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United States Region III Region III EPA 903-R-03-002
Environmental Protection Chesapeake Bay Water Protection October 2004
Agency Program Office Division
In coordination with the Office of Water/Office of Science and Technology, Washington, DC
Ambient Water Quality
Criteria for Dissolved
Oxygen, Water Clarity and
Chlorophyll a for the
Chesapeake Bay and Its
Tidal Tributaries
f \ \ c •
2004 Addendum
October 2004
A
A
K ft*
V
Ambient Water Quality Criteria
M
for Dissolved Oxygen, Water Clarity
and Chlorophyll a for the Chesapeake Bay
and Its Tidal Tributaries
2004 Addendum
October 2004
U.S. Environmental Protection Agency
Region III
Chesapeake Bay Program Office
Annapolis, Maryland
and
Region III
Water Protection Division
Philadelphia, Pennsylvania
in coordination with
Office of Water
Office of Science and Technology
Washington, D.C.
72)
,^3/h/73
*7} 1
LC Control Number
2006 530195
Ill
Contents
Acknowledgments . v
I. Introduction . 1
II. Shortnose Sturgeon Temperature Sensitivity Analyses . 3
III. Key Findings Published in the EPA ESA
Shortnose Sturgeon Biological Evaluation . 9
Consultation History . 9
Biological Evaluation Findings . 11
Biological Evaluation Conclusions . 13
Literature Cited . 15
IV. Key Findings Published in the NOAA ESA
Shortnose Sturgeon Biological Opinion . 17
Chlorophyll a Criteria . 17
Water Clarity Criteria . 17
Dissolved Oxygen Criteria . 18
Sea turtles . 18
Shortnose sturgeon . 18
Incidental Take Statement . 20
Amount and Extent of Take Anticipated . 20
Extent of take from 2004-2009 . 22
Extent of take in 2010 and beyond . 23
Reasonable and Prudent Measures . 23
Literature Cited . 24
V. Guidance for Attainment Assessment of Instantaneous
Minimum and 7-Day Mean Dissolved Oxygen Criteria . 27
Background . 27
Current Status . 27
Assessment of Instantaneous Minimum Criteria
Attainment from Monthly Mean Data . 28
Reference points with respect to depth . 29
Data assemblage and manipulation . 29
Designated use assignments . 36
Findings . 36
Contents
IV
Assessment of 7-Day Mean Criteria Attainment
from Monthly Mean Data Findings . 64
Findings . 66
Literature Cited . 66
VI. Guidance for Deriving Site Specific Dissolved Oxygen Criteria
for and Assessing Criteria Attainment of Naturally Low
Dissolved Oxygen Concentrations in Tidal Wetland
Influenced Estuarine Systems . 67
Natural Conditions/Features Indicating Role of
Wetlands in Low Dissolved Oxygen Concentrations . 68
Surface to volume ratios/large fringing wetland areas . 68
Water quality conditions . 68
Dissolved oxygen/temperature relationships . \ . 71
Low variability in dissolved oxygen concentrations . 71
Approaches for Addressing Naturally Low Dissolved Oxygen
Conditions Due to Tidal Wetlands . 73
Derivation of Site-Specific Dissolved Oxygen Criteria Factoring
in Natural Wetland-Caused Dissolved Oxygen Deficits . 76
Scientific research-based estimates of wetland respiration .... 77
Model-based wetland-caused oxygen deficits . 77
Monitoring-based estimates of wetland-caused oxygen deficits 78
Site-specific dissolved oxygen criteria derivation . 81
Site-specific criteria biological reference curve . 82
Literature Cited . 83
VII. Upper and Lower Pycnocline Boundary Delineation
Methodology . 85
Determination of the Vertical Density Profile . 86
Determination of the Pycnocline Depths . 86
Literature Cited . 87
VIII. Updated Guidance for Application of Water Clarity Criteria
and SAV Restoration Goal Acreages . 89
Water Clarity Criteria Application Periods . 90
Shallow-w ater Habitat Acreages . 91
SAV restoration acreage to shallow-water habitat acreage ratio 91
SAV Restoration Goal Acreages . 92
Determining Attainment of the Shallow-w ater Bay Grass Use . . 93
Literature Cited . 94
IX. Determining Where Numerical Chlorophyll a Criteria
Should Apply to Local Chesapeake Bay and
Tidal Tributary Waters . 87
Recommended Methodology . 97
Literature Cited . 99
Appendix A: Wetland Area, Segment Perimenter/Area/Volume
and Water Quality Parameter Statistics for Chesapeake Bay
Tidal Fresh and Oligohaline Segments . 101
Contents
V
Acknowledgments
This addendum to the April 2003 Water Quality Criteria for Dissolved Oxygen,
Water Clarity • and Chlorophyll a for Chesapeake Bay and Its Tidal Tributaries was
developed and documented through the collaborative efforts of the members of the
Chesapeake Bay Program's Water Quality Standards Coordinators Team: Richard
Batiuk, U.S. EPA Region III Chesapeake Bay Program Office; Joe Beaman, Mary¬
land Department of the Environment; Gregory Hope, District of Columbia
Department of Health; Libby Chatfield, West Virginia Environmental Quality Board;
Tiffany Crawford, U.S. EPA Region III Water Protection Division; Elleanore Daub,
Virginia Department of Environmental Quality; Lisa Huff, U.S. EPA Office of
Water; Wayne Jackson, U.S. EPA Region II; James Keating, U.S. EPA Office of
Water; Robert Koroncai, U.S. EPA Region III Water Protection Division; Benita
Moore, Pennsylvania Department of Environmental Protection; Shah Nawaz,
District of Columbia Department of Health; Scott Stoner, New York State Depart¬
ment of Environmental Conservation; David Wolanski, Delaware Department of
Natural Resources and Environmental Control; and Carol Young, Pennsylvania
Department of Environmental Protection.
The individual and collective contributions from members of the Chesapeake Bay
Program Office and NOAA Chesapeake Bay Office staff are also acknowledged:
Danielle Algazi, U.S. EPA Region III Chesapeake Bay Program Office; David
Jasinski, University of Maryland Center for Environmental Science/Chesapeake Bay
Program Office; Marcia Olson, NOAA Chesapeake Bay Office; Gary Shenk, U.S.
EPA Region III Chesapeake Bay Program Office; and Howard Weinberg, University
of Maryland Center for Environmental Science/Chesapeake Bay Program Office.
Acknowledgments
1
chapter |
Introduction
In April 2003, the U.S. Environmental Protection Agency (EPA) published the
Ambient Water Quality > Criteria for Dissolved Oxygen, Water Clarity and Chloro¬
phyll a for the Chesapeake Bay and Its Tidal Tributaries (Regional Criteria
Guidance) in cooperation with and on behalf of the six watershed states — New York,
Pennsylvania, Maryland, Delaware, Virginia and West Virginia — and the District of
Columbia. The culmination of three years of work, the Regional Criteria Guidance
document was the direct result of the collective contributions of hundreds of regional
scientists, technical staff and agency managers and the independent review by recog¬
nized experts across the country.
At the time of publication of the Regional Criteria Guidance document, a number of
technical issues still remained to be worked through, resolved and documented. The
Chesapeake Bay Water Quality Standards Coordinators Team — water quality stan¬
dards program managers and coordinators from the seven Chesapeake Bay
watershed jurisdictions and EPA’s Office of Water, Region 2 and Region 3 — took on
the responsibility on behalf of the Chesapeake Bay watershed partners to collectively
work through these technical issues. The work on these issues was largely in support
of the four jurisdictions with bay tidal waters who were formally adopting the
published Chesapeake Bay water quality criteria, designated uses and criteria attain¬
ment procedures into their states’ water quality standards regulations.
This first EPA published addendum to the 2003 Ambient Water Quality Criteria for
Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its
Tidal Tributaries documents the resolution of and recommendations for addressing
the following technical issues and criteria attainment procedures.
• Guidance to the jurisdictions on where and when to apply the temperature-based
open-water 4.3 mg liter1 instantaneous minimum dissolved oxygen criteria
required to protect the endangered shortnose sturgeon (Chapter 2).
• Key findings published in the Endangered Species Act required EPA shortnose
sturgeon biological evaluation of the potential impacts and benefits from publica¬
tion of the Regional Criteria Guidance (Chapter 3).
chapter i
Introduction
2
• Summary of findings, incidental take and recommended reasonable and prudent
measures published in the Endangered Species Act required NOAA shortnose
sturgeon biological opinion on the potential impacts and benefits from state adop¬
tion of the Regional Criteria Guidance into water quality standards (Chapter 4).
• Guidance to the jurisdictions on when and where attainment of the instantaneous
minimum, 1-day mean and 7-day mean dissolved oxygen criteria can be assessed
using monthly mean water quality monitoring data (Chapter 5).
• Guidance to the jurisdictions for deriving site-specific dissolved oxygen criteria
and assessing criteria attainment of those tidal systems where naturally low
dissolved oxygen concentrations are due to extensive adjacent tidal wetlands
(Chapter 6).
• Documentation of the methodology for delineating the upper and lower bound¬
aries of the pycnocline used in defining the vertical boundaries between
open-water, deep-water and deep-channel designated uses (Chapter 7).
• Updated guidance to the jurisdictions for potential combined application of the
numerical water clarity criteria to shallow water habitats and submerged aquatic
vegetation (SAV) restoration goal acreages for defining attainment of the shallow-
water bay grass designated use (Chapter 8).
• Guidance to the jurisdictions for determining where numerical chlorophyll a
criteria should apply to local Chesapeake Bay and tidal tributary waters (Chapter
9).
Through publication by EPA as a formal addendum to the 2003 Chesapeake Bay
Regional Criteria Guidance document, this document should be viewed by readers
as supplemental chapters and appendices to the original published Regional Criteria
Guidance document. The publication of future addendums by EPA is likely as
continued scientific research and management application reveal new insights and
knowledge to be incorporated into revisions of state water quality standards regula¬
tions in upcoming triennial reviews.
chapter i
Introduction
3
chapter 1 1
Shortnose Surgeon Temperature
Sensitivity Analyses
For water column temperatures greater than 29°C, documented as stressful to short-
nose sturgeon, EPA established a Chesapeake Bay open-water dissolved oxygen
criterion of 4.3 mg liter-1 instantaneous minimum to protect survival of this listed
sturgeon species (U.S. EPA 2003). An investigation was conducted to determine if
there were water column habitats within Chesapeake Bay and its tidal tributaries
where water column temperatures routinely exceed 29°C. States would need to apply
the 4.3 mg liter-1 instantaneous minimum dissolved oxygen criterion in such open-
water habitats.
Bottom water temperature data were examined for the June through September
period for the years 1996 through 2002 for all Chesapeake Bay tidal water quality
monitoring stations throughout the mainstem Bay and tidal tributaries. Observations
greater than 29°C at a station were expressed as a percentage of the total number of
observations at the station for the 1996 through 2002 summer time period. These
percentages were then interpolated and displayed on a map (Figure II- 1). Due to the
high density of stations within the District of Columbia’s tidal waters, this region
was examined in greater detail (Figure II-2).
Areas with a higher percentage of tidal water temperatures above 29°C were almost
exclusively in the tidal fresh and oligohaline regions of the tidal tributaries. The tidal
fresh James and Appomattox rivers had the highest percentages with 16^40 percent
of the summer bottom water temperatures exceeding 29°C. In the Northeast, Elk,
Bohemia, Sassafras, and tidal fresh segmemts of the Chester, Patuxent, Potomac,
Rappahannock, Mattaponi and Pamunkey rivers, temperatures exceeded 29°C 5-15
percent of the time.
Examining the District of Columbia’s water quality monitoring stations’ bottom
temperature data, it appeared that there were some stations with fairly high percent¬
ages of temperatures exceeding the 29°C temperature threshold (Figure II-2). But on
closer examination, these stations were infrequently sampled and, therefore, the
percentages were misleading. Based on a more strict evaluation of the total number
of exceedences by station, it did not appear that elevated bottom water temperatures
chapter ii
Shortnose Sturgeon Temperature Sensitivity Analyses
Temperature Threshhold Violations
by Percent Occurence
0%
1-5
mm 6-15
Figure 11-1 . Interpolated percent occurrence of bottom water temperatures greater than
29°C from June-September 1996-2002 at the Chesapeake Bay Water Quality Monitoring
Program stations. Data were drawn from 48 monitoring cruises over the 7 year period.
Source: Chesapeake Bay Water Quality Monitoring Program database.
http://www.chesapeakebay.net/data
chapter ii
Shortnose Sturgeon Temperature Sensitivity Analyses
5
Figure 11-2. Percent occurrence of bottom water temperatures greater than 29°C from
June- September 1996-2002 at the Chesapeake Bay Water Quality Monitoring Program
stations located in the District of Columbia's tidal waters.
Source: Chesapeake Bay Water Quality Monitoring Program database.
http://www.chesapeakebay.net/data
were high enough to trigger routine application of the 4.3 mg liter 1 instantaneous
minimum criterion in District of Columbia tidal waters (Figure II-3).
To further narrow down on those tidal water habitats where the temperature-based
4.3 mg liter 1 instantaneous minimum dissolved oxygen criterion would likely
routinely apply, the baywide data set described previously was examined for the
number of bottom water dissolved oxygen concentrations less than 4.3 mg liter1
when the corresponding bottom water temperature exceeded 29°C. Over the summer
periods of 1996 through 2002, there were a total of 20 incidences of these two condi¬
tions among 9 stations. Five of the stations were in the Southern Branch Elizabeth
River and there was one station each in the tidal fresh segments of the Choptank,
Patuxent, and Pamunkey rivers and in the oligohaline segment of the Rappahannock
River (Figure II-4).
chapter ii
Shortnose Sturgeon Temperature Sensitivity Analyses
6
Figure 11-3. The number of times the bottom water temperatures were greater than 29°C
from June-September 1996-2002 at the Chesapeake Bay Water Quality Monitoring
Program stations located in the District of Columbia's tidal waters.
Source: Chesapeake Bay Water Quality Monitoring Program database.
http://www.chesapeakebay.net/data
Based on these evaluations, there appear to be no widespread tidal water habitats
exceeding the 29°C threshold, thereby requiring routine application of the
temperature-based 4.3 mg liter 1 instantaneous minimum dissolved oxygen criteria.
Jurisdictions are advised to evaluate water column temperatures prior to assessing
attainment of the open-water dissolved oxygen criteria to determine if, w'here and
when this temperature-based dissolved oxygen criterion should be applied to protect
the open-water designated use.
LITERATURE CITED
U. S. Environmental Protection Agency. 2003. Ambient Water Quality Criteria for Dissolved
Oxygen . Water Clarity' and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.
EPA 903-R-03-002. Region III Chesapeake Bay Program Office, Annapolis, Maryland.
chapter ii • Shortnose Sturgeon Temperature Sensitivity Analyses
7
Figure 11-4. Chesapeake Bay Water Quality Monitoring Program stations where both
bottom water dissolved oxygen concentrations were less than 4.3 mg liter1 and bottom
water temperatures were greater than 29°C from June-September 1996-2002.
Source: Chesapeake Bay Water Quality Monitoring Program database.
http://www.chesapeakebay.net/data
chapter ii
Shortnose Sturgeon Temperature Sensitivity Analyses
chapter hi
Key Findings Published in the
EPA ESA Shortnose Sturgeon
Biological Evaluation
In November of 2000, EPA initiated a voluntary informal consultation with NOAA
National Marine Fisheries Service (NOAA Fisheries) under Section 7(a)(2) of the
Endangered Species Act (ESA) for the issuance of guidance for Chesapeake Bay
specific water quality criteria for dissolved oxygen, water quality and chlorophyll a.
Upon publication of Ambient Water Quality Criteria for Dissolved Oxygen, Water
Clarity - and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries
( Regional Criteria Guidance) (U.S. EPA 2003a), EPA initiated formal consultation
with NOAA Fisheries. At the same time, EPA submitted its final Biological Evalua¬
tion for the Issuance of Ambient Water Quality Criteria for Dissolved Oxygen, Water
Clarity / and Chlorophyll a for the Chesapeake Bay and its Tidal Tributaries (U.S.
EPA 2003b) to NOAA Fisheries. This chapter provides a concise summary of key
findings published in EPA’s biological evaluation.1
CONSULTATION HISTORY
EPA sent a letter to NOAA Fisheries on November 24, 2000, requesting comments
on the list of federally listed threatened or endangered species and/or designated crit¬
ical habitat for listed species under the jurisdiction of NOAA Fisheries. NOAA
Fisheries responded in a letter dated January 8, 2001. In this letter, NOAA Fisheries
indicated that the endangered and threatened species under its jurisdiction in the
vicinity of the Chesapeake Bay and its tidal tributaries were: federally threatened
loggerhead ( Caretta caretta), and endangered Kemp’s ridley ( Lepidochelys kempii ),
green ( Chelonia my das), hawksbill ( Eretmochelys imbricata) and leatherback
(Dermochelys coriacea) sea turtles; federally endangered North Atlantic right
‘The entire biological evaluation document can be viewed and downloaded at:
http://www.chesapeakebay.net/pubs/subcommittee/wqsc/BE_final.pdf
chapter iii
Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation
10
(Eubalaena glacialis), humpback ( Megaptera novaeangliae ), fin ( Balaenoptera
physalus), sei ( Balaenoptera borealis ) and sperm (Physter macrocephalas ) whales;
and federally endangered shortnose sturgeon ( Acipenser brevi rostrum). In this letter,
NOAA Fisheries indicated to EPA that the revised dissolved oxygen criteria should
be evaluated for effects on shortnose sturgeon survival, foraging, reproduction and
distribution due to the lowering of dissolved oxygen criteria in the Chesapeake Bay.
On December 20, 2002, EPA sent a letter to NOAA Fisheries requesting concurrence
with EPA’s conclusion that the proposed criteria and refined designated uses would
not adversely affect the listed species under NOAA Fisheries’ jurisdiction. Included
with this letter were a Biological Evaluation regarding the shortnose sturgeon and a
copy of the draft criteria document. In a January 7, 2003 letter, NOAA Fisheries
replied to EPA and indicated that it concurred with EPA’s conclusion as it applied to
federally listed sea turtles and marine mammals but that NOAA Fisheries could not
concur that the revised dissolved oxygen criteria would not adversely affect short¬
nose sturgeon. NOAA Fisheries provided several comments to EPA on the contents
of the biological evaluation regarding the effects of the dissolved oxygen standards
on shortnose sturgeon and indicated that EPA should revise the biological evaluation.
Subsequent to receiving this letter, NOAA Fisheries and EPA staff communicated
informally to revise the contents of the biological evaluation.
In February 2003, several meetings and conference calls took place between EPA
and NOAA Fisheries staff. Included in these meetings was a discussion as to how the
formal consultation would be conducted. The complicating factor was that while
EPA was issuing the Regional Criteria Guidance document as guidance to the states,
the states were not obligated to adopt the criteria exactly as outlined in the Regional
Criteria Guidance document. It was determined between EPA and NOAA Fisheries
staff that a programmatic approach would be taken in developing an appropriate
biological opinion. In this scenario, EPA would consult with NOAA Fisheries on the
effects of issuing the guidance document to the states and District of Columbia since
EPA would evaluate the States and District of Columbia’s revised water quality
criteria in light of the Chesapeake Bay specific guidance. Then, when the states had
developed their water quality standard regulations and submitted them to EPA, EPA
would consult again with NOAA Fisheries on the effects of EPA approving the stan¬
dards proposed by the states. This type of programmatic consultation was
particularly appropriate as the pollutant loads from each State and the District of
Columbia mix in the Chesapeake Bay and the water quality in the Bay and its tidal
tributaries would be a result of the combined pollutant loads from the various states
and the District of Columbia. The consultation that is the subject of EPA’s final
biological evaluation published April 25, 2003 and NOAA Fisheries final biological
opinion dated April 16, 2004 serves as the first in a series of consultations that will
take place between EPA and NOAA Fisheries on the effects of EPA’s issuing water
quality criteria and approving water quality standards for the Chesapeake Bay and
its tidal tributaries.
chapter Hi
Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation
11
In April 2003, EPA published the final Regional Criteria Guidance document. At
that time, EPA indicated that it had not made any irreversible or irretrievable
commitment of resources that would foreclose the formulation or implementation of
any reasonable and prudent alternatives to avoiding jeopardizing endangered or
threatened species.
