Sulfate Reduction in Freshwater Wetland Soils and the Effects of Sulfate and Substrate Loading

Elevated sulfate and organic C loadings in freshwater wetlands could stimulate dissimilatory sulfate reduction that oxidizes organic C, produces hydrogen sulfide and alkalinity, and sequesters trace metals. We determined the extent of sulfate reduction in two freshwater wetland soils, that is, black gum ( Nyssa biflona ) swamp soils and titi ( Cliftonia monophylla ) swamp soils, in northern Florida. We also investigated the potential of sulfate reduction in the wetland soils by adding sulfate, organic substrate, and lime. Sulfate reduction was found to be an active process in both swamp soils without any amendment, where the pore 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 through sulfate reduction in the swamp soils. Sulfate loading, liming, and substrate addition significantly increased sulfate reduction in the black gum swamp soil, but none of those treatments increase sulfate reduction in the titi swamp soil. The limiting factor for sulfate reduction in the titi swamp soil were likely texture and soil aggregate related properties. The results suggested that wastewater loading may increase sulfate reduction in some freshwater wetlands such as the black swamps while it has no stimulating effect on other wetlands such as the titi swamps.