U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2004-5142

Prepared as part of the U.S. Geological Survey Place-Based Studies Initiative and the

U.S. Department of the Interior Critical Ecosystem Studies Initiative of the National

Park Service, Everglades National Park

Water Flow and Nutrient Flux from Five Estuarine

Rivers along the Southwest Coast of the

Everglades National Park, Florida, 1997-2001
Cover: Landsat 7 Enhanced Thematic Mapper sensor image taken on 

February 5, 2000 (scale 1:100,000)
Water Flow and Nutrient Flux from Five 

Estuarine Rivers along the Southwest 

Coast of the Everglades National Park, 

Florida, 1997-2001

By Victor A. Levesque

Prepared as part of the U.S. Geological Survey Place-Based Studies Initiative and the 

U.S. Department of the Interior Critical Ecosystem Studies Initiative of the National Park Service, 

Everglades National Park

Scientific Investigations Report 2004-5142

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 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.

Suggested citation:

Levesque, V.A., 2004, Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast 

of the Everglades National Park, Florida, 1997-2001: U.S. Geological Survey Scientific Investigations Report 

2004-5142, 24 p.
iii

Contents

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

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

Purpose and Scope ............................................................................................................................. 2

Acknowledgments ............................................................................................................................... 2

Description of Study Area .................................................................................................................. 2

Methods ......................................................................................................................................................... 5

Water-Level and Velocity Measurements ....................................................................................... 5

Discharge Measurements .................................................................................................................. 6

Water-Quality Sampling ...................................................................................................................... 6

Computation of Discharge ........................................................................................................................... 7

Cross-Sectional Area Relation .......................................................................................................... 7

Index-Velocity Relation ....................................................................................................................... 7

Estimation of Discharge Error ............................................................................................................ 7

Discharge Characteristics ............................................................................................................... 10

Discharge and Water-Level Synopsis ..................................................................................................... 12

Lostmans Creek Station .................................................................................................................... 17

Broad River Station ........................................................................................................................... 17

Harney River Station ......................................................................................................................... 17

Shark River Station ............................................................................................................................ 17

North River Station ............................................................................................................................ 18

Water Quality and Nutrient Flux ............................................................................................................... 18

Water-Quality Characteristics ......................................................................................................... 18

Nutrient Flux ....................................................................................................................................... 18

Summary ...................................................................................................................................................... 19

References Cited ........................................................................................................................................ 24
iv

Figures

 1-2. Maps showing:

 1. Location of USGS discharge stations, Everglades National Park rainfall stations, 

and S-12-A, B, C, and D structure locations ............................................................................ 3

 2. Location of USGS discharge stations ....................................................................................... 4

 3-10. Graphs showing:

 3. Index velocity to mean velocity regression relations for Lostmans Creek, Broad 

River, Harney River, Shark River, and North River stations .................................................. 8

 4. Residual plots of index-to-mean velocity regression relations for Lostmans Creek, 

Broad River, Harney River, Shark River, and North River stations .................................... 11

 5. Typical instantaneous discharge cycle for five stations along the southwest coast 

of the Everglades National Park .............................................................................................. 12

 6. Monthly mean residual discharge for the five southwest coast stations, 

S-12-A, B, C, and D monthly mean discharge, and ENP average monthly total 

rainfall for 1997–2001 ............................................................................................................13-15

 7. Southwest coast stations monthly mean residual discharge to S-12-A, B, C, 

and D monthly mean discharge regression relation ............................................................ 15

 8. Monthly mean and 2-year average residual discharge distributions for selected 

periods of concurrent data between 1998-2000 ................................................................... 16

 9. Southwest coast stations discharge to nutrient flux regression relations .................20-21

 10. Southwest coast three and five station total nitrogen and total phosphorus flux 

distributions for selected periods of concurrent data ......................................................... 23

Tables

 1. Southwest coast discharge station identification numbers and locations ....................... 4

 2. Southwest coast station cross-sectional area regression equations ................................ 7

 3. Index velocity regression equations and discharge error estimates using standard 

error estimate method ................................................................................................................ 9

 4. Computed discharge error estimation based on measured discharge and Wilcoxon 

Signed Ranks probability for determining median error is different from zero ................. 9

 5. Southwest coast station nitrogen concentration basic statistics ..................................... 19

 6. Southwest coast station phosphorus concentration basic statistics .............................. 19

 7. Regression equations used to estimate total nitrogen flux ................................................ 22

 8. Regression equations used to estimate total phosphorus flux .......................................... 22
v

Conversion Factors, Acronyms, 

Abbreviations and Datum

Multiply By To obtain

Length

inch (in.) 25.4 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

square foot (ft2) 929.0 square centimeter

square foot (ft2) 0.09290 square meter

square mile (mi2) 259.0 square hectare

square mile (mi2) 2.590 square kilometer

Volume

cubic foot (ft3) 28.32 cubic decimeter

cubic foot (ft3) 0.02832 cubic meter

Flow rate

foot per second (ft/s) 0.3048 meter per second

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

Mass

ton, short (2,000 lb) 0.9072 megagram

ton per day (ton/d) 0.9072 metric ton per day

ton per day (ton/d) 0.9072 megagram per day

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer

SI to Inch/Pound

Multiply By To obtain

Volume

liter (L) 33.82 ounce, fluid (fl. oz)

liter (L) 2.113 pint (pt)

liter (L) 1.057 quart (qt)

liter (L) 0.2642 gallon (gal)

liter (L) 61.02 cubic inch (in2)

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)
vi

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit 

(°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius 

(°C) as follows:

°C=(°F-32)/1.8

Specific conductance is given in microSiemens per centimeter at 25 degrees 

Celsius (μS/cm).

Concentrations of chemical constituents in water are given in milligrams per 

liter (mg/L).

Acronyms

ADAPS Automated Data Processing System

CESI U.S. Department of the Interior Critical Ecosystem Studies Initiative

ENP Everglades National Park

kHz kilohertz

MHz megahertz

NPS National Park Service

NWIS National Water Information System

PBS U.S. Geological Survey Place-Based Studies Initiative

PVC polyvinylchloride

S-12 Water control structures

R2 Coefficient of determination

USGS U.S. Geological Survey

WSR Wilcoxon signed ranks test

Datum

Horizontal coordinate information is referenced to the North American 

Datum of 1983 (NAD 83)
Abstract

Discharge and nutrient fluxes for five tidally affected 

streams were monitored and evaluated as a part of the U.S. 

Geological Survey Place-Based Studies Initiative and the U.S. 

Department of the Interior Critical Ecosystem Studies Initiative. Locations on Lostmans Creek, and Broad, Harney, Shark, 

and North Rivers were selected using the criterion that a large 

amount of the water that flows through Shark River Slough 

must pass these sites. Discharge and nutrient-concentration 

data collection started at the Broad, Harney, and Shark River 

stations in January 1997 and ended in early 2001. Discharge 

and nutrient-concentration data collection started at the 

Lostmans Creek and North River stations in April 1999 and 

ended in early 2001. Each station was equipped with a vertically oriented acoustic-velocity sensor, water-level pressure 

transducer, bottom water-temperature thermistor, and specific 

conductance four-electrode sensor. Data collected using a 

vessel-mounted acoustic discharge measurement system were 

used to calibrate regression models of the mean river velocities and the in-situ index velocities. Information from these 

stations, in conjunction with data from other ongoing studies, 

will help to determine environmental effects on the southwest 

coast estuaries as changes in water management of the Everglades National Park continue.

Discharges from the Lostmans Creek, and Broad, Harney, 

Shark, and North River stations are influenced by semidiurnal 

tides, meteorological events, and surface- and ground-water 

inflow. Each of the five rivers is usually well mixed, having no greater than 500 microSiemens per centimeter at 25 ̊ 

Celsius difference in specific conductance from top to bottom 

during flood and ebb tides. Instantaneous flood discharges 

(water moving upstream) are typically of greater magnitude and shorter duration than instantaneous ebb discharges 

(water moving downstream).

Instantaneous discharge data were filtered using a 

low-pass filter to remove predominant tidal frequencies, and 

the filtered data were used to compute daily mean and monthly 

mean residual discharges. Lostmans Creek, and Broad, Harney 

and Shark Rivers each contributed from 20 to 27 percent of 

the total measured discharge to the Gulf of Mexico, whereas 

North River contributed approximately 4 percent. The main 

discharge region of the Shark River Slough extends from as 

far north as Lostmans Creek to as far south as North River. 

North River discharge has similar response characteristics to 

the other four rivers measured, but with a lesser magnitude of 

discharge. Comparisons of monthly mean discharges from the 

Tamiami Canal flow control structures S-12-A, B, C, and D 

located on U.S. Highway 41 (Tamiami Trail) to the five station 

total monthly mean discharges indicate that the discharges 

from the five rivers are approximately 2 to 3 times the S-12-

A, B, C, D discharges, and that the measured southwest coast 

discharge peaks lead the S-12-A, B, C, D discharge peaks by 

approximately 1 month.

Residual total nitrogen and total phosphorus fluxes were 

estimated using linear regression models of discharge and flux. 

