Location: Water Quality and Ecology ResearchTitle: Contrasting nutrient mitigation and denitrification potential of agricultural drainage environments with different emergent aquatic macrophytes
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2015
Publication Date: 7/10/2015
Publication URL: http://handle.nal.usda.gov/10113/62066
Citation: Taylor, J.M., Moore, M.T., Scott, J.T. 2015. Contrasting nutrient mitigation and denitrification potential of agricultural drainage environments with different emergent aquatic macrophytes. Journal of Environmental Quality. 44:1304–1314. https://doi.org/10.2134/jeq2014.10.0448.
Interpretive Summary: Excess nitrogen in runoff from agricultural areas can negatively impact water quality in rivers, lakes, and coastal areas. Water resource managers and agricultural producers seek simple cost-effective practices for reducing the movement of excess nitrogen from agricultural areas to sensitive freshwater and marine environments. Denitrification is a natural process that converts nitrogen in waters and soils to nitrogen gas, thereby returning excess nitrogen to the atmosphere. Scientists from ARS and the University of Arkansas investigated how managing different vegetation types in ditches influences the capture and removal of nitrogen from agricultural runoff. Experimental ditches planted with cutgrass or cattails removed > 90% of the nitrogen from runoff water compared to < 65% for ditches without plants over a 48 hour period. Additionally, cutgrass converted nitrogen dissolved in water to nitrogen gas at rates 30 times higher than observed for ditches with cattails or without plants. Results indicate, that cutgrass has the potential to permanently remove 50% of captured nitrogen through the denitrification process. Results from this experiment suggest that vegetated agricultural ditches have the potential to serve as an important nitrogen mitigation practice on agricultural lands.
Technical Abstract: Remediation of excess nitrogen (N) in agricultural runoff can be enhanced by establishing wetland vegetation but the role of denitrification in N removal is not well understood in drainage ditches. We quantified differences in N retention during experimental runoff events followed by stagnant periods in mesocosms planted in three different vegetation treatments: unvegetated; cutgrass (Leersia orizoides (L.) Sw.); and common cattail (Typha latifolia L.). We also quantified denitrification rates using membrane inlet mass spectrometry (MIMS) from intact cores extracted from each mesocosm treatment. All treatments retained 60% or more of NO3--N loads during the 6 h experimental runoff event, but mesocosms planted with cutgrass had significantly higher (68%) retention compared to cattail (60%) or unvegetated (61%) treatments. After the runoff event, mesocosms planted in cattails reduced NO3--N concentrations by > 95% within 24 h and cutgrass achieved similar reductions within 48 h, whereas reductions in unvegetated mesocosms were significantly less (65%). Cores from cutgrass mesocosms had significantly higher average denitrification rates (5.93 mg m-2 h-1) accounting for as much as 56% of the immobilized NO3--N within 48 h, whereas denitrification rates were minimal in cores from unvegetated (-0.19 mg m-2 h-1) or cattail (0.2 mg m-2 h-1) mesocosms. Our findings have implications for mitigating excess NO3--N in agricultural runoff. While vegetated treatments removed excess NO3--N from the water column at similar and significantly higher rates than unvegetated treatments, the high denitrification rates observed for cutgrass highlight the potential for permanent removal of excess N from agricultural runoff in vegetated ditches and wetlands.