Glaciers play key roles in capturing, storing, and transforming global carbon and nitrogen, thereby contributing markedly to their cycles. However, an integrated mechanistic approach is still lacking regarding glacier's primary producers (PP), in terms of stable dissolved inorganic carbon isotope (δ13C-DIC) and its relationship with dissolved carbon and nitrogen transformation dynamic changes/cycling. Here, we sampled waters from glaciers, streams, tributaries, and the Indus River (IR) mainstream in the Upper IR Basin (UIRB), Western Himalaya. Dissolved organic matter (DOM) appears to fluctuate when passing from glaciers to streams-tributaries-IR mainstream continuum, implying that DOM originates from glaciers PP and is subsequently degraded. The corresponding fluctuations are observed for fluorescent DOM (FDOM), dissolved organic nitrogen (8.0‒106.8%), NO3‒-N (‒13.5/+16.6%), NH4+-N (‒8.8/+13.0%), and NO2‒-N (70.7-217.5%). These variations are associated with overall DOM/FDOM transformations, with the production of ending byproducts (e.g. CO2/DIC). The δ13C-DIC values fluctuated from glaciers (−5.3±2.5‰) to streams (−4.4±2.1‰), tributaries (−4.3±1.6‰), and IR mainstream (−4.2±1.3‰). The δ13C-DIC data are consistent with C transformations that involve lighter CO2 emission into the atmosphere, whereas highly depleted DIC/CO2 is the signature of DOM degradation after its fresh production from glaciers PP which originated by photosynthetic activities. The conceptual model (Figure) depicts the production processes of photosynthetically-derived OM in glaciers, as occurring by uptake of atmospheric CO2 (δ13C-DIC, 8.4‰) and followed by release of FDOM, DIC, and nutrients by photoinduced and/or biological respiration. The net C emissions as CO2 is calculated approximately 226.5 g/s or 7.1 ×109 g/year in the UIRB based on DOC mineralization, wand the net C sequestration based on increasing DOC is approximately 596.88 g/s or 1.9 ×1010 g/year. Similarly, the net N emission based on decreasing TN is approximately 61 g/s or 1.9 ×109 g/year, and the net N sequestration based on increasing TN is ~107 g/s or 3.4 ×109 g/year. Our results highlight the substantial contribution of western Himalayan glaciers-derived DOM to the global C and N cycles.
Prof. Khan M.G. Mostofa and Prof. Si-Liang Li and supervise this study.
Paper reference: Bhat MA, Li S.-L., Liu CQ, Senesi N, Senesi GS, Vione D, Yuan J, Shammi M, Mostofa KMG (2024) Dynamic changes, cycling and downward fate of dissolved carbon and nitrogen photosynthetically-derived from glaciers in upper Indus river basin. Environmental Research. 263, 120117. https://doi.org/10.1016/j.envres.2024.120117
