Hydrochemical and stable isotopic characteristics of waters in and around an eutrophic lake—Ooty, Tamil Nadu, India

Abstract

Ooty Lake, one of the famous tourist destinations in south India, deteriorates due to tourism activities and urbanisation. The present study aims in characterising the quality of lake water (both surface and depth) and groundwater besides addressing its suitability for various purposes by collecting samples during premonsoon, monsoon and post monsoon seasons of the years 2015 to 2017. Collected samples are analysed for physicochemical parameters using potentiometric technique. Major ions, trace metals and stable isotopes are determined by titrimetric, spectroscopy techniques. Statistical analysis involves principal component and cluster analysis with correlation coefficient. Major chemistry of lake water and groundwater exhibits Ca2+Na+HCO3− type and mainly dominated by silicate weathering. Water chemistry and statistical study indicate that chromium, zinc and cobalt in groundwater and lake water are attributed to the dominance of rock weathering. Copper, chromium along with zinc and lead in stream and inlet locations can be attributed to the influence of domestic waste water entering the lake. Phosphorous in the lake is also derived mainly through the domestic waste entering the lake. Water quality and heavy metal pollution indices show unsuitability of lake water for drinking, whereas, ecological risk assessment indicates that water is safe for aquatic life. Sodium absorption ratio, permeability index, residual sodium carbonate and sodium percentage of water samples indicate suitability for agricultural activities. Stable isotopic composition of lake water and groundwater samples shows possible southwest monsoon precipitation as the major source. Ineffective water treatment at inlet and stream water chemistry affects the lake water quality, which could be focussed for enriching quality.