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Title:   Author  item
                                            FOX, R - UNIVERSITY OF MARYLANDitem
                                            GUSTAFSON, A - UNIVERSITY OF MARYLANDitem
                                            FISHER, T - UNIVERSITY OF MARYLANDitem
                                            KANA, T - UNIVERSITY OF MARYLANDitem
                                            ATOR, S - U.S. GSWSCitem
                                            DENVER, J - U.S. GSWSCitem
                                            JORDAN, T - SMITHSONIAN RESEARC CTRitem
                                            Lang, Meganitem
                                            McCarty, Gregory
  Submitted to: Society of Wetland Scientists
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 4/7/2009
                                    Publication  Date: 6/21/2009
                                    Citation: Fox, R.J., Gustafson, A.B., Fisher, T.R., Kana, T., Ator, S., Denver, J., Jordan, T., Lang, M.W., McCarty, G.W. 2009. Denitrification in restored and constructed wetlands adjacent to crop fields on the Mid-Atlantic coastal plain [abstract]. Society of Wetland Scientists. 2009 CDROM.Interpretive Summary:
                                Technical Abstract: Fertilizer applications on crop fields are a significant source of nitrate (NO3), and groundwater concentrations are frequently 500-1000 μM. We show that groundwater transport of agricultural NO3 results in significant denitrification in adjacent wetlands in the Choptank Basin on the Delmarva Peninsula. We use piezometers for groundwater sampling, and two gas collection methods for vadose zone sampling. We quantify gases associated with soil respiration using quadrapole mass spectrometers and gas chromatographs. Excess N2 and CO2 are defined as the difference between observed concentrations and those expected or measured at equilibrium with air at recharge temperatures. In transects from fields to wetlands, we have observed large horizontal concentration gradients of NO3 (e.g., 7-54 μmoles L-1 m-1) and large accumulations of excess N2 gas, CO2, N2O, and CH4. Accumulation of excess N2 and N2O was negatively associated with declining O2 and NO3, whereas accumulation of CH4 (20 - 400 μM) increased rapidly following depletion of O2 and NO3. Excess N2 frequently represented 10 to >100% of the measured NO3, and N2O was in the range of 1-5% of excess N2. These data strongly support the use of natural, restored, or constructed wetlands in the vicinity of agricultural fields as a mitigation strategy to remove agricultural NO3. However, since the greenhouse gases N2O and CH4 can be generated under conditions of NO3 depletion, there may be optimal ratios of crop field to wetland to ensure adequate NO3 removal without excess production of greenhouse gases.


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