Water Quality in Big Cypress National 

Preserve and Everglades National 

Park—Trends and Spatial Characteristics

of Selected Constituents

By Ronald L. Miller, U.S. Geological Survey, St. Petersburg, Florida;

Benjamin F. McPherson, U.S. Geological Survey, Tampa, Florida; and

Robert Sobczak, and Christine Clark, Big Cypress National Preserve, Ochopee, Florida

U.S. Department of the Interior

U.S. Geological Survey

Water Resources Investigations Report 03-4249
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virgina: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.
iii

Contents

Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Data Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Objective and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Problems in Long-Term Trend Analyses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Trends in Rainfall, Water Levels, and Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Water Quality in South Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Water Quality Changes Over Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Eastern Everglades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Taylor Slough Bridge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Shark River Slough. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Western Everglades and Big Cypress Swamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Site P-34 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Bridge 105 Site. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Spatial Patterns in Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Park Boundary Water-Quality Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

L-28 Interceptor (L-28I) Drainage System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Barron River Canal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

S-12s Gated Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

L-31 Canal and C-111 Canals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Median Concentrations of Selected Constituents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Trace Elements in Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Pesticides and Other Organic Compounds in Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Pesticides and Other Organic Compounds in Bed Sediment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Water-Quality Monitoring Network Design for Future Studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figures

1. Map showing Big Cypress National Preserve and Everglades National Park with major 

features and sampling sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

2. Timeline showing major human and climatic events that might affect water quality . . . . . . . . . . . . . . . . .3

3-13. Graphs showing:

3. Average annual rainfall at 20 sites in south Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

4. Average monthly water elevation in feet above NGVD29 at wells S-196 and S-196A 

near Homestead, Florida . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

5. Average annual discharge under the Tamiami Trail. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

6. Average annual discharge at S-332. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
iv

7. Stage (water level) and water-quality data with loess smooth lines for period of record at 

Taylor Slough Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

8. Variation in stage and concentration of total phosphorus with time, and variation of 

concentration of total phosphorus with discharge at Taylor Slough Bridge. . . . . . . . . . . . . . . . . . 12

9. Stage (water level) and water-quality data with loess smooth lines for the period of record 

at P-33. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

10. Concentration of sulfate at P-33 and discharge under Tamiami Trail; sulfate at P-33 and 

stage; total phosphorus at P-33 and stage; and chloride concentration at P-34 and stage. . . . 14

11. Stage (water level) and water-quality data with loess smooth lines for period of record 

at P-34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

12. Stage (water level) and water-quality data with loess smooth lines for period of record 

at Bridge 105 and 40-Mile Bend section. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

13. Stage (water level) and concentration and water level at Bridge 105 and concentrations 

of sulfate (times 100) and total phosphorus (times 1,000) at Bridge 105 from January 1996 

to January 1999. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

14-20. Maps showing:

14. Median specific conductance at Big Cypress National Preserve and Everglades 

National Park sites and nearby canal sites, 1991-2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

15. Median chloride concentrations at Big Cypress National Preserve and Everglades 

National Park sites and nearby canal sites, 1991-2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

16. Median sulfate concentrations at Big Cypress National Preserve and Everglades National 

Park sites and nearby canal sites, 1991-2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

17. Median total phosphorus concentrations at Big Cypress National Preserve and Everglades

National Park sites and nearby canal sites, 1991-2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

18. Median total nitrogen concentrations at Big Cypress National Preserve and Everglades

National Park sites and nearby canal sites, 1991-2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

19. Median concentrations of nitrite plus nitrate at Big Cypress National Preserve and 

Everglades National Park sites and nearby canal sites, 1991-2000. . . . . . . . . . . . . . . . . . . . . . . . . . . 25

20. Median concentrations of ammonia plus ammonium ion at Big Cypress National Preserve 

and Everglades National Park sites and nearby canal sites, 1991-2000 . . . . . . . . . . . . . . . . . . . . . . 26

21. Boxplots showing trace element concentrations in water at Big Cypress National Preserve 

and Everglades National Park sites and nearby canal sites, 1991-2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Tables

1. Summary of most frequently detected pesticides and other organic compounds in water 

for the period of record at selected sites in and near Big Cypress National Preserve 

and Everglades National Park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2. Most frequently detected pesticides and other organic compounds in water for period of 

record at selected sites in and near Big Cypress National Preserve and 

Everglades National Park. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3. Most frequently detected pesticides and other organic compounds in bed sediment at seven 

canal sites near Big Cypress National Preserve and Everglades National Park. . . . . . . . . . . . . . . . . . . . 30
v

Conversion Factors, Acronyms, Abbreviations, 

and Datums

Acronyms and Abbreviations

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD29); horizontal coordinate information is referenced to the North American Datum of 1927 

(NAD27).

Multiply By To obtain

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2

) 2.59 square kilometer (km2)

foot per day (ft/d) 0.3048 meter per day (m/d)

foot squared per day (ft2/d) 0.0929 meter squared per day (m2/d)

cubic foot per day (ft3/d) 0.028317 cubic meter per day (m3/d)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

foot per year (ft/yr) 0.3048 meter per year (m/yr)

BICY Big Cypress National Preserve

DOM Dissolved organic matter

EVER Everglades National Park

μg/kg micrograms per kilogram

μg/L micrograms per liter

μS/cm microsiemens per centimeter

mg/L milligrams per liter

NPS National Park Service

OFW Outstanding Florida Waters

ONRW Outstanding Natural Resource Waters

SOFIA South Florida Information Exchange

SFWMD South Florida Water Management District

TSB Taylor Slough bridge

TN Total nitrogen

TP Total phosphorus

USGS U.S. Geological Survey
vi
Water Quality in Big Cypress National Preserve and 

Everglades National Park—Trends and Spatial 

Characteristics of Selected Constituents

By Ronald L. Miller, U.S. Geological Survey, St. Petersburg, Florida;

Benjamin F. McPherson, U.S. Geological Survey, Tampa, Florida; and

Robert Sobczak, and Christine Clark, Big Cypress National Preserve, Ochopee, Florida

Abstract

Seasonal changes in water levels and flows in Big 

Cypress National Preserve (BICY) and Everglades National 

Park (EVER) affect water quality. As water levels and flows 

decline during the dry season, physical, geochemical and 

biological processes increase the breakdown of organic 

materials and the build-up of organic waste, nutrients, and 

other constituents in the remaining surface water. For example, concentrations of total phosphorus in the marsh are less 

than 0.01 milligram per liter (mg/L) during much of the year. 

Concentrations can rise briefly above this value during the 

dry season and occasionally exceed 0.1 mg/L under drought 

conditions.

Long-term changes in water levels, flows, water 

management, and upstream land use also affect water quality 

in BICY and EVER, based on analysis of available data 

(1959-2000). During the 1980’s and early 1990’s, specific 

conductance and concentrations of chloride increased in the 

Taylor Slough and Shark River Slough. Chloride 

concentrations more than doubled from 1960 to 1990, 

primarily due to greater canal transport of high dissolved 

solids into the sloughs. Some apparent long-term trends in 

sulfate and total phosphorus were likely attributable, at least 

in part, to high percentages of less-than and zero values and 

to changes in reporting levels over the period of record. High 

values in nutrient concentrations were evident during dry 

periods of the 1980’s and were attributable either to 

increased canal inflows of nutrient-rich water, increased 

nutrient releases from breakdown of organic bottom 

sediment, or increased build-up of nutrient waste from 

concentrations of aquatic biota and wildlife in remaining 

ponds. Long-term changes in water quality over the period of 

record are less pronounced in the western Everglades and the 

Big Cypress Swamp; however, short-term seasonal and 

drought-related changes are evident.

Water quality varies spatially across the region because 

of natural variations in geology, hydrology, and vegetation 

and because of differences in water management and land 

use. Nutrient concentrations are relatively low in BICY and 

EVER compared with concentrations in parts of the northern 

Everglades that are near agricultural and urban lands. Concentrations of total phosphorus generally are higher in BICY 

(median values, 1991-2000, were mostly greater than 

0.015 mg/L) than in EVER (median values, 1991-2000, less 

than 0.01 mg/L), probably because of higher phosphorus in 

natural sources such as shallow soils, rocks, and ground 

water in the Big Cypress region than in the Everglades 

region. Conversely, concentrations of chloride and sulfate 

are higher in EVER (median values in Shark River Slough, 

1991-2000, mostly greater than 2 mg/L sulfate and 50 mg/L 

chloride) than in BICY (median values, 1991-2000, less than 

1 mg/L sulfate and at most sites less than 20 mg/L chloride), 

probably because of the canal transport system, which conveys more water from an agricultural source into EVER than 

into BICY.

Trace elements and contaminants such as pesticides 

and other toxic organic compounds are in relatively low 

concentrations in BICY and EVER compared with 

concentrations in parts of the northern Everglades near 

agricultural and urban sources. Concentrations rarely 

exceeded aquatic life criteria in BICY and EVER. Atrazine 

was the only pesticide found in water that exceeded the 

criteria (in 2 out of 304 samples). The pesticides heptachlor 

expoxide, lindane, and p,p′ -DDE exceeded criteria in canal 

bed sediments in 1, 2, and 16 percent of the samples, 

respectively.
2 Water Quality in Big Cypress National Preserve and Everglades National Park

Introduction

The extreme southern tip of the Florida peninsula is an 

extensive subtropical wetland that includes the Everglades, the 

Big Cypress Swamp, and the coastal mangrove forests (fig. 1). 

The Everglades is a wide, flat expanse of grassland and tree 

islands that historically served as the primary drainage path for 

runoff from water overflowing the southern bank of Lake 

Okeechobee, as well as from direct rainfall. Water drains south 

and southwest toward Florida Bay and the Gulf of Mexico. The 

Big Cypress Swamp, west of the Everglades, is characterized by 

cypress domes, elongated bands of cypress trees called strands, 

and meandering marshy areas called sloughs. Water in the Big 

Cypress Swamp generally drains southwest towards the coast.

South Florida wetlands are dominated by a "sheetflow" 

flooding regime, thus named because the landscape becomes 

covered with a shallow (1-3 ft deep) and continuous expanse of 

water during the wet season (generally during the summer and 

fall) that flows at a slow velocity towards the coast. Land 

surface differences of less than 3 ft determine the distribution 

and abundance of plant communities (sawgrass prairie, marsh, 

pinelands, cypress, hardwood hammocks), and influence the 

volume, timing, and duration of surface-water flows. Drainage 

basins are often difficult to define because of the relative 

flatness of the south Florida landscape and the redirection of 

water with gates and pumps.

Major physical alteration of the landscape and associated 

water management practices, including canal and levee 

Everglades

National

Park

Gulf of Mexico

Florida Bay

0 5 MILES

Everglades

Agricultural Area

Miami Canal

L-28N

New River

Canal

Interceptor

Canal

L-28I

North

West

Feeder

Feeder

Taylor

Slough

Shark

River

Slough

L-67 Ext

L-28

L-67 A

Barron

River Ca

n

al

L-67 C

75

A5

C-111

S-332

L-28

STATION Location

and number

CONTROL

STRUCTURE

Location and number

LEVEE Location

and number

−

−

−

EXPLANATION

Alligator Alley

Ponce de

Leon Bay

Whitewater

Bay

40 Mile

Bend

Tamiami Trail 41

Monroe

Turner

River

NE1

S-190

S-140

AB

AB C D

S-344

S-343

S-12sS-333

S-332

S-177

S-18C

Big Cypress

National Preserve

L-31

Water

Conservation

Area 3A

A2 A12

A1

A3

A13

BR105

(A6)

A14

A4

A9

A5

P-37

TSB

P-35

P-34

P-36

P-33

EP

NP-201 US41

Chokoloskee

Bay

Water

Conservation

Area 2A

Fakahatchee Strand

LOCATION OF

STUDY AREA

Florida

EVERGLADES

BIG CYPRESS

SWAMP

Figure 1. Map showing Big Cypress National Preserve and Everglades National Park and major 

features and sampling sites.
Introduction 3

construction, agriculture and residential development, and 

operation of pumps and flood gates in the 1900’s, have substantially altered the volume, timing, distribution, and quality of 

surface water in this system (fig. 2). Everglades National Park 

(EVER, established in 1947) and Big Cypress National Preserve (BICY, established in 1974) were both established by 

