Biological index and pollution assessment of Damghanroud river in the Semnan province

Fresh water rivers are one of the most important aquatic ecosystems in arid and semi-arid regions of iran in viewpoint of biodiversity and drinking water. damghanroud river is one of the rivers in the semnan province that during past years has been threatened by drought and anthropogenic pollutions. this river supplies some parts of drinking water of damghan city and some vicinity villages. the aim of the present study was biological index assessment of the damghanroud river. at this study, seven sampling stations were determined based on limnological standard method along the river. sampling of invertebrates and water were performed respectively to calculate biological index and biochemical oxygen demand (bod) seasonally during the study period. the results showed that the first station (cheshmeh-ali) is free of pollution while the fourth sampling station (doab) is the most polluted region at the river because the first station has no pollutant resource but the fourth station directly receives wastewater of the agricultural activities and rural wastewaters. according to biomonitoring and water bod measurement findings, damghanroud river has relatively polluted situation and is classified in β- mezosaprobe class and benthos biological index has been deteriorated at this river.