Hydrogeochemical characterization and CO₂ consumption in the Maqu catchment of the Qinghai-Tibetan Plateau by multiple hydrogeochemical methods

The Qinghai-Tibetan Plateau (TP) is the source of many large Asian rivers and has significant social, ecological and economic importance. However, few hydrogeochemistry and stable isotope studies have been performed in the Maqu catchment of the eastern TP. In this study, the hydrogeochemical composition and stable isotopes (δD and δ ¹⁸O) of surface water and groundwater samples collected in the Maqu catchment were analysed to characterise the surface water and groundwater, investigate the contributions of different sources, and determine CO ₂ consumptions. Different techniques were used, including inverse modelling, end member mixing analysis (EMMA), and a forward mass balance model. The results indicated that all water samples are of the HCO ₃-Ca type. Both the surface water and groundwater are of meteoric origin and there is close contact between them (except wetlands). Water in the wetlands is substantially evaporated (0–45%). Calcite and illite generally precipitate, whereas chlorite and CO ₂ generally dissolve along groundwater flow paths in the east. The mean contributions of fresh surface waters, mountain-front groundwaters, and anthropogenic inputs to the surface water samples are 56%, 16%, and 28%, respectively. Carbonate and silicate weathering are the dominant sources of major cations. Moreover, high CO ₂ consumption rates in both the surface runoff and groundwater make the Maqu catchment an important carbon sink in the Yellow River Basin. With many newly-found conclusions on the Maqu catchment, the present study not only provides insight into the catchment but also contributes to a comprehensive understanding of the water cycle and CO ₂ consumptions on the TP.