Sub-canopy Evapotranspiration from Floating Vegetation and Open Water in a Swamp Forest

Among previous studies, there are large discrepancies in the difference between evapotranspiration from wetland vegetation and evaporation from open water. In this study, we investigate evapotranspiration differences between water and vegetation in a scenario that has otherwise not been extensively investigated: evapotranspiration from floodwaters in the sub-canopy environment. This study was conducted under a closed canopy baldcypress-ash-tupelo swamp forest in southeastern Louisiana. Water levels were measured in paired, partially-submerged evaporation pans, one with floating aquatic vegetation and the other without. Over the 5 month measurement period (June-November), average evapotranspiration rates from floating vegetation and open water were approximately 1.35 +/- 0.10 and 1.36 +/- 0.06 mm day(-1), respectively. Open water evaporation was generally higher in summer, and evapotranspiration from the vegetated water surface was higher in fall, likely due to changes in the sub-canopy energy environment related to both regional climate and site canopy phenology.