Watershed

Oral

394616 - Pocket Wetlands” for Nutrient Removal in Tile-drained Agriculture

Tuesday, June 5
2:00 PM - 3:30 PM
Location: Greenway IJ
Co-Authors: Karl Rockne, IL – University of Illinois at Chicago (UIC)

Midwestern states have agreed to reduce nutrient releases to combat Gulf of Mexico hypoxia by focusing on the ~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, W2 in 2017) in high-yield corn/soybean cropland in IL. Inlet/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 in W1 during 2016, with concentrations frequently >16 mg/L during the late spring and summer. Nitrate accounted for 98% of the total DIN in the inlet flow to the wetland. SRP averaged 0.18 mg/l in 2016 with a DIN/SRP ratio >65. Such high DIN/SRP ratios indicate that N has a significantly greater potential for release and export via drain tiles than P. Overall, 1000 kg of N was removed in 2016, but with relatively low efficiency, which we attribute to limited denitrification in the wetland sediment. In year 2, W1 nitrate removal efficiency increased significantly after a complete year of plant growth, die-back, and subsequent incorporation into the wetland sediment. Water depth and hydraulic loading also plays a role in N removal, as significantly less precipitation resulted in longer hydraulic residence times.

Lessons learned from the operation of W1 have been employed in the construction and operation of pocket wetland W2. Better data on the tile system allowed accurate sizing, and full flow was prevented in W2 until the wetland plants had grown to fully cover the wetland. Data from initial operation in W2 demonstrate the importance of proper conditions to support the microbial denitrification process.

Mahsa Izadmehr, PhD student

Graduate Research Assistant
University of Illinois at Chicago (UIC)

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394616 - Pocket Wetlands” for Nutrient Removal in Tile-drained Agriculture



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