Sources, Instream Transport, and Trends of 

Nitrogen, Phosphorus, and Sediment in the 

Lower Tennessee River Basin, 1980-96

By ANNE B. HOOS, JOHN A. ROBINSON, ROBERT A. AYCOCK, 

RODNEY R. KNIGHT, and MICHAEL D. WOODSIDE 

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 99-4139

Nashville, Tennessee

2000
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Any use of trade, product, or firm names in this report is for identification

purposes only and does not constitute endorsement by the

U.S. Geological Survey.

For additional information write to: Copies of this report may be purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

640 Grassmere Park, Suite 100 Box 25286

Nashville, Tennessee 37211 Denver, Colorado 80225-0286

Information regarding the National Water-Quality Assessment (NAWQA) Program is available on the 

Internet via the World Wide Web. You may connect to the NAWQA home page at:

http://water.usgs.gov/nawqa/nawqa_home.html
FOREWORD

The mission of the U.S. Geological Survey 

(USGS) is to assess the quantity and quality of the 

earth resources of the Nation and to provide information that will assist resource managers and policymakers at Federal, State, and local levels in making sound 

decisions. Assessment of water-quality conditions and 

trends is an important part of this overall mission.

One of the greatest challenges faced by waterresources scientists is acquiring reliable information 

that will guide the use and protection of the Nation’s 

water resources. That challenge is being addressed by 

Federal, State, interstate, and local water-resource 

agencies and by many academic institutions. These 

organizations are collecting water-quality data for a 

host of purposes that include: compliance with permits 

and water-supply standards; development of remediation plans for specific contamination problems; operational decisions on industrial, wastewater, or watersupply facilities; and research on factors that affect 

water quality. An additional need for water-quality 

information is to provide a basis on which regionaland national-level policy decisions can be based. Wise 

decisions must be based on sound information. As a 

society we need to know whether certain types of 

water-quality problems are isolated or ubiquitous, 

whether there are significant differences in conditions 

among regions, whether the conditions are changing 

over time, and why these conditions change from 

place to place and over time. The information can be 

used to help determine the efficacy of existing waterquality policies and to help analysts determine the 

need for and likely consequences of new policies.

To address these needs, the U.S. Congress appropriated funds in 1986 for the USGS to begin a pilot program in seven project areas to develop and refine the 

National Water-Quality Assessment (NAWQA) Program. In 1991, the USGS began full implementation of 

the program. The NAWQA Program builds upon an 

existing base of water-quality studies of the USGS, as 

well as those of other Federal, State, and local agencies. 

The objectives of the NAWQA Program are to:

• Describe current water-quality conditions for a 

large part of the Nation’s freshwater streams, 

rivers, and aquifers.

• Describe how water quality is changing over 

time.

• Improve understanding of the primary natural 

and human factors that affect water-quality

conditions.

This information will help support the development 

and evaluation of management, regulatory, and monitoring decisions by other Federal, State, and local 

agencies to protect, use, and enhance water resources. 

The goals of the NAWQA Program are being 

achieved through ongoing and proposed investigations 

of 60 of the Nation’s most important river basins and 

aquifer systems, which are referred to as study units. 

These study units are distributed throughout the 

Nation and cover a diversity of hydrogeologic settings. 

More than two-thirds of the Nation’s freshwater use 

occurs within the 60 study units and more than twothirds of the people served by public water-supply systems live within their boundaries.

National synthesis of data analysis, based on 

aggregation of comparable information obtained from 

the study units, is a major component of the program. 

This effort focuses on selected water-quality topics 

using nationally consistent information. Comparative 

studies will explain differences and similarities in 

observed water-quality conditions among study areas 

and will identify changes and trends and their causes. 

The first topics addressed by the national synthesis are 

pesticides, nutrients, volatile organic compounds, and 

aquatic biology. Discussions on these and other waterquality topics will be published in periodic summaries 

of the quality of the Nation’s ground and surface water 

as the information becomes available.

This report is an element of the comprehensive 

body of information developed as part of the NAWQA 

Program. The program depends heavily on the advice, 

cooperation, and information from many Federal, 

State, interstate, Tribal, and local agencies and the 

public. The assistance and suggestions of all are 

greatly appreciated.

Robert M. Hirsch

Chief Hydrologist

Contents v

CONTENTS

Glossary ................................................................................................................................................................................. viii

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

Introduction ........................................................................................................................................................................... 3

Purpose and Scope....................................................................................................................................................... 3

Description of the Lower Tennessee River Basin........................................................................................................ 5

Previous Investigations................................................................................................................................................ 5

Acknowledgments ....................................................................................................................................................... 10

Approach and Methods.......................................................................................................................................................... 10

Sources of Nitrogen and Phosphorus..................................................................................................................................... 16

Point Sources ............................................................................................................................................................... 16

Wastewater Discharge ....................................................................................................................................... 16

Nonpoint Sources ........................................................................................................................................................ 16

Atmospheric Deposition .................................................................................................................................... 22

Inputs to Agricultural Lands.............................................................................................................................. 22

Fertilizer Application............................................................................................................................... 23

Nitrogen Fixation..................................................................................................................................... 23

Crop Uptake............................................................................................................................................. 23

Livestock Waste....................................................................................................................................... 24

Additional Sources of Nitrogen and Phosphorus ........................................................................................................ 24

Sources of Sediment .............................................................................................................................................................. 25

Instream Transport of Nitrogen, Phosphorus, and Sediment................................................................................................. 25

Relation of Concentrations to Season, Streamflow, and Reach Location ................................................................... 25

Relation of Concentrations to Season................................................................................................................ 25

Relation of Concentrations to Streamflow ........................................................................................................ 30

Downstream Variations in Concentrations ........................................................................................................ 33

Instream Loads ............................................................................................................................................................ 43

Comparison of Inputs from Nutrient Sources with Nutrient Yields............................................................................ 57

Trends of Nitrogen, Phosphorus, and Sediment .................................................................................................................... 60

Trends of Inputs........................................................................................................................................................... 60

Trends of Instream Concentration ............................................................................................................................... 60

Conclusions ........................................................................................................................................................................... 65

Implications for Data Collection and Analysis............................................................................................................ 65

Implications for Resource Management...................................................................................................................... 65

References Cited.................................................................................................................................................................... 66

Appendix A. Sites where historical water-quality data collected from water year 1980 to 1996 are 

included in nutrient- and sediment-data analyses, lower Tennessee River Basin ................................................... 71

Appendix B. Limitations of instream load estimates ............................................................................................................ 75

Appendix C. Methods for quantifying inputs of nitrogen and phosphorus from point and nonpoint sources ...................... 81

Appendix D. Variation in nutrient concentrations with streamflow, and model estimate of streamflow 

variation in concentration, at selected sites in the lower Tennessee River Basin, 1980-96 .................................... 87

Appendix E. Streamflow-duration characteristics for period of streamflow record, compared with 

characteristics for period of load computation, for load-computation sites in the 

lower Tennessee River Basin................................................................................................................................... 95
vi Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

FIGURES

1-4. Maps showing:

1. Location of the lower Tennessee River Basin NAWQA study unit .................................................................. 4

2. Subunits, major hydrologic units, and location of selected monitoring sites and 

basin boundaries in the lower Tennessee River Basin....................................................................................... 6

3. Land use and land cover, major hydrologic units, and location of selected monitoring 

sites and basin boundaries in the lower Tennessee River Basin ....................................................................... 7

4. Location of wastewater dischargers and estimated wastewater input of total nitrogen 

and total phosphorus in the lower Tennessee River Basin in 1995 ................................................................... 8

5. Graph showing basin characteristics of tributary sites in the lower Tennessee River Basin 

where instream loads were estimated......................................................................................................................... 13

6. Diagram showing anthropogenic sources and fluxes of nitrogen within an agricultural watershed.......................... 22

7-18. Graphs showing:

7. Seasonal variation in nutrient concentrations and model estimate of seasonal 

pattern at selected sites in the lower Tennessee River Basin, 1980-96 ............................................................. 31

8. Variation in total nitrite plus nitrate and total phosphorus concentrations with 

streamflow and model estimate of streamflow variation in concentration at 

selected sites in the lower Tennessee River Basin, 1980-96 ............................................................................. 32

9. Relation of median value of total nitrogen concentrations during low streamflow 

conditions and median value of total nitrogen load during low streamflow 

conditions to wastewater-discharge input to the watershed .............................................................................. 34

10. Nutrient concentrations at selected sites on the Tennessee River, 1980-96, 

for total nitrogen, total nitrite plus nitrate, total ammonia, and total phosphorus ............................................. 35

11. Nutrient concentrations at selected sites on the Duck River, 1980-96, for total 

nitrogen, total nitrite plus nitrate, total ammonia, and total phosphorus........................................................... 39 

12. Annual yield and flow-weighted mean concentration of total nitrogen, total nitrite plus 

nitrate, total ammonia, and total ammonia plus organic nitrogen at selected 

sites in the lower Tennessee River Basin .......................................................................................................... 50

13. Annual yield and flow-weighted mean concentration of total phosphorus, 

dissolved orthophosphorus, and suspended sediment at selected sites in 

the lower Tennessee River Basin....................................................................................................................... 51

14. Total nitrogen input and export at selected sites in the lower Tennessee River Basin ...................................... 52

15. Total phosphorus input and export at selected sites in the lower Tennessee River Basin................................. 53

16. Comparison of distribution of flow-weighted mean concentrations at lower 

Tennessee River Basin sites with national distribution ..................................................................................... 55

17. Monthly instream load of total nitrogen at Elk River near Prospect, 

Tennessee, water years 1990-92 ........................................................................................................................ 56

18. Relation of total nitrogen export to the balance of land-phase inputs to agricultural land ............................... 58

19. Map showing trends of instream concentrations of nitrogen, phosphorus, and suspended 

sediment in the lower Tennessee River Basin ............................................................................................................ 61

20. Graph showing temporal variation in nutrient concentrations during 1980-96 and model 

estimate of trend at selected sites in the lower Tennessee River Basin for total 

nitrogen, total nitrite plus nitrate, total ammonia, and total phosphorus.................................................................... 63
Contents vii

TABLES

1. Streamflow characteristics of sites in the lower Tennessee River Basin where 

instream loads were estimated.................................................................................................................................... 11

2. Summary of procedures used to combine nutrient constituent data from different analytical methods.................... 15

3. Nitrogen inputs and export for selected basins in the lower Tennessee River Basin................................................. 17

4. Phosphorus inputs and export, and ratio of nitrogen to phosphorus export, 

for selected basins in the lower Tennessee River Basin............................................................................................. 18

5. Nitrogen inputs for major hydrologic units in the lower Tennessee River Basin ...................................................... 19

6. Phosphorus and sediment inputs for major hydrologic units in the lower Tennessee River Basin............................ 20

7. Summary of methods for quantifying inputs of nitrogen and phosphorus to tributary basins and 

major hydrologic units ............................................................................................................................................... 21

8. Calibration results for the seven-parameter log-linear regression model of nutrient and 

sediment concentrations for selected sites in the lower Tennessee River Basin........................................................ 26

9. Instream load, yield, and flow-weighted mean concentration for selected constituents 

and basins in the lower Tennessee River Basin, 1980-96 .......................................................................................... 44

10. Pearson correlation coefficients among 1992 export, inputs, and other factors......................................................... 59

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of

1929—a geodetic datum derived from a general adjustment of the first-order level nets of

the United States and Canada, formerly called Sea Level Datum of 1929.

ABBREVIATIONS AND ACRONYMS

ADEM Alabama Department of Environmental Management

FCWP Flint Creek Watershed Project

GSA Geological Survey of Alabama

KDEP Kentucky Department for Environmental Protection

LOWESS Locally weighted scatter-plot smoothing

LTEN Lower Tennessee

NAWQA National Water-Quality Assessment

ORSANCO Ohio River Valley Sanitation Commission

STORET STOrage and RETrieval data base of the U.S. Environmental Protection Agency

TDEC Tennessee Department of Environment and Conservation

TVA Tennessee Valley Authority

U.S. EPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

WATSTORE WATer STOrage and REtrieval system data base of the U.S. Geological Survey

Multiply By To obtain

inch (in.) 2.54 centimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

square mile (mi2

) 2.590 square kilometer

cubic foot per second (ft3

/s) 0.02832 cubic meter per second

pound (lb) 0.4536 kilogram

pound per day (lb/d) 0.4536 kilogram per day

pound per year (lb/yr) 0.4536 kilogram per year

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

ton per square mile per year [(ton/mi2)/yr] 0.003503 metric ton per hectare per year

ton per acre (ton/acre) 2.242 metric ton per hectare

pound per acre (lb/acre) 1.121 kilogram per hectare

million gallons per day (Mgal/d) 0.04381 cubic meter per second
viii Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

GLOSSARY

Export. Equivalent to yield, and used in place of that term in comparisons with input to a 

watershed.

Flow-weighted mean concentration. The ratio of instream load of a constituent to the 

mean discharge during the period of transport (dimensions of mass per volume); and 

equivalent computationally to the flow-weighted mean of the model estimates of 

daily concentration. Expressed in units of concentration [milligrams per liter 

(mg/L)]. This quantity is used, in place of load or yield, for evaluating average waterquality conditions at the site, and for comparing water quality among sites with differing discharge characteristics.

Instream delivery processes. Processes such as channel storage and aquatic biological 

assimilation that control how much of the stream input is transported along the channel and is exported from the watershed. 

Instream load. The mass of a constituent moving past a specified point in a channel (for 

example, the mouth of a river basin) during a specified period of time. The instream 

load can be estimated by monitoring the concentration of the constituent periodically, 

and streamflow continuously, at the specified point. 

Land-water delivery processes. Transport of a portion of land-phase inputs, overland or 

in the subsurface, from the point of deposition or application on the land surface to 

the stream channel (Smith and others, 1997). Some of the factors influencing landwater delivery include distance to the channel, land slope and runoff characteristics, 

soil-drainage characteristics, biological processing or storage within the vegetative 

cover or soil, and hydrogeology.

Land-phase input. The mass of a constituent deposited on (through natural processes or 

human activities) or derived from (through erosion of natural materials) the land surface in the watershed. Land-phase inputs are the basis for estimating the contribution 

from most nonpoint sources of constituents, inputs from which cannot be otherwise 

quantified. Only a portion of the land-phase input reaches the stream channel by 

overland or subsurface transport processes, referred to as land-water delivery processes.

Nonpoint source. A source of a water-quality constituent that is not discharged directly to 

the stream channel at a discrete location, but rather originates as land-phase inputs to 

broad source areas. An unknown percentage of a nonpoint-source input is transported 

overland or subsurface and reaches the stream channel as diffuse input. 

Point source. A source of a water-quality constituent that is discharged directly to the 

stream channel from a discrete location (for example a pipe, tank, or pit).

Stream input. The mass of a constituent delivered to the stream channel from sources in 

the watershed. Stream inputs include inputs discharged directly from sources to the 

stream channel (such as wastewater discharges), as well as the portion of land-phase 

input that reaches the stream channel. 

Trend. The change in the concentration of a water-quality constituent over time.

Yield. The ratio of instream load of a constituent to the area of the watershed (dimensions 

of mass per time per area). This area-normalized load is used, in place of load, to 

compare instream loads among watersheds with different drainage areas, and to compare with inputs to the watershed. 
Abstract 1

Sources, Instream Transport, and Trends of Nitrogen, 

Phosphorus, and Sediment in the Lower Tennessee 

River Basin, 1980-96

By Anne B. Hoos, John A. Robinson, Robert A. Aycock, Rodney R. Knight, and

Michael D. Woodside

Abstract

In 1997, the U.S. Geological Survey 

(USGS) began an assessment of the lower Tennessee River Basin as part of the National WaterQuality Assessment Program. Existing nutrient 

and sediment data from 1980 to 1996 were compiled, screened, and interpreted to estimate watershed inputs from nutrient sources, provide a 

general description of the distribution and transport of nutrients and sediments in surface water, 

and evaluate trends in nutrient and sediment concentrations in the lower Tennessee (LTEN) River 

Basin. 

Nitrogen inputs from major sources varied 

widely among tributary basins in the LTEN River 

Basin. Point source wastewater discharges contributed between 0 and 0.61 tons per square mile 

per year [(tons/mi2)/yr]. Of the nonpoint sources 

of nitrogen for which inputs were estimated 

(atmospheric deposition, nitrogen fixation, fertilizer application, and livestock waste) livestock 

waste contributed the largest input in about twothirds (7 out of 11) of the tributary basins, and fertilizer application contributed the largest input in 

the remaining 4 basins. Nitrogen input from fertilizer application was the most variable spatially 

among the nonpoint sources of nitrogen, ranging 

from 1.5 to 23 (tons/mi2)/yr. Atmospheric deposition estimates varied the least from basin to basin, 

ranging from 1.6 to 2.0 (tons/mi2)/yr. Estimates of 

nitrogen input from livestock waste ranged 

between 2.0 to 13 (tons/mi2)/yr. The percentage 

of the input from each of these nonpoint sources 

that entered the surface-water system is not 

known.

Wastewater discharge contributed between 

0 and 0.14 (ton/mi2)/yr of phosphorus to tributary 

basins. Livestock waste contributed most of the 

input in 8 out of the 11 basins, and fertilizer application contributed the most in the remaining 3 

basins. Estimates of phosphorus input for fertilizer 

application ranged from 0.35 to 5.1 (tons/mi2)/yr 

and from 0.62 to 4.3 (tons/mi2)/yr from livestock 

waste. 

Reservoirs on the main stem of the Tennessee River and on the Duck and Elk Rivers affect 

nutrient transport because hydrodynamic conditions in the reservoirs promote assimilation by 

aquatic plants and deposition of particulate matter. Observed decreases in total nitrite plus nitrate 

and dissolved-orthophosphorus concentrations in 

reservoirs or at sites downstream of reservoirs 

during summer months were probably related to 

seasonality of plant growth.

Nutrient and sediment data used to estimate 

annual instream loads and yields were compiled 

from various water-quality monitoring programs 

and represent the best available data in the LTEN 

River Basin, but these data have several characteristics that limit accuracy of load estimates. 

Many of the monitoring programs were not 

designed with the objective of annual load estimation, and data representing storm transport are, 

therefore, sparse; sampling and analytical methods varied through time and among the monitoring programs, hampering spatial and temporal 

comparisons. The load estimates computed from 
2 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

these data are useful for evaluating broad spatial 

patterns of instream load, and comparisons of 

instream load to inputs, but may not be sufficiently accurate for local-scale evaluations of 

water quality. 

Estimates of the mean annual instream load 

of total nitrogen entering (Chattanooga, Tenn.) 

and leaving (Paducah, Ky.) the LTEN River Basin 

were 29,000 and 60,000 tons per year (tons/yr), 

respectively. These estimates represent a gain of 

31,000 tons/yr, on average, across the area 

(18,930 mi2) between these inlet and outlet sites. 

The sum of the mean annual instream load from 

gaged tributaries to the main stem within the 

study unit was 14,000 tons/yr; however, this number cannot be directly compared with the gain 

between the inlet and outlet sites because (1) the 

gaged area represents only 30 percent of the total 

area and (2) the period of record at many tributary 

sites did not correspond with the period of record 

at the inlet or outlet sites.

Estimates of mean annual instream load of 

total phosphorus at the inlet and outlet sites of the 

LTEN River Basin were 1,300 and 5,000 tons/yr, 

respectively, representing a gain of 3,700 tons/yr, 

on average, across the study unit. The sum of the 

gaged tributary load, representing only 28 percent 

of the area contributing to the main stem, was 

4,300 tons/yr. Although this number cannot be 

closely compared with the gain throughout the 

study unit, for the same reasons given for total 

nitrogen, a general comparison suggests that the 

main stem of the Tennessee River and the tributary embayments along the main stem function as 

a sink for total phosphorus, removing a substantial amount from the water column through deposition or assimilation.

The estimates of inputs can be compared 

and correlated with yields (area-normalized 

instream loads); significant correlations between 

estimates of inputs and yields might be useful as 

predictive tools for instream water quality where 

monitoring data are not available. Yields of nitrogen correlated moderately well with inputs from 

nonpoint sources, based on 1992 estimates. Nitrogen yield was highest [3.5 (tons/mi2

)/yr] for Town 

Creek, for which the balance of nonpoint-source 

inputs to agricultural lands (fertilizer application 

plus nitrogen fixation plus livestock waste minus 

harvest) was also the highest [15 (tons/mi2)/yr]. 

Nitrogen yield was low [1.0 (tons/mi2)/yr] for the 

Buffalo River, for which the balance of agricultural nonpoint-source input was correspondingly 

low [3.2 (tons/mi2)/yr, the second lowest]. Correlation of wastewater discharge with yield was 

poor, and contrasted with the significant correlation between wastewater discharge and median 

nitrogen concentration during low streamflow. 

The poor correlation between wastewater discharge and annual yield was expected, however, 

as wastewater discharge is a small fraction compared with annual yield.

In contrast with nitrogen, phosphorus yield 

did not correlate well with any estimated inputs or 

land-use types for the tributary basins. Phosphorus yield was highest [1.1 and 0.93 (tons/mi2

)/yr] 

at two sites along the Duck River and at Elk River 

near Prospect [0.89 (ton/mi2)/yr]; however, estimates of inputs at these sites were in the middle of 

their respective ranges. The influence of the outcrop of phosphatic limestone formations of the 

brown-phosphate districts in the lower Duck and 

lower Elk River Basins might be responsible for 

the poor correlation between estimated inputs and 

yields of phosphorus. The outcrop pattern of these 

phosphatic limestones are an important factor to 

consider as regional boundaries are established 

for attainable, region-specific water-quality criteria for total phosphorus.

Estimates of sediment input from cropland 

soil erosion in 1992 ranged from 51 to 

540 (tons/mi2)/yr among the major hydrologic 

units in the LTEN River Basin. Information was 

not available to estimate this input for individual 

tributaries. Sediment yield estimates ranged from 

65 to 263 (tons/mi2)/yr for the three tributary 

monitoring basins for which instream data were 

available, and from 17 to 26 (tons/mi2)/yr for the 

Tennessee River at South Pittsburg and at Pickwick Landing Dam, respectively. Lower sediment 

yields for the main stem sites compared with the 

tributary sites is probably due to sediment deposition in the main stem of the Tennessee River and 

tributary embayments along the main stem.
Introduction 3

Most of the significant trends in nutrient 

concentrations from about 1985 to about 1995 

were decreasing trends, except for total nitrite 

plus nitrate, which increased at one site on the Elk 

River. The spatial distribution of decreasing 

trends of total nitrogen and total ammonia corresponds with the spatial variation among basins in 

wastewater loading rate. The time period of 

observed trends corresponds to the period of 

improvements in municipal treatment, thus 

decreases in wastewater effluent concentrations of 

nitrogen might be responsible for the decreasing 

trend in instream concentrations at these sites. 

Concentrations of total phosphorus did not 

decrease during this period at these sites, as might 

have been expected considering the reductions in 

wastewater input of phosphorus during this 

period.

INTRODUCTION

In 1997, the U.S. Geological Survey (USGS) 

began an assessment of the lower Tennessee (LTEN) 

River Basin as part of the National Water-Quality 

Assessment (NAWQA) Program. The lower Tennessee River Basin corresponds to the lower half of the 

Tennessee River Valley (fig. 1). Surface-water-quality 

data collected in the LTEN River Basin from 1980 to 

1996 have been compiled, screened, and evaluated to 

provide a general description of water-quality conditions, to identify trends in selected water-quality constituents, and to assist the design of NAWQA datacollection activities within the LTEN River Basin. 

Assessment efforts have been focused on nitrogen, 

phosphorus, and suspended sediment because these 

water-quality constituents have been identified by 

Federal, State, and local resource-management and 

regulatory agencies in the basin as the issues of greatest concern to the quality of surface-water resources.

State water-quality regulatory agencies within 

the LTEN River Basin have documented that although 

the quality of surface water in the basin is generally 

good, poor water quality impairs beneficial uses locally 

in 109 stream segments and 3 lakes (Alabama Department of Environmental Management, 1996; Georgia 

Department of Natural Resources, 1996; Kentucky 

Natural Resources and Environmental Protection Cabinet, 1996; Mississippi Department of Environmental 

Quality, 1996; Tennessee Department of Environment 

and Conservation, 1996). Nutrient overenrichment is 

listed as causing impairment in 37 stream segments 

and 2 lakes. Although nitrogen and phosphorus are 

essential nutrients for plant and animal growth, nutrient 

overenrichment of streams and lakes can promote 

excessive growth of algae and other aquatic plants. The 

subsequent decay of this growth in organic matter may 

deplete dissolved oxygen and adversely affect fish and 

other aquatic life. Excessive growth of algae and other 

aquatic plants also is accompanied by increased levels 

of dissolved organic matter that may cause taste and 

odor problems. These problems increase watertreatment costs and thus impair the use of the water 

resource as a drinking-water supply.

Although nutrient overenrichment is a major 

cause of impairment, siltation and suspended sediment 

are the dominant causes of impairment in streams 

throughout the LTEN River Basin. Siltation and suspended sediment are listed by State water-quality regulatory agencies as causing impairment in 63 of the 

109 impaired stream segments in the basin. The 

increased turbidity associated with elevated 

suspended-sediment concentrations reduces light penetration and primary productivity of the water bodies. 

In addition, excessive sediment deposition (siltation) 

on streambeds degrades habitat for benthic organisms 

and reduces spawning grounds for fish. Excessive sediment deposition in reservoirs interferes with recreational use (in the tributary embayments), obstructs 

commercial navigation channels, and reduces storage 

capacity (D. Meinert, Tennessee Valley Authority, 

written commun., 1998).

Purpose and Scope

The purposes of this report are to (1) describe 

and quantify the major sources of nitrogen and phosphorus to surface waters in the LTEN River Basin; 

(2) describe the seasonal and spatial patterns and temporal trends of concentrations and loads of nitrogen, 

phosphorus, and sediment; and (3) relate spatial and 

temporal patterns of nutrient concentrations and loads 

to spatial and temporal variation in sources and other 

environmental factors. The analyses presented in this 

report are based on historical water-quality data collected at 49 monitoring sites during the period October 

1979-September 1996 (water years 1980-96), and on 

information on nutrient sources for several years during this period. Comparison of nutrient sources with 

loads is based on data from 1992. The water-quality 
4 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

KENTUCKY

88

87

86

o

o

o

36o

35o

Duck

River

Elk

River

Clar ks

River

Buffalo

River

Sho a l Creek

Bear

Creek

Flint Creek

Flint

Paint R ock Ri v er

Beech River

Sequatchie River

Paducah

River

Kentucky

Lake

Wheeler

Lake Wilson Lake

Pickwick L ake

Tennessee

River

Woods

Reservoir

Normandy

Lake

Tims Ford

Lake

Nickajack

Lake

Guntersville

Lake

Big Sandy River

TENNESSEE

GEORGIA

Chattanooga

Columbia

TENNESSEE

ALABAMA

MISSISSIPPI

Huntsville Scottsboro

Decatur

Florence

10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

0

1:2,000,000 digital line graph

Figure 1. Location of the lower Tennessee River Basin NAWQA study unit.

NAWQA study units

Town

Creek

Base from U.S. Geological Survey,

Study unit

Georgia Mississippi Alabama

Kentucky

Tennessee

Index map

Lower Tennessee River

Basin study unit

Figure 1. Location of the lower Tennessee River Basin NAWQA study unit.
Introduction 5

data were obtained from various monitoring programs 

and special studies conducted by the Alabama Department of Environmental Management (ADEM), Flint 

Creek Watershed Project (FCWP), Geological Survey 

of Alabama (GSA), Kentucky Department for Environmental Protection (KDEP), Ohio River Valley Sanitation Commission (ORSANCO), Tennessee 

Department of Environment and Conservation 

(TDEC), Tennessee Valley Authority (TVA), and 

USGS. Water-quality constituents used in the analyses 

included total nitrogen, total ammonia plus organic 

nitrogen, total nitrite plus nitrate nitrogen, total ammonia nitrogen, total phosphorus, dissolved orthophosphorus, and suspended sediment. The data analyses 

included graphic summaries of nutrient concentrations, regression analysis of nutrient and sediment 

concentrations to estimate instream loads and trends, 

and correlation analysis of instream nutrient loads 

with watershed inputs.

Description of the Lower Tennessee River 

Basin

The LTEN River Basin NAWQA study unit 

covers a 19,500-square-mile (mi2

) area in the lower 

half of the Tennessee River Valley (fig. 1). The study 

unit upstream boundary, which coincides with the 

downstream boundary of the upper Tennessee River 

Basin study unit, is located at river mile 465 on the 

main stem of the Tennessee River at Chattanooga, 

Tennessee. The study unit encompasses parts of Tennessee, Georgia, Alabama, Mississippi, and Kentucky 

that drain to the Tennessee River and its tributaries 

between river mile 465 and the confluence with the 

Ohio River at Paducah, Kentucky (Woodside and 

Mitchell, 1998). 

The LTEN River Basin is subdivided into 14 

major hydrologic units (fig. 2). Seven of these units, 

representing 37 percent of the basin area, make up the 

drainage areas of five major tributaries to the Tennessee River: the Elk (two units), Duck (two units), 

Sequatchie, and Buffalo Rivers, and Bear Creek. The 

remaining units, representing 63 percent of the basin, 

correspond to direct drainage to the main stem of the 

Tennessee River, or to groupings of minor tributaries 

to the main stem (no individual tributary draining 

more than 600 mi2, or 3 percent of the basin).

The spatial variation in concentrations and loads 

of nitrogen, phosphorus, and sediment within hydrologic units is affected by both natural and anthropogenic factors. Natural factors that affect water quality 

include geology, physiography, soils, land cover, climate, and hydrology. Kingsbury and others (1999) 

used geologic and physiographic boundaries to divide 

the LTEN River Basin into subunits in which natural 

factors affecting water quality are relatively homogeneous (fig. 2). 

Anthropogenic factors that affect water quality 

include reservoirs, land use, population distribution, 

and urban, industrial, and agricultural activities. The 

distribution of urban and agricultural land use in the 

LTEN River Basin (fig. 3) corresponds to the distribution and amount of nonpoint sources (terms in bold

can be found in the Glossary) of nitrogen, phosphorus, 

and sediment in the basin. The influence of certain 

urban and industrial activities is represented by the 

distribution of point-source discharges of wastewater 

(fig. 4). A more thorough discussion of the environmental setting of the LTEN River Basin is given in 

Kingsbury and others (1999).