Monthly mean total nitrogen residual fluxes for the five southwest coast rivers ranged from approximately 0 to 390 short 

tons, whereas monthly mean total phosphorus residual fluxes 

ranged from approximately 0 to 6 short tons. Total nitrogen 

and total phosphorus residual fluxes at Lostmans Creek, and 

Broad, Harney, and Shark Rivers were similar in magnitude, 

each accounting for between 20 to 29 percent of the total 

measured residual flux. North River contributed between 3 to 

4 percent of the total nitrogen and total phosphorus residual 

flux from the five rivers.

Water Flow and Nutrient Flux from Five Estuarine Rivers 

along the Southwest Coast of the Everglades National 

Park, Florida, 1997–2001

By Victor A. Levesque

Abstract 1
Introduction

A study of water flows and nutrient fluxes was conducted 

at five tidally affected rivers that receive freshwater from 

the Shark River Slough located in Everglades National Park, 

Florida (ENP) (fig. 1). The study was funded from 1996 to 

2001 through the U.S. Geological Survey (USGS) Place-Based 

Studies Initiative (PBS), and partially funded for the final 

year (2001) by the U.S. Department of the Interior Critical 

Ecosystem Studies Initiative (CESI) in cooperation with ENP. 

The fundamental scientific goals of the PBS are to clarify 

the interactions between ecosystem stresses and responses to 

provide relevant, high-quality, impartial, scientific information to enable resource-management agencies that require 

an improved scientific information base to make informed 

planning decisions and to help resolve and prevent resourcemanagement conflicts (U.S. Geological Survey, 1999). The 

CESI was established to provide sound scientific information 

for restoring ecosystems on Department of the Interior lands 

in South Florida, particularly in ENP. The CESI focuses on 

addressing urgent science information gaps and emerging 

research needs (U.S. Geological Survey, 2004).

Estuaries along the southwest coast of ENP receive the 

majority of surface water from the Shark River Slough. The 

slough is a broad southwest-trending arc of continuous wetland, dotted throughout with numerous tree islands (Schomer 

and Drew, 1982). The southwest coast of ENP is recognized as 

an important part of the Everglades system, and information 

on the timing and magnitude of discharge and nutrient flux is 

required to assess existing water management practices and 

to document changes brought about by rehabilitation efforts 

in the Everglades. Data described in this report are available 

from the USGS National Water Information System (NWIS). 

Additional data are available from the ENP Marsh and Marine 

Monitoring Network, the USGS mangrove dynamics stations, 

the Southeast Environmental Research Program water-quality 

monitoring program, and other ecological studies. Discharge 

data for this area of ENP were previously collected by the 

USGS between 1960-1967, and are available in out-of-print 

reports (U.S. Geological Survey, 1970, 1975).

Purpose and Scope

This report describes the timing and magnitude of water 

flows and nutrient fluxes for five estuarine river stations 

located along the southwest coast of Everglades National 

Park (figs. 1 and 2). The study began in late 1996 and ended 

in early 2001. Discharge data were collected at three stations 

from early 1997 through early 2001, and nutrient-concentration data were collected at these stations from February 1997 

through August 2000. Discharge data were collected at two 

additional stations from April 1999 through May 2001, and 

nutrient-concentration data were collected at these additional 

stations from May 1999 through August 2000. Station descriptions and characteristics, equipment selected for monitoring 

the rivers, and procedures used for estimation of discharge and 

discharge errors are presented in this report. Brief descriptions 

of hydrodynamic characteristics at each station are presented 

in the Methods section of this report. Water-quality methods 

used to collect water samples, an overview of water-quality 

data collected, and procedures used for the estimation of nutrient flux also are presented in the Methods section.

Acknowledgments

Thanks are extended to DeWitt Smith, Tom Smith, 

numerous Dutch exchange students, Kevin Kotun, and others 

at the Everglades National Park Research Station who helped 

accomplish this study. Special thanks to Gordon Anderson of 

USGS, Miami for assisting with numerous field trips, arranging for exchange students to assist with field trips, and as a 

valuable source of information about the southwest coast study 

area.

Description of Study Area

The west coast of ENP is a subtropical mangrove forest 

and wetland area with many stream channels, lagoons, and 

back bays interwoven through the mangrove forests. Red 

mangroves dominate the land margins adjacent to the streams. 

Some mangroves are approximately 60 ft in height along the 

banks of the Shark and Harney Rivers closer to the Gulf of 

Mexico.

The headwaters of the five streams selected for this study 

are located near Lake Okeechobee and are influenced by rain 

events and water control structures located along the Tamiami 

Trail (U.S. Highway 41) (fig. 1). Drainage basin boundaries 

of the rivers are indeterminate due to a lack of elevation data 

and the flatness of the terrain. Drainage basin boundaries of 

these rivers within ENP have been estimated based on aerial 

photographs and the alignment of vegetation in satellite imagery. Within the ENP, the river basins overlap. As water in the 

Shark River Slough flows towards the southwest coast, distinct 

stream channels form and transport the water to back-country 

bays and the Gulf of Mexico.

 The Everglades basin has a tropical savanna to subtropical climate characterized by a relatively long dry season 

(November to April) and a wet season (May to October) 

(Hela, 1952; Fernald and Patton, 1984). Annual rainfall typically ranges from 48 to 60 in., with approximately 80 percent 

occurring during the wet season (Schomer and Drew, 1982). 

Additionally, longer-term (greater than 5 years) rainfall averages exhibit a bimodal distribution pattern with a peak in 

May-June and a second peak in September-October (Thomas, 

1974). Rainfall data collected by ENP personnel between 1996 

and 2001 continue to exhibit the bimodal pattern. Average 

temperatures typically range from the mid-60s in the winter 

to low-90s (degrees Fahrenheit) in the summer (Schomer and 

Drew, 1982).

2 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001
24o

30'

EXPLANATION

82o

15' 80o

00'

Base from U.S. Geological Survey digital data, 1992

Universal Transverse Mercator projection, Zone 17, Datum NAD83

Broad River station

USGS DISCHARGE STATION —

 Location and name

Miami

NP202

41

Alligator Alley

Tamiami Trail

Everglades Parkway

Tamiami Canal

BIG

CYPRESS

NATIONAL

PRESERVE

BOUNDARY

EVERGLADES

NATIONAL PARK

BOUNDARY

North River station

Shark River station

Harney River station

Broad River station

Lostmans Creek station

Ponce de Leon

 Bay

Whitewater

 Bay

Florida

Bay

ENP RAINFALL STATION —

 Location and name

P38

P34

P36 NP206

P33

NP205 NP202

997

9336

Gulf

of

Mexico

Atlantic

Oce an

26o

30'

0

0

25 MILES

25 KILOMETERS

75

Study 

Area

shown

ALABAMA

GEORGIA

FLORIDA

Lake 

Okeechobee

MONROE

DADE

BROWARD COLLIER

HENDRY CHARLOTTE PALM BEACH

Figure 1. Location of USGS discharge stations, Everglades National Park rainfall stations, and S-12-A, B, C, and D 

structure locations.

Introduction 3
Discharge and nutrient monitoring stations (fig. 2) were 

established in the Broad, Harney, and Shark Rivers between 

October 1996 and January 1997, and were discontinued in 

March 2001. Additional discharge and nutrient monitoring 

stations were established in Lostmans Creek and North River 

between January and April 1999 and were discontinued in 

March and May 2001 respectively. “Left and right bank” and 

“edge of water” terms used in the following station descriptions refer to their location when viewed looking downstream 

(direction of positive discharge or flow towards the Gulf of 

Mexico).

The Lostmans Creek station is the northernmost station (fig. 2, table 1). The station is approximately 13 river 

miles from the Gulf of Mexico and about 1 mi upstream of 

Big Lostmans Bay. Both riverbanks are lined with mostly 

red mangroves, which are 5 to 15 ft tall. The river is approximately 300 ft wide at the station, with depths ranging from 

Ponce de Leon

 Bay

Shark River Slough Flows

Whitewater 

 Bay

North River station

Gunboat Island

Shark River station

Harney River station

Broad River station

Lostmans Creek station

Big Lostmans

Bay

Tarpon 

Bay

Lostmans Riv er

Shark River

Broad River 

Bay

Harney River

North Harney River

81o15' 81o00'

25o00'

25o30'

MONROE COUNTY

Base from U.S. Geological Survey digital data, 1992

Universal Transverse Mercator projection, Zone 17, Datum NAD83

Broad River station

EXPLANATION

USGS DISCHARGE

STATION LOCATION—

 and name

0 5 MILES

0 5 KILOMETERS

Table 1. Southwest coast discharge station identification numbers 

and locations.

Station name and ID Latitude Longitude

Lostmans Creek, 2290904 25o 33’ 54” N 081o 03’ 18” W

Broad River, 252953081011900 25o 29’ 53” N 081o 01’ 19” W

Harney River, 252551081050900 25o 25’ 51” N 081o 05’ 09” W

Shark River, 252230081021300 25o 22’ 30” N 081o 02’ 13” W

North River, 022908205 25o 20’ 18” N 080o 54’ 48” W

Figure 2. Location of USGS discharge stations.

