Chemical weathering and CO_2 consumption of a high-erosion-rate karstic river: a case study of the Sanchahe River, southwest China

The Sanchahe River in southwest China is a tributary of the Wujiang River and experiences high erosion rates. Geochemical analysis was conducted on Sanchahe River basin samples collected in the wet and dry seasons of 2014 in order to better understand local chemical weathering processes, anthropogenic influences, and associated CO2 consumption. The samples' total dissolved solid concentrations were found to be significantly higher than that of the global river average. Ca2+was the dominant cation in the samples and accounted for 64 % and73 % of the total cations in the dry and wet seasons,respectively. HCO3-and SO42-were the dominant anions,accounting for 92 % of the total anions. Stoichiometry analyses of the river waters suggested that the water chemistry is controlled by carbonate dissolution by both carbonic and sulfuric acid. The chemical weathering rates of carbonate and silicate evaporites in the Sanchahe River basin were estimated to be approximately 109.2 and 11.0 t/(km2a), respectively, much higher than both the global mean values and the Wujiang River, a typical karstic river.The CO2 consumption by carbonate and silicate weathering are estimated to be 597.4 9 103 and 325.5 9 103mol/(km2a), which are much higher than corresponding values in the Wujiang River, indicating a high erosion rate in the Sanchahe River basin.