Chesapeake Bay Program Dissolved Oxygen Criteria Team Final Responses to Comments on the July 3, 2001 Working Draft Chesapeake Bay Dissolved Oxygen Criteria Document

December 19, 2001
Chesapeake Bay Program Dissolved Oxygen Criteria Team
Final Responses to Comments on the July 3,2001
Working Draft Chesapeake Bay Dissolved Oxygen Criteria Document

From Erik Winchester

1. If I recall correctly, both myself and Jim Pletl expressed some concern for using the
instantaneous values, but I do not recall the rationale for going with the instantaneous
values.

Response: See response to comment 4.

2. I will see what other info we need to justify the species deletions. Based on my reading of
the AWQC guidelines, it does appear that the species would not be deleted, but again it
probably can be supported with the work group's knowledge of the bay biology.

Response: See response to comment 3.

From Charlie Delos, EPA OW OST

3. The Bay criterion incorporates a site-specific recalculation procedure, but that procedure
does not appear to follow the EPA 1995 guidance. It appears that taxa have been deleted if
the genus is not present in the Bay. However, EPA's guidance says to delete species only if
the phylum is absent. According to the 1995 guidance, Table m-2 should not only have the
columns for species and genus; it should also have columns for order, class, and phylum.

It is not absolutely necessary to follow the guidance procedure, if there are good technical
reasons for preferring an alternative procedure. However, no such rationale is provided.

Note that states merely need to demonstrate that they are using a reasonable procedure.

EPA, on the other hand, is more bound to follow its own guidance, unless it explains why an
alternative is preferable.

Finally, note that no recalculation is necessary if you believe that the species in the Virginia
Province data set represent the range of sensitivity of the tested and untested species of
Chesapeake Bay. Unless it is politically necessary, it might be better not to use the
recalculation procedure.

Response: The original decision to drop selected species from the effects data base was
based on the Dissolved Oxygen Criteria team's objective to derive Chesapeake Bay
specific criteria. To prevent any concerns about not adhering to EPA criteria
derivation guidelines, the four non-Chesapeake Bay species have been included in the
derivation of Bay specific criteria. However, as can be seen from the working draft
criteria document, there is no difference in the ultimate draft Bay criteria when the
four selected non-Chesapeake Bay species are kept in the effect data base.

Note there are over 300 species of fishes that use the Chesapeake Bay yet all of these
species comprise only a single phylum (personal communication Dave Secor,

University of Maryland). The team still believes that taxonomy is not the concern

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here; what is important is the diversity of responses to hypoxia for species acclimizated
and adapted to Bay conditions.

4. On page 18, the instantaneous maximum application of a criterion based on growth effects
defies logic, and tends to undermine trust in other judgment calls throughout the document.
The explanation for the instantaneous maximum application is inadequate. One wonders
whether given the option, the author might prefer to apply all EPA chronic criteria as
instantaneous maximums. To improve this section, I suggest taking a look at the freshwater
ammonia document for good examples of the type of things that need to be considered in
setting averaging periods.

Response: The instantaneous minimum criteria reflect the fact that daily average
criteria will not be fully protective of aquatic organisms in the Chesapeake Bay and
tidal tributaries. Within the implementation guidelines chapter, it is recommended
that where semi-continuous data are available, criteria attainment should be judged on
the basis of the lowest concentration averaged over a six hours time period within a 24
hour period. The six hour period reflects the time over which effects were observed in
the laboratory and/or field. Agencies and others are encouraged to collect the data
necessary to evaluate concentrations at periods less than 24 hours to ensure full
protection, and yet not define non-attainment when the criteria is in fact attained. A
more complete rationale for the instantaneous minimum criteria has been added to the
revised draft criteria document.

5. On page 21, the translation between observing sturgeon effects within six hours and setting
the criterion as an instantaneous maximum is problematic. First of all, it is essential to
indicate what the measured exposure concentration was that yielded effects within six
hours. Second, assuming that concentrations marginally above 3.5 mg/L actually do yield
observable effects within six hours, this does not necessarily seem to be the same as
instantaneous. I would be cautious about assuming that everyone will view this as a minor
rounding error. Some additional explanation is in order.

Response: See response to comment 4. Concentrations below, not above, 3.5 mg/L
were found to lead to effects within 6 hours.

6. Table III-7 needs a column that refers back to the section where each value is derived.
Response: An additional column has been added to Table IEI-7 with a narrative
reference back to the effect being protected within the respective designated use.

From James J. Pletl, Ph.D.

7. I sent an email to you on May 14, 2001 listing qualifications that I requested to be included
in the draft document. Three topics were addressed: continuous exposures in lab tests
versus cyclic exposures in the field, attrition rate assumptions of EPA's recruitment model,
and the assumption that stress from unacceptably low D.O. is instantaneous. I believe the
draft document adequately addresses the first two comments, but the text that I offered on
the assumption of instantaneous D.O. stress should be included in the final criterion
document. This comment takes on even greater importance given the inclusion of an

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"instantaneous" criterion. I put this word in quotations because it does not appear that the
D.O. Team has yet achieved consensus on the meaning of this term. I can provide the
original email text that I sent in May if you can not locate it.

Response: The following text, with minor edits, has been added to the revised draft
criteria document:

"EPA's saltwater D.O. criteria document states that effects of low D.O. are
instantaneous. However, cyclic periods without food resulting from inactivity during
low D.O. exposure is unlikely to impact larval growth based on data for several species
(Anger, et al., 1981). Figure 11 and data from Appendix H of EPA's criteria document
also suggest that there is a threshold for cyclic exposure which must be exceeded
before impact on growth occurs. Figure 10 of this same document illustrates that
juveniles for several species are twice as tolerant to D.O. stress for a one-hour duration
as they are for a 24-hour duration. Again, duration of exposure does play a role in
response even when that exposure may be very brief. This assumption also does not
recognize the ability of organisms to adapt their behavior and metabolism in response
to stressors for short periods of time. There is no doubt that significant D.O. stress
impacts organisms at the cellular level and beyond, but EPA's document does not
account for the fact that short durations of exposure to moderate or marginal D.O.
stress may not ultimately affect growth. Appendix H of EPA's document presents data
showing no impact on growth under these conditions. Therefore, this assumption may
lead to conservatism in defining criteria."

Anger, K., Dawirs, R.R., Anger, V. and J.D. Costlow. 1981. Effects of early starvation
periods on zoeal development of brachyuran crabs. Biol. Bull., 161:199-2

8. As I have stated in previous comments regarding the development of these criteria, a
frequency component must be included to define how often the criteria can be exceeded
without unacceptable impacts on aquatic life. One should consider how States and EPA
Regions often define compliance with standards. Compliance is not typically made with
instantaneous measurements but based on a percent (10%, for example) of the entire
database for a particular station. I believe the Chesapeake Bay Program uses a 10%
criterion as its benchmark when characterizing a water segment to determine whether D.O.
is a stressor. D.O. is concluded to be a stressor by the Bay Program, as I understand the
process, if 10% of the data exceeds the standard. The frequency component is incorporated
into most other criteria proposed by EPA and must be addressed in this document to support
decisions regarding monitoring and compliance with water quality standards based on these
criteria.

Response: The revised criteria document include a comprehensive set of
implementation guidance which specifically address how often the criteria can be
exceeded without unacceptable impacts on aquatic life.

