Geochemistry of the dissolved load of the Changjiang Basin rivers: Anthropogenic impacts and chemical weathering

Abstract

This study focuses on the chemical and Sr isotopic compositions of the dissolved load of the rivers of the Changjiang Basin, one of the largest riverine systems in the world. Water samples were collected in August 2006 from the main tributaries and the main Changjiang channel. The chemical and isotopic analyses indicated that four major reservoirs (carbonates, silicates, evaporites and agriculture/urban effluents) contribute to the total dissolved solutes. The overall chemical weathering (carbonate and silicate) rate for the Changjiang is approximately 40 ton/km 2/year or 19 mm/kyr, similar to that of the Ganges–Brahmaputra system, and the basin is characterized by carbonate and silicate weathering rates ranging from 17 to 56 ton/km 2/year and from 0.7 to 7.1 ton/km 2/year, respectively. In the lower reach of the Changjiang main channel, the weathering rates are estimated to be 36 and 2.2 ton/km 2/year for carbonates and silicates, respectively. It appears that sulphuric acid may dominate chemical weathering reactions for some sub-basins. The budgets of CO 2 consumption are estimated to be 646 × 10 9 and 191 × 10 9 mol/year by carbonate and silicate weathering, respectively. The contribution of the anthropogenic inputs to the cationic TDS of the Changjiang is estimated to be 15–20% for the most downstream stations. Our study suggested that the Changjiang is strongly impacted by human activities and is very sensitive to the change of land use.