Previous Investigations

Although many investigators have reported 

nutrient and sediment concentration data from ambient 

monitoring sites in the LTEN River Basin (Tennessee 

Valley Authority, 1972; Carriker and others, 1981; 

Meinert, 1991; Parr, 1991; Meinert and Fehring, 

1992), few reports have presented estimates of 

instream loads, yields, or trends. Parr (1991) 

reported streamflow-concentration relations and temporal trends for selected water-quality constituents, 

including nutrients, in data collected during 1986-89 at 

sites in the TVA fixed-station tributary monitoring network. Trimble and Carey (1984) combined reservoir 

sediment-accumulation data with suspended-sediment 

load data from samples from the 1930’s, 1960’s, and 

from 1975 to 1982 to estimate instream sediment loads 

for several subbasins in Tennessee, including part of 

the LTEN River Basin. Estimates of sediment yields 

for central and eastern Tennessee basins (including 

those in the LTEN River Basin) were about 800 tons 

per square mile per year [(tons/mi2)/yr], whereas sediment yields for western Tennessee basins, which are 

intensively agricultural and channelized, ranged from 

700 to 1,000 (tons/mi2)/yr. The similarities in these 

values did not match the expected result that sediment 

yields for western Tennessee basins would far exceed 

sediment yields for central and eastern Tennessee 
6 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

88

87

86

o

o

o

36o

35o

1:2,000,000 digital line graph

EXPLANATION

From Kingsbury and others, 1999; modified

from Griffith and others, 1997, King and

Beikman, 1974, Osborne and others, 1989,

and Smalley, 1983

Base from U.S. Geological Survey,

KENTUCKY

TENNESSEE

TENNESSEE

ALABAMA

MISSISSIPPI

GEORGIA

Coastal Plain

Transition

Western Highland Rim

Outer Nashville Basin

Inner Nashville Basin

Eastern Highland Rim

Cumberland Plateau

Plateau escarpment and

valleys

Valley and Ridge

06040006 MAJOR HYDROLOGIC UNIT BOUNDARY AND NUMBER (SEE TABLE 6)

BASIN BOUNDARY OF SELECTED MONITORING SITE

NUTRIENT MONITORING SITE (SEE TABLE 1)

SEDIMENT MONITORING SITE (SEE TABLE 1)

06040006

06040005

06040003

06040001

06040004

06030005

06030006

06030002

06030001

06020004

06020001

06030003

06040002 06030004

7

8

1

6

2

5

16

7

8 10

9

4 3

17

18

11

MONITORING SITE FOR WHICH TRENDS (BUT NOT LOADS) 20

19

12

20

13

14

15

SUBUNITS

(Lower Duck River)

(Lower Elk River)

(Upper Elk River)

(Sequatchie River)

(Bear Creek)

(Buffalo River)

(Upper Duck River)

WERE ESTIMATED (SEE APPENDIX A)

Figure 2. Subunits, major hydrologic units, and location of selected monitoring sites

and basin boundaries in the lower Tennessee River Basin.

Figure 2. Subunits, major hydrologic units, and location of selected monitoring sites and basin boundaries in the lower 

Tennessee River Basin.
Introduction 7

88

87

86

o

o

o

36o

35o

1:2,000,000 digital line graph

Base from U.S. Geological Survey,

KENTUCKY

TENNESSEE

TENNESSEE

ALABAMA

MISSISSIPPI

GEORGIA

06040006 MAJOR HYDROLOGIC UNIT BOUNDARY AND NUMBER (SEE TABLE 6)

BASIN BOUNDARY OF SELECTED MONITORING SITE

NUTRIENT MONITORING SITE (SEE TABLE 1)

SEDIMENT MONITORING SITE (SEE TABLE 1)

06040006

06040005

06040003

06040001

06040004

06030005

06030006

06030002

06030001

06020004

06020001

06030003

06030004

06040002

7

8

1

6

2

5

16

7

8

9

4 3

17

18

11

10

EXPLANATION

Land use and land cover digital data provided by TVA (Frank Sagona, TVA,

written commun., 1998). Land cover data were derived spectrally from

satellite imagery (from period 1989-92), and ground truthed using infrared

aerial photography. Boundaries for certain land-use classifications (urban

and wetland areas) were digitized from topographic maps.

MONITORING SITE FOR WHICH TRENDS (BUT NOT LOADS)

WERE ESTIMATED (SEE APPENDIX A)

OPEN WATER

WETLANDS

PASTURE

CULTIVATED

FOREST

URBAN

20

14

15

13

20

12

19

Figure 3. Land use and land cover, major hydrologic units, and location of selected

monitoring sites and basin boundaries in the lower Tennessee River Basin.

Figure 3. Land use and land cover, major hydrologic units, and location of selected monitoring sites and basin boundaries in the 

lower Tennessee River Basin.
8 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

88

87

86

o

o

o

36o

35o

KENTUCKY

TENNESSEE

TENNESSEE

ALABAMA

MISSISSIPPI

Huntsville GEORGIA

Decatur

Florence

Chattanooga

Paducah

Columbia

EXPLANATION

0 TO 30

GREATER THAN 30

NOT ESTIMATED

(A)

WASTEWATER INPUT OF TOTAL NITROGEN

AS N, IN TONS PER YEAR

Figure 4. Location of wastewater dischargers and estimated wastewater input of (A) total nitrogen

and (B) total phosphorus in the lower Tennessee River Basin in 1995.

1:2,000,000 digital line graph

Base from U.S. Geological Survey,

Figure 4. Location of wastewater dischargers and estimated wastewater input of (A) total nitrogen and (B) total phosphorus in the 

lower Tennessee River Basin in 1995.
Introduction 9

88

87

86

o

o

o

36o

35o

KENTUCKY

TENNESSEE

TENNESSEE

ALABAMA

MISSISSIPPI

Huntsville GEORGIA

Decatur

Florence

Chattanooga

Paducah

Columbia

1:2,000,000 digital line graph

Base from U.S. Geological Survey,

(B)

EXPLANATION

0 TO 7.5

GREATER THAN 7.5

NOT ESTIMATED

WASTEWATER INPUT OF TOTAL PHOSPHORUS

AS P, IN TONS PER YEAR

Figure 4. Location of wastewater dischargers and estimated wastewater input of (A) total nitrogen

and (B) total phosphorus in the lower Tennessee River Basin in 1995ÑContinued.

Figure 4. Location of wastewater dischargers and estimated wastewater input of (A) total nitrogen and (B) total phosphorus in the 

lower Tennessee River Basin in 1995—Continued.
10 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

basins because of the greater availability of loose sediment in western Tennessee watersheds compared with 

other parts of the State. Trimble and Carey (1984) 

explained these results by citing the regional differences in land-water and instream delivery processes.

Acknowledgments

The authors gratefully acknowledge the following Federal and State agencies for their cooperation in 

providing data and interpretations used in this report: 

Tennessee Valley Authority (TVA), Tennessee Department of Environment and Conservation (TDEC), Alabama Department of Environmental Management 

(ADEM), Kentucky Department for Environmental 

Protection (KDEP), Ohio River Valley Sanitation 

Commission (ORSANCO), Geological Survey of Alabama (GSA), Mississippi Department of Environmental Quality (MDEQ), and Georgia Department of 

Natural Resources (GDNR). Sherry Wang of TDEC, 

Frank Sagona and Dennis Meinert of TVA, and 

M.W. Treece and Douglas Harned of USGS provided 

excellent technical guidance and review throughout 

this effort. The authors also thank several individuals 

who gave special assistance in compiling the data: 

E.A. Thornton and Glenda Gose of TVA; Steve Fishel 

and Jack Hughes of TDEC; Hubert Savoy of the University of Tennessee, Agricultural Extension Service; 

Steve Foster, Tom Cleveland, and Mike Reif of 

ADEM; Sydney DeJarnette of GSA; Glen Odom of 

MDEQ; and Vicky Prather of KDEP.

APPROACH AND METHODS

During the period 1980-96, Federal, State, and 

local agencies and universities collected water-quality 

samples at more than 700 stream and reservoir sites in 

the LTEN River Basin. Most of the water-quality data 

analyzed in this report were collected as part of ambient monitoring programs conducted by TVA, TDEC, 

ADEM, KDEP, ORSANCO, and USGS. Some additional data were collected as part of special studies 

conducted by ADEM and TVA (Sweatt, 1996), the 

FCWP (1996), and as part of a sediment datacollection network conducted by USGS.

Data from the ambient monitoring programs of 

TVA, ORSANCO, and State agencies were obtained 

from the STOrage and RETrieval (STORET) data base 

of the U.S. Environmental Protection Agency (U.S. 

EPA). Data from USGS monitoring programs were 

obtained from the WATer data STOrage and REtrieval 

system (WATSTORE) data base of USGS. 

Instream loads of nutrients and sediment were 

estimated for water-quality monitoring sites for which 

samples were collected at least quarterly for a period 

of 5 consecutive years during which daily streamflow 

data also were collected (or could be adapted from a 

nearby gage). Sites that met these criteria are shown in 

figures 2 and 3 and are listed as sites 1-18 in 

Appendix A. Most of these sites were sampled quarterly, but four sites (sites 1, 11, 12, and 18) were sampled monthly.

Instream nutrient loads were estimated at 16 of 

the sites (all sites except 3 and 8, where only sediment 

data were collected). Streamflow data for 11 of the 

18 sites were collected by USGS; TVA provided 

streamflow data for the remaining sites (E.A. Thornton, Tennessee Valley Authority, written commun., 

March 1998). Additional information for the streamflow-gaging sites is provided in table 1. Instream loads 

of sediment were estimated at five of the USGS sites 

(sites 2, 3, 8, 16, and 17).

Of the 18 sites for which loads were computed, 

11 are in free-flowing, or riverine, reaches of tributaries to the Tennessee River, 2 are on flow-regulated 

sections of tributaries (sites 4 and 9), and 5 are on 

flow-regulated sections along the main stem of the 

Tennessee River (sites 14-18). Each drainage basin 

contributing to the tributary sites (sites 1-13) is shown 

in relation to environmental setting (figs. 2 and 3) to 

illustrate the composition of each basin with respect to 

subunits and land use/land cover. Summaries of subunit and land use/land cover for each tributary basin 

are shown in figure 5. The combined percentage in 

pasture, cultivated, and urban land use/land cover in 

this set of basins ranges from 29 percent (site 2, Buffalo River near Flat Woods) to 80 percent (site 1, 

Clarks River at Almo). Land use and subunit summaries are not shown for the sites along the main stem of 

the Tennessee River (sites 14-18) because the many 

large impoundments along the main stem in both the 

upper and lower parts of the Tennessee River alter the 

instream transport of nutrients and sediment, confounding comparison between basin characteristics 

and water quality for those sites.

Eight of the 18 water-quality monitoring sites 

were not colocated with a corresponding streamflowgaging station, but were located some distance 

upstream or downstream from a gaging station (drainage areas listed in table 1 indicate a difference for the 
A

pproachandMethods11

Table 1. Streamflow characteristics of sites in the lower Tennessee River Basin where instream loads were estimated—Continued

Related streamflow gaging sit

Site 

identification 

(fig. 2)

Surface-water station/site location Streamflow gaging station Period 

of 

record 

(water 

year)

Streamflow chara

teristics for perio

of record

Number Name

Drainage 

area 

(mi2)

Type

of 

site

Number Agency

Drainage area 

(mi2)

Median 

flow 

(ft3/s)

Media

runo

(in.)

1 PRI038 Clarks River at Almo, Ky. 134 R 03610200 USGS 134 1982-CY 31.8 3.2 2 03604000 Buffalo River near Flat Woods, 

Tenn.

447 R 03604000 USGS 447 1921-CY 392 11.9 

3 03596000 Duck River below Manchester, 

Tenn.

107 R 03596000 USGS 107 1935-87 64.1 8.1 

4 001025 Duck River below Normandy 

Dam, Tenn.

195 FR Dam tailwater TVA 195 1922-31, 73-75, 

87-CY

155 10.7 

5 001065 Duck River at Williamsport, 

Tenn.

1,448 R 03599500 USGS 1,208 1905-08, 

21-CY

709 8.0 

6 475793 Duck River above Hurricane 

Mills, Tenn.

2,557 R 03603000 TVA 2,557 1926-CY 1,823 9.7 

7 002395 Shoal Creek at Highway 43 near 

Lawrenceburg, Tenn.

176 R 03588500 USGS 348 See entry for site 8 

8 03588500 Shoal Creek at Iron City, Tenn. 348 R 03588500 USGS 348 1926-94 324 12.7 9 001207 Elk River below Tims Ford Dam, 

Tenn.

529 FR Dam tailwater TVA 529 1967-75, 82-CY 409 10.4 

Table 1. Streamflow characteristics of sites in the lower Tennessee River Basin where instream loads were estimated[mi2, square miles; ft3/s, cubic feet per second; in., inches; R (riverine), tributary site at which streamflow is not regulated or a major component of the streamflow is 

located in an impoundment or at which streamflow is strongly influenced by an upstream impoundment; USGS, U.S. Geological Survey; TVA, Tennessee Valley Authtrend computation varies slightly among constituents]
12 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96 10 475796 Elk River near Prospect, Tenn. 1,784 R 03584600 TVA 1,805 1905-07, 20-CY 1,441 10.8 

11 FLCR7 Flint Creek near Falkville, Ala. 86.3 R 03576500 USGS 86.3 1953-70, 93-97 41.5 6.5 

12 TOWN CREEK

15a

Town Creek near Geraldine, Ala. 157 R 03572900 TVA 141 1958-CY 129 12.4 

13 002375 Sequatchie River at Valley Road, 

Tenn.

578 R 03571000 USGS 402 1921-94 341 11.5 

14 03609750 Tennessee River at Highway 60 

near Paducah, Ky.

40,330 FR 03609500 TVA 40,200 1890-

1984

43,700 14.6 

15 202832 Tennessee River at mile 23, Ky. 40,200 FR 03609500 TVA 40,200 See entry for site 14 16 03593005 Tennessee River at Pickwick 

Landing Dam, Tenn.

32,820 FR 03593500 USGS 33,140 1931-CY 40,794 16.7 

17 03571850 Tennessee River at South Pittsburg, Tenn. 22,640 FR 03571850 USGS 22,640 1931-87 31,121 18.6 18 003315 Tennessee River below Raccoon 

Mountain, Tenn.

21,730 FR 03568000 USGS 21,400 1875-CY 29,288 18.6 

aStation number in Alabama Department of Environmental Management study is t5.

Table 1. Streamflow characteristics of sites in the lower Tennessee River Basin where instream loads were estimated—Continued

Related streamflow gaging site

Site 

identification 

(fig. 2)

Surface-water station/site location Streamflow gaging station Period 

of 

record 

(water 

year)

Streamflow charac

teristics for perio

of record

Number Name

Drainage 

area 

(mi2)

Type

of 

site

Number Agency

Drainage area 

(mi2)

Median 

flow 

(ft3/s)

Media

runof

(in.)
Approach and Methods 13

100

90

80

70

60

50

40

30

20

10

0

1

1

2 3 4 5 6 7 8 9 10 11 12 13

LAND USE / LAND COVER, IN PERCENT

SITE NUMBER

OTHER (INCLUDING

WETLANDS AND

OPEN WATER)

URBAN

CULTIVATED

EXPLANATION

PASTURE

FOREST

SITE NUMBERÑCorresponds

with monitoring site number

in table shown above and

shown in figures 2 and 3

Figure 5. Basin characteristics of tributary sites in the lower Tennessee River

Basin where instream loads were estimated.

Figure 5. Basin characteristics of tributary sites in the lower Tennessee River Basin where instream loads were 

estimated.

Percentage of basin area in subunit or land use/land cover

Subunit Land use/land cover

Site 

number

(fig. 2) Surface-water station name

1 Clarks River at Almo, Ky. 95 0 5 0 0 0 0 0 14 58 20 3 5

2 Buffalo River near Flat Woods, Tenn. 0 1 99 0 0 0 0 0 68 25 4 0 3

3 Duck River below Manchester, Tenn. 0 0 0 1 0 99 0 0 18 45 16 1 20

4 Duck River below Normandy, Tenn. 0 0 0 34 0 65 0 0 35 42 9 1 13

5 Duck River at Williamsport, Tenn. 0 0 1 49 39 11 0 0 34 56 5 1 4

6 Duck River above Hurricane Mills, Tenn. 0 0 34 36 24 7 0 0 47 45 4 1 3

7 Shoal Creek at Highway 43 near Lawrenceburg, Tenn.0 0 100 0 0 0 0 0 42 46 8 2 2

8 Shoal Creek at Iron City, Tenn. 0 1 99 0 0 0 0 0 59 34 4 1 2

9 Elk River below Tims Ford Dam, Tenn. 0 0 0 11 0 64 14 12 42 41 11 1 5

10 Elk River near Prospect, Tenn. 0 0 7 61 0 24 5 3 44 47 6 0 3

11 Flint Creek near Falkville, Ala. 0 0 0 0 0 14 0 85 56 40 2 0 2

12 Town Creek near Geraldine, Ala. 0 0 0 0 0 0 0 100 31 57 10 0 2

13 Sequatchie River at Valley Road, Tenn. 0 0 0 0 0 0 64 36 67 29 2 0 2 Coastal Plain Transition Western Highland Rim Outer Nashville Basin Inner Nashville Basin Eastern Highland Rim Cumberland Plateau Plateau Escarpment and Valleys Forest Pasture Cultivated Urban Other

Agriculture
14 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

eight sites). To adjust for these differences in drainage 

areas, the estimates of instream load at these eight 

water-quality monitoring sites were multiplied by the 

ratios between the drainage areas of the paired streamflow and water-quality monitoring sites. A ratio within 

0.8 to 1.2 was considered to be acceptable. Two of the 

sites, however, fell outside of this criterion: Sequatchie 

River at Valley Road (site 13), and Shoal Creek at 

Highway 43 (site 7), had ratios of 1.4 and 0.5, respectively. These sites were included in the set of instreamload computation sites to provide representation for a 

particular combination of land use and subunit for 

which no other sites were available (as shown by combinations in fig. 5), but the load estimates are presented with the qualifier that the estimation error may 

be significantly larger than for other sites.

Trends in concentration were estimated at sites 

for which samples were collected at least quarterly for 

5 consecutive years, and for which streamflow data 

were available for each sample (either from a nearby 

continuous-recording streamflow gage or from measurements of instantaneous streamflow concurrent 

with sample collection) so that concentrations could 

be adjusted based on streamflow. Flow adjustment of 

concentration data eliminates variation in concentration related to streamflow, allowing for more accurate 

detection of time trends in water quality. The sites that 

met the data requirements for this analysis were the 18 

instream-load computation sites (table 1), and sites 19 

and 20 (figs. 2 and 3 and Appendix A) sampled as part 

of a special study conducted by ADEM and TVA in 

the Cumberland Plateau area in Alabama (Sweatt, 

1996).

Downstream variations in nutrient concentrations along the Tennessee and Duck Rivers were evaluated by summarizing data from numerous monitoring 

sites along the rivers where at least 20 samples had 

been collected during 1980-96 and with record extending past 1989. (The last criterion was relaxed to 1985 

in screening for sites on the Duck River, where only a 

few sites had data extending past 1985.) Of the more 

than 400 monitoring sites located on the main stem 

Tennessee River and Duck River (based on nutrient 

data in the STORET or WATSTORE data bases), 37 

sites met this criterion and are listed in Appendix A.

Data were reviewed to ensure comparability 

between data from the different monitoring networks, 

despite variations in analytical methods and datareporting levels among agencies. Analytical data 

derived from various analytical procedures were 

grouped when appropriate (table 2) to construct the 

most complete nutrient data sets possible. Differences 

in minimum reporting levels (MRL) among sites tend 

to confound spatial comparisons of instream loads, 

thus load estimates for sites and constituents with high 

MRL’s (compared with other sites) are reported with a 

qualifier.

Instream load of nitrogen, phosphorus, and sediment was calculated as the product of daily streamflow and estimated daily concentration using the 

Cohn’s Estimator model (Cohn and others, 1989; 

Cohn and others, 1992; Gilroy and others, 1990). This 

model includes a seven-parameter log-linear regression analysis of constituent concentrations against 

measured environmental variables:

ln[C] = β0 + β1(ln[Q/Q′] + β2(ln[Q/Q′])2 (1)

+ β3[T-T′] + β4[T-T′]

2 + β5sine[2πT] 

+ β6cosine[2πT] + e

where

ln[ ] is natural logarithm function;

C is estimated daily concentration, in 

milligrams per liter;

Q is daily streamflow, in cubic feet per second;

T is time, in decimal years;

π is 3.14169;

β0 - β6 are calibration coefficients of the regression 

model;

e is model error;

Q′ is centering variable defined so that β1 and 

β2 are statistically independent; and

T′ is centering variable defined so that β3 and 

β4 are statistically independent.

The regression analysis assumes that model 

errors (e) are independent and normally distributed, 

with zero mean and variance. The Minimum Variance 

Unbiased Estimator (Bradu and Mundlak, 1970) is 

included in the model to correct for the retransformation bias associated with log-linear regression models; 

the model also employs the Adjusted Maximum Likelihood Estimator (Cohn, 1988), which statistically 

addresses censored data and multiple reporting limits. 

Additional information about the data requirements of 

Cohn’s Estimator model is given in Appendix B.

Variations in concentrations of nitrogen, phosphorus, and sediment with season, streamflow, and 

time were displayed for sites 1 to 20 with scatterplots, 

and quantified with the multivariate log-linear regression component of Cohn’s Estimator model. A significance level of 0.05 was used as the criterion for 

statistical significance to interpret regression analyses 

and correlations. 
A

pproachandMethods15

a Nutrient constituent derived from another combination procedure.

Table 2. Summary of procedures used to combine nutrient constituent data from different analytical methods[Modified from Frick and others, 1996; mg/L, milligrams per liter; N, nitrogen; P, phosphorus]

Nutrient constituent

Parameter from source data bases

Procedure

Parameter

code Parameter name

Total nitrite plus nitrate, as N 00630 Nitrogen, nitrite plus nitrate, total (mg/L as N) Use if available 

00631 Nitrogen, nitrite plus nitrate, dissolved (mg/L as N) Use if 00630 not availa

Total ammonia, as N 00610 Nitrogen, ammonia, total (mg/L as N) Use if available 

00608 Nitrogen, ammonia, dissolved (mg/L as N) Use if 00610 not availa

Total ammonia plus organic 

nitrogen, as N

00625 Nitrogen, ammonia plus organic, total (mg/L as N) Use if available 00635 Nitrogen, ammonia plus organic, single determination (mg/L as N) Use if 00625 not availa00605+00610 Nitrogen, organic, total (mg/L as N) + total ammonia, as Na Use if 00625 and 00635 

not available

Total nitrogen, as N 00600 Nitrogen, total (mg/L as N) Use if available 

[total nitrite plus nitrate, as N] + [total ammonia plus organic nitrogen, as N]a Use if 00600 not availa

Total phosphorus, as P 00665 Phosphorus, total (mg/L as P) Use if available Dissolved orthophosphorus, as P 00671 Phosphorus, orthophosphate, dissolved (mg/L as P) Use if available 

00666 Phosphorus, dissolved (mg/L as P) Use if 00671 not availa
16 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

SOURCES OF NITROGEN AND 

PHOSPHORUS

Inputs from several sources of nitrogen and 

phosphorus were compiled to compare the magnitude 

of inputs among the various sources, to identify areas 

in the basin with higher nitrogen and phosphorus 

inputs, and to compare inputs with instream loads. 

Two distinct types of input estimates are presented: 

land-phase inputs (mass applied to the land surface 

of the watershed) and stream inputs (mass discharged 

directly to the stream channel). Estimates of landphase inputs cannot be compared directly to estimates 

of stream inputs or instream loads.

Sources of nutrients to watersheds and to 

streams and reservoirs include both point sources

(wastewater and stormwater discharge, combined 

sewer overflows) and nonpoint sources (atmospheric 

deposition, fertilizer application, livestock waste, 

urban runoff, failing septic systems, contaminated 

ground water, and natural sources). Inputs from wastewater discharge, atmospheric deposition, fertilizer 

application, and livestock waste were quantified for 

11 sites on the tributary streams and reservoirs and for 

the major hydrologic units in the LTEN River Basin 

(tables 3, 4, 5, and 6). Inputs from wastewater discharge are direct stream inputs, and inputs from nonpoint sources are land-phase inputs. Data from 1992 

were used to estimate inputs where possible because 

more data were available in the data sets for sources, 

land use, and instream loads during this period than in 

any other period. Inputs from the other listed sources 

are discussed in the section “Additional Sources of 

Nitrogen and Phosphorus” but are not quantified in 

this report.

Sites on the main stem of the Tennessee River 

were excluded from the analysis of inputs because the 

main stem of the lower Tennessee River carries considerable load from the upper Tennessee (UTEN) 

River Basin, and the intent of this report is to interpret 

sources and transport only in the LTEN River Basin. 

Treece and Johnson (1997) and Johnson and Treece 

(1998) describe nitrogen and phosphorus sources, 

yields, and trends for the upper Tennessee River Basin. 

In addition, the many large impoundments along the 

main stem in both the upper and lower parts of the 

Tennessee River alter the instream transport of nutrients and sediment, confounding direct comparison of 

inputs with instream loads for the main stem sites.

Point Sources

Point sources discharge directly to the stream 

channel from a discrete location and include municipal 

and industrial wastewater discharges, municipal and 

industrial stormwater discharges, and sanitary and 

combined sewer overflows. Data were not available to 

estimate nutrient inputs from stormwater discharges 

and sewer overflows; therefore, the only point-source 

inputs estimated in this report are municipal and 

industrial wastewater discharge.

Wastewater Discharge

In 1992, an estimated 730 municipal and industrial facilities discharged wastewater into streams and 

reservoirs in the LTEN River Basin. Nitrogen and 

phosphorus inputs were estimated for the individual 

wastewater discharges (fig. 4) using methods 

described in Appendix C and summarized in table 7. 

These estimates were then summed for the tributary 

basins and the major hydrologic units. The input estimates were normalized by watershed drainage area to 

allow comparisons among basins and hydrologic units. 

Estimated inputs of nitrogen from wastewater 

discharge for selected tributary monitoring basins 

(table 3) ranged from 0 (ton/mi2)/yr (site 11, Flint 

Creek near Falkville) to 0.61 (ton/mi2)/yr (site 1, 

Clarks River at Almo), and of phosphorus (table 4), 

from 0 (ton/mi2)/yr (site 11, Flint Creek near 

Falkville) to 0.14 (ton/mi2

)/yr (site 1, Clarks River at 

Almo). Estimated inputs of nitrogen for major hydrologic units (table 5) ranged from 0.021 (tons/mi2)/yr 

(hydrologic unit 06020004, Sequatchie River basin) to 

5.5 (tons/mi2)/yr (hydrologic unit 06040006, area contributing to below Kentucky Dam) and of phosphorus 

(table 6), from 0.005 (ton/mi2)/yr (hydrologic unit 

06020004, Sequatchie River basin) to 0.11 (ton/mi2)/yr 

(hydrologic unit 06030002, area contributing to 

Wheeler Reservoir).

Nonpoint Sources

Nonpoint-source inputs to a watershed have diffuse source areas, ranging from a few square miles to 

the entire watershed area. Only a part of the input from 

these sources reaches the stream channel; the remainder accumulates within the watershed or is lost 

through processes such as crop harvest and export and 

denitrification. Nonpoint-source inputs of nutrients 

estimated in this report (atmospheric deposition, fertilizer application, and livestock waste) primarily are 

related to human activities.
S

ourcesofNitrogenandPhosphorus17

Table 3. Nitrogen inputs and export for selected basins in the lower Tennessee River Basin[Inputs and export reported in tons per year of nitrogen; unit-area inputs and yield reported in tons per square mile per year; --, not estimated; <, less than; -, negative a nutrient sink; balance of land-phase input is calculated as the sum of inputs from fertilizer application, nitrogen fixation, and livestock waste, minus removal as crop at sites where record was available for that year]

Stream input Land-phase input

Wastewater Atmospheric Fertilizer Nitrogen Harvest (crop) Livestoc

Site Surface-water station discharge deposition application fixation uptake) waste 

identi- (1995 or 1992) (1992) (1991) (1992) (1992) (1992) 

fication Unit- Unit- Unit- Unit- Unit- U

(fig. 2) Number Name Input area Input area Input area Input area Input area Input a

input input input input input in

Tributary sites

1 PRI038 Clarks River at Almo, Ky. 82 0.61 210 1.6 3,000 23 1,000 7.6 -3,300 -24 500 2 03604000 Buffalo River near 26 .06 800 1.8 1,600 3.6 130 .3 -1,200 -2.6 880 

Flat Woods, Tenn.

4 001025 Duck River below Normandy 52 .27 350 1.8 890 4.5 290 1.5 -990 -5.1 990 

Dam, Tenn.

5 001065 Duck River at Williamsport, Tenn. 300 .21 2,600 1.8 5,200 3.6 1,100 .8 -6,000 -4.2 9,500 6 475793 Duck River above Hurricane 320 .12 4,600 1.8 6,700 2.6 1,300 .5 -8,000 -3.1 12,000 

 Mills, Tenn.

7 002395 Shoal Creek at Highway 43, 75 .43 320 1.8 1,200 6.6 100 .6 -850 -4.8 730 

near Lawrenceburg, Tenn.

9 001207 Elk River below Tims Ford 93 .18 960 1.8 3,200 6.0 850 1.6 -3,200 -6.0 3,100 

Dam, Tenn.

10 475796 Elk River near Prospect, Tenn. 160 .092 3,200 1.8 7,600 4.3 1,700 1.0 -7,800 -4.4 11,000 11 FLCR7 Flint Creek near Falkville, Ala. 0 .00 160 1.9 180 2.1 34 .4 -150 -1.8 1,100 112 TOWNCREEK15 Town Creek near Geraldine, Ala. 0.55 <.01 310 2.0 730 4.7 96 .6 -490 -3.1 2,000 113 002375 Sequatchie River at Valley 13 .02 1,000 1.8 860 1.5 200 .3 -960 -1.7 1,300 

Road, Tenn.

Main stem sites

14 03609750 Tennessee River at Highway 60 -- -- -- -- -- -- -- -- -- -- -- 

 near Paducah, Ky.

15 202832 Tennessee River at mile 23, Ky. -- -- -- -- -- -- -- -- -- -- -- 16 03593005 Tennessee River at Pickwick -- -- -- -- -- -- -- -- -- -- -- 

Landing Dam, Tenn.

17 03571850 Tennessee River at South -- -- -- -- -- -- -- -- -- -- -- 

Pittsburg, Tenn.

18 003315 Tennessee River below Raccoon -- -- -- -- -- -- -- -- -- -- -- 

Mountain, Tenn.

a Estimate for 1994.b Estimate for 1982.
18 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

Table 4. Phosphorus inputs and export, and ratio of nitrogen to phosphorus export, for selected basins in the lower Tennessee River [Inputs and export reported in tons per year of phosphorus; unit-area inputs and yield reported in tons per square mile per year; --, not estimated; -, negative number bsink; balance of land-phase input calculated as the sum of inputs from fertilizer application and livestock waste, minus removal as crop harvest; export was estimated available for that year]

Stream input Land-phase input

Site 

identi- Surface-water station Wastewater Atmospheric Fertilizer Nitrogen Harvest (crop Livestock Bala

fica- discharge deposition application fixation uptake) waste land

tion (1995 or 1992) (1992) (1991) (1992) (1992) (1992) input 

(fig. 2) cultu

Unit- Unit- Unit- Unit- Unit- Unit- 

Number Name Input area Input area Input area Input area Input area Input area Inpu

input input input input input input 

Tributary sites

1 PRI038 Clarks River at Almo, Ky. 19 0.14 -- -- 690 5.1 -- -- -430 -3.2 170 1.2 430 2 03604000 Buffalo River near 6 .014 -- -- 410 .93 -- -- -140 -.32 280 .62 550 

Flat Woods, Tenn.

4 001025 Duck River below Normandy 10 .050 -- -- 230 1.2 -- -- -120 -.60 280 1.4 390 

Dam, Tenn.

5 001065 Duck River at Williamsport, 67 .046 -- -- 1,300 .92 -- -- -700 -.48 2,700 1.9 3,300 

Tenn.

6 475793 Duck River above Hurricane 71 .028 -- -- 1,700 .67 -- -- -930 -.36 3,500 1.4 4,200 

Mills, Tenn.

7 002395 Shoal Creek at Highway 43, 13 .072 -- -- 300 1.7 -- -- -100 -.61 220 1.2 400 

near Lawrenceburg, Tenn.