4 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001
about 3 ft at the edges to about 6 ft near the center of the river 

at mean high tide. Normal tidal range is less than 1 ft, and 

velocities are less than 1 ft/s during flood or ebb tides. The left 

and right river edges are nearly vertical and composed of 

peat and fine mud. The river bottom consists of soft mud near 

the banks, grading to hard-packed mud littered with mollusk 

shells near the center of the river. Underwater visibility is 

usually about 4 to 6 ft.

The Broad River station is located approximately 10 river 

miles upstream from the Gulf of Mexico, about 1 mi upstream 

from Broad River Bay (fig. 2, table 1). Both riverbanks are 

lined mostly with red mangroves of 8 to 16 ft height. The 

river is approximately 200 ft wide at the station, with depths 

ranging from about 6 ft at the river edges to about 8 ft near 

the center. Riverbanks are vertical and consist of peat and fine 

sediments. The river bottom is covered with mud near the 

edges (approximately 1 to 3 ft from the edges) transitioning 

to exposed limestone with ridges, holes, and pinnacles less 

than 1⁄2 ft in elevation. Occasional small limestone spires and 

mollusk-encrusted limestone are distributed across the river 

bottom. Underwater visibility is usually 6 to 8 ft.

The Harney River station is located approximately 5 river 

miles from the Gulf of Mexico and about 1,800 ft downstream 

of the North Harney and Harney River confluence (fig. 2, 

table 1). Riverbanks are lined mostly with red mangroves 

of spectacular heights, some more than 60 ft. The river is 

approximately 350 ft wide with depths ranging from 0 ft at 

the right bank, sloping rapidly to about 13 ft near the center. 

The river bottom then gradually slopes up to about 9 ft at the 

vertical left bank. The sloped right bank is a sand beach about 

10 to 20 ft wide at low tide, grading to muddy sediments as the 

water deepens. Within 50 ft of the right bank, these sediments 

transition to exposed limestone that extends across the river to 

within about 40 ft of the left bank. Near the left bank, the river 

bottom is composed of muddy sediments with a vertical peat 

bank. Most of the bottom at this station is exposed limestone 

with ridges, holes, and pinnacles less than 1⁄2 ft in elevation. Mollusks cover much of the exposed limestone bottom. 

Underwater visibility is usually between 2 and 4 ft.

The Shark River station is located approximately 6 river 

miles upstream from the Gulf of Mexico and about 1,000 ft 

downstream of Gunboat Island (fig. 2, table 1). The riverbanks 

are lined mostly with red mangroves of moderate heights 

(30 to 40 ft). The river is approximately 400 ft wide, with 

depths ranging from 7 ft at the right bank sloping to 8 or 9 ft 

near the center and gradually decreasing in depth back to 7 ft 

at the left bank. Both banks are nearly vertical and consist of 

peat. Some areas of mud are located along the river bottom 

within 1 to 3 ft from the riverbanks. The remaining cross 

section is exposed limestone with ridges, holes, and pinnacles 

approximately 1 ft in elevation. Mollusks are attached to the 

exposed limestone bottom. Underwater visibility is usually 

6 to 8 ft.

The North River station is located approximately 4 river 

miles upstream from Whitewater Bay and about 16 mi from 

the Gulf of Mexico (fig. 2, table 1). Riverbanks are lined 

mostly with red mangroves of relatively short stature, with 

heights of only 5 to 8 ft. The river is approximately 250 ft 

wide with depths ranging from 4 ft at the right bank to 5 ft 

near the center of the river, and gradually decreasing in depth 

up to 3 ft at the left bank. Both riverbank edges are vertical 

and composed of peat and fine sediments. The bottom is 

composed of packed mud over harder bottom. The bottom of 

the river near the center is composed of fine sediments having 

a “pudding-like” consistency. Underwater visibility is usually 

between 2 and 4 ft.

Methods

The Broad, Harney, and Shark River monitoring station 

locations were selected based on an initial reconnaissance of 

the study area in June 1996 that included bathymetry, hydrodynamic characteristics, and water-quality. Aerial photography 

also was used to locate the monitoring stations. These three 

stations were established between November 1996 and January 1997. A second field reconnaissance conducted in December 1997, and a meeting with ENP personnel in October 1998, 

were used to locate two additional discharge and nutrient flux 

monitoring stations. Station installations at Lostmans Creek 

and North River were completed in April 1999.

Continuous monitoring of water-level, stream velocity, 

and specific conductance combined with periodic discharge 

measurements and collection of water-quality samples were 

required to compute the discharge and nutrient flux from the 

five estuarine river stations. Stream velocity (index-velocity) 

data were used to estimate the mean cross-section channel 

velocity (mean velocity) that was measured using a vesselmounted acoustic Doppler discharge measurement system. 

Stream velocity data were used with the measured mean 

channel velocity to develop index-to-mean velocity relations. 

Each station was equipped with similar instrumentation. Data 

collected at each station were reviewed for accuracy and 

entered into the USGS NWIS database. Data for each station 

were then used to develop regression equations that were used 

to estimate water discharge and nutrient flux.

Water-Level and Velocity Measurements

Water level was measured at each station using Design 

Analysis Associates H-310 vented-submersible pressure 

sensors that were mounted within 2-in. inside-diameter polyvinylchloride (PVC) pipes with end caps, which functioned 

as stilling wells. Quarter-inch holes were drilled around the 

perimeter of the PVC pipe within 6 in. of the bottom. Pressure 

sensors were programmed to average over an 8-second period 

every 15 minutes. Distances to water-level surfaces were measured from fixed reference points every 4 to 6 weeks and compared to the water levels measured by the pressure transducers. 

Water-surface reference measurements varied less than 0.02 ft 

from the pressure transducer water levels during the study. 

Methods 5
Two types of vertically oriented acoustic Doppler 

velocity systems were used to measure 2-min averages of 

velocity through the water column every 15 minutes:

(1) SonTek ADP 1.5 and 3 MHz velocity profilers, and

(2) SonTek Argonaut-XR 3 MHz depth-averaging

 velocity sensors.

Vertically oriented velocity profilers were used because 

vertical stratification of flow was possible, and because these 

sensors allow variations in the velocity profiles in the water 

column to be measured during all conditions. It has been suggested (Chiu and Said, 1995) that if the maximum velocities 

in an open channel can be measured, then all other velocities 

in a cross section can be theoretically estimated using channel 

geometry. Therefore, the use of vertically oriented velocity 

systems should allow the systems to be placed in regions of 

maximum velocities, where the maximum amount of information about open-channel flow is contained (Chiu and Said, 

1995). Theoretically, the most reliable relations between index 

velocity and measured-mean velocity could be acquired using 

this method. Unfortunately, maximum flood and maximum 

ebb velocities often do not occur in the same region of the 

river cross section. However, repeatable relations between 

index and mean velocities can be calculated despite this 

characteristic.

One drawback to using a vertically oriented indexvelocity system is the limited amount of across-channel 

volume that is measured. In rivers and streams with variable cross-channel flow distribution, this could prove to be a 

problem. If water flow is relatively uniform and flow patterns 

are always the same across the channel, vertically oriented 

sensors can provide an alternative to horizontally oriented 

index-velocity systems.

Discharge Measurements

River discharge was measured directly using a vesselmounted acoustic discharge system (Simpson and Oltmann, 

1992). An RD Instruments 1.2 MHz acoustic Doppler discharge measurement system was used to measure discharge for 

calibration and validation of the index-to-mean velocity relation at all stations every 4 to 6 weeks. The discharge section 

edges were marked with buoys and unmeasured edge section 

distances were measured using optical and laser range finders. 

Discharge values were calculated using manufacturer’s software. Individual discharge measurements took between 4 to 10 

minutes to complete.

Discharge measurements were collected over varying 

ranges of tidal level and tidal phase for about one year to 

develop an index-to-mean velocity relation for each station. 

Multiple measurements were made during 3- to 6-hour periods 

to better characterize variations in flow caused by variations 

in tide, inflow, and wind effects, and to reduce serial correlations between measurement sets. Discharge data collected 

after the calibration period were used to check the accuracy 

of the water-level/velocity/discharge relations for the duration 

of the study and to apply corrections or shifts to the index-tomean velocity relations if required. Corrections to the velocity 

regressions were not required at four of the five stations during 

the study. The Harney River station index-velocity data were 

corrected for June 1998 because of an electronics problem that 

caused the index-velocity data to be biased low.

Water-Quality Sampling

Water-quality samples also were collected every 4 to 6 

weeks during trips for discharge measurement and equipment 

maintenance. Daily fluctuation in water quality was assumed 

to be represented by samples collected near flood maximum 

and ebb maximum based on previous studies in west-central 

Florida (Stoker and others, 1995, 1996). Water-quality samples 

were collected for the determination of total nitrogen and total 

phosphorus concentrations and to estimate total nitrogen and 

total measured phosphorus flux at the southwest coast stations. 

