INORGANIC SULFUR CYCLING IN MID AND LOWER CHESAPEAKE BAY SEDIMENTS

Concentrations of dissolved and solid-phase inorganic sulfur compounds and sulfate reduction (SR) rates were measured in sediments along a lateral transect in the mesohaline region of the Chesapeake Bay estuary (USA). Areal SR rates varied seasonally from 2 to 10, 5 to 60, and 10 to 90 mmol m-2 d-1 in deep channel, channel slope and western flank sediments respectively, and with temperature according to an apparent activation energy of ca 83 kJ mol-1. March through November integrated SR rates were 1.3, 5.3 and 7.3 mol m-2 yr-1 at the 3 locations respectively. Summer SR rates in other mid-bay central channel and lower bay sediments were comparable to the highest rates found along the mid-bay transect. Sulfate reduction was maximal in the top 2 to 4 cm (0.2 to 2 mmol l-1 d-1) of sediment and decreased several-fold with depth to 12 cm in both mid- and lower bay sediments. Mid-bay central channel sediments underlying anoxic bottom water during the summer exhibited high concentrations (1 to 5 mM) of dissolved sulfide (DS), whereas bioturbated flank sediments had 5- to 10-fold lower DS concentrations (0.1 to 1 mM). In lower bay sediments, DS concentrations were < 0.1 mM in the upper 12 cm despite intense SR (25 to 100 mmol m-2 d-1). Solid phase reduced sulfur concentrations in mid- and lower bay sediments were not correlated with SR rates. Comparison of annual SR with reduced sulf ur burial indicated that < 30 % of total sulfide production is permanently retained in mid-bay sediments. A similar fraction of sulfide retention is expected to occur in lower bay sediments. Our results indicate that sulfur cycling accounts for a substantial portion of carbon mineralization and oxygen consumption over a large area of the mid- and lower Chesapeake Bay benthos.