Title page for ETD etd-08132008-150224

Type of Document

Master's Thesis

Author

Lenhart, Hayes Austin,

Author's Email Address

halenhar@ncsu.edu

URN

etd-08132008-150224

Title

A North Carolina field study to evaluate the effect of a coastal stormwater wetland on water quality and quantity and nitrogen accumulation in five wetland plants in two constructed stormwater wetlands.

Degree

Master of Science

Graduate Program

Biological and Agricultural Engineering

Advisory Committee

Advisor Name	Title
William F. Hunt III	Committee Chair
Dennis J. Werner	Committee Member
Michael R. Burchell II	Committee Member

Keywords

nitrogen
wetland
BMP
stormwater
plant uptake

Date of Defense

2008-08-01

Availability

unrestricted

Abstract

A stormwater wetland in River Bend, North Carolina, was instrumented to collect water quality samples and monitor water quantity between June 2007 and May 2008. Inflow and outflow water quality concentrations and loads were compared for total kjeldahl nitrogen (TKN), nitrate and nitrite (NO2-3-N), ammonium (NH4-N), total nitrogen (TN), total phosphorus (TP), ortho phosphorus (OP), and total suspended solids (TSS). Inflow and outflow runoff peaks and volumes were also examined.
A total of 24 and 11 storms for water quantity and water quality have been collected and statistically compared, respectively. The wetland reduced peak flow rates by 80% and runoff volumes by 54%. Both peak flow rates and runoff volumes were significantly (p<0.05) reduced. Mean concentration reductions of TKN, NO2-3-N, NH4-N, TN, TP, OP and TSS were -70%, 9%, -53%, -51%, 0%, 39% and -30%, respectively; while mean load reductions were 35%, 41%, 42%, 36%, 47%, 61% and 49%, respectively. There was no significant difference (p>0.05) between inflow and outflow concentrations for all but one of the previously mentioned pollutants. Inflow concentrations of OP were significantly greater (p<0.05) than outflow concentrations. There was no significant difference (p<0.05) between inflow and outflow loads for all but two of the previously mentioned pollutants. Inflow loads for OP and NH2-3-N were significantly greater (p<0.05) than outflow loads. There was no significant difference in pollutant loads (p<0.05) between the growing and non-growing seasons.
Mean influent and effluent concentrations were compared with background stream concentrations in the same watershed to better quantify wetland water quality. Mean influent and effluent concentrations from other wetland studies in North Carolina and those from River Bend were compared in order to determine how well the wetland is functioning with reference to other statewide wetlands.
Phosphorus deposition was also monitored by taking soil samples at specific locations in the wetland every 2 months for a year. It was found that there was a significantly greater (p<0.05) concentration of P in soils closer to the inlet of the wetland compared to P concentrations at the outlet. The P concentration profile from the wetland substrate did not appear to change substantially over time; therefore, no evidence of P migration along the wetland bottom existed. This suggested that the wetland had become saturated with P and was no longer effectively removing P.
Vegetation was harvested in two stormwater wetlands located in Smithfield and Pactolus, North Carolina, to evaluate the ability of five wetland plant species to sequester 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 September and October 2007 and analyzed for nutrient content on a % N of biomass basis. At the Pactolus wetland the Pontederia cordata, Scirpus cyperinus and Schoenoplectus tabernaemontani biomass retained significantly (p<0.05) more nitrogen than Sagittaria latifolia and Saururus cernuus. At the Smithfield wetland, Pontederia cordata and Sagittaria latifolia biomass retained significantly more nitrogen than Scirpus cyperinus and Saururus cernuus.
A positive relationship was noticeable between the density of harvested biomass and nitrogen removal for two species, Scirpus cyperinus and Sagittaria latifolia. A model for estimating total nitrogen loading in Coastal Plain watersheds in North Carolina was used to determine that harvested vegetation from a wetland in the Tar-Pamlico River basin could potentially account for 21% of nitrogen entering the Pactolus wetland on an annual basis. The implementation of stormwater wetland harvesting as a maintenance activity appears to be a potentially important practice for nitrogen removal.

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