Impact of extreme flooding on the diversity of macrobenthic assemblages in the lower reaches of the Gorganroud River, Golestan Province

In recent decades, floods have changed riverine ecosystems drastically. The Gorganroud River in northern Iran experienced an extreme flood in March 2019. To examine the impact of this flood on the diversity of macrobenthic assemblages, a 2 yr study was conducted with over 6 surveys at 3 sites, with 3 replicates at each site, in the lowest reaches of the river. The results showed that Chironomidae, which were the dominant taxa before flooding, almost disappeared due to the flooding. In addition, the abundance of macrobenthic taxa was significantly reduced. Contrarily, the richness of the taxa did not change. Furthermore, although the abundance of macrobenthic taxa was immediately reduced after the flood, it was not fully recovered 1 yr after it. Additionally, this flood happened after a prolonged drought, a circumstance that enhanced the impact of the flood. Thus, providing rivers with unrestricted flow would be more beneficial to the macrobenthic communities in rivers that feature dam constructions.