Water Quality

in Southern Florida

Florida, 1996–98

U.S. Department of the Interior

U.S. Geological Survey

Circular 1207
POINTS OF CONTACT AND ADDITIONAL INFORMATION

Front cover: Everglades National Park (photograph by Benjamin F. McPherson). 

Back cover: Left, Southern Everglades C-111 agricultural basin, irrigation of crops; center, Northern Everglades, 

slough and tree islands; right, areal view of Miami (photographs by Benjamin F. McPherson). 

The companion Web site for NAWQA summary reports:

http://water.usgs.gov/nawqa/

Southern Florida contact and Web site:

USGS State Representative: Carl Goodwin

U.S. Geological Survey

Water Resources Division

227 N. Bronough St., Suite 3015

Tallahassee, FL 32301

state rep fl@usgs.gov

http://water.usgs.gov/pubs/nawqa/

National NAWQA Program:

Chief, NAWQA Program

U.S. Geological Survey

Water Resources Division

12201 Sunrise Valley Drive, M.S. 413

Reston, VA 20192

http://water.usgs.gov/nawqa/

River Basin Assessments

Albemarle-Pamlico Drainage Basin (Circular 1157)

Allegheny and Monongahela River Basins (Circular 1202)

Apalachicola-Chattahoochee-Flint River Basin (Circular 1164)

Central Arizona Basins (Circular 1213)

Central Columbia Plateau (Circular 1144)

Central Nebraska Basins (Circular 1163)

Connecticut, Housatonic and Thames River Basins (Circular 1155)

Eastern Iowa Basins (Circular 1210)

Georgia-Florida Coastal Plain (Circular 1151)

Hudson River Basin (Circular 1165)

Kanawha-New River Basins (Circular 1204)

Lake Erie-Lake Saint Clair Drainages (Circular 1203)

Las Vegas Valley Area and the Carson and Truckee River Basins

(Circular 1170)

Lower Illinois River Basin (Circular 1209)

Long Island-New Jersey Coastal Drainages (Circular 1201)

Lower Susquehanna River Basin (Circular 1168)

Mississippi Embayment (Circular 1208)

Ozark Plateaus (Circular 1158)

Potomac River Basin (Circular 1166)

Other NAWQA summary reports

Puget Sound Basin (Circular 1216)

Red River of the North Basin (Circular 1169)

Rio Grande Valley (Circular 1162)

Sacramento River Basin (Circular 1215)

San Joaquin-Tulare Basins (Circular 1159)

Santee River Basin and Coastal Drainages (Circular 1206)

South-Central Texas (Circular 1212) 

South Platte River Basin (Circular 1167)

Trinity River Basin (Circular 1171)

Upper Colorado River Basin (Circular 1214) 

Upper Mississippi River Basin (Circular 1211)

Upper Snake River Basin (Circular 1160)

Upper Tennessee River Basin (Circular 1205)

Western Lake Michigan Drainages (Circular 1156)

White River Basin (Circular 1150)

Willamette Basin (Circular 1161)

National Assessments

The Quality of Our Nation‘s Waters—Nutrients and Pesticides (Circular 1225)
Water Quality in Southern Florida

Florida,1996–98

By Benjamin F. McPherson, Ronald L. Miller, Kim H. Haag, and Anne Bradner

U.S. GEOLOGICAL SURVEY CIRCULAR 1207
Library of Congress Cataloging-in-Publications Data

The use of firm, trade, and brand names in this report is for identification purposes only and

does not constitute endorsement by the U.S. Government.

Free on application to the

U.S. Geological Survey

Information Services

Box 25286 Federal Center

Denver, CO 80225

Or call: 1-888-ASK-USGS

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

2000

Water quality in Southern Florida, Florida, 1996–98 / by Benjamin F. McPherson...[et al.].

p. cm. -- (U.S. Geological Survey Circular ; 1207)

Includes bibliographical references.

ISBN 0-607-95413-2 (alk. paper)

1. Water quality--Florida--Everglades. 2. Watersheds--Florida. I. McPherson, Benjamin F. II. Geological 

Survey (U.S.) III. Series.

TD224.F6 W3723 2000

363.739’42’0975939--dc21

00-049463
CONTENTS

Contents III

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM ............................................................... IV

SUMMARY OF MAJOR FINDINGS.................................................................................................... 1

Surface-Water Highlights .............................................................................................................. 1

Ground-Water Highlights .............................................................................................................. 2

INTRODUCTION TO THE SOUTHERN FLORIDA NAWQA STUDY UNIT ........................................ 3

Rainfall .......................................................................................................................................... 6

MAJOR FINDINGS ............................................................................................................................. 7

Nutrient enrichment is prevalent in surface water......................................................................... 7

NATIONAL PERSPECTIVE—Nutrient concentrations vary widely in southern Florida 

and the Nation............................................................................................................................ 7

Nutrient concentrations in ground water are highly variable ......................................................... 9

Dissolved organic carbon concentrations are often high .............................................................. 9

Pesticides are present in most surface-water samples................................................................. 10

NATIONAL PERSPECTIVE—Pesticide detections vary with land use in southern Florida 

and the Nation............................................................................................................................ 11

Regional patterns of pesticides, VOCs and trace elements are evident in ground water ............. 12

NATIONAL PERSPECTIVE—What combinations of pesticides occur most frequently 

in southern Florida and the Nation?........................................................................................... 13

Pesticides, PCBs, other organics and trace elements have accumulated in bottom 

sediment and fish ...................................................................................................................... 15

Mercury is a contaminant in the Southern Florida Study Unit ...................................................... 16

Biological communities are influenced by water quality................................................................ 18

NATIONAL PERSPECTIVE—Southern Florida aquatic communities in a national context ......... 20

Exotic species are a threat to native biota .................................................................................... 21

STUDY UNIT DESIGN........................................................................................................................ 22

GLOSSARY ........................................................................................................................................ 24

REFERENCES ................................................................................................................................... 25

APPENDIX A—WATER-QUALITY DATA FROM SOUTHERN FLORIDA IN 

A NATIONAL CONTEXT............................................................................................................... 27
NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

IV National Water-Quality Assessment Program 

THIS REPORT summarizes major findings about water quality in the southern Florida area studied by the U.S. 

Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program between 1996 and 1998. 

Water quality is discussed in terms of local and regional issues and compared to conditions found in all 36 

NAWQA study areas, called Study Units, assessed to date. Findings also are explained in the context of selected 

national benchmarks, such as those for drinking-water quality and the protection of aquatic organisms. The 

NAWQA Program was not intended to assess the quality of the Nation’s drinking water, such as by monitoring 

water from household taps. Rather, the assessments focus on the quality of the resource itself, thereby 

complementing many ongoing Federal, State, and local drinking-water monitoring programs. The comparisons 

made in this report to drinking-water standards and guidelines are only in the context of the available untreated 

resource. Finally, this report includes information about the status of aquatic communities and the condition of 

stream habitats as elements of a complete water-quality assessment.

Many topics covered in this report reflect the concerns of officials of State and Federal agencies, water-resource 

managers, and members of stakeholder groups who provided advice and input during the Southern Florida 

assessment. Basin residents who wish to know more about water quality in the areas where they live will find this 

report informative as well. 

THE NAWQA PROGRAM seeks to improve scientific and public understanding of water quality in the Nation’s 

major river basins and ground-water systems. Better understanding facilitates effective resource management, 

accurate identification of water-quality priorities, and successful development of strategies that protect and restore 

water quality. Guided by a nationally consistent study design and shaped by ongoing communication with local, 

State, and Federal agencies, NAWQA assessments support the investigation of local issues and trends while 

providing a firm foundation for understanding water quality at regional and national scales. The ability to integrate 

local and national scales of data collection and analysis is a unique feature of the USGS NAWQA Program.

The southern Florida area is one of 51 water-quality assessments initiated since 1991, when the U.S. Congress 

appropriated funds for the USGS to begin the NAWQA Program. As indicated on the map, 36 assessments have 

been completed, and 15 more assessments will conclude in 2001. Collectively, these assessments cover about onehalf of the land area of the United States and include water resources that are available to more than 60 percent of 

the U.S. population.

NAWQA Study Units

Assessment Schedule

1991_95

1994_98

1997_2001

Not Yet

Scheduled

High Plains Regional

Ground Water Study,

1999_2004

Southern Florida

NAWQA Study Unit
Summary of Major Findings 1 

SUMMARY OF MAJOR FINDINGS

Surface-Water Highlights

The environment in southern Florida is being 

degraded by human activities. Native biota have been 

reduced greatly in abundance and diversity by drainage, development, alteration of water flows, degradation of water quality, and by continuing invasions of 

exotic species.The Everglades ecosystem, which is 

adapted to water that has an extremely low phosphorus 

concentration, is being altered by agricultural activities 

that produce high levels of phosphorus in water. Nutrient loading in the major rivers is contributing to overenrichment of Lake Okeechobee and estuaries such as 

Charlotte Harbor. Mercury has accumulated in Everglades game fish, and consumption of the fish poses a 

potential human health risk. Mercury has accumulated 

in the Everglades food web because natural 

conditions and human influences enhance 

methylation of mercury to its organic form and 

because high atmospheric mercury deposition 

rates (among the highest in the Nation) sustain 

mercury methylation. 

 Federal and State agencies and environmental groups agree that parts of southern Florida 

should be restored to predevelopment conditions. Restoration will require massive changes 

in the water-management system to restore predevelopment drainage patterns, improve water 

quality, and protect native biota. 

Major findings on water quality and biology 

from this study: 

• Concentrations of total phosphorus (TP) at the 

Southern Florida (SOFL) National WaterQuality Assessment (NAWQA) Program sites 

were above Everglades background levels and 

exceeded the U.S. Environmental Protection 

Agency’s (USEPA) Everglades water-quality 

standard of 0.01 milligram per liter (mg/L). A 

major source of the high TP is fertilizer from 

agriculture. 

• Concentrations of dissolved organic carbon 

(DOC) in southern Florida water were relatively high compared with those in other 

waters of the Nation. High DOC concentrations provide food for bacteria to grow, 

reduce light penetration in the water, and 

enhance transport and cycling of pesticides 

and trace elements such as mercury. 

• Pesticides were detected in almost all SOFL 

samples. Most concentrations were below 

aquatic-life criteria; however, the criteria do 

not address potential effects of mixtures of 

pesticides and their degradation products, which 

were common in the samples. 

• Organochlorine pesticides, such as DDT and its 

degradation products, are still prevalent in bottom 

sediment and fish tissue at the SOFL sites, even 

though most uses of these compounds have been 

discontinued in recent decades. The mobilization of 

these pesticides by the reflooding of Everglades 

farm lands could lead to food-web contamination.

• Of 21 NAWQA basins nationwide, the Everglades 

has the second highest ratio of methylmercury to 

mercury in sediment.This enrichment in methylmercury enhances mercury uptake by the biota.

• The frequency of external anomalies (lesions, 

ulcers, and tumors) on fish collected at two SOFL 

agricultural canal sites was in the top 25 percent of 

41

STUDY-UNIT

BOUNDARY

ATLANTIC OCEAN

GULF OF MEXICO

STRAITS OF FLORIDA

St. Lucie

River

Black Creek

Canal

Barron River

Canal

St. Lucie

Canal

Biscayne

Bay

West

Palm

Beach

Fort

Lauderdale

Miami

Homestead

0 25 50 MIL

0 50 KILOMETERS 25

ES

Other public lands

NATIVE AMERICAN LANDS

WATER CONSERVATION AREA

MODIFIED KISSIMMEEOKEECHOBEE-EVERGLADES

BOUNDARY

25°

26°

Everglades National Park

Big Cypress National Preserve

PUBLIC LANDS

OTHER

AGRICULTURAL LAND

URBAN LAND

EXPLANATION

Naples

Alva

Fort

Myers

Arcadia

Florida Keys

Tamiami Canal L−67A

C111 WCA

2

WCA

3

WCA

3

WCA

1

Beach

Canal 

Caloosahatchee

Canal

West Palm

North New

River Canal

Hillsboro

Canal

Charlotte

Harbor

Florida Bay

27°

Peace River

Myakka River

Kissimmee

River Lake

Okeechobee

28°

83° 82° 81° 80°

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′

Caloo sah River atchee

Miami Canal and River

LOCATION

OF STUDY

AREA

ALABAMA GEORGIA

FLORIDA

Tamiami Trail

Urban, agricultural, Native American, public lands and other 

important features in the Southern Florida NAWQA Study Unit 

(McPherson and Halley, 1996).
2 Water Quality in Southern Florida, 1996–98

144 NAWQA sites sampled nationwide. Anomalies 

can be indications that fish are stressed by contamination.

• Exotic animals and plants are a threat to native 

biota. Ten of the 54 exotic fish species established 

in the region were collected at the SOFL sites. 

Several herbicides used to control exotic plants 

were detected in surface water.

Major Influences on Surface Water

and Ecology

• Drainage modifications and wetland destruction.

• Runoff from agricultural and urban areas.

• High concentrations of DOC and its effects on the 

transport of mercury and the attenuation of light.

• Deliberate or accidental release of exotic species.

Ground-Water Highlights

In much of the SOFL region, ground water in the 

surficial aquifers, such as the Biscayne aquifer, is of 

good quality and usually meets Federal and State drinking-water quality standards. Contaminants are usually 

in low concentrations, presumably because of rapid 

flushing and recharge as a result of high annual rainfall 

(about 55 inches) and shallow aquifers and porous limestone that allow the easy interchange of surface and 

ground water. However, because of the shallow aquifers 

and porous limestone, ground water is vulnerable to 

surface contamination and to saltwater intrusion.

Major findings on ground-water quality from this 

study include the following: 

• Nitrate concentrations were below the drinkingwater standard (10 mg/L) in 108 SOFL wells 

Small Streams Major Rivers

Agricultural Pasture/

Forest

Selected Stream-Quality Indicators

Mixed

Land Uses

1 Insecticides, herbicides, and pesticide metabolites, sampled in water.

2 Total phosphorus (TP) sampled in water. Aquatic-life guidelines based on USEPA Everglades standard of 0.01 mg/L TP for small Everglades streams

 and on USEPA national goal of 0.1 mg/L TP for major rivers.

3 Nitrate (as nitrogen), sampled in water.

4 Organochlorine compounds including DDT and PCBs, sampled in fish tissue.

5 Solvents, refrigerants, fumigants, and gasoline compounds, sampled in water.

Nutrients 2

Pesticides 1

Organochlorines 4

Percentage of samples with concentrations equal to or greater than a health-related national guideline for drinking water, aquatic life, or water-contact 

recreation; or above a national goal for preventing excess algal growth (a Percentage is 1 or less and may not be clearly visible)

Percentage of samples with concentrations less than a health-related national guideline for drinking water, aquatic life, or water-contact recreation; 

or below a national goal for preventing excess algal growth

Percentage of samples with no detection (b Percentage is 1 or less and may not be clearly visible)

Not assessed

Selected Ground-Water Quality Indicators

Shallow Ground Water Supply Wells

Urban Agricultural Public

Nitrate 3

Pesticides 1

Radon

Volatile

organics 5

b b b

b

a a,b a,b

b b

(Biscayne and other surfical aquifers), except for 

two shallow wells in the unnamed surficial aquifer 

of the citrus area.

• Pesticides were detected in more than 85 percent of 

the SOFL wells and beneath every type of land use 

studied, but no concentrations exceeded any USEPA 

or State of Florida drinking-water standard.

• Pesticides detected in shallow ground water were 

associated with specific land uses. For example, the 

herbicides bromacil and norflurazon were detected 

almost exclusively in citrus areas. Metolachlor and 

simazine were common in mixed agricultural areas 

near the southern Everglades.

• Volatile organic carbon compounds (VOCs) commonly were detected in water from shallow and 

deep wells in the Biscayne aquifer. Concentrations 

of one industrial VOC, vinyl chloride, exceeded the 

USEPA maximum contaminant level (MCL) of 

2 micrograms per liter (μg/L) for drinking water in 

two samples.

• Radon-222 radioactivity exceeded the proposed 

MCL (300 picocuries per liter ([pCi/L]) in the majority of samples from the Biscayne aquifer, including untreated water from the public-supply wells.

Major Influences on Ground Water

• Porous, shallow limestone aquifers overlain by thin 

layers of sandy, permeable soils.

• Water-management practices involving canals, 

pumps, gates, locks, and saltwater-control structures.

• Agricultural and urban land-use practices and 

aquatic-weed control.
Introduction to the Southern Florida NAWQA Study Unit 3

INTRODUCTION TO THE SOUTHERN FLORIDA NAWQA STUDY UNIT

In the mid-1800s southern Florida was a lush, subtropical wilderness of pine forest, hardwood 

hammocks, swamps, marshes, estuaries, and bays. Wetlands dominated the landscape. The region 

contained one of the largest wetlands in the continental United 

States, the Everglades, which was 

part of a larger watershed—the 

Kissimmee-Okeechobee-Everglades—which extended more than 

half the length of the Florida peninsula (fig. 1). Wetlands of the Everglades, Big Cypress Swamp, and 

Mangrove and Coastal Glades 

stretched continuously across much 

of the southern part of the peninsula south of Lake Okeechobee 

(fig. 1). To the north, much of the 

Flatwoods physiographic province 

also was wetlands; upland habitats 

were primarily on the narrow Lake 

Wales and Atlantic Coastal Ridges. 

Freshwater in the Everglades and 

other wetlands generally moved as 

sheetflow in 

marshes, sloughs, 

and cypress 

strands. Numerous 

small streams and 

rivers near the 

coast, such as the 

Miami River, 

drained into mangrove forests and 

tidal waters and 

provided the freshwater that sustained 

the highly productive and abundant 

coastal fisheries 

around the southern 

end of the peninsula (McIvor and 

others, 1994).

