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Water Quality Criteria: Notice of Ambient Aquatic Life Water Quality Criteria for Dissolved Oxygen (Saltwater): Cape Cod to Cape Hatteras
Note: EPA no longer updates this information, but it may be useful as a reference or resource.
[Federal Register: November 30, 2000 (Volume 65, Number 231)]
[Notices]
[Page 71317-71321]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr30no00-51]
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ENVIRONMENTAL PROTECTION AGENCY
[FRL-6909-8]
Water Quality Criteria: Notice of Ambient Aquatic Life Water
Quality Criteria for Dissolved Oxygen (Saltwater): Cape Cod to Cape
Hatteras
AGENCY: Environmental Protection Agency (EPA).
ACTION: Notice of availability of ambient aquatic life water quality
criteria for dissolved oxygen (saltwater): Cape Cod to Cape Hatteras.
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SUMMARY: Pursuant to section 304(a)(1) of the Clean Water Act (CWA),
the Environmental Protection Agency announces the availability of the
[[Page 71318]]
completed document titled, Ambient Aquatic Life Water Quality Criteria
for Dissolved Oxygen (Saltwater): Cape Cod to Cape Hatteras. The
document contains EPA's recommended national 304(a) criteria for
dissolved oxygen in saltwater to protect aquatic life. These water
quality criteria recommendations apply to coastal waters (waters within
the territorial seas, defined as within three miles from shore under
section 502(8) of the CWA) of the Virginian Province (Cape Cod to Cape
Hatteras). However, with appropriate modifications they may be
applicable to coastal waters (as defined under section 502(8) of the
CWA) in other provinces of the United States. Under the CWA, States,
Territories, and Tribes are to adopt water quality criteria to protect
designated uses. EPA has promulgated regulations to implement this
requirement (see 40 CFR part 141). EPA's recommended water quality
criteria do not substitute for the Act or regulations, nor is it a
regulation itself. Thus, EPA's recommended water quality criteria do
not impose legally-binding requirements. States, Territories, and
authorized Tribes retain the discretion to adopt, where appropriate,
other scientifically defensible water quality standards that differ
from these recommendations. EPA may change these section 304(a)
criteria recommendations in the future.
Because these criteria were under development prior to the Agency's
revision and implementation of its current processes for notice of data
availability and criteria development (see Federal Register, December
10, 1998, 63 FR 68354 and in the EPA document titled, National
Recommended Water Quality--Correction EPA 822-Z-99-001, April 1999),
and because EPA believes it is important to invite and consider public
input in development of draft criteria, we enabled the public to submit
significant scientific information and views to EPA (see Federal
Register, January 19, 2000, 65 FR 2954) that might not have otherwise
been identified during development of these criteria. EPA has reviewed
the scientific information and views submitted by the public and has
made revisions to the criteria where appropriate. Even though we are
not required to respond to specific issues submitted by the public, we
have provided a brief summary of some of the issues that lead to a
revision, along with our response, in the section titled Supplementary
Information.
This document has been approved for publication by the Office of
Science and Technology, Office of Water, U.S. Environmental Protection
Agency. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
ADDRESSES: Copies of the complete document, titled: Ambient Aquatic
Life Water Quality Criteria for Dissolved Oxygen (Saltwater): Cape Cod
to Cape Hatteras can be obtained from EPA's National Service Center for
Environmental Publications (NSCEP) 1-800-490-9198. Alternatively, the
document and related fact sheet can be obtained from EPA's web site at
http://www.epa.gov/waterscience/standards/dissolved/ on the Internet.
FOR FURTHER INFORMATION CONTACT: For questions regarding the
development of the criteria contact Erik L. Winchester, USEPA, Health
and Ecological Criteria Division (4304), Office of Science and
Technology, 1200 Pennsylvania Avenue, NW., Washington, DC 20460; or
call (202) 260-6107; fax (202) 260-1036; or e-mail
winchester.erik@epa.gov. For questions regarding implementation issues
under State water quality standards programs contact Jim Keating,
USEPA, Standards and Health Protection Division, (202) 260-3845; or
email keating.jim@epa.gov.
