Water-Quality Assessment of Southern Florida: 

An Overview of Available Information on Surface 

and Ground-Water Quality and Ecology

By Kirn H. Haag, Ronald L. Miller, Laura A. Bradner, 

and David S. McCulloch

U.S. Geological Survey

Water-Resources Investigations Report 96-4177

Prepared as part of the

National Water-Quality Assessment Program

Tallahassee, Florida 

1996
FOREWORD

The mission of the U.S. Geological Survey (USGS) is to assess the quantity and quality of the earth resources of the 

Nation and to provide information that will assist resource managers and policymakers at Federal, State, and local levels 

in making sound decisions. Assessment of water-quality conditions and trends is an important part of this overall mission.

One of the greatest challenges faced by water-resources scientists is acquiring reliable information that will guide 

the use and protection of the Nation's water resources. That challenge is being addressed by Federal, State, interstate, and 

local water-resource agencies and by many academic institutions. These organizations are collecting water-quality data for 

a host of purposes that includes: compliance with permits and water-supply standards; development of remediation plans 

for a specific contamination problem; operational decisions on industrial, wastewater, or water-supply facilities; and 

research on factors that affect water quality. An additional need for water-quality information is to provide a basis on which 

regional and national-level policy decisions can be based. Wise decisions must be based on sound information. As a society 

we need to know whether certain types of water-quality problems are isolated or ubiquitous, whether there are significant 

differences in conditions among regions, whether the conditions are changing over time, and why these conditions change 

from place to place and over time. The information can be used to help determine the efficacy of existing water-quality 

policies and to help analysts determine the need for and likely consequences of new policies.

To address these needs, the Congress appropriated funds in 1986 for the USGS to begin a pilot program in seven 

project areas to develop and refine the National Water-Quality Assessment (NAWQA) Program. In 1991, the USGS began 

full implementation of the program. The NAWQA Program builds upon an existing base of water-quality studies of the 

USGS, as well as those of other Federal, State, and local agencies. The objectives of the NAWQA Program are to:

 Describe current water-quality conditions for a large part of the Nation's freshwater streams, rivers, and aquifers.

 Describe how water quality is changing over time.

 Improve understanding of the primary natural and human factors that affect water-quality conditions.

This information will help support the development and evaluation of management, regulatory, and monitoring 

decisions by other Federal, State, and local agencies to protect, use, and enhance water resources.

The goals of the NAWQA Program are being achieved through ongoing and proposed investigations of 60 of the 

Nation's most important river basins and aquifer systems, which are referred to as study units. These study units are 

distributed throughout the Nation and cover a diversity of hydrogeologic settings. More than two-thirds of the Nation's 

freshwater use occurs within the 60 study units and more than two-thirds of the people served by public water-supply 

systems live within their boundaries.

National synthesis of data analysis, based on aggregation of comparable information obtained from the study units, 

is a major component of the program. This effort focuses on selected water-quality topics using nationally consistent 

information. Comparative studies will explain differences and similarities in observed water-quality conditions among 

study areas and will identify changes and trends and their causes. The first topics addressed by the national synthesis are 

pesticides, nutrients, volatile organic compounds, and aquatic biology. Discussions on these and other water-quality topics 

will be published in periodic summaries of the quality of the Nation's ground and surface water as the information becomes 

available.

This report is an element of the comprehensive body of information developed as part of the NAWQA Program. The 

program depends heavily on the advice, cooperation, and information from many Federal, State, interstate, Tribal, and local 

agencies and the public. The assistance and suggestions of all are greatly appreciated.

Robert M. Hirsch 

Chief Hydrologist

Contents III
IV Contents
CONTENTS

Foreword...............................................................................................................................................................^

Abstract........................................................................................................................................................^ 1

Introduction...................................................................................................................................................^ 1

Purpose and Scope........................................................................................................................................................... 4

Surface-Water Quality in Southern Florida ............................................................................................................................... 4

Overview of Surface-Water Quality and Hydrology........................................................................................................ 6

Issues of Regional Importance to Surface-Water Quality................................................................................................ 8

Altered Patterns of Water Flow.............................................................................................................................. 8

Relation of Atmospheric Deposition to Surface-Water Quality ............................................................................ 9

Nutrient Enrichment............................................................................................................................................. 10

Pesticides and Other Organic Compounds in Water and Sediment..................................................................... 12

Radioactivity........................................................................................................................................................ 18

Ground-Water Quality in Southern Florida ............................................................................................................................. 18

Overview of Ground-Water Quality and Hydrogeology................................................................................................ 18

Issues of Regional Importance to Ground-Water Quality.............................................................................................. 19

Saltwater Intrusion............................................................................................................................................... 19

Nutrient Enrichment............................................................................................................................................. 2

Occurrence and Distribution of Pesticides........................................................................................................... 22

Volatile Organic Compounds............................................................................................................................... 22

Metals and Trace Elements ..................................................................................................................................23

Radioactivity ................................................................

Aquatic Ecology in Southern Florida ...................................................................................................................................... 25

Overview of Aquatic Ecology........................................................................................................................................ 25

Issues of Regional Importance to Aquatic Ecology.......................................................................................................28

Altered Hydropatterns..........................................................................................................................................28

Influence of Nutrient Enrichment on Habitat Integrity........................................................................................ 28

Occurrence and Distribution of Mercury .............................................................................................................29

Endocrine Disruption and Other Effects of Pesticides on Biota.......................................................................... 30

Spread of Exotic Plant and Animal Species......................................................................................................... 31

Summary .................................................................................................................................................................^

References Cited.........................................................................^

Appendix: Data Sources and Computation Methods Used for Pie Diagrams of Estimated Nutrient Loads 

in Southern Florida................................................................................................................._^

FIGURES

1. Map showing surface-water basins in southern Florida.................................................................................................... 2

2. Map showing major canals, control structures, and other hydrologic features in southern Florida.................................. 5

3. Pie charts showing estimated phosphorus loading from point and nonpoint sources in surface-water basins in

southern Florida............................................................................................................................................................... 13

4. Pie charts showing estimated nitrogen loading from point and nonpoint sources in surface-water basins in

southern Florida............................................................................................................................................................... 14

5-8. Maps showing:

5. Estimated total phosphorus loads for selected canal and river outflows from surface-water basins in

southern Florida.......................................................................................................................................................... 16

6. Estimated total nitrogen loads for selected canal and river outflows from surface-water basins in southern Florida....... 17

7. Aquifer systems in southern Florida and extent of peat in the Everglades region ..................................................... 20

8. Occurrence of hydrogenated aliphatic and monocyclic aromatic hydrocarbons in ground water in southern Florida 

number of water utilities with untreated water samples in which concentrations of halogenated aliphatic 

hydrocarbons exceeded drinking-water guidance concentrations; number of water utilities with untreated 

water samples in which concentrations of monocyclic aromatic hydrocarbons exceeded drinking-water guidance 

concentrations; number of background wells in which halogenated aliphatic hydrocarbons were detected in 

water samples; number of background wells in which monocyclic aromatic hydrocarbons were detected in 

water samples......................................................................................................................................................^

Contents V
Tables

1. Average nutrient concentrations in precipitation at selected sites in Florida, 1990-92.......................................

2. Estimated annual atmospheric loading of nitrogen and phosphorus at selected sites in Florida ........................

3. Estimates of nitrogen and phosphorus inputs to drainage basins in the Southern Florida NAWQA study unit.

4. Extent of wetlands in drainage basins in southern Florida..................................................................................

.10 

.11 

.15

.25

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

Multiply

square meter (m2)

hectare (ha)

square kilometer (km2)

cubic meter (m3)

meter (m)

meter per second (m/s)

liter (L)

centimeter (cm)

centimeter per year (cm/yr)

centimeters per kilometer (cm/km)

kilometer (km)

kilometer per day (km/d)

kilogram

square kilometer (km2)

megagram (Mg)

By

0.0002471

2.471

247.1

35.31

3.281

3.281

0.2642

0.3937

0.3937

0.6239

0.6214

0.6214

2.2046

0.3861

1.016

To obtain

acre

acre

acre

cubic foot

foot

foot per second

gallon

inch

inch per year

inch per mile

mile

mile per day

pound

square mile

ton

Degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) by use of the following equation: °F = (9/5)(°C) + 32

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)-a geodetic datum derived 

from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.

Abbreviated water-quality units used in this report: Chemical concentrations and water temperatures are given in metric units. Chemical 

concentration is given in milligrams per liter (mg/L) or micrograms per liter (ug/L). Milligrams per liter is a unit expressing the concentration 

of chemical constituents in solution as weight (milligrams) of solute per unit volume (liter) of water. One thousand micrograms per liter is 

equivalent to one milligram per liter. For concentrations less than 7,000 mg/L, the numerical value is the same as the concentration in parts 

per million.

ADDITIONAL ABBREVIATIONS

BCNP Big Cypress National Preserve

BNRP Broward County Department of Natural Resource Protection

DERM Dade County Environmental Resource Management

EAA Everglades Agricultural Area

ENP Everglades National Park

FDEP Florida Department of Environmental Protection

FGFWFC Florida Game and Freshwater Fish Commission

LEC Lower East Coast

NFS National Park Service

SFWMD South Florida Water Management District

STA Stormwater Treatment Area

SWFWMD Southwest Florida Water Management District

USAGE U.S. Army Corps of Engineers

USEPA U.S. Environmental Protection Agency

USFWS U.S. Fish and Wildlife Service

USGS U.S. Geological Survey

WCA Water Conservation Area

CHEMICAL ABBREVIATIONS

BHC hexachlorocyclohexane

DDE 1' (2,2-dichloroethenylidene)bis[4-chlorobenzene]

DDT 1' 92,2,2-trichloroethenylidene)bis[4-chlorobenzene]

EBDC ethylenebisdithiocarbamates

EDB ethylene dibromide

MSMA monosodium methanearsonate

PAH polyaromatic hydrocarbons

PCB polychlorinated biphenyl

VOC volatile orcanic carbon

ppm parts per million

ppb parts per billion

pCI/L picocuries per liter

ug/L micrograms per liter

mg/L milligrams per liter

< less than

> greater than

VI Contents
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Any use of trade, product, or firm names in this publication is for descriptive purposes only 

and does not imply endorsement by the U.S. Geological Survey.

For additional information Copies of this report can be

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

Suite 3015 Box 25286

227 N. Bronough Street Denver, CO 80225

Tallahassee, FL 32301
Water-Quality Assessment of Southern Florida: 

An Overview of Available Information on Surfaceand Ground-Water Quality and Ecology

By Kim H. Haag, Ronald L. Miller, Laura A. Bradner, and David S. McCulloch

Abstract

This report summarizes water-quality conditions, issues of concern, and management efforts 

underway in southern Florida. The report is 

designed to provide a conceptual framework for the 

Southern Florida National Water Quality Assessment (NAWQA) study that began in 1994. The 

report makes reference to the most important waterquality literature pertaining to southern Florida, to 

water-quality studies that are underway or planned, 

and to topics which are of high priority in the study 

unit. These topics include: the availability and suitability of water for competing demands; nutrient 

enrichment of the Everglades; transport, degradation, and effects of pesticides; and the sources and 

cycling of mercury in the ecosystem.

The report also includes a retrospective analysis and conceptual presentation of nutrient loading, which is a high priority for the national 

NAWQA Program and for regional water-quality 

managers. Nutrient contributions from point and 

nonpoint sources are estimated for nine basins in 

the study area and are discussed in relation to land 

use. Fertilizer is the dominant source of phosphorus in eight basins and the dominant source of 

nitrogen in at least five basins. Atmospheric 

sources of nitrogen contribute more than 20 percent of the total nitrogen input to all basins and are 

the dominant source of nitrogen input to Lake 

Okeechobee and the Everglades.

Nutrient loads are also estimated in selected 

canal and river outflows in southern Florida to provide a spatial overview of the magnitude of nutrient 

loading to coastal waters. Annual phosphorus loads 

from the Peace River are the highest in the study 

unit; annual phosphorus loads from the Caloosahatchee River and the major Palm Beach canals are 

also high, compared to other parts of southern Florida. Estimated annual loads of phosphorus from 

parts of the Big Cypress Basin and the S-12 watercontrol structures of the Tamiami Canal are low 

compared with estimated phosphorus loads in outflows in the northern part of the study unit. Annual 

nitrogen loads in southern Florida were highest in 

outflows from the Caloosahatchee River Basin and 

the major Palm Beach canals. Nitrogen loads in outflows from parts of the Big Cypress subbasin were 

lower than those estimated to the north.

INTRODUCTION

The Southern Florida National Water Quality 

Assessment (NAWQA) study unit encompasses about 

50,500 km2 . It is part of a regional ecosystem which 

includes coastal waters between Charlotte Harbor on 

the Gulf of Mexico and the St. Lucie River on the 

Atlantic Ocean and the lands that drain into these 

waters (fig. 1). The elevation in the study unit ranges 

from about 90 m above sea level to sea level along the 

coast. The climate is subtropical and humid with mean 

temperatures ranging from about 15° C in the winter to 

about 27° C in summer (Florida Department of Natural 

Resources, 1974; Duever and others, 1994). Average 

annual rainfall ranges from 100 to 1,075 cm, and more 

than half of the rainfall occurs in the wet season from 

June through September (Thomas, 1974).

Introduction
83° 82° sr 80°

28°

27°

26°

25°

SOUTHERN FLORIDA

NAWQA STUDY AREA

BOUNDARY LOCATION

OF

STUDY 

UNIT

Lakeland 

Tampa

Lake 

Qkeechobee 

echobee

West 

Palm 

Beach

Charlotte 

Harbor Caloosa^hatche

Boca 

|( Raton 

Fort 

uflerdale

EXPLANATION 

Big Cypress

SURFACE WATER BASIN 

BOUNDARY AND NAME

s

Florida Keys

50 MILES

50 KILOMETERS

Base from U.S. Geological Survey digital data, 1:2,000,000,1972

Albers Equal-Area Conic projection

Standard Parallels 29°30' and 45°30', central meridian -83°00'

Figure 1. Surface-water basins in southern Florida.

Water-Quality Assessment of Southern Florida: An Overview of Available Information
Southern Florida is underlain by shallow-marine 

carbonate sediments that contain three major aquifers 

systems the surficial, intermediate, and Floridan. 

Wetlands are a predominant feature of the landscape 

and are maintained as a result of abundant rainfall and 

the absence of surface relief. Wetlands in the northern 

part of the study unit are drained by several large rivers 

that include the Kissimmee, Peace, Myakka, and 

Caloosahatchee Rivers. In the southern part of the 

study unit, much of the land is inundated during the wet 

season, and water moves by sheetflow toward the 

coast. The Everglades is a vast freshwater marsh originally covering about 10,000 km2 and extending from 

the southern edge of Lake Okeechobee south to Florida 

Bay. The Everglades Basin has an almost imperceptible 

slope to the south, averaging less than 3 cm/km. The 

Big Cypress Basin to the west of the Everglades is on 

slightly higher ground. The land surface is relatively 

flat with numerous, low limestone outcrops and depressions. Water in the Big Cypress Basin drains to the 

south and southwest through cypress strands into the 

coastal mangrove forest. The Florida Keys is a series of 

low limestone islands extending 225 km southwest of 

the mainland. The physiography, climate, geology, and 

hydrology of the south Florida region are described 

more fully by McPherson and Halley (1996).

The ecosystem in southern Florida has undergone 

significant alteration over the past century, principally 

in response to the demands of a growing population. 

Activities included extensive drainage and development. When the initial alterations began, understanding 

and appreciation of the value and function of wetlands 

was very limited. Once the effects of drainage and 

development became evident and began to affect the 

environment, efforts turned towards restoration. Initial 

data-gathering efforts focused on studies of water supply, water use, and flood prevention. During the 1970's, 

an awareness of the importance of water-quality and 

habitat protection emerged. Of particular interest are 

the effects of pesticides, trace elements, and excess 

nutrients on water quality and aquatic ecology. Among 

the most active agencies gathering data in southern 

Florida are the Florida Department of Environmental 

Protection (FDEP), the Florida Game and Freshwater 

Fish Commission (FGFWFC), the National Biological 

Service (NBS), the National Park Service (NPS), the 

National Atmospheric and Oceanic Administration 

(NO A A), the South Florida Water Management 

District (SFWMD), the Southwest Florida Water 

Management District (SWFWMD), the U.S. Geological Survey (USGS), the U.S. Army Corps of 

Engineers (USAGE), the U.S. Fish and Wildlife Service (USFWS), and the U.S. Environmental Protection 

Agency (USEPA). Other organizations which actively 

study water quality in southern Florida include several 

county governments, Duke University, the Florida 

Institute of Technology, Florida International University, Louisiana State University, the University of 

Florida, and the University of Miami. Numerous individuals have also published information relevant to 

water quality and ecology in southern Florida.

