Surface Water Quality Evaluation under Land Use Changes (Case study: Mahabad Chai Watershed)

Not only have recent global challenges including drought, climate change, land degradation and land use change impacted the quantity of available surface water and groundwater, but also water quality has been affected as well. To study this impact, Landsat 5 satellite images and water quality data were obtained to compare the effects of land use changes on surface water quality between July of 1992 and 2011. The maximum likelihood algorithm was used for preparing and processing land use maps in ENVI 4.8 and Arc GIS9.3. For land use classification, the Jeffreys–Matusita, Kappa coefficient, and overall accuracy indexes were used. The results showed that the values ​​of Kappa coefficients and overall accuracy were 84.23 and 87.72% for 1992 and 93.84% and 95.55% for 2011, respectively. Most land use changes were related to dryland agriculture and residential land use, which increased 1.46 and 2.45 times, respectively. The results for water quality parameters showed that electrical conductivity (EC) and total dissolved solids (TDS) increased during the study period and that their values ​​at Gardeh Yaghub station (basin outlet) were higher relative to the Cotter station (upstream). This observation can be explained by the fact that the Mahabad River flows through agricultural lands between Cotter and Gardeh Yaghub stations. It can be concluded that land use changes have played a major role in changing surface water quality parameters in the region and have reduced water quality of the Mahabad River during the period from 1992 to 2011.