National Water-Quality Assessment Program

Century-Scale Perspective on Water Quality in Selected 

River Basins of the Conterminous United States

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012–5225
Cover: Schuylkill River from below South Street, Philadelphia. Cover illustration from 

the collection of Adam E. Levine / http://www.phillyh2o.org/. Used with permission.
Century-Scale Perspective on Water 

Quality in Selected River Basins of the 

Conterminous United States

By Edward G. Stets, Valerie J. Kelly, Whitney P. Broussard, III, Thor E. Smith, and 

Charles G. Crawford

National Water-Quality Assessment Program

Scientific Investigations Report 2012–5225

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: 2012

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Suggested citation:

Stets, E.G., Kelly, V.J., Broussad, W.P., III, Smith, T.E., and Crawford, C.G., 2012, Century-scale perspective on water 

quality in selected river basins of the conterminous United States: U.S. Geological Survey Scientific Investigations 

Report 2012–5225, 108 p.
iii

Contents

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

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

Nutrient Pollution..................................................................................................................................1

Historical Perspective on Water-Quality Problems ........................................................................2

Water-Quality Issues in the 19th Century ................................................................................2

The Water Sanitation Era ...........................................................................................................3

The Rise of Industrial Waste......................................................................................................5

Growth Era ....................................................................................................................................5

Recent History .............................................................................................................................7

Methods...........................................................................................................................................................9

Stream-Gaging Station Selection ......................................................................................................9

Data Sources.........................................................................................................................................9

Parameter Codes Used in this Study...............................................................................................12

Nitrogen and Phosphorus Codes ............................................................................................12

Inorganic Carbon Codes...........................................................................................................12

Stream Discharge and Runoff Calculations ...................................................................................15

Ancillary Data Methodology .............................................................................................................15

Recent Ancillary Data for all Basins.........................................................................................................16

Population ............................................................................................................................................16

Farmland Area.....................................................................................................................................16

Non-Point Sources of Nitrogen and Phosphorus from Fertilizer and Livestock ......................17

Corn Production ..................................................................................................................................19

Specific Basins of Interest.........................................................................................................................20

Eastern Basins.....................................................................................................................................20

Connecticut River ......................................................................................................................22

Data Sources.....................................................................................................................22

Delaware River...........................................................................................................................25

Data Sources.....................................................................................................................27

Schuylkill River ..........................................................................................................................28

Data Sources.....................................................................................................................28

Potomac River............................................................................................................................31

Data Sources.....................................................................................................................33

James River................................................................................................................................35

Data Sources.....................................................................................................................35

Great Lakes Basins.............................................................................................................................38

Saint Lawrence River................................................................................................................40

Data Sources.....................................................................................................................42

Maumee River............................................................................................................................44

Data Sources.....................................................................................................................46
iv

Specific Basins of Interest—Continued

Central Basins .....................................................................................................................................48

Ohio River ...................................................................................................................................53

Data Sources.....................................................................................................................55

Illinois River.................................................................................................................................58

Data Sources.....................................................................................................................60

Des Moines River.......................................................................................................................63

Data Sources.....................................................................................................................63

Missouri River ............................................................................................................................66

Data Sources.....................................................................................................................66

Arkansas River...........................................................................................................................69

Data Sources.....................................................................................................................69

Brazos River................................................................................................................................72

Data Sources.....................................................................................................................72

Upper Mississippi River............................................................................................................75

Data Sources.....................................................................................................................75

Middle Mississippi River...........................................................................................................75

Data Sources.....................................................................................................................77

Lower Mississippi River............................................................................................................77

Data Sources.....................................................................................................................78

Upper Colorado River Basins............................................................................................................82

Green River.................................................................................................................................85

Colorado River at Cisco ............................................................................................................85

Gunnison River ..........................................................................................................................85

San Juan River...........................................................................................................................86

Colorado River at Lees Ferry....................................................................................................86

Data Sources..............................................................................................................................86

Western Basins ..................................................................................................................................88

Santa Ana River .........................................................................................................................90

Data Sources.....................................................................................................................92

San Joaquin River......................................................................................................................93

Data Sources.....................................................................................................................95

Willamette River.........................................................................................................................96

Data Sources.....................................................................................................................98

Summary........................................................................................................................................................99

References Cited..........................................................................................................................................99

Contents—Continued
v

Figures

Figure 1. Map showing land-cover data and river basins included in this study.

Monitoring stations are the reference stream gaging stations for all river

reaches of interest ........................................................................ 10

Figure 2. Map showing physiographic provinces of the conterminous United States

along with river basins in this study. Monitoring stations are the reference

stream gaging stations for all river reaches of interest................................. 11

Figure 3. Graph showing population density from 2000 census for all river basins

included in this study........................................................................ 16

Figure 4. Graph showing agricultural land use in 2002 for all river basins included in this

study .......................................................................................... 17

Figure 5. Graphs showing average nonpoint sources of nitrogen and phosphorus from

fertilizer and animal livestock for all river basins included in this study, 1997–2001 18

Figure 6. Graph showing average corn harvested per square kilometer of drainage area

for 2000–2010 for all river basins included in this study................................. 19

Figure 7. Graphs showing historical changes in population density, corn harvest,

percentage of basin area in any farmland usage, percentage of basin area in

cropland, and fertilizer and animal livestock sources of nitrogen and

phosphorus in the Eastern basins ......................................................... 21

Figure 8. Map showing Connecticut River basin ................................................... 23

Figure 9. Map showing Delaware River basin ...................................................... 26

Figure 10. Map showing Schuylkill River basin ...................................................... 29

Figure 11. Map showing Potomac River basin ...................................................... 32

Figure 12. Map showing James River basin ......................................................... 36

Figure 13. Graphs showing historical changes in population density, corn harvest,

percentage of basin area in any farmland usage, percentage of basin area in

cropland, and fertilizer and animal livestock sources of nitrogen, and

phosphorus in the Great Lakes basins ................................................... 39

Figure 14. Map showing Saint Lawrence River basin ............................................. 41

Figure 15. Map showing Maumee River basin ...................................................... 45

Figure 16. Graphs showing historical changes in population density, corn harvest,

percentage of basin area in any farmland usage, percentage of basin area in

cropland, and fertilizer and animal livestock sources of nitrogen and

phosphorus in the Central basins east of the main stem of the Mississippi

River .......................................................................................... 49

Figure 17. Graphs showing historical changes in population density, corn harvest,

percentage of basin area in any farmland usage, percentage of basin area in

cropland, and fertilizer and animal livestock sources of nitrogen and

phosphorus in the Central basins west of the main stem of the Mississippi

River .......................................................................................... 51

Figure 18. Graphs showing historical changes in population density, corn harvest,

percentage of basin area in any farmland usage, percentage of basin area in

cropland, and fertilizer and animal livestock sources of nitrogen, and

phosphorus in the basins of interest on the main stem of the Mississippi River ... 52

Figure 19. Map showing Ohio River basin, Ohio...................................................... 54

Figure 20. Map showing Illinois River basin ......................................................... 59

Figure 21. Map showing Des Moines River basin ................................................... 64

Figure 22. Map showing Missouri River basin ...................................................... 67
vi

Figure 23. Map showing Arkansas River basin ...................................................... 70

Figure 24. Map showing Brazos River basin ......................................................... 73

Figure 25. Map showing Mississippi River basin ................................................... 76

Figure 26. Map showing Upper Colorado River basins ............................................. 83

Figure 27. Graphs showing historical changes in population, corn harvest, percentage of

basin in any farmland usage, percentage of basin in cropland, and fertilizer

and animal livestock sources of nitrogen and phosphorus in the basins of

interest in the Upper Colorado River ...................................................... 84

Figure 28. Graphs showing historical changes in population, corn harvest, percentage of

basin in any farmland usage, percentage of basin in cropland, and fertilizer

and animal livestock sources of nitrogen and phosphorus in the basins of

interest in the Western United States ................................................... 89

Figure 29. Map showing Santa Ana River basin...................................................... 91

Figure 30. Map showing San Joaquin River basin ................................................... 94

Figure 31. Map showing Willamette River basin ................................................... 97

Figures—Continued

Tables

Table 1. River basins included in this study and their associated reference stream

gaging station .............................................................................. 9

Table 2. Parameter codes used in nitrogen and phosphorus calculations ..................... 13

Table 3. Alkalinity parameter codes shown in descending hierarchy along with their

frequency in the database used in this study .......................................... 14

Table 4. Connecticut River basin data sources ................................................... 24

Table 5. Delaware River data sources ............................................................ 27

Table 6. Schuylkill River data sources ............................................................ 30

Table 7. Potomac River data sources................................................................ 34

Table 8. James River basin data sources ......................................................... 37

Table 9. Saint Lawrence River basin data sources................................................ 43

Table 10. Maumee River basin data sources ...................................................... 47

Table 11. Ohio River basin data sources ............................................................ 56

Table 12. Illinois River basin data sources ......................................................... 61

Table 13. Des Moines River data sources............................................................ 65

Table 14. Missouri River basin data sources ...................................................... 68

Table 15. Arkansas River basin data sources ...................................................... 71

Table 16. Brazos River basin data sources ......................................................... 74

Table 17. Mississippi River basin data sources ................................................... 79

Table 18. Upper Colorado River basin data sources................................................ 87

Table 19. Santa Ana River basin data sources ...................................................... 92

Table 20. San Joaquin River basin data sources ................................................... 95

Table 21. Willamette River basin data sources...................................................... 98
vii

Conversion Factors and Datums

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.004047 square kilometer (km2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

million gallons (Mgal) 3,785 cubic meter (m3)

cubic foot (ft3) 0.02832 cubic meter (m3) 

acre-foot (acre-ft) 1,233 cubic meter (m3)

gallon 3.78 liter (L)

Flow rate

acre-foot per day (acre-ft/d) 0.01427 cubic meter per second (m3/s)

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m3/yr)

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

cubic foot per second per square 

mile [(ft3/s)/mi2]

 0.01093 cubic meter per second per square 

kilometer [(m3/s)/km2]

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

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

Mass

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

ton per day (ton/d) 0.9072 metric ton per day

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Application rate

pounds per acre per year 

[(lb/acre)/yr]

 1.121 kilograms per hectare per year 

[(kg/ha)/yr]
viii

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd) 

kilometer (km) 0.6214 mile (mi)

Area

square meter (m2) 0.0002471 acre 

square kilometer (km2) 247.1 acre

square meter (m2) 10.76 square foot (ft2) 

square kilometer (km2) 0.3861 square mile (mi2)

Volume

cubic kilometer (km3) 0.2399 cubic mile (mi3) 

Flow rate

cubic meter per second (m3/s) 70.07 acre-foot per day (acre-ft/d) 

centimeter per year (cm/yr) 3.937 inch per year (in/yr) 

millimeter per year (mm/yr) 0.03937 inch per year (in/yr) 

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

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.