Samples were collected at each station at least once daily, and 

typically were collected during flood, ebb, and slack tides.

Depth-integrated samples were collected at three crossstream locations using a stainless-steel-weighted TeflonTM 

bottle. A modified downrigger was used to regulate descent 

and ascent speed of the weighted TeflonTM bottle. Depthintegrated water samples from the three cross-stream locations 

were combined and mixed in a polyethylene churn and then 

distributed to individual sample bottles. Water sample bottles 

were then bagged in plastic and placed in a cooler with ice. 

All water-quality samples were analyzed at the USGS laboratory in Ocala, Fla. Water samples were analyzed for total and 

dissolved ammonia, ammonia-plus-organic nitrogen, nitrateplus-nitrite, nitrite, phosphorus, and orthophosphate. Analytical methods used in this study are documented in Fishman and 

Freidman (1989). Field measurements of water temperature, 

specific conductance, dissolved oxygen, and pH were collected concurrently during water-quality sample collection at 

each location to identify cross-stream and vertical variability.

Approximately 20 percent of the water samples collected 

were field quality-assurance samples. Two types of qualityassurance samples were collected: (1) duplicate samples and 

(2) equipment blanks. Field quality-assurance samples were 

sent to the laboratory with routine samples. Field measurement 

sensors were calibrated at the beginning of each day for each 

parameter.

In-situ temperature and specific conductance sensors 

were used to collect 15-minute-interval data near the water 

surface and at the bottom of the water column at each station. 

Near surface temperature and conductance sensors were 

removed after 3 years at the Broad, Harney, and Shark River 

stations because data indicated the rivers to be well-mixed 

from the top to the bottom of the water column. In-situ temperature and specific conductance sensors were checked for 

accuracy every 4 to 6 weeks both before and after cleaning 

6 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001
using three conductance standards. Any adjustments to data 

from the sensors based on field calibrations were made using 

variable shifts in the USGS Automated Data and Processing 

System (ADAPS).

Computation of Discharge

Discharge was computed using both a water depth to 

cross-sectional area relation and an index-to-mean velocity 

relation. Water depth to cross-sectional area relations were 

developed using 2nd-order polynomial equations. Velocity relations were developed using linear regression analysis 

of measured data. Random and systematic instantaneous 

discharge errors were evaluated.

Cross-Sectional Area Relation

River station cross-section bathymetry was measured 

using a 200 kHz recording fathometer. Cross-section elevation data not measured directly with the fathometer were 

measured using stadia rod and laser distance measurements. 

Water-level data were used with cross-section bathymetry data 

to determine cross-sectional area for any given water level. 

The water-level to cross-sectional area relation equations are 

shown in table 2.

using multiple-linear regression techniques. The independent 

variables used in the multiple-linear regression analysis 

were index velocity, index-velocity squared, and water level; 

whereas the dependent variable was mean-channel velocity (mean velocity). Index velocity was the only significant 

linear predictor of mean velocity for each station. However, 

the index-velocity relations had significant changes in slope 

for positive (downstream) and negative (upstream) velocities 

at the Broad, Harney, and Shark River stations. Index-to-mean 

velocity relation plots for the five stations are shown in figures 

3A-E. The index-to-mean velocity equations and basic statistics are shown in table 3. Instantaneous discharge for each 

river station was computed by multiplying estimated mean 

velocity (using the index-to-mean velocity relation equations) 

by area (using the water level to cross-sectional river area 

relation equations).

Estimation of Discharge Error

Uncertainty in estimating instantaneous discharge is 

produced by random and systematic errors. Random discharge 

errors can be removed by data averaging, whereas systematic discharge errors cannot be removed by averaging. Two 

principal sources of error in the estimate of instantaneous 

discharge are instrument errors associated with measurement 

of water depth and index velocity, and errors associated with 

the cross-sectional area and mean-velocity equations (Sloat 

and Gain, 1995). Two methods of estimating discharge error 

are discussed in this report. The first method uses the standard 

error of the estimate of the regression equations for estimating 

mean velocity in the river; the second method compares the 

difference of computed discharge (estimated using regression 

equations) to measured discharge and then uses the Wilcoxon 

Signed-Ranks test to determine if the median difference 

between the values is different from zero. A difference from 

zero indicates a bias in the computed discharge.

The first method estimates instantaneous discharge error 

by multiplying the standard error estimate for each indexto-mean velocity regression equation by the corresponding 

median cross-sectional area. The instantaneous discharge 

errors using the standard error and median cross-sectional 

areas are listed in table 3 along with basic regression statistics 

for the velocity regression equations. Residual plots of the 

index-to-mean velocity regression equations were analyzed 

and appear to be random, indicating that biases are unlikely. 

Maximum instantaneous discharge errors were approximately 

213, 65, 326, 453, and 193 ft3/s for Lostmans Creek, Broad 

River, Harney River, Shark River, and North River, respectively (table 3). The maximum discharge errors as a percentage of maximum instantaneous discharge are 9, 2, 2, 4, and 18 

percent for Lostmans Creek, Broad River, Harney River, Shark 

River, and North River, respectively. Random errors associated 

with individual acoustic discharge measurements were estimated to be less than 3 percent of the true discharge based on 

a simple random error model for acoustic discharge measureTable 2. Southwest coast station cross-sectional area regression 

equations.

[Area in square feet; depth, water level in feet]

Station name Water-depth-to-cross-sectional 

area equation

Lostmans Creek Area = 0.19 * depth2 + 277.2 * depth +10.2

Broad River Area = 0.28 * depth2

 + 185.9 * depth + 256.1

Harney River Area = 2.20 * depth2

 + 365.0 * depth + 1527.8

Shark River Area = 0.35 * depth2 + 423.9 * depth + 901.6

North River Area = 0.37 * depth2 + 246.6 * depth + 5.9

Index-Velocity Relation

Linear index-to-mean velocity regression models (indexvelocity relations) were developed for each station relating 

index velocity to mean velocity computed from measured 

discharge. Mean velocity was computed by dividing the 

measured discharges by the cross-sectional area (determined 

from the cross-sectional area equations) of the channel for the 

mid-time of the discharge measurement. Index velocities were 

then plotted against the mean channel velocities and analyzed 

Computation of Discharge 7
Broad River Velocity Rating

February 1997 - May 1998

Harney River Velocity Rating

February 1997 - January 1998

Shark River Velocity Rating

February 1997 - January 1998

INDEX VELOCITY, IN FEET PER SECOND

E

North River Velocity Rating

April 1999 - August 2000

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

MEAN VELOCITY, IN FEET PER SECOND

Lostmans Creek Velocity Rating

April 1999 - August 2000

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

A B

C D

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

Velocity

Regression line

Velocity

Positive regression line

Negative regression line

Velocity

Positive regression line

Negative regression line

Velocity

Positive regression line

Negative regression line

Velocity

Regression line

Figure 3. Index velocity to mean velocity regression relations for Lostmans Creek, Broad River, Harney River, Shark River, 

and North River stations.

8 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001
ment systems (Simpson and Bland, 2000). Simpson and Bland 

(2000) also noted that the measurement of less than the entire 

river cross section for an index velocity may result in sampling 

bias (systematic error). The index-velocity methods used in 

this study sampled a relatively small horizontal cross section 

of the rivers and could be biased. Other methods of indexvelocity measurement such as horizontal-averaging velocity 

systems can also be biased, so care must be used when determining any index-to-mean velocity relation.

The second method for estimating instantaneous 

discharge error provides information about discharge random 

error and bias. Discharge errors were calculated by subtracting the computed discharge from the measured discharge, 

and then basic statistics (minimum, maximum, mean, and 

standard deviation) were calculated for the discharge errors. 

The standard deviations of the discharge error are similar 

to the errors computed using the first method (table 3). 

Additional discharge measurements that were not used to 

develop the index-velocity relations were used in this method 

for three of the five stations (Broad, Harney, and Shark Rivers 

which had data-collection periods that were 2 years longer).

The Wilcoxon-Signed-Ranks test (WSR) was used to 

compare the difference between the medians of computed 

discharges and measured discharges. The WSR test can 

provide information relating to biases between the computed 

and measured discharges. The median values for discharge 

error are not significantly different from zero for four of 

the five stations based on the WSR probabilities (table 4). 

Table 3. Index velocity regression equations and discharge error estimates using standard error estimate method.