9. I stated above that the D.O. workgroup has not yet determined how to define the duration of
instantaneous criteria being proposed in the draft document. It is therefore not possible to
comment in a meaningful manner on the validity and appropriateness of these criteria. I

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have expressed my concerns via conference calls with the D.O. Criteria Team that the
criteria should reflect the time scale of the lab tests used to support those criteria. An
instantaneous measurement, in the strictest sense, would be considered a duration of a
minute or less. In most cases, if not all, the durations of the lab tests used to calculate the
instantaneous criteria proposed are much longer than this (relatively speaking). We also
should not define these criteria based on restrictions due to the methods currently used to
monitor the Bay; this is a resource issue rather than one driven by the sensitivity of Bay
species. Furthermore, I believe we will be doing a disservice by adopting instantaneous
criteria in the strictest sense because there will be no incentive to collect more data. If any
single data point collected instantaneously can be used to determine non-compliance, the
probability of non-compliance being concluded increases as the data set size increases. We
should provide incentive to collect more data where it is technically defensible.

Response: See response to comment 4.

10. Perhaps my biggest concern with the document is that it has not yet addressed
implementation issues such as how to address natural conditions, the dimensions of water
parcels being protected and represented by monitoring data, and habitat delineations. For
example, it seems that the spatial extent of hypoxia relative to that of recruitment must be
significant before impact on a population would occur. Hypoxia exposure will vary across
the Bay and variability in exposure to hypoxia will increase as the spatial extent of
recruitment increases. Habitat delineations will determine which criteria apply and when,
therefore the applications of the criteria are not yet clear. For these reasons it is not possible
to comment on all aspects of the document. It will be necessary to distribute the document
to the public again and request comments after these issues have been addressed.

Response: The revised criteria document include a comprehensive set of
implementation guidance which specifically address the frequency component of
defining how often the criteria can be exceeded without unacceptable impacts on
aquatic life.

From Chesapeake Bay Program Living Resources Subcommittee

drafted by Steve Jordan, July 30, 2001

11. One major issue is that of monitoring attainment of the DO criteria. Criteria exposure
durations range from monthly means to instantaneous (not to go below a given
concentration for any period of time). The Bay water quality monitoring program measures
DO at many stations throughout the Bay and tributaries biweekly. Since there is not
complete spatial or temporal coverage by the monitoring program, many violations of the
criteria could occur without being observed, with possibly serious consequences for the
biota. For example, there are a number of fish kills in the Bay each summer that are
attributed to hypoxia, yet seldom is the hypoxia observed until after the damage has been
done.

Response: See response to comment 12.

12. DO data from the monitoring program have been compared with data collected from several
continuous monitoring stations where DO concentrations were measured every few minutes

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for several weeks. This information was used to develop probability-based models to
estimate attainment of DO goals from point measurements made by the monitoring program
or long term means simulated by the Bay water quality model. The concept is
straightforward—given the variations in DO concentrations observed by continuous
monitors, the probability of achieving or failing to achieve a criterion concentration can be
estimated from point measurements or mean concentrations. Since DO can vary greatly over
short time scales (hours to days), an approach of this type will be essential to evaluate the
degree of attainment of the criteria.

Response: The attainment procedure, described in the above comment, was originally
published as part of the 1992 Chesapeake Bay Dissolved Oxygen Restoration Goals. A
significantly revised and strengthened procedure is described in the revised draft
criteria document's implementation guidelines for dissolved oxygen.

13. The Subcommittee should gain a thorough understanding of probability-based approaches to
estimating compliance, and consider what level of confidence will be acceptable (e.g., 95%
confidence in 90% compliance). It must be recognized that 100%) attainment of the criteria
will be not be measurable, even if it is attained, and that we will never have 100%>
confidence in estimates of compliance.

Response: The revised draft document recommends 95 percent of the observed values
be equal to or above the applicable criterion value in order to define the subject region
as in attainment.

14. Another major issue, closely related to the preceding, is one of interpretation. Suppose,
based on point monitoring data, that we estimate 90% attainment of the instantaneous
minimum criterion of 3.5 mg/L for shallow and open water habitats in a segment of the Bay.

Will we view this level of attainment as a categorical violation of the criteria? How would
we treat 80%, 95%, 99% or 99.9% attainment? From the discussion in the previous
paragraph, note that if we are willing to accept nothing less than 100% attainment, we can
never know if the criteria have been achieved. The implication is that in addition to
exposure criteria, we need interpretive criteria. An earlier application of this idea defined
>90%) attainment, estimated by probability, as "acceptable habitat," 50-90% as "marginal
habitat," and <50% as "unacceptable habitat" (Jordan et al. 1992). Once formal criteria are
adopted, a much narrower, categorical interpretation probably will be necessary, e.g., >90%
estimated attainment as compliant with the criteria, <90% attainment as not compliant. This
situation is quite different from the typical application of water quality criteria, where
measured point concentrations or means over some well-defined area or time period can be
used in a straightforward manner to evaluate compliance. It is the large amplitude, high
frequency variability of DO in response to physical, chemical and biological processes that
makes it different from other water quality constituents.

Response: See responses to comments 12-13 above.

References

Jordan, S., C. Stenger, M. Olson, R. Batiuk and K. Mountford. 1992. Chesapeake Bay Dissolved

Oxygen Goal for Restoration of Living Resources Habitats: a Synthesis of Living Resources

Habitat Requirements with Guidelines for their Use in Evaluating Model Results and Monitoring

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Information. USEPA Chesapeake Bay Program, Annapolis, Maryland. CBP/TRS 88/93.

Thursby, G., D. Miller, S. Poucher, L. Coiro, W. Munns and T. Gleason. 2000. Ambient aquatic

life water quality criteria for dissolved oxygen (saltwater): Cape Cod to Cape Hatteras. EPA-

822-R-00-012. U.S. Environmental Protection Agency, Washington, D.C.

From WASH-COG

15. The proposed saltwater criteria are based on Chesapeake Bay-specific modifications of
U.S.EPA's (2000) Virginian Province criteria document; whereas the proposed freshwater
values are taken directly from EPA's (1986) national freshwater criteria document.

Response: Restatement of what's contained in the criteria document. No changes
made to text.

16. The draft criteria for tidal freshwaters are taken directly from EPA's (1986) freshwater
criteria document. Three of the eight species used by EPA (1986) however, are not
components of the tidal freshwater community of the Chesapeake Bay (white sucker,
northern pike, and walleye) but are relatively sensitive to low DO. If these EPA freshwater
criteria are applied directly to the Bay, they should be reevaluated excluding these three
non-resident species, and considering inclusion of data for other Bay resident species in a
manner consistent with the modifications of the Virginian Province saltwater criteria and
U.S. EPA National Guidelines (1994).

Response: A decision has been made to be consistent with EPA criteria derivation
guidelines and not drop the non-Chesapeake Bay species from effects data base prior
to derivation of Bay specific dissolved oxygen criteria. This is reflected in the revised
draft dissolved oxygen criteria document. See response to comment 4 for details.
Given the small number of species within the freshwater effects database (8), there was
not the justification drop any of the non-Bay species from the effects database.

