The Wakulla Springs Woodville Karst Plain Symposium

THE WAKULLA SPRINGS
WOODVILLE KARST PLAIN SYMPOSIUM
OCTOBER 9, 1998

TRANSACTIONS

COMPILED AND EDITED BY
WALTER SCHMIDT, JACQUELINE M. LLOYD
AND CINDY COLLIER

FLORIDA GEOLOGICAL SURVEY
SPECIAL PUBLICATION NO. 46

STATE OF FLORIDA
DEPARTMENT OF ENVIRONMENTAL PROTECTION
David B. Struhs, Secretary

DIVISION OF RESOURCE ASSESSMENT AND MANAGEMENT
Edwin J. Conklin, Director

FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist and Chief

SPECIAL PUBLICATION NO. 46

THE WAKULLA SPRINGS WOODVILLE KARST
PLAIN SYMPOSIUM TRANSACTIONS
OCTOBER 9, 1998

Compiled by Walter Schmidt, Jacqueline M. Lloyd
and Cindy Collier

Published by the

FLORIDA GEOLOGICAL SURVEY
Tallahassee, Florida
2000

LETTER OF TRANSMITTAL

FLORIDA GEOLOGICAL SURVEY

April 2000

Governor Jeb Bush
Florida Department of Environmental Protection
Tallahassee, FL 32301

Dear Governor Bush:

The Florida Geological Survey (FGS), Division of Resource Assessment and
Management, Department of Environmental Protection, is publishing as our Special Publication
No. 46, the Transactions from the Wakulla Springs Woodville Karst Plain Symposium, held at
the FSU Center for Professional Development on October 9th, 1998. This conference brought
together numerous professionals involved with natural sciences and resources research and
land-use planning on the Woodville Karst Plain, located between the Cody Scarp and the Gulf of
Mexico coast in the big bend of north Florida. This conference demonstrated the usefulness
and need for multidiscipline research expertise to address holistic environmental conservation
concerns. This successful gathering also served as the kick-off for Earth Science Week in
Florida. We hope this week in the future will serve to highlight other events which demonstrate
the importance of understanding applied earth sciences to the future of Florida and our
environmental sustainability.

Respectively yours,

Walter Schmidt, Ph.D., P.G.
State Geologist & Chief
Florida Geological Survey

/ws

This collection of papers represents the authors written manuscript of their talk
presented at the Wakulla Springs Karst Plain Symposium. The editors have reviewed
the submitted texts for basic spelling errors and gross figure irregularity and prepared
necessary reformatting of text for consistency. Interpretive concepts, figures, and other
professional opinions are clearly the responsibility of the authors and no endorsement
by the Florida Geological Survey or the Department of Environmental Protection is
intended. Authors who presented their talk but were not able to provide a complete
manuscript are represented here by their abstract.

Printed for the Florida
Geological Survey

TALLAHASSEE, FL 2000

ISSN 0085-0640

PREFACE

The first annual Earth Science Week was celebrated the second full week of October in 1998. This
celebration was initially conceived by the American Geological Institute to celebrate their 50th anniversary.
The Association of American State Geologists representing the 50 State Geological Surveys immediately
supported the concept to raise the visibility and awareness of the Earth Sciences among the public and
professional environmental community. Over thirty Governors had signed proclamations designating
Earth Science Week within their respective State, Congress adopted a resolution into the Congressional
record designating such, and President Clinton saluted the effort by signing a letter recognizing the
contributions earth science makes to society and the well being of all Americans. In Florida, Governor
Chiles signed a proclamation designating October 11-17, 1998, as Earth Science Week in Florida.

One of the goals of Earth Science Week is to encourage geoscientists to do something in their community
to promote earth science understanding and to foster further appreciation for the subject. In Florida, we
at the Florida Geological Survey viewed this as a logical and natural means to promote what the Florida
Department of Environmental Protection had been endorsing for several years, namely holistic
ecosystem management concepts. This management principle must be based on sound scientific
understanding of our natural physical systems and their interconnectedness to be successful. Three
activities were organized to kick-off Earth Science Week and to highlight these issues in the Big Bend of
Florida. On Friday, October 9, 1998, scientists, land and water managers, and others with an interest in
the science behind the Wakulla Springs Basin and its water resources, came together at the Wakulla
Springs Karst Plain Symposium at the FSU Center for Professional Development, in Tallahassee, FL.
Participants included geologists, hydrogeologists, biologists, botanists, cave divers, engineers, land use
and resource managers and planners, government officials, and the public. This publication represents a
compilation of the papers presented at the symposium on that day. Mr. Kirby Green, the Deputy
Secretary of the Department of Environmental Protection provided introductory and welcoming remarks to
those in attendance. This was followed by comments from the Honorable Janegale Boyd, Representing
District 10 in the Florida House of Representatives (which covers most of the area covered by the
symposium presentations). Representative Boyd is an active and dedicated member of the House Water
Resources Management Committee.

On Saturday, October 10th, the public was the primary focus at the Wakulla Springs Earth Science
Fair. Beginning at 10 a.m. at the Wakulla Springs State Park, the Fair gave everyone the chance to
enjoy and learn more about this valuable resource. Exhibits explained the importance of karst geology to
the springs, the threats to water quality throughout the Wakulla Springs Basin, and how cave divers have
mapped the underground cave system that brings water to the Springs. Demonstrations and field trips
also were incorporated into the day's activities by the many agencies and various firms participating. The
demonstrations covered several aspects of water quality monitoring, the use of satellites for mapping
systems such as the network of caves that lead into the springs, how divers negotiated the caves, the
damage done to local ecosystems by exotic plants -- and more. Visitors were able to take field trips to
see some of the sinkholes and springs that are important components of the Wakulla Springs system and
learn how they offer avenues through which pollution can enter the spring system. Visitors also were able
to take the river boat and glass-bottom boat tours of the springs to learn more about the waters that
bubble up from deep in the earth, and the ecosystems around the spring and river. The park entrance
fee was waived during the Fair. The Fair was sponsored and organized by the Florida Department of

Environmental Protection, the Florida Geological Survey, the Florida Association of Professional
Geologists and the Wakulla Springs Water Quality Working Group, which is composed of all the federal,
regional, state, and local agencies that are working to protect water quality in the springs. Over 1,200
people attended the day's festivities.

On the following Monday, October 12, 1998, the Florida Geological Survey hosted an Open House at the
Herman Gunter Building, the headquarters of the FGS in Tallahassee, FL. Geoscience colleagues,
environmentalists, government employees, friends, and the public attended to view FGS displays, and
learn about our programs and facilities. All in all the first Earth Science Week was a very successful
event for the geological community in north Florida. The FGS hopes to orchestrate continuing outreach
activities in Florida during Earth Science Week on an annual basis.

Walt Schmidt, Ph.D., P.G.
State Geologist & Chief
Florida Geological Survey

TABLE OF CONTENTS
Page

Schmidt/Earth Systems Understanding: The Foundation of Environmental Regulatory
Support, Land-Use Planning Decisions, Natural Resources Conservation, and the Basis
of Ecosystem Management 1

Rupert/Regional and Local Geologic Setting of the Woodville Karst Plain 4

Clemens, Hatchett, Hartnett/Hydrogeology of the St. Marks River Basin 11

Davis/Regional Hydrology of the Upper Floridan Aquifer of North-Central Florida and
Southwestern Georgia (Abstract Only) 21

Chen, Donoghue, Hoenstine, Rupert, Spencer, Ladner, Lane, Faught/A Buried Karst
Plain on the Northeastern Gulf of Mexico Shelf, NW Florida: Origin and Relation to
Onshore Karst 22

Singleton/St. Marks River Basin: Water Resource Vulnerability (Abstract Only) 26

Werner/Determination of Groundwater Flow Patterns From Cave Exploration in the
Woodville Karst Plain, Florida 37

Cowart, Osmond, Dabous, Miller, Cao/Uranium and Strontium Isotope Character of
Waters in theWakulla Karst Plain 45

Katz/Hydrochemical Interactions Between Ground Water and Surface Water in the
Woodville Karst Plain, Northern Florida (Abstract Only) 61

Maddox/The Big Picture: Aquifer Vulnerability Mapping Efforts in the Woodville Karst
Plain of Northern Florida (Abstract Only) 62

Burnett, Chanton, Rutkowski, Corbett, Dillon, Cable/Tracing Groundwater Flow
into the Northeastern Gulf of Mexico Coastal Zone (Abstract Only) 63

Pratt/Physical Framework For Understanding Floridan Aquifer Groundwater Flow and
Nutrient Transport within the Woodville Karst Plain (Abstract Only) 64

Lane/The Spring Creek Submarine Springs Group, Wakulla County, Florida 65

Kwader/Restoration of the Floridan Aquifer to Potable Conditions, St. Marks Peninsula,
St. Marks, Florida 78

Macmillan/St. Marks River Watershed Surface Water Improvement and Management
(SWIM) Program 83

Livingston/Stormwater Concerns and Management on the Wakulla Karst Plain 88

Page

Swanson/Water Quality Status in Leon County, Florida: What's Happening Upstream 89

Lee/Wakulla Springs Water Clarity Model 92

Landing/The Politics and Economics of Environmental Neglect (Abstract Only) 97

Stevenson/Wakulla Springs Water Quality Working Group An Interagency Ecosystem
Process (Abstract Only) 99

Means/Lakes and Ponds in the Wakulla Karst Plain; Their Importance to Local and
Regional Biodiversity (Abstract Only) 100

Frydenborg/Biological Assessment of the St. Marks River Basin In Leon, Jefferson, and
Wakulla Counties, Florida 101

Bartodziej, Leslie/Waterhyacinth as a Biological Indicator of Water Quality 107

Rudloe/Fresh Water Impacts in Coastal Ecosystems 116

Ladner, Hoenstine, Dabous, Harrington/A Geological Investigation of Sedimentation
and Accretion Rates of Marine Coastal Wetlands Within Apalachee Bay 120

Cook/Wakulla Springs Quality of Life 140

Webb/Two Cycles of Late Pleistocene Sinkhole Filling in the Middle Aucilla River,
Jefferson County, Florida 142

Wisenbaker/Aboriginal Settlement in the Apalachee Region of Florida 154

Savery/Water Visibility and Rainfall at Wakulla Springs A Short History 160

Bell/Non Market Values of Natural Resource Use (Abstract Only) 172

Colaninno/The Apalachicola National Forest Staying One Step Ahead of the Threat 173

Sheftall/Soils of the Karst Plain and Their Ecological Communities: Correlations and
Constraints for Sustainable Use (Abstract Only) 175

Bennett/Florida Yards and Neighborhoods (FYN) Program in the St. Marks/Wakulla
River Watershed (Abstract Only) 177

Reinman/Wildlife Habitat Management on St. Marks National Wildlife Refuge
(Abstract Only) 178

Donovan/Are One To Five Acre Lots the Answer? (Abstract Only) 179

EARTH SYSTEMS UNDERSTANDING: THE FOUNDATION OF
ENVIRONMENTAL REGULATORY SUPPORT, LAND-USE PLANNING
DECISIONS, NATURAL RESOURCES CONSERVATION, AND THE BASIS OF
ECOSYSTEM MANAGEMENT

Walter Schmidt, State Geologist and Chief, Florida Geological Survey, 903 W. Tennessee Street, Tallahassee, FL
32304-7700

ABSTRACT

Each and every environment that exists on the face of the earth, is the cumulative dynamic result of
the interactions between four Earth Systems. And without a basic understanding of these Earth Systems
there can be no real understanding or predictive capabilities for environmental change, and hence, natural
resources conservation or "sustainability" as popularly defined. These systems include: the Geosystem
(the solid earth framework of the earth), the Hydrosystem (the hydrologic cycle or the aqueous portion of
the earth), the Atmosystem (the meteorological and climate aspects of our planet), and the Ecosystem
(the interaction of the biologic assemblages with each other and the physical systems).
Here, I will champion the need for a greater emphasis on the Geosystem, the solid earth framework.
This I believe is critical to our species survival, our societal life style, and indeed all life. Water supply and
protection concerns are not isolated issues only involving the study and planning for surface and ground
water resources. To fully understand and protect our precious, life sustaining water resources, knowledge
of the medium which the water flows through and over must also be considered. The geologic framework
serves as the "bucket" that contains the water, and it contributes dissolved minerals and elements which
characterizes the ambient water component and is the most critical of the precusor for the soils. Why do I
say the solid earth component is the most critical of the systems? Because; we walk on it, we grow our
food on and in it, we get our water resources from within it, we dispose of our waste on and within it, we are
subject to all the natural hazards it has to offer (such as sinkholes, coastal and fluvial erosion, expansive
clays and other soils, if we were from another state I'd mention volcanoes and earthquakes), and we obtain
all our mineral resources from it to build our roads, homes, schools, malls, government buildings, cars,
computers, clothes, packages, medicines, etc.
We must learn about earth systems, so that we may understand our surroundings. To remain
ignorant of geological reality, jeopardizes the future welfare of our society. To quote Dr. Gene Shinn from a
recent paper: "No Rocks, No Water, No Ecosystem!"

INTRODUCTION

Earth Systems are commonly thought of as:
Volcanoes, Earthquakes, Landslides, and Tsunamis.
And a typical response to us in Florida is, we don't
have to worry about these things here. Well let me
explain to you, that not only are we subject to the
dynamic actions of earth systems in Florida, but they
clearly are the fundamental aspect of understanding
our various environments. For without this awareness,
we cannot implement defendable environmental
regulations, we cannot conserve or preserve our
natural resources, we cannot approach a sustainable
society as popularly defined, and we cannot do an
adequate job of protecting threatened & endangered
species, or degraded habitats.

Viewing a satellite image of hurricane Georges
clearly demonstrates a powerful earth system
impacting our State. It's the resultant manifestation of
land heating, warm ocean circulation, and dynamic
atmospheric response. It's forces effect our corner of
the earth in: Coastal erosion, inland wind damage to

structures and vegetation, coastal flooding, upland
flooding, mud slides, sediment build-up at estuaries
resulting from increased sediment loading during flood
stage events, surficial aquifer loading, changed
surface water / groundwater interactions, critical
sinkhole development, among many others. Clearly,
we are seriously impacted by physical earth systems.
When we consider how other parts of the earth must
deal with many other geologic hazards, it easy to see
why WILL DURANT said: "Civilization exists by
geological consent, subject to change without notice."
And how author H.G. WELLS came to say: "Human
history becomes more and more a race between
education and catastrophe." But we are not here to
dwell on the awesome power of earth systems, we are
here to nurture an appreciation for the need to
understand how they work, for the benefit for society
and our co-inhabitants of this earth.

Our society and cultural habits tend to have a
great impact on the workings of these earth systems.
We must understand the impacts of our actions if we
are to conserve our natural environment or minimize

our pollution impact. For example: forest fires,
logging, road construction, urban development, dam
operations, or agricultural draining, all can and do send
a rush of sediment into streams and rivers, changing
the river's environment and ecological system. Excess
sand into a riverine system can degrade fish habitat or
increase the potential for flooding. Sediment transport
is a function of not only the fluid regime, but the grains
lithology, SP gravity, size, roundness, sorting, among
other factors.

De-watering an area for development can
change the soil type by changing it from a reducing
environment to an oxidized environment. The
available elements and nutrients which plants depend
on would be dramatically altered. The surficial water
table may cease being available for the local plant
assemblage. It may cease recharging the local
aquifer, a spring discharge area could become an
aquifer recharge area, sinkholes could be triggered,
saltwater intrusion into the local aquifer could
contaminate the freshwater resource. These are but a
few of the obvious impacts of an apparent simple
modification to a local water table for development
purposes.

In Florida in 1990, we saw about 19 acres per
hour of wetlands and agricultural land being developed
into urban uses. We have through the P2000 and
other programs been able to conserve over 1,000,000
acres of land since then. So significant efforts are
being made. But we can't buy everything, nor do we
have any business suggesting it. But we must include
all the "stakeholders" in the discussion. Science in
public policy has rarely been so needed as it is in
today's complex political forum. Society demands
resources to maintain a standard of living
commensurate with people's expectations and a
suitable level of environmental quality is inherent to this
demand. Tradeoffs are inevitably made between the
activities that provide energy, minerals, timber, food,
and water, and the need to and desire to preserve
ecosystem services and conserve our environment.
Such tradeoffs are often highly controversial and
politically volatile, and maintaining detachment, not
taking sides on issues, is not easy for the scientist or
informed citizen. Differences between geological and
ecological views may reflect real and inherent tensions
arising from the growth of industrialized society, but
scientists must seek common ground in order to
balance resource and environmental goals. Failure will
likely result in alternating extremes of exploitation and
preservation. The use of a popular phrase or a current
buzz-word can change the course of public opinion, but
fundamental geologic and biologic processes are not
swayed by polls. We must be careful that true
conservation will not be lost in rhetoric and scrambling
for dominance of perspective.

LOCAL PERSPECTIVE

The Leon / Wakulla / Jefferson Counties area
has increased in human population about 110% the
last twenty five years. It now represents over a quarter
of a million people. The NWFWMD estimates that the
area withdraws about 116 Mgal/day from the aquifers.
This area is a great natural laboratory to implement a
multidiscipline, multiagency, public / private attempt to
mesh our best efforts for the good of the environment,
for the conservation of our natural resources, and
ultimately to the benefit of us all. We have a growing
urban / metropolitan area in Tallahassee. We have
several small towns with their own public facilities
(such as Perry, Crawfordville, and Woodville), we have
widespread areas of rural farms and small
homesteads, there are vast unpopulated uplands in
timber, pristine uplands and coastal wetlands, a
National Refuge and State Parks. There exists a
great variety of environmental and geographic
landforms in and around the Woodville Karst Plain.

Ecosystem management principals and
programs, water shed management; natural resources
conservation; environmental regulatory program
foundations; land-use, planning, zoning, and
management decisions; threatened and endangered
species assessment and protection; invasive and
exotic species geographic assessment; groundwater
and surface water conservation and protection;
geologic hazards understanding; minerals resources
planning for society's needs; among many other
issues, all have at their base, a fundamental need for
data and interpretations of the solid earth.

Of course all living things need air, water, and
mineral and elemental components to survive. Why do
I say the solid earth is the most important from our
point of view? It's the substrate to everything we do,
we walk on it, we grow our food on and in it, we get our
life sustaining water from within it, we dispose of our
waste in it, we are subject to all the natural hazards it
can dish out, we get all our materials and supplies to
build our homes, malls, schools, cars, cloths, etc. from
it, and every single square inch of the surface of the
earth is a unique environment resulting from the
composite dynamic interactions of the solid earth
terrain with the hydrosphere and atmosphere, which in
turn creates our ecosystems with their associated
biologic assemblages. Forested uplands, dry inland
ridges, wetlands, and coastal swamps, to name only a
few, all owe their existence to the local shallow
subsurface geology and hydrogeologic regime. All
species exist in the habitat from which they evolved
and for which they are best adapted. Why does an
area function as a wetland? It is a groundwater
discharge area? Is it a low relief karst prairie, or is it
flooded as a part of an episodic fluvial system? Is it
the result of a perched surficial water table because of
an impermeable hard pan or clay bed in the subsoil
zone? How does this change seasonally going wet to
dry back to wet again? Do these alternating oxidizing

and reducing conditions change the available minerals
and elemental nutrients? Why do certain species of
plants grow in selected defined regions? Are they
dependent on the near-surface mineralogical nutrient
sources? Are they in need of well drained sediments?
Do they require certain groundwater or surface water
geochemistry? What accounts for the various types of
surface water chemistry we see in Florida? Where do
the various elemental and chemical components come
from? A clear understanding of the solid earth system
is an essential aspect of any successful environmental
assessment. I like to say,.....the solid earth is the
"bucket" that contains our precious water resources.

RESOLVE

So, this is our big picture problem as
geoscientists and as environmental scientists from all
disciplines, to communicate this to the public, to
elected and appointed government officials, to
planners, and others. A basic understanding of these
concepts is lacking by the general public. Earth
Science is not required in our public school systems,
so most members of the lay public have never been
exposed to these basic earth system concepts. They
continue to think of geoscience as the science of
mining, oil & gas, and rock and mineral collections from
their Boy/Girl Scout days. True natural resource
conservation towards a sustainable environment can
never be achieved until the general public grasps an
overall systems understanding and an appreciation for
the interconnectedness of these systems. We must
continue and expand our outreach programs to be
successful.

I thank Dr. Lee C. Gerhard, State Geologist of
Kansas, and Dr. Morris W. Leighton (past State
Geologist of Illinois) whose many publications and
several discussions on this topic provided a basis for
these thoughts.

REGIONAL AND LOCAL GEOLOGIC SETTING
OF THE WOODVILLE KARST PLAIN

Frank R. Rupert, Florida Geological Survey, 903 W. Tennessee Street, Tallahassee, FL 32304-7700

ABSTRACT

The Woodville Karst Plain (WKP) is situated in the eastern Florida panhandle bordering the Gulf of
Mexico. It extends from central Wakulla County, Florida, eastward through southernmost Jefferson County
and around the coastal Big Bend region to the Steinhatchee River in southwestern Taylor County. The
WKP is characterized as a very-gently-seaward-sloping, sandy, swampy subzone of the Ocala Karst District
geomorphic province. It is underlain by shallow, karstic, carbonate bedrock covered by a veneer of
undifferentiated sand. Land surface elevations typically vary between 0 and 50 feet. Doline features, such
as sinks, collapse depressions, disappearing streams and caves are common throughout the region. The
WKP is bounded on the west by an elevationally-higher region of clayey sands with few karst surface
features. To the east and south the WKP is bounded by elevationally higher and less karstic zones. The
northern boundary of the WKP is a relict Pleistocene marine escarpment named the Cody Scarp, which
forms a relatively abrupt transition from the flat, sandy, karst plain into higher clayey sand hills of the
Tallahassee and Madison Hills geomorphic zones. The southern edge of the WKP borders the Gulf of
Mexico, and the seaward extension of the carbonate plain continues offshore to the edge of the continental
shelf.
The origin of the WKP, as well as its underlying stratigraphy, have been significantly influenced by
adjacent subsurface structural features. The rocks comprising the shallow bedrock in the WKP are Eocene
and younger carbonates. These units dip and thicken to the west-southwest into a broad structural basin
named the Apalachicola Embayment. Eocene through Miocene carbonate strata are brought close to the
surface in the WKP as the units lap up onto the flank of the Ocala Platform, a broad, southeast-trending,
positive structure located to the southeast of the WKP. Eocene Ocala Limestone forms the bedrock
adjacent to the crest of the Ocala Platform at the southeast end of the WKP. The Ocala Limestone typically
consists of white to pale orange, skeletal, very fossiliferous Eocene (38 Mya [million years ago]) marine
limestone and dolostone. It ranges in depth from surface outcrop near the Steinhatchee River in Taylor
County to over 400 feet bls at the western edge of the WKP.
Progressively younger geologic units are exposed on the northern and western flanks of the Ocala
Platform. Suwannee Limestone unconformably overlies the Ocala Limestone and comprises the shallow
bedrock in most of Taylor County and southern Jefferson County. The Suwannee is an Oligocene (33 to
30 Mya) white to gray to pale orange calcarenitic marine limestone and dolostone, comprised largely of
foraminiferal tests and small mollusks. In the WKP the top of the unit varies from approximately 150 feet
below land surface at the western edge of the plain to surface exposure in the eastern part. A network of
large subsurface karst conduits mapped in the WKP are developed in Suwannee Limestone. The Miocene
(25-20 Ma) St. Marks Formation unconformably overlies the Suwannee Limestone and forms the shallow
bedrock under the western end of the WKP, comprising westernmost Jefferson County, southernmost Leon
County, and all of Wakulla County. It is typically a pale orange to light gray to white, calcarenitic limestone,
generally very fossiliferous, well indurated, and commonly dolomitic. The St. Marks Formation crops out
over much of southern Wakulla County, and many area sinks expose this unit. St. Marks Formation also
forms the ledge overhanging the vent in Wakulla Spring, rims the spring pool, and forms the bed of the
Wakulla River. The St. Marks Formation and the underlying Suwannee Limestone and Ocala Limestone
are components of the Floridan aquifer system.
Variably-thick Pleistocene undifferentiated sands and clayey sands overlie the carbonate bedrock
throughout the WKP. These surficial sands are largely reworked marine sediments, deposited by high-
standing Pleistocene seas. Relict Pleistocene marine and aeolian features, such as dunes, bars, and
beach ridges are common in many areas of the WKP.

INTRODUCTION
and Crawfordville, in Wakulla County, around the
The Woodville Karst Plain (WKP) is situated in Florida Big Bend, encompassing portions of southern
the eastern Florida panhandle, bordering the Gulf of Leon, eastern Wakulla, southern Jefferson, and
Mexico (Figure 1). It extends east-southeastward from western Taylor Counties. The Steinhatchee River
an approximate line connecting the towns of Panacea forms the southern boundary of the WKP. The WKP is

characterized as a flat-to-gently rolling, seaward-
sloping plain, underlain by shallow Tertiary carbonate
bedrock. Undifferentiated Quaternary sands thinly
blanket the surface, and karst doline features such as

GEO R G IA i I I %
- - ---- 4

'-~ ^
..A _. ."
----... -- -- -.
SKULL / -

-\ -. ,y l p / ,
~ I -

Figure 1. Location of the Woodville karst Plain.

collapse depressions, sinkholes, disappearing streams,
springs, and extensive underground caves are
common throughout the area.

PREVIOUS STUDIES

Studies leading to the delineation of the region
now called the Woodville Karst Plain have spanned
much of the present century. Early descriptions of
northern Florida's surface features, completed before
detailed topographic maps and extensive subsurface
geological data were available, were based on field
observations of land forms. The early literature
generally recognized differences in elevation and land
surface shape between the highlands in the northern
part of the panhandle and the lower, flatter coastal
plain bordering the Gulf of Mexico. Wilder et al. (1906)
noted the topographic differences between the clayey-

Figure 2. Geomorphic map of the eastern
Florida panhandle (modified from White, 1964).

sand highlands of northern Leon County and the low,
sandy, undulating plain extending from southern Leon
County to the Gulf; these authors correctly attributed
the terrain differences to variations in the underlying
geology. They also cited the shallow limestone
substrate occurring in the region south of Tallahassee
noting the numerous sinks and the underground
drainage systems.

In his early botanical studies, Roland Harper
(1910) took a geomorphic approach to descriptions of
the local terrain, dividing the state into geographic
regions. Harper (1910) included the Leon County
portion of what is now the WKP in his Limesink region,
and placed the Wakulla County portion in his Gulf
Hammocks region. He also used the term Red Hills to
describe the stream-dissected highlands of northern
Leon, Jefferson, and Madison Counties, which at that
time, he included in his Middle Florida Hammock Belt.
Later, Harper (1914) noted that the floral assemblages
in the Limesink and Gulf Hammock regions, which
correspond to the modern WKP, were distinctly
different from surrounding areas and coined the term
Tallahassee Red Hills for the highlands in Leon County
bordering the northern edge of what would be later
named the WKP.

Sellards (1910, 1914) and Sellards and Gunter
(1912) broadly described the geomorphology of the
counties that would one day contain the Woodville
Karst Plain. The only elevation data available for
Sellard's studies, however, had been shot along the
railroad grades of his day. Therefore, vast expanses of
land lay unmapped, and he could not see the
geomorphic features which would be used to define the
WKP.

The first true regional geomorphic zone
encompassing the entire extent of the modern WKP
was named the Coastal Lowlands by Cooke (1939).
He recognized the Coastal Lowlands as terraced plains
representing the sea bottoms of high-standing
Pleistocene seas. These were observable as a series
of elevational terraces, flat erosional sea floors
punctuated by small scarps, approximately paralleling
the modern coastline. Cooke also differentiated the
broad geomorphic region of stream-dissected
highlands between the Apalachicola and
Withlacoochee Rivers, extending from Tallahassee
north into Georgia, giving it the name Tallahassee
Hills.