Congress to preserve and protect large areas of the south Florida 

ecosystem that had remained relatively intact and free of agricultural and urban development. Waters in BICY and EVER 

currently are designated by the State of Florida as Outstanding 

Florida Waters (OFW) and Outstanding Natural Resource 

Waters (ONRW), respectively. However, because these waters 

are located at the downgradient end of the altered system, they 

are subject to the effects of upstream water management practices. Water flow and water quality in EVER are most affected 

because the Park receives surface water from canals that drain 

nutrient-enriched upstream agricultural lands. In comparison, 

water quality in BICY has remained relatively unaffected by 

upstream land use because the original BICY boundary encompassed a predominantly self-contained, rain-driven watershed, 

in which headwater flows were diverted into bypass canals 

around and downstream of the Preserve. To the east of BICY, 

headwaters flowed into the northeast corner of Water Conservation Area (WCA) 3A through the L-28 Interceptor (L-28I) canal 

drainage system, and to the west of BICY, headwaters flowed 

from agricultural areas in the north down the Barron River 

Canal into Chokoloskee Bay (fig. 1). The threat posed to the 

quality of water in the Preserve by these upstream sources has 

increased recently because: (1) new areas to the northeast and 

west have been included in the preserve's boundaries by Congressional legislation and include lands that either abut or 

encompass these bypass canals; (2) future restoration plans 

include diverting a portion of the canal waters into the preserve 

that previously had bypassed it; and (3) land-use activities that 

impair water quality have intensified in the upstream watersheds. Similar concerns are raised for EVER because of its 1989 

1900-09 1910-19 1920-29 1930-39 1940-49 1950-59 1960-69 1970-79 1980-89 1990-99

Unregulated

flows

Tamiami Trail and canal

construction inititiated

Last unimpeded flows

from Lake Okeechobee

to Everglades occur

Tamiami Trail

and canal

completed

Everglades

National Park

established

Central and Southern Florida

Flood Control Project begins

L-31 canal

extended

south of

Tamiami

Trail

L-31 canal

construction

begins

L-67 and L-28

canals

constructed

Everglades

Forever Act

begins

Rainfall Plan

initiated

for S-12s

S-332 begins

pumping water

into Taylor Slough

Main C-111 canal

system completed

Central and Southern Florida

Flood Control Project

nearly completed

Comprehensive

Everglades

Restoration Plan

(CERP) begins

L-67

extended

9.5 miles

south of

Tamiami

Trail

Barron River road,

railgrade, and canal

completed

Logging and farming

occur in the

Big Cypress Swamp

Construction of

Turner River, Birdon,

and Wagon Wheel roads

L-28 canal and levee

completed, and Water

Conservation Areas closed

L-28 Interceptor

and Tieback

constructed

Big Cypress

National

Preserve

established

S-343 (A and B) and S-344

constructed to allow more

flow into Big Cypress Swamp

Stopgate weirs

added to Barron

River Canal

Work performed

to restore flows to

the Turner River

Figure 2. Timeline showing major human and climatic events that might affect water quality.
4 Water Quality in Big Cypress National Preserve and Everglades National Park

boundary expansion into the northeastern portion of Shark 

River Slough where future restoration efforts will increase 

water levels and flows. As a result, water quality in BICY and 

EVER will become increasingly vulnerable to degradation as 

land development (especially conversion to high intensity agricultural activities) along upstream boundaries is coupled with 

restoration activities that increase surface-water flows into the 

Park and Preserve.

Data Sources

Water-quality analyses and studies have been conducted in 

EVER for over four decades and have increased in number and 

scope in recent years. The most extensive water-quality database is maintained by the South Florida Water Management 

District (SFWMD) and includes data collected since 1984. 

SFWMD has recently begun publishing annual summaries of 

these data (for example, see South Florida Water Management 

District, 2000), including baseline conditions (October 1, 1987-

September 30, 1988) and yearly exceedances from Class III criteria in EVER (Florida Department of Environmental Protection, 

1996, Criteria for surface water; Class III: Recreation, propagation and maintenance of a healthy well-balanced population of 

fish and wildlife). In addition, SFWMD has monitored pesticide 

residues in water and sediment in canals that are near EVER for 

more than 10 years and now posts quarterly summaries of the 

data at http://www.sfwmd.gov/curre/pest/pestindex.htm. 

Water-quality data collection and studies in BICY have been 

fewer, but extend back to at least the early 1970’s when the proposed Big Cypress “Jetport” triggered a flurry of environmental 

investigations (Duever and others, 1979; Klein and others, 1970 

and 1975; U.S. Department of the Interior, 1969).

Networks of hydrologic monitoring stations (hydrostations) are maintained in BICY and EVER to measure the surface-water level (stage) and monitor water-quality conditions 

(fig. 1). Data have been collected at these sites since 1984, providing a historical baseline for assessing hydrologic conditions 

and making a wide range of management decisions. Collection 

and analysis of water-quality samples at BICY and EVER are 

performed under cooperative agreements with the SFWMD. 

Under these agreements, the National Park Service (NPS) collects water samples in the field and the SFWMD provides sampling equipment and laboratory analysis (Germain, 1998). In 

EVER, water-quality samples have been collected at nine 

“internal marsh” sites on a monthly basis since 1984. In BICY, 

water-quality samples have been collected at 10 “internal” sites 

on a bimonthly basis since 1995. In recent years, the number of 

sampling sites increased to 14. Additional water-quality data 

were analyzed by a private laboratory (Thornton Laboratories, 

Inc., Tampa, Florida) between 1988 and 1994, but not under the 

agreement with SFWMD. Water-quality data collected at the 

BICY and EVER stations have been archived at SFWMD, and 

the data from EVER have been summarized in the SFWMD 

Everglades Consolidated Report (2000).

In addition to the water-quality data currently being collected in the park and preserve, other agencies and individuals 

have collected water-quality data and information over the 

years. Some of these sources extend coverage of water-quality 

conditions back into the 1960’s and 70’s (Duever and others, 

1979; Kolipinski and Higer, 1969; Kolipinski and others, 1971; 

Klein and others, 1970; McPherson, 1970; Klein and others, 

1975; Waller, 1982). Some of this earlier information is 

included in this report to provide the longest record possible for 

water-quality conditions in BICY and EVER.

Objective and Scope

The overall objective of this report is to describe and summarize the results of analyses of surface water-quality data collected in freshwaters in or near EVER and BICY. The analyses 

include an evaluation of seasonal and long-term trends, and possible effects of hydrologic, climatic, and human-induced perturbations. Included in the report are: (1) an analysis of long-term 

trends for selected properties, such as specific conductance, 

chloride, sulfate, total phosphorus (TP), and total nitrogen 

(TN); (2) an evaluation of baseline water-quality conditions; 

(3) a comparison of selected water-quality indicators across the 

landscape; and (4) an evaluation of water-quality network 

design with regard to frequency of sampling and optimal number of sites and their locations. The database developed for this 

report is available at South Florida Information Exchange 

(SOFIA) web site at http://sofia.usgs.gov.

Data Analysis

Analysis of water-quality data focused on a comprehensive review of all water-quality data collected in BICY and 

EVER. Data from 1984 to 2000 were from the South Florida 

Water Management District (SFWMD) DBHYDRO database. 

Manual data entry was required for the water-quality data at 

BICY predating 1995. Other sources of water-quality data, primarily from the USGS, were reviewed and integrated into the 

analysis. Data related to water quality, such as water levels and 

flow, also were compiled. Land-use and water management 

changes in watersheds upstream of BICY and EVER (fig. 2) 

were evaluated to determine the effects of these changes on 

water quality. Data collected at selected canal sites near the 

parks also were included in the study.

We selected specific conductance, chloride, sulfate, TP, 

and TN for evaluation of long-term trends. Specific conductance and chloride were selected because they are the most 

chemically and biologically conservative water-quality indicators and tracers, and because they usually have a long and reliable analytical record. Sulfate was selected because concentrations naturally are low in remote freshwater wetlands in south 

Florida and thus, a good indicator of human activities. Sulfate 

also is important in mercury methylation, a major environmental concern in south Florida. TP was selected because 
Data Analysis 5

concentrations naturally are low in freshwater wetlands that 

have not been affected by agricultural and urban development, 

and because TP is considered to be the primary growth-limiting 

nutrient for plants and controlling the ecological balance of the 

Everglades. TN was selected because nitrogen is an important 

micronutrient that can influence the ecological balance, and 

because TN serves as an indicator of ecological conditions, 

especially in tidal and estuarine waters.

Some water-quality constituents were compared to others 

using chemical logic checks to assess data quality. Additionally, chemical logic and statistical or graphical checks of the 

data were used together when feasible, to eliminate erroneous 

data or outliers that could bias interpretations.

Problems in Long-Term Trend Analyses

Analysis of water-quality data to determine long-term 

trends is confounded by three basic problems: (1) the variety 

and complexity of environmental causes of trends; (2) changes 

over time in the protocols and methods used to collect and analyze water samples; and (3) changes in frequency or timing of 

sampling. Natural changes in rainfall, water flow, and water 

level, and changes in water management practices, land use, and 

water treatment may produce water-quality trends. Hydrologic 

changes can be partially compensated for by using statistical 

computer programs, such as S-ESTREND (Slack and others, 

2003), that fit a relationship between concentration and flow or 

between concentration and water level, and use the relationship 

to minimize effects of wet and dry seasons on concentrations. 

Consequently, an apparent trend in concentration during a long 

drought may not produce a statistically valid trend because the 

stage adjustment compensated adequately for the effects of 

stage on concentration. Changes in water management, however, may alter the adjustment or relation between water quality 

and flow over time, and can be evaluated using a residual time 

plot. Statistical computer programs such as S-ESTREND 

require sufficient data with suitable distribution throughout the 

period of interest to meet the requirements of S-ESTREND for 

reliable statistical analysis.

Analytical laboratory methods and reporting levels for 

constituents have changed over the years, and these changes can 

affect the results of some trend analyses; this is especially true 

if many of the concentrations are near to or less than the minimum reporting level for the analytical methods. For example, 

the laboratory procedures for some trace elements were 

changed in early 1994 when BICY switched from using a private laboratory to using the SFWMD laboratory. Consequently, 

some differences in concentrations before and after 1994 may 

be due to changes in the analytical method rather than to environmental changes. Minimum reporting levels also have varied 

over the years within and between agencies. The USGS 

reported TP concentrations as low as 0.01 mg/L in the 1970’s 

and 1980’s; in the mid-1980’s, SFWMD began reporting TP 

concentrations as low as 0.004 mg/L. The TP concentrations, 

therefore, appear to decrease after 1985 because of the lower 

minimum reporting level, suggesting an apparent downward 

trend over time, even though the concentrations may have been 

the same during both periods. Additionally, trend determinations are more difficult if a large percentage of the data are 

reported as less-than values (censored data; data reported as less 

than a minimum reporting level for the method of measurement). Because all measurements have random errors and some 

have biases associated with them, low concentrations near the 

reporting levels can be influenced and biased by such errors 

even though the data are not censored. For example, if the 

earliest sulfate reporting level is less than 5 mg/L and the variability is +/- 3 mg/L, a “true” concentration of 3 mg/L could be 

reported as 6 mg/L. If in 1988, the analytical method changed 

and the reporting level was revised to less than 2 mg/L, a “true” 

concentration of 3 mg/L could be reported by the laboratory as 

3 mg/L. Thus, the latter method could report one half the concentration of the former for the same sample. In addition to lessthan data, low concentrations of some constituents were 

reported as zeroes instead of less-than values in the earliest data 

available. The factors discussed above are most likely to affect 

our trend analyses of sulfate and TP data for sites with the lowest concentrations. Data for specific conductance, chloride, and 

TN were well above the reporting levels, and therefore, were 

less influenced by changes in analytical methods. We have 

attempted to recognize and minimize such problems in the 

data analyses. The S-ESTREND programs have the ability to 

minimize some of the effects of changes in minimum reporting 

levels.

Changes in the frequency or timing of sampling can affect 

results of water-quality analyses. For example, if sampling frequency increases during a year, seasonal trends will be more 

obvious. An increase in sampling frequency also will increase 

the chance of collecting samples during extreme rainfall and 

storms or during droughts, both of which may result in a large 

range in water quality not evident with fewer samples.

Statistics

We used loess (locally weighted scatter-plot smoothing) 

plots (Slack and others, 2003) to evaluate long-term data and to 

show the generalized direction of change in concentration with 

time. Loess smoothing is especially useful for visualizing trends 

in data when the data are highly scattered or messy. Loess 

smoothing also was used for adjusting concentrations for flow 

or stage changes in order to reduce the normal seasonal changes 

in concentration due to variations in flow or stage. Without 

these adjustments, cyclical variations in concentrations due to 

seasonal or drought-related changes in flow or stage make it difficult to determine if there are real long-term trends in concentration due to other changes within the drainage basin. One of 

the advantages of using loess smoothing for flow and stage 

adjustment of water-quality data is that no advanced knowledge 

is needed about the relation between the two variables. Loess 

smoothing allows the user to describe a relation between two 

variables even when simple or commonly used equations do not 
6 Water Quality in Big Cypress National Preserve and Everglades National Park

describe the relation between them. Loess smoothing is accomplished by fitting a linear regression for many small parts of the 

x-axis (horizontal axis) and piecing together a line. The loess 

regression weights the close (local) data points more than more 

distant data points, and is similar to a moving average. When 

viewing plots of data and loess smooth lines, the reader may 

perceive a trend in concentration that is not statistically significant especially when the statistical programs adjust for severe 

wet and dry periods. 

