Discharge and temperature effects on weathering fluxes in alpine and perialpine basins in Switzerland

Chemical weathering exerts a key control on atmospheric CO2 and hence on Earth's temperature. Knowledge of the influence of discharge and temperature on weathering product loads and fluxes through rivers is important to evaluate the possible influence of climate change on weathering. The role of hydrology on such loads and fluxes is clear, but the effect of temperature is difficult to investigate, particularly in big rivers. We use long term (1974-2015) measurements of hydrological and chemical parameters in 20 Swiss stations in large, median-sized, and small rivers. This is to calculate the effect of discharge and temperature on annual loads in each station and in mean fluxes of silicic acid (SA) and calcium linked to carbonate (Ca-car) considering all 20 stations together. SA and Ca-car loads are good proxies of carbonate and silicate weathering. Mean annual loads of SA and Ca-car depend mostly on discharge. They decrease with temperature when the dependence is evaluated by univariate linear regression. Multiple linear regression analysis, however, reveals that the real influence of temperature, when taking into account discharge, is positive in several cases for SA and is mostly non-significant for Ca-car. Runoff and lithology are the main positive factors on SA fluxes, whereas temperature is the main positive factor in Ca-car fluxes. In both cases, the fraction of impounded water in the catchment is the main negative influence. No significant temporal trend in loads are detected in 18 out of the 20 stations despite the general increase of water temperature, which is consistent with the small effect of temperature on loads found in the present work.

Automated summary

Chemical weathering plays a crucial role in atmospheric CO2 and Earth's temperature. Understanding the influence of discharge and temperature on weathering product loads is important for assessing the impact of climate change. By analyzing long-term measurements in Swiss rivers, it is found that discharge has a significant impact on the loads of silicic acid and calcium linked to carbonate, while the effect of temperature is relatively small.