As topographic map coverage expanded in the
panhandle area through the 1950s, and more geologic
well data became available, better delineation of
geomorphic features was possible. White (1964)
produced the first color geomorphic map of the Florida
panhandle (Figure 2). In it he incorporated Cooke's
(1939) zones and added the important bounding
feature known as the Cody Scarp. The Cody Scarp is a
relict, east-west-trending marine escarpment

representing the shoreline of the Wicomico sea. The
escarpment forms a distinct break between the
Tallahassee Hills to the north and the Coastal
Lowlands stretching from the toe of the scarp
southward to the Gulf. It is best developed near the
community of Cody in Jefferson County, for which it is
named. At Tallahassee, the toe of the Cody Scarp lies
at about 50 to 60 feet above mean sea level (msl), with
the crest at approximately 150-200 feet above msl.
Locally the scarp is modified by dissolution of the
underlying carbonates and by erosion to the extent that

Figure 3. Regional subsurface structures of
north Florida.
the scarp face is not as well defined as in areas to the
east; here it consists of a series of coalesced sand hills
in the transition from highlands to lower karst plain.
White also included names for two of the larger relict
marine features in the Gulf Coastal Lowlands. At the
edge of the Cody Scarp, near Tallahassee, are a
series of relict sand bars and dunes associated with
the Wicomico sea named the Lake Munson Hills.
Crests of the dunes attain elevations of 80-100 feet
above msl. Similarly, the Wakulla Sand Hills in
southeastern Leon County are a series of Pamlico sea
dunes attaining elevations of about 50 feet msl.

In 1966 Hendry and Sproul published a bulletin
on the geology of Leon County, in which they further
refined existing geomorphic zones and erected several
new subdivisions. They proposed the name Woodville
Karst Plain (after the town of Woodville, located on the
plain in southeastern Leon County) for the gently-
sloping, relatively low plain extending from the edge of
the Tallahassee Hills south to the Gulf of Mexico, and
eastward from the edge of their topographically higher
Apalachicola Coastal Lowlands zone into Jefferson
County. They characterized the WKP area as "loose
quartz sands thinly veneering a limestone substrata

that has resulted in a sinkhole and dune topography."
Later in 1966, Yon published a bulletin on the geology
of Jefferson County and extended the WKP eastward
to approximately the Aucilla River. These works
established the basic geomorphic boundaries of the
WKP, which defined the extent of the zone for most of
the last 30 years. In subsequent studies, Lane (1986)
illustrated the extent of the WKP in Leon and Wakulla
Counties, and Rupert and Spencer (1988) provided a
more detailed definition of the WKP in Wakulla County.

Scott (1998a in preparation) has extended the
WKP southeastward from its original arbitrary boundary
at the Aucilla River, through Taylor County, to the
Steinhatchee River. This seems a logical step as karst
terrain similar to that mapped by the original WKP
authors occurs throughout the coastal Big Bend region.

SUBSURFACE STRUCTURE AND GEOLOGY OF
THE WOODVILLE KARST PLAIN

The WKP straddles a transitional area
between two major subsurface geologic structures
(Figure 3). It is situated along the eastern edge of a
broad depositional basin named the Apalachicola
Embayment. This basin is filled with approximately
15,000 feet of Jurassic to Quaternary age sediments.
Geologic units deepen and thicken to the west-
southwest into the trough of the Apalachicola
Embayment.

The WKP is also located on the western flank
of a large, dome-like structure named the Ocala
Platform. This features brings Middle Eocene rocks
close to the surface over its crest in Levy County.
Progressively younger units lap onto the structure from
the west-southwest. The origin of this feature is
somewhat uncertain. In early literature it was named
the Ocala Uplift (Applin, 1951; Vernon, 1951),
assuming that it was the result of structural movement.
It was later given the name Ocala "Platform" (Scott,
1988), eliminating the structural connotation to the
name. It may simply be a positive region that has
undergone less compaction and downwarping than
peripheral areas to the west-southwest. The Ocala
Platform has had significant influence on the geology
of the WKP. Figure 4 illustrates a cutaway view of the
Florida Big Bend area, with the different geologic strata
shaded for reference. The vertical scale is greatly
exaggerated to illustrate the dip of the units. The
Ocala Platform brings the oldest rock exposed in
Florida, Middle Eocene Avon Park Formation, to the
surface over its crest in northwestern Levy County.
Younger Upper Eocene Ocala Limestone laps over the
structure, forming the shallow bedrock in the central
Big Bend region, which encompasses the southern
WKP. Still younger Oligocene Suwannee Limestone
laps onto the flanks of the structure from the
southwest, forming the bedrock from western Jefferson
through most of Taylor County before pinching out in

southern Taylor County. Lower Miocene St. Marks
Formation shallows from the west as it laps over
Suwannee Limestone, forming the bedrock in the

Figure 4. Block diagram of the Florida Big Bend
region (from Rupert and Arthur, 1997).

southeastern Leon and Eastern Wakulla Counties.
The Ocala Platform has thus helped shape the areal
pattern of the shallow bedrock throughout the WKP.

Figure 5 shows the Big Bend portion of the
geologic map of Florida (from Scott, 1998b, in

Figure 5. Geologic map of the eastern Florida
panhandle (from Scott, 1998a).
preparation). The older-to-the-southeast pattern of
shallow rock units imposed on the area by the Ocala
Platform is evident. Referring to Figure 5, Miocene St.
Marks Limestone (Tsmk) forms the bedrock at the
western end of the WKP, the Oligocene Suwannee
Limestone (Ts) extends through the central part, and
the Eocene Ocala (To) comprises the southernmost
portion of the plain. While most of the WKP is covered
by variably-thick Quaternary quartz sand, areas
covered by sands in excess of 20 feet thick (Qu, Qbd)
are mapped in white.

The shallow structure and geomorphology of
the WKP is readily observed in cross section. Figure 6
is a west-to-east section across northern Wakulla
County. The local bedrock limestone of the St. Marks
Formation gently rises from the west to a very shallow
position in central and eastern Wakulla County. Here it
is mantled by thin porous undifferentiated sands, relicts
of the Pleistocene marine transgressions over the
area. Surface drainage streams are uncommon; the
only major streams in the western part of the WKP are
the Wakulla and St. Marks Rivers, both spring-fed and
flowing in channels incised in the underlying bedrock.
Precipitation falling in this area percolates directly
down to the rock. Over thousands of years this
meteoric water has dissolved the limestone, forming
numerous sinks, underground drainage conduits and
other karst features. In the western part of Figure 6,
immediately west of the WKP, a major contrast is
seen. The land surface is higher, and is underline by
thick clayey sands. Three additional geological units,
the Pliocene Jackson Bluff and Intracoastal Formations
and the Miocene Torreya Formation, pinch out from the
west. The thick clayey overburden sediments have
served to protect the underlying limestone from
dissolution, thus land surface lowering due to
dissolution has been reduced, karst features are fewer
in number, and the area contains numerous swampy,
standing-water bays. Streams following in western
Wakulla County, such as Lost Creek, are captured by
underground drainage as they flow onto the WKP.

Figure 7 is a section extending from
Tallahassee, in Leon County, south to Apalachee Bay.
Tallahassee is mostly located above the Cody Scarp,
in the Tallahassee Hills geomorphic zone. Hills in this
zone locally attain elevations of 200 or more feet
above msl. The Tallahassee Hills have a core of
Miocene Hawthorn Group sands, clays and
carbonates. Capping the hills are the red clayey sands
of the Plio-Pleistocene Miccosukee Formation,
observable in roadcuts throughout northern Leon
County. The Cody Scarp, a former shoreline of the
Pleistocene Wicomico sea, forms an abrupt boundary
between the Tallahassee Hills and the WKP. The
scarp trends east-to-west across the eastern
panhandle, passing through Tallahassee just south of
the fairgrounds. Shallow St. Marks Formation
limestone, overlain by variably-thick undifferentiated
sands, forms the bedrock near the scarp and extends
under the Tallahassee Hills. High and well-drained
relict sand dunes at the northern edge of the WKP
support a flora of pines, black-jack, and turkey oak
trees. In contrast, wetter areas to the south are
populated by cypress and bay trees (Hendry and
Sproul, 1966). Harper (1914) described 30 tree
species, seven species of woody vines, 30 shrubs, and
109 species of herbs growing within the WKP zone.

WEST

WOODVILLE KARST PLAIN

Figure 6. West-to-east geologic cross section in the Woodville Karst Plain (from Rupert and
Spencer, 1988).

NORTH

SOUTH

CROSS SECTION
c LOCATION
C3
S^LEON CO

,MICCOSUKEE FM. z
S5
,TORREYA FM. I

2 UNDIFFERENTIATED SAND
/\ AND CLAY 0

SUWANNEE

LIMESTONE

0 5 MILES
I I
0 8 KILOMETERS

LO

-L1 t~r -. N y APALACHEE BAY

VERTICAL EXAGGERATION = 350
TIMES TRUE SCALE

Figure 7. North-to-south geologic cross section in the Woodville Karst Plain (from Rupert, 1993).

-0 200

200- 60

150-
40
100-

-20
50

0+0

EAST

r100

-250

At the southern edge of the WKP, the limestone
bedrock extends offshore into the Gulf of Mexico and
onto the broad Big Bend continental shelf. Boulders
and pinnacles of Suwannee Limestone are common in
the shallows off the central Big Bend coastline.
Extensive salt marshes are developed along most of
the coastal portion of the WKP, from Wakulla County
eastward through Taylor County. Organic-rich muds
and silts, resting on the shallow carbonate substrate,
support a marsh flora of predominantly Juncus and
Spartina grasses (Clewell, 1981). Formation of open
coastal marshes is attributable to the zero-energy
nature of the Big-Bend coast. Sand movement is
minimal, and beaches are virtually absent due to a lack
,f-n- Irti~,ti (Drir'Q Q1OZ T7nn-r I QAn\

GULF OF MEXICO

Figure 8. Lineaments in the eastern panhandle-
northwestern peninsula area of Florida.

BEDROCK LITHOLOGY

The oldest rock forming near-surface bedrock
in the WKP is the Upper Eocene (38 Mya [million years
ago]) Ocala Limestone. The Ocala Limestone (Dall and
Harris, 1892) is a calcarenitic marine limestone
containing abundant microfossils, mollusks, bryozoans,
corals, algal fragments, and rare vertebrate fossils.
Guide fossils include the pelecypod Amusium
ocalanum, and the benthic foraminifera Lepidocyclina
ocalana and Nummulites spp. In its type area near
Ocala, Marion County, Florida, it is a nearly pure
calcium carbonate coquina of large benthic
foraminifera and other fossil fragments, cemented with
micrite. In the coastal regions of the WKP, it is
commonly dolomitized and/or silicified to varying
degrees as a result of interactions with groundwater
and subaerial exposure. The Ocala Limestone is
exposed along the Steinhatchee River and in sinks in
the southern end of the WKP. It ranges in depth from
surface exposure in southern Taylor County to over
400 feet bls (below land surface) in Wakulla County.

The Oligocene (33 to 30 Mya) Suwannee
Limestone (Cooke and Mansfield, 1936) is a white to
gray, pale orange, or brown recrystallized calcarenitic

limestone, commonly comprised largely of small
miliolid foraminifera tests, mollusks, and bryozoans.
Guide fossils include the echinoid Rhyncholampus
gouldii and the benthic foraminifera Dictyoconus
cookei, Rotalia mexicana var. mecatepecensis,
Discorinopsis gunteri, and Coskinolina floridana. It
also is commonly dolomitized or silicified in the WKP.
Chert from the Suwannee provided material for early
indian tools and weapons. Many of the underground
conduit systems in the WKP are developed in
Suwannee Limestone. The Suwannee limestone
varies in depth from surface exposure in coastal Taylor
and Jefferson Counties to over 150 feet bls along the
western edge of the WKP.

The youngest bedrock in the WKP is the Lower
Miocene (25-20 Mya) St. Marks Formation (Puri and
Vernon, 1964). The St. Marks Formation is a pale
orange to light gray, to white, argillaceous, moderately
indurated calcaren itic-to-massive limestone and
dolostone with abundant casts and molds of mollusks
(Mansfield, 1937) and the large benthic foraminifera
Sorites sp. It commonly crops out along the major
streams and sinks in western-most Jefferson County
and eastern Wakulla County. The type location for the
St. Marks Formation is in a sink named the Swirl, just
southeast of Crawfordville in Wakulla County.

All three rock units are components of the
Floridan aquifer system. The Floridan aquifer system
is the primary freshwater source for the WKP area.
Throughout most of the WKP the local water table is
the top of the Floridan aquifer system. Recharge to the
Floridan aquifer system occurs in areas in Georgia and
northern Florida as well as locally by direct percolation
of precipitation through the porous sands blanketing
the carbonate bedrock. Surface runoff also enters the
aquifer through the numerous sinks in the region.

A number of surface lineations, primarily in the
form of aligned sinkholes, stream courses, and lake
and Gulf coastal shorelines are evident on both aerial
photographs and topographic maps of the Big Bend
Region. Figure 8 is a compliation of lineaments
mapped by various authors in county studies as well as
additional FGS in-house FGS maps. The map reveals
an abundance of linear patterns, thought to possibly
reflect joints, fractures, or faults in the limestone
bedrock. Two primary directions are prevalent:
northwest-southeast and northeast-southwest, with
others varying in bearing between these directions.
The general directional bearings of the lineaments
mirror the alignment of faults in the Mesozoic and older
basement rocks of Florida, and may be related.
However, research is lacking on this subject. If the
lineaments represent fractures, which are commonly
observed in dry caves, they would offer paths of least
resistance to groundwater flow, and as a result
facilitate karst dissolution along their trends. In
addition to the obvious linear alignment of sinkholes in
the region, many of the underground cave segments
mapped by cave divers appear to correspond with

these directional trends. Thus fractures may have
significant impact on regional and local groundwater
flow patterns within the WKP.

REFERENCES

Applin, P.L., 1951, Preliminary report on buried pre-
Mesozoic rocks in Florida and adjacent states:
U.S. Geological Survey Circular 91, 28 p.

Clewell, A.F., 1981, Natural setting and vegetation of
the Florida panhandle: U.S. Army Corps of
Engineers, Miscellaneous Report, Contract No.
DACWO1-77-C-01014.

Cooke, C.W., 1939, Scenery of Florida interpreted by a
geologist: Florida Geological Survey Bulletin 17,
120 p.

Cooke, C.W., and Mansfield, W.C., 1936, Suwannee
Limestone of florida {abs.}: Geological Society of
America Proceedings for 1935, p. 71-72.

Dall, W.H., and Harris, G.D., 1892, Correlation Papers
Neocene: U.S. Geological Survey Bulletin 84,
349 p.

Harper, R.M., 1910, Preliminary report on the peat
deposits of Florida: Florida Geological Survey 3rd
Annual Report, p. 197-397.

1914, Geography and vegetation of
northern Florida: Florida Geological Survey 6th
Annual Report, p. 163-437.

Hendry, C.W., and Sproul, C.R., 1966, Geology and
groundwater resources of Leon County, Florida:
Florida Geological Survey bulletin 47, 178 p.

Lane, B.E., 1986, Karst in Florida: Florida Geological
Survey Special Publication 29, 100 p.

Mansfield, W.C., 1937, Mollusks of the Tampa and
Suwanee Limestones of Florida: Florida
Geological Survey Bulletin 15, 334 p.

Price, W.A., 1953, The low energy coast and its new
shoreline types on the Gulf of Mexico: IV
Congress de I'Association Internationale pour
I'Etude du Quaternaire (INQUA), Rome, 8 p.

Puri, H.S., and Vernon, R.O., 1964, Summary of the
Geology of Florida and a guidebook to the classic
exposures: Florida Geological Survey, Special
Publication 5, 225 p.

Rupert, F.R., 1993, Karst features of northern Florida,
in: Kish, S.A., (ed.), 1993, Geologic Field Studies
of the Coastal Plain in Alabama, Georgia, and
Florida: Southeastern Section, Geological Society
of America, Meeting guidebook, April, 1998,
Tallahassee, FL, p. 49-61.

Rupert, F.R., and Spencer, S.M., 1988, Geology of
Wakulla County, Florida: Florida Geological
Survey Bulletin 60, 46 p.

and Arthur, J., 1997, Geology and
geomorphology: in, Coultas, C.L. and Hseih, Y.,
(eds.), 1997, Ecology and management of Tidal
Marshes, a model from the Gulf of Mexico: Delray
beach, St. Lucie press, p. 35-75.

Scott, T.M., 1988, The lithostratigraphy
Hawthorn Group (Miocene) of Florida:
Geological Survey Bulletin 59, 146 p.

of the
Florida

__ 1998a (in preparation), Geomorphic map of
the state of Florida.

1998b (in preparation), Geologic map of the
state of Florida.

Sellards, E.H., 1910, A preliminary report on the
Florida phosphate deposits: Florida Geological
Survey Third Annual Report, p 17-41.

1914, Mineral industries and resources of
Florida: Florida Geological Survey 6th Annual
Report, p. 23-64.

Sellards, E.H., and Gunter, H., 1912, The water supply
of west-central and west Florida: Florida
Geological Survey 4th Annual Report, p. 139-141.

Tanner, W.F., 1960, Florida coastal classification: Gulf
Coast Association of Geological Societies
Transactions, v. 10, p. 259-266.

Vernon, R.O., 1951, Geology of Citrus and Levy
Counties, Florida: Florida Geological Survey
Bulletin 33, 256 p.

White, W.A., 1964, Physiographic map of West Florida,
in: Puri, H., and Vernon, R.O., 1964, Summary of
the geology of Florida and a guidebook to the
classic exposures: Florida Geological Survey
Special Publication 5, 225 p.

Wilder, H.J., Drake, J.A., Jones, G.B., and Geib, W.J.,
1906, Soil Survey of Leon County, Florida: U.S.
Department of Agriculture, Advance sheets-Field
Operations of the Bureau of Soils, 1905, 30 p.

Yon, J.W., Jr., 1966, Geology of Jefferson County,
Florida: Florida Geological Survey Bulletin 48,
119 p.

HYDROGEOLOGY OF THE ST. MARKS RIVER BASIN

Linda Ann Clemens, Department of Environmental Protection, Division of Water Facilities, Basin Planning &
Management, 2600 Blair Stone Road, MS 3565, Tallahassee, FL 32399-2400
Lyle Hatchett, Department of Environmental Protection, Division of Water Facilities, Basin Planning & Management,
2600 Blair Stone Road, MS 3565, Tallahassee, FL 32399-2400
Frances M. Hartnett, Department of Environmental Protection, Division of Water Facilities, Basin Planning &
Management, 2600 Blair Stone Road, MS 3565, Tallahassee, FL 32399-2400

ABSTRACT

Understanding the geologic framework of an area and the way that water moves through that
framework is fundamental to understanding water quality and biological community health issues. In the St.
Marks River Basin, four hydrostratigraphic units are present: the surficial aquifer system, the intermediate
aquifer system, the Floridan aquifer system, and the sub-Floridan confining unit. Of the three aquifer
systems, the Floridan aquifer is the major carrier of water. Water flow through the Floridan aquifer is
ultimately driven by rainfall. Water enters the aquifer through limestone outcrops, sinkholes, lakes, and the
thin, sandy soil of the Woodville Karst Plain. Water leaves the aquifer through natural discharges, including
Wakulla Springs, and through water well withdrawals. There is a strong connection between surface water
and ground water in the St. Marks River Basin.

INTRODUCTION

The St. Marks River Basin is located in the Big
Bend Region of Florida (Figure 1). The St. Marks
River is approximately 35 miles long and drains 1,161
square miles. Approximately ten percent of the basin
area is in Georgia; the remainder is in Florida.
Communities within the St. Marks River Basin include
portions of Thomasville, Georgia, and Tallahassee, St.
Marks, and Crawfordville in Florida.

In the St. Marks River Basin, there is a strong
connection between surface water and ground water.
An abundance of rainfall has shaped the landforms into
river basins and ground water flow systems which
carry this water from where it falls to the Gulf of Mexico
and the Atlantic Ocean. The flow of water within this
combined system is governed by the landforms, or
geomorphology, and by the nature of the materials
through which the water flows.

GEOMORPHOLOGY

The St. Marks River Basin traverses two
regional geomorphic districts in parts of two states.
The Florida Geological Survey is currently creating a
new geomorphic map of Florida which will maintain
continuity of geomorphic names across state borders.
In the St. Marks River Basin, Dr. Tom Scott (oral
communication) identifies two major geomorphic
regions: the Tifton Upland District, which includes the
Tifton Upland District of Georgia (Clark and Zisa, 1976)
and the Northern Highlands of Florida (Puri and
Vernon, 1964); and the Gulf Coastal Lowlands District
(Puri and Vernon, 1964). The boundary between the
two geomorphic regions is the Cody Scarp, a
prominent and extensive east-west trending paleo
wave-cut escarpment (Rupert and Spencer, 1988).
Displaying up to 150 feet of elevation change in a miles

distance (Lane and Rupert, 1996), the Cody Scarp
separates a marine terrace below the scarp (the Gulf
Coastal Lowlands) from the deltaic deposits of the
Tifton Uplands above the Scarp. Figure 2 shows the
geomorphic regions and sub-regions in the St. Marks
River Basin.

Tifton Upland District

In the St. Marks River Basin, the Tifton Upland
District extends from approximately the Cody Scarp
northward and comprises the whole northern section of
the St. Marks River Basin. Only one geomorphic sub-
zone is found in the Tifton Uplands of the St. Marks
River Basin:

The Tallahassee Hills subzone consists of a
series of topographic highlands extending northward
from approximately the Cody Scarp into south Georgia,
where it is known as the Red Hills (after Rupert, 1991).
In the St. Marks River Basin, the tallest of the
Tallahassee Hills is approximately 260 feet above
mean sea level (msl). The area was once a deltaic
plain and is composed of sands, silts, clays, and
gravels eroded from the Appalachian Mountains and
carried by rivers to the Gulf of Mexico (Hendry and
Sproul, 1966). Erosion of this plain has left a series of
gently rolling hills with relief of up to 120 feet.

Gulf Coastal Lowlands District

The Gulf Coastal Lowlands District,
characterized by generally flat, sandy terrain, extends
from the coast inland to the Cody Scarp. Elevation
ranges from near sea level to approximately 100 feet
above msl. In this area, the deltaic sediments which
make up the Tallahassee Hills were removed by
erosion during former high sea level stands.
Geomorphic sub-zones include:

Ch[odroee~ver

REGIONAL AREA MAP OF THE

ST. MARKS RIVER BASIN

( FIGURE 1)

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00000 O000 OOOOOOQOOOOOQOOOOOC

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oI II II I II I "I I II I I I
I i I I I 1

M DOUG HERTy PLAIN DL STRICT
E TIFTON UPLAND DISTRICT
- APALACHICOLA COASTAL LOWLANDS
SWOODVILLEKARSTPLAIN

REGIONAL GEOMORPHOLOGY

OF THE

ST. MARKS RIVER BASIN

(FIGURE 2 )

The Appalachicola Coastal Lowlands are characterized
by flat, sandy surfaces marked with shallow "bays"
(densely-wooded, swamp-like areas)
and poorly-defined creeks (Hendry and Sproul, 1966).
The water table is generally close to the land surface
and during the rainy season much of the area is
swampy.

The Woodville Karst Plain is characterized by
elevations of less than 35 feet msl, gentle slopes, and
thin, sandy soils lying directly upon a limestone
surface. Naturally acidic ground water has dissolved
the limestone at or near the land surface into the many
karst or solution features that distinguish this area.
Sinkholes, springs, caves, and disappearing rivers are
all present in the Woodville Karst Plain. In some
areas, crests of relict sand dunes rise to 20 feet above
the surrounding land. In the Woodville Karst Plain, rain
which falls on the land surface tends to soak directly
into the ground or to drain into shallow depressions in
the land surface.

HYDROSTRATIGRAPHY

Three aquifer systems, or water bearing units,
are present in the St. Marks River Basin: the surficial
aquifer system, the intermediate aquifer system, and
the Floridan aquifer system. These aquifer systems,
and the rock formations in which they occur, are shown
on Figure 3. The surficial aquifer system and
intermediate system aquifers are present mainly in the
Tallahassee Hills physiographic region. The Floridan
aquifer system is present within the entire St. Marks
River Basin. The sub-Floridan confining unit underlies
the Floridan aquifer.

Surficial Aquifer System

The surficial aquifer system is predominantly
found in the unconsolidated sands and gravels near
the land surface in the Tallahassee Hills. Isolated
surficial aquifer zones may also occur in the northern
portions of the Gulf Coastal Lowlands. The surficial
aquifer system is generally less than 50 feet thick and
produces only limited amounts of water. Before the
widespread use of modern drilling methods, the
surficial aquifer was often tapped by hand-dug wells,
and used for domestic and farm supply. Water within
the surficial aquifer system occurs under unconfined or
water-table conditions. Rainfall directly recharges the
surficial aquifer system and the water table fluctuates
according to the amount of rainfall.

Intermediate Aquifer System

The intermediate aquifer system exists as a
group of interlayered clayey sediments, dolostones,
and limestone formations, which retard the movement
of water between the Floridan aquifer system below
and the surficial aquifer system above. Discontinuous
water-bearing zones occur within the coarser
sediments and carbonate beds. In the Tallahassee

Hills, the intermediate aquifer system ranges from
about 50 feet to over 150 feet thick. Water reaches the
intermediate aquifer system by leakage from the
surficial aquifer system and from sinkhole-drained
lakes. Water leaves the intermediate aquifer system
through downward leakage to the Floridan aquifer
system, through baseflow to streams, through ground
water flow to sinkholes, and through limited use for
domestic water supply.

Floridan Aquifer System

The major carrier of water in the St. Marks
River Basin is the Floridan aquifer system, one of the
world's most prolific aquifers. The Floridan aquifer
system occurs in the thick sequence of carbonate
rocks deposited on the Florida Platform and also in
parts of Alabama, Georgia, and South Carolina during
Paleocene through Middle Miocene time. The aquifer
thickens from about 100 feet in south Georgia to over
2,000 feet in southern Wakulla County (Pratt, et al.
1996).

In the St. Marks River Basin, the Floridan
aquifer system is comprised of a series of clean,
porous, and permeable fossiliferous limestones and
dolomites: the Chattahoochee or St. Marks
Formations; the Suwannee Limestone; the Ocala
Limestone Group; the undifferentiated Claiborne
Group; and the hydraulically connected portion of the
Wilcox Group (Pratt, et al. 1996). The base of the
Floridan aquifer system, the sub-Floridan confining
unit, is formed by low permeability sediments, which
prevent the downward movement of water.

The Floridan aquifer system is generally an
excellent transmitter of water, allowing huge amounts
of water to flow through it. Transmissivities in the
Floridan aquifer system in the St. Marks River Basin
range from as low as 5,000 feet squared per day in a
small area near the coast to over 125,000 feet
squared per day in the highest zones (Pratt, et al.
1996). Sever (1966) indicates that similar high
transmissivity values were found in tests at the
Thomasville, Georgia municipal well field.
Transmissivity, the capacity of an aquifer to transmit
water, is a function of the total thickness of the aquifer
and the permeability of the rocks which comprise it.

