Water-Resources Investigations Report 00-4057

Distribution, Movement, and Fate of Nitrate in

the Surficial Aquifer Beneath Citrus Groves,

Indian River, Martin, and St. Lucie Counties,

Florida

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the

Institute of Food and Agricultural Sciences, University of Florida
Distribution, Movement, and Fate of Nitrate in the 

Surficial Aquifer Beneath Citrus Groves, Indian 

River, Martin, and St. Lucie Counties, Florida

By C.A. Crandall

U.S. Geological Survey

Water-Resources Investigations Report 00-4057

Prepared in cooperation with the

INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES, UNIVERSITY OF FLORIDA

Tallahassee, Florida

2000
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

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

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

For additional information Copies of this report can be 

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

Suite 3015 Box 25286

227 N. Bronough Street Denver, CO 80225

Tallahassee, FL 32301 888-ASK-USGS

Additional information about water resources in Florida is available on the World Wide 

Web at http://fl.water.usgs.gov
Contents III

CONTENTS

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

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

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

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

Description of the Study Area ............................................................................................................................................. 3

Hydrogeology ............................................................................................................................................................ 4

Water Use and Supply ............................................................................................................................................... 5

Land-Use and Agricultural Practices ........................................................................................................................ 6

Methods ............................................................................................................................................................................... 9

Site Selection ............................................................................................................................................................. 9

Well Installation .......................................................................................................................................................10

Water-Level Measurements ......................................................................................................................................11

Sample Collection and Analysis ..............................................................................................................................11

Rainfall and Ground-Water-Flow Patterns .........................................................................................................................13

Rainfall Patterns .......................................................................................................................................................13

Ground-Water-Flow Patterns and Age of Water ......................................................................................................13

Isotopes ....................................................................................................................................................................18

Carbon, Oxygen, and Deuterium ....................................................................................................................19

Tritium and Helium-3 .....................................................................................................................................20

Distribution of Nitrate and Other Agricultural Constituents .............................................................................................21

Major Ions ................................................................................................................................................................21

Trace Elements .........................................................................................................................................................31

Nutrients ...................................................................................................................................................................32

Ammonium, Organic Nitrogen, and Phosphorus ...........................................................................................32

Nitrate .............................................................................................................................................................32

Fate of Nitrate in Ground Water ........................................................................................................................................34

Summary .............................................................................................................................................................................39

References Cited ................................................................................................................................................................40

Appendix I.—Attributes of Sampling Sites in This Study ................................................................................................43

Appendix II.—Sampling Schedule of Chemical Constituents, by Site .............................................................................47

Appendix III.—Water-Quality Data, 1996-98 ...................................................................................................................51

Figures

1. Map showing citrus sites, reference site, and irrigated citrus areas, Indian River, Martin, and 

St. Lucie Counties, Fla. ...........................................................................................................................................3

2. Graphs showing irrigated citrus acreage in Indian River, Martin, and St. Lucie Counties, Fla., compared to 

each other and to total production, 1966-98 ............................................................................................................6

3. Diagram of a typical citrus block showing beds, tree rows, canals, furrows, monitoring wells, and soil layers ....7

4-6. Photographs of: 

4. Drainage canal with furrow drain pipes extending out of the wall of the canal, St. Lucie County, Fla. ..........8

5. Microsprinkler irrigating a citrus tree, Martin County, Fla. .............................................................................8

6. Wells at the reference site in a natural pine and palmetto habitat, St. Lucie County, Fla. .............................10

7-18. Graphs showing:

7. Hourly water levels in wells and canal at site 2, July through October 1998, Indian River County, Fla. ......14

8. Water levels measured at the reference and citrus sites, December 1996 through July 1998, 

Indian River, Martin, and St. Lucie Counties, Fla. .........................................................................................15

9. Values of delta 13C and calcite saturation index, by site and well, May 1998 ...............................................19

10. Values of delta 18O and delta deuterium at sites 2 and 5, May 1998 ..............................................................20
IV Contents

11. Major ion distribution, nitrate, and dissolved-solids concentrations on Durov diagram for site 2 and the 

reference site, May 1998 ................................................................................................................................ 21

12. Major ions and nutrients at study sites, December 1996 and May 1998, Indian River, Martin, and

St. Lucie Counties, Fla. .................................................................................................................................. 24

13. Major ions and nutrients at citrus sites, by depth, December 1996 and May 1998, Indian River, 

Martin, and St. Lucie Counties, Fla. .............................................................................................................. 30

14. Chloride and nitrate concentrations compared by depth at sites 1, 2, 6, and the reference site ..................... 33

15. Correlations of nitrate concentrations with other constituent concentrations in samples from the 

citrus sites, Indian River, Martin, and St. Lucie Counties, Fla. ..................................................................... 34

16. Nitrate, delta 15N, and excess N2 gas, by depth, at sites 2, 4, 5, and the reference site, July 1997 and 

May 1998 ....................................................................................................................................................... 36

17. Values of delta 15N of NO3 and concentrations of excess N2 gas compared to NO3, sites 2, 4, and 5, 

July 1997 and May 1998 ................................................................................................................................ 37

18. Concentrations of dissolved argon and N2 in ground water compared to equilibrium concentrations 

of air in water at sites 2, 4, 5, and the reference site, May 1998 ................................................................... 38

Tables

1. Generalized geologic sections and hydrogeologic units in east-central Florida ............................................................4

2. Water use in Indian River, Martin, and St. Lucie Counties, Fla., 1995 ..........................................................................5

3. Primary soil series, management practices, and crop variety/vegetation for each sampling site, Indian River, 

Martin, and St. Lucie Counties, Fla.,...............................................................................................................................9

4. Annual total rainfall for 1997 and 1998 and average annual rainfall, in inches, at the citrus sites and at the

reference site, Indian River, Martin, and St. Lucie Counties, Fla. ...............................................................................13

5. Tritium age, corrected age of recharge water, and vertical velocity of ground water in deep wells at selected 

sites, May 1998 ............................................................................................................................................................20

6. Geochemical water types, December 1996 and May 1998 ..........................................................................................21

7. Median and range in values of field parameters, and concentrations of major ions, nutrients, and selected trace

elements in ground-water and surface-water samples, by site, December 1996 and May 1998 ..................................22

8. Median and range in values of field parameters, and concentrations of major ions, nutrients, and selected trace 

elements, by depth, at citrus sites, December 1996 and May 1998 .............................................................................25

9. Median and range in values of field parameters, and concentrations of major ions, nutrients, and selected trace 

elements, by depth, at the reference site, December 1996 and May 1998 ...................................................................27

10. Dissolved gas concentrations in ground water and estimated excess N2, recharge temperature, and excess air 

from midlevel and deep wells, May 1998 ....................................................................................................................29

11. Median trace-element concentrations, ranges, detection levels, and minimum percentage of samples below 

detection level in ground and surface water from all sites, December 1996 ................................................................31
Contents V

Conversion Factors, Acronyms, and Abbreviations

Temperature can be converted between degrees Fahrenheit (F) and degrees Celsius (C) as follows:

°F = 9/5 (°C) + 32

°C = 5/9 (°F - 32)

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

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

Multiply By To obtain

inch (in.) 25.4 millimeter

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

foot (ft) 0.3048 meter

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

acre 0.4047 hectare

pound per acre (lb/acre) 1.12 kilogram per hectare

million gallons per day (Mgal/d) 0.04381 cubic meter per second

DOC = dissolved organic carbon

MCL = maximum contaminant level

SI = saturation indices

TU = tritium units

USEPA = U.S. Environmental Protection Agency

USGS = U.S. Geological Survey

μg/L = micrograms per liter

mg/L = milligrams per liter

cm3

/L = cubic centimeter per liter
VI Contents
Abstract 1

Distribution, Movement, and Fate of Nitrate in the 

Surficial Aquifer Beneath Citrus Groves, Indian River, 

Martin, and St. Lucie Counties, Florida

By C.A. Crandall

Abstract

The surficial aquifer system beneath citrus 

groves in Indian River, Martin, and St. Lucie Counties, Florida, was studied to determine the effects of 

citrus agriculture on ground-water quality. The 

surficial aquifer is the primary drinking-water 

source for Martin and St. Lucie Counties and 

furnishes about 33 percent of the drinking-water 

for Indian River County. Water-quality samples 

and water-level data were collected from December 1996 through October 1998. Nitrate concentrations in ground water exceeded 10 milligrams 

per liter (mg/L), the U.S. Environmental Protection 

Agency’s maximum contaminant level for nitrate 

reported as nitrogen, in 5 percent of the samples 

from citrus groves. These exceedances occurred in 

samples from wells with depths of 10 feet or less at 

citrus groves, and mostly in samples collected 

during or immediately following fertilizer applications. Samples from wells with depths of 20-25 feet 

contained little or no nitrate. The decreased nitrate 

concentrations in ground water with depth was not 

consistent with chloride and dissolved-solids 

concentrations, two other common indicators of 

agricultural activity. Chloride and dissolved-solids 

concentrations remained elevated in ground-water 

samples from all depths at citrus groves; median 

chloride and dissolved-solids concentrations in 

samples from citrus sites were 125 and 779 mg/L, 

respectively. In comparison, samples from the 

reference site had maximum chloride and 

dissolved-solids concentrations of 61 and 366 mg/L, 

respectively. Based on the age of ground water at 

20-25 foot depths (3-50 years, measured with 

tritium and helium-3 concentration ratios), nitrate 

concentrations also should have remained elevated 

with depth because fertilizers have been used for at 

least 20-30 years at these citrus groves. Nitrate 

concentrations decreased with depth as a result of 

denitrification. This could have occurred because 

favorable conditions for denitrification existed in 

the aquifer, including high concentrations of 

dissolved organic carbon and iron (median concentrations of 25.5 and 1.75 mg/L, respectively at 

citrus sites) and low concentrations of dissolved 

oxygen (median concentration of 0.9 mg/L at 

citrus sites), which indicates that reducing conditions were present. Evidence that denitrification 

occurred included the enrichment of ground water 

with depth in the heavier isotope of nitrogen, nitrogen-15 (15N). Ground water from wells screened 

10-15 feet below land surface had a median δ 15N 

value of 24.6 per mil, whereas ground water from 

wells screened 5-10 feet below land surface had a 

median δ 15N value of 9.4 per mil. Fertilizer 

samples had a median δ 15N value of 3.0 per mil. 

Increased δ 15N values coincident with decreased 

nitrate concentrations with depth indicates that 

fractionation occurred during denitrification reactions. Finally, excess nitrogen gas, a byproduct of 

denitrification reactions, was detected at concentrations ranging from 0-8 mg/L in samples from 

wells screened 10-25 feet below land surface. 
2 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

INTRODUCTION

Large quantities of nitrogen in fertilizers in 

various forms, such as ammonium nitrate (NH4 NO3) 

and potassium nitrate (KNO3), are applied annually 

to citrus groves in Florida to improve the quality and 

production of fruit. Much of the nitrogen is readily 

converted to nitrate, a highly soluble and mobile 

species that has the potential to leach to underlying 

aquifers. The surficial aquifer is the primary drinkingwater source in Indian River, Martin, and St. Lucie 

Counties (Alvarez and Bacon, 1988). Concern for 

public drinking-water supplies owing to the high 

application rates of nitrogen-containing fertilizers and 

the proximity of the water table to land surface in 

citrus-producing areas prompted this study. 

Ground-water contamination from nitrogen in 

fertilizers has caused considerable concern in many 

agricultural areas in the United States and Europe 

(U.S. Department of Agriculture, 1991; McNeal and 

others, 1994, 1995; Mueller and others, 1995; Tucker 

and others, 1995; Graham and Alva, 1996). Several 

studies of water quality in citrus areas of central 

Florida have reported nitrate concentrations greater 

than the U.S. Environmental Protection Agency’s 

(USEPA) maximum contaminant level (MCL) of 10 

milligrams per liter (mg/L). Fifty to 100 percent of 

samples collected from shallow ground-water wells in 

citrus areas of Florida exceeded the USEPA MCL for 

nitrate (McNeal and others, 1994, 1995; German, 

1996; Graham and Alva 1996). Nitrate concentrations 

in water from wells screened at deeper levels in the 

saturated zone were less than 10 mg/L (McNeal and 

others, 1995). 

Factors that can affect nitrate distribution, 

movement, and fate in ground water include land-use 

patterns, agricultural practices, and soil characteristics. Changes in land-use patterns in Indian River, 

St. Lucie, and Martin Counties include substantial 

increases in citrus acreage. From 1966 to 1996, irrigated citrus acreage increased from 41,000 to 67,000 

in Indian River County; from 22,000 to 47,000 in Martin 

County; and from 64,000 to 107,000 in St. Lucie 

County (Florida Agricultural Statistics Service, 1996, 

1998). Agricultural practices also have changed. 

Agricultural practices vary by grove, based on fertilizer placement (over root zone or directly on trees), 

the timing of applications (in rainy season or not), the 

number of split applications per year, types of irrigation practices, and the form of nitrogen applied 

(reduced ammonium or oxidized nitrate) (Tucker and 

others, 1995). Soil characteristics such as permeability, 

pH, and exchangeable bases, are variable from one 

grove to another and have a profound influence on the 

movement and fate of nutrients. In some areas with 

poorly drained soils, denitrification reactions (conversion of nitrate (NO3) to N2 or N2O by microbial processes) are an important pathway for nitrogen loss 

from the subsurface, thus preventing excessive nitrate 

from reaching the deeper surficial aquifer. 

In 1996, the U.S. Geological Survey began a 

cooperative study with the Institute of Food and 

Agricultural Sciences (IFAS), University of Florida, to 

evaluate the factors controlling nitrate concentrations 

in ground water in citrus-growing areas of Indian 

River, Martin, and St. Lucie Counties. The goals of 

this study were to determine the distribution, 

movement, and fate of nitrate in ground water at 

selected citrus groves.

Purpose and Scope

The purpose of this report is twofold: (1) to 

describe the distribution of nitrate and other constituents 

in ground water beneath citrus groves, and (2) to 

determine the fate of nitrate in the surficial aquifer 

system and its rate of lateral and vertical migration in 

ground water. Wells were installed in the surficial 

aquifer system and surface-water sites were established 

at six groves and one nonagricultural (reference) site. 

Water was sampled for nutrients, major ions, dissolved 

organic carbon, dissolved gases, and selected isotopes 

from the fall of 1996 through the summer of 1998. 

The groves were selected based on representative soil 

series; management practices; the age, health, and type 

of citrus trees; and the willingness of grove owners to 

cooperate with this study.

Acknowledgments

The author would like to thank Dr. Brian 

Boman, Marion Parsons, and the entire IFAS staff for 

their generous help and support, and the six citrus 

growers who consented to allow this study to occur on 

their property. The author also thanks the following 

U.S. Geological Survey employees: L. Niel Plummer 

and Carol Kendall for their insightful reviews, and 

Marian Berndt, Brian Katz, Gary Mahon, and J.K. 

Bohlke for their support and guidance on this project.
Description of the Study Area 3

DESCRIPTION OF THE STUDY AREA 

The study area is located within the Indian River 

citrus-production area in Indian River, Martin, and 

St. Lucie Counties, Fla., (fig. 1). The citrus production 

area in these three counties makes up nearly 286,000 

contiguous acres of irrigated citrus crops. The area is 

adjacent to the Atlantic Coast in the central and 

southern part of the Flatwoods Physiographic Province 

(Caldwell and Johnson, 1982), which is characterized 

by poorly drained spodosol soils that have an organic 

horizon (Tucker and others, 1995). Soils in the 

Flatwoods Province are generally underlain by calcium 

carbonate deposits (Tucker and others, 1995).

1

2

3

4

5

6

Reference

Site

Lake

Okeechobee

Indian River

St Johns Marsh

Allapattah Flats

Tenmile Creek

St. Lucie Canal

Sebastian River

ATLANTIC

OCEAN

Blue

Cypress

Lake

OKEECHOBEE

INDIAN RIVER

ST. LUCIE

MARTIN

BREVARD

27°45′

81°45′ 81°30′ 81°15′

27°30′

27°15′

27°

EXPLANATION

IRRIGATED CITRUS

WETLANDS

STUDY SITE AND 

 IDENTIFIER

0 5 10 MILES

0 5 10 KILOMETERS

1

Vero

Beach

Fort

Pierce

Stuart

LOCATION OF

STUDY AREA

Figure 1. Citrus sites, reference site, and irrigated citrus areas, Indian River, Martin, and St. Lucie Counties, Fla.
4 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

The climate of the study area is characterized as 

subtropical humid with long, warm, and mostly wet 

summers and short, dry winters. Mean annual temperatures range from 72.4 °F at Vero Beach to 74.1 °F at 

Stuart, Fla., (Owenby and Ezell, 1992). Most years have 

few days of frost or freezing temperatures. Approximately 60 percent of all rainfall occurs between June and 

October (Schiner and others, 1988); summer rainfall is 

due to convective activity whereas winter rainfall is due 

to large continental cold fronts. Occasionally, tropical 

storms or hurricanes may produce up to 10-20 inches 

(in.) of total rainfall, substantially increasing the annual 

total (Schiner and others, 1988). Average annual rainfall 

is 50.06 in. at Fort Pierce, 53.08 in. at Vero Beach 

(station 4W) and 54.32 in. at Stuart, Fla., (Owenby and 

Ezell, 1992). In 1997, pan evaporation measured at Vero 

Beach was 63.28 in. (National Oceanic Atmospheric 

Administration, 1997). Pan evaporation commonly is 

greater than actual evapotranspiration (to get a more 

accurate estimate of actual evapotranspiration, pan 

evaporation is usually multiplied by 0.7). Evapotranspiration has been estimated to average 42 in. per year in 

Indian River County (Schiner and others, 1988). 

Land-surface altitudes in Indian River, St. Lucie, 

and Martin Counties generally are less than 30 feet (ft) 

above mean sea level (Earle, 1975; Miller, 1978; Schiner 

and others, 1988); altitudes average about 28 ft above 

mean sea level. Land-surface altitudes range from 0-60 ft 

in St. Lucie County (Bearden, 1972), from 0-50 ft in 

Indian River County (Schiner and others, 1988), and 

from 0-20 ft in Martin County (Lichtler, 1957).

Hydrogeology

The top 700-1,500 ft of sediments composing the 

study area range in age from Eocene to Holocene and 

form the surficial and Floridan aquifer systems (table 1). 

The uppermost undifferentiated sediments consist of up 

to 100 ft of unconsolidated sand, clay, coquinas, and 

organic material (Miller, 1978; Schiner and others, 

1988). Below the undifferentiated sediments are the 

Anastasia, Fort Thompson, and Caloosahatchee Formations of Pleistocene age and the Tamiami Formation of 

Pliocene age, which total 100-400 ft in thickness 

(Lichter, 1957; Miller, 1978; Miller, 1986; Schiner and 

others, 1988). The Anastasia, Fort Thompson, and 

Caloosahatchee Formations generally consist of sand, 

coquina, limestone, marl, and sandstone (Schiner and 

others, 1988). The Tamiami Formation consists of clay, 

sandy clay, and shells with some cemented zones. These 

post-Miocene-age strata form the surficial aquifer 

system, which is bounded beneath by the Hawthorn 

Group of Miocene age; the Hawthorn Group forms the 

intermediate confining unit of the Floridan aquifer 

system. Below the intermediate confining unit lies the 

Floridan aquifer system, which consists of the Suwannee and Ocala Limestones and the Avon Park and 

Oldsmar Formations. The Suwannee Limestone of 

Oligocene age underlies the Hawthorn Group in parts of 

the study area; in other areas, where the Suwannee 

Limestone is missing, the Ocala Limestone of Eocene 

age underlies the Hawthorn Group. The Avon Park and 

Oldsmar Formations of Eocene age underlie the Ocala 

Limestone and make up the lower part of the Floridan 

aquifer system (Schiner and others, 1988).

Table 1. Generalized geologic sections and hydrogeologic units in east-central Florida 

[Lichtler, 1960; Miller, 1986; Schiner and others, 1988]

System Series Stratigraphic Unit Hydrogeologic Unit 

Quaternary

Holocene Undifferentiated sediments

Pleistocene Surficial aquifer system

Anastasia Formation

Fort Thompson Formation

Caloosahatchee Formation

Tertiary

Pliocene Tamiami Formataion

Miocene Hawthorn Group Intermediate confining unit

Oligocene Suwannee Limestone

Floridan aquifer system

Eocene

Ocala Limestone

Avon Park Formation

Oldsmar Formation
Description of the Study Area 5

In the study area, the surficial aquifer system 

generally is unconfined; however, locally, it may be 

confined or semiconfined where beds of low permeability are present (Schiner and others, 1988). The 

water table usually is within 5 ft of the surface (Izuno 

and others, 1988). Most natural recharge to the surficial 

aquifer system is from rainfall. The surficial aquifer 

system can receive discharge from the Floridan aquifer 

system where the upper confining unit is leaky; water 

in the Upper Floridan aquifer is under artesian pressure 

in the study area. The surficial aquifer system responds 

rapidly to rainfall or to drought (Izuno and others, 

1988). The natural potentiometric surface of the surficial aquifer system (equivalent to the water table) 

roughly approximates land surface topography (Healy, 

1982). The water table usually lies within 1-2 ft of land 

surface in flat, poorly drained areas such as Indian 

River and St. Lucie Counties. The water table usually 

is deeper in Martin County (8-10 ft below land surface) 

(Healy, 1982). Natural discharge from the surficial 

aquifer system occurs as evapotranspiration, discharge 

to canals, and discharge to the Indian River, St. Johns 

Marsh, (Earle, 1975; Schiner and others, 1988), 

Tenmile Creek, Allapattah Flats, St. Lucie Canal, or 

Sebastion River (Miller, 1978; Kane, 1992a,b). 

Seepage of shallow ground water from the surficial 

aquifer system to the extensive network of local drainage canals has been estimated to range from 0.3-2.8 

cubic feet per second per mile per foot of head difference between ground water and the canal (Beardon, 

1972). Water levels in the surficial aquifer system 

fluctuate continuously as a result of changes in 

recharge and discharge. Water levels also may fluctuate 

in response to pumping and manipulation through the 

canals in the study area (Schiner and others, 1988). 

The surficial aquifer system is the primary 

source of drinking water in the study area (Earle, 1975; 

Miller, 1978; Schiner and others, 1988; and Marella, 

1999). Water from the Floridan aquifer system, which 

is commonly the source of drinking water in Florida, 

tends to be high in dissolved solids (sulfate, chloride, 

and sodium) in the study area, whereas water from the 

surficial aquifer system is low in dissolved solids 

(chloride and sodium) (Schiner and others, 1988; 

Marella, 1999). 

Water Use and Supply

Total freshwater withdrawal in Indian River, 

Martin, and St. Lucie Counties was nearly 700 million 

gallons per day (Mgal/d) in 1995 (table 2; Marella, 

1999). Of this total, 70 percent (485 Mgal/d) was 

withdrawn from surface-water sources and the remaining 30 percent (207 Mgal/d) was withdrawn from 

ground-water sources. Agricultural irrigation 

accounted for nearly 95 percent of the total surface 

water withdrawn (458 Mgal/d). Surface water in the 

study area largely consists of a network of canals 

augmented by ground water, rainfall, and water from 

Lake Okeechobee and the St. Johns River headwaters. 

In 1995, agricultural irrigation accounted for 63 

percent of the ground water withdrawn (131 Mgal/d), 

most of which (80 percent; 105 Mgal/d) was obtained 

from the Floridan aquifer system. The source of most 

drinking water (public supply and domestic selfsupplied) in the three counties is ground water. The 

surficial aquifer system accounted for about 94 percent 

of the public-water supply for Martin and St. Lucie 

Counties in 1995. The surficial aquifer system and the 

Floridan aquifer system each accounted for about 33 

percent of the public-water supply for Indian River 

County in 1995 (Marella, 1999). 

Table 2. Water use in Indian River, Martin, and St. Lucie 

Counties, Fla., 1995

[Drinking water includes public supply and domestic self-supplied. Other 

includes commercial-industrial, self-supplied, recreation, and power 

generation. Withdrawals are in million gallons per day. ( ) = percentage 

of water from the Floridan aquifer system. From Marella, 1999]

County Ground 

water

Surface 

water Totals

Indian River

Agricultural irrigation 56.3 (90) 135.2 191.5

Drinking water 18.1 (33) 0.0 18.1

Other 2.2 (50) 1.1 3.3

Totals 76.6 136.3 212.9

Martin

Agricultural irrigation 23.1 (75) 100.2 123.3

Drinking water 21.6 ( 6) 0.0 21.6

Other 5.1 ( 0) 20.1 25.2

Totals 49.8 120.3 170.1

St. Lucie

Agricultural irrigation 51.5 (75) 222.1 273.6

Drinking water 24.5 ( 6) 0.0 24.5

Other 4.8 ( 0) 7.0 11.8

Totals 80.8 229.1 309.9

Indian River, Martin, and 

St. Lucie

Agricultural irrigation 131.0 (81) 457.5 588.5

Drinking water 64.2 (14) 0.0 64.2

Other 11.9 ( 4) 28.1 40.0

Totals 207.1 (76) 485.6 692.7
6 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Land-Use and Agricultural Practices

About 35 percent of Florida’s irrigated citrus 

acreage is in Indian River, Martin, and St. Lucie 

Counties (Florida Agricultural Statistics Service, 

1996). Although the total citrus acreage in the state 

decreased from 1966 to 1998, the total citrus acreage 

in Indian River, Martin, and St. Lucie Counties 

increased 170 percent (fig. 2) (Florida Agricultural 

Statistical Service, 1966, 1998). 

Soil and water resources in citrus groves are 

highly managed. Citrus groves on moderate to poorly 

drained soils, such as those in the study area, are 

bedded with rectangular blocks of trees (Jackson and 

others, undated; Ferguson and Taylor, 1993) (fig. 3). 

A bed is an elevated, mounded row of soil approximately 5 ft high and flattened on top. One to two rows 

of trees are planted on each bed. A block of trees contains 15-40 beds (15-80 rows of trees), and is approximately 220-240 yards long and 100-200 yards wide.

1966 1966

1974 1974

1982 1982

1990 1990

1998 1998

1970 1970

1978 1978

1986 1986

YEAR

120,000

100,000

80,000

60,000

40,000

20,000

0

IRRIGATED CITRUS, IN ACRES IRRIGATED CITRUS, IN ACRES

State total

St. Lucie

Total for Martin, St Lucie, and

Indian River Counties

Martin

Indian River

1994 1994

1,000,000

750,000

500,000

250,000

0

Figure 2. Irrigated citrus acreage in Indian River, Martin, and St. Lucie Counties, Fla., 

compared to each other and to total production, 1966-98.
Description of the Study Area 7

Furrow

Supply canal (S1) "A"

cluster

"B"

cluster

S2

SANDY MATERIAL SANDY MATERIAL SHELLY MATERIAL SPODIC LAYER

B20

B5

B5F

B10

Figure 3. Typical citrus block showing beds, tree rows, canals, furrows, monitoring wells, and soil layers.
8 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Trees typically are spaced 10-15 ft apart within rows and 24 ft 

apart between rows (Tucker and others, 1992; Ferguson and 

Taylor, 1993). Between each bed is a drainage ditch, or furrow, that conveys water to a nearby drainage canal (figs. 3 

and 4). Irrigation water is delivered to the trees either 

through micro-irrigation or by seepage irrigation (fig. 5). 