Further, evaluation of Figure 1 from the 1986 EPA freshwater dissolved oxygen
criteria document shows that even dropping the white sucker, northern pike, and
walleye effects data points would not change the overall conclusion regarding the need
for a 7 day mean of 6 mg/L to be fully protective of early life stage freshwater fish
species.

17. It is questionable whether compliance with an instantaneous minimum value of 5.0 mg/L
can be achieved during spring under natural ambient conditions throughout the tidal Bay
system through application of even the most rigorous management practices (particularly
the shallow tidal embayments). Historic and ongoing databases should be evaluated to
determine if compliance with this instantaneous minimum is achievable and, if not, to
identify those areas where compliance is not expected and specifically exclude them from
the implementation or provide alternative criteria for those areas/times.

Response: EPA 304(a) criteria, even those derived for specific regional waterbodies
like Chesapeake Bay, are based solely on data and scientific judgments. They do not
consider economic impacts or the technological feasibility of meeting the criteria in
ambient waters.

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Direct application of EPA freshwater dissolved oxygen criteria is inappropriate for a Bay-

specific value (p. 12).

18. The effect thresholds identified in the draft criteria for four of the effects components (i.e.,
larval recruitment effects, growth effects, threatened/endangered species and scientific
literature) support a long-term average exposure criteria of 5.0 mg/L except the protection
of early life stages for tidal freshwater species. The Bay-specific long-term (30-40 days)
average DO for protection against larval recruitment effects was estimated at 4.7 mg/L in
the draft criteria. By comparison, the U.S.EPA's freshwater criteria (EPA 1986) are a 7-day
average of 6.0 mg/L and instantaneous minimum of 5.0 mg/L. The Bay-specific criteria
propose the application of the EPA freshwater criteria during the primary spawning and
nursery period of 15 February-10 June.

Response: Restatement of what's contained in the criteria document. No changes
made to text.

19. The EPA DO criteria for freshwater were promulgated in 1986 based on a qualitative
evaluation of data for freshwater species available at that time. The development procedure
used for the EPA's (2000) Virginian Province saltwater criteria has a stronger scientific
basis using a more quantitative assessment of the available data.

Response: Restatement of what's contained in the criteria document. No changes
made to text.

20. Because much of the laboratory data on sensitivity of early life stages to low DO conditions
that were used for the Virginian Province criteria collected at salinities of 5 ppt or greater,
the draft Bay-specific criteria have applied U.S. EPA's freshwater criteria to the tidal
freshwater habitats of the Bay tributaries. For protection of survival and growth of juveniles
and adults this is essentially equivalent to the process used for saline habitats in the Bay;
however, the freshwater criteria were not re-evaluated and adjusted for Bay-specific
conditions.

Response: There were numerous reasons and documented rationale for taking specific
actions to generate a set of Bay specific criteria from the Virginian Province criteria's
effects database documented throughout the working draft criteria document, the
principal reason being the need to derive criteria protective of the five proposed draft
designated uses. There is not a parallel need nor a sufficient set of effects data to
recalculate the EPA freshwater criteria specific to Chesapeake Bay tidal fresh
habitats.

21. EPA freshwater criteria for protection of early life stages were based on 8 species; three of
these (white sucker, northern pike, and walleye) are relatively sensitive to low DO, but are
not components of the tidal freshwater community of the Chesapeake Bay. Furthermore,
walleye and northern pike are often grouped for criteria calculations with cold-water habitat
species (EPA 1986) which is also inappropriate for application to the tidal freshwaters of the
Bay's tributaries. If the EPA freshwater criteria are applied for protection to resident tidal
freshwater species in the Bay, they should be reevaluated excluding these three species and
considering inclusion of other Bay resident species in a manner consistent with the

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modifications of the Virginian Province saltwater criteria made for the Bay-specific open
water criteria and U.S. EPA's National Guidelines (1994).

Response: See response to comment 16.

22. Because it has been 15 years since the freshwater criteria were developed, we recommend
that an update and recalculation of the freshwater criteria specific to the Bay be performed
consistent with EPA guidance by conducting a literature review to identify more recent data
that may be available for freshwater species that are residents of the tidal freshwater reaches
of the Bay and its tributaries. We also recommend that the recruitment effects model
approach be used to evaluate threshold DO levels for early life stages of resident species in
tidal freshwater habitat similar to the approach for deep and open water use habitats.

Response: See response to comment 20.

Migratory spawning and nursery designated use instantaneous criteria may not be appropriate

or achievable.

23. It is questionable whether compliance with an instantaneous minimum value of 5.0 mg/L
can be achieved during spring under natural ambient conditions throughout the tidal Bay
system through application of even the most rigorous management practices. This is
particularly of concern in shallow embayments in the Bay tributaries. It is recommended
that historical and ongoing databases be evaluated to determine if compliance with this
instantaneous minimum is reasonably achievable and, if not, to identify the extent of those
areas where compliance is not expected and specifically exclude those areas from the
implementation or provide alternative criteria for those areas/times.

Use of instantaneous minimum versus daily averaged minimum as criteria (p. 15-16).

24. The case being made in this paragraph in favor of an instantaneous minimum criterion is
neither clear nor particularly logical. The case presented in the draft is that generally only
one data point is available for a day, but that when there is semi-continuous data using an
average value would mask periods of risk due to low DO. However, a strong case could be
made that with only one or two measurements you don't know what may be missed. The
better approach might be to require semi-continuous monitoring at a particular location
where a risk is thought to exist during critical periods. Rather than use an instantaneous
value, resource managers could apply a statistical approximation of the range of the
minimum concentration (e.g., the lower 10th or 20th percentile) or more specific temporal
limits on short duration exposure.

Response: See response to comment 4.

The spatial and temporal extent of the larval recruitment model is not addressed (p. 9-10).

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25. While the larval recruitment model effectively integrates duration and intensity to assess the
effects of low DO conditions, a significant limitation of the model is the failure to
incorporate a spatial component. While the designated use habitat categories attempt to
account for variation in habitat use over the Bay, the defined uses do not adequately reflect
the variability of habitat use by individual species. Given the size and complexity of the Bay
and its tidal tributaries relative to the spatial distribution of some of the target species
evaluated with the model, some of the assumptions relative to temporal exposure to low DO
conditions may significantly over-estimate potential effects and thus establish overly
protective criteria. The Virginian Province criteria (pages 1 and 40) caution that, "even if
the DO at a site is low enough to significantly affect aquatic life, the environmental
manager will have to judge whether the hypoxia is widespread enough [relative to aquatic
resources] for concern " Changes in the application of the model can provide a tool to assist
environmental manager in making this judgement.

Response: It is not the model that fails to incorporate a spatial component. The user
can adjust the "p" value in the model (representing the probability of exposure) to
incorporate horizontal space. In the application of the larval recruitment effects
model to Chesapeake Bay, only the vertical distribution is factored in as that's where
the best information was available. However, the model does not care why a
particular portion of a cohort is not exposed. The model responds to what proportion
of the cohort that is exposed.

26. The application of the recruitment model to striped bass is an example of the influence of
spatial factors in the Bay specific criteria development. The Chesapeake Bay model
assumes that striped bass spawn over a 30-40 day period that may accurately represent the
spawning period across all of the tidal tributaries to Chesapeake Bay. However, an
examination of some data for striped bass egg abundance (Rutherford 1992, Olney et al.
1991) indicates that there may be a progression of spawning within the Bays tributaries and
that most spawning in a given tributary may occur over a much shorter period of 7-21 days.