9 001207 Elk River below Tims Ford 22 .042 -- -- 820 1.5 -- -- -400 -.76 980 1.8 1,400 

Dam, Tenn.

10 475796 Elk River near Prospect, Tenn. 39 .022 -- -- 1,900 1.1 -- -- -950 -.53 3,100 1.7 4,100 11 FLCR7 Flint Creek near Falkville, Ala. 0 .00 -- -- 30 .35 -- -- -17 -.19 320 3.7 340 12 TOWNCREEK15 Town Creek near 0.15 .001 -- -- 120 .77 -- -- -61 -.39 680 4.3 740 

Geraldine, Ala.

13 002375 Sequatchie River at Valley 3 .005 -- -- 220 .38 -- -- -110 -.19 390 .68 500 

Road, Tenn.

Main stem sites

14 03609750 Tennessee River at Highway 60 -- -- -- -- -- -- -- -- -- -- -- -- -- 

near Paducah, Ky.

15 202832 Tennessee River at mile 23, Ky. -- -- -- -- -- -- -- -- -- -- -- -- -- 16 03593005 Tennessee River at Pickwick -- -- -- -- -- -- -- -- -- -- -- -- -- 

Landing Dam, Tenn.

17 03571850 Tennessee River at South -- -- -- -- -- -- -- -- -- -- -- -- -- 

Pittsburg, Tenn.

18 003315 Tennessee River below Raccoon -- -- -- -- -- -- -- -- -- -- -- -- -- 

Mountain, Tenn.

a Instream estimate for 1982.
Sources of Nitrogen and Phosphorus 19

Table 5. Nitrogen inputs for major hydrologic units in the lower Tennessee River Basin[Inputs reported in tons per year of nitrogen; unit-area inputs reported in tons per square mile per year; -, negative number because crop harvest represents a nutrient calculated as the sum of inputs from fertilizer application, nitrogen fixation, and livestock waste, minus removal as crop harvest]

Stream input Land-phase input

Wastewater Atmospheric Fertilizer Nitrogen Harvest (crop) 

Major hydrologic unit discharge deposition application fixation uptake) 

(1995 or 1992) (1992) (1991) (1992) (1992) 

Hydrologic Unit- Unit- Unit- Unit- Unit- 

unit Name Input area Input area Input area Input area Input area In

code input input input input input 

06020001 Area contributing to Nickajack 34 0.073 880 1.9 540 1.1 68 0.14 -440 -0.94 1

Reservoir

06020004 Sequatchie River basin 13 .021 1,100 1.8 860 1.5 200 .34 -970 -1.6 106030001 Area contributing to Guntersville 330 .16 3,900 2.0 6,400 3.2 1,900 .93 -5,900 -2.9 14

Reservoir

06030002 Area contributing to Wheeler 7,400 2.5 5,500 1.9 16,000 5.6 3,500 1.2 -10,500 -3.6 13

Reservoir

06030003 Upper Elk River basin 130 .10 2,300 1.8 6,000 4.6 1,500 1.2 -6,100 -4.8 706030004 Lower Elk River basin 36 .038 1,800 1.8 3,000 3.1 410 .43 -2,500 -2.6 406030005 Area contributing to Pickwick/ 930 .41 4,100 1.8 10,000 4.5 1,000 .44 -4,800 -2.1 6

Wilson Reservoir

06030006 Bear Creek basin 39 .042 1,700 1.8 1,300 1.4 220 .23 -790 -.83 306040001 Area contributing to upper Kentucky 72 .035 3,300 1.6 3,700 1.8 960 .46 -3,700 -1.7 3

Reservoir

06040002 Upper Duck River basin 190 .16 2,100 1.8 4,400 3.7 920 .78 -5,000 -4.2 806040003 Lower Duck River basin 130 .088 2,600 1.7 2,500 1.6 450 .30 -3,300 -2.2 406040004 Buffalo River basin 37 .049 1,300 1.7 1,900 2.5 180 .24 -1,600 -2.1 106040005 Area contributing to lower Kentucky 290 .16 2,900 1.6 3,500 1.9 1,000 .55 -3,900 -2.1 2

Reservoir

06040006 Area contributing to below 3,800 5.5 1,100 1.6 7,300 10 2,800 4.0 -8,500 -12 2

Kentucky Dam
20 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

Table 6. Phosphorus and sediment inputs for major hydrologic units in the lower Tennessee River Basin[Inputs reported in tons per year; unit-area inputs reported in tons per square mile per year; --, not estimated; -, negative number because crop harvest represents a nutcalculated as the sum of inputs from fertilizer application and livestock waste, minus removal as crop harvest; rates of soil erosion by wind and water on cropland (U.Resources Conservation Service, 1997) were multiplied by area of cropland in the major hydrologic unit]

Phosphorus

Stream input Land-phase input 

Balan

Wastewater Atmospheric Fertilizer Nitrogen Harvest (crop) Livestock land-

Major hydrologic unit discharge deposition application fixation uptake) waste input 

(1995 or 1992) (1992) (1991) (1992) (1992) (1992) cultur

Hydrologic Unit- Unit- Unit- Unit- Unit- Unit- 

unit Name Input area Input area Input area Input area Input area Input area Input 

code input input input input input input 

06020001 Area contributing to Nickajack 8.1 0.017 -- -- 110 0.24 -- -- -51 -0.11 400 0.85 460 

Reservoir

06020004 Sequatchie River basin 3.0 .0050 -- -- 220 .38 -- -- -110 -.19 390 .67 500 06030001 Area contributing to 71 .036 -- -- 1,100 .55 -- -- -700 -.35 4,500 2.2 4,900 

Guntersville Reservoir

06030002 Area contributing to Wheeler 300 .11 -- -- 2,800 .96 -- -- -1,300 -.44 4,000 1.4 5,500 

Reservoir

06030003 Upper Elk River basin 30 .023 -- -- 1,500 1.2 -- -- -760 -.59 2,300 1.8 3,100 06030004 Lower Elk River basin 8.5 .0088 -- -- 690 .71 -- -- -300 -.31 1,300 1.4 1,700 06030005 Area contributing to 130 .059 -- -- 1,800 .80 -- -- -610 -.27 2,100 .94 3,300 

Pickwick/Wilson Reservoirs

06030006 Bear Creek basin 10 .010 -- -- 200 .21 -- -- -92 -.10 1,100 1.1 1,200 06040001 Area contributing to upper 17 .0081 -- -- 930 .45 -- -- -450 -.21 1,400 .67 1,900 

Kentucky Reservoir

06040002 Upper Duck River basin 40 .034 -- -- 1,100 .95 -- -- -580 -.49 2,300 1.9 2,800 06040003 Lower Duck River basin 31 .021 -- -- 640 .42 -- -- -400 -.26 1,300 .85 1,600 06040004 Buffalo River basin 9.1 .012 -- -- 490 .64 -- -- -200 -.26 400 .53 690 06040005 Area contributing to lower 33 .018 -- -- 860 .47 -- -- -500 -.27 960 .52 1,300 

Kentucky Reservoir

06040006 Area contributing to below 72 .10 -- -- 1,600 2.3 -- -- -1,100 -1.5 840 1.2 1,400 

Kentucky Dam
Sources of Nitrogen and Phosphorus 21

Table 7. Summary of methods for quantifying inputs of nitrogen and phosphorus to tributary basins and major hydrologic units

[NADP/NTN, National Atmospheric Deposition Network/National Trends Network; mg/L, milligrams per liter; lb/acre, pounds per acre; 

lb/bushel, pounds per bushel]

Nitrogen or 

phosphorus source

Methods

Description of spatial 

data Description of calculations Coefficients used in calculations

Wastewater discharge Annual mean flow rate 

and (where available) effluent concentration data 

from wastewater 

dischargers.

Multiply annual mean flow rate by 

reported effluent concentration, 

or (for nitrogen) by empirically 

adjusted effluent ammonia concentration, or by typical concentration of nitrogen and 

phosphorus for discharge 

categories.

Typical concentration for municipal wastewater: 

nitrogen - 15 mg/L, 

phosphorus - 3.5 mg/L, for 

industrial wastewater, estimates from National Oceanic 

and Atmospheric Administration (1993).

Atmospheric deposition Precipitation chemistry 

data from the 

NADP/NTN 

network.

Weight NADP/NTN nitrate and 

ammonia wet deposition rates to 

each basin; multiply weighted 

nitrate wet deposition rate for 

each basin by regional coefficient to calculate nitrate dry deposition rate; combine wet and 

dry deposition rates to arrive at 

total nitrogen deposition rate; no 

deposition rate calculated for 

phosphorus.

Regional dry nitrate coefficients;

Tennessee: 0.7826

Alabama: 0.8571

Kentucky: 0.8333.

Fertilizer application—

sales.

County estimates of 

commercial sales of 

nitrogen and phosphorus fertilizers.

No calculations No coefficients

Fertilizer application—

recommended rates.

County estimates of 

harvested acreage, 

by crop type.

Multiply harvested acreage by recommended fertilizer application 

rates for medium-soil test 

results.

Recommended fertilizer application rates, varying by crop:

nitrogen—rates range from 

0 (soybeans) to 

200 (tobacco) lb/acre

phosphorus—rates range from

20 (soybeans) to 

90 (tobacco) lb/acre.

Nitrogen fixation County estimates of 

harvested acreage 

of soybeans.

Multiply harvested acreage of soybean crop by nitrogen fixation 

rate.

Nitrogen-fixation rate for soybeans: 105 lb/acre.

Crop uptake County estimates of 

harvested amount, 

by crop type.

Multiply harvested amount by coefficients of nitrogen and phosphorus uptake rates, expressed 

as pounds per acre of nutrient 

removed per harvested amount 

per acre; simplify to pounds per 

harvested amount.

Nitrogen and phosphorus uptake 

rates, varying by crop;

nitrogen—rates range from

1.75 (corn) to 

5.15 (soybeans) lb/bushel

phosphorus—rates range from

0.22 (corn) to 

0.46 (soybeans) lb/bushel.

Livestock waste County estimates of 

nitrogen and phosphorus in livestock 

waste, by livestock 

class.

Sum estimates for each livestock 

class.
22 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

Nitrogen oxides Atmospheric ammonium

and nitrate

Fertilizer application

Nitrogen fixation

Volatilization

Volatilization

Atmospheric deposition

Exported

agricultural

products

Grains/vegetables

Imported

food

products

Meat,

eggs, milk

Humans

Livestock

Livestock waste

Forage/feed

Manure use

Crop

uptake

Cultivated

and

pasture

land

Instream load

Channel network

Municipal

wastewater

discharge

INPUTS TO THE WATERSHED FROM

VARIOUS SOURCES

FLUXES AMONG COMPONENTS IN

THE WATERSHED

EXPORTS FROM THE WATERSHED

Note: Italic text indicates loads (fluxes)

were estimated in this study

EXPLANATION

Overland

runoff/

subsurface

flow

Overland

runoff/

subsurface

flow

Exported

manure

Figure 6. Anthropogenic sources and fluxes of nitrogen within an agricultural watershed

(modified from Jordan and Weller, 1996).

Atmospheric Deposition

More than 3.2 million tons of nitrogen is deposited in the United States each year from atmospheric 

deposition (Puckett, 1994). The combustion of fossil 

fuels such as coal and oil is the major source of nitrogen in atmospheric deposition. Atmospheric deposition of nitrogen may be in a wet form as rain, snow, 

hail, fog, and freezing rain, or in a dry form as particulates, gases, and droplets. Atmospheric deposition of 

phosphorus is not considered a significant source of 

phosphorus to watersheds in general and is not estimated for this report; however, atmospheric deposition 

may contribute significant amounts of phosphorus in 

some locales (Harned, 1995).

The methods used for developing estimates of 

inputs of nitrogen from atmospheric deposition are 

described in Appendix C and summarized in table 7. 

Estimated inputs of nitrogen for selected tributary monitoring basins (table 3) ranged from 1.6 (tons/mi2)/yr 

(site 1, Clarks River at Almo) to 2.0 (tons/mi2)/yr 

(site 12, Town Creek near Geraldine). Estimated inputs 

of nitrogen for major hydrologic units (table 5) covered 

this same range; from 1.6 (tons/mi2)/yr (areas contributing to lower and upper Kentucky Reservoir and to below 

Kentucky Dam, hydrologic units 06040001, 06040005, 

and 06040006, respectively) to 2.0 (tons/mi2

)/yr (area 

contributing to Guntersville Reservoir, hydrologic unit 

06030001). These estimates fall near the upper part of 

the range [0.9-1.8 (tons/mi2

)/yr] reported in a national 

assessment (Puckett, 1994).

Inputs to Agricultural Lands

Agricultural lands are associated with major 

nutrient sources and sinks at the land surface. Major 

sources include fertilizer application to crop, nitrogen 

fixation by leguminous crops, and livestock waste 

released from feedlots and husbandry operations 

(fig. 6). Part of the nutrient mass applied to cropland 

(in both inorganic fertilizer and livestock manure) is 

utilized by plants and incorporated into plant biomass. 

Figure 6. Anthropogenic sources and fluxes of nitrogen within an agricultural watershed (modified from 

Jordan and Weller, 1996).
Sources of Nitrogen and Phosphorus 23

This mass, along with the amount of nitrogen assimilated through biological fixation, is removed from the 

basin when crop plants are harvested and exported. 

The amount of applied nutrient not removed from the 

basin by crop uptake and harvest may be transported, 

overland or in the subsurface, to the stream channel. 

To obtain a general estimate of the balance of sources 

and sinks available to enter the overland and subsurface transport phase, the estimate of crop uptake is 

subtracted from the sum of estimates of fertilizer 

application, nitrogen fixation, and livestock waste. 

However, this estimate does not reflect other processes, such as accumulation or denitrification in the 

soil, which may represent major components of the 

nutrient budget in agricultural lands.

Fertilizer Application

Commercial nitrogen fertilizer is applied as 

either ammonia or nitrate. Part of the nitrogen is 

absorbed by the growing crop, part is released in gaseous form to the atmosphere, and part remains as 

nitrate in the soil. Nitrate is soluble in water and 

readily leached from soils, allowing the rapid transport 

of nitrate into streams and ground-water systems. 

Phosphorus fertilizer is commonly applied as phosphate, which readily adheres to clay particles and is 

relatively insoluble in water. Soil erosion and transport 

is, therefore, the primary process by which significant 

amounts of particulate phosphate travel to streams.

The methods used to quantify inputs of nitrogen 

and phosphorus from fertilizer application are 

described in Appendix C and summarized in table 7. 

Input estimates of nitrogen for selected tributary monitoring basins (table 3) ranged from 1.5 (tons/mi2

)/yr 

(site 13, Sequatchie River at Valley Road) to 

23 (tons/mi2)/yr (site 1, Clarks River at Almo), and of 

phosphorus (table 4), from 0.35 (tons/mi2

)/yr (site 11, 

Flint Creek near Falkville) to 5.1 (tons/mi2

)/yr (site 1, 

Clarks River at Almo). Estimated inputs of nitrogen 

(table 5) for major hydrologic units ranged from 

1.1 (tons/mi2)/yr (area contributing to Nickajack Reservoir, hydrologic unit 06020001) to 10 (tons/mi2

)/yr 

(area contributing to below Kentucky Dam, hydrologic unit 06040006), and of phosphorus (table 6), 

from 0.21 (tons/mi2)/yr (Bear Creek basin, hydrologic 

unit 06030006) to 2.3 (tons/mi2)/yr (area contributing 

to below Kentucky Dam, hydrologic unit 06040006). 

The spatial distribution of nitrogen and phosphorus 

inputs generally corresponds to the distribution of cultivated land (figs. 3 and 5).

Nitrogen Fixation

Leguminous crops, such as soybeans, absorb 

atmospheric nitrogen from Rhizobium bacteria which 

infect their roots (nitrogen fixation). The mass of 

nitrogen fixed by crops through biological fixation 

was estimated because this mass is part of the balance 

between applied fertilizer, livestock manure, and crop 

uptake, but is not an expected input to water bodies.

The methods used to quantify inputs of nitrogen 

from nitrogen fixation are described in Appendix C 

and summarized in table 7. Estimated inputs of nitrogen for selected tributary monitoring basins (table 3) 

ranged from 0.30 (ton/mi2

)/yr (site 2, Buffalo River 

near Flat Woods, and site 13, Sequatchie River at Valley Road) to 7.6 (tons/mi2)/yr (site 1, Clarks River at 

Almo). Input estimates for the major hydrologic units 

(table 5) ranged from 0.14 (tons/mi2

)/yr (area contributing to Nickajack Reservoir, hydrologic unit 

06020001) to 4.0 (tons/mi2

)/yr (area contributing to 

below Kentucky Dam, hydrologic unit 06040006).

Crop Uptake

The nutrient mass applied to cropland as fertilizer, along with the mass fixed biologically, is partly 

removed from the land surface when crops are harvested. Part of the plant remains on the land as residue 

after harvest; therefore, the mass removed as harvested 

crop is somewhat less than crop uptake. The methods 

used to quantify nutrient removed as harvested crop are 

described in Appendix C, and summarized in table 7. 

Estimates are reported as negative values because harvest represents removal of nitrogen. Crop uptake estimates of nitrogen for selected tributary monitoring 

basins (table 3) ranged from -1.7 (tons/mi2

)/yr (site 13, 

Sequatchie River at Valley Road) to -24 (tons/mi2

)/yr 

(site 1, Clarks River at Almo), and of phosphorus 

(table 4), from -0.19 (tons/mi2)/yr (site 11, Flint Creek 

near Falkville and site 13, Sequatchie River at Valley 

Road) to -3.2 (tons/mi2

)/yr (site 1, Clarks River at 

Almo). Crop uptake estimates of nitrogen for major 

hydrologic units (table 5) ranged from -0.83 (tons/mi2

)/yr 

(Bear Creek basin, hydrologic unit 06030006) to 

-12 (tons/mi2

)/yr (area contributing to below Kentucky Dam, hydrologic unit 06040006), and of phosphorus (table 6), from -0.10 (tons/mi2

)/yr (Bear Creek 

basin, hydrologic unit 06030006) to -1.5 (tons/mi2)/yr 

(area contributing to below Kentucky Dam, hydrologic unit 06040006). 
24 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

Livestock Waste

Nationwide, approximately 7 billion farm animals generate millions of tons of manure containing 

some 6.5 million tons of nitrogen and 2 million tons of 

phosphorus each year. Organic nitrogen and urea in 

the manure are converted to ammonia (part of which 

volatilizes) and ultimately to nitrate (Mueller and 

Helsel, 1996). Most organic phosphorus is converted 

to phosphate, which adheres to soil particles and may 

become mobile through soil erosion. Confined animal 

feeding operations, which concentrate animals, feed, 

and manure on a small land area, have a greater potential to contribute nutrients to surface runoff and ground 

water. Manure produced by these operations may be 

applied to pasture land and crop land, becoming available for either crop uptake or losses to the environment (fig. 6).

The methods used to quantify inputs of nitrogen 

and phosphorus from livestock waste are described in 

Appendix C and summarized in table 7. Estimated 

inputs of nitrogen for selected tributary monitoring 

basins (table 3) ranged from 2.0 (tons/mi2)/yr (site 2, 

Buffalo River near Flat Woods) to 13 (tons/mi2)/yr 

(site 12, Town Creek near Geraldine), and of phosphorus (table 4), from 0.62 (tons/mi2

)/yr (site 2, Buffalo River near Flat Woods) to 4.3 (tons/mi2

)/yr 

(site 12, Town Creek near Geraldine). Input estimates 

of nitrogen (table 5) for major hydrologic units ranged 

from 1.5 (tons/mi2)/yr (area contributing to lower 

Kentucky Reservoir, hydrologic unit 06040005) to 

7.0 (tons/mi2

)/yr (area contributing to Guntersville 

Reservoir, hydrologic unit 06030001), and of phosphorus (table 6), from 0.52 (tons/mi2)/yr (area contributing to lower Kentucky Reservoir, hydrologic unit 

06040005) to 2.2 (tons/mi2)/yr (area contributing to 

Guntersville Reservoir, hydrologic unit 06030001). 

The spatial distribution of nitrogen and phosphorus 

input generally corresponds to the distribution of 

pasture land (figs. 3 and 5).

Additional Sources of Nitrogen and 

Phosphorus

Several other sources of nutrients have been 

identified, but quantitative information for these 

sources is not available. Urban runoff and combined 

sewage overflow are potentially large sources of nutrients from urban areas, but may be comparatively small 

sources in the LTEN River Basin because of the relatively small urban component in the basin. Nutrient 

contribution from natural sources, such as weathering 

and erosion of geologic materials in the watershed, 

may be significant, but is difficult to quantify. 

Nutrient contribution from leachate from failing 

septic systems may be significant in residential areas 

experiencing high rates of failure. A general estimate 

of nutrient loads in surface runoff from these areas 

(presented in this section) is derived from runoffmonitoring data from a residential area near Scottsboro, Alabama, which experienced a high rate (60 percent) of septic-system failure during the period 1983-

85 (Sagona, 1988). Surface-runoff loads of total nitrogen and total phosphorus during 1985 in this area were 

1.9 and 0.34 (lbs/acre)/storm event, respectively. 

These estimates were adjusted to account for other 

nutrient sources, such as lawn fertilizer, by subtracting 

the estimate for average runoff load from an adjacent 

residential area with a lower rate of septic-system 

failure (45 percent). 

Annual estimates of unit-area surface-runoff 

load from failing septic systems were calculated by 

multiplying the adjusted average runoff load by the 

average number of runoff events per year for the area 

(Steurer and Nold, 1986) as 42 (tons/mi2)/yr nitrogen, 

and 6.7 (tons/mi2

)/yr phosphorus. These estimates 

may be conservative due to sampling bias: the period 

of runoff monitoring at the high-failure-rate site did 

not include the wet season, when leachate amounts are 

highest; and the presence of some septic-system 

leachate in the samples from the adjacent, lowerfailure-rate site probably caused the adjustment for 

background to be too large. 

The estimates from the residential area near 

Scottsboro are at least an order of magnitude higher 

than estimates of unit-area input from wastewater discharge for most of the tributary basins (tables 3 and 4). 

However, these rates cannot be compared directly 

because the septic system loading rates apply to local 

areas with high failure rate, which may represent only 

a small part of the watershed area, whereas the wastewater discharge loading rates apply to the entire watershed. Because watershed-wide data on septic-system 

failure rates for unsewered areas were not available, 

extrapolation of these rates to produce basin estimates 

of nitrogen and phosphorus inputs, similar to the other 

sources in this report, was not possible.
Instream Transport of Nitrogen, Phosphorus, and Sediment 25

SOURCES OF SEDIMENT

Sediment is transported into streams by the erosion of uplands as a stream naturally evolves. The rate 

of erosion can be increased by natural disturbances, 

such as fires and floods, and by human disturbances, 

such as agricultural and construction activities. These 

disturbances can change the geomorphology of a 

stream by increasing the erosion of stream banks and 

beds, which serves as an additional source of sediment.

The Natural Resources Conservation Service 

has estimated rates of annual soil erosion from cropland, by major hydrologic unit, using the universal 

soil loss equation (U.S. Department of Agriculture, 

Natural Resources Conservation Service, 1997). Unitarea annual erosion rates from cropland for 1992 

ranged from 2,200 (tons/mi2

 of cropland)/yr (hydrologic unit 06020004, Sequatchie River Basin) to 

5,200 (tons/mi2 of cropland)/yr (hydrologic unit 

06030005, area contributing to Pickwick/Wilson reservoirs). These rates were multiplied by the percentage 

of cropland in each major hydrologic unit in 1992 to 

obtain an estimate of sediment input from cropland 

soil erosion to the hydrologic unit (table 6); estimates 

ranged from 51 to 540 (tons/mi2)/yr. 

Quantification of the various natural and human 

inputs of sediment presents a complex challenge 

because few sources of ancillary data can be related to 

the numerous potential sources of sediment. An extensive analysis of the sources of sediment was not compiled for the selected monitoring basins because the 

limited data set of instream sediment loads (at three 

tributary sites) was insufficient for input/instream load 

comparisons. Furthermore, only one of these three 

sites drained basin areas large enough to compare with 

the estimates of sediment inputs based on major 

hydrologic unit.

INSTREAM TRANSPORT OF NITROGEN, 

PHOSPHORUS, AND SEDIMENT

The following three sections describe spatial 

and temporal variations in instream transport of nutrients and sediment. The first section examines the relation of nutrient transport to the environmental 

variables: season, hydrologic condition at the time of 

sample collection, and physical location along the 

stream channel. The second section describes estimated nutrient and sediment instream loads. The third 

section compares nutrient yields to inputs from nutrient sources and other factors influencing transport. 

Relation of Concentrations to Season, 

Streamflow, and Reach Location

Interpretation of the relation of nutrient and sediment concentrations to season and streamflow is confounded because season and streamflow variables 

generally do not operate independently of one another. 

For example, an observed seasonal pattern in nutrient 

concentration may be caused by correlation between 

concentration and streamflow, rather than directly by 

seasonal change in water-quality processes. A stratified statistical analysis, such as multiple linear regression, provides a way to identify the confounding 

effects of different variables. In this approach, the 

influence of each variable is interpreted independently 

by examining the statistical significance of each 

regression coefficient (Cohn and others, 1992). The 

results of seven-parameter log-linear regressions of 

nutrient and sediment concentration data are organized 

by constituent for each of the 20 water-quality monitoring sites (table 8). The period of record used in the 

regression analysis varied among sites and is indicated 

in table 8 along with the statistical significance and 

sign (positive or negative) of the regression coefficients. 

Statistical significance of β1 indicates that 

streamflow, independent of other influences, is a good 

predictor of concentration. Statistical significance of 

both β5 and β6 indicates a significant seasonal pattern 

in concentration data (fitted to a simple sine wave 

function), independent of other influences. Temporal 

trends in nutrient and sediment concentration are interpreted based on the statistical significance of β3; these 

are discussed in the section “Trends of Nitrogen, Phosphorus, and Sediment.”

Relation of Concentrations to Season

Seasonal variation in nutrient concentrations is 

commonly attributed to assimilation by algae and 

aquatic macrophytes. During the summer months, 

concentrations of bioavailable forms of nitrogen and 

phosphorus may decrease as a result of aquatic plant 

growth in water bodies with long hydraulic-residence 

time. Other possible causes of seasonal variation 

include seasonal fertilizer application, temperaturedriven nitrification and volatilization, and seasonal 

flow variation. The extent to which seasonal processes 
26 Sources, Instream

Transport, and Trends of Nitrogen, Phosphorus,

and Sediment in the Lower Tennessee River Basin, 1980-96

Table 8. Calibration results for the seven-parameter log-linear regression model of nutrient and sediment concentrations for selected sites in the lower Tennessee 

River Basin

[The numerical values of the coefficients β1-β6 are not shown; rather, the table entries indicate the time period spanned by the calibration data sets, which varied among sites and constituents; the colors of 

the numbers indicate the statistical significance and the sign (positive or negative) of the regression coefficients β1-β6 (see eq. 1); 1985-95, coefficient significant and positive; 1985-95, coefficient

significant and negative; 1985-95, coefficient not significant; β1 significant and positive (negative) indicates that concentrations increase (decrease) with increasing streamflow; β3 significant and positive 

(negative) indicates an increasing (decreasing) temporal trend in concentration; β5 and β6 significant indicate that concentrations vary in a seasonal pattern, the patterns are illustrated at the bottom of the 

table; additional interpretation of the significance and sign of each coefficient is explained in the text; other regression statistics, such as coefficient of determination and standard error, are reported with load 

estimates in table 9; --, not estimated, and results not shown on fig. 19 because record during common period was insufficient; entries in italics are subject to larger error than the other entries, for various 

reasons (described in footnotes); R (riverine), tributary site at which streamflow is not regulated, or at which a major component of streamflow is not regulated; FR (flow regulated), site located in an

impoundment or where streamflow is strongly influenced by an upstream impoundment; common period, the time span of the calibration data set used to obtain trend estimates for this common period is 

indicated in the table entries]

Common

Site β1 β5 β6 period

identi- (Logarithm β3 (Sine (Cosine β3

fication Surface-water station/site location Site of (Decimal {2 * π {2 * π (Decimal

(fig. 2) Number Name type streamflow) time) * time}) * time}) time)

Total nitrogen as N

1 PR1038 Clarks River at Almo, Ky. R 1985-95 1985-95 1985-95 1985-95 1985-94

2 03604000 Buffalo River near Flat Woods, Tenn. R 1982-95 1982-95 1982-95 1982-95 1985-94

4 001025 Duck River below Normandy Dam, Tenn. FR 1986-95 1986-95 1986-95 1986-95 --

5 001065 Duck River at Williamsport, Tenn. R 1982-94 1982-94 1982-94 1982-94 1982-94

6 475793 Duck River above Hurricane Mills, Tenn. R 1986-93 1986-93 1986-93 1986-93 1985-94

7 002395 Shoal Creek at Highway 43 near R 1983-92 1983-92 1983-92 1983-92 --

Lawrenceburg, Tenn. a

9 001207 Elk River below Tims Ford Dam, Tenn. FR 1984-94 1984-94 1984-94 1984-94 1985-94

10 475796 Elk River near Prospect, Tenn. R 1987-92 1987-92 1987-92 1987-92 --

11 FLCR7 Flint Creek near Falkville, Ala. R 1993-97 1993-97 1993-97 1993-97 --

12 TOWNCREEK15 Town Creek near Geraldine, Ala. R 1988-96 1988-96 1988-96 1988-96 --

13 002375 Sequatchie River at Valley Road, Tenn. a R 1983-95 1983-95 1983-95 1983-95 1985-94

14 03609750 Tennessee River at Highway 60 near Paducah, Ky. FR 1980-84 1980-84 1980-84 1980-84 --

15 202832 Tennessee River at mile 23, Ky. b FR 1990-94 1990-94 1990-94 1990-94 --

16 03593005 Tennessee River at Pickwick Landing Dam, Tenn. FR 1980-96 1980-96 1980-96 1980-96 1985-94

17 03571850 Tennessee River at South Pittsburg, Tenn. FR 1980-85 1980-85 1980-85 1980-85 --

18 003315 Tennessee River below Raccoon Mountain, Tenn. FR 1981-94 1981-94 1981-94 1981-94 1985-94

Total ammonia as N

1 PRI038 Clarks River at Almo, Ky. R 1985-95 1985-95 1985-95 1985-95 1986-94

2 03604000 Buffalo River near Flat Woods, Tenn. R 1987-92 1987-92 1987-92 1987-92 --

4 001025 Duck River below Normandy Dam, Tenn. FR 1987-95 1987-95 1987-95 1987-95 --

5 001065 Duck River at Williamsport, Tenn. R 1984-94 1984-94 1984-94 1984-94 1986-94

6 475793 Duck River above Hurricane Mills, Tenn. R 1987-94 1987-94 1987-94 1987-94 --
Instream Transport of 

Nitrogen, Phosphorus, and Sediment 27

Table 8. Calibration results for the seven-parameter log-linear regression model of nutrient and sediment concentrations for selected sites in the lower Tennessee

River Basin—Continued

Common

Site β1 β5 β6 period

identi- (Logarithm β3 (Sine (Cosine β3

fication Surface-water station/site location Site of (Decimal {2 * π {2 * π (Decimal

(fig. 2) Number Name type streamflow) time) * time}) * time}) time)

Total ammonia as N—Continued

7 002395 Shoal Creek at Highway 43 R 1984-94 1984-94 1984-94 1984-94 1986-94

near Lawrenceburg, Tenn. a

9 001207 Elk River below Tims Ford Dam, Tenn. FR 1984-94 1984-94 1984-94 1984-94 1986-94

