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Stephen K. Hamilton and others W.K. Kellogg Biological Station and Department of Zoology, Michigan State University, 3700 E. Gull Lake Drive, Hickory Corners, Michigan 49060, USA, Abstract: The complex floodplains of large rivers offer a striking example of how geomorphology, by dictating patterns in the frequency and duration of soil saturation and surface flooding, influences ecosystem structure and function. This study draws on multiple sources of remote sensing data, together with ground observations and water sampling, to distinguish floodplain ecosystems in the Madre de Dios River, a tributary of the Amazon River in Perú. This remote tropical river meanders across sub-Andean alluvial deposits in a tectonically active region, creating fluvial terraces of varying ages. Data from Landsat ETM+, JERS-1 radar, and the Shuttle Radar Topography Mission were integrated in an object-oriented image analysis approach to distinguish five floodplain vegetation classes. Vegetation classes generally correspond with successional age, reflecting the activity of the riverine meander belt. Stage data for the river show erratic fluctuations and an annual range exceeding 8 m, but the maximum depth of floodplain inundation varied from >1 m close to the river to ca. 0.1 m on more elevated terraces. The major ion composition of standing waters on the floodplain during the dry season indicated the importance of local groundwater emergence in maintaining saturated soils, particularly further from the river, where backswamp vegetation is distinct and includes palm swamps. There is thus a hydrological continuum from deep but sporadic river inundation near the river to chronic soil saturation by groundwater in distant backswamps, reflecting the geomorphological origin and age of the floodplain deposits, and this continuum results in fundamental ecological differences. The exceptionally rich biodiversity of the sub-Andean region may be ascribed in part to the habitat diversity associated with fluvial geomorphological features, and thus conservation planning must account for the role of fluvial dynamics. |
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