The wetlands of southern Florida 

made much of the region inhospitable for human habitation. Settlers 

and developers in the late 1800s 

and early 1900s began to drain the 

wetlands for commercial and safety 

reasons. Loss of lives as a result of 

hurricane flooding in the 1920s 

accelerated drainage projects. 

Today, many of the region’s original 

wetlands have been drained. Water 

in the region is now intensively 

managed, with more that 1,400 

miles of primary canals and more 

0 25 50 MILES

0 50 KILOMETERS 25

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′

P

25°

83° 82° 81° 80°

28°

27°

26°

L

ATLANTIC OCEAN

GULF OF MEXICO

STRAITS OF FLORIDA

Florida Keys

Charlotte

Harbor

Florida Bay

St. Lucie River

Biscayne

Bay

Peace River

Myakka River

Kissimmee

River

Caloosah River atchee

EVERGLADES

BIG CY RESS SWAMP

F L A T W O O D S

Lake Wales Ridge

STUDY−UNIT BOUNDA

EXPLANATION

NATURAL KISSIMMEE

OKEECHOBEE−EV

WATERSHED BOUNDA

MANGROVE AND

COASTAL GLADES

NTIC COASTAL RIDGE

ATLA

RY

−

ERGLADES

RY

ake

Okeechobee

Figure 1. Physiographic provinces of southern Florida. 

(Modified from Davis, 1943; Parker and others, 1955.)

The Southern Florida (SOFL) National Water-Quality Assessment study encompasses about 19,500

square miles. It is part of a regional ecosystem that 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. The elevation in the study area ranges from about 300 feet above sea level to sea level along the

coast. It includes a large and rapidly growing urban population (about 5 million people) along the Atlantic coast and a less rapidly growing population (over a million people) along the gulf coast, areas of

intense agricultural development around Lake Okeechobee and along the southeastern edge of the

Everglades, and vast regions of wetlands, including the Everglades National Park (ENP), Big Cypress

National Preserve, and other parks, preserves, and conservation areas that are mostly in public ownership. Ground water from the shallow, highly porous Biscayne aquifer is the source of most of the drinking water for the densely populated southeast coast. 

The Everglades are remarkable for....the absolute purity 

of the water there, which contrary to popular idea, is 

clear as crystal....—Alanso Skinner, Bird Lore, XIII, no. 6, 

Nov.-Dec. 1911.

Both these glade rivers (Miami and New Rivers) are singularly beautiful. Their waters, clear and limpid, are 

fringed on either shore by all the wild growths of the 

hammock...pine and prairie, reflecting every change of 

scene like mirrors.—J.N. MacGonigle, 1896, The geography of the southern peninsula of the United States:

National Geographic Magazine, v. 7, no. 12, p. 381–394.
4 Water Quality in Southern Florida, 1996–98

than 100 water-control structures. 

The larger rivers, such as the Kissimmee and Caloosahatchee Rivers, 

have been canalized and controlled 

to enhance their ability to move 

water. About half the Everglades 

have been lost to drainage and 

development since the early 1900s; 

the remaining Everglades, included 

in the Everglades National Park 

(ENP), conservation areas, and the 

Loxahatchee National Wildlife 

Refuge, are protected from physical destruction, but it has been 

degraded by altered quantity, quality, and timing of freshwater 

inflows.

Drainage and development of 

wetlands have adversely affected 

water quality and ecology throughout southern Florida. Water 

Complex canal system in northern Everglades. Northern Big Cypress Swamp.

pumped into canals from agricultural lands commonly has high 

concentrations of nutrients and pesticides. The high nutrient concentrations and loads entering Lake 

Okeechobee and the Everglades 

from farms and cattle lands have 

degraded water quality. Phosphorus 

concentrations in Lake Okeechobee have increased two and 

one-half times since the 1970s, and 

massive algal blooms have become 

more frequent and persistent. The 

increased nutrient loading to the 

Everglades is stressing native vegetative communities. Sawgrass, 

which is adapted to a low-nutrient 

environment, is being replaced by 

cattails in parts of the northern 

Everglades where nutrient loading 

has been excessive. Drainage and 

development also has resulted in 

loss of peat soils, contamination by 

pesticides, saltwater intrusion into 

aquifers near the coast, mercury 

buildup in the biota, fragmentation 

of landscape, loss of wetland functions, widespread invasion by 

exotic species, increased algal 

blooming, seagrass die-off, and 

declines in fishing resources in 

coastal waters.

An abundant and uncontaminated supply of freshwater was a 

primary environmental characteristic of southern Florida in predevelopment times. Increased human 

population and activity have 

brought not only increased need for 

water but also a decrease in water 

supply and deterioration in water 

quality. These changes in the 

hydrologic system, wrought by 

growth and development, are 

thought to be the major causes of 

the substantial declines in the 

health of the remaining natural 

ecosystem.

A consensus has begun to 

emerge among environmental 

groups and Federal and State agencies that southern Florida, and particularly the Everglades, should be 

restored to the extent possible to 

the predevelopment ecosystem. A 

first and primary step in this undertaking is the restoration of predevelopment hydrologic conditions 

to the remaining natural system. 

Plans are to change the manmade 

water-conveyance system and 

restore the natural hydrologic cycle 

of the predevelopment Everglades 

as a means of contributing to overall ecosystem restoration.

Everywhere and at all 

seasons of the year, the 

water in the glades is clear, 

pure, and though sometimes 

warm, palatable, without the 

least staleness or stagnancy.—Edwin Asa Dix and Rev. 

John N. MacGonigle, Century 

Magazine, February 1905.
Introduction to the Southern Florida NAWQA Study Unit 5

Aquifers and Water Use

Southern Florida, which is underlain by shallow 

marine carbonate sediments to depths of 

20,000 feet, contains three major aquifer systems: 

the Floridan, the intermediate, and the surficial 

aquifer systems (figs. 2a,b). The confined Floridan 

aquifer system is the principal source of water for 

human use in the northern part of the south Florida 

area, but water from this aquifer is too mineralized 

for most uses in the southern part of the area. The 

semiconfining layers of the intermediate aquifer 

system, which overlies the Floridan, serves as the 

confining unit for the Floridan and is a source of 

freshwater for public supply along the gulf coast. 

The surficial aquifer system includes the highly 

permeable Biscayne aquifer, which is the principal 

source of potable water for the more than 5 million 

people in southeastern Florida. The Biscayne 

aquifer has been designated as a “sole-source” 

drinking-water supply by the USEPA. 

Most of the potable water supply in southern 

Florida is withdrawn from shallow aquifers, generally from wells less than 250 feet deep. Ground 

water supplied 94 percent (872 million gallons per 

day [Mgal/d]) of the water used by most of the 

5.8 million people in the SOFL Study Unit in 1990. 

Water used for agriculture in 1990 (2,735 Mgal/d) 

was nearly evenly divided between ground-water 

and surface-water sources (Richard L. Marella, 

U.S. Geological Survey, written commun., 1990). 

Caloosahatchee

River

0 25 50 MILES

0 50 KILOMETERS 25

25°

83° 82° 81° 80°

28°

27°

26°

A A'

°° °

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 meridan -83 00'

ATLANTIC OCEAN

GULF OF MEXICO

STRAITS OF FLORIDA

Florida Keys

Charlotte

Harbor

Florida Bay

St. Lucie River

Biscayne

Bay

Peace River

Myakka River

Kissimmee

River

STUDY-UNIT

BOUNDARY

FLORIDAN

AQUIFER

UNNAMED 

SURFICIAL

AQUIFERS AND

INTERMEDIATE

AQUIFERS,

UNDIFFERENTIATED

Naples BISCAYNE

AQUIFER

Lake

Okeechobee

Figure 2a. The three main aquifer systems of southern 

Florida.

SHALLOW AQUIFER

A A ′

BISCAYNE AQUIFER

FLORIDAN AQUIFER SYSTEM

SURFICIAL AQUIFER

SYSTEM

INTERMEDIATE AQUIFER SYSTEM

(zone of low yield)

250

250

500

750

1,000

SEA

LEVEL

FEET

GULF OF

MEXICO

ATLANTIC

OCEAN

NAPLES

BIG CYPRESS

SWAMP

THE

EVERGLADES

VERTICAL SCALE

GREATLY EXAGGERATED

0 50 KILOMETERS

0 50 MILES

Figure 2b. Generalized subsurface section A–A′ showing 

Agricultural irrigation, eastern Everglades area. aquifers of southern Florida (Klein and others, 1975).
6 Water Quality in Southern Florida, 1996–98

 

• Drainage basins are poorly defined.

• Surface and ground water are closely connected.

• Sheetflow is common through the “River of Grass” and other wetlands.

• Surface-water flow in canals and rivers is highly managed and regulated.

• Organic soils (peats) are abundant, but much has been lost to oxidation.

• The farming season is in winter.

• Coastal meteorological effects often dominate.

• Tropical storms are common.

• Nutrient concentrations are naturally low in the Everglades and other pristine 

wetlands.

• Dissolved organic carbon concentrations are high.

• Water color is dark in some rivers and wetlands. 

• There are extensive subtropical wetlands and public lands, including four 

national parks, preserves, or refuges.

• Many exotic species thrive in the subtropical climate.

HOW IS THE SOUTHERN FLORIDA NAWQA DIFFERENT FROM 

OTHER NAWQA STUDY UNITS?

Rainfall

Annual rainfall in southern 

Florida ranges from about 40 to 

65 inches. The east coast usually 

receives the greatest amount of 

rainfall, whereas the Florida Keys 

80

70

60

50

40

30 –20

–10

0

10

20

30

DIFFERENCE FROM AVERAGE,

IN INCHES

ANNUAL RAINFALL, IN INCHES

Intensive Sampling

Phase, 1996–98

Above average annual rainfall

 is shown above the line

Below average annual rainfall

 is shown below the line

1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

For 20 stations in southern Florida

AVERAGE ANNUAL

RAINFALL IS 51.1 INCHES

Figure 3. Annual rainfall was above average during the 1996–98 sampling period. (Data from 

the National Oceanic and Atmospheric Administration’s National Climate Center.)

and areas near Lake Okeechobee 

and Charlotte Harbor usually 

receive the least. More than half the 

rainfall occurs from June through 

September and is associated with 

thunderstorms and tropical 

cyclones. Rainfall during the 

remainder of the year usually is the 

result of large frontal systems and 

is broadly distributed rather than 

localized. April and May typically 

have the least rainfall. Annual and 

seasonal rainfalls vary from year to 

year (fig. 3).
Major Findings 7 

MAJOR FINDINGS

24 20 21 25

NUMBER OF SAMPLES

MEDIAN VALUE

29

Kissimmee River at S-65E

47

Hillsboro Canal

36

Tamiami Canal at BR-105

28

Caloosahatchee River at Alva

51

C-111 Canal at S-177

P33

P34

P35

P36

1.1

1.0

0.9

0.8

0.7

0.6

0.5

1.2

24

Peace River at Arcadia Peace River

36

U.S. Sugar Canal 1 U.S. Sugar value of 0.34

EXPLANATION

USEPA

 National Recommended Goal

 Everglades Water-Quality

 Standard

0

0.05

0.10

0.15

0.20

0.25

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

NAWQA Sites

ENP Reference Sites

Figure 4. Concentrations of total phosphorus (TP) at SOFL 

NAWQA sites during 1996–98 frequently exceeded the 

USEPA recommended goal of 0.1 mg/L and Everglades 

standard of 0.01 mg/L. Concentrations of TP at Everglades 

National Park reference sites were near or below 0.01 mg/L.

Nutrient enrichment is prevalent in surface 

water

Water quality has been degraded in large parts of 

southern Florida by human activities that result in high 

nutrient concentrations and over-enrichment. Nutrient 

concentrations at the SOFL NAWQA sites are elevated 

when compared with Everglades background concentrations (see box below). The high nutrient concentrations, 

primarily from agricultural runoff, have contributed to 

overenrichment of surface water, including Lake 

Okeechobee, estuaries such as Charlotte Harbor, and the 

northern Everglades. The high phosphorus concentrations in agricultural runoff entering the northern Everglades are a significant cause of ecosystem degradation. 

The USEPA recently (May 26, 1999) approved a new 

water-quality standard of 0.01 mg/L or less for phosphorus in the Miccosukee Federal Indian reservation 

lands of the Everglades. The State of Florida is reviewing additional scientific information and plans to adopt 

a numerical phosphorus standard for other parts of the 

Everglades.

Nutrient concentrations of the national NAWQA and the SOFL NAWQA 

study areas, national background, and Everglades background sites in mg/L

[SW, surface water; GW, shallow ground water; <, less than; --, no data]

Nutrient

NAWQA Background

National, 

1993–98, 

median2

SOFL, range 

of medians3, 

05/96–09/98

National1

(undeveloped 

areas)

Everglades4 

05/96–09/98

Total phosphorus (SW) 0.12 0.006–0.79 0.1 <0.004

Total nitrogen (SW) 1.3 0.7–2.6 1.0 1.1

Nitrite plus nitrate (SW) 0.71 0.006–0.59 0.6 0.005

Ammonia (SW) 0.046 0.017–0.25 0.1 <0.015

Ammonia (GW) 0.02 0.24–0.438 -- --

Nitrite plus nitrate (GW) 1.85 <0.05–0.44 2.0 --

Orthophosphate (GW) 0.11 0.013–0.028 0.02 -- 1

U.S. Geological Survey, 1999.

2

Flow-weighted concentrations.

3

Medians for routinely sampled (BFS) sites (SW) and for land-use categories (GW).

4

Everglades National Park, site P–34, medians; data from South Florida Water 

 Management District (1992).

Concentrations of nutrients in surface water at the SOFL 

sites vary widely compared with national NAWQA median 

concentrations. Generally, the high nutrient concentrations 

in southern Florida are at canal and river sites north of the 

Tamiami Trail and are associated with agricultural activities. 

Concentrations of phosphorus in surface water of the more 

pristine Everglades (south of the Tamiami 

Trail) are more than an order of magnitude 

lower than national background concentrations. The Everglades ecosystem is adapted 

to water that has extremely low phosphorus 

concentrations and is being adversely 

affected by agricultural runoff with high 

concentrations of phosphorus. Concentrations of phosphorus in southern Florida are 

highest in the Peace River (fig. 4) and are 

well above national median concentrations. 

The high concentrations in the Peace River 

are associated with natural sources (phosphatic deposits) as well as mining and agricultural activities in the basin.

Concentrations of nutrients in shallow 

ground water at SOFL wells generally are 

lower than or comparable with the national 

background concentrations. Median concentrations of nitrate in the southern Florida wells are onefourth the national background concentration, and median 

concentrations of orthophosphate are comparable to the 

national background concentration. Concentrations of nutrients at the SOFL sites are plotted against corresponding 

national nutrient ranges for different land uses in Appendix A.

NUTRIENT CONCENTRATIONS VARY WIDELY IN SOUTHERN FLORIDA 

AND THE NATION
8 Water Quality in Southern Florida, 1996–98

All routinely sampled SOFL 

sites (BFS sites, see Glossary) had 

phosphorus concentrations that 

exceeded the USEPA Everglades 

standard of 0.01 mg/L, but the two 

southern sites, Canal C-111 and 

Tamiami Canal at bridge 105, had 

median concentrations near the 

0.01-mg/L Everglades standard 

(fig. 4). The ENP reference sites 

had median phosphorus concentrations below 0.01 mg/L and are 

characteristic of pristine Everglades water.

Seasonal changes in total phosphorus concentrations often are 

related to changes in water levels 

Ground-water sampling, eastern 

Everglades C-111 agricultural basin.

DAILY MEAN DISCHARGE,

IN CUBIC FEET PER SECOND

0

500

1,000

1,500

2,000

3,000

2,500

No Discharge Data

Discharge

Data

0

0.02

0.04

0.06

0.08

0.10

0.12

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

M J J A SOND J FMAM J J A SOND J FMAM J J A S

1996 1997 1998

Total

Phosphorus

Figure 5. Total phosphorus concentrations increased as 

discharge and water levels declined at Tamiami Canal at 

Bridge 105, Big Cypress National Preserve.

and flows. Generally, concentrations were below 0.02 milligram 

per liter (mg/L) at the Big Cypress 

Swamp reference site (Br 105) during 1996–98, but increased to more 

than 0.10 mg/L as water flows and 

levels declined during the dry season (fig. 5). The increase in phosphorus concentrations occurs when 

fish, wading birds, and other 

aquatic organisms congregate in 

ponded waters and their wastes 

contribute nutrients to the remaining inundated areas. The relatively 

greater ground-water contributions 

to surface water during the dry season also may increase nutrient concentrations. The background marsh 

sites in the ENP had very low concentrations of phosphorus (less 

than 0.01 mg/L) throughout the 

1996–98 sampling period, and 

effects of seasonal low water levels 

on nutrients were not evident.

The dominant source of phosphorus loading in southern Florida 

is fertilizer (fig. 6). Manure and 

atmospheric sources are also 

important in some subbasins. 

Annual phosphorus loads estimated 

for selected canals and rivers were 

highest in the Peace River and lowest in the eastern Big Cypress 

Swamp. Much more phosphorus 

has been transported seaward from 

the northern Everglades and 

Okeechobee basins by the Caloosahatchee River, St. Lucie Canal, and 

major canals of Palm Beach 

County than is transported seaward 

in the southern Everglades (Haag 

and others, 1996).