10 475796 Elk River near Prospect, Tenn. R 1987-94 1987-94 1987-94 1987-94 --

11 FLCR7 Flint Creek near Falkville, Ala. R 1993-97 1993-97 1993-97 1993-97 --

12 TOWNCREEK15 Town Creek near Geraldine, Ala. c R 1988-96 1988-96 1988-96 1988-96 --

13 002375 Sequatchie River at Valley Road, Tenn. a R 1983-95 1983-95 1983-95 1983-95 1986-94

15 202832 Tennessee River at mile 23, Ky.

 b FR 1990-94 1990-94 1990-94 1990-94 --

16 03593005 Tennessee River at Pickwick Landing Dam, Tenn. FR 1980-96 1980-96 1980-96 1980-96 --

17 03571850 Tennessee River at South Pittsburg, Tenn. FR 1980-86 1980-86 1980-86 1980-86 --

19 SCARHAMCREEK03 Scarham Creek near Kilpatrick, Ala. R 1988-96 1988-96 1988-96 1988-96 --

Total ammonia plus organic nitrogen as N

1 PRI038 Clarks River at Almo, Ky. R 1985-95 1985-95 1985-95 1985-95 1986-93

2 03604000 Buffalo River near Flat Woods, Tenn. R 1982-95 1982-95 1982-95 1982-95 1986-93

4 001025 Duck River below Normandy Dam, Tenn. FR 1986-95 1986-95 1986-95 1986-95 --

5 001065 Duck River at Williamsport, Tenn. R 1981-92 1981-92 1981-92 1981-92 1986-93

6 475793 Duck River above Hurricane Mills, Tenn. R 1986-93 1986-93 1986-93 1986-93 1986-93

7 002395 Shoal Creek at Highway 43, R 1983-94 1983-94 1983-94 1983-94 1986-93

near Lawrenceburg, Tenn. a

9 001207 Elk River below Tims Ford Dam, Tenn. FR 1984-94 1984-94 1984-94 1984-94 1986-93

10 475796 Elk River near Prospect, Tenn. R 1986-93 1986-93 1986-93 1986-93 1986-93

11 FLCR7 Flint Creek near Falkville, Ala. R 1993-97 1993-97 1993-97 1993-97 --

12 TOWNCREEK15 Town Creek near Geraldine, Ala. R 1988-96 1988-96 1988-96 1988-96 --

13 002375 Sequatchie River at Valley Road, Tenn. a R 1983-95 1983-95 1983-95 1983-95 1986-93

14 03609750 Tennessee River at Highway 60 near Paducah, Ky. FR 1980-84 1980-84 1980-84 1980-84 --

15 202832 Tennessee River at mile 23, Ky.

 b FR 1990-94 1990-94 1990-94 1990-94 --

16 03593005 Tennessee River at Pickwick Landing Dam, Tenn. FR 1986-93 1986-93 1986-93 1986-93 1986-93

17 03571850 Tennessee River at South Pittsburg, Tenn. FR 1980-85 1980-85 1980-85 1980-85 --

18 003315 Tennessee River below Raccoon Mountain, Tenn. FR 1981-94 1981-94 1981-94 1981-94 1986-93

19 SCARHAMCREEK03 Scarham Creek near Kilpatrick, Ala. R 1988-96 1988-96 1988-96 1988-96 --
28 Sources, Instream Transport, and Trends of 

Nitrogen, Phosphorus,

and Sediment in the Lower Tennessee River Basin, 1980-96

Table 8. Calibration results for the seven-parameter log-linear regression model of nutrient and sediment concentrations for selected sites in the lower Tennessee 

River Basin—Continued

Common

Site β1 β5 β6 period

identi- (Logarithm β3 (Sine (Cosine β3

fication Surface-water station/site location Site of (Decimal {2 * π {2 * π (Decimal

(fig. 2) Number Name type streamflow) time) * time}) * time}) time)

Total nitrite plus nitrate as N

1 PRI038 Clarks River at Almo, Ky. R 1985-95 1985-95 1985-95 1985-95 1985-94

2 03604000 Buffalo River near Flat Woods, Tenn. R 1986-93 1986-93 1986-93 1986-93 1985-94

4 001025 Duck River below Normandy Dam, Tenn. FR 1987-95 1987-95 1987-95 1987-95 --

5 001065 Duck River at Williamsport, Tenn. R 1982-93 1982-93 1982-93 1982-93 --

6 475793 Duck River above Hurricane Mills, Tenn. R 1987-93 1987-93 1987-93 1987-93 --

7 002395 Shoal Creek at Highway 43, Tenn. a R 1983-94 1983-94 1983-94 1983-94 1985-94

9 001207 Elk River below Tims Ford Dam FR 1984-94 1984-94 1984-94 1984-94 1985-94

10 475796 Elk River near Prospect, Tenn. R 1987-93 1987-93 1987-93 1987-93 --

11 FLCR7 Flint Creek near Falkville, Ala. R 1993-97 1993-97 1993-97 1993-97 --

12 TOWNCREEK15 Town Creek near Geraldine, Ala. R 1988-96 1988-96 1988-96 1988-96 --

13 002375 Sequatchie River at Valley Road, Tenn. a R 1983-95 1983-95 1983-95 1983-95 1985-94

14 03609750 Tennessee River at Highway 60 near Paducah, Ky.FR 1980-84 1980-84 1980-84 1980-84 --

15 202832 Tennessee River at mile 23, Ky. b FR 1990-94 1990-94 1990-94 1990-94 --

16 03593005 Tennessee River at Pickwick Landing Dam, Tenn. FR 1980-96 1980-96 1980-96 1980-96 1985-94

17 03571850 Tennessee River at South Pittsburg, Tenn. FR 1980-85 1980-85 1980-85 1980-85 --

18 003315 Tennessee River below Raccoon Mountain, Tenn. FR 1981-94 1981-94 1981-94 1981-94 1985-94

19 SCARHAMCREEK03 Scarham Creek near Kilpatrick, Ala. R 1988-96 1988-96 1988-96 1988-96 --

20 SOUTHSAUTYCK03 South Sauty Creek, Ala. R 1988-96 1988-96 1988-96 1988-96 --

Total phosphorus as P

1 PRI038 Clarks River at Almo, Ky. R 1985-95 1985-95 1985-95 1985-95 1985-93

2 03604000 Buffalo River near Flat Woods, Tenn. R 1983-95 1983-95 1983-95 1983-95 1985-93

4 001025 Duck River below Normandy Dam, Tenn. FR 1987-94 1987-94 1987-94 1987-94 --

5 001065 Duck River at Williamsport, Tenn. R 1981-93 1981-93 1981-93 1981-93 1985-93

6 475793 Duck River above Hurricane Mills, Tenn. R 1988-93 1988-93 1988-93 1988-93 --

7 002395 Shoal Creek at Highway 43 near R 1983-94 1983-94 1983-94 1983-94 1985-93

 Lawrenceburg, Tenn. a

9 001207 Elk River below Tims Ford Dam, Tenn. FR 1983-94 1983-94 1983-94 1983-94 1985-93

10 475796 Elk River near Prospect, Tenn. R 1986-94 1986-94 1986-94 1986-94 --

14 03609750 Tennessee River at Highway 60 near Paducah, Ky.FR 1980-84 1980-84 1980-84 1980-84 --

15 202832 Tennessee River at mile 23, Ky. b FR 1990-94 1990-94 1990-94 1990-94 --
Instream Transport of 

Nitrogen, Phosphorus, and Sediment 29

Table 8. Calibration results for the seven-parameter log-linear regression model of nutrient and sediment concentrations for selected sites in the lower Tennessee

River Basin—Continued

Common

Site β1 β5 β6 period

identi- (Logarithm 

fication Surface-water station/site location Site 

(fig. 2) Number Name type 

Total phosphorus as P—Continued

16 03593005 Tennessee River at Pickwick Landing Dam, Tenn. FR 1980-93 1980-93 1980-93 1980-93 1985-93

17 03571850 Tennessee River at South Pittsburg, Tenn. FR 1980-86 1980-86 1980-86 1980-86 --

Dissolved orthophosphorus as P

2 03604000 Buffalo River near Flat Woods, Tenn. R 1984-95 1984-95 1984-95 1984-95 --

6 475793 Duck River above Hurricane Mills, Tenn. R 1986-91 1986-91 1986-91 1986-91 --

10 475796 Elk River near Prospect, Tenn. R 1987-91 1987-91 1987-91 1987-91 --

11 FLCR7 Flint Creek near Falkville, Ala. c R 1993-97 1993-97 1993-97 1993-97 --

12 TOWNCREEK15 Town Creek near Geraldine, Ala. c R 1988-96 1988-96 1988-96 1988-96 --

16 03593005 Tennessee River at Pickwick Landing Dam, Tenn. FR 1983-93 1983-93 1983-93 1983-93 --

15 202832 Tennessee River at mile 23, Ky. b FR 1990-94 1990-94 1990-94 1990-94 --

19 SCARHAMCREEK03 Scarham Creek near Kilpatrick, Ala. R 1988-96 1988-96 1988-96 1988-96 --

Suspended sediment

2 03604000 Buffalo River near Flat Woods, Tenn. R 1982-95 1982-95 1982-95 1982-95 --

3 03596000 Duck River below Manchester, Tenn. d R 1979-83 1979-83 1979-83 1979-83 --

8 03588500 Shoal Creek at Iron City, Tenn. d R 1979-83 1979-83 1979-83 1979-83 --

16 03593005 Tennessee River at Pickwick Landing Dam, Tenn. FR 1980-93 1980-93 1980-93 1980-93 --

17 03571850 Tennessee River at South Pittsburg, Tenn. FR 1980-86 1980-86 1980-86 1980-86 --

a

 Regression results are subject to error because streamflow-measurement and water-quality-sampling sites were not colocated. b

 Regression results are subject to error due to grab sampling methods at this vertically stratified site. c

 Regression results are subject to error due to variable minimum reporting level and large percentage of observations below minimum reporting level. d

 The calibration data set included data from 1979 in order to have sufficient length of record.

Seasonal patterns:

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

β5 and β6 significant and positive— Annual peak in winter β5 and β6 significant and negative—

Annual peak in summer

β5 significant and positive,

β6 significant and negative—

Annual peak in spring β5 significant and negative,

β6 significant and positive—

Annual peak in fall
30 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

influence nutrient transport in the LTEN River Basin is 

indicated by the significance of the seasonal regression coefficients (β5 and β6) for the bioavailable 

forms of nutrients (total nitrite plus nitrate and dissolved orthophosphorus, table 8). These results will 

indicate seasonal effects independent of flow variation, which is accounted for by the regression coefficient β1.

Statistically significant seasonal variation of 

total nitrite plus nitrate concentrations was observed at 

9 of the 18 sites tested. Seasonal variation was closely 

correlated with site type: 7 of the 9 sites showing significant seasonal variation were in reservoirs or were 

influenced by reservoir tailwater, suggesting strong 

seasonal influence by aquatic plants in water bodies 

with long hydraulic-residence times. The seasonal pattern of total nitrite plus nitrate for most of the sites 

influenced by reservoirs was annual maximum concentrations in winter and annual minimum concentrations in summer. 

Significant seasonal variation was observed at 

less than half of the sites for the other nutrient constituents, except for dissolved orthophosphorus. Of the 

eight sites with dissolved-orthophosphorus data, four 

showed statistically significant seasonal variation of 

this constituent. The detected pattern at the reservoir 

sites (sites 16 and 15, Tennessee River at Pickwick 

Landing Dam and at river mile 23, respectively) was 

slightly offset (annual maximum concentrations in fall 

rather than winter, and annual minimum concentrations in the spring) from the pattern for total nitrite 

plus nitrate, but may be caused by the same phenomenon of aquatic-plant assimilation.

Scatterplots of concentration and time of year of 

sampling (fig. 7) illustrate seasonal patterns in nitrate 

and total phosphorus at a few selected sites. Comparison of these patterns with the regression result (statistical significance of β5 and β6, also shown on fig. 7) 

illustrates how the regression analysis isolates the 

influences of different environmental variables. For 

example, concentrations of nitrite plus nitrate appear 

to indicate a seasonal pattern at site 2 (Buffalo River at 

Flat Woods); however, the regression analysis did not 

detect a statistically significant pattern. The apparent 

pattern may be caused instead by a seasonal bias in 

sampled streamflow conditions (five of the six highest 

streamflows sampled occurred during the month of 

January) combined with a strong correlation between 

concentration and streamflow (β1 is significant and 

positive, table 8).

A separate possible cause of seasonal variations 

in nutrient concentrations, the agricultural planting 

cycle, may cause episodic increases in concentrations 

of nutrients derived from fertilizer application and of 

suspended sediment following periods of soil preparation and fertilizer application and when storm runoff is 

frequent (during April through June). The relation 

between the planting cycle and instream nutrient 

transport is not examined in this report, however, 

because the data from most of the sites are from quarterly monitoring programs rather than from programs 

designed to detect episodic, storm-related increases in 

concentrations. 

Relation of Concentrations to Streamflow

The variation of nutrient concentrations with 

streamflow generally reflects the dominant sources in 

the watershed (point versus nonpoint sources). Transport of nonpoint-source-derived constituents mainly 

occurs during periods of high surface runoff and high 

base flow; therefore, higher concentrations are 

expected during high streamflow in watersheds dominated by nonpoint sources. Point-source discharges are 

generally independent of runoff; consequently, 

instream concentrations of constituents from these 

sources are expected to decrease during high streamflow. 

Scatterplots of concentration and streamflow are 

shown (fig. 8), along with regression results for β1 

(coefficient on streamflow), for total nitrite plus nitrate 

and total phosphorus at a few selected monitoring 

sites. Scatterplots and model regression results are 

included for the full set of load-computation sites for 

total nitrite plus nitrate, total ammonia, total phosphorus, and dissolved orthophosphorus (Appendix D). 

Interpretation of the relation of concentration to 

streamflow at flow-regulated sites is of less interest 

than at riverine sites in this examination of dominant 

sources in the watershed because at flow-regulated 

sites the observed streamflow-concentration relation 

reflects controlled impoundment releases rather than 

hydrologic processes such as runoff. Therefore, 

regression results are not shown on the concentrationstreamflow scatterplots for flow-regulated sites in 

Appendix D. The flow corresponding to maximum 

turbine capacity is indicated on the scatterplots for 

these sites as a cutoff below which a relation based on 

hydrologic conditions in the contributing watershed is 

unlikely; above this cutoff, at least some component of 

streamflow reflects hydrologic conditions upstream 
Instream Transport of Nitrogen, Phosphorus, and Sediment 31

0.01

0.1

1

10

0.01

0.1

1

10

DJ F MA MJ J A S ON

DJ FM AMJ J A SON

0.01

0.1

1

10

0.01

0.1

1

10

0.01

0.1

1

10

Elks Ford below Tims Ford Dam, Tenn.

(site 9, fig. 2)

Duck River below Normandy Dam, Tenn.

(site 4, fig. 2)

Buffalo River near Flat Woods, Tenn.

(site 2, fig. 2)

Elk River below Tims Ford Dam, Tenn.

(site 9, fig. 2)

Duck River below Normandy Dam, Tenn.

(site 4, fig. 2)

Tennessee River at Highway 60 near

Paducah, Ky. (site 14, fig. 2)

Tennessee River at Pickwick Landing Dam,

Tenn. (site 16, fig. 2)

Clarks River at Almo, Ky.

(site 1, fig. 2)

0.01

0.1

1

10

EXPLANATION

SEASONAL PATTERN OF CONCENTRATION

(calculated by Cohn's Estimator model)

Not significant (p-value for β5, β6 greater

than 0.05)

Significant, annual peak in winter

Significant, annual peak in spring

Significant, annual peak in summer

Significant, annual peak in fall

RIVERINE SITE

FLOW-REGULATED SITE

Figure 7. Seasonal variation in concentrations and model estimate of seasonal pattern at selected sites

in the lower Tennessee River Basin, 1980-96.

TOTAL PHOSPHORUS CONCENTRATION AS P,

IN MILLIGRAMS PER LITER

TOTAL AMMONIA CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL NITRITE PLUS NITRATE CONCENTRATION AS N, IN MILLIGRAMS PER LITER

0.01

0.1

1

10

0.01

0.1

1

10

W

Sp

Su

F

W

W

Su

Sp

W

F

Su

Figure 7. Seasonal variation in nutrient concentrations and model estimate of seasonal pattern at 

selected sites in the lower Tennessee River Basin, 1980-96.
32 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

EXPLANATION

100 100,000 1,000 10,000 0.001

10

0.01

0.1

1

100 100,000 1,000 10,000 0.001

10

0.

01

0.1

1

100,000 100 100,000 1,000 10,000 0.001

10

0.

01

0.1

1

DAILY MEAN STREAMFLOW, IN CUBIC

FEET PER SECOND

DAILY MEAN STREAMFLOW, IN CUBIC

FEET PER SECOND

100 1,000 10,000 0.001

10

0.01

0.1

1

0.1 10,000 1 10 100 1,000 0.001

10

0.01

0.1

1

100 10,000 200 500 1,000 2,000 5,000 0.001

10

0.01

0.1

1

100 10,000 200 500 1,000 2,000 5,000 0.001

10

0.01

0.1

1

TOTAL PHOSPHORUS CONCENTRATION AS P, IN MILLIGRAMS PER LITER

TOTAL NITRITE PLUS NITRATE CONCENTRATION AS N, IN MILLIGRAMS PER LITER

STREAMFLOW VARIATION IN

CONCENTRATION (calculated

by Cohn's Estimator model)

β1 IS POSITIVE AND SIGNIFICANT

(p-value for β1 is less than or equal

to 0.05)

RIVERINE SITE

Figure 8. Variation in total nitrite plus nitrate and total phosphorus concentrations with streamflow and

model estimate of streamflow variation in concentration at selected sites in the lower Tennessee River

Basin, 1980-96.

Buffalo River near Flat Woods, Tenn.

(site 2, fig. 2)

Duck River above Hurricane Mills, Tenn.

(site 6, fig. 2)

Duck River above Hurricane Mills, Tenn.

(site 6, fig. 2)

Elk River near Prospect, Tenn.

(site 10, fig. 2)

Buffalo River near Flat Woods, Tenn.

(site 2, fig. 2)

Duck River at Williamsport, Tenn. (site 5, fig. 2)

Flint Creek near Falkville, Ala.

(site 11, fig. 2)

Figure 8. Variation in total nitrite plus nitrate and total phosphorus concentrations with streamflow and 

model estimate of streamflow variation in concentration at selected sites in the lower Tennessee River 

Basin, 1980-96.
Instream Transport of Nitrogen, Phosphorus, and Sediment 33

from the impoundment (E.A. Thornton and 

D.L. Meinert, Tennessee Valley Authority, written 

commun., 1998). 

Comparison between the relative influence of 

nonpoint sources and point sources on instream water 

quality in the selected tributary basins can be examined by comparing the statistical significance of the 

streamflow regression coefficient, β1 (table 8 and 

fig. 8) with a ranking of these basins according to estimates of inputs from these sources. For total nitrite 

plus nitrate, β1 was significant and positive at 5 sites 

(sites 2, 6, 10, 11, and 20) of the 11 riverine sites 

tested, and was positive in all of these cases, suggesting that nonpoint sources were the dominant source of 

input for total nitrite plus nitrate during the periods 

spanned by the calibration data sets. These results 

match the ranking of basins by nitrogen input reasonably well; the largest nitrogen inputs from nonpoint 

sources (the sum of atmospheric deposition and fertilizer application and livestock waste) relative to point 

sources (wastewater discharge) were for sites 11, 20, 

12, 13, 10, and 2. β1 was significant and positive for 

total phosphorus at three of the six riverine sites (sites 

2, 5, and 6), suggesting that nonpoint sources are the 

dominant source of phosphorus input in these watersheds. The nonpoint source might be a natural source, 

as for sites 5 and 6; suspended sediment at these sites 

is naturally phosphate rich as a result of phosphatic 

limestone in the watershed. The regression results for 

total phosphorus might, therefore, be explained by 

movement of sediment during high flows.

Dominance of point sources, such as wastewater 

discharge, is indicated by a negative concentrationstreamflow relation, that is, by a significant and negative value for β1. β1 was significant and negative for 

total phosphorus concentrations at site 1 (Clarks River 

at Almo), suggesting dominance of point-source discharges or some other runoff-independent source at 

this site. Clarks River at Almo was ranked second out 

of 11 based on the ratio of point-source input (wastewater discharge) to nonpoint-source inputs of phosphorus. Data for dissolved orthophosphorus, which 

might have provided additional information about the 

influence of wastewater sources, were not available 

for this site.

The relation between nutrient concentration and 

streamflow has important implications for resource 

management apart from the issue of the relative contributions of nonpoint and point sources to nutrient load. 

The occurrence of high concentrations during low 

streamflows and the sources that cause high concentrations during low streamflows (for example, wastewater discharges) may not be significant for 

characterizing annual nutrient transport. However, 

these occurrences and sources of high concentration 

are of particular concern for evaluating impairment of 

a water body caused by constituent concentrations at 

harmful levels for short periods, for example during 

critical low streamflow periods. Although the monitoring networks from which these data were collected 

were not designed to detect impairment during critical 

periods, some insight as to where these conditions 

might occur can be gained by comparing concentrations of nitrogen constituents during low streamflows. 

The median concentration of total nitrogen from 

the set of samples collected when streamflow was 

below the 80th percentile (the flow exceeded 80 percent of the time at that site) was plotted against estimated input of total nitrogen from wastewater in the 

watershed (fig. 9a). The correlation between these 

variables is significant (r = 0.71, p = 0.01) and suggests that wastewater discharges are significant contributors to the amount of nitrogen in transport during 

periods of low streamflow. That wastewater-discharge 

input is large (almost equal to or exceeding) compared 

to the median of observed daily loads during low 

streamflow (calculated as the product of observed concentration and daily streamflow) at most sites supports 

this conclusion (fig. 9b).

Downstream Variations in Concentrations

Box plots of nutrient concentrations at different 

water-quality sites along a river reach illustrate how 

nutrient concentrations vary with distance. Downstream variations in nutrient concentrations are illustrated as truncated box plots (Helsel and Hirsch, 1992) 

for the main stem Tennessee River (fig. 10) and for the 

Duck River, the largest tributary within the LTEN 

River Basin (fig. 11). Data from eight of the loadcomputation sites on the main stem Tennessee and the 

Duck Rivers were included in these graphical displays, 

in addition to data from 29 additional long-term monitoring sites on these rivers (as described in the section 

“Approach and Methods”). 

Median total nitrogen concentrations were generally less than 0.7 mg/L throughout the main stem of 

the Tennessee River (fig. 10B) compared to median 

values greater than 1.0 mg/L at many sites on the Duck 

River (fig. 11B). Variation of nitrite plus nitrate concentrations throughout the main stem of the Tennessee 

River was closely correlated with reservoir forebay 

areas (immediately upstream from the dams, fig. 10C). 

The range in concentration at a site reflects the seasonal variation of nitrite plus nitrate in reservoirs; concentrations decreased to below the minimum reporting 

level (MRL) during the summer months in the forebay 
34 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

10

11 2 6-Duck 4-below Normandy

13 9-below Tims Ford

12-Town 5-Duck

5-Duck

7-Shoal

1-Clarks

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

WASTEWATER-DISCHARGE INPUT OF TOTAL NITROGEN,

IN TONS PER SQUARE MILE PER YEAR

r = 0.71

p = 0.01

(A)

EXPLANATION

EXPLANATION

NUMBER IS SITE IDENTIFICATION (fig. 2)ÑConcentration value

is median value from set of samples collected when streamflow was

below the 80th percentile

WASTEWATER-DISCHARGE INPUT, IN TONS PER SQUARE

MILE PER YEAR

LOW-FLOW LOAD, IN TONS PER SQUARE MILE PER DAY * 365Ñ

Median value from set of samples collected when streamflow was below

the 80th percentile

0.00

0.20

0.40

0.60

0.80

1 2 4 5 6 7 9 10 11

0.005

0

12 13

(B)

Sequatchie

Flint Buffalo

-Elk

MEDIAN VALUE OF LOW-FLOW CONCENTRATION OF

TOTAL NITROGEN AS N, IN MILLIGRAMS PER LITER

TOTAL NITROGEN, IN TONS PER

SQUARE MILE PER YEAR

SITE NUMBER

Figure 9. Relation of (A) median value of total nitrogen concentrations and

loads during low streamflow conditions with wastewater-discharge input

and (B) of median value of daily total nitrogen load during low streamflow

conditions with wastewater-discharge input to the watershed.

Figure 9. Relation of (A) median value of total nitrogen concentrations during low 

streamflow conditions and (B) median value of total nitrogen load during low 

streamflow conditions to wastewater-discharge input to the watershed.
Instream Transport of Nitrogen, Phosphorus, and Sediment 35

0.1

10

1

0 75 150 225 300 375 450

DISTANCE, IN RIVER MILES UPSTREAM FROM THE MOUTH OF THE TENNESSEE RIVER

SITE IDENTIFICATION (Appendix A)

TOTAL NITROGEN CONCENTRATION AS N, IN MILLIGRAMS PER LITER

24

130

26

21

20

17

48

12 29

24

38 25

30

27

18

31

18

41

20

38

42

14

158

t5

t23t40t51t85t89

t112

t206t207t230t260t277t295t307t350t375t396t418t425t433t444

t430

t6

Kentucky Dam

New Johnsonville

mouth of Duck River

Pickwick Landing

Dam

Wilson Dam

Wheeler Dam

Decatur

Huntsville

Guntersville Dam

Nickajack Dam

mouth of

Elk River

EXPLANATION

NUMBER OF SAMPLES

PERCENTILE OF CONCENTRATION

DISTRIBUTION

MINIMUM REPORTING

LEVEL

SITE AND IDENTIFICATION

NUMBER CORRESPONDING

TO RIVER NAME AND MILE

(see Appendix A)

90th

75th

50th

25th

10th

12 CONCENTRATION

OF INDIVIDUAL

SAMPLE

Figure 10. Nutrient concentrations (A) at selected sites on the Tennessee River, 1980-96, for (B) total nitrogen,

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorus.

t5 (site 14) t6 t23 (site 15)

t40

t51

t85

t89

t112

t135

t189

t207 t206

(site 16)

t230

t260

t277

t295t307

t350

t375

t396

t444

(site 18) t433

t433

t418

(site 17)

t425

Tennessee

Tennessee

River

River

Lower Tennessee River Basin

(B)

(A)

t430

Huntsville

Figure 10. Nutrient concentrations (A) at selected sites on the Tennessee River, 1980-96, for (B) total nitrogen, 

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorus.
36 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

DISTANCE, IN RIVER MILES UPSTREAM FROM THE MOUTH OF THE TENNESSEE RIVER

SITE IDENTIFICATION (Appendix A)

TOTAL NITRITE PLUS NITRATE CONCENTRATION AS N, IN MILLIGRAMS PER LITER

0.01

0.1

1

10

0 75 150 225 300 375 450 t5 t23 t40 t51 t85 t89 t112 t135 t189 t206 t207 t230 t260 t277 t295 t307 t350 t375 t396 t418 t425 t433v t6t444 t430 Kentucky Dam New Johnsonville mouth of Duck River Pickwick Landing Dam Wilson Dam Wheeler Dam Decatur Huntsville Guntersville Dam Nickajack Dam mouth of Elk River

52

144

36

22

22

17

63

12 21 24

77

33 39

32

50

27 18

32

18

42

43

37

49

14

166

(C)

EXPLANATION

NUMBER OF SAMPLES

PERCENTILE OF CONCENTRATION

DISTRIBUTION

MINIMUM REPORTING

LEVEL

SITE AND IDENTIFICATION

NUMBER CORRESPONDING

TO RIVER NAME AND MILE

(see Appendix A)

90th

75th

50th

25th

10th

12 CONCENTRATION

OF INDIVIDUAL

SAMPLE

t5 (site 14) t6 t23 (site 15)

t40

t51

t85

t89

t112

t135

t189

t207 t206

(site 16)

t230

t260

t277

t295t307

t350

t375

t396

t444

(site 18) t433

t433

t418

(site 17)

t425

Tennessee

Tennessee

River

River

Lower Tennessee River Basin

(A)

t430

Huntsville

Figure 10. Nutrient concentrations (A) at selected sites on the Tennessee River, 1980-96, for (B) total nitrogen,

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorusÑContinued.

Figure 10. Nutrient concentrations (A) at selected sites on the Tennessee River, 1980-96, for (B) total nitrogen, 

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorus—Continued.
Instream Transport of Nitrogen, Phosphorus, and Sediment 37

DISTANCE, IN RIVER MILES UPSTREAM FROM THE MOUTH OF THE TENNESSEE RIVER

SITE IDENTIFICATION (Appendix A)

TOTAL AMMONIA CONCENTRATION AS N, IN MILLIGRAMS PER LITER

0.01

0.1

1

10

0 75 150 225 300 375 450 t5 t23 t40 t51 t85 t89 t6t112 t135 t189 t206 t207 t230 t260 t277 t295 t307 t350 t375 t396 t418 t425 t433 t444 t430 Kentucky Dam New Johnsonville mouth of Duck River Pickwick Landing Dam Wilson Dam Wheeler Dam Decatur Huntsville Guntersville Dam Nickajack Dam mouth of Elk River

52

144

36 22

22

17

42

12

22

24

77

33

39

32 50

27

18

32

18

42

43

37

47

14

138

(D)

EXPLANATION

NUMBER OF SAMPLES

PERCENTILE OF CONCENTRATION

DISTRIBUTION

MINIMUM REPORTING

LEVEL

SITE AND IDENTIFICATION

NUMBER CORRESPONDING

TO RIVER NAME AND MILE

(see Appendix A)

90th

75th

50th

25th

10th

12 CONCENTRATION

OF INDIVIDUAL

SAMPLE

t5 (site 14) t6 t23 (site 15)

t40

t51

t85

t89

t112

t135

t189

t207 t206

(site 16)

t230

t260

t277

t295t307

t350

t375

t396

t444

(site 18) t433

t433

t418

(site 17)

t425

Tennessee

Tennessee

River

River

Lower Tennessee River Basin

(A)

t430

Huntsville

Figure 10. Nutrient concentrations (A) at selected sites on the Tennessee River, 1980-96, for (B) total nitrogen,

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorusÑContinued.

Figure 10. Nutrient concentrations (A) at selected sites on the Tennessee River, 1980-96, for (B) total nitrogen, 

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorus—Continued.
38 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

DISTANCE, IN RIVER MILES UPSTREAM FROM THE MOUTH OF THE TENNESSEE RIVER

SITE IDENTIFICATION (Appendix A)

TOTAL PHOSPHORUS CONCENTRATION AS P, IN MILLIGRAMS PER LITER

0.01

0.1

1

10

0 75 150 225 300 375 450 t5 t23 t40 t51 t85 t89 t6t112 t135 t189 t206 t207 t230 t260 t277 t295 t307 t350 t375 t396 t418 t425 t433 t444 t430 Kentucky Dam New Johnsonville mouth of Duck River Pickwick Landing Dam Wilson Dam Wheeler Dam Decatur Huntsville Guntersville Dam Nickajack Dam mouth of Elk River

53

141

36

22

22

17

76

12

21

22

74

33

39

32

50

33

23

33

18

43

47

37

49

14

179

(E)

EXPLANATION

NUMBER OF SAMPLES

PERCENTILE OF CONCENTRATION

DISTRIBUTION

MINIMUM REPORTING

LEVEL

SITE AND IDENTIFICATION

NUMBER CORRESPONDING

TO RIVER NAME AND MILE

(see Appendix A)

90th

75th

50th

25th

10th

12 CONCENTRATION

OF INDIVIDUAL

SAMPLE

t5 (site 14) t6 t23 (site 15)

t40

t51

t85

t89

t112

t135

t189

t207 t206

(site 16)

t230

t260

t277

t295t307

t350

t375

t396

t444

(site 18) t433

t433

t418

(site 17)

t425

Tennessee

Tennessee

River

River

Lower Tennessee River Basin

(A)

t430

Huntsville

Figure 10. Nutrient concentrations (A) at selected sites on the Tennessee River, 1980-96, for (B) total nitrogen,

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorusÑContinued.

