Geoscience Reference
In-Depth Information
streams, reservoirs, and portions of lakes too deep
for emergent vegetation are not included. Neither
are water areas that are so temporary as to have
little or no effect on the development of moist-soil
vegetation (Shaw and Fredine 1956).
The dei nition of wetlands utilized by the U.S.
Fish and Wildlife Service was elaborated subse-
quently by Cowardin et al. (1979), and this
dei nition has been cited widely, adopted or
modii ed by others.
Figure 2-1.
The island of Vormsi merges into the
shallow Väinimeri (Strait Sea) in the left foreground
with the deeper Gulf of Finland in the far background.
Water salinity here, at the eastern end of the Baltic Sea,
is quite low. View northward from Förby, Vormsi,
Estonia. Kite aerial photo by J.S. Aber and S.W. Aber.
Wetlands are lands transitional between terrestrial
and aquatic systems where the water table is usually
at or near the surface or the land is covered by
shallow water . . . wetlands must have one or more
of the following attributes: 1) at least periodically,
the land supports predominantly hydrophytes, 2)
the substrate is predominantly undrained hydric
soil, and 3) the substrate is nonsoil and is saturated
with water or covered by shallow water at some
time during the growing season of each year.
part of the year. And i nally, Mitsch and Gos-
selink (2007, p. 25) emphasized the presence
of standing water for some period during the
growing season, unique soil conditions, and
organisms, especially vegetation, adapted to or
tolerant of saturated soils.
From these several dei nitions, it is clear that
three aspects
-
water, soil, and vegetation
-
are accepted as the basis for recognizing and
describing wetland environments (Schot 1999).
This triad is the modern approach for wetland
dei nition under many circumstances that
include vastly different environments. Further-
more, wetlands typically occupy transitional
settings or intervening positions between dry,
upland environments and deep-water habitats
(Fig. 2-1). Each of these primary aspects is
briel y described in the following sections and
elaborated in subsequent chapters.
The U.S. Army Corps of Engineers (USACE) and
the Environmental Protection Agency (EPA)
have agreed on the following dei nition, which
they use for legal recognition of wetlands under
the U.S. Clean Water Act.
The term “wetlands” means those areas that are
inundated or saturated by surface or ground water
at a frequency and duration sufi cient to support,
and that under normal circumstances do support,
a prevalence of vegetation typically adapted for
life in saturated soil conditions. Wetlands generally
include swamps, marshes, bogs, and similar areas
(USACE 1987).
According to Charman (2002, p. 3), the distin-
guishing features of wetlands are: a) the pres-
ence of water at or near the land surface, b)
unique soil conditions that are most often char-
acterized by low oxygen content, and c) special-
ized biota, particularly plants, that are adapted
to growing in these environments. Greb,
DiMichele and Gastaldo (2006, p. 2) stated that
wetlands are characterized by water at or near
the soil surface for some part of the year, soils
that are inl uenced by water saturation all or
part of the year, and plants that are adapted to
living in conditions of water saturation all or
2.2 Water
Ground water (water table or zone of satura-
tion) is at the surface or within the soil root
zone during all or part of the growing season.
Water may be obvious in shallow pools, pannes,
puddles and channels, or it may lie just beneath
the surface (Fig. 2-2). Water l ow ranges from
turbulent streams to essentially stagnant ponds,
and water level may l uctuate; tidal l ats are