GROUNDWATER FLOW WITHIN THE ST. MARKS
RIVER BASIN

Water moves downward from the surficial
aquifer system or the land surface where the
Intermediate system is absent, thin, or as in Leon
County, breached by sinkholes. This movement of
naturally acidic rain and surface water has allowed the
limestone within the Floridan aquifer system to
dissolve, creating a very permeable, cavernous aquifer
with rapid and dynamic movement of groundwater.
Water within the Floridan aquifer system in the St.
Marks River Basin generally flows from north to south.

NORTH SOUTH STRATIGRAPHIC SECTION FOR THE ST, MARKS RIVER BASIN

SOUTH GEORGIA BASIN AREA

PANHANDLE FLORDA BASIN AREA

TMSERIES AGE MY GI LHOLOGIC DESCRIION DS S | O L -IOLOGIC DESCRIPTION HR
i_ sAicn urA iUz. UNiT i GRA____UNIT

HOLOCENE <10,000
YEARS

k hV

UNDIFFERENTIAED
HOLOCENE/

PLEISTOCENE
Sediment

CTRONELLE FORMATION
MKCCOSUKEE
FORMATION

Sediments compared of
undifferenlataed quartz sands, clys

These are the surfild sediments
found In sevenia locallons In he
study area,

Coss-bedded sands gavels and
clas deposited by streams and rives
Moderately sorted to poorly sorted
coarse flhi-graned, varicolored,
caye, quartz sand; and kadlnfc,

5 MY I montmarillin s.

o4A r IV

HAWTHORN GROUP
- TORREYA FORMATION

CHATTAHOOCHEE
FORMATION

A slicaclasltt unit coniting of
fine to medlum-grained, clyey sands
to sandy, silty clays, containing varying
amounts of limestone dolomite and
minor amounts of phosphate

Terriglnous and shallow water
sediments comprised of 11ts clays
and doomnte

White to Ilght.gray, coaue to fine
DLGOCENE SUWANNEE UMESIONE ained wel induratld s~sm rous
marine mnestone, contafino nodules
of clastc limestone, and chert.
36 MY
Pinkih-wh e finely crystalline, oolit,
OCALA LMESTONE folslderos lT mes one, gording down-
word into an interlayered dark-brown
EOCENE recrysalled, dolomtfi limestone,
Deltalc and marine classics; cross
CLAIBORNE GROUP bedded awndstones; cioaleous,
56MY carbon ceous, and foarllueous shale

AX ,IVm

WILCCK GROUP

Core-graned snds wilh clay
clost. Iminaled clays, and massive

5 6 MY Imicaceous s

UNDIFFERENIAIED

SURGICAL
AQUIFER
SYSiEM

INTERMEDIATE
AQUIFER
SYSTEM

FLORDAN

AQSIFER

SYSTEM

SUB-
FLORIDAN
CONFINING
UNIT

UNDIFFERENTIATED
HOOCENE /

Sedlments comprised of
undfferenlated quartz sands, clys,

cM Wandc and gOavel,
PLEISOCENE These are the surflcial sedmertls
Sediments found tn several locations n the
study area.

I E Modertely sorted to poorly soited
MICOKEE coase to fn aned, varicolored,
FORMON clay, quarlz sand; and oollntlic,
montmonrinlic soand clays
JAKSON BUFF Poor consolidated clayey quarlz
FORMATION sands and sandy sh beds

IMNIRCQASWI
FORMATION

HAWTHORN GROUP
- ORREYA FORMATION

ST1 MARKS FORMATION

Ollvegray. Sandy, highly mcro-
fossiffeous poorly consolidated
oa)carenttc marine liestone
A sllocloskfc unit consing of fine to
medium-gained, clayey sands to
silty clays; minor amounts of phosphate,
and quartz-sandy, clayey limestone.
Pale to grays-o nge fne to
med wrmalned, partly rcrystaed
sily to sandy imestones; dolomltlzed
In difflern amourri.

While to Ilghfgry, coaoe to fine
groined wel induacted fosslerous
SUWANNEE UMESONE marine nmesione, conta ng some
dolomite, with sand as a minor
component

Ught-brown, alghily glaconllo,
Ocala Lmesone fossilferous limestone, grading
downward Into a socchioldal
fine crystalline dolomite.
Fosslierous limestones; and
CLAIBORNE GROUP glaucorntc, aglaoceous
IImestones
Pale orange argllceou
WILCOX GROUP calclulte containing dolomte
gypsam. chert and glauconlne

UNDIFFERENTIATED

SURFICIAL
AQUIFER
SYSTEM

INTERMEDIATiE
QIUFER
WSYSM

FLORIDAN

AQUIFER

7I.-
,

SUB-
FLORIDAN
CONFINING
UNIT

( FIGURE 3)

PLEISTOCENE

PLOCENE

MIOCENE

PALEOCENE

CREACEOUS
AND OLDER

I :-------- I

]
S

HYDROGEOLOGY OF THE ST, MARKS RIVER BASIN

TALLAHASSEE HILLS

WOODVILLE KARST
PLAIN

GULF OF

SURFICIAL AQUIFER SYSTEM
INTERMEDIATE AQUIFER SYSTEM
FLORIDAN AQUIFER SYSTEM

%N SUB FLORIDAN CONFINING UNIT
UNDIFFERENTIATED SANDS AND CLAYS
IDEALIZED CONDUITS

( FIGURE 4 )

LL2ZJ

However, because of the well developed conduit
system within the aquifer rocks, localized flow may be
in any direction.

Inflows

To the north of the St. Marks River Basin,
water enters the Floridan aquifer system where
limestones of the aquifer are exposed at land surface
in Georgia (Davis, et al., 1989). Recharge to the
Floridan aquifer system occurs in the Tallahassee Hills
physiographic region, through minor downward
leakage from the intermediate system aquifers, or
through sinkholes (Hendry and Sproul, 1966). Large
lakes in this region have periodically drained because
of loss of water through active sinkholes. The
Woodville Karst Plain acts as another major recharge
area for the Floridan aquifer system, where the aquifer
receives rainfall through the overlying sands or from
runoff or stream flow into sinkholes (Scott, et al., 1991).

Disappearing Streams

At least four streams in the St. Marks River
Basin flow underground into sinkholes, including the
St. Marks River at Natural Bridge, Fisher Creek,
Munson Slough at Ames Sink and Lost Creek near
Crawfordville. Fisher Creek, Lost Creek, and Munson
Slough at Ames Sink all flow under ground through
sinkholes and "disappear." The St. Marks River at
Natural Bridge also goes underground, but re-
emerges, augmented by additional Floridan aquifer
system water, at St. Mark Springs.

Lakes

Many lakes are found within the study area,
ranging in size from a few acres to hundreds of acres.
Lakes in the St. Marks River Basin are either small and
deep, created by sinkholes extending into the
underlying rock, or they are large, elongated, and
shallow. The large lakes are only found in the
Tallahassee Hills and were formed by the dissolution of
large areas of limestone, either along stream valleys or
in the underlying rock in fractured areas (Hendry and
Sproul, 1966). These large lakes naturally drain
periodically, through a combination of low rainfall, high
evaporation, and flow through sinkholes in the lake
bottoms.

Lake Miccosukee is located along the Leon
and Jefferson County line in the Tallahassee Hills
province of the Tifton Upland District. A large sinkhole
in the northwestern part of the lake formerly allowed
water to drain from the lake, but the sinkhole is now
surrounded by a dam to prevent this from occurring
(Swanson, et al. 1988). Lake Lafayette, located in east
central Leon County, is another of the shallow,
sinkhole drained lakes of the Tallahassee Hills. Lake
Munson is a shallow, 255-acre impounded lake on the
south side of the City of Tallahassee (Ryan and
Hemmert, 1997). Munson Slough flows into Lake

Munson and from Lake Munson to Ames Sink, where it
goes underground into the Floridan aquifer system.

Sinkholes

Sinkholes are closed depressions found on
land surfaces underlain by limestone, formed either by
the collapse of a cave roof or by solution as
descending water enlarges a crack in limestone. If a
sinkhole is deep enough, it intercepts the water table
and fills with water, forming a pond or a lake. A
sinkhole can also form in an aquifer conduit, creating a
karstt window." The water continues to flow through
the conduit, and is briefly exposed at the land surface
through the sinkhole "window."

The St. Marks River Basin area contains
numerous sinkholes of various surface areas and
depths. Examination of aerial photos shows a linear
pattern to the arrangement of many of these sinkholes,
which may be due to fractures existing in the sub-
surface limestone units. Many ongoing studies are
attempting to show subsurface connections between
these sinks by tracing the movement of ground water
as it flows south toward the Gulf of Mexico. There are
far too many sinkholes in the study area to name
individually, but more prominent sinkhole areas or
sinkholes include: The Leon Sinks State Geological
Area (including Big Dismal Sink and many others), the
Riversinks, Cherokee Sink, Bream Fountain in
Crawfordville, and Ames Sink, which drains Lake
Munson.

Outflows

Major discharges for the Floridan aquifer
system in the St. Marks River Basin include springs
and seeps within the St. Marks and Wakulla Rivers;
Wakulla, Spring Creek, and other springs; and the
submarine springs and underwater exposures of the
limestones of the Floridan aquifer system in the Gulf of
Mexico. Water is also withdrawn from wells in various
amounts for various uses.

Springs

A spring is water that leaks from an aquifer, or
water-bearing formation, through a natural hole in the
ground. Springs are abundant in the St. Marks River
Basin. According to Rosenau, et al. (1977) six of
Florida's twenty-seven first magnitude springs, or
springs with flows greater than 100 cubic feet per
second, are located in the St. Marks River Basin. Nine
other named springs and countless unnamed smaller
springs and seeps are also found here. Table 1 shows
the names, county location, and discharges of springs
found in the St. Marks River Basin.

Table 1: Springs in the St. Marks River Basin

Name County Discharge (cfs) Comments

Horn Springs Leon 29

Natural Bridge Spring* Leon 106 see note 1

Rhodes Springs Leon 14 to 22 4 small springs

St. Marks Spring* Leon 519 avg. 1958-73

Indian Springs Wakulla 0.11

Newport Spring Wakulla 8.24

Kini Spring* Wakulla 176 see note 1

Panacea Mineral Springs Wakulla 0.11 several small springs

River Sink Spring* Wakulla 165 see note 1

Spring Creek Springs* Wakulla 2,000 see note 2

Wakulla Springs* Wakulla 390

Mc Bride Spring Wakulla **

Sally Ward Spring Wakulla **

Shepherd Spring

Wakulla

no data

WATER USE IN THE ST. MARKS RIVER BASIN

Most of the water used in the St. Marks River
Basin is derived from ground water, primarily from the
Floridan aquifer system. Water use data from 1990,
the most recent year available, is provided by US
Environmental Protection Agency (1998). A total of
39.17 million gallon per day (mgd) of water was
withdrawn for use in the St. Marks River Basin. A total

of 97.7 percent, or 38.27 mgd, was supplied by ground
water; the remaining 2.3 percent, or 0.90 mgd, is
drawn from surface water sources.

The major water use in the St. Marks River
Basin is for public water supply, comprising about 63
percent of total use. Irrigation and self supplied
domestic use follow, making up 17.5 and 15 percent of
the total use, respectively. Remaining uses

Source: Rosenau, et al., 1977
* First Magnitude Springs listed by Rosenau, et al., 1977
** Very minor flow generally combined with Wakulla Springs discharge
Note 1: These springs have been reclassified (Wilson and Skiles, 1989) as karst windows. They are now
considered to be aquifer conduits, temporarily exposed to the surface because of collapse of the conduit roof.
Although the water is exposed at the land surface, it remains within its conduit and continues its flow through
the aquifer.
Note 2: Flow at Spring Creek Springs has been measured twice: on 05/30/74 at 2,000 cfs and again on
11/01/91 at 307 cfs (Davis, 1996).

(commercial, industrial, power generation and
livestock) account for less than 5 percent of total use.

SUMMARY

Understanding the way that water moves through a
natural system is essential to understanding how that
system functions. Figure 4 provides a summary of the
hydrogeology of the St. Marls River Basin. Important
features include the following:

* In the St. Marks River Basin, there is a strong
connection between surface water and
groundwater. Springs contribute groundwater to
surface water bodies; surface water streams flow
underground to become groundwater.
* There are two distinct geomorphic districts in the
St. Marks River Basin. The Tifton Uplands District
is a deltaic plain with gently rolling hills of sands,
silts, clays and gravels in various thicknesses
covering the underlying limestone. In the Gulf
Coastal Lowlands, these plastic materials have
been removed by the erosive action of higher sea
levels and the limestone is exposed at the land
surface, or covered with a thin layer of sandy soil.
The two regions are separated by the Cody Scarp,
a wave cut escarpment, which displays an
elevation change of up to 150 feet change in
elevation in a mile's distance (Lane and Rupert,
1996).
* Four hydrostratigraphic units are present in the St.
Marks River Basin: the surficial aquifer system,
the intermediate aquifer system, the Floridan
aquifer system, and the sub-Floridan confining unit.
The surficial aquifer system is found primarily in
the Tifton Uplands, the intermediate aquifer system
occurs only in the Tifton Uplands, and the Floridan
aquifer system and the sub-Floridan confining unit
underlie the entire St. Marks River Basin.
* The Floridan aquifer is the main source of water
supply in the area. It is a very productive aquifer of
regional extent which supplies abundant water. It
is the source of the large springs in the St. Marks
River Basin.
* Water flows into the Floridan Aquifer through
recharge areas in southern Georgia, through
leakage from the surficial and intermediate aquifer
systems, where present, through sinkholes, and
through the thin, sandy soils of the Woodville Karst
Plain.
* Water flows out of the Floridan aquifer system
through discharge to springs and seeps, through
water well withdrawals, and through offshore
discharge to the Gulf of Mexico.

ACKNOWLEDGMENTS

We would like to thank our colleagues, Tom
Singleton, Donna Tterlikkis, Deborah Mekeel, Tom
Greenhalgh, and Richard Hicks for their review of this
document in its formative stages.

REFERENCES

Clark, W.Z., Jr., and Zisa, A.C., 1976, Physiographic
map of Georgia: Atlanta: Georgia Dept. of Nat.
Resources, scale 1:2,000,000, 1 sheet.

Davis, Hal, 1996, Hydrogeologic investigation and
simulation of ground-Water flow in the Upper
Floridan Aquifer of North-Central Florida and
Southwestern Georgia and delineation of
contributing areas for selected city of
Tallahassee, Florida Water -Supply Wells, US
Geological Survey Water Resources
Investigations Report 95-4296, 56 p.

Davis, K.R., Donahu, J.C., Hutcheson, R.H., and
Waldrop, D.L., 1989, Most significant ground-
water recharge areas of Georgia: Georgia
Geologic Survey Hydrologic Atlas 16.

Hendry, C.W., and Sproul, C.R., 1966, Geology and
ground-water resources of Leon County, Florida:
Florida Geological Survey Bulletin No. 47, 174 p.

Lane, E. and Rupert, F.R., 1996, Earth systems: The
foundation of Florida's ecosystems: Florida
Geological Survey Poster.

Pratt, T.R., Richards, C.J., Milla, K.A., Wagner, J.R.,
Johnson, J.L., and Curry, R.J. 1996,
Hydrogeology of the Northwest Florida Water
Management District: Northwest Florida Water
Management District, Special Report 96-4.

Puri, H.S., and Vernon, R.O., 1964, Summary of the
geology of Florida and a guidebook to the classic
exposures, Revised 1964, Florida Bureau of
Geology Special Publication No. 5, 312 p.

Rosenau, J.C., Faulkner, G.L., Hendry, Jr., C.W., and
Hull, R.W., 1977, Springs of Florida: Florida
Bureau of Geology Bulletin No. 31 (revised), 198
P.

Rupert, F.R., 1991, The geomorphology and geology
of Liberty County, Florida: Florida Geological
Survey Open File Report Number 43, 9 p.

Rupert, F.R., 1988, The geology of Wakulla Springs:
Florida Geological Survey Open File Report No.
22, 18 p.

Rupert, F.R., and Spencer, S.M., 1988, Geology of
Wakulla County, Florida: Florida Geological
Survey Bulletin No. 60, 46 p.

Ryan, P.L., and Hemmert, E., 1997, St. Marks River
watershed surface water improvement and
management plan: Northwest Florida Water
Management District Program Development
Series 97-1.

Scott, T.M., Lloyd, J.M., and Maddox, G.L., (eds.),
1991, Florida's ground water quality monitoring
program, hydrogeological framework: Florida
Geological Survey Publication No. 32, 97 p.

Sever, C.W., 1966, Reconnaissance of the ground
water and geology of Thomas County, Georgia:
United States Geological Survey Information
Circular 34.

Swanson, H.R., Hatim, A., Greene, T.A., Hodges,
S.M., Kebart, K.K., Lewis, R., McWilliams, K.,
and Ross, W.S., 1988, Environmentally sensitive
areas of Leon County, Florida: Leon County
Department of Public Works, Tallahassee,
Florida.

US Environmental Protection Agency, 1998, Surf your
watershed, Apalachee Bay-St. Marks,
http://www.epa.gov/surf/HUCS/hucinfo/03120001.

Wilson, W.L., and Skiles, W.C., 1989, "Partial
reclassification of first-magnitude Springs in
Florida": in The Proceedings of the 3rd
Multidsciplinary Conference on Sinkholes and the
Environmental Impacts of Karst: St. Petersburg,
Florida, October 4 7, 1989.

REGIONAL HYDROLOGY OF THE UPPER FLORIDAN AQUIFER OF NORTH-
CENTRAL FLORIDA AND SOUTHWESTERN GEORGIA

James H. Davis, United States Geological Survey, 227 N. Bronough Street, Suite 3015, Tallahassee, FL 32301

ABSTRACT

Within north-central Florida and southwestern Georgia (referred to as the study area) the Upper
Floridan aquifer includes all or parts of the Oldsmar Formation, Avon Park Formation, Ocala Limestone,
Suwannee Limestone, St. Marks Formation, and Chattahoochee Formation. The altitude of the top of the
Upper Floridan aquifer ranges from about 200 ft above sea level in the Dougherty Plain to greater than 400
ft below sea level in parts of the Apalachicola Delta District and Tifton Uplands. The altitude of the base of
the aquifer ranges from 100 ft above sea level in the northern part of the study area to greater than 2,200 ft
below sea level in the south. The aquifer thickens from about 100 ft in the north to greater than 2,000 ft in
the southwest.
The ultimate source of recharge to the Upper Floridan aquifer is precipitation. Recharge rates are
relatively high in the karst areas because the aquifer is exposed at land surface or covered only by a thin
veneer of sediments. Precipitation falling in these areas can rapidly infiltrate through the overlying
sediments or directly enter the aquifer through sinkholes and sumps. Outside the karst areas, the aquifer is
overlain by low-permeability sediments. Recharge rates in these areas are less than in the karst areas
because the low-permeability sediments cause a large proportion of precipitation to become overland runoff
to streams.
In areas where the overlying low-permeability sediments confine the Upper Floridan aquifer, the rate
of recharge (leakage downward) is dependent on: (1) the difference in head between the water table and
the potentiometric surface of the Upper Floridan aquifer, and (2) the thickness and vertical hydraulic
conductivity of the low-permeability sediments. In the Barwick Arch area (a subsurface feature located in
extreme southern Georgia), the Upper Floridan aquifer is unconfined but overlain by low-permeability
sediments. Here, the rate of leakage is not dependent on the head in the Upper Floridan aquifer so
fluctuations in the Upper Floridan aquifer water levels do not effect the rate of recharge through the
overlying sediments. The base of the Upper Floridan aquifer is formed by low-permeability marine
sediments that are at least two orders of magnitude lower in hydraulic conductivity than sediments of the
Upper Floridan aquifer.
The transmissivity of the Upper Floridan aquifer varies greatly, ranging from 1,300 ft2/d to 1,300,000
ft2/d. The highest transmissivity values generally occur within the karst areas of the Dougherty Plain, the
Ocala Uplift, and the Tifton Uplands where the overlying low-permeability sediments are thinnest or absent.
The lowest transmissivity values occur within the Apalachicola Embayment Gulf Trough where the
overlying low-permeability sediments are thickest.
Discharge of ground water from the Upper Floridan aquifer occurs as spring flow, seepage into
rivers and the Gulf of Mexico, and withdrawals from wells. Rivers within the karst areas are hydraulically
connected to the Upper Floridan aquifer, but rivers (or reaches of rivers) not in the karst areas are generally
separated from the aquifer by low-permeability sediments. Major springs draining the Upper Floridan aquifer
in the study area are the Spring Creek Spring group, Wakulla Spring, St. Marks Spring group, and the
Wacissa Spring group. These four springs are among the eight largest springs in Florida. Discharges
measured on November 1, 1991, were: Spring Creek Spring group (307 ft3/s), Wakulla Spring (350 ft3/s), St.
Marks Spring group (602 ft3/s), and Wacissa Spring group (319 ft3/s). Some discharge also occurs in
smaller springs along the coast and directly from the aquifer to the Gulf of Mexico.

A BURIED KARST PLAIN ON THE NORTHEASTERN GULF OF MEXICO SHELF,
NW FLORIDA: ORIGIN AND RELATION TO ONSHORE KARST

Z.-Q. Chen, Dept. of Geology, Florida State University, Tallahassee, FL 32306
J.F. Donoghue, Dept. of Geology, Florida State University, Tallahassee, FL 32306;
R.W. Hoenstine, F.R. Rupert, S.M. Spencer, L.J. Ladner, and E. Lane, Florida Geological Survey, 903 W.
Tennessee St., Tallahassee, FL 32304;
M.K. Faught, Dept. of Anthropology, Florida State University, Tallahassee, FL 32306

ABSTRACT

More than 800 km of high-resolution seismic surveys, vibracoring, and sea-floor sediment sampling
have revealed the buried topography and geology of the offshore component of the Woodville Karst Plain
on the NW Florida coast of the Gulf of Mexico. Detailed seismic interpretation and correlation with
vibracores and boreholes have outlined the geographic distribution of the offshore karst plain, which covers
approximately 3,000 km2 of inner continental shelf, trending south-southeastward from the present day
Ochlockonee River mouth. The submarine karst plain is distinguished by high freshwater seepage rates,
extensive dissolution of the near-surface Tertiary limestones, isolated paleofluvial channels, sinkholes, and
submarine springs. Based on the array of available information it can be postulated that a significant part of
the karst plain has developed since 9,000 yr BP--a time when global climate was considerably wetter than
during the present--and that at least some of the karst was developed in a submarine setting. The
development and evolution of the karst plain both onshore and offshore was assured by a relatively stable
tectonic setting, and was predominantly controlled by climate-induced fluctuations of the regional fluvial and
groundwater systems of the coastal plain and shelf.

INTRODUCTION

General

The Florida carbonate platform has been
subject to extensive karstification due to its relatively
stable tectonic setting, large-scale limestone aquifer
systems, high precipitation rates, and numerous rivers
and springs. However, the majority of karst
investigations both in Florida and elsewhere have
been, and still are, conducted in terrestrial settings.
Most karst features, such as sinkholes, are still
believed to be the result of exclusively subaerial
exposure (Esteban and Wilson, 1993). Paleokarst
unconformities are widely considered as a sea-level
indicator (e.g., Schlanger and Silva, 1986).

Not until recently has the importance of
offshore karst processes and antecedent topography to
coastal development been fully realized. Among
others, Hine et al. (1988) documented the extremely
irregular Paleogene bedrock on the inner continental
shelf and broad coastline in an area of the northwest
Florida coast. They postulated that the antecedent
topography, a product of karstification and dissolution
processes, not only controls coastal stratigraphic
development, but also strongly influences the structure
and preservation potential of coastal bioherms.

Further south, along the Florida Gulf peninsula
coast, Evans et al. (1989) and Evans and Hine (1991)
described the extensive isolated karst depressions and
fracture-controlled elongated limestone troughs within
the Charlotte Harbor lagoonal and estuarine system.
They linked the karst effects imprinted upon the early-
to middle Pleistocene seismic unconformities to the

repeated sea-level fluctuations and coastal migrations
that have recurred in southwest Florida throughout
Quaternary time.

Using seismic and side-scan sonar imagery
techniques, Land et al. (1995) provided a
hydrogeologic mechanism for the formation of offshore
sinkholes. They argued that sinkhole and other karst
features may not reflect exclusively a subaerial
exposure condition. Rather, they may be an indicator
of the pattern and intensity of ground-water circulation
beneath continental margins.

Faught and Donoghue (1997) described the
discontinuous nature of the offshore karst drainage
system on the northeastern Gulf of Mexico inner
continental shelf off northwest Florida. They linked the
karstification process to complex groundwater flow,
which directly or indirectly discharges through the
seafloor of the continental shelf and outer margin at
places where coastal aquifers crop out on the sea
floor. Interestingly, these outcrops, identified as
offshore karst depressions and paleofluvial features,
are often the ideal spot for conducting underwater
geoarchaeological research, and hunting for
Paleoindian and Early to Middle Archaic artifacts.

Hypotheses

In this study, the following hypotheses were
tested. The first is that the terrestrial Woodville Karst
Plain has an offshore equivalent. Its existence is not
obvious, due to burial beneath Quaternary sediments,
but shallow seismic profiling can be used to delineate
its extent. A second hypothesis involves the general
belief that the karst plain was a product of the long-

term Quaternary sea-level and coastal environmental
change (Lane, 1986). However, the observations
made in this study imply another possibility: the onset
of the major part of the karst may not have occurred
until approximately 10,000-9,000 yr BP, when global
climate finally entered a pluvial post-glacial stage
(Jacobson et al., 1987), with precipitation in the
southeastern U.S. reaching levels 30% greater than
during the present day (Kutzbach, 1987; Kutzbach et
al., 1998). A final hypothesis involves the prevalent
belief in traditional karst investigations that, because
the meteoric water of continental interiors is the
primary agent of dissolution (e.g., Palmer, 1990),
subaerial exposure is considered to be necessary for
karst development (Esteban and Wilson, 1993). Based
on the evidence from this study and others'
observations, it is reasonable to hypothesize that karst
features and especially the aligned sinkholes and
depressions in the offshore submarine environment
may be related to subaqueous karst processes. In this
view karst development is carried out mainly by
groundwater seepage through the shelf seafloor along
structural or tectonic zones of high permeability, such
as regional joint systems, aided by the migration of
coastal fluvial systems along the shoreline, and by the
advance and retreat of coastal fluvial systems back
and forth across the shelf.

Study Area

As part of an interdisciplinary cooperative
program between Florida State University and the
Florida Geological Survey, we examined the
distribution, stratigraphy and topography of the
subsurface karst features on the upper continental
shelf of the northwest Florida coast of the Gulf of
Mexico. Included in the investigation were seismic
profiles, vibracores and sediment sampling. The
purpose of this investigation was to document the
stratigraphic expression of the shallow karst structure,
to examine the role that karst development has played
in the hydrogeologic evolution of this portion of the
continental shelf, and to determine what these features
can reveal about sedimentary processes and
paleoclimatologic and paleohydrogeologic changes
that have occurred within the region. Figure 1 shows
the study area and the grid of seismic lines generated
in this study. An additional goal of the work was to
provide a framework for re-evaluating the role that the
karst-influenced offshore groundwater flow has played
in water balance and budget calculations for nutrients
and dissolved constituents -- such as 222Rn and CH4,
to the Gulf of Mexico and the world ocean.

Background Geology

Rupert (this volume) describes in detail the
background geology of the study area. Rupert and
Spencer (1988) and Rupert (1993) detailed the
geomorphology, stratigraphy, and hydrogeology of the
Woodville Karst Plain. They documented a number of
karst features, such as karst springs, sinks, dissolution

depressions, natural bridges, and subaqueous
conduits. They described the complex regional
hydrogeologic processes that participate in the regional
karst drainage system. The Woodville Karst Plain--
whose offshore extension is the subject of this study--
has an area of approximately 1,000 km2 (Lane, 1986).
However, when combined with its offshore counterpart,
its total area exceeds 4,000 km2.

