"Pocket Wetlands" for Nutrient Removal in Tile-Drained Agriculture

Midwestern states have agreed to reduce nutrient releases to combat Gulf of Mexico hypoxia by focusing on the approximately 80% of N and 50% of P loading resulting from agriculture. In support of this effort, we are working with The Wetlands Initiative to develop " Pocket Wetlands" to capture and treat drain tile water by microbial denitrification and nutrient sequestration. Two wetlands were built, W1 in 2015 and W2 in 2017, in high-yield corn/soybean cropland in IL. Inlet and outlet flow and nutrient data have been used to assess treatment performance and learn lessons about construction and operation to increase nutrient removal. NO3--N levels averaged 11.7 mg/l, and SRP averaged 0.18 mg/l in W1 during 2016 with a DIN/SRP ratio >65. Overall, 1100 kg of N was removed in 2016 from W1, but with relatively low efficiency. In the second year, W1 nitrate removal efficiency increased significantly with total removal of 1700 kg of N and 200 kg of P. Lessons learned from the operation of W1 have been employed in the construction and operation of wetland W2. Data from initial operation in W2 demonstrate the importance of proper conditions to support the microbial denitrification process.