U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006-5204

In cooperation with the Kentucky Department of Agriculture

Concentrations, and Estimated Loads and Yields of 

Nutrients and Suspended Sediment in the 

Little River Basin, Kentucky, 2003-04
Cover Photograph. Art depiction of land protected with conversation buffers and other practices by 

Scott Patton, USDA, Natural Resources Conversation Service.
Concentrations, and Estimated Loads and Yields of 

Nutrients and Suspended Sediment in the 

Little River Basin, Kentucky, 2003-04

By Angela S. Crain

In cooperation with the Kentucky Department of Agriculture 

Scientific Investigations Report 2006-5204

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

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Suggested citation:

Crain, A.S., 2006, Concentrations, and Estimated Loads and Yields of Nutrients and Suspended Sediment in the Little 

River Basin, Kentucky, 2003-04: U.S. Geological Survey Scientific Investigations Report 2006-5204, 31 p.

The U.S. Geological Survey does not discriminate on the basis of race, color, national origin, sex, age, religion or 

disability and provides on request, reasonable accommodations including auxiliary aids and services necessary to 

afford an individual with a disability an equal opportunity to participate in all services, programs, and activities. These 

materials can be provided in alternative format to any individual with a disability. This work was supported, in part, 

by a grant from the U.S. Environmental Protection Agency under §319(h) of the Clean Water Act through the Kentucky 

Division of Water to the Kentucky Department of Agriculture, Grant # C9994861-01 KY.
iii

Contents 

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

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

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

Description of the Little River Basin ..................................................................................................2

Geology..........................................................................................................................................4

Streamflow....................................................................................................................................6

Land Use........................................................................................................................................6

Study Design and Methods..........................................................................................................................6

Sample-Site Selection and Sampling Frequency............................................................................6

Sampling Methods................................................................................................................................6

Analytical Methods.............................................................................................................................10

Quality Control.....................................................................................................................................10

Statistical Analysis of Nutrients and Suspended Sediment........................................................10

Load-Estimation Methods .................................................................................................................11

Sources of Nitrogen and Phosphorus......................................................................................................11

Nonpoint-Source Contributions .......................................................................................................11

Atmospheric Deposition ...........................................................................................................13

Commercial Fertilizer and Livestock Waste..........................................................................13

Nitrogen Fixation by Soybeans................................................................................................14

Point-Source Contributions...............................................................................................................14

Concentrations, and Estimated Loads and Yields of Nutrients............................................................15

Concentrations....................................................................................................................................15

Spatial Variability .......................................................................................................................15

Seasonal Variability...................................................................................................................17

Estimated Loads and Yields...............................................................................................................17

Concentrations, and Estimated Loads and Yields of Suspended Sediment.......................................22

Concentrations....................................................................................................................................22

Spatial Variability .......................................................................................................................23

Seasonal Variability...................................................................................................................23

Estimated Loads and Yields...............................................................................................................23

Conclusions...................................................................................................................................................26

Acknowledgments.......................................................................................................................................26

References Cited..........................................................................................................................................27

Appendix 1: Statistical summary of concentrations of ammonia nitrogen, nitrite plus 

nitrate, total phosphorus, orthophosphate, and suspended sediment in the Little 

River Basin, Kentucky, 2003-04 ....................................................................................................29
iv

Figures

1.-5. Maps showing:

1. Location of the surface-water-sampling sites in the Little River Basin, Kentucky, 

2003-04..................................................................................................................................3

2. Surficial geology in the Little River Basin, Kentucky, 2003-04.......................................................4

3. Location of sinkholes in the Little River Basin, Kentucky, 2003-04 ...............................................5

4. Location of surface-water samplings sites and graphs showing precipitation and daily 

mean streamflow at selected sites in the Little River Basin, Kentucky, 2003-04 .....7

5. Land cover in the Little River Basin, Kentucky, 2001.......................................................................8

6.-10. Boxplots showing:

6. Concentrations of nitrite plus nitrate, total phosphorus, and orthophosphate at all 

sampling sites in the Little River Basin, Kentucky, 2003-04 .......................................16

7. Seasonal distribution of concentrations of nitrite plus nitrate for four fixed-network 

sites in the Little River Basin, Kentucky, 2003-04.........................................................18

8. Seasonal distribution of concentrations of total phosphorus and orthophosphate for 

four fixed-network sites in the Little River Basin, Kentucky, 2003-04 ......................19

9. Concentrations of suspended sediment at all sampling sites in the Little River Basin, 

Kentucky, 2003-04 .............................................................................................................24

10. Seasonal distribution of concentrations of suspended sediment for four fixed-network 

sites in the Little River Basin, Kentucky, 2003-04.........................................................25

Tables

1. Description of surface-water-sampling sites in the Little River Basin, Kentucky, 2003-04...........9

2. Reporting limits for nutrients as established by the U.S. Geological Survey National 

Water-Quality Laboratory..........................................................................................................10

3. Summary of replicate-sample data for nutrients and suspended sediment in the 

Little River Basin, Kentucky, 2003-04 .......................................................................................11

4. Loads of nutrients and suspended sediment at three sites in the Little River Basin, 

Kentucky, 2003-04, using LOADEST predefined and user-defined models .......................12

5. Estimated mean annual loads of total nitrogen and total phosphorus from nonpoint and 

point sources in the Little River Basin, Kentucky, 2003-04...................................................13

6. Estimated mean annual loads of total nitrogen and total phosphorus from municipal 

wastewater discharge in the Little River Basin, Kentucky, 2003-04...................................14

7. Estimated mean annual load and yield of nutrients and suspended sediment at 

the fixed-network sites in the Little River Basin, Kentucky, 2003-04..................................20

8. Regression coefficients and coefficients for determination (R2) for load models used 

to estimate nitrite plus nitrate, total phosphorus, orthophosphate, and suspended 

sediment at three sites in the Little River Basin, Kentucky, 2003-04..................................21
Conversion Factors and Abbreviations

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

acre 0.4047 square hectometer (hm2) 

acre 0.004047 square kilometer (km2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

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

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Application rate

pounds per acre (lb/acre) 1.121 kilograms per hectare (kg/ha)

pounds per day (lb/d) 0.4536 kilogram per day (kg/d)

pounds per year (lb/yr) 0.4536 kilograms per year (kg/yr)

pounds per square mile (lb/mi2) 0.17514 kilograms per square kilometer (kg/km2)

pounds per square mile per year 

((lb/mi2)/yr)

0.17514 kilograms per square kilometer per year 

((kg/km2)/yr)

pounds per year per square mile 

((lb/yr)/mi2)

0.17514 kilograms per year per square kilometer 

((kg/yr)/km2)

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

°F=(1.8×°C)+32

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

or micrograms per liter (μg/L).
vi

Abbreviations

AIC - Akaike Information Criterion 

EDI - equal-discharge increment

EWI - equal-width increment 

mL - milliliter

MCL - maximum contaminant level

N – normal

NADP - National Atmospheric Deposition Program 

NPDES – National Pollutant Discharge Elimination System

NWQL - National Water Quality Laboratory

PCS – Permit Compliance Section

RPD - relative percent difference

TMDL - total maximum daily load

USEPA - U.S. Environmental Protection Agency

USGS - U.S. Geological Survey
Abstract

Nutrients, primarily nitrogen and phosphorus compounds, 

naturally occur but also are applied to land in the form of 

commercial fertilizers and livestock waste to enhance plant 

growth. Concentrations, estimated loads and yields, and 

sources of nitrite plus nitrate, total phosphorus, and orthophosphate were evaluated in streams of the Little River Basin 

to assist the Commonwealth of Kentucky in developing “total 

maximum daily loads” (TMDLs) for streams in the basin. 

The Little River Basin encompasses about 600 square miles 

in Christian and Trigg Counties, and a portion of Caldwell 

County in western Kentucky. Water samples were collected in 

streams in the Little River Basin during 2003-04 as part of a 

study conducted in cooperation with the Kentucky Department 

of Agriculture. A total of 92 water samples were collected at 

four fixed-network sites from March through November 2003 

and from February through November 2004. An additional 

20 samples were collected at five synoptic-network sites during the same period. 

Median concentrations of nitrogen, phosphorus, and suspended sediment varied spatially and seasonally. Concentrations of nitrogen were higher in the spring (March-May) after 

fertilizer application and runoff. The highest concentration 

of nitrite plus nitrate—5.7 milligrams per liter (mg/L)—was 

detected at the South Fork Little River site. The Sinking Fork 

near Cadiz site had the highest median concentration of nitrite 

plus nitrate (4.6 mg/L).

The North Fork Little River site and the Little River near 

Cadiz site had higher concentrations of orthophosphate in the 

fall and lower concentrations in the spring. Concentrations 

of orthophosphate remained high during the summer (JuneAugust) at the North Fork Little River site possibly because of 

the contribution of wastewater effluent to streamflow. Fiftyeight percent of the concentrations of total phosphorus at the 

nine sites exceeded the U.S. Environmental Protection Agency 

recommended maximum concentration limit of 0.1 mg/L.

Concentrations of suspended sediment were highest 

in the spring during runoff and lowest in the fall. The highest concentration of suspended sediment (1,020 mg/L) was 

observed at the Sinking Fork near Cadiz site. The median 

concentration of suspended sediment for all sites sampled was 

12 mg/L. A nonparameteric statistical test (Wilcoxson ranksum) showed that the median concentrations of suspended 

sediment were not different among any of the fixed-network 

sites.

The Little River near Cadiz site contributed larger 

estimated mean annual loads of nitrite plus nitrate 

(2,500,000 pounds per year (lb/yr)) and total phosphorus 

(160,000 lb/yr) than the other three fixed-network sites. Of the 

two main upstream tributaries from the Little River near Cadiz 

site, the North Fork Little River was the greatest contributor 

of total phosphorus to the study area with an estimated mean 

annual load of 107,000 lb/yr or about 64 percent of the total 

estimated mean annual load at the Little River near Cadiz site. 

The other main upstream tributary, South Fork Little River, 

had an estimated mean annual load of total phosphorus that 

was about 20 percent of the mean annual load at the Little 

River near Cadiz site. Estimated loads of suspended sediment 

were largest at the Little River near Cadiz site, where the estimated mean annual load for 2003-04 was about 

84,000,000 lb/yr. The North Fork Little River contributed an 

estimated 36 percent of the mean annual load of suspended 

sediment at the Little River near Cadiz site, while the South 

Fork Little River contributed an estimated 18 percent of the 

mean annual load at the Little River near Cadiz site.

The North Fork Little River site had the largest estimated 

mean annual yield of total phosphorus (1,600 pounds per year 

per square mile (lb/yr/mi2)) and orthophosphate 

(1,100 lb/yr/mi2). A principal source of phosphorus for the 

North Fork Little River is discharge from wastewater-treatment facilities. The largest estimated mean annual yield of 

nitrite plus nitrate was observed at the South Fork Little River 

site. The North Fork Little River site had the largest estimated 

mean annual yield of suspended sediment (450,000 lb/yr/mi2). 

