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 > SO₄ ²⁻ > 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 SO₄ ²⁻ 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 SO₄ ²⁻, 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 SO₄ ²⁻ 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 SO₄ ²⁻, NO₃ ⁻ and Cl⁻ reflect anthropogenic inputs from the immediate catchment.