U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006–5175

Prepared in cooperation with the

Oklahoma Water Resources Board

Phosphorus Concentrations, Loads, and Yields in the Illinois 

River Basin, Arkansas and Oklahoma, 2000–2004

Illinois River near Watts, Oklahoma
Cover Photograph Credit: Picture is Illinois River near Watts, Adair County, Oklahoma, downstream from U.S. Highway 59 bridge, taken October 11, 2002. Flow is 155 

cubic feet per second. Photographer: Royce E. Johnson, U.S. Geological Survey.
Phosphorus Concentrations, Loads, and 

Yields in the Illinois River Basin, Arkansas 

and Oklahoma, 2000–2004

By Robert L. Tortorelli and Barbara E. Pickup

Prepared in cooperation with the Oklahoma Water Resources Board

Scientific Investigations Report 2006–5175

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

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

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

reproduce any copyrighted materials contained within this report.

Suggested citation:

Tortorelli, R.L., and Pickup, B.E., 2006, Phosphorus concentrations, loads, and yields in the Illinois River basin, Arkansas and Oklahoma, 2000–2004: U.S. Geological Survey Scientific Investigations Report 2006–5175, 38 p.
iii

Contents

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

Introduction.....................................................................................................................................................1

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

Study Area Description........................................................................................................................4

Streamflow in the Illinois River Basin ...............................................................................................4

Acknowledgments................................................................................................................................4

Methods...........................................................................................................................................................4

Water-Quality Data Collection and Analysis....................................................................................4

Streamflow Separation........................................................................................................................8

Statistical Tests .....................................................................................................................................8

Load and Yield Estimation....................................................................................................................8

Phosphorus Concentrations, Loads and Yields in the Illinois River Basin...........................................9

Concentrations....................................................................................................................................11

Estimated Mean Annual Loads.........................................................................................................11

Estimated Mean Seasonal Loads.....................................................................................................11

Estimated Mean Yields.......................................................................................................................11

Estimated Mean Flow-Weighted Concentrations .........................................................................20

Estimated Mean Annual Phosphorus Loads into Lake Tenkiller.................................................20

Summary........................................................................................................................................................20

Selected References...................................................................................................................................23

Appendixes ...................................................................................................................................................27

1. Instantaneous streamflows, total phosphorus concentrations, and flow

category for Illinois River near Watts, Oklahoma, from 2000–2004....................................29

2. Instantaneous streamflows, total phosphorus concentrations, and flow

category for Flint Creek near Kansas, Oklahoma, from 2000–2004 ....................................31

3. Instantaneous streamflows, total phosphorus concentrations, and flow

category for Illinois River at Chewey, Oklahoma, from 2000–2004....................................33

4. Instantaneous streamflows, total phosphorus concentrations, and flow

category for Illinois River near Tahlequah, Oklahoma, from 2000-2004.............................35

5. Instantaneous streamflows, total phosphorus concentrations, and flow

category for Baron Fork at Eldon, Oklahoma, from 2000–2004............................................37

Figures

1. The Illinois River basin, Arkansas and Oklahoma, with locations of selected

streamflow and water-quality stations in the basin and of towns with

wastewater-treatment plants that discharge into streams in the basin.............................2

2. Land use in the Illinois River basin, Arkansas and Oklahoma...............................................5

3. Streamflow divided into total flow and base flow, and base-flow and runoff water

samples collected at water-quality stations in the Illinois River basin, Oklahoma,

2000–2004 .......................................................................................................................................7

4. Total phosphorus concentrations from base-flow and runoff water samples

collected at water-quality stations in the Illinois River basin, Oklahoma, 2000–2004.....14
iv

5. Distributions of base-flow total phosphorus concentrations from water samples

collected at water-quality stations in the Illinois River basin, Oklahoma, periods

2000–2002, 2001–2003, and 2002–2004.....................................................................................15

6. Distributions of runoff total phosphorus concentrations from water samples

collected at water-quality stations in the Illinois River basin, Oklahoma, periods

2000–2002, 2001–2003, and 2002–2004.....................................................................................16

7. Instantaneous total phosphorus concentrations from water samples collected

at water-quality stations in the Illinois River basin, Oklahoma, periods 2000–2002,

2001–2003, and 2002–2004 .........................................................................................................21

Tables

1. Station information and streamflow statistics for continuous streamflow gaging

and ungaged stations used for water-quality monitoring in the Illinois River basin,

Oklahoma .......................................................................................................................................6

2. Regression models developed using total phosphorus concentrations from water

samples collected at water-quality stations in the Illinois River basin, Oklahoma,

periods 2000–2002, 2001–2003, and 2002–2004 ......................................................................10

3. Summary statistics of total phosphorus concentrations from base-flow and runoff

water samples collected at water-quality stations in the Illinois River basin,

Oklahoma, periods 2000–2002, 2001–2003, and 2002–2004 ..................................................12

4. Wilcoxon rank-sum test results comparing base-flow total phosphorus

concentrations to runoff total phosphorus concentrations from water samples

collected at water-quality stations in the Illinois River basin, Oklahoma, periods

2000–2002, 2001–2003.................................................................................................................13

5. Estimated mean annual total phosphorus loads and yields estimated from total

phosphorus concentrations in water samples collected at water-quality stations in

the Illinois River basin, Oklahoma, periods 2000–2002, 2001–2003, and 2002–2004.........17

6. Number of days of base flow and runoff designated by Base-Flow Index (BFI)

program at water-quality stations in the Illinois River basin, Oklahoma, periods

2000–2002, 2001–2003, and 2002–2004.....................................................................................18

7. Estimated mean seasonal total phosphorus loads estimated from total phosphorus 

concentrations in water samples collected at water-quality stations in the Illinois

River basin Oklahoma, periods 2000–2002, 2001–2003, and 2002–2004 .............................19

8. Estimated mean annual total phosphorus loads, mean annual streamflows, and

mean flow-weighted total phosphorus concentrations at water-quality stations in

the Illinois River basin, Oklahoma, periods 2000–2002, 2001–2003, and 2002–2004.........22

9. Summary of estimated total phosphorus loads to Lake Tenkiller, Oklahoma, periods

2000–2002, 2001–2003, and 2002–2004.....................................................................................23
Conversion Factors and Definitions

Multiply By To obtain

Length

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

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

Mass

pound (lb) 0.4536 kilogram (kg) 

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

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

pound per year per square mile 

(lb/yr/mi2)

 0.1751 kilogram per year per square

kilometer (kg/yr/km2)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

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

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

Estimated concentration (“E” remark code)—Positive detections below the LRL are not 

censored. Detected analytes with concentrations between the LT–MDL and the LRL are 

reported as estimated (“E” remark code). This is because a detection in this region should have 

a ≤1-percent probability of being a false positive (Childress and others, 1999). There are several 

circumstances that dictate this code, this is one of the most common.

Laboratory reporting level (LRL)—Generally equal to twice the yearly determined LT–MDL. 

The LRL controls false negative error. The probability of falsely reporting a non-detection 

for a sample that contained an analyte at a concentration equal to or greater than the LRL 

is predicted to be less than or equal to 1 percent. The value of the LRL will be reported with 

a “less than” remark code for samples in which the analyte was not detected. The National 

Water Quality Laboratory collects quality-control data from selected analytical methods on 

a continuing basis to determine long-term method detection levels (LT–MDL’s) and establish 

laboratory reporting levels (LRL’s). These values are re-evaluated annually based on the most 

current quality-control data and may, therefore, change (Childress and others, 1999).

Long-term method detection level (LT–MDL)—A detection level derived by determining the 

standard deviation of a minimum of 24 MDL spike sample measurements over an extended 

period of time. LT–MDL data are collected on a continuous basis to assess year-to-year 

variations in the LT–MDL. The LT–MDL controls false positive error. The chance of falsely 

reporting a concentration at or greater than the LT–MDL for a sample that did not contain the 

analyte is predicted to be less than or equal to 1 percent (Childress and others, 1999).

Method detection limit (MDL)—Minimum concentration of a substance that can be measured 

and reported with 99-percent confidence that the analyte concentration is greater than zero. 

It is determined from the analysis of a sample in a given matrix containing the analyte (U.S. 

Environmental Protection Agency, 1997). At the MDL concentration, the risk of a false positive is 

predicted to be less than or equal to 1 percent (Childress and others, 1999).

Minimum reporting level (MRL)—Smallest measured concentration of a constituent that may be 

reliably reported by using a given analytical method (Timme, 1995).
Abstract

The Illinois River and tributaries, Flint Creek and Baron 

Fork, are designated scenic rivers in Oklahoma. Recent 

phosphorus levels in streams in the basin have resulted in the 

growth of excess algae, which have limited the aesthetic benefits of water bodies in the basin, especially the Illinois River 

and Lake Tenkiller. The Oklahoma Water Resources Board has 

established a standard for total phosphorus not to exceed the 

30-day geometric mean concentration of 0.037 milligram per 

liter in Oklahoma Scenic Rivers. The U.S. Geological Survey, 

in cooperation with the Oklahoma Water Resources Board, 

conducted an investigation to summarize phosphorus concentrations and provide estimates of phosphorus loads, yields, and 

flow-weighted concentrations in the Illinois River and tributaries from January 2000 through December 2004. Data from 

water-quality samples collected from 2000 to 2004 were used 

to summarize phosphorus concentrations and estimate phosphorus loads, yields, and mean flow-weighted concentrations 

in the Illinois River basin for three 3-year periods—

2000–2002, 2001–2003, and 2002–2004, to update a previous 

report that used data from water-quality samples from 1997 

to 2001. This report provides information needed to advance 

knowledge of the regional hydrologic system and understanding of hydrologic processes, and provides hydrologic data and 

results useful to multiple parties for interstate compacts.

Phosphorus concentrations in the Illinois River basin 

were significantly greater in runoff samples than in base-flow 

samples. Phosphorus concentrations generally decreased 

with increasing base flow, from dilution, and decreased in 

the downstream direction in the Illinois River from the Watts 

to Tahlequah stations. Phosphorus concentrations generally 

increased with runoff, possibly because of phosphorus resuspension, stream bank erosion, and the addition of phosphorus 

from nonpoint sources.

Estimated mean annual phosphorus loads were greater 

at the Illinois River stations than at Flint Creek and Baron 

Fork. Annual total loads in the Illinois River from Watts to 

Tahlequah, increased slightly for the period 2000–2002 and 

decreased slightly for the periods 2001–2003 and 2002–2004. 

Estimated mean annual base-flow loads at stations on the 

Illinois River were about 11 to 20 times greater than base-flow 

loads at the station on Baron Fork and 4 to 10 times greater 

than base-flow loads at the station on Flint Creek. Estimated 

mean annual runoff loads ranged from 68 to 96 percent of the 

estimated mean annual total phosphorus loads from 

2000–2004. Estimated mean seasonal base-flow loads were 

generally greatest in spring (March through May) and were 

least in fall (September through November). Estimated mean 

seasonal runoff loads generally were greatest in summer (June 

through August) for the period 2000–2002, but were greatest 

in winter (December through February) for the period 2001–

2003, and greatest in spring for the period 2002–2004.

Estimated mean total yields of phosphorus ranged from 

192 to 811 pounds per year per square mile, with greatest 

yields being reported for Illinois River near Watts (576 to 811 

pounds per year per square mile), and the least yields being 

reported for Baron Fork at Eldon for the periods 2000–2002 

and 2001–2003 (501 and 192 pounds per year per square mile) 

and for Illinois River near Tahlequah for the period 2002–2004 

(370 pounds per year per square mile).

Estimated mean flow-weighted concentrations were more 

than 10 times greater than the median (0.022 milligram per 

liter) and were consistently greater than the 75th percentile of 

flow-weighted phosphorus concentrations in samples collected 

at relatively undeveloped basins of the United States 

(0.037 milligram per liter). In addition, flow-weighted phosphorus concentrations in 2000–2002 at all Illinois River stations and at Flint Creek near Kansas were equal to or greater 

than the 75th percentile of all National Water-Quality Assessment Program stations in the United States (0.29 milligram per 

liter).

The estimated mean annual phosphorus load entering 

Lake Tenkiller ranged from about 391,000 pounds per year to 

712,000 pounds per year, and from about 83 to 90 percent of 

the load was transported to the lake by runoff.

Introduction

The Oklahoma Scenic Rivers Act of 1970 designated the 

Illinois River, and two tributaries, Flint Creek and Baron Fork 

(formerly named Barren Fork), in northeastern Oklahoma 

(fig. 1) as a Scenic River to protect water quality and preserve 

fish, wildlife, and outdoor recreational values for the benefit 

of the people of Oklahoma and visitors to the state (Oklahoma 

Phosphorus Concentrations, Loads, and Yields in the 

Illinois River Basin, Arkansas and Oklahoma, 2000–2004

By Robert L. Tortorelli and Barbara E. Pickup

Introduction 
Flin t C re e k

Ill ni o

si R

vi e r

C ane y C reek

B aron Fo rk

Lake

Tenkiller

Lake

Frances

O s a g e

C reek

Rogers

Westville

Tahlequah

Springdale

Fayetteville

Prairie Grove

Siloam Springs

Base from U.S. Geological Survey digital data, 1:100,000, 1983Stream data from U.S. Environmental Protection Agency enhanced River Reach File 1Albers Equal Area Conic projection, North America Datum 1983

Oklahoma Arkansas

ARKANSAS

OKLAHOMA

36°00

35°45'35°30'

’

36°15'

95°00’ 94°45' 94°30' 94°15' 94°00’ 93°45'

07196500

07197000

07196090

07196000

07195500

Tahlequah

Eldon

Chewey

Kansas

Watts

U.S Geological Surveywater-quality monitoringsite and number (table 1)Locations of towns withwastewater-treatmentplants that dischargeinto streams in theIllinois River basinWatershedLakesStreams

Boundary

Stateline

U.S Geological Survey

streamflow monitoringstations and numbers(table 1).