Lake

Okeechobee

[kg/yr, kilograms per year]

PHOSPHORUS SOURCES

EXPLANATION

KISSIMMEE RIVER

12,370,000 kg/yr

BIG CYPRESS

NATIONAL PRESERVE

5,831,000 kg/yr

EVERGLADES

NATIONAL PARK

3,508,000 kg/yr

MYAKKA RIVER and

PEACE RIVER

11,390,000 kg/yr

ST. LUCIE RIVER

5,339,000 kg/yr

EAST COAST

URBAN AREA

6,478,000 kg/yr

LAKE OKEECHOBEE

241,000 kg/yr

CALOOSAHATCHEE

RIVER

3,773,000 kg/yr

FERTILIZER

MANURE

ATMOSPHERIC DEPOSITION

SEPTIC TANKS

MAJOR CANALS AND RIVERS

WASTEWATER TREATMENT

 FACILITIES

EVERGLADES

AGRICULTURAL AREA

12,860,000 kg/yr

Figure 6. Estimated phosphorus loading from point and 

nonpoint sources in surface-water basins in southern 

Florida (Haag and others, 1996).
Major Findings 9 

Table 1. Dissolved phosphorus concentrations varied widely in shallow 

wells in southern Florida during 1997–98. (Different detection levels 

were reported for different survey types during the period)

[B, Biscayne aquifer; S, unnamed surficial aquifer; <, less than]

Survey type Number of wells 

and samples

Range, 

mg/L Median mg/L

Urban/residential (B) 32 <0.01–0.30 <0.01

Urban background (B) 3 <0.01–0.07 <0.01

Citrus (S) 31 <0.01–0.79 0.023

Citrus background (S) 5 <0.004–0.036 <0.01

Mixed agricultural 

(Canal C-111) (B) 7 0.001–0.019 0.003

Public supply (B) 30 <0.01–0.34 <0.01

SOFL citrus land-use survey was 

the highest of 47 NAWQA agricultural surveys nationwide. Median 

concentrations of ammonia in the 

SOFL urban and study-unit survey 

(public water supply) ranked second and fifth highest, respectively, 

in these categories nationally. 

 Dissolved phosphorus concentrations in SOFL wells ranged from 

0.001 to 0.79 mg/L; most land-use 

areas had median concentrations 

less than 0.01 mg/L (table 1). Concentrations above 0.05 mg/L 

occurred in some wells in all landuse and public-supply surveys, but 

highest concentrations generally 

were in the deeper public-supply 

wells of the Biscayne aquifer and 

in the citrus land-use area. The 

source of the relatively high concentrations of phosphorus in 

ground water may be fertilizers or 

naturally occurring phosphatic 

materials associated with silt and 

clays.

Dissolved organic carbon 

concentrations are commonly 

high

Dissolved organic carbon (DOC) 

originates from natural sources, 

such as living and decaying plants, 

and from human sources. DOC 

represents about half the dissolved 

organic matter (DOM) in natural 

waters (Hem, 1985). In southern 

Florida, DOC concentrations commonly are high compared with 

Nutrient concentrations in 

ground water are highly 

variable

High nitrate concentrations 

(greater than 10 mg/L) in drinking 

water can cause a life-threatening 

illness in infants known as “bluebaby syndrome.” Nitrate concentrations in ground water were low 

(commonly not detected) in most 

of the 108 wells sampled in the 

SOFL Study Unit, but a few occasionally were elevated in areas with 

agricultural land use. Wells located 

in or near the mixed-agricultural 

land-use area (including publicsupply wells) tended to yield water 

with detectable concentrations of 

nitrate, but no nitrate concentrations exceeded the drinking-water 

standard of 10 mg/L. More than 

half of the wells located in citrus 

groves yielded water with no 

detectable nitrate concentrations, 

but two wells had nitrate concentrations above the drinking-water 

standard. With a few exceptions, 

shallow Biscayne aquifer wells in 

the urban land-use area contained 

water with relatively low concentrations of nitrate.

Ammonia concentrations in 

ground water in the SOFL Study 

Unit were relatively high compared 

with concentrations in other 

NAWQA Study Units across the 

Nation. The median ammonia concentration (0.396 mg/L) in the 

other natural waters in the Nation 

and may constitute, as DOM, a 

significant fraction of the dissolved 

solids (table 2). 

Concentrations of DOC ranged 

from 4.8 to 52.0 mg/L at the SOFL 

surface-water sites, and from 0.6 to 

80 mg/L at the ground-water sites 

(table 4). The highest DOC concentrations (median of 34.0 mg/L) 

occurred at Hillsboro Canal at S-6 

in the northern Everglades downgradient from the Everglades Agricultural Area, which has highly 

organic muck soils that are thought 

to be a source of DOC. In contrast, 

the Big Cypress Swamp reference 

site at Tamiami Trail Bridge 105 

had the lowest concentrations 

(median of 9.5 mg/L) of the routinely sampled sites. This site is 

characterized by natural swamp 

vegetation and thin carbonate soils 

and rock. Concentrations of DOC 

at sites along the Tamiami Trail 

(1996–97) ranged from 4.8 to 

26.9 mg/L (table 2), and tended to 

be low in the central and eastern 

Big Cypress Swamp and higher in 

the western Big Cypress and to the 

east in the Everglades (Miller and 

others, 1999).

The amount of DOC in water is 

significant. It can (1) contribute to 

water color, which absorbs sunlight 

and reduces the amount of light 

available for use by submerged 

aquatic plants and phytoplankton; 

Citrus groves north of Big Cypress Swamp.
10 Water Quality in Southern Florida, 1996–98

(2) serve as a source of carbon for 

bacterial growth; (3) form complexes with trace elements, such as 

mercury, and make them more 

soluble and mobile in water (Reddy 

and others, 1999); (4) reduce bioavailability of nonionic organic 

compounds through sorption, 

entrapment, or sequestering the 

compounds (Nowell and others, 

1999, p. 296); (5) increase the 

solubilities of relatively insoluble 

compounds, such as p,p′-DDT, 

PCBs, and lindane (Chiou and 

others, 1986); and (6) react with 

chemicals used to disinfect public 

water supplies and produce undesirable by-products, such as chloroform and other trihalomethanes, 

Table 3. Water color for southern Florida surface-water sites, 1913–

1999 (Color is reported in platinum-cobalt units. Data from U.S. 

Geological Survey data bases)

Sampling site Range Median

Number

of

samples

Period of 

record

Kissimmee River, S-65E 25–240 85 51 1959–75

Peace River, Arcadia 0–320 82.5 414 1930–99

Caloosahatchee River at S-79 5–500 62.5 144 1953–88

Hillsboro Canal at S-6 30–560 120 89 1945–84

Tamiami Canal at Bridge 105 10–100 30 56 1967–99

Canal, C-111 at S-18-C 0–40 5 40 1970–83

Everglades P-33 10–120 45 82 1959–85

878 southern Florida sites in 

Miami USGS data base

0–640 55 11,457 1913–99

Naturally occurring dissolved organic matter 

(DOM) causes the tea-colored water in many of 

Florida’s rivers and swamps. Water color can 

have significant ecological effects by decreasing 

available light in the water column and reducing 

algal and aquatic plant productivity and growth. 

In the Peace River and upper Charlotte Harbor, 

for example, color can contribute up to about half 

of the total light attenuation in the water column, 

and this high attenuation limits algal phytoplankton and seagrass growth (McPherson and Miller, 

1987). The range in color for southern Florida 

water, including the NAWQA sites, is shown in 

table 3.

that may have harmful effects on 

human health.

Pesticides are present in 

most surface-water samples

Pesticides are widely used in 

southern Florida to control insects, 

fungi, weeds, and other undesirable 

organisms. These compounds vary 

in their toxicity, persistence, and 

transport. Some of the more persistent pesticides, such as DDT, chlordane, dieldrin, and aldrin, have been 

discontinued for use in Florida, but 

their residues persist in the environment. Although pesticides usually 

are applied to specific areas and 

directed at specific organisms, these 

compounds often become widely 

distributed and pose potential hazards to nontarget organisms. 

Intensive pesticide sampling (up 

to weekly sampling) was conducted at three SOFL sites (IFS 

sites, see Glossary) that represented three different agricultural 

land uses — mixed vegetable crops 

(C-111 basin), sugarcane (S-6), and 

citrus (U.S. Sugar). Pesticides were 

detected in all but one sample from 

the three intensive-sampling sites 

during 1996–98. The most 

frequently detected pesticides 

included those with highest annual 

application rates, such as the herbicides atrazine, bromacil, simazine, 

2-4-D, and diuron. Atrazine, the 

most frequently detected pesticide 

overall, was detected in about 

90 percent of all samples. The 

other most frequently detected 

pesticides overall were metachlor, 

simazine, tebuthiuron, norflurazon, bromacil, and diuron. 

Pesticide application in vegetable 

farming area.

Table 2. Concentrations of dissolved organic carbon, in milligrams per liter, at 

surface- and ground-water sites in southern Florida, 1996–98

[Dissolved organic carbon (DOC) in natural water typically is 45 to 55 percent of the dissolved organic 

matter (DOM; Robert Wershaw and Jerry Leenheer, oral commun., 1997) and averages about 50 percent of the DOM that also includes other elements such as oxygen, hydrogen, nitrogen, phosphorus;

 --, no data]

Sampling site Range Median

Number 

of DOC 

samples

DOM as a 

percentage of

 dissolved solids

Surface Water

Kissimmee River at S-65E 13.0–22.0 16.0 29 20–39

Peace River Arcadia 8.6–26.0 15.0 30 6–36

Caloosahatchee River at Alva 13.0–22.0 16.0 27 5–15

Hillsboro Canal at S-6 15.0–52.0 34.0 48 7–13

U.S. Sugar 17.0–30.0 20.0 37 11–16

Tamiami Canal at Bridge 105 7.1–14.0 9.5 35 5–18

Canal C-111 at S-177 5.0–18.0 6.6 51 4–9

All 7 Basic Fixed Sites 5.0–52.0 16.0 257 4–39

Tamiami Trail, SOFL data (1996–97) 4.8–26.9 12.5 43 -- Ground Water

Urban/residential land-use wells 1.9–36 11.5 32 --

Citrus wells 2.7–80 24 29 --

Public-supply wells 0.6–22 9.4 30 --
Major Findings 11 

Concentrations of pesticides in 

water were seasonal and related to 

land use. Concentrations of atrazine 

peaked at all three sites in late winter 

and spring (fig. 7). Concentrations 

were highest at the S-6 site, where 

some samples had atrazine concentrations that exceeded the Canadian 

aquatic-life criterion of 2 μg/L and 

the USEPA MCL of 3 μg/L. Concentrations at the other two sites were 

significantly lower, with maximum 

values less than 1 μg/L. 

A pesticide of particular concern, 

endosulfan, was detected mainly at 

the Canal C-111 site (fig. 8). 

Endosulfan was detected by the 

South Florida Water Management 

U.S. Sugar

Outfall

Canal

(citrus)

Hillsboro

Canal at S–6

(sugarcane)

Sixty-two

agricultural

streams 1

nd nd nd nd

 1 U.S. Geological Survey, 2000.

 2 Kolpin and others, 1998.

nd No data available

Canal C–111

at S–177

(mixed

agriculture)

SAMPLES WITH DETECTIONS, IN PERCENT

0 100 0 100 0 100 100 0

Study Unit

survey (publicsupply wells)

Urban

land

use

all

NAWQA

wells2

Agricultural

 land

use (citrus)

0 100 0 100 0 100 100 0

Atrazine

Deethylatrazine

Metolachlor

Simazine

Fenuron

Tebuthiuron

Norflurazon

Bromacil

Diuron

Endosulfan I

Alachlor

EPTC

Cyanazine

Ethoprop

Chlorpyrifos

Malathion

Carbaryl

Methomyl

Prometon

Carbofuran

SOUTHERN FLORIDA SURFACE WATER NATIONWIDENATIONWIDESOUTHERN FLORIDA GROUND WATER

HERBICIDE

INSECTICIDE

EXPLANATION

Data censored at 0.01 microgram

per liter, except when asterisk (*

)

indicates data censored at

0.05 microgram per liter

nd

nd

nd

nd

nd

*

*

*

*

*

Different patterns of pesticide detections were evident in surface and ground water of the different land-use areas of 

southern Florida. For example, norflurazon and bromacil frequently were detected in citrus land-use areas but seldom 

detected in other agricultural and urban areas. Detections of prometon and fenuron were relatively high in the publicsupply wells of the Biscayne aquifer but were much lower in other areas. Many of the same pesticides were detected in 

surface and ground water nationwide, but a few such as alachlor, cyanazine, and carbofuran were mostly absent in 

southern Florida. The most commonly detected pesticides, such as atrazine, simazine, and metolachlor, were more common in surface water than in ground water in both southern Florida and the Nation. Concentrations of selected herbicides 

at SOFL sites are plotted against corresponding national herbicide ranges for different land uses in Appendix A.

A SO N D J FM AM J J A SO N D J FM AM J J A SO N D

1996 1997 1998

ATRAZINE, IN MICROGRAMS PER LITER

0

1.0

0

0.5

U.S. Sugar Outfall Canal (citrus)

15

0

5

10

0

0.2

0.1

Hillsboro Canal at S–6 (sugarcane)

Canal C–111 at S–177 (mixed vegetables)

Figure 7. Concentrations 

of atrazine at the Intensive 

Fixed Sites, August 1996–

December 1998, showing 

similar seasonal occurrence 

patterns but different 

concentrations.

PESTICIDE DETECTIONS VARY WITH LAND USE IN SOUTHERN 

FLORIDA AND THE NATION
12 Water Quality in Southern Florida, 1996–98

District (SFWMD) over a number 

of years in the C-111 basin at levels 

considered to be a threat to aquatic 

life in the basin and in nearby 

Florida Bay (Miles and Pfeuffer, 

1997). During the intensive sampling period of the SOFL study 

(1996–98), endosulfan concentrations were 0.05 μg/L or less 

(fig. 8), which is just below the 

Florida Department of Environmental Protection criterion 

(0.056 mg/L) for Class III (recreation, propagation and maintenance of a healthy, well-balanced 

population of fish and wildlife) 

freshwater. Detections of endosulfan were frequent in 1996 but 

became less frequent in the following 2 years, as the use of this pesticide was discouraged and an 

alternate, imidacloprid, was introduced.

 Mixtures of pesticides were 

common in samples from SOFL 

and other national NAWQA sites 

0.06

0

0.01

0.02

0.03

0.04

0.05

– Last sample on September 1, 1998

A SO N D J FM AM J J A SO N D J FM AM J J A SO N D

ENDOSULFAN, IN

MICROGRAMS PER LITER

Canal C–111 at S–177 (mixed vegetables)

1996 1997 1998

Figure 8. Concentrations of endosulfan at Canal C-111 at 

S-177, August 1996-September 1998.

exceeded USEPA or State of Florida drinking-water standards or 

health advisories.

 VOCs commonly were detected 

in water from shallow, residential 

land-use wells and deeper publicsupply (study-unit survey) wells in 

the Biscayne aquifer (fig. 9). Vinyl 

chloride, trichloroethylene, tetrachloroethylene, cis-1,2-dichloroethene, and methyl tert-butyl ether 

(MTBE) were detected more commonly in the older residential and 

industrial areas and in public-supply 

wells near mixed agricultural lands. 

Toluene, p-isopropyltoluene, and 

1,2,4-trimethyl-benzene commonly were detected in the newer 

residential areas and in public-supply wells near mixed agricultural 

lands. Two samples from publicsupply wells in more industrialResidential land near Fort Lauderdale.

Toluene

p-Isopropyltoluene

Chloroform

cis-1,2-Dichloroethene

Methyl tert-butyl ether

Methylethyl ketone

Acetone

Carbon disulfide

Tetrahydrofuran

o-Dichlorobenzene

Bromodichloromethane

Bromoform

Chlorobenzene

Methylchloride

Chlorodibromomethane

Dichlorodifluoromethane

Trichloroethylene

Vinyl chloride

0

30

40

20

10

PERCENTAGE OF

VOC DETECTIONS

0.1 μg/L OR GREATER

Study-Unit public-supply survey – Biscayne aquifer

Urban land-use survey – Biscayne aquifer

Agriculture land-use surveys – Biscayne and

 unnamed surficial aquifer

Figure 9. Percentages of common volatile organic carbons 

(VOCs) detected in water from shallow urban (residential) 

and agricultural wells and from deeper public-supply wells 

(see Study Unit Design on page 22 for locations).

The NAWQA Program uses 

Federal drinking-water standards 

and guidelines to assess the 

quality of drinking water in 

potential surface- or ground-water 

sources prior to treatment and 

distribution. This complements 

many ongoing Federal, State, and 

local monitoring programs that 

assess drinking water after treatment and distribution.

(see figure on page 13). The effects 

of pesticide mixtures on biota or 

humans are not included in criteria, 

which are based on the results of 

single-species, single-chemical 

toxicity tests conducted in the laboratory. As a result, analyses of individual pesticides may underestimate potential adverse effects 

of contaminants on biota (Nowell 

and others, 1999).

Regional patterns of 

pesticides, VOCs, and trace 

elements are evident in 

ground water

Pesticides were detected in 

ground water from more than 

85 percent of the 108 SOFL wells 

and beneath every type of land use 

studied. No pesticide concentration 
Major Findings 13 

WHAT COMBINATIONS OF PESTICIDES OCCUR MOST FREQUENTLY 

IN SOUTHERN FLORIDA AND THE NATION?

The composition of the most common pesticide 

mixtures in surface water of agricultural areas in 

the SOFL Study Unit is similar to, but generally 

lower than, that of mixtures in agricultural areas 

nationwide. Atrazine, deethylatrazine (DEA), 

simazine, and metolachlor are found together most 

frequently in both southern Florida and the Nation.

Ground water in the SOFL Study Unit, however, 

has a different composition of pesticide mixtures 

than is found in ground water in other areas of the 

Nation. Norflurazon and bromacil were found 

together most frequently as mixtures in the SOFL 

Study Unit; these pesticides commonly are used on 

citrus crops. 

The composition of the most common pesticide 

mixtures in ground water in urban areas in the 

SOFL Study Unit also differs from that throughout 

the rest of the Nation: the most common pesticides 

in mixtures were atrazine and DEA in the SOFL 

Study Unit compared with simazine and prometon 

nationwide. The atrazine and DEA in shallow 

ground water of the southern Florida urban study 

area may originate from local residential lawn herbicide applications or may be transported from 

nearby agricultural lands, either through the atmosphere or in canals. Canals that drain agricultural 

lands recharge shallow ground water in this urban 

area.

