Seasonal variations in the water quality and antibiotic resistance of microbial pollution indicators in the Mandovi and Zuari estuaries, Goa, India.

The two adjacent estuaries of the rivers Mandovi and Zuari, along the Goa coast in the central west coast of India, are a large complex aquatic system hosting diverse natural habitats. The water quality in these habitats is affected by various anthropogenic activities as they are extensively used for transportation, fisheries and various recreational activities. In the present study, changes in the water quality and levels of microbial pollution during the pre-monsoon, monsoon and post-monsoon seasons were determined. The water quality index was estimated based on the parameters: temperature, salinity, pH, dissolved oxygen, biochemical oxygen demand and nutrients. The seasonal changes in the microbial pollution load were also assessed based on the abundance of pollution indicator organisms and their resistivity towards multiple antibiotics. Results show that the water quality index status was 'poor' in the pre-monsoon and post-monsoon seasons and it was 'good' only in the monsoon period. Levels of pollution indicator organisms determined show that the counts were the highest in the pre-monsoon season, which reduced in the monsoon and further declined during the post-monsoon season. However, the estimated multiple antibiotic resistance (MAR) index suggests that bacterial isolates in monsoonal water and sediment samples have maximum resistance towards antibiotics. This shows that, though the basic water quality improved during the monsoon, possibly due to substantial dilution, the increased terrestrial inputs brought harmful pathogens into these estuarine waters, which may be of potential health risk. Understanding the ecological status of the estuarine habitats is important for successful environmental management and sustainable development.