Estimation of carbon sinks in chemical weathering in a humid subtropical mountainous basin

The fluvial geochemistry of the mainstream and tributaries of the Zengjiang River was investigated, and the mass balance approach and deduction methods were used to estimate the uptake of atmospheric CO(2) through rock chemical weathering. The results showed that the chemical runoff mainly consisted of HCO(3) (-), Ca(2+), Na(+), and dissolved Si, and that silicate mineral weathering was significant, but carbonate mineral weathering was a minor source of dissolved loads in the Zengjiang River basin because of the low amount of interlayered carbonate rock strata in the catchment. The ion composition indicated that atmospheric CO(2) was the primary erosive agent for rock chemical weathering in the Zengjiang River basin. The CO(2) consumption fluxes caused by rock chemical weathering were (3.50-3.81) x 10(5) mol km(-2) a(-1), which is just lower than that in tropical and subtropical basalt and carbonate regions, and is much higher than that in temperate and cold-temperate regions, indicating that surficial chemical weathering processes in the humid and hot monsoon current influencing the low-middle latitude zone of the Northern Hemisphere constitutes a significant carbon sink in the global biogeochemical cycle.