Seasonal composition, abundance, and biodiversity of benthos assemblages in Gorganroud River, Golestan Province

An annual survey of benthos fauna in a river can provide accurate information on contamination levels for other researchers. According to the entering of municipal and agricultural wastewater into the Gorganroud River, the purpose of this study was a determination of the composition, abundance, and diversity of the benthic communities in this river as a part of the nutritional levels of this aquatic ecosystem. This study was conducted in 5 different stations on a monthly basis during a one-year sampling period between 2009-2010. Sampling operation was carried out using a Surber sampler (With an area of 1600 centimeters) with 3 replications. Based on the results, 3 phyla and 16 genera of benthos fauna were identified that annelids, arthropods, and mollusks had 3, 4 and 9 genera, respectively. The highest biodiversity of 2.67 and 0.86 was in obtained autumn and the lowest biodiversity with a seasonal mean of 2.16 and 0.81 was obtained in summer. Based on the comparison of benthic communities, the average density of the final benthos assemblages of four seasons in the determined stations was significantly different (P<0.05), but the average density of the seasons was not significantly different (P>0.05). According to these results, there was no significant difference between temperature, dissolved oxygen, and acidity level of different stations (P>0.05), and depth showed the significant difference between different stations (P<0.05). Also, correlation analysis of water factors and density of benthos communities showed a lack of correlation between them at different stations (P> 0.05).