Bathymetry, Sedimentation Rate and Physico-Chemical Characteristics of Mansar Lake in the Himalayan Foothills, Jammu and Kashmir, India

An attempt has been made to workout the bathymetry, determine the rate of sedimentation and the physico-Chemical characteristics of the Mansar lake of Jammu region. The bathymetric survey conducted using Range-Line method shows present lake surface area is 0 59x10⁶ m² and volume to be 11 57x10⁶ m³. The rate of sedimentation determined using ¹³⁷Cs and ²¹⁰Pb radiometric dating technique in the lake varies between 0 14 cm/y to 0 37 cm/y with a mean rate of 0 23 cm/y±0 002 cm/y. The variation of temperature, pH, electrical conductivity, dissolved oxygen, hardness and alkalinity suggest that Mansar lake undergoes two distinct stages, viz complete mixing stage in the months of January and February and stratified stage in other months. The catchment lithology contributes a large part of the major constituents in lake water, Ca and Mg account 70 to 85% of the cations and HCO₃ accounts for 77 to 91% of the total anion, and equivalent ratio of Ca Mg varies from 0 45 to 6 40. The average (Ca+Mg)/HCO₃ equivalent ratio of 1 04, major contribution of (Ca+Mg) to total cations and high (Ca+Mg)/(Na+K) ratio indicate that weathering of calcareous sandstones and mudstones of the Siwalik Group could be the primary source of major ions in the lake water. Results of phosphorous show that Mansar lake has entered the eutrophic stage.