7-Anthropogenic impact on hydrological balance and water quality in Sambhar Lake Rajasthan

Abstract

Sambhar Lake covers an area of about 90 km2 is the Largest Saline Playa Lake in India extending in SW-NE direction. The lake represents a closed drainage basin receiving the major sediment and water influx by the monsoonal precipitation through two main streams namely Mandha and Rupangarh. The annual precipitation over this region ranges from 100 mm to 500 mm, while the temperature averages around 23° C with a maximum of 45° C. (Biswas et al. 1982). The major rock assemblage of Sambhar Lake catchment area mainly comprises of Precambrian quartzite, mica schist and quaternary sand dunes. Sambhar Lake plays an important roll in hydrological biological and climatic process in the desert. Therefore Sambhar Lake was designated as a Ramsar site in 1990. Presently Sambhar Lake faces serious threat for its existence, because manmade small dams restrict water availability in the lake from natural sources. Simultaneously government and private salt production firms are involved in overexploitation of ground water that caused deep water levels. We made an effort to monitor the hydrological balance in Sambhar Lake using 50 year rainfall and lake level data; simultaneously we collected shallow and deep subsurface water samples from Sambhar lake area to assess water quality. We find that the annual rain fall and lake level is not matching with each other after 1984, simultaneously the production of brine was increased. The geochemical analysis of water samples show 3 ppm to 6 ppm fluoride concentration in the shallow lake subsurface water, while Sambhar Lake city drinking water samples contain fluoride concentration between 1 to 7 ppm. Similarly Nawa and Guddah Salt drinking water contain fluoride concentration around 5 ppm. Two very deep (225 and 245 feet) subsurface water from Nawa salt production area has unusual fluoride concentration 13 and 14 ppm. Hence we concluded that the mixing of deep ground water in fresh drinking water around Sambhar Lake is responsible for the fluoride contamination. Also the overexploitation of water and construction of small dames are responsible for disturbance in the water balance in the region.