Irrigation water usually is supplied by pumping water from 

a supply canal, which is commonly a separate canal on the 

site (fig. 3). Some supply canals also serve as drainage 

canals. Over half of all groves have irrigation systems 

designed to deliver fertilizers or pesticides through the irrigation systems (Ferguson and Taylor, 1993; Smajstrla and 

others, 1993). Irrigation systems are used more commonly 

during the spring because of the normally drier weather, 

coincident with the peak application period of fertilizers 

(Ferguson and Taylor, 1993). Citrus groves using seepageirrigation use furrows to provide both irrigation and drainage. Seepage irrigation entails filling furrows with water 

from the adjacent canal to near the top of the beds, thereby 

flooding the grove. This process usually takes 24 hours to 

complete. The high water level is maintained for approximately 1 day, and then the furrows are drained by pumping 

excess water to adjacent drainage canals (Smajstrla, 

1993).The drainage process takes approximately 24 hours.

Figure 4. Drainage canal with furrow drain pipes extending out of the wall of the canal, St. Lucie County, Fla.

Figure 5. Microsprinkler irrigating a citrus tree, Martin 

County, Fla.
Methods 9

Approximately 175-225 pounds per acre (lb/acre) 

of nitrogen, generally as NH4NO3 or KNO3 dry and 

liquid fertilizer formulations, is applied annually to 

groves. In most citrus operations, fertilizer is broadcast 

to the soil in two to three applications (McNeal and 

others, 1995). Most citrus growers use water-soluble 

dry fertilizer (Ferguson and Taylor, 1993); however, 

some growers use both liquid and dry fertilizer. Each 

year about one-third of the total annual nitrogen fertilizer is applied in the fall with the remaining two-thirds 

applied before June (Tucker and others, 1995). Other 

micro- and macro-nutrients, necessary for citrus health 

and nutrition, are applied with the nitrogen fertilizer. 

Other nutrients in fertilizer include carbon, hydrogen, 

oxygen, nitrogen, phosphorus, potassium, magnesium, 

sulfur, and calcium, boron, molybdenum, iron, manganese, copper, and zinc (Ferguson and Davies, 1995). 

Substantial amounts of chloride and sulfate are also 

included in fertilizers as salts. Calcium carbonate or 

dolomite also may be applied to soils to control soil 

pH—the target pH for optimal citrus health is 6.0 

(Tucker and others, 1995).

METHODS

Sampling sites were established at six citrus 

groves in Indian River, Martin, and St. Lucie Counties; 

one reference site was established in St. Lucie County. 

Water samples were collected and analyzed for a 

variety of chemical and isotopic constituents to determine the water character. Water levels were measured 

monthly from December 1996 through July 1998 to 

determine flow patterns in the surficial aquifer. Hydrologic and chemical data were collected and statistical 

analyses were performed to determine water-quality 

trends and characteristics.

Site Selection

Sampling sites were selected based on representative soil properties, tree age and health, grove-management practices, distribution of groves throughout the 

study area, and the willingness of owner(s) to participate (table 3) (Boman and others, 1998; Boman, 1999). 

Sites were selected in areas representing the most 

common soil series used for citrus production in the 

three-county area—Riviera, Pineda, Wabasso, Oldsmar 

or related soil series. Blocks of trees were selected to 

minimize differences in tree size and age, as much as 

possible. Trees typically were 20-30 years old, and 

trees within each selected block were evaluated for 

health, uniformity, and type of fruit variety. Fruit 

produced within these six selected blocks included 

some of the most common orange and grapefruit 

varieties produced in the study area, such as Valencia 

oranges and Ruby-red grapefruit. Sites 1, 2, 4, 5, and 6 

use micro-emitter sprinkler systems to deliver irrigation water, whereas site 3 uses seepage irrigation—

both microsprinkler emitter and seepage irrigation 

methods are common in the study area. Citrus blocks at 

sites 1, 2, and 4 are double-bedded (two tree rows per 

bed); blocks at sites 3, 5, and 6 are single bedded.

The selected sites included the most common 

soil series used to grow citrus in the study area. The 

soil series found at sampling sites 1, 2, 4, 5, 6, and the 

reference site include the Wabasso, Riviera, Pineda, 

Nettles, Oldsmar, and Pineda series, respectively, 

which are characterized as well-drained sandy to fine 

sandy soils. Soil series in the study area are differentiated by the presence of either a spodic or argyllic 

layer at depths of 30-40 in. below land surface, which 

can restrict or impede the downward movement of water 

(Watts and Stankey, 1980; McCollum and Cruz, 1981; 

Wettstein and others, 1987; Boman, and others, 1998). 

Table 3. Primary soil series, management practices, and crop variety/vegetation for each 

sampling site, Indian River, Martin, and St. Lucie Counties, Fla.

[FS, fine sand; LS, loamy sand; n/a, not applicable]

Site Soil Series Restricting 

layer

Planting 

date

Management 

practices

Row 

type

Crop variety/

vegetation

1 Oldsmar FS Spodic 1964 Microspray Double Pineapple oranges

2 Riviera FS Argillic mid-1960’s Microspray Double Valencia oranges

3 Winder LS Argillic 1920’s Flood irrigation Single Valencia oranges

4 Pineda sand Argillic mid-1960’s Microspray Double Ruby-red grapefruit

5 Nettles FS Spodic 1965 Microspray Single White grapefruit

6 Wabasso FS Spodic mid-1960’s? Microspray Single Valencia oranges

Reference Pineda sand Argillic n/a n/a n/a Palmetto/pine
10 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

The Oldsmar (site 1), Nettles (site 5), and Wabasso 

(site 6) series are sandy soils containing spodic 

(organic) layers; whereas the Riviera (site 2) and 

Pineda (site 4) series are fine soils containing argyllic 

(clay) layers. Sampling site 3 is composed of the 

Winder series, a heavy, poorly drained loamy sand 

containing an argyllic layer (table 3) (Watts and 

Stankey, 1980; McCollum and Cruz, 1981; Wettstein 

and others, 1987). The reference site, located in a 

natural pine and palmetto savannah habitat, is underlain by Pineda soils. The reference site has never been 

used for any type of crop production (fig. 6).

Well Installation 

During October and November 1996, wells 

were installed by using a portable hollow-stem auger 

and by following standard USGS procedures for the 

installation of water-quality monitoring wells (Lapham 

and others, 1995). At each of the six groves, two 

clusters of four wells each and, depending on supply 

and drainage canal arrangements, one or two surfacewater sites were established. At the reference site, six 

wells were installed in two clusters, and an adjacent 

surface-water site was established in a similar layout at 

the citrus sites.

At each site, an upgradient (“A”) well cluster 

was located near the middle of the citrus block, usually 

15-25 trees (100-200 ft) in from the end of the block 

(fig. 3). Surveying techniques were used to define 

relative northing, easting, and elevation coordinates at 

each site based on an arbitrary datum to compare water 

levels to compute hydraulic gradients between wells. 

The downgradient (“B”) well cluster was located 

closer to the drainage canal, about two to three trees 

(20-50 ft) in from the end of the block. Within each 

cluster, wells were installed at the top of the beds 

between trees in tree rows at the following three depth 

intervals: (1) shallow, 4-10 ft deep (called A5 in the 

“A” cluster and B5 in the “B” cluster); (2) midlevel, 

7-15 ft deep (called A10 in the “A” cluster and B10 in 

the “B” cluster); and (3) deep, 20-25 ft deep (called 

A20 in the “A” cluster and B20 in the “B” cluster). 

Figure 6. Wells at the reference site in a natural pine and palmetto habitat, St. Lucie County, Fla.
Methods 11

An additional shallow well (called A5F in the “A” 

cluster and B5F in the “B” cluster) was located within 

or near the drainage furrow near each cluster at each 

citrus grove site; no furrow wells were installed at the 

reference site (fig. 3). The depths of the furrow wells 

ranged from 4-10 ft. Most were fitted with 2.5-ft-long 

slotted screens, but the midlevel wells at sites 1 and 4 

were equipped with 5-ft-long slotted screens because 

of concern about poor well production (app. I). 

Surface-water sampling sites were established 

along the supply canal (S1) and along the drainage 

canal (S2), which drains the studied bed (app. I). 

At site 2 and at the reference site, the same canal 

functioned as both irrigation supply and drainage canal 

for the studied blocks, so only one surface-water site 

was established.

Reference elevations, and northing and easting 

coordinates were established at each well and canal 

sampling point by using an arbitrary datum at each site. 

These elevations and coordinates were used to compare 

water-levels and compute distance and gradients. 

Reference coordinates and elevations are available in 

appendix I.

Water-Level Measurements

Water levels were measured monthly in most 

wells and twice monthly during peak fertilizer application periods. In furrow wells and drainage canals, water 

levels were measured quarterly and during sampling. 

Eight pressure transducers, one rain gage, and a 

barometric pressure logger were monitored at site 2 

(except in well A5F) from May through October 1998 

to determine relative surface-water elevations, waterlevel changes among wells and the drainage canal, and 

ground-water response to rainfall. Monthly total 

rainfalls was recorded at each site from 1996 through 

1998.

Sample Collection and Analysis

Ground-water samples were collected by using a 

portable peristaltic low-volume pump outfitted with 

silicone-rubber tubing. Surface-water samples were 

collected using a steel drop sampler and polyethylene 

churn splitter. Rainfall samples were collected using a 

clean 5-gallon polyethylene bucket. Procedures outlined in Horowitz and others (1994) and Koterba and 

others (1995) were implemented in the collection of all 

samples and in the measurement of field parameters, 

including values of pH, temperature, specific conductance, and concentrations of dissolved oxygen (DO). 

Field parameters were measured onsite using portable 

meters with probes encased in a closed, flow-through 

chamber to prevent contact with the atmosphere. 

In December 1996, water samples were 

collected from 43 wells, 11 canals, and a rainfall site 

near the reference site. Water samples could not be 

collected from 10 shallow and furrow wells and from 

the drainage canal at site 6 because the wells could not 

sustain pumping at this time and the canal was dry. 

Analyses included field parameters, major ions, nutrients, dissolved organic carbon (DOC), trace elements, 

and stable isotopes of oxygen and hydrogen. The 

rainfall sample collected during a storm event on 

December 8, 1996, was analyzed only for stable 

isotopes of oxygen and hydrogen.

In July 1997, a subset of wells and canals was 

sampled to determine if a seasonal component might 

exist in nitrate concentrations. Water samples were 

collected from the “A” cluster wells at sites 2, 5, and 

the reference site and from the drainage canals at these 

three sites. Water from 14 wells and three canals were 

analyzed for nutrients, field parameters, and stable 

isotopes of nitrogen in NO3 and NH4.

In May 1998, water samples were collected from 

28 wells and 6 canals at sites 2, 4, 5, and the reference 

site. Additionally, three samples of dry fertilizer (one 

from each of the three citrus sites), a precipitation 

sample, and a microsprinkler-emitter sample (from 

site 5) were analyzed only for nutrients and/or stable 

isotopes of nitrogen, oxygen, and hydrogen. A rainfall 

sample was collected near the reference site following 

an overnight storm on June 8, 1998. Ground-water 

samples from shallow and furrow wells were analyzed 

for field parameters, major ions, nutrients, DOC, isotopes of oxygen, hydrogen, nitrogen, and carbon. Analyses in ground-water samples from midlevel and deep 

wells included major ions; nutrients; DOC; field 

parameters; dissolved gases; isotopes of oxygen, 

hydrogen, nitrogen, and carbon. Tritium and helium 

were analyzed in deep wells only. The number of sites 

had to be limited because of the cost associated with 

the extensive analyses performed on these samples. 

Sites 2, 4, and 5 were chosen for further study because 

of their representative soil and agricultural practices. 
12 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Analyses of major ions included calcium (Ca), 

magnesium (Mg), sodium (Na), potassium (K), iron 

(Fe), manganese (Mn), chloride (Cl), sulfate (SO4), 

bicarbonate (HCO3), bromide (Br), fluoride (F), silica 

as (Si) SiO2, and dissolved solids (DS). Nutrient 

analyses included concentrations of nitrite (NO2), 

nitrate (NO3), ammonia (NH4), organic nitrogen 

(organic N), total phosphorus (total P), and orthophosphate (PO4). In this report, concentrations of nitrogen 

and phosphorus species are reported in units of mg/L 

as nitrogen or phosphorus, respectively. Additionally, 

all nitrate values were computed as the sum of nitrate 

plus nitrite unless otherwise stated. Analyses of trace 

elements included arsenic (As), aluminum (Al), 

barium (Ba), beryllium (Be), cadmium (Cd), 

chromium (Cr), cobalt (Co), copper (Cu), lead (Pb), 

molybdenum (Mo), nickel (Ni), selenium (Se), silver 

(Ag), and zinc (Zn). Analyses of major ions, nutrients, 

dissolved organic carbon (DOC), and trace elements 

were conducted at the USGS laboratory in Ocala, Fla. 

Concentrations of major ions, nutrients, trace 

elements, and DOC are reported as dissolved species 

(operationally defined as able to pass through a 0.45-

μm filter). Ten percent of all samples collected were 

quality-assurance samples consisting of both field and 

equipment blanks and duplicate samples. Most of the 

sampling schedule is included in appendix II. 

Analyses of dissolved gases included argon 

(Ar), oxygen (O2), carbon dioxide (CO2), nitrogen 

(N2), methane (CH4) and hydrogen sulfide (H2S). 

Dissolved gas analyses were performed by the U.S. 

Geological Survey Dissolved Gas Laboratory in 

Reston, Va. Dissolved gassamples were collected by 

using methods developed by Pearson and others 

(1978) and Busenberg and Plummer (1992); H2S 

samples were collected and analyzed in the field using 

a colorimetric method (methylene blue) and a portable 

field spectrophotometer (Hach Company, 1992). 

Dissolved gas analysis can be useful in determining 

the oxidation state of water and the likely occurrence 

of biogeochemical reactions (Korom, 1992). 

Concentration ratios of stable isotopes of 

oxygen (18O/16O), hydrogen (2

H/1H) or the deuteriumprotium (D/P) ratio, carbon (13C/12C), and nitrogen 

(

15N/14N) were determined in ground- and surfacewater samples. In this report, values of 15N/14N in NO3

and NH4 are reported as dissolved concentrations. 

Isotopic values were reported using standard δ (delta) 

notation (Gonfiantini, 1981) as defined by the following expression:

δ (per mil) = [(Rsample/Rstandard) – 1] * 1,000 , (1)

for δ 18O, R = 18O/16O; for δ D, R=D/H; for δ 13C, 

R = 13C/12C; and for δ 15N, R = 15N/14N. Analyses of 

δ 18O, δ D, δ 13C, and δ 15N in water samples were 

performed in the USGS Isotope Fractionation Laboratory in Reston, Va.

Analyses of δ18O and δ D were used in this 

study to determine mixing ratios along probable flow 

paths, based on water-level data, and sources of water. 

Measurements of δ13C provide additional information 

on sources of carbon and potential rock-water interaction. For example, degradation of organic matter 

results in δ13C values that are much lower than when 

the source of carbon is the dissolution of limestone 

(Katz and others, 1999). The carbon isotopic composition of most carbonate minerals is approximately 0 + 5 

per mil (Veizer and Hoefs, 1976); however, the carbon 

isotopic compositions of CO2 in soils with similar 

natural vegetation and climate to the study area are 

generally -23.2 to -19.0 per mil (Rightmire and 

Hanshaw, 1973).

Nitrogen isotopic analyses are used primarily to 

determine sources of nitrogen in ground water. For 

instance, δ15N of NO3 values ranging from -2 to +3 per 

mil generally indicate inorganic fertilizer as the source 

of NO3; δ 15N values ranging from +9 to +22 per mil 

indicate animal wastes as the source of nitrate (Kreitler 

and others, 1978). Enriched values of δ15N may also be 

due to microbial reactions involving NO3, such as 

denitrification. Ground-water NO3 becomes enriched in 

the heavier isotope of 15N due to fractionation, a process 

by which microbes preferentially uptake NO3 containing the lighter isotope, 14N (Mariotti and others, 1988).

The age of ground-water recharge (in years) was 

estimated by measuring tritium (3

H) and tritogenic 

helium (3

He or helium-3) concentrations in water and 

comparing these values to the long-term 3

H-input 

function of rainfall measured at the International 

Atomic Energy Agency precipitation monitoring station 

at Ocala, Fla., (Michel, 1989). Tritium, with a half-life 

of 12.43 years, decays to 3

He; by measuring 3H/3He, the 

3

H input can be corrected, improving the accuracy of 

the age of recharge estimate. Concentrations of 3

H and 

3

He were determined only for samples from deep wells 

(20-25 ft) at sites 2, 4, 5, and the reference site because 

of the low yields from the shallower wells and the cost 

of the analysis. Water samples were collected and 

analyzed by using procedures developed by Michel 
Rainfall and Ground-Water-Flow Patterns 13

(1989) and by Schlosser and others (1989). Equilibrium 

values of neon and non-tritogenic helium were used, 

when available and reasonable, to correct the age of 

water generated only from the 3

H/3He ratios. Tritium, 

helium, and neon concentrations in water were determined by the Noble Gas Laboratory of the LamontDoherty Earth Observatory of Columbia University. 

Tritium activity is reported in tritium units (TU).

Data were described using nonparametric 

statistics, including the Kruskal-Wallis, Spearman 

correlation, and Tukey tests. P-values were calculated; 

values less than 0.05 were considered significant. 

Medians, maxima, mimima, ranges, boxplots, and 

x-y plots were utilized to describe data relations.

The chemical speciation program, PHREEQC 

(Parkhurst, 1995), was used to calculate calcite 

saturation indices. Input data included solute concentrations of major ions, nutrients, pH, dissolved oxygen, 

and temperature.

RAINFALL AND GROUND-WATER-FLOW 

PATTERNS

Ground-water-flow patterns must be determined 

in order to properly interpret geochemical data. 

Without velocity and directional information about 

water movement, geochemical interpretations may be 

in error. In the following discussion, rainfall patterns 

during the study are discussed and water levels are 

used to determine potentiometric gradients and direction of flow. Additionally, stable isotope data are used 

to estimate water sources, mixing ratios, and ages of 

recharge water.

Rainfall Patterns

Measured rainfall totals for 1997 and 1998 at 

the study sites generally were greater than but within 

15 percent of annual long-term (1960-90) normal 

precipitation totals for Fort Pierce (50.06), Vero Beach 

(53.08), and Stuart (54.32), Fla., with the exception of 

site 1 (table 4; Owenby and Ezell, 1992). Annual longterm total rainfall data at the study sites were unavailable, so long-term NOAA climate station data from 

Stuart, Ft. Pierce, and Vero Beach were compared with 

rainfall at the study sites. Total rainfall for 1997 and 

1998 at site 1 was 40 percent greater than the annual 

long-term normal for Vero Beach (table 4). Rainfall 

totals were lowest for the reference site. Rainfall 

during the study period generally was characterized by 

episodic flooding and drought conditions as a result of 

the El Niño and La Niña weather patterns. For 

example, although above average rainfall occurred in 

early 1998, severe drought conditions existed from 

March through May 1998, causing water levels in 

canals to drop, prompting the need for irrigation.

Ground-Water-Flow Patterns and 

Age of Water

Ground-water levels at site 2, which were 

measured from July through October 1998 using 

pressure transducers, were extremely variable and 

responded rapidly to rainfall and irrigation events 

(fig. 7). Water levels in the shallow wells (A5 and B5) 

responded slightly sooner and maintained higher water 

levels than midlevel or deep wells. Although significant correlation (p-value less than 0.01) was found 

between water levels in most of the wells, water levels 

in the B5F furrow well were more strongly correlated 

to the stage of water in the drainage canal. 

At all citrus sites, hydraulic gradients indicated 

that water from shallow wells located on top of the 

beds moved rapidly downward toward midlevel wells 

and laterally and downward toward furrow wells. 

Water levels usually were highest in A5 wells at all 

sites except site 6, where water levels in the B5 well 

usually were higher than in other wells (fig. 8).

Table 4. Annual total rainfall for 1997 and 1998 and average annual rainfall, in inches, 

at the citrus sites and at the reference site, Indian River, Martin, and St. Lucie 

Counties, Fla.

Year Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Reference

site

1997 80.3 61.0 60.9 63.9 55.8 61.9 49.6

1998 68.4 61.6 55.3 56.7 59.2 62.9 53.3

Average 74.4 61.3 58.1 60.3 57.5 62.4 51.5
14 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Vertical gradients from A5 and B5 wells to furrow 

wells (A5F and B5F, respectively) ranged from 0.002-

9.8 foot per foot (ft/ft); units of vertical and horizontal 

gradient were calculated by dividing the vertical difference in water elevation by the difference in the depth or 

the distance between wells, respectively. Median gradients were then calculated for each pair of wells. Vertical gradients were greatest between shallow and furrow 

wells; gradients were 0.9 and 4.9 ft/ft at sites 2 and 6, 

respectively. Vertical gradients may have been greatest 

at these two sites due to the thicker spodic or argyllic 

soil layers. Tucker and others (1995) found that water 

tended to move rapidly downward during rainfall or 

irrigation until encountering a spodic or argyllic horizon, where it began moving laterally. 

Exceptions to predominant flow patterns were 

also detected. Water levels in the A5F well generally 

were higher than water levels in the A5 wells at site 4, 

and water levels in the A20 wells at sites 2, 3, and 5 

were higher than water levels in the A5 wells in about 

50 percent of the measurements. These water levels 

indicate that, for a substantial period of time, the 

potential existed for water to move upward from 

deeper wells toward shallow (A5) wells at these sites 

(fig. 8). Downward gradients usually were present 

between shallow, midlevel, and deep wells. Median 

vertical gradients from the shallow to midlevel wells 

ranged from 0.09-0.45 ft/ft. 

At the citrus sites, vertical water flow was much 

slower and the patterns more variable in the midlevel 

and deeper parts of the aquifer. Downward water 

movement from the midlevel wells to the deep wells 

was not common but did occur—for instance at site 2, 

water levels in the B10 well were higher than those in 

the B20 well 100 percent of the time (the median 

difference between water levels in wells B10 and B20 

was 0.13 ft). Water levels in midlevel wells were 

higher than water levels in deep wells in 50 percent or 

more of the measurements at sites 1, 2, and the reference site (fig. 8). Vertical gradients between midlevel 

and deep wells ranged from 0.01-0.08 ft/ft. At the four 

remaining sites, water levels in midlevel wells were 

equal to or less than water levels in deep wells and, as 

a result, the composition of water from midlevel wells 

was more likely to be a mixture of water from shallow 

and deep wells. 

7 15 20 25 31 10 5 10 15 20 25 31 5 10 15 20 25 30 5 10 15 20 25 28

July August September October

1998

100

99

98

97

96

95

94

ELEVATION OF WATER RELATIVE TO AN ARBITRARY DATUM, IN FEET

4

3

2

1

0

PRECIPITATION IN INCHES

A10

(midlevel)

A20

(deep)

A5

(shallow)

B10

(midlevel)

B20

(deep)

B5

(shallow)

B5F

(furrow)

S1

(canal)

SITE 2

Figure 7. Hourly water levels in wells and canal at site 2, July through October 1998, Indian River County, Fla.
Rainfall and Ground-Water-Flow Patterns 15

99

98

97

96

95

94

93

92

SITE 1

D J FMAM J J A S O N D J FMAM J J

1996 1997 1998

A5 (shallow)

A5 (shallow)

A10 (midlevel)

A10 (midlevel)

A20 (deep)

A20 (deep)

A5F (furrow)

A5F (furrow)

B5 (shallow)

B5 (shallow)

B10 (midlevel)

B10 (midlevel)

B20 (deep)

B20 (deep)

B5F (furrow)

B5F (furrow)

S2 (drainage canal)

S1 (pump and

drainage canal)

D J FMAM J J A A S S O O N D J FMAM J J

1996 1997 1998

100

99

98

97

96

95

SITE 2

ELEVATION OF WATER RELATIVE TO AN ARBITRARY DATUM, IN FEET

Figure 8. Water levels measured at the reference and citrus sites, December 1996 through July 1998, Indian River, 

Martin, and St. Lucie Counties, Fla. 
16 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

D J FMAM J J ASOND J FMAM J J

1996 1997 1998

SITE 4

D J FMAM J J A SO ND J FMAM J J

1996 1997 1998

98.5

98.0

97.5

97.0

96.5

96.0

95.5

95.0

94.5

94.0

97.5

97.0

96.5

96.0

95.5

95.0

94.5

94.0

93.5

93.0

SITE 3

92.13

98.24

A5 (shallow)

A10 (midlevel)

A20 (deep)

A5F (furrow)

B5 (shallow)

B10 (midlevel)

B20 (deep)

B5F (furrow)

S2 (drainage canal)

ELEVATION OF WATER RELATIVE TO AN ARBITRARY DATUM, IN FEET

Figure 8. Water levels measured at the reference and citrus sites, December 1996 through July 1998, Indian River, 

Martin, and St. Lucie Counties, Fla. (Continued)
Rainfall and Ground-Water-Flow Patterns 17

90.75 91.34 91.29 90.86

D J FMAM J J A A S S O O N D J FMAM J J

1996 1997 1998

100

99

98

97

96

95

94

SITE 5

D J FMAM J J ASOND J FM A M J J ASO

1996 1997 1998

100

98

96

94

92

90

88

SITE 6

A5 (shallow)

A10 (midlevel)

A20 (deep)

A5F (furrow)

B5 (shallow)

B10 (midlevel)

B20 (deep)

B5F (furrow)

S2 (drainage canal)

ELEVATION OF WATER RELATIVE TO AN ARBITRARY DATUM, IN FEET

Figure 8. Water levels measured at the reference and citrus sites, December 1996 through July 1998, Indian River, 

Martin, and St. Lucie Counties, Fla. (Continued)
18 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Horizontal gradients were generally one to 

two orders of magnitude lower than vertical gradients. 

However, between the “B” cluster wells and drainage 

canals, horizontal gradients were comparable in magnitude to the lower vertical gradients, ranging from 

0-0.09 ft/ft. Water levels in A5 wells usually were 

higher than those of B5 wells, indicating that water at 

shallow well depths generally moved from the “A” to 

the “B” cluster, except at sites 5 and 6 where gradients 

were reversed (0.001 and 0.02 ft/ft, respectively). 

Other generalizations about horizontal groundwater circulation patterns at the midlevel and deepwell depths were difficult to make because no predominant flow direction prevailed. In furrow wells, water 

generally moved from the B5F to the A5F wells. In the 

deeper wells, water typically moved from the A20 to 

the B20 wells at sites 1, 3, and 4, although horizontal 

gradients were low, ranging from 0.005-0.007 ft/ft. 

Generally, water moved from the B20 to the A20 wells 

at sites 2 and 6 where horizontal gradients ranged from 

0.002-0.003 ft/ft. At site 5, ground-water gradients 

between the A20 and B20 wells were reversed at least 

50 percent of the time probably due to raised canal 

water levels. At all but one of the sites, water levels in 

deep wells were higher than water levels in the drainage 

canal (fig. 8). At site 2, water levels in wells A20 and 

B20 were lower than or equal to water levels in the 

drainage canal (S1). 

Isotopes

Isotopes of carbon, oxygen, hydrogen, and 

helium are useful in determining (1) the source of 

water, (2) mixing ratios, and (3) the age of water. 

Carbon in ground water resulting from the dissolution 

of carbonate minerals, is enriched in the heavier 

isotope of carbon, carbon-13 (13C), whereas carbon in 

ground water resulting from the decay of organic 

matter, is depleted in the heavier isotope. Carbon 

sources may be identified using this information. 

Stable isotope ratios of oxygen and hydrogen can be 

used to estimate mixing ratios if valid flow paths are 

identified from water-level data, and if sources of 

water have independent signatures. Tritium and 

helium-3 can be used to estimate the age of recharge 

water, which is important in identifying land-use 

practices that may affect water quality at the time of 

recharge.

