science for a changing world 

Prepared in cooperation with the 

National Exposure Research Laboratory, U.S. Environmental Protection Agency, 

Athens, Georgia, and the North Carolina Department of Environment and Natural 

Resources, Division of Water Quality. Groundwater section 

Geochemistry and Characteristics of Nitrogen 

Transport at a Confined Animal Feeding Operation 

in a Coastal Plain Agricultural Watershed, and 

Implications for Nutrient Loading in the Neuse 

River Basin, North Carolina, 1999-2002 

Scientific Investigations Report 2004-5283 

U.S. Department of the Interior 

U.S. Geological Survey
Cover photographs. Left: Sandy Run near the Lizzie Research Station, Greene County, North Carolina. Right: Ground-water sampling 

site L18 at the Lizzie Research Station.
Geochemistry and Characteristics of 

Nitrogen Transport at a Confined Animal 

Feeding Operation in a Coastal Plain 

Agricultural Watershed, and Implications 

for Nutrient Loading in the Neuse River 

Basin, North Carolina, 1999–2002

By T.B. Spruill, A.J. Tesoriero, H.E. Mew, Jr., K.M. Farrell, S.L. Harden, 

A.B. Colosimo, and S.R. Kraemer

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the National Exposure Research Laboratory, U.S. Environmental Protection 

Agency, Athens, Georgia, and the North Carolina Department of Environment and Natural Resources, 

Division of Water Quality, Groundwater Section

Scientific Investigations Report 2004–5283
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

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

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

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

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Research for this report was funded in part by the U.S. Environmental Protection Agency under Interagency Agreement 

DW14938792-01 to the U.S. Geological Survey; however, the report does not necessarily reflect the views of the Agency 

and no official endorsement should be inferred.

Suggested citation:

Spruill, T.B., Tesoriero, A.J., Mew, H.E., Jr., Farrell, K.M., Harden, S.L., Colosimo, A.B., and Kraemer, S.R., 2005, 

Geochemistry and characteristics of nitrogen transport at a confined animal feeding operation in a Coastal Plain 

agricultural watershed, and implications for nutrient loading in the Neuse River Basin, North Carolina, 1999–2002: U.S. 

Geological Survey Scientific Investigations Report 2004–5283, 57 p.
 iii

Contents

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

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

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

Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Ground-Water Sampling Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Surface-Water Sampling Sites and Weather Station. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

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

Load Estimation Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site. . . . . . . . . . . . . 14

Ground-Water Age-Dating, Chemistry, and Nitrogen Fate and Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Ground-Water and Surface-Water Interactions: Nutrient Chemistry, Surface-Water Origin and 

Residence Time, and Pathways of Nutrients to Surface Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Effects on Ground-Water Quality of Changing to Swine-Waste Fertilizer from Inorganic Fertilizer . . . . . 31

Nutrient Loading in the Neuse River Drainage Basin During Calendar Years 2000 and 2001 in Relation to 

Background Loads, and Implications of Findings from the Lizzie Research Station Study . . . . . . . . . . . 34

Atmospheric Nutrient Loads in the Plum Tree Branch and Sandy Run Subbasins. . . . . . . . . . . . . . . . . . . . . 38

Little Contentnea Creek Subbasin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Contentnea Creek Subbasin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Neuse River Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Loads and Sources of Nutrients to the Neuse Estuary, Calendar Year 2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

References Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Figures

1. Locations of Lizzie Research Station and multimedia integrated modeling system 

(MIMS) sampling sites in the Neuse River basin, North Carolina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2. Locations of surface-water and ground-water sampling sites at the Lizzie Research Station, 

North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3. Photograph of weather station at the Lizzie Research Station, North Carolina . . . . . . . . . . . . . . . . . . . . . 11

4. Cross sections showing conceptual models of (A) stratigraphy and (B) hydrogeologic units 

of the Lizzie Research Station, North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5. Piezometric head values and contours and flow directions for the (A) surficial and (B) Yorktown 

aquifers on December 13, 2000, at the Lizzie Research Station, North Carolina. . . . . . . . . . . . . . . . . . . . . 16

6. Piezometric head values and contours along (A) cross-section A-A’ and (B) cross-section B-B’ . . 17

7. (A) Recharge dates and isopleths using chlorofluorocarbon concentrations, (B) isopleths and 

tritium concentrations, and (C) silica concentrations in ground water along transect A-A’ . . . . . . . . . 19

8. Tritium concentrations in ground-water samples plotted against recharge year . . . . . . . . . . . . . . . . . . 20

9. Ground-water residence time interpreted from chlorofluorocarbon (CFC) concentrations 

plotted against silica concentrations in samples from the Lizzie Research Station, 

North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
iv 

10. Delineation of terminal electron-accepting processes along transect A-A’. Nitrate and excess 

nitrogen concentrations also are shown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

11. Sequence of oxidation-reduction reactions involved with oxidation of carbon (electron donor) 

and terminal electron acceptors preferred by bacteria in the saturated zone. . . . . . . . . . . . . . . . . . . . . . 21

12. Dissolved argon and nitrogen concentrations in ground water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

13. Redox-active species as a function of ground-water residence time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

14. Nitrate and ammonium concentrations, phosphorus, and discharge for (A) Middle Swamp 

and (B) Plum Tree Branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

15. Trilinear diagrams of water chemistry in ground water, streams, and artificial drainages at 

the Lizzie Research Station, North Carolina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

16. Concentrations of silica in ground- and surface-water samples collected at the Lizzie 

Research Station, North Carolina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

17. Terminal electron-accepting zones along transect L2 to Plum Tree Branch near site FP 

and concentrations of (A) methane, iron, dissolved oxygen, and nitrate; and (B) silica, 

dissolved organic carbon, nitrate, and ammonium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

18. Percent of nitrate flux increase along Plum Tree Branch reach from S7 to S2 that is attributed 

to tile drain SR5-T1, and discharge at Plum Tree Branch at S2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

19. Chemical constituent concentrations in ground water from wells L2 and L6 at the Lizzie 

Research Station, North Carolina, for 1995 (before swine-waste spray was used) and 1999 

(after 4 years of swine-waste spraying) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

 20. Nitrite-plus-nitrate concentrations in ground-water samples from well L6 at the Lizzie 

Research Station, North Carolina, 1995–2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

 21. Concentrations of nitrite plus nitrate in ground water from shallow aquifers beneath four 

areas with selected land uses in the Coastal Plain of North Carolina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

 22. Concentrations of nitrate in fields fertilized with conventional inorganic fertilizer, sprayed 

swine waste, and wastewater-treatment plant sludge in the Little Contentnea Creek subbasin, 

North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

 23. Loads of (A) total nitrogen and (B) total phosphorus transported at 15 stations in calendar 

years 2000 and 2001 in relation to results from the Lizzie Research Station study, 

North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

24. Annual total nitrogen yield at selected stations in the Little Contentnea Creek subbasin, 

North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

25. Annual total phosphorus yield at selected stations in the Little Contentnea Creek subbasin, 

North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

26. Annual total nitrogen yield at selected stations in the Contentnea Creek subbasin, 

North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

27. Annual total phosphorus yield at selected stations in the Contentnea Creek subbasin, 

North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

28. Annual total nitrogen yield at selected stations in the Neuse River basin, North Carolina . . . . . . . . . . 40

 29. Annual total phosphorus yield at selected stations in the Neuse River basin, North Carolina. . . . . . . 41

 30. Sources of total nitrogen, estimated by three different methods, delivered to the Neuse River 

estuary at New Bern, North Carolina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

31. Sources of total phosphorus delivered to the Neuse River estuary at New Bern, North Carolina, 

in calendar year 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
 v

Tables

1. Land use and basin characteristics for 14 sampling sites in the Neuse River drainage 

basin, North Carolina, 1999–2002. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2. Soil type, streamflow characteristics, and nutrient data for 14 sampling sites in the Neuse 

River drainage basin, North Carolina, 1999–2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3. Screened intervals and median concentrations of selected chemical constituents in 

ground-water samples collected from aquifers and riparian zones at the Lizzie Research 

Station, North Carolina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4. Recharge dates and concentrations of dissolved gases and tritium in ground-water samples 

collected at the Lizzie Research Station, North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5. Seasonal and annual loads and annual yields of total nitrogen and phosphorus at 14 stations 

in the Neuse River basin, North Carolina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

6. Annual estimated background loads and yields for total nitrogen and total phosphorus 

for 14 stations in the Neuse River basin, North Carolina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Appendix Tables

1. Data available for stations included in the Lizzie Research Station study . . . . . . . . . . . . . . . . . . . . . . . . . . 54

2. Ninety-five percent confidence intervals for annual loads and methods of load estimation

used in the Lizzie Research Station study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

Flow rate

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

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

Mass

ton, short (2,000 lb) 0.9072 megagram (Mg)

ton, long (2,240 lb) 1.016 megagram (Mg)

ton per year (ton/yr) 0.9072 megagram per year (Mg/yr)

ton per year (ton/yr) 0.9072 metric ton per year (ton/yr)

Radioactivity

picocurie per liter (pCi/L) 0.037 becquerel per liter (Bq/L)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 x °C) + 32
vi 

Datum, Abbreviations, and Acronyms

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

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or 

micrograms per liter (μg/L).

AMLE Adjusted Maximum Likelihood Estimator

ASW air-saturated water

ASWEA air-saturated water with excess air

Ca2+ calcium

CAFO confined animal feeding operation

CFC chlorofluorocarbon

CFC-11 trichlorofluoromethane

CFC-12 dichlorodifluoromethane

CFC-113 trichlorotrifluoroethane

Cl- chloride

DIN dissolved inorganic nitrogen

DNRA dissimilatory nitrate reduction to ammonium

DO dissolved oxygen

DWQ Division of Water Quality

ELI eutrophication loading index

HCO3

- bicarbonate

ICP/MS inductively coupled plasma and mass spectrometry

LA Linear Attribution

LAD Least Absolute Deviation

lbs/acre pounds per acre

μm micrometer

mg/sec milligram per second

MIMS multimedia integrated modeling system

MLE Maximum Likelihood Estimator

N nitrogen

N2 nitrogen gas

NAWQA National Water-Quality Assessment Program

NCDENR North Carolina Department of Environment and Natural Resources

NCSU North Carolina State University

NERL National Exposure Research Laboratory

NO3

- nitrate

NPDES National Pollutant Discharge Elimination System

P phosphorus

pg/kg picogram per kilogram

SiO2 silica

SO4

2- sulfate

SPARROW spatially referenced regression on watershed model

TEAP terminal electron acceptor

TMDL total maximum daily load

ton/mi2 ton per square mile

ton/mi2/yr ton per square mile per year

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

WWTP wastewater-treatment plant
Geochemistry and Characteristics of Nitrogen Transport 

at a Confined Animal Feeding Operation in a Coastal 

Plain Agricultural Watershed, and Implications for 

Nutrient Loading in the Neuse River Basin, 

North Carolina, 1999–2002

By T.B. Spruill1, A.J. Tesoriero1, H.E. Mew, Jr.2, K.M. Farrell3, S.L. Harden1, A.B. Colosimo4, and S.R. Kraemer5

Abstract

Chemical, geologic, hydrologic, and age-dating 

information collected between 1999 and 2002 were used to 

examine the transport of contaminants, primarily nitrogen, in 

ground water and the pathways to surface water in a coastal 

plain setting in North Carolina. Data were collected from more 

than 35 wells and 4 surface-water sampling sites located in a 

0.59 square-mile basin to examine detailed hydrogeology and 

geochemical processes affecting nutrient fate and transport. 

Two additional surface-water sampling sites were located 

downstream from the primary study site to evaluate basin-scale 

effects. Chemical and flow data also were collected at an 

additional 10 sites in the Coastal Plain portion of the Neuse 

River basin located between Kinston and New Bern, North 

Carolina, to evaluate loads transported in the Neuse River and 

primary tributary basins. 

At the Lizzie Research Station study site in North 

Carolina, horizontal flow is induced by the presence of a 

confining unit at shallow depth. Age-dating, chemical, and 

piezometric data indicate that horizontal flow from the surficial 

aquifer is the dominant source of ground water to streamflow. 

Nitrogen applied on cultivated fields at the Lizzie Research 

Station is substantially reduced as it moves from recharge to 

discharge areas. Denitrification in deeper parts of the aquifer 

and in riparian zones is indicated by a characterization of redox 

conditions in the aquifer and by the presence of excess nitrogen 

gas. Direct ground-water discharge of nitrate to surface water 

during base-flow conditions is unlikely to be significant 

because of strongly reducing conditions that occur in the 

riparian zones of these streams. Nitrate loads from a drainage 

tile at the study site may account for much of the nitrate load in 

the receiving stream, indicating that a major source of nutrients 

from ground water to this stream is artificial drainage. During 

base-flow conditions when the streams are not flowing, it is 

hypothesized that the mineralization of organic matter on the 

streambed is the source of nitrate and(or) ammonium in the 

stream. Base flow is a small contributor to nitrogen loads, 

because both flows and inorganic nitrogen concentrations are 

low during summer months. 

Effects of a confined hog operation on ground-water 

quality also were evaluated. The use of sprayed swine wastes to 

fertilize crops at the Lizzie Research Station study site since 

1995 resulted in increased concentrations of nitrate and other 

chemical constituents in ground water beneath spray fields 

when compared to ground water beneath fields treated with 

commercial fertilizer. The nitrate concentration in ground water 

from the spray field well increased by a factor of 3.5 after 4 

years of spray applications. Nitrate concentrations ranged from 

1U.S. Geological Survey, Raleigh, North Carolina.

2North Carolina Department of Environment and Natural Resources, Division of Water Quality, Raleigh, North Carolina.

3North Carolina Geological Survey, Division of Land Resources, Raleigh, North Carolina.

4Monroe Community College, Department of Chemistry and Geosciences, Rochester, New York.

5U.S. Environmental Protection Agency, National Exposure Research Laboratory/Office of Research and Development, 

Athens, Georgia.
2 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

10 to 35 milligrams per liter, and one concentration as high as 

56 milligrams per liter was observed in water from this well in 

spring 2002. This finding is in agreement with findings of other 

studies conducted in the Coastal Plain of North Carolina that 

nitrate concentrations were significantly higher in ground water 

from cultivated fields sprayed with swine wastes than from 

fields treated with commercial fertilizer.

Loads and yields of nitrogen and phosphorus in 14 streams 

in the Neuse River basin were evaluated for calendar years 2000 

and 2001. Data indicate that anthropogenic effects on nitrogen 

yields were greatest in the first-order stream studied (yields 

were greater than 2 tons per square mile [ton/mi2] and 

1 ton/mi2 or less in second- and higher-order streams) in the 

Little Contentnea Creek subbasin. Nitrogen yields in streams in 

the Contentnea Creek subbasin ranged from 0.59 to 2 ton/mi2

with typical yields of approximately 1 ton/mi2

. Contentnea 

Creek near Evansdale had the highest yield (2 ton/mi2

), 

indicating that a major source of nitrogen is upstream from this 

station. Nitrogen yields were lower at Contentnea Creek at 

Hookerton in 2000 and 2001 compared to previous yield 

estimates based on 1990 data. Along the main stem of the Neuse 

River, nitrogen yields during 2000 and 2001 ranged from 

3.4 ton/mi2

 in Bear Creek, a tributary west of Kinston, North 

Carolina, to 0.55 ton/mi2 in the Trent River. The total nitrogen 

load delivered to the Neuse estuary in 2000 was 4,807 tons or 

9.61 million pounds, and the total phosphorus load was 

425 tons or 850,000 pounds. It is estimated that about 

17 percent of the delivered total nitrogen load is from 

background sources—35 percent from point sources and 

48 percent from nonpoint sources.

Annual phosphorus yields in the Little Contentnea Creek 

subbasin for 2000 and 2001 ranged from 0.02 to about 

0.15 ton/mi2. In contrast with total nitrogen yields, the larger 

total phosphorus yields were in higher-order streams (about 

three times greater), indicating either that the major source of 

phosphorus in the Little Contentnea Creek subbasin originates 

in the larger streams or the phosphorus is deposited by sediment 

eroded from low-order headwater streams and deposited on the 

bed. Phosphorus yields in the Contentnea Creek subbasin 

ranged from 0.02 to 0.15 ton/mi2. Phosphorus yields for 

Contentnea Creek at Hookerton were about 5 to 6 times the 

expected background yield, although yields for phosphorus 

reported for 2000 and 2001 for Contentnea Creek at Hookerton 

were considerably lower than those reported for 1990. 

Phosphorus yields in the Neuse River basin ranged from 0.02 to 

0.29 ton/mi2, with the highest yields occurring near New Bern 

in the vicinity of the upper Neuse estuary. 

The total phosphorus load transported to the Neuse estuary 

in 2000 was 425 tons. No recently published information was 

found on total point-source contributions of phosphorus to the 

Neuse River near Fort Barnwell for this study; therefore, 

general estimates from past studies were used. Based on this 

analysis, about 7 percent of the total phosphorus load in 2000 

was from background sources, about 41 percent was from 

anthropogenic point sources, and 52 percent was from 

anthropogenic nonpoint sources. 

Effects of cultural eutrophication with respect to 

phosphorus enrichment in coastal plain streams of the Neuse 

River basin are much greater than for nitrogen. The 

eutrophication loading index of phosphorus ranged between 2 

and 12 times, and values typically were 5 to 6 times the 

estimated background yield for second- and higher-order 

streams. The eutrophication loading index of total nitrogen 

ranged between 1 and 5 times, and values typically were about 

2 times the estimated background yield. 

 Introduction

Eutrophication has been identified as a primary problem in 

the Albemarle-Pamlico estuaries, and excess algal growth and 

fish kills in the estuaries have been attributed to the occurrence 

of excess nitrogen. Worldwide, nitrate is recognized as the most 

ubiquitous contaminant of ground water (Spaulding and Exner, 

1993) and in agriculture as the most extensive source of nitrate 

to ground and surface water (Hallberg, 1989). According to the 

Clean Water Action Plan (U.S. Environmental Protection 

Agency and U.S. Department of Agriculture, 1998), 

overenrichment by nutrients is the largest overall source of 

impairment in the Nation’s rivers and streams. In the 

southeastern United States, streams and receiving waters have 

been adversely affected by eutrophication (Pinckney and 

others, 1997), increased hypoxia (Paerl and others, 1998), fish 

kills (Burkholder and others, 1995), and outbreaks of toxic 

species (Burkholder and Glasgow, 1997). In general many 

researchers agree that excessive nutrient loading to the Neuse 

River and estuary, particularly nitrogen, has been the primary 

contributing factor for fish kills and algal blooms in the Neuse 

estuary (Stow and Borsuk, 2003). 

 Within North Carolina’s Neuse River basin, nonpointsource nutrient loads have been identified as a major component 

of increased estuarine nutrient loading (Spruill and others, 

1998; Stow and Borsuk, 2003). In particular, confined animal 

feeding operations (CAFOs), which have increased five-fold 

over the past two decades in the North Carolina Coastal Plain 

(Mallin, 2000), appear to have a substantial effect on nitrogen 

and phosphorus loading to streams (Glasgow and Burkholder, 

2000). The predominant wastewater-treatment system used in 

CAFOs is lagoons and spray fields, in which waste is flushed 

from confined animal housing into large earthen lagoons and 

then periodically sprayed onto agricultural fields in accordance 

with State regulations. Reactive nitrogen in the sprayed 

wastewater does one or more of the following: volatilizes into 

the atmosphere, becomes assimilated by crops, runs off into 

adjacent streams, or infiltrates into the ground-water system and 

eventually discharges to streams. Although more than 

70 percent of the streamflow in the Coastal Plain may be 

derived from ground water (McMahon and Lloyd, 1995), the 

fate and transport of nitrate (NO3

-

) from these CAFOs, as it 

moves from field to stream through the ground-water system, 

has not previously been assessed in North Carolina.
Introduction 3

The National Exposure Research Laboratory (NERL) of 

the U.S. Environmental Protection Agency's (USEPA) Office 

of Research and Development began a project in 1998 to 

develop a multimedia integrated modeling system (MIMS). The 

system is intended to represent the transport and fate of 

nutrients and chemical stressors over multiple scales and 

through air, ground water, and surface water. MIMS is intended 

to improve the environmental management community's ability 

to evaluate the effects of air quality and watershed management 

practices on streams and estuarine conditions. The USEPA 

recognized the importance of a multimedia data set for 

developing and testing the modeling system.

The MIMS project was developed with two parallel 

objectives: (1) to methodically account, through scientific 

study, for the advective transport of stressors, such as nutrients, 

through the atmospheric-hydrospheric system; and (2) to 

develop integrated multimedia software to model the 

transformation of these nutrients as they move through multiple 

environmental media. The U.S. Geological Survey (USGS) and 

the North Carolina Department of Environment and Natural 

Resources (NCDENR) were involved in the first of these 

objectives, primarily by providing data adequate to test the 

results of the developed models. The general developmental 

approach of the USEPA MIMS effort was presented in Johnston 

and others (2000). 

A thorough understanding of environmental processes, 

ranging from local to watershed scales, is necessary to develop 

accurate predictive environmental models. This concept of a 

multiple-scale study forms the basis for understanding 

environmental processes taking place within a watershed and is 

an integral part of the USGS National Water-Quality 

Assessment (NAWQA) Program. With a multiple-scale study 

in mind, the Neuse River basin was selected for study because 

of poor water-quality conditions observed in the Neuse River 

estuary and Pamlico Sound due to excess nutrients (North 

Carolina Department of Environment and Natural Resources, 

1999). The USGS, NCDENR, and USEPA NERL 

cooperatively worked together to provide information on 

movement of a contaminant from a (1) source (atmosphere, 

plants, fertilizer, animal manure, and(or) other sources) near 

land surface, through the (2) unsaturated zone to the water table, 

and then from the (3) recharge area laterally and vertically 

through the aquifer in the saturated zone into (4) natural streams 

(through the hyporheic zone and into the stream channel) or 

artificial channels (through drainage tiles or ditches). 

