Seasonal variation in the major ion chemistry of Pandoh Lake, Mandi District, Himachal Pradesh, India Anshumali, A.L. Ramanathan * Laboratory of Biogeochemistry and Hydrogeochemistry (209), School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110 067, India Available online 30 March 2007 Abstract Pandoh is a beautiful Lake surrounded by Shivalik sequences (Lesser Himalaya) in the Mandi District of Himachal Pradesh. A comprehensive and systematic study on the seasonal pattern of major ions (Cl  , PO 3 4 , HCO  3 , NO  3 , SO 2 4 , Na + ,K + , Ca 2+ , Mg 2+ ) and SiO 2 was carried out to understand the geochemical processes controlling water quality. There is marked seasonal variation for almost all ions. Carbonate weathering and atmospheric precipitation are strong factors controlling the chemistry of major ion such as Ca 2+ , Mg 2+ and HCO  3 in the winter and summer seasons. In the monsoon season, relatively low concentrations of all the ions were observed due to dilution effects. Ca 2+ , Mg 2+ and HCO  3 generally account for about 70% of the total ions throughout the year. The ratios Ca 2+ + Mg 2+ /Na + + Cl  , HCO  3 /(Ca 2+ + Mg 2+ ), (Ca 2+ + Mg 2+ )/T þ z , ðNa þ þ K þ Þ=T þ z indicate that carbonate weathering is the main control on water chemistry in con- trast to other Himalayan lakes. The low concentrations of Na + and K + indicate a minimal contribution from the weath- ering of silicate minerals to Pandoh Lake. Correlation matrix and principal component analysis were used to identify various factors influencing the ionic strength of Pandoh Lake waters. The overall water quality variation (in space and time) as well as comparison with the quality of other Himalayan lake water indicates that this lake is non polluted, however there are indications of possible enrichment of nutrients (eutrophication) in the near future in the Himalayan region of the Indian subcontinent. Hence Pandoh Lake deserves further detailed attention for management of the water resource to pre- serve its eco-hydrological status. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction The geochemical study of lake water reveals the pattern and linkage between evaporation, chemical weathering and precipitation. Generally the lake water chemistry describes the seasonal changes in the behavior of the major ions and catchment char- acteristics. Pandoh Lake is an important protected water body in the Lesser Himalaya. Its water is used for generation of hydropower, fishing, agricultural activities, etc. A few unpublished preliminary reports containing general hydro-chemical informa- tion on the lake are available (Kaushal et al., 1978). Kaushal et al. (1978) provide a limnological profile of Pandoh Lake. Thermal stratification between 13 and 14 m has been reported, the temperature dropping from 16.5 to 10.5 °C at the surface to 19 m. 0883-2927/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.apgeochem.2007.03.045 * Corresponding author. E-mail addresses: alr0400@mail.jnu.ac.in, alr_jnu@yahoo. co.in (A.L. Ramanathan). Applied Geochemistry 22 (2007) 1736–1747 www.elsevier.com/locate/apgeochem Applied Geochemistry