0 5 10 15 20 25 30 35 40

SURFACE WATER

GROUND WATER

GROUND WATER

PERCENTAGE OF SAMPLES IN WHICH

COMBINATIONS OF PESTICIDES OCCUR TOGETHER

AT OR ABOVE 0.01 MICROGRAM PER LITER 

DEA is deethylatrazine.

National data from U.S. Geological Survey, 1999.

Atrazine+DEA+Simazine

Atrazine+DEA

Atrazine+DEA+Simazine+Metolachlor

Atrazine+DEA+Simazine+Metolachlor+Tebuthiuron

Atrazine+DEA

Atrazine+DEA+Metolachlor

Atrazine+DEA+Metolachlor+Prometon

Atrazine+DEA+Metolachlor+Prometon+Simazine

Atrazine+DEA+Metolachlor+Prometon+Simazine+Alachlor

Norflurazon+Bromacil

Norflurazon+Bromacil+Diuron

Norflurazon+Bromacil+Diuron+Simazine

Atrazine+DEA

Atrazine+DEA+Metolachlor

Atrazine+DEA+Metolachlor+Prometon

Atrazine+DEA+Metolachlor+Prometon+Simazine

Atrazine+DEA

Atrazine+DEA+Tebuthiuron

Atrazine+DEA+Tebuthiuron+Diuron

Atrazine+DEA+Tebuthiuron+Diuron+Fenuron

Simazine+Prometon

Simazine+Prometon+Atrazine

Nation

AGRICULTURAL LANDS

Southern

Florida Nation

AGRICULTURAL LANDS

Southern

Florida Nation

URBAN LANDS

Southern

Florida

ized areas had vinyl chloride concentrations (4.68 and 3.18 μg/L) 

slightly above the USEPA MCL of 

2 μg/L. 

Urban and agricultural activities 

are sources of trace-element contamination in ground water. 

Arsenic and copper are used as 

fungicides in citrus groves. Arsenic 

(in the herbicide monosodium 

meth-anearsonate) is used in turfgrass maintenance on golf courses, 

and concentrations of arsenic in 

shallow ground water are sometimes elevated (Swancar, 1996). 

Arsenic has been implicated as 

causing several cancers. Because of 

this health concern, the USEPA is 

considering lowering the MCL for 

arsenic from 50 to about 5 μg/L. 

Concentrations of arsenic in shallow ground water exceeded 5 μg/L 

in some of the urban and citrus 

land-use SOFL wells. Concentrations of copper in the SOFL ground 

-water samples reached 19 μg/L, 

which is well below the drinkingwater MCL of 1,300 μg/L. 

Uranium and radon-222, two 

naturally occurring radioactive 

elements that are potential carcinogens, exceeded drinking-water 

standards in some shallow ground 

water in the SOFL Study Unit. 

Uranium exceeded the MCL in 5 of 

116 samples. Radon-222, a gaseous 

radionuclide that, when released to 

the air and inhaled is a significant 

cause of lung cancer, exceeded the 

proposed MCL of 300 picocuries 

per liter (piC/L) in more than 

75 percent of the samples from the 

Biscayne aquifer. 
14 Water Quality in Southern Florida, 1996–98

Transport of Herbicides and their Breakdown Products

To evaluate the geochemical transport of herbicides, water and bed-sediment samples were collected in 

May 1997 and February 1998 from six SOFL sites (fig. 10) representing different land uses. The samples 

were analyzed after the methods of Thurman and others (1990) and Meyer and others (1993) for a suite of 

herbicides and breakdown products. Low levels (0.05 to 2.5 μg/L) of one or more herbicides were detected in 

water at all sites, including atrazine at every site. Other herbicides detected include ametryn, prometryn, 

and metolachlor at the sugarcane site, simazine and metolachlor at a mixed-agricultural (vegetable) site, and 

ametryn, simazine, and terbutryn at a citrus site. Atrazine (at trace levels) and ametryn (exceeding 40 

micrograms per kilogram (μg/kg)) were detected in the sediment samples from the sugarcane site (S-6) in 

both years. The only other herbicides detected in sediments were trace levels of ametryn and alachlor at the 

mixed-agricultural (vegetable) site (Canal C-111). A breakdown product of alachlor, 2,6-diethylaniline, was 

detected in water at the same site. At the sugarcane site, S-6, the ratio of sediment-to-water concentration for 

ametryn was 240 (1997) and 580 (1998) and was zero for atrazine both years, which indicates that ametryn is 

transported primarily in sediment and atrazine is transported primarily in water. 

The ratio of the concentration of deethylatrazine to the parent herbicide atrazine (DAR) has been used as 

an indicator of herbicide transport and surface- and ground-water interaction in the Midwestern States. 

Generally, a ratio greater than 1.0 indicates slow unsaturated zone transport and ground-water contributions to surface water (Adams and Thurman, 1991; Thurman and others, 1991; 1992). An elevated ratio also 

can be caused by photodecomposition of atrazine to deethylatrazine during atmospheric transport of herbicides (Goolsby and others, 1997). A ratio less than 0.1 indicates rapid overland-flow transport to surface 

water shortly after herbicide application. In southern Florida, DAR values were less than 0.1 at the sugarcane site (S-6), suggesting rapid transport of the herbicide into canal water shortly after herbicide application. The DAR at three other sites was between 0.1 and 1.0, which suggests post-application runoff. The 

DAR value of 1.0 at the background site (Br-105) presumably is from low-level atmospheric transport and 

photodecomposition because this site is remote from any farm runoff or ground-water sources of atrazine. 

The higher values above 1.0 at the citrus site (U.S. Sugar) and Canal C-111 at S-178 could indicate groundwater contributions (as in the Midwest) or more rapid photodegradation of atrazine in southern Florida 

because of higher temperatures, stronger sunlight, or greater soil organic carbon content and soil moisture 

than in the Midwest. 

OLD ATRAZINE

(Ground-water contributions to surface water?)

POST-APPLICATION

(Runoff contributions to surface water)

HERBICIDE APPLICATION

(Runoff contributions to surface water)

10

1

0.1

0.01

RATIO OF

DEETHYLATRAZINE TO ATRAZINE

Hillsboro

Canal S–6,

(May 1997)

S–6

(February 1998)

C–111 at S–177

(May 1997)

C–111 at S–177

(February 1998)

C–111 at S–178

(February 1998)

U.S. Sugar

(May 1997)

U.S. Sugar

Bridge 105

(May 1997)

(February 1998)

S–12D

(May 1997)

SUGARCANE MIXED CROPS

LAND USE

CITRUS 25°

82° 80°

27°

26° Monroe

Tamiami Trail

and Canal

Barron River

Canal

Miami

P-34

Bridge

105

S-8

S-177

S-18C

S-7

S-6

S-79

S-65E

P-33

P-36

P-35

40-Mile BendS-12AS-12BS-12CS-12D

ATLANTIC OCEAN

GULF OF MEXICO

Charlotte

Harbor

Florida Bay

St.

Lucie M

Peace

River yakka

River

River

Kissimmee

River

Caloosah River atchee

0 25 50 MILES

0 25 50 KILOMETERS

Biscayne

Bay

Lake

Okeechobee

C-111

81°

P-35

S-177 CONTROL STRUCTURE--Location

 and number

SAMPLING SITE--Location and number

EXPLANATION

Canal

Arcadia

S-178

Figure 10. Ratio of deethylatrazine to atrazine (DAR) in surface water at selected sites, 1997–98 (M.T. Meyer, U.S. Geological 

Survey, written commun., 1998).
Major Findings 15 

Other organochlorine compounds and PCBs detected in the 

composite whole-fish samples 

collected during 1995–96 include 

polychlorinated biphenyls (PCBs) 

and the pesticides dieldrin, mirex, 

and various compounds of chlordane (cis-chlordane, oxy-chlordane, trans-chlordane, transnonachlor, and cis-nonachlor). 

Maximum concentrations of pesticides occurred primarily in fish 

collected in Hillsboro Canal at S-6. 

PCBs were detected in three separate fish samples; the maximum 

concentration (140 μg/kg) was in 

fish collected from Black Creek 

Canal. Dieldrin and toxaphene 

were two other pesticides commonly detected in composite fish 

samples from the Everglades in the 

early 1970s. Concentrations of 

dieldrin in largemouth bass were as 

high as 130 μg/kg, and concentrations of toxaphene were as high as 

5,000 μg/kg. In 1995, dieldrin concentrations ranged from less than 

5 to 18 μg/kg, and 5 of 27 fish 

samples had detectable dieldrin. 

Toxaphene was not detected in fish 

collected during 1995–96, but the 

analytical method was not very 

sensitive for toxaphene (only levels 

greater than 200 μg/kg could be 

detected). 

endosulfan, and other 

semivolatile organic 

compounds, including 

polycyclic aromatic 

hydrocarbons (PAHs).

 The most frequently 

detected pesticides in 

fish at 15 SOFL sites 

also were DDT and its 

breakdown products. 

Largemouth bass and 

(or) Florida gar were 

collected at each site, 

and one or more samples (5–8 

whole fish) were analyzed for pesticides. DDT compounds were 

detected in 25 of the 27 composited 

fish samples. Concentrations of 

total DDT ranged from less than 

5 to 1,170 μg/kg in Florida gar and 

from less than 5 to 610 μg/kg in 

largemouth bass. The most commonly detected and abundant DDT 

product was p,p′-DDE. Total DDT 

concentrations exceeded the 200-

μg/kg guidelines (Newell and 

others, 1987) for the protection of 

fish-eating wildlife in 4 of 27 fish 

samples. Highest concentrations of 

total DDT were in canals of the 

northern Everglades near agricultural lands. For comparison, during 

1970–73 concentrations of total 

DDT in 49 composite fish samples 

from 12 sites in southern Florida ranged from 

6 to 800 μg/kg. In 1978, 

total DDT concentrations in 23 fish samples 

ranged from 3 to 

1,650 μg/kg (Haag and 

McPherson, 1997). 

Pesticides, PCBs, other 

organics, and trace elements 

have accumulated in bottom 

sediment and fish

Many pesticides, other trace 

organic compounds, and trace elements are hydrophobic; that is, in 

aquatic environments they tend to 

be associated with sediment particles and biological tissues rather 

than dissolved in water. For this reason, sampling bottom sediment and 

fish is an effective way to assess the 

occurrence of these contaminants in 

the aquatic environment.

The most frequently detected 

pesticides in bottom sediment at 

the SOFL sites during 1996–98 

were DDT and its breakdown products DDE and DDD, ranging from 

2.4 to 670 micrograms per kilogram (μg/kg). DDE exceeded the 

Canadian sediment quality guidelines probable effects level (PEL) 

of 6.75 μg/kg (Environment Canada, 1999) at four of the 

seven fixed sites, including the 

Hillsboro Canal at S-6 (308 μg/kg) 

and the Kissimmee River at S-65E 

(670 μg/kg). More than 40 organic 

compounds were detected in bedsediment from the Hillsboro Canal 

at S-6, including ametryn, chlordane, DDT compounds, dieldrin, 

 Row crops, C-111 basin, southern Florida.

Fish sampling in Big Cypress Swamp as part of the 

southern Florida NAWQA study.
16 Water Quality in Southern Florida, 1996–98

The types and amounts of pesticides used in Florida have changed 

over the years because of new technology, land use, and State and 

Federal regulations. One of the 

most frequently detected herbicides in bed sediment in southern 

Florida, ametryn, is used in relatively small amounts on sugarcane 

crops (6 tons per year [tons/y]) 

(Miles and Pfeuffer, 1997). By far, 

the greatest frequency of insecticide detection was the organochlorine insecticides, such as DDD, 

DDE, DDT, dieldrin, and heptachlor. DDT was banned for most 

uses in the Nation in 1973. These 

insecticides also are the most 

frequently detected pesticides in 

bottom sediments (Shahane, 1994). 

Although most organochlorine 

pesticides such as DDT and chlordane are no longer sold in the 

United States, they persist in the 

environment and continue to pose 

potential threats to wildlife and 

humans. Persistent organochlorine 

pesticides were detected beginning 

in the late 1960s and early 1970s 

(Kolipinski and Higer, 1969; 

McPherson, 1973) in bottom sediment and fish that are a part of the 

food chain in the Everglades. 

Reflooding of farm lands for Everglades restoration potentially could 

lead to mobilization of persistent 

organochlorine pesticides and 

foodweb contamination, as 

occurred in Lake Apoka just north 

of the study area. Many organochlorine pesticides and PCBs also 

have been linked to hormone disruption and reproductive problems 

in aquatic animals (Colborn and 

others, 1993). 

Polynuclear aromatic hydrocarbons (PAHs) are contaminants in 

soils and sediments and originate 

from such sources as crude oil and 

tar and from forest fires and incomplete combustion of fossil 

fuels. Bottom-sediment 

samples were collected at 

10 sites in a survey of the 

Barron River Canal in 1998 to 

evaluate the occurrence of 

PAHs and other semivolatile 

organic compounds in the 

vicinity of the Big Cypress 

National Preserve (Miller and 

McPherson, U.S. Geological 

Survey, in press). PAHs normalized to organic carbon had 

patterns of distribution that 

indicated sources to be roads, 

vehicles, or an old creosote 

wood-treatment facility. Concentrations of phthalate esters 

and the trace elements arsenic, 

cadmium, and zinc in the 

Barron River Canal appear to 

have a nonpoint source and to 

be influenced by local bedsediment properties, such as 

sediment particle size and 

organic content. At some 

Barron River Canal sites, lead, 

copper, and zinc, normalized to 

aluminum, exceeded background 

levels and may be enriched by 

human activities. Trace elements in 

bottom-sediment samples from the 

Barron River Canal sites did not 

exceed the Canadian PEL for freshwater sediment.

Mercury is a contaminant in 

the Southern Florida Study 

Unit

Game fish in the Everglades 

have concentrations of mercury 

that exceed recommended levels 

(1.5 micrograms per gram, μg/g) for 

human consumption (Ware and 

others, 1990; fig. 11). The maximum concentrations of mercury 

found in edible portions of largemouth bass (4.4 μg/g) collected 

from the Everglades exceeded 

mercury concentrations in game 

fish from all other parts of the State 

(Stober and others, 1995). The 

NAWQA Program specifies that 

trace elements (including mercury) 

be determined for fish livers. Thus, 

the data are not directly comparable to data from studies analyzing 

fish fillets (the edible portion of the 

fish). Mercury concentrations in 

composite samples of largemouth 

bass livers from the SOFL sites 

ranged from 0.4 μg/g in Black 

Creek Canal to 42 μg/g in Miami 

Canal at S-8. Mercury concentrations in Florida gar livers ranged 

from 2.1 μg/g in the Caloosahatchee River at Alva to 190 μg/g 

in the Miami Canal at S-8. Largemouth bass and gar are top predators; on average, mercury 

concentrations in gar livers were 

about four times higher than 

mercury concentrations in largemouth bass livers.

P-34P-33

STUDY-UNIT

BOUNDARY

ATLANTIC OCEAN

GULF OF MEXICO

25°

26°

Caloosahatchee Canal

Miami

Canal

27°

Kissimmee

Lake

Okeechobee

28°

83° 82° 81° 80°

° ° °

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 meridan -83 00'

River

Caloosahatchee

0 25 MILES 

0 25 KILOMETERS

River

EXPLANATION

MERCURY

CONCENTRATIONS

IN BASS TISSUE

(μg/g)

MEDIAN SULFATE

 CONCENTRATION–In

 milligrams per liter

0.5 to 1.5

Greater than 1.5

50 10

25

25

22

5

4

<1

<1

58

SAMPLING SITE–Location

 and number P-34

Figure 11. Mercury concentrations in largemouth bass tissue equaled or exceeded 

0.5 μg/g in an area in southern Florida. 

(Lambou and others, 1991). Median sulfate 

concentrations at SOFL sites, P-33 and P-34, 

in mg/L, 1996-98 (P-site data from South 

Florida Water Management District).
Major Findings 17 

The high concentrations of 

mercury in fish result from foodweb bioaccumulation of methylmercury, the most biologically 

available form of mercury in the 

environment (fig. 12). Buildup in 

the Everglades food web begins 

with high rates of bacterial mercury 

methylation at the sediment-water 

interface and subsequent transport 

of methylmercury from this interface into the water column. The 

Everglades region had one of the 

highest methylmercury to mercury 

ratios in sediment of the 21 

NAWQA basins sampled in 1998 

(Krabbenhoft and others, 1999a).

Mercury methylation rates in the 

Everglades are affected by complex 

physical-chemical-biological processes that vary widely from day to 

night, from season to season, and 

along spatial gradients. Two of the 

most important controls on mercury methylation are availability of 

sulfur and bacterial cycling of sulfur. Sulfur inputs to the Everglades 

have increased over background 

levels during the 20th century as a 

result of runoff containing agricul-

 

PEAT ADVECTION / DIFFUSION / SEDIMENT RESUSPENSION PEAT

SAWGRASS

SLOUGH

TREE

ISLAND

BEDROCK

METHYLATION

BIOACCUMULATION

PERIPHYTON

REDUCTION

DEMETHYLATION

Hg(0)

DOC,

Other Nutrients

VOLATILIZATION (Hg0)

and

DEPOSITION

(Hg(II), CH3Hg)

CH3Hg

CH3Hg

Hg(II)

Hg(II)

Figure 12. High concentrations of mercury in Everglades fish, birds, and other organisms is a 

result of food web bioaccumulation of methylmercury, which originates primarily at the sediment 

and periphyton-water interface (modified from Krabbenhoft, 1996).

tural fertilizers. Large inputs of 

sulfur in parts of the northern Everglades have stimulated sulfate 

reduction that would normally 

favor methylation, but very high 

levels of sulfide in the eutrophic 

areas have an inhibitory effect on 

methylation rates. Lower levels of 

sulfur contamination in the central 

Everglades (fig. 11) have increased 

sulfate reduction and mercury 

methylation without the inhibitory 

effects of excess sulfide on methylation rates (Benoit and others, 

1999; Orem and others, 1999, 

p. 79). Concentrations of mercury 

are higher in fish and other organisms in the more remote and lownutrient waters of the central and 

southern Everglades than in the 

high-nutrient waters of the northern 

Everglades (Cleckner and others, 

1998; Gilmour and others, 1998; 

Hurley and others, 1998).