The uncensored seasonal Kendall test and Tobit regression 

procedures, provided with the S-ESTREND program, were 

used to analyze water-quality data for trends. A 95-percent confidence level (p = 0.05) was used for all of the statistical tests. 

The uncensored seasonal Kendall test requires that a minimum 

of 5 years of data be available, that censored (less than) data be 

no more than about 5 percent of the data set, and that there is 

only one censoring level. In addition, there are requirements for 

a minimum abundance of data in the first and last fifth of the 

time span being tested. This test allows water-quality data to be 

flow or stage adjusted. The uncensored seasonal Kendall test 

was used to test for trends in specific conductance, chloride, and 

TN. The uncensored seasonal Kendall test is considered robust; 

that is, it is not sensitive to outliers in the data (Schertz and others, 1991). The uncensored seasonal Kendall test permits the 

user to compare only data from the same seasons over the 

period of record, which reduces the effect of seasonal waterquality changes and improves one’s ability to determine longterm trends. Three seasons were used in most cases. Comparisons were made between concentrations in the same seasons in 

the first year and each following year to count the number of 

increases and decreases. Then, comparisons were made 

between concentrations in the same seasons in the second year 

and each following year, and so on. For each season, a single 

value was selected for use in the seasonal Kendall test. For seasons with multiple values, the most central value with respect to 

time, that is also paired with discharge or stage, was selected to 

represent the season (Schertz and others, 1991). Because of this 

selection process, some of the data that are visible on a graph 

and that influence the shape of the loess smooth plots, may not 

be used by the seasonal Kendall test procedure. Consequently, 

graphs showing all of the data points over time may appear to 

show a trend that is not found to be statistically significant using 

this procedure.

The Tobit regression analysis was used to test for trends in 

sulfate and TP concentrations. This was necessary because the 

percentage of censored data was often more than the 5-percent 

limit suggested for the uncensored seasonal Kendall test, and 

because the sulfate and TP data sets usually contained more 

than one censoring level, making the data set unsuitable for the 

uncensored seasonal Kendall test.

Data requirements for using the S-ESTREND program 

sometimes prevented the use of the full period of record for statistical analysis. In addition, the S-ESTREND program assumes 

a monotonic trend (tends to increase, decrease, or have no trend, 

but not change from an increase to a decrease or vice versa) in 

concentration, which is not the case for sites where an increase 

in concentration was followed by a decrease. Consequently, we 

used loess smooth plots to decide where to break the data sets 

into shorter periods for trend analysis. Common linear regressions were used to look for trends in stage over time.

Trends in Rainfall, Water Levels, and Flows

Water quality in the BICY and EVER is affected by seasonal and long-term changes in rainfall (fig. 3), water levels, 

and flows. During the period when water-quality data are available, annual water conditions in the Everglades have been 

described as being dry in 1974-76 and 1985, and very dry in 

1989-91 (Frederick and Ogden, 2001). Low water levels in the 

marshes and sloughs generally result in ponding and increased 

major ion and nutrient concentrations because of the enhanced 

breakdown of organic material and the build-up of wastes from 

aquatic and terrestrial wildlife that concentrate in and near the 

remaining surface water. Conversely, high water levels and 

flowing water may decrease concentrations by dilution or flushing major ions and nutrients out of the marsh, or may increase 

concentrations by introducing water enriched in major ions and 

nutrients from agricultural or urban sources. Tropical storms 

and hurricanes might be expected to affect water quality 

because of heavy rainfall and high winds, but it appears that 

such effects are minimal, at least in remote regions of EVER, 

where little change was seen in water quality after Hurricane 

Andrew passed over the park on August 24, 1992 (Roman and 

others, 1994).

Water levels and flows in the eastern Everglades have been 

altered by development and water management. The eastern 

Everglades (including the eastern part of Everglades National 

Park) encompasses a vegetative region know as the southern 

marl-forming marsh (Davis and others, 1994)—an area of rugged limestone at the surface (Miami Rock Ridge), marl marshes 

and prairies, mangrove-lined creeks near the coast, and a few 

deeper water sloughs, including Taylor Slough. Annual fluctuations in water levels were dampened in the 1970’s (fig. 4) by 

changes in water management, primarily the construction of the 

L-31 canal and later the C-111 canal system.

Shark River Slough, the major drainage feature in the central Everglades, lies to the west of the marl-forming marsh of 

the eastern Everglades. The Slough originally extended about 

100 miles in a southwesterly direction and drained into the mangrove forests and Ponce de Leon Bay of southwest Florida. The 

Tamiami Trail (US 41), constructed across the Slough in the 

1920’s, was the first impediment to the Slough’s flow. Drainage 

and impoundment to the north of the Trail in the 1960’s and 

70’s further isolated the Slough from its headwaters in the central Everglades. The L-67 canals, which were dug in the early 

1960’s, brought water from the northern Everglades to the 

newly constructed S-12 structures (S-12s), where waters flowed 

into EVER along the western side of the Slough. In 1966-67, the 

L-67 canal was extended south from the Tamiami Trail along 

what was then the eastern boundary of the park and conveyed 
Trends in Rainfall, Water Levels, and Flows 7

1960 1965 1980 1985 2000

RAINFALL, IN INCHES

YEAR

1955 1970 1975 1990 1995

20

30

40

50

60

70

Figure 3. Average annual rainfall at 20 sites in south Florida.

10

9

8

7

6

5

4

3

2

1

0

-1

-2

GROUND-WATER ELEVATION,IN

FEET ABOVE AND BELOW NGVD OF 1929

1932 50 60 70 80 90 2000 35 45 40 55 65 75 85 95

YEARS

Figure 4. Average monthly water elevation in feet above NGVD 29 at wells S-196 and S-196A near Homestead, FL.
8 Water Quality in Big Cypress National Preserve and Everglades National Park

waters into the Slough 9.5 miles south of the Trail. In the early 

1980’s, the gates of the S-12s were left open, so waters flowed 

to EVER based on hydraulic gradient. In 1985, a Rainfall Plan 

was initiated so that water flowed to the park following a more 

natural pattern that reflected upstream rainfall. Compared to the 

high rainfall and flows in 1969-70, annual flows to EVER 

across the Tamiami Trail were low during the 1970’s and 

1980’s (fig. 5). The years 1989 and 1990 were dry with little 

flow to EVER. Annual flows increased in the 1990’s and 

peaked in 1996 (fig. 5). Also during the 1990’s, proportionally 

more water passed through the eastern section of the Tamiami 

Trail (L-30 to L-67) into the Shark River Slough than in earlier 

years. Efforts currently are underway to divert even more water 

to the eastern part of the Slough to more closely mimic natural 

(predevelopment) flow patterns.

West of Shark River Slough lies the slightly higher lands 

of the western Everglades and the Big Cypress Swamp. These 

lands are a mosaic of cypress strands and sloughs, rocky 

marshes, and slightly higher pine forests. Disruption of natural 

flows has been minimal in the Swamp compared with the 

effects on Shark River Slough and the eastern Everglades. The 

Tamiami Trail, constructed in the 1920’s, is regarded as having 

less effect on flows in BICY than in EVER. Canals in the Big 

Cypress Swamp are small and have less effect on hydrology 

than the larger canals in the Everglades. Water in the Big 

Cypress Swamp flows under the Trail through numerous culverts and bridges. Flows in the Big Cypress Swamp have been 

affected by the L-28 Interceptor Canal drainage system (fig. 1), 

which was constructed in the mid-1960’s and blocked flows to 

the swamp from the Everglades, and by the Barron River Canal 

(fig. 1), which was completed in 1926 and intercepted flows 

from the Okaloacoochee Slough and Deep Lake Strand and discharged water to the coast near Everglades City. Structures 

(S-343A, S-343B, and S-344) were cut in the L-28 levee in 

1983-85 to allow water to flow from the western Everglades 

(WCA 3A) into the eastern Big Cypress Swamp. Flows in the 

section of Tamiami Trail from 40-Mile Bend to Monroe (fig. 1) 

increased markedly in the mid-1990’s, as a result of abundant 

rainfall and the construction of the S-343A, S-343B, and S-344 

water control structures (fig. 5).

Water Quality in South Florida

Water quality in freshwater marshes and sloughs of BICY 

and EVER is characterized by low specific conductance (typically in the range of 200-400 microsiemens per centimeter 

(μS/cm) at 25° C), a predominance of calcium and bicarbonate 

ions, low nutrient concentrations, and high dissolved organic 

matter (DOM). Water quality in canals of the region is characterized by specific conductance usually greater than 400 μS/cm 

at 25° C, relatively more chloride, sodium, and magnesium 

ions; higher (darker) color, and higher DOM and nutrient concentrations than in marshes and sloughs (McPherson and others, 

1976).

Seasonal changes in water quality in the wetlands of BICY 

and EVER are a result of natural processes, water management, 

and land-use activities. As water levels and flows decline during 

the dry season (November to May), ionic concentrations 

increase due to evaporation and geochemical and biological 

processes especially in ponded water (Waller, 1982). Drought 

and fire can cause geochemical changes in Everglades peat that 

L-30 TO L-67

S-12s

40-MILE BEND TO MONROE

MONROE TO CARNESTOWN

BARRON RIVER

1960 1970 1990

TOTAL DISCHARGE ACROSS TAMIAMI TRAIL,

IN CUBIC FEET PER SECOND

YEAR

1950 1980 2000

0

1,000

2,000

3,000

4,000

5,000

Figure 5. Average annual discharge under the Tamiami Trail. L-30 to L-67A; S-12s, 40-Mile Bend to Monroe, and Monroe to 

Carnestown, and Barron River. [Discharge measurements started during the 1960’s in some sections.]
Water Quality in South Florida 9

stimulates release of constituents such as sulfate and nutrients 

to surface waters after the peat is reflooded (Krabbenhoft and 

Fink, 2000). A decline in water level in these wetlands can 

result in greater inflows from the canals, changing wetland 

water quality (Waller, 1982; McPherson and others, 1970; 

Walker, 1997). Land-use activities in the urban and agricultural 

areas affect water quality in canals and in wetlands that receive 

the canal inflows. Concentrations of phosphorus at inflows to 

EVER (S-12 structures; S-12s) increased in the late 1970’s and 

the 1980’s (Walker, 1997). Walker attributed the increases to 

the expansion of agricultural land use, changes in water management, and long-term nutrient enrichment in the WCAs. In 

water years (October to September) 1985 and 1986, water managers kept the S-12s structures open and water levels in WCA3A were low, which resulted in the increased transport of phosphorus–rich canal flow to EVER. After about 1991, concentrations of phosphorus at the S-12s decreased. Walker speculated 

that this decrease may reflect post-1991 changes in water management and water treatment, and shifts in agricultural crops 

away from vegetables. Rice and others (2002) estimated that 

implementation of best management practices in the Everglades 

Agricultural Area (EAA) reduced farm phosphorus loads an 

average of 55 percent between water years 1996-98.

Water-quality conditions in EVER sometimes exceed 

Class III water-quality criteria established by the State. The 

SFWMD (2000, p. 4-63–4-64) summarized baseline and yearly 

water-quality exceedances of Class III criteria for inflow and 

interior sites of EVER. An exceedance is a concentration or 

other water-quality value that is outside of the acceptable range 

specified in a criterion. Highest percentages of exceedance of 

the criteria were for dissolved oxygen (from about 24 to 82 percent), followed by total iron at interior sites (from about 4 to 

20 percent). Small percentages of exceedances occurred for pH, 

specific conductance, total cadmium, total lead, total zinc, 

turbidity, and unionized ammonia.

Water Quality Changes Over Time

To address the questions, “Has water quality changed over 

time in BICY and EVER?” and “If changes have occurred, then 

have they been similar across the region?” selected sites in different regions that had long-term water-quality records were 

evaluated. These regions include Taylor Slough in the eastern 

Everglades (along the eastern boundary of EVER), Shark River 

Slough, and the western Everglades and Big Cypress Swamp.

Eastern Everglades

Taylor Slough Bridge

Taylor Slough bridge (TSB), located near the headwaters 

of the Taylor Slough, serves as a long-term (1960-2000) waterquality reference site for the eastern Everglades. Water discharged from S-332 (1980-2000) into the Slough several miles 

north of TSB increased in the mid-1990’s (fig. 6). Waller 

(1982), using regression analysis, reported that there were no 

long-term changes in ionic concentrations in the Taylor Slough 

drainage from 1960 to 1977, but his analysis preceeded the 

large increase in discharge at S-332.

We evaluated trends in stage and water-quality constituents at TSB both graphically (fig. 7) and statistically for the 

period of record, 1960-2000. Statistically, stage, specific conductance, and chloride increased significantly (fig. 7A, B, C). 

