Major ion geochemistry of the Nansihu Lake basin rivers, North China: chemical weathering and anthropogenic load under intensive industrialization

Abstract

To explore the chemical weathering processes and the anthropogenic disturbance of weathering, 20 water samples were collected from the tributaries in the Nansihu Lake basin, a growing industrial area. The major ions in river waters were analyzed to identify and quantify the contributions of the different reservoirs. Based on stoichiometric analyses and end-member determination, the contributions of individual reservoirs were calculated for each tributary. In the study region, the averaged contributions of atmospheric inputs, anthropogenic inputs, evaporite weathering, carbonate weathering and silicate weathering were 2, 37, 28, 25 and 8 %, respectively. Combined with information regarding runoff and drainage area, the annual average contribution of TDS to waters was estimated to be 1.90 ± 0.95 ton/km2 from silicate weathering, 5.68 ± 2.84 ton/km2 from carbonate weathering. Furthermore, the associated consumption of CO2 was calculated to be approximately 7.50 × 109 mol/a. The industrial and mining activities were the main sources for anthropogenic inputs, and they produced non-CO2 acids (NCA). Of all protons involved in chemical weathering, 34 % was presumed to be originated from NCA, causing 2.74 × 109 mol/a of CO2 degassing. Moreover, industrial inputs could play a major role in the modification of the chemicals in the water system, and they could even change the carbonate weathering rate in such an intensively industrializing region. In North China, the chemical weathering associated with NCA was found to be significant for the first time.