This section focuses on wetlands as water resources
within a watershed
and, specifically,
how they are both a product of and an influence on watershed
hydrology and water quality.
Fens
Fens are peat-accumulating wetlands that form at low points in the
landscape or near slopes where ground water intercepts the soil surface
(Mitsch and Gosselink 1993). Water levels are fairly constant all year
because the water supply is provided by ground water inputs. Fens,
like bogs, tend to be glacial in origin and are found in the northern
United States or on mountains and mountainsides. Fens are dominated by
herbaceous plants, such as grasses and sedges, typically lack the
Sphagnum moss that predominates in bogs, and look like meadows.
Fens may represent an earlier successional stage of peat accumulation
than bogs, and over geologic time, fens may become bogs. Unlike bogs,
fens receive minerals and nutrients from ground water, because they
have built up less peat and ground water is still sufficiently close
to the surface. Fens are less acidic than bogs because they have
little or no Sphagnum, and because ground water inputs tend to be
neutral or alkaline. The pH of fens ranges from 4.0 - 8.0, depending
on vegetation and peat type (Camp, Dresser, and McKee 1981). Fens
provide less stressful growing conditions for plants and microbes and
thus have higher primary productivity and a greater variety of flora and
fauna than bogs.
Fens may depend on aquifers that are recharged in uplands. These upland
recharge areas may be distant from the wetlands (Brinson 1993). Thus,
excessive withdrawal or interception of ground water for municipal and
agricultural uses, and reduced urban ground water recharge as a result
of increased impervious surfaces can decrease water supply to fens,
potentially leading to degradation of these wetland communities
(USEPA 1993b).
Values related to watershed management
In addition to their ground water inputs and precipitation, fens may
receive runoff and other surface water. They tend to contribute more
to downgradient surface water supplies than do bogs because of
additional ground and surface water inputs to fens. Fens may help
maintain surrounding water tables, exerting influence on the recharge
and discharge of local aquifers and thus on the hydrology of other
water resources (O'Brien 1988).
Life support
Fens, like bogs, support a great diversity of wildlife species in
relatively limited quantities. Like bogs, they are increasingly
important habitat for moose, deer, black bear, beaver, lynx, fishers,
snowshoe hare, otter, and mink because of development elsewhere
(Mitsch and Gosselink 1993). Because fens are more productive than
bogs, they support a greater variety of small mammals and are host
to greater numbers of their predators. Many bird species (including
migratory birds) breed, nest, feed, and find refuge in fens. The
greater sandhill crane, great gray owl, short eared owl, sora rail,
and sharp-tailed sparrow depend on fens and bogs for survival. Fens
provide habitat for more fish species than bogs because fens may have
inflow and outflow streams. Species such as pike, walleye, bluegill,
smallmouth bass, brook trout, brown trout, and killifish may inhabit
fens or streams fed by fens (Camp, Dresser, and McKee 1981). One third
of fish taxa in the deserts of the southwestern United States are
completely dependent on ground water-fed wetlands and downstream riparian
marshes (cienegas) (Meffe, 1989).
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