Assessment of the impact of anthropogenic activities on the groundwater hydrology and chemistry in Tarsus coastal plain (Mersin, SE Turkey) using fuzzy clustering, multivariate statistics and GIS techniques

Tarsus coastal plain (TCP) is an economically and ecologically important area situated in between the fertile fluvio-deltaic plains of two rivers, Deliçay and Tarsus (Mersin, SE Turkey), where anthropogenic activities (agricultural, industrial, and domestic) are very intense. Twenty-four water quality parameters were surveyed at 193 groundwater and 10 surface water sites during August 2008. The objective was to characterize the physico-chemical properties of groundwaters in TCP, assess the impact of anthropogenic activities on the groundwater hydrology and chemistry, and identify the major hydrogeochemical processes occurring in the area. Groundwater samples were grouped into hydrochemically distinct and spatially continuous four water classes (i.e., C1, C2, C3, and C4) using the fuzzy c-means (FCM) clustering method, where membership values were interpolated using the ordinary kriging technique. Principal components analysis (PCA) was used to decipher various underlying natural and anthropogenic processes creating these distinct water classes. Four principal components (PCs) were extracted in PCA which explained more than 73% of the total variance in water quality. Major factors responsible for the variations in chemistries of water classes are identified as: (1) water–rock interaction and nitrate contamination; (2) salinization by seawater intrusion and evaporite dissolution; (3) geogenic/anthropogenic Cr, Fe, and Mn; and (4) anthropogenic Zn pollution. Overexploitation of the aquifer is clearly evident, especially at settlements located near the coastal zone, where the water table is lowered 2–5 m below the sea level. Salinization is well known in the area and is attributed not only to seawater intrusion, but also to dissolution of evaporitic series from the Handere formation. Hydrochemical evidence also suggest that in the area subsurface paleo-river channels and the deposits infilling the ancient lagoon area within Quaternary–Recent alluvial deposits act as significant hydrological features where preferential groundwater flow occurs along them.