New estimate of chemical weathering rate in Xijiang River Basin based on multi-model.

Hydrochemistry and Sr isotope compositions were measured in water samples collected during high- and low-water periods from the main stream and tributaries of the Xijiang River Basin in southern China. The primary weathering end-members were analyzed and calculated using the multi-model combination and classic hydrogeochemical method. During the high-water period, structural factors were found to be the main factors controlling chemical weathering in the basin, whereas anthropogenic activity and other random factors had a negligible influence. During the low-water period, both structural and random factors controlled chemical weathering. Through path-model and semi-variance analyses, we determined and quantified the relationship between the main weathering sources, whose results were stable; this is consistent with the inversion model. The total dissolved substances were mainly derived from carbonate weathering, which was approximately 76% (0-96%) while silicate weathering accounted for only 14% (5-19%). The inversion model results showed that the optimum silicate weathering rate was 7.264-35.551 × 103 mol/km2/year, where carbonic acid was the main factor that induces weathering. The CO2 flux consumed by rock weathering in the basin during the study period was 150.69 × 109 mol/year, while the CO2 flux consumed by carbonic acid weathering of carbonate (CCW) and silicate rocks (CSW) was 144.47 and 29.45 × 109 mol/year, respectively. The CO2 flux produced by H2SO4 weathered carbonate (SCW) was 23.23 × 109 mol/year.