Investigation of the Trend of Groundwater Quality Changes in Dezful Aquifer

In this study, modified Mann-Kendall test by removing the effects of internal autocorrelation, slope of trend line test and Pettitt test were used to investigate the time and spatio-temporal changes of the quality parameters of the groundwater of Dezful aquifer in the period of 1999-2017. In this regard, the parameters of potassium, sodium, magnesium, calcium, sulfate, chlorine, bicarbonates, acidity, total dissolved solids and electrical conductivity were used in 30 wells in Dezful aquifer. The results of examining the trend of changes in the investigated values based on the modified Mann-Kendall statistic showed that on average, 74% of the investigated wells experienced an increasing trend in the mentioned qualitative values. While the trend of changes in pH values in the entire studied range was decreasing, the trend of increasing changes in potassium, sodium, magnesium, calcium, sulfate, chlorine, bicarbonates, total dissolved solids and electrical conductivity was in 4, 10, 10, 0, 14, 37, 37, 27 and 27% of the wells are significant at the 5% level, respectively. According to the investigation of the time of changing point of trend in the studied qualitative values, the results showed that the time of changing of the trend in qualitative variables started from 2000 in potassium, sulfate and chlorine variables and included other variables until 2001. The decreasing changes of pH values at the level of the studied area also started in 2005. The increase in the changes of the investigated qualitative values, especially in the central and southeastern regions, has caused a decrease in the usefulness of groundwater in the studied region, and this issue affects its use in different sectors. Investigating the changes in the qualitative values of groundwater is one of the important methods in monitoring the quality of groundwater, and using the obtained results, restrictions can be applied regarding its use in different sectors.