History
Although similar to bogs, fens
support marshy vegetation and present a greater diversity of plant species. A
fen is a peat land with a fluctuating water table at the surface. The water
table is not stagnant, but moves through the peat very slowly by seepage and, in
some cases, in open channels.
Fens are wetlands
that are fed primarily by underground water (rather than surface water) and that
have peat soils. Unlike most soil, which is primarily mineral matter with bits
of decomposing organic matter mixed in it, peat consists of layer upon layer of
packed vegetation that has not been able to get enough oxygen to decompose, and
so has become a very fine, oxygen- and mineral-deprived, highly saturated mass.
In many cases, the peat that you see in fens today has been accumulating for
thousands of years.
Marble bedrock
and
gravel lie
in layers throughout and at the bottom of the mountain plateau. That means that
the groundwater that runs through those layers and then supplies most fens in
this landscape is alkaline, or "sweet," in composition, leading the fens
themselves to be known as "calcareous" because they contain a lot of calcium
compounds and ions. Calcareous fens are the most rare type of wetlands in our
landscape, but some of the world's healthiest examples of them can be found
here.
Dominated by
grassy-looking plants known as "sedges," fens typically shelter a rich diversity
of species. The calcareous nature of local fens also makes them home to many
rare species that depend upon alkaline "sweet " water, including the showy lady
slipper.
The Crooked Lake Floating Fens
