Botkin Environmental Science Earth as Living Planet 8th txtbk

388 CHAPTER 18 Water Supply, Use, and Management
Natural Service Functions of Wetlands
Wetland ecosystems may serve a variety of natural service
functions for other ecosystems and for people, including
the following:
Freshwater wetlands are a natural sponge for water. During
high river flow, they store water, reducing downstream
flooding. Following a flood, they slowly release
the stored water, nourishing low flows.
Many freshwater wetlands are important as areas of
groundwater recharge (water seeps into the ground
from a prairie pothole, for instance) or discharge (water
seeps out of the ground in a marsh fed by springs).
Wetlands are one of the primary nursery grounds for fish,
shellfish, aquatic birds, and other animals. It has been
estimated that as many as 45% of endangered animals
and 26% of endangered plants either live in wetlands or
depend on them for their continued existence. 17
Wetlands are natural filters that help purify water; plants
in wetlands trap sediment and toxins.
Wetlands are often highly productive and are places
where many nutrients and chemicals are naturally
cycled.
Coastal wetlands buffer inland areas from storms and
high waves.
Wetlands are an important storage site for organic carbon;
carbon is stored in living plants, animals, and rich
organic soils.
Wetlands are aesthetically pleasing to people.
Freshwater wetlands are threatened in many areas.
An estimated 1% of the nation’s total wetlands are lost
every two years, and freshwater wetlands account for
95% of this loss. Wetlands such as prairie potholes in
the midwestern United States and vernal pools in Southern
California are particularly vulnerable because their
hydrology is poorly understood and establishing their
wetland status is more difficult. 18 Over the past 200
years, over 50% of the wetlands in the United States have
disappeared because they have been diked or drained for
agriculture or filled for urban or industrial development.
Perhaps as much as 90% of the freshwater wetlands have
disappeared.
Although most coastal marshes are now protected in
the United States, the extensive salt marshes at many of the
nation’s major estuaries, where rivers entering the ocean
widen and are influenced by tides, have been modified
or lost. These include deltas and estuaries of major rivers,
(a)
FIGURE 18.16 Several types of wetlands: (a) aerial view of part
of the Florida Everglades at a coastal site; (b) cypress swamp water
surface covered with a floating mat of duckweed, northeast Texas;
and (c) aerial view of farmlands encroaching on prairie potholes,
North Dakota.
(b)
(c)