On April 25, 2003, EPA submitted a final Biological Evaluation to NOAA Fisheries
along with the published Regional Criteria Guidance and a letter requesting that
NOAA Fisheries initiate formal consultation on the effects of the issuance of the
dissolved oxygen criteria on shortnose sturgeon. The date April 25, 2003, serves as
the initiation of formal consultation on the shortnose sturgeon for the issuance of the
Regional Criteria Guidance.
During the formal consultation process, EPA and NOAA Fisheries staff continued to
hold discussions regarding the evaluation of the effects of EPA’s regional criteria on
the shortnose sturgeon. On October 30, 2003, EPA management and staff traveled to
NOAA Fisheries offices in Gloucester, Massachusetts, to provide technical informa¬
tion and background information on the Chesapeake Bay Program’s ambient water
quality criteria, designated uses, monitoring program and predictive modeling
assessments of water quality conditions of the Bay. Subsequently, communication
between the respective staffs continued, through which EPA provided NOAA Fish¬
eries with requested data necessary to complete a determination analysis for the
biological opinion. NOAA Fisheries communicated informally to the EPA that it
concurred with EPA’s determination that the issuance of the Chesapeake Bay
specific criteria would not affect endangered and threatened whales and that the
issuance of the criteria for water clarity and chlorophyll a likely would beneficially
affect federally listed sea turtles and the endangered shortnose sturgeon. However,
NOAA Fisheries indicated that the issuance of the dissolved oxygen criteria may
affect shortnose sturgeon and sea turtles. The effect of EPA’s issuance of the ambient
water quality criteria on shortnose sturgeon and sea turtles was the subject of the
consultation.
BIOLOGICAL EVALUATION FINDINGS
The EPA determined through consultation with the U.S. Fish and Wildlife Service
and the NOAA National Marine Fisheries Service that the only endangered or threat¬
ened species under the NOAA Fisheries jurisdiction in the evaluation area that would
potentially be affected was the endangered shortnose sturgeon ( Acipenser brevi-
rostrum). All the other federally-listed species within the Chesapeake Bay and its
tidal tributaries would either not be affected or would be beneficially affected by the
issuance of the Regional Criteria Guidance.
The EPA determined that the recommended water clarity criteria would not likely
adversely effect the listed species evaluated. Furthermore, the EPA determined that
chapter iii
Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation
12
the proposed water clarity criteria would beneficially affect preferred habitat,
spawning areas and food sources that the listed shortnose sturgeon depends.
The EPA determined that the recommended chlorophyll a criteria would not likely
adversely affect the listed species evaluated. Furthermore, the EPA determined that
the recommended chlorophyll a criteria would beneficially affect preferred habitat,
spawning habitat and food sources on which the listed species depends.
The EPA determined that the collective application of dissolved oxygen criteria for
the migratory fish spawning and nursery and open-water fish and shellfish desig¬
nated uses were fully protective of shortnose sturgeon survival and growth for all life
stages based on the following:
• The migratory spawning and nursery 6 mg liter-1 7-day mean and 5 mg instanta¬
neous minimum criteria will fully protect spawning shortnose sturgeon. The
February 1 through May 3 1 application period for the migratory spawning and
nursery criteria fully encompasses the mid-March through mid-May spawning
season documented previously from the scientific peer-reviewed literature.
• The individual components of the open-water criteria protect shortnose sturgeon
growth (5 mg liter-1 30-day mean), larval recruitment (4 mg liter-1 7-day mean)
and survival (3.2 mg liter-1 instantaneous minimum). A 4.3 mg liter-1 instanta¬
neous minimum criterion applies to open waters with temperatures above 29°C
considered stressful to shortnose sturgeon.
• The open-water criteria applied to tidal fresh waters include a 5.5 mg liter-1
30-day mean criterion providing extra protection of shortnose sturgeon juveniles
inhabiting tidal freshwater habitats.
The EPA determined that adoption of the proposed dissolved oxygen criteria into
Maryland, Virginia, Delaware and the District of Columbia’s state water quality stan¬
dards and their eventual attainment would beneficially affect shortnose sturgeon
spawning, nursery, juvenile and adult habitats and food sources by driving wide¬
spread nutrient loading reduction actions leading to increased existing ambient
dissolved oxygen concentrations. EPA stated that this determination was consistent
with and pursuant to Endangered Species Act provisions that the responsible federal
agency — EPA in this case — use its authority to further the purpose of protecting
threatened and endangered species (see 16 U.S.C. § 1536(a)). EPA also stated that
its determination was also consistent with the NOAA National Marine Fisheries
Recovery Plan for shortnose sturgeon which recommends working cooperatively
with states to promote increased state activities to promote best management prac¬
tices to reduce non-point sources (NOAA National Marine Fisheries Service 1998).
The EPA determined that adoption, implementation and eventual full attainment of
the states’ adopted dissolved oxygen water quality standards would result in signifi¬
cant improvements in dissolved oxygen concentrations throughout the tidal waters to
levels last observed consistently more than four to five decades ago in Chesapeake
Bay and its tidal tributaries.
chapter iii
Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation
13
The EPA recognized in the biological evaluation that dissolved oxygen criteria for
June through September for the deep-water seasonal fish and shellfish and the deep-
channel designated uses were at or below levels that protect shortnose sturgeon. The
EPA believed there were strong lines of evidence that shortnose sturgeon historically
have not used deep-water and deep-channel designated use habitats during the
summer months due to naturally pervasive low dissolved oxygen conditions based
on the following:
• Published findings in the scientific literature regarding salinity preferences (tidal
fresh to 5 ppt) and salinity tolerances (<15 ppt) clearly indicated shortnose stur¬
geon habitats were unlikely to overlap with the higher salinity deep-water and
deep-channel designated use habitats.
• The EPA concluded, based on extensive published scientific findings and in-depth
analysis of the 1400 record U.S. Fish and Wildlife Service Reward Program data¬
base, that these same deep-water and deep-channel regions have not served as
potential habitats for sturgeon during the June through September time period
when there is a natural tendency for low dissolved oxygen conditions to occur.
• The EPA recognized the potential limitations of the U.S. Fish and Wildlife Service
data set. However, the EPA believed the significant extent of the capture records —
400 stations and 1400 individuals caught — provided substantial evidence for the
lack of a potential conflict between shortnose habitat and seasonally applied deep¬
water and deep-channel designated uses.
The EPA determined that the recommended dissolved oxygen criteria for the refined
designated uses would not likely adversely affect the listed species evaluated in this
document. Furthermore, the EPA determined that the Chesapeake Bay dissolved
oxygen criteria would beneficially affect critical habitat and food sources on which
the listed species was dependent.
BIOLOGICAL EVALUATION CONCLUSIONS
Shortnose sturgeon are endangered throughout their entire range (NOAA National
Marine Fisheries Service 2002). According to NOAA, in the Final Biological
Opinion for the National Pollutant Discharge Elimination System Permit for the
Washington Aqueduct, this species exists as 19 separate distinct population segments
that should be managed as such. Specifically, the extinction of a single shortnose
sturgeon population risks permanent loss of unique genetic information that is crit¬
ical to the survival and recovery of the species (NOAA National Marine Fisheries
Service 2002). The shortnose sturgeon residing in the Chesapeake Bay and its tribu¬
taries form one of the 19 distinct population segments.
Adult shortnose sturgeon are present in the Chesapeake Bay based on the 50 captures
via the U.S. Fish and Wildlife Service Atlantic Sturgeon Reward Program. However,
the presence and abundance of all life stages within the evaluation area itself are
unknown. Preliminary published scientific evidence suggests that the shortnose
chapter iii
Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation
14
sturgeon captured in the Chesapeake Bay may be part of the Delaware distinct popu¬
lation segment using the C & D Canal as a migratory passage. However, the NOAA
National Marine Fisheries Service recommended that more studies utilizing nuclear
DNA needed to be conducted before this can be proven conclusively.
Section 9 of the Endangered Species Act and Federal regulations pursuant to section
4(d) of the Endangered Species Act prohibit the take of endangered and threatened
species, respectively, without special exemption. ‘Take' is defined as to harass, harm,
pursue, hunt, shoot, wound, kill, trap, capture or collect, or to attempt to engage in
any such conduct. ‘Harm’ is further defined by NOAA National Marine Fisheries
Service to include any act that kills or injures fish or wildlife. Such an act may
include significant habitat modification or degradation that actually kills or injures
fish or wildlife by significantly impairing essential behavioral patterns including
breeding, spawning, rearing, migrating, feeding, or sheltering. ‘Harass’ is defined by
U.S. Fish and Wildlife Service as intentional or negligent actions that create the like¬
lihood of injury to listed species to such an extent as to significantly disrupt normal
behavior patterns which include, but are not limited to, breeding, feeding or shel¬
tering. ‘Incidental take’ is defined as take that is incidental to, and not the purpose
of, the carrying out of an otherwise lawful activity.
The shortnose sturgeon recovery plan further identifies habitat degradation or loss
(resulting, for example, from dams, bridge construction, channel dredging, and
pollutant discharges) and mortality (resulting, for example, from impingement on
cooling water intake screens, dredging and incidental capture in other fisheries) as
principal threats to the species’ survival (NOAA National Marine Fisheries Service
1998). The recovery goal is identified as delisting shortnose sturgeon populations
throughout their range, and the recovery objective is to ensure that a minimum popu¬
lation size is provided such that genetic diversity is maintained and extinction is
avoided.
Considering the nature of the Regional Criteria Guidance , the effects of the recom¬
mended criteria, and future cumulative effects in the evaluation area, the issuance of
Regional Criteria Guidance was not likely to adversely affect the reproduction,
numbers, and distribution of the Chesapeake Bay distinct population segment in a
way that appreciably reduces their likelihood of survival and recovery in the wild.
This contention was based on the following: (1) the adoption of the recommended
dissolved oxygen criteria into state water quality standards and subsequent attain¬
ment upon achievement of the Chesapeake Bay watershed’s nutrient loading caps
would provide for significant water quality improvements to the tributaries to the
Chesapeake Bay (such as the Susquehanna, Gunpowder, and Rappahannock rivers)
where the shortnose sturgeon would most likely spawn and spend their first year of
life; (2) the main channel of the Chesapeake Bay most likely experienced reductions
in dissolved oxygen before large-scale post-colonial land clearance took place, due
to natural factors such as climate-driven variability in freshwater inflow; and
(3) there was strong evidence that shortnose sturgeon have historically not used
chapter iii
Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation
15
deep-water and deep-channel designated use habitats during the summer months due
to naturally pervasive low dissolved oxygen conditions.
Based on the evaluations conducted in the biological evaluation, EPA concluded that
the issuance of the Regional Criteria Guidance would not adversely affect the
continued existence of the Chesapeake Bay district population segment of shortnose
sturgeon. No critical habitat has been designated for this species and, therefore, none
will be affected. In fact, the EPA believed state adoption of the criteria into water
quality standards would directly lead to increased levels of suitable habitat for short-
nose sturgeon.
LITERATURE CITED
NOAA National Marine Fisheries Serv ice. 1998. Recovery Plan for the Shortnose Sturgeon
(Acipenser brevirostrum) . Prepared by the Shortnose Sturgeon Recovery Team for the
National Marine Fisheries Service, Silver Spring, Maryland.
NOAA National Marine Fisheries Service. 2002. Final Biological Opinion for the Motional
Pollutant Discharge Elimination System Permit for the Washington Aqueduct. Gloucester,
Massachusetts.
U.S. Environmental Protection Agency. 2003a. Ambient Water Quality' Criteria for Dissolved
Oxygen , Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.
EPA 903-R-03-002. Region III Chesapeake Bay Program Office, Annapolis. Maryland.
U. S. Environmental Protection Agency. 2003b. Biological Evaluation for the Issuance of
Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for
the Chesapeake Bay and its Tidal Tributaries. Region III Chesapeake Bay Program Office,
Annapolis, Maryland.
chapter iii
Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation
17
cha pter i\/
Key Findings Published in the
NOAA ESA Shortnose Sturgeon
Biological Opinion
In response to EPA’s submission of a biological evaluation and request for formal
consultation under Section 7 (a)(2) of the Endangered Species Act as described in
Chapter 2, the NOAA National Marine Fisheries Service published a biological
opinion (NOAA National Marine Fisheries Service 2004). This chapter provides an
extracted summary of key findings, the incidential take statement and recommended
reasonable and prudent measures published in NOAA’s biological opinion 2.
CHLOROPHYLL A CRITERIA
NOAA Fisheries determined that the chlorophyll a criteria will beneficially affect
the food sources for several species of listed sea turtles and benefit the habitat of
shortnose sturgeon and sea turtles (NOAA Fisheries 2004). This is based on the
finding that the recommended Chesapeake Bay chlorophyll a criteria provide
concentrations characteristic of desired ecological trophic conditions and protective
against water quality and ecological impairments (U.S. EPA 2003a). When the
chlorophyll a criteria are met, light levels and dissolved oxygen levels in the Chesa¬
peake Bay system should improve (U.S. EPA 2003b). The proposed chlorophyll a
concentrations should be protective against these water quality impairments. The
criteria should significantly improve water quality conditions in the Bay, particularly
for underwater Bay grasses.
WATER CLARITY CRITERIA
NOAA Fisheries determined that shortnose sturgeon and sea turtles are expected to
benefit from the improved water quality resulting from the adoption of the proposed
2The entire biological opinion document can be viewed and downloaded at:
http://www.chesapeakebay.net/pubs/BONMFS.pdf
chapter iv
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion
18
water clarity criteria (NOAA Fisheries 2004). The endangered green sea turtle feeds
directly on sea grasses while other sea turtle species feed on shellfish which are
dependent on the underwater grasses for habitat. The criteria for water clarity fully
support the survival, growth and propagation of balanced, indigenous populations of
ecologically important fish and shellfish inhabiting vegetated shallow-water habitats
(U.S. EPA 2003b). As the water clarity criteria will lead to increased water quality and
an increased forage base for sea turtles, NOAA Fisheries believed that these criteria
will beneficially affect listed sea turtles. While shortnose sturgeon are not directly
dependent on underwater grasses, these grasses are an important part of the food chain
making the protection of bay grasses beneficial to shortnose sturgeon as well.
DISSOLVED OXYGEN CRITERIA
SEA TURTLES
After reviewing the best available information on the status of endangered and
threatened species under NOAA Fisheries jurisdiction, the environmental baseline
for the action area, the effects of the action, and the cumulative effects, it was NOAA
Fisheries’ opinion that the EPA’s approval of the dissolved oxygen criteria for Chesa¬
peake Bay and its tidal tributaries was not likely to adversely affect loggerhead,
leatherback, Kemp’s ridley, green, or hawksbill sea turtles. Because no critical
habitat is designated in the action area, none will be affected by the project.
NOAA Fisheries believed that the dissolved oxygen criteria would beneficially affect
endangered and threatened sea turtles that may be present in the Chesapeake Bay.
Loggerhead, Kemps ridley, leatherback and green sea turtles are likely to be present
in the action area. The occurrence of a hawksbill turtle in the area would be a rare
occurrence. The effect of the dissolved oxygen levels on juvenile and adult turtles
have been assessed. As turtles are air breathers, there are not likely to be any direct
effects to sea turtles as a result of these dissolved oxygen criteria. As the dissolved
oxygen conditions in the Bay were expected to continually improve over the next
several years until the nutrient and sediment enrichment goals were met, NOAA
Fisheries anticipated that as habitat conditions improve in the Bay and habitat was
restored, there would be an increased forage base for sea turtles.
SHORTNOSE STURGEON
NOAA Fisheries determined that the water clarity and chlorophyll a criteria were
expected to improve water quality conditions in the Bay and its tidal tributaries,
beneficially affecting all native species of the Bay including shortnose sturgeon
(NOAA Fisheries 2004). While the dissolved oxygen levels authorized by this set of
criteria may result in some short-term adverse effects to shortnose sturgeon, no
chronic or lethal effects were expected.
chapter iv
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion
19
In addition, NOAA Fisheries determined that the adoption of the dissolved oxygen
criteria would result in significantly improved water quality conditions in the Bay,
elimination of anoxic zones and the improvement in the quality and quantity of
habitat available to shortnose sturgeon as well as improving the chances for recovery
of the Chesapeake Bay population of shortnose sturgeon and the long term sustain¬
ability of this population (NOAA National Marine Fisheries Service 2004).
This determination was based on the following conclusions:
• The effects of the ambient water quality criteria for the Chesapeake Bay and its
tidal tributaries have been analyzed on the Chesapeake Bay population of short¬
nose sturgeon. While the dissolved oxygen levels authorized by this set of criteria
may result in some short-term adverse effects to shortnose sturgeon through
displacement or other behavioral or physiological adjustments, no chronic effects
are expected. No lethal effects are expected as a result of the dissolved oxygen
criteria and significant protections are being provided to essential habitats
including deep water, spawning and nursery habitats.
• The adoption of the dissolved oxygen criteria will result in significantly improved
water quality conditions in the Bay, elimination of anoxic zones and the improve¬
ment in the quality and quantity of habitat available to shortnose sturgeon as well
as improving the chances for shortnose sturgeon recovery in the Bay and
improving the likelihood of long-term sustainability of this population.
• NOAA Fisheries believes that the issuance of these criteria, as currently stated,
would not reduce the reproduction, numbers and distribution of the Chesapeake
Bay shortnose sturgeon population or the species as a whole in a way that appre¬
ciably reduces the likelihood of the species’ survival and recovery in the wild.
This conclusion was supported by the following: (1) no lethal takes of any life
stage of shortnose sturgeon are anticipated to occur; (2) the demonstrated ability
of shortnose sturgeon to avoid hypoxic areas and move to areas with suitable
dissolved oxygen levels; (3) the availability of adequate habitat with not only
suitable temperature, salinity and depth, but suitable dissolved oxygen levels; (4)
the seasonal nature of the anticipated effects (i.e., no effects anticipated from
October 1-May 3 1 of any year); (5) adequate protection of essential spawning and
nursery areas protecting not only spawning adults but eggs and larvae from
hypoxic conditions; (6) the elimination of anoxic areas within the Bay; (7) a large
portion of the deep-water areas have low temperatures and adequate dissolved
oxygen levels allowing shortnose sturgeon to be less dependent on the deepest
areas of the Chesapeake Bay (deep-channels) for thermal refiigia; and (8) the
significant improvement in Bay water quality conditions and increased avail¬
ability of suitable habitat for all life stages of shortnose sturgeon.
As such, it was NOAA Fisheries’ biological opinion that the approval of these
criteria by EPA may adversely affect the Chesapeake Bay population of endangered
shortnose sturgeon through displacement to suboptimal habitat or other behavioral
and metabolic responses to hypoxic conditions but was not likely to jeopardize the
chapter iv
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion
continued existence of the Chesapeake Bay population of shortnose sturgeon or the
species as a whole (NOAA National Marine Fisheries Service 2004).
INCIDENTAL TAKE STATEMENT
Section 9 of the ESA and Federal regulations pursuant to section 4(d) of the ESA
prohibit the take of endangered and threatened species, respectively. “Incidental
take” is defined as take that is incidental to, and not the purpose of, the carrying out
of an otherwise lawful activity (50 CFR 402.02). Under the terms of section 7(b)(4)
and section 7(o)(2) of the ESA, taking that is incidental to and not intended as part
of the agency action is not considered to be prohibited under the ESA provided that
such taking is in compliance with the terms and conditions of this Incidental Take
Statement.
