Environmental Impact Assessment of Aquaculture Effluent On Benthic Fauna; Case Study: Gomishan Wetland, Golestan Province

Aquaculture is one of the human activities in which uncontrolled development has negative effects on the environment and biomonitoring can be used to explore it. In this study, the environmental impacts of shrimp farms effluents on macroinvertebrate communities in Gomishan Wetland were investigated. Sampling was performed from six stations monthly for one year and five biological indices were used to investigate the quality status. The results showed that the average density of macroinvertebrate communities was 31934 individual/m2 and the most frequent family was Pyrgulidae. The maximum density among stations was observed in Gorganrood River mouth station. The comparison of density in different months showed that in the first three months of the year, the it was higher than the others; Then, the frequency decreased in summer. Along with the depletion of shrimp farms effluents into the Gomishan Wetland in August, the average abundance of macroinvertebrates increased, but it reduced again in the last four months of the year. The Margalf and Shannon-Weiner indices in different months and stations indicated pollution in this wetland. By calculating the Simpson index, it was found that by increasing the pollution, along with the reduction of water volume, the distribution of macroinvertebrates became more uniform. Pielou index with the mean of 0.4 showed no significant differences between different stations and months. Also, the study of distribution index confirmed the clumped distribution. The water quality in Gomishan Wetland was undesirable, indicating the necessity of effective management policies to improve the water quality in this international wetland.