Functional Assessment for a Proposed Stormwater Treatment Wetland

Abstract

Urbanization can dramatically alter the hydrologic cycle and water quality, causing adverse effects on urban streams and floodplain wetlands. A proposed regional stormwater treatment wetland on a forested floodplain of South Buffalo Creek is planned. The wetland should improve water quality and stream habitat in an urban watershed found in Greensboro, NC, USA. The objectives of this research were to (1) characterize in-stream stormwater concentrations of sediment and nutrients and species composition of macroinvertebrates within South Buffalo Creek, (2) determine geomorphic properties of the stream channel upstream, within, and downstream of the proposed stormwater treatment wetland, (3) establish baseline water table hydrology on the floodplain of the proposed stormwater treatment wetland, and (4) determine the composition of the existing forest stand. The proposed wetland will remove from stormflow an estimated 1092 to 163 g/m2/yr (3111 to 4666 tons/mi2/yr) total suspended sediment (TSS) per unit area of the wetland with an accumulation of 0.08 cm/yr (0.20 in/yr). Total nitrogen and total phosphorus will be removed from floodwater in the wetland at a rate of 67% and 46% respectively. Reduction of peak flow and shear stress during storm flow should decrease channel erosion and lead to increased stream stability. Average depth to the local water table level on the floodplain should decrease, leading to an increased area of functioning wetland. Forest vegetation should likely shift to more wetland species with changes occurring in the herbaceous and understory layers first. Overall, the proposed stormwater treatment wetland should improve water quality and increase stream stability in South Buffalo Creek.