Figure 10. Nutrient concentrations (A) at selected sites on the Tennessee River, 1980-96, for (B) total nitrogen, 

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorus—Continued.
Instream Transport of Nitrogen, Phosphorus, and Sediment 39

DISTANCE, IN RIVER MILES UPSTREAM FROM THE MOUTH OF THE DUCK RIVER

Figure 11. Nutrient concentrations (A) at selected sites on the Duck River, 1980-96, for (B) total nitrogen,

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorus.

SITE IDENTIFICATION (Appendix A)

TOTAL NITROGEN CONCENTRATION AS N, IN MILLIGRAMS PER LITER

0.1

1

10

0 75 150 225 300

Note: Data for sites d8, d133, d181, and d221 are limited to

the period 1980-85, whereas data for other sites extended

through 1992 or later.

d8

d26

d113

d133d181d221d246d249d252d259d262d265

39

44

57

43

41

42

38

67

64

12

28

26

Columbia

Shelbyville

Normandy Dam

EXPLANATION

NUMBER OF SAMPLES

PERCENTILE OF CONCENTRATION

DISTRIBUTION

SITE AND IDENTIFICATION

NUMBER CORRESPONDING

TO RIVER NAME AND MILE

(see Appendix A)

90th

75th

50th

25th

10th

12 CONCENTRATION

OF INDIVIDUAL

SAMPLE

d8

d265

Tennessee

Tennessee

Duck

River

River

River

Lower Tennessee River Basin

(B)

(A)

d26

(site 6)

d113

(site 5)

d133

d181

d221

d246

(site 4)

d249,

d252

d265

d259,

d262

Columbia

Figure 11. Nutrient concentrations (A) at selected sites on the Duck River, 1980-96, for (B) total nitrogen, (C) total 

nitrite plus nitrate, (D) total ammonia, and (E) total phosphorus.
40 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

DISTANCE, IN RIVER MILES UPSTREAM FROM THE MOUTH OF THE DUCK RIVER

SITE IDENTIFICATION (Appendix A)

TOTAL NITRITE PLUS NITRATE CONCENTRATION AS N, IN MILLIGRAMS PER LITER

0.01

0.1

1

10

0 75 150 225 300 d8 d26 d113 d133 d181 d221 d246 d249 d252 d259 d262 d265 Columbia Shelbyville Normandy Dam

42

57 67

45

42

45

38

68

123

84

34

26

NAWQA Background Level

(C)

Figure 11. Nutrient concentrations (A) at selected sites on the Duck River, 1980-96, for (B) total nitrogen,

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorusÑContinued.

Note: Data for sites d8, d133, d181, and d221 are limited to

the period 1980-85, whereas data for other sites extended

through 1992 or later.

EXPLANATION

NUMBER OF SAMPLES

PERCENTILE OF CONCENTRATION

DISTRIBUTION

MINIMUM REPORTING

LEVEL

SITE AND IDENTIFICATION

NUMBER CORRESPONDING

TO RIVER NAME AND MILE

(see Appendix A)

90th

75th

50th

25th

10th

42 CONCENTRATION

OF INDIVIDUAL

SAMPLE

d8

d265

Tennessee

Tennessee

Duck

River

River

River

Lower Tennessee River Basin

(A)

d26

(site 6)

d113

(site 5) d181

d133

d221

d246

(site 4)

d249,

d252

d265

d259,

d262

Columbia

Shelbyville

Figure 11. Nutrient concentrations (A) at selected sites on the Duck River, 1980-96, for (B) total nitrogen, (C) total 

nitrite plus nitrate, (D) total ammonia, and (E) total phosphorus—Continued.
Instream Transport of Nitrogen, Phosphorus, and Sediment 41

DISTANCE, IN RIVER MILES UPSTREAM FROM THE MOUTH OF THE DUCK RIVER

SITE IDENTIFICATION (Appendix A)

TOTAL AMMONIA CONCENTRATION AS N, IN MILLIGRAMS PER LITER

0.01

0.1

1

10

0 75 150 225 300 d26 d113 d246 d249 d252 d259 d262 d265 Columbia Shelbyville Normandy Dam

57 45

34

68

123

84

34

26 NAWQA Background Level

(D)

Note: Data for sites d8, d133, d181, and d221 are limited to

the period 1980-85, whereas data for other sites extended

through 1992 or later.

EXPLANATION

NUMBER OF SAMPLES

PERCENTILE OF CONCENTRATION

DISTRIBUTION

MINIMUM REPORTING

LEVEL

SITE AND IDENTIFICATION

NUMBER CORRESPONDING

TO RIVER NAME AND MILE

(see Appendix A)

90th

75th

50th

25th

10th

45 CONCENTRATION

OF INDIVIDUAL

SAMPLE

d8

d265

Tennessee

Tennessee

Duck

River

River

River

Lower Tennessee River Basin

(A)

d26

(site 6)

d113

(site 5) d181

d133

d221

d246

(site 4)

d249,

d252

d265

d259,

d262

Columbia

Shelbyville

Figure 11. Nutrient concentrations (A) at selected sites on the Duck River, 1980-96, for (B) total nitrogen,

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorusÑContinued.

Figure 11. Nutrient concentrations (A) at selected sites on the Duck River, 1980-96, for (B) total nitrogen, (C) total 

nitrite plus nitrate, (D) total ammonia, and (E) total phosphorus—Continued.
42 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

DISTANCE, IN RIVER MILES UPSTREAM FROM THE MOUTH OF THE DUCK RIVER

SITE IDENTIFICATION (Appendix A)

TOTAL PHOSPHORUS CONCENTRATION AS P, IN MILLIGRAMS PER LITER

0.01

0.1

1

10

0 75 150 225 300

NAWQA Background Level

d26

d8

d113

d133d181d221d246d249d252d259d262d265

Columbia

Shelbyville

Normandy Dam

59

63 78

61

60

61

38

67

93

135

34

26

60

Note: Data for sites d8, d133, d181, and d221 are limited to

the period 1980-85, whereas data for other sites extended

through 1992 or later.

EXPLANATION

NUMBER OF SAMPLES

PERCENTILE OF CONCENTRATION

DISTRIBUTION

BROWN PHOSPHATE DISTRICT

(Smith and Whitlatch, 1940)

MINIMUM REPORTING

LEVEL

SITE AND IDENTIFICATION

NUMBER CORRESPONDING

TO RIVER NAME AND MILE

(see Appendix A)

90th

75th

50th

25th

10th

CONCENTRATION

OF INDIVIDUAL

SAMPLE

d265

(E)

Figure 11. Nutrient concentrations (A) at selected sites on the Duck River, 1980-96, for (B) total nitrogen,

(C) total nitrite plus nitrate, (D) total ammonia, and (E) total phosphorusÑContinued.

d8

Tennessee

Tennessee

Duck

River

River

River

Lower Tennessee River Basin

(A)

d26

(site 6)

d113

(site 5) d181

d133

d221

d246

(site 4)

d249,

d252

d265

d259,

d262

Columbia

Shelbyville

Figure 11. Nutrient concentrations (A) at selected sites on the Duck River, 1980-96, for (B) total nitrogen, (C) total 

nitrite plus nitrate, (D) total ammonia, and (E) total phosphorus—Continued.
Instream Transport of Nitrogen, Phosphorus, and Sediment 43

areas. In contrast, concentrations of ammonia and total 

phosphorus did not vary much longitudinally 

(figs. 10D and 10E); instead they fluctuated for short 

distances (for example, near Tennessee River miles 

100 and 300), possibly in response to point- or nonpoint-source inputs.

Concentrations of all nutrient constituents varied widely with distance along the Duck River, and 

appear to be strongly influenced by Normandy Reservoir (from river mile 248.6 to 265.4, fig. 11). Median 

nitrite plus nitrate concentrations were less than 

0.3 mg/L within the reservoir, compared with median 

values of 0.6 mg/L or greater upstream and downstream from the reservoir (fig. 11C); total nitrogen 

concentrations were somewhat lower in the reservoir 

with median values less than 0.7 mg/L, compared with 

median values of 1.0 mg/L or greater upstream and 

downstream of the reservoir. Median total phosphorus 

concentrations were as low as 0.01 mg/L within the 

reservoir, compared with a range in median values of 

0.08 to 0.3 mg/L at sites upstream and downstream 

from the reservoir (fig. 11E). This pattern probably 

reflects depletion of these nutrients caused by assimilation by aquatic plants in the reservoir during the 

summer months and, in the case of total phosphorus, 

by settling associated with sediment. A study of the 

nutrient balance in Normandy Reservoir by Broach 

and others (1995, p. 70) found that the reservoir functions as a sink for nitrite plus nitrate and organic nitrogen, but that ammonia outflow from the reservoir 

exceeds inflow by about threefold. The illustration of 

variation in total nitrogen (fig. 11B), which shows tailwater concentrations about equal to upstream concentrations, suggests that the reservoir may not be a sink 

for total nitrogen. The high concentrations of ammonia 

within Normandy Reservoir and in the tailwater 

(median value as high as 0.1 mg/L, fig. 11D) might be 

due to nitrate reduction and ammonification in the 

oxygen-deficient layer of the reservoir during summer 

months (Broach and others, 1995). 

Background levels for nitrate, ammonia, and 

total phosphorus for 20 NAWQA study units are 

included to compare water quality in the Duck River 

with other rivers in the Nation (fig. 11). Average concentration for “undeveloped” basins was summarized 

as 0.7 mg/L for nitrate and 0.1 mg/L for ammonia and 

total phosphorus (Mueller and others, 1995). These 

background levels were not compared with concentrations on the main stem Tennessee River (fig. 10) 

because the levels do not reflect the effects of instream 

processing of nutrients in large rivers.

The median values of concentrations of total 

nitrite plus nitrate and total phosphorus observed for 

many of the riverine sites on the Duck River exceeded 

NAWQA background levels of 0.7 mg/L for nitrate 

and 0.1 mg/L for total phosphorus (figs. 11C and 11E). 

The high phosphorus concentrations (greater than 

0.2 mg/L) relative to the NAWQA background level in 

the lower reach of the river (from near Duck River 

Mile 120 to the mouth) were probably caused by contribution of phosphate-rich sediment, from soils 

formed on the outcrop of phosphatic limestones in the 

brown-phosphate districts (figs. 11A and 11E) of middle Tennessee (Smith and Whitlatch, 1940). Ammonia 

data were sparse in the riverine sections downstream 

and upstream of the Normandy Reservoir; median values at the five riverine sites with data were below the 

NAWQA background level of 0.1 mg/L (fig. 11D).

Instream Loads

This section presents estimates of nutrient and 

sediment instream loads and yields for 18 sites in the 

LTEN River Basin (table 9). These estimates are used 

in interpretations of spatial patterns of instream loads 

and comparisons of instream loads with inputs. 

Instream loads were calculated for total nitrogen (16 

sites), total ammonia (13 sites), total ammonia plus 

organic nitrogen (16 sites), total nitrite plus nitrate 

nitrogen (16 sites), total phosphorus (12 sites), dissolved orthophosphorus (7 sites), and suspended sediment (5 sites). Several estimates of annual load were 

produced for each site-constituent combination. The 

first set of estimates—mean, minimum, and maximum 

annual load for the available period of record for load 

computation (concurrent water-quality and streamflow 

record)—is provided to indicate long-term transport 

conditions at the site. Load estimates can vary significantly in years with low or high annual streamflows. 

At each of the 18 sites where loads were estimated, 

streamflow durations during the period of load estimation were compared with long-term streamflow duration (Appendix E). At most sites, streamflows during 

these two periods were similar.

Transport of nutrients into the LTEN River Basin 

near Chattanooga, Tennessee, is characterized by the 

instream load estimate at site 18 (Tennessee River 

below Raccoon Mountain). Transport out of the basin is 

characterized by the estimate at site 14 (Tennessee 
44 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus,

and Sediment in the Lower Tennessee River Basin, 1980-96

Table 9. Instream load, yield, and flow-weighted mean concentration for selected constituents and basins in the lower Tennessee Riv[r2, coefficient of determination; s, standard deviation, in log units; MRL, minimum reporting limit of the analytical method; mi2, square miles; mg/L, milligrams per estimation error than the other entries, for various reasons (described in footnotes); <, less than; --, not estimated; regression statistics r2 and s are from the multivariatagainst streamflow, season, and time; annual load, yield, and flow-weighted mean concentration were estimated for a common period: water year 1992. Where water-data from a year with similar hydrologic conditions to 1992 were used instead; the width of the model-calculated confidence interval partly indicates the error associasources of error are not accounted for in this interval, including sampling bias and data sparseness (see Appendix B)]

Annual load 

No. of 95-percen

Site Period of observations For a in

identi- record for Less Regression For the period of available record single Lower 

fication Surface-water station/site location load than statistics Mean Minimum Maximum year limit 

(fig. 2) Number Name estimates MRL Total r

2 s (tons) (tons) (tons) (tons) (tons) 

Total nitrogen

1 PRI038 Clarks River at Almo, Ky. 1985-95 0 132 0.15 0.38 490 220 1,000 320 240 

[1987] [1989] [1992]

2 03604000 Buffalo River near Flat 1982-95 0 36 .20 .55 490 280 710 460 310 

Woods, Tenn. [1986] [1983] [1992]

4 001025 Duck River below Normandy 1986-95 0 27 .28 .41 220 84 280 200 140 

Dam, Tenn. [1988] [1989] [1992]

5 001065 Duck River at Williamsport, 1982-94 0 52 .36 .33 3,800 1,500 6,400 3,000 2,100 

Tenn. [1986] [1983] [1992]

6 475793 Duck River above Hurricane 1986-93 0 44 .48 .36 4,700 2,200 7,600 4,500 3,200 

Mills, Tenn. [1986] [1989] [1992]

7 002395 Shoal Creek at Highway 43, 1983-92 0 32 .31 .39 480 200 950 500 230 

near Lawrenceburg, Tenn. a [1988] [1983] [1992]

9 001207 Elk River below Tims Ford 1984-94 0 36 .32 .37 620 160 1,100 530 370 

Dam, Tenn. [1988] [1994] [1992]

10 475796 Elk River near Prospect, Tenn. 1987-92 0 43 .64 .30 6,600 1,600 10,000 5,300 3,600 

 [1988] [1989] [1992]

11 FLCR7 Flint Creek near Falkville, Ala. 1993-97 0 67 .32 .57 220 140 290 200 110 

 [1995] [1997] [1994]

12 TOWNCREEK15b Town Creek near Geraldine, Ala. 1988-96 0 72 .47 .40 880 550 1,900 550 460 

 [1992] [1989] [1992]

13 002375 Sequatchie River at Valley 1983-94 0 39 .32 .44 960 370 1,500 810 620 

Road, Tenn. a [1988] [1982] [1992]

14 03609750 Tennessee River at Highway 60 1980-84 0 30 .53 .36 60,000 21,000 89,000 56,000 45,000 

near Paducah, Ky. [1981] [1983] [1982]

15 202832 Tennessee River at mile 23, 1990-94 0 26 .61 .20 52,000 38,000 65,000 38,000 32,000 

Ky. c [1992] [1991] [1992]

16 03593005 Tennessee River at Pickwick 1980-95 0 64 .53 .28 43,000 20,000 66,000 36,000 29,000 

Landing Dam, Tenn. [1988] [1990] [1992]

17 03571850 Tennessee River at South 1980-85 0 37 .15 .58 38,000 21,000 53,000 43,000 23,000 

Pittsburg, Tenn. [1981] [1984] [1982]

18 003315 Tennessee River below Raccoon 1981-94 0 152 .39 .49 29,000 10,000 51,000 20,000 17,000 

Mountain, Tenn. [1988] [1982] [1992]
Instream Transport of Nitrogen, Phosphorus, and Sediment 45

Table 9. Instream load, yield, and flow-weighted mean concentration for selected constituents and basins in the lower Tennessee Riv

Annual load 

No. of 95-percen

Site Period of observations For a in

identi- record for Less Regression For the period of available record single Lower 

fication Surface-water station/site location load than statistics Mean Minimum Maximum year limit 

(fig. 2) Number Name estimates MRL Total r2 s (tons) (tons) (tons) (tons) (tons) 

Total ammonia

1 PRI038 Clarks River at Almo, Ky. 1985-95 70 133 .19 1.13 25 11 53 11 <1 

 [1993] [1989] [1992]

2 03604000 Buffalo River near Flat 1987-92 3 28 .39 .52 15 8.0 18 17 7.7 

Woods, Tenn. [1988] [1989] [1992]

4 001025 Duck River below Normandy 1987-95 0 27 .70 .92 40 21 45 38 18 

Dam, Tenn. [1995] [1990] [1992]

5 001065 Duck River at Williamsport, 1984-94 7 43 .47 .82 250 100 540 160 45 

Tenn. [1994] [1984] [1992]

6 475793 Duck River above Hurricane 1987-94 12 53 .12 1.10 230 110 400 220 <1 

Mills, Tenn. [1993] [1989] [1992]

7 002395 Shoal Creek at Highway 43, 1984-94 14 38 .41 .95 29 6.1 56 31 <1 

near Lawrenceburg, Tenn. a [1993] [1983] [1992]

9 001207 Elk River below Tims Ford 1984-94 8 37 .45 1.00 120 17 220 130 11 

Dam, Tenn. [1988] [1984] [1992]

10 475796 Elk River near Prospect, Tenn. 1987-94 8 57 .30 .87 820 57 2,700 720 <1 

 [1988] [1991] [1992]

11 FLCR7 Flint Creek near Falkville, Ala. 1993-97 4 66 .30 .86 10 5.0 14 10 3.1 

 [1995] [1993] [1994]

12 TOWNCREEK15 Town Creek near Geraldine, 1988-96 40 77 .14 1.27 30 17 55 17 5.5 

Ala. d [1992] [1989] [1992]

13 002375 Sequatchie River at Valley Road, 1983-94 12 41 .37 1.06 99 19 400 50 19 

Tenn. a [1988] [1983] [1992]

15 202832 Tennessee River at mile 23, Ky. c 1990-94 5 33 .33 .91 5,000 2,900 8,700 4,000 770 

 [1990] [1994] [1992]

16 03593005 Tennessee River at Pickwick 1980-92 2 45 .35 .58 2,300 880 4,700 1,900 1,100 

Landing Dam, Tenn. [1988] [1980] [1992]

Total ammonia plus organic nitrogen

1 PRI038 Clarks River at Almo, Ky. 1986-93 0 101 .29 .43 200 76 550 100 62 

 [1987] [1989] [1992]

2 03604000 Buffalo River near Flat 1982-95 21 61 .32 .83 200 73 400 140 86 

Woods, Tenn. [1995] [1983] [1992]

4 001025 Duck River below Normandy 1987-95 0 27 .20 .53 140 59 170 140 81 

Dam, Tenn. [1988] [1989] [1992]

5 001065 Duck River at Williamsport, 1981-92 1 53 .29 .62 2,300 500 4,900 1,700 220 

Tenn. [1981] [1983] [1992]

6 475793 Duck River above Hurricane 1986-93 1 47 .33 .59 2,800 930 5,400 2,600 130 

Mills, Tenn. [1986] [1989] [1992]
46 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

Table 9. Instream load, yield, and flow-weighted mean concentration for selected constituents and basins in the lower Tennessee Riv

Annual load 

No. of 95-percen

Site Period of observations For a in

identi- record for Less Regression For the period of available record single Lower 

fication Surface-water station/site location load than statistics Mean Minimum Maximum year limit 

(fig. 2) Number Name estimates MRL Total r2 s (tons) (tons) (tons) (tons) (tons) 

Total ammonia plus organic nitrogen—Continued

7 002395 Shoal Creek at Highway 43, 1983-94 0 39 .52 .66 140 49 380 94 <1 

near Lawrenceburg, Tenn. a [1993] [1983] [1992]

9 001207 Elk River below Tims Ford 1984-94 3 39 .39 .64 280 77 620 190 94 

Dam, Tenn. [1988] [1984] [1992]

10 475796 Elk River near Prospect, Tenn. 1986-93 0 49 .60 .53 2,900 570 5,900 2,800 960 

 [1988] [1989] [1992]

11 FLCR7 Flint Creek near Falkville, Ala. 1993-97 4 60 .28 .72 82 49 160 69 35 

 [1995] [1997] [1994]

12 TOWNCREEK15 Town Creek near Geraldine, Ala. 1988-96 4 76 .51 .56 140 63 430 78 60 

 [1995] [1988] [1992]

13 002375 Sequatchie River at Valley Road, 1983-94 4 42 .24 .79 300 100 660 220 120 

Tenn. a [1988] [1983] [1992]

14 03609750 Tennessee River at Highway 60 1980-84 0 41 .24 .49 37,000 14,000 53,000 30,000 22,000 

near Paducah, Ky. [1981] [1984] [1982]

15 202832 Tennessee River at mile 23, Ky. c 1990-94 0 32 .34 .31 24,000 16,000 32,000 16,000 12,000 

 [1992] [1990] [1992]

16 03593005 Tennessee River at Pickwick 1986-93 3 36 .45 .41 16,000 11,000 22,000 14,000 11,000 

Landing Dam, Tenn. [1988] [1989] [1992]

17 03571850 Tennessee River at South 1980-85 3 40 .18 .94 23,000 9,500 35,000 25,000 3,900 

Pittsburg, Tenn. [1981] [1984] [1982]

18 003315 Tennessee River below Raccoon 1981-94 4 158 .39 .66 16,000 5,000 31,000 9,300 7,500 

Mountain, Tenn. [1988] [1983] [1992]

Total nitrite plus nitrate nitrogen

1 PRI038 Clarks River at Almo, Ky. 1985-95 0 133 .16 .55 320 150 580 220 150 

 [1987] [1989] [1992]

2 03604000 Buffalo River near Flat 1986-93 5 38 .47 .58 230 120 400 220 82 

Woods, Tenn. [1986] [1989] [1992]

4 001025 Duck River below Normandy 1987-95 0 27 .78 .50 89 22 140 69 47 

Dam, Tenn. [1988] [1991] [1992]

5 001065 Duck River at Williamsport, Tenn. 1982-93 0 56 .16 .30 1,900 780 2,700 1,800 1,300 

 [1986] [1983] [1992]

6 475793 Duck River above Hurricane 1987-93 2 48 .41 1.09 3,200 2,200 4,700 2,800 1,200 

Mills, Tenn. [1988] [1987] [1992]

7 002395 Shoal Creek at Highway 43, 1983-94 0 40 .25 .37 280 140 460 250 200 

near Lawrenceburg, Tenn. a [1988] [1983] [1992]

9 001207 Elk River below Tims Ford 1984-94 0 39 .42 .68 450 70 1,500 420 160 

Dam, Tenn. [1988] [1994] [1992]

10 475796 Elk River near Prospect, Tenn. 1987-93 0 51 .22 .41 3,100 1,000 4,700 2,700 2,000 

 [1988] [1991] [1992]

11 FLCR7 Flint Creek near Falkville, Ala. 1993-97 1 67 .69 .57 150 100 200 140 48 

 [1995] [1997] [1994]

12 TOWNCREEK15 Town Creek near Geraldine, Ala. 1988-96 0 77 .46 .60 570 440 790 440 330 

 [1992] [1989] [1992]
Instream Transport of Nitrogen, Phosphorus, and Sediment 47

Table 9. Instream load, yield, and flow-weighted mean concentration for selected constituents and basins in the lower Tennessee Riv

Annual load 

No. of 95-percen

Site Period of observations For a in

identi- record for Less Regression For the period of available record single Lower 

fication Surface-water station/site location load than statistics Mean Minimum Maximum year limit 

(fig. 2) Number Name estimates MRL Total r2 s (tons) (tons) (tons) (tons) (tons) 

Total nitrite plus nitrate nitrogen—Continued

13 002375 Sequatchie River at Valley Road, 1983-94 12 43 .15 .71 680 250 1,400 640 400 

Tenn. a [1988] [1994] [1992]

14 03609750 Tennessee River at Highway 60 1980-84 0 41 .58 .55 27,000 7,400 38,000 23,000 15,000 

near Paducah, Ky. [1981] [1984] [1982]

15 202832 Tennessee River at mile 23, Ky. c 1990-94 8 33 .77 .95 79,000 41,000 120,000 62,000 <1 

 [1990] [1994] [1992]

16 03593005 Tennessee River at Pickwick 1980-94 6 77 .70 .39 24,000 8,500 40,000 18,000 13,000 

Landing Dam, Tenn. [1988] [1980] [1992]

17 03571850 Tennessee River at South 1980-85 0 38 .37 .24 13,000 8,000 16,000 14,000 12,000 

Pittsburg, Tenn. [1981] [1983] [1982]

18 003315 Tennessee River below Raccoon 1981-94 0 158 .43 .40 13,000 4,700 19,000 11,000 9,900 

Mountain, Tenn. [1988] [1982] [1992]

Total phosphorus

1 PRI038 Clarks River at Almo, Ky. 1985-95 0 132 .57 .49 62 29 160 40 27 

 [1995] [1989] [1992]

2 03604000 Buffalo River near Flat 1983-95 9 56 .25 .74 27 12 52 19 9 

Woods, Tenn. [1995] [1983] [1992]

4 001025 Duck River below Normandy 1987-95 6 24 .68 .91 20 3.0 34 15 <1 

Dam, Tenn. [1994] [1990] [1992]

5 001065 Duck River at Williamsport, Tenn. 1981-93 0 68 .11 .86 1,700 390 3,300 1,300 120 

 [1981] [1983] [1992]

6 475793 Duck River above Hurricane 1988-93 0 43 .33 .63 2,900 1,500 4,700 2,900 <1 

Mills, Tenn. [1993] [1991] [1992]

7 002395 Shoal Creek at Highway 43, 1983-94 2 39 .30 .93 39 14 60 26 10 

near Lawrenceburg, Tenn. a [1994] [1983] [1992]

9 001207 Elk River below Tims Ford 1983-94 16 41 .68 1.10 68 2.0 140 17 <1 

Dam, Tenn. [1994] [1987] [1992]

10 475796 Elk River near Prospect, Tenn. 1986-94 0 56 .31 .60 1,400 290 3,100 1,600 330 

 [1988] [1991] [1992]

14 03609750 Tennessee River at Highway 60 1980-84 0 31 .50 .31 5,000 2,000 6,900 4,800 3,900 

near Paducah, Ky. [1981] [1980] [1982]

15 202832 Tennessee River at mile 23, Ky. c 1990-94 0 34 .40 .41 4,900 3,200 6,300 3,200 2,100 

 [1992] [1989] [1992]

16 03593005 Tennessee River at Pickwick 1980-93 1 71 .16 .48 3,600 1,300 6,500 3,900 2,300 

Landing Dam, Tenn. [1988] [1991] [1992]

17 03571850 Tennessee River at South 1980-86 2 40 .23 .45 1,300 520 2,000 1,600 1,200 

Pittsburg, Tenn. [1986] [1980] [1982]
48 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

Table 9. Instream load, yield, and flow-weighted mean concentration for selected constituents and basins in the lower Tennessee Riv

Annual load 

No. of 95-percen

Site Period of observations For a in

identi- record for Less Regression For the period of available record single Lower 

fication Surface-water station/site location load than statistics Mean Minimum Maximum year limit 

(fig. 2) Number Name estimates MRL Total r2 s (tons) (tons) (tons) (tons) (tons) 

Dissolved orthophosphorus

2 03604000 Buffalo River near Flat 1984-95 18 54 .26 .43 10 4.5 18 11 3.2 

Woods, Tenn. [1986] [1989] [1992]

6 475793 Duck River above Hurricane 1986-91 0 38 .25 .43 870 220 1,500 940 81 

Mills, Tenn. [1986] [1989] [1990]

10 475796 Elk River near Prospect, Tenn. 1987-91 0 38 .22 .45 800 230 1,300 820 300 

 [1988] [1989] [1987]

11 FLCR7 Flint Creek near Falkville, Ala. d 1993-97 15 62 .73 .39 12 5.5 16 13 9.0 

 [1995] [1993] [1994]

12 TOWNCREEK15 Town Creek near Geraldine, 1988-96 29 74 .28 1.55 47 21 110 21 2.1 

Ala. d [1992] [1996] [1992]

15 202832 Tennessee River at mile 23, Ky. c 1990-94 1 33 .64 .56 3,200 1,900 4,200 3,500 1,300 

 [1990] [1991] [1992]

16 03593005 Tennessee River at Pickwick 1983-93 11 49 .49 .52 2,200 520 5,000 2,600 700 

Landing Dam, Tenn. [1988] [1991] [1992]

Suspended sediment

2 03604000 Buffalo River near Flat 1982-95 0 65 .50 .71 29,000 9,800 92,000 20,000 <1 

Woods, Tenn. [1986] [1983] [1992]

3 03596000 Duck River below Manchester, 1979-83 0 30 .71 .46 11,000 820 17,000 16,000 <1 

Tenn. e [1981] [1980] [1982]

8 03588500 Shoal Creek at Iron City, 1979-83 1 29 .56 .74 91,000 3,900 240,000 41,000 <1 

Tenn. e [1981] [1983] [1982]

16 03593005 Tennessee River at Pickwick 1980-93 0 68 .09 .71 850,000 260,000 1,800,000 1,000,000 330,000 1

Landing Dam, Tenn. [1986] [1991] [1992]

17 03571850 Tennessee River at South 1980-86 0 43 .22 .61 390,000 140,000 600,000 480,000 260,000 

Pittsburg, Tenn. [1986] [1980] [1982]

a Estimates are subject to error because streamflow-gaging and water-quality-sampling sites were not colocated.b Station number in Alabama Department of Environmental Management study is t5.c Load estimates are subject to error due to grab sampling methods at this vertically stratified site.d Load estimates are subject to error due to variable MRL (ranging from 0.03 to 0.2 mg/L), and the large percentage of observations below MRL. e Included data from 1979 for calibration and load estimation, in order to have sufficient length of record.f Annual yield and flow-weighted mean concentration for sediment were estimated for the period of available record, rather than for the single year, because a common overlapp
Instream Transport of Nitrogen, Phosphorus, and Sediment 49

River at Highway 60 near Paducah), except that the 

watershed for this site does not include the Clarks River 

drainage. Estimates of mean annual instream load of 

total nitrogen at the inlet (site 18) and outlet (site 14) 

were 29,000 tons/yr (for the period 1981-94) and 

60,000 tons/yr (for the period 1980-84), respectively 

(table 9), representing a gain of 31,000 tons/yr, on average, across the area (18,930 mi2) between these two 

sites. The sum of the mean annual instream load from 

gaged tributaries to the main stem within the study unit 

was 14,000 tons/yr (period variable); however, this 

number cannot be compared with the gain between the 

inlet and outlet sites because the gaged area represents 

only 30 percent of the total area and the period of 

record at many tributary sites did not correspond with 

the period of record at the inlet or outlet sites. 

