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Implementing constructed wetlands for nutrient reduction at watershed scale Case study in the upper East Fork of the Little Miami River Watershed, Ohio
Citation:
Nietch, C. Implementing constructed wetlands for nutrient reduction at watershed scale Case study in the upper East Fork of the Little Miami River Watershed, Ohio. UC Engineering Graduate Seminar, Cincinnati, OH, February 10, 2023.
Impact/Purpose:
Understanding the cost effectiveness of mitigating nutrient pollution in watershed is a research priority for the USEPA. To this end, we modeled nutrient management cost effectiveness in the Upper East Fork Watershed in Southwestern, Ohio. Constructed wetland placement feasibility was assessed and innovative design were developed and are demonstrated.
Description:
The East Fork Watershed Cooperative (EFWCoop) leverages expertise to address nutrient pollution in the 892 km2 upper East Fork of the Little Miami River watershed (UEFW) in Southwestern Ohio. The UEFW is 64% agriculture with 422 km2 of row crops (RCs) contributing 71% of the system’s nutrient load. Understanding the cost effectiveness of mitigating nutrient pollution is a research priority for the USEPA. To this end, we model nutrient management in the UEFW. Among a list of eight alternatives, constructed wetlands ranked high, i.e., low costs per kilogram of nutrient removed. The model suggested that the runoff from 85% of the RC area would need to be treated by the equivalent of 3.61 km2 of wetlands to meet a watershed-wide phosphorus (P) reduction target at an estimated cost of $2.5 million annually ($50 million over 20 years). This prompted a series of EFWCoop projects designed to understand the feasibility of retrofitting the system with 3.61 km2 of constructed wetlands. The practicalities of sighting and constructing this coverage, while leading to innovation in unit-level design, has highlighted the underestimation of resources needed for achieving the P target with wetlands. Approximately $1.5 million have been spent thus far and an additional feasibility study projects a $38 million price tag. However, the combined expenditures would only achieve an estimated 11% of the required treatment. These results highlight the importance of considering field-scale realities in watershed-scale nutrient reduction simulations using constructed wetlands.