0 10 20 5 Miles

0 10 20 5 Kilometers

07195500

07196090

Figure 1. The Illinois River basin, Arkansas and Oklahoma, with locations of selected streamflow and water-quality stations in the basin and of towns with wastewater-treatment plants that discharge into streams in the basin (Modified from Pickup and others, 2003).

   Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Legislature, 1970). The Oklahoma Scenic Rivers Commission 

was created on May 3, 1977, to enforce the stipulations of this 

Act (Oklahoma Legislature, 1977).

Streams in the Illinois River basin are used for primary 

body contact recreation (in which there is a possibility of 

human ingestion of water) and fisheries. Water from these 

streams also is used for public and private water supply and 

non-irrigation agriculture (Oklahoma Water Resources Board, 

2000). About 400,000 tourists spend an estimated $12 million 

per year in the basin (Ed Fite, Oklahoma Scenic Rivers Commission, written commun., 2006). The Illinois River flows into 

Tenkiller Ferry Lake (referred to as Lake Tenkiller). An estimated $16.5 million is generated annually by about 1,500,000 

visitors per year to the area around this lake (John Marnell, 

U.S. Army Corps of Engineers, written commun., 2001).

Phosphorus enters streams in discharges from wastewater-treatment plants (point-source components) and in agricultural and urban runoff (nonpoint-source components) (Oklahoma Water Resources Board, 2002a). Streams in the Illinois 

River basin are susceptible from both point and nonpoint 

sources. Elevated phosphorus concentrations promote algae 

growth in streams (Sharpley, 1995), and accelerate eutrophication of lakes (Daniel and others, 1998). Phosphorus levels 

in streams in the basin have resulted in the growth of excess 

algae, which have degraded the aesthetic benefits of water 

bodies in the basin, especially in the Illinois River and Lake 

Tenkiller (Oklahoma Water Resources Board, 2002b). The 

recreation-based economy of the area relies on maintenance of 

aesthetically pleasing water quality in the Illinois River basin.

The 1998 Federal Clean Water Action Plan directs the 

states, in conjunction with the U.S. Environmental Protection 

Agency, to develop numeric criteria for nutrients, including 

phosphorus, (U.S. Environmental Protection Agency, 1998). 

Oklahoma Water Resources Board has established a standard 

for total phosphorus concentration not to exceed 0.037 milligram per liter (mg/L) (30-day geometric mean concentration) in Oklahoma Scenic Rivers. The standard was approved 

by the U.S. Environmental Protection Agency in December 

2003 and will be fully implemented by 2012 (Oklahoma Water 

Resources Board, 2004). The standard is based on the 75th 

percentile of flow-weighted total phosphorus concentrations 

from streams draining 85 relatively undeveloped basins from 

across the United States (referred to as relatively undeveloped 

basins of the United States) selected from three programs 

of the U.S. Geological Survey (USGS)—the Hydrologic 

Benchmark Network, the National Water-Quality Assessment 

program, and the USGS Research Program (Clark and others, 

2000). Total phosphorus (referred to as phosphorus) is the concentration of dissolved phosphorus and particulate phosphorus 

in the sample.

The Hydrologic Benchmark Network program, initiated 

by the USGS in 1958, was established to track water-quality trends in streams draining basins free from anthropogenic 

influence and to study cause and effect relation between various physiologic, meteorologic, and hydrologic variables (Cobb 

and Biesecker, 1971). The Hydrologic Benchmark Network is 

primarily composed of relatively undeveloped basins encompassing a wide variety of natural environments nationwide 

(Mast and Turk, 1999).

The National Water-Quality Assessment program, initiated by the USGS in 1991, is a primary source for long-term, 

nationwide information on the quality of streams, ground 

water, and aquatic ecosystems. The information gathered 

through the program supports national, regional, state, and 

local decision making and policy formation for water-quality 

management (Gilliom and others, 2001). Long-term goals of 

the program are to describe the status and trends in the quality 

of the Nation’s surface- and ground-water resources and determine the natural and anthropogenic factors affecting water 

quality (Gilliom and others, 1995).

The USGS Research Program provided research data 

for the assessment in Clark and others (2000) from 20 USGS 

research basins. These were small basins, ranging in size from 

about 0.04 to 8.5 square miles, that were located predominately in the Appalachian and Rocky Mountains (Clark and 

others, 2000).

Historical water-quality data collection in the Illinois 

River basin has been biased towards sampling during baseflow (non-runoff) conditions. Because of insufficient historic 

sampling during runoff events, calculations using historic data 

may have underestimated true phosphorus concentrations, 

loads, and yields. In July 1999, the USGS, in cooperation with 

the Oklahoma Scenic Rivers Commission and the Oklahoma 

Water Resources Board, supplemented fixed period, bimonthly 

water-quality sampling with six runoff-event samplings 

per year to better determine water quality over the range of 

streamflows in the basin. Pickup and others (2003) described 

phosphorus concentrations, loads and yields for the period of 

1997–2001. Water-quality samples collected during 

1997–1999 had relatively few runoff-event samples. Increases 

and shifts in seasonal trends of estimated annual loads and 

estimated seasonal loads and yields may have been partly 

attributable to the beginning of runoff-event sampling in the 

basin in July 1999. The period 2000–2004 encompasses a 

period where the runoff-event sampling protocol was in effect 

during the entire period. The U.S. Geological Survey, in cooperation with the Oklahoma Water Resources Board, conducted 

an investigation to summarize phosphorus concentrations and 

provide estimates of phosphorus loads, yields, and flowweighted concentrations in the Illinois River and tributaries 

from January 2000 through December 2004.

 Purpose and Scope

The purpose of this report is to summarize phosphorus 

concentrations and provide estimates of phosphorus loads, 

yields, and flow-weighted concentrations in the Illinois River 

and tributaries, Flint Creek and Baron Fork, from January 

2000 through December 2004 and for three 3-year periods—

2000–2002, 2001–2003, and 2002–2004. This report updates 

the work of Pickup and others (2003), which used water-qualIntroduction 
ity and streamflow data from 1997 to 2001, and comprises a 

preliminary analysis of data collected for a multi-year monitoring program.

Phosphorus concentrations are compared among stations 

in the Illinois River basin, and to those measured at relatively 

undeveloped basins of the United States. Phosphorus loads are 

computed using S-LOADEST, a program to compute mean 

constituent loads in rivers using the rating-curve method (Dave 

Lorenz, USGS, written commun., 2006). S-LOADEST, based 

on LOADEST, uses instantaneous phosphorus concentrations 

and daily mean streamflows to estimate annual and seasonal 

(spring, summer, fall, and winter) average phosphorus loads 

for the study period (Crawford, 1999; Runkel and others, 

2004). The report provides information needed to advance 

knowledge of the regional hydrologic system and understanding of hydrologic processes, and provides hydrologic data and 

results useful to multiple parties for interstate compacts.

Study Area Description

The Illinois River basin is about equally divided between 

northeastern Oklahoma and northwestern Arkansas (fig. 1). 

The basin is in the southwestern part of the Ozark Plateaus 

physiographic province (Fenneman, 1938), and is underlain by 

the cherty limestone of the Springfield Plateau aquifer (Adamski and others, 1995; Renken, 1998).

The basin is dominated by about equal proportions of 

agricultural (pasture and cropland) and forest land uses and is 

interspersed with minor amounts of commercial and residential land uses (fig. 2). Livestock production on pasture is the 

primary form of agriculture in the basin; about 48 percent of 

agricultural land use is pasture for cattle and horses. Numerous large-scale poultry and swine production facilities are in 

the basin and poultry and swine manures are used to fertilize 

pastures (Sims and Wolf, 1994). Approximately 226 million 

laying hens, broilers, or turkeys; 96,000 hogs; and 12,000 

dairy cattle and 200,000 unconfined cattle are raised in the 

basin, mostly in the upstream part of the basin in Arkansas 

(Oklahoma Conservation Commission, 2000).

There also are several municipal wastewater-treatment 

plants that discharge phosphorus containing wastewater to 

the Illinois River and tributaries (Oklahoma Water Resources 

Board, 2002a; fig. 1). The basin is the site of one of the fastest-growing Metropolitan Statistical Areas in the United States 

(Fayetteville-Springdale-Rogers, Arkansas).

Streams in the Illinois River basin are exposed to potentially large concentrations of phosphorus from point sources 

(such as wastewater-treatment plants) and nonpoint sources 

(such as runoff from fertilized pastures). Phosphorus concentrations in Ozark streams are typically greater in streams 

draining agricultural lands than in those draining forested 

lands (Petersen and others, 1998; 1999) because runoff from 

pastures fertilized with animal manure are probably substantial 

sources of phosphorus to the rivers in this basin (Arkansas 

Department of Environmental Quality, 2000). Streams receiving municipal wastewater from treatment plants can have 

phosphorus concentrations substantially greater than those 

in streams draining agricultural areas (Petersen and others; 

1998, 1999). The Illinois River and Flint Creek (fig. 1) receive 

discharges from wastewater-treatment plants, whereas, Baron 

Fork does not.

Streamflow in the Illinois River Basin

Streamflow in the Illinois River basin was highly variable 

and generally increased with basin drainage area (table 1, 

fig. 3). The maximum daily mean streamflow during the study 

period occurred in April 2004 for Illinois River near Watts and 

June 2000 for the rest of the stations, and the minimum daily 

mean streamflow during the study period occurred in August 

2003 at all stations (table 1, fig. 3). Greatest mean monthly 

streamflows occurred from February through June and least 

mean monthly streamflows occurred from July through 

October at all stations (Blazs and others, 2001–2006). Continuous streamflow was not measured at the Illinois River near 

Chewey, so estimated daily mean streamflows were computed 

by adding streamflow from Illinois River near Watts to streamflow from Flint Creek near Kansas (fig. 1, table 1).

Acknowledgments

The authors thank many people for their contributions to 

the data collection and data analysis presented in this report. 

There were numerous USGS personnel that participated in the 

bimonthly and runoff-event water-quality sampling, the entire 

Oklahoma Water Science Center Data Section at all three 

field offices added to the effort, but special thanks goes to the 

Tulsa Field Office for their contribution to the data collection. 

Additional special thanks go to Dave Lorenz for his help with 

load estimations, the S-LOADEST program, and his statistical 

guidance; Joel Galloway for his statistical guidance; and Dave 

Mueller for his insight into load estimation equations.

Methods

This section describes the water-quality collection and 

analysis protocol, method of streamflow separation into base 

flow and runoff, statistical tests used to compare groups of 

data, and methods used to estimate total phosphorus loads and 

yields.

Water-Quality Data Collection and Analysis

The USGS operates several continuous streamflow gaging stations and ungaged stations and collects water-quality 

data in the Illinois River basin in Oklahoma. Four continuous 

streamflow gaging stations were selected for use in this report: 

Illinois River near Watts, Flint Creek near Kansas, Illinois 

   Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Rogers

Westville

Tahlequah

Springdale

Fayetteville

Prairie Grove

Siloam Springs

Base from U.S. Geological Survey digital data, 1:100,000, 1983Stream data from U.S. Environmental Protection Agency enhanced River Reach File 1Land Cover from U.S. Geological Survey NLCD 1992Albers Equal Area Conic projection, North America Datum 1983

Oklahoma Arkansas

07196500

07197000

07196090

07196000

07195500

ARKANSAS OKLAHOMA

Tahlequah

Eldon

Chewey

Kansas

Watts

95°00’ 94°45' 94°30' 94°15' 94°00’ 93°45'

35°30'35°45'36°15

36°00’

'

Land Cover Classes

U.S Geological Surveywater-quality monitoringsite and number (table 1)Locations of towns withwastewater-treatmentplants that dischargeinto streams in theIllinois River basinSamplingWatershed BoundaryLake TenkillerWatershedStreams

Boundary

Open WaterResidentialCommercial/

Transportation

Forest/ShrublandPasture/GrasslandsCroplandsWetlandsStatelineU.S Geological Surveystreamflow monitoringstations and numbers(table 1)

0 10 20 5 Miles0 10 20 5 Kilometers

07195500

07196090

Figure 2. .Land use in the Illinois River basin, Arkansas and Oklahoma (Modified from Pickup and others, 2003)

Methods 
Table 1. Station information and streamflow statistics for continuous streamflow gaging and ungaged stations used for water-quality monitoring in the 

Illinois River basin, Oklahoma.[WY, water year; ddmmss, degrees, minutes, seconds; mi2, square mile; ft3/s, cubic foot per second; NA, not applicable]

Station name

(number)

Period of

record for 

station (WY)

Latitude

(ddmmss)

Longitude

(ddmmss)

Drainage

area

(mi2

)

Mean annual streamflow

(ft3/s)

Minimum and maximum

daily mean streamflow for study 

period, 2000-2004

(ft3/s)

2000-2002 2001-2003 2002-2004 Period of record 2 Minimum (date) Maximum (date) 

Illinois River nearWatts (07195500)

1955–present 360748 943419 635 639 539 552 631 83

(08/28/2003) 

19,200

(04/24/2004) 

Flint Creek near Kansas (07196000)

1955–1976;1979–1990;

1993–present

361111 944224 110 105 77.7 93.6 119 10

(08/27/2003)

7,820

(06/21/2000) 

Illinois River atChewey (07196090)1

NA 360615 944657 820 745 616 645 NA 94

(08/28/2003) 

26,000

(06/21/2000) 

Illinois River nearTahlequah (07196500)

1936–present 355522 945524 959 990 787 829 940 93

(08/28/2003) 

32,800

(06/22/2000) 

Baron Fork atEldon (07197000)

1949–present 355516 945018 307 327 250 270 330 23

(08/27/2003)

22,300

(06/21/2000) 

1The Illinois River at Chewey is ungaged; streamflow is estimated by adding streamflow from Illinois River near Watts to streamflow from Flint Creek near Kansas.2Based on streamflow statistics through Water Year 2004.