Datums

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

(NAVD 88).

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

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

Conversion Factors and Datums—Continued

Conversion Factors—Continued
Century-Scale Perspective on Water Quality in Selected 

River Basins of the Conterminous United States

By Edward G. Stets, Valerie J. Kelly, Whitney P. Broussard, III, Thor E. Smith, and Charles G. Crawford

Abstract

Nutrient pollution in the form of excess nitrogen and 

phosphorus inputs is a well-known cause of water-quality 

degradation that has affected water bodies across the Nation 

throughout the 20th century. The recognition of excess 

nutrients as pollution developed later than the recognition 

of other water-quality problems, such as waterborne illness, 

industrial pollution, and organic wastes. Nevertheless, 

long-term analysis of nutrient pollution is fundamental to 

our understanding of the current magnitude of the problem, 

as well the origins and the effects. This report describes the 

century-scale changes in water quality across a range streams 

in order to place current water-quality concerns in historical 

context and presents this history on a national scale as well 

as for selected river reaches. The primary focus is on nutrient 

pollution, but the development and societal responses to other 

water-quality problems also are considered. Land use and 

agriculture in the selected river reaches also are analyzed to 

consider how these factors may relate to nutrient pollution. 

Finally, the availability of relevant nutrient and inorganic 

carbon data are presented for the selected river reaches. 

Sources of these data included Federal agencies, State-level 

reports, municipal public works facilities, public health 

surveys, and sanitary surveys. The availability of these data 

extends back more than a century for most of the selected river 

reaches and suggests that there is a tremendous opportunity to 

document the development of nutrient pollution in these river 

reaches.

Introduction 

Input of excess nutrients in the form of nitrogen 

and phosphorus is a well-known cause of water-quality 

degradation that has affected water bodies across the Nation 

throughout the 20th century. Water effluent from farming 

operations, municipalities, and industries all contribute to 

elevated nutrient inputs, and water bodies downstream of 

these sources are at risk of eutrophication. However, drawing 

explicit connections between century-long changes in nutrient 

concentrations and factors believed to be causing those 

changes requires long-term water-quality and ancillary (for 

example, land use) data. This report presents the sources of 

long-term nutrient data for 26 river basins along with brief 

historical descriptions of events likely to affect water quality 

within the basins. This study was conducted to evaluate 

the availability of long-term nutrient concentration data for 

selected river basins around the country. A strong emphasis 

was placed on locating data collected by government agencies 

involved with drinking water quality, biogeochemical 

investigations, human health and sanitation, as well as 

resource utilization, such as fisheries management. The 

availability of ancillary data including streamflow, population 

density, and land-use characteristics in the river basins of 

interest also was evaluated in order to put the rivers into 

context with respect to one another and on a national scale. 

Comparable water-quality data from many different sources 

were gathered to document the availability of data for selected 

river reaches around the country. For most sites, the oldest 

data identified were collected over a century ago. 

Nutrient Pollution

Nutrient pollution is fundamentally caused by excess 

inputs of nitrogen and phosphorus to water bodies. Humans 

have dramatically altered the natural cycling of these nutrients. 

In the case of the nitrogen cycle, humans have added reactive 

nitrogen to the biosphere through synthetic fertilizer usage, 

human waste, fossil fuel combustion, and agricultural 

animal production (Galloway and others, 2004). Phosphorus 

also is used as a fertilizer and is found in both human and 

animal waste, mobilized by soil erosion, and contained 

in many synthetic compounds including some detergents 

(Edmondson, 1991). Phosphorus is an important component 

of urban runoff (Novotny, 2003). Additionally, there can be 

interactions between the phosphorus and nitrogen cycles such 

that excessive phosphorus inputs stimulate bacterial nitrogen 

fixation (Schindler, 1977). The global carbon cycle also is 

experiencing tremendous perturbation through the burning 

of fossil fuels and changes to biomass production (Le Quéré 

and others, 2009). Inorganic carbon dissolved in water is not 

a pollutant, but it can indicate other large-scale anthropogenic 
2 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

disturbances, such as land-use changes (Oh and Raymond, 

2006) and hydrologic connectivity, between terrestrial and 

aquatic environments (Raymond and others, 2008).

Nutrient pollution has resulted in lost biodiversity, 

eutrophication, and the development of hypoxia in many 

coastal areas around the world (Diaz, 2001). In the United 

States, the Gulf of Mexico hypoxic zone stands as perhaps 

the largest manifestation of anthropogenic nutrient pollution. 

Agricultural use of synthetic fertilizer is currently a primary 

driving force of pollution in aquatic ecosystems and the 

heavily cultivated Mississippi River basin exemplifies these 

effects. Uneven distribution of nutrient pollution throughout 

the country reflects both the diversity of agricultural practices 

(Broussard and Turner, 2009) and differential biogeochemical 

processing of nutrients in different regions (Schaefer and 

Alber, 2007). 

Several studies successfully used long-term datasets to 

analyze the relation between changes in land use and stream 

chemistry. Broussard and Turner (2009) combined modern 

stream chemistry data, data collected by the U.S. Geological 

Survey (USGS) in the early 20th century, and the U.S. 

Department of Agriculture (USDA) Census of Agriculture 

to explore the correlation between increasing stream nitrate 

concentrations and agricultural intensity in the Midwestern 

United States. Robinson and others (2003) compared modern 

stream chemistry with data collected by the Massachusetts 

State Department of Health from 1900 to 1914 to explore 

how stream chemistry has changed with road salting, fertilizer 

usage, and sulfate aerosol emissions. Goolsby and others 

(1999) synthesized long-term data from a number of sources 

including the USGS, the Illinois Environmental Protection 

Agency, and the Illinois State Water Survey to develop a mass 

balance model of net nitrogen inputs to the Mississippi River 

basin. The model strongly implicated anthropogenic fertilizers 

in total nitrogen concentrations and loads (Goolsby and 

others, 1999). These analyses and others like them provide a 

foundation upon which to build additional studies considering 

century-scale trends in water quality and the land-use factors 

leading to these changes.

In this publication, the history of water-quality issues 

since the mid-19th century and the societal response to those 

issues are briefly discussed, focusing on government actions 

aimed at improving water access or water quality. The goal 

of this discussion is to present the evolving nature of waterquality problems and to place current water-quality problems 

in the context of a long trajectory of change. After discussing 

the history of national-scale changes in water-quality issues 

and corresponding management and legislative decisions, 

methods are summarized for data assembly and management 

including an algorithm used to synthesize relevant data 

from disparate collecting agencies. The synthesis of data 

describing population, land use, and agricultural intensity in 

the river basins of interest is also summarized. Finally, the 

individual river reaches of interest and the relevant sources 

of data are presented for each river reach. In most cases, data 

exist from several sites close to the primary station for a river 

reach. The comparability of these sites for nutrient analyses 

depends on the nutrient being considered, the time frame of 

the analysis, and the ultimate goal of the analysis. Specific 

recommendations about which sites could be combined for 

analytical purposes are not made.

Historical Perspective on Water-Quality 

Problems

Access to clean and abundant fresh water is fundamental 

to human welfare and development, but water usage, whether 

agricultural, industrial, or household, always results in some 

degree of water-quality degradation. Thus, water-quality issues 

have become more severe with the expansion of water usage 

beginning in the mid-19th century (Tarr, 1996). The nature of 

water-quality concerns and the coincident societal response 

changed over time. Sometimes the solution to existing waterquality problems spawned new problems, as was the case with 

the first sanitary sewers that successfully conveyed untreated 

wastewater away from densely populated areas but resulted 

in regional waterborne disease outbreaks as the raw waste 

was delivered to nearby rivers (Tarr, 1996). For the most part, 

however, new issues arose as societal pressures on water 

resources increased, such as the emergence of pollution from 

synthetic organic compounds after World War II (Tarr, 1996). 

The causes and impacts of water-quality degradation are 

complex, almost always involving multiple aspects of societal 

development and multiple classes of stakeholders. In this 

section, the history of water-quality problems in the United 

States is briefly discussed, including the responses to these 

problems. In presenting this history, we hope to emphasize 

that water-quality issues have changed over time, as has as our 

understanding of what is needed to successfully address those 

issues.

