U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5078

Prepared in cooperation with Missouri Department of Natural Resources

Surface-Water Quality Conditions and Long-Term Trends at 

Selected Sites within the Ambient Water-Quality Monitoring 

Network in Missouri, Water Years 1993–2008
A

F

E

B

C

D

Cover photos. A, Upstream view of the Grand River near Sumner site (Jacob Morris, U.S. Geological Survey). B, Upstream view of the 

South Fabius River near Taylor site (Dean Fryer, U.S. Geological Survey). C, Downstream view of the Gasconade River above Jerome site 

(Bruce Ponzer, U.S. Geological Survey). D, Upstream view of the Current River near Doniphan site (Dean Fryer, U.S. Geological Survey). 

E, Downstream view of the Elk River near Tiff City site (Bruce Ponzer, U.S. Geological Survey). F, Upstream view of the Wilson Creek 

near Brookline site (Matthew Williams, U.S. Geological Survey). 
Surface-Water Quality Conditions and 

Long-Term Trends at Selected Sites within 

the Ambient Water-Quality Monitoring 

Network in Missouri, Water Years 

1993–2008

By Miya N. Barr and Jerri V. Davis

Prepared in cooperation with the Missouri Department of Natural Resources

Scientific Investigations Report 2010–5078

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Barr, M.N. and Davis, J.V., 2010, Surface-water quality conditions and long-term trends at selected sites within the 

ambient water-quality monitoring network in Missouri, 1993–2008: U.S. Geological Survey Scientific Investigations 

Report 2010–5078, 42 p.

ISBN 978–1–4113–2838–9 
iii

Contents

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

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

The Ambient Water-Quality Monitoring Network............................................................................2

Description of Study Area ...................................................................................................................2

Physiography................................................................................................................................2

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

Climate...........................................................................................................................................6

Summary of Hydrologic Conditions ..........................................................................................6

Methods of Study...........................................................................................................................................6

Description of Sampling Network......................................................................................................8

Sample Collection and Analysis Methods......................................................................................10

Data Analysis Methods .....................................................................................................................10

Assessment of Water Quality ....................................................................................................................11

Water-Quality Conditions...................................................................................................................11

Streamflow, Dissolved Oxygen, Physical Properties, and Total Suspended Solids ......14

Nutrients......................................................................................................................................17

Fecal Indicator Bacteria...........................................................................................................17

Trace Elements...........................................................................................................................21

Long-Term Trends ...............................................................................................................................22

Flow-Adjusted Trends ...............................................................................................................22

Dissolved Oxygen and Physical Properties..................................................................22

Nutrients.............................................................................................................................22

Fecal Indicator Bacteria..................................................................................................33

Trace Elements..................................................................................................................33

Non-Flow Adjusted Trends.......................................................................................................36

Total Suspended Solids....................................................................................................36

Nutrients.............................................................................................................................36

Trace Elements..................................................................................................................36

Summary and Conclusions.........................................................................................................................39

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

Figures

1–3. Maps showing—

1. Location of study sites........................................................................................................3

2. Physiographic regions of Missouri...................................................................................5

3. Land use in Missouri, 2001.................................................................................................7

4–5. Graphs showing—

4. Departure from normal total annual precipitation during the study period 

collected at precipitation gages near sites, calendar years 1993 

through 2008 .........................................................................................................................8

5. Annual mean streamflow for each site, water years 1993 through 2008 ...................9

6. Box plots showing elected constituents by site, water years 1993 through 2008 ...........15

7–8. Plots showing—

7. Relation of Escherichia coli and fecal coliform bacteria density to 

streamflow, water years 1993 through 2008..................................................................19

8. Relation of Escherichia coli and fecal coliform bacteria density to month, 

water years 1993 through 2008........................................................................................20

9. Graphs showing correlation of total recoverable lead and zinc with total 

suspended solids at sites 1 and 2, water years 1993 through 2008....................................21

10–11. Plots showing—

10. Flow-adjusted trends in physical properties, water years 1993 through 2008........27

11. Flow-adjusted trends in dissolved nitrate plus nitrite (as nitrogen) and total 

phosphorus concentrations, water years 1993 through 2008 ....................................30

12. Box plot showing total phosphorous concentrations before and after introduction 

of advanced phosphorous reduction system at the City of Springfield Southwest 

Wastewater Treatment Facility, located downstream from site 4......................................33

13–16. Plots showing—

13. Flow-adjusted trends in Escherichia coli and fecal coliform densities, 

water years 1993 through 2008........................................................................................34

14. Flow-adjusted trends in zinc concentrations at site 4, water years 1993 

through 2008 .......................................................................................................................36

15. Non-flow adjusted trends in total suspended solids, dissolved nitrate plus 

nitrite (as nitrogen), and total phosphorus concentrations, water years 1993 

through 2008 .......................................................................................................................37

16. Non-flow adjusted trends in total recoverable lead and zinc concentrations, 

water years 2000 to 2008 ..................................................................................................38

Tables

1. Information for selected Missouri Ambient Water-Quality Monitoring Network sites.....4

2. Summary statistics for selected constituents, water years 1993 through 2008...............12

3. State stream classifications and use designations of site streams ..................................14

4. Recreational classes, State standards, geometric means pertaining to the State 

Escherichia coli standards during the recreational season (April to October), and 

median values, water years 1993 through 2008.....................................................................18

5. Model output for flow-adjusted trends in concentrations, water years 1993 

through 2008 ................................................................................................................................23
v

Conversion Factors and Datums

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

square mile (mi2

) 2.590 square kilometer (km2) 

Flow rate

cubic foot per second (ft3

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

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

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

 °F=(1.8×°C)+32

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

 °C=(°F-32)/1.8

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

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

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

or micrograms per liter (μg/L).

Water year in U.S. Geological Survey reports is the 12-month period October 1 through 

September 30. The water year is designated by the calendar year in which it ends and which 

includes 9 of the 12 months. Thus, the year ending September 30, 2008, is called the “2008 water 

year”.

6. Model output for non-flow-adjusted trends in concentrations, water years 

1993 through 2008 .......................................................................................................................25

7. Agricultural census statistics in Missouri counties containing river basins 

where significant trends in nutrient data were detected....................................................32
vi
Surface-Water Quality Conditions and Long-Term Trends 

at Selected Sites within the Ambient Water-Quality 

Monitoring Network in Missouri, Water Years 1993–2008

By Miya N. Barr and Jerri V. Davis

Abstract

The U.S. Geological Survey, in cooperation with the Missouri Department of Natural Resources, collects data pertaining to the surface-water resources of Missouri. These data are 

collected as part of the Missouri Ambient Water-Quality Monitoring Network and constitute a valuable source of reliable, 

impartial, and timely information for developing an improved 

understanding of water resources in the State. 

Six sites from the Ambient Water-Quality Monitoring 

Network, with data available from the 1993 through 2008 

water years, were chosen to compare water-quality conditions 

and long-term trends of dissolved oxygen, selected physical 

properties, total suspended solids, dissolved nitrate plus nitrite 

as nitrogen, total phosphorous, fecal indicator bacteria, and 

selected trace elements. The six sites used in the study were 

classified in groups corresponding to the physiography, main 

land use, and drainage basin size, and represent most stream 

types in Missouri. 

Long-term trends in this study were analyzed using flowadjusted and non-flow adjusted models. Highly censored datasets (greater than 5 percent but less than 50 percent censored 

values) were not flow-adjusted. Trends that were detected can 

possibly be related to changes in agriculture or urban development within the drainage basins. Trends in nutrients were 

the most prevalent. Upward flow-adjusted trends in dissolved 

nitrate plus nitrite (as nitrogen) concentrations were identified 

at the Elk River site, and in total phosphorus concentrations at 

the South Fabius and Grand River sites. A downward flowadjusted trend was identified in total phosphorus concentrations from Wilson Creek, the only urban site in the study. 

The downward trend in phosphorus possibly was related to a 

phosphorus reduction system that began operation in 2001 at 

a wastewater treatment plant upstream from the sampling site. 

Total suspended solids concentrations indicated an upward 

non-flow adjusted trend at the two northern sites (South Fabius 

and Grand Rivers). The increase in total suspended solids 

concentrations could be because of soil erosion from land 

cultivated for row crops. Most trace element data examined 

in the study were highly censored and could not be used for 

flow-adjusted trend analyses. 

Water-quality conditions were assessed to explore relations between data from sites and to the State water-quality 

standards where applicable for selected constituents. Streamflow varied at each site because of drainage area, land use, and 

groundwater inputs. Dissolved oxygen and water temperature 

were similar at all sites except the urban site located on Wilson 

Creek. Specific conductance was similar between the most 

northern (South Fabius and Grand River sites) and the most 

southern sites (Current and Elk River sites). Total suspended 

solids concentrations were near the method reporting level at 

all sites, except the northern sites. Streams in northern Missouri are more turbid than streams in southern Missouri and 

are affected by large volumes of sediment deposition because 

of soil erosion from land cultivated for row crops. 

Geometric means of Escherichia coli were calculated 

from the recreational seasons within the study period. Only the 

Grand River site exceeded the whole-body-contact standard 

for frequently used waters. The South Fabius and Grand River 

sites and the Wilson Creek site had statistically larger densities 

of both fecal indicator bacteria types than the remaining sites. 

Introduction

The U.S. Geological Survey (USGS), in cooperation 

with the Missouri Department of Natural Resources (MDNR), 

collects data pertaining to the surface-water resources of Missouri. These data are collected as part of the Missouri Ambient Water-Quality Monitoring Network (AWQMN) and are 

stored and maintained by the USGS National Water Information System (NWIS) database. These data constitute a valuable source of reliable, impartial, and timely information for 

developing an improved understanding of the water resources 

of the State. To make this information readily available, these 

data have been published annually by water year (October 1 

through September 30) since the inception of the AWQMN in 

1964 (U.S. Geological Survey, 1964–2005; U.S. Geological 

Survey 2006–2008). Historical as well as current data also can 
2 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

be accessed from the Internet-based version of NWIS at http://

waterdata.usgs.gov/nwis (U.S. Geological Survey, 2010).

The MDNR is responsible for the implementation of the 

Federal Clean Water Act (CWA) in Missouri. Section 305(b) 

of the CWA requires that each State develop a water-quality 

monitoring program and periodically report the status of its 

water quality (U.S. Environmental Protection Agency, 1997). 

Water-quality status is described in terms of the suitability 

of the water for various uses, such as drinking water, fishing, 

swimming, and aquatic life; these uses are formally defined 

as “designated uses” in State and Federal Regulations. Section 303(d) of the CWA requires that certain waters that do 

not meet applicable water-quality standards be identified and 

Total Maximum Daily Loads (TMDLs) be determined for 

these waters (U.S. Environmental Protection Agency, 1997). 

TMDLs establish the maximum amount of a contaminant that 

a water body can assimilate and still meet the water-quality 

standards. Separate TMDLs address each contaminant for each 

water body.

Missouri has an area of approximately 69,000 square 

miles (mi2

) with 22,216 miles (mi) of classified streams 

that support recreation, agriculture, industry, transportation, 

and public utilities. An estimated 8,541 mi of streams are 

adversely affected or impaired by various physical changes or 

chemical contaminants. These impairments can result in the 

loss of at least one of the water body uses designated for these 

streams (Missouri Department of Natural Resources, 2009).

Public agencies that protect and manage water resources 

have a critical need for information gained through waterquality monitoring. Information from water-quality monitoring 

is needed to assess the existing conditions of water resources; 

to design preservation, management, and remediation programs; and to evaluate the effectiveness of such programs 

(Intergovernmental Task Force on Monitoring Water Quality, 

1995). Monitoring also is needed to document compliance 

with local, State, and Federal regulations and permits. In 

addition, the results of water-quality monitoring are needed to 

detect and define trends in water quality and to identify emerging water-quality concerns.

The Ambient Water-Quality Monitoring Network

The AWQMN was established in 1964 with 18 surfacewater quality sites and increased to 41 sites by 1986. During 

the early 1990’s, the network decreased to only 5 sites because 

of State funding limitations, but by 1994, the AWQMN 

increased to 39 sites. By the 2008 water year, the program 

consisted of 67 sites (Otero-Benítez and Davis, 2009b).

The objectives of the AWQMN are to (1) obtain information on the quality and quantity of surface water within the 

State; (2) provide a historical water-quality database that can 

be used by State planning and management agencies to make 

informed decisions about cultural effects on the surface waters 

of the State; and (3) provide consistent data-collection methods, laboratory analysis, and data reporting (Otero-Benítez and 

Davis, 2009a, 2009b). 

The purpose of this report is to describe the water-quality 

assessment, including water-quality conditions and long-term 

trends, at six AWQMN sites from water years 1993 through 

2008. Constituents used in this report are dissolved oxygen 

(DO), physical properties (specific conductance and water 

temperature), total suspended solids (TSS), nutrients (dissolved nitrate plus nitrite as nitrogen and total phosphorous), 

fecal indicator bacteria [Escherichia coli (E. coli) and fecal 

coliform], and trace elements (dissolved and total recoverable lead and zinc). Other constituents also analyzed during 

the study period but not used for analysis include major ions, 

other trace elements, and pesticides at selected sites. The six 

sites were chosen for this study based on their geographical 

distribution within the physiographic regions, main land use, 

and drainage basin size to represent the stream diversity within 

Missouri, as well as their long period of record. 

Description of Study Area

The sites used in the study (fig. 1) are classified in groups 

corresponding to the physiography, main land use, or unique 

station type (Otero-Benítez and Davis, 2009a, 2009b; table 1). 

Sites also were used based on their long period of record.

Physiography

Missouri has three major physiographic provinces within 

its State boundaries—Central Lowland, Ozark Plateaus, and 

Coastal Plain (Fenneman, 1938; fig. 2). The Central Lowland Province occupies a large amount of area in the central 

United States. Within Missouri, the province is divided into 

two different sections: the Dissected Till Plains section north 

of the Missouri River and the Osage Plains section in western 

Missouri (fig. 2). The Osage Plains section was not affected by 

glaciation (Fenneman, 1938) and is underlain mostly by soft 

shales with interbedded sandstones and limestones (Adamski 

and others, 1995). The Dissected Till Plains section is a mostly 

flat till plain, covered by loess (Fenneman, 1938). The topography typically is gently rolling hills with some steeper slopes 

near streams. Streams in this section are less steep than those 

in the Ozark Plateaus Province. Springs in the Plains sections 

are smaller and do not contribute to overall streamflow (Vineyard and Feder, 1974).