[All equations are for mean velocity in the stream, in feet per second. R2, correlation coefficient; ft/s, feet per second; ; ft2, square feet; ; ft3/s, cubic feet per 

second; Vm, mean velocity in feet per second; Vi, measured index velocity in feet per second; S.E.E, standard error of the estimate]

Station

Number of

discharge

measurements

Equation R2

Standard

error of the

estimate

(ft/s)

Median crosssectional area 

(ft2)

Instantaneous

discharge

error for median 

cross-sectional area

(ft3/s)

(S.E.E. * median area)

Lostmans Creek 58 Vm = 1.031 Vi + 0.092 0.92 0.23 927 213

Broad River

 Positive velocity 86 Vm = 0.8182 Vi + 0.012 0.98 0.05 1,379 65

 Negative velocity 47 Vm = 0.919 Vi - 0.001 0.98 0.04 1,379 54

Harney River

 Positive velocity 53 Vm = 0.9388 Vi - 0.02 0.98 0.06 4,521 254

 Negative velocity 71 Vm = 0.827 Vi + 0.005 0.96 0.07 4,521 326

Shark River

 Positive velocity 89 Vm = 0.6926 Vi - 0.054 0.94 0.10 4,362 453

 Negative velocity 47 Vm = 0.7564 Vi + 0.0007 0.94 0.08 4,362 331

North River 131 Vm = 0.7017 Vi - 0.04181 0.60 0.17 1,143 193

Table 4. Computed discharge error estimation based on measured discharge and Wilcoxon Signed Ranks probability for determining 

median error is different from zero.

[Error = computed discharge minus measured discharge; ft3/s, cubic feet per second; WSR, Wilcoxon Signed Ranks test]

Station name

Number of

discharge

measurements

Minimum 

error

(ft3/s)

Maximum 

error

(ft3/s)

Mean

(ft3/s)

Median

(ft3/s)

WSR probability that 

median difference is zero

Standard 

deviation

(ft3/s)

Lostmans Creek 69 -334 490 16 6 0.85 209

Broad River 227 -350 335 -9 -5 0.29 98

Harney River 196 -1,268 900 -10 -31 0.67 337

Shark River 205 -1,208 1,055 74 125 0.002 398

North River 131 -378 510 12 3 0.62 192

Computation of Discharge 9
The median values not significantly different from zero 

(probabilities 0.29 to 0.85) indicate that bias in the discharge is 

unlikely. However, the Shark River WSR probability less than 

0.002 indicates that the median error for discharges is significantly different from zero, which could indicate a positive bias 

for computed discharge.

The Shark River instantaneous discharge bias based on 

the WSR is between 74 and 125 ft3/s (table 4), indicating that 

the true discharges for the Shark River may be slightly lower 

than the values in this report. This bias may be attributed in 

part to the confluence of a small creek that enters the Shark 

River upstream of the discharge measurement section that was 

not well represented using the index-velocity system.

The North River station had the greatest percentage error 

in instantaneous discharge, as expected based on the velocity regression model (R2

 = 0.60 compared to 0.92 to 0.98 for 

the other stations). However, the long-term North River mean 

discharge should be close to the actual discharge because 

residual plots (figs. 4A-E) of the index-to-mean velocity 

regression data and Wilcoxon-Signed-Ranks test (table 4) 

indicate the uncertainty is random and the mean and median 

WSR errors are not significantly different from zero. The poor 

index-to-mean velocity regression model for the North River 

indicates the velocity sensor was located in a section of the 

river that did not represent the mean channel velocity all of 

the time. In addition, a relatively low tidal range (typically 

less than 1⁄2 ft) measured at this station could allow the flow 

distribution across the channel to be easily changed by wind 

forcing. Additionally, the channel geometry (wide and relatively shallow with no distinct center channel and confluence 

of two river sections upstream of the station) also could have 

contributed to a poor index-to-mean velocity relation. 

Discharge Characteristics

Discharges from the Lostmans Creek, Broad, Harney, 

Shark, and North Rivers are predominantly influenced by 

semidiurnal astronomical tides, longer period astronomical 

tides, wind events, and water inflow (rain, surface water, and 

ground water). Discharge flow direction at these stations was 

one dimensional except for brief periods (less than 20 minutes) during slack water between flood and ebb tide. During 

these periods, flow was vertically and horizontally bidirectional (moving upstream and downstream). For a typical tidal 

cycle, the flood discharges (water moving upstream, denoted 

as negative values) were usually of greater magnitude and 

shorter duration (4 to 5 hours) than the ebb discharges. Ebb 

discharges (water moving downstream, denoted as positive 

values) were slightly less magnitude than the flood discharges 

but longer duration (5 to 7 hours) (fig. 5). 

Residual discharge in this report refers to the discharge 

data after filtering the instantaneous discharge with a digital 

filter. Filtering allows the computation of daily mean and 

monthly mean discharge values without aliasing the data. 

Aliasing of data causes the introduction of a false signal that 

is not contained in the original data. Aliasing occurs when the 

sampling frequency is less than twice the highest frequency 

contained in the measured data (Orfanidis, 1996). A 9th order 

Butterworth low-pass filter was used to attenuate semidiurnal 

tidal fluctuations of less than about 40 hours in the instantaneous discharge data (Roberts and Roberts, 1978). The order 

of the Butterworth filter comes from the selection of the corner 

frequencies (normalized passband frequency (1/80), and 

normalized stopband frequency (1/60)), the passband ripple 

(1 decibel), and the stopband attenuation (15 decibel). The 

corner frequencies are normalized to the Nyquist frequency 

(Nyquist, 1928). These parameters are used to determine the 

minimum order of the Butterworth low-pass filter (9th order) 

in the Matlab Signal Processing Toolbox (The MathWorks, 

Inc., 1998). After the minimum order of the filter is determined, the Matlab Signal Processing Toolbox is used to design 

a Butterworth filter based on the order of the filter and the 

cutoff frequency. The cutoff frequency is a number between 

0 and 1 where 1 corresponds to one-half the sampling frequency (The MathWorks, Inc., 1998). After all these values 

are determined, the input data are processed through a forward 

and reverse digital filter that preserves the original phase of the 

input data. Data resulting from this process are called residual 

data.

Values of residual discharge include freshwater inflow, 

ground-water inflow, and storage due to prevailing winds or 

long-term (greater than 40 hours) astronomical tides. Storm 

events with strong associated winds are noticeable in the 

residual discharge data. Daily mean and monthly mean data 

were determined using the residual discharge data. 

The five station’s total monthly mean discharges were 

compared to ENP monthly rain totals and USGS discharges 

from the S-12 A, B, C, and D (S-12) structures along the 

Tamiami Trail (U.S. Highway 41) (fig. 1, figs. 6A-E). Residual 

discharge responses to rainfall for the Lostmans Creek, Broad, 

Harney, and Shark River stations show similar patterns and 

magnitudes, whereas the North River station residual discharge response was similar to the other four stations but 

with a lesser magnitude (figs. 6A-E). Negative mean residual 

discharges are typical in the southwest coast estuaries from 

March to May, as the mean water level in the Gulf of Mexico 

begins to increase after reaching a low in late winter and 

surface runoff is reduced because of lower rainfall during the 

winter. Residual discharge peaks at the coast stations typically lead the discharge peaks at the S-12 structures by about 

1 month. The relatively flat terrain and the rapid response of 

the measured coast discharges to rainfall in the Shark River 

Slough may explain the measured coast discharge peak leading the S-12 discharge peak. It also is possible that the flow 

releases through the S-12 structures do not begin until water 

levels on the upgradient side of the structures begin to rise. 

Linear regression analysis of S-12 total discharge to the five 

station total discharge (lagged by 1 month) indicate that the 

total monthly mean discharge for the five rivers is approximately two to three times greater than the total discharge at 

structures S-12 (fig. 7).

10 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

Lostmans Creek Index-to-Mean Velocity Residuals

INDEX VELOCITY, IN FEET PER SECOND

RESIDUALS, IN FEET PER SECOND

Broad River Index-to-Mean Velocity Residuals

-1.5 -1 -0.5 0 0.5 1 1.5

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Harney River Index-to-Mean Velocity Residuals

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

Shark River Index-to-Mean Velocity Residuals

North River Index-to-Mean Velocity Residuals

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 2 1.5 2.5

A B

C D

E

Figure 4. Residual plots of index-to-mean velocity regression relations for Lostmans Creek, Broad River, Harney River, Shark 

River, and North River stations.

Computation of Discharge 11
The Lostmans Creek, Broad River, Harney River, and 

Shark River stations had approximately equal residual flow 

between 20 to 27 percent of the total measured coast discharge 

when total measured residual discharge was between about 

1,250 to 3,000 ft3/s (figs. 8A-E). Residual flow distribution 

estimates for the five rivers were made based on 6 months 

of residual monthly mean discharges when all stations had 

complete months of residual discharge data. Over a longer 

11-month period with concurrent data during 1998, the Broad, 

Harney, and Shark Rivers residual flows were evenly divided, 

with each river accounting for 30 to 35 percent of the threestation total residual discharge. The similarity in residual 

discharge between Lostmans Creek, Broad, Harney, and Shark 

Rivers indicates that the Shark River Slough outflow region 

extends at least as far north as Lostmans Creek, and possibly 

as far south as North River. However, residual flow magnitudes decrease significantly at North River. North River typically accounted for only about 4 percent of the total residual 

flow for all stations during periods with concurrent data. 

