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ARS Home » Plains Area » El Reno, Oklahoma » Oklahoma and Central Plains Agricultural Research Center » Livestock, Forage and Pasture Management Research Unit » Research » Publications at this Location » Publication #406927
Research Project: Integrated Agroecosystem Research to Enhance Forage and Food Production in the Southern Great Plains

Location: Livestock, Forage and Pasture Management Research Unit

Title: A comparison of FVS, MREA, and CEC methods to partition evapotranspiration in tallgrass prairies

Author
item Wagle, Pradeep
item RAGHAV, PUSPHENDRA - University Of Alabama
item KUMAR, MUKESH - University Of Alabama
item SCANLON, TODD - University Of Alabama
item Northup, Brian
item Moffet, Corey
item Gunter, Stacey
item XIAO, XIANGMING - University Of Oklahoma

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 10/4/2023
Publication Date: 12/5/2023
Citation: Wagle, P., Raghav, P., Kumar, M., Scanlon, T., Northup, B.K., Moffet, C., Gunter, S.A., Xiao, X. 2023. A comparison of FVS, MREA, and CEC methods to partition evapotranspiration in tallgrass prairies [abstract]. American Geophysical Union. 2023:H13D-06.

Interpretive Summary:

Technical Abstract: Several methods viz. Flux Variance Similarity (FVS), Modified Relaxed Eddy Accumulation (MREA), and Conditional Eddy Covariance (CEC) are developed to partition evapotranspiration (ET) into transpiration (T) and evaporation (E) using high-frequency eddy covariance (EC) data. The FVS method uses different approaches to parametrize intercellular carbon dioxide concentrations (ci) to calculate water use efficiency (WUE). In FVS, some ci parameterization approaches (i.e., constant ci and constant ci/ca ratio) allow for C3 or C4 options and adjustable ci. In contrast, MREA, CEC, and the optimum (i.e., optimized WUE approach) in FVS do not require prior approximations of ci or C3 and C4 species. We evaluated the performance of MREA, CEC, and three ci parameterization approaches in FVS, along with sensitivity analysis and dynamic ci parameterizations for constant value and constant ratio for two differently managed (grazed vs. hay harvest) C3-C4 mixed tallgrass prairies, which were dominated by warm-season C4 grasses. The T:ET ratios from MREA and CEC showed similar temporal dynamics, but with larger magnitudes of T:ET ratios than those from FVS. For CEC and MREA methods, many half-hourly T:ET ratios equaled 1 (i.e., 100% T), while the minimum E was around 10-15% for FVS, resulting in slightly higher (by 10-15%) T:ET ratios at seasonal and annual scales. The T:ET ratios from constant value and constant ratio FVS methods were similar (within 1-2%) at annual and seasonal scales, regardless of whether they were calculated using C4 parameterization only or a dynamic C3-C4 parameterization. Greater agreement among the partitioning methods was found when the correlation coefficient ('qc) between carbon (c) and water vapor (q) concentrations was between -0.1 and 0.1 (i.e., a balance between stomatal and non-stomatal exchange). Significant variations in T:ET ratios were observed across methods when stomatal ('qc <-0.8) and non-stomatal ('qc >0.8) fluxes dominated.