Geoscience Reference
In-Depth Information
Figure 2-18.
Aerial overview of fjords along the
southwestern coast of Greenland. These deep glacier-
carved valleys descend hundreds of meters below sea
level and extend from the inland ice sheet (visible in
background) to the edge of the continental shelf. Photo
by J.S. Aber.
Figure 2-17.
Both rocky cliffs and sandy beach are
well-known tourist attractions at Canon Beach on the
Pacii c coast of Oregon, United States. Kite aerial photo
by J.S. Aber and S.W. Aber.
rivers. Fjords and drowned coasts, where
supply of river sediment is insufi cient to
ini ll estuary basins (Fig. 2-18).
• Riverine - Freshwater, perennial streams
comprising the deep-water habitat contained
within a channel. This restrictive system
excludes l oodplains adjacent to the channel
as well as habitats with more than 0.5‰
salinity (Fig. 2-19).
• Lacustrine - Inland water bodies that are
situated in topographic depressions, lack
emergent trees and shrubs, have less than
30% vegetation cover, and occupy at least 20
acres (8 ha). Includes lakes, larger ponds,
sloughs, lochs, and bayous (Fig. 2-20).
• Palustrine - All non-tidal wetlands that
are substantially covered with emergent
vegetation
-
trees, shrubs, moss, etc. Most
bogs, swamps, l oodplains and marshes fall
into this system (Fig. 2-21), which also
includes small bodies of open water (
and energy occur within wetlands and between
wetlands and other habitats; a holistic approach
is necessary to investigate, understand, develop,
and manage wetlands successfully.
A signii cant portion of this topic deals with
the palustrine system of wetland environments
as well as other water bodies not more than 6 m
(20 feet) deep, according to the broad Ramsar
dei nition. The palustrine system includes
several classes that are recognized on the basis
of substrate conditions or dominant vegetation
cover (Schot 1999), including rock bottom,
unconsolidated bottom, aquatic bed, unconsoli-
dated shore, moss-lichen wetland, emergent
wetland, scrub/shrub wetland, and forested
wetland.
<
2.6 Peatland
8 ha),
as well as playas, mudl ats and salt pans that
may be devoid of vegetation much of the
time. Water chemistry is normally fresh but
may range to brackish and saline in semiarid
and arid climates.
The classii cation scheme outlined above deals
mainly with the suri cial aspects of wetlands. As
most wetlands exist in topographic depressions,
they tend to accumulate sediment through time.
Furthermore, wetland soils are typically anaero-
bic, which often leads to the preservation of
organic remains, namely peat. It is the living
vegetation combined with accumulation of pre-
served plant debris that distinguishes peatlands
All of these systems may interface with each
other or with dryland and deep-ocean habitats,
so that an environmental continuum exists
across the Earth's surface. Flows of materials
