Identifying environmental drivers of methane fluxes in freshwater wetlands of the Florida Everglades

Zhuoran Yu, Christina L. Staudhammer and Gregory Starr, Biological Sciences, University of Alabama, Tuscaloosa, AL, Sparkle Malone and Steven F. Oberbauer, Biological Sciences, Florida International University, Miami, FL

Background/Question/Methods
Wetlands are among the most productive ecosystems in the world but are also considered the largest natural source of methane (CH4). Yet the contribution of wetlands towards the global CH4 budget is still unclear and the factors driving CH4 from subtropical natural wetlands have not been identified. Developing a better understanding of these wetlands’ contributions are important considering the global atmospheric CH4 concentration has doubled since the beginning of the industrial revolution. In this study, we compared a short and long hydroperiod wetland in the Florida Everglades, the largest subtropical wetland in the US, to improve our knowledge of its CH4 dynamics. We use CH4 flux data collected from 2016 to 2019 via the eddy covariance method to answer the following questions: 1) What are the diurnal and seasonal patterns in CH4 emissions? 2) What are the biotic and abiotic drivers of CH4 in freshwater marshes? And 3) Are patterns and drivers similar between the two sites? We used linear mixed effects models and wavelet analysis to examine patterns and identify the environmental drivers of CH4 in each study site.
Results/Conclusions
Both short- and long-hydroperiod freshwater wetlands lacked diurnal patterns but showed a similar seasonal pattern across the study period with more CH4 release during the summer wet seasons and lower CH4 emission in the winter dry seasons. Compared with the short-hydroperiod site, the long-hydroperiod site had a stronger seasonal pattern, emitted more CH4 annually. The linear mixed effects models indicated that higher water level, air temperature (Ta) and net ecosystem exchange (NEE) were significantly associated with increased CH4 emissions in the short hydroperiod site. At the long hydroperiod site, Ta had a similar positive association with CH4 emissions. In addition, greater daily pressure difference also led to increased CH4 release. However, both water level and gross ecosystem exchange (GEE) were negatively associated with CH4 fluxes. Pressure difference, water level, and GEE all had a stronger impact during the wet seasons for the long hydroperiod site. Both climate change and water management are expected to alter hydroperiods in the Everglades, therefore, this research improves our understanding of how changes in conditions will influence CH4 in the future.