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What is a Wetland?
Inland
Wetlands
Where
are all the Wetlands?
Wetlands
for the Future
People
and Wetlands
Classroom
Activities
Facts
Links
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 What's
the big deal about wet soil?
If
you can squeeze a fist full of soil into a ball, you've got soil
with no room for much oxygen. And that's bad news for most plants,
because oxygen is an essential part of their respiration. They
absorb the oxygen from the soil through their roots. These oxygen
starved (anaerobic) soils often smell like sulfur or rotten eggs
due to the bacteria that thrive under anaerobic conditions.
The dampness also causes chemical reactions in the elements of
the soil; for example, iron will oxidize and mottle the soil with
orange.
Scientists
recognize two major types of wetland soils: organic and
mineral.
- Organic
soil
has an obvious amount of decomposing plants; this kind of soil
is often black or dark brown.
- Mineral
soil
contains few decomposing plants; instead, it is comprised of
materials such as clay, sand, or silt. Wetland mineral soils
may be gray, greenish, or bluish gray; they also might be mottled.
Lucky for
scientists, color charts exist that key soil color with the amount
of water in the soil. The U.S. Natural Resource Conservation Service
also publishes a list of hydric soils.
Soil content
also determines the speed of draining. For example, water seeps
through sandy soils faster than clay soils. Sand particles are
large and irregularly shaped; they have more air pockets through
which water can move. Clay particles are smaller and they can
compress when wet; their smaller air pockets fill more quickly
and completely.
 Identifying
Wetlands....Wet Roots
Plants
that live in wet soil must adapt to the lack of oxygen. Reeds
and sedges, found in freshwater wetlands, have hollow structures
that enable the little oxygen they obtain to travel quickly through
the plant. Mangrove trees, found in saltwater (marine) wetlands,
have a tangle of roots that are exposed periodically to the atmosphere
as the tides ebb and flow.
Cypress trees,
which grow in freshwater swamps, have knobs or "knees" of root
material that emerge from the water; scientists speculate that
these knees absorb oxygen. The roots of floating plants, such
as duckweed or lilies, dangle into water and absorb oxygen. Wetlands
plants also must be efficient at absorbing other nutrients such
as nitrogen and phosphorus.
For example,
in wetlands, nitrogen is most often available as ammonia (NH4+),
thus many wetlands plants have become super-efficient absorbers
of ammonia.
Sometimes
Wetlands Are Hard to Identify
OK,
you're looking at a spot that someone insists is not a
wetland. By looking at the plants, this person might be right—no
wetlands plants grow here. But look again. This might be what
is sometimes called a "problem wetland," one that is hard to identify
due to its brief season or because it appears only during wet
years.
These types of wetlands include playas, potholes, vernal pools,
and ephemeral ponds.
So take a
look at the location: is it on high ground or a depression, slough,
or other low ground? Sample the soil and study its color and composition.
For example, some prairie potholes in the Dakotas may remain dry
during a prolonged drought. When the rains and snow return, though,
they reappear and continue to provide excellent habitat for ducks
and other creatures.
Soil alone
won't identify these potholes, though, because even dry grasslands
contain soils that resemble hydric soils. To confirm the presence
of a pothole during a drought, you need to look for a layer of
decomposed vegetation in the soil, lots of mottling, and the remains
of aquatic insects and other invertebrates near the surface.
Learn
about How Scientists Mark Wetlands
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