Urban wetlands of Delhi, India: water quality and pollution status

The present study aims to understand the water quality of four urban wetlands of Delhi-NCR (Sanjay lake, Okhla bird sanctuary, Indira Gandhi stadium lake and Bhalswa lake). Several surface water samples from these wetlands were studied in two seasons (winter and summer) for various physico-chemical properties (temperature, pH, dissolved oxygen, biological oxygen demand, chemical oxygen demand, electrical conductivity, alkalinity, major cations and anions) including trace metals. Water from all these wetlands are alkaline and show seasonally varying chemical composition. Hydrogeochemistry (Piper plot and Gibb's diagram) indicates that water from Bhalswa lake is Na+ - SO42- type and shows an evaporation dominance regime, whereas water from the other three wetlands is Na+ - SO42- and Ca2+ - Mg2+ - SO42- type, and show a dominance of rock-water interaction. The water quality index reveals that water from all the wetlands is poor to unsuitable for drinking. Concerning irrigation water quality, water from Bhalswa lake is unsuitable, whereas water from other wetlands is marginal to suitable. Both drinking and irrigational water quality deteriorate during summer. In light of the immense ecological importance of these wetlands, urgent measures are required to arrest their deteriorating health.