Hydrochemistry of inland rivers in the north Tibetan Plateau: Constraints and weathering rate estimation

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The geographic region around the northern and northeastern Tibetan Plateau is the source of several inland rivers (e.g. Tarim River) of worldwide importance that are generated in the surrounding mountains systems of Tianshan, Pamir, Karakorum, and Qilian. To characterize chemical weathering and atmospheric CO2 consumption in these regions, water samples from the Tarim, Yili, Heihe, Shule, and Shiyang Rivers were collected and analyzed for major ion concentrations. The hydrochemical characteristics of these inland rivers pronouncedly distinguish them from large exorheic rivers (e.g., the Yangtze River and the Yellow River), as reflected in very high total dissolution solids (TDS) values. TDS was 115–4345mgl−1 with an average of 732mgl−1, which is an order of magnitude higher than the mean value for world rivers (65mgl−1). The Cheerchen River, Niya River, Keliya River and the terminal lakes of the Tarim River and the Heihe River have TDS values higher than 1gl−1, indicating saline water that cannot be directly consumed. Therefore, the problem of sufficient and safe drinking water has become increasingly prominent in the northwestern China arid zone. According to an inversion model, the contribution from evaporite dissolution to the dissolved loads in these rivers is 12.5%–99% with an average of 54%. The calculated silicate and carbonate weathering rates are 0.02–4.62tkm−2y−1 and 0.01–11.7tkm−2y−1 for these rivers. To reduce the influence of lithology, only the silicate weathering rates in different parts of the Tibetan Plateau are compared. A rough variation tendency can be seen in the rates: northern regional (0.15–1.73tkm−2y−1)<northeastern regional (0.74–4.62)≈western regional (1.75)<eastern regional (0.18–16.4)≈southeastern regional (3.5–10.6)<southern regional (13.5–38.0). The weathering rates did not show a noticeable correlation with a single influencing factor, such as temperature, elevation, vegetation, and physical erosion rates. Rainfall and runoff, however, seems to have a positive correlation with silicate weathering rates.