N FMAM D J J J A A S S O O N D J FMAM J J

1996 1997 1998

98

96

94

92

90

88

REFERENCE SITE

A5 (shallow)

A10 (midlevel)

A20 (deep)

A5F (furrow)

B5 (shallow)

B10 (midlevel)

B20 (deep)

B5F (furrow)

S1 (drainage canal)

ELEVATION OF WATER RELATIVE TO

AN ARBITRARY DATUM, IN FEET

Figure 8. Water levels measured at the reference and citrus sites, December 1996 through July 1998, Indian River, 

Martin, and St. Lucie Counties, Fla. (Continued)
Rainfall and Ground-Water-Flow Patterns 19

Carbon, Oxygen, and Deuterium

Ratios of 13C/12C were analyzed and calcite 

saturation indices were calculated for samples 

collected in May 1998 from sites 2, 4, 5, and the reference site to determine the source of water. Carbon in 

ground water is derived mainly from carbonate minerals in sediments, soil humus, and the decay of landplant biomass (Coplen, 1993). The δ 13C values of 

most carbonate minerals is usually 0 + 5 per mil 

(Veizer and Hoefs, 1976), whereas in areas with natural 

vegetation and climate similar to that of the study area, 

the δ 13C values of soil CO2 range from -23.2 to -19.0 

per mil (Rightmire and Hanshaw, 1973). Calcite saturation indices were calculated using PHREEQC 

(Parkhurst, 1995), a geochemical speciation and 

mixing model. Calcite saturation indices are likely to 

be near zero when ground water is at equilibrium with 

the mineral calcite in the aquifer. Negative indices 

indicate that water is undersaturated and is theoretically capable of dissolution of calcite, whereas positive 

indices indicate that water is oversaturated with respect 

to calcite and is theoretically capable of precipitation. 

The δ 13C values plotted against calcite saturation indices (SI) show two distinct zones of water—one 

zone that is undersaturated with calcite and depleted in 

δ 13C and a second zone that is near saturation with 

calcite and enriched in δ 13C (fig. 9). Water from the 

shallow wells and a few midlevel wells generally was 

depleted in δ 13C (between -19 and -23 per mil) and 

undersaturated with calcite (SI values less than -2); 

which indicated that organic carbon, converted to CO2

in various microbial reactions, was the most likely 

source of carbon. Water from deep wells (A20 and 

B20) and water from the canals generally was 

saturated with respect to calcite (SI values between -1 

and 1) and was more highly enriched in δ 13C (values 

between -6 and -14 per mil; fig. 9). Water from deep 

wells and water from the canals may be a mixture of 

water from the shallow depleted zone and from a 

deeper part of the aquifer where the carbonate mineral 

content is high. Water from the midlevel wells and 

from one furrow well seems to be a mixture of water 

from deep wells (or canals) and water from shallow 

wells. The similarity of δ 13C and calcite saturation 

indices between water from canals and water from the 

deep wells indicates that one of these is either the 

source of water for the other or they share a common 

source of water. Water-level measurements at most 

citrus sites indicate that water occasionally moves 

laterally from the deep wells to the drainage canals and 

vertically upward to the midlevel wells.

Results of δ 18O and δ D analyses also 

suggest that mixing may occur in midlevel and 

some deep wells at sites 2 and 5. At other sites, 

δ 18O and δ D values indicate that mixing has 

occurred, however, plausible mixing scenarios 

could not be developed because of disagreement with water-level and gradient data. 

Mixing ratios of water were calculated for 

plausible flow paths using δ 18O and δ D values 

from samples collected in May 1998. Results 

for site 2 indicate that water from well A10 

may have been composed of about 40 percent 

water from A5 and 60 percent water from A20 

(using δ D to compute mixing ratios; fig. 10). 

At site 5, water from A5 and B20 may have 

contributed 46 and 54 percent, respectively, of 

the water to well A20. Canal water may have 

been another contributing water source or may 

have been composed of deep well water that 

had undergone evaporation.

-8 -6 -4 -2 0 2 4

CALCITE SATURATION INDEX

-6

-8

-10

-12

-14

-16

-18

-20

-22

-24

Site 5 B10

Site 4 A10

Site 2 B5F

Site 2 B10

Site 4 B10

Site 2 A10

reference site B10

δ13C, IN PER MIL

SHALLOW

FURROW

MIDLEVEL

DEEP

CANALS

Figure 9. Values of delta 13C and calcite saturation index, by site 

and well, May 1998.
20 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Tritium and Helium-3

Concentrations of 3H and 3He were analyzed in 

samples from deep wells (19-24 ft deep) to estimate 

age of recharge water and velocity of water in the 

aquifer. Values of 3

H and 3He can be useful for age 

dating. In the early 1950’s, 3

H was introduced in large 

quantities to the atmosphere when atmospheric testing 

of nuclear weapons began; before the 1950’s, concentrations in ground water did not exceed 0.2 TU. Since 

reaching a peak during 1963-64, 3

H concentrations in 

the atmosphere and in precipitation have declined with 

few exceptions in response to the cessation of aboveground nuclear testing in the 1970’s (Michel, 1989). 

Atmospheric 3

H was introduced to ground water 

through recharge. Because the radioactive decay of 3

H 

produces tritogenic helium (3

He), measurements of the 

3

H/3He ratio in ground water provides a more reliable 

estimate of the age of young water (less than 30 years 

old) than the measurement of 3

H alone (Plummer and 

others, 1998). Fractionation from biological activity is 

generally not a concern in 3

H and 3He concentrations 

(Plummer and others, 1992). 

Measurements of neon and non-tritogenic helium 

concentrations (used to correct 3

H/3He ages) were not 

possible in some samples and may have been due to gas 

stripping. This occurs when the total pressure of gases 

in ground water exceeds 1 atmosphere and the suction 

pressure of the pump is not high enough to keep the 

gases in solution; helium and other gases can bubble out 

of solution and adhere to the sidewalls of the sampling 

tube.

Ground water was generally oldest at sites 5 and 

2 and youngest at site 4 and the reference site indicating that water may travel more slowly, have a longer 

flow path, and(or) a greater component of water may 

originate from deeper in the aquifer at sites 2 and 5 

compared to site 4 and the reference site (table 5). 

Vertical ground-water velocities were estimated from 

water ages and well depths. The average vertical 

velocity of water at sites 2 and 5 was similar (ranging 

from 0.4-1.0 ft/yr, respectively) and much slower than 

the average vertical velocities at site 4 and the reference site (ranging from 2.0-8.5 ft/yr, respectively). 

Similarities in the soil profiles would explain the 

similar vertical velocities at sites 2 and 5; site 5 is 

underlain by a 20-in-thick spodic layer, the top of 

which is approximately 3 ft below land surface; site 2 

is underlain by a 30-in-thick argyllic layer that is about 

2 ft below land surface. Both site 4 and the reference 

site are located on Pineda soils, which contain 12-15 

in-thick argyllic layers lying within about 1 ft of land 

surface. Breaches from decayed root channels or other 

causes are common in this layer and can facilitate 

rapid infiltration and transport of water.

-4 -3 -2 -1

PRECIPITATION

0

B5 B5F

A5

A5F

B10

S1

A20

A10

B20

SITE 5

MAY 1998

SITE 2

MAY 1998

A5 B5

B10

B20

A10 S2 A20

S1

-4 -3 -2 -1 δ DEUTERIUM, PER MIL, VSMOW δ DEUTERIUM, PER MIL, VSMOW

0

δ O, PER MIL, VSMOW 18

δ O, PER MIL, VSMOW 18

1 2

30

20

10

0

-10

-20

-30

10

0

-10

-20

-30

A5F

B5F

3

Meteoric water line

Meteoric water line

Figure 10. Values of delta 18O and delta deuterium at 

sites 2 and 5, May 1998.

Table 5. Tritium age, corrected age of recharge water, and 

vertical velocity of ground water in deep wells at selected sites, 

May 1998

[ft/yr, foot per year; --, unable to measure]

* Uncorrected tritium age used to compute vertical velocity.

** Age of water corrected using equilibrium values of neon and 

non-tritogenic helium.

Site Well Date

Tritium/

Helium-3 age 

(years)

Corrected 

age (years)**

Vertical 

velocity 

(ft/yr)

2 A20 5/18/98 14.8 ±0.6 19.7 ±0.8 1.0

B20 5/19/98 15.6 ±0.9 22.8 ±1.2 0.9

4 A20 5/11/98 7.2 ±0.5 10.2 ±1.0 2.3

B20 5/12/98 2.6 ±0.4 -- -- 8.5*

5 A20 5/20/98 31.8 ±7.4 24.4 ±7.3 0.8

B20 5/14/98 51.8 ±0.6 48.9 ±2.6 0.4

Reference A20 5/6/98 5.1 ±0.8 -- -- 4.1
Distribution of Nitrate and Other Agricultural Constituents 21

DISTRIBUTION OF NITRATE AND 

OTHER AGRICULTURAL CONSTITUENTS

Factors that can affect the chemical composition 

of ground water include quality and quantity of rainfall 

as recharge, aquifer properties such as rock type and 

permeability, circulation patterns in the aquifer, leakage 

or recharge from deeper aquifers, and land-use 

practices. Chemical composition and water quality 

were evaluated by analyzing major ions, trace 

elements, and nutrients (nitrogen and phosphorus). 

Oxidation conditions were evaluated based on 

dissolved-gas data.

Major Ions

Distinct differences were noted between the major 

ion composition of ground water and surface water at the 

six citrus sites compared to that of the reference site. 

Eighty-one percent of all samples consisted of a mixed 

water type (no dominant ions), and water types were 

consistent between groves during low and high fertilization periods (table 6; fig. 11). Water is designated as a 

“mixed” water type when no single cation or anion 

makes up more than 60 percent of the sum of equivalent 

cations and anions. A cation or anion is considered a 

dominant ion when the percentage of the ion is greater 

than 60 percent of the total cation or anion concentration. The predominance of mixed water types for 

samples from the citrus sites contrasts sharply with the 

water types for samples collected from the reference 

site; only 1 of the 12 samples collected at the reference 

site (8 percent) was a mixed water type (table 6). 

The predominance of mixed water types associated with 

citrus areas may reflect the contribution of irrigation 

water and the addition of fertilizers to the soil—masking 

the natural water types. Samples from shallow wells at 

the reference site consisted either of a Na-Cl or a mixedCl water type, suggesting that rainfall was the dominant 

source of water. Ground water from the deep well at the 

reference site and from two deep wells at the citrus sites 

was a Ca-HCO3 type, suggesting the presence and dissolution of carbonate aquifer materials approximately 20 ft 

below land surface. 

Table 6. Geochemical water types, December 1996 and 

May 1998

Type 

of well

Distribution (number of samples)

Mixed* Ca, Mg, 

SO4

Ca, 

HCO3

NaCl Mixed 

Cl

Mixed 

HCO3

Citrus

Shallow 9 1 2

Furrow 9 1

Midlevel 15 1 2

Deep 16 2

Floridan 1

Surface water 11 4

Reference

Shallow 1 2 1

Midlevel 1 3

Deep 2

Surface water 1 1

*Mixed water type indicates that no single cation or anion makes 

up more than 60 percent of the total cation or anion composition, in 

milliequivalent per liter.

SITE 2

May 1998

REFERENCE SITE

May 1998

EXPLANATION

80

60

40

20

80

60

40

20 80

60

40

20

Ca

Mg

Na+K

80

60

40

20

80

60

40

20

80

60

40

20

Cl

SO4

HCO3

80

60

40

20

80

60

40

20 80

60

40

20

Ca

Mg

Na+K

80

60

40

20

80

60

40

20

80

60

40

20

Cl

SO4

HCO3

0

0

750

1500

TDS TDS

0 20 40

NO3

NO3

DEEP

MIDLEVEL

SHALLOW

FURROW

CANALS

200

400

0 0.075 0.150

Figure 11. Major ion distribution, nitrate, and dissolvedsolids concentrations on Durov diagram for site 2 and the 

reference site, May 1998.
22 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Concentrations of most major ions in ground 

water and surface water (canals) were significantly 

higher at the citrus sites compared to the reference site 

(table 7; fig. 12). Potassium concentrations were 

highest in samples from midlevel and shallow wells at 

the citrus sites; median concentrations at these two 

well depths were 14 mg/L each (table 8). Potassium 

concentrations were lowest in samples from the reference site (median of 0.8 mg/L; table 7). Calcium and 

bicarbonate concentrations were significantly higher in 

the deep wells at all sites probably reflecting the fact 

that these wells were screened in shelly (limestone) 

materials. Only concentrations of DO, iron, 

ammonium, and total phosphorus measured in samples 

from the reference site were both similar in magnitude 

and distribution to concentrations in samples collected 

from the six citrus sites. Water-quality data are 

presented in appendix III. 

Table 7. Median and range in values of field parameters, and concentrations of major ions, nutrients, and selected 

trace elements in ground-water and surface-water samples, by site, December 1996 and May 1998

[Concentrations are in milligrams per liter except where noted; n, number of samples; n = 23, except as shown; °C, degrees Celsius]

Site 1

(n=7)

Site 2

(n=18)

Site 3

(n=9)

Site 4

(n=14)

Site 5

(n=20)

Site 6

(n=6)

Reference Site

(n=12)

Citrus Sites

(n=74)

Temperature °C

Median 23.7 23.9 23.8 24.0 23.4 24.0 24.4 23.8

Range 23.2-26.6 16.8-29.3 20.5-24.3 17.7-28.2 16.2-31.2 19.5-24.3 22.0-28.0 16.2-31.2

n n=23 n=7 n=15 n=24 n=7 n=15 n=82

pH

Median 6.7 7.1 6.9 7.0 6.0 7.0 5.6 7.0

Range 4.7-7.0 4.1-7.6 6.8-7.8 6.5-7.2 3.9-7.6 6.9-8.4 3.6-7.2 3.89-8.4

n n=22 n=15 n=24 n=7 n=16 n=85

Dissolved solids (DS)

Median 1,360 749 1,190 796 514 604 171 779

Range 1,020-1,980 298-1,370 732-2,060 462-1260 294-1,540 522-1,020 80.0-366 294-2060

n

Dissolved oxygen (DO)

Median 0.8 0.9 1.2 0.9 0.9 0.7 0.7 0.9

Range 0.6-0.9 <0.1-4.5 <0.1-3.0 0.6-7.3 <0.1-7.2 0.5-5.6 0.3-5.6 <0.1-7.3

n n=6 n=12 n=23 n=5 n=15 n=68

Calcium (Ca)

Median 150 120 160 155 52.5 150 11.6 115

Range 84-280 42-250 74-290 51-260 24.0-200 84.0-200 0.9-71 24-290

n

Magnesium (Mg)

Median 57 18 33 18 15.5 12 2.7 18

Range 6.0-100 10-26 11-73 11-27 8.0-44.0 4.0-42.0 0.6-5.0 4-100

n

Sodium (Na)

Median 160 59 150 71.5 53.0 31.5 15 65

Range 67-260 6.9-88 58-400 30-130 29.0-150 13.0-60 7.4-29.0 6.9-400

n

Potassium (K)

Median 8.2 8.7 12 7.0 4.8 3.0 0.8 7.5

Range 0.9-69 0.6-26 1.4-17 1.3-16 0.6-24.0 1.6-18 0.2-1.0 0.6-69

n

Chloride (Cl)

Median 540 130 420 110 110 76.0 22.5 125

Range 290-580 19-250 130-580 35-240 54.0-470 26.0-110 13.0-61.0 19-960

n

Sulfate (SO4)

Median 210 210 120 260 120 85.0 4.6 160

Range 150-530 81-380 77-310 41-430 3.9-340 30.0-280 0.2-13.0 3.9-530

n

Bicarbonate (HCO3)

Median 168 191 368 280 25.6 351 31.7 198

Range 5.2-302 1.5-417 130-500 112-405 1.2-254 156-414 1.2-240 1.2-500

n n=81
Distribution of Nitrate and Other Agricultural Constituents 23

Iron (Fe) μg/L

Median 2,600 1,400 400 315 4,550 2,100 2,850 1750

Range 20-89,000 20-8,700 <3-7,300 5-19,000 9.0-47,000 10.0-7,000 110-5,500 <3.0-89,000

n

Manganese (Mn) μg/L

Median 37 230 49 61.5 27.0 26.5 8.0 40

Range <0.3-480 8.2-540 10-490 6.9-240 <0.3-110 4.3-150 2.6-56 <0.3-540

n

Silica (Si)

Median 17 11.5 14 12.5 11.5 14.5 9.4 12

Range 7.3-40 9-20 10-17 5.3-18 0.4-26 4.8-18.0 7.4-18.0 0.4-40

n

Bromide (Br)

Median 1.3 0.44 1.4 0.39 0.35 0.3 0.1 0.45

Range 0.83-2 0.09-0.8 0.48-3.4 0.14-0.9 0.1-1.6 0.14-0.44 0.05-0.2 0.09-3.4

n

Fluoride (Fl)

Median 0.2 0.41 0.5 0.5 0.25 0.4 <0.1 0.4

Range <0.1-0.6 0.19-0.6 0.4-1.1 0.2-0.7 <0.1-0.5 0.2-0.5 <0.1-0.2 <0.1-1.1

n

Nitrate (NO3) as N

Median 0.06 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02

Range <0.02-13.9 <0.02-26.0 <0.02-<0.02 <0.02-1.4 <0.02-31 <0.02-17.9 <0.02-0.13 <0.02-31

n n=25 n=26 n=7 n=17 n=88

Ammonia (NH4) as N

Median 0.4 0.36 0.07 0.06 0.71 0.67 0.18 0.58

Range 0.19-4.4 <0.01-6.2 <0.01-0.84 <0.01-1.0 <0.01-6.7 <0.01-1.2 <0.01-0.54 <0.1-6.7

n n=25 n=26 n=7 n=17 n=78

Organic nitrogen

Median 0.35 0.82 0.31 0.52 0.7 0.8 0.54 0.68

Range <0.1-0.9 0.55-2.79 0.03-0.7 0.29-0.94 0.27-1.8 0.54-1.1 0.11-1.31 <0.1-2.79

n n=25 n=26 n=7 n=17 n=78

Orthophosphate (PO4) as P

Median <0.01 <0.01 0.04 <0.01 <0.01 <0.01 0.02 <0.01

Range <0.01-<0.01 <0.01-0.14 <0.01-0.21 <0.01-0.22 <0.01-0.08 <0.01-0.04 <0.01-0.19 <0.01-0.22

n n=25 n=26 n=7 n=17 n=88

Phosphorus (P) total as P

Median 0.02 0.02 0.04 0.02 0.02 0.02 0.02 <0.02

Range 0.02-0.02 0.02-0.36 0.02-0.33 0.02-0.25 0.02-0.14 0.02-0.04 <0.01-0.23 <0.02-0.36

n n=25 n=26 n=7 n=17 n=88

Dissolved organic carbon (DOC)

Median 39 17.5 66 35 20.5 21 46.0 25.5

Range 12-79 8.4-55 33-95 3.7-77 10.0-78 7.7-79 13.0-79.0 3.7-9

n n=7 n=72

Arsenic (As) μg/L

Median <1 1.4 <1 1.5 1.65 1.6 2.4 1.35

Range <1-16 <1-2.8 <1-16 <1-5.5 <1.0-11 <1.0-6.6 <1.0-9.8 <1-16

n n=9 n=10 n=7 n=10 n=7 n=6 n=50

Cadmium (Cd) μg/L

Median <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5

Range <0.5-7.0 <0.5-0.7 <0.5-0.7 <0.5-1.1 <0.5-3.3 <0.5-<0.5 <0.5-<0.5 <0.5-7.0

n n=9 n=10 n=7 n=10 n=7 n=6 n=50

Copper (Cu) μg/L

Median <1 <1 <1 <1 1.1 <1.0 1.25 <1.0

Range <1-1.5 <1-12.0 <1-2.7 <1-2.6 <1.0-11.0 <1.0-3.2 <1.0-10.0 <1.0-12.0

n n=9 n=10 n=7 n=10 n=7 n=6 n=50

Zinc (Zn)

Median 1.9 4.8 6.2 3.6 9.0 2.9 3.55 4.7

Range <1-61 <1-150 1.5-15 1.2-10 2.0-44 1.6-15 <1.0-13.0 <1.0-150

n n=9 n=10 n=7 n=10 n=7 n=6 n=50

Table 7. Median and range in values of field parameters, and concentrations of major ions, nutrients, and selected 

trace elements in ground-water and surface-water samples, by site, December 1996 and May 1998 (Continued)

[Concentrations are in milligrams per liter except where noted; n, number of samples; n = 23, except as shown; °C, degrees Celsius]

Site 1

(n=7)

Site 2

(n=18)

Site 3

(n=9)

Site 4

(n=14)

Site 5

(n=20)

Site 6

(n=6)

Reference Site

(n=12)

Citrus Sites

(n=74)
24 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

300

200

100

0

300

200

100

0

2000

1500

1000

500

0

500

400

300

200

100

0

100

80

60

40

20

0

100

10.0

1.00

0.10

0.01

0.001

600

500

400

300

200

100

0

600

500

400

300

200

100

0

1

1

1

1

1

1

1

1

2

2

2

2

2

2

2

2

3

3

3

3

3

3

3

3

4

4

4

4

4

4

4

4

5

5

5

5

5

5

5

5

6

6

6

6

6

6

6

6

reference

site

reference

site

reference

site

reference

site

reference

site

reference

site

reference

site

reference

site

CALCIUM CONCENRTATION,

IN MILLIGRAMS PER LITER

BICARBONATE CONCENRTATION

IN MILLIGRAMS PER LITER

MAGNESIUM CONCENRTATION,

IN MILLIGRAMS PER LITER

SULFATE CONCENRTATION,

IN MILLIGRAMS PER LITER

SODIUM PLUS POTASSIUM

CONCENRTATION,

IN MILLIGRAMS PER LITER

CHLORIDE CONCENRTATION,

IN MILLIGRAMS PER LITER

IRON CONCENRTATION,

IN MILLIGRAMS PER LITER

DISSOLVED SOLIDS

CONCENRTATION,

IN MILLIGRAMS PER LITER

SITE SITE

90th PERCENTILE

75th PERCENTILE

MEDIAN

25th PERCENTILE

10th PERCENTILE

EXPLANATION

Figure 12. Major ions and nutrients at study sites, December 1996 and May 1998, Indian River, Martin, and 

St. Lucie Counties, Fla.
Distribution of Nitrate and Other Agricultural Constituents 25

Table 8. Median and range in values of field parameters, and concentrations of 

major ions, nutrients, and selected trace elements, by depth, at citrus sites, 

December 1996 and May 1998

[Concentrations are in milligrams per liter except where noted; n, number of samples; n=23, 

except as shown; °C, degrees Celsius]

Deep

(n=23)

Midlevel

(n=22)

Shallow

(n=12)

Furrow

(n=10)

Surface 

water

(n=15)

Temperature °C

Median 24 24.1 23.0 23.5 23.7

Range 23.0-25.5 21.4-26.6 20.5-26.8 20.5-27.0 16.2-31.2

n n=25 n=24 n=14 n=11 n=17

pH

Median 7.0 6.9 6.2 6.6 7.2

Range 6.7-7.2 4.7-7.4 4.1-7.8 3.9-7.5 6.2-8.4 n n=25 n=23 n=16 n=11 n=17

Dissolved solids (DS)

Median 800 789 725 614 792

Range 464-1,670 526-1,540 298-1,980 410-1,340 294-1,340 n

Dissolved oxygen (DO)

Median 0.5 0.9 1.4 0.9 1.9

Range 0.4-1.0 0.3-2.4 0.06-3.7 <0.1-2.2 <0.1-7.3 n n=21 n=8 n=11 n=17

Calcium (Ca)

Median 160 140 69.0 90.5 91.0

Range 72.0-290 44.0-260 24.0-200 25.0-200 25.0-130 n

Magnesium (Mg)

Median 14 22.0 16.0 17.5 18.0

Range 4.0-33.0 10.0-57.0 10.0-100 10.0-49.0 11.0-60.0 n

Sodium (Na)

Median 62.0 58.0 50.0 45.5 79.0

Range 19.0-180 13.0-160 6.9-190 31.0-110 29.0-260 n

Potassium (K)

Median 1.3 14.0 14.0 8.35 5.5

Range 0.6-7.4 1.6-25.0 3.3-69.0 3.1-24.0 2.2-11.0 n

Chloride (Cl)

Median 120 140 110 110 170

Range 26.0-430 41.0-540 19.0-540 39.0-370 54.0-580 n

Sulfate (SO4)

Median 210 245 225 155 120

Range 19.0-380 46.0-460 81.0-530 77.0-340 3.9-200 n

Bicarbonate (HCO3)

Median 238 179 40.2 146 212

Range 190-415 5.2-405 1.2-415 8.2-500 36.6-254 n n=13 n=11 n=16

Iron (Fe) μg/L

Median 6,900 2,520 375 3,500 40.0

Range 1,500-23,000 6.0-89,000 <3.0-47,000 200-11,088 10-1,400 n

Manganese (Mn) μg/L

Median 49.0 59.0 61.0 128 12.0

Range 16.0-150 0.3-340 26.0-540 9.3-490 <3.0-56.0 n

Silica (Si)

Median 13.0 9.9 13.5 14.0 9.1

Range 10.0-18.0 5.4-26.0 7.7-40.0 11.0-25.0 0.4-17.0 n

Bromide (Br)

Median 0.4 0.4 0.36 0.42 0.53

Range 0.14-1.4 0.1-1.6 0.09-1.3 0.2-1.0 0.15-2.0 n
26 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Concentrations of SO4 in ground water were 

high at the citrus sites (median 160 mg/L) in contrast to 

the reference site (median 4.6 mg/L and maximum 

13 mg/L), thus suggesting that there were few natural 

sources of SO4 (fig. 12; tables 7, 8, and 9). High SO4

concentrations in ground water from midlevel and deep 

wells at citrus sites were not expected because reducing 

conditions were indicated by low DO, high Mn and Fe 

concentrations, and the presence of sulfide and 

methane (table 10). Sulfate contributions from fertilizer can be substantial, but other oxidized species in 

fertilizers, such as NO3, were not detected or were 

detected in much lower concentrations in deep and 

midlevel wells at citrus sites. Sulfate is a byproduct of 

a denitrification reaction involving the mineral pyrite 

(FeS2), and can form in recent sediments rich in organic 

matter (Postma and others, 1991). Fertilizer as a source 

of SO4 at citrus sites was indicated by significant 

positive correlations (p-values less than 0.05) between 

concentrations of SO4 and concentrations of K, Cl, Ca, 

Mg, NH4, Mn, NO3 (other common components of 

fertilizer, potash, or liming agents). 