 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Illinois River near Watts

101

102

103

104

105

Flint Creek near Kansas

TIME

Illinois River near Tahlequah

2000 2001 2002 2003 2004

Illinois River at Chewey

101

102

103

104

105

TIME

Baron Fork at Eldon

101

102

103

104

105

2000 2001 2002 2003 2004

Total flow

Base flow

Base-flow water-quality sample

Runoff water-quality sample

(Instantaneous streamflow)

(Instantaneous streamflow)

(Daily mean streamflow)

(Daily mean streamflow)

EXPLANATION

STREAMFLOW, I

N CUBIC FEET PER SECOND

Figure 3. Streamflow divided into total flow and base flow, and base-flow and runoff water samples collected at waterquality stations in the Illinois River basin, Oklahoma, 2000–2004. Base flow estimated by Base-Flow Index program (Institute of 

Hydrology, 1980a, 1980b.)

Methods 
River near Tahlequah, and Baron Fork at Eldon (table 1, fig. 

1). The Illinois River at Chewey is an ungaged station at which 

streamflow is only measured when water-quality samples are 

collected (table 1, fig. 1). Stream gages were operated and 

streamflows were measured according to methods described in 

Rantz and others (1982). The data used for surface-water quality analyses should represent different flow conditions (from 

low to high) and be reasonably balanced among seasons (A.V. 

Vecchia, USGS, written commun., 2005). Prior to July 1999, 

only bimonthly water-quality samples were collected at these 

stations. Starting in July 1999, six additional water-quality 

samples were collected annually during runoff events at these 

stations (fig. 3). Representative water-quality samples were 

collected using equal-width increment methods (Edwards and 

Glysson, 1999).

The USGS National Water Quality Laboratory in Lakewood, Colorado, analyzed the water-quality samples for total 

phosphorus using methods described in Patton and Truitt 

(1992). The total phosphorus concentrations are reported as 

values if they are above the laboratory reporting level (LRL). 

The LRL is set to reduce false positive error, and is equal to 

twice the yearly determined long-term method detection level. 

Censored values are the value of the LRL reported with a “less 

than” remark code for samples in which the concentration was 

not detected. Estimated values are detected concentrations 

with concentrations between the long-term method detection 

level and the LRL are reported with an “E” remark code (Childress and others, 1999).

Streamflow data and phosphorus concentrations measured from 2000 through 2004 are analyzed in this report. All 

streamflow and water-quality data are available through the 

world wide web at http://water.usgs.gov/ok/nwis.

Streamflow Separation

Streamflow was separated into base-flow and runoff components using a hydrograph separation program, Base-Flow 

Index (Institute of Hydrology, 1980a, 1980b; Wahl and Wahl, 

1995) (fig. 3). Base flow is the sustained runoff or fair-weather 

flow of the stream and is largely composed of ground-water 

seepage (Langbein and Iseri, 1960). The minimum daily mean 

flow was identified in consecutive 5-day increments, and minimums less than 90 percent of adjacent minimums were defined 

as turning points (Wahl and Wahl, 1988; Wahl and Tortorelli, 

1997). The Base-Flow Index program estimated the base-flow 

hydrograph by drawing straight lines through successive turning points. Runoff components were calculated as the difference between total streamflow and base-flow components.

Each day was designated to be either base flow or runoff. 

Base-flow days in this report were defined as days when base 

flow was greater than or equal to 70 percent of total flow; runoff days were defined as days when runoff contributed more 

than 30 percent of total flow.

Statistical Tests

Streamflow data and water-quality data were divided into 

three 3-year periods: 2000–2002, 2001–2003, and 2002–2004, 

based on calendar year. Three-year periods were used to emulate a 3-year moving average.

The Mann-Whitney rank-sum test (Helsel and Hirsch, 

1992), used to compare two groups of data, was used to 

determine the statistical significance of differences between 

base-flow and runoff phosphorus concentrations at each station within each period. The Kruskal-Wallis test (Helsel and 

Hirsch, 1992, p. 159, 355), used to compare multiple data sets 

at one time, was used to determine the statistical significance 

of differences in phosphorus concentrations among stations in 

the Illinois River basin within base-flow and runoff groups of 

data.

The tests were selected because neither test requires 

normally distributed data. The null hypotheses of both tests 

indicate that there are no differences in median concentrations 

between the data sets being compared. The null hypothesis 

was rejected and medians were described as being significantly different if the two-sided p-value of the test was less 

than or equal to 0.05 (Helsel and Hirsch, 1992). If the null 

hypothesis of the Kruskal-Wallis test was rejected and the 

medians were described as significantly different, the multiple-stage Kruskal-Wallis test, which is new Kruskal-Wallis 

tests on smaller subsets of data, was applied to determine 

which sites were different and which were not (Helsel and 

Hirsch, 1992).

All tests conducted included censored values (values less 

than the laboratory reporting level) entered as one-half the 

laboratory reporting level values for analyses during 

2000–2004. This was done for two reasons: (1) to be consistent with Pickup and others (2003); and (2) a comparison 

using censored value summary statistics with the traditional 

summary statistics using the one-half substitution showed very 

little difference in the results. Two sites had no censored values, Flint Creek near Kansas and Illinois River at Chewey; two 

sites had only one censored value, Illinois River near Watts 

and Tahlequah; and one site had eight censored values, Baron 

Fork near Eldon (Appendixes 1-5).

Load and Yield Estimation

Linear regression was used to evaluate relations between 

total streamflow and phosphorus concentrations for each 

of the periods. Regression methods have been developed to 

estimate daily constituent loads, because water-quality data 

were collected intermittently. The regression method requires 

daily mean streamflow data and discrete water-quality samples 

collected over several years. Sample dates, times, instantaneous streamflows, and phosphorus concentrations used in 

this analysis are provided in Appendixes 1–5 and through the 

world wide web at http://water.usgs.gov/ok/nwis.

 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Linear regression models developed by S-LOADEST 

for the estimation of phosphorus loads for all 3-year periods 

at each station are listed in table 2. Constituent load (L) is the 

product of streamflow (Q) and the constituent concentration in 

the water (C) multiplied by a conversion factor for consistent 

units. Load is the amount of a constituent transported past a 

selected point in a stream in a given amount of time, usually 

one year. The S-LOADEST program (Dave Lorenz, USGS, 

written commun., 2006) was used to estimate constituent 

loads by the rating-curve method (Cohn and others, 1989; 

Crawford, 1991) in the Illinois River, Flint Creek, and Baron 

Fork. S-LOADEST is based on LOADEST (Crawford, 1999; 

Runkel and others, 2004) and is incorporated in the computer 

program S-Plus (Insightful Corporation, 2005) to facilitate 

graphical analysis and tabular results. S-LOADEST estimates 

rating-curve parameters and mean daily loads using several 

regression methods and a ratio estimator. Because some of the 

constituent concentrations included in this analysis were censored, parameters were estimated by the adjusted maximum 

likelihood estimation method (Cohn, 1988; Cohn and others, 

1992). In the absence of censored data, the method converts 

to the maximum likelihood estimation method (Dempster and 

others, 1977; Wolynetz, 1979). An estimate of the uncertainty 

in the estimated load was obtained using the method described 

by Likes (1980) and Gilroy and others (1990). S-LOADEST 

contains nine predefined rating-curve models that can test the 

relation between constituent load and streamflow. The model 

used for this report (equation 1) includes a time variable and 

seasonality variables to model the relation between the natural 

logarithms of L, Q and Q2:

ln(L) = bo + b1 lnQ + b2 lnQ2 + b3T + b4 sin SS + b5 cos SS

where

 ln is natural logarithm

 L is constituent load, in 

 pounds per day (lb/d);

 b0 is regression constant, 

 dimensionless;

 b1, b2, b3, b4, b5 are regression coefficients, 

 dimensionless;

 Q is daily mean streamflow,

 in cubic feet per second 

 (ft3/s);

 T is dectime, time parameter 

 in decimal years;

 sin is sine;

 cos is cosine; and

 SS is seasonality parameter 

 (2πdectime).

Data from stations on the Illinois River at Chewey and 

near Tahlequah, and Flint Creek, generally appeared to fit 

the model better than data from Illinois River near Watts and 

Baron Fork. Other S-LOADEST predefined regression models 

using various combinations of streamflow, time, and seasonal 

coefficients did have lesser residuals than the model used for 

this report; however, the “best” model indicated in S-LOADEST was different for each station and time. However, this 

one general model (equation 1) was chosen for all stations 

and periods: (1) to be consistent with general methodology 

in the previous Pickup and others (2003) report, (2) to use a 

consistent general model to estimate loads for all stations and 

periods in a basin, (3) because an analysis of the “best” models compared with this general model indicated a very small 

improvement in reduction in variance, and (4) because seasonality parameters were present in the majority of the “best” 

models and this general model had a much lower variance than 

the simpler model used in Pickup and others (2003).

Three-year periods were used to emulate a 3-year moving 

average. Different model coefficients for each 3-year period 

were used (1) to allow the slope between L and Q to vary with 

time instead of having one slope for the 5-year period, and 

(2) because the model variances were lower using different 

3-year models instead of a single 5-year model, indicating a 

better model fit.

Estimated mean annual phosphorus loads and estimates 

of the standard deviations of the mean loads were calculated 

by S-LOADEST using all base-flow and runoff data. The daily 

load values generated by S-LOADEST were then separated 

into base-flow and runoff sample sets according to the number 

of base-flow days and the number of runoff days in each 

3-year period. Estimated mean annual base-flow loads were 

calculated as the mean of the base-flow day sample set. Estimated mean annual runoff loads were calculated as the mean 

of the runoff day sample set. Estimated seasonal base-flow 

and runoff loads were calculated in the same way based on the 

number of base-flow and runoff days in each season of each 

period. In this report, spring is March through May, summer 

is June through August, fall is September through November, 

and winter is December through February.

Phosphorus yields for each of the three periods at each 

station were calculated by dividing mean annual phosphorus 

loads by drainage area (table 1). Flow-weighted concentrations 

for each of the three periods at each station were calculated 

by dividing mean annual phosphorus loads by mean annual 

streamflow and multiplying by a conversion factor to adjust 

the units.

Phosphorus Concentrations, Loads and 

Yields in the Illinois River Basin

Phosphorus in the Illinois River basin is described in 

terms of three 3-year periods (2000–2002, 2001–2003, and 

2002–2004) of mean concentrations, loads, and yields in baseflow and runoff samples, and in terms of mean flow-weighted 

concentrations. All annual and seasonal loads, yields, and 

flow-weighted concentrations are estimated mean values that 

were calculated by S-LOADEST. All total phosphorus values 

are referred to as phosphorus.

Phosphorus Concentrations, Loads and Yields in the Illinois River Basin 
Table 2. Regression models developed using total phosphorus concentrations from water samples collected at water-quality stations in the Illinois River basin, Oklahoma, 

periods 2000–2002, 2001–2003, and 2002–2004.[no., number; obs., observations; ln, natural logarithm; L, daily load in pound per day; Q, mean daily streamflow in cubic foot per second; T, dectime, time parameter in decimal years; SS, seasonality parameter, (2πdectime); R2, coefficient of determination]

Station name

(number) 

3-year

period

No. of

obs.

