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The
Green Swamp
In the heart of Central Florida just
west of Highway 27 in Polk, Lake, Sumter, Hernando and Pasco Counties
lies a unique natural area known as the Green Swamp. This area exists
as a distinct recognizable unit primarily due to underlying geology.
Beneath the ground's surface a large raised plateau of limestone
approaches (and at times becomes) the surface. With the physical
increase in altitude of the  limestone
is lifted the groundwater (potentmetric) surface of the Floridan
Aquifer. This geologic feature is known variously as the Polk High,
Green Swamp High or Central Florida High. The raised nub of underlying
limestone and associated groundwater in conjunction with the relatively
large surface area of the swamp available to accept recharge water
(approximately 870 square miles) accounts for the fact that the
Green Swamp is the source for multipl rivers and streams and supports
large wetland systems.
The Green Swamp River Systems rank
possibly second only to the Florida Everglades in terms of hydrologic
and environmental significance to the state. Overlying an important
zone of groundwater recharge for peninsular Florida and the highest
elevation potentiometric surface of the Floridan Aquifer, the Green
Swamp ecosystem is important to the preservation of clean potable
groundwater supplies. As noted above, the Swamp also includes the
headwaters of various rivers including the Hillsborough, Withlacoochee,
Little Withlacoochee, Oklawaha and Peace.
In the upper reaches of the Green
Swamp River Systems, the floodplain forests and swamps promote natural
detention of flood waters and provide habitat for many wildlife
species. In addition to the rivers and their associated floodplains,
habitats within the Green Swamp River Systems include a mosaic of
cypress and hardwood forests, pine flatwood, prairies and sandhills.
The wilderness aspects of the Swamp and resources of the groundwater
and river systems are adjacent and accessible to the rapidly growing
urban areas of Central Florida. Overall, the area has been noted
for exceptional resource value related to: recharge, aquifer pressurization,
aquifer water quality, flood water attenuation, wildlife/habitat,
and open/green space.
I. Surface
Water Quality
Water quality protection in the Green
Swamp is an important issue due to its overall position in the natural
geologic landscape in Florida, the resultant high potentiometric
surface of the Floridan Aquifer, combined with the lack of a strong
confining unit between surface waters and groundwater over much
of the Swamp. Presently, water quality is excellent in the major
river components of the Withlacoochee, Little Withlacoochee and
the Big Creek and Little Creek portions of the Palatlakaha. These
separate riverine headwaters each derive from the Green Swamp high
and exhibit water quality typical of a natural filtering wetland
system (i.e., generally highly colored with natural tannins and
detritus breakdown products, with an acidic pH).
II. Groundwater
Quantity & Quality
Due to the relative direct interconnection
of surface and groundwater over much of the Green Swamp, protection
of surface waters is protection of groundwater (i.e., they are one
and the same). From a resource perspective (call it ecosystem perspective),
primary issues for groundwater protection in the Green Swamp revolve
around:
* limitation of water consumption/water use to maintain "the
swamp"; and,
* protection of the existing relatively
good water quality that acts to recharge the Floridan Aquifer which
is so important to the greater Central Florida area.
Quantity
and Pressurization
Principle features of the Green Swamp
are related to its geologic position and make-up in the Central
Florida landscape. The Green Swamp serves important functions of
recharge and pressurization of the Floridan Aquifer because it:
* is the highest elevation of
Floridan Aquifer limestone in peninsula Florida (i.e., like
a water tank sits high and uses gravity to ensure pressurization);
* is a large volume of porous
limestone with relatively low groundwater transmisivity and,
as noted above, is positioned at a higher elevation than surrounding
Floridan limestone (i.e., the area has a lot of water storage
capacity); and,
* represents approximately 870
square miles of surface area to provide Floridan aquifer recharge
and pressurization (recharge varies from very high to low. On
average, the Green Swamp can be considered an area of moderate
recharge. Nevertheless, the water budget input to the Green
Swamp/Floridan Aquifer
potentiometric high is almost exclusively derived via rainfall
recharge within the area).
