FWS/OBS- 84/09 May 1984 THE ECOLOGY OF DELTA MARSHES OF COASTAL LOUISIANA: A Community Profile 105 L8 G67 Fish and Wildlife Service Corps of Engineers U.S. Department of the Interior U.S. Department of the Army :5EJP Salt marshes along the Mississippi deltaic channels (Photograph by Charles Sasser) . coast characterized by extensive tidal /05' FWS/OBS-84/09 May 1984 THE ECOLOGY OF DELTA MARSHES OF COASTAL LOUISIANA: A COMMUNITY PROFILE by James G. Gosselink Center for WefTahd Resources Louisiana State University Baton Rouge, LA 70803 ni- si i _D ': □" : 3- ; _D ; nj '• a i ° • c-=l \ CD : m I D I CD Project Officer Edward C. Pendleton National Coastal Ecosystems Team Fish and Wildlife Service 1010 Gause Boulevard Slidell, LA 70458 U.S. Performed for National Coastal Ecosystems Team Division of Biological Services Research and Development Fish and Wildlife Service U.S. Department of the Interior Washington, DC 20240 The findings in this report are not to be construed as an official U.S. Fish and Wildlife Service position unless so designated by other authorized documents. Library of Congress Card Number 34-601047. This report should be cited: Gosselink, J.G. 1984. The ecology of delta marshes of coastal Louisiana: a community profile. U.S. Fish Wildl. Serv. FWS/OBS-84/09. 134 pp. PREFACE This report is one of a series of U.S. Fish and Wildlife Service Community Profiles synthesizing the available liter- ature for selected critical ecosystems into comprehensive and definitive refer- ence sources. The objective of this particular account is to review the infor- mation available on the marshes of the Mississippi River Deltaic Plain. The river system is the largest in North America. It drains an area of 3,344,560 km^. Over the past 5,000 years the river has built a delta onto the continental shelf of the Gulf of Mexico covering about 23,900 km^. This low land is primarily marshes and represents about 22 percent of the total coastal wetland area of the 48 conterminous United States. The delta is notable for its high primary productivity, its valuable fishery and fur industry, and the recreational fishing and hunting it supports. At the same time, the Mississippi River Deltaic Plain marshes are subject to the unique problem of extremely rapid marsh degradation due to a complex mixture of natural processes and human activities that include worldwide sea-level rise; subsidence; navigation and extractive industry canal dredging; flood control measures that channel the river; and pollution from domestic sewage, exotic organic chemicals, and heavy metals. The future of the marshes in this region is in jeopardy, and if they are to be saved, it is important to know how they function and what measures can be taken to arrest the present trends. Any questions or comments about this publication or requests for the report should be directed to the following address. Information Transfer Specialist National Coastal Ecosystems Team U.S. Fish and Wildlife Service NASA/SI idell Computer Complex 1010 Gause Boulevard SI idell, LA 70458 m CONVERSION TABLE Metric to U.S. Customary Mul tiply BiL millimeters (mm) 0.03937 centimeters (an) 0.3937 meters (m) 3.281 kilometers (km) 0.6214 square meters (m") 2 square kilometers (km ) 10.76 0.3861 hectares (ha) 2.471 liters (1) 0.2642 cubic meters (m^) 35.31 cubic meters 0.0008110 mill igrams (mg) 0.00003527 grams (g) 0.03527 kilograms (kg) metric tons (t) 2.205 2205.0 metric tons 1.102 kilocalories (kcal ) 3.968 Cel sius degrees 1.8(C°) + 32 To Obtain inches inches feet mil es square feet square miles acres gal Ions cubic feet acre- feet ounces ounces pounds pounds short tons British thermal units Fahrenheit degrees U.S. Customary to Metric inches inches feet (ft) fathoms miles (mi) nautical miles (nmi) square feet (ft") acres ^ square miles (mi ") gallons (gal) cubic feet acre- feet (ft') ounces (oz) pounds (lb) short tons (ton) British thermal units Fahrenheit degrees (BTU) 25.40 2.54 0.3048 1.829 1.609 1.852 0.0929 0.4047 2.590 3.785 0.02831 1233.0 28.35 0.4536 0.9072 0.2520 0.5556(F° - 32) mill imeters centimeters meters meters kilometers kil ometers square meters hectares square kilometers 1 iters cubic meters cubic meters grams kil ograms metric tons kil ocal ories Celsius degrees IV CONTENTS Page PREFACE i i 1 CONVERSION TABLE iv F IGURES vi i TABLES xii ACKNOWLEDGMENTS xi v INTRODUCTION 1 MAN IN THE MISSISSIPPI RIVER DELTA l HISTORY OF DELTA RESEARCH 4 WETLAND DEFINITIONS, TYPES, LOCATION, AND EXTENT 5 CHAPTER ONE. THE REGIONAL SETTING 9 THE CLIMATE, THE OCEAN, AND THE RIVER 9 Insolation 9 Temperature 10 Water Balance 10 GEOLOGICAL PROCESSES 14 Pleistocene sea levels 14 Modern Mississippi Delta 18 CHAPTER TWO. TEMPORAL AND SPATIAL GRADIENTS IN DELTA MARSHES 28 TEMPORAL GRADIENTS 28 SPATIAL GRADIENTS 32 Flooding 33 Soils 34 Sal t 35 Soil Nutrients 36 Vegetation 37 CHAPTER THREE. ECOLOGICAL PROCESSES IN DELTA MARSHES... 43 PRIMARY PRODUCTION 43 Emergent Vascular Plants 44 Epiphytic Algae 54 Benthic Microflora in Marsh Ponds 55 Submerged Grasses in Marsh Ponds 55 DECOMPOSI TION 55 CONSUMERS 60 Benthos 60 Nekton 61 Wildlife 63 Carbon Budget 71 NUTRIENT CYCLES 74 Nitrogen 74 Phosphorus 76 Sulfur 77 STORMS 77 CHAPTER FOUR. THE MARSH IN THE COASTAL BASIN 79 COUPLINGS AMONG ECOSYSTEMS 79 Intra-Basin Couplings 79 Extra-Basin Couplinqs 80 Intercontinental Couplings 81 TEMPORAL USE OF MARSHES 81 CHAPTER FIVE. WETLAND VALUES, HUMAN IMPACTS, AND MANAGEMENT 84 WETLAND VALUES 84 Wetland Harvest 84 Environmental Quality 85 Esthetics 86 Confl icting Values 86 WETLAND EVALUATION 87 WETLAND MANAGEMENT 89 Marsh Loss and Salt Intrusion 89 Habitat Qual ity 93 Water Quality 96 REFERENCES 100 APPENDICES 116 1. Plant species composition of salinity zones in the Louisiana coastal marshes 116 2. Marsh plant decomposition rates, Mississippi River delta marshes 118 3. Fishes of the Mississippi River Deltaic Plain that are found in marshes and associated water bodies.. 120 4. Representative vertebrate species of marsh habi- tats in the Mississippi River Deltaic Plain ^28 VI FIGURES Number Page Frontispiece. Salt marshes along the Mississippi deltaic coast characterized iMcinp by extensive tidal channels COVER 1 The groves of trees in the middle of this broad expanse of marsh identify the site of old Indian villages 2 2 The oil storage facility for the nations' s only superport is constructed in a salt dome in the middle of a Mississippi delta brackish marsh. The maze of pipes is the primary aboveground expression. An old oilfield also sits atop this submerged salt dome as shown by the network of tree-lined oilwell access canals 3 3 Across this expanse of marsh and swamp looms the Mew Orleans skyline through the haze, a reminder of the proximity of heavy industries and concentrated popul ations 4 4 Louisiana oil and gas production 5 5 Map of the Mississippi River Deltaic Plain showing the hydrologic units 7 6 The seasonal variation of insolation at various latitudes. The computation assumes a transmission coefficient of 0.7 throughout 9 7 Mean monthly air temperature at New Orleans, Louisiana 10 8 Generalized water budget for the Mississippi delta marshes 10 9 Average water budget for the upper Barataria basin, 1914-1978. P=precipitation, PE=potential evapotranspiration, AE=actual evapotranspi ration 11 10 Freshwater inflows to the Mississippi Delta. Discharges are in cumecs. All discharges are for water year 1978 except Mississippi River, which is a long-term mean representing the combined average annual discharge above the confluence of the lower Mississippi (10400 cumecs) and the Atchafalaya (5000 cumecs) Rivers 12 11 Water level trends in delta marshes:, a) long term; b) seasonal; c) daily 13 12 Tide levels at Shell Beach, in the Pontchartrain-Lake Borgne basin, associ ated wi th ni ne major storms 14 vii Number Page 13 The relationship of glacial advance and retreat to continental shelf exposurs and sedimentation during the Late Quarternary 25 14 Location of major buried river channels formed during the Wisconsin gl acial period 15 15 The position of major delta lobes on the gulf coast during the previous 25,000 years. (A) Late Wisconsin, 25,000 - 20,000 yr B. P. (B) Late Wisconsin, 15,000 yr B. P. (C) Early Holocene, 12,000 - 10,000 yr B. P. (D) Present, 5,000 - 1,000 yr B. P 17 If) Deltaic lobes of Mississippi River deltas 18 17 Satellite image of the Mississippi Delta Region showing delta lobes of different ages 19 13 Six subdeltas of the modern Mississippi Balize Delta recognized from maps and sediment analysis. Dates indicate year of crevasse opening 20 19 Plan view and cross sections through A-A' and B-B' of environments of deposition in a crevasse 21 20 Sequential development of Cubits Gap subdelta 22 21 Linear, areal , and volume growth curves for the Cubits Gao subdelta 23 22 Composite subaerial growth curve, Mississippi River subdeltas. Total subaerial land determined from averages at 10-yr intervals 24 23 The accelerating wetland loss rate in the Mississippi Delta 24 24 Conputerized re-creation of the west side of Barataria Bay showing the change in wetlands between 1945 (a) and 1980 (b). Black is open water; marshes are shown as varying shades of grey 25 25 Environmental succession of an idealized delta cycle 29 26 Mineral content of marsh soils in Mississippi delta hydrologic units, arranged in order of increasing age 30 27 Marsh soil salinity and percent fresh marsh in Mississippi delta marshes by hydrologic unit, arranged in order of increasing age. Soil salinity is a mean for the whole basin weighted by ares of each marsh zone. The fresh marsh is percent of total marsh area 30 28 Marsh edge length :area ratio and total marsh edge length for delta hydrologic units. The units are arranged in order of increasing age 31 29 Net primary production and fishery yield of Mississippi River Deltaic Plain hydrologic units. Production calculated from average production of each habitat type and its area in the hydrologic unit. Shrimp data from Barrett and Gillespie (1975). Basins are, in order of increasing aye: I - Pontchartrain-Lake Borgne, II - Balize, III -Barataria, IV - Terrebonne, V - Atchafalaya , VI -Vermilion 31 viii Number Pag*? 30 Seasonal salt marsh inundation patterns 34 31 Variation in soil density and soil carbon content with distance inland from the strean edge in a salt marsh in the Barataria basin 34 32 Sedimentation rates on the Barataria saline marsh. (A) Mean seasonal sedimentation 1975 - 78. (B) Mean seasonal sedimentation 1975 - 79. Sedimentation rates were highest during the winters of 1975 - 78. Hurricane Bob and tropical storm Claudette passed through the area during the summer of 1979, resulting in very high deposition rates 34 33 The decrease in free soil water salinity (mg/g) of chenier plain marshes with distance (km) from the gulf 36 34 Concentrations of available Na, Ca, K, Mg, P, and N in different marsh zones 37 35 Vegetation zones in the Mississippi River delta marshes ■^g 36 A deltaic plain brackish marsh. Note the "hummocky" appearance which is typical of Spartina patens stands. The birds with black-tipped wi ngs are white pel icans , the smal ler ones ducks , mostly teal 40 37 A diverse deltaic plain fresh marsh scene. Species are: Sagittaria falcata (foreground), Typha sp. (right edge), mixed grasses and vines, Myrica shrubs in rear 41 38 Vegetation zonation in an intermediate marsh transition zone in the Barataria basin. Factors arise from statistical clustering techniques and are identified by the dominant species 41 39 Effects of substrate drainage conditions on the dry weight accumulation by (A) Spartina alterni flora and (B) S^. cynosuroides 42 40 A conceptual model of a typical wetland ecosystem, showing major coTiponents and processes 44 41 Monthly growth rates of Panicum hemitomon and Spartina alterniflora 45 42 Seasonal changes in live and dead biomass of Phragmites austral is and Spartina patens during 1973 - 1975 47 43 Production of intertidal S. alterniflora vs. mean tide range for various Atlantic coastal marshes. Different symbols represent di f ferent data sources 49 44 Variation in total aboveground biomass and height of Spartina alterniflora with distance inland from the marsh edge in a Barataria basin sal t marsh 50 45 Gulf-inland variations in live and total biomass in Spartina al terni flora marshes 50 46 Effects of NaCl concentration in the root medium on the rate of Rb ix Number Page absorption by excised root tissue of S^. a1 terni flora and D. spicata 51 47 Metabolic conversions of pyruvic acid. This "key" intermediate in metabolism can be converted to a variety of end products, depending on the organism and the electron acceptors available 52 48 Marsh soil transfonnations that result from tidal flooding 53 49 Seasonal changes in various physical, chemical, and biotic factors in a Barataria basin salt marsh 54 50 Net epiphytic production on stens of Spartina a1 terni flora collected at the water's edge and inland 1.5 m with the averages, extremes, and fitted curve for the water's edge production superimposed 55 51 Number of shore-line epiphytic diatans/cm culm surface area of Spartina al terni f1 ora. Results are pooled averages for four stations and height classes 55 52 Disappearance of S^. patens litter from litter bags in the Pontchartrain-Borgne basi n 58 53 Decomposition rates (mg/g/day) of S^. al terni flora litter incubated in 2 -mm mesh bags in different locations 59 54 Major pathways of organic energy flow in a Mississippi River deltaic salt marsh and associated water bodies 51 55 Length class frequency of qulf menhaden captured in and near Lake Pontchartrai n 52 56 Density of vegetation, detritus, and consumers at the edge of the salt marsh 53 57 Pelt production from marsh zones in coastal Louisiana 55 53 Annual muskrat harvest from a 52,200-ha brackish Scirpus ol neyi marsh in the Mississippi Delta 55 59 Ground plan of a typical muskrat house with underground runways and surface trail s 55 60 A muskrat "eat-out" in the brackish marsh in the Barataria basin. Note the high densi ty of muskrat houses 57 61 Carbon dioxide flux measurements in a deltaic salt marsh communi ty 72 62 Carbon budget of a Mississippi River deltaic salt marsh (see Table 29 for sources). Rates (g C/m^/yr) are from CO2 flux measurements, except numbers in parentheses, which are fran other sources 72 63 A schematic outline of the redox zones in a submerged soil showing some of the N transfonnations. The aerobic layer has been drawn thick for clarity. In reality it is seldom over 1-2 mm in flooded marshes 75 X Number Page 64 Nitrogen and phosphorus budgets for a Mississippi deltaic salt marsh 75 65 Conceptual diagram illustrating the coupling of delta marshes to other ecosystems 79 66 Patterns of estuarine use by nektonic organisms in the Barataria basin, Louisiana 80 67 The life cycle of the brown shrimp 81 63 Major duck migration corridors to gulf coast marshes 82 69 Seasonal use of wetlands by migratory birds, shellfish, and fish 83 70 The increase in open water in natural and impounded wetlands. The pattern of greater wetland loss in impoundments is consistent in both fall, when water levels are low, and winter when impoundments are f 1 ooded 92 71 Wildlife management areas in the Mississippi Delta 94 72 A weir in the deltaic plain marshes. The strong flow of water across the weir is an indication of the effectiveness of the barrier. These structures are favorite sport fishing spots 95 73 Cumulative number of days per year that ponds in the study area will equal or exceed certain percentages of bottom exposure. Based on depth contours of 48 ponds and 20 years of tide data on the central Louisiana coast 96 74 The percentage of different types of vegetation in impoundments in the Rockefeller State Wildlife Refuge 97 75 Habitat type, vegetative cover, and fish and wildlife values achieved with water management programs operating on the Rockefeller Refuge 98 XI TABLES Nu"iber Page 1 Salinity values (ppt) recorded by various investigators for delta marshes 6 2 Classification of coastal marshes of the Mississippi River Delta, and area of different marsh zones in 1978 6 3 Average coastal subnergence on the U.S. east and gulf coasts 13 4 Land-use changes along the northwest edge of the Barataria basin, on the Bayou Lafourche natural levee 26 5 Land use changes, in hectares, in the Mississippi Delta, 1955-78 27 5 Regression analyses relating net primary production (NPP) and inshore shrimp production (1955-74) in hydrologic units to various physical parameters 32 7 The annual duration and frequency of inundation of marshes in the Barataria basin, Louisiana 33 3 Marsh accretion rates (mm/yr) in Louisiana delta marshes, based on the 1963 ^''Cs fallout peak 35 9 Concentration (C) and accumulation rates (A) of organic carbon, nitrogen, phosphorus, iron, and manganese in Louisiana delta marsh soil s 35 10 Multiple linear regression models of soil ions showing what factors control their distribution 36 11 The ratio of the major cations to the chloride ion in normal seawater and in the saline, brackish, inte mediate, and fresh marshes of Louisiana 37 12 Percent cover of the dominant plant species in major marsh zones of the Louisiana coast 38 13 Production of marsh vascular plant species in the Mississippi Delta .... 45 14 Belowground biomass of Mississippi delta marsh plant species 48 15 Production estimates for a Spartina alterniflora stand based on different techniques 48 xi i Number ^age 16 Year-to-year variations in peak live biomass of Spartina alterni flora at a single site in the Barataria basin 49 17 Spartina alterni flora root alcohol dehydrogenase (ADH) activity, adenosine triphosphate (ATP) and ethanol concentrations, and soil Eh in a Louisiana sal t marsh 52 18 Percentage of marsh community ;netabolism by Spartina alterniflora 54 19 Submerged aquatic plant species composition of ponds and lakes by marsh zone along the Louisiana coast 55 20 Range and mean loss rates (mg/g/day) of litter from different marsh plant species (summarized from Appendix 2) 59 21 Monthly occurrence and abundance of the fish species collected in smal 1 sal t marsh ponds 62 22 Wildlife species richness (number of species) in the chenier plain marshes 64 23 Muskrat house-building activity in 10-ha brackish and salt marsh areas in Barataria basin 66 24 Density of waterfowl (number/100 ha) by marsh zone in the Barataria basin in 1980-81 68 25 Density of ponds and lakes of various size classes in marsh zones along the Louisiana coast, August, 1968 69 26 The percent of the area of ponds and lakes covered with submerged vegetation in August, 1968 by size and marsh zone 70 27 Density of wading birds and pelicans (number/100 ha) by marsh zone, in the Barataria basin, 1980-81 70 28 Birds of the Mississippi Deltaic Plain on the Audubon Society "Blue List," indicating that their populations are declining 71 29 Estimates of different components of the carbon budget of a Mississippi deltaic salt marsh community 73 30 Influence of Spartina alterniflora plants on recovery of ^^N-ammonium added over 18 weeks to soil cores 76 31 The estimated economic value of harvests from the Barataria basin, Louisiana 85 32 Estimates of the economic value of Louisiana's coastal wetlands comparing willingness-to-pay approaches with energy analysis approaches 89 33 Major wetland issues and human impacts in Mississippi delta wetlands .... 89 34 Impacts of canals in Louisiana coastal marshes leading to habitat loss, and mechanisms and management practices to minimize these impacts 90 xiii ACKNOWLEDGMENTS This profile is dedicated to the graduate students in Marine Sciences and Fisheries at Louisiana State University (LSU), Baton Rouge, who carried out much of the original field research upon which this profile is based. I have been privi- leged to work closely with thirteen of them. Fifty- six literature citations in the profile are authored or coauthored by students. They have made a major contri- bution toward unravelling the ecology of our coastal ecosystems. have been of coworkers fortunate to for the last enjoy a 15 years group who introduced me to participated with me in stiiiiul ation of wetland contributions are cited work. They are Len Charles Hopkinson, Stone, Gene Turner, Costanza, Flora Wang, Bob Baumann, Deborah Fuller, Gary Paterson, and Charles Sasser. the marshes and the intellectual research. Their throughout this Bahr, John Day, Roland Parrondo, Jim and more recently Bob Special thanks are extended to Jim Coleman, who drafted the geology section of this report, and to Linda Deegan and Jean and Walt Sikora for information and advice on the benthos and nekton sections, respectively. John Day and Irv Mendelssohn (LSU), Gerry Bodin [U.S. Fish and Wildlife Service (FWS), Lafayette, La.], Ed Pendleton (FWS National Coastal Ecosystems Team), and Suzanne Hawes , and John Corps of Engineers, New reviewed an early draft helpful suggestions Thanks to Kathryn Steve Matheis, Weber (U.S. Army Orleans District) and provided many for improving it. Lyster and Susan Lauritzen (FWS National Coastal Eco- systems Team); they edited and did the layout for the profile, respectively. Dawnlyn M. Harris provided word processing assistance. Diane Baker, as usual, did a superb job drafting the figures. She created the cover. My wife, Jean, showed great forbearance and understanding while I labored long hours over the word processor. Much of the research cited in this manuscript was supported by the National Sea Grant Program and the U.S. Army Engineers District, New Orleans. The preparation of this profile has been sponsored by the Office of the Chief of Engineers in association with the Water- ways Experiment Station, the Lower Mississippi Valley Division, and the New Orleans District, Anny Corps of Engineers, and the Fish and Wildlife Service. XIV INTRODUCTION The history of the marshes of the Mississippi River Delta is inextricably intertwined with the history of the river itself. Like some ancient god, it broods over the coastal plain, implacable in its power, its purpose inscrutable. With its sediment it spawns the flat, verdant marshes of the delta, nourishes them with its nutrients, and finally abandons them to senesce slowly under the influence of time and subsidence, while it renews the cycle elsewhere along the coast. This community profile deals with the facts and the quantitative analysis of this cycle. But the cold numbers often defy our comprehension. How much is 15,400 cubic meters per second (cLnecs) , the average discharge of the Mississippi River? How large is 0.2 y, the size of a bacterium? And what does it mean to say that there are one thousand million of then in a cubic centimeter of marsh soil? These scales are almost unimaginably different, yet understanding a natural ecosystem demands the ability to deal with both. As one examines the technical details of a system like a coastal marsh, the complexity becomes increasingly apparent, and the cold, technical analysis breaks down more and more often into a sense of wonder at the system's sophistication and the delicate interplay of parts that make up the whole. Migratory waterfowl's ability to respond to subtle environmental cues and navigate thousands of miles from Alaskan prairie potholes to the Louisiana coastal marshes rivals our most sophisticated inertial guidance systems. After years of study we still have little understanding of how passively floating shrimp larvae in the Gulf of Mexico find their way through estuarine passes into the coastal marshes. The idea of energy flow in ecological systems is still only a guiding principle; the complex details of molecular biochemistry in the marsh substrate and the complexity of the meiofaunal food chain are still largely unexplored. This monograph details the human struggle to understand, and through understanding to manage the Mississippi delta marshes. I will emphasize what we know - and that is considerable - but I hope that the presentation of technical detail does not obscure the large areas of uncertainty about how to manage the system. Above all I hope that it does not reduce the delta marshes to cold statistics; for understanding, I believe, is heightened by emotional involvement. MAN IN THE MISSISSIPPI RIVER DELTA When de Soto found and named the Rio del Esperitu Santo, now the Mississippi River, in 1543, the Indians had been living on the coast for 12,000 years. They preferred the easy living of the marshes to the uplands because food was abundant and easy to harvest. Oysters and the Ranqia clam were in nearly endless supply. Fish, turtles, and edible plants were plentiful. The tribes now known as Tchefuncte, Marksville, Troyville, Coles Creek, Caddoan, Mississippian, and Plaquemine settled on the slightly elevated banks of river distributaries where they literally ate themselves up out of the water. As they ate oysters and clams, the shells accumulated beneath them. The evidence of these prehistoric villages now dots the marshes as small groves of trees on slightly elevated shell mounds in an otherwise treeless vista (Figure 1). De Soto approached the river from the Florida Peninsula. It was 140 years before the next European, LaSalle, explored the coast in 1682, having approached from upriver. He claimed the great basin drained by the river for France and in 1584 led an expedition to establish a colony at the mouth of the river. Although he failed in this attempt, and lost his life, he was followed by Iberville, who explored and mapped the river and by Bienville, who established New Orleans in 1718. Thus began a settlenent phase that resulted in the development of the distributary (a diversion near the mouth of a river that distributes water out of the main channel) levees for agriculture. Rice, indigo, tobacco, corn, cotton, and later sugarcane were the large plantation crops, but many other crops brought in from Europe and elsewhere were also grown. During this period Germans settled part of the coast, beginning in about 1720. In 1760 an influx of French refugees from Eastern Canada began. These poor farmers, trappers, and fishermen brought with them a strong culture still characteristic of the coastal villages (Kane 1943). One hundred years ago Louisiana had only about 900,000 inhabitants (Kniffen 1968). Many developments led to the present industrialized state. The construction of levees along the Figure 1. The groves of trees in the middle of this broad expanse of marsh identify the site of old Indian villages (Photograph courtesy of Louisiana State University Museum of Geosciences, Robert Newman, curator). Mississippi River did much to develop a sense of permanence and encourage industrial expansion. The levees also promoted waterborne transportation by channelling the Mississippi River and its Dredging to create new ones These fostered and stimulated distributaries, channels and commonpl ace. transportation deepen became more further commercial expansion. New industries developed based on Louisiana's coastal resources. The late 1800' s and early 1900' s were a time of widespread harvesting of the extensive cypress forests of the coast. The fishing and fur-trapping industries expanded. But the most significant event in the state's life was the discovery of oil in Jennings in 1901. Oil reserves in concentrated around salt Louisiana are domes that occur across the coastal wetlands and on the continental shelf. The inland fields were developed first. An enormous expansion of petroleum demand began in the war years of 1941-45. This resulted in dredging thousands of miles of canals through the coastal wetlands for access to drilling sites and for pipelines, constructing enormous refineries and petrochemical processing facilities, and secondarily stimulating many other industries (Fi-gures 2 and 3). As oil and gas reserves were depleted in the inland marshes, production moved offshore. This shift increased pressure for more and deeper navigation canals to link the offshore rigs with land-based facilities. Production of oil and gas reached its peak in 1971 and has since been declining (Figure 4). However, the search for new oil continues, and wetland modification has by no means stopped. Louisiana's wetland management problems continue to be related to its Figure 2. The oil storage facility for the nation's only superport is constructed in a salt dome in the middle of a Mississippi delta brackish marsh. The maze of pipes is the primary aboveground expression. An old oilfield also sits atop this submerged salt dome as shown by the network of tree-lined oilwell access canals (Photograph by Robert Abernathy) . major coastal industries - and fossil fuel extraction, HISTORY OF DELTA RESEARCH transportation Investigations of geological and biological aspects of the Mississippi Delta both followed the same historic trend from descriptive accounts to greater emphasis on functional processes. In geology early studies are typified by that of Lerch et al. (1892), who carried out a fairly inclusive preliminary survey of Louisiana that included geology, soils, and groundwater. Davis' (1899) physiographic interpretation ushered in the "golden age" of coastal geomorphol ogy (Fisk 1939, 1944; Fisk and McFarlan 1955; Russell 1936, 1967; Kolb and Van Lopik 1958; and many others). This was a period of deciphering the geomorphol ogy of the delta on a regional scale and qualitatively documenting the major i^ormative processes. In the last 20 years the emphasis has shifted to intensive investigation, usually at specific locations, of nrocess-response rel ationships . In the biological arena early comments on delta biota were common, at first emphasizing economically important animals such as furbearers. De Montigny (1753, as quoted in Gowanloch 1933), who spent 25 years in Louisiana, and Le Page du Pratz (1758) observed fish and terrestrial animals in the coastal zone. In the early 1800' s Rafinesque, a professor at Transylvania University, Lexington, Kentucky, described many fish species of the South (Gowanloch 1933). John J. Audubon and Alexander Wilson described Louisiana birds in the early 1800' s. George E. Beyer published "The Figure 3, Across this expanse of marsh and swamp looms the New Orleans skyline through the haze, a reminder of the proximity of heavy industries and concentrated populations (Photograph by Charles Sasser). 1915 1925 1936 1946 1965 1975 1985 Figure 4. Louisiana oil and gas production (Costanza and Cleveland 1984). beneficial effect of the Mississippi River water and nutrients on aquatic productivity was generally understood (Gunter 1938; Viosca 1927; Riley 1937). Also during this decade articles devoted specifically to marsh plants were published (Brown 1936; Penfound and Hathaway 1936). These were soon followed by articles that focused on the relation of environmental factors, particularly salinity and inundation, to plant occurrence (Hathaway and Penfound 1936; Penfound and Hathaway 1938; Brown 1944; Walker 1940). Since that time the focus of biotic research has shifted to the processes that control the distribution and abundance of organisms and to analyses of whole communities and ecosystems. While this was a national trend, on the Louisiana coast it was seen in a series of studies funded by the Louisiana Sea Grant program in the early 1970' s. WETLAND EXTENT DEFINITIONS, TYPES, LOCATION, AND Avifauna of Louisiana" in 1900, a classic description. A.B. Langlois collected 1,200 plants near Plaquemine in the late 1800's; Riddill, Hale, and Carpenter collaborated between 1839 and 1859 to publish a list of 1,800 names of Louisiana plants, excluding grasses and sedges. Cocks (1907) stated that Langlois' collec- tion was shipped to St. Louis University and that most of the Riddel 1 et al . collection was lost. Cocks incorporated their lists into his own list of the flora of the Gulf Biologic Station at Cameron, Louisiana. This station also published pioneering studies on oysters (Kellogg 1905; Cary 1907) and shrimp (Spaulding 1908) during this period. The 1930' s brought a sudden wealth of publications. Noteworthy are a series of bulletins published by the Louisiana Department of Conservation on birds, fur animals and fishes (La. Dept. of Conservation 1931; Gowanloch 1933) that sumnarized the available knowledge on these topics. By the late 1930' s the general life history pattern of the commercially valuable estuarine organisms of the delta had been described, and the The marshes considered in this monograph are classified by Cowardin et al. (1979) as persistent or nonpersistent emergent wetlands. Most of them lie within the estuarine intertidal or palustrine systems of this classification scheme, although some could be construed to be riverine, particularly where the Mississippi and Atchafalaya river flows are not confined by levees. In Louisiana these marshes are further subdivided as freshwater, intermediate, brackish, or salt, based on vegetation associations established by Penfound and Hathaway (1938) and Chabreck (1972), rather than on salinity per se. However, the salinity ranges for these associations have been determined by various investigators (Table 1). They correspond fairly closely with the salinity modifiers - fresh, oligoha- line, mesosaline and polysaline - of Cowardin et al . (1979) as shown in Table 2. This table also shows the area of each marsh type in the Mississippi Delta region. In both Figure 5, a map of the delta marshes, and in Table 2 the region is divided into drainage basins, the natural ecosystem units of the delta (Costanza et Table 1. Salinity values (ppt) recorded by various investigators for delta marshes (from Wicker et al. 1982). Investigator Delta marshes Fresh Intermediate Brackish Sal ine Penfound & Hathaway 1938 5 N.A.* 5 -20 20+ O'Neil 1949 5 N.A. 0.7-18 18+ Allan 1950 0 -10 8 -35 N.A. 30 -50 Lemaire 1960 1 - 2 1 - 6 4.5-21.6 9.5-26 Wright et al . 1960^ Giles 1965 1 - 2 2 -10 10 -20 20+ N.A. 2.4- 7 7 -12 11.5-17 Chabreck 1972 1.1- 6.7 2.7- 2.8 4.7-18.4 0.6-30 USDI/FVJS unpubl. Palmisano 197r 0 - 1 0.5- 5.9 0.9-19 1.5-26 1.1- 3.2 2.7- 2.8 4.7-18 17.3-29 USACh 1974 0 - 5 5 -10 10 -20 20+ Montz 1975 0 - 1 1 - 8 8 -18 18+ USDA/SCS no date 0 - 5 0.4- 9.8 0.4-28 O.G-52 Data not available. Salinity contours established by Dept. of Oceanography and Meteorology, Texas A.X M. jj College, 1959. Average minimum and maximum annual range of soil water salinity. .Fruge (1980) pers. comm.; extrenes of recorded salinity range from 1963 sampling. Water salinity range of vegetative types in hydrologic unit I. Table 2. Classification of coastal marshes of the Mississippi Delta, and area of marsh in 1978 within each major hydrologic basin (Cowardin et al . 