SUPPLEMENTARY INFORMATION:
Introduction
Section 304(a)(2) of the CWA calls for information on the
conditions necessary ``to restore and maintain biological integrity of
all * * * waters, for the protection and propagation of shellfish, fish
and wildlife, to allow recreational activities in and on the water, and
to measure and classify water quality.'' EPA has not previously issued
saltwater criteria for dissolved oxygen (DO) because, until recently,
the available effects information was insufficient. This criteria
document is the result of an extensive multi-year research effort to
produce sufficient information to support the development of saltwater
DO criteria. The water quality criteria presented in the document
represent EPA's best estimates, based on the data available, of DO
concentrations necessary to protect aquatic life and uses associated
with aquatic life.
Overview of the Problem
Hypoxia is defined in this document as the reduction of DO
concentrations in water below air saturation. Oxygen is essential in
aerobic organisms for the proper functioning of cellular processes.
When hypoxia exists, organisms may get an insufficient amount of oxygen
into their system which results in reduction in cellular energy and a
subsequent loss of ion balance in cellular and circulatory fluids. If
oxygen insufficiency persists, death will ultimately occur, although
some aerobic animals also possess anaerobic metabolic pathways, which
can delay lethality for short time periods (minutes to days). The
animals most sensitive to hypoxia are those inhabiting well oxygenated
environments which are not normally exposed to low DO levels. EPA's
Environmental Monitoring and Assessment Program (EMAP) for the
estuaries in the Virginian Province (defined as Cape Cod to Cape
Hatteras) has shown that 25% of the area of the Province is exposed to
some degree to DO concentrations less than 5 mg/L. Persistent DO levels
below 5 mg/L can have an adverse effect on various life stages of
aquatic organism. EMAP also has generated field observations that
correlate many of the biologically degraded benthic areas with low DO
in the lower water column. These two reports serve to emphasize that
low DO (hypoxia) is a major concern within the Virginian Province. Even
though hypoxia is a major concern for many waters, a strong technical
basis for developing benchmarks for low DO effects has been lacking
until recently.
In the Virginian Province, hypoxia is essentially a warm water
phenomenon. In the southern portions of the Province, such as the
Chesapeake Bay and its tributaries, reduced DO may occur any time
between May and October; in the more northern coastal and estuarine
waters, it may occur at any time from late June into September. Hypoxic
events can occur on seasonal or diel (daily) time scales. Seasonal
hypoxia often develops as a consequence of water column stratification,
which prevents mixing of well oxygenated surface water with deeper
water. Diel cycles of hypoxia often occur in non-stratified shallow
habitats where nighttime respiration temporarily depletes DO levels.
Hypoxia may also persist more or less continuously over a season (with
or without a cyclic component) or be episodic (i.e., of irregular
occurrence and indefinite duration). The fauna most at risk from
hypoxic exposure in the Virginian Province are primarily summer
inhabitants of subpycnocline (i.e., bottom) waters.
Overview of the Protection Approach
The approach to determine DO criteria to protect saltwater animals
within the Virginian Province takes into account both continuous (i.e.,
persistent) and cyclic (e.g., diel, tidal, or episodic) exposures to
low levels of DO.
[[Page 71319]]
The continuous situation considers exposure durations of 24 hours or
greater. Criteria for cyclic situations cover hypoxic exposures of less
than 24 hours, but which may be repeated over a series of days. Both
scenarios cover three areas of protection that are summarized here, and
explained in more detail in the criteria document: (1) Protection for
juvenile and adult survival; (2) Protection for chronic (growth)
effects; and (3) Protection for larval recruitment effects (estimated
with a generic recruitment model).
The approach to derive these DO water quality criteria combines
features of traditional water quality criteria with a new biological
framework that uses a mathematical model to integrate time (replacing
the concept of an averaging period) and establish protection limits for
different life stages (i.e., larvae versus juveniles and adults). Where
practical, data were selected and analyzed in manners consistent with
the Guidelines for Deriving Numerical National Water Quality Criteria
for the Protection of Aquatic Organisms and Their Uses (hereafter
referred to as the Guidelines).
The saltwater DO criteria segregate effects on juveniles and adults
from those on larvae. The survival data on the sensitivity of the
juveniles and adults are handled in a traditional Guidelines manner. To
address cumulative effects of low DO on larval recruitment to the
juvenile life stage (i.e., larval survival as a function of time), the
new biological approach to deriving criteria uses a mathematical model
that evaluates the effect of DO conditions on larvae by tracking
intensity and duration of effects across the larval recruitment season.
