Introduction
Lake Apopka is located in central Florida about 11 kilometers northwest
of Orlando. It covers an area of approximately 125 square kilometers,
and is located in both Orange County and Lake County. Before the
lake’s marshes were eradicated from the lake it spanned approximately 52,000
acres—after drainage of the marshes it was reduced to 31,000 acres.
It is a shallow lake with average depths between 5 and 6 feet, and at present
can be classified as a hypereutrophic system (Thomas, 1999).
Disturbance to this system ultimately began in 1880 with the construction
of the Apopka-Beauclair Canal. Upon its construction, water leaving
Lake Apopka was no longer naturally filtered by the swamp system prior
to being introduced into Lake Beauclair. In 1922 a sewage treatment plant
began pumping effluent from the town of Winter Garden directly into the
lake, and it wasn’t until 1980 that this practice was halted. Coincidentally,
a citrus farm began to discharge its wastes directly into Lake Apopka.
A drastic change to the lake system occurred in 1941 with the formation
of the Zellwood Drainage and Water Control District that was responsible
for the construction of a levee built between the lake and the marshes
located on the north shore. This sectioned off marshes, which were
then drained, exposing the nutrient rich soils for agricultural use.
“Muck farms” began establishing themselves around the lake—primarily at
the northern shore—and they too discharged wastes directly into the lake.
External nutrient loading—particularly nitrogen (N) and phosphorus
(P)—into the system from the surrounding farms eventually led to a massive
algal bloom in 1947, which began a transformation of the lake from a macrophyte
dominant to a phytoplankton dominant system (Battoe, 1999). An experiment
conducted by Dillon and Rigler (1974) suggests a positive correlation between
phosphorus concentrations and algal biomass; thus as concentrations of
phosphorus increased in Lake Apopka algal biomass also increased.
Many of the fish species native to Lake Apopka began to be replaced
by gizzard shad (Dorosoma cepedianum), a species that is more tolerant
to pollution (Williams, 1999). Gizzard shad are detritivorous fish,
feeding primarily on benthic organic matter—the result of which releases
nutrients to the water column that otherwise would remain stored in bottom
sediment. Liberated phosphorus can then stimulate the growth of phytoplankton
populations, and, consequently, influence water quality giving the lake
its now characteristic pea-soup color. Furthermore, releases of nutrients
to the system have been found to have a negative affect on species diversity
(Schaus et al, 1997).
The farms surrounding Lake Apopka are also responsible for the introduction
of many types of pesticides and chemicals into the Lake Apopka system.
Compounds like DDT, DDE, dicofol (mixture of the pesticides DDT and DDE),
PCB’s, dioxin and diethlstibestrol (DES) contribute to the disruption of
the endocrine systems of organisms (Gillis, 1995). Abnormal development
of the reproductive system has been observed as a result of the introduction
of various compounds (Lebanc, 1998). There have been instances where
birds have been born with such severely malformed beaks that they were
incapable of eating (Williams, 1999). Alligators have been examined
and found to have shrunken penises, and in some instances have possessed
both male and female sexual organs.
In 1985 the Lake Apopka Restoration Act was passed by Congress, which
provided a source of funding for the restoration of Lake Apopka.
Then in 1996 and 1997 Congress passed an act giving the St. Johns Water
Management District (SJWMD) the funds and the freedom of action to purchase
farm lands located on the north shore of Lake Apopka.
The SJWMD was also given the task of developing a restoration plan
for Lake Apopka, and has outlined their restoration intentions with several
projects that may help to improve the lake. A significant reduction
in phosphorus loading, in order to destabilize algal dominance and encourage
a shift towards a macrophyte-dominated community, is essential to the improvement
of the lake’s water quality. The surrounding muck farms are the major
contributors of phosphorus to the lake—they are responsible for more than
90 percent of the incoming nutrients—therefore the SJWMD has deemed it
of the utmost importance that these sources of nutrient inputs be abated
or, if possible, altogether stopped (3). Lake Apopka contains high
concentrations of nutrients (particularly P) that must be removed from
the system. Methods of removal of P are by filtering water through
a specially designed wetland called the Marsh Flow-Way, and by the laborious
removal of gizzard shad. Also planned for the lake is the recreation
of the littoral zone. Jay Polinkas (1999) of the SJWMD states:
“The overall goals of this effort are to, restore the water in Lake
Apopka to meet Class III water quality standards, to restore the functional
capabilities of the lake's natural systems, to re-establish previous recreational
and aesthetic values, and to implement a comprehensive basin management
plan.”