1979; Wicker 1980; Wicker et al. 1980a, 1980b). Level of cl assification CI assification System/subsystem Cl ass Subclass Modifiers Tide Sal inity (ppt) Marsh designation Basin Salt Estuarine intertidal Pal us trine Emergent wetl and Persistent Persistent or nonpersistent Tidal Nontidal Irregularly exposed to Intennittently flooded to regularly or irregularly intermittently exposed flooded Polyhaline Mesohaline 01 igohal ine Fresh 18-30 5-18 0.5 - 5 0.5 Brackish and intermediate Fresh Total I Pontchartrain II Balize III Barataria IV Terrebonne V Atchafalaya VI Vermilion 45,793 0 19,388 57,866 0 2,541 129,487 hectares - 14,519 189,799 10,386 15,397 26,783 79,483 65,358 164,229 92,010 69,423 219,299 0 23,855 23,855 77,902 20,233 100,676 Total 125,588 389,268 209,785 724,641 ( V STUDY AREA HYDDOLOGK UNIT BOuNIIARIE; . , fT^no,,:,... I PONTCHARTRAINj h^, \ lA ^4; '-^ j^RR^BO^Nrft^^.J S G(/tF OF MEXICO Figure 5. Map of the Mississippi River Deltaic Plain showing the hydrologic units, al. 1983). These data and maps are from a recent Fish and Wildlife Service study of the Mississippi Delta Plain Region (Wicker 1980; Wicker et al. 1980a, 1980b). The drainage basins are interdistributary basins formed by shifts in the major distributary of the river. Thus they forni a time series of delta lobes of different ages and allow one to see in space the time sequence of the development and decay of the marshes of a delta lobe. The active Mississipoi River delta, the Balize Delta, is next youngest. It receives two-thirds of the flow of the Mississippi River, but it is debouching into deep water at the edge of the continental shelf. Most of this basin is fresh also, but there has been marine invasion of abandoned around the edges distributaries, and the brackish. subdelta lobes of the main marshes here are The youngest basin is the Atchafalaya, which is actively prograding out through the shallow Atchafalaya Bay. It receives one-third of the flow of the combined Mississippi and Red river systems, whose freshwater flows into the shallow bay keep the whole basin fresh or nearly fresh all year. All the marshes in this basin are fresh. In succession Barataria, Terrebonne, Vermilion-Cote Blanche, and the Pontchartrain-Lake Borgne basins are of increasing age. They all have extensive marshes with well-developed salt and brackish zones. These six basins together form the Mississippi Delta Plain Region, one of the best-developed deltas in the world. The Mississippi Delta Plain Region is also the largest continuous wetland systan in the United States with addition to these renewable resources the 725,000 ha of marshes, not including the delta is also the scene of intensive forested wetlands at the inland extremes mineral extraction; the Mississippi River of the basins. The delta supports the ports between New Orleans and Baton Rouge nation's largest fishery, produces more handle yreater tonnage than any other port furs than any other area in the United in the United States; and dense urban. States, and is an important wintering industrial, and agricultural activity ground for iiiigratory waterfowl. In crowds the distributary levees. CHAPTER ONE THE REGIONAL SETTING The unique characteristics of the region and its marshes result froin the interaction of three forces - the subtropical climate, the oceanic regime, and the river - all acting on the physiographic template of the northern gulf coast. The forces control the geomorphic processes that have formed the delta and also the biological characteristics of the delta marshes. For individual plants on the coastal marsh these forces resolve into insola- tion, tenperature, and water. Insola- tion and temperature determine the poten- tial and the rate, respectively, of biotic productivity. Within the constraints set up by these two parameters water is the major controlling function which makes a wetland wet and determines, directly or indirectly, its characteristics. It is also the most complex of the three parame- ters. Insolation and tenperature are determined primarily by latitude, with only minor modification by local circum- stances. But, the water available to marshes, the depth and duration of flood- ing, current velocity, and water quality are complex functions of marine energy, fluvial processes, rainfall, and evapora- tion, operating over an irregular surface. THE CLIMATE, THE OCEAN, AND THE RIVER Insolation There is apparently no weather station in the Mississippi Delta region that routinely records insolation. Existing records of this important parameter are scattered and fragmentary. However, the insolation reaching the top of the atmosphere is a constant that varies seasonally at a particular point on the earth's surface, depending on latitude. Assuming an atmospheric transmission coefficient of 0.7, Crowe (1971) showed how insolation varied seasonally with latitude (Figure 5). In the Mississippi Delta region, at about 30° north latitude, solar energy reaching the earth's surface varies from about 200 cal/cm^/day during the winter to a peak of nearly 600 cal/cm^/day in June and July. During the summer insolation at this latitude is higher than anywhere else on the globe; it falls off both north toward the Arctic and south toward the Equator. Therefore, midsummer growth potential in terms of solar energy is as high in the Mississippi Delta as it is anywhere on earth. Cloud cover diminishes the potential irradiance, and on the coast where daytime seabreezes move moisture-laden gulf waters inshore, there are clouds almost every day during the hot summer. Consequently the CAL'Cm'/ oay eoo 600 400 300 200 100 JFMAMJ J I A I S I O I N I D J F m|a|m|j|j|a|s|o|n|d Figure 6. The seasonal variation of insolation at various latitudes. The computation assumes a transmission coefficient of 0.7 throughout (Copyright. Reprinted from "Concepts of Climatology," 1971, by P.R. Crowe wi th permi ssion of Longman Group Ltd., England). seasonal insolation cjrve for the delta skewed to the left with in May, falling off and July because of coast is probably peak insolation somewhat in June clouds . Temperature As one might expect, seasonal air tenperatures follow insolation closely. Mean monthly temperatures range from a Decenber/January low of about 14°C to a midsummer high of about 30°C. Temperature at the U, S. Weather Bureau station in New Orleans (Figure 7) is fairly representative of the coast because New Orleans is surrounded by marshes and water. Because of the moderating effect of the water bodies and the high humidities, midday temperatures seldom exceed the low 30's (Celsius) despite the high insolation. During winter in the coastal marshes, freezes are infrequent, and the average number of frost- free days is about 300. In fact, the barrier island. Grand Isle, was chosen for the site of a sugar cane breeding laboratory by the Louisiana State University (LSU) Agricultural Experiment Station because the lack of frost allowed sugar cane fruit to ripen there. Since most of the inshore waters are less than 1 m deep. 90 - 80 ?x z lU uj 70 tr (T ^ < < u. 60 cc UJ w 0. u 2 liJ 50 UJ T I- O a 40 30 30- 20 UJ a < a. (3 t- 2 UJ O 03 UJ C 10 o J F M A M J J A S 0 N D MONTHS Normal Maximum Minimum water temperature follows air temperature closely, with a lag time of a few hours at most. Water Balance The water budget includes rain, evapotranspiration, local runoff from adjacent uplands, upstream discharge into wetlands by rivers entering the region, and marine water pumped in and out by tidal and meteorologic forces (Figure 8). Each of these varies in both time and place; the resultant flooding frequency, volume, and water quality on the marsh are at present predictable only as average trends. No present models capture the details adequately. Precipi tation. Annual averages about 160 cm spread over the year (Figure 9). to be the driest month and test, but torrential rains that any month can be either dry experience precipitation of up to 50 precipitation fairly evenly October tends July the wet- are common so or cm. Muller (Wax et al. 1978) analyzed the atmospheric circulation of the Louisiana coast. Typically high pressure systems moving in from the north and west bring cool, dry air. They dre easily recog- nized during the winter as "cold fronts" but occur throughout the year. They are typically followed by atmospheric condi- tions that bring warm gulf air in from the coast, usually with heavy cloud cover and rain. About two-thirds of the coastal rainfall is associated with frontal activ- ity of this kind. During 1971-74 about 13 percent of the rainfall was from infre- quent, severe tropical storms and hurri- canes. EVAPOTRANSPIRATION Figure 7. Mean monthly air temperature at New Orleans, Louisiana (NCAA 1979). Figure 8. Generalized water budget for the Mississippi delta marshes. 10 5 E ■ DEFICIT LJ SURPLUS ,»». 5 E ^"^ 2 "> a o u a. Ill < B > a uj PE 'M '"^^1 , 1 rn r "1 I r J J A MONTH T~r Figure 9. Average water budget for the upper Barataria basin, 1914-1978 (Sklar 1983). P=precipi tation, PE=potential evapotranspiration, AE=actual evapotran- spiration. Evapotranspiration and rainfall sur- plus. The effect of precipitation depends not so much on the absolute amount but on the relationship between rainfall and evaporation from water and plant surfaces. Although apparently no one has recorded evapotranspiration directly in the delta marshes, water balances have been calcu- lated from equations developed by Thorn- thwaite and Mather (1955), These show that water surpluses occur during the winter months, but during the summer precipitation and evaporation tend to be fairly closely balanced, with occasional deficits in May through August (Figure 9). Annual rainfall surplus is about 60 cm along the northern edge of the delta marshes (Gagliano et al. 1973), decreas- ing to about 40 cm on the coast. This surplus is important in the total water balance of the marshes that includes riverine inputs and gulf marine water, as will be discussed in the following sections. Upstream freshwater inflows. The largest source of freshwater to delta marshes is the Mississippi River and its major distributary, the Atchafalaya River. The combined annual flow of these two rivers averages about 15,400 cumecs. The flow is strongly seasonal, peaking in late spring, fed by melting snow and spring rains in the upper Mississippi watershed (Figure 10). River flow can be nearly independent of local rainfall because of the size of the Mississippi River watershed, but often spring rains along the coast reinforce the river flow. The older basins of the delta are isolated from direct riverine input by natural and manmade levees. Therefore the rivers debouch through the Balize and Atchafalaya hydrologic units and in extreme floods through the Bonnet Carre control structure into Lake Pontchartrain. Their waters flow on out into the gulf and are carried westward along the coast, freshening the tidal water that moves in and out of the Barataria, Terrebonne, and Vermilion basins. Thus, while these three basins have almost no direct freshwater inflow except from local runoff, the salt marshes are never strongly saline because of the moderated salinities offshore. In addition to the Mississippi and Atchafalaya Rivers, smaller rivers also feed freshwater into the coastal marshes (Figure 10). The Pearl River delivers its water to the mouth of the Pontchartrain basin, freshening the Lake Borgne marshes and through tidal action the lower Lake Pontchartrain marshes. Other small rivers flow into the northern edge of Lake Pontchartrain. The other basins receive negligible stream flow, however, the interior marshes are maintained as fresh marshes by the precipitation surplus. Water fluxes in marshes are driven by the water differences across the estuary. change in three time scales: long seasonal, and daily. Since the reached its approximate present about 7,000 years ago, it has been relative to the land at a rate Marine processes delta level These term, ocean level rising measured in centimeters per century. The term "coastal submergence" is used to long-term process, which is to true sea- level rise but subsidence as discussed in section on geoiTiorphology. identify this due not only also to land the following In the last 20 years the rate of submergence has accelerated. Presently in delta marshes it averages about a 11 Mississippi Amife Tickfaw Pearl eo i \^[j^EP[MILIOli_.* , "^ ^T^Lwi, n I PONTCHARTRAIN. jATCHAFALAyA\ 1 G U i /^ MISSISSIPPI ,'^^v|R DELTA O F M £ X / C Figure 10. Freshwater inflows to the Mississippi Delta. (Oata from IJSGS 1978). Discharges are in cuinecs. All discharges are for water year 1978 except Mississippi River, which is a long-term mean representing the combined average annual discharge above the confluence of the lower Mississippi (10400 cumecs) and the Atchafalaya (5000 cumecs) Rivers. centimeter per year (Figure 11a). This is double the rate anywhere else along the eastern United States coast (Table 3). Superimposed on this long-term trend is a seasonal variation in mean water level that itself has an excursion of 20 - 25 cm. This bimodal variation (Figure lib) occurs consistently throughout the different salinity zones of the delta, with peaks in the spring and late sunmer. In the Barataria basin the spring maximum increases in an inland direction, that is from salt toward fresh marshes, possibly because of the considerable volume of surplus precipitation during this time of the year (Baumann 1980). The seasonal changes in water level are attributed to several interacting factors. Water level varies inversely with barometric pressure which averages 1,021 millibars (mb) during December and January and 1,015 mb during early summer and fall. Several investigations have shown that water level decreases nearly 1 cm for each mb increase in barometric pressure (e.g. Lisitzin and Pattullo 1951). Thus the expected mean seasonal range in water level as a response to barometric pressure is approximately 6 cm or 25 percent of the total observed range. In addition, the seasonal warming (expansion) and cooling (contraction) of nearshore waters contribute to a seasonal high in the late summer and a low in January and February. These astronomical events can be modeled and compared to the actual water levels. When this is done (Byrne et al. 1976) there is always a significant 12 residual which is presumably due to other forces and changes dramatically from year to year. Dominant among these other forces and responsible for the secondary maximum in spring and the following secondary minimun in mid-summer is the seasonally changing, dominant wind regime over the Gulf of Mexico (Chew 1962),. Maximum east and southeast winds in spring and fall result in an onshore transport of water. During winter and summer westerly winds (southwest in summer, northwest in winter) strengthen the Mexican Current and draw a return flow of water from the estuaries (Baumann 1980). Superimposed on the seasonal water level change is a diurnal tide averaging Airplane Lake 7 krti (fom GuH ' ' ' ' October 1972 Figure 11. marshes: a) daily. Water level trends in delta long term; b) seasonal; c) about 30 cm at the coast. Because of the broad, shallow expanse of the coastal estuaries, the tides attenuate in an inland direction. Figure lie shows how the normal tide range decreases from salt to freshwater marshes. In this example tides are still perceptible 50 km inland fran the tidal passes because of the extremely slight slope of the land. It would be misleading to infer that water levels slavishly follow predictable daily and seasonal cycles. In reality they are modified strongly by stochastic meteorologic events which set up or set down water in the bays and marshes. The effect is clearly shown in Figure lie, where gradually decreasing water levels associated with a "cold front" began on 12 October. Then the water levels suddenly rose on 19-22 October when the wind came around to the south. Typically, "cold fronts" moving across the coast lower water levels dramatically. "Warm fronts" with winds from the southern quadrant set up water in the estuaries. The magnitude of these wind effects is often 40-50 cm, which when combined with astronomic tides can result in water level shifts of over a meter within 12 hours. Table 3. Average coastal submergence on the U.S. east and gulf coasts (Bruun 1973 compiled by Hicks). Location Record yr Rate Eastport, Maine Portsmouth, N.H. Woods Hole, Mass. Newport , R. I. New London, Conn. New York, N.Y. Sandy Hook, N.J. Baltimore, Md. Washington, D.C. Portsmouth, Va. Charleston, S.C. Fort Pul aski , Ga. May port, Fla. Miami Beach, Fla. Pensacola, Fla. Eugene Island, La, Galveston, Tex. cm/yr 1930-1969 0.338 1927-1970 0.165 1933-1970 0.268 1931-1970 0.210 1939-1970 0.229 1893-1970 0.287 1933-1970 0.457 1903-1970 0.259 1932-1970 0.244 1936-1970 0.341 1922-1970 0.180 1936-1970 0.198 1929-1970 0.155 1932-1970 0.192 1924-1970 0.040 1040-1970 0.905 1909-1970 0.430 13 These meteorologically driven water level changes are common events. Tropical storms are much more unusual . When they occur water levels can be dramatically elevated. The water level height/fre- quency curve for Shell Beach, southeast of New Orleans (Figure 12), shows that wind tides as high as 3.5 m have been recorded, and l.S-m tides occur about once every eight years. On a coast with a slope of about n.2 mm/km (Byrne et al . 1976) a 1.5-m tide can cause flooding hundreds of kilometers inland. The ecological effects of such flooding can be dramatic. GEOLOGICAL PROCESSES The Mississippi River, the largest river systan in North America, drains an area of 3,344,560 km^ (Coleman 1976). The average discharge of the river at the delta apex is approximately 15,360 cimecs with a maximum and minimim of 57,900 and 2,830 cijmecs, respectively. Sediment discharge is generally about 2.4x10^^ kg annually. The sediments brought down by the river to the delta consist primarily of clay, silt, and sand. The sediments are 70 percent cl ay. The river has had a pronounced influence on the development of the northern Gulf of Mexico throughout a long period of geologic time. In the Tertiary Period (70 - 1 million years before the present) the large volumes of sediment < UJ CO z < > O CD < 100 50 OCCURRENCES/ 100 YEARS Figure 12. Tide levels at Shell Beach, in the Pontchartrain-Lake Borgne basin, associated with nine major storms (Wicker et al. 1982). brought down by the Mississippi River created a major sedimentary basin, and many of the subsurface deposits, especially those that formed in localized centers of deposition, have been prolific hydrocarbon-produci ng reservoi rs . In more recent geologic times, changing sea levels associated with the advance and retreat of inland glaciers during the Pleistocene Ice Ages have strongly influenced the sedimentary patterns off the coast. In order to understand the development of the present-day coastal wetlands it is necessary to view the progradation of the delta and its adjacent coastal plains in relationship to several time scales. These scales range from the long periods of geologic time associated with changing sea levels to the changes in the last 100 years in the patterns of minor subdeltas that foniied the most recent deltaic lobe, the Balize Delta. In addition, the heavy sediment load deposited by the river during the last several million years has caused excessive subsidence. This factor has to a large degree controlled the construction rate and the rate of coastal wetland loss throughout much of the recent geologic history. Pleistocene Sea Levels During the Pleistocene Epoch, some 1.8 - 2.5 million years long, sea level fluctuated several times. Most authorities agree on at least four major low sea-level stands and four or five high level stands. In addition to these major changes in sea level, numerous more rapid fluctuations took place. The minor changes in level undoubtedly affected the development of the delta marshes, but in the younger Pleistocene deposits it is extremely difficult to document the pre- cise changes. At the lower sea-level stands, the ocean surface was 150 - 200 m below its present level. During the higher stands water surfaces were slightly above or near present sea level. These fluctuations resulted in periodic valley cutting during the low stands and valley filling or terrace formation during the high sea-level stands. This concept is diagrammed in Figure 13. Fisk's 1944 paper should be consulted for details of 14 Figure 13. The relationship of glacial advance and retreat to continental shelf exposure and sedimentation during the Late Quarternary (after Fisk 1956). the relationship of sea level changes to delta and river valley response. In addition to causing cutting and valley filling, changes in sea level resulted in migration of the site of sediment deposition. During falling sea level, deposition shifted seaward, depositing deltaic sediments at or near the edge of the continental shelf. The progradation of the deltas seaward over thick sequences of shelf clays resulted in major sedimentary loading of the underlying clays, causing rap-id downbowing and subsidence. As sea level began to rise, the delta site shifted landward. expanses of coastal wetlands, some 50 - 60 percent larger than present-day wetlands, existed along the Louisiana coast. Borings along the present-day coastline and offshore often hit these buried freshwater marsh and swamp deposits. Warming of the Late Pleistocene climate returned polar meltwaters to the ocean basins, raised sea level, and progressively decreased the stream gradients and carrying capacities of the rivers. As a result, the channels filled and large expanses of coastal wetlands were buried beneath the present continental shelf. Sedi.nentation could not keep pace with the rising sea level and the rapid subsidence, and a series of deltas were left stranded on the present continental shelf. Seismic data and offshore foundation borings have been used to reconstruct the major deltaic lobes at various times during the last major rise of sea level. The positions of these lobes, shown in Figure 15 a through d, illustrate that at different times in the past the area of the coastal wetlands was governed by the locus of deposition of the major deltaic lobe. The presence of numerous delta lobes, now buried beneath the continental shelf deposits, points out the role that submergence plays in controlling the total area of coastal marshes. If submergence did not occur along the Louisiana coast, many of these older deltaic lobes would still be present, and the present-day coastal marshes would be much more extensive. The most recent cycle of sea- level lowering and subsequent rise to its present level began about 80,000 years ago (Fisk and McFarlan 1955). This Late Quaternary cycle began in response to cooling Pleistocene climates. Sea level was lowered approximately 150 - 170 m below its present level by withdrawal of water into the expanding Wisconsin-stage glaciers. Streams along the gulf coast and Mississippi River eroded extensive valleys across the shelf and dumped their sediment at or near the present-day shelf edge. The generalized locations of these river channels, now buried beneath the younger deltaic sediments, are shown in Figure 14. During this period large The latest phase of the Quaternary cycle, characterized by relative stability of climates and relatively small changes in sea level, began approximately 5,000 - 5,000 years ago. This sequence involves the modern delta cycles described by Fisk and McFarlan (1955) and Frazier (1967). Figure 16 illustrates the major Mississippi River delta lobes that have developed during this period. Although numerous, slightly differing terminologies have evolved to describe the individual delta systems and their ages, most authorities agree on at least seven delta lobes. The result of the building and subsequent abandonment of the Late Recent delta lobes was construction of a modern 15 deltaic coastal plain which has a total area of 28,568 km^ of which 23,900 km^ is exposed above the sea surface (subaerial) (Coleman 1976). In one of its earlier channels the river built the Sale-Cypremont Delta along the western flanks of the present Mississippi River Delta Plain. In approximately 1,200 years an extensive coastal marshland emerged before the river switched its course to another locus of deposition, the Cocodrie system. A similar sequence of events continued, and site of deposition was new del ta lobe began a buildout. This process each delta completing a with time this abandoned and a period of active has continued. cycle of progradation that requires approximately 1,000 - 1,500 years. Over approximately the last 500 years, the most recent delta cycle has formed the modern birdfoot or Balize Delta (Figure 16). The modern delta has nearly completed its progradation cycle, and in the recent past a new distributary, the Atchafalaya River, began tapping off a portion of the Mississippi River's water and sediment discharge. A new delta is beginning its progradational phase (Van Heerden and Roberts 1980; Wells et al. 1982). In each progradational phase of the delta cycle, broad coastal marshes are constructed. Scruton (1960) referred to this as the constructional phase. However, once the river begins to abandon its major deposition site, the unconsoli- dated mass of deltaic sediments is immedi- ately subjected to marine reworking pro- cesses and subsidence. Waves and coastal currents, and subsidence result in pro- gressive inundation of the marshes, and within a few thousand years the delta lobe Figure 14. Location of major buried river channels fomied during the Wisconsin glacial period (after Fisk 1954). 16 Figure 15. The position of major delta lobes on the gulf coast during the previous 25,000 years. (A) Late Wisconsin, 25,000 - 20,000 yr B. P. (B) Late Wisconsin, 15,000 yr B. P. (C) Early Holocene, 12,000 - 10,000 yr B. P. (0) Present, 5,000 - 1,000 yr B. P. SL = relative sea level. has sunk beneath the marine waters. Scruton (1960) referred to this stage of the delta cycle as the destructional phase. Thus, in a relatively short period of geologic time both land gain and land loss occur, a function of the stage of the normal delta cycle. The initial phase of delta progradation is characterized by formation of coastal marshes associated with the advancing delta.^ Coastal marshes deteriorate when a delta lobe is aban- doned, and a new delta cycle begins else- where. Figure 17, a satellite image of the eastern portion of the Mississippi Delta Plain, shows several delta lobes in different stages of construction and destruction. The oldest shown on this image is the St. Bernard Delta, a delta lobe that was actively prograding some 3,000 years before present. This delta lobe remained active for approximately 1,200 years, forming a broad, coastal marshland along the eastern deltaic plain. Approximately 1,800 years ago, the Lafourche channel began its progradation. In the St. Bernard Delta, deprived of its sediment load, marine processes and subsidence (primarily compaction) became dominant. The Lafourche distributary gradually increased its sediment yield and within 1,000 years built out a major delta lobe west of the modern or Balize Delta. During this time the St. Bernard Delta continued to be dominated by marine processes and subsidence. Marine waters began to intrude into the formerly fresh- water marshes, and marshland deterioration 17 Figure 16. Deltaic lobes of Mississippi River deltas (modified from Kolb and Van Lopik 1958). increased rapidly. Initially the interior marshes deteriorated, and the coastal barrier islands were attached to the ends of the fonner distributaries. Eventually the Lafourche Delta system reached its maximum development and the modern delta lobes (Plaqueinine and Balize) began their progradation. The Lafourche Delta was then subjected to marine reworking and compaction. During the past 800 or so years subsidence in the St. Bernard Delta has reached a stage in which little or no freshwater marshes exist, and the reworked barrier islands have been sepa- rated from the mainland. During this same period the Lafourche Delta has lost land, mainly by saltwater intrusion and opening of the marshland behind a coastal barrier still attached to the fonner distributar- ies. Meanwhile, in the modern Balize Delta the river has constructed a major delta lobe. The river would abandon this lobe in favor of the Atchafalaya River course if manmade river control structures at Simmesport did not limit diversion to about one-third of the Mississippi River's discharge. Even with this limited flow the modern Atchafalaya River will continue to build its delta onto the continental shelf for the next several hundred years. Modern Mississippi Delta The modern Balize Delta has been constructed during the past 500 years. Because it is relatively young, it offers an opportunity to evaluate the short-term processes responsible for delta building and deterioration. When a break (or crevasse) occurs in the levee of one of the river distributaries, water rushing through the break deposits sediment in the adjacent bay. These bay fill deposits form the major coastal marshes of the subaerial delta. Figure 18 illustrates the bay fill sequences within the modern delta during the past few hundred years. Of the six crevasses shown, four have been 18 dated historically, developnent can be maps. and much traced by of their historic After an initial break in the levee of a major distributary during flood stage, flow through the crevasse gradually increases through successive floods, reaches a peak of maximum deposition, wanes, and is cut off (Coleman 1976). As a result of compaction, the crevasse system is inundated by marine waters and reverts to a bay environment, thus com- pleting its sedimentary cycle. These crevasse systems are similar to the larger delta lobes but develop faster so that the details of the processes responsible for their fomnation can be adequately evalu- ated. New Orleans . Bernard delta Belize delta Figure 17. Satellite image of the Mississippi Delta Region showing delta lobes of different ages (NASA photograph 1973). 19 MODERN MISSISSIPPI RIVER SUBDELTAS A Dry Cypress Bayou Complex B Grand Liord Complex C West Boy Complex r- ,- D Cubits Gap Complex i-- _ j^ ^.)i£^\?' E Baplisle Collette Complex '^i?^ 1 i^f*''«'"s*>,j/~F ^Garden Island Bay Compli ^10?/r u Sect CSI LSU Figure 18. Six subdeltas of the modern Mississippi Balize Delta recognized from maps and sediment analysis. Dates indicate year of crevasse opening (Wells et al. 1982). In cross section, the prodel ta clays constitute the base of the sequence (Figure 19b). The lowermost clay marks the first introduction of sediment into the bay. Above the prodel ta clays are the coarser-grained silts and sands that form the delta front environment. These sandy deposits are laid down immediately in front of the advancing river mouth. Once active sedimentation ceases in the crevasse system, compaction and retreat dominate. For a time marsh growth can keep pace with compaction, but eventually large bays tend to develop, and the shoreline retreats rapidly. Small beaches accumulate near the major distributaries where coarser-grained sediment is available for reworking. Oyster reefs may find a foothold along the old channel margins of the submerged levee ridges . Historic maps of one of these crevasses, Cubits Gap, can be used to illustrate a cycle of delta building and abandonment. Figure 20 shows the sequential development of the Cubits Gap crevasse. The 1838 map was surveyed prior to the break and shows a narrow, natural levee separating the Mississippi River from the shallow Bay Rondo. The idealized sequence is shown in the plan view in Figure 19. The crevasse initiates as a break in the major distrib- utary levee in the vicinity of point A. During the early formative years coarse- grained sediments are deposited in the immediate vicinity of the break. With time new channels fonn, bifurcate and reunite, forming an intricate pattern of distributaries. Later, some distributar- ies are abandoned and become inactive. When a systematic channel pattern develops, the bay fill front advances rapidly into the bay, resulting in the deposition of a sheet of relatively coarse sediment thickening locally near the channels. Seaward of the active channel mouths, fine-grained sediments settle out in deposits commonly referred to as prodel ta clays. Other parts of the crevasse system which have been abandoned or dre deprived of a continuing sediment supply compact rapidly, and many areas tend to open up and revert to shallow marine bays . In 1862 a ditch excavated by the daughters of an oyster fishennan na:;ied Cubit to allow passage by shallow draft boats caused the crevasse break. The original ditch was about 120 m wide; the flood of 1862 enlarged the opening, and by 1868 the the break was 740 m wide. By 1834 the map shows the initial buildout of a complex series of distributary channels that had deposited relatively coarse sediment near the break. Note also the shoaling in the bay caused by subaqueous deposition of the finer-grained deposits. The map of 1905 shows that many of the major distributaries had developed and that rapid progradation had taken place in the 11-year period since 1884. A major portion of the crevasse had been constructed by 1922; some small bays were already beginning to open up, indicating that some parts of the crevasse system were being deprived of sediments. The 1946 map shows that sedimentation was 2U V^-^-riy^^ Bay (s' t Carlo Secl.i j;.;:n;;ii;;n;U2Hnin;;::;;;;;:;;:;i;;;;H;H;;;;H;H;;;;;::; SHALLOW -^ MARINE Oyster Reefx Beach Sea Level -i:r^^^^Carto Sect .CSI.LSU- Figure 19. Plan view and cross sections through A-A' and B-B' of environments of deposition in a crevasse (after Coleman and Gagliano 1964). 21 Figure 20. al. 1982). Sequential development of Cubits Gap subdelta (Wells et 22 primarily taking place at the seaward ends of selected distributaries and that marshland loss was beginning to take place. By 1971 a large part of the crevasse system was being inundated by marine waters, and marsh loss was becoming significant. The only deposition was at the seaward ends of some of the distributaries and subaqueously in the bay fill front. Note that land loss begins first near the crevasse break. Here sedimentation is extremely slow, depending only on overbank flooding, whereas higher sedimentation rates are still prevailing near the distal parts of the crevasse system. Figure 21 illustrates the crevasse growth and deterioration. Figure 22 shows on a single plot the cyclic nature of four of the Mississippi River crevasses; each cycle consisted of growth followed by deterioration. Projection of the present-day trends indicates a life cycle for a crevasse system that lasts 115 - 175 years. KO A CUBITS GAP Jt ' 175 /^\ ^M ■ 150 / '-\' 125 ■ ^' Volume *. p too /j \ / 75 50 25 ■s. ai o 1 • 1 o 1 > 1 u 1 #' y J Arso . 0 • l, » 4D 1 i OB o CD s 1900 1910 1920 1930 1940 1950 o % 10 Growth rates during progradation ranged from 0.8 kmVyr to 2,7 kmVyr. Degradation rates averaged from 1.0 to 4.1 kmVyr. This growth and deterioration cycle of bay fills, although representing a relatively short time period, is similar to the cycle of major delta lobes de- scribed earlier. The delta cycle is on a much longer time scale - a growth period that approaches 800 - 1,000 years and a deterioration period that can be as long as 2,000 years. These bay fills provide an excellent model for evaluation of the future growth of the newly formed Atchafalaya Delta (Wells et al. 1982) and for the deterioration of the former Mississippi River delta lobes. The composite curve in Figure 22 shows a peak in the early 1940' s, followed by a rapid loss of marshes that continues, with a tenporary reversal during the flood years of the 1970' s, to the present. The rapid degradation of this delta lobe, even though river flow has been maintained, is not well understood. In the Mississippi River Deltaic Plain as a whole the same rapid marsh loss is found. This is more understandable since, with the exception of the Atchafalaya Delta, the other hydro! ogic units are all abandoned, degrading lobes. Across the delta the marsh loss rates have been accelerating rapidly during this century to the present rate of 1.5 percent per year or about 100 km^/year (Gagliano et al . 1981; Figure 23, 24). This rapid degradation rate is cause for considerable alarm. Strong evidence supports the contention by many that superimposed on the natural processes described in this newer changes, both natural that are strongly affecting marshes today. These changes 1 ocal to global . geomorphic section are and human, the coastal range from Figure 21. Linear, areal , and volume growth curves for the Cubits Gap subdelta (Wells et al. 1982). At the global scale the rate of sea-level rise has accelerated in recent years, as has been discussed (Figure 11). The acceleration has been imputed to the increase in the atmosphere's carbon dioxide resulting from burning fossil fuels and clearing forests. Increased carbon dioxide in turn creates a 23 1800 1820 1840 1860 1880 1900 Date 1920 1940 1960 1980 Figure 22. Composite subaerial growth curve, Mississippi River subdeltas. Total subaerial land determined from averages at 10-yr internals (Wells et al, 1982). "greenhouse" effect that is wanning the earth's surface and melting the polar ice caps. The net affect of both true sea- level rise and coastal subsidence has been a change in the coastal submergence rate from about 0.27 cm/yr during 1948 to 1959, to nearly 1.3 on/yr between 1959 and 1971. Although these data are for a gauge at 1.5 1 25- 1 0- 0-5 Years spanned by estimate Midpoint Reference 1 Adams et at 1976 20ozier 1983 3Gaqliano f. Van Beck 1970 1 940 YEAR Figure 23. The accelerating wetland loss rate in the Mississippi Delta (based on data from Dozier 1983). Bayou Rigaud in the Barataria basin, the trend is similar along the whole Louisiana coast (Gosselink et al . 1979). In order to remain at intertidal elevations marshes must accrete vertically as rapidly as they are sinking. The rapid rate of marsh degradation indicates that they are not doing so, an observation supported by recent research (Delaune et al. 1983). One reason is that the Mississippi River no longer supplies as much sediment to the coast as it has historically. Keown et al . (1980) reported that sediment supplies are only about 60 percent of what they used to be, despite the presumed increase in erosion that accompanies forest clearing on the upper watershed. The reduction is presumably due to the construction of dams on the upper reaches of the river and its tributaries. The dams also remove the coarser sediments selectively, so that the sediments reaching the coast are depleted of the sand that is the main foundation material for delta growth. This means that the river can no longer support as 24 Figure 24. Computerized re-creation of the west side of Barataria Bay showing the change in wetlands between 1945 (a) and 1980 (b). Black is open water; marshes are shown as varying shades of grey (Dozier 1983). large a delta as it has historically. In addition, channel ing and leveeing the river entrains much of the sediment, preventing spring overbank flooding that nourishes the interdistributary marshes . There is now strong evidence that the rate of marsh loss is being accelerated by local human activities in addition to the reduction in the river's sediment load. Canals are the major culprit in this scenario. Formerly, rain runoff from adjacent uplands flowed across wetlands, dropping its load of sediment and nourishing the marshes. Now a network of drainage canals along the marsh-upland interfaces of the delta estuaries carries this runoff directly into estuarine lakes and bays, bypassing the swamps and marshes (Conner and Day 1982). If runoff flowed across the wetlands, the trapped sediment would help minimize wetland subsidence and the quality of the runoff water would be improved before it entered the lakes and bays. Instead, the portions of the estuaries near urban areas are becoming increasingly turbid and eutrophic (Craig et al. 1977). At the other end of the estuary, navigation canals, especially those that cross the barrier islands, cause major disruption of circulation. The canals are straight and deep in estuaries that have an average depth of only 1 or 2 m. There- fore they capture flow from smaller 25 channels and allow the intrusion of salt water deep into the estuary. Saltwater accelerates the conversion of fresh and intermediate marshes to saline marshes. When increases are sudden, sal t-intolerant vegetation can be killed, and the marsh may erode before other vegetation can be established. There is also some suggestion that the biochemistry of marsh sediments changes with salinity, making the marsh more vulnerable to erosion (Dozier 1983). A network of medium-sized canals that are dredged for access to oil and gas well sites is linking the navigation canals to the inner marsh and to the flood drainage canals. These canals are extensive; their impacts are multiple. The canals themselves act like the navigation canals and, in combination with them, change circulation patterns extensively. For example, in the Leeville oilfield (Terrebonne basin) the density of natural channels declined as dredged channels captured the flow of water (R. E. Turner, LSU Center for Wetland Resources; pers. comm.). These canals also allow salt intrusion. Their spoil banks block the flow of water across marshes, depriving them of sediments and nutrients. This is especially noticeable where canals intersect and their spoil banks interlock to impound or partially impound an area. The effect has not been rigorously quantified, but aerial photographs showing the loss of marsh in these semi-impounded areas are too striking to ignore. Analysis of marsh loss rates between 1955 and 1978 (mapped by Wicker 1980) shows a direct linear relationship between canal density and the marsh loss rate (Turner et al . 