Protection for larvae of all species is provided by using toxicological
data on the larval stages of nine sensitive aquatic organisms.
The approach used to derive the new DO criteria deviates somewhat
from EPA's traditional approach for toxic chemicals outlined in the
Guidelines. However, where practical, data selection and analysis
procedures are consistent with the Guidelines. Most of the terminology
and the calculation procedures are the same, but one should consult the
Guidelines for a more complete understanding of how these DO criteria
were derived.
The juvenile/adult survival and the growth criteria provide
boundaries within which to judge the DO status of a given site. If the
DO conditions are above the chronic growth criterion (4.8 mg/L), then
this site would meet objectives for protection. If the DO conditions
are below the juvenile/adult survival criterion (2.3 mg/L), then this
site would not meet objectives for protection. When the DO conditions
are between these two values, then the site would require evaluation
using the larval recruitment model that integrates duration and
intensity of hypoxia to determine suitability of habitat for the larval
recruitment objective.
The DO criteria are based entirely on laboratory findings. Field
observations on the impact of low DO levels support the findings of
laboratory studies. Field acute effects occurred in juvenile and adult
animals at 2.0 mg/L, which would be predicted based on the 2.3 mg/L
juvenile/adult criterion. In the field, behavioral effects generally
occurred within the range where many of the laboratory sublethal
effects occurred.
Revisions to the Draft Document
Approximately half of the views and information submitted by the
public on the draft DO criteria addressed science or technical issues,
and the other half addressed implementation issues. EPA considered only
the science issues when making revisions to the criteria. EPA will
review the implementation issues when developing future implementation
guidance. The more significant revisions due to science issues are
summarized here.
First, some commentors indicated that the larval recruitment model
should not be based on the mud crab (Dyspanopeus sayi) alone. Based on
further review of the toxicity information for other species, we have
revised the dose-response curve in Figure 5 by using a final acute
value (FAV) approach (see the Guidelines) to generate a new final
larval survival curve that reflects responses of all nine species
tested. Figures 5a and 5b have been replaced by a ``Final Larval
Survival Curve'', and Figure 5c has been removed. These changes to the
larval recruitment approach necessitated that changes also be made to
Figures 6, 7, 12, 14 and 17. Overall, these changes had minimal effect
on the criteria. The point (4.64 mg/L) at which the larval recruitment
curve levels off in the revised criteria is only slightly greater than
the point (4.45 mg/L) in the draft document.
Second, some commentors raised issues about the effect that
differences in larval life history requirements among species in the
Virginian Province might have on the applicability of the larval
recruitment model across species and regions in the Province. The
consideration of all nine species in development of the larval
recruitment model addresses this issue. Also, in an appendix we added
an assessment of sensitivity that might be expected with the life
history model parameters D (duration of larval development) and R
(length of larval recruitment season). The sensitivity analysis was
performed using the individual larval recruitment curve for the mud
crab. The sensitivity of the model to these two parameters was
evaluated by increasing or decreasing D while holding R constant, by
holding L constant and increasing R, and varying both D and R at the
same time. A range of values were chosen for this analysis that we
believe encompass a reasonable range in species-specific larval life
history requirements in the Virginian Province, and because the upper
and lower ranges are relatively extreme values that can test the
overall assumptions and sensitivity of the model. The results indicate
that the DO curve associated with no greater than 5 percent cumulative
impairment of seasonal larval recruitment is most sensitive to a
simultaneous decrease in D and increase in R. Under these conditions,
the protective DO value at 44 days (the length of mud crab larval
development season) decreases. This evaluation shows that the model can
easily be adjusted to account for latitudinal variations in life larval
life history requirements, or even seasonal variations in timing of
hypoxia events concurrent with larval development periods. The results
also indicate the Virginia Province criteria are protective of most
species under most conditions, but that in some site-specific
situations they may be overprotective. In the absence of site-specific
data that would suggest a lower level of DO may be acceptable, EPA
believes that in order to ensure that most organisms and their uses are
protected it is appropriate to derive Province-wide criteria that may
be overprotective in some cases.
Third, some commentors suggested that the 5 percent cumulative
reduction in larval seasonal recruitment may be too low a protection
goal. EPA disagrees. Larval life stages are important and this
protection goal is meant to protect them at a critical point in their
development and transition to the juvenile life stage, which for many
species corresponds to times of the year when hypoxia conditions occur.
