using discriminant analysis to examine ecological effects of rainbow trout farms wastewater on benthic community structure, a case study with the gamasiab river

the gamasiab river has one of the highest discharge in the western iran receiving wastewater of trout frames. the present study investigated effects of wastewater using bioassessment of benthic organisms. the benthos were sampled over four seasons using a surber sampler on four stations, upstream, on the farm outlet, 500 and 1000 m down the farm outlet. 5454 benthic fauna were identified that were belonged to 11 orders, 22 families and 25 genera. the ephemeropterids had the highest abundance belonged to four families and six genera. over all seasons, macroinvertebrates abundance and ept percentage decreased on the inlet. the taxonomic richness decreased over the spring and autumn and increased in the summer, which was not significant statistically. the shannon-weiner diversity index showed no significant changes in most sampling stations. based on the hilsinhoff biotic index, the water quality in the sampling stations were very good, good and suitable. using the discriminant analysis, the outlet of the farm had the highest difference with the sampling stations in the upstream area, and the benthic structure had the highest difference with the samples collected in other seasons. a negative correlation was detected between shannon-weiner and ept/chir when the sampling stations were examined, and a positive correlation when sampling times (seasons) were examined using discriminant analysis. in conclusion, the water quality improved 1 km downstream of the farm but the benthic structures were not fully recovered.