The USGS and NCDENR Division of Water Quality, 

Groundwater Section, began data-collection activities in March 

1999 to provide hydrogeologic and water-quality information 

on transport and fate of nitrogen in a small watershed, the Lizzie 

Research Station (fig. 1), in the Little Contentnea Creek 

subbasin. In addition, the effects of swine-waste application as 

fertilizer on ground-water quality were evaluated by comparing 

water-quality characteristics in wells sampled at the Lizzie 

Research Station by the USGS as part of the NAWQA Program 

in 1995 prior to the application of swine wastes to the fields. In 

2000, water-quality data collection began at 12 additional 

surface-water sites to evaluate surface-water loading 

characteristics in the Contentnea Creek subbasin and the Neuse 

River basin. The Contentnea Creek subbasin was selected 

because of the large nitrogen and phosphorus loads contributed 

to the Neuse River—as much as 45 percent of the phosphorus 

load and 35 percent of the nitrogen load delivered to the Neuse 

estuary (Spruill and others, 1996). All sites were sampled for 

18–24 months to estimate loads of nitrogen and phosphorus. 

Data collected as part of the RiverNet Program at North 

Carolina State University also were used to evaluate the 

adequacy of techniques used to calculate annual stream loads 

(North Carolina State University, 2004). 

This report summarizes activities of the USGS for the 

MIMS project between 1999 and 2002, including data collected 

during the study and general findings regarding geology, 

hydrology, and the fate and transport of nitrogen in ground 

water and streams. This information is presented for watersheds 

ranging in size from 0.59 square mile (mi2) at Plum Tree Branch 

(site S2, fig. 2; tables 1, 2) to about 153 mi2 at Little Contentnea 

Creek near Willow Green (site S6, fig. 1; tables 1, 2) to 

characterize processes occurring in smaller coastal plain 

watersheds. In addition, information is provided for larger-scale 

stream systems, including the Neuse River estuary near New 

Bern (fig. 1), which drains more than 4,000 mi2

, to evaluate 

implications that these processes may have on nitrogen and 

phosphorus transport in the Neuse River. Some of the data 

presented herein were obtained from USGS NAWQA studies 

(Spruill and others, 1998) and from another cooperative project 

between NCDENR and the USEPA directed at evaluating the 

effects of artificial drains on surface-water quality (Harden and 

Spruill, 2004).

Description of the Study Area

The Lizzie Research Station study site is located southeast 

of Farmville in Greene County, in the North Carolina Coastal 

Plain (fig. 1), south of the confluence of Sandy Run and Middle 

Swamp (fig. 2). The site has been under study by the NCDENR 

since 1993. Most of the Lizzie Research Station study site is 

drained by a first-order stream (for a definition of stream orders, 

see Strahler, 1963), known locally as Plum Tree Branch (fig. 2), 

which is a tributary to Sandy Run and drains 0.59 mi2. Land use 

in the area primarily is agricultural, with row crops typically of 

corn, wheat, and soybeans. 

Farming practices at the Lizzie Research Station changed 

during the mid-1990’s. Prior to 1995, crops were fertilized by 

using inorganic ammonium nitrate applied at the suggested 

agronomic rate for corn (about 150–200 pounds per acre 

(lbs/acre), North Carolina State University, 1992). After 1995, 

crops were fertilized with sprayed swine-waste lagoon effluent. 

Construction of five hog houses and a lagoon began in 1994, 
4 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

Figure 1. Locations of Lizzie Research Station and multimedia integrated modeling system 

(MIMS) sampling sites in the Neuse River basin, North Carolina.
Introduction 5

Figure 2. Locations of surface-water and ground-water sampling sites at the Lizzie Research Station, North Carolina.

Table 1. Land use and basin characteristics for 14 sampling sites in the Neuse River drainage basin, North Carolina, 1999–2002.

[NPDES, National Pollutant Discharge Elimination System; mi2, square mile]

Map no. (figs. 1 and 2) 

and station name

USGS 

station 

no.

Population NPDES 

sites

Drainage 

area 

(mi2

)

Land use (in percent) Swine 

population Crops (average) Forest Urban Water Wetland

N1-Bear Creek at Mays Store 208925200 11,348 0 58.62 59.9 22.9 11.9 0.7 4.4 40,624

N2-Neuse River at Kinston 2089500 1,027,971 126 2,709.00 25.3 42.6 23.1 1.5 6.6 527,583

S2-Plum Tree Branch near Lizzie 209173190 14 0 0.59 48.1 38.5 3.9 0 9.4 5,000

S4-Sandy Run near Lizzie 209173200 2,282 0 31.12 49.4 33.3 4.2 .2 13 96,405

S5-Middle Swamp near Farmville 2091736 4,192 0 51.29 50.1 32.7 5.4 .2 11.4 104,805

S6-Little Contentnea near Willow Green 2091737 15,072 1 152.60 47.1 31.7 5.8 .3 12.3 132,200

S16-Little Contentnea at Scuffleton 2091740 18,000 1 172.00 49.2 31.8 6.3 .4 12.3 179,045

S11-Contentenea Creek near Lucama 2090380 18,287 4 159.00 26.4 46.3 16.8 1.6 8.2 8,300

S14-Contentnea Creek near Evansdale 2090519 50,819 8 263.80 28.6 38.2 21.1 1.4 10.1 11,841

S10-Nahunta Swamp near Shine 2091000 8,964 3 79.91 50.7 30.5 10.7 .3 7.5 44,080

S18-Contentnea Creek at Hookerton 2091500 103,483 20 734.79 40.2 32.1 15 .9 11.1 178,068

N3-Neuse River near Fort Barnwell 2091814 1,185,642 155 3,951.00 31 38.8 19.6 1.3 8.4 1,081,669

N5-Trent River near Trenton 2092500 5,291 0 166.64 31.3 43.3 4.7 .2 19.5 150,476

N4-Swift Creek near Streets Ferry 209205053 43,351 3 265.41 36.2 30.2 7.4 .4 23.3 61,014
Table 2. Soil type, streamflow characteristics, and nutrient data for 14 sampling sites in the Neuse River drainage basin, North Carolina

[in., inch; mg/L, milligram per liter; ft3/s, cubic foot per second]

Map no. (figs. 1 and 2) 

and station name

Percent 

A/B soils

aDual hydrologic soil groups: A–(Low runoff potential). The soils have a high infiltration rate even when thoroughly wetted. They chiefly consist of deep, well 

sively drained sands or gravels. They have a high rate of water transmission. B–The soils have a moderate infiltration rate when thoroughly wetted. They chiefly ar

to deep, moderately well drained to well drained soils that have moderately fine to moderately coarse textures. They have a moderate rate of water transmission (UAgriculture, 2002).

a

Percent 

C/D soils

bDual hydrologic soil groups: C–The soils have a slow infiltration rate when thoroughly wetted. They chiefly have a layer that impedes downward movement o

moderately fine to fine texture. They have a slow rate of water transmission. D–(High runoff potential). The soils have a very slow infiltration rate when thorough

chiefly consist of clay soils that have a high swelling potential, soils that have a permanent high water table, soils that have a claypan or clay layer at or near the su

soils over nearly impervious material. They have a very slow rate of water transmission (U.S. Department of Agriculture, 2002).

b Average slope

Base-flow index 

(annual base flow 

[in.] / annual total 

flow [in.])

Median total nitrogen 

([mg/L] / range 

[mg/L] / number of 

observations)

Median total phosphorus 

([mg/L] / range 

[mg/L] / number of 

observations)

Med

N1-Bear Creek at Mays Store 54.5 45.5 0.9068 68.1 3.1 / 2.2–4.6 / 23 0.1 / 0.04–0.66 / 23 3N2-Neuse River at Kinston 57.2 42.8 2.6518 64.8 0.56 / 0.51–1 / 48 0.12 / 0.057–0.195 / 49 1,32S2-Plum Tree Branch near Lizzie 34.2 65.8 .7192 51.8 6.5 / 1.6–13 / 27 0.08 / 0.03–0.86 / 27 0.09 S4-Sandy Run near Lizzie 38.3 61.7 .6714 53.4 1.4 / 0.15–2.3 / 29 0.34 / 0.11–0.81 / 33 2.2 S5-Middle Swamp near Farmville 35.9 64.1 .6584 51.2 0.97 / 0.51–1.4 / 22 0.33 / 0.11–1.08 / 31 7.4 S6-Little Contentnea near Willow Green 34.9 65.2 .7383 53.9 0.98 / 0.63–1.4 / 25 0.27 / 0.08–0.60 / 31 3S16-Little Contentnea at Scuffleton 59.1 40.9 .7689 61.5 0.9 / 0.59–1.3 / 20 0.19 / 0.08–0.53 / 23 S11-Contentenea Creek near Lucama 60.5 38.9 2.3193 53.9 0.82 / 0.01–0.97 / 20 0.037 / 0.02–0.07 / 20 6S14-Contentnea Creek near Evansdale 56.9 42.7 1.9495 76.4 1.3 / 0.05–2.73 / 20 0.11 / 0.04–0.38 / 20 17S10-Nahunta Swamp near Shine 51.4 48.5 1.1623 64.6 1.4 / 0.91–2.1 / 21 0.08 / 0.02–0.17 / 20 S18-Contentnea Creek at Hookerton 53.4 46.4 1.467 70.9 1.2 / 0.86–1.9 / 72 0.138 / 0.019–0.255 / 72 4N3-Neuse River near Fort Barnwell 54.2 45.7 2.1958 71.8 1.1 / 0.66–1.6 / 21 0.11 / 0.03–0.166 / 21 2,00N5-Trent River near Trenton 35.6 64.4 .7276 53 0.94 / 0.42–4.6 / 95c

cData collected by the North Carolina Department of Environment and Natural Resources.

0.01 / 0.09–0.83 / 95c 67 

N4-Swift Creek near Streets Ferry 14.1 85.8 .6118 20.5 0.5 / 0.2–2.5 / 147c 0.13 / 0.04–1.3 / 147c 
Introduction 7

and in late 1995, a confined animal feeding operation with 

approximately 5,000 animals began in the central part of the 

study area (fig. 2). A lagoon was constructed on the site to hold 

waste drained from the five hog houses. Liquid from the lagoon 

provided the primary source of nitrogen sprayed onto about 

90 acres of fields (with about 70 acres inside the Plum Tree 

Branch watershed) in the northwestern portion of the Lizzie 

Research site (fig. 2). All property within the Lizzie study site 

is privately owned.

In addition to gaining an understanding of surface- and 

ground-water relations at the Lizzie Research site, a major 

objective of the MIMS study was to determine nutrient loading 

and discharge characteristics in drainages of the Neuse River 

basin. Seventeen stream sites (figs. 1, 2) were sampled and 

streamflow was measured to characterize flow and nutrient 

loads or to investigate short-term transport processes and 

behavior (sites S3, S7, and SR5-T1, fig. 2). The natural streams 

studied range in drainage area from about 0.59 mi2

 at Plum Tree 

Branch to almost 4,000 mi2

 at the Neuse River near Fort 

Barnwell (table 1). A small tile-drain site, SR5-T1 (fig. 2), 

drains an area of about 0.01 mi2

 into Plum Tree Branch. A 

weather station was established at this site and near one of the 

surface-water gages to evaluate atmospheric inputs of nitrogen 

into the basin. General land use, soil, and drainage-basin 

characteristics in the study area are presented in tables 1 and 2.

Hydrologic conditions in the Neuse River basin between 

1999 and 2002 were highly variable. At the most downstream 

station, the Neuse River near Fort Barnwell (site N3, fig. 1), the 

highest daily flow of 57,000 cubic feet per second (ft3/s) 

occurred on September 20, 1999 (Ragland and others, 2003) 

during Hurricane Floyd, whereas the lowest daily mean of 

340 ft3/s occurred on June 27, 2002 (Ragland and others, 2003). 

The years for which complete data were collected for the 

current study include calendar years 2000 and 2001. The 

average daily flow of 3,679 ft3

/s in calendar year 2000 was 

closer to the long-term average daily flow of 4,217 ft3/s 

(1997–2004) than in calendar year 2001 (2,464 ft3/s).

Methods

Methods used for conducting the study are presented in the 

following sections. Information on basic well construction and 

location, surface-water site locations, sample-collection 

procedures for surface-water and ground-water sampling, 

laboratory analytical procedures, and statistical methods used 

for analysis of load data are included.

Ground-Water Sampling Sites

The NCDENR Division of Water Quality (DWQ), 

Groundwater Section, installed 27 wells at 12 sites in the basin 

(Ted Mew, North Carolina Department of Environment and 

Natural Resources, Division of Water Quality, written 

commun., 2000) beginning in 1993. In 2000, eight new wells 

were installed on the site. The locations of wells at the Lizzie 

Research site are shown in figure 2, and screen-interval 

information for each of the wells is presented in table 3. The 

DWQ Drilling Unit constructed all wells in the study area 

according to general procedures established for monitoringwell construction by the State of North Carolina.

Surface-Water Sampling Sites and Weather 

Station

In order to evaluate interactions of ground water with 

surface water in the study area and to characterize hydrology 

and chemical quality of water draining the site, six primary 

streamgaging sites were established (fig. 2). Three streamgages 

were installed in 1999 at the Lizzie Research site—a gage on 

Sandy Run (S4, fig. 2), a weir and gage on a small first-order 

tributary (S2, fig. 2) on the west side of the study area, and a 

weir and recorder on a drainage ditch near the center of the 

study site (S3, fig. 2). An ungaged sampling site upstream from 

the S2 gage (S7, fig. 2) was selected as a supplementary 

sampling site to evaluate the chemical quality of water in areas 

upstream from the hog-farm operation. Two more gages, one at 

Middle Swamp near Farmville (S5, fig. 2) and one at Little 

Contentnea Creek near Willow Green (S6, fig. 1) were installed 

to evaluate basin-scale effects on water chemistry and nutrient 

loading. 

In addition to the six primary sampling sites, several sites, 

including Contentnea Creek at Hookerton (S18), Nahunta 

Swamp near Shine (S10), Contentnea Creek near Lucama 

(S11), Contentnea Creek near Evansdale (S14), Bear Creek at 

Mays Store (N1), Neuse River at Kinston (N2), and Neuse 

River near Fort Barnwell (N3, fig. 1), were sampled to 

characterize seasonal nutrient concentrations and loading from 

streams in the Contentnea Creek basin down to the 

downstream-most station at Fort Barnwell, N.C. Flow data from 

two additional stations in tributaries to the Neuse River—Trent 

River near Trenton (N5, fig. 1) and Swift Creek at Streets Ferry 

(N4, fig. 1)—also were included. Water-quality data collected 

by the DWQ for the Trent River and Swift Creek were used in 

conjunction with USGS streamflow data in order to calculate 

nutrient loads to the Neuse River estuary. A weather station 

with a recorder (fig. 3) also was established initially at one 

location (S1-A, fig. 2) and later moved to a more suitable 

location about 1,000 feet (ft) away (S1-B, fig. 2). Measured 

properties include temperature, humidity, solar radiation, wind 

speed, wind direction, and soil moisture at 0.16, 0.32, and 

0.98 ft below land surface. 
Table 3. Screened intervals and median concentrations of selected chemical constituents in ground-water samples collected from 

aquifers and riparian zones at the Lizzie Research Station, North Carolina.

[NGVD 29, National Geodetic Vertical Datum of 1929; mg/L, milligram per liter; N, nitrogen; <, less than; —, no data. Units are milligrams per liter unless 

otherwise noted. Most samples were collected from March 1999 to June 2002]

Well name

Well name and 

location shown in 

figure 2 (several wells 

may be colocated)

Screened interval 

(feet above NGVD 29)a Dissolved 

oxygen 

(mg/L)

pH 

(units)

Calcium 

(mg/L)

Magnesium 

(mg/L)

Potassium 

(mg/L)

Bottom Top

Surficial aquifer (unconfined)

L2 L2 61.0 70.9 3.4 4.6 3.5 3.6 .7

L2S L2 72.5 75.5 4.2 5.1 2.2 2.5 .7

L2D L2 57.4 59.4 .6 5.2 6.0 1.1 3.9

L3 L2 39.0 54.1 .4 5.1 2.4 .4 2.0

L4 L4 54.5 59.4 5.5 5.3 27 4.6 5.2

L4S L4 56.4 59.4 4.2 4.2 28 7.1 9.1

L4D L4 52.5 54.5 3.1 5.0 35 5.4 7.0

L5 L6 44.3 54.1 .1 4.4 3.5 .6 1.5

L6 L6 66.3 69.6 2.8 4.3 41 15 9.2

L6S L6 70.5 72.5 1.0 4.7 41 14 13

L6D L6 55.4 57.4 .3 4.5 1.9 .7 1.9

L9 L9 52.8 62.7 .2 6.0 38 2.5 1.7

L15 L15 52.8 63.0 1.7 4.1 15 7.6 2.4

L15D L15 50.5 52.5 1.1 5.9 25 3.7 1.5

L18D L18 46.6 48.6 1.9 5.3 13 .9 1.4

L20 L21 59.4 69.2 .1 4.9 3.3 .3 .5

L23 L23 68.9 73.8 2.1 5.3 3.6 .1 .2

L24 L23 53.8 58.7 .5 7 88 1.8 .9

L27 L27 59.7 69.6 4.5 5.0 .8 .2 .1

Alluvial aquifer (unconfined)

L7 L8 20.7 40.7 7.8 4.7 13 7.4 4.5

L8S L8 40.7 45.9 6.7 4.3 12 6.2 4.4

L8D L8 25.9 27.9 1.8 4.7 15 6.6 4.3

L11S L11 40.0 44.9 3.4 5.1 9.1 2.2 5.0

L11D L11 24.6 26.6 4.3 4.5 16 5.7 7.1

L11 L11 31.8 41.7 3.2 5.0 7.9 2.3 4.6

Yorktown aquifer (confined and unconfined)

L10 L11 2.3 17.1 0.2 6.2 32 1.4 1.6

L12 L12 8.5 28.5 .1 7.5 59.0 2.2 2.0

L14 L15 18.0 28.2 .1 7.45 51.9 2.0 1.1

L16 L4 14.1 29.2 .4 7.4 60.5 1.7 2.2

L17 L18 11.5 31.5 .1 7.4 55.0 1.8 1.7

L19 L21 12.1 37.4 .1 7.5 61.1 1.4 1.4

L22 L22 17.7 37.7 .1 7.3 66 1.4 1.1

L26 L27 7.9 27.9 .6 7.5 52.5 1.2 1.3

Peedee Formation (confined)

L25 L23 -33.5 -25.9 0.1 7.3 61.2 2.4 2.2

L55 L2 7.2 27.6 .1 7.2 35.1 1.3 1.9

Streambed and riparian zone

Streambed-center (GR089) Drainage ditch at S3 2.0 1.6 0.1 5.2 8.2 2.3 2.9

Riparian/upland boundary 

(GR157)

FP 5.2 4.9 .3 4.5 7.2 5.5 4.0

Streambed-center (GR155) Plum Tree near FP 2.0 1.6 .3 5.5 15 2.7 4.0

Streambank-right (GR156) Plum Tree near FP 2.6 2.3 .2 5.3 9.8 3.1 7.9

Streambed-center (GR149) Plum Tree at S2 2.0 1.6 .3 5.0 5.4 1.1 1.7

Streambed-center (GR148) Plum Tree at S2 4.3 3.9 1.1 5.1 6.0 1.1 1.2

Streambed-center (GR152) Sandy Run at S4 2.6 2.3 .3 6.0 28 1.8 2.3

Streambed-right (GR151) Sandy Run at S4 2.6 2.3 .3 6.0 20 1.2 1.9

Streambed-right (GR150) Sandy Run at S4 2.0 1.6 .3 5.7 17 1.5 3.4

Streambank-right (GR153) Sandy Run at S4 1.3 1.0 .2 5.7 11 1.5 1.8

8 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002
Table 3. Screened intervals and median concentrations of selected chemical constituents in ground-water samples collected 

from aquifers and riparian zones at the Lizzie Research Station, North Carolina.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; mg/L, milligram per liter; N, nitrogen; <, less than; —, no data. Units are milligrams per liter unless 

otherwise noted. Most samples were collected from March 1999 to June 2002]

Well name

Well name and location 

shown in figure 2 

(several wells may be 

colocated)

Sodium 

(mg/L)

Bicarbonate 

(mg/L)

Chloride 

(mg/L)

Silica 

(mg/L)

Sulfate 

(mg/L)

Ammonia 

(as N)

Surficial aquifer (unconfined)

L2 L2 2.4 1 9.1 5.6 9.3 <0.04

L2S L2 5.3 — 10 6.7 3.4 .12

L2D L2 14 10 23 9.9 10 <.04

L3 L2 4.3 3 11 17 8.5 <.04

L4 L4 3.9 10 20 4.9 14 <.04

L4S L4 6.5 1 33 5.4 16 <.04

L4D L4 7.1 8 37 5.6 36 <.04

L5 L6 4.8 — 9.8 16 14 <.04

L6 L6 39 1 95 7.9 17 <.04

L6S L6 30 7 76 9.6 18 .10

L6D L6 7.4 2 10 13 17 <.04

L9 L9 5.2 38 26 13 60 .03

L15 L15 3.7 — 25 6.7 16 <.04

L15D L15 4.6 19 20 9.8 41 <.04

L18D L18 7.8 5 11 8.4 26 <.04

L20 L21 3.4 8 7.1 15 .9 .03

L22 L22 7.2 226 5.1 33 .8 .03

L23 L23 17 9 22 12 12 .07

L24 L23 17 293 20 37 5.1 <.04

L27 L27 2.1 3 3.4 4.7 1.3 <.04

Alluvial aquifer (unconfined)

