Document Type : Research Paper
Understanding the changes in groundwater quality has an important role on the planning and sustainable management of water and soil resources in any region. In this study, trends of groundwater quality of Shabestar – Soofian plain using the information of the 18 deep wells and four Qanats were analyzed during 1998– 2011. For this purpose, the non – parametric Mann – Kendall method were used. Before conducting the MK test, the effect of significant lag – 1 serial correlation was removed from the data set. Hydro - geochemical variables that analyzed were the total Anions, total Cations, pH, EC,SO42-,Na%, Na+, Ca2+, Mg2+, TDS, SAR, Cl- and HCO3- which were measured twice in a year, wet and dry periods. The magnitudes of trends were computed using the Sen’s estimator method. Change points identified using the Pettitt test. Results showed that in most of the Qanats many variables showed decreasing trends and some of them showed increasing (but insignificant) trends. In the wet period, 21 percent of the stations and in the dry period, 22 percent of the stations experienced significant increasing trend in more than half of the variables. Results of trend line slope showed that in wet period groundwater quality is going to be improving but it is not true in dry period. Increasing trends observed in both periods in the southern plain overlooking the Urmia Lake. The steepest trend line slope belonged to the Shendabad (Farahnak) station, which was about 400 µS/cm. Among the whole of the time series about 63 percent of them experienced significant trends (in unsuitable direction).