Plant Nutrient Uptake in Full-Scale Floating Treatment Wetlands in a Florida Stormwater Pond: 2016-2020

Nutrient enrichment of surface waters degrades water quality. Municipalities need effective and economical solutions to remove nutrients from surface waters. From July 2016 to May 2020, full-scale (900 m(2), 5% cover) floating treatment wetlands (FTWs) were deployed in Wickham Park pond, a eutrophic water body (0.13 mg/L total phosphorus (P), 0.96 mg/L total nitrogen (N)). The plants in FTWs in close proximity to a SB10000 mixer fixed N and P more efficiently. The rate of N (g/m(2)/year) fixed within tissues was highest for Juncus effusus (13.5), Agrostis alba (13.2), and Sagittaria lancifolia (12.1). The rate of P (g/m(2)/year) fixed within plant tissues was similar for all species (3.77, Agrostis alba, Canna spp., Iris hexagona, Juncus effusus, and Sagittaria lancifolia) save Pontederia cordata (2.52) volunteer species (1.41). The N and P removed with plant harvest were similar for non-mixed and mixed FTWs. Notably, the N:P ratio in plant tissues in 2017 (pre-mixer installation) was 11:1; after mixer installation (2018-2020), N:P ratios averaged 2.7:1, indicating increased P fixation within plant tissues. In 2017, 12,828 kg of plant tissues was harvested, removing 334 kg of N and 29.5 kg of P. In 2019, 32,958 kg of plant biomass was harvested from the pond, removing 425 kg of N and 138 kg of P. In 2020, 27,945 kg of biomass was harvested from FTWs, removing 267 kg of N and 95 kg of P. From 2016 to 2020, 73,000 kg of biomass was harvested, removing 1026 kg of N and 262 kg of P from Wickham Park pond. Knowing the total fresh biomass of tissues removed from FTWs at harvest is critical for accuracy in reporting nutrient removal aided by FTWs.

Automated summary

The study shows that floating treatment wetlands can effectively remove nitrogen and phosphorus from water bodies. Different plant species have varying efficiency in fixing nitrogen and phosphorus, but the amounts of nitrogen and phosphorus removed after plant harvest are similar. Harvesting plants can effectively reduce the nitrogen and phosphorus content in surface waters.