83 
be ‘healthy,’ i.e., that demonstrably support growth and reproduction of the living 
resources targeted for protection by these criteria. 
The biological reference levels are, by definition, based on ambient dissolved 
oxygen conditions exhibited by areas supporting high functioning living resources. 
Even if this definition were abandoned in favor of a curve or curves based on specific 
natural impairments, then the Mattaponi and Pamunkey segments would have to 
serve as their own reference sites, which is difficult to rationalize. In the absence of 
sufficient data necessary to generate a biological reference curve, EPA recommends 
application of a normal distribution curve representing approximately 10 percent 
allowable criteria exceedence (U.S. EPA 2003a). 
LITERATURE CITED 
Anderson, I. C., C. R. Tobias, B. B. Neikirk and R. L. Wetzel. 1997. Development of a 
process-based mass balance model for a Virginia Spartina alterniflora salt marsh: Implica¬ 
tions for net DIN flux. Marine Ecology Progress Series 159:13-27. 
Cai, W. J., L. R. Pomeroy, M. A. Moran and Y. Wang. 1999. Oxygen and carbon dioxide mass 
balance for the estuarine-intertidal marsh complex of five rivers in the southeastern U.S. 
Limnology' and Oceanography 44:639-649. 
Neubauer, S. C., I. C. Anderson, J. A. Constantine and S. A. Kuehl. 2001. Sediment deposi¬ 
tion and accretion in a mid-Atlantic (U.S.A.) tidal freshwater marsh. Estuarine Coastal and 
Shelf Science. 54:713-727. 
Neubauer, S. C., W. D. Miller and I. C. Anderson. 2000. Atmospheric C0 2 evasion, dissolved 
inorganic carbon production and net heterotrophy in the York River estuary. Limnology and 
Oceanography. 45:1701-1717. 
Neubauer, Scott. June 6, 2003 and June 19, 2003. Personal communication. Smithsonian 
Institute Environmental Research Center, Edgewater, Maryland. 
Tobias, C.R., EC. Anderson, E.A. Canuel, and S.A. Mako. 2001. Nutrient cycling through a 
fringing marsh—aquifer ecotone. Marine Ecology Progress Series. 210:25-39. 
U.S. EPA. 2003a. Ambient Water Quality' for Dissolved Oxygen, Water Clarity / and Chloro¬ 
phyll a for the Chesapeake Bay and Its Tidal Tributaries. EPA 903-R-03-002. Region III 
Chesapeake Bay Program Office, Annapolis, Maryland. 
U.S. EPA. 2003b. Technical Support Documentation for Identification of Chesapeake Bay 
Designated Uses and Attainability'. EPA 903-R-03-004. Region III Chesapeake Bay Program 
Office, Annapolis, Maryland. 
chapter vi 
Guidance for Deriving Site Specific Dissolved Oxygen Criteria 
