Climatic Variabilities Control the Solute Dynamics of Monsoon Karstic River: Approaches from C-Q Relationship, Isotopes, and Model Analysis in the Liujiang River

摘要

The dynamics of riverine solutes' contents and sources reflect geological, ecological, and climatic information of the draining basin. This study investigated the influence of climatic variability on solute dynamics by the high-frequency hydrogeochemical monitory in the Liujiang River draining karst terrain of Guangxi Province, SW (Southwestern) China. In the study river, the content-discharge (C-Q) patterns of riverine solutes indicate that the majority of riverine solutes show similar dilution and near chemostatic behaviors responding to increasing discharge, especially geogenic solutes (such as weathering products from carbonate, silicate, and sulfide oxidation), whereas exogenous solutes (such as atmospheric input to riverine sulfate) and biological solutes (such as soil CO2) show higher contents with increasing discharge. Besides, the biological carbon is the main driver of the chemostatic behaviors of total dissolved inorganic carbon (DIC). The forward model results show that carbonate weathering dominates the water chemistry, and the weathering rates are intensified during high flow period due to additional inputs of weathering agents, i.e., the biologic carbonic acid from dissolution of soil CO2, indicated by delta C-13(DIC). In addition, there exists the strong capacity of CO2 consumption that is heavily dependent on climatic variables such as precipitation and air temperature in this study river. Our study highlights the impact of climatic variability on solutes dynamics and chemical weathering and thus must be better addressed in C models under future climate change scenarios.