L7 L8 2.4 2 18 6.2 3.9 <0.04

L8S L8 2.1 1 17 6.5 6.3 <.04

L8D L8 2.7 2 15 6.4 34 <.04

L11S L11 2.3 4 9.2 2.8 8.6 <.04

L11D L11 2.1 1 24 3.4 16 <.04

L11 L11 2.2 4 8.3 2.4 9.0 <.04

Yorktown aquifer (confined and unconfined)

L10 L11 4.7 49 13 11 39 <0.04

L12 L12 8.5 200 5.5 35 5.2 .07

L14 L15 4.1 151 7.5 16 16 <.04

L16 L4 7.1 210 3.1 40 1.7 .06

L17 L18 6.4 184 3.4 29 3.2 <.04

L19 L21 4.9 198 4.1 25 1.1 <.04

L26 L27 17 193 4.2 25 6.2 <.04

Peedee Formation (confined)

L25 L23 8.6 218 4.4 27 0.4 0.06

L55 L2 4.1 116 7.0 23 5.0 .02

Streambed and riparian zone

Streambed-center (GR089) Drainage ditch at S3 7.1 23 27 16 3.1 0.09

Riparian/upland boundary 

(GR157)

FP 9.0 — 29 6.6 11 <.04

Streambed-center (GR155) Plum Tree near FP 6.9 54 41 8.2 4.3 1.1

Streambank-right (GR156) Plum Tree near FP 10 32 44 10 10 .63

Streambed-center (GR149) Plum Tree at S2 8.2 7.5 25 12 10 .29

Streambed-center (GR148) Plum Tree at S2 7.8 15 23 12 9.0 .22

Streambed-center (GR152) Sandy Run at S4 7.4 81 12 18 1.3 .84

Streambed-right (GR151) Sandy Run at S4 8.1 59 13 11 28 .60

Streambed-right (GR150) Sandy Run at S4 6.6 66 13 16 2.0 4.3

Streambank-right (GR153) Sandy Run at S4 5.3 49 14 9.8 .7 1.6

Introduction 9
Table 3. Screened intervals and median concentrations of selected chemical constituents in ground-water samples collected 

from aquifers and riparian zones at the Lizzie Research Station, North Carolina.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; mg/L, milligram per liter; N, nitrogen; <, less than; —, no data. Units are milligrams per liter 

unless otherwise noted. Most samples were collected from March 1999 to June 2002]

Well name

Well name and location 

shown in figure 2 

(several wells may be 

colocated)

Ammonia plus 

organic 

nitrogen 

(as N)

Nitrate 

(as N)

Phosphorus Carbon Iron Manganese

Surficial aquifer (unconfined)

L2 L2 <0.2 4.1 <0.02 0.6 0.21 0.01

L2S L2 .29 2.6 <.02 1.4 .17 .01

L2D L2 <.2 .89 .02 .5 .63 .05

L3 L2 <.2 <.05 .08 .2 5.06 .01

L4 L4 <.2 15 <.02 .6 <.003 .10

L4S L4 .21 19 .18 1.4 .02 .17

L4D L4 .14 19 .02 1.0 .17 .15

L5 L6 <.2 .14 <.02 .2 .79 .02

L6 L6 .33 41 .01 1.6 .07 .19

L6S L6 .36 35 <.02 2.0 .02 .21

L6D L6 <.1 .12 <.02 .3 .70 .02

L9 L9 <.2 <.05 .11 .8 2.48 .05

L15 L15 .14 12 .02 .7 .02 .06

L15D L15 <.1 1.4 .04 .3 .06 .10

L18D L18 .17 .46 .15 .4 .03 .08

L20 L21 <.2 <.05 .27 .6 .66 .01

L22 L22 <.2 <.05 .11 .6 2.45 .05

L23 L23 .24 .07 .03 — .31 .01

L24 L23 .19 <.05 .06 3.2 1.49 .04

L27 L27 <.2 <.05 .07 .3 .11 .00

Alluvial aquifer (unconfined)

L7 L8 <0.1 11.8 0.50 0.3 <0.01 0.03

L8S L8 <.1 11.6 .05 .4 .01 .03

L8D L8 <.1 6.5 .70 .4 .05 .05

L11S L11 <.1 5.2 .02 .6 <.01 .03

L11D L11 <.1 7.7 .05 .4 .01 .04

L11 L11 <.1 3.9 .02 .5 — .02

Yorktown aquifer (confined and unconfined)

L10 L11 0.09 0.05 0.51 0.4 1.15 0.05

L12 L12 .09 <.05 .11 .5 .27 .07

L14 L15 .38 <.05 .15 .2 .86 .06

L16 L4 <.2 <.05 .06 .4 .29 .06

L17 L18 .15 <.05 .13 .4 .93 .09

L19 L21 <.2 <.05 .08 .3 1.19 .02

L26 L27 <.2 <.05 .28 .7 .83 .02

Peedee Formation (confined)

L25 L23 0.16 <0.05 0.12 0.6 1.2 0.08

L55 L2 .06 <.05 .15 .3 2.3 .06

Streambed and riparian zone

Streambed-center (GR089) Drainage ditch at S3 0.28 0.63 <0.02 2.4 8.0 0.04

Riparian/upland boundary 

(GR157)

FP .11 6.4 <.02 1.1 .09 .04

Streambed-center (GR155) Plum Tree near FP 1.5 <.05 .07 9.0 14 .04

Streambank-right (GR156) Plum Tree near FP .99 <.05 .08 12 9.6 .03

Streambed-center (GR149) Plum Tree at S2 .47 <.05 .12 4.3 8.2 .03

Streambed-center (GR148) Plum Tree at S2 .32 <.05 .18 3.2 10 .04

Streambed-center (GR152) Sandy Run at S4 .87 <.05 .89 2.7 .04 .20

Streambed-right (GR151) Sandy Run at S4 .65 <.05 .87 2.2 .08 .03

Streambed-right (GR150) Sandy Run at S4 3.9 <.05 1.0 25 4.1 .04

Streambank-right (GR153) Sandy Run at S4 2.0 <.05 .78 8.5 6.2 .04

10 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

a

For streambed and riparian wells, screen interval is given as depth below land surface, in feet.
Introduction 11

Sample Collection and Analysis

Surface-water-quality samples and discharge 

measurements were collected approximately monthly at the six 

primary sampling sites beginning in April 1999 and continuing 

through September 2002; samples were collected at the 

remaining nine sites approximately monthly or more frequently 

beginning in June 2000 and continuing through September 

2002. Selected precipitation events also were targeted to obtain 

additional samples during various flow conditions. Surfacewater samples were collected and processed according to 

procedures presented in Wilde and others (1998). During 

sample collection, field measurements of pH, dissolved oxygen, 

specific conductance, and temperature were obtained. Total 

nitrogen and total phosphorus concentration data were collected 

from surface-water stations (figs. 1, 2) and used for load 

calculations (table 2). A summary of selected chemical 

constituents at ground-water sites is presented in table 3. 

Selected data for inert gases and tritium collected at groundwater sites and used for age dating the water are listed in table 4. 

Surface-water sampling sites instrumented by the USGS 

include a drainage ditch (S3), Plum Tree Branch (S2), Sandy 

Run (S4), and Middle Swamp (S5, fig. 2). Ground-waterquality sampling was conducted according to the USGS 

NAWQA protocols (Koterba and others, 1995). Submersible or 

peristaltic pumps and Teflon lines were used for all waterquality sampling except for chlorofluorocarbon (CFC) 

sampling for which copper tubing was used. 

Dissolved-oxygen concentrations and pH were measured 

using electrodes placed in a flow cell chamber to minimize 

atmospheric interactions. Alkalinity was determined in the field 

by titration. Water samples for major ions and nutrients were 

filtered using a 0.45-micrometer (μm) capsule filter. Sulfate 

(SO4

2-) was analyzed by ion chromatography. Magnesium, 

silica (SiO2), iron, and manganese were analyzed by using 

inductively coupled plasma and mass spectrometry (ICP/MS). 

Nitrate, nitrite, ammonium, and bromide were analyzed by 

using colorimetric methods. Detailed descriptions of the 

analytical methods for the above-mentioned major ions and 

nutrients are provided in Fishman and Friedman (1989). 

Dissolved organic carbon was analyzed by ultraviolet promoted 

persulfate oxidation and infrared spectrometry (Brenton and 

Arnett, 1993). All of the above-listed analyses were conducted 

at USGS laboratories in Denver, Colorado, and Ocala, Florida. 

Samples for CFCs (trichlorofluoromethane, CFC-11; 

dichlorodifluoromethane, CFC-12; trichlorotrifluoroethane, 

CFC-113) and dissolved gases (nitrogen and argon) were 

collected and analyzed as described in Busenberg and Plummer 

(1992) and Busenberg and others (1993), respectively. A list of 

all sites sampled for this study and accessibility of the data is 

presented in Appendix 1. Data for major ions, nutrients, 

streamflow, stream stage, precipitation, wind speed, and wind 

direction have been published previously (U.S. Geological 

Survey, 1999–2002). 

Figure 3. Weather station at the Lizzie Research Station, North Carolina.
Table 4. Recharge dates and concentrations of dissolved gases and tritium in ground-water samples collected at the Lizzie Research Statio

[pCi/L, picocurie per liter; pg/kg, picogram per kilogram; <, less than; —, no data; >, greater than. Units are milligrams per liter unless otherwise noted. Most samples to June 2002]

Well name Well location (fig. 2) CH4 N2 Ar Excess N2 Tritium (pCi/L) CFC-12 (pg/kg) Rec

d

Surficial aquifer (unconfined)

L2D L2 0.001 22.4 0.689 2.1 33 171 19L3 L2 .001 22.6 .695 1.8 29 14 19L6S L6 .002 18.8 .646 <1 26 259 19L6D L6 <.001 22.8 .668 3.6 48 75 19L15D L15 .005 24.3 .635 7 30 236 19L18D L18 — — — — 31 — >19L20 L21 .014 21.3 .681 1.3 36 12 19L23 L23 — — — — 29 — >19L24 L23 — — — — <1 — <19L27 L27 <.001 17.3 .650 <1 18 256 19

Alluvial aquifer (unconfined)

L7 L8 <0.001 17.7 0.630 <1 23 284 19L8S L8 <.001 16.0 .595 <1 19 288 19L8D L8 <.001 19.3 .638 1.9 22 — L11S L11 .005 18.0 .641 <1 19 281 19L11D L11 <.001 19.1 .685 <1 19 — 19

aCFC-12 contamination is suspected. Recharge date is based on SF6 data.

Yorktown aquifer (confined and unconfined)

L10 L11 0.155 27.3 0.667 8.2 28 108 19L14 L15 .002 22.3 .704 1.1 10 19 19L16 L4 .011 22.1 .743 <1 <1 2 19L17 L18 .004 21.7 .732 <1 <1 — <19L19 L21 .003 22.4 .743 <1 <1 5 19L26 L27 <.001 21.7 .722 <1 2.6 32 19

Peedee aquifer (confined)

L25 L23 0.003 23.0 0.752 <1 <1 — <19L55 L2 .006 23.0 .742 <1 11 9 19

Streambed and riparian zone

Streambed-center (GR089) Drainage ditch at S3 0.001b

bSamples have outgassed. Values given underestimate actual concentrations.

17.2b 0.531b — — — 

Riparian/upland boundary (GR157) FP .011 20.1 .632 — — — Streambed-center (GR155) Plum Tree near FP .002b 11.5b .364b — — — Streambank-right (GR156) Plum Tree near FP .011 20.1 .638 — — — Streambed-center (GR149) Plum Tree at S2 .090b 16.3b .542b — — 51.8 19Streambed-center (GR148) Plum Tree at S2 .002 18.8 .612 2 — 68.5 19Streambed-center (GR152) Sandy Run at S4 14.9b 1.4b .046b — — — Streambed-right (GR151) Sandy Run at S4 6.63b 3.8b .150b — — — Streambed-right (GR150) Sandy Run at S4 14.7b 2.2b .105b — — — 
Introduction 13

Load Estimation Methods 

The transport (mass discharge) of a constituent past a 

monitoring site in a given amount of time is referred to as the 

constituent load. Constituent loads were estimated by the 

rating-curve method (Cohn and others, 1989; Crawford, 1991). 

Because some of the constituent concentrations included in this 

assessment were less than the detection limit, parameters of the 

rating curve were estimated by maximum-likelihood methods 

(Dempster and others, 1977; Wolynetz, 1979) or the linearattribution method (Chatterjee and McLeish, 1986). An 

estimate of the uncertainty in the estimated loads was obtained 

by using the method described by Likes (1980) and Gilroy and 

others (1990) for maximum-likelihood estimates and by the 

jackknife method (Efron, 1982) for linear-attribution estimates. 

A detailed description of these methods is presented in 

Crawford (1996). 

Estimates of annual mass loads at 13 stations were made 

using the procedures referred to above. The eight models 

considered in the model-selection procedure are:

model 1: ln(load) = b0 + b1 ln(flow)

model 2: ln(load) = b0 + b1 ln(flow) + b2 ln(flow)2

model 3: ln(load) = b0 + b1 ln(flow) + b2 dectime

model 4: ln(load) = b0 + b1 ln(flow) + b2 sin(dectime)

+ b3 cos(dectime)

model 5: ln(load) = b0 + b1 ln(flow) + b2 ln(flow)2

+ b3 dectime 

model 6: ln(load) = b0 + b1 ln(flow) + b2 ln(flow)2

+ b3 sin(dectime) + b4 cos(dectime)

model 7: ln(load) = b0 + b1 ln(flow) + b2 sin(dectime)

+ b3 cos(dectime) + b4 dectime

model 8: ln(load) = b0 + b1 ln(flow) + b2 ln(flow)2

+ b3 sin(dectime) + b4 cos(dectime) + b5 dectime

The natural logarithm of the load is considered as a 

function of up to eight combinations of parameters representing 

discharge (flow and flow2

), time (dectime), and seasonality 

(sin[dectime] and cos[dectime]), which best account for the 

variability of constituent concentrations. The b parameters, or 

regression coefficients, of the model are estimated from the 

data. The best model is selected automatically in the USGS load 

estimator program (Loadest) subroutines implemented in 

S-PlusTM. When the log-transformed loads are converted back to 

daily loads, one of four estimators—the Adjusted Maximum 

Likelihood Estimator (AMLE), Maximum Likelihood 

Estimator (MLE), Least Absolute Deviation (LAD), or Linear 

Attribution (LA)—is selected by the program, depending on the 

distribution of the residuals. Seasonal loads were computed by 

summing loads for winter (December–February), spring 

(March–May), summer (June–August), and fall (September–

November). 

Because not enough continuous-flow data and samples 

were available for Plum Tree Branch (site S2, fig. 2; tables 1, 2) 

for use with Loadest, the mean daily discharge for calendar year 

2000 was multiplied times the annual median concentration for 

both total nitrogen and total phosphorus and summed to obtain 

an annual load estimate. Confidence intervals for total nitrogen 

and total phosphorus loads and estimation methods used for 

each station are given in Appendix 2.

In order to obtain an estimate of the accuracy of the loadestimation procedures used in this report, USGS gaging-station 

flow data and USGS nitrate data collected approximately twice 

monthly in 2001 from the Neuse River near Fort Barnwell 

(site N3, fig. 1) were compared to the estimated loads, using 

hourly data, collected by North Carolina State University 

(NCSU), Raleigh, N.C. Hourly measurements of nitrate, pH, 

dissolved oxygen, and other constituents were measured by 

NCSU as part of the River Net Program in 2001 (William 

Showers, North Carolina State University, written commun., 

2003). These data are available at http://rivernet.ncsu.edu/

index.html. Using hourly NCSU nitrate data collected by a 

continuous sampler/analyzer in conjunction with USGS daily 

discharge data for the same site, the hourly NCSU nitrate 

concentrations were averaged into daily values and analyzed by 

using the load-estimation procedures described for stations 

included in this report. 

The annual nitrate load, using the 365 daily average 

concentrations and flows for 2001, was 1,138 tons. When only 

21 daily nitrate values from USGS discrete water-quality 

samples were used to calculate the annual nitrate load at Fort 

Barnwell using the same load-estimation procedures, the result 

was 963 tons for 2001, about 15 percent lower than the results 

for the complete data set. In addition, the annual nitrate load for 

the Neuse River near Fort Barnwell also was computed by 

summing all 365 daily nitrate loads, using the nitrate data from 

NCSU and flow data from the USGS. The resulting load 

(1,148 tons) is considered to be the best estimate of the true load 

because it includes all days with daily mean nitrate 

concentrations and all days with mean flow—it is simply a 

direct numeric integration of all flow and concentration data 

(Richards, 1997). Thus, the USGS estimate, using only 21 

samples, is about 16 percent lower than the true load computed 

using all data. The observed difference between the estimated 

loads is probably because the load estimate based on the 21 

samples collected by the USGS included only 5 percent of the 

365 samples collected by NCSU and did not cover the entire 

range of flow events. Specifically, the lack of samples during 

high flows may result in estimates that are somewhat low, 

particularly when the regression approach is used (Richards, 

1997). Based on this brief comparative analysis, however, loads 

for this report are expected to be within 15 to 20 percent of the 

true loads transported.

Flow was generated at stations for streams that were not 

gaged, including Contentnea Creek near Evansdale (site S14, 
14 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

fig. 1) and Little Contentnea Creek at Scuffleton (S16, fig. 1). 

Daily flow values at Evansdale were estimated using daily 

mean flow data from Contentnea Creek at Hookerton (S18, 

fig. 1) by proportion of drainage area (flow at Evansdale = 

0.359 x flow at Hookerton). Similarly, flows at Scuffleton (S16, 

fig. 1) were generated using flow data from Contentnea Creek 

near Willow Green (S6, fig. 1) (flow at Scuffleton = 1.13 x flow 

at Willow Green). 

Flows from tidally affected streams also must be corrected 

because of periodic flow reversals. Swift Creek is tidally 

influenced near Streets Ferry, and several reported daily flow 

values were negative. Because positive daily flows were 

required for analysis, unit values recorded every 15 minutes 

were filtered and modeled to generate positive daily net flows. 

Acknowledgments

The U.S. Environmental Protection Agency, through its 

Office of Research and Development, partially funded the 

research described in this report through Interagency 

Agreement DW14938792-01 to the U.S. Geological Survey.

The authors acknowledge Dr. H.E. “Ted” Mew, Jr., 

(1942–2005), a friend and colleague, whose knowledge and 

insights contributed greatly to the concepts and ideas presented 

in this report. The work conducted at the Lizzie Research 

Station would not have been possible without his tireless 

enthusiasm and dedication.

The authors would like to thank all of the landowners who 

graciously allowed access to their property. Thanks also to Scott 

Caldwell, Terry Middleton, and Cassandra Pfeifle of the U.S. 

Geological Survey for their dedication and long hours toward 

maintaining instrumentation and collection of hydrologic and 

water-quality data during the study. Finally, the authors greatly 

appreciate comments and suggestions of the numerous 

reviewers of the manuscript who provided new perspectives on 

many topics that were incorporated into the final report.

Hydrogeology, Geochemistry, and 

Nitrogen Transport at the Lizzie 

Research Station Study Site

The Lizzie Research Station study site is in the Coastal 

Plain Physiographic Province (fig. 1, inset map), a landscape 

characterized by a series of progressively younger 

paleoshorelines and intervening terraces that step down in 

altitude and age toward the coast and into drainages. The relic 

landscape is mostly of Pliocene through Quaternary age, with 

modern drainages bordered by a series of nested PlioPleistocene paleovalleys that are separated by remnants of older 

interfluves. The Lizzie site straddles the boundary between the 

Wicomico plain interfluve (60 to 90-ft terrace lying east of the 

Surry Scarp paleoshoreline, toe at 90 ft [Daniels and Kane, 

Hog houses in Greene County, North Carolina.
Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site 15

2001]) and the 36-ft Sandy Run flood plain, with two sets of 

lower terraces separated by the 60-ft and 48-ft scarps (fig. 4A; 

cross-section A-A' in fig. 2; Farrell and others, 2003). 

Landforms characterizing the Plum Tree Branch watershed 

include the poorly drained, wet flat upland headwaters, known 

locally as Half Moon Pocosin, and the generally well to 

moderately well drained, dry flat uplands and valley side slopes 

composing the Plum Tree Branch upland valley. Plum Tree 

Branch drains into Sandy Run, an alluvial paleovalley with 

riverine landforms along the valley bottoms.

At the Lizzie Research Station site, a Late Cretaceous 

marine shelf deposit resembling the Peedee Formation 

functions as the lower boundary for the shallow ground-water 

system of near-surface aquifers and confining units (fig. 4B). 

Overlying the Cretaceous section is the Pliocene-age Yorktown 

Formation and several poorly exposed Pliocene to Pleistocene 

units that are difficult to age date and correlate because of 

widespread carbonate dissolution. Stephenson and Johnson 

(1912) prepared the first detailed hydrogeologic maps of 

ground-water resources in the North Carolina Coastal Plain, 

Figure 4. Conceptual models of (A) stratigraphy and (B) hydrogeologic units of the Lizzie Research Station, North Carolina.
16 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

associating the surficial aquifer with Pleistocene terrace 

deposits, and equated the first confining unit and underlying 

confined aquifer with the Yorktown Formation. More recently, 

the surficial aquifer was generalized to include post-Yorktown 

deposits of Quaternary age (Winner and Coble, 1996).