Fluoride (Fl)

Median 0.3 0.28 0.50 0.4 0.4

Range 0.16-0.7 <0.1-0.8 <0.1-0.8 <0.1-1.1 0.22-0.60 n

Nitrate (NO3) as N

Median <0.02 0.22 1.8 <0.02 <0.02

Range <0.02-0.03 <0.02-4.9 <0.02-26.0 <0.02-31.0 <0.02-0.08 n n=26 n=24 n=16 n=12 n=17

Ammonia (NH4) as N

Median 0.61 0.38 0.7 0.54 0.03

Range 0.08-1.1 <0.01-4.4 <0.01-6.2 0.09-6.7 <0.01-0.40 n n=26 n=24 n=16 n=12 n=17

Organic nitrogen

Median 0.38 0.66 0.85 0.88 0.76

Range 0.22-1.12 <0.1-1.0 0.31-2.79 0.3-2.6 0.18-1.83 n n=26 n=24 n=16 n=12 n=17

Orthophosphate (PO4) as P

Median <0.01 <0.01 <0.01 <0.01 0.02

Range <0.01-0.08 <0.01-0.1 <0.01-0.08 <0.01-0.1 <0.01-0.22 n n=26 n=24 n=16 n=12 n=17

Phosphorus (P) total as P

Median <0.02 <0.02 <0.02 <0.02 0.03

Range <0.02-0.36 <0.02-0.12 <0.02-0.11 <0.02-33.0 <0.02-0.25 n n=26 n=24 n=16 n=12 n=17

Dissolved organic carbon (DOC)

Median 21.0 17.0 16.0 24.5 36.0

Range 3.7-79.0 5.7-77.0 7.7-67.0 11.0-95.0 12.0-79.0 n n=21 n=13

Arsenic (As) μg/L

Median 1.0 1.0 1.45 2.1 <1.0

Range 0.44-3.1 0.49-6.6 1.0-5.1 <1.0-16.0 <1.0-2.0

n n=12 n=12 n=8 n=7 n=10

Cadmium (Cd) μg/L

Median <0.5 <0.5 <0.5 <0.5 <0.5

Range <0.5-1.1 <0.5-7.0 <0.5-3.3 <0.5-0.8 <0.5-<0.5 n n=12 n=12 n=8 n=7 n=10

Copper (Cu) μg/L

Median <1.0 <1.0 2.55 <1.0 2.45

Range <1.0-2.2 <1.0-3.2 <1.0-12.0 <1.0-4.0 <1.0-11.0 n n=12 n=12 n=8 n=7 n=10

Zinc (Zn)

Median 1.65 3.85 14 6.8 10.45

Range <1.0-15.0 1.4-61 1.9-150 2.2 12.0 1.9-44.0 n n=12 n=12 n=8 n=7 n=10

Table 8. Median and range in values of field parameters, and concentrations of 

major ions, nutrients, and selected trace elements, by depth, at citrus sites, 

December 1996 and May 1998 (Continued)

[Concentrations are in milligrams per liter except where noted; n, number of samples; n=23, 

except as shown; °C, degrees Celsius]

Deep

(n=23)

Midlevel

(n=22)

Shallow

(n=12)

Furrow

(n=10)

Surface 

water

(n=15)
Distribution of Nitrate and Other Agricultural Constituents 27

Table 9. Median and range in values of field parameters, and 

concentrations of major ions, nutrients, and selected trace elements, 

by depth, at the reference site, December 1996 and May 1998

[Concentrations are in milligrams per liter except where noted; n, number of samples; 

n=23, except as shown; °C, degrees Celsius]

Deep

(n=3)

Midlevel

(n=5)

Shallow

(n=4)

Surface 

water

(n=2)

Temperature °C

Median 23.9 24.5 23.8 27.5

Range 23.7-24.2 24.0-26.3 22.0-27.6 27.0-28.0

n n=4 n=6 n=5

pH

Median 6.8 5.4 4.0 7.1

Range 6.7-6.8 5.0-5.4 3.6-5.9 7.1-7.2

n n=4 n=6 n=5 n=3

Dissolved solids (DS)

Median 240 156 114 276

Range 214-240 128-350 80-126 186-366

n

Dissolved oxygen (DO)

Median 0.4 0.7 1.0 5.6

Range 0.4-0.6 0.4-1.0 0.8-1.5 0.3-5.6

n n=4 n=6 n=3

Calcium (Ca)

Median 54.0 8.2 2. 49.5

Range 47.0-54.0 5.5-21.0 0.9-8.0 28.0-71.0

n

Magnesium (Mg)

Median 4.1 2.4 1.0 4.3

Range 3.0-4.1 2.0-5.0 0.6-1.2 3.6-5.0

n

Sodium (Na)

Median 18.0 15.0 9.6 22.0

Range 18.0-21.0 11.0-26.0 7.4-13.0 15.0-29.0

n

Potassium (K)

Median 0.8 0.9 0.5 0.7

Range 0.7-0.8 0.8-0.9 0.2-1.0 0.4-1.0

n

Chloride (Cl)

Median 20.0 26.0 16.5 39.0 

Range 16.0-20.0 21.0-61.0 13.0-26.0 24.0-54.0

n

Sulfate (SO4)

Median 0.2 4.3 6.3 9.5

Range 0.2-0.9 4.3-6.6 1.8-8.1 6.0-13.0

n

Bicarbonate (HCO3)

Median 213 20.7 4.4 224

Range 200-239 11.2-46.3 1.2-87.0 96.3-229

n n=4

Iron (Fe) μg/L

Median 5,500 3,200 2,300 150

Range 3,700-5,500 2,400-4,600 1,800-5,300 110-190

n

Manganese (Mn) μg/L

Median 9.2 8.3 13.6 3.6

Range 7.1-9.2 7.7-11.0 3.7-56.0 2.6-4.5

n

Silica (Si)

Median 11.0 10.0 7.9 9.1

Range 11.0-13.0 8.2-18.0 7.4-8.7 8.2-10.0

n

Bromide (Br)

Median 0.1 0.1 0.08 0.12

Range 0.1-0.1 0.1- 0.2 0.05-0.1 0.09-0.15

n

Fluoride (Fl)

Median 0.17 <0.1 <0.1 0.19

Range 0.17-0.2 <0.1-<0.1 <0.1-<0.1 0.18-0.2

n
28 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Iron concentrations were generally high in 

ground water, but were significantly higher (p-values 

less than 0.01) in samples from deep wells (tables 8 

and 9). The overall median iron concentration in 

ground water was 1.75 mg/L at citrus sites and 

2.85 mg/L at the reference site. Berndt and Katz 

(1992) reported that iron concentrations are generally 

high in ground water from the surficial aquifer system 

in Florida. Iron is released under reducing conditions 

in aquifers where materials are coated with iron 

hydroxides. Iron concentrations in canal samples were 

significantly lower than in ground water (tables 8 and 9; 

fig. 13). 

In samples from all wells, values of pH and 

concentrations of Ca, Fe, and HCO3 increased with 

depth as indicated by significant positive correlations 

with depth (p-values of 0.01, <0.01, 0.03, and <0.01, 

respectively). Increases in concentration with depth 

were probably the result of increased mineral dissolution of aquifer materials (limestone) with depth. 

Significant negative correlations with depth, for concentrations of DO, K, Mn, and NO3 were detected, 

(p-values of <0.01, <0.01, 0.02, and <0.01, respectively). 

Decreased concentrations of these constituents with 

depth were likely the result of biological activity, 

cation exchange, precipitation, tree uptake, or dilution. 

Nitrate (NO3) as N

Median <0.02 <0.02 <0.02 0.04

Range <0.02-<0.02 <0.02-<0.02 <0.02-0.1 <0.02-0.13

n n=4 n=6 n=5 n=3

Ammonia (NH4) as N

Median 0.51 0.22 0.06 0.02

Range 0.43-0.54 0.18-0.31 0.05-0.13 <0.01-0.04

n n=4 n=6 n=5 n=3

Organic nitrogen

Median 0.28 0.75 0.59 0.51

Range 0.21-0.35 0.54-1.28 0.45-1.31 0.48-0.56

n n=4 n=6 n=5 n=3

Orthophosphate (PO4) as P

Median 0.18 0.02 0.05 <0.01

Range 0.15-0.19 0.02-0.04 <0.01-0.15 <0.01-<0.01

n n=4 n=6 n=5 n=3

Phosphorus (P) total as P

Median 0.19 <0.02 0.05 <0.02

Range 0.17-0.23 <0.02-<0.02 <0.02-0.3 <0.02-<0.02

n n=4 n=6 n=5 n=3

Dissolved organic carbon (DOC)

Median 13.0 53.0 38.5 47.0

Range 13.0-52.0 28.0-79.0 18.0-60.0 21.0-73.0

n

Arsenic (As) μg/L

Median 0.58 0.78 2.4 <1

Range 0.56-9.8 0.56-4.1 1.4-3.4

n n=3 n=4 n=2 n=1

Cadmium (Cd) μg/L

Median <0.5 <0.5 <0.5 <0.5

Range <0.5-<0.5 <0.5-<0.5 <0.5-<0.5

n n=3 n=4 n=1

Copper (Cu) μg/L

Median <1.0 5.5 2.7 <1

Range <1.0-<1.0 <1.0-10.0 1.5-3.9

n n=3 n=2 n=2 n=1

Zinc (Zn)

Median <1.0 5.1 8.1 2.4

Range 4.0-6.1 3.1-13.0

n n=1 n=4 n=2 n=1

Table 9. Median and range in values of field parameters, and 

concentrations of major ions, nutrients, and selected trace elements, 

by depth, at the reference site, December 1996 and May 1998 

(Continued)

[Concentrations are in milligrams per liter except where noted; n, number of samples; 

n=23, except as shown; °C, degrees Celsius]

Deep

(n=3)

Midlevel

(n=5)

Shallow

(n=4)

Surface 

water

(n=2)
Distribution of Nitrate and Other Agricultural Constituents 29

Dissolved-solids and chloride concentrations at 

citrus sites were significantly higher than concentrations at the reference site (fig. 12). Water in the surficial aquifer system in Florida generally contains low 

DS (less than 500 mg/L) (Franks, 1982; Berndt and 

Katz, 1992). Dissolved-solids concentrations of ground 

water at citrus sites ranged from 294-2,060 mg/L with 

a median of 779 mg/L—more than four times the 

median concentration at the reference site (median of 

171 mg/L) (table 7). The median chloride concentration in samples from the six citrus sites was 125 mg/L 

compared to 22.5 mg/L at the reference site. Dissolvedsolids concentrations in samples from citrus groves 

were positively correlated with concentrations of Cl, K, 

Mn, Ca, Mg, Si, Na, HCO3, Br, SO4, F, PO4, and 

organic nitrogen (p-values less than 0.05). Three factors that may have contributed to the high DS and Cl 

concentrations in ground water at the citrus sites were: 

(1) the high volume of irrigation water that was recirculated through canals and the aquifer; (2) the addition 

of at least 200 lbs/acre per year of fertilizer and liming 

agents (Sarooshi, and others, 1994; Tucker and others, 

1995; Guazzelli and others, 1996); and (3) the use of 

water from the Upper Floridan aquifer as an irrigation 

source. The median concentration of DS in the Upper 

Floridan aquifer was about 2,500 mg/L in the area 

(Katz, 1992). Dissolved-solids concentrations were 

highest at sites 1 and 3 where sources of irrigation 

water included water from the Upper Floridan aquifer. 

A water sample collected in December 1996 from a 

well at site 3, which taps the Upper Floridan aquifer, 

had a dissolved-solids concentration of 960 mg/L. 

Leaking capped wells that tap the Floridan aquifer 

system also may have increased DS concentrations 

in the surficial aquifer in some groves (Schiner and 

others, 1988). 

Table 10. Dissolved gas concentrations in ground water and estimated excess N2, recharge 

temperature, and excess air from midlevel and deep wells, May 1998

[Concentrations are in milligrams per liter (mg/L); cc STP/L, cubic centimeter per liter standard temperature pressure per 

liter; NA, data not available; H2S measured only once at each well]

Sample 

(site-well) N2 Ar O2 CO2 CH4 H2S

Median 

estimated 

excess N2

(mg/L as N)

Median 

estimated 

recharge

(degrees 

Celsius)

Median 

estimated 

excess air

(cc STP/L)

Site 2

A10 18.113 0.489 0.062 7.878 0.006 0.013 6 22.8 -2.1

A10 17.877 .489 .078 7.993 .004 -- 6 22.8 -2.1

A20 18.983 .509 .292 33.911 .059 .001 6 22.9 -0.9

A20 16.868 .471 .104 28.948 .072 -- 6 23.0 -3.1

B20 17.532 .440 .066 20.225 .022 .022 8 22.6 -5.2

B20 17.420 .439 .065 20.367 .021 -- 8 22.7 -5.2

Site 4

A10 15.109 .539 .062 117.138 .006 .044 0 22.8 0.9

A10 17.174 .577 .066 124.274 .006 -- 0 22.4 2.9*

B10 18.589 .563 .066 34.380 .002 .001 2 23.7 2.8

B10 18.653 .564 .195 33.915 .002 -- 2 23.7 2.9

A20 31.831 .723 3.264 59.679 .011 .033 6 23.0 12 *

A20 19.103 .503 .235 50.407 .012 -- 6 23.0 -1.2

B20 18.447 .539 .060 35.309 .001 .001 3 22.8 0.8

B20 18.393 .538 .065 34.038 .001 -- 3 22.7 0.8

Site 5

A10 19.154 .545 .190 46.918 .208 .028 4 21.9 0.6

A10 19.258 .545 .198 47.215 .222 -- 4 21.8 0.7

B10 23.009 .624 .324 19.660 .001 .028 3 23.9 6.6*

B10 17.453 .522 .288 15.758 .381 -- 3 23.9 0.5

A20 16.438 .509 1.665 22.815 2.793 .020 3 22.7 -1.0 

A20 16.505 .510 1.666 22.015 2.781 -- 3 22.8 -0.9

B20 15.657 .518 2.106 31.666 3.536 .019 2 21.7 -1.0

B20 15.497 .514 2.134 31.275 3.640 -- 2 21.8 -1.2

Reference

A10 15.792 .557 .089 93.253 .045 0.312 0 21.7 1.3

A10 15.754 .560 .168 94.583 .173 -- 0 21.1 1.1

A20 17.420 .581 .539 51.838 .761 NA 0 22.3 3.1

A20 16.296 .559 .532 48.645 .801 -- 0 22.9 2.1

* Values are high as the result of air leaks in the laboratory.
30 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

300

200

100

0

300

200

100

0

100

10.0

1.00

0.10

0.01

500

400

300

200

100

0

100

80

60

40

20

0

100

10.0

1.00

0.10

0.01

0.001

600

500

400

300

200

100

0

600

500

400

300

200

100

0

CALCIUM CONCENRTATION,

IN MILLIGRAMS PER LITER

BICARBONATE CONCENRTATION,

IN MILLIGRAMS PER LITER

MAGNESIUM CONCENRTATION,

IN MILLIGRAMS PER LITER

SULFATE CONCENRTATION,

IN MILLIGRAMS PER LITER

SODIUM PLUS POTASSIUM

CONCENRTATION,

IN MILLIGRAMS PER LITER

CHLORIDE CONCENRTATION,

IN MILLIGRAMS PER LITER

IRON CONCENRTATION,

IN MILLIGRAMS PER LITER

NITRATE PLUS NITRITE

CONCENRTATIONS, IN

MILLIGRAMS PER LITER AS N

DEEP DEEP

DEEP

DEEP

DEEP

DEEP

DEEP

DEEP

FURROW FURROW

FURROW

FURROW

FURROW

FURROW

FURROW

FURROW

MIDLEVEL MIDLEVEL

MIDLEVEL

MIDLEVEL

MIDLEVEL

MIDLEVEL

MIDLEVEL

MIDLEVEL

SHALLOW SHALLOW

SHALLOW

SHALLOW

SHALLOW

SHALLOW

SHALLOW

SHALLOW

SURFACE

WATER

SURFACE

WATER

SURFACE

WATER

SURFACE

WATER

SURFACE

WATER

SURFACE

WATER

SURFACE

WATER

SURFACE

WATER

CITRUS SITES ONLY

90th PERCENTILE

75th PERCENTILE

MEDIAN

25th PERCENTILE

10th PERCENTILE

EXPLANATION

Figure 13. Major ions and nutrients at citrus sites, by depth, December 1996 and May 1998, Indian River, Martin, 

and St. Lucie Counties, Fla.
Distribution of Nitrate and Other Agricultural Constituents 31

The pH values were higher in ground water from 

shallow wells at the citrus sites (median of 6.2) than at 

the reference site (median of 4.0) (tables 8 and 9). High 

pH values, especially in shallow parts of the aquifer, 

are indicative of liming—the practice of applying 

calcium carbonate or dolomite to soils to raise the soil 

pH to optimal levels (6.0) for plant uptake of minerals 

and nutrients (Tucker and others, 1995). At all citrus 

sites, the median pH of water in the deep wells (7.0) 

was similar to the pH of the canal water (7.2) which 

suggests that, at least in part, water from deeper parts 

of the aquifer infiltrated upwards into the canals.

At all seven sites, DOC concentrations were high 

and DO concentrations were low. The median DOC 

concentration was 25.5 mg/L for samples from citrus 

sites and 46.0 mg/L for samples from the reference site. 

DOC concentrations in ground water are generally less 

than 2 mg/L (Thurman, 1985). DOC concentrations 

ranged from 3.7-95 mg/L and did not differ significantly by site (table 7) or depth (tables 8 and 9). DOC 

concentrations ranged from 13-79 mg/L at the reference site, indicating that DOC naturally occurred at 

high concentrations throughout the study area, most 

likely due to the decay of organic matter (table 9). 

The median DO concentration was 0.7 mg/L in ground 

water from the reference site and 0.9 mg/L in ground 

water from citrus sites, indicating suboxic or anoxic 

conditions. For instance, concentrations were lowest in 

the deep wells (medians ranged from 0.4-0.5 mg/L), 

progressively greater in the midlevel and furrow wells 

(medians ranged from 0.7-0.9 mg/L), and highest in 

the shallow wells (medians ranged from 1.0-1.4 mg/L) 

(tables 8 and 9). Dissolved oxygen concentrations 

were generally greater in the canal water than in 

ground water. 

Trace Elements

Trace elements are a concern in water because 

high concentrations may harm fisheries and impair 

drinking water (U.S. Environmental Protection Agency, 

1999). Trace element analyses were performed on water 

samples (table 11) to determine overall water-quality 

conditions at citrus sites and the reference site; Ba Cu, 

Zn, and Mo are applied as micronutrients in fertilizer, 

and As, Cd, and Se may be inadvertently included in 

sludge applied to citrus-production areas (Tucker and 

others, 1995). Concentrations of As, Be, Cd, Co, Cu, 

Mo, Se, Ag, and Zn in ground water from citrus sites 

were similar to those in samples from the reference 

site. At all sites, the maximum concentration of As at 

each site exceeded the recommended criteria for human 

consumption of 0.018 μg/L (U.S. Environmental 

Protection Agency, 1999) and maximum concentrations 

of Cd at sites 1 and 5 exceeded the recommended 

continuous and maximum criteria for the health of 

aquatic organisms of 2.2 and 4.3 μg/L, respectively 

(U.S. Environmental Protection Agency, 1999). 

Table 11. Median trace-element concentrations, ranges, 

detection levels, and minimum percentage of samples below 

detection level in ground and surface water from all sites, 

December 1996

[Concentrations are in micrograms per liter; <, less than the 

detection level]

Constituent Median Range

Detection 

level

Minimum 

percent-

 age

below 

detection 

level

Ground Water (44 samples)

Arsenic (As) <1 <1.0-16 <1 50

Aluminum (Al) 21 <3-1700 <3 5

Barium (Ba) 74 6-180 <0.5 0

Beryllium (Be) <0.5 <0.5-0.7 <0.5 95

Cadmium (Cd) <0.5 <0.5-7 <0.5 50

Chromium (Ch) <1.0 <1.0-4.3 <1.0 75

Cobalt (Co) <1.0 <1.0-8.6 <1.0 50

Copper (Cu) <1.0 <1.0-12 <1.0 50

Lead (Pb) <1.0 <1.0-13 <1.0 75

Molybdenum (Mo) 2.75 <2-51 <2.0 25

Nickel (Ni) 2 <1.0-11 <1.0 10

Selenium (Se) <1.0 <1.0-1.8 <1.0 50

Silver (Ag) <1.0 <1.0-<1.0 <1.0 100

Zinc (Zn) 4.2 <1-150 <1.0 5

Surface Water (11 samples)

Arsenic (As) <1 <1.0-2 <1 50

Aluminum (Al) 5 <3-350 <3 5

Barium (Ba) 43 13-63 <0.5 0

Beryllium (Be) <0.5 <0.5-<0.5 <0.5 100

Cadmium (Cd) <0.5 <0.5-<0.5 <0.5 100

Chromium (Ch) <1.0 <1.0-<1.0 <1.0 100

Cobalt (Co) <1.0 <1.0-<1.0 <1.0 100

Copper (Cu) 2.3 <1.0-11 <1.0 25

Lead (Pb) <1.0 <1.0-<0.1 <1.0 100

Molybdenum (Mo) <2.0 <2.0-25 <2.0 50

Nickel (Ni) 1.1 <1.0-11 <1.0 25

Selenium (Se) <1.0 <1.0-1.6 <1.0 50

Silver (Ag) <1.0 <1.0-<1.0 <1.0 100

Zinc (Zn) 8.9 1.9-44 <1.0 0
32 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Maximum concentrations of Al, and Zn also exceeded 

the continuous and maximum recommended criteria 

for aquatic life of 0.75 and 0.12 mg/L, respectively 

(U.S. Environmental Protection Agency, 1999). The 

maximum Cu concentrations in samples from sites 2, 5, 

and the reference site were very close to the recommended freshwater criteria of 13 μg/L (U.S. Environmental Protection Agency, 1999). Only concentrations 

of Al, Ba, Cr, Pb, and Ni differed significantly (p-values 

<0.05) between the reference site and the citrus sites. 

Of these constituents, only Ni concentrations were 

higher in ground water from citrus sites; Al, Cr, and 

Pb concentrations were higher in ground water from 

the reference site, indicating that these trace elements 

are derived from natural sources. Trace element occurrence, concentrations, and distributions are presented 

in table 11 and appendix II.

Nutrients

Nutrients discussed in this report include 

various nitrogen and phosphorus species. Several 

forms of nitrogen (NH4, NO3, and organic nitrogen) 

and phosphorus are applied annually to citrus trees to 

improve the growth of the trees and fruit production. 

Nitrogen in the form of NO3 sometimes leaches into 

aquifers, impairing the use of ground water as a 

potable drinking-water source. Nitrate is known to 

cause “blue-baby syndrome” (methemoglobinemia), 

which can be a potentially lethal illness in small 

children. Nitrogen and phosphorus also produce algal 

blooms in surface water, and reduce oxygen availability to organisms.

Ammonium, Organic Nitrogen, and Phosphorus

Overall, concentrations of NH4, organic N, and 

phosphorus were fairly low in ground water and 

surface water. However, a few relatively high NH4

concentrations (maximum of 6.7 mg/L) were found in 

samples from shallow wells and furrow wells at the 

citrus sites (table 8). Although concentrations of NH4

from the reference site never exceeded 1.0 mg/L, they 

were not significantly lower than those from the citrus 

sites, indicating that there are natural sources of NH4. 

Concentrations of NH4 were lowest in midlevel and 

furrow wells and highest in shallow and deep wells 

from the citrus sites (table 8). Only 5 percent of NH4

concentrations in ground water were below the detection level of 0.01 mg/L; most concentrations were 

below the USEPA 1-hour, 3-year average aquatic 

criteria for NH4. Concentrations of NH4 in canal 

samples also never exceeded the criteria. 

Median concentrations of organic N were less 

than 1 mg/L in all samples. Concentrations of organic 

N were highest in samples from shallow, midlevel, 

and furrow wells and from site 2 (tables 7, 8, and 9). 

Urea, used in some fertilizer mixes, may account for 

these higher concentrations. Organic N also was 

relatively high in samples from the reference site 

(maximum of 1.31 mg/L), suggesting that organic 

nitrogen was naturally occurring in ground water in 

that area. 

At least 50 percent of all sample concentrations 

of PO4 and total P in ground water and surface water 

were below detection levels of 0.01 and 0.02 mg/L, 

respectively. Median concentrations of PO4 and total P 

were equal to or less than 0.04 mg/L at all sites (table 7). 

Median concentrations of PO4 and total P at the reference site were similar to those at the citrus sites, indicating natural sources (table 7). The carbonate material 

composing the aquifer at the level of the screened 

interval in the deep wells may have contained some 

phosphorus.

Nitrate

Concentrations of NO3 in samples from shallow 

wells and some furrow wells at the citrus sites were 

substantially higher than NO3 concentrations in ground 

water from deeper wells and from the reference site. 

Concentrations of NO3 in samples from five shallow 

wells and furrow wells from sites 1, 2, 5, and 6 

exceeded the USEPA MCL for NO3 in drinking water. 

The three highest NO3 concentrations (all greater than 

20 mg/L) at citrus sites were found in samples 

collected immediately following the highest fertilizer 

applications of the year. For example, 114 lbs/acre of 

nitrogen (in fertilizer) were applied as two applications 

in March and May 1997 at site 2; NO3 concentrations 

in samples from the shallow wells and furrow wells 

collected in July 1997, exceeded 20 mg/L (table 8). 

Concentrations of NO3 in ground water at the reference site never exceeded 0.1 mg/L. A seasonal 

increase in concentrations was detected in samples 

from midlevel wells in citrus areas only during spring 

and summer. Median NO3 concentrations in samples 

from midlevel wells increased from below the detection level in December 1996 to 0.87 mg/L in samples 

collected in July 1997 and May 1998.
Distribution of Nitrate and Other Agricultural Constituents 33

Concentrations of NO3 were significantly correlated with K, DO, and SO4 (p-values < 0.01), but no 

significant correlation was found between NO3 concentrations and DS and Cl—both indicators of agricultural 

activity. Nitrate and K concentrations were significantly higher in samples from shallow and furrow 

wells at the citrus sites than in midlevel and deep wells, 

whereas DS and Cl concentrations were not statistically different by depth (table 8). If Cl was assumed to 

be a conservative tracer and indicator of agricultural 

activity, the presence of Cl in deeper wells and the lack 

of NO3 and K in samples from midlevel and deep wells 

in citrus areas would indicate that NO3 and K were not 

behaving in a conservative manner (fig. 14). Significant negative correlations (p-values < 0.05) were found 

between NO3 and HCO3 and Fe, which indicates that 

biological reactions may have been occurring in 

ground water (fig. 15). 

0 0 10 10 20 20 30 30

0

5

10

15

20

25

0

5

10

15

20

25

DEPTH OF WELL, IN FEET DEPTH OF WELL, IN FEET

0 0 200 200 400 400 600

CHLORIDE

NITRATE

CITRUS SITE 1

December 1996

CITRUS SITE 2

May 1998

CITRUS SITE 6

December 1996

REFERENCE SITE

May 1998

0 50 100 150 0 50 100

5

10

15

20

25

30

5

10

15

20

25

30

0 10 20 30 0 5 10 15 20

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER AS N

NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER AS N

NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER AS N

NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER AS N

Figure 14. Chloride and nitrate concentrations compared by depth at sites 

1, 2, 6, and the reference site.
34 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

FATE OF NITRATE IN GROUND WATER

Any elevated NO3 concentration in ground 

water is cause for concern because the surficial aquifer 

system supplies the majority of drinking water for 

Indian River, Martin, and St. Lucie Counties. About 

24 percent (23 out of 95) of the samples collected 

from the citrus sites had NO3 concentrations equal to 

or exceeding 0.2 mg/L, and only 5 percent (5 samples) 

had concentrations exceeding the USEPA MCL of 

10 mg/L. Concentrations exceeded 10 mg/L in 

samples from shallow and furrow wells following 

heavy fertilizer applications. 

Several factors or processes may explain why NO3

concentrations, which sometimes exceeded 20 mg/L in 

ground water at depths less than 7 ft, dropped to nearly 

zero at depths of about 20 ft. Possible explanations for 

the substantial decreases in NO3 concentrations include 

dilution, tree uptake, movement off site, ammonification, 

and denitrification. Dilution probably contributed to 

reduced NO3 concentrations in the midlevel wells. 