Water-Quality Issues in the 19th Century

Population and industrial growth beginning in the 19th 

century prompted interest in securing adequate water supplies 

to densely populated areas, primarily located in central and 

eastern areas of the Nation. The first public waterworks 

was built in 1802 in Philadelphia to bring water from the 

Schuylkill River to the city (Tarr, 1996). By 1860, there were 

136 public waterworks in the United States and by 1880, 

they numbered nearly 600 (Tarr, 1996). The availability of 

tap water allowed affluent citizens to use water much more 

freely, especially as a means of conveying waste away from 

households. Substantial increases in per capita water usage 

and wastewater generation typically occurred after the 

construction of public waterworks. Most urban areas had a 

system of cesspools that were designed to capture household 

and industrial wastewater. When the cesspool was full, the 

waste was collected and transported to vacant lands, nearby 

waterways, or sometimes used as fertilizer (Tarr, 1996). These 

informal systems were quickly overwhelmed after tap water 
Introduction 3

became available and wastewater volumes increased. By the 

1870s, there was widespread recognition of the dangers of 

water-quality degradation from wastewater contamination 

(Merchant, 2002). Local disease outbreaks and generally 

unpleasant conditions prompted many cities to contemplate 

methods for removing wastewater from densely populated 

areas via sewer systems.

Early sewer systems in the United States were 

constructed for the sole purpose of transporting wastewater 

away from cities and into nearby rivers and streams with 

no consideration given to wastewater treatment. Most 

large cities used combined sewers designed to carry both 

stormwater runoff and wastewater, including raw sewage. 

Sewer construction was accomplished through actions by 

local water authorities while the Federal government remained 

strictly concerned with protecting navigation on the Nation’s 

riverways (Scarpino, 1985). Wastewater treatment was 

considered expensive and unnecessary for many years because 

running water was believed to be capable of purifying itself 

(Rauch, 1889). Indeed, studies hailing the ability of heavily 

polluted streams to rid themselves of waste continued into 

the 1920s (Hoskins and others, 1927). Nevertheless, the 

diversion of untreated sewage into streams and rivers had 

the predictable effect of degrading water quality within the 

Nation’s waterways. 

Increases in waterborne diseases during the 1880s and 

1890s have been attributed to the relatively primitive sewerage 

system in the United States (Lewis, 1906; Tarr, 1996). 

Outbreaks of cholera and typhoid fever increasingly alerted 

the public to the dangers of discharging untreated wastewater 

into rivers. For example, recurring typhoid fever and cholera 

outbreaks in Chicago were linked to contamination of the 

drinking water source, Lake Michigan (Novotny, 2003). 

As a response, the Chicago Sanitary and Ship Canal was 

constructed to reverse the flow of the Chicago River thereby 

preventing sewage and urban runoff from contaminating the 

lake; the river was diverted from Lake Michigan to discharge 

into the Des Plaines River, which drains into the Illinois River, 

and ultimately the Mississippi River. In other States, public 

officials began to recognize the need for wastewater treatment 

and a handful of States responded by creating State public 

health boards, which were intended to regulate and oversee 

wastewater discharges into rivers. 

Although the initial goal of many State public health 

boards was to induce wastewater treatment by municipalities, 

it was quickly discovered that drinking water treatment, 

primarily through filtration or chlorination, was an effective 

and much cheaper means of improving drinking water quality 

and reducing the incidence of waterborne disease (Tarr, 

1996). For example, Pennsylvania tasked the public health 

board with enacting strict guidelines limiting the discharge 

of untreated waste into rivers following a serious typhoid 

fever outbreak in Butler, Pa., in 1903. However, when the 

Pennsylvania Public Health Board required Pittsburgh to 

produce a plan to treat all of its wastewater in 1910, sanitary 

engineers working for the city demonstrated that the cost 

of treating Pittsburgh wastewater would be greater than 

providing drinking water treatment for 26 downstream cities. 

The health board refused to proceed and granted Pittsburgh a 

permit to continue discharging untreated waste into the Ohio 

River. The permit remained in effect until 1939 (Tarr, 1996). 

This incident exemplifies the cost-benefit analysis that allowed 

drinking water treatment to prevail as the preferred method of 

combating the problem of untreated wastewater discharge into 

the Nation’s rivers.

Modern water quality laws explicitly designate a role 

for the Federal government in guaranteeing water quality. 

However, this idea developed very slowly. The Federal role 

in water issues was essentially limited to navigation and flood 

control in the 19th and early 20th centuries. By one estimate, 

more than 100 bills relevant to water-quality standards were 

introduced to Congress and failed to be enacted before the 

first, ineffective, national Water Pollution Control Act became 

law in 1948 (Melosi, 2000). Although the earliest Federal 

legislation dealing with water quality was the Rivers and 

Harbors Act of 1899, which declared it unlawful to discharge 

refuse into navigable waters without a permit (Patrick, 1992), 

the law narrowly authorized enforcement by the U.S. Army 

Corps of Engineers (USACE) only if pollution interfered with 

navigation (Scarpino, 1985). On the Mississippi River, the 

primary concerns were the removal of snags (fallen trees stuck 

in the river channel) and ensuring the presence of a navigable 

channel through the use of wing dams and dredging. Later, 

flood control on the lower Mississippi River was incorporated 

into the USACE responsibilities (Barry, 1997). Despite the 

substantial changes in water quality that were occurring in the 

late 19th and early 20th centuries, prevailing wisdom at the 

time dictated that water-quality issues were best decided at the 

State and local level.

The Water Sanitation Era

Attitudes about Federal responsibilities to safeguard 

sustainable uses of natural resources, including water, began to 

change during the reform-minded administration of President 

Theodore Roosevelt (1901–09). Passage of the Reclamation 

Act of 1902 permitted a Federal role in the development of 

water resources in Western States (National Research Council, 

2004), and established the Hydrographic Branch of the U.S. 

Geological Survey, later changed to the Water Resources 

Branch. In 1908, the Inland Waterways Commission, a 

Presidential Commission tasked with finding the most 

appropriate role for the Federal government in guiding water 

development projects, strongly advocated “multiple-use” 

projects (Scarpino, 1985). “Multiple-use” development 

meant that water resources should be managed to provide the 

greatest overall good, rather than to guarantee the primacy of 

navigation or flood control. Although the recommendations 

of the Inland Water Commission were never acted upon, they 

reflect the evolving perceptions of water as a resource and the 

appropriate role of the Federal government in managing that 

resource. 
4 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

The Public Health Service Act of 1912 specifically 

directed the Federal U.S. Public Health Service to study “the 

pollution, direct and indirect, of the navigable waters of the 

United States” (Cumming and others, 1916). The passage of 

this legislation was an acknowledgment that water-quality 

problems in navigable waters were regional in scale and not 

adequately addressed at the State level. Nevertheless, this 

bill stopped short of authorizing Federal agencies to enforce 

pollution controls (Scarpino, 1985). The Public Health Service 

conducted large-scale studies of pollution in the Ohio River 

(1914–15), the lower Potomac River (1916), and tidal waters 

in several Mid-Atlantic States (1916–17). The authors of 

these studies recognized the negative effects of untreated 

sewage disposal on water quality, and the link to disease 

outbreaks. They also began to approach the topic of industrial 

wastes; although, by at least one account, industrial wastes 

were considered “not poisonous or otherwise pathogenic” 

(Cumming and others, 1916), and instead were viewed simply 

as an impediment to the ability of a river to naturally purify 

itself (Phelps, 1914). 

Concerns over industrial pollution increased as industrial 

output increased during and after World War I (Merchant, 

2002). Demand for petroleum-based fuels and lubricants 

grew rapidly as internal combustion engines began to 

replace coal-fired steam engines. Petroleum spills and leaks 

also increased rapidly and raised public awareness of the 

nuisance of industrial pollution and the potential to pollute 

waterways (Scarpino, 1985). This concern coalesced into 

the Oil Pollution Act of 1924, which authorized the USACE 

to prohibit vessels from discharging oil into tidal waters 

and to study the effect oil pollution in rivers may have on 

navigation and commerce (Scarpino, 1985). This law was the 

first permitting direct Federal regulation of water pollution, 

although it was extremely narrow in scope and did nothing to 

address the problem of water pollution more broadly.

Although drinking water treatment successfully decreased 

the occurrence of cholera and typhoid fever in large cities 

during the early part of the 20th century (Melosi, 2000), other 

negative impacts associated with stream pollution continued to 

grow. Pollution and overfishing destroyed the inland fisheries 

in the Illinois River by 1923 (Thompson, 2002). By 1926, the 

Upper Mississippi River near Minneapolis-St. Paul, Minn., 

was nearly devoid of fish and was declared a “public health 

problem” (Twin Cities Metropolitan Council, 2006). In the 

early 1920s, the American Water Works Association found 

248 separate instances of water supplies being harmed by 

industrial wastes (American Water Resources Association, 

1923). The harmful effects of nonpoint source pollution on 

rivers also began to be recognized. Researchers at the U.S. 

Fish and Wildlife Service identified pollution as a primary 

cause for the demise of freshwater mussels throughout the 

Midwestern United States. Notably, silt eroding from farmland 

in the Mississippi River basin was believed to be the chief 

culprit causing the destruction of mussel habitat (Scarpino, 

1985). Similarly, the Izaak Walton League recognized the 

link between nonpoint sources of pollution and water quality. 

Their drive to preserve the Upper Mississippi River rested 

upon the understanding that riparian development would harm 

fish and wildlife populations and would increase flood risks 

for downstream communities (Scarpino, 1985). The pressure 

exerted by the Izaak Walton League prompted the U.S. 

Congress to approve the creation of the Upper Mississippi 

River Fish and Wildlife Refuge in 1924 thereby preventing 

development of river bottomlands between Rock Island, 

Illinois and Wabasha, Minnesota. However, broad steps to 

curtail nonpoint source pollution did not occur until after 

passage of the Federal Water Pollution Control Act (Clean 

Water Act) in 1972.

River assessments from this time period often noted the 

presence of high biological oxygen demand (BOD) that arose 

from inputs of organic material and could result in anoxia, fish 

kills, and the production of offensive reduced gases (Purdy, 

1923; Iowa Division of Public Health Engineering, 1934; 

Gleeson, 1972). Sanitary sewers and industrial effluent were 

believed to be the primary cause of elevated BOD in rivers. 

