The role of macrophytes in the greenhouse gas fluxes from a constructed wetland system in Phoenix, AZ.

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Macrophytes can increase nutrient retention in wetlands constructed to reduce nutrient pollution and for this reason, Typha spp., are frequently planted in constructed wetland systems (CWS). However, these macrophytes also play a role as a significant pathway of 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 (CWS) in the CAP LTER in Phoenix, AZ. 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). Preliminary analysis shows that CH₄ fluxes are not different between, transects, subsites, time, and plant height. However, summer CH₄ fluxes are significantly greater from lower parts Typha spp. and show an interaction effect between with subsite and transect factors. N₂O fluxes are not different between transect, subsite, and time. In contrast to CH₄, winter N₂O fluxes are greater from higher parts of Typha spp. and show a significant interaction effect with subsite. As we continue to analyze the 2015 gas samples, we will contribute to a more precise and comprehensive quantification of GHG emission from a constructed wetland system in Phoenix, AZ.