Floating treatment wetland aided remediation of nitrogen and phosphorus from simulated stormwater runoff

• We quantify season-long nutrient removal aided by floating treatment wetlands.
• We quantify plant (Canna and Juncus) contributions to nutrient removal.
• Higher nutrient loading results in lower nutrient removal percentages.
• Floating treatment wetlands decrease water temperature, pH, and dissolved oxygen.
• Whole plant harvest is a key management strategy for low nutrient environments.

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.