Concentrations, and Estimated Loads and Yields of 

Nutrients and Suspended Sediment in the 

Little River Basin, Kentucky, 2003-04

By Angela S. Crain
Inputs of nitrogen and phosphorus to streams from point 

and nonpoint sources were estimated for the Little River 

Basin. Commercial fertilizer and livestock-waste applications 

on row crops are a principal source of nutrients for most of the 

Little River Basin. Sources of nutrients in the urban areas of 

the basin mainly are from effluent discharge from wastewatertreatment facilities and fertilizer applications to lawns and golf 

courses.

Introduction

Nitrogen and phosphorus are essential nutrients for the 

growth of plants and animals. Nitrogen and phosphorus compounds occur naturally, but also are applied to land in the form 

of commercial fertilizers and livestock waste to enhance plant 

growth. Nutrients that are not utilized by crops or stored in the 

soil can travel in runoff to streams or through soil to ground 

water. Suspended sediment plays a major role in the transport 

and fate of contaminants because contaminants may sorb onto 

the surface of the suspended sediments and be transported 

and deposited in other areas downstream. Concentrations of 

suspended sediment are affected by natural conditions (soil 

erosion, streambed resuspension) and by human activities 

(construction, timber harvesting, and certain agricultural 

practices). 

Excess nutrients and suspended sediment in the environment can be detrimental to aquatic ecosystems and to the 

health of organisms living in and using water. Section 303(d) 

of the Clean Water Act requires that each State identify surface 

waters that do not meet applicable water-quality standards. 

In Kentucky, about 520 stream miles are impaired because of 

nutrients and about 470 stream miles are impaired because of 

suspended sediment (U.S. Environmental Protection Agency, 

2006a). The Kentucky Environmental and Public Protection 

Cabinet—Division of Water has listed some streams in the 

Little River Basin (fig. 1) as impaired streams for nutrients and 

suspended sediment in the State’s 2002 305(b) Report to Congress on Water Quality and in the 2002 and 2004 303(d) List 

of Waters for Kentucky report (Kentucky Environmental and 

Public Protection Cabinet, 2002, 2003, and 2005). The State 

must develop plans to restore and maintain the water quality of 

the streams in the Little River Basin because of these impairments. The plans establish a “total maximum daily load” 

(TMDL) for the impaired streams. A TMDL represents the 

total amount of contaminant a water body can assimilate without violating the designated water-quality standard established 

by the U.S. Environmental Protection Agency (USEPA). The 

State currently (2006) is developing TMDLs specifically for 

the North Fork Little River and the South Fork Little River.

In 2003, the U.S. Geological Survey (USGS), in cooperation with the Kentucky Department of Agriculture, began 

a study to determine concentrations and estimate loads and 

yields of nutrients and suspended sediment in the Little River 

Basin. Information from this study will assist State and local 

water managers and planners, who are responsible for implementing TMDLs for streams in the Little River Basin to make 

informed management decisions on nutrients and suspended 

sediment. The purpose of the study was to determine the 

presence and distribution of nutrients and suspended sediment 

in streams in the Little River Basin study area and to estimate loads and yields of nutrients and suspended sediment at 

selected sites in the basin. Pesticides and pesticide degradates 

also were collected during this study and their results can be 

found in Crain (2006).

Purpose and Scope 

This report summarizes the occurrence and distribution 

of nutrients and suspended sediment and provides estimates of 

nutrient and suspended-sediment loads and yields from samples collected from streams in the Little River Basin during 

2003-04. The spatial and seasonal variability in concentrations 

of nutrients and suspended sediment is presented. Nutrient and 

suspended-sediment loads are computed using LOADEST, a 

USGS software program used to compute mean constituent 

loads in rivers using regression models. Estimated loads and 

yields of nutrients and suspended sediment are presented for 

three sites in the basin. 

Description of the Little River Basin

The Little River Basin encompasses about 600 mi2

(fig. 1). The Little River discharges into Lake Barkley Reservoir on the Cumberland River. Water quality throughout the 

basin is directly affected by natural (geology, climate, soils) 

and human (population, land use) factors. The Little River 

Basin has a high “hydrogeologic sensitivity rating” indicating it is highly vulnerable to effects from runoff, because 

much of the area is underlain by karst (Ray and others, 1994). 

The hydrologic sensitivity of an area is defined as the ease 

and speed with which a contaminant is transported within a 

ground-water system (Ray and others, 1994). Some streams 

in the Little River Basin are listed as impaired streams in the 

State’s 303(d) List of Waters for Kentucky report (Kentucky 

Environmental and Public Protection Cabinet, 2005). The 

Kentucky Division of Water has listed the causes of impairments to the streams in the basin as siltation, nutrients, pathogens, organic enrichment (low dissolved oxygen), and habitat 

alterations (Kentucky Environmental and Public Protection 

Cabinet, 2005, p. 134-136). 

   Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
0 5 10 Miles

0 5 10 Kilometers

88

37

36 42'

87 20'

##

#

#

KENTUCKY

Study area

Base from U.S. Geological Survey digital data, 2004, NAD83, Lambert Conformal Conic

CALDWELL COUNTY

LYON COUNTY

LYON COUNTY

TRIGG COUNTY

CALDWELL COUNTY

TRIGG COUNTY

CALDWELL COUNTY

CHRISTIAN COUNTY

TRIGG COUNTY

CHRISTIAN COUNTY

CHRISTIAN COUNTY

TODD COUNTY

Cadiz

Hopkinsville

Little River at Crute Road

03438080

Sinking Fork 

near Cadiz

03438040

Muddy Fork

03438024

Sinking Fork near

Hopkinsville

03438028

Little River

near Cadiz

03438000

Casey Creek

03437990

North Fork Little River

03437400

South Fork Little River

03437600

Little River at

KY 345

03437680

Muddy Fork

Sinking Fork

Little River

Casey Creek

EXPLANATION

Little River Basin

Fixed-network sampling site

Synoptic-network sampling site

#

Lake Barkley

Figure 1. Location of the surface-water-sampling sites in the Little River Basin, Kentucky, 2003-04. 

Introduction   
Geology

The Little River Basin mostly is underlain by karstic 

limestone formations of late Mississippian age (fig. 2). The 

limestone units of significance within the Little River Basin 

study area are the St. Louis and Ste. Genevieve Limestone. 

The St. Louis Limestone mostly is composed of sequences of 

massively bedded (tabular) limestones, and the Ste. Genevieve 

Limestone mostly is composed of thin-bedded, cherty limestones.

Overlying the Ste. Genevieve and St. Louis Limestone 

on the northeastern side of the study area is a thick sequence 

of limestone, sandstone, and shale formations of Chesterian age (late Mississippian) that are divided into upper and 

lower parts. The lower Chesterian is composed of alternating 

sandstone and limestone strata that includes the Golconda 

Formation (sandstone dominated) and the Girkin Limestone 

(McDowell, 1986). The upper rocks of the Chesterian-age 

formations are mainly composed of siltstone and shale with 

alternating minor beds of limestone. 

Numerous karst features including sinkholes (fig. 3), 

sinking streams, and springs are present in the study area. 

The exposure of Ste. Genevieve Limestone at the land surface 

allows for water from surface-water streams to enter the 

underground cavities through sinkholes. Water also enters 

the Ste. Genevieve and Girkin Limestones through sinkholes 

developed in the sandstone members of the Golconda Formation. Potential contaminants may enter the karstic limestone 

aquifers with surface runoff drained by sinkholes in the St. 

Louis and Ste. Genevieve Limestone and through sinking 

streams.

88

37

36 42'

87 20'

Base from U.S. Geological Survey digital data, 2004, NAD83, Lambert Conformal Conic

Stratographic data source: McDowell, R.C., and others.

0 5 10 Miles

0 5 10 Kilometers

EXPLANATION

# Fixed surface-water-sampling

site

Synoptic surface-water-sampling

site

Mcl - lower Chesterian

Mgl - Ste. Genevieve, St. Louis limestone

Mcu - upper Chesterian

Mw - Warsaw limestone

Mississippian

Kt - Tusculoosa formation 

Cretaceous

Pca - Caseyville formation

Pennsylvanian

Mgl

Mcl

Mcu

Mw

Kt

Pca

##

#

#

Figure 2. Surficial geology in the Little River Basin, Kentucky, 2003-04. 

   Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
36 42'

88 56' 87 20'

37

Source: Kentucky Geological Survey, A GIS Sinkhole Coverage for the Karst Areas of Kentucky, 2003.

EXPLANATION

Sinkholes

Little River Basin

0 5 10 Miles

0 10 Kilometers 5

Figure 3. Location of sinkholes in the Little River Basin, Kentucky, 2003-04.

Introduction   
Streamflow

Direct surface runoff and ground-water discharge are the 

major sources of streamflow in the Little River Basin. Another 

source is interflow, which is part of the subsurface flow that 

moves at shallow depths and potentially can reach the surface 

channels in a short period of time. During a storm, interflow 

slowly increases until the end of the storm, then gradually 

decreases (Viessman and others, 1989, p. 171). 

Annual mean flow differs appreciably from year to year, 

with variations in weather conditions. Mean annual streamflow 

of the Little River near Cadiz site (water years 1940-2004) was 

about 360 ft3/s. It was 479 ft3/s in 2003 and 299 ft3/s in 2004. 

Mean monthly streamflow usually peaks in the spring (March–

May); however, there is often a second peak in the winter 

(December–February). Low streamflow conditions typically 

occur from late summer (June–August) to early fall (September–November). The mean daily streamflows for the Little 

River near Cadiz site in 2003 ranged from 27 ft3/s (November 

7) to 5,170 ft3/s (May 7); mean daily streamflows in 2004 

ranged from 33 ft3/s (October 11) to 2,670 ft3/s (April 24).

Mean annual precipitation for the Little River Basin was 

55.8 in. in 2003 and 54.0 in. in 2004 (National Oceanic and 

Atmospheric Administration, 2003 and 2004). About 63 percent of the mean annual precipitation in 2003 (34.9 in.) and 

about 57 percent of the mean annual precipitation in 2004 

(31.0 in.) occurred during the growing season from April 

through October (fig. 4). The long-term mean annual precipitation for the Little River Basin is about 50 in. 

Land Use

Streams in the Little River Basin drain a diverse landscape of forest, agricultural areas, and urban areas around 

Hopkinsville and Cadiz, Kentucky. Forested land represents 

about 31 percent of the Little River Basin. The southern and 

western parts are the most densely forested areas in the basin.