Chloride concentrations ranged from less than 5 to 25 mg/L 

during most of the 1960’s and 70’s, except for a few higher values in the early 1960’s, and increased significantly in the mid 

1980’s through early 1990’s, with several values greater than 

50 mg/L (fig. 7C). The loess smooth line for chloride concentrations decreased in the 1990’s, but the decline is not yet

statistically significant.

Sulfate concentrations at TSB ranged from about 1 to 

62 mg/L, with most concentrations less than 20 mg/L. Statistical tests on sulfate indicate that concentrations increased significantly in the late 1980’s and decreased significantly in the 

1990’s (fig. 7D). However, 28 percent of the sulfate data were 

less-than or zero values and there were changes in the reporting 

levels (0.0, <0.1, <5.0, < 2.0, <1.0 mg/L), indicating that the 

trend could be false.

Concentrations of TP at TSB generally were less than 

0.02 mg/L, except in the late 1980’s when values were sometimes higher. There was a significant downward trend from 

about 1988 to 2000 (fig. 7E). Like sulfate, the high percentage 

1985 1990

YEAR

1980 1995 2000

0

50

100

150

200

250

S-332

300

DISCHARGE, IN CUBIC FEET PER SECOND

Figure 6. Average annual discharge at S-332.
10 Water Quality in Big Cypress National Preserve and Everglades National Park

E F

YEAR

0

0.05

0.10

0.15

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

0

1

2

3

TOTAL NITROGEN,

IN MILLIGRAMS PER LITER

62 mg/L

3/30/1962

0

20

40

60

90

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

10

30

50

70

0

10

20

30

40

SULFATE, IN MILLIGRAMS PER LITER

YEAR

80

1960 1970 1980 1990 2000 1960 1970 1980 1990 2000

C D

A B

0

200

400

600

800

SPECIFIC CONDUCTANCE, IN

MICROSIEMENS PER CENTIMETER

AT 25 DEGREES CELSIUS

0

4

6

STAGE, IN FEET

ABOVE NGVD OF 1929

3

5

2

1

Figure 7. Stage (water level) and water-quality data with loess smooth lines for period of record at Taylor Slough Bridge.

[Trends or lack of trends at the 95-percent confidence level follows. (a) Linear regression for stage gave a significant upward trend for 

1960-2000. (b) Uncensored seasonal Kendall test for specific conductance using stage adjustment gave significant upward trends for 

1966-1992 and 1966-2000 and no significant trends for 1993-2000. (c) Uncensored seasonal Kendall test for chloride with stage adjustment 

gave significant upward trends for 1966-2000, 1966-1993, and 1983-1993 and no significant trend for 1993-2000 and 1966-1983. (d) Tobit regression for sulfate gave a significant downward trend for 1989-1999; a significant upward trend for 1983-1990; and no significant trends 

for 1984-1998, 1981-1989, and 1981-1999. The trends may be influenced by changes in reporting levels for sulfate and may not be valid. 

(e) Tobit regression for total phosphorus gave a significant downward trend for 1978-2000; and no significant trends for 1986-1999; 1978-

1985; 1978-1986; 1978-1987, and 1985-2000. The trends may be influenced by changes in reporting levels for total phosphorus and may not 

be valid. The clusters of data at the reporting levels are visible on the graph. (f) Uncensored seasonal Kendall test for total nitrogen with 

stage adjustment gave significant upward trends for 1980-2000 and 1984-1996 and no significant trends for 1982-1988, 1988-2000, 1980-

1990, and 1990-2000.]
Water Quality in South Florida 11

(27 percent) of less-than or zero values and changes in reporting 

levels (<0.01, < 0.02, 0.004, and 0.00 mg/L) may mean that the 

trend is not valid. Effects of the reporting levels can be seen by 

the clusters of data points at 0.01, 0.02, and 0.004 mg/L 

(fig. 7E). The higher concentrations of TP during the late 

1980’s were associated with low water levels (fig. 8A) and low 

flows in the Slough (fig. 8B). Higher phosphorus concentrations also could be related to increased nutrient inputs from 

upstream canal sources. Walker (1991) reported an increasing 

trend of over 20 percent per year in TP at S-332 (which 

discharges into the headwaters of the Slough) for the period 

1983-89.

Concentrations of TN at TSB ranged from less than 

0.5 mg/L to nearly 2.5 mg/L. TN increased significantly over 

the period 1980-2000 (fig. 7F), but not during other time 

periods that were tested (fig. 7F).

Shark River Slough

Water-quality records in Shark River Slough go back to at 

least 1959. Flora and Rosendahl (1981) reported that before 

construction of levee L-29 (in 1962) along the Tamiami Trail, 

water in the Slough was dominated by calcium and bicarbonate 

ions with a mean specific conductance of 272 μS/cm at 25° C, 

and a sodium-to-calcium ratio of 0.34; after 1962, mean specific 

conductance increased to 653 μS/cm at 25° C, and the sodiumto-calcium ratio changed to 0.88 in the late 1970’s. Waller 

(1982) also described changes in water quality in the Slough 

during 1959-77; he attributed the increases in ionic concentrations and changes in water color to channelization that allowed 

more mineralized and darker colored water to flow from L-67A 

directly into Shark River Slough.

Several long-term water-level and water-quality sites 

(P-sites) are located along the length of the Shark River Slough 

south of Tamiami Trail. Trends for stage and water-quality 

constituents at one of these sites, P-33, were evaluated for the 

period of record, 1959-2000 (fig. 9). Stage increased 

significantly during the period; the increase was most 

noticeable in the 1990’s (fig. 9A). Both specific conductance 

and chloride concentrations also increased significantly during 

the period (fig. 9B, C); however, chloride concentrations 

decreased significantly from 1993-2000 (fig. 9C). Increases in 

chloride from 1960 to the mid-1990’s were due primarily to 

increased canal transport of high dissolved-solids water from 

the north by the L-67 Canals, which were constructed in 1962-

63 (Waller, 1982; Walker, 1997). In 1966-67, the L-67 Canal 

extension was dug 9.5 miles south of the Tamiami Trail and 

delivered canal water to within 3 miles of site P-33. Dry periods 

in the 1960-90 time span also probably contributed to the high 

chloride values. During dry periods, the inflow of canal water 

probably increases relative to sheetflow from the interior of 

WCAs and surrounding marshes. The decrease in chloride 

concentrations in the 1990’s probably is due to increased marsh 

inflow, fewer droughts, higher water levels, and changes in 

upstream water management and treatment.

Most concentrations of sulfate at site P-33 were less than 

20 mg/L for the period of record, 1960-2000 (fig. 9D), except 

for a few high concentrations at low-water periods (fig. 10B). 

Sulfate tended to increase when flow through the L-30 to 

40-Mile Bend reach of the Tamiami Trail increased (fig. 10A). 

Although sulfate concentrations graphically appeared to 

increase until the early 1990’s, and then decrease until the end 

of 2000, trends were not statistically significant. Concentrations 

of sulfate increased with increasing flows under the Tamiami 

Trail (fig. 10A). Stober and others (2001) showed high 

concentrations of sulfate in the vicinity of P-33 during both wet 

and dry seasons of 1995 and 1996 (presumably transported to 

the vicinity by the L-67 Canal extension), but lower sulfate 

concentrations in 1999, when the L-67 Canal extension no 

longer transported water. Our data at P-33 (fig. 10B and 10C) 

have a few relatively high concentrations of sulfate 

(10-25 mg/L) in 1999; however, these data were collected 

at different times and a different location and are not directly 

comparable to those of Stober and others (2001).

Concentrations of TP at site P-33 showed a significant 

downward trend from 1972 to 2000; this trend probably is 

related to a decrease in the laboratory reporting level (from 

<0.01 to <0.004 mg/L) in the mid-1980’s and a high percentage 

(19 percent) of less-than or zero values (fig. 9E). The effect of 

changes in reporting level is visible, with numerous values at 

0.01 and 0.004 mg/L (fig. 9E). Concentrations remained low 

(less than 0.05 mg/L), other than a few high values (spikes) 

associated with sharp drops in water level (fig. 10C), over the 

entire period of record, even though the concentrations of TP 

increased at the S-12 inflows to EVER during 1977-89 (Walker, 

1991). Site P-33 is about 3 miles from the nearest canal 

(L-67 Canal extension), and much of the phosphorus transported by the canal is probably taken up in the marsh before 

reaching P-33 (McPherson and others, 1976). The few high 

spikes of phosphorus concentrations associated with a sharp 

decline in water level (fig. 10C) may result from a combination 

of the following:

1. large phosphorus loading from canals that reaches P-33 

during droughts;

2. breakdown of organic matter and the accumulation of 

biological waste in the marsh at low water levels when 

ponding may occur;

3. contamination of samples because of difficulty in 

collecting water samples in shallow water without 

disturbing phosphorus-rich bottom sediments.

It is also possible that increased sampling frequency (particularly at low stage) might result in more high-phosphorus concentrations by increasing the likelihood of sampling very high 

concentrations.

Western Everglades and Big Cypress Swamp

The two sites with the longest water-quality records in 

these regions are P-34 (in EVER just south of the BICY boundary) and the 40-Mile-Bend-to-Monroe section of the Tamiami 
12 Water Quality in Big Cypress National Preserve and Everglades National Park

A

1986

FM AM J J A S O ND

1987

F M A M J J A S O ND

1988

FMAM J J ASOND 0

0.02

0.04

0.06

0.08

0.10

0

2

4

STAGE, IN FEET ABOVE NGVD OF 1929

TOTAL PHOSPHORUS, IN

MILLIGRAMS PER LITER

J J J

DETECTIONS

LESS-THAN

VALUES 1

3

5

0 100 200 300 400

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

DISCHARGE, IN CUBIC FEET PER SECOND

500 0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

DETECTIONS

LESS-THAN VALUES

B

GAGE

HEIGHT

Figure 8. (A) Variation in stage and concentration of total phosphorus with time, and (B) variation of concentration of total 

phosphorus with discharge at Taylor Slough Bridge.
Water Quality in South Florida 13

E F

YEAR

1960 1970 1980 1990 2000 1970 1960 1980 1990 2000

YEAR

0

0.01

0.04

0.05

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

TOTAL NITROGEN,

IN MILLIGRAMS PER LITER

0

1

2

3

4

0.02

0.03

C D

0

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

0

20

10

30

SULFATE, IN MILLIGRAMS PER LITER

50

100

150

SPECIFIC CONDUCTANCE, IN

MICROSIEMENS PER CENTIMETER

AT 25 DEGREES CELSIUS

STAGE, IN FEET

ABOVE NGVD OF 1929

0

200

400

600

1,000

1,200

800

3

4

5

6

7

8

A B

Figure 9. Stage (water level) and water-quality data with loess smooth lines for the period of record at P-33. 

[Trends or lack of trends at the 95-percent confidence level follows. (a) Linear regression for stage gave a significant upward trend for 

1959-2000. (b) Uncensored seasonal Kendall test for specific conductance with stage adjustment gave significant upward trends for 

1959-1975, 1959-1995 and 1959-2000 and no significant trends for 1980-1993 and 1994-2000. (c) Uncensored seasonal Kendall test with 

stage adjustment for chloride gave significant upward trends for 1959-2000 and 1959-1982, no significant trend for 1982-1993, and significant downward trend for 1993-2000. (d) Tobit regression for sulfate gave no significant trend for 1977-2000. (e) Tobit regression for total 

phosphorus gave a significant downward trend for 1972-2000 and no significant trends for 1986-2000 and 1972-1986. The clusters of data points at the reporting level of 0.01 mg/L before 1985 and 0.004 mg/L after 1985, when lower reporting levels began, make the influence of the reporting levels on less-than and reported values visible on the graph. Although 19-percent of the data were less-than or 

zero values, the influence of the change in reporting levels also appears to have influenced many of the reported (not less than or zero) 

values and the trend is appears to be false. (f) Uncensored seasonal Kendall test for total nitrogen with stage adjustment gave no 

significant trend for 1975-2000.]
14 Water Quality in Big Cypress National Preserve and Everglades National Park

DETECTIONS

LESS THAN

VALUES

B P-33

A P-33

C P-33

D P-34

0

20

40

60

80

100

3

4

5

6

7

8

SULFATE CONCENTRATION,

IN MILLIGRAMS PER LITER

0

TOTAL PHOSPHPHORUS,

IN MILLIGRAMS PER LITER 0.1

0.2

0.3

0.4

0.5

0.7

0

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER 10

20

30

40

50

STAGE, IN FEET

ABOVE NGVD OF 1929

0

1

2

3

4

5

0

2,000

4,000

6,000

8,000

DAILY DISCHARGE, IN

CUBIC FEET PER SECOND

1991

YEARS

1992 1993 1994 1995 1996 1997 1998 1999 2000

1972

YEARS

1975

1980

YEARS

1985 1990 2000 2002

1995

YEARS

1996 1997 1998 1999 2000

1

3

4

5

6

7

8

0

10

20

30

40

SULFATE CONCENTRATION,

IN MILLIGRAMS PER LITER

7,000

5,000

3,000

1,000

DAILY DISCHARGE,

L30-40 Mile

SULFATE

CONCENTRATION

1956 1960 1965 1970 1975 1995

2

0.6

1980 1985 1990 1995 2000

GAGE HEIGHT

GAGE HEIGHT

GAGE HEIGHT

STAGE, IN FEET

ABOVE NGVD OF 1929

STAGE, IN FEET

ABOVE NGVD OF 1929

Figure 10. (A) Concentration of sulfate at P-33 and discharge under Tamiami Trail (L-30-40-Mile Bend); (B) sulfate at P-33 and 

stage; (C) total phosphorus at P-33 and stage; (D) chloride concentration at P-34 and stage.
Water Quality in South Florida 15

Trail, which includes Bridge 105 and is referred to as 

Bridge 105.