Discharge and Water-Level 

Synopsis

The following sections include brief discussions of 

discharge characteristics of individual stations comparing 

the tidal ranges and response of each station to significant 

hydrologic events. To allow easy comparison of tidal ranges, 

water levels were converted to mean-normalized water levels 

(normalized water level). The mean water level during the 

1999-2001 period was subtracted from the water level to 

compute a normalized water level. Because of their remoteness, the stations were not surveyed to a vertical datum. The 

mean water level of the rivers is typically lower during the 

winter and early spring along the southwest coast of Florida, 

and it is not unusual for strong southeast winds to precede a 

cold front and force water out of the estuaries. Then, strong 

northwest winds (20 to 25 miles per hour) occur after the front 

that forces water back into the estuaries.

00:00 04:48 09:36 14:24 19:12 00:00 04:48 09:36 14:24 19:12 00:00

-12,000

-10,000

-8,000

-6,000

-4,000

-2,000

0

2,000 

4,000

6,000

8,000

10,000

12,000

August 10 - 11, 1999

DISCHARGE, IN CUBIC FEET PER SECOND

Southwest Coast Station Instantaneous discharges

Ebb tide Flood tide

24 - HOUR TIME

Lostmans Creek

Broad River

Harney River

Shark River

North River

Figure 5. Typical instantaneous discharge cycle for five stations along the southwest coast of the 

Everglades National Park.

12 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001
Figure 6. Monthly mean residual discharge for the five southwest coast stations, S-12-A, B, C,and D monthly mean 

discharge, and ENP average monthly total rainfall for 1997-2001.

Discharge and Water-Level Synopsis 13

1997

A

0

5

10

15

20

1997

J F M A M J J A S O N D

J F M A M J J A S O N D

J F M A M J J A S O N D

J F M A M J J A S O N D

-500

0

500

1,000

1,500

S12

Broad River

Harney River

Shark River

MONTHLYMEAN RAINFALL, 

IN INCHES

MONTHLYMEAN RAINFALL, 

IN INCHES

MONTHLYMEAN DISCHARGES, 

IN CUBIC FEET PER SECOND

MONTHLYMEAN DISCHARGES, 

IN CUBIC FEET PER SECOND

B

1998

1998

-500

0

500

1,000

1,500

S12

Broad River

Harney River

Shark River

0

5

10

15

20
14 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001

2000

1999

1999

D

C

-500

0

500

1,000

1,500

-500

0

500

1,000

1,500

2000

0

5

10

15

20

0

5

10

15

20

J F M A M J J A S O N D

J F M A M J J A S O N D

J F M A M J J A S O N D

J F M A M J J A S O N D

MONTHLYMEAN RAINFALL, 

IN INCHES

MONTHLYMEAN RAINFALL, 

IN INCHES

MONTHLYMEAN DISCHARGES, 

IN CUBIC FEET PER SECOND

MONTHLYMEAN DISCHARGES, 

IN CUBIC FEET PER SECOND

S12

Lostmans Creek

Broad River

Harney River

Shark River

North River

S12

Lostmans Creek

Broad River

Harney River

Shark River

North River

Figure 6. Monthly mean residual discharge for the five southwest coast stations, S-12-A, B, C,and D monthly mean 

discharge, and ENP average monthly total rainfall for 1997-2001. (Continued)
Figure 6. Monthly mean residual discharge for the five southwest coast stations, S-12-A, B, C,and D monthly mean 

discharge, and ENP average monthly total rainfall for 1997-2001. (Continued)

2001

E

0

5

10

15

20

-500

0

500

1,000

1,500

S12

Lostmans Creek

Broad River

Harney River

Shark River

North River

J F M A M J J A S O N D

J F M A M J J A S O N D

2001

MONTHLYMEAN RAINFALL, 

IN INCHES

MONTHLYMEAN DISCHARGES, 

IN CUBIC FEET PER SECOND

-1,000

0

1,000

2,000

3,000

4,000

5,000

6,000

0 200 400 600 800 1,000 1,200 1,400 1,600

S-12-A,B,C,D TOTAL DISCHARGE, 

 IN CUBIC FEET PER SECOND

SOUTHWEST COAST FIVE STATION TOTAL DISCHARGE, 

IN CUBIC FEET PER SECOND

Figure 7. Southwest coast stations monthly mean residual discharge (coast station discharges 

lagged by 1 month) to S-12-A, B, C, and D monthly mean discharge regression relation.

Discharge and Water-Level Synopsis 15
Broad

River

35%

Harney 

River

33%

Shark 

River

32%

FEBRUARY 1998, 1,330 CUBIC FEET PER SECOND NOVEMBER 1999, 3,200 CUBIC FEET PER SECOND 

SEPTEMBER 1998, 1,250 CUBIC FEET PER SECOND 

Broad

River

37%

Harney 

River

28%

Shark 

River

35%

Lostmans

Creek

34%

Broad

River

39%

Harney 

River

2%

Shark 

River

14%

North

River

11%

JUNE 2000, 600 CUBIC FEET PER SECOND 

Lostmans 

Creek

20%

Broad 

River

26%

Harney

River

23%

Shark

River

27%

North

River

4%

A 

B 

C 

D 

E 

Average Southwest Coast

Flow Distribution

North

River

5% Lostmans

Creek

23%

Broad

River

26%

Harney

River

20%

Shark

River

26%

Figure 8. Monthly mean and 2-year average residual discharge distributions for selected periods of 

concurrent data between 1998-2000.

16 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001
Discharge and Water-Level Synopsis 17

Lostmans Creek Station

The Lostmans Creek normalized water level ranged from 

-1.64 to 2.13 ft during the study. Index velocities greater than 

1 ft/s occurred during less than 10 percent of the study period. 

Computed instantaneous discharges at the Lostmans Creek 

station ranged from -2,600 ft3/s during the passage of Tropical 

Storm Harvey on September 21, 1999, to +2,400 ft3/s during the passage of Hurricane Irene on October 15, 1999. The 

maximum residual discharge of +1,560 ft3/s also occurred during the passage of Hurricane Irene, and the minimum residual 

discharge of -835 ft3/s occurred on March 27, 2000, during the 

passage of a strong cold front during a period of lower mean 

water level at the station.

Residual discharge for January through December 2000 

was less than during 1999 because of less rainfall. Approximately 70 in. of rainfall fell on ENP in 1999 (average of 16 

stations shown in fig. 1), whereas only 51 in. fell in 2000 

(Everglades National Park, 1996-2001). The daily mean 

residual discharge during the study period ranged from -610 to 

+1,470 ft3/s. A strong cold front in March 2000 caused water 

to pile up in the mangrove forests and resulted in the largest 

negative daily mean residual discharge for the study period 

of -610 ft3/s. The rest of the year was relatively uneventful, 

with a maximum daily mean residual discharge of approximately 800 ft3

/s, which was about half the maximum for 1999. 

Lostmans Creek absolute residual discharge (absolute value 

of residual discharge) was greater than 500 ft3/s for 20 percent 

of the study period, and absolute instantaneous discharge 

(absolute value of instantaneous discharge) was greater than 

500 ft3/s approximately 50 percent of the study period.

Broad River Station

The Broad River station normalized water levels ranged 

from -2.03 to +2.05 ft during the study, with a typical springtide water-level range of approximately 2 ft. The maximum 

index velocity recorded was +2.99 ft/s during the passage of 

Hurricane Irene in October 1999, and the minimum index 

velocity, -1.78 ft/s, occurred during the passage of a strong 

cold front in January 2001. Computed instantaneous discharges at the Broad River station ranged from -2,400 ft3

/s 

during the passage of a frontal storm system on April 30, 

1999, to +3,500 ft3/s during the passage of Hurricane Irene on 

October 15, 1999. There were some periods when the instantaneous discharge did not reverse (move upstream) for as long 

as a month. The maximum residual discharge was +2,500 ft3/s 

during the passage of Hurricane Irene, whereas the minimum 

residual discharge was -1,700 ft3/s during the passage of a cold 

front on February 4, 1998. The Broad River station daily mean 

residual discharge ranged from -1,320 to +2,040 ft3/s.

Harney River Station

The Harney River station normalized water levels ranged 

from -2.95 to +3.42 ft, with a typical spring-tide water-level 

range of approximately 4 ft. Maximum velocities for flood 

tide occurred right of river center (looking downstream), 

and maximum ebb flows occurred left of river center based 

on acoustic discharge measurements. The maximum index 

velocity recorded was 2.7 ft/s during the passage of Tropical 

Storm Harvey on September 21, 1999, and the minimum index 

water velocity recorded was -3.2 ft/s earlier on the same day 

as winds blew onshore. Computed instantaneous discharges at 

the Harney River station ranged from -12,000 to +10,000 ft3/s 

during the study. The daily mean residual discharge during the 

study period ranged from -2,290 to +4,860 ft3/s. 

