Biophysical Processes and Feedback Mechanisms Controlling the Methane Budget of an Amazonian Peatland
Fenghui Yuan1*, Timothy Griffis1 (firstname.lastname@example.org), Jeffrey D. Wood2, Daniel T. Roman3, Angela Lafuente4, Erik Lilleskov5, Daniel Ricciuto6, Jhon Rengifo7, Lizardo Fachin7, Hinsby Cadillo-Quiroz8, Randall Kolka9, Rod Chimner4, Craig Wayson3
1Department of Soil, Water, and Climate, University of Minnesota–Twin Cities, Minneapolis/St. Paul, MN; 2School of Natural Resources, University of Missouri, Columbia, MO; 3International Programs, USDA Forest Service, Washington, D.C.; 4Michigan Technological University, Houghton, MI; 5USDA Forest Service, Houghton, MI; 6Oak Ridge National Laboratory, Oak Ridge, TN; 7Instituto de Investigaciones de la Amazonía Peruana, Iquitos, Peru; 8Arizona State University–Tempe, AZ; 9Northern Research Station, USDA Forest Service, Grand Rapids, MN
Tropical peatlands play a significant role in the global carbon (C) budget. However, little is known about the biogeochemistry of these peatlands and in particular the C cycle processes and their responses to hydrometeorological conditions. This leads to large uncertainties when constraining land surface models designed to forecast C budgets for tropical peatlands. This research made fundamental advances by providing the first ecosystem-scale carbon dioxide (CO2) and methane (CH4) flux observations in an Amazonian peatland and was the first to represent these systems within the E3SM Land Model (ELM) framework. Researchers found that the sink strength of natural palm swamp Amazonian peatlands is large but vulnerable to future warmer and drier conditions. Initial analyses of ecosystem-scale CO2 and CH4 fluxes showed the palm swamp peatland to be a large C sink (e.g., 440±187 g C m-2 y-1 in 2019). However, more recent data indicate that variations in hydrometeorological forcing can lead to a switch to a net C source. This change could be attributed to large scale climate variations, such as oscillations in La Niña/El Niño cycles. Field chamber observations showed unexpected subecosystem-scale C flux behavior, indicating complex partitioning of ecosystem-scale C emissions into soil and stem sources across seasons. Significant seasonal variation was observed in soil and stem CO2 fluxes (increasing during the dry season) and soil CH4 fluxes (decreasing during the dry season). However, there were no significant differences in stem CH4 fluxes between wet and dry seasons. Moreover, stem fluxes varied significantly among tree species and along their height profiles. Using these novel observations, the team improved ELM’s ability to simulate CO2 and CH4 fluxes and the energy balance of tropical peatlands by advancing three tropical-specific biophysical functions and by using multiobjective parameter optimization. Global sensitivity analyses suggested strong control of parameters associated with vegetation photosynthetic activities. Further, the modeling assessments highlighted the knowledge gaps that need to be addressed in simulating tropical vegetation phenological physiology and the CH4 transport from non-aerenchymatous tissues, such as stems. Subecosystem-scale and ecophysiological measurements are needed to characterize and develop parameterizations of these processes to improve model capabilities and to advance ongoing modeling efforts to extend the C budget estimate to the Pastaza-Marañón foreland basin, which is the most extensive peatland complex in the Amazon basin.