Major element chemistry of the Changjiang (Yangtze River)

The chemistry of major elements (Ca, Mg, Na, K, HCO3, SO4, Cl, and Si) in the river water of the Changjiang (Yangtze River) was studied, based on continuously monitored data at 191 stations in the drainage basin for the period 1958–1990. The results show that the total dissolved solid (TDS) concentration of the Changjiang varies over an order of magnitude throughout the basin (49.7–518.1 mg/l), with a medium TDS concentration of 205.9 mg/l, about three times the global average. In contrast, the TDS at a given main-channel station varies only slightly in different seasons with a variation factor less than 2.0, despite a substantial water dilution in the summer flood season. The major element chemistry of the Changjiang is mainly controlled by rock weathering, with the anion HCO3 and the cation Ca dominating the major ion composition, due to the abundance of carbonate rocks in the basin. A persistently increasing trend has been observed in the concentrations of SO4 and, to a lesser extent, Cl in the Changjiang, a signature of considerable anthropogenic impacts (e.g., acid deposition). Flux calculations at Datong (the most downstream main-channel station without tidal influence) indicate that the Changjiang transports ca. 154×106 tons/year of TDS to the sea, second only to the Amazon in the world.