Greenhouse gas emissions from a constructed wetland in southern Sweden

This paper investigates the greenhouse gas emissions from a Swedish wetland, constructed to decrease nutrient content in sewage treatment water. To evaluate the effect of the construction in terms of greenhouse gas emissions we carried out ecosystem-atmosphere flux measurements of CO2, CH 4 and N2O using a closed chamber technique. To evaluate the importance of vascular plant species composition to gas emissions we distributed the measurement plots over the three dominating plant species at the field site, i.e., Typha latifolia, Phragmites australis and Juncus effusus. The fluxes of CO2 (total respiration), CH4 and N2O from vegetated plots ranged from 1.39 to 77.5 (g m-2 day -1), -377 to 1387 and -13.9 to 31.5 (mg m-2 day -1) for CO2, CH4 and N2O, respectively. Presence of vascular plants lead as expected to significantly higher total respiration rates compared with un-vegetated control plots. Furthermore, we found that the emission rates of N2O and CH 4 was affected by presence of vascular plants and tended to be species-specific. We assessed the integrated greenhouse warming effect of the emissions using a Global Warming Potential over a 100-year horizon (GWP 100) and it corresponded to 431 kg CO2 equivalents m -2 day-1. Assuming a 7-month season with conditions similar to the study period this is equal to 90 tonnes of CO2 equivalents annually. N2O emissions were responsible for one third of the estimated total greenhouse forcing. Furthermore, we estimated that the emission from the forested bog that was the precursor land to Magle constructed wetland amounted to 18.6 tonnes of CO2 equivalents annually. Hence, the constructed wetland has increased annual greenhouse gas emissions by 71.4 tonnes of CO2 equivalents for the whole area. Our findings indicate that management processes in relation to wetland construction projects must consider the primary function of the wetland in decreasing eutrophication, in relation to other positive aspects on for instance plant and animal life and recreation as well as possible negative climatic aspects of increased emissions of CH4 and N2O. © 2006 Springer Science+Business Media B.V.