A study on macrobenthic communities in the lower zone of Ghaersou river- Golestan province

The aim of this research conducted in the lower zone (or estuary) of Gharesou River was to study biodiversity of the macrobenthos and changes in sedimentary organic matter in river litter. No sample collected in summer 2018 due to drying river. Sampling was undertaken over five surveys, (May, June, November, and December 2018 and March 2019), in four sites (with two replications). The results of split plot analysis showed that sedimentary organic matter in river litter reduced significantly in autumn 2018 and winter 2019 (P<0.05). Whilst, biodiversity indices like species abundance, species richness, and evenness showed significant differences among surveys, Shannon, Simpson, and Berger-Parker indices had no significant differences (P>0.05). Species abundance reduced to -0.87 in autumn, and also species richness reduced to 3 species in autumn, including Tubificidae, Chironomidae, and Spionidae (Streblospio sp.). In addition, Species abundance was the only biodiversity index which had significant difference among sampling sites (P<0.05), as species abundance reached to the highest level (i.e., -0.7) in the fourth site. Thus, river drying in summer reduced species abundance and richness in autumn. But, when water reflowed in river in autumn, two species belonging to Tuificidae and Shironomidae were emerged first in river, which might be associated to the higher resistance of these two families to the rigid environmental conditions, like river drying.