Abstract: On the basis of analyzing the relationship among hydrological process,habitat variation and wetland ecology,it’s pointed out that flood and drought are important factors to drive the ecological process of wetland transition zone. The Okeechobee lake in Florida is taken as a test area to study the variation of submerged transition zone area of lake wetland under different water level frequencies. The effect of underlying surface variation on the ecology is quantitatively and qualitatively evaluated by using HSI (Habitat Suitability Indices) model. The causes of the ecological effects are analyzed. Measured data of migratory birds are employed to calibrate the results. It is concluded that the typical moderate flood and drought process is favorable for the diversity of biological species in the wetland transition zone.

Key words: flood , drought , lake wetland , transition zone variation , ecological effect