Investigating the Long-Term Annual and Seasonal Changes in River Quality (Case Study: Aleshtar River)

Abstract

The expansion of urbanization along with industrial and agricultural activities on the banks of the Alshar River and subsequent discharge of wastewater into water sources have caused water contamination by various pollutants. In this study, seasonal and annual changes in the long-term water quality changes in the Alshar River were evaluated. For this purpose, water quality data used were recorded at the Sarab Sayyed Ali hydrometric station located at the outlet of the Alshar River from 1970 to 2018. For analysis, 11 water quality variables were selected. Man-Kendall test was used to examine the trend of changes. The results showed that the patterns were similar for changes in parameters at both annual and seasonal scales, with decreasing concentrations of HCO3, Na, pH and SAR and increasing concentrations of Mg, Ca, TH, TDS, EC, Cl, and SO4. In the annual period, the trend of change of all qualitative parameters except Na was statistically significant at 99% level. During the summer seasons, there were more intense upward and slower downward trends, with the strongest increase in concentration during this season. However, in the winter, the results were in contrary with the summer. In most of the qualitative parameters, the decreasing and increasing trends were higher in spring than in autumn. The reason for this could be attributed to the fact that winter snow melting from the altitudes occurs in the spring, causing increased surface currents and a relative decrease in concentrations.

Keywords

• aleshtar
• man-kendall
• quality
• river
• trend