According to the EPA Ambient Water Quality Criteria for Dissolved Oxygen, Water
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries
{Regional Criteria Guidance ), the goal of this program is that states will adopt water
quality standards consistent with the Regional Criteria Guidance and further imple¬
ment those water quality standards so that nutrient and sediment load reductions will
be achieved by 2010. At that time, EPA expects that the dissolved oxygen criteria
will be met for all designated uses. This Incidental Take Statement accounts for take
that will occur before the 2010 goals are met and after the goals are met. Unless
NOAA Fisheries revokes, modifies or replaces this Incidental Take Statement, this
Incidental Take Statement is valid for as long as the EPA’s guidance document
remains in effect (NOAA National Marine Fisheries Service 2004). When the States
and the District of Columbia seek EPA approval of their dissolved oxygen criteria,
NOAA Fisheries will verify at that time that EPA's approval of the state water quality
criteria will also be subject to this programmatic take statement. At that time, NOAA
Fisheries may revise this Incidental Take Statement based on a particular State’s
implementation plan, for example to include additional terms and conditions to mini¬
mize the likelihood of take.
AMOUNT AND EXTENT OF TAKE ANTICIPATED
The proposed action is reasonably certain to result in incidental take of shortnose
sturgeon. NOAA Fisheries stated it is reasonably certain the incidental take
described here will occur because (1) shortnose sturgeon are known to occur in the
action area; and (2) shortnose sturgeon are known to be adversely affected by low
dissolved oxygen levels as low dissolved oxygen levels cause them to avoid areas,
increase surfacing behavior, and undergo metabolic changes. Based on the evalua¬
tion of the best available information on shortnose sturgeon and their use of the
Chesapeake Bay, NOAA Fisheries has concluded that the issuance of the dissolved
oxygen criteria for seasonal deep water, deep channel and open water aquatic life
chapter iv
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion
21
uses was likely to result in take of shortnose sturgeon in the form of harassment of
shortnose sturgeon, where habitat conditions (i.e., dissolved oxygen levels below
those protective of shortnose sturgeon) will temporarily impair normal behavior
patterns of shortnose sturgeon (NO A A National Marine Fisheries 2004). This
harassment will occur in the form of avoidance or displacement from preferred
habitat and behavioral and/or metabolic compensations to deal with short-term
hypoxic conditions. Neither lethal takes (see below) nor harm are anticipated in any
Bay area due to the extent of available habitat in the Bay with dissolved oxygen
levels protective of shortnose sturgeon and the demonstrated ability of shortnose
sturgeon to avoid hypoxic areas and move to areas with suitable dissolved oxygen
levels. Shortnose sturgeon displaced from hypoxic areas were expected to seek and
find suitable alternative locations within the Bay. While shortnose sturgeon may
experience temporary impairment of essential behavior patterns, no significant
impairment resulting in injury (i.e., “harm”) was likely due to: the temporary nature
of any effects, the large amount of suitable habitat with adequate dissolved oxygen
levels, and the ability of shortnose sturgeon to avoid hypoxic areas.
As outlined in the Biological Opinion, generally shortnose sturgeon are adversely
affected upon exposure to dissolved oxygen levels of less than 5mg liter 1 and lethal
effects are expected to occur upon even moderate exposure to dissolved oxygen
levels of less than 3.2mg liter-1. Because dissolved oxygen levels are known to be
affected by various natural conditions (e.g., tides, hurricanes or other weather events
including abnormally dry or wet years) beyond the control of EPA or the States and
District of Columbia and can fluctuate greatly within any given period of time, a
monthly average dissolved oxygen level has been determined to be the best measure
of this habitat condition within the Bay. As indicated in the Biological Opinion, an
area that achieves a 5mg liter-1 monthly average will also achieve at least a 3.2mg
liter-1 instantaneous minimum dissolved oxygen level. As shortnose sturgeon are
reasonably certain to be adversely affected by dissolved oxygen conditions below
these levels, these levels can be used as a surrogate for take. As such, for puiposes
of this Incidental Take Statement areas failing to meet a 5mg liter-1 monthly average
of dissolved oxygen will be a surrogate for take of shortnose sturgeon. As noted
above, this take is likely to occur in the form of avoidance or displacement from
preferred habitat and behavioral and/or metabolic compensations to deal with short¬
term hypoxic conditions (defined as harassment in this situation). The amount of
habitat failing to meet an instantaneous minimum of 3.2mg liter-1 could be used as
a surrogate for lethal take of shortnose sturgeon; however, due to limitations of the
model developed by EPA (U.S. EPA 2003c), the amount of habitat failing to reach a
3.2mg liter-1 instantaneous minimum could not be modeled. However, an analysis of
the likelihood of lethal take can be based on the amount of habitat failing to reach a
3mg liter -1 monthly average (which would also likely be failing to meet a 3.2mg
liter-1 instantaneous minimum). While a small portion of the Bay will fail to meet
the 3 mg liter-1 monthly average, shortnose sturgeon are likely to be able to avoid
these areas. Lethal effects are only expected to occur after at least 2-4 hours of expo¬
sure to dissolved oxygen levels of less than 3.2mg liter-1, and this is not likely to
chapter iv
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion
22
occur given the mobility of shortnose sturgeon and the availability of suitable
habitat. Therefore, no lethal take is expected to occur.
The probability of lack of attainment of dissolved oxygen levels protective of short-
nose sturgeon when the 2010 sediment and nutrient reduction goals are met has been
modeled by EPA (U.S. EPA 2003c) and was the basis for determining the extent of
take anticipated. As such, take levels can be determined for each of the designated
uses where take is anticipated (open water, deep-water and deep-channel). As indi¬
cated in the biological opinion, take is likely to occur only in the summer months
(June 1-September 30). Based on the analysis documented in the accompanying
biological opinion, the area of the Bay designated uses that fail to meet a 5mg liter1
monthly average dissolved oxygen level can be used as a surrogate for take of short-
nose sturgeon by harassment. As shortnose sturgeon are benthic fish, the modeling
runs done for the bottom layer of the Bay have been used to determine the extent of
take. To further refine this analysis, the “tolerate” habitat threshold has been used;
that is, the estimate of area that will have temperatures <28°C, salinity <29 ppt and
depth <25 meters which can be reasonably expected to be the areas of the Bay where
shortnose sturgeon may be present in the summer months (U.S. EPA 2003c).
Despite the use of the best available scientific and commercial data, NOAA Fisheries
cannot quantify the precise number of fish that are likely to be taken. Because both
the distribution of shortnose sturgeon throughout the Bay and the numbers of fish
that are likely to be in an area at any one time are highly variable, and because inci¬
dental take is indirect and likely to occur from effects to habitat, the amount of take
resulting from harassment is difficult, if not impossible, to estimate. In addition,
because shortnose sturgeon are aquatic species who spend the majority of their time
on the bottom and because shortnose sturgeon are highly mobile while foraging in
the summer months, the likelihood of discovering take attributable to this proposed
action is very limited. In such circumstances, NOAA Fisheries uses a surrogate to
estimate the extent of take. The surrogate must be rationally connected to the taking
and provide an obvious threshold of exempted take which, if exceeded, provides a
basis for reinitiating consultation. For this proposed action, the spatial and temporal
extent of the area failing to meet dissolved oxygen standards protective of shortnose
sturgeon provides a surrogate for estimating the amount of incidental take.
EXTENT OF TAKE FROM 2004-2009
Using data provided by EPA, the extent of take occurring from the time of the adop¬
tion of the guidance3 could be estimated. As habitat conditions in the Bay are
expected to improve over time as interim measures are achieved before the 2010
goals are met, it is reasonable to assume that this surrogate level of take will decrease
3Adoption of the guidance by the states and District of Columbia and approval by EPA is expected to
occur in 2004 and 2005.
chapter iv
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion
over time. Using the EPA model of dissolved oxygen conditions in 2000 in the
bottom layer of habitat that was rated “tolerate” (see above) the following conditions
were observed:
23
Designated Use
Percent of area failing to meet 5mg liter1 monthly
averaqe 2004-2009 (see U.S. EPA 2003c)
Open Water
9.2
Deep Water
47.3
Deep Channel
78.3
Each year in the summer months, no more than the above percentages of the partic¬
ular designated use areas were expected to fail to meet a 5 mg liter1 monthly
average dissolved oxygen level between 2004 and 2009. The extent of take would be
limited to those percentages of each designated use area in the Bay. As such, for the
period 2004 through 2009, NOAA Fisheries would consider take to have been
exceeded when upon review of the annual monitoring data, NOAA Fisheries was
able to determine that for the preceding summer, the dissolved oxygen data for any
30 days during the June 1 -September 30 time frame indicate that any of the desig¬
nated use area failed to meet the above goals.
EXTENT OF TAKE IN 2010 AND BEYOND
Using the EPA model, the extent of take anticipated in 2010 and beyond can be
determined. Using the EPA model of dissolved oxygen conditions anticipated
when the 2010 nutrient and sediment reduction goals were met and using the bottom
layer of habitat that is rated “tolerate” (see above) the following conditions were
anticipated:
Designated Use
Percent of area failing to meet 5mg liter1 monthly
average 2010 and beyond (see U.S. EPA 2003c)
Open Water
5.7
Deep Water
33.0
Deep Channel
65.9
As conditions were expected to be improving over time, no more than the above
percentages of the particular habitats were expected to fail to meet a 5mg liter 1
monthly average dissolved oxygen level in 2010 and beyond. As such, for the period
of 2010 and beyond, NOAA Fisheries will consider take to have been exceeded
when upon review of the annual monitoring data, NOAA Fisheries was able to deter¬
mine that for the preceding summer, the dissolved oxygen data for any 30 days
during the June 1-September 30 time frame indicate that any of the designated use
area failed to meet the above goals.
REASONABLE AND PRUDENT MEASURES
Reasonable and prudent measures are those measures necessary and appropriate to
minimize incidental take of a listed species. For this particular action, however, it is
chapter iv
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion
24
not possible to design reasonable and prudent measures that are necessary and
appropriate to minimize take, because the best available science has demonstrated
that the EPA criteria are the limit of feasibility based on current technology. The
purpose of the reasonable and prudent measure below is to monitor environmental
conditions in the Bay and to monitor the level of take associated with this action. In
order to monitor the level of incidental take, monitoring of dissolved oxygen and
accompanying temperature conditions in the Bay must be completed each summer.
In order to be exempt from the prohibitions of section 9 of the ESA, the EPA must
comply with the following terms and conditions, which implement the reasonable
and prudent measure described above and outline the required reporting require¬
ments. These terms and conditions are non-discretionary.
1. By April 1 of each year (beginning in 2005), EPA shall provide an annual report
to NOAA Fisheries outlining the progress towards nutrient and sediment load
reductions, including a discussion of any best management practices or other
strategies put in place to achieve the target nutrient and sediment load reductions.
2. EPA shall continue using the results of the Chesapeake Bay Interpolator to
extrapolate measured data to assess water quality conditions in the Bay. The
Chesapeake Bay Interpolator extrapolates water quality concentrations
throughout the Chesapeake Bay and/or tributary rivers from water quality meas¬
ured at point locations. The purpose of the Interpolator is to assess water quality
concentrations at all locations in the 3 -dimensional water volume or as a 2-
dimensional layer. The results from the Interpolator will be used by EPA to
develop an annual report (see below).
3. By April 1 of each year (beginning in 2005), EPA shall provide an annual report
to NOAA Fisheries on water quality conditions in the Bay, including tempera¬
ture, dissolved oxygen, depth and salinity. The data provided will express actual
monitoring data in volumetric figures (cubic kilometers) as well as bottom
habitat area (squared kilometers) extrapolated from the Chesapeake Bay Inter¬
polator. This report should include information on the percent of each designated
use that failed to meet the 5mg liter-1 monthly average for June, July, August and
September of the preceding year.
By April 30, 2010, EPA shall submit a report to NOAA Fisheries assessing the
dissolved oxygen condition in the Bay which highlights the dissolved oxygen condi¬
tions in the Bay during the June 1 -September 30 time frame for each of the years
2004 through 2009. In this report, EPA will determine the percent of each designated
use that failed to attain a 5mg liter-1 monthly average. Included in this report will be
an analysis of the likely causes of failures (i.e., weather events, point sources).
LITERATURE CITED
NOAA National Marine Fisheries Service. 2004. National Marine Fisheries Ser\'ice Endan¬
gered Species Act Biological Opinion— Ambient Water Quality 1 Criteria for Dissolved
chapter iv
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion
25
Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.
F/NER/2003/00961 . Northeast Region, Gloucester. Massachusetts.
U.S. Environmental Protection Agency. 2003a. Ambient Water Quality Criteria for Dissolved
Oxygen, Water Clarity > and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.
EPA 903-R-03-002. Region Ill Chesapeake Bay Program Office, Annapolis, Maryland.
U.S. Environmental Protection Agency. 2003b. Biological Evaluation for the Recommended
Ambient Water Quality > Criteria and Designated Uses for the Chesapeake Bay and its Tidal
Waters Under the Clean Water Act Section 1 17. Region III Chesapeake Bay Program Office,
Annapolis, Maryland.
U.S. Environmental Protection Agency. 2003c. Unpublished Analysis of Shortnose Sturgeon
Habitat Quality Preferences under Monitoring Program Observed data from 1985-1994 and
Water Quality Modeling Estimated Water Quality Conditions for 2010. Region III Chesa¬
peake Bay Program Office. Annapolis, Maryland.
chapter iv
Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion
27
chapter \/
Guidance for Attainment
Assessment of Instantaneous
Minimum and 7-Day Mean
Dissolved Oxygen Criteria
BACKGROUND
As published in the Ambient Water Quality Criteria for Dissolved Oxygen, Water
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries (U.S.
EPA 2003), it is accepted that concentration minima need to be defined, which if
exceeded for some defined (short) duration result in lethal or other adverse effects.
Instantaneous minimum criteria have been derived and published for protection of
each of the five tidal water designated uses. A 1 -day mean dissolved oxygen crite¬
rion was also determined to be necessary for the protection of the deep-water
designated use. In addition, a 7-day mean criterion has been derived for protection
of the open-water designated use (U.S. EPA 2003).
However, it is also acknowledged that assessing the attainment status of these criteria
requires data collections at temporal and spatial scales that are simply not practicable
nor sustainable across all Chesapeake Bay and tidal tributary waters. To address this
issue, there are ongoing efforts to develop statistical methods to estimate attainment
of these dissolved oxygen criteria using a synthesis of: 1) seasonal and inter-annual
patterns found in the long term, low-frequency, spatially-limited monitoring data; 2)
the short-term patterns of temporal variability found in high-frequency, spatially
uneven ‘buoy’ data; and 3) the small-interval patterns of variability observed in data
records generated through the ‘data-flow’ and ‘scan-fish’ sampling devices.
CURRENT STATUS
These methods are in the exploratory and trial application phases. However, we can
still address the question of how best to assess attainment of these criteria given the
almost two-decade record of dissolved oxygen concentrations for Chesapeake Bay
tidal waters. First, there are some Chesapeake Bay Program segments, such as the
deep-channel mid-Chesapeake Bay mainstem segments and the lower Potomac
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
28
River, whose hypoxic/anoxic conditions are of long standing and whose dynamics
are well enough understood to be modeled mathematically and relatively precisely.
There are other segments that have long term monthly and twice monthly dissolved
oxygen concentration records whose station coverage is considered to represent the
whole segment adequately or at least areas most likely to have dissolved oxygen
concentrations below saturation levels. The Chesapeake Bay Program partners have
previously demonstrated (see Chesapeake Bay Dissolved Oxygen Goal for Restora¬
tion of Living Resource Habitats ; Jordan et al. 1992) that relatively good predictive
models can be developed for segments that suffer hypoxia at some regular frequency
and so far have demonstrated no long term trend in dissolved oxygen concentrations.
These models produce estimates of the percent of time the segment depth is below
some specified concentration. These monitoring data-based models reflect only
daytime measurements, but can be enhanced (and validated) by the in-situ contin¬
uous records from the buoy deployments.
The remaining segments not characterized above are those segments where the long¬
term fixed monitoring stations, sampled on a monthly to twice-monthly basis, do not
well represent dissolved oxygen conditions elsewhere in the segment. Typically
these segments have a moderately deep channel with flanking nearshore areas of
significant size. In these segments, tidal pulses from downstream, inflows from
upstream, and local land-based influences vary in their dominance, and the current
long-term water quality monitoring data do not capture ephemeral events or the near¬
shore conditions very well. The new shallow water monitoring component of the
larger Chesapeake Bay Water Quality Monitoring Program is designed to generate
the additional data necessary to assess criteria attainment in these segments. The
Chesapeake Bay Program partners are now accumulating such data for a growing
number of Chesapeake Bay Program segments.
ASSESSMENT OF INSTANTANEOUS MINIMUM
CRITERIA ATTAINMENT FROM MONTHLY MEAN DATA
By overlaying information from the buoy data about diurnal variability and the
frequency of common hypoxic events, such as those caused by phytoplankton bloom
respiration and decay, pycnocline tilting, etc., on top of the long-term fixed-station
monitoring data record, we can better understand the relationship between attain-
ment/non-attainment of the 30-day mean and instantaneous minimum criteria. The
reader should keep several things in mind. The temporal record of the long-term,
fixed-station monitoring program is considered “low-frequency” relative to the high
frequency record of the “continuous” data record from the buoy deployments. The
available continuous records chronicle a few days to months of a single year. Each
measurement is closely related to the previous and next measurement, providing a
detailed record of the dissolved oxygen response to the specific conditions of that
period. These buoy data records are measuring conditions at a single fixed point in
the water column, usually about a meter off the bottom in these data sets. The sensors
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
29
are fixed, but the water mass moves past, back and forth with the tide and the various
complexities of the local riverine and estuarine circulation. The majority of the avail¬
able buoy data were collected through buoy deployments that were sited using
stratified random design considerations or to answer location-specific questions, but
not directly to address the relationship between instantaneous minimum and monthly
mean concentrations.
In contrast, the long term monitoring program includes a vast network of stations
sited specifically to represent overall water quality conditions of the 78 Chesapeake
Bay Program segments. The low-frequency monitoring record captures a snapshot of
conditions only once or twice a month, but that series of snapshots now extends over
an 19-year period and is ongoing. Each snapshot consists of synoptic measurements
forming a relatively dense three-dimensional spatial data grid. The grid is formed
horizontally by the network of mainstem and tidal tributary monitoring stations and
vertically by the dissolved oxygen profiles measured at 1- to 2-meter intervals from
water column surface to bottom water-sediment interface. A single summer ‘snap¬
shot cruise' typically includes over a thousand individual dissolved oxygen
concentration measurements.
REFERENCE POINTS WITH RESPECT TO DEPTH
Dissolved oxygen levels are strongly related to depth, bathymetry, and flow and
circulation patterns. Table V-l provides information that helps to decide how repre¬
sentative the long-term fixed-station monitoring data and the continuous buoy data
records are of their respective Chesapeake Bay Program segment. Table V-l presents
segment volume, the depth of the Chesapeake Bay Water Quality Program moni¬
toring station(s) in the segment, and the segment-wide bottom depth distribution i.e.,
maximum depth, the depth encompassing 90 percent, 75 percent, 50 percent (the
median) and 25 percent of the bottom depths, as well as the minimum depth.
DATA ASSEMBLAGE AND MANIPULATION
Table V-2 lists the 147 continuous buoy data sets available for analysis through the
Chesapeake Information Management System (partner network of Chesapeake Bay
data and information servers), latitude/longitude location information, the time interval
between measurements, the total duration of deployment, water depth and depth of the
sensor at the site and in what depth category the sensor depth falls, based on the depth
distributions listed in Table V-l. The list of data sets has been categorized according to
Chesapeake Bay Program segment so that it is obvious which segments have or do not
have such high frequency information available for evaluating and establishing the 30-
day mean and instantaneous minimum concentration relationship.
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7 -Day Mean Dissolved Oxygen Criteria
30
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Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
DESIGNATED USE ASSIGNMENTS
Both the low frequency long-term fixed station and the continuous buoy data records
were assessed relative to the published Chesapeake Bay dissolved oxygen criteria.
The criteria are specific to different designated uses and, therefore, seasons (U.S.
EPA 2003). With very few exceptions, the buoy data currently available were
summer deployments (June-September). One exception begins at the end of April;
this one and a couple of other deployments extend through October, and one extends
to November.