1982). The rate of loss per unit of canal is higher in recently formed deltas where the sediments are less consolidated than in older deltas (Oeegan et al. 1983). It seems to be maximum where fresh marshes are experiencing salt intrusion (Dozier 1983). Turner et al. (1982) found that the intercept of the regression of marsh loss on canal density (that is where canal density is zero) was always less than 10 percent of the total loss and usually nearly zero. This Table 4. Land-use changes along the northwest edge of the Barataria basin, on the Bayou Lafourche natural levee (Dozier 1983). a. Change in developed land Year Developed Rate of land area increase 1945 1955 1969 1980 (ki) 19.27 20.80 39.41 71.69 (km /yr) 0.13 1.43 2.93 b. Loss of marsh to indicated category, 1945-80 Area Marsh loss To canal To development To open water (km) 39 52.4 127.6 (percent) 5 8.2 20 Total to nonmarsh 218 34 indicates that nearly all the loss can be attributed to canals. The direct impact of canals (the area they occupy) is less than 10 percent of the total loss. If the spoil area is taken to be three to five times the canal area (Johnson and Gosselink 1982), the direct loss of marsh due to canals is less than 50 percent of the total loss. The rest is attributed to indirect effects of circulation disruption by the canal and its spoil. An independent, lesser source of marsh loss is direct impoundment and drainage for agriculture or other develop- ment. Several large reclamation projects were initiated early in the century. Most of these were destroyed by floods like the one in 1927 and now appear as large, square lakes in the coastal zone. How- ever, reclamation along the natural levees is proceeding apace, as is shown for the Bayou Lafourche levee on the northwestern side of Barataria basin (Table 4). Over the region as a whole, especially in the urban areas, agricultural land has been converted to urban and industrial use without a large net reclamation of new marsh (Table 5). 26 Table 5. Land use changes, in hectares, in the Mississippi Delta, 1955-73 (Wicker et al , 1980a). Unit Urban/ 1955 industrial 1978 area Change Aqricul tural area Net change 1955 1978 Chanqe I 27,987 55,116 27,129 45,008 23,949 -21,059 6,070 II 1,979 2,058 79 37 81 44 123 III 8,279 19,622 11,343 13,772 14,118 346 11,589 IV 1,278 2,680 1,402 5,100 6,639 1,539 2,941 V 387 575 188 742 1,043 301 489 VI 2,145 4,364 2,219 41,366 40,772 -594 1,625 Total 22,937 27 CHAPTER TWO TEMPORAL AND SPATIAL GRADIENTS IN DELTA MARSHES The ecology of a marsh is determined by the biota as constrained by the regional geologic platform on which it develops, and by the water regime. These create physical gradients that are closely related to variations across the delta in marsh vegetation, fauna and ecological processes. Furthermore, in the Mississippi Delta geologic processes are so rapid that the platform cannot be assumed to be constant in the time scale of human generations . As we have seen, a typical delta lobe has a life cycle of about 5,000 years. But the accretionary phase is \/ery rapid. Wells et al. (1982) showed subdelta cycles in the modern birds foot delta of 115 - 175 years. In the Atchafalaya Delta about 20 km^ of new land has appeared since 1973. And with current subsidence rates of about 1 cm/yr even the destrjctional phase of a delta is rapid; marsh degradation to open water is occurring at a net rate of about 75 km^/yr for the deltaic plain as a whole. As a result, the spatial gradients are not constant but vary with the age of the delta lobe. In this chapter we will consider the spatial and temporal gradients of Mississippi delta marshes, particularly as they control the physical substrate, water and water chemistry, and vegetation. TEMPORAL GRADIENTS Gagliano and Van Beek (1975) suggested that the geologic cycle of delta growth, abandonment, and destruction is paralleled by a cycle of biological productivity. The biotic cycle lags the geologic one so that peak productivity occurs during the delta lobe's destructional phase (Figure 25). In order to throw some further light on this interesting hypothesis, i t is pertinent to describe the way marshes develop in the context of whole basin systems. To do this, ! have used data from the delta hydrologic units, arranged by age to get an instant snapshot of a basin's development over time. This approach is not ideal. The hydrologic units are i nterdistributary, except for the active deltas, and thus represent the active sedimentation of more than one river distributary. For exa^nple, the west side of the Sarataria basin was formed when the Lafourche distributary was active; the east side is strongly influenced by recent Mississippi River sediments. However, biological data have, in general, been collected by hydrologic unit, and a rough tine sequence of six units can be identified, ranging from modern to about 5,000 years old. When a delta lobe first begins to form, it is overwhelmingly riverine. The mineral sediment load is high, and water is fresh. As a result, the newly emerged sediments are mineral, and the first marshes to appear are fresh (Figures 25 and 27). As the delta grows, the fresh marshes expand. As described in Chapter 1, the expansion is not uniform; as subdeltas are cut off from stream flow, they become more and more influenced by marine tidal waters. Consequently, sal ini ty increases, and brackish and saline marshes begin to appear. When the river diverts to another delta site, the periphery of the abandoned 28 BIOLOGICAL PRODUCTIVITY AS A FUNCTION OF THE DELTA CYCLE SALINITY SUBAERIAL DEVELOPMENT LENGTH OF LAND - WATER INTERFACE BIOLOGICAL PRODUCTIVITY © Maringouin /?\ ^ ^ . (3) St. Bernard (D Teche W Lafourche ©Plaquemines High (0 UJ z - 2 UJ = a ± o Low Marine ^XD> Subaqueous Growth NATURAL ENVIRONMENTS OPEN BAY SUBAQUEOUS LEVEES MUDFLATS FRESH MARSH BRACKISH MARSH SALINE MARSH SWAMP LAKES OYSTER REEFS MARGINAL BEACHES BARRIER ISLANDS Rapid Subaerial Growth Time Span Deterioration Figure 25. Environmental Van Beek 1975). succession of an idealized delta cycle (fiagliano and delta becomes saline and is modified by marine processes which typically rework the delta edge into a series of barrier reefs and islands that protect the inner estuary. Riverine hydraulic energy is much reduced and sediment loads decline. Further marsh development is increasingly controlled by the productivity of the vegetation, which forms peat. This is especially true at the landward edge of the basin. Here, too far from the coast to experience much tidal activity and with the river's sediment supply cut off, organic material produced in situ is the only material available for marsh accretion. Thus, as Figure 26 shows, fresh marshes start out as highly mineral, but as the delta lobe ages become increasingly organic. Salt marsh sediments, subject turbid tidal washes, are high in mineral content. to frequent, always fairly The general sequence is clear in the figure, but some exceptions deserve com- ment. Sediment mineral content decreases with distance from the river source (that is, from fresh toward salt marshes) in active deltas (units II and V) but de- creases with distance from the marine sediment source in the abandoned basins. This trend is consistent in all basins. However, compared to the low mineral contents in the recently abandoned basins III and IV, marshes of the older basins I and VI have relatively high mineral con- centrations. This probably reflects the continued sediment- laden freshwater input into these systems. 29 INCREASING AGE ^ PONCHARTRAIN L BORGNE VI VERMILION FRESH INTERMEDIATE ^""'j BRACKISH SAl I Mineral order of Figure 26. arranged in PERCENT MINERAL CONTENT content of marsh soils increasing age (data from 100 50 0 in Mississippi Chabreck 1972). delta hydro! ogic units. The Ponchartrain-Lake Borgne basin (Unit I) is fed by a number of small, local streams, by the Pearl River, and periodically by diversion of the Missis- sippi River through the Bonnet Carre '■'-- ■■ ^'-" The Vermil ion The Pontchartrain-Lake Borgne unit is exceptional in that the mean salinity is high, but so is the proportion of fresh marshes. This may be a result of the physiography of the system. The gradient is compressed into the lower half of the basin by the location of the mouth of the Pearl River, the primary freshwater source, and by the small passes into Lake Pontchartrain which restrain free flow of saline water into the lake. Within a hydrologic unit of constant size, wetland area and land:water ratio a a > I- <0 O in #100- X (0 K < (A III i INCREASING »Gg> J V II ATCHAF- MIS8.R. ALAVA DELTA III BARA- TARIA IV I TERRE- PONT- BONE CHAR- TRAIN VI VER- MILION Figure 27. Marsh soil salinity and percent fresh marsh in Mississippi Delta marshes by hydrologic unit, arranged in order of increasing age. Soil salinity is a mean for the whole basin weighted by area of each marsh zone. The fresh marsh is percent of total marsh area (data from Chabreck 1972). 30 increase during active delta growth to a inaxiinuin when the distributary is abandoned, and then decrease as marshes subside and degrade back to open water bodies. The length of the interface between the marsh and adjoining water bodies (the marsh edge) is small in young delta lobes because the new marsh is fairly solid. After abandonment, however, the marsh edge increases as marshes open up and more and more tidal streams interfinger through them. This is reflected in the ratio of marsh edge length to marsh area (m/m^) in different marsh zones. There are no measurements of this ratio available for the delta, but in the neighboring chenier plain's fairly solid fresh and intenriedi- ate marshes the ratio is 15 and 17, respectively. As tidal energy increases, the ratio increases to 39 in brackish marshes and 50 in salt marshes (Gosselink et al. 1979). Applying these ratios to the delta hydrologic units, the mean edge length per unit area of marsh, weighted for the area of different marsh zones in a hydrologic unit, increases with the age of the unit (Figure 28). However, because younger units have more marsh, the total length of the marsh edge (the product of the ratio and the marsh area) is greatest in the recently abandoned Barataria and Terrebonne units (III and IV, Figure 28). "e 1'° -•o 0 y A X Lenglh -»/ \ I / \ tn E \ c , \ < \ 3 30 -115 ~ »a \ u. O \ O Z m V < _i \ UJ * q: UJ Length , / A < 20 -O10 Area \ o 1 \ I LU 1 \ t- 1 \ O -I 1 \ z < 1 ■v lU 1- ^ -■ 10 o t- - 1 u : o t o 1 UJ cC ^x^-- J X^X S \\\^ s f^ =^ \'\'; . s^ \\\V rs^J n\\V V II III IV I VI HYDROLOGIC UNIT Figure 28. Marsh edge length:area ratio and total marsh edge length for delta hydrologic units. The units are arranged in order of increasing age (data from Chabreck 1972). How are these differences in the physical characteristics of hydrologic units related to biological productivity? Two measures of productivity d.rQ net primary production and the inshore shrimp harvest (Figure 29). Total net productiv- ity is lowest in the active deltas and highest in the Pontchartrain hydrologic unit - mostly a function of the size of the unit. Primary production per unit area, however, is highest in the Barataria and Terrebonne basins. Inshore shrimp yield is also highest in the same basins. Since these basins are in the early destructional phase, these data support the hypothesis of Gagliano and Van Beek (1975). Regressions of biological productiv- ity on salinity, marsh area, and edge length (Table 6) should be taken with caution because they are based on data from only six hydrologic jnits. Neverthe- less, they make for interesting specu- lation. Average net primary production o crnoo D O O - Px a - 3 r E O __ Whif Sttrlmp V II III IV I VI NET PRIMARY PRODUCTION V Hill IV I VI NET PRIMARY PRODUCTION/m' II iiirv I VI INSHORE SHRIMP CATCH 1955-74 Figure 29. Net primary production and fishery yield of Mississippi River Deltaic Plain hydrologic units. Production calculated fran average production of each habitat type and its area in the hydro- logic unit. Shrimp data from Barrett and Gillespie (1975). Basins are, in order of increasing age: I - Pontchartrain-Lake Borgne, II - Balize, III - Barataria, IV - Terrebonne, V - Atchafalaya, VI - Verm il ion. 31 Table 5. Regression analyses relating net primary production (NPP) and inshore shrinp production (1955-74) in hydrologic units to various physical parameters. NPP was calcu- lated from the mean productivity and area of each habitat type (Costanza et al . 19S3). Shrimp catch is from Barrett and Gillespie (1975). R is the proportion of the varia- bility in the dependent variable accounted for by variations in the independent vari- able. Independent variabl e Dependent variable NPP NPP/area Shrimp catch Equation R Equation R Equation R Total unit area Y=1.22E5X+0.5 0.96 Not computed Y=0.2E5X+2.4 0.09 Total marsh area Y=4.4E5X+0.92 0.72 Y=0.02X+318 0.20 Y=1.04E5X+0.22 0.76 Marsh/total area Not computed Y=17.2X+881 0.98 Not computed Total brackish & sa It Y=0.1E5X+1.4 0.79 Not computed Y=1.6E5X-0.01 0.58 Marsh edge length Y=1.16X+1.2 0.83 Not computed Y=0.285X-13 0.75 Edge length/area Y=0.41X-6.5 0.77 Not computed -- 0.01 Mean sal inity Y=1.57X-1.02 0.85 Y=37.5X+1150 0.18 -- 0.01 NPP Not computed Y=0.25X+1.7 0.20 per unit area is very closely related to the proportion of marsh in the unit because -narsh productivity is higher than aquatic productivity; therefore, average productivity increases with the proportion of marsh. Total net primary production is, as might be expected, closely related to the total area of the hydrologic unit. In contrast, inshore shrimp catch, which in these estuaries is quite a good index of total shrimp yield (R. Condrey, LSU Center for Wetland Resources; pers. comm. ) , is poorly related to most single factors in the analysis. This may be because of the animal's complex migratory life history. For example, shrimp yield is not related to total hydrologic unit area, nor to total net primary production. The best relationship is to the marsh area and to the total marsh edge length in the unit. This suggests that accessibility to the marsh and marsh refugia are important fishery productivity, indicated by the marsh area ratio) increases the del ta lobe . Si nee marsh area decreases as the delta de- grades, the total accessible marsh is maximum in the early destructional geo- logic phase. These tentative correlations between marsh edge length and fisheries productiv- components of Accessibility (as edge length:marsh with the age of ity need to be verified with additional research, but the implications are inter- esting and important. First, they support Gagliano and Van Beek's hypothesis and provide a reason why biological productiv- ity peaks in degrading basins. Second, if the hypothesis is correct, it has significant implications for the future of Louisiana fisheries. We are currently enjoying the results of past delta building by the Mississippi River. Modifications of the river have signifi- cantly affected its ability to build new wetlands. As a result we are not now producing the geological resource for our future fisheries. If there is a signif- icant lag time before new delta growth can support efficient fishery production, we can not afford to wait until the present bounty disappears before encouraging new delta fonnation. SPATIAL GRADIENTS Within any delta basin a spatial gradient is set up by the land's slope and by the source and magnitude of freshwater compared to marine water inflow. In the Barataria basin the mean water slope from the coast to the swamp forests 80 km inland is about 2 mm/km (Byrne et al . 1976). Since coastal marsh elevations approximate the local mean water level 32 (Sasser 1977; Baumann 1980), the land slope is also exceedingly snail. The slope of the water is slightly steeper in the Atchafalaya basin because of the enormous river inflow. Generally, across the coast it is so slight that "downhill" changes daily, depending on the astronomical tide stage, wind direction and strength, rain- fall, local runoff, and river flow. On a smaller scale of meters rather than kilometers, a slope also exists on the marsh surface from the edge of tidal streams inland. Water overflowing stream banks on flood tides slows and drops much of its sediment load near the stream edge as it moves inland, creating a slight crest or levee next to the stream. Because of this, water tends to drain away fran streams into small marsh chan- nels that eventually carry the water back through the natural levee. The natural creekbank levee, which is usually measured in centimeters, and the slight marsh sur- face slope are enough to create a gradient of inundation, water chemistry and biotic activity. These hydraul ical ly mediated gradients dre responsible for much of the observed biotic diversity in the delta marshes. F1 ooding Information on the frequency and duration of marsh flooding is rather scarce. Sasser (1977) and Baumann (1980) measured marsh elevations relative to local mean water levels and calculated inundation statistics for a number of different species and associations from nearby tide gauge records. Byrne et al. (1976) plotted frequency and duration of flooding at locations in the Barataria basin corresponding to salt, brackish and fresh marshes. They did not measure the elevation of any marshes relative to these data. However, by interpolating Sasser's elevations on the graphs by Byrne et al . it is possible to come up with several estimates of marsh inundation (Table 7). Considering the variability in these estimates, it appears that the total duration of flooding during the year is about constant across the whole marsh from coast to upland. But the regular, daily tidal flushing of the salt marsh is replaced by a more infrequent flooding inland where wind tides and upstream runoff play a much larger role. The delta marshes appear to be flooded about 50 per- cent of the time. The average duration of a flooding increases from 12 to 16 hours at the coast to almost 5 days in fresh marshes. Notice that the streamside marsh, some 10 - 15 an above the inland marsh, is inundated almost as often but for much shorter time periods, so that it is flooded only about 12 percent of the year. Baumann (1980) showed that inundation characteristics are not constant throughout the year (Figure 30). Flooding frequency does not vary much, but because the water level varies seasonally, the Table 7. The annual duration and frequency of inundation of marshes in the Barataria basin, Louisiana. Figures in parentheses indicate the percentage of the year inundated. Marsh zone Reference Duration Frequency Duration/event (hr/yr) (No. /.yr) (hr) Sal t (inland) Baumann 1980 4396 (50) 263 15 Byrne et al. 1976 4400 (50) 200 22 Sasser 1977 4100 (47) 150 27 (streamside) Byrne et al. 1976 1050 (12) 160 6.6 Brackish Byrne et al . 1976 3700 (42) 75 50 Sasser 1977 3500 (40) 125 28 Intermediate Sasser 1977 2300 (26) 32 29 Fresh Byrne et al . 1976 3700 (42) 32 115 Spartina patens and Sagittaria falcata association. 33 80- 60- 40 20- 0 40 Frequency % Time / '*> 1 — I — I — r J F M A — I — r MONTHS -I — r A S 1 — I — r O N D Figure 30. Seasonal salt marsh inundation patterns (Baumann 1980). also varies. duration of October when During this inundated more water depth over the marsh There is a sharp peak in flooding in September and water levels are highest, time the salt marshes are than 80 percent of the time Soil s As discussed in the previous section on changes in an aging delta lobe, the mineral content of marsh soil is directly related to the hydraulic energy of the system. In abandoned interdistributary environments this means that sediment delivery to the marsh decreases inland coast (Units III, IV, I, and VI 26) and also into the marsh from of local tidal streams (Figure frail the in Figure the edge 31). According to Baumann (1980), most of the sediment is deposited during frequent winter storms and rare summer tropical disturbances, probably by redistribution of sediment from bay bottoms (Figure 32). As expected, the sediment size fraction also varies with the hydraulic energy. There is hardly any sand in delta marshes, but the fraction of clays increases inland with decreasing hydraulic energy (Gosselink et al . 1977). Rates of sediment rather well known, both (Cs) profiles and from laid down on the surface time (Hatton 1981, Table deposition are from ^" Cesium marker horizons and tracked over 8). Streams ide 5 0 o o < o (O *-> (11 c ■n o •f— m +-> c- lO m s- +-> (/) c O) -1 o o c _1 n <_) c •'~ 0) CT' \n Lo CVJ -- CO ro cni CNJ .— . — ' ,— . + 1 +1 +1 +1 cT' \r> 1— < en -"■ cr LO rj Ln cr> r— ro ("-1 u- r- a- ui- O CC CC r^ CC •^ cr oc c O ^ t^ \C o o + 1 +1 o o +1 *l CM CD CO c^ ^ -"d- cr. CO -"d- -X- (NJ KO CO -^ UD r~- KO KO *d- 'JD U-. O ro o O f" cr T, T? CO ** +1 ^ cr Lo u:) LT* LT) CO CC CC CC CM ro +1 +1 CO ^ o o +1 +1 C^J CD CO CO ■— 1^ E --- cr o CM LT) ■«3- «3- en CJO m o cn o ro CM CVJ ^ ^ ^ -Xi cn -x s* + 1 +1 +1 CVl 'a- + 1 LT) r- CM «d- CO OJ en CVJ CO CSV CM CVJ CN( ^ "^ ..^ O o *3- O o CVJ o O O 5 cr O o +1 o O CO o +1 CO o o CVJ O o o-i cr> CM CM- o o o o o o c o 1- o CO o +1 en o o lO o +t m CD O "3- O + 1 cr- LO «3- o ^ o r-. o ^ o ^ o in o ^■8 35 10 20 30 DISTANCE FROM GULF (km) in free soil chenier plain from the gul f Figure 33. The decrease water salinity (mg/g) of marshes with distance (km) (Rainey 1979). Soil Nutrients The nutrient content of delta marshes is quite well known from a comprehensive set of surface sediment samples taken across the whole coast by R. H. Chabreck, LSU, in 1968 and analyzed by Brupbacker et al. (1973). Rainey (1979) used the same data set to draw a number of conclusions about the factors controlling sediment nutrient concentrations. Because the density of marsh soils varied from 0.05 to 0.97 in Chabreck's data set, a 20-fold range, Rainey converted all nutrient con- centrations to a volumetric basis as recommended by Boelter and Blake (1954), Clarke and Hannon (1967), and Mehl ich (1972, 1973). When analyzed on a volumetric basis (dry mass/volume wet soil), the distribu- tion of nutrients across the marshes falls into a predictable pattern. As one would expect, the soluble ions associated with sea water [sodium {Ha), chloride (CI), potassium (K), magnesium (Mg), and total soluble salts] are closely controlled by the surface water salinity (Table 10). This is also shown in Table 11, which compares the ratio of soluble nutrients to chloride in seawater and in the different marsh zones. Sodium, K, and Mg ratios in the marsh are never more than twice the seawater ratio. Compared to the soluble ions, some of the total available ions (the soluble plus the exchangeable fractions) behave some- what differently. Total available Na is closely related to surface water salinity since it is a major component of sea water. However most available K and Mg are held in the soil exchange complex. Therefore, available K and Mg are strongly influenced by the adsorptive capacity of the soil mineral component as indicated by their high regression coefficients with bulk density in Table 10. Phosphorus distribution is also strongly related to the mineral component of the soil. The major source of phosphorus to the marsh is probably from mineral sediment deposits. Neither total nitrogen (N) nor cal- cium (Ca) (either soluble or exchangeable) are closely related to salinity or to bulk density. Unlike the other soluble cations, Ca is abundant in freshwater, and runoff from the surrounding upland areas into the fresh marsh contains high quantities of Ca. This explains the high Ca/Cl ratios Table 10. Multiple linear regression models of soil ions showing what factors control their distribution in Louisiana marshes (Rainey 1979). For each nutrient the first soil factor entering the model is shown with its R value. The total proportion of the variability accounted for when salinity, bulk density and or- ganic matter are all entered in the model is also shown. In general, one factor accounts for most of the variability. Soil nutrient Soil R Total factor* R ** Total soil salts Sal ini ty 0.741 0.754 Soluble chloride Sal inity 0.748 0.753 Soluble sodium Sal inity 0.760 0.767 Available sodium Sal inity 0.760 0.789 Solubl e potassium Sa 1 i n i ty 0.643 0.744 Available potassium Density 0.573 0.707 Solubl e magnesium Sa 1 i n i ty 0.604 0.622 Available i.iagnesium Density 0.580 0.617 Avail abl e phosphorus Density 0.673 0.707 Total nitrogen Organic 0.189 Avail abl e calcium 0.246 *Independent variable that explains greatest part of the variability, and the the R value associated with it. **Total proportion of the variability in the dependent variability explained by var- iations in the soil factors. 36 found in fresh marshes (Table 11). Cal- cium is tightly bound to organic material. (However, on a volumetric basis neither Ca nor organic content shows a wide range of values, and as a result the statistical association is not strong). Nitrogen distribution is similarly affected. It is relatively constant in organic material (C:N = 16.5; Chabreck 1972), and most of the N in the sediment is tied up in organ- ic form. Sulfate distribution is interesting because the major source is presumably seawater, but the concentration in marsh sediments is as much as four times that expected from the sulfate:chloride ratio in seawater. However, the biochemistry of sulfur (S) in anaerobic soils is complex; sulfates are reduced to insoluble sulfides that can accumulate in the soil and later be re-oxidized to sulfate. Summarizing, the distribution of nutrient elements in the delta marsh zones (Figure 34) is understandable in light of the source of each and its soil chemistry. The ions Na , K, and Mg, associated with sea water, decrease from salt to fresh marshes as salinity decreases. Phosphorus also decreases, but for a different reason; it is carried into the marsh with sediment and sedimentation rates decrease inland. Calcium increases inland since it is derived mostly from upland runoff. Nitrogen is fairly constant across the marshes since it is closely associated with organic matter. Vegetation I have discussed the physical and chemical traits of the vegetation zones in delta marshes in some detail. It is time now to consider the vegetation itself. Based on a classification from early studies by Penfound and Hathaway (1938), Chabreck surveyed and classified the Louisiana marshes in 1968 and 1978. I S 2.5V .'Aa) 2- z o ; 1-5 c ►- z 111 u I ' o .5- im S B I F SB I F Na MG S B I F K S B I F Ca SB I F P S B I F N Figure 34. Concentrations of available Na, Ca, K, Mg, P, and N in different marsh zones (Rainey 1979) . Table 11. The ratio of the major cations to the chloride ion in nomal seawater and in the saline, brackish, intermediate, and fresh marshes of Louisiana (Rainey 1979). Cation Seawater'' Mar; ,h zone Salt Brackish \\ itemiedia te Saline Soluble sodium 0.556 0.585 0.576 0.613 0.560 Solubl e magnesium 0.057 0.070 0.085 0.090 0.107 Soluble calcium 0.021 0.034 0.040 0.077 0.135 Soluble potassium 0.021 &.028 0.026 0.030 0.040 Soluble sulfate 0.140 0.250 0.341 0.407 0.533 From Riley and Chester (1971), 37 Table 12, Percent cover of the dominant plant species marsh zones of the Louisiana coast (Chabreck 1972). in major Species Mai -"sh zone Salt Brackish Intermed' iate Fresh Batis maritima 4.41 0 0 0 Distichlis spicata 14.27 13.32 0.36 0.13 Juncus roemerianus 10.10 3.93 0.72 0.60 Spartina alterni flora 62.14 4.77 0.86 0 Eleocharis parvula 0 2.46 0.49 0.54 Ruppia maritima 0 3.83 0.64 0 Scirpus ol ne^i 0 4.97 3.26 0.45 Scirp^us robustus 0.66 1.78 0.68 0 Spartina patens 5.99 55.22 34.01 3.74 Bacopa monnieri 0 0.92 4.75 1.44 Cyperus odoratus 0 0.84 2.18 1.56 Echinochloa wal teri 0 0.36 2.72 0.77 Paspalum vaginatum 0 1.38 4.46 0.35 Phra^mites austral is 0 0.31 6.63 2.54 A1 ternanthera phi 1 oxeroides 0 0 2.47 5.34 Eleocharis sp. 0 0.82 3.28 10.74 Hydrocotyl Lmbellata 0 0 0 1.93 Panicum hemitomon 0 0 0.76 25.62 Saqittaria falcata 0 0 6.47 15,15 Other species 2.43 5.09 25.26 29.10 Total 100.00 100.00 100.00 100.00 Total number of species 17 40 54 93 have used his grouping of the marshes into four broad zones in the discussion of temporal and spatial gradients earlier in this chapter. The 1968 survey (Chabreck 1972) is still the best description avail- able of the broad marsh vegetation pat- terns, including the species associated with each marsh zone and their relative importance as indicated by percent cover (Table 12, Figure 35, Appendix 1). Spartina a1 terni flora and S^. patens dominate the saline marsh, with Juncus roemerianus , Distichi is spicata and Batis maritima as subdoininants (see Frontis- piece) . Chabreck identified 12 addi- tional species in this vegetation zone. In the brackish zone S. patens is dominant. D. spicata, S^. aTterni flora. J. roemerianus _ and Sci rpus" olneyi are also common species of this zone. Notice that many of the species are the same in both zones, but their order of dominance is changed. Often the brackish marsh has a distinct "hummocky" appearance associ- ated with the clumped growth of S^. patens (Figure 36). Forty species are on the brackish marsh 1 ist. The intermediate marsh is difficult for the novice to identify. The species are not, on the whole, different from those found in the fresh marsh, but all but one of the four dominant species in these two zones are different. Inter- mediate marsh dominants are again S^. patens, with Phragmites austral is, Sagi ttaria falcata^ and Bacopa monnieri . In the fresh marsh the dominants are Panicim hemitomon, S^. falcata, Eleocharis Al ternanthera philoxeroides. increases from salt to and dominance decreases. are often very diverse with different species of grasses and spp., and Species richness fresh marsh Fresh marshes many broad-leaved annuals waxing and waning throughout the growing season (Figure 37). 38 VEGETATION TYPES: ^■1- FRESH MARSHES INTERMEDIATE MARSHES BRACKISH MARSHES SALINE MARSHES ■ NL>N-MARSH AREAS Figure 35. Vegetation zones in the Mississippi River Delta marshes (Chabreck and Linscombe 1978). Chabreck': data are for the coastal marshes of the whole state. There is some difference in the species found in the western chenier plain compared to the delta, but these are minor. More impor- tant is that the species list is a com- posite from many different, sites. No one site would be expected to contain all the species, especially in the intermediate and fresh marshes. Each major zone is actually a complex mosaic of many sub- associations. The primary zones are, as the names indicate, determined by the salinity tolerance of the plants. Within each zone detailed mosaics result from much more complex factors including soil nutrients and elevation (hence flooding frequency and duration). For example, a 90-km^ site in the intermediate marsh in the Barataria basin was mapped from aerial imagery, and intensive ground surveys were conducted. Six plant associations were identified using statistical clustering techniques (Figure 38), and even more complex visual patterns are seen in the aerial imagery. The observed patterns seem to result from the interaction of brackish water entering the marsh from the east and south, and fresh upland runoff from the west, com- bined with slight elevation differences (Sasser et al . 1982). Vegetation studies in the Atchafalaya basin fresh marshes show the importance of elevation and exposure to direct river flow versus stagnating backwater flooding in controlling the species distribution (Johnson et al., LSU Center for Wetland Resources; unpublished). Greenhouse studies on salt marsh species from the delta clearly show differences in the ability of different species to tolerate flooding (Parrondo et al . 1978). In these studies, although S^. al terniflora and S. cynosuroides appeared to be equally weTl adapted to salt, the latter was far less tolerant of flooding (Figure 39). The greenhouse studies quantify qualitative observations that S^. cynosuroides is found in slightly elevated locations in the marsh. 39 ^■ S*2J**^^^Ii^' ^.V^. Figure 36. A deltaic plain brackish marsh. Note the "hunmocky" appearance wh typical of Spartina patens stands. The birds with black-tipped wings are pelicans, the smaller ones ducks, mostly teal (Photograph by Robert Abernathy) . '«^ ich is white The roles of chance and competition in marsh plant distribution have not been extensively studied in the delta marshes. We usually assume that seed sources are abundant so that a supply of propagules does not limit invasion by a species and the presence of one species does not prevent another adapted species from invading. In fact, competition is probably a very strong distribution factor. With the exception of a few true obligate halophytes (represented on the gulf coast by Batis mari tima and several species of Sal icornia), the salt-tolerant species will all grow well in fresh or nearly fresh substrates. Since these species are not found in salt-free areas, presumably they are confined to saline areas because they cannot compete well with fresh marsh species in a fresh environment. Another example of competition is the observation that the thick layer of dead vegetation covering a stand of the perennial grass ^. patens excludes S_. olneyi and annual grasses. It is common to burn S_. patens stands to encourage these other species which are nore desirable as food for ducks and muskrats (Hoffpauir 1968). In early literature on delta marsh plants it was assumed that the vegetation modified the landscape so that the envi- ronment was changed, allowing other spe- cies to invade. For example, Penfound and Hathaway (1938) outlined a successional sequence fran saline through fresh marshes to upland forests. The sequence was based on the idea that marsh plants, by produc- ing peat, could elevate the sites they grew on until upland species could invade and survive there. This idea of autogenic succession arose before we understood the rapidity of subsidence on the gulf coast. It is clear now, I think, that most vege- tation changes in the delta marshes occur because of allogenic processes. In a sense, the most the biota can do is resist and slow down the inevitable change from 40 K- Figure 37. A diverse deltaic plain fresh marsh scene. Species are: Sagittaria falcata (foreground), Typha sp. (right edge), mixed grasses and vines, Myrica shrubs in rear (Photograph by Charles Sasser). F.ciof I I ; High WIregrass F.clor 2 E::n;;::H High Bulllongue ^^H Medium Builtongua H^H High Salt Grass and Oystsr Grass [■ , ' ) Medium Salt Grass and Oyster Grass I I HighSpikerush ■ dor 6 I I High'Mixed Fresh' I High Coast Bacopa Figure 38. Vegetation zonation in an intermediate marsh transition zone in the Barataria basin (Sasser et al. 1982). Factors arise from statistical clustering techniques and are identified by the dominant species. 41 fresh to saline conditions associated with the overriding geomorphic processes. Perhaps one exception to this gener- alization is the fresh floating marsh. This marsh is a thick (up to 1 m) mat of interwoven roots binding decaying peat into a platform that floats on the water. It supports a diverse flora of emergent species dominated by Panicum hemitomon. The origins of these mats is Russell (1942) suggested that by growing out into lakes from line. O'Neil (1949) thought began as anchored marshes that from their substrate during not known, they arise the shore- that they broke loose a high-water period because of the bouyant force of the mat. The fresh floating marshes are in many respects highly self-controlled. Since they float they are never deeply flooded, but by the same token the water level is always near the marsh surface. The production of organic matter maintains the floating mat. Thus the vagaries of water supply are effectively controlled, and the hydrologic environment of the floating marsh is nearly constant. c re a I g III > a. o Flooded Sediments [rrprrirrfi SSSSy Drained Sediment k ^l . k t* S B. h ^ h L3. R C P S ALTERNI FLORA S CYNOSUROIDES R- Roots C- Culms P - Plant Figure 39. Effects of substrate drainage conditions on the dry weight accumulation by (A) Spartina alterniflora and (B) S^. cynosuroides (reproduced from Bot. Gazette, 1978 by R.T. Parrando, J.G. Gosselink, and C.S. Hopkinson with per- mission of The University of Chicago). 