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3. Determine a fixed or multivariate compensation factor to ‘adjust’ (upward) the 
observed dissolved oxygen concentration values. The adjusted values would be 
substituted for observed values in the criteria attainment assessment protocol used 
for all affected designated uses, i.e., comparing the cumulative frequency distri¬ 
bution curve of observed values to the biological reference curve. 
4. Derive a set of site-specific dissolved oxygen criteria values that factor in the 
natural dissolved oxygen deficit. 
The first approach—a completely new designated use—was rejected because the 
species and habitat requirements of those species that should be protected in these 
tidal wetland dominated segments are the same species that occupy other open-water 
designated use tidal water segments of similar salinity regimes. The assumption is 
that in these areas, the species’ dissolved oxygen requirements are the same but that 
they may modify their behavior, utilize the area differently or otherwise make 
accommodation for the natural effect of the tidal wetlands on ambient dissolved 
oxygen concentrations with some level of adverse effects. 
The second approach—developing a separate biological reference curve—was 
rejected because the biological reference levels are, by definition, based on ambient 
dissolved oxygen conditions exhibited by areas supporting high functioning living 
resources. Even if this definition were abandoned in favor of a curve or curves based 
on specific natural impairments, then the Mattaponi and Pamunkey segments would 
have to serve as their own reference sites since there are no other comparable 
segments within the Chesapeake Bay system. Taking this approach to deriving 
biological reference curves was difficult to rationalize. 
The third approach—to find an appropriate adjustment factor for observed concen¬ 
trations—was rejected because of concerns that the criteria, not the attainment 
procedures, should directly reflect the natural dissolved oxygen deficits caused by 
extensive tidal wetlands. 
The fourth option—derive a set of set specific dissolved oxygen criteria values—was 
recommended as the best approach to factor in the natural wetlands-caused dissolved 
oxygen deficit directly for the reasons and technical basis documented below. 
DERIVATION OF SITE-SPECIFIC DISSOLVED OXYGEN 
CRITERIA FACTORING IN NATURAL WETLAND-CAUSED 
DISSOLVED OXYGEN DEFICITS 
Through evaluation of three independent sources of information—scientific findings 
published in the peer reviewed literature, Chesapeake Bay water quality model simu¬ 
lations, and the long-term Chesapeake Bay Water Quality Monitoring Program data 
record—efforts were made to quantify the deficit in dissolved oxygen concentrations 
below oxygen saturation levels due to natural tidal wetland processes. Once 
quantified, the wetland-caused oxygen deficits could then be subtracted from 
chapter vi 
Guidance for Deriving Site Specific Dissolved Oxygen Criteria 
