Floating treatment wetlands are potential alternatives to traditional constructed wetlands for remediating
nutrient-rich water. This study examined the remediation efficacy of floating treatment wetlands
planted with Canna flaccida and Juncus effusus in a replicated trough system over two growing seasons
at two nutrient loading rates. Plant growth parameters were measured on a biweekly basis, and water
quality parameters were monitored weekly. Plant shoots and roots were harvested at the end of the first
growing season, and biomass was dried, ground, and analyzed for nutrient content. Juncus plants fixed
28.5 ± 3.4 g N per m2 and 1.69 ± 0.2 g P per m2, while Canna fixed 16.8 ± 2.8 g N per m2 and 1.05 ± 0.2 g
P per m2. More N and P were fixed in the below-mat biomass of both species than in the above-mat
biomass, thus whole-plant harvest may be a critical management strategy for floating treatment wetlands.
During the first season, when nutrient addition rates simulated stormwater loading conditions, effluent
nutrient concentrations were very low and averaged 0.14 ± 0.04 mg L−1 total N and 0.02 ± 0.01 mg L−1
total P. During the second season, nutrient-loading rate into treatment wetlands was doubled to simulate
a more nutrient-rich runoff, and effluent nutrient concentrations averaged 0.79 ± 0.3 mg L−1 total
N and 0.12 ± 0.03 mg L−1 total P. Floating treatment wetlands may prove most effective in low nutrient
environments where it is necessary to polish water quality to extremely low P concentrations