use of benthic invertebrates population structure and distribution pattern for biological monitoring and water quality assessment in sharhrud river (qazvin province)

biological monitoring using benthic organisms is one of the best and the most inexpensive methods for anthropogenic activities evaluation in aquatic ecosystems. the purpose of present investigation was biological monitoring of shahrud river that was performed in the qazvin province using by macro benthic invertebrates population. in the present investigation macro benthic invertebrate samples were collected by surber sampler at 8 sampling stations with 3 replicates in each station for a period of one year. the collected samples were preserved in 4% formalin solution and transported to the laboratory for identification and counting. about 11636 individuals of benthic organisms were identified consist of 32 genera from 31 families, 9 orders, 5 classes and 4 phylum. the most important of benthic organisms were included trichoptera (42.27%), diptera (23.77%), ephemeroptera (16.64%) and pelecoptera (11.74%) according to abundance. from upstream to downstream population- biological indices values and abundances of sensitive organisms decreased in the other hand abundances of resistant organisms increased. the lowest and highest values of bmwp/aspt were 7.06 and 3.51 for station 4 and 8 respectively. evaluation of indicators revealed less water quality at stations 2 and 8 that received agricultural , industrial and residential sewages respectively. based on bmwp/aspt annual average value (5.51) shahrud water quality classified on low polluted level.