The study of surface- and ground-water quality and 

aquatic ecology in the southern Florida ecosystem has 

a long history. The amount of available data is tremendous and a brief summary of all available water-quality 

and ecological data is beyond the scope of this report. 

For example, the SFWMD alone operates 26 major 

water-quality monitoring programs that incorporate 

984 sampling stations. Much of the retrospective data 

available through 1994 was collected by missionoriented agencies to address strictly defined regulatory 

issues, answer specific questions in the context of 

resource utilization, or provide guidance for resource 

management within a single watershed. Although these 

data have unquestioned utility, they often cannot be 

used to answer questions which involve multiple 

watersheds or address more complex water-quality 

issues. Among the most important water-quality 

questions being addressed in southern Florida in the 

1990's are:

 What is the availability and suitability of water 

for competing demands?

 What key components of the hydrologic system 

are needed to support a diverse, self-sustaining 

ecosystem?

 How does atmospheric deposition influence 

surface-water quality?

 Are contaminants from human activities 

widespread, and do they adversely affect 

ecosystems?

 What are the processes that transform and 

transport nutrients?

 What are the origins and pathways for the 

cycling of mercury in the ecosystem?

There are several important, broadly based, environmental programs now underway in southern Florida that 

address these and related questions (South Florida Water 

Management District, 1995). Everglades water-quality 

litigation was filed by the Federal Government in 1988 

and resolved by a negotiated State-Federal settlement

Introduction
agreement in 1991. One goal of the settlement was to 

establish long-term limits on phosphorus concentrations 

for the Arthur R. Marshall Loxahatchee National Wildlife Refuge and the Everglades National Park.

In 1993, the South Florida Ecosystem Restoration 

Task Force was formed to initiate an interagency effort 

to reestablish and maintain the ecosystem integrity of 

southern Florida. The Task Force is composed of Federal and State agencies involved in Everglades restoration. In 1994, Florida passed the Everglades Forever 

Act to initiate restoration of the Everglades and Florida 

Bay. The area identified for restoration and protection 

by the act is called the Everglades Protection Area and 

is comprised of the Everglades National Park (ENP) 

and the Water Conservation Areas (WCAs): WCA-1 

(the Arthur R. Marshall Loxahatchee National Wildlife 

Refuge), WCA-2, and WCA-3 (fig. 2). The Everglades 

Protection Area encompasses a total of about 

810,000 ha. Two major components of the act are:

 The Everglades Construction Project, which will 

entail construction of more than 16,200 ha of 

wetlands called Stormwater Treatment Areas 

(STAs) designed to remove nutrients (specifically phosphorus) and other contaminants from 

agricultural stormwater runoff from the 

Everglades Agricultural Area (EAA); and

 Implementation of on-farm Best Management 

Practices for reduction of nutrient loads from the 

EAA, which produces about 45 percent of the 

phosphorus load to the Everglades.

The Everglades Water Quality Model is being developed and tested by the SFWMD in support of the act 

and to evaluate the efficacy of the Everglades Nutrient 

Removal Project (South Florida Water Management 

District, 1995).

In 1993, the USEPA initiated a program of research, 

monitoring, and regulatory efforts to determine the 

sources, extent, transport, transformation, and pathways 

of mercury in southern Florida ecosystems. This initiative is a part of the USEPA Regional Environmental 

Monitoring and Assessment Program (U.S. Environmental Protection Agency, 1993). Since 1995, the USGS 

has provided multidisciplinary hydrologic, cartographic, 

and geologic data that relate to the mainland of southern 

Florida, Florida Bay, and the Florida Keys and Reef ecosystems, as a part of the USGS South Florida Ecosystem 

Program (U.S. Geological Survey, 1995).

A recent consensus has emerged that agencies and 

individuals must go beyond a mere assessment and 

understanding of the southern Florida environment and 

begin to protect the remaining natural system and 

restore some watersheds to predevelopment waterquality conditions and patterns of hydrologic function. 

The USGS is committed to providing scientific information that will contribute to the protection and restoration effort in southern Florida (McPherson and 

Halley, 1996).

Purpose and Scope

This report was written as part of the retrospective 

analysis of existing data and information for the Southern Florida NAWQA. Surface-water quality, groundwater quality, and aquatic ecology are closely related in 

southern Florida and are difficult to discuss separately. 

Nevertheless, they are covered in separate sections of 

this report to be consistent with other reports of the 

national NAWQA Program. The report briefly:

(1) summarizes relevant published water-quality and 

ecological information pertaining to southern Florida;

(2) describes selected regional conditions, trends, and 

issues of importance to surface- and ground-water 

quality and ecology; (3) suggests possible relations of 

water quality and ecology to natural and human factors; (4) indicates what types of water-quality and ecological data are lacking; and (5) presents a conceptual 

description of nutrient loading in surface waters of 

southern Florida. The report will be used to help 

develop a study plan for the Southern Florida NAWQA 

and to provide information to the NAWQA National 

Synthesis Team for incorporation into the nationwide 

synthesis of water-quality information.

SURFACE-WATER QUALITY IN 

SOUTHERN FLORIDA

Many factors influence surface-water quality in the 

watersheds of southern Florida. A short description of 

historical conditions and a summary of the major alterations which have occurred as a result of human activities in south Florida are presented. A brief overview of 

available surface-water-quality data and a brief discussion of important water-quality issues is presented in this 

report to provide a framework for the study design of the 

NAWQA Program in the Southern Florida study unit.

Water-Quality Assessment of Southern Florida: An Overview of Available Information
83° 82° 81° 80<

28°

27°

26°

25°

Warn

Mineral

Springs

ChailoL 

Harbor

O 

O

Atlantic

Coastal

Ridge

EXPLANATION

WATER CONSERVATION 

AREAS. WCA 1 IS ALSO 

ARTHUR R. MARSHALL 

LOXAHATCHEE NATIONAL 

WILDLIFE REFUGE

SOUTHERN FLORIDA 

NAWQA STUDY AREA 

BOUNDARY

Military 

Canal

SO MILES

50 KILOMETERS

J_ _L

Base from U.S. Geological Suivey digital data, 1:2,000,000, 1972

Abets Equal-Area Conic project! 

Standard Parallels 29°30' and 4!5°30', central meridian -83°00'

Figure 2. Major canals, control structures, and other hydrologic features in southern Florida.

Surface-Water Quality in Southern Florida 5
Overview of Surface-Water Quality and 

Hydrology

Historically, southern Florida was characterized by 

large areas of wetlands that were drained by numerous, 

small coastal streams and several large rivers. The 

Peace, Myakka, and Caloosahatchee Rivers drained the 

northwestern parts of the study area and emptied into 

Charlotte Harbor and the Gulf of Mexico. The Kissimmee River meandered through the central part of the 

study area and drained into Lake Okeechobee. Most of 

the land south of Lake Okeechobee was wetlands, 

including the Everglades and Big Cypress Swamp, 

where surface water moved slowly by sheetflow to the 

south and southwest into Florida Bay and the Gulf of 

Mexico (Davis, 1943). During high-water periods, 

surface and ground water also spilled and seeped into 

coastal waters of the Atlantic Ocean, including Biscayne Bay (Parker, 1974). Seasonal flows of freshwater 

created salinity conditions which supported highly productive estuarine and marine fisheries (Lindall, 1973). 

Much surface water was lost through evapotranspiration and returned to the system between June and October as rainfall. Water levels in the Everglades fluctuated 

seasonally over several meters during years with normal rainfall.

Historically, the Everglades was a low-nutrient 

system where ecosystem productivity was primarily 

limited by phosphorus. The algae and vascular plants 

that comprise the marsh ecosystem developed under 

conditions of low nutrient inputs that are characteristic 

of pristine rainfall (Davis, 1994). Nutrient inputs from 

rainfall were so rapidly taken up by the extensive 

marsh vegetation that nutrient concentrations in surface waters were very low. Nutrient loading to coastal 

waters was dispersed over broad areas by sheetflow.

Southern Florida has been greatly altered by 

construction of drainage canals, agriculture, and urban 

development. Construction of drainage canals began in 

the 1800's and continued into the 1960's. The St. Lucie 

and the Caloosahatchee Rivers were connected to Lake 

Okeechobee; both rivers were enlarged and channelized to carry water to the coast. The Kissimmee River 

was straightened and channelized to eliminate seasonal 

flooding on the river's flood plain. Several large canals, 

including the West Palm Beach, Hillsboro, North New 

River, and Miami Canals were dug to carry water from 

Lake Okeechobee to the Atlantic Ocean. A levee was 

built around the south rim of Lake Okeechobee to prevent spillage of water to the northern Everglades.

Drainage lowered the water table by as much as 

2.0 m and resulted in severe fires, land subsidence, and 

saltwater intrusion. Subsequently, regional water management efforts were modified and redesigned to lessen 

these severe effects, to provide flood protection for 

continued urban and agricultural development, and to 

ensure an adequate water supply for urban growth. A 

complex system of canals, levees, pumps, and watercontrol structures was eventually completed.

In the northern Everglades about 324,000 ha was 

converted to agriculture and designated as the Everglades Agricultural Area (EAA) (fig. 1). Principal 

crops are sugarcane and winter vegetables. More than 

360,000 ha of additional land in the northern Everglades was converted to shallow impoundments (the 

WCAs) to provide flood protection during the wet season and water supply during the dry season (Cooper 

and Roy, 1991).

Parts of the southern Everglades and the Big 

Cypress still retain some of the predevelopment surface-water characteristics. These areas include the ENP 

and the Big Cypress National Preserve (BCNP). In 

general, water management has lowered water levels 

and reduced the frequency and duration of inundation 

in the Everglades.

Surface-water basins are often ill-defined in parts 

of southern Florida because of low relief, a lack of distinct drainage divides, and the interconnection of 

canals. However, for the purposes of this report the 

Southern Florida study unit is divided into 10 major 

surface-water basins that differ in their surface-water 

and land-use characteristics (fig. 1). They are: the 

Myakka River and Peace River Basin; the Caloosahatchee River Basin; the Big Cypress Basin; the St. 

Lucie River Basin; the Kissimmee River Basin; Lake 

Okeechobee; the Everglades; the Everglades Agricultural Area; the East Coast Urban Area; and the Florida 

Keys. The Florida Keys do not have significant freshwater features and, therefore, are not discussed further 

in this section of the report.

The Myakka River and Peace River Basins in the 

northwestern part of the study unit are drained by small 

rivers that have not been channelized. Water quality in 

the Myakka River is generally good, and parts of the 

river have been designated as an Outstanding Florida 

Water (Livingston, 1991). Natural ground-water inputs 

are negligible in the Myakka River Basin, and river 

flow in the dry season is often comprised solely of 

highly mineralized ground water originating as runoff 

from irrigated farmland (Livingston, 1991). Rainwater

6 Water-Quality Assessment of Southern Florida: An Overview of Available Information
runoff is typically acidic and low in total mineral content in this part of Florida. Rangeland and agricultural 

land use are significant sources of nutrients. There is 

little urban influence within the watershed. Phosphate 

mining occurs in the headwaters and both sulfate and 

phosphorus concentrations are reported to have 

increased from 1963-85 in surface waters (Hammett,

1990). Water quality in the Peace River is extensively 

influenced by land use and other human activities. The 

Peace River has its headwaters in areas with rich phosphate deposits, and the discharge of wastewater by the 

phosphate mining and fertilizer industries is the most 

significant influence on water quality in the basin 

(Lewelling and Wylie, 1993). The annual discharge of 

the Peace River at Arcadia has shown a significant 

long-term decline during 1931-85, which is not attributable solely to deficient rainfall (Hammett, 1990) but 

may be associated with increased pumpage of ground 

water. The surface-water data indicate that there were 

long-term increasing trends during 1957-85 for total 

organic nitrogen, chloride, sulfate, and dissolvedsolids concentrations, and decreasing trends for total 

phosphorus and orthophosphorus concentrations 

(Hammett, 1990).

The Caloosahatchee River has been highly modified by channelization and the construction of locks 

and water-control structures (Livingston and Fernald,

1991), which now control the flow and stage of the 

river. Water quality in the Caloosahatchee River and its 

tributaries is influenced primarily by low relief, discharge from Lake Okeechobee, and land use (Drew and 

Schomer, 1984). During 1978-80, inflow from Lake 

Okeechobee contributed 55 percent of the total flow in 

the Caloosahatchee River, 62 percent of the total nitrogen, and 64 percent of the chloride (Miller and others, 

1982). The principal types of land use in the eastern 

part of the basin are cattle, citrus, and vegetable production. Land uses in the western part of the basin are 

agriculture and urban. Increases in agricultural and 

urban land uses in the Caloosahatchee River Basin are 

causing significant changes in water quality.

The Big Cypress Basin consists of numerous 

sloughs and cypress-dominated strands where water 

flows southwest and discharges to the Gulf of Mexico. 

Agriculture is prevalent in the northern part of the 

basin; Native American lands also are present in the 

northern part of the basin. In the southern part of the 

basin, most of the land is undeveloped and publicly 

owned. Water-quality studies in the 1970's indicated 

that surface water was uncontaminated in remote undrained parts of the Big Cypress Basin, but the studies 

indicated that in other parts of the basin human activities had degraded surface-water quality (McPherson, 

1974; Duever, 1984). Nitrogen concentrations were 

low (0.03-0.10 mg/L) in this basin compared to concentrations in the urban canals of southern Florida 

(Klein and others, 1970). There is generally a lack of 

recent water-quality data in the Big Cypress Basin, 

although the BCNP began a water-sampling program 

in the 1980's. Collier County Environmental Services 

Division (1994) identified some trace elements 

(chromium, silver, lead, and zinc) in bed-sediment 

samples at concentrations which are indicative of 

human influences.

Principal surface-water features in the St. Lucie 

Basin include wetlands, the St. Lucie Canal, the St. 

Lucie River, and several smaller streams and canals. 

Agriculture and wetlands are the two principal types of 

land cover in the basin; agricultural activities are 

mainly improved pasture and citrus production. Water 

quality in the St. Lucie Canal was reported to be similar 

to water quality in Lake Okeechobee (Parker and others, 1955), which the canal periodically drains. Stormwater inflow influences dissolved-oxygen, suspendedsediment, and nutrient concentrations in canals 

throughout the basin (Graves and Strom, 1992). Large, 

sporadic freshwater discharges from canals have had a 

detrimental effect on biota in the St. Lucie Estuary 

(Haunert and Startzman, 1985; Haunert, 1988; Steward 

and others, 1993).

Surface-water chemistry varies spatially and temporally in the Kissimmee River, Lake Okeechobee, and 

Everglades Basins. The pH is neutral to slightly basic, 

and dominant ions are calcium and bicarbonate. Much 

of the surface water is highly buffered due to contact 

with periphytic marl, limestone, calcareous sand, or 

fossilized deposits. WCA-1 and some deep peat ponds 

are more acidic than surface waters in contact with 

limestone deposits. Dissolved-solids concentrations 

and conductivity are often high, and dissolved-oxygen 

concentrations are typically low. Nutrient retention is 

high in the marshes of the Everglades, as a result of 

tight cycling between the plant community and the sediments (Steward and Ornes, 1975). Phosphorus concentrations are low and this element is considered to be 

the limiting nutrient for plant growth. Total phosphorus 

concentrations ranged from 0.03 to 0.25 mg/L during 

1973-78 in streams of the Kissimmee River Basin 

(Federico, 1982) and were generally less than concentrations measured in rainfall. Canal waters in

Surface-Water Quality in Southern Florida
agricultural areas of the EAA contain high nutrient 

concentrations. For example, average concentrations 

of total phosphorus at 144 sites in the EAA during 

1990-92 ranged from 0.10 to 1.32 mg/L. Water quality 

in some northern parts of the WCA's are affected by 

canal waters that drain the EAA and other farm lands. 

Total nitrogen and phosphorus concentrations in parts 

of WCA-2 and WCA-3 that receive canal inflows from 

the EAA are among the highest in southern Florida 

(Germain, 1994). Interior marshlands of WCA-1 are 

unaffected by high nutrient concentrations, although 

peripheral wetlands are affected by canal inflows. 

Nutrient concentrations in the southern Everglades, 

including the ENP, are naturally low (Waller, 1975; 

Waller and Earle, 1975). At nine sites in the interior of 

the ENP, mean total phosphorus concentrations ranged 

from 0.01 to 0.06 mg/L during 1986-93 and mean total 

nitrogen concentrations ranged from less than 0.01 to 

2.5 mg/L (Germain, 1994).