Agricultural land uses represent about 60 percent of the 

study area (fig. 5). Most of the agricultural land (34 percent) is 

used for corn, soybeans, wheat, hay, and tobacco production; 

the remaining 26 percent is used for pasture. Corn is the principal row crop harvested in the basin, followed by soybeans. 

In 2003, about 95,000 acres of corn were harvested for seed, 

grain, silage, or sweet corn; about 76,500 acres were harvested 

for soybeans (Kentucky Agricultural Statistics Service, 2004). 

Urban areas represent about 9 percent of the land use 

in the basin. The most heavily populated communities in the 

Little River Basin are Hopkinsville and Cadiz. Hopkinsville 

has a population of about 30,000; Cadiz has a population of 

about 2,400 (U.S. Census Bureau, 2002).

Study Design and Methods 

Stream-sampling sites in the Little River Basin were 

selected to assess the spatial and seasonal variability of nutrients and suspended sediment in subbasins consisting of mixed 

land use and different types of agricultural land. Samples 

were collected on three Little River main-stem sites and five 

tributaries—the North Fork Little River, South Fork Little 

River, Muddy Fork, Sinking Fork, and Casey Creek (fig. 1 and 

table 1). 

Sample-Site Selection and Sampling Frequency

Water-quality and suspended-sediment samples were 

collected monthly (March 2003 through November 2003 and 

February 2004 through November 2004) at four fixed-network 

sites. The sites included North Fork Little River, South Fork 

Little River, Sinking Fork near Cadiz, and Little River near 

Cadiz. These sites were sampled to monitor seasonal changes 

in water quality resulting from a variety of land-use activities. 

An additional four samples were collected at each of these 

sites for three high-flow events and one low-flow event.

In addition to the routine sampling at the four fixed-network sites, five synoptic-network sites were sampled twice 

each year in 2003 and 2004. The sites included Little River 

at KY 345, Muddy Fork, Sinking Creek near Hopkinsville, 

Casey Creek, and Little River at Crute Road. A total of three 

high-flow events and one low-flow event were collected over 

the 2 years to evaluate the spatial distribution of nutrients and 

suspended sediment in the Little River Basin.

Ninety-two samples were collected for nutrient and 

suspended sediment at the fixed-network sites, and 20 samples 

were collected at the synoptic-network sites. Twenty-two 

samples were collected for quality assurance/quality control 

(blanks and replicates). 

Sampling Methods

Representative water samples were collected by means 

of the equal-width increment (EWI) method, in which depthintegrated samples are collected at equal distances across 

the entire stream width and composited, or by means of the 

equal-discharge increment (EDI) method, in which equal-volume, depth-integrated samples are collected at the center of 

each EDI across the stream width and composited (Edwards 

and Glysson, 1998). All sampling material was constructed of 

Teflon to minimize contamination. Equipment used to collect 

and process nutrient samples was pre-cleaned with a 0.1-percent nonphosphate detergent, triple rinsed with tap water, 

acid rinsed with 5-percent hydrochloric acid for 30 minutes 

(nonmetal equipment only), triple rinsed with deionized water, 

air dried, and stored in a dust-free environment prior to sample 

collection (Webb and others, 1999).

   Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
87 20'

37

Hopkinsville

Cadiz

EXPLANATION

# Fixed surface-water-sampling site

Precipitation data source: National Oceanic and Atmospheric Administration, 2003, 2004

S ni k ni g Fork

Little River

1,5001,000

500

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

2003 2004

Estimated daily mean streamflow,

in cubic feet per second

North Fork Little River

near Hopkinsville, Kentucky

Sampling event

6,0004,5003,0001,500

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

2003 2004

Daily mean streamflow, in cubic feet per second Little River near Cadiz, Kentucky Sampling event 1,500 1,000 5000 J F M A M J J A S O N D J F M A M J J A S O N D

2003 2004

Estimated daily mean streamflow,

 in cubic feet per second

South Fork Little River

near Hopkinsville, Kentucky

Sampling event

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Monthly precipitation, in inches

20032004

Hopkinsville, Kentucky

10

86420 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Monthly precipitation, in inches

20032004

Cadiz, Kentucky

10

86420

36 42'

88 56' Little River

near Cadiz

03438000

North Fork Little River

03437400

South Fork Little River

03437600 0 5 10 Miles

0 10 Kilometers 5

#

#

#

Figure 4. Location of surface-water-sampling sites and graphs showing precipitation and daily mean streamflow at selected sites in the Little River Basin, Kentucky, 2003-04.

Study Design and Methods 
88

37

36 42'

87 20'

Base from U.S. Geological Survey digital data, 2004, NAD83, Lambert Conformal Conic

Land-cover source: Kentucky Land Cover Data Set 2001, Kentucky Commonwealth Office of Technology, November 1, 2005.

0 5 10 Miles

0 5 10 Kilometers

Land cover

Urban

Forest

Agriculture

Pasture

Cultivated

Water

EXPLANATION

# Fixed-network sampling site

Synoptic-network

sampling site

##

#

#

Figure 5. Land cover in the Little River Basin, Kentucky, 2001.

Water samples for dissolved nutrients were filtered using 

a 0.45-micrometer (μm) pore-size filter that was pre-rinsed 

with deionized water and filtered native stream water and 

collected in the appropriate bottle types. Whole-water (unfiltered) nutrient samples were preserved using 1 milliliter (mL) 

of 4.5N sulfuric acid. All nutrient samples were chilled and 

shipped on ice by overnight air express to the USGS National 

Water Quality Laboratory (NWQL) in Lakewood, Colorado, 

for analysis. Suspended-sediment samples were shipped to the 

USGS Kentucky Water Science Center Sediment Laboratory 

in Louisville, Kentucky.

Field measurements of stream discharge, air temperature, 

barometric pressure, water temperature, specific conductance, 

pH, concentrations of dissolved oxygen (DO), and turbidity were measured at the time of sampling. Alkalinity and 

concentrations of bicarbonate were determined by titrating 

filtered sample water with 0.16N sulfuric acid using a digital 

titrator. Discharge was measured according to standard USGS 

guidelines as described by Rantz and others (1982). The field 

measurement data is available online at http://ky.water.usgs.

gov/.

A continuously recording (15-minute interval) waterquality monitor was installed at the USGS streamflow-gaging 

station on Little River near Cadiz, Kentucky (station number 03438000), on April 1, 2003. Water-quality properties 

measured with the monitor during April 2003–November 

2004 included water temperature, specific conductance, pH, 

dissolved oxygen, and turbidity. Measurements were transmitted every 4 hours via satellite to the USGS office in Louisville, 

Kentucky, and were made available in near-real time on the 

Internet at URL http//ky.water.usgs.gov/. The water-quality 

monitor was inspected onsite by USGS personnel approximately every 3 to 4 weeks to maintain calibration. Guidelines 

and standard operating procedures for maintaining the site and 

reporting the data are described in Wagner and others (2000).

 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
Table 1. Description of surface-water-sampling sites in the Little River Basin, Kentucky, 2003-04.

[USGS, U.S. Geological Survey; mi2, square mile; Ky., Kentucky; N/A, not applicable]

Percentage of basin area in indicated 

land use1

USGS

site

number USGS site name

Abbreviated

site name

Drainage

area

(mi2)

Site

type Agriculture Forest Urban Water

03437400 North Fork Little River at 

Gary Lane Bridge near 

Hopkinsville, Ky.

North Fork 

Little River

58 Fixed 50 36 13 1

03437600 South Fork Little River at 

KY 107 near 

Hopkinsville, Ky.

South Fork 

Little River

67 Fixed 63 26 11 0

03438000 Little River near Cadiz, Ky. Little River 

near Cadiz

244 Fixed 57 35 6 2

03438040 Sinking Fork at Kings 

Chapel Road near Cadiz, 

Ky.

Sinking Fork 

near Cadiz

107 Fixed 68 26 6 0

03437680 Little River at KY 345 near 

Hopkinsville, Ky.

Little River at 

KY 345

134 Synoptic2 N/A N/A N/A N/A

03438024 Muddy Fork near 

Hopkinsville, Ky.

Muddy Fork 7.9 Synoptic2 N/A N/A N/A N/A

03438028 Sinking Fork near 

Hopkinsville, Ky.

Sinking Fork 

near Hopkinsville

44 Synoptic2 N/A N/A N/A N/A

03437990 Casey Creek at KY 525 

near Cadiz, Ky.

Casey Creek 35.7 Synoptic2 N/A N/A N/A N/A

03438080 Little River at Crute Road 

near Cadiz, Ky.

Little River at 

Crute Road

400 Synoptic2 N/A N/A N/A N/A

1

Kentucky Land Cover Data Set, 2001, Kentucky Commonwealth Office of Technology, November 1, 2005.

2

Site located within the 10-digit hydrologic-unit code of one of the four fixed-network sites.

Study Design and Methods 
Analytical Methods

The USGS NWQL analyzed the water-quality samples 

for nutrients. Water-quality samples for dissolved (filtered) 

and suspended (unfiltered) species of nitrogen and phosphorus were analyzed by colorimetric methods (Fishman, 1993; 

Patton and Truitt, 1992; Patton and Kryskalla, 2003; U.S. 

Environmental Protection Agency, 1993). These analyses 

quantified sample concentrations of dissolved nitrite plus 

nitrate, dissolved ammonia nitrogen, dissolved orthophosphate, and total phosphorus (table 2). Concentrations of 

nutrients discussed in this report represent their concentrations 

expressed as either nitrogen or phosphorus. For example, a 

concentration of nitrite plus nitrate expressed as 10 milligrams 

per liter (mg/L) refers to a concentration of nitrite plus nitrate 

of 10 mg/L as nitrogen.

The USGS Kentucky Water Science Center in Louisville, Kentucky, analyzed the suspended-sediment samples by 

filtering samples through a pretared 0.45-μm membrane filter. 

The filtrate was rinsed with deionized water to remove salts, 

and the insoluble material and filter were dried at 103°C and 

weighed (Fishman and Friedman, 1989).

Table 2. Reporting limits for nutrients as established by the 

U.S. Geological Survey National Water-Quality Laboratory. 

[mg/L, milligrams per liter; N, nitrogen; P, phosphorus]

 Constituent Laboratory reporting level

Ammonia (as N), dissolved 0.04 mg/L as N

Nitrite plus nitrate (as N),

 dissolved

.06 mg/L as N

Phosphorus (as P), total .004 mg/L as P

Orthophosphate (as P),

 dissolved

.006 mg/L as P

Quality Control

Quality-control information is needed to estimate the 

bias and variability that result from sample collection, sample 

processing, and laboratory analysis in order to ensure proper 

interpretation of water-quality data. About 20 percent of all 

samples submitted to the laboratory were quality-control 

samples, which included equipment blanks and field blanks 

to measure contamination and bias, and replicate samples to 

measure variability.

