Sensitivity assessment of the National Sanitation Foundation Water Quality Index (NSFWQI) and IRan Water Quality Index for Surface Water Resources (IRWQIsc) on the water quality of the Neka River

In recent years, the improper increase of agricultural activities along riverbanks and discharge of household, agricultural, and industrial wastewater into them has led to a significant reduction in the quality of surface water. Polluted or contaminated water sources can have a negative impact on the entire life cycle. In this study, the trend of changes in the water quality of Neka River, from its source to its connection to the Caspian Sea, has been investigated. Samples were collected at three different points along the river during different seasons in 2021 and were analyzed using IRWQIsc and NSFWQI standards. Results showed that, based on the IRWQIsc index, the river is relatively good quality, and according to the NSFWQI index, it is of moderate quality, but at station 3, the river's quality is relatively poor using both indexes. The overall water quality follows a downward trend from the source to the outlet, with greater declines in quality during warmer seasons due to increased agricultural activities in the river basin, with the largest decrease in quality observed in spring and the smallest decrease in quality in the colder seasons, especially in winter.