NATURAL CONDITIONS/FEATURES INDICATING 
ROLE OF WETLANDS IN LOW DISSOLVED 
OXYGEN CONCENTRATIONS 
A future objective is to define more fully the natural conditions and physical features 
in Chesapeake Bay tidal systems that would indicate that tidal wetlands are playing 
a significant role in naturally reducing ambient dissolved oxygen concentrations. 
Those natural conditions/features have not yet been firmly established but Tables 
VI-1 and VI-2 provide some key physical and water quality statistics for the tidal 
Mattaponi and Pamunkey rivers. Appendix A provides similar data for other tidal 
fresh and oligohaline regions in the Chesapeake Bay and its tidal tributaries for 
comparison. Four natural conditions/features have been evaluated here to document 
and help quantify the influence of tidal wetlands on the dissolved oxygen deficit 
observed in the tidal Mattaponi and Pamunkey rivers. 
SURFACE TO VOLUME RATIOS/LARGE FRINGING WETLAND AREAS 
The tidal fresh and oligohaline segments in the Mattaponi and Pamunkey rivers are 
among the smallest volume, with a small surface to volume ratio and large areas of 
fringing tidal marsh—1.5 times larger than the tidal surface water area—relative to 
other segments throughout the Bay’s tidal waters (Table VI-1; Appendix A, Table A-l). 
WATER QUALITY CONDITIONS 
Table VI-2 gives some water quality statistics for recent years. These years happen 
to have had dry to record-dry summers and that low flow regime should be borne in 
mind. Severe low dissolved oxygen conditions (concentrations < 3 mg liter 1 ) are not 
obvious, but average dissolved oxygen concentrations, in both surface and bottom 
waters, are about 2.5 to 3 mg liter' 1 below calculated oxygen saturation levels (Table 
VI-2). Chlorophyll a concentrations are comparatively low, as are the total nitrogen 
concentrations (with the exception of the oligohaline Pamunkey River segment 
PMKOH). Phosphorus concentrations range from mid to high compared to other 
tidal systems. 
The dissolved oxygen deficit in these two tidal systems is among the highest 
observed in the Chesapeake Bay’s tidal tributaries. The dissolved oxygen deficits 
observed in the recent dry years (Table VI-2) are similar to those observed over the 
1985-2002 Chesapeake Bay water quality monitoring program data record (Figure 
VI-1). These findings indicate that the processes driving the recorded dissolved 
oxygen deficits are due largely to natural processes internal to the tidal system and 
not as much to external nonpoint nutrient loadings (which are naturally reduced 
during the recent dry years due to decreased surface runoff). 
chapter vi 
Guidance for Deriving Site Specific Dissolved Oxygen Criteria 
