Assessment of impact of shrimp farming on coastal groundwater using Geographical Information System based Analytical Hierarchy Process

Impact assessment of shrimp farming on groundwater needs selection of representative sampling units. In the coastal region, complex sources invariably influence the groundwater flow and its quality. This warrants multicriteria evaluation techniques consequent to which Geographical Information System (GIS) based Analytical Hierarchy Process (AHP) was used for the selection of groundwater sampling units in an effort to assess the impact of shrimp farming. Thematic maps of eight base layers viz. distance from the aquaculture ponds, drainage pattern in the study area, lineament, soil texture, slope, landuse/landcover, geomorphology and lithology were prepared using ARCGIS 10 as these were the main factors that could impact groundwater quality. Information on the relative importance of the evaluation criteria was obtained by assigning weights to each criterion defined by pairwise comparison for all the above eight factors. Pairwise comparison revealed that the consistency ratio was less than the threshold value (0.1) indicating perfection in comparison of each evaluation criterion. Eight criteria of distance, seven criteria of drainage, three criteria of lineament, seven criteria of soil, eight criteria of landuse, three criteria of slope, seven criteria of geomorphology and five criteria of geology were computed and combined to develop a priority classification map related to the influence of brackish water aquaculture on the salinisation of the groundwater in an effort to precisely assess the impact. On analysis, 29 sampling well locations were identified with three priority classes viz., (i) high priority (10), (ii) moderate priority (13) and (iii) low priority (6). Groundwater samples from all these sampling units were collected bimonthly starting from October 2011 till June 2013 and analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS), and chloride (Cl). Results revealed no significant relationship of groundwater quality as per the priority classification. Hierarchical cluster analysis clearly elucidated the variation of different water quality parameters being independent of the location of aqua farms indicating multiple sources for variation. From the spatial distribution map, it could be concluded that groundwater quality is independent of shrimp farming.