The Ozark Plateaus Province is divided into two sections known as the Salem Plateau and the Springfield Plateau 

(Fenneman, 1938; fig. 2). The Salem Plateau predominantly 

is dolomite whereas the Springfield Plateau is abundant in 

limestone and chert. Precambrian igneous rocks crop out in 

an area known as the St. Francois Mountains in southeastern 

Missouri. The Salem Plateau is intensely wooded, has steep, 

rugged topography with narrow valleys, dendritic drainages, 

and steep main channel gradients. The Springfield Plateau has 

less relief than the Salem Plateau with gently rolling hills that 
Introduction 3

RAY

BATES

CASS

POLK

SALINE

HENRY

PETTIS

VERNON

BENTON

HOLT

NODAWAY

JOHNSON

CLAY

ST CLAIR

CARROLL

CEDAR

DAVIESS

JACKSON

GENTRY

PLATTE

LAFAYETTE

ATCHISON MERCER

GRUNDY

DE KALB

ANDREW

CLINTON

HICKORY

WORTH

HARRISON

LIVINGSTON

CALDWELL

BUCHANAN

PIKE

LINN MACON

BOONE

FRANKLIN

ADAIR KNOX

OSAGE

MILLER

LEWIS

CALLAWAY

AUDRAIN

CLARK

RALLS MONROE

LINCOLN

COLE

CHARITON

SULLIVAN

MORGAN

COOPER

SHELBY

ST LOUIS

MARION

WARREN

JEFFERSON

HOWARD

ST CHARLES

RANDOLPH

GASCONADE

SCOTLAND

MONITEAU

MONTGOMERY

SCHUYLER

ST LOUIS

TEXAS

BARRY

IRON

HOWELL

OZARK

WAYNE SHANNON

TANEY

DADE

OREGON RIPLEY BUTLER

LACLEDE

PHELPS

WRIGHT

DOUGLAS

JASPER

GREENE

STODDARD

BARTON

NEWTON

PERRY

MARIES

PULASKI

SCOTT

CARTER

MADISON

CHRISTIAN

MCDONALD

STONE

REYNOLDS

CRAWFORD

DUNKLIN

WEBSTER

WASHINGTON

LAWRENCE

BOLLINGER

NEW MADRID

PEMISCOT

MISSISSIPPI

ST 

FRANCOIS

CAPE 

GIRARDEAU

STE 

GENEVIEVE

DENT

CAMDEN

DALLAS

PUTNAM

 94° 92° 90°

40°

38°

Base from U.S. Geological Survey digital data, 1991, 1:100,000 and 1:2,000,000 

Universal Transverse Mercator projection 

Zone 15

IOWA

ARKANSAS

MISSOURI

36°

06930800; site 3

07052152; site 4

07189000; site 6

07068000; site 5

05500000; site 1

06902000; site 2

Kansas

City

St. Louis

Springfield

Palmyra

Sumner

Anderson Doniphan

Jerome Rolla

Bella Vista, Arkansas

0 25 50 75 KILOMETERS 100

0 25 50 75 MILES 100

EXPLANATION

U.S. Geological Survey streamflow-gaging 

 station and site number

Site drainage basins and class— 

 modified from Otero-Benítez and Davis, 2009a, 2009b

National Weather Service precipitation gage

South Fabius River—Dissected Till Plains, agriculture

Grand River—Dissected Till Plains, agriculture

Gasconade River—Salem Plateau, forested and agriculture

Wilson Creek—Springfield Plateau, urban

Current River—Salem Plateau, forested and agriculture

Elk River—Springfield Plateau, agriculture and forested

05500000; site 1

Figure 1. Location of study sites.
4 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri Table 1. Information for selected Missouri Ambient Water-Quality Monitoring Network sites. [USGS, U.S. Geological Survey; mi2, square miles; ft3/s, cubic feet per second;°, degrees; ′, minutes; ′′, seconds] Site number (fig. 1) USGS station number Latitude Longitude Drainage area (mi2

)

Basin land use

(percent) Stream classificationa Period of recordb Mean annual streamflowc (ft3/s) Agriculture Forest Urban

South Fabius River near Taylord

1 05500000 39°53′47.9′′ 91°34′48.6′′ 620 74 21 4 Dissected Till Plains, agriculture November 1992 

to current year

527

Grand River near Sumnerd

2 06902000 39°38′24.1′′ 93°16′25.3′′ 6,880 76 18 5 Dissected Till Plains, agriculture August 1967 to 

current year

4,782

Gasconade River above Jerome

3 06930800 37°55′12′′ 91°58′33′′ 2,570 35 60 5 Salem Plateau, forested and 

agriculture

January 1978 to 

current year

2,539

Wilson Creek near Brookline

4 07052152 37°08′49.7′′ 93°22′31.7′′ 51 14 10 76 Springfield Plateau, urban October 1993 to 

current year

e68

Current River at Doniphand

5 07068000 36°37′19′′ 90°50′51′′ 2,038 13 83 3 Salem Plateau, forested and 

agriculture

November 1992 

to current year

2,912

Elk River near Tiff City

6 07189000 36°37′53′′ 94°35′12′′ 872 42 51 7 Springfield Plateau, agriculture 

and forested

November 1992 

to current year

866

aModified from Otero-Benítez and Davis, 2009a, 2009b.bDate range shown as period of record is not the entire period of record available for some sites. The period shown is the largest period with no interruption in collection between water 

years.

cMean annual streamflow shown is calculated from the date range listed in period of record. Steamflow gaging stations may have longer period of record than the water-quality collection 

period used in this table (U.S. Geological Survey, 1964–2005, 2006–2008, 2010).

dAbout 1 percent of the land use in this basin is water.eStreamflow data from water year 2001 to current year (2010).
Introduction 5

EXPLANATION

Central Lowland Province—Osage Plains

Ozark Plateaus Province—Salem Plateau

Ozark Plateaus Province—Springfield Plateau

Coastal Plain Province—Mississippi Alluvial Plain

Base from U.S.Geological Survey digital data, 1991, 2001, 1:100,000 and 1:2,000,000

Universal Transverse Mercator projection 

Zone 15

Horizontal coordinate information referenced to the

North American Datum of 1983 (NAD 83)

96° 94° 92° 90°

40°

38°

36°

0 25 50 100 MILES

0 50 100 KILOMETERS

Central Lowland Province—Dissected Till Plains

St. Francois Mountains

25 75

75

IOWA

ARKANSAS

MISSOURI

U.S. Geological Survey streamflow-gaging 

 station and site number

05500000; site 1

Drainage basin boundary

Physiographic regions— 

 modified from Fenneman, 1938

07052152; site 4

Springfield

07189000; site 6

07068000; site 5

06930800; site 3

06902000; site 2

05500000; site 1

07068000; site 5

07052152; site 4

Springfield

07189000; site 6

St. Louis

Kansas City

Figure 2. Physiographic regions of Missouri.
6 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

generally are equally divided between wooded and pasturelands. Sinkholes and springs are common in both the Salem 

and Springfield Plateaus, but are more prevalent and larger in 

the Salem Plateau (Vineyard and Feder, 1974). 

The Coastal Plain Province is located in the area commonly referred to as the “boot heel” of Missouri and is known 

as the Mississippi Alluvial Plain (fig. 2). This province has a 

very gentle slope in the delta and bottomlands of the Mississippi River and its tributaries (Fenneman, 1938). 

The six sites chosen for this study represent all physiographic regions except the Mississippi Alluvial Plain section 

(fig. 2) and are classified within the Salem and Springfield 

Plateaus and the Dissected Till Plains section. Each category 

is subdivided into more distinct classes based on land use 

(table 1).

Land Use

Land use in Missouri primarily is agricultural and forested (fig. 3). In the Dissected Till Plains, land use is agricultural and includes row crops such as corn, soybeans, and 

wheat, and livestock such as cattle, hogs, and poultry. Land 

use in the Ozark Plateaus Province predominantly is agricultural (cattle and poultry production) in the Springfield Plateau 

and mainly is forested with some agriculture in the Salem 

Plateau. Agricultural land use in the Mississippi Alluvial Plain 

mostly is row crops, such as cotton, rice, and sorghum. Three 

major urban areas are located in Missouri—Kansas City, 

St. Louis, and Springfield (figs. 1, 3). The estimated population of Missouri is 5.88 million people (U.S. Census Bureau, 

2008). Land-use percentages of the drainage basins for the six 

sites used in this study are listed in table 1. 

Climate

Missouri has a temperate climate with a mean annual 

temperature of 55 degrees Fahrenheit (o

F) from 1993 through 

2008, and a mean annual precipitation of 43.5 inches per year 

(in/yr) across the State (National Oceanic and Atmospheric 

Administration, 2009). The climate of Missouri follows a gradient diagonally across the State from northwest to southeast, 

with lower temperatures in the northwest and larger annual 

precipitation in the southeast (University of Missouri, 2009). 

Typically, most rainfall in Missouri occurs from April through 

July. Thundershowers are common in September and October, 

but can occur at any time. Measurable precipitation occurs 

approximately 100 days a year, with nearly one-half of the 

days as thunderstorms. Snowfall varies from 18 to 24 inches 

(in.) north of the Missouri River to an average of 8 to 12 in. 

in the southern one-half of the State (University of Missouri, 

2009).

Rainfall departures from normal total annual precipitation (1993 to 2008) were analyzed at National Weather Service 

precipitation gages located near the six sites used in the study 

(fig. 1). Annual departures were available for calendar years 

1993 through 2008 for all precipitation gages except the 

Sumner gage (site 2; fig. 1), which did not have data for 1993 

(fig. 4; National Oceanic and Atmospheric Administration, 

1993–2008). A precipitation gage was available in the town 

of Jerome (site 3; fig. 1); however, the data available were 

limited and the gage was discontinued in 1999. The nearest 

weather station located in the nearby town of Rolla was used 

to assess the precipitation departures for the study period. All 

gages recorded above-average precipitation in 1993 and 2008. 

All gages recorded above-average precipitation in 1998 except 

the Doniphan gage (site 5; fig. 1), which recorded a slight 

negative departure from average precipitation (fig. 4). Belowaverage precipitation was recorded at all gages in 2000 and 

2005 (fig. 4).

Summary of Hydrologic Conditions

Surface-water streamflow conditions in Missouri vary 

seasonally and tend to reflect precipitation patterns. A 100-

year flood occurred along the Missouri and Mississippi Rivers 

during the 1993 water year as a result of an abnormally large 

and persistent increase of precipitation in the region (Johnson 

and others, 2004). Many smaller streams in the State also were 

affected by the flooding. During the 2007 water year, Missouri 

once again experienced storm systems that produced flooding during the spring and summer. In the 2008 water year, 

Missouri had its wettest year to date, with 57.28 in.; 16.52 

in. above the State’s long-term mean based on precipitation 

data collected since 1895 (National Oceanic and Atmospheric 

Administration, 2009).

Annual mean streamflows at the six sites were plotted 

for the study period (fig. 5). Annual data were available at all 

sites for the entire study period except site 4, which only had 

streamflow data from the 2001 through 2008 water years. The 

five remaining sites followed similar trends in annual mean 

streamflow during the study period. The highest annual mean 

for the entire period of record for sites 1, 2, and 6 was the 

1993 water year. Sites 3 and 5 recorded the highest annual 

mean in the 1985 water year, which was another flood year. 

The streamflow at site 4 is affected by effluent discharges 

from the Springfield Southwest Wastewater Treatment Plant 

(SWWTP), particularly at low flows, and may not exhibit 

streamflow patterns typical of streams where the flow is 

determined primarily by precipitation and groundwater inputs. 

Annual mean streamflow data for each site are shown in 

table 1.

Methods of Study

The six sites within the AWQMN were chosen to evaluate water-quality conditions and long-term trends of selected 

physical properties and constituents from the 1993 through 

2008 water years. Hereinafter, each site will be referred to 

as a site number (1 through 6). The numerical reference will 
Methods of Study 7

94° 92° 90°

40°

38°

36°

Land cover data modified from the 30-meter U.S. Geological Survey

national land cover dataset 2001; reclassified to open water, urban,

agricultural land, and forest

Base from U.S. Geological Survey digital data, 1991, 2001, 1:100,000 and 1:2,000,000

Universal Transverse Mercator projection 

Zone 15

05500000; site 1

07068000; site 5

07189000; site 6

07052152; site 4

Springfield

06930800; site 3

06902000; site 2

07052152; site 4

07189000; site 6

07068000; site 5

05500000; site 1

St. Louis

Kansas City

EXPLANATION

Open water

Urban

Agricultural land

Forest

0 25 50 75 KILOMETERS 100

0 25 50 75 MILES 100

U.S. Geological Survey streamflow-gaging 

 station and site number

05500000; site 1

Drainage basin boundary

IOWA

ARKANSAS

MISSOURI

Figure 3. Land use in Missouri, 2001.
8 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

follow the same downstream order as the USGS station identifiers (table 1; fig. 1). Sites will be referred to as the following: site 1, South Fabius River near Taylor (USGS identifier 

05500000); site 2, Grand River near Sumner (USGS identifier 

06902000); site 3, Gasconade River above Jerome (USGS 

identifier 06930800); site 4, Wilson Creek near Brookline 

(USGS identifier 07052152); site 5, Current River at Doniphan 

(USGS identifier 07068000); and site 6, Elk River near Tiff 

City (USGS identifier 07189000).

Description of Sampling Network

The six sites from the AWQMN were chosen based on 

their location, stream classification, main land use, and drainage basin size (table 1). Each site has a different classification, 

land use, or size that represents most stream types in Missouri. 

The sites also were chosen because of the long-term period of 

record available and the sampling frequency during the period 

of record. Each site had at least 15 years of water-quality data 

available. The sampling frequency at the six sites varied over 

the period of record, but was consistent enough to include 

data for all months. Sampling frequency within the AWQMN 

is determined by several factors, including the size of the 

drainage basin, effects from land use and human-influenced 

activity, history of the water chemistry, the need for data, and 

cost (Otero-Benítez and Davis, 2009a, 2009b). 