A landmark study published in 1925 provided a mathematical 

description of the process of oxygen depletion and re-aeration 

in rivers. The so-called Streeter-Phelps dissolved oxygen sag 

curve is still in use; it was developed specifically for point 

sources of BOD and highlights the emphasis placed on point 

sources of pollution (Streeter and Phelps, 1925). Low oxygen 

concentrations in rivers continued to be a problem throughout 

most of the 20th century. In the most heavily polluted rivers, 

periods of low oxygen conditions may affect the interpretation 

of nitrogen concentration data. This is especially relevant if 

only a single form of nitrogen, such as nitrate, is analyzed. 

Low oxygen conditions can induce denitrification or can 

inhibit ammonium oxidation and affect interpretation of these 

data. 

Continued calls to improve navigation and flood control 

resulted in significant water infrastructure development 

throughout the country, although these accomplishments 

sometimes directly contradicted goals to improve river water 

quality. The Rivers and Harbors Act of 1927 mandated that 

the Corps of Engineers maintain a 9-foot navigational channel 

from Cairo, Ill. to St. Louis, Mo. This was accomplished 

through dredging and construction of wing-dams and so did 

not disrupt the ability of the river to carry wastewater away 

from population centers. After passage of the 1930 Flood 

Control Act, the Army Corps of Engineers began extending 

the 9-foot navigational channel upstream to Minneapolis-St. 

Paul, which required that a series of locks and dams be 

built on the Upper Mississippi River (Scarpino, 1985). The 

presence of these structures created slack water pools, which 

did severely curtail the ability of the river to remove municipal 

wastewater. Lock and Dam 2 in Hastings, Minn., was 

completed in 1931 and the slack water pool became the final 

resting place of most of the waste generated by Minneapolis 

and St. Paul. The resulting conditions eventually prompted the 

Twin Cities to build the first wastewater treatment plant on 

the Upper Mississippi (Scarpino, 1985). Construction of this 

treatment plant began in 1934 and was subsidized by grants 
Introduction 5

from the Public Works Administration, which was created as 

part of the New Deal (Scarpino, 1985). The willingness of 

the Federal government to become involved in such projects 

re-invigorated the stagnating field of wastewater treatment 

(Melosi, 2000).

Federal spending on water treatment projects increased 

substantially during the New Deal era. Franklin Roosevelt’s 

Public Works Administration completed nearly 2,500 water 

projects including wastewater treatment plants (Merchant, 

2002). Approximately three-quarters of all projects 

financed went to towns with populations of 1,000 people 

or less (Melosi, 2000) and filled an important gap in water 

infrastructure and sanitation. Small communities began 

to share in the progress that large cities had made toward 

combating waterborne disease. National rates of typhoid fever 

infections decreased from 34 cases per 100,000 people in 1932 

to fewer than 4 cases per 100,000 people in 1945 (Merchant, 

2002).

During the late 1920s and early 1930s, the United States 

also was experiencing arguably the worst environmental 

disaster in its history—the Dust Bowl. Eroding sediment 

and drought conditions were largely to blame for the severe 

dust storms experienced throughout semi-arid plains. 

However, water-driven gully and sheet erosion also were 

widespread and deposited enormous amounts of sediment into 

waterbodies throughout the agricultural region (Hansen and 

Libecap, 2004). At least one study connected serious habitat 

degradation in rivers and streams with erosion from heavily 

cultivated areas (Ellis, 1936).

The Rise of Industrial Waste

New Deal investments provided much needed momentum 

to the goal of improving water quality, but with the outbreak 

of World War II, emphasis shifted toward promoting industrial 

output rather than safeguarding water supplies. Improvements 

made during the New Deal continued to reduce water-quality 

degradation due to municipal sewage releases (Paavola, 2006), 

but industrial pollution was significantly increasing. As a 

result, industrial waste became the largest source of water 

pollution by the end of World War II (Murphy, 1961). There 

was growing awareness among public health officials that 

industrial wastes were becoming an important threat to water 

supplies. In 1942, the Public Health Service recommended for 

the first time that water-quality standards include maximum 

permissible concentrations for industrial waste products 

having severe physiological effects, such as heavy metals and 

some synthetic organic compounds (Tarr, 1996). Concern over 

the quality of waters within the Nation’s rivers also increased. 

During the opening decades of the 20th century, improving 

water quality was understood to mean decreasing the risk of 

contracting waterborne illness from consumption of polluted 

water. With that goal largely accomplished by the early 1940s, 

more attention began to be paid to improving conditions in 

the rivers themselves. The U.S. Geological Survey began 

regularly collecting and publishing water-quality data from 

streams around the Nation, reflecting the increased emphasis 

on water quality. However, attempts to improve water-quality 

standards were largely set aside during World War II because 

of the need to increase wartime industrial production (Murphy, 

1961).

The development of synthetic organic compounds 

combined with a reluctance to regulate industry during 

World War II led to a dramatic shift in the magnitude and 

nature of water pollution following the end of World War 

II. Synthetic detergents and chlorinated hydrocarbons were 

widely produced and released into surface waters for the first 

time and posed a long-term threat to human and ecological 

health (Tarr, 1996). Groundbreaking work by M.M. Ellis at the 

newly created U.S. Fish and Wildlife Service demonstrated the 

dangers of DDT (dichlorodiphyenyltrichloroethane) on aquatic 

life (Scarpino, 1985). Recognizing the need for strengthened 

water-quality laws, the U.S. Congress began drafting bills 

specifying greater involvement of the Federal government 

in enforcement of water-quality standards. Their work 

culminated in passage of the 1948 Federal Water Pollution 

Control Act.

Growth Era

By most measures, the 1948 Water Pollution Control 

Act was an ineffective piece of legislation that had very little 

impact on water pollution in the United States, even though 

it was the first Federal attempt to deal with overall water 

pollution. The importance of this act stems from the fact that 

it laid the foundation for a series of improvements ultimately 

resulting in the 1972 Clean Water Act. As passed in 1948, the 

Water Pollution Control Act was limited to interstate waters, 

those that crossed or formed State borders, and authorized the 

Surgeon General to focus only on pollution that endangered 

the “health or welfare of persons in a State other than that in 

which the discharge originated” (Milazzo, 2006). Enforcement 

of the law was left to the States, and the Surgeon General 

could only initiate Federal involvement if the polluting 

State agreed. As a result, in 8 years of existence, not a single 

pollution abatement order was issued under the 1948 law 

(Milazzo, 2006).

In 1947, the conversion of a former munitions plant in 

Muscle Shoals, Ala., to the first large-scale synthetic fertilizer 

plant also proved to be a pivotal moment for the future of 

both farming and water quality in the United States. The 

plant originally used the Haber-Bosch process to produce 

ammonium nitrate for use in explosives during World War II. 

After the cessation of hostilities, the demand for explosives 

decreased, so this material began to be used as fertilizer on 

farms around the country (Pollan, 2006). Fertilizer application 

to agricultural fields was not a new phenomenon in 1947, 

as farmers relied upon animal manure to enrich soil before 

synthetic fertilizers became widely available. However, 

fertilizer usage became much more prevalent once synthetic 

fertilizers were developed in the middle part of the 20th 

century. Between 1945 and 1951, the amount of fertilizer 
6 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

nitrogen applied to agricultural fields doubled from 0.5 to 

1.0 million tons per year and by 1989, it reached 10 million 

tons per year (Alexander and Smith, 1990; Ruddy and others, 

2006); although present in fertilizer in smaller quantities, 

agricultural applications of phosphorus also were increasing 

during this time. The acres of cropland on which commercial 

fertilizer was applied nearly doubled between 1954 and 1978 

from 123 to 226 million acres.

During the middle of the 20th century, there was a largescale shift from agriculture based on small farms relying on 

organic fertilizers to large and intensively operated industrial 

farms that focused on growing single crops in monoculture 

(Novotny, 2003). The advent of an industrial agricultural 

system highly reliant on synthetic fertilizers paved the way 

for tremendous increases in yield, and has been implicated in 

prevalent and widespread nutrient pollution observed in many 

streams and rivers around the country (Goolsby and others, 

1999). Annual yield for corn ranged from 20 to 30 bushels per 

acre from 1867 to 1944 but began to increase substantially 

thereafter (National Agricultural Statistics Service, 2010). 

By 1960, yield reached 50 bushels per acre and then tripled 

to 150 bushels per acre by 2009 (National Agricultural 

Statistics Service, 2010). The success in increasing yield 

occurred through the development of new corn varieties and 

changes to agricultural practices, including the widespread 

use of pesticides, but all of it was made possible by the 

availability of nutrient fertilizers to increase plant growth. 

Widespread fertilizer application also resulted in elevated 

nitrogen concentrations in groundwater and surface water 

and eventually contributed to eutrophication in the Nation’s 

waterways, particularly in coastal areas.

Coincident with the increase in industrialization and 

specialization in crop production during this time, animal 

production was developing in a similar direction (MacDonald 

and McBride, 2009). Livestock increasingly began to be 

raised at high densities in indoor facilities called concentrated 

animal feeding operations (CAFOs). CAFOs were introduced 

during the 1950s to grow poultry and later expanded to 

include cattle and swine during the 1970s and 1980s. By the 

turn of the century, CAFOs produced most animals utilized 

for human consumption in the United States (Burkholder and 

others, 2007). These concentrations of livestock in a limited 

area produce excess concentrations of manure-based nutrients 

that enter streams and rivers from large manure lagoons that 

may be poorly constructed or that overflow during large 

precipitation events. Although both nitrogen and phosphorus 

are present in animal waste, CAFOs are an especially 

important source for phosphorus (Sharpley and Moyer, 2000; 

Ruddy and others, 2006). 

