Nocturnal Evapotranspiration in Eddy-Covariance Records from Three Co-Located Ecosystems in the Southeastern U.S.: Implications for Annual Fluxes

dc.contributor.authorNovick, Kimberly A.
dc.contributor.authorOren, Ram
dc.contributor.authorStoy, Paul C.
dc.contributor.authorSiqueira, Mario B. S.
dc.contributor.authorKatul, Gabriel G.
dc.description.abstractNocturnal evapotranspiration (ETN) is often assumed to be negligible in terrestrial ecosystems, reflecting the common assumption that plant stomata close at night to prevent water loss from transpiration. However, recent evidence across a wide range of species and climate conditions suggests that significant transpiration occurs at night, frustrating efforts to estimate total annual evapotranspiration (ET) from conventional methods such as the eddy-covariance technique. Here, the magnitude and variability of ETN is explored in multiple years of eddy-covariance measurements from three adjacent ecosystems in the Southeastern U.S.: an old grass field, a planted pine forest, and a late-successional hardwood forest. After removing unreliable data points collected during periods of insufficient turbulence, observed ETN averaged 8–9% of mean daytime evapotranspiration (ETD). ETN was driven primarily by wind speed and vapor pressure deficit and, in the two forested ecosystems, a qualitative analysis suggests a significant contribution from nocturnal transpiration. To gapfill missing data, we investigated several methodologies, including process-based multiple non-linear regression, relationships between daytime and nighttime ET fluxes, marginal distribution sampling, and multiple imputation. The utility of the gapfilling procedures was assessed by comparing simulated fluxes to reliably measured fluxes using randomly generated gaps in the data records, and by examining annual sums of ET from the different gapfilling techniques. The choice of gapfilling methodology had a significant impact on estimates of annual ecosystem water use and, in the most extreme cases, altered the annual estimate of ET by over 100 mm year−1, or ca. 15%. While no single gapfiling methodology appeared superior for treating data from all three sites, marginal distribution sampling generally performed well, producing flux estimates with a site average bias error of <10%, and a mean absolute error close to the random measurement error of the dataset (12.2 and 9.8 W m−2, respectively).en_US
dc.description.sponsorshipU.S. Department of Energy (DOE) Office of Biological and Environmental Research (BER) Terrestrial Carbon Processes (TCP) program (Grants # 10509-0152, DE-FG02-00ER53015, and DE-FG02-95ER62083); United States-Israel Binational Agricultural Research and Development (BARD, Research Grant No. IS3861-06); National Science Foundation (NSF-EAR 06-28342 and 06-35787) Graduate Research Fellowship Program; James B Fellowship program at Duke Universityen_US
dc.identifier.citationNovick, Kimberly A., Oren, Ram, Stoy, Paul C., Siqueira, Mario B. S., Katul, Gabriel G. “Nocturnal Evapotranspiration in Eddy-Covariance Records from Three Co-Located Ecosystems in the Southeastern U.S.: Implications for Annual Fluxes.” Agricultural and Forest Meteorology 149, no. 9 (September 2009): 1491–1504. doi:10.1016/j.agrformet.2009.04.005.en_US
dc.rightsThis Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).en_US
dc.titleNocturnal Evapotranspiration in Eddy-Covariance Records from Three Co-Located Ecosystems in the Southeastern U.S.: Implications for Annual Fluxesen_US
mus.citation.journaltitleAgricultural and Forest Meteorologyen_US
mus.identifier.categoryLife Sciences & Earth Sciencesen_US
mus.relation.collegeCollege of Agricultureen_US
mus.relation.departmentLand Resources & Environmental Sciences.en_US
mus.relation.universityMontana State University - Bozemanen_US


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