The Impact of Green Infrastructure on Stormwater Quality: A Sewershed-Scale Analysis of the Effects of Blueprint Columbus on Nutrients, Sediments, and Metals

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The discharge of pollutants to surface waters via stormwater runoff is a societal challenge. Among other impacts, these pollutants cause harmful algal blooms and eutrophication resulting in degraded water quality, threats to public health and potable water, and reduced tourism, cultural activities, and coastal economies. Waterborne pollutants can be unsightly, including plastics, garbage, and sediment, or less visible, including nutrients and soluble metals. Stormwater runoff is a major source of nutrients, sediment, and metals to aquatic ecosystems. Green infrastructure (GI) is a novel way to reduce stormwater to improve water quality to protect ecosystems, public health, and coastal economies. While the ability for GI to reduce stormwater pollution has been demonstrated for single installations and at a smaller scale of less than 10 ha, there are still important unknowns about water quality benefits of a network of GI across entire sewersheds. These questions were the focus of this research. GI reduces directly connected impervious area through the use of stormwater control measures including bioretention cells and permeable pavement. Using soil and plants as natural filters, these solutions have been shown to individually improve water quality. This improvement is made possible by increasing sewershed storage and infiltration to counter impermeable surfaces typical in urban areas. As part of the Blueprint Columbus project, several hundred bioretention cells and 8,742 m2 of permeable pavement roads have been implemented in the Clintonville neighborhood of Columbus, OH. Also, redirecting downspouts, implementing sump pumps, and lining sanitary sewer laterals have been used to lessen sanitary sewer overflows, and large underground tunneled to lessen combines sewer overflows. Bioretention and permeable pavement are the focus of this thesis. Using automated samplers, event mean water quality samples were collected and analyzed for nutrients, sediment, and metals over three and a half years at the outfall of three sewersheds (11.5 to 111.5 ha) located in the Clintonville neighborhood of Columbus, Ohio. Tipping bucket rain gauges and flow meters were utilized to characterize sewershed hydrology. GI was installed in two sewersheds while the third served as a control to account for annual and seasonal changes in rainfall, runoff, and pollutant generation. A before-after, control-impact paired sewershed approach was applied to obtain a robust comparison of pollutant concentrations and loads before and after the installation of GI. Water quality samples were collected at the discharge point of three sewersheds located in the Clintonville neighborhood of Columbus, Ohio. A network of various technologies, including tipping rain gauges, area-velocity meters, and ISCO water samplers were utilized to continuously collect water quality data, including nutrients, sediment, and metals. This network was able to sense precipitation and collect samples throughout the duration of the precipitation event, producing event mean pollutant concentrations. Pollutant loads were calculated as the product of this event mean pollutant concentration and measured stormwater runoff volume. Total nitrogen, phosphorus, and suspended solid concentrations decreased by 13.7-24.1, 20.9-47.4, and 61.6-67.7%, respectively. Loads reductions for these pollutants were in the range of 24.0-25.4, 27.8-32.6, and 59.5-78.3%, respectively. Significant reduction in both particulate and dissolved pollutants were observed due to GI installation at a sewershed scale. Lead, copper, and zinc concentrations decreased in the range of 25.2-58.3% and loads in the range of 21.3-52.3%. Storm event loads were significantly reduced for every heavy metal analyzed herein. Bioretention was better suited to treat TSS, Cu, and Pb for smaller storm events. Since these results are for 1 or 2 years following the installation of GI, inherent limitations exist with sampling size, especially when trying to make statistical conclusions with 1 year of post-GI data. Sustained monitoring will be needed to evaluate future impacts of the system on water quality.


Poster Division: Math, Physical Sciences, and Engineering: 2nd Place (The Ohio State University Edward F. Hayes Graduate Research Forum)


Bioretention, Permeable Pavement, Watershed, Water Quality, Eutrophication