Hydrochemical characteristics and estimation of the dissolved inorganic carbon flux in the Donghe River Basin of western Hunan

In order to examine the hydrochemical characteristics and quantify the contribution of petrochemical weathering processes to the absorption of atmospheric CO2, this paper selects the Donghe River Basin in western Hunan as the study area, and 32 water samples from July, 2016 to August, 2016 were collected and analyzed. The results show that the river water has the pH value of 8.31 and is slightly alkaline. The variation ranges of EC and TDS are large, which are mainly related to the distribution of lithology in the basin. The ions in water are dominated by Ca2+ and HCO-3 and the hydrochemical type is HCO3-Ca type. The hydrochemical compositions of the water samples are affected by lithology. HCO-3, Ca2+ and Mg2+ are mainly derived from the weathering of carbonate rocks, and sources of the other ions are affected by human activities. In the main ions of the water in the Donghe River Basin, HCO-3, Ca2+ and Mg2+ show a decreasing trend from upstream to downstream, reflecting that rivers flow from carbonate rocks to clastic rocks. The growth trend of NO-3, K+, Na+, F-, Cl-and SO2-4 shows that the influence of artificial pollution on the Donghe River is significant and can reflect the intensity of human activities. It is found from the subbasin investigation that hydrochemistry of the upper reaches of the basin is mainly controlled by limestone and dolomite, the middle reaches, by limestone, and the lower reaches, by sandstone, mudstone and other clastic rocks. The observed data of a hydrological year at the Jishou observation station was collected and the hydrochemical-runoff method is used to estimate the amount of inorganic carbon flux in the Donghe River Basin as 60477.33 tCO2/a and the carbon sink intensity as 71.15 tCO2/(km2·a).