Silicate weathering rate and its controlling factors: A study from small granitic watersheds in the Jiuhua Mountains

Silicate weathering is intimately linked to global climate. To investigate the controlling factors of silicate weathering rate, we collected monthly or half-monthly river water samples from ten small granitic watersheds in the Jiuhua Mountains. Mass balance calculation shows that agricultural activity, atmospheric input, silicate weathering, carbonate weathering and evaporite dissolution contribute 2.0%, 16.9%, 58.7%, 13.5% and 8.9% cations to the river water, respectively. The disproportionate contribution of carbonate rocks with an exposed area of < 5% demonstrates the importance of trace carbonate minerals in these small granitic watersheds. The average silicate weathering and CO2 consumption rates at our sites are 7.0 t km(-2) y(-1) and 3.4 x 10(5) mol km(-2) y(-1), respectively. There is no correlation between silicate weathering rates (SWR) and the suspended solid concentrations (an index of physical erosion rate), but there is a strong positive correlation between SWR and temperature, consistent with the kinetic-limited chemical weathering regime in alpine areas. A compilation of literature data from global small granitic watersheds in different climatic zones shows positive correlations between temperature, runoff and SWR. A multiple linear regression between SWR, temperature and runoff yielded an adjusted R-squared of 0.61, showing that climatic factors can account for 61% of the variation in SWR. In addition, for catchments where the elevation difference between the highest point of the headwater and sampling point (an approximate topographical parameter) exceeds 400 m, the R-squared value obtained from the temperature and SWR regression analysis is significantly increased, indicating that temperature is likely the most important factor controlling silicate weathering in the alpine region where a kinetic-limited regime dominates.