It is stated that the primary interest is, "to capture the period of predominant recruitment,
rather than observance of the first and last date [of] presence". Thus, for anadromous
species it may be necessary to consider the period of exposure for spawning habitat within
each primary spawning tributary to accurately characterize the potential effects of low DO
on spawning and recruitment.

Response: Shortening the spawning period for striped bass has only a minimal effect
on the output of the recruitment model. This is because of the sensitivity to low
dissolved oxygen concentrations. The dissolved oxygen dose response curve seems to
controlling the response more than the spawning period, at least between one and four
to five weeks. At the same time, two papers published by Dave Secor listed below
describe the importance of spawning time and spawning duration and spatial egg
placement to striped bass recruitment. The gist of these papers is that striped bass
spawners cannot predict which portion of the entire spawning period will result in
recruitment. Over years and decades, its important for the system to support
recruitment from all parts of the spawning season.

Secor, D.H. 2000. Spawning in the nick of time? Effect of adult demographics on

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spawning behavior and recruitment of Chesapeake Bay striped bass. ICES J. Mar. Sci.
57: 403-411.

Secor, D. H. and E. D. Houde. 1995. Temperature effects on the timing of striped bass
egg production, larval viability, and recruitment potential in the Patuxent River
(Chesapeake Bay). Estuaries 18(3):527-533.

27. Another issue related to the spatial application of the larval recruitment model is an
understanding of the size, distribution, and transport of populations relative to the area of
exposure to low DO conditions. In the case of estuarine/marine species that spawn over a
wide extent of coastal and estuarine water (e.g., bay anchovy [Rilling and Houde 1999])
with transport and mixing of larvae in and out of estuaries, the relative proportion of the
overall population that may be exposed to low DO conditions in a given segment of the Bay
may be very small. This could result in a significant overestimate of potential effects and
overprotective criteria. We recommend that model be evaluated and applied on a species-
specific basis incorporating spatial segmentation of the designated use habitats based on
species life history factors and distribution within the Bay and areas on non-attainment
within the Bay.

Response: The information necessary to apply the larval recruitment model "on a
species-specific basis incorporating spatial segmentation of the designated use habitats
based on species life history factors and distribution within the Bay and areas on non-
attainment within the Bay" is just not available for the species contained in the effects
data base.

Deep water use designation, egg/larval recruitment effects model assumptions and application

require re-evaluation(p. 27)

28. The criteria for the deep water use designation is driven by the egg and larval recruitment
effects model based on a 5 percent impairment benchmark. As indicated in the Criteria
Components section and documented by Rilling and Houde (1999), bay anchovy eggs and
larvae are widely distributed throughout the mainstem Bay and the water column. A more
explicit linkage of the population distribution between the upper and lower portions of water
column in the model would provide a more defensible and reliable estimate of low DO
effects on the overall population of bay anchovy eggs and larvae in the Bay than the
unsupported assumption of "50 percent exposure" made in the draft development document.
That is, estimates (based on field abundance data) of the relative distribution of the
population between the shallow/open water habitat and the deep water habitat should be
incorporated to estimate the potential spatial extent of exposure to low DO before
calculating the cumulative effect percent. Based on the documented differences in low DO
conditions and persistence in the main Bay north and south of the approximate location of
the mouth of the Potomac River and the apparent higher densities of bay anchovy larvae in
the lower Bay, consideration should also be given to segmenting the model based on the
longitudinal morphometry and hydrology of the Bay.

Response: Given the complexity already built into the draft Bay dissolved oxygen
criteria with 1-3 individual criterion values applied on a seasonal basis to five different

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set of designated uses, yielding 17 different designated use-criterion-season
combinations, to then add a spatially explicit larval recruitment modeling component
on top becomes too complex to implement. The designated uses, which vary
themselves in time (migratory spawning and nursery) and vertical space (open water,
deep water, deep channel) have been established to reflect longitudinal differences in
morphometry and hydrology of the Bay and its tidal tributaries. As one moves further
south down the mainstem Bay, the application of open water/deep water/deep channel
designated use changes, therefore, the applicable dissolved oxygen criteria changes as
well. The information available for "the relative distribution of the population
between the shallow/open water habitat and the deep water habitat" is non-existent for
most species. In the case of Bay anchovy, the information is really only available in
terms of the vertical water column.

The use of 5 percent as the cumulative reduction in larval recruitment value may not be the most
appropriate endpoint (p. 11).

Response: See response to comment 29.

29. Similar to the Virginian Province criteria, the Bay-specific application of the larval
recruitment model sets a benchmark for protection against greater than a 5 percent
cumulative reduction in larval recruitment. The draft criteria document indicates that this is
the same level of protection afforded juvenile and adult life stages. This approach is based
strictly of the ability to detect a statistically significant difference in conditions with and
without anoxia, not biological significance to the population. In addition, it fails to
recognize the relative value of individuals at different life stages to the overall population
equilibrium.

Response: The 5 percent value is not based on the ability to detect a statistically
significant difference. The 5 percent was originally chosen in the Virginian Province
criteria document in an attempt to be consistent with the 5 percent level of protection
given to other criteria (e.g., FAV and FCV). Choosing a value other than 5 percent
must be based on a similar set of acceptable losses. The purpose of the 5 percent value
is not to say that a given population can not withstand a greater impact, but rather
that 5 percent is assumed to be an insignificant increase in impairment relative to no
hypoxia. Thus, "normal" effects on a population (such as predation or harvesting) will
not be significantly impaired.

30. For most species with a broadcast spawning strategy (e.g., bay anchovy, striped bass) egg
production is high and natural mortality rates are very high for early life stages, declining
steadily with age. For thousands of eggs spawned only one individual may survive to
maturity and spawn; thus, losses sustained at the egg and larval stages would have
considerably less impact on the population than the same loses sustained by juveniles or
adults. One population model commonly used for impact assessment is the Equivalent Adult
Model (Goodyear 1978) that takes these factors into account and uses natural mortality rates
by age to extrapolate losses through a range of life stages to numbers of adults that would
otherwise have survived to a comparable specified age. For species that fill a major niche as
forage for larger piscivores, such as bay anchovy, similar biomass loss models are available

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to account for losses at various life stages in terms of biomass of adults potentially lost to
the system. It is recommended that an equivalent adult or similar models be evaluated as a
means of estimating losses to the adult population and the potential percent reduction.

Response: The Equivalent Adult Model (EAM) is flawed in that it stipulates life table
probabilities, assuming a steady state population without due consideration of variance
in these vital rates. Of greatest concern are the rates that affect early survival. The
EAM typically calculates early vital rates based on poor assumptions or solves for
these by assuming population growth rate lambda=l (r=0). This invariably leads to
the conclusion that we are affecting a trivial no. of adults through the removal of x
larvae or juveniles (so we should stock that many juvenile fish, etc). It should be now
clear to everyone that striped bass and other Bay fishes are periodic strategists - their
populations grow and contract in fits and bursts; thus it is not the rate of the early
survival that is critical, rather it is it's variance, and providing habitats that preserve
the capacity for population growth through salubrious conditions that favor high
recruitments.

