Determination of temporal and spatial variability of groundwater irrigation quality using geostatistical techniques on the coastal aquifer of Çarşamba Plain, Turkey, from 1990 to 2012

The present study was conducted to investigate variations in groundwater quality parameters between 1990 and 2012, and to assess the suitability of groundwater for irrigation. Groundwater samples were taken in the summers of 1990 and 2012, and hydrochemical characteristics were investigated through Piper and USSL diagrams. The electrical conductivity (EC), sodium percentage (%Na), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), magnesium hazard (MR), potential salinity (PS), and Kelly’s ratios (KI) were used as the indicators for the water quality. Water quality parameters were assessed through geostatistical techniques and geographical information systems. Initially, semivariograms were determined for each water quality index, and spatial distribution maps were created for each sampling period through ordinary kriging techniques. Results revealed excessive increases in EC, Na, and Cl values with time. EC values of groundwater were over 1.25 dS/m in 4.64% of the study area in 1990. The area increased to 37.38% in the year 2012. With regard to the Kelly Index, there were not any problems in the study area in 1990, but problems were encountered over 5.75% of the study area in the year 2012. While the ratio of problematic sites with regard to RSC was 2.44% in 1990, the ratio increased to 12.13% in the year 2012. Similar increases were also observed in other water quality parameters except for MR. Higher deteriorations were observed in water quality parameters through the eastern sections of the study area. From 1990 to 2012, increased deteriorations were observed in water quality parameters, and excessive groundwater withdrawal and resultant seawater intrusion were considered as the basic reasons for such deteriorations. Therefore, groundwater withdrawals along the coastal lines should be performed in a controlled fashion, and water quality should continuously be monitored.