Tile Water Nitrogen Reduction in a Constructed Wetland and Wetland Mesocosms in Southern Minnesota.

The need for understanding the effectiveness of constructed treatment wetlands in Minnesota continues to grow in order to limit the amount of nitrogen and phosphorous released into the Mississippi River and other water bodies. Improving technologies and best management practices to reduce these nutrients’ releases into the environment is especially significant as states set stretch goals to reduce nutrients contributing to algal blooms similar to and including that of the dead zone in the Gulf of Mexico. This study focuses on the effectiveness of a recently constructed tile-drain treatment wetland. In 2013 a 0.54 acre, 3-cell treatment wetland was constructed to remove nitrates from row-crop tile drainage discharging into Elm Creek in southern Minnesota. The drainage area switches between 10 and 25 acres depending on drainage needs following rain events. This continuing study aims to understand the effectiveness of this constructed wetland as well as the contributions of the ecology in the wetland at reducing nitrogen and phosphorus flowing into the nearby creek from tile drainage. Water sampling results indicate an improvement in nitrate load reduction of 37.1-43.3% in the first growing season to 49.5-57.2% reduction in the second season. The vegetation and soil are currently being studied using wetland mesocosms to better understand the contributions of some of the wetland’s plant species and soil in denitrification. qPCR is also being used to estimate the populations of denitrifying bacteria in the soils of this wetland compared to those of two other wetlands. Results from this study will be useful for designing other wetlands used to treat tile drainage by integrating structural and ecological components to develop a more effective treatment wetland.