Both Bridge 105 and P-34 represent relatively unaltered 

hydrologic conditions, but the Bridge 105 site is affected 

locally by US Highway 41 and the adjacent borrow canal. Site 

P-34 is in a location remote from canals and probably best represents long-term undisturbed water-quality conditions in the 

region. Waller (1982) reported no long-term changes in water 

quality at site P-34 between 1959 and 1976.

Site P-34

We evaluated trends for stage and selected water-quality 

constituents at site P-34 for the period of record, 1959-2000 

(fig. 11). There was a small but significant increasing trend for 

stage and stage-adjusted specific conductance, even though the 

loess plot shows no obvious trend for the unadjusted specific 

conductance (fig. 11 A, B). Changes in water quality at P-34 

were small and may simply be related to changes in rainfall. 

Concentrations of chloride, which ranged from less than 10 to 

about 60 mg/L (fig. 11C), appeared to decrease in the 1990’s

with increasing water levels, but the stage-adjusted seasonal 

Kendall test did not detect significant trends. This suggests that 

the apparent decline in chloride concentration in the late 1980’s 

could be due to increasing stage during that period. Higher chloride values typically were associated with lower water levels 

(fig. 10D).

Most sulfate concentrations at site P-34 were less than 

10 mg/L, although a few values (not shown) exceeded 20 mg/L 

before the early 1970’s (fig. 11D). Although the Tobit regression analysis computed a statistically significant downward 

trend in sulfate, the trend appears to be the result of the high percentage (57 percent) of less-than or zero values and the changes 

in reporting levels (0 mg/L through 1980, <5 mg/L from 1987 

until early 1988, <2 mg/L in 1988 through 1995, <1 mg/L 1995 

through 1998, and <0.1 mg/L in 1999) over the period of 

record. Some of the effect can be seen in the clustering of data 

at 5, 2, and 1 mg/L and the shape of the loess smooth line.

Concentrations of the nutrients, TP and TN, at P-34 

showed no significant trends over the period of record 

(fig. 11E, F). Ninety percent of TP concentrations were less 

than 0.03 mg/L. An apparent downward trend in the loess plot 

for TP (fig. 11D) is probably due to the decrease in reporting 

levels between 1975 and 1985, and in later years. The change in 

reporting levels can be seen (fig. 11D) by the clustering of data 

at 0.01 mg/L from about 1975 to 1983 and at 0.004 and 

0.005 mg/L after about 1986.

Bridge 105 Site

The stage and water-quality data used for analysis of the 

Bridge 105 site (1967-2000) was a mix of samples collected at 

Bridge 105 and samples composited from flow at Bridge 105 

and other bridges between 40-Mile Bend and Monroe along the 

Tamiami Trail that had flow at the time of sampling (fig. 12). 

The stage recorder is located at Bridge 105. There was a 

significant increasing trend for stage (fig. 12A), but no significant trends for specific conductance or chloride (fig. 12 B, C). 

The increase in stage in the 1990’s is related to abundant rainfall 

during that period and the release of water through the S-343 

and S-344 structures into southeastern BICY.

Concentration of sulfate at Bridge 105 showed a significant downward trend from 1970-1999 (fig. 12D). The decline in 

sulfate possibly is influenced by changes in laboratory reporting 

levels (0, <1, <0.1, and <0.2 mg/L) and 21 percent less-than or 

zero values (fig. 12D). High values for sulfate were associated 

with low water levels (fig. 13).

Concentrations of TP at Bridge 105 showed a significant 

trend upward for 1970-80, a significant downward trend for 

1990-1999, and no trend for 1970-1999 (fig. 12E). Only 6 percent of the TP data were less-than or zero values (most occurred 

in the 1980’s); it is unlikely that either loess plots or Tobit 

regression trend results would be biased by the less-than values. 

The statistical analysis of trends is based on Tobit regressions 

and does not correlate with the loess smooth plot. For example, 

a few high phosphorus values in the late 1960’s and early 

1970’s cause the loess smooth line to start high and decrease 

during the 1970’s. However, the Tobit regression results in an 

upward trend between 1970 and 1980 because there are only 

3 data values greater than 0.1 mg/L in the first half of that 

decade and 8 data values greater than 0.1 mg/L in the second 

half. Higher values for TP concentrations were associated with 

low water levels (fig. 13), and were probably caused by ponding 

of water, accumulation of biological waste, and the chemical 

breakdown of organic material in the water remaining in the 

Tamiami Canal.

Concentrations of TN at Bridge 105 for the period of 

record (1975-1999) remained at about 1 mg/L along the loess 

smooth line with 90 percent of the values ranging between 0.4 

and 1.2 mg/L. The uncensored seasonal Kendall tests gave a 

significant downward trend for 1975 to 1999, but no trend for 

1975 to 1985 (fig. 12 F).

Lietz (2000) analyzed trends in water quality at the Tamiami Trail section (40-Mile Bend to Monroe) over the period 

1967 to 1993. He used flow-adjusted and unadjusted concentrations and parametric and nonparametric statistics in the analysis, and reported significant increasing or decreasing trends for 

13 out of 37 constituents or measurements (Lietz, 2000, pg. 19). 

He labeled an upward trend as a deterioration in water quality 

for eight constituents including specific conductance and dissolved solids, and a downward trend as an improvement in 

water quality for five constituents including ammonia and 

nitrite plus nitrate. Our analysis differed from that of Lietz, in 

that we evaluated data extending into 1999 and used stage 

adjustment for the uncensored seasonal Kendall tests for specific conductance, chloride, and TN. Discharge approaches zero 

as the stage approaches about 6.9 feet, resulting in ponding near 

Bridge 105, but the stage ranged from 2.85 to 8.98 feet.
16 Water Quality in Big Cypress National Preserve and Everglades National Park

E F

YEAR

1960 1970 1980 1990 2000

0

0.01

0.03

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

1960 1980 1990 2000 1970

YEAR

TOTAL NITROGEN,

IN MILLIGRAMS PER LITER

0

1

2

3

0.02

C D

0

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

SULFATE, IN MILLIGRAMS PER LITER

0

20

40

60

5

10

15

20

SPECIFIC CONDUCTANCE, IN

MICROSIEMENS PER CENTIMETER

AT 25 DEGREES CELSIUS

STAGE, IN FEET

ABOVE NGVD OF 1929

0

200

400

600

1,000

800

0

1

2

3

4

5

A B

Figure 11. Stage (water level) and water-quality data with loess smooth lines for period of record at P-34.

[Trends or lack of trends at the 95-percent confidence level follows. (a) Linear regression for stage gave a significant upward trend for 

1959-2000. (b) Uncensored seasonal Kendall test for specific conductance with stage adjustment gave a significant upward trend for 

1959-2000 and no trend 1986-2000. (c) Uncensored seasonal Kendall test with stage adjustment for chloride gave no significant trends 

for 1959-2000 and 1986-2000. (d) Tobit regression for sulfate gave a significant downward trend that is almost certainly a false trend 

due to changes in laboratory reporting level for 1986-2000. Less-than and zero values comprised 57 percent of the sulfate data and the 

influence of clusters of data at the reporting levels of 1, 2, and 5 mg/L is visible on the graph. (e) Tobit regression for total phosphorus 

gave no significant trends for 1986-2000. (f) Uncensored seasonal Kendall test for total nitrogen with stage adjustment gave no

significant trend for 1986-2000.]
Water Quality in South Florida 17

E F

YEAR

1965 1970 1975 1980 1985 1990 1995 2000

0

0.1

0.2

0.3

TOTAL PHOSPHORUS,

IN MILLIGRAMS PER LITER

1965 1980 1970 1975 1990 1985 2000 1995

YEAR

0

1

2

3

TOTAL NITROGEN,

IN MILLIGRAMS PER LITER

C D

0

20

40

60

80

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

10

30

50

70

0

10

5

15

SULFATE, IN MILLIGRAMS PER LITER

0

200

400

600

800

SPECIFIC CONDUCTANCE, IN

MICROSIEMENS PER CENTIMETER

AT 25 DEGREES CELSIUS

2

4

6

8

10

STAGE, IN FEET

ABOVE NGVD OF 1929

9

3

5

7

A B

Figure 12. Stage (water level) and water-quality data with loess smooth lines for period of record at Bridge 105 and 40-Mile Bend 

section.

[Trends or lack of trends at the 95 percent confidence level follows. (a) Linear regression for stage gave a significant upward trend for 

1967-1999. (b) Uncensored seasonal Kendall test for specific conductance with stage adjustment gave no significant trends for 1967-

1999, 1967-1988, and 1989-1999. (c) Uncensored seasonal Kendall test with stage adjustment for chloride gave no significant trends for 

1967-2000, 1967-1980, and 1981-2000. (d) Tobit regression for sulfate gave significant downward trends that may be influenced by 

changes in laboratory reporting level for 1970-1999 and 1980-1999. No significant sulfate trends were found for 1970-1980, 1970-1990, 

1970-1996, 1980-1990, 1985-1999, and 1990-1999. Less-than and zero values comprised 29 percent of the sulfate data. (e) Tobit regression for total phosphorus gave a significant upward trend for 1970-1980; a significant downward trend for 1990-1999; and no significant 

trends for 1970-1999; 1980-1990; 1980-1999. Only 5 percent of the total phosphorus data were less-than values, so trends should not be 

influenced much by changes in reporting levels. (f) Uncensored seasonal Kendall test for total nitrogen with stage adjustment gave no 

significant trend for1975-1985 and a significant downward trend for 1975-1999.]
18 Water Quality in Big Cypress National Preserve and Everglades National Park

Spatial Patterns in Water Quality

Water quality varies spatially across the study area 

because of natural variations in geology, hydrology, and vegetation, and because of differences in water management and 

land use. Wetlands dominate the landscape, but canals also are 

important hydrologic features, especially along the borders of 

EVER and, to a lesser extent, BICY. Water-quality conditions 

in the boundary canals can influence water quality in the interior 

of the parks, depending on the quality, amount, and timing of 

water released from canals into the parks. Restoration of the 

Everglades will involve changes in the amount, timing and location of inflows, all of which can affect water quality in the 

parks, and therefore, are of concern.

Park Boundary Water-Quality Conditions

Water quality along the boundaries of BICY and EVER 

were evaluated in the L-28I drainage system, the Barron River 

Canal, the S-12s control structure, and the L-31 and C-111 

canals (fig. 1).

L-28 Interceptor (L-28I) Drainage System

The L-28I drainage system is in or near the northeastern 

part of BICY. The system was constructed in the mid-1960’s to 

provide flood protection to the Seminole Reservation, and consists of three main canals—L-28I canal, the North Feeder canal, 

and the West Feeder canal. The north and west feeders convey 

water south and southeast through the S-190 pump station into 

the L-28I Canal, ultimately discharging into WCA 3A. Currently, water is confined to the canals until it discharges into 

WCA 3A, but restoration plans being considered include releasing some water from the West Feeder canal into the northern 

BICY to reestablish historic hydrologic flows to several cypress 

strands. Waters in the L-28I and the North Feeder canal are 

enriched in nutrients from agricultural lands to the north, 

whereas water in the West Feeder canal contains relatively low 

nutrient concentrations. For example, the average concentration 

of TP in the North Feeder canal was 0.25 mg/L during 1996-97, 

compared with 0.06 mg/L in the West Feeder canal (Germain, 

1998). Nutrient concentrations tend to increase in the West 

Feeder canal during the dry season when S-190 is closed and 

some water from the North Feeder canal backs up into the West 

Feeder canal (R. Sobczak, National Park Service, written commun., 2002).

Barron River Canal

The Barron River Canal is located along the western 

boundary of BICY. The canal and the adjacent Highway 29 

roadbed act as a major hydrologic barrier to the wetlands of the 

BICY. The canal drains predominately agricultural lands north 

of the Preserve and discharges into Chokoloskee Bay and 

EVER.