A blank is a water sample that consists of water that has 

undetectable concentrations of analytes of interest. Blankwater samples are used to test for bias that could result from 

contamination during any stage of sample collection or analysis process. Field-blank samples were collected to demonstrate 

that (1) equipment has been adequately cleaned to remove 

contamination introduced by samples obtained at previous 

sites; (2) sample collection and processing have not resulted in 

contamination; and (3) sample handling, transport, and laboratory analysis have not introduced contamination (Mueller and 

others, 1997). The procedure for blank samples was to use 

pesticide-free water through all of the sampling and filtration 

steps as a typical water-quality sample. Field-blank sample 

concentrations for nutrients did not indicate any contamination 

from the equipment or sample-processing methods. 

Replicate samples are a set of two or more environmental 

samples considered to be essentially identical in composition. 

Concurrent replicates are prepared by using one sampler and 

alternating collection of the samples into two or more compositing containers. All replicates collected in the Little River 

Basin were concurrent replicates. 

Data obtained from the six sets of replicate samples 

were used to access the variability of the overall sampling and 

analytical process. Replicate samples were compared by using 

relative percent differences (RPDs). RPD’s for each analyte 

and replicate sample pair was calculated by the following 

equation: 

RPD S = 1 – S2 e   S1 + S2 e 2x100 (1)

where

S1 is equal to the concentration in the environmental 

sample, in mg/L (nutrients and suspended 

sediment); and 

S2 is equal to the concentration in the replicate sample, 

in mg/L (nutrients and suspended sediment).

The larger the RPD, the greater the variability in those 

samples. Concentration differences, as measured by RPD, 

within replicate sets ranged from 0 to 5 percent for nutrients 

and were 15 percent for suspended sediment (table 3). If the 

RPD of replicate samples was 15 percent or less, then the data 

from the collected samples were determined to meet the precision objectives of the project.

Statistical Analysis of Nutrients and Suspended 

Sediment

The S-Plus software program (Insightful, 2005) was used 

to calculate summary statistics such as the mean, median, 

minimum, and maximum concentrations for nutrients and 

suspended sediment (Appendix 1). The Wilcoxson rank-sum 

nonparameteric statistical test (Helsel and Hirsch, 1992) was 

used to compare concentrations of nutrients and suspended 

sediment at the four fixed-network sites in the basin. The 

Wilcoxson rank-sum tests rank the data points to determine the 

statistical significance of differences in concentrations among 

groups of data. Differences among the groups of data with 

probability (p) values of 0.05 or less were considered significant in this study.

10 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
Load-Estimation Methods

Nutrient (ammonia nitrogen, nitrite plus nitrate, total 

phosphorus, and orthophosphate) loads and suspended sediment loads were estimated with the USGS software, LOADEST. This software uses time-series streamflow data and 

constituent concentrations to calibrate a regression model that 

describes constituent loads in terms of various functions of 

streamflow and time (Runkel and others, 2004). A complete 

discussion of the theory and principles behind the calibration 

and estimation methods can be found in Runkel and others 

(2004). 

The LOADEST software allows the user to choose 

between selecting the general form of the regression from 

several predefined models and letting the software automatically select the best-defined model, on the basis of the Akaike 

Information Criterion (AIC) (Akaike, 1981). The predefined 

model with the lowest value for the AIC was then selected for 

use in load estimation. A user-defined model was used for this 

study. User-defined results and results defined by the software 

are listed in table 4. The RPD’s between the two methods 

ranged from about 0 to 14 percent (table 4). 

The output regression equations have the following general form: 

2

2

1n  L  = a + b1n Q  + c 1nQ + d > sin  2 S T @

+ e > co s  2 S T @ + fT + gT

(2)

where

 L is the constituent load, in lb/d;

 Q is the stream discharge, in ft3/s;

 T is the time, in decimal years, from the 

beginning of the calibration period; and

a,b,c,d,e,f,g are regression coefficients.

Sources of Nitrogen and Phosphorus

Sources of nutrients into the Little River Basin are 

categorized as nonpoint or point source. Contaminant sources 

that are diffuse and do not have a single point of origin into 

receiving streams are called nonpoint sources. Nonpoint 

sources of nutrients include atmospheric deposition, fertilizer 

applications from agricultural and residential areas, feed-lot 

discharges, septic systems, and urban runoff. Point sources differ from nonpoint sources in that they discharge directly into 

a receiving stream at a discrete point. Point sources primarily 

consist of a variety of large and small wastewater-treatment 

facilities, but nutrient inputs also can come from storm-water 

runoff and sewer overflows.

Nonpoint-Source Contributions

Nonpoint-source inputs of nutrients for the Little River 

Basin estimated in this report include atmospheric deposition, 

commercial fertilizer application, livestock waste, and nitrogen 

fixation from soybeans (table 5). Nutrient inputs from urban 

runoff, combined sewer overflows, and septic systems were 

not included in the nonpoint source estimates of this report 

because of minimal or no data. 

Table 3. Summary of replicate-sample data for nutrients and suspended sediment in the 

Little River Basin, Kentucky, 2003-04. 

[RPD, relative percent difference; <, less than]

Constituent

Number of

replicate

sample sets Median RPD Maximum RPD

Ammonia (as N), dissolved 6 0 <1

Nitrite plus nitrate (as N),

 dissolved

6 .14 2

Phosphorus (as P), total 6 .94 5

Orthophosphate (as P),

 dissolved

6 1.1 3

Suspended sediment 5 0 15

Sources of Nitrogen and Phosphorus 11
Table 4. Loads of nutrients and suspended sediment at three sites in the Little River Basin, 

Kentucky, 2003-04, using LOADEST predefined and user-defined models.

[lb/yr, pound per year; ---, unable to determine from available data]

Constituent

Predefined

LOADEST

model results

(lb/yr)

User-defined

LOADEST model

results

(lb/yr)

Relative

difference

(in percent)

North Fork Little River near Hopkinsville, Ky. (03437400)

Ammonia as (N), dissolved 13,000 13,000 0

Nitrite plus nitrate as (N), dissolved 470,000 450,000 4.3

Phosphorus as (P), total 105,000 107,000 1.9

Orthophosphate as (P), dissolved 75,000 74,000 1.3

Suspended sediment 26,000,000 30,000,000 14

South Fork Little River near Hopkinsville, Ky. (03437600)

Ammonia as (N), dissolved --- --- ---

Nitrite plus nitrate as (N), dissolved 803,000 780,000 4.6

Phosphorus as (P), total 28,000 32,000 13

Orthophosphate as (P), dissolved 13,000 14,000 7.4

Suspended sediment 18,000,000 18,000,000 0

Little River near Cadiz, Ky. (03438000)

Ammonia as (N), dissolved --- --- ---

Nitrite plus nitrate as (N), dissolved 2,700,000 2,500,000 5.6

Phosphorus as (P), total 145,000 166,000 13

Orthophosphate as (P), dissolved 59,000 65,000 9.7

Suspended sediment 91,000,000 84,000,000 8.0

12 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
Table 5. Estimated mean annual loads of total nitrogen and total 

phosphorus from nonpoint and point sources in the Little River 

Basin, Kentucky, 2003-04.

[lb/yr, pound per year; NA, not applicable]

Constituent

Mean annual

load of total

nitrogen

(lb/yr)

Mean annual

load of total

phosphorus

(lb/yr)

Inputs to land

Atmospheric 

 deposition2 2,600 NA

Farm fertilizer3 9,800,000 2,100,000

Nonfarm fertilizer3 68,000 4,000

Livestock waste1 3,000,000 1,000,000

Nitrogen fixation4 20,000 NA

Input to streams

Municipal wastewater 

 discharge5 221,000 102,000

1

U.S. Department of Agriculture, 2004.

2

Data from National Atmospheric Deposition Program, 2006. 

 Dry deposition nitrogen not included in atmospheric deposition.

3

Ruddy and others, 2006. Data from 2001.

4

Kentucky Agricultural Statistics Service, 2004.

5

U.S. Environmental Protection Agency, 2006b

Atmospheric Deposition

Atmospheric deposition of nitrogen has been measured 

since December 1994 at a site in the Land between the Lakes 

National Recreation Area (KY99) in Trigg County, Kentucky. 

The wet-deposition data from the National Atmospheric 

Deposition Program (NADP) include nitrate and ammonia. No 

dry deposition data are measured; therefore, total atmospheric 

deposition of nitrogen cannot be obtained. Atmospheric 

deposition of phosphorus is not measured by NADP because 

concentrations generally are not appreciable and samples are 

subject to contamination (National Atmospheric Deposition 

Program, 2006). 

Rates of wet deposition of total nitrogen in 2003 and 

2004 were 2,900 and 2,300 lb/mi2, respectively. The 8-year 

mean rate (1995-2004) of wet deposition of total nitrogen 

was 2,200 lb/mi2. The wet-deposition inputs for total nitrogen 

during 2003-04 were higher than the 8-year mean, reflecting above-average precipitation for those 2 years. The NADP 

provides annual-summary reports which are available online at 

http://nadp.sws.uiuc.edu/.

Commercial Fertilizer and Livestock Waste

Commercial fertilizers applied to agricultural lands has 

become a primary nonpoint source of nitrogen and phosphorus 

in the United States. Commercial nitrogen fertilizer is applied 

as either ammonia or nitrate and commercial phosphorus 

fertilizer commonly is applied as phosphate. Application 

of nitrogen and phosphorus in commercial fertilizers in the 

United States during 1945-2001 increased by about 22 and 3.6 

percent, respectively (Ruddy and others, 2006). 

County-level data for nitrogen and phosphorus from 

commercial fertilizer (farm and nonfarm) and livestock waste 

were compiled in a national data set (Ruddy and others, 2006). 

The methods for allocating data on State total fertilizer sales to 

individual counties and for estimating livestock-waste inputs 

from livestock populations are described in detail by Ruddy 

and others (2006). The use of county-level data has some limitations in its application, because fertilizer and livestock waste 

sources are not evenly distributed within counties. The use of 

county-level data generally is more applicable to large drainage basins that encompass entire counties than smaller drainage basins that encompass only parts of one or more counties. 

However, the study area encompasses large portions of Christian and Trigg Counties, which are mostly homogenous in land 

use. Thus, any introduced error from using estimates of farm 

fertilizer and livestock waste inputs should not be appreciable. 

Farm-fertilizer inputs of nutrients in 2001 were 9,800,000 

lb of nitrogen and 2,100,000 lb of phosphorus in Christian 

and Trigg Counties, which are average applications of about 

8,100 lb/mi2/yr of nitrogen and 1,700 lb/mi2/yr of phosphorus. The amount of cultivated-agricultural land in the Little 

River Basin is about 34 percent, or about 200 mi2. Nitrogen 

and phosphorus fertilizers generally are applied to corn in 

spring just before seeding. Livestock waste also can be used 

during this time. Nitrogen fertilizer is reapplied to corn fields 

6 to 10 weeks after planting; phosphorus fertilizer is applied 

to corn and soybeans at the time of planting. Nitrogen and 

phosphorus fertilizers and livestock waste are applied in late 

summer through early fall for cool-season pasture, hay fields, 

and wheat fields (University of Kentucky, 2001).

