Identification and study of benthic organisms abundance and biomass to determine the water quality of Balikhli-Chai river in Ardabil

In this research, the identification and estimation of benthos biomass of Balikhli chai and downstream river of Yamchi dam in Ardabil province was performed to water quality determination for aquaculture. Sampling of benthos organisms in rivers conducted in 4 stations. After identification of benthos, their distribution percent, was determined the ratio of the frequency of individual of three orders of Ephemeroptera, Plecoptera, and Trichoptera to the frequency of individual in Chironomidae family and the Hilsenhoff Family Biological Index (FBI) to determine water quality condition at the stations was calculated. 11 orders and 21 families were identified from the study of river benthic species. Chironomidae family had highest number of observation and was present in 97 percent of the samplings. In terms of mean abundance and biomass, the Gammaridae family showed the highest value in station 1. Also, sensitive groups with grade 4 tolerance, namely Gammaridae, Baetidae, Heptagenidae and Hydropsychidae, were mainly present in stations 1 and 2. Biological index showed that station 1 had the lowest value of 4.4 and then, station 2 was 5.7. EPT/C index showed that stations 2 and 1 had the highest numerical values ​​of 49.5±81.7 and 10.8±16.9, respectively. In general, it was concluded from benthos investigation that according to the observation of very good to excellent biological index in station 1 and 2, which were closer to Yamchi Dam, there were more suitable conditions for aquaculture in these stations.