Reduced sulfur compounds in the bottom sediments of meromictic lakes

Abstract

This paper presents data on the content of reduced sulfur compounds in the bottom sediments of two meromictic reservoirs: Mogilnoe Lake (Barents Sea) and Lake Trekhtsvetnoe (White Sea). A distinctive feature of both reservoirs is the high content of hydrogen sulfide in the anaerobic monimolimnion. The total content of reduced sulfur compounds, characterized by the ƩS_H2S parameter, averaged 0.500% for Mogilnoe Lake and 0.994% for Lake Trekhtsvetnoe. The main form of sulfur for both lakes was pyrite (more than 60% for Mogilnoe Lake and up to 80% for Lake Trekhtsvetnoe). Significant amounts of sulfur associated with organic matter were noted in the surface layers. The contents of acid-soluble monosulfides and elemental sulfur were not significantly different (no more than 10% of ƩS_H2S). This distribution of forms in the composition of ƩS_H2S makes the bottom sediments of the studied lakes similar to sea sediments. The high level of accumulation of reduced sulfur compounds in sediments is due to their provision of a sufficient amount of organic matter, which comes mainly from the chemocline zone.