Oral Presentation Society for Freshwater Science 2026 Annual Meeting

Linking oxygen and carbon dynamics to characterize dominant biogeochemical processes in headwater wetlands (134011)

Carla López Lloreda 1 , James Maze 2 , Emily Mulcahy 3 , Nicholas Corline 4 , Katherine Wardinski 2 , Daniel McLaughlin 5 , Nate Jones 6 , Durelle Scott 7 , Margaret Palmer 8 , Erin R Hotchkiss 1
  1. Biological Sciences, Virginia Tech, Blacksburg, VA, USA
  2. Water Institute, University of Florida, Gainesville, FL, USA
  3. Biology, University of Louisiana, Lafayette, LA, USA
  4. Wildlife, Fish, and Conservation Biology, University of California, Davis, CA, USA
  5. Forestry and Environmental Conservation, Virginia Tech, Blacksburg, VA, USA
  6. Biological Sciences, University of Alabama, Tuscaloosa, AL, USA
  7. Biological and Agricultural Engineering, North Carolina State University, Raleigh, NC, USA
  8. Entomology, University of Maryland, College Park, MD, USA

Wetlands are important control points for carbon cycling from local to global scales. Carbon dioxide (CO2) in wetlands is produced and consumed by primary producers and microbes, while groundwater acts as an additional major contributor of CO2. In addition, physical processes also alter CO2 concentrations in wetlands. And although the individual biogeochemical processes influencing CO2 dynamics are relatively well understood, how these processes change with dynamic environmental conditions, particularly in small, hydrologically dynamic wetlands, requires a more integrated ecosystem-scale approach. Further, while wetlands are generally framed as carbon sinks, recent work highlights their potential role as carbon sources due to their significant carbon emissions.

We used a dissolved oxygen (DO) and CO2 framework to characterize dominant biogeochemical processes across sites and seasons in three depressional forested wetlands that varied in size and inundation regime. This framework evaluates departures of DO and CO2 from an expected theoretical metabolic 1:-1 line, where deviations indicate processes beyond photosynthesis and respiration (e.g., anaerobic metabolism, groundwater inputs, or physical controls). We deployed DO and CO2 sensors, monitored wetland water levels, and collected quarterly surface water for water chemistry. To test how site and seasonal differences influenced biogeochemical processes, we calculated the offset for each paired DO-CO2 observation from the expected 1:-1 metabolic line.

At the ecosystem scale, wetlands were substantially more depleted in oxygen (range = -406.3-207.7μM) and more enriched in CO2 (range = -4.5-1331.9μM) than lakes and rivers. The largest, hydrologically stable wetland had lower offsets compared to the smaller wetlands, suggesting stronger controls of aerobic metabolism relative to other controls, likely due to greater light availability. Offsets during the drier summer and fall were higher, pointing to potentially increasing groundwater influence. There were periods of undersaturation, particularly in the large, hydrologically stable wetland, that point to potential periods of CO2 sink behavior. Together, these results highlight the variability in processes influencing CO2 dynamics and how these are mediated by hydrology, seasonality, and size. Understanding these controls will be critical to understanding the vulnerability of the wetland carbon cycle to future climatic changes, such as warming temperatures, storms, and droughts.