NUTRIENTS AND HEAVY METALS IN KUMAUN HIMALAYAN LAKES

Abstract

The Kumaun Himalayan lakes, Nainital Bhimtal, Sattal and Naukuchiatal, situated in the administrative state of Uttarakhand, are one of the major tourist attractions in the northern part ofIndia. The increasing tourism and population around these lakes are a major concern for the ecology and good sustenance ofthe lakes. The present study is aimed to understand the behavior of nutrients and metals in the lake sediments and their association with different chemical forms in the sediments deposited during the past few decades. The study was accomplished by collection of water samples at different depths and core sediment samples from the deepest part of the lakes. Major ions and dissolved metals concentrations were analyzed in the surface water, deep water and interstitial (pore) waters. The core samples were sliced at different depth intervals and analyzed for major oxides composition at each depth sample; nutrient fractionation (easily exchangeable, reducible, CaC03 bound+ biogenic apatite, detrital apatite, organic) and heavy metals fractionation (water dissolvable, exchangeable, carbonates, manganese oxides, amorphous iron oxide, crystalline iron oxide, oxidisable and residual) in each sample were also carried out following standard sequential extraction procedure. The total concentration of nutrients (P, Nand S) and metals (Fe, Mn, Co, Cr, Ni, Cu, Pb and Zn) in the water column, interstitial water and the sediments varied differently. The major water chemistry (major ion composition) and sediment chemistry (major oxides composition) along with the Ca+Mg: Na+K ratio, chemical index of alteration, and A1203/K20 ratios in the water and sediments respectively, indicate the major influence of catchment lithology, especially carbonate weathering and soil erosion in the catchment area. The high concentration of chloride, sulfate and ammonium in the interstitial waters show processes such as denitrification, sulfidization and sulfide oxidation dominating the anoxic bottom of the lakes. The metal chemistry shows that, the Nainital Lake is more polluted in Tallital basin compared to the Mallital basin. The high concentrations of the metals, copper, zinc, chromium and nickel indicate contributions from domestic and agricultural wastes and vehicular pollution inputs in to these lakes. The saturation indices in water show the formation of iron oxide minerals, goethite, ferrihydrite and others, in the oxic layer of the lakes. These minerals are dissolved in the anoxic bottom layers of the highly anoxic Nainital Lake; the metals form carbonate phase rather than the oxide phase. The other three lakes show that all the oxide minerals are not reduced in the anoxic condition, thus leaving behind some metals in the sediments. The relationship between phosphorus and other major elements in the sediments shows the preference of phosphorus for calcium, rather than for iron and aluminum in these lakes. The presence of carbonate flour apatite, inferred from the high concentration of phosphorus in this fraction, acts as a main sink for phosphorus in sediments. The trace metal geochemistry in the sediments also shows the major influence of source rocks. The geo-accumulation index shows, the Nainital Lake to be moderately polluted with respect to chromium and nickel, and strongly polluted with zinc, copper and cobalt, where as the other lakes show high levels of lead and cobalt contamination in the sediments. The metal fractionation studies show the influence of catchment lithology and redox potential in the speciation of metals. The high anoxic condition of the Nainital Lake shows that the metals are associated with the dominant carbonate phase compared to the oxide phase, where as in the other lakes, chromium and nickel prefer iron oxide phase, cobalt prefers manganese oxide phase, and zinc is associated with organic matter. The study shows the catchment lithology, organic matter and redox potential, significantly 11 affecting the speciation and bioavailability of phosphorus and metals in the lake sediments. The overall geochemical processes taking place in the lakes are inferred from the present study. The precipitation of the oxy-hydroxides acts a major sink for the metals and phosphorus in the water column. The oxy-hydroxides are reduced in the anoxic layer, resulting in the release ofthe metals and phosphorus; sulfidisation ofthe metals takes place at the anoxic layer. The dominance of carbonate in the Nainital Lake acts as major sink for the metals and phosphorus into the sediments. In other lakes, the organic complexes act as a significant sink for the metals and the carbonates for phosphorus. The diffusive metal flux estimated for the Nainital lake shows that the metal flux is high for redox sensitive metals (Fe, Mn, Ni) compared to the less sensitive metals (Cu, Pb, Zn). The positive flux values indicate release of the metals from the sediments. Taking the observed lake processes, suitable remediation methods may be suggested in future studies. The study shows that the metals and phosphorus are mainly sequestered onto the sediments by carbonates in the Nainital Lake., The change in pH may result in the dissociation of carbonates, and thus the metals and phosphorus. Providing sand capping to the bottom sediments and any suitable amendment material, may reduce the metal and phosphorus flux from sediments to water. The Nainital Lake is more urbanized and polluted compared to the other three lakes, Bhimtal, Sattal and Naukuchiatal, may be due to abundant vegetation and less urbanization around these lakes. Thethesis on "Nutrients and Heavy Metals in Kumaun Himalayan Lakes" has been organized in to six chapters. Abrief introduction, outline and objective of the study have been described in Chapter 1. Details ofthe study area are presented in Chapter 2. Chapter 3 deals with nutrient fractionation in the lake sediments, and in Chapter 4 deals with fractionation of heavy metals in sediments. Chapter 3 and Chapter 4 have been covered with literature on global lake studies, objective, methodology, and results and discussion of the data obtained from the selected Kumaun Himalayan lakes. A gist of the lake processes in operation in the present study, flux and suggested remedial measures are enumerated in Chapter 5. The major conclusions from the study are presented in Chapter 6, followed by all the references cited in the thesis.