31. This recommended approach still would not address the issue of the significance of the 5
percent benchmark to populations. Although a predicted 5 percent cumulative reduction was
selected as an acceptable assessment benchmark for the Virginian Province criteria, it is not
necessarily an indication of potential impact to populations. As described in the Virginian
Province criteria (page 12) document, "This does not mean that a population cannot
withstand a greater percentage effect with no significant effect on recruitment. Rather, the
5% means that this level of effect should be insignificant relative to recruitment in the
absence of hypoxic events The effect of a 5 percent reduction in larval recruitment will

vary widely among various species or even among various populations/spawning stocks of a
given species. For many species 5 percent will be overprotective, while for others 5 percent
may be insufficient protection. Although it can be difficult to determine precisely what level
of reduction is acceptable, such an evaluation should be made on a species by species basis.
Response: We see no systematic means of conducting such a species by species analysis
to determine the acceptable level of effect with no significant effect on recruitment.
The comment already answers why we don't need a higher value that 5 percent when
stating "it can be difficult to determine precisely what level of reduction is acceptable",
given the complexities of Chesapeake Bay food webs and species interactions.

Implementation Issues

32. The most significant comments related to these criteria concern the implementation process
that has not been proposed at this time. It is difficult to provide a thorough review of the
criteria and their development without a clear understanding of the implementation goals
and process. As clearly stated in the development document, unlike common toxic
contaminants that can be directly monitored and regulated at the point of discharge and via
sediment management practices, anoxia and hypoxia are symptoms of complex interactions
of a variety of natural physical, chemical, and biological processes, and anthropogenic
stresses and inputs to the ecosystem. While DO can be monitored, the causative factors of
low DO conditions are not so easily distinguished or readily monitored.

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Response: See response to comments 35-38.

33. It is clear that low oxygen conditions can and have existed exclusive of human activities in
the Bay watershed and that these conditions can be highly variable in intensity, extent and
duration. In the discussion of Oxygen Dynamics it is pointed out that, "The Chesapeake Bay
has a built-in, natural tendency towards reduced dissolved oxygen conditions, particularly
within the deeper waters because of the physical morphology and estuarine circulation". In
the Section Low Dissolved Oxygen: Historical and Recent Past, it is documented that
anoxic and hypoxic conditions have existed through geologic time, although with greater
frequency and extent over the past 50-100 years. Under certain atmospheric conditions there
are also occasional intrusions of low DO water from deep-water habitat into the shallow and
open water habitat. In fact, it is recognized in Refined Designated Uses for the Chesapeake
Bay and Tidal Tributary Waters that, "In the seasonal anoxic region, there will be periods
from May through September when the deep channel dissolved oxygen criteria will be
unattainable'". Furthermore, hypoxic and anoxic, "conditions are likely to persist
throughout [the deep channel] even under the best management conditions that can be
achieved'. It is also recognized that similar conditions exist in many of the Bay's shallow
embayments.

Response: See response to comments 35-38.

34. The implementation of these criteria, particularly for the deep channel use designation,
needs to delineate and account for these areas that are unattainable even under the best
management scenarios. Such areas need to be clearly defined and excluded from the
designated use criteria; alternative management goals could be established for these regions
outside of the criteria implementation process. If these criteria are implemented without
such exclusions, the alternative of dealing with these areas through the variance or site-
specific criteria process has the potential to considerably burden the environmental
management, restoration, and regulatory process.

Response: The revised draft criteria document incorporates detailed implementation
guidance addressing application of the dissolved oxygen criteria to each of the
designated use categories including the deep channel.

35. While it is stated that the averaging periods are specified with a recognition that short term
exposures to low DO are allowable, it is not clear how the criteria recognize and account for
periods of natural anoxia/hypoxia in some areas of the Bay's deeper waters and occasionally
in the shallow and open waters. This is a critical concern that must be accounted for as part
of the implementation of these criteria.

Response: The revised criteria document includes a comprehensive set of
implementation guidance which specifically address how often the criteria can be
exceeded without unacceptable impacts on aquatic life.

36. Another significant issue for implementation is designation of the boundary between tidal
freshwater and shallow/open water or deep-water habitats. The transition zone in tidal
tributaries may exhibit a salinity range of zero to several parts per thousand on a daily
and/or seasonal basis. The biotic community may vary significantly seasonally and between

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years. Drought years and wet years will affect the location of the salt front within these
tributaries. Where and when a reach is considered to be freshwater can have a significant
influence on whether that reach is in compliance, because the tidal freshwater criteria as
currently proposed are considerably more stringent than the saltwater criteria.

Response: This issue is specifically addressed in the implementation guidance included
in the revised draft criteria document.

37. Another consideration is the level of effort required to monitor and document the existence
and extent of anoxic conditions seasonally and annually. Unlike toxic chemicals that can be
monitored and regulated at points of discharge by the regulated community, DO will need to
be extensively monitored within the Bay and its tributaries. Low DO may be the result of a
number of factors including excess nutrients and organic carbon and the combination of
factors will likely vary in different parts of the Bay system. These physical and chemical
factors will also require ongoing Bay-wide monitoring. Consequently, there is also a
significant built-in lag that must be recognized between monitoring, regulation, and
recovery.

Response: There is a clear recognition by the management and scientific community as
to the built-in lag between implementation of load reduction actions and response in
the tidal system.

38. EPA's draft criteria document also makes the important point that due to its morphometry
and circulation, the Bay is very efficient at conserving and recycling nutrients. Thus excess
nutrients and organic carbon already in the system may require an extended period of time
to be flushed from the system before recovery due to regulatory control efforts will be
recognized. This also adds to the complexity of understanding the spatial and circulatory
linkages between the potential sources (e.g., point and non-point sources in tidal and non-
tidal reaches of tributaries and in the mainstem Bay) of materials that may affect low DO
conditions and the locations at which the low DO conditions are observed in the main Bay.

That is, the reliability of hydrological water quality model will be a critical factor for
environmental managers moving from classification of an area as non-attainment to
identification of where and how management efforts can effectively be applied.

Response: The role that the Bay models will play in determination of criteria
attainment is a topic still under discussion at this time.

Data Gaps

Low salinity/freshwater data for survival

39. Much of the laboratory-based data for the effects of low DO on survival and growth of
aquatic organisms used in development of the Virginian Province criteria was generated at
EPA's Narragansett Laboratory; as a consequence of the Laboratory's location on
Narragansett Bay in Rhode Island most of the tests were conducted at salinities of 5 ppt or
greater. In order to "bridge the information gap " and establish criteria for the freshwater
tidal reaches of the Chesapeake Bay, this draft document defaults to the EPA freshwater DO
criteria that are generally more restrictive than the Virginian Province saltwater criteria.
Laboratory studies of the effects of low DO on survival and growth of resident species of

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the tidal freshwater reaches of the Chesapeake Bay and tributaries would provide the
necessary data to develop site specific tidal freshwater criteria for the Bay.

Response: See responses to comments 16, 20-22.