The East Coast Urban area includes slightly higher 

land along the Atlantic Coastal Ridge from Loxahatchee River to the Florida Keys. The East Coast 

Urban area is home to almost 5 million people and 

includes high-density residential, commercial and 

industrial land uses. Water-quality characteristics and 

nutrient loadings in the basin have been studied in the 

past (Lutz, 1977a; Dickson, 1980), and the Biscayne 

Bay SWIM Plan (South Florida Water Management 

District, 1994a) summarizes results of studies carried 

out in the southern part of the basin since 1984. Contamination of Biscayne Bay comes principally from the 

Miami Canal and other canals. Water quality in these 

urban canals is adversely affected by agricultural and 

urban runoff, and sewage effluent (Florida Department 

of Environmental Regulation, 1988). Dissolvedoxygen concentrations are frequently less than 4.0 

mg/L in the canals and streams in the basin. Nonpoint 

source pollution from lawn and landscape fertilizer and 

pesticides, automobile emissions, seepage from landfills, septic tanks, and disposal wells, and construction 

runoff is significant in the basin.

Issues of Regional Importance to SurfaceWater Quality

Surface water in southern Florida comprises a 

complex, intensively regulated system of wetlands, 

lakes, canals, and rivers. Watersheds are not welldefined, and discharge in some streams and canals may 

cease or be reversed at certain times of the year when

back-pumping is used to manage local water levels and 

regional water supply. The quality of surface water has 

been and continues to be profoundly influenced by 

altered patterns of water flow, atmospheric deposition, 

runoff from agriculture and livestock operations, phosphate mining, urban runoff, municipal wastewater 

discharge, and other human activities.

Altered Patterns of Water Flow

Widespread canal construction and drainage 

manipulation throughout southern Florida have inexorably changed the spatial and temporal patterns of 

water flow. These hydrologic alterations can have complex, and sometimes subtle but pervasive, effects on 

water quality.

The Kissimmee River was channelized for flood 

control between 1962 and 1971, resulting in increased 

depth, altered patterns of flow, and increased sedimentation. The elimination of flood plains resulted in a 

lower basin retention time for many constituents and a 

subsequently higher nutrient input to Lake Okeechobee 

(Loftin and others, 1990a,b). Restoration of the Kissimmee River to ameliorate the environmental effects of 

channelization is underway as a joint project of the 

USAGE, the SFWMD, the FGFWFC, and the USFWS 

(Carroll and Banner, 1991; U.S. Army Corps of Engineers, 1991; South Florida Water Management 

District, 1991, 1993). A demonstration project involving 19.5 km of river was initiated in the mid-1980's and 

the resulting data will be used to guide full-scale restoration efforts. Thus far, the capacity of the wetlands to 

filter sediment and nutrients has been reestablished in 

the newly created flood plain adjacent to the demonstration project, and data indicate that dissolvedoxygen concentrations in the river may be increasing 

(Toth, 1993).

The Caloosahatchee and St. Lucie Canals divert 

water out of Lake Okeechobee to maintain lake level 

schedules and prevent floods. This diversion limits the 

amount and timing of water delivered to the southern 

Everglades. Levees around the southern edge of the 

lake further guard against overflow from the lake to the 

south. Another series of levees and canals in Palm 

Beach and Dade Counties prevent sheetflow from the 

Everglades from flowing to the east coast urban area. In 

the Everglades, water-quality changes can be directly 

related to the movement of water by canals through the 

WCA's (Kushlan, 1991; Walker, 1991). The SFWMD 

regulates the amount of water discharged through

8 Water-Quality Assessment of Southern Florida: An Overview of Available Information
structures throughout the area. In years of high annual 

rainfall, this delivery pattern is problematic for the 

ENP, and naturally high water levels in the Park are 

even higher (South Florida Water Management District, 1995). Moreover, drawdown and reflooding of 

marshlands in the WCA's may increase the release of 

inorganic phosphorus (Gleason, 1974; Swift and 

Nicholas, 1987; Worth, 1988).

The construction of canals in southern Florida has 

resulted in a much greater transport of nutrients, suspended sediment, trace elements, and other contaminants in water than occurred when most water moved 

overland to the coasts by sheetflow (Carter and others, 

1973). Canals in the northern Everglades were constructed to drain water and to create agricultural land 

(the EAA). Intensive agriculture in this area contributes significant amounts of nutrients to surface waters 

in southern Florida. Soil subsidence (due to physical, 

chemical, and microbiological processes) is a direct 

result of drainage and exposure of Everglades soil to 

air, and is a severe threat to agriculture in the EAA 

(Science Sub-Group, 1994).

Demand for water in the East Coast Urban area is 

out of phase with the natural seasonal hydrologic cycle, 

necessitating the artificial movement of water. Balancing water needs for the ENP with needs for the urban 

population (about 5 million) of the East Coast Urban 

area (Miami, West Palm Beach, Boca Raton, Ft. Lauderdale) is critical to the region. Although rainfall provides most of the recharge to ground water, which in 

turn provides most of the drinking-water supply, water 

carried into the area by canals supplements this 

recharge during the dry season. The South Dade Conveyance System provides a mandated supply of water 

to the ENP and also supplies water to other southern 

Dade County canals to prevent saltwater intrusion 

(Cooper and Lane, 1987). The Lower East Coast 

Regional Water Supply Plan, when fully implemented, 

will aid in achieving the critical balance (South Florida 

Water Management District, 1995).

When ecosystem restoration is implemented in 

southern Florida, patterns of water flow in many areas 

will again be changed this time back toward historical patterns (South Florida Water Management District, 1995). More water will be moved through 

historical flow paths, such as Shark River and Taylor 

Sloughs. Water quality, however, could be poor (contain high concentrations of nutrients, pesticides, and 

sediment) if water is diverted directly from agricultural 

or urban lands where fertilizers and pesticides are

intensively applied. Redirection of water to the Everglades Protection Area will be beneficial to the ecosystem only if the water quality is good and concentrations 

of nutrients, pesticides, and other contaminants are 

low. Projects are underway to evaluate appropriate 

water-quality standards for waters entering the Everglades and to implement treatment of storm water runoff from the EAA in Stormwater Treatment Areas so 

that surface-water inflows will cause no imbalance in 

Everglades flora and fauna (South Florida Water Management District, 1995).

Relation of Atmospheric Deposition to SurfaceWater Quality

The atmosphere is recognized as a principal pathway by which nutrients, pesticides, and other organic 

and inorganic compounds are transported and deposited in areas frequently far removed from their sources 

(Majewski and Capel, 1995). The chemical composition of rainfall is influenced by natural factors such as 

fires, oceanic sources of sea salts, and the frequency of 

thundershowers which produce oxides of nitrogen; and 

by human activities such as agriculture, application of 

lawn-care chemicals, burning of fossil fuels in powerplants and vehicles, and waste processing.

Atmospheric deposition is a significant source of 

many contaminants detected in surface water in southern Florida, including nutrients, pesticides, PCB's, and 

mercury. Bulk precipitation (dry-fall and rainfall) is a 

major source of nutrients in southern Florida surface 

waters (Waller, 1975). However, accurate measurements of atmospheric concentrations of nutrients are 

subject to a number of complicating factors. Consequently, estimates of atmospheric deposition of nutrients may vary significantly with location, date, and 

method of collection (Irwin and Kirkland, 1980; Alien 

and Sutton, 1990; Baker, 1991; South Florida Water 

Management District, 1992b; Peters and Reese, 1994). 

The SFWMD (1992b) has a network of 273 rainfallquantity stations, 4 long-term (10-14 years) rainfallquality stations, and several other short-term rainfallquality stations. During 1974-86, most samples collected were bulk precipitation; after May 1986, separate samples of wet and dry atmospheric precipitation 

were collected (South Florida Water Management 

District, 1992b). The mean concentration of phosphorus during 1979-89 ranged from 0.03 to 0.11 mg/L; 

concentrations were highest at sites that were affected 

by airborne particles from soil, agricultural activities, 

and fires (South Florida Water Management District,

Surface-Water Quality in Southern Florida
Table 1. Average nutrient concentrations in precipitation at selected 

sites in Florida, 1990-92

[South Florida Water Management District sites sampled during 1990-92. 

(See Germain, 1994); mg/L, milligrams per liter]

Total nitrogen Total phosphorus

Site

Kissimmee River at S65A 

Lake Okeechobee Field

Average Range, 

(mg/L) (mg/L)

1.01 <0.50-5.43 

1.11 0.52-11.70

Average Range, 

(mg/L) (mg/L)

0.065 <0.004 - 0.792 

0.026 <0.004 - 0.452

Station

Lake Okeechobee, southeast 0.98 0.56 - 4.59 

shore

Pump Station S-7 1.07 0.54-2.60

Everglades Nutrient Removal 0.77 0.54 - 2.04 

Project

Water Conservation- Area 1.45 <0.50 -7.18 

3A near Pump Station S-140

Everglades National Park 1.21 0.51-21.40 

Research Center

0.058 <0.004 - 0.424

0.042 <0.004 - 0.379

0.012 <0.004-0.112

0.098 <0.004- 1.135

0.014 <0.004 - 0.203

1992b). During 1990-92, concentrations of nitrogen 

and phosphorus were determined in wet and dry atmospheric precipitation collected at seven sites in southern Florida (table 1) following NADP protocols 

(Stansland and others, 1983; Peden, 1986; Bigelow and 

Dossett, 1989), except that samples were collected 

every 2 weeks. After March 1992, samples were collected weekly to satisfy NADP protocols. Average 

phosphorus concentrations ranged from 0.012 to 0.098 

mg/L, and average nitrogen concentrations ranged 

from 0.77 to 1.45 mg/L.

Estimates of atmospheric deposition rates (loading) of nitrogen and phosphorus are available for the 

southern Florida study area and other parts of Florida 

(table 2). Total phosphorus loading from precipitation 

in WCA-1, WCA-2, and WCA-3 was estimated to be 

54,56, and 56 (kg /km2)/yr, respectively (South Florida 

Water Management District, 1992a). The SFWMD 

(1992a) estimated that rainfall contributed 40 percent 

of the total phosphorus input to the WCAs during 

1979-88. Efforts continue to refine estimates of the relative contribution to nutrient loading from atmospheric 

deposition, as well as from the other nonpoint sources.

Several national studies of atmospheric sources of 

pesticides include data from sites in southern Florida. 

At least 10 organochlorine insecticides and at least 5 

organophosphorus insecticides have been detected in 

air, rain, or fog at sample sites in Florida (Majewski 

and Capel, 1995). Dieldrin, alpha and gamma HCH, 

diazinon, and malathion are all used on cropland in 

southern Florida and were all detected in air samples 

collected at sites in southern Florida (Majewski and

Capel, 1995). Aldrin was detected in air samples collected in Florida City (Tabor, 1965). Several pesticides, 

including chlordane, oxychlordane, parathion, and 

methylparathion, were detected in air samples collected in Miami in 1975 (Kutz and others, 1976). The 

relatively wide distribution of PCBs in Florida is most 

likely a result of volatilization and transport by aerosols and fallout with dust or rain (Pfeuffer, 1991). 

Vast amounts of mercury continually enter the 

atmosphere from natural sources, vaporized from the 

Earth's crust and mobilized from marine sediments. 

Burning coal and other industrial activities add to the 

global atmospheric mercury burden. Most mercury 

entering the aquatic habitat from the atmosphere is primarily in the inorganic form, which is only moderately 

toxic and has a short retention time. Under acidic conditions, anaerobic bacteria in many aquatic systems can 

convert inorganic mercury to highly toxic methyl mercury. Mercury in southern Florida is principally of 

interest because of its effects on the biota; consequently, mercury is discussed in greater detail in the 

section of this report on issues of regional importance 

to aquatic ecology.

Nutrient Enrichment

Human activities are the principal source of nutrient inputs to surface water in southern Florida. Application of fertilizers and other agricultural activities in 

many parts of the study unit have significantly 

increased nutrient input to surface waters above historical levels. For example, high nutrient concentrations 

in the Kissimmee River primarily are attributable to

10 Water-Quality Assessment of Southern Florida: An Overview of Available Information
Table 2. Estimated annual atmospheric loading of nitrogen and phosphorus at selected sites in Florida 

[SFWMD, South Florida Water Management District; SWIM, Surface Water Improvement and Management; -, not available]

Atmospheric loading, 

in kilograms per square kilometer per year

Description of data Source of data

Total Total 

phosphorus nitrogen

Nitrogen,

ammonia

plus nitrate

Nitrogen, 

nitrate

Bulk precipitation; statewide'; collected during 1970's

Bulk precipitation; south Florida

Bulk precipitation; three Water Conservation Areas2

Bulk precipitation; uncontaminated areas of south 

Florida

Wet + dry precipitation; Gary Forest northeast of 

Gainesville; 1988-89

Wetfall only; five Florida sites; 1993; volumeweighted

Irwin and Kirkland( 1980) 130 1,400

SFWMD SWIM Program (1992b) 65

SFWMD SWIM Program (1992b) 55

SFWMD SWIM Program (1992b) 39

Alien and Sutton (1990) 1 5 660

National Atmospheric Deposition 

Program (1994)

330

Wetfall only; four Tampa sites; 8-10 events during 

1975-80

Wetfall only; not volume-weighted;average of seven 

sites in south Florida

Wetfall only; quantity estimated from rain gage at 

Okeechobee Field Station; 04/92-04/93

Wetfall only; quantity estimated from rain gage at 

Structure S-65A; 04/92-04/94

Wetfall only; quantity estimated from rain gage at 

Structure S-7; 05/92-05/94

Lopez and Giovanelli (1984)

Germain(1994)

Computed from SFWMD data

Computed from SFWMD data

Computed from SFWMD data

250

59

20

42

18

1,300

1,400

1,800

1,400

1,300

330

-

-

'Based on 130 centimeters average annual precipitation. 

2Based on 118 centimeters average annual precipitation.

runoff from improved pasture and dairy operations. 

Nutrient concentrations in the Taylor Creek, Nubbin 

Slough, Lower Kissimmee River, and Arbuckle Creek 

subbasins (fig. 2) are influenced by feedlot and cattle 

operations (Germain, 1994). Nutrient concentrations in 

the St. Lucie River Basin during 1976-77 were highest 

during periods of highest discharge and were influenced by agricultural runoff (Federico, 1983). The 

range of average nitrogen concentrations was 1.38 to 

1.58 mg/L and the range of average phosphorus concentrations was 0.11 to 0.26 mg/L in surface waters 

during 1976-77 (Federico, 1983).

Urban land use is the most important influence on 

surface-water quality in parts of the study unit. Urban 

stormwater runoff from Fort Myers and La Belle contributes significant amounts of nutrients to the Caloosahatchee River (Environmental Science and 

Engineering, 1977). Effluent from waste water treatment plants in Lakeland, Winter Haven, and Bartow 

contributes nitrogen to the streams of the Peace River 

Basin (Fraser, 1991; Irwin and Swihart, 1993). Total 

nitrogen concentrations in the Peace River, which often 

exceed 1.0 mg/L (German and Schiffer, 1988), are also 

influenced by agricultural runoff and the discharge of 

citrus processing operations. In at least one part of the 

study unit, natural sources of nutrients are important.

The Peace River is naturally enriched with phosphorus, 

because the river flows through phosphate deposits. 

However, mining activities in the basin accelerate the 

rate at which phosphorus enters surface waters. 

The Peace River has the second highest phosphate concentration of all of Florida's rivers. During 1974-82, 

total phosphorus concentrations commonly exceeded 

0.1 mg/L (German and Schiffer, 1988).

Lake Okeechobee is naturally eutrophic, but due to 

human influence, the lake has become hypereutrophic. 

The lake acts as a sink for nutrients, which are retained 

in the organic bottom sediment. The concentration of 

total phosphorus almost doubled, from 49 |ig/L in 1973 

to 98 |ig/L in 1984 (Aumen, 1995). More than 50 percent of the phosphorus and 30 percent of the nitrogen 

inputs to the lake are from the Kissimmee River and 

from Taylor Creek/Nubbin Slough (Federico and others, 1981; Jones, 1987; Janus and others, 1990). Also, 

nutrient-laden waters discharged from the EAA were 

formerly channeled to Lake Okeechobee (Dickson and 

others, 1978). In recent years, however, efforts have 

been made to keep these nutrient-laden waters out of 

Lake Okeechobee. As a result, back pumping of water 

from the EAA to the lake has decreased, but more of 

this nutrient-enriched water has entered the WCAs 

(Lutz, 1977b). Total nitrogen concentrations at sites in

Surface-Water Quality in Southern Florida 11
the northern Everglades influenced by the EAA are 

now among the highest in southern Florida. Mean total 

nitrogen concentrations ranged from 1.10 to 5.60 mg/L 

in the WC As during the period of record, and mean 

total phosphorus concentrations ranged from 0.01 to 

0.91 |ig/L (Germain, 1994). Estimates of phosphorus 

concentrations flowing into and out of the WCAs indicates that the WCAs are efficient at assimilating the 

phosphorus loads (South Florida Water Management 

District, 1992a). Phosphorus concentrations in water in 

WCA marshlands generally follow a gradient of high 

to low from the input point to interior marsh locations 

(Whalen and others, 1992; Reddy and others, 1993; 

Urban and others, 1993; Davis, 1994). This pattern is 

most conspicuous in WCA-2, where water from canals 

flows into the interior marshes. In WCA-1, land surface 

elevation is greater in the marsh interior than along the 

perimeter; therefore, water tends to flow along the 

periphery of the marsh instead of through it.

