THE FLORIDA
EVERGLADES
The Effects of a Smaller Everglades
Less Water, Fewer Habitats
From: FICUS
Network - USF University of South Florida
Including the Everglades itself, the
system's original watershed was more than 8,100 square
miles. The remaining marsh now comprises about 2,300
square miles-of which almost three-fifths is impounded
in the Water Conservation Areas. Two-thirds of the
original Everglades now subsists on the rain that falls
on one-third of the original watershed. On an areal
basis, the current Everglades has about half the water
of the original. Everglades National Park makes up less
than one-fifth of the historic Everglades.
These profound changes have reduced
the availability of water and altered the Everglades
hydroperiod. Historically, water in the Everglades was
generally deeper for a longer period. In the remnant
Everglades, however, the slow, dry-season recession of a
much larger quantity of flowing water no longer takes
place. Instead, impounded pools that accumulated during
the wet season are rapidly drawn down.
Not only has most habitat vanished as
a result of these massive changes, but less water is
available for the remaining wildlife. Fourteen animal
species in the Everglades are now endangered. Many
others are threatened or, while not formally listed, are
declining.
Scientists use wading birds as a
measure of a wetland ecosystem's environmental health.
For every bird you now see in the Everglades, in the
early 1900s you would have seen at least ten. In other
words, at least 90 percent have vanished. A drought
between 1988 and 1991 exacerbated the damage to wading
birds and water animals by destroying their food base
and also increased the competition among human and
wildlife needs. By 1989 only 5,000 wading-bird nests and
15 major colonies were counted, a very low number. In
1990, the number of nests dropped to about 1,000.
While some birds such as hawks, green
herons, and anhingas are less sensitive to drought than
other species, much ecologically specialized wildlife
has died or been forced out of the region. In Everglades
National Park, the alligator population has dropped from
50,000 to 10,000 in the last two years. Everglade or
snail kites (of which fewer than 500 are left) and wood
storks are now seen in Central Florida because their
primary Everglades habitat is gone. Since the 1960s
nesting wood storks have dropped 80 percent in the
Everglades. Some scientists believe the bird is an
indicator species that heralds the decline of other
wading birds. (See Chapter 5 on Florida's Wetland and
Freshwater Ecosystems for more information on the wood
stork.)
THE SPREAD OF EXOTIC PLANTS
Still
more habitat destruction in the Everglades is being
caused by invasions of exotic plants. Brazilian pepper
is a major problem. Far worse is the melaleuca tree,
particularly east of the levees enclosing the Water
Conservation Areas. Introduced in an early attempt to
dry out the region, the trees consume so much water that
they can dry entire swamps. Unfortunately, by the time
the importance of preserving the system's natural water
flows and habitats was recognized, the melaleuca was
firmly established. It deprives native plants of habitat
because it grows so densely that no other vegetation can
compete, and wildlife can find little food. (See
Chapter 8 on Exotic Species in Florida for more
information on these and other exotic invasions.)
Everglades National Park is still
largely melaleuca-free because a buffer zone has been
established around the park, and young melaleucas are
removed as they appear. The park, however, is under
continual biological assault. At the moment, human
vigilance and expensive maintenance are all that is
keeping melaleuca from taking over the remnant
Everglades.
ALTERED WATER CHEMISTRY
The Everglades is a highly
oligotrophic system. That is, in their natural state,
its native communities are in balance with the very low
nutrient supplies provided by unpolluted rainfall. In
the natural Everglades, the rate of plant growth is
probably limited by phosphorus availability. Nutrients
such as nitrogen and phosphorus added by human
activities cause profound imbalances that result in eutrophication,
a surfeit of organic matter that accelerates a water
body's aging.
Where nutrient-rich agricultural
drainage water is discharged from the Everglades
Agricultural Area to the Everglades, the characteristic
periphyton mats of algae and microorganisms disappear,
and blue-green algae appear in their place. Dense
monocultures of cattails force out native plant
communities and take over marsh, wet prairie, and
slough, rapidly closing off open places where birds once
fed. In the Loxahatchee National Wildlife Refuge, which
occupies Water Conservation Area 1, 6,000 acres of
cattails expanded to 20,000 acres between 1978 and 1990,
an area so large it can be seen from space.
Because of the plants' rapid growth
rate, detritus forms an anaerobic ooze under the
cattails. Dissolved oxygen in the water is nearly zero.
Other than air-breathing gambusia, no fish can survive
in the water.
When the Everglades Agricultural Area
was drained, oxygen entered the soil, and microorganisms
then completed the process of consuming it. The soil
continues to oxidize, turning to a fine dust. As a
result, in 60 years the soil surface of the EAA has
dropped about five feet. The microbes also excrete
phosphorus-which then drains off and eventually enters
the Everglades. According to a recent estimate, as many
as 260 metric tons of phosphorus are released from the
EAA's farms each year.
Not much is known about how rapidly
the effects of phosphorus contamination are spreading in
the remnant Everglades. Almost 50 square miles have so
far been affected. Ordinarily, vegetation forms organic
soil that buries phosphorus. Where nutrient supplies are
so great that other factors limit plant growth and
phosphorus storage, though, the phosphorus is passed on,
and the process begins again in new territory. No one
knows how long the contamination will continue
spreading, but it could eventually affect the entire
system.
Owners of EAA lands have raised doubts
about the seriousness of the contamination. Elsewhere,
widespread agreement exists. The few individuals who
dispute the nature, extent, and significance of
Everglades degradation appear to be employed, directly
or indirectly, by agribusiness, the major pollution
source.
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For information on the
Everglades and the Florida panther, contact the
following agencies (see the listing of governmental
agencies in the back of the guide):