Community Description
Lake Apopka is a hypereutrophic lake with a bottom that is entirely
covered by organic sediments. The organic sediments supply a basis
for the high turbidity of the lake caused by suspended phytoplankton and
surficial sediments (4). The remaining “highland marshes” of Lake
Apopka, and other marshes located in the same region, are unstable due
to the capacity for extreme variations in subsurface drainageways (Myers
et al, 1990). Deevey (1988) studied hydrographs of lakes throughout
Central Florida and found that water levels seem to change in unison with
each other. This may be attributed to the fact that much of the lakes
in Northern and Central Florida respond to variations in the Floridan Aquifer.
Lake Apopka overlies both the Fort Preston Formation, and lower marine
and estuarine terrace deposits (Vernon et al, 1964). Soils of lower
marine and estuarine terrace deposits are alluvium, marl and peat, and
sand for the Fort Preston Formation. See Picture 1 for the location
of Lake Apopka.
Picture 1
Disruptive Agent
A major disrupter to the Lake Apopka system has been the persistent
loading of phosphorus as a result of discharges from muck farms located
along the lake. Phosphorus loading supports populations of gizzard
shad, which do particularly well in high nutrient waters such as Lake Apopka.
This detritivorous fish is a major contributor for the transport of nutrients
from the benthic zone to the water column. Benthic foraging by the
gizzard shad dislodges nutrients that would otherwise be held in sediment.
Some of the nutrients are incorporated into the fish’s body tissue and
some is made available to phytoplankton, which has helped change the lake
into a hypereutrophic system (Battoe, 1999). Phosphorus inputs need
to be greatly reduced, and mass removal of the gizzard shad must occur
to help shift the lake to a more stable environment.
Another disruptive agent to the Lake Apopka system has been the release
of chemical pollutants from agricultural farms. Discharged chemicals
include the organochlorine pesticides DDT, its derivative DDE, dieldrin
and aldrin, polychlorinated biphenyls (PCBs), dioxin, dicofol, furans and
phthalates (The Lancet, 1995). Studies have repeatedly suggested
that many of these pesticide compounds alter the normal functioning of
the endocrine system in organisms. This important system controls
the release of hormones into the body by various organs and glands such
as the pancreas, ovaries and testis, and thyroid, pituitary and adrenal
glands—which all act to influence the rate of functioning of almost all
the body’s cells. High pesticide levels in Lake Apopka were found
in populations of large mouth bass, and tests suggest that increased levels
may have a feminizing effect on males. Increased concentrations of estrogen
were also found in female populations (Gross, 1995). Similar results
were received in a study performed on alligators in Lake Apopka—generally,
estrogen concentrations increased, while testosterone concentrations decreased
(Gross, 1995). Pesticide introduction into the system must be halted
or vastly reduced because it seems likely that prolonged discharges will
only continue to threaten populations of organisms tied into the Lake Apopka
ecosystem.
Restoration Initiatives
With the creation of the Lake Apopka Restoration Council by Florida
Legislature in 1985 the St. Johns Water Management District was given the
assignment of creating a plan for the restoration of Lake Apopka.
In 1985 the Surface Water Improvement and Management Act (SWIM) was passed
which instructed SJWMD to implement a plan for Lake Apopka’s restoration.
Other organizations have worked, and continue to work, in conjunction with
SJWMD, producing studies on various aspects of the lake, and increasing
public concern and involvement in the effort. The SJWMD is conducting
this restoration project on the lake and its surrounding littoral zone,
as well as on the 14,000 acres of drained farmland located on the North
Shore (see Picture 1 for drained farmland location). The necessity
to restore Lake Apopka lies in the benefits gained from attaining better
water quality. Increased water quality will improve the aesthetics
of the lake, increase species diversity of both vegetation and plants,
and generally create a healthier environment.
There are several stages to the restoration of Lake Apopka, a few of
which have already been implemented and completed. The restoration
of Lake Apopka by the reduction of pollution was made a primary goal for
the SJWMD by the 1985 Lake Apopka Restoration Act and the 1987 Surface
Water Improvement and Management Act. An Allowable Waste Load Rule
for Lake Apopka was attempted by the SJWMD in 1994, but a ruling by the
State of Florida deemed SJWMD did not have the authority to implement such
a regulation. The Lake Apopka Restoration Act of 1996 was later passed
effectively giving SJWMD the authority to put into practice pollution regulations,
as well as allocating to its disposal $20 million towards the purchasing
of lakeside farms. Another Florida Legislative program in 1997 also
provided additional funding to be used for the buyout of these farms (1).
In 1998 approximately 95% of the agricultural farms had been bought, and
by spring of the same year construction of the Marsh Flow-Way system was
underway (2).
