Nitrogen and phosphorus removal using tile‐treatment wetlands: A 12‐year study from the midwestern United States

• Published in: Journal of environmental quality Vol. 51; no. 5; pp. 797 - 810
• Main Authors: Lemke, A. Maria, Kirkham, Krista G., Wallace, Michael P., VanZomeren, Christine M., Berkowitz, Jacob F., Kovacic, David A.
• Format: Journal Article
• Language: English
• Published: United States 01.09.2022
• Subjects: Agriculture; Glycine max; Nitrates; Nitrogen; Phosphates; Phosphorus; Wetlands; Zea mays
• ISSN: 0047-2425; 1537-2537
• DOI: 10.1002/jeq2.20316

Nutrient enrichment from tile‐drained agricultural lands to the Mississippi River is a leading cause of hypoxia in the Gulf of Mexico. Small edge‐of‐field wetlands can effectively treat nitrate‐nitrogen (NO3–N) export from tiles, although less research exists on their capacity to treat phosphorus (P). Additionally, long‐term data are needed to incorporate variability of weather and farming practices into assessments of wetland performance longevity. Research conducted over 12 yr quantified size‐effectiveness of wetlands to reduce NO3–N and dissolved P (orthophosphate [ORP]) loadings from subsurface tile systems. Nitrate‐N export was significantly higher during corn (Zea mays L.) than soybean [Glycine max (L.) Merr.] production years, during which 80–84% of mean annual loadings were exported during spring. Wetlands representing 3% (W1) of tile‐drained farmland area reduced 15–38% of NO3–N export, with cumulative reductions of 39–49 and 49–57% observed in wetlands representing 6 (W2) and 9% (W3) areas, respectively. Mass NO3–N removal ranged from 28 to 52%. Twelve‐year total ORP load reductions for W1 ranged from 53 to 81%, with cumulative reductions of 35–91% and 32–95% for W2 and W3 wetlands, respectively. Mass ORP removal ranged from 71 to 85%. Results emphasize how incorporating constructed wetlands into state and watershed‐level conservation planning can significantly contribute toward reducing excess N and P export to river systems and ultimately to the Gulf of Mexico. Core Ideas A 12‐yr study tested how wetland size affected nutrient removal from tile drainage. Small wetlands effectively treat excess NO3–N and dissolved P losses from tiles. Annual reductions of NO3–N and dissolved P remained high throughout the 12‐yr study. Implementing wetlands at scale could improve local and regional water quality.