Linkage and/or segmentation of recruitment model for deep and shallow habitat and up and

down Bay

40. A critical factor for evaluating the potential effects of low DO, particularly as it relates to
the larval recruitment model, is the exposure potential. As indicated in the Virginian
Province saltwater criteria document, an assessment against these criteria may indicate the
potential for impact associated with low DO in a particular area; however, it is up to the
environmental manager to make a professional judgment as to whether the exposure affects
a significant portion of the population. For species with sufficient distributional data, it
would be valuable to integrate into the recruitment effects model, proportionate
distributions for eggs and larvae within the various use designation areas and up and down
Bay relative to the bathymetric ridge in the vicinity of the mouth of the Potomac River. This
would provide the Bay's resource managers with a model/tool to explicitly and directly
account for the proportion of the population exposed to low DO conditions that are likely to
cause significant impairment.

Response: See responses to comments 25-28.

Sturgeon Distribution and Spawning

41. Shortnose and Atlantic sturgeon survival and growth are the driving factors for the
instantaneous criteria for the shallow water, open water, deep water, and deep channel water
use designation habitats. A thorough synthesis of available information on the seasonal
distribution and location of potential spawning habitat should be developed to more
accurately define where and when criteria driven by these two species are applicable.
Response: The sturgeon survival and growth effects data are only directly factored
into the shallow/open water criteria, but apply to the deep water and deep channel
designated uses during the cooler months of the year when cooler water temperatures
and lack of stratification. The draft document contains a synthesis of the available
information gathered by one of the world's leading experts on sturgeon, Dave Secor at
the University of Maryland Chesapeake Biological Laboratory. The more complete
record of sturgeon occurrences (depth, latitude, and longitude) collected in recent
years by the USFWS Chesapeake Bay Field Office through a reward and tagging
program shows sturgeons of both species using a diversity of habitat zones among
seasons in the Chesapeake Bay. It is unclear what information is still missing.

References

Goodyear, C.P. 1978. Entrainment impact estimates using the equivalent adult approach. Report

No. FWS/OBS-78/65. U.S. Fish and Wildlife Service, Washington, D.C.

Jordan, S., 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

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Habitat Requirements with Guidelines for Their Use I Evaluating Model Results and Monitoring
Information. Prepared for Living Resources Subcommittee and the Implementation Committee's
Nutrient Reduction Strategy Reevaluation Workgroup of the Chesapeake Bay Program.

Reevaluation Report #7c, CBP/TRS 88/93. The Maryland Department of Natural Resources
Tidewater Administration, Chesapeake Bay Research and Monitoring Division, Annapolis,

Maryland.

Olney, J.E., J.D. Field, and J.C. McGovern. 1991. Striped bass egg mortality, production, and
female biomass in Virginia Rivers, 1980-1989. Trans. Amer. Fish. Soc. 120:354-367.

Rilling, G.C. and E.D. Houde. 1999. Regional and temporal variability in distribution and
abundance of bay anchovy (Anchoa mitchilli) eggs, larvae, and adult biomass in the Chesapeake
Bay. Estuaries 22: 1096-1109.

Rutherford, E.S. 1992. Relationship of Larval Stage Growth and Mortality to Recruitment of
striped bass, Morone saxatili.v, in Chesapeake Bay. Dissertation submitted to the Faculty of the
Graduate School of the University of Maryland in partial fulfillment of the requirements for the
degree of Doctor of Philosophy.

Rutherford, E.S., E.D. Houde, and R.M. Nyman. 1989. Cohort-specific growth and mortality
sates of striped bass and white perch in the Potomac River, 1987. Presented at Emergency
Striped Bass Act Program Workshop, Richmond, Virginia, 25-26 January 1989.

U.S. Environmental Protection Agency (U.S.EPA). 2000. Ambient Aquatic Life Water Quality
Criteria for Dissolved Oxygen (Saltwater): Cape Cod to Cape Hatteras. (EPA-822- R-00-012).
Office of Water, Office of Science and Technology, Office of Research and Development
National Health and Environmental Effects Research Laboratory Atlantic Ecology Division.
Washington, D.C., Narragansett, Rhode Island.

U.S. EPA. 1986. Ambient Aquatic Life Water Quality Criteria for Dissolved Oxygen
(Freshwater). (EPA-440/5-86-003). Office of Research and Development Environmental
Research Laboratories, Duluth, Minnesota, Narragansett, Rhode Island.

From CBF

42. We are pleased with the extent of the literature review and use of existing methods, such as
the EPA Saltwater Criteria Methods, in establishing the draft numbers. However, we are
concerned that the actual criteria were set more closely to the levels that could be met
relatively easily versus levels that should be met to improve water quality. The objective of
the Clean Water Act is to restore and maintain the chemical, physical, and biological
integrity of the Nation's waters through such mechanisms as water quality standards, even if
the standards are technology forcing. As stated by CBP, development of these criteria
intends to adhere to the development of the national ecoregional nutrient criteria, yet
"(w)ater quality criteria developed under section 304(a) are based solely on data and
scientific judgments. They do not consider economic impacts or the technological feasibility

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of meeting the criteria in ambient water." Nutrient Criteria Development; Notice of
Ecoregional Nutrient Criteria (January 9, 2001) 66 Fed. Reg. 1671, 1672. (emphasis added)
Response: EPA 304(a) criteria, even those derived for specific regional waterbodies
like Chesapeake Bay, are based solely on data and scientific judgments. They do not
consider economic impacts or the technological feasibility of meeting the criteria in
ambient waters.

43. CBF has several concerns related to the development of the Dissolved Oxygen (DO)
criteria. First, only species commonly inhabiting Bay or tributary tidal waters were used in
the derivation of the criteria. We question whether any rare species have been omitted that
may be more sensitive than common species. This concern is magnified by CBP's decision
to consider only one threatened or endangered species "whose habitat would be directly
influenced by state adoption of the proposed three criteria." (p.65) (emphasis added) Given
the lists of threatened and endangered species in Tables B-l and B-2, more consideration
should be given to the influence of these criteria on these other species in order to comply
with Section 7(a)(2) of the federal Endangered Species Act (ESA) which provides that
Federal agencies shall insure that actions authorized or funded by the federal government
are not likely to jeopardize the continued existence of any endangered or threatened species
or result in adverse modification of habitat of such species. 16 U.S.C. Section 1536(a)(2)

CBF is concerned that by limiting the development of the criteria to direct habitat
influences on common species, CBP may not be providing protection to threatened and
endangered species which inhabit the Bay, and their habitat, as required by the ESA.

Response: As described in more detail on page 8 of the July 3, 2001 working draft
document, a total of 36 species of fish, crustaceans, and molluscan shellfish are in the
Virginian Province effects database. Only four species, none of which were listed as
rare, threatened or endangered were originally proposed to be dropped from the
effects database given they were species not resident in Chesapeake Bay. These four
non-Bay species have been maintained in the effects data base used to derive the Bay
dissolved oxygen criteria. See response to comment 3 for more details. The text has
been revised to not use the word "commonly" as that does not accurately reflect the list
of 32 species used in derivation of the Bay dissolved oxygen criteria. A review of the
complete listing of endangered species listed in Appendix B by the four states with
tidal waters yields sturgeon (2 species), sea turtles (5 species), and whales (3 species)
once all terrestrial species are moved to the side. Of these remaining species, only
sturgeon would be influenced by dissolved oxygen conditions in the Chesapeake Bay as
whales and sea turtles are air breathers. These criteria were derived with actual
shortnose and Atlantic sturgeon effects data, the only two listed species in Bay tidal
waters that would be influenced by these criteria.

