Diurnal dynamics of minor and trace elements in stream water draining Dongkemadi Glacier on the Tibetan Plateau and its environmental implications

Global warming has resulted in rapid glacier retreat on the Tibetan Plateau (TP), and the impacts of glacier melting on downstream ecosystems remain largely unknown. Minor and trace elements in stream water draining Dongkemadi Glacier (DG) were examined during the ablation season of 2013. Dominant ions and elements are HCO₃ ⁻, Ca²⁺, Fe and Sr. Water chemistry is controlled by the weathering of calcite, oxidation of pyrite and dissolution of evaporites. Correlations suggests the hydrological (e.g. meltwater generation and routing, water residence time) and physicochemical (e.g. sorption, precipitation, oversaturation) controls on species concentrations. The distribution of metals is featured by the mixture of soluble metal and non-metal ligand complexes and free monovalent and divalent ions. Downstream increased concentrations and/or fluxes of some metals and metalloid (e.g. Cr, Cu and As) suggest potential environmental impacts. Discharge-normalized cation denudation rate (372 Σ^∗meq⁺m⁻³) in the DG basin is larger than those from alpine and polar glaciers, suggesting a stronger weathering of carbonate with greater abundance on the TP in comparison to other mountain and polar glacial catchments. The maximum Fe concentration exceeds the USEPA guideline, and Al, Zn and Pb are close to or of the same order of magnitude as liminal values. This implies that the TP may face a challenge of ecosystem health and environmental issue in a warming climate.