42 CHAPTER THREE ECOLOGICAL PROCESSES IN DELTA MARSHES In the previous chapter, I considered marsh changes across spatial gradients and also those temporal changes that are measured in hundreds or thousands of years. But within any fairly homogeneous patch of marsh, many complex interacting processes occur and reoccur in cycles that are measured in days and seasons. In order to understand the marsh ecosystem, it is necessary to understand how these processes operate and how they interact. However, it is not clear how best to study them. One can analyze the individual components of the systan and from these attempt to reconstruct the whole. Or conversely, it is possible to examine the system from a "macroscopic" point of view, almost as an independent organism which acts as an integrated individual. Both approaches have their strengths and weaknesses. The latter "systems" approach has been emphasized in Mississippi delta marshes in studies supported by the Louisiana Sea Grant program, and I will draw heavily on them in this chapter. In addition, much excellent research has also focused on individual species, especially fish, mammals, and birds. Without these studies it would not have been possible to draw as complete a picture as we now have. In the systems approach one often relies heavily on ecosystem models which conceptually organize and simplify the ecosystem under study. Although more sophisticated, quantitative models of delta marshes have been published (Day et al. 1973; Hopkinson and Day 1977; Costanza et al. 1983), I will use a simple conceptual model to focus the reader's attention on the most important coiTiponents and processes in the marsh ecosystem. Each of these will then be considered further. This model (Figure 40) emphasizes the importance of (1) primary production and its control, (2) decomposition, detritus, and the role of micro-organi sns, (3) the benthos, (4) the food chain to vertebrates - fish, water- fowl, and fur animals, and (5) nutrient cycles. Throughout this discussion the role of hydrology will be emphasized. This property makes wetlands unique. Nearly everything that happens in wetlands is influenced by the flooding properties of the site. Some of these - flooding dynamics, chemical and physical properties of the substrate, vegetation zones - have already been considered. In addition, each of the five groups of processes emphasized in Figure 40 is influenced by hydrology. The extent of hydrology's influence should become increasingly clear in the following discussion. PRIMARY PRODUCTION It is convenient to consider marsh plants in four different groups. (1) The most extensively studied are the emergent vascular plants, most of them grasses which are responsible for most inarsh photosynthesis. (2) Almost always associated with the emergent plants on the mud surface, and especially on the lower parts of the vascular plant stems, is an active community of epiphytic filamentous algae and diatoms along with many microscopic consumers. (3) The benthic algal community in marsh ponds, almost always submerged, is a rich surface coating of diatoms and other unicellular green and blue-green algae. (4) Finally, in many marsh ponds submerged macrophytes such as Ruppia maritima, Eleocharis 43 ADJACENT \ WATER Figure 40, A conceptual and processes. O DEPOSITS IN DEEP SEDIMENTS model of a typical wetland ecosystem, showing major components parvula, Chara vulgaris and Potomageton spp. are found. Emergent Vascular Plants The energent vascular plants are by far the most intensively studied of these four groups. Much plant biomass infonnation about delta marsh species has been generated during the past decade. Seven studies of marsh grass productivity covering nine plant species have been performed (Table 13) . The most common infonnation related to production is peak end-of-season biomass. In iiore northerly climates where all growth ceases and the plants are killed to the ground during the winter, this is often an excellent estimate of true net production. But in the subtropical climate of the gulf coast peak biomass has been shown to underestimate production by a factor of 1.6 to over 4, even in those species that have a single growth cycle each year (Hopkinson et al . 1978a). As a result, one must interpret peak bianass data with caution. Table 13 shows production estimates vary considerably, but most estimates are very high compared to studies in other localities in the temperate zone. This is because production generally increases with decreasing latitude (Turner 1976). The seasonal growth of marsh plants in Louisiana shows two patterns (Figure 41). One is characteristic of annual plants and many species witii perennial roots that die to the ground every winter. These species have a single, smooth growth curve which builds from near zero in January to a peak sometime between July and September. Each year almost all of the new stems anerge at once when growth commences in the spring. In Figure 41 P_. austral is illustrates this group. For species like this, peak biomass represents about 40 - 60 percent of annual net production. The rest is accounted for by shedding of leaves during the spring and some continued growth into the fall that is masked by mortality after the peak is attained. Sagittaria falcata appears to follow the same growth pattern, but actually the individual leaves of this species have a short lifespan and are replaced constantly throughout the year. 44 Table 13. Production of marsh vascular plant species in the Mississippi Delta (g dv;/m^ biomass and g dw/mVyr production). Species Si te Yr Peak 1 ive Production Ref. t >iomass Different techniques Best estimate Sal t marsh Spartina alterniflora Streamside Barataria 70 1,018 1,410 a 2,645 b 2,645 1 Inland Barataria 70 788 1,006 a 1,323 b 1,323 1 Intermediate or Barataria 74-5 754 1,000 a unstated Barataria 80 Lake Borgne 75 831 1,070 1,673 c 1,381 d 2,178 b 1,086 a 1,494 b 1,445 e 2,220 f 1,527 a 2,895 b 2,178 1,445 2,895 2 3 4 Distichlis spicata Barataria 74-5 Lake Borgne 75 991 750 700 a 1,010 c 1,967 d 2,881 b 1,291 a 1,162 b 2,881 1,291 2 4 Juncus roemerianus Barataria 74-5 1,240 1,200 a Lake Borgne 75 1,550 1,850 c 3,295 d 3,257 b 1,740 a 1,806 b 3,257 1,806 2 4 Spartina cynosuroides Barataria 74-5 808 1,767 b 1,134 d 398 c 1,134 2 Brackish marsh Spartina patens Terrebonne 74 Lake Borgne 75 1,376 1,350 2,000 a 2,500 c 4,159 d 5,812 b 1,342 a 1,428 b 4,159 1,428 2 4 Terrebonne 74 Lake Pont- chartrain N.O. East 78 Walker 78 Canal (Continu 45 800 1,248 2,159 ed) 2.128 a 2,605 a 3,056 b 3,053 b+ 4,411 a 3,464 b 5,509 b+ 2,128 3,053 5,509 5 6 6 Tabl e 13. Concluded, bpecies Site Yr Peak 1 ive biomass Production Ref. Different 3est techniques estimate Interiiediate narsh Phragmites communis Sagi ttaria falcata Fresh marsh Sci rpus val idus Panicum hemitomon Goose Point 78 2,130 Irish Bayou 78 2,466 Barataria 74-5 990 Terrebonne 74-5 648 2,541 a 2,487 b 3,075 b+ 3,192 a 2,861 b 3,595 b+ Terrebonne 74 360 2,364 1,402 2,310 1,113 700 508 Terrebonne 74 800 Barataria 80 1,150 1,261 a 1,700 b 1,810 f 3,075 3,595 2,364 2,310 608 1,261 1,700 6 2 2 5 5 7 Techniques : a - Smalley 1958 b - Wiegert and Evans 1964 b+- Wiegert and Evans 1954, modified c - Mortality, Hopkinson et al . 1980 d - Williams and Murdoch 1972 e - Lomnicki et al . 1968 f - Density and longevity, Sasser et al. 1982 Reference : 1 - Ki rby and Gosselink 1976 2 - Hopkinson et al . 1980 3 - Kaswadji 1982 4 - White et al . 1978 5 - Payonk 1975 6 - Cramer and Day 1980 7 - Sasser et al. 1982 At the other extreme, Spartina patens is an example of a species that grows throughout the year, continuously adding foliage and losing it through death in a kind of steady state. Biomass fluctuates widely around a mean, and there is little if any seasonal pattern. For species like these, peak biomass tells almost nothing about annual production, which is three to four times higher. S_. alterni flora falls between these two extremes. It continues to grow slowly during the winter and always has some green foliage, but superimposed on this is a distinct seasonal cycle. Figure 42 contrasts the monthly growth pattern of S_. al terniflora with that of the fresh marsh species Panicum hemitomon. The latter has a broad peak in its growth rate during the spring; growth E 500 o a P. hemitomon .J. .. .„ STREAMSIDE • • INLAND ]- tllmrntllora Figure 41. Monthly growth rates of Panicum hemitomon (Sasser et al. 1982) and Spartina alterni flora (Kirby 1971). 46 p. australis 1600 E X -8 a 4000 |- 3500 3000 2500 - 2000 1500 1000 DEAD -k. 1974 '-I-—. / A972 I' - 0 3i00r E 2600 2100 1600 J J J A Tim«, monthj 1100 600 DEAD 1975,' /V'''.'\ 1973 M J J A Tim«, months Figure 42. Seasonal changes in live and dead biomass of Phragmites austral isand Spartina patens during 1973 - 1975 (Copyright. Reprinted from "Aboveground production of seven coastal marsh plant species in coastal Louisiana " in Ecology, 1978, by C.S. Hopkinson, J.G. Gosselink, and R.T. Parrondo with permission of Ecological Society of America). gradually tapers into the fall with a resurgence after the hottest months, and the plants die to the ground each winter. S^. al terni fl ora maintains active growth throughout the year, with a maximum rate during the early summer. The pattern of streamside and inland plants is similar, but the inland rates are lower. All the production data reported so far have been for aboveground growth. Root production is difficult to measure because it is difficult to determine, in a substrate that is nearly all root material, which roots are living. Table 14 lists reports of root biomass from a number of studies in the delta. The reported biomass varies widely, partly as a result of differences in techniques. Fresh and brackish marsh species in established, highly organic marshes have enormous belowground biomass, whereas the same species (for example, Sagittaria spp.. Table 14) in the mineral sediments of the Atchafalaya Delta produce few roots. Outside of the del ta, root production measurements have been almost as variable. Good et al, (1982) reported S_. al terni- flora root production estimates ranging from 220 to 3500 g/mVyr for tall form (streamside) locations and 420 to G200 g/m^/yr for short form (inland) locations. High root:shoot ratios have been con- sidered indicative of unfavorable soil conditions requiring greater root surface area to support a unit of aboveground material (Shaver and Billings 1975). This relationship seems to hold in marshes 47 Table 14. Belowground biomass of Mississippi Delta narsh plant spe- cies (g dw/m^). Species Month Biomass Percent* Comment Ref. Salt marsh Spartina alterniflora 100-250+ 25 Lake Borgne a Brackish marsh Spartina patens Oct. 1,375 57 Terrebonne b Jan. 1,957 58 1) Scirpus val idus Oct. 3,598 73 " Jan. 11,917 96 II I nte mediate marsh Sagittaria falcata Oct. 2,775 96 Terrebonne b Jan. 7,093 99 II Fresh marsh Pan i cum hemitomon Mean 8,000 90 Barataria c Cyperus di f fornii s Fall 52 39 Atchafalaya d Prod. /y r 117 e Saqittaria lati fol ia Prod. /y r 140 e Sa^ittaria sp. Fall 114 d Typha lati fol ia Fall 214 d *Percentage of total biomass. References : a - White et al . 1978 b - Payonk 1975 c - Sasser et al . , LSD, unpubl d - Johnson et al. LSU, unpubl. e - Mendelssohn, LSU, unpubl. where, for example, S_. al terni flora root:shoot ratios increase from 1-8 streamside to 1.2 - 49 inland (Good et al. 1982). As vn'th root biomass estimates, aboveground production estimates vary widely, even for a single species. Again this is partly because of methodological problems. Production is calculated from at least two sets of measurements - biomass and sone measure of mortality during the interval between sampling. The latter introduces a large element of uncertainty in the estimate. One study can generate several estimates that vary from each other by as much as a factor of three, depending on the assumptions made. Shew et al. (1931) have an excellent discussion of this topic. For example Kaswadji's (1982) study was designed to compare four different techniques for detemiining production in a S^. al terni flora marsh. The four methods resulted in estimates of annual production (g/m2) varying fron 641 to 2,220 (Table 15). The higher estimates are commonly, but not universally, considered the more realistic in gulf coast marshes. Aside from tlie variation in reported production due to the nethods of analysis. Table 15. Production estimates for a Spartina al terni flora stand based on different techniques (Kaswadji 1982). Technique E s t i na te (g/mVyr) Milner & Hughes^ 641 Peak standing live biomass 831 Smal ley 1085 Wiegert-Evans 1496 Lomnicki 1445 Stem longevity/density 2220 ^See Table 13 for references to tech- niques. 48 there is still a good deal of real variation in the productivity of a single species in different environments. This is best shown by differences in peak bioinass, which although not equivalent to production are a pretty good index of relative production. These differences are temporal as well as spatial. At Airplane Lake in the Barataria basin, peak biomass has varied by over 300 g/m^ from year to year (Table 16). Turner (1979) found a positive rela- tionship between biomass and potential evaporation (which is in turn related to the average air tenperature) during the growing season. By implication, dif- ferences in biomass among years at one location should be related to annual differences in the accumulated potential evaporation. While this kind of relationship has been confirmed for many agricultural crops, it has not been studied in marshes, perhaps because long-term data sets are not available. Spatial variations in biomass have been the subject of many investigations, both to determine the correlation of biomass with environmental variables and to identify the physiological mechanisms of adaptation to the marsh environment. Figures 43, 44, and 45 show three typical examples of spatial variations in marsh biomass. It is instructive to examine them because they throw light on the physiological responses of plants. The first of these is the "tidal subsidy", discussed by Oduin and Fanning (1973) as a reason for the high produc- tivity of coastal marshes. Tides Table 16. Year-to-year variation in peak 1 ive biomass of Spartina al terniflora at a singl e site in the Barataroa basin. Year Biomass n Source (g/m^) 1970 903 10 Kirby 1971 1976 701±245 6 Buresh 1978 1978 700 10 Sasser et al. 1982 1979 700 10 " 1980 790 10 " 1981 748±377 10 " 1982 1,047±190 10 2000 -□ La (3) 1600 o o o °^ °0 A 1200 800 n nn ^^ 400 C 1 1 2 TIDE RANGE (m) Figure 43. Production of intertidal S_. al terni flora vs. mean tide range for various Atlantic coastal marshes. Different symbols represent different data sources (adapted from Steever et al. 1975). Note the position of Mississippi delta marshes on the graph. media facto size, secon illus north propo that study much tidal te such plant growth-influencing rs as nutrient supply, sediment grain Hrainano 5oii Oxygenation, and drainage 1 dary chemical changes. m lims tration, peak plant biomass along the Atlantic coast is directly rtional to the tide range. Notice biomass from one Louisiana delta does not fit the trend. Biomass is higher than expected considering the range. In this The second example illustrates the well-known "streamside" effect - the stimulation of growth along the edge of natural streams, or conversely its inhibition inland. This effect is similar to the tidal subsidy in that tidal action is weaker inland than streamside so the plants receive less "subsidy." 49 500 Plan Biomass Plant Heighl 5 ID 15 20 DISTANCE FROM STREAM (m) 70 50 I O z < -30 10 Figure 44. Variation in total aboveground biomass and height of Spartina a1 terni flora with distance inland from the marsh edge in a Barataria basin salt marsh (Buresh 1978). Live y//A ■ Total ^H 2000 1 1 1800 1 1 '^ 1600 1 1400 w 1200 3 1000 S 800 < a 600 o 5 400 200 /; ?1 INLAND POSITION ON TRANSECT GULF Figure 45. Gulf-inland variations in live and total biomass in Spartina alterniflora marshes (Gosselink et al . 1977y] The third example shows the increase in biomass from the coast inland. The first two examples illustrate complex gradients in the physiological sense; the last may be due simply to a gradient of decreasing salinity. Physiologically a plant growing in a marsh has to solve one or both of two problems. All marsh plants are periodically exposed to high salt concentrations and to anoxic soil conditions and accompanying sediment chemical changes. As indicated earlier, the dominant salt and brackish marsh plants are salt tolerant rather than salt requiring. Generally, growth is depressed as salt concentration increases (Parrondo et al . 1978). One reason for this is that the high concentration of salt surrounding the roots makes it osmotically difficult for plant cells to absorb water. The plant could get around this problem by simply absorbing salt to decrease the internal osmotic potential. But this leads to biochemical problems because the Na and CI ions interfere with the activity of many enzymes, probably through steric effects. For example, the enzyme-mediated absorption of the radio- tracer, rubidium (Rb) by excised roots of S^. al terniflora and D. spicata is strongly inhibited by salt in the root medium (Figure 46). This may occur be- cause Na replaces Ca, which has been shown to stimulate ion uptake, on the cell membranes. Plants have adapted to the problems posed by salt in a number of ways. These all involve mechanisms to exclude or selectively absorb only certain ions, to raise the osmotic concentration of the plant cells to overcome the water uptake problem, and/ or to secrete unwanted ions. S_. al terni flora has apparently evolved all three mechanisms. The osmotic concentration of its cells is always slightly higher than the substrate concentration, creating a favorable gradient for water flow into the plant. This is accomplished both by absorption of salts from the external medium and by production of osmotically active organic compounds. The absorption of salt is not a passive process. The relative concentrations of different ions within the plant cells indicate that absorption is selective, with the exclusion of Na and 50 D. spicata c E o CO O o (A a> 3 z g a cc O CO OQ < cc NaCI (mM/l) Figure 46. Effects of NaCl concentration in the root medium on the rate of Rb absorption by excised root tissue of S. alterniflora and D. spicata (1 mM Rb; 2 mM Ca; reprinted from Bot. Gazette, 1981, by R.T. Parrando, J.G. Gosselink, and C.S. Hopkinson with permission of The Univer- sity of Chicago) . the concentration of other ions such as K (Smart and Barko 1978). Finally, the plant leaves have secretory glands called hydathodes which selectively secrete cer- tain ions. All this regulatory activity requires extra energy expenditure by the plant. It is not surprising then that the growth rate decreases as the external salt concentration increases. The problem of anoxia is complex because it affects not only the plant Itself but also the microblally mediated biochemical reactions that occur in the soil around the roots. Oxygen is required as an electron acceptor in aerobic cell respiration. Its presence allows the efficient oxidation of organic sugars to carbon dioxide and water to produce high energy-reduced organic compounds and the cell's ready energy currency adenosine triphosphate (ATP). In the absence of oxygen, cell metabolism is incomplete; less energy is released from an equivalent amount of sugar (1 mole of glucose yields 2 moles of ATP under anaerobic conditions compared to 36 moles under aerobic conditions); and organic "waste products" like ethanol and lactic acid accumulate because they cannot be oxidized to carbon dioxide (Figure 47). In the surrounding root medium, when oxygen is depleted, other materials act as electron acceptors, almost always through some microbial intermediary rather than through strictly inorganic chemical transfonnations. Many ionic species are reduced. The reduced form of metallic ions such as manganese and iron is more soluble than the oxidized form, and the ions can accumulate to toxic levels. At very low reduction potentials, sulfate is reduced to the highly toxic sulfide. Since the substrate is largely organic and micro-organisms are active, organic toxins such as ethylene can also potentially be produced. Marsh plant species have developed a number of adaptations to cope with anoxia, but even with these the plants are stressed by sublethal effects of anaerobiosis (Mendelssohn and McKee 1982). One of the main adaptations of nearly all wetland plant species is the extensive development of aerenchyna tissues in the leaves, stems, and roots, which allow the diffusion of oxygen from aerial plant parts into the roots Teal and Kanwisher evidence that this nomially enough to metabolic requirements In addi tion, diffusion of oxygen out roots can buffer the effect of soil (Etherington 1975, 1966). There is oxygen source is satisfy the root of wetland plants, of the anoxia by creating a thin, oxidized layer in the rhizosphere. Mendelssohn and Postek (1982) eloquently denonstrated through scanning electron microscopy and x-ray microanalysis that the brown precipitate often seen surrounding S_. al terni flora roots is indeed highly enriched in oxidized iron (Fe) and manganese (Mn). to Another adaptation of wetland plants anoxia is the evolution of the ability 51 Figure 47. Metabolic conversions of pyruvic acid. This "key" intemiediate in metabolism can be converted to a variety of end products, depending on the organism and the electron acceptors available (Nester et al. 1973). to shift from aerobic to anaerobic (fennentation) metabolism. In one study, enzymatic alcohol dehydrogenase (ADH) activity, a measure of the cells' ability to convert acetaldehyde to ethanol during alcoholic fermentation, was much higher in inland sites where the soil reduction potential was intense than in a nearby less-reduced streamside marsh (Table 17). Alcohol did not accumulate in inland plant Table 17. Spartina al terni fl ora root alcohol dehydrogenase (ADH) activity, adenosine triphosphate (ATP) and ethanol concentrations, and soil Eh in a Louisiana salt marsh (Mendelssohn et al . 1982). Variable Unit Location Strediaside Inl and ^71" ADH nmoles NADH oxi- 36 t 9 325 dized/g fw/hr ATP umoles/g dw 218 -23 248 -25 Ethanol umoles/g fw 1.17t .07 1.10* .08 Eh mV 174 t30 -131 ^22 Meantstandard error of mean. tissues in spite of the high ADH activity, indicating that it was able to diffuse out of the roots. In spite of these adaptations marsh plants in highly reduced environments are stressed, as shown by reduced growth rates, and in severe cases, death. Comparison of streamside to inland sites in the salt marsh provides good examples of the intensity of the stressing agents, their relationship to tidal flooding, and their effects on plant growth. Figure 48 shows schematically a few of the transfonnations that result from tidal action, and their effects on plant growth. When the tide rises it carries minerals, both particulate and dissolved, onto the marsh. Because the water slows as it crosses the natural levee, most of the sediment is deposited close to the stream bank, less inland (Table 9). At the same time, flooding water reduces the diffusion rate of oxygen into the marsh soil. The result is usually anoxic soils, especially where organic concentration is high. The streamside dred is flooded as regularly as 52 WIND AND LUNAR TIDES ^ 0, EXCHANGE, SEDIMENT AND NUTRIENT INFLUX SOIL REDOX POTENTIAL J MICROBIAL ^ ANAEROBIC "nIO" METABOLISM J '■"flONS Figure 48. Marsh soil transformations that result from tidal flooding. inland, but for shorter periods of time (Table 7), and the inland floodwaters are more slowly exchanged. Furthermore, the streamside marshes drain better on falling tides because their sediments are coarser. They also contain more reducible mineral ions to buffer redox changes. All these factors lead to stronger reducing potentials in inland marshes than streamside. The strongly potential . nutrient, availabl e chemistry of many minerals is influenced by the redox Phosphorus, a key plant is much more soluble (and hence to plants) under reduced than oxidized conditions (Delaune et al. 1981). Inorganic nitrogen, the primary limiting nutrient in marshes, is reduced to the aimonium ion which is readily absorbed by plant roots. More nutrients are delivered to streamside than to inland sites; this should favor streamside plant growth rates. Organic nitrogen is also more rapidly mineralized to ammonium in streamside sites (Brannon 1973). Other minerals may be transformed to toxins or accumulate in toxic concentra- tions (for example, sulfide) (Hollis 1967). Toxic byproducts of anaerobic microbial metabolism may accumulate. In general, the levels of these potential toxins are higher in inland marshes than streamside marshes, increasing the stress on inland plants. Finally, referring again to Figure 48, the direct flushing of marsh soils and the leaching of olant leaves can dilute toxic materials, reducing their activity. Flushing occurs more readily in streamside sites, reducing the potential for accumulation of toxins. With all these potential effects it is not surpris- ing that plant production is higher along streams than inland. Soil analyses can, at times, mislead. For example, it has been found that ammonium in marsh soil interstitial water is more concentrated inland than stream- side. This is not expected, considering the higher rates of ammonium production in streamside areas. Apparently, however, the interstitial water concentration is controlled by the rate of plant root up- take. The concentration is maintained at low levels by streamside plants; it accu- mulates in inland sites because the less robust inland plants are unable to use all the ammonium available to them. Figure 49 summarizes typical seasonal patterns for various physical and biologi- cal processes in marsh soils. Soil water salinity is highest during the summer but probably does not reach levels that ax-& biologically limiting for the euryhaline marsh species. The low winter and early spring salinities correspond with winter rains and low transpiration rates, indi- cating flushing of the marsh by rainwater. Soil-reducing potential (Eh) is least negative (least anaerobic) during the winter, but even during this period it is too low to support any free oxygen. The seasonal Eh curve is the inverse of the tenperature curve - the soil becomes more and more reduced as temperatures rise and biological activity increases. Soils begin to become less anoxic in late summer as temperature drops, even though the marsh is flooded almost all the time during these months. Free sulfide follows the redox curve closely. It is generally highest when the Eh is lowest. Extract- able manganese is an example of a metal ion that is fairly easily reduced. The substrate is always anoxic enough to reduce the manganic ion and the reduced 53 fonii is present year round. Free ammoniuin is the only forn of inorganic nitrogen available to plants in these reduced soils. In streamside marshes it is naintained at a low level of 1 - 2 pg/ml by plant uptake during the spring and suiii'iier, building up in the fall when plant growth tapers off. Epiphytic Algae Where emergent grasses and algae grow together the grass is probably nearly always the dominant producer. Certainly it develops the largest biomass, but this is not a good criterion for comparison because the turnover rate of algae is much faster than that of grass. In a study in which the carbon dioxide uptake of both of these groups was measured simultaneously (Gosselink et al. 1977), the algal community was responsible for only 4-11 percent of the photosynthesis but 61 - 76 percent of the total respiration (Table 18). It has not been possible to separate out from the plants the respiratory associated with the active - bacteria, fungi, protozoans, invertebrates - found in this activi ty consumers and other communi ty . Stowe (1972) found that only along the edges of the marsh where adequate light penetrated did photosynthesis exceed respiration (Figure 50). He estimated that net carbon (C) fixation amounted to about 60 g C/m^ annually at the water's edge, compared to -18 g C/m^ inland. The inland community was consuming more organic carbon than it produced. Nearly all of the photosynthetic activity was associated with organisms growing on the base of S_. al terniflora culms rather than on the sediment surface. Filamentous algal production was dominated by the genera Enteromorpha and Ectocarpus in the winter and Bostrichia and Polysiphonia in the summer. The diatom community was also abundant; the cells clustered on the intertidal portion of the culms, decreasing in concentration upward into the drier environment (Figure 51). Although quantitatively the algal community appears to be rather insignificant, the cells are much higher Table 18. Percentage of marsh community metabolism by Spartina al terniflora (Gosselink et al . 1977), December March May 1975 1976 1976 Figure 49. Seasonal changes in various physical, chemical, and biotic factors in a Barataria basin salt marsh. Gross photosynthes 89± 6 92±6 96+3 Respiration 36±11 36±5 24±9 Mean±standard deviation. 54 '^ 1 1 1 1 1 1 0/ 3 30 VYS 60 90 120 150 180 210 240 270 300 330 Figure 50. Net epiphytic production on stems of Spartina al terni f1 ora collected at the water' c edge and inland 1.5 m with the averages, extremes, and fitted curve for the water's edge production superimposed (Stowe 1972). in protein than the dominant grasses. Furthermore the diatoms are already "bite-sized" and may be much more readily available to the consuming members of the community. Therefore they may be more important metabol ical ly than has been commonly real ized. Benthic Microflora in Marsh Ponds There have been no studies on the gulf coast of the benthic flora found in marsh ponds. Most individuals who have taken the trouble to examine these ponds when they are exposed at low tide can testify that there is almost always a golden sheen to the mud surface. Under the microscope this sheen is resolved into a dense layer of diatoms of many species. Recently Moncreiff (1983) studied the algal mats found on the edges of the V CO « S~ 3 o^ I-'" \ 9 J ^^ UJ H < ' ^0 h lU u z < oc < UJ 5 0. a. < V) a Jan Jun SUB- MERGED IN BAYOU Jan Jun Jan Jun STREAMSIDE INLAND MARSH MARSH Figure 53. Decomposition rates (mg/g/day) of S. a1 terniflora litter incubated in different 2-mm mesh bags (Kirby 1971). in locations roeme nanus slow to decompose. J_ decomposes rapidly for a species with a low surface to volume ratio. S_. falcata , a broad-leaved monocot with high leaf N content, decomposes extremely rapidly, apparently at any tenperature. Nitrogen availability often limits the decay rate of detritus (Teal 1983). Since most animals have low C:N ratios (under 10) while litter from such plants as S_. al terniflora has a ratio well over 20, the decomposers must either select high H residues from the litter or sup- plement the litter with N from other sources. In a laboratory test Gosselink and Kirby (1974) found that litter became increasingly fragmented as it decomposed, and that the C:N ratio, after an initial increase, dropped rapidly so that the finely decomposed material had a N content up to 8 percent (C:N = 6). This increase in N was not simply a concentration of litter N by respiration of the C. Rather, N was absorbed from inorganic sources in the environment. This is not surprising since it has been known for many years that when a mulch is used in an agricul- Tabl e 20. Range and mean loss rates (mg/g/day) of litter from different marsh plant species (summarized from Appendix 2). Species Range Mean Sal t marsh Spartina al terni f1 ora Spartina cynosuroides Distichl is spicata Juncus roemerianus Bracki sh inarsh Spartina patens Intennediate & fresh m Phragmites austral is Sagittaria falcata " 4.0-21.9 8.4 2.7- 5.4 4.6 2.2- 9.0 4.6 5.9-14.4 9.3 2.8- 5.4 6.0 rsh 1.3- 6.2 3.8 24.1-25.7 24.9 tural crop the soil micro-organisms use it as an energy substrate and compete with the crop plant for available nitrogen. Although this laboratory test suggested that litter can be converted to high protein microbial biomass efficient- ly, several recent studies showed that the bacterial and fungal biomass associated with detritus is quite small (Rublee et al. 1978, Wiebe and Pomeroy 1972). This may be at least partially because the bacteria are cropped as rapidly as they are produced by the ineiofauna. Other forms of nitrogen are extracellular coinpounds produced by microbes and proteins bound to oxidized phenolic compounds (degradation products of plant lignins). Many of these compounds are relatively resistant to decomposition and poor sources of organic energy to detritus feeders. The aerobic decomposers comprise a bewildering array of species and physiological strains. Meyers et al . (1971) identified the species Pichia spartinae and Kluyveromyces drosophil arum as dominant yeasts in the sTTt marsh sediment surface. Hood and Colmer (1971) characterized a number of physiological groups of bacteria. They found that the soil -root interface of the grass was the site of most intense microbial activity. Maltby (1982) found that the ratios of actinomycetes to bacteria and of 59 filainentous fungi to yeasts changed predictably in different wetlands depending on their history. Mixed with these decomposers on the soil surface is an active community of autotrophic algae, chiefly diatoms, that enter the food web at the same level as the decomposers and may be an important additional energy source. Most investigators, however, are concerned more with the biochemical activity mediated by the microbiota than with species identification. They are satisfied to get some relative index of microbial bioTiass like that afforded by total ATP activity, or to characterize the microbiota by their chemical activity (White et al. 1979). The decomposition of underground biomass has been studied very little. No studies are available from the Louisiana delta marshes. The best infonnation on the subject comes from studies in Atlantic coast salt marshes summarized by Valiela et al. (1982), Teal (1983), and Howarth and Hobbie (1982). Since the soil environment is anoxic, most of the decomposition must be anaero- bic. The leaching phase of decomposition is the same as aboveground, but subse- quently the disappearance of organic material is slower. Nitrogen stimulates the decomposition rate, indicating that it is limiting belowground as well as in an aerobic environment. One reason is that nitrate may control the metabolic rate by acting as an electron acceptor in the absence of oxygen. Most underground pro- duction, however, is decomposed through the fennentation and sulfate reduction pathways (Howarth and Teal 1979). CONSUMERS Benthos In terms of energy transfer it is assumed that' the microflora act as the intermediary between the organic production of the higher plants and the higher trophic levels. At first investigators thought that the macroscopic deposit feeders were ingesting bacteria-laden detritus; skimming the bacteria from it; and fragmenting. packaging, and inoculating the detritus with bacteria in fecal pellets. It appears now that bacterial density is too low on most detrital material to provide a sufficient food source for the macro-benthos (Wiebe and Pomeroy 1972). This change in viewpoint is reflected in the trophic diagram of Figure 54. The meiofauna are seen to have a crucial role in energy transfer (1 in Figure 54). They are distinguished from macrofauna primarily by size. Both are found in or on the substrate during all or part of their life cycles. Meiobenthos are generally microscopic; macrobenthos are larger and include such taxonomic groups as snails, mussels, and crabs. Sikora et al . (1977) found that meiobenthic nematodes account for 70 - 90 percent of ttie sediment ATP, indicating that nearly all living biomass in anoxic marsh sedi;nents is meiofaunal, not bacterial. These organisms are thought to be siiial 1 enough to graze the bacteria efficiently and "package" that organic energy supply in bite-sized portions for slightly larger macrobenthic deposit feeders (3 in Figure 54). Sikora (1977) showed that the chelae of the grass shrimp (Pal eomonetes spp.) are about the right size to capture nematodes and speculated that grass shrimp are more likely to use this food than detritus. Bell's study (1980) supports this idea. She found that meiobenthic polychaete and copepod densities increased in caged exclosures that reduced macro- faunal predation. Gut analyses seldom turn up nematodes, the dominant meiofaunal taxon, but this is probably because their soft bodies are dissolved rapidly. Macro- benthic deposit feeders are thus ingesting and using as an energy source meiofauna, which in turn have been cropping bacteria. The deposit feeders themselves are prey for the many small fish, shellfish, and birds that use the marsh, marsh creeks, and small marsh ponds (3 and 4, Figure 54). Although apparently each step in this energy transfer can be quite efficient - net growth efficiencies up to 50 percent for bacteria (Payne 1970), 38 percent for nematodes (Marchant and Nicholas 1974) - the trophic pathway from detritus to microbes to meiofauna to 60 1 Bacteria Fungi Protozoa Nematodes Turbellarians Gastrotrichs Polychaete larvae Harpacticoid copepods Ostracods Polychaetes Amphipods 01 igochaetes Tenaiads Isopods Melampus sp. Caridean shrimp Fiddler crabs Small blue crabs Littorina snails Neritina snails Carol ina marsh clam Penaeid shrimp Blue crab Sea catfish Blue catfish Channel catfish Largemouth bass Black drum Red drum Striped mullet Silver perch Spotted gar Alligator gar Yellow bass f ^F~)» Microbes * I Detmus j'-f I J 1 Macro - Denthos MetobenTfTos Clapper rail Sora Belted kingfisher Fish crow Black duck Least bittern Northern shoveler Hooded merganser American avocet Western sandpiper Solitary sandpiper Wil son' s phalarope Common snipe Dunl in Piping plover Kill deer Speckled trout Gizzard shad Hogchoker Pinfish (juvenile) Spot Tidewater silverside Atlantic croaker American alligator Snapping turtle Mississippi mud turtle Red-eared turtle Graham's water snake Western ribbon snake Figure 54. Major pathways of organic marsh and associated water bodies. energy \/^^ Muskrat --v-^ Raccoon I Mink River otter r^^ Deposii 5 Feeders Southern painted turtle Sheepshead Pinfish American coot Brown snake Canada goose Garter snake Seaside sparrow Nutria Pied- billed grebe 6 Eared grebe Oyster Great blue heron Mussel s Little blue heron Clams Green heron Snowy egret Gulf menhaden Great egret Threadfin shad Glossy ibis Sand seatrout White ibis Bay anchovy King rail Atlantic croaker Virginia rai 1 ( < 25 mm) / flow in a Mississi ppi River del taic salt macrofauna to fish is long. The overall energy transferred to the nektonic level is a small fraction of primary production. Figure 54 also shows a feedback loop from macrobenthos to detritus. Macrobenthic animals actively shred and break up detritus in their feeding activity, increasing its surface area and making it more readily decomposed. For example, Val i el a et al . (1982) estimated that exclosures that keep detritivores away from decaying litter reduce the decomposition rate by as much as 30-50 percent. Nekton Numerous fish species are found in the delta marshes (Appendix 3). These include a broad array of year-round residents with varying salinity tolerance 61 and migrating as juveniles these species represent the species that use the marsh for a nursery. Many of are benthic feeders and next link in the benthic food chain section. described in the previous Ruebsamen (1972) studied the stomach contents of fish captured by seine in small, shallow intertidal marsh ponds in the Barataria basin (Table 21). Of the nine most abundant species, six were described as feeding on benthic infauna such as copepods, amphipods, ostracods, mysidaceans, polychaetes, tendipedid larvae, nematodes, and annelid worms. Two were described as detritus eaters, (which probably means that they were using the meiofauna in the sediment). The small marsh ponds are frequented primarily by resident fish, while migratory fish are found in the deeper marsh creeks. In Ruebsamen' s study of small marsh ponds, spot (Leiostomus xanthurus) was the only migratory species found in large numbers. Variation in the particular species reported to use marsh ponds is often related to differences in gear used and Table 21. Monthly occurrence and abundance of the fish species collected in small salt marsh ponds (Ruebsamen 1972). definitions of what comprises a marsh pond. Nevertheless, much evidence points to heavy use of the marsh by nekton for both food and shelter. Ruebsamen (1972) found only the small fish in the intertidal marsh ponds. As they grew they usually disappeared from the samples. Hinchee (1977) found 20 to 25-mm menhaden along the edges of Lake Ponchartrain, apparently as they moved into the estuary from the gulf. These small juveniles moved into the marsh where they stayed until they reached about 50 mm, after which they began their emigration back out through the lake to the open gulf (Figure 55). When conditions permit, many nektonic organisms move up into the marsh itself. Sikora (1977) found this true for the grass shrimp in Georgia, and Wernie (1981) found 30 percent of the silverside (Menidia menidia) and mummichog ( Fundulus heterocl itus) in a north Atlantic estuary up in the marsh at high tide. Kelley (1965) sampled fish in marsh ponds in the active Balize Delta. In this nearly freshwater area he found mullet and blue catfish the most abundant, but he also reported plentiful croaker, spot, sand seatrout, spotted seatrout, and menhaden. It is interesting that Species Month Relative ^ abundance A S ONDJFIAMJJA Cyprinodon varieqatus Adinia xenicd Menid Id beryl 1 ina Fundulus ±r^u^^ s Poecil ia latipinna Fundulus pul vereus Lucania parva Leijstonius xanthurus Fundulus simil is Mu^il cephalus Gobiunellus boleosona Anchoa mi tchil 1 i Ldjiodon rhoinboides Gainbusia affinis Brevoortia patronus Sciaenops ocellatus Cynoscion nebulosus Achinjs 1 inea tus Evorthodus tyricus El ops saurus Sphaeroides parvus Archosarqus probatocepha f 14,3Si 4,763 2,662 2.272 2,064 343 304 212 139 86 35 28 27 22 12 7 5 4 3 2 2 2 *••••••__ •**• ***** US -- Gobiosoma bosci Le^isosteus sp. Synqnaathus scovel 1 i Pot^onias cromi s Microqobius qulosus 2 1 1 1 1 ILake Stations J (Based on 237 Menhaden) I Marsh Stations l(Based on 15,927 Menhaden) 35- 30- r t "" |~ z UJ 15- 3 O UJ '0- 5- 0- PI D 10 20 IIvIVHiII Pi PPPi 1 30 40 so 60 70 80 90 100 .Total cauijht during study. Present, ***** abundant. LENGTH CLASSES (mm) Figure 55. Length class frequency of gulf menhaden captured in and near Lake Pontchartrain (Hinchee 1977). 