Field Test Results for Nitrogen Removal by the Constructed Wetland

ALLRED, B. J.; GAMBLE, D. L.; LEVISON, P. W.; SCARBROUGH, R. L.; Brown, L. C.; Fausey, N. R.

Field Test Results for Nitrogen Removal by the Constructed Wetland

2014

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.

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