Nutrient Retention in the First Full Year by a Wetlaculture Mesocosm System in the Former Great Black Swamp Upstream of the Highly Eutrophic Western Lake Erie

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Human-induced non-point sources of nitrogen and phosphorus have contributed to the world widely common occurrence of harmful algal blooms, such as the serious eutrophication issue of western Lake Erie in the Laurentian Great Lakes of North America. A sustainable wetland-agriculture integration system (we call it “wetlaculture”) is proposed for reducing high nutrient loaded flows into natural waters and recovering farmland soil conditions by applying wetland treatment system. A physical wetlaculture mesocosm model has been developed on agricultural land in the northwestern edge of the former 4,000 km2 ‘Great Black Swamp’ which was drained entirely in the 19th century. Twenty-eight vertical-flow mesocosms (Rubbermaid tubs 122 x 76 x 61 cm) were installed in the ground with appropriate plumbing in 2017 and planted in October 2017 with the sedge Schoenoplectus tabernaemontani. Drainage ditch water containing agricultural runoff is added by gravity to the mesocosms when there is ditch flow (normally from March to June plus November). In a 2x2x7 experiment the mesocosms were randomly assigned to 2 water depths and 2 hydraulic loading rates (HLR) with seven replicates of each treatment. Started in March 2018, inflow and outflow water samples were collected and analysis for soluble reactive phosphorus (SRP), total phosphorus (TP), nitrate+nitrite (NO3+NO2-N), total Kjeldahl nitrogen (TKN), and total nitrogen (TN) every two other weeks during sampling hydroperiods. TP and TN in the inflow water were 0.130±0.013 mg-P/L (n=34) and 5.982±0.128 mg-N/L (n=34) respectively, in the first year. Early data in 2018 suggest the wetlands have already become nutrient sinks with a positive removal rate of TP (32±5% (n=167) and TN (82±0.4% (n=208)). After 3 or 4 years, these wetland mesocosms will be flipped (rotated) to a commercial agricultural crop over a several year period to determine x number of years wetlands that are needed to produce y number of years of crops without the addition of fertilizers. This study will provide a valuable information on restoring wetlands from farmlands in the former Great Black Swamp strategically focused on reducing the nutrient loading to western Lake Erie from the Maumee River Basin. Eventually dynamic and spatial mathematical models basing on wetlaculture mesocosm data will be developed to predict the behavior of created and restored wetlands at a landscape-scale for protection of downstream aquatic ecosystems including Lake Erie.

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Presented at the 19th Annual American Ecological Engineering Society Meeting, Enabling Future Generations to Solve Our Planet’s Grand Challenges, June 2019, Asheville, NC