Hydrogeochemistry of Dal Lake and the potential for present, future management by using facies, ionic ratios, and statistical analysis

Abstract

This paper presents the inventory study on the Dal Lake, the second largest fresh water lake in Kashmir Valley, India. A total of 336 water samples were monthly collected to assess the present scenario of weathering and anthropogenic impact on water for hydrological year (2012–2013). The results showed a significant spatio-temporal (monthly and basinal) variability in the concentration of the physical and chemical characteristics (major ions) of the lake water. The lake water is alkaline in nature (pH: 7.1–8.7) characterized by medium total dissolved solids of 80.8–230.7 mg L−1 and electrical conductivity of 126.3–384.6 µs cm−1. The order of major cations and anions is Ca2+ > Mg2+ > Na+ > K+ and HCO3 > SO42− > Cl− > NO3−, respectively. The geochemical processes suggested that the lake water composition is mostly influenced by the lithology of the catchment. Ca–Mg–HCO3 was found to be the dominant hydrochemical facies followed by mixed type of water (throughout the hydrological year). From sub-basin point of view all the four basins show Ca–Mg–HCO3 type water, but Hazratbal and Nigeen basins also show shift towards SO4 and Cl type of water reflecting the anthropogenic inputs in these two basins. Basin wise the average concentration of Ca2+, Mg2+, HCO3−, Cl−, and NO3− were highest in Nigeen basin due to high resistance time of water within the basin and Na+, K+, and SO42− in Hazratbal basin from the silicate weathering, and sewage plant sources. The Gagribal basin showed lowest values of Ca2+, Na+, K+, HCO3−, and Cl−, whereas Boddal and Hazratbal basin showed lowest values of SO42−, NO3−, and Mg2+, respectively. On monthly basis Ca2+, Na+, K+, and HCO3− were highest in April, Mg2+, and NO3− in January, Cl− in December and SO42− in September, lower value of Ca2+, and Cl− were observed in July, Mg2+ in April and HCO3−, and K+ in August. The study suggested that the predominant processes influencing water chemistry were congruent carbonate dissolution (61.9 %) and incongruent silicate weathering (12.7 %) and cation exchange of Na+ in rocks for Ca2+ and Mg2+ (10 %). The high major-ion concentrations indicated long water–rock interactions and long residence time of water in the lake. The higher concentrations SO42−, NO3− and Cl− reflect anthropogenic inputs from the immediate catchment.