Analysis of the Trends of Groundwater Quality Changes by Using the Spearman Test in Mazndaran Plain, Northern Iran

Analyzing the trend of changes in groundwater quality is very important for programming and stable managing of water resource in every area. This study aims to use non-parametric Spearman test for analyzing groundwater quality changes trend in 24 piezometric stations located in Mazandaran plain in annual time scales, from 1373 to 1389. Hydrogeochemical parameters of groundwater such as Total Cation, Total Anion, PH, Electrical Conductivity (EC), total dissolved solids (TDS), sodium (Na), potassium (k), calcium (Ca), magnesium (Mg), bicarbonate (Hco), sulphate (So) and SAR were investigated. Sen’s estimator was used to estimate line slope trend. Three significance levels, 1%, 5% and 10% were used to test the trends. The results showed that the line slope of the density changes of groundwater qualitative variables was downward in 43 percent of variables and upward in 57 percent of them. The most positive trend, which was identified with statistic Z (7.14), was the sulfate ion in the mass analyzed in Darvish Babylon station in the eastern region. The results were also indicative of the increase in chemical density and the decrease in quality of the well water in Mazandaran plain at all piezometric stations.