干旱区生态环境知识资源中心

The chemical and strontium isotopic compositions of four major rivers (Heihe, Shule, Beida, and Shiyang) around the Badain Jaran Desert, northwestern China, were measured to understand the solute sources of surface water and rock weathering in the arid region. These rivers have high total cationic charge (TZ(+)) and total dissolved solids (TDS), averaging at 7379 mu Eq and 511 mg l(-1), which are significantly higher than the global river average. The increase in TDS and major ions (Na+, Cl-, and SO42-) and TDS concentrations from upper to lower reaches is ascribed to the evaporite dissolution and the effect of evaporation in the arid and semiarid areas. Sr-87/Sr-86 isotopic ratios of these rivers range between 0.71019 and 0.71628, with an average of 0.71328. The chemical and Sr-87/Sr-86 isotopic analyses indicate that three reservoirs (evaporites, carbonates, and silicates) contribute to the total dissolved loads. The contributions of the different reservoirs to the dissolved load are first calculated using a forward method in this area. The calculated results show that the dissolved cation load is dominated by carbonates weathering and evaporites dissolution, and their contribution account for about 80 % of the total dissolved cations for the rivers around the Badain Jaran Desert. The proportion of the dissolved cations from silicates weathering is 23.5, 10.8, 12.1, and 18.2 %, and the weathering rate of silicates is 0.81, 0.76, 2.04, and 0.93 ton km(-2) a(-1) for Heihe, Shule, Beida, and Shiyang, respectively.