Degradation of methylmercury 

also is a dynamic process that 

varies from day to night and spatially across the Everglades. 

Microbial demethylation rates in 

the sediments do not show strong 

spatial patterns, whereas photodemethylation rates in the water 

column do show a strong north to 

south upward trend, ranging from 

2 to 15 percent per day, as a result 

of decreasing DOM in the water 

column from north to south and 

the resulting increase in light penetration in the south (Krabbenhoft 

and others, 1999b). 

Atmospheric sources supply 

mercury that sustains methylation 

and food-web biomagnification in 

the Everglades. The southern 

Florida area has one of the highest 

atmospheric mercury deposition 

rates (25 micrograms per square 

meter per year, μg/m2

/y) in the 

United States (Krabbenhoft and 

others, 1999a). Atmospheric inputs 

have local sources, such as medical, municipal, and industrial incinerators, landfills, power plants, and 

other urban activities, and global 

sources. Local sources are considered by most investigators to be 

primarily responsible for the relatively high atmospheric mercury 

inputs in southern Florida.
18 Water Quality in Southern Florida, 1996–98

Biological communities are 

influenced by water quality

The distribution of fish, invertebrates, and algae within a river or 

canal is influenced by natural conditions and human activities that 

affect water quality and available 

habitat. Generally, a diverse aquatic 

community composed of a variety 

of species and dominated by no 

single species or group of species is 

an indicator of favorable biotic 

conditions and an absence of contaminants and other environmental 

stresses. Although human activities 

have caused significant changes in 

many southern Florida freshwater 

habitats, it is important to understand how unique natural conditions in southern Florida influence 

the composition of aquatic communities there.

Sixty-three species of fish in 

26 families were collected in the 

seven canals and rivers sampled in 

the SOFL Study Unit during 1996–

98. The fish community included 

43 native species and 10 exotic or 

non-native species. Additionally, 

10 species of marine fish that periodically inhabit portions of canals 

and rivers in southern Florida also 

were collected. The chemical composition of freshwater in southern 

Caloosahatchee

River

Kissimmee

River

Peace

River

EPHEMEROPTERA (mayflies) OTHER AQUATIC INVERTEBRATES

PLECOPTERA (stoneflies)

TRICHOPTERA (caddisflies)

ODONATA (dragonflies / damselflies)

COLEOPTERA (beetles)

DIPTERA (true flies)

MIXED LAND USE

Tamiami

Canal

UNDEVELOPED

Canal

C–111

Hillsboro

Canal

U.S. Sugar

Canal

AGRICULTURAL LAND USE

EXPLANATION

Figure 13. Diptera (true flies) dominated the insect community at the Southern Florida National Water-Quality Assessment 

Study Unit Sites, 1996–98.

Florida, in particular the concentrations of sodium, chloride, and 

calcium, facilitates the invasion and 

occasional establishment of fishes 

with broad salinity tolerance 

(Loftus and Kushlan, 1987). No 

fish species listed as threatened or 

endangered in the United States or 

Florida were collected in southern 

Florida during the NAWQA study.

Florida rivers have smaller 

drainage basins and fewer fish 

species than rivers in the adjacent 

Southeastern United States (Swift 

and others, 1986). Natural conditions, in this case the repeated rise 

and fall of sea level over geologic 

time, have reduced the number of 

freshwater fish species in the 

Florida peninsula. The present fish 

community represents the most 

recent reinvasion following sealevel withdrawal (Bass, 1990). The 

most important natural factors limiting the diversity of the fish community are unsuitability of habitat 

and climate for temperate species 

(Loftus and Kushlan, 1987).

The rivers in southern Florida 

have very low gradients, typically 

only a few inches per mile 

(McPherson and Halley, 1996), as 

well as slow current velocities, 

high water temperatures, and low 

dissolved-oxygen concentrations. 

Fish and invertebrate communities 

are characterized by species that 

prefer these conditions and by the 

absence of related species that are 

found only in cool, swiftly flowing, 

well-oxygenated streams. The 

number of fish species collected at 

SOFL sites, or the species richness 

of the community, tended to 

increase with increasing mean 

annual dissolved-oxygen concentrations. Some game-fish species, 

such as bass, were absent at sites 

with the lowest dissolved-oxygen 

concentrations. One entire group of 

invertebrates (Plecoptera: stoneflies), which prefer cool running 

waters, usually are not found anywhere in the waters of southern 

Florida. Diptera (true flies) was the 

dominant insect group at all sites 

(fig. 13). Many of the Diptera were 

species in the family Chironomidae 

(midges), which are adapted to 

aquatic environments with sandy 

substrates and very low dissolvedoxygen concentrations, such as 

those prevalent in southern Florida 

surface waters. Species in this 

family are also tolerant of nutrient 

enrichment and contaminants.
Major Findings 19 

In the canals and some of the rivers of southern Florida, habitat 

alteration is significant. The canal 

channels are rectangular in crosssection, and they have been channelized and are routinely dredged 

to facilitate navigation and the 

movement of water. There are few 

areas of shallow water (littoral 

zone) to provide sufficient light for 

attached algae (periphyton) and 

suitable spawning areas for fish. 

Moreover, aquatic vegetation is 

periodically removed for watermanagement purposes, further 

reducing habitat for small fish and 

invertebrates that serve as food for 

fish. The species richness of fish 

and the total numbers of fish collected generally were lowest in the 

canals of southern Florida in basins 

with agricultural land use (fig. 14). 

The canals and channelized rivers 

have little suitable habitat of any 

kind for many aquatic insects that 

prefer hard substrate, such as caddisflies (Trichoptera) and some 

mayflies (Ephemeroptera); snags 

(woody debris) are scarce because 

bankside vegetation is usually 

cleared, and hard surfaces, such as 

rock, are limited to porous limestone outcroppings.

Fish can be categorized 

on the basis of their ability 

to tolerate a range of environmental conditions. 

There were no intolerant 

fish species collected in 

any of the canals in southern Florida (fig. 14). The 

presence of intolerant species in the Peace River 

during the SOFL study, as 

well as in earlier studies 

(Champeau, 1990), indicates favorable biotic conditions. The Peace River is 

unique among the rivers 

sampled in southern Florida because it has not been 

channelized, and the main channel 

is connected to the flood plain 

during periods of high water. The 

flood plain provides a refuge for 

fish during high flow, perhaps 

enhancing survival and reproduction. Also, periodic flooding results 

in input of particulate organic matter and dissolved organic carbon 

from the flood plain, which 

increases the productivity of the 

river and increases its ability to 

support a diverse fish community. 

The environmental conditions in 

the Peace River also supported a 

diverse aquatic insect community 

compared to most other SOFL sites 

(fig. 13). For example, the Peace 

River had the highest mean dissolved-oxygen concentration of 

any southern Florida site. Hard 

substrates, such as the woody snags 

preferred by many aquatic insects, 

were abundant. Seasonal input of 

leaf debris (particulate organic 

matter) from the flood plain provides a valuable food source for 

many aquatic invertebrates. In 

contrast, Hillsboro Canal, a relatively degraded SOFL site, had 

insects from a number of different 

groups, but few of the pollutionC–111 Canal

Caloosahatchee River

Hillsboro Canal

Kissimmee River

Peace River

Tamiami Canal

U.S. Sugar Canal

UNDEVELOPED

0

21 28 32 34 24 23 26

500

1,000

1,500

2,000

2,500

SITE LOCATION

NUMBER OF FISH SPECIES COLLECTED

NUMBER OF FISH

MIXED LAND USE AGRICULTURAL

LAND USE

INTOLERANT

MODERATELY

 TOLERANT

TOLERANT

Figure 14. Environmentally tolerant fish are common in 

southern Florida canals and rivers.

sensitive insects, including caddisflies, were present.

In many parts of the United 

States, the abundance of a group of 

invertebrate taxa referred to as the 

EPT taxa (Ephemeroptera, Plecoptera, Trichoptera) is used to assess 

the biotic condition of streams and 

rivers. Species in these insect 

groups generally thrive in conditions of flowing water, moderate to 

high dissolved oxygen, and low 

suspended sediment and are intolerant of contaminants and habitat 

disturbance. The relative abundance of EPT taxa compared to the 

more tolerant Diptera taxa can be 

used to assess and compare sites. 

However, this metric must be used 

with caution because Plecoptera 

usually are not found in southern 

Florida. The Peace River had the 

highest EPT/Diptera ratio compared to the other SOFL sites. The 

Peace River also supported a 

diverse algae community with the 

greatest species richness (220 species) of all the SOFL sites. Total 

phosphorus and nitrogen concentrations were high in the Peace 

River compared to other SOFL 

sites because of natural conditions 

and human activities. The availability of these essential 

nutrients, combined with 

an unmodified habitat and 

more shallow-water areas, 

may contribute to a more 

diverse algal community.

The Tamiami Canal is 

unique among the SOFL 

canal sites because land 

within its basin is mostly 

undeveloped, limiting the 

input of contaminants. 

However, the environmental conditions are stressful 

because the shallow canal 

has almost no flow, the 

water is warm, and dissolved-oxygen concentra-
20 Water Quality in Southern Florida, 1996–98

tions typically are very low. 

Nutrient concentrations were 

among the lowest of the SOFL 

sites. The insect community was 

dominated by Diptera, although 

some Trichoptera that are adapted 

to still or slow-flowing conditions 

were collected. Bluegreen algae 

were relatively abundant. The fish 

community showed little similarity 

to any of the other sites and was 

Algae Siltation Index 

Algae collected at the seven southern Florida NAWQA sites 

were compared to algae at 140 national NAWQA sites by using 

the Siltation Index (Bahls and others, 1992). This index is the 

relative abundance of the motile diatoms Navicula, Nitzschia, 

Cylindrotheca, and Surirella in a diatom count. These diatoms 

are able to move through silt particles, and because they are able 

to avoid being buried, they are considered more tolerant of sedimentation than other diatoms. The values for this index are higher for 

streams in agricultural basins. Based on the relative abundance of these diatoms, the undeveloped Southern Florida site (Tamiami Trail 

Canal) falls into the less degraded stream category, whereas the agricultural sites are between the 25th and 50th percentile, and two of the 

three major river sites in the mixed land-use category are near or above the 75th percentile. See pages 18–20 for how algae communities 

compare at sites within the SOFL Study Unit.

Invertebrate Community Status Index (ICSI)

Invertebrate communities at the seven southern Florida 

NAWQA sites were compared to invertebrate communities at 

NAWQA sites nationwide by using a multimetric index. The 

index combines 11 metrics, including ones that assess taxa richness and diversity, taxa richness of mayflies, stoneflies, and caddisflies, and various measures of environmental tolerance. Using 

the ICSI, all seven of the Southern Florida sites ranked above the 75th percentile, indicating that they are among the most degraded sites in 

the Nation. Use of the ICSI in southern Florida must be approached with caution because background environmental conditions prevalent 

at all sites, including slow water velocities and low dissolved-oxygen concentrations, probably contribute to the high index values and may 

obscure differences in invertebrate communities because of other factors, such as land use or changes in habitat. The dominance of Diptera 

(true flies), insects that are tolerant of degraded environmental conditions, and low diversity of insects overall contribute to the high ICSI 

scores for Southern Florida. See pages 18–20 for how insect communities compare at sites within the SOFL Study Unit. 

Fish Status Index

To facilitate comparisons, fish collected at NAWQA sites 

across the Nation were classified based on four fish metrics (percentage of tolerant, ominvorous, non-native individuals, and percentage of individuals with external anomalies). Nationwide, 

higher values suggest a more degraded stream site. Six of the 

SOFL sites, including the reference site, ranked in the highest 25th 

percentile cataegory for the Nation. Environmental conditions mentioned above for invertebrates also may contribute to stress in the fish 

community at sites including the reference site. This environmental stress can lead to dominance of tolerant fish, favorable conditions for 

exotic species, and increased external anomalies at some sites in the SOFL Study Unit, leading to higher values compared with other sites 

nationwide. See pages 18–20 for a discussion of how fish communities compare at sites within the SOFL Study Unit.

UNDEVELOPED

AGRICULTURAL

MIXED

TOLERANT ALGAE, IN PERCENT

0 20 40 60 80 100

NATIONAL RANGE

STUDY UNIT VALUE

75th PERCENTILE

25th PERCENTILE

EXPLANATION

UNDEVELOPED

AGRICULTURAL

MIXED

INVERTEBRATE STATUS INDEX

0 20 40 60 80 100

NATIONAL RANGE

STUDY UNIT VALUE

75th PERCENTILE

25th PERCENTILE

EXPLANATION

UNDEVELOPED

AGRICULTURAL

MIXED

TOLERANT FISH SPECIES,

IN PERCENT

0 5 10 15 20

NATIONAL RANGE

STUDY UNIT VALUE

75th PERCENTILE

25th PERCENTILE

EXPLANATION

SOUTHERN FLORIDA AQUATIC COMMUNITIES IN A NATIONAL CONTEXT

characterized by an abundance of 

minnows and Florida gar. The 

Tamiami Canal had the smallest 

proportion (5 percent) of fish with 

external anomalies. External 

anomalies, such as eroded fins, 

lesions, ulcers, tumors, and 

external parasites, can be an 

indication that fish are stressed by 

environmental conditions or 

contaminants. The highest 

percentages of fish with external 

anomalies were from the Hillsboro 

(32 percent) and C-111 Canals 

(22 percent). Anomalies at these 

two sites were primarily external 

parasites, eroded fins, and anatomical deformities. These two sites 

were in the top 25 percent of 

144 NAWQA sites sampled 

nationwide.
Major Findings 21 

Exotic species are a threat to 

native biota

Exotic or non-native species of 

fish, as well as other animals and 

plants, represent a major threat to 

native biota in southern Florida. 

Exotic fish compete with native 

species for food and habitat. Exotic 

plants crowd out native species and 

can form dense monocultures that 

alter habitat for birds, fish, and 

other native biota. Ten exotic fish 

species were collected at the SOFL 

sites during 1996–98 (fig. 15).

Cichlids were the most numerous 

and widespread exotic species, 

including the black acara, Mayan 

cichlid, peacock cichlid, blue tilapia, spotted tilapia, and the oscar. 

The other exotic species collected 

(pike killifish, grass carp, walking 

catfish, and sailfin catfish) were all 

rare and found at only one or two 

sites each. Fifty-four exotic fish 

species have been recorded in 

southern Florida, and the total 

statewide exceeded 125 species by 

1998 (Fuller and others, 1999). 

Nearly all the exotic fish species 

were originally imported for the 

aquarium trade and either escaped 

from fish farms or were released by 

individuals with home aquariums. 

Exotic fish usually are most abunThe Asian swamp eel, Monopterus albus, 

continues to spread.

The exotic sailfin catfish, 

Pterygoplichthys disjunctivus, is a 

South American invader.

dant in streams that have been 

altered by human activity (Moyle, 

1986). Generally, the canal sites in 

southern Florida had more exotic 

species than the major rivers. The 

number of species of exotic fish at 

SOFL sites ranked in the top onethird of NAWQA sites nationwide.

The swamp eel (Monopterus 

albus), recently introduced from 

Southeast Asia, is a potentially 

dangerous invader. The swamp eel 

can breathe air for extended periods of time, enabling it to inhabit 

stagnant water and even live out of 

water. This characteristic also 

enhances its ability to disperse 

widely. It is a voracious general 

predator, making it a threat to 

native fishes, amphibians, and 

aquatic invertebrates. The swamp 

eel was not collected at any of the 

SOFL sites during 1996–98. However, this species has affected 

regional water-management practices. Selected water-control structures in the vicinity of established 

populations are not being opened to 

prevent or at least retard dispersal, 

particularly into waters of ENP. 

In addition to fish, other exotic 

species are of great concern in 

Florida. At least 25 percent of all 

plant species in the State are exotic 

(Langeland, 1998). Melaleuca, a 

wetland tree, covers almost 

400,000 acres in the State and is 

particularly troublesome in the 

Water Conservation Areas 

(Laroche, 1994). Brazilian pepper, 

a wetland shrub, has infested more 

than 100,000 acres in the ENP 

(Ferriter, 1997). Hydrilla, water 

hyacinth, water milfoil, and water 

lettuce are the most abundant 

exotic aquatic plant species infesting canals throughout southern 

Florida. Efforts to control or eradicate exotic plant species involve 

the use of mechanical, chemical, 

and biological control methods. 