A significant component of ongoing southern Florida ecosystem restoration efforts is the reduction of 

phosphorus loading to WCA-1 and the ENP (South 

Florida Water Management District, 1995). The 

SFWMD and the FDEP are conducting research to 

define acceptable nutrient concentrations for the protection and restoration of the Everglades, with the 

emphasis on phosphorus concentrations. This research 

began in WCA-2 in 1994 and has several components. 

Data are being collected along a nutrient gradient in the 

marsh where sawgrass has been replaced by cattails. 

Data are also being collected from a series of "dosing 

chambers" placed in the marsh which are treated with 

known amounts of phosphorus and then monitored for 

changes in vegetation. In addition, State and Federal 

agencies are jointly sponsoring dosing threshold 

research being conducted by Florida International University.

Development of a nutrient budget for southern 

Florida is a goal of the SFWMD, as well as other agencies involved in ecosystem restoration in the region. 

Estimates of nutrient inputs and outflows is an initial 

step in this complex process (Puckett, 1994). In this 

report, the relative contributions of various point and 

nonpoint sources of phosphorus (fig. 3) and nitrogen 

(fig. 4) were estimated in nine surface-water basins in 

the Southern Florida study unit (see Appendix for data 

sources and computation methods). Fertilizer and 

manure from agriculture account for much of the nutrient inputs. Fertilizer is the dominant source of phosphorus in eight basins and of nitrogen in at least five

basins. Canal inflow is the largest source of phosphorus 

input to Lake Okeechobee and the second largest 

source of nitrogen input to the lake, after atmospheric 

deposition. Atmospheric sources of nitrogen contribute 

more than about 20 percent of the total nitrogen input 

to all basins and are the dominant source of input to 

Lake Okeechobee and the Everglades.

The total nutrient input from all sources was estimated for the nine southern Florida surface-water 

basins (table 3). Total phosphorus inputs ranged from 

100 (kg/ km2)/yrin Lake Okeechobee to 4,800 (kg/ 

km2)/yr in the EAA. Total nitrogen inputs ranged from 

2,900 (kg/ km2)/yrin the Everglades to 9,200 (kg/ km2)/ 

yr in the EAA.

Estimates of nutrient loads in selected canal and 

river outflows in southern Florida were calculated for 

this report from data collected by the SFWMD and the 

USGS (figs. 5-6). Annual phosphorus loads from the 

Peace River (fig. 5) are the highest in the study unit; 

annual phosphorus loads from the Caloosahatchee 

River and the major Palm Beach canals are also high, 

compared to loads in other parts of southern Florida. 

Estimated annual loads of phosphorus from the S-12 

water-control structures and parts of the Big Cypress 

Basin (Tamiami Trail; 40-Mile Bend to Monroe) are 

low compared with estimated loads in the northern part 

of the study unit (fig. 5). Annual nitrogen loads (fig. 6) 

were highest in outflows from the Caloosahatchee 

River Basin and the major Palm Beach canals. Nitrogen loads in outflows from parts of the Big Cypress 

subbasin (Tamiami Trail; 40-Mile Bend to Monroe) 

were lower than estimated loads to the north.

Pesticides and Other Organic Compounds in 

Water and Sediment

Pesticides are widely used in southern Florida for 

agriculture; for maintenance of highway right-of-ways, 

domestic lawns, and golf courses; and for control of 

aquatic weeds and mosquitoes. Application to agricultural crops constitutes the major use of pesticides in 

southern Florida, where citrus, sugar cane, and vegetables are the principal crops. Petroleum distillates and 

ethion are the principal insecticides (on a weight basis) 

used on citrus crops. Methomyl is the main insecticide 

used on vegetables (corn, peppers, and tomatoes), and 

ethoprop and phorate are the main insecticides used on 

sugarcane. Chlorpyrifos is another widely applied 

insecticide, with approximately equal amounts used on 

vegetables, citrus, domestic lawns, and golf courses.

12 Water-Quality Assessment of Southern Florida: An Overview of Available Information
MYAKKA RIVER AND

PEACE RIVER

11,390000 kg/yr

KISSIMMEE RIVER 

12,370,000 kg/yr

CALOOSAHATCHEE RIVER 

3,773,000 kg/yr

BIG CYPRESS 

5,831,000 kg/yr

EVERGLADES 

3,508,000 kg/yr

ST. LUCIE RIVER 

5,339,000 kg/yr

LAKE OKEECHOBEE 

241,000 kg/yr

EVERGLADES 

AGRICULTURAL

AREA 

12,860,000 kg/yr

EAST COAST 

URBAN AREA 

6,478,000 kg/yr EXPLANATION 

PHOSPHORUS SOURCES 

__ FERTILIZER 

I I MANURE

I I ATMOSPHERIC DEPOSITION 

| SEPTIC TANKS 

| MAJOR CANALS AND RIVERS

| WASTEWATER TREATMENT 

FACILITIES

[kg/yr, kilograms per year]

Figure 3. Estimated phosphorus loading from point and nonpoint sources in surface-water basins in southern 

Florida (see appendix for information on data sources and computational methods).

Surface-Water Quality in Southern Florida 13
MYAKKA RIVER AND 

PEACE RIVER KISSIMMEE RIVER 

68.070.000kg/vr

CALOOSAHATCHEE RIVER 

18,200,000 kg/yr

BIG CYPRESS 

26,780000 kg/yr

EVERGLADES 

27,320,000 kg/yr

ST. LUCIE RIVER 

26,87pJOOOkg/yr

LAKE OKEECHOBEE 

5,994,000 kg/yr

EVERGLADES 

AGRICULTURAL

AREA 

24,660.000 kg/yr

EAST COAST

SL kg/yr EXPLANATION 

NITROGEN SOURCES 

FERTILIZER 

[ I MANURE

I | ATMOSPHERIC DEPOSITION 

| SEPTIC TANKS 

| MAJOR CANALS AND RIVERS

WASTEWATER TREATMENT 

FACILITIES

[kg/yr, kilograms per year]

Figure 4. Estimated nitrogen loading from point and nonpoint sources in surface-water basins in southern 

Florida (see appendix for information on data sources and computational methods).

14 Water-Quality Assessment of Southern Florida: An Overview of Available Information
Table 3. Estimates of nitrogen and phosphorus inputs to drainage basins in the Southern Florida 

NAWQA study unit

Basin

Big Cypress

Caloosahatchee River

East Coast Urban Area

Everglades

Everglades Agricultural Area

Kissimmee River

Lake Okeechobee

St. Lucie River

Myakka River and Peace River

Total 

nitrogen 

input 

(kilograms 

per year)

26,800,000

18,200.000

23,200,000

27,300,000

24,700,000

68,100,000

6,000,000

26,900,000

56,700,000

Total 

phosphorus 

input 

(kilograms 

per year)

5,830,000

3.770.000

6,480,000

3,510,000

12,900,000

12,400,000

241,000

5,340.000

11,400,000

Basin 

area 

(hectares)

649,000

349,000

412,000

935,000

270,000

1,060,000

181,000

351,000

840,000

Nitrogen 

input 

(kilograms 

per hectare 

per year)

41

52

56

29

91

64

33

77

67

Phosphorus 

input, 

(kilograms 

per hectare 

per year)

9

11

16

4

48

12

1

15

14

Atrazine, the major herbicide used in southern Florida, 

is applied primarily on sugarcane, but also on vegetables. Bromacil, diuron, glyphosate, and simazine are all 

used on citrus crops, and monosodium methanearsonate (MSMA) is the main herbicide used on golf 

courses. Agricultural application also leads in the use 

of fungicides. Sulfur and copper hydroxides are the 

most frequently applied fungicides on citrus crops, and 

EBDCs (ethylenebisdithiocarbamates) and chlorothalonil are used mostly frequently on vegetables 

(primarily tomatoes). Fenamiphos is the major nematocide used, and it is applied primarily on golf courses. 

Methyl bromide and chloropicrin are the major soil 

fumigants used, and they are used exclusively on 

tomatoes and peppers (RJ. Miles and C.J. Pfeuffer, 

SFWMD, written commun., 1994).

The occurrence, distribution, and fate of pesticides 

has been a long-standing water-quality concern in 

southern Florida. In the late 1960's and early 1970's, 

pesticides were detected in water, bed sediment, and 

fish in the Everglades (Kolipinski and Higer, 1969; 

Kolipinski and others, 1971; McPherson, 1973). Other 

studies reported relatively high concentrations of chlorinated hydrocarbons in southern Lake Okeechobee, 

Hillsboro Canal, and Miami Canal (Pfeuffer, 1985). 

In the early 1970's, PCBs were determined to be 

widely distributed in the southern Florida environment 

(Klein and others, 1970). Early studies of pesticides in 

southwestern Florida indicated few detections in water, 

but more frequent detections in bed sediment 

(McPherson 1969; U.S. Environmental Protection 

Agency, 1972; Carter and others, 1973). For example, 

in the Big Cypress Basin pesticides were detected in

low concentrations in water samples and at high concentrations in bed sediment (Klein and others, 1970). 

DDT and its degradation products were the most commonly detected compounds in bed sediment during 

1969-70; the mean reported concentration of DDT in 

the BCNP was 5.1 Jig/kg. Soil samples collected in the 

eastern part of the ENP indicated that concentrations 

of PCBs and DDT were very low within the ENP, 

although concentrations in soil samples from agricultural fields within 2 km of the ENP boundary were two 

orders of magnitude higher (Requejo and others, 1979).

The SFWMD initiated a district-wide pesticide 

monitoring program in 1984. During 1984-90, atrazine 

was the only pesticide consistently detected in surfacewater samples; most of the detections were between 0.1 

and 1.0 jig/L. The greatest frequency of atrazine detections was along the south shore of Lake Okeechobee, 

and in canals draining the EAA, indicating that atrazine 

use may be significant in areas adjacent to these sites 

(Pfeuffer, 1991). Atrazine concentrations in basins 

within the EAA are frequently above the State criteria 

(South Florida Water Management District, 1995).Residues of DDD and DDE were detected in bed-sediment 

samples collected at these sites, as well as in canals 

adjacent to agricultural land to the east of the ENP. 

Detectable concentrations of ethion and DDT were 

consistently measured in areas adjacent to citrus 

agriculture. An ongoing SFWMD pesticide monitoring 

program continues to detect herbicides, including atrazine, ametryn, bromacil, and simazine, and the insecticide endosulfan (South Florida Water Management 

District, 1995).

Surface-Water Quality in Southern Florida 15
PEACE RIVER AT ARCADIA 

500,000 kg/yr

KISSIMMEE RIVER AT S-65E 

100,000 kg/yr

CALOOSAHATCHEE RIVER

AT S-79 

200,000 kg/yr

BIG CYPRESS, TAMIAMI CANAL,

40 MILE BEND TO MONROE

4,000 kg/yr

ST LUCIE CANAL AT S-80 

80,000 kg/yr

MAJOR PALM BEACH

COUNTY CANALS

200,000 kg/yr

MAJOR DADE

COUNTY CANALS

30,000 kg/yr

S-12 STRUCTURES 

10,000 kg/yr

4,000_kg/yr EXPLANATION

ESTIMATED TOTAL PHOSPHORUS

LOADS, IN KILOGRAMS PER YEAR

[kg/yr, kilograms per year]

DIRECTION OF CANAL FLOW 

OR DISCHARGE

SURFACE WATER 

A GAGING STATION

Figure 5. Estimated total phosphorus loads for selected canal and river outflows from 

surface-water basins in southern Florida.

In the Barren River Canal, d-BHC (benzene 

hexachloride) (99 jug/kg) and aldrin (1.3 jug/kg) were 

detected in bed sediment samples during 1989-91 

(Collier County Environmental Services Division, 

1994). Stream-bed sediment has been sampled 

repeatedly since 1990 in Collier County; eight organochlorine pesticides have been detected at 15 of 26 

sites sampled. Concentrations of chlordane in the 

Coconut Palm River, d-BHC in the Barron River 

Canal, and endosulfan sulfate in the Haldeman Canal 

were the highest concentrations of these pesticides in

bed sediment reported to date in Florida (Collier 

County Environmental Services Division, 1994).

In the Caloosahatchee River, several agricultural 

pesticides (aldrin, dieldrin, DDT, and chlordane) have 

been detected at concentrations exceeding the Florida 

Water Quality Standards (Drew and Schomer, 1984). 

Urban stormwater runoff from Ft. Myers and LaBelle 

also contributes pesticides to the Caloosahatchee 

River, which is a primary or secondary source of drinking water for basin residents (Environmental Science 

and Engineering, Inc., 1977).

16 Water-Quality Assessment of Southern Florida: An Overview of Available Information
PEACE RIVER AT ARCADIA 

1,000,000 kg/yr

KISSIMMEE RIVER AT S-65E 

1,000,000 kg/yr

CALOOSAHATCHEE RIVER

AT S-79 

2,000,000 kg/yr

BIG CYPRESS, TAMIAMI CANAL,

40 MILE BEND TO MONROE

300,000 kg/yr

ST LUCIE CANAL AT S-80 

700,000 kg/yr

MAJOR PALM BEACH

COUNTY CANALS

2,000,000 kg/yr

S-12 STRUCTURES 

800,000 kg/yr

300,000 kg/yr EXPLANATION

ESTIMATED TOTAL NITROGEN 

LOADS, IN KILOGRAMS PER YEAR 

[kg/yr, kilograms per year]

DIRECTION OF CANAL FLOW 

OR DISCHARGE

SURFACE WATER 

A GAGING STATION

Figure 6. Estimated total nitrogen loads for selected canal and river outflows from 

surface-water basins in southern Florida.

In the East Coast Urban Basin, pesticides associated 

with citrus farming have been detected in the Ten Mile 

Creek subbasin. Bromacil, metalaxyl, simazine, diazinon, ethion, malathion, and endosulfan sulfate are 

among the 14 pesticides detected in water samples during 1993-95 (Graves and Strom, 1995a,b). Biscayne Bay 

has a significant pesticide input due to agricultural land 

use (24 percent of the watershed). An estimated 200,000 

kg of 35 common pesticides are used per year in the 

basin. Among the pesticides of greatest concern are

atrazine, 2,4-D, endosulfan, and chlorpyrifos (Pait and 

others, 1992). Contaminants of greatest concern in the 

East Coast Urban area are trace elements, PCBs, PAHs, 

and pesticides. Endosulfan degradation products have 

been detected at five water-control structures in south 

Dade County (C.J. Miles and R.J. Pfeuffer, SFWMD, 

written commun., 1995), occasionally at concentrations 

which exceeded the Florida surface-water-quality standard for endosulfan (0.056 |ig/L) (Florida Department of 

Environmental Protection, 1995).

Surface-Water Quality in Southern Florida 17
In the ENP aldrin, heptachlor, and toxaphene were 

detected in surface-water samples collected during 1980 

(Pfeuffer, 1985). Endosulfan and endosulfan oxide residues have been detected in water samples collected at all 

water control structures in south Dade County since 

1987 (C.J. Miles and RJ. Pfeuffer, SFWMD, written 

commun., 1995). Maximum concentrations of endosulfan (0.03-0.29 |Llg/L) occurred in late winter and early 

spring, and exceeded the FDEP standard for Class IE 

waters (0.056 |Llg/L) (Florida Department of Environmental Protection, 1995) on more than one sampling 

date. Concentrations of DDD and/or DDE in bed sediment in the ENP during August 1984-July 1988 were 

lower than those routinely measured during previous 

SFWMD monitoring (Pfeuffer, 1991).

Monitoring of pesticides in water and bed sediment 

has been carried out for many years in southern Florida, but there is little information or understanding of 

processes of pesticide transport, degradation, uptake, 

and biological effects. Recent studies suggest that there 

are widespread effects of low-level concentrations of 

pesticides and other organic compounds on wildlife 

reproduction and human health (Colborn and others, 

1993). More information is needed before the degree 

that these contaminants are affecting the southern Florida ecosystem can be assessed.

