Application of floating wetlands for the improvement of degraded urban waters: Findings from three multi-year pilot-scale installations

Abstract

Floating Treatment Wetlands (FTWs) are an emerging ecological engineering technology being applied the restoration of eutrophic urban water bodies. Documented water-quality benefits of FTW include nutrient removal, transformation of pollutants, and reduction in bacterial contamination. However, translating findings from short-duration lab and mesocosm scale experiments, into sizing criteria that might be applied to field installations is not straightforward. This study presents the results of three well established (>3 years) pilot-scale (40–280 m2) FTW installations in Baltimore, Boston, and Chicago. We quantify annual phosphorus removal through harvesting of above-ground vegetation and find an average removal rate of 2 g-P m−2. In our own study and in a review of literature, we find limited evidence of enhanced sedimentation as a pathway for phosphorus removal. In addition to water-quality benefits, FTW planted with native species, provide valuable wetland habitat; and theoretically improve ecological function. We document efforts to quantify the local effect of FTW installations on benthic and sessile macroinvertebrates, zooplankton, bloom-forming cyanobacteria, and fish. Data from these three projects suggest that, even on a small scale, FTW produce localized changes in biotic structure that reflect improving environmental quality. This study provides a simple and defensible method for sizing FTW for nutrient removal in eutrophic waterbodies. We propose several key research pathways which would advance our understanding of the effects FTW have on the ecosystem they are deployed in.