Himalayan rivers play pivotal roles in regional water and food supplies, global sediments, and carbon budgets. We studied a transboundary mountainous Kosi River in the Himalayas by utilizing ultraviolet–visible spectroscopy and excitation–emission matrix coupled with parallel factor analysis. We have found that agricultural land use promoted the production of abundant proteinlike fluorescence in the surface waters [∼1.1–1.8 Raman unit (RU) for two proteinlike components that accounts for ≥97% of relative abundance] as opposed to natural vegetation land cover (e.g., forests and grasslands), despite the low dissolved organic carbon (DOC, 0.50–1.02 mg L^–1), implying more reactive fluorescent dissolved organic matter (FDOM) that can potentially cause more CO₂ outgassing. Furthermore, we observed a decreasing trend of slope ratio (S_R) and proteinlike fluorescence with elevation as opposed to a humiclike component, potentially due to more concentrated croplands and consequent nutrient inputs to rivers at lower elevations. In addition, poststorm samples shifted to more humiclike FDOM and chromophoric DOM (CDOM) sides compared to baseflow water. These findings highlighted the importance of land uses and other environmental conditions, such as elevation and hydrology, on DOM characteristics and dynamics and water quality, which can potentially be amplified due to the steep gradients in mountainous watersheds. Measures should be taken for proper and sustainable land uses to mitigate river water eutrophication and pollution and to protect drinking water sources for millions of populations.

中文翻译：

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跨境喜马拉雅流域的溶解有机物特征：与土地利用，海拔和水文的关系

喜马拉雅河在区域水和粮食供应，全球沉积物和碳预算中起着关键作用。我们利用紫外可见光谱和激发发射矩阵结合并行因子分析研究了喜马拉雅山的跨界山区科西河。我们发现，与天然植被的土地覆盖相比，农业土地的使用促进了地表水中大量蛋白质样荧光的产生[〜1.1-1.8拉曼单位（RU），两种蛋白质样成分占相对丰度的≥97％]（例如森林和草原），尽管溶解有机碳含量较低（DOC，0.50–1.02 mg L ^–1），这意味着更多的反应性荧光溶解有机物（FDOM）可能会导致更多的CO ₂排放。放气。此外，我们观察到坡度比（S _R）和类似荧光的蛋白质（与类似腐殖质的成分相比具有较高的荧光性），这可能是由于耕地更加集中以及随之而来的营养素输入较低海拔的河流所致。此外，与基流水相比，暴风雨后的样本向更像腐殖质的FDOM和发色DOM（CDOM）侧移动。这些发现凸显了土地利用和其他环境条件（例如海拔和水文状况）对DOM特性，动态和水质的重要性，由于山区流域的陡坡，这些潜在条件可能会被放大。应采取适当和可持续的土地利用措施，以减轻河水富营养化和污染，并保护数百万人口的饮用水源。