W3 Seminar: Quantifying the hydrology & water quality efficacy of wetland and green infrastructure projects

Details

Presenter:
Joey Smith, Research Scientist, Department of Food, Agricultural and Biological Engineering, Ohio State University

Title:
Quantifying the hydrology and water quality efficacy of large-scale wetland and green infrastructure projects in Ohio

Abstract:
“I’m swamped!” Wetlands in Ohio were drained for the same reason wetlands carry a negative connotation in the English language: westward expansion. The Great Black Swamp was a large, glacially fed wetland in northwest Ohio that was drained and converted to agricultural land. The destruction of the Great Black Swamp, which filtered nutrients from runoff, contributed to the harmful algal blooms in and the eutrophication of Lake Erie. Today, wetlands and green infrastructure (GI) are being adopted on large scales in Ohio to combat ongoing nutrient pollution and eutrophication problems throughout the state. This presentation quantifies the hydrology and water quality efficacy of two such projects.

Williamsburg Wetland — In response to recurring harmful algal blooms in Harsha Lake, Clermont County, Ohio, a riparian wetland was constructed in the floodplain of the East Fork Little Miami River, which drains to Harsha Lake and ultimately the Ohio River. The 4-ha constructed wetland system consists of three contiguous treatment zones: a wintering pool (forebay); a 3-acre detention basin (repurposed from a retired drinking water reservoir); and a 7-acre highly sinuous wetland. For the overall system, statistically significant (n = 8, p ≤ 0.05) pollutant load retention was: 93% TSS; 64% total phosphorus (TP); 47% total nitrogen (TN).

Blueprint Columbus — The City of Columbus, Ohio began retrofitting GI into existing development through a multi-decade project in response to a sanitary sewer overflow consent decree. Primary design goals were reducing TSS loads in runoff by 20% and stormwater infiltration and inflow to the sanitary sewer. Through this paired watershed study, nutrients, sediment, and heavy metal reductions were observed in an 11.5-ha watershed where three online bioretention cells treated 66.5% of the imperviousness. TN, TP, and TSS event mean concentrations (EMCs) decreased by 13.7–24.1%, 20.9–47.4%, and 61.6–67.7%, respectively. Runoff attenuation by GI contributed to pollutant load reductions of 24.0–25.4% (TN), 27.8–32.6% (TP), and 59.5–78.3% (TSS). Reductions in TSS concentration were similar (within a margin of 5%) to the percent of the watershed imperviousness treated by GI. GI also contributed to modest heavy metal reductions at the watershed scale.