The drainage basins of the six sites vary in size and 

land use (table 1; figs. 1–3). Site 1 is located within the 

South Fabius River Basin, which drains mostly agricultural 

land and drains directly into the Mississippi River. Site 2 

is located in the Grand River Basin, the largest basin in the 

-15

-10

-5

0

5

10

15

20

25

30

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Palmyra (site 1)

Sumner (site 2)

Rolla (site 3)

Springfield (site 4)

Doniphan (site 5)

Anderson (site 6)

DEPARTURE FROM NORMAL PRECIPITATION, IN INCHES

CALENDAR YEAR

Precipitation gage and associated site

Figure 4. Departure from normal total annual precipitation during the study period collected at precipitation gages near 

sites, calendar years 1993 through 2008.
Methods of Study 9

STREAMFLOW, IN CUBIC FEET PER SECOND

WATER YEAR

1,000

10,000

 1993 1995 1997 1999 2001 2003 2005 2007 2008

Site 5

 1993 1995 1997 1999 2001 2003 2005 2007 2008

100

1,000

2,000 Site 6

1,000

10,000

300

20,000 Site 2

1,000

400

5,000 Site 3 Site 4

Site 1

100

1,000

50

2,000

100

30

200

Figure 5. Annual mean streamflow for each site, water years 1993 through 2008.
10 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

study, and drains mostly agricultural land directly into the 

Missouri River. This basin is not confined to Missouri but 

also has approximately one-third of its drainage area in Iowa 

(U.S. Geological Survey, 2001). The basins containing site 3 

(Gasconade River Basin) and site 5 (Current River Basin) are 

located next to each other, but drain in different directions. 

The Gasconade River Basin drains north into the Missouri 

River, whereas the Current River Basin drains south into the 

Black River in Arkansas, which, in turn, flows into the Mississippi River. The Gasconade River drains forested and some 

agricultural land, most of which is dedicated to cattle grazing. 

The Current River drains mostly forested and some agricultural lands. The smallest basin in the study is Wilson Creek, 

which contains site 4 and drains into the James River. This site 

is mostly urban (76 percent; U.S. Geological Survey, 2001) 

and is located downstream from the SWWTP. Site 6 drains 

forested and agricultural land, most of which is dedicated to 

poultry production and cattle grazing. Site 6 also has a small 

portion of its drainage area outside of Missouri, with approximately one-fourth of the Elk River Basin in Arkansas (U.S. 

Geological Survey, 2001).

Sample Collection and Analysis Methods

The methods used by the USGS for collecting and 

processing representative surface-water quality samples are 

presented in detail in U.S. Geological Survey (variously 

dated). Onsite measurements including DO, pH, specific 

conductance, and water temperature were performed at each 

site in accordance to methods described in Wilde (chapter 

sections variously dated). Samples collected and analyzed for 

fecal indicator bacteria (E. coli and fecal coliform) used the 

membrane filtration procedure described in Myers and others 

(2007). Methods used by the USGS for collecting and processing representative samples for suspended solids and nutrients 

are presented in U.S. Geological Survey (2006) and Wilde and 

others (2004). 

All chemical analyses were performed by the USGS 

National Water Quality Laboratory (NWQL) in Lakewood, 

Colorado, using procedures described in Fishman and Friedman (1989) and Fishman (1993). The NWQL uses method 

reporting conventions (Childress and others, 1999) for establishing the minimum concentration above which a quantitative 

measurement can be made. These reporting conventions are 

the method reporting level (MRL) and the laboratory reporting 

level (LRL). The MRL is defined by the NWQL as the smallest measured concentration of a substance that can be reliably 

measured using a given analytical method. The method detection level (MDL) is the minimum concentration of a substance 

that can be measured and reported with 99 percent confidence 

that the concentration is greater than zero (Childress and others, 1999). A long-term method detection limit (LT-MDL) is a 

detection level obtained by determining the standard deviation 

of 20 or more MDL spiked-sample measurements conducted 

over an extended period of time. The LRL is computed as 

twice the LT-MDL. 

About 10 to 15 percent of all water-quality samples collected annually for the AWQMN were quality-control (QC) 

samples, which were collected to assure data were of sufficient quality to meet the needs of the State of Missouri. Field 

equipment blanks were collected to detect contamination and 

carry-over between environmental samples. Replicate environmental samples also were collected to monitor consistency 

in sample collection and processing techniques and analytical 

precision. Thirty-two field equipment blanks and 47 replicate 

environmental samples were collected among the 6 sampling 

sites during the study period (U.S. Geological Survey, 1993–

2005; U.S. Geological Survey 2006–2008). Most constituent 

concentrations were equal to or less than the MRL or LRL in 

the field equipment blanks with the following exceptions: one 

dissolved zinc detection [LRL 4 μg/L (micrograms per liter), 

detected concentration of 5 μg/L] and one total recoverable 

zinc detection (LRL 2 μg/L, detected concentration of 6 μg/L). 

These results indicate that samples are not being contaminated, and carry-over between environmental samples is not 

occurring during sample collection and processing. Most constituent concentrations in the replicate environmental samples 

were comparable and within laboratory analytical error. These 

results indicate that there is consistency in sample collection 

and processing techniques and analytical precision.

Data Analysis Methods 

Boxplots are used to graphically display the distribution 

of data at multiple sites (Helsel and Hirsch, 2002). Boxplots 

provide a visual summary of the 25th, 50th, and 75th percentiles 

and any extreme values in the distribution. The boxplot consists of the median value (50th percentile) plotted as a horizontal line, and a box is drawn from the 25th percentile to the 

75th percentile. The box length, also known as the interquartile 

range (IQR), represents one-half of the values. The IQR is 

insensitive to the presence of extreme values in the distribution. If a median value does not divide the box into two equal 

parts, it indicates asymmetry in the data distribution. Adjacent 

values are outside the box and, if within 1.5 times the IQR, 

are shown as whisker lines. The length of the whisker connected to the 75th percentile represents the value of the largest 

adjacent value; the length of the whisker connected to the 25th

percentile represents the smallest adjacent value. Values that 

are more extreme in either direction than the adjacent values 

are plotted individually. The values equal to 1.5 to 3.0 times 

the IQR are called “far-out values” and are represented by 

an ‘x’ (D.R. Helsel, U.S. Geological Survey, written comm., 

1989). Values greater than the “far-out values” are represented 

by a circle. If the median of the data equals the 25th percentile, 

no center line is shown. If the median of the data equals both 

the 25th and 75th percentiles, the box will be plotted as a single 

line. Concentration values reported less than the MRL, less 

than the LRL, or as “E” (estimated to be below the MRL or 
Assessment of Water Quality 11

LRL) were included in each distribution as a concentration 

value equal to the MRL or LRL, depending on the constituent reporting convention. Although the reporting levels of the 

constituents analyzed varied throughout the study period as 

laboratory technologies and the data requirements of the State 

changed, censored data (data reported as less than a given 

value) for each constituent were set to one reporting level in 

order to use nonparametric statistical analyses. The censoring 

level selected for statistical analyses of each constituent was 

the highest reporting level reported during the study period. 

Any boxplots made with these censored data were modified by 

making the lower limit of the box equal to the reported value. 

Constituents that were highly censored, such as dissolved lead, 

were not plotted because so few measurements were greater 

than the censoring level.

The nonparametric Kruskal-Wallis rank-sum test (Helsel 

and Hirsch, 2002) was used to test for significant differences 

in the medians of the data among the six sites. Median values 

of the constituents were determined to be significantly different when the “attained significance level” (p-value) was less 

than 0.05. If significant differences were noted, a Tukey’s 

multiple comparison test was performed on the rank-transformed data to identify similarities between all sites (Helsel 

and Hirsch, 2002). Nonparametric ranking tests were used 

because data for constituents such as TSS, nutrients, and trace 

elements were highly censored. In order to correctly represent 

the censored values, the ranks were tied at a value lower than 

the censoring level selected for each constituent (Helsel and 

Hirsch, 2002). For instance, if there were 19 censored values 

in the dataset, all censored values would be assigned a rank of 

10, which is the mean of ranks 1 through 19. The next highest 

value above the censoring level obtained the rank of 20, so 

that all data above the censoring level had ranks identical to 

what would have been obtained had no censored data been 

present (Helsel and Hirsch, 2002). If censoring was greater 

than 50 percent of the total dataset, the Tukey test was not 

performed.

All long-term trend analyses were performed in the 

TIBCO Spotfire S+® program using the USGS library package ESTREND. The ESTREND library uses a system known 

as S-ESTREND to manage data for multiple stations and 

constituents for long periods of time. All constituents were 

analyzed using a Seasonal Kendall test (Helsel and Hirsch, 

2002) to define the maximum number of seasons with available data in the study period. Some constituents were analyzed 

using a flow-adjusted trend test on concentrations, whereas 

datasets with large amounts of censored values were analyzed 

by non-flow adjusted trend tests. The determination of which 

adjustment was best for a constituent was based on the amount 

of censored values in the dataset. If censored values were 

5 percent or less of the total dataset, a flow-adjusted trend test 

was performed. If the values were highly censored (between 

6 and 50 percent of the entire dataset), no flow-adjustment 

could be used, and only a linear regression could be performed. No trend tests were performed if censored values 

exceeded 50 percent of the dataset.

The flow-adjustment models initially were chosen by the 

prediction error sum of squares (PRESS) statistic. The PRESS 

statistic can be used to assess the quality of a multiple regression equation when conducting analyses utilizing standardized 

residuals (Helsel and Hirsch, 2002). The standardized residuals also are known as a measure of outliers in the direction of 

y. Streamflow was used as the standard (x) to which all constituents (y) were adjusted to, unless the censored values were 

greater than 5 percent, in which case no flow adjustment was 

used. The S-ESTREND system fits 11 different models, evaluated by means of the PRESS statistic, to find the most appropriate model for the constituent while adjusting the constituent 

to streamflow. Other models such as log-based and LOWESS 

(LOcally WEighted Scatterplot Smoothing) models also were 

analyzed to find the absolute best model for the constituent. 

Model selection was based on the p-value associated with 

each regression model and the quantile plots of the concentration of each constituent in relation to the streamflow. If a 

trend was detected for a constituent, the significance (upward, 

downward, or no significance) was determined by the p-value 

and the estimated trend in percent per year from the model 

calculations.

Step-trend analysis was used to study changes in concentrations from before and after a known event. The Wilcoxon 

rank-sum test was used to test whether or not data collected 

before and after an event differed (Helsel and Hirsch, 2002). A 

significant difference was noted if the associated p-value was 

less than 0.05.

Assessment of Water Quality

Water-quality conditions were assessed to explore the 

relations between data from sites as well as the State waterquality standards where applicable. Long-term trends were 

used to determine if water-quality conditions at the six sites 

have improved, declined, or remained the same from water 

year 1993 through 2008. Water-quality data are available 

in the USGS National Water Information System (http://

waterdata.usgs.gov/nwis).

Water-Quality Conditions

The comparison of data among sites (also known as status) was used to determine the water-quality conditions at all 

six sites from water years 1993 through 2008. All sites were 

compared by streamflow, DO, physical properties (specific 

conductance and water temperature), TSS, nutrients [dissolved 

nitrate plus nitrite as nitrogen (hereinafter referred to as dissolved nitrate plus nitrite) and total phosphorus], fecal indicator bacteria (E. coli and fecal coliform), and trace elements 

(dissolved and total recoverable lead and zinc). Summary 

statistics were calculated for selected water-quality constituents during the study period (table 2).
12 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri Table 2. Summary statistics for selected constituents, water years 1993 through 2008.—Continued [ft3/s, cubic feet per second; mg/L, milligrams per liter; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; N, nitrogen; P, phosphorous; E. coli, Escherichia coli; col/100 mL, colonies per 100 milliliters; μg/L, micrograms per liter; <, less than] Streamflow (ft3/s) Dissolved oxygen (mg/L) Dissolved oxygen (percent saturation) Specific conductance (μS/cm at 25 °C) Water temperature (°C) Water hardness (mg/L) Total suspended solids (mg/L) Dissolved nitrate plus nitrite (mg/L as N) Total phosphorous (mg/L as P) E. coli (col/100 mL) Fecal coliform (col/100 mL) Dissolved lead (μg/L) Total recoverable lead (μg/L) Dissolved zinc (μg/L) Total recoverable zinc (μg/L) Site 1, South Fabius River near Taylor (05500000) Number of samples 187 187 185 186 187 64 121 186 176 132 186 50 50 47 44 Censored values 0 0 0 0 0 0 35 52 12 0 0 40 23 32 5 Minimum .5 4.5 58 81 .1 33 <10 <.06 <.06 1 1 <1 <1 <4 <2 25th percentile 15 8.0 86 281 4.4 135 <10 <.06 .06 11 25 <1 <1 <4 2 Median 75 10.2 96 360 13.8 175 17 .46 .10 65 115 <1 1 <4 3 75th percentile 270 12.9 104 437 22.9 200 55 .87 .21 260 620 <1 3 4 10 Maximum 15,300 19.2 175 716 32.5 310 2,000 7.5 1.4 62,000 160,000 7 64 124 80 Site 2, Grand River near Sumner (06902000) Number of samples 190 189 188 189 191 101 98 189 175 127 188 32 32 29 32 Censored values 0 0 0 0 0 0 12 50 1 0 0 25 11 16 1 Minimum 66 4.0 40 131 .1 53 <10 <.06 <.06 1 2 <1 <1 <4 <2 25th percentile 350 7.1 79 301 2.9 130 19 <.06 .12 23 41 <1 <1 <4 3 Median 1,000 9.3 90 387 12.7 180 81 .52 .20 66 160 <1 2 <4 6 75th percentile 3,600 11.9 98 461 23.8 210 240 .93 .37 570 1,400 <1 9 4 22 Maximum 128,000 16.5 142 631 32.0 280 2,400 3.1 3.1 25,000 120,000 2.1 65 151 166 Site 3, Gasconade River above Jerome (06930800) Number of samples 188 188 188 188 188 67 99 184 173 130 184 33 33 30 33 Censored values 0 0 0 0 0 0 65 2 73 0 0 27 26 20 7 Minimum 120 5.2 47 130 .5 61 <10 <.06 <.06 1 1 <1 <1 <4 <2 25th percentile 640 7.6 83 298 8.8 140 <10 .12 <.06 3 7 <1 <1 <4 2 Median 1,200 9.1 91 329 15.8 170 <10 .24 .06 10 18 <1 <1 <4 2 75th percentile 2,700 10.9 100 347 23.0 180 12 .49 .06 35 67 <1 <1 4 3 Maximum 29,300 16.7 162 775 28.9 220 260 1.3 .31 5,200 8,200 1 7.1 22 12
Assessment of Water Quality 13