62 marsh edges shelter is grass stans pers. comm.) freshwater coastal marsh/ aquatic systems represented by the Balize and Atchafalaya Deltas are found to function in very much the same way as saline estuaries, with the same suite of marine/estuarine fish and shellfish. In addi tion, freshwater species like gars (Lepisosteus spp.), gizzard shad Dorosoma cepedianum), and blue catfish Ictalurus furcatus) are common (Kelley 1965, Thompson and Deegan 1983). Even when they are seldom found up in the marsh itself or in the small marsh ponds, other species concentrate along the where food is abundant and available in the streamside For example, Peterson (LSU; was unsuccessful in capturing larval spotted sea trout until he began to seine along the very edge of marshes as compared to more open aquatic environments. Spotted sea trout are just one example of the concentration of both the food supply and the aquatic organisms that depend on it. Biological activity is concentrated at the marsh edge (Figure 56). For reasons already discussed, pi ant production is highest along the marsh edge. Finely decomposed detritus from the previous year's plant crop is flushed from the marsh during the winter and accumulates along the marsh edge in deep deposits known to local shrimpers as "coffee grounds." Nematode numbers are highest here as are the concentrations of small deposit feeders. It is no wonder that larger invertebrates - shrimp and crabs - and larval and juvenile fish are also attracted to this feast. Virtually every kind of organism enumerated has been found to concentrate along marsh edges. Figure 56. detritus and salt marsh. Density of consumers at the vegetation , edge of the The importance of this energy flow pathway in marshes can be seen qualitatively by comparing the list of nektonic species in Figure 54 that use the benthic pathway predominantly with those that use the planktonic pathway. Of the abundant species only the gulf menhaden, the bay anchovy, and the juvenile Atlantic croaker are filter feeders. Crabs, shrimp, drum, gar, mullet and nearly all the small resident marsh fish are benthic feeders. This benthic food pyramid is the dominant one in salt marshes. Meiofauna, particularly nematodes, graze the bacteria on decomposing grass, are ingested in turn by deposit feeders which are a major source of food to nektonic fish, shellfish and birds. The marsh-dependent fish, especially the \/ery small ones, graze and shelter up in the marsh when it is flooded and lie in the small marsh ponds and along the edges of fine feeder creeks at other times. As they grow they frequent deeper, more open water. Wildlife Wildlife species that use Mississippi delta marshes are abundant. Table 22 sum- marizes taxonomic found in chenier Louisiana the same richness the species of different groups that are likely to be different marsh zones in the plain region of southwestern The deltaic plain has about species. In general, species is highest in the fresh marsh, decreasing into saline areas. No amphibi- ans and only 4 reptile species are found 63 Table 22. Wildlife species richness (number of species) in the chenier plain marshes (Gosselink et al . 1979). Wildlife Swamp Marsh zone group Fresh Inte rmediate Brack ish Salt Amphibians 18 18 6 5 0 Reptiles 32 24 16 16 4 Birds 120 84 89 89 92 Mammals 25 14 11 10 8 in salt marshes, for example, whereas 13 amphibian and 24 reptilian species inhabit the fresh marsh. Bird species richness does not vary much over these zones, per- haps because birds are mobile and can easily move from one area to another. The richness of swamp forest habitats is included in the table for comparison. It is higher for all groups, probably re- flecting the higher structural heterogene- i ty of that habitat. Although preferred habitat conditions vary with individual species, Weller (1978) suggested that the following characteristics can lead to increased wetland use: (1) Diversity of plant communities. Wildlife are usually more densely distributed where several dif- ferent plant zones occur than in homoge- neous stands. The structure of the habi- tat is apparently more important for nest- ing than the particular taxonomic makeup. Bird species that prefer tall, robust vegetation, for example, seen to be equal- ly satisfied with cattails, bulrushes, or small willows. This is not true for feed- ing since decided preferences are found, especially for annual plants such as mil- lets with abundant seed and for tuberous species. (2) High edge zone:marsh ratio. Apparently both the edges between differ- ent vegetation zones and between vegeta- tion and water are important. For example, the ideal in midwestern pothole marshes appears to be a "henimarsh" that has a 1:1 or 1:2 ratio of marsh to water with good interspersion between the two (Weller 1978). For' waterfowl, the size and depth of shallow marsh ponds is particularly important. In the delta marshes, waterfowl studies have emphasized their distribution with respect to the broad vegetation zones of the coast. Studies of local marsh:water relationships, marsh breakup, and plant diversity as thay relate to waterfowl are rare. Perhaps this is inevitable in a wetland area as large as the Mississippi Delta. The availability, in the past few years, of good remote sensing data and new technologies to process large data sets gives us the capability of examining in much greater detail the complex wi Idl ife:habi tat rel ationships . In midwestern pothole marshes, habi tat quality for wildlife is closely hound to an approximate 10-year cycle of energent-floating-submergent vegetation succession that seems to be controlled bv water levels and herbivory, especially muskrat herbivory. In Louisiana's coastal marshes, water levels controlled by the level of the Gulf of Mexico arp more stable in that time scale, and the dominant trend is a long-tern (100+ year) change from fresh to saline and from solid marsh to broken-up marsh to open water. However, within this long tine frame O'Neil (1949) identified 10- to 14-year cycles that are related to severe storms and muskrat and goose "eat-outs." One the most Al 1 igators. dramatic success stories in wildlife conservation in Louisiana is the return of the alligator from a threatened classification (Endangered Species Tech. Bull. 2(2), Feb. 1977) to the present abundance that makes possible a controlled harvest each year. The soecies was threatened by severe hunting pressure, not habitat loss. When that pressure was removed, its numbers increased rapidly. Alligators are abundant in fresh and slightly brackish bayous and lakes. They reach their highest densities in internediate wetland zones (Joanen and McNease 1972). They build nests in marshes and on levees. One favorite microhabitat is the wax myrtle thickets canmon in fresh marshes. In 1982 we counted 23 nests in a fresh floating marsh fringing a small shallow lake; a night count along a fresh marsh bayou revealed over four alligators per km (Sasser et al. 1982). 64 Crawfish, and in brackish areas blue crabs, are major alligator foods, but alligators are also reported to eat birds, fiddler crabs, fish, insects, nuskrats, nutria, turtles, shrimp, snails, and grasses (Chabreck 1971b). In the Florida Everglades they make "wallows" that are ecologically important for fish during the dry season, but this has not been reported in delta marshes. The muskrat the nutria Muskrat and nutria. (Ondatra zibethicus) and ..._ ,„ (Myocastor coypus), both herbivores, are the dominant mammals in the delta marshes. The nutria is an introduced species. It is debatable whether muskrats are native or not. O'Neil (1949) stated that although early surveyors' records provide an unconfirmed record of high density muskrat populations in the Barataria- Lafitte area in 1840, fur harvesting did not begin until the first years of the twentieth century, and old-time trappers all claimed that no "rats" were seen much prior to that time. However, Arthur (1931) , in a Louisiana Department of Conservation Bulletin, quotes from the journal of Father Jacques Gravier describing travels down the Mississippi River. He described the dress of the Tunica Indians in a November, 1700 entry: "Most of the men have long hair and have no dress but a wretched deerskin. Sometimes they, as well as the women, also have mantels of turkey feathers or muskrat skins well woven and worked." (Figure 57), the nutria prefers fresh marsh and swamp forests and often ventures into nearby ricefields to feed. There is some evidence (Lowery 1974) that the present muskrat distribution results from the invasion of fresh marshes by the more robust nutria which displace muskrats into less desirable brackish areas. Although both species often exist side-by-side in the same area, they appear to have very much the same food habits, and it has been noted that when nutria are heavily trapped, the muskrat population can soar (Evans 1970). Muskrats often seem to be the primary agents in a 10- to 14-year cycle of marsh growth and collapse (Figure 58). They < o o o o 3 Q O oc Q. UJ a. 700- 600- 500- 400- 300- 200- 100- 0- MUSKRAT TO 6,478 H Fresh Intermediate Brackish About the Houmas Indians he stated: "The women wear a fringed skirt, which covers them from the waist to below the knee. When they go out of their cabins they wear a robe of muskrat skins or of turkey feathers." These reports seem to indicate that the muskrat has been abundant in the coastal region for at least several hundred years. The nutria is a native of South America. It was introduced by the Mcllhennys to Avery Island; it escaped in 1938 and rapidly spread throughout the Louisiana coast. Whereas the muskrat is found most abundantly in brackish marshes o < NUTRIA o 900 P o o ^ 7t)0 - \ z o 600 - \- o 450 - 3 Q O 300 - OC Q. 150 - 1- -1 0 _ UJ a Fig ure 57 zones in 1972). MAX MEAN SS:^ s ^ Fresh Intermediate Brackish Pelt production from marsh coastal Louisiana (Palmisano 65 1920 1945 Figure 58. Annual muskrat harvest from a 52,200-hd brackish Scirpus ojneyi marsh in the Mississippi Delta (O'Neil 1949). kill much vegetation digging for the preferred roots. In addition, their house-building activity, underground runs, and surface trails (Figure 59) destroy much more marsh than is directly eaten. For example, in a ID-ha brackish marsh area that contained 24 active and 30 inactive houses in April 19S2, 31 new houses were built and 10 "refurbished" during the next year (Table 23). Sixty percent of the active houses and 57 percent of the inactive ones simply disappeared. When muskrat populations are dense, all this activity can decimate a marsh, creating large "eat-outs" especially in the favored brackish marsh three-corner grass (Sci rpus olneyi ) (Figure 60). Subsequently the local popul ation, with no Figure 59. Ground plan of a typical muskrat house with underground runways and surface trails (barred lines) (Arthur 1931). food, crashes. If water levels are low for a year or two to allow regrowth of the vegetation, the marsh may recover (and the muskrat population with it), but often the damage extends so deeply into the marsh that recovery is poor at best. Severe storms may reset this cycle by destroying nests and burrows and drowning the predatory disease organisms they harbor. The muskrat population often comes back strongly after these storms (O'Neill 1949). It is interesting that "eat-outs" are seldan found outside of brackish marshes and are always attributed to muskrats, not nutria (O'Neil 1949). The nutria has a much longer gestation period (130 days compared to 28 days for the muskrat) so that its potential for response to environmental change is much slower than the muskrat' s. Consequently, its population is more stable. Muskrat "eat-outs" in fresh marshes have been recorded (O'Neil 1949) but the preference for brackish marsh makes this a more likely site. "Eat-outs" are much rarer today than in the 20's and 30's because trapping keeps the population down to nondamaging levels. In light of the apparent local importance of plant-eating furbearers and the earlier discussion of the relative lack of herbivory in marshes, it is informative to reconsider the importance Table 23. Muskrat house-building activity in 10-ha brackish and salt marsh areas in Barataria basin (Sasser et al. 1982). status Number of houses Brackish Salt Apr. 1982 Apr. 1983 Apr. 1982 Apr. 1983 Ac 1 1 ve Inactive Total Status change 24 30 54 47 22 69 26 12 38 40 48 Brackish Salt Active to active Active to inactive Active to gone Inactive to active Inactive to inactive Inactive to gone New active New inactive 6 (25%) 3 (12*) 15 (62%) 10 (33%) 3 (10%) 17 (57%) 31 16 19 (73%) 3 (12%) 4 (15%) 1 ( 8%) 0 ( 0%) 11 (92%) 20 5 66 Figure 60. A muskrat "eat-out" in the brackish marsh in the Barataria basin. Note the high density of muskrat houses (Photograph by Robert Abernathy). of herbivory. Huskrats are reported to eat one-third of their weight per day (O'Neil 1949), and a nutria consumes 1.5 - 2 kg of vegetation each day (Lowery 1974). The average population of nutrias and muskrats from Point au Chien Wildlife Management Area in the delta, from 1973 to 1981, was 1.2 and 0.8/ha, respectively (from Sasser et al. 1982, assuming the population is double the catch (O'Neil 1949). If a nutria eats 2 kg/day, a muskrat 0.3 kg/day (a muskrat weighs about a kilogram), and the vegetation is 20 percent dry weight, then their combined intake is about 150 kg/ha/yr, compared to a plant productivity of about 30,000 kg/ha/yr. Direct grazing is thus less than 1 percent of production. O'Neil (1949) reported a peak harvest of 46 muskrats/ha in a brackish marsh (Figure 59). With the same assumptions, that many animals would eat as much as 7 percent of the vegetation. If damage from burrowing. building nests, and digging for roots was 10 times greater than ingestion, it is easy to see that a significant portion of the vegetation would be destroyed. Deer. Although one-third of Louisiana's white-tailed deer (Odocoileus virqinianus) population is reported to live in the coastal marshes (which comprise only 13 percent of the state) (St. Amant 1959), very few studies have been made of their feeding and habitat requirements in this environment. Apparently, fresh marshes are preferred almost to the exclusion of brackish and sal ine marshes . Based upon data gathered over 20 years, J. B. Kidd (La. Wildlife and Fisheries Commission), in a 1972 letter (as reported in Self 1975), estimated that the "potential" density of deer by marsh type was one deer per 12 ha in the fresh marsh, 1 per 330 ha in the brackish marsh, and 1 per 2900 ha in the salt marsh. This 67 assessment of carrying capacity for fresh marsh agrees well with observations by Jessie Fontenot (Morgan City, La., 1983; pers. comm.) about the deer density in his 1600-ha hunting lease in a fresh marsh in the Atchafalaya hydrologic unit. He reported 180 deer (about one per 9 ha) on his lease, which he said was overstocked. White-tailed deer prefer areas slightly elevated above the marsh such as natural levees and spoil banks which can be used for travel, bedding, and fawning. From a browse study made on spoil levees in the fresh marsh in the Rockefeller Wildlife Refuge in the chenier plain of Louisiana, and from rumen analyses of deer killed in that area. Self (1975) determined that deer ate nearly any plants that were succulent and green. Important food plants during the fall were Al ternanthera philoxeri odes , Bacopa hal imifol ia, Vigna luteol a, Sal i x nigra, B_. monnieri , Echinochloa wal teri i , Kosteletzkya vi rginica, Leptochloa fascicul aris , Panic um dicotomiflorum, and Paspalum vaginatum. During the spring and summer the same species and Phragmi tes austral is. Iva annua, Cyperus vi rens, and Typha angustifol ia were browsed. All these species are found in fresh and intermediate marshes. The brackish marsh grass Spartina patens was grazed in proportion to its abundance but was not a preferred species. Waterfowl, coots, and wading birds. Functionally, birds that use Louisiana's delta marshes can be divided into dabbling or puddle ducks and coots, diving ducks, geese, wading birds, birds of prey, and other marsh birds (Appendix 4). The waterfowl and coots are by far the most abundant. They are mostly winter residents that migrate as far north as the Arctic Circle each summer. Of this group, only the mottled duck breeds in Louisiana marshes with any regularity. Duck populations are highly variable in censuses because of their mobility, but peak populations in the deltaic plain are usually over 2 million birds. Table 24 shows the density of the most common species along transects through Barataria basin. Gadwall (Anas strepera) , blue-winged teal (A. discors) , and mallard (A_. platyrhynchosT were the most common Table 24. (nuiiiber/100 ha) Barataria basin fl ights; Sasser Density of waterfowl by marsh zone in the in 1980-31 (total for 13 et al. 1982). Species^ Marsh zone Salt Brackish Fresh Gadwall 90.0 212.2 11.2 American Coot 25.8 198.4 82.2 Blue-winged Teal 30.8 65.5 25.3 Mallard 10.3 24.0 26.3 Northern Pintail 11.2 53.8 3.5 Green-winged Teal 17.3 1.5 0.0 Mottled Duck 3.8 12.6 12.2 Northern Shovel er 4.5 9.4 0.3 American Wigeon 1.7 2.9 0.7 Red-breasted Merganser 2.1 0.0 0.1 Hooded Merganser 1.7 0.2 0.0 Scaup spp. 0.4 0.9 0.1 Bufflehead 0.2 0.0 0.0 Ruddy Duck 0.1 0.0 0.0 Ringneck Duck 0.1 0.0 0.0 Common Goldeneye 0.02 0.0 0.0 Total Density^ 199.9 579.9 161.7 Flight Mean'^ 15.4 44.6 12.4 L^For scientific names see Appendix 4. Includes intennediate marsh. ^Total number of ducks/13 flights/100 ha. Total density divided by number of survey fl ights. puddle ducks 1982). In Wildlife and the past 10 green-winged blue-winged ( Ful ica common, is not in this study (Sasser et al. Louisiana Department of Fisheries surveys taken over years in the same area, the teal {^. crecca) replaces the teal. The Aiierican coot americana) , which is also very a duck but in the rail However, because of its habits it family is usually included with the puddle ducks. The diving ducks - scaup (Ay thy a spp.), ring-necked duck ^. coll aris) and hooded merganser (Lophodytes cucul latus) - are also common. General ly, geese are found only in the active Balize Delta. They are much more common along the southwestern coast of Louisiana. Puddle ducks prefer marshes interspersed with small, shallow ponds 68 (less than 5 ha) from a few centimeters to about one-half meter deep. They are primarily herbivores, and good stands of submerged grasses improve the quality of the habitat. Ruppia maritima (widgeongrass) is the preferred food in brackish ponds; Potamogeton pu s i 1 1 u s (pondweed), Najas quadalupensis (naiad), and Lemna spp. (duckweed) in freshwater ponds. In brackish marshes Scirpus olneyi (three-cornered grass), Bacopa monnieri (water hyssop), and Eleochari s parvul a (dwarf spikerush) are desirable foods. Echinochloa walteri (wild millet), fascicularis (sprangletop) , Leptochloa Panicum sp , (fal 1 panicum) , and other annuals that produce abundant seeds are good fresh marsh foods. The succulent roots and tubers of species such as S^. olneyi and Sagittaria platyphyl 1 a (delta duck potato) are also favorite foods, especially for geese. It is easy to see why fresh and brackish marshes in the delta support so many dabbling ducks. There are thousands of small marsh ponds in all salinity zones (Table 25), and the dominant plant species in brackish to fresh ponds are considered excellent duck food. Ponds 0.4 - 4 ha in size have the best growth of submerged grasses, possibly because wind-induced turbulence is low in these small ponds. Saline ponds are poorly vegetated (Table 26). Because of this and because the plant species of this marsh zone make poor duck foods, the saline marshes are rela- tively poor puddle duck habitat. Much attention has been focused on the habitat conditions of arctic and subarctic nesting grounds and their in- fluence on the growth of duck populations. Much less attention has been directed toward the importance of wintering grounds for reproductive success. A recent study by Heitneyer and Fredrickson (1931), however, emphasized this important aspect of wintering grounds. They found a direct linear relationshio between winter precip- itation in the Mississippi delta riparian hardwoods (an index of pond number and hence habitat quality) and reproductive success of mallards as measured by the ratio of young to mature mallards. In their multiple regression models both the wintering ground quality index and the numbers of ponds in the nesting area in May and June were significantly positively related to mallard age ratios. The study implies that the quality of deltaic plain marshes may also be important in duck reproductive success. In contrast to puddle ducks, diving ducks usually prefer deep water. They are carnivores, diving to depths of over 10 meters in some cases to obtain their food. Because of this preference they are usual- ly found in open water and along the nearshore zone. However, they are also known to feed on the vegetation of shallow Table 25. Density of ponds and lakes of various size classes in marsh zones along the Louisiana coast in August, 1968 (Chabreck 1971a). Pond and lake size class Marsh zone Salt Brackish Intermediate Fresh (acres) 0.01 0.01-0.10 0.10-1.0 1.0-10 10-80 80-640 640-3,200 3,200-16,000 16,000-32,000 64,000 (number per 100,000 acres) 27,700.2 118,841.7 55,952.2 59,181.2 16,749.0 62,162.2 45,024.0 47,637.4 4,702.6 14,139.0 10,432.8 9,796.8 700.0 1,376.1 759.1 1,070.5 32.2 179.5 73.2 108.8 30.2 12.4 2.6 25.1 5.2 3.2 0 4.5 0.5 0.6 0 0.2 0 0.2 0 0.3 0 0.1 0 0 69 Table 25. The percent of the area of ponds and lakes covered with submerged vegetation in August, 1968 (Chabreck 1971a). Pond and lake size Marsh zone Entire cl ass Salt Brackish Intermediate Fresh coast (acres) (percent) 0.01 0 8.5 11.4 53.2 20.0 0.01-0.10 0 15.4 29.1 75.6 35.4 0.10-1.0 0 8.1 37.7 71.7 31.1 1.0-10 0 10.7 19.5 55.4 23.9 10-80 0 15.3 13,1 28.4 15.0 30-540 0 7.1 0 29.5 15.1 640-3,200 0 7.9 0 4.0 3.8 3,200-15,000 0 0 0 0 0 16,000-32,000 0 0 0 0 0 64,000 0 0 0 0 0 ponds (Bell rose 1930) and in this case are associated with marsh habitats. Compared to ducks, much less inforna- tion is available about wading bird ecolo- gy in delta marshes. This is surprising when it is considered that they are abun- dant year-round residents. The herons and egrets (Table 27) are mostly carnivorous, catching frogs, small fish, snakes, craw- fish, and a wide assortinent of wornis and insects (Mabie 1976). They prefer to fish in very shallow marsh ponds and along the bayous that drain marshes. They also nest in marshes or in close-by mangrove thickets, wax myrtles, and uplands. They appear to prefer the brackish marsh zone for feeding. Densities range up to 100 or more per 100 ha, and average from 6 to 25 per 100 ha (Sasser et al . 1982). A number of heronries occur in the delta marshes (Portnoy 1977). They are aban- doned and refonned in other places fairly frequently. For example, of 27 sites identified by Portnoy (1977) in the Barataria basin only 17 were active in 1932, and at least 4 new nesting colonies were found (Sasser et al. 1982). It would be interesting to know whether the nesting of wading birds in a congested area made much impact on the local nutrient cycles. Certainly this has been shown for other birds, especially where huge guano deposits have resulted (Deevey 1970). Rails (Rail us spp.), the seaside sparrow (Ain;nospiza maritima) , the great- Table 27. Density of wading birds and pelicans (number/100 ha) by marsh zone, in the Barataria basin, 1980-81 (total for 6 fl ights; Sasser et al. 1982). Speci es Marsh zone Salt Brackish Fresh Snowy Egret 8.2 23.9 35.5 Great Common Egret 9.4 25.9 23.1 Anerican White Pel ican 8.6 39.3 1.3 White-faced Ibis 1.1 31.9 16.1 White Ibis 2.2 21.1 14.7 Great Blue Heron 3.6 5.3 3.6 Little Blue Heron 2.4 8.0 4.8 Louisiana Heron 1.4 2.7 1.3 Cattle Egret 0.02 1.5 4.2 Black-crowned Night Heron 1.0 1.1 0.8 Reddish Egret 0.04 0 0 Brown Pel ican 0.02 0 0 Total Density^ 38.0 150.5 105.4 Fl ight ftean 6.3 26.8 17.6 .For scientific names see Appendix 4 , Includes intermedi ate marsh. ^Total number of ducks/6 flights/100 ha. Total density divided by number of survey fl ights. 70 tailed grackle (Quiscalus mexicanus) and the red-winged blackbird ( Agel aius phoeni ceus) are the most numerous of the other marsh birds. The latter two species, especially, are abundant during the spring breeding season. They are migratory and are absent during the winter. Northern harriers are also seen frequently in all marsh environments. Some of these species are endangered or rare (Table 28). The beautiful brown pelican, in particular, has been almost lost from the delta (King et al . 1977). It has been reintroduced from Florida and is found in two nesting colonies on man- groves on Queen Bess Island in Barataria Bay and North Island just west of the Chandeleur Island chain. Carbon Budget One v/ay of summarizing quantitatively the productivity and trophic relations discussed is with a C budget. Most C budgets are primarily input-output budgets that treat the ecosystem under study as a black box so that internal details of the trophic structure are ignored, and metabo- lism of all consumers is lumped as commu- nity respiration. In particular, higher consumers contribute little to community respiration and are usually ignored. Both Day et al. (1973) and Costanza et al . (1983) are exceptions to this generaliza- tion; they calculated metabolic rates for Table 28. Birds of the Mississippi Deltaic Plain on the Audubon Society "Blue List," indicating that their populations are declining (Mabie 1976). Brown Pel ican (Pelecanus occidental is) American White Pel ican (P. erythrorhynchos) Reddish Egret (Egretta rufescens) White- faced Ibis (PI egad is chihi ) White Ibis (Eudocimus albusl Black-crowned Night Heron (Nycticorax nycticorax) Red-shouldered Hawk (Buteo 1 ineatus) Northern Harrier (Circus cyaneus) Osprey (Pandion hal iaetusT Bl ac k vul ture (Coragyps atratus) Loggerhead Shrike (Lanius ludovicianus) Endangered species, a number of consumer groups. However, I will consider the overall input-output budget without this detail. Unfortunately, several key flows in the budget are still not quantified. As a result, any carbon balance inust be considered tentative even today. Day et al . (1973) published the first budget for a delta salt marsh. It was based almost entirely on aboveground primary production, benthic commmunity respiration, and calculated energy flow through the abundant consumers. Loss to deep sediments was assumed to come from root production, and both were ignored in the balance. These authors concluded that 50 percent of net production was exported from the marsh. It has not been possible to measure this organic export directly. Happ et al . (1977) calculated the export of total organic carbon (TOC) from the Barataria estuary to the nearshore gulf from the gradient of decreasing TOC across the passes and an estimate of the turnover rate of bay water. They estimated that the export of TOC was about 150 g/m^/yr. Since aquatic primary production and community respiration in the bay appear to be about equal (Allen 1975), this export from the estuary must reflect marsh export. It amounted to about one-half of the Day et al. estimate. Hopkinson et al . published additional salt marsh respiration data in 1978. Since then Smith et al . (1982) published an incomplete carbon budget for the same area which includes estimates of methane evolution and new data on CO2 evolution. I have attempted to create a new budget from all this information and some direct carbon dioxide flux measurements of photosynthesis that include root production (Gosselink et al . 1977). The weakest links in all these budgets are the paucity of root production infonnation and our inability to measure marsh export directly. Figure 51 shows measurements of CO2 flux through a S_. al terni flora stand at different seasons. The cuvette used to collect these data enclosed 0.07 m^ of marsh, including sediment and aboveground vegetation, so the data should represent the whole community. Notice that nearly 71 S«pt«*lb«('7S il Is •I ir ri OP m fil ^ fc r*i ~ rt n i 1 - \ rii i 1 1 1 1 i 1 .N'-, -f '— ' -T- ■^ -f-i u Lj. _ 1 1 I y 4^ - y y Figure 61. Carbon dioxide flux measurements in a deltaic salt marsh community (unpublished data; see Gosselink et al. 1977). all the production can the grass. be attributed to Most of the respiration is associated with the diatom and microbial community (aufwuchs) on the base of the plant culms and sediment surface. In Figure 62 I show annual C fluxes calculated from these data, adjusted for the difference in average biomass in the cuvette compared to the surrounding marsh but not corrected for light intensity, marsh flooding, and temperature variation (see Gosselink et al . 1977 for details of the technique). Comparable data from other delta salt marsh studies is displayed for comparison in Table 29. Organic matter has been converted to carbon by multiplying by 0.4 (Smith et al. 1932a). The differences from earlier budgets are startling. Gross community production was estimated to be METHANE (5) GROSS PRODUCTION 4680 SALT MARSH LEACHING (140) ABOVE GROUND BELOW GROUND ►(850)-! ► 2680-' 3265 PLANT CONSUMERS ▼ SEDIMENTS (265) EXPORTED AND -► UNEXPLAINED SALT 1120 RESPIRATION 1010 RESPIRATION 2140 Figure 62. Carbon budget of a Mississippi River deltaic salt marsh (see Table 29 for sources). Rates (g C/m^/yr) are from CO2 flux measurements, except numbers in parentheses, which are from other sources. 72 4,680 g C/mVyr, most of the einerjent grass. Net tion was 3,670 g/m^/yr. other figures comparable direct measurement. which is due to primary produc- There are no to these from Net aboveground production from clip plot studies is only about 850 g/m^/yr. leaving an estimated 2,800 g/mVyr under- ground production. That is not impossible but is certainly very high. Community respiration was about 3,150 g/m^/yr, which is not too different from the estimates of Day et al . (1973) and Hopkinson and Day (1977) of around 3000 g/mVyr; but in their studies 90 percent of this was plant Table 29. Estimates of different components of the carbon budget of a Mississippi deltaic salt marsh community (g C/m^/yr). Carbon flux Technique Reference Input Gross community primary production 4,680 Net plant primary production (above and belowground) 3,670 Aboveground einergents 793 578 871 1,158 Mean 850 Belowground production 2,820 Output Community respiration Emergent plant respiration Consumers Leaching from live plants Methane production Lost to deep sediments 3.150 3,081 1,010 2,750 2,140 302-316 140 5 265 Balance (export and unaccounted) Net community production 1,260 300 300 150 CO2 flux II M CI ip plot 11 II M II II II II II Difference (3,670-850) a b c d Mean CO2 flux a Sed. oxygen flux & calc. pi ant resp. f ,g CO2 flux a calculated from other studies f,g CO2 difference a Oxygen flux & calc. for large consumers f,g Leaching studies i Methane flux h Subsidence rate X sed. C content j from CO 2 a from organic balance f,g from N bal ance j from estuary export & bay P:R ratio k References : a - Gossel ink et al . 1977 and unpubl. b - Kirby 1971 c - Kaswadji 1982 d - Hopkinson et al. 1978 e - White et al . 1978 f - Hopkinson and Day 1977 q ■ - Day et al . 1973 h ■ - Smith et al. 1982 i ■ - Turner 1978 j ■ - DeLaune and Patrick 1979 k • ■ Happ et al. 1977 73 respiration (calculated from literature values). In the CO; flux studies, two- thirds is associated with the aufwuchs coinmuni ty and the sediments. The experi- mentally detennined data for consumer respiration are 2,140 g/m^/yr from CO2 flux measurements and about 300 g/m^/yr from O2 flux. The CO2 flux was determined with the marsh unflooded, the Oj flux when the marsh surface was submerged. About 140 g/m'^/yr may be lost through leaching, 265 g/m^ /yr are lost to deep sediments, and another 5 g/m-^/yr are lost as methane. Over the whole community the net balance unaccounted for (that is, the organic C available for export) is 1,120 g/m^/yr. Export of all the aboveground production would not equal this. Hopkin- son's estimate of about 300 g exported/m^/ yr is also the balance left over when all other inputs and outputs are considered. It is a reasonable figure in that it matches the estimate of Happ et al . (1977). Furthermore, the H budget (see Nutrient Cycling), which is derived from different assumptions and measurements, also makes a value of about 300 g C reasonable, assuming that the exported N is all organic with a C:N ratio of 21.6 (Delaune et al. 1981), The discrepancy between 300 and 1,120 g/m^/yr is large. The best that can be said for the C balance in deltaic salt marshes at present is that there appears to be a large amount of organic production for which the fate is unknown. Part of it is certainly exported, but we do not know how much. Methodological differences certainly contribute to the uncertainty. We know even less about C balances in zones other than the salt marsh. Burial of C in deep sediments does not vary much from salt to fresh marshes. However, as sulfate availability decreases, methane production increases. The annual loss of C as methane increases from 5 g/m^ in salt marshes to 73 g/m^ in brackish marshes and 160 g/m^ in fresh marshes (Smith et al . 1982a). On the other hand, because flushing energies are lower than in salt marshes one would expect waterborne organic export to decrease toward fresh areas. The brackish marsh, in particular, is very poorly understood. Its production is high, probably higher than the salt marsh. Because flushing energy is low, export is expected to be low also. This suggests that respiration must be very high, but decomposition studies (White et al . 