Harney and Shark Rivers are both connected to Tarpon 

Bay. Acoustic discharge measurements on the Harney River 

approximately 300 ft downstream of Tarpon Bay from the 

June 1996 reconnaissance identified a short period of time 

when the Harney River flow was flooding (moving upstream), 

while the Shark River flow slightly downstream of Tarpon 

Bay had been ebbing a short time before. These measurements suggest that during specific periods, water can move 

upstream into Tarpon Bay from the Harney River while Tarpon 

Bay water is flowing downstream into the Shark River. The 

contrary flood and ebb flows are believed to be a rapid occurrence (duration less than 15 minutes), because flow in the 

Shark River was upstream (flooding) when it was measured 

about 10 minutes later. These contrary flows would tend to 

reduce the daily mean residual discharge values for the Harney 

River station while artificially increasing those at the Shark 

River station. However, the short duration of the flows and the 

uncertainty of how often the contrary flows occur suggest they 

will probably not significantly affect long-term mean residual 

discharges for either station.

Shark River Station

The Shark River station normalized water levels 

ranged from -2.63 to +3.08 ft. The maximum water level 

occurred during the passage of Tropical Storm Harvey on 

September 21, 1999, and the minimum water level occurred 

as Hurricane Georges passed offshore in the Gulf of Mexico 

on September 25, 1998. Similar to the Harney River station, 

maximum velocities for flood flows occurred right of the river 

center and maximum velocities for ebb flow occurred left of 

river center based on acoustic discharge measurements. Index 

velocities ranged from -2.5 to +3.0 ft/s, and a typical tidal 

cycle range was usually ±2 ft/s. The maximum water velocity occurred during the passage of Tropical Storm Harvey on 

September 21, 1999, and the minimum occurred during the 

passage of Tropical Storm Mitch on November 5, 1998. The 
passage of Tropical Storm Mitch on November 5, 1998. The 

Shark River station instantaneous discharges were slightly 

less than the Harney River station and ranged from -10,000 

to +8,000 ft3/s. The daily mean residual discharge during the 

study period ranged from -1,970 to +3,790 ft3/s. 

North River Station

The North River station normalized water levels ranged 

from -1.67 to +2.06 ft. The maximum water level occurred 

during the passage of Tropical Storm Harvey on September 21, 

1999, whereas the minimum water level occurred during the 

passage of a cold front on January 15, 2000. Index velocities 

ranged from -1.1 to +1.8 ft/s and a typical tidal cycle range 

was -0.2 to +0.4 ft/s. The maximum water velocity occurred 

during the passage of Hurricane Irene on October 15, 1999, 

and the minimum velocity occurred during the passage of 

Tropical Storm Harvey on September 21, 1999. The North 

River station instantaneous discharges were the lowest of the 

five stations and ranged from -1,100 to +1,100 ft3/s. The daily 

mean residual discharge during the study period ranged from 

-360 to +530 ft3/s.

Water Quality and Nutrient Flux

Water-quality data consisted of nutrient-concentrations 

from water samples collected during the study and in-situ

water-quality measurements. Concentrations of constituents 

in duplicate samples were within 5 percent of original sample 

concentrations, and equipment blank sample concentrations 

indicated there was no significant contamination from the 

sampling procedure. Nutrient-concentrations and the in-situ

water-quality parameters generally exhibited seasonal variations, although short-term variation of concentrations and 

water-quality measurements also occurred.

Water-Quality Characteristics

Broad, Harney, and Shark Rivers were well mixed, with a 

difference in specific conductance from top to bottom usually no greater than 500 μS/cm during flood and ebb tides. 

Lostmans Creek and North River were usually well mixed, 

but there were occurrences of slightly stratified flows (topto-bottom difference 2,000 μS/cm) near the beginning of 

the wet season, or after significant rainfall events. Specific 

conductance at the Lostmans Creek and Broad River stations 

remained at 250 to 800 μS/cm from August through December 

1999 because of rainfall from the summer season and two lateseason tropical systems (39 in. of rainfall). Specific conductance at the Lostmans Creek and Broad River stations was less 

than 1,000 μS/cm for 30 percent of the study period.

All stations had relatively high total nitrogen concentrations of about 1 to 2 mg/L and very low total phosphorus 

concentrations, typically less than 0.04 mg/L (tables 5 and 6). 

Concentrations for total nitrogen and total phosphorus were 

very similar in magnitude and range at all five stations. Infrequently, a duplicate sample’s phosphorus concentration was 10 

to 20 percent different than the original sample concentration. 

Discussions with the USGS laboratory personnel identified 

possible interference with the low-level phosphorus analysis 

method, when used on saline water, that could result in erroneous phosphorus concentrations. Nitrite and nitrate concentrations were detected at very low levels and ranged from below 

the detection limit of 0.002 to 0.070 mg/L. 

Total nitrogen concentrations were approximately 75 to 

85 percent dissolved nitrogen, and total phosphorus concentrations were approximately 35 to 50 percent dissolved 

phosphorus. Dissolved nutrients are readily available to plants, 

and analyses indicated that approximately three-quarters of the 

total nitrogen and half of the total phosphorus are available in 

the dissolved form.

Total nitrogen concentrations for the five stations 

generally were inversely related to specific conductance 

(saltier water had lower nitrogen concentrations), but the relations were not statistically significant. However, at four of the 

five stations (all but the Shark River station), total phosphorus 

concentrations were directly related to specific conductance 

and the relations were statistically significant (p = 0.0 to 

0.11), which means that as the water became saltier (increased 

specific conductance water from the Gulf of Mexico), the 

total phosphorus concentrations increased. Two models were 

tested for estimating total measured phosphorus flux. One 

model used specific conductance as the independent variable 

to estimate phosphorus concentration for any given specific 

conductance. The second model is a more direct method 

that used discharge as the independent variable to estimate 

total phosphorus flux for any given discharge. In the second 

method, nutrient-concentration is multiplied by instantaneous 

discharge at the time of sample collection and a conversion 

factor to yield flux in short tons (2,000 pounds) per day. 

The flux values are then used as the dependent variable and 

discharge is the independent variable, and a linear regression 

equation is used to describe the relation (Helsel and Hirsch, 

1992). The two models gave similar results for monthly mean 

phosphorus flux. The second more direct method of estimating total nitrogen and total phosphorus flux was selected to 

estimate total station fluxes. 

Nutrient Flux

Nutrient fluxes were estimated for the five stations to 

provide information about loading to the estuarine system and 

the Gulf of Mexico from the upgradient regions of Everglades 

National Park. Instantaneous nitrogen and phosphorus fluxes 

were estimated using regression methods based on total 

18 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001
measured nitrogen flux and total measured phosphorus flux 

(dependent variables) and 15-minute instantaneous discharge 

(independent variable) (figs. 9A-J; tables 7 and 8).

Residual nutrient fluxes were calculated by processing 

the instantaneous nutrient flux data with the same 9th order 

Butterworth low-pass filter that was used to calculate residual 

discharge. Nutrient fluxes are a function of discharge; therefore, the nutrient fluxes for the five stations are proportional 

to discharge. Residual nutrient flux distributions for the five 

stations with concurrent data are shown in figures 10A-D. 

Total residual nitrogen fluxes and total residual phosphorus 

fluxes at the Lostmans Creek, Broad, Harney, and Shark River 

stations were evenly distributed, with each station accounting 

for between 23 to 27 percent of the five station total fluxes 

during low and high flow conditions. The North River station 

total residual nitrogen and total residual phosphorus fluxes 

accounted for 4 percent of the five station total fluxes, a value 

similar to the residual discharges for that station. 

 Total residual nitrogen flux from the five river stations 

was about 1,280 short tons for August 1999 through January 

2000, the highest flow period during the study. Total residual 

phosphorus flux from the five river stations was about 17 short 

tons for the same period, reflecting the low total phosphorus 

concentrations measured in the five rivers.

Summary

A study of discharge and nutrient fluxes was conducted 

at five tidally affected rivers that receive freshwater from the 

Shark River Slough of Everglades National Park, Florida. The 

study was funded through the U.S. Geological Survey Placed 

Based Studies Initiative, and partially funded for the final year 

by the U.S. Department of the Interior Critical Ecosystem 

Studies Initiative in cooperation with Everglades National 

Park (ENP). Data collection began at three stations between 

November 1996 and January 1997, and two additional stations 

were added in April 1999.

This study quantified residual discharge and residual 

nutrient flux from five estuarine rivers along the southwest 

coast of ENP. This is the first phase of a long-term effort to 

monitor estuarine river discharge to the southwest coast of 

Florida and evaluate estuarine discharge from ENP and Big 

Cypress National Preserve as rehabilitation of the Everglades 

System progresses.

River discharges were estimated using acoustic velocity 

systems and linear regression models. Instantaneous discharges for each station varied between -2,600 to +2,400 ft3

/s 

for the Lostmans Creek station; -2,400 to +3,500 ft3/s for the 

Broad River station; -12,0000 to +10,000 ft3/s for the Harney 

Table 5. Southwest coast station nitrogen concentration basic statistics.

[mg/L, milligrams per liter]

Station name Number of

samples

Total nitrogen (mg/L) Dissolved nitrogen (mg/L)

Maximum Minimum Mean Maximum Minimum Mean

Lostmans Creek 22 1.30 0.54 0.88 1.10 0.38 0.72

Broad River 60 1.60 0.48 0.94 1.32 0.45 0.80

Harney River 71 1.62 0.55 0.87 1.22 0.46 0.73

Shark River 65 1.13 0.54 0.83 1.12 0.42 0.70

North River 23 1.70 0.56 1.10 1.31 0.20 0.80

Table 6. Southwest coast station phosphorus concentration basic statistics.

