SULFATE REDUCTION IN FRESH-WATER WETLAND SOILS AND THE EFFECTS OF SULFATE AND SUBSTRATE LOADING

Elevated sulfate and organic C loadings in freshwater wetlands could s timulate dissimilatory sulfate reduction that oxidizes organic C, prod uces hydrogen sulfide and alkalinity, and sequesters trace metals. We determined the extent of sulfate reduction in two freshwater wetland s oils, that is, black gum (Nyssa biflona) swamp soils and titi (Clifton ia monophylla) swamp soils, in northern Florida. We also investigated the potential of sulfate reduction in the wetland soils by adding sulf ate, organic substrate, and lime. Sulfate reduction was found to be an active process in both swamp soils without any amendment, where the p ore water pH was as low as 3.6 and sulfate concentration was as low as 5 mg L-1, Without amendment, 11 to 14% of organic C was oxidized thro ugh sulfate reduction in the swamp soils. Sulfate loading, liming, and substrate addition significantly increased sulfate reduction in the b lack gum swamp soil but none of those treatments increase sulfate redu ction in the titi swamp soil. The limiting factor for sulfate reductio n in the titi swamp soil were likely texture and soil aggregate relate d properties, The results suggested that wastewater loading may increa se sulfate reduction in some freshwater wetlands such as the black swa mps while it has no stimulating effect on other wetlands such as the t iti swamps.