No. of

censored

obs.1

Regression model

Estimated

residual

variance2

R2

(percent)

Illinois River nearWatts (07195500)

2000–20022001–20032002–2004

303331

110

ln(L) = 7.93 + 1.18*lnQ + 0.0538*lnQ2 + 0.0643*T - 0.138*sin SS + 0.0286*cos SSln(L) = 7.55 + 1.24*lnQ + 0.0352*lnQ2 - 0.116*T - 0.225*sin SS - 0.101*cos SSln(L) = 7.25 + 1.42*lnQ + 0.0869*lnQ2 - 0.239*T - 0.351*sin SS - 0.298*cos SS

0.3140.3570.224

939196

Flint Creek near Kansas (07196000)

2000–20022001–20032002–2004

313031

000

ln(L) = 6.29 + 1.42*lnQ + 0.0491*lnQ2 + 0.0559*T - 0.120*sin SS - 0.0784*cos SSln(L) = 5.23 + 1.33*lnQ + 0.0726*lnQ2 + 0.183*T - 0.0924*sin SS - 0.0657*cos SSln(L) = 5.42 + 1.28*lnQ + 0.0716*lnQ2 + 0.0042*T - 0.0505*sin SS - 0.0522*cos SS

0.0450.0290.031

999999

Illinois River atChewey (07196090)

2000–20022001–20032002–2004

273231

000

ln(L) = 8.12 + 1.33*lnQ + 0.0400*lnQ2 + 0.0587*T - 0.0220*sin SS - 0.0254*cos SSln(L) = 7.59 + 1.36*lnQ + 0.0638*lnQ2 - 0.119*T - 0.185*sin SS - 0.119*cos SSln(L) = 7.04 + 1.45*lnQ + 0.162*lnQ2 - 0.168*T - 0.257*sin SS - 0.295*cos SS

0.0870.0840.062

999899

Illinois River nearTahlequah (07196500)

2000–20022001–20032002–2004

313331

110

ln(L) = 7.93 + 1.48*lnQ + 0.0158*lnQ2 + 0.0491*T - 0.0906*sin SS - 0.110*cos SSln(L) = 7.37 + 1.45*lnQ + 0.0586*lnQ2 + 0.0197*T - 0.102*sin SS - 0.154*cos SSln(L) = 7.13 + 1.46*lnQ + 0.0838*lnQ2 - 0.257*T - 0.270*sin SS - 0.214*cos SS

0.0590.0700.072

999999

Baron Fork atEldon (07197000)

2000–20022001–20032002–2004

323231

832

ln(L) = 6.15 + 1.68*lnQ + 0.0258*lnQ2 + 0.115*T - 0.466*sin SS - 0.239*cos SSln(L) = 5.26 + 1.60*lnQ + 0.0689*lnQ2 - 0.0842*T - 0.389*sin SS - 0.149*cos SSln(L) = 5.32 + 1.71*lnQ + 0.101*lnQ2 - 0.147*T - 0.377*sin SS - 0.0890*cos SS

0.2760.1820.107

989899

 1Censored observations are a result of an analysis value lower than the laboratory minimum reporting level.

2Estimated residual variance is the maximum likelihood estimation variance corrected for the number of observations, number of censored observations, and number of parameters in the regression 

model.

10 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Concentrations

 Phosphorus concentrations were significantly greater 

(p ≤ 0.05) in runoff samples than in base-flow samples for all 

three periods, 2000–2002, 2001–2003, and 2002–2004, at all 

stations (tables 3 and 4, fig. 4).

Phosphorus concentrations in base-flow samples during all 3-year periods significantly decreased (p ≤ 0.05) in 

the downstream direction in the Illinois River from the Watts 

to Tahlequah stations (fig. 5), as has been reported for other 

point-source affected streams in the region (Haggard, 2000; 

Haggard and others, 2001). Phosphorus concentrations in 

base-flow samples from the Illinois River generally decreased 

with increasing streamflow (fig. 4, table 3). As base flow 

increased by addition of ground water, dilution reduced the 

concentration of phosphorus from point sources. The Illinois 

River and Flint Creek received phosphorus concentrations 

from point sources, but Baron Fork did not. Consequently, 

phosphorus concentrations in base-flow samples from Baron 

Fork were significantly less than those in base-flow samples 

from the Illinois River and Flint Creek during all 3-year periods (fig. 5).

Phosphorus concentrations in runoff samples for all 

3-year periods were not significantly different among the two 

upstream stations on the Illinois River and Flint Creek for 

the periods 2000-2002 and 2001-2003; and not significantly 

different among the three stations on the Illinois River and 

Flint Creek for the periods 2002-2004 (fig. 6). However, the 

concentrations at Baron Fork were significantly less than at all 

other stations for all periods, except at Tahlequah during 

2000-2002 (fig. 6). Phosphorus concentrations in runoff 

samples from the Illinois River, Flint Creek, and the Baron 

Fork generally increased with increasing streamflow (fig. 

4). Possible causes of larger concentrations of phosphorus 

during runoff events than in base flow are resuspension of 

phosphorus from the streambed and lakebed sediment, stream 

bank erosion, and the addition of phosphorus from nonpoint 

sources. Svendsen and others (1995) reported that about half 

the phosphorus transported during runoff in lowland streams 

in Denmark resulted from resuspension of phosphorus in 

streambed sediments.

Estimated Mean Annual Loads

Estimated mean annual phosphorus loads were substantially greater at the Illinois River stations than at Flint Creek 

and Baron Fork, primarily because of greater streamflow at 

the stations on the Illinois River (tables 1 and 5). Annual total 

loads from Watts to Tahlequah in the Illinois River, increased 

slightly for the period 2000–2002 (table 5) and decreased 

slightly for the periods 2001–2003 and 2002–2004 (table 5).

Estimated mean annual base-flow loads were least in the 

Baron Fork, despite a larger drainage basin and greater base 

flow than Flint Creek, which receives phosphorus from wastewater discharges (fig. 2). Annual base-flow loads at stations on 

the Illinois River were about 11 to 20 times greater than baseflow loads at the station on Baron Fork and were about 

4 to 10 times greater than base-flow loads at the station on 

Flint Creek. Annual base-flow phosphorus loads decreased 

from Watts to Tahlequah in the Illinois River within all three 

periods and between periods in the basin from 2000–2004 

(table 5).

Estimated mean annual runoff loads in the basin 

increased with increasing drainage area and with increasing 

streamflow (tables 1 and 5). The portion of annual phosphorus load contributed by runoff increased in the downstream 

direction in the Illinois River (Watts to Tahlequah) (table 5). 

Runoff components of the annual total load for Flint Creek 

ranged from 68 to 84 percent from 2000 to 2004 (table 5). At 

the Illinois River stations, the range in the runoff component 

of the annual total load was 75 to 88 percent (table 5). Runoff 

components of the annual total load at Baron Fork ranged 

from 91 to 96 percent (table 5). These runoff loads were from 

small proportion of the time with less than 39 percent of the 

days including substantial runoff (runoff component greater 

than 30 percent of total flow) (table 6). Annual runoff loads 

appeared to be greater in the 2000–2002 period compared to 

the other two time periods at all stations in the basin. The most 

significant decrease occurred between the 2000–2002 period 

and the 2001–2003 period, which coincides with the drop in 

mean annual streamflow (table 1).

Estimated Mean Seasonal Loads

Estimated mean seasonal base-flow phosphorus loads 

generally were least in fall (September through November) 

and greatest in spring (March through May) for all periods at 

all stations in the Illinois River basin (table 7). The summer 

season (June through August) in the period 2002–2004 also 

was a high load season.

Estimated mean seasonal runoff phosphorus loads were 

least in fall for all periods at all stations. Runoff loads generally were greatest in summer (June through August) for the 

period 2000–2002, but were greatest in winter (December 

through February) for the period 2001–2003, and greatest in 

spring for the period 2002–2004. The shift in seasonal patterns 

between the 3-year periods may be a result of the sampling 

of large runoff events. For example, streamflows and phosphorus concentration data collected during runoff events in 

June 2000 (maximum streamflow event for most stations for 

the 2000–2002 period; table 1, fig. 3) and April 2004 (maximum streamflow event for Illinois River near Watts for the 

2002–2004 period; table 1, fig. 3) may have been sufficient to 

shift the greatest seasonal loads from summer to spring at all 

stations from the period 2000–2002 to the period 2002–2004.

Estimated Mean Yields

Estimated mean total yields of phosphorus ranged from 

192 to 811 pounds per year per square mile (lbs/yr/mi2), with 

Phosphorus Concentrations, Loads and Yields in the Illinois River Basin  11
Table 3. Summary statistics of total phosphorus concentrations from base-flow and runoff water samples collected at water-quality stations in the Illinois River basin, 

Oklahoma, periods 2000–2002, 2001–2003, and 2002–2004.

[Obs, number of observations; Cens obs, number of censored observations; mg/L, milligram per liter as P; <, less than the laboratory reporting level]

Station name

(number) 3-year period

Total phosphorus concentrations

Base-flow Runoff

Minimum

(mg/L)

Median 

(mg/L)

Mean

(mg/L)

Maximum

(mg/L) Obs Cens obs2 Minimum (mg/L) Median (mg/L) Mean (mg/L) Maximum (mg/L) Obs Cens obs2

Illinois River nearWatts (07195500) 1

2000–20022001–20032002–2004

0.180.100.07

0.310.220.15

0.310.260.20

0.540.540.54

111212

000

<0.06<0.06

0.04

0.410.370.37

0.490.450.44

0.931.061.06

192119

110

Flint Creek near Kansas (07196000)

2000–20022001–20032002–2004

0.110.110.14

0.140.150.16

0.140.160.17

0.150.200.20

111114

000

0.110.110.14

0.260.230.24

0.420.280.33

1.660.850.72

201917

000

Illinois River atChewey (07196090)

2000–20022001–20032002–2004

0.140.090.05

0.170.150.12

0.200.170.14

0.300.300.30

9

1012

000

0.180.150.08

0.450.280.28

0.500.380.36

0.960.860.78

182219

000

Illinois River nearTahlequah (07196500) 1

2000–20022001–20032002–2004

0.070.060.04

0.110.110.09

0.100.110.09

0.150.150.15

99

13

000

<0.06<0.06

0.06

0.260.220.24

0.340.280.30

0.820.820.82

222418

110

Baron Fork atEldon (07197000) 1

2000–20022001–20032002–2004

<0.04<0.04<0.04

<0.04<0.04<0.04

<0.04<0.04<0.04

0.040.040.04

101114

632

<0.05

0.020.02

0.140.090.09

0.320.160.23

1.650.741.08

222117

200

1All concentration data, including censored data, were used to calculate statistics. 2Censored data (concentrations less than the laboratory reporting level) were entered in the calculations as one-half the laboratory reporting level.

12 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Table 4. Wilcoxon rank-sum test results comparing base-flow total phosphorus concentrations to runoff total phosphorus 

concentrations from water samples collected at water-quality stations in the Illinois River basin, Oklahoma, periods 

2000–2002, 2001–2003, and 2002–2004.

[z, normal test statistic with correction for ties; p, probability value; p-values in bold indicate statistically significant differences between groups 

of data at 95-percent confidence level (probability value less than or equal to 0.05)]

 Station name (number)

3-year period2

2000–2002 2001–2003 2002–2004

Illinois River near Watts (07195500) 1 z = -2.132 z = -2.115 z = -2.596

p = 0.0330 p = 0.0344 p = 0.0094

Flint Creek near Kansas (07196000) z = -3.425 z = -3.049 z = -3.925

p = 0.0006 p = 0.0023 p = 0.0001

Illinois River at Chewey (07196090) z = -3.345 z = -3.131 z = -3.630

p = 0.0008 p = 0.0017 p = 0.0003

Illinois River near Tahlequah (07196500) 1 z = -3.574 z = -3.600 z = -4.104

p = 0.0004 p = 0.0003 p < 0.0001

Baron Fork at Eldon (07197000) 1 z = -3.809 z = -4.021 z = -4.172

p = 0.0001 p = 0.0001 p < 0.0001

1

All concentration data, including censored data, were used to calculate statistics.

2

Censored data (concentrations less than the laboratory reporting level) were entered in the calculations as one-half the laboratory reporting 

level.

Phosphorus Concentrations, Loads and Yields in the Illinois River Basin  13
Flint Creek near Kansas

0.01

0.1

1

IIlinois River near Watts

2

0.01

0.1

1

Illinois River at Chewey

2

101 102 103 104 105

IIlinois River near Tahlequah

TOTAL PHOSPHORUS CONCENTRATION, IN MILLIGRAMS PER LITER AS PHOSPHORUS

101 102 103 104 105

INSTANTANEOUS DISCHARGE,

IN CUBIC FEET PER SECOND

0.01

0.1

1

2000 Base-flow phosphorus concentration

2001

2002

2003

2004

2000 Runoff phosphorus concentration

2001

2002

2003

2004

0.037 milligram per liter phosphorus concentration

Baron Fork at Eldon

2

EXPLANATION

[75th percentile of flow-weighted phosphorus concentrations

from relatively undeveloped basins of the United States

(Clark and others, 2000)]

INSTANTANEOUS DISCHARGE,

IN CUBIC FEET PER SECOND

Figure 4. Total phosphorus concentrations from base-flow and runoff water samples collected at water-quality stations in 

the Illinois River basin, Oklahoma, 2000–2004.

14 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
TOTA

L PHOSPHORUS CONCENTRATION, IN MILLIGRAMS PER LITER AS PHOSPHORUS

]

[



Figure 5. Distributions of base-flow total phosphorus concentrations from water samples collected at water-quality stations in the 

Illinois River basin, Oklahoma, periods 2000–2002, 2001–2003, and 2002–2004.

Phosphorus Concentrations, Loads and Yields in the Illinois River Basin  15
TOTA

L PHOSPHORUS CONCENTRATION, IN MILLIGRAMS PER LITER AS PHOSPHORUS

Distributions with the

same letter are not

significantly different

(p 0.05) two letters

indicate tests run on

smaller sub-sets of data



0.037 milligram per liter

phosphorus concentration

[75th percentile of flow-weighted

phosphorus concentrations from

relatively undeveloped basins of

the United States

(Clark and others, 2000)]

Figure 6. Distributions of runoff total phosphorus concentrations from water samples collected at water-quality stations in the Illinois 

River basin, Oklahoma, periods 2000–2002, 2001–2003, and 2002–2004.

