Measurement And Theoretical Calculation Of Daily Evapotranspiration Of The Wetland Plant-Reeds

With the increasing problem of water shortage, wetlands in arid areas are threatened by decreasing water supply. When the decline of water supply exceeds a threshold, wetlands will face irreversible damages. Therefore, accurate calculation of evapotranspiration (ET) of wetland plants is a key link in wetland protection and restoration.The objective of this thesis is to measure ET of the wetland plant–reeds by lysimeter measurement and develop a new method for calculate ET based on principles of SPAC theory. For lysimeter measurement, daily evapotranspiration of reeds was recorded for different water supply conditions from April 6, 2005 to November 13, 2005, using lysimeters, whose inflow was controlled by Marriot bottles that can supply water at a stable water table. The results showed that ET of reeds increased with the growing stages of the plant, and decreased with the dying of the plant in the late growing season; it rises in the clear and sunny days and drops sharply in rainy or cloudy weather condition.Based on the principle of water movement in a soil-plant-atmosphere continuum, i.e.water moves from high potential to low potential, the current water potential concept was modified on the basis of the Gibb's energy function. The modification enhanced the meaning of water potential and pointed out that total water potential is the driving force for water movement in SPAC. A new model and equation for calculating ET was proposed based on the modified water potential concept. The new ET calculating equation was validated by comparing with observed ET of reeds. Empirical coefficients used in the equation were calibrated with part of the observed results. Analysis on the errors between the calculated and observed ET shows that the proposed new equation can predict ET of reeds satisfactorily. The new equation has advantages of requiring fewer meterological parameters, being easy to use and accurate.