Unravelling the hydrological effects on spatiotemporal variability of water chemistry in mountainous rivers from Southwest China

Understanding the effects of hydrological processes on solute dynamics is critical to interpret biogeochemical processes. Water chemistry and isotopic compositions of surface water (δ¹⁸O_w and δD_w) were investigated in rivers from Southwest China to study the effects of hydrological variability on biogeochemical processes. The inverse relationship between deuterium excess (d-excess) and δ¹⁸O_w could be ascribed to non-equilibrium fractionation processes, and the slope of the Local River Water Line was much lower than the Local Meteoric Water Line, suggesting the post-precipitation evaporation pattern. The evaporation fraction (1–f) was estimated by the d-excess method, varying from 0.01 to 0.18. (1–f), was a function of water temperature and drainage mean elevation, indicating that evaporation easily occurs at high temperatures in low-elevation regions. The hydrological processes co-varied with solute dynamics in the river network, and fluid transit time and temperature were likely responsible for the co-variations. Also, we found that hydrological processes played an important role in solute dynamics through shifting the geochemical processes (e.g., enrichment, water-rock reaction, photosynthesis, and secondary mineral precipitation). This study highlights that biogeochemical processes co-vary with hydrological processes, and we suggest that investigating hydrological processes can help to understand biogeochemical processes.