Algal blooms resulting from the eutrophication of surface waters represent a significant ecological and water treatment issue. The potential for wetland systems to act as sinks for various types of pollutants indicates their potential for mitigating algal blooms. Although nutrient uptake in terrestrial treatment wetland systems has received substantial attention in the literature, relatively little is known about the mechanisms involved in floating constructed wetland (FCW) function for algal control and whether plant species can optimise performance. Here, the effect of FCWs on water quality including nutrient levels and algal biomass was investigated, along with the effect of planting with different species of macrophyte. All the planted FCWs showed significant potential for algal bloom mitigation in both hypereutrophic and mesotrophic systems; algal biomass control is proposed to be due to the direct uptake of nitrate and phosphate via macrophyte roots, rather than algaecidal effect of phenolic compounds. Dissolved organic carbon (DOC) release was found to differ between species, with implications for drinking water treatment.

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The objective of this study was to monitor a newly constructed wetland (CW) in north Wales, UK, to assess whether it contributes to an improvement in water quality (nutrient removal) of a nearby drinking water reservoir. Inflow and outflow of the Free Water Surface (FWS) CW were monitored on a weekly basis and over a period of 6 months. Physicochemical parameters including pH, conductivity and dissolved oxygen (DO) were measured, as well as nutrients and dissolved organic and inorganic carbon (DOC, DIC) concentration. The CW was seen to contribute to water quality improvement; results show that nutrient removal took place within weeks after construction. It was found that 72 % of initial nitrate (N03 (-)), 53 % of initial phosphate (PO4 (3-)) and 35 % of initial biological oxygen demand (BOD) were removed, calculated as a total over the whole sampling period. From our study, it can be concluded that while inorganic nutrients do decline in CWs, the DOC outputs increases. This may suggest that CWs represent a source for DOC. To assess the carbon in- and output a C budget was calculated.