16  Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Table 5. Estimated mean annual total phosphorus loads and yields estimated from total phosphorus concentrations in water samples collected at water-quality 

stations in the Illinois River basin, Oklahoma, periods 2000–2002, 2001–2003, and 2002–2004.[mi2, square mile; lb/yr, pound per year; lb/yr/mi2, pound per year per square mile; SEP, standard error of prediction; P, phosphorus. Differences between total load and the sum of the base-flow load plus runoff loads are due to rounding.]

Station name 

(number)

Drainage 

area

(mi2

)

3-year

period

Estimated mean annual total phosphorus

Total load 1

(+/- SEP1

)

 (lb/yr as P)

Total yield

(lb/yr/mi2 as P)

Base-flow 

load 2

(lb/yr as P)

Base-flow 

yield

(lb/yr/mi2 as P)

Runoff load 3

(lb/yr as P)

Runoff yield 

(lb/yr/mi2 as P)

Load delivered 

during runoff 

(percent)

Illinois River nearWatts (07195500)

635 2000–2002

2001–20032002–2004

515,000 (71,500)384,000 (62,600)366,000 (53,400)

811604576

116,000

96,10063,900

182151101

399,000288,000302,000

629453476

787582

Flint Creek near Kansas (07196000)

110 2000–2002

2001–20032002–2004

70,000 (6,340)32,300 (1,590)49,500 (2,610)

637293450

11,10010,20012,000

101

93.0

109

58,90022,00037,500

536200341

846876

Illinois River atChewey (07196090)

820 2000–2002

2001–20032002–2004

549,000 (43,100)348,000 (27,000)405,000 (45,800)

670425494

94,90077,30059,100

116

94.272.1

454,000271,000346,000

554330422

837885

Illinois River nearTahlequah 

(07196500)

959 2000–2002

2001–20032002–2004

559,000 (40,000)331,000 (24,000)355,000 (29,400)

583346370

65,70060,90053,400

68.563.555.7

493,000271,000302,000

514282314

888285

Baron Fork atEldon (07197000)

307 2000–2002

2001–20032002–2004

154,000 (45,400)59,000 (10,100)120,000 (28,400)

501192389

5,6605,3605,000

18.417.516.3

148,000

53,600

115,000

482175373

969196

1Calculated by S-LOADEST and are statistics of all data in the 3-year period.2Means of the base-flow loads are calculated from base-flow days data only.3Means of the runoff loads are calculated from runoff days data only.

Phosphorus Concentrations, Loads and Yields in the Illinois River Basin  17
Table 6. Number of days of base flow and runoff designated by Base-Flow Index (BFI) program at water-quality stations in the Illinois River basin, Oklahoma, periods 

2000–2002, 2001–2003, and 2002–2004.[Spring is March through May, Summer is June through August, Fall is September through November, and Winter is December through February]

 Station name 

(number)

3-year

period

Spring Summer Fall Winter Total Percent of 

runoff days in 

period

Base 

flow Runoff Base flow Runoff Base flow Runoff Base flow Runoff Base flow Runoff

Illinois River nearWatts (07195500)

2000–20022001–20032002–2004

168169136

108107140

180206198

967078

208200215

657358

153145176

118125

95

709720725

387375371

353434

Flint Creek near Kansas (07196000)

2000–20022001–20032002–2004

188196157

8880

119

185189173

9187

103

197193205

768068

188177192

839379

758755727

338340369

313134

Illinois River atChewey (07196090)

2000–20022001–20032002–2004

169175140

107101136

181207197

956979

209201211

647262

155147177

116123

94

714730725

382365371

353334

Illinois River nearTahlequah (07196500)

2000–20022001–20032002–2004

165166128

111110148

164182189

112

9487

195195210

787863

149149178

122121

93

673692705

423403391

393736

Baron Fork atEldon (07197000)

2000–20022001–20032002–2004

159179156

117

97

120

185204194

917282

207202208

667165

139132171

132138100

690717729

406378367

373434

18  Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Table 7. Estimated mean seasonal total phosphorus loads estimated from total phosphorus concentrations in water 

samples collected at water-quality stations in the Illinois River basin Oklahoma, periods 2000–2002, 2001–2003, and 

2002–2004.

[Values are loads in pound per season as total phosphorus, Spring is March through May, Summer is June through August, Fall is September 

through November, and Winter is December through February]

Flow type Station name (number) Estimated mean seasonal total phosphorus loads

Spring Summer Fall Winter

2000–2002

Base flow Illinois River near Watts (07195500) 34,900 28,100 24,800 28,000

Flint Creek near Kansas (07196000) 3,900 2,760 1,440 3,000

Illinois River at Chewey (07196090) 34,100 22,700 15,400 22,700

Illinois River near Tahlequah (07196500) 27,700 15,400 7,710 14,900

Baron Fork at Eldon (07197000) 2,430 1,320 643 1,270

Runoff Illinois River near Watts (07195500) 95,600 145,000 25,600 133,000

Flint Creek near Kansas (07196000) 6,070 39,200 2,000 11,700

Illinois River at Chewey (07196090) 104,000 192,000 19,500 139,000

Illinois River near Tahlequah (07196500) 99,000 240,000 19,900 135,000

Baron Fork at Eldon (07197000) 20,400 95,200 3,450 29,000

2001–2003

Base flow Illinois River near Watts (07195500) 31,500 26,400 17,500 20,800

Flint Creek near Kansas (07196000) 4,260 2,130 1,380 2,460

Illinois River at Chewey (07196090) 27,800 20,500 12,500 16,400

Illinois River near Tahlequah (07196500) 25,800 14,200 7,670 13,200

Baron Fork at Eldon (07197000) 2,430 930 685 1,320

Runoff Illinois River near Watts (07195500) 96,200 35,300 22,800 133,000

Flint Creek near Kansas (07196000) 6,910 2,150 1,420 11,600

Illinois River at Chewey (07196090) 88,600 28,300 16,600 137,000

Illinois River near Tahlequah (07196500) 94,400 26,700 14,300 135,000

Baron Fork at Eldon (07197000) 15,700 4,500 2,360 31,100

2002–2004

Base flow Illinois River near Watts (07195500) 16,300 22,700 12,900 12,100

Flint Creek near Kansas (07196000) 4,080 3,200 2,000 2,730

Illinois River at Chewey (07196090) 15,800 20,500 11,600 11,200

Illinois River near Tahlequah (07196500) 16,400 16,900 8,710 11,400

Baron Fork at Eldon (07197000) 1,860 868 802 1,470

Runoff Illinois River near Watts (07195500) 188,000 69,100 17,700 26,900

Flint Creek near Kansas (07196000) 18,400 12,800 3,330 2,950

Illinois River at Chewey (07196090) 228,000 80,300 16,900 21,400

Illinois River near Tahlequah (07196500) 201,000 60,800 17,200 22,900

Baron Fork at Eldon (07197000) 97,000 7,490 6,540 3,560

Phosphorus Concentrations, Loads and Yields in the Illinois River Basin  19
greatest yields being reported for Illinois River near Watts 

(576 to 811 lbs/yr/mi2), and the least yields being reported 

for Baron Fork at Eldon for the periods 2000–2002 and 

2001–2003 (501 and 192 lbs/yr/mi2) and for Illinois River near 

Tahlequah for the period 2002–2004 (370 lbs/yr/mi2) (table 5). 

The greater yields in Illinois River near Watts may be caused 

by resuspension of phosphorus from the streambed and the 

lakebed of Lake Frances, stream bank erosion, and the addition of phosphorus from nonpoint sources.

Estimated mean base-flow yields decreased at the Illinois 

River stations and remained about the same on Flint Creek 

and Baron Fork over the three periods. Base-flow yields also 

decreased downstream in the Illinois River possibly because of 

dilution.

Estimated mean runoff yields appeared to be greater in 

the 2000–2002 period compared to the other two time periods at all stations in the basin. The most substantial decrease 

occurred between the 2000–2002 period and the 2001–2003 

period. Because yield (mean load divided by drainage area) is 

proportional to load, this decrease again might be partly attributable to the drop in mean annual streamflow (table 1).

Estimated Mean Flow-Weighted Concentrations

Estimated mean flow-weighted phosphorus concentrations at the stations in the basin were more than 10 times 

greater than the median flow-weighted concentrations 

(0.022 mg/L) and were consistently greater than the 75th 

percentile of flow-weighted phosphorus concentrations in 

relatively undeveloped basins of the United States (0.037 

mg/L, Clark and others, 2000; fig. 7, table 8). In addition, 

flow-weighted phosphorus concentrations in 2000–2002 at all 

Illinois River stations and at Flint Creek were approximately 

equal to or greater than the 75th percentile of all National 

Water-Quality Assessment program stations in the United 

States (0.29 mg/L, David Mueller, U.S. Geological Survey, 

written commun., 2003).

Estimated mean flow-weighted phosphorus concentrations were consistently greater than the median phosphorus 

concentrations shown in figure 7. The collected water-quality 

data has a wide range (table 3) and high outliers can greatly 

effect the computation of the mean flow-weighted concentrations. For example, the maximum concentration during 

2002–2004 at Baron Fork at Eldon (1.08 mg/L, table 3) 

was collected during a high runoff event in April 2004 and 

resulted in a large mean annual load that was proportionally a 

much greater increase from 2001–2003 than all other stations 

(table 5). This resulted in a large increase in estimated mean 

flow-weighted phosphorus concentration from 2001–2003 to 

2002–2004 at Baron Fork at Eldon (fig. 7).

Estimated Mean Annual Phosphorus Loads into 

Lake Tenkiller

Estimated mean annual phosphorus loads entering Lake 

Tenkiller can be estimated by adding the loads of Baron Fork 

and the Illinois River near Tahlequah. Phosphorus loads at 

these stations do not represent the entire phosphorus load into 

Lake Tenkiller, but the drainage area of these stations accounts 

for more than 80 percent of the drainage basin of the lake.

The Illinois River and Baron Fork contributed a mean 

annual phosphorus load that ranged from about 391,000 

pounds per year (lbs/yr) to 712,000 lbs/yr (table 9) and from 

about 83 to 90 percent of the annual phosphorus load was 

transported to Lake Tenkiller by runoff. The Illinois River 

transported about 10 times more phosphorus load during base 

flow and about 3 times more phosphorus load during runoff to 

the lake than Baron Fork (table 9).

Summary

The Illinois River and tributaries, Flint Creek and the 

Baron Fork, are designated scenic rivers in Oklahoma. Streams 

in the Illinois River basin are susceptible to potentially large 

concentrations of phosphorus from point sources and nonpoint 

sources. Recent phosphorus levels in streams in the basin 

have resulted in excess algae growth, which have limited 

the aesthetic benefits of water bodies in the basin, especially 

the Illinois River and Lake Tenkiller. The Oklahoma Water 

Resources Board has established a standard for total phosphorus not to exceed the 30-day geometric mean concentration of 

0.037 milligram per liter of phosphorus in Oklahoma Scenic 

Rivers.

In July 1999, the U.S. Geological Survey, in cooperation with the Oklahoma Scenic Rivers Commission and the 

Oklahoma Water Resources Board, supplemented fixed period, 

bimonthly water-quality sampling with six runoff-event 

samplings per year to better determine water quality over the 

range of streamflows in the basin. Phosphorus concentrations, 

loads, and yields were determined from January 2000 through 

December 2004, and for three 3-year periods—2000–2002, 

2001–2003, and 2002–2004.

Phosphorus concentrations in the Illinois River basin 

were significantly greater in runoff samples than in base-flow 

samples. Phosphorus concentrations generally decreased 

with increasing base flow, from dilution, and decreased in 

the downstream direction in the Illinois River from the Watts 

to Tahlequah stations. Phosphorus concentrations generally 

increased with runoff, possibly because of phosphorus resuspension, stream bank erosion, and the addition of phosphorus 

from nonpoint sources.

Estimated mean annual phosphorus loads were greater 

at the Illinois River stations than at Flint Creek and Baron 

Fork. Annual total loads from Watts to Tahlequah in the 

20 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Figure 7. Instantaneous total phosphorus concentrations from water samples collected at water-quality stations in the Illinois 

River basin, Oklahoma, periods 2000–2002, 2001–2003, and 2002–2004. Mean flow-weighted total phosphorus concentrations are 

calculated from loads estimated by S-LOADEST.

Summary 21

0.01

0.1

1

TOTAL PHOSPH

ORUS CONCENTRATION, IN MILLIGRAM

S PER LITER AS PHOSPH

ORUS

Illinois River

near Watts

(07195500)

(33) (32) (31)(31)

(31)

(31) (30) (27) (31) (33) (31)

(32)

(32)

(31)

5

Illinois River

at Chewey

(07196090)

Flint Creek

near Kansas

(07196000)

Illinois River

near Tahlequah

(07196500)

Baron Fork

at Eldon

(07197000)

EXPLANATION

2000-2002

2001-2003

2002-2004

Estimated mean flow-weighted

phosphorus concentration (table 8)

0.037 milligram per liter

phosphorus concentration

[75th percentile of flow-weighted phosphorus

concentrations from relatively undeveloped

basins of the United States

(Clark and others, 2000)]

(30) Number of samples

Outlier

Data value less than or equal to 1.5 times

the interquartile range beyond the box

75th percentile

25th percentile

Median

Outlier

Interquartile

range

(30)
Illinois River increased slightly for the period 2000–2002 and 

decreased slightly for the period 2001–2003 and 2002–2004.