Radioactivity

The Peace River and Myakka River Basins have 

significant inputs of radionuclides from the naturally 

high radioactivity associated with phosphate deposits 

that occur within the basins and from phosphate mining 

and processing. In the upper Peace River Basin, much 

of the radioactivity tends to be transported on particles 

such as clays and other fines that are washed downstream, whereas in the lower part of the basin ground 

water introduces significant amounts of soluble 

radium-226 (Miller and others, 1990). Occasionally, 

dikes that contain waste clays (slimes) from phosphate 

mines rupture and release large volumes of these fines 

into the Peace River. Miller and Morris (1981) reported 

22 slime-pond spills into the Peace River between 1942 

and 1980. These accidental spills have the potential to 

release enough ion-exchangeable radium-226 to equal 

the annual load of natural radium-226 transported by 

the river (Miller and McPherson, 1987). Radium-226 

concentrations in estuarine water in Charlotte Harbor 

are approximately an order of magnitude higher than 

for water in many other estuaries in the Nation, due to

the inflow of radium-226 rich ground water. Radium226 and radon-222 have been used to identify areas of 

significant ground-water inflow; radium-226 has been 

used as a natural tracer to estimate the rate of groundwater inflow into the Charlotte Harbor estuary (Miller 

and others, 1990). Radium-226 radioactivity approximately doubled in the Myakka River below where 

Warm Mineral Springs flows into the river (Miller and 

others, 1990). Disposal of the highly concentrated 

reject water from reverse osmosis plants in coastal 

areas of southwestern Florida is another potentially 

important source of radioactivity in surface water as 

the treatment of saline water for public consumption 

becomes more common.

GROUND-WATER QUALITY IN 

SOUTHERN FLORIDA

Ground water is the most important drinking-water 

resource in southern Florida. About 5.5 million people 

depend on ground water as a primary source of drinking water, and about 4.7 million of those people use 

water from wells less than 60 m deep. Ground water in 

southern Florida is vulnerable to contamination 

because of its close proximity to the surf ace.The focus 

of the NAWQA Program's study of ground-water 

quality in southern Florida is on assessing human 

influences on shallow ground water.

Overview of Ground-Water Quality and 

Hydrogeology

The hydrogeologic features of southern Florida's 

principal aquifers have been described previously by 

Parker and others (1955) and many other authors. The 

principal aquifers in southern Florida are the Biscayne 

aquifer, the surficial and intermediate aquifer systems, 

and the Floridan aquifer system. Waters in all the aquifer systems in the study unit are primarily a calcium 

bicarbonate type, mostly because shell, limestone, or 

dolomite is predominant in the aquifers. The waters are 

generally considered to be hard to very hard.

The Biscayne aquifer is a surficial aquifer that 

underlies all of Dade, Broward, and parts of Palm 

Beach and Monroe Counties and consists of a very 

permeable interbedded limestone and sandstone. 

The Biscayne aquifer has a water table that is close to 

the land surface and has a high recharge rate of approximately 98 cm/yr. The Biscayne aquifer is aerobic in

18 Water-Quality Assessment of Southern Florida: An Overview of Available Information
the upper 9 m or so, and anaerobic (reducing) in the 

deeper parts. Waters from the Biscayne aquifer are 

used extensively for public supply. Pumping of the 

aquifer is managed carefully to minimize saltwater 

intrusion. Concentrations of most water-quality constituents in the aquifer do not exceed primary drinkingwater standards (Anderson and Shaw, 1991). Waterquality constituents, which may be of concern where 

ground water is the source of drinking water include: 

sodium, chloride, and dissolved solids in areas affected 

by saltwater intrusion; hydrocarbons in urban-industrial areas; nitrate in localized areas of urban or suburban development; and organic carbon in areas where 

overlying peat deposits occur.

The surficial and intermediate aquifer systems, 

located to the west and north of the Biscayne aquifer, 

consist of interlayered beds of sand, peat, clayey sand, 

silt, and shell, with minor limestone beds. The surficial 

aquifer system can be further subdivided into: the 

medium-to-fine sand and clayey sand of the Lake Wales 

Ridge area (fig. 2); and the interbedded layers of sand, 

silt, and shell or limestone that are present in the central 

part of the study area (fig. 7). The surficial aquifer system in the Lake Wales Ridge area has a moderate 

recharge rate of approximately 25 to 38 cm/yr, and an 

aerobic saturated zone. The surficial aquifer system 

within the Lake Wales Ridge area is used primarily for 

domestic supply and small-scale agricultural irrigation 

supply. The sand, silt, and shell surficial aquifer system 

in the central and southern part of the study area generally has a water table close to the land surface, a low 

recharge rate of 2.5 to 23 cm/yr, and an anaerobic saturated zone.

The Biscayne aquifer and parts of the other surficial aquifer system are overlain by a layer of peat in the 

Everglades region (fig. 7). The peats of the Everglades 

are an accumulation of 0.3 to 3.3 m of peat, muck, and 

marl (Davis, 1943) which generally has a low permeability. The water table in the peats usually is less than 

0.6 m below land surface in areas where the Everglades 

is not inundated.

The intermediate aquifer system is similar to the 

sand, silt, and shell surficial aquifer system but is somewhat deeper. The waters in the sand, silt, and shell surficial and intermediate aquifer systems are used 

extensively for public supply in all areas south of Lake 

Okeechobee and in cities along the western coastlines. 

Saltwater intrusion and free-flowing deeper artesian 

wells have rendered parts of these aquifer systems nonpotable. Concentrations of VOCs in ground water used

for drinking-water supply are often of concern in urban 

areas on the east coast, and high radioactivity has been 

measured in ground water in the western part of the 

study area where saline water contacts phosphate 

deposits rich in natural radioactivity (Miller and 

Sutcliffe, 1985).

The Floridan aquifer system underlies the entire 

study unit and occurs near the land surface in the northern part but drops to 150 m below land surface in the 

southern part (McPherson, 1996). It consists of limestone and dolomite beds that are generally highly transmissive. The Floridan aquifer system generally 

contains older water or a mix of recent and older water. 

It is used extensively for public supply and agriculture 

in the northern part of the study area because goodquality water is relatively close to the surface and easily accessible. Conversely, in the southern part, the 

aquifer contains nonpotable water due to high salinity. 

Concentrations of most water-quality constituents in 

waters from the Floridan aquifer system generally do 

not exceed applicable drinking-water standards, 

although high concentrations of nitrate and pesticides 

may occur in ground water near current or former citrus 

grove operations.

Issues of Regional Importance to GroundWater Quality

Ground water in southern Florida is vulnerable to 

many sources of contamination (Herr and Shaw, 1989). 

Issues of greatest concern are saltwater or brackishwater intrusion, nutrient enrichment, pesticides, metals 

and trace elements, volatile organic compounds, and 

radioactivity. Contaminants indirectly reach the 

ground-water systems in southern Florida from landfill 

leachates, spills of industrial organic solvents, and 

areal application of fertilizers and pesticides; and 

directly from leaking fuel storage tanks, septic systems, 

and drainage wells (Kimrey and Fayard, 1984; Irwin 

and Bonds, 1987; Bradner, 1991). Saltwater or brackish-water from remnant or recent seawater, and radioactivity from phosphatic deposits reach ground-water 

systems as a result of natural processes, but their occurrence may also be affected by human activities.

Saltwater Intrusion

Saltwater intrusion became a significant problem 

for urban water supply along the urban southeast coast 

in the I940's and 1950's. Increased demand for freshwater resulted in increased pumping of the surficial

Ground-Water Quality in Southern Florida 19
83

28° -

27° -

26°

25° -

rSEMINOLE^ I 

--.__ \J 

ORANGE X

IHILLSBOROUGH

EXPLANATION 

BISCAYNE AQUIFER

SANDY SURFICIAL 

AQUIFER SYSTEM

SAND, SILT, AND SHELL 

SURFICIAL AND INTERMEDIATE 

AQUIFER SYSTEMS

AREA OVERLAIN BY 

EVERGLADES PEAT

I I

25 50 KILOMETERS

Base from U.S. Geological Survey digital data, 1:2,000,000,1972

Albers Equal-Area Conic projection

Standard Parallels 29°30' and 45°30', central meridian -83°00'

Figure 7. Aquifer systems in southern Florida and extent of peat in the Everglades region.

20 Water-Quality Assessment of Southern Florida: An Overview of Available Information
aquifer system. At the same time, canals were dredged 

to drain land for development. These activities lowered 

water tables and allowed saltwater to move inland 

within the aquifer. The most severe problems have 

been somewhat alleviated through impoundment and 

storage of water in the WCAs which is later released to 

maintain sufficient water levels during dry seasons, and 

by restricting canal flow to the ocean during the dry 

season (Howie, 1987; Sonntag, 1987; Miller, 1988; 

Radell and Katz, 1991). Other strategies for improving 

the quality of the public-water supplies have included 

desalinization, rotation of well pumpage, and relocation of well fields to inland areas (Sonenshein and Hofstetter, 1990).

Saltwater intrusion also has occurred on the southwest coast of Florida in areas of urban development 

(Duerr and others, 1988; Duerr and Enos, 1991; Florida 

Geological Survey, 1992; Trommer, 1993). Saltwater 

intrusion into highly phosphatic zones of the intermediate aquifer can release large amounts of radium -226 

into the ground water (Miller, 1992). Brackish water 

from deep, free-flowing, abandoned irrigation wells 

has infiltrated many localized areas in the central part 

of the study unit. Strategies for improving the quality 

of the surficial aquifer in these areas involve plugging 

abandoned wells and backplugging saltwater-flow 

zones in deep wells (LaRose, 1990; Bradner, 1994).

Nutrient Enrichment

Sources of nutrient enrichment of ground water in 

southern Florida include fertilizer application, stormwater runoff, and wastewater disposal. Nutrients in 

ground water are a concern in southern Florida because 

of their potential effect on human health and on surface 

waters. Nutrients such as nitrate and ammonia present 

in high concentrations in ground water may pose a 

threat to human health because most drinking water in 

southern Florida is from ground-water sources. Shallow ground water and surface water in southern Rorida 

are closely connected and rapidly interchange. Therefore, nutrient-rich ground water that seeps or is pumped 

into surface-water bodies can contribute to nutrient 

enrichment and undesirable algal growth.

Fertilizer applied to citrus groves, vegetable crops, 

golf courses, and residential areas is a source of nitrate, 

ammonia, and phosphorus in ground water in southern 

Florida. For example, nitrate concentrations exceeding 

30 mg/L have been detected in ground water beneath 

citrus growing areas in the Lake Wales Ridge area

(German, 1996) and in the upper part of the Biscayne 

aquifer in the vicinity of vegetable-growing areas 

(Florida Department of Environmental Protection, 

Public Water System, written commun., 1995). The 

highest number of wells yielding water exceeding the 

drinking-water standard for nitrate (10 mg/L) (Florida 

Department of State, 1993) are in Polk and Highlands 

Counties near the citrus-growing areas (822 domestic 

supply wells) and in Dade County near the vegetablegrowing areas (7 noncommunity supply wells) (Florida 

Department of Environmental Protection, Pesticide 

Contaminant Monitoring System, written commun., 

1995). Generally, as recharge water with high organic 

nitrogen concentration enters anaerobic zones of the 

aquifer system, conversion to ammonia occurs by mineralization. High ammonia concentrations have been 

detected in ground water in the Biscayne aquifer near a 

golf course (Swancar, 1996). Although phosphorus is 

not typically a problem in ground water, runoff of 

phosphorus-rich ground water used for irrigation may 

result in algal blooms in wetlands, lakes, and streams.

Stormwater runoff may enter ground water through 

drainage wells or percolation ponds. Shallow drainage 

wells in Dade and Broward Counties that divert stormwater into the Biscayne aquifer may be a source of 

ammonia contamination (Kimrey and Fayard, 1984). 

Drainage wells in Orange County that divert stormwater 

by gravity flow into the Floridan aquifer system are also 

a source of ammonia contamination (Bradner, 1991).

Wastewater disposal is a widespread sources of 

nutrient contamination to ground water. For example, 

citrus processing wastes and wastewater treatment 

plant effluent are often applied to sprayfields or placed 

into percolation ponds (Bradner, 1991; Sumner and 

Bradner, 1996). Wastes from dairy operations contain 

high concentrations of phosphorus and nitrogen 

(Federico, 1977; Lake Okeechobee Technical Advisory Council, written commun., 1989; South Florida 

Water Management District, 1989) which may be 

transported in surface-water runoff and subsequently 

contaminate shallow ground water overlain by sandy 

soils. Nutrients from septic tanks and shallow disposal 

wells can potentially seep into surface water and contribute to enrichment and degradation of surface water 

and ground water. In the Florida Keys, there are more 

than 25,000 septic tanks, 5,000 cesspools, and 600 

shallow drainage wells that release nutrient-rich water 

into very porous limestone. There is concern that nutrients from these sources may seep into shallow marine

Ground-Water Quality in Southern Florida 21
waters and adversely affect this environment, including 

the coral reefs. Recent studies have reported high concentrations of ammonia in shallow ground water offshore of the Keys (Shinn and others, 1994; Paul and 

others, 1995).

Occurrence and Distribution of Pesticides

Pesticide use in southern Florida includes ground 

and aerial application of pesticides for agriculture, 

mosquito control, and aquatic weed control; and pesticide use on golf courses, residential property, and 

power and transportation right-of-ways. Many pesticides reach shallow ground water by runoff and percolation through the soil; however, the transport and 

degradation of pesticides in ground water are not well 

understood. Pesticides detected in wells tapping the 

surficial aquifer system include the herbicides bromacil, diuron, and propazine; and the insecticides 1,2- 

Dibromoethane (EDB), aldicarb, carbofuran, and 

endosulfan sulfate (Florida Department of Environmental Protection, Groundwater Monitoring Program, 

written commun., 1995).

A widespread source of ground-water contamination by pesticides in southern Florida is heavy application in citrus groves. Bromacil is widely applied to 

citrus groves and has been frequently detected in citrus-growing areas. Untreated water samples from more 

than 800 domestic-supply wells in Polk and Highlands 

Counties contained detectable concentrations of 

bromacil (Florida Department of Environmental Protection Groundwater Monitoring Program, written 

commun., 1995). By 1995,56 of these wells had water 

samples with bromacil concentrations greater than the 

health-advisory concentration of 90 |ig/L (Florida 

Department of Environmental Regulation, 1989; Florida Department of Health, Environmental Toxicology, 

written commun., 1995). Diuron is commonly combined with bromacil for application in citrus groves; 

however, detections of diuron are less frequent and 

generally at lower concentrations than bromacil (Florida Department of Environmental Protection, Groundwater Monitoring Program, written commun., 1995). 

The herbicide propazine, used for weed control in sorghum (a common feed crop for cattle), was detected in 

several background wells in Collier, Glades, Hendry, 

and Lee Counties. The extent of propazine contamination has not been determined because the counties 

cover large areas of land and the background wells are 

sparsely located.

One of the most publicized contaminants is EDB, 

which was banned for agricultural use in Florida in 

1983 (Katz, 1993). By 1995, more than 1,000 domestic 

supply wells in the sandy ridge area of Polk and Highlands Counties were contaminated by EDB (Florida 

Department of Environmental Protection, Pesticide 

Contaminant Monitoring System, written commun., 

1995). Many of the contaminated wells are located in 

areas where former citrus groves were converted to residential developments. In these developments, drinking water is supplied by individual shallow wells. 

Traces of EDB also are detected in ground water in 

other parts of the study area. Sources of EDB contamination in areas away from citrus groves have not been 

determined.The fumigant methyl bromide is now being 

used instead of EDB as an insecticide in southern Florida; further studies are needed to determine whether 

ground water has been contaminated in areas where 

methyl bromide is being used.

Aldicarb, a carbamate insecticide, has been 

detected in water samples from more than 100 wells 

that tap the surficial aquifer system in current and 

former citrus-growing areas in Orange, Polk, and Highlands Counties (German, 1996), as well as in water 

samples from background wells (Florida Department 

of Environmental Protection, Groundwater Monitoring 

Program, written commun., 1995). Carbofuran, 

another carbamate insecticide, was detected in water 

from one background monitoring well, but has not been 

detected in water from domestic supply wells in the 

areas where other insecticides have been detected 

(Florida Department of Environmental Protection, 

Ground Water Monitoring Program, written commun., 

1995) Endosulfan I and II, insecticides that are used on 

vegetables and citrus, have been detected in surface 

waters in southern Florida (R.J. Miles and C.J. 

Pfeuffer, SFWMD, written commun., 1995). Only 

endosulfan sulfate, a less hazardous breakdown product of the two parent compounds, has been detected in 

ground water in the study area.