1978) show slower loss rates than in salt marshes. NUTRIENT CYCLES In coastal marsh ecosystems, as in other types, organic productivity depends on the availability of inorganic nutrients in the right proportions at the right times. Growth limitation due to both nutrient limitation and toxicity can and probably do occur in marshes. However, of the 12 inorganic minerals known to be required by plants, only N appears to be regularly limiting to marsh plant growth. Iron limitations have been reported (Adams 1963), but subsequent studies have not supported this observation (Haines and Dunn 1976). In fact Fe and Mn are much more likely to be in toxic concentrations in i.iarsh soils because of their increased availability under anaerobic conditions. For example, Fe is found in marsh plant tissues in concentrations up to 1,800 ppm (Haines and Dunn 1976), which is well over 10 times the concentration in most agri- cultural crops. Marshes are open systems, and the absorption and release of nutrients can have strong effects on adjacent waters. Marshes have been said to reduce eutro- phication by removing nutrients from these water bodies and, conversely, to be a source of nutrients that supplements aquatic production. The evidence for Mississippi delta salt marshes is that they are sinks for all nutrients, that they absorb inorganic N and release part of it as reduced ammonia and organic fonns, and that they export organic C. Ecologically the most important nutrients in the marsh are N, P, and S. Ni trogen Nitrogen, as mentioned earlier, has been found to limit growth in most marshes (see Mendelssohn et al . 1982). Nitrogen chemistry in anoxic soils is extremely complex and is made even more so by the 74 proximity of aerobic and anaerobic layers in marsh sediments (Figure 53). In the aerobic layer, oxidation of ammonium to nitrate occurs. This is an extremely thin layer in most delta marshes because the rate of diffusion of oxygen into the flooded soil is not fast enough to supply the demand by the large microbial population. The nitrate can diffuse down into the anaerobic zone where it is reduced to nitrous oxide and nitrogen gas and lost from the marsh ecosystem. Nitrate can also be reduced all the way to ammonium, and perhaps as much as 50 percent of it is reduced to this form under the environmental conditions of a delta salt marsh (Smith et al . 1932a). Either the oxidized nitrate or the reduced ammonium can be taken up by the emergent grasses, but free nitrate is present in only the thin aerobic layer. Undoubtedly, nearly all the N absorbed by the marsh plants is ammonium. The nitrification of ammonium and its subsequent denitrifica- tion to N2 is facilitated by the vertical movement of the aerobic-anaerobic inter- face as the tide rises and falls. The ions do not even have to diffuse from one NH, ji. * ^s oa"^ ■ NH:-N+N0-2-N+ NOi-Nj t NITRIFICATION ^^'Ji LAYER NAEROBIC ..„,.,.„„ SOIL UPWARD LAYER DIFFUSION X DIFFUSION |^|_|t DOWNWARD DIFFUSION Nj.N^O ■* O"*^*""- " MINERALIZATION DENITRIFICATION LEACHING ..^ -NOa'-N Figure 63. A schematic outline of the redox zones in a submerged soil showing some of the N transformations (Copyright. Reprinted from "Nitrogen in Agricultural Soils," 1982, with permission of the American Society of Agronomy). The aerobids layer has been drawn thick for clarity. In reality, it is seldom over 1-2 mm in flooded marshes. zone to another - the zones migrate to the ions. Most of the N in the substrate is organic; mineralization (the decomposition of organic material and release of in- organic nutrients) of this material yields nearly all of the ammonium available for absorption and for nitrification (Patrick 1982). As much as 3.8 yg N/ml soil/week (inland) to 11.1 ug/ml/week (streamside) is mineralized under optimum conditions (Brannon 1973). This compares to a peak demand by S_. al terni flora of about 2.1 ug/ml/week based on the Tiaximimum growth rates detennined by Ki rby (1971). Kirby's estimate does not include root production so it is an underestimate, but the indication is that mineralization can provide nearly all the inorganic N that the plant takes up. Delaune and Patrick (1979) came to the same conclusion based on average annual rates. It is likely, for two reasons, that plant uptake tracks mineralization closely during the active part of the growing season: (1) Nitrogen is limiting plant growth so the plants would be expected to take it up as it became available. (2) During the active growing season, sediment ammo ni urn- N remains at a very low concentration of less than 1 ug/ml , increasing to higher levels of 6 - 7 ug/ml during October and November when the plant growth demand is much reduced (Brannon 1973). Ammonium not taken up by plants is likely to be lost through deni trif ication. Vegetated marsh plots retained 93-94 percent of added labelled ammonium-N in the plant and soil, whereas in soil cores without plants only 56 percent of the labelled N was recovered (Table 30). However, denitrif ication and other gaseous losses of N are reported to be low in delta salt marshes, probably because plants absorb ammonium before it can be denitrified. Smith et al. (1982a) reported that only about 50 mg N/m^/yr are released as N2O, and estimated that about 5 g N/m^/yr is released as Nj through deni trif ication. Nitrogen fixation is also relatively minor. Casselman et al . (1981) measured fixation rates of 15 and 4.5 g N/m^/yr in a streamside and an inland marsh, respectively. 75 Table 30. al terni flora Influence plants on of Spartina recovery of •'^N- ammonium added over 18 weeks to soil cores (Buresh et al. 1982) . Recovery of added N Soil Aboveground Total tissue Soil core with plants Bare soil core 42±2.3 56 51±3.5 93 ±4 56 Includes belowground tissue. The overall N budget for a salt marsh is summarized in Figure 64. There is a large reserve in the sediment. New N is introduced in particulate fonn in tidal water. DeLaune et al . (1981) estimated this source to be about 23 g/m^/yr from the N concentration in sediment trapped in shallow pans mul tipl ied by detennined from sediments are a ■>et the i^'Cs sink marshes are subsiding quite accurately from about 16 g/m^/yr. surface water, the balance the budget, into the marsh, sedi.iientation rate profiles. The deep for N, because the This loss, known ^"Cs profiles, is Nitrogen export in amount needed to is 14 g/mVyr. Presumably this is primarily bound up in organic fonn. Notice that there are no estimates of the flux of dissolved N in the water column. Nobody has made even a first order estimate of that. Phosphorus At first glance the P budget appears to be much less complex than the N budget. PLANT TOP ISOOgOM 13gN 1.3gP PRODUCTION y , 2900qOM N FIXATION^ ° ^5^ 1 IgN OVERLAND FLOW 23gN 2.5gP -\— \-l ► 1450gOM\ I DENITRIFICATION OVERLAND FLOW 14 OgN 0 6gP PERMANENT SINK 1 5gN 1.75gP Figure 64. Nitrogen and phosphorus budgets for a Mississippi deltaic salt marsh (adapted from DeLaune and Patrick 1979). 76 Phosphorus has no volatile forms, so sources and losses must occur through water flow across the marsh. Studies in Georgia salt marshes have shown that P accuTiulates in estuarine sediments, fonning an enormous reservoir of many years supply (Pomeroy and Wiegert 1981). In aerobic soils P rapidly becomes unavailable because it is tied up with Fe, Ca and aluminum (Al). But under anoxic conditions the ferric phosphates are reduced to the more soluble ferrous form, phosphate anions can exchange between clay and organic anions, sulfides can replace phosphate in ferric phosphates, and hydrolysis of phosphate compounds can occur. The P budget for a delta salt marsh is presented in Figure 64. Extractable (and presumably available) P averages between 4 and 3 g/m^ in the sediment over the year (Brannon 1973). Since the annual demand for P by the emergent plants is only about 2.6 g/m^ there does not seem to be any lack of P for plant growth. About 2.3 g/m^ is brought in with sediments, and 1.7 g/m^ is lost to deep sediments. This leaves a balance of 0.6 g P/m^ exported, again probably as organic P. Sul fur The S cycle is interesting not because S has been reported to limit plant growth in marshes, but because of its important role in energy transfer. This is a new and still not fully understood role. When oxygen and nitrate are depleted in flooded soil s, sul fate can act as a terminal electron acceptor and is reduced to sulfide in the process. (This gives the marsh its characteristic rotten egg odor). In anoxic salt marsties sulfate is a major electron acceptor. In fresh marshes where the supply of sulfate is limited, C is reduced to methane instead. The sulfide radical is a form of stored energy that can be tapped by S bacteria in the presence of oxygen or other oxidants (Howarth et al. 1983). In a northeast Atlantic coast marsh the energy flow through reduced inorganic S compounds was equivalent to 70 percent of the net belowground primary productiv- ity of the dominant grasses. Apparently most of the stored sulfides are reoxidized annually, by oxygen diffusing into the substrate from the marsh grass roots (Howarth and Teal 1979), but there is a possibility of soluble sulfides being flushed from the marsh to become a source of biological energy elsewhere. In the marsh cited above, Howarth et al . (1983) estimated that 2.5 to 5.3 moles of reduced S/m^/yr are exported by pore water exchange with adjacent creeks. This amounts to about 3-7 percent of the S reduced in the sediment, and as much as 20 - 40 percent of net aboveground pro- duction. No one has investigated whether the export of reduced S compounds is signifi- cant in Mississippi delta marshes. Brannon (1973) measured the total S content of salt marsh sediments (Figure 49) and found the same kind of seasonal variation reported by Howarth et al . (1983). A crude estimate of the amount of reduced S lost to deep sediments by marsh subsidence shows it to be in the neighbor- hood of 1 g (0.3 mol)/m^/yr. This is about the same amount of S deposited by precipitation in southeastern forests (Swank et al . 1984). We have no idea of the reduced S flux from the marsh. STORIES The role of severe storms on marshes has received little attention, mostly because their occurrence is unpredictable and their immediate effects difficult to document. Storms occur with remarkable frequency on the delta plain. A 1.5-m wind tide occurs about every 8 years. (Figure 12), and smaller storms are annual events. Most of the sediment is deposited in the coastal marshes during these high water periods or during winter storms (Figure 32). Day et al . (1977) reported that Hurricane Carmen in 1974 defoliated swamp forests in its path two months earlier than nornial leaf fall. A large amount of organic C, N, and P was flushed from the swamp to the fresh, brackish, and salt marshes of the lower estuary by the accompanying torrential rains. Part of this material undoubtedly resulted from 77 the early defoliation, but visual evidence pointed to thorough flushing of stored detritus froui the swamp floor which would not wash out under nonnal weather conditions . On the other hand, a survey of salt marsh biomass in the Barataria and Terrebonne basins in progress at the time of the same hurricane (Gosselink et al . 1977) showed no evidence that dead biomass collected from the marsh surface was any different in plots sampled before the hurricane than after. Short-term effects of Hurricane Camille on species composition in fresh and brackish marshes near the mouth of the Mississippi River were described by Chabreck and Palmisano (1973). They found that an increase in salinity caused by the hurricane tide was ephemeral. The major effect seened to be widespread destruction of vegetation, especially woody species, by wind and water which uprooted and ripped apart stands of plants. Recovery of most species was rapid so that prehur- ricane levels of abundance were approached within a year. In the small lakes and ponds, however, the submerged and floating vegetation was slow to recover. Probably the most dramatic alteration documented in marshes is that described by Valentine (1977) in the chenier plain of southwestern Louisiana. One hundred sixty thousand ha of CI adium jamai cense (sawgrass) were killed by the saline tide of Hurricane Audrey in 1957. The following year 86 percent of this area was open water. During the drought years of the early 50' s annual grasses and sedges became abundant. By 1972 Sagittaria falcata (bulltongue) occupied 74 percent of the area and Nymphaea odorata (white water-lily) 11 percent. C_. jamaicense never reestablished itself in any extensive areas, oerhaps because seed viability was very low. Secondary effects of these vegetation changes on duck feeding habits were dramatic. Prior to 1959 C^. jamaicense seeds were an important component of duck diets. In the years immediately following the hurricane, duck stomachs contained primarily rice seeds, indicating heavy dependence on agricultural areas outside the marshes. During succeeding drought years, when the marshes produced large quantities of annual grass seeds, large numbers of both ducks and geese were attracted to these habitats. It seems likely, therefore, that hurricanes are major forces on gulf coast marshes, initiating changes that can have significant consequences for years following the storm. 78 CHAPTER FOUR THE MARSH IN THE COASTAL BASIN flarshes are open ecosystems; that is, they are not isolated islands out of touch with their surroundings. Quite the contrary, the main reason that they are of particular interest to environmentalists and conservationists is because they are strongly coupled with surrounding ecosystems. In Chapter 2 we say that the main physical driving forces for marshes are the upstream river and the downstream ocean. Both are outside the marsh, but the annual variation in river flow, the periodic switching of its channel and thereby its nutrients and sediment, and the periodic variation in the gulf water level and salinity all determine the character of the marsh. Similarly, marshes are open biotically - they contribute biologically to many other ecosystems. Figure 65 illustrates these couplings with other ecosystems: marsh zone to marsh zone; marsh to estuary; marsh/estuary to gulf, river and adjacent uplands; and intercontinental couplings. COUPLINGS AMONG ECOSYSTEMS Intra-Basin Couplings The coastal basin can be viewed as a set of coupled subsystems, for indeed the marshes, bays and streams in the basin are tightly coupled. A typical basin is organized by the internal freshwater-salt MARSH ZONE TO MARSH ZONE Figure 65. Conceptual diagram illustrating the coupling of delta marshes to other ecosystems. 79 census, individual fresh marsh or in freely among the taking advantage conditions. The water gradient. We take the organization for jranted, but brackish areas are always between fresh and salt areas. The marshes next to the uplands are usually fresher than marshes in the interior of the basin because they receive rain runoff; salt marshes are more naturally dissected by channels than fresh marshes because they receive stronger tidal energy, and so forth. Similarly, biotic assemblages are organized along these gradients. We have seen that one of the chief consumer groups in the marsh, the waterfowl, partitions itself within the different marsh zones according to the tolerance of individual species for salt and preference for available foods, marsh ponds, and water depths. But these preferences are only average ones. On any single aerial bird flocks may be found in salt marsh. They inove different marsh zones, of favorably changing increased waterfowl density when marshes changed from sawgrass to annuals, mentioned in the previous chapter, is an example of the mobility of the fauna among marsh zones. The possible displacement of muskrats toward saline marshes by the invading nutria is another. Nektonic organisms provide particularly good examples of the use of multiple subsystems within the coastal basin (Figure 56). Many year-round residents of the estuary are euryhaline and move freely throughout the basin. Such species as the bay anchovy, mullet, alligator gar, rainwater killifish, and tidewater silverside are found from salt to freshwater, many of them in the small creeks that border the marshes. Others, like the threadfin shad, the blue and channel catfish, and the river shrimp move down basin during the fall and winter as brackish areas freshen. The marine- spawned croaker, menhaden, and blue crab use the whole estuary as a nursery area, penetrating all the way through salt and brackish zones to fresh marshes in their migrations. Extra-Basin Couplings FISH & SHELLFISH WHirr iiHRiMP TEAL & PINTAIL WAGING BIRDS BLACKBIRDS & CRACKLES ent The marine-spawned, estuarine-depend- fish and shellfish mentioned above Figure 66. Patterns of estuarine use by nektonic organisms in the Barataria basin, Louisiana (Chambers 1980). are, from an economic point of view, the most important group of consumers that frequent the coastal marshes. Typically they spawn on the continental shelf, move into estuaries as juveniles, and return to the Gulf of Mexico as adults to continue the cycle. Nearly all the commercially important nektonic species on the gulf coast are estuarine-dependent (Gunter 1957). Within the estuary marsh habitat is crucial for these species. For example. Turner (1977) showed that both along the gulf coast and worldwide, the commercial shrimp harvest is directly related to the marsh area in the inshore nursery. The relationship is to the total marsh area - not just salt marsh; the relationship of yield to the inshore open water area is poor. The brown shrimp life cycle is typi- cal for these estuarine-dependent species (Figure 67). Early in their juvenile stage they can be found deep in the marsh in small bayous and ponds. As they in- crease in size, they move slowly out into 80 Spfi Figure 67. The life cycle of the brown shrimp (Gosselink 1980), larger, deeper water bodies which they appear to use as "staging areas" for emigration. These anigrations occur primarily at night and are keyed to the phase of the lunar tidal cycle, with greatest movement during periods of high- est tides (Blackmon 1974). In the Mississippi Delta there appear to be no fish species that spawn in fresh water and move to the ocean as they mature. But in other locations these species make extensive use of the marshes through which they pass on these migra- tions. A different kind of migratory use of marshes is that of numerous bird species which move daily in and out of the marshes to feed. Wading birds, for example, may nest in adjacent upland areas and along beach rims but feed along the marsh edges and in marsh ponds during the day. Their daily travels may cover many miles. One manber of this group, the white ibis, has been reported to travel as much as 80 km from its nesting site to feed (Lowery 1960). In a similar vein,Tamasier (1976) found wintering green-winged teal and pintail resting during the day on large. shallow ponds. The birds then spread out to forage elsewhere at night. Deer and other mammals may also venture out into marshes to forage from upland resting areas (Schitoskey and Linder 1979). Intercontinental Couplings The most dramatic inter-ecosystem couplings are those of the migratory birds that link Canadian and Alaskan pothole wetlands to gulf coast marshes. The Mississippi delta wetlands are at the southern extreme of the major duck and goose migration corridors (Figure 68). Many songbird species winter further south and are found moving through the delta marshes only during fall and spring migra- tions. As mentioned earlier, we have wery poor information about the importance of winter-habitat quality of birds that nest in the far north, but all indications are that it is extremely important for nesting success. TEMPORAL USE OF MARSHES It is interesting to observe how different migrating species use coastal wetlands at different times. (Figure 69). 81 Figure 58. Major duck migration coast marshes (Bellrose 1980). corridors to gulf Bird populations sre largest during the winter when ducks and geese are abundant. It is misleading to group all these species, however, as sone migrate on through to South America, as shown for the pintail and teals. These two species reach peak abundance late in the year and again in the spring, apparently because a large proportion of the population moves south across the gulf in mid-winter. Wading bird densities in the marsh peak during the summer. Although they are year-round residents, they appear to be much more active in marshy areas during the summer (Mabie 1975). About 60 species of land birds, mostly songbirds, migrate through the delta to South America each year. They do not use the marsh exten- sively, but usually fly over it. However, during northward spring migrations they frequently encounter strong head winds and take refuge on the first landing sites, the cheniers and slightly elevated marsh ridges. During these occasions their densities can be very high, and the marshes can be important for their sur- vival. Some of these songbirds, like the red-winged blackbird and the great-tailed grackle, nest in the coastal marshes in 82 o o X HI s u. O 3 MARINE-SPAWNED JUVENILES (EURYHALINE) FRESHWATER ADULTS Micropogonias undulalus ,use oppe- esiuai^ (ReslriLlod lo (rrshesi .irc.is) Lepomts gulosus Nolemigonus crysoleucas BrevoOflia palronus Mugil cephalus Parahcthys lethostigma Call.necles sap.dus Lale w.n.er and early .pr^iq »isho-e .mm.gral.on ^ Penaeus spp L.irv-ie Pc.Haivae Juveniles ^^ Subadults Summer and tall oMsHore emigration J MARINE-SPAWNED JUVENILES FRESHWATER ADULTS (MESOHALINE) Carani hippos Cf^nsienls m upper bflsn lUn.. ,nin ntanhalme IcIalUfUS punclalUS nuiinq niqn s^iiniiv perioas) Pomatomus sallatnx '»'"■ ■" '" """ -""■' Iclaluius lurcalus when marine lorms are absent) Macrobrachium ohione Potydaclylus octonemus pTionolus tnbulus Oorosoma pelenense Dorosoma cep«dt3num Scomberomorus maculalus Anus lelis /^ Late lalt and early wnniet AnchOa hepsetuS summer and e.^.^ t.V\ »^s^orP mov-m^nl / e«tensK>n mlo tow sahrnty ^if^-i J ' Lale wmter and early spring retreat Lare lall and early winler emmtqralion j^ lo (resti *aler lakes and bayous " i»,a. ,o„.rt EURYHALINE ADULTS AND JUVENILES (Yeir round residenis) Anchoa milchilli 'psidenis) Gobiosoma spp. Lucania parva Menidia berytlina Palaemoneles spp Lepisosteus spalula (0 lU < -I o z < Q. < oc UJ I- < X (/) c SALINE (20-35 ppD BAflATAfllA BAY BRACKISH (0.5-20 ppl) LITTLE LAKE -LAKE SALVADOR FRESH (0-0 5 ppt) LAKE CATAOUATCME-LAC DES ALLEMANOS Figure 69. Seasonal use of wetlands by migratory birds, shellfish, and fish. large numbers. They disappear during the winter when they migrate south. Similarly, nektonic species appear to partition the marsh ponds and creeks seasonally. The most abundant commercial species peak in ^y and June (brown shrimp), October to December (white shrimp), and March to May (croaker and menhaden). The top carnivores, spotted seatrout and red drum, reach greatest densities in September and October. Up in the shallow marsh ponds, the year-round residents peak in early spring (Ruebsamen 1972). The hot months of July and August seem to be the periods of least activity in the marsh, perhaps because many species move into deeper, cooler bay waters during that time. The migratory habits of the many species that inhabit the delta marshes emphasize the importance of inanagement objectives that take into account the high degree of coupling of the marsh with other ecosystems. Marshes cannot be managed in isol ation. 83 CHAPTER FIVE WETLAND VALUES, HUMAN IMPACTS, AND MANAGEMENT The terai "value" imposes an anthropocentric orientation on the discussion of marshes. The term can be used in an ecological sense to refer to functional processes, for example, when we speak of the "value" of primary production in providing the food energy that drives the ecosysten or the "value" of a predator in controlling the size of herbivore populations. But it is important to distinguish this use of the term from its ordinary use which refers to the services wetlands perfonn for man. The reasons that wetlands are legally protected have to do with their value to society, not with any abstruse ecological processes that proceed therein; this is the sense in which "value" is used in this chapter. These perceived values arise out of the functional ecological processes described in the previous chapters, but are detennined also by the location of a particular marsh, the human population pressures on it, and the extent of the resource. The extent of the marsh, in particular, has been one factor that has lowered the value of gulf coast marshes in human eyes. There is so much marsh that losing a few acres for any specific project has not been seen to be of much consequence. In this chapter I will first review the services natural wetland systems provide for society, then discuss the problems of trying to compare the values of natural ecosystems with more conventional economic systems. Finally, I will outline what appear to me to be the major management issues in Mississippi del ta marshes . WETLAND VALUES Wetl and Harves t The easiest wetland value to discuss and quantify is the harvest of animals that depend on it. Aside from the important fur animals, most commercially important species associated with wetlands are migratory, requiring habitats in addition to marsh to complete their life cycles. This group includes all commercially important fish and shellfish, recreational fish species, and hunted waterfowl. Qual i tatively, i t is clear that delta marshes are important habitats for these species, and the completion of their normal life cycles depends on the marshes. This dependence has been the rationale for imputing the whole economic value of the harvest to the marsh, although this is not without problems from an economist's point of view. The Louisiana coast fishery harvest is the largest in poundage in the country, and the wild fur harvest is also without equal. Sport fishing and recreational hunting generate comparable revenues. The per acre dollar value of these harvests has been detennined by a number of individuals. The figures in Table 31 for the Barataria basin are representative. Cited values usually range from $50 to $200/ha/yr, depending on the geographic area and the assumptions made. Other measures of wetland value for harvested species would be the weight of harvested animals or the number of hides and carcasses. These measures would not be subject to year-to-year variability in prices, but from an economic point of view they are not much good for comparison to other commodities. 84 Table 31. The estimated economic value of harvests from the Barataria basin, Louisiana (Mumphrey et al . 1978). Ac t i V i ty Annual Present return value ($/acre) ii) Commercial fishing 286.36 5,540 Noncommercial fishing 3.19 46 Commercial trapping 11.69 170 Recreation Economic impact of recreation expenditures 60.08 874 Econanic value of user-benefits 104.33 2,428 Total $465.65 $9,058 Capitalized value for indicated annual return. Environmental Quality Another set of values society receives from wetlands can be grouped under the heading of environmental quality. This includes a number of ecological functions of coastal wetlands that contribute to the improvement of water and air quality taken in the broadest sense. Much has been made of the ability of wetlands to remove organic and inorganic nutrients and toxic materials from the water that flows across them. In the delta, Meo et al.(1975) found that fresh marshes effectively removed nearly all the organic material and most of the nutrients from a menhaden processing plant's effluent when that effluent was allowed to filter through the marsh. There have been similar reports of efficient waste-water treatment from a number of other studies elsewhere (Bastian and Reed 1979; Kadlec 1975; Kadlec and Kadlec 1979). Nevertheless, these reports can not be taken uncritically. Most studies have been short term, and there is a persisting question of what happens if and when the system becomes saturated with the pollutant. The answer depends on the circumstances. In some systems the pollutants begin to appear in the outflow. Other marshes have been used for 20 - 50 years and still seem to function effectively. Where environmental circumstances are appropriate, nitrogen may be denitrified and lost to the air. But other pollutants such as heavy metals and phosphorus must accumulate or be washed out. There have been no long-tenn studies in the Mississippi delta, but the capacity for permanent storage of nutrients in these marshes is unusually high because of the rapid subsidence rate. Craig et al . (1977) showed that the upper part of the Barataria basin was heavily polluted, but that water quality rapidly improved downstream. This improvement would not have occurred if the marshes and streams were unable to "remove" the pollutants from the water. In spite of this cleansing capacity, the delta marshes are not used explicitly, with one or two minor exceptions, for water quality improvement. Marshes function in the maintenance of water and air quality on a much broader scale. Nitrogen and S are good examples. The natural supply of ecologically useful N comes from the fixation of atmospheric nitrogen gas (N2) by a small group of plants and microorganisms that can convert it into organic form. Today the produc- tion of ammonia from N2 for fertilizers is about equal to all natural fixation (Delwiche 1970). Wetlands may be important in returning part of this "excess" N to the atmosphere through denitrifi cation. The close proximity of an aerobic and a reducing environment, such as the marsh surface, is ideal for deni trif ication as discussed in Chapter 3. The denitrif ication rate seems to increase with the nitrate supply (Reddy et al . 1980; Engler et al. 1976). Because coastal wetlands are the downstream receivers of fertilizer-enriched river runoff and are ideal environments for deni trif ication, it is likely that they are important in the world's fixed N balance. Sulfur is another element whose cycle has been modified by man. The atmospheric sulfate load has been greatly increased by fossil fuel burning. VJhen sulfates are washed out of the atmosphere by rain they acidify oligotrophic lakes and streams. However, when washed into marshes, the intensely reducing environment of the sediment reduces them to sulfides which form insoluble complexes with phosphate and metal ions. In salt marshes this 85 effect is masked hy the abundance of sulfate in seawater, so perhaps sulfide accumulation in freshwater wetlands is a better index oF atmospheric input. In delta fresh marshes about 20 mq S/mVyr as sulfide is sequestered in deep sediments (Hatton 1981). This is more or less pennanently removed from circulation in the S cycle. Marshes are also valuable because they act as giant water reservoirs during floods. The vegetation may provide some resistance to the flow of water, slowing it down and thus protecting inland areas, but most of the benefit is probably its storage capacity. This is best seen on rivers where large riparian areas store storm waters and decrease the river stage downstream, reducing flood damage. On the Charles River in nassachusetts, this role was deemed effective enough by the U.S. Army Engineers that they purchased the river flood plain rather than build expensive flood-control structures to protect Boston (D.S. Army Engineers 1972). The broad, coastal expanse of the Mississippi Delta acts more as a storm buffer. Its value has to be seen in the context of marsh conservation vs. development. The full fury of a coastal storm hits the barrier islands and marshes first and it attenuated as it crosses them, damaging little property of societal value. Buildings and other structures in this coastal zone are vulnerable to the same storms, and damage is often high. Inevitably the public pays much of the cost of this damage through taxes for relief, rebuilding public services such as roads and utilities, and federally guaranteed insurance. Esthetics A very real but difficult aspect of the marsh to capture is its esthetic value, often hidden under the dry tenn "nonconsumpti ve use values", which simply means that people enjoy being out in marshes. The Mississippi delta marshes are a rich source of information on our cultural heritage. The remains of prehistoric Indian villages, mounds of shells or middens, have contributed to our understanding of both their culture and the physical geography of the delta (Mclntire 1959). Smardon (1979) described wetlands as visually and educationally rich environments because of their ecological interest and diversity. Their complexity makes wetlands excellent sites for research. Many artists have been drawn to tiiem, notably the Georgia poet Sidney Lanier, the painters John Constable and John Singer Sargent, the Louisiana photographer Clyde Lockwood, and many other artists of lesser public recognition. Each year thousands of these artists paint and photograph marshes. I suspect that many wetland visitors use hunting and fishing only as excuses to experience its wildness and solitude, expressing that frontier pioneering instinct that may lurk in us all. Confl icting Values With this long list of marsh values one might expect marsh conservation to be an issue that everyone would support. This is not so, and the reason is simple. The private owner of a marsh tract benefits financially from very few of these services. In Louisiana land can be leased to trappers and hunters for perhaps $25/ha/yr (Chabreck, LSU School of Forestry and Wildlife Management; pers. comm.). The owner has no monopoly on, and cannot sell, the fishery resources and the improved air and water quality associated with the marshes. To the owner the wetland is valuable primarily for development - drainage for construction or agriculture, or dredging and drilling for subsurface mineral resources - that can bring in thousands of dollars per hectare annually. This conflict between private ownership and public services is becoming more intense everywhere as population density increases, but it is particularly impassioned in wetlands for several reasons. First, population density and development pressure are particularly high on coasts; second, marshes are open systems that cannot be considered in isolation; and third, marsh development is essentially irreversible. 86 Recognizing the value of wetlands and educating the public and public officials to these values are important milestones that have led to legislation (particularly Section 404 of the Clean Water Act of 1977) protecting marshes from unconsidered modification. Wetland management did not begin with this legislation, hut certainly the Clean Water Act has focused attention on many wetland issues. Some of these Issues, particularly those that relate directly to Mississippi delta marshes, will be discussed in the rest of this chapter. Probably the most used instruments for ecological evaluations in general are the U.S. Fish and Wildlife Service Habitat Evaluation Procedures (HEP, USFWS 1980) and the U. S. Army Engineers Habitat Evaluation System (HES, USAE 1980). Both were developed for upland sites. HES has not been adapted for wetlands, and HEP wetland applications are still evolving. These procedures are most valuable when used to compare two different areas or to compare an area before modification to the expected state afterward. WETLAND EVALUATION One important component of wetland management is the evaluation of proposed actions in wetlands. Under Section 404 of the Clean Water Act of 1977 a perniit is required for wetland activities that might affect water quality. For activities that require an environmental impact statement (as required by the National Environmental Policy Act) two different kinds of evaluation are involved. First, the ecological value of the area in question is determined - that is, the quality of the site as compared to other similar sites or its suitability for supporting wildlife. Second, the ecological value of the habitat is compared to the economic value of some proposed activity that would destroy or modify the habitat - in other words, a benefit:cost analysis. Both pro- cedures are fraught with difficulties. Both require an evaluation of the relative values of different commodities, like com- paring apples and oranges. Above all, both require numerous value judgments about what is ecologically desirable. The HEP procedure, probably the aiore detailed, illustrates both the potential and the problems of evaluation. In this procedure the suitability of a site is evaluted for a number of different game species, commercially important species, and species of special interest for ecosystem structure or function. For each species, habitat suitability is evaluated on a scale of 0 - 1.0 for a number of habitat characteristics. These Habitat Suitability Indices (HSI's) are multipl ied by the area of each species' habitat under consideration to yield Habitat Units (HU's). Thus both habitat quality and area are combined in one number. Schamberger et al. (1979) listed the assumptions of the system: (1) habitat value can be quantified; (2) habitat suitability for a species of concern can be evaluated from habitat characteristics; (3) overall habitat value can be determined by assessing suitability for selected species; (4) habitat quantity and quality are directly related to animal numbers. It is apparent that the community HSI's depend on the species selected for evaluation. Essentially all proceaures now in use assess the relative value of wildlife habitat. Lonard et al . (1981) evaluated 20 different wetland valuation systems. The enphasis in all of them was overwhelmingly on the evaluation of the ecological habitat function of wetlands. Hydrology functions are poorly documeted and difficult to quantify. Evaluation of silviculture, heritage, and recreation functions are also considered open for improvement (Lonard et al . 1981). The result of the HEP analysis is a set of HU's for individual species for the site or sites in question. The HU's can be compared within a site or among sites for determining best management scenarios. The values can be used to help make a management decision about the site, as for instance, offsetting project impacts through mitigation. In this case, sites with equal value in terms of HU's are created or set aside for use by the species in question. 