Estimated mean annual base-flow loads at stations on the 

Illinois River were about 11 to 20 times greater than base-flow 

loads at the station on Baron Fork and 4 to 10 times greater 

than base-flow loads at the station on Flint Creek. Estimated 

mean annual runoff phosphorus loads increased with increasing drainage area and increasing streamflow. Runoff components of the annual total phosphorus load ranged from 68 to 96 

percent from 2000–2004.

Estimated mean seasonal base-flow loads were generally 

greatest in spring (March through May) and were least in fall 

(September through November). Estimated mean seasonal 

runoff loads generally were greatest in summer (June through 

August) for the period 2000–2002, but were greatest in winter 

(December through February) for the period 2001–2003, and 

greatest in spring for the period 2002–2004.

Estimated mean total yields of phosphorus ranged from 

192 to 811 pounds per year per square mile, with greatest 

yields being reported for Illinois River near Watts (576 to 811 

pounds per year per square mile), and the least yields being 

reported for Baron Fork at Eldon for the periods 2000–2002 

and 2001–2003 (501 and 192 pounds per year per square mile) 

and for Illinois River near Tahlequah for the period 2002–2004 

(370 pounds per year per square mile). Estimated mean 

annual base-flow yields generally decreased at the Illinois 

River stations and remained about the same on Flint Creek 

and Baron Fork over the three periods. Base-flow yields also 

decreased downstream in the Illinois River possibly because 

of dilution. Estimated mean annual runoff yields appeared to 

decrease from the 2000–2002 period compared to the other 

two time periods at all stations in the basin. The most substantial decrease occurred between the 2000–2002 period and the 

2001–2003 period.

Estimated mean flow-weighted concentrations were 

more than 10 times greater than the median and were consistently greater than the 75th percentile of flow-weighted 

phosphorus concentrations in samples collected at relatively 

undeveloped basins of the United States (0.022 milligram per 

liter and 0.037 milligram per liter, respectively). In addition, 

flow-weighted phosphorus concentrations in 2000–2002 at 

all Illinois River stations and at Flint Creek were equal to or 

greater than the 75th percentile of all National Water-Quality 

Assessment Program stations in the United States (0.29 milligram per liter).

The Illinois River and Baron Fork contributed an estimated mean annual load that ranged from about 391,000 

pounds per year to 712,000 pounds per year and from about 83 

Table 8. Estimated mean annual total phosphorus loads, mean annual streamflows, and mean flowweighted total phosphorus concentrations at water-quality stations in the Illinois River basin, Oklahoma, 

periods 2000–2002, 2001–2003, and 2002–2004.

[lb/yr, pound per year; ft3/s, cubic foot per second; mg/L, milligram per liter]

Station name 

(number)

3-year 

period

Estimated mean annual

Total phosphorus 

load 

(lb/yr)

Streamflow 

for 3-year period 

(ft3/s)

Flow-weighted total 

phosphorus 

concentration 

(mg/L)

Illinois River near

Watts (07195500)

2000–2002

2001–2003

2002–2004

515,000

384,000

366,000

639

539

552

0.409

0.362

0.337

Flint Creek near 

Kansas (07196000)

2000–2002

2001–2003

2002–2004

70,000

32,300

49,500

105

77.7

93.6

0.339

0.211

0.269

Illinois River at 

Chewey (07196090)

2000–2002

2001–2003

2002–2004

549,000

348,000

405,000

745

616

645

0.374

0.287

0.319

Illinois River near

Tahlequah (07196500)

2000–2002

2001–2003

2002–2004

559,000

331,000

355,000

990

787

829

0.287

0.214

0.217

Baron Fork at

Eldon (07197000)

2000–2002

2001–2003

2002–2004

154,000

59,000

120,000

327

250

270

0.239

0.120

0.226

22 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
to 90 percent of the estimated mean annual phosphorus load 

was transported to Lake Tenkiller by runoff.

Selected References

Adamski, J.C., Petersen, J.C., Friewald, D.A., and Davis, J.V., 

1995, Environmental and hydrologic setting of the Ozark 

Plateaus study unit, Arkansas, Kansas, Missouri and Oklahoma: U.S. Geological Survey Water-Resources Investigations Report 94–4022, 69 p.

Arkansas Department of Environmental Quality, 2000, Water 

quality inventory report, 2000: Arkansas Department of 

Environmental Quality, variously paginated.

Blazs, R.L., Walters, D.M., Coffey, T.E., White, D.K., Boyle, 

D.L., and Kerestes, J.F., 1998, Water resources data, Oklahoma, water year 1997: U.S. Geological Survey Water-Data 

Report OK–97–1, 447 p.

Blazs, R.L., Walters, D.M., Coffey, T.E., Boyle, D.L., Kerestes, J.F., and Johnson, R.E., 1999, Water resources data, 

Oklahoma, water year 1998: U.S. Geological Survey WaterData Report OK–98–1, 367 p.

Blazs, R.L., Walters, D.M., Coffey, T.E., Boyle, D.L., and 

Kerestes, J.F., 2000, Water resources data, Oklahoma, water 

year 1999: U.S. Geological Survey Water-Data Report 

OK–99–1, 364 p.

Blazs, R.L., Walters, D.M., Coffey, T.E., Boyle, D.L., and 

Wellman, J.J., 2001, Water resources data, Oklahoma, water 

year 2000: U.S. Geological Survey Water-Data Report 

OK–00–1, 382 p.

Blazs, R.L., Walters, D.M., Coffey, T.E., Boyle, D.L., and 

Wellman, J.J., 2002, Water resources data, Oklahoma, water 

year 2001: U.S. Geological Survey Water-Data Report 

OK–01–1, 349 p.

Table 9. Summary of estimated total phosphorus loads to Lake Tenkiller, Oklahoma, periods 

2000–2002, 2001–2003, and 2002–2004.

[ lb/yr, pound per year] 

Flow type 3-year period

Lake Tenkiller Illinois River 

near Tahlequah

Baron Fork

at Eldon

Estimated mean annual 

phosphorus load 1

per period 

(lb/yr)

Component 

per period 

(percent)

Component 

per period 

(percent)

Base flow 2 2000–2002

2001–2003

2002–2004

71,400

66,300

58,400

92

92

91

8

8

9

Runoff 3 2000–2002

2001–2003

2002–2004

641,000

325,000

417,000

77

83

72

23

17

28

Total 4 2000–2002

2001–2003

2002–2004

712,000

391,000

475,000

78

85

75

22

15

25

1

Loads to Lake Tenkiller are calculated by adding loads from Illinois River near Tahlequah to loads from Baron Fork 

at Eldon (table 5).

2

Means of the base-flow loads are calculated from base-flow day data only by S-LOADEST and are statistics of all 

data in the 3-year period.

3

Means of the runoff loads are calculated from runoff day data only by S-LOADEST and are statistics of all data in the 

3-year period.

4

Differences between total loads and the sum of the base-flow loads plus runoff loads are due to rounding.

Selected References 23
Blazs, R.L., Walters, D.M., Coffey, T.E., Boyle, D.L., and 

Wellman, J.J., 2003, Water resources data, Oklahoma, water 

year 2002: U.S. Geological Survey Water-Data Report 

OK–02–1, 375 p.

Blazs, R.L., Walters, D.M., Coffey, T.E., Boyle, D.L., and 

Wellman, J.J., 2004, Water resources data, Oklahoma, water 

year 2003: U.S. Geological Survey Water-Data Report 

OK–03–1, 394 p.

Blazs, R.L., Walters, D.M., Coffey, T.E., Boyle, D.L., and 

Wellman, J.J., 2005, Water resources data, Oklahoma, water 

year 2004: U.S. Geological Survey Water-Data Report 

OK–04–1, 408 p.

Blazs, R.L., Walters, D.M., Coffey, T.E., Boyle, D.L., and 

Wellman, J.J., 2006, Water resources data, Oklahoma, water 

year 2005: U.S. Geological Survey Water-Data Report 

OK–05–1, 473 p.

Childress, C.J.O., Foreman, W.T., Connor, B.F., and Maloney, 

T.J., 1999, New Reporting Procedures Based on Long-Term 

Method Detection Levels and Some Considerations for 

Interpretations of Water-Quality Data Provided by the U.S. 

Geological Survey National Water Quality Laboratory: U.S. 

Geological Survey Open-File Report 99–193, 19 p.

Clark, G.M., Mueller, D.K., and Mast, M.A., 2000, Nutrient 

concentrations and yields in undeveloped stream basins of 

the United States: Journal of the American Water Resources 

Association, v. 36, no. 4, p. 849–860.

Cobb, E.D., and Biesecker, J.E., 1971, The National Hydrologic Benchmark Network: U.S. Geological Survey Circular 

460–D, 38 p.

Cohn, T.A., 1988, Adjusted maximum likelihood estimation of 

the moments of lognormal populations from type I censored 

samples: U.S. Geological Survey Open-File Report 88–350, 

34 p.

Cohn, T.A., 1995, Recent advances in statistical methods for 

the estimation of sediment and nutrient transport in rivers: 

Reviews of Geophysics, v. 33 (Supplement), p. 1117–1124.

Cohn, T.A., DeLong, L.L., Gilroy, E.J., Hirsch, R.M., and 

Wells, D.K., 1989, Estimating constituent loads: Water 

Resources Research, v. 25, no. 5, p. 937–942.

Cohn, T.A., Gilroy, E.J., and Baier, W.G., 1992, Estimating 

fluvial transport of trace constituents using a regression 

model with data subject to censoring: Proceedings of the 

Joint Statistical Meeting, Boston, August 9–13, 1992, 

p. 142–151.

Crawford, C.G., 1991, Estimation of suspended-sediment rating curves and mean suspended-sediment loads: Journal of 

Hydrology, v. 129, p. 331–348.

Crawford, C.G., 1996, Estimating mean constituent loads in 

rivers by the rating-curve and flow-duration, rating-curve 

methods: Bloomington, Indiana University, Ph.D. dissertation, 245 p.

Crawford, C.G., 1999, Read.me file, LOADEST2, v 2.0: 

accessed April 9, 2001, at http://srv1dinind.er.usgs.gov

Daniel, T.C., Sharpley, A.N., and Lemunyon, J.L., 1998, 

Agricultural phosphorus and eutrophication—A symposium 

overview: Journal of Environmental Quality, v. 27, no. 2, 

p. 251–257.

Dempster, A.P., Laird, N.M., and Rubin, D.B., 1977, Maximum likelihood from incomplete data via the EM algorithm: Journal of the Royal Statistical Society, Series B, 

v. 39, no. 1, p. 1–38.

Edwards, T.K, and Glysson, G.D., 1999, Field methods for 

measurement of fluvial sediment: U.S. Geological Survey 

Techniques of Water-Resources Investigations, book 3, 

chap. C2, 89 p.

Fenneman, N.M., 1938, Physiography of eastern United 

States: New York, McGraw-Hill, p. 631–662.

Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1995, Design of 

the National Water-Quality Assessment Program—Occurrence and distribution of water-quality conditions: U.S. 

Geological Survey Circular 1112, 33 p.

Gilliom, R.J., Hamilton, P.A., and Miller, T.L., 2001, The 

National Water-Quality Assessment Program—Entering a 

new decade of investigation: U.S. Geological Survey Fact 

Sheet 071–01, 8 p.

Gilroy, E.J., Hirsch, R.M., and Cohn, T.A., 1990, Mean square 

error of regression-based constituent transport estimates: 

Water Resources Research, v. 26, no. 9, p. 2069–2077.

Haggard, B.E., 2000, Stream nutrient retention in the Lake 

Eucha—Spavinaw Basin: Stillwater, Oklahoma State University, Ph.D. dissertation, 165 p.

Haggard, B.E., Storm, D.E., and Stanley, E.H., 2001, Effect of 

a point source input on stream nutrient retention: Journal of 

the American Water Resources Association, v. 37, no. 5, 

p. 1291–1299.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in 

water resources: Amsterdam, Netherlands, Elsevier, 522 p.

Insightful Corporation, 2005, S-Plus 7.0 for Windows Professional Developer Edition with Release 3.0 of the U.S. 

Geological Survey S-PLUS library: Seattle, Washington.

Institute of Hydrology, 1980a, Low flow studies: Wallingford, 

Oxon, United Kingdom, Report No. 1, 41 p.

Institute of Hydrology, 1980b, Low flow studies: Wallingford, 

Oxon, United Kingdom, Report No. 3, p. 12–19.

24 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Langbein, W.B., and Iseri, K.T., 1960, General introductions 

and hydrologic definitions: U.S. Geological Survey WaterSupply Paper 1541–A, 29 p.

Likes, Jiri, 1980, Variance of the MVUE for lognormal variance: Technometrics, v. 22, no. 2, p. 253–258.

Mast, M.A., and Turk, J.T., 1999, Environmental characteristics and water quality of Hydrologic Benchmark Network 

Stations in the Midwestern United States, 1963–95: U.S. 

Geological Survey Circular 1173–B, 130 p.

Oklahoma Conservation Commission, 2000, FY 1997 319(h) 

Task 400—Institutionalization of Conservation District 

Non-Point Source Pollution Programs of the Illinois River 

with Programs of the Oklahoma Scenic Rivers Commission 

(OCC Task #089) Final Report: Oklahoma Conservation 

Commission, 17 p.