Nonfarm-fertilizer inputs of nutrients in 2001 were 

68,000 lb of nitrogen and 14,000 lb of phosphorus in Christian 

and Trigg Counties. These applications average about 

56 lb/mi2/yr of nitrogen and 12 lb/mi2/yr of phosphorus. 

Nitrogen and phosphorus in livestock waste potentially 

can be a major source of nitrogen and phosphorus loads in 

streams draining agricultural areas. Animal-feeding operations 

and concentrated animal-feeding operations, which concentrate animals, feed, and waste on a small land area, have 

greater potential to contribute nutrients to surface runoff and 

ground water. Wastes produced by these operations may be 

applied to pasture land and crop land, becoming available for 

either crop uptake or losses to the environment. An animalfeeding operation in Kentucky is defined as a facility where 

animals are confined and fed for a total of 45 days or more 

in any 12-month period and where crops, vegetation forage 

Sources of Nitrogen and Phosphorus 13
growth, or post-harvest residues are not sustained over any 

portion of the facility in the normal growing season (Kentucky 

Environmental and Public Protection Cabinet, 2006). In order 

for an animal-feeding operation to be defined as a confined 

animal-feeding operation, the facility has more than 300 

animal units confined and there is a discharge to the Waters 

of the Commonwealth, or if more than 1,000 head of beef 

cattle, 700 head of dairy cattle, 2,500 pigs, 25,000 broilers, or 

82,000 laying hens or pullets are present at the facility. There 

are 11 animal-feeding operations and 0 confined animal-feeding operations within the southern portion of the Little River 

Basin as of July 2006 (James Seay, Kentucky Environmental 

and Public Protection Cabinet–Kentucky Division of Water, 

written commun., 2006).

In Kentucky, the average inputs of nutrients from livestock waste were 1,100,000 lb of nitrogen and 320,000 lb of 

phosphorus in 1997. In Christian and Trigg Counties, nutrient inputs from livestock waste in 1997 were 3,000,000 lb of 

nitrogen and 1,000,000 lb of phosphorus. These nutrient inputs 

average about 2,500 lb/mi2/yr of nitrogen and 830 lb/mi2/yr of 

phosphorus throughout the basin. Actual nitrogen inputs to the 

land probably were lower because of volatilization of ammonia from the waste and nitrification and de-nitrification.

Nutrient-input estimates from livestock waste were based 

on county-level livestock-population data collected by the U.S. 

Census Bureau during the Census of Agriculture. The method 

and assumptions used in Ruddy and others (2006) to estimate 

nitrogen and phosphorus content of livestock waste produced 

by the various types of livestock are described by Goolsby and 

others (1999). The livestock groups used to estimate nutrient 

inputs from livestock waste include beef cattle, dairy cows, 

hogs, and poultry.

Nitrogen Fixation by Soybeans

Nitrogen fixation by soybeans is an important source of 

nitrogen in the Little River Basin because of the large acreage 

of soybeans in the study area; however, the fixation of nitrogen from soybeans is not used in computations of nonpointsource inputs of nitrogen because little nitrogen is available 

to enter the surface and ground water. The amount of nitrogen 

produced by fixation from soybeans in the basin is based on 

the area of soybeans planted and an annual nitrogen fixation 

rate of 105 lb/acre, as used by Hoos and others (1999) from 

Craig and Kuenzler (1983) for soybeans in the southeast. This 

rate was multiplied by 2003-04 harvested acres for soybeans 

(Kentucky Agricultural Statistics Service, 2004) to estimate 

the amount of fixed nitrogen. The estimated nitrogen fixation 

for the Little River Basin was 20,000 lb/mi2/yr.

Point-Source Contributions

The only point-source inputs of nitrogen and phosphorus estimated in this report are municipal-wastewater 

discharge (table 5). Only facilities with a mean flow greater 

than 0.1 Mgal/d were available for input computations for 

this study (table 6). The exclusion of minor privately owned 

discharge facilities (<0.1 Mgal/d) in the study area, if totaled, 

could be an appreciable source of nitrogen and phosphorus to 

the basin. 

Table 6. Estimated mean annual loads of total nitrogen and total phosphorus from municipal wastewater discharge in the Little River 

Basin, Kentucky, 2003-04.

[Mgal/d, million gallons per day; lb/yr, pounds per year; WWTP, wastewater-treatment plant]

Mean annual load

Facility name County Receiving stream

Effluent

flow

(Mgal/d)1

Total

nitrogen

(lb/yr)

Total

phosphorus

(lb/yr)

Hopkinsville Hammond 

Wood WWTP

Christian North Fork Little River 3.35 123,000 87,200

Hopkinsville Northside 

WWTP

Christian North Fork Little River 2.30 86,200 13,900

Cadiz WWTP Trigg Little River .32 11,800 1,200

Total 221,000 102,300

1

U.S. Environmental Protection Agency, 2006b

14 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
The nutrient inputs are based on information from the 

NPDES permitting program of the USEPA. The required 

monitoring data for NPDES discharges are stored in the 

USEPA’s PCS database. All of the wastewater-treatment facilities in the Little River Basin monitor effluent for ammonia and 

total phosphorus, but concentrations of total nitrogen were not 

available. A regression equation, developed from more than 

800 observations of effluent concentrations from municipal 

wastewater-treatment facilities in Virginia and North Carolina, 

was used to estimate concentrations of total nitrogen from 

concentrations of ammonia nitrogen (McMahon and Lloyd, 

1995, p. 70-71). The regression equation is as follows:

Total nitrogen = 11.97 + 0.55 (ammonia) (3)

where concentrations are in mg/L, as nitrogen.

Nitrogen and phosphorus inputs to streams from municipal wastewater-treatment facilities were estimated using the 

following equation:

L = (RQ)(C)(f)(T) (4)

where

L is nutrient load in lb/yr;

RQ is wastewater effluent flow in ft3/s;

C is the mean concentration of nutrient in mg/L;

f is a unit conversion factor of 5.3943; and

T is time in days per year.

The estimated inputs from wastewater discharge were 

221,000 lb/yr for nitrogen and 102,300 lb/yr for phosphorus 

for the Little River Basin. Wastewater discharges to the Little 

River ranged from 33 to 50 percent of the annual mean streamflow during 2003-04.

Concentrations, and Estimated Loads 

and Yields of Nutrients

Summary statistics for the concentrations of nutrients 

(ammonia nitrogen, nitrite-plus-nitrate nitrogen, total phosphorus, and orthophosphate) from March 2003 through 

November 2003 and from February 2004 through November 

2004 at all sampling sites are shown in Appendix 1. These 

data provide the basis for analysis of concentrations, and estimated loads and yields at the selected sampling sites. 

Concentrations

Although nutrients such as nitrogen and phosphorus are 

necessary for plant and animal life, in excessive quantities they 

can accelerate the growth of aquatic plants and cause algal 

blooms. Excessive aquatic growth may result in unsuitable 

habitat conditions for aquatic animals and can interfere with 

recreational activities such as fishing, swimming, and boating. 

Decomposition of aquatic-plant growth can cause odor and 

taste concerns in drinking water supplies and can consume dissolved oxygen, which can adversely affect aquatic life.

Spatial Variability

Concentrations of nitrate greater than 10 mg/L in drinking water can have adverse human-health effects. Concentrations of nitrite plus nitrate ranged from 0.36 to 5.7 mg/L at the 

nine sites (fig. 6 and Appendix 1). The highest concentration 

of nitrite plus nitrate, 5.7 mg/L, was measured at the South 

Fork Little River site. The lowest concentration of nitrite plus 

nitrate, 0.36 mg/L, was measured at the Casey Creek site. 

The median concentration of nitrite plus nitrate for all sites 

sampled was 3.6 mg/L. The Sinking Fork near Cadiz site had 

the highest median nitrogen concentration of 4.6 mg/L. Concentrations of ammonia nitrogen ranged from <0.04 to 0.66 

mg/L at the nine sites (Appendix 1). The highest concentration 

of ammonia nitrogen was observed at the South Fork Little 

River site.

Phosphorus is a common element in rocks; other sources 

of phosphorus include fertilizer, human and animal waste, and 

some detergents. Although no established aquatic-life criterion 

exists for total phosphorus, the USEPA recommends a maximum concentration of total phosphorus of 0.1 mg/L to discourage excessive growth of aquatic plants and algae. Concentrations of total phosphorus in 58 percent of the samples were 

greater than 0.1 mg/L (fig. 6). The median concentration of 

total phosphorus for all sites sampled was 0.13 mg/L. Concentrations of orthophosphates ranged from <0.006 to 2.0 mg/L. 

The highest concentration of orthophosphate was measured at 

the North Fork Little River site: 2.0 mg/L. This sampling site 

is located immediately downstream from a wastewater-treatment facility. Sources of orthophosphate include weathering 

of soils, human and animal waste, some detergents, decaying 

plants, and fertilizer.

A Wilcoxson rank-sum nonparameteric statistical test 

(Helsel and Hirsch, 1992) was used to compare concentrations 

of nitrite plus nitrate, total phosphorus, and orthophosphate 

among the four fixed-network sites. A total of 23 samples 

were collected at each of the four fixed-network sites during 

2003-04. 

Concentrations, and Estimated Loads and Yields of Nutrients 15
Data outside

10th and 90th percentile

90 percent

75 percent

Median

25 percent

10 percent

EXPLANATION

(4) Number of samples collected

Concentration, in milligrams per liter

MCL Maximum contaminant level

(23) North Fork Little River

(23) South Fork Little River

(4) Little River at KY 345

(23) Little River near Cadiz

(4) Little River at Crute Road

(4) Muddy Fork

(4) Sinking Fork near Hopkinsville

(23) Sinking Fork near Cadiz

(4) Casey Creek

MCL

Nitrite plus nitrate

12

10

4

2

0

8

6

2.5

2.0

1.5

1.0

0.5

0.0

Total phosphorus

2.5

2.0

1.5

1.0

0.5

0.0

Orthophosphate

Figure 6. Concentrations of nitrite plus nitrate, total phosphorus, and orthophosphate at all 

sampling sites in the Little River Basin, Kentucky, 2003-04.

16 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
The fixed-network sites sampled in the Little River Basin 

represent drainage areas in predominantly agricultural areas, 

forested areas, or a mixture of both. Urban areas represent 

only a small portion of the study area. Median concentrations 

of nitrite plus nitrate were lowest at the North Fork Little 

River site, which had the least agricultural and most urban 

land use (fig. 6). However, the North Fork Little River site had 

higher median concentrations of both total phosphorus and 

orthophosphate than samples from the other fixed-network 

sites, likely because of the urban sources in the North Fork 

Little River subbasin. The Sinking Fork near Cadiz site had 

a higher median concentration of nitrite plus nitrate than the 

other fixed-network sites, likely because this site had a higher 

percentage of drainage area in row crops. Median concentrations of total phosphorus and orthophosphate were lowest at 

the Sinking Creek near Cadiz site.