Rate of Freshwater Seepage Through the Shelf
Seafloor

Groundwater is believed to be an important
source of nutrients and other dissolved constituents to
the coastal marine and continental shelf environments,
particularly when the concentrations of these dissolved
components are elevated in groundwater relative to
seawater (Johnannes,1980). Furthermore, changes in
quality (e.g., the nutrient and pollutant load) and
quantity of groundwater transport may have a
significant influence on coastal water ecology and
human activity (Snyder et al., 1995). For instance, the
groundwater seepage through nearshore sediments
into Great South Bay, New York, is estimated to be as
much as 15-20% of the total freshwater discharge to
the Bay (Bokuniewicz, 1980). Moore (1996) found a
similar result for the coastline of the Atlantic Bight:
groundwater seepage through the seafloor was
equivalent to approximately 40% of freshwater riverine
input.

Similar to the Snyder et al. (1995) study on the
nutrient-rich margins of the North Carolina continental
shelf, Young et al. (1995) and Cable et al. (1996)
attempted to quantify the coastal groundwater seepage
on the NW Florida Gulf coast. Young and colleagues
utilized the trace gas 222Rn to construct a
conservative, advection/diffusion model, cross-checked
by the qualitative groundwater tracer, methane (CH4).
The 222Rn sources in this system include benthic
sediment-water exchange, water column production of
226Ra, and groundwater seepage. The sinks include
radon decay and atmospheric exchange. Cable et al.
(1996) measured the concentrations of the trace gases
(222Rn and CH4) and thus calculated freshwater
discharge rates to coastal waters. By comparing with
average sea water 222Rn concentration in the offshore
area (less than 10 dpm m-2 d-1 disintegrationss per
minute per square meter per day)), and locating and
quantifying sources of freshwater seepage, they
discovered that, compared with the diffusion rate
through the seafloor (178 + 56 dpm m-2 d-1), other
sources, such as direct injection via submarine spring
flow (5,200+1,800 dpm m-2 d-1) play a more
significant role in groundwater discharge to the coastal
ocean. Their data confirmed a long-held belief that
dissolution of carbonate bedrock in the coastal zone,
shelf, and even continental margin (e.g., Land et al.,
1995), may create direct groundwater conduits for

supporting offshore freshwater seepage and spring
flow.

Using similar techniques, Cable et al. (1997)
determined the magnitude and variations of
groundwater seepage along the NW Florida shoreline.
They found that groundwater seepage through
sediments into the ocean in the study area occurs at a
flow rate up to 4.4 m3 sec-1. They further determined
that the main control on temporal variations of
groundwater flow in the region is precipitation, not tidal
height nor barometric pressure, because recharge is
governed largely by precipitation levels and the size of
the recharge area. Employing Cable et al's (1997) mid-
range measured seepage rate, Faught and Donoghue
(1997) calculated that the inner shelf seafloor of Florida
discharges freshwater at a rate of more than 64,000
cfs (or 1,812 m3 sec-1), nearly equal to the combined
flow of Florida's 20 largest rivers.

Rate of Carbonate Platform Surface Degradation

The lowering of the land surface on a regional
scale is thought to be inherent in the formation of karst
terrain. Regional land surface lowering is the
cumulative effects of local karst processes. Since
Sellards' (1909) attempt, many investigations have
sought to calculate the lowering rate or the surficiall
degradation rate". The rate calculated varies widely,
ranging from 2 to 10 cm/1,000 yr in Florida, depending
on carbonate rock properties and hydrogeologic
processes (Lane, 1986). In his study of the structural
geology and hydrologic features on the Woodville Karst
Plain and adjacent areas, Fennell (1969) reported
surface-lowering rates of 1.3 cm/1,000 yr (in Rainbow
Springs), 2.1 cm/1,000 yr (in Itchetuknee Springs) and
3.5 cm/1,000 yr (in Silver Springs). However, another
study of the same three sites showed somewhat larger
surface-lowering rates of 2.0, 3.1 and 5.3 cm/1,000 yr
respectively (Lane, 1986). Other reported estimates of
surface-lowering rates by karst processes in Florida
include 3.0-5.2 cm/1,000 yr in the Suwannee river
drainage basin (Brooks, 1967), and 17.8 cm/1,000 yr
in Tampa (Sinclair, 1982)

Based on the occurrence of marine fossils of
Pleistocene age in the high (42-49 m) terrace deposits
of the northern Florida peninsula, Opdyke et al. (1984)
postulated a lowering rate of approximately 1 m in
38,000 yr, or 2.6 cm/1,000 yr. They calculated an
isostatic uplift rate of 1 m per 41,000 yr, or 2.4
cm/1,000 yr, due to compensation at depth for the
removed mass of carbonate rock. They argued that
the northern Florida peninsula was at or near sea level
during the deposition of Miocene and Pliocene
sediments, and that karst development began during
the late Miocene and fluctuated during the Pleistocene
as global glaciation intensified. The elevated marine
terraces that contain Pleistocene marine fossils were
attributed to compensating isostatic uplift of the
carbonate platform by approximately 40 meters in

response to karstification and the resultant dissolution
of the carbonate bedrock.

Recent studies (Wilson et al., 1987; Wilson
and Beck, 1992; Wilson and Shock, 1996, among
others) have indicated that previous estimates of the
intensity and frequency of karst activities in Florida are
probably conservative. This would imply that karst
processes exert a much stronger influence on the
Florida platform's hydrology and geology -- both
onshore and offshore. Thus the inner continental shelf
-- the drowned lower portions of the coastal plain -- has
been heavily influenced by karst processes during
Quaternary time.

METHODS

Approximately 800 km of high-resolution
seismic survey lines were collected in a multi-year
survey on the inner shelf of northwest Florida, from
East Bay eastward to a longitude of 83055' (Figure 1).
Seismic data were acquired primarily with a Geopulse
3.5 KHz high-resolution sub-bottom profiling system.
Some lines were also profiled using a Uniboom
system. A velocity of 1500 m/s, calibrated by
correlation with borehole records (Schnable and
Goodell, 1968; Schmidt, 1984; Donoghue, 1992), was
used to convert acoustic travel time to sediment depth.
The seismic data were analyzed using the methods of
Vail et al. (1977) and Donoghue (1992).

Taking advantage of long and continuous
seismic track lines enabled identification of prominent
reflectors by continuously tracking similar seismic
patterns throughout most of the profiles. Navigational
fixes were obtained approximately every five minutes,
and at all course changes. Navigation utilized a GPS
system or, in estuaries, fixed reference points such as
channel. Subbottom lithologic control of the seismic
data was established using borehole records and
vibracores from Schnable(1966), Donoghue (1992),
and Chen et al. (1996; 1998). Cores were logged and
described using standard methods (Chen, unpub. data;
Ladner et al., 1995, 1996, and 1997).

RESULTS

A typical subbottom seismic profile of the near-
surface offshore karst plain is shown in Figure 2. All of
the seismic profiles from the offshore extension of the
karst plain show a first-order, distinctive, and very
irregular reflector ranging in depth from 20 to 50
milliseconds (two-way travel time), or at approximate
depths of 15 to 38 m below MSL. Deepening
westward, this seismic reflector represents the
fundamental building baseline of sedimentary
successions, namely, the surface of the offshore
extension of the Woodville Karst Plain. We interpret it
as a regional unconformity, the top of the St. Marks
Limestone of early Miocene age.

Immediately above this reflector, the seismic
expression of overlying sedimentary units is usually
characterized by a weakly reflective to reflection-free
pattern in the western part of the study area, indicating
subaerial exposure and erosion, and a rapid and
homogeneous infilling (Evans et al., 1994). In the
central area, however, the seismic expression of the
overlying units is dominated by wavy-parallel to
subparallel patterns (Figure 2), which reflects generally
a gradual sedimentation process, accompanied by
sedimentary deformation during the dissolution of the
underlying St. Marks Formation of early Miocene age.

In the western portions of the study area, west
of Turkey Point (approximately 84030'), an additional
seismic reflector is often observed, approximately 0.5-3
m above the strong and irregular reflector discussed
above. We interpret this seismic unit as being the
early Neogene -- but post-St. Marks -- sedimentary
units that are observed in boreholes in the western part
of the study area (Scott, 1992; Rupert and Spencer,
1988). Toward the east, this unit pinches out or
becomes too thin to be detectable as a discrete
seismic unit.

The paleokarst -- as well as ongoing
karstification -- can be readily observed (e.g., Figure
2). The features have a vertical relief averaging 6-9 m,
and a width ranging from 50 to 250 m. They are
densely distributed throughout the far-western
subsurface St. Marks Formation.

Figure 2 shows the active karstification in the
western portion of the study area, characterized by an
irregular upper surface and densely developed
sinkholes of 10-50 m in diameter and 3 m in average
depth. These sinkholes can be described as "buried
dissolution sinkholes" using Wilson and Shock's (1996)
classification. They form a highly irregular pattern in
the seismic profiles, and are widely distributed
throughout the region. Many other morphologies of
sinkholes can be found in the offshore sub-bottom
carbonate units as well, such as the karstt depression",
elongate karstt trough", and collapse structure in
offshore subbottom seismic records.

Figure 3 shows an isolated paleofluvial
channel or a paleokarst trough (here presented in
multiple traverses of the same buried feature -- labeled
F-3 in Figure 1), in which dissolution of the carbonate
bedrock and subsequent subsidence and perhaps
collapse of the infilling sediments can be observed.
This feature is comparable in morphology and scale to
what Wilson and Shock (1996) have observed in
subsurface radar images onshore at Champney
Sinkhole, Orange County, Florida.

Although karst processes act on both the St.
Marks Formation and the overlying younger units, the
St. Marks Formation has undergone more severe
karstification. Besides the greater age of the St.
Marks, this has occurred because the St. Marks has a

lithology more conducive to karstification. The unit is
composed of moderately indurated moldic calcilutite
and dolomite. The overlying units are composed
primarily of poorly indurated sandy/clayey calcilutite or
clayey quartz sand (Rupert and Spencer, 1988). This
explains in part why karst features are not readily
observed in the upper seismic unit. In this study,
therefore, the designation "offshore Woodville Karst
Plain" refers predominantly to the karstified inner-shelf
components of the St. Marks Formation.

Figure 4 shows the distribution of the major
geomorphologic divisions of the offshore Woodville
Karst Plain. These include: 1) the western region of
intensive karst, where the St. Marks Formation not only
lies deeply beneath the Intracoastal Formation and
recent sediments (Table 1), but also has been
karstified; 2) the central transitional region where the
St. Marks Formation is overlain by the thinning
Intracoastal Formation and/or the Quaternary
sediments; 3) the eastern karst region where the
offshore karst plain is best developed, contiguous to
the traditional onshore Woodville Karst Plain; 4) the
outcrop region where the St. Marks Formation is
exposed in many places on the seafloor, and where
the karst process is primarily influenced by the
magnitude and variation of local groundwater seepage.

DISCUSSION

Resting upon the stable foundation of the
Paleogene Florida Platform throughout the study area
(Figure 1), the St. Marks Limestone has served as a
basis for the development and evolution of the late
Cenozoic geology -- and especially the Quaternary
stratigraphy and sedimentology -- of the northeastern
Gulf shelf (Rupert and Spencer, 1988; Donoghue,
1993). With its karst-enhancing lithology and petrology,
along with changes in regional tectonics, the St. Marks
Limestone has passed through various stages of
deformation and alteration. Among the most striking
changes to affect this sedimentary unit have been
dissolution and karstification.

Age of the Offshore Karst Plain

Although the process of karstification may
have occurred as early as Early Neogene, shortly after
the formation of the St. Marks Limestone, the notable
karst features of the present day may have had a much
later origin, perhaps as late as Wisconsinian time. This
would be the case if we accept the assumption that the
dominant, strong, and irregular seismic reflector in
most of the study area (e.g., Figures 2 and 3) is the
upper surface of the St. Marks Formation, which has
experienced multiple episodes of subaerial erosion
since early Miocene time.

During the approximately 15 million years
since the St. Marks formed, it could have experienced
various events of dissolution and karstification.
However, due to weathering, the surficial karst features

of earlier times may not be evident today. It is possible,
in fact, that any pre-Wisconsinan karst may not have
survived recognizably through the lengthy periods of
subaerial weathering during the Quaternary.

There is support for the hypothesis that,
beginning in the Late Paleogene, the Mississippi River
significantly diminished its sedimentological influence
on this part of the Gulf Basin (Bouma et al., 1978;
Perlmutter, 1985). The Paleo-Apalachicola River
system (Figure 1) gradually became the major player
in refabricating and constructing the geological
environments of the northeastern Gulf coast during the
intervening time (Donoghue, 1993).

During the Wisconsinian sea-level low stand,
the Apalachicola River and the smaller coastal rivers of
the NE Gulf of Mexico region incised a dense network
of paleofluvial channels on the present-day continental
shelf (Donoghue, 1993; Faught and Donoghue, 1997).
As a result, a complex hydrologic system was
established, incorporating the paleochannel network
and paleokarst features. Along with the dramatic
change of coastal landscapes, the freshwater hydraulic
head might have dropped by as much as 80-100
meters in response to sea level change (Anderson and
Thomas, 1991). A new episode of karstification would
have begun to act upon the St. Marks Limestone,
superimposed upon older Late Neogene erosion
surfaces.

In the western region of the study area (see
Figure 4), both the St. Marks and the Intracoastal
Formations can be traced in the seismic records.
However, the lower reflector (top of St. Marks) is more
"irregular", distinctive, and broadly traceable
throughout the rest of the study area. The
Intracoastal/Torreya Formations are not present in the
eastern half of the study area, with the result that the
St. Marks Formation is the uppermost carbonate unit in
that region. It is noteworthy that the topographic relief
of the St. Marks Formation in the western region (see
Figure 4) is much greater than that in the other regions
(Figures 2-4). In the western region, the relief of the
buried karst features is generally 10 m or greater; in
the rest of the regions, the relief is approximately 3 m
or less.

The St. Marks Limestone surface in the
western region exhibits a different style of karstification
than that in the east. In the west, no dissolution
features are observed that cut through the overlying
Intracoastal Formation and reach the St. Marks
surface. The karstic rim on the limestone surface
possesses approximately the same thickness--there
are no V-shaped dissolution features or sinkholes
observed on the topographic lows or the paleofluvial
valleys on the St. Marks surface.

This evidence implies that, although there may
be multiple generations of karstification imprinted on
the St. Marks Formation, it appears that the youngest

and most distinct karst features on the St. Marks
surface were developed during relatively recent
geological time via a major hydrogeologic event. This
event not only modified the older St. Marks surface, but
also imprinted its new evidence of karstification onto
the St. Marks surface. That surface appears in high
relief in the west region of the study area, but gradually
becomes more subdued in the rest of the regions,
where the St. Marks surface has been exposed to
multiple Quaternary episodes of subaerial erosion
(Figures 2 and 3).

Regional Paleoclimatic Background

Based on a convergence of glacial lake data
(Hu et al., 1997), paleofluvial information (Leigh and
Feeney, 1995), GCM modeling (Kutzbach, 1987;
Kutzbach et al., 1998), pollen analyses (Watts, 1969,
1971, and 1975; Grimm, et al., 1993), granulometric
data (Tanner, 1992; Chen et al., 1998), and paleo-
environmental index studies (Chen et al., 1996; Chen
et al., 1998), a wetter than present-day climate (10-
30% greater precipitation) has widely been inferred for
parts of the Holocene for the southeastern United
States. This wetter climate occurred worldwide
beginning in the early Holocene (9,000-8,500 yr BP),
extending to approximately 5,500 yr BP (Leigh and
Feeney, 1995). This event corresponds to a major
change in the seasonal solar-radiation cycle, which
took place 9,000-6,000 yr BP (Kutzbach, 1987), and to
the possible final step in Wisconsinan deglaciation at
8,000-6,000 yr BP (Jacobson et al., 1987).

As a result, the onset of much of the
karstification of the Woodville Karst Plain and its
offshore counterpart may have occurred approximately
9,000 yr BP. The pluvial conditions may have
enhanced the process of karst development and the
consequent lowering of the surface. The karst-induced
surface lowering rate for the coastal plain during that
time could easily have exceeded 2.6 cm / 1,000 yr--an
average rate Opdyke et al. (1984) calculated for the
northern Florida peninsula during the past 1.5 Ma. The
rate might even have reached as high as 17.8
cm/1,000 yr--a surface lowering rate Sinclair (1982)
calculated for the present-day karst-rich Tampa area.

After the pluvial period, a dryer and perhaps
warmer climate followed (Baker et al., 1992; Webb et
al., 1993; Yu et al., 1997). The dry climate was
initiated earlier in the north and later in the south. For
instance, it began between 8,000-5,000 yr BP in
Minnesota (Webb et al., 1983; Web et al., 1993), and
5,500-3,000 yr BP in southern Ontario, eastern Iowa
and southern Wisconsin (Yu et al., 1997; Winkler et al.,
1986; Baker et al.,1992). In the southeast, a few dry
swings occurred 6,000 1,500 yr BP, with a final shift
to dryer climate beginning at approximately 1,500 yr
BP (Watts, 1971). During the dryer periods, karst
development might be expected to have slowed down
and surface subsidence rates would have been
significantly reduced.

The offshore karst features, as revealed in the
subsurface seismic data, provide some insight into the
paleoclimatic changes that have dominated the
topography of the region. Figure 3 shows the multiple
subsidence and collapse structures of infilling
sediments in a feature that appears to be a
paleofluvial-paleokarst trough or sinkhole. The
subsidence/collapse unit is highly recognizable by its
distinctive seismic reflection pattern. In detailed
examination of the unit, a number of sub-layers can be
recognized, indicating that the paleochannel or karst
trough may have gone through a number of dissolution
and subsidence stages.

A possible scenario to explain the karst
features observed in the eastern karst region of the
study area is as follows: starting with the onset of wet
conditions in the southeast approximately 9,000 yr BP,
karstification accelerated on the exposed St. Marks
surface. Most of the karst development could have
occurred during the subsequent few millenia;
thereafter, with the continuing post-glacial sea-level
rise and inundation of the karst field, infilling and
collapse commenced.

Other studies in the same offshore region have
revealed similar features of subsidence and collapse.
Donoghue et al. (1995) described Ray Hole Spring, a
sub-bottom paleosinkhole spring in the southeastern
corner of the study area (see Figure 1). According to
Donoghue et al. (1995, and unpubl. data), Ray Hole is
characterized by two asymmetric, irregularly-shaped
dissolution crevices. Each is approximately 10 m deep
below the modern seafloor and with a total diameter of
approximately 50 m. Both of the dissolution features
narrow downward, and are filled with a sedimentary
sequence from brackish (?) shell-rich sediments to
marine sands, implying a relatively rapid filling of the
karst features.

Faught and Donoghue (1997) described the
J&J Hunt paleosinkhole on the eastern border of the
study area. A string of filled or partly filled dissolution
features ranging 50 to 100 m in diameter, including the
Fitch Site and the J&J Hunt paleosink system, defines
the paleo-Aucilla River fluvial channel in an intensely
karstified zone of the NE Gulf of Mexico. These
paleokarst features are located offshore from the
modern Aucilla River mouth in the NE portion of Figure
1.

Implications of Dynamic Offshore Groundwater
Seepage

Relatively acidic freshwater dissolution has
long proven to be the most significant agent in
karstification (Brooks, 1967). As described above,
fresh and acidic groundwater seepage through the
floor of the inner shelf accounts for a significant
amount (ranging from 10 to 36%) of coastal water
budgets (Brock et al. 1982; Lane, 1986; Shaw et al.,

1990; Lee and Hollyday, 1993; Cable et al., 1996;
Cable et al., 1997).

The seismic expression of the upper contact of
the St. Marks Formation is commonly characterized by
an impressive irregular reflector. The strong seismic
reflector reveals a ragged surface that is characterized
by densely distributed buried sinkholes. Similar sub-
bottom karst features can be observed immediately
offshore from the modern Carrabelle River, a small
coastal river adjacent to the Apalachicola River system
(Figure 1). Similar extensive karst features can also be
observed in several other submarine environments.
An example is the central transitional region (Figure 4),
in which the Ochlockonee, St. Marks, Aucilla and
Econfina Rivers converge, and a number of karst
structures, such as paleochannels, submarine
sinkholes, and offshore freshwater springs are present
(Figure 1) (Donoghue et al., 1995; Faught and
Donoghue, 1997).

It is quite clear that, despite the distance
(several to several tens of kilometers) between the
present-day shoreline and these offshore sites of
heavy karst development (Figure 1), the sub-bottom
karst development at these sites appears very similar
in terms of their density and karst topography (Figures
2 and 3). This implies that the St. Marks Formation at
these sites has experienced a similar degree of
dissolution through most of late Wisconsinian and
Holocene time.

It can be observed that in the western deep-
karst region of the study area (Area I in Figure 4), the
St. Marks Limestone surface is buried to a greater
depth, and shows evidence of more robust weathering.
However, among these deeply incised, subaerial
erosional paleochannel deposits, no funnel-shaped
dissolution sinkholes nor infilled collapse structures
were found. This implies that in the far west area, the
groundwater seepage and dissolution front may move
primarily in a lateral fashion, along the heavily
weathered paleoerosional surface. Alternatively, the
dissolution front may follow a joint system or
paleofluvial network, rather than vertically percolating
through the clayey/sandy layered sediment overlying
the St. Marks Limestone surface.

The explanation for this phenomenon may lie
in the fact that the St. Marks Limestone surface in this
study area dips westward at a slope of approximately
1:1,000 (Hendry and Sproul, 1966; Cable et al., 1997),
which is steeper than that of the modern continental
shelf, and, arguably should exert a greater hydraulic
head. This perhaps was especially effective during
sea-level lowstands. Recent studies (Cable et al.,
1996; Cable et al., 1997) have clearly demonstrated
that the groundwater seepage rates at an offshore
submarine spring (Lanark Spring, approximately 10
km west of Turkey Point on Figure 1) is significantly
greater than that of the surrounding seafloor (60 vs. 20
mL m-2 min-1).

The environmental significance of this effect is
that the localized salinity at the offshore spring drops
by as much as 2 /oo (from 32 to 30 /oo), and the
nutrients and other dissolved constituents, such as
CH4 and Rn222, are elevated by several orders of
magnitude relative to the surrounding seawater (1,500
vs. 0.0 nM for CH4; and 100 vs. 0.0 dpm L-1 for
222Rn). The fresher and more nutrient-rich water at
these sites can enhance not only the chemical
dissolution of the seafloor carbonate bed, but also the
biochemical weathering process.

Fluvial Migration, Groundwater Seepage, and
Geomorphological Development

Dissolution and karstification have played a
significant role in re-fabricating the enormous (350,000
2
km ), flooded, broad, flat carbonate platform (Hine et
al., 1988), re-shaping the antecedent topography, and
controlling the distribution of subsequent sedimentation
in the northeastern Gulf of Mexico coast. It is
reasonable to hypothesize that at the initial stage, the
fluvial systems and groundwater transport systems of
NW Florida were developed along structural or tectonic
zones of preferential dissolution, such as regional joint
systems. The structural zone would subsequently
undergo mechanical, chemical and biological
weathering, forming topographic lows, where not only
the fluvial system transports and removes sediments,
but also where geochemical processes begin the
development of karst. Faught (1996), Faught and
Donoghue (1997) and Chen et al. (1998) have reported
this type of phenomenon in the paleo-Aucilla river in
the southeastern portion of this study.

We relate the isolated sinkholes and especially
the aligned sinkholes/ depressions in the offshore
submarine environment to subaqueous karst
developments, which are carried out mainly by either
groundwater seepage in zones of weakness or
dynamic intrusion of a fluvial system. It is interesting to
note the case of the modern Carrabelle River, a small
distributary stream in the Ochlockonee River
watershed. The river mouth has migrated in recent
times from west to east. The result appears to be a
consequent shift of karst development from west to
east. Similar features are observed along the modern
Ochlockonee River, where the river mouth has
undergone several stages of migration from west to
east.

This and other evidence implies that rapid
development of karstification not only has etched the
upper contact of the St. Marks into a high relief (Figure
3), but also has set the architectural framework for the
subsequent topography in the northeastern Gulf coast
and shelf. Hine et al. (1988), in an investigation
immediately east of the study area, reported the
intense karstification of what they called "marsh
archipelago" (in their Figure 5) which appears almost to

be a modern analog of the buried karst topography
observed in the western region of the present study
area. They define "marsh archipelago" as an area that
is dominated by numerous marsh islands, and has an
elevated, irregular, rocky surface, flanked by adjacent
broad "shelf embayments" or topographic lows. They
postulated that a subaerial stage plays a significant
role in the development of these karst features.

It can be inferred, however, that a subaerial
stage is not absolutely necessary for the development
of such features because there is no fundamental
difference between the "marsh archipelagoes" and the
topographic lows in terms of spring/seepage density
and local groundwater discharge systems over spatial
scales of 100's of meters, as in the study by Hine et al.
(1988). Instead, based on the present study, it can be
inferred that the migration of coastal fluvial systems
along the shoreline, the advance and retreat of coastal
fluvial systems back and forth on the shelf, and the
seepage of groundwater through the shelf floor, can
create an architecture similar to a "marsh archipelago"
and associated topographic lows on the NE Gulf shelf.

Investigations of the lower continental slope
offshore New Jersey (Robb, 1982) and of the Straits of
Florida (Jordan, 1954, 1964; Malloy and Hurley, 1970;
Land et al., 1995) have also demonstrated that karst
processes are not restricted to subaerial conditions,
and can take place over a broad range of water
depth-hundreds and even thousands of meters below
the sea level (Land et al., 1995)

Possible Mechanisms for Development of the Karst
Plain

Postulating an explanation for the occurrence
of the high elevation (42-49 m above MSL) marine
beach ridges of Pleistocene age near the border of
northern Florida and southern Georgia, Opdyke et al.
(1984) proposed an epeirogenic uplift mechanism to
explain the occurrence of the raised terraces, the karst
development of the Florida Platform, and the evolution
of the Florida Platform from Late Neogene to Holocene
time. Noting that the sedimentary wedges and any
resulting isostatic changes are present mainly on the
fringe of the Florida platform, and that there is little
tectonic influence and no significant fault displacement,
they concluded that the robust surficial or near-surficial
karst processes have removed mass at a minimum
rate of 1.2 x 106 m3 / yr. They calculated that this
mass loss may have resulted in lowering of the karst
surface by approximately 2.6 cm/1,000 yr and a
compensating epeirogenic uplift of the north Florida
Platform by approximately 2.4 cm/1,000 yr. Their
speculation pointed out a largely unpursued line of
research in this field, and quantified in a simple format
the magnitude of post-Miocene karstification in Florida.

However, the epeirogenic uplift mechanism
contrasts with other regional geophysical observations,
with the result that alternative mechanisms need to be

considered. For example, Meade (1971) contoured
crustal movement rates for the eastern United States,
and categorized the region of the northern Florida
peninsula between Pensacola and Fernandina west to
east, and between Savannah, Georgia, and Cedar
Keys north to south, as primarily a stable region
(vertical crustal movement rate of approximately 0
mm/yr). Using precise releveling and mareography
data, Holdahl and Morrison (1974) likewise found that
the northern Florida peninsula principally lies in a
stable or slightly subsiding zone at a vertical elevation
change rate of -2 to 0 mm/yr.