The Yorktown aquifer is composed of gravelly sands and 

a phosphatic gravelly, shelly sand, overlain by a sandy clayey 

silt with beds of Mulinia congesta that function as the 3 to 21-ft 

thick Yorktown confining unit. The tidally bedded surficial 

deposits of the Wicomico plain form the upland surficial or 

terrace aquifer at the Lizzie site. These deposits of medium- to 

fine-grained flaser-bedded sand and silt initially settled into 

low-lying depressions in the relic landscape, infilling 

paleovalleys and other channel-like features that cut into the 

Yorktown. Overlying these sands is a sheet of heterogeneous, 

extensively bioturbated, 2 to 6-ft thick, surficial layer of tidal 

flat or interdistributary bay-like deposits that evolve upward 

into salt-marsh deposits. 

Within the Sandy Run paleovalley, earlier erosion 

truncated the surficial and Yorktown formations, and the 

Yorktown confining unit completely is eroded below the 50-ft 

scarp. Subsequent middle Pleistocene fluvial to estuarine 

deposition, associated with sea-level rises, overlaid fine to 

coarse sands in the valley. Modern flood-plain deposits rich in 

detrital plant debris form a riparian zone along Sandy Run and 

lower portions of Plum Tree Branch. Hydrologically, the 

paleovalley substrate breaches the Yorktown confined aquifer 

and functions as an unconfined alluvial valley aquifer. As 

determined during the current study, water from the alluvial 

aquifer in Sandy Run and Middle Swamp was found to be 

chemically distinct from both the surficial and Yorktown 

aquifers.

The principal shallow aquifer, termed the surficial aquifer, 

includes several post-Yorktown units (W, PL, and N units, 

fig. 4) that are likely Pleistocene in age. These surficial units are 

underlain by the areally extensive Yorktown confining unit 

(Ty-4 – Morgarts Beach Member) and the Yorktown aquifer 

(Ty-2, Ty-3). The Yorktown aquifer includes two facies (Ty-2 

and Ty-3). Because the Yorktown confining unit is eroded 

along the Sandy Run and Middle Swamp drainages, the 

Yorktown aquifer (Ty-2 and Ty-3) is unconfined in these areas 

and is connected to the surficial aquifer. 

Head values for December 13, 2000, are shown for the 

surficial and Yorktown aquifers (fig. 5). Flow directions in the 

surficial aquifer indicate that much of the ground water 

underlying the western part of the study site discharges to Plum 

Tree Branch. Along the southeast-northwest cross-section B-B' 

(fig. 2), large downward gradients occur between the surficial 

and Yorktown aquifers as the stream is approached, indicating 

that ground water from the Yorktown does not discharge to 

Plum Tree Branch (fig. 6B). Plum Tree Branch does not breach 

the Yorktown confining unit (fig. 6B) but flows above it. Direct 

Figure 5. Piezometric head values and contours (in feet above NGVD 29) and flow directions for the (A) surficial and (B) Yorktown 

aquifers on December 13, 2000, at the Lizzie Research Station, North Carolina.
Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site 17

discharge to streams also occurs along the northern part of the 

site, with flow to both Sandy Run and Middle Swamp. Head 

differences between the surficial and Yorktown aquifers along 

the south-north cross-section A-A' (fig. 2) are several feet in the 

upland areas but decrease to less than 0.3 ft along the slope 

toward the alluvial valley (fig. 6A). Beneath this alluvial valley, 

the confining unit has been eroded, and the Yorktown aquifer 

sediments have been overlain by fluvial to estuarine deposits, 

creating a 45- to 50-ft thick unconfined alluvial aquifer.

Three distinct flow regimes are present at the site and can 

be characterized by the overlying landscape settings—poorly 

drained upland wet flats, moderate to well-drained upland 

valleys, and broad riverine alluvial valleys. These landscape 

features typically are found in the middle Coastal Plain 

environment and have been mapped across the entire North 

Carolina Coastal Plain (Haven, 2003). A pocosin is present at 

the upgradient end of the transect.

Flow is largely horizontal in the surficial aquifer 

underlying the upland flats and valley slopes to Plum Tree 

Branch, with seeps observed roughly 300 ft south of toe-slope 

well L4 (fig. 2) during wetter periods of the year. Downward 

flow occurs along the terraced valley slopes to the Sandy Run 

Figure 6. Piezometric head values and contours (in feet above NGVD 29) along (A) cross-section A-A’ and (B) cross-section 

B-B’.
18 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

bottomlands. The confining unit along this slope has been 

significantly leached and likely has increased the hydraulic 

conductivity of the unit in this area. Seeps have not been 

observed at the outcrop of the confining unit, as would be 

expected if the unit were to retard the downward migration of 

water. The chemistry (for example, pH, alkalinity) of samples 

collected from this zone are similar to those from the surficial 

aquifer, which supports the conclusion that the confining unit 

has been leached by the more acidic water present in the 

surficial aquifer. 

Ground-Water Age-Dating, Chemistry, and 

Nitrogen Fate and Transport 

The date that ground water recharges an aquifer (defined 

as the time the water loses contact with the atmosphere) can 

provide information on the prevailing flux through the groundwater flow system and the fate of contaminants. The residence 

time of ground water and surface water was estimated based on 

concentrations of as many as three chemical markers: 

chlorofluorocarbons (CFCs), tritium, and silica (Tesoriero and 

others, 2005). Concentrations of CFCs increased in the 

atmosphere beginning in the 1940s when they were produced 

for a variety of uses (for example, propellants, aerosols) until 

recently when restrictions on CFC production were established. 

CFCs have been successfully used to track changes in 

contaminants over time (for example, Böhlke and Denver, 

1995; Tesoriero and others, 2000). Chlorofluorocarbons and 

tritium concentrations in ground water were measured to 

estimate the age since the time of recharge. 

Not surprisingly, the poorly drained upland or pocosin has 

a recharge age profile indicative of slow percolation rates. 

Recharge-age isopleths are tightly spaced with old (before 

1955) ground water occurring at the base of the aquifer (fig. 7A; 

table 4). In contrast, along the intermediate part of the flow 

system, moderately well-drained soils are present, and faster 

recharge is indicated by the spreading of the recharge-age 

isopleths. Ground water at the base of the surficial aquifer is 

approximately 30 years old. Piezometric head values indicate 

that as Sandy Run is approached, incision of the surficial 

aquifer increases and the vertical component of ground-water 

flow increases (fig. 6). 

Along the alluvial valley slopes, recent recharge-date 

isopleths occur at greater depths than in upland areas indicating 

that the alluvial aquifer is a recharge area. Upwelling of older 

water toward streams is not indicated by these data, as 

upwelling would result in the presence of older water as the 

stream is approached. The young age of ground water in the 

alluvial aquifer is consistent with the hypothesis that water in 

this aquifer is derived from short flow paths originating from 

directly above or from movement of water from Sandy Run 

and(or) Middle Swamp into the aquifer. 

Tritium concentrations in the atmosphere are derived from 

atmospheric testing of nuclear weapons. As such, tritium is a 

particularly helpful marker of whether recharge occurred before 

or after the onset of atmospheric testing (approximately 1953). 

The intensity of atmospheric testing has varied since its 

inception. Using a chronological record of atmospheric tritium 

concentrations and the half life for tritium (12.4 years), a profile 

of expected tritium concentrations as a function of groundwater age has been constructed for this site. When both a tritium 

concentration and a CFC-based ground-water age were 

available, observed and expected tritium concentrations were 

compared to provide an independent test of the validity of the 

CFC-based ground-water ages (fig. 8). Nondetectable levels of 

tritium for CFC-based ages prior to 1953 provide a definitive 

verification that these samples represent water recharged prior 

to 1953. Tritium levels as a measure of the accuracy of CFC 

ages become less quantitative with more recent age dates 

because a single tritium level may represent recharge from 

widely different time periods. Further, mixing of water from 

different ages can have a dramatic effect on tritium levels 

because of the non-uniform tritium profile caused by bombtesting peaks.

With a few exceptions, tritium levels in ground water 

match the value expected by CFC-based age. No tritium was 

detected in samples with CFC-based recharge ages prior to 

1953. As has been observed elsewhere (Böhlke and Denver, 

1995), tritium levels that correspond to the bomb peak in the 

late 1960s were not found and may be a result of the mixing of 

waters recharged during the bomb peak with waters either 

before or after the peak. Although sample L26 has a CFC age of 

1964, it has too little tritium to have recharged at that time 

(fig. 8). The sample has tritium levels consistent with recharge 

in the early 1950s. Although peak tritium levels were not 

observed when tritium concentrations were plotted in crosssection A-A' (fig. 7B), the higher concentrations of tritium 

observed at the base of the surficial aquifer (except beneath the 

upland wet flats) correspond to CFC-based ages that are 

consistent with bomb peak periods. The nondetectable 

concentrations of tritium at the base of the surficial aquifer 

beneath the upland wet flats is consistent with the slow rate of 

recharge that is expected in this part of the aquifer. 

Geochemical tracers also have been used to determine the 

relative amounts of streamwater derived from different flow 

paths. Flow paths in a watershed range from short overland flow 

paths on the order of hours to long ground-water flow paths on 

the order of years. Silica (SiO2) has been used as a chemical 

tracer because these pathways often have distinctly different 

silica concentrations, which tend to increase as a function of 

residence time. The availability of silica and age-dating 

information provides an opportunity to determine the relation 

between silica concentrations and residence time, which is 

typically modeled (Scanlon and others, 2001). Silica 
Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site 19

Figure 7. (A) Recharge dates and isopleths using chlorofluorocarbon concentrations, (B) isopleths and tritium concentrations, and 

(C) silica concentrations in ground water along transect A-A’.
20 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

concentrations in the unconfined aquifers in this study area 

increase linearly as residence times increase (R2=0.95, fig. 9). 

As a result, silica concentrations in 

the unconfined aquifer may be used 

as a first approximation of the 

residence time for samples for 

which direct estimates (CFCs, 

tritium) of residence times are not 

available. In the confined aquifers 

(primarily Yorktown), there also is a 

relation between silica concentrations and residence time; however, 

the slope indicates a faster rate of 

silica dissolution (fig. 9). In a later 

section of this report, the relation 

between silica and residence time is 

used to distinguish between the 

various sources of surface water, 

such as overland flow and shallow 

ground water.

Shallow ground water beneath 

the site often has concentrations of 

nitrate exceeding the drinking-water 

standard of 10 milligrams per liter 

(mg/L) as nitrogen. Nitrate 

concentrations decrease quickly 

with depth, with levels below 1 mg/L less than 15 ft below the 

water table (fig. 10). Two processes may be responsible for the 

sharp decrease in nitrate with 

depth: (1) nitrate-contaminated 

water from agricultural activity 

may not have reached deeper 

portions of the flow system (in 

other words, the age of deep, lownitrate ground water pre-dates 

intensive fertilizer application) 

and(or) (2) nitrate is denitrified as 

it moves deeper in the aquifer 

system. Coupling age-dating and 

water-chemistry data can discern 

between these two processes.

Based on the dominant 

terminal electron acceptor, 

concentrations of redox-active 

constituents in ground water can 

be used to delineate the 

geochemical zones of an aquifer. 

Redox reactions occur in 

sequence, with the more 

thermodynamically favorable 

reactions occurring first (fig. 11). 

With respect to nitrate, 

denitrifying bacteria are 

facultative anaerobes and, as a 

result, prefer to use oxygen as an 

electron acceptor if it is present. 

Consequently, nitrate will not be 

denitrified in portions of the 

Figure 8. Tritium concentrations in ground-water samples plotted against recharge year. 

Recharge year was interpreted from chlorofluorocarbon (CFC) data. Low tritium concentration 

in sample L26 indicates recharge year calculated using CFCs is erroneous.

Figure 9. Ground-water residence time interpreted from chlorofluorocarbon (CFC) concentrations plotted against silica concentrations in samples from the Lizzie Research Station, 

North Carolina.

70 

60 

50 

40 

30 

20 

10 

0

TRITIUM CONCENTRATION, IN PICOCURIES PER LITER

1945 1955

Expected profile

1965 1975 1985 1995

RECHARGE YEAR (based on CFCs)

Observed tritium concentrations 

 in ground water

L26
Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site 21

Figure 10. Delineation of terminal electron-accepting processes along transect A-A’. Nitrate and excess nitrogen (italics) 

concentrations also are shown. (See figures 1 and 2 for well locations and line of section.)

Figure 11. Sequence of oxidation-reduction reactions involved with oxidation 

of carbon (electron donor) and terminal electron acceptors preferred by bacteria 

in the saturated zone (modified from Korom, 1992).
22 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

aquifer containing oxygen. Conversely, if high levels of 

dissolved iron are present, iron-reducing conditions are 

indicated and nitrate is not stable. 

Dominant terminal electron acceptors (TEAPs) were 

delineated along flow paths through both the surficial and 

Yorktown aquifers in the study area to determine the portions of 

these aquifers where transformations of nitrate and other redoxactive contaminants may occur. Dominant TEAPs were 

determined by using the classification system of Chapelle and 

others (1995). Oxygen-reducing conditions were indicated 

when concentrations of dissolved oxygen (DO) exceeded 

0.5 mg/L. Nitrate-reducing conditions were considered 

dominant when DO levels were below 0.5 mg/L and nitrate 

concentrations were above 0.5 mg/L. Iron-reducing conditions 

were considered dominant when both DO and nitrate levels 

were below 0.5 mg/L and iron concentrations exceeded 

0.5 mg/L. When seasonal variations in TEAPs occurred, the 

TEAP that was dominant for most of the year was selected.

Dominant TEAPs along a south to north transect across the 

study site indicate that only in the uppermost portions of the 

surficial aquifer (< 16 ft below the water table) is nitrate 

expected to be stable (fig. 10). Ground water becomes 

anaerobic at shallow depths (fig. 6), indicating that the 

consumption of oxygen by microbial respiration (fig. 11) 

quickly exceeds the supply. In deeper portions of the surficial 

aquifer and in most of the Yorktown aquifer iron-reducing 

conditions are present, and nitrate is not stable in this 

environment. Oxygen-reducing conditions occur at depth only 

at the northern terminus of the flow path where the confining 

unit is not present.

Selected ground-water samples were analyzed for 

dissolved nitrogen and argon gas to estimate the amount of 

nitrogen derived from atmospheric sources. Nitrogen and argon 

are incorporated in ground water during recharge by air-water 

equilibration processes. Air bubbles also can be transported to 

the saturated zone resulting in concentrations of nitrogen and 

argon in excess of equilibrium (Heaton and Vogel, 1981). 

Nitrogen gas that is derived from atmospheric sources (both airwater equilibrium and excess air) can be estimated by using 

nitrogen to argon ratios for samples from aerobic portions of the 

aquifer where denitrification is not expected (Dunkle and 

others, 1993). Aerobic samples have nitrogen to argon ratios 

that may suggest recharge water temperatures varying from 12 

to 16 degrees Celsius (°C; fig. 12). A recharge temperature of 

14 °C was used for the recharge temperature in calculations of 

excess nitrogen. The uncertainty in the recharge temperature 

(14 °C ± 2 °C) translates into ± 1 mg/L excess nitrogen. 

As expected, aerobic samples plotted on or near the 14 °C 

air-saturated water with excess air (ASWEA) line, indicating 

that little, if any, denitrification has occurred in this portion of 

the aquifer (fig. 12). In contrast, most post-1953 (defined by 

detectable levels of tritium) anaerobic samples from the 

surficial aquifer and the unconfined portion of the Yorktown 

aquifer plot significantly to the right of the ASWEA line, 

indicating that varying amounts of denitrification has occurred 

in these portions of the aquifer. This indicates that the water 

samples contained elevated nitrate levels prior to entering an 

Figure 12. Dissolved argon and nitrogen concentrations in ground water. Air-saturated water (ASW) line 

depicts range of values expected for air-water at varying temperature. Air-saturated water with excess air 

(ASWEA) lines depict range of values for one recharge temperature but with varying amounts of excess 

air. Values to the right of the ASWEA line representing the recharge temperature for the sample indicate 

excess nitrogen from denitrification.
Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site 23

anaerobic portion of the aquifer where the nitrate was 

subsequently denitrified. Pre-1953 samples were from the 

confined portion of the Yorktown aquifer. Although these 

samples also were anaerobic, they plotted on or near the 12 °C 

ASWEA line, which indicates that these samples had little or no 

excess nitrogen. Nitrogen applications to the land surface were 

lower prior to 1953 than more recently. 

The combined use of age-dating, nitrate, excess nitrogen, 

and other redox-active constituents provides insight into the 

fate and history of nitrate contamination in the surficial and 

Yorktown aquifers (fig. 13). Three regimes regarding the 

history of nitrate contamination are apparent. Ground water that 

is less than 10 years old tends to be oxic and has elevated nitrate 

concentrations, reflecting both the stability of nitrate and a 

recharge time of high nitrogen applications. Ground water that 

is greater than 10 but less than 30 years old has low nitrate and 

DO concentrations, which indicate that nitrate is not stable, 

although the increased excess nitrogen values indicate that the 

water at one time contained elevated nitrate concentrations. 

Ground water more than 30 years old also has low nitrate and 

DO concentrations and high levels of iron, indicating that 

nitrate also is not stable in this environment. However, these 

samples have little or no excess nitrogen, which suggests that 

the ground water did not contain elevated nitrate at an earlier 

point along the flow path.

Ground-Water and Surface-Water Interactions: 

Nutrient Chemistry, Surface-Water Origin and 

Residence Time, and Pathways of Nutrients to 

Surface Water

In Plum Tree Branch, nitrate was the dominant form of 

inorganic nitrogen throughout most of the year (fig. 14B). Only 

during base-flow conditions in the summer was ammonium the 

dominant form of inorganic nitrogen, with dissolved 

phosphorus concentrations also peaking during base-flow 

conditions in both Plum Tree Branch and Middle Swamp 

(fig. 14). As such, the annual nitrogen flux was primarily 

dominated by nitrate transported during the non-summer 

months. Ammonium became the dominant form in the summers 

of 2000 and 2002 likely because flows and nitrate inputs were 

reduced because of high levels of evapotranspiration, resulting 

in generally reducing conditions in Plum Tree Branch and 

Middle Swamp during low-flow periods. The mineralization of 

organic matter (eq. 1) then becomes the primary source of 

inorganic nitrogen and probably phosphorus as well, although 

release of phosphorus sorbed on sediment is also a possible 

mechanism (Spruill, 2000). Conversion to nitrate by 

nitrification (eq. 2) does not occur to a large degree because of 

the typically low dissolved-oxygen (DO) concentrations during 

Figure 13. Redox-active species as a function of ground-water residence time.
24 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

Figure 14. Nitrate and ammonium concentrations, phosphorus, and discharge for (A) Middle Swamp and 

(B) Plum Tree Branch.
Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site 25

the summer (table 5). Low DO levels facilitate removal of 

nitrate by denitrification (eq. 3) from Plum Tree Branch and 

Middle Swamp and release phosphorus during low-flow 

periods. The summer of 2001 was wetter than the summers of 

2000 and 2002, so the nitrate (and oxygen) fluxes from ground 

water were sufficient to maintain high nitrate concentrations 

and aerobic conditions.

C106H263O110N16P 107O2 14H+ + + 106CO2

16NH+ HPO4

2-

+ ++ 108H2O

→

NH4

+ 2O2 NO3- 2H+ + → + + H2O

5CH2O 4NO3

 - 4H + 5CO2 2N2 + + → + + 7H2O

(1)

(2)

(3)

Inorganic nitrogen concentrations were much lower in 

both Sandy Run and Middle Swamp than in Plum Tree Branch, 

whereas dissolved phosphorus concentrations were about 3–5 

times higher (fig. 14; table 2). With respect to nitrogen, this may 

reflect more efficient nitrogen processing (reduction by 

nitrogen loss to the atmosphere) in the riparian and hyporheic 

zones and the wider riparian forests in the larger basins. For 

phosphorus, which cannot be biologically converted and 

removed from the stream to the atmosphere, these data indicate 

that the higher-order streams accumulate phosphorus from 

eroded sediment, organic debris, and possibly point sources, 

which provide long-term sources of phosphorus and which can 

then be moved to points downstream in a natural fluvial system 

only by erosion or, temporarily, by biological uptake. Similar 

seasonal trends in nitrate, phosphorus, and DO were observed 

in all three watersheds, with significant decreases during the 

summer. Low DO and nitrate, associated with reducing 

conditions in the stream, indicate that denitrification during the 

summer base-flow periods may be responsible for much of the 

decline in nitrate and for increased dissolved phosphorus 

concentrations. 

By comparing the major ion chemistry of the aquifers and 

streams, it is possible to discern the origin of surface waters. 

Ground water from the Yorktown aquifer was dominated by 

calcium (Ca2+) and bicarbonate (HCO3

-

, fig. 15). In contrast, 

water from the surficial and alluvial aquifers had a more varied 

mix of cations and anions and was dominated by chloride (Cl-

) 

and nitrate (NO3

-

). Water from the alluvial aquifer had anion 

and cation chemistry that resembled the chemistry of the 

surficial aquifer but not that of the Yorktown aquifer. However, 

sodium to potassium ratios and other indicators suggest that the 

surficial and alluvial aquifers may have different sources of 

ions. The cation chemistry of Plum Tree Branch, Sandy Run, 

and Middle Swamp was bounded by the range in cation 

chemistry found in the surficial and alluvial aquifers (fig. 15). 

In contrast, the anion chemistry of all three streams, but 

particularly Sandy Run and Middle Swamp, trended from Cl-

 to 

NO3

-

-dominated water, similar to that of the surficial aquifer, to 

HCO3

-

-dominated water, similar to that of the Yorktown 

aquifer (fig. 15). Bicarbonate, however, is not conservative and 

may be generated by biologically mediated reactions occurring 

in the stream. Thus, the primary sources of ions in these streams 

are likely the surficial and alluvial aquifers. As will be 

discussed below, SiO2 concentrations in these streams were 

much lower than in the Yorktown aquifer, suggesting that little 

of the streamwater is derived from this aquifer.

