Monitoring the Spatial and Temporal Variations in Water Quality of the Haraz River : A Comparative Study of IRWQIsc and NSFWQI Index

Situated in northern Iran, the Haraz River stands out as a significant ecosystem, hosting diverse aquatic life and serving as a vital water source for dynamic commercial and industrial activities in its vicinity. This study employed both the Iran Surface Water Quality Indicators (IR-WQIsc) and the National Health Foundation Quality Index (NSF-WQI) to evaluate the water quality of the Haraz River.

Monthly water samples were collected from the central segment of the Haraz River, at a depth of 30 cm, throughout the year (1399-1400). An array of parameters including water temperature, pH, dissolved oxygen (DO), electrolyte conductivity (EC), total dissolved solids (TDS), turbidity, ammonium nitrogen (N-NH+ 4), nitrate nitrogen (N-NO3), phosphate (PO4), biochemical oxygen demand (BOD5), and total suspended solids (TSS) were meticulously measured and subjected to analysis.

According to the IR-WQIsc index, the Haraz River's water quality shifts from relatively good in the upstream direction to relatively poor as it progresses downstream during the spring, autumn, and winter seasons. Notably, spring marks the peak of upstream water quality, while winter exhibits the highest downstream quality. However, during summer, the river's water quality is comparably lower than in other seasons. On average, as per the IR-WQIsc index, water quality is categorized as "relatively good" during spring, autumn, and winter, while it declines to a "moderate" level in summer. Conversely, analysis using the NSF-WQI index reveals that river water quality is at its best during spring and least favorable in summer. In autumn and winter, water quality demonstrates consistent patterns and maintains an average level. An in-depth interseasonal assessment consistently identifies the summer season as having the lowest water quality across all three monitoring stations.

The assessment of water quality across seasons through distinct indicators yields insightful findings. The summer season experiences reduced water quality due to tourist activity in northern regions and environmental factors such as heightened temperatures. Furthermore, a discernible trend emerges wherein water quality demonstrates improvement from downstream to upstream, likely influenced by population density fluctuations along the river's trajectory. Conclusively, a comparative analysis of the two methods indicates a degree of concurrence in water quality assessment outcomes. However, the IR-WQIsc index emerges as a more precise classifier, underscoring its efficacy in such evaluations.