Emission of the Greenhouse Gases Nitrous Oxide and Methane from Constructed Wetlands in Europe

The potential atmospheric impact of constructed wetlands (CWs) should be examined as there is a worldwide increase in the development of these systems. Fluxes of N2O, CH4, and CO2 have been measured from CWs in Estonia, Finland, Norway, and Poland during winter and summer in horizontal and vertical subsurface flow (HSSF and VSSF), free surface water (FSW), and overland and groundwater flow (OGF) wetlands. The fluxes of N2O-N, CH4-C, and CO2-C ranged from -2.1 to 1000, =32 to 38 000, and -840 to 93 000 mg m-2 d-1, respectively. Emissions of N2O and CH4 were significantly higher during summer than during winter. The VSSF wetlands had the highest fluxes of N2O during both summer and winter. Methane emissions were highest from the FSW wetlands during wintertime. In the HSSF wetlands, the emissions of N2O and CH4 were in general highest in the inlet section. The vegetated ponds in the FSW wetlands released more N2O than the nonvegetated ponds. The global warming potential (GWP), summarizing the mean N2O and CH4 emissions, ranged from 5700 to 26000 and 830 to 5100 mg CO2 equivalents m-2 d-1 for the four CW types in summer and winter, respectively. The wintertime GWP was 8.5 to 89.5% of the corresponding summertime GWP, which highlights the importance of the cold season in the annual greenhouse gas release from north temperate and boreal CWs. However, due to their generally small area North European CWs were suggested to represent only a minor source for atmospheric N2O and CH4.