44. Second, the document states that a larval recruitment model was used to confirm the criteria
for the migratory spawning and nursery designated use. While the CBP literature review
supports a larval release season of 120 days or more, a more "conservative" timeframe of 75
to 100 days was chosen "to capture the period of predominant recruitment, rather than
observance of the first and last dates for zoeal presence in the water column" (p.9). Again,
we question whether conservative levels of protection will meet the goals.

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Response: Note the larval recruitment model was used to confirm, not derive the
criteria for the migratory spawning and nursery designated use. A change of 20 days
in the recruitment season will not make a significant change in the larval recruitment
effects information to show the derived migratory spawning and nursery designated
use criteria were not already protective enough.

45. As for the actual DO and Chlorophyll a criteria, the phytoplankton reference communities
used to determine the draft Chlorophyll a criteria were based on existing assemblages,
although "there are presently no undisturbed sites in Chesapeake Bay." (p.4) Thus, while
the actual Chlorophyll a criteria seem reasonable, they are based on the "best" disturbed
conditions. Similarly, the DO criteria appear to be set at the "minimum amount of oxygen
(mg/L) needed to survive by species" (Batuik, 8/22/01 presentation to CBF staff). This
would mean that no margin of safety has been incorporated. The document does not say
anything about a margin of safety being included in the development of these criteria and
the values and study results cited in the text indicate that the proposed numbers are quite
close to the levels where negative effects begin to be seen. Yet the draft document states
that the DO criteria "are sufficiently protective under most Chesapeake Bay conditions
where aquatic organisms are not otherwise unduly stressed." (p. 16) The document
continues, however, to point out that both temperature and behavioral effects are not
addressed within these criteria, although they could cause "otherwise unduly stressed"
conditions. Acknowledgement of these concerns warrants the addition of an explicit margin
of safety to the criteria.

Response: The derived criteria are not at the absolute minimum amount of oxygen
required for survival. A cross comparison of the actual lethal and growth effects
values on a species by species basis with the draft criterion values applicable to the
appropriate designated use clearly illustrates none of the individual species would not
be protected by the draft criteria. Conservative assumptions have been built in
throughout the criteria derivation process given the recognized inability to generate
effects information for the hundreds to thousands of aquatic species living in the tidal
waters. EPA's criteria derivation methodology which calculates the acute:chronic
ratio to better more fully account for sensitivity to chronic impacts (e.g. growth) is just
one example. The revised draft criteria text has been edited to better highlight where
assumptions to build in some level of conservative given lack of full information.

From Virginia DEQ

46. Efforts toward revising Virginia's water quality standards, as an outcome of this process,
will have the benefit of correcting deficiencies in the existing dissolved oxygen standard.
One such deficiency was the definition and use of natural conditions. The Commonwealth
has no interest in creating similar problems with the other criteria under development for
water clarity and chlorophyll, such as applying unobtainable clarity requirements in areas of
turbidity maximum and naturally high sediment resuspension, or stringent chlorophyll
levels in areas with historically elevated concentrations, again due to natural conditions
(e.g., in small embayments and creeks).

Response: The revised draft criteria document incorporates a comprehensive set of

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implementation guidelines which address application the criteria in these
circumstances.

47. The document desusesdoc7-3-01.pdf states, "In part of the mainstem Bay south of the mouth
of the Rappahannock River, the 'open water' designated use habitat extends all the way
down to the bottom. Although this region can exhibit relatively strong stratification, it
exhibits little dissolved oxygen deficiency. Proximity to the mouth of Chesapeake Bay
allows for continuous replenishment of subpycnocline waters with oxygenated ocean
water".

It is DEQ's position that the designation of the entire Virginia main Bay area as 'open
water' in the draft document is inappropriate and considerable further study of this issue is
needed. Ultimately, Virginia has the regulatory authority and responsibility to delineate
where the designated uses apply in it's main Bay and tidal rivers. Therefore, this specific
designation should be removed from the draft documentation. This designation does
nothing to resolve the problems encountered under the current standards. It also works
against the goal of having consistency among the jurisdictions, where just across the state
line Maryland's main Bay waters have areas designated as 'deep water' and 'deep channel'.
We feel that "deep water" and "deep channel" uses apply to areas of Virginia's tributaries as
well.

Further evaluation of this issue is underway in Virginia, and we expect to have discussions
on the physical, chemical, and biological characteristics of Virginia's main Bay region to
ensure it's proper designation. We agree that the open ocean has an influence on this area,
as evidenced by the fact that much of Virginia's main Bay is not listed as "impaired". Part
of our analysis will be aimed at better understanding the extent of the ocean influence and
its impact on water quality conditions.

Response: See the response to comment 89 within the designated use comments
summary.

48. Designating the entire main channel of the James, York, and Rappahannock rivers as
"migratory spawning and nursery" habitat may be appropriate. However, we note that the
lines in the draft documents, showing where these areas begin as one moves upstream, do
not correspond to the NOAA maps depicting Environmentally Sensitive Areas
(spring/summer) for anadromous fish. This discrepancy needs to be resolved.

Response: See the response to comment 90 within the designated use comments
summary.

From Maryland DNR

Deep Water and Deep Channel Habitats

49. The proposed dissolved oxygen criteria for defined Spawning and Nursery Water, Shallow
Water and Open Water uses appear to be well documented and should be protective of
aquatic life in the State's tidal waters if comments that follow are adequately addressed.

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The proposed criteria for Deep Water and Deep Channel uses, however, do not support all
aquatic life uses - specifically fish habitat year-round. That these proposed criteria do not set
goals for year-round support does not meet federal or State water quality goals and lowers
expectations for Bay restoration and effective aquatic habitat of the Bay.

Recommendation

A more protective approach would be to develop year-round criteria that support all aquatic
life in these areas and define natural conditions that may occur that keep these criteria from
being met.

Response: The above comments seems to have missed the whole point behind
development of a designated use and corresponding dissolved oxygen that differ over
time and with vertical depth. The proposed deep water and deep channel uses do
provide for year round protection of aquatic life uses, only different uses at different
times of the year. The applicable dissolved oxygen criteria differ according to the time
of year as well.

Seasonal Application of Criteria

50.	The proposed criteria establish reasonable seasonal periods for different criteria for
Spawning/Nursery Areas, Deep Waters and Deep Channel areas, but seasonal variations in
the assessment measures are unexplained (e.g. no 30-day mean in Spawning/Nursery Areas
from mid-Feb to mid June; no 7-day mean in Deep Water from April to Sept.; no 7-day or
30-day mean in Deep Water and Channel areas from April to Sept.). Are these intentional
omissions or aspects of the criteria that still need to be developed?

Response: The criteria concentration/duration/temporal application, which are
complete with no omissions, will vary depending on the designated use to which they
apply given the underlying scientific information used in their derivation. All of this is
laid out in detail throughout the working draft criteria document.

Benthic Communities

51.	The protection of benthic communities are not explicitly addressed in Shallow Water and
Deep Water habitats where most of the benthic community resides and plays a critical role
as a source of food for fish and crabs. While it may be presumed that the criteria for these
organisms are less stringent than for fish, and therefore they are protected if conditions for
fish are adequate, there are natural circumstances that may cause benthic communities to
experience significantly lower oxygen levels than observed in the overlying water column.

