There are many definitions of riparian wetlands. A hydro-logical definition defines riparian wetlands as lowland terrestrial ecotones which derive their high water tables and alluvial soils from drainage and erosion of adjacent uplands on the one side or from periodic flooding from aquatic ecosystems on the other (McCormick, 1979)
A functional definition states that riparian areas are three-dimensional ecotones of interaction that include terrestrial and aquatic ecosystems, that extend down to the groundwater, up above the canopy, outward across the floodplain, up the near-slopes that drain to the water, laterally into the terrestrial ecosystem, and along the water course at a variable with (Ilhard et al., 2000).
Both definitions point to the ecotonal character of riparian wetlands between water bodies on one side and the upland on the other. Riparian wetlands can be, at the smallest scale, the immediate water's edge where some aquatic plants and animals form a distinct community, and pass to periodically flooded areas of a few tens of meters width. At medium scale they form bands of vegetation, and at the largest scale they form extended floodplains of tens of kilometers width along large rivers. In this case, complexity of the riparian wetlands increases so much that many scientists give them the status of specific ecosystems (see Floodplains).
There are several concepts that deal with different aspects of stream and river ecology but two of them are of specific interest to rivers and riparian zones (see Rivers and Streams: Ecosystem Dynamics and Integrating Paradigms). The 'river continuum concept' (RCC) of Vannote et al., describes the longitudinal processes in the river channel and the impact of the riparian vegetation on the physical and chemical conditions and as carbon source to the aquatic communities in the channel. The 'flood pulse concept' (FPC) of Junk eta/. stresses the lateral interaction between the floodplain and the river channel and describes the specific physical, chemical, and biological processes and plant and animal communities inside the floodplain. The predictions of the RCC fit well for rivers with narrow riparian zones but with increasing lateral extent and complexity of the riparian zone the FPC becomes more important. Here, we restrict our discussion to riparian wetlands along streams and low-order rivers. Since lateral extent of the riparian zone along low-order rivers can vary considerably in different parts of the same river or between different rivers of the same river order, the applicability of the concepts may also vary.
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