Comparisons on the effects of temperature, runoff, and land-cover on carbonate weathering in different karst catchments: insights into the future global carbon cycle

Abstract

This study compares and analyzes high-frequency hydrochemical data from three karst catchments in the mountainous Gadenalpe (GAC, Austrian Alps), Tsanfleuron-Sanetsch (TSC, Swiss Alps), and Banzhai (BZC, SW China) regions, to differentiate the effects of temperature, runoff, and land-cover on carbonate weathering. The results show that when bare rock dominates in the recharge area, as in the GAC and TSC, the seasonal discharge variations account for the most significant change in HCO3− concentration. In these two alpine catchments, maximum HCO3− concentrations occurred in the cold season when the areas were covered by snow and discharge was low, whereas minimum HCO3− concentrations occurred in the warm season, when snowmelt and/or glacier melt caused higher discharge and dilution. In contrast, control by the strong seasonal variation in soil respiration in the subtropical catchment (BZC), caused by the well-developed forest cover, exceeded the negative impact of temperature on carbonate weathering. This led to higher HCO3− concentrations during the summer growing season than in the winter dormant season. This study demonstrates that the occurrence of different soils/vegetation has a profound impact on the behavior of carbonate weathering on land, from negative temperature- and discharge-driven correlations in alpine catchments to positive soil CO2-driven correlation in subtropical catchments. Based on the equilibrium modeling of HCO3− concentration for a global temperature range, it is predicted that under future global warming, karst regions in cold climates with vegetation cover will have increasing CO2 consumption potential, whereas karst regions in warm climates will have decreasing CO2 consumption potential.