Effects of added manganic and ferric oxides on sulfate reduction and sulfide oxidation in intertidal sediments

Freshly precipitated iron or manganese oxides were added to surface sediments from a salt marsh and from the intertidal region of Lowes Cove, Maine. In the presence of added manganese, sulfate was formed under anoxic conditions, suggesting a manganese dependent sulfide oxidation. Sulfate formation was not observed with iron additions. Sulfate reduction was substantially but not completely inhibited by either metal oxide, even though both were added at levels well in excess though both were added at levels well in excess of natural concentrations. Manganese-catalysed sulfide oxidation was further documented using a combination of radiolabel, metal oxide, and inhibitor additions, Results from this study suggested that losses of radiolabelled sulfide could result in underestimates of gross sulfate reduction rates in the presence of significant manganic oxide concentrations. In addition, manganic oxides may facilitate the anaerobic regeneration of sulfate from sulfides.