Nitrous oxide exchanges with the atmosphere of a constructed wetland treating wastewater Parameters and implications for emission factors

Static chamber measurements of N 2 O fluxes were taken during the 1998 and 1999 growth seasons in a Swedish constructed wetland receiving wastewater. The dominating plant species in different parts of the wetland were Lemna minor L ., Typha latifolia L . , Spirogyra sp . and Glyceria maxima (Hartm.) and Phalaris arundinacea (L.), respectively. There were large temporal and spatial variations in N 2 O fluxes, which ranged from consumption at –350 to emissions at 1791 μg N 2 O m −2 h −1 . The largest positive flux occurred in October 1999 and the lowest in the middle of July 1999. The average N 2 O flux for the two years was 130 μg N 2 O m −2 h −1 (SD = 220). No significant differences in N 2 O fluxes were found between the years, even though the two growing seasons differed considerably with respect to both air temperature and precipitation. 15% of the fluxes were negative, showing a consumption of N 2 O. Consumption occurred on a few occasions at most measurement sites and ranged from 1–350 μg N 2 O m −2 h −1 . 13–43% of the variation in N 2 O fluxes was explained by multiple linear regression analysis including principal components. Emission factors were calculated according to IPCC methods from the N 2 O fluxes in the constructed wetland. The calculated emission factors were always lower (0.02–0.27%) compared to the default factor provided by the IPCC (0.75%). Thus, direct application of the IPCC default factor may lead to overestimation of N 2 O fluxes from constructed wastewater-treating wetlands. DOI: 10.1034/j.1600-0889.2003.00034.x