Abstract
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 m2, 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/m2/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/m2/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.
Highlights
The N and P removed with plant harvest were similar for non-mixed and mixed floating treatment wetlands (FTWs)
Water column mixing enhanced the rate of nitrogen and phosphorus fixed within plant tissues of those plants initially established within the island, with N removal rates over 2019 ranging from 7.42 (Iris) to 13.5 (Juncus effusus) g/m2 /year and P removal rates ranging from 2.52 (Pontederia cordata) to 3.91 (Canna spp.) g/m2 /year
Similar nutrient uptake in mixed and non-mixed treatments could partially be explained by the contributions of volunteer species that fixed more nutrients in non-mixed FTWs than mixed FTWs, offsetting the increased nutrient uptake by the initial plant species installed within the FTWs
Summary
The presence of excess nutrient, metal, organic, and pathogen contaminants often impairs the quality of surface and ground water [1,2,3,4]. Nutrient contaminants are of specific concern to inland and coastal communities due to the persistence, frequency, and consequences of algal blooms [5,6,7]. Algal blooms are an increasing problem in the USA, both inland and in coastal areas. In the USA, the state of Florida administers water resources at the regional level using five water management districts [8]. Among the water management districts’ core mission areas is water quality, addressing water quality issues through various practices, including monitoring and restoration. Within the St. Johns River Water Management District, water quality efforts are coordinated among many partners, including the Florida Department of Environmental Protection
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