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United States Department of Agriculture

Agricultural Research Service

Research Project: Preserving Water Quality and Availability for Agriculture in the Lower Mississippi River Basin

Location: Delta Water Management Research

Title: Measurement of sub-canopy evaporation in a flooded forest

item Allen, Scott
item Edwards, Brandon
item Keim, Richard
item Reba, Michele

Submitted to: American Society of Agricultural and Biological Engineers
Publication Type: Proceedings
Publication Acceptance Date: 4/7/2014
Publication Date: 4/11/2014
Citation: Allen, S.T., Edwards, B.L., Keim, R.F., Reba, M.L. 2014. Measurement of sub-canopy evaporation in a flooded forest. Proceedings of the American Society of Agricultural and Biological Engineers. Meeting held in Raleigh, North Carolina, April 7-11, 2014, 9 pp.

Interpretive Summary: Subcanopy water flux was measured from a forested wetland in southern Louisiana in a closed-canopy of bald-cypress in the Atchafalaya River Basin in southern Louisiana (30.0715 N, -91.3114 W). Mean water flux of 0.7 mm per day were measured. Standard eddy covariance methods did not yield useful sub-daily results due to inadequate turbulence under the canopy. Bowen-ratio methods require precise equipment, but provide a feasible option because heat and vapor gradients were stable. Although sub-daily measurements are possible, daily and weekly BREB measurements were more reliable. Floating vegetation affected measured energy, temperature and vapor gradients.

Technical Abstract: Evapotranspiration is the dominant water efflux in many forested wetlands, but few studies have quantified the contribution of subcanopy evaporation. The goal of this study is to investigate the subcanopy energy balance to more fully understand physical controls over evaporation. We used Bowen ratio energy balance calculations and eddy covariance to investigate the partitioning of energy in the subcanopy of a flooded baldcypress-water tupelo forested wetland. Results from daily and weekly Bowen ratio energy balances indicate that when flooded, available energy was primarily partitioned to latent heat exchange, resulting in a mean flux of 0.7 mm per day. Standard eddy covariance methods did not yield useful sub-daily results because of inadequate turbulence. Sub-daily Bowen ratio calculations were unreliable because of difficulties in measuring relatively weak fluxes and gradients in temperature and vapor pressure. Although measuring the water surface temperature usually mitigates this issue in lake system, this approach was complicated by the thick layer of floating macrophytes that affected temporal energy patterns.

Last Modified: 09/19/2017
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