The vertical movement of water upward from the deep 

wells to the midlevel wells occurred, at least occasionally, at all of the sites except the reference site. The 

occurrence of high Cl and DS in samples from wells at 

CITRUS DATA ONLY

EXPLANATION

SIGNIFICANT NEGATIVE CORRELATION

SIGNIFICANT POSITIVE CORRELATION

NO SIGNIFICANT CORRELATION

0

0 0

100

100

200

200 1 9 2 3 5

300

300

400

400 4

500

500

600

6 8 7

0 100 200 300 400 500 600 700 800 900 1000

CHLORIDE CONCENTRATION,

IN MILLIGRAMS PER LITER

SULFATE CONCENTRATION,

IN MILLIGRAMS PER LITER

BICARBONATE CONCENTRATION,

IN MILLIGRAMS PER LITER

IRON CONCENTRATION,

IN MILLIGRAMS PER LITER

100

10.0

1.00

0.10

0.01

100

10.0

1.00

0.10

0.01

100

10.0

1.00

0.10

0.01

100

10.0

1.00

0.10

0.01

100

10.0

1.00

0.10

0.01

100

10.0

1.00

0.10

0.01

DISSOLVED OXYGEN,

IN MILLIGRAMS PER LITER

0 1 2 3 4 5 6 7 8

NITRATE PLUS NITRITE CONCENTRATIONS, IN MILLIGRAMS PER LITER AS N

POTASSIUM CONCENTRATION,

IN MILLIGRAMS PER LITER

0 10 20 30 40 50 60 70

Figure 15. Correlations of nitrate concentrations with other constituent concentrations in 

samples from the citrus sites, Indian River, Martin, and St. Lucie Counties, Fla.
Fate of Nitrate in Ground Water 35

all depths indicates that dilution probably was not the 

dominant process responsible for the decrease in NO3

with depth. Tree uptake of nitrogen primarily occurs 

above the water table; it is possible that when the water 

table rose in response to rainfall or irrigation, some nitrogen was removed from the ground water by tree uptake. 

The offsite movement of NO3 was unlikely. Water-level 

data indicate that shallow ground water moved predominantly downward from the shallow wells and furrow 

wells; NO3 concentrations in midlevel wells, deep wells, 

and in the canals (upgradient sites) were low or usually 

below detection levels. Ammonification also was not a 

likely process responsible for decreases in NO3 concentrations, because the conversion of NO3 to NH4 generally 

preserves nitrogen in the system by increasing NH4

concentrations; NH4 concentrations remained less than 

1 mg/L in most samples. Consequently, denitrification 

was probably the primary process responsible for the 

reduction in NO3 concentrations with depth in the aquifer.

Geochemical factors required for denitrification 

to occur include: the presence of NO3, denitrifying 

microbes, a suitable electron donor, and suboxic or 

anoxic (reduced) conditions (generally DO concentrations less than 2.0 mg/L) (Gillham, 1992; Korom, 1992). 

For substantial denitrification to occur, there must be 

adequate amounts of materials capable of electron (e) 

donation, such as organic carbon, pyrite, hydrogen 

sulfide, Mn, or Fe(II)-silicates (Postma and others, 

1991). Organic carbon, if available, is thermodynamically favored to become the electron donor due to 

greater energy levels yielded by the reaction (Korom, 

1991). Denitrification will proceed if the concentration 

of organic carbon equals or exceeds the concentration 

of NO3 (Korom, 1992). The denitrification reaction in 

the presence of organic carbon is summarized as:

4NO3

-

 + 5C0 + 3H2O = 2N2 + 5HCO3

-

 + H+ (2)

(Korom, 1992; Kendall and others, USGS, written 

commun., 1995). Note that N2 and HCO3 are products 

of the reaction. Denitrification reactions using pyrite 

(FeS2) as the electron donor are also very common 

when organic carbon is not available. Denitrification 

using pyrite is summarized as: 

5FeS2 + 14NO3

-

 + 4H+ = 7N2 + 10SO4

2-

+ 5Fe2+ + 2H2O (3)

(Postma and others, 1991). Note that N2, SO4, and Fe 

are products of this reaction. 

Conditions favorable for denitrification existed 

in ground water at each of the sites. Elevated concentrations of Fe and Mn, low DO concentrations, and the 

presence of CH4 and sulfide indicate that reduced 

conditions were present in ground water. Concentrations of DOC and Fe were high in ground water 

throughout the study area, indicating that both organic 

carbon and pyrite were probably available as potential 

electron donors. Denitrification using organic carbon 

or pyrite would have resulted in increases in Fe, HCO3

and SO4 with depth, which is exactly what was observed 

at most sites. Quantifying denitrification using 

increases in these constituents was not possible 

because of the large amounts of SO4 applied in fertilizers, HCO3 from liming materials, and possible pyrite 

and carbonate dissolution in deep wells from aquifer 

materials. DOC concentrations were lower in samples 

from the midlevel wells than the shallow or deep wells, 

which may have been the result of consumption of 

organic carbon during denitrification reactions. Other 

evidence of denitrification came from measurements of 

nitrogen isotope ratios, δ 15N of NO3 in ground water 

and measurements of N2 gas.

Substantially enriched δ 15N values of NO3

nitrogen were detected in samples from midlevel wells 

(median of +24.6 per mil) compared to those values 

observed in the shallow (median of +9.4 per mil) and 

furrow wells (median of +6.1 per mil) (fig. 16). Enrichment in δ 15N values of NO3 is produced by preferential 

uptake of the lighter 14N isotope and can indicate that 

denitrification occurs with depth. Values of δ 15N of 

NO3 could not be determined for samples from deep 

wells or from the reference site because NO3 concentrations were too low. Fertilizer samples collected from 

sites 2, 4, and 5 had a median δ 15N of NO3 of +3.0 per 

mil with values ranging from +1.3 to +4.5 per mil. 

Enrichment in δ 15N in samples from midlevel wells 

agreed with water-level data, which indicated that water 

moved relatively rapidly from the shallow wells to 

furrow wells but more slowly to the midlevel wells. 

This relatively rapid movement of water in the shallow 

part of the aquifer reduced the amount of denitrification 

that may have occurred if the water had moved more 

slowly. Water movement from the shallow and furrow 

wells to the midlevel wells was much slower (vertical 

gradients were generally one order of magnitude lower), 

allowing time for more denitrification to occur. 
36 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

An inverse relation was observed between 

δ 15N values of NO3 and NO3 concentrations (fig. 17) 

and may have been related to processes occurring 

along the ground-water flow paths. For example, the 

NO3 concentration in water from a shallow well at 

site 2 was 26 mg/L and the δ 15N value was +1.3 per 

mil; however, the NO3 concentration in water from a 

midlevel well at this same site was 0.87 mg/L and the 

δ 15N was +26.3 per mil from the deeper well at this 

site. The relation between NO3 and δ 15N could be 

attributed to either: (1) two distinct sources of water, 

where one source is depleted in δ 15N with high NO3

concentrations and the other source is enriched in 

δ 15N with low NO3 concentrations; or (2) denitrification and fractionation of the nitrogen isotopes of NO3. 

Both processes likely occurred in ground water at the 

midlevel well depths, based on probable flow paths.

Values of δ15N of NO3 and NO3 concentrations 

can be used to estimate enrichment factors (ε), which 

are useful to semiqualitatively compare denitrification 

rates in ground water. Mariotti and others (1988) 

found that for a single-step, nonreversible reaction, 

δ 15N increases proportionally with the logarithm of 

the residual NO3 fraction according to the Rayleigh 

distillation equation. This equation is used to determine how the isotope ratio of a reactant changes as a 

reaction proceeds due to fractionation. The Rayleigh 

distillation equation (Mariotti and others, 1988) is:

δ 15Ni = δ 15N0+ εlnCi/C0 , (4)

where δ 15Ni is the concentration of δ 15N in the final 

reacted water, δ 15N0 is the δ 15N concentration of the 

initial source of nitrate, ε is the enrichment factor, ln is 

the natural log, and Ci

/C0 is the ratio of final NO3 concentration to initial concentration. Enrichment factors 

in the range of -5 to -10 indicate rapid denitrification 

reactions (Mariotti and others, 1988).

Enrichment factors calculated for the study sites 

indicate that denitrification reactions not only occurred, 

but they occurred rapidly in the aquifer between the 

shallow and midlevel depths. For example, at site 2, 

ground water from shallow well A5 had a NO3 concentration of 26 mg/L and a δ 15N value of +1.3 per 

mil (similar to that of fertilizer); ground water from 

midlevel well A10 had a NO3 concentration of 0.87 mg/L 

and a δ 15N value of +26.3 per mil. The fact that the 

δ 15N values increased with depth and the NO3 concentrations decreased with depth indicates that denitrification occurred. The calculated enrichment factor (-7.4) 

indicates that denitrification occurred rapidly in 

ground water at site 2 (Mariotti and others, 1988). 

DEEP

FURROW

MIDLEVEL

SHALLOW

CONCENTRATION OF NITRATE (NO ),

IN MILLIGRAMS PER LITER AS N 3 δ N OF NITRATE (NO ),IN PER MIL

15

3 EXCESS N GAS,

IN MILLIGRAMS PER LITER AS N 2

0.01 0.1 1 10 100

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0

2

4

6

8

10

12

14

16

18

20

22

24

26

0

2

4

6

8

10

12

14

16

18

20

22

24

26

DEPTH OF WELL, IN FEET

0 30 10 20 0 6 8 2 4 10

Figure 16. Nitrate, delta 15N, and excess N2 gas, by depth, at sites 2, 4, 5, and the reference site, 

July 1997 and May 1998.
Fate of Nitrate in Ground Water 37

The enrichment factor calculated for samples collected 

from site 5 at wells A5F and A10 was -6.0. These 

enrichment factors were similar to those found in the 

literature for ground water undergoing rapid denitrification (Cline and Kaplan, 1975; Wada and others, 

1975; Black and Waring, 1977; Vogel and others, 1981; 

Mariotti and others, 1988; Bohlke and Denver, 1995). 

Nitrogen gas is generated during denitrification 

reactions, thus, the presence of excess (above equilibrium concentrations) N2 in ground water is an indication that denitrification has occurred. Results of 

analyses of N2 and Ar gas concentrations can be used 

to estimate the concentrations of excess N2 through an 

iterative trial and error approach. Equilibrium concentrations of Ar and N2 exist in recharge water at specific 

temperatures at the time of recharge. Any excess N2 in 

ground water at the time of sampling can be estimated 

by guessing N2 concentrations until the recalculated 

values of recharge temperature are “reasonable,” and 

there is good agreement between the two samples 

(samples were collected in duplicate) from each well 

(Heaton and Vogel, 1981). Reasonable values of 

ground-water recharge temperature are generally 

similar to the average annual temperature. Because the 

actual recharge temperature was not known at the sites, 

two bounds were placed on estimates of recharge 

temperature. First, the minimum recharge temperature 

was assumed to be 2.5 o

C less than the field-measured 

ground-water temperatures, or roughly the average 

difference between recharge temperatures and groundwater field temperatures of samples with no excess N2

(samples from the reference site and one sample from 

site 4). The minimum recharge temperature was similar 

to the annual average temperature. Second, the 

maximum recharge temperature was assumed to be 

equal to the measured ground-water field temperature. 

These two bounds on recharge temperature provided 

an upper and lower limit on the estimates of excess N2. 

Using minimum estimates of recharge temperature, 

maximum estimates of excess N2 were calculated; 

using maximum estimated recharge temperatures, 

minimum estimates of excess N2 were calculated (L. Niel 

Plummer, U.S. Geological Survey, written commun., 

1999). 

0 5 10 15 20 25 30 35

CONCENTRATION OF NITRATE (NO), IN MILLIGRAMS PER LITER AS N 3

30

20

10

0

δ N OF NITRATE (NO ) IN PER MIL, AND EXCESS N GAS,

IN MILLIGRAMS PER LITER AS N

15

3 2

δ

δ

δ

15

15

15

N per mil in shallow wells

N per mil in furrow wells

N per mil in midlevel wells

Excess N in midlevel wells

Excess N in deep wells

2

2

Probable

ground-water

flow path at

site 2

Probable

ground-water

flow path at

site 5

Figure 17. Values of delta 15N of NO3 and concentrations of excess N2 gas compared to NO3, 

sites 2, 4, and 5, July 1977 and May 1998.
38 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Excess air concentrations also were calculated 

in the computation. Median values of estimated 

excess N2, recharge temperature, and excess air were 

calculated from the maximum and minimum 

estimates, and the medians then were used as the final 

concentrations and temperatures for each sample 

(table 10). Differences in the estimated maximum and 

minimum excess N2 concentrations from each sample 

were less than or equal to 1 mg/L. Three sample 

bottles had leaks in the laboratory, and so the values 

of excess air were not reliable; however, these 

samples were able to be used in calculations of excess 

N2 and recharge temperature. A median recharge 

temperature of 22.8 °C and an excess air content of 

0.6 cubic centimeters per liter (cm3

/L) at standard 

temperature and pressure conditions were calculated 

for all samples. The recharge temperature was in good 

agreement with the average annual air temperature 

for the study area (approximately 23 °C). The median 

excess air value was lower than atmospheric conditions (2.0 cm3

/L) probably due to degassing (bubbling 

out) at the water table due to the amount of the excess 

N2 present. This supposition was supported by the 

many negative values of excess air.

Excess N2 was measured in 10 of 13 samples 

collected (figs. 16 and 18). Median estimated excess 

N2 concentrations ranged from 0-8 mg/L (figs. 16 and 

18; table 10). The median excess N2 of all samples was 

3 mg/L. Estimated excess N2 concentrations in 

samples from deep wells ranged from 0 (reference site, 

well A20) to 8 mg/L (site 2, well B20). The median 

and the maximum estimated excess N2 in samples 

from deep wells (3 and 8 mg/L, respectively) was 

greater than the median and maximum concentrations 

in midlevel wells (2 and 6 mg/L, respectively), thus 

indicating that the highest rates of denitrification may 

have occurred in the zone between the midlevel and 

deep wells. Excess N2 concentrations in samples from 

the reference site were 0 (table 10), which agreed well 

with the extremely low or nondetectable NO3 concentrations in ground water and indicated that denitrification was not occurring at the reference site. 

0 10 20 30 40 50

DISSOLVED NITROGEN (N ), IN MILLIGRAMS PER LITER AS N 2

1.4

1.2

1.0

0.8

0.6

0.4

ARGON (Ar), IN MILLIGRAMS PER LITER

0

5

10

15

200

10

30

20

WEA Line

Excess Air, in cc

Recharge Temperature,

in degrees C.

excess N2

WEA = Water in Equilibrium with Air

Figure 18. Concentrations of dissolved argon and N2 in ground water compared 

to equilibrium concentrations of air in water at sites 2, 4, 5, and the reference site, 

May 1998.
Summary 39

SUMMARY

Water quality was analyzed at citrus groves in 

Indian River, Martin, and St. Lucie Counties, Florida, 

where the surficial aquifer system is the primary source 

of drinking water. Nitrate contamination of the surficial 

aquifer system is a concern in these three counties 

because of nitrogen in fertilizers, irrigation practices, 

sandy soils, high intensity rainfall events, and the 

proximity of the water table to the land surface. Six 

citrus grove sites in Indian River, Martin, and St. Lucie 

Counties and one reference site in St. Lucie County 

were selected to evaluate the distribution and the 

movement and fate of nitrate in ground water in citrus 

production areas. Groves were selected based on representative characteristics such as soil type, tree age, and 

management practices. Well arrangement in each grove 

consisted of eight wells in two clusters and one or two 

surface-water sites, depending on the pump and drainage canal arrangement. At the reference site, six wells 

were installed in two clusters in a layout similar to the 

citrus sites; one canal site was also established.

Wells and canals were sampled during one low 

fertilization period and during two high fertilization 

periods. Quality-assurance samples were also collected. Water samples were analyzed for field parameters, dissolved major ions, nutrients, trace elements, 

dissolved organic carbon (DOC), dissolved gases, 

isotopes of oxygen, hydrogen, nitrogen and carbon, 

tritium and tritogenic helium. The geochemical speciation program PHREEQC was used to calculate saturation indices and phase distribution. Water levels were 

measured monthly in most wells, twice monthly during 

peak fertilizer application periods, and quarterly in furrow wells and drainage canals. Pressure transducers, 

installed in the wells and the canal at site 2, measured 

relative water-level elevations in response to rainfall 

and irrigation from May 1998 through October 1998.

Water-level measurements and data from 

pressure transducers were used to establish patterns of 

ground-water flow to determine whether high NO3 

concentrations in shallow ground water were likely to 

affect the ground-water quality of the surficial aquifer 

system. Hydraulic gradients indicated that water 

moved rapidly from the shallow well depths downward 

to the deeper furrow wells. Deeper vertical circulation 

was much slower and more variable. The chemical 

composition of water in deep and midlevel wells was 

likely a mixture of deeper and shallower ground water 

(depending on canal levels and water levels in deeper 

parts of the aquifer). The δ 13C, calcite saturation 

indices, δ 18O, and δ D data also suggest that water in 

the midlevel wells may have been a mixture of water 

from deeper and shallower ground water. The age of 

water, determined by 3

H/3He, was oldest in samples 

from deep wells at sites 5 (30-50 years) and 2 (20-23 

years). The age of ground water from site 4 and the 

reference site was much younger (3-10 years).

Concentrations of the major and nutrient components of fertilizers, such as Cl, SO4, NO3, K, NH4, and 

Mg, and some minor components such as Mn, were 

substantially higher in ground water from citrus sites 

than from the reference site. Mixed water types were 

the most common in samples from citrus sites, probably reflecting the contribution of irrigation water and 

the addition of fertilizers to the soil, thereby masking 

the natural water types. Dissolved-solids and chloride 

concentrations were high in ground water from the 

citrus sites compared with the reference site. DOC 

concentrations were high at every site. The median 

DOC concentration from citrus sites was 25.5 mg/L, 

which was relatively high for ground water. Reducing 

conditions also existed—DO concentrations were low 

throughout, and H2S and CH4 were detected at low 

levels. Trace element concentrations in ground water 

were generally low in the study area.

Concentrations of nutrients, NH4, organic N, 

PO4, and total P, were relatively low in all samples. 

The median NH4 concentration in samples from citrus 

sites was not substantially higher than those of the 

reference site. Median concentrations of organic 

N were less than 1 mg/L in all samples. At least 

50 percent of all sample concentrations of PO4 and 

total P in ground water and surface water were below 

detection levels of 0.01 and 0.02 mg/L, respectively. 

Nitrate concentrations in samples from shallow 

and some furrow wells at the citrus sites were substantially higher than NO3 concentrations in ground water 

from deeper wells at the citrus sites and ground water 

from the reference site. Samples from five shallow 

wells and furrow wells from sites 1, 2, 5, and 6 had 

NO3 concentrations that exceeded the USEPA MCL of 

10 mg/L for NO3 in drinking water. The three highest 

NO3 concentrations (all greater than 20 mg/L) 

occurred in samples collected in May 1998 or July 

1997 from shallow or furrow wells at the citrus sites. 

Nitrate concentrations were substantially lower in 

samples from midlevel wells, deep wells, and canals. 

Nitrate concentrations in ground water were also significantly correlated with only two major components 
40 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

of fertilizer, K and SO4 (p=<0.01), but no significant 

correlation was found between NO3 concentrations 

and other prominent indicators of agricultural activity, 

such as dissolved solids and Cl. 

Several processes may be occurring that would 

explain why NO3 concentrations, which sometimes 

exceeded 30 mg/L in ground water at depths near 7 ft, 

dropped to near zero at depths of about 20 ft. Dilution 

probably played some role in the decrease in NO3; the 

upward movement of water from deep wells to midlevel wells was documented at some sites. However, 

the absence of NO3 and the relatively low NH4

concentrations in samples from deep wells at the citrus 

sites indicated that denitrification probably was the 

main explanation for the decrease in NO3. Conditions 

favoring denitrification were present in the aquifer—

low DO and high DOC and Fe concentrations in 

ground water throughout the study area—both organic 

carbon and pyrite were probably available as potential 

electron donors. Higher δ 15N values were detected in 

samples from the midlevel wells than in samples from 

the shallow and furrow wells, thus indicating that 

denitrification was occurring and causing fractionation 

and enrichment. Excess N2, found in 10 of 13 groundwater samples collected from midlevel and deep wells 

in May 1998, also indicated denitrification. Excess N2

concentrations in samples from deep wells were 

typically greater than excess N2 concentrations in 

samples from midlevel wells, indicating that higher 

rates of denitrification may have occurred in the zone 

between the midlevel and deep wells.

REFERENCES CITED

Alvarez, J.A., and Bacon, D.D., 1988, Production zones of 

major public water supply wellfields for the counties of 

the South Florida Water Management District: West 

Palm Beach, South Florida Water Management District, Resource Planning Department, Technical Publication 88-4, Appendix II, 17 p.

Beardon, H.W., 1972, Water available in canals and shallow 

sediments in St. Lucie County, Florida: Tallahassee, 

Florida Bureau of Geology Report of Investigations 

No. 60, 50 p. 

Berndt, M.B, and Katz, B.G., 1992, Hydrochemistry of the 

surficial and intermediate aquifer systems in Florida: 

U.S. Geological Survey Water-Resources Investigations Report 91-4186, 24 p. 

Black, A.S., and Waring, S.A., 1977, The natural abundance 

of 15N in the soil-water system of a small catchment 

area: Australian Journal of Soil Research, v. 15, 

p. 51-57.

Bohlke, J.K., and Denver, J.M., 1995, Combined use of 

groundwater dating, chemical, and isotopic analyses to 

resolve the history and fate of nitrate contamination in 

two agricultural watersheds, Atlantic coastal plain, 

Maryland: Water Resources Research, v. 31, no. 9, 

p. 2319-2339.

Boman, B.J., Crandall, C., and Zhong, H., 1998, Groundwater 

nitrate in coastal Florida citrus groves: Proceedings 

Ground Water Managment Symposium, Reston, Va., 

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42 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

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Appendix I 43

APPENDIX I

ATTRIBUTES OF SAMPLING SITES IN THIS STUDY
44 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Appendix I. Attributes of sampling sites in this study

[-, not applicable; relative elevation, northing and easting are based on an arbitrary datum at each site]

Sample 

identifier

Depth of

sampling point 

(feet below land 

surface)

Sample

Category

Screen

length

(feet)

Diameter

of well

(inches)

Relative

elevation of

measuring 

point (feet)

Relative

northing

coordinate

(feet)

Relative

easting

coordinate

(feet)

Site 1

A5 4.7 shallow well 2.5 1.5 100.21 10010.86 9766.65

A10 9.9 midlevel well 5 1.5 100.00 10010.58 9768.69

A20 20.65 deep well 2.5 1.5 100.30 10007.23 9770.72

A5F 4.7 furrow well 2.5 1.5 99.13 10019.82 9767.09

B20 20.45 deep well 2.5 1.5 99.71 10006.61 9929.24

B5 4.9 shallow well 2.5 1.5 99.43 10013.50 9930.00

B10 9.74 midlevel well 5 1.5 99.19 10011.78 9927.09

B5F 3.8 furrow well 2.5 1.5 96.94 10024.32 9928.78

S1 - supply canal - - - - -

S2 - drainage canal - - 85.20 10004.95 10015.17

Site 2

A5 4.35 shallow well 2.5 1.5 100.00 10262.35 9984.37

A10 9 midlevel well 2.5 1.5 100.00 10260.78 9984.71

A20 20.35 deep well 2.5 1.5 100.76 10258.85 9990.32

A5F 4.95 furrow well 2.5 1.5 98.99 10262.63 9975.28

B20 19.6 deep well 2.5 1.5 100.51 10042.86 9991.59

B5 5.04 shallow well 2.5 1.5 100.05 10046.02 9981.80

B10 9.05 midlevel well 2.5 1.5 99.93 10044.23 9982.03

B5F 4.9 furrow well 2.5 1.5 98.97 10043.05 9973.64

S1 - supply/drainage 

canal

- - 100.20 9984.10 9616.86

FERTILIZER - fertilizer sample - - - - -

Site 3

A5 6.65 shallow well 2.5 1.5 100.07 9719.68 10012.90

A10 7.71 midlevel well 2.5 1.5 100.00 9717.70 10014.35

A20 20.86 deep well 2.5 1.5 99.98 9719.51 10006.97

A5F 4.92 furrow well 2.5 1.5 99.00 9717.32 10003.59

B20 20.15 deep well 2.5 1.5 99.60 9939.10 10008.26

B5 4.9 shallow well 2.5 1.4 99.92 9936.68 10015.95

B10 9.81 midlevel well 2.5 1.5 99.77 9937.63 10012.00

B5F 4.72 furrow well 2.5 1.5 99.02 9937.49 10005.12

S1 - supply canal - - - - -

S2 - drainage canal - - 100.79 10020.51 10017.60

FLORIDAN - Floridan well - - - - -

Site 4

A5 6.8 shallow well 2.5 1.5 100.10 9794.04 9976.17

A10 9.8 midlevel well 5 1.5 100.00 9792.59 9976.25

A20 23 deep well 2.5 1.5 100.43 9793.24 9981.30

A5F 4.55 furrow well 2.5 1.5 98.13 9796.41 9964.21

B20 22.05 deep well 2.5 1.5 100.61 9948.29 9993.87

B5 7.25 shallow well 2.5 1.5 100.07 9946.81 9985.26
Appendix I 45

B10 9.4 midlevel well 5 1.5 99.81 9948.20 9986.41

B5F 4.65 furrow well 2.5 1.5 97.89 9949.26 9976.41

S1 - supply canal 

well

- - - - -

S2 - drainage canal - - 101.08 10021.18 9816.74

FERTILIZER - fertilizer sample - - - - -

Site 5

A5 7.2 shallow well 2.5 1.5 100.93 9813.16 9797.88

A10 12.35 midlevel well 2.5 2 100.04 9809.05 9796.40

A20 19.2 deep well 2.5 2 99.92 9809.17 9798.64

A5F 7.3 furrow well 2.5 2 100.00 9808.28 9793.81

B20 21.15 deep well 2.5 2 99.53 9811.42 9919.02

B5 7.45 shallow well 2.5 1.5 100.48 9816.34 9920.42

B10 12.35 midlevel well 2.5 2 99.63 9811.54 9916.74

B5F 7.5 furrow well 2.5 2 99.68 9810.97 9913.85

S1 - supply canal - - - - -

S2 - drainage canal - - 83.56 10014.36 9988.36

MICROJET - micro-sprinkler 

sample

- - - - -

FERTILIZER - fertilizer sample - - - - -

Site 6

A5 10.1 shallow well 2.5 1.5 101.03 9826.37 9852.64

A10 13.7 midlevel well 2.5 2 99.90 9825.08 9859.67

A20 24.3 deep well 2.5 2 100.00 9823.66 9858.51

A5F 9.55 furrow well 2.5 2 99.84 9826.88 9860.58

B20 24.05 deep well 2.5 2 100.08 9948.53 9864.23

B5 9.95 shallow well 2.5 1.5 101.06 9948.12 9858.03

B10 14.7 midlevel well 2.5 2 100.32 9944.01 9863.43

B5F 9.45 furrow well 2.5 2 99.96 9943.56 9865.14

S1 - supply canal 

well

- - - - -

S2 - drainage canal - - 81.86 10018.00 10016.44

Reference Site

A5 5.16 shallow well 2.5 1.5 98.04 9829.70 9985.07

A10 12.96 midlevel well 2.5 2 100.47 9819.13 9994.85

A20 21.04 deep well 2.5 1.5 97.34 9821.93 9997.81

A13 13 test well well 2.5 2 100.00 9808.82 9989.91

B5 5.2 shallow well 2.5 1.5 97.79 9974.01 10009.15

B10 9.59 midlevel well 2.5 1.5 98.00 9963.60 10008.84

S1 - drainage canal - - 91.39 10024.07 10003.84

RAINFALL - rainfall sample - - - -

Appendix I. Attributes of sampling sites in this study (Continued)

