Hydrochemistry of Lake Rara: A high mountain lake in western Nepal

High altitude ecosystems have important natural ecological functions but are under increasing impacts from human activities and climate change. A detailed analysis of the water chemistry of Lake Rara, a high mountain lake in western Nepal, was carried out in October 2015 and April 2016. A total of 31 water samples were collected. Major ions (Ca 2+ , Mg 2+ , Na + , K + , SO 4 2− , NO 3 − and Cl − ) were analysed by ion chromatography. Si and PO 4 3− were analysed following the standard protocols. Conductivity, pH, total dissolved solids (TDS), turbidity and dissolved oxygen (DO) were measured on‐site. The lake is oligotrophic characterized by low PO 4 3− concentration (0.06 ± 0.01 mg/L), high DO values (6.73 ± 0.06 and 10.89 ± 0.86 mg/L), alkaline pH (8.42 ± 0.3 and 8.32 ± 0.23) and low conductivity (189.93 ± 5.3 and 189.22 ± 5.8 μS/cm). The concentrations of the major cations were in the order of Ca 2+ > Mg 2+ > K + > Na + (during both seasons), and for anions, it was HCO 3 − > SO 4 2− > Cl − > NO 3 − and HCO 3 − > Cl − > NO 3 − > SO 4 2− during postmonsoon and premonsoon, respectively. One‐way ANOVA revealed significant seasonal variations ( p < 0.05) in most of the physicochemical parameters. The increased concentrations of most of the ions in the premonsoon time probably reflect long‐range transport of materials through dry deposition, whereas higher concentrations of NO 3 − and Cl − in some sites possibly reflect the localized impacts of settlement and grazing. The lake water was classified as Ca(Mg)HCO 3 . High (Ca 2+ + Mg 2+ )/Tz + ratio (0.97 in postmonsoon and 0.95 in premonsoon) and low (Na + + K + )/Tz + ratio (0.03 in postmonsoon and 0.04 in premonsoon) confirm carbonate weathering as the principal source of major ions with bedrock geology governing the water chemistry. The findings of this study build on the baseline dataset for assessing future anthropogenic influence on the lake and subsequent development for future lake management strategies.