Each data record was assigned to a designated use within a Chesapeake Bay Program
segment based on following method. Using the Chesapeake Bay Water Quality Moni¬
toring Program data, the depth of the upper and lower pycnoclines, if any, were
calculated for each station for each cruise date and the segment averages for the
month/year were determined. These segment-averaged pycnocline depths were then
merged by corresponding dates with the buoy sensor depths in those segments where
deep-water and deep-channel designated uses apply. It is important to remember that
pycnocline depths may be fairly stable in some areas, but changeable and ephemeral
in others, even within the same segment. An average pycnocline depth for the month
may have a lot of variability around it, and thus the designated use assignments for
some buoy data records may not be correct. Where the buoy dissolved oxygen
concentrations suggested an incorrect assignment, the monitoring data at stations and
dates nearest in time and space to the buoy deployment were examined in detail and
any appropriate changes to the designated use assignment were made accordingly.
FINDINGS
Day/Night Differences In Dissolved Oxygen Concentration
A commonly expressed concern about the Chesapeake Bay Water Quality Moni¬
toring Program’s dissolved oxygen data is that they reflect daytime dissolved oxygen
levels, the time period when active photosynthesis by algae, and consequent gener¬
ation and introduction of new oxygen into the water column, may mask lower
nighttime concentrations. To address this concern, the buoy data were partitioned
into day (defined as 9:00 AM to 5:00 PM) and night (defined as after 5:00 PM to
before 9:00 AM) periods and summarized. Table V-3 provides the following statis¬
tics for the day and night periods: minimum concentration, the concentration of the
lowest 1 percent of measurements, the lowest 1 0 percent, the median, mean, standard
deviation, and coefficient of variation, separately for day and night periods each
month, and the number of measurements taken in that month.
Table V-4 pools all the continuous buoy data for a station’s designated use to show
average day/night differences at each site. The difference between the daytime mean,
minimum, 1 percent, etc. and the equivalent nighttime statistic was computed for
each date of deployment and the means of the daily day-night differences are shown
in the table (difference = daytime concentration minus nighttime concentration).
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
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chapter v • Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
46
With some clear exceptions, the day-night concentration differences in these buoy
data are small. Back River (segment BACOH), a tidal river known to be stressed by
discharges from a large urban sewage treatment facility, exhibits the largest day-
night difference in mean and median concentrations: -2.24 mg liter'1 and -4.51 mg
liter 1 , respectively (Table V-4). Note that here the nighttime concentration is higher
than during the daytime, which seems counterintuitive. But, in fact, the average
day/night difference in the daily means and medians is almost always negative in this
table. A buoy site in the lower Potomac River (POTMH) and one in upper Potomac
River (POTTF) showed day-night differences greater than 1 mg liter 1 in the daily
mean or median or both, but all other sites showed differences less than 1 mg liter-1.
The average day-night differences in the daily minimum concentration and lowest
1 percent value were similarly generally small, but with more sites exhibiting day-
night differences in excess of 1 mg liter-1: mesohaline Patapsco River (PATMH),
tidal fresh (POTTF) and mesohaline (POTMH) Potomac River, tidal fresh James
River (JAMTF), middle central and lower western mainstem Chesapeake Bay
segments CB4MH and CB6PH, respectively, and Tangier Sound (TANMH). In
contrast to the findings for the daily mean and median, the concentration minima and
lowest 1 percent were generally higher in the daytime than at night.
30-Day Mean and Instantaneous Minimum Criteria Attainment
Table V-5 shows how the continuous dissolved oxygen measurements stack up
against the corresponding designated use dissolved oxygen criteria. The dissolved
oxygen criteria are to be assessed for each segment/designated use separately. Thus,
in this analysis, the day and night measurements are pooled and the mean, 1 percent
concentration and other statistics are calculated within month, if the data record
extends over multiple months. Asterisks flag the continuous buoy data records where
the 30-day mean criterion is not achieved (i.e., monthly mean dissolved oxygen
concentration is lower than the applicable criterion) or where the measured 1 percent
dissolved oxygen concentration is lower than the instantaneous minimum criterion.
Looking down the columns in Table V-5 labeled “30-day Mean” and “Instantaneous
Minimum” under the heading “Criterion Not Achieved”, it can be seen frequently
that if the 30-day mean criterion was achieved, the instantaneous minimum criterion
was also achieved. Conversely, if the 30-day mean criterion was not achieved, the
instantaneous minimum criterion also was not achieved. Further, if only one
dissolved oxygen criterion was not achieved, then it was usually the instantaneous
minimum criterion that was not achieved.
Table V-6 summarizes the criteria achieved/not achieved rate by segment and desig¬
nated use and Table V-7 pools the Table V-6 findings by designated use. For the
open-water designated use, in 80 out of 94 cases (—85 percent), if the 30-day mean
criterion was achieved/not achieved, then the same was the case for the instantaneous
minimum criterion. In deep-water designated use habitats, this condition was true in
15 out of 26 cases (~57 percent). The diversity of buoys deployed in deep-channel
designated use habitats is too small for drawing very specific conclusions at this time.
chapter v • Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
47
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chapter v • Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
Table V-7. Summary of continuous dissolved oxygen buoy data achievementynon-achievement of the applicable 30-day mean and
instantaneous minimum dissolved oxygen criteria summarized Bay-wide by designated use.
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chapter v • Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
52
Predicting the Lowest 1 Percent Concentration From The Mean
Down the left side of Figure V-l are plots of the 1 percent measured dissolved
oxygen concentration versus the measured monthly mean concentration for each
designated use (all buoy records parsed by month and pooled within designated use).
Down the right side of Figure V-l are plots of the same sets of measurements only
for an individual segment, CB4MH as an example, where multiple buoys or records
including multiple months were available. Both solid circles and open triangles are
displayed on the plots. The circles are the observed 1 percent concentration data; the
triangles are concentrations predicted by a simple regression model including the
observed monthly mean and the coefficient of variation. In these examples, the
prediction model does pretty well because of the relative large number of observa¬
tions and thus the very good estimate of the monthly mean and 1 percent
concentrations, as well as the close relationship of each observation to the next. As
the number of available continuous buoy data records increases for a wider array of
segments and designated uses, the Chesapeake Bay Program partners should be in a
position to develop a more generalized model for designated uses by segment that
would enable the user to predict the 1 percent concentration from the monthly means
obtained from the long-term fixed-station monitoring data.
One question still under investigation is how well those observed monthly means
compare to the means obtained from the continuous buoy data records. Figure V-2,
which shows the fixed station twice monthly monitoring data and semi-continuous
buoy data plotted together, provides some current insights into answering this ques¬
tion. Down the left side of Figure V-2 are plots of the observed 1 percent
concentrations versus observed monthly mean dissolved oxygen concentrations
(June-September) obtained from fixed station monitoring data and plotted for open-
water, deep-water and deep-channel designated uses in segment CB4MH. Down the
right side of Figure V-2 are the plots from the continuous buoy data for CB4MH. The
vertical and horizontal reference lines cutting each graph into 4 quadrants represent
the 30-day mean and instantaneous minimum dissolved oxygen criteria concentra¬
tions. Again, a regression model using the mean and coefficient of variation of the
monitoring data has been used to predict the 1 percent concentration. As illustrated
in Figure V-l, solid circles represent the observed concentrations and open triangles
represent the predicted concentrations. As expected from the fixed station moni¬
toring data, the fit of predicted to observed is not as tight as with the buoy data. These
regression models can be improved with the addition of more explanatory variables.
The point is that in some, possibly many segments, the relationship of the monthly
mean with the 1 percent concentration evidenced in monitoring data is similar to that
found in the buoy data records. The regression models output illustrated in Figures
V-l and V-2 can be improved by including other explanatory variables to better
predict the variability detected and quantified in the buoys.
Figure V-3 shows similar plots of the 1 percent concentration versus the monthly
mean obtained from monitoring data in various other example segments. Note how
tight the relationship is in segment BOHOH (Bohemia River) in contrast to the
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
53
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Figure V-l . Plots of monthly mean dissolved oxygen concentration (mg liter1) versus the 1 percentile dissolved
oxygen concentration as measured by sensors on individual buoys. Plots on left side show patterns of dissolved
oxygen concentration data pooled across Chesapeake Bay Program segments within open-water, deep-water and
deep-channel uses. Plots on the right side show patterns of dissolved oxygen concentration data from middle cen¬
tral Chesapeake Bay, segment CB4MH. Circles are observed dissolved oxygen concentration data; open triangles are
dissolved oxygen concentrations predicted by the regression model: 1 percent dissolved oxygen concentration as a
function of monthly mean dissolved oxygen and the coefficient of variation.
Source: Chesapeake Bay Water Quality Monitoring Program database.
http://www.chesapeakebay.net/data
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
54
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Figure V-2. Plots of monthly mean dissolved oxygen concentration (mg liter1) versus the 1 percentile dissolved
oxygen concentration in middle central Chesapeake Bay, segment CB4MH. Plots on left side show the pattern of
observed dissolved oxygen concentration data from the Chesapeake Bay Water Quality Monitoring Program
(May-September 1985-2003). Plots on right side show observed dissolved oxygen data from segment CB4MH as
measured during various buoy deployments. Circles are observed dissolved oxygen concentrations; open triangles
are dissolved oxygen concentrations predicted by the regression model: 1 percent dissolved oxygen concentration
as a function of monthly mean dissolved oxygen concentration and coefficient of variation.
Source: Chesapeake Bay Water Quality Monitoring Program database.
http://www.chesapeakebay.net/data
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
55
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Figure V-3. Plots of monthly mean ambient dissolved oxygen concentration versus the one percentile dissolved
oxygen concentrations in several example Chesapeake Bay Program segments: the northern Chesapeake Bay
(CB1TF), Bohemia River (BOHOH), open-water and deep-water lower eastern Chesapeake Bay (CB7PH), Magothy
River (MAGMH) and the lower York River (YRKPH). These graphics show patterns of dissolved oxygen data from the
Chesapeake Bay Water Quality Monitoring Program from May-September 1985-2003. Circles are observed dissolved
oxygen concentration data; open triangles are dissolved oxygen concentrations predicted by the regression model:
1 percent dissolved oxygen concentration as a function of monthly mean dissolved oxygen concentration and
coefficient of variation.
Source: Chesapeake Bay Water Quality Monitoring Program database.
http://www.chesapeakebay.net/data
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
56
scatter of points in the plot for segment MAGMH (Magothy River), indicating large
between-segment differences in variability and predictability.
The plots in Figure V-3 illustrate the differences among segments in their patterns of
criteria non-achievement. The four quadrants bounded by the reference lines in the
plots represent the four possible results from a two-criteria achievement assessment.
Let the quadrants be numbered clockwise 1 through 4, beginning with the upper
right hand quadrant. Any data points in quadrant 1 achieve both the 30-day mean and
instantaneous minimum criteria. Data points in quadrant 2 achieve the 30-day mean
criterion, but do not achieve the instantaneous minimum criterion. Data points in
quadrant 3 do not achieve both the 30-day mean and instantaneous minimum
criteria. Data points in quadrant 4 achieve the instantaneous minimum criterion, but
do not achieve the 30-day mean criterion. In a fully restored Chesapeake Bay, one
would expect that most data points would fall in quadrant 1. In impaired segments,
where low dissolved oxygen conditions are frequent or chronic, one would expect
most data points to fall in quadrant 3. In segments where low dissolved oxygen
events are episodic, ranging from occasional to frequent, one would expect a dense
population of data points in quadrant 2. And, where dissolved oxygen concentrations
are chronically reduced, but really low dissolved oxygen concentrations are rare,
then one would expect some data points in quadrant 4.
Providing plots such as those presented in Figure V-3 for each designated use for
every segment is impractical for this document. Instead, Table V-8 shows the number
of points in a representative data set that would be in each quadrant, if the data were
plotted as in Figure V-3 using the summer only data from a recent 10-year period:
June-September, 1993-2002.
There are 66 segments that have only open-water designated uses. A total of 28 of
these segments achieve both the 30-day mean and instantaneous minimum criteria,
i.e., which have all their data points in quadrant 1 and none or only one data point in
the other quadrants. These segments are marked with a single asterisk in Table V-8.
In these open-water only segments, assessment of attainment of the instantaneous
minimum criterion can be directly based on assessment of attainment of the 30-day
mean criterion (Table V-9).
A total of 18 segments with only open-water designated uses had the vast majority
(greater than two-thirds) of their data points in either quadrant 1 or quadrant 3. These
segments are marked with double asterisks in Table V-8. The assessment of attain¬
ment of the instantaneous minimum criterion can be directly based on assessment of
attainment of the 30-day mean criterion in these segments (Table V-9).
In five segments with only open-water designated uses there were sufficient data
points in quadrant 2 indicating a much higher occurrence where the 30-day mean
criterion was achieved yet the instantaneous minimum criterion was not achieved.
These segments are marked with a single dash in Table V-8. These five segments
were: upper Chesapeake Bay (CB20H), Magothy River (MAGMH), Severn River
(SEVMH), Mobjack Bay (MOBPH) and Little Choptank River (LCHMH). Users
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
57
Table V-8. Characterization of the Chesapeake Bay Program segments based on
occupied quadrants in a plot of the 1 percent dissolved oxygen concentration
versus observed monthly mean dissolved oxygen concentration1.
Number of Data Points By Quadrant by Designated Use
CBP
Segment
Open
-Water
Deep-Water
Deep-Channel
1
2
3
4
1
2
3
4
1
2 3
4
CB1TF*
39
0
0
0
CB20H-
12
19
8
0
CB3MH
38
2
0
0
2
34
4
0
3
17 18
0
CB4MH
35
5
0
0
1
8
31
0
2
2 36
0
CB5MH
36
4
0
0
6
29
5
0
11
20 9
0
CB6PH
31
9
0
0
32
8
0
0
CB7PH
36
4
0
0
33
5
2
0
CB8PH*
39
1
0
0
BSHOH*
37
0
0
1
GUNOH**
38
0
1
1
MIDOH*
40
0
0
0
BACOH**
36
0
0
4
PATMH
40
0
0
0
0
7
33
0
1
1 7
0
MAGMH-
8
16
16
0
SEVMH-
7
9
19
4
SOUMH**
3
2
31
3
RHDMH**
37
0
1
1
WSTMH**
28
3
5
3
PAXTF*
40
0
0
0
WBRTF*
40
0
0
0
PAXOH**
31
0
2
7
PAXMH
25
15
0
0
8
11
21
0
POTTF*
39
1
0
0
PISTF**
38
2
0
0
MATTF*
39
1
0
0
POTOH*
39
1
0
0
POTMH
39
1
0
0
5
25
10
0
10
7 22
0
RPPTF*
39
0
0
0
RPPOH*
39
0
0
0
RPPMH
35
4
1
0
24
15
1
0
22
8 3
0
CRRMH**
20
2
11
7
PIAMH**
38
2
0
0
MPNTF
29
0
0
8
MPNOH
25
0
0
13
PIMKTF
26
0
3
10
PMKOH
22
0
0
17
YRKMH**
30
0
2
8
YRKPH**
35
0
0
5
32
2
3
1
MOBPH-
25
14
1
0
JMSTF*
40
0
0
0
APPTF*
39
0
0
0
JMSOH*
40
0
0
0
CFIKOH*
40
0
0
0
JMSMH*
40
0
0
0
JMSPH*
39
0
0
1
WBEMH**
31
0
1
7
SBEMH
22
0
4
13
29
0
3
2
EBEMH
25
0
2
12
LAFMH**
17
0
0
3
ELIPH**
36
0
3
1
NORTF*
40
0
0
0
continued
C&DOH*
40
0
0
0
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
Table V-8 (continued). Characterization of the Chesapeake Bay Program segments
based on occupied quadrants in a plot of the 1 percent dis¬
solved oxygen concentration versus observed monthly mean
dissolved oxygen concentration1 .
Number of Data Points By Quadrant by Designated Use
CBP
Segment
Open-
-Water
1
2
3
4
BOHOH*
39
0
0
1
ELKOH*
39
0
0
0
SASOH*
39
0
0
1
CHSOH*
39
0
0
1
CHSMH
37
2
1
0
EASMH
39
1
0
0
CHOOH**
34
0
0
6
CHOMH2**
26
2
9
3
CHOMH1 **
33
6
1
0
LCHMH-
4
11
24
0
FSBMH*
36
0
0
1
NANTF**
35
0
0
5
NANMH*
38
0
0
0
WICMH
28
0
0
10
MANMH*
37
0
0
1
B1GMH*
38
0
0
0
POCTF
18
0
3
19
POCMH*
40
0
0
0
TANMH**
27
6
5
1
Deep-Water
12 3 4
12 8 14 1
1 13 20 2
Deep-Channel
12 3 4
2 0 3 0
2 0 2 0
'Quad 1 : both 30-day mean and instantaneous minimum criteria achieved; quad 2: 30-day mean criterion
achieved, instantaneous minimum criterion not achieved; quad 3: both 30-day mean and instantaneous minimum
criteria not achieved; quad 4: 30-day mean criterion not achieved, instantaneous minimum criterion achieved.
Based on data from the Chesapeake Bay Water Quality Monitoring Program twice monthly cruises between June
and September, 1993 through 2002 (most recent 10 years).
Single asterisk (*): Open-water use only segment with all data points in quadrant 1 and none or only one data
point in the other three quadrants.
Double asterisk (**): Open-water use only segment with a vast majority of data points (greater than two-thirds)
in either quadrant 1 or quadrant 3.
Single dash(-): Open-water use only segment with sufficient data points in quadrant 2 indicating a much higher
occurrence where the 30-day mean criterion was achieved yet the instantaneous minimum criterion was not
achieved.
Boldface type: Open-water use only segment with a large number of data points in quadrant 1 and quadrant 4 and
none or very few data points in the other two quadrants.
Source: Chesapeake Bay Water Quality Monitoring Program database.
http://www.chesapeakebay.net/data
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
Table V-9. Chesapeake Bay Program segments and tidal water designated uses where attainment of the instantaneous minimum, 1-day
mean and 7-day mean dissolved oxygen criteria can be assessed using 30-day mean data or dissolved oxygen criteria
attainment assessment may require collection and evaluation of data of higher frequency than 30-day means.
59
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CB1TF
CB20II
CB3MH
CB4MH
CB5MH
CB6PH
CB7PH
CB8PH
BSHOH
GUNOH
MIDOH
BACOH
PATMH
MAGMH
SEVMH
SOUMH
RHDMH
WSTMH
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Northern Chesapeake Bay
Upper Chesapeake Bay
Upper Central Chesapeake Bay
Middle Central Chesapeake Bay
Lower Central Chesapeake Bay
Western Lower Chesapeake Bay
Eastern Lower Chesapeake Bay
Mouth of the Chesapeake Bay
Bush River
Gunpowder River
Middle River
Back River
Patapsco River
Magothy River
Severn River
South River
Rhode River
West River
Upper Patuxent River
Western Branch Patuxent River
Middle Patuxent River
Lower Patuxent
Upper Potomac River
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
continued
Table V-9 (continued). Chesapeake Bay Program segments and tidal water designated uses where attainment of the instantaneous min¬
imum, 1-day mean and 7-day mean dissolved oxygen criteria can be assessed using 30-day mean data or dis¬
solved oxygen criteria attainment assessment may require collection and evaluation of data of higher frequency
than 30-day means.