Water and bed sediment in the canal contain a number of 

pesticides and other contaminants that are a potential source of 

contaminants to the bay and the extreme northwestern part of 

EVER (Miller and McPherson, 2001: Shahane, 1994). Because 

1996

FM AM J J A S O ND

1997

F M A M J J A S O ND

1998

FMAM J J ASOND 0

100

200

300

400

500

5

7

9

STAGE, IN FEET ABOVE NGVD OF 1929

SULFATE (x 100) AND TOTAL PHOSPHORUS (X 1,000),

IN MILLIGRAMS PER LITER

J J J

6

8

10

SULFATE

TOTAL

PHOSPHORUS

GAGE

HEIGHT

Bridge 105

Figure 13. Stage (water level) at Bridge 105 and concentration of sulfate (times 100) and total phosphorus (times 1000) from January 

1996 to January 1999.
Water Quality in South Florida 19

the current direction of flow in the canal is south into 

Chokoloskee Bay or west into the Fakahatchee Strand, and 

because restoration plans call for even more diversion of water 

to the west, these areas have a greater potential of receiving 

contaminants from the Barron River than BICY.

S-12s Gated Structures

The S-12s are gated structures (A, B, C, D) along the 

Tamiami Canal between the L-67A and L-28 canals. The S-12s 

were constructed in the early 1960’s and release water south 

into the Shark River Slough in EVER. A large amount of waterquality data (particularly nutrients) has been collected over the 

years at these structures. Walker (1991) reported increasing 

trends in concentrations of TP for 1977-89 and decreasing 

trends for 1992-96 (Walker, 1997). As part of restoration in 

recent years, more water is being diverted east from the S-12s 

into the northeastern portion of the Shark River Slough. This 

trend is planned to increase, so that more of the water from the 

L-67 canals will flow away from the S-12s.

L-31 Canal and C-111 Canals

Construction of the L-31 canal began in 1951, and the 

canal was extended south of the Tamiami Trail in the late 

1950’s and early 60’s. Pumping station S-332 was completed 

and began pumping water in 1981 into Taylor Slough in EVER. 

The main C-111 canal system, south of the L-31 canal system, 

was completed by 1982. These canal systems drain water from 

the Tamiami Canal and from mixed agricultural lands east of 

EVER. Water interchanges rapidly between surface- and 

ground-water sources in the porous limestone of the region. 

Large amounts of water-quality data have been collected in 

these canal systems over the years. Hydrologic restoration 

activities are underway and there are concerns that diversion of 

more water into EVER could alter water quality in the slough 

and in the estuarine wetlands bordering Florida Bay (Sutula and 

others, 2001).

Median Concentrations of Selected Constituents

Median concentrations of selected constituents were used 

to illustrate spatial patterns for the period 1991-2000 (figs. 14-

20). The 10-year period, 1991-2000, was selected as a baseline 

because this length of time provides a broad range of hydrologic 

conditions and sufficient water-quality data at most sites, and 

because this time span covers a period when sampling and laboratory protocols were relatively consistent.

Median values for specific conductance generally were 

higher at canal and slough sites than at most other interior sites 

(fig. 14). At the interior sites, the highest values were at site EP, 

at sites in Shark River Slough of EVER, and at a canal site 

northeast of BICY. The high median value at site EP in EVER 

may result from nearby coastal influences. The high values in 

Shark River Slough probably are due to inflow of higher conductance waters from the L-67 canal through S-12D and S-333 

into the slough. The source of the high values in the northwest 

BICY is possibly saltier ground water released from oil drilling 

operations.

Median concentrations of chloride were highest in EVER; 

most median concentrations were greater than 30 mg/L, and 

seven median concentrations were greater than 60 mg/L 

(fig. 15). Median concentrations at all sites in BICY were less 

than 30 mg/L, except at a canal site (S-190; 39 mg/L) northeast 

of the preserve and an interior site in the extreme northwest 

(A1: 53 mg/L). Site A1 is located near an oil drilling operation 

and the high median chloride concentration may be due to contamination from this source. The sources of most of the high 

chloride concentrations in EVER are canals that drain lands to 

the north or coastal water to the south.

Median concentrations of sulfate were highest at several 

Everglades canal sites, somewhat lower at the Everglades 

marsh sites, and lowest at the interior BICY sites (fig. 16). The 

source of the high concentrations of sulfate in the Everglades is 

primarily agricultural drainage, which has been enriched by fertilizer applications (Bates and others, 2002).

Median concentrations of TP generally were higher in 

BICY than in EVER and its adjacent canals (fig. 17). Several 

possible sources for the high concentrations in BICY include: 

(1) high phosphorus content in surficial (in or near the land surface) rocks, soils, or ground water; (2) a larger release or 

smaller uptake of phosphorus by soils and vegetation of the Big 

Cypress Swamp compared with the Everglades; (3) shallower 

water, less flow, and more ponding in Big Cypress Swamp that 

could favor chemical or biological processes that increase phosphorus release to the water, or simply accumulation of higher 

concentrations of waste from wildlife; or (4) an influence from 

high-phosphorus canal waters near the Preserve boundaries. For 

example, sites A1 and A2 have high median concentrations and 

are near the northwestern boundary and the Barron River Canal, 

and sites A5, A6, and A9 also have high median concentrations 

and are near the eastern boundary and the L-28 canal system. 

Miller and others (1999, fig. 7) found a general east-to-west 

increase in TP in water along the Tamiami Canal in the wet and 

dry seasons, and this suggests that surficial geology may be a 

dominant influence.

Brand (2001) reported that phosphorus concentrations are 

substantially higher in shallow coastal water south of Big 

Cypress Swamp in the 10,000 Islands area, compared with 

waters farther to the east in Florida Bay. He attributes the source 

of the higher phosphorus in the west to phosphate deposits in 

central Florida. The phosphorus from these deposits may be 

made available by erosion enhanced by phosphate mining and 

transport down the Peace River and along the southwest coast, 

and by ground water moving through the deposits and transporting phosphorus up into coastal waters (Top and others, 2001). 

More evidence is needed, however, to prove that shallow 

ground water is a source of elevated phosphorus in BICY 

compared with EVER.
20 Water Quality in Big Cypress National Preserve and Everglades National Park

Everglades

National

Park

Gulf of Mexico

Florida Bay

0 5 MILES

Miami Canal

L-28N

New River

Canal

Interceptor

Canal

L-28I

North

West Feeder

Feeder

P-35

Taylor

Slough

Shark

River

Slough

L-67 Ext

L-28

L-67 A

Barron

River Ca

nal

L-67 C

75

C-111

Alligator Alley

Ponce de

Leon Bay

Whitewater

Bay

40 Mile

Bend

Tamiami Trail 41

BR105

(A6)

Monroe

Big Cypress

National Preserve

L-31

US41

(506)

P-36

(515)

P-33

(535) P-34

(307)

P-37

(319)

TSB

(454)

S-332

(515)

EP

(567)

S-18C

(529)

S-177

(519)

NE1

(550)

NP-201

(479)

S-333

(625)

(314)

A9

(435)

(265)

A4

(367)

A5

(269)

(298)

S-12A

(601)

S-12D

A14

(503)

A13

(267)

A3

(373)

A12

(310)

A2

(489)

A1

(433)

S-190

(555)

L-28

EXPLANATION

STATION Location and

number. Red bar and

number in parenthesis

represent median

specific conductance

in milligrams per liter

LEVEE Location

and number

−

−

P-34

(307)

Turner

River

Water

Conservation

Area 3A

Chokoloskee

Bay

Water

Conservation

Area 2A

Figure 14. Median specific conductance at Big Cypress National Preserve and Everglades National Park sites and nearby canal sites, 1991-2000.
Water Quality in South Florida 21

Turner

River

Water

Conservation

Area 3A

Chokoloskee

Bay

Water

Conservation

Area 2A

Everglades

National

Park

Gulf of Mexico

Florida Bay

0 5 MILES

Miami Canal

L-28N

New River

Canal

Interceptor

Canal

L-28I

North

West Feeder

Feeder

P-35

Taylor

Slough

Shark

River

Slough

L-67 Ext

L-28

L-67 A

Barron

River Ca

nal

L-67 C

75

C-111

Alligator Alley

Ponce de

Leon Bay

Whitewater

Bay

40 Mile

Bend

Tamiami Trail 41

BR105

(A6)

Monroe

Big Cypress

National Preserve

L31

US41

(65)

P-36

(63)

P-33

(63)

P-34

(18)

P-37

(25)

TSB

(37)

S-332

(38)

S-18C

(39)

S-177

(36)

NE1

(65)

NP-201

(51)

S-333

(68)

(16)

A9

(14)

(13)

A4

(22)

A5

(9)

(17)

S-12A

(67)

S-12D

A14

(21)

A13

(13)

A3

(24)

A12

A2 (9) (26)

A1

(53) S-190

(39)

L-28

EXPLANATION

STATION Location and

number. Red bar and

number in parenthesis

represent median

chloride concentration

in milligrams per liter

LEVEE Location

and number

−

−

P-34

(18)

EP

(80)

Figure 15. Median chloride concentrations at Big Cypress National Preserve and Everglades National Park sites and nearby canal sites, 1991-2000.
22 Water Quality in Big Cypress National Preserve and Everglades National Park

Turner

River

Water

Conservation

Area 3A

Chokoloskee

Bay

Water

Conservation

Area 2A

Everglades

National

Park

Gulf of Mexico

Florida Bay

0 5 MILES

Miami Canal

L-28N

New River

Canal

Interceptor

Canal

L-28I

North

West Feeder

Feeder

P-35

Taylor

Slough

Shark

River

Slough

L-67 Ext

L-28

L-67 A

Barron

River Ca

nal

L-67 C

75

C-111

Alligator Alley

Ponce de

Leon Bay

Whitewater

Bay

40 Mile

Bend

Tamiami Trail 41

BR105

(A6)

Monroe

Big Cypress

National Preserve

L-31

US41

(2)

P-36

(3)

P-33

P-34 (5)

(0.0)

P-37

(0.0)

TSB

(2)

S-332

(4)

EP

(10)

S-18C

(12)

S-177

(4)

NE1

(2) NP-201

(5)

S-333

(10)

(0.4)

A9

(0.0)

(0.1)

A4

(0.8)

A5

(0.0)

(0.0)

S-12A

S-12D

A14

(0.0)

A13

(0.0)

A3

(0.0)

A12

(0.3)

A2

(0.4)

A1

(0.3)

S-190

(10)

L-28

EXPLANATION

STATION Location and

number. Red bar and

number in parenthesis

represent median

sulfate concentration

in milligrams per liter

LEVEE Location

and number

−

−

P-35

(2)

Figure 16. Median sulfate concentrations at Big Cypress National Preserve and Everglades National Park sites and nearby canal sites, 1991-2000.
Water Quality in South Florida 23

Turner

River

Water

Conservation

Area 3A

Chokoloskee

Bay

Water

Conservation

Area 2A

Everglades

National

Park

Gulf of Mexico

Florida Bay

0 5 MILES

Miami Canal

L-28N

New River

Canal

Interceptor

Canal

L-28I

North

West Feeder

Feeder

P-35

Taylor

Slough

Shark

River

Slough

L-67 Ext

L-28

L-67 A

Barron

River Ca

nal

L-67 C

75

C-111

Alligator Alley

Ponce de

Leon Bay

Whitewater

Bay

40 Mile

Bend

Tamiami Trail 41

BR105

(A6)

Monroe

Big Cypress

National Preserve

L-31

US41

(0.007)

P-36

(0.006)

P-33

(0.005)

P-34

(0.005)

P-37

(0.001)

TSB

(0.004)

S-332

(0.007)

EP

(0.004)

S-18C

(0.007)

S-177

(0.007)

NE1

(0.007)

NP-201

(0.004)

S-333

(0.011)

(0.010)

A9

(0.016)

(0.019)

A4

(0.010)

A5

(0.018)

(0.008)

S-12A

(0.01)

S-12D

A14

(0.009)

A13

(0.012)

A3

(0.009)

A12

(0.016)

A2

(0.016)

A1

(0.018)

S-190

(0.05)

L-28

EXPLANATION

STATION Location and

number. Red bar and

number in parenthesis

represent median

total phosphorus

concentration in

milligrams per liter

LEVEE Location

and number

−

−

P-34

(0.005)

Figure 17. Median total phosphorus concentrations at Big Cypress National Preserve and Everglades National Park sites and nearby canal sites, 1991-2000.
24 Water Quality in Big Cypress National Preserve and Everglades National Park

Median concentrations of TN ranged from 0.64 to 

1.8 mg/L; there were no obvious patterns between canals and 

interior sites or across the landscape (fig. 18). The inorganic 

forms of nitrogen (nitrite plus nitrate), however, tended to be 

higher in canals near the Everglades than in the interior marshes 

of either BICY or EVER (fig. 19). Median concentrations of 

nitrite plus nitrate (N02+N03) were greater than 0.03 mg/L in 

C-111 basin canals, whereas median concentrations at most 

sites in the interior were less than 0.01 mg/L. Median concentrations of ammonia plus ammonium ion (NH3 + NH4

+1) were 

0.04 mg/L or less, except at several C-111 basin canals (fig. 20). 

