the biological assessment of the zaringol stream using the structure of benthic macroinvertebrates (golestan province)

this study was conducted to assess water quality level of zarin gol stream on macrobenthic invertebrates. macrobenthic fauna were sampled from 9 selected sampling stations along the stream with an average distance of 22 km by using a surber sampler every 45 days during the year. sampling was replicated 9 times in each sampling station. collected samples were fixed with 4% formalin, isolated, and then identified. the number of total abundance of macrobenthic fauna were counted to 2749.021 ± 1301.8 (ind/m2) belonging to 15 orders and 81 groups (families and genus). the minimum and maximum of total abundance (ind/m2) was at station 1 (370.63 ± 231.1) and at station 5 (215. 73 ± 101.75), respectively. the main orders of macro benthic invertebrate communities in zaringol stream included diptera, ephemeroptera, trichoptera, plecoptera, oligocheta, odonata and amphipoda. population structure of macro benthic invertebrates were analyzed by biotic indices and the results showed significant differences in ept and ept/chir indices at different sampling stations (p0.05) along the stream. evaluation of indicators revealed less water quality at stations 2 and 5 where located at the lowermost of fish farms. this reduction might be implicated to the effluents of water damps from fish farms running into the stream as diversity and total abundance (%) of succible macro-invertebrates decreased and that of resistant macrofauna increased due to water pollution. hence, from the obtained results, this can be concluded that the use of benthic macro-invertebrates as bioindicator for the assessment of water quality of the stream is desirable.