Table 2. Summary statistics for selected constituents, water years 1993 through 2008.—Continued[ft3/s, cubic feet per second; mg/L, milligrams per liter; μS/cm at 25 °C, microsiemens per centimeter at 25 degrees Celsius; °C, degrees Celsius; N, nitrogen; P, phosphorous; E. coli, Escherichia coli; col/100 mL, 

colonies per 100 milliliters; μg/L, micrograms per liter; <, less than]

Dissolved Specific Total Dissolved Fecal Total Total Dissolved Water Water Total E. coli Dissolved Dissolved Streamflow oxygen conductance suspended nitrate coliform recoverable recoverable oxygen temperature hardness phosphorous (col/100 lead zinc (ft3/s) (percent (μS/cm solids plus nitrite (col/100 lead zinc (mg/L) (°C) (mg/L) (mg/L as P) mL) (μg/L) (μg/L) saturation) at 25 °C) (mg/L) (mg/L as N) mL) (μg/L) (μg/L)

Site 4, Wilson Creek near Brookline (07052152)

Number of samples 118 119 117 119 119 57 85 116 111 94 117 35 35 33 35Censored values 0 0 0 0 0 0 69 0 0 0 0 25 18 0 0Minimum 13 7.5 95 297 10.5 89 <10 1 .09 2 1 <1 <1 15 1625th percentile 38 13.0 154 840 15.4 180 <10 7 .23 16 30 <1 <1 27 26Median 48 14.6 166 957 19.3 190 <10 10 .43 73 100 <1 <1 39 4075th percentile 63 16.5 175 1,100 23.0 220 <10 14 2 175 330 1 2 59 51Maximum 340 19.9 202 1,400 28.0 230 62 28 6 4,800 7,500 7 7.8 132 130

Site 5, Current River at Doniphan (07068000)

Number of samples 193 191 191 193 193 66 126 192 179 132 192 55 55 53 52Censored values 0 0 0 0 0 0 88 1 144 0 0 45 31 34 30

Minimum 940 4.4 56 140 2.3 100 <10 <.06 <.06 1 1 <1 <1 <4 <2

25th percentile 1,500 8.4 88 271 10.3 150 <10 .20 <.06 2 4 <1 <1 <4 <2Median 2,000 9.4 95 305 15.4 165 <10 .24 <.06 6 11 <1 <1 <4 <275th percentile 3,100 10.6 103 329 21.4 180 10 .30 <.06 16 29 <1 1.5 4 2.1Maximum 36,400 14.2 132 423 28.5 200 470 .60 .43 1,900 5,700 4 19 51 30

Site 6, Elk River near Tiff City, Missouri (07189000)

Number of samples 185 169 168 183 183 86 111 186 179 155 175 53 39 50 39Censored values 0 0 0 0 0 0 89 1 9 0 0 47 31 34 22

Minimum 12 4.5 61 190 3.9 95 <10 <.06 <.06 1 1 <1 <1 <4 <2

25th percentile 160 8.4 88 272 10.3 130 <10 1.1 .06 10 17 <1 <1 <4 <2Median 460 9.7 100 294 16.0 135 <10 1.6 .06 21 33 <1 <1 <4 <275th percentile 1,100 11.8 115 317 22.6 140 <10 1.9 .13 49 82 <1 <1 4 2Maximum 9,700 18.1 169 440 31.8 160 130 3.6 .50 7,200 13,000 1 1.5 33 5
14 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

Water-quality standards for DO, water temperature, fecal 

indicator bacteria, and trace elements are listed in Missouri 

Department of Natural Resources (2008). These criteria are 

modified every 3 years to assess the current water-quality 

conditions. The criteria are based on several different stream 

classifications as defined by the MDNR. Some of the streams, 

or sections of the streams in which the sites are located, are 

classified in three or more of the following categories: irrigation; livestock and wildlife watering; protection of aquatic 

life; drinking-water supply; whole-body contact recreation, 

such as swimming (class A) and less frequently used waters 

(class B); secondary-contact recreation, such as boating or 

streambank activities such as fishing, where body contact with 

the water can be possible; and cool- and cold-water fisheries. 

The six sites and the Missouri stream classifications and use 

designations are listed in table 3. Not all of the classifications 

and use designations listed apply to the location of the sites 

used in this study; however, the State criteria are shown on the 

boxplots in figure 6 as a reference.

Streamflow, Dissolved Oxygen, Physical 

Properties, and Total Suspended Solids 

Streamflow varied at each site because of drainage area, 

land use, and groundwater inputs. Instantaneous streamflow 

measured at the time the surface water-quality samples were 

collected has been used to evaluate the status of conditions 

over the study period. Median instantaneous streamflows 

ranged from 48 cubic feet per second (ft3

/s) at site 4 to 2,000 

ft3

/s at site 5. All six sites had statistically different median 

streamflows for the study period except sites 2 and 3 (fig. 6). 

Site 2 has a drainage area almost three times larger than site 3; 

and the drainage areas of sites 3 and 5 are similar (table 1). 

Springs, which contribute substantially to streamflow in 

the Ozark Plateaus, are prevalent in the Salem Plateau. Big 

Spring, which is the largest spring in the Ozark region of 

Missouri and Arkansas (Vineyard and Feder, 1974) with a 

mean discharge of 446 ft3

/s (U.S. Geological Survey, 2010), is 

located upstream from site 5. 

The DO was determined by two different measurements—concentration in milligrams per liter and percent 

saturation. The State criteria for DO refer to the milligrams per 

liter measurement and require a value no less than 5 milligrams per liter (mg/L) for warm-water and cool-water fisheries 

and 6 mg/L for cold-water fisheries (Missouri Department of 

Natural Resources, 2008; fig. 6). Most of the statistical analyses in this study used percent saturation of DO. Median DO 

concentration and percent saturation ranged from 9.1 mg/L 

at site 3 to 14.6 mg/L at site 4 and 90 percent at site 2 to 166 

percent at site 4 (table 2). The graphical representation of DO 

in milligrams per liter and percent saturation indicates site 4 as 

the most significantly different (fig. 6). Site 4 is located downstream from the Springfield SWWTP and is the only urban site 

in the study (fig. 1). Wastewater-treatment (WWT) facilities 

generally use ozone during the disinfection treatment. Ozone 

is unstable and once released from the SWWTP, decays to 

ordinary diatomic oxygen when mixed with the native stream 

waters, resulting in super saturation conditions likely causing 

the elevated DO measurements at site 4.

Specific conductance measurements provide an indication of dissolved ion concentrations. Median specific conductance values ranged from 294 microsiemens per centimeter 

at 25 degrees Celsius (μS/cm at 25 oC) at site 6 to 957 μS/cm 

at 25 o

C at site 4 (table 2). Specific conductance was similar 

between the most northern sites (sites 1 and 2) and between 

the most southern sites (sites 5 and 6; fig. 6). The IQR at sites 

3, 5, and 6 is smaller than at the other sites (fig. 6). Springs 

contribute to streamflow at these three sites throughout the 

year. Spring discharge is dependent on the amount of rainfall 

that infiltrates to the subsurface. The specific conductance of 

the spring water is determined by subsurface residence time 

and is fairly constant throughout the year, thus attenuating 

changes in specific conductance in the stream. Springs do not 

contribute substantially to the streamflow at sites 1 and 2, and 

thus specific conductance tended to increase as precipitation 

Table 3. State stream classifications and use designations of site streams.

[USGS, U.S. Geological Survey; IRR, irrigation; LWW, livestock and wildlife watering; AQL, protection of aquatic life; DWS, 

drinking-water supply; WBC, whole-body contact recreation; SCR, secondary contact recreation; CLF, cool-water fishery; 

CDF, cold-water fishery; X, designation applies; --, not applicable]

Site 

number 

(fig. 1)

USGS 

station 

number

Stream 

Classification/use designationa

IRR LWW AQL DWS WBC SCR CLF CDF

1 05500000 South Fabius River X X X -- X -- -- --

2 06902000 Grand River X X X X X X -- --

3 06930800 Gasconade River -- X X -- X X X --

4 07052152 Wilson Creek -- X X -- X -- -- --

5 07068000 Current River -- X X -- X X -- X

6 07189000 Elk River X X X -- X X X --

a

Recreation classifications and use designations as listed in Missouri Department of Natural Resources (2008). Stream 

reaches in which the listed classification and uses are shown may vary and may not include the site location. 
Assessment of Water Quality 15 Figure 6. Selected constituents by site, water years 1993 through 2008.

PERCENT SATURATION

Dissolved oxygen

50

250

200150100

0

0

MICROSIEMENS PER CENTIMETER 

AT 25 DEGREES CELSIUS 800 600 400

200

1,6001,4001,2001,000

Dissolved oxygen

25201510

50

MILLIGRAMS PER LITER

10

MILLIGRAMS PER LITER (mg/L) 50 500 100 1,000

Total suspended solids

1,500

0

DEGREES CELSIUS

Water temperature

40302010

CUBIC FEET PER SECOND

0.1

1

10

100

1,000

10,000

100,000

o

xxxxxx

xxx

o

xxxxx

xxxx

xxxx

xxxx

185 188 188 117 191 168

BC A AB E BC CD

Specific conductance

xx o

ooo

xxxxxx

o

xx

xxx

xxx

186 189 188 119 193 183

BC C B

D

A A

1 2 3 4 5 6

SITE

o o

x

xxxx

oooooooooooo

xxxxx

ooooo

oooooooooo

ooooooooo

121 98 99 85 126 111

METHOD REPORTING LEVEL = 10 mg/L

B C A A A A

1 2 3 4 5 6

Instantaneous streamflow

x

xx

o

xxx

o

xxxxx

187 190 188 118 193 185

B D D A E C

x

x

xxxx

x

187 189 188 119 191 169

B AB A C AB AB

187 191 188 119 193 183

A A A B A AB

1 2 3 4 5 6

State criteria for cool-water fisheryState critieria for cold-water fishery

30 Number—Number of samples 

EXPLANATION 

o

xx

o

Upper far-out valueUpper outlierUpper adjacent75th percentileMedian25th percentileLower adjacentLower outlierLower far-out value

A Distributions associated with the same letter for each constituent are not significantly different (p-value less than 0.05)

Laboratory reporting levelAverage State criteria (based on mean of 25th percentile of water hardness concentrations) for acute zinc allowed in the protection of aquatic lifeState critieria for whole-body contact (class A) recreationState critieria for whole-body contact (class B) recreationState critieria for secondary-contact recreation

Geometric mean calculated for the recreational season (April–October) during study period

1,000,000
16 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

COLONIES PER 100 MILLILITER 10 100 1,000 10,000

100,000

Escherichia coli

1

MICROGRAMS PER LITER (μg/L)50

100

51

10

COLONIES PER 100 MILLILITER MICROGRAMS PER LITER (μg/L)

1

100

5

5010

51

Total phosphorous

0.05

0.50.1

0.01

xx

ooooooooooooo

ooooo

x

176 175 173 111 179 179

LABORATORY REPORTING LEVEL = 0.06 mg/L

C D B E A C

SITE

SITE

xx

oooooo

x

oo

xxxx

o

Total recoverable lead

LABORATORY REPORTING LEVEL = 1 μg/L

50 32 33 35 55 39

BC C AB ABC ABC A

1 2 3 4 5 6

1

10

100

1,000

10,000

100,000

1,000,000

x

xxxxxx x

xxx

o

xxxxxxxxxxxxx

186 188 184 117 192 175

Fecal coliform

D D B D A C

MILLIGRAMS PER LITER (mg/L)

Dissolved nitrate plus nitrite (as nitrogen)

1

10

0.1

0.01

xxxx

o

xxx

xxxxxxx

o

LABORATORY REPORTING LEVEL = 0.06 mg/L

186 189 184 192 186 116

AB B AB D A C

5010

100

51

Total recoverable zinc

oo

x

ooooooo

ooooo

LABORATORY REPORTING LEVEL = 2 μg/L 

44 32 33 35 52 39

BC C AB D A A

1 2 3 4 5 6

xx

xxx xx

x

o

xxxxxxxx

132 127 130 94 132 155

C C A C A B

ooooooooooo

ooooo

ooooo

oooooooo

oooooooooo

47 29 30 33 53 50

Dissolved zinc

LABORATORY REPORTING LEVEL= 4 μg/L 

A A A B A A

1 2 3 4 5 6

SITE

Figure 6. Selected constituents by site, water years 1993 through 2008.—Continued
Assessment of Water Quality 17

decreases, and dilution of ions is less likely to occur (Vineyard 

and Feder, 1974). The overall effect is a wider range of specific conductance values at sites 1 and 2 than at sites 3, 5, and 

6 as illustrated by the IQR (table 2).

Water temperature was similar for all sites in the study 

except site 4; however, sites 4 and 6 were similar. Site 4 has 

a substantially smaller drainage area and streamflow than the 

other sites (table 1; fig. 6), and much of the flow is contributed 

by discharges from the Springfield SWWTP, particularly at 

low flow. Water temperatures would be expected to be greater 

at site 4 than the other sites and less affected by ambient air 

temperatures. Large variations were shown in sites 1 and 2 

(fig. 6). Both sites are located in the northern one-half of the 

State and are more susceptible to freezing conditions in the 

winter, yet still had a large increase in temperatures during the 

summer.

The TSS concentrations generally were reported at the 

MRL of 10 mg/L, except for sites 1 and 2 and some samples 

collected during higher streamflows at all sites (fig. 6). Median 

and maximum TSS concentrations were 17 and 2,000 mg/L at 

site 1 and 81 and 2,400 mg/L at site 2 (table 2). The median 

at the remaining sites was less than (<) 10 mg/L, and the largest maximum concentration at sites other than sites 1 and 2 

was 470 mg/L at site 5. Streams in northern Missouri are 

more turbid than southern streams and are affected by large 

volumes of sediment deposition because of soil erosion from 

land cultivated for row crops (Missouri Department of Natural 

Resources, 2009).