Volatile Organic Compounds

Detections of volatile organic compounds (VOCs) 

in ground water are common in urban areas and sporadic in rural areas in southern Florida. The principal 

VOCs detected in untreated ground water used for public supplies are the halogenated aliphatic hydrocarbons, 

particularly trichloroethene, vinyl chloride, and tetrachloroethene; and the monocyclic aromatics hydrocarbons such as benzene, toluene, and xylenes.

22 Water-Quality Assessment of Southern Florida: An Overview of Available Information
A study of public-water supplies in Broward, 

Dade, and Palm Beach Counties reported that 27 large 

public water systems had detectable levels of VOCs in 

the raw water supplied to the utilities (Vincent, 1984). 

Numerous drinking-water utilities in southeastern 

Florida treat raw ground water contaminated by halogenated aliphatic hydrocarbons (fig. 8a) and monocyclic aliphatic hydrocarbons (fig. 8b). Concentrations of 

these compounds in raw untreated water samples 

sometimes exceed drinking-water guidance concentrations. Many of these water-supply systems are using air 

stripping techniques to remove significant quantities of 

vinyl chloride and trichloroethene from raw water as a 

part of the treatment process (FDEP Public Water 

Supply, written commun., 1995). Samples from background monitoring wells were also reviewed for detections of halogenated aliphatic hydrocarbons (fig. 8c) 

and monocyclic aromatics hydrocarbons (fig. 8d). The 

highest densities of background monitoring wells with 

detections of these VOCs in raw water samples were in 

Polk, Martin, Dade, and Palm Beach Counties.

Metals and Trace Elements

Natural iron sources are widespread in southern 

Florida's aquifer systems. Sources include oxidation of 

pyrite and organic compounds, and the dissolution of 

iron oxide and silicate minerals (Florida Geological 

Survey, 1992). Iron can be mobile in some ground 

water environments and can occur in relatively high 

concentrations (>1.0 mg/L). Iron in ground water is an 

issue of concern primarily for esthetic reasons, and it 

can be easily removed using conventional treatment 

methods.

Trace elements are generally present at low 

(<0.001 mg/L) concentrations in ground water in 

southern Florida (Florida Geological Survey, 1992). 

Lead, arsenic, and mercury in ground water are of concern because of their potentially toxic effects on the 

biota. Lead concentrations in ground water samples 

from background monitoring wells sometimes exceed 

the 50 M-g/L primary drinking water standard, but some 

of these detections may be artifacts of well contamination. Lead mobility should be limited by sorption on 

clays and organic compounds (Florida Geological 

Survey, 1992).

Arsenic has been a contaminant around old cattledipping pits in the vicinity of cattle ranches (Blasland, 

Bouck, and Lee, 1992), but these areas are very small 

compared to the large size of the ranch (usually thousands of hectares in drained prairie wetland compared 

to about 1 ha of contamination). Arsenic has been 

detected in the bed sediment of canals in southern Florida (Sherwood and others, 1973); further studies are 

needed to determine whether the ground water in these 

areas has been contaminated. Arsenic has also been 

detected in ground water beneath golf courses where 

the arsenic-containing compound MSMA has been 

applied for weed control (Swancar, 1996).

Mercury is generally in low concentrations in 

ground water in southern Florida, but an abundance of 

dissolved organic compounds in ground water is conducive to the transport of mercury. Surficial ground 

water in the Everglades may be enriched in certain constituents that enhance mercury cycling. Sulfate-reducing bacteria in peat soils of the Everglades may 

enhance the transformation of inorganic mercury to 

methyl mercury, a toxic form that concentrates in the 

biota. Studies are underway by the U.S. Geological 

Survey to evaluate biogeochemical processes in the 

Everglades peat that might control mercury cycling 

(Krabbenhoft and Rickert, 1995).

Radioactivity

Much of the northwestern part of the study unit is 

underlain by phosphatic deposits containing phosphate 

ore (pebbles) that typically contains 100 to 150 ppm of 

uranium, mainly uranium-238 (Guimond and Windom, 

1975). Uranium is not very soluble in the reducing 

environment typical of ground water. Consequently, 

many of the studies of radioactivity in Florida have 

been related to uranium-238 daughter radionuclides 

such as radium-226 in drinking-water sources (Kaufmann and Bliss, 1977; Miller and Sutcliffe, 1985) or in 

ground water near phosphate chemical plants and 

mines (Miller and Sutcliffe, 1984); radon-222 in water 

and dwellings (Nagda and others, 1987); and polonium-210 in water (Harada and others, 1989) because 

of the cancer risk associated with ingestion or inhalation of these radionuclides. Phosphate ore occurs in 

greatest concentration in the intermediate aquifer, but 

the ore also occurs in other parts of the surficial aquifer 

system in southwestern Florida. Radium-226 in ground 

water often exceeds drinking-water regulations (5.0 

pCi/L) in coastal counties and its radioactivity usually 

increases with dissolved-solids concentration due to 

ion exchange reactions (Miller and Sutcliffe, 1985). 

The highest radium-226 activity that Miller and Sutcliffe (1985) measured was 110 pCi/L in a sample with

Ground-Water Quality in Southern Florida 23
EXPLANATION

NUMBER OF WATER 

UTILITIES WITH 

UNTREATED WATER 

SAMPLES IN WHICH 

CONCENTRATIONS OF 

HALOGENATED ALIPHATIC 

HYDROCARBONS EXCEEDED 

DRINKING-WATER GUIDANCE 

CONCENTRATIONS

I LESS THAN 3 

EH3TO5

11

EXPLANATION

NUMBER OF WATER 

UTILITIES WITH 

UNTREATED WATER 

SAMPLES IN WHICH 

CONCENTRATIONS OF 

MONOCYCLIC AROMATIC 

HYDROCARBONS EXCEEDED 

DRINKING-WATER GUIDANCE 

CONCENTRATIONS

I I LESS THAN 1

r~h TO 2 

 GREATER THAN 2

 1

t

EXPLANATION

NUMBER OF

BACKG ROU N D WELLS * 

IN WHICH HALOGENATED 

ALIPHATIC HYDROCARBONS 

WERE DETECTED IN 

WATER SAMPLES

I LESS THAN 2 

E32TO6

EXPLANATION

NUMBER OF 

BACKGROUND WELLS 

IN WHICH MONOCYCLIC 

AROMATIC HYDROCARBONS 

WERE DETECTED IN 

WATER SAMPLES

I LESS THAN 2 

CH2TO4

!THAN 4

Figure 8. Occurrence of hydrogenated aliphatic and monocyclic aromatic hydrocarbons in ground water in 

southern Florida.

24 Water-Quality Assessment of Southern Florida: An Overview of Available Information
a specific conductance of 19,000 microsiemens per 

centimeter at 25° C. Efforts have been made to provide 

treated water from public water utilities to people living in areas with elevated radium-226 to reduce cancer 

risks associated with ingesting this bone-seeking radionuclide. Radon-222 concentrations in ground water in 

central Florida ranged from 20 to 46,000 pCi/L (Kaufmann and Bliss, 1977). Polonium-210 in ground water 

ranged from less than 0.05 to greater than 4.5 pCi/L; 

tended to occur in shallow ground water with low pH, 

high sulfide, and high radon-222; and may be released 

by bacterial action (Harada and others, 1989).

AQUATIC ECOLOGY IN SOUTHERN 

FLORIDA

The biological communities of aquatic ecosystems 

in southern Florida reflect past and present water-quality conditions and simultaneously influence the nature 

of future water quality through a series of complex and 

dynamic interactions.

Overview of Aquatic Ecology

Wetlands are the dominant aquatic systems in the 

surface-water basins of southern Florida (table 4). 

These wetlands include a variety of ecosystem types 

including cypress strands, cypress domes, flatwoods 

sloughs, hardwood swamps, prairies, marshes, and riverine/lacustrine flood plains (Livingston and Fernald, 

1991). Freshwater wetlands merge with coastal wetlands and sustain them through seasonal sheetflow of 

waters with low nutrient concentrations. A large number of canals cut through the wetlands of southern Florida and are isolated from the ecosystems of the adjacent 

wetlands. These canals are often dredged to facilitate 

maximum discharge and have habitat characteristics 

very different from surrounding wetlands, natural rivers, and streams. Unchannelized rivers, such as the 

Myakka and the Peace Rivers, constitute a relatively 

small part of the surface water ecosystem in southern 

Florida.

The Big Cypress Basin, including the Big Cypress 

Swamp and the BCNP, is a unique wetland environment in southern Florida. The Big Cypress Basin 

differs from the adjacent Everglades in that it has relatively higher land elevation, thinner soils of marl or 

sand, and widespread forest vegetation (McPherson, 

1974). Natural drainage in the Big Cypress is by slow, 

overland flow of water to the south, and well-defined 

streams generally do not exist (McPherson, 1984).

Freshwater vegetation in the Big Cypress Basin 

primarily consists of cypress forests, mixed swamp 

forests, willow thickets, prairies, marshes, and ponds 

(Duever, 1984); cypress and hardwood vegetation is 

dominant (table 4). Periphyton is also an important 

component of wet prairies, coastal marsh, and dwarf 

cypress communities. Blue-green algae precipitate

Table 4. Extent of wetlands in drainage basins in southern Florida

Basin

Big Cypress

Caloosahatchee River

Everglades Agricultural Area

Everglades

Florida Keys

Kissimmee River

St. Lucie River

Lake Okeechobee

Peace and Myakka Rivers

East Coast Urban Area

Total basin 

area, in

hectares

649,000

349,000

270,000

935,000

39,400

1,060,000

351,000

181,000

840,000

412,000

Hectares of wetlands1

Cypress

184,000

7,240

0

55,900

0

13,600

5,890

15

4,790

126

Hardwoods

75,300

5,960

49,900

96,500

0

37,600

5,270

4,620

55,600

12,100

Marsh

and

slough

51,500

18,200

351

111,000

0

96,800

50,300

10,200

40,300

48,300

Lakes

1,360

377

49

61

0

79,600

491

88,600

21,200

5,940

Canals

and

rivers

358

1,070

769

1,930

0

3,510

2,360

878

1,360

2,350

Mangrove

58,200

1,090

0

125,000

12,300

0

1,060

0

13,700

7,090

Odll Coif 

marsh

9,260

200

0

24,000

59

0

91

0

2,320

1,390

'Modified from U.S. Department of the Interior, Fish and Wildlife Service, National Wetlands Inventory, 1979-81.

Aquatic Ecology in Southern Florida 25
considerable amounts of calcium carbonate, which 

forms calcitic mud or marl found throughout the Big 

Cypress (Duever and others, 1986).

Little is known about the ecology of the invertebrates in the Big Cypress Basin (Drew and Schomer, 

1984). Among the most abundant fish in the Big 

Cypress Basin are the Florida gar, the bowfin, the lake 

chubsucker, the swamp darter, species of killifish, and 

the mosquito fish (Drew and Schomer, 1984; Duever 

and others, 1986). The Big Cypress Basin is perhaps 

the most ecologically undisturbed natural wetlands 

system in southern Florida (Duever, 1984). Major contemporary perturbations to the ecology of the Big 

Cypress include agriculture and residential development on the periphery of the basin, oil exploration, offroad vehicle use, construction of roads and an airport, 

and limerock quarrying.

The Kissimmee River, Lake Okeechobee, and the 

Everglades watersheds are a complex, highly modified 

system where watershed boundaries and ecological 

relations are difficult to assess. The Kissimmee River is 

in a state of transition as a result of efforts to restore the 

hydrology of the Kissimmee-Okeechobee-Everglades 

system to an approximation of predevelopment conditions.

Historically, the Kissimmee River meandered for 

about 160 km through its watershed and periodically 

overflowed its banks to inundate an adjacent wetland 

mosaic of broadleaf marsh, wet prairie, and wetland 

shrub communities (Milleson and others, 1980), which 

made up 20 percent of the watershed (Kushlan, 1991). 

By the early 1980's the Kissimmee River had been 

transformed into a canal (sometimes called C-38) about 

90-km long, fitted with a number of water-control 

structures.

Wetlands are much reduced in extent, and the wetlands that remain are homogeneous plant communities 

confined to the lower, impounded parts of each pool 

(Toth, 1993). At least 39 species of native freshwater 

fishes were present in the pre-impounded Kissimmee 

River Basin (Bass, 1991). Following canalization, only 

17 fish species were collected, and the proportion of 

game species decreased from 43 to 28 percent (Davis 

and others, 1990). Macroinvertebrate communities in 

the canalized reaches are generally characterized by 

low invertebrate density and low species richness (Rutter and others, 1986; Toth, 1993). Restoration of the 

Kissimmee River, including a 4-year demonstration 

project designed to recreate hydrologic conditions 

prevalent during predevelopment times, has provided a 

focus for recent ecological studies (Toth, 1993).

Lake Okeechobee is a shallow, naturally eutrophic 

lake which is extensively influenced by nutrient enrichment from human activities. Primary production is 

limited by nutrient concentration and/or light. In some 

years algal blooms of blue-green species (cyanobacteria) cover more than 40 percent of the lake surface in 

late June and early July (Brezonik and others, 1987). 

Average annual chlorophyll a concentrations (a common measure of productivity of algal populations) 

ranged from 19 to 27 |ig/L during 1974-84 (Canfield 

and Hoyer, 1988). The highest chlorophyll a concentrations were measured in the northern and western parts 

of the lake (Phlips and others, 1994). The relative 

importance of factors contributing to frequency and 

intensity of algal blooms has not been determined. 

Phosphorus inputs, disturbance and resuspension of 

nutrient-rich bed sediments, and other factors are all 

being studied to quantify their relative contributions to 

blooms of blue-green algae. The lake contains large nuisance populations of several exotic aquatic macrophytes, including water hyacinth, hydrilla, and water 

lettuce. Periodic application of herbicides for control of 

nuisance macrophytes results in greater light penetration and greater availability of plant nutrients, which in 

turn promotes subsequent algal blooms.

The Everglades is a large, peat-based wetland 

that historically covered about 11,000 km2 . In modern 

times, the Everglades watershed south of Lake Okeechobee has been drained and divided into the EAA, the 

WCAs, and the ENP. The EAA is an area of drained 

wetlands used for large-scale agricultural production of 

sugar cane, winter vegetables, and rice. The WCAs are 

diked, vegetated, shallow-water reservoirs designed 

for flood control and water supply. The ENP contains 

about 20 percent of the original Everglades system now 

preserved for wilderness and wildlife habitat.

The majority of the wetlands already lost from the 

Everglades system may never be restored because restoration would come at an incalculable cost to agriculture and the millions of residents living on the already 

drained land. Maintaining the remaining wetlands in 

the Everglades system as a self-sustaining multi-use 

resource which provides water supply, flood control, 

and water-quality enhancement is the goal of present 

(1995) interagency efforts.

The Everglades has been described as the most 

intensely studied wetlands in the world (Kushlan, 

1991). Historically, the Everglades was dominated by 

sawgrass, Cladiumjamaicense. This dominance is presumably due to the tolerance of sawgrass for very low 

nutrient concentrations (Steward and Ornes, 1975).

26 Water-Quality Assessment of Southern Florida: An Overview of Available Information
Sawgrass does not have a competitive advantage over 

other macrophytes, such as cattail, under high-nutrient 

conditions.

Periphyton is an important component of the ecosystem in many areas of the Everglades; periphyton 

varies in composition according to nutrient concentration and hydropattern (defined as the depth of water, 

and the duration and timing of freshwater inundation). 

Desmids, filamentous green algae, and certain species 

of diatoms are present in acid, low-mineral, low-nutrient habitats such as those present in the interior of 

WCA-1. Rainfall is the primary source of water-quality 

constituents in these habitats. In marsh areas with low 

nutrient concentrations but high dissolved-mineral 

content, calcareous blue-green algae and diatoms dominate the periphyton community. These areas occur in 

interior parts of WCA-2 and WCA-3, and in parts of 

the ENP. Marsh areas adjacent to and fed by the EAA 

canals carrying drainage water with high nutrient and 

dissolved-mineral concentrations typically contain periphyton dominated by filamentous, nutrient-tolerant, 

blue-green algae and diatoms (Swift, 1984; Swift and 

Nicholas, 1987). Calcareous periphyton and the formation of an algal mat are characteristic of Taylor Slough 

and other areas where the hydroperiod (the duration of 

freshwater inundation) is 6 to 7 months. At sites with a 

longer hydroperiod, approaching year-round flooding, 

periphyton composed of green algae, especially 

desmids, is common (Browder and others, 1981).

A review of data on periphyton food utilization by 

macroinvertebrates and vertebrate animals in the Everglades indicates that diatoms are a preferred food 

source; green algae are consumed less frequently, and 

blue-green algae are likely an unsuitable food for many 

invertebrates, fish, and other organisms (Browder and 

others, 1994).