The understanding of the role of inorganic nutrients, 

especially nitrogen and phosphorus, as pollutants developed 

slowly during the second half of the 20th century. 

Eutrophication of lakes and rivers became increasingly 

common, but the underlying factors causing these conditions 

were not widely understood until the 1970s. Phosphoruscontaining synthetic detergents are now known to be a 

particularly acute cause of eutrophication in inland waters, 

but in 1961, the organizers of a conference about Great 

Lakes Pollution stated that detergents caused unsightly 

foam in the water, but were otherwise harmless (De Paul 

University, 1961). As late as 1969, the offered explanations 

for eutrophication ranged from increased water temperature to 

the presence of growth hormones (Schindler, 2006). Richard 

Vollenweider generally is credited with providing the first 

scientific explanation of the link between eutrophication of 

aquatic ecosystems and changes occurring on land, which 

result in greater nutrient input to waterbodies (Schindler, 

2006). Yet his theories continued to be debated well into the 

1970s (Schindler, 1977, 2006). Accordingly, water pollution 

laws did not address nutrient pollution until the 1970s and 

originally focused only on phosphates arising from wastewater 

and detergents.

Aside from the emerging recognition of eutrophication 

as a nutrient issue, general concerns about water supply 

and water quality also were increasing in the middle of the 

20th century. Water usage continued to increase during the 

1950s due to rising affluence, placing further demands on 

aging sewerage and water-treatment facilities. Per capita 

water usage increased from 137 to 157 gal/d between 1955 

and 1965 (Melosi, 2000). Water supply concerns arising 

from increased usage were further compounded because 

many treatment facilities had reached or surpassed their 

design age and capacity, and water sanitation technology had 

largely stagnated since the 1930s (Melosi, 2000; Milazzo, 

2006). However, the response of sanitary engineers to these 

challenges would lead a top official from the U.S. Public 

Health Service to retrospectively declare the 1950s the 

“Decade of Reawakening” for water sanitation (Milazzo, 

2006).

The focus of water sanitation and water quality with the 

original emphasis on preventing waterborne disease, which 

was largely overcome in previous decades, shifted toward 

increasing water supply to support postwar economic growth 

(Milazzo, 2006). The number of people served by public 

waterworks nearly doubled between 1945 and 1965 from 94 

million to 160 million (Melosi, 2000). It was recognized that 

water pollution contributed to water shortages by decreasing 

the ability of cities and towns to reuse existing water. People 

also became increasingly aware of the consequences of 

water pollution because growing affluence allowed them 

the leisure time to participate in outdoor activities (Poston, 

1961). Updates to the Water Pollution Control Act passed in 

1956 provided for greater Federal support to State programs 

to reduce pollution in interstate, coastal, or Great Lakes 

waters (Everts and Dahl, 1957). The act preserved State 

primacy in setting water-pollution standards with the Federal 

role limited to technical guidance, as well as a Federal grant 

system to assist in the construction of sewage treatment 

plants. Federal grants were authorized for projects aiming 

to improve water quality for the purpose of increasing water 

supplies for agriculture and industrial use, or “propagation of 

fish and aquatic life and wildlife” (Everts and Dahl, 1957). 
Introduction 7

This shift emphasized the emerging thinking that in-stream 

water quality was a legitimate reason for water treatment. The 

act also called for substantially increasing the collection of 

basic chemical and biological water-quality data to document 

existing conditions.

Despite the renewed interest, however, water quality 

in streams and lakes continued to deteriorate. Water usage 

increased 40 percent between 1950 and 1955 from 185 to 262 

billion gal/d (Melosi, 2000). Larger water-quality problems 

accompanied increased water usage, as had been the case 

since the 1870s. In 1952, the Cuyahoga River caught fire and 

caused $1.5 million in damage (Melosi, 2000), beach closures 

due to pollution occurred in every major city on the Great 

Lakes in 1960 (Chesrow and Hurwitz, 1961), and Lake Erie 

was recognized as being heavily polluted and eutrophic by the 

1960s (Davis, 1961; Melosi, 2000).

Federal involvement in setting water-quality standards 

was strengthened considerably by passage of the 1965 Water 

Quality Act. In a departure from earlier legislation, States 

were required to set water-quality criteria for interstate 

waters along with plans for implementation and enforcement 

(Milazzo, 2006). The Secretary of Health, Education, and 

Welfare oversaw the program and was permitted to set or 

enforce the criteria if States failed to do so (Melosi, 2000). 

The act also created the Federal Water Pollution Control 

Administration, which was tasked with carrying out its 

objectives. The act attempted to balance the growing needs 

of water-quality regulation with respect for the tradition of 

State supremacy in setting water-quality standards. Finding a 

middle ground between those goals proved difficult, resulting 

in an ambiguous enforcement environment (Melosi, 2000). 

The funding of water-quality improvement plans also was 

insufficient and some of the approved State plans did very 

little to improve water quality. Therefore, once again, water 

quality continued to worsen. Yet, this piece of legislation 

proved to be highly significant as a direct predecessor to the 

1972 Clean Water Act.

The magnitude of national water-quality problems at 

the end of the 1960s was expressed in the Second Annual 

Report of the President’s Council on Environmental Quality: 

the number of fish killed from pollution reached 41 million in 

1969, up from 15 million in 1968 and 6 million in 1960; the 

shrimp harvest in 1965 was 0.2 percent of what it was in 1936; 

and, more than 90 percent of drainage basins were considered 

polluted (Adler and others, 1993). These examples highlight 

what had become a nearly ubiquitous problem in the United 

States—water pollution was a serious and rapidly expanding 

problem.

Government agencies were reorganized in 1970, and the 

U.S. Environmental Protection Agency (EPA) was established 

to replace the Federal Water Pollution Control Administration. 

The EPA was vested with the responsibility to administer 

and enforce all Federal laws dealing with the environment, 

including water quality. Shortly after, in 1972, Congress 

passed the historic amendment to the Federal Water Pollution 

Control Act, commonly known as the Clean Water Act. This 

legislation was a substantial departure from the approach taken 

in the past. Although Federal involvement in water pollution 

control had been evolving since at least 1948, the burden of 

proof always laid with enforcement officials to demonstrate 

that a particular entity was polluting a given body of water 

and that this pollution was negatively affecting some aspect of 

the water usage. The stated goal of the Clean Water Act was 

to “restore and maintain the chemical, physical and biological 

integrity of the Nation’s waters” (Adler and others, 1993). 

Therefore, the logical starting point was that the Nation’s 

waters ought to be free from pollution and entities wishing to 

discharge waste into waterways needed to provide justification 

and receive permission to do so. 

The Clean Water Act, therefore, reversed the previous 

approach by requiring dischargers to obtain a permit via the 

National Pollution Discharge Elimination System (NPDES), 

which defines the allowable limit for the pollution load they 

could discharge into a waterway. Implicit in this approach 

is a distinction between point sources of pollution, defined 

as discharges, whose sources can be clearly identified and 

controlled, and nonpoint or diffuse sources. This second 

category was defined in the Clean Water Act as a range of 

pollution sources primarily from runoff and atmospheric 

deposition, or sources that cannot be precisely identified 

and are difficult to measure and quantify (Novotny, 2003). 

Delivery of pollutants from nonpoint sources is often sporadic, 

linked to events such as storms that generate runoff from 

agricultural fields or urban areas. Therefore, these sources are 

more difficult to control than discharges from traditional point 

sources.

Recent History 

Following the requirement in the 1972 Clean Water Act 

that dischargers of pollution must abide by limits established 

by the NPDES permit, treatment of effluent wastewater was 

greatly enhanced. The Act specified that municipal sewage 

treatment facilities provide the best treatment practicable or 

available by the late 1970s and early 1980s, with a minimum 

of secondary treatment that includes on-site biological 

oxidation of organic wastes in wastewater (Patrick, 1992). 

States were directed to define water-quality standards for all 

State waters, and prepare water-quality management plans for 

achieving those standards based on establishing relationships 

between water quality and land use. The plans were mandated 

to quantify total maximum daily loads (TMDLs) for pollutants 

in streams that did not meet the standards, defining the 

permitted load for each target constituent from all contributing 

sources, including point and nonpoint sources. Nonpoint 

sources generally were assumed to encompass all agricultural 

operations, including runoff from fields, irrigation return 

flows, and stormwater discharges from CAFOs. 
8 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

The primary emphasis in the Clean Water Act was 

municipal and industrial point sources, whose discharges were 

limited and controlled by the NPDES permits. No mechanisms 

for control of nonpoint sources were implemented by the Act, 

and no incentives for complying with pollution abatement 

programs were specified for these sources. Nonetheless, the 

enactment of a land-use planning process in the development 

of management plans represented the first formal recognition 

that control of point sources would not be sufficient to solve 

the full range of pollution problems in the country (Patrick, 

1992).

During subsequent years, the Clean Water Act was 

amended. In 1974, health- and nuisance-related standards for 

drinking water were established. In 1977, amendments added 

the Rural Clean Water Program to support implementation 

of best management practices controlling pollution from 

nonpoint sources (Patrick, 1992). More emphasis was placed 

on developing measures to control agriculturally related 

pollution, with guidance provided by the Department of 

Agriculture. Gradually, legislative focus began to incorporate 

explicit land use changes in the form of wetland protection 

with the passage of the Wetlands Resources Act in 1986, 

which provided Federal funding for acquisition and 

conservation of wetlands. In 1987, further amendments to the 

Clean Water Act required States to develop more stringent 

management programs specifically targeting nonpoint 

sources, including agricultural sources. Still, legislation was 

largely ineffective because of insufficient funding and limited 

consequences of noncompliance. A significant component of 

the dilemma relative to controlling nonpoint source pollution 

lay in the strong relationship between land use and nonpoint 

source discharges, because management of land use was not 

a Federal concern but rather within the legislative domain of 

State and local government (Patrick, 1992). 