[-, not applicable; relative elevation, northing and easting are based on an arbitrary datum at each site]

Sample 

identifier

Depth of

sampling point 

(feet below land 

surface)

Sample

Category

Screen

length

(feet)

Diameter

of well

(inches)

Relative

elevation of

measuring 

point (feet)

Relative

northing

coordinate

(feet)

Relative

easting

coordinate

(feet)
46 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida
Appendix II 47

APPENDIX II

SAMPLING SCHEDULE OF CHEMICAL CONSTITUENTS, BY SITE
48 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

Appendix II. Sampling schedule of chemical constituents, by site

[1, sampling occurred in November-December 1996; 2, sampling occurred in July 1997; 3, sampling occurred in May-June 1998]

Sample identifier Major

ions Nutrients

Dissolved

organic 

carbon

Trace

elements

15N/14N

of nitrate,

15-nitrogen/

14-nitrogen

ratios

15N/14N

of ammonia

15-nitrogen/

14-nitrogen

ratios

13C/12C

of carbon,

13-carbon/

12-carbon

ratios

18O/16O

and D/P, 

18-oxygen/ 

16-oxygen

ratios

Dissolved

gases

3H/3He,

Tritium/

helium 

ratios

Site 1

A5

A10 1 1 1 1 1

A20 1 1 1 1 1

A5F

B20 1 1 1 1 1

B5 1 1 1 1 1

B10 1 1 1 1 1

B5F

S1 1 1 1 1 1

S2 1 1 1 1 1

Site 2

A5 1,3 1,2,3 1,3 1 2,3 2,3 3 1,3

A10 1,3 1,2,3 1,3 1 2,3 2,3 3 1,3 3

A20 1,3 1,2,3 1,3 1 2,3 2,3 3 1,3 3 3

A5F 1,3 1,2,3 1,3 1 2,3 2,3 3 1,3

B20 1,3 1,2,3 1,3 1 2,3 2,3 3 1,3 3 3

B5 1,3 1,2,3 1,3 1 2,3 2,3 3 1,3

B10 1,3 1,3 1,3 1 2,3 2,3 3 1,3 3

B5F 1,3 1,3 1,3 1 2,3 2,3 3 1,3

S1 1,3 1,2,3 1,3 1 2,3 2,3 3 1,3

FERTILIZER 3 3

Site 3

A5 1 1 1 1 1

A10 1 1 1 1 1

A20 1 1 1 1 1

A5F 1

B20 1 1 1 1

B5

B10 1 1 1 1 1

B5F 1 1 1 1 1

S1 1 1 1 1 1

S2 1 1 1 1 1

FLORIDAN 1 1 1 1 1

Site 4

A5 3 3 3 3

A10 1,3 1,3 1,3 1 3 3 3 1,3 3

A20 1,3 1,3 1,3 1 3 3 3 1,3 3 3

A5F

B20 1,3 1,3 1,3 1 3 3 3 1,3 3 3

B5 1,3 1,3 1,3 1 3 3 3 1,3

B10 1,3 1,3 1,3 1 3 3 3 1,3 3

B5F

S1 1,3 1,3 1,3 1 3 3 1,3

S2 1,3 1,3 1,3 1 3 3 1,3

FERTILIZER 3 3
Appendix II 49

Site 5

A5 1,2,3 1,2,3 1,3 1 2,3 2,3 3 1,3

A10 1,2,3 1,2,3 1,2,3 1 2,3 2,3 3 1,3 3

A20 1,2,3 1,2,3 1,2,3 1 2,3 2,3 3 1,3 3 3

A5F 1,2,3 1,2,3 1,3 1 2,3 2,3 3 1,3

B20 1,3 1,3 1,3 1 2,3 2,3, 3 1,3 3 3

B5 1,3 1,3 1,3 1 3 3 3 1,3

B10 1,3 1,3 1,3 1 3 3 3 1,3 3

B5F 1,3 1,3 1,3 1 3 3 3 1,3

S1 1,3 1,2,3 1,3 1 3 3 3 1,3

S2 1,3 1,3 1,3 1 3 3 3 1,3

MICROJET 3 3 3 3

FERTILIZER 3 3

Site 6

A5

A10 1 1 1 1 1

A20 1 1 1 1 1

A5F 1 1 1

B20 1 1 1 1 1

B5 1 1 1 1

B10 1 1 1 1 1

B5F 1 1 1 1 1

S1 1 1 1 1 1

S2

Reference Site

A5 1,3 1,2,3 1,3 1 2,3 2,3 3 1,3

A10 1,3 1,2,3 1,3 1 2,3 2,3 3 1,3 3

A20 1,3 1,2,3 1,3 1 2,3 2,3 3 1,3 3 3

A13

B5 1,3 1,3 1,3 1 3 3 3 1,3

B10 1,3 1,3 1,3 1 3 3 3 1,3 3

S1 1,3 1,2,3 1,3 1 3 3 3 1,3

RAINFALL 3 1,3

Appendix II. Sampling schedule of chemical constituents, by site (Continued)

[1, sampling occurred in November-December 1996; 2, sampling occurred in July 1997; 3, sampling occurred in May-June 1998]

Sample identifier Major

ions Nutrients

Dissolved

organic 

carbon

Trace

elements

15N/14N

of nitrate,

15-nitrogen/

14-nitrogen

ratios

15N/14N

of ammonia

15-nitrogen/

14-nitrogen

ratios

13C/12C

of carbon,

13-carbon/

12-carbon

ratios

18O/16O

and D/P, 

18-oxygen/ 

16-oxygen

ratios

Dissolved

gases

3H/3He,

Tritium/

helium 

ratios
50 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida
Appendix III 51

APPENDIX III

WATER-QUALITY DATA, 1996-98
52 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

APPENDIX III. WATER-QUALITY DATA, 1996-98

[<, below detection level;--,analysis not available]

 PH PH 

 WATER WATER NITROGEN NITROGEN NITROGEN

 SPECIFIC WHOLE WHOLE AMMONIA NITRITE AMMONIA +

 TEMPER- CON- OXYGEN, FIELD LAB DIS- DIS- ORGANIC

 LOCAL ATURE DUCT- DIS- (STAND- (STAND- SOLVED SOLVED DISSOLVED

 IDENTIFIER DATE WATER ANCE SOLVED ARD ARD (MG/L (MG/L (MG/L 

 (DEGoC) (μS/CM) (MG/L) UNITS) UNITS) AS N) AS N) AS N) 

Site 6

A10 12-19-96 24. 743. 0.6 7.01 7.33 .14 <.01 .93 

A20 12-19-96 23.3 963. .65 6.99 7.87 .96 .03 1.5 

B20 12-18-96 24.1 780. .5 6.96 7.12 1.1 <.01 2.2 

B5 12-18-96 24.3 878. -- 7.53 -- .67 .084 1.7 

B10 12-18-96 24.1 1087. .7 6.93 7.12 1.2 <.01 2. 

B10 12-18-96 24.1 1087. .7 6.93 7.21 1.2 <.01 1.7 

B5F 12-18-96 23.3 1315. -- 7.15 7.36 .26 <.01 1.2 

S1 12-13-96 19.5 876. 5.6 8.42 8.2 .01 <.01 .69 

S1 12-13-96 19.5 876. 5.6 8.42 8.18 .011 <.01 .71 

S1 12-19-96 -- -- -- -- 5.63 <.01 <.01 <.2 

Site 5

MICROJET 05-14-98 -- -- -- -- -- -- -- -- 

MICROJET 05-14-98 -- -- -- -- -- <.01 <.01 1.3 

A5 12-17-96 22.8 479. 1.2 5.9 5.89 .44 .012 1.6 

A5 07-14-97 24.5 643. .06 5.72 -- 1.2 .012 1.9 

A5 07-14-97 24.5 643. .06 5.72 -- 1.2 .011 2.1 

A5 05-20-98 22.9 585. 1.7 6.01 5.62 .73 <.01 1.9 

A10 12-17-96 22.5 785. 1. 5.87 5.52 1.1 .012 2.1 

A10 07-15-97 24.1 772. .9 5.58 -- 3.2 .012 3.7 

A10 05-20-98 23.1 657. .75 5.59 5.31 2. .016 2.7 

A20 12-17-96 23.3 983. .5 7.21 7.43 .76 <.01 1.2 

A20 07-14-97 23.4 1052. .5 7.22 -- .93 <.01 1.2 

A20 05-20-98 24. 904. .4 7.03 7.32 .83 <.01 1.2 

A20 05-20-98 -- -- -- -- 7.24 .83 <.01 .95 

A5F 12-17-96 21.6 562. 1. 5.86 5.85 .09 .02 1.4 

A5F 07-15-97 24.8 838. .5 5.56 -- 1.1 <.01 1.8 

A5F 05-20-98 25.1 1367. .85 5.55 5.97 6.7 <.01 7. 

B20 12-16-96 23.7 798. .5 6.96 7.19 .66 <.01 1. 

B20 05-14-98 23. 808. .5 6.92 6.89 .68 <.01 1. 

B5 12-16-96 -- 1649. -- 5.8 4.74 .91 .018 1.5 

B5 05-14-98 23. 1369. 1.2 4.73 4.16 .78 .013 1.3 

B10 12-16-96 22.9 1916. .3 10.48 9.31 1.4 .016 2. 

B10 05-14-98 25.1 1008. .95 6.67 6.68 .68 <.01 1.2 

B5F 12-16-96 21.5 662. -- 3.89 5.64 .34 <.01 1.2 

B5F 05-14-98 24.4 904. .7 5.47 5.37 .35 <.01 .92 

S1 12-13-96 16.2 549. 4.6 7.23 7.23 .046 <.01 1.1 

S1 07-14-97 31.19 562. 7.22 7.28 -- .018 <.01 .89 

S1 05-21-98 26.5 614. 1.9 6.83 7.19 .034 <.01 1.1 

S2 12-13-96 16.5 412. 2.8 7.57 6.86 .018 <.01 .76 

S2 05-21-98 24. 574. .0 6.23 6.89 .27 <.01 2.1 

FERTILIZER 07-08-98 -- -- -- -- -- -- -- -- 

Site 4

FERTILIZER 07-08-98 -- -- -- -- -- -- -- -- 

A5 05-12-98 22.5 1109. -- 6.48 7.01 <.01 <.01 .9 
Appendix III 53

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

NITRO- PHOS- 

 GEN, PHOS- PHORUS CARBON, MAGNE- POTAS-

 NO2+NO3 PHORUS ORTHO, ORGANIC CALCIUM SIUM, SODIUM, SIUM,

 DIS- DIS- DIS- DIS- DIS- DIS- DIS- DIS- 

 LOCAL SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED

 IDENTIFIER DATE (MG/L (MG/L (MG/L (MG/L (MG/L (MG/L (MG/L (MG/L 

 AS N) AS P) AS P) AS C) AS CA) AS MG) AS NA) AS K) 

Site 6

A10 12-19-96 <.02 .02 .02 21. 120. 10. 13. 18. 

A20 12-19-96 .03 .04 .01 21. 150. 12. 29. 2.9 

B20 12-18-96 <.02 .04 .04 25. 150. 4. 19. 1.8 

B5 12-18-96 18. <.02 <.01 7.7 -- -- -- -- 

B10 12-18-96 <.02 .03 <.01 18. 160. 18. 34. 1.6 

B10 12-18-96 <.02 .03 <.01 17. 170. 19. 36. 1.7 

B5F 12-18-96 <.02 <.02 <.01 26. 200. 42. 39. 3.1 

S1 12-13-96 <.02 .04 <.01 79. 84. 12. 60. 4.4 

S1 12-13-96 <.02 .03 <.01 79. 87. 12. 57. 4.4 

S1 12-19-96 <.02 <.02 <.01 .8 .02 .004 <.1 <.1 

Site 5

MICROJET 05-14-98 -- -- -- -- -- -- -- -- 

MICROJET 05-14-98 <.02 .14 .08 -- -- -- -- -- 

A5 12-17-96 <.02 .02 .02 32. 24. 14. 34. 7.6 

A5 07-14-97 2.1 .03 <.01 -- -- -- -- -- 

A5 07-14-97 2.3 .02 <.01 -- -- -- -- -- 

A5 05-20-98 .2 <.02 .01 19. 26. 13. 31. 8. 

A10 12-17-96 <.02 .02 .01 27. 44. 24. 59. 11. 

A10 07-15-97 1.3 .02 <.01 -- -- -- -- -- 

A10 05-20-98 4.2 <.02 .01 17. 52. 24. 32. 11. 

A20 12-17-96 <.02 .05 .05 78. 72. 11. 96. 3.2 

A20 07-14-97 <.02 .04 .01 -- -- -- -- -- 

A20 05-20-98 <.02 <.02 .04 10. 90. 11. 62. 2. 

A20 05-20-98 .03 <.02 .03 11. 87. 11. 59. 1.9 

A5F 12-17-96 .69 .02 .01 30. 34. 17. 38. 8.8 

A5F 07-15-97 2.1 .02 <.01 -- -- -- -- -- 

A5F 05-20-98 31. <.02 <.01 14. 130. 44. 49. 24. 

B20 12-16-96 <.02 .09 .08 72. 88. 8. 46. .8 

B20 05-14-98 <.02 .04 .04 12. 75. 11. 45. .6 

B5 12-16-96 .03 .02 <.01 10. 62. 31. 150. 3.3 

B5 05-14-98 .04 <.02 <.01 12. 58. 30. 140. 4.1 

B10 12-16-96 <.02 .02 <.01 11. 200. 15. 150. 2.4 

B10 05-14-98 .03 <.02 .01 14. 67. 12. 110. 2.5 

B5F 12-16-96 <.02 .03 <.01 23. 25. 14. 64. 4. 

B5F 05-14-98 <.02 <.02 <.01 11. 53. 30. 68. 5.9 

S1 12-13-96 <.02 .06 <.01 31. 38. 16. 38. 7.9 

S1 07-14-97 <.02 .02 <.01 -- -- -- -- -- 

S1 05-21-98 <.02 <.02 .02 22. 34. 18. 48. 7. 

S2 12-13-96 .02 .03 <.01 33. 25. 11. 29. 5.4 

S2 05-21-98 <.02 .05 .05 36. 34. 17. 57. 2.2 

FERTILIZER 07-08-98 -- -- -- -- -- -- -- -- 

Site 4

FERTILIZER 07-08-98 -- -- -- -- -- -- -- -- 

A5 05-12-98 .09 .04 .04 13. 93. 16. 74. 15. 
54 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 CHLO- FLUO- SILICA, BERYL- 

 RIDE, SULFATE RIDE, DIS- ARSENIC BARIUM, LIUM, CADMIUM

 DIS- DIS- DIS- SOLVED DIS- DIS- DIS- DIS- 

 LOCAL SOLVED SOLVED SOLVED (MG/L SOLVED SOLVED SOLVED SOLVED

 IDENTIFIER DATE (MG/L (MG/L (MG/L AS (μG/L (μG/L (μG/L (μG/L 

 AS CL) AS SO4) AS F) SIO2) AS AS) AS BA) AS BE) AS CD) 

Site 6

A10 12-19-96 41. 46. .2 7.5 2.2 38. <.5 <.5 

A20 12-19-96 58. 110. .4 15. 1.6 42. <.5 <.5 

B20 12-18-96 26. 30. .4 18. 1.6 44. <.5 <.5 

B5 12-18-96 -- -- -- -- 1.5 78. <.5 <.5 

B10 12-18-96 94. 140. .5 15. 6.6 53. <.5 <.5 

B10 12-18-96 96. 140. .5 15. 6.6 56. <.5 <.5 

B5F 12-18-96 100. 280. .4 14. 3.6 140. <.5 <.5 

S1 12-13-96 110. 60. .3 4.8 1. 30. <.5 <.5 

S1 12-13-96 110. 60. .3 4.9 <1. 30. <.5 <.5 

S1 12-19-96 <.1 <.2 <.1 .02 <1. <.2 <.5 <.5 

Site 5

MICROJET 05-14-98 -- -- -- -- -- -- -- -- 

MICROJET 05-14-98 -- -- -- -- -- -- -- -- 

A5 12-17-96 67. 89. .5 11. 1.1 37. <.5 <.5 

A5 07-14-97 -- -- -- -- -- -- -- -- 

A5 07-14-97 -- -- -- -- -- -- -- -- 

A5 05-20-98 73. 130. .3 10. -- -- -- -- 

A10 12-17-96 110. 190. .2 11. <1. 88. <.5 .8 

A10 07-15-97 -- -- -- -- -- -- -- -- 

A10 05-20-98 82. 180. .18 9.8 -- -- -- -- 

A20 12-17-96 140. 63. .4 12. 3.1 35. <.5 <.5 

A20 07-14-97 -- -- -- -- -- -- -- -- 

A20 05-20-98 120. 78. .16 10. -- -- -- -- 

A20 05-20-98 120. 74. .16 10. -- -- -- -- 

A5F 12-17-96 72. 120. .4 12. <1. 53. <.5 <.5 

A5F 07-15-97 -- -- -- -- -- -- -- -- 

A5F 05-20-98 140. 340. .49 17. -- -- -- -- 

B20 12-16-96 110. 19. .3 12. 1.8 33. <.5 .6 

B20 05-14-98 110. 24. .2 13. -- -- -- -- 

B5 12-16-96 380. 230. <.1 21. 5.1 140. <.5 3.3 

B5 05-14-98 280. 240. .14 26. -- -- -- -- 

B10 12-16-96 470. 170. .1 5.4 1. 180. <.5 <.5 

B10 05-14-98 180. 160. .16 13. -- -- -- -- 

B5F 12-16-96 120. 120. <.1 18. 11. 46. <.5 .8 

B5F 05-14-98 140. 220. <.1 25. -- -- -- -- 

S1 12-13-96 68. 110. .4 3. 2. 32. <.5 <.5 

S1 07-14-97 -- -- -- -- -- -- -- -- 

S1 05-21-98 93. 90. .38 .4 -- -- -- -- 

S2 12-13-96 54. 70. .3 6.4 1.5 24. <.5 <.5 

S2 05-21-98 90. 3.9 .36 3.6 -- -- -- -- 

FERTILIZER 07-08-98 -- -- -- -- -- -- -- -- 

Site 4

FERTILIZER 07-08-98 -- -- -- -- -- -- -- -- 

A5 05-12-98 120. 230. .49 12. -- -- -- -- 
Appendix III 55

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 CHRO- MANGA- MOLYB- 

 MIUM, COBALT, COPPER, IRON, LEAD, NESE, DENUM, NICKEL,

 DIS- DIS- DIS- DIS- DIS- DIS- DIS- DIS- 

 LOCAL SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED

 IDENTIFIER DATE (μG/L (μG/L (μG/L (μG/L (μG/L (μG/L (μG/L (μG/L 

 AS CR) AS CO) AS CU) AS FE) AS PB) AS MN) AS MO) AS NI)

Site 6

A10 12-19-96 <1. 1.1 3.2 940. <1. 6.9 <2. 5.2 

A20 12-19-96 <1. <1. 2.2 2600. <1. 38. 4. 2.3 

B20 12-18-96 <1. <1. <1. 1600. <1. 150. <2. 1. 

B5 12-18-96 <1. <1. 3. -- <1. -- 4.2 1.9 

B10 12-18-96 <1. <1. <1. 5000. <1. 15. 2.4 5. 

B10 12-18-96 <1. <1. <1. 5100. <1. 15. 2.2 5.5 

B5F 12-18-96 <1. 1.2 <1. 7000. <1. 96. 4.7 6.2 

S1 12-13-96 <1. <1. <1. 10. <1. 4.3 <2. 1.1 

S1 12-13-96 <1. <1. 1.1 10. <1. 4.3 <2. 1.6 

S1 12-19-96 <1. <1. 6.5 <1. <1. <.2 <2. <1. 

Site 5

MICROJET 05-14-98 -- -- -- -- -- -- -- -- 

MICROJET 05-14-98 -- -- -- -- -- -- -- -- 

A5 12-17-96 1.2 1.1 3. 5000. <1. 26. <2. 1.6 

A5 07-14-97 -- -- -- -- -- -- -- -- 

A5 07-14-97 -- -- -- -- -- -- -- -- 

A5 05-20-98 -- -- -- 3600. -- 37. -- -- 

A10 12-17-96 <1. 1.9 1.2 9400. <1. 35. <2. 2.4 

A10 07-15-97 -- -- -- -- -- -- -- -- 

A10 05-20-98 -- -- -- 5500. -- 32. -- -- 

A20 12-17-96 <1. <1. <1. 1900. <1. 97. 2.2 <1. 

A20 07-14-97 -- -- -- -- -- -- -- -- 

A20 05-20-98 -- -- -- 6900. -- 110. -- -- 

A20 05-20-98 -- -- -- 6500. -- 100. -- -- 

A5F 12-17-96 1.3 <1. 4. 2700. <1. 22. <2. 2.1 

A5F 07-15-97 -- -- -- -- -- -- -- -- 

A5F 05-20-98 -- -- -- 200. -- 32. -- -- 

B20 12-16-96 <1. <1. <1. 8200. <1. 28. <2. <1. 

B20 05-14-98 -- -- -- 23000. -- 19. -- -- 

B5 12-16-96 <1. 4.2 <1. 47000. 2.6 56. <2. 3.7 

B5 05-14-98 -- -- -- 26040. -- 45. -- -- 

B10 12-16-96 <1. <1. <1. 9. <1. .3 3.8 4.2 

B10 05-14-98 -- -- -- 4100. -- 9.2 -- -- 

B5F 12-16-96 <1. 2.8 <1. 11000. <1. 9.3 3.1 1.9 

B5F 05-14-98 -- -- -- 11088. -- 12. -- -- 

S1 12-13-96 <1. <1. 8.8 1400. 1. 12. <2. 1.9 

S1 07-14-97 -- -- -- -- -- -- -- -- 

S1 05-21-98 -- -- -- 250. -- 11. -- -- 

S2 12-13-96 <1. <1. 11. 180. <1. 12. <2. 11. 

S2 05-21-98 -- -- -- 1000. -- 34. -- -- 

FERTILIZER 07-08-98 -- -- -- -- -- -- -- -- 

Site 4

FERTILIZER 07-08-98 -- -- -- -- -- -- -- -- 

A5 05-12-98 -- -- -- 40. -- 27. -- -- 
56 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 ALKA- SOLIDS, C-13/ 

 ALUM- SELE- LINITY RESIDUE C-12 

 SILVER, ZINC, INUM, NIUM, WAT DIS AT 180 BROMIDE STABLE 

 DIS- DIS- DIS- DIS- TOT IT DEG. C DIS- ISOTOPE

 LOCAL SOLVED SOLVED SOLVED SOLVED FIELD DIS- SOLVED RATIO 

 IDENTIFIER DATE (μG/L (μG/L (μG/L (μG/L MG/L AS SOLVED (MG/L PER 

 AS AG) AS ZN) AS AL) AS SE) CACO3 (MG/L) AS BR) MIL 

Site 6

A10 12-19-96 <1. 1.6 5.7 <1. 287. 526. .28 -- 

A20 12-19-96 <1. 1.7 8.2 <1. 328. 674. .24 -- 

B20 12-18-96 <1. 15. 23. <1. 340. 522. .14 -- 

B5 12-18-96 <1. 4.1 3.3 <1. 128. -- -- -- 

B10 12-18-96 <1. 2.9 13. <1. 288. 732. .35 -- 

B10 12-18-96 <1. 14. 17. <1. 288. 734. .35 -- 

B5F 12-18-96 <1. 2.8 29. <1. 312. 1020. .44 -- 

S1 12-13-96 <1. 5.2 5. <1. 174. 534. .32 -- 

S1 12-13-96 <1. 5.5 4.8 <1. 174. 542. .32 -- 

S1 12-19-96 <1. 3.3 <3. <1. -- 12. <.1 -- 

Site 5

MICROJET 05-14-98 -- -- -- -- -- -- -- -- 

MICROJET 05-14-98 -- -- -- -- -- -- -- -- 

A5 12-17-96 <1. 10. 300. <1. 18.6 364. .26 -- 

A5 07-14-97 -- -- -- -- -- -- -- -- 

A5 07-14-97 -- -- -- -- -- -- -- -- 

A5 05-20-98 -- -- -- -- -- 402. .3 -20.92 

A10 12-17-96 <1. 9.5 250. 1.1 19. 554. .33 -- 

A10 07-15-97 -- -- -- -- 21. -- -- -- 

A10 05-20-98 -- -- -- -- -- 528. .1 -- 

A20 12-17-96 <1. 5.5 17. <1. 208. 566. .5 -- 

A20 07-14-97 -- -- -- -- 156. -- -- -- 

A20 05-20-98 -- -- -- -- -- 540. .4 -10.29 

A20 05-20-98 -- -- -- -- -- 520. .6 -- 

A5F 12-17-96 <1. 8.5 490. <1. 17.6 430. .23 -- 

A5F 07-15-97 -- -- -- -- 21. -- -- -- 

A5F 05-20-98 -- -- -- -- -- 938. .2 -21.06 

B20 12-16-96 <1. 2. 29. <1. 186. 500. .36 -- 

B20 05-14-98 -- -- -- -- -- 464. .3 -8.55 

B5 12-16-96 <1. 13. 260. 1.5 -- 966. 1.3 -- 

B5 05-14-98 -- -- -- -- -- 834. 1. -21.42 

B10 12-16-96 <1. 2.5 11. 1.4 134. 1540. 1.6 -- 

B10 05-14-98 -- -- -- -- -- 656. .8 -19.63 

B5F 12-16-96 <1. 6.8 230. <1. -- 450. .5 -- 

B5F 05-14-98 -- -- -- -- -- 598. .4 -22.17 

S1 12-13-96 <1. 23. 350. <1. 44. 376. .18 -- 

S1 07-14-97 -- -- -- -- -- -- -- -- 

S1 05-21-98 -- -- -- -- -- 404. .2 -10.24 

S2 12-13-96 <1. 44. 140. <1. 30. 294. .15 -- 

S2 05-21-98 -- -- -- -- -- 380. .5 -6.6 

FERTILIZER 07-08-98 -- -- -- -- -- -- -- -- 

Site 4

FERTILIZER 07-08-98 -- -- -- -- -- -- -- -- 

A5 05-12-98 -- -- -- -- -- 718. .5 -- 
Appendix III 57

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 H-2/ O-18/ N15/N14 N15/N14 SPE- ANC 

 H-1 O-16 NO3 NH4 CIFIC UNFLTRD

 STABLE STABLE N15/N14 N15/N14 FRAC FRAC CON- TIT 4.5

 ISOTOPE ISOTOPE NO3 NH4 WATER WATER DUCT- LAB 

 LOCAL RATIO RATIO FRAC FRAC FLTRD FLTRD ANCE (MG/L 

 IDENTIFIER DATE PER PER SOIL SOIL 0.45 U 0.45 U LAB AS 

 MIL MIL PER MIL PER MIL PER MIL PER MIL (μS/CM) CACO3)

Site 6

A10 12-19-96 -16.4 -3.45 -- -- -- -- 744. 290. 

A20 12-19-96 -6.1 -1.9 -- -- -- -- 934. 314. 

B20 12-18-96 -9.1 -2.5 -- -- -- -- 772. 349. 

B5 12-18-96 -9.1 -2.4 -- -- -- -- -- -- 

B10 12-18-96 -6.3 -1.84 -- -- -- -- 1050. 286. 

