Spatially explicit environmental impact assessment of commercial brackish water aquaculture along the northwestern coast of the Bay of Bengal using a multiparameter index approach

The present study attempted to apply a comprehensive aquaculture impact index to assess the environmental impacts caused by the proliferation of commercial shrimp farming along the northwestern coast of the Bay of Bengal. The locale of the study was restricted to three community development blocks, viz. Contai-I, Deshapran, and Ramnagar-II in the Medinipur coastal plain of eastern India. Surface water and soil samples were collected from 195 sites during the postmonsoon season deploying a stratified random sampling method. Surface water samples were tested for pH, electrical conductivity, biochemical oxygen demand, dissolved oxygen, chemical oxygen demand, total nitrogen, total phosphorus, chloride, total dissolved solids, and free ammonia. Soil samples were analyzed for pH, electrical conductivity, total organic carbon, total nitrogen, total phosphorus, and total potassium. Spline interpolation was conducted to portray parameter-wise spatial concentration of these samples. To develop the index, principal component analysis was employed as a weightage assignment technique towards characterizing the pollutants that dominate the regional water and soil chemistry. Results indicated that water quality factors have wide spatial reach and influence the aquatic environ of the entire region, mainly in terms of pH, electrical conductivity, and biochemical oxygen demand. High values of aquaculture impact index (> 0.7) indicating greater aquaculture-induced pressure on the landscape were observed along the eastern inland and nearshore southwestern parts, whereas its lower values (< 0.3), indicating lower aquaculture influence on the immediate environs, were primarily observed in the more inland northwestern portions. Settlements along the coastal tracts with very high prevalence of brackish water aquaculture depicted alarming aquatic pollutant loads, whereas mostly localized influences were observed for soil parameters. This revealed that aquaculture activities have significantly altered the regional aquatic environs but not the edaphic dynamics yet.