Estimates of mean annual instream load of total 

phosphorus at the inlet (site 17) and outlet (site 14) 

were 1,300 tons/yr (1980-86) and 5,000 tons/yr (1980-

84), respectively, representing a gain of 3,700 tons/yr, 

on average, across the study unit (table 9). For this 

comparison, site 17 (Tennessee River at South Pittsburg) was substituted as the inlet site because total 

phosphorus load was not estimated at site 18. The sum 

of the gaged tributary load, representing only 28 percent of the area contributing to the main stem between 

sites 17 and 14, was 4,300 tons/yr (period variable). 

Although this number cannot be closely compared 

with the gain throughout the study unit, for the same 

reasons given for total nitrogen, a general comparison 

suggests that the main stem of the Tennessee River and 

the tributary embayments along the main stem function as a sink for total phosphorus, removing a substantial amount from the water column through 

assimilation or deposition.

Load and yield estimates for a single water year 

also are presented for each site (table 9) to provide a 

common period for better spatial comparisons among 

sites. Data from 1992 were used for comparison where 

possible because more data were available on instream 

loads and sources during 1992 than for any other year. 

Hydrologic conditions during 1992 were close to average at all sites (except for Clarks River at Almo, which 

had relatively low flow in 1992). For those sites without load estimates for 1992, the estimate from a hydrologically similar year was used. 

The range between the upper and lower limits of 

the 95-percent confidence intervals (table 9) indicates 

precision of the model estimates and is an important 

consideration for interpreting these data. The load 

estimates are useful for evaluating broad spatial patterns of instream load, and comparisons of instream 

load to inputs, but may not be sufficiently accurate for 

local-scale evaluations of water quality. A discussion 

of limitations of the data and error in the model estimates is contained in Appendix B. 

An additional consideration in spatial interpretation is the extent to which the set of monitoring sites 

represent conditions in the LTEN River Basin. The 

gaged tributary area represents a relatively small part 

of the study unit (less than 30 percent for most constituents); therefore, spatial extrapolations must be made 

with caution. In addition, the tributary sites in Alabama were monitored as part of special studies of 

known water-quality problems, compared to tributary 

sites in other states that were part of ambient monitoring networks, which may bias conclusions about 

basin-wide water quality.

To facilitate spatial comparisons of instream 

loads at sites draining watersheds of greatly differing 

size and streamflow characteristics, the load estimates 

at each site were normalized in two ways: by dividing 

each estimate by the watershed area (producing an 

estimate of yield in tons per square mile), and by 

dividing each estimate by the mean streamflow at the 

site for the load-computation period (producing the 

equivalent of flow-weighted mean of the modelestimated daily concentrations, in milligrams per 

liter). The model-estimated daily concentrations are 

used rather than the set of observed concentrations to 

derive the estimate of flow-weighted mean concentration because the former account for flux during 

unsampled periods and are considered to better represent average concentration during a specified period. 

Estimates of flow-weighted mean concentration 

are useful for evaluating average water-quality conditions at the site and for comparisons (which follow) 

with national data sets and guidelines; estimates of 

yield are useful for comparisons with inputs in a mass 

balance analysis. Both yields and flow-weighted mean 

concentrations are reported in table 9 and displayed 

graphically in figures 12 and 13, and estimates of yield 

of total nitrogen and total phosphorus are displayed on 

maps in figures 14 and 15. Because runoff characteristics for site 1, Clarks River at Almo (median runoff for 

period of load computation is 3.0 in., table 1), differed 

from the other tributary sites (median runoff ranges 

from 8 to 13 in.), the ranking of this site for constituent 

transport estimated by flow-weighted mean concentration differs substantially from the ranking based on 

yield estimates (compare in figure 12). 
50 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

0.1

0.2

0.3

0.4

0.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

SITE IDENTIFICATION

YIELD, IN TONS PER SQUARE MILE YIELD, IN TONS PER SQUARE MILE

0.5

1.0

1.5

2.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

SITE IDENTIFICATION

0

1

2

3

4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 0

0 0

1

2

3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

FLOW-WEIGHTED MEAN CONCENTRATION,

IN MILLIGRAMS PER LITER

FLOW-WEIGHTED MEAN CONCENTRATION,

IN MILLIGRAMS PER LITER

TOTAL NITROGEN AS N TOTAL NITRITE PLUS NITRATE AS N

TOTAL AMMONIA AS N TOTAL AMMONIA PLUS ORGANIC

NITROGEN AS N

Figure 12. Annual yield and flow-weighted mean concentration of total nitrogen, total nitrite plus nitrate, total

ammonia, and total ammonia plus organic nitrogen at selected sites in the lower Tennessee River Basin. Not estimated Not estimated Not estimated Not estimated Not estimated Not estimated Not estimated Not estimated Not estimated Not estimated Not estimated

14 15

6

5

2

7 16 8 10

4 3

9

11

12

17

13 18

18

1

SITE AND IDENTIFICATION

NUMBER (table 1)

YIELD

FLOW-WEIGHTED MEAN

CONCENTRATION

EXPLANATION

Lower Tennessee River Basin

Tennessee

Tennessee

Duck

River

River

River

Figure 12. Annual yield and flow-weighted mean concentration of total nitrogen, total nitrite plus nitrate, total 

ammonia, and total ammonia plus organic nitrogen at selected sites in the lower Tennessee River Basin.
Instream Transport of Nitrogen, Phosphorus, and Sediment 51

0

0.5

1.0

1.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

0

0.1

0.2

0.3

0.4

0.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

18

SITE AND IDENTIFICATION

NUMBER (table 1)

YIELD

FLOW-WEIGHTED MEAN

CONCENTRATION

Note: Estimates for suspended-sediment

yield and flow-weighted mean concentration are for the period of available

record.

EXPLANATION

TOTAL PHOSPHORUS AS P

SUSPENDED SEDIMENT

DISSOLVED

ORTHOPHOSPHORUS

AS P

Not estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimated

Not estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimatedNot estimated Not estimated

Not estimated

SITE IDENTIFICATION

SITE IDENTIFICATION

YIELD, IN TONS PER SQUARE MILE YIELD, IN TONS PER SQUARE MILE

FLOW-WEIGHTED MEAN CONCENTRATION,

IN MILLIGRAMS PER LITER

FLOW-WEIGHTED MEAN CONCENTRATION,

IN MILLIGRAMS PER LITER

14 15

6

5

2

7 16 8 10

4 3

9

11

12

13 18

1

Lower Tennessee River Basin

Tennessee

Tennessee

Duck

River

River

River

17

Figure 13. Annual yield and flow-weighted mean concentration of total phosphorus, dissolved orthophosphorus,

and suspended sediment at selected sites in the lower Tennessee River Basin.

Figure 13. Annual yield and flow-weighted mean concentration of total phosphorus, dissolved orthophosphorus, and 

suspended sediment at selected sites in the lower Tennessee River Basin.
52 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus,

and Sediment in the Lower Tennessee River Basin, 1980-96

W

<0.01

A

F

N

L 13

H E

H E

L 12

N

W A F

0.00

W

A

F

N

L

H

E

W

A

F 6.6

N

L

H

E (1994)

W

A F

N

L

H

E

-6-4-2

0246

E

H

L 6.6

N

F

A

W

E

H -24

L

F 23 N 7.5

A W

W

A

F

N

L

H

E

W

A

F

N

L

H

E

Site 6 Site 5 Site 4 

TONS PER SQUARE MILE

PER YEAR

-6-4-2

0246

TONS PER SQUARE MILE

PER YEAR

-6-4-2

0246

TONS PER SQUARE MILE

PER YEAR

Site 10 -6

-4-2

0246

TONS PER SQUARE MILE

PER YEAR

Site 12 -6

-4-2

0246

TONS PER SQUARE MILE

PER YEAR

Site 11 -6

-4-2

0246

TONS PER SQUARE MILE

PER YEAR

Site 7 -6

-4-2

0246

TONS PER SQUARE MILE

PER YEAR

Site 2Site 1

-6-4-2

0246

TONS PER SQUARE MILE

PER YEAR

-6-4-2

0246

TONS PER SQUARE MILE

PER YEAR

Figure 14. Total nitrogen input and export at selected sites in the lower Tennessee River Basin.

1

2

5 6

10 13

11 12

4

9

7

Figure 14. Total nitrogen input and export at selected sites in the lower Tennessee River Basin.
Instream Transport of Nitrogen, Phosphorus, and Sediment 53

W

0.07

F L

H E (-0.15)

W

0.02

F

L

H E

E

-0.04

H

L W F

0.01

E

H -3.1

L

F 5.1

W

W

0.05

F L

H E -0.08

W

0.05

F

L

H E

W

0.03

F

L

H

E

-3-2

-1

0

1

23

W

0.0

Site 6 Site 5 TONS PER SQUARE MILE

PER YEAR

-3-2

-1

0

1

23

TONS PER SQUARE MILE

PER YEAR

-3 Site 4-2

-1

0

1

23

TONS PER SQUARE MILE

PER YEAR

-3 -2

-1

0

1

23

TONS PER SQUARE MILE

PER YEAR

-3 Site 1-2

-1

0

1

23

TONS PER SQUARE MILE

PER YEAR

-3 Site 2-2

-1

0

1

23

TONS PER SQUARE MILE

PER YEAR

-3 Site 7-2

-1

0

1

23

TONS PER SQUARE MILE

PER YEAR

-3-2

-1

0

1

23

TONS PER SQUARE MILE

PER YEAR

Site 10

Figure 15. Total phosphorus input and export at selected sites in the lower Tennessee River Basin.

1

2 4

5

6

7

9

10 13

11 12

INPUT AND 

PHOSPHOR

INPUT T

W Waste

LAND-PH

**

EX

A AtmoF FertilL LivesH HarvE Expo* Values 

negativfrom th

Insufficien

0.90 - 11.11 - 2

1

YIELD OF TO

ENTIRE UP

AREA, IN T

MILE PER 

SITE AN

for deta

Figure 15. Total phosphorus input and export at selected sites in the lower Tennessee River Basin.
54 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

Estimates of annual flow-weighted mean concentration of total nitrogen range from 0.53 to 2.8 mg/L

as nitrogen (table 9), representing a fivefold difference 

among the watersheds. The smallest estimates were at 

site 2 (Buffalo River near Flat Woods) and site 4 

(Duck River below Normandy Dam), which represent 

a minimally developed watershed (with 29 percent 

combined urban and agricultural land use, fig. 5) and 

tailwater from a tributary reservoir, respectively. The 

largest estimate, at site 1 (Clarks River at Almo), is 

from the watershed with the largest areal percentages 

of urban and agricultural land use (corresponding to 

80 percent combined urban and agricultural land use, 

fig. 5), and with the largest amount of wastewater discharge (table 3), suggesting that human activity 

increases instream transport of total nitrogen by as 

much as fivefold. The difference in flow-weighted 

mean concentration at sites 1 and 2 might not be 

caused by human activity alone, however, because the 

natural basin characteristics also differ for these two 

sites (fig. 2).

Estimates of annual flow-weighted mean concentration of total phosphorus range from 0.02 to 

0.73 mg/L as phosphorus (table 9), representing a 

fortyfold difference among the watersheds. The smallest estimate was for site 2 (Buffalo River near Flat 

Woods), which is a minimally-developed watershed. 

The largest three estimates, 0.73, 0.53, and 0.52 mg/L 

(from sites 6 and 5 on the Duck River and site 10 on 

the Elk River, respectively), probably represent a natural source: the phosphatic limestone formations of the 

brown-phosphate district outcrop in the watersheds for 

these three sites (figs. 11A and 11E). The outcrop pattern of these phosphatic limestones is an important 

factor to consider as regional boundaries are established for attainable region-specific water-quality criteria for total phosphorus (U.S. Environmental 

Protection Agency, 1998). The estimate of 0.35 mg/L 

for site 1 (Clarks River at Almo) is a twentyfold difference from site 2 and better indicates to what extent 

human activity has increased instream transport of 

total phosphorus in the LTEN River Basin. 

The range of annual flow-weighted mean concentration for each constituent can be placed in 

national context by comparing with the statistical distribution of estimated values of annual flow-weighted 

mean concentration from about 200 basins monitored 

during 1993-94 as part of the NAWQA program 

(D. Mueller, U.S. Geological Survey, written commun., 1998). The distributions for total ammonia, 

dissolved orthophosphorus, and total nitrite plus 

nitrate at the LTEN River Basin sites match the 

national distributions reasonably well (fig. 16); 

median values for the LTEN River Basin sites fall 

within the 45 to 65 percentile range of the national distribution. Distributions for total nitrogen and total 

phosphorus at LTEN River Basin sites, however, 

depart more from the national distributions (fig. 16); 

median values for the LTEN River Basin sites are 

lower (corresponding to the 35 percentile in both 

cases). The maximum value of total phosphorus flowweighted mean concentration (0.73 mg/L for site 6, 

Duck River above Hurricane Mills, table 9) falls at the 

high end of the national distribution. The nine sites in 

the national data base with higher values than for site 6 

were predominantly from western States or were from 

small (drainage area less than 80 mi2), intensively cultivated, watersheds (D. Mueller, USGS, written commun., 1998). The flow-weighted mean concentration 

of total phosphorus for site 6 is an extreme value 

within the context of both the national and the regional 

(LTEN River Basin) distributions, and further emphasizes the significance of the phosphatic limestone formations in the basin for this site. Flow-weighted mean 

concentrations for site 5 (Duck River at Williamsport, 

0.53 mg/L) and site 10 (Elk River near Prospect, 

0.52 mg/L) also are extreme. 

The spatial distribution of tributary annual flowweighted mean concentration indicates which areas of 

the basin contribute more nutrients, on a dischargeweighted basis, to downstream receiving waters and, 

therefore, which water bodies may be at greatest risk 

for eutrophication and consequent ecological disruption. Although the trophic status of a water body 

relates not only to nutrient influx but also to assimilative capacity (which includes factors such as light 

attenuation and residence time), nutrient influx is a 

major factor. Watersheds contributing the largest 

amounts of total nitrogen on a discharge-weighted 

basis are sites 1, 12, and 10 (Clarks River at Almo, 

Town Creek near Geraldine, and Elk River near Prospect, respectively, table 9). Watersheds contributing 

the largest amounts of total phosphorus, on a 

discharge-weighted basis, are sites 6, 5, and 10 (Duck 

River above Hurricane Mills and at Williamsport and 

Elk River near Prospect, respectively). These sites also 

have small nitrogen-to-phosphorus (N:P) ratios (less 

than 4:1, compared to a range of 8:1 to 29:1 for the 

other tributary sites, table 4; values greater than 7:1 

indicate that phosphorus is the limiting nutrient). 
Instream Transport of Nitrogen, Phosphorus, and Sediment 55

FLOW-WEIGHTED MEAN CONCENTRATION

10

1

0.1

0.01

NATIONAL

LTEN

NATIONAL

LTEN

NATIONAL

LTEN

NATIONAL

LTEN

NATIONAL

LTEN

Figure 16. Comparison of distribution of flow-weighted mean concentrations at lower Tennessee River Basin

sites with national distribution.

Total ammonia Total nitrogen Total phosphorus Total nitrite plus

nitrate

Dissolved

orthophosphorus

211 14 186 8

202

17

200

16

206

12

EXPLANATION

SITES IN NATIONAL DATA SET

(D. Mueller, U.S. Geological

Survey, written commun., 1998)

NUMBER OF SITES

PERCENTILE

90th

75th

50th

25th

10th

202

12

NATIONAL

LTEN SITES IN LOWER TENNESSEE

RIVER BASIN

NUMBER OF SITES

VALUE FOR SINGLE SITE

50th PERCENTILE

Figure 16. Comparison of distribution of flow-weighted mean concentrations at lower Tennessee River Basin sites with 

national distribution.
56 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

0

500

1,000

1,500

2,000

2,500

3,000

3,500

O ND J FM AM J J A SO ND J FMAM J J A SOND J FM AM J J A S

1990

Annual mean of monthly

loading rate

1991 1992

MONTHLY INSTREAM LOAD, IN TONS PER MONTH

Figure 17. Monthly instream load of total nitrogen at Elk River near Prospect, Tennessee,

water years 1990-92.

Furthermore, inflow from these tributaries appears to 

cause a decreasing trend of N:P ratio along the main 

stem of the Tennessee River (27:1 at site 17, Tennessee River at South Pittsburg, compared with 12:1 at 

site 15 near the mouth), towards a less phosphoruslimited system.

Although water-quality criteria limiting nutrient 

influx have not been established, the National Technical Advisory Committee (1968) recommendation of 

0.05 mg/L phosphorus for waters entering impoundments can be compared with the annual estimate of 

phosphorus flow-weighted mean concentrations at 

each monitoring site (table 9). The annual flowweighted mean concentrations exceeded the recommended value at five of the eight tributary sites and 

three of the four main stem Tennessee River sites. Furthermore, these phosphorus concentrations exceeded 

the value of 0.1 mg/L, recommended by Mackenthun 

(1969) to prevent algal blooms in streams, by threefold 

or more at four of the eight tributary sites. The phosphorus influx to consider for evaluating ecological risk 

to water bodies may not be the annual mean influx, 

however, but rather the influx during spring and summer, which is the season of algae and macrophyte 

growth. Mean rates of influx for this period are different from the mean annual rate, due to seasonal variation in loading rate (illustrated in fig. 17). 

Estimates of flow-weighted mean concentration 

of nutrients during the period March-July are reported 

in table 9 along with the annual estimates to illustrate 

differences in annual influx and seasonal influx. Estimates of seasonal flow-weighted mean concentration 

were about 50 percent lower than annual estimates; the 

range for the tributary sites was from 0.28 mg/L (site 2, 

Buffalo River near Flat Woods) to 1.2 mg/L (site 1, 

Clarks River at Almo) of total nitrogen, and from less 

than 0.01 mg/L (site 9, Elk River below Tims Ford 

Dam) to 0.18 mg/L (site 5, Duck River at Williamsport) of total phosphorus. The seasonal estimate of 

total phosphorus flow-weighted mean concentration 

was above the value of 0.05 mg/L, recommended for 

water entering impoundments, at four of the eight tributary sites, but was much closer to this value than the 

corresponding annual estimates.

Whereas water-quality impairment from 

eutrophication is related to excessive nutrient influx 

over a period of weeks or months, other types of 

impairment (for example, acute toxicity of ammonia) 

result from short-term fluctuations of concentrations. 

The estimates of annual or seasonal yield and flowweighted mean concentration are not useful for 

addressing this latter type of water-quality impairment. 

Information about the spatial distribution of ammonia 

concentration during prolonged periods of low streamflow, similar to the information presented in figure 9A, 

Figure 17. Monthly instream load of total nitrogen at Elk River near Prospect, Tennessee, water years 

1990-92.
Instream Transport of Nitrogen, Phosphorus, and Sediment 57

would be more useful in assessing where impairment 

caused by ammonia toxicity is likely to occur.

Sediment yield estimates ranged from 

65 (tons/mi2)/yr (site 2, Buffalo River near Flat Woods) 

to 260 (tons/mi2

)/yr (site 8, Shoal Creek at Iron City) 

for the three tributary monitoring basins for which data 

were available, and from 17 to 26 (tons/mi2

)/yr for the 

two main stem sites (Tennessee River at South Pittsburg and Tennessee River at Pickwick Landing Dam, 

respectively, table 9). Lower sediment yields for the 

main stem sites compared with the tributary sites is 

probably due to sediment deposition in the main stem 

of the Tennessee River and tributary embayments 

along the main stem. The sediment yield estimates for 

the tributary sites are lower than the estimate from 

Trimble and Carey (1984) of 800 (tons/mi2

)/yr for 

basins in central and eastern Tennessee. 

Comparison of Inputs from Nutrient Sources 

with Nutrient Yields

The estimates of nitrogen and phosphorus loading from major sources varied widely among the 11 

tributary basins for which estimates were prepared, 

and are expected to represent the variability in these 

sources across the LTEN River Basin (figs. 14 and 15). 

Of the sources of land-phase nitrogen inputs (atmospheric deposition, fertilizer application, and livestock 

waste), livestock waste contributed the largest input in 

about two thirds (7 out of 11) of the load-computation 

basins (table 3 and fig. 14), and fertilizer application 

contributed the largest input in the remaining four 

basins (sites 1, 2, 7, and 9). Estimates of nitrogen input 

from fertilizer application were the most variable spatially among the land-phase nitrogen inputs, ranging 

from 1.5 to 23 (tons/mi2)/yr. Atmospheric deposition 

estimates varied the least from basin to basin, ranging 

from 1.6 to 2.0 (tons/mi2

)/yr. The balance of landphase nitrogen inputs on agricultural lands (fertilizer 

application plus nitrogen fixation plus livestock waste 

minus harvest) ranged from 2.4 to 15 (tons/mi2)/yr of 

nitrogen (table 3). Wastewater discharge contributed 

between 0 and 0.61 (tons/mi2

)/yr of nitrogen (table 3); 

wastewater input of nitrogen is therefore equivalent to 

a relatively small part (less than 27 percent) of the 

annual instream nitrogen load, whereas the contribution of wastewater discharge during low flow is much 

more significant (fig. 9B).

The estimates of inputs can be compared and 

correlated with export yields; significant correlations 

between estimates of inputs and exports might be useful as predictive tools for instream water quality where 

monitoring data are not available. Export of nitrogen 

correlated moderately well with the balance of landphase inputs to agricultural lands for the tributary sites 

(fig. 18). For example, nitrogen export was highest 

[3.5 (tons/mi2)/yr] for site 12 (Town Creek near Geraldine), for which the balance of agricultural land-phase 

input was also the highest [15 (tons/mi2

)/yr]. Nitrogen 

export was low [1.0 (tons/mi2

)/yr] for site 2 (Buffalo 

River at Flat Woods), for which the balance of agricultural land-phase input was correspondingly low 

[3.2 (tons/mi2

)/yr, the second lowest]. The matrix of 

Pearson correlation for nutrient input, percentage land 

use and land cover, and export is shown in table 10. 

Among all the estimated nitrogen inputs and land-use 

types, there were significant correlations between the 

balance of agricultural land-phase input and export 

(r = 0.65, p = 0.03, shown in fig. 18) and between percentage pasture land and export (r = 0.67, p = 0.03). 

Nonparametric rank correlation analysis showed similar results, addressing the concern that the large values 

of export, livestock-waste input, and percentage pasture land at site 12 (Town Creek near Geraldine) might 

skew the correlation results. Correlation of wastewater 

discharge with nitrogen export was poor (r = 0.06), 

and contrasts with the significant correlation (r = 0.71, 

p = 0.01, fig. 9A) between wastewater discharge and 

nitrogen concentration during low streamflow. The 

poor correlation between wastewater discharge and 

annual export was expected, however, as wastewater 

discharge is a small fraction compared with annual 

instream nitrogen load.

The relation between total nitrogen export and 

the balance of agricultural land-phase input is shown 

in figure 18, with a line fitted to the data points using a 

simple linear regression. The y-intercept of the fitted 

line, 0.95 (ton/mi2

)/yr, could be interpreted as the 

expected nitrogen export from a watershed without 

agricultural inputs. The results from sites 4 and 9 

(Duck River below Normandy Dam and Elk River 

below Tims Ford Dam, respectively) represent the 

largest residuals from the regression line, and may 

reflect the effects of the reservoirs on instream delivery processes. Large residuals for sites 7 and 10 (Shoal 

Creek at Highway 43 and Elk River near Prospect, 

respectively) could be due to a difference in the landwater delivery process (such as different soil-drainage 

characteristics) in the watersheds for these sites, as 

compared with the other sites in the data set.
58 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

0 5 10 15 20

BALANCE OF AGRICULTURAL LAND-PHASE INPUT OF TOTAL NITROGEN, IN TONS PER

SQUARE MILE PER YEAR

0

4.5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

EXPORT OF TOTAL NITROGEN,

IN TONS PER SQUARE MILE PER YEAR

10- Elk

7-Shoal

12-Town

1-Clarks

2-Buffalo

4-below Normandy

5-Duck

6-Duck 13-Sequatchie

9-below Tims Ford

11-Flint Y = 0.95 + 0.15*X

r = 0.65, p = 0.03

EXPLANATION

NUMBER IS SITE IDENTIFICATION (fig. 2)

Upper limit of 95-percent-confidence interval

Estimate of export

Lower limit of 95-percent confidence interval

6

Balance of agricultural land-phase input is calculated

as a combination of several inputs related to agricultural

activities: fertilizer application plus nitrogen fixation plus

livestock waste minus harvest

Figure 18. Relation of total-nitrogen export to the balance of land-phase inputs

to agricultural land.

Among the sources of land-phase phosphorus 

inputs (fertilizer application and livestock waste), livestock waste contributed most of the total input in 8 out 

of the 11 tributary basins (fig. 15 and table 4), and fertilizer application contributed most in the basins for 

sites 1, 2, and 7 (Clarks River at Almo, Buffalo River 

near Flat Woods, and Shoal Creek at Highway 43, 

respectively). The balance of agricultural land-phase 

inputs of phosphorus ranged from 0.87 (tons/mi2

)/yr 

(site 13, Sequatchie River at Valley Road) to 

4.7 (tons/mi2

)/yr (site 12, Town Creek near Geraldine). Wastewater discharge contributed from 0 to 

0.14 (tons/mi2

)/yr, equal to as much as 1.2 times 

(site 9, Elk River below Tims Ford Dam) the corresponding phosphorus export from the basin. 

In contrast with nitrogen, phosphorus export did 

not correlate well with any estimated inputs or landuse types (table 10). Phosphorus export was highest 

[1.1 and 0.93 (tons/mi2)/yr] for sites 6 and 5 (on the 

Duck River) and at site 10 [0.89 (tons/mi2)/yr, Elk 

River near Prospect]; however, estimates of inputs and 

percentage of each land-use type at these sites were 

not in the high end of respective ranges (table 4). The 

influence of a known natural source, outcrop of phosphatic limestone formations of the brown phosphate 

district, in the lower Duck and lower Elk River Basins 

(fig. 11A and 11E) was examined by removing sites 5, 

6, and 10 from the correlation data set. The significant 

correlations between phosphorus export and wastewater discharge (r = 0.97) and between phosphorus 

export and fertilizer application (r = 0.94) for this 

Figure 18. Relation of total nitrogen export to the balance of land-phase inputs to agricultural 

land.
Instream Transport of Nitrogen, Phosphorus, and Sediment 59

trimmed data set (table 10) should be interpreted with 

caution because of the small number of sites (n = 5). 

Two related conclusions are suggested: (1) inputs from 

wastewater discharge and fertilizer application are 

strongly linked with instream transport of phosphorus 

in watersheds where the natural phosphorus source is 

not present and (2) the natural source, where it is 

present, might be the largest contributor to instream 

transport of phosphorus. A regression equation was 

not developed between total phosphorus export and 

any of these sources due to the small number of sites 

in the trimmed data set.

That the correlation between phosphorus export 

and percentage of pasture land (r = 0.85) is very different from the correlation between export and livestock 

waste (r = -0.06) is difficult to explain because the 

estimate for livestock waste is partly derived from distribution of pasture land; however, the estimate for 

livestock waste also accounts for distribution of animal populations, and, because of feedlot operations, 

this distribution may differ substantially from the distribution of pasture land. The apparent contradiction in 

correlation results might indicate that pasture land 

influences instream loads of phosphorus through 

processes apart from runoff from land areas with livestock waste, or that some controlling factor is coincidentally correlated with percentage pasture land.

The spatial pattern of estimated inputs and 

exports may be influenced by several factors other 

than sources and transport processes. These other factors, some of which are listed below, may confound 

meaningful interpretation of the correlation results:

1. Inaccuracy in estimates of export caused by sparseness of monitoring data and lack of flowstratified sampling for load estimation (discussed 

in Appendix B). 

2. Low variability in export, which reduces the ability 

to detect spatial patterns. For example, the relatively low variability in nitrogen export (only one 

half of an order of magnitude) may reflect conditions throughout the basin, or may result from 

network bias (lack of representation of the full 

range of conditions in the basin or lack of sufficiently homogeneous basins). Phosphorus export, 

ranging through almost two orders of magnitude, 

was more variable than was nitrogen export.

3. Other sources of nutrients not quantified in this 

analysis (such as urban runoff, failing septic 

a

 Calculated for nitrogen as the sum of inputs from fertilizer application and nitrogen fixation and livestock waste, minus removal as crop 

harvest; calculated for phosphorus as the sum of inputs from fertilizer application and livestock waste, minus removal as crop harvest.

Table 10. Pearson correlation coefficients among 1992 export, inputs, and other factors

[n, number of observations in the correlation data set; --, not estimated; **, correlation significant (p-value < 0.05); sites with known natural 

source of phosphorus (excluded from n=5 data set) are sites 5, 6, and 10 (Duck River at Williamsport, Duck River above Hurricane Mills, and 

Elk River near Prospect, respectively)]

Correlation coefficient (r)

Input, land use, or other 

factor

Total nitrogen export

(n = 11)

Total phosphorus export

All sites (n = 8)

Excluding sites with 

known natural source 

(n = 5)

Wastewater discharge 0.06 -0.24 0.97**

Atmospheric deposition .29 -- --

Fertilizer application .17 -.27 .94**

Livestock waste .57 .40 -.06

Balance of agricultural 

land-phase input a .65** -.14 .70

Percent forest land -.41 -.06 -.80

Percent cultivated land .14 -.42 .82

Percent pasture land .67** .46 .85

Percent urban land .18 -.04 .90**

Site type (riverine = 1, 

flow-regulated = 2)

-.58 -.52 -.53
60 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

systems, or natural sources) might be responsible 

for much of the observed variability in export.

4. The pairwise correlation analysis (table 10) allows 

examination of correlations of export with individual input variables, but does not test the correlation with co-occurrence of variables. The small 

size of the data set prevented testing combinations of variables using stepwise multiple regression analysis.

5. Regional variability in soil and other geologic factors causes variability in land-water delivery processes and therefore affects the relation between 

sources (particularly land-phase loads) and 

export. The influence of regional differences in 

natural environmental setting on interactions 

between sources and exports could be examined 

with a larger set of monitoring sites, provided 

that the monitoring network was sufficiently 

stratified by environmental setting (that is, 

included several watersheds representing each 

type of environmental setting). 

TRENDS OF NITROGEN, PHOSPHORUS, 

AND SEDIMENT

An objective of this analysis of historical data is 

to describe temporal trends in nutrient and sediment 

concentrations during the period 1980-96 and to interpret the trends with respect to changes in sources during this period. Although quantitative data on temporal 

variation of sources are sparse, a comparison of general information about source changes with observed 

trends of instream concentration is possible.

Trends of Inputs

The primary sources of nitrogen and phosphorus 

for which data are available for the LTEN River Basin 

are wastewater discharge, fertilizer, and livestock 

waste (tables 3 and 4). The volume of wastewater discharge increased during the period 1980-96 as a result 

of population growth. Concentrations of nitrogen and 

phosphorus in wastewater decreased during this 

period, however, because of legislated control of 

municipal-effluent quality implemented through construction and upgrading of treatment plants to bring all 

dischargers to secondary or tertiary treatment standards. Concentrations of phosphorus in wastewater 

decreased dramatically starting around 1988, when 

reductions in the phosphate content of commerciallyavailable detergents were made to reduce the 

phosphorus input to wastewater treatment plants 

(S. Fishel, Tennessee Department of Environment and 

Conservation, oral commun., 1997).

Significant changes have occurred in effluent 

concentration of certain constituents of total nitrogen; 

specifically in the relative amounts of reduced and 

oxidized forms of nitrogen. Because the reduced forms 

of nitrogen (organic nitrogen and ammonia) deplete 

instream oxygen levels and because ammonia is toxic 

to fish and aquatic life, advanced treatment processes 

have focused on converting ammonia and organic 

nitrogen to nitrate (U.S. Environmental Protection 

Agency, 1993). These processes have resulted in 

decreases in effluent loads of ammonia and increases 

in effluent loads of nitrate.

