The Bacterial Population and the Processes of Hydrogen Sulphide Oxidation in the Black Sea

Abstract

Methods are described to study the mechanism and rate of sulphide oxidation in water using ³⁵S. These methods were used in the Black Sea together with measurements of O₂, H₂S, Eh, bacterial biomass and production. Sulphide oxidation proceeds via two main steps: chemical oxidation of sulphide to sulphate and thiosulphate, and the biological oxidation of thiosulphate to sulphate. The rate of sulphide oxidation varied from 0·4–0·9 g H₂S/m² day. The maximum rate of oxidation took place at depths of 150–170 m at Eh –10 to –20 mV, and at a maximum rate of chemosynthesis of 8 mg C/m³/day. Data are given for the biomass of the microflora and its production in the water column. The maximum efficiency of chemosynthesis was 15%. The results are discussed in relation to the budget of the organic matter.