Investigating the effect of land use type on surface water quality in the Talar watershed in Mazandaran

Objective: To study changes in water resource quality with emphasis on the role of existing land use and geological characteristics during the period 2011-2021 using satellite imagery and quantitative and qualitative data on groundwater resources in the Talar watershed.Method: The Talar is one of the mountainous watersheds in the north of Iran and is located in central Alborz. Landsat 7 and 8 satellite images were used to study land use in the Talar basin during the period 2011-2021. To produce the land use map, atmospheric, geometric and radiometric errors were first corrected, then a land use map was produced using false colour combinations and training samples separately for each year. The used softwares were ArcMap, ENVI 5.6 and Google Earth Engine. Google Earth Pro7.3.6 software was also used to check and control the ground points. Pearson correlation was then used to determine the relationship between different factors on water quality. The kappa coefficient was also used to check the validity of land use. Then, considering the current situation, some parameters of EC, TDS, pH, Ca2+, Mg2+, Na+, K+, HCO3-, CO3-2, Cl-, SO42- were studied using RSC index, agricultural standards and Schuler diagram.Results: The results of the parameter investigation showed that the parameters Cl and SAR with values of 1.13 and 51.6 were below the standard limit, but the parameter EC with a value of 24.755 was above the standard limit. The highest percentage of land use was pasture (71%) and the lowest percentage of land use was water resources (0.01%). Based on the kappa coefficient, all maps have a good accuracy. Residential land use was the main factor changing the quality of water resources in the Talar catchment, while forests and pastures had the least negative impact on water quality. Based on the measurements, the concentration of water quality elements in the Talar River is lower than the average agricultural standard and is in two categories: C1S1 and C2S1, and is suitable for agricultural use. The water quality classification based on SAR parameters, sodium percentage, RSC index and Schuler diagram indicates that the quality is good and suitable for agriculture and drinking. The results show that land use changes in the Talar basin have been progressive, with a decrease in pasture and forest land and an increase in barren and residential land.Conclusions: Considering the location of the Talar basin, it was found that the presence of industrial and agricultural uses along the river, and agricultural activities, increased use of pesticides and fertilizers, and the discharge of agricultural effluents into this river, as well as sewage and waste from residential and industrial areas, are among the factors affecting changes in water quality. Therefore, information on land use changes to examine their factors and causes over a period of time can be of interest to planners and managers and help them make the necessary decisions.