These geophysical observations may be a
reflection of the long-term tectonic history of this
region. The closing of the Suwannee Straits in the
Mid-Cenozoic (Chen, 1965; Schmidt, 1984; Scott,
1992) would have led to thickening of the lithosphere
due to infilling of sediments, and to cooling of the
underlying aesthenosphere (McKenzie, 1978; Royden
et al., 1980). As a consequence, this part of the
Florida Platform would undergo long-term subsidence.

These observations indicate that an
epeirogenic uplifting mechanism may not be the sole
candidate for explaining the origin of the elevated
terraces of NE Florida. Other processes may also
participate in the development and evolution of both
the onshore and offshore karst plains. As mentioned
above, post-Miocene tectonic movement in this region
has been primarily in a stable or a subsidence mode
due to the thickening of the lithosphere and cooling of
the underlying asthenosphere. This region of the Gulf
coast is marked by a low energy level and sediment
starvation, removing the likelihood of isostatic change
due to sediment loading (Tanner, 1960; Hine et al.,
1988; Donoghue and Tanner, 1992). Evidence for
reactivation of pre-Pleistocene faults is lacking
(Opdyke et al., 1984; Nunn, 1985). The influence of
glacial ice and meltwater on the Florida Platform is
relatively insignificant in comparison with more
northern regions, because the ice-induced hydro-
isostasy is generally considered to be proportional to
the proximity of deep water (Bloom, 1967). The wide,
shallow shelf of the northern Gulf of Mexico therefore
makes this factor less important.

As a consequence, we postulate that the
coastal and offshore groundwater system and the
coastal river systems in this area (Figure 1) have been
the primary agents controlling the development and
evolution of both the onshore and offshore Woodville
Karst Plain. In particular the potentially high rate of
groundwater flux to the shelf--via springs and seepage-
-may have played a major role in development of the
regional karst. This would be especially true during
wet periods, such as the mid-Holocene, when seepage
rates might be expected to have been even greater
than at present.

SUMMARY

One can observe the relentless processes of
dissolution and karstification over a broad
geographical range of both onshore and offshore
environments in the northeastern Gulf coast of
northwest Florida. By tracing the seismic sequence
boundary of the top of the St. Marks Formation, the
areal extent of the offshore Woodville Karst Plain--
more than 3,000 km2 -- can be delineated on the inner
Gulf of Mexico shelf.

Based on the array of available information it
can be postulated that the onset of a significant part of
the Woodville Karst Plain may have occurred
approximately 9,000 yr BP, a time when global climate
was considerably wetter than today. The development
and evolution of the karst plain both onshore and
offshore were assured by a relatively stable tectonic
setting, and predominantly controlled by the temporal-
spatial variations of the fluvial system on the coastal
plain and shelf. The geographic distribution and
volumetric quantity of the groundwater seepage to this
part of Gulf probably have been significantly
underestimated previously, because prior to this study
there was no systematic documentation of the
geomorphology, sub-bottom stratigraphy, and spatial
variation of the sub-bottom karst in this offshore region.
Based on the sub-bottom features, submarine
environments, and geographic extent of the offshore
karst features, four geomorphologic regions of the
offshore karst plain have been established.

It appears that the older subaerial erosion
surface--the upper contact of the St. Marks Formation--
may have served as a surface conduit for groundwater
seepage. This may be especially true in the western
region of the study area where the St. Marks
Limestone surface is characterized by high relief (10 m
and greater). Paleofluvial systems often co-exist with
the present-day springs or sinkholes or karst troughs
both onshore and offshore, implying a similar
controlling influence on the development of such
features. The development of the Woodville Karst Plain
-- both onshore and offshore -- appears to have been
closely associated with regional structural geology,
sea-level fluctuation, climatic change, and the
magnitude and variations of groundwater seepage.

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Figure 1. Study area in NE Gulf of Mexico off northwest Florida. Inset map
shows location in NW Florida. Offshore grid of high-resolution seismic lines is
shown. The solid bars on the seismic survey lines labeled "F-" denote the location
of the subbottom profiles shown in the corresponding figures.

__ __ :
_I __ '. -

Figure 2. Seismic profile of karst features in the central transitional region of the
study area. Relief on the upper surface of the St. Marks Formation is 3-5 m. See
Figure 1 for location of the profile.

0)q"a

gJ
~B;e`
r

Sry~~w

Figure 4. Extent of the four major geomorphologic divisions of the offshore
extension of the Woodville Karst Plain. I. Western intensive karst region. II.
Central transitional region. III. Eastern karst region. IV. Outcrop region. See
text for explanation.

0R-
ft

FA

2 =~
E

o 46
ar if 9

II

5 .

ST. MARKS RIVER BASIN:
WATER RESOURCE VULNERABILITY

Tom Singleton, Department of Environmental Protection, Division of Water Facilities, Basin Planning &
Management, 2600 Blair Stone Road, MS 3565, Tallahassee, FL 32399-2400

ABSTRACT

Three maps were developed using Geographic Information Systems (GIS), to evaluate water
resource vulnerability in the St. Marks River Basin.
Surface water vulnerability This map was created by combining four different factors: distance
weighted vicinity to major wetlands and water bodies, soil runoff characteristics, soil composition, and slope.
The most vulnerable areas of the St. Marks River Basin are: the areas above the Cody Scarp, where most
water flow is in streams and wetlands on the land surface, and in the coastal regions immediately adjacent
to Apalachee Bay. Individual sinkholes and ponds are areas of vulnerability, as are the courses of the St.
Marks and Wakulla Rivers. The area with the lowest vulnerability to surface water problems is a large area
in the center of the basin. This marks the area of karst development in the Woodville Karst Plain where
there is no surface water flow. Rainfall directly infiltrates into the groundwater.
Ground water vulnerability This map was created by combining two factors: soil runoff
characteristics and underlying geology. Areas with differing degrees of vulnerability coincide fairly well with
the geomorphic provinces of the region. The area where ground water is most vulnerable is the Woodville
Karst Plain, followed by the Gulf Coastal Lowlands. The least vulnerable area is above the Cody Scarp, in
the Tallahassee Hills.
Combined surface water and ground water vulnerability This map was created by combining the
surface water and groundwater vulnerability maps. The areas with the highest vulnerability are at the coast,
along the surface water drainage systems, and at the lakes and sinkholes scattered throughout the basin.
The Woodville Karst Plain is highly vulnerable to groundwater contamination. A large area of the
Tallahassee Hills, including the Lake Lafayette Drainage Basin, is the next most vulnerable. The Gulf
Coastal Lowlands, roughly the western one third of the basin, is the least vulnerable area.
The maps are standardized on a scale from 0 to 10 to indicate relative water resource vulnerability.
Darker colors indicate areas with a higher vulnerability. It should not be construed that areas with higher
vulnerability should never be developed. Special design criteria must be developed for these areas to
insure that impacts are minimized. Similarly, areas with lower vulnerability should not be construed to be
suitable for all types of development. The maps suggest that with prudent use, impacts to ground water and
surface water should be minimal.
In the St. Marks River Basin, only the movement of water is constant. Where and how the water
moves and what it carries with it changes with the form and nature of the land, soils, and rock. When
surface water and ground water vulnerabilities are placed on a map, the wise and unwise use of water
resources can be identified.

DETERMINATION OF GROUNDWATER FLOW PATTERNS FROM CAVE
EXPLORATION IN THE WOODVILLE KARST PLAIN, FLORIDA

Christopher Werner, Woodville Karst Plain Project

ABSTRACT

The Woodville Karst Plain (WKP), located in the panhandle of Northern Florida, is characterized by a
layer of unconsolidated sediments 3-20 m thick, predominantly sands, with shell and clay, overlying an
extensive sequence of carbonate deposits, 150-600 m thick. The surface of this area is distinguished by
the presence of numerous sinkholes, karst windows, sinking streams, and large springs. There are over 42
km of surveyed underwater cave passages present in several large systems within the WKP. These include
Indian Spring, Sally Ward Spring, Wakulla Springs, Shepherd Spring and the Leon Sinks Cave System.
Several physical controls are observed to operate, with varying degree, in cave passage development,
including lithology, stratigraphy, regional and local groundwater flow patterns, and water table elevation
directly influenced by sea-level fluctuations. These parameters are considered in the context of cave-
system development presently charted in the WKP. Regional groundwater flow extends from southern
Georgia through the WKP and south to the Gulf of Mexico. The orientations of cave passages within the
WKP suggest a nearly parallel alignment with regional flow. Current drainage patterns primarily transport
groundwater south through these conduits toward the Gulf. However, notable exceptions to this trend occur
within Wakulla Spring cave and Indian Spring cave. Geomorphic features, cave passage orientation,
current branchwork drainage patterns and flow directions suggest paleoflow directions during conduit
formation in the above mentioned caves were most likely in contrast to present day observations.

REGIONAL GEOLOGY AND HYDROLOGY

The exploration and survey of underwater
cave systems south of Tallahassee by the Woodville
Karst Plain Project (WKPP) has significantly
improved the ability of hydrologists to understand the
complexity of groundwater flow in a multiple-porosity
medium such as the carbonates of the WKP. The
improvement in understanding has been hampered in
the past by the lack of qualified scientists to visit the
remote and hostile environment of deep underwater
caves. There is no substitute for detailed
observations in improving the quality and quantity of
information needed to advance scientific
understanding within this multifaceted system of fluid
flow.

While the recent observations are an
important glimpse into the groundwater flow regime, it
should be noted that they represent a significantly
limited data set. The small size of the data set and
its relation to the regional groundwater flow pattern
may be restricted, but this does not mean that it is
insignificant. Reasonable assumptions may be
made, such that a greater overall understanding of
the evolution of this complex groundwater drainage
basin may emerge. This paper is an endeavor to add
accurate and thorough scientific observations to the
current body of knowledge. By using reasonable
assumptions in conjunction with detailed
observations, it is expected that significant
conclusions may be drawn which aid in the
understanding of this unique resource.

The WKP developed in Leon, Wakulla, and
Jefferson Counties, Florida, is characterized by a thin
veneer of unconsolidated and undifferentiated
Pleistocene quartz sand and shell beds, overlying a thick
sequence of relatively horizontal carbonates (Hendry
and Sproul, 1966). The WKP is a gently sloping
topographic region of low sand dunes and exposed
carbonates rising northward from the Gulf of Mexico to
approximately 20 m in elevation within Leon County,
terminating at the Cody Scarp. The loosely consolidated
Pleistocene sands, being very porous and permeable,
allow rapid infiltration of precipitation. Important to our
study, the St. Marks and Suwannee limestones,
underlying the unconsolidated sands, comprise
hydrostratigraphic units of the Upper Floridan aquifer
system (FAS). These limestones, being very porous,
permeable and soluble, have undergone considerable
dissolution from groundwater movement (Hendry and
Sproul, 1966). Consequently, the topography is karstic
in nature, with numerous sinkholes, karst windows,
sinking streams, and large springs (Rupert & Spencer,
1988).

The St. Marks is a predominately fine to
medium-fine grained, partially recrystallized, silty to
sandy limestone that has undergone degrees of
secondary dolomitization (Hendry and Sproul, 1966). It
also contains extensive shallow conduits in portions of
the Leon Sinks cave system, Chips Hole cave and
Indian Springs cave. It pinches out against the

INTRODUCTION

IOG MK --

D IHTGLE PON

SALLY VMD oPRM

0 .5 1
0 .5 1 1.5

SCALE

Figure 1. Plan view map of the western Woodville Karst Plain illustrating the Leon Sinks cave system
(comprising northernmost Sullivan sink and Big Dismal sink to southernmost Turner sink), Chips Hole cave,
Indian Springs cave, Sally Ward Spring cave, McBride's Slough Spring cave and Wakulla Springs cave
system.

Suwannee limestone in southwestern Jefferson County
and reaches a maximum thickness of approximately
60-m in western Wakulla County.

The Suwannee limestone, Oligocene in age,
reaches a maximum thickness of 160 m at
approximately 30-150 m below land surface within
Leon and Wakulla Counties (Davis, 1996). The
thickest portion of the Suwannee is found south at the
Gulf of Mexico and the thinnest is located near the
Georgia border (Hendry and Sproul, 1966). It consists
of two types of permeable rock: (1) a crystalline tan,
highly fossiliferous limestone and (2) a white to cream,
finely crystalline limestone containing foraminifer with
micritic limestone pellets (Davis, 1996). The
Suwannee limestone is the principal lithology
transporting much of the groundwater of the Upper
FAS within the WKP. The majority of dissolution
conduits within the WKP are primarily developed in the
Suwannee limestone.

The regional recharge area for WKP extends
north of the Georgia border for over 80 km and covers
portions of over five Georgia Counties (Davis, 1996).
The regional groundwater flow pattern, taken from
piezometric contour maps, shows overall south
trending flow lines (Davis, 1996; Fig. 32, Scott et al.,
1991). There is an interesting feature of the
piezometric contour maps which show a saddle or
potentiometric low area extending well into the WKP.
This indicates a convergent flow line pattern toward the
south-central region of the karst plain. In this area,
there are several first-order magnitude springs
including Wakulla Springs, St. Marks Springs and
Spring Creek Springs. The regional convergence of
flow is thought to originate from the fact that the WKP
confining unit is absent. Thus, flow through Leon
County, being confined by the Miccosukee and
Hawthorn Formations, converges in the WKP, where
the lack of confining units allows groundwater transport
to result in artesian flow at the surface.

We will turn our attention to the south-central
region within the WKP. Within this region, where the
majority of springs discharge and the majority of caves
have been explored, there are several interesting
features. The first is the numerous sinkholes. These
depressions are readily observed on 7% minute
quadrangles, as well as easily identifiable in the field.
As an example, the Leon Sinks cave system connects
over 25 sinkholes through multiple underground
conduits (Fig. 1).

The second is the dimensions of the conduits.
Many of the large conduits, herein referred to as
primary conduits, have interior dimensions that
typically exceed heights of 15 m and widths of 20 m.
Most are easily recognized as having a phreatic origin,
where a slight few appear to have been modified by
vadose entrenchment. These primary conduits
typically extend several kilometers in length and

transport great volumes of groundwater. There are
several smaller dimension passages, which in most
cases serve as tributaries to the larger primary
conduits. The exception is where the primary conduit
ceiling has collapsed blocking the conduit. In these
cases, of which there are many, flow has been
captured or redirected along a smaller tributary.

The third and most interesting feature is the
apparent convergence of groundwater flow lines in the
vicinity of Spring Creek. Here as many as ten springs
continually discharge groundwater into the Apalachee
Bay of the Gulf. Spring Creek appears to be the
convergence of a branchwork dendriticc) groundwater
drainage pattern (Palmer, 1991). It may include waters
from as close as newly discovered caves a few
kilometers north of Spring Creek to those of the Leon
Sinks cave system, Chip's Hole cave, and Wakulla
Springs cave.

CAVE PASSAGE ORIENTATION

Surveys and plan-view maps of the conduits,
obtained from the WKPP divers (Irvine, 1998), were
utilized to infer orientation of many of the primary
conduits. The maps clearly exhibit a roughly north-
south trendline (Fig. 1). In fact, a majority of the
primary conduits show slight deviations from the
regional hydraulic gradient. With this in mind, it is
reasonable to infer that the evolution of this drainage
basin has resulted from a nearly continues southward-
directed regional hydraulic gradient. In so much as this
hydraulic gradient has not been entirely steady, it is
reasonable to suggest that it has remained, for the
most part, in its present state for some time. It is
obvious, from glacial and interglacial records of the
Quaternary, that sea level has not been constant this
entire time, but has fluctuated significantly. Given
these fluctuations and the proximity of the WKP to the
present sea level in the Gulf, it is reasonable to
suggest that the overall drainage pattern directions
have not been significantly altered during this brief
geologic time scale.

To better visualize the cave passage
trendlines, rose diagrams were created for some of the
major cave systems (Fig 2). The compass directions
from the surveys were calculated to have an error no
greater than +4.60. Given the large error inherent in
these underwater surveys, the orientation plots
provided clearly illustrate the significant trendlines
found in most of the cave systems of the WKP.

Sinkholes constitute the most prevalent
geomorphic feature of the WKP. Sinkholes form from
the collapse of large cavernous voids within the
carbonates underlying the land surface. The
cavernous voids are the result of dissolution of the
carbonate rock by chemically aggressive waters.
Sinkholes form as the ceilings of these large voids

become unstable and collapse. The distribution of
sinkholes is not without patterns or trends.

To better understand the spatial distribution of
sinkholes, it is important to realize that sinkholes are
indicative of collapsed caves and/or caverns. These
void spaces are not formed in isolation from other void
spaces, but are typically formed in response to the
concentrated flow of aggressive waters. Concentrated
flow routes are generally interconnected forming the
precursor toward primary conduit formation. As
aggressive waters are concentrated, extensive
dissolution of limestone occurs initiating connections
between the void spaces. The subsequent increase in
void space and/or porosity allows the influx of larger
volumes of aggressive waters, reinforcing the
interconnected flow route. As time progresses, this
system may evolve to become a primary flow route

270 -7 --

270 -1 15 1 -in

transporting groundwater. During this evolution,
primary conduits are formed and enlarged by the
imposed hydraulic gradient and the positive feedback
loop.
As the size of the primary conduits is
systematically enlarged, many parts of the ceiling
become unstable and collapse forming a sinkhole. To
envision this, we will refer to the earlier example of the
Leon Sinks cave system (Fig. 1). Here, there have
been over 25 collapsed cave ceilings producing
sinkholes, which are all direct entrances for divers into
the cave system. The sinkholes formed in response to
enlargement of the primary conduits comprising the
cave system. These sinkholes are aligned, in most
cases, directly above primary conduits. This sinkhole
alignment provides invaluable evidence for locating
primary conduits.

10 5 -20 ----90

Figure 2. Cave passage orientations from Leon Sinks cave system (top)
and Shepherd Spring cave (bottom).

wj

I &

It

I t

Figure 3. Map of southwestern WKP at 1/300,000. Grey dots are sinkholes, thin black lines
surface streams and rivers, dark grey lines are primary cave passages and lines with
arrows are inferred branchwork dendriticc) drainage lines.
Refer to Fig. 1 for specific cave and sinkhole names.

b>
^ 1

Topographic maps, aerial photographs and USGS
orthoquadrangles were employed to locate additional
sinkholes south of the Leon Sinks and Wakulla cave
systems. These sinks, as well as others not detectable
on published maps, were located and surveyed in the
field and plotted (Fig. 3). The constructed map
indicated several possible primary conduit locations.
One of the more interesting features of the sinkhole
location map (Fig. 3) was the nearly north-south
trendlines of the majority of the sinkholes. This is
consistent with the sinkhole alignment of the Leon
Sinks cave system. In addition, the sinkhole trendlines
are also consistent with the regional hydraulic gradient
within the WKP.

CAVE PASSAGE FLOW PATTERNS

The majority of subsuface conduit flow moves
from north to south, which is in agreement with the
regional flow pattern. However, there are some
exceptions to this trend. The two most notable
exceptions occur in Wakulla Springs cave and Indian
Springs cave.

In Wakulla Springs cave, the primary conduit
discharging water to the spring mouth, A-tunnel, flows
north for upwards of approximately 1.5 km. The
interface between northward and southward flowing
water varies considerably within the cave. It appears
to be dependent on head conditions. During periods of
low precipitation and low head conditions, the interface
between the divergent flowing water occurs near the
junction of A-tunnel and D-tunnel, a distance of 0.65
km from the spring mouth. Conversely, following
periods of extensive precipitation and high head
conditions, the interface between northward and
southward flowing water occurs at a penetration
distance of 2.3 km inside the cave at the junction of O-
tunnel and A-tunnel. Here at the interface, the
northward flowing water travels up A-tunnel 2.3 km to
the spring mouth. Both of these conditions transport
water in the opposite direction to the regional and local
flow regimes.

In Indian Springs cave, a similar situation
occurs. Approximately 0.2 km inside the spring mouth,
in a northward trending passage, there is a junction
between the upstream and downstream tunnel. Here
the downstream tunnel continues north for 0.55 km
where it terminates in a debris cone from a collapse.
Slightly before the debris cone there is a small
siphoning southwestward trending passage. The
upstream tunnel trends westward for 0.85 km and then
turns and trends northward for another 0.8 km.

During high head conditions, a majority of
water flows from the upstream tunnel and turns south
exiting the cave at the spring mouth. A small
proportion of water turns north into the downstream
tunnel and flows into the downstream siphon. During
extended periods of low head, the majority of water

flowing from the upstream tunnel turns north and flows
toward the downstream siphon. Usually in these
conditions, there is no discharge of water from the
upstream tunnel into the spring mouth. In cases of
extremely low head conditions, water flowing from the
upstream tunnel is entirely diverted to the northward
directed downstream tunnel and flows to the
downstream siphon. In addition, water from the spring
basin is siphoned back into the cave and flows north
0.75 km to the downstream siphon. Thus, depending
on head conditions, the water in the front section of the
cave, from the spring mouth to the junction of the
upstream and downstream tunnels, can flow either
north or south.

PALEOFLOW PATTERNS

In order to gain further insight into the conduit
system drainage patterns, it is necessary to envision
the present drainage system during its Pleistocene
evolution. In addition to existing passage enlargement
and increased connections (permeability) of large
secondary-porosity voids, sea level height was
fluctuating significantly. There are indications that sea
level was at the Cody Scarp 100,000 years BP and
approximately 100 m lower 18,000 years BP (Rupert &
Spencer, 1988; Chappell & Shackleton, 1986). These
extreme variations may have greatly affected fresh and
salt water mixing zones, as well as alter drainage basin
size and extent. In as much as the conduit and
geomorphic features are indicative of N-S paleoflow, it
is important to realize that there were several
mechanisms working to varying degrees and during
particular times, in order to have produced the present
drainage system.

Following careful study of the geomorphic
features and the current extent of explored passages a
key observation becomes relevant. There are four
large sinks north of Wakulla Springs located parallel to
FL highway 61. These sinks are in linear alignment
with the Leon Sinks cave system and Wakulla Springs
Cave system. It appears, after land and in-water dive
surveys, that the surface area and volume of Cherokee
sink, Wakulla Springs basin, and the large sink directly
north of Wakulla on Rt. 61 are all of approximately the
same magnitude. Noting how these sinks trend
linearly south, there is sufficient evidence to make a
hypothesis as to their origin and evolution.

First, it is proposed that Wakulla Springs A-
tunnel passage formed from southward directed flow
along the hydraulic gradient. This indicates that
paleoflow was at one time directed south from the
spring mouth toward Cherokee sink. This is reinforced
by the passage dimensions of A-tunnel and O-tunnel,
which have nearly the same overall box-canyon/
phreatic tube shape and size.

Second, it is proposed that there was a large
conduit, the size of A-tunnel, connecting the large sink

on Rt. 61 north of Wakulla and Wakulla Springs A-
tunnel (Fig. 1). This passage appears to have been a
primary conduit of the paleodrainage basin and
originated somewhere near the termination of Munson
slough or Eight Mile Pond (Fig. 3). This is in alignment
with the four large sinks which parallel Rt. 61.

Last, it is proposed that there was a large
collapse of this primary paleoconduit at the present
Wakulla Spring location. This collapse caused a
complete blockage of the southward directed flow. The
collapse feature evolved into the large spring now
present.

OVERFLOW VALVE

It is necessary to place Wakulla Springs cave
system in the context of the regional drainage basin
patterns to understand its flow evolution to its present
state. The WKPP has believed for some time that
Wakulla Springs cave, the Leon Sinks cave system, as
well as many of the other caves south of these, were at
one time connected or are still physically connected at
present (Irvine, 1998). This assumption has been a
major driving force in the continued exploration of this
area. When the southwestern extent of the WKP is
displayed in the context of the cave systems, the
regional hydraulic gradient, and sinkhole alignment, it
becomes clear that a drainage basin trend emerges.

This trend, coupled with the presence of the
sinking surface streams, indicates a very large
branchwork dendriticc) drainage pattern (Palmer,
1991). Each cave system, after proposed drainage
lines connecting the systems along sinkhole trendlines
are drawn (Fig. 3), appears to be part of the larger
branchwork drainage system. The terminal mouth of
this system also appears to be Spring Creek Springs,
at the edge of the Gulf.

With this in mind, following large precipitation
events and/or a large head gradient within the basin,
flow backs up at Spring Creek and other springs near
the coast. This causes an overall decrease in the
ability of the conduit system to effectively transport
water to the Gulf. Increased flow at several springs,
such as Shepherd Spring and Wakulla Springs,
becomes the direct result of this inefficiency. A very
large head gradient appears to be responsible for the
extreme fluctuations in discharge seen at Wakulla
Springs.

This intricate and complex feedback loop is
typical of karst groundwater / surface water flow
regimes (White, 1988). There are several examples of
these conditions in the literature, of which Mammoth
Cave, Kentucky is the most notable (White & White,
1989). The observations of Indian Springs made
above are also consistent with the proposed model
above.

CONCLUSIONS

It is evident that the alignment of regional
groundwater flow lines with primary conduits and
sinkholes are not a coincidence. They are intimately
related surface and subsurface features. Much of the
subsurface flow through the cave passages are tied to
surface water flow. This indicates that the entire
drainage basin, both surface and subsurface, must be
considered in any further study. It also becomes clear
that the evolution of the drainage basin has been
intricate and complex through its history. The
seemingly anomalous cave passage flow patterns may
be explained by simple groundwater / surface water
interactions during varying hydraulic head conditions.
These observations, models and conclusions should
provide a foundation for continued exploration and
research into this unique drainage basin.

REFERENCES

Chappell, J. & Shackleton, N. J., 1986, Oxygen
isotopes and sea level: Nature, v. 324, 137-
140.

Davis, H., 1996, Hydrogeologic investigation and
simulation of ground-water flow in the Upper
Floridan Aquifer of North-Central Florida and
delineation of contributing areas for selected
city of Tallahassee, Florida, water supply wells:
USGS Water-Resources Investigation Report
95-4296, 56 p.

Hendry, C. W., and Sproul, C. R., 1966, Geology and
groundwater resources of Leon County,
Florida: Florida Geologic Survey Bulletin 47,
178 p.

Irvine, G., 1998, Woodville Karst Plain Project:
www.wkpp.orq, personal communication.

Palmer, A. N., 1991, Origin and morphology of
limestone caves: GSA Bulletin, v. 103, p. 1-4.

Rupert, F.R., and Spencer, S.M., 1988, Geology of
Wakulla County, Florida: Florida Geologic
Survey Bulletin 60, 46 p.

Scott, T.M., Lloyd, J.M,, and Maddox, G., 1991,
Florida's Groundwater quality monitoring
program: Hydrogeological framework: Florida
Geological Survey Special Publication No. 32,
1991,97 p.

White, W. B., 1988, Geomorphology and hydrology of
karst terrains: Oxford University Press, New
York.

White, W. B. and White, E. L., 1989, Karst hydrology:
Concepts from the mammoth cave area, Van
Nostrand Reinhold, N.Y.

Wisenbaker, M., 1998, Woodville Karst Plain Project:
www.wkpp.org, personal communication.

URANIUM AND STRONTIUM ISOTOPE CHARACTER OF WATERS
IN THE WAKULLA KARST PLAIN

J.B. Cowart, J.K. Osmond, Adel A. Dabous, Tom Miller, Hongshen Cao, Department of Geological
Sciences, Florida State University, Tallahassee, FL 32306

ABSTRACT

Both uranium and strontium are conservative elements in oxic natural waters, and both exhibit
readily measurable isotopic variations that can be used to characterize water sources. The activity ratio of
234U to 238U, normally high in surficial run-off and swamp water, is unusually low in Wakulla Springs and
related karstic ground waters. This can be shown to be the result of changes in Upper Floridan aquifer
water as it moves southward and becomes oxic and aggressive at the margins of confining beds near the
Cody Scarp in Leon County. The mass ratio of 87Sr to 86Sr has increased through geologic time at a rate
that can be used to characterize limestone formations and their included ground waters. These same
ground waters exhibit significant increases in this ratio if exposed to shaley strata and soils high in
potassium. As a result of these two isotopic fingerprint approaches, we estimate that most of the aquifer
effluence and surficial drainage in Wakulla Karst Plain springs and sinks is derived directly from the
southward flow of the Floridan Aquifer.