Oklahoma Legislature, 1970, Scenic Rivers Act, 82 O.S., 

Sec. 1451–1471.

Oklahoma Legislature, 1977, Scenic Rivers Act, 82 O.S., 

Sec. 1461.

Oklahoma Water Resources Board, 2000, Oklahoma water 

quality standards, variously paginated: accessed July 11, 

2003, at http://www.owrb.state.ok.us/rules/Chap45.pdf

Oklahoma Water Resources Board, 2002a, Phosphorus in 

Oklahoma’s Scenic Rivers—Justification for 0.037 mg/L: 

presentation to Oklahoma State Legislature, House Environmental and Natural Resources Committee, April 23, 2002, 

accessed July 11, 2003, at http://www.owrb.state.ok.us/

reports/presentations/Phosphorus%2004_23_2002.pdf

Oklahoma Water Resources Board, 2002b, Illinois River 

basin tour: presentation for OWRB meeting in Tahlequah, 

Oklahoma, August 12, 2002, accessed July 11, 2003, at 

http://www.owrb.state.ok.us/reports/presentations/Illinois%

20River%20Basin%20Tour%20Guide.pdf

Oklahoma Water Resources Board, 2004, 2003 Annual 

Report: Oklahoma Water Resources Board. 12 p.

 Patton, C.J., and Truitt, E.P., 1992, Methods of analysis by 

the U.S. Geological Survey National Water-Quality Laboratory—Determination of total phosphorus by a Kjeldahl 

digestion method and an automated colorimetric finish that 

includes dialysis: U.S. Geological Survey Open-File Report 

92–146, 39 p.

Peterson, J.C., Adamski, J.C., Bell, R.W., Davis, J.V., Femmer, 

S.R., Freiwald, D.A., and Joseph, R.L., 1998, Water quality 

in the Ozark Plateaus, Arkansas, Kansas, Missouri, and 

Oklahoma, 1992-1995: U.S. Geological Survey Circular 

1158, accessed July 11, 2003, at http://water.usgs.gov/pubs/

circ/circ1158

Peterson, J.C., Adamski, J.C., Bell, R.W., Davis, J.V., Femmer, 

S.R., Freiwald, D.A., and Joseph, R.L., 1999, Quality of 

Ozark streams and ground water, 1992–95: U.S. Geological 

Survey Fact Sheet FS–092–99, 4 p.

Pickup, B.E., Andrews, W.J., Haggard, B.E., and W.R. Green, 

2003, Phosphorus concentrations, loads, and yields in the 

Illinois River basin, Arkansas and Oklahoma, 1997–2001: 

U.S. Geological Survey Water-Resources Investigations 

Report 03–4168, 39 p.

Rantz, S.E. and others, 1982, Measurement and computation 

of streamflow—Volume 2. Computation of discharge: U.S 

Geological Survey Water-Supply Paper 2175, v. 2, 

285–631 p.

Renken, R.A., 1998, Ground water atlas of the United States—

Segment 5, Arkansas, Louisiana, Mississippi: U.S. Geological Survey Hydrologic Atlas 730–F, 28 p.

Runkel, R.L., Crawford, C.G., and Cohn, T.A., 2004, Load 

Estimator (LOADEST)—A FORTRAN Program for 

Estimating Constituent Loads in Streams and Rivers: U.S. 

Geological Survey Techniques and Methods Book 4, Chapter A5, 69 p. (online only), accessed October 12, 2005, at 

http://pubs.usgs.gov/tm/2005/tm4A5/

Sharpley, A.N., 1995, Fate and transport of nutrients—Phosphorus: U.S. Department of Agriculture, Agricultural 

Research Service Working Paper No. 8, 28 p.

Sims, J.T. and Wolf, D.C., 1994, Poultry waste management—Agricultural and environmental issues: Advances in 

Agronomy, v. 52, p. 1-83.

Svendsen, L.M., Kronvang, Brian, Kristensen, P., and Graesbol, P., 1995, Dynamics of phosphorus compounds in a lowland river system—Importance of retention and nonpoint 

sources: Hydrological Processes, v. 9, p. 119–142.

Timme, P.J., 1995, National Water Quality Laboratory 1995 

Services Catalog: U.S. Geological Survey Open-File Report 

95–352, p. 92.

U.S. Environmental Protection Agency, 1997, Guidelines 

establishing test procedures for the analysis of pollutants 

(App. B, Part 136, Definition and procedures for the determination of the method detection limit): U.S. Code of Federal Regulations, Title 40, revised July 1, 1997, p. 265–267.

U.S. Environmental Protection Agency, 1998, Clean Water 

Action Plan: accessed June 20, 2006, at http://www.epa.

gov/history/topics/cwa/03.htm

Wahl, K.L., and Tortorelli, R.L., 1997, Changes in flow in the 

Beaver-North Canadian River basin upstream from Canton 

Lake, western Oklahoma: U.S. Geological Survey WaterResources Investigations Report 96–4304, 58 p.

Selected References 25
Wahl, K.L., and Wahl, T.L., 1988, Effects of regional groundwater level declines on streamflow in the Oklahoma Panhandle, in Proceedings of Symposium on Water-use data for 

water resources management, Tucson, Ariz., August 1988: 

American Water Resources Association, p. 239–249.

Wahl, K.L., and Wahl, T.L., 1995, Determining the flow of 

Comal Springs at New Braunfels, Texas, in Proceedings 

of Texas Water, ‘95, A Component Conference of the First 

International Conference on Water Resources Engineering, American Society of Civil Engineers Symposium, San 

Antonio, Texas, August 16–17, 1995: American Society of 

Civil Engineers, p. 77–86.

Wolynetz, M.S., 1979, Algorithm 139—Maximum likelihood 

estimation in a linear model with confined and censored 

data: Applied Statistics, v. 28, p. 195–206.

26  Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Appendixes

Appendixes 27
Appendix 1. Instantaneous streamflows, total phosphorus concentrations, and flow category for Illinois River 

near Watts, Oklahoma, from 2000–2004.

[ft3/s, cubic foot per second; mg/L, milligram per liter; P, phosphorus; <, less than the laboratory reporting level; all water-quality 

and streamflow data available at http://water.usgs.gov/ok/nwis]

Date Sample time

Instantaneous 

streamflow

 (ft3/s)

Total phosphorus

concentrations

(mg/L as P) 1

Flow category 2

02/18/2000 0835 1,560 0.29 Runoff

04/12/2000 0920 1,270 0.27 Runoff

05/07/2000 1052 2,410 0.59 Runoff

06/18/2000 0950 10,600 0.57 Runoff

06/22/2000 0745 24,100 0.65 Runoff

07/18/2000 1345 398 0.20 Base flow

08/15/2000 1445 191 0.26 Base flow

09/26/2000 1530 341 0.30 Runoff

10/24/2000 1030 176 0.38 Base flow

11/07/2000 0720 1,400 0.34 Runoff

12/08/2000 1430 279 0.21 Base flow

01/30/2001 1100 2,740 0.30 Runoff

02/15/2001 1100 7,660 0.67 Runoff

04/18/2001 1115 352 0.18 Base flow

05/18/2001 1120 851 0.88 Runoff

06/15/2001 1230 3,930 <0.06 Runoff

08/15/2001 1530 163 0.37 Base flow

09/18/2001 1250 815 0.36 Runoff

10/11/2001 1230 2,490 0.59 Runoff

10/23/2001 0800 236 0.31 Base flow

12/11/2001 1515 284 0.36 Base flow

12/17/2001 1420 17,300 0.59 Runoff

02/01/2002 1115 4,400 0.41 Runoff

03/20/2002 1108 8,210 0.40 Runoff

04/08/2002 1215 14,400 0.91 Runoff

04/17/2002 0755 1,170 0.19 Runoff

06/12/2002 1515 562 0.33 Base flow

08/14/2002 1640 7,490 0.93 Runoff

10/10/2002 0730 146 0.54 Base flow

12/09/2002 1400 169 0.23 Base flow

03/27/2003 1030 429 0.144 Runoff

04/23/2003 1045 219 0.181 Base flow

05/16/2003 1400 911 0.200 Runoff

05/17/2003 0920 3,590 0.390 Runoff

Appendixes 29
Appendix 1. Instantaneous streamflows, total phosphorus concentrations, and flow category for Illinois River 

near Watts, Oklahoma, from 2000–2004.

[ft3/s, cubic foot per second; mg/L, milligram per liter; P, phosphorus; <, less than the laboratory reporting level; all water-quality 

and streamflow data available at http://water.usgs.gov/ok/nwis]

Date Sample time

Instantaneous 

streamflow

 (ft3/s)

Total phosphorus

concentrations

(mg/L as P) 1

Flow category 2

05/21/2003 1150 1,970 0.370 Runoff

06/02/2003 1145 2,490 1.060 Runoff

06/10/2003 0745 312 0.158 Base flow

06/12/2003 1250 1,160 0.220 Runoff

07/14/2003 1355 817 0.310 Runoff

08/28/2003 1100 86 0.210 Base flow

08/30/2003 1815 410 0.280 Runoff

09/02/2003 1200 997 0.250 Runoff

10/30/2003 0800 120 0.144 Base flow

12/08/2003 1630 171 0.095 Base flow

02/18/2004 1500 301 0.036 Runoff

03/04/2004 1115 3,930 0.760 Runoff

04/13/2004 1100 416 0.102 Runoff

04/23/2004 1540 10,500 0.780 Runoff

06/17/2004 1430 241 3 E0.135 Base flow

08/17/2004 1345 260 0.122 Base flow

10/14/2004 1540 167 0.127 Base flow

11/01/2004 1530 5,450 0.660 Runoff

12/16/2004 1000 548 0.070 Base flow

1

Year 2003 and 2004 values are reported as 3 significant digits because the precision of the analytical method changed.

2

Base flow and runoff designated by Base-Flow Index (BFI) program (Institute of Hydrology, 1980a, 1980b). 

3

 Rerun analyzed past analyical method holding time limit.

—Continued

30 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Appendix 2. Instantaneous streamflows, total phosphorus concentrations, and flow category for Flint Creek 

near Kansas, Oklahoma, from 2000–2004.

[ft3/s, cubic foot per second; mg/L, milligram per liter; P, phosphorus; all water-quality and streamflow data available at

http://water.usgs.gov/ok/nwis]

Date Sample time Instantaneous 

streamflow (ft3/s)

Total phosphorus 

concentration (mg/L 

as P) 1

Flow category 2

02/18/2000 0830 81 0.14 Runoff

04/17/2000 1200 48 0.14 Base flow

05/07/2000 0922 170 0.19 Runoff

06/17/2000 1200 5,150 1.66 Runoff

06/21/2000 1700 5,450 0.90 Runoff

06/28/2000 1430 8,970 1.17 Runoff

07/19/2000 1520 102 0.15 Base flow

08/15/2000 0730 47 0.14 Base flow

10/11/2000 1230 33 0.12 Base flow

10/27/2000 1100 73 0.17 Runoff

11/06/2000 2000 191 0.26 Runoff

12/12/2000 1020 64 0.12 Base flow

01/29/2001 1130 191 0.11 Runoff

02/15/2001 0830 678 0.28 Runoff

02/24/2001 1435 4,090 0.85 Runoff

04/17/2001 1335 85 0.11 Base flow

06/15/2001 1040 304 0.26 Runoff

08/14/2001 1035 26 0.14 Runoff

10/11/2001 1045 224 0.22 Runoff

10/30/2001 1430 34 0.12 Base flow

12/06/2001 1330 55 0.15 Base flow

12/17/2001 1045 1,030 0.32 Runoff

02/01/2002 0915 256 0.20 Runoff

03/20/2002 0948 339 0.26 Runoff

04/08/2002 1115 1,390 0.56 Runoff

04/16/2002 1145 139 0.14 Runoff

05/13/2002 1130 454 0.24 Runoff

06/11/2002 1555 100 0.15 Base flow

08/14/2002 1125 407 0.41 Runoff

10/10/2002 1130 24 0.14 Base flow

12/10/2002 1600 23 0.15 Base flow

02/25/2003 1100 75 0.200 Runoff

04/22/2003 1000 55 0.200 Base flow

05/16/2003 1940 550 0.300 Runoff

Appendixes  31
Appendix 2. Instantaneous streamflows, total phosphorus concentrations, and flow category for Flint Creek 

near Kansas, Oklahoma, from 2000–2004.

[ft3/s, cubic foot per second; mg/L, milligram per liter; P, phosphorus; all water-quality and streamflow data available at

http://water.usgs.gov/ok/nwis]

Date Sample time Instantaneous 

streamflow (ft3/s)

Total phosphorus 

concentration (mg/L 

as P) 1

Flow category 2

05/21/2003 1030 273 0.200 Runoff

06/09/2003 1215 43 0.200 Base flow

06/11/2003 1400 90 0.200 Runoff

07/14/2003 1220 73 0.230 Runoff

08/28/2003 1600 11 0.170 Base flow

08/31/2003 0115 38 0.196 Runoff

10/30/2003 0940 26 0.184 Base flow

12/09/2003 0800 30 0.181 Base flow

01/18/2004 1010 214 0.230 Runoff

02/18/2004 1130 51 0.160 Base flow

03/04/2004 0945 1,410 0.580 Runoff

03/05/2004 1130 984 0.360 Runoff

04/08/2004 1400 80 0.164 Base flow

04/24/2004 1040 3,230 0.720 Runoff

06/18/2004 0830 65 0.196 Base flow

08/18/2004 1235 80 0.162 Base flow

10/18/2004 1245 25 0.158 Base flow

11/01/2004 1325 2,050 0.640 Runoff

12/17/2004 1430 112 0.144 Base flow

1

Year 2003 and 2004 values are reported as 3 significant digits because the precision of the analytical method changed.

