As with all aquatic systems, rigid definitions
lead to difficulties with habitats which
are clearly transitional.
An area of floodplain marsh may be fed
by groundwater during the dry season,
thereby remaining permanently waterlogged and taking on the characteristics of a
fen. Whether it is then classified as a fen or a flood wetland, or simply a hybrid
between the two, is a matter of subjectivity. If its soil is dominated by peat it is
probably a fen that is occasionally flooded by a river, whereas if dominated by
mineral soils, such as riverine silts, it is a flood wetland with fen-like characteristics.
Similarly, as a fen forms over the site
of a lake or pond, it passes through a
transitional stage, and a distinction must be drawn between a small lake which
supports a large fringing wetland, and an open pool formed in a hollow-within a
mire.
