chapter \/i 
Guidance for Deriving Site 
Specific Dissolved Oxygen 
Criteria for Assessing Criteria 
Attainment of Naturally Low 
Dissolved Oxygen 
Concentrations in Tidal Wetland 
Influenced Estuarine Systems 
Tidal wetlands are a valuable component of estuarine systems. In the Pamunkey 
River, they have been shown to be net sinks for sediments (Neubauer et al. 2001) and 
in most cases also serve to remove nutrients from overlying water (Anderson et al. 
1997). High rates of organic production, accompanied by high rates of respiration 
(Neubauer et al. 2000), can significantly reduce dissolved oxygen and enhance 
dissolved inorganic carbon levels both in sediment pore water and overlying water 
in wetland systems. Another process that can deplete dissolved oxygen in wetland 
sediments is nitrification, which converts ammonium to nitrite and nitrate (Tobias et 
al. 2001). 
Subsequent to publication of Ambient Water Quality' for Dissolved Oxygen, Water 
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries (U.S. 
EPA 2003a), Virginia, Maryland, Delaware and the District of Columbia initiated 
their respective processes for adopting new and/or revising existing state water 
quality standards. In so doing, Virginia requested support and guidance from EPA in 
determining the appropriate dissolved oxygen criteria/designated use/attainment 
procedures for the tidal Mattaponi and Pamunkey rivers for addressing the naturally 
lower ambient dissolved oxygen concentrations. Based on the scientific literature 
and personal communications with Chesapeake Bay wetland scientists, EPA recog¬ 
nized the need to explore accommodations for the special circumstances in these 
tidal wetland influenced estuarine systems with respect to criteria levels, designated 
uses and/or criteria attainment assessment. 
chapter vi 
Guidance for Deriving Site Specific Dissolved Oxygen Criteria 
