BIOGEOCHEMICAL TRANSFORMATIONS OF SULPHUR IN THE SALINE LAKES OF TRANSBAIKALIA

Biogeochemical transformations of sulphur in the saline lakes of southeastern Transbaikalia have been studied. Quantitative measurements show that hydrogen sulphide is present in the water and bottom sediments of most of the lakes studied. In addition to hydrogen sulphide, the presence of sulphate, thiosulphate, and elemental sulphur was detected in the water column, while sulphate and elemental sulphur were found in the bottom sediments. It was established that elemental sulphur exists in the lakes primarily in the form of suspension and colloids, as well as polysulphidic sulphur, the amount of which increases with increasing water pH. It is concluded from the isotopic ratios of sulphur for sulphate, hydrosulphide ions, and elemental sulphur that sulphur in the studied natural systems is controlled by biological and geochemical processes. One of the processes controlling the behaviour of sulphate ions in the lakes is sulphate reduction, which leads to the enrichment of sulphate sulphur and depletion of sulphur in hydrogen sulphide with the 34S isotope. It is shown that oxidation of reduced sulphur in the lakes proceeds with the participation of oxygen, iron, manganese, as well as various bacteria. The presence of an additional source of sulphur and/or absence of sulphur reduction causes 32S accumulation in sulphate ions. It is determined that the loss of sulphate ions due to their bacterial reduction in bottom sediments is most pronounced in the chloride and soda lakes of the I and III subtypes. In the sulphate and soda lakes of the II subtype, an increase in the amount of sulphate ions was detected.