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The Lake Chany complex and nearby lakes in western Siberia (Russian Federation) were studied to constrain the S cycle in these terrestrial lake environments. Surface water chemistry was characterized by Na-SO(4)-Cl composition, comparable to other inland basins in semi-arid climatic zones associated with marine evaporite-bearing formations at depth. Dissolved sulfates showed elevated delta(34)S (up to +32.3 parts per thousand). These values are quite distinct from those in similar saline lakes in northern Kazakhstan, the Aral Sea, Lake Barhashi, and a gypsum deposit in the Altai Mountains. The localized distribution of such a unique S isotopic signature in dissolved SO(4) negates both aeolian and catastrophic flooding hypotheses previously suggested for the genesis of the dissolved salts. The probable source of the dissolved SO(4) in Lake Chany basin is inherited from hidden saline groundwaters (whose location and origins remain unclear) from eastern Paleozoic ranges with Upper Devonian formations with heavy S isotope values. Post-depositional enrichment of heavy S in the dissolved SO(4) from saline sediments may be caused by local activity Of SO(4)-reducing bacteria under the ambient supply of electron donors (dissolved river load organic matter and decaying bacterial mats) in the lake complex. Such microbial processes can remove up to ca. 60% Of SO(4) from the system. Extensive and intensive evaporation of lake fluids, ca. 40%, was indicated by the progressive enrichment of delta(18)O values in meteoric water samples collected along the river and lake system. This evaporation process compensates the microbial loss Of SO(4) dissolved in the incoming river water. (c) 2008 Elsevier Ltd. All rights reserved.