Groundwater
Quality
The Green Swamp area acts as natural
water quality filtration system to deliver clean water to the Floridan
Aquifer because:
* over much of its area, from
the Lake Wales Ridge westward towards the Polk and Lake County
lines there is a wedge of undifferentiated clayey sand over
the Floridan limestone (thickest on the east and thinning to
the west); and,
* over much of the area wetlands exist which provide the normal
wetland functions of water attenuation, detention, pollutant
trapping and filtration.
"Groundwater quality data is
available for the surficial and Upper Floridan aquifers. Very little
groundwater quality data is available for the intermediate aquifer
(where present) in the hydrologic Green Swamp area. In these areas
the intermediate aquifer is very thin and discontinuous making groundwater
quality data difficult to obtain. Few monitoring wells are constructed
such that the samples may be obtained exclusively from the intermediate
aquifer.
Groundwater quality in the surficial
aquifer is generally good. Concentrations of dissolved ions are
usually very low, well below Drinking Water Standards. However,
in some locations nitrate concentrations can be higher in the surficial
aquifer than in either the intermediate or Upper Floridan aquifers
(SWFWMD), 1991). The higher concentrations of nitrates may be attributed
to the following: septic tanks, livestock, sludge disposal and the
use of nitrate fertilizers for agriculture.
Groundwater quality in the Upper
Floridan aquifer is also good. However, concentrations of calcium,
bicarbonate, and hardness are higher in the hydrologic Green Swamp
area than in surrounding areas (SWFWMD, 1991). The Upper Floridan
aquifer is either unconfined or semi-confined in the hydrologic
Green Swamp area. Therefore, the hydrologic Green Swamp is considered
to be a recharge area for the Upper Floridan aquifer. Although the
hydrologic Green Swamp is a recharge area, the hydraulic
conductivity of the Upper Floridan aquifer in this area is relatively
low. The low hydraulic conductivity is one of the contributing factors
for the existence of the Green Swamp Potentiometric High. Therefore,
residence time of the groundwater in the vicinity of the hydrologic
Green Swamp is relatively long. The long residence time enables
the groundwater
to stay in contact with the mineralized matrix of the Upper Floridan
aquifer, allowing the concentration of dissolved ions to increase."
[From the Green Swamp Task Force Report, July 1992]
III. Sources
of Water Quality Degradation
Wastewater
and Wastewater Residual Disposal
A majority of the Green Swamp is
an area of wetlands and uplands with a high seasonal water table
(i.e., generally saturated soil conditions). Less saturated soils
representing old dune lines are found in ridges (generally oriented
north to south) especially on the eastern side of the Swamp. Soils
in these ridges are sandy. In fact, mining of these sandy ridges
within the Swamp to market to the central Florida construction industry
is an active business along with citrus production. Due to the prevalence
of wetlands, high groundwater levels, frequency of seasonal flooding
or porous sandy conditions in much of the Green Swamp, disposal
of wastewater effluent or septage presents problems of groundwater
or surface water contamination. Percolation ponds, spray fields,
septic systems or land application of wastewater treatment plant
residuals each experience similar difficulties relating to a limited
treatment ability presented by the prevailing soil conditions.
As noted, much of the Green Swamp
has a high seasonal water table or poor soils for assimilating (i.e.,
providing treatment) the wastewater effluent. Nevertheless, the
natural conditions of the area are well suited for sub-surface lateral
and surface conveyance of inadequately treated wastewater into creeks,
wetlands, lakes and the aquifer. Unfortunately, without advanced
treatment most treated wastewater effluent is nutrient laden. Thus,
it is very hard to locate a site that will perform as for a land
application method (perc/evaporation ponds, spray fields, drainfields).
Typically for this area, a system may work fine during the winter
dry months ... then comes the summer rainy season and effluent disposal
and treatment problems appear.
For septic systems the problem of
siting is equally difficult. If fact, within the Green Swamp, off
the sandy ridges, septic systems generally rely on a raised mound
of imported soils for drainfield construction. Due to the water
table being near or at the ground surface the problem of "capillary
fringe action" up into raised drainfield mounds also is common
(i.e., wicking action of groundwater up into the mounded systems
further restricting the ability of the system to function). In addition,
erosion of the raised drainfield mounds due to inadequate maintenance
by home owners is an observed problem.
