Data from: Carbon dioxide and methane fluxes from different surface types in a created urban wetland

<p><span>Many wetlands have been drained due to urbanization, agriculture, forestry or other purposes, which has resulted in losing their ecosystem services. To protect receiving waters and to achieve services such as flood control and stormwater quality mitigation, new wetlands are created in urbanized areas. However, our knowledge of greenhouse gas exchange in newly created wetlands in urban areas is currently limited. In this paper we present measurements carried out at a created urban wetland in boreal climate.</span></p> <p><span>We conducted measurements of ecosystem CO₂flux (NEE) and CH₄ flux (F_CH4) at the constructed stormwater wetland Gateway in Nummela, Vihti, Southern Finland using eddy covariance (EC) technique. The measurements were commenced the fourth year after construction and lasted for one full year and two subsequent growing seasons. Besides ecosystem scale fluxes measured by EC tower, the diffusive CO₂andCH₄ fluxes from the open-water area (F_w_CO₂ and F_w_CH_4,respectively) were modelled based on measurements of CO₂andCH₄concentration in the water. Fluxes from vegetated area were estimated by applying a simple mixing model using above-mentioned fluxes and footprint-weighted fractional area. The half-hourly footprint-weighted contribution of diffusive fluxes from open water ranged from 0 to 25.5 % in year 2013.</span></p> <p><span>The annual NEE of the studied wetland was 8.0 g C-CO₂m^-2 yr^-1with the 95 % confidence interval between-18.9 and 34.9 g C-CO₂m^-2 yr^-1and F_CH4was 3.9 g C-CH₄ m^-2 yr^-1 with the 95 % confidence interval between 3.75 and 4.07 g C-CH₄ m^-2 yr^-1. The ecosystem sequestered CO₂during summer months (June-August), while the rest of the year it was a CO₂ source. CH₄ displayed strong seasonal dynamics, higher in summer and lower in winter, with a sporadic emission episode in the end of May 2013. Both CH₄and CO₂fluxes_,especially those obtained from vegetated area, exhibited strong diurnalcycle during summer with synchronized peaks around noon. The annual F_w_CO₂was 297.5 g C-CO₂m^-2 yr^-1and F_w_CH₄was 1.73 g C-CH₄m^-2 yr^-1. The peak diffusive CH₄ flux was 137.6 nmol C-CH₄ m^-2 s^-1, which wassynchronized with the F_CH4.</span></p> <p><span>Overall, during the monitored time period, the established stormwater wetland had a climate warming effect with 0.263 kg CO₂-eq m^-2 yr^-1ofwhich 89 % was contributed by CH₄. The radiative forcing of the open-water exceeded the vegetation area (1.194 kg CO₂-eq m^-2 yr^-1 and0.111 kg CO₂-eq m^-2 yr^-1, respectively), which implies that, when considering solely the climate impact of a created wetland over a 100-year horizon, it would be more beneficial to design and establish wetlands with large patches of emergent vegetation, and to limit the areas of open-water to the minimum necessitated by other desired ecosystem services.</span></p>