Numerous herbicides are applied, 

including 2,4-D, copper sulfate, 

diquat, endothall, fluridone, 

glyphosate, imazapyr, triclopyr, 

and others. At least two of these 

compounds (2,4-D and triclopyr) 

have been detected in surface water 

at the SOFL sites. MIXED LAND USE

UNDEVELOPED

AGRICULTURAL

LAND USE

C–111 Canal

Caloosahatchee River

Hillsboro Canal

Kissimmee River

Peace River

Tamiami Canal

U.S. Sugar Canal

NUMBER OF FISH SPECIES

0

10

20

30

25

35

5

15

SITE LOCATION

MARINE FISH

EXOTIC FISH

NATIVE FISH

Figure 15. Exotic fish species were 

collected at all SOFL sites, 1996-98.
22 Water Quality in Southern Florida, 1996–98

STUDY UNIT DESIGN

EXPLANATION

Lake

Okeechobee

Peace

River at

Arcadia

(B)

Kissimmee

River at S-65E

 (B)

C-111 at

S-177

(B/I)

S-6

 (B/I)

S-178

Four S-12

structures

P-33

P-34

P-35

U.S. Sugar

(B/I)

BR-105

(B)

Caloosahatchee

River at Alva

 (B)

Water Conservation

 Areas 1,2, and 3

Big Cypress National

 Preserve

Everglades National Park

Basic Fixed Site (BFS)

Basic Fixed Site and 

 Intensive Fixed Site (IFS)

Intensive pesticide

 sampling site

Cooperative sampling site

Contaminants in fish tissue

 sampling site

Water chemistry,

 bottom sediment,

 aquatic biology,

 sediment toxicity,

 process studies, and

 storm sampling site

Nutrient / pesticide /

 algae synoptic site

(B)

(B/I)

STUDY COMPONENTS

USED TO ASSESS WATER

QUALITY AND AQUATIC

BIOLOGY IN THE

SOFL STUDY UNIT

N

Lake

Okeechobee

Tamiami Trail

Canal

Urban land-use

survey

Biscayne

aquifer and

Study-Unit survey

(public supply)

Mixed-agricultural

land-use survey,

C-111 basin

Agricultural

land-use survey

(unnamed surficial

aquifer)

C-111

GROUND-WATER SAMPLING

SURFACE-WATER AND

AQUATIC-BIOLOGY SAMPLING
Study Unit Design 23 

Study 

component

(Type of site)

Objectives Brief description and

water-quality parameters

Number

of sites

Sampling 

frequency 

during water 

year

Historical

data

available

SURFACE WATER

Bottomsediment 

survey (BFS)

Determine presence of potentially 

toxic compounds in sediment at 

selected sites

Sample the depositional zone for pesticides, 

other synthetic organic compounds, and trace 

elements at water-chemistry sites

7 1

(1996) some

Waterchemistry 

sites (BFS)

Describe concentrations and loads 

of major ions and nutrients at 

selected sites

Sample near-continuous streamflow sites for 

major ions, nutrients, organic carbon, and 

suspended sediment

7

2–6 in 1996

12–31 in 1997

12 in 1998

 data at some 

sites

Cooperative

sampling

program (BFS)

Assess the influence of

sampling method and location

on water-quality data

Sample water-chemistry sites on the same day 

as the SFWMD using both USGS methods 

and SFWMD methods

5

2–6 in 1996

12–31 in 1997

12 in 1998

none

Storm 

sampling (BFS)

Assess effects of runoff during 

high-flow conditions on surfacewater quality

Sample water-chemistry sites during highflow conditions for major ions, nutrients, 

organic carbon, and suspended sediment

variable

variable

(1997 and 

1998)

some

Nutrient/

pesticide 

synoptic 

studies 

Determine the concentration of 

nutrients and pesticides across 

southern end of Study Unit during 

high and low flow

Sample sites along the Tamiami Trail Canal 

during low flow (June) and high flow 

(August) for major ions, mercury, nutrients, 

organic carbon, and pesticides

30

3

(Aug. 1996, 

June and August 

1997)

limited

Process 

studies

Describe processes controlling the 

degradation and biological 

availability of pesticides

Deploy and collect semipermeable membrane 

devices at selected sites. Collect water and 

bottom-sediment samples 

variable 4

(1997–98)

undetermined

Intensive 

pesticide

sampling (IFS)

Determine seasonal variation in the 

occurrence and concentrations of 

nutrients and pesticides at waterchemistry sites

Sample water-chemistry sites that are located 

in specified agricultural land-use areas 

(citrus, sugarcane, and vegetables) for 

nutrients and pesticides

3

2 in 1996; 

weekly/biweekly 

in 1997;

monthly in 1998

some

GROUND WATER

Urban 

land-use 

survey

Describe water quality in a residential and light commercial land-use 

area in a shallow aquifer susceptible to contamination

Sample monitoring wells for major ions, 

nutrients, organic carbon, pesticides, radionuclides, trace elements, and volatile organic 

compounds (VOCs)

38 wells 1

(1997) some

Ground-water

and surface-water

synoptic survey

Determine which water-quality 

constituents are transported through 

shallow ground water into surface 

water in an agricultural land-use 

area 

Sample shallow wells and surface-water sites 

for major ions, nutrients, pesticides, and 

VOCs before and during a surface-water 

release in a canal that drains agricultural land

7 wells;

9 

surfacewater sites

1–5

(1997) none

Agricultural

land-use 

survey

Describe the effects of citrus land 

use on water quality in a shallow 

aquifer. 

 Sample new wells for major ions, nutrients, 

pesticides, radionuclides, and trace elements 30 wells 1

(1998) some

Study-unit 

survey (public 

supply)

Describe overall water quality in 

the Biscayne aquifer, which is used 

for drinking-water supply

Sample existing wells for major ions, nutrients, organic carbon, pesticides, radionuclides, trace elements, and VOCs

30 wells 1

(1998) some

AQUATIC BIOLOGY

Contaminants

in fish tissue

Determine the presence of 

contaminants that can 

accumulate in fish tissue

Collect largemouth bass and Florida gar at a 

large number of sites. Sample composites of 

whole fish for organic compounds and fish 

livers for trace elements

15 1

(1996) limited

Sediment

toxicity 

testing

Evaluate potential toxicity of bed 

sediment at the water-chemistry 

sites

Collect bed-sediment samples and evaluate 

their potential toxicity by using ASTM methods and Hyallela azteca

7 1

(1996) none

Aquatic 

biology

Assess biological communities and 

stream habitat at the Basic Fixed 

Sites 

Quantitatively sample fish, macroinvertebrates, and algae near water-chemistry sites. 

Quantitatively describe stream habitat for 

these organisms

7

3

(1 per year during

1996–98)

limited

Algae

synoptic

studies

Determine the influence of nutrients on the algal community along 

a nutrient gradient in the southern 

part of the basin

Collect algae using artificial substrate samplers at sites across the Tamiami Trail Canal 10–13

3

(June, August,

November, 1997)

none
GLOSSARY

24 Water Quality in Southern Florida, 1996–98

Aquatic-life criteria - Water-quality guidelines for protection of aquatic life. Often refers to U.S. Environmental 

Protection Agency water-quality criteria for protection of 

aquatic organisms. 

Aquifer - A water-bearing layer of soil, sand, gravel, or rock 

that will yield usable quantities of water to a well.

Basic Fixed Sites (BFS) - Sites on streams or canals at 

which streamflow is measured and samples are routinely 

collected for temperature, salinity, major ions, nutrients, 

and organic carbon. Samples may also be periodically collected for contaminants in bottom sediment, biota, storm 

effects, or other constituents.

Breakdown products - Compounds resulting from transformation of an organic substance through chemical, photochemical, and/or biochemical reactions.

DDT - Dichloro-diphenyl-trichloroethane. An organochlorine 

insecticide no longer registered for use in the United States. 

DDT degradation products include DDE and DDD.

Drinking-water standard or guideline - A threshold concentration in a public drinking-water supply, designed to 

protect human health.

Ecosystem - The interacting populations of plants, animals, 

and microorganisms occupying an area, plus their physical environment.

Intensive Fixed Sites (IFS) - Basic Fixed Sites with 

increased sampling frequency during selected seasonal 

periods and analysis of dissolved pesticides for 1 year.

Load - General term that refers to a material or constituent in 

solution, in suspension, or in transport; usually expressed 

in terms of mass or volume.

Maximum contaminant level (MCL) - Maximum permissible level of a contaminant in water that is delivered to 

any user of a public water system. MCLs are enforceable 

standards established by the U.S. Environmental Protection Agency.

Methylation - The addition of a methyl group (–CH3) to a 

molecule or atom through a chemical reaction.

Micrograms per liter (μg/L) - A unit expressing the concentration of constituents in solution as weight (micrograms) of solute per unit volume (liter) of water; 

equivalent to one part per billion in most stream water and 

ground water.

Nutrient - Element or compound essential for animal and 

plant growth. Common nutrients in fertilizer include nitrogen, phosphorus, and potassium.

Organochlorine insecticide - A class of organic insecticides 

containing a high percentage of chlorine. Includes dichlorodiphenylethanes (such as DDT), chlorinated cyclodienes (such as chlordane), and chlorinated benzenes 

(such as lindane). 

Periphyton - Organisms that grow on underwater surfaces; 

periphyton include algae, bacteria, fungi, protozoa, and 

other organisms.

Pesticide - A chemical applied to crops, rights of way, 

lawns, or residences to control weeds, insects, fungi, nematodes, rodents or other “pests.”

Phosphorus - A nutrient essential for growth that can play a 

key role in stimulating aquatic growth in lakes and 

streams.

Phthalates - A class of organic compounds containing 

phthalic acid esters [C6H4(COOR)2] and derivatives. 

Used as plasticizers in plastics. Also used in many other 

products (such as detergents, cosmetics) and industrial 

processes (such as defoaming agents during paper and 

paperboard manufacture, and dielectrics in capacitors).

Polychlorinated biphenyls (PCBs) - A mixture of chlorinated derivatives of biphenyl, marketed under the trade 

name Aroclor with a number designating the chlorine content (such as Aroclor 1260). PCBs were used in transformers and capacitors for insulating purposes and in gas 

pipeline systems as a lubricant. Further sale for new use 

was banned by law in 1979.

Polycyclic aromatic hydrocarbon (PAH) - A class of 

organic compounds with a fused-ring aromatic structure. 

PAHs result from incomplete combustion of organic carbon (including wood), municipal solid waste, and fossil 

fuels, as well as from natural or anthropogenic introduction of uncombusted coal and oil. PAHs include 

benzo(a)pyrene, fluoranthene, and pyrene.

Recharge - Water that infiltrates the ground and reaches the 

saturated zone.

Reference site - A sampling site selected for its relatively 

undisturbed conditions.

Trace element - An element found in only minor amounts 

(concentrations less than 1.0 mg/L) in water or sediment; 

includes arsenic, cadmium, chromium, copper, lead, mercury, nickel, and zinc.

Volatile organic compounds (VOCs) - Organic chemicals 

that have a high vapor pressure relative to their water solubility. VOCs include components of gasoline, fuel oils, 

and lubricants, as well as organic solvents, fumigants, 

some inert ingredients in pesticides, and some by-products 

of chlorine disinfection.

Water-quality criteria - Specific levels of water quality 

which, if reached, are expected to render a body of water 

unsuitable for its designated use. 

Water-quality standards - State-adopted and U.S. Environmental Protection Agency-approved ambient standards 

for water bodies. Standards include the use of the water 

body and the water-quality criteria that must be met to 

protect the designated use or uses.

Water year - The 12-month period October 1 through 

September 30, designated by the calendar year in which it 

ends.
REFERENCES

References 25 

Adams, C.D., and Thurman, E.M., 1991, Formation and transport of deethylatrazine in the soil and vadose zone: Journal 

of Environmental Quality, v. 20, no. 3, p. 540–547.

Bahls, L.R., Burkantis, R., and Tralles, S., 1992, Benchmark 

biology of Montana reference streams: Helena, Montana, 

Department of Health and Environmental Science, Water 

Quality Bureau, 47 p.

Bass, D.G., Jr., 1990, Monitoring Florida’s riverine fish 

communities: Florida Science, v. 53, no. 1, p. 1–10.

Benoit, J.M., Gilmour, C.C., Mason, R.P., and Heyes, A., 

1999, Sulfide controls on mercury speciation and bioavailability to methylating bacteria in sediment and pore 

waters: Environmental Science and Technology, v. 33, 

p. 951–957.

Champeau, T.R., 1990, Ichthyofaunal evaluation of the 

Peace River, Florida: Florida Scientist, v. 53, p. 302–311.

Chiou, C.T., Malcolm, R.L., Brinton, T.I., and Kile, D.E., 

1986, Water solubility enhancement of some organic pollutants and pesticides by dissolved humic and fulvic 

acids: Environmental Science and Technology, v. 20, 

p. 502–508.

Cleckner, L.A., Garrison, P.J., Hurley, J.P., Olson, M.O., and 

Krabbenhoft, D.P., 1998, Trophic transfer of methyl mercury in the northern Florida Everglades: Biogeochemistry, v. 40, p. 347–361.

Colborn, T., vom Saal, F.S., and Sota, A.M., 1993, Developmental effects of endocrine-disrupting chemicals in wildlife and humans: Environmental Health Perspectives, 

v. 101, p. 378–384.

Davis, J.H., Jr., 1943, The natural features of southern 

Florida, especially the vegetation, and the Everglades: 

Florida Geological Survey Bulletin 25, 311 p.

Environment Canada, 1999, Canadian sediment quality 

guidelines for the protection of aquatic life, Summary 

tables: accessed September 17, 1999 at 

http://www.ec.gc.ca/ceqg-rcqe/sediment.htm.

Ferriter, A.P., 1997, Brazilian pepper management plan for 

Florida: West Palm Beach, Fla., Florida Exotic Pest Plant 

Council, 38 p.

Fuller, P.L., Nico, L.G., and Williams, J.D., 1999, Nonindigenous fishes introduced into inland waters of the United 

States: Bethesda, Md., American Fisheries Society, Special Publication, v. 27, 613 p.

Gilmour, C.C., Riedel, G.S., Ederington, M.C., Bell, J.T., 

Benoit, J.M., Gill, G.A., and Stordal, M.C., 1998, 

Mercury methylation and sulfur cycling across a trophic 

gradient in the northern Everglades: Biogeochemistry, v. 

40, p. 327–345.

Goolsby, D.A., Thurman, E.M., Pomes, M.L., Meyer, M.T., 

and Battaglin, W.A., 1997, Herbicides and their metabolites in rainfall: Origin, transport, and deposition patterns 

across the Midwestern and Northeastern United States, 

1990–1991: Environmental Science and Technology, 

v. 31, p. 1325–1333. 

Haag, K.H., and McPherson, B.F., 1997, Organochlorine pesticides and PCBs in southern Florida fishes—Then and 

Now: U.S. Geological Survey Fact Sheet FS–110–97, 4 p.

Haag, K.H., Miller, R.L., Bradner, L.A., and McCulloch, D.S., 

1996, Water-quality assessment of southern Florida—An 

overview of available information on surface and ground 

water and ecology: U.S. Geological Survey WaterResources Investigations Report 96–4177, 42 p. 

Hem, J.D., 1985, Study and interpretation of the chemical 

characteristics of natural water (3d ed.): U.S. Geological 

Survey Water-Supply Paper 2254, 263 p.

Hurley, J.P., Krabbenhoft, D.P., Cleckner, L.B., Olson, M.L., 

Aiken, G., and Rawlik, P.S., Jr., 1998, System controls on 

aqueous mercury distribution in the northern Everglades: 

Biogeochemistry 40, p. 293–311. 

Klein, Howard, Armbruster, J.T., McPherson, B.F., and 

Freiberger, H.J., 1975, Water and the south Florida environment: U.S. Geological Survey Water-Resources 

Investigation 24–75, 165 p.

Kolipinski, M.C., and Higer, A.L., 1969, Some aspects of the 

effects of the quantity and quality of water on biological 

communities in Everglades National Park: U.S. Geological Survey Open-File Report, 97 p.

Kolpin, D.W., Barbash, J.E., and Gilliom, R.J., 1998, Occurrence of pesticides in shallow ground water of the United 

States—Initial results from the National Water-Quality 

Assessment Program: Environmental Science and Technology, v. 32, 558–566 p.

Krabbenhoft, D.P., 1996, Mercury studies in the Florida Everglades: U.S. Geological Survey Fact Sheet FS–166–96, 

4 p.

Krabbenhoft, D.P., Wiener, J.G., Brumbaugh, W.G., Olson, 

M.L., DeWild, J.F., and Sabin, T.J., 1999a, A national 

pilot study of mercury contamination of aquatic ecosystems along multiple gradients, in Morganwalp, D.W., and 

Buxton, H.T., eds., U.S. Geological Survey Toxic Substances Hydrology Program—Proceedings of the Technical Meeting, Charleston, SC, March 8–12, 

1999—Contamination of hydrologic systems and related 

ecosystems: U.S. Geological Survey Water-Resources 

Investigations Report 99–4018B, v. 2, p. 147–160.

Krabbenhoft, D.P., Hurley, J.P., Marvin-DiPasquale, M., 

Orem, W.H., Aiken, G.R., Schuster, P.J., Gilmour, C.C., 

and Harris, R., 1999b, The aquatic cycling of mercury in 

the Everglades (ACME) project: A process-based investigation of mercury biogeochemistry in a complex environmental setting, in Gerould, Sarah, and Higer, Aaron, 

compilers, U.S. Geological Survey, Program on the 

South Florida Ecosystem—Proceedings of South Florida 

Restoration Science Forum, May 17–19, 1999, Boca 

Raton, Florida: U.S. Geological Survey Open-File 

Report 99–181, p. 54–56.

Lambou, V.W., Barkay, T., Braman, R.S., Delfino, J.J., 

Jansen, J.J., Nimmo, D., Parks, J.W., Porcella, D.B., 

Rudd, J., Schultz, D., Stober, J., Watras, C., Wiener, J.G., 

Gill, G., Huckabee, J., and Rood, B.E., 1991, Mercury 

technical advisory committee interim report to the Florida Governor’s Mercury in Fish and Wildlife Taskforce 

and the Department of Environmental Regulation: Tallahassee, Fla., Center for Biomedical and Toxicological 

Research and Waste Management, 60 p.

Langeland, K.A., 1998, Help protect Florida’s natural areas 

from non-native invasive plants: Gainesville, University 
26 Water Quality in Southern Florida, 1996-98

of Florida, Cooperative Extension Service, Institute of 

Food and Agricultural Sciences, Circular 1204, 6 p.

