Denitrification in marsh-pond-marsh constructed wetlands treating swine wastewater at different loading rates

Denitrification in constructed wetlands can be very important in the treatment of swine lagoon effluent when land application areas are limited. The objectives of this investigation were to determine (i) the denitrification enzymeactivity (DEA) in themarsh sediments ofmarsh-pond-marsh (MPM) constructed wetlands, (ii) changes in DEA with additions of carbon and nitrate, and (iii) the response of DEA to dif-ferent wastewater N loading rates. Swine wastewater was applied to six MPM wetlands located at North Carolina A&T State University, Greensboro, NC, at rates of 4 to 35 kg N ha21 d21. Soil samples were obtained from the top 25 mm of the marsh sections on four dates for determination of DEAvia the acetylene blockage method (blocked at N2O). Headspace N2O was measured via gas chromatography. In the control treatment, they ranged from 0.06 to 1.13 and 0.16 to 0.79 mg N2O-N kg21 soil hr21 in the first and second marshes, respectively