极端洪水下荆江洲滩植被响应研究OA

To investigate the differential effects of natural floods and engineering-regulated floods on riverine shoal vegetation in the middle Yangtze River,this study took Guanzhou Island,a typical mid-channel bar in the upper Jingjiang Reach,as the research object.Two extreme flood events in 1998 and 2020,comparable in magnitude but with distinctly different hydrological boundary conditions,were selected for comparative analysis.Based on the Google Earth Engine platform,a multi-source time-series remote sensing dataset of Guanzhou Island was constructed by integrating Landsat surface reflectance products,Sentinel-2 multispectral imagery,and high-temporal-resolution data from the moderate resolution imaging spectroradiometer(MODIS).Combined with discharge,water level,and suspended sediment concentration series from Zhicheng Hydrological Station,the correspondence among flood processes,water-sediment conditions,and responses of riverine shoal vegetation was analyzed.Results indicate that the 1998 flood,under natural evolution,exhibits characteristics of high peak discharge,long duration,and high sediment concentration,causing significant vegetation greenness decline and bare flat expansion in the low-lying flats and marginal areas of Guanzhou Island under the combined effects of sustained high water levels and high sediment-laden flows.Although the 2020 flood also occurred against a background of basin-wide heavy rainfall,cascade reservoirs'joint operation substantially reduces the released flood peak and sediment load,imparting stronger anthropogenic regulation characteristics to the flood process;consequently,the core vegetation zone on the mid-to-high flats of Guanzhou Island is preserved,and post-flood recovery is faster than in 1998.Zonal analysis reveals that the artificial forest-farmland composite zone at higher elevations with relatively stable surfaces exhibits stronger tolerance to regulated floods,while the low-lying bare flat and water-fringing zones remain the most sensitive area to flood disturbance.Over the long term,after the operation of the Three Gorges Project,vegetation expansion and woody encroachment on the shoals of the Jingjiang Reach have intensified.These changes may alter local flood discharge conditions by increasing the roughness of the shoals.This study concludes that riverine shoal vegetation responses under extreme floods are jointly controlled by flood peak intensity,continuous inundation duration,sediment conditions,and microtopography,and that engineering regulation has substantially altered the disturbance mode of floods on vegetation.