Location: Soil Drainage Research
Title: Field test results for nitrogen removal by the constructed wetland component of an agricultural water recycling system Authors
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 16, 2014
Publication Date: June 11, 2014
Citation: Allred, B.J., Gamble, D.L., Levison, P.W., Scarbrough, R.L., Brown, L.C., Fausey, N.R. 2014. Field test results for nitrogen removal by the constructed wetland component of an agricultural water recycling system. Applied Engineering in Agriculture. 30(2):163-177. Interpretive Summary: Constructed wetlands are currently being promoted for reintroduction into agricultural landscapes to receive subsurface drainage discharge waters and to provide treatment to remove nitrogen transported with the drainage water. When untreated drainage water carrying nitrogen reaches the streams, offsite effects such as harmful algal blooms and degraded drinking water supplies may result. There is scant data available to indicate the efficacy and efficiency of nitrogen removal from drainage waters in constructed wetlands. We added natural waters containing known concentrations of nitrogen into an established constructed wetland in four separate tests to examine the effectiveness of the wetland to remove the nitrogen before the water exited the wetland. The results indicate that the constructed wetland removed significant amounts of the nitrogen present in the water. This information will be useful for conservation planners and wetland designers for design and placement of constructed wetlands.
Technical Abstract: Wetland Reservoir Subirrigation Systems (WRSIS) are innovative agricultural water recycling systems that can provide economic and environmental benefits. A constructed wetland is a main component of WRSIS, and an important function of this constructed wetland is drainage water treatment of nitrogen nutrients. Four field tests were therefore conducted at a northwest Ohio WRSIS wetland to evaluate nitrate (NO3--N), ammonium (NH4+-N), and total nitrogen (TN) removal effectiveness. Tests 1 and 2 had lower inflow volumes, shorter effective retention times, and smaller nitrogen nutrient input loads. Test 3 had an intermediate inflow volume, intermediate effective retention time, and intermediate nitrogen nutrient input load, while Test 4 had a high inflow volume, long effective retention time, and large nitrogen nutrient input load. Based on nitrogen mass balance calculations, wetland processes produced 11.0% NO3--N, 61.7% NH4+-N, and 13.2% TN decreases during Test 1, 10.8% NO3--N, 41.7% NH4+-N, and 11.7% TN decreases during Test 2, 44.0% NO3--N, 87.5% NH4+-N, and 44.9% TN decreases during Test 3, and 15.6% NO3--N, 81.1% NH4+-N, and 16.1% TN decreases during Test 4. For the three tests conducted in May and June, 2009, Test 3 had the longest effective retention time, which may account for the better nitrogen nutrient reduction results achieved with Test 3 as compared to Tests 1 and 2. Cooler temperatures for Test 4 during October and November, 2009 may have decreased denitrifying bacterial activity, in turn suppressing the amount of NO3--N and TN reduction obtained with Test 4. Overall results of this study indicate that WRSIS wetlands are capable of providing water quality benefits by removing significant amounts of nitrogen nutrients present in drainage waters.