B046-0008
Direct Partitioning of Eddy-Covariance Water Vapor and Carbon Fluxes into Surface and Plant Components

Thursday, 10 December 2020
Poster
Einara Zahn1, Elie Bou-Zeid2, Stephen P Good3, William P Kustas4, Marcelo Chamecki5, Jose D Fuentes6, Nelson Luis Dias7, Joseph G Alfieri4, Nicolas E Bambach-Ortiz8, John H Prueger9, Maria Mar Alsina10, Zhiqiu Gao11, Zexia Duan12, Will Richardson13 and Gabriel George Katul14, (1)Princeton University, Princeton, NJ, United States, (2)Princeton University, Civil and Environmental Engineering, Princeton, NJ, United States, (3)Oregon State University, Department of Biological & Ecological Engineering, Corvallis, OR, United States, (4)U. S. Department of Agriculture, Agricultural Research Service, Hydrology and Remote Sensing Laboratory, Beltsville, MD, United States, (5)University of California, Los Angeles, Atmospheric and Oceanic Sciences, Los Angeles, CA, United States, (6)Penn State University, Department of Meteorology and Atmospheric Science, University Park, PA, United States, (7)University Federal Parana, Environmental Engineering, Curitiba, Brazil, (8)University of California Davis, Davis, CA, United States, (9)U. S. Department of Agriculture, Agricultural Research Service, National Laboratory for Agriculture and Environment, Ames, IA, United States, (10)E&J Gallo, Modesto, United States, (11)State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry，Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, (12)Nanjing University of Information Science and Technology, Climate and Weather Disasters Collaborative Innovation Center, Nanjing, China, (13)Oregon State University, Corvallis, OR, United States, (14)Nicholas School of the Environment, Duke University, Durham, NC, United States
Abstract:
The partitioning of observed total evapotranspiration into canopy/surface evaporation (E) and stomatal transpiration (T) is essential for a better quantification of water and energy budgets, and for validation of land-surface models. Similarly, the associated partitioning of total carbon dioxide flux into ecosystem respiration (R) and photosynthesis (P) is required to advance the understanding of the role of various biomes as carbon sinks or sources. Because of the importance of obtaining reliable estimates of these components, many partitioning techniques have been proposed. Promising approaches are partitioning models based on analysis of conventional high frequency eddy-covariance data, which require a smaller number of input parameters and can be applied to the network of flux towers existing world-wide. In this work, we compare three partitioning methods (all based on eddy covariance data) applied to measurements from a hazelnut orchard, rice field, vineyard, and the Amazon forest. The first method relies on flux-variance similarity between the two scalars and requires ecosystem water use efficiency as an input parameter; the second is a combination of relaxed-eddy accumulation and quadrant analysis; while the last model is a novel and simple approach proposed here that relies only on quadrant analysis. We found different levels of agreement across the models and sites. In all tests, the components of the carbon flux showed greater variability than those of the water flux because of the opposite directions of the two components (R and P have to add to the total flux, but their respective values are unbounded). While the present analyses cannot confirm which method is more accurate since that would require independent and reliable estimates of the components in each site, our results can identify some physical limitations of the various models, the conditions where they give similar results, and the distinct drivers of the partitioning in different ecosystems.
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