First, steep oxyclines from surface to bottom often occur during warmer months in poorly-
flushed tidal systems, often resulting in low oxygen levels (< 2 mg/1) in the lower meter of
the water column when near surface or mid water column concentrations are above 5mg/l.
Second, there are often wide fluctuations on a diel basis in these same systems, frequently
resulting in very low oxygen levels in early morning hours. Finally, in all Bay waters,
especially during warmer months, there is a thin boundary layer where oxygen declines
appreciably in a matter of a few cm between typical water column levels and those
experienced at or near the bottom sediments. Unlike fish, benthic organisms cannot

20

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typically escape these localized low oxygen zones.

Recommendation

Protection of benthic communities from low dissolved oxygen conditions should be
explicitly addressed in Shallow Water and Deep Water habitats. Literature values for
oxygen tolerances of various benthic organisms need to be compared to oxygen levels in the
bottom boundary layer where these organisms actually live for a technically valid
assessment of attainment. The literature describing the relationship between water column
oxygen concentrations and those in the benthic environment should be carefully examined
so that extrapolations can be made between near-bottom (e.g. 0.5 - 1.0 m above bottom)
monitoring values and those to be expected in the benthic environment under specific
hydrodynamic conditions.

Response: The shallow water, open water and deep water criteria are fully protective
of infaunal and epifaunal benthic communities. However, it would be logistically
impossible to establish and then enforce a different set of criteria strictly protective of
benthic organisms only applicable in the last few centimeters of the water column just
before reaching the bottom sediments.

Assessment and Monitoring - General

52. There is very little detail about how attainment would be defined and how it would be
monitored. Particular concerns exist in obtaining sufficient data to capture episodic events
and in assessing conditions where gradients, such as vertical oxyclines, exist within a
designated use zone.

Recommendation

It is recommended that standardized measurement and statistical analysis methods be
defined for assessing criteria for all designated uses and time periods of averaging (e.g.
location of multiple vertical measures, frequency of sampling, spatial density of sampling,
instantaneous measures, etc.).

Response: The revised draft criteria document incorporates a comprehensive set of
implementation guidelines which address all the above listed implementation issues.

Assessment and Monitoring - Bottom Layer

53. None of the existing monitoring programs adequately monitor dissolved oxygen conditions
in the near-bottom layer (less than one meter from the bottom) to determine whether oxygen
levels support benthic life.

Recommendation

Assessing benthic oxygen conditions should be explicitly addressed in the development of
criteria implementation and monitoring programs to assess the dissolved oxygen criteria.
New monitoring technologies or extrapolations from existing programs should be
considered. A surrogate measure of acceptable habitat conditions (including dissolved
oxygen levels) could be addressed by identifying "healthy" benthic communities. The

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limitation of this approach, however, is that when benthic communities fail to meet
expectations it may not be possible to determine whether the impairment was due to low
oxygen levels or to other anthropogenic or natural habitat impacts. The feasibility of
measuring dissolved oxygen impacts through benthic community metrics should be
explored.

Response: Given sampling logistics when working over a water column often 10-30
meters in depth, measurements of low dissolved oxygen are made generally a meter
above the bottom. We know of no existing instrumentation, other then a tripod or
other similar apparatus, that can provide for measurements less than a meter from the
bottom during routine monitoring cruises. There is an existing benthic index of biotic
integrity for Chesapeake Bay that has been applied as recommended in the comment.

Assessment - Natural Conditions

54. Dr. Butt's review of conditions where waters are naturally low in dissolved oxygen is
focused on the Main Bay. This review needs to be extended into tributary areas to address
some of the unique situations that occur there. For example, in some tributary areas,

Maryland fish kill records have suggested low oxygen conditions resulting from respiration
of large schools of fish and low oxygen conditions (winter kill) when respiration exceeds
oxygen production/reaeration during periods of ice and snow cover. Other naturally-
occurring conditions or extremes that need to be addressed include conditions related to low
freshwater flow near the head of tide during drought conditions and epibenthic conditions
(within a meter of the bottom) that are rarely monitored.

Recommendation

It is recommended that exceptions to the recommended criteria in time and space due to
natural causes be well defined in future drafts and the final document.

Response: The revised draft criteria document incorporates a comprehensive set of
implementation guidelines which address all the above listed implementation issues.

From Pennsylvania DEP

55. There is a section in the Recommended Implementation Procedures portion of each
document for the "factoring in" of naturally occurring violations of the proposed criteria.
Although it may be acceptable for a clarity criterion not to be met in the turbidity maximum
zone, high chlorophyll levels in poorly flushed embayments may be hard to justify as
exceptions. Also, if these areas of natural violation are delineated by the Water Quality
Model, some assurance must be made that model results from a "natural" scenario are not
over-stepping the bounds of the model calibration.

We have no comments on the designated uses and dissolved oxygen criteria documents at
this time.

Response: Thank you!

From LRSC (Aug 1, 2001)

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Please note: no responses were given to the below as they were not actual comments

received.

Issues for the ad hoc task members to consider should include the following:

56. Look at the designated uses to see that they collectively will provide levels of protection to
Bay living resources,

57. Investigate the probabilistic approach to linking monitoring data to short-term DO
variations, and

58. How do you use probabilities of compliance or non-compliance in a regulatory or policy
mode?

59. There are several issues related to the designated uses that may need further clarification.
Currently, boundary delineation between the open/deep/deep channel are largely determined
by measuring depths of the upper and lower boundaries of the pycnocline. For example,
deep water designated use are waters located"..between the measured depths of the upper
and lower boundaries of the pycnocline in areas where a measured pycnocline is present and
represents a barrier to oxygen replenishment." Unfortunately, this approach lacks any
quantitative metric.

One option may be to use the degree of stratification present in the water column. As
written, the deep channel are ".. .waters at depths below the measured lower boundary of the
pycnocline over and within isolated deep channels. In the mainstem, the deep channel
designated use habitat is located along the deep central trough running north-south." Is this
sufficient, or are some predetermined depths needed? For example, Chesapeake Bay is a
shallow estuary with a mean depth of just 8.4 meters. The modern bay formed when the
post-glacial sea level rise flooded the paleo-Susquehanna River. Today, a deep trench with
depths to 50 m runs along the center of the mainstem. In order to protect aquatic organisms,
should the open water delineation be based on the presence or absence of a pycnocline or on
mean depth?

60. In the 1992 document, the Dissolved Oxygen Goals for Restoring Living Resource Habitats
in Chesapeake Bay used a sliding scale of impairment as a way to evaluate model scenarios
(acceptable, marginal and unacceptable habitat based on percent compliance). Numbers 2
and 3 are essential parts of the process that have hardly been touched by the criteria work
group. It is doubtful that 100% compliance is neither measurable nor attainable in the real
world. Therefore, do we need to consider some type of probabilistic approach similar to

that accomplished in 1992?

61. How does one go about assessing and implementing a "minimum 1 day instantaneous"
metric? For example, dissolved oxygen measurements are taken as a vertical profile every
meter. What happens when the "minimum 1 day instantaneous" value is exceeded in the
last 5 depths. Does this count as a single violation or five separate violations? Do we need

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some qualitative metric (as proposed above) to measure compliance or non-compliance in a
regulatory or policy mode?

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