87 This or any other evaluation system nust play off bewildering detail against simplifying integrations to facilitate the decisionmaking process. The evaluator must integrate mentally the information about a number of different individual species in order to make the decision. The ideal solution is a compromise between extremes - simple enough to allow a decision to be made, but detailed enough for the decisionmaker to feel confident about it. All procedures developed to make decisions about wetlands are based on human values and human judgments about what is good and what is not. They reflect what humans think is important, and that fact is a basic ingredient in all management. In the case of HEP, the procedures have been standardized, individuals can be trained and certified to carry them out, and reproducibility is quite good. These facts often make us forget the value-laden nature of the whole enterprise. When habitat values are monetized for benefit :cost analyses, a whole new set of assumptions are superimposed on the ecological evaluation. I do not intend to discuss these because they are well covered by several other authors (Shabman and Batie 1978; McAllister igS'"). The methodology has evolved from economic theory that assumes that in a free economy the market price reflects the value of a commodity (the willingness-to-pay approach). This leads to real problems in monetizing nonmarket commodities like pure water and air, and in pricing marshes whose monetary value in the marketplace is determined by their value as real estate, not their "free services" to society. Consequently, attempts to monetize marsh values have generally emphasized the commercial "crops" from marshes - fish, shellfish, furs, and recreational fishing and hunting for which pricing methodologies are available. As Odum (1979) pointed out, this kind of pricing ignores ecosystem-level values related to hydrology and productivity, and global values related to clean air and water and other "life support" functions. One controversial approach uses the idea that energy flow through an ecosystem or the similar concept "embodied energy" (the total energy required to produce the commodity, Costanza 1980) is a valid index of the totality of ecosystem functions; and that furthermore, this index is applicable to human systems as well. Thus natural and human systems can be evaluated on the basis of one common currency: "embodied energy." (Since there is a linear relationship between embodied energy and dollars, that more familiar currency can also be used.) The general response to this kind of approach is probably fairly summed up by Reppert and Sigleo (1979): "Certain aspects of the evaluation structure .... are too theoretical and unsubstantiated to be considered for general application, particularly those involving the analysis of energy flows and the conversion of energy values to monetary values." However, in recent years both the theoretical base and the methodology have been much improved . Using better assumptions, Costanza (1933) showed that the economist's willingness-to-pay approach and energy analysis converge to a surprising degree. In Table 32 the average gross benefits arrived at by summing the gross economic value of different marsh resources ($342/acre/yr) are roughly equivalent to the latest value arrived at from the embodied energy of biological productivity ($300/acre/yr). This convergence suggests an integrated methodological framework for evaluation. The approach has the real merit of being equally applicable to both natural and human systems, but like e^ery other approach it simplifies by converting everything into one currency. Since the purpose of the exercise is to compare apples to oranges or oil wells to marshes, some kind of equivalence must be established, but it seems to me dangerous to lose sight of the real 88 Table 32. Estimates of the economic value of Louisiana's coastal wetlands comparing willingness-to-pay approaches with energy analysis approaches (Costanza 1983). Approach Shadow Refer- value* ence oriented (Table 33). I will discuss briefly each major issue or problem, bringing in the role of the various human activities as they apply. Since habitat loss (marsh loss) is by far the most pressing problem, it will receive the major emphasis. 1979 $/acre/yr) Willingness-to-pay approaches Consumer surplus Gross benefits Average of gross benefits Net benefits Replacement value Energy Analysis approaches Biological productivity 25 3 155 241 352 544 231 342 237 ,662 ,120 7,374 300 d b d Marsh Loss and Salt Intrusion As discussed in Chapter 1 (Figure 23), the rate of marsh loss to open water has been accelerating over the past 50 years to the present rate of about 1.5 percent of the delta marshes being lost annually. Although the circumstances leading to this loss are complex and involve natural processes beyond human control , there is good evidence that a significant part of the problem is a result of human modification of the Mississippi River and the deltaic plain. This discussion will be limited to these latter factors, that is, those which man can hope to manage on a regional scale. *Price that would prevail in a perfect market. References : a - Humphrey et al . b - Gossel ink et al c - Vora 1974 d - Costanza 1983 1978 1974 structures involved. One compromise has been suggested by Lichfield et al. (1975), who used a planning balance sheet to list the major commodities exchanged and to identify the recipients of the cost and the benefits. This procedure ensures that the important factors in the benefit:cost analysis are explicitly recognized rather than being lumped into a single dollar value. WETLAND MANAGEMENT In the Mississippi River Deltaic Plain the major wetland management issues are marsh loss, salt intrusion, and the maintenance of habitat and water quality. These are interrelated problems. They are affected by a number of human activities, but the major ones can be grouped as either development or conservation- All the development activites listed in Table 33 contribute to marsh loss. Reclamation does so because it impounds and drains wetlands, essentially turning them into upland habitat. Although marsh "reclamation" is still occurring, the pace of development is much slower than it was early in this century (Gossel ink et al . 1979), and the cost of impounding, draining and maintaining an area is becoming so prohibitive that economics Table 33. Major wetland issues and human impacts in Mississippi delta wetlands. ENVIRONMENTAL ISSUES MINERAL EXTRACTON FLOOD CONTROL NAVIGATION O RECLAMATION _ HABITAT PROTECTION & ENHANCNG HABITAT CREATION + ? 0 + 89 dictates against this practice for purposes . ;iiost The impact of mineral extraction, flood control, and navigation on marsh loss occurs primarily through the canals dredged for these operations. Table 34 lists the major ecological effects of canals in the deltaic marshes, the kinds of iiiechanisns that should minimize these ecological impacts, and the specific management practices that are being used or could be used to implement these mechanisms. Because good experimental evidence is often lacking, many of the effects and mitigation procedures are inferred. I will document those statanents that can be documented. But many are merely reasonable extrapolations from what is known. Canals alter marshes by accelerating salt intrusion, changing hydrology, and affecting benthic and aquatic organisms. Salt intrusion is closely tied to changes in hydrology. It occurs when deep, straight channels connect low-salinity areas to high-salinity zones. Large navigation channels that link the marshes directly to the gulf are particularly efficient in allowing salt intrusion (Gosselink et al . 1979), but a channel from a saline bay into a less saline marsh also allows salt intrusion. Salt intrusion into fresh and i ntennediate marshes stresses the vegetation. We do not know exactly how the fairly subtle changes in salinity operate, but the result is often death of the plants and, as the roots die, loss of their peat-binding capacity. If the salinity changes so rapidly that the plants are not replaced immediately by more salt-tolerant species, often the underlying peat rapidly erodes and large, shallow lakes appear (Dozier 1933). These changes are linked to biocheinical and microbial changes in the peat associated with salt intrusion (Dozier 1983). Canals also change hydrologic patterns that inodify a marsh independently of any salt effect. Straight, deep canals in shallow bays, lakes, and marshes capture flow, depriving the natural channels of water (L. Gosselink 1934; Turner, pers. comm.). Canals are hydrological ly efficient, allowing more rapid runoff of fresh water than the normal sinuous channels. As a result, water levels fluctuate more rapidly than in unmodified marshes, and minimum levels are lowered (Light 1976). Sheet flow of water across the marsh surface is reduced by the spoil banks that almost always line a canal. Consequently, the sediment supply to the marsh is reduced, and the water on the marsh is more likely to stagnate than when freely flooded. Since canals change the marsh water budget, the salt budget, and the sediment supply, any mechanisms that can influence these three factors might be useful ways of minimizing the effects of canals. Table 34 lists several mechanisms. Generally, an increased freshwater supply Table 34. Impacts of canals in Louisiana coastal marshes leading to habitat loss, and mechanisms and management practices to minimize these impacts. Type of impact Mechanisms to minimize impacts Management practices 1. Salt intrusion 1. 2. Hydrologic 9 change 3. 4. 5. 6. Increase fresh water supply 1. Increase sediment supply 2. Reduce salt intrusion 3. Maintain slow, sinuous natural 4. water flows Maintain overland flow 5. Maintain water levels 6. Fresh water diversion Reduce number of canals Control canal location Improve engineering design Backfill canals Require mitigation fee for lost resources 90 to a marsh also increases the sediment load since rain runoff and river water are both generally quite turbid. Mechanisms that maintain slow, sinuous, shallow natural channels and overland flow will generally also reduce salt intrusion and stabilize water levels. They may also reduce the sediment-carrying capacity of the water, but this has to be balanced against the increased overland flow. A number of practices are already being used or are potentially useful to minimize marsh loss (Table 34). They can be grouped as those that build new marshes to replace those lost and those that minimize the loss of existing marshes. Day and Craig (1982) assessed the potential for reduction in wetland loss by several mitigation techniques. They concluded that diversion of fresh water to baild new marshes could only create 1-3 km^ of marsh a year, and the Atchafalaya had the potential of building about 18 km^/yr. The largest potential for saving marshlands (30 - 40 km^/yr), therefore, was by strict regulatory control of new canal s. We have little experimental experience on which to outline the best canal ing technology. Prohibition against new canals would be the best solution, but prohibition against crossing barrier islands, connecting basin interiors to the periphery, and creating canals that shunt upland runoff around marshes would be partial solutions. Directional drilling is a well- established technology that would eliminate the need to dredge canals for many well heads. It has not been used often in the coastal marshes, and good studies comparing the extra cost of directional drilling against the environmental cost of the canal are needed. Another technology that needs to be explored is the use of air cushion vehicles to traverse the marshes. These are used in the tundra and might provide a way to approach well sites and even transport drilling rigs without damaging the marsh extensively and without the need for canal dredging. There are also possibilities for better design of canals. Where possible, they should follow natural channels in order to maintain natural circulation patterns. Spoil deposits are usually placed on both sides of the canal, isolating the canal from the adjacent marsh. Any design that breaks the spoil barrier to allow better exchange with the marsh would probably be an improvenent. Unfortunately, there are no studies upon which to base detailed recommendations. It is common practice to require that when canals cross natural streams and other canals, they must be blocked to mini- mize the danger that the new canal will capture the flow of the other channels and/or allow salt intrusion. Some fairly straightforward engineering work is needed to improve the design of these barriers. Earth fill, shell, or rock are usually used. These materials have densities much greater than the organic marsh, and their weight tends to settle and load down the adjacent marsh. As a result, the barriers are constantly breaching, especially at their ends. It would seem that an inert plastic material of the same density as the surrounding marsh, perhaps anchored into place with a mininum number of pil- ings, could be more effective. Many canals can be backfilled - cer- tainly all those dredged for pipelines and also many that lead to dry or depleted wells. Yet we know little about the relative value of backfilling compared to open canals. Work in progress (Men- delssohn, Sikora and Turner, Center for Wetland Resources, LSU) points to the effectiveness of backfilling canals because the practice removes spoil banks and also raises the bottom of the canal (although it seldom fills it completely because of the oxidation and dissipation of sediments when they are exposed in spoil banks) to a depth where the water column does not stratify. Oxygen is then available to the sediments, and a healthy benthic infauna can grow. In addition, there is some evidence that these shallow ditches, if left open in areas where marsh circulation is poor, can improve the quality of adjacent marshes. Such research on canals can yield major bene- fits to the State by providing practical means of reducing marsh degradation. 91 Recently some permits for dredging in the delta marshes have included require- ments for marsh improvement elsewhere to mitigate the damage in the permit area. This is a creative mechanism for conserv- ing marsh, although at the expense of other marsh tracts. Unfortunately, the methodology for assessing the true envi- ronmental cost of canals is rudimentary, so the relationship between the canal damage and the mitigation effort is some- wh a t a rb i t ra ry . If environmental costs of development in wetlands are to be internalized by the developer, we need much better information about how to assess these costs. In a recent article /Vnft et al . (in review) present a methodology and make a bene- fitrcost assessment of an oil well access canal in the chenier plain. Based on their methodology, they suggest that a conservative estimate of the environmental cost for a typical exploratory well is $380,000 (1981 dollars) per kilometer of access canal . common in the chenier plain than in the delta, primarily because the firner substrate in the cheniers makes levee construction much less expensive and more effective. The idea behind these impoundments is to prevent salt intrusion and thus retard marsh loss. Unfortunately, there is little evidence to show that they are effective, and some evidence to suggest that they are not. Baumann, Conner, and Gosselink (LSU Center for Wetland Resources; unpubl, MS.) analyzed marsh loss rates in impoundments compared to adjacent unimpounded areas, and concluded that loss rates ivere actually higher in impoundments than outside them (Figure 70). Wicker et al, (1983) also measured marsh loss rates in different kinds of impoundments in the Rockefeller Wildlife Refuge. Although they presented no comparative data, it is apparent from their maps that marsh degra- dation is occurring in all the impound- ments except perhaps those with pumps for water level control . A word needs to be said about some current practices that do not seen to effectively retard marsh loss. One of these is channelizing upland runoff. In fairness, this practice is not used to minimize marsh loss, but it is a common flood control measure. The impact on marshes is negative because it shunts the sediments of rivers and runoff away from marshes, both by leveeing rivers to prevent overbank flooding and by digging deep-dredged channels to deliver flood water through and around marshes instead of over them. This is a case of conflicting interests in the coastal zone. Until recently, flood control interests took ascendancy over marsh loss concerns. A more balanced evaluation of this "solution" to flooding is needed. Another common practice is the construction of levees and impoundments to prevent marsh loss. In recent years, all over the deltaic and the chenier plain marshes small levees no nore than a meter high have been thrown up by private land owners. Marsh impound-nents are also common in State and Federal wildlife management areas where they were created to improve habitat for waterfowl and fur animals. These levees are much more The problem, I think, is that sediment input is a key element in the ability of a marsh to accrete fast enough to keep up with subsidence. Impounding /f"-4 z 111 a. ; o o NATimAL tUfiSH IMPOUNDED MARSH , K" 1962 YEAR YEAR Figure 70. The increase in open water in natural and impounded wetlands. The pattern of greater wetland loss in impoundments is consistent in both fall, when water levels ire low, and winter, when impoundments are flooded (W. Conner and R. Baumann, Center for Wetland Resources, Louisiana State University; pers. comm.). 92 cuts off the sediment supply. In i nterdistributary basins which have very little surface fresh water input, most of the sediments come from tidal action. Under these circumstances attempts to retard salt intrusion also restrict sediment input. In addition to marsh loss caused by salt intrusion and hydrologic changes, canals also directly change benthic and nektonic habitat quality (Table 34). The deep canals are depauperate in benthic organisms because, at least in bulkheaded channels, the lower part of the water column and the sediments are anoxic most of the year (W. Sikora, LSU Center for Wetland Resources; pers. comm.). On the other hand, canals might enable nektonic organisms to penetrate marsh areas where they previously had no access, although the presence of spoil banks would cancel this benefit. Fish can use the deep water of canals as a refuge during cold spells when the shallow natural streams become almost as cold as the air above them. Habitat Qua! ity In the wildlife management areas of the delta (Figure 71) several kinds of marsh modifications are practiced to improve habitat quality. Generally this means improved quality for waterfowl and fur animals, sometimes at the expense of fishery species. But in recent years the aim has been a diversified habitat that will support a broad range of species. Where water level management is active, the opening and closing of water control structures is timed to increase the availability of the managed area to migratory fish and shellfish species. The simplest control structure is the weir (Figure 72); this Is a common device found all over the coastal zone, especially in areas managed by State or Federal authorities. It is a dam placed in tidal creeks to maintain a minimum water level In the marshes drained by the creek. Usually the top of the weir Is about 15 cm below the average marsh surface. The purpose of the weir is to stabilize water levels to encourage the growth of submerged aquatic plants and reduce marsh erosion by keeping the marsh from drying out and oxidizing. Weirs seem fairly effective for stabilizing water levels (Figure 73) and for promoting growth of submerged aquatic plants (Chabreck 1968). On the other hand, the evidence from the study of Steever et al . (1976; see Figure 43) that marsh plant biomass is directly proportional to tide range makes it likely that marsh productivity is reduced by these structures. As far as erosion prevention is considered, there is no evidence that weirs are effective. Weirs are the cheapest kind of marsh management. Because of the increase in submerged vegetation, the ponds behind weirs attract more wintering waterfowl than unwei red ponds (Spiller 1975). They also improve conditions for fur animals. The next level of control device is the flap gate and/or variable level dam in a completely Impounded marsh. The flap gate allows water to flow one way through the control structure. Modern ones are reversible, but in Louisiana, with its high rainfall, they are usually set to allow freshwater to flow out of the impoundment and to prevent saltwater from moving in. Because of the surplus rainfall, all impounded areas become fresher with time. The variable height device, which is often incorporated in the same structure, allows the manager to set minimum water levels behind the weir. With this "gravity drainage" systen, if the weather cooperates it is possible to draw down the water In the spring to allow seeds of annual emergents to germinate. It can then be raised in the winter to make shallow ponds for ducks. The most sophisticated water level control Is obtained by pumping water out of or into the impoundment (forced drain- age). The effectiveness of these manage- ment measures can be judged by the kinds and diversity of vegetation produced (habitat quality) and the use of the impoundment by birds, fur animals, fish, and shellfish. Wicker et al . (1983) summarized the effectiveness of impoundments in the Rockefeller Wildlife Refuge. Annual vegetation surveys carried out since 1958 93 STUDY AREA — -- HYDROLOGIC UNIT BOUNDARIES GULF OF MEXICO 1 PAUL J. RAINEY WILDLIFE REFUGE 2 LOUISIANA STATE WILDLIFE REFUGE 3 RUSSELL SAGE FOUNDATION WILDLIFE REFUGE 4 ATCHAFALAYA WMA 5 SALVADOR STATE WMA 6 JEAN LAFITTE NATIONAL HISTORICAL PARK 7 JOYCE WMA 8 MANCHAC STATE WMA 9 POINTE-AU-CHIEN STATE WMA Figure 71. Wildlife mdnagement areas in the Mississippi Delta. 94 10WISNER STATE WMA 1 1 ST. TAMMANY STATE WMA 12 PEARL RIVER WMA 13 BILOXI WMA 14 BOHEMIA STATE WMA 15 DELTA NATIONAL WILDLIFE REFUGE 16 PASS A LOUTRE STATE WMA 17 BRETON NATIONAL WILDLIFE REFUGE lb Figure 72. A weir in the deltaic plain marshes. The strong flow of water across the weir is an indication of the effectiveness of the barrier. These structures are favorite sport fishing spots (Photograph by Robert Chabreck). show that the production of the desired emergent annuals and aquatic plants was variable. Even with pumps it was not possible to control water level in very rainy years like 1973, and the level of control decreased as the sophistication of the control devices decreased. In general, the better the water level management, the greater the diversity and desirability of the vegetation (Figure 74). Water level management in the Rockefeller Wildlife Refuge is credited with increasing waterfowl use from a peak population of about 75,000 ducks in 1951 - 1952 to over 400,000 dabbling ducks, 40,000 coots and 10,000 diving ducks in 1958 - 1959 when the control structures were put into use (Chabreck 1951). The freshwater impoundments attract the most ducks; use of brackish water impoundments (usually areas in which water exchange with the surrounding marsh is not completely cut off) is comparable to unmanaged marshes (Chabreck et al. 1975; Davidson and Chabreck 1983). The value of freshwater impoundments for species other than ducks is not as clear; fur animals, geese, and marine organisms are not benefitted (Chabreck 1975). However, crawfish can be successfully raised in impoundments managed for ducks (Perry et al. 1970). Brackish marsh impoundments seen to yield excellent crops of marine shellfish and fish if the control gates are managed to allow the juvenile organisms access during their immigration periods (Davidson and Chabreck 1983). Figure 75 summarizes the effectiveness of impoundments. Marshes, inside impoundments and out, are often burned as a management practice. 95 (0 > < Q cr III 03 z UJ > 3 O 20 40 60 80 100 BOTTOM EXPOSURE (%) Figure 73. year that equal or bottom exposure, of 43 ponds and Cumulative number of days per ponds in the study area will exceed certain percentages of Based on depth contours 20 years of tide data on the 1979 central Louisiana coast (Chabreck Chabreck (1975) questioned the value of most of this effort. However, he acknowledged that burning can be useful to remove a heavy vegetation thatch to allow annual species to germinate and to give three-cornered grass an earlier start during the growing season. Burning is widely practiced to attract snow geese to an area. Trappers find burned areas inuch easier walking, and animal trails are much more noticeable. However^ nutria and raccoon often move from a burned marsh because of the lack of adequate cover. Water Qual i ty Water quality is a major issue in Louisiana wetlands as in inany other areas of the country, but it has received relatively little attention, probably because the much more pressing issue of marsh loss has taken the spotlight. The source of delta sediments, the Mississippi River itself, is heavily polluted with exotic chenicals which become incorporated in the sediments of any marshes created. because of hydrocarbon strength; it reintroduced 1975). here they can be magnified into chain, leading to the kind of species that pelican. That from the del ta of chlorinated on egg shell recently been From the food effects on individual occurred with the brown s|-iecies was extirpated the effect pesticides has only from Florida (Blus et al Local runoff from urban and agricultural areas is also a serious problem. Seaton and Day (1979), Seaton and Day (1980), and Kemp (1973) documented the effects of urban runoff from the New Orleans area into the Sarataria basin and Lake Pontchartrai n. Gael and Hopkinson (1979) showed that eutrophi cation of water bodies is accelerated by canals which shunt the water around marshes instead of over them. High coliform counts have resulted in oyster bed closures in much of the estuarine area soutli of New Orleans and east of the Mississippi River. In all these examples the primary concern has been with the quality of water in the coastal lakes and bays. If 'iiore runoff water was allowed to flow across the marshes instead of bypassing it through flood drainage canals, it is likely that water quality would improve significantly. With all the oil and gas production activity in wetlands, it is surprising that so little is known about the effect of oilspills on wetlands. In the delta only one group of studies is available. This research showed that chronic, low-level oilspills resulted in fairly high levels of hydrocarbons in marsh sediments (Bishop et al . 1976) in the Leeville oilfield. These high concentrations are reflected in the aromatic hydrocarbon concentration in tissues of benthic organisms such as oysters and mussels. The emergent grasses and free-swimming organisms such as the grass shrimp and killifish had high concentrations of unresolved hydrocarbon components (Milan and Whelan 1979). The influence of this pollution on biota could not be separated 96 O 80 - Dnll'D Id :|liiillliU 158 60 66 70 74 O 80' I I AQUATIC PLANTS i; '|;| EMERGENT ANNUALS ^M EMERGENT PERENNIALS MANAGEMENT EVENTS 1955-LEVEES BUILT METAL FLAP -GATE CULVERTS INSTALLED FLAP-GATE CULVERTS LFAKING CONCRETE VARIABLE CREST REVERSIBLE MANAGEMENT EVENTS LEVEE REPAIRS WEST SIDE SOME FLAP-GATE CULVERTS PLUGGED FLAP-GATE STRUCTURES i ALL FLAP-GATE CULVERTS REMOVED SEPT 1965 SEVERE MARSH BURN FOLLOWED BY HIGH SALINE TIDES CAUSED MARSH LOSS O 80- M ^iufliuil MANAGEMENT EVENTS iUMil 1 1965- LEVEES CONSTRUCTED METAL FLAP-GATE CULVERTS INSTALLED VEAR FmP- GATE CULVERTS LEAKING WOODEN BOX FLAP- GATES INSTALLED MANAGEMENT EVENTS CONCRETE VARIABLE CREST REVERSIBLE LEVEE REPAIRS - EASTSIOE SOME FLAP-GATE CULVERTS PLUGGED FLAP GATE STRUCTURES' ALL FLAP-GATE CULVERTS REMOVED. WOODEN BOX FLAP-GATE CULVERTS PLUGGED VEAR METAL FLAP-GATE CULVERTS MAINTAINED AS PERMANTLV FLOODED FRESHWATER IMPOUNDMENT BEGAN SPRING AND SUMMER DRAW-DOWN DROUGHT FLOODED IN SUMMER FOR MOTTLED DUCK NESTING DOUBLE DIVERGENT . PUMPING UNIT Figure 74. The percentage of different types of vegetation Rockefeller State Wildlife Refuge (Wicker et al . 1983). in impoundments in the from the effect of the associated dense network of canals and spoil banks, but the density of marsh grass culms and average height was lower than in control areas (R. E. Turner; pers. comm.). Amphipods, total crustaceans, and total benthic organisms were reduced 50 percent compared to non-oilfield control areas (Lindstedt 1978). Killifish abundance was substantially less in oil- field marsh ponds than at control sites, although not statistically so because of the large confidence limits. However, the fecundity of Fundulus grandis in oilfield marshes was significantly lower than at control sites, especially the condition index of females 61-80 mm long (May 1977). It is apparent that we need to know much more about the effects of chronic low-level oilspills. From a management point of view, water pollution is a good example of the need to manage on many different levels. Water quality of the Mississippi River must be improved. This is a problem national in scope because of the river's enormous watershed. The control of urban runoff in the delta itself is a regional problem that affects marshes and estuaries in the New Orleans area more than other delta 97 TARGET HABITAT TYPE WATER MANAGEMENT PROGKAMi PASSIVE ESTUARINE CONTROLLED ESTUARINE GRAVITY DRAINAGE Wakefield Weirs at -0.5 ft MSL FORCED DRAINAGE Concrete Variable Crest Reversible Flap-Gates Concrete 36-in and i8-in Flap-Gates Radial Concrete Variable Crest Lift Gates Reversible Flap-Gates Pumps UNCONTROLLED Nonexisting or Non operable Structures EMERGENT PERENNIAL VEGETATION: Ve-H . Du-P, Mu-P, Nu-P Intermediate Ve-A Ve-M; Mu-F, Ge-F Du-P Nu-F Ve-M; Du-P, Mu-P^ Ve-M; Du-P Ge-F, Nu-f rtu-F, De-P, Nu-F Ce-F Ve-H; Du-P, Mu-P. Ve-A Nu-P, Ge-G Ve-H. Ce-G, Du-P, Mu-F, Nu-C, De-F Vp-H; Du-P, Mu-P, Nu-F, De-P, Ge-G Ve-M; Du-P. Mu-F, Ge-G, Nu-F, De-P Ve-M; Du-P, Mu-F, Ge-C, Nu-F, De-P, Ve-L; Du-P. Mu-P. Nu-P. De-P Ve-H; Du-P. Mu-F Nu-F, Ge-G Ve-H; Du-P. Mu-P. Nu-P. Ge-G EMERGENT ANNUAL VEGETATION: Fresh Ve-A Intermediate Ve-A Ve-L; Du-F, Nu-P. Ge-P Ve-M. Du-C. Nu-F. Mu-P Ve-M; Du-G. Mu-P, Nu-F, De-P, Cc-P Ve-L, Du-F, Ve-H; Du-E. Mu-P, Nu-P, Mu-P, Ge-P. Ce-P Nu-F, De-F Ve-L; Du-F Ve-H; Du-E. Mu-P Mu-P, Nu-P, Nu-F, De-F. Ge-P Dc-P, Ce-P Ve-H ; Du-E, Mu-P, Ve-A Nu-F, De-F Ve-L; Du-F, Mu-P, Nu-P, Ge-P Ve-L; Du-P, Mu-P, Nu-P, Ge-P Ve-1 ; Du-F, Mu-P, Nu-P, Ce-P AQUATIC VEGETATION: Intermediate Ve-M; Du-G, Mu-P, Ge-P Ve-M; Du-G Mu-P, Nu-F Ce-P Ve-M. Du-G Mu-P. Nu-F De-P. Ge-F Ve-L; Du-F, Mu-P, Ge-F, Nu-P, De-P Ve-L, Mu-P. De-P. Du-F. Nu-P, Ge-P Ve-L; Du-F, Mu-P. Ge-P, Nu-P. De-P Ve-L. Ce-P. Mu-P, De-P Ve-M, Du-G, Mu-P, Nu-G, De-F Ve-M ; Du-C; Mu-P, Nu-P Ve-L, Du-F, Mu-P, Nu-P, Ce-P FRESH-TO- INTERMEDIATE WATER BODIES ESTUARINE WATER BODIES Ff-G, Cr-P, Wb-E, Al-E. Ot-C Ff-P. Cr-P. Ot-P, Al-F, Wb-P Cr-G. Ff-P. Wb-C. Wb-C. Al-F. Ot-P Ef-E, Al-F. Sh-E. Ot-G. Wb-E, Sb-G Ef-E, Sh-E. Ot-G. Al-G, Wb-E. Sb-F Ef-P, Ot-P. Al-P, Wb-F Ff-C , Cr-F , Al-F, Ot-F, Wb-P Ef-G, Sh-G, Al-P, Ot-F, Sb-E, Wb-G SPECIES SYMBOLS Vegetation Geese Dabbling ducks Shorebirds Wading birds Muskrats Nutria Deer Alligators Shrimp Crayfish Freshwater Fish Estuarine Fish Otters Ve Ge Du Sb Wb Hu Nu De Al Sh Cr Ff Ef Ot RATING OF MANAGEMENT TECHNIQUE FOR PRODUCJNC FLORA AND FAUNA FLORA (Relative vegetative cover): High H Medium H Lou L Absent A FAUNA (Habitat value) Excellent E Good G Fair F Poor P SPECIAL NOTES Water salinities in these zones are as fol lows : Fresh 0-2 ppt Intermediate 2-5 ppt Brackish 5-15 ppt Saline over 15 ppt 2 Furbearer populations on Rockefeller are presently at a low point in their cycle, but this management technique has been success- fully used in other areas, especially with proper burning . This aplies only to Unit 9. All forced drainage units are of intermediate salinities. Figure 75. 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Prepared for Coastal Management Section, Louisiana Depart- ment of Natural Resources, Baton Rouge. Wiebe, W. J., and L. R. Pomeroy. 1972. ^1icroorganis;ns and their association witii aggregates and detritus in the sea: a microscopic study. Mem. 1st. Ital. Idrobiol. 29 (suppl.): 325-352. Wiegert, R. G. , and F. C. Evans. 1964. Primary production and the disappear- ance of dead vegetation in an old field in southwestern Michigan. Ecology 45:49-63. Williams, R. 8., and M. B. Murdoch. 1972. Conpartmental analysis of the produc- tion of Juncus roemerianus in a North Carol ina sal t marsh. 13:69-79. Chesapeake Sci Wright, R. , J. Sperry, and D. Huss. 1960. Vegetation type mapping studies of the marshes of southeastern Louisiana. Texas A and M Research Fd., College Station. Project 191. Prepared for U.S. Bur. Sport Fish. Wildl., U.S. Dep. Inter. Contract 14-16-003-538. 42 pp. 115 Appendix 1. Plant species composition of salinity zones in the Louisiana coastal marshes (Chabreck 1972). Scientific names conform with the National List of Scientific Plant Names (Soil Conservation Service 1982). CaTHon name Saline Vegp itative type Species Brackish Intemediate i^resh Po("(~ont' Aeschynomene viryinica Sensitive jointweed rtriLrf.lL _--- .07 Al ternanthera phi 1 oxeroides Al 1 igator-weed - - . . 2.4^ 5.34 Ainaranthus austral is Bel le-dani3 - - .10 .30 .0? Aster sp. Aster - - .08 .41 .13 Avicennia jemiinans Black iianijrove .50 - - - - - . Azol 1 a carol iniana Water fern - - - - - - - - Baccharis halimifolia Backbrush - - .10 .56 .0? Bacopa carol ini ana Carol ina bacopa - - - . .78 .34 Bacopa cionnieri Water hyssop - - .92 4.75 1.44 Bacopa rotundi fol ia Round leaf bacopa - - .11 .3? - - Batis niari tima Batis 4.41 - - - - - - Bidens laevis 3ur-marigolii - - - - - - .08 Borrichia frutescens Sea-oxeye .67 .11 - - - - Brasenia schreberi VJater shield - - - - - - .67 Cabomba carol iniana Fan wort - . . - - - .71 Carex sp. Carex - - - - - - .o:^ Centella erecta - - - - .16 .12 Cephal anthus occidental is Button-bush - - - - - - .21 Ceratophyl 1 jin deniersiji Coontai 1 - - - - - - 1.50 CI adium jamaicense Saw-grass - - - - - - .8" Colocasia antiquorun Elephantsear - - - - - - .39 Cuscjta indecora Dodder - - .0?. - - - - Cynodon dactylon Bermuda grass - - - - - - .10 Cyperus compressus Sedge - - - - - - .0'' Cyperus odoratus - - .84 2.18 1.55 Decodon vert ici 1 1 atus Water wil low - - - - - - .51 Dichromena colorata Star sedge - - - - - - .03 Distichl is spicata Sal t Trass 14.77 13.32 .36 .13 Echinochloa walteri Wal ter' s mill et - - .36 2.72 .77 Eichhornia crassipes Water hyacinth - - - - - - 1.43 Eleocharis parvula Dwarf spikerush - - 2.46 .49 .54 Eleocharis sp. Spikerush - - .82 3. 28 10.74 Eupatoriuni capil 1 i fol lum Yankee weed - - - - - - .05 Eupatorium sp. Boneset - - - - .OS .03 Fimbristyl is castanea Sand rush .04 .11 .12 - - Gerardia mari tima .01 .OF - - - - Heliotropiun curassavicuii Seas irie hel i otrope - - .02 . - - . Hibiscus moscheutos Marsh mal low - - - - .10 .05 Hydrocotyle bonariensis - - - - - - .02 Hydrocotyle ranunculoides - - - - - - .11 Hydrocotyle umbel lata Water pennywort - - - - - - 1.93 Hymenocallis occidental is Sp i d e r lily - - - - .04 .14 Ipomoea stolonifera Morning glory - - - - - - .03 Ipoinoea sagittata Morning glory - - .ll .84 .1" Iva frutescens Marsh elder .03 .10 - - - . Juncus effusus Soft rush - - - - - - .11 Juncus roenerianus Black rush n.io 3.93 .72 .60 Kosteletzkya virqinica Pink hibiscus - - .0? .18 .07 Le'iina mi nor Duckweed - - .02 .16 2.31 Leptochloa fasciculans Sprangle top - - .32 2.17 .49 Leptochloa f i 1 i formis Red sprangle top - - - - .04 - - Linnobiun sponyia Frogbit - - - - - - .16 Lud^iyia suffruticosa Water primrose - - - - - - .24 Ludwigia sp. Wi 1 1 ow pri'iirose - - - - - - .84 Lyciuin carol i ni anuin Sal t matrimony vine .07 - - - - - - Lythrjn lineare Looses tri fe .01 .16 .18 .07 Myrica cerifera Wax myrtle - - - - - - .16 Myriuphyllum heterophyl lum Eurasian watennill foi' 1 - - - - - - .19 Myriophyl lum spicatum Variable watermill foT 1 - - .IS .44 1.56 Cont inued 1 116 Appendix 1. Concluded. Common Name Vegetative Type Species Sal ine Brackish Intern ediate Fresh Pprrpnt ----.-.-.