Seasonal changes in the water quality of Sardab river: dual perspectives of the Iran Water Quality Index for Surface Water Resources – Conventional Parameters (IRWQIsc) and the National Sanitation Foundation Water Quality Index (NSFWQI)

The quality of river water is of great importance due to the limited availability of freshwater resources and the increased demand for water in the drinking water, agriculture, and other sectors. Rivers are one of the sources of this water supply, which are exposed to indiscriminate discharge of industrial, agricultural and human wastewater without proper environmental considerations.The study area in this research is the Sardabrud River located in Mazandaran province. The required data for conducting the research were collected from three stations along the river throughout a hydrological year and analyzed. In this study, the Iranian River Water Quality Index for surface waters (IRWQIsc) and the National Sanitation Foundation Water Quality Index (NSFWQI) were used to evaluate the river water quality. Based on the results, the values of the IRWQIsc index varied between 92.12-30.42 and the NSFWQI index between 92.35-48.075, indicating very good quality in spring and bad quality in winter for IRWQIsc, and excellent quality in spring and bad quality in summer for the NSFWQI, respectively.. Among the most important factors polluting the water of this river along its course are the discharge of agricultural and human sewage into the middle and downstream reaches, land use changes, and climate changes - which have caused a decrease in water quality along the river's path.Using the obtained results and current understanding, measures can be taken to prevent these polluting sources from entering the river to improve its water quality.