Seasonal Variability

Concentrations of nutrients vary seasonally. Concentrations of nitrite plus nitrate tended to be highest during spring 

and lowest in the fall in the Little River Basin. During late fall, 

plants become dormant and limit the uptake of available nutrients allowing for nutrients to build up in the soil. An increase 

in precipitation in the spring allows for the runoff of nutrients 

into the streams. In addition, nitrogen fertilizers are applied 

in the spring to row crops such as corn, adding more available 

nutrients to the soil that potentially can runoff into the streams. 

Precipitation decreases in the fall allowing plants to take up 

much of the available nutrients in the soil; thus, concentrations of nitrite plus nitrate decrease in streams. An insufficient 

number of samples were collected in the winter to perform a 

statistical analysis.

Differences in median concentrations of nitrite plus 

nitrate were minimal between fall and spring at the South Fork 

Little River site and the Sinking Fork near Cadiz site (fig. 7). 

The other fixed-network sites showed no difference between 

fall and spring. The South Fork Little River site also showed 

a difference between spring and summer (p value: 0.008). No 

difference was shown between fall and summer at any of the 

sites.

Seasonal variation in concentrations of total phosphorus 

was minimal, with the exception of the North Fork Little River 

site (fig. 8). The North Fork Little River site and the Little 

River near Cadiz site had high concentrations of orthophosphate in the fall and low concentrations of orthophosphate 

during spring (fig. 8). Concentrations of orthophosphate 

always were higher at the North Fork Little River site than 

at the other sites. A possible explanation is the effluent from 

the wastewater-treatment facilities on the North Fork Little 

River considerably contributes to streamflow. The percentage 

of total phosphorus that is orthophosphate varies seasonally. 

Concentrations of total phosphorus and orthophosphate are 

similar in the fall and summer at the fixed-network sites, but 

concentrations of orthophosphate are lower than concentrations of total phosphorus in the spring (fig.8). This probably is 

because orthophosphate is readily consumed by aquatic plants 

and algae during the spring growing season.

The Wilcoxson rank-sum test showed that median 

concentrations of total phosphorus and orthophosphate were 

different between fall and spring (p value: 0.024 and 0.014, 

respectively) and between summer and spring (p value: 0.001 

for both constituents) at the North Fork Little River site. Only 

median concentrations of orthophosphate at the Little River 

near Cadiz site were notable during the same seasons. Median 

concentrations of total phosphorus and orthophosphate were 

not similar among any of the three seasons at the South Fork 

Little River site and the Sinking Fork near Cadiz site.

Estimated Loads and Yields

Load represents the mass (usually pounds or tons) of a 

given waterborne constituent moving past a given point per 

unit of time. Annual loads can vary depending upon drainage 

basin size, hydrologic conditions, and land uses within a basin. 

Mean annual loads (in lb/yr) for nutrients were estimated using 

the LOADEST program at three of the four fixed-network 

sampling sites from samples collected March through November 2003 and February through November 2004 (table 7). The 

95-percent confidence interval for each estimated annual load 

of ammonia nitrogen, nitrite plus nitrate, total phosphorus, and 

orthophosphate was calculated from the standard error of prediction provided by the LOADEST program. The confidence 

interval is shown in pounds per year. Loads were not estimated 

at the Sinking Fork near Cadiz site, because a streamflow 

relation between this site and the Little River near Cadiz site 

could not be established; however, estimates for this site are 

available (Michael C. Ierardi (U.S. Geological Survey, unpub. 

data., 2006) (table 7).

The coefficients of determination (R2) for the bestfit regression models for loads of nitrite plus nitrate, total 

phosphorus, orthophosphate, and suspended sediment are 

listed in table 8. High R2 values indicate that the models for 

all four constituents successfully simulated the variability in 

constituent loads at the three fixed-network sites. Overall, the 

model simulations for nitrite plus nitrate showed the highest R2

 values. Based on R2 values, the model simulations for 

total phosphorus showed a better fit than the orthophosphate 

model. The better fit for total phosphorus likely is related to 

the suspended components of total phosphorus. Generally, 

suspended material has a stronger relation to streamflow than 

do dissolved components such as orthophosphate. Model 

simulations for suspended sediment showed high R2 values for 

all three fixed-network sites. 

The largest estimated mean annual load of nitrite plus 

nitrate among the three fixed-network sites was at the Little 

River near Cadiz site (2,500,000 lb/yr) (table 7). This site also 

had the largest estimated mean annual load of total phosphorus (166,000 lb/yr). The estimated mean annual load of 

orthophosphate was 65,000 lb/yr, which is about 40 percent 

of the mean annual load of total phosphorus at this site. 

Concentrations, and Estimated Loads and Yields of Nutrients 17
Data outside

10th and 90th percentile

90 percent

75 percent

Median

25 percent

10 percent

EXPLANATION

Concentration, in milligrams per liter as N

Fall Summer Spring Fall Summer Spring

MCL Maximum contaminant level

MCL

Sinking Fork near Cadiz

0

2

4

6

8

10

12

MCL

Little River near Cadiz

South Fork Little River

MCL

0

2

4

6

8

10

12

MCL

North Fork Little River

Figure 7. Seasonal distribution of concentrations of nitrite plus nitrate for four fixed-network sites in the Little River 

Basin, Kentucky, 2003-04.

18  Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
0.0

0.5

1.0

1.5

2.0

2.5

0.0

0.5

1.0

1.5

2.0

2.5

Fall Summer Spring Fall Summer Spring

Little River near Cadiz Sinking Fork near Cadiz

North Fork Little River South Fork Little River

Concentration, in milligrams per liter as P

Data outside

10th and 90th percentile

90 percent

75 percent

Median

25 percent

10 percent

EXPLANATION

Total phosphorus

Orthophosphate

Figure 8. Seasonal distribution of concentrations of total phosphorus and orthophosphate for four fixed-network 

sites in the Little River Basin, Kentucky, 2003-04.

Concentrations, and Estimated Loads and Yields of Nutrients 19
Table 7. Estimated mean annual load and yield of nutrients and suspended sediment at the fixed-network sites in the 

Little River Basin, Kentucky, 2003-04.

[lb/yr, pound per year; lb/yr/mi2, pounds per year per square mile; DA, drainage area; mi2, square miles; ---, not available]

95-percent confidence

interval

Constituent

Mean

annual load

(lb/yr) Lower Upper

Standard

error of

prediction

Mean annual

yield

(lb/yr/mi2)

North Fork Little River near Hopkinsville, Ky.

(DA = 58 mi2)

Ammonia (as N),

 dissolved 13,000 7,800 20,000 3,000 190

Nitrite plus nitrate

 (as N), dissolved 450,000 396,000 516,000 31,000 6,700

Phosphorus (as P), total 107,000 87,000 129,000 10,000 1,600

Orthophosphate (as P)

 dissolved 74,000 60,000 90,000 7,500 1,100

Suspended sediment 30,000,000 7,000,000 23,000,000 4,400,000 450,000

South Fork Little River near Hopkinsville, Ky.

(DA=67 mi2)

Ammonia (as N),

 dissolved --- --- --- --- ---

Nitrite plus nitrate

 (as N), dissolved 780,000 678,000 890,000 54,000 13,000

Phosphorus (as P), total 32,000 14,500 62,000 12,000 550

Orthophosphate (as P)

 dissolved 14,000 6,100 29,000 5,900 240

Suspended sediment 18,000,000 3,500,000 55,000,000 14,000,000 310,000

Little River near Cadiz, Ky.

(DA = 244 mi2)

Ammonia (as N),

 dissolved --- --- --- --- ---

Nitrite plus nitrate

 (as N), dissolved 2,500,000 230,000 2,800,000 103,000 10,000

Phosphorus (as P), total 166,000 102,000 250,000 39,000 660

Orthophosphate (as P)

 dissolved 65,000 46,000 89,000 11,000 270

Suspended sediment 84,000,000 59,000 620,000 150,000 340,000

Sinking Fork near Cadiz, Ky.1

(DA = 107 mi2)

Total nitrogen 1,200,000 -- -- 660,000 12,000

Phosphorus (as P), total 114,000 -- -- 67,000 1,000

1

Data from Michael C. Ierardi, U.S. Geological Survey, unpub. data, 2006.

20 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
Table 8. Regression coefficients and coefficients for determination (R2) for load models used to estimate nitrite plus nitrate, 

total phosphorus, orthophosphate, and suspended sediment at three sites in the Little River Basin, Kentucky, 2003-04.[Site locations are shown in figure 1. The regression equation is ln(L) = a + b(lnQ) + c(lnQ2) + d[sin(2πT)] + e[cos(2πT)] + fT + gT2 : where L is the constituent load, in pounds per day; Q is stream discharge, in cubic feet per second; T is time in decimal years from the beginning of the calibration period; a,b,c,d,e,f,g are regression coefficients; R2 represents the amount of variance explained by the model] 

Site name

Regression coefficient

R2

(percent) a b c d e f g

Nitrite plus nitrate

North Fork Little River near Hopkinsville, Ky. 6.09 0.750 -0.002 -0.059 -0.209 0.343 0.527 92South Fork Little River near Hopkinsville, Ky. 6.24 1.008 -.049 .273 -.208 .013 -.016 97Little River near Cadiz, Ky. 7.67 1.000 -.040 .084 -.068 .152 -.144 99

Total phosphorus

North Fork Little River near Hopkinsville, Ky. 4.72 .855 .124 -.436 -.146 .751 -.306 86South Fork Little River near Hopkinsville, Ky. 1.91 1.46 .158 .328 -.052 -.127 .478 85Little River near Cadiz, Ky. 4.35 1.22 .181 -.199 .026 .246 .404 88

Orthophosphate

North Fork Little River near Hopkinsville, Ky. 4.41 .583 .030 -.494 -.271 .985 -.501 81South Fork Little River near Hopkinsville, Ky. 1.16 1.52 .084 -.897 -.164 -.250 .681 77Little River near Cadiz, Ky. 3.83 1.02 .063 -.349 -.048 .479 -.126 84

Suspended sediment

North Fork Little River near Hopkinsville, Ky. 8.47 2.21 -.041 .131 -.473 -.394 -1.22 94South Fork Little River near Hopkinsville, Ky. 6.59 2.08 .247 -.041 .016 .035 .798 86Little River near Cadiz, Ky. 8.32 2.02 .179 .176 -.876 -.108 1.11 91

Concentrations, and Estimated Loads and Yields of Nutrients 21
Estimates of mean annual total load of nitrite plus nitrate and 

total phosphorus during 1985-97 reported by Crain (2001) 

and estimates reported by Michael C. Ierardi (U.S. Geological 

Survey, unpub. data, 2006) are similar to the estimates in this 

report. The estimated mean annual load of nitrite plus nitrate 

and total phosphorus reported during 1985-97 was 2,100,000 

and 212,000 lb/yr, respectively (Crain, 2001). Estimated mean 

annual loads for total nitrogen were 2,000,000 lb/yr and for 

total phosphorus were 210,000 lb/yr (Michael C. Ierardi, 

U.S. Geological Survey, unpub. data, 2006). Although Michael 

C. Ierardi (U.S. Geological Survey, unpub. data, 2006) 

reported mean annual loads for total nitrogen and not nitrite 

plus nitrate, the major form of nitrogen in the Little River 

Basin is nitrite plus nitrate (about 87 percent of total nitrogen) 

(Crain, 2001). Load estimates with long periods of record are 

more reliable than estimates from sites with short periods of 

record. 

