CONTROLS ON THE MAJOR ION CHEMISTRY OF THE URUMQI-RIVER, TIAN-SHAN, PEOPLES-REPUBLIC-OF-CHINA

Water and snow samples were collected in May of 1990 and 1992 in headwater basins and along a longitudinal transect of the Urumqi River, located in northwestern China. Surface waters were dominated by Ca2+ and HCO3- at all sites. Maximum measured SO42- concentrations in surface waters were 550 mu eq L(-1), and were balanced by Ca2+ and HCO3-; pH was slightly alkaline at all locations, Several independent analyses each concluded that the solute composition of surface waters was dominated by dissolution of rocks with rapid weathering kinetics, such as calcite and dolomite, Preliminary analysis of stable sulfur ratios in headwater basins shows delta(34)S values of +6.8 for snow and +3.3 for surface waters. Changes in the delta(34)S value of surface waters with increasing basin area were variable, suggesting changes in the stable sulfur ratios of source materials. The large amounts of HCO3- and base cations at all sites indicates that the Urumqi River is not sensitive to acidification from atmospheric deposition.