2

Base flow and runoff designated by Base-Flow Index (BFI) program (Institute of Hydrology, 1980a, 1980b). 

—Continued

32 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Appendix 3. Instantaneous streamflows, total phosphorus concentrations, and flow category 

for Illinois River at Chewey, Oklahoma, from 2000–2004.

[ft3/s, cubic foot per second; mg/L, milligram per liter; P, phosphorus; all water-quality and streamflow data 

available at http://water.usgs.gov/ok/nwis ]

Date Sample time

Instantaneous 

streamflow

 (ft3/s)

Total phosphorus 

concentrations 

(mg/L as P) 1

Flow category 2

02/16/2000 1105 231 0.17 Base flow

04/12/2000 1445 1,400 0.37 Runoff

05/07/2000 1450 3,340 0.47 Runoff

06/18/2000 1235 16,800 0.86 Runoff

06/22/2000 1215 34,700 0.96 Runoff

08/16/2000 1310 251 0.16 Base flow

09/26/2000 1330 840 0.23 Runoff

10/23/2000 1430 230 0.22 Base flow

11/07/2000 1230 1,900 0.27 Runoff

12/07/2000 1255 415 0.14 Base flow

01/30/2001 1245 4,980 0.40 Runoff

02/15/2001 1320 6,670 0.83 Runoff

02/25/2001 1010 20,600 0.46 Runoff

04/18/2001 1715 518 0.14 Base flow

05/18/2001 1635 1,220 0.24 Runoff

06/27/2001 0945 376 0.18 Runoff

08/15/2001 1300 200 0.25 Base flow

10/11/2001 1605 1,110 0.22 Runoff

12/11/2001 1210 335 0.26 Base flow

12/17/2001 1740 17,400 0.86 Runoff

02/01/2002 1345 7,420 0.53 Runoff

03/20/2002 1220 9,540 0.65 Runoff

04/08/2002 1400 11,600 0.78 Runoff

06/14/2002 1040 1,640 0.27 Runoff

08/15/2002 1210 3,230 0.44 Runoff

10/17/2002 1315 156 0.30 Base flow

12/11/2002 1000 216 0.15 Base flow

03/27/2003 1315 584 0.123 Base flow

04/23/2003 1320 293 0.144 Base flow

05/16/2003 1815 1,440 0.210 Runoff

05/17/2003 1120 5,030 0.510 Runoff

05/21/2003 1335 2,730 0.350 Runoff

06/02/2003 1520 621 0.151 Runoff

06/03/2003 1340 2,000 0.280 Runoff

Appendixes  33
Appendix 3. Instantaneous streamflows, total phosphorus concentrations, and flow category 

for Illinois River at Chewey, Oklahoma, from 2000–2004.

[ft3/s, cubic foot per second; mg/L, milligram per liter; P, phosphorus; all water-quality and streamflow data 

available at http://water.usgs.gov/ok/nwis ]

Date Sample time

Instantaneous 

streamflow

 (ft3/s)

Total phosphorus 

concentrations 

(mg/L as P) 1

Flow category 2

06/12/2003 1550 1,380 0.180 Runoff

07/14/2003 1610 951 0.250 Runoff

08/27/2003 1730 117 0.172 Base flow

08/30/2003 1945 286 0.183 Runoff

09/02/2003 1430 845 0.210 Runoff

10/28/2003 1530 162 0.122 Base flow

11/18/2003 1605 1,600 0.200 Runoff

12/08/2003 1415 234 0.088 Base flow

02/19/2004 1530 421 0.051 Base flow

03/04/2004 1345 5,120 0.420 Runoff

04/14/2004 1255 686 0.075 Runoff

04/23/2004 1310 9,590 0.770 Runoff

06/17/2004 1225 367 0.199 Base flow

08/18/2004 1130 379 0.109 Base flow

10/14/2004 1430 327 0.112 Base flow

11/02/2004 1000 4,780 0.430 Runoff

12/17/2004 1130 695 0.079 Base flow

1

Year 2003 and 2004 values are reported as 3 significant digits because the precision of the analytical method 

changed.

2

Base flow and runoff designated by Base-Flow Index (BFI) program (Institute of Hydrology, 1980a, 1980b). 

—Continued

34 Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Appendix 4. Instantaneous streamflows, total phosphorus concentrations, and flow category 

for Illinois River near Tahlequah, Oklahoma, from 2000-2004.

[ft3/s, cubic foot per second; mg/L, milligram per liter; P, phosphorus; <, less than the laboratory reporting level; 

all water-quality and streamflow data available at http://water.usgs.gov/ok/nwis]

Date Sample time

Instantaneous 

streamflow

(ft3/s)

Total phosphorus 

concentration 

(mg/L as P) 1

Flow category 2

02/15/2000 1700 268 0.09 Base flow

04/13/2000 0910 1,150 0.15 Runoff

05/08/2000 0920 3,010 0.28 Runoff

06/18/2000 1635 14,800 0.62 Runoff

06/22/2000 1630 33,900 0.80 Runoff

07/20/2000 1200 677 0.12 Base flow

08/29/2000 1630 189 0.09 Base flow

09/26/2000 1045 1,040 0.15 Runoff

10/19/2000 1415 251 0.11 Base flow

10/27/2000 1600 582 0.16 Runoff

11/07/2000 1400 1,540 0.19 Runoff

12/12/2000 1215 420 0.07 Base flow

01/31/2001 1040 3,840 0.21 Runoff

02/16/2001 1315 10,200 0.38 Runoff

02/25/2001 1505 25,200 0.75 Runoff

04/23/2001 1430 588 0.11 Base flow

05/19/2001 1410 2,070 0.23 Runoff

06/26/2001 1530 645 0.13 Runoff

08/16/2001 1110 312 0.10 Runoff

10/12/2001 1100 2,660 0.22 Runoff

10/24/2001 0850 368 <0.06 Runoff

11/05/2001 1250 1,690 0.35 Runoff

12/05/2001 1330 828 0.15 Runoff

12/18/2001 1210 19,500 0.54 Runoff

02/02/2002 1100 4,090 0.28 Runoff

03/21/2002 1200 7,940 0.31 Runoff

04/09/2002 1130 17,900 0.82 Runoff

06/10/2002 1300 794 0.15 Base flow

08/15/2002 1447 7,360 0.61 Runoff

10/23/2002 1145 192 0.11 Base flow

12/09/2002 1010 293 0.08 Base flow

Appendixes  35
Appendix 4. Instantaneous streamflows, total phosphorus concentrations, and flow category 

for Illinois River near Tahlequah, Oklahoma, from 2000-2004.

[ft3/s, cubic foot per second; mg/L, milligram per liter; P, phosphorus; <, less than the laboratory reporting level; 

all water-quality and streamflow data available at http://water.usgs.gov/ok/nwis]

Date Sample time

Instantaneous 

streamflow

(ft3/s)

Total phosphorus 

concentration 

(mg/L as P) 1

Flow category 2

02/22/2003 1000 738 0.152 Runoff

04/21/2003 1340 304 0.114 Base flow

05/16/2003 1020 2,090 0.260 Runoff

05/19/2003 1030 2,760 0.200 Runoff

05/22/2003 1030 2,480 0.230 Runoff

06/04/2003 1120 1,900 0.200 Runoff

06/10/2003 1200 512 0.108 Base flow

06/13/2003 0915 1,270 0.130 Runoff

07/15/2003 1130 886 0.157 Runoff

08/28/2003 1830 91 0.128 Base flow

08/30/2003 2200 205 0.130 Runoff

09/03/2003 1245 750 0.160 Runoff

10/28/2003 1330 180 0.087 Base flow

12/08/2003 1145 293 0.060 Base flow

02/19/2004 1130 482 0.035 Base flow

03/05/2004 0830 9,870 0.470 Runoff

04/13/2004 1400 926 0.056 Runoff

04/24/2004 1057 25,100 0.550 Runoff

06/23/2004 1050 439 0.086 Base flow

07/26/2004 1115 3,310 0.240 Runoff

08/17/2004 1100 453 0.081 Base flow

10/12/2004 1410 213 0.090 Base flow

11/02/2004 1325 9,340 0.460 Runoff

12/15/2004 1700 995 0.074 Base flow

1

Year 2003 and 2004 values are reported as 3 significant digits because the precision of the analytical method 

changed.

2

Base flow and runoff designated by Base-Flow Index (BFI) program (Institute of Hydrology, 1980a, 1980b). 

—Continued

36  Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004
Appendix 5. Instantaneous streamflows, total phosphorus concentrations, and flow category 

for Baron Fork at Eldon, Oklahoma, from 2000–2004.

[ft3/s, cubic foot per second; mg/L, milligram per liter; P, phosphorus; <, less than the laboratory reporting level; 

E, estimated value between the laboratory reporting level and the method detection limit; all water-quality and 

streamflow data available at http://water.usgs.gov/ok/nwis]

Date Sample time Instantaneous 

streamflow (ft3/s)

Total phosphorus 

concentration 

(mg/L as P) 1

Flow category 2

02/16/2000 0730 66 <0.05 Base flow

04/13/2000 1050 350 <0.05 Runoff

05/07/2000 1645 985 0.08 Runoff

06/17/2000 1540 7,520 1.12 Runoff

06/21/2000 1345 49,100 1.65 Runoff

06/28/2000 1630 5,350 0.98 Runoff

07/20/2000 0930 150 E0.04 Base flow

08/30/2000 1100 50 <0.05 Base flow

10/24/2000 1435 51 <0.06 Base flow

10/27/2000 1320 110 E0.04 Runoff

11/07/2000 0930 1,180 0.10 Runoff

12/20/2000 1530 192 <0.06 Runoff

01/30/2001 1015 1,270 0.13 Runoff

02/16/2001 1145 3,300 0.17 Runoff

02/25/2001 1240 4,900 0.26 Runoff

04/23/2001 1610 153 <0.06 Base flow

05/18/2001 1500 673 E0.04 Runoff

06/25/2001 1630 231 E0.04 Runoff

08/16/2001 0930 51 E0.03 Base flow

10/11/2001 1740 927 0.15 Runoff

10/23/2001 1555 136 0.13 Runoff

12/05/2001 1245 231 E0.04 Runoff

12/17/2001 1400 6,650 0.15 Runoff

02/01/2002 1045 1,700 0.15 Runoff

02/15/2002 1615 215 <0.06 Base flow

03/20/2002 1015 6,200 0.47 Runoff

04/08/2002 1607 8,030 0.49 Runoff

04/17/2002 0945 928 0.09 Runoff

06/13/2002 0845 174 E0.03 Base flow

08/14/2002 1340 4,580 0.74 Runoff

10/23/2002 1030 41 E0.04 Base flow

12/09/2002 1130 51 <0.04 Base flow

Appendixes  37
Appendix 5. Instantaneous streamflows, total phosphorus concentrations, and flow category 

for Baron Fork at Eldon, Oklahoma, from 2000–2004.

[ft3/s, cubic foot per second; mg/L, milligram per liter; P, phosphorus; <, less than the laboratory reporting level; 

E, estimated value between the laboratory reporting level and the method detection limit; all water-quality and 

streamflow data available at http://water.usgs.gov/ok/nwis]

Date Sample time Instantaneous 

streamflow (ft3/s)

Total phosphorus 

concentration 

(mg/L as P) 1

Flow category 2

02/22/2003 1155 258 0.023 Runoff

04/21/2003 1145 94 0.020 Base flow

05/16/2003 1200 228 0.039 Runoff

06/03/2003 1120 561 0.078 Runoff

06/10/2003 0950 133 0.025 Base flow

06/12/2003 1015 441 0.069 Runoff

07/15/2003 1310 120 0.031 Runoff

08/28/2003 0810 27 0.029 Base flow

08/30/2003 2320 61 0.031 Runoff

09/03/2003 1049 211 0.040 Runoff

10/28/2003 1245 56 0.025 Base flow

12/08/2003 1230 115 0.024 Base flow

02/19/2004 1220 202 0.016 Base flow

03/04/2004 1645 996 0.104 Runoff

03/05/2004 1415 2,370 0.310 Runoff

04/13/2004 1245 297 0.015 Base flow

04/23/2004 1035 14,900 1.080 Runoff

06/23/2004 1140 609 0.057 Runoff

08/17/2004 1230 115 0.028 Base flow

10/12/2004 1300 52 0.029 Base flow

11/02/2004 1215 1,820 0.157 Runoff

12/16/2004 0800 312 0.030 Base flow

1

Year 2003 and 2004 values are reported as 3 significant digits because the precision of the analytical method 

changed.

2

Base flow and runoff designated by Base-Flow Index (BFI) program (Institute of Hydrology, 1980a, 1980b). 

—Continued

38  Phosphorus Concentrations, Loads, and Yields in the Illinois River Basin, Arkansas and Oklahoma, 2000–2004