Fish are an important component of the Everglades 

ecosystem, and they function at many levels of the food 

web ranging from primary consumers of vegetation 

and detritus, to secondary consumers of invertebrates, 

and finally as top predators (Loftus and Eklund, 1994). 

Forty-three species of fishes in 18 families, including at 

least four exotic species, were collected in the Everglades during 1962-74 (Dineen, 1974). Only two longterm, quantitative studies of Everglades freshwater 

fishes have been conducted, and both occurred within 

the ENP (Loftus and Eklund, 1994). It is likely that the 

intensity of human activities in southern Florida will 

result in ecosystem alterations that will influence the 

fish community composition.

The Myakka River, Peace River, Caloosahatchee 

River, and other streams are locally important components of surface-water systems in the northwestern part 

of the study unit. The Myakka River is one of southern 

Florida's most pristine rivers (Estevez and others, 

1991), and the lower two-thirds of the river is designated as an Outstanding Florida Water (Livingston, 

1991). The basin still contains areas of forested wetlands and large amounts of instream and bankside logs, 

branches, roots and other snag habitats. Submersed 

aquatic vegetation is relatively scarce (Canfield and 

Hoyer, 1988), perhaps due to shading, and food chains 

are based on detrital inputs (Estevez and others, 1991). 

One exception is the natural in-stream lakes which are 

typically wide, grassy, and shallow lentic reaches in the 

main riverbed. In these habitats, insects are the most 

abundant invertebrates in the upstream reaches, 

whereas crustaceans dominate in the downstream parts 

of the river (Estevez and others, 1991).

In contrast to the Myakka River, the Peace River 

Basin contains a relatively small amount of undisturbed and public land, and the few remaining natural 

areas in the basin are being diminished by expanding 

citrus operations and phosphate mining. Blue-green 

algae with the capacity to fix nitrogen dominate the 

phytoplankton community in the phosphate-enriched 

streams of the Peace River Basin (Fraser, 1991). The 

Peace River contained 34 species of native freshwater 

fishes and a number of exotic species during 1983-88. 

The most abundant species collected were the Florida 

gar, bluegill, largemouth bass, and redear sunfish 

(Bass, 1991).

In the Caloosahatchee River, very low streamflow 

velocity and the presence of numerous oxbow lakes 

along the main channel allows the establishment of 

floating aquatic macrophyte communities including 

alligator weed, floating maidencane, water lettuce, and 

primrose willow. In the main channel of the river, 

emergent and floating vegetation is rare, and algae 

dominate the plant community (Drew and Schomer, 

1984). Chlorophyll a concentrations in the Caloosahatchee River vary seasonally, and maximum chlorophyll a concentrations coincide with algal blooms of 

blue-green algal species including Anabaenaflosaquae 

and Microsystis aeruginosa. Algal blooms occur 

downstream of wastewater treatment plants, and also 

downstream from sources of agricultural runoff including flower nurseries and citrus groves. At least 31 species of native freshwater fishes have been collected in 

the Caloosahatchee River (Bass, 1991).

Aquatic Ecology in Southern Florida 27
Issues of Regional Importance to Aquatic 

Ecology

The intensity and pervasive nature of human activities in southern Florida has significant consequences 

for the ecology of the aquatic habitats in the region. 

Although there are many issues of importance relating 

to aquatic ecology in southern Florida, those which are 

of particular interest include altered hydropatteras, the 

influence of nutrient enrichment, the occurrence and 

distribution of mercury, endocrine disruption and other 

effects of pesticides and other organic compounds, and 

the spread of exotic plant and animal species.The many 

factors relating to aquatic ecology in southern Florida 

are discussed separately in this report, for ease of presentation. However, in many cases these factors interact in complex ways, with consequences of greater 

magnitude for the biota than would otherwise be 

expected.

Altered Hydropatterns

Hydropatteras have been significantly altered in 

southern Florida from historical times. The hydroperiod in the Everglades marshes was 5 to 10 months, 

but under present conditions, many Everglades 

marshes are wet only 2 to 5 months per year. The dense 

saw grass once covering the northern Everglades likely 

slowed the southward flow of water from rainfall and 

Lake Okeechobee overflow, resulting in a prolonged or 

continuous hydroperiod for the marshes farther south 

(Fennema and others, 1994). The conversion of the 

sawgrass marsh in the northern Everglades to agricultural fields and drainage canals may have had an indirect effect on hydropattern in the sawgrass marshes to 

the south in the WCAs, accelerating the rate of water 

flow and changing the timing of water supply (Walters 

and others, 1992). One goal of the Everglades Construction Project is to use treated water from the proposed STAs to improve seasonal water supply in the 

Everglades and specifically to reestablish sheetflow to 

the WCAs.

Changes in hydropattern have many ramifications 

for aquatic ecosystem structure (numbers and types of 

organisms) and function (processing and cycling of 

food and energy). Altered hydropatterns have influenced historic fire patterns in the BCNP (Duever and 

others, 1986). There appears to be a general increase in 

fires in the BCNP since 1971, although inconsistent 

records prior to 1970 preclude statistical analysis of 

these changes (Duever and others, 1986). Changes in

dominant flora, for example a shift from sawgrass to 

cattail, may result from changes in hydrologic and fire 

regimes (Urban and others, 1993; Davis and others, 

1994). Studies indicate that marshes with a longer 

hydroperiod have greater densities of macroinvertebrates than marshes with a shorter hydroperiod (Loftus 

and others, 1990). Densities of many small fish species 

that provide a food source for wading birds have been 

positively correlated with the number of months of 

marsh inundation (Loftus and Eklund, 1994). Two 

long-term, quantitative studies of Everglades fishes 

focus on the response of fish communities to changing 

hydroperiod (Kushlan, 1976; Loftus and Kushlan, 

1987) and indicate that populations of larger predatory 

fish are enhanced during periods when the hydroperiod 

is extended.

Data from studies in the Kissimmee River Basin 

indicate that wetland communities can revert to predevelopment types within a year once the hydrologic 

regime is restored (Toth and others, 1993). Data also 

indicate that maintenance of diverse and self-sustaining littoral and flood-plain vegetation requires maintenance of continuous flow and widely varying stage and 

discharge regimes (Toth and others, 1993). Macroinvertebrate communities sampled adjacent to the Kissimmee River main channel following flow restoration 

indicate increased species richness especially of current-loving species (Rutter and others, 1989). However, unless water levels are deep enough for long 

enough, fish species cannot utilize marsh habitat to any 

extent in the Kissimmee watershed, and enhancement 

of game fish populations will not occur (Toth, 1993).

Influence of Nutrient Enrichment on Habitat 

Integrity

Historically, nutrient concentrations were low in 

the Everglades and controlled by nutrient concentrations in rainfall (Waller, 1982). In recent times, numerous areas of southern Florida have been subjected to 

nutrient enrichment. The EAA is the source of 45 percent of the phosphorus load discharged to the Everglades (South Florida Water Management District, 

1995). During 1978-87 WCA-2 received at least 1,825 

Mg of nitrogen and 61 Mg of phosphorus per year from 

adjacent canals (South Florida Water Management District, 1992b). During 1978-91, an estimated mean 

annual load of 204 Mg of total phosphorus was transported by EAA drainage/runoff water with 85 percent 

going to the south (South Florida Water Management

28 Water-Quality Assessment of Southern Florida: An Overview of Available Information
District, 1992b). A north-to-south gradient of decreasing nitrogen and phosphorus concentrations has been 

documented across the WCAs (Belanger and others, 

1989). Nutrient concentrations of up to 30 times the 

background concentration have been measured in canal 

water adjacent to the ENP (Gordon and others, 1986); 

however, the annual phosphorus input to the ENP has 

increased very little over predrainage inputs (Davis, 

1994). Data indicate that phosphorus is more important 

than nitrogen as a limiting nutrient for plant growth in 

the Everglades system as a whole (Davis, 1994).

Studies show that algae and macrophytes respond 

rapidly (within days or weeks) to increased nutrient 

availability (Belanger and others, 1989; Grimshaw and 

others, 1993). Experimental additions of phosphorus at 

field sites in WCA-2 resulted in increased phosphorus 

uptake and increased biomass production by sawgrass 

communities (Craft and others, 1995). No significant 

change in macrophyte species diversity or expansion of 

cattail stands was observed in experimental plots 

receiving nutrient additions, but the duration of the 

study (2 years) may have been too short to show 

effects.

Numerous other studies indicate that nutrient 

enrichment in the Everglades has resulted in or contributed to the replacement of sawgrass and slough communities by cattail and disappearance of the native 

blue-green algae/ diatom-dominated periphyton mats 

(Flora and others, 1988; Belanger and others, 1989; 

Scheidt and others, 1989; Davis, 1991; South Florida 

Water Management District, 1992b). Increases in nutrient concentrations, however, do not fully explain the 

distribution of cattail in the Everglades. Urban and others (1993) monitored sawgrass and cattail densities in 

WCA-2 and reported that deep water, fire, and nutrient 

enrichment synergistically stimulated cattail expansion 

into sawgrass communities. Physical disturbance of 

any kind appears to provide cattail with a competitive 

advantage over sawgrass because cattail is adapted 

to function as an early colonizer in these habitats 

(Davis, 1994).

In the Everglades ecosystem, the dominant macrophyte type (sawgrass or cattail) can exert a profound 

influence on the ecology of the habitat (Belanger and 

others, 1989). Cattails have a shorter life cycle than 

sawgrass, so the production of detrital material (and 

associated biological oxygen demand) is greater. The 

shape and size of cattail leaves reduces reaeration and 

light availability at the water surface, thus reducing 

benthic algal photosynthesis and lowering dissolvedoxygen concentrations. Changes in organic bedsediment texture, dissolved-oxygen concentration, 

transpiration rate, and the community composition of 

microbial, periphyton, and macroinvertebrate populations occur following nutrient enrichment (Davis, 

1994). Richardson (1994) and Craft and others (1995) 

reported a significant decline of the Utricularia-penphyton mat after only 1 year of nutrient additions and 

subsequent expansion of Chara (musk-grass) populations to replace the floating periphyton mat. Several 

studies have reported that macroinvertebrate diversity 

in the Everglades is naturally low (Waller, 1976; Loftus 

and others, 1990). Following a shift from sawgrass to 

cattail stands, a reduction in numbers of Diptera, snails, 

and isopods was observed, whereas the density of 

annelid worms doubled (Davis, 1994). Rader and Richardson (1992) reported no reduction in diversity, 

although their analyses of macroinvertebrate data were 

preliminary. Implications of a shift in macroinvertebrate community composition for the Everglades food 

chain are poorly understood but may be significant 

(Davis, 1994) and warrant further investigation.

The goal of the Everglades Construction Project is 

to reduce the phosphorus loading to the Everglades 

Protection Area by creating six STAs comprising about 

16,000 ha of wetlands. In combination with implementation of on-farm Best Management Practices in the 

EAA, the STAs should keep phosphorus inflows to the 

Everglades Protection Area from exceeding 50 ppb 

(South Florida Water Management District, 1994b). 

The Everglades Nutrient Removal Project is a prototype STA and operation was initiated in 1994 (South 

Florida Water Management district, 1994b). Data 

collected from this 1,600-ha constructed wetland will 

be used to refine and improve design, operation, and 

management of the Everglades Construction Project.

Occurrence and Distribution of Mercury

The build up of mercury in the environment is 

widespread in many parts of the world (National Academy of Sciences, 1978). Concentrations of mercury 

have increased worldwide in the atmosphere over the 

last 100 years, presumably as a result of industrialization. In Florida and particularly in the Everglades, the 

build up of mercury in bed sediment and biota has been 

pronounced (Atkeson, 1994). Analysis of bedsediment cores in the Everglades indicates that mercury accumulation rates are presently about six times 

higher than in 1900 (Delfino and Crisman, 1993).

Aquatic Ecology in Southern Florida 29
Most mercury entering the aquatic habitat from the 

atmosphere is primarily in the inorganic form. Mercury 

is then transformed by bacteria to the more toxic 

organic form (methyl mercury) in many aquatic systems. Most mercury detected in freshwater fish is 

methyl mercury (Grieb and others, 1990), which 

bioaccumulates through uptake from water or diet.

In 1989, high concentrations of mercury were 

detected in freshwater fish that were collected in a joint 

monitoring project by the FGFWFC, the Florida Health 

and Rehabilitative Services Department of Environmental Health, and the FDEP (Ware and others, 1990). Concentrations of mercury greater than 0.5 (ig/kg were 

detected in largemouth bass collected from remote and 

urban lakes and rivers throughout Florida (Ware and others, 1990). Since that time, health advisories have been 

issued for more than 810,000 ha of aquatic habitat in 

southern Florida, including the BCNP, WCA-2, WCA-3, 

and the Shark River drainage in the ENP. During 1990- 

91, mercury concentrations were determined in largemouth bass from 53 sites in Florida. Mercury concentrations increased with fish age and size at all study sites, 

and exceeded the Florida health advisory standard 

(0.5 (ig/kg) in fish from 24 of the 53 lakes sampled. 

Maximum concentrations of mercury detected in largemouth bass (4.4 mg/kg) and bowfin (7 mg/kg) from the 

Everglades are the highest concentrations detected in 

Florida (Stober and others, 1994).

A 1993 study of mercury in southern Florida indicated the presence of a north-to-south (high to low) 

gradient for total mercury and methyl mercury in water. 

Gradients were reversed (low to high) for total mercury 

in bed sediment and mosquito fish tissue (Stober and 

others, 1995). Bed sediment from Military Canal had 

the highest concentrations of mercury of any site in 

Dade County (SFWMD, 1994), and mobilization from 

the bed sediment into the food chain may occur. Mercury accumulation through the food web may suppress 

the breeding success of wading birds (Frederick and 

Spalding, 1994) and contribute to the endangered status of the Florida panther (Roelke and others, 1991).

Sources of mercury in southern Florida ecosystems 

are not well understood. Atmospheric transport and 

deposition from global and regional sources is one 

likely source. Periodic inundation of natural mineral 

and peat deposits during fluctuating water levels may 

facilitate mercury mobilization (Delfino and Crisman, 

1993; Lange and others, 1993). Other waterborne 

sources may include release from limestone formations 

underlying the Everglades, and runoff from periodically burned croplands in the EAA. Definitive studies 

of the influence of water quality on mercury transformation and uptake are not complete, and at this time 

(1996) correlations between other water-quality constituents and mercury concentrations in biota have not 

been substantiated. Numerous studies of mercury 

occurrence and distribution in water, bed sediment, and 

biota, as well as process-oriented studies of mercury 

mobilization, transformation, and bioaccumulation, are 

underway in southern Florida (Mercury Technical 

Committee, 1991).

Endocrine Disruption and Other Effects of 

Pesticides on Biota

Pesticides and other organic compounds are 

detected throughout the ecosystems of the world 

(Simonich and Kites, 1995). The same suite of characteristics which make pesticides effective (persistence, 

low volatility, low water solubility, high lipid solubility, and low rate of biodegradation) also may lead to 

bioaccumulation and biomagnification with resultant 

toxicity in nontarget wildlife and humans (Bason and 

Colborn, 1992). Pesticide use is so widespread in 

southern Florida that documenting the extent of use is 

difficult (Scheldt, 1989). As of the late 1980's, at least 

88 pesticide compounds were used in southern Florida 

agriculture (Scheldt, 1989). Principal regional pesticide uses include ground and aerial spraying of pesticides for agriculture, mosquito control, and aquatic 

weed control, and application of pesticides on golf 

courses, on residential property, and on power and 

transportation right-of-ways.

The only long-term pesticide monitoring program 

in southern Florida is carried out by the SFWMD; longterm quarterly monitoring sites for a suite of 68 pesticides in surface water and hydrosoil are confined to the 

canal system and no marsh sites are included (Scheldt, 

1989). No ongoing programs to monitor pesticides in 

wildlife existed as of the late 1980's (Scheldt, 1989).

Fish were collected in the WCAs during 1971-72 

and in the ENP during 1969-70 for pesticide analyses. 

Measurable concentrations of DOT (6-218 (ig/kg), 

dieldrin (6-130 u.g/kg), toxaphene (2,200-5,000 

(ig/kg), and PCBs (10-100 (ig/kg) were detected in tissue from largemouth bass, bluegill, and several sunfish 

species (McPherson, 1973). No detectable concentrations of aldrin, endrin, heptachlor, lindane, or chlordane were measured in that study. Measurable 

concentrations of several pesticides including

30 Water-Quality Assessment of Southern Florida: An Overview of Available Information
chlordane, oxychlordane, p,p DDE, and nonachlor 

were detected in fish fillet tissue samples collected in 

Collier County in 1995 (Al Ruth, Collier County Environmental Services Division, written commun., 1995). 

