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FEN
(fen)
Low-lying
wetland, as a swamp Common
clues: Swamp;
Marsh; Wetland; Boggy land; Quagmire; Waterlogged lowland;
Marshland Crossword
puzzle frequency:
2 times a year Frequency
in English language:
10579 / 86800 Video: Congaree
Swamp Lake
A
fen is a type of wetland fed by surface and/or groundwater. The
flora of fens is characterized by their water chemistry. Fens are
often confused with bogs, which are fed primarily by rainwater
and often inhabited by certain sphagnum moss, making them acidic.
Like other wetlands, fens will ultimately fill in and become a
terrestrial community such as a woodland through the process of
ecological succession.
Marsh
in Long Point, Ontario, Canada
The
ecological succession begins with fresh water filling a
depression in the land surface. However, the subsequent course of
development depends on the conditions; the acidity of the water,
the climate and so on. In a north European climate, given a
near-neutral or somewhat basic pH, submerged plants will colonize
the lake while from its margin, emergent vegetation, typically a
reed bed will spread.
The
decayed vegetation, with clay particles and precipitated
carbonates (lime) will form ooze, held in place by the still
water among the rhizomes and stems of the reeds. That in turn,
will exclude air so that decomposition organisms will not fully
work on the dead vegetation which subsequently sinks into it. In
this way, peat will form. As the peat accumulates to near the
surface level of the lake, a fen will develop on it. Provided it
continues to be fed by chemically basic spring or runoff water,
it will continue to grow out of the lake as long as oxygen is
excluded from the peat.
If
achievement of the saturation by water comes to be by way of
direct rainfall, the fen will become acidic to the point where it
is a bog. It can then grow on, above the level of the fen,
receiving its moisture from the sky. Thus, a fen develops
readily, in a moderately rainy climate. Where there is too little
rain, seasonal dryness will allow air into the peat. This will
permit its decay. Alternatively, too much rain washes the
hydroxide (HO-) ions out of the peat and it becomes bog owing to
the carbonic acid from dissolved carbon dioxide in the rain,
added to the humic acid naturally in the peat.
This
article is licensed under the GNU
Free Documentation License.
It uses material from the Wikipedia
article "Fen".
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