Nutrients

Nutrients, such as nitrogen and phosphorus, are important to all life and can be introduced to surface waters from 

natural or human influences. Some natural sources of nutrients are runoff from forests or other natural habitats, erosion 

of soils, and decay of plants and animals. Human influenced 

sources of nutrients can be from sewage effluent, leaking 

septic tanks, waste runoff from urban areas, improper management of concentrated animal feeding operations (CAFO), 

runoff from fertilized fields, pasturelands where cattle are 

grazed and where manure has been applied as fertilizer, and 

industrial or domestic waste discharges. Dissolved nitrate 

plus nitrite and total phosphorus concentrations were chosen 

to determine the nutrient status at the sites because nutrients 

in these forms most commonly are found in natural waters, 

and the laboratory methods have not varied during the study 

period.

Dissolved nitrate plus nitrite concentrations were significantly different at sites 4 and 6 than other sites (fig. 6). Median 

dissolved nitrate plus nitrite concentrations ranged from 0.24 

mg/L at sites 3 and 5 to 10 mg/L at site 4 (table 2; fig. 6). Dissolved nitrate plus nitrite concentrations ranged from 1 mg/L 

to 28 mg/L at site 4 throughout the study period. Nitrogen 

concentrations, including nitrate plus nitrite, can be large in 

WWT plant effluent, and when concentrations are large, algal 

blooms in receiving streams can result. The lowest median 

dissolved nitrate plus nitrite concentrations were detected at 

sites 3 and 5, which are located in predominantly forested 

areas where there are fewer nutrient sources. The large amount 

of row crop agriculture in the basins containing sites 1 and 2 

could produce larger concentrations of dissolved nitrate plus 

nitrite as the result of fertilizer use and soil erosion. Livestock, 

such as hogs and cattle, also are prevalent near sites 1 and 

2. Site 6 is located in an agricultural area as well but mostly 

consists of poultry and cattle production rather than row crops. 

The water-quality standard for nitrate as nitrogen is 10 mg/L 

for a drinking-water supply (Missouri Department of Natural 

Resources, 2008). 

Median total phosphorus concentrations ranged from 

<0.06 mg/L at site 5 to 0.43 mg/L at site 4 (table 2; fig. 6). In 

1993, the Springfield SWWTP completed facility improvements that decreased the phosphorus concentration in 

effluent discharged into Wilson Creek by an average of 40 

percent. In March 2001, the SWWTP introduced an advanced 

phosphorus reduction system, which decreased the typical 

phosphorus discharge levels to less than 0.5 mg/L (City of 

Springfield, 2009); the median total phosphorus concentration at site 4 was 0.43 mg/L. Of the three sites in basins 

containing large percentages of agricultural land (sites 1, 2, 

and 6; table 1; fig. 3), the median total phosphorus concentration at site 2 was significantly different. Total phosphorus 

concentrations never exceeded 0.5 mg/L at sites 3 and 5 during the study period.

Fecal Indicator Bacteria

Of the constituents analyzed in this study, fecal indicator bacteria are among the most stringently monitored by the 

MDNR. The fecal indicator bacteria standards apply only to 

the recreational period of April 1 through October 31. The 

E coli standard began in 2005 and was the only whole-bodycontact standard used after December 31, 2008; fecal coliform 

was used for the State standard before that date. Missouri has 

three recreational classes of waters: (1) whole-body contact 

class A (WBC-A) used for high-use waters; (2) whole-body 

contact class B (WBC-B) for less frequently used waters; and 

(3) secondary-contact recreation (SCR) such as fishing, wading, boating, or any other activity that does not involve swimming or floating in the water (Missouri Department of Natural 

Resources, 2008). 

The MDNR uses a geometric mean of all samples 

collected at a particular site during the recreation period 

to determine if the E. coli standard has been exceeded. A 

geometric mean is the average of the natural logarithms converted back to their original units and should be close to the 

median (Helsel and Hirsch, 2002). The current standard for 

E. coli is 126 colonies per 100 milliliters (col/100 mL) for 

WBC-A, 206 col/100 mL for WBC-B, and 1,134 col/100 mL 

for SCR waters (Missouri Department of Natural Resources, 

2008; table 4). The whole-body-contact standards apply to 

most stream reaches where the sites are located. The sites 

and their State classification are listed in table 4, as well as 
18 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

the geometric mean computed for the recreational seasons 

during the study period. The geometric mean for each site 

also is included on figure 6 for comparison with the median 

densities.

The geometric means of E. coli were calculated from 

the recreational seasons within the study period, and they 

indicate that only site 2 exceeded the WBC-A standard of 

126 col/100 mL by 55 colonies (table 4; fig. 6). The WBC-B 

and SCR standards (206 col/mL and 1,134 col/mL) were not 

exceeded at any sites within the recreational seasons during 

the study period. The geometric means of the E. coli densities 

ranged from 7 col/100 mL at site 5 to 181 col/100 mL at site 

2 (table 4; fig. 6). The geometric means and median densities 

of E. coli were relatively similar at all sites except sites 1 and 

2; the geometric means were nearly twice the median densities at both sites relative to the other four sites (table 4). The 

difference in the geometric mean of the seasonal data and the 

median density of all data collected at sites 1 and 2 possibly 

was the result of larger streamflows during sample collection or because higher colony densities were measured during 

the recreational season than during the winter at these two 

sites. Fecal indicator bacteria generally are associated with 

suspended sediment. Sites 1 and 2 are located on streams in 

northern Missouri that are more turbid because of soil erosion. Although bacteria density increases generally are related 

to suspended sediment increases in surface water (Wilkinson 

and others, 1995), regression analyses at the predominantly 

agricultural sites were not possible. No suspended-sediment 

concentrations were collected at the sites, and the TSS concentration data were only collected two to four times per water 

year until the 2001 water year, which created a small dataset 

for linear regressions.

The fecal indicator bacteria show median densities 

for all sites were at or less than the State standards for the 

study period (table 2; fig. 6). Median densities ranged from 6 

col/100 mL at site 5 to 73 col/100 mL at site 4 for E. coli, and 

11 col/100 mL at site 5 to 160 col/100 mL at site 2 for fecal 

coliform (table 2). The largest maximum densities were at 

site 1 (62,000 col/100 mL for E. coli and 160,000 col/100 mL 

for fecal coliform) and site 2 (25,000 col/100 mL for E. coli

and 120,000 col/100 mL for fecal coliform). These sites 

are located in agricultural areas, where large CAFOs are in 

operation and manure is used as fertilizer on crop and pastureland. Median densities at site 4 for both fecal indicator 

bacteria types (73 col/100 mL for E. coli and 100 col/100 mL 

for fecal coliform) were similar to sites 1 and 2. However, 

the maximums for each (4,800 col/100 mL for E. coli and 

7,500 col/100 mL for fecal coliform) were more similar to 

the maximum for site 3 (5,200 col/100 mL for E. coli and 

8,200 col/100 mL for fecal coliform), which is mostly forested 

(table 1). Similarities between sites were consistent between 

the two fecal indicator bacteria types. Sites 1, 2, and 4 were 

statistically similar for both E. coli and fecal coliform. Sites 3 

and 5 had similar E. coli densities, but different fecal coliform 

densities. Site 6 was significantly different from all sites for 

both fecal indicator bacteria types (fig. 6).

Most of the fecal indicator bacteria samples were collected during base-flow conditions through the study period, 

but some samples were collected during high-flow conditions 

(fig. 7). In addition, samples collected at the six sites were 

distributed rather equally among the recreational period (April 

through October) and the non-recreational months (November 

through March; fig. 8). Samples were collected during a larger 

range of streamflow conditions for sites 1, 2, and 6, resulting 

in a larger range in bacteria densities (fig. 7). Sites 1, 2, and 6 

Table 4. Recreational classes, State standards, geometric means pertaining to the State Escherichia coli 

standards during the recreational season (April to October), and median values, water years 1993 through 2008.

[USGS, U.S. Geological Survey; col/100 mL, colonies per 100 milliliters; WBC, whole-body-contact recreation; B, less frequently used 

waters; --, not applicable; A, high-use waters; SCR, secondary-contact recreation]

Site 

number 

(fig. 1)

USGS 

station 

number

Stream 

Recreation classa State standard for class Geometric 

mean 

(col/100 mL)

Medianb

Primary Secondary Primary Secondary (col/100 mL)

1 05500000 South Fabius River WBC-B -- 206 -- 121 65

2 06902000 Grand River WBC-A SCR 126 1,134 181 66

3 06930800 Gasconade River WBC-A SCR 126 1,134 13 10

4 07052152 Wilson Creek WBC-B -- 206 -- 74 73

5 07068000 Current River WBC-A SCR 126 1,134 7 6

6 07189000 Elk River WBC-A SCR 126 1,134 30 21

a

Recreation classifications as listed in Missouri Department of Natural Resources (2008). Stream reaches in which the listed classification are shown may vary and may not include the site location. 

b

Median values also shown in table 2 and are calculated from all available data from water years 1993 through 2008.
Assessment of Water Quality 19

STREAMFLOW, IN CUBIC FEET PER SECOND

0.1

1

10

100

1,000

10,000

100,000

0.1

1

10

100

1,000

10,000

100,000

0.1

1

10

100

1,000

10,000

100,000

FECAL COLIFORM, IN COLONIES PER 100 MILLILITERS

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

Site 1 Site 2

Site 3 Site 4

Site 5 Site 6

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

EXPLANATION

Sample

0.1

1

10

100

1,000

10,000

100,000

ESCHERICHIA COLI, IN COLONIES PER 100 MILLILITERS

0.1

1

10

100

1,000

10,000

100,000

0.1

1

10

100

1,000

10,000

100,000

Site 1 Site 2

Site 3 Site 4

Site 5 Site 6

Figure 7. Relation of Escherichia coli and fecal coliform bacteria density to streamflow, water 

years 1993 through 2008.
20 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

MONTH

FECAL COLIFORM, IN COLONIES PER 100 MILLILITERS

0.1

1

10

100

1,000

10,000

100,000

0.1

1

10

100

1,000

10,000

100,000

0.1

1

10

100

1,000

10,000

100,000

0.1

1

10

100

1,000

10,000

100,000

0.1

1

10

100

1,000

10,000

100,000

0.1

1

10

100

1,000

10,000

100,000

ESCHERICHIA COLI, IN COLONIES PER 100 MILLILITERS

Site 1 Site 2

Site 3 Site 4

Site 5 Site 6

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

Site 1 Site 2

Site 3 Site 4

Site 5 Site 6

EXPLANATION

Sample

Figure 8. Relation of Escherichia coli and fecal coliform bacteria density to month, water years 

1993 through 2008.
Assessment of Water Quality 21

also drain a large percentage of agricultural land (table 1). 

Fecal indicator bacteria densities can increase in streams 

because of runoff from row crops as well as pasturelands 

where cattle are grazed and where manure has been applied as 

fertilizer, and as a result of improperly managed animal waste 

from hog and poultry production in CAFOs (Francy and others, 2000). 

Trace Elements

Water samples collected at the sites also were analyzed 

for selected trace elements, including dissolved and total 

recoverable lead and zinc. The State standards for lead and 

zinc vary with the hardness of the water and stream classifications (Missouri Department of Natural Resources, 2008). 

Dissolved lead concentrations analyzed during the study 

period seldom exceeded the LRL of 1 μg/L (table 2) and are 

not shown in figure 6. Most total recoverable lead concentrations were equal to or less than the LRL at sites 3, 4, 5, 

and 6. Median total recoverable lead concentrations at site 2 

were significantly different from those at the other sites. The 

largest total recoverable lead concentrations were detected in 

samples from sites 1 (64 μg/L) and 2 (65 μg/L). Trace elements, including lead, generally are associated with suspended sediment, and concentrations will tend to increase as 

suspended-sediment concentrations increase (Hem, 1985). No 

suspended-sediment concentration data were collected during 

the study period, but TSS data were available. To determine 

if total recoverable lead and zinc data from sites 1 and 2 are 

correlated with TSS, regression analyses were performed 

(fig. 9). The correlation used Kendall’s tau and measured 

the strength of association between two constituents (Helsel 

TOTAL RECOVERABLE LEAD,IN MICROGRAMS PER LITER

TOTAL RECOVERABLE ZINC,IN MICROGRAMS PER LITER

TOTAL SUSPENDED SOLIDS, IN MILLIGRAMS PER LITER

0

10

20

30

40 Site 1

R2=0.94

y= 1.03x+0.018

0

20

40

60

80 Site 2

R2

y= 0.26x+0.03

=0.87

0

20

40

60

80

100

120 Site 1

0 500 1,000 1,500 2,000

R2

y= 2.9x+0.06

=0.93

0

50

100

150

Site 2

0 500 1,000 1,500 2,000 2,500

R2

y= 2.4x+0.074

=0.93

EXPLANATION

R2 Correlation coefficient

Line equation

Sample

y= 1.03x+0.018

Figure 9. Correlation of total recoverable lead and zinc with total suspended solids at sites 1 and 2, water years 

1993 through 2008.
22 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

and Hirsch, 2002). A completely linear correlation will have 

a correlation coefficient (R2

) equal to 1. The R2 values were 

greater than 0.80 for both total recoverable lead and zinc with 

TSS at sites 1 and 2, indicating good correlations (fig. 9). One 

data point (sample collected on January 6, 1993) was removed 

from the total recoverable lead dataset for the correlation 

analysis at site 1, which made the R2 value more representative of the entire dataset. The total recoverable lead outlier did 

not fit historical data and could not be associated with higher 

streamflow or other possible effects. Before this data point was 

removed, the correlation was poor (R2

 = 0.26). 

Median dissolved zinc concentrations for all sites were 

equal to the LRL of 4 μg/L except at site 4. Median total 

recoverable zinc concentrations were at or less than the LRL 

of 2 μg/L at sites 3, 5, and 6, and similar to total recoverable lead. Sites 1 (3 μg/L) and 2 (6 μg/L) had median total 

recoverable zinc concentrations significantly larger than 

concentrations at sites 3, 5, and 6. The median concentrations 

of dissolved and total recoverable zinc were 39 and 40 μg/L 

at site 4, which were significantly larger than the other sites. 

The typical zinc concentration in effluent from the SWWTP is 

40 μg/L (City of Springfield, 2009). 

