calculated oxygen saturation concentrations to determine the natural background 
oxygen levels that could be sustained within these wetland dominated tidal rivers 
absent any external anthropogenic nutrient pollutant loadings. 
SCIENTIFIC RESEARCH-BASED ESTIMATES OF 
WETLAND RESPIRATION 
As part of the analysis to examine dissolved oxygen criteria attainment in the various 
tidal wetland dominated segments, the Chesapeake Bay Water Quality Model was 
calibrated to account for wetland oxygen demand by applying a universal sediment 
oxygen demand of 2 grams 0 2 /meter 2 -day to all Chesapeake Bay tidal wetland areas. 
This value is a best professional judgement based on values published in the scien¬ 
tific literature and communication with Chesapeake Bay wetland scientists 
(Neubauer 2003). The scientific literature indicates wetland sediment oxygen 
demand in Northeastern United States ranges from 1 to 5.3 grams 0 2 /meter 2 -day 
(Neubauer et al. 2000; Cai et al. 1999). 
The value for sediment oxygen demand used in the previous 1998 Chesapeake Bay 
water quality model calibration (2 grams 0 2 /meter 2 -day) was re-examined and deter¬ 
mined to be accurate for the Mattaponi and Pamunkey rivers. Scott Neubauer of the 
Smithsonian Environmental Research Center (personal communication June 19, 
2003) estimates the marsh sediment oxygen consumption for Sweet Hall marsh, a 
freshwater marsh in the Pamunkey River, to range between 0.99-2.59 grams 
0 2 /meter 2 -day. Neubauer’s estimated ranges further support the sediment oxygen 
demand of 2 grams 0 2 /meter 2 -day that was used in the previous model calibration. 
Neubauer also concurred that the Mattaponi and Pamunkey systems are very similar 
(Neubauer 2003). Therefore, there was no need to recalibrate the sediment oxygen 
demand for either tidal tributary. 
MODEL-BASED WETLAND-CAUSED OXYGEN DEFICITS 
The impact of wetland oxygen demand on ambient dissolved oxygen concentrations 
was quantified for both the Mattaponi and Pamunkey segments through application 
of the Chesapeake Bay water quality model. A series of water quality model 
scenarios ‘with wetlands’ and ‘without wetlands’ were run to estimate the difference 
in model-adjusted interpolated monthly averaged dissolved oxygen concentration in 
the Mattaponi and Pamunkey segments. In the ‘with wetlands’ scenario, the water 
quality model simulated the full influence of the extensive adjacent tidal wetlands on 
ambient water quality conditions. In the ‘without wetlands' scenario, the tidal 
wetland functions of the model were turned off in the Mattaponi and Pamunkey 
model cells in order to simulate ambient water quality conditions in the absence of 
any influence by tidal wetlands. The summer monthly averaged dissolved oxygen 
concentration difference simulated by the ‘with wetlands’ scenario minus the 
‘without wetlands’ scenario was 3 mg liter” 1 , i.e., the open-water dissolved oxygen 
concentrations in the Mattaponi and Pamunkey segments with the presence of the 
chapter vi 
Guidance for Deriving Site Specific Dissolved Oxygen Criteria 