-_. Najas guddalupensis Southern naiad rciLfrrlL ------------ 1.03 1.07 Nelumbo lutea American lotus - - - - - - .54 Nymphaea odorata/ tuberosa White water lily - - - - - - 1.15 Nymphoides aquatica Floating heart - - - - - - .11 Osnunda regal is Royal fern - - - - .16 .43 Ottel ia al ismoides - - - - - - .03 Pari cum hemitonon Ma idencane - - - - .76 25.62 Panican repens Dog tooth grass - - - - .92 .24 Panicum vi rgatum Feather grass - - .14 2.51 .45 Paniciin sp. - - - - - - .10 Paspaluin dissectum - - - - .40 .42 Paspalum vaginatum - - 1.38 4.46 .35 Philoxerus vennicularis Sal t al 1 i'jator weed - - - - .08 .01 Phragmi tes austral is Roseau - - .31 6.63 2.54 Phyla nodiflora - - - - - - .06 Pluchea foetida Stinking fleabane - - - - - - .02 Pluchea campliorata Camphorweed - . .37 2.26 .36 Polygonum sp. Smartweed - - - - - - .56 Pontederia cordata Pickerel weed - - - - - - .07 Potamoqeton nodosus Longleaf pondweed - - - - .28 .03 Potamogeton pusillus Slender pondweed - - - - .24 .62 Ruppia mari tima Widgeongrass - - 3.83 .64 - - Sacciolepis striata Bagscale - - - - - - .06 Sagittaria falcata Bull tongue - - - - 6.47 15.15 Sagittaria latifolia Wapato - - - - - - .21 Sagittaria platyphyl la Del ta duckpotato - - - - - - .23 Sagittaria sp. - - - - .03 - - Sal icornia bigel ovi i Gl asswort .13 - - - - - - Sal icornia vi rginica Glasswort .53 - - - - - - Sal ix nigra Bl ack wil low - - - - - - .05 Saururus cernuus Lizzard's tail - - - - - - .16 Scirpus americanus Freshwater three square - - - - 1.27 .13 Scirpus californicus Hardstem bul Irush - - - - 1.83 .42 Scirpus olneyi Three-cornered grass - - 4.97 3.26 .45 Scirpus robustus Leafy three square .66 1.78 .68 - - Sci rpus val idus Soft stem bulrush - - .08 - - - - Sesbania exaltata - - .06 .20 - - Sesbania sp. Rattlebox _ . - - .04 .17 Sesuviun portulacastrim Marsh purslane - - .04 - - - - Setaria glauca Ye 1 low foxtail - - .06 - - - - Setaria magna Giant foxtail - - - - - - .03 Sol idago sp. Goldenrod - - - - .04 .08 Spartina alterniflora Oyster grass 62.14 4.77 .86 - - Spartina cynosuroides Hog cane - - .89 1.19 .02 Spartina patens Marsh hay cordgrass 5.99 55.22 34.01 3.74 Spartina spartinae ^ .01 .04 1.48 - - Spirodela polyrhiza Duckweed - - - - - - .20 Suaeda linearis Sea-bl ite .23 . - - - - - Taraxacun officinale Dandel ion - - - - .02 - - Taxodium distichum Baldcypress - - - - - - .02 Thelypteris thelypteroides Southern marsh fern Triadenum virginicum Marsh St. John' s wort - - - - - - .07 Typha spp. Cattail - - - - .98 1.57 Utricularia cornuta Horned bladderwort - - - - - - 1.68 Utricularia subulata Zigzag bladderwort - - - - - - .21 Vallisneria americana Wildcelery - . .08 - - - - Vigna luteola Deerpea - - 1.20 3.84 1.43 Woodwardia vi rginica Vi rginia chain fern - - - - - - .28 Zi zani opsis mil iacea Giant cutgrass ~ ~ " " * ~ 1.20 117 Appendix 2. Marsh plant decomposition rates, Mississippi River delta marshes . Species Month initiated Loss rate Comment Citation (mg/g/day) 5-mm mesh bags on marsh 3 Open plots in marsh 4 5-mm mesh bags on marsh 3 Open plots in marsh 4 Open plots in marsh 4 Open plots in marsh 4 5-mm mesh bags on marsh 1 2-mm mesh bags in bayou 2 2-mm mesh bags, streamside marsh 2-mm mesh bags, inland marsh 5-mm mesh bags on marsh 3 Open pi ots in marsh 4 Open pi ots on marsh 4 (Continued) Distichli s spicata June 6.6 September 4.2 December 2.2 Sumnier 9.0 Winter 5.7 Juncus roeiierianus June 7.7 Summer 14.4 '/J inter 5.9 Phragmites austral is Summer 6.2 Winter 1.3 Sagittaria falcata Summer 25.7 Winter 24.1 Spartina al terni fl ora March 8.2 July 12.6 September 10.7 December 5.6 June 13.8 January 5.5 June 9.2 January 4.6 June 5.5 January 4.2 May 21.9 September 9.2 December 4.3 Summer 7.0 Winter 4.0 Spartina cynosuroides Summer 5.4 Winter 2.7 118 Appendix 2. Concluded. Species Month initiated Loss rate Comment Citation Spartina patens June Summer Winter June 4.6 11.9 9.1 5-mm mesh bags on marsh Open plots in marsh 2.8-3.0 2-mm mesh bags on marsh 3 4 Ci tations: 1 - White and Trapani 1982 2 - Kirby 1971 3 - White et al . 1978 4 - Hopkinson et al. 1978 5 - Cramer and Day 1980 119 Appendix 3. Fishes of the Mississippi River Deltaic Plain that are found in marshes and associated water bodies (compiled by Gosselink et al , 1979; Deegan and Thompson 1984; see these documents for original sources). Scientific and common names conform to Robins et al. (1980), Ecological affinity Trophic relations Local distribution Relative and seasonal abundance Economic imoortance FAMILY DASYATIDAE STINGRAYS Dasyatis sabina (Lesueur) Atlantic Stingray FAMILY LEPISOSTEIDAE GARS Lepisosteus oculatus (Winchell) Spotted Gar lepisosteus osseus (Linnaeus) Longnose Gar Lepisosteus spatul a Lacepede All igator Gar FAMILY AMIIDAE BOWFINS Atnia caWa (Linnaeus) Bov/f in FAMILY ELOPIOAE TARPONS Elops saurus (Linnaeus) Ladyfish - Adults Ladyflsh - Young Carnivore; predator on meiofauna Carnivore; predator/ scavenger on fishes, macroinvertebrates Carnivore; predator on fishes, macro- and micro-fauna Carnivore; predator/ scavenger on fishes, larger invertebrates Carnivore; predator/ scavenger on fishes, amphibians, macro- invertebrates Carnivore; predator on small fishes, invertebrates, zoo- plankton Same as adu1 ts Broadly euryhallne; to freshwater; widespread Fresh to brackish areas, principally in protected areas; swamps, bayous, canals Broadly euryhaline; wide- spread , hut mainly in freshwater areas, rivers, canals, 1 akes See longnose gar entry; less rheophil ic than L. osseus Fresh to si ightly brackish ared^ only; mainly In quiet water, swamps, canals, ditches, bayous, fresh lakes Pelagic; mainly in high salinity areas; lower passes Pelagic; broadly euryhaline; to fresh areas; larvae and juveniles widespread in inland open-water areas Abundant, especially in open bay areas, larger canal s Locally abundant, esoecially in fresh swamps, hayous, canal s Moderately abundant in rivers, canal s, 1 akes Moderately abundant in upper bays, canals, lakes, bayous Locally abundant Locally abundant Moderately abundant along marsh edges, April- June None Limited value as cofmercial fish ( tranmel nets) ; much less impor- tant than other gars Minor value as coimerclal fish (tratmel nets) Moderate value as coiTiTiercial fish (trammel nets) (most important of gars) Limited value as gamefish None None FAMILY ANGUILLIOAE FRESHWATER EELS Angullla rostrata (Lesueur) Anerican Eel - Adults HA Carnivorous; predators on fishes , macro- Invertebrates Demersal ; broadly euryhaline but mainly In brackish to fresh areas except during spawning migration; river channel, upper bay, larger bayous Sparse; very cryptic; occasionally taken in trawls, seines , hook and 1 ine Anerican Eel - Young FAMILY CLUPEIDAE HERRINGS Alosa chrysochlorls (Rafinesque) Skipjack Herring - Adults Skipjack Herring - Young Carnivore; predator on fishes, inverte- brates, -forage species -forage species Planktonic larvae mainly offshore; demersal elvers widespread in bays, bayous , lakes Broadly euryhaline, hut mainly in fresher areas; river channels, upper bays, fresh lakes Platonic larvae mainly in rivers Sparse; ■very cryotic; occasionally taken by trawls, seines Very cyclic; year-class strengths seem to fluctuate radically; can be moderately abundant in some years See above entry; in "good" years larvae moderately abundant April - July; juveniles moderately abundant June - October Limited value as baltfish (dip- 1 ines) , crawfish traps None (Continued) 120 Appendix 3. Continued, Ecological affinity Trophic relations Local distribution Relative and seasonal abundance Economic importance Brevoortia patronus Goode Gulf Menhaden Dorosoma ceped i an jn (Lesueur) Gizzard Shad - Adults Gizzard Shad - Young Dorosoma petenense (Gunther) Threadfin Shad - Adults Threadfin Shad - Young Fil ter feeder on plankton, suspended benthic algae, and detritus Omni vore: fil ter feeder of plankton detritus, benthic algae -forage species Onnivore; strainer of plankton, detritus* benthic algae -forage species -forage species Euryhaline; juveniles found from fresh to sal ine marshes Broadly euryhaline, hut Tiainly in fresher areas, where very widespread Planktonic larvae mainly in rivers Same as gizzard shad Same as gizzard shad Very abundant bundant, locally Larvae abundant late March - June; juveniles moderately ahundant June - October Same as gizzard shad Larvae abundant May - September; juveniles abundant June - November *\Dderflte v-ilue in soring dipnet fishery for bait, troutl ines , and crawfish traps None Limited value as haitfish FAMILY ENGRAULIDAE ANCHOVIES Anchoa mitchill i (Valenciennes) Bay Anchovy - Adults Bay Anchovy - Young FAMILY CYPRINIDAE MINNOWS AND CARPS Cyprinus carpio Linnaeus Carp NoteiTii_qonus crysoleucas (Mitchill) Golden Shiner FAMILY liJALDRIDAE BULLHEAD CATFISHES Ictalurus furcatus (Lesueur) Blue Catfish - Adults Blue Catfish - Young Ictalurus natal is (Lesueur) Yellow Bullhead Ictalurus punctatus (Rafinesque) Channel Catfish - Adults Carnivore; predator on fishes, inverte- brates -forage species -forage species Oinivore; grazer/ sucker-type feeder on plants, benthic inyertebrates,. detritus, carrion Onnivore; midwater and surface grazer/preda- tor on zoopl ankton, filamentous algae, periphyton, fouling invertebrates -forage species ftrinivore; mainly carnivorous; predator/ grazer on fishes , macro-invertebrates , carrion Omnivore; sifnilar to adults but using more insect larvae, smaller invertebrates, detritus Omnivore, predator/ grazer on benthic invertebrates , carrion, detritus See blue catfish entry Pelagic; broadly euryhal ine to fresh water; widespread Planktonic larvae widespread; juveniles as adults Fresh to brackish areas; widespread , larvae planktonic; post larvae and juveniles mainly in temporarily flooded areas Fresh to brackish areas; widespread Fresh to moderate sal ini ty areas; mainly in fresh and brackish areas; river channel , bayous, uoper bay, Tiarsh lakes Essential ly as adul ts but preferring fresh areas; river channel Fresh to si ightly brackish; swanps, bayous, canals, ditches See blue catfish entry; this species si ightly less salt-tolerant and tends to prefer quieter water areas than K furcatus Abundant; increasingly so in suiTimer; ijsually taken in seines, trawls, cast-nets JVbundant year-round, oeak usually in early sumner Moderately abundant fresh areas; young abundant 1 ate March through suriTier Locally abundant Abundant; often taken in trawls, coimercial nets , hook and 1 ine Locally abundant; see habitat entry Locally abundant, esnecially in small canals, ditches, swamps See blue catfish entry; tends to predominate in fresher areas Mone None Minor co'iponent of freshwater hoopnet fisherv "Jone; fthose sold as bait brought in fron ■ni nnow farms outside the area) f^opular Ta'iefish major conponent of inland trout- line, hoopnet , trammel net catches; used in local fish cul- ture None See blue catfish entry; this snecies tends ti oredQininate in *"resher areas and laore henthic situations (Continued) 121 Appendix 3. Continued, Ecological af f ini ty Trophic relations Local distribution Relative and seasonal abundance Economic imooT-tance Pylodictis ol ivaris (Rafmesque) Flathead Carfish FAMILY ARIIDAc SEA CATFISHES Aru|_s fe_Hs (Linnaeus) Hardhead Catfish ^sqre marinus (Mitchill) Gafftopsail Catfish ESM Carnivore; predator on f isnes , macro- invertebrates Onnivore; grazer/ scavenger on carrion, detritus, macro- and meio-benthos Omnivore; grazer/ scavenger on carrion, detritus, macro- and meio-henthos Fresh to brackish areas; ■nainly in river channel Broadly euryhaline, hut mainly in high to moderate salinity areas; To moderate sal ini ty areas; -nainly limited to high sal ini ty; lower bays, passes Sparse Local ly abundant , -nainly during warm months Sparse; found in and around marshes in warn months only ^opul ar qame- fish; minov cnmponpnt n*" inland hoopnet and trotl ine catch fi-in% of indus- trial bottom- fish catch Minor coapo- nent of bottom- fish catch; not distinguished fron Sea Cat- fish FW\U GOHIESOCIDAE CLINGFISHES Gobiesox strunosus Cope Skilletfish FAMILY HELONIOAE NEEDLEFISHES Strongylura marina (Walbaum) Atlantic Needlefish FAMILY CYPRINOOONTIDAE KILLFISHES Adinia xenica (Jordan and Gilbert) Diamond Ki! 1 if ish Cyprinodon variegatus Lacepede Sheepshead Minnow Fundulus chrysotus (Gunther) Golden Topninnow Fundulus 'jrandi s Baird and Gi ra rd Gulf Killifish Fundulus Jenkins i (Evennann) Saltmarsh Topininnow Carnivore; feeds on macro- and meio- benthos ESM Carnivore; predator (jn fishes , macro- invertebrates Omnivore; mainly herbivorous; grazer on algae, periphyton, detritus ftnnivore; primarily herbivorous; grazer on algae , detri tus , benthic invertebrates , periphyton -forage species -forage species Omnivore; mainly carnivorous; predator/ grazer on small invertebrates, fishes, detritus -forage species -forage species High to moderate salinity areas; mainly near reefs, pilings, letties Broadly euryhaline; to freshwater; widespread Broadly euryhal ine; to freshwater, but mainly in high to moderate salinities; mainly along edges of protected areas (marshes); ponds, ditches, canals Broadly euryhaline; wide- spread along shores and in protected marsh waters Fresh to si ightly brackish areas; mainly in fresh swamps, ditches, canal s, borrow pits See sheepshead minnow entry Broadly euryhaline; in protected marsh areas Sparse; occasionally taken in trawls, dredges; larvae in plankton near reefs, late winter, spring Moderately abundant but seldom concentrated; often taken in seine, castnets Locally abundant, esnecially in winter and spring Abundant, peaks observed in winter and soring Locally abundant; esnecially quiet marshy areas See sheepshead ninnow entrv ^are, occasionally seined in marsh ditches, ponds None Minor value as haitfish Minor value as haitfish Fundulus pul vereus (Evennann) ES Bayou Ki 1 1 if ish Fundulus simil i s [ Bai rd and Gi rard) ES Longnose Kil 1 ifish Carnivore; predator/ grazer on smal 1 invertebrates Omnivore; predator/ grazer on benthic invertebrates , detritus Broadly euryhaline; in protected marsh areas; bayous, canals, ditches, ponds Broadly euryhaline but greatest concentrations in moderate to high salinities; along beaches, edges of marsh lakes, bayous Locally abundant, winter through spring Locally abundant; lower bavs, high salinity marshes (Continued) 122 Appendix 3. Continued. Lucam a parva (Baird) "Rainwa'ttjr Kill if ish FAfllLr ^'0^■:CILIIDA£ LlVtRBEAREtlS Ecoloyical affinity Trophic rel ations Local distribution Relative and seasonal abundance Onnivore; priinarily carnivorous; predator/ qrdier on invertebrates, detritus -forage species Sa^ne as sheepshead ininnnw Locally -jhijndant, nea-:s in SuniTier economic rtport-incf* Gdmbus_i_d af f im s (Baird and Gir.jrd) Mosqji tof isn Heterandria fornosa Agassi z Least Kill ifish Onnivore; primarily carnivorojs; predator/ grazer on invertebrates -forage species Herbivore; -jrdZBr on ep ip^ytes , hentb ic algae -forage species Broadly euryhaline, ^>st Tiainly in fresh to brackisH areas; along edges of protected areas; swanps, marshes, canals, ditches, bayo'js, ponds Fresh and brackish areas only; swanps, ditches, borrow pits; usually in ■larshy areas Loral 1 y abundant, in fresh areas Rare; occasionally \a^en in di tchps , borrow oits Poecil ia 1 atipinna (Lesueur) Sailfin Molly FAMILY ATHERINIUAE SILVERSIDES Labidesthes sicculus ( Cope ) Brook Silverside Membra^ martinica (Valenciennes) Rough Si 1 vers ide Memdi a beryl l_i_n_a (Cope) Inland Silverside FAMILY SYNGNATHIDAE PIPEFISHES AND SEAHORSES Herbivore; -jrazer on epiphytes, benthic algae, detritus Carnivore; predator on neustomc inverte- brates, zooplankton -forage soecies Carnivore, predator on small inverte- brates -forage species Carnivore, predator/ grazer on zooplanktnn other smal 1 inverte- brates -forage snecies Rroadly euryhaline to freshwater; widespread along protected shores, open beaches, bayous, ditches, canals, nonds Fresh areas onl small streais Broadly euryhaline; to freshwater; ^nainly along marshy shores of bays, lakes, lar^jp ranals, bayous Locally abundant vear-round Broadly euryhal i ne ■^iread Locally ^hundant in fro^h areas t.ocally abundant during suimier wide- Abundant, riealrs in sum^ier Synqnathus louisianae Gunther Cham Pipefish Carnivore; predator on small invertebrates High to noderate salinity areas; nainly associated with vegetation Rare; occasionally taken by seines in higher salinity narsh nonds, ditchps Syngnathus scovel 1 1 (Evermann and Kendall) Gulf Pipefish FAMILY PERCICHTHYIDAE TEMPERATE BASSES Mo rone chrysops (Raf inesgue) White Bass Mo rone mississippiensis Jordan and Eigeninann Yellow Bass Mo rone saxatil is (Walbaum) Striped Bass Carnivore; predator on small invertebrates Carnivore, predator :iai nly on fishes Carnivore; predator mainly on fishes Larmvore; voracious predator on smal 1 fisb Broadly euryhaline; to freshwater; widespread along edges and areas having dense vegetation; ditches, canals, nonds "broadly euryhaline but nainly in fresh and brackish areas; pelagic in open waters of river channel, large bayous, canals, lakes, upper hays See white bass entry; this fonn slightly "tore salt tolerant and nore common in snail er water bodi es Mai nly in i nl and waters Local 1 y abundant Lor^l 1 y abundant in fresher areas Locally ■ibundant; nainly in fresh areas , f"! vpr channel , swa^ips Rare; occasionally caudbt ^v book -ind 1 i traiTinel nets "i nor val UP 'i' ga ipf isb Minor valije as gaief ish Lviited valyo ■IS gamp^is^ (Continued) 123 Appendix 3. Continued. Ecological af f ini ty Trophic relations Local distribution Relative and seasonal abundance ficonoinic imoortance FAMILY CENTRARCHIDAE SUNFISHES Centrarchus macropterus (Lacepede) Flier Leponis cyanel lus Rafinesque Green Sunfish Lepomis gulosus (Cuvier) Wa mouth Lepomis macrochirus Rafinesque Sluegill Lepomis marginatus (Holbrook) Dollar Sunfish Lepomis megalotis (Rafinesque) Longear Sunfish Lepomis microlophus (Gunther) Redear Sunfish Lepomis punctatus (Valenciennes) Spotted Sunfish Lepomis symmetricus Forbes Bantam Sunfish Micropterus salmoides (Lacepede) Largemouth Bass - Adults FW Carnivore; predator on sinal 1 fishes , macro- invertebrates Carnivore; predator on fishes , macro- invertebrates Carnivore; predator on fishes , macro- invertebrates Omnivore; predator/ grazer on inverte- brates, algae Carnivore; predator/ qrdzer on inverte- brates, especially insects Fresh to si ightly brackish areas; swamps, marshes, hayous, sluggish streams Fresh to brackish areas; backwaters of streams, swamps, ditches, canals Fresh to brackish areas; swamps, borrow pits, canals, bayous Fresh to brackish areas; widespread in fresh habitats Fresh to brackish areas; especially swamps, borrow pits Fresh areas only; mainly i n rivers , creeks Omnivore; primarily Fresh to brackish areas; carnivorous; predator/ mainly in swamps, borrow grazer on inverte- pits, canals, bayous, brates , mainly mollusks lakes See redear sunfish entry Carnivore; predator mainly on fishes, macroinvertebrates Fresh areas only; mainly in swamps Fresh to brackish areas; common in swamps, borrow pits, ditches Fresh to brackish; widespread in lentic situations, especial ly in areas of low turbidity Sparse Sparse Local ly abundant; especially in swamps Locally abundant Locally abundant in fresh areas Sparse Moderately abundant in fresh lakes, ponds, borrow pits Local ly abundant Abundant in lentic habitats, sluggish streams, canals, bayous Limited value as qamefish None Minor value as gamef ish Minor value as qanefish None Minor value as gamef ish Minor value as gamef ish pQDular qamefish; large quantities caunht in marsh ponds , impound- ments Largefnouth Bass - Toung Pomox 1 s nigromacuTatus (Lesueur) FH Black Crapple FAMILY CARANGIDAE JACKS Oligopl Ues saurus (Schneider) ESM Leatherjacket - Young FAMILY GERREIDAE HOJARRAS Eucinostanus argenteus Balrd E94 Spotfln Mojarra - Young FAt4ILY SPARIDAE PORGIES Archosarqus probatocephalus (Walbaum) E9^ Sheepshead - Adults Carnivore; predator on zooplankton, later Insects, small fishes Minimally in fresh areas; shallow marginal zones of swamps, stream backwaters Carnivore; predator Fresh to brackish; on fishes, macro- widespread In Invertebrates; larvae low turbid lentic feed an zooplankton situations Carnivore; predator on small fishes. Invertebrates Carnivore; predator/ grazer on benthlc invertebrates Broadly euryhal Ine; to freshwater, but mainly moderate to high salinity areas; bay shores, bayous, marsh lakes Broadly euryhallne, hut mainly In moderate to high salinities; wide- spread Omnivore; grazer/ predator on perlphyton, macroinvertebrates. Mainly In high salinity areas, lower bays, tidal passes; near pll Inqs, reefs Moderately abundant In lentk freshwater areas, April through summer Moderately abundant in fresh areas, esoeclally quiet, weedy areas Moderately abundant during warn months Moderately ahundant In shore seines during warm months Moderately abundant, year-round; often taken by anglers, trairmel nets Popular gameflsh Minor value as comnercial fish (trarmel net); popular gameflsh (Continued) 124 Appendix 3. Continued- Ecological affinity Trophic relations Local dtstributlon Relative and seasonal abundance Economic importance Sheepshead - Young Lagodon rhoinboides (Linnaeus) Pinfish - Adults Pinfish - Young FAMILY SCIAENIOAE DRUMS Aplodinotus grunniens Raf Inesque Freshwater Dru« - Adults Freshwater Drun - Young Bairdlella chrysoura (Lacepede) Silver Perch ESM Oinnivore; predator/ grazer on fishes , detritus, inverte- brates, algae Carnivore; predator/ grazer on benthic Invertebrates , espe- cial ly mol lusks , and fishes Chinlvore; larvae predators on zooplank- ton; juveniles grazers on benthtc inverte- brates, detritus Carnivore; adults predatory on small fishes, benthic invertebrates Broadly euryhaline; wide- spread In protected waters, marsh bayous, canals , lakes ftoderately abundant, mainly spring, early sunmer Broadly eurytiallne, but mainly in high to moderate salinity areas; lower bays, bayous Broadly eurytiallne; to freshwater; widespread along shores and in marsh bayous, ditches, ponds Fresh to brackish areas; especially river channel larvae planktonic In river, upper bays, demersal, especially over soft mud/detritus bottoms Broadly euryhaline but nainly 1n inoderate to high salinity; widespread Moderately abundant, especially during warm months Abundant, late winter through suntner Locally abundant year- round Locally abundant, Hay through early fal 1 Locally abundant , especially as postlarval and early juveniles, April through early sunmer Major component of Inland hoop- net catch; minor gamefish Cynosc 1 on arenarlus Ginsburg Sand Seatrout - Adults Sand Seatrout - Young Cynosclon nebulosus (Cuvler) Spotted Seatrout Leiostomus xanthurus Lacepede Spot - Young Spot - Adul ts MIcropogonUs undulatus {Linnaeus) Atlantic Croalter Carnivore; predator on fishes , macro- invertebrates ESM Carnivore; predator on fishes and macro- Invertebrates Oinnivore; primarily carnivorous on zoo- plankton; grazer on detritus Graze on benthic invertebrates and detri tus ESM Onnivores; grazers on benthic Invertebrates , detritus, small fishes; young subsist on zooplankton Moderate to high salinity areas; widespread In bays, marsh lakes, bayous Moderately abundant, declining In cold months Abundant, April early Fall through Abundant year-round, except winter Broadly euryhaline; wide- spread; very smal 1 juveniles prefer protected marsh waters Abundant schooling fish In saline and brackish areas, often found in marsh bayous and shallow lakes, especially juveniles Broadly euryhaline, but Abundant, especially late mainly In moderate to high spring through sifimer salinity areas; postlarvae and early juveniles mainly in protected marsh waters; older juveniles widespread Adults move offshore in fall Euryhaline, preferring salinity areas around marshes as juveniles, moving to saline areas wl th maturity Very abundant; moving offshore in winter Ponular game- fish; minor com- nonent of inland tranmel net catch None Popular sport- fish 5-71 of indus- trial bototmfish catch in spring and sumner; moderately valu- able as qamefish More than S of Industrial hottomflsh catch Poqonlas cromis (Linnaeus) ESM Black Drun - Adults Black Orim - Young Carnivore predator/ grazer on benthic invertebrates, espe- cially blvalue tnol lusks Predatory on small benthic Invertebrates Broadly euryhaline, but mainly in high to moderate sal tnity areas; lower passes; mainly near reefs Larvae mainly In offshore areas; postlarvae and Juveniles occasionally entering bays , lower marshes Moderately abundant, often taken by tranmel nets, hook and line Sparse; occasionally taken in seines Same value as sportfish and and cornnerclal fish None (Continued) 125 Appendix 3. Continued, ScUenops occl latus (Linnaeus) Red Drun Stel 1 tfer lanceoUtus (Holbrook) Star DrijTi Ecological affinity Trophic relations Carnivores; predators on fishes and crus- taceans Local distribution Widespread in saMne and brackish areas, often In shal low marsh, ponds, and streams Mainly In high salinity areas; lower bays, passes Relative and seasonal abundance Economic importance Abundant especially In fall and early winter Sparse; occasionally taken In trawls Valuable game- fish FAMILY EPHIPPIDAE SPADEflSHES Chaetodipterus faber Atlantic Spadefish fAJ^JLY MUCILIOAE MULLETS Young Mu^il cephalus Linnaeus Striped **]llet - Adults Striped HjI let - Young ttnnivore; grazer on attached algae, foul log Invertebrates Onni vore; primarl ly herbivorous; -forage species Onnlvore; primarily herbivorous Mainly In high sal Inlty areas, near tidal passes Broadly euryhaline; to freshwater; Broadly euryhaline; to freshwater; widespread; planktonic larvae offshore Moderately abundant, locally, especially during sunrier and fall Abundant , v^ar-round Abundant, especially late winter, early spring None FAMILY ELEOTRIOAE SLEEPERS Dormitator maculatus (Bloch) ES fat Sleeper El eotrls pisonis (Gmel In) ES Splnycheek Sleeper FAMILY GOBIIDAE GOBIES Evorthodus lyricus (Girard) ES Lyre Goby Gobioides broussoneti Lacepede ES Violet Goby Goblonel lus boleosoma (Jordan and ES Gilbert) Darter Goby GobloncUus hastatus Girard ES Sharptail Goby Goblonel lus s^kj feldtl (Jordan and ES Elgenmann) Freshwater Goby Goblosawa bosci (Lacepede) ES Naked Goby Gobiosoma robustuw Glnsburg ES Code Goby Microqoblus gulosus (Girard) ES Clown Goby Mlcroqobius thalassinus {Jordan ES and Gilbert) Green Goby Carnivore; predator on fishes , macro- Invertebrates Same as fat sleeper Onnlvore; grazer on algae, benthlc invertebrates Broadly eurytial ine; mainly In ditches, canals, bayous Broadly euryhaline; hut mainly In fresh or brackish areas; canals, ditches Broadly euryhal Ine; but mainly in moderate to high sal Inl ty areas; dl tches , canal s , marsh ponds Broadly euryhaline; but mainly In high salinity areas; open bays, bayous, marsh lakes Broadly euryhal Ine; widespread Broadl y euryhal Ine; widespread Broadly eurytial Ine, hut mainly in fresh to brackish areas, where widespread Carnivore; predator/ Broadly euryhaline, scavenger on benthlc widespread Invertebrates, carrion Carnivore; predator/ grazer on benthlc Invertebrates Onnlvore; predator/ qraier on benthic Invertebrates, algae Broadly euryhaline. hut mainly In moderate to high salinities; mainly associated with vegetation Broadly euryhal ine, widespread; mainly near vegetation Broadly euryhaline, but mainly In high salinity areas; near vegetation Moderately abundant, local ly Very rare Local ly abundant Sparse; occasionally taken In trawls Local ly abundant, esfieclally during cold months Sparse; occasionally taken In trawls Locally abundant Locally abundant, on reefs, marsh ponds, ditches Sparse, occasionally taken In seines Sparse; occasionally taken in trawls, seines Very rare; occasionally taken In seines (Continued) 126 Appendix 3, Concluded. FWILY BOTHIOAE LEFTEYE FLOUNDERS CI tharlchth^s macrops Dresel Spotted Whiff Ecologtcal affinity Trophic relations Carnivore; predator on small crustaceans Local distribution Relative and seasonal abundance Limited to high sal Inlty areas; lower bays, passes Rare; occasionally taken in trawls Economic importance Paral Ichthys lethostiqma Jordan and Gilbert Southern Flounder E^ Carnivore; predator on small fishes, macro! nvertebrates Euryhallne; juveniles and adults found from freshwater to gul f saMnitles. in tidal channels and shallow lakes; larvae offshore Fairly ahundant, esoecially during warm months Valuable snort and connercial fish FWILY SOLEIOAE SOLES Achirus 1 ineatus (Linnaeus) Lined Sole Trinectes maculatus (Bloch and Schneider) Hogchoker - Adul ts Syrnphurus plaglusa (Linnaeus) BlacVcheek Tongueflsh Grazer on melo- and macro-benthos . detrl tus Carnivore; predator on benthk inverte- brates Broadly euryhal Ine. but mai nly in high to moderate sal Inlty; widespread Broadly euryhal Ine; to freshwater, but mainly In brackish to high sal Inity Broadly euryhallne, but mainly In moderate to high salinity; widespread Moderately abundant, late sumner, fall Abundant, mainly spring and summer Abundant , mai nly in snring None None FW = freshwater MA = marine ES = estuarine ESM = estuarine-marine (migratory) 127 Appendix 4. Representative vertebrate species of marsh habitats in the Mississippi River Deltaic Plain (compiled by Mabie, 1976 and Gosselink et al. 1979; see these documents for original sources) (F = Fresh, I = Intermediate, B = Brackish, S = Saline). Scientific and common names of amphibians and reptiles conform to Collins et al. (1982); birds to American Ornithologists' Union (1983); and mammals to Jones et al . (1975). Species Seasonal peaks of abundance or activi ty AHPHIBIANS Anbystoind opacun Marbled salamander Aiiib^stoind texanuiii Snallmouth sal aitiarider Notophthalrrujs vindescens Central newt Amphiuma tridactylum Three-toed amphiuna Siren intermedid Lesser siren Eur_ycea quadr idigitJta FI Dwarf salamander Bufo vail iceps Gulf coast toad Bufo woodhousel Woodhouse's toad FIB Acris crepitans Northern cricket frog Hj'l a cinerea Green treefrug FI Hyla crucifer Spring peeper Hyl a squirel la Squirrel treefrog Pseudacns trisenata Upland chorus frog Rana catesbeiana Bull frog Rana clamitans Bronze frog FIB Rana qryl lo Pig frog Rana sphenocephal a Southern leopard frog FIB Gastrophryne carol inensis FIB Insects Eastern narrownouth toad REPTILES Alligator miss issippiensis FIBS American al 1 igator Chel^dra serpentina FIB Snapping turtle Macroci enys teminincki i F Alligator snapping turtle Ha 1 a cl emy s terrapin BS Diamondback terrap in Kinos ternon subrubrun F IB Eastern mud turtle Sternotherus odoratus FI Stinkpot 61t crayfish; also birds, fiddler crabs, fish, insects, muskrats, turtles, shrinif), grasses, snaiK Fish (3S.41), other vertebrates (l.U), carnon (19.61), invertebrates (7.8%), plant material (36. 2t) Fish, frogs, snakes, other turtles, mussels, various aquatic grasses Fish, crustaceans, mollusks. insects Insects, smal 1 snails Fish (46.31), mollusks (40.11), also crayfish, insects, plant material for Michigan (Continued) Endangered - Te» Threatened - la. 128 Appendix 4. Continued. species Food Seasonal peaks of abundance or activity Remarks Pseudemjs conci nna River cooter Pseudemys floridana Missouri si ider Pseudemys pi eta Southern painted turtle Pseudemys scripta Red-eared turtle Deirochelys reticularia Chicken turtle Graptemys kohni i Mississippi map turtle Graptemys pseudogeographica Sabine map turtle Trionyx spini ferus Spiny sof tshel 1 Anol is carol ini ens is Coluber constrictor Racer Farancia abacura Lampropel tis getulus Speckl ed ki ng snake Me rod 1 a cycl op ion Green water snake Ne rod i a fasciata cl arki i Gul f sal t marsh snake fterodia fasci ata conf luens Broad-banded water snake Nerodia rhombi fera Diamondback water snake Reqina grahami i Graham's crayfish snake Regina rigida Glossy crayfish snake Storerla dekayi Brown snake Fie Thamnophis proximus Western ribbon snake Thamnophis sirtal is Comnon garter snake Aqki strodon plsci vorus Cottonmoutn FIB F FIB FIB BS FIB FIB Largely aquatic vegetation Largely aquatic vegetation Juvenile: 13i plant, 85% animal Adult: 881 plant, 10% animal Juvenile: 30% plant, 70% animal (e.g., amphipods) Adult: 89% plant, 11% animal (e.g., crayfish) Tadpoles, crayfish, plant material FI FIB Carnivorous Insects and spiders Insects, frogs, snakes, young birds /Vnphiunna, Si ren, frogs Other snakes, small birds, lizards, mice, rats C^mbusia (77.6%); other fish (18.6%); tadpoles (3.5%) Fish, fiddler crab Fish (86.9%); frogs and toads (6.4%); tadpoles (4.3%) Fish (92.7%); frogs and toads (1.0%}; tadpoles (6.1%) Crayfish (inOi) Si ren, fish, crayfish Earthworms, snails. Insects, small frogs, fish Insects, fish, frogs, salamanders, mice, toads Earthworms, moUusks, insects, fish, salamanders, toads, frogs, small manmals, small birds Fish, salamanders, frogs, reptiles, birds, mammals Breeds: May Hatch: July- Sept. Mar. -Oct. Mar. -Sept. Mar. -Oct. f^r.-Sept. BIRDS GREBES & WATERFOML Podilymbus podiceps Pied-billed grebe Podiceps nigricol 1 is Eared grebe Dendrocygna bicolor Fulvous whistling-duck FIBS Mostly animal: aquatic worms and Insects, snails, Oct. -Apr. small frogs and fish, plants: seeds and soft parts Insects, shrimp, some water plants, feathers Oct. -Nay Mostly seeds of grasses and weeds; also grasses, Apr. -Sept. grain (Continued) 129 Appendix 4. Continued. species Anser albifrons Greater white- fronted yoose FIBS Food Grain, tender shoots, occasional Insects Seasonal peaks of abundance or activity Remarks Nov. -Mar. Anas strepera Gadl^aTT Anas americana American wujeon Aythya col lans Ring-necked duck Ay thy a aff mis Lesser scaup Bucephala albeola bufflehead Lophodytes cucul latus Hoocfed inerganser Qxyura jamaicensis Ruddy duck Porphyrul a martirnca Purple gal 1 inule Ga 1 1 inula chloropus Common inoortien Ful Kd djnencana Ainerican coot Chen caerulescens Snow goose Branta canadensis Canada goose Anas crecca 5reen-w1ng ed teal Anas njbripes American black duck Anas ful vigula Mottled duck Anas platyrtiynchos Mallard Anas acuta Northern pintal 1 Ana_s discors B1ue-Hlnged teal Anas clypeatd Northern shovel er FIBS FIBS FIBS FIBS FIBS FI FIBS FIB FIBS FIBS FIBS FIBS FIBS FIBS FIBS FIBS FIBS Principally plants Oct. -Mar. 90% plant. 101 animal (from Sept. -Apr.) Oct. -Apr. 19% animal: Insects, mollusks; 81% plant: aquatic Oct. -Apr. plants, sedges, grasses, smartweeds Similar to A. marl 1 a Oct. -Apr. 79% animal: insects, crustaceans, mollusks, fish; Nov. -Mar. 21% plant: pondweeds , misc. Mostly insects; also small fish, frogs, mollusks, Nov. -Apr. crayfish, roots of aquatic plants, seeds, grain 72% plant: aquatic plants, grasses, sedges; Nov, -Apr. 28% animal: Insects, mollusks, crustaceans Rice, other seeds, worms, mollusks Apr. -Sept. Seeds, roots, soft parts of aquatic plants, snails Apr. -Nov. insects, worms Leaves, fronds, seeds and roots of aquatic plants; Sept. -Apr. wild celery, algae; worms, snails. Insects, small fish, tadpoles Almost wholly plants: grain, roots and culms of Oct. -Apr. grasses; some insects, mol lusks Almost wholly plants: aquatic plants, marsh grasses Oct. -Feb. sedges; some mollusks, crustaceans 10% animal: Insects, mollusks, crustaceans Oct, -Mar. 90% plant: sedges, pondweeds and grasses (62%); other (28%) Mast, grain, mollusks, crustaceans Oct. -Mar. 40% animal: mollusks. Insects, crayfish, small fish; 60% plant: inostly grasses (plants and seeds) 90% plant: sedges, grasses, smartweeds, pondweeds, duckweeds, tubers, mast; 10% animal: Insects, crustaceans, mollusks, fish 13% animal: mollusks, crustaceans. Insects 87% plant: pondweed , sedges and grasses (60%); other (27%) 30% animal: worms, mollusks, insects, tadpoles 70% plant: sedges, pondweeds and grasses (43,6%); other (26.4%) Animal: worms, small mollusks, insects, shrimp, Oct. -Apr. small fish, small frogs. Plant: buds and young shoots of rushes and other aquatics; grasses Oct. -Mar. Feb. -Apr.; Sept. -Nov. WADING 81RDS Botdurus lentiglnosus 'Vnerican bittern Ixubrychus exil is Least bittern Ardea herodias Great blue heron Casjnerodius albus Great egret FIB FIBS FIBS FIBS Mollusks, crayfish. Insects, small fish, frogs, lizards, small snakes, mice Oct. -May Slugs, leeches, insects, small fish, tadpoles, small Apr. -Sept. frogs, lizards, small mammals Mostly fish; also crustaceans. Insects, frogs, llzarxjs, snakes, birds, small manmals Small fish, snails, fiddlers. Insects, frogs, lizards, small snakes, mice, some plant material (Continued) Year- Round "Blue List" Natl. Aud. Soc. (1976) 130 Appendix 4. Continued. Speci es Seasonal peaks of abundance or activity Remarks Egretta thuJa FIBS Snowy egret Egretta caerulea F I BS Little blue heron Egretta tricolor FIBS Tricolored heron Egretta rufescens BS Reddish egret Bubulcus ibis Cattle egret Butorides striatus Green-backed heron Nycticorax nycticorax Black-crowned night-heron Nycticorax violaceus FIBS Yel low-crowned night heron Eudociinus albus FBS White ibis Plegadis falcinel lus Glossy ibis Plegadis chihi White-face3"ibis Hycteria americana Wood stork SHORE BIROS Pluvial is squatarola Bl ac k- bellied plove r Charadrius sanipalinatus Semipalmated plover FIBS Shrimp, small fish, fiddlers, snails, insects. Mar, -Oct. crayfish, small lizards, small frogs, small snakes Crayfish, small crabs, insects, fish, frogs, lizards Mar. -Oct. Slugs, snails, crayfish, insects, small fish, Mar. -Nov. 1 izards, frogs Mar, -Oct. Small fish, earthworms. Insects, tadpoles, frogs. Mar. -Oct. snakes, small maimials Mostly fish (alive or dead), worms, crustaceans. Mar. -Sept. Insects Snails, crayfish, crabs, fish, small reptiles, small Mar. -Sept. mamnals and birds Mostly crayfish; also other crustaceans, slugs Mar. -Sept. snails, small snakes, insects Insects, crayfish, young snakes Earthworms, crayfish, mollusks, insects, small fish and frogs, newts, leeches Fish, aquatic reptiles, insects Jun.-Sept. Marine worms, sanded armadillo Sylvllagus aquaticus Swamp rabKit Oryzomys palustns ice rat ryzomys p Harsfi ri Ondatra zibethicus Common musk rat Hyocastor coypus Nutria Proc^on lotor Northern raccoon Hu stela vison Hink Lut ra canadens is ^T7er otter Ddqcoilcus yirginianus Uhite-tailed deer FIBS FIBS FIBS FIBS FI FIBS FIB FIBS FIB Insects Insects Insects Insects, plant material Green plants Plant material, insects, crustaceans, bird eggs and young 61% crayfish; also crabs, birds, fish, Insects Aquatic vegetation Animals and plant material Crayfish, rodents, birds, fish, crabs, frogs Crabs, crayfish, fish, frogs, turtles, snakes Plant material Active year-round in warm weather; mating in spring Active year-round in warm weather; young born May- June Active year-round in warn weather; young born In June Breeds in July-Auq. Breeds Jan. -Sept. Breeds Mar. -Oct. Active year-round; breeding peaks Nov . and Har. Breeds Oec.-Jan. Active year-round, young born In early spring Breeds in late fall Breeds in Sept. -Mar. 134 i0?7?-10l REPORT DOCUMENTATION PAGE 1 REPORT NO FWS/OBS-84/09 2 3 t(*CiP'-n:'^ *«CC*iV>On No 4. Title »r>{r SubtMi* The Ecology of Delta Marshes of Coastal Louisiana: A Community Profile 5 ftfoon D»i» May 1984 fc 7. AulhOf(*) James Gossel ink 6 Peiiofm.ng 0'g«nTi»\ion Rep*. No 9 Author' s Affil iation Center for Wetland Resources Louisiana State University Baton Rouge, LA 70803 10 fro'fc:, T?i. 'v,o'* jn : Nc U ContfSCtlC) Of GranUGi Nc (C, (G) Fish and Wild! i f e Service Division of Biological Services Department of the Interior Washington, D.C. 20240 J3 Ttoe 0' Repon t ^c'