Inferences about the watershed residence times of surface 

water can be made by comparing SiO2 concentrations in surface 

water to the relation between SiO2 and ground-water residence 

time. Flow paths in a watershed range from short overland flow 

paths on the order of hours to long ground-water flow paths on 

the order of years. Because these pathways often have distinctly 

different SiO2 concentrations, SiO2 often is used as a chemical 

tracer (for example, Scanlon and others, 2001). The availability 

of SiO2 and age-dating information provides an opportunity to 

determine the relation between SiO2 concentrations and 

residence time. 

At the Lizzie site, concentrations of SiO2 increased as a 

function of ground-water age, with the shallowest parts of the 

surficial aquifer having the lowest SiO2 levels and the confined 

parts of the Yorktown having the highest levels (fig. 7). 

Inferences about the residence times of surface water in the 

watershed can be made by comparing SiO2 concentrations in 

surface water to the relation between SiO2 and ground-water 

residence time (fig. 9). The usefulness of SiO2 concentrations as 

indicators of both the source and residence times of streamflow 

is limited by the effect that biological activity has on SiO2

concentrations in streams. A bloom dominated by diatoms is 

indicated by a decrease in SiO2 concentrations in Middle 

Swamp, Sandy Run, and Plum Tree Branch during late winter 

or early spring followed by a return to normal levels. This 

pattern has been observed in streams elsewhere and has been 

attributed to a spring diatom bloom followed by summer 

blooms with a mixed phytoplankton population. As a result, 

some of the lowest SiO2 concentrations (for example, bottom 

quartile) observed in Middle Swamp, Sandy Run, and Plum 

Tree Branch may not be reliable indicators of watershed 

residence time.

Concentrations of SiO2 in Plum Tree Branch were always 

in the range indicated by the surficial aquifer (fig. 16). This 

indicates that water in Plum Tree Branch during base flow is 

derived largely from the surficial aquifer, having a watershed 

residence time of 15 years or less. Little or no contribution from 

the Yorktown aquifer is expected since this stream does not 

breach the confining unit separating the surficial aquifer from 

the Yorktown. Overland flow and other fast pathways having 

low SiO2 concentrations due to low contact time with sediments 

are not indicated as major sources in Plum Tree Branch during 

base flow. In contrast to Plum Tree Branch, Middle Swamp and 

Sandy Run occasionally incise through the confining unit and 

into the Yorktown, so some Yorktown discharge into these 

streams is more likely. However, SiO2 concentrations in Middle 

Swamp and Plum Tree Branch are not intermediate between 

unconfined and confined aquifers. In fact, SiO2 concentrations 

are much lower than those found in the unconfined aquifers, 

indicating that a large portion of flow in these streams has a 
26 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

Table 5. Seasonal and annual loads and annual yields of total nitrogen and phosphorus at 14 stations in the Neuse River basin, North 

Carolina.

[USGS, U.S. Geological Survey; tons/mi2, tons per square mile]

Station name USGS station 

number

Seasonal total nitrogen load (tons) Annual total 

nitrogen 

load

(tons)

Annual total 

nitrogen yield

(tons/mi2 Winter Spring Summer ) Fall

Calendar year 2000

Bear Creek at Mays Store 208925200 98 36 42 24 201 3.4

Neuse River at Kinston 2089500 1,427 621 774 446 3,268 1.2

Plum Tree Branch 209173190 .79 .24 .28 .17 1.4 2.5

Sandy Run near Lizzie 209173200 16 3.8 6.0 .76 27 .86

Middle Swamp near Farmville 2091736 23 5.4 6.8 3.0 38 .74

Little Contentnea near Willow Green 2091737 56 15 19 6.3 97 .63

Little Contentnea at Scuffleton 2091740 82 29 37 13 160 .93

Contentenea Creek near Lucama 2090380 59 16 50 13 139 .87

Contentnea Creek near Evansdale 2090519 292 168 42 25 526 2.0

Nahunta Swamp near Shine 2091000 61 13 23 12 109 1.4

Contentnea Creek at Hookerton 2091500 461 149 178 150 939 1.3

Neuse River near Fort Barnwell 2091814 1,778 774 1,023 618 4,192 1.2

Trent River near Trenton 2092500 75 30 82 20 207 1.2

Swift Creek near Steets Ferry 209205053 171 69 145 22 408 1.5

Calendar year 2001

Bear Creek at Mays Store 208925200 50 44 40 16 150 2.6

Neuse River at Kinston 2089500 579 791 480 177 2,027 .75

Sandy Run near Lizzie 209173200 4.1 5.2 1.1 .18 11 .34

Middle Swamp near Farmville 2091736 7.8 7.4 2.2 .01 17 .34

Little Contentnea near Willow Green 2091737 15 25 10 1.1 51 .33

Little Contentnea at Scuffleton 2091740 30 45 24 3.8 102 .59

Contentenea Creek near Lucama 2090380 37 37 15 4.8 94 .59

Contentnea Creek near Evansdale 2090519 189 256 32 8.4 486 1.8

Nahunta Swamp near Shine 2091000 32 22 13 5.8 72 .91

Contentnea Creek at Hookerton 2091500 219 247 113 42.5 622 .85

Neuse River near Fort Barnwell 2091814 709 969 576 220 2,474 .63

Trent River near Trenton 2092500 42 36 12 2.4 92 .55
Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site 27

Station name USGS station 

number

Seasonal total phosphorus load (tons) Annual total 

phosphorus 

load

(tons)

Annual total 

phosphorus 

yield

(tons/mi2

)

Winter Spring Summer Fall

Calendar year 2000

Bear Creek at Mays Store 208925200 4.3 1.7 3.2 0.6 9.9 0.17

Neuse River at Kinston 2089500 115 57 85 38 294 .11

Plum Tree Branch 209173190 .01 .00 .00 .00 .02 .03

Sandy Run near Lizzie 209173200 2.3 .74 1.3 .19 4.5 .14

Middle Swamp near Farmville 2091736 2.7 1.1 1.9 .65 6.3 .12

Little Contentnea near Willow Green 2091737 7.3 3.2 4.9 1.2 17 .11

Little Contentnea at Scuffleton 2091740 9.1 5.1 9.0 2.8 26 .15

Contentenea Creek near Lucama 2090380 4.4 .78 1.6 .52 7.3 .05

Contentnea Creek near Evansdale 2090519 8.0 3.7 4.2 3.8 20 .07

Nahunta Swamp near Shine 2091000 3.8 1.1 1.5 .41 6.7 .08

Contentnea Creek at Hookerton 2091500 34 16 25 14 88 .12

Neuse River near Fort Barnwell 2091814 100 65 106 43 313 .08

Trent River near Trenton 2092500 11 4.1 16 2.5 34 .20

Swift Creek near Steets Ferry 209205053 27 11 36 4.0 78 .29

Calendar year 2001

Bear Creek at Mays Store 208925200 2.0 3.4 3.2 0.28 8.9 0.15

Neuse River at Kinston 2089500 47 83 60 17 207 .08

Plum Tree Branch 209173190 .00 .00 .00 .00 .01 .02

Sandy Run near Lizzie 209173200 .58 .9 .31 .04 1.8 .06

Middle Swamp near Farmville 2091736 1.1 1.7 .83 .04 3.7 .07

Little Contentnea near Willow Green 2091737 1.9 4.2 2.8 .27 9.2 .06

Little Contentnea at Scuffleton 2091740 3.8 8.4 6.5 1.3 20 .12

Contentenea Creek near Lucama 2090380 1.6 1.4 .41 .25 3.6 .02

Contentnea Creek near Evansdale 2090519 4.8 5.2 3.3 2.3 16 .06

Nahunta Swamp near Shine 2091000 1.6 1.3 .75 .24 3.8 .05

Contentnea Creek at Hookerton 2091500 17 29 17 3.8 67 .09

Neuse River near Fort Barnwell 2091814 45 100 69 18 232 .06

Trent River near Trenton 2092500 3.8 3.8 1.3 .17 9.2 .05

Table 5. Seasonal and annual loads and annual yields of total nitrogen and phosphorus at 14 stations in the Neuse River basin, North 

Carolina.—Continued

[USGS, U.S. Geological Survey; tons/mi2, tons per square mile]
28 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

Figure 15. Trilinear diagrams of water chemistry in ground water, streams, and artificial drainages at the Lizzie 

Research Station, North Carolina. Unconfined aquifer data include both the surficial aquifer and the alluvial aquifer. 

Confined aquifer data include confined portions of the Yorktown aquifer and Peedee Formation.
Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site 29

short residence time (for example, < 3 years) and is likely 

derived from overland flow, discharge of young water from 

recharge into near-stream alluvial deposits, and the discharge of 

young water from bank storage after flood events. Thus, the 

alluvial and terrace deposits in second- and higher-order 

streams act as both recharge and discharge areas, depending on 

prevailing hydrologic conditions, discharging to streams during 

dry periods and recharging during wet periods. 

High nitrate concentrations in the surficial aquifer (median 

nitrate concentration of 6.4 mg/L excluding wells in the 

pocosin) are the likely source of nitrate in Plum Tree Branch 

(median nitrate concentration of 3.6 mg/L). The two transport 

mechanisms considered for the elevated nitrate concentrations 

in Plum Tree Branch were direct discharge of nitrate in ground 

water to surface water and tile-drain discharge from site SR5-

T1 (fig. 2). Overland runoff from stormflow was not considered 

in this study because individual storm events were not 

monitored and only moderate- to low-flow conditions are 

represented. Ground- and surface-water samples were collected 

along a transect extending from site L2 to site FP (fig. 2) and 

analyzed for nutrients and redox-active constituents to assess 

the likelihood of direct discharge of nitrogen to Plum Tree 

Branch. 

High DO concentrations indicate that aerobic conditions 

exist upgradient from the riparian zone with high 

concentrations of nitrate found beneath the spray field (fig. 17). 

As ground water enters the subsurface riparian zone, DO and 

nitrate concentrations are very low, and iron and 

methane concentrations increase, indicating that 

conditions are sufficiently reducing to assure that 

nitrate passing through this zone is likely to be 

denitrified (eq. 3) prior to discharging to Plum Tree 

Branch. Dilution of aerobic, nitrate-laden, shallow 

ground water with a large fraction of deeper anaerobic 

water can yield similar riparian zone concentrations of 

redox-active constituents to those found near Plum 

Tree Branch. However, SiO2 concentrations remained 

essentially constant along the transect, indicating that 

the same portion of the ground-water system was 

being sampled (fig. 17). As such, denitrification is the 

likely nitrate removal mechanism in the riparian zone. 

Unfortunately, dissolved gas samples collected in the 

riparian zone and in the streambed contained too much 

methane and carbon dioxide to obtain a meaningful 

estimate of excess nitrogen. 

Increases in ammonium levels occurred (0.22 to 

4.3 mg/L, table 3) in the riparian zone. Although 

dissimilatory nitrate reduction to ammonium (DNRA) 

may be responsible for a small amount of nitrate 

reduction, mineralization of organic matter (eq. 1) is 

considered the more likely process for ammonium 

generation in riparian zones (Duff and Triska, 2000). 

Denitrification, DNRA, and plant uptake are possible 

pathways for nitrate removal. Increase in ammonium 

levels occurring in the riparian zone are very small 

relative to upgradient nitrate concentrations, 

indicating that DNRA may be responsible for only a small 

fraction of nitrate reduction. Consequently, plant uptake and(or) 

denitrification are the likely nitrate-removal mechanisms in the 

riparian zone. Mineralization of organic matter also appears to 

be a likely mechanism for high concentrations of phosphorus 

(> 0.5 mg/L) occurring in stream and riparian zone wells 

sampled along Sandy Run (table 3).

Ground water that is intercepted by the tile drain in the 

spray field is routed directly to Plum Tree Branch (fig. 2); as a 

result, riparian zone processes that lower nitrate fluxes are 

bypassed. The nitrate flux from the tile drain remained fairly 

constant throughout the year (fig. 18) and can account for 

approximately 30 percent of the increase in nitrate flux along 

the reach from S7 to S2 (fig. 2) based on instantaneous 

measurements. Nitrate flux from the tile drain decreased to 

about 15 percent of the total increase in nitrate flux during 

periods of high discharge (fig. 18). Overland flow and, perhaps, 

direct ground-water discharge that pass through the riparian 

zone too quickly to be denitrified are possible sources of 

increased nitrate flux during high-discharge periods. 

Dissolved inorganic nitrogen (DIN) concentrations are 

much lower in both Sandy Run (mean DIN = 0.3 mg/L) and 

Middle Swamp (0.3 mg/L) than in Plum Tree Branch 

(5.4 mg/L). This may reflect more efficient nitrogen processing 

in the riparian zone and(or) greater separation of agricultural 

land from streams in these larger basins because of wider 

riparian buffer zones. Strongly reducing conditions are present 

Figure 16. Concentrations of silica in ground- and surface-water samples 

collected at the Lizzie Research Station, North Carolina.
30 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

Figure 17. Terminal electron-accepting zones along transect L2 to Plum Tree Branch near site FP 

and concentrations of (A) methane, iron, dissolved oxygen, and nitrate; and (B) silica, dissolved 

organic carbon, nitrate, and ammonium.
Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site 31

in the riparian zone and streambed of Sandy Run (table 3), 

indicating that direct discharge of nitrate to surface water during 

base-flow conditions is not likely in this drainage.

Effects on Ground-Water Quality of Changing to 

Swine-Waste Fertilizer From Inorganic 

Fertilizer

In addition to characterizing fate and transport of nitrogen 

in a coastal plain stream-aquifer system, the Lizzie Research 

site provided an excellent opportunity to evaluate the effects on 

ground-water and surface-water quality of using swine wastes 

for fertilizing crops, specifically nitrogen and phosphorus. The 

Lizzie Research site was included in a 1995 USGS NAWQA 

study as a secondary flow-path study site. (The primary flowpath site was in the Pete Mitchell Swamp watershed in the TarPamlico River basin [Spruill and others, 1998]). The objectives 

of the NAWQA flow-path studies were to evaluate chemical 

characteristics of ground water in a coastal plain aquifer and 

changes that occur in ground-water chemistry from recharge to 

discharge areas of the shallow aquifer at selected sites along a 

ground-water flow path. Five wells (L2, L4, L5, L6, and L16, 

fig. 2; see table 3 for locations) were selected from a set of more 

than 40 wells installed for a recharge study at the Lizzie 

Research site by the DWQ Groundwater Section. Well L2, 

located upgradient from cultivated fields, was selected by the 

NAWQA study team to represent water quality least affected by 

intensive agricultural operations. Wells L6 and L5 were located 

in cultivated fields used for growing corn, soybeans, and wheat. 

Wells L4 and L16 were located at the field edge, downgradient 

from the fields where crops were grown. 

The source of nitrogen fertilizer used at the study site 

changed in 1995. Prior to 1995, the primary nitrogen fertilizer 

used at the site was ammonium nitrate, applied at the rate of 

100–200 lbs/acre as recommended for growing corn in North 

Carolina (North Carolina State University, 1992). The 

recommended rate for soybeans in the Coastal Plain at this time 

was 30–50 lbs/acre and for wheat, 80–100 lbs/acre (North 

Carolina State University, 1992). These recommended 

application rates remain essentially the same (North Carolina 

State University, 2003). Fertilizer is generally applied to corn 

and soybeans at least two times per growing season, first in 

March or April and again in June. Both crops are planted in the 

spring, and corn is harvested during late summer and soybeans 

are harvested in the fall. The fields then may be left fallow or 

planted in late fall in winter wheat. During the late spring of 

1995, wastewater from a newly constructed lagoon was applied 

to fertilize crops on about 90 acres east and south of the lagoon 

(fig. 2). Other than this change in fertilizer type, other farming 

practices, recommended fertilization rates, general application 

times, and the crops planted remained the same. 

Changes in the quality of shallow ground water beneath 

and downgradient from the spray fields were observed between 

Figure 18. Percent of nitrate flux increase along Plum Tree Branch reach from S7 to S2 that is 

attributed to tile drain SR5-T1, and discharge at Plum Tree Branch at S2.
32 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

1995 and 1999. Five wells (L2, L4, L5, L6, L16; fig. 2; table 3) 

at the Lizzie Research Station were sampled in March 1995 as 

part of the NAWQA secondary flow-path study for dissolved 

major ions, nutrients, selected pesticides, and organic carbon 

(Smith and others, 1996). Well L2 was located upgradient from 

cultivated fields and represented shallow ground water. Well L6 

represented shallow ground-water quality beneath the 

cultivated field, which 

had been planted in corn 

the previous growing 

season. Well L4 also 

represented shallow 

ground-water 

downgradient from the 

cultivated fields. Wells 

L5 and L16 tapped the 

first confined aquifer 

(Yorktown aquifer) 

beneath the cultivated 

field and were used to 

evaluate whether water 

was moving from the 

shallow to the deep 

aquifer. Concentrations of 

selected constituents, 

including dissolved 

nitrate, calcium, 

magnesium, sodium, and 

potassium, in the 1995 

ground-water samples 

from two of the wells, L2 

(the upgradient well) and 

L6 (the field well), are 

shown in figure 19.

By 1999 when the 

MIMS project began, 

lagoon wastes had been 

applied to fields used for 

growing corn, wheat, and 

soybeans for 

approximately 4 years. 

Samples were collected in 

March 1999 from these 

same wells. 

Concentrations of all 

constituents were 

approximately the same 

in 1999 in the upgradient 

well (L2), but 

concentrations of all 

constituents except 

phosphorus increased in 

the field well (L6) and the 

downgradient well (L4) 

by a factor of 2 or greater. The nitrate concentration in well L6 

increased from 10 mg/L in 1995 to 35 mg/L in 1999. The 15N 

value of 21.8 in well L6, indicative of swine wastes (Karr and 

others, 2001; Spruill and others, 2002) was higher than the 

8.7 per mil value of 15N in water from well L2. By 2002, nitrate 

concentrations had remained relatively unchanged from 1995 in 

the upgradient well (L2), whereas nitrate concentrations had 

Figure 19. Chemical constituent concentrations in ground water from wells L2 and L6 at the Lizzie Research 

Station, North Carolina, for 1995 (before swine-waste spray was used) and 1999 (after 4 years of swine-waste 

spraying).
Hydrogeology, Geochemistry, and Nitrogen Transport at the Lizzie Research Station Study Site 33

varied between 2 and 5 times higher since 1999 in well L6 

(fig. 20). 

The use of sprayed swine wastes at this site resulted in 

increased concentrations of nitrate and other chemical 

constituents. No change in dissolved phosphorus concentrations 

was observed in the spray field well (L6, fig. 2), and no 

concentration exceeded 0.02 mg/L, suggesting that phosphorus 

is adsorbed to the soil matrix before reaching shallow ground 

water. The nitrite-plus-nitrate concentration in ground water 

beneath the spray field (well L6, fig. 2) increased by a factor of 

3.5 within 4 years of spray application—from 10 to 35 mg/L, 

and a concentration as high as 56 mg/L was observed in this 

well in spring 2002 (fig. 20). 

The finding that nitrate concentrations are higher in 

ground water sprayed with swine wastes in ground water 

beneath crops fertilized with commercial fertilizer is 

consistent with recent findings from other studies being 

conducted in North Carolina and indicates that this site is 

representative of other hog-producing farms in the Coastal 

Plain (Spruill and others, 2002). Examination of nitratenitrogen concentrations in ground water beneath cultivated 

fields in the North Carolina Coastal Plain having different 

sources of nitrogen applied as fertilizer (Spruill and others, 

2002) reveals that highest concentrations occur in ground 

water beneath fields sprayed with swine wastes and 

fertilized with poultry litter (fig. 21). Statistically, using a 

Kruskal Wallis test (Conover, 1980), concentrations of 

nitrate in ground water beneath fields sprayed with swine 

wastes were significantly (p < 0.01) higher (median=

26 mg/L) than in ground water beneath fields fertilized 

with inorganic commercial fertilizer (median=14.5 mg/L). 

Results of another cooperative study in the Contentnea 

Creek drainage basin (Ragland and others, 2003; Harden and 

Spruill, 2004), specifically in the Sandy Run and Middle 

Swamp area where the Lizzie Research Station is located, also 

indicate that nitrate concentrations in drainage tiles located in 

fields where swine wastes were sprayed on crops were 

significantly higher than in drainage tiles located in fields where 

commercial fertilizer was used (fig. 22). 

Why are nitrate concentrations higher in both ground 

water and tile drainage from fields fertilized with sprayed swine 

wastes than in ground water and tile drainage from fields 

fertilized with commercial fertilizer? Results of previous 

studies indicate that increasing nitrogen fertilizer rates 

generally result in higher nitrateconcentrations and offsite 

transport in subsurface tile drainage, regardless of the nitrogen 

source (Baker and Johnson, 1981; Evans and 

others, 1984; Randall and others, 2000; Jaynes 

and others, 2001). Results of these studies were 

based on applications of conventional 

fertilizers (urea, anhyrdous ammonia) and(or) 

animal wastes (swine-lagoon effluent and dairy 

manure). Randall and others (2000) applied 

dairy manure and urea at equivalent rates of 

available nitrogen to different plots over a 

4-year period and found no differences in NO3

-

concentrations and field losses in subsurface 

tile drainage. In the current study and a tile 

drain study conducted in the Sandy Run and 

Middle Swamp basins, all sites (including the 

Lizzie Research Station site) receiving swinelagoon effluent as a fertilizer source had 

substantially higher NO3

-

 concentrations and 

yields compared to sites receiving 

conventional fertilizer, indicating that more 

total nitrogen probably is applied to the spray 

sites relative to the conventional sites. 

