Seasonal control of CO2 and CH4 dynamics in a temporarily flooded subtropical wetland

Authors: GOMEZ-CASANOVAS, NURIA - University Of Illinois; DELUCIA, NICHOLAS - University Of Illinois; DELUCIA, EVAN - University Of Illinois; BLANC-BETES, ELENA - University Of Illinois; BOUGHTON, ELIZABETH - Archbold Biological Station; SPARKS, JED - Cornell University; Bernacchi, Carl

Submitted to: Journal of Geophysical Research-Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2020
Publication Date: 3/14/2020
Citation: Gomez-Casanovas, N., DeLucia, N.J., DeLucia, E.H., Blanc-Betes, E., Boughton, E., Sparks, J., Bernacchi, C.J. 2020. Seasonal control of CO2 and CH4 dynamics in a temporarily flooded subtropical wetland. Journal of Geophysical Research-Biogeosciences. 125(3). https://doi.org/10.1029/2019JG005257.
DOI: https://doi.org/10.1029/2019JG005257

Interpretive Summary: Subtropical pastures are very important ecosystems for a variety of reasons including their ability to store organic carbon, but they are strong emitters of greenhouse gases. The mechanisms driving the uptake of organic carbon and greenhouse gases, however, are unclear leading to significant uncertainty in ecosystem and global models. This research measured the exchange of carbon dioxide, which is taken up by photosynthesis and leads to organic carbon formation, and of methane, which is a potent greenhouse gas, for a large wetland nested within an agricultural setting in Central Florida. The results show that the wetland is a large source of methane, and that water, temperature, and photosynthesis all contributed to the control of methane release, however, the extent of the control varied based on a number of factors. This improved understanding of wetland carbon and methane fluxes will improve global emission modeling and allow better understanding of wetland function into the future.

Technical Abstract: Subtropical and tropical wetlands play a prominent role in the global C cycle. However, the mechanisms driving CO2 and CH4 fluxes in these systems remain uncertain. Using the eddy covariance technique, we determined the exchange of CO2 and CH4 fluxes between a temporarily flooded subtropical wetland and the atmosphere to investigate drivers controlling these fluxes at annual and seasonal scales. The wetland was a net CO2 sink from the atmosphere (-469 g C-CO2 m-2 in 2013, -308 g C-CO2 m-2 in 2014 and -361 g C-CO2 m-2 in 2015) and a source of CH4 (25.1 g C- CH4 m-2 in 2013, 26.1 g C- CH4 m-2 in 2014, 32.1 g C- CH4 m-2 in 2015). Combining fluxes of CO2 and CH4, the wetland was a net sink of C but a net source of GHGs. Hydrology played a major role in regulating C fluxes from this ecosystem. Higher water tables increased Gross Primary Productivity (GPP), and increased ecosystem respiration (Reco) only when soils were not flooded. When soils were inundated, however, increases in water tables decreased Reco. GPP and CH4 fluxes were positively correlated only when soils were flooded, demonstrating the need to incorporate the response of CH4 fluxes to soil flooding conditions in biogeochemical models. The contribution of dry season CH4 emissions to annual CH4 budget was large (41-to-49%), reflecting the importance of continuous observations of CH4 fluxes for accurate estimates of the C budget of subtropical wetlands. Incorporating the mechanisms that drive C fluxes in subtropical flooded wetlands as influenced by soil flooding conditions in biogeochemical models will help improve predictions, particularly as the hydrological cycle intensifies with global climate change.