Measurable concentrations of endrin were detected in 

fish tissue samples collected in a remote area of Fakahatchee Strand State Preserve, and dieldrin was 

detected in fish tissue samples collected in Lake Trafford. The focus of recent monitoring efforts couples 

analyses of water and bed sediment with analyses of 

biota at various levels in the food chain (filterers, gatherers, predators) to obtain information on bioaccumulation and biomagnification of pesticides and other 

organic compounds.

A large number of pesticides and other organic 

compounds with widespread distribution in the environment are reported to have endocrine-disrupting 

effects (Colborn and others, 1993). Reproductive 

anomalies have been observed in fish, wading birds, 

the American alligator, and other animals living in ecosystems polluted by compounds that disrupt the endocrine system (Davis and Bradlow, 1995). The National 

Biological Service has collected fish from several sites 

in southern Florida as well as from numerous sites 

throughout the United States; analyses to determine 

estrogen/testosterone ratios were in progress in 1996 

(Wade Bryant, National Biological Service, written 

commun., 1995). Coupled with analyses of fish tissue 

for the presence of pesticides and other organic compounds, these data may indicate areas in southern Florida where organisms are at greatest risk from pesticide 

contamination.

Spread of Exotic Plant and Animal Species

Exotic aquatic and wetlands plants are spreading 

rapidly through many parts of southern Florida. Invading plant species of greatest concern include melaleuca 

(Melaleuca quinquinervid), Australian pine (Casuarina equisetifolid), Brazilian pepper (Schinus terebinthifolius), hydrilla (Hydrilla verticillata), and water 

hyacinth (Eichornia crassipes) (Exotic Pest Plant 

Council, 1993). Melaleuca has invaded more than 

200,000 ha in Florida. Infestations occur in Lake 

Okeechobee's marshes, the WCAs, the BCNP, and 

areas east of the ENP. The BCNP is vulnerable to invasion of aggressive exotic plant species, particularly in 

areas disturbed by off-road vehicles, fire-control activities, construction, and drainage projects. The northwestern quadrant of the BCNP is most vulnerable to

establishment of melaleuca forest because of the area's 

deep sandy soils, which are preferred by melaleuca 

(Duever and others, 1986). Agricultural activities associated with conventional crop farming, including alteration of patterns of periodic floods and fires, have also 

facilitated the invasion of a number of exotic species 

especially in the northern part of the area (Duever, 

1984).

By the early 1990s, 15 to 17 species of exotic fishes 

were considered to be well established in southern 

Florida, and at least 7 of these species were present in 

the Everglades (Robertson and Frederick, 1994).The 

detrimental effects of exotic fish species include predation on native fish species and competition with native 

fish species for habitat and food. These activities can 

result in negative impacts on animals at other levels of 

the food chain. However, some exotic fish species are 

highly productive in marsh habitats and may produce a 

significant amount of food for predatory bird species 

(Robertson and Frederick, 1994), thereby making these 

exotic fish species valuable to the food web in southern 

Florida. The National Biological Service is presently 

collecting data on distribution, abundance, and food 

habits of exotic fish species in southern Florida to 

assess their role and effect on the ecosystem.

SUMMARY

Historically, southern Florida surface waters were 

characterized by large areas of wetlands that were 

drained by numerous small coastal streams and several 

large rivers. Today, surface water exists in southern 

Florida in a complex system of highly modified and 

intensively managed wetlands, lakes, canals, and regulated rivers. Surface-water basins are not well-defined 

and discharge in some rivers and canals may cease or 

be reversed at times of the year when backpumping is 

used to manage local water levels and regional water 

supply. The quality of surface water has been and continues to be profoundly influenced by altered patterns 

of water flow, atmospheric deposition of nutrients and 

other contaminants, runoff from agriculture and livestock operations, phosphate mining, urban runoff, 

municipal wastewater discharge, and other human 

activities.

Development of a nutrient budget for southern 

Florida is a goal of several agencies involved in ecosystem restoration in the region. The relative contributions 

of various point and nonpoint sources of phosphorus

Summary 31
and nitrogen were estimated in nine surface-water 

basins in the Southern Florida NAWQA study unit. 

Fertilizer and manure from agriculture account for 

much of the nutrient inputs. Fertilizer is the dominant 

source of phosphorus in eight basins and the dominant 

source of nitrogen in at least five basins. Canal inflow 

is the largest source of phosphorus input to Lake 

Okeechobee and the second largest source of nitrogen 

input to the lake. Atmospheric sources of nitrogen contribute more than 20 percent of the total nitrogen input 

to all basins and are the dominant source of nitrogen 

input to Lake Okeechobee and the Everglades.

Nutrient loads in selected canal and river outflows 

in southern Florida were estimated using data collected 

by the SFWMD and the USGS. Annual phosphorus 

loads from the Peace River are the highest in the study 

unit; annual phosphorus loads from the Caloosahatchee 

River and the major Palm Beach canals are also high, 

compared to other parts of southern Florida. Estimated 

annual loads of phosphorus from parts of the Big 

Cypress Basin and the S-12 water-control structures of 

the Tamiami Canal are low compared with estimated 

phosphorus loads in outflows in the northern part of the 

study unit. Annual nitrogen loads in southern Florida 

were highest in outflows from the Caloosahatchee 

River Basin and the major Palm Beach canals. Nitrogen loads in outflows from parts of the Big Cypress 

subbasin were lower than those estimated to the north.

The principal aquifers in southern Florida are the 

Biscayne aquifer, the surficial and intermediate aquifer 

systems, and the Floridan aquifer system. Waters in all 

the aquifer systems are primarily a calcium bicarbonate 

type, mostly because shell, limestone, or dolomite is 

abundant in the aquifers. The waters are generally hard 

to very hard. Ground water is the most important drinking-water resource in southern Florida; about 5.5 million people depend on ground water as a primary 

source of drinking water.

Ground water in southern Florida is vulnerable to 

contamination because of its close proximity to the surface. Ground-water contamination issues of greatest 

concern include: saltwater or brackish-water intrusion, 

nutrient enrichment, pesticides, metals and trace elements, volatile organic compounds, and radioactivity. 

Most contaminants reach the ground-water system in 

southern Florida indirectly through the land surface 

from landfill leachate, spills of industrial organic solvents, and areal application of fertilizers and pesticides; and directly from leaking fuel storage tanks, 

septic systems, and drainage wells. Saltwater or brackish

water from remnant or recent seawater, and radioactivity from phosphatic deposits reach ground-water 

systems as a result of natural processes, but their occurrence may also be affected by human activities.

Wetlands are the dominant aquatic ecosystem type 

in the surface-water basins of southern Florida, and 

include the cypress forests of the Big Cypress Basin, 

the sawgrass marshes of the Everglades, and the mangrove forests of coastal waters. Freshwater wetlands 

merge with coastal wetlands and sustain them through 

seasonal sheetflow of waters with low nutrient concentrations. A large number of canals cut through the wetlands of southern Florida and are isolated from the 

ecosystems of the adjacent wetlands. These canals are 

often enriched with nutrients, are periodically dredged 

to facilitate maximum discharge, and have habitat characteristics very different from surrounding wetlands, 

natural rivers, and streams. The biological communities of aquatic ecosystems in southern Florida reflect 

past and present water-quality conditions and simultaneously influence the nature of future water quality 

through a series of complex and dynamic interactions.

The intensity and pervasive nature of human activities in southern Florida has had significant consequences for the ecology of the aquatic habitats in the 

region. Although there are many issues of importance 

to aquatic ecology in southern Florida, those which are 

critical to the ecosystem include: altered hydropatterns; 

the influence of nutrient enrichment; the occurrence 

and distribution of mercury; endocrine disruption and 

other effects of pesticides and other organic compounds; and the spread of exotic plant and animal species.The many factors influencing aquatic ecology in 

southern Florida interact in complex ways, with consequences of greater magnitude for the biota than those 

expected if the individual factors acted separately.

Surface-water quality, ground-water quality, and 

aquatic ecology in southern Florida are being studied 

(1996) in the context of ecosystem restoration by 

numerous Federal, State, and local agencies, and by 

private organizations. There is a widespread commitment to develop a fundamental understanding of 

ecosystem function in southern Florida. Efforts are 

underway to formulate and implement a broadly based, 

basin-wide water management strategy for the region 

in order to restore and maintain a sustainable ecosystem in southern Florida. The U.S. Geological Survey is 

a participant in these efforts, and the data collected in 

the Southern Florida NAWQA study unit will contribute to ecosystem restoration efforts in south Florida.

32 Water-Quality Assessment of Southern Florida: An Overview of Available Information
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40 Water-Quality Assessment of Southern Florida: An Overview of Available Information
Appendix

Data Sources and Computation Methods Used for Pie Diagrams of Estimated 

Nutrient Loads in Southern Florida

Fertilizer and Manure

Fertilizer and manure loads were calculated using a 

combination of county-level estimates for fertilizer and 

manure and large-scale land use and land cover (LULC) digital maps. Fertilizer estimates were obtained from the Florida 

Department of Agriculture and Consumer Services. Manure 

data were computed by R.B. Alexander (U.S. Geological 

Survey, written commun., 1992) using data on county animal 

populations obtained from the 1987 Census of Agriculture 

and the manure nutrient content in units of kilograms per 

year as N and P. Computations are based on estimates of the 

nutrient content of daily wastes produced per 454 kg of animal weight. Estimates obtained from the Soil Conservation 

Service, April 1992, the Agricultural Waste Management 

Field Handbook, Chapter 4. Estimates of nutrient content, in 

some cases, represent an average of the reported range of 

values or are assumed values.

Fertilizer and manure data were available for each 

county in the study unit, but not for the designated surfacewater basins. In order to determine estimates for the designated surface-water basins, it was necessary to determine the 

proportion of cropland in the basins for fertilizer estimates 

and the proportion of other agricultural land in the basins for 

manure estimates, compared to total cropland and total other 

agricultural land in the county. The proportion of cropland 

was used to calculate the fertilizer use estimates for the 

basin. The proportion of other agricultural land was used to 

calculate the manure estimates for the basin.

The cropland estimates used are based on Water Management District (WMD) land cover and land use digital 

maps. The Southern Florida NAWQA study unit falls under 

the jurisdictions of three Water Management Districts: South 

Florida (SFWMD), Southwest Florida (SWFWMD), and St. 

Johns River (S JRWMD). The LULC data for SFWMD were 

compiled in 1988. SWFWMD LULC digital maps were 

compiled from aerial photography dated from 1989-91. S JRWMD LULC digital maps were compiled from aerial photography dated from 1986-91.

The specific LULC classification systems differed slightly 

between Water Management Districts. For SFWMD, the following LULC categories were used for the fertilizer calculations: cropland, including sugar cane, truck crops, rice groves, 

ornamentals, nurseries, tropical fruits, and sod farms. For 

manure calculations the following LULC categories were used: 

improved and unimproved pasture, confined feeding operations, including cattle, dairy, fish, horse, and poultry farms.

For SWFWMD and SJRWMD, the following categories 

were used for fertilizer calculations: row crops, field crops, 

citrus, fruit, other groves, tree nurseries, sod farms, ornamentals, vineyards, floriculture, and timber seedlings. For 

manure calculations, the following categories were used: 

pasture, improved pastured, woodland pasture, feeding operations, including, cattle, poultry, swine, horse, dairies, kennels, and fish farms.

Atmospheric Deposition

Three South Florida Water Management District precipitation-quality sites were used. These sites were selected 

where water quality could be matched with data from nearby 

daily precipitation-quality collectors. Only precipitationquality data collected after March 1992 were used (when 

SFWMD began using NADP protocols). The precipitationquantity data (wetfall only) were summed for the 7 days preceding the Tuesday morning collection of the precipitationquality sample. This approach was used because precipitation often falls in the afternoon or evening during much of 

the year. If precipitation-quantity/quality data were missing, 

the nearest before and after data were averaged to compute 

an estimated value to avoid assuming zero loading during the 

gaps in data. To compute the weekly atmospheric loading, 

the 7-day sum of precipitation quantity in inches was multiplied by the concentration of total nitrogen or total phosphorus in milligrams per liter and by a conversion factor of 

25.4 L kg mg' 1 inch' 1 km'2 to get a weekly loading in kilograms per square kilometer. The weekly periods at the beginning and end of the 1 - or 2-year summing period were 

adjusted by multiplying by the number of days in the period 

of computation and then dividing by 7 days. The weekly 

sums were then added together to get total atmospheric loading. If a 2-year period was summed the load was divided by 

2 to get an annual atmospheric loading of total nitrogen or 

total phosphorus in kilograms (kg) of N or P per square kilometer (km 2) per year. The designated basins were converted 

to a grid consisting of 1-km2 grid cells. The three annual 

average precipitation loadings were interpolated/extrapolated to the centers of the grid cells using the ARC/INFO 

inverse distance weighting function. The interpolated/ 

extrapolated values were summed to produced total nitrogen 

and phosphorus loads per basin.

Appendix 41
Total atmospheric deposition of nitrogen and 

phosphorus includes wet and dry components, although the 

dry deposition is generally not measured and is poorly 

understood (Edgerton and Lavery, 1990); total deposition is 

usually estimated using a ratio of dry to wet deposition (Gerald Morrison, South Florida Water Management District, 

written commun., 1992). Estimates of the dryfall to wetfall 

ratio in Florida range from 0.30 (CH2M Hill, 1992) to 2.04 

(Environmental Science and Engineering, 1977; Zarback 

and others, 1994). We have chosen the lower ratio as a conservative estimate for southern Florida and have multiplied 

the wet deposition by 1.3 to obtain a total atmospheric deposition.

Septic Tanks

The nitrogen and phosphorus loads for septic tanks were 

calculated using county estimates of septic tank numbers and 

drainage basin population data. The septic tank data were 

obtained from Marella (1994). In order to determine the 

number of septic tanks within each basin from the county 

estimate, the proportion of population within the basin was 

calculated from county population estimates for census 

block groups. For example, if 90 percent of a county's 1990 

population lived within a given basin, then 90 percent of the 

septic tanks for that county were allocated to that basin.

In order to determine nitrogen and phosphorus loads 

from numbers of septic tanks, estimates were obtained for 

the amount of nitrogen and phosphorus potentially generated 

by a septic tank. According to Tchobanoglous (1991), 11 

kg/yr of nitrogen and 4 kg/yr of phosphorus can be generated 

per septic tank. Therefore, the number of septic tanks in a 

given basin was multiplied by 11 and 4 to obtain nitrogen 

and phosphorus loads, respectively, for that basin.

Major Canals and Rivers

Loads of total phosphorus and total nitrogen from major 

canals and rivers were estimated for use in table 3 and figures 

5 and 6. For most sites, these loads were estimated using 

average annual discharge during 1980-89 (South Florida 

Water Management District, 1993) reported in 1,000 acrefeet per year times the mean concentration of total phosphorus or total nitrogen (Germain, 1994) reported in milligrams 

per liter times a unit conversion factor of 1233.482 (L 

kg)/(thousands acre-ft mg). The computation was done using 

a FORTRAN program.

Loads for 3 major canals and rivers were computed from 

different data sources. Loads for the Peace River at Arcadia 

were computed from USGS discharge and nutrient-concentration data collected during 1984-93 using the Estimator 

program written by Timothy Cohn of the USGS. The use of 

Estimator is described by Baier and others (1993). The nutrient loads for the St. Lucie Canal were estimated using the 

mean USGS discharge data for the St. Lucie Canal at structure S80 collected during 1953-91 and the mean nutrient 

concentration data collected during 1989-91 by Germain 

(1994). Nutrient loads to the Big Cypress Basin were estimated from USGS discharge data collected during 1964-94 

at 40-Mile Bend to Monroe and mean nutrient concentration 

data collected at Tamiami Trail Bridge 105, as reported in the 

SFWMD data base (DBHYDRO) from 1984-93.

Wastewater Treatment Facilities

Nitrogen and phosphorus loads generated by wastewater treatment facilities were calculated using wastewater discharge amounts and disposal source. The amount of 

nutrients in wastewater is determined primarily by the level 

of treatment. Most wastewater treatment in Florida is secondary (Sharon Sowicki, Florida Department of Environmental Protection, written commun., 1996). Only those 

facilities that discharged wastewater within the designated 

basins were included in the calculations. Wastewater treatment facilities that discharged treated wastewater directly to 

the Atlantic Ocean were removed from the calculations. 

According to David York (Florida Department of Environmental Protection, Draft Domestic Wastewater Management 

Section for Chapter 10 (Water Management Programs), Florida Water Atlas, table 1, written commun., 1996), secondarily treated wastewater can contain 15 mg/L nitrogen and 8 

mg/L phosphorus, so these amounts, along with the discharge amounts, were used to determine nitrogen and phosphorus loads.

42 Water-Quality Assessment of Southern Florida: An Overview of Available Information