Irrigation systems involving applications of 

Figure 20. Nitrite-plus-nitrate concentrations in ground-water samples from well L6 

at the Lizzie Research Station, North Carolina, 1995–2003.

Figure 21. Concentrations of nitrite plus nitrate in ground water from 

shallow aquifers beneath four areas with selected land uses in the 

Coastal Plain of North Carolina (modified from Spruill and others, 2002).
34 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

swine-lagoon effluent are designed such that the total nitrogen 

applied can be utilized by the growing crop to avoid runoff or 

excessive leaching; however, problems may result from adverse 

weather conditions or application rates that exceed crop 

utilization (Evans and others, 1984; Smith and Evans, 1998). 

Thus, the higher nitrogen loadings for the Lizzie site, as well as 

other spray sites in the Sandy Run and Middle Swamp 

watersheds, indicate over-application or applications at times 

when crops are not growing.

Nutrient Loading in the Neuse River 

Drainage Basin During Calendar Years 

2000 and 2001 in Relation to 

Background Loads, and Implications of 

Findings from the Lizzie Research 

Station Study

Chemicals and sediment are naturally removed from 

watersheds by moving water derived from recharge 

(precipitation) in both surface and ground water through 

processes of corrasion (physical erosion) or corrosion 

(dissolution). Although sediment is transported primarily by 

water through the physical movement of solid or colloidal 

particles from the land surface, soluble chemicals typically are 

dissolved in rainwater as it falls onto the land surface and moves 

either through soils to the water table (percolation) or in runoff 

to streams. 

Chemical loads in rivers are computed according to 

the following general equation:

L CQ = × , (4)

where L = mass transport through time; C = concentration 

of the chemical constituent (mass/volume); and Q = 

discharge, in volume per unit time. 

Excess plant nutrients, primarily nitrogen and 

phosphorus, in aquatic ecosystems are associated with 

contamination caused by humans and human activities 

(Schlesinger, 1997). Increased loading of nutrients, 

primarily nitrogen, through time has been implicated as a 

reason for environmental problems in the Neuse River 

basin in North Carolina (North Carolina Department of 

Environment and Natural Resources, 2001). Spruill and 

others (1996) noted that Contentnea Creek was 

responsible for 35 percent of the total nitrogen and 

45 percent of the total phosphorus delivered downstream 

from both the Neuse River at Kinston and Contentnea 

Creek at Hookerton, indicating that this drainage has a 

major effect on the Neuse River water quality. Because 

nitrogen has been implicated by several researchers as the 

primary nutrient responsible for algal blooms in the Neuse 

River (Paerl, 1987; Paerl and others, 1995) and because recent 

research indicates increases in total nitrogen loading, the State 

of North Carolina in 1997 required a reduction of 30 percent in 

all sources of nitrogen in the Neuse River basin in order to 

improve water quality. 

Loads of chemical constituents carried by rivers are 

indicative of the relative abundance of the chemicals in the 

watershed and may be associated with particular geologic, 

biologic, and anthropogenic sources. Various nutrient load 

estimates have been made for the Neuse River since 1992 

(Dodd and others, 1992; Harned and others, 1995; McMahon 

and Woodside, 1997; Stow and Borsuk, 2003). Within the same 

drainage and same time period, loads can be useful in assessing 

major sources of particular chemical constituents and in 

determining likely areas where mass and water are gained or 

lost in the reach. 

While comparisons of stream loads of chemical 

constituents are particularly useful for identifying possible 

constituent sources in a basin, it is more difficult to use stream 

loads to determine temporal trends or to relate to anthropogenic 

factors. This is largely because flow, which typically is highly 

variable, has such a large influence on load relative to 

concentration. For example, flow in the Neuse River at Kinston 

for the period April 1999 to September 2002 ranged from 

260 ft3/s to more than 35,000 ft3/s (a ratio of 136 to 1) compared 

to the range in nitrate concentration for the same period of 

0.05 mg/L to about 1 mg/L (ratio of 20 to 1). The calculated 

load for such a river is influenced more strongly by the 

relatively large variability in discharge and factors that affect 

discharge, such as climate and precipitation, relative to 

concentration. Large apparent changes in load occur in response 

Figure 22. Concentrations of nitrate in fields fertilized with conventional 

inorganic fertilizer (Conv), sprayed swine waste (Spray), and wastewatertreatment plant sludge (WWTP) in the Little Contentnea Creek subbasin, 

North Carolina (Harden and Spruill, 2004).
Nitrogen Loading in the Neuse River Basin 2000 and 2001 in Relation to Background Loads 35

to hydrologic changes during dry or wet years, months, or days; 

therefore, the effects of change on constituent loads as a result 

of factors other than climatic factors are difficult to detect. The 

importance of climatic change on load and the resulting 

problems associated with causal analysis was noted by 

Burkholder and others (2004), who found that a series of 

drought years lowered loads (associated with reduced flow 

only) and complicated assessment of the effectiveness of bestmanagement practices and other nutrient load-reduction 

strategies.

A potentially useful technique for evaluating 

anthropogenic effects on constituent loads was used by 

Simmons and Heath (1982) to estimate predevelopment or 

background concentrations for rivers in different geochemical 

zones in North Carolina. By using a background concentration 

to calculate a load using current flow data, the effect on loads 

from anthropogenic activities can be assessed without 

considering effects due to flow. Possible shortcomings of this 

technique include (1) incorrect estimated background 

concentrations and (2) the possibly incorrect assumption that 

background concentrations estimated for small streams are the 

same as for large rivers. However, Simmons and Heath (1982) 

estimated background concentrations with the best information 

possible for the area and selected a small number of streams 

from about 200 stream sites that appeared to be as minimally 

affected by human activities as possible. Caldwell (1992) later 

updated estimates of background nutrient concentrations for 

these selected streams. 

Assumptions about whether background concentrations 

for small rivers are the same as for large rivers appear to be 

reasonable for nitrogen and phosphorus, which are the only 

constituents considered herein. The issue of stream nutrientprocessing efficiency, particularly with respect to nitrogen, in 

small as opposed to large streams (Alexander and others, 2000) 

and its effect on total nitrogen concentrations is assumed to be 

of minimal importance under presettlement conditions. The 

primary assumption is that the entire Neuse River basin was 

forested before European settlement, thus implying a low-level, 

relatively homogeneous source of nutrients to streams in the 

area. If it is assumed that during predevelopment times, erosion 

was minimal (meaning no or low transport of sorbed 

phosphorus on soil particles from uplands) and that nitrogen 

sources were limited to only fixed nitrogen from vegetation, 

then the presence or ability of microflora to process compounds 

with nitrogen and phosphorus would be of low significance, 

since concentrations in sediment and water would be low 

because there were no major sources (relative to current sources 

of nutrients) of either element for dissolution. 

Estimates of background loads using total nitrogen and 

phosphorus concentration data from Simmons and Heath 

(1982) were applied to the Neuse River basin (Harned, 1982) 

and to the Cape Fear River basin (Crawford, 1985) to evaluate 

anthropogenic effects on stream loads for several chemical 

constituents. Background nutrient concentrations for streams in 

the Neuse River basin were selected for the current study by 

using the middle value between the highest value (0.69 mg/L) 

and lowest value (0.37 mg/L), or about 0.52 mg/L for total 

nitrogen and 0.02 mg/L for total phosphorus (highest value is 

0.03 mg/L and lowest value is 0.01 mg/L) in geochemical zones 

II, IV, and V (Simmons and Heath, 1982). More recently, Smith 

and others (2003) presented nutrient yield information based on 

data collected between 1976 and 1997 from streams located in 

14 ecoregions of the United States. Median background 

concentrations for rivers in the eastern Coastal Plain were about 

0.55 mg/L for total nitrogen and 0.015 mg/L for total 

phosphorus, which appear to be very comparable to background 

concentrations used in this study. 

Although large main-stem drainages were investigated in 

previous studies (McMahon and Woodside, 1997; North 

Carolina Department of Environment and Natural Resources, 

2001), no studies have been conducted to evaluate smaller 

(< 500 mi2) subdrainages that could contribute significant 

nitrogen and phosphorus loads to the middle and lower Neuse 

River basin. In order to evaluate load contributions by small to 

large streams, annual and seasonal loads were calculated for 14 

stations in the Neuse and Contentnea Creek drainage basins for 

calendar years 2000 and 2001 (table 5; fig. 23) using techniques 

already described. In this report, loads are shown for 2000–

2001 for all stations for which complete data were collected. 

Flow data were incomplete for sites S2 (Plum Tree Branch) and 

N4 (Swift Creek near Streets Ferry) for 2001; therefore, only 

data for these sites for 2000 are given in table 5. Because flow 

so greatly affects load calculations, loads are shown for both 

years where data are available; although as previously 

indicated, the average daily flow for 2000 (3,679 ft3/s for the 

Neuse River near Fort Barnwell, Ragland and others, 2003) was 

closer to the long-term (1997–2001) average daily flow for this 

station (4,707 ft3

/s, Ragland and others, 2003) than in 2001 

(2,464 ft3

/s). Thus, estimated loads for calendar year 2000 were 

used in making load comparisons with other work conducted in 

the Neuse River basin and other locations. 

Abnormally high primary productivity of streams, lakes, 

and estuaries—or eutrophication—is often the result of elevated 

nutrient inflows from human activities and has resulted in a 

variety of undesirable effects in streams draining the 

Albemarle-Pamlico drainage basin, such as algal blooms and 

fish kills (Spruill and others, 1998). Large nutrient additions to 

the environment, including nitrogen and phosphorus 

concentrations from such human activities as agriculture and 

urban waste disposal, have been referred to by several authors 

as “cultural eutrophication” (Schlesinger, 1997). The relative 

effects of human activities on water-quality impairment with 

respect to nutrients, or cultural eutrophication effects, may be 

evaluated by comparing post-European settlement nutrient 

concentrations or loads (current conditions in rivers and 

streams) with pre-European settlement concentrations or loads 

(background conditions). This comparison for yields (load per 

unit area) was made in this report by computing the ratio of 
36 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

current annual yield to background annual yield and is referred 

to as the eutrophication loading index (ELI). 

Background loads for calendar years 2000 and 2001 were 

computed by summing the mean daily flows for each year times 

the mean daily background concentration for either nitrogen 

(0.52 mg/L) or phosphorus (0.02 mg/L). Background loads for 

14 stations for calendar years 2000 and 2001 are presented in 

table 6. Yields shown in table 6 for both total nitrogen and 

phosphorus are comparable to the estimated background yields 

presented in Smith and others (2003). The median total nitrogen 

yield in the Neuse River was 0.49 ton per square mile per year 

(ton/mi2

/yr) for the 14 stations, slightly lower than the overall 

background estimated yield of 0.56 ton/mi2

/yr for the Coastal 

Plain of the eastern United States as estimated by Smith and 

others (2003). The median total phosphorus yield for the 

14 stations in the Neuse River was 0.019 ton/mi2/yr, nearly 

identical to the 0.018 ton/mi2

/yr estimated by Smith and 

others (2003) for the Coastal Plain of the eastern United States. 

The ELI for both nitrogen and phosphorus is presented in 

table 6.

Figure 23. Loads of (A) total nitrogen and (B) total phosphorus transported at 15 stations in calendar years 2000 and 

2001 in relation to results from the Lizzie Research Station study, North Carolina.
Table 6. Annual estimated background loads and yields for total nitrogen and total phosphorus for 14 stations in the Neuse River basin, N

[USGS, U.S. Geological Survey; tons/mi2, tons per square mile]

Station name USGS station number

Background 

total nitrogen

load

(tons)

Background 

total nitrogen

yield

(tons/mi2)

Background total 

phosphorus

load

(tons)

Background total 

phosphorus

yield

(tons/mi2)

Eutrophicati

aActual yield divided by estimated background yield.

Calendar year 2000

Bear Creek at Mays Store 208925200 30 0.5 1.2 0.02 6.7 Neuse River at Kinston 2089500 1,348 .5 54 .02 2.4 Plum Tree Branch 209173190 .0001 .002 .0001 .0001 1,048 Sandy Run near Lizzie 209173200 9.2 .3 .4 .01 2.9 Middle Swamp near Farmville 2091736 16 .3 .6 .01 2.4 Little Contentnea near Willow Green 2091737 47 .3 1.9 .01 2.1 Little Contentnea at Scuffleton 2091740 83 .5 3.3 .02 1.9 Contentenea Creek near Lucama 2090380 86 .5 3.5 .02 1.6 Contentnea Ceek near Evansdale 2090519 136 .5 5.4 .02 3.9 Nahunta Swamp near Shine 2091000 32 .4 1.3 .03 3.4 Contentnea Ceek at Hookerton 2091500 378 .5 15 .02 2.5 Neuse River near Fort Barnwell 2091814 1,867 .5 75 .03 2.2 Trent River near Trenton 2092500 96 .6 3.9 .02 2.2 Swift Creek near Streets Ferry 209205053 158 .6 6.3 .02 2.6 

Calendar year 2001

Bear Creek at Mays Store 208925200 22 0.4 0.9 0.01 7 Neuse River at Kinston 2089500 930 .3 37 .01 2.2 Sandy Run near Lizzie 209173200 3.9 .1 .2 .01 2.7 Middle Swamp near Farmville 2091736 7.4 .1 .3 .01 2.4 Little Contentnea near Willow Green 2091737 26 .2 1.0 .01 2 Little Contentnea at Scuffleton 2091740 50 .3 2 .01 2.1 Contentenea Ceek near Lucama 2090380 58 .4 2.3 .01 1.6 Contentnea Ceek near Evansdale 2090519 93 .4 3.7 .01 5.2 Nahunta Swamp near Shine 2091000 22 .5 .9 .01 3.3 Contentnea Ceek at Hookerton 2091500 260 .4 10 .01 2.4 Neuse River near Fort Barnwell 2091814 1,184 .3 47 .01 2.1 Trent River near Trenton 2092500 41 .2 1.6 .01 2.3 

Total 

nitrogen
38 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

Atmospheric Nutrient Loads in the Plum Tree 

Branch and Sandy Run Subbasins

Monthly precipitation totals measured at a weather station 

near Lizzie, N.C. (stations 0209173196, S1-A, fig. 2, and 

353137077332801, S1-B, fig. 2), were summed to produce 

annual precipitation totals for 2000 and 2001. The drainage 

areas of Plum Tree Branch and Sandy Run were then multiplied 

by these totals, and the results were converted to liters and 

multiplied by the median measured concentration of nitrogen 

from precipitation samples. Based on this method, atmospheric 

deposition at Plum Tree Branch (S2, fig. 2) was estimated to be 

1.14 tons of nitrogen in 2000 (about 2 tons/mi2) and 0.51 ton in 

2001 (about 1 ton/mi2

). In Sandy Run (S4, fig. 2), atmospheric 

deposition was determined to be 60 tons of nitrogen in 2000 and 

26.7 tons in 2001. In 2000, atmospheric phosphorus deposition 

in the Plum Tree Branch watershed was estimated to be 

0.0012 ton, and 0.006 ton in the Sandy Run watershed. Loads 

for 2001 were not calculated because the detection limit was too 

high (all values were reported as < 0.007 mg/L in 2001).

Little Contentnea Creek Subbasin

Annual nutrient loads in the Little Contentnea Creek 

drainage subbasin for calendar years 2000 and 2001 for Plum 

Tree Branch (S2), Sandy Run (S4), Middle Swamp (S5), Little 

Contentnea Creek near Willow Green (S6), and Little 

Contentnea Creek at Scuffleton (S16, fig. 2) ranged from about 

0.8 ton to about 160 tons for total nitrogen and from 0.02 ton to 

26 tons for total phosphorus (fig. 23). Yields for total nitrogen 

ranged from 0.33 to 2.53 tons/mi2

 (fig. 24) and for total 

phosphorus from 0.02 to about 0.15 ton/mi2 (fig. 25). Based on 

nitrogen and phosphorus seasonal load data (table 5), 69 to 

87 percent of the total nitrogen and 55 to 81 percent of the total 

phosphorus load was transported during the winter and spring.

All streams included in this study had lower nitrogen 

yields (less than 1 ton/mi2) than the first-order Plum Tree 

Branch (2.53 tons/mi2

). Sandy Run, a second-order stream that 

drains about 30 mi2

, transported between 0.3 and 0.8 ton/mi2 

during 2000–2001. The next two downstream sampling points 

S5 (Middle Swamp near Farmville, drainage area = 51 mi2

) and 

S6 (Little Contentnea Creek near Willow Green, drainage 

area=152 mi2) transported between 0.3 and 0.74 ton/mi2

(fig. 24; tables 1, 2). Little Contentnea Creek at Scuffleton 

(S16) transported slightly more nitrogen, 0.9 ton/mi2

 in 2000 

and 0.6 ton/mi2 in 2001. During 2000 and 2001, the total 

nitrogen loads were more than 1,000 times the estimated 

background loads for the first-order stream, Plum Tree Branch, 

and about two times or less the estimated background loads in 

the third- and higher-order streams in the Little Contentnea 

Creek drainage basin. Total nitrogen yields for second- or 

higher-order streams ranged from 0.35 to about 0.95 ton/mi2

, 

with a median load of about 0.60 ton/mi2

. However, nitrogen 

Figure 24. Annual total nitrogen yield at selected stations in 

the Little Contentnea Creek subbasin, North Carolina.

Figure 25. Annual total phosphorus yield at selected stations in 

the Little Contentnea Creek subbasin, North Carolina.
Nutrient Loading in the Neuse River Basin During 2000 and 2001 in Relation to Background Loads 39

transport from the small first-order stream, Plum Tree Branch, 

was much higher relative to the larger second- and higher-order 

streams, implying loss of nitrogen as it moved through the 

drainage basin. 

Phosphorus behaves differently, however. Although total 

phosphorus yields in Plum Tree Branch were more than 300 

times the estimated background loads and second- and higherorder streams in the subbasin transported approximately 8–12 

times the estimated background phosphorus load in 2000 and 

2001, overall phosphorus yields were higher in larger streams 

than in the first-order Plum Tree Branch (fig. 25) and remained 

fairly constant at downstream stations. In contrast to total 

nitrogen yields, larger total phosphorus yields were found in the 

higher-order streams (about three times greater), indicating 

either that a major source of phosphorus in the Little Contentnea 

Creek subbasin originates in the larger streams, such as detritus 

from vegetation deposited in sediments, or that phosphorus load 

estimates for Plum Tree Branch are too low, perhaps because of 

inadequate sampling of high-flow events. The low phosphorus 

loads measured in Plum Tree Branch may be because extreme 

high flows that could mobilize sediment movement were not 

represented by the monthly water samples. 

Anthropogenic activities in the basin have caused much 

greater increases in phosphorus loads than nitrogen loads 

relative to expected background loads, with greatest effect of 

phosphorus enrichment occurring in the higher-order streams. 

Geochemical processes that occur in this basin, as demonstrated 

at the Lizzie Research Station site, suggest that coincident 

processes and mobilization and release of phosphorus under 

reducing conditions in aquifers and streams in this region may 

account for the relatively greater observed anthropogenic 

enrichment of phosphorus relative to nitrogen.

Contentnea Creek Subbasin

Contentnea Creek is considered a major contributor of 

nitrogen and phosphorus to the Neuse River (Spruill and others, 

1996). Nutrient loads transported at four stations in the 

Contentnea Creek basin are shown in figures 26 and 27. The 

most upstream station sampled for this study, Contentnea Creek 

near Lucama (S11, fig. 1), which drains about 159 mi2 and is 

located just downstream from Buckhorn Reservoir, transported 

0.87 and 0.6 ton/mi2 of total nitrogen in 2000 and 2001, 

respectively, which is about 1.6 times more than the estimated 

background load for total nitrogen (fig. 26). This station 

transported about 0.05 and 0.02 ton/mi2 of total phosphorus in 

2000 and 2001, respectively, which is about 2 and 1.5 times the 

expected background load (fig. 27). Contentnea Creek near 

Lucama had the lowest ELI (1.6 for nitrogen and 2.1 for total 

phosphorus, table 6) of all streams included in this 

investigation. This may be in part because the station is located 

downstream from a reservoir, which may remove much of the 

nitrogen and phosphorus load. Seasonally, between 55 and 

92 percent of the total nitrogen and 56 and 81 percent of the 

total phosphorus were transported during the winter and spring 

(table 5).

The next site downstream, Contentnea Creek near 

Evansdale (S14, fig. 1), transported 2.0 and 1.84 tons/mi2

 of 

total nitrogen in 2000 and 2001 (fig. 26), which were about 5.2 

and 3.8 times, respectively, the expected background total 

nitrogen load for these years. This site apparently receives 

substantial quantities of nitrogen and has the highest yields in 

the basin, which decrease downstream to Hookerton (fig. 26). 

Contentnea Creek near Evansdale (S14) transported about 0.07 

and 0.06 ton/mi2

 of total phosphorus in 2000 and 2001 (fig. 27), 

which were about 3.6 and 4 times the estimated background 

loads (table 6). 

Nahunta Swamp, the next major tributary inflow to 

Contentnea Creek, also transported more than three times the 

estimated background load for total nitrogen. Phosphorus yields 

increased at the next downstream station, Contentnea Creek at 

Hookerton (S18, fig. 1), indicating new sources of phosphorus. 

This site, which is the most downstream station in the 

Contentnea Creek drainage basin before receiving inflow from 

Little Contentnea Creek, transported 1.28 and 0.85 ton/mi2

 of 

total nitrogen in 2000 and 2001, respectively (fig. 26), about 

two times the expected total nitrogen background load. This 

station transported 0.12 and 0.09 ton/mi2

 of total phosphorus, 

the second highest observed in the subbasin and about five to 

six times the expected background load. As noted for the Little 

Contentnea Creek subbasin, the generally greater ELI of 

phosphorus relative to nitrogen may be because of reducing 

Figure 26. Annual total nitrogen yield at selected 

stations in the Contentnea Creek subbasin, North 

Carolina.
40 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

conditions in aquifer sediments and streams in the watershed 

that reduce nitrogen and release phosphorus. 