Over the course of the last two decades of the 20th 

century, a number of important research programs were 

implemented to investigate the association between land use 

and nonpoint pollution. The Soil and Water Resources Act 

of 1977 mandates that the Secretary of Agriculture conduct 

studies via the Soil Conservation Service to assess national 

soil and water conditions, and to develop conservation 

programs in partnership with the States. The USDA initiated 

the Rural Clean Water Program in 1980, which provides 

funding for long-term watershed projects focused on 

identifying successful approaches to controlling nonpoint 

pollution from agricultural sources (Novotny, 2003). The 

National Urban Runoff Project was carried out in the 1980s 

to study the characteristics of urban runoff; results laid the 

foundation for the expansion of the NPDES permit coverage 

in the mid-1990s to include runoff from urban and industrial 

sources (Novotny, 2003). Finally, in 1983, the States of 

Pennsylvania, Maryland, and Virginia, as well as the mayor 

of the District of Columbia and the administrator of the EPA, 

established the Chesapeake Bay Agreement to investigate 

the causes of declining water quality in Chesapeake Bay. 

Excess nutrients from upstream sources were found to be a 

significant factor. The drainage basin model produced by this 

collaboration provided the means to articulate the relative 

contribution of point and nonpoint sources, and especially to 

identify specific areas associated with elevated nutrient loads 

(Novotny, 2005). This program is ongoing and among the 

forefront in the Nation for developing management programs 

to assist farmers in reducing soil and nutrient losses. 

Despite these efforts, more than 50 percent of receiving 

water bodies were not meeting the water-quality goals 

established by the Clean Water Act by the end of the 

20th century (Novotny, 2003). As a result of this lack of 

comprehensive progress, dozens of lawsuits were filed in the 

mid-1990s against the EPA and the States by environmental 

groups to implement the TMDL requirement of the Clean 

Water Act. Although subject to legal challenge, the TMDL 

process is currently recognized as the most effective legal 

tool that can result in minimizing pollution loads from 

nonpoint sources, which are widely recognized to be primarily 

agricultural and urban sources (Novotny, 2003). 

In the last decade of the 20th century, new water-quality 

concerns arose about the effect of hydraulic fracturing 

(fracking) procedures utilized in commercial natural gas 

production from shale formations (Curtis, 2002). Abundant 

natural gas resources have been identified in shale basins that 

include the Barnett Shale, New Albany Shale, Lewis Shale, 

and Marcellus Shale, potentially affecting a number of rivers 

in our study (Kargbo and others, 2010). Fracking procedures 

include injecting water horizontally through deep well 

casings at sufficient pressure to create fractures in shale-gas 

formations so that the gas can be extracted. This technique 

requires large volumes of fresh water augmented by drilling 

additives. The wastewater contains chemicals found in the 

geological formation as well as those found in the additives 

(Kargbo and others, 2010). Contaminants associated with 

fracking include ammonium and other salts, toxic metals, a 

wide range of organic compounds, and radionuclides (Kargbo 

and others, 2010). At the time this report was written, effective 

treatment or regulation of fracking wastewater was not well 

developed, although the EPA was beginning to develop 

national standards for fracking wastewater discharged to 

natural streams (Kusnetz, 2011).

This study is focused on compiling data from selected 

river basins that will be useful to evaluate how these long-term 

changes in policy have coincided with changes in nutrient 

concentrations. The emphasis is on acquiring data to support 

assessment of changes throughout the entire course of the 

20th century, to the greatest degree possible. This perspective 

is unprecedented and challenging to develop, especially 

given the changes in sampling and analytical methodologies 

over such a lengthy period. Nonetheless, it is a valuable and 

critical one for understanding the impact and effectiveness 

of legislation in controlling excess delivery of nutrients to 

streams and rivers of the Nation.
Methods 9

Methods

Stream-Gaging Station Selection

Sites were selected based on the availability of data 

and for representation of different basin types in the study. 

Therefore, basins were included to represent a high degree 

of agricultural development, some with urban development, 

some with very little overall development, and sites which 

represented different regions of the conterminous United 

States. In all, 26 individual stations were selected along rivers 

reaches of interest (table 1, fig. 1). In some cases, several 

stations were selected within the same river basin with the 

result that some basins are nested within other larger basins. 

River basins with multiple stations nested within them include 

the Mississippi, the Illinois, the Ohio, and the Upper Colorado 

(table 1, fig. 1). For the purposes of describing water-quality 

history and ancillary data trends, the river basin names as 

they appear in table 1 are used. Additionally, river basins 

and associated USGS stream-gaging stations are shown in 

table 1 and described in greater detail in individual river basin 

sections. In order to place the river basins into greater spatial 

context, we describe them in terms of physiographic provinces 

(fig. 2).

Data Sources

An initial assessment of data availability was performed 

by aggregating all data available in the USGS National 

Water Information System (NWIS; http://waterdata.usgs.gov/

nwis) and the EPA Storage and Retrieval System (STORET; 

http://www.epa.gov/storet). Data outside of these databases 

were found by searching the USGS Publications Warehouse, 

State agency publications, water-treatment facilities, and 

Canadian Federal agencies, and U.S. Federal agencies outside 

of the USGS and EPA. The availability of data for each site 

described in this publication reflects the ultimate outcome of 

these searches. Streamflow, nutrient, and inorganic carbon data 

availability are reported, but often major ions, measures of 

oxygen demand, and other field parameters, such as turbidity, 

residue on evaporation, and water temperature are available as 

well.

Table 1. River basins included in this study and their associated reference stream gaging station.

[Abbreviations: No., number; USGS, U.S. Geological Survey]

Geographic 

region River basin Station name USGS station No. Latitude Longitude

Eastern Connecticut Connecticut River at Thompsonville, Conn. 01184000 41°59'14" 72°36'19"

Delaware Delaware River at Trenton, N.J. 01463500 40°13'18" 74°46'41"

Schuylkill Schuylkill River at Philadelphia, Pa. 01474500 39°58'04" 75°11'19"

Potomac Potomac River (adjusted) near Washington, D.C. 01646502 38°56'58" 77°07'39"

James James River at Cartersville, Va. 02035000 37°40'16" 78°05'09"

Great Lakes Maumee Maumee River at Waterville, Ohio 04193500 41°30'00" 83°42'46"

St. Lawrence St. Lawrence River at Cornwall Ontario, near Massena, N.Y. 04264331 45°00'22" 74°47'42"

Central Middle Ohio Ohio River at Louisville, Ky. 03294500 38°16'49" 85°47'57"

Lower Ohio Ohio River at Cairo, Ill. 03614500 36°59'45" 89°08'36"

Des Moines Des Moines River at Keosauqua, Iowa 05490500 40°43'40" 91°57'35"

Middle Illinois Illinois River at Kingston Mines, Ill. 05568500 40°33'11" 89°46'38"

Lower Illinois Illinois River at Valley City, Ill. 05586100 39°42'12" 90°38'43"

Upper Mississippi Mississippi River at Grafton, Ill. 05587450 38°58'05" 90°25'44"

Missouri Missouri River at Hermann, Mo. 06934500 38°42'35" 91°26'19"

Middle Mississippi Mississippi River at Thebes, Ill. 07022000 37°12'59" 89°28'03"

Arkansas Arkansas River at Murray Dam, near Little Rock, Ark. 07263450 34°47'35" 92°21'30"

Lower Mississippi Mississippi River at Baton Rouge, La. 07374000 30°26'44" 91°11'30"

Brazos Brazos River at Richmond, Tex. 08114000 29°34'57" 95°45'28"

Upper

Colorado 

River

Gunnison Gunnison River near Grand Junction, Colo. 09152500 38°58'60" 108°27'02"

Colorado at Cisco Colorado River near Cisco, Utah 09180500 38°48'38" 109°17'36"

Green Green River at Green River, Utah 09315000 38°59'10" 110°09'04"

San Juan San Juan River near Bluff, Utah 09379500 37°08'49" 109°51'53"

Colorado at Lee’s Ferry Colorado River at Lees Ferry, Ariz. 09380000 36°51'53" 111°35'18"

Western Santa Ana Santa Ana River below Prado Dam, Calif. 11074000 33°53'00" 117°38'43"

San Joaquin San Joaquin River near Vernalis, Calif. 11303500 37°40'34" 121°15'59"

Willamette Willamette River at Salem, Oreg. 14191000 44°56'39" 123°02'34"
10 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 1. Land-cover data and river basins included in this study. Monitoring stations are the reference stream gaging stations for all river reaches of 

interest (see table 1).

tac12-0694_fig01-All

-125° -95° -65° -70° -75° -80° -85° -90° -100° -105° -110° -115° -120° -130°

45°40°35°30°25°20°

Lake Huron

Lake Ontario

Lake Superior

Green 

River

Lower Ohio

Middle Ohio James River

Brazos River

St. Lawrence

Maumee River

Potomac River

Lower

Colorado San Juan

River

UpperColorado Gunnison

River

Arkansas River

Missouri 

River

Lower 

Illinois

Delaware River

Santa Ana River

Middle 

Illinois

Des Moines 

River Schuylkill River

Willamette River

San Joaquin River

Lower Mississippi

Upper 

Mississippi

Connecticut River

Middle 

Mississippi

Lake Huron

Lake Ontario

Lake Superior

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

0 200 400 MILES0 200 400 KILOMETERS

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

Chicago Sanitary and Ship Canal

Appalachian Mountains

Gulf of Mexico

Philadelphia

Chicago Lake Michigan

Nashville

St. Louis

MinneapolisSt. Paul

Denver

Chicago River

Des Plaines River

Butler

Pittsburgh

Cairo

Hastings

Muscle Shoals

Lake Erie Cuyahoga River

Chesapeake Bay

San Bernardino

Riverside

ORANGE COUNTY

Great Plains

Atchafalaya River

South Platte River

LaurentialGreat Lakes

Canadian Shield

Ri o Grande

Gulf of Mexico

Philadelphia

Chicago Lake Michigan

Nashville

St. Louis

MinneapolisSt. Paul

Denver

Chicago River

Chicago Sanitary and Ship Canal

Des Plaines River

Butler

Pittsburgh

Cairo

Hastings

Muscle Shoals

Lake Erie Cuyahoga River

Chesapeake Bay

San Bernardino

Riverside

ORANGE COUNTY

Great Plains

Atchafalaya River

South Platte River

LaurentianGreat Lakes

Canadian Shield

Ri o Grande

Appalachian Mountains
Methods 11 Figure 2. Physiographic provinces of the conterminous United States along with river basins in this study. Monitoring stations are the reference stream gaging stations for all river reaches of interest (see table 1).