INTRODUCTION

part of the decay series headed by 238U.

U and Sr isotopes in natural waters

Knowledge of the source and pathway of
groundwater flow is essential in the protection of our
water resources. To this end, any characteristic of the
groundwater which retains a "memory" of the location
of its recharge into the ground or of the formations
through which it has traveled is useful in gaining
understanding of the underground flow system.
Generally, substances dissolved in the water provide
the most useful clues. Concentrations or relative
concentrations of major or minor elements or ions are
often helpful; isotopic ratios of certain elements can be
equally or even more useful. In this investigation, we
have utilized the isotopes of the two elements, uranium
(U) and strontium (Sr) to gain insight into the
groundwater system of the Wakulla Karst Plain.

Uranium is a heavy metal that can be found as
a trace constituent in all natural waters. In oxygen rich
("oxic") water U is soluble whereas in oxygen poor
("reducing") water it is very sparingly soluble. In oxic
waters the concentration of U may vary over many
orders of magnitude. In our study area U is generally
found in the range from 0.05 to 10 micrograms per liter
(pg/l) but even at these relatively low concentrations it
can be measured easily and accurately because of the
radioactivity of all of its isotopes. U-238 is a nuclide
that has been present on Earth for the entire history of
our planet. Because it is a slightly unstable nuclide it
takes about 4.5 billion years for half of an amount of it
to decay into another nuclide (234Th). However, 234Th
is also unstable (radioactive), so it, in turn, is
transformed into yet a different nuclide. Thus, a
cascade is formed with each member having a
different rate of radioactive decay (half-life). The
cascade ends at the element lead. Figure 1 shows

In a closed system, one in which no atoms can
enter or leave, the physical laws governing radioactivity
dictate that the radioactivity ("activity") of each member
of the decay series must be the same; in such cases
the ratio of activities of any two members of the series
is equal to exactly 1.0. However, in many systems in
which minerals are in contact with water it is found that
the radioactivities of various members of the decay
series are not equal; that is, they are in radioactive
disequilibrium. The disequilibrium is especially
pronounced in the waters of the Earth. Because each
element has a different chemistry than any other
element, it is easy to understand how different
elements might separate because of their different
solubilities. However, the two isotopes of U in the
series, 238U and 234U, are almost always found to be in
disequilibrium in natural waters, despite the fact that
they are separated in the decay series only by two very
short lived and highly insoluble nuclides.

In most natural waters 234U is found to have
greater radioactivity than 238U. However, a zone in
Florida, extending from the Tallahassee area to the
vicinity of Tampa and including the Wakulla Karst
Plain, contains waters which are quite different in that
many of them contain dissolved U in which the activity
ratio 234U238U is less than 1.0 (Osmond, et al., 1968;
Kaufman, 1968; Rydell, 1969; Macesich, 1993;
Whitecross, 1995). The usual situation (activity of
234U/238U > 1.0) is thought to occur because the 4U
has been physically recoiled out of the outer boundary
("rind") of the mineral as a result of radioactive decay
(Figure 2) or by selective leaching of 234U from
damaged sites in the mineral which resulted from the
radiogenic origin of the 234U. These two processes can
occur under both oxic and reducing conditions.

If the surrounding waters are gaining 234U by
either or both of these processes, then the mineral
itself must be deficient in 234U (Figure 2). In the
situation wherein low U concentration reducing ground
waters bathing the minerals are replaced quickly
(geologically speaking) by oxic and somewhat acid
waters a profound change may occur. The aggressive
oxic waters have the capability of adding U by the
dissolution of the minerals containing U. In the case of
carbonate minerals the dissolution can be significant.
The portion of the mineral dissolved releases all of the
U that was associated with it. Because it is the "rind"
of the minerals that is most likely to be dissolved, the U
released is not only in higher concentration than
formerly but also is relatively deficient in 234U (activity
of 234U23U < 1.0). Under ideal conditions the activity
of 234U/238U ("AR") can approach 0.5 in aquifer waters.
Waters with relatively high U concentrations and ARs
less than 1.0 are often found downflow from sinkholes
or scarps, places where reducing waters are displaced
by or mixed with aggressive oxic waters. Thus, the
presence of a water having such characteristics
provides a clue as to its source (Osmond and Cowart,
1976, 1992).

In a locale having waters with a variation in U
concentration of at least several orders of magnitude (a
common occurrence) and a significant variation in the
AR (also common), water sources and their histories
can often be deduced. Systematic variation of these
parameters is well displayed on a graph plotting AR
versus the reciprocal of the U concentration (Osmond,
et al., 1974; Osmond and Cowart, 1976, 1992)). This
display, shown in Figure 3, is termed by us a "mixing
diagram" and it can be used to help calculate the
relative contribution of up to three separate sources of
U to a resultant water (such as a spring).

Strontium is an alkaline earth element that
behaves rather similarly to Ca. Therefore, the
abundant marine calcium carbonate rocks always
contain a minor amount of Sr. Strontium has no
naturally occurring radioactive isotopes and has four
stable isotopes. However, one of these, 8Sr, is formed
by the radioactive decay of 7Rb which means that its
relative abundance has changed through geologic
time. The ratio of 8Sr to the stable, non-radiogenic
86Sr is used as a measure of this change. For the past
forty million years or so the 87Sr/86Sr ratio has generally
changed monotonically, as may be seen in Figure 4.
This means that determination of the Sr isotope ratio in
a Neogene marine carbonate rock is a measure of its
age. But it also means that ground water which
solubilizes some of the incorporated Sr from the rock
through which it is flowing will eventually have a Sr
ratio similar to that of the rock. As such water flows to
other places, it will retain, at least for a period of time,
an isotopicc memory" of the rocks along its earlier
travel path.

Regional Hydrology

The area of this investigation can be identified
as the possible catchment and source region for
Wakulla Springs water (Hendry and Sproul, 1966;
Miller, 1986; Rupert and Spencer, 1988; Davis, 1996).
This includes southern Leon County and northern
Wakulla County (Figure 5). Geologically it includes the
region just north of the Cody Scarp where the Floridan
aquifer is capped by clays and clayey sands and is
generally confined, although dotted with sinkholes, and
the region south of the scarp where the marine
carbonate host rock of the aquifer is exposed or thinly
veneered with sand (Figure 6).

ISOTOPIC CHARACTER OF WAKULLA KARSTIC
WATERS

Waters issuing from Wakulla springs, Spring
Creek, and other first magnitude springs in the area
are notable for having uranium ARs less than 1.0
(Osmond, et al., 1968; Kaufman, 1968; Rydell, 1969;
Macesich, 1993; Whitecross, 1995). Values from 0.5
to 0.9 are usual, as are U concentrations greater than
0.5 pg/l. On the basis of at least 15 analyses done
over more than 30 years, the values for Wakulla
Springs are 0.85 with a U concentration of 0.65 pg/l,
with virtually no variation over that time. Surficial
swamp waters in the same area are characterized by
AR values ranging from 1.0 to 1.3 and U
concentrations usually less than 0.2 pg/l. As a
consequence, it is relatively easy to determine water
mass mixing volumes in the karst region when the two
source types, spring and surface waters, are involved.
As an example, water from the St. Marks river is
somewhat higher in AR than is that of the Wakulla
River because of a surface-derived U component.

ISOTOPIC CHARACTER OF FLORIDAN AQUIFER
WATERS

The Tallahassee municipal water supply is
derived from the Upper Floridan Aquifer. Samples of
this water analyzed for their U isotopic composition
before and during this investigation (Korosy, 1984;
Whitecross, 1995; Miller, 1998; Osmond et al., 1998)
exhibit, with few exceptions, ARs of 0.76 to 1.15 and U
concentrations of 0.3 to 0.8 pg/l. (Table 1 and Figure
7). These values, although not extreme, are more
variable than would be expected of a major confined
aquifer. A logical explanation for such variability would
be admixture of surface water infiltrating through the
relatively thin and sinkhole-punctured confining layer
overlying the Floridan Aquifer (Katz, et al., 1997).
However, simple mixing does not explain the
observation that some down-flow waters have higher
concentration and lower ARs than up-flow waters. We
interpret this to mean that the infiltrating waters are
acting not only as diluents of the aquifer but also acting
to leach and/or dissolve the aquifer rocks containing U
(and Sr). If the mobilized U from the rocks has an AR
close to 0.5 (see Figure 2) then it is possible to

calculate the residual excess of 234U (Figure 7) as it
becomes diluted from north to south in the area
(Figures 8).

ISOTOPIC CHARACTER OF SURFACE WATERS

Like surface drainage world-wide, the streams
and lakes of Leon County have relatively low U
concentrations coupled with AR's greater than about
1.0 (Table 2 and Figure 9). The few samples which
carry more than one ppb of U are suspected of being
contaminated (Osmond, et al., 1998). Karstic springs
have low AR values, consistent with travel through the
deep aquifer.

SOURCES OF WAKULLA SPRINGS WATERS

Uranium Isotopes

Using available U isotope data and plotting all
reasonable source waters for the Wakulla Springs
discharge, we see that the Springs values (Osmond, et
al., 1998) lie entirely outside the surface water regime
but within the aquifer regime (Figure 9). We conclude
that the primary source of Wakulla Springs is
southward flowing Floridan Aquifer water. If and when
the Wakulla Springs conduits have been accurately
and repeatedly sampled, we should be able to make
quantitative estimates of the contributions of the two
sources types. We anticipate that Wakulla Springs
discharge will be shown to be composed of at least
90% deep aquifer water.

Strontium Isotopes

The Sr isotope ratios from waters in the area of
investigation fall into three distinct groups (Table 3 and
Figure 10). One group, consisting of analyzed
samples taken from wells known to produce water from
the Floridan Aquifer, has the lowest ratios, ratios that
are consistent with those associated with the marine
carbonates which make up the Floridan Aquifer.
Another group, the one having the highest Sr ratios,
consists of samples which come from surficial clayey
areas and are unlikely to have mixed with Floridan
Aquifer water nor with significant amounts of urban
runoff. The ratios for this group are much greater than
those of the marine carbonates. The third group
consists mainly of samples that have a large urban
runoff component. An exception appears to be the two
samples of Lost Creek, a stream that originates within
the Apalachicola National Forest and flows just south
of Crawfordville before being captured by underground
drainage. In this case, the ratio may result from a
mixing of surface runoff from the clayey sands of the
headwaters and upwelling Floridan Aquifer waters lying
just below the veneer of surficial sediments.

The Sr isotope ratio for water from Wakulla
Springs falls within the values obtained from Floridan
Aquifer waters. Thus, it seems that the source of
waters feeding the spring are unlikely to be solely from

nearby local recharge; rather, it comes from waters
which have spent considerable time in contact with the
marine carbonates that comprise the matrix of the
Floridan Aquifer.

ACKNOWLEDGEMENTS

We are grateful to Rosemarie Raymond for
help in the preparation of figures. This work was
supported by the Florida Department of Environmental
Protection, Storm Water and Nonpoint Source
Management Section.

REFERENCES

Burke, W.H., Denison, R.E., Hetherington, E.A.,
Koepnick, R.B., Nelson, H.F., and Otto, J.B.,
1982, Variation of sea water 87Sr/86Sr
throughout Phanerozoic time: Geology v. 10,
p. 516-519.

Davis, H., 1996, Hydrologic investigation and
simulation of ground-water flow in the Upper
Floridan Aquifer of North-Central Florida and
Southwestern Georgia and delineation of
contributing areas for selected City of
Tallahassee, Florida, water-supply wells: U.S.
Geol. Survey Water-Resources Investigations
Report 95-4296, 56 p.

Hendry, C.W. and Sproul, C.R., 1966, Geology and
ground-water resources of Leon County,
Florida: Florida Geological Survey Bulletin 47,
174 p.

Katz, B.G., Coplen, T.B. Bullen, T.B., Davis, J.H.,
1997, Use of chemical and isotopic tracers to
characterize the interactions between ground
water and surface water in mantled karst:
Ground Water, v. 35, p. 1014-1028.

Kaufman, M.I., 1968, Uranium isotope investigation of
the Floridan Aquifer and related natural waters
of North Florida: Unpublished MS Thesis,
Florida State University, 89 p.

Korosy, M.G., 1984, Groundwater flow pattern as
delineated by uranium isotope distributions in
the Ochlocknee River area: Unpublished MS
Thesis, FSU, 179 pp.

Macesich, M., 1993, Uranium isotopic disequilibrium
of Wakulla Springs: Unpublished MS Thesis,
Florida State University, 146 p.

Miller, J.A., 1986, Hydrologic framework of the
Floridan aquifer system in Florida and parts of
Georgia, Alabama. and South Carolina: U. S.
Geological Survey Professional Paper 1403-B,
91 p.

Miller, T., 1998, Groundwater and surface water
interaction within the Lake Lafayette sub-basin:
a uranium disequilibrium mixing line analysis:
MS Thesis, Florida State University, in prep.

Osmond, J.K., Rydell, H.S., and Kaufman, M.I., 1968,
Uranium disequilibrium in groundwaters: an
isotope dilution approach in hydrologic
investigations: Science v, 162, p. 997-999.

Osmond, J.K., Kaufman, M.I., and Cowart, J.B., 1974,
Mixing volume calculations, sources and aging
trends of Floridan aquifer water by uranium
isotopic methods: Geochimica et
Cosmochimica Acta, vol. 38, p. 1083-1100.

Osmond, J.K., and Cowart, J.B., 1976, Theory and
uses of natural uranium isotopic variations in
hydrology: Atomic Energy Reviews v. 14, p.
621-679.

Osmond, J.K., and Cowart, J.B., 1992, Groundwater,
Chapter 9: in Uranium Series Disequilibrium,
2nd edition, Ivanovich, M. and Harmon, R.,
Eds, Oxford Univ. Press, p. 290-333.

Osmond, J.K., Cowart, J.B., Dabous, A.A., Miller, T.,
and Cao, H., 1998, Surface water and ground
water budgets from Tallahassee to Wakulla
Springs by dissolved uranium and strontium
isotopes: Final Report of Project #WM622,
Florida Department of Environmental
Protection, Storm Water and Nonpoint Source
Management Section

Rupert, F.R., and Spencer, S.M., 1988, Geology of
Wakulla County, Florida: Florida Geolological
Survey Bulletin 60, 18 p.

Rydell, H.S., 1969, Implications of the uranium isotope
distributions associated with the Floridan
Aquifer of North Florida: Unpublished PhD
Dissertation, Florida State University, 119 p.

Whitecross, L., 1995, Ground water and surface water
interaction from Tallahassee, Florida, to the
Woodville Karst Plain: a study utilizing
uranium disequilibrium modelling:
Unpublished MS Thesis, Florida State
University, 98 p.

S.N. LOC COLL

4862 W-1 6/96 0.50 13.761 0.07
4970 2 3/97 0.91 0.50 2.02
4482 4 3/97 1.03 0.58 1.72
4973 5 3/97 1.01 0.53 1.89
4975 6 3/97 0.76 0.52 1.92
4976 7 3/97 1.01 0.40 2.49
4480 8 6/96 0.83 0.51 1.96
4972 9 3/97 1.01 0.48 2.08
4497 11 6/96 1.15 0.57 1.75
4967 12 3/97 0.88 0.47 2.13
4813 13 4/96 0.92 0.75 1.33
4484 14 1/94 0.98 0.37 2.70
4471 15 1/94 0.97 0.56 1.79
4467 17 7/97 1.14 0.31 3.23
4487 18 9/97 0.99 0.31 3.23
4473 19 9/97 1.01 0.47 2.13
4478 20 9/96 0.91 0.43 2.33
4903 21 9/96 0.93 0.42 2.38
4477 22 1/94 1.06 0.35 2.86
4465 23 1/97 0.93 0.59 1.69
5042 26 7,/97 0.72 0.58 1.74
4966 27 3/97 0.88 0.49 2.04
4485 29 1/94 0.95 0.37 2.70
5043 30 9/97 0.99 0.47 2.13

Table 1. Representative U Isotopic data for selected City of Tallahassee Wells

A.R. CON

1/C

GEOGRAPHIC
GROUP

LOCAL
GROUP

MEDIAN VALUES
U CON U AR
(ppb)

NUMBER OF
SAMPLES

L Jackson
drainage area

L Munson
drainage area

L LaFayette
drainage area

St. Marks R

Karst Plain

high springs
drainage ditches
Lake Jackson

high springs
West lakes
West ditches (hi U)
West ditches (lo U)
Munson Slough
Lake Munson (& Crk)

Upper Lake drainage
Lower Lake drainage
Lake LaFayette
Mosquito Canal

above Natural Bridge

sinking streams

0.02
0.17
0.03

0.03
1.34
1.50
0.20
0.60
0.20

0.10
0.06
0.05
0.03

1.21
1.15
1.49

1.24
1.05
1.00
1.00
1.40
1.30

1.00
1.90
1.30
1.40

0.25 0.95

0.05 1.20

TOTAL

Table 2. Summary of U Isotopic Data in Surface Waters

SAMP DATE
NUMB COLL

87Sr/86Sr RATIO

LOCALITY

SURFACE WATERS AND HIGH SPRINGS

+/-0.000055
+/-0.000010
+/-0.000011
+/-0.000009
+/-0.000030
+/-0.000010
+/-0.000010
+/-0.000039
+/-0.000010
+/-0.000036
+/-0.000009
+/-0.000040
+/-0.000011
+/-0.000008
+/-0.000009

Spring Meyer's Park
NW Corner Tallahassee Mall
Tallahassee Mall Drainage
Park Ave near Gov Sq
Gov Sq drainage
Piney Z Lake
U L Lafayette @ Falls Chase
U L Lafayette @ Falls Chase
Lower L Lafayettee
Outlet L L Lafayettee (Chaires)
St Marks R @ US27
Munson Slough @ Capital Circle
Munson Slough @ Orange Ave
Lost Creek (Crawfordville)
II Io

FLORIDAN AQUIFER WATER

+/-0.000008
+/-0.000007
+/-0.000008
+/-0.000011
+/-0.000052

6923
it
City
City
City

Hanging Vine Way
(N of L. Lafayette)
Well #2
Well #17 (CapCir/Apalachee)
Well #12 Country Club Dr

WAKULLA SPRINGS

5053 09/20/97
5052 09/20/97

0.708279 +/-0.000017
0.708235 +/-0.000011

Main pool
Tunnel "D"

Table 3. Strontium Isotopic Data

0.710462
0.709030
0.709407
0.709172
0.708991
0.709193
0.708765
0.709314
0.710376
0.710495
0.710548
0.709335
0.709071
0.709033
0.709133

4943
4907
4915
4916
4908
4879
4878
5018
5014
4919
4896
4927
5000
4894
4922

4846A
4846B
4970
4975
4967

09/12/97
06/14/97
09/06/97
06/15/97
06/13/97
09/08/97
12/18/96
06/19/97
06/19/97
06/15/97
09/10/97
09/19/97
04/30/97
12/30/96
06/15/97

07/31/97
07/31/97
06/18/97
09/19/97
09/17/97

0.708151
0.708140
0.708283
0.708338
0.708201

U-238 Series
U-238 U-234
U 4.5x 109y 2.48x105y
Pa-234 /
Pa a 1.18 m

S Th-234 Th-230
24.1 d 75.2x103 y

Ac a

Ra Ra-226
1622 y

Fr a

Rn Rn-222
3.825 d
Figure 1. Early part of U-series decay scheme. The principal nuclides of interest are mU and 2U.
The reason for the variation in relative activity of the two U isotopes, and their usefulness in
identifying ground water sources, is one subject of this paper.

Figure 2. High and low A.R. schematics. Recoil displacement as a result of alpha decay of 2"U to
produce mU can be invoked to explain both high and low AR in ground water. (1) recoil
directly into aquifer waters produces high A.R. in water and low A.R. in solid; (2) subsequent
leaching of the solid by water mobilizes low A.R. U.

3.0

D
0

/// '_ EQUIL.
< A

ro
J1NM

I 2 3

RECIPROCAL

U conc. (lug-')

Figure 3. U isotopic mixing diagram. The U activity ratio and concentration data can be used to infer
water mass evolution and mixing. By plotting the A.R. values against reciprocal of U
concentration, such evolutionary trends and mixing proportions show up as straight lines.

.7080--

MIOCENE

J. U -

I OLIGOCENE

AGE (x 106Y)
Figure 4. Sr isotopes evolution. The ratio of e8Sr/"Sr in ground water can be used to infer the ages of
aquifer host limestone strata, because ocean water and associated chemical sediments have
experienced a gradual evolutionary increase in 87Sr/eSr ratio with time (modified from Burke et
al., 1982).

-T

.7095

.7090

.7085

N

i -

.707f

P

EOCENE

L

I

**44

S-I I I 1-

' *

W-1

"t,.

LAKE
BRADFORD

Figure 5. Study.Area. The area of study includes parts of Southern Leon County and Northern Wakulla
County and includes the area from which Wakulla Karst Plain waters are derived.

SOUTI I-SOUTlHEAST

NORTI I-NORTI IWES'T

TALLAHASSEE I ILLS

200 feet

100 reet

61 meters

WOODVILLE KARST PLAIN
30.5 mclers

i I St. Marks Formation Pleistocene hands

Sw n -30.5

Suvwanncc Limenstone

-100 feet \

SECTION A-A'

Figure 6. Hydrostratigraphic profile of the study area. The St. Marks and Suwannee Limestones
constitute the Upper Floridan Aquifer, while the Hawthorn and Miccosukee Formations are
aquicludes.

1.2

1.1

o 0.9

0.7m

0.6

0.5
0 0.5 1 1.5 2 2.5 3
RECIP CON

Figure 7. Mixing diagram of City of Tallahassee water wells. These wells sample Upper Floridan
Aquifer water. Variation of U concentration and A.R. across the region could appear to be
random. However, each sample can be regarded as a mixture of leachate U with A.R. near
0.5 (y-axis intercept) and relatively dilute hgh A.R. aquifer water (joined by a mixing line). The
slope of this line has units of "Excess U". The line shown has slope of 0.20 ppb (U-
equivalent) excess 34U. Sample points shaded are from the northwest sectors of the city and
have generally higher excess values; the unshaded are from the southeast and have generally
lower values.

0 5
I K I M I
KM

BM
Figure 8. Regional variations of excess 24U in the study area. Data points from wells in Leon and
Gadsden counties are plotted. For orientation, the FSU campus (A) and Wakulla Springs (B)
are shown. Infiltration from the surface causes the aquifer water to be diluted with respect to its
conservative excess 4U. As a result the regional variation shows aquifer flow direction,
generally from north to south.

1.6

1.4 -

1.2-

.S.
0.8

0.6

0.4
0 5 10 15 20 25 30 35
RECIP CONC

Figure 9. Mixing plot of U in waters from Wakulla Springs, Floridan Aquifer, and regional streams
and lakes. The shaded squares are surface streams and lakes, characterized by low
concentration (to the right) and high A.R. values, 0.95 and above. The polygon shows the
plotted area of Floridan Aquifer water as represented by Tallahassee wells (Figure 7). The
water from Wakulla Springs plots within the aquifer region and well below the surface water
region.

4 0

0.710F

0.709

0.708'

* MODERN
SEAWATER
1111111111

I'I

0

Figure 10. Strontium isotopic ratios of surficial, aquifer, and karstic waters In the study area.
Group 1: samples from Floridan Aquifer; Group 2: samples having significant urban
drainage component, including input from clayey confining layer; Group 3: samples in
contact only with clays of confining layer. Triangles represent water analyzed from Wakulla
Springs.

nDo
o?

HYDROCHEMICAL INTERACTIONS BETWEEN GROUND WATER AND
SURFACE WATER IN THE WOODVILLE KARST PLAIN, NORTHERN FLORIDA

Brian G. Katz, U.S. Geological Survey, 227 N. Bronough Street, Suite 3015, Tallahassee, FL 32301

ABSTRACT

Hydrochemical interactions between surface water and ground water in the Woodville karst plain in
Leon and Wakulla Counties have resulted in water-quality impacts on both resources. Karst features such
as sinkholes, springs, disappearing streams, and solution conduits, provide direct pathways for surface
water to enter the Upper Floridan aquifer (UFA), the source of potable water in these two counties. In parts
of Leon County, ground-water samples analyzed for stable isotopes (d'80, dH, and d13C) along with results
from geochemical mass-balance modeling indicate that isotopically-enriched surface water from sinkhole
lakes enters the UFA and mixes with shallow ground water in proportions ranging from 0.07 to nearly 0.90.
Ground water in deeper parts of the UFA also had an enriched isotopic signature, indicating mixture
proportions of as much as 0.25 surface water. Based on tritium age-dating, the shallow and deep ground
water was recharged during the past 30 years, indicating a very dynamic system through the full thickness
of the aquifer. Blackwater streams, such as Fisher Creek and Lost Creek, flow directly into the UFA through
sinkholes and transport large amounts of organic carbon (such as tannins and lignins) into the aquifer.
When these naturally-occurring organic compounds react with chlorine during disinfection of the water
supply, harmful products such as trihalomethanes are produced. The unconfined Upper Floridan aquifer in
the karst plain also is vulnerable to contamination by nitrate from nonpoint and point sources, such as septic
tanks (at least 4,000 in the eastern half of Wakulla County), fertilizers, publicly-owned treatment works, and
stormwater runoff. In recent years, nitrate-N concentrations have increased to approximately 1 mg/L in
Wakulla Springs. Because Wakulla Springs is a first magnitude spring and drains ground water from a
large regional area, there is concern about a widespread increase in nitrate levels in ground water and the
potential for increased algal growth in this State-designated priority water body.

THE BIG PICTURE:
AQUIFER VULNERABILITY MAPPING EFFORTS IN
THE WOODVILLE KARST PLAIN OF NORTHERN FLORIDA

Gary Maddox, Environmental Manager, Department of Environmental Protection,Division of Water Facilities,
Ambient Monitoring Section, 2600 Blair Stone Road, MS 3525, Tallahassee, FL 32399-2400

ABSTRACT

For the last twelve years, state and local government agencies involved in ground-water monitoring
and protection efforts have developed aquifer vulnerability maps as a generalized tool to depict relative
susceptibility of aquifer systems to contamination. Several vulnerability mapping efforts have focused on or
included the Woodville Karst Plain subdivision of the Gulf Coastal Lowlands. Pilot vulnerability mapping
projects have centered on this region and the adjacent Northern Highlands, due to the wide range in
potential vulnerability of the Floridan aquifer system within these adjacent geomorphic areas.
DRASTIC, a widely-used aquifer vulnerability mapping system developed jointly by the U.S.
Environmental Protection Agency and the National Water Well Association, has been mapped in the
Woodville Karst Plain by Northwest Florida and Suwannee River Water Management Districts, the Florida
Geological Survey, and the Ambient Monitoring Section of the Department of Environmental Protection
(DEP). DRASTIC is complete for the Floridan and surficial aquifer systems in this area, and the coverages
are currently available in the DEP GIS map library. These maps were originally developed as a tool to aid in
the selection of DEP ground-water monitoring efforts designed to quantify the impact of various land use
types on ground-water quality. Subsequently, these coverages have also served as regional planning tools
useful to local and state governments charged with consideration of aquifer impacts resulting from land use
changes.
KARSTIC, developed by Leon County, incorporates karst features into a vulnerability mapping
product similar to DRASTIC. KARSTIC has only been mapped for Leon County. Florida Aquifer
Vulverability Assessment (FAVA) and Aquifer Vulnerability Assessment Model (AVAM) are two proposed
vulnerability assessment methodologies which are designed to better portray potential aquifer vulnerability
in Florida. Pilot mapping projects using both methods are in progress in portions of the Woodville Karst
Plain. A unified Florida-specific mapping methodology, incorporating karst features, will result from this
effort.

