Monitoring the Pollution Intensity of Wetlands of Coimbatore, Tamil Nadu, India

In the semiarid region in India, rainfall cannot be relied on for irrigation of crops due to its irregularities in availability as well as quantity. Tank irrigation is the best alternate solution for crops; but due to unscientific anthropogenic practices, the water quality of wetlands has degraded. Coimbatore city is currently facing acute water crisis because of degradation of the quality of water. The wetlands, which recharge the groundwater aquifers, have degraded in quality due to the discharge of domestic and industrial sewage. Continuous monitoring of surface water is essential for ensuring groundwater quality. The seven major tanks of the city were selected for the present study. The Water Quality Index of the wetlands during the premonsoon ranged from 41.23 for Perur lake to 82.03 for Ukkadam lake. The water type of the wetlands of the study area predominantly is of Ca(HCO₃)₂, Mg(HCO₃)₂, NaHCO₃ and NaCl type. The suitability of water for irrigation purposes was analysed using USSL (US Salinity Laboratory) classification system, and it was found that the water from three of the wetlands fall under S1C1 class, which indicate low salinity hazard. The Kurichi lake comes under S1C2 class and the other wetlands fall under S1C2 and S1C3 class. The study showed that the water from Singanallur wetland, Ukkadam wetland and Selvachinthamani wetland is unsuitable for irrigation due to high SAR (Sodium Adsorption Ratio) and electrical conductivity. The seasonal variation study showed that the wetland water quality parameters during premonsoon were higher than that of post monsoon. Ukkadam wetland and Singanallur wetland showed a degraded water quality due to continuous discharge of domestic and industrial sewage.