Sediment and hydro biogeochemistry of Lake Nainital, Kumaun Himalaya, India

The picturesque Nainital Lake, in the Uttarakhand state of India, is one of the major tourist attractions in the northern part of India. The increasing tourism and population around these lakes are a major concern for the ecology and good sustenance of the lakes. The present study is aimed to understand the behaviour of nutrients and metals in the sediment and their association with chemical forms in the lake. The study was accomplished by studying the water, interstitial water and sediments for major oxides, nutrients and metals in the lake. The different chemical forms of phosphorus and metals in the sediments were done using sequential extraction procedures. The water chemistry (Ca + Mg:Na + K) and the sediment chemistry (CIA and Al₂O₃/K₂O) show that the rocks in the catchment area play an important role in the geochemistry of the lake. The metals in the water also show that the Tallital basin is more polluted than the Mallital basin, may be due to the influence of Bus station. The high concentration of chloride, NH₄, SO₄ and metals in the sediment water interface and the interstitial water shows denitrification, sulfidisation and sulfide oxidation in the anoxic bottom water. The sediment composition shows that the phosphorus in the water is sequestered as carbonate flour apatite, and the metals precipitate as carbonate. The geo- accumulation index shows that the metals zinc, cobalt and nickel show moderate polluted nature than other metals. In general, the lake is less affected by anthropogenic activities. The chemical processes undergoing within the lake, like sulfidisation and sulfide oxidation, oxide dissolution and denitrification and organic matter degradation play an important role in the remobilization of the metals from the lake sediments.