tac12-0694_fig.02-Physio

60° 64° 68° 72° 76° 80° 84° 88° 92° 96° 100° 104° 108° 112° 116° 120° 124° 128° 132°

46°42°38°34°30°26°22°18°14°

Upper 

Colorado

Canadian Shield

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

00 250 500 KILOMETERS

250 500 MILES

Explanation

Green River

Lower Ohio

Middle Ohio James River

Brazos River

St. Lawrence

Maumee 

River

Potomac River

Lower 

Colorado

San Juan River

Upper 

Colorado

Gunnison River

Arkansas River

Lower Illinois

Missouri River

Delaware River

Santa Ana River

Middle 

Illinois Des Moines River

Schuylkill River

Willamette River

San Joaquin River

Lower Mississippi

Upper Mississippi

Connecticut River

Middle 

Mississippi

Canadian Shield

Watershed boundary

Monitoring station

New EnglandCoastal PlainPiedmont PlateauBlue RidgeValley and Ridge

St. Lawrence ValleyAppalachian Plateau

Superior UplandsAdirondackInterior Low PlateausCentral LowlandsGreat Plains

Ozark PlateausOuachita

Southern Rocky MountainsWyoming BasinMiddle Rocky MountainsNorthern Rocky MountainsColumbia Plateau

Colorado PlateauBasin and Range

Cascade-Sierra MountainsPacific BorderLower Californian No data

EXPLANATION
12 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Parameter Codes Used in this Study

Nitrogen and Phosphorus Codes

In our analysis of the availability of nitrogen data, 

several nitrogen species were considered including nitrate, 

ammonium, organic nitrogen, and total nitrogen. For 

phosphorus, both dissolved and total phosphorus were 

considered. Where necessary, concentrations were transformed 

so that all were reported consistently at the elemental level 

(for example, ammonia was transformed to N). Algorithms to 

calculate missing nutrient species were utilized when possible 

and the calculated values were considered to be equivalent to 

the reported values. Nitrate plus nitrite is reported as nitrate if 

the latter was missing. Similarly, filtered and unfiltered nitrate 

measurements are considered equivalent because nitrate is 

typically a small portion of the particulate pool (Harrington 

and Harrington, 2009). Table 2 lists the parameter codes used 

in the algorithms to identify and calculate (where necessary) 

the range of nitrogen and phosphorus species in this analysis. 

Inorganic Carbon Codes

At least 32 separate parameter codes express some form 

of inorganic carbon in NWIS and STORET. In order to make 

these parameter codes comparable, dissolved inorganic carbon 

was calculated, in milligrams carbon per liter (mg C/L), for 

any sample reporting dissolved inorganic carbon, alkalinity, 

acid-neutralizing capacity, or bicarbonate. In some cases, 

a sample listed several parameters relating to dissolved 

inorganic carbon. Parameters were preferentially used that 

would produce the best estimate of dissolved inorganic carbon 

in a given sample. Filtered, field-titrated measurements were 

given highest priority because significant changes to alkalinity 

and acid neutralizing capacity (ANC) can occur in the holding 

time between field and laboratory observations. Reported 

alkalinity or ANC values were preferred over reported HCO3 

values because HCO3 was determined in older samples by 

titration to pH 4.5, which has been shown to be dependent on 

temperature and ionic strength of the water sample (Barnes, 

1964). All alkalinity parameter codes, their priority of 

selection, and the frequency of occurrence in our database are 

listed in table 3. Parameter code 00410 comprised 65 percent 

of all alkalinity observations in our database. Prior to 1980, 

measurements of unfiltered water titrated to pH 4.5 were 

reported as parameter code 00410 regardless of whether the 

titration was performed in the field or the laboratory. However, 

it is assumed that most of these samples were analyzed in 

a laboratory setting (U.S. Geological Survey, 1988). In the 

USGS database, roughly 80 percent of the observations 

having parameter code 00410 occur prior to 1980. Subsequent 

to 1980, parameter code 00410 was reserved for analyses 

performed in the field and parameter code 90410 was used to 

denote the same analysis performed in a laboratory. Roughly 

7 percent of all of the alkalinity observations originate from 

parameter code 90410. Parameter code 00440 (bicarbonate), 

determined by fixed endpoint titration on unfiltered water 

samples in the field, comprised approximately 10 percent of 

the database. This parameter code was used most frequently 

between 1950 and 1970. Analyses of alkalinity by incremental 

titration performed in the field, parameter code 39086, also 

comprised roughly 10 percent of the observations. All other 

parameters were less common, none of which made up more 

than 2 percent of the total number of observations.

Alkalinity and ANC are expressed in terms of the 

amount of inorganic carbon available to react with divalent 

calcium (Ca2+), given in the units mg CaCO3 L-1. Converting 

to mg C L-1 requires both stoichiometric conversion and 

consideration of the charge on the inorganic carbon molecule, 

because twice as much carbon is available to react with 

Ca2+ if it exists as HCO3

-

 than if it exists as CO3

2-. In order 

to calculate the distribution of inorganic carbon species, 

dissociation constants Ka1 and Ka2 were calculated as 

functions of temperature (Plummer and Busenberg, 1982) and 

the proportionate distribution of CO3

2- and HCO3-

 (rc) as

r

H

K

C =

+



  















+

1

1

2

, (1)

where [H+] is the hydrogen ion concentration, calculated as 

10-pH. Individual constituents of dissolved inorganic carbon 

were then calculated as:

HCO 3 mg C L ALK mg CaCO L - -1

3

-1 = − ( ) 1 0 r × × . ( 24 ) C (2)

CO3 mg C L ALK mg CaCO L 2- -1

3

-1 = × rC 0 1. ( 2× ) (3)

CO mg L HCO H

2

-1 3 = × ×

− + ( )( )

12 1000 Ka1

(4)

where ALK is the reported alkalinity or ANC, and HCO3

-

 in 

equation (4) was calculated as in equation (1) and expressed in 

mg C L-1. Dissolved inorganic carbon was then calculated as 

the sum of CO2, HCO3

-

, and CO3

2-.
Methods 13

Table 2. Parameter codes used in nitrogen and phosphorus calculations.

Constituent Abbreviation Parameter

code Parameter description

Organic N TON 00605 Organic nitrogen, water, unfiltered, milligrams per liter

Ammonia NH3 00610 Ammonia, water, unfiltered, milligrams per liter as nitrogen

71845 Ammonia, water, unfiltered, milligrams per liter as NH4

71846 Ammonia, water, filtered, milligrams per liter as NH4

00608 Ammonia, water, filtered, milligrams per liter as nitrogen

NH3 + Organic N TON + NH3 00625 Ammonia plus organic nitrogen, water, unfiltered, milligrams per liter as nitrogen

00635 Ammonia plus organic nitrogen, water, unfiltered, milligrams per liter as nitrogen

Nitrite NO2 00615 Nitrite, water, unfiltered, milligrams per liter as nitrogen

71855 Nitrite, water, unfiltered, milligrams per liter

71856 Nitrite, water, filtered, milligrams per liter

Nitrate NO3 00620 Nitrate, water, unfiltered, milligrams per liter as nitrogen

71850 Nitrate, water, unfiltered, milligrams per liter

00618 Nitrate, water, filtered, milligrams per liter as nitrogen

71851 Nitrate, water, filtered, milligrams per liter

Nitrate + Nitrite 1NO3 00630 Nitrate plus nitrite, water, unfiltered, milligrams per liter as nitrogen

00631 Nitrate plus nitrite, water, filtered, milligrams per liter as nitrogen

Total nitrogen TN 00600 Total nitrogen, water, unfiltered, milligrams per liter

62855 Total nitrogen (nitrate + nitrite + ammonia + organic-N), water, unfiltered, 

analytically determined, milligrams per liter

71887 Total nitrogen, water, unfiltered, milligrams per liter as nitrate

Dissolved phosphorus TDP 00666 Phosphorus, water, filtered, milligrams per liter as phosphorus

71888 Phosphorus, water, filtered, milligrams per liter as phosphate

00671 Orthophosphate, water, filtered, milligrams per liter as phosphorus

00660 Orthophosphate, water, filtered, milligrams per liter

91004 Orthophosphate, water, filtered, micrograms per liter as phosphorus

99122 Orthophosphate, water, filtered, field, milligrams per liter

99893 Phosphorus, water, filtered, modified jirka method, milligrams per liter

Total phosphorus TP 00665 Phosphorus, water, unfiltered, milligrams per liter as phosphorus

71886 Phosphorus, water, unfiltered, milligrams per liter as phosphate

1

 NO3 and NO2 + NO3 are considered equivalent in historical data because NO2 concentration is typically much lower than NO3 concentration.
14 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Table 3. Alkalinity parameter codes shown in descending hierarchy along with their frequency in 

the database used in this study.

