Spatiotemporal variations of hydrogeochemistry and its controlling factors in the Gandaki River Basin, Central Himalaya Nepal

Ramesh Raj Pant; Fan Zhang; Faizan Ur Rehman; Guanxing Wang; Ming Ye; Chen Zeng; Handuo Tang

doi:10.1016/j.scitotenv.2017.12.063

Spatiotemporal variations of hydrogeochemistry and its controlling factors in the Gandaki River Basin, Central Himalaya Nepal

Sci Total Environ. 2018 May 1:622-623:770-782. doi: 10.1016/j.scitotenv.2017.12.063. Epub 2017 Dec 13.

Authors

Ramesh Raj Pant¹, Fan Zhang², Faizan Ur Rehman³, Guanxing Wang⁴, Ming Ye⁵, Chen Zeng⁶, Handuo Tang⁴

Affiliations

¹ Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China; Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China; CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China; Central Department of Environmental Science, Tribhuvan University, Nepal.
² Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China; Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China; CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China. Electronic address: zhangfan@itpcas.ac.cn.
³ Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China; Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China; CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China; Department of Earth Sciences, COMSATS Institute of Information Technology, Abbottabad, Pakistan.
⁴ Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China; Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China; CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, China; University of Chinese Academy of Sciences, Beijing, China.
⁵ Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, FL, USA.
⁶ Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China; Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China.

PMID: 29223904
DOI: 10.1016/j.scitotenv.2017.12.063

Abstract

The characterization and assessment of water quality in the head water region of Himalaya is necessary, given the immense importance of this region in sustaining livelihoods of people and maintaining ecological balance. A total of 165 water samples were collected from 55 sites during pre-monsoon, monsoon and post-monsoon seasons in 2016 from the Gandaki River Basin of the Central Himalaya, Nepal. The pH, EC values and TDS concentrations were measured in-situ and the concentrations of major ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl^-, SO₄^2-, NO₃^-) and Si were analyzed in laboratory. Correlation matrices, paired t-test, cluster analysis, principal component analysis (PCA), the Piper, Gibbs, and Mixing plots, and saturation index were applied to the measurements for evaluating spatiotemporal variation of the major ions. The results reveal mildly alkaline pH values and the following pattern of average ionic dominance: Ca²⁺>Mg²⁺>Na⁺>K⁺ for cations and HCO₃^->SO₄²^->Cl^->NO₃^- for anions. The results of PCA, Gibbs plot and the ionic relationships displayed the predominance of geogenic weathering processes in areas with carbonate dominant lithology. This conclusion is supported by geochemically different water facies identified in the Piper plot as Ca-HCO₃ (83.03%), mixed Ca-Mg-Cl (12.73.0%) and Ca-Cl (4.24%). Pronounced spatiotemporal heterogeneity demonstrates the influence of climatic, geogenic and anthropogenic conditions. For instance, the Ca²⁺-SO₄^2-, Mg²⁺-SO₄^2- and Na⁺-Cl^- pairs exhibit strong positive correlation with each other in the upstream region, whereas relatively weak correlation in the downstream region, likely indicating the influence of evapo-crystallization processes in the upstream region. 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. 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.

Keywords: Chemical weathering; Controlling factors; Himalayan River Basin; Major ions; Spatiotemporal variations.