Of the two main tributaries upstream from the Little 

River near Cadiz site, the North Fork Little River site contributed the greatest amount of total phosphorus to the study area 

with an estimated mean annual load of 107,000 lb/yr or about 

64 percent of the total mean annual load at the Little River 

near Cadiz site, from about 27 percent of the overall drainage 

area. The South Fork Little River site contributed an estimated 

mean annual load of total phosphorus of 32,000 lb/yr, which 

was about 20 percent of the total mean annual load at the Little 

River near Cadiz site, from 24 percent of the overall drainage 

area. 

The estimated mean annual loads for orthophosphate for 

the North Fork Little River site and South Fork Little River 

site were 74,000 and 14,000 lb/yr, respectively. The mean 

annual load of orthophosphate represented a larger percentage of the mean annual load of total phosphorus at the North 

Fork Little River site (68 percent) than at the South Fork 

Little River site (44 percent). A possible reason for the larger 

percentage of orthophosphate to total phosphorus at the North 

Fork Little River site is a wastewater-treatment facility, which 

discharges just upstream from the sampling site. The estimated mean annual load of nitrite plus nitrate for the South 

Fork Little River site was 780,000 lb/yr. The North Fork Little 

River site had an estimated mean annual load of nitrite plus 

nitrate of 450,000 lb/yr. 

Yields are defined as the amount of load per unit area and 

are useful for comparing basins with varying size, land use, 

and physiography. Yields for ammonia nitrogen, nitrite plus 

nitrate, total phosphorus, and orthophosphate were computed 

for each of the three fixed-network sites (table 7). 

Estimated historical mean annual yields (Crain, 2001; 

Michael C. Ierardi, U.S. Geological Survey, unpub. data, 2006) 

of nitrite plus nitrate and total phosphorus for the Little River 

near Cadiz site were similar to those computed from samples 

collected during 2003-04. The estimated mean annual yields 

of nitrite plus nitrate and total phosphorus reported by Crain 

(2001) were 8,600 and 870 (lb/yr)/mi2, respectively. Estimated 

mean annual yields of total nitrogen and total phosphorus 

from Michael C. Ierardi (U.S. Geological Survey, unpub. data, 

2006) were 8,200 and 860 (lb/yr)/mi2, respectively; whereas, 

the estimated mean annual yield of nitrite plus nitrate was 

10,000 (lb/yr)/mi2 and the estimated mean annual yield for 

total phosphorus was 660 (lb/yr)/mi2 for 2003-04 at the Little 

River near Cadiz site. Mean annual streamflow for the Little 

River near Cadiz site was 389 ft3/s for water years 2003-04, 

compared to 372 ft3/s for water years 1985-97, and 355 ft3/s 

for the period reported by Michael C. Ierardi (U.S. Geological 

Survey, unpub. data, 2006).

The North Fork Little River site had the largest estimated 

mean annual yield of total phosphorus (1,600 (lb/yr)/mi2) and 

orthophosphate (1,100 (lb/yr)/mi2). Thirteen percent of the 

land is considered urban in this subbasin. A principal source 

of phosphorus for the North Fork Little River is discharge 

from wastewater-treatment facilities. The mean annual yields 

for total phosphorus and orthophosphate for the Little River 

near Cadiz site and the South Fork Little River site were much 

lower, with the Little River near Cadiz site having slightly 

larger yields of the two (table 7). The South Fork Little River 

site had the largest estimated mean annual yield of nitrite 

plus nitrate (13,000 (lb/yr)/mi2), followed by the Little River 

near Cadiz site (10,000 (lb/yr)/mi2), and the North Fork Little 

River site (6,700 (lb/yr)/mi2). Estimated mean annual yields 

for nitrogen and phosphorus from Crain (2001) and Michael 

C. Ierardi (U.S. Geological Survey, unpub. data, 2006) were 

similar to the mean annual yields estimated in this report.

Concentrations, and Estimated Loads 

and Yields of Suspended Sediment

Summary statistics for the concentrations of suspended 

sediment from March 2003 through November 2003 and from 

February 2004 through November 2004 at all sampling sites 

are shown in Appendix 1. These data provide the basis for 

analysis of concentrations, and estimated loads and yields at 

the selected sampling sites. 

Concentrations

Suspended sediment is all particulate matter suspended in 

the water column resulting from streambed resuspension, rock 

weathering, and soil erosion. Concentrations of suspended 

sediment are affected by natural conditions (streambank erosion, steep slopes, and forest fires) and anthropogenic activities (construction, timber harvesting, and certain agricultural 

practices).

High concentrations of suspended sediment can cause 

habitat destruction and limit light penetration throughout the 

water column. In addition, suspended sediment has a major 

role in the transport and fate of contaminants. Contaminants 

may sorb onto the surface of the suspended sediments and be 

transported and deposited in other areas downstream. 

22 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
Spatial Variability

Concentrations of suspended sediment generally were 

low in the Little River Basin (fig. 9). The median concentration of suspended sediment for all sites sampled was 12 mg/L. 

The highest concentration of suspended sediment was measured at the Sinking Fork near Cadiz site (1,020 mg/L) during 

a spring runoff event. 

Concentrations of suspended sediment for the four fixednetwork sites were grouped by site and compared by means of 

the Wilcoxson rank-sum test. Differences in median concentrations of suspended sediment were not significant (p value: 

>0.05) among any of the fixed-network sites.

Seasonal Variability

Concentrations of suspended sediment were higher during spring and low during the fall (fig. 10). Concentrations of 

suspended sediment were grouped by season and compared by 

means of the Wilcoxson rank-sum test. Differences in median 

concentrations of suspended sediment were not significant 

(p value: >0.05) at the South Fork Little River site among 

any season, while samples from the Little River near Cadiz 

site had differences in median concentrations of suspended 

sediment that were significant among all seasons. Differences in median concentrations of suspended sediment at the 

North Fork Little River site were significant between summer 

and fall (p value: 0.04) and between spring and fall (p value: 

0.006). The Sinking Fork near Cadiz site and the Little River 

near Cadiz site had differences in median concentrations of 

suspended sediment that were significant between spring and 

summer (p value: 0.01 and 0.03, respectively). 

Estimated Loads and Yields

Mean annual loads (in lb/yr) for suspended sediment 

were estimated using the LOADEST program at three of 

the four fixed-network sites from samples collected during 

2003-04 (table 7). The 95-percent confidence interval for 

each estimated annual load of suspended sediment has been 

calculated from the standard error of prediction provided by 

the LOADEST program; the confidence interval is shown in 

pounds per year. Loads of suspended sediment were not estimated at the Sinking Fork near Cadiz site, because a streamflow relation between this site and the Little River near Cadiz 

site could not be established. Annual loads vary depending 

upon drainage basin size, hydrologic conditions, and land uses 

within a basin. 

Estimated loads of suspended sediment were largest at 

the Little River near Cadiz site, where the mean annual load 

for 2003-04 was about 84,000,000 lb/yr (table 7). The largest estimated mean annual yield was 450,000 (lb/yr)/mi2

 at 

the North Fork Little River site. The smallest mean annual 

loads and yields of suspended sediment, 18,000,000 lb/yr and 

310,000 (lb/yr)/mi2, respectively, were estimated at the South 

Fork Little River site. 

Concentrations, and Estimated Loads and Yields of Suspended Sediment 23
24 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04

Figure 9. Concentrations of suspended sediment at all sampling sites in the 

Little River Basin, Kentucky, 2003-04. Concentration, in milligrams per liter

0

200

400

600

800

1,000

1,200

(23) North Fork Little River

(23) South Fork Little River

(4) Little River at KY 345

(23) Little River near Cadiz

(4) Little River at Crute Road

(3) Muddy Fork

(3) Sinking Fork near Hopkinsville

(23) Sinking Fork near Cadiz

(4) Casey Creek

Data outside

10th and 90th percentile

90 percent

75 percent

Median

25 percent

10 percent

EXPLANATION

(4) Number of samples collected
0

200

400

600

800

1000

1200

0

50

100

150

200

250

0

50

100

150

200

250

0

50

100

150

200

250

Little River near Cadiz Sinking Fork near Cadiz

North Fork Little River South Fork Little River

Fall Summer Spring Fall Summer Spring

Data outside

10th and 90th percentile

90 percent

75 percent

Median

25 percent

10 percent

EXPLANATION

Concentration, in milligrams per liter

Figure 10. Seasonal distribution of concentrations of suspended sediment for four fixed-network sites in the Little 

River Basin, Kentucky, 2003-04.

Concentrations, and Estimated Loads and Yields of Suspended Sediment 25
Conclusions

Concentrations and estimated loads and yields of nitrite 

plus nitrate, total phosphorus, orthophosphate, and suspended 

sediment were evaluated in streams of the Little River Basin 

of western Kentucky. Water samples were collected in streams 

in the Little River Basin during 2003-04 as part of study in 

cooperation with the Kentucky Department of Agriculture. A 

total of 92 water samples were collected at four fixed-network 

sites from March through November 2003 and from February 

through November 2004. An additional 20 samples were collected at five synoptic-network sites during the same period. 

The Little River Basin encompasses about 600 square miles 

in Christian and Trigg Counties, and a portion of Caldwell 

County.

Median concentrations of nitrogen, phosphorus, and 

suspended sediment varied spatially and seasonally. Concentrations of nitrogen were higher in the spring (March-May) 

after fertilizer application and runoff. The highest concentration of nitrite plus nitrate, 5.7 milligrams per liter (mg/L), 

was detected at the South Fork Little River site. The Sinking 

Fork near Cadiz site had the highest median concentration of 

nitrite plus nitrate (4.6 mg/L). Median concentrations of nitrite 

plus nitrate were notable between spring and fall (SeptemberNovember) at the South Fork Little River site and the Sinking Fork near Cadiz site. The median concentrations at the 

other fixed-network sites showed no differences between the 

seasons.