We selected this Province-wide protection goal because it is consistent
with the approach outlined in the 1985 Guidelines for deriving ambient
aquatic life water quality criteria, because 5 percent is also
consistent with the level of protection afforded to juvenile and adult
life stages, and because, in absence of data that suggests otherwise,
this level of reduced larval recruitment from DO alone is believed to
be
[[Page 71320]]
protective of most species. EPA recognizes that large losses of larval
life stages occur naturally, and that many species may be able to
withstand a greater than 5 percent loss of larvae, from low DO or
otherwise, without an appreciable effect on juvenile recruitment. On
the other hand, this may not be the case for certain highly sensitive
species or populations that are already highly stressed, for example an
endangered species. This may also not be the case where there are other
important natural or anthropogenic stressors that contribute to a loss
of the larval life stage. In such situations, it may be that a 5
percent loss in larval recruitment from DO alone is not protective
enough, and environmental risk managers may need to evaluate the
Province-wide 5 percent protection goal in light of their site-specific
factors that may contribute to a cumulative loss in seasonal larval
recruitment. Also in response to this issue, an appendix was added to
the document that shows, by using the mud crab as an example, how the
larval recruitment criterion would change if the acceptable percentage
impairment was increased. This example demonstrates the flexibility in
the criteria approach and how one might change the protection goals on
a site-specific basis should States and authorized Tribes choose to do
so and have the data to support such a change, while still protecting
designated uses. EPA believes the 5 percent cumulative reduction level
in seasonal larval recruitment is appropriate and protective of
populations in the Virginian Province in absence of data that suggest
otherwise.
Implementation Overview
Implementation of DO criteria may be slightly different from that
of chemical toxicants, but not for reasons associated with either
biological effects or exposure. The primary reason that DO might be
implemented differently from toxic compounds is because controlling the
effects of low DO is not accomplished by directly regulating DO.
Rather, hypoxia is a symptom of a problem, not the direct problem. Thus
DO would be regulated primarily through the control of nutrients (e.g.,
nitrogen and phosphorus) and oxygen demanding wastes. As a stressor, DO
also differs from most toxic compounds in that there can be a large
natural component to the cause of hypoxic conditions in any given water
body.
The DO criteria may also be appropriately used in a risk assessment
framework. The criteria and management approach presented in the
document could be used to compare DO conditions among areas and
determine if DO conditions would be adequate to support aquatic life.
Using the criteria, environmental managers could determine which sites
need the most attention and what are the spatial and temporal extent of
hypoxic problems from one year to the next. Environmental planners
could also use the criteria in a risk assessment framework to evaluate
how conditions would improve under different management scenarios,
helping them make better management decisions.
EPA recommends that States and authorized Tribes within the
Virginian Province adopt numeric DO criteria for saltwater applicable
at all times of the year for all marine waters designated for the
protection of aquatic life or for waters whose existing uses include
aquatic life. States and Tribes may adopt numeric criteria based on
EPA's ambient water quality criteria for DO, such criteria modified to
reflect site-specific conditions, or other scientifically defensible
methods, 40 CFR 131.11(b)(1). States and Tribes should adopt narrative
criteria where numeric criteria cannot be established or to supplement
numeric criteria, 40 CFR 131.11(b)(2). Because EPA has issued
recommended section 304(a) criteria for DO, numeric criteria for DO can
be established. Numeric criteria for DO can be implemented in NPDES
permits by determining the need for and calculating specific limits for
oxygen demanding wastes and nutrients that spur excess algal growth and
subsequent decay of aquatic plants. Such criteria also serve as a
definitive benchmark for determining impairment of waters for Clean
Water Act Section 303(d) listing purposes and then as a starting point
for establishing TMDL's, wasteload allocations for point sources, and
load allocations for nonpoint sources.
To take full advantage of the flexibility allowed in the DO
criteria methodology for determining specific protective DO levels, it
is necessary to characterize both the diurnal and season patterns of DO
concentrations in response to natural and anthropogenic pollutant
loadings for the location where the criteria are applied. Simplified
approaches to establishing protective criteria that ensure a level of
protection consistent with the detailed approach outlined in the DO
criteria document are acceptable. Any approach a State or Tribe chooses
to use to implement the DO criteria must be reflected in the State's or
Tribe's water quality standards and submitted to EPA for review and
approval. To determine the scientific defensibility of a State's or
Tribe's approach as part of the Clean Water Act section 303(c) review
and approval/disapproval process, EPA will review information
concerning the characterization of diurnal and seasonal patterns of DO
concentration in relation to the geographic areas and the times of the
year the criteria applies, and would want the State or Tribe to provide
all of the data and information the State or Tribe relied on for its
rationale.