Laroche, F.B., ed., 1994, Melaleuca management plan for 

Florida: West Palm Beach, Florida Exotic Pest Plant 

Council, 88 p.

Loftus, W.F., and Kushlan, J.A., 1987, Freshwater fishes of 

southern Florida: Gainesville, Fla., Bulletin of the Florida 

State Museum of Biological Sciences, v. 31, no. 4, 344 p.

McIvor, C.C., Ley, J.A., and Bjork, R.D., 1994, Changes in 

freshwater inflow from the Everglades to Florida Bay 

including effects on biota and biotic processes—A 

review, in Davis, S.M., and Ogden, J.C., eds., Everglades—The ecosystem and its restoration: Delray 

Beach, Fla., St. Lucie Press, p. 117–146.

McPherson, B.F., 1973, Water quality in the conservation 

areas of the central and southern Florida Flood Control 

District, 1970–72: U.S. Geological Survey Open-File 

Report 73–014, 39 p.

McPherson, B.F., and Halley, Robert, 1996, The south 

Florida environment—A region under stress: U.S. Geological Survey Circular 1134, 61 p. 

McPherson, B.F., and Miller, R.L., 1987, The vertical attenuation of light in Charlotte Harbor, a shallow, subtropical estuary, southwestern Florida: Estuarine, Coastal, 

and Shelf Science, v. 25, p. 721–737.

Meyer, M.T., Mills, M.S., and Thurman, E.M., 1993, Automated solid-phase extraction of herbicides from water 

for gas chromatographic-mass spectrometric analysis: 

Journal of Chromatography, v. 629, p. 55–59.

Miles, C.J., and Pfeuffer, R.J., 1997, Pesticides in canals of 

south Florida: Archives of Environmental Contamination and Toxicology, v. 32, p. 337–345.

Miller, R.L., and McPherson, B.F., in press, Occurrence and 

distribution of contaminants in bottom sediment and water 

of the Barron River Canal, Big Cypress National Preserve, 

Florida, October 1998: Florida Scientist, v. 64, no. 1.

Miller, R.L., McPherson, B.F., and Haag, K.L., 1999, Water 

quality in the southern Everglades and Big Cypress 

Swamp in the vicinity of the Tamiami Trail, 1996–97: 

U.S. Geological Survey Water-Resources Investigations 

Report 99–4062, 16 p.

Moyle, P.B., 1986, Fish introductions into North America—Patterns and ecological impact, in Mooney, H.A., 

and Drake, J.A., eds., Ecology of biological invasions of 

North America and Hawaii: New York, Springer-Verlag, 

p. 27–43.

Newell, A.J., Johnson, D.W., and Allen, L.K., 1987, 

Niagara River Project—Fish flesh criteria for piscivorous wildlife: New York State Department of Environmental Conservation Technical Report 87–3. 

Nowell, L.H., Capel, P.D., and Dileanis, P.D., 1999, Pesticides in stream sediment and aquatic biota—Distribution, trends, and governing factors: Boca Raton, Fla., 

Lewis Publishers, 1001 p. 

Orem, W.H., Bates, A.L., Lerch, H.E., Corum, Margo, and 

Boylan, Ann, 1999, Sulfur contamination in the 

Everglades and its relation to mercury methylation, in

Gerould, Sarah, and Higer, Aaron, comps., U.S. Geological Survey Program on the South Florida Ecosystem—Proceedings of South Florida Restoration Science 

Forum, May 17–19, 1999, Boca Raton, Florida: U.S. 

Geological Survey Open-File Report 99–181, 121 p.

Parker, G.G., Ferguson, G.E., Love, S.K., and others, 1955, 

Water resources of southeastern Florida, with special reference to geology and ground water of the Miami area: 

U.S. Geological Survey Water-Supply Paper 1255, 965 p.

Reddy, M.M., Aiken, G.R., and Schuster, P.F., 1999, Mercury-dissolved organic carbon interactions in the Florida 

Everglades—A field and laboratory investigation, in

U.S. Geological Survey, Program on the south Florida 

ecosystem, Proceedings of South Florida Restoration 

Science Forum, May 17–19, 1999, Boca Raton, Fla.: 

U.S. Geological Survey Open-File Report 99–181, 

p. 86–87.

Shahane, A.N.,1994, Pesticide detections in surface waters 

of Florida—Toxic substances and the hydrologic sciences: American Institute of Hydrology, p. 408–416.

Stober, Q.J., Jones, R.D., and Scheidt, D.J., 1995, Ultra 

trace level mercury in the Everglades ecosystem, a 

multi-media canal pilot study: Water, Air, and Soil 

Pollution, v. 80, p. 991–1001.

Swancar, Amy, 1996, Water quality, pesticide occurrence, 

and effects of irrigation with reclaimed water at golf 

courses in Florida: U.S. Geological Survey WaterResources Investigations Report 95–4250, 85 p.

Swift, C.C., Gilbert, C.R., Bortone, S.A., Burgess, G.H., 

and Yerger, R.W., 1986, Zoogeography of the freshwater 

fishes of the southeastern United States—Savannah 

River to Lake Pontchartrain, in Hocutt, C.H. and Wiley, 

E.O., eds., The zoogeography of northern American 

freshwater fishes: New York, John Wiley and Sons, 

p. 213–265.

Thurman, E.M., Goolsby, D.A., Meyer, M.T., and Kolpin, 

D.W., 1991, Herbicides in surface waters of the Midwestern United States—The effect of the spring flush: Environmental Science and Technology, v. 25, p. 1794–1796.

Thurman, E.M., Goolsby, D.A., Meyer, M.T., Mills, M.S., 

Pomes, M.L., and Koplin, D.W., 1992, A reconnaissance 

study of herbicides and their metabolites in surface 

water of the Midwestern United States using immunoassay and gas chromatography/mass spectrometry: Environmental Science and Technology, v. 26, p. 2440–2447.

Thurman, E.M., Meyer, M.T., Pomes, M.L., Perry, C.A., 

and Schwab, P., 1990, Comparison of an enzyme-linked 

immunosorbent assay and gas chromatography/mass 

spectrometry for the analysis of herbicides in water: 

Analytical Chemistry, v. 62, p. 2043–2048.

U.S. Geological Survey, 2000, Pesticides in surface and 

ground water of the United States: Summary of results of 

the National Water-Quality Assessment Program 

(NAWQA): accessed Aug. 18, 2000, at http://wwwdcascr.wr.usgs.gov/pnsp/allsum_sw.html.

———1999, The quality of our Nation’s waters: U.S. Geological Survey Circular 1225, 82 p.

Ware, F. J., Royals, H., and Lange, T., 1990, Mercury contamination in Florida largemouth bass: Proceedings of 

the Annual Conference Southeastern Association of Fish 

and Wildlife Agencies, no. 44, p. 5–12. 
Water-Quality Data in a National Context 27 

Streams in agricultural areas 

Streams in urban areas

Streams and rivers draining mixed land uses 

Shallow ground water in agricultural areas

Shallow ground water in urban areas 

Major aquifers 

Detected concentration in Study Unit

Frequencies of detection, in percent. Detection frequencies 

were not censored at any common reporting limit. The lefthand column is the study-unit frequency and the right-hand 

column is the national frequency 

Not measured or sample size less than two

Study-unit sample size. For ground water, the number of 

samples is equal to the number of wells sampled

National ranges of detected concentrations, by land use, in 36 

NAWQA Study Units, 1991–98—Ranges include only samples

in which a chemical was detected

Drinking-water quality (applies to ground water and surface water)

Protection of aquatic life (applies to surface water only)

Prevention of eutrophication in streams not flowing directly into 

lakes or impoundments

No benchmark for drinking-water quality

No benchmark for protection of aquatic life

*

**

66 38

Other herbicides detected

Alachlor (Lasso, Bronco, Lariat, Bullet) **

Benfluralin (Balan, Benefin, Bonalan) * **

Bentazon (Basagran, Bentazone) **

Butylate (Sutan +, Genate Plus, Butilate) **

Cyanazine (Bladex, Fortrol) 

CHEMICALS IN WATER

Concentrations and detection frequencies, Southern Florida, 

1996–98—Detection sensitivity varies among chemicals and, thus, 

frequencies are not directly comparable among chemicals

Lowest

25 percent

Middle

50 percent

Highest

25 percent

National water-quality benchmarks

National benchmarks include standards and guidelines related to 

drinking-water quality, criteria for protecting the health of aquatic life, and 

a goal for preventing stream eutrophication due to phosphorus. Sources 

include the U.S. Environmental Protection Agency and the Canadian 

Council of Ministers of the Environment

|

|

|

--

This appendix is a summary of chemical concentrations 

and biological indicators assessed in Southern Florida. 

Selected results for this Study Unit are graphically 

compared to results from as many as 36 NAWQA Study 

Units investigated from 1991 to 1998 and to national 

water-quality benchmarks for human health, aquatic life, or 

fish-eating wildlife. The chemical and biological indicators 

shown were selected on the basis of frequent detection, 

detection at concentrations above a national benchmark, 

or regulatory or scientific importance. The graphs illustrate 

how conditions associated with each land use sampled in 

Southern Florida compare to results from across the 

Nation, and how conditions compare among the several 

land uses. Graphs for chemicals show only detected 

concentrations and, thus, care must be taken to evaluate 

detection frequencies in addition to concentrations when 

comparing study-unit and national results. For example, 

norflurazon concentrations in Southern Florida ground 

water in agricultural areas were similar to the national 

distribution, but the detection frequency was much higher 

(72 percent compared to 2 percent).

CONCENTRATION, IN MICROGRAMS PER LITER

 0.0001 0.001 0.01 0.1 1 10 100 1,000 

Study-unit frequency of detection, in percent

National frequency of detection, in percent

Pesticides in water—Herbicides

Study-unit sample size

12

Atrazine (AAtrex, Atrex, Atred, Gesaprim) 

95 88 | | 121 -- 86 | | 0 -- 87 | | 0

28 40 | 29 53 30 | 32 72 18 | 29

Bromacil (Hyvar X, Urox B, Bromax) 

18 1 | | 118 -- 2 | | 0 -- 1 | | 0

62 2 | 29 0 3 | 32 0 <1 | 29

2,4-D (Aqua-Kleen, Lawn-Keep, Weed-B-Gone) 9 15 | | 118 -- 18 | | 0 -- 11 | | 0

0 <1 | 26 0 1 | 32 0 <1 | 29

Deethylatrazine (Atrazine breakdown product) * ** 83 75 121 -- 62 0 -- 75 0

10 39 29 50 28 32 62 19 29

Diuron (Crisuron, Karmex, Diurex) **

18 13 | 118 -- 22 | 0 -- 20 | 0

48 4 | 29 12 3 | 32 52 2 | 29

Metolachlor (Dual, Pennant) 

63 81 | | 121 -- 64 | | 0 -- 83 | | 0

3 18 | 29 3 9 | 32 28 5 | 29

Norflurazon (Evital, Predict, Solicam, Zorial) * **

25 4 118 -- <1 0 -- 3 0

72 2 29 0 <1 32 3 <1 29

Simazine (Princep, Caliber 90) 64 61 | | 121 -- 77 | | 0 -- 74 | | 0

38 21 | 29 6 18 | 32 28 5 | 29

Tebuthiuron (Spike, Tebusan) 

56 22 | | 121 -- 39 | | 0 -- 32 | | 0

3 3 | 29 19 7 | 32 76 3 | 29

APPENDIX—WATER-QUALITY DATA FROM SOUTHERN FLORIDA IN 

A NATIONAL CONTEXT

For a complete view of Southern Florida data and for additional information about specific benchmarks used, visit our Web site at http://water.usgs.gov/nawqa/. 

Also visit the NAWQA Data Warehouse for access to NAWQA data sets at http://water.usgs.gov/nawqa/data. 
28 Water Quality in Southern Florida

CONCENTRATION, IN MICROGRAMS PER LITER

 0.0001 0.001 0.01 0.1 1 10 100 1,000 

DCPA (Dacthal, chlorthal-dimethyl) * **

Dicamba (Banvel, Dianat, Scotts Proturf) 

2,6-Diethylaniline (Alachlor breakdown product) * **

EPTC (Eptam, Farmarox, Alirox) * **

Fenuron (Fenulon, Fenidim) * **

Linuron (Lorox, Linex, Sarclex, Linurex, Afalon) * 

Metribuzin (Lexone, Sencor) 

Napropamide (Devrinol) * **

Prometon (Pramitol, Princep) **

Pronamide (Kerb, Propyzamid) **

Propanil (Stam, Stampede, Wham) * **

Terbacil (Sinbar) **

Triclopyr (Garlon, Grandstand, Redeem, Remedy) * **

Herbicides not detected

Acetochlor (Harness Plus, Surpass) * **

Acifluorfen (Blazer, Tackle 2S) **

Bromoxynil (Buctril, Brominal) * 

Chloramben (Amiben, Amilon-WP, Vegiben) **

Clopyralid (Stinger, Lontrel, Transline) * **

2,4-DB (Butyrac, Butoxone, Embutox Plus, Embutone) * **

Dacthal mono-acid (Dacthal breakdown product) * **

Dichlorprop (2,4-DP, Seritox 50, Lentemul) * **

Dinoseb (Dinosebe) 

Ethalfluralin (Sonalan, Curbit) * **

Fluometuron (Flo-Met, Cotoran) **

MCPA (Rhomene, Rhonox, Chiptox) 

MCPB (Thistrol) * **

Molinate (Ordram) * **

Neburon (Neburea, Neburyl, Noruben) * **

Oryzalin (Surflan, Dirimal) * **

Pebulate (Tillam, PEBC) * **

Pendimethalin (Pre-M, Prowl, Stomp) * **

Picloram (Grazon, Tordon) 

Propachlor (Ramrod, Satecid) **

Propham (Tuberite) **

2,4,5-T **

2,4,5-TP (Silvex, Fenoprop) **

Thiobencarb (Bolero, Saturn, Benthiocarb) * **

Triallate (Far-Go, Avadex BW, Tri-allate) * 

Trifluralin (Treflan, Gowan, Tri-4, Trific) 

Study-unit frequency of detection, in percent

National frequency of detection, in percent

Pesticides in water—Insecticides

Study-unit sample size

Volatile organic compounds (VOCs) in ground water

These graphs represent data from 16 Study Units, sampled from 1996 to 1998

Study-unit frequency of detection, in percent

National frequency of detection in percent Study-unit sample size

CONCENTRATION, IN MICROGRAMS PER LITER

 0.001 0.01 0.1 1 10 100 1,000 10,000 

Other VOCs detected

tert-Amylmethylether (tert-amyl methyl ether (TAME)) * 

Benzene 

Bromochloromethane (Methylene chlorobromide) 

Bromodichloromethane (Dichlorobromomethane) 

2-Butanone (Methyl ethyl ketone (MEK)) * 

Carbon disulfide * 

1-Chloro-2-methylbenzene (o-Chlorotoluene) 

Chlorobenzene (Monochlorobenzene) 

Chlorodibromomethane (Dibromochloromethane) 

Chloromethane (Methyl chloride) 

Dibromomethane (Methylene dibromide) * 

1,3-Dichlorobenzene (m-Dichlorobenzene) 

1,4-Dichlorobenzene (p-Dichlorobenzene) 

Dichlorodifluoromethane (CFC 12, Freon 12) 

1,1-Dichloroethane (Ethylidene dichloride) * 

1,1-Dichloroethene (Vinylidene chloride) 

trans-1,2-Dichloroethene ((E)-1,2-Dichlorothene) 

cis-1,2-Dichloroethene ((Z)-1,2-Dichloroethene) 

Dichloromethane (Methylene chloride) 

1,2-Dichloropropane (Propylene dichloride) 

Diethyl ether (Ethyl ether) * 

1,2-Dimethylbenzene (o-Xylene) 

1,3 & 1,4-Dimethylbenzene (m-&p-Xylene) 

1-4-Epoxy butane (Tetrahydrofuran, Diethylene oxide) * 

Ethylbenzene (Phenylethane) 

p-Isopropyltoluene (p-Cymene) * 

4-Methyl-2-pentanone (Methyl isobutyl ketone (MIBK)) * 

Methylbenzene (Toluene) 

Naphthalene 

2-Propanone (Acetone) * 

Tetrachloroethene (Perchloroethene) 

Tribromomethane (Bromoform) 

1,1,2-Trichloro-1,2,2-trifluoroethane (Freon 113) * 

Trichloroethene (TCE) 

Trichloromethane (Chloroform) 

1,2,4-Trimethylbenzene (Pseudocumene) *

Carbaryl (Carbamine, Denapon, Sevin) 7 9 | | 121 -- 46 | | 0 -- 16 | | 0

0 <1 | 29 0 2 | 32 0 1 | 29

p,p'-DDE 2 8 | | 121 -- 2 | | 0 -- 4 | | 0

3 4 | 29 0 2 | 32 7 2 | 29

Other insecticides detected 

Carbofuran (Furadan, Curaterr, Yaltox) 

Chlorpyrifos (Brodan, Dursban, Lorsban) 

Dieldrin (Panoram D-31, Octalox, Compound 497) 

Ethoprop (Mocap, Ethoprophos) * **

Malathion (Malathion) 

Methomyl (Lanox, Lannate, Acinate) **

Methyl parathion (Penncap-M, Folidol-M) **

Propoxur (Baygon, Blattanex, Unden, Proprotox) * **

Insecticides not detected

Aldicarb (Temik, Ambush, Pounce) 

Aldicarb sulfone (Standak, aldoxycarb) 

Aldicarb sulfoxide (Aldicarb breakdown product) 

Azinphos-methyl (Guthion, Gusathion M) * 

Diazinon (Basudin, Diazatol, Neocidol, Knox Out) 

Disulfoton (Disyston, Di-Syston) **

Fonofos (Dyfonate, Capfos, Cudgel, Tycap) **

alpha-HCH (alpha-BHC, alpha-lindane) **

gamma-HCH (Lindane, gamma-BHC) 

