Geochemical characteristics of water and sediment from the Dal Lake, Kashmir Himalaya: constraints on weathering and anthropogenic activity

Two hundred and forty water samples (in four seasons) and seventeen sediment samples have been analyzed to monitor the natural and anthropogenic influences on the water and sediment chemistry of the Dal Lake, Kashmir Himalaya. The scatter diagrams [(Ca + Mg)/total cations (TZ(+)), (Ca + Mg)/HCO3, (Ca + Mg)/(HCO3 + SO4), (Na + K)/TZ(+); (Ca + Mg)/(Na + K)] and the geological map of the study area suggest predominance of carbonate and silicate weathering. Lower pH and high total dissolved solids, electrical conductivity and NO3- values in the Gagribal basin and in some patches of other basins reflect anthropogenic inputs in the form of sewage from surrounding population, houseboats, hotels, etc. The Dal Lake is characterized by high chemical index of alteration (CIA: 87-95), reflecting extreme weathering of the catchment area. Relative to the average carbonates, the lakebed sediments are enriched in Al, Ti, Zn, Cu and Co and depleted in Ni and Mn. Compared to the post-Archean Shale the sediments have higher Al, Zn and Cu contents and lower Ni and Co. There are distinct positive anomalies of Al, Mn, Zn and Cu and negative anomalies of Ni and Pb with respect to the upper continental crust. Geoaccumulation index (I-geo) and the US Environmental Protection Agency sediment quality standards indicate that the Gagribal basin and some patches of the Nagin basin are polluted with respect to Zn, Cu and Pb. These data suggest that the Dal Lake is characterized by differential natural and anthropogenic influences.