Limitations of the Criteria
These water quality criteria recommendations apply to coastal
waters (waters within the territorial seas, defined as within three
miles from shore under section 502(8) of the CWA) of the Virginian
Province (southern Cape Cod, MA to Cape Hatteras, NC) of the Atlantic
coast of the United States. The document provides the necessary
information for environmental planners and regulators within the
Virginian Province to address the question: are the DO conditions at a
given site sufficient to protect coastal or estuarine aquatic life? The
approach outlined in the document could be used to evaluate existing
localized DO standards or management goals or establish new ones. The
criteria do not address direct behavioral responses (i.e., avoidance)
or the ecological consequences of behavioral responses, such as
increased or decreased predation rates or altered community structure,
nor do they address the issue of spatial significance of a DO problem.
In addition, as with all criteria, these criteria do not account for
changes in sensitivity to low DO that accompany other stresses, such as
high temperature, extremes of salinity, or toxicants. Chief among these
concerns would be high temperature because high temperature and low DO
often appear together. Generally, low DO would be more lethal at water
temperatures approaching the upper thermal limit for species. EPA
believes the DO limits provided in the document are sufficiently
protective under most conditions where aquatic organisms are not
otherwise unduly stressed.
Although the DO criteria for the Virginian Province may be over- or
underprotective of aquatic life in other regions, the approach used to
develop the criteria is considered to be applicable to other regions
with appropriate regional modifications. Organism adaptations to lower
oxygen requirements may have occurred in locations where oxygen
concentrations have historically been reduced due to high temperatures,
or in systems with non-anthropogenic high oxygen demand. Conversely,
organisms in another region could be adapted to colder temperature and
higher DO
[[Page 71321]]
regimes than those covered in the document, and thus may have different
sensitivity to DO concentrations. In addition, effects of hypoxia may
vary latitudinally, or site-specifically, particularly as reproductive
seasons determine exposure risks for sensitive early life stages. For
these reasons, an environmental risk manager would need to carefully
evaluate water quality and biological conditions within the specific
location and decide if the Virginian Province criteria would apply or
if region-or site-specific considerations would need to be made.
Endangered or Threatened Species Policy Recommendations
When a threatened or endangered species occurs at a site and
sufficient data are available to indicate that it is sensitive at
concentrations above the recommended criteria, it would be appropriate
to consider deriving site-specific DO criteria.
Future Implementation Information and Applications
In the future additional information will be provided that will
specifically address implementation issues. In the current document,
implementation issues are discussed in a more general manner,
summarizing important issues that environmental managers should
consider in adopting and implementation of DO water quality standards.
The future implementation information will provide more detailed
discussion of implementation issues by using real world example data
sets where possible, or hypothetical data sets that show users how to
integrate their data and management goals. Application of this guidance
to marine waters outside the Virginian Province may also be discussed.
As a component of the implementation guidance, EPA originally
envisioned publishing a visual basic-based computer program that would
allow States and other users to derive DO criteria to meet the larval
recruitment protection goal for coastal and estuarine animals. However,
the recent revisions in the criteria (i.e., the use of multiple species
in the larval recruitment model) has precluded use of the visual basic
model in its current format. Therefore, the model when available will
likely be provided as a spreadsheet application compatible with
commonly used software packages. EPA anticipates providing the
additional implementation guidance in late 2001.
EPA believes the approach used to develop the criteria can be
applied, with minor modifications and regional specific data, to derive
DO criteria for other coastal and estuarine regions of the United
States. Therefore, in the future EPA plans to prepare similar DO
criteria for other provinces based on this approach. At such time, EPA
intends to publish a Notice of Data Availability and formally request
submission of data from parties interested in the development of DO
criteria for other provinces.
Dated: November 14, 2000.
Geoffrey H. Grubbs,
Director, Office of Science and Technology.
[FR Doc. 00-30542 Filed 11-29-00; 8:45 am]
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