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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 N(2)O, CH(4), and CO(2) 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 N(2)O-N, CH(4)-C, and CO(2)-C ranged from -2.1 to 1000, -32 to 38 000, and -840 to 93 000 mg m(-2) d(-1), respectively. Emissions of N(2)O and CH(4) were significantly higher during summer than during winter. The VSSF wetlands had the highest fluxes of N(2)O during both summer and winter. Methane emissions were highest from the FSW wetlands during wintertime. In the HSSF wetlands, the emissions of N(2)O and CH(4) were in general highest in the inlet section. The vegetated ponds in the FSW wetlands released more N(2)O than the nonvegetated ponds. The global warming potential (GWP), summarizing the mean N(2)O and CH(4) emissions, ranged from 5700 to 26000 and 830 to 5100 mg CO(2) 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 N(2)O and CH(4).

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We studied concentrations of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) in the eutrophic Temmesjoki River and Estuary in the Liminganlahti Bay in 2003-2004 and evaluated the atmospheric fluxes of the gases based on measured concentrations, wind speeds and water current velocities. The Temmesjoki River was a source of CO 2 , CH 4 and N 2 O to the atmosphere, whereas the Liminganlahti Bay was a minor source of CH 4 and a minor source or a sink of CO 2 and N 2 O. The results show that the fluxes of greenhouse gases in river ecosystems are highly related to the land use in its catchment areas. The most upstream river site, surrounded by forests and drained peatlands, released significant amounts of CO 2 and CH 4 , with average fluxes of 5,400 mg CO 2 -C m -2 d -1 and 66 mg CH 4 -C m -2 d -1 , and concentrations of 210 lM and 345 nM, respectively, but N 2 O concentrations, at an average of 17 nM, were close to the atmospheric equilibrium concentration. The downstream river sites surrounded by agricultural soils released significant amounts of N 2 O (with an average emission of 650 lg N 2 O-N m -2 d -1 and concentration of 22 nM), whereas the CO 2 and CH 4 concentrations were low compared to the upstream site (55 lM and 350 nM). In boreal regions, rivers are partly icecovered in wintertime (approximately 5 months). A large part of the gases, i.e. 58% of CO 2 , 55% of CH 4 and 36% of N 2 O emissions, were found to be released during wintertime from unfrozen parts of the river.