A novel device with macrophytes and bio balls as a rehabilitation tool for small eutrophic urban ponds: a mesocosm approximation

During the last century, the human-derived impact on freshwater systems has been severe all around the world. Artificial eutrophication has an outstanding relevance in urban aquatic ecosystems and it is recognized as one of the most common problems associated with water deterioration in urban lakes and ponds. Therefore, more studies regarding the trophic interactions and the potential rehabilitation methods should be encouraged. Our aim is to evaluate at a mesocosm scale, a device composed of native aquatic plants, either submerged (SPD) or floating (FPD), including an extra artificial potential refuge (bio balls rolls) for zooplankton as a rehabilitation tool for urban ponds. As regards the impact of the tested devices on water quality variables, FPD provoked a decrease in TP and pH. In turns, SPD maintained the dissolved oxygen concentrations above those registered in FPD. Transparency was significantly higher in the presence of plants at final time. Differences in phytoplankton morpho-functional group diversity and zooplankton functional feeding groups were registered by the end of the experiment. Zooplankton abundance at the artificial refuges was higher than at the water column; a study of the efficiency of the bio balls rolls as potential active/passive refugees is merited.Considering benefits on water quality variables, we suggest that a device combining floating macrophytes plus the bio ball rolls deserves to be further tested at a greater scale in order to be considered as a water rehabilitation tool, including plant harvest.