3-Hydroxycarbofuran (Carbofuran breakdown product) * **

Methiocarb (Slug-Geta, Grandslam, Mesurol) * **

Oxamyl (Vydate L, Pratt) **

Parathion (Roethyl-P, Alkron, Panthion, Phoskil) * 

cis-Permethrin (Ambush, Astro, Pounce) * **

Phorate (Thimet, Granutox, Geomet, Rampart) * **

Propargite (Comite, Omite, Ornamite) * **

Terbufos (Contraven, Counter, Pilarfox) **

Chloroethene (Vinyl chloride) 1 

0 1 | 32 7 <1 | 29

Methyl tert-butyl ether (MTBE) 1 

0 4 | 12 3 16 | 32 31 6 | 29

1 Many of the samples in this study were diluted prior to laboratory analysis and therefore the 

actual detection frequency may be larger than the value listed.
Water-Quality Data in a National Context 29 

CONCENTRATION, IN MILLIGRAMS PER LITER

 0.001 0.01 0.1 1 10 100 1,000 10,000 100,000 

CONCENTRATION, IN MILLIGRAMS PER LITER

 0.001 0.01 0.1 1 10 100 1,000 10,000 100,000 

Nutrients in water

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

CONCENTRATION, IN MILLIGRAMS PER LITER

 0.001 0.01 0.1 1 10 100 1,000 10,000 100,000 

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

Dissolved solids in water

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

VOCs not detected

Bromobenzene (Phenyl bromide) * 

Bromoethene (Vinyl bromide) * 

Bromomethane (Methyl bromide) 

n-Butylbenzene (1-Phenylbutane) * 

sec-Butylbenzene * 

tert-Butylbenzene * 

3-Chloro-1-propene (3-Chloropropene) * 

1-Chloro-4-methylbenzene (p-Chlorotoluene) 

Chloroethane (Ethyl chloride) * 

1,2-Dibromo-3-chloropropane (DBCP, Nemagon) 

1,2-Dibromoethane (Ethylene dibromide, EDB) 

trans-1,4-Dichloro-2-butene ((Z)-1,4-Dichloro-2-butene) * 

1,2-Dichlorobenzene (o-Dichlorobenzene) 

1,2-Dichloroethane (Ethylene dichloride) 

2,2-Dichloropropane * 

1,3-Dichloropropane (Trimethylene dichloride) * 

trans-1,3-Dichloropropene ((E)-1,3-Dichloropropene) 

cis-1,3-Dichloropropene ((Z)-1,3-Dichloropropene) 

1,1-Dichloropropene * 

Diisopropyl ether (Diisopropylether (DIPE)) * 

Ethenylbenzene (Styrene) 

Ethyl methacrylate * 

Ethyl tert-butyl ether (Ethyl-t-butyl ether (ETBE)) * 

1-Ethyl-2-methylbenzene (2-Ethyltoluene) * 

Hexachlorobutadiene 

1,1,1,2,2,2-Hexachloroethane (Hexachloroethane) 

2-Hexanone (Methyl butyl ketone (MBK)) * 

Iodomethane (Methyl iodide) * 

Isopropylbenzene (Cumene) * 

Methyl acrylonitrile * 

Methyl-2-methacrylate (Methyl methacrylate) * 

Methyl-2-propenoate (Methyl acrylate) * 

2-Propenenitrile (Acrylonitrile) 

n-Propylbenzene (Isocumene) * 

1,1,2,2-Tetrachloroethane * 

1,1,1,2-Tetrachloroethane 

Tetrachloromethane (Carbon tetrachloride) 

1,2,3,4-Tetramethylbenzene (Prehnitene) * 

1,2,3,5-Tetramethylbenzene (Isodurene) * 

1,2,4-Trichlorobenzene 

1,2,3-Trichlorobenzene * 

1,1,1-Trichloroethane (Methylchloroform) 

1,1,2-Trichloroethane (Vinyl trichloride) 

Trichlorofluoromethane (CFC 11, Freon 11) 

1,2,3-Trichloropropane (Allyl trichloride) 

1,2,3-Trimethylbenzene (Hemimellitene) * 

1,3,5-Trimethylbenzene (Mesitylene) *

CONCENTRATION, IN PICOCURIES PER LITER

Trace elements in ground water

Arsenic 

77 58 | 31 69 36 | 32 45 37 | 29

Chromium 

100 85 | 31 94 79 | 32 90 73 | 29

Radon-222 

-- 99 | 0 100 100 | 32 100 97 | 29

Uranium 

58 64 | 31 56 35 | 32 31 33 | 29

CONCENTRATION, IN MICROGRAMS PER LITER

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

 0.01 0.1 1 10 100 1,000 10,000 100,000 

 0.01 0.1 1 10 100 1,000 10,000 100,000 

Ammonia, as N * **

98 84 132 -- 86 0 89 75 87

90 78 29 94 71 32 93 70 29

Dissolved ammonia plus organic nitrogen, as N * ** 100 78 131 -- 74 0 100 62 87

100 28 29 97 30 32 93 24 29

Dissolved nitrite plus nitrate, as N ** 86 95 | 132 -- 97 | 0 92 91 | 87

41 81 | 29 28 74 | 32 52 71 | 29

Orthophosphate, as P * **

76 79 131 -- 72 0 100 74 86

90 59 29 66 52 32 97 61 29

Total phosphorus, as P * ** 100 92 | 130 -- 90 | 0 100 88 | 81

Dissolved solids * ** 100 100 131 -- 100 0 100 100 86

100 100 29 100 100 32 100 100 29
30 Water Quality in Southern Florida

Fish tissue from streams in agricultural areas

Fish tissue from streams in urban areas

Fish tissue from streams draining mixed land uses

Sediment from streams in agricultural areas 

Sediment from streams in urban areas 

Sediment from streams draining mixed land uses

Protection of fish-eating wildlife (applies to fish tissue)

Protection of aquatic life (applies to bed sediment)

No benchmark for protection of fish-eating wildlife

No benchmark for protection of aquatic life

|

|

**

CHEMICALS IN FISH TISSUE

AND BED SEDIMENT

Concentrations and detection frequencies, Southern Florida, 

1996–98—Detection sensitivity varies among chemicals and, thus, 

frequencies are not directly comparable among chemicals. Study-unit 

frequencies of detection are based on small sample sizes; the 

applicable sample size is specified in each graph

Lowest

25 percent

Middle

50 percent

Highest

25 percent

National benchmarks for fish tissue and bed sediment

National benchmarks include standards and guidelines related to 

criteria for protection of the health of fish-eating wildlife and aquatic 

organisms. Sources include the U.S. Environmental Protection Agency, 

other Federal and State agencies, and the Canadian Council of 

Ministers of the Environment

*

Other organochlorines detected

Dieldrin+aldrin (sum of dieldrin and aldrin) **

Endosulfan I (alpha-Endosulfan, Thiodan) * **

Mirex (Dechlorane) **

Organochlorines not detected

Chloroneb (Chloronebe, Demosan) * **

DCPA (Dacthal, chlorthal-dimethyl) * **

Endrin (Endrine) 

gamma-HCH (Lindane, gamma-BHC, Gammexane) * 

Total-HCH (sum of alpha-HCH, beta-HCH, gamma-HCH, and delta-HCH) **

Heptachlor epoxide (Heptachlor breakdown product) * 

Heptachlor+heptachlor epoxide (sum of heptachlor and heptachlor epoxide) **

Hexachlorobenzene (HCB) **

Isodrin (Isodrine, Compound 711) * **

p,p'-Methoxychlor (Marlate, methoxychlore) * **

o,p'-Methoxychlor * **

Pentachloroanisole (PCA) * **

cis-Permethrin (Ambush, Astro, Pounce) * **

trans-Permethrin (Ambush, Astro, Pounce) * **

Toxaphene (Camphechlor, Hercules 3956) * **

CONCENTRATION, IN MICROGRAMS PER KILOGRAM

(Fish tissue is wet weight; bed sediment is dry weight)

 0.1 1 10 100 1,000 10,000 100,000 

CONCENTRATION, IN MICROGRAMS PER KILOGRAM

(Fish tissue is wet weight; bed sediment is dry weight)

 0.1 1 10 100 1,000 10,000 100,000 

National ranges of concentrations detected, by land use, in 36 

NAWQA Study Units, 1991–98—Ranges include only samples

in which a chemical was detected

Detected concentration in Study Unit

Frequencies of detection, in percent. Detection frequencies 

were not censored at any common reporting limit. The lefthand column is the study-unit frequency and the right-hand 

column is the national frequency

Not measured or sample size less than two

Study-unit sample size

66 38

--

12

Organochlorines in fish tissue (whole body)

and bed sediment

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

2 The national detection frequencies for total PCB in sediment are biased low because about 

30 percent of samples nationally had elevated detection levels compared to this Study Unit. 

See http://water.usgs.gov/nawqa/ for additional information.

Other trace elements detected

Lead 

Selenium 

Zinc

Trace elements not detected

Cadmium 

Total Chlordane (sum of 5 chlordanes) 

33 38 | 12 -- 75 | 1 0 56 | 8

33 9 | 3 -- 57 | 0 0 11 | 4

o,p'+p,p'-DDD (sum of o,p'-DDD and p,p'-DDD) * 

50 49 12 -- 69 1 0 50 8

100 27 | 3 -- 50 | 0 0 20 | 4

p,p'-DDE * ** 92 90 12 -- 94 1 88 92 8

100 48 3 -- 62 0 50 39 4

o,p'+p,p'-DDE (sum of o,p'-DDE and p,p'-DDE) * 

92 90 12 -- 94 1 88 92 8

100 48 | 3 -- 62 | 0 50 39 | 4

Total DDT (sum of 6 DDTs) **

92 90 | 12 -- 94 | 1 88 93 | 8

100 49 3 -- 66 0 50 41 4

o,p'+p,p'-DDT (sum of o,p'-DDT and p,p'-DDT) * 

33 31 12 -- 53 1 0 29 8

33 19 | 3 -- 38 | 0 0 11 | 4

Dieldrin (Panoram D-31, Octalox) * 42 53 12 -- 42 1 0 38 8

33 13 | 3 -- 30 | 0 0 9 | 4

Total PCB 2

17 38 | 12 -- 81 | 1 0 66 | 8

33 2 | 3 -- 21 | 0 0 9 | 4
Water-Quality Data in a National Context 31 

CONCENTRATION, IN MICROGRAMS PER KILOGRAM, DRY WEIGHT

 0.1 1 10 100 1,000 10,000 100,000 

Study-unit frequency of detection, in percent

National frequency of detection, in percent

Semivolatile organic compounds (SVOCs)

in bed sediment

Study-unit sample size

Other SVOCs detected

Acenaphthene 

Acenaphthylene 

Acridine **

Anthracene 

Benz[a]anthracene 

Benzo[a]pyrene 

Benzo[b]fluoranthene **

Benzo[ghi]perylene **

Benzo[k]fluoranthene **

Butylbenzylphthalate **

Chrysene 

p-Cresol **

Di-n-butylphthalate **

Di-n-octylphthalate **

Dibenz[a,h]anthracene 

Diethylphthalate **

1,6-Dimethylnaphthalene **

Dimethylphthalate **

9H-Fluorene (Fluorene) 

Indeno[1,2,3-cd]pyrene **

1-Methyl-9H-fluorene **

2-Methylanthracene **

4,5-Methylenephenanthrene **

1-Methylphenanthrene **

1-Methylpyrene **

Naphthalene 

Phenanthrene 

Phenanthridine **

Pyrene 

2,3,6-Trimethylnaphthalene **

SVOCs not detected

C8-Alkylphenol **

Azobenzene **

Benzo[c]cinnoline **

2,2-Biquinoline **

4-Bromophenyl-phenylether **

4-Chloro-3-methylphenol **

bis(2-Chloroethoxy)methane **

2-Chloronaphthalene **

2-Chlorophenol **

4-Chlorophenyl-phenylether **

1,2-Dichlorobenzene (o-Dichlorobenzene) **

1,3-Dichlorobenzene (m-Dichlorobenzene) **

1,4-Dichlorobenzene (p-Dichlorobenzene) **

1,2-Dimethylnaphthalene **

3,5-Dimethylphenol **

2,4-Dinitrotoluene **

2-Ethylnaphthalene **

Isophorone **

Isoquinoline **

Nitrobenzene **

N-Nitrosodi-n-propylamine **

N-Nitrosodiphenylamine **

Pentachloronitrobenzene **

Quinoline **

1,2,4-Trichlorobenzene **

CONCENTRATION, IN MICROGRAMS PER GRAM

(Fish tissue is wet weight, bed sediment is dry weight)

 0.01 0.1 1 10 100 10,000 1,000 

Study-unit frequency of detection, in percent

National frequency of detection, in percent

Trace elements in fish tissue (livers) and 

bed sediment

Study-unit sample size

Anthraquinone **

33 21 3 -- 83 0 25 39 4

9H-Carbazole **

67 19 3 -- 76 0 50 33 4

Dibenzothiophene **

67 12 3 -- 64 0 25 30 4

2,6-Dimethylnaphthalene **

100 65 3 -- 74 0 100 77 4

bis(2-Ethylhexyl)phthalate **

100 91 3 -- 99 0 100 95 4

Fluoranthene 

100 66 | 3 -- 97 | 0 100 78 | 4

Phenol **

100 81 3 -- 82 0 100 80 4

Arsenic * 

100 56 7 -- 38 1 80 76 5

100 99 | 3 -- 98 | 0 33 97 | 3

Cadmium * 

57 77 7 -- 72 1 80 95 5

100 98 | 3 -- 100 | 0 33 98 | 3

Chromium * 29 62 7 -- 72 1 0 54 5

100 100 | 3 -- 99 | 0 100 100 | 3

Copper * 100 100 7 -- 100 1 100 100 5

100 100 | 3 -- 99 | 0 100 100 | 3
32 Water Quality in Southern Florida

Biological indicator value, Southern Florida, by land use, 

1996–98

Biological status assessed at a site

National ranges of biological indicators, in 16 NAWQA Study 

Units, 1994–98

Streams in undeveloped areas

Streams in agricultural areas

Streams in urban areas

Streams in mixed-land-use areas

75th percentile

25th percentile

BIOLOGICAL INDICATORS

Higher national scores suggest habitat disturbance, water-quality 

degradation, or naturally harsh conditions. The status of algae, 

invertebrates (insects, worms, and clams), and fish provide a 

record of water-quality and stream conditions that waterchemistry indicators may not reveal. Algal status focuses on the 

changes in the percentage of certain algae in response to 

increasing siltation, and it often correlates with higher nutrient 

concentrations in some regions. Invertebrate status averages 11 

metrics that summarize changes in richness, tolerance, trophic 

conditions, and dominance associated with water-quality 

degradation. Fish status sums the scores of four fish metrics 

(percent tolerant, omnivorous, non-native individuals, and percent 

individuals with external anomalies) that increase in association 

with water-quality degradation

 0 10 20 30 40 50 60 70 80 90 100

CONCENTRATION, IN MICROGRAMS PER GRAM

(Fish tissue is wet weight, bed sediment is dry weight)

 0.01 0.1 1 10 100 10,000 1,000 

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

 0 5 10 15 20

 Algal status indicator

Undeveloped

Agricultural

Urban

Mixed

 Invertebrate status indicator

Undeveloped

Agricultural

Urban

Mixed

 Fish status indicator

Undeveloped

Agricultural

Urban

Mixed

Lead * 

0 11 7 -- 41 1 20 41 5

100 100 | 3 -- 100 | 0 100 99 | 3

Mercury * 

100 71 7 -- 59 1 100 80 5

100 82 | 3 -- 97 | 0 100 93 | 2

Nickel * **

29 42 7 -- 44 1 60 50 5

100 100 3 -- 100 0 100 100 3

Selenium * 100 99 7 -- 100 1 100 99 5

-- 100 | 0 -- 100 | 0 -- 100 | 0

Zinc * 

100 100 7 -- 100 1 100 100 5

100 100 | 3 -- 99 | 0 100 100 | 3
A COORDINATED EFFORT

Coordination among agencies and organizations is an integral part of the NAWQA Program. We thank the following agencies and organizations who contributed data used in this report or participated in the Study Unit liaison 

committee.

Federal Organizations Native American

National Park Service Miccosukee Tribe of Indians of Florida

National Oceanic and Atmospheric Administration Seminole Tribe of Florida

U.S. Army Corps of Engineers

U.S. Department of Agriculture Universities

U.S. Environmental Protection Agency University of Miami

U.S. Fish and Wildlife Service University of Florida

National Marine Fisheries Service Florida International University 

State Agencies

Florida Marine Research Institute Local Agencies

Florida Department of Agriculture and Consumer Services City of Naples

Florida Department of Environmental Protection Metropolitan Dade County

Florida Game and Freshwater Fish Commission Palm Beach County

Florida Geological Survey Broward County

Florida Park Service Collier County

South Florida Water Management District

Southwest Florida Water Management District

Private Organizations

Nature Conservancy 

Special thanks to U.S. Geological Survey employees for their contributions:

Bruce Bernard, lead technician for SOFL, John Byrnes, Mark Zucker for data collection. Becky Deckard, Teresa Embry, Pat Mixson, and

Ron Spencer for production of the report, including editing, layout, and illustrations. Michael Meyers for his contribution on pesticide degradation.

Appreciation also is extended to those individuals and agencies that reviewed this report: Edward Oaksford, U.S. Geological Survey, 

Michael Thurman, U.S. Geological Survey, Richard Pfeuffer, South Florida Water Management District.
McPherson and others— Water Quality in Southern Florida

U.S. Geological Survey Circular 1207

National Water-Quality Assessment (NAWQA) Program

Southern Florida

Lake

Okeechobee

Miami

Tampa

Kissimmee R.

Caloosahatchee R.

Peace River

NAWQA