'Swamp Thing' was released on this day in 1982

Word of the Day – Monday, February 19th



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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
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"