A new vegetation chamber to investigate the role of macrophytes in the CH4 and N2O gas fluxes from constructed wetland in Phoenix, AZ

Background/Question/Methods

Macrophytes can increase nutrient retention in wetlands constructed to reduce nutrient pollution and for this reason, Typha spp., are frequently planted in constructed wetlands (CW). However, these macrophytes also play a role as a significant pathway of important greenhouse gases, methane (CH₄) and nitrous oxide (N₂O) emissions from wetlands. Their aerenchyma structure, allows them to transport oxygen to their roots, as well as to ventilate gases directly from the roots to the atmosphere. With a new macrophyte-specific gas chamber, we are investigating CH₄ and N₂O fluxes from Typha spp. at Tres Rios CW. During July and November of 2014, we collected gas fluxes from two subsites (shoreline and water) at the inlet and outlet transects of the CW. The fluxes were collected at 15-min intervals over a 45-min flux time at two times of day (morning and afternoon) from two Typha spp.heights (low and high).

Results/Conclusions

Means of all CH₄ fluxes are not different between, transects, subsites, time, and plant height. However, summer CH₄ fluxes are significantly greater at low-height Typha spp. and show a significant interaction effect with subsite and transect factors. Means of all N₂O fluxes show gas uptake and are not different between transect, subsite, and time. Fall N₂O fluxes are greater from high-height parts of Typha spp. and show a significant interaction effect with subsite. Significant fluxes show higher CH₄ fluxes in July and outlet; and for N₂O, higher in shoreline subsite and in the afternoon. Our results emphasize the need to develop new and more feasible methods to better resolve the role of vegetation in the biogeochemical cycling of methane and nitrous oxide fluxes as an important component of closing the gap in the greenhouse gas fluxes from novel wetland ecosystems. Due to the increased development of CW worldwide, it is important not just to study their effectiveness in purifying water but also the design factors, vegetation, & environmental conditions that control greenhouse gas fluxes.