Aquatic Ecosystems 145© Dan Leeth/Alamy Limitedrivers flood their banks, wetlands
are capable of holding or even ab-
sorbing the excess water, thereby
helping to control flooding. The
floodwater then drains slowly back
into the rivers, providing a steady
flow of water throughout the year.
Wetlands also serve as groundwa-
ter recharging areas. One of their
most important roles is to trap and
hold pollutants in the flooded soil,
thereby cleansing and purifying the water.
Although wetlands are afforded some legal protec-
tion, they are still threatened by pollution, development,
agriculture, and dam construction. (See Chapter 10 for
more on threats to freshwater ecosystems.)Freshwater wetlands include
marshes, dominated by grass-
like plants, and swamps, domi-
nated by woody trees or shrubs
(Figure 6.14). Wetland soils are
waterlogged for variable periods
and are therefore anaerobic
(without oxygen). They are rich
in accumulated organic materials, partly because anaero-
bic conditions discourage decomposition.
With their productive plant communities, wetlands
provide excellent wildlife habitat for migratory water-
fowl and other bird species, as well as for beaver, otters,
muskrats, and game fish. In addition to providing unique
wildlife habitat, wetlands serve other important environ-
mental functions, known as ecosystem services. When
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Freshwater swamps are inland areas covered by water and dominated by trees, such as baldcypress.
Photographed in Lake Martin, at the edge of the Atchafalaya Basin, Louisiana.
freshwater
wetlands Lands that
shallow fresh water
covers for at least part
of the year; wetlands
have a characteristic
soil and water- tolerant
vegetation.ecosystem
services Important
environmental
benefits, such as
clean air to breathe,
clean water to
drink, and fertile
soil in which to
grow crops, that the
natural environment
provides.