روند تغییرات رواناب و کیفیت آب سطحی در رودخانه گرگانرود

The statistical and trend analysis of water quality and water quantity are important in assessment, planning control and management program of streams. The time series of yearly values of five water quality variables (,, SAR, TDS, TH) and the discharge at seven selected stations in  the period 1971-2009 were selected for this analysis. Stations were selected on the basis of sample size, period of reporting, and availability of flow data. Four non-parametric trend tests (the Sen’s slope estimator, the Mann-Kendall, the Spearman’s Rho, and the Hodges-Lehmann) are adapted in this study. In most cases, the first three tests provide the same conclusion about trend existence but Hodges-Lehmann test doesn't reveal a significant trend. An overview of results is as follows: 1.  concentration at Tangrah, Galikesh, Tamar monitoring stations decreased, while no significant trend is observed in other selected stations, 2.  exhibited positive significant trend in Ramiyan monitoring station 3. Spearman's rho test of trend shows an increasing and decreasing trend of TDS for Tamar and Galikesh monitoring stations respectively, while Mann-Kendall test and Sen estimator of trend show an increasing trend of TDS for Tamar and Galikesh monitoring station, while TDS exhibited positive trends at Ramiyan station. 4. SAR concentration at Tagi Abad, Galikesh, Tamar and Lazoreh increased while no significant trend is observed in other selected stations, 5. Significant positive trends were found for TH in Tnagrah and Galikesh monitoring stations. Only two monitoring stations, one at Tamar station and the other at the Ramiyan station, had decreasing trends for discharge.