60
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Chesapeake Bay Program Segment
Segment
Code
ANATF
PISTF
MATTF
POTOH
POTMH
RPPTF
RPPOH
RPPMH
CRRMH
PIAMH
MPNTF
MPNOH
PMKTF
PMKOH
YRKMH
YRKPH
MOBPH
JMSTF
APPTF
JMSOH
CHKOH
JMSMH
JMSPH
Segment Name
Anacostia River
Piscataway Creek
Mattawoman Creek
Middle Potomac River
Lower Potomac River
Upper Rappahannock River
Middle Rappahannock River
Lower Rappahannock River
Corrotoman River
Piankatank River
Upper Mattaponi River
Lower Mattaponi River
Upper Pamunkey River
Lower Pamunkey River
Middle York River
Lower York River
Mobjack Bay
Upper James River
Appomattox River
Middle James River
Chickahominy River
Lower James River
Mouth of the James River
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
61
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SBEMH
EBEMH
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ELKOH
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CHSOH
CHSMH
EASMH
CHOTF
CHOOH
CHOMH2
CHOMH1
LCHMH
HNGMH
FSBMH
NANTF
Segment Name
Western Branch Elizabeth River
Southern Branch Elizabeth River
Eastern Branch Elizabeth River
Lafayette River
Mouth to mid-Elizabeth River
Lynnhaven River
Northeast River
C&D Canal
Bohemia River
Elk River
Sassafras River
Upper Chester River
Middle Chester River
Lower Chester River
Eastern Bay
Upper Choptank River
Middle Choptank River
Lower Choptank River
Mouth of the Choptank River
Little Choptank River
Honga River
Fishing Bay
Upper Nanticoke River
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
continued
Table V-9 (continued). Chesapeake Bay Program segments and tidal water designated uses where attainment of the instantaneous min¬
imum, 1-day mean and 7-day mean dissolved oxygen criteria can be assessed using 30-day mean data or dis¬
solved oxygen criteria attainment assessment may require collection and evaluation of data of higher frequency
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chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
63
assessing attainment of 30-day mean and instantaneous minimum dissolved oxygen
criteria within these five segments are cautioned to not automatically assume attain¬
ment of the 30-day mean criterion reflects attainment of the instantaneous minimum
criterion (Table V-9). Site-specific buoy deployments may be necessary to either
better quantify a relationship or assess attainment using both low- and high-
frequency data sources.
Seven segments with only open-water designated uses had a large number of data
points in quadrant 1 (both criteria were achieved) and in quadrant 4 (instantaneous
minimum criterion achieved, but the 30-day mean criterion not achieved) and none
or very few data points in other quadrants were marked in bold typeface in Table V-
8. These seven segments were: upper (MPNTF) and lower (MPNOH) Mattaponi,
upper (PMKTF) and lower (PMKOH) Pamunkey River, Eastern Branch Elizabeth
River (EBEMH), Wicomico River (WICMH), and upper Pocomoke River (POCTF.)
The segments in the Pamunkey and Mattaponi rivers (segments PMKTF, PMKOH
and MPNTF, MPNOH, respectively) are known to be strongly influenced by rela¬
tively large expanses of fringing wetlands along the entire length of both tidal rivers.
The Wicomico River (WICMH) and upper Pocomoke River (POCTF) also have
large areas of tidal wetlands along particular reaches of these two rivers. The natural
influences of extensive fringing tidal wetlands systems, described in more detail in
Chapter 6, are the likely reason for why the 30-day mean/instantaneous minimum
relationship does not fully apply to these seven segments. More site specific evalua¬
tion of the data and conditions within the Eastern Branch of the Elizabeth River
(EBEMH) is required to understand what’s happening in this tidal system.
Users assessing attainment of the 30-day mean and instantaneous minimum
dissolved oxygen criteria within these seven segments are cautioned not to automat¬
ically assume that attainment of the 30-day mean criterion reflects attainment of the
instantaneous minimum criterion (Table V-9). Site-specific buoy deployments may
be necessary either to better quantify a relationship or assess attainment using both
low- and high-frequency data sources.
For the remaining seven segments with only open-water designated uses, there were
insufficient buoy data available to assess whether attainment of the 30-day mean
criterion reflected attainment of the instantaneous minimum criterion. These
segments are marked with a “N/D” in Table V-9.
Of the thirteen segments with deep-water or deep-water and deep-channel desig¬
nated uses, eleven of the segments had the vast majority (greater than two-thirds) of
their open-water designated use data points in quadrant 1 (Table V-8), directly
supporting the assessment of attainment of the instantaneous minimum criterion
directly based on assessment of attainment of the 30-day mean criterion in these
segments (Table V-9). Users assessing attainment of the 30-day mean and instanta¬
neous minimum dissolved oxygen criteria within the lower Patuxent River
(PAXMH) and Southern Branch Elizabeth River (SBEMH) are cautioned not to
automatically assume that attainment of the 30-day mean criterion reflects attain¬
ment of the instantaneous minimum criterion.
chapter v
Guidance for Attainment Assessment of instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
64
Ten of these thirteen segments with deep-water or deep-water and deep-channel
designated uses also showed evidence of a strong relationship between achieved/not
achieved in the assessment of the instantaneous minimum using monthly mean data
for the deep-water and/or deep channel designated uses (Table V-8). These segments
were: middle central Chesapeake Bay (CB4MH), western lower Chesapeake Bay
(CB6PH), eastern lower Chesapeake Bay (CB7PH), Patapsco River (PATMH), lower
Potomac River (POTMH) [deep-channel use only], lower Rappahannock River
(RPPMH) [deep-channel use only], lower York River (YRKPH), Southern Branch
Elizabeth River (SBEMH), lower Chester River (CSHMH), and Eastern Bay
(EASMH) [deep channel use only] (Table V-9).
In the cases of the upper central Chesapeake Bay (CB3MH), lower central Chesa¬
peake Bay (CB5MH), lower Patuxent River (PAXMH), lower Potomac River
(POTMH) [deep-water use only], lower Rappahannock River (RPPMH) [deep-water
use only] and Eastern Bay (EASMH) [deep-water use only] there are sufficient data
points in quadrant 2 indicating a higher occurrence where the 30-day mean criteria
were achieved yet the instantaneous minimum criteria were not achieved in deep¬
water and/or deep-channel designated use habitats (Table V-8). Users assessing
attainment of 30-day mean and instantaneous minimum dissolved oxygen criteria
within these seven segments and their respective deep-water/deep channel desig¬
nated uses are cautioned not to automatically assume that attainment of the 30-day
mean criterion reflects attainment of the instantaneous minimum dissolved oxygen
criterion (Table V-9). Site-specific buoy deployments may be necessary either to
better quantity a relationship or assess attainment using both low- and high-
frequency data sources.
ASSESSMENT OF 7-DAY MEAN CRITERIA ATTAINMENT
FROM MONTHLY MEAN DATA
The open-water designated use habitats are also subject to a 7-day mean criterion.
The continuous buoy data were examined to look for relationships between the 30-
day mean and the 7-day mean values. Buoy data records with durations over 14 days
(at least two 7-day periods) were examined. Figure V-4 shows plots of the sequen¬
tial as opposed to a rolling series of 7-day means versus the 30-day mean for the
more limited number of data records that were available. There is more scatter in
these relationships than in the 30-day mean versus instantaneous minimum relation¬
ships. However, a significant majority of the data points are found in the first and
third quadrants, where the data points both achieve (quadrant 1) or both do not
achieve (quadrant 3) the 30-day mean and 7-day mean criteria. There is clearly a
strong relationship between achieving/not achieving of the 30-day mean and 7-day
mean criteria. The remaining data points tended to be in the second quadrant where
the data points do not achieve the 30-day mean criterion but achieve the 7-day mean
criterion. Only 3 data points were located in the fourth quadrant.
chapter v • Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
65
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Monthly Mean Dissolved Oxygen Concentration
PAXMH Open— Water
Monthly Mean Dissolved Oxygen Concentration
Figure V-4. Plots of monthly mean dissolved oxygen concentration (mg liter1) versus the 7-day mean dissolved
oxygen concentration (mg liter1) in several example Chesapeake Bay Program segments: open-water and deep¬
water middle central Chesapeake Bay (CB4MH), Mobjack Bay (MOBPH), lower Choptank River (CHOMH1), middle
Potomac River (POTOH) and lower Patuxent River (PAXMH).
Source: Chesapeake Bay Water Quality Monitoring Program database.
http://www.chesapeakebay.net/data
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
66
FINDINGS
For the majority of Chesapeake Bay Program segments and the designated use habi¬
tats within those segments identified in Table V-9, dissolved oxygen concentration
data collected through monthly to twice monthly sampling at the Chesapeake Bay
Water Quality Monitoring Program fixed-stations can be used to assess attainment
of all higher frequency dissolved oxygen criteria components including the 7-day
mean, 1-day mean and instantaneous minimum criteria. For the remaining segments
and identified designated uses, further targeted buoys deployments are required to
more fully characterize and quantify the relationships between the monthly mean, 7-
day mean, 1-day mean and instantaneous minimum concentrations. Further work is
underway to factor in additional variables to strengthen the predictive relationships
between the 30-day mean, 7-day mean, 1-day mean and instantaneous minimum
values and therefore, the assessment of attainment of the instantaneous minimum, 1-
day mean and 7-day mean criteria using monthly mean observations.
LITERATURE CITED
Jordan, S.J., C. Stenger, M. Olson, R. Batiuk and K. Mountford. 1992. Chesapeake Bay
Dissolved Oxygen Goal for Restoration of Living Resource Habitats: A Synthesis of Living
Resource Requirements with Guidelines for Their Use in Evaluating Model Results and
Monitoring Information. CBP/TRS 88/93. Region III Chesapeake Bay Program Office,
Annapolis, Maryland.
U.S. Environmental Protection Agency. 2003. Ambient Water Quality • Criteria for Dissolved
Oxygen. Water Clarity' and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.
EPA 903-R-03-002. Region III Chesapeake Bay Program Office, Annapolis, Maryland.
chapter v
Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria
chapter \/i
Guidance for Deriving Site
Specific Dissolved Oxygen
Criteria for Assessing Criteria
Attainment of Naturally Low
Dissolved Oxygen
Concentrations in Tidal Wetland
Influenced Estuarine Systems
Tidal wetlands are a valuable component of estuarine systems. In the Pamunkey
River, they have been shown to be net sinks for sediments (Neubauer et al. 2001 ) and
in most cases also serve to remove nutrients from overlying water (Anderson et al.
1997). High rates of organic production, accompanied by high rates of respiration
(Neubauer et al. 2000), can significantly reduce dissolved oxygen and enhance
dissolved inorganic carbon levels both in sediment pore water and overlying water
in wetland systems. Another process that can deplete dissolved oxygen in wetland
sediments is nitrification, which converts ammonium to nitrite and nitrate (Tobias et
al. 2001).
Subsequent to publication of Ambient Water Quality' for Dissolved Oxygen, Water
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries (U.S.
EPA 2003a), Virginia, Maryland, Delaware and the District of Columbia initiated
their respective processes for adopting new and/or revising existing state water
quality standards. In so doing, Virginia requested support and guidance from EPA in
determining the appropriate dissolved oxygen criteria/designated use/attainment
procedures for the tidal Mattaponi and Pamunkey rivers for addressing the naturally
lower ambient dissolved oxygen concentrations. Based on the scientific literature
and personal communications with Chesapeake Bay wetland scientists, EPA recog¬
nized the need to explore accommodations for the special circumstances in these
tidal wetland influenced estuarine systems with respect to criteria levels, designated
uses and/or criteria attainment assessment.
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
NATURAL CONDITIONS/FEATURES INDICATING
ROLE OF WETLANDS IN LOW DISSOLVED
OXYGEN CONCENTRATIONS
A future objective is to define more fully the natural conditions and physical features
in Chesapeake Bay tidal systems that would indicate that tidal wetlands are playing
a significant role in naturally reducing ambient dissolved oxygen concentrations.
Those natural conditions/features have not yet been firmly established but Tables
VI- 1 and VI-2 provide some key physical and water quality statistics for the tidal
Mattaponi and Pamunkey rivers. Appendix A provides similar data for other tidal
fresh and oligohaline regions in the Chesapeake Bay and its tidal tributaries for
comparison. Four natural conditions/features have been evaluated here to document
and help quantify the influence of tidal wetlands on the dissolved oxygen deficit
observed in the tidal Mattaponi and Pamunkey rivers.
SURFACE TO VOLUME RATIOS/LARGE FRINGING WETLAND AREAS
The tidal fresh and oligohaline segments in the Mattaponi and Pamunkey rivers are
among the smallest volume, with a small surface to volume ratio and large areas of
fringing tidal marsh — 1.5 times larger than the tidal surface water area — relative to
other segments throughout the Bay’s tidal waters (Table VI- 1; Appendix A, Table A-l).
WATER QUALITY CONDITIONS
Table VI-2 gives some water quality statistics for recent years. These years happen
to have had dry to record-dry summers and that low flow regime should be borne in
mind. Severe low dissolved oxygen conditions (concentrations < 3 mg liter 1 ) are not
obvious, but average dissolved oxygen concentrations, in both surface and bottom
waters, are about 2.5 to 3 mg liter'1 below calculated oxygen saturation levels (Table
VI-2). Chlorophyll a concentrations are comparatively low, as are the total nitrogen
concentrations (with the exception of the oligohaline Pamunkey River segment
PMKOH). Phosphorus concentrations range from mid to high compared to other
tidal systems.
The dissolved oxygen deficit in these two tidal systems is among the highest
observed in the Chesapeake Bay’s tidal tributaries. The dissolved oxygen deficits
observed in the recent dry years (Table VI-2) are similar to those observed over the
1985-2002 Chesapeake Bay water quality monitoring program data record (Figure
VI- 1). These findings indicate that the processes driving the recorded dissolved
oxygen deficits are due largely to natural processes internal to the tidal system and
not as much to external nonpoint nutrient loadings (which are naturally reduced
during the recent dry years due to decreased surface runoff).
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
69
Table VI-1 . Some physical characteristics of the Mattaponi and Pamunkey tidal fresh (MPNTF and TMKTF,
respectively) and oligohaline (MPNOH and PMKOH, respectively) segments: depth distribution
based on depth of cells in the Chesapeake Bay Program volumetric interpolator, acres of fringing
tidal wetlands, segment perimeter, segment water surface area, segment water column volume
and segment water surface area:water column volume ratio.
Maximum
CBP Depth
Segment (meters)
75th
Percentile
(meters)
Median
Depth
(meters)
25th
Percentile
(meters)
Minimum
Depth
(meters)
Wetland
Acreage
(acres)
Segment
Perimeter
(meters)
Segment
Surface Area
(meters2)
Segment
Volume
(meters3)
Surface Area
to Volume
Ratio
MPNTF
12
3
2
1
1
1,125
108,327
8,573,187
15,337,500
0.6
MPNOH
15
5
3
2
1
3,360
109,059
8,660,891
35,390,000
0.2
PMKTF
15
4
2
1
1
1,652
264,699
16,229,024
28,630,000
0.6
PMKOH
18
5
3
2
1
5,374
119,417
14,093,807
66,680,000
0.2
Source: Chesapeake Bay Program http://ww\
v.chesapeakebay.net/data
Table VI-2. Recent summer averaged water quality conditions in the Mattaponi and Pamunkey tidal fresh
(MPNTF and PMKTF, respectively) and oligohaline (MPNOH and PMKOH, respectively) segments for
2000-2002, dry to record dry summers.
CBP
Segment
Water
Water Column
Column Depth
Layer (meters)
Salinity
(PPO
Temperature
(°C)
Dissolved
Oxygen
Concentration
(mg liter1)
Dissolved
Oxygen
Deficit
(mg liter'1)
Chlorophyll a
Concentration
(ug liter1)
Total
Suspended
Solids
Concentration
(mg liter1)
Total Total
Nitrogen Phosphorus
Concentration Concentration
(mg liter1) (mg liter1)
MPNTF
S 0.7
0.0
27.3
5.6
2.4
5.9
10.3
0.61
0.079
MPNTF
B 3.0
0.0
27.2
5.6
2.4
•
12.3
0.61
0.080
MPNOH
S 0.7
7.4
26.8
5.6
2.1
10.6
35.4
0.76
0.115
MPNOH
B 14.3
8.4
26.5
5.0
2.7
100.6
0.94
0.174
PMKTF
S 0.7
0.3
26.9
5.3
2.5
6.2
18.3
0.61
0.084
PMKTF
B 6.1
0.3
26.8
5.5
2.6
31.0
0.68
0.107
PMKOH
S 0.7
6.6
26.2
5.0
2.9
12.6
46.0
0.73
0.105
PMKOH
B 5.2
7.0
26.2
4.9
3.0
139.9
1.11
0.220
S = surface
B = bottom
Source: Chesapeake Bay Water Quality Monitoring Program database, http: www.chesapeakebay.net data
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
70
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MPNTF Surface
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Figure VI-1. Time series plots of ambient dissolved oxygen concentrations (mg liter1) and calculated dissolved
oxygen saturation concentrations (mg liter1) and resultant calculated dissolved oxygen deficit (saturation
concentration minus ambient concentration) in surface and bottom waters of the tidal fresh segments of the
Mattaponi (MPNTF) and Pamunkey (PMKTF) rivers.
Source: Chesapeake Bay Water Quality Monitoring Program database, http://www.chesapeakebay.net/data
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
71
DISSOLVED OXYGEN/TEMPERATURE RELATIONSHIPS
Another natural feature of tidal systems strongly influenced by extensive adjacent
tidal wetlands would be a strong relationship between the ambient dissolved oxygen
concentrations (and dissolved oxygen deficit) and water temperature, useful for
separating out the wetlands’ effect on dissolved oxygen versus an anthropogenic
effect. Figure VI-2 shows dissolved oxygen concentration and dissolved oxygen
deficit plotted versus water temperature for the tidal fresh and oligohaline segments
of the Mattaponi and Pamunkey rivers and for the tidal fresh and oligohaline
segments of the Rappahannock and Patuxent rivers for comparison. All the plots
illustrated in Figure VI-2 show dissolved oxygen concentrations going down as
water temperature rises due to decreasing saturation concentrations and likely
increased biological/chemical demand.
In the Rappahannock and Patuxent segments, however, dissolved oxygen concentra¬
tions begin to trend back upward (and the dissolved oxygen deficit levels out) as
temperatures continue to increase. Presumably the generation of oxygen from plank¬
tonic algal photosynthesis at these increasing temperatures provides the beneficial
boost during the daytime when these measurements were collected.
This trend effect in which dissolved oxygen concentrations increase as temperatures
continue to increase is not evident in the Mattaponi and Pamunkey segments. Based
on a comparison of the values in Table VI-2 and Appendix A, the difference in
chlorophyll a concentrations in Rappahannock and Patuxent (higher concentrations)
versus Mattaponi and Pamunkey river segments (lower concentrations) supports this
hypothesis. These findings lend further evidence of the lack of a strong influence of
planktonic algal photosynthesis on dissolved oxygen concentrations with the
Mattaponi and Pamunkey rivers.
LOW VARIABILITY IN DISSOLVED OXYGEN CONCENTRATIONS
One could also hypothesize that, within the temperature trend described above and
illustrated in Figure VI-2, there should be less scatter in the data points in a system
whose ‘stressor’ exerted its effect in a relatively constant manner, as the wetlands
might. While this hypothesis may be true and is suggested in the plots provided in
Figure VI-2, the differences among the segments in the number and diversity of
stations contributing data points is confounding a clearer conclusion. Table VI-3,
however, provides further quantitative information on dissolved oxygen concentra¬
tion variability in the Mattaponi and Pamunkey segments which does support that
hypothesis.
Through the long-term Chesapeake Bay Water Quality Monitoring Program,
Virginia has been collecting monthly or twice monthly dissolved oxygen measure¬
ments (surface and bottom) at fixed stations in the Mattaponi and Pamunkey tidal
fresh and oligohaline segments since 1985. The data are collected in the daytime and
each measurement represents one point in time in the month or two-week interval.
chapter v
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
72
MPNTF Surface
MPNOH Surface
Water Temperature
Water Temperature
PMKTF Surface
PMKOH Surface
Water Temperature
Water Temperature
RPPTF Surface
RPPOH Surface
Water Temperature
Water Temperature
PAXTF Surface
PAXOH Surface
Water Temperature
Water Temperature
Figure VI-2. Plots of measured ambient dissolved oxygen concentrations (•, mg liter1) and calculated dissolved
oxygen deficit (o, mg liter1) versus water temperature (°C) in tidal fresh and oligohaline segments of the Mattaponi
(MPNTF and MPNOH, respectively) and Pamunkey (PMKTF and PMKOH, respectively) rivers and in the tidal fresh
and oligohaline segments of Rappahannock (RPPTF and RPPOH, respectively) and Patuxent (PAXTF and PAXOH,
respectively) rivers for comparison.
