Macrophyte performance in floating treatment wetlands on a suburban stormwater pond: Implications for cold climate conditions

Stormwater ponds (also called detention basins or retention ponds) are a commonly employed method to control runoff flow from developed lands. They function to reduce peak discharge and provide settling of suspended particulate pollutants but do not perform well in removing fine particulates or dissolved nutrients. Floating treatment wetlands (FTWs) are modular floating vegetated mat systems gaining attention as potential stormwater pond retrofits to improve pollutant removal performance. This study presents data on the FTW suitability of four plant species native to the Northeast region of the United States and commonly referenced in other FTW studies: Juncus effusus L. (Common Rush), Schoenoplectus tabernaemontani (C.C. Gmel.) Palla (Softstem Bulrush), Carex comosa Boott (Longhair Sedge), and Pontederia cordata L. (Pickerel Weed). Species were evaluated for suitability of FTW in cold climates based on their survival rate, biomass development, phosphorus (P) uptake and storage in shoots, and root architectural features. S. tabernaemontani survived the winter most successfully with greater than 95% of planted plugs resprouting the following spring after the first winter. P. cordata suffered a nearly complete loss. C. comosa produced the most biomass (35.6 ± 12.8 g/plant individual) and P. cordata produced the least (3.6 ± 3.98 g/plant). A self-seeded species populated all of the mats at the study site (Bidens vulgata) and produced sizable biomass over the growth season but with a large range (12.4 ± 12.0 g/plant individual) due to the variable growing time of each individual. P. cordata and B. vulgata had the highest P concentration (5.72 ± 0.71 g/kg and 7.49 ± 0.15 g/kg respectively). When controlled for individual plant mass, C. comosa had the greatest P content per plant individual. The longest measured root segments were associated with the C. comosa (32.6 ± 15.8 cm) and B. vulgata (29.4 ± 16.9 cm). P. cordata produced the shortest root segments (11.9 ± 5.1). S. tabernaemontani and J. effusus had similar root lengths (19.6 ± 11.1 and 18 ± 6.8 cm, respectively). C. comosa had higher root surface area than any other species studied and had a greater than 90% survival over the winter. Overall, C. comosa was the best performing species and may be more suitable for FTW in stormwater ponds in cold climates.