Greenhouse gas emissions from a constructed wetland system in Phoenix, AZ

Wetlands support ecological functions that result in valuable services to society, including the purification of water through processes such as denitrification, plant uptake, and soil retention. Wetlands are also significant sources of greenhouse gases, such as nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂). Many free-water surface constructed treatment wetland systems (CWS) in North America have been developed to remove nutrients from secondarily-treated water, but little is known about the contributions of CWS on greenhouse gas emissions, especially in arid regions. We proposed to link ongoing denitrification and plant uptake investigations in the Tres Rios CWS in Phoenix, AZ to quantify the greenhouse gas fluxes of N₂O, CH₄, and CO₂. Since the spring of 2012, we have been utilizing the floating chamber technique to collect and measure gas samples from three subsites (shoreline, vegetation, and open water) along two transects within the CWS. No differences have been observed within the three field campaigns in March, May, and July. So far, there have been no differences observed between the three subsites (shoreline, vegetation, and open water) of each transect. During the summer months, differences have been observed between the transect closest to the inflow and the transect closer to the outflow for CH₄ and CO₂. Since starting these observation in the spring of 2012, averaged CO₂ fluxes (17.56 µg CO₂-C cm-2 hr-1) were greater than averaged CH₄ (1.31 µg CH₄-C cm-2 hr-1) and averaged N₂O (0.06 µg N₂O-N cm-2 hr-1) across the CWS. We expect that our results will show what tradeoffs exist between the ecosystem processes desired from the CWS and greenhouse gas emissions in an arid-urban region.