Nitrogen accumulation for five native North Carolina wetland plant species in stormwater wetlands

Abstract

As the use of constructed stormwater wetlands to treat stormwater runoff becomes more frequent, strategies for maintaining their pollutant removal over time must be examined. One potential strategy is plant harvesting to remove nutrients that would otherwise be deposited back into the wetland during senescence. Vegetation was harvested in two stormwater wetlands located in Smithfield and Pactolus, North Carolina, in 2007 to evaluate the ability of five wetland plant species to uptake nitrogen. Biomass samples from harvested emergent vegetation for Pontederia cordata (Pickerelweed), Saururus cernuus (Lizard Tail), Scirpus cyperinus (Wool Grass), Sagittaria latifolia (Arrowhead) and Schoenoplectus tabernaemontani (Softstem Bulrush) were collected in October 2007 and analyzed for nutrient content. At the Pactolus wetland Pontederia cordata, Scirpus cyperinus and Schoenoplectus tabernaemontani biomass retained significantly (p<0.05) more nitrogen than Sagittaria latifolia and Saururus cernuus. While at the Smithfield wetland, Pontederia cordata and Sagittaria latifolia biomass retained significantly more nitrogen than Scirpus cyperinus and Saururus cernuus. No Schoenoplectus tabernaemontani was found in the Smithfield wetland. Wetland maturity had a direct relationship to harvestable nitrogen which could explain the change in significance of Scirpus cyperinus, and Sagittaria latifolia between the two wetlands. A model for estimating total nitrogen loading in Piedmont watersheds in North Carolina was used to determine that harvested vegetation from a wetland in the Tar-Pamlico River basin could potentially account for approximately 21% of nitrogen entering the system on an annual basis. The implementation of stormwater wetland harvesting as a maintenance activity appears to be a potentially important practice for nitrogen removal.