Reduction of nutrient loads from agricultural subsurface drainage water in a small, edge-of-field constructed treatment wetland

Authors: GORDON, BRAD - University Of Minnesota; LENHART, CHRISTIAN - University Of Minnesota; PETERSON, HEIDI - Sand County Foundation; NIEBER, JOHN - University Of Minnesota; Gamble, Joshua; CURRENT, DEAN - University Of Minnesota

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2020
Publication Date: 2/1/2021
Citation: Gordon, B., Lenhart, C., Peterson, H., Nieber, J., Gamble, J.D., Current, D. 2021. Reduction of nutrient loads from agricultural subsurface drainage water in a small, edge-of-field constructed treatment wetland. Ecological Engineering. 160. Article 106128. https://doi.org/10.1016/j.ecoleng.2020.106128.
DOI: https://doi.org/10.1016/j.ecoleng.2020.106128

Interpretive Summary: Constructed treatment wetlands are a common practice for removing nutrients from agricultural tile drainage in the Midwest. Wetland size recommendations vary, but little is known about the effectiveness of wetlands with an area as small as 0.11 hectares. A small, edge-of-field wetland treating tile drainage from a 10.1-ha row-crop field was constructed in 2013 adjacent to Elm Creek in Martin County, MN. The water, nitrate (NO3), and phosphorus (P) budgets were determined for 2013 to 2016. Over the four years of study, the wetland removed 67% of the input NO3, but TP removal was inconclusive. The majority of NO3 was removed in the shallow groundwater flow after it infiltrated from the surface. Approximately 0.35 kg-P yr-1 was removed by harvesting the vegetation in the wetland. Therefore, NO3 removal in the shallow groundwater and TP removal through vegetation harvest were the primary means of removing each nutrient. These findings are important for the design of treatment wetlands because they demonstrate that mechanisms of nitrate and phosphorus removal differ in small, edge-of-field treatment wetlands and also suggest possible ways to further improve removal. The findings of this research will be of interest to NRCS who have developed a treatment wetland standard, watershed districts, researchers, and producers/producer groups with interest in reducing tile drainage nitrate and phosphorus losses in harvest were the primary means of removing each nutrient.

Technical Abstract: Constructed treatment wetlands are a common practice for filtering nitrogen from agricultural sub-surface (i.e. tile) drainage in the Midwest. Wetland size recommendations vary, but little is known about the effectiveness of wetlands with a pooled area as small as 0.11 hectares. A small, edge-of-field wetland treating tile drainage from a 10.1-ha row-crop field was constructed in 2013 adjacent to Elm Creek in Martin County, MN. The water, nitrate (NO3), and phosphorus (P) budgets were determined for 2013 to 2016. The wetland received 55,268 m3 drainage water, 738 kg nitrate-nitrogen (NO3-N), and 5.2 kg total phosphorus (TP) over the four years of this study. It removed 67% of the input NO3, but TP removal was inconclusive. The majority of NO3 was removed in the shallow groundwater flow after it infiltrated from the surface. Approximately 0.35 kg-P yr-1 was removed by harvesting the vegetation in the wetland. Therefore, NO3 removal in the shallow groundwater and TP removal through vegetation harvest were the primary means of removing each nutrient.