Sludge
(Domestic Wastewater Residuals/Biosolids)
The application of domestic wastewater
residuals/bio-solids (sludge) from wastewater treatment facilities
to the lands of the Green Swamp has been practiced. The residuals
come from a variety of wastewater treatment plants in Florida. The
impact to the groundwater and surface waters of the Green Swamp from
this practice has not been studied. As with the siting of treatment
plant effluent disposal discussed above, the high groundwater levels,
poor soils and the mosaic of wetlands has raised concerns in regards
to the the application of these residuals.
Presently, there is no requirement
for a ground water monitoring plan (or surface water where applicable)
for septage disposal sites in the Green Swamp. Thus, it is difficult
to determine when sludge disposal is resulting in deterioration
of water quality or changes in the biota of adjacent natural systems.
Sludge is monitored at the treatment facilities for various contaminants
so that it can be graded for use prior to decisions on acceptable
disposal areas.
Reuse Water
Treated wastewater effluent can be
reclaimed for reuse. Chapter 62-610 and 62-6,F.A.C., provide the
design requirements to ensure water destined for reuse on these
sites is properly treated to minimize adverse effects. Nevertheless,
DEP has seen some problems with the reuse of effluent on some of
the areas such as golf courses. The problem is with a high level
of nitrates (>10 mg/l) showing up in groundwater monitoring wells.
Interestingly, the effluents from the treatment facilities are low
in nitrates going to the courses. It is suspected that the problem
is with the management of the golf courses and the amount of fertilizer
being applied on the courses. The reuse water seems to be a transportation
method for moving the nitrates and possibly pesticides into the
shallow aquifer. The Department is investigating this problem at
the present.
MINING
Within the Green Swamp, sand mining
is a principle activity though some peat and limestone mining may
occur. The mining of sand in this area often occurs along the old
dune ridges that extend in a north to south direction between large
strands of hardwood, cypress and and open freshwater swamps. The
deposits of sand are mined to a depth of 20 to 50 feet, and a substantial
void is eventually created which cannot be restored to reflect pre-mining
conditions. The deposits do not necessarily follow the surface sand
ridges and at times occur under large strands of hardwood, cypress
and and open freshwater swamps. In addition, the sand ridges are
not always continuous and some limited movement of large mining
dredges occurs through intervening wetlands and through smaller
isolated wetlands which lie in the planned mining path. Whether
through the wetlands or the sandy ridge areas, an eventual outcome
of sand mining is a "land of lakes" situation. Thus, in
the Green Swamp ecosystem, where open lake systems are not common,
sand mining results in lake creation. The relative impact of these
operations (estimated at 100 acres per year) to the total Green
Swamp, weighed against the economic value of the mining to the area
becomes one of extent and comparative value of the existing uplands
and wetlands to post-mining lakes.
IV. Flora
and Fauna
Contrary to the implications of its
name, the Green Swamp is made up of a diverse mixture of upland
and wetland habitats. Within the study area of the Green Swamp Task
Force 1992 report, 26.72% is upland (7 vegetative associations),
35.09% is wetlands (5 vegetative associations), 2.70% is open water,
and 35.48% is disturbed lands (mostly agricultural) (figures are
based on an analysis of 1987 LANDSAT data). This variety of vegetative
associations supports an estimated 335 species of wildlife.
Soils data indicate that the Green
Swamp was historically composed of (1) low hammocks of live oak,
laurel oak, water oak, runner oak, cabbage palm, and slash and longleaf
pines in the better drained areas; (2) seasonally wet flatwoods
supporting slash pine, some longleaf pine, cabbage palm, gallberry,
fetterbush, wax myrtle, saw palmetto, and a variety of grasses and
sedges in more poorly drained areas; and (3) wooded swamps composed
of cypress, blackgum, bay, red maple, water oak, ironwood, pond
pine, and maidencane and pickerelweed marshes in sloughs, river
floodplains, and other areas of seasonally ponded water.