TRACING GROUNDWATER FLOW INTO THE
NORTHEASTERN GULF OF MEXICO COASTAL ZONE

William C. Burnett, Jeffery Chanton, Christine Rutkowski, D. Reide Corbett, Kevin Dillon and Jane
Cable, Florida State Unversity, Oceanography Department, Tallahassee, Florida 32306-3048

ABSTRACT

Submarine springs and seeps deliver an unknown quantity of groundwater to the coastal ocean,
lakes, and rivers. This process has been demonstrated to be ecologically significant as a nutrient input or
contaminant source in some local areas. Is the process important on a wider scale? Some information
suggests that inputs of various chemicals via submarine discharge of groundwater may be regionally
significant. The problem is how to quantify this diffusive flow.
Our research team has been developing an assessment method based on measurements of: (1)
naturally-occurring tracers, such as radon and methane, found at very high concentrations in groundwater
relative to surface waters; and (2) artificial tracers such as SF6 and 1311 that can be traced from specific
points after injection. Thus far, only the natural tracer approach has been applied in the coastal Gulf of
Mexico. We have also made direct measurements of groundwater seepage using seepage meters in the
same areas where we are collecting the tracer information. Both the tracer data and the direct
measurements indicate that groundwater flow into this area is significant.

PHYSICAL FRAMEWORK FOR UNDERSTANDING FLORIDAN
AQUIFER GROUNDWATER FLOW AND NUTRIENT
TRANSPORT WITHIN THE WOODVILLE KARST PLAIN

Tom Pratt, Bureau Chief, Northwest Florida Water Management District, Ground Water Management, Route 1, Box
3100, Havana, FL 32333

ABSTRACT

The Northwest Florida Water Management District and the U.S. Geological Survey are currently
engaged in a four-year investigation of the fate and transport of nutrients within the Floridan Aquifer in Leon
and Wakulla counties. Understanding the transport of nutrients through a karst flow system requires
knowledge of the physical context in which nutrient transport is occurring. This paper presents a discussion
of major aspects of the ground water flow system beneath the Woodville Karst Plain. The major inflows and
outflows and their relative magnitudes are described. One of the goals of the project is to create a simple
predictive model that can be used to estimate nutrient concentrations in the outflow, given various nutrient
input functions. Creation of such a model requires linking the volumetric inflows to the outflows. Various
conceptualizations of ways to create this linkage are discussed.

THE SPRING CREEK SUBMARINE SPRINGS GROUP,
WAKULLA COUNTY, FLORIDA

Ed Lane, Florida Department of Environmental Protection, Florida Geological Survey, 903 W. Tennessee Street,
Tallahassee, Florida 32304-7700

ABSTRACT

Submarine springs are offshore discharges of ground water, usually associated with a coastal karst
area. Submarine karst springs and sinkholes on the Florida Platform constitute integral parts of Florida's
hydrogeological regime. They are some of the ultimate down-gradient discharge points for fresh water from
Florida's aquifers. Knowledge of their location, hydrology, and stratigraphy will add to an understanding of the
overall structure and extent of Florida's aquifer systems. Conceivably, they may represent supplementary
sources for fresh water supplies. In addition, they are micro-environments for fish nurseries; and some are
known to contain archaeological artifacts. They are key elements in the linked Earth systems among Florida's
environments and ecosystems: the uplands, the coasts, and the continental shelf marine realms.
The Florida Geological Survey is gathering information on these karst features as part of ongoing
Florida coastal research programs. This report documents the results of the first investigation, to locate and
determine the physical characteristics of the Spring Creek Submarine Springs Group, Wakulla County, Florida.

INTRODUCTION

Submarine springs occur on continental
shelves around the world. Figure 1 shows the location
of the better known submarine springs and sinkholes
that occur around Florida's coastline, or on the Florida
Platform. The Florida Geological Survey has several
ongoing coastal research programs along the coastlines
of Florida. An important part of these programs is
gathering information on these submarine springs,
sinkholes, and other karst features. This report
documents the results of the first investigation of
submarine springs, on the Spring Creek Springs Group,
Wakulla County, Florida.

The purpose of the present investigation is to
gather background information on the largest group of
submarine springs in the Big Bend area of the
northeastern Gulf of Mexico, the Spring Creek Springs
Group. The immediate goal is to locate and determine
the physical characteristics of the springs. The long-term
goals for future research will be to determine the
linkages between the land and the ocean, and to
determine the role of submarine springs in those
linkages. More specifically, what are the linkages among
the ecosystems and environments of the uplands, the
coast, the coastal marshes, the marine realm, and the
springs and sinkholes that occur in all of them?

Location of Study Area the Woodville Karst
Plain

The study area is on the southern coast of
Wakulla County, in the Big Bend area of the Florida
panhandle (Figure 1). The study area is in the Woodville
Karst Plain, which includes the entire eastern half of
Wakulla County, extending eastward into Jefferson
County, and northward to the Cody Scarp at Tallahassee
in Leon County (Hendry and Sproul, 1966) (Figure 2).

This part of the northeastern Gulf of Mexico is a low
energy coast, characterized by muddy or fine grained
sediments, small tidal ranges of one to three feet,
extensive marshes, and low gradient tidal streams.

WATER RESOURCES

The region's climate is semi-tropical and an
occasional hurricane delivers enough rain to cause
extensive flooding. Convective storms and
thunderstorms occur year-round, many of which drop
large quantities of rain in a short time. For the 30-year
period of record from 1951 to 1980, average annual
rainfall was between 56 and 60 inches. Also, during this
time the maximum amount of rainfall for the entire state
during any 12-month period, 107 inches, was recorded at
St. Marks, just seven miles east of Spring Creek (Fernald
and Patton, 1984). Because of this large amount of
annual rainfall, the local water table is usually close to
land surface. Even in periods of low rainfall, though, the
water table only drops a few feet.

The Floridan aquifer system underlies all of
Wakulla County (Miller, 1986). In the study area the
Floridan aquifer system extends from land surface to
about 2,400 feet below sea level (Scott et al., 1991). The
carbonate St. Marks Formation and the Suwannee
Limestone constitute the upper part of the Floridan
aquifer system in the study area, and they supply all of
the potable ground water used. In the Woodville Karst
Plain there are no low-permeability units between land
surface and the carbonate aquifer units, so the Floridan
aquifer is unconfined (i.e., it is at atmospheric pressure)
and its potentiometric surface is essentially the elevation
of the water table.

Ground-Water Recharge and Discharge

The ultimate source of all recharge to the
aquifers in the study area is from precipitation (Davis,
1996). The eastern part of Wakulla County (the
Woodville Karst Plain) is classified as a high recharge
area to the Floridan aquifer system, with rapid infiltration
of rainfall through the thin layer of clean sand that
overlies the limestone aquifer, as well as direct recharge
through karst solution features, such as sinkholes that
breach the overburden (Scott, et al., 1991). In addition,
large quantities of ground water moves down gradient
from adjacent areas, supplying water to Wakulla Springs
and the Spring Creek Springs Group.

Discharge from the aquifers is from pumpage,
upward leakage and evaporation from lakes that
intercept the water table, point-source terrestrial and
submarine springs, and diffuse submarine discharge that
takes place offshore along the coast. It is probable that
undetermined quantities of ground water alternately
recharge-discharge through interbasin flow, especially
when their locally adjacent potentiometric surfaces
fluctuate irregularly due to uneven distribution of rainfall,
or during droughts.

SPRING CREEK SPRINGS GROUP

Previous Investigations

Spring Creek is a low-gradient tidal stream in the
northwest part of Apalachee Bay (Figure 3). It is aptly
named, for there may be as many as 14 large submarine
springs in its lower reaches. Rosenau et al. (1977)
showed the locations of eight springs, and assigned
numbers 1 through 8 to them (Figure 3 ). Figure 4 is an
aerial photograph of the study area.

In 1972, 1973, and 1974, the U.S. Geological
Survey collected water quality samples and estimated
flow rates for the spring group. The results of their
investigations were reported by Rosenau et al. (1977).
On May 30, 1974 the USGS measured aggregate
stream flows of about 2,000 cubic feet per second (cfs)
(3,096 million gallons per day (mgd)), attributable to the
eight springs, and apparently to many other submarine
springs thought to exist in the area (Rosenau et al.,
1977). For comparative purposes, the maximum
recorded flow of Wakulla Springs was 1,910 cfs (2,957
mgd) on April 11, 1973 (Rosenau et al., 1977).

Woodville Karst Plain Project

The Woodville Karst Plain Project is a continuing
program to map the underground conduit systems that
link the sinkholes and springs throughout the plain. The
project was formally initiated in 1986, although sporadic,
uncoordinated, scuba cave diving activities go back to
the 1950s. Investigations under the present project are
conducted by experienced, certified cave divers,
because all of the conduits are flooded year-round. The
main thrust has been to find and map, or otherwise

prove, direct connections between the up-gradient
components of the karst drainage system, starting with
Big Dismal Sink in Leon County, and the main down-
gradient discharge point, which is thought to be Wakulla
Springs.

Physical Descriptions of the Spring
Springs Group

Creek

Several of these submarine springs were
investigated by the Florida Geological Survey in August
and September 1995, November 1997, and September
1998, to gather background data on them. Three new
springs, not described by Rosenau et al. (1977), were
located (numbers 9, 10, 11 on Figure 3). Springs 1, 2, 3,
and 8 were located by their surface boils, but springs 4,
5, 6, and 7 of Rosenau et al. (1977) were not located;
their flows may have been too small to create surface
boils at the time of these investigations.

Spring Creek and its tributaries meander
through low-lying coastal marshes. Stream beds are silt,
mud, and mollusk debris. However, at low tide, when the
water is clear, fragmented limestone boulders can be
seen in places around the rims of the springs' basins,
apparently exposed where the springs' discharges scour
away the thin sediments.

A Sitek Model HE-203 sonic depth indicator,
with a strip-chart recorder, was modified to obtain
continuous cross-section profiles of the springs. (Any use
of trade names is for descriptive purposes only and does
not imply endorsement by the FGS). To obtain depth
recordings, several boat-runs were made over each
spring, from varying directions, in order to get the best
quality print-out. Some shallow spot-depths were taken
using a lead line. The springs' basins and pools
appeared to be relatively symmetrical, varying from
broad, shallow bowl-shaped pools to steep-walled,
conical shapes, as shown on Figures 5 through 9.

Spring 1 (Spring Creek Rise): It was not
possible to obtain a depth profile across Spring 1 due to
the enormous amount of discharge, which created so
much boiling, surface turbulence that the boat could not
be held steady over the spring. The active boil is about
40 to 50 feet in diameter and, in places, can rise nearly a
foot above the level of the stream's surface. Rosenau et
al. (1977) reported its depth as being 100 feet.

During high, onshore tidal surges caused by
hurricanes, reversal of flow into Spring 1 has been
observed, taking brackish estuarine water and flotsam
into the aquifer (pers. comm., Mr. Spears, 1995). The
reversal of flow caused by the relatively small amount of
increased head over Spring 1's orifice due to hurricane
tidal surge indicates that its potentiometric surface is so
low that its flow is in tenuous balance with the marine
environment. By inference, then, it appears that a
change of only a few inches of head on the upland side
of the aquifer system can make the difference between
discharge from, or recharge to, the local aquifer system

supplying the springs. The same thing could happen if
the springs are exploited and pumped to such an extent
that salt-water intrusion is induced.

Spring 2: This spring's basin is about 75-feet
across. A small canal extends to the northeast, and a
narrow channel on its southeastern side connects to
Spring 3. This spring has the largest and deepest basin
of any measured during this investigation. Approaching
the pool from any direction the floor falls away
precipitously, dropping to 90-feet deep or more. Based
on the sizes of the surface boil and the pool, this spring
may rival Spring 1 in magnitude of flow.

Spring 3: This spring's pool is circular, about 50
feet in diameter, and its pool floor drops precipitously to
about 40-feet deep. Crumbling concrete and cement-
block walls outline its southeastern side. These walls
enclose what appears to be a very shallow, rectangular,
wading pool, possibly the remnants of an old spa or
hotel, which no longer exists.

Spring 8: This spring's basin is about 80 feet in
diameter, resembling a shallow bowl in cross section,
whose bottom slopes gradually to about 30-feet deep,
then drops steeply to 45-feet deep. Although not as deep
as Spring 2, it appears to have a large flow, since its
surface boil was about as large and as turbulent as that
of Spring 2.

Spring 9: This spring was located by a surface
boil that was about 30 feet in diameter in the channel of
Spring Creek, several hundred feet to the southwest of
Spring 1. Its basin appears to have a symmetrical cone
shape, with a depth of about 30 feet. The size and
turbulence of its surface boil indicates a large flow. It was
the only spring observed to be discharging muddy water.

Spring 10: The basin of this spring is circular,
about 75 feet in diameter, with a narrow canal entering
its northern side. The pool has a gently sloping bottom
that drops steeply to 45-feet deep. As with Spring 8, the
large, turbulent boil indicated considerable flow.

Spring 11: This spring was located by a surface
boil that was about 30 feet in diameter in the channel of
Spring Creek, several hundred feet to the southwest of
Spring 10. Its pool resembles that of Spring 9, although
not as deep. The size and activity of its boil indicates
significant flow.

Pulsating Flow

All the springs were observed to exhibit
pulsating flow, a phenomenon characterized by
alternating surges of boiling surface turbulence, followed
by relatively quiescent flow. Each phase could take as
long as a minute or more to complete. Some of the more
active boiling phases had noisy, splashing turbulence,
that was created by what appeared to be large bubbles
of water that suddenly erupted upward above the stream
surface.

A possible explanation for this phenomenon may
lie in the spring group's underground karst drainage
system. It seems reasonable to assume that the springs
are fed by a complex, even tortuous, interconnected
network of large-diameter tunnels, similar to those
supplying Wakulla Springs (Stone, 1989; Rupert, 1988;
Rosenau et al., 1977), which lies only 10 miles north on
the Woodville Karst Plain. Scuba divers have established
that some of Wakulla Springs' largest conduits' flows
change direction, and that their local source of water also
changes (George Irvine, Director, Woodville Karst Plain
Project, pers. comm., March, 1998).

These phenomena are controlled by the state of
Wakulla Springs' local potentiometric surface. Large
rains over Wakulla Springs' recharge basin can change
its potentiometric surface so that ground water is routed
differently within the underground drainage system
supplying the springs. A change of only a foot or two in
the potentiometric surface in various parts of the
recharge basin can change both the direction of flow and
the source of ground water supplying individual conduits.
This balance of recharge-discharge routing within the
underground drainage system is so sensitive to changes
in head that it also appears to be influenced by tidal
effects on the springs (George Irvine, pers. comm.,
1998). The water surface of Wakulla Springs' main pool
is less than five feet above sea level, and the Wakulla
River is tidally influenced at least as far upstream as the
bridge at US 319, about two-miles below the springs,
and possibly even further upstream to the spring-head,
itself.

Given that the Spring Creek Springs Group
probably has a similar maze-like "plumbing" system, it is
easy to visualize how enormous quantities of water,
moving rapidly and turbulently through the conduits,
could create blockages and pressure surges that would
propagate through the system. In this scenario, a tunnel
feeding a particular spring that had a pressure surge
would momentarily get more of the system's water,
resulting in an increase in its discharge. That surge
would relieve pressure in that part of the system and the
spring's discharge would decrease; then another tunnel
would experience an increase in pressure, causing a
pulse of water to its orifice; and so on.

SUMMARY

The geological element that controls or greatly
influences most of Florida's coastal environments and
ecosystems is the karstified limestone that underlies the
state. These karstified limestones form a common,
unifying linkage among the uplands, the coastal and
estuarine environments, and the continental shelf marine
realms; they link the terrestrial environments to the
marine environments. Submarine springs discharging
large quantities of terrestrial ground water can have
profound affects on the estuarine, marsh, or littoral
environments they discharge into. For example,
significant effects on salinity will determine the marine

biota that can live in the local area affected by the
springs' discharges.

Empirical evidence indicates that the spring
group's flow regime is in precarious balance with the
local water table's potentiometric surface. When water in
the creek rises approximately two or more feet above low
tide some of the springs, at least, appear to stop flowing
or they exhibit reversal of flow. Such a situation argues
against the use of the springs as a source for large-scale
withdrawals of fresh water, as has been suggested
recently. Heavy pumpage of the springs' source water
from the local water table would probably induce rapid
infiltration of brackish creek water into the aquifer.

REFERENCES

Davis, H., 1996, Hydrogeologic investigation and
simulation of ground-water flow in the Upper
Floridan aquifer of north-central Florida and
southwestern Georgia and delineation of
contributing areas for selected City of Tallahassee,
Florida, water-supply wells: U.S. Geological Survey
Water-Resources Investigations Report 95-4296,
55 p.

Fernald, E.A. and Patton, D.J., 1984, Water Resources
Atlas of Florida: Institute of Science and Public
Affairs, Florida State University, Tallahassee, 291 p.

Hendry, C.W., Jr., and Sproul, C.R., 1966, Geology and
ground-water resources of Leon County, Florida:
Florida Geological Survey, Bulletin 47,178 p.

Miller, J.A., 1986, Hydrologic framework of the Floridan
aquifer system in Florida and in parts of Georgia,
Alabama, and South Carolina: U.S. Geological
Survey Professional Paper 1403-B, 91 p.

Rosenau, J.C., Faulkner, G.L., Hendry, C.W., Jr., and
Hull, R.W., 1977, Springs of Florida: Florida
Geological Survey, Bulletin 31 (revised), 461 p.

Rupert, F.R., 1988, The Geology of Wakulla Springs:
Florida Geological Survey, Open File Report 22, 18
P.

Scott, T.M., Lloyd, J.M., and Maddox, G., 1991, Florida's
ground water quality monitoring program -
hydrogeological framework: Florida Geological
Survey, Special Publication 32, 97 p.

Stone, W.C., 1989, The Wakulla Springs Project: U.S.
Deep Caving Team, Derwood, MD, 210 p.

SUBMARINE SPRINGS
1. Bear Creek Spring
2. Cedar Island Spring
3. Cedar Island Springs
4. Choctawhatchee Springs
5. Crays Rise
6. Crescent Beach
7. Crystal Beach Spring
8. Freshwater Cave
9. Mud Hole
10. Ocean Hole Spring
11. Ray Hole Spring
12. Red Snapper Sink
13. Spring Creek Springs Group
14. Tarpon Springs
15. Jewfsh Hole
16. Unnamed Spring No. 4

I

Figure 1. Map of Florida showing locations of 16 submarine springs described by
Rosenau et al. (1977). Study area is at No. 13, Spring Creek Springs.

EXPLANATION

I WOODVILLT KARST PLAIN

SU.S. HMIHWAY

SSTATEiCOUNTY ROAD I
0= CROSS SECTION LOCATION

73- '

ISON COUNTY
WAKULA COUNTY

MILES
N. \

01 23,46 / ,. .,.
024 6
KILOMETERS

gr

o4 ,TALLAHASSEE( 1
-16
?L \ s
lJ.3a^Cf

OF MEXICO

Figure 2. Map of Leon and Wakulla Counties showing extent of the Woodville
Karst Plain (after Rupert, 1988)

Co -

a a

l tdand

dk ,l
SpringCreek pringsGroup

~L~L~Z~~

Figure 4. Northeasterly oblique aerial view of the Spring Creek area from an altitude of 1,000 feet,
October 1998 (FGS photograph).

A I l-
50 79

...40 e 65 66

7.

spot depth

00

best

A 7 A'

0 26 feet

5 mters
Horizontal and Vertical Scale

SPRING CREEK SPRINGS GROUP
Spring No. 2 +
Figure 5. Plan and cross section of Spring 2.

SPRING CREEK SPRINGS GROUP
Spring No. 3

11

x'9
N,<
1L

A -

0 25 feet

5 maters

Horizontal and Vertical Scale

Figure 6. Plan and cross section of Spring 3.

wads

am
pool
amo

-A'

* O 39+

SPRING CREEK SPRINGS GROUP
Spring No. 8

Sspot depth

0 25 feet
1 1 1 1 t /
5 meters
Horizontal and Vertical Scale

'I
I 4

Figure 7. Plan and cross section of Spring 8.

*A'

/00

'V

SPRING CREEK SPRINGS GROUP
Spring No. 9

0 25 feet

5 meter

Horizontal and Vertical Scale

SPRING CREEK SPRINGS GROUP
Spring No. 10

approx. 30' dia.
surface boil

V

stream
flow

NW

% 30+

canal
I-
A

0 25 feet

5 meters

Horizontal and Vertical Scale

A VA'

/

I 45

Figure 8. Cross section of Spring 9 (in main channel of Spring Creek), and plan
and cross section of Spring 10.

SPRING CREEK SPRINGS GROUP
Spring No. 11

approx. 30' dia.
surface boil

NW

S 20

stream
flow

O 25 feet

5 meters
Horizontal and Vertical Scale

Figure 9. Cross section of Spring 11, in main channel of Spring Creek.

//00,000

RESTORATION OF THE FLORIDAN AQUIFER TO POTABLE CONDITIONS, ST.
MARKS PENINSULA, ST. MARKS, FLORIDA

Thomas Kwader, Woodward/Clyde Consultants, 3676 Hartsfield Road, Tallahassee, FL 32303

ABSTRACT

In the late 1950's the City of Tallahassee began withdrawing ground water as a source of make-up
cooling water for a small electric generating station located in the St. Marks peninsula, Wakulla County,
Florida. The peninsula is formed by the meeting of the St. Marks River (east) and the Wakulla River (west).
Both of these rivers serve as a discharge line for the Floridan aquifer as noted by the numerous seeps and
springs observed along their banks.
The earliest wells, located near the St. Marks River, initially supplied abundant quantities of good
quality water for cooling purposes. After a few seasons of pumping it was observed that the water quality
had deteriorated in the wells located nearest the St. Marks River. Additionally, wells were drilled away from
the river and northward towards the mainland. Located approximately 800 feet apart this practice continued
until nine (9) wells had been drilled of which seven (7) had been abandoned due to deterioration in water
quality.
In 1995 a study was initiated to determine how the city should proceed to secure a good quantity of
good quality water on the peninsula, however it was necessary to implement a resource management plan
to spread the pumping stress over a larger area. This was accomplished primarily by alternating the
pumping on a weekly basis between two sets of wells to minimize upcoming of poorer quality water from
lower depths in the aquifer.
Three formerly abandoned wells were redeveloped, geophysically logged and pump tested. From
these tests a decision was made to plug back a portion of the open borehole. As a result, no new wells
were needed to attain the quantities or groundwater required under current operating conditions.

The St. Marks Peninsula is located in the
Florida Panhandle approximately 20 miles south of
Tallahassee (Figure 1). The peninsula is a triangular-
shaped area formed by the convergence of the
Wakulla River on the west and St. Marks River on the
east. The Gulf of Mexico is located about two miles
south of the convergence of the rivers. The peninsula
is a low-lying sandy area underlain by the St. Marks
Limestone at a depth of generally less than 10 feet.
The St. Marks Limestone crops out along the river
banks and can be seen in both river beds.

Discharge of ground water from the Floridan
Aquifer (St. Marks Limestone) occurs throughout the
area from numerous springs and seeps in the river
beds. Although millions of gallons of fresh water per
day discharge from this area through the river systems,
the ground water quality deteriorates rapidly with
depth. The sources of the poor quality water are
deeper waters of poorer quality and water from the toe
of the saline wedge underlying the peninsula.

In the late 1950s, the City of Tallahassee
began withdrawing ground water as a source of make-
up cooling water for a small electric generating station
located in the St. Marks Peninsula.

The earliest wells, located near the St. Marks
River, initially supplied abundant quantities of good
quality water for cooling purposes. After a few

seasons of pumping, it was observed that the water
quality had deteriorated in the wells located nearest the
St. Marks River. Additionally, wells had been drilled
away from the river and northward towards the
mainland. This practice continued until nine (9) wells,
located approximately 800 feet apart had been drilled.
Seven (7) of these wells have been abandoned
due to deterioration in water quality (Figure 2).

The wells typically had 50 to 100 feet of
casing, with an additional 50 to 100 feet of open hole
section in the limestone. Many of the wells were
completed open hole at 150 to 200 feet, near the
interface of poor quality water. The fresh-brackish
interface is deepest near the center of the peninsula
and shallowest near the rivers.

The life of the well, (the time at which an
individual well's water quality would deteriorate) would
depend upon proximity to the river, total depth, and
rate at which the wells were pumped. Pumping rates
generally ranged from 200 to 500 gallons per minute
(gpm). However, the wells generally pumped
continuously 24 hours a day to supply make-up water
for the power plant's boilers.

The life of the wells ranged from one year to
nearly ten years. Wells 1, 2, and 3 were drilled from
the edge of the St. Marks River, westward towards the
center of the peninsula, where a power line extended
northward along the water edge of the peninsula.

Distances between the wells were generally 500 to 800
feet.

In 1995, a study was commissioned by the City
of Tallahassee to locate a long-term source of ground
water for the electric generating facility. During the
gathering of data for the abandonment of the existing
wells, it was determined that the lower section of the
abandoned wells was fresh (i.e., the wells had been
restored to redevelopment conditions). It was then
theorized that wells had been over-pumped, and the
poorer quality water at depth had been drawn to the
wells.

Since the water quality in the wells appeared
to have returned to prepumping conditions, variable
rate pumping tests were conducted to assess the safe
yield of the wells in the peninsula. It was reported that
pumping the wells continuously in the 300 to 500 gpm
range was exceeding the safe yield for the area.
Pumping test data were modeled and evaluated for
long-term safe yield pumping rates. Specific capacities
measured in eight (8) wells on the peninsula ranged
from 9 to 78 gpm/feet of drawdown, with most of the
wells in the 15 to 27 gpm/feet of drawdown range.
Transmissivities generally ranged from 33,000 to
59,000 gallons per day/feet.

Step drawdown tests were conducted for this
study on abandoned Wells 6 and 7. Prior to running
the pumping tests, borehole geophysical logs were run
on Wells 3, 4, 5, 6, and 7 to determine construction
specifications and water quality in each well.

Water quality parameters chloridess and
specific conductance) were monitored for changes
during each of the pumping steps. Only a slight
degradation of water quality was detected in Well 7.
Based on the borehole geophysical logs and pumping
tests, it was decided to plug the lower portion of the
open hole from 213 to 150 feet to help assure the
poorer quality water from the lower depths would not
be drawn to the producing zone of the well.

Although water quality results are not well
documented, it appears the background water quality
for most of the peninsula is in the range of<5 to 10 for
chloride, 300 to 350 pmhos for specific conductance.
Water quality was measured in Well 9 in 1994, with
chlorides at 101 mg/L and specific conductance at 782
pmhos.

Safe yield was determined to be in the range
of 300 to 400 gpm at a continuous pumping rate.
However, other factors affected these figures,
particularly distance and rate of pumping of other wells
in the area and precipitation conditions which recharge
the Floridan in this area.