State water-quality standards for lead and zinc are 

in place for the protection of aquatic life, drinking water, 

and groundwater uses. The State criteria for aquatic life 

protection are based on dissolved trace element concentrations, except mercury, whereas drinking water and all other 

beneficial uses are based on total recoverable trace element 

concentrations (Missouri Department of Natural Resources, 

2008). The State standard for lead is 15 μg/L and 5,000 μg/L 

for zinc in drinking water (Missouri Department of Natural 

Resources, 2008). The lower 56 river miles of the Grand 

River is the only stream reach designated as a drinking-water 

supply source. To calculate the State criteria for select trace 

elements for the protection of aquatic life, the water hardness 

is used. The State determines the hardness of the stream in 

question by calculating the 25th percentile of a representative 

number of samples from the water body in question (Missouri Department of Natural Resources, 2008). Each site in 

the study has different water hardness (table 2), but for comparison purposes, the mean of the 25th percentiles of hardness 

concentrations for all sites was computed to get a mean hardness for the six sites studied, which was then used to find the 

chronic toxicity concentration to aquatic life for dissolved 

lead and zinc. The mean of the 25th percentile of hardness 

concentrations for all sites was about 145 mg/L. The corresponding chronic toxicity concentration for dissolved lead 

was about 3 μg/L, and the chronic toxicity concentration for 

dissolved zinc was about 129 μg/L (fig. 6). Samples with 

concentrations of dissolved lead and zinc that exceeded 

chronic toxicity concentrations were less than 25 percent of 

the total number of samples from all sites (fig. 6; table 2).

Long-Term Trends

Long-term trends were analyzed for each site and constituent. The number of seasons used in the trend tests was 

analyzed, and 12 seasons (or monthly analyses) best represented all sites in the study, except site 4. Because site 4 has 

the smallest dataset, the best seasonal analysis for constituents 

collected during the study period was six (or bi-monthly). 

Some constituents were analyzed using a flow-adjusted trend 

test, whereas datasets with greater than 5 percent but less 

than or equal to 50 percent censored values, were analyzed 

by non-flow adjusted trend tests. Because datasets with more 

than 50 percent censored values can decrease the power of a 

trend test, no trend test was conducted on any constituent with 

censoring above this level. All TSS, dissolved lead, and total 

recoverable lead values were censored greater than 5 percent, 

but only sites 1 and 2 had less than 50 percent censored datasets. Data inputs for each model and the model outputs for flow 

and non-flow adjusted trends are in tables 5 and 6.

When flow-adjusted trend analyses were used, a large 

part of the variability in concentrations because of the natural 

fluxes in streamflow was removed, allowing for trends caused 

by other occurrences such as human-influenced effects to be 

assessed directly. When no flow adjustment could be used, all 

aspects of variability from natural and human influences were 

evaluated simultaneously. 

Flow-Adjusted Trends

Dissolved Oxygen and Physical Properties

DO, specific conductance, and water temperature were 

analyzed for long-term trends using flow-adjusted models. 

No data were censored for DO and any physical properties 

(table 5).

No significant long-term trends were detected for DO or 

water temperature. The p-values calculated by the trend tests 

indicated no significant differences during the study period 

(p-value < 0.05). Trends in water temperature would be rare 

because it is seasonally dependent and follows a diurnal or 

sinusoidal trend both daily and seasonally. Significant trends 

in specific conductance were determined for three sites; a 

downward trend at site 1 and upward trends at sites 3 and 6 

(table 5; fig. 10). Many natural and human-influenced occurrences can cause an increase or decrease in dissolved ion 

concentrations, thus causing a similar change in specific conductance. These occurrences could be because of increased 

contaminant loadings, such as wastewater discharges or land 

application of wastes. 

Nutrients

Flow-adjusted models were used for dissolved nitrate 

plus nitrite datasets at all sites except sites 1 and 2, which 

contained more than 5 percent censored values. Of the four 
Assessment of Water Quality

23

Table 5. Model output for flow-adjusted trends in concentrations, water years 1993 through 2008.—Continued[USGS, U.S. Geological Survey; R2, coefficient of determination between observed and predicted concentrations; significant trend if p-value is less than 0.05; --, poor model fit]

Site 

number 

(fig. 1)

USGS

 station 

number

Model calibration information Model properties

Median 

value

Number 

of 

samples

Number of 

censored 

values

Dataset 

start 

date

Dataset 

end 

date

Number 

of 

seasons

Coefficient R2

p-value 

(from 

trend test)

Model 

estimated 

trend 

(percent per 

year)

Trend 

significance

Dissolved oxygen, in percent saturation

1 05500000 96 185 0 11/18/1992 9/3/2008 12 60 0.03 0.79 -0.08 None2 06902000 90 188 0 11/12/1992 9/2/2008 12 114 .12 .48 -.27 None

3 06930800 91 188 0 11/17/1992 9/3/2008 12 96 .03 .54 -.08 None4 07052152 166 117 0 11/24/1993 9/4/2008 6 174 .14 .74 .01 None5 07068000 95 191 0 11/12/1992 9/8/2008 12 132 .05 .46 -.17 None6 07189000 100 168 0 11/18/1992 9/9/2008 12 106 .04 .78 -.09 None

Specific conductance, in microsiemens per centimeter at 25 degrees Celsius

1 05500000 360 186 0 11/18/1992 9/3/2008 12 91 0.43 0.03 -1.4 Down

2 06902000 387 189 0 11/12/1992 9/2/2008 12 717 .56 .11 -.54 None3 06930800 329 188 0 11/17/1992 9/3/2008 12 -115 .36 .004 .30 Up

4 07052152 957 119 0 11/24/1993 9/4/2008 6 6.8 .59 .19 -.65 None

5 07068000 305 193 0 11/12/1992 9/8/2008 12 733 .73 .32 .13 None

6 07189000 294 183 0 11/18/1992 9/9/2008 12 228 .47 .01 .71 Up

Water temperature, in degrees Celsius

1 05500000 13.8 187 0 11/18/1992 9/3/2008 12 11.4 0.02 0.66 -0.23 None

2 06902000 12.7 191 0 11/12/1992 9/2/2008 12 13.3 .002 .12 .59 None

3 06930800 15.8 188 0 11/17/1992 9/3/2008 12 9.8 .12 .90 -.09 None

4 07052152 19.3 119 0 11/24/1993 9/4/2008 6 14.6 .13 .23 .31 None

5 07068000 15.4 193 0 11/12/1992 9/8/2008 12 10.4 .08 .14 .50 None

6 07189000 16.0 183 0 11/18/1992 9/9/2008 12 14.4 .10 .30 .43 None

Dissolved nitrate plus nitrite (as nitrogen), in milligrams per liter

1 05500000 -- -- -- -- -- -- -- -- -- -- --

2 06902000 -- -- -- -- -- -- -- -- -- -- --

3 06930800 0.24 184 2 11/17/1992 9/3/2008 12 -1.4 0.44 0.75 0.5 None

4 07052152 10 116 0 11/24/1993 9/4/2008 6 -15.6 .16 .61 .97 None

5 07068000 .24 192 1 11/12/1992 9/8/2008 12 .34 .25 .73 -.2 None6 07189000 1.6 186 1 11/18/1992 9/9/2008 12 2.03 .36 .04 1.8 Up
24 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri Table 5. Model output for flow-adjusted trends in concentrations, water years 1993 through 2008.—Continued [USGS, U.S. Geological Survey; R2, coefficient of determination between observed and predicted concentrations; significant trend if p-value is less than 0.05; --, poor model fit] Model calibration information Model propertiesModel Site USGS Number Number of Dataset Dataset Number p-value estimated number station Median Trend of censored start end of Coefficient R2 (from trend (fig. 1) number value significance samples values date date seasons trend test) (percent per year) Total phosphorus, in milligrams per liter 1 05500000 0.10 176 12 11/18/1992 9/3/2008 12 -2.1 0.58 0.005 3.2 Up 2 06902000 .20 175 1 11/12/1992 9/2/2008 12 -1.5 .51 .01 8.8 Up 3 06930800 -- -- -- -- -- -- -- -- -- -- -- 4 07052152 .43 111 0 11/24/1993 9/4/2008 6 .1 .11 .004 -38 Down 5 07068000 -- -- -- -- -- -- -- -- -- -- -- 6 07189000 .06 179 9 11/18/1992 9/9/2008 12 .09 .09 .61 -33 None Escherichia coli, in colonies per 100 milliliters 1 05500000 65 132 0 10/16/1997 9/3/2008 12 13,826 0.24 0.89 -3.2 None 2 06902000 66 127 0 10/21/1997 9/2/2008 12 4.7 .42 .60 -57 None 3 06930800 10 130 0 10/8/1997 9/3/2008 12 5,573 .45 .88 -8 None 4 07052152 70 94 0 11/5/1997 9/4/2008 6 2,485 .14 .08 -45 None 5 07068000 6 132 0 10/22/1997 9/8/2008 12 -513 .03 .73 -5.9 None 6 07189000 21 155 0 5/18/1994 9/9/2008 12 -155 .63 .48 21 None Fecal coliform, in colonies per 100 milliliters 1 05500000 115 186 0 11/18/1992 9/3/2008 12 18,702 0.12 0.19 18.6 None 2 06902000 160 188 0 11/12/1992 9/2/2008 12 4.7 .43 .74 -17.7 None 3 06930800 18 184 0 11/17/1992 9/3/2008 12 -267 .69 .62 8.8 None 4 07052152 100 117 0 11/24/1993 9/4/2008 6 3,099 .15 .31 -12.4 None 5 07068000 11 192 0 11/12/1992 9/8/2008 12 -1,650 .09 .18 30.6 None 6 07189000 33 175 0 11/18/1992 9/9/2008 12 -255 .52 .15 30.4 None Dissolved zinc, in micrograms per liter 1 05500000 -- -- -- -- -- -- -- -- -- -- -- 2 06902000 -- -- -- -- -- -- -- -- -- -- -- 3 06930800 -- -- -- -- -- -- -- -- -- -- -- 4 07052152 39 33 0 1/26/1994 7/16/2008 4 19 0.02 0.006 -7.3 Down 5 07068000 -- -- -- -- -- -- -- -- -- -- -- 6 07189000 -- -- -- -- -- -- -- -- -- -- -- Total recoverable zinc, in micrograms per liter 1 05500000 -- -- -- -- -- -- -- -- -- -- -- 2 06902000 -- -- -- -- -- -- -- -- -- -- -- 3 06930800 -- -- -- -- -- -- -- -- -- -- -- 4 07052152 39 35 0 1/26/1994 7/16/2008 4 31 -0.02 0.002 -5.8 Down 5 07068000 -- -- -- -- -- -- -- -- -- -- -- 6 07189000 -- -- -- -- -- -- -- -- -- -- --
Assessment of Water Quality

25

Table 6. Model output for non-flow adjusted trends in concentrations, water years 1993 through 2008.—Continued[USGS, U.S. Geological Survey; R2, coefficient of determination between observed and predicted concentrations; significant trend if p-value is less than 0.05; --, poor model fit; Inf, not computed because sign of trend is different from sign of Kendall’s tau]

Site 

number 

(fig. 1)

USGS 

station 

number

Model calibration information Model properties

Median 

value

Number 

of 

samples

Number 

of 

censored 

values

Dataset 

start 

date

Dataset end 

date

Number 

of 

seasons

Coefficient R2

p-value 

(from trend 

test)

Model 

estimated 

trend 

(percent 

per year)

Trend 

significance

Total suspended solids, in milligrams per liter

1 05500000 17 121 35 1/19/2000 9/3/2008 4 -- -- 0.05 9.4 Up

2 06902000 81 98 12 1/4/2000 9/2/2008 4 -- -- .01 10 Up

3 06930800 -- -- -- -- -- -- -- -- -- -- --

4 07052152 -- -- -- -- -- -- -- -- -- -- --

5 07068000 -- -- -- -- -- -- -- -- -- -- --

6 07189000 -- -- -- -- -- -- -- -- -- -- --

Dissolved nitrate plus nitrite (as nitrogen), in milligrams per liter

1 05500000 0.46 186 52 11/18/1992 9/3/2008 12 -- -- 0.51 0.95 None2 06902000 .52 189 50 11/12/1992 9/2/2008 12 -- -- .71 -.64 None3 06930800 -- -- -- -- -- -- -- -- -- -- --

4 07052152 -- -- -- -- -- -- -- -- -- -- --

5 07068000 -- -- -- -- -- -- -- -- -- -- --

6 07189000 -- -- -- -- -- -- -- -- -- -- --

Total phosphorus, in milligrams per liter

1 05500000 -- -- -- -- -- -- -- -- -- -- --

2 06902000 -- -- -- -- -- -- -- -- -- -- --

3 06930800 0.69 173 73 11/17/1992 9/3/2008 12 -- -- 0.61 Inf None

4 07052152 -- -- -- -- -- -- -- -- -- -- --

5 07068000 -- -- -- -- -- -- -- -- -- -- --

6 07189000 -- -- -- -- -- -- -- -- -- -- --
26 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri Table 6. Model output for non-flow adjusted trends in concentrations, water years 1993 through 2008.—Continued [USGS, U.S. Geological Survey; R2, coefficient of determination between observed and predicted concentrations; significant trend if p-value is less than 0.05; --, poor model fit; Inf, not com- puted because sign of trend is different from sign of Kendall’s tau] Model calibration information Model properties Model Site USGS Number Number Dataset Number p-value estimated number station Median of Dataset end Trend of start of Coefficient R2 (from trend trend (fig. 1) number value censored date significance samples date seasons test) (percent values per year) Total recoverable lead, in micrograms per liter 1 05500000 1.0 50 23 1/19/2000 7/8/2008 4 -- -- 0.66 0.60 None 2 06902000 1.8 32 11 1/4/2000 7/9/2008 4 -- -- .21 .22 None 3 06930800 -- -- -- -- -- -- -- -- -- -- -- 4 07052152 -- -- -- -- -- -- -- -- -- -- -- 5 07068000 -- -- -- -- -- -- -- -- -- -- -- 6 07189000 -- -- -- -- -- -- -- -- -- -- -- Total recoverable zinc, in micrograms per liter 1 05500000 3.0 44 5 1/19/2000 7/8/2008 4 -- -- 0.29 Inf None 2 06902000 6.0 32 1 1/4/2000 7/9/2008 4 -- -- .60 0.60 None 3 06930800 2.0 33 7 1/13/2000 7/31/2008 4 -- -- .10 Inf None 4 07052152 -- -- -- -- -- -- -- -- -- -- -- 5 07068000 -- -- -- -- -- -- -- -- -- -- -- 6 07189000 -- -- -- -- -- -- -- -- -- -- --
Assessment of Water Quality 27

