Nutrient Removal Potential of Constructed Wetlands in Grand Lake St. Marys Watershed

Constructed wetlands are becoming an increasingly important management tool to reduce nutrient rich agricultural runoff in the Great Lakes region. The objective of this study was to assess the removal efficiency of two constructed wetlands operating on tributaries of Grand Lake St. Marys (Prairie Creek and Coldwater Creek) located in northwest Ohio. Water samples were collected weekly during 2019 year from inflow and outflow points where they were analyzed for nutrient (nitrate-N, total phosphorus, dissolved reactive phosphorus) concentrations following standard EPA colorimetric methods. Overall, while both wetlands experienced high mean nutrient inputs (concentrations in mg/L) across both fall and summer seasons ranging from 0.5 to 13+ NO3-N, 0.1 to 1.5+ TP, and 0.05 to 0.75+ DRP, respectively, high removal efficiencies (often in excess of 75%) produced significantly reduced outflow concentrations (paired t tests; p\u3c0.05) largely consistent with EPA recommended TMDL target values for sub watersheds of these size (~20mi2: 1.0 mg/L NO3, 0.10 mg/L TP). Extending these concentration reductions to effect size and loading, wetland flow through rates, and daily stream discharge data from USGS gauging stations revealed that PC and CC Treatment Train Wetlands were found to have collectively removed approximately 10,000 lbs of nitrogen, 150,000 lbs of sediment, and 750 lbs of phosphorus throughout the year. This study continues to demonstrate the importance of constructed wetlands towards freshwater conservation strategies.https://corescholar.libraries.wright.edu/lake_research_symposium_abstracts/1006/thumbnail.jp