Understanding how dissolved trace elements chemically evolve in the Ganga River from source to sink is important to understand subcatchment contributions and chemical variability across space and time but remains poorly constrained. What exists is site‐specific data sets that are focused on capturing contamination “hotspots.” Here, we present riverine trace element concentrations of 38 targeted locations in the Ganga Basin. Samples in the headwater and the upstream segments of the river were collected during the premonsoon, monsoon, and postmonsoon seasons of 2014, 2015, and 2016, and the downstream samples were collected in 2016. In addition, monthly time‐series samples were collected at a downstream site to capture the geochemical variability at a higher temporal‐resolution. To evaluate the geogenic contributions, groundwater, rainwater, snow, glacier‐ice, and sediment samples were also analyzed. We find that the river chemistry displays a wide spatio‐temporal variability. Headwater samples are characterized by high concentrations of trace elements that are primarily controlled by ice meltwater, intense weathering, and interactions with glacial flour and are therefore geogenic in nature. Moreover, high concentrations of trace metals were also observed in a few localized downstream sites. However, such enriched signals are not persistent further downstream as they get diluted by the joining of large tributaries. We show that the dissolved trace element concentrations in the Ganga River are low compared to existing datasets and are comparable to the global average river water composition. We additionally quantified the present‐day “baseline” concentration ranges to facilitate future water quality assessment in the Ganga Basin.

中文翻译：

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追踪恒河中从源到汇的溶解痕量和重金属：判断未来变化的基线

了解恒河中溶解的微量元素如何从源头到汇水如何化学演化对于了解子汇水面积贡献和跨时空化学变化的重要性很重要，但仍然受限制。现有的是特定于站点的数据集，这些数据集专注于捕获污染“热点”。在这里，我们介绍了恒河盆地38个目标地区的河流微量元素浓度。在2014年，2015年和2016年的季风，季风和季风后季节采集上游水源和河流上游段的样本，并于2016年采集下游样本。此外，每月的时间序列样本在下游站点以更高的时间分辨率捕获地球化学变异性。为了评估地质成因，地下水，雨水，积雪，还分析了冰川和沉积物样本。我们发现河流化学显示出很大的时空变化。水源样品的特征在于高含量的痕量元素，这些元素主要受融冰水，强烈的风化作用以及与冰粉的相互作用控制，因此具有自然成因。此外，在一些局部下游位置也观察到高浓度的痕量金属。然而，这种富集的信号在下游并没有持续存在，因为它们被大支流的连接稀释了。我们显示，与现有数据集相比，恒河中溶解的痕量元素浓度较低，可与全球平均河水成分相媲美。