50

90

130

170 Site 1

0

40

80

120

Site 2

40

80

120

160 Site 3

80

120

160

200 Site 4

50

70

90

110

130 Site 5

50

70

90

110

130

150

170 Site 6

WATER YEAR

DISSOLVED OXYGEN, IN PERCENT SATURATION

Sample

Raw data trend

Flow-adjusted trend

EXPLANATION

Downward trend

Upward trend

1994 1996 1998 2000 2002 2004 2006 2008 1994 1996 1998 2000 2002 2004 2006 2008 

Figure 10. Flow-adjusted trends in physical properties, water years 1993 through 2008.
28 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

0

200

400

600

100

200

300

400

500

600

100

200

300

400

150

200

250

300

350

400

450

WATER YEAR

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER AT 25 DEGREES CELSIUS

Site 1 Site 2

Site 5 Site 6

1994 1996 1998 2000 2002 2004 2006 2008 1994 1996 1998 2000 2002 2004 2006 2008 

0

200

400

600

800 Site 3

100

500

900

1,300

Site 4

Figure 10. Flow-adjusted trends in physical properties, water years 1993 through 2008.—Continued
0

10

20

30

0

10

20

30

0

5

10

15

20

25

30

10

15

20

25

0

5

10

15

20

25

30

0

10

20

30

WATER YEAR

WATER TEMPERATURE, IN DEGREES CELSIUS

Site 1 Site 2

Site 3 Site 4

Site 5 Site 6

1994 1996 1998 2000 2002 2004 2006 2008 1994 1996 1998 2000 2002 2004 2006 2008 

Figure 10. Flow-adjusted trends in physical properties, water years 1993 through 2008.—Continued
30 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

sites adjusted by streamflow, only site 6 showed a significant 

upward trend (table 5; fig. 11). Site 6 is located in the Elk 

River Basin, which is largely agricultural, including poultry 

(chickens and turkey) and cattle production (table 1; fig. 3). 

Poultry waste is used as a fertilizer for pastureland and row 

crops in the basin and could be introduced to the Elk River 

during storm runoff, increasing the dissolved nitrate plus 

nitrite concentrations. Agricultural statistics from the 1997, 

2002, and 2007 census studies indicate that the number of 

cattle operations in the Elk River Basin, as well as the amount 

of commercial fertilizers applied, have stayed relatively 

stable during the study period, whereas poultry production 

has slightly increased (U.S. Department of Agriculture, 2007; 

table 7). In 1997, 506 operations housing about 25 million 

head of poultry were located in Barry, McDonald, and Newton 

Counties. Fertilizers were applied to about 177,000 acres of 

pasture and row crop fields. In 2007, there were 605 operations housing about 29 million head of poultry, and about 

186,000 acres fertilized. No manure fertilizers were computed 

in the 1997 census to compare to the approximate 85,000 acres 

that were computed during the 2007 census.

The census data obtained from the U.S. Department of 

Agriculture were totaled for all counties containing parts of 

the river basins for sites with significant trends in nutrient concentrations. The animal head and crop counts may be greater 

than the information shown in table 7 because some data were 

not released by the U.S. Department of Agriculture to avoid 

disclosing information for individual farms. The census values 

referred to in this report have been rounded to the nearest 

whole number.

0

1

2

3

Site 6

0.0

0.1

0.2

0.3

0.4

0.5

0.6 Site 5

DISSOLVED NITRATE PLUS NITRITE (AS NITROGEN),

IN MILLIGRAMS PER LITER

0

5

10

15

20

25

Site 4

0.0

0.4

0.8

1.2

Site 3

WATER YEAR

1994 1996 1998 2000 2002 2004 2006 2008 1994 1996 1998 2000 2002 2004 2006 2008 

Sample

Raw data trend

Flow-adjusted trend

EXPLANATION

Downward trend

Upward trend

Figure 11. Flow-adjusted trends in dissolved nitrate plus nitrite (as nitrogen) and total phosphorus 

concentrations, water years 1993 through 2008.
Assessment of Water Quality 31

A USGS study in the Upper Elk River Basin from 2004 

to 2006 (Smith and others, 2007), included the analysis of the 

nutrients in surface water as well as streambed sediments. The 

study determined that nitrate as nitrogen varied in proportion 

to streamflow, indicating the larger concentrations possibly 

were caused by runoff from non-point sources. Seepage runs 

were performed in 2004 and again in 2006 to calculate nutrient 

loads over the course of the study. During the 2006 seepage 

run, nitrate as nitrogen concentrations increased in Little Sugar 

Creek, a tributary of the Elk River, particularly downstream 

from Bella Vista, Arkansas, whereas total phosphorus concentrations decreased (Smith and others, 2007). The population of 

the Bella Vista area as well as the number of large golf courses 

upstream from site 6 has increased during the past several 

years. Increased urban development, in addition to increased 

poultry populations during the study period, possibly caused 

the upward trend in dissolved nitrate plus nitrite concentrations at site 6 (fig. 11). 

Total phosphorus data at all sites contained censored values. Sites 1, 2, 4, and 6 were analyzed by flow-adjusted models, and sites 1, 2, and 4 showed significant long-term trends in 

the data (table 5; fig. 11). Total phosphorus concentrations at 

sites 1 and 2 show an upward trend with time, whereas site 4 

shows a downward trend. 

The increase in total phosphorus concentrations at sites 

1 and 2 possibly was because of the agricultural land use in 

the basin. Cattle and crop production such as corn, soybeans, 

and wheat totaled for counties within the South Fabius River 

Basin (site 1) have stayed relatively stable from the 1997 

agricultural census to the 2007 census (table 7). Poultry and 

hog production have changed substantially within the basin 

counties during the 10-year period. In 1997, the agricultural 

census estimated 153 operations housing about 3,800 head of 

poultry, and 307 hog operations housing about 153,000 hogs 

were located in the South Fabius River Basin counties (U.S. 

Department of Agriculture, 2007; table 7). During the 2002 

census, hog operations had decreased to 181, and the hog 

population decreased to about 138,000 head, whereas the poultry operations and total head increased slightly (241 operations and about 4,900 head). Then during the 2007 census, 

poultry operations stayed about the same (228 operations), 

but the number of poultry increased to about 69,000 head; and 

WATER YEAR

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

0.0

0.1

0.2

0.3

0.4

0.5 Site 6

0

1

2

3 Site 2

0.0

0.4

0.8

1.2

Site 1

Site 4

-2

0

2

4

6

1994 1996 1998 2000 2002 2004 2006 2008 1994 1996 1998 2000 2002 2004 2006 2008 

Figure 11. Flow-adjusted trends in dissolved nitrate plus nitrite (as nitrogen) and total phosphorus 

concentrations, water years 1993 through 2008.—Continued
Table 7. Agricultural census statistics in Missouri counties containing river basins where significant trends in nutrient data were detected.

[--, data not available. Data obtained from U.S. Department of Agriculture, National Agricultural Statistics Service, Census of Agriculture, 1997, 2002, 2007; accessed August 2009 at http://agcensus.usda.gov. Census data were totaled for all counties containing portions of the river basins in which significant trends in nutrient concentrations at study sites were detected. Animal head and crop counts may be greater than shown in table because some data were not released by U.S. Department of Agriculture to avoid disclosing information for individual farms.]

Census 

year

Poultrya Cattleb Hog Crop fields, in acres Fertilizer applied, in acresc

Head Operations Head Operations Head Operations Corn Soybean Wheat Annual total Commerciald Manure Annual total

South Fabius River Basin; site 1

1997 3,837 153 75,379 1,859 153,130 307 227,058 316,393 39,974 583,425 516,984 -- 516,9842002 4,918 241 86,998 2,020 137,853 181 195,862 336,440 34,457 566,759 578,680 31,719 610,3992007 68,624 228 80,593 1,769 198,767 146 183,788 319,512 56,420 559,720 610,592 22,435 633,027

Grand River Basin; site 2

1997 12,582 497 280,685 6,813 361,582 710 419,044 813,580 74,769 1,307,393 1,087,610 -- 1,087,6102002 20,155 735 298,545 6,591 113,966 363 428,326 836,796 41,039 1,306,161 1,252,918 41,984 1,294,9022007 22,972 750 304,159 6,069 554,307 303 524,643 777,890 59,641 1,362,174 1,469,720 63,933 1,533,653

Elk River Basin; site 6

1997 25,597,750 506 115,686 3,684 12,378 152 3,337 4,073 5,888 13,298 177,441 -- 177,4412002 23,598,881 618 133,154 3,572 1,160 89 4,297 3,660 5,508 13,465 197,572 91,306 288,878

2007 29,035,895 605 118,549 2,875 1,185 92 16,374 4,096 2,876 23,346 186,349 85,295 271,644

aPoultry head and operations used in table were totaled from chickens (broilers, layers, and pullets) and turkeys.bCattle head and operations used in table were totaled from beef, milk, and feedlot cattle.cFertilizers in table were applied to both cropland and pastureland.dCommercial fertilizers used in table include lime and soil conditioners.
hog operations decreased to 146 operations, but the number 

of hogs being housed increased to about 199,000 head (U.S. 

Department of Agriculture, 2007; table 7). Between the 2002 

and 2007 census, the number of family owned hog and poultry 

farms likely began to decrease as large commercial operations 

moved into the counties (John Ford, Missouri Department of 

Natural Resources, written commun., 2009). 

In the Missouri counties within the Grand River Basin 

(site 2), the agricultural census in 1997 recorded 497 operations housing about 12,000 head of poultry (table 7). By the 

2007 census, the operation totals increased about 50 percent to 

750 housing about 23,000 head of poultry (U.S. Department 

of Agriculture, 2007; table 7). Cattle production was relatively 

stable between the 3 census years. Hog totals, similar to those 

in the South Fabius River Basin, changed between the 2002 

and 2007 census years when private farms closed as large 

commercial operations moved into the basin. In 1997, 710 hog 

operations had about 360,000 hogs. By 2002 those numbers 

had decreased to 363 operations and about 114,000 hogs. As 

the commercial operations became established, the number 

of operations in the counties was near 300, but the number of 

hogs increased to about 550,000 head. Corn production in the 

basin counties increased, whereas soybean and wheat production decreased. In 1997, about 420,000 acres of corn, 814,000 

acres of soybean, and 75,000 acres of wheat were cultivated. 

By 2007, corn production increased to about 525,000 acres, 

whereas soybean production decreased to about 780,000 acres 

and wheat decreased to about 60,000 acres. Fertilizer use 

steadily increased each census, as commercial fertilizers were 

applied to about 1 million acres in 1997, increasing to about 

1.5 million acres in 2007. Of the 1.5 million acres fertilized, 

about 64,000 acres were fertilized with manure to both crop 

and pasturelands (U.S. Department of Agriculture, 2007; 

table 7). 

The additional phosphorus reduction system at the 

SWWTP in 2001 has substantially decreased the phosphorus concentration in effluent discharged into Wilson Creek, 

contributing to a downward trend (table 6; fig. 11). A flowadjusted long-term trend is not the best trend test for site 4 

because a known point in time exists where a distinct change 

in total phosphorus concentrations occurred; therefore, a 

step-trend analysis was performed on the total phosphorus 

data. The step-trend compared concentrations from before 

the phosphorus reduction system began operation in March 

2001 to concentrations afterwards. The p-value from the 

step-trend test was less than 0.05, indicating a significant 

difference in the median from before and after the reduction 

system began. The median total phosphorus concentration 

for data collected before the reduction system began was 

2.5 mg/L and for data collected after was 0.25 mg/L. The 

SWWTP phosphorus reduction is likely responsible for the 

significant downward trend in total phosphorus concentrations at site 4 (fig. 12).

Fecal Indicator Bacteria

All sites were analyzed for flow-adjusted trends in 

E. coli and fecal coliform bacteria. No significant long-term 

trends in E. coli or fecal coliform bacteria densities were 

detected because p-values were all greater than 0.05 (table 5; 

fig. 13).

Trace Elements

Most trace element data used in the study were highly 

censored and could not be used for flow-adjusted trend analyses. Site 4 was the only site with uncensored dissolved and 

total recoverable zinc data. Larger concentrations of zinc at 

site 4 are to be expected because zinc is detected in the effluent of the Springfield SWWTP (City of Springfield, 2009). 

Downward trends were detected for both dissolved and total 

recoverable zinc concentrations (table 5; fig. 14). No processes 

EXPLANATION 

x

x

o

o

Upper adjacent

75th percentile

Median

25th percentile

Lower adjacent

Lower outlier

Lower far-out value

Upper far-out value

Upper outlier

p-value—Significance

 level from the Wilcoxon 

 rank-sum test (considered 

 significantly different when

 p-value is less than or equal

 to 0.05)

x

x

0.05

0.10

0.50

1.00

5.00

66 45

Before phosphorous

reduction system was installed 

(November 1993 to February 2001)

After phosphorous

reduction system in operation

(March 2001 to September 2008)

p-value = 0

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

66 Number of samples

p = 0

Figure 12. Total phosphorous concentrations before and 

after introduction of advanced phosphorous reduction system 

at the City of Springfield Southwest Wastewater Treatment 

Facility, located downstream from site 4.
ESCHERICHIA COLI, IN COLONIES PER 100 MILLILITERS

 0

40,000

90,000

140,000

Site 1

0

2,000

4,000

6,000

8,000 Site 3

0

1,000

3,000

5,000

Site 5

0

3,000

7,000

11,000

Site 6

0

2,000

4,000

6,000

8,000 Site 4

0

30,000

70,000

110,000

Site 2

WATER YEAR

1994 1996 1998 2000 2002 2004 2006 2008 1994 1996 1998 2000 2002 2004 2006 2008 

Sample

Raw data trend

Flow-adjusted trend

EXPLANATION

Figure 13. Flow-adjusted trends in Escherichia coli and fecal coliform densities, water years 1993 

through 2008.
1,000

3,000

5,000

7,000

0

20,000

40,000

60,000

0

4,000

9,000

14,000

19,000

24,000

0

1,000

2,000

3,000

4,000

5,000

0

1,000

2,000

3,000

4,000

5,000

0

500

1,000

1,500

2,000

FECAL COLIFORM, IN COLONIES PER 100 MILLILITERS

WATER YEAR

0

Site 1

Site 3

Site 6

Site 4

Site 2

1994 1996 1998 2000 2002 2004 2006 2008 

Site 5

1994 1996 1998 2000 2002 2004 2006 2008 

Figure 13. Flow-adjusted trends in Escherichia coli and fecal coliform densities, water years 1993 

through 2008.—Continued
36 Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri

have been used at the SWWTP to decrease zinc concentrations 

in the effluent. However, two circuit board manufacturers and 

several chrome plating operations that discharged effluent 

into the SWWTP along Wilson Creek have slowly decreased 

production during the past several years and have eventually 

gone out of business (James Burks, City of Springfield, Public 

Works Department, oral commun., 2009), which could have 

resulted in decreases in the zinc concentrations.

