Anthropogenic stress on a Ramsar site, India: Study towards rapid transformation of the health of aquatic environment

Abstract

The East Kolkata Wetlands (EKW) region is an important Ramsar Site (huge provisional, regulatory, cultural and spiritual ecosystem services) which is located at the eastern periphery of Kolkata Metropolitan City (India). But in the recent years, illegal land acquisition, wetlands conversion, aquatic species depletion as well as water pollution related diseases have been experienced in different pockets of EKW region. The main objective is to determine regulating factors and stages of eutrophication. The water samples of consecutive three years 2017, 2018 and 2019 (pre and post monsoon) have been obtained from selective 20 wetlands in EKW. The important physicochemical parameters (temperature, electrical conductivity (EC), turbidity, total alkalinity, pH, total hardness, total dissolved solids (TDS), dissolved oxygen (DO), inorganic nitrogen, total phosphorus, potassium, ammonium-nitrogen (NH4+-N), biological oxygen demand (BOD), Secchi disk depth, chlorophyll - a), trophic status index and statistical techniques (like principal component analysis, hierarchical cluster analysis) have been considered to analyze the water quality of these wetlands. The results portray that the magnification of inorganic nitrogen, total phosphorus, potassium and ammonium-nitrogen accelerates the mechanism of eutrophication in the selective wetlands. The DO level has been diminished during 2019 while the BOD level and chlorophyll concentration have been accelerated amidst 2019.The results reveal that about 40% of wetlands i.e. wetland no. 5, 7, 10, 16, 17 (TSI value – 50–70) and wetland no. 8 and 11 (TSI value – 70–100) come under eutrophic and hyper-eutrophic stages respectively due to higher accumulation of nitrogen and phosphorus contents in the wetlands from various non-point sources and these principal components stimulate the processes of eutrophication of the water bodies. Some relevant mitigation measures have been recommended to protect the “kidney of Kolkata Metropolitan City”.