Publication
Authors
Joseph S. Smith, PhD Candidate, Department of Food, Agricultural and Biological Engineering (FABE), Environmental Science Graduate Program
Ryan J. Winston, Assistant Professor, FABE and Department of Civil, Environmental, and Geodetic Engineering, College of Engineering
David M. Wituszynski, Former PhD Student, FABE; Research & Development Fellow, Engineering Industries International
R. Andrew Tirpak, Research Scientist, FABE
Kathryn M. Boening-Ulman, Lecturer and PhD Candidate, FABE
Jay F. Martin, Professor, FABE
Quick Take
The puddles on parking lots aren’t as innocent as you may think. As urban areas expand, soil and vegetation are replaced with concrete and asphalt—materials which typically don’t allow water to pass through. After rainstorms, stormwater collects in puddles and eventually goes down manmade drains, bringing along with it all the lawn fertilizers, pesticides, trash, vehicle emissions, and sediment that end up on the ground in developed areas. This urban runoff can end up in lakes, rivers, and oceans without treatment, and potentially harm humans, wildlife, and entire ecosystems.
Low impact development (LID) tries to mitigate these negative effects by using stormwater control measures that imitate natural hydrology, or the way that water naturally moves through landscapes. A typical part of LID is green infrastructure (GI), which improves stormwater quality and reduces runoff by allowing water to escape into the soil and air. Researchers in the Department of Food, Agricultural and Biological Engineering studied three watersheds (two experimental and one control) in the Clintonville neighborhood north of Columbus, Ohio, to determine how effectively the newly implemented green infrastructure improved the water quality and hydrology in the neighborhood.
Results
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Total nitrogen levels, but especially organic nitrogen levels, were significantly reduced by over 13% (19.6% for organic nitrogen) with the introduction of green infrastructure. This was primarily accomplished through nitrification (an important step in the nitrogen cycle that eventually allows plants to absorb nitrogen from the soil), sedimentation (which removes suspended solids from water), and filtration (which removes particulate matter).
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Total phosphorus concentration was reduced by 20.9% to 47.4%, and loads following storm events were reduced by 27.8% to 32.6%, after the researchers introduced GI.
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Total suspended solids (TSS) concentration, which includes any solids that are suspended—not dissolved—in water, was reduced by over 60% in both experimental watersheds after GI was introduced. The rate of this reduction closely followed the percentage of surfaces treated by GI.
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The annual loads of ammonia, nitrate, total nitrogen, total phosphorus, and total suspended solids decreased significantly after GI was introduced. Organic phosphorus decreased in one watershed, but it increased in the more forested watershed.
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The control watershed did not show significant changes to water quality, suggesting that the improvements in runoff quality in the watersheds were caused by the newly implemented GI.
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The study authors noted that more research is needed to determine the specifics of what types of GI and their placement in the watershed are most effective at improving water quality, which will likely prove useful for engineers, municipalities, and environmental regulators looking to implement GI in their cities.
Citation
Smith, J. S., Winston, R. J., Wituszynski, D. M., Tirpak, R. A., Boening-Ulman, K. M., Martin, J. F. “Effects of watershed-scale green infrastructure retrofits on urban stormwater quality: A paired watershed study to quantify nutrient and sediment removal.” Ecological Engineering, January 2023, 186. https://doi.org/10.1016/j.ecoleng.2022.106835