Trends of Groundwater Quality of Ardabil Plain Using the Spearman Method

Study of groundwater quality trend in any region is very important from the view of scheduling and sustainable water resources management. In the present study trend analysis conducted on groundwater quality based on information of 32 piezometeric stations located in the Ardabil plain from 1993 to 2008 using the non-parametric Spearman test. Hydrogeochemical variables studied here are Total anions, Total Cations, calcium, magnesium, sodium (Na+), potassium (K), chloride (Cl-), bicarbonate (HCO3-), total hardness (TH), electrical conductivity (EC), sulfate (SO4-2), total dissolved solids (TDS), Na% and pH, which are measured two times a year.One measurement belonged to the month in which groundwater level reach to its highest level that named wet month and other in lowest level that named these as dry months in the present study. Trend line slope estimated using the Sen’s estimator approach. Results showed that concentration of all groundwater quality variables exhibited upward trends at all stations. TDS is the parameter that witnessed the most significant trend in two mentioned months (wettest and driest). For the detected rising trends, the most significant parameters are Cations, EC, Ca and TDS in the most of stations. Median of slopes was positive in the case of all variables. Results for slope of trend lines were shown by Box and Whisker plots for four parameters. In general, quality of Ardebil plain groundwater decreased in the study time period. Strong positive trends observed for water quality in the north, central and east part of the Ardabil plain.