Sources of sulfur in Deccan Trap rivers: A reconnaissance isotope study

Sulfur isotopic composition (delta S-34) of dissolved SO42- was measured in waters of rivers draining the Deccan Trap basalts in order to elucidate the source(s) of elevated SO42- content in some of these rivers, observed in an earlier study. The delta S-34 values range from 8.7 parts per thousand. to 19.5 parts per thousand, with an average of 14.5 +/- 2.8 parts per thousand, values generally enriched in S-34 compared to data available from other Indian rivers. The Bhima River (a tributary of the Krishna) and most of its tributaries have (delta S-34 within the 14 +/- 2 parts per thousand range and high dissolved SO42- concentrations (256-1556 mu M). Measured delta S-34 of 7 of the saline/alkaline soils suggest that the high dissolved SO42- in the Bhima river system is likely derived from this source and/or gypsum concretions in the soils. The (delta S-34-SO4 relationship for the Krishna River and its smaller tributaries follows a mixing pattern of two end-members, rainwater with low SO42- and low delta S-34 and an unknown, likely a pollution, source with intermediate SO42- content and heavy delta S-34. The most important finding that this study brings out is the minimal role that the weathering of basalt-sulfides play in contributing to the dissolved SO42- in the rivers. This rules out the role of H2SO4-, and supports H2CO3-mediated weathering as the dominant process in the Deccan settings. (C) 2010 Elsevier Ltd. All rights reserved.