Changes in stream inputs of nitrogen and phosphorus from fertilizer and livestock waste between 

1980 and 1996 are more difficult to estimate, even 

qualitatively. As with wastewater, these land-phase 

inputs increased during this period, based on pounds 

of fertilizer applied and animal census data; however, 

the extent to which improvements in nonpoint-source 

controls have offset the increased inputs by reducing 

delivery of land-phase to stream inputs is impossible 

to generalize.

Trends of Instream Concentration

Trends of instream concentration of nitrogen, 

phosphorus, and sediment were quantified with the 

multivariate log-linear regressions included in Cohn’s 

Estimator program (Cohn, 1988). Trends were estimated by examining the statistical significance of the 

coefficient on time (β3 in equation 1). The direction 

(increasing or decreasing) of significant trends was 

determined from the sign of β3. Positive values of β3 

indicate an increasing trend; negative values of β3 

indicate a decreasing trend. Trend results are reported 

for two separate periods—the period of available 

record between 1980-96 and a common period of 

record (last column of table 8). 

The trend results for the period of available 

record constitute a larger data set and span a longer 

time period, compared with results for the common 

period of record, and thus are more useful for at-site 

interpretations of instream trends with respect to 

trends in sources. The trend results for the common 

period of record, however, are more useful for comparing results among sites (fig. 19). The common 

period used for this second set of tests (generally from 

mid-1980’s to mid-1990’s) differed slightly among 

constituents but is consistent for results at all sites for a 
Trends of Nitrogen, Phosphorus, and Sediment 61

1

13 9

16 7

2 2

18

1

6

5

13 9

10

16 7

2

18

1

6

5

13 9

16 18

Total nitrite plus nitrate,

1985-94

Total ammonia plus organic nitrogen,

1986-93

Total nitrogen,

1985-94

Tenn.

Ala.

Tenn.

Ala.

Tenn.

Ala.

Miss.

Ga.

Ky. Ky. Ky.

Ky. Ky. Ky.

Miss.

Ga.

Miss.

Ga.

1

5

16

2

9

17

8

16

3

Total phosphorus,

1985-93

2

7

1

5

13 9

7

Total ammonia,

1986-94

Tenn.

Ala.

Tenn.

Ala.

Tenn.

Ala.

Miss.

Ga.

Miss.

Ga.

Miss.

Ga.

9

Figure 19. Trends of instream concentrations of nitrogen, phosphorus, and suspended sediment in the

lower Tennessee River Basin.

Suspended sediment,

variable time period

TREND IN WATER-QUALITY

CONSTITUENTÑNumber is

site identification in table 1

Increasing trend

Decreasing trend

No trend

Note: Trend results for other time spans are

reported for these sites and four additional

sites (4, 11, 19, and 20) in table 8.

EXPLANATION

Figure 19. Trends of instream concentrations of nitrogen, phosphorus, and suspended sediment in the lower Tennessee River 

Basin.
62 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

constituent. Trend tests could not be done for a common period of record for suspended sediment, however, because there were too few sites and the periods 

of available record generally did not overlap.

The time series of concentration residuals (from 

a regression against flow and season) for selected sites 

and constituents are shown in figure 20. Use of residuals, rather than actual concentrations, in these displays 

shows more clearly how concentration varies with 

time, independent of other influences (season and 

streamflow). A smoothed curve of the residuals calculated by locally weighted scatter-plot smoothing 

(LOWESS) is displayed with the residuals to illustrate 

the trend pattern. The trend estimate from the analysis 

of the common period of record is also shown on these 

plots in the inset boxes, for comparison. 

All significant trends in nutrient concentrations 

during the common period of record (mid-1980’s to 

mid-1990’s) were decreasing trends, except for total 

nitrite plus nitrate, which increased at site 9 (Elk River 

below Tims Ford Dam). The constituents for which 

significant downward trends were most commonly 

observed were total ammonia and total nitrogen. Sites 

with decreasing trends in ammonia concentration during the period 1986-94 were also sites which ranked 

relatively high (compared with the other sites) in 

wastewater inputs compared to other inputs, and the 

timeframe of the observed trends spans the period of 

changes in wastewater loading. These lines of evidence suggest that the ammonia trends at site 1 (Clarks 

River at Almo), site 5 (Duck River at Williamsport), 

and site 7 (Shoal Creek at Highway 43) result from 

decreases in wastewater effluent concentrations. Concentrations of total phosphorus did not decrease during 

the period 1985-93 at the sites with decreasing ammonia trends, however, as might have been expected considering reductions in wastewater loading of 

phosphorus during this period.

The common-period trend results for site 18, 

Tennessee River below Raccoon Mountain, are apparently contradictory (fig. 19); no significant trend is in 

concentrations of nitrite plus nitrate or ammonia plus 

organic nitrogen, but a significant decreasing trend 

exists in total nitrogen concentration, which is calculated as the sum of concentrations of the first two constituents. This discrepancy can be explained by the 

slightly different time periods used as the common 

period for each constituent: 1986-93 for ammonia plus 

organic nitrogen, and 1985-94 for nitrite plus nitrate 

and for total nitrogen. Decreasing trends for site 18 for 

all three nitrogen constituents for the period of available record (1981-94, table 8) are reasonable: decreasing trends exist in concentrations of all three 

constituents.

The trend results include periods other than the 

common period used for spatial interpretation (table 8). 

Total ammonia increased at site 15 (Tennessee River at 

mile 23) during the period 1990-94, dissolved orthophosphorus increased at sites 12 and 19 (Town Creek 

near Geraldine and Scarham Creek near Kilpatrick) 

during the period 1988-96, and total nitrogen 

increased at site 14 (Tennessee River at Highway 60 

near Paducah) during the period 1980-84. The increasing trends in dissolved orthophosphorus at the Town 

and Scarham Creek sites (12 and 19) were not expected, 

because the period of trend analysis (1988-96) corresponds to a period of many recognized improvements 

in management of poultry-waste runoff in the watershed for the sites. This suggests that the predominant 

input of phosphorus in these basins is from another 

source(s). A separate explanation, however, is that the 

improvements in source control may have had the 

desired effect of causing decreases in instream concentrations and loads of total phosphorus and particulate 

phosphorus, but with a corresponding conversion of 

part of the particulate-phase phosphorus to dissolved 

forms (for example, in sediment detention areas), thus 

causing the increasing trend in dissolved orthophosphorus (Holt and others, 1970). Unfortunately, this 

hypothesis cannot be tested because of insufficient 

data for total phosphorus at these sites.

It is important to emphasize that these trend 

results only describe the net change in concentrations 

between the start and end of the period of analysis. 

Temporary fluctuations in concentration, caused by 

temporary changes in sources, for example, are not 

detected by these trend tests. These fluctuations are 

evident, however, in the time series of concentration 

residuals (fig. 20). The time series and LOWESSsmoothed line of total ammonia and total nitrogen 

concentrations at site 9 (Elk River at Tims Ford Dam) 

suggest a temporary decline in the late 1980’s, but then 

an increase and return to early 1980’s levels, with no 

net change or trend. This pattern might be caused by 

increases in sources other than wastewater during this 

period, superposed on and offsetting declines in wastewater in the early part of the period; or this pattern 

might correspond with temporary reductions in 

nonpoint-source loads because of decreased runoff 

during the drought of 1985-88.
Trends of Nitrogen, Phosphorus, and Sediment 63

1980 1985 1990 1995

-1.5

-1

-0.5

0

0.5

1

1.5

1980 1985 1990 1995

-1.5

-1

-0.5

0

0.5

1

1.5

Figure 20. Temporal variation in nutrient concentrations during 1980-96 and model estimate of trend at

selected sites in the lower Tennessee River Basin, for (A) total nitrogen, (B) total nitrite plus nitrate,

(C) total ammonia, and (D) total phosphorus.

(A)

REGRESSION RESIDUAL OF TOTAL NITROGEN CONCENTRATION

Clarks River at Almo, Ky.

(site 1, fig. 2)

Elk River below Tims Ford Dam,

Tenn. (site 9, fig. 2)

Duck River at Williamsport,Tenn.

(site 5, fig. 2)

-3

-2

-1

0

1

2

1980 1985 1990 1995 1980 1985 1990 1995

-3

-2

-1

0

1

2

LOWESS LINE

RESIDUAL FROM REGRESSION

1985-94 TREND IN CONCENTRATION,

FLOW- AND SEASON-ADJUSTED

(Calculated by Cohn's Estimator

model)

Increasing trend

Decreasing trend

No trend

RIVERINE SITE

FLOW-REGULATED SITE

EXPLANATION

REGRESSION RESIDUAL OF TOTAL NITRITE PLUS NITRATE CONCENTRATION

(B)

Clarks River at Almo, Ky.

(site 1, fig. 2)

Elk River below Tims Ford Dam,

Tenn. (site 9, fig. 2)

Duck River at Williamsport,Tenn.

(site 5, fig. 2)

Figure 20. Temporal variation in nutrient concentrations during 1980-96 and model estimate of trend at selected 

sites in the lower Tennessee River Basin for (A) total nitrogen, (B) total nitrite plus nitrate, (C) total ammonia, and 

(D) total phosphorus.
64 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

-3

-2

-1

0

1

2

3

1980 1985 1990 1995

1980 1985 1990 1995

-3

-2

-1

0

1

2

3

REGRESSION RESIDUAL OF TOTAL AMMONIA CONCENTRATION

(C)

-4

-3

-2

-1

0

1

2

3

4

1980 1985 1990 1995 1980 1985 1990 1995

-4

-3

-2

-1

0

1

2

3

4

REGRESSION RESIDUAL OF TOTAL PHOSPHORUS CONCENTRATION

(D)

Clarks River at Almo, Ky.

(site 1, fig. 2)

Elk River below Tims Ford

Dam, Tenn. (site 9, fig. 2)

Duck River at Williamsport,Tenn.

(site 5, fig. 2)

Clarks River at Almo, Ky.

(site 1, fig. 2)

Elk River below Tims Ford Dam,

Tenn. (site 9, fig. 2)

Duck River at Williamsport,Tenn.

(site 5, fig. 2)

LOWESS LINE

RESIDUAL FROM REGRESSION

TREND IN CONCENTRATION, FLOWAND SEASON-ADJUSTED (Calculated

by Cohn's Estimator model)Ñ

1986-94 for total ammonia (C)

1985-94 for total phosphorus (D)

Increasing trend

Decreasing trend

No trend

RIVERINE SITE

FLOW-REGULATED SITE

EXPLANATION

Figure 20. Temporal variation in nutrient concentrations during 1980-96 and model estimate of trend at

selected sites in the lower Tennessee River Basin for (A) total nitrogen, (B) total nitrite plus nitrate,

(C) total ammonia, and (D) total phosphorusÑContinued.

Figure 20. Temporal variation in nutrient concentrations during 1980-96 and model estimate of trend at selected 

sites in the lower Tennessee River Basin for (A) total nitrogen, (B) total nitrite plus nitrate, (C) total ammonia, and 

(D) total phosphorus—Continued.
Conclusions 65

CONCLUSIONS

Implications for Data Collection and Analysis

By their nature, ambient water-quality monitoring programs cover large geographic areas and operate 

over long time periods. This broad spatial and temporal coverage makes them well suited to broad-scale 

assessment of transport of constituents in a large river 

basin, but can also restrict interpretations of these data. 

Resource limitations and logistics in operating a large, 

long-term monitoring network often force difficult 

design trade-offs, favoring a sampling design that is 

prescribed more by schedule than by targeting a wide 

variety of environmental conditions. Use of the data 

for interpreting constituent transport as a function of 

environmental conditions is, therefore, hampered. Heterogeneous characteristics of the large watersheds 

contributing to many of the ambient monitoring sites 

confound spatial comparisons of input to export; 

meaningful comparisons require a network of sites 

draining watersheds that are homogeneous with 

respect to both natural and human-influenced environmental setting.

Data-collection requirements depend on the 

water-quality evaluation to be made: the important 

water-quality indicator for evaluating risk to the ecological health of a receiving water body caused by 

nutrient overenrichment is nutrient loading rate from 

its tributaries, rather than concentrations in these tributaries. Estimation of loading rate requires continuous 

streamflow record at the tributary sampling site and 

requires a fully stratified sampling program that covers all possible combinations of season and runoff condition. Evaluation of ecological risk may also require 

estimates of loading rates during the period of the year 

when growth of aquatic plants responds most rapidly 

to nutrient influx: the period of long hydraulicresidence time and warm, clear water in the receiving 

water body. Although the data sets used in this report 

are sufficiently large for estimating annual loading 

rates, they are too sparse when stratified by season to 

allow accurate estimation of loading rate during a 

specified, critical season. Accurate estimation of transport during a critical season requires targeting sampling efforts to cover the full range of runoff and 

streamflow conditions during that season. Data from a 

fully stratified sampling program will also produce 

more accurate estimates of temporal trends and can be 

used to distinguish between loading patterns of nonpoint sources and loading patterns of point sources.

Implications for Resource Management

Estimates of 1992 annual flow-weighted mean 

concentration of total nitrogen ranged from 0.53 to 

2.8 mg/L as nitrogen, representing a fivefold difference in instream transport among watersheds in the 

LTEN River Basin. The smallest estimate was for a 

minimally developed watershed, and the largest estimate was for a watershed with the largest areal percentages of urban and agricultural land use and largest 

amounts of wastewater discharge, suggesting that 

human activity increased exports of total nitrogen by 

as much as fivefold. The range in estimates of annual 

flow-weighted mean concentration of total phosphorus, from 0.02 to 0.73 mg/L as phosphorus, represents 

nearly a fortyfold difference in instream transport 

among the watersheds. The largest three estimates, 

0.73, 0.53, and 0.52 mg/L, probably represent a natural source in those watersheds: the phosphatic limestones of the brown-phosphate districts. The outcrop 

pattern of these phosphatic limestones may be an 

important factor to consider as regional boundaries are 

established for attainable region-specific water-quality 

criteria for total phosphorus (U.S. Environmental 

Protection Agency, 1998).

Nutrient overenrichment caused impairment in 

37 of the 109 impaired stream segments in the LTEN 

River Basin in 1996. Impairment is caused by influx of 

nutrients and growth of algae and aquatic macrophytes 

during critical periods of the year; therefore, estimates 

of seasonal flow-weighted mean concentration may be 

more useful than annual estimates in evaluating ecological risk to water bodies, and in establishing waterquality criteria. Seasonal estimates of flow-weighted 

mean concentration generally were less than half of the 

annual estimates, and ranged from 0.28 to 1.2 mg/L 

total nitrogen, as nitrogen, and from less than 0.01 to 

0.18 mg/L total phosphorus, as phosphorus.

Nitrogen from wastewater discharge represents 

a small part (less than 27 percent) of the annual nitrogen export in 11 tributary basins, and variability in 

wastewater discharge among basins correlates poorly 

with annual export. Wastewater discharge may 

account for a larger part of nitrogen yield during low 

streamflow, however, and does correlate well (r = 0.71, 

p = 0.01) with total nitrogen concentration during low 

streamflow. Phosphorus from wastewater discharge 
66 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

represents as much as 1.2 times the annual phosphorus 

export, and correlates well with annual export except in 

watersheds with outcrops of the phosphatic limestones. 

The estimates of input from other sources 

(atmospheric deposition, fertilizer application, and 

livestock waste) cannot be compared as a fraction of 

export in the same way as for wastewater discharges 

because these estimates are the land-phase inputs from 

these sources, rather than inputs directly to the stream 

channel. The fraction of export contributed by a source 

may be inferred indirectly based on correlations 

between inputs and export. The significant correlation 

(r = 0.65, p = 0.03) between the estimate of agricultural land-phase input within a watershed and exported 

nitrogen might mean that these sources contribute to 

annual instream loads in significant amounts.

Concentrations of total ammonia and total nitrogen decreased during the period 1985-94 at about half 

of the sites where temporal trends could be tested. The 

spatial distribution of decreasing trends corresponds 

with the spatial variation among basins in wastewater 

input, and the time period of observed trends corresponds to the period of improvements in municipal 

treatment; thus, decreases in wastewater effluent concentrations of nitrogen might be responsible for the 

decreasing trend in instream concentrations at these 

sites. 

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Appendixes

Appendix A 71

Appendix A. Sites where historical water-quality data collected from water year 1980 to 1996 are included in nutrient- and sediment-d

River Basin—Continued

Hydrologic cataloging 

unit code 

(for sites 

1-20)

Site 

identification 

(fig. 2, 

10, or 11)

Surface-water station/Site location

Agency and

monitoring 

network

River 

mile

Period

of 

record

(water year)

Number Name 

Site identification

(fig. 2)

06040006 1 PRI038 Clarks River at Almo, Ky. KDEP-AMP 53.5 1981-95 06040004 2 03604000 Buffalo River near Flat Woods, Tenn. USGS-NASQAN 58.7 1963-95 06040002 3 03596000 Duck River below Manchester, Tenn. USGS-S 265.4 1967-89 06040002 4, d246a 001025 Duck River below Normandy Dam, 

Tenn.

TDEC-AMN 246.9 1981-96 

06040003 5, d113a 001065 Duck River at Williamsport, Tenn. TDEC-AMN 113.9 1978-95 

06040003 6, d26a 475793 Duck River above Hurricane Mills, 

Tenn.

TVA-FSN 26.0 1973-95 

06030005 7 002395 Shoal Creek at Highway 43 near 

Lawrenceburg, Tenn.

TDEC-AMN 32.2 1982-95 

06030005 8 03588500 Shoal Creek at Iron City, Tenn. USGS-S 22.3 1974-94 06030003 9 001207 Elk River below Tims Ford Dam, 

Tenn.

TDEC-AMN 133.0 1982-96 

06030004 10 475796b Elk River near Prospect, Tenn. TVA-FSN 41.5 1971-95 

06030002 11 FLCR7 Flint Creek near Falkville, Ala. FCWP-SS 33.4 1993-96 06030001 12 TOWNCREEK15c Town Creek near Geraldine, Ala. ADEM-SS 14.1 1980-90 06020004 13 002375 Sequatchie River at Valley Road, 

Tenn.

TDEC-AMN 6.3 1988-96 

(multiple) 14, t5d 03609750 Tennessee River at Highway 60 near 

Paducah, Ky.

USGS-NASQAN 5 1974-88 

(multiple) 15, 

t23d

202832 Tennessee River at mile 23, Ky. TVA-VS 23 1960-95 

Appendix A. Sites where historical water-quality data collected from water year 1980 to 1996 are included in nutrient- and sediment-d

River Basin

[Period of record represents entire period of record in source data base as of 1996; however, only data since October 1979 were included in data analysis in this report; variation analyses (DS) are shown only in figs. 10 and 11, all other sites are shown in fig. 2; d246, denotes Duck River and river mile; t5, denotes Tennessee River and DRM, Duck River mile; ADEM-TMN and ADEM-SS, Alabama Department of Environmental Management trend monitoring network and special study, respectivelyDepartment for Environmental Protection ambient monitoring program and special study, respectively; TDEC-AMN, Tennessee Department of Environment and ConsTVA-FSN, TVA-VS, and TVA-SS, Tennessee Valley Authority fixed station monitoring network, vital-signs monitoring network, and special study, respectively; USGcal Survey National Stream-Quality Accounting Network and suspended-sediment network, respectively; ORSANCO-MN, Ohio River Valley Sanitation Commission Creek Watershed Project special study; S, seasonal variation in nutrient concentration; Q, variation in nutrient concentration with streamflow; DS, downstream variatioinput loads; EL, annual export loads; T, trend estimation; STORET, STOrage and RETrieval data base of the U.S. Environmental Protection Agency; WATSTORE, WAbase of the U.S. Geological Survey; GSA, digital file from Geological Survey of Alabama; ADEM, digital file from Alabama Department of Environmental Managem
72 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96 Site identification (fig. 2)—Continued (multiple) 16, t206d 03593005 Tennessee River at Pickwick Land- ing Dam, Tenn. USGS-NASQAN 206.7 1975 -96 

(multiple) 17, t418d 03571850 Tennessee River at South Pittsburg, Tenn. USGS-NASQAN 418.2 1967-87 (multiple) 18, t444d 003315 Tennessee River below Raccoon Mountain, Tenn. TDEC-AMN 444 1978-96 06030001 19 SCARHAMCREEK03e Scarham Creek near Kilpatrick, Ala. ADEM-SS 7.7 1988-96 

06030001 20 SOUTHSAUTYCK03f South Sauty Creek, Ala. ADEM-SS 16.7 1988-96 

Site identification (fig. 10) Sites on the Tennessee River main stem (in addition to sites 14-18) t6 TR-6.0M, 

and TR-5.0M

Tennessee River at Paducah (TRM 5 

and 6)

ORSANCO-MN 5 1971-95 

t40 CLN132 Jonathan Creek embayment (TRM 

40.0)

KDEP-SS 40.0 1990-93 

t51 CLN130 Blood River embayment (TRM 51.3) KDEP-SS 51.3 1990-93 t85 477403 Kentucky Reservoir (TRM 85.0) TVA-VS 85.0 1990-96 t89 003610 Tennessee River at Shirley’s Light 

(TRM 89.0)

TDEC-AMN 89.0 1970-95 

t112 475015 Kentucky Reservoir (TRM 112.0) TVA-VS 112.0 1960-95 

t135 003460 Tennessee River (circa TRM 135) TDEC 135 1960-95 t189 003455 Tennessee River (TRM 189.9) TDEC 189.9 1990-95 t207 476799 Pickwick Forebay (TRM 207.3) TVA-VS 207.3 1981-96 t230 016923 Pickwick Reservoir (TRM 230.0) TVA-VS 230.0 1960-96 t260 016912 Tennessee River upstream from Wilson Dam (TRM 260.8) TVA-VS 260.8 1960-96 

t277 016900 Tennessee River upstream from 

Wheeler Dam (TRM 277.0)

TVA-VS 277.05 1960-95 

t295 017009 Tennessee River/Wheeler Lake 

below Fox Creek (TRM 295.87)

TVA-VS 295.87 1960-95 

t307 017012 Tennessee River/ Wheeler Lake 

(TRM 307.52, near Decatur)

TVA-VS 307.52 1960-91 

t350 017261 Tennessee River/Guntersville Lake 

at Honey Bluff (TRM 350.0)

TVA-VS 350.0 1980-96 

Appendix A. Sites where historical water-quality data collected from water year 1980 to 1996 are included in nutrient- and sediment-da

River Basin—Continued

Hydrologic cataloging 

unit code 

(for sites 

1-20)

Site 

identification 

(fig. 2, 

10, or 11)

Surface-water station/Site location

Agency and

monitoring 

network

River 

mile

Period

of 

record

(water year)

Number Name 
Appendix A 73 a Site has an additional identification in figure 11, including river mile. b Site is a composite of site 475796 (river mile 41.5) and site 477330 (river mile 36.5). c Station number in ADEM study is t5. d Site has an additional identification in figure 10, including river mile. e Station number in ADEM study is sc3. f Station number in ADEM study is ss3.

Site identification

(fig. 10)—Continued

Sites on the Tennessee River main stem (in addition to sites 14-18)—Continued

t375 017522 Tennessee River/Guntersville Res at 

Mink Creek (TRM 375.2)

TVA-VS 375.2 1980-96 

t396 017101 Tennessee River/Guntersville Res at 

Coffee Ferry (TRM 396.8)

TVA-VS 396.8 1971-91 

t425 476344 Tennessee River/Nickajack Reservoir (TRM 425.5) TVA-VS 425.5 1980-95 

t430 003325 Tennessee River below Hales Bar 

Light (TRM 430.7, Nickajack Reservoir)

TDEC-AMN 430.7 1981-95 

t433 476239 Tennessee River/Nickajack Reservoir (TRM 433.0) TVA-VS 433.0 1970-91 

Site identification

(fig. 11)

Sites on the Duck River main stem (in addition to sites 4, 5, and 6)

d8 001135 Duck River at Waverly Waterworks 

Intake (DRM 8.0)

TDEC-AMN 8 1970-85 

d133 001050 Duck River (DRM 133.92) TDEC-AMN 133 1960-85 d181 001040 Duck River (DRM 181.0) TDEC-AMN 181.0 1960-85 d221 001030 Duck River (DRM 221.41) TDEC-AMN 221.41 1960-85 d249 NORMANDY01 Normandy Reservoir at the Dam 

(DRM 249)

TDEC-SS 249 1991-92 

d252 476244 Normandy Reservoir - Riley Creek 

(DRM 252.0)

TVA-SS 252.0 1980-95 

d259 476172 Normandy Reservoir - Anthony 

Branch (DRM 259.4)

TVA-SS 259.4 1971-92 

d262 476429 Normandy Reservoir (DRM 262.0) TVA-SS 262.0 1981-95 d265 TN001019 Duck River at Powers Bridge (DRM 

265.5)

TDEC-SS 265.5 1991-92 

Appendix A. Sites where historical water-quality data collected from water year 1980 to 1996 are included in nutrient- and sediment-d

River Basin—Continued

Hydrologic cataloging 

unit code 

(for sites 

1-20)

Site 

identification 

(fig. 2, 

10, or 11)

Surface-water station/Site location

Agency and

monitoring 

network

River 

mile

Period

of 

record

(water year)

Number Name 

Appendix B 75

Appendix B. Limitations of instream load estimates

Figure B1. Distribution of nutrient samples within season classes for load-computation sites in the

lower Tennessee River Basin, 1980-96 .................................................................................................................. 77

Figure B2. Distribution of nutrient samples within decile-flow classes for load-computation sites in the 

lower Tennessee River Basin, 1980-96................................................................................................................... 78
76 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

Appendix B. Limitations of instream load 

estimates

Most of the nutrient and sediment water-quality 

data used in this assessment are from monitoring networks that were not designed for estimating transport. 

This section examines the validity of load estimates 

from these data sets by evaluating the issues of sampling error caused by sparse data and sampling bias, 

the suitability of the data sets to Cohn’s Estimator 

model assumptions, and calibration error.

Successful calibration of a regression model 

requires a minimum number of observations for each 

regression variable—a general rule of thumb for data 

sufficiency is 10 observations for each variable (or 

regression coefficient), with at least 20 percent of the 

observations above the minimum reporting level, or 

MRL (T.A. Cohn, U.S. Geological Survey, written 

commun., 1995). This data-sufficiency criterion translates to a minimum of 70 observations for the sevenparameter regression analysis in Cohn’s Estimator 

model. This requirement was relaxed for this application because many of the data sets had fewer than (in 

some cases, less than half) the prescribed 70 observations; the accuracy of the load estimates for these data 

sets is expected to be lower. The estimates of dissolved 

orthophosphorus at site 11 (Flint Creek near Falkville) 

are subject to substantial error because fewer than 

20 percent of observations were above the MRL.

The data sets are relatively unbiased with 

respect to season of sampling (fig. B1), because samples were collected on a quarterly basis. Quarterly 

sampling leaves to chance the representation of high 

flow events: the hydrologic condition during which a 

large percentage of transport at riverine sites occurs 

for many nutrient species. Examination of the distribution of nutrient samples within the streamflow distribution (fig. B2) shows that the data sets are biased 

against higher streamflows (the 0-10 deciles of 

streamflow). The under-representation of higher 

streamflows, especially noticeable at site 6 (Duck 

River above Hurricane Mills) among the riverine sites, 

reduces the accuracy of model calibration for high 

streamflows, and thus substantially reduces the accuracy of load estimates.

Regression results were examined for two standard assumptions in least squares theory (Draper and 

Smith, 1981): normality of residuals and constancy in 

error variance throughout the range of values of 

regression variables (homoscedasticity). These 

assumptions were satisfied in only about half of the 

data sets examined, which leads to uncertainty that the 

log-linear regressions were able to adequately model 

constituent transport from these data. Data sparseness 

and sampling bias may contribute to this problem.

The calibration error statistics of Cohn’s Estimator regression models can be used as a partial indication of model accuracy and precision, although these 

statistics cannot account for the errors introduced by 

sampling bias, data sparseness, and data characteristics 

that do not match model assumptions. The coefficient 

of determination, r2

, represents the amount of variance 

in the concentration data that is explained by the 

regression variables; therefore, the value of r2 is a 

measure of the fit of the regression model to the data. 

A high value of r2 indicates that the regression equation can estimate daily concentration, and thus daily 

and annual load, with a high degree of accuracy. The 

standard error, s, is the estimate of standard deviation 

about the regression. The smaller the value of s, the 

more precise the estimates of daily concentration and 

load. The upper and lower bounds of the 95-percent 

confidence interval for each load estimate are calculated from s, and are similar measures of the precision 

of the estimate given the values of the independent 

variables. The values of r2 ranged from 0.09 to 0.78, 

and the values of s (log units) ranged from 0.20 to 

1.55. Although load estimates are reported for all data 

sets, regardless of values of r2 and s, the estimates 

from data sets with small r2

 and large s are probably 

less accurate. 

Despite these limitations, the accuracy of the 

estimates of instream load presented in this report are 

considered to be the best possible based on the available data. The model-calculated errors in individual 

estimates generally are less than differences among 

sites for a single year, and among years with different 

hydrologic conditions (wet, dry). Therefore, interpretations with these data of broad spatial patterns of 

instream load and comparison of instream load to 

input are considered valid.
Appendix B 77

20

SEASON

SEASON

40

20 10

0

20

10

0

20

10

0

20

10

0

20

10

0

20

10

0

20

10

0

20

10

0

20

10

0

20

10

0

20

10

0

20

10

0

20

10

0

60

30

0

20

10

0

0

40

20

0

SEPT-NOV

DEC-FEB

MAR-MAY

SEPT-NOV

JUNE-AUG

DEC-FEB

MAR-MAY

JUNE-AUG

Buffalo River near

Flat Woods, Tenn.

(site 2, fig. 2)

Duck River below

Manchester, Tenn.

(site 3, fig. 2)

Duck River below

Normandy Dam, Tenn.

(site 4, fig. 2)

Duck River above

Hurricane Mills, Tenn.

(site 6, fig. 2)

Duck River at

Williamsport, Tenn.

(site 5, fig. 2)

Shoal Creek at

Highway 43 near Lawrenceburg,

Tenn. (site 7, fig. 2)

Shoal Creek at

Iron City, Tenn.

(site 8, fig. 2)

Elk River near

Prospect, Tenn.

(site 10, fig. 2)

Elk River below

Tims Ford Dam, Tenn.

(site 9, fig. 2)

Flint Creek near

Falkville, Ala.

(site 11, fig. 2)

Sequatchie River at

Valley Road, Tenn.

(site 13, fig. 2)

Town Creek near

Geraldine, Ala.

(site 12, fig. 2)

Tennessee River at

Highway 60 near Paducah,

Ky. (site 14, fig. 2)

SEPT-NOV

DEC-FEB

MAR-MAY

SEPT-NOV

JUNE-AUG

DEC-FEB

MAR-MAY

JUNE-AUG

20

10

0

Tennessee River at mile 23, Ky.

(site 15, fig. 2)

Tennessee River at

Pickwick Landing Dam,

Tenn. (site 16, fig. 2)

Clarks River at Almo, Ky.

(site 1, fig. 2)

(Sediment only)

(Sediment only)

Figure B1. Distribution of nutrient samples within season classes for load-computation sites in the

lower Tennesse River Basin, 1980-96.

Tennessee River at

South Pittsburg, Tenn.

(site 17, fig. 2)

Tennessee River below

Raccoon Mountain, Tenn.

