Phytoplankton diversity recovers slowly and cyanobacterial abundance remains high after the reflooding of drained marshes

Wetland restoration with the goal of restoring natural ecosystem functioning is receiving attention worldwide. Mesopotamian marshes, which had been suffering from a water shortage since the 1970s, were reflooded in 2003, and have been assessed to be at least partly recovered from certain physical, chemical, or biological point of views. Our focus was in the phytoplankton community and through that in the aquatic food web in order to understand the recovery of the normal functioning of the marsh ecosystem. We sampled eight separate marshes that formed a continuum from a wet to a desertified area during the desiccation period. Three to five years after the reflooding, we measured the biomass, diversity and structure of the phytoplankton community and its controlling physical and chemical factors 11 times irregularly. In most cases, the dried and reflooded marshes had a less diverse phytoplankton community than the marsh that had never dried up. The community structure of the latter differed from all dried marshes and was the most divergent from the marshes that had been succumbed to desertification and were situated farthest away from the freshwater rivers. We conclude that the aquatic food web and thus the natural wetland ecosystem functioning recover more slowly than single physical or chemical factors. Cyanobacteria species abundance may be of concern from a management point of view for a long period of time.