 The 2000 and 2001 yields for nitrogen 

and phosphorus reported for Contentnea 

Creek at Hookerton are considerably lower 

than those reported by McMahon and 

Woodside (1997) for 1990 (total nitrogen 

yield = 1.83 tons/mi2

; total phosphorus 

yield = 0.21 ton/mi2). Average streamflow 

in 1990, 2000, and 2001 for Contentnea 

Creek at Hookerton was 677, 767, and 

529 ft3

/s, respectively (U.S. Geological 

Survey, 2004); therefore, the change in load 

was probably not due to a major difference 

in streamflow. Harned (2003) reported a 

decrease in both total nitrogen and 

phosphorus concentrations between 1974 

and 2003 and suggested that part of this 

decrease could be a result of the 

implementation of the 1997 NCDENR 

DWQ management rules to reduce nitrogen 

loading to the Neuse River. Another 

possibility is that the percentage of 

agricultural land since the late 1980s in the 

entire Contentnea Creek watershed has 

decreased from 50 percent in 1987 

(McMahon and Lloyd, 1995) to 42 percent in 1999 (Harned, 

2003).

Neuse River Basin

Total nitrogen yields for five stations in the Neuse River 

drainage basin are shown in figure 28. Bear Creek (N1, fig. 1), 

which drains into the Neuse River just west of Kinston, N.C., 

transported 3.4 and 2.6 tons/mi2 of total nitrogen in 2000 and 

2001, respectively, about seven times the expected background 

load. The ELI for this site is one of the highest observed for all 

sites included in this study (table 6). Total phosphorus yields at 

this site were 0.17 and 0.15 ton/mi2

, or about 8–10 times the 

background yield (fig. 29; table 6). Because no National 

Pollutant Discharge Elimination System (NPDES)-permitted 

dischargers are reported to be in the Bear Creek watershed, it is 

assumed that the entire nutrient load is derived from nonpoint 

sources. Because Bear Creek had some of the highest yields for 

both nitrogen and phosphorus, further study of this watershed 

could provide useful information about the fate and transport of 

nutrients and provide an opportunity to evaluate the 

effectiveness of land-management practices. The Bear Creek 

basin has the highest percentage of cropland (59 percent) of all 

basins included in this study (table 1), and a previous study 

(Woodside and Simerl, 1995) indicated that this basin had more 

than 1.5 million poultry in 1994.

Figure 27. Annual total phosphorus yield at selected 

stations in the Contentnea Creek subbasin, North 

Carolina.

Figure 28. Annual total nitrogen yield at selected stations in the Neuse River basin, 

North Carolina.
Nutrient Loading in the Neuse River Basin During 2000 and 2001 in Relation to Background Loads 41

The Neuse River at Kinston (N2, fig. 1) yield was 1.21 and 

0.75 tons/mi2 for 2000 and 2001, respectively, two times higher 

than the background yield for nitrogen (fig. 28; table 6). The 

total phosphorus yields were 0.11 and 0.08 ton/mi2 (fig. 29), 

about five times the expected loading rate for background 

conditions. These nutrient yields are slightly lower than those 

reported for 1990 by McMahon and Woodside (1997), when the 

total nitrogen yield was 1.62 tons/mi2 and the total phosphorus 

yield was 0.12 ton/mi2. 

The Neuse River near Fort Barnwell (N3, fig.1) had total 

nitrogen yields of 1.06 and 0.63 tons/mi2 in 2000 and 2001, 

respectively (fig. 28), about twice the estimated background 

yield (table 6). Total phosphorus transported at this site, 0.08 

and 0.06 ton/mi2 (fig. 29), was four and five times the expected 

background load. 

The Trent River near Trenton (N5, fig. 1) transported 1.24 

and 0.55 tons/mi2 of nitrogen in 2000 and 2001, respectively, 

and Swift Creek near Streets Ferry (N4, fig. 1) transported 

1.54 tons/mi2 in 2000 (fig. 28). Nitrogen yields were between 

two and three times the background, similar to other streams in 

the Neuse River basin. Phosphorus yields in 2000 from the 

Trent River (0.2 ton/mi2) and Swift Creek (0.29 ton/mi2; 

fig. 29) were the highest observed for all of the streams included 

in this study and 8 and 12 times, respectively, the estimated 

background yields (table 6). The combined total phosphorus 

load from Swift Creek and Trent River for 2000 was 114 tons, 

about 26 percent of the total load entering the Neuse River 

estuary at New Bern (fig. 1), which represents only about 

10 percent of the contributing drainage area. Because these 

two streams are located so near the upper Neuse estuary where 

eutrophication effects are an issue, 

determining the reasons the loads of 

phosphorus near New Bern are elevated is 

worthy of further investigation. Possible 

reasons for elevated phosphorus loads from 

these streams are geochemically reducing 

ground water moving from aquifers that 

may contain high phosphorus 

concentrations and water moving through 

phosphorus-laden sediment that could 

contribute substantial phosphorus loads to 

the estuary near New Bern. 

Because both Swift Creek and the 

Trent River directly discharge to the Neuse 

River estuary, the large amount of 

phosphorus entering from these two streams 

is likely to cause nitrogen to be the growthlimiting element for phytoplankton in this 

portion of the estuary, particularly during 

summer months when 32 percent of the 

phosphorus load to the estuary is from both 

Swift Creek and the Trent River (table 5). 

Because few point-source dischargers are 

located in Swift Creek and none in the Trent 

River (sites N4 and N5, table 1), it appears 

likely that phosphorus from these two 

watersheds is derived from nonpoint sources.

Loads and Sources of Nutrients to the Neuse 

Estuary, Calendar Year 2000

Water quality of the Neuse River and estuary has been 

impaired in the past by an overabundance of nutrients (Tedder 

and others, 1980; Paerl, 1987; Paerl and others, 1995; 

Burkholder and Glasgow, 1997; Spruill and others, 1998; Stow 

and Borsuk, 2003). Section 303D of the Clean Water Act of 

1972 requires that States identify impaired water bodies and 

implement a total maximum daily load (TMDL) for each 

problem contaminant (McMahon and others, 2003). The 

NCDENR DWQ (North Carolina Department of Environment 

and Natural Resources, 2001) determined that excessive 

chlorophyll a occurs in the estuary between the Streets Ferry 

Bridge and Cherry Point and, based on research conducted over 

the last decade, found that “nitrogen has the best potential to 

limit chlorophyll a in the estuary.” According to the NCDENR 

(1999), phosphorus was eliminated as a nutrient to control 

chlorophyll a primarily because (1) nitrogen to phosphorus 

ratios generally indicate nitrogen limitation in the Neuse River 

estuary, (2) much of the phosphorus loading in the Neuse 

estuary was naturally occurring and extremely difficult to 

manage, and (3) phosphorus loads have decreased over much of 

the basin, so that reducing phosphorus loads will not have as 

much effect as reducing nitrogen loads. Thus, nitrogen was the 

primary nutrient targeted to control the occurrence of 

chlorophyll a in the Neuse estuary (North Carolina Department 

Figure 29. Annual total phosphorus yield at selected stations in the Neuse River basin, 

North Carolina.
42 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

of Environment and Natural Resources, 2001). A 30-percent 

reduction from 9.65 million pounds baseline load to 

5.92 million pounds for New Bern (North Carolina Department 

of Environment and Natural Resources, 2001) was adopted as 

the total nitrogen TMDL. 

 In order to reach the Neuse TMDL goal, an accurate 

accounting of the amount of nitrogen entering the estuary is 

necessary before the effectiveness of nitrogen reductions can be 

measured. In addition to the total quantity of a nutrient 

delivered, an accurate accounting of the quantity delivered by 

individual source categories is required in order to determine 

where and how much each nutrient can be reduced. A major 

objective of this study is to characterize nitrogen loading in 

streams draining the Neuse River, not just for simple accounting 

of loads transported by various streams but also in light of 

processes that appear to be occurring in the watershed at varied 

scales. Findings from research activities conducted at the Lizzie 

Research Station to improve understanding of nutrient transport 

could assist in management of the Neuse River.

In order to understand nutrient transport in the Neuse River 

and the Neuse River estuary, several studies have attempted to 

account for nitrogen loading (Dodd and others, 1992; Harned 

and others, 1995; North Carolina Department of Environment 

and Natural Resources, 2001; McMahon and others, 2003) and 

nitrogen and phosphorus (McMahon and Woodside, 1997). 

Some of the more recent efforts associated with development of 

a nitrogen TMDL are described in NCDENR (2001). 

The following discussion includes estimates of total 

nitrogen loads delivered to the Neuse River estuary in 2000 

(fig. 30) made in this study and in two other recent studies 

(North Carolina Department of Environment and Natural 

Resources, 2001; McMahon and others, 2003) to provide and 

compare estimation methods to management with respect to the 

accuracy and practical application of each method, and to 

provide possible reasons why the estimates differ. Because 

many of the TMDL discussions in NCDENR (2001) refer to 

pounds as the unit of mass transported, pounds of nutrients are 

shown with tons transported for the reader’s convenience. 

Estimates for phosphorus loads also are discussed. Nutrient 

loads at the Neuse River near Fort Barnwell (N3), Swift Creek 

near Streets Ferry (N4), and Trent River near Trenton (N5, 

fig. 1) are presented for calendar year 2000 only because 

discharge data from Swift Creek near Streets Ferry were 

incomplete for calendar year 2001 and because, hydrologically, 

calendar year 2000 was closer to the average flow conditions for 

the Neuse River, as indicated previously. 

Based on results from this study, the total nitrogen load 

delivered to the Neuse River estuary near New Bern, N.C. 

(fig. 1), in 2000 was 4,807 tons (table 5), or 9.61 million 

pounds, and 425 tons for total phosphorus (table 5), or 

850,000 pounds. It is estimated that about 17 percent 

(1,630,000 pounds) of the delivered total nitrogen load is due to 

background sources based on the background total nitrogen 

concentration of 0.50 mg/L used in this analysis. This 

background estimate is larger than the 8.6-percent 

(830,000 pounds) background total nitrogen load reported by 

NCDENR (2001) for 1995, but less than the 30 percent 

estimated by the USGS spatially referenced regression on 

watershed (SPARROW) attributes study (McMahon and others, 

2003) for 1992. The average total nitrogen load, based on data 

from Fort Barnwell, Trent River, and wastewater-treatment 

plants (WWTP) below Fort Barnwell and delivered to the 

Neuse estuary, was 9.65 million pounds for the base period 

(1991–95; North Carolina Department of Environment and 

Natural Resources, 2001). The load reported herein for calendar 

year 2000 (9.61 million pounds) is comparable to the load for 

the base period.

The background load estimate from this report 

(1.63 million pounds), based on the percentage of forested land 

in each basin in 2000 multiplied by the sum of background 

loads for 2000 from Fort Barnwell, Swift Creek near Streets 

Ferry, and Trent River near Trenton, assuming 100-percent 

forested land cover for all three basins (4.24 million pounds), 

was used as a basis for estimating anthropogenic contributions 

of nitrogen. The total 9.61 million pounds of total nitrogen 

delivered during 2000 minus the estimated background load of 

1.63 million pounds (which consists primarily of loads from 

forested land), yielded an anthropogenic load, by difference, of 

approximately 7.98 million pounds. Using the 1995 pointsource contribution of 3.32 million pounds as an estimate of 

point-source load (North Carolina Department of Environment 

and Natural Resources, 2001), the anthropogenic nonpointsource load in the Neuse basin would be 4.66 million pounds, 

somewhat less than the 5.5 million pounds estimated to be from 

nonpoint sources reported by NCDENR (2001) and 8.12 

million pounds estimated from 1992 data using SPARROW 

(McMahon and others, 2003, and Gerard McMahon, U.S. 

Geological Survey, written commun., 2004).

 The variation of load estimates by three different 

approaches raises questions about accuracy and comparability 

of different methods used to estimate loads from different 

sources. Primary reasons for the observed variability in 

methods relate to flow conditions used in computations and 

methods used to compute individual source loads. The 

percentages of total nitrogen in water transported from the 

Neuse River basin into the Neuse estuary from background and 

anthropogenic point and nonpoint sources from this study, the 

NCDENR TMDL study (North Carolina Department of 

Environment and Natural Resources, 2001), and from the 

SPARROW model (McMahon and others, 2003, and Gerard 

McMahon, U.S. Geological Survey, written commun., 2003) 

are shown in figure 30. These graphs show relatively wide 

variations in loads transported to the Neuse estuary, from 

14 million pounds in 1992 (SPARROW model, McMahon and 

others, 2003), 9.65 million pounds for the period 1991–95 

(North Carolina Department of Environment and Natural 

Resources, 2001), and 9.61 million pounds in 2000, as reported 

in this study. Individual source category load estimates also 

varied widely. Background loads ranged from 9 percent (North 

Carolina Department of Environment and Natural Resources, 

2001) to more than 30 percent of the total nitrogen load 

determined by the SPARROW model (McMahon and others, 
Nutrient Loading in the Neuse River Basin During 2000 and 2001 in Relation to Background Loads 43

Figure 30. Sources of total nitrogen, estimated by three different methods, delivered to the 

Neuse River estuary at New Bern, North Carolina.
44 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

2003, and Gerard McMahon, U.S. Geological Survey, written 

commun., 2004). The point-source load varied from 9 percent 

in 1992 to more than 30 percent in both 1995 and 2000 (fig. 30).

Because data from NCDENR were used in two of the three 

methods—North Carolina Department of Environment and 

Natural Resources (2001) and this study—based on information 

filed by individual dischargers to the North Carolina DWQ for 

1995, the resulting large difference in point-source load 

contribution between the SPARROW model and this study and 

the NCDENR (2001) report underscores the need for a standard 

reproducible method to compute point-source loads to streams. 

Although possible, it appears unlikely that the point-source load 

was lower (1.33 million pounds from the SPARROW model) in 

1992 than in 1995, particularly assuming improved treatment 

technology through time. One likely reason for the observed 

difference is the method used for point-source load 

determination. Because point-source loads are the most 

regulated and controllable source information for nutrients, 

improved data (minimum of daily discharge with daily 

concentration data), improved data storage and retrieval 

capability, and standard methods of reporting and computing 

point-source discharge data could greatly increase the accuracy 

and reduce the variability of this very important, if not the most 

important, source of nutrient load information.

Background nitrogen estimates used for the three different 

methods also account for much of the variability observed. 

McMahon and others (2003) used a SPARROW model 

coefficient of 0.51 ton/mi2. This method resulted in a 

background load of about 4.6 million pounds delivered to the 

Neuse estuary, or 30 percent of the total load, under the average 

flow conditions used for developing the SPARROW model. 

The background load for the Neuse used by NCDENR (2001) 

also was determined by using land delivery coefficients 

(0.53 ton/mi2

) from Dodd and others (1992), which resulted in 

86,000 pounds, the lowest background load of the three 

methods considered. According to methods used for 

development of the TMDL reported by NCDENR (2001), 

expected yields in tons per acre from each source were 

computed for each land-use category and then proportionally 

allocated to the annual load that remained after subtracting the 

estimated point-source load from the total delivered nitrogen 

load. For this report, as described previously, the background 

concentration of 0.50 mg/L was used for forested land, the 

expected load was computed from the actual amount of forested 

land in each basin, and then this amount was subtracted from the 

total load at New Bern, N.C. 

The advantage of the method used for calculating 

background loads for this report, compared to the other two 

methods described, is that the background load (1) is calculated 

independently of the other loads used in the total load 

calculations and (2) is based on measured concentrations from 

streams that are thought to best represent background 

conditions. As shown earlier, these concentrations compare 

favorably with concentrations derived independently by Smith 

and others (2003). In addition, because the background quantity 

used for this report is a concentration, monthly, seasonal, or 

annual loads also can be calculated easily using available flow 

information. Both the SPARROW and NCDENR (2001) 

methods are dependent on the point loads used in the 

computation—loads are allocated across the remaining source 

categories after the point-source load has been subtracted. 

Therefore, the difference in point-source load magnitude used 

in McMahon and others (2003) and by NCDENR (2001) could 

largely account for the widely different background loads 

reported. 

The total phosphorus load transported to the Neuse estuary 

in 2000 was 425 tons. As for nitrogen, accurate and easily 

available point-source information is necessary for computing 

meaningful phosphorus loads. Because of the focus on nitrogen 

over the last decade, however, no recent published information 

was found on total point-source contributions of phosphorus to 

the Neuse River near Fort Barnwell; therefore, general 

estimates from past studies were used. Based on previous 

estimates of total phosphorus load of 0.04 ton/mi2

 from point 

sources in the Albemarle-Pamlico drainage basin (Stanley, 

1989), which also was used by McMahon and Woodside 

(1997), about 175 tons of phosphorus were estimated delivered 

to the estuary by point sources in 2000. Also, as was done for 

nitrogen, background phosphorus was calculated by 

multiplying the actual percentage of forested area in each of the 

three basins by the total background loads computed assuming 

100 percent forested land cover for each basin. By adding the 

estimated background load of 31 tons obtained using the 

background phosphorus concentration of 0.02 mg/L (Simmons 

and Heath, 1982; Smith and others, 2003) to the point-source 

load of 175 tons and subtracting this sum from the total load to 

the Neuse estuary, the resulting nonpoint total phosphorus load 

was 219 tons in 2000. Based on this analysis, about 7 percent 

was from background sources with about 93 percent of the total 

phosphorus load in 2000 derived from anthropogenic point 

(41 percent) and nonpoint (52 percent) sources (fig. 31).

The analysis of phosphorus loads from this study raises 

questions regarding background sources of phosphorus because 

previous researchers have indicated very high background 

sources in the Neuse River basin (Paerl, 1987; Spruill and 

Figure 31. Sources of total phosphorus delivered to the Neuse 

River estuary at New Bern, North Carolina, in calendar year 2000.
Nutrient Loading in the Neuse River Basin During 2000 and 2001 in Relation to Background Loads 45

others, 1998; North Carolina Department of Environment and 

Natural Resources, 2001), and yet the estimated background 

load in this study yielded only 7 percent of the total delivered 

phosphorus load to the Neuse River estuary (fig. 31). 

There are several reasons for the apparent discrepancy 

between what the available data indicate with respect to 

background phosphorus (only 7 percent of the total phosphorus 

load to the Neuse River estuary) and what previous researchers 

have reported with respect to background, such as high ambient 

concentrations (Paerl, 1987) and high phosphorus from 

geologic sources (Spruill and others, 1998). In general, 

however, the primary reason for this apparent discrepancy is 

that the sources of phosphorus are not particularly well 

understood and defined with respect to time, space, and scale or 

landscape position in a watershed in the nutrient-source 

accounting process. For example, where ground water 

discharges to a stream and is a source of phosphorus, the origin 

of the phosphorus must be determined—is it an anthropogenic 

source, such as derived from the land surface from some 

anthropogenic activity and transported to the water table and 

then discharged to surface water; or a background source, such 

as directly discharged from an unconfined or confined aquifer 

with phosphorus-containing matrix material; or simply 

transported into surface water by ground water flowing through 

recent fluvial streambed deposits that have been eroded from 

uplands as part of some anthropogenic activity (farming) and 

then deposited in the streambed? 

Some clues to the answer to the above question can be 

obtained from work conducted for this study at the Lizzie 

Research Station and from previous work. Spruill and others 

(1998) indicated geologic sources of phosphorus in the Neuse 

and Tar-Pamlico basins as evidenced by elevated phosphorus 

concentrations (0.1 mg/L) that are not reflected in the 

phosphorus concentration data reported for small streams by 

Simmons and Heath (1982) or Smith and others (2003). Spruill 

and others (1998) reported a significant correlation between 

ground-water and surface-water concentrations of dissolved 

phosphorus in coastal plain streams, indicating that phosphorus 

most likely was derived either from the bed material of streams 

or from aquifer material from which ground water is 

discharged. If the phosphorus were contained in water from a 

confined aquifer, such as the Yorktown (table 3) with water 

ages of greater than 30–50 years, it is likely that the age of the 

streamwater would reflect the ground-water contribution from 

this source. Using silica data, the median age of water from the 

larger streams at the Lizzie Research Station site, Sandy Run 

and Middle Swamp (fig. 16), was determined to be less than 

5 years, which indicates very little contribution of ground water 

by the confined aquifer and no geologic source. Therefore, the 

relatively young age of water in Sandy Run and Middle Swamp 

indicates discharge of young ground water through bed material 

that contains phosphorus, derived either from decomposing 

vegetation and(or) from sediment eroded from uplands. As 

described in Spruill (2000), phosphorus on the bed material can 

be deposited as a result of sediment containing high phosphorus 

concentrations eroded from uplands and then released by 

organic carbon-rich (1–25 mg/L, table 3), oxygen-deficient 

(generally less than 0.3 mg/L, table 3), geochemically reducing 

ground water as it passes through the streambed sediments and 

riparian areas before discharging to the stream. In addition, 

reducing conditions that occur in the streams in the Little 

Contentnea watershed during the summer low-flow periods, 

which tend to reduce nitrate (fig. 14), are the same conditions 

that can chemically liberate phosphorus. 