B10 12-18-96 -- -- -- -- -- -- 1050. 286. 

B5F 12-18-96 -6.7 -1.98 -- -- -- -- 1280. 309. 

S1 12-13-96 .6 -.48 -- -- -- -- 833. 197. 

S1 12-13-96 -- -- -- -- -- -- 833. 197. 

S1 12-19-96 -- -- -- -- -- -- 1.2 4.2 

Site 5

MICROJET 05-14-98 3. .25 -- -- -- -- -- -- 

MICROJET 05-14-98 -- -- -- -- -- -- -- -- 

A5 12-17-96 -18.7 -3.76 -- -- -- -- 468. 16. 

A5 07-14-97 -- -- -- -- 11.8 15.8 -- -- 

A5 07-14-97 -- -- -- -- -- -- -- -- 

A5 05-20-98 -13.7 -3. -- -- 9.4 11.8 566. 7.8 

A10 12-17-96 -17. -3.59 -- -- -- -- 748. 8.3 

A10 07-15-97 -- -- -- -- 11.5 13.3 -- -- 

A10 05-20-98 -12.4 -3.03 -- -- 8.7 16.3 708. 6.1 

A20 12-17-96 1.2 -.14 -- -- -- -- 942. 201. 

A20 07-14-97 -- -- -- -- -- -- -- -- 

A20 05-20-98 -2.1 -.81 -- -- -- 6. 844. 162. 

A20 05-20-98 -- -- -- -- -- -- 837. 164. 

A5F 12-17-96 -20.5 -4.08 -- -- -- -- 552. 16. 

A5F 07-15-97 -- -- -- -- 8.6 17.5 -- -- 

A5F 05-20-98 -12.1 -2.82 -- -- 3.5 16.7 1330. 13. 

B20 12-16-96 7. 1.29 -- -- -- -- 740. 189. 

B20 05-14-98 6.6 1.07 -- -- -- 4.3 667. 165. 

B5 12-16-96 -14.5 -3.01 -- -- -- -- 1620. 1.6 

B5 05-14-98 -11.6 -2.54 -- -- 7.3 9.4 1380. <1. 

B10 12-16-96 -7.2 -1.96 -- -- -- -- 1920. 18. 

B10 05-14-98 -10.9 -2.57 -- -- -- 5.6 1020. 36. 

B5F 12-16-96 -15.4 -3.12 -- -- -- -- 639. 11. 

B5F 05-14-98 -11.6 -2.41 -- -- -- 7.4 905. 6.7 

S1 12-13-96 -8. -1.54 -- -- -- -- 548. 41. 

S1 07-14-97 -- -- -- -- -- -- -- -- 

S1 05-21-98 11.5 2.27 -- -- -- -- 616. 52. 

S2 12-13-96 -12.6 -2.98 -- -- -- -- 407. 30. 

S2 05-21-98 -2.4 -.63 -- -- -- .4 578. 140. 

FERTILIZER 07-08-98 -- -- 1.3 -.7 -- -- -- -- 

Site 4

FERTILIZER 07-08-98 -- -- 3. -.6 -- -- -- -- 

A5 05-12-98 -10.6 -2.49 -- -- -- -- 1100. 117. 
58 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 PH PH 

 WATER WATER NITROGEN NITROGEN NITROGEN

 SPECIFIC WHOLE WHOLE AMMONIA NITRITE AMMONIA +

 TEMPER- CON- OXYGEN, FIELD LAB DIS- DIS- ORGANIC

 LOCAL ATURE DUCT- DIS- (STAND- (STAND- SOLVED SOLVED DISSOLVED

 IDENTIFIER DATE WATER ANCE SOLVED ARD ARD (MG/L (MG/L (MG/L 

 (DEGoC) (μS/CM) (MG/L) UNITS) UNITS) AS N) AS N) AS N) 

Site 4 (Continued)

A10 12-12-96 23.9 1636. .7 6.74 6.92 .56 <.01 1.4 

A10 05-11-98 26.6 1757. 1. 6.62 7.01 .38 <.01 1.1 

A20 12-12-96 25.5 1286. .6 7.1 7.1 1. <.01 1.5 

A20 05-11-98 24.2 1174. .7 7.01 7.38 .69 <.01 .98 

B20 12-11-96 24.5 817. .9 6.85 7.46 .083 <.01 .45 

B20 05-12-98 24. 1058. -- 6.99 7. .076 <.01 .4 

B5 12-11-96 22.5 -- -- 6.87 7.54 <.01 .068 .48 

B5 05-13-98 22.7 1563. .9 7.02 -- -- -- -- 

B10 12-11-96 23.2 1121. .9 6.96 7.5 .026 .058 .41 

B10 05-12-98 25. 1436. .9 7.04 7.29 <.01 .028 .4 

S1 12-12-96 17.67 1128. 7.28 6.74 8.04 .012 <.01 .87 

S1 05-13-98 27.3 728. .9 6.87 7.28 .056 <.01 1. 

S2 12-12-96 19.99 970. 2.9 7.06 7.57 .054 <.01 .59 

S2 05-13-98 28.2 1359. 1.4 7.16 6.96 <.01 <.01 .62 

S2 05-13-98 -- -- -- -- 5.68 <.01 <.01 <.2 

Site 3

A5 12-03-96 23.8 1020. -- 7.8 7.44 .03 <.01 .34 

A10 12-02-96 23.8 1382. 1.3 6.81 7.27 .071 <.01 .39 

A20 12-02-96 24. 2200. 1. 6.87 7.09 .17 <.01 .39 

A5F 12-03-96 -- -- -- -- -- -- -- -- 

B20 12-03-96 24.3 2090. .5 6.84 7.21 .1 <.01 .32 

B10 12-03-96 23.8 1340. 1.3 6.92 7.35 .017 <.01 .22 

B5F 12-03-96 -- 1912. -- 6.77 7.12 .84 .012 1.4 

S1 12-04-96 20.48 2017. 2.96 7.37 7.74 <.01 <.01 .67 

S2 12-04-96 21.06 2005. .1 7.68 7.86 .016 <.01 .74 

FLORIDAN 12-13-96 -- 3520. -- 7.77 8.21 .51 <.01 .54 

Reference Site

A5 11-22-96 23.8 98.8 .9 3.96 3.9 .052 .015 .84 

A5 07-09-97 27.6 387. 1. 3.64 -- .086 .018 1.4 

A5 05-07-98 24.9 129.6 .75 3.81 3.1 .052 <.01 .63 

A10 11-22-96 24.5 137.3 .35 5.03 5.06 .22 .016 1.1 

A10 07-09-97 26.3 115. .6 5.17 -- .18 <.01 .72 

A10 05-07-98 24.4 132. .7 5.42 5.69 .31 <.01 .92 

A20 11-22-96 24. 349. .5 6.81 7.22 .43 <.01 .64 

A20 07-08-97 24.2 459. .6 6.72 -- .48 <.01 .69 

A20 05-06-98 23.7 387. .35 6.79 7.1 .54 <.01 .89 

A20 05-06-98 -- -- -- -- 7.16 .55 <.01 .93 

B5 11-26-96 23.6 88.7 -- 5.8 5.78 .064 <.01 .51 

B5 05-08-98 22. 137.3 1.5 5.91 5.65 .13 <.01 .64 

B10 11-26-96 -- -- -- -- 5.63 <.01 <.01 <.2 

B10 11-26-96 24.7 306. .55 5.41 5.53 .22 .014 1.5 

B10 11-26-96 24.7 306. .55 5.41 5.62 .23 .015 1.5 

B10 05-08-98 24. 219. 1. 5.32 5.62 .21 .01 1.1 

S1 11-26-96 -- 532. 5.6 7.13 7.83 .042 .01 .55 

S1 11-26-96 -- 532. 5.6 7.13 7.83 .042 .01 .55 

S1 11-26-96 -- 532. 5.6 7.13 7.83 .042 .01 .55 

S1 07-09-97 27. 522. .3 7.2 -- .02 <.01 .5 
Appendix III 59

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 NITRO- PHOS- 

 GEN, PHOS- PHORUS CARBON, MAGNE- POTAS-

 NO2+NO3 PHORUS ORTHO, ORGANIC CALCIUM SIUM, SODIUM, SIUM,

 DIS- DIS- DIS- DIS- DIS- DIS- DIS- DIS- 

 LOCAL SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED

 IDENTIFIER DATE (MG/L (MG/L (MG/L (MG/L (MG/L (MG/L (MG/L (MG/L 

 AS N) AS P) AS P) AS C) AS CA) AS MG) AS NA) AS K) 

Site 4 (Continued)

A10 12-12-96 <.02 .02 <.01 77. 230. 26. 66. 14. 

A10 05-11-98 <.02 .05 <.01 11. 260. 27. 90. 15. 

A20 12-12-96 <.02 <.02 <.01 58. 160. 16. 86. 1.3 

A20 05-11-98 <.02 <.02 <.01 8.8 150. 15. 85. 2.1 

B20 12-11-96 <.02 <.02 <.01 48. 100. 11. 51. 6.5 

B20 05-12-98 <.02 .02 <.01 3.7 160. 15. 38. 7.4 

B5 12-11-96 1.5 <.02 <.01 55. 200. 23. 42. 15. 

B5 05-13-98 -- -- -- -- -- -- -- -- 

B10 12-11-96 1.4 <.02 <.01 47. 170. 18. 30. 15. 

B10 05-12-98 .75 .12 .1 5.7 240. 23. 37. 16. 

S1 12-12-96 <.02 <.02 .02 52. 100. 18. 100. 5.5 

S1 05-13-98 .04 .25 .22 23. 51. 11. 69. 3.9 

S2 12-12-96 .03 <.02 <.01 54. 130. 19. 77. 5.2 

S2 05-13-98 <.02 .02 <.01 12. 110. 22. 130. 4.7 

S2 05-13-98 <.02 <.02 <.01 <.1 <.02 .002 <.1 <.1 

Site 3

A5 12-03-96 .03 .04 .04 67. 160. 11. 58. 17. 

A10 12-02-96 <.02 <.02 .02 70. 160. 20. 85. 14. 

A20 12-02-96 <.02 .04 .05 70. 290. 33. 150. 2. 

A5F 12-03-96 -- -- -- -- -- -- -- -- 

B20 12-03-96 <.02 .06 <.01 66. 210. 14. 180. 1.4 

B10 12-03-96 <.02 <.02 <.01 66. 140. 13. 100. 13. 

B5F 12-03-96 <.02 .33 .1 95. 200. 49. 110. 14. 

S1 12-04-96 <.02 .2 .21 54. 110. 40. 200. 11. 

S2 12-04-96 <.02 .23 .21 54. 110. 39. 210. 11. 

FLORIDAN 12-13-96 <.02 <.02 <.01 33. 74. 73. 400. 12. 

Reference Site

A5 11-22-96 <.02 .13 .15 60. 1.2 .6 7.4 .2 

A5 07-09-97 <.02 .05 .06 -- -- -- -- -- 

A5 05-07-98 .07 .05 .05 37. .9 1.2 11. .2 

A10 11-22-96 <.02 .02 .04 64. 5.5 2. 15. .8 

A10 07-09-97 <.02 <.02 .04 -- -- -- -- -- 

A10 05-07-98 <.02 <.02 .02 28. 8.2 2.4 11. .9 

A20 11-22-96 <.02 .21 .15 52. 47. 3. 21. .7 

A20 07-08-97 <.02 .23 .16 -- -- -- -- -- 

A20 05-06-98 <.02 .17 .19 13. 54. 4.1 18. .8 

A20 05-06-98 <.02 .19 .22 14. 54. 4.1 17. .8 

B5 11-26-96 .1 <.02 <.01 40. 4.4 .8 8.2 1. 

B5 05-08-98 <.02 <.02 .02 18. 8. 1.1 13. .8 

B10 11-26-96 <.02 <.02 <.01 2.5 <.01 <.002 <.1 <.1 

B10 11-26-96 <.02 <.02 <.01 79. 21. 5. 26. .9 

B10 11-26-96 <.02 <.02 <.01 77. 22. 5. 28. .9 

B10 05-08-98 <.02 <.02 .01 53. 15. 3.3 20. .8 

S1 11-26-96 .04 <.02 .01 73. 71. 5. 29. .4 

S1 11-26-96 .04 <.02 .01 73. 71. 5. 29. .4 

S1 11-26-96 .04 <.02 .01 73. 71. 5. 29. .4 

S1 07-09-97 <.02 <.02 <.01 -- -- -- -- -- 
60 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 CHLO- FLUO- SILICA, BERYL- 

 RIDE, SULFATE RIDE, DIS- ARSENIC BARIUM, LIUM, CADMIUM

 DIS- DIS- DIS- SOLVED DIS- DIS- DIS- DIS- 

 LOCAL SOLVED SOLVED SOLVED (MG/L SOLVED SOLVED SOLVED SOLVED

 IDENTIFIER DATE (MG/L (MG/L (MG/L AS (μG/L (μG/L (μG/L (μG/L 

 AS CL) AS SO4) AS F) SIO2) AS AS) AS BA) AS BE) AS CD) 

Site 4 (Continued)

A10 12-12-96 160. 320. .2 18. 5.5 120. <.5 1.4 

A10 05-11-98 160. 430. .28 13. -- -- -- -- 

A20 12-12-96 97. 290. .5 16. <1. 74. <.5 1.1 

A20 05-11-98 75. 260. .44 15. -- -- -- -- 

B20 12-11-96 35. 150. .7 15. 3. 46. <.5 <.5 

B20 05-12-98 49. 270. .61 14. -- -- -- -- 

B5 12-11-96 100. 340. .5 7.7 1.5 120. <.5 <.5 

B5 05-13-98 -- -- -- -- -- -- -- -- 

B10 12-11-96 74. 260. .5 6.6 1.6 96. <.5 <.5 

B10 05-12-98 82. 430. .57 7.3 -- -- -- -- 

S1 12-12-96 220. 110. .4 5.4 <1. 39. <.5 <.5 

S1 05-13-98 140. 41. .22 5.3 -- -- -- -- 

S2 12-12-96 120. 200. .6 15. <1. 45. <.5 <.5 

S2 05-13-98 240. 140. .43 12. -- -- -- -- 

S2 05-13-98 <.1 <.2 <.1 <.01 -- -- -- -- 

Site 3

A5 12-03-96 130. 97. .8 14. 2.1 94. <.5 <.5 

A10 12-02-96 190. 140. .6 14. <1. 89. <.5 <.5 

A20 12-02-96 430. 310. .4 17. <1. 44. <.5 <.5 

A5F 12-03-96 -- -- -- -- 1.8 120. <.5 <.5 

B20 12-03-96 420. 150. .4 15. <1. 39. <.5 .7 

B10 12-03-96 200. 85. .8 10. <1. 130. <.5 <.5 

B5F 12-03-96 370. 77. 1.1 14. 16. 130. <.5 <.5 

S1 12-04-96 450. 120. .5 10. <1. 43. <.5 <.5 

S2 12-04-96 450. 120. .5 10. <1. 44. <.5 <.5 

FLORIDAN 12-13-96 960. 130. .5 13. <1. 27. <.5 <.5 

Reference Site

A5 11-22-96 14. 1.8 <.1 8.7 1.4 16. <.5 <.5 

A5 07-09-97 -- -- -- -- -- -- -- -- 

A5 05-07-98 19. 5.9 <.1 8.1 -- -- -- -- 

A10 11-22-96 26. 4.3 <.1 8.2 4.1 19. <.5 <.5 

A10 07-09-97 -- -- -- -- -- -- -- -- 

A10 05-07-98 21. 4.3 <.1 10. -- -- -- -- 

A20 11-22-96 16. .9 .2 13. 9.8 23. <.5 <.5 

A20 07-08-97 -- -- -- -- -- -- -- -- 

A20 05-06-98 20. .2 .17 11. -- -- -- -- 

A20 05-06-98 20. .2 .17 11. -- -- -- -- 

B5 11-26-96 13. 6.7 <.1 7.4 3.4 6. <.5 <.5 

B5 05-08-98 26. 8.1 <.1 7.6 -- -- -- -- 

B10 11-26-96 <.1 <.2 <.1 .1 <1. <.2 <.5 <.5 

B10 11-26-96 61. 6.6 <.1 18. 1. 37. <.5 <.5 

B10 11-26-96 61. 6.5 <.1 19. 1.4 38. <.5 <.5 

B10 05-08-98 41. 4.9 <.1 15. -- -- -- -- 

S1 11-26-96 54. 6. .2 10. <1. 13. <.5 <.5 

S1 11-26-96 54. 6. .2 10. <1. 13. <.5 <.5 

S1 11-26-96 54. 6. .2 10. <1. 13. <.5 <.5 

S1 07-09-97 -- -- -- -- -- -- -- -- 
Appendix III 61

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 CHRO- MANGA- MOLYB- 

 MIUM, COBALT, COPPER, IRON, LEAD, NESE, DENUM, NICKEL,

 DIS- DIS- DIS- DIS- DIS- DIS- DIS- DIS- 

 LOCAL SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED

 IDENTIFIER DATE (μG/L (μG/L (μG/L (μG/L (μG/L (μG/L (μG/L (μG/L 

 AS CR) AS CO) AS CU) AS FE) AS PB) AS MN) AS MO) AS NI) 

Site 4 (Continued)

A10 12-12-96 <1. 1.4 <1. 19000. 1.3 240. 13. 5.5 

A10 05-11-98 -- -- -- 15527. -- 130. -- -- 

A20 12-12-96 <1. <1. <1. 15000. <1. 100. 31. 5. 

A20 05-11-98 -- -- -- 11077. -- 100. -- -- 

B20 12-11-96 <1. <1. <1. 5100. <1. 84. 51. 2.8 

B20 05-12-98 -- -- -- 15094. -- 140. -- -- 

B5 12-11-96 <1. <1. 2.1 5. <1. 29. 31. 3.9 

B5 05-13-98 -- -- -- -- -- -- -- -- 

B10 12-11-96 <1. <1. <1. 90. <1. 67. 38. 2.8 

B10 05-12-98 -- -- -- 6. -- 27. -- -- 

S1 12-12-96 <1. <1. 2.6 60. <1. 6.9 3.9 1.3 

S1 05-13-98 -- -- -- 540. -- 36. -- -- 

S2 12-12-96 <1. <1. <1. 40. <1. 56. 25. 1.4 

S2 05-13-98 -- -- -- 40. -- 10. -- -- 

S2 05-13-98 -- -- -- 2. -- <.2 -- -- 

Site 3

A5 12-03-96 <1. <1. 1.3 3. <1. 66. 27. 2.1 

A10 12-02-96 <1. <1. <1. 830. <1. 51. 15. 1.5 

A20 12-02-96 <1. <1. <1. 1500. <1. 100. 2.2 <1. 

A5F 12-03-96 <1. <1. <1. -- <1. -- 13. 8. 

B20 12-03-96 <1. <1. <1. 7300. <1. 49. 17. <1. 

B10 12-03-96 <1. <1. <1. 400. <1. 10. 21. 1.6 

B5F 12-03-96 <1. 2. <1. 2500. <1. 490. 25. 5.2 

S1 12-04-96 <1. <1. 2.7 30. <1. 34. 2.7 1.3 

S2 12-04-96 <1. <1. 2.3 30. <1. 43. 3.1 1. 

FLORIDAN 12-13-96 <1. <1. <1. 20. <1. 14. <2. <1. 

Reference Site

A5 11-22-96 2.9 <1. 3.9 2500. 13. 8.2 <2. 1.7 

A5 07-09-97 -- -- -- -- -- -- -- -- 

A5 05-07-98 -- -- -- 2100. -- 3.7 -- -- 

A10 11-22-96 4.3 <1. 10. 2400. 4.4 7.7 <2. 1.3 

A10 07-09-97 -- -- -- -- -- -- -- -- 

A10 05-07-98 -- -- -- 3200. -- 8.3 -- -- 

A20 11-22-96 <1. <1. <1. 3700. <1. 7.1 5.3 <1. 

A20 07-08-97 -- -- -- -- -- -- -- -- 

A20 05-06-98 -- -- -- 5500. -- 9.2 -- -- 

A20 05-06-98 -- -- -- 5600. -- 9. -- -- 

B5 11-26-96 1.6 <1. 1.5 1800. <1. 19. <2. 1.2 

B5 05-08-98 -- -- -- 5300. -- 56. -- -- 

B10 11-26-96 <1. <1. <1. <1. <1. <.2 <2. <1. 

B10 11-26-96 3.3 <1. <1. 4600. <1. 11. <2. <1. 

B10 11-26-96 3.3 <1. <1. 4800. <1. 12. <2. <1. 

B10 05-08-98 -- -- -- 3400. -- 7.7 -- -- 

S1 11-26-96 <1. <1. <1. 190. <1. 4.5 <2. <1. 

S1 11-26-96 <1. <1. <1. 190. <1. 4.5 <2. <1. 

S1 11-26-96 <1. <1. <1. 190. <1. 4.5 <2. <1. 

S1 07-09-97 -- -- -- -- -- -- -- -- 
62 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 ALKA- SOLIDS, C-13/ 

 ALUM- SELE- LINITY RESIDUE C-12 

 SILVER, ZINC, INUM, NIUM, WAT DIS AT 180 BROMIDE STABLE 

 DIS- DIS- DIS- DIS- TOT IT DEG. C DIS- ISOTOPE

 LOCAL SOLVED SOLVED SOLVED SOLVED FIELD DIS- SOLVED RATIO 

 IDENTIFIER DATE (μG/L (μG/L (μG/L (μG/L MG/L AS SOLVED (MG/L PER 

 AS AG) AS ZN) AS AL) AS SE) CACO3 (MG/L) AS BR) MIL 

Site 4 (Continued)

A10 12-12-96 <1. 10. 41. <1. 332. 1110. .49 -- 

A10 05-11-98 -- -- -- -- -- 1260. .4 -13.83 

A20 12-12-96 <1. 4.3 35. <1. 270. 848. .37 -- 

A20 05-11-98 -- -- -- -- -- 800. .3 -10.91 

B20 12-11-96 <1. 1.2 16. <1. 228. 528. .14 -- 

B20 05-12-98 -- -- -- -- -- 783. .2 -8.53 

B5 12-11-96 <1. 1.9 <3. 1.2 254. 956. .28 -- 

B5 05-13-98 -- -- -- -- -- -- -- -12.91 

B10 12-11-96 <1. 1.4 <3. 1.3 228. 790. .23 -- 

B10 05-12-98 -- -- -- -- -- 1060. .2 -11.04 

S1 12-12-96 <1. 8.9 <3. <1. 176. 792. .71 -- 

S1 05-13-98 -- -- -- -- -- 462. .8 -11.02 

S2 12-12-96 <1. 3.6 4.9 <1. 208. 740. .4 -- 

S2 05-13-98 -- -- -- -- -- 814. .9 -7.54 

S2 05-13-98 -- -- -- -- -- 4. <.05 -- 

Site 3

A5 12-03-96 <1. 15. 3.6 <1. 340. 732. .48 -- 

A10 12-02-96 <1. 2.5 5. 1.1 296. 856. .65 -- 

A20 12-02-96 <1. 1.4 6.9 <1. 306. 1670. 1.4 -- 

A5F 12-03-96 <1. 12. <3. <1. -- -- -- -- 

B20 12-03-96 <1. 2.5 21. <1. 302. 1420. 1.4 -- 

B10 12-03-96 <1. 1.5 <3. <1. 304. 806. .67 -- 

B5F 12-03-96 <1. 9.9 3.9 1.4 410. 1340. 1. -- 

S1 12-04-96 <1. 14. <3. 1.6 190. 1190. 1.5 -- 

S2 12-04-96 <1. 14. 4.7 1.4 186. 1190. 1.6 -- 

FLORIDAN 12-13-96 <1. 1.5 <3. <1. 107. 2060. 3.4 -- 

Reference Site

A5 11-22-96 <1. 13. 1100. 1. -- 126. <.1 -- 

A5 07-09-97 -- -- -- -- -- -- -- -- 

A5 05-07-98 -- -- -- -- -- 106. <.05 -- 

A10 11-22-96 <1. 4. 1700. 1.4 9.2 156. <.1 -- 

A10 07-09-97 -- -- -- -- 26. -- -- -- 

A10 05-07-98 -- -- -- -- -- 128. .1 -- 

A20 11-22-96 <1. <1. 16. <1. 196. 214. <.1 -- 

A20 07-08-97 -- -- -- -- 186. -- -- -- 

A20 05-06-98 -- -- -- -- -- 240. .1 -- 

A20 05-06-98 -- -- -- -- -- 236. .1 -- 

B5 11-26-96 <1. 3.1 540. 1.2 -- 80. <.1 -- 

B5 05-08-98 -- -- -- -- -- 122. <.05 -20.38 

B10 11-26-96 <1. <1. <3. <1. -- <1. <.1 -- 

B10 11-26-96 <1. 6.1 1100. 1.2 38. 350. .15 -- 

B10 11-26-96 <1. 2.4 1100. 1.1 38. 354. .14 -- 

B10 05-08-98 -- -- -- -- -- 248. .2 -22.09 

S1 11-26-96 <1. 2.4 4.3 1. 188. 366. .15 -- 

S1 11-26-96 <1. 2.4 4.3 1. 188. 366. .15 -- 

S1 11-26-96 <1. 2.4 4.3 1. 188. 366. .15 -- 

S1 07-09-97 -- -- -- -- 184. -- -- -- 
Appendix III 63

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 H-2/ O-18/ N15/N14 N15/N14 SPE- ANC 

 H-1 O-16 NO3 NH4 CIFIC UNFLTRD

 STABLE STABLE N15/N14 N15/N14 FRAC FRAC CON- TIT 4.5

 ISOTOPE ISOTOPE NO3 NH4 WATER WATER DUCT- LAB 

 LOCAL RATIO RATIO FRAC FRAC FLTRD FLTRD ANCE (MG/L 

 IDENTIFIER DATE PER PER SOIL SOIL 0.45 U 0.45 U LAB AS 

 MIL MIL PER MIL PER MIL PER MIL PER MIL (μS/CM) CACO3) 

Site 4 (Continued)

A10 12-12-96 -15.6 -2.94 -- -- -- -- 1570. 288. 

A10 05-11-98 -11.3 -2.65 -- -- -- 6.2 1720. 281. 

A20 12-12-96 -8.7 -2.34 -- -- -- -- 1250. 237. 

A20 05-11-98 -9.8 -2.52 -- -- -- 5.2 1140. 236. 

B20 12-11-96 -11. -2.89 -- -- -- -- 804. 215. 

B20 05-12-98 -23.2 -4.15 -- -- -- -- 1020. 196. 

B5 12-11-96 -22.8 -4.36 -- -- -- -- 1360. 236. 

B5 05-13-98 -13.5 -2.83 -- -- 28.3 -- -- -- 

B10 12-11-96 -22.7 -4.27 -- -- -- -- 1110. 216. 

B10 05-12-98 -16.8 -3.45 -- -- 27.1 -- 1430. 246. 

S1 12-12-96 -.9 -1.09 -- -- -- -- 1220. 172. 

S1 05-13-98 .9 -.48 -- -- -- -- 723. 92. 

S2 12-12-96 -11.4 -2.33 -- -- -- -- 1140. 201. 

S2 05-13-98 -2.6 -1.14 -- -- -- -- 1380. 187. 

S2 05-13-98 -- -- -- -- -- -- 1200. 4.4 

Site 3

A5 12-03-96 -18.8 -3.38 -- -- -- -- 1180. 314. 

A10 12-02-96 -14.5 -3.19 -- -- -- -- 1400. 305. 