From the 1987 LANDSAT analysis, it
appears that three major blocks of vegetation occur within today's
Green Swamp. Two large, distinctly different, blocks of relatively
undisturbed vegetation remain. One of these lies in immediately
west of the Lake Wales Ridge in northeastern Polk County and southern
Lake County, and is characterized by a conspicuous pattern of north-south
relic dunes, much of which have been converted to agriculture, and
swales that are dominated by cypress. Almost all of this area is
in private ownership. The second lies in eastern Pasco County, southern
Hernando and Sumter counties, southwestern Lake County, and the
northwestern tip of Polk County, and does not show a banded arrangement
of uplands and wetlands. Most of this land is in public ownership.
The third
category of vegetation type is disturbed lands, most of which are
privately owned and have been converted to agriculture or low-density
residential uses. Although this area has been disturbed, portions
of it still have the potential for utilization by a variety of wildlife
species, including listed species (e.g., the threatened Florida
sandhill crane).
V. Ecosystem
Protection
Ecosystem protection for the Green
Swamp focuses on:
* the importance of its size
and the interdependence of its composite natural biological
systems to the underlying Green Swamp geology and related potentiometric
high;
* the existing situation of limited
areal fragmentation; and,
* the often critical role of
hydrology, and water chemistry to long-term continuance of existing
plant and animal communities.
The Green Swamp and the diversity
of plant communities and wildlife it holds exemplifies an area that
should be viewed and managed from an ecosystem approach. An ecosystem
is any system in which there is an interdependence and interaction
between living organisms and their immediate physical, chemical
and biological environments. The Green Swamp exists as an identifiable
ecological unit specifically because of its unique physical position
relative to the underlying Floridan aquifer limestone and the interdependence
and interaction between resultant surface water, land conditions
and biological
communities.
Problems
Fragmentation and reduction in size
of an ecosystem results in a reduction of its species carrying capacity
(number of species or biodiversity). Such fragmentation can occur
for a variety of reasons but is often directly related to land development
activities (removal of natural vegetation, alterations in the land's
hydrology - usually a drying out from resulting from surface draining
and/or groundwater drawdowns, road development or, from the impacts
of pollutants).
To approach the Green Swamp from
an ecosystem perspective, the natural functions and the interconnections
of upland and wetland habitats for wildlife species must be better
understood, and protective measures developed. Because of the potential
for significant ecological impacts from inappropiate land uses,
special attention should be given encouraging land use decisions
which are compatible with maintaining ecological functions. Planning
efforts have recognized the value of maintaining a contiguous network
of high-quality habitats and the need to address some level of restoration
where habitats have been fragmented.
Consumptive
Use of Water and The Green Swamp
A lowering of the groundwater levels
in this area would result in substantial changes in the existing
natural communities. Due to the fact that the Floridan Aquifer and
the interconnected surficial aquifers are at, or near, the land's
surface, lowering of groundwater levels would negatively impact
Green Swamp ecosystems (a drying out or reduction in natural hydroperiods
would occur). The tremendous growth of the Tampa, Lakeland and Orlando
urban areas and the corresponding reliance on use of
groundwater to meet water demands elevates the need for vigilance
to ensure plentiful water for the continued maintenance of the Green
Swamp Ecosystem.
Land Acquisition
and Management Efforts
The DEP and the WMD's include, as
a part of their land acquisition and management efforts within the
Green Swamp, flora and fauna corridor development to link WMD Save
Our River Lands, Conservation and Recreation Lands (CARL), Withlacoochee
State Forest Lands, Lake Lousia State Park Lands and Area of Critical
State Concern (ACSC) Green Swamp Core Area lands. Efforts to identify
and maintain the natural biodiversity in the Central Florida area
have emphasized that the Green Swamp serves as an
important core area through which other relatively undisturbed areas
connect, such as, the Hillsborough River and Withlacoochee River
Corridors. These two corridors extend out beyond the area of the
Green Swamp (to the southwest and the northwest respectively). Such
natural land and water linkages provide the means by which localized
animal and plant populations can maintain access to other proximate
populations. Intact corridor/linkages help to sustain the genetic
health of species promoting longterm survival.
