Enhanced Nitrate Reduction within a Constructed Wetland System: Nitrate Removal within Groundwater Flow

Within the Midwest United States, agricultural fields are drained by tile drainage systems. These systems are emplaced to enhance crop production, but they serve as a direct flowpath to surface streams, delivering excess nutrients to the streams. Identifying and establishing methods to reduce excess nutrient delivery to surface streams has become a priority. Surface processes within wetlands, both natural and constructed, have been shown to abate excess nutrients. This work explores the benefit associated with the subsurface flow of seepage from a wetland. Water level monitoring and geochemical analyses were used to ascertain the reduction of nitrate occurring in the subsurface following leakage from a wetland. Receiving only tile-drainage water, the wetland waters had a mean nitrate as nitrogen (NO3-N) concentration of 19.80 mg/L, which is a magnitude larger than the measured NO3-N concentration in the upgradient groundwater of 1.53 mg/L. As water travels in subsurface away from the wetland, the NO3-N concentrations decrease to 10.99 mg/L, a 44.5% reduction. The reduction occurs over a distance of 47 m, representing a 0.16 mg/L decrease in NO3-N per meter of travel distance.