A20 12-02-96 -8.5 -2.3 -- -- -- -- 2380. 304. 

A5F 12-03-96 -- -- -- -- -- -- -- -- 

B20 12-03-96 -9.4 -2.21 -- -- -- -- 2110. 291. 

B10 12-03-96 -14.6 -2.94 -- -- -- -- 1350. 294. 

B5F 12-03-96 -8.1 -2.14 -- -- -- -- 2020. 416. 

S1 12-04-96 -1.3 -1.14 -- -- -- -- 2000. 185. 

S2 12-04-96 -1.8 -1.1 -- -- -- -- 2040. 185. 

FLORIDAN 12-13-96 -2.8 -1.43 -- -- -- -- 3530. 102. 

Reference Site

A5 11-22-96 -10.1 -2.7 -- -- -- -- 104. <1. 

A5 07-09-97 -- -- -- -- -- -- -- -- 

A5 05-07-98 -14.9 -3.11 -- -- -- -- 136. <1. 

A10 11-22-96 -15.4 -3.34 -- -- -- -- 144. 5.3 

A10 07-09-97 -- -- -- -- -- 4.3 -- -- 

A10 05-07-98 -14. -3.01 -- -- -- 4.1 115. 12. 

A20 11-22-96 -11.1 -2.77 -- -- -- -- 411. 168. 

A20 07-08-97 -- -- -- -- -- -- -- -- 

A20 05-06-98 -13. -2.96 -- -- -- 6. 375. 164. 

A20 05-06-98 -- -- -- -- -- -- 368. 160. 

B5 11-26-96 -7.9 -2.3 -- -- -- -- 84. 7.1 

B5 05-08-98 -17.9 -3.77 -- -- -- 4.4 130. 6.2 

B10 11-26-96 -- -- -- -- -- -- <1. 4.2 

B10 11-26-96 -17.9 -3.99 -- -- -- -- 295. 23. 

B10 11-26-96 -- -- -- -- -- -- 291. 23. 

B10 05-08-98 -14.4 -3.34 -- -- -- 2.6 212. 22. 

S1 11-26-96 -10.4 -2.38 -- -- -- -- 535. 187. 

S1 11-26-96 -10.4 -2.38 -- -- -- -- 535. 187. 

S1 11-26-96 -10.4 -2.38 -- -- -- -- 535. 187. 

S1 07-09-97 -- -- -- -- -- -- -- -- 
64 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 PH PH 

 WATER WATER NITROGEN NITROGEN NITROGEN

 SPECIFIC WHOLE WHOLE AMMONIA NITRITE AMMONIA +

 TEMPER- CON- OXYGEN, FIELD LAB DIS- DIS- ORGANIC

 LOCAL ATURE DUCT- DIS- (STAND- (STAND- SOLVED SOLVED DISSOLVED

 IDENTIFIER DATE WATER ANCE SOLVED ARD ARD (MG/L (MG/L (MG/L 

 (DEGoC) (μS/CM) (MG/L) UNITS) UNITS) AS N) AS N) AS N) 

Reference Site (Continued)

S1 07-09-97 27. 522. .3 7.2 -- .02 <.01 .5 

S1 07-09-97 27. 522. .3 7.2 -- .02 <.01 .5 

S1 05-08-98 28. 258. 5.55 7.08 7.49 .013 <.01 .57 

S1 05-08-98 28. 258. 5.55 7.08 7.49 .013 <.01 .57 

S1 05-08-98 28. 258. 5.55 7.08 7.49 .013 <.01 .57 

RAINFALL 11-26-96 -- -- -- -- -- -- -- -- 

RAINFALL 06-08-98 -- -- -- -- -- S.265 .033 .371 

Site 2

FERTILIZER 07-10-98 -- -- -- -- -- -- -- -- 

A5 12-10-96 20.5 793. -- 7.3 7.31 2.5 .013 3.3 

A5 07-10-97 26.8 1195. 2. 4.08 -- 6.2 <.01 7.8 

A5 05-18-98 24. 310. 3.7 6.8 6.85 .02 <.01 .69 

A10 12-10-96 22.4 1257. 1. 6.1 7.7 .014 .38 .7 

A10 07-10-97 25.2 1268. .7 7.21 -- .026 .11 .83 

A10 05-18-98 25.1 1124. .85 7.14 7.54 <.01 .032 .75 

A20 12-10-96 23.4 1753. .7 6.7 7.26 .33 <.01 1.3 

A20 12-10-96 23.4 1753. .7 6.7 7.16 .33 <.01 1.3 

A20 07-10-97 24.1 1624. .6 7.07 -- .28 <.01 1.4 

A20 05-18-98 24. 1559. .5 7.03 7.15 .36 <.01 1.3 

A5F 12-10-96 20.5 893. -- 6.93 7.59 .47 <.01 1.6 

A5F 07-10-97 27. -- 2.2 -- -- 1.4 <.01 4. 

A5F 05-18-98 23.2 619. 1.5 6.63 7.02 .35 <.01 1.4 

B20 12-09-96 23.2 1551. .85 7.24 7.33 .54 <.01 1.3 

B20 07-28-97 -- -- -- -- -- .57 <.01 1.6 

B20 05-19-98 23.9 1629. .5 7.1 7.43 .64 <.01 1.2 

B5 12-09-96 20.8 1231. -- 7.24 6.91 .59 .022 1.4 

B5 07-28-97 -- -- -- -- -- .81 .024 3.6 

B5 05-19-98 23.5 456. 1.6 5.11 4.55 .09 .02 1.1 

B10 12-09-96 21.4 1153. -- 7.36 7.42 .97 <.01 1.6 

B10 07-28-97 -- -- -- -- -- -- -- -- 

B10 05-19-98 24.7 902. 2.4 7.24 7.57 .17 .12 .72 

B5F 12-09-96 24.1 1094. -- 7.35 7.68 .76 <.01 1.6 

B5F 05-19-98 23.5 827. .1 7.49 7.56 .6 <.01 1.5 

S1 12-09-96 16.83 1100. 4.53 7.32 7.89 .076 <.01 .84 

S1 12-09-96 16.83 1100. 4.53 7.32 7.84 .078 <.01 .9 

S1 07-10-97 29.25 980. 1.8 7.14 -- .064 .014 .86 

S1 05-19-98 27. 1199. .1 7.58 8.16 <.01 <.01 .83 

Site 1

A10 12-06-96 26.6 1664. -- 5.9 5.98 1.5 .019 2. 

A20 12-06-96 23.4 1696. .6 6.86 7.12 .19 <.01 .54 

B20 12-05-96 23.2 1707. .7 6.7 7.1 .24 <.01 .62 

B5 12-05-96 -- 2740. -- 5.61 6.11 2.4 .053 3.3 

B10 12-05-96 24. 2390. -- 4.68 5.02 4.4 .034 4.5 

S1 12-06-96 23.74 2150. .85 7.04 7.69 .4 .02 .58 

S1 12-06-96 23.74 2150. .85 7.04 7.69 .4 .02 .58 
Appendix III 65

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 NITRO- PHOS- 

 GEN, PHOS- PHORUS CARBON, MAGNE- POTAS-

 NO2+NO3 PHORUS ORTHO, ORGANIC CALCIUM SIUM, SODIUM, SIUM,

 DIS- DIS- DIS- DIS- DIS- DIS- DIS- DIS- 

 LOCAL SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED

 IDENTIFIER DATE (MG/L (MG/L (MG/L (MG/L (MG/L (MG/L (MG/L (MG/L 

 AS N) AS P) AS P) AS C) AS CA) AS MG) AS NA) AS K) 

Reference Site (Continued)

S1 07-09-97 <.02 <.02 <.01 -- -- -- -- -- 

S1 07-09-97 <.02 <.02 <.01 -- -- -- -- -- 

S1 05-08-98 .13 <.02 <.01 21. 28. 3.6 15. 1. 

S1 05-08-98 .13 <.02 <.01 21. 28. 3.6 15. 1. 

S1 05-08-98 .13 <.02 <.01 21. 28. 3.6 15. 1. 

RAINFALL 11-26-96 -- -- -- -- -- -- -- -- 

RAINFALL 06-08-98 .212 .01 .022 -- -- -- -- -- 

Site 2

FERTILIZER 07-10-98 -- -- -- -- -- -- -- -- 

A5 12-10-96 4. .03 .03 25. 76. 16. 29. 26. 

A5 07-10-97 26. .07 .08 -- -- -- -- -- 

A5 05-18-98 .51 <.02 <.01 8.7 45. 10. 16. 13. 

A10 12-10-96 .83 <.02 .01 33. 120. 24. 70. 19. 

A10 07-10-97 4.9 <.02 .02 -- -- -- -- -- 

A10 05-18-98 .87 <.02 .01 9.3 130. 21. 51. 14. 

A20 12-10-96 <.02 <.02 <.01 55. 250. 21. 82. .7 

A20 12-10-96 <.02 <.02 <.01 55. 250. 21. 83. .6 

A20 07-10-97 <.02 <.02 .01 -- -- -- -- -- 

A20 05-18-98 <.02 <.02 <.01 18. 220. 18. 80. .6 

A5F 12-10-96 <.02 <.02 <.01 50. 120. 18. 37. 7.9 

A5F 07-10-97 <.02 <.02 .02 -- -- -- -- -- 

A5F 05-18-98 <.02 <.02 .02 17. 60. 10. 31. 5.7 

B20 12-09-96 <.02 <.02 <.01 55. 220. 24. 61. 1.2 

B20 07-28-97 <.02 .36 <.01 -- -- -- -- -- 

B20 05-19-98 <.02 <.02 <.01 15. 240. 26. 61. 1. 

B5 12-09-96 2.4 <.02 <.01 16. 110. 23. 71. 18. 

B5 07-28-97 20. .11 .01 -- -- -- -- -- 

B5 05-19-98 8.3 <.02 .01 11. 42. 14. 6.9 9.4 

B10 12-09-96 .02 <.02 <.01 43. 140. 16. 57. 6.7 

B10 07-28-97 -- -- -- -- -- -- -- -- 

B10 05-19-98 .97 <.02 .01 8.4 120. 15. 37. 10. 

B5F 12-09-96 .07 .06 .06 45. 100. 15. 76. 11. 

B5F 05-19-98 <.02 .03 .05 12. 81. 13. 42. 11. 

S1 12-09-96 .03 .04 .03 55. 130. 20. 88. 8. 

S1 12-09-96 .03 .04 .03 -- 120. 20. 90. 7.6 

S1 07-10-97 .06 .12 .14 -- -- -- -- -- 

S1 05-19-98 <.02 .03 .03 14. 120. 18. 79. 5.5 

Site 1

A10 12-06-96 .39 <.02 <.01 12. 84. 57. 120. 25. 

A20 12-06-96 <.02 <.02 <.01 48. 260. 6. 78. .9 

B20 12-05-96 <.02 <.02 <.01 79. 280. 8. 67. .9 

B5 12-05-96 14. <.02 <.01 30. 150. 100. 190. 69. 

B10 12-05-96 .04 <.02 <.01 -- 170. 46. 160. 14. 

S1 12-06-96 .08 <.02 .01 -- 91. 60. 260. 8.2 

S1 12-06-96 .08 <.02 .01 -- 91. 60. 260. 8.2 
66 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 CHLO- FLUO- SILICA, BERYL- 

 RIDE, SULFATE RIDE, DIS- ARSENIC BARIUM, LIUM, CADMIUM

 DIS- DIS- DIS- SOLVED DIS- DIS- DIS- DIS- 

 LOCAL SOLVED SOLVED SOLVED (MG/L SOLVED SOLVED SOLVED SOLVED

 IDENTIFIER DATE (MG/L (MG/L (MG/L AS (μG/L (μG/L (μG/L (μG/L 

 AS CL) AS SO4) AS F) SIO2) AS AS) AS BA) AS BE) AS CD) 

Reference Site (Continued)

S1 07-09-97 -- -- -- -- -- -- -- -- 

S1 07-09-97 -- -- -- -- -- -- -- -- 

S1 05-08-98 24. 13. .18 8.2 -- -- -- -- 

S1 05-08-98 24. 13. .18 8.2 -- -- -- -- 

S1 05-08-98 24. 13. .18 8.2 -- -- -- -- 

RAINFALL 11-26-96 -- -- -- -- -- -- -- -- 

RAINFALL 06-08-98 -- -- -- -- -- -- -- -- 

Site 2

FERTILIZER 07-10-98 -- -- -- -- -- -- -- -- 

A5 12-10-96 46. 220. .5 13. 1.4 99. <.5 <.5 

A5 07-10-97 -- -- -- -- -- -- -- -- 

A5 05-18-98 45. 81. .33 15. -- -- -- -- 

A10 12-10-96 170. 240. .6 9.2 1.2 82. <.5 <.5 

A10 07-10-97 -- -- -- -- -- -- -- -- 

A10 05-18-98 140. 250. .5 12. -- -- -- -- 

A20 12-10-96 250. 370. .2 10. 1.2 110. <.5 .7 

A20 12-10-96 250. 370. .2 10. 1.3 120. <.5 .7 

A20 07-10-97 -- -- -- -- -- -- -- -- 

A20 05-18-98 200. 320. .19 11. -- -- -- -- 

A5F 12-10-96 70. 190. .3 16. 1.5 100. <.5 <.5 

A5F 07-10-97 -- -- -- -- -- -- -- -- 

A5F 05-18-98 39. 130. .42 12. -- -- -- -- 

B20 12-09-96 210. 320. .3 12. <1. 110. <.5 <.5 

B20 07-28-97 -- -- -- -- -- -- -- -- 

B20 05-19-98 210. 380. .25 11. -- -- -- -- 

B5 12-09-96 160. 290. .6 12. 1.1 75. <.5 .7 

B5 07-28-97 -- -- -- -- -- -- -- -- 

B5 05-19-98 19. 140. .56 20. -- -- -- -- 

B10 12-09-96 100. 280. .2 9. 2.8 110. <.5 .5 

B10 07-28-97 -- -- -- -- -- -- -- -- 

B10 05-19-98 79. 200. .42 9.4 -- -- -- -- 

B5F 12-09-96 120. 180. .4 11. 2.1 68. <.5 <.5 

B5F 05-19-98 39. 120. .44 13. -- -- -- -- 

S1 12-09-96 180. 160. .4 9.1 1.5 63. <.5 <.5 

S1 12-09-96 180. 160. .4 9.1 1.6 64. <.5 <.5 

S1 07-10-97 -- -- -- -- -- -- -- -- 

S1 05-19-98 170. 160. .41 10. -- -- -- -- 

Site 1

A10 12-06-96 340. 300. .1 7.3 1.2 72. <.5 1.3 

A20 12-06-96 310. 200. .2 17. 1.6 53. <.5 <.5 

B20 12-05-96 290. 210. .3 18. 1.3 54. <.5 .6 

B5 12-05-96 540. 530. <.1 40. <1. 75. <.5 <.5 

B10 12-05-96 540. 460. <.1 26. <1. 74. .7 7. 

S1 12-06-96 580. 150. .6 17. 1. 57. <.5 <.5 

S1 12-06-96 580. 150. .6 17. 1. 57. <.5 <.5 
Appendix III 67

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 CHRO- MANGA- MOLYB- 

 MIUM, COBALT, COPPER, IRON, LEAD, NESE, DENUM, NICKEL,

 DIS- DIS- DIS- DIS- DIS- DIS- DIS- DIS- 

 LOCAL SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED SOLVED

 IDENTIFIER DATE (μG/L (μG/L (μG/L (μG/L (μG/L (μG/L (μG/L (μG/L 

 AS CR) AS CO) AS CU) AS FE) AS PB) AS MN) AS MO) AS NI)

Reference Site (Continued)

S1 07-09-97 -- -- -- -- -- -- -- -- 

S1 07-09-97 -- -- -- -- -- -- -- -- 

S1 05-08-98 -- -- -- 110. -- 2.6 -- -- 

S1 05-08-98 -- -- -- 110. -- 2.6 -- -- 

S1 05-08-98 -- -- -- 110. -- 2.6 -- -- 

RAINFALL 11-26-96 -- -- -- -- -- -- -- -- 

RAINFALL 06-08-98 -- -- -- -- -- -- -- -- 

Site 2

FERTILIZER 07-10-98 -- -- -- -- -- -- -- -- 

A5 12-10-96 <1. 1.1 12. 50. <1. 540. <2. 4.6 

A5 07-10-97 -- -- -- -- -- -- -- -- 

A5 05-18-98 -- -- -- 30. -- 280. -- -- 

A10 12-10-96 <1. <1. 2.4 20. <1. 270. 5. 4.4 

A10 07-10-97 -- -- -- -- -- -- -- -- 

A10 05-18-98 -- -- -- 30. -- 340. -- -- 

A20 12-10-96 <1. <1. <1. 8700. <1. 58. 5.1 <1. 

A20 12-10-96 <1. <1. <1. 8300. <1. 59. 5.6 <1. 

A20 07-10-97 -- -- -- -- -- -- -- -- 

A20 05-18-98 -- -- -- 6600. -- 42. -- -- 

A5F 12-10-96 <1. <1. <1. 4300. <1. 160. <2. 1.8 

A5F 07-10-97 -- -- -- -- -- -- -- -- 

A5F 05-18-98 -- -- -- 6700. -- 170. -- -- 

B20 12-09-96 <1. <1. <1. 2600. <1. 30. 5.1 <1. 

B20 07-28-97 -- -- -- -- -- -- -- -- 

B20 05-19-98 -- -- -- 2900. -- 16. -- -- 

B5 12-09-96 <1. 3.1 8.4 1400. <1. 430. <2. 9.8 

B5 07-28-97 -- -- -- -- -- -- -- -- 

B5 05-19-98 -- -- -- 600. -- 500. -- -- 

B10 12-09-96 <1. <1. <1. 6800. <1. 240. 7.8 2.6 

B10 07-28-97 -- -- -- -- -- -- -- -- 

B10 05-19-98 -- -- -- 270. -- 220. -- -- 

B5F 12-09-96 <1. <1. <1. 1400. <1. 290. 9.2 1.5 

B5F 05-19-98 -- -- -- 2700. -- 290. -- -- 

S1 12-09-96 <1. <1. 3.5 40. <1. 18. 3.6 <1. 

S1 12-09-96 <1. <1. 3.6 40. <1. 18. 4. <1. 

S1 07-10-97 -- -- -- -- -- -- -- -- 

S1 05-19-98 -- -- -- 30. -- 8.2 -- -- 

Site 1

A10 12-06-96 <1. 4.8 <1. 13000. <1. 91. <2. 4.7 

A20 12-06-96 <1. <1. <1. 2600. <1. 37. <2. <1. 

B20 12-05-96 <1. <1. <1. 7500. <1. 36. <2. <1. 

B5 12-05-96 <1. 1.1 1.5 150. <1. 480. <2. 1.3 

B10 12-05-96 <1. 8.6 <1. 89000. 4.3 220. <2. 11. 

S1 12-06-96 <1. <1. <1. 20. <1. 3. <2. <1. 

S1 12-06-96 <1. <1. <1. 20. <1. 3. <2. <1. 
68 Distribution, Movement, and Fate of Nitrate in the Surficial Aquifer Beneath Citrus Groves, Indian River, Martin, 

and St. Lucie Counties, Florida

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 ALKA- SOLIDS, C-13/ 

 ALUM- SELE- LINITY RESIDUE C-12 

 SILVER, ZINC, INUM, NIUM, WAT DIS AT 180 BROMIDE STABLE 

 DIS- DIS- DIS- DIS- TOT IT DEG. C DIS- ISOTOPE

 LOCAL SOLVED SOLVED SOLVED SOLVED FIELD DIS- SOLVED RATIO 

 IDENTIFIER DATE (μG/L (μG/L (μG/L (μG/L MG/L AS SOLVED (MG/L PER 

 AS AG) AS ZN) AS AL) AS SE) CACO3 (MG/L) AS BR) MIL 

Reference Site (Continued)

S1 07-09-97 -- -- -- -- 184. -- -- -- 

S1 07-09-97 -- -- -- -- 184. -- -- -- 

S1 05-08-98 -- -- -- -- -- 186. .09 -13.65 

S1 05-08-98 -- -- -- -- -- 186. .09 -13.65 

S1 05-08-98 -- -- -- -- -- 186. .09 -13.65 

RAINFALL 11-26-96 -- -- -- -- -- -- -- -- 

RAINFALL 06-08-98 -- -- -- -- -- -- -- -- 

Site 2

FERTILIZER 07-10-98 -- -- -- -- -- -- -- -- 

A5 12-10-96 <1. 150. 61. 1.4 -- 542. .17 -- 

A5 07-10-97 -- -- -- -- -- -- -- -- 

A5 05-18-98 -- -- -- -- -- 298. .1 -- 

A10 12-10-96 <1. 4.8 6.9 1.8 -- 774. .52 -- 

A10 07-10-97 -- -- -- -- 141. -- -- -- 

A10 05-18-98 -- -- -- -- -- 788. .4 -12.82 

A20 12-10-96 <1. 1.4 23. 1.3 -- 1370. .71 -- 

A20 12-10-96 <1. 3.2 17. 1.2 -- 1420. .72 -- 

A20 07-10-97 -- -- -- -- 190. -- -- -- 

A20 05-18-98 -- -- -- -- -- 1150. .8 -9.72 

A5F 12-10-96 <1. 2.2 26. <1. -- 630. .46 -- 

A5F 07-10-97 -- -- -- -- -- -- -- -- 

A5F 05-18-98 -- -- -- -- -- 410. .3 -- 

B20 12-09-96 <1. <1. 6.4 1.6 -- 1210. .63 -- 

B20 07-28-97 -- -- -- -- -- -- -- -- 

B20 05-19-98 -- -- -- -- -- 1220. .6 -11.67 

B5 12-09-96 <1. 53. 140. 1.6 -- 754. .42 -- 

B5 07-28-97 -- -- -- -- -- -- -- -- 

B5 05-19-98 -- -- -- -- -- 332. .09 -- 

B10 12-09-96 <1. 11. 21. 1.3 -- 744. .42 -- 

B10 07-28-97 -- -- -- -- -- -- -- -- 

B10 05-19-98 -- -- -- -- -- 598. .2 -11.43 

B5F 12-09-96 <1. 4.6 8.8 1.4 -- 690. .46 -- 

B5F 05-19-98 -- -- -- -- -- 498. .3 -12.21 

S1 12-09-96 <1. 12. 6.6 1.5 -- 804. .53 -- 

S1 12-09-96 <1. 9.5 7.7 1.2 -- 776. .53 -- 

S1 07-10-97 -- -- -- -- 173. -- -- -- 

S1 05-19-98 -- -- -- -- -- 806. .5 -- 

Site 1

A10 12-06-96 <1. 30. 150. 1.6 18. 1020. .83 -- 

A20 12-06-96 <1. <1. 5.1 <1. 228. 1480. .93 -- 

B20 12-05-96 <1. 1.6 21. 1.3 248. 1360. .86 -- 

B5 12-05-96 <1. 40. 690. 1.3 23. 1980. 1.3 -- 

B10 12-05-96 <1. 61. 720. 1.5 -- 1520. 1.5 -- 

S1 12-06-96 <1. 1.9 6.8 <1. 138. 1340. 2. -- 

S1 12-06-96 <1. 1.9 6.8 <1. 138. 1340. 2. -- 
Appendix III 69

APPENDIX III. WATER-QUALITY DATA, 1996-98 (Continued)

[<, below detection level;--,analysis not available]

 H-2/ O-18/ N15/N14 N15/N14 SPE- ANC 

 H-1 O-16 NO3 NH4 CIFIC UNFLTRD

 STABLE STABLE N15/N14 N15/N14 FRAC FRAC CON- TIT 4.5

 ISOTOPE ISOTOPE NO3 NH4 WATER WATER DUCT- LAB 

 LOCAL RATIO RATIO FRAC FRAC FLTRD FLTRD ANCE (MG/L 

 IDENTIFIER DATE PER PER SOIL SOIL 0.45 U 0.45 U LAB AS 

 MIL MIL PER MIL PER MIL PER MIL PER MIL (μS/CM) CACO3) 

Reference Site (Continued)

S1 07-09-97 -- -- -- -- -- -- -- -- 

S1 07-09-97 -- -- -- -- -- -- -- -- 

S1 05-08-98 -3.9 -1.01 -- -- 1.9 -- 262. 79. 

S1 05-08-98 -3.9 -1.01 -- -- 1.9 -- 262. 79. 

S1 05-08-98 -3.9 -1.01 -- -- 1.9 -- 262. 79. 

RAINFALL 11-26-96 -14. -3.97 -- -- -- -- -- -- 

RAINFALL 06-08-98 -18. -3.9 -- -- -- -- -- -- 

Site 2

FERTILIZER 07-10-98 -- -- 4.5 -.7 -- -- -- -- 

A5 12-10-96 -21.7 -4.46 -- -- -- -- 797. 47. 

A5 07-10-97 -- -- -- -- 1.3 14.5 -- -- 

A5 05-18-98 -11.4 -2.38 -- -- -- -- 331. 34. 

A10 12-10-96 -6.3 -1.73 -- -- -- -- 1200. 101. 

A10 07-10-97 -- -- -- -- -- -- -- -- 

A10 05-18-98 -7.5 -1.87 -- -- 26.3 -- 1130. 105. 

A20 12-10-96 -4.1 -1.52 -- -- -- -- 1750. 175. 

A20 12-10-96 -- -- -- -- -- -- 1760. 174. 

A20 07-10-97 -- -- -- -- -- -- -- -- 

A20 05-18-98 -5. -1.52 -- -- -- 6.1 1540. 191. 

A5F 12-10-96 -11.3 -2.76 -- -- -- -- 885. 161. 

A5F 07-10-97 -- -- -- -- -- 5.6 -- -- 

A5F 05-18-98 -10.3 -2.39 -- -- -- 7. 611. 120. 

B20 12-09-96 -6.1 -1.44 -- -- -- -- 1560. 195. 

B20 07-28-97 -- -- -- -- -- -- -- -- 

B20 05-19-98 -7. -1.76 -- -- -- 9.1 1600. 164. 

B5 12-09-96 -8.6 -2.21 -- -- -- -- 1140. 33. 

B5 07-28-97 -- -- -- -- -- -- -- -- 

B5 05-19-98 -11.7 -2.88 -- -- -- -- 455. 1.2 

B10 12-09-96 -12.2 -2.76 -- -- -- -- 1090. 157. 

B10 07-28-97 -- -- -- -- -- -- -- -- 

B10 05-19-98 -9.6 -2.38 -- -- 24.6 9.4 919. 153. 

B5F 12-09-96 -11.6 -2.55 -- -- -- -- 1030. 157. 

B5F 05-19-98 -11.5 -2.63 -- -- -- 10.4 818. 342. 

S1 12-09-96 -1.8 -.92 -- -- -- -- 1240. 203. 

S1 12-09-96 -- -- -- -- -- -- 1240. 204. 

S1 07-10-97 -- -- -- -- -- -- -- -- 

S1 05-19-98 .4 -.46 -- -- -- -- 1180. 199. 

Site 1

A10 12-06-96 -10.3 -2.69 -- -- -- -- 1700. 13. 

A20 12-06-96 -9.2 -2.65 -- -- -- -- 1700. 214. 

B20 12-05-96 -10.4 -2.63 -- -- -- -- 1710. 242. 

B5 12-05-96 -11.3 -2.62 -- -- -- -- 2800. 25. 

B10 12-05-96 -5.8 -2.08 -- -- -- -- 2410. 4.3 

S1 12-06-96 -3.6 -1.61 -- -- -- -- 2370. 133. 

S1 12-06-96 -3.6 -1.61 -- -- -- -- 2370. 133.