Investigation of seasonal composition, abundance and biodiversity of macroinvertebrate communities in Khormarud river, Golestan province

Benthic macroinvertebrate communities are a biological indicator in aquatic ecosystems. The aim of this study was to investigate the abundance and biodiversity of macroinvertebrate communities in Khormarud River, Golestan Province. Macroinvertebrate samples were collected seasonally from 5 stations with three replications in 2020 using a Vanveen grab with a cover area (225 cm2). A total of 819 specimens of macroinvertebrate belonging to 6 orders and 10 families were identified, with the highest diversity belonging to the order of insects with 7 families and the highest abundance belonging to Chironomidae (31.5%) and then Tubificidae (22.47%). Spring with 45% had the highest and winter with 22% had the lowest abundance. The highest distribution of macroinvertebrate was obtained in station 1 in upstream (40.66%) and the lowest in station 5 in downstream (5.86%). The results showed that the highest Shannon and Simpson diversity indices were obtained in station 1 in upstream of autumn season (1.96 ± 0.32) and (0.85 ± 0.11), respectively. Also, the highest values ​​of Margalf species richness index in station 3 in midstream of winter (2.06 ± 0.4) and Pielou's evenness index in station 3 (0.94 ± 0.19) were spring. According to the Multidimensional Scale Analysis (MDS), the distribution of macroinvertebrate among the stations showed three distinct groups. PCA results showed that organic matter and clay are the most important environmental factors in the changes of macroinvertebrate communities in Khormarud river, Golestan province. The results showed that this river due to increased organic matter from agricultural areas, adjacent urban and rural wastewater caused increased contamination of the benthos resistant to the pollution, including Tubificidae and Chironomidae, these indicators could be used as useful tools for evaluating water supplies quality.