Geoscience Reference
In-Depth Information
Figure 2-8.
Peat exposed in a cliff along the North Sea
coast, northwestern Denmark. The peat accumulated in
bogs during the Iron Age about 2000 years ago. Sand
dunes later buried the peat, and recent coastal erosion
has uncovered the peat layer. Scale pole marked in
20-cm intervals; photo by J.S. Aber.
Figure 2-10.
Sangre de Cristo Formation exposed near
Cuchara in south-central Colorado, United States (see
Color Plate 2-10). Several thousand meters of red
sandstone, shale and conglomerate accumulated as
alluvial fans during the Permian when the Ancestral
Rocky Mountains were uplifted. The red color indicates
oxidizing conditions in the depositional environment.
These strata were tilted upward later, when the modern
Rocky Mountains were deformed in the Eocene. Photo
by J.S. Aber.
nearly bare playas and mudl ats. The inclusion
of rice, the world's most important crop, shows
that wetlands may be cultural as well as natural
features.
Hydrophytes have various special adapta-
tions for dealing with submergence and lack of
oxygen. Some wetland plants can tolerate sub-
stantial variations in soil moisture and water
level, but others have strict water requirements
for survival. On this basis, wetland vegetation is
grouped into four general ecological categories,
depending mainly on growth position in rela-
tion to water level (Whitley et al. 1999):
Figure 2-9.
Highvale coal mine in central Alberta,
Canada. A thick seam of Cretaceous coal is extracted
for generating electricity in a nearby power plant.
Photo by J.S. Aber.
state. The latter is often observed in ancient soils,
known as paleosols, preserved in the geologic
record, for example red beds (Fig. 2-10). Modern
wetland soils typically display both mottled
greenish-gray and orange patches, lenses or
layers, which demonstrate alternating reducing
and oxidizing chemical environments.
• Shoreline - Plants that grow in wet soil on
raised hummocks or along the shorelines
of streams, ponds, bogs, marshes, and lakes.
These plants are situated at or above the
level of standing water; some may be rooted
in shallow water (Fig. 2-11).
• Emergent - Plants that are rooted in soil that
is underwater most of the time. These plants
grow up through the water, so that stems,
leaves and l owers emerge in air above water
level (Fig. 2-12).
• Floating - Plants whose leaves mainly l oat
on the water surface. Much of the plant body
2.4 Vegetation
Plants that grow in standing water or saturated
soils, such as moss, sedges, reeds, cattail and
horsetail, mangroves, cypress, rice and cranber-
ries, are called hydrophytes. Emergent vegeta-
tion ranges from heavily forested swamps to