Possible reasons for the higher inorganic nitrogen in the canals 

include: (1) less biological uptake in the canals due to less 

contact with vegetation and bottom sediments and their associated micro-organisms, (2) greater inputs of ground water 

enriched in inorganic nitrogen into canals than into marshes, or 

(3) greater inputs of fertilizers to canals because of proximity to 

agriculture.

Most concentrations of unionized ammonia (NH3, the 

most toxic form of ammonia) were below Class III criteria 

(0.02 mg/L) indicative of adverse effects on aquatic life; 

median values in BICY, EVER, and nearby canals were less 

than 0.001 mg/L. The SFWMD (2000) reported that NH3 periodically exceeded Class III criteria in EVER; most years there 

were few or no exceedances and the maximum number of 

exceedances (13.6 percent) occurred in 1992.

Turner

River

Water

Conservation

Area 3A

Chokoloskee

Bay

Water

Conservation

Area 2A

Everglades

National

Park

Gulf of Mexico

Florida Bay

0 5 MILES

Miami Canal

L-28N

New River

Canal

Interceptor

Canal

L-28I

North

West Feeder

Feeder

P-35

Taylor

Slough

Shark

River

Slough

L-67 Ext

L-28

L-67 A

Barron

River Ca

nal

L-67 C

75

C-111

Alligator Alley

Ponce de

Leon Bay

Whitewater

Bay

40 Mile

Bend

Tamiami Trail 41

BR105

(A6)

Monroe

Big Cypress

National Preserve

L-31

US41

(1.5)

P-36

(1.6) P-33

(1.5)

P-34

(1.0)

P-37

(0.8)

TSB

(0.79)

S-332

(0.89)

EP

(1.1)

S-18C

(0.68)

S-177

(0.92)

NE1

(1.8)

NP-201

(1.3)

S-333

(1.4)

(0.91)

A9

(1.0)

A4

(0.8)

A5

(1.2)

(1.0)

S-12A

(1.4)

S-12D

A14

(0.64)

A13

(0.82)

A3

(0.98)

A12

(0.85)

A2

(1.3)

A1

(1.5)

S-190

L-28

EXPLANATION

P-34

(1.0)

STATION Location

and number. Red

bar and number in

parenthesis represent

median total nitrogen

in milligrams per liter

LEVEE Location

and number

−

−

Figure 18. Median total nitrogen concentrations at Big Cypress National Preserve and Everglades 

National Park sites and nearby canal sites, 1991-2000.
Water Quality in South Florida 25

Trace Elements in Water

Waller (1982) summarized trace element concentrations in 

water from 20 stations in and near EVER during 1959-1977. 

Average concentrations generally were lower in canals than in 

marshes, which he speculated was due to the more stable chemical and biological processes in the canals. Most average trace 

element concentrations were below the U.S. Environmental 

Protection Agency’s aquatic life criteria of 1977.

The SFWMD (2000) summarized spatial and temporal 

trends of total (unfiltered and digested) trace elements in EVER 

for the 19-year period of record (water years 1981-1999). Only 

cadmium, copper, lead, and zinc exceeded the Class III criteria 

(table 4-12). The interior marsh sites had the highest number of 

exceedances for total iron (> 1 mg/L) compared with other 

locations in the Everglades. Total iron was correlated (r2 = 0.61) 

with turbidity and this suggested a possible source of the iron 

was from sediment re-suspension.

We summarized trace element data for total arsenic, cadmium, copper, lead, iron, and zinc in water samples collected in 

BICY, EVER, and nearby canals over the baseline period 1991-

2000 in figure 21. Few trace elements exceeded the Class III 

criteria for aquatic life. The greatest percentage of exceedances 

was for total iron from marsh sites in EVER where 8 percent of 

the samples exceeded the criterion of 1.0 mg/L.

Turner

River

Water

Conservation

Area 3A

Chokoloskee

Bay

Water

Conservation

Area 2A

Everglades

National

Park

Gulf of Mexico

Florida Bay

0 5 MILES

Miami Canal

L-28N

New River

Canal

Interceptor

Canal

L-28I

North

West Feeder

Feeder

P-35

Taylor

Slough

Shark

River

Slough

L-67 Ext

L-28

L-67 A

Barron

River Ca

nal

L-67 C

75

C-111

Alligator Alley

Ponce de

Leon Bay

Whitewater

Bay

40 Mile

Bend

Tamiami Trail 41

BR105

(A6)

Monroe

Big Cypress

National Preserve

L-31

US41

(0.019)

P-36

(0.009)

P-33 P-34 (0.005) (0.004)

P-37

(0.010)

TSB

(0.008)

S-332

(0.040)

EP

(0.008)

S-18C

(0.051)

S177 (0.045)

NE1

(0.006)

NP-201

(0.008)

S-333

(0.045)

(0.019)

A9

(0.006)

(0.016)

A4

(0.006)

A5

(0.009)

(0.011)

S-12A

S-12D

A14

(0.006)

A13

(0.007)

A3

(0.007)

A12

A2 (0.009) (0.005)

A1

(0.009)

S-190

(0.015)

L-28

EXPLANATION

STATION Location and

number. Red bar and

number in parenthesis

represent nitrite plus

nitrate concentration in

milligrams per liter

LEVEE Location

and number

−

−

P-35

(0.019)

(0.041)

Figure 19. Median concentrations of nitrite plus nitrate at Big Cypress National Preserve and 

Everglades National Park sites and nearby canal sites, 1991-2000.
26 Water Quality in Big Cypress National Preserve and Everglades National Park

Turner

River

Water

Conservation

Area 3A

Chokoloskee

Bay

Water

Conservation

Area 2A

Everglades

National

Park

Gulf of Mexico

Florida Bay

0 5 MILES

Miami Canal

L-28N

New River

Canal

Interceptor

Canal

L-28I

North

West Feeder

Feeder

P-35

Taylor

Slough

Shark

River

Slough

L-67 Ext

L-28

L-67 A

Barron

River Ca

nal

L-67 C

75

C-111

Alligator Alley

Ponce de

Leon Bay

Whitewater

Bay

40 Mile

Bend

Tamiami Trail 41

BR105

(A6)

Monroe

Big Cypress

National Preserve

L-31

US41

(0.010)

P-36

(0.042)

P-33

P-34 (0.028)

(0.001)

P-37

(0.010)

TSB

(0.001)

S-332

(0.167)

EP

(0.012)

S18C

(0.065)

S-177

(0.118)

NE1

NP-201 (0.040) (0.023)

S-333

(0.025)

(0.040)

A9

(0.001)

(0.031)

A4

(0.001)

A5

(0.001)

(0.021)

S-12A

S-12D

A14

(0.001)

A13

(0.001)

A3

(0.001)

A12

(0.013)

A1

(0.011)

S-190

(0.016)

L-28

EXPLANATION

STATION Location and

number. Red bar and

number in parenthesis

represent ammonium

ion concentration in

milligrams per liter

LEVEE Location

and number

−

−

P-35

(0.010)

(0.021)

A2

(0.014)

Figure 20. Median concentrations of ammonia plus ammonium ion at Big Cypress National 

Preserve and Everglades National Park sites and nearby canal sites, 1991-2000.
Water Quality in South Florida 27

0

2

4

6

8

10

TOTAL ARSENIC, IN

MICROGRAMS PER LITER

0

2

4

6

8

10

TOTAL COPPER, IN

MICROGRAMS PER LITER

0

0.2

0.4

0.6

0.8

1.0

TOTAL CADMIUM, IN

MICROGRAMS PER LITER

0

10

20

30

40

50

TOTAL ZINC, IN

MICROGRAMS PER LITER

0

0.5

1.0

1.5

2.0

TOTAL LEAD, IN

MICROGRAMS PER LITER

0

0.5

1.0

1.5

2.0

TOTAL IRON, IN

MILLIGRAMS PER LITER

CANALS EVERGLADES

NATIONAL

PARK

INTERIOR

BIG CYPRESS

NATIONAL

PRESERVE

INTERIOR

Class criteria is

50 micograms per liter

III Class criteria is

6.5-21 micrograms per liter

III

Class criteria is

0.66-2 micrograms per liter

III Class criteria is

1.3-7.7 micrograms per liter

III

Class criteria is

1.0 milligram per liter

III Class criteria is

59-191 micrograms per liter

III

Class Criteria III

MAXIMUM VALUE

Class criteria III CLASS AQUATIC

LIFE CRITERIA

III

EXPLANATION

99th PERCENTILE

95th PERCENTILE

75th PERCENTILE

MEAN VALUE

MEDIAN VALUE

25th PERCENTILE

5th PERCENTILE

99th PERCENTILE

MAXIMUM VALUE

CANALS EVERGLADES

NATIONAL

PARK

INTERIOR

BIG CYPRESS

NATIONAL

PRESERVE

INTERIOR

Figure 21. Trace element concentrations in water at Big 

Cypress National Preserve and Everglades National Park sites 

and nearby canals, 1991-2000. (Class III aquatic life criteria are 

indicated for each element. Criteria that are dependent on hardness were calculated using average hardness values. Less-than 

values were set to 1⁄2 of the lowest reported less-than value.)
28 Water Quality in Big Cypress National Preserve and Everglades National Park

Pesticides and Other Organic Compounds 

in Water 

The most frequently detected pesticides and other organic 

compounds in water at EVER, BICY, and nearby canal sites are 

listed in tables 1 and 2. Out of 556 samples, each sample, on 

average, had one pesticide detection. The only pesticide concentrations that exceeded aquatic life criteria were two detections of the herbicide atrazine.

In an earlier study, Waller (1982) summarized data on pesticide analyses from water samples collected at 20 stations in 

EVER and surrounding areas during 1965-1977. Two percent 

of the over 1,700 samples analyzed had detectable pesticides 

(very low concentrations reported as “trace” to 0.017 μg/L), 

with the most frequently detected being dieldrin, diazinon, 

DDT, DDE, DDD, 2,4-D, and silvex.

In more recent studies (Miller and McPherson, 2001; 

Miller and others, 1999; McPherson and others, 2000), several 

pesticides were detected in water from the Barron River Canal, 

the Tamiami Canal, and the C-111 canal at S-177. In the Barron 

River Canal, nine pesticides (18 detections including estimated 

values) were detected in water samples collected in October 

1998. The most commonly detected pesticides included 

atrazine, deethylatrazine, and tebuthiuron; however, no concentrations exceeded Canadian aquatic-life criteria (Canadian 

Council of Ministers of the Environment, 2001). At the C-111 

Canal at S-177, the most commonly detected pesticides in a 

3-year intensive sampling period, 1996-98, were atrazine, 

metolachlor, tebuthiuron, and endosulfan. Detections and concentrations were seasonal, and generally peaked in winter and 

spring. During the 3-year sampling period, detections of the 

insecticide, endosulfan, were frequent in 1996, but became less 

frequent in the following 2 years (McPherson and others, 2000).

Pesticides and Other Organic Compounds in 

Bed Sediment

The most frequently detected pesticides or other organic 

compounds in bed sediment from seven canal sites near EVER 

or BICY are given in table 3. Canadian aquatic life criteria 

(Environment Canada, 1999) were exceeded for p,p ́-DDE 

(16 percent of the samples), lindane (3 percent), and heptachlor 

expoxide (1 percent).

Waller (1982) reported that one or more chlorinated 

hydrocarbon insecticide residues (DDT, DDE, DDD, chlordane, dieldrin) were detected in bottom sediment from nearly all 

20 stations sampled in and around EVER and at every station in 

the Park. Average concentrations in EVER for dieldrin, chlordane, DDD, DDE, and DDT were 0.2, 1.8, 3.5, 4.2, and 

0.9 μg/kg, respectively.

Table 1. Summary of most frequently detected pesticides and other organic compounds in water for the period of record at selected 

sites in and near Big Cypress National Preserve and Everglades National Park 

[μg/L, micrograms per liter]

Compound

Number of 

detections 

by compounds

Number of 

determinations by compounds

Detections

per determination

Highest 

measured 

concentration

Lowest

measured 

concentration1

Aquatic 

life

criteria

Number 

of 

exceedances

Class III 

criteria,

fresh 

waters4

Atrazine, unfiltered, μg/L 116 304 0.382 13.2 0.01 2

1.8 2

Atrazine, filtered, μg/L 90 99 0.909 0.87 0.00347 2

1.8 0

Metolachlor, filtered, μg/L 83 99 0.838 0.0635 0.0036 27.8

Deethylatrazine, filtered, μg/L 73 99 0.737 0.0225 0.00107

Tebuthiuron, filtered, μg/L 61 99 0.616 0.0494 0.0027 2

1.6 0

Endosulfan sulfate, unfiltered, μg/L 43 374 0.115 0.45 0.0033

EPTC, filtered, μg/L 29 99 0.293 0.0148 0.00081

2,6-Diethylaniline, filtered, μg/L 23 99 0.232 0.0054 0.00098

Simazine, filtered, μg/L 20 99 0.202 0.0979 0.00361 210 0

Chlorpyrifos, filtered, μg/L 19 99 0.192 0.0234 0.00249

Endosulfan I, unfiltered, μg/L 17 55 0.309 0.05 0.001 0 0.056

Malathion, filtered, μg/L 16 99 0.162 0.0837 0.00324 30.1 0 0.1

Hexazinone, unfiltered, μg/L 15 153 0.098 0.031 0.019

1

There are less-than values in the data set that might represent concentrations lower than the reported “lowest measured concentrations.” 2

Environment Canada, 1999, Canadian Interim Criteria.