Source: Chesapeake Bay Water Quality Monitoring Program database, http://www.chesapeakebay.net/data
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
73
In 2003, in-situ, continuous monitoring devices were deployed by the Virginia Insti¬
tute of Marine Science at a number of sites within both tidal rivers and all four
salinity-based segments. These ‘buoys’ were deployed to collect data at time-scales
more relevant to the Chesapeake Bay dissolved oxygen criteria, which have 7-day
mean and instantaneous minimum as well as the 30-day mean averaging periods
(U.S. EPA 2003a). These buoys collect dissolved oxygen concentration and other
physical data continuously at 15-minute intervals.
For the comparisons in Table VI-3, the mean and other statistics of the long-term
daytime Chesapeake Bay Water Quality Monitoring Program measurements were
computed for each month over the 18-year record, separately for surface (water
column depth = 1 meter) and bottom (where the water column depth was >1 meter)
waters. The continuous buoy data were divided into day (6:00 AM-5:59 PM) and
night (6:00 PM-5:59 AM) periods. All the buoys were deployed at the fixed depths
listed in Table VI-3.
The low variability in dissolved oxygen concentrations measured in the Mattaponi
and Pamunkey segments are documented by four separate measures: 1) the small
within-month range of concentrations measured in the Chesapeake Bay Water
Quality Monitoring Program over the 18-year data record; 2) the small dissolved
oxygen concentration differences between surface and deeper waters (long-term
water quality monitoring program data station); 3) the good agreement between
dissolved oxygen concentrations measured at the long-term water quality monitoring
program stations and the continuous buoy sites; and 4) the small differences between
day and night concentrations recorded in the continuous buoy data. Similar compar¬
isons are becoming possible in other Chesapeake Bay and tidal tributary segments
with expanded implementation of shallow water and continuous buoy deployment
monitoring programs. This expanding data record will be evaluated in the future to
further confirm low-variability in dissolved oxygen concentrations are an important
characteristic of segments where extensive tidal wetlands are directly influencing
ambient dissolved oxygen concentrations.
APPROACHES FOR ADDRESSING NATURALLY
LOW DISSOLVED OXYGEN CONDITIONS
DUE TO TIDAL WETLANDS
Four approaches for addressing naturally low ambient dissolved oxygen concentra¬
tions due to adjacent extensive tidal wetlands within the context of state water
quality standards were considered:
1. Define a completely new designated use with the appropriate dissolved oxygen
criteria.
2. Develop a separate biological reference curve that would account for lower
dissolved oxygen values in wetland-dominated tidal water segments.
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
74
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chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
76
3. Determine a fixed or multivariate compensation factor to ‘adjust’ (upward) the
observed dissolved oxygen concentration values. The adjusted values would be
substituted for observed values in the criteria attainment assessment protocol used
for all affected designated uses, i.e., comparing the cumulative frequency distri¬
bution curve of observed values to the biological reference curve.
4. Derive a set of site-specific dissolved oxygen criteria values that factor in the
natural dissolved oxygen deficit.
The first approach — a completely new designated use — was rejected because the
species and habitat requirements of those species that should be protected in these
tidal wetland dominated segments are the same species that occupy other open-water
designated use tidal water segments of similar salinity regimes. The assumption is
that in these areas, the species’ dissolved oxygen requirements are the same but that
they may modify their behavior, utilize the area differently or otherwise make
accommodation for the natural effect of the tidal wetlands on ambient dissolved
oxygen concentrations with some level of adverse effects.
The second approach — developing a separate biological reference curve — was
rejected because the biological reference levels are, by definition, based on ambient
dissolved oxygen conditions exhibited by areas supporting high functioning living
resources. Even if this definition were abandoned in favor of a curve or curves based
on specific natural impairments, then the Mattaponi and Pamunkey segments would
have to serve as their own reference sites since there are no other comparable
segments within the Chesapeake Bay system. Taking this approach to deriving
biological reference curves was difficult to rationalize.
The third approach — to find an appropriate adjustment factor for observed concen¬
trations — was rejected because of concerns that the criteria, not the attainment
procedures, should directly reflect the natural dissolved oxygen deficits caused by
extensive tidal wetlands.
The fourth option — derive a set of set specific dissolved oxygen criteria values — was
recommended as the best approach to factor in the natural wetlands-caused dissolved
oxygen deficit directly for the reasons and technical basis documented below.
DERIVATION OF SITE-SPECIFIC DISSOLVED OXYGEN
CRITERIA FACTORING IN NATURAL WETLAND-CAUSED
DISSOLVED OXYGEN DEFICITS
Through evaluation of three independent sources of information — scientific findings
published in the peer reviewed literature, Chesapeake Bay water quality model simu¬
lations, and the long-term Chesapeake Bay Water Quality Monitoring Program data
record — efforts were made to quantify the deficit in dissolved oxygen concentrations
below oxygen saturation levels due to natural tidal wetland processes. Once
quantified, the wetland-caused oxygen deficits could then be subtracted from
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
calculated oxygen saturation concentrations to determine the natural background
oxygen levels that could be sustained within these wetland dominated tidal rivers
absent any external anthropogenic nutrient pollutant loadings.
SCIENTIFIC RESEARCH-BASED ESTIMATES OF
WETLAND RESPIRATION
As part of the analysis to examine dissolved oxygen criteria attainment in the various
tidal wetland dominated segments, the Chesapeake Bay Water Quality Model was
calibrated to account for wetland oxygen demand by applying a universal sediment
oxygen demand of 2 grams 02/meter2-day to all Chesapeake Bay tidal wetland areas.
This value is a best professional judgement based on values published in the scien¬
tific literature and communication with Chesapeake Bay wetland scientists
(Neubauer 2003). The scientific literature indicates wetland sediment oxygen
demand in Northeastern United States ranges from 1 to 5.3 grams 02/meter2-day
(Neubauer et al. 2000; Cai et al. 1999).
The value for sediment oxygen demand used in the previous 1998 Chesapeake Bay
water quality model calibration (2 grams 02/meter2-day) was re-examined and deter¬
mined to be accurate for the Mattaponi and Pamunkey rivers. Scott Neubauer of the
Smithsonian Environmental Research Center (personal communication June 19,
2003) estimates the marsh sediment oxygen consumption for Sweet Hall marsh, a
freshwater marsh in the Pamunkey River, to range between 0.99-2.59 grams
02/meter2-day. Neubauer’s estimated ranges further support the sediment oxygen
demand of 2 grams 02/meter2-day that was used in the previous model calibration.
Neubauer also concurred that the Mattaponi and Pamunkey systems are very similar
(Neubauer 2003). Therefore, there was no need to recalibrate the sediment oxygen
demand for either tidal tributary.
MODEL-BASED WETLAND-CAUSED OXYGEN DEFICITS
The impact of wetland oxygen demand on ambient dissolved oxygen concentrations
was quantified for both the Mattaponi and Pamunkey segments through application
of the Chesapeake Bay water quality model. A series of water quality model
scenarios ‘with wetlands’ and ‘without wetlands’ were run to estimate the difference
in model-adjusted interpolated monthly averaged dissolved oxygen concentration in
the Mattaponi and Pamunkey segments. In the ‘with wetlands’ scenario, the water
quality model simulated the full influence of the extensive adjacent tidal wetlands on
ambient water quality conditions. In the ‘without wetlands' scenario, the tidal
wetland functions of the model were turned off in the Mattaponi and Pamunkey
model cells in order to simulate ambient water quality conditions in the absence of
any influence by tidal wetlands. The summer monthly averaged dissolved oxygen
concentration difference simulated by the ‘with wetlands’ scenario minus the
‘without wetlands’ scenario was 3 mg liter”1, i.e., the open-water dissolved oxygen
concentrations in the Mattaponi and Pamunkey segments with the presence of the
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
78
extensive tidal wetlands were simulated to be 3 mg liter 1 lower than model esti¬
mated dissolved oxygen saturated concentrations. The model estimated 3 mg liter"1
oxygen deficit is fully consistent with the average dissolved oxygen deficits
observed in monitoring data collected in these segments (see text below, Tables VI-
2 and VI-3, Figure VI- 1 ).
MONITORING-BASED ESTIMATES OF WETLAND-CAUSED
OXYGEN DEFICITS
The dissolved oxygen concentration and oxygen saturation levels were calculated
from the 1985-2002 Chesapeake Bay Water Quality Monitoring Program data
collected at stations in the Mattaponi and Pamunkey segments. Over the 18-year data
record, these stations were sampled at least monthly — sometimes twice monthly —
as part of the long-term water quality monitoring program. The almost two-decade
data record covers years of varying climatic and hydrologic conditions in the water¬
shed. Continuous, high frequency dissolved oxygen concentration data were also
available for these segments, as described previously, but in most cases the duration
of the data records is less than one year. Based on findings presented above,
dissolved oxygen conditions characterized by the data collected at long-term (day¬
time) monitoring stations were very similar to those revealed by the continuous
dissolved oxygen recording devices: short-term temporal and spatial variations in
dissolved oxygen concentrations were relatively small; and deep nocturnal dips in
dissolved oxygen concentrations were not observed in these segments.
For this analysis, the long-term water quality monitoring data were partitioned into
surface and bottom depths and into ‘cold’ (sampling events when water column
temperatures were less than or equal to 15° C) and ‘warm’ (greater than 15° C)
temperature categories. Table VI-4 shows: the calculated mean dissolved oxygen
saturation concentration over the 18 year data record; the difference between calcu¬
lated oxygen saturation and actual observed dissolved oxygen concentrations, i.e.,
the dissolved oxygen deficit; the number and percent of dissolved oxygen measure¬
ments below the 5 mg liter 1 30-day mean criterion and below a 4 mg liter"1
concentration value; and the average magnitude of those episodic excursions below
the 5 and 4 mg liter 1 values. Dissolved oxygen concentrations are always well above
the 5 mg liter 1 30-day mean criterion in the cold months in the Mattaponi and
Pamunkey river segments, so the cold month statistics are not discussed further.
As presented earlier and previewed in Table VI-2, the average dissolved oxygen
deficit in the warm (>15° C) months was 2.6 +/- 0.8 mg liter”1 (Table VI-4). This
long-term average monitoring data-based oxygen deficit value overlaps with the
oxygen deficit of 3 mg liter"1 estimated through the Bay water quality model simu¬
lation of tidal dissolved oxygen concentrations with and without tidal wetlands.
The calculated dissolved oxygen saturation concentration in the Mattaponi and
Pamunkey segments in the warm months was 8.5 +/- 0.7 mg liter"1. That means that,
in the absence of any anthropogenic pollutant influences on water quality conditions,
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
79
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much of the time the fully saturated ambient dissolved oxygen concentrations would
still above the 5 mg liter 1 30-day mean criterion level. However, from 13 to greater
than 30 percent of the warm months’ monitoring-based observations fell below a
monthly mean of 5 mg liter1 with the magnitudes of these exceedences up to 0.7 mg
liter1. These observations indicate that the segments would likely fail a summer¬
time application of the 5 mg liter1 30-day mean criteria. Tested against a monthly
mean concentration of 4 mg liter however, the percentage of observations falling
below this concentration is less than 7 percent in most cases, and the magnitude of
the exceedance is ~0.5 mg liter1 (Table VI-4).
The warm months calculated dissolved oxygen saturation concentration of 8.5
+/-0.7 mg liter1 directly translates into a dissolved oxygen concentration range of
7.8 to 10.2 mg liter-1. Similarly, the warm months average oxygen deficit of 2.6
+/-0.8 mg liter 1 converts into a oxygen deficit concentration range of 1.6 to 3.4 mg
liter-1. Assuming a maximum long-term average oxygen deficit of 3.4 mg liter-1, we
could anticipate an ambient dissolved oxygen range of 6.8 to 4.4 mg liter-1 upon
factoring in the oxygen deficit to a saturated water column condition. These are the
best dissolved oxygen conditions, assuming the maximum oxygen deficit, one could
ever hope to measure in the absence of any anthropogenic nutrient pollutant loading
influence on ambient dissolved oxygen conditions. Even without any human
impacts, the 5 mg liter 1 30-day mean dissolved oxygen criterion would be not
attained all times in the warm months of the year, setting up the basis for a site-
specific criterion based on natural conditions preventing attainment of the use (U.S.
EPA 2003b).
SITE-SPECIFIC DISSOLVED OXYGEN CRITERIA DERIVATION
Factoring a natural tidal wetlands-based oxygen deficit into the oxygen saturation
levels, based on the 18-year data record (see above), along with recognition that the
antropogenic pollutant loads can be reduced but not eliminated (U.S. EPA 2003b), a
site specific 4 mg liter-1 30-day mean criterion is recommended in place of the
published 5 mg liter-1 30-day mean and 4 mg liter 1 7-day mean open-water desig¬
nated use criteria. The EPA-published 3.2 mg liter-1 instantaneous minimum
dissolved oxygen criterion still applies to these waters year round (U.S. EPA 2003a).
The 4 mg liter 1 30-day mean site-specific criterion applies only to the tidal fresh and
oligohaline segments of the Mattaponi and Pamunkey rivers during the time period
of June 1 through September 30. Outside of this time period, the EPA-published set
of open- water designated use dissolved oxygen criteria apply (U.S. EPA 2003a). The
water column temperatures during the October through May time-frame are such
that higher levels of oxygen saturation are maintained and the biological processes
driving the natural tidal wetland oxygen deficits do not have nearly the same level of
influence on ambient dissolved oxygen concentrations.
This approach assumes that the nature of the wetland effect on dissolved oxygen is
relatively constant within season and that there are no other major stresses on
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
82
dissolved oxygen in the system as documented previously. This results in relatively
stable dissolved oxygen concentrations, which although sometimes below the 5 mg
liter1 30-day mean criterion level due to natural oxygen deficits, remain substantially
above the instantaneous minimum criterion. The magnitude of the wetland-caused
oxygen deficit is not enough to cause the calculated oxygen saturated concentrations
to fall below the 3.2 mg liter-1 instantaneous minimum. Therefore any future observed
exceedences of this criterion value are likely due to anthropogenic nutrient pollutant
loadings, not natural wetland-caused oxygen deficits.
At attainment levels sustained for long periods of time just above the 4 mg liter-1
criterion concentration (e.g., very few observed concentrations above 4 mg liter-1),
survival of open-water aquatic species in their larval, juvenile and adult lifestages
will not be impaired but there is likely to be some unquantified level of growth-
related impairments. However, the 18-year data record indicates a maximum of less
than one-third of the segment-based dissolved oxygen concentrations would not
attain a 5 mg liter-1 concentration (Table VI-4). Therefore, combined with imple¬
mentation of further nutrient reduction actions in the upstream watersheds yielding
higher measured ambient dissolved oxygen concentrations in the future, the number
of exceedences of the 5 mg liter-1 concentration will be even less, further limiting
growth effects.
With a 30-day mean criterion of 4 mg liter-1, these segments are likely to pass or
come close to passing a formal criteria assessment under current conditions. Given
that some fraction of oxygen depletion in these segments is definitely caused by
controllable nutrient inputs, tributary-based nutrient reduction strategies should be
more than adequate to raise ambient oxygen levels above the 4 mg liter-1
concentration.
SITE-SPECIFIC CRITERIA BIOLOGICAL REFERENCE CURVE
The criteria assessment protocol for all segments and designated uses employs moni¬
toring data to develop cumulative frequency distribution (CFD) curves of
exceedance, which are compared to biological reference curves specific to desig¬
nated uses, salinity regimes, and seasons. Monitoring data are interpolated over a
fixed three-dimensional grid to obtain dissolved oxygen concentrations for each grid
cell. These are compared to appropriate criteria values and yield a grid-cell by grid¬
cell estimate of the volume or area of criteria exceedance. The percentages of a
segment’s volume/area exceeding the criteria levels are accumulated over all obser¬
vation dates in the assessment period. The CFD generated from these data reflect
exceedance (and by difference, attainment) in both space and time. (See Chapter 6
of Ambient Water Quality Criteria for Dissolved Oyxgen, Water Clarity and Chloro¬
phyll a for the Chesapeake Bay and Its Tidal Tributaries (U.S. EPA 2003a) for more
details on the criteria attainment assessment protocol.) The biological reference
curve is the CFD of exceedances in segments or other areas that are determined to
chapter Vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
83
be ‘healthy,’ i.e., that demonstrably support growth and reproduction of the living
resources targeted for protection by these criteria.
The biological reference levels are, by definition, based on ambient dissolved
oxygen conditions exhibited by areas supporting high functioning living resources.
Even if this definition were abandoned in favor of a curve or curves based on specific
natural impairments, then the Mattaponi and Pamunkey segments would have to
serve as their own reference sites, which is difficult to rationalize. In the absence of
sufficient data necessary to generate a biological reference curve, EPA recommends
application of a normal distribution curve representing approximately 10 percent
allowable criteria exceedence (U.S. EPA 2003a).
LITERATURE CITED
Anderson, I. C., C. R. Tobias, B. B. Neikirk and R. L. Wetzel. 1997. Development of a
process-based mass balance model for a Virginia Spartina alterniflora salt marsh: Implica¬
tions for net DIN flux. Marine Ecology Progress Series 159:13-27.
Cai, W. J., L. R. Pomeroy, M. A. Moran and Y. Wang. 1999. Oxygen and carbon dioxide mass
balance for the estuarine-intertidal marsh complex of five rivers in the southeastern U.S.
Limnology' and Oceanography 44:639-649.
Neubauer, S. C., I. C. Anderson, J. A. Constantine and S. A. Kuehl. 2001. Sediment deposi¬
tion and accretion in a mid- Atlantic (U.S. A.) tidal freshwater marsh. Estuarine Coastal and
Shelf Science. 54:713-727.
Neubauer, S. C., W. D. Miller and I. C. Anderson. 2000. Atmospheric C02 evasion, dissolved
inorganic carbon production and net heterotrophy in the York River estuary. Limnology and
Oceanography. 45:1701-1717.
Neubauer, Scott. June 6, 2003 and June 19, 2003. Personal communication. Smithsonian
Institute Environmental Research Center, Edgewater, Maryland.
Tobias, C.R., EC. Anderson, E.A. Canuel, and S.A. Mako. 2001. Nutrient cycling through a
fringing marsh — aquifer ecotone. Marine Ecology Progress Series. 210:25-39.
U.S. EPA. 2003a. Ambient Water Quality' for Dissolved Oxygen, Water Clarity / and Chloro¬
phyll a for the Chesapeake Bay and Its Tidal Tributaries. EPA 903-R-03-002. Region III
Chesapeake Bay Program Office, Annapolis, Maryland.
U.S. EPA. 2003b. Technical Support Documentation for Identification of Chesapeake Bay
Designated Uses and Attainability'. EPA 903-R-03-004. Region III Chesapeake Bay Program
Office, Annapolis, Maryland.
chapter vi
Guidance for Deriving Site Specific Dissolved Oxygen Criteria
85
chapter VII
Upper and Lower Pycnocline
Boundary Delineation
Methodology
Vertical stratification is foremost among the physical factors affecting dissolved
oxygen concentrations in some parts of Chesapeake Bay and its tidal tributaries. If
the density discontinuity is great enough to prevent mixing of the layers and consti¬
tutes a vertical barrier to diffusion of dissolved oxygen, then a pycnocline is said to
exist (Figure VII- 1). For the purposes of water quality criteria attainment assessment,
the Chesapeake Bay and tidal tributary waters are separated into a surface mixed
layer (e.g., open-water designated use), an inter-pycnocline layer (e.g., deep-water
designated use) and a lower mixed layer (e.g., deep-channel designated use) (U.S.
EPA 2003a, 2003b).
Accurate estimates of the pycnocline are important for assessing criteria attainment.
The method documented here for assessing upper and lower mixed layer depths
differs from the standard Chesapeake Bay Water Quality Monitoring Program field
sampling cruise method (Chesapeake Bay Program 1996) in that this methodology
uses a measured density gradient based on salinity and temperature rather than
relying on the field surrogate, conductivity.
