Spatial Distribution and Release Flux of Carbon and Nitrogen Components in Glacial Watersheds of Eastern Tibetan Plateau

Abstract

The carbon cycle stands as a cornerstone among the Earth’s material cycles, carrying profound implications for global climate dynamics and humanity’ s sustenance and advancement. Additionally, nitrogen, as a vital nutrient element, plays a pivotal role in biogeochemical processes, exerting significant influence on the ecological environment within watersheds. In this study, an analysis of the carbon (C) and nitrogen (N) components in the river water of 12 alpine basins on the eastern margin of the Tibetan Plateau (TP) reveals that the average dissolved organic carbon (DOC) concentration in the river water is 0.76 ± 0.67 mg/L, indicating a lower level compared to the global river average organic carbon content. Specifically, the average DOC concentrations were 0.42 ± 0.22 and 1.56 ± 0.68 mg/L in the glacial and non-glacial basins, respectively. The average dissolved inorganic carbon (DIC) concentration in the eastern TP is 27.04 ± 20.19 mg/L, with the lowest DIC observed at Dagu Glacier and the highest at Daxia River. Furthermore, the average dissolved total carbon (DTC) concentration in glacier river water was 18.87 ± 12.65 mg/L, contrasting with 48.23 ± 21.07 mg/L in non-glacial basins. The mean concentration of total nitrogen (TN) in the eastern TP averaged 0.97 ± 0.54 mg/L, with the glacial basin registering 1.01 ± 0.47 mg/ L and the non-glacial basin at 0.89 ± 0.70 mg/L. Evaluating the release fluxes of carbon and nitrogen across 12 river basins revealed a range of DTC emission fluxes from 0.32 × 10⁹ to 31.02 × 10⁹ g·C/a, with inorganic carbon comprising 71.0% to 99.5%. Consequently, the carbon emission flux for seven glacier basins totaled 15.91 × 10⁹ g·C/a, while for the five non-glacial river basins, it reached 87.37× 10⁹ g·C/a. The total TN release fluxes across 12 small river basins amounted to 2.46 × 10⁹ g·N/a, with 0.84 × 10⁹ g·N/a released in glacial basins and 1.62 × 10⁹ g·N/a in the non-glacial basin. This study elucidates the spatial distribution and transport mechanisms of carbon and nitrogen elements within the glacial and downstream non-glacial basins, offering valuable insights into the biogeochemical cycles of carbon and nitrogen in the eastern Tibetan Plateau.

Keywords

carbon cycle / total nitrogen / eastern Tibetan Plateau / glacier basin / release flux

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