3U.S. Environmental Protection Agency, 1999.

4

Florida Department of Environmental Protection, 1996.
Water Quality in South Florida 29

Table 2. Most frequently detected pesticides and other organic compounds in water for period of record at selected sites in and near 

Big Cypress National Preserve and Everglades National Park

[Other compounds were detected such as chlorinated pesticides, but at lower frequencies]

Site

Atrazine, unfilteredAtrazine, filteredMetolachlor, filteredDeethylatrazine, filteredTebuthiuron, filteredEndosulfan sulfate, unfilteredEPTC, filtered2,6-Diethylaniline, filteredSimazine, filtered Chlorpyrifos, filteredEndosulfan I, unfilteredMalathion, filtered Hexazinone, unfilteredNumber of sample collected 

(not all samples were were analyzed for the compound of interest)

Average detections per sample 

(some values are approximate)

Bridge 105 0 2 0 1 0 0 0 0 0 0 0 0 0 7 0.43

S-333 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0.00

S-18C 17 0 0 0 0 2 0 0 0 0 0 0 0 72 0.26

TSB 0 0 0 0 0 0 0 0 0 0 0 0 0 15 0.00

P-33 0 2 0 2 3 0 0 0 0 0 0 1 0 18 0.44

P-36 0 0 0 0 0 0 0 0 0 0 0 0 0 12 0.00

P-35 0 0 0 0 0 0 0 0 0 0 0 0 0 16 0.00

S-177 0 84 80 68 58 0 28 23 19 19 16 16 0 85 4.84

S-177 SFWMD 15 0 0 0 0 5 0 0 0 0 0 0 2 65 0.34

S-178 SFWMD 13 1 1 1 0 36 1 0 0 0 1 0 0 67 0.81

S-175 SFWMD 24 0 0 0 0 0 0 0 0 0 0 0 4 26 1.08

S-332 SFWMD 39 0 0 0 0 0 0 0 0 0 0 0 9 100 0.48

S-12D 0 3 2 3 3 0 0 0 1 0 0 0 0 3 4.00

US41-25 8 0 0 0 0 0 0 0 0 0 0 0 0 64 0.13

Total for all sites 116 90 83 73 61 43 29 23 20 19 17 16 15 556 1.09
30 Water Quality in Big Cypress National Preserve and Everglades National Park

Table 3. Most frequently detected pesticides and other organic compounds in bed sediment at seven canal sites near Big Cypress National Preserve and Everglades National Park (S-333, S-18C, S-177, S-178, S-175, S-332, US41-25)

[μg/kg, micrograms per kilogram]

Compound

Number of 

detections by 

compound

Number of 

determinations by

compound

Detections 

per

determination

Highest

measured 

concentration

Lowest 

measured 

concentration

Aquatic 

life 

criteria

Number 

of 

exceedances

p,p ́-DDE, bottom material, μg/kg 50 170 0.294 89 1.4 115

1Gilliom and others, 1998

27

Endosulfan sulfate, bottom material, μg/kg 17 168 0.101 120 1.6

Endosulfan beta, bottom material, μg/kg 15 168 0.089 24 0.67

p,p ́-DDD, bottom material, μg/kg 13 171 0.076 15 1.7

Chlordane technical, bottom material, μg/kg 12 185 0.065 155 0.2

p, p ́-DDT, bottom material, μg/kg 10 182 0.055 11.6 0.28

Heptachlor, bottom material, μg/kg 10 185 0.054 12.9 0.25

Endosulfan alpha, bottom material, μg/kg 9 168 0.054 16 1.1

Lindane, bottom material, μg/kg 8 185 0.043 34.2 0.19 11.38 5

Aldrin, bottom material, μg/kg 8 185 0.043 600 0.2

α-BHC, bottom material, μg/kg 6 182 0.033 6.62 1.1

β-Benzene hexachloride, bottom material, μg/kg 5 181 0.028 40.6 1.4

δ-Benzene hexachloride, bottom material, μg/kg 5 174 0.029 35.2 6.17

2,4-D, bottom material, μg/kg 4 177 0.023 1090 12.8

Endrin, bottom material, μg/kg 3 185 0.016 2.12 0.22 142 0

Heptachlor epoxide, bottom material, μg/kg 3 185 0.016 35 1.53 2.742

2

Canadian Council of Ministers of the Environment, 2001

2

2,4,5-T, bottom material, μg/kg 3 175 0.017 1130 1.4

o,p’-DDT, bottom material, μg/kg 2 25 0.080 1.85 1.02

Arochlor 1254 (PCB), bottom material, μg/kg 2 113 0.018 2.3 1.3

Arochlor 1016 (PCB), bottom material, μg/kg 1 102 0.010 235.4 235.4

Malthion, bottom material, μg/kg 1 185 0.005 4200 4200

Atrazine, bottom material, μg/kg 1 171 0.006 9.14 9.14

Mirex, bottom material, μg/kg 1 66 0.015 15.7 15.7

Dieldrin, bottom material, μg/kg 0 185 0 0 0 1 110 0

Miller and McPherson (2001) sampled bed sediment at 

nine sites on the Barron River and one site on the Turner River 

in October 1998. No pesticides were detected in bed sediment, 

except for two measurable concentrations of p,p ́-DDE and one 

of p,p ́-DDD, neither of which exceeded aquatic-life criteria.

Earlier studies have reported pesticides and other organic 

compounds in the Barron River Canal. Law Engineering and 

Environmental Services (1993) found high concentrations of 

semivolatile organic compounds in bed sediments near a creosote wood treatment facility near Jerome, Florida. Grabe (1996) 

found 99 parts per billion (μg/kg) of α-BHC (a degradation 

product of lindane) in bed sediments of the canal. A number of 

pesticides have been reported in surface water and bed sediment 

in Collier County, Florida, during 1989-92, including aldrin, 

α-BHC, chlordane, dieldrin, endosulfan sulfate, endosulfan I, 

endrin, and heptachlor (Shahane, 1994).
Water-Quality Monitoring Network Design for Future Studies 31

Water-Quality Monitoring Network 

Design for Future Studies 

At least three objectives for water-quality monitoring in 

BICY and EVER can be identified: (1) continued documentation of baseline water-quality conditions, (2) early detection of any changes that may occur as a result of water-management alterations, and (3) documentation of possible 

effects of restoration activities on water quality. To adequately document baseline water-quality conditions, at least 

some of the current long-term, remote sites need to be maintained and sampled. Continued sampling at these sites provides a way to gage changes in water-quality conditions 

resulting from natural events or human activities over many 

years. These sites are located where hydrologic data, such as 

water levels and discharge, are available. Maintaining sampling parameters, protocols, and frequencies similar to those 

that have been carried out for previous years will help ensure 

effective statistical evaluations. Monthly sampling has been 

identified as an appropriate frequency for some types of monitoring (Robertson and Roerish, 1999; Stansfield, 2001), but 

budget considerations may require some modifications. The 

second objective of providing early detections of changes in 

water quality may require establishing of new sites and different sampling frequencies or parameters from those used for 

the baseline sites. Changes in agricultural and domestic chemicals used to control weeds and pests may dictate the need to 

analyze new compounds. To detect the effects of upstream 

water modifications, it may be desirable to sample near the 

park boundary, to sample during runoff-events, and to sample 

a small selected number of constituents more frequently than 

monthly. Automatic sampling or continuous monitors may be 

appropriate, and sampling along transects may help identify 

sources of constituents. Both baseline water-quality monitoring and question-driven monitoring will help document 

potential effects of restoration on water quality.

Summary

Major physical alteration of the south Florida landscape 

and associated water management practices, including canal 

and levee construction, agriculture and residential development, and operation of pumps and flood gates in the 1900’s, 

have greatly altered both the volume, timing, distribution, and 

quality of surface water in this system. Everglades National 

Park (EVER, established 1947) and Big Cypress National 

Preserve (BICY, established 1974) were both established by 

Congress to preserve and protect large areas of the south Florida 

ecosystem that had remained relatively intact and free of agricultural and urban development. Because they are located at the 

downgradient end of the altered system, they are subject to 

effects of upstream water management practices.

The National Park Service (NPS) maintains hydrologic 

monitoring sites for measuring water level (stage) and water 

quality in EVER and BICY. Water-quality data collection and 

analyses have been carried out in EVER for over four decades, 

and in BICY since at least the early 1970’s when the proposed 

Big Cypress “Jetport” triggered a flurry of environmental investigations. These long-term data sets provide a historical baseline 

(beginning as early as 1959) for assessing hydrologic conditions and making a wide range of management decisions. We 

assessed selected water-quality data collected in the Park and 

Preserve and in nearby canals between 1959 and 2000. The data 

used were primarily from the South Florida Water Management District (SFWMD), but also includes data from the U.S. 

Geological Survey (USGS), and the NPS.

Seasonal changes in water levels and flows in BICY and 

EVER affect water quality. As water levels and flows decline 

during the dry season, physical, geochemical, and biological 

processes increase the breakdown of organic materials and the 

build-up of organic waste, nutrients, and other constituents in 

the remaining surface water. For example, during much of the 

year, concentrations of total phosphorus in the marshes of BICY 

and EVER usually are less than 0.01 milligram per liter (mg/L), 

but during the dry season, concentrations can rise briefly above 

this value, and occasionally, usually under drought conditions, 

exceed 0.1 mg/L.

Long-term changes in water levels, flows, water management, and upstream land use also affect water quality in BICY 

and EVER, based on analysis of available data (1959-2000). 

Specific conductance and concentrations of chloride increased 

in Taylor Slough and Shark River Slough in the mid-1980’s and 

early 1990’s. For example, chloride concentrations more than 

doubled from 1960 to the 1990’s, primarily due to canal transport of high dissolved-solids water into the sloughs. Trends in 

concentrations of sulfate and total phosphorus during the period 

are likely attributable, at least in part, to high percentages of 

less-than and zero values combined with changes in reporting 

levels over the period of record. High values in nutrient concentrations in marshes of BICY and EVER were evident during dry 

periods, and attributable to increased nutrient releases from 

breakdown of organic bottom sediment, or to increased buildup of nutrient waste from concentrations of aquatic biota and 

wildlife in remaining ponds, or in the EVER, to an increased 

ratio of nutrient-rich canal water to marsh water. Long-term 

changes in water quality are less pronounced in western EVER 

and BICY, however, seasonal and drought-related changes are 

evident.

Water quality varies spatially across the region because of 

natural variations in geology, hydrology, and vegetation and 

because of differences in water management and land use. 

Nutrient concentrations are relatively low in BICY and EVER 

compared to concentrations in parts of the northern Everglades, 

near agricultural and urban lands. Concentrations of total phosphorus generally are higher in BICY (median values, 1991-

2000, were mostly greater than 0.015 mg/L) than in EVER 

(median values, 1991-2000, less than 0.01 mg/L), probably 

because of higher phosphorus in natural sources such as 
32 Water Quality in Big Cypress National Preserve and Everglades National Park

shallow soils, rocks, and ground water in the Big Cypress region 

than in the Everglades region. Concentrations of chloride and 

sulfate are higher in EVER (median values in Shark River 

Slough, 1991-2000, mostly greater than 2 mg/L of sulfate and 

50 mg/L of chloride), than in BICY (median values, 1991-2000, 

less than 1 mg/L of sulfate and at most sites less than 20 mg/L 

of chloride), probably because of the canal transport system, 

which conveys more water from an agricultural source into 

EVER than into BICY.

Trace elements and contaminants such as pesticides and 

other toxic organic compounds are in relatively low concentrations in BICY and EVER compared to concentrations found in 

parts of the northern Everglades near agricultural and urban 

sources. Atrazine was the most frequently detected pesticide in 

water; atrazine exceeded the aquatic-life criteria in less than 

1 percent of the samples, or in 2 out of 304 samples. The pesticides heptachlor expoxide, lindane, and p,p’-DDE exceeded 

aquatic-life criteria in canal bed sediments in 1, 3, and 

16 percent of the samples, respectively.

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