Defining the depth of the upper mixed layer based on the physical barrier of a density
gradient is discussed in Brainerd and Gregg 1995. Culver and Perry (1999) and
Larsson et al. (2001 ) propose particular density gradient thresholds for defining this
layer. The critical density gradient is dependent on many factors, most importantly
the strength of the turbulent mixing. Generally, for the Chesapeake Bay the upper
pycnocline depth, defining the surface mixed layer, is the shallowest occurrence of a
density gradient of 0. 1 kg/m4 or greater. The lower mixed layer depth is the deepest
occurrence of a density gradient of 0.2 kg/m4, if a lower mixed layer exists below it.
These limits were based on an extensive review of thousands of density profiles
throughout the Chesapeake Bay and its tidal tributaries throughout 19-year record of
the Chesapeake Bay Water Quality Monitoring Program. These density gradient
thresholds are consistent with the values published for other tidal water bodies and
with similar studies in the Chesapeake Bay (Fisher 2003). Since pycnocline delin-
chapter vii
Upper and Lower Pycnocline Boundary Delineation Methodology
86
eation is based on hydrodynamics and not bathymetry, the depth of the pycnocline
and hence the boundaries of the designated uses changes on a monthly basis.
DETERMINATION OF THE VERTICAL DENSITY PROFILE
The vertical water column density profile (sigma-t) is calculated using the following
equations:
Sigma_t = tsum+((sigo+0.1324)*( l-sa+sb*(sigo -0.1324)))
Where:
tempc = water temperature in degrees Celsius
salinity = salinity in grams per liter
sigo = -0.069+(( 1 .47808*((salinity - 0.03)/1.805))(0.00157*
(((salinityBO. 03 )/l. 805 )**2))+0. 0000398*
(((salinityB0.03)/l .805)**3)));
tsum = (-l*(((tempc - 3.98)**2)/503.57))* ((tempc+283)/(tempc+67.26));
sa = ( 10**-3)*tempc)*(4.7867 - (0.098 185*tempc)+(0. 0010843*
(tempc**2))),
and
sb = (( 10**-6)*tempc)*( 18.030-(0.8164*tempc)+(0.01667*(tempc**2))).
DETERMINATION OF THE PYCNOCLINE DEPTHS
To determine the depths of the pycnocline, the following rules are applied to the
density profile:
1) From the water surface downward, the first density slope observation that is
greater than 0.1 kgnr4 is designated as the upper pycnocline depth provided that:
a) that observation is not the first observation in the water column; and
b) the next density slope observation below is positive.
2) From the bottom sediment-water interface upward, the first density slope obser¬
vation that is greater than 0.2 kg nr4 is designated as the lower pycnocline depth
provided that:
a) an upper pycnocline depth exists;
b) there is a bottom mixed layer, defined by the first or second density
slope observation from the bottom sediment-water interface being less
than 0.2 kg m'4; and
c) the next density slope observation above is positive.
chapter vii
Upper and Lower Pycnocline Boundary Delineation Methodology
87
Figure VIM. Example of a vertical density profile with calculated pycnocline boundaries
and observed dissolved oxygen concentrations with depth. Monitored water column
density and observed dissolved oxygen concentrations with depth are illustrated with the
upper (dashed line) and lower (dotted line) pycnocline depths overlaid for station CB4.3 in
the middle Chesapeake Bay mainstem on June 10, 1986.
LITERATURE CITED
Brainerd, K. E. and M. C. Gregg. 1995. Surfaced mixed and mixing layer depths. Deep-Sea
Research 42: 1521-1543
Chesapeake Bay Program. 1996. Recommended Guidelines for Sampling and Analyses in the
Chesapeake Bay Monitoring Program. EPA 903-R-96-006. CBP/TRS 148/96. Chesapeake
Bay Program Office, Annapolis, Maryland.
Culver, M. E. and M. J. Perry. 1999. The response of photosynthetic absorption coefficients
to irradiance in culture and in tidally mixed estuarine waters. Limnology > and Oceanography
44: 24-36.
Fisher, Tom. 2003. Personal communication/unpublished manuscript. University of Mary¬
land Center for Environmental Science, Horn Point Laboratory, Cambridge, Maryland.
Larsson, U., S. Hajdu, J. Waive, and R. Elmgren. 2001. Baltic Sea nitrogen fixation estimated
from the summer increase in upper mixed layer total nitrogen. Limnology ; and Oceanography
46: 811-820.
U.S. Environmental Protection Agency. 2003a. Ambient Water Quality ; Criteria for Dissolved
Oxygen, Water Clarity’ and Chlorophyll a far the Chesapeake Bay and Its Tidal Tributaries.
EPA 903-R-03-002. Region III Chesapeake Bay Program Office. Annapolis, Maryland.
U.S. Environmental Protection Agency. 2003b. Technical Support Document for Identifica¬
tion of Chesapeake Bay Designated Uses and Attainability. EPA 903-R-03-004. Region III
Chesapeake Bay Program Office, Annapolis, Maryland.
chapter vii
Upper and Lower Pycnocline Boundary Delineation Methodology
89
chapter \/BIi
Updated Guidance for
Application of Water Clarity
Criteria and SAV Restoration
Goal Acreages
With publication of the Ambient Water Quality Criteria for Dissolved Oxygen, Water
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries
(Regional Criteria Guidance) (U.S. EPA 2003a) and the Technical Support Docu¬
ment for Identification of Chesapeake Bay Designated Uses and Attainability-
(Technical Support Document) (U.S. EPA 2003b), the jurisdictions were provided
with extensive guidance for how to determine attainment of the shallow-water bay
grass designated use.
Specifically, the EPA Regional Criteria Guidance document provided the following
guidance to the jurisdictions:
To determine the return of water clarity conditions necessary to support
restoration of underwater grasses and, therefore, attainment of the shallow-
water designated use, states may: 1) evaluate the number of acres of
underwater bay grasses present in each respective Chesapeake Bay Program
segment, comparing that acreage with the segment’s bay grass restoration
goal acreage; and/or 2) determine the attainment of the water clarity criteria
within the area designated for shallow-water bay grass use. The shallow-
water bay grass use designated use area may be defined by either:
1) applying the appropriate water clarity criteria application depth (i.e., 0.5,
1 or 2 meters) along the entire length of the segment's shoreline (with excep¬
tion of those shoreline areas determined to be bay grass no-zone grow zones;
see U.S. EPA 2003 [Technical Support Document ] for details); or
2) determining the necessary total acreage of shallow-water habitat within
which the water clarity criteria must be met using a salinity regime specific
ratio of underwater bay grass acres to be restored within a segment to acres
of shallow-water habitat that must meet the water clarity criteria within the
same segment (regardless of specifically where and at what exact depth
those shallow water habitat acreages reside within the segment).
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Updated Guidance for Application of Water Clarity Criteria and SAV Restoration Goal Acreages
90
These approaches to assessing attainment of the shallow-water bay grass designated
use were described in more detail in Chapter 6 of the Regional Criteria Guidance
document (U.S. EPA 2003a). Since the 2003 publication of both the Regional
Criteria Guidance and the Technical Support Document , new information has
become available to the watershed jurisdictions and EPA in support of state adoption
of SAV restoration goal, shallow water habitat and shallow-water existing use
acreages into their water quality standards regulations. This new information will
also help the four jurisdictions with Chesapeake Bay tidal waters adopt consistent,
specific procedures for determining attainment of the shallow-water bay grass desig¬
nated uses into their regulations. (Note the terms ‘underwater bay grasses’ and
‘submerged aquatic vegetation’ or ‘SAV’ are used interchangeably in this document.)
EPA continues to support and encourage the jurisdictions’ adoption of the Chesapeake
Bay Program segment-specific submerged aquatic vegetation (SAV) restoration goal
acreages and the corresponding water clarity criteria attaining shallow-water acreage
necessary to support restoration of those acreages of SAV into each jurisdictions’
respective water quality standards regulations. Achievement of the SAV restoration
goal and shallow-water acreages are two additional means, beyond numerical water
clarity criteria applied to segment-specific application depths, for defining attainment
of the shallow-water bay grass designated use.
WATER CLARITY CRITERIA APPLICATION PERIODS
The temporal application periods for the water clarity criteria were determined based
on the growing seasons for the salinity-based SAV plant communities: April 1
through October 31 for tidal fresh, oligohaline and mesohaline salinity regimes and
March 1 through May 31 and September 1 through November 30 for polyhaline
regimes (U.S. EPA 2003a; Batiuk et al. 1992, 2000). The tidal fresh, oligohaline and
mesohaline salinity regimes application period was based on the combined growing
seasons for tidal fresh to middle salinity SAV species communities. The polyhaline
temporal application periods were based on the bimodal Zoster a marina or eelgrass
growing seasons (Batiuk et al. 1992).
Given that Ruppia maritima or widgeon grass, principally a mesohaline species, has
been found growing along with eelgrass in a majority of the polyhaline regions of
the Chesapeake Bay and its tidal tributaries in Virginia waters (Moore et al. 2000),
the water clarity criteria temporal application period for polyhaline waters should be
an inclusive combination of the mesohaline and polyhaline temporal application
periods or March 1 through November 30. This expanded temporal application
period should apply to polyhaline Chesapeake Bay Program segments where there is
evidence of past or present widgeon grass growth or the potential for future growth.
chapter vii
Updated Guidance for Application of Water Clarity Criteria and SAV Restoration Goal Acreages
91
SHALLOW-WATER HABITAT ACREAGES
New information on shallow-water habitat acreages has been published in the Tech¬
nical Support Document for Identification of Chesapeake Bay Designated Uses and
Attainabilit)'-2004 Addendum (U.S. EPA 2004). These updated shallow-water
habitat acreages factor in the full extent of the 0 to 2 meter depth contour area of
shallow water habitat, minus the delineated SAV no-grow zones. Through compar¬
ison with the expanded restoration acreages, described below, new segment-specific
expanded restoration acreages as a percentage of the shallow-water habitat acreages
have also been published in the Technical Support Document 2004 Addendum.
SAV RESTORATION ACREAGE TO SHALLOW-WATER HABITAT
ACREAGE RATIO
There is scientific documentation originally published in both the Ambient Water
Quality - Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the
Chesapeake Bay and its Tidal Tributaries (U.S. EPA 2003a) and the Technical
Support Document for Identification of Chesapeake Bay Designated Uses and
Attainability (U.S. EPA 2003b) supporting the findings that suitable shallow-water
habitat must be at acreages greater than the corresponding SAV restoration goal to
support restoration of SAV to those acreages.
Text on page 198 in the Regional Criteria Guidance states:
Restoring underwater water grasses within a segment requires that the
particular shallow-water habitat meet the Chesapeake Bay water clarity
criteria across acreages much greater than those actually covered by bay
grasses. The ratio of underwater bay grass acreage to the required shallow-
water habitat acreage achieving the necessary level of water clarity to
support return of those underwater bay grasses varies based upon the
different species of bay grasses inhabiting the Chesapeake Bay’s four
salinity regimes. The baywide average ratio of underwater bay grass acreage
to suitable shallow-water habitat acreage is approximately one acre of
underwater bay grasses for every three acres of shallow-water habitat
achieving the Chesapeake Bay water clarity criteria.
The salinity regime and, therefore, bay grass community-specific under¬
water bay grass acreage to shallow-water habitat acreage ratios have been
derived through an evaluation of extensive underwater bay grass distribution
data within tidal-fresh, low (oligohaline), medium (mesohaline) and high
(polyhaline) salinity regimes (reflecting different levels of coverage by
different bay grass communities). The Technical Support Document for the
Identification of Chesapeake Bay Designated Uses and Attainability docu¬
ments the methodology followed and the resulting bay grasses acreage to
shallow water habitat acreage ratios derived for each of the four salinity
regimes (U.S. EPA 2003).
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92
Text on page 123 in the Technical Support Document states:
As described previously, the restoration of underwater bay grasses within a
segment requires that shallow-water habitat meet the Chesapeake Bay water
clarity criteria over a greater acreage than the underwater bay grasses will
actually cover. The ratio of underwater bay grass acreage to the required
shallow-water habitat acreage varies based on the different species of under¬
water bay grasses that inhabit the Bay’s four salinity regimes. Shallow-water
habitat acreage ratios have been derived scientifically through evaluation of
extensive underwater bay grasses distribution data within tidal fresh, low,
medium and high salinity regimes (reflecting different levels of coverage by
different underwater bay grass communities).
The Chesapeake Bay Program segment-specific restoration goal acreage and
corresponding shallow-water designated use acreage (to the previously
determined maximum depth of abundant and persistent underwater plant
growth) listed in Table IV- 15 were summed by major salinity regimeBtidal
fresh (0-0.5 ppt), oligohaline (> 0.5-5 ppt), mesohaline (> 5ppt— 1 8 ppt) and
polyhaline (>18 ppt). The underwater bay grasses acreage to shallow-water
habitat acreage ratios were then expressed as a percentage of the total
shallow-water designated use habitat. Compared with a baywide value of 38
percent, the tidal-fresh (37 percent), mesohaline (39 percent) and polyhaline
(41 percent) values were all very close to the baywide value as well as the
other salinity regime-specific values (Table IV- 16). These values are consis¬
tent with findings published in the scientific literature and the 35 to 48
percent range derived from evaluation of the 1930s through early 1970s
historical data record by Naylor (2002) and Moore (1999, 2001). Influenced
by the natural presence of the estuarine turbidity maximum, the value was
21 percent in oligohaline habitats.
The scientific literature along with analysis of the multi-decadal SAV aerial survey
data record confirm that healthy SAV beds cover only a portion of the available suit¬
able habitat due to a variety of natural reasons. Given that the information
summarized above and further documented in the Technical Support Document-2004
Addendum indicates ratios from 1 :2 to 1 :3 in terms of the area covered by SAV beds
compared to available shallow-water habitat area, a 1:2.5 ratio is recommended for
determining the segment-specific acreage of shallow-water habitat that needs to
achieve the applicable water clarity criteria required to support restoration of the
segment specific SAV goal acreage.
SAV RESTORATION GOAL ACREAGES
The adopted Chesapeake Bay Program SAV restoration goal acreages were based on
single best year coverages artificially clipped for shoreline and segment-specific
water clarity criteria application depths, undercounting the actual mapped SAV
acreages. In some segments, this resulted in the existing use acreages being higher
than the restoration goal acreage. The chosen solution, described in more detail in
chapter vii
Updated Guidance for Application of Water Clarity Criteria and SAV Restoration Goal Acreages
93
the Technical Support Document-2004 Addendum , was to count all of the SAV
acreage for a given segment that occurred within the single best year regardless of
any shoreline, bathymetry data limitations or water clarity application depth restric¬
tions.
The Technical Support Document-2004 Addendum documents the ‘expanded
restoration acreage’, updated existing use acreage and the available shallow-water
habitat area for each Chesapeake Bay Program segment (U.S. EPA 2004). As
described in the addendum:
The ‘expanded restoration acreage’ is the greatest acreage from among the
updated existing use acreage (1978-2002; no shoreline clipping), the Chesa¬
peake Bay Program adopted SAV restoration goal acreage (strictly adhering
to adopted single best year methodology with clipping) and the goal acreage
displayed without shoreline or application depth clipping and including SAV
from areas still lacking bathymetry data. This ‘expanded restoration
acreage’ is being documented here and provided to the partners as the best
acreage values that can be directly compared with SAV acreages reported
through the baywide SAV aerial survey. These acreages are not the officially
adopted goals of the watershed partners; they are for consideration by the
jurisdictions when adopting refined and new water quality standards
regulations.
The Chesapeake Bay Program SAV restoration goal of 185,000 acres and the
segment-specific goal acreages stand as the watershed partners’ cooperative restora¬
tion goal for this critical living resource community (Chesapeake Executive Council
2003). EPA recommends that the jurisdictions with Chesapeake Bay tidal waters
consider adopting the expanded restoration acreages (which factor in the updated
existing use acreages) and shallow-water habitat acreages determined using the 1 :2.5
ratio into their refined and new water quality standards regulations.
DETERMINING ATTAINMENT OF THE
SHALLOW-WATER BAY GRASS USE
In addition to the methods previously described in the Technical Support Document
(U.S. EPA 2003b) for determining attainment of the shallow-water bay grass desig¬
nated use, there is an additional methodology which integrates both progress towards
to the SAV restoration goal acreage and measurement of suitable shallow water
habitat acreage necessary to support restoration of the remaining SAV beds needed
to reach the goal acreage. This methodology calls for assessing attainment of the
shallow-water designated use in a segment through a combination of mapped SAV
acreage and meeting the applicable water clarity criteria in an additional, unvege¬
tated shallow water surface area equal to 2.5 times the remaining SAV acreage
necessary to meet the segment’s restoration goal (SAV restoration goal acreage
minus the mapped SAV acreage). In other words, a segment’s shallow-water bay
grass designated use would be considered in attainment if there are sufficient acres
chapter vii
Updated Guidance for Application of Water Clarity Criteria and SAV Restoration Goal Acreages
94
of shallow-water habitat meeting the applicable water clarity criteria to support
restoration of the remaining acres of SAV, beyond the SAV beds already mapped,
necessary to reach that segment’s SAV restoration goal acreage. These measure¬
ments of SAV acreages and water clarity levels would be drawn from three years of
data as previously described in the Regional Criteria Guidance (U.S. EPA 2003a).
Here’s a hypothetical example of determining attainment of the shallow-water bay
grass use using both mapped SAV acreage and shallow-water habitat acreage
meeting the water clarity criteria. Segment X has an SAV restoration goal acreage of
1,400 acres. Over the past three years, SAV beds totaling 1,100 acres have been
mapped within the segment for at least one of the three years. Therefore, the
remaining SAV acreage necessary to meet the segment’s restoration goal is 1,400
acres (SAV restoration goal) minus 1,100 acres (SAV currently mapped) or 300
acres. Beyond the currently vegetated shallow-water habitat, an additional 750 acres
of shallow-water habitat (2.5 times 300 acres) would need to attain the water clarity
criteria in order to determine that this segment is attaining the shallow-water bay
grass use in combination with the 1,100 acres of mapped SAV.
LITERATURE CITED
Batiuk, R. A., P. Bergstrom, M. Kemp. E. Koch, L. Murray, J. C. Stevenson, R. Bartleson, V.
Carter, N. B. Rybicki, J. M. Landwehr, C. Gallegos, L. Karrh, M. Naylor, D. Wilcox, K. A.
Moore, S. Ailstock and M. Teichberg. 2000. Chesapeake Bay Submerged Aquatic Vegetation
Water Quality and Habitat-Based Requirements and Restoration Targets: A Second Technical
Synthesis. CBP/TRS 245/00 EPA 903-R-00-014. U.S. EPA Chesapeake Bay Program,
Annapolis, Maryland.
Batiuk. R. A., R. Orth, K. Moore, J. C. Stevenson. W. Dennison. L. Staver, V. Carter, N. B.
Rybicki, R. Hickman, S. Kollar and S. Bieber. 1992. Chesapeake Bay Submerged Aquatic
Vegetation Habitat Requirements and Restoration Targets: A Technical Synthesis. CBP/TRS
83/92. U.S. EPA Chesapeake Bay Program, Annapolis, Maryland.
Chesapeake Executive Council. 2003. Chesapeake Executive Council Directive No. 02-03:
Meeting the Nutrient and Sediment Reduction Goals. Annapolis, Maryland.
Moore, K„ D. Wilcox, R. Orth and E. Bailey. 1999. Analysis of historical distribution of
submerged aquatic vegetation (SAV) in the James River. Special Report No. 355 in Applied
Marine Science and Ocean Engineering. Virginia Institute of Marine Science, School of
Marine Science, College of William and Mary, Gloucester Point, Virginia.
Moore, K. A., D.J. Wilcox and R. J. Orth. 2000. Analysis of the abundance of submersed
aquatic vegetation communities in the Chesapeake Bay. Estuaries 23 ( 1 ): 1 15-127.
