Spatial heterogeneity in CO2 and CH4 fluxes: insights from airborne eddy covariance measurements over the Mid-Atlantic region

Authors: HANNUN, R. - Goddard Space Flight Center; WOFLE, G. - Goddard Space Flight Center; KAWA, S - Goddard Space Flight Center; HANISCOL, T. - Goddard Space Flight Center; NEWMAN, P. - Goddard Space Flight Center; Alfieri, Joseph; BARRICK, J - Langley Airforce Base; CLARK, K. - US Department Of Agriculture (USDA); DIGANGI, K. - Langley Airforce Base; DISKIN, G. - Langley Airforce Base; KING, J. - North Carolina State University; Kustas, William - Bill; MITRA, B. - Texas A&M University; NOORMETS, A. - North Carolina State University; NOWAK, J. - Langley Airforce Base; THORNHILL, K. - Langley Airforce Base; VARGAS, R. - Collaborator

Submitted to: Ecological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2020
Publication Date: 3/6/2020
Citation: Hannun, R., Wofle, G., Kawa, S., Haniscol, T., Newman, P., Alfieri, J.G., Barrick, J., Clark, K., Digangi, K., Diskin, G., King, J., Kustas, W.P., Mitra, B., Noormets, A., Nowak, J., Thornhill, K., Vargas, R. 2020. Spatial heterogeneity in CO2 and CH4 fluxes: insights from airborne eddy covariance measurements over the Mid-Atlantic region. Ecological Research. 15/035008. https://doi.org/10.1088/1748-9326/ab7391.
DOI: https://doi.org/10.1088/1748-9326/ab7391

Interpretive Summary: Trace gases such as carbon dioxide (CO2) and methane (CH4) can influence regional weather and climate but continuous spatially- distributed measurements can be challenging. Thus, processes must be modeled. In turn, to develop and test the models, accurate data describing the exchange of these trace gases is needed. Using data collected over the Mid-Atlantic region, this study invested an airborne method for collecting those data while focusing on the effects of variability in the landscape. The study showed that the aerial measurements agreed well with surface measurements over a variety of ecosystems including wetlands, forests, and crops. This suggests the measurements could prove to be a valuable monitoring method.

Technical Abstract: The exchange of carbon between the Earth’s atmosphere and biosphere influences the atmospheric dynamics of carbon dioxide (CO2) and methane (CH4). Airborne eddy covariance can quantify surface-atmosphere exchange from landscape-to-regional scales, offering a unique perspective on carbon cycle dynamics. We use extensive airborne measurements to quantify fluxes of energy, CO2, and CH4 across multiple ecosystems in the Mid-Atlantic region. Flights took place during September 2016 and May 2017. In conjunction with footprint analysis and land cover information, we use the airborne dataset to explore the effects of landscape heterogeneity on measured fluxes. Our results demonstrate large variability in CO2 uptake over mixed agricultural and forested sites, with fluxes ranging from -3.4 ± 0.7 to -11.5 ± 1.6 µmol m-2 s-1 for croplands and -9.1 ± 1.5 to -22.7 ± 3.2 µmol m-2 s-1 for forests. We also measured large CH4 emissions of 32.3 ± 17.0 to 76.1 ± 29.4 nmol m-2 s-1 from a brackish herbaceous wetland and 58.4 ± 12.0 to 181.2 ± 36.8 nmol m-2 s-1 from a freshwater forested wetland site. Additionally, we compared ecosystem-specific aircraft observations with measurements from eddy covariance flux towers along the flight path to demonstrate that towers capture ~30–75% of the regional variability in ecosystem flux. Additionally, diel patterns measured by the tower sites demonstrate that peak, midday flux measurements from aircraft can predict net daily CO2 exchange. We also discuss next steps in applying airborne observations to evaluate bottom-up flux models and improve understanding of the biophysical processes that drive carbon exchange from landscape-to-regional scales.