Sulphur, organic carbon and iron relationships in estuarine and freshwater sediments: effects of sedimentation rate

Abstract

Concentrations of S, organic C and Fe were investigated in profiles of sediments from two estuarine systems in the SW of Western Australia. In marine-affected sediments, inorganic S dominates total S and concentrations of total S correlate with Fe and not with organic C. In freshwater sediments, organic S dominates total S and concentrations of total S correlate with organic C and not with Fe. Molar Fe/S ratios in the estuarine sediments decrease with increasing salinity and approach unity for marine conditions. Net accumulation rates of S in sediments were estimated with a numerical computer model, calibrated with published data on profiles of marine sediments for diffusion of SO 2− 4, sedimentation rates and distributions of S. Measured depth-integrated reduction rates of SO 2− 4 in the marine-affected estuarine sediments approach those obtained for Fe-limited marine conditions at similar rates of sedimentation. Measured concentrations of inorganic S in anoxic freshwater sediments fit a numerically calculated relationship between inorganic S and sedimentation rate.