The Himalayan ranges extending approximately 2400 km generates rivers such as Brahmaputra, Indus, Koshi, and Gandaki rivers. The characterization and assessment of water quality in the headwater region of Himalaya is necessary, given the immense importance of this region in sustaining livelihoods of people and maintaining ecological balance.
PhD candidate Mr. Ramesh Raj Pant, a member of Professor Fan Zhang’s team of the CAS center for excellence in Tibetan Plateau earth sciences and the institute of Tibetan Plateau Research, and the co-authors, collected a total of 165 water samples from 55 sites during pre-monsoon, monsoon and post-monsoon seasons in 2016 from the Gandaki River Basin of the Central Himalaya, Nepal (Fig. 1). The pH, EC values and TDS concentrations were measured in-situ, the concentrations of major ions (（Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl^-, SO₄^2-, NO₃^-), Si were analyzed in laboratory, and HCO₃^- was calculated by charge balance. The results reveal mildly alkaline pH values and the following pattern of average ionic dominance: Ca²⁺>Mg²⁺> Na⁺> K⁺ for cations and HCO₃^->SO₄^2->Cl^->NO₃^- for anions. Geogenic weathering processes predominated in this area with carbonate dominant lithology and its hydrochemical type was mainly Ca_-HCO₃(> 83%) (Fig. 1). Pronounced spatiotemporal heterogeneity demonstrates the influence of climatic, geogenic and anthropogenic conditions, especially the variation of river discharge in different seasons in the upstream and downstream. Analyses of the suitability of the water supply for drinking and irrigation reveal that the river has mostly retained its natural water quality but poses safety concern at a few locations, illustrated by the NO₃^-concentrations at several sites in the downstream close to residential locations. Data and knowledge obtained through this study can contribute to the sustainable management of water quality in the climatically and lithologically distinct segments of the Himalayan river basins.

This research was financially supported by the International Partnership Program of Chinese Academy of Sciences (Grant No. 131C11KYSB20160061) and the National Natural Science Foundation of China (Grant No. 41422101).

Paper linkage：http://www.sciencedirect.com/science/article/pii/S0048969717334824

Citation：Pant, R. R., F. Zhang*, F.-R. Qaiser, G. Wang, M. Ye, Z. Chen, H. Tang. Spatiotemporal variations of hydrogeochemistry and its controlling factors in the Gandaki River Basin, Central Himalayas, Nepal. Science of Total Environment. 622-623: 770-782 (2018)

Fig.1 Locations of sampling points in the Gandaki River, Gibbs plot of water chemistry, Piper diagram of water facies, seasonal variation of upstream and downstream runoff-TDS-precipitation and principal component analysis results