MEPS 260:55-70 (2003)  -  doi:10.3354/meps260055

Benthic sulfate reduction along the Chesapeake Bay central channel. II. Temporal controls

M. C. Marvin-DiPasquale1,*, W. R. Boynton2, D. G. Capone3

1Water Resource Division, US Geological Survey, MS 480, 345 Middlefield Road, Menlo Park, California 94025, USA
2Chesapeake Biological Laboratory, Center for Environmental Science, University of Maryland, 1 Williams St., Solomons, Maryland 20688, USA
3Department of Biological Sciences, University of Southern California, AHF107, Los Angeles, California 90089-0371, USA

ABSTRACT: Seasonal and interannual controls of benthic sulfate reduction (SR) were examined at 3 sites (upper [UB], mid- [MB] and lower [LB] bay) along the Chesapeake Bay central channel, from early spring through fall, for 6 yr (1989 to 1994). The combined influences of temperature, sulfate, organic loading and bioturbation affected seasonal SR rates differently in the 3 regions. Consistently low SR rates at UB resulted from low overlying-water sulfate concentrations and the dominance of refractory organic terrestrial material. Combined seasonal variation in temperature and sulfate accounted for 50% of the annual variability in 0 to 2 cm depth interval SR rates, while sediment organic content had no significant seasonal influence. In contrast, MB and LB sites had high rates of SR fostered by high levels of overlying water SO42- and organic input dominated by labile phytoplankton detritus. New organic loading (measured as chl a) stimulated 0 to 2 cm SR during spring at both sites. Combined organic quantity (as particulate C and/or N) and temperature accounted for >75% of the variability in 0 to 2 cm SR at MB during spring and fall. Molecular diffusion supplied 25 to 45% of the SO42- needed to fuel 0 to 12 cm depth interval SR at MB, with the balance presumably supplied by S-recycling. Interannual differences in summertime SR rates were linked to the extent of freshwater flow during spring, with high-flow years associated with high SR rates at UB and MB, and low rates at LB. The negative trend between benthic SR and river flow at LB may result from the up-estuary transport of senescing organic matter in bottom water, which increases in the lower reach of the estuary with increasing freshwater inflow.

KEY WORDS: Sulfate reduction · Benthic metabolism · Sediment · Estuary · Chesapeake Bay

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