Non-Flow Adjusted Trends

Total Suspended Solids

The TSS data were highly censored at all sites. Many 

of Missouri’s streams commonly have TSS concentrations 

that are less than the MRL, making long-term trend detection 

difficult (U.S. Geological Survey, 1964–2005, 2006–2008; 

Otero-Benítez and Davis, 2009a, 2009b). Non-flow adjusted 

trends were performed on TSS data from sites 1 and 2, which 

both had datasets with less than 50 percent censored values. 

The long-term trends could be determined only on data for 

the last 8 water years (2000 through 2008) because samples 

for TSS data analyses were not regularly collected before 

the 2000 water year. Statistically significant upward trends 

were detected at both sites (table 6; fig. 15). The increase in 

TSS concentrations could be because of soil erosion from an 

increase in land cultivated for row crops. However, TSS is 

related to streamflow, and because this trend analysis was not 

flow adjusted, the upward trends may be related to flow as 

well as human-influenced effects.

Nutrients

Most nutrient data at the six sites were analyzed with 

flow-adjusted trend tests. Dissolved nitrate plus nitrite 

concentrations at sites 1 and 2 exceeded the 5 percent limit 

of censored values as did total phosphorus concentrations at 

site 3 and, therefore, were tested for non-flow adjusted trends. 

No significant trends were detected (table 6; fig. 15). 

Trace Elements

Trace element data were highly censored at all sites. 

Trace element data were collected four times per water year 

during the study period, which made determining trends 

40

80

120

DISSOLVED ZINC,

IN MICROGRAMS PER LITER

0

40

80

120

TOTAL RECOVERABLE ZINC,

IN MICROGRAMS PER LITER

WATER YEAR

0

1994 1996 1998 2000 2002 2004 2006 2008 

Sample

Raw data trend

Flow-adjusted trend

EXPLANATION

Downward trend

WATER YEAR

1994 1996 1998 2000 2002 2004 2006 2008 

Figure 14. Flow-adjusted trends in zinc concentrations at site 4, water years 1993 through 2008.
0

2

4

6

8 Site 1

DISSOLVED NITRATE PLUS NITRITE (AS NITROGEN),

 IN MILLIGRAMS PER LITER

WATER YEAR

TOTAL PHOSPHORUS,

 IN MILLIGRAMS PER LITER

0.02

0.07

0.12

0.17

0.22

0.27

0.32 Site 3

0

1

2

3 Site 2

2,000

1,500

1,000

500

0

2,000

1,500

1,000

500

0

2,500

TOTAL SUSPENDED SOLIDS, 

IN MILLIGRAMS PER LITER

Site 1 Site 2

2000 2002 2004 2006 2008 2000 2002 2004 2006 2008

1994 1996 1998 2000 2002 2004 2006 2008 

WATER YEAR

1994 1996 1998 2000 2002 2004 2006 2008 

Sample

Raw data trend

EXPLANATION

Upward trend

Figure 15. Non-flow adjusted trends in total suspended solids, dissolved nitrate plus nitrite (as nitrogen), and 

total phosphorus concentrations, water years 1993 through 2008.
TOTAL RECOVERABLE LEAD,

IN MICROGRAMS PER LITER

Site 1

0

20

40

60

Site 2

Site 1 Site 2

TOTAL RECOVERABLE ZINC, IN MICROGRAMS PER LITER

0

20

40

60

80

WATER YEAR

WATER YEAR

13 Site 3

11

9

7

5

3

1

2000 2002 2004 2006 2008

2000 2002 2004 2006 2008

0

50

100

150

0

20

40

60

Sample

Raw data trend

EXPLANATION

Figure 16. Non-flow adjusted trends in total recoverable lead and zinc concentrations, water years 2000 to 

2008.
more difficult. Long-term trends could be calculated for total 

recoverable lead concentrations at sites 1 and 2, and for total 

recoverable zinc concentrations at sites 1, 2, and 3. Only data 

from 2000 to 2008 were used because data collected before 

the 2000 water year were not collected consistently (table 6). 

No trends were indicated in the total recoverable lead and zinc 

concentrations at the three sites (table 6; fig. 16). Because the 

datasets were highly censored, the power of the trend tests was 

decreased, making the determination of a true trend difficult. 

No flow adjustment could be used because of the large amount 

of censored values; therefore, any long-term trend may be 

masked by year-to-year variability caused by streamflow 

differences. 

Summary and Conclusions

The U.S. Geological Survey (USGS), in cooperation 

with the Missouri Department of Natural Resources (MDNR), 

collects data pertaining to the water resources of Missouri. 

These data are collected as part of the Missouri Ambient 

Water-Quality Monitoring Network (AWQMN) and constitute 

a valuable source of reliable, impartial, and timely information 

for developing an improved understanding of water resources 

of the State. Information from water-quality monitoring performed by the USGS is needed to assess the existing conditions of water resources; to design preservation, management, 

and remediation programs; and to evaluate the effectiveness 

of such programs, as well as document compliance with local, 

State, and Federal regulations and permits. In addition, the 

results of water-quality monitoring are needed to detect and 

define trends in water quality and to identify emerging waterquality concerns.

Six sites from the AWQMN, with available data from 

the 1993 through 2008 water years, were chosen to study the 

water-quality conditions and long-term trends of dissolved 

oxygen, physical properties (specific conductance and water 

temperature), total suspended solids, nutrients (dissolved 

nitrate plus nitrite as nitrogen and total phosphorous), fecal 

indicator bacteria [Escherichia coli (E. coli) and fecal coliform], and trace elements (dissolved and total recoverable 

lead and zinc). The six sites used in the study are classified 

in groups corresponding to the physiography, main land use, 

and drainage basin size, and represent the stream diversity 

within Missouri. Sites used in the study were referred to as 

the following: site 1, South Fabius River near Taylor (USGS 

identifier 05500000); site 2, Grand River near Sumner (USGS 

identifier 06902000); site 3, Gasconade River above Jerome 

(USGS identifier 06930800); site 4, Wilson Creek near Brookline (USGS identifier 07052152); site 5, Current River at 

Doniphan (USGS identifier 07068000); site 6, Elk River near 

Tiff City (USGS identifier 07189000).

Water-quality conditions were assessed to explore 

relations between data from sites and to the State waterquality standards where applicable for selected constituents. 

Streamflow varied at each site because of drainage area, land 

use, and groundwater inputs. All six sites had statistically different streamflows for the study period, except sites 2 and 3. 

Dissolved oxygen concentrations were significantly different 

at site 4, which was the only urban site in the study. Specific 

conductance was similar between the most northern sites (sites 

1 and 2) and between the most southern sites (sites 5 and 6) 

in the study. Water temperature was similar for all sites in the 

study except site 4. Total suspended solids concentrations generally were reported at the method reporting level at all sites, 

except sites 1 and 2. Streams in northern Missouri are more 

turbid than streams in southern Missouri and are affected by 

large volumes of sediment deposition because of soil erosion 

from land cultivated for row crops. 

Site 4, located downstream from the Springfield Southwest Wastewater Treatment Plant (SWWTP), had the largest 

concentrations of dissolved nitrate plus nitrite during the study 

period; the median concentration was 10 milligrams per liter. 

In 1993, the SWWTP completed facility improvements that 

decreased the phosphorus concentration in effluent discharged 

into Wilson Creek by an average of 40 percent. In March 

2001, the SWWTP introduced an advanced phosphorus reduction system, which decreased the average phosphorus discharge levels to 0.5 milligram per liter. Of the three sites with 

basins containing large percentages of agricultural land (sites 

1, 2, and 6), median total phosphorus concentration at site 2 

was significantly different. Total phosphorus concentrations 

never exceeded 0.5 milligram per liter at sites 3 and 5 during 

the study period. 

The MDNR has set statewide standards for fecal indicator bacteria and are among the most stringently monitored 

constituents by the State. The State standards are used for 

Escherichia coli and apply only to the recreational period 

of April 1 through October 31. The standard is calculated 

from the geometric mean of all samples collected during the 

recreation period. The geometric means of Escherichia coli

calculated from the recreational seasons within the study 

period show that only site 2 exceeded the whole-body-contact 

standard for frequently used waters. The whole-body-contact 

standard for less frequently used waters and the secondary 

contact recreation standard were not exceeded at any of the 

sites during the study period. The most northern sites (sites 1 

and 2) and the only urban site (sites 4) in the study had statistically larger densities of both fecal indicator bacteria types than 

the remaining sites. Fecal indicator bacteria samples primarily were collected during base-flow conditions through the 

water year, but some samples were collected during high-flow 

conditions as well as the non-recreational months (November 

through March). 

Dissolved lead concentrations analyzed during the study 

period seldom exceeded the laboratory reporting level of 

1 microgram per liter. Median total recoverable lead data were 

equal to or less than the laboratory reporting level at all sites 

except the two northern sites. Median total recoverable lead 

concentrations at sites 1 and 2 were significantly larger than 

concentrations as sites 3, 5, and 6. The median concentrations 
of dissolved and total recoverable zinc were 39 and 40 micrograms per liter at site 4, which are significantly larger than the 

other sites, but are typical of concentrations in the SWWTP 

effluent. The State standards for lead and zinc varied with the 

hardness of the water and stream classifications.

 Long-term trends were analyzed at each site and for 

each constituent. All constituents were analyzed using the 

Seasonal Kendall test. Some constituents were analyzed using 

a flow-adjusted trend test, whereas datasets with greater than 

5 percent but less than or equal to 50 percent censored values 

were analyzed by non-flow adjusted trend tests. 

No significant long-term trends were detected for dissolved oxygen or water temperature. Significant trends in specific conductance were determined for three sites; a downward 

trend at site 1, and an upward trend at sites 3 and 6. 

Dissolved nitrate plus nitrite concentrations for all sites, 

except sites 1 and 2 (which contained more than 5 percent 

censored values), could be analyzed by flow-adjusted models. 

Of the four sites adjusted by streamflow, only site 6 showed 

a significant trend (upward). The Elk River Basin is largely 

agricultural, most of which is poultry and cattle production. 

Agricultural statistics from the 1997, 2002, and 2007 census 

studies show that the number of cattle operations in the Elk 

River Basin, as well as the amount of commercial fertilizers 

that were applied, have stayed relatively stable over the study 

period, whereas poultry production increased. The increase 

in urban development upstream and the increase in poultry 

populations within the basin possibly have caused the upward 

trend in nutrient concentrations at the site. 

Total phosphorus concentrations at four of the six sites 

were analyzed by flow-adjusted models. All of the sites 

showed significant long-term trends in the data except the site 

6. The two northern sites showed an upward trend, whereas 

the urban site (site 4) had a downward trend in concentrations 

for the study period. The increase in total phosphorus concentrations at the northern sites could be from an increase in agricultural land use in the basins. The SWWTP upstream from 

site 4 on Wilson Creek began using a phosphorus reduction 

system in March 2001 that decreased the average phosphorus 

discharge levels to 0.5 milligram per liter, contributing to the 

downward trend in total phosphorus concentrations in Wilson 

Creek. A step-trend analysis was performed on the total phosphorus concentrations collected at site 4 to analyze the data 

before and after the phosphorus reduction system began operation at the treatment plant. A statistically significant difference 

was indicated between concentrations, indicating the reduction 

system was likely responsible.

Site 4 contained no censored values for dissolved and 

total recoverable zinc datasets and could be analyzed using 

flow-adjusted tests. Median concentrations of both dissolved 

and total recoverable zinc at the urban site are near the typical 

effluent zinc concentration of 40 micrograms per liter. Significant downward trends in dissolved and total recoverable zinc 

concentrations were indentified at the urban site. Two circuit 

board manufacturers and several chrome plating operations 

that discharged effluent into the wastewater treatment plant 

have gone out of business during the past several years, which 

may have contributed to the significant downward trend in 

zinc concentrations.

Total suspended solids concentrations were highly 

censored at all sites. Only datasets from the two northern sites 

were censored less than 50 percent and could be analyzed by 

non-flow adjustment tests. Statistically significant upward 

trends were detected at both sites. The increase in total suspended solids concentrations could be because of soil erosion 

from land cultivated for row crops.

Trace element data at all sites were highly censored. 

Long-term trends could be calculated for total recoverable lead 

datasets at the two northern sites, and for total recoverable 

zinc datasets at sites 1, 2, and 3 using non-flow adjusted tests. 

No trends were indicated in the total recoverable lead and zinc 

data at the three sites. 

The significant trends identified in the study were mainly 

among nutrient constituents. Most of the nutrient trends can 

be related to changes in agriculture and urban development. 

Other significant trends were identified in total suspended 

solids, particularly at the two northern sites where agriculture, 

soil erosion, and runoff are more pronounced. Analysis of 

additional long-term sites within the Ambient Water-Quality 

Monitoring Network would help determine if other trends in 

dissolved oxygen, physical properties, total suspended solids, 

nutrients, or trace elements can be detected within the State’s 

surface waters.

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Publishing support provided by:

Rolla Publishing Service Center

For more information concerning this publication, contact:

Director, USGS Missouri Water Science Center

1400 Independence Road

Rolla, MO 65401

(573) 308–3667

Or visit the Missouri Water Science Center Web site at:

http://mo.water.usgs.gov
References Cited 43
Barr and Davis—Surface-Water Quality Conditions and Long-Term Trends within the Ambient Water-Quality Monitoring Network in Missouri—SIR 2010—5078

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