LYSIMETER STUDY OF EVAPOTRANSPIRATION OF CATTAILS AND COMPARISON OF 3ESTIMATION METHODS

A lysimeter was designed and installed in a cattail marsh as part of t he Everglades Nutrient Removal project in South Florida (26 degrees 38 ' N, 80 degrees 25' W) to measure evapotranspiration (ET) of cattails (Typha domingensis). The fully automated lysimeter with a surface area of 9.8 m(2) was located inside the marsh to measure cattail ET in a m arsh environment with sufficient fetch and minimum oasis effect on the lysimeter. The average measured ET rate was 3.9 mm per day for the pe riod of 12 February to 19 December 1993. The Penman-Monteith equation was applied to estimate daily ET using physically based resistance par ameter estimates and high resolution weather data. Also, average albed o (0.17) was computed for the vegetation for possible future computati on of net radiation from solar radiation data. The Penman combination model was applied with new wind function coefficients developed for th e study site and the Priestley-Taylor model was applied with an estima ted average coefficient (alpha) value of 1.18. Seven-day mean of measu red and estimated data were compared. The Penman-Monteith method had t he least error of estimation of 0.39 mm day(-1) with an r(2) value of 0.89 while the Penman combination equation had an error of estimation of 0.57 mm day(-1) with r(2) value of 0.86 and a least intercept of 0. 03 mm. The Priestley-Taylor method with an a value of 1.18 had standar d error of estimate 0.53 mm day(-1) with an r(2) value of 0.79. The Pr iestley-Taylor method has the potential to estimate ET in south Florid a when climatic data is limited, More data is needed to evaluate each equation to estimate ET of wetland features in humid areas such as sou th Florida.