Hydro-chemical characteristics of biring and Tangting Rivers (Nepal) and evaluation of water quality for drinking and irrigation purposes.

Although river water is vital for drinking, irrigation and domestic needs, it faces threats from natural processes and human activities. Small and medium-sized rivers, especially in Nepal, remain understudied despite their vital importance in providing water to densely populated areas. This study evaluated the suitability for drinking and irrigation and the hydro-chemical characteristics of the Biring and Tangting rivers in Koshi province, Nepal. The results showed that turbidity, pH, EC, TDS, TH, NH4+, K+, Ca2+, Mg2+, Na+, Cl-, SO42-, HCO3- and NO3- values of all sampling sites in the Biring and Tangting rivers, except for the turbidity value of 10.39 NTU recorded in the PT9 site of the Tangting River, did not exceed maximum limit values set for drinking water. However, according to Water Quality Index results, the water of both rivers was in poor condition for drinking due to domestic wastewater discharges and cremation activities which caused high NH4+ levels. The major cations in both rivers were listed as Ca2⁺ > Na⁺ > K⁺ > Mg2⁺, while the major anions were listed as HCO3⁻ > Cl⁻ > SO42⁻ > NO3⁻. Gibbs and Piper diagrams showed that geogenic weathering of carbonate rocks prevailing in the region affected the hydrochemistry in both rivers. Evaluation based on seven different irrigation indices and US salinity laboratory diagram revealed that the water of both rivers was suitable for irrigation despite some magnesium-related limitations.

Water quality, criticality, and sustainability of mountain springs-a case study from the Nepal Himalaya.

In the hilly terrain of Nepal, springs are the main source of drinking water. With the increasing population, rapid urbanization, and unabated climate change, springs are under the risk of survival. There is increasing evidence that springs in the mid-hills of Nepal are drying up, or are reducing in discharge, or are deteriorating by water quality. As a result, local communities are facing unprecedented water stress. On this background scenario, assessment of water quality of the springs in the Marin Watershed of Sindhuli district of Nepal was carried out in this study. Spring water samples were collected during the pre-monsoon and post-monsoon of 2020 and their hydrochemistry was analyzed. Further, springs' discharge was measured in situ and their criticality and sustainability were studied through community interaction. Results have revealed seasonal variation in spring discharge and spring water quality. Out of 39 flowing springs, water quality of 13, 8, and 6 springs, respectively, was very poor, poor, and unsuitable for drinking in the pre-monsoon. The count of springs with very poor, poor, and unsuitable drinking water quality during the post-monsoon was 8, 3, and 1, respectively. Occurrence of pathogenic bacteria (Escherichia coli) was identified in five spring samples which makes the spring water unsafe for drinking. Again, out of 51 springs studied, 12 are already dried up, and another 12 of the 39 flowing springs have become seasonal with very low discharge (0.03-0.07 L/s). The study highlights and emphasizes the need to protect the flowing springs and rejuvenate the dying springs of the Himalaya and of other parts of the world.

Climate change and river health of the Marshyangdi Watershed, Nepal: An assessment using integrated approach.

Climate change alters the river flow regimes causing significant changes in the structure and function of an aquatic ecosystem, ultimately affecting river health. This study applied a customized framework consisting of 1-index, 4-components, 6-indicators, and 43-metrics, to assess river health for two seasons and future periods, in the Marshyangdi Watershed, Nepal. Hydrological, water quality, biological and physical conditions were assessed using simulated results from a hydrological model, physiochemical analysis of water samples, macroinvertebrates assemblages analysis, and physical habitat condition assessment, respectively. Climate change impact on river health was assessed based on projected climate (precipitation and temperature) based on regional climate models under representative concentration pathways (RCP) 4.5 and 8.5 scenarios until the mid-century. Results showed moderate river health condition in both the seasons and it's deterioration for future scenarios and periods. It reveals the need to formulate appropriate measures for the conservation of the river health.