Aquatic marginal wetlands are created
by open water bodies - rivers, lakes and the
sea - which act as the source of water. They can be conveniently subdivided into
fringe wetlands and flood wetlands.
Fringe wetlands have a continuous or very
frequent (at least once per day)
hydrologi-cal connection with the parent water body and are typical of the shallow
edges of lakes and slow-flowing rivers, being characterised by emergent
vegetation.
Flood wetlands are, for most of the time,
hydrologically separated from the parent
water body, becoming connected only during high water. Typical examples are river
floodplain marshes, inundated frequently or for long periods during the wet season.
Coastal saltmarshes incorporate both wetland
types: areas subjected to daily
inundation ('low marsh') are flooded with a frequency and regularity adequate to
describe them as fringe wetlands, whereas infrequently flooded areas ('high
marsh') are flood wetlands.
During the interval between flood events,
flood wetlands will lose their water through
drainage and evapotranspiration, and may, in some cases, dry out completely.
The terms 'riverine wetland' and 'riparian
wetland' have been applied to flood
wetlands. However, these terms are usually applied to freshwater wetlands
associated with rivers. This overlooks the important functional and ecological
similarities these systems share with infrequently flooded coastal systems.