The buyout project is the portion of the restoration plan that will
reduce inputs of nutrients to Lake Apopka, but the actual removal of phosphorous
from the lake will also be necessary. The Marsh Flow-Way will remove
phosphorous from the water by filtering it through 13 marsh “cells”, and
redistributing the cleaned water to the lake. The total volume of
the lake’s water will be cycled through this system two times a year.
Phosphorous and algae will be buried in the marsh sediment by the natural
process of vegetation growth and decay (3).
The mass removal of gizzard shad by fishermen, paid for by the St.
Johns Water Management District (SJWMD), is another method that has been
utilized for the removal of phosphorous from Lake Apopka. This system
of phosphorous removal has proved quite successful despite proving to be
very expensive and labor intensive (1). Therefore, due to these two
reasons, this method will be stopped once population numbers have decreased—making
them harder to catch—or when populations of game fish have increased sufficiently.
The importance of littoral zone recreation has been recognized; therefore
this aspect of the restoration project involves the planting of native
species of vegetation in selected sections of the shore. The SJWMD
accomplishes this task by attaching the desired plant to a sand-filled
sock, which sinks the invention at the preferred location and allows the
plant to take root in the sediment (1).
Discussion
Through the purchasing of “muck” farms the SJWMD has decreased
the discharge of phosphorous into Lake Apopka by as much as 90 percent
(3). A press release by SJWMD on October 13th, 1999 stated that due
to the restoration effort, involving, in particular, the reduction and
removal of phosphorous from Lake Apopka, there appears to have been a 31
percent reduction in phosphorous concentrations since 1995. Also
announced was that lake water clarity has also increased by 29 percent
since 1995 (8). Additionally, gizzard shad harvesting has been estimated
at about 4 million pounds—resulting in the extrication from the Lake Apopka
system of about 28,000 pounds of phosphorous contained within the fish—since
1993 (1). The Marsh Flow-Way system removes 30 metric tons of phosphorous
per year, and clears the lake’s water by removing a great deal of suspended
particles. SJWMD biologists have observed the natural reestablishment
of vegetation that has been absent from the lake for many years (1).
The St. Johns Water Management District accumulated about $106 million
for the specific use of purchasing farmland. In addition to this
amount, $4 million was necessary for the construction of the Marsh Flow-Way,
as was approximately the same amount for the harvesting of gizzard shad.
The total cost for the restoration of Lake Apopka has been estimated at
about $120 million dollars. Some of this money has been, and continues
to be used for the clean up of soil severely contaminated by pesticides.
This area of the lake had been flooded, shortly after which birds began
to die. To prevent further bird kills the area was drained, and tests
are being conducted to determine the best way to manage the site.
Such a restoration plan as this one carried out on Lake Apopka can
be conducted on other systems with similar problems. A decrease in
phosphorous concentration is the result of a reduction in phosphorous loading
(Battoe, 1999). Therefore, all that would remain is, basically, the
removal of the excess phosphorous from the system.
Any system with exorbitant amounts of phosphorous inputs can be made
to have lower concentrations of phosphorous by reducing the inputs of phosphorous
into the system (Battoe, 1999). Reducing phosphorous levels can destabilize
populations of algae that rely the phosphorous; thus the system can be
made to shift towards macrophytic dominance. As Dillon and Rigler
(1974) suggest: reduce phosphorous concentrations and algal biomass will
also decrease. The removal of gizzard shad would benefit the system
by minimizing the release of phosphorous from the benthic zone of the lake
permitting its metabolism by algae and phytoplankton (Schaus, 1997).
Some researchers have concluded that contaminants can be held
accountable for the adverse affects they have on wildlife as well as on
human populations. There have been decreases in sperm count, and
increases in incidences of breast and prostate cancer, including other
affects on the endocrine system of humans (The Lancet, 1995).
Conclusion
The problems found in Lake Apopka are not limited to this system alone.
Poor water quality has become a problem for those lakes and ponds that
receive water from the lake via rivers, streams and channels. This
alerts one to the fact that any progress toward the restoration of Lake
Apopka will also improve surrounding ecosystems that are, no doubt, also
of significant importance—since 15 percent of the water leaving the Marsh
Flow-Way will travel to downstream systems (2).
The restoration of Lake Apopka appears to have been quite successful
if one were to solely regard its improvement as a response to phosphorous
reduction and removal, and the reintroduction of a littoral zone.
Yet, this is not the end of the Lake Apopka restoration, for the riddance
of persistent chemical compounds is the next task that must be initiated.
The threat to wildlife and humans is too real, an intense plan to reduce
or remove them is essential.
References
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