Determination of the Sulfate-removing Ability of Freshwater Sediments by a Convenient Method based on the HPLC Analysis of Sulfate

Abstract

To estimate the sulfate-removing ability of a freshwater pond, sulfate-reducing activities were measured in sediments of the pond by a convenient method based on the HPLC analysis of sulfate. In this method, samples suspended with an assay solution were anaerobically incubated, and rates of sulfate reduction (μmol of sulfate reduced/hr) were determined by monitoring sulfate concentrations in assay mixtures. During anaerobic incubation of assay solution inoculated with pure cultures of sulfatereducing bacteria, sulfate reduction proceeded at constant rates until the sulfateconcentration decreased to about 70, μM. The rate of sulfate reduction was propor tional to the inoculum size of sulfate-reducing bacteria. The threshold value of sulfate concentration and the activation energy for sulfate reduction were about 20 μM and 20 kcal, respectively. The sulfate-reducing activity and the density of sulfate-reducing bacteria were determined in sediment layers sampled from the pond. In all layers of the sediment down to 35 cm depth, sulfate-reducing activities (umol/h/cm³ of sediment sample) were detected in the range of 4.5-32.1 at 30°c, and sulfate-reducing bacteria were enumerated at the densities of 10⁴ CFU/cm³ level. In this pond, the sulfateremoving ability was estimated to exceed 46 mmol/m²/day in summer.