Temporal and spatial variations of macrobenthic invertebrate community and water quality of Pasikhan River, Guilan

Water quality assessment using water quality indices and biotic indices is a group of suitable methods. This study was carried out to determine temporal and spatial variations of benthos in Pasikhan River, north of Iran. Therefore, 6 sampling stations were set up along the river mainstream and the macrobenthic invertebrate community samples were collected from these stations during 4 seasons (from autumn 2015 to summer 2016), seasonally. The benthos samples were collected by surber sampler (25×25 cm) in sixteen replicates, then were identified and counted. The results of the benthic communities of Pasikhan River showed the dominant taxa of the invertebrates collected belonged to aquatic insects group. In this study, 18 families of 9 orders of benthic macroinvertebrates were identified. BMWP index at sixth station, showed the lowest annual average score (5.50±2.38) with so bad quality and the second station, showed the highest average score (41.00±16.39) with medium quality. Also, according to the annual average ASPT, second station had the highest score (5.83±0.38), and showed suspected to water pollution. The sixth station with the lowest score (2.50±0.91) was classified in high pollution group. Among the seasons, the highest and the lowest amount of both BMWP and ASPT were observed in winter and autumn, respectively.
The results of Hilsenhoff index between stations showed that first station with average score (5.26±1.10) was categorized in medium class and fourth station with average score (4.58±0.56) was categorized in good class. This could be due to sand mining before first station (Bodab Bridge). Based on the results, biotic indices showed that water quality in Nokhale station (Station 6) that is located in downstream is the lowest that may be due to anthropogenic activities, discharge of domestic wastewater and agricultural runoff and sand mining.