The acquisition and management of
Green Swamp lands by the State and the Southwest Florida and St.
Johns River Water Management Districts (SWFWMD and SJRWMD, respectively)
are directed toward sensitive areas such as large wetlands, riverine
bottomland hardwoods and identified valuable flora and fauna habitats.
Recent progress toward acquisitions by the State includes Cabinet
approval to proceed with buying of 1353 acres of land adjacent to
Highway U.S. 27 in Lake County next to Lake Lousia State Park from
Charles E. Bradshaw, Jr.. An additional 2000 acres is under negotiation
and is proceeding toward acquisition. Appraisals on an additional
10,300 acres in the eastern Phase I portion (Lake County) of the
project area has been undertaken.
"Proposed land acquisition projects
total approximately 141,500 acres, comprised of the Green Swamp
Project (126,000 acres CARL program with SJRWMD participating) and
SWFWMD's proposed additions (15,500 acres) to present holdings.
Together with other state lands (e.g., the Richloam Tract and the
Withlacoochee State Forest) there is an estimated more or less 150,000
acres in public protective ownership within the Green Swamp area.
If the proposed 141,500 acres are acquired, the total acerage of
protected lands within the Green Swamp would reach 291,000 acres,
representing nearly 52% of the entire Green Swamp region."
[ from Report On The Green Swamp Area Of Critical State Concern,
SWFWMD and SJRWMD, December 31, 1993]
Further, the Green Swamp is the northern "terminal hub"/habitat
core area for the phosphate district Integrated Habitat Network
(greenway) and a part of the statewide greenways system. Additionally,
the James Van Fleet Rail-to-Trail bisects the swamp proper. This
existing trail follows an old rail line up through Polk and Lake
Counties and provides access to some excellent wilderness in relative
close proximity to the Orlando urban area.
Land Use
Planning and the Green Swamp
In the 1970s the Florida Legislature
recognized the sensitive nature of the Green Swamp and designated
a large portion of it as an Area of Critical State Concern under
Chapter 380, F.S.. Under this designation the local governments
of Polk and Lake Counties have been working with the state's land
planning agency, the Department of Community Affairs (DCA) to address
land development
activities. The statute lays out "Principles for Guiding Development"
which local land development plans and regulations must be consistent
with.
In addition, identification of natural
land development limitations and suitabilities was required by the
1985 Local Comprehensive Planning Act (Chapter 163, F.S.). Lake,
Polk, Citrus, Sumter and Hernando Counties each have developed future
land use designations for the Green Swamp within their jurisdiction
and corresponding goals, objectives and policies to direct land
development commensurate with the natural suitabilities. In general,
these local land use plans exhibit the low density and intensity
of land use historic to the area; a level compatible with the continued
protection of the sensitive
natural resources.
Recently, the SWFWMD designated the
whole of the swamp as the Green Swamp Wilderness Preserve to emphasize
a significant statewide natural resource that needs and deserves
long-term protection. In addition, this Department and a number
of others such as the Department of Health & Rehabilitative
Services (HRS) responded to a legislative mandate to review agency
rules and actions in regards to the Green Swamp and to report to
the State Administrative Commission on what actions we might need
to take to better reflect the Principles for Guiding Development
as provided for the Swamp under Chapter 380, F.S.. These reports
were finalized in January 1994 and submitted to the Commission with
recommendations
Note:
This article is an adaptation of a report entiled, "Green
Swamp Area of Critical State Concern Report To The Administreative
Commission", by the FDEP, December 1993. Also, we want to
thank Margit Crowell of the SWFWMD for the maps of the Green Swamp
and Hydrologic Features. The article, by Dan Pennington, appeared
in the FDEP publication the Environmental Exchange Point, May
1994.
* The online Recreation Guide
site is provided by the Southwest Florida Water Management District.
The purpose of this site is to provide the public with information
about the lands which are available for recreational activities
including those in the Green Swamp: http://www.swfwmd.state.fl.us/recguide/recguide.htm
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