Moore, K., D. Wilcox and B. Anderson. 2001. Analysis of historical distribution of
submerged aquatic vegetation (SAV) in the York and Rappahannock rivers as evidence of
historical water quality conditions. Special Report No. 375 in Applied Marine Science and
Ocean Engineering. Virginia Institute of Marine Science, School of Marine Science, College
of William and Mary, Gloucester Point, Virginia.
chapter vii
Updated Guidance for Application of Water Clarity Criteria and SAV Restoration Goal Acreages
Naylor, M.D. 2002. Historic distribution of submerged aquatic vegetation (SAV) in Chesa¬
peake Bay, Maryland. Maryland Department of Natural Resources, Annapolis, Maryland.
U.S. Environmental Protection Agency. 2003a. Ambient [Voter Quality Criteria for Dissolved
Oxygen, Water Clarity ; and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.
EPA 903-R-03-002. Chesapeake Bay Program Office, Annapolis, Maryland.
U.S. Environmental Protection Agency. 2003b. Technical Support Document for Identifica¬
tion of Chesapeake Bay Designated Uses and Attainability. EPA 903-R-03-004. Region III
Chesapeake Bay Program Office, Annapolis, Maryland.
U.S. Environmental Protection Agency. 2004. Technical Support Document for Identification
of Chesapeake Bay Designated Uses and Attainability-2004 Addendum. EPA 903-R-04-006.
Region 111 Chesapeake Bay Program Office, Annapolis, Maryland.
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Updated Guidance for Application of Water Clarity Criteria and SAV Restoration Goal Acreages
97
cha pter IX
Determining Where Numerical
Chlorophyll a Criteria Should
Apply to Local Chesapeake Bay
and Tidal Tributary Waters
As published in Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity
and Chlorophyll a for Chesapeake Bay and Its Tidal Tributaries (U.S. EPA 2003):
The EPA expects states to adopt narrative chlorophyll a criteria into their
water quality standards for all Chesapeake Bay and tidal tributary waters.
The EPA strongly encourages states to develop and adopt site-specific
numerical chlorophyll a criteria for tidal waters where algal-related impair¬
ments are expected to persist even after the Chesapeake Bay dissolved
oxygen and water clarity criteria have been attained.
The Chesapeake Bay Program partners developed a general methodology for
possible use by the jurisdictions with tidal waters to determine consistently which
local tidal waters will likely attain the published Chesapeake Bay dissolved oxygen
and water clarity criteria yet algal-related water quality impairments will persist. The
methodology is for application by Maryland, Virginia, Delaware and the District of
Columbia to assist in their future determinations of where they need to derive and
apply numerical chlorophyll a criteria for localized tidal waters.
RECOMMENDED METHODOLOGY
The jurisdictions should evaluate the available Chesapeake Bay Water Quality Moni¬
toring Program’s time series of spring and summer chlorophyll a concentrations on
a station by station, segment by segment basis and compare these concentrations to
a range of season and salinity regime-based target chlorophyll a concentrations.
Target concentrations, examples given in Table IX- 1, should be derived from
published chlorophyll a concentrations associated with an array of water quality and
biological community effects and impairments. The jurisdictions should then iden¬
tify those stations/segments that are persistently higher than the applicable target
chlorophyll a concentrations with the individual jurisdictions developing their own
chapter ix
Determining Where Numerical Chlorophyll a Criteria Should Apply
98
Table IX-1 . Example numerical chlorophyll a thresholds (p g liter1) drawn from Ambient Water Quality Criteria
for Dissolved Oxygen, Water Clarity and Chlorophyll a for Chesapeake Bay and its Tidal Tributaries'
reflective of an array of historical concentrations, ecosystem trophic status, potential harmful algal
blooms, water quality impairments, user perceptions and state water quality standards.
Chlorophyll a Concentration Thresholds (pg liter'1)
Salinity
Regime
Historical
Chesapeake
Bay Levels 2J
Ecosystem
Trophic Status
Phytoplankton
Reference
Communities6
Potentially
Harmful Algal
Blooms7
Water Quality
Impairments8
User
Perceptions
State Water
Quality
Standards"
Tidal Fresh
Spring: 4
Summer: 7
Mainstem
(annual): 3
2-1 54
Spring: 4.3
Summer: 8.6
Microcystis
aeruginosa: 15
Water Clarity:
9-16
Dissolved
Oxygen:
4-5 ~
Vermont Lakes:
< 159
Minnesota
Lakes: < 1 51"
AL: 16-27 (res.)
CN: 2-15 (meso.)
GA: 5-20 (lakes)
NC: 15(lakes,
res.)
Oligohaline
Spring: 6
Summer: 8
Mainstem
(annual): 3
Spring: 9.6
Summer: 6.0
Microcystis
aeruginosa: 15
Water Clarity
9-16
Dissolved
Oxygen:
7-12
NC: 40 (tidal)
Mesohaline
Spring: 6
Summer: 8
Mainstem
(annual): 4
Spring: 5.6
Summer: 7.1
Prorocentrum
minimum: 5
Water Clarity:
<8
Dissolved
Oxygen:
5-6
NC: 40 (tidal)
Polyhaline
Spring: 4
Summer: 4
Mainstem
(annual): 1
2-7 5
Spring: 2.9
Summer: 4.4
Prorocentrum
minimum: 5
Water Clarity:
<8
Dissolved
Oxygen:
4-5
NC: 40 (tidal)
HW: 2; 5 <10%;
10 <2%
Sources: 1. U.S. EPA 2003; 2. Olson 2002; 3. Harding and Perry 1997; 4. Wetzel 2001, Ryding and Rast 1989, Smith et al. 1998,
Novotny and Olem 1994; 5. Smith. 1998, Molvaer 1997; 6. U.S. EPA 2003; 7. U.S. EPA 2003; 8. U.S. EPA 2003; 9. Smeltzer and
Heiskary 1 990; 1 0.Heiskary and Walker 1 988; 1 1 . U.S. EPA 2003.
decision rules for defining “persistently higher”. The jurisdictions should finally
evaluate the degree of non-attainment of the dissolved oxygen and/or water clarity
criteria within surrounding or “downstream” tidal waters. If these waters are in
attainment of the dissolved oxygen and water clarity criteria, yet are persistently
higher than the applicable target chlorophyll a concentrations, then these waters
should be targeted for adoption of numerical chlorophyll a criteria.
The jurisdictions should also evaluate results from Chesapeake Bay water quality
model-simulated water quality conditions with achievement of the assigned
nitrogen, phosphorus and sediment cap load allocations. The jurisdictions would
then identify those Chesapeake Bay Program segments where the model simulated
surface chlorophyll a concentrations are above a range of season and salinity regime-
based target concentrations. The jurisdictions are encouraged to factor in findings
from state-generated local TMDL modeling in the smaller tidal tributaries and
embayments (e.g., Nanticoke River in Delaware, Anacostia River in the District of
Columbia and several tidal tributaries in Maryland) as an additional source of
chapter ix
Determining Where Numerical Chlorophyll a Criteria Should Apply
99
information on anticipated chlorophyll a concentrations upon attainment of the
dissolved oxygen and/or water clarity criteria. Given that these model-simulated
results reflect tidal water quality conditions estimated to attain the dissolved oxygen
criteria4, these segments should be targeted for adoption of numerical chlorophyll a.
The jurisdictions should note that management-applicable Chesapeake Bay water
quality model results are not available for all 78 Chesapeake Bay Program segments
(Linker et al. 2002).
LITERATURE CITED
Harding, L. W. Jr. and E. S. Perry. 1997. Long-term increase of phytoplankton biomass in
Chesapeake Bay, 1950-1994. Marine Ecology > Progress Series 157:3952.
Heiskary, S. A. and W. W. Walker. 1988. Developing phosphorus criteria for Minnesota lakes.
Lake and Reservoir Management 4: 1-10.
Linker, L.C., G. W. Shenk, P. Wang, C. F. Cerco, A. J. Butt, P. J. Tango and R. W. Savidge.
2002. A Comparison of Chesapeake Bay Estuary Model Calibration With 1985-1994
Observed Data and Method of Application to Water Quality’ Criteria. Modeling Subcom¬
mittee, Chesapeake Bay Program Office, Annapolis, Maryland.
Molvaer, J., J. Knutzen, J. Magnusson, B. Rygg, J. Skei and J. Sorensen. 1997. Environ¬
mental quality classification in fjords and coastal areas. Statens Forurensningstilsyn
TA1467, Norway. 36 pp.
Novotny V. and Olem H. 1994. Water Quality’: Prevention. Identification and Management of
Diffuse Pollution. Van Nostrand Reinhold. New York, New York. 1054pp.
Olson, M. 2002. Benchmarks for nitrogen, phosphorus, chlorophyll and suspended solids in
Chesapeake Bay. Chesapeake Bay Program Technical Report Series, Chesapeake Bay
Program, Annapolis, Maryland.
Ryding, S. O. and W. Rast. 1989. The control of eutrophication of lakes and reservoirs. Man
and the Biosphere Series, Volume /, UNESCO, Parthenon Publication Group, Park Ridge,
New Jersey. 314 pp.
Smeltzer, E. and S. A. Heiskary. 1990. Analysis and Applications of Lake User Surv ey Data.
Lake and Reservoir Management 6( 1 ): 1 09- 1 1 8.
Smith, V. H. 1998. Cultural eutrophication of inland, estuarine and coastal waters. In: Pace,
M. L. and P. M. Groffman (eds.). Successes, Limitation and Frontiers in Ecosystem Science.
Springer- Verlag, New York, New York. Pp. 7-49.
U.S. Environmental Protection Agency. 2003. Ambient Water Quality’ Criteria for Dissolved
O.xvgen, Water Clarity’ and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.
EPA 903-R-03-002. Region III Chesapeake Bay Program Office, Annapolis, Maryland.
Wetzel, R. G. 2001. Limnology’— Lake and River Ecosystems, 3rd Edition. Academic Press,
New York, New York.
4The applicable water clarity may not be attained within the model simulated output given suspended
sediment contributions to reduced water clarity conditions independent of the algal contribution to
reduced water clarity conditions.
chapter ix
Determining Where Numerical Chlorophyll a Criteria Should Apply
s
appendix
Wetland Area, Segment
Perimeter/Area/Volume
and Water Quality
Parameter Statistics for
Chesapeake Bay
Tidal Fresh and
Oligohaline Segments
102
Table A-1. Wetland area, perimeter, surface area and volume statistics for Chesapeake Bay tidal fresh and
oligohaline segments.
Chesapeake Bay Program Segment
Wetland
Acreage
(acres)
Segment
Perimeter
(meters)
Segment
Surface Area
(meters2)
Segment
Volume
(meters1)
Surface Area
to Volume
Ratio
Western Branch Patuxent River-tidal fresh region
WBRTF
5181
131511
Appomattox River-tidal fresh region
APPTF
168938
8011611
1510000
5.3
Piscataway Creek-tidal fresh region
PISTF
15219
3708997
2850000
1.3
Chester River-tidal fresh region
CHSTF
60350
4084016
3362500
1.2
Pocomoke River-tidal fresh region
POCTF
77456
3998871
4470000
0.9
Nanticoke River-tidal fresh region
NANTF
69276
4608463
6615000
0.7
Mattawoman Creek-tidal fresh region
MATTF
37045
7280895
9500000
0.8
* Patuxent River-tidal fresh region
PAXTF
55373
4408622
11025000
0.4
*Choptank River-tidal fresh region
CHOTF
153218
9466475
15322500
0.6
Bohemia River-oligohaline region
BOHOH
79964
11927636
1 7000000
0.7
Pocomoke River-oligohaline region
POCOH
116755
13821501
18000000
0.8
Back River-oligohaline region
BACOH
64832
16175354
22375000
0.7
C&D Canal-oligohaline region
C&DOH
35654
3565828
24130000
0.1
Middle River-oligohaline region
MIDOH
93914
16214070
25000000
0.6
Northeast River-tidal fresh region
NORTF
40617
15817689
26500000
0.6
*Patuxent River-oligohaline region
PAXOH
76397
14243456
27180000
0.5
Chester River-oligohaline region
CHSOH
124641
14790537
28875000
0.5
Nanticoke River-oligohaline region
NANOH
238038
16455330
45000000
0.4
*Choptank River-oligohaline region
CHOOH
142681
14477365
45125000
0.3
Chickahominy River-oligohaline region
CHKOH
355816
27969270
48562500
0.6
Bush River-oligohaline region
BSHOH
107046
30542696
49250000
0.6
* Rappahannock River-oligohaline region
RPPOH
1 12097
19536530
53580000
0.4
Gunpowder River-oligohaline region
GUNOH
163323
41998392
64250000
0.7
Sassafras River-oligohaline region
SASOH
161366
33085712
84187500
0.4
Elk River-oligohaline region
EFKOH
138710
37270004
101250000
0.4
* Rappahannock River-tidal fresh region
RPPTF
252716
36503308
107437500
0.3
James River-tidal fresh region
JMSTF
562776
95301848
286187500
0.3
Chesapeake Bay-tidal fresh region
CB1TF
216814
151620944
360000000
0.4
James River-oligohaline region
JMSOH
271459
127749032
43 1 500000
0.3
* Potomac River-tidal fresh region
POTTF
365926
153841616
484750000
0.3
*Potomac River-oligohaline region
POTOH
312495
214963696
852250000
0.3
Chesapeake Bay-oligohaline region
CB20H
246410
275239520
1237000000
0.2
*Segments with similar characteristics or geographically close to the Mattaponi and Pamunkey segments.
Source: Chesapeake Bay Program http://chesapeakebay.net/data
appendix a
103
Table A-2. Summer average conditions in other tidal fresh and oligohaline Chesapeake Bay Program segments,
2000-2002.
Total
CBP
Segment
Water
Column
Layer
Water
Column
Depth
(meters)
Salinity
(ppt)1
Temperature
(°C)
Dissolved Dissolved
Oxygen Oxygen
Concentration Deficit
(mg liter'1) (mg liter'1)
Chlorophyll a
Concentration
(pg liter')
Suspended Total
Solids Nitrogen
Concentration Concentration
(mg liter') (mg liter')
Total
Phosphorus
Concentration
(mg liter')
APPTF
S
0.7
0.09
27.90
8.45
-0.50
44.5
35.5
1.0771
0.1169
APPTF
B
5.7
0.09
27.44
7.68
0.31
67.7
1.1839
0.1656
CB1TF
S
0.5
0.68
25.92
7.32
0.79
8.4
8.0
1.1310
0.0389
CB1TF
B
4.8
0.86
25.58
6.79
1.36
6.7
10.1
1.1603
0.0387
JMSTF
S
0.7
0.30
27.56
7.82
0.13
22.4
15.9
0.9022
0.0989
JMSTF
B
8.8
0.37
27.24
6.94
1.04
75.1
1.1113
0.1388
MATTF
S
0.3
0.19
24.46
6.98
1.38
18.1
8.1
0.9551
0.0608
NANTF
S
0.5
0.63
25.86
5.68
2.45
15.6
23.1
2.3553
0.0667
NANTF
B
4.1
0.67
25.77
5.44
2.69
14.6
50.4
2.3513
0.0891
NORTF
S
0.5
0.24
25.93
8.70
-0.57
44.3
22.0
1.1431
0.0847
NORTF
B
1.8
0.24
25.66
7.91
0.26
42.2
25.7
1.1207
0.0876
PAXTF
S
0.2
0.22
24.27
7.37
1.02
36.2
34.4
1.3724
0.1547
PAXTF
B
9.4
0.68
25.18
7.28
0.96
66.3
99.9
1.3846
0.2731
PISTF
S
0.2
0.00
24.22
6.97
1.45
14.2
10.3
1.3197
0.0962
POCTF
S
0.5
0.61
26.13
4.63
3.46
7.6
12.4
1.6927
0.1206
POCTF
B
4.9
0.72
26.00
4.64
3.46
7.8
25.8
1 .6005
0.1408
POTTF
S
0.5
0.16
26.54
7.60
0.45
20.4
13.0
1.5054
0.0769
POTTF
B
10.9
0.24
25.97
6.36
1.76
18.7
35.1
1.6021
0.1047
RPPTF
S
0.7
0.71
26.89
7.20
0.84
31.0
23.4
0.9105
0.0776
RPPTF
B
5.1
0.75
26.68
6.84
1.10
.
37.1
0.9543
0.0883
WBRTF
S
0.0
0.01
21.97
6.82
1.94
12.8
37.1
1.1804
0.1868
BACOH
S
0.5
2.82
25.18
7.92
0.24
81.9
24.9
2.4796
0.2564
BACOH
B
0.8
2.92
25.17
7.26
0.89
66.9
23.9
2.1900
0.2347
BOHOH
S
0.5
1.27
26.68
7.73
0.26
24.7
21.6
0.8554
0.0653
BOHOH
B
1.8
1.30
26.43
7.27
0.75
21.2
22.6
0.9143
0.0666
BSHOH
S
0.5
1.16
25.82
8.19
-0.05
28.7
24.0
0.9170
0.0699
BSHOH
B
1.2
1.17
25.61
7.64
0.53
28.7
25.8
0.9117
0.0696
C&DOH
S
0.5
2.03
25.74
6.68
1.41
10.5
17.8
1.2866
0.0715
C&DOH
B
12.3
2.08
25.53
6.54
1.57
3.4
30.7
1.2121
0.0808
CB20H
S
0.5
5.11
24.72
6.68
1.41
6.5
9.9
0.9548
0.0526
CB20H
B
1 1.7
8.14
24.21
4.47
3.57
5.5
24.6
0.8730
0.0675
CHKOH
S
0.7
2.05
26.41
6.33
1.68
19.1
24.7
0.6205
0.0873
CHKOH
B
3.9
2.10
26.21
6.24
1.78
.
62.5
0.7355
0.1338
CHOOH
S
0.5
1.09
26.28
5.66
2.40
18.3
28.2
1.6772
0.1042
CHOOH
B
7.5
1.19
25.93
5.36
2.74
17.1
47.5
1.8115
0.1311
CHSOH
S
0.5
0.69
26.47
8.13
-0.09
61.2
53.2
2.2028
0.1619
CHSOH
B
4.0
0.71
26.18
7.86
0.23
59.6
65.9
2.1452
0.1747
ELKOH
S
0.5
1.68
25.89
6.80
1.27
4.1
11.7
1.1244
0.0584
ELKOH
B
11.4
1.77
25.62
6.59
1.52
3.5
25.7
1.1267
0.0736
GUNOH
S
0.5
2.23
25.12
7.13
1.06
10.3
16.3
0.6558
0.0476
GUNOH
B
0.9
2.24
25.08
6.55
1.64
10.5
18.8
0.6600
0.0489
JMSOH
S
0.7
6.20
26.71
6.77
1.03
8.9
22.8
0.5089
0.0828
JMSOH
B
10.1
7.00
26.69
6.49
1.28
.
73.5
0.6217
0.1202
MIDOH
S
0.5
3.67
25.42
7.63
0.45
19.3
10.1
0.6698
0.0493
MIDOH
B
2.7
4.14
25.07
5.90
2.20
15.7
13.7
0.6727
0.0478
PAXOH
S
0.5
3.33
26.36
5.87
2.10
17.3
28.6
0.8689
0.1378
PAXOH
B
3.6
3.61
26.08
5.38
2.61
18.0
56.1
0.9835
0.1912
POTOH
S
0.5
3.00
25.80
6.59
1.44
8.2
12.1
1.1141
0.0896
POTOH
B
7.8
3.77
25.66
5.92
2.09
3.8
50.9
1.1603
0.1258
RPPOH
S
0.7
3.12
26.84
7.40
0.55
19.5
21.9
0.6160
0.0753
RPPOH
B
7.2
3.63
26.51
6.40
1.57
.
73.3
0.8002
0.1198
SASOH
S
0.5
0.46
26.98
8.30
-0.32
71.6
23.2
1.6423
0.1170
SASOH
B
5.2
0.53
26.49
6.62
1.43
66.3
31.9
1.5082
0.1254
Source: Chesapeake Bay Program http://chesapeakebay.net/data
appendix a
LIBRARY OF CONGRESS
0 016 080 847 0
U.S. Environmental Protection Agency
Region III
Chesapeake Bay Program Office
Annapolis, Maryland
1-800-YOUR-BAY
and
Region III
Water Protection Division
Philadelphia, Pennsylvania
in coordination with
Office of Water
Office of Science and Technology
Washington, D.C.
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