Assessment of spatial variability of some parameters affecting three water quality of Zarin Gol River in Golestan Province

With an increase in population and greater demand for agricultural and aquaculture activities, the importance of water resource quality and quantity have increased and, consequently, surface water resources are faced with more pollution than other water resources. Generalizing point measurements of water quality characteristics to maps is of special significance in most water resource-related studies. Interpolation techniques may be used to estimate unknown parameter values. The aim of this study is to use the best interpolation method for water quality assessment of Zarin Gol River and the effect of different human activities. For this purpose, samples were collected from 12 study stations in winter and spring 2016. Then, the spatial variations of physical and chemical parameters of surface water were determined including DO, NO3, PO4, Turbidity, pH and TSS and Hilsenhoff index (water quality index) using interpolation functions based on cross validation technique (lowest value of RMSE, highest value of R2 and lowest close to zero values of spatial data MBE and MAE) of deterministic and geo-statistical methods in a GIS environment. The results showed that, for all the studied parameters, the kriging method was more suitable than the IDW method and was selected for mapping. The results of the modelling showed that the maximum value of the Helsenhoff index was observed in stations 2 and 10 (5.31 and 5.2, respectively) during the winter season with a relatively weak class in terms of water quality. The results of indices showed that stations located downstream of fish farms were more polluted than those located upstream of or away from farms and enjoyed the self-purification process. Investigation of special variations in the environmental characteristics of water showed that increasing the physical and chemical parameters of surface water along the river, including wastewater discharge from villages, fish farms and agricultural activities, has a direct impact on water quality and the pollution level increases and the river water quality decreases from upstream to downstream.