Climatic, land cover, and anthropogenic controls on dissolved organic matter quantity and quality from major alpine rivers across the Himalayan-Tibetan Plateau

Alpine rivers in mountainous regions are crucial not only for land-ocean transfer of chemical species and sediments, but also for water, food, and energy security. Here, we examined dissolved organic matter (DOM) from the major alpine waters on the Tibetan Plateau. Our results revealed a decreasing trend of DOM quantity juxtaposed to an increasing trend of aromaticity from the northern to southern plateau. This is potentially caused by a general decreasing gradient of dust load combined with an increasing gradient of precipitation and vegetation from the NW to SE plateau. Furthermore, most proglacial streams and smaller tributaries were found to be relatively dominated by tyrosine-like fluorescent DOM from glaciers. In contrast, most main stems of rivers and tributaries within larger catchment basins were more controlled by humic-like fluorescent DOM from terrestrial origins. Condensed aromatics accounts for 14-21% of molecular formulas for riverine DOM, much higher than the world's average of similar to 11%, which indicated anthropogenic black soot pollution. In addition, there isa higher level of DOM amount in the monsoon season than in winter, and DOM characteristics varied more widely (dissolved organic carbon concentration: 0.2-37 mg-C L-1, Fluorescence Index: 1.2-1.8) on the Tibetan Plateau in comparison to other global alpine watersheds. This suggests heterogeneous land cover, anthropogenic, and climatic factors at play, which is reflected in DOM quantity and quality, over the highest plateau on Earth. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Alpine rivers in the Tibetan Plateau exhibit a decreasing trend of dissolved organic matter (DOM) quantity and an increasing trend of aromaticity from the northern to southern plateau, influenced by dust load, precipitation, and vegetation. Proglacial streams are dominated by tyrosine-like fluorescent DOM, while main stems of rivers within larger catchment areas are controlled by humic-like fluorescent DOM. The presence of condensed aromatics in riverine DOM suggests anthropogenic black soot pollution, and seasonal variations in DOM amount and characteristics indicate heterogeneous land cover, anthropogenic activities, and climatic factors at play on the highest plateau on Earth.