[mg/L, milligrams per liter; <, less than]

Station name Number of

samples

Total phosphorus (mg/L) Dissolved phosphorus (mg/L)

Maximum Minimum Mean Maximum Minimum Mean

Lostmans Creek 22 0.032 0.005 0.014 0.016 < 0.002 0.005

Broad River 60 0.024 0.003 0.012 0.012 < 0.002 0.004

Harney River 71 0.042 0.010 0.021 0.024 0.003 0.009

Shark River 65 0.034 0.007 0.015 0.105 < 0.002 0.008

North River 23 0.028 0.005 0.015 0.013 < 0.002 0.006

Water Quality and Nutrient Flux 19
-1,500 -1,000 -500 0 500 1,000 1,500

-4

-3

-2

-1

0

1

2

3

4

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND

TOTAL NITROGEN FLUX, IN SHORT 

TONS PER DA

Y

Lostmans Creek Instantaneous Discharge To

Total Nitrogen Flux A B

C D

E

-2,000 -1,500 -1,000 -500 0 500 1,000 1,500 2,000

-6

-4

-2

0

2

4

6

Broad River Instantaneous Discharge To

Total Nitrogen Flux

Data

Regression line

Data

Regression line

Data

Regression line

-8,000 -6,000 -4,000 -2,000 0 2,000 4,000 6,000 8,000

-20

-15

-10

-5

0

5

10

15

20

Shark River Instantaneous Discharge To

Total Nitrogen Flux

-8,000 -6,000 -4,000 -2000 0 2,000 4,000 6,000 8,000

-20

-15

-10

-5

0

5

10

15

20

Harney River Instantaneous Discharge To

Total Nitrogen Flux

Data

Regression line

North River Instantaneous Discharge To

Total Nitrogen Flux

-500 -400 -300 -200 -100 0 100 200 300 400 500

-1.5

-1

-0.5

0

0.5

1

1.5

Data

Regression line

Figure 9. Southwest coast stations discharge to nutrient flux regression relations.

20 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001
Lostmans Creek Instantaneous Discharge To

Total Phosphorus Flux F G

H I

J

Broad River Instantaneous Discharge To

Total Phosphorus Flux

-2,000 -1,500 -1,000 -500 0 500 1,000 1,500 2,000

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

-1,500 -1,000 -500 0 500 1,000 1,500

-8,000 -6,000 -4,000 -2,000 0 2,000 4,000 6,000 8,000

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Harney River Instantaneous Discharge To

Total Phosphorus Flux

TOTAL PHOSPHORUS FLUX, IN SHORT 

TONS PER DA

Y

INSTANTANEOUS DISCHARGE, IN CUBIC FEET PER SECOND

Data

Regression line

Data

Regression line

Data

Regression line

Data

Regression line

Data

Regression line

Shark River Discharge To

Total Phosphorus Flux

-500 -400 -300 -200 -100 0 100 200 300 400 500

-0.025

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

North River Instantaneous Discharge To

Total Phosphorus Flux

-8,000 -6,000 -4,000 -2,000 0 2,000 4,000 6,000 8,000

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

Figure 9. Southwest coast stations discharge to nutrient flux regression relations. (Continued)

Water Quality and Nutrient Flux 21
River station; -10,000 to +8,000 ft3

/s for the Shark River 

station; and -1,100 to +1,100 ft3/s for the North River station. 

Maximum instantaneous discharge errors were approximately 

213, 65, 326, 453, and 193 ft3/s for Lostmans Creek, Broad 

River, Harney River, Shark River, and North River, respectively. The maximum discharge errors as a percentage of maximum instantaneous discharge are 9, 2, 2, 4, and 18 percent for 

Lostmans Creek, Broad River, Harney River, Shark River, and 

North River, respectively. Instantaneous discharge data were 

filtered using a 9th order Butterworth low-pass filter to remove 

predominant tidal frequencies, and the filtered data were used 

to compute daily mean and monthly mean residual discharges. 

The similarity in residual discharge between Lostmans Creek, 

Broad, Harney, and Shark Rivers indicates that the Shark 

River Slough outflow region extends at least as far north as 

Lostmans Creek, and possibly as far south as the North River. 

Regression analysis of monthly mean residual discharges 

indicate that the Lostmans Creek, Broad River, Harney River, 

Shark River, and North River systems discharge approximately two to three times the amount of water flowing through 

the Tamiami canal S-12 structures along U.S. Highway 41. 

Monthly mean residual discharges at the five stations along 

the southwest coast are at a maximum approximately 1 month 

before the S-12 structures reach their maximum discharges. 

Most of the total daily mean residual discharge from the five 

rivers is evenly distributed between Lostmans Creek, Broad, 

Harney, and Shark Rivers with each river contributing between 

20 to 27 percent of the residual discharge. In contrast, the 

North River typically discharged only 4 percent of the total 

residual discharge during the same period.

Table 7. Regression equations used to estimate total nitrogen flux.

[All equations are for total nitrogen flux in short tons per day. Q, discharge in cubic feet per second;

 R2, correlation coefficient]

Station

Number of 

water quality 

samples

Total nitrogen flux equation 

(short tons per day) R2

Standard error of the 

estimate

(short tons per day)

Lostmans Creek 22 Flux = 0.00235 Q - 0.00385 0.96 0.34

Broad River 60 Flux = 0.00252 Q - 0.04141 0.95 0.60

Harney River 71 Flux = 0.00231 Q + 0.53058 0.96 2.14

Shark River 65 Flux = 0.00221 Q + 0.21612 0.97 1.46

North River 23 Flux = 0.00269 Q - 0.05611 0.90 0.21

Table 8. Regression equations used to estimate total phosphorus flux.

[All equations are for total phosphorus flux in short tons per day. Q, discharge in cubic feet per second;

 R2, correlation coefficient]

Station

Number of

water quality

samples

Total phosphorus flux equation 

(short tons per day) R2

Standard error of the 

estimate 

(short tons per day)

Lostmans Creek 22 Flux = 0.00003501 Q - 0.002378 0.80 0.012

Broad River 60 Flux = 0.00003170 Q - 0.001453 0.88 0.013

Harney River 71 Flux = 0.00005428 Q - 0.012177 0.95 0.064

Shark River 65 Flux = 0.00004390 Q - 0.008485 0.96 0.037

North River 23 Flux = 0.00003626 Q - 0.000306 0.84 0.004

22 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001
The concentrations of total nitrogen and total phosphorus 

were similar in magnitude and range at all five stations; 

therefore, nitrogen and phosphorus flux distributions resemble 

the residual discharge distributions. Total nitrogen and total 

phosphorus residual fluxes from the five rivers were estimated 

using linear regression models of total nitrogen and total 

phosphorus flux to instantaneous discharge. Instantaneous 

nutrient flux data also were filtered using a 9th order Butterworth low-pass filter to remove predominant tidal frequencies, 

and the filtered data were used to compute residual nutrient 

fluxes. Total nitrogen residual flux was 1,280 short tons, and 

the total phosphorus residual flux was 17 short tons for a high 

flow period between August 1999 and January 2000. The 

distribution of residual fluxes was similar to the distribution 

of residual discharges. Lostmans Creek, and Broad, Harney, 

and Shark Rivers contributed approximately equal amounts of 

total nitrogen (20 to 27 percent of the total), whereas the North 

River contributed 4 percent of the total nitrogen. Lostmans 

Creek, and Broad, Harney, and Shark River stations discharged 

between 23 to 27 percent of the five station total phosphorus 

residual flux, whereas the North River discharged 3 percent of 

the five station total phosphorus residual flux.

A 

Broad

River

36%

Harney 

River

30%

Shark 

River

34%

B 

Broad 

River

31%

Harney 

River

44%

Shark 

River

25%

THREE STATION TOTAL PHOSPHORUS FLUX, 2 SHORT TONS

FEBRUARY TO DECEMBER, 1998 

C 

Lostmans

Creek

20%

Broad 

River

22%

Harney 

River

28%

Shark 

River

27%

North

River

3%

FIVE STATION TOTAL NITROGEN FLUX, 1,280 SHORT TONS

AUGUST 1999 TO JANUARY, 2000

 THREE STATION TOTAL NITROGEN FLUX, 680 SHORT TONS

FEBRUARY TO DECEMBER, 1998

D 

Lostmans

Creek

23%

Broad 

River

Harney 23%

River

23%

Shark 

River

27%

North

River

4%

 FIVE STATION TOTAL PHOSPHORUS FLUX, 17 SHORT TONS

AUGUST 1999 TO JANUARY, 2000 

Figure 10. Southwest coast three and five station total nitrogen and total phosphorus flux distributions for selected 

periods of concurrent data.

Summary 23
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24 Water Flow and Nutrient Flux from Five Estuarine Rivers along the Southwest Coast of the ENP, Florida, 1997-2001