EVAPOTRANSPIRATION FROM A WET PRAIRIE WETLAND UNDER DROUGHT CONDITIONS: PAYNES PRAIRIE PRESERVE, FLORIDA, USA

Evapotranspiration and other surface-energy balance components of a wet prairie community dominated by Panicum hemitomon (maiden cane), Ptilimnium capillaceum (mock bishop's weed), and Eupatorium capillifolium (dog fennel) in Central Florida, USA were investigated. Drought conditions resulted in water-table levels from 0.58 to 1.20 m below ground level and variable soil wetness conditions during the observation period. Energy-balance measurements were made using the eddy correlation approach. The overall evapotranspiration rate was 4.16 mm d−1, and the average Bowen ratio was 0.42. Energy partitioning had an enhanced sensible heat-flux component and a dampened latent heat-flux component when the volumetric soil water content was less than or equal to 0.09 for the sandy soil. Evapotranspiration was classified into a two stages, first stage (wet) and second stage (dry) based on the soil water availability. The Penman-Monteith model gave good results for the first stage evapotranspiration. The Priestley-Taylor and the Penman models overestimated first stage evapotranspiration. A simple second stage evapotranspiration model, developed by applying a reduction factor based on soil moisture to the Penman-Monteith model, provided improved estimates of evapotranspiration for second stage observations.