Historical trends of heavy metal contamination and eutrophication in an aquatic system from Kashmir Himalaya, India

Abstract

Long-term trends of heavy metal pollution in aquatic systems are significant for assessing the influence of human activities and adopting relevant management strategies. In this study, we present analyses of heavy metals (iron, manganese, copper, zinc, cobalt, nickel, and lead) in 210Pb/137Cs dated sediment cores from Ahansar lake (Kashmir Himalaya, India) covering a time span of the last 200 years. Additionally, the relative water quality analyses and compilation of historical water quality data (since 1983 CE) were performed to understand the long-term eutrophication status of Ahansar lake system. The heavy metal concentrations varied very little in pre-anthropogenic sediments (before 1980 CE) and represent geochemical background concentrations. Since the 1980s, the heavy metals (Pb, Zn and Cu) began to increase gradually corresponding to the population expansion in the region and the beginning of industrialization. Similarly, the ecological risk index (ERI) values for all heavy metals lies below 40, indicating less toxic impact of Pb, Cu, Zn and Ni. However, the increasing trend of ERI observed in Pb and Zn since 1980, indicates deterioration of the lake ecosystem. Further, the water quality parameters revealed deteriorating trend from ∼2000 CE, with an increase of total phosphorus, ammonia, nitrate and a decrease of dissolved oxygen. The present day (∼2020 CE) quantitative assessment of Ahansar lake water quality using trophic level index (TLI) reflected the eutrophic condition of the lake waters. The long-term baseline information from this study will aid policy makers and environmentalists for the development, management and restoration of water resources.