Quantitative delineation of water sources in a large river system is essential for the sustainable use of water. In the present study, we have tested two different methodologies to estimate the contribution from different water sources in the river Ganga. The first model uses stable isotopes and physicochemical parameters of water to delineate the contribution of glacier-melt, groundwater, and surface runoff in different stretches of the river Ganga. The end member-based mixing model provides glacier-melt contribution of ~31.2%, ~5.5%, and ~0.5% in the upper, middle, and lower stretch of the river Ganga. The model showed maximum contribution from groundwater (~66.3%) in the middle stretch and surface runoff (~57.2%) in the lower stretch of the river Ganga. However, the uncertainties in the estimates from the three-component mixing model were significantly high due to temporal variability in the end member values. To provide estimates with lower uncertainty, an alternate method (discharge dependent budget estimation [DDBE]) has been proposed which delineates the contribution of groundwater and surface runoff in small segments of the river. The DDBE model confines the calculation for budget estimates to smaller segments of the river and hence leads to lower uncertainties in the results, providing improved systematic estimation of water budget for large river systems. In the present study, estimates from the DDBE model suggest that groundwater contributes ~79% of the additional water whereas the contribution from surface runoff is ~21% in the middle and lower stretch of the river Ganga. The DDBE model was successfully applied in 5 small segments along the stretch of the river Ganga and the methodology used shows great potential for systematic delineation of water sources in large river system.

中文翻译：

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使用稳定水同位素定量描述恒河水源

对大型河流系统中的水源进行定量划分对于水的可持续利用至关重要。在本研究中，我们测试了两种不同的方法来估计恒河不同水源的贡献。第一个模型使用水的稳定同位素和物理化学参数来描述恒河不同河段冰川融化、地下水和地表径流的贡献。基于端元的混合模型提供了恒河上游、中游和下游河段的冰川融化贡献分别为~31.2%、~5.5%和~0.5%。该模型显示，恒河中段的地下水贡献最大（约 66.3%），下游的地表径流贡献最大（约 57.2%）。然而，由于最终成员值的时间变化，三分量混合模型的估计的不确定性非常高。为了提供不确定性较低的估计，提出了一种替代方法（与流量相关的预算估计[DDBE]），该方法描述了河流小段中地下水和地表径流的贡献。DDBE 模型将预算估算的计算限制在河流的较小部分，因此结果的不确定性较低，从而为大型河流系统提供了改进的水预算系统估算。在本研究中，DDBE 模型的估计表明，在恒河中下游，地下水贡献了约 79% 的额外水量，而地表径流的贡献约为 21%。DDBE 模型已成功应用于恒河沿岸的 5 个小段，所使用的方法显示出系统描绘大型河流系统水源的巨大潜力。