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 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).

Emission of greenhouse gases from constructed wetlands for wastewater treatment and from riparian buffer zones.

We measured N2O, CH4 and CO2 fluxes in horizontal and vertical flow constructed wetlands (CW) and in a riparian alder stand in southern Estonia using the closed chamber method in the period from October 2001 to November 2003. The average rates of N20, CH4 and CO2 emission from the riparian gray alder stand were from -0.4 to 58 microg N2O-N m(-2) h(-1) and 0.1-265 microg CH4-C m(-2) h(-1), 55-61 mg CO2-C m(-2) h(-1), respectively. The average N2O-N emission from the microsites above the inflow pipes of horizontal subsurface flow (HSSF) CWs was 6.4-31 microg N2O-N m(-2) h(-1), whereas the outflow microsites emitted 2.4-8 microg N2O-N m(-2) h(-1). In vertical subsurface flow (VSSF) beds the same value was 35.6-44.7 microg N2O-N m(-2) h(-1). The average CH4 emission from the inflow and outflow microsites in the HSSF CWs differed significantly ranging from 640 to 9715 and from 30 to 770 microg CH4-C m(-2) h(-1), respectively. The average CO2 emission was somewhat higher in VSSF beds (140-291 mg CO2-C m(-2) h(-1)) and at inflow microsites of HSSF beds (61-140 mg CO2-C m(-2) h(-1)). The global warming potential (GWP) from N2O and CH4 was comparatively high in both types of CWs (4.8 +/- 9.8 and 6.8 +/- 16.2 t CO2 eq ha(-1) a(-1) in the HSSF CW 6.5 +/- 13.0 and 5.3 +/- 24.7 t CO2 eq ha(-1) a(-1) in the hybrid CW, respectively). The GWP of riparian alder forest from both N2O and CH4 was relatively low (0.4 +/- 1.0 and 0.1 +/- 0.30 t CO2 eq ha(-1) a(-1), respectively), whereas the CO2-C flux was remarkable (3.5 +/- 3.7 t ha(-1) a(-1). The global influence of CWs is not significant. Even if all the global domestic wastewater were treated by wetlands, their share in the trace gas emission budget would be less than 1%.

Nitrous oxide, dinitrogen and methane emission in a subsurface flow constructed wetland.

N2O, N2 and CH4 fluxes were measured from a horizontal subsurface flow (HSSF) constructed wetland (CW) for wastewater treatment in Estonia. The closed chamber method was used in the field and the He-O method (intact soil core analyses) in the lab throughout the period from October 2001 to June 2002. The average flux of N2O-N, N2-N and CH4-C from various microsites ranged from 0.1 to 59, 4.1 to 1,458 and -0.04 to 2,094 mg m(-2) d(-1), respectively. A significantly higher flux of N2O was found in chambers installed above the inlet pipes, while the methane flux was higher in the inlet part of the bed with wetter conditions. The groundwater table significantly correlates with gas emission rates of all the gases studied; N2 emission was enhanced by higher temperature of wastewater. PO4(3-) and NH4+ content significantly enhanced, and NO2- and NO3- content inhibited, both N2O and CH4 fluxes. NH4+ showed a negative correlation with N2 flux. Nitrification and denitrification are the main processes of the N removal in the CW covering 42.9%. The specific global warming potential was highest in the wet bed and lowest in the dry bed with lowered water table (32 and 9 g CO2 pe(-1) d(-1), respectively).