Based on the pumping tests, it was
recommended that:

* Four wells would function as supply wells for the
power plant (Wells 6, 7, 8, and 9), with only even
or odd wells pumping at the same time in order to
maximize the distance between pumping centers.
* Wells would be equipped with four identical
submergible pumps which would be capable of
pumping only 150 to 175 gpm at the wellhead
under pressure conditions (two miles of pipeline
plus 80 feet of elevated storage).
* Wells would be controlled by radio telemetry to turn
off once the elevated tank read full conditions.
* Pumping would be rotated between the even and
odd pairs on a daily (minimum) to weekly
(maximum) time interval.

All recommendations were adapted and
implemented in late 1994. The latest water quality
data available (late 1998) indicate that the quality is
very similar to background water quality for the area,
without any sign of deterioration.

A substantial cost savings was realized by not
drilling new wells and laying additional pipeline. A
considerable cost savings from the limited use of
chemicals to demineralize the water was also realized,
not to mention the improvement of the water quality in
the Floridan aquifer through the peninsula for other
users of the aquifer.

ST. MARKS
WELLS

POWER PLANT

LEGEND \

* PRODUCTION WELL
o ABANDONED WELL
A MONITORING WELL

1 MILE
1-/2
1/2

GULF OF MEXICO
3 MILES

K:\ACAD\0WGS\93\g3Fr564\gF56401 -A

STUDY AREA

FIG-1: Power Plant and Location
of Production Wells

WEST

WAKULLA RIVER

50

MSL 0.

-50

-100

-150

-200

FIG-2: HYDROGEOLOGIC CROSS-SECTION THROUGH ST. MARKS PENINSULA

K:\ACAD\DWGS\93\93F564\STMARKS-XS

ST. MARKS PENINSULA

SOUTH OF U.S. 98

EAST

NORTH

STATUS= ABD

AUGUST JULY
1960 1962
#3 #4

PLUGGED BACK
1994

MONITOR PROD. P
ABD ABD WELL WELL V

^-N STATIC WATER LEVEL
TYPICALLY 5-10 ft.

500-700'
ROD. PROD. PROD.
JELL WELL WELL

FIG-3: PROFILE OF PRODUCTION WELL CONSTRUCTION SPECIFICATIONS

K:\CDRIVE\0WG\JOB\93r564\WELLS

SEPT.
1948
#1

APRIL
1959
#2

T 1" T T I I I -

50_

50

100 __

150 ___

200

250

ABD

SOUTH

ST. MARKS RIVER WATERSHED SURFACE WATER
IMPROVEMENT AND MANAGEMENT (SWIM) PROGRAM

Tyler Macmillan, Section Director, Resource Planning, Northwest Florida Water Management District, Route 1, Box
3100, Havana, FL 32333

ABSTRACT

The St. Marks River watershed covers approximately 1, 170 square miles extending from Thomas
County in the red clay hills region of southern Georgia to the Gulf of Mexico. The watershed includes the
St. Marks River, its major tributary the Wakulla River, Apalachee Bay, and lakes Miccosukee, Lafayette, and
Munson. In May 1997 the NWFWMD completed the first SWIM Plan for the St. Marks River Watershed in
accordance with the SWIM Act, which was enacted by the Florida Legislature in 1987 and amended in
1989.
The St. Marks River Watershed SWIM Plan was developed in cooperation with the St. Marks River
Technical Advisory Committee (TAC), made up of representatives from various jurisdictions in the
watershed, resource management agencies, and other technical experts. The plan addresses priority
issues identified by the TAC (water quality, land use, pollution, environmental factors, and public
awareness) through four programs: Watershed Management, Biological Concerns, Water Quality, and
Public Awareness. Each of the programs has a set of goals, issues, and objectives to guide its
implemention as well as a number of projects that have been identified to address specific issues.
The following St. Marks River SWIM Plan Projects are either currently underway or scheduled to
commence during Fiscal Year 1999-2000:
1. Planning and Coordination This project includes coordination of the TAC; coordination with the
DEP Ecosystem Management Team, other agencies, and local governments; general program oversight;
project tracking and administration; monitoring or relevant planning and development activities within the
watershed; efforts to supplement SWIM funding through grants.
2. Land Use/Land Cover Mapping for the Entire Watershed This project entails analysis of detailed
land use and land cover information for the watershed. Tasks will include obtaining existing land use and
cover data from DEP and developing map layers and watershed specific acreage tables using Geographic
Information System (GIS). A watershed future land use map will be developed using local government
comprehensive plan future land use maps. A general environmental land use assessment will be
developed, considering historic change and potential future development, as they relate to water resources
and various government jurisdictions.
3. Baseline Biological and Water Quality Assessment and Monitoring This project will provide
comprehensive water quality, sediment, and biological assessments of sites in the St. Marks River Basin.
Monitoring will be concentrated in the lower basin, with a few upper basin sites at locations suspected to
have a significant, direct influence on water quality in the lower basin. In order to estimate pollutant
loadings, flows will be measured at selected tributaries, and in the main channel.
4. Inventory of On-Site Sewage Disposal Systems (OSDS) This project will determine the number
and location of on-site sewage disposal systems (OSDS) within the Woodville Karst Plain portion of the St.
Marks River Watershed. GIS coverages representing the spatial distribution of septic tanks in the study
area and estimates of nitrate load from OSDS will be used in the following SWIM project.
5. Examination and Prediction of Nitrate Flux through the Surface Water-Ground Water System in the
Wakulla Karst Plain This project will identify the dominant hydrochemical processes that control the
movement and fate of nitrate in shallow and deep parts of the ground water flow system in the Woodville
Karst Plain. At present, a network of wells is being established to provide for ground water sampling and
water level data collection.
6. Public Education and Awareness Public education and awareness initiatives will focus on informing
area residents and tourists of all ages about the significance of local habitats, natural resources and unique
geological characteristics such as the area's karst features. These efforts will address issues such as: the
proper use and maintenance of on-site disposal systems; the necessity of surface and groundwater
protection; the impact of point and nonpoint source pollution; the importance of fostering land and water
stewardship; ecosystem management and various environmental concerns related to the St. Marks and
Wakulla Rivers and Apalachee Bay.

FLORIDA'S SWIM PROGRAM

Florida's Surface Water Improvement and
Management (SWIM) Act was enacted by the State
Legislature in 1987 and amended in 1989. The Act
recognized that water quality in many of the state's
surface waterbodies is degraded or is in danger of
degradation, and directed the state's five water
management districts to develop and implement plans
to improve water quality and related aspects of
threatened surface waters.

Prior to plan development, each district was
required to determine which waterbodies were eligible
for the SWIM program and then prioritize those
waterbodies based upon the need for restoration and
preservation. Prioritizing SWIM waterbodies is an
iterative task, with review and updating of priority lists
required every three years. The current Northwest
Florida Water Management District (NWFWMD) SWIM
priority list consists of fourteen waterbodies, four of
which-Lake Munson, Lake Lafayette, Lake
Miccosukee, and St. Marks River-are located within
the St. Marks River basin.

The SWIM Act directs the District to develop
SWIM plans, in priority order, to include activities,
schedules, and budgets for preservation and/or
restoration. The Department of Environmental
Protection (DEP), Florida Game and Fresh Water Fish
Commission (FGFWFC), Department of Agriculture
and Consumer Services (DACS), Department of
Community Affairs (DCA), and local governments are
cooperators in this process. Once developed, the
plans are to be reviewed and, if needed, revised a
minimum of once every three years.

Currently the SWIM program is funded
primarily by legislative appropriation to the Ecosystem
Management and Restoration Trust Fund, which is
administered by the DEP Office of Water Policy. The
NWFWMD is guaranteed at least ten percent of the
Fund in any given year, with 50 percent available for
statewide discretionary distribution. Funding for the
SWIM program has been inconsistent and generally
decreasing since its initiation. Annual statewide
budgets have ranged from fifteen million dollars in FY
87-88 through FY 89-90 to zero in FY 95-96 and FY
97-98. This situation limits the overall effectiveness of
the SWIM program by hindering long-term planning
and delaying or precluding project implementation.
Project planning and implementation are time-
consuming, and monitoring of trends and progress are
inherently long-term activities.

NWFWMD SWIM program expenditures
include more than SWIM Trust Fund dollars. A twenty
percent local match (often divided among local
governments and the NWFWMD) is required to secure
funds from the SWIM Trust Fund. Additional funding is
derived from a variety of sources, including various
state and federal granting agencies.

ST. MARKS RIVER WATERSHED SWIM PLAN

The St. Marks River Watershed SWIM Plan
was completed in May 1997 (NWFWMD, 1997). The
plan's coverage is restricted to those waters in the
lower basin that have direct flow connections to the St.
Marks or Wakulla rivers. (Three closed or semi-closed
basins in the upper watershed-Lake Munson, Lake
Lafayette, and Lake Miccosukee-are scheduled for
future separate SWIM plans.) The St. Marks River
plan is organized into a hierarchy of programs, goals,
issues, objectives, and projects. Programs are general
categories that have been used to divide the plan into
distinct subject areas based upon priority issues
identified for the watershed by the Technical Advisory
Committee (TAC). The St. Marks River TAC is made
up of representatives of the various jurisdictions in the
watershed, resource management agencies, and other
technical experts. The TAC should play an integral
role in the development and implementation of the
SWIM plan by providing a forum for agency and
technical review and input. An active TAC also helps
maintain other agency and jurisdiction commitments to
watershed management. The St. Marks River
Watershed TAC is a joint committee serving the DEP
Ecosystem Management Program as well as the SWIM
program.

The plan addresses the priority issues (water
quality, land use, pollution, environmental factors, and
public awareness) through the following four programs:
Watershed Management Program, Biological Concerns
Program, Water Quality Program, and Public
Awareness Program. Each of the programs has a set
of goals, issues, and objectives to guide its
implementation as well as projects. The program goals
are broad based, identify ultimate program objectives,
and provide the underlying framework for the plan.
Under each program a number of projects have been
identified to address specific issues.

The four St. Marks River Watershed SWIM
Plan programs with their goals, issues, objectives, and
projects are described below:

Watershed Management Program

Goal:

Provide comprehensive, coordinated

management of the watershed in order to
preserve and protect the watershed
environment.
Issues: Information regarding location of
sinkholes, small streams, and various
resource features.

Information regarding existing and future land
uses for the entire basin and the impact of land
uses upon water resources.

Multiple government entities responsible for
managing components of the system.

Need to apply existing research and define
data gaps for further research to guide
management strategies and decisions.

Objectives: Implement and update as necessary a
comprehensive plan for the watershed
and develop the research necessary to
guide the management program.
Projects: M1-Administration, Planning and
Coordination
M2-Analysis of Permitted Activities
M3-Land Use/Land Cover Mapping for
the Entire Watershed
M4-Institutional/Regulatory Assessment
M5-Economic Valuation

Biological Concerns Program

Goal: Conserve and protect the biological
resources of the St. Marks and Wakulla
rivers and Apalachee Bay ecosystem.
Issues: Estuarine/saltwater resources and
environmental conditions of Apalachee
Bay.

Biological and water quality information.

Adverse impacts of exotic aquatic plants.

Adverse impacts resulting from proposed
oil drilling operations in the Gulf of
Mexico.

Identification of specific biological
resources and habitat within the basin.

Adverse impacts resulting from water
withdrawals.
Objectives: Increase information available about the
natural resources of the St. Marks and
Wakulla rivers and Apalachee Bay.

Obtain and utilize the information
necessary to assess and project changes
in the St. Marks and Wakulla rivers and
Apalachee Bay system.

Projects: B1-Baseline Biological and Water Quality
Assessment and Monitoring
B2-Seagrass Mapping, Monitoring, and
Restoration
B3-Riverine/Estuarine Ecological
Assessment

Water Quality Program

Goal: Maintain or improve current water quality
conditions within the St. Marks River
watershed.
Issues: Characterize ambient fresh and saltwater
quality and water quality trends.

Objectives:

Relationship between surface and ground
water in the watershed.

Nonpoint pollution sources.

Cumulative impacts of point and nonpoint
sources of pollution.

Potential threat to water quality due to the
impacts of various land use activities.

The potential impacts to water quality and
habitat from recreation.

Potential adverse impacts of on-site
disposal systems (OSDS) on groundwater
quality, and the possible resulting impacts
on surface waters.
Identify and quantify both point and
nonpoint sources of pollution in the
watershed and develop management
strategies that will protect and preserve
water quality.

Document water and sediment quality
and relate ambient conditions and
changes in water quality to specific
activities, such as land use, shoreline
alteration and nutrient inputs in order to
improve the management of the system.

Determine ground and surface water
interactions/relationships and identify
possible sources of water quality
problems.
Projects: W1-Point and Nonpoint Source
Assessment
W2-Sediment Assessment of the St.
Marks River at the City of St. Marks
W3-Development of Total Maximum
Daily Loads (TMDLs) and Pollution Load
Reduction Goals (PLRGs)
W4-lnventory of On-Site Sewage
Disposal Systems (OSDS)
W5-Examination of On-site Sewage
Disposal Systems (OSDS) Construction
and Maintenance Standards to Determine
Effectiveness in Karst Areas
W6-River Users Sanitary Facility Survey
W7-Examination and Prediction of Nitrate
Flux Through the Surface Water-Ground
Water System in the Wakulla Karst Plain
W8-Evaluation of Surface and
Groundwater Pollution Potential Within
the St. Marks River watershed

Public Awareness Program

Goal:

Promote sustainability of the resources of
the St. Marks River watershed by
providing for public education
opportunities to increase public

awareness of the problems and issues
associated with the system.
Issues: Lack of public awareness of natural
resources within the watershed and
human impact upon those resources.
Objective: Improve public awareness about the St.
Marks and Wakulla rivers and Apalachee
Bay ecosystem through an aggressive
public education campaign that informs
citizens about basin habitats and natural
resources, on-site disposal systems
(OSDS), responsible recreational
behavior, and responsible land and water
stewardship.
Projects: P1-Public Education and Awareness

STATUS OF ST. MARKS RIVER WATERSHED
SWIM PROJECTS

In addition to project M1, Administration,
Planning and Coordination, which is continuously
active throughout the life of the SWIM plan, the
following projects have been initiated as of November
1998.

M3-Land Use/Land Cover Mapping.

This project entails analysis of detailed land
use and land cover information for the watershed.
Tasks include obtaining existing land use and cover
data from DEP and developing map layers and
watershed specific acreage tables using Geographic
Information System (GIS). A watershed future land
use map will be produced using local government
comprehensive plan future land use maps. A general
environmental land use assessment will be developed,
considering historic change and potential future
development, as they relate to water resources and
various government jurisdictions. To date a scope of
work has been developed for this project and initial
data collection efforts have begun.

B1-Baseline Biological and Water Quality
Assessment.

This project is currently in the experimental
design/quality assurance plan stage. The project will
be similar in concept to a joint DEP/NWFWMD study
conducted in the Deer Point Lake watershed in 1990-
91 (DEP Biology Section, 1992). Repeated
measurements of a broad range of biological and water
quality parameters will be performed in order to
quantify natural variation in baseline conditions.
Approximately fifteen sampling sites will be distributed
from the upper reaches of the St. Marks and Wakulla
Rivers through Apalachee Bay. Many of these sites
will correspond to those selected for a DEP pilot study
conducted in 1996 (Singleton et al. 1997). Water
quality grab samples (nutrients, dissolved oxygen, pH,
conductivity, suspended solids) will be collected
monthly, while biological sampling benthicc
macroinvertebrates, algae, bacteria) will be done

bimonthly for two years. Algal growth assays will be
conducted either quarterly or every four months, and
24-hour dissolved oxygen measurements will be done
at a subset of sampling stations bimonthly. Sediments
will be sampled for nutrients, metals, and petroleum
hydrocarbons at the beginning and the end of the
study. Sampling is expected to begin in early spring,
1999.

W4-lnventory of On-site Sewage Disposal Systems.

This project involves determining which areas
in Leon & Wakulla counties rely on septic tanks,
identifying the type of structure occupying each parcel
with a septic tank, applying HRS OSDS flow rates
according to structure type, and calculating flow rates.
GIS coverages will be developed to represent the
spatial distribution of septic tanks in the study area.
Estimates of nitrate load from OSDS will be used in the
following SWIM projects: Examination of On-Site
Disposal Systems Construction and Maintenance
Standards to Determine Effectiveness in Karst Area
and Examination and Prediction of Nitrate Flux
Through the Surface and Ground Water System in the
Woodville Karst Plain. Preliminary data gathering
efforts have begun and current information sources
include: Tallahassee-Leon County, Wakulla County,
Talquin Electric, and HRS.

W7-Examination and Prediction of Nitrate Flux

Through the Surface Water-Groundwater
System in the Wakulla Karst Plain. This project will
identify the dominant hydrochemical processes that
control the movement and fate of nitrate in shallow and
deep parts of the ground water flow system in the
Woodville Karst Plain. At present, a network of wells is
being established to provide for ground water sampling
and water level data collection. A Quality Assurance
Plan for the work has been submitted to FDEP and is
awaiting approval. Additionally, the Inventory of On-
site Sewage Disposal Systems Project is in progress
and an order of magnitude ground water budget for the
study area has been calculated.

P1-Public Education and Awareness.

Public education and awareness initiatives
focus on informing area residents and tourists of all
ages about the significance of local habitats, natural
resources and unique geological characteristics such
as the area's karst features. To accomplish this, the
comprehensive educational program will include: a
portable educational display about the District and local
environmental issues, interagency coordination and
general public awareness activities such as special
exhibits, media relations, community events and other
endeavors. St. Marks River watershed educational
display has been featured at the Humantee Festival,
Springtime Tallahassee, and the Wakulla Springs
Earth Science Fair. Various program issues and
needs of existing area public education programs

(Wakulla Springs State Park, Gulf Specimen Marine
Lab, FSU Marine Lab, St. Marks Wildlife Refuge) have
been identified as well as ways the District can
facilitate the education programs currently operating
within the watershed.

REFERENCES

DEP Biology Section, 1992, Biological Water Quality of
the Deer Point Lake Drainage Basin, Bay County
Florida: Unpublished report, 89 p.

Singleton, T., Lee, P., Hand, J., Frydenborg, R.,
Castellanos, M., Tterlikkis, D., Harnett, F.,
Clemens, L., Hatchett, L., and Hulbert. J., 1997,
St. Marks River Watershed Pilot Project: A Model
for Basin Planning and Management: Florida
Department of Environmental Protection.

NWFWMD, 1997, St. Marks River Watershed Surface
Water Improvement and Management Plan:
Program Development Series 97-1, 102 p.

STORMWATER CONCERNS AND MANAGEMENT
ON THE WOODVILLE KARST PLAIN

Eric H. Livingston, Environmental Administrator, Department of Environmental Protection, Division of Water
Facilities, Stormwater Section, MS 3570, 2600 Blair Stone Road, Tallahassee, FL 32399-2400

ABSTRACT

Nonpoint sources of pollution are the largest contributor of pollutant loading to be surface and
ground water systems of the Woodville Karst Plain. In patricular, urban stormwater runoff from the City of
Tallahassee that drains into Lake Munson, along with contributions of runoff that drain into Lake Lafayette
are the major sources of pollutant loading to these waters. This talk will present a brief introduction to the
stormwater problem but will focus mainly on what actions are being taken, or need to be taken, to minimize
stormwater pollution. Current structural improvements planned by the City of Tallahassee and Leon
County, along with other suggested improvements will be reviewed.

WATER QUALITY STATUS IN LEON COUNTY, FLORIDA:
WHAT'S HAPPENING UPSTREAM...

Helge Swanson, Consultant, 834 Watt Drive, Tallahassee, FL 32303

ABSTRACT

Leon County and its primary urban complex, the City of Tallahassee, sit atop the clayhill and sandhill
covering a vast and dynamic karstic substrata, including, among other things, the southern tip of the
Floridan aquifer. Area groundwater discharges include Wakulla Springs and numerous other springs and
associated riverine systems of this generally wet natural environment. The past 15 years (or so) of local
environmental history has included a recognition of this and other related surface water and ground water
quality and quantity phenomena, resulting in considerable research, planning, management and regulation.
However, the effectiveness of these efforts remain unclear. While a comprehensive and objective
evaluation of effectiveness is well beyond the scope of this talk, if we had to guess, based on what we know
now, where are we?

Four reasons come to mind for discussing Leon
County's lakes at a Woodville Karst Plain Symposium:

1. the obvious reason is that they are all uphill and
that whether by surface connection or ground
water connection, or both, there are direct
hydrologic connections;
2. what Leon County has learned about the sensitive
ecology of these waterbodies is at least generally
applicable to the future ecology of the WKP's
surface water and ground water habitats;
3. the programmatic and policy history of pain and
struggle may be prophetic as the WKP, the coastal
marsh belt and the maritime of Apalachee Bay feel
the impacts of urbanization; and,
4. perhaps the most frightening reason is that our city
and county politicians are developing what is
euphemistically referred to as a "south side
strategy". Consider a subtle but significant
precedent set by the giant Southwood
development, portions of this project actually fall
south of the Cody Scarp!

From a long-term ecological perspective, Leon
County's clayhill, closed-basin lakes give a historic
account of the adverse threshold effects of the
anthropogenic impacts. In the period following
European settlement, a continuous process of land
change began, from agriculture, to silviculture and
most recently, urban-culture have incrementally altered
and re-altered the landscape. Land use intensification
facilitated economic development on the one hand,
while, in the aggregate, adversely affecting local and
regional biogeochemical processes, on the other. As a
result, a consistent and increasingly urgent scientific
literature has focused on the elimination and decline of
many area natural features. Unfortunately, this
scientific awareness has yet to effect the full range of
necessary remedial actions.

Consider for example, that in the early 1970's,
the Florida Division of State Planning published its
concerns that increasing urbanization and associated
stormwater pollution entering through the Megginnis
Arm watershed would eventually lead to degraded lake
quality. Since then there have been numerous
additional episodes, so many in fact, that from time to
time, it has been difficult to tell the random noise from
the clear warnings. Unfortunately, Lake Jackson and
other Leon County lakes continue to show signs of
urban stormwater pollution and associated natural
aquatic habitat deterioration.

Lack of follow-through and polarized rhetoric
have both confused the picture and served to damper
the enactment of effective policy. The problems of the
Kissimmee-Okeechobee-Everglades system, well
documented by the mid-1970s, led not to corrective
measures but to squabbling over who was most to
blame and who now has to pay to fix the problem. This
discussion has been going on for 25 years. Central
Florida's Lake Apopka went hypereutrophic in the
1960s and is still the focus of much fruitless debate.
The pollution-induced problems of Apalachicola Bay,
with its productive oyster beds and spartina marshes
also began to show up in the early 1970s, and so on
and so on. Environmental literature around the world
is full of similar case studies. Tallahassee-Leon
County is not unique in its under-functioning when it
comes to being stewards of the natural world.

In fact, this may be part of the problem that it
is the natural world suffering. When people, our
money or our property suffer adverse environmental
impacts, amazing things happen with incredible speed!
A fact of the contemporary world especially the
western, industrialized world is that most of us are
several steps removed from nature, often oblivious to
its presence unless the weather is bad, the
infrastructure goes out, or worse, both. How many of

us actually miss drinking lake water while we swim?
How many of us even miss swimming in lakes?

A confusing aspect for the public has been the
frequent arguing among experts. However, what
sounds like uncertainty and disagreement over Lake
Jackson's fate, for example is really semantics an
argument over the adjectives used to describe its
condition. Words and phrases like "dying lakes", "sick
fish", "toxic algae", and so forth become the focus.
There is no real disagreement among experts that
stormwater run-off is polluting our lakes.

Another confusing issue is the role of
regulation. If we have so many tough environmental
regulations, why does surface water quality continue to
decline and the list of adverse ecological changes
continue to grow larger? The answer lies in what we
have not done, which I will discuss in a moment.

Lake impacts began with the early settlers; the
biggest hit was probably pre-1960s when, as a part of
public policy, most of the creeks, marshes, sloughs
and swamps leading to area lakes were ditched,
drained, diverted and culverted. Subsequently, the
ecology of the entire system was affected. Streams
meandering through vegetated floodways and sloughs
are nature's way of cleaning water before it enters the
receiving waterbody. When streams are eliminated,
the problem-causing sediments, nutrients and other
pollutants go right into the lake. The final assault was
the placement of non-regulated roads and strip
commercial developments upstream of the water
bodies. In the Lake Munson Basin, for example, much
of the polluted stormwater comes from the pre-
ordinance development throughout downtown
Tallahassee, the Gaines Street corridor, FSU and
FAMU areas, among others. The same is true for
Upper Lake Lafayette, where most of eastern
Tallahassee drains highly polluted runoff into the
ground water.

Lake's Jackson, Lafayette, Munson, Hall and
now, lamonia have, to varying degrees, early signs of
adverse ecological changes from stormwater pollution.
Not little dead canaries, as the metaphor suggests, but
subtle changes in lake ecologies more frequent and
longer lasting algae blooms, turbid water, liquid mud
replacing sandy bottoms, invading exotics replacing
native plants, nutrient over-enrichment, fish kills and a
variety of chemical changes including higher ammonia
levels and declining dissolved oxygen and so forth.

However, despite the slow call to arms, some
steps have been taken. One victory as noted, are the
tough standards that new development are required to
meet. However, what we have not done is gone back
to retrofit all the already impacted watersheds, bringing
them up to current standards of treatment. This water
quality retrofit requirement, by the way, is one of many
failed promises made to the community in the
Tallahassee-Leon County Comprehensive Plan.

This, however, is old news. The state-required
Evaluation and Appraisal Report (EAR), lists all the
unaddressed objectives, policies and program
initiatives of the comprehensive plan. The critical point
here is that until we retrofit for water quality treatment,
the lakes will continue to decline and as the ecological
effects of decline increase from threshold to threshold,
the costs of lake restoration will increase exponentially
until such undertakings become unaffordable.

Water quality retrofit is not to be confused with
flood control; these are two different objectives,
although with careful planning and design the same
measures can work for both objectives. Pursuing duel
design objectives is particularly important given that
city flooding inevitably pollutes the downhill county
lakes. Unfortunately, up through the present, the city
and county have been unable to coordinate resolution
of this issue in spite of agreeing in the
comprehensive plan that their regulatory and
stormwater management programs should be
consolidated, or at the very least, coordinated.
(Another failed item mentioned in the EAR Report). In
the meantime, the city is moving ahead to improve
stormwater conveyances and flood control within its
jurisdiction but stonewalling in meeting its
environmental responsibility to join the county downhill
in lake management. The county on the other hand,
still does not have a handle on the extent of the lake
problem, how to address it and most importantly, how
to pay for it. In this regard, the county has botched
several previous efforts to secure appropriate funding.
Let us hope that this interjurisdictional squabbling is
not a sign of things to come between uphill neighbors
of Leon County and Tallahassee and those downhill
including Wakulla and Franklin Counties.

This is not to say that no progress has been
made in the Leon County lakes issues. There are
many examples of good, albeit uncoordinated, water
quality management. Some positive examples include
the Gum Swamp and Lake Henrietta restorations
(Leon County); the Piney-Z restoration (City of
Tallahassee); greenway acquisitions wherever
floodplains, riparian forests, creeks, ravines and lake
shores have been involved; the advances in GIS and
watershed planning; stormwater utilities; and the
dredging of polluted sediments from the Megginnis
Arm of Lake Jackson (Northwest Florida Water
Management District), and so forth. However, the
problem remains one of lack of a coordinated, informed
and aggressive water quality program that takes our
science seriously, recognizing the increasing urgency
of the matter.

In achieving this, several steps must be taken.
First, combine the regulatory and stormwater
management programs of the city and county into one
holistic group responsible for all elements of the
system. Second, develop a water quality retrofit plan
for all the currently problematic watersheds (there are
probably 25 to 30 of them at this point). Include an

	Front Cover
	Front Matter
	Table of Contents
	Main

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