Effects of cultural eutrophication with respect to 

phosphorus enrichment in coastal plain streams of the Neuse 

River basin are much greater than for nitrogen. The ELI range 

for phosphorus was 2–12 times with values typically 5–6 times 

the estimated background yield for second- and higher-order 

streams. The ELI range for total nitrogen was 1–5, with values 

typically about 2 times the estimated background yield. This 

finding contrasts with those of Smith and others (2003) that 

enrichment from background with respect to nitrogen was 

generally greater (6.4) than for phosphorus (2.0). The nitrogen 

and phosphorus enrichment reported here is in agreement with 

Simmons and Heath (1982), who found that agricultural 

streams in North Carolina had 2–13 times the baseline 

concentrations of phosphorus during stormflow conditions 

compared to 1–5 times baseline concentrations for total 

nitrogen.

The higher ELI for phosphorus relative to nitrogen in the 

Neuse River basin may be because phosphorus is closely 

associated with sediment (Schlesinger, 1997) and because 

sediment erosion rates in many areas are substantially higher 

today than a few centuries ago as a result of clearing of 

vegetation for agriculture and development (Pimentel and 

others, 1995). A possible reason that phosphorus yields are 

higher than nitrogen yields compared to background yields in 

the Neuse River basin is again provided by process-oriented 

studies conducted at the Lizzie Research Station. Oxidationreduction (redox) conditions in bed sediment and riparian zones 

along rivers that tend to reduce oxidized chemical species in 

ground water, such as nitrate, that result from farming practices 

and discharge to streams are the same processes that can 

mobilize phosphorus. Thus, denitrification, which takes place 

in the streambed sediments prior to ground water discharging to 

the stream, is a natural mechanism that can reduce nitrogen 

loading by converting part of the nitrogen, as nitrate, to nitrogen 

gas (fig. 17).

The loading rate for phosphorus in the Neuse River basin 

is greatest in the upper Neuse estuary, where potential effects on 

algal growth are substantial. Based on data presented in Qian 

and others (2000), phosphorus concentrations remain near 

0.2 mg/L at three stations in the upper Neuse estuary just above 

and below New Bern, N.C. Although both phosphorus and 

nitrogen concentrations have declined throughout much of the 

Neuse basin since 1990 (Qian and others, 2000), phosphorus 

declines are less evident near New Bern; nevertheless, Qian and 

others (2000) concluded that the upper estuary has shifted to 

phosphorus limitation. High loading rates for phosphorus from 

Swift Creek near Streets Ferry and Trent River near Trenton, 

however, during the summer months could sustain phosphorus 
46 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

concentrations in the upper Neuse estuary, thus favoring 

nitrogen limitation.

While management actions to control nitrogen throughout 

the basin may help in controlling nuisance algal blooms and fish 

kills under average hydrologic conditions, large amounts of 

nitrogen moving into the estuary as a result of extreme events, 

such as during hurricanes or extended wet periods, may cause 

algal growths of much greater severity than would occur if 

phosphorus discharges from Swift Creek and the Trent River 

were lower. This is because the potential for algal growth is 

greater as more phosphorus is available—a pound of 

phosphorus has the potential for producing as much as 

77 pounds of algal cells (Lamb, 1985). Thus, if 0.1 mg/L of 

phosphorus is available, 7.7 mg/L of algal biomass may be 

produced if nitrogen is not limiting. It becomes even more 

important to control phosphorus sources if phosphorus is the 

growth-limiting nutrient. At any rate, this potential problem 

warrants further investigation into the cause of high phosphorus 

concentrations in the Neuse River at New Bern, N.C., and 

consideration for managing phosphorus loads into the estuary. 

Such a study could result in findings to support application of 

management techniques to control phosphorus that could 

substantially improve water quality and have long-term benefits 

for the Neuse River estuary.

Evidence from this study indicates that most of the water 

in second- and higher-order streams is apparently composed of 

relatively young water, as determined by the evaluations of 

tritium and silica data (fig. 16), and that most of the base flow 

in the basin is derived from ground water in alluvial aquifers 

located in riparian areas adjacent to streams. Therefore, a 

logical method for preventing nonpoint-source contaminants 

from entering streams would be to limit or prevent development 

within riparian corridors along streams. Alluvial aquifers in 

riparian areas appear to be the source of most of the water in the 

Neuse River and its larger tributaries, and any activities along 

river terraces and riparian areas that could be a source of 

nutrients (particularly nitrate) or other contaminants are more 

likely to affect the water quality of the receiving stream. The 

actual widths of riparian areas required to minimize nitrate 

contamination from nonpoint sources could be determined by 

incorporating estimates of ground-water velocities toward the 

discharge points during wet periods, nitrogen loading rates to 

fields, and estimated rates of denitrification derived from field 

studies in different hydrologic settings. In addition, because 

very little nitrogen loss takes place in larger streams (Alexander 

and others, 2000) and because point-source discharges of 

nitrogen and phosphorus are a significant part of the 

anthropogenic load in the Neuse River (greater than 30 percent 

according to North Carolina Department of Environment and 

Natural Resources, 2001), substantial improvements in water 

quality in the Neuse River could be made by identifying 

discharge points that have major effects on river water quality 

and by improving wastewater-treatment capabilities of the 

discharge facilities.

Summary and Conclusions

Chemical, geologic, hydrologic, and age-dating 

information collected from 1999 to 2002 was used to examine 

the transport of contaminants, primarily nitrogen, in ground 

water and their pathways to surface water in a coastal plain 

setting in the southeastern United States—the Lizzie Research 

Station near Lizzie, N.C. Data were collected from more than 

35 wells and 4 surface-water sampling sites located in a 

0.59 -mi2 basin to examine detailed hydrogeology and 

geochemical processes affecting nutrient fate and transport. 

Two additional surface-water sampling sites were located 

downstream from the primary study site to evaluate basin-scale 

effects. Chemical and flow data also were collected at an 

additional 10 sites in the Coastal Plain portion of the Neuse 

River basin between Kinston and New Bern, N.C., to evaluate 

loads transported in the Neuse River and primary tributary 

basins. 

At the Lizzie Research Station site, horizontal flow is 

induced by the presence of a confining unit at shallow depth. 

Age-dating, chemical, and piezometric data all indicate flow 

from the surficial and alluvial aquifers as the dominant source 

of ground water to streamflow. In the uplands, the upper several 

feet of saturated thickness of the surficial aquifer is the only 

zone in which nitrate is stable. Denitrification in deeper parts of 

the aquifer and in the riparian zones is indicated by a 

characterization of redox conditions in the aquifer and by the 

presence of excess levels of nitrogen. Direct ground-water 

discharge of nitrate to surface water during base-flow 

conditions is unlikely to be significant because of strongly 

reducing conditions in the riparian zones of the streams. 

Instantaneous nitrate loads from a drainage tile at the Lizzie 

Research Station study site may account for much of the nitrate 

load in the receiving stream, which suggests that artificial 

drainage is a major source of nutrients from ground water to this 

stream. During base-flow conditions, when these artificial 

drainages are not flowing, it is hypothesized that the 

mineralization of organic matter on the streambed is a major 

source of nitrate and(or) ammonium in the stream. Base flow is 

only a small contributing factor to loads, because both flow and 

inorganic nitrogen concentrations are low. 

The use of sprayed swine wastes on fields planted in crops 

at the Lizzie Research Station study site resulted in increased 

concentrations of nitrate and other chemical constituents in 

ground water beneath spray fields compared to ground water 

beneath crops treated with commercial fertilizer. No change in 

dissolved phosphorus concentrations was observed in ground 

water beneath the spray field, and no phosphorus concentration 
Summary and Conclusions 47

exceeded 0.02 mg/L, which indicates that phosphorus is 

primarily adsorbed in the soil matrix prior to reaching shallow 

ground water. The nitrate concentration in ground water from 

the spray field well increased by a factor of 3.5 after 4 years of 

spray applications. Nitrate concentrations ranged from 10 to 

35 mg/L, and one concentration as high as 56 mg/L was 

observed in water from this well in spring 2002. Overapplication of swine wastes is a possible cause of elevated 

nitrate concentrations in ground water and the tile drainage 

beneath fields in the study area.

Based on published data about background concentrations, 

nitrogen and phosphorus concentrations in the Neuse River 

basin, and discharge data collected in calendar years 2000 and 

2001, nitrogen yields in the Neuse River basin typically were 

about two times background yields at most sites in the study 

area. Phosphorus yields typically were six times higher than 

background yields, which indicates that phosphorus pollution 

from human activities generally is more pronounced in the 

Neuse River basin. A possible reason for this is that conditions 

are favorable for denitrification in coastal plain watersheds, and 

reducing conditions in the bed and riparian areas of the study 

streams are favorable for mobilizing phosphorus from 

decomposing vegetation or from eroding sediment from 

uplands that then is deposited.

Data from this study indicate that anthropogenic effects on 

nitrogen yields were greatest in first-order streams (yields were 

greater than 2 tons/mi2

), and 1 ton/mi2 or less in second- and 

higher-order streams in the Little Contentnea Creek subbasin. 

Nitrogen yields in the Contentnea Creek subbasin ranged from 

0.59 to 2 tons/mi2, with typical yields of approximately 

1 ton/mi2

. Contentnea Creek near Evansdale had the highest 

yield (2 tons/mi2

), indicating that a major source of nitrogen is 

upstream from this station. Nitrogen yields were lower at 

Contentnea Creek at Hookerton in 2000 and 2001 compared to 

previous yield estimates based on 1990 data. Along the main 

stem of the Neuse River, nitrogen yields during 2000 and 2001 

ranged from 3.4 tons/mi2

 in Bear Creek, a tributary west of 

Kinston, N.C., to 0.55 ton/mi2

 in the Trent River. 

Annual phosphorus yields in the Little Contentnea Creek 

subbasin for 2000 and 2001 ranged from 0.02 to about 

0.15 ton/mi2

. In contrast with total nitrogen yields, the larger 

total phosphorus yields were in higher-order streams (about 

three times greater), indicating either that the major source of 

phosphorus in the Little Contentnea Creek subbasin originates 

in the larger streams or the phosphorus is deposited by sediment 

eroded from low-order headwater streams and deposited on the 

bed. Phosphorus yields in the Contentnea Creek subbasin 

ranged from 0.02 to 0.12 ton/mi2

. Contentnea Creek at 

Hookerton had the highest phosphorus yield observed in the 

subbasin, about five to six times the expected background yield, 

although yields for phosphorus reported for 2000 and 2001 for 

Contentnea Creek at Hookerton were considerably lower than 

those reported for 1990. Phosphorus yields in the Neuse River 

basin ranged from 0.02 to 0.29 ton/mi2

, with the highest yields 

occurring near New Bern in the vicinity of the upper Neuse 

estuary. 

The total nitrogen load delivered to the Neuse estuary in 

2000 was 4,807 tons or 9.61 million pounds, and the total 

phosphorus load was 425 tons or 850,000 pounds. It is 

estimated that about 17 percent (1,630,000 pounds) of the 

delivered total nitrogen load is from background sources, based 

on the background total nitrogen concentration of 0.50 mg/L 

used in this analysis. This background estimate is larger than the 

8.6 percent (830,000 pounds) background total nitrogen load 

reported by the North Carolina Department of Environment and 

Natural Resources for 1995, but less than the 30 percent 

estimated by the USGS spatially referenced regression on 

watershed model for 1992. The average total nitrogen load, 

based on data from Fort Barnwell, Trent River, and wastewatertreatment plants below Fort Barnwell and delivered to the 

Neuse estuary was 9.65 million pounds for the base period 

(1991–95). The total nitrogen load of 9.61 million pounds 

reported in this study for calendar year 2000 is comparable to 

the base period total nitrogen load.

The total phosphorus load transported to the Neuse estuary 

in 2000 was 425 tons. No recently published information was 

found on total point-source contributions of phosphorus to the 

Neuse River at Fort Barnwell for this study; therefore, general 

estimates from past studies were used. Based on this analysis, 

about 7 percent of the total phosphorus load in 2000 was from 

background sources, and about 93 percent of the total 

phosphorus load was derived from anthropogenic point 

(41 percent) and nonpoint (52 percent) sources. 

Effects of cultural eutrophication with respect to 

phosphorus enrichment in coastal plain streams of the Neuse 

River basin are much greater than for nitrogen. The 

eutrophication loading index for phosphorus ranged between 2 

and 12 times, and values typically were 5 to 6 times the 

estimated background yield for second- and higher-order 

streams compared to the eutrophication loading index range for 

total nitrogen of 1 to 5 times, and values typically were about 2 

times the estimated background yield. This finding is in 

agreement with nutrient enrichment previously reported for 

agricultural streams, but contrasts with recent (Smith and 

others, 2003) findings that nutrient enrichment from 

background sources generally was greater for nitrogen (6.4) 

than for phosphorus (2.0) in streams throughout the United 

States. One possible reason why this occurs in the Neuse River 

basin is provided by process-oriented studies conducted at the 

Lizzie Research Station. Redox conditions in bed sediment and 

riparian zones along rivers that tend to reduce oxidized forms of 

nitrate as it moves from recharge to discharge areas near 

streams are the same conditions that can mobilize phosphorus 

from bed sediments and maintain elevated concentrations in 

streamwaters in the Coastal Plain. Thus, the reducing 

conditions in streams in the Neuse River basin tend to 
48 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

exacerbate anthropogenic effects of phosphorus release and 

mitigate effects of nitrogen release into the environment.

The potential loading rate in the Neuse River basin for 

phosphorus is greatest in the upper Neuse estuary, where effects 

of nutrients on algal growth can be substantial. The high yields 

of phosphorus from Swift Creek near Streets Ferry and Trent 

River near Trenton may be one important reason that the upper 

Neuse estuary is often nitrogen limited. While management 

actions to control nitrogen throughout the basin likely help in 

controlling nuisance algal blooms and fish kills under average 

conditions, large amounts of nitrogen moving into the estuary as 

a result of extreme events may potentially cause algal growths 

of much greater severity than would occur if phosphorus 

discharges from Swift Creek and the Trent River were lower. 

Determining the sources of elevated phosphorus concentrations 

in these two tributary streams warrants further investigation that 

could result in application of management techniques that can 

have substantial water-quality improvement benefits for the 

Neuse River estuary.

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Appendix Tables

1. Data available for stations included in the Lizzie Research Station study.

2. Ninety-five percent confidence intervals for annual loads and methods of load 

estimation used in the Lizzie Research Station study.
54 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

Appendix table 1. Data available for stations included in the Lizzie Research Station study.

Site number Station name Web address

Surface-water stations

0208925200 Bear Creek at Mays Store http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=0208925200

02089500 Neuse River at Kinston http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02089500

0209173190 Unnamed tributary to Sandy Run near Lizzie http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=0209173190

0209173200 Sandy Run near Lizzie http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=0209173200

02091736 Middle Swamp near Farmville http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02091736

02091737 Little Contentnea near Willow Green http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02091737

02091740 Little Contentnea at Scuffleton http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02091740

02090380 Contentnea Creek near Lucama http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02090380

02090519 Contentnea Creek near Evansdale http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02090519

02091500 Contentnea Creek at Hookerton http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02091500

02091764 Contentnea Creek at Grifton http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02091764

02091814 Neuse River near Fort Barnwell http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02091814

02092500 Trent River near Trenton http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02092500

0209205053 Swift Creek near Streets Ferry http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=0209205053

02091000 Nahunta Swamp near Shine http://waterdata.usgs.gov/nc/nwis/inventory/?site_no=02091000

Weather station

0209173196 S1 Weather station near Lizzie (MIMS) http://waterdata.usgs.gov/nc/nwis/nwisman/?site_no=

0209173196&agency_cd=USGS

353137077332801 Weather station no. 2 near Lizzie http://waterdata.usgs.gov/nc/nwis/nwisman/?site_no=

353137077332801&agency_cd=USGS

Ground-water stations

353103077333401 L2 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353103077333401

353103077333402 L2D http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353103077333402

353103077333404 L2S http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353103077333404

353103077333403 L3 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353103077333403

353122077334901 L4 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353122077334901

353122077334903 L4D http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353122077334903

353122077334904 L4S http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353122077334904

353111077334401 L5 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353111077334401

353111077334402 L6 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353111077334402

353111077334404 L6D http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353111077334404

353111077334403 L6S http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353111077334403

353052077335501 L9 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353052077335501

353148077332103 L11S http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353148077332103

353127077333702 L15 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353127077333702

353127077333704 L15D http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353127077333704

353135077332704 L18D http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353135077332704

353027077340102 L20 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353027077340102

353051077333401 L22 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353051077333401

353050077333401 L23 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353050077333401

353050077333402 L24 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353050077333402

353042077334502 L27 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353042077334502

353142077332701 L7 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353142077332701

353142077332702 L8S http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353142077332702

353142077332703 L8D http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353142077332703

353148077332101 L10 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353148077332101
Appendix Tables 55

Ground-water stations (continued)

353148077332102 L11D http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353148077332102

353149077332101 L11 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353149077332101

353134077334601 L12 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353134077334601

353127077333701 L14 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353127077333701

353122077334902 L16 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353122077334902

353135077332701 L17 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353135077332701

353027077340101 L19 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353027077340101

353042077334501 L26 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353042077334501

353050077333403 L25 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353050077333403

353103077333406 L55 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353103077333406

353137077334603 GR089 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353137077334603

353104077334307 GR155 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353104077334307

353104077334308 GR156 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353104077334308

353137077334605 GR149 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353137077334605

353137077334604 GR148 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353137077334604

353153077333204 GR152 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353153077333204

353153077333203 GR151 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353153077333203

353153077333202 GR150 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353153077333202

353153077333206 GR153 http://waterdata.usgs.gov/nc/nwis/gwsi/?site_no=353153077333206

Appendix table 1. Data available for stations included in the Lizzie Research Station study.—Continued

Site number Station name Web address
56 Nitrogen Transport at a Confined Animal Feeding Operation in an Agricultural Watershed in the Neuse River Basin, 1999–2002

Appendix table 2. Ninety-five percent confidence intervals for annual loads and methods of load estimation used in the Lizzie 

Research Station study.

[Methods for load estimation: AMLE, Adjusted Maximum Likelihood Estimate; SUM, Sum of daily flows times mean concentrations for calendar year 2000; 

LAD, Least Absolute Deviation Method (cannot compute confidence interval with this method); LA, Linear Attribution Method (cannot compute confidence 

interval with this method)]

Station name

Total

nitrogen

load

(tons per year)

Lower 95% Upper 95% Estimation 

method

2000

Bear Creek at Mays Store 201 182 221 AMLE

Neuse River at Kinston 3,268 3,023 3,521 AMLE

Plum Tree Branch near Lizzie 1.4 0.0 4.4 SUM

Sandy Run near Lizzie 27 LAD

Middle Swamp near Farmville 38 34 42 AMLE

Little Contentnea near Willow Green 97 LA

Little Contentnea at Scuffleton 160 139 184 AMLE

Contentnea Creek near Lucama 139 LAD

Contentnea Creek near Evansdale 526 LA

Nahunta Swamp near Shine 109 95 123 AMLE

Contentnea Creek at Hookerton 939 872 996 AMLE

Neuse River near Fort Barnwell 4,192 3,722 4,703 AMLE

Trent River near Trenton 207 LAD

Swift Creek near Streets Ferry 508 LAD

2001

Bear Creek at Mays Store 150 134 167 AMLE

Neuse River at Kinston 2,027 1,880 2,183 AMLE

Sandy Run near Lizzie 11 LAD

Middle Swamp near Farmville 17 15 19 AMLE

Little Contentnea near Willow Green 51 LA

Little Contentnea at Scuffleton 102 91 115 AMLE

Contentnea Creek near Lucama 94 LAD

Contentnea Creek near Evansdale 486 LA

Nahunta Swamp near Shine 72 64 81 AMLE

Contentnea Creek at Hookerton 622 588 657 AMLE

Neuse River near Fort Barnwell 2,474 2,300 2,654 AMLE

Trent River near Trenton 92 LAD
Appendix Tables 57

Station name

Total

phosphorus

load

(tons per year)

Lower 95% Upper 95% Estimation 

method

2000

Bear Creek at Mays Store 9.9 7.7 12 AMLE

Neuse River at Kinston 294 LA

Plum Tree Branch near Lizzie 0.0 0 0.1 SUM

Sandy Run near Lizzie 4.4 3.2 5.4 AMLE

Middle Swamp near Farmville 6.3 5.1 7.7 AMLE

Little Contentnea near Willow Green 17 14 20 AMLE

Little Contentnea at Scuffleton 26 22 30 AMLE

Contentnea Creek near Lucama 7.2 5.4 8.8 AMLE

Contentnea Creek near Evansdale 20 15 25 AMLE

Nahunta Swamp near Shine 6.7 LA

Contentnea Creek at Hookerton 88 LAD

Neuse River near Fort Barnwell 313 LA

Trent River near Trenton 34 LA

Swift Creek near Streets Ferry 78 68 108 AMLE

2001

Bear Creek at Mays Store 8.9 6.2 12 AMLE

Neuse River at Kinston 207 LA

Sandy Run near Lizzie 1.8 1.3 2.6 AMLE

Middle Swamp near Farmville 3.7 3.0 4.3 AMLE

Little Contentnea near Willow Green 9.1 6.0 12 AMLE

Little Contentnea at Scuffleton 20 18 23 AMLE

Contentnea Creek near Lucama 3.6 2.8 4.3 AMLE

Contentnea Creek near Evansdale 16 13 19 AMLE

Nahunta Swamp near Shine 3.8 LA

Contentnea Creek at Hookerton 67 LAD

Neuse River near Fort Barnwell 232 LA

Trent River near Trenton 9.1 LA

Appendix table 2. Ninety-five percent confidence intervals for annual loads and methods of load estimation used in the Lizzie 

Research Station study.—Continued

[Methods for load estimation: AMLE, Adjusted Maximum Likelihood Estimate; SUM, Sum of daily flows times mean concentrations for calendar year 2000; 

LAD, Least Absolute Deviation Method (cannot compute confidence interval with this method); LA, Linear Attribution Method (cannot compute confidence 

interval with this method)]