The North Fork Little River site and the Little River near 

Cadiz site had higher concentrations of orthophosphate in the 

fall and lower concentrations in the spring. Concentrations 

of orthophosphate remained high during the summer (JuneAugust) at the North Fork Little River site probably because of 

the contribution of wastewater effluent to streamflow. Fiftyeight percent of the concentrations of total phosphorus at the 

nine sites exceeded the U.S. Environmental Protection Agency 

recommended maximum concentration limit of 0.1 mg/L.

Concentrations of suspended sediment were high in the 

spring during runoff and low in the fall. The highest concentration of suspended sediment (1,020 mg/L) was observed at 

the Sinking Fork near Cadiz site. The median concentration 

of suspended sediment for all sites sampled was 12 mg/L. A 

nonparameteric statistical test (Wilcoxson rank-sum) showed 

that the median concentrations of suspended sediment were 

not different among any of the fixed-network sites.

Commercial-fertilizer and livestock-waste application on corn and soybean fields is the principal source of 

nutrients for most of the Little River Basin. Some of these 

nutrients from agricultural nonpoint sources eventually are 

transported to streams by surface runoff, erosion of sediment, 

or ground-water discharge. Sources of nutrients in the urban 

areas (Hopkinsville) mainly are from effluent discharge from 

wastewater-treatment facilities and fertilizer applications 

to lawns and golf courses. The Little River near Cadiz site 

contributed larger estimated mean annual loads of nitrite plus 

nitrate (2,500,000 pounds per year (lb/yr)) and total phosphorus (160,000 lb/yr) than the other three fixed-network sites. Of 

the two main tributaries upstream from the Little River near 

Cadiz site, the North Fork Little River was the greatest contributor of total phosphorus to the study area with an estimated 

mean annual load of 107,000 lb/yr or about 64 percent of the 

total mean annual load at the Little River near Cadiz site. The 

other main upstream tributary, South Fork Little River, had an 

estimated mean annual load of total phosphorus that was about 

20 percent of the mean annual load at the Little River near 

Cadiz site. Estimated loads of suspended sediment were largest at the Little River near Cadiz site, where the mean annual 

load for 2003-04 was about 84,000,000 lb/yr. The North Fork 

Little River contributed an estimated 36 percent of the mean 

annual load of suspended sediment at the Little River near 

Cadiz site; the South Fork Little River contributed an estimate 

of 18 percent of the mean annual load at this site.

The North Fork Little River site had the largest estimated 

mean annual yield of total phosphorus (1,600 pounds per year 

per square mile (lb/yr)/mi2) and orthophosphate 

(1,100 (lb/yr)/mi2). A principal source of phosphorus for the 

North Fork Little River is discharge from wastewater-treatment facilities. The largest estimated mean annual yield of 

nitrite plus nitrate was at the South Fork Little River site. The 

North Fork Little River site had the largest estimated mean 

annual yield of suspended sediment (450,000 (lb/yr)/mi2). The 

smallest estimated mean annual loads and yields of suspended 

sediment were at the South Fork Little River site.

Acknowledgments

The author is grateful for the technical reviews by Terence Messinger (USGS West Virginia Water Science Center) 

and Brenda Smith (USGS Missouri Water Science Center). 

The agricultural crop sales data provided by Ernest Collins 

(Kentucky Department of Agriculture) is appreciated. Donnie 

Keeling, R. Steven Darnell, and James Filbeck (USGS Kentucky Water Science Center, Paducah field office, Paducah, 

Ky.) and Greg McCombs and Zeke Hensley (USGS Kentucky 

Water Science Center, Louisville, Ky.) are thanked for their 

assistance in collecting samples for this study. Joseph Vrabel 

(USGS Texas Water Science Center) is thanked for providing assistance on computing the loads. Aimee Downs (USGS 

Kentucky Water Science Center, Louisville, Ky.) is thanked for 

assistance with GIS illustrations and summarizing the agricultural crop sales data. Bonnie Stich Fink (USGS Publishing 

Network, PSC 8, Louisville, Ky.) is thanked for editing and 

preparing the report for publication.

26 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
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28  Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
Appendix 1. Statistical summary of concentrations of ammonia nitrogen, nitrite plus nitrate, total phosphorus, orthophosphate, and 

suspended sediment in the Little River Basin, Kentucky, 2003-04.

[N, nitrogen; P, phosphorus; <, less than; ---, not applicable]

Concentrations,

in milligrams per liter

Constituent

Number

of

samples

Number

of

detections Minimum

25th

percentile Mean Median

75th

percentile Maximum

North Fork Little River near Hopkinsville , Kentucky

(03437400)

Ammonia (as N),

 dissolved

23 15 <0.04 <0.04 0.06 <0.04 0.05 0.48

Nitrite plus nitrate

 (as N), dissolved

23 23 1.3 2.2 3.1 2.9 3.8 5.3

Phosphorus (as P),

 total

23 23 .14 .36 .81 .60 1.1 2.1

Orthophosphate

 (as P), dissolved

23 23 .05 .26 .70 .48 1.0 2.0

Suspended 

 sediment

23 --- 1 4 35 7 56 201

South Fork Little River near Hopkinsville , Kentucky

(03437600)

Ammonia (as N),

 dissolved

23 3 <.04 <.04 .07 <.04 <.04 .66

Nitrite plus nitrate

 (as N), dissolved

23 23 1.4 3.4 3.8 4.0 4.5 5.7

Phosphorus (as P),

 total

23 23 .02 .04 .09 .06 .10 .39

Orthophosphate

 (as P), dissolved

23 22 <.006 .02 .05 .03 .05 .25

Suspended 

 sediment

23 --- 1 3 28 5 39 182

Little River near Cadiz, Kentucky

(03438000)

Ammonia (as N),

 dissolved

23 4 <.04 <.04 .03 <.04 <.04 .11

Nitrite plus nitrate 

 (as N), dissolved

23 23 2.5 3.2 3.6 3.7 3.9 4.7

Phosphorus (as P),

 total

23 23 .06 .11 .17 .16 .20 .49

Orthophosphate

 (as P), dissolved

23 23 .03 .05 .1 .08 .13 .21

Suspended

 sediment

23 --- 2 5 38 14 28 175

Appendix 1 29
Appendix 1. Statistical summary of concentrations of ammonia nitrogen, nitrite plus nitrate, total phosphorus, orthophosphate, and 

suspended sediment in the Little River Basin, Kentucky, 2003-04.—Continued

[N, nitrogen; P, phosphorus; <, less than; ---, not applicable]

Concentrations,

in milligrams per liter

Constituent

Number

of

samples

Number

of

detections Minimum

25th

percentile Mean Median

75th

percentile Maximum

Sinking Fork near Cadiz, Kentucky

(03438040)

Ammonia (as N),

 dissolved

23 3 <0.04 <0.04 0.02 <0.04 <0.04 0.10

Nitrite plus nitrate

 (as N), dissolved

23 23 1.2 3.7 4.3 4.4 5.2 5.7

Phosphorus (as P),

 total

23 23 .03 .06 .14 .07 .11 1.0

Orthophosphate

 (as P), dissolved

23 23 .008 .03 .05 .04 .05 .14

Suspended

 sediment

23 --- 1 5 93 14 30 1,020

Little River at KY 345 near Cadiz, Kentucky

(03437680)

Ammonia (as N),

 dissolved

4 2 <.04 <.04 .07 <.04 .07 .22

Nitrite plus nitrate

 (as N), dissolved

4 4 2.0 2.7 3.0 3.0 3.3 3.8

Phosphorus (as P),

 total

4 4 .17 .29 .31 .34 .37 .39

Orthophosphate

 (as P), dissolved

4 4 .05 .10 .17 .15 .22 .31

Suspended

 sediment

4 --- 67 67 103 68 120 173

Muddy Fork near Hopkinsville, Kentucky

(03438024)

Ammonia (as N),

 dissolved

4 2 <.04 <.04 <.04 <.04 <.04 .05

Nitrite plus nitrate

 (as N), dissolved

4 4 2.0 2.2 3.5 3.5 4.7 5.0

Phosphorus (as P),

 total

4 4 .04 .05 .15 .08 .18 .40

Orthophosphate 

 (as P), dissolved

4 4 .03 .03 .04 .04 .05 .06

Suspended

 sediment

3 --- 42 46 55 50 62 74

30 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04
Appendix 1. Statistical summary of concentrations of ammonia nitrogen, nitrite plus nitrate, total phosphorus, orthophosphate, and 

suspended sediment in the Little River Basin, Kentucky, 2003-04.—Continued

[N, nitrogen; P, phosphorus; <, less than; ---, not applicable]

Concentrations,

in milligrams per liter

Constituent

Number

of

samples

Number of

detections Minimum

25th

percentile Mean Median

75th

percentile Maximum

Sinking Fork near Hopkinsville, Kentucky

(03438028)

Ammonia (as N),

 dissolved

4 1 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04

Nitrite plus nitrate

 (as N), dissolved

4 4 1.3 1.8 2.3 2.4 2.9 3.1

Phosphorus (as P),

 total

4 4 .04 .10 .18 .19 .28 .30

Orthophosphate

 (as P), dissolved

4 4 .01 .02 .05 .04 .06 .09

Suspended

 sediment

3 --- 40 100 157 161 216 271

Casey Creek near Cadiz, Kentucky

(03437990)

Ammonia (as N),

 dissolved

4 0 <.04 <.04 <.04 <.04 <.04 <.04

Nitrite plus nitrate

 (as N), dissolved

4 4 .36 1.7 1.8 2.3 2.3 2.4

Phosphorus (as P),

 total

4 4 .03 .03 .05 .04 .06 .07

Orthophosphate

 (as P), dissolved

4 3 <.006 .02 .02 .02 .02 .03

Suspended

 sediment

4 --- <1 1 18 2 27 53

Little River at Crute Road near Cadiz, Kentucky

(03438080)

Ammonia (as N),

 dissolved

4 3 <.04 <.04 <.04 <.04 .05 .06

Nitrite plus nitrate

 (as N), dissolved

4 4 2.8 3.2 3.4 3.5 3.7 3.7

Phosphorus (as P),

 total

4 4 .08 .08 .24 .12 .28 .63

Orthophosphate

 (as P), dissolved

4 4 .05 .05 .08 .08 .11 .11

Suspended

 sediment

4 --- 5 9 142 22 154 518

Appendix 1 31
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32 Concentrations, and Est. Loads and Yields of Nutrients and Suspended Sediment in the Little River Basin, Ky., 2003-04

Angela S. Crain— Concentrations, and Estimated Loads and Yields of Nutrients and Suspended Sediment in the 

Little River Basin, Kentucky, 2003-04—Scientific Investigations Report 2006-5204