WETLANDS - Water Quality Engineering in Natural Systems - page 288

Figure 8.4. Aerial view of a bog wetland. Source : Aber (2001).
Copyright: J.S. Aber.

needed for plant growth, a condition that is enhanced
by acid-forming peat mosses. The unique and demand-
ing physical and chemical characteristics of bogs result
in the presence of plant and animal communities that
demonstrate many adaptations to low nutrient levels,
waterlogged conditions, and acidic waters, such as car-
nivorous plants. In the United States, bogs are found in
the glaciated northeast and Great Lakes regions, where
they are referred to as northern bogs , and bogs are also
found in the southeast, where they are referred to as
pocosins . Bogs serve an important ecological function
in preserving downstream flooding by absorbing pre-
cipitation, and bogs have been recognized for their role
in regulating the global climate by storing large amounts
of carbon in peat deposits.

Figure 8.5. Typical fen. Source : McGlynn (2005).

improving water quality, and providing habitat for
unique plant and animal communities.
Bogs and fens are sometimes collectively referred to
as peatlands , since they are both peat-accumulating
systems. Moors and muskegs are other names given to
peatlands.

8.2.2 Delineation of Wetlands

8.2.1.4 Fens. Fens are peat-forming wetlands that
receive nutrients from sources other than precipitation,
usually from upslope sources through surface runoff
over surrounding mineral soils. A typical fen is illus-
trated in Figure 8.5, where the sloping land above the
fen is shown clearly in the background. Fens differ from
bogs in that they are less acidic and have higher nutrient
levels, which make them able to support a much more
diverse plant and animal community. Fens are often
covered by grasses, sedges, rushes, and wildflowers. Fens
are mostly a northern hemisphere phenomenon, occur-
ring in the northeastern United States, Great Lakes
region, the rocky Mountains, and much of Canada.
Fens are generally associated with low temperatures
and short growing seasons, where ample precipitation
and high humidity cause excessive amounts of moisture
to accumulate. Fens provide important benefits in a
watershed, including preventing or reducing flood risks,

A variety of definitions are used around the world to
delineate wetlands. In the United States, wetlands are
defined as “those areas that are inundated or saturated
by surface or groundwater at a frequency and duration
sufficient to support, and that under normal circum-
stances do support, a prevalence of vegetation typically
adapted for life in saturated soil conditions” (USACE,
1987). Wetlands that are delineated for regulatory pur-
poses are called jurisdictional wetlands . In the United
States, three factors must generally be considered in
delineating a wetland: vegetation, soils, and hydrology.

8.2.2.1 Vegetation. Wetland vegetation is defined as
macrophytes that are adapted to inundated or saturated
conditions. For purposes of delineation, plants can be
grouped into five categories: obligate wetland plants
(OBLs), facultative wetland plants (FACWs), faculta-