Major ion chemistry, catchment weathering and water quality of Renuka Lake, north-west Himalaya, India

The water samples collected from Renuka Lake during pre-monsoon, monsoon and post-monsoon seasons were analyzed to know water quality related to major ion chemistry and other essential parameters. The water is found to be slightly alkaline having pH value 7.22–8.66. Both Ca²⁺ and Mg²⁺ are observed as the dominant cations, whereas SO₄²⁻ and HCO₃⁻ are dominant anions during all seasons. The Piper plot has shown Ca²⁺–HCO₃⁻ type of water during pre- to post-monsoon seasons. Alkaline earth metals (Ca²⁺ and Mg²⁺) are noticed to exceed over alkali metals (Na⁺ and K⁺), and weak acid (HCO₃⁻) surpass over strong acid (SO₄²⁻) in all seasons. The carbonate weathering of surrounding rocks is found to be the dominant source of major ions for the lake during pre- to post-monsoon. The WQI values 176.45–184.91 from monsoon to pre-monsoon have revealed that the water of Renuka Lake is unsuitable for drinking. The higher value of WQI is mainly due to increased concentration of F⁻, which is produced from the fluorapatite, cryolite and mica etc., and anthropogenic activities. Its concentration more than standard permissible limit may be very harmful for human being and aquatic species. However, based on sodium per cent (11.88–15.62%), sodium adsorption ratio (0.48–0.61) and residual sodium carbonate (< 2.5 meq/L), the water quality is determined  fit for irrigation. The lake has indicated seasonal variations of Ca²⁺, Mg²⁺, Na⁺, K⁺ and HCO₃⁻, etc., which may be due to changing temperature, monsoon rain and human activities. Thus, stringent mitigation measures are required to reduce increased concentration of various physiochemical parameters and preservation of the Renuka Lake.