(site 18, fig. 2)

NUMBER OF NUTRIENT SAMPLES

Figure B1. Distribution of nutrient samples within season classes for load-computation sites in the lower Tennessee River Basin, 

1980-96.
78 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

NUMBER OF NUTRIENT SAMPLES

25 15

10

5

0

15

10

5

0

15

10

5

0

15

10

5

0

15

10

5

0

15

10

5

0

15

10

5

0

15

10

5

0

15

10

5

0

15

10

5

0

20

15

10

5

0

DECILES OF FLOW (highest flows on the left)

DECILES OF FLOW

(highest flows on the left)

(Sediment only)

(Sediment only)

Clarks River at

Almo, Ky.

(site 1, fig. 2)

Buffalo River near

Flat Woods, Tenn.

(site 2, fig. 2)

Duck River below

Manchester, Tenn.

(site 3, fig. 2)

Duck River at

Williamsport, Tenn.

(site 5, fig. 2)

Duck River above

Hurricane Mills, Tenn.

(site 6, fig. 2)

Shoal Creek at Highway 43

near Lawrenceburg, Tenn.

(site 7, fig. 2)

Duck River below

Normandy Dam, Tenn.

(site 4, fig. 2)

Elk River below

Tims Ford Dam, Tenn.

(site 9, fig. 2)

Elk River near

Prospect, Tenn.

(site 10, fig. 2)

Flint Creek near

Falkville, Ala.

(site 11, fig. 2)

Shoal Creek at

Iron City, Tenn.

(site 8, fig. 2)

0-5

6-10

11-20

21-3031-4041-5051-6061-7071-8081-90

91-100

0-5

6-10

11-20

21-3031-4041-5051-6061-7071-8081-90

91-100

0-5

6-10

11-20

21-3031-4041-5051-6061-7071-8081-90

91-100

0-5

6-10

11-20

21-3031-4041-5051-6061-7071-8081-90

91-100

Figure B2. Distribution of nutrient samples within decile-flow classes for load-computation sites in the

lower Tennessee River Basin, 1980-96.

{{{

{

Figure B2. Distribution of nutrient samples within decile-flow classes for load-computation sites in the lower Tennessee River Basin, 

1980-96.
Appendix B 79

NUMBER OF NUTRIENT SAMPLES

Tennessee River at

Pickwick Landing Dam, Tenn.

(site 16, fig. 2)

Tennessee River at

South Pittsburg, Tenn.

(site 17, fig. 2)

Tennessee River below

Raccoon Mountain, Tenn.

(site 18, fig. 2)

Town Creek near

Geraldine, Ala.

(site 12, fig. 2)

Sequatchie River at

Valley Road, Tenn.

(site 13, fig. 2)

Tennessee River at Highway 60

near Paducah, Ky.

(site 14, fig. 2)

Tennessee River at

mile 23, Ky.

(site 15, fig. 2)

DECILES OF FLOW (highest flows on the left)

DECILES OF FLOW

(highest flows on the left)

0-5

6-10

11-20

21-3031-4041-5051-6061-7071-8081-90

91-100

0-5

6-10

11-20

21-3031-4041-5051-6061-7071-8081-90

91-100

0-5

6-10

11-20

21-3031-4041-5051-6061-7071-8081-90

91-100

0-5

6-10

11-20

21-3031-4041-5051-6061-7071-8081-90

91-100

15

10

5

0

15

10

5

0

15

10

5

0

15

10

5

0

15

10

5

0

25

20

15

10

5

0

10

8

6

4

2

0

{{{

{

Figure B2. Distribution of nutrient samples within decile-flow classes for load-computation sites in the

lower Tennessee River Basin, 1980-96ÑContinued.

Figure B2. Distribution of nutrient samples within decile-flow classes for load-computation sites in the lower Tennessee River Basin, 

1980-96—Continued.

Appendix C 81

Appendix C. Methods for quantifying inputs of nitrogen and phosphorus from point and 

nonpoint sources

Table C1. Comparison of results from two methods of estimating fertilizer inputs of nitrogen and 

phosphorus for selected basins in the lower Tennessee River Basin ...................................................................... 84
82 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

Appendix C. Methods for quantifying 

inputs of nitrogen and phosphorus from 

point and nonpoint sources

Wastewater Discharge

Nitrogen and phosphorus inputs from wastewater discharge were calculated from effluent monitoring 

data reported to State agencies by permitted wastewater dischargers in the LTEN River Basin. State agencies provided discharger-reported monitoring data 

(effluent-quality sampling data and effluent flowmeasurement data for 1992 or 1995) and Standard 

Industrial Codes (SIC) for 729 permitted wastewater 

dischargers (J. Hughes, TDEC, written commun., 

1998; M. Rief and T. Cleveland, ADEM, written commun., 1998; V. Prather, KDEP, written commun., 

1998; G. Odom, MDEQ, written commun., 1998). 

Annual mean concentrations of total nitrogen and total 

phosphorus were estimated from self-reported concentrations or, where complete data were not available, 

were estimated using one of the following methods. 

Where ammonia-nitrogen (NH3-N) concentration data were reported but total nitrogen (TN) data 

were lacking, a regression equation was used to calculate TN from NH3-N. The regression equation was 

developed from more than 800 observations of effluent concentrations from municipal wastewater treatment plants in Virginia and North Carolina, and thus 

applies only to municipal wastewater. This equation 

took the form:

TN = 11.97 + 0.55 (NH3-N) (2)

where concentrations are given in milligrams per liter, 

as nitrogen (McMahon and Lloyd, 1995, p. 70-71).

In the absence of ammonia-nitrogen and total 

nitrogen concentration data, the average value of 

15 mg/L, as nitrogen, was assumed for total nitrogen 

concentration of municipal wastewater effluent. In the 

absence of phosphorus data, a concentration of 

3.5 mg/L, as phosphorus, was assumed for total phosphorus concentration of municipal wastewater effluent 

(S. Fishel, TDEC, oral commun., 1998). Values from 

literature were used for industrial wastewater when 

data were lacking. National Oceanic and Atmospheric 

Administration (1993) provides tables with average 

wastewater effluent concentrations of total nitrogen 

and total phosphorus based on the type of industry and 

the SIC of the facility.

Nutrient loads were estimated as the product of 

effluent annual mean concentration (estimated or measured) and effluent annual mean discharge (estimated 

or measured). Effluent discharge data were obtained 

from self-reported information from 264 of the 729 

dischargers in the LTEN River Basin (representing the 

264 sites for which effluent discharge data were available in digital format). At these sites, the annual mean 

discharge for calendar year 1992 (or 1995 in some 

cases) was calculated from daily, monthly, or semiannual effluent discharge measurements. Of the 264 

dischargers with digital discharge data, 64 were classified as major dischargers [that is, they discharged 

more than 1 million gallons per day (Mgal/d) each, or 

were industrial facilities with specific process wastewater of concern]. These 64 major dischargers contributed 13,000 Mgal/d (90 percent) of the total 

wastewater discharge, 9,000 tons/yr (68 percent) of the 

nitrogen load, and 640 tons/yr (83 percent) of the 

phosphorus load from all 264 dischargers.

Most of the remaining unestimated discharges 

(465 sites, fig. 4) are small domestic and commercial 

dischargers, such as trailer parks and schools, discharging less than 0.1 Mgal/d each. The contributions 

of discharge and nutrient load from these dischargers 

should be negligible in comparison with the contributions from the 264 estimated dischargers (S. Fishel, 

TDEC, written commun., 1998).

Atmospheric Deposition

Deposition data were obtained from the 

National Atmospheric Deposition Program/National 

Trends Network (NADP/NTN), a national system of 

precipitation chemistry monitoring stations operated 

in cooperation between State agricultural experiment 

stations, USGS, U.S. Department of Agriculture, and 

numerous other governmental and private entities. 

Data from several NADP/NTN monitoring stations in 

proximity to the LTEN River Basin were selected to 

calculate atmospheric deposition calculations: these 

included data from Dixon Springs Agricultural Center, 

Illinois (IL63); Land between the Lakes, Kentucky 

(KY38); Walker Branch Watershed, Tennessee 

(TN00); Hatchie National Wildlife Refuge, Tennessee 

(TN14); and Wilburn Chapel, Tennessee (TN98). Deposition data were retrieved for each of these NADP/ 

NTN monitoring stations for 1992 to coincide with the 

most recent data for other sources. 

Atmospheric deposition of total nitrogen was 

calculated as the sum of nitrate wet and dry deposition 
Appendix C 83

and ammonia wet deposition. Nitrate dry deposition 

rates were calculated from nitrate wet deposition rates, 

by multiplying the wet values by a dry/wet deposition 

ratio determined by Sisterson (1990). Because highelevation (> 610 meters) terrain and urban areas were 

of very limited areal extent in the LTEN River Basin, 

nitrate droplet deposition, nitrate urban wet deposition, and nitrate urban dry deposition were assumed to 

be negligible and were not included in the analysis. 

Organic-nitrogen deposition was not monitored at the 

NADP/NTN stations and therefore was not included in 

this analysis; however, monitoring studies in other 

parts of the Nation (for example, Harned, 1995) indicate that this may be a significant component of wet 

deposition of nitrogen.

Wet deposition rates for the selected 

NADP/NTN monitoring stations ranged from 0.33 to 

0.68 kilogram per hectare (kg/ha) for ammonia, and 

from 0.53 to 0.73 kg/ha for nitrate. This variability 

among stations preempted selection of a single basinwide average deposition rate for the LTEN River 

Basin. Instead, the total nitrogen deposition rates calculated for each NADP/NTN monitoring station (in 

tons per square mile per year) were weighted to each 

of the tributary basins and major hydrologic units, 

based on the station’s distance to the centroid of each 

basin and major hydrologic unit. 

Fertilizer Application

Estimates of fertilizer inputs to agricultural 

lands in the LTEN River Basin were calculated using 

two sources of information: fertilizer sales data and 

fertilizer application recommendations. County-level 

estimates of the amount of nitrogen fertilizer sold were 

computed by Jerald Fletcher (West Virginia University, written commun., 1992), by disaggregating statelevel estimates of the amount of fertilizer sold in 1991 

(obtained from the National Fertilizer and Environmental Research Center of TVA) to county-level estimates. Disaggregation was done by multiplying the 

state-level estimates by a ratio of county-to-state 

expenditures based on the 1987 Census of Agriculture 

(U.S. Department of Commerce, 1989). 

Fertilizer application recommendations were 

selected after comparing published recommended 

application recommendations for Tennessee (Savoy 

and Joines, 1998) and Alabama (Adams and others, 

1994) with the recommendations made by county agricultural extension agents. Published fertilizer application recommendations are based on crops and soil-test 

results, which are used to determine the availability of 

common agricultural nutrients, including nitrogen, 

phosphorus, and potassium. Agricultural extension 

agents from a number of counties across the LTEN 

River Basin were interviewed to determine typical soil 

ratings for the basin. Because of the great variability in 

soil-test results within individual counties, agents suggested using a medium soil rating to arrive at a basinwide average fertilizer application recommendation 

for each crop. 

Application recommendations for selected crops 

(corn, wheat, tobacco, soybeans, cotton, and hay) were 

multiplied by 1992 county-level data on harvested 

acreage (U.S. Department of Commerce, 1994) to 

derive an estimate of applied fertilizer for nitrogen and 

phosphorus for each crop in each county for 1992. The 

estimates were then summed by crop to provide a single fertilizer application estimate for each county.

County-level input estimates from both methods 

were weighted to provide estimates for selected 

basins. The weighting algorithm apportions the county 

input to each basin based on the portion of cultivated 

land, by county, encompassed within each basin. Estimates of nitrogen and phosphorus fertilizer inputs 

were also calculated for each major hydrologic unit 

using the same land-use weighting approach. This 

weighting approach may give inaccurate results in 

areas where cropping practices vary greatly across the 

agricultural land within a county, but the error introduced in this step is not significant for larger basins 

(those that include large parts of one or more counties).

A comparison of basin-level input estimates 

from the two computation methods (table C1) reveals 

significant differences in results for some basins. 

Sales-based nitrogen inputs were consistently higher 

than crop application recommendations (ranging from 

6 to 49 percent higher). Sales-based estimates for 

phosphorus differed from crop application recommendations by as much as 46 percent, but were not consistently higher or lower across all the basins. Several 

factors may contribute to these differences:

1. Estimates based on application recommendation 

are calculated for fertilizer applied to harvested 

acres only, not to total agricultural lands. The 

areas for which nitrogen sales-based estimates 

are almost 50 percent higher than application 

recommendation-based estimates may 
84 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus,

and Sediment in the Lower Tennessee River Basin, 1980-96

Table C1. Comparison of results from two methods of estimating fertilizer inputs of nitrogen and phosphorus for selected basins in the [Estimates are reported in tons per year of nitrogen (N) or phosphorus (P); fertilizer sales method [A] based on State and county sales information (J. Fletcher, West V1992; fertilizer application recommendation method [B] based on recommendations from Savoy and Joines (1998), Adams and others (1994); difference between estipercent]

Estimated input

from fertilizer

Estimated application 

Site input from recommendation 

identi- fertilizer sales method 

fica- method (1991) (1992) 

tion Surface-water station/site location

A

B 

(fig. 2) Number Name

N P N P 

1 PRI038 Clarks River at Almo, Ky. 3,042 689 2,554 589 2 03604000 Buffalo River near Flat Woods, Tenn. 1,613 414 1,083 379 4 001025 Duck River below Normandy Dam, Tenn. 885 227 706 224 5 001065 Duck River at Williamsport, Tenn. 5,192 1,333 4,617 1,775 6 475793 Duck River above Hurricane Mills, Tenn. 6,651 1,707 6,245 2,401 7 002395 Shoal Creek at Highway 43, near 1,158 297 764 249 

Lawrenceburg, Tenn.

9 001207 Elk River below Tims Ford Dam, Tenn. 3,178 816 2,414 714 

10 475796 Elk River near Prospect, Tenn. 7,591 1,948 6,061 2,032 11 FLCR7 Flint Creek near Falkville, Ala. 182 30 94 44 12 TOWNCREEK15 Town Creek near Geraldine, Ala. 730 121 372 116 13 002375 Sequatchie River at Valley Road, Tenn. 862 221 667 259 
Appendix C 85

correspond to areas where farmers apply commercial nitrogen fertilizer to pasture land.

2. Application recommendation-based estimates are 

calculated based on medium soil-test results, but 

soils in some parts of the LTEN River Basin do not 

match that result. Application recommendationbased estimates for phosphorus may exceed 

sales-based estimates for soils that have high natural phosphorus content, such as in the basins for 

sites 5 and 6 (Duck River at Williamsport and 

above Hurricane Mills).

3. The use of manure to fertilize agricultural areas is 

not taken into account in the sales-based estimates. This may account for smaller estimates of 

phosphorus based on sales for areas where 

manure is commonly applied.

4. Estimates based on fertilizer sales do not account 

for the possibility that fertilizer may be purchased in one county but applied in another 

county.

Sales-based input estimates were generally viewed as 

the more reliable of the two estimates and were used in 

comparison among sources for the selected basins and 

for major hydrologic units.

Nitrogen Fixation

Estimates of nitrogen input were adopted from 

literature values for nitrogen fixation and county-level 

estimates of 1992 harvested acreage for soybeans (the 

only legume with significant acreage in the LTEN 

River Basin). The rate of nitrogen fixation by soybeans was based on comparison of rates reported in 

Tennessee, Alabama, Kentucky, and North Carolina 

agricultural literature. Reported rates varied little geographically. A rate of 105 lb/acre was applied throughout the study area (Craig and Kuenzler, 1983). The 

rate was multiplied by 1992 harvested acres for soybeans (U.S. Department of Commerce, 1994) to estimate the amount of biologically fixed nitrogen, in 

tons. Estimates were then converted from county to 

basin level using the same land-use weighting algorithm described for fertilizer application. 

Crop Uptake

The mass of nutrients incorporated into crop 

biomass was calculated using literature values of rates 

of nutrient uptake and 1992 county-level data of 

harvested amounts. Nutrient uptake rates varied 

among literature sources (Savoy, 1999; Mitchell, 

1998; McMahon and Lloyd, 1995), but because most 

of the LTEN River Basin is located within Tennessee, 

rates reported by the University of Tennessee Agricultural Extension Service (Savoy, 1999) were used for 

this analysis. To derive the mass of nutrient removal 

for each harvested crop, the nutrient uptake rate 

(pounds per acre for the harvested amount per acre) 

was multiplied by the harvested amount (in pounds, 

bushels, or tons) (U.S. Department of Commerce, 

1994). Estimates of nutrient removal in tons per year 

were totaled by county for all crops, then converted 

from county level to basin level by using the same 

land-use weighting algorithm described for fertilizer 

application. 

Livestock Waste

County-level estimates of the mass of nutrients 

from livestock waste have been compiled for all livestock categories, including cattle, hogs, and chickens 

(U.S. Department of Commerce, 1994). These estimates were calculated for each livestock category 

from county-level animal census data and from estimates of the nutrient content of daily wastes (Barth 

and others, 1992), by using the following equation:

[nutrient mass in livestock waste, in pounds per year] = 

[census estimate of number of animals] x [average 

weight of animal per 1,000 pounds] x [nutrient content 

of waste, in pounds per day per 1,000 pounds animal] x 

[365 days per year] (3)

Nutrient mass estimates for 1992 were converted from 

county level to basin level using a land-use weighting 

algorithm similar to the one used for weighting fertilizer application, except that the weighting was based 

on the distribution of pasture land.

Estimates of nutrient input from livestock waste 

are associated with two separate double-counting 

problems in a mass-balance analysis of sources and 

sinks. First, if the livestock producing the waste are 

fed fertilized crops grown within the watershed, the 

nutrient input is double-counted as both applied fertilizer and produced waste. Second, the ammonia volatilized from manure contributes to atmospheric nitrogen, 

so that nutrient input may be double-counted as both 

produced waste and measured atmospheric deposition. 

These discrepancies cannot be accounted for with the 

available data.

Appendix D 87

Appendix D. Variation in nutrient concentrations with streamflow, and model estimate of 

streamflow variation in concentration, at selected sites in the lower Tennessee River 

Basin, 1980-1996

Figure D1. Variation in total nitrite plus nitrate concentrations with streamflow and model 

estimate of streamflow variation in concentration at selected sites in the 

lower Tennessee River Basin, 1980-96................................................................................................................... 88

Figure D2. Variation in total ammonia concentrations with streamflow and model estimate of 

streamflow variation in concentration at selected sites in the 

lower Tennessee River Basin, 1980-96................................................................................................................... 90

Figure D3. Variation in total phosphorus concentrations with streamflow and model estimate of 

streamflow variation in concentration at selected sites in 

the lower Tennessee River Basin, 1980-96 ............................................................................................................. 92

Figure D4. Variation in dissolved orthophosphorus concentrations with streamflow and model estimate of 

streamflow variation in concentration at selected sites in 

the lower Tennessee River Basin, 1980-96 ............................................................................................................. 94
88 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus,

and Sediment in the Lower Tennessee River Basin, 1980-96

1 10 100 1,000 10,000 100 200 500 1,000 2,000 5,000 10,000 10 1

100 1,000 10,000 100,000 100 1,000 10,000 100,000 100 200 

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

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

TOTAL NITRITE PLUS NITRATE CONCENTRATION AS N, IN MILLIGRAMS PER LITER

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

DAILY MEAN STRE

RESERVO

THIS VA

STREAMF

Cohn's Es

Not signif

β1 is posi

RIVERINE FLOW-REG

variation 

Clarks River at Almo, Ky. (site 1, fig. 2)

Buffalo River near Flat Woods, Tenn. (site 2, fig. 2 ) Duck River belo

Duck River at Williamsport, Tenn. (site 5, fig. 2 ) Duck River above Hurricane Mills, Tenn. (site 6, fig. 2 )

Elk River below Tims Ford Dam, Tenn. (site 9, fig. 2 ) Elk River near Prospect, Tenn. (site 10, fig. 2 )

Shoal Creek a

Appendix D1. Variation in total nitrite plus nitrate concentrations with streamflow and model estimate of streamflow variation in conat selected sites in the lower Tennessee River Basin, 1980-96.

Figure D1. Variation in total nitrite plus nitrate concentrations with streamflow and model estimate of streamflow variation in conce

lower Tennessee River Basin, 1980-96.
Appendix D 89

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

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

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

10,000 20,000 50,000 100,000 1,000 100,000 10,000 1,000,000

1,000 

10,0

10 100 10,000 1,000 10 100 

Flint Creek near Falkville, Ala. (site 11, fig. 2) Town Creek near Geraldine, Ala. (site 12, fig. 2) Sequatchie Rive

Tennessee River at Highway 60 near

Paducah, Ky. (site 14, fig. 2)

Tennessee River at mile 23, Ky. (site 15, fig. 2)

Tennessee River at South Pittsburg,Tenn. (site 17, fig. 2) Tennessee River below Raccoon Mountain, Tenn. (site 18, fig. 2)

Tennessee R

Te

TOTAL NITRITE PLUS NITRATE CONCENTRATION AS N, IN MILLIGRAMS PER LITER

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

DAILY MEAN STREA

Appendix D1. Variation in total nitrite plus nitrate concentrations with streamflow and model estimate of streamflow variation in concenat selected sites in the lower Tennessee River Basin, 1980-96ÑContinued.

RESERVO

THIS VA

STREAM

Cohn's E

Not sign

β1 is po

RIVERINFLOW-RE

variation 

Figure D1. Variation in total nitrite plus nitrate concentrations with streamflow and model estimate of streamflow variation in concentrat

Tennessee River Basin, 1980-96—Continued.
90 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

TOTAL AMMONIA CONCENTRATION AS N, IN MILLIGRAMS PER LITER

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

DAILY MEAN STREAM

Appendix D2. Variation in total ammonia concentrations with streamflow and model estimate of streamflow variation in concentrationat selected sites in the lower Tennessee River Basin, 1980-96.

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

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

100 1,000 100,000 10,000 100 500 200 1,000 2,000 5,000 10,000

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

100 500 200 

Clarks River at Almo, Ky. (site 1, fig. 2) Buffalo River near Flat Woods, Tenn. (site 2, fig. 2 ) Duck River below N

Duck River at Williamsport, Tenn. (site 5, fig. 2 ) Duck River above Hurricane Mills, Tenn. (site 6, fig. 2 )

Elk River below Tims Ford Dam, Tenn. (site 9, fig. 2 ) Elk River near Prospect, Tenn. (site 10, fig. 2 )

Shoal Creek at H

Te

E

RESERVOIR 

THIS VALU

STREAMFLO

Cohn's Estim

Not signific

β1 is positiv

RIVERINE SFLOW-REGU

variation no

Figure D2. Variation in total ammonia concentrations with streamflow and model estimate of streamflow variation in concentration at 

Tennessee River Basin, 1980-96.
Appendix D 91

10

521

0.50.20.1

0.050.020.01

0.0050.0020.001

10

521

0.50.20.1

0.050.020.01

0.0050.0020.001

10

521

0.50.20.1

0.050.020.01

0.0050.0020.001

10

521

0.50.20.1

0.050.020.01

0.0050.0020.001

10

521

0.50.20.1

0.050.020.01

0.0050.0020.001

TOTAL AMMONIA CONCENTRATION AS N, IN MILLIGRAMS PER LITER

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

DAILY MEAN STRE

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

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

10 

1

Flint Creek near Falkville, Ala. (site 11, fig. 2) Town Creek near Geraldine, Ala. (site 12, fig. 2)

Tennessee River at mile 23, Ky. (site 15, fig. 2) Tennessee River at Pickwick Landing Dam,

Tenn. (site 16, fig. 2)

Sequatchie Ri

RESERV

THIS V

STREAM

Cohn's 

Not sig

RIVERINFLOW-R

variatio

Appendix D2. Variation in total ammonia concentrations with streamflow and model estimate of streamflow variation in concentrationat selected sites in the lower Tennessee River Basin, 1980-96ÑContinued.

Figure D2. Variation in total ammonia concentrations with streamflow and model estimate of streamflow variation in concentration at 

Tennessee River Basin, 1980-96—Continued.
92 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

TOTAL PHOSPHORUS CONCENTRATION AS P, IN MILLIGRAMS PER LITER

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

DAILY MEAN STRE

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

Clarks River at Almo, Ky. (site 1, fig. 2) Buffalo River near Flat Woods, Tenn. (site 2, fig. 2 ) Duck River belo

Duck River above Hurricane Mills, Tenn. (site 6, fig. 2 )

Duck River at Williamsport, Tenn. (site 5, fig. 2 )

Elk River below Tims Ford Dam, Tenn. (site 9, fig. 2 ) Elk River near Prospect, Tenn. (site 10, fig. 2 )

Shoal Creek 

1 10 100 1,000 10,000 100 500 200 1,000 2,000 5,000 10,000 10 1

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

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

100 

200 

RESERVO

THIS VA

STREAMF

Cohn's Es

Not signif

β1 is posiβ1 is neg

RIVERINE FLOW-REG

variation 

Appendix D3. Variation in total phosphorus concentrations with streamflow and model estimate of streamflow variation in concentraat selected sites in the lower Tennessee River Basin, 1980-96.

Figure D3. Variation in total phosphorus concentrations with streamflow and model estimate of streamflow variation in concentration 

Tennessee River Basin, 1980-96.
Appendix D 93

TOTAL PHOSPHORUS CONCENTRATION AS P, IN MILLIGRAMS PER LITER

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SEC

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10,000 100,000 1,000,00010,000 20,000 50,000 100,000

Tennessee River at Highway 60 near

Paducah, Ky. (site 14, fig. 2)

Tennessee River at mile 23, Ky.

(site 15, fig. 2)

Tennessee 

10

1

0.1

0.01

0.001

Tennessee River at South Pittsburg, Tenn.

(site 17, fig. 2)

10

1

0.1

0.01

0.001

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

EXPLANATION

RESERVOIR DISCHARGE GREATER THAN

THIS VALUE INCLUDES SPILLWAY FLOW

STREAMFLOW VARIATION (calculated by

Cohn's Estimator model)

Not significant (p-value for β1 greater than 0.05

β1 is positive and significant

RIVERINE SITEFLOW-REGULATED SITE (model estimate of

variation not reported)

Appendix D3. Variation in total phosphorus concentrations with streamflow and model estimate of streamflow variation in concentrationat selected sites in the lower Tennessee River Basin, 1980-96ÑContinued.

Figure D3. Variation in total phosphorus concentrations with streamflow and model estimate of streamflow variation in concentration a

Tennessee River Basin, 1980-96—Continued.
94 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10

1

0.1

0.01

0.001

10 100 10,000 1,000 100 1,000 100,000 10,000 100 1,00

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

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

1,000 

10,00

Buffalo River near Flat Woods, Tenn. (site 2, fig. 2) Duck River above Hurricane Mills, Tenn. (site 6, fig. 2) Elk River ne

Flint Creek near Falkville, Ala. (site 11, fig. 2)

Tennessee River at Pickwick Landing Dam,

Tenn. (site 16, fig. 2)

Tennessee R

Town Creek near Geraldine, Ala. (site 12, fig. 2)

Appendix D4. Variation in total orthophosphorus concentrations with streamflow and model estimate of streamflow variation in conceat selected sites in the lower Tennessee River Basin, 1980-96.

DISSOLVED ORTHOPHOSPHORUS CONCENTRATION AS P, IN MILLIGRAMS PER LITER

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

EXPLANATION

RESERVOIR DISCHARGE GREATER THAN

THIS VALUE INCLUDES SPILLWAY FLOW

STREAMFLOW VARIATION (calculated by

Cohn's Estimator model)

Not significant (p-value for β1 greater than 0.05)

β1 is positive and significant

RIVERINE SITEFLOW-REGULATED SITE (model estimate of

variation not reported)

Figure D4. Variation in dissolved orthophosphorus concentrations with streamflow and model estimate of streamflow variation in conc

lower Tennessee River Basin, 1980-96.
Appendix D 95

100

100,000

200

500

1,000

2,000

5,000

10,000

20,000

50,000

EXPLANATION

10

100,000

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

100

10,000

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0 100 20 40 60 80

100

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

1

10,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000 Clarks River at Almo, Ky.

(site 1, fig. 2)

Buffalo River near Flat Woods, Tenn.

(site 2, fig. 2)

Duck River below Manchester, Tenn.

(site 3, fig. 2)

Duck River below Normandy Dam, Tenn.

(site 4, fig. 2)

Duck River at Williamsport, Tenn.

(site 5, fig. 2)

Duck River above Hurricane Mills, Tenn.

(site 6, fig. 2)

Shoal Creek at Iron City, Tenn.

(streamflow record used for

sites 7 and 8, fig. 2)

Elk River below Tims Ford Dam, Tenn.

(site 9, fig. 2)

10

10,000

20

50

100

200

500

1,000

2,000

5,000

0 100 20 40 60 80

10

10,000 10,000

20

50

100

200

500

1,000

2,000

5,000

14 years of

record

76 years of

record

23 years of

record

53 years of

record

69 years of

record 80 years of

record

71 years of

record

24 years of

record

PERCENT OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED

10

1,000

20

30

40

50

70

100

200

300

400

500

700

PERIOD OF RECORD

PERIOD OF LOAD COMPUTATION

LOW FLOW YEAR

HIGH FLOW YEAR

Appendix E. Streamflow duration characteristics for period of streamflow record, compared

with characteristics for period of load computation, for load-computation sites in the lower

Tennessee River Basin.

Appendix E. Streamflow-duration characteristics for period of streamflow record, compared with characteristics for 

period of load computation, for load-computation sites in the lower Tennessee River Basin.
96 Sources, Instream Transport, and Trends of Nitrogen, Phosphorus, 

and Sediment in the Lower Tennessee River Basin, 1980-96 DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

0.1

1,000

0.2

0.5

1

2

5

10

20

50

100

200

500

1

10,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

100

100,000

200

500

1,000

2,000

5,000

10,000

20,000

50,000

PERCENT OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED

10

10,000

20

50

100

200

500

1,000

2,000

5,000

10,000

1,000,000

20,000

30,000

40,000

50,000

70,000

100,000

200,000

300,000

400,000

500,000

700,000

1,000

1,000,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

0 100 20 40 60 80 10,000

1,000,000

20,000

30,000

40,000

50,000

70,000

100,000

200,000

300,000

400,000

500,000

700,000

0 100 20 40 60 80 1,000

1,000,000

2,000

5,000

10,000

20,000

50,000

100,000

200,000

500,000

Elk River near Prospect, Tenn.

(site 10, fig. 2)

Flint Creek near Falkville, Ala.

(site 11, fig. 2)

Town Creek near Geraldine, Ala.

(site 12, fig. 2)

Sequatchie River at Valley Road, Tenn.

(site 13, fig. 2)

Tennessee River at Highway 60 near

Paducah, Ky. (streamflow record used

for sites 14 and 15, fig. 2)

Tennessee River at Pickwick Landing Dam, Tenn.

(site 16, fig. 2)

Tennessee River at South Pittsburg, Tenn.

(site 17, fig. 2)

Tennessee River below Raccoon Mountain, Tenn.

(site 18, fig. 2)

80 years of

record

23 years of

record

31 years of

record

74 years of

record

95 years of

record

66 years of

record

57 years of

record

122 years of

record

EXPLANATION

PERIOD OF RECORD

PERIOD OF LOAD COMPUTATION

LOW FLOW YEAR

HIGH FLOW YEAR

Appendix E. Streamflow-duration characteristics for period of streamflow record, compared with characteristics for 

period of load computation, for load-computation sites in the lower Tennessee River Basin—Continued.