[Symbol: <, less than]

Constituent Parameter

code Frequency Percentage of frequency

Dissolved inorganic carbon (DIC) 00691 2,273 0.56

Alkalinity – Filtered, field 29802 934 0.23

39086 40,084 9.85

00418 204 0.05

39036 6,580 1.62

Bicarbonate – Filtered, field 63786 0 0

00453 663 0.16

29804 1 <0.01

Acid-neutralizing capacity – 

Unfiltered, field

29813 0 0

00419 3,944 0.97

00410 264,963 65.14

00416 7 <0.01

00417 3,710 0.91

90410 28,603 7.03

95410 56 0.01

00413 56 0.01

00431 3,058 0.75

00685 482 0.12

Bicarbonate – Unfiltered, field 00450 1 <0.01

99440 50 0.01

00440 41,903 10.3

00449 0 0

90440 27 0.01

00451 5,886 1.45

95440 223 0.05

Alkalinity – Filtered, laboratory 29803 669 0.16

39087 56 0.01

00421 0 0

29801 1,641 0.4

Bicarbonate – Filtered, laboratory 29806 0 0

Acid-neutralizing capacity – 

Unfiltered, setting not specified

00431 0 0

00425 688 0.17
Methods 15

Stream Discharge and Runoff Calculations

All discharge and runoff values presented in this 

publication were derived from information obtained from 

NWIS. Annual discharges were calculated from the annual 

average discharge reported in NWIS and averaged over at 

least 10 years. In most cases, annual discharge was averaged 

over much longer time periods. For drainage basins in which 

discharge was subject to significant hydrologic modification, 

water withdrawals, or water infrastructure development, 

annual averages are presented from after the modification. 

Therefore, the values presented should reflect modern annual 

discharge unless otherwise noted. 

Runoff was calculated as annual discharge divided by 

drainage area and expressed as millimeters per year and used 

as a general descriptive characteristic of water availability in 

the basins, as well as a way of comparing the river reaches 

of interest to one another. In some cases, drainage basins 

contain significant non-contributing areas, such as endorheic 

basins. For these basins, in NWIS, the contributing drainage 

area is sometimes distinguished from total drainage area. In 

these cases, we calculated runoff from total drainage area but 

discuss how runoff may differ if only contributing area was 

used.

Ancillary Data Methodology

We analyzed ancillary data that are presumed to be 

relevant to understanding the changes in water quality 

associated with each of the basins of interest. In this sense, 

ancillary data were considered to represent potential causative 

factors of observed water chemistry in these river basins. 

The ancillary data presented in the following sections are 

not meant to be exhaustive, but rather allow us to place 

river basins in context historically and with respect to one 

another. These potential causative factors include indicators of 

agricultural intensity, fertilizer usage, nitrogen and phosphorus 

inputs from livestock, and population density. 

In order to investigate changes in land use associated with 

agriculture, county-level data were evaluated from the Census 

of Agriculture beginning in 1870. Census of Agriculture data 

from 1870 to 1910 are from public document ICPSR 2896 

(Haines and Inter-university Consortium for Political and 

Social Research, 2004). Agricultural data from 1930 and 1940 

were derived from the decennial population census conducted 

in those years. For census years 1920, 1949, and all years 

from 1954 to 2002, Census of Agriculture data tables were 

digitized and organized into data files (M. Haines, University 

of Colgate, written commun., 2004). Fertilizer data were used 

from two USGS publications, the first reported annual countylevel data from 1945 to 1985 (Alexander and Smith, 1990) and 

the second reported county-level fertilizer usage from 1987 to 

2001 (Ruddy and others, 2006). No fertilizer usage data were 

available for 1986 and so this year was excluded from our 

analysis. 

In each case, nitrogen and phosphorus inputs were 

calculated from both farm and non-farm fertilizer usage. 

Nitrogen and phosphorus inputs were also estimated from 

livestock and farm animals using Census of Agriculture data 

and following the general methods explained in Ruddy and 

others (2006). County-level population data were downloaded 

from the National Historical Geographic Information System 

(Minnesota Population Center, 2011). Population census data 

are available on a decadal basis, and Census of Agriculture 

data are available on a decadal basis from 1870 to 1920 with 

subsequent agricultural census years more frequent, every 4 to 

5 years, up to 2002. State-level data from the USDA National 

Agricultural Statistical Service annual survey were also used 

to estimate corn harvest on an annual basis. County-level corn 

harvest data from the closest agricultural census year were 

used to estimate the proportion each county contributed to 

state-level corn harvest. State-level survey data were used to 

estimate county-level corn harvest in the non-census years.

Animal manure is a nonpoint source of nitrogen and 

phosphorus so the production of nitrogen and phosphorus also 

was calculated in the basins of interest. To calculate animal 

livestock contributions to nitrogen and phosphorus inputs, we 

tabulated the population of several animal groups, calculated 

the production of nutrients by each animal group, and then 

summed the contribution of each animal group to calculate 

total animal contribution of nitrogen and phosphorus. The 

animal groups consisted of cattle, horses, sheep, chickens, and 

turkeys. These groupings and animal nutrient production rates 

were identical to those presented in Ruddy and others (2006), 

except that all cattle were included in a single group rather 

than being divided into sub-categories. Animal contributions 

to nitrogen and phosphorus production were calculated for the 

agricultural census years and then interpolated on an annual 

time scale to allow direct comparison with annual fertilizer 

input data.

Agricultural and population statistics on a basin scale 

were calculated by spatially relating county-level data to basin 

geography. The historical U.S. County boundary file was used 

to create lists of counties contained or partially contained in 

each river basin at 10-year intervals beginning in 1870 and 

continuing through 2010. 

The contribution of each county to basin characteristics 

was tabulated on an areal basis such that the metrics reported 

for any county were weighted by the areal proportion of 

the county residing within the river basin. For example, if 

a county lies entirely within a river basin, all of the people 

and farmland of that county were considered to contribute 

to the river basin total. For counties partially inside a basin, 

the county totals were multiplied by the areal proportion of 

the county inside the basin. This approach has the limitation 

of assuming that farmland and population are all distributed 

evenly throughout a county, which is often a poor assumption. 

For large basins encompassing many counties, the assumption 

probably has minimal effect on our calculations. However, 

for smaller drainage basins, significant artifacts can be 

introduced. One extreme example is the Santa Ana River 
16 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

basin, which is situated in small, densely populated areas of 

San Bernardino, Riverside, and Orange Counties in southern 

California. Riverside and San Bernardino Counties are large 

with population centers clustered in the Santa Ana River basin. 

The result is that when calculated on a county-wide basis, 

the population density of the Santa Ana River basin appears 

to be small. Because this river basin was such an outlier, a 

different approach was used to calculate population density. 

We used census tract data, which is presented at a finer spatial 

scale, from 1950 and 2000 to determine the proportion of the 

county population residing within the river basin and used 

this coefficient to calculate population density for each of 

the population census years. Population densities calculated 

for other river basins were reasonably close to values 

published elsewhere (Benke and Cushing, 2005), so no further 

corrections were made.

For basins located partially within Canada, including 

the Missouri, Mississippi, Connecticut, and Saint Lawrence, 

the Canadian portion of the basin was excluded from our 

calculation of ancillary basin characteristics. For the Missouri, 

Mississippi, and Connecticut River basins, this had a minimal 

impact on our analysis because only a very small fraction 

of the drainage basin is located within Canada (1.4, 0.7, and 

1.2 percent, respectively). However, more than 40 percent 

of the Saint Lawrence River basin is located within Canada 

so it must be assumed that basin characteristics are similar 

in Canada and the United States. This issue is addressed in 

greater detail in section, “Saint Lawrence River.”

Recent Ancillary Data for all Basins

Population

According to the 2000 population census, the most 

densely populated basin in this study was the Santa Ana 

River, with almost 330 people/km2 (U.S. Census Bureau, 

2000) (fig. 3). The Schuylkill River basin, which includes 

parts of Philadelphia and western suburbs, also had more 

than 300 people/km2; and the Illinois River, which includes 

densely populated areas of northern and central Illinois, had 

a population density of 150 and 240 people/km2 in the lower 

and middle sections, respectively (fig. 3). By contrast, the 

five stations considered in the Colorado River basin had the 

lowest population densities, ranging from approximately 2 

to 6 people/km2 (fig. 3). Overall, approximately one-half 

of the river basins included in our study had population 

densities greater than the national average in the year 2000 of 

31 people/km2 (fig. 3).

Farmland Area

Figure 4 shows the percentage of each river basin with 

land usage specified as farmland, according to the 2002 

Census of Agriculture (U.S. Department of Agriculture, 

2005). Farmland was separated into two categories: cropland 

and non-cropland (which includes rangeland and other uses). 

Figure 3. Population density from 2000 census (U.S. Census Bureau, 2000) for all river basins 

included in this study.

Population density in the year 2000, in people per square kilometer 

0 50 100 150 200 250 300 350

River basin

Santa Ana

Schuylkill

Middle Illinois

Lower Illinois

Delaware

Potomac

Middle Ohio

Maumee River

Lower Ohio

Connecticut

Upper Mississippi

Saint Lawrence

Willamette

James

Lower Mississippi

San Joaquin

Des Moines

Middle Mississippi

Brazos

Arkansas

Missouri

Colorado At Cisco

San Juan River

Gunnison River

Colorado at Lees Ferry

Green River

National population density in 2000
Recent Ancillary Data for all Basins 17

Cropland typically is more intensively managed, so basins 

where farmland is primarily cropland can be viewed as having 

a high degree of agricultural intensity. Ten of the river basins 

included in this study had greater than 60 percent of the basin 

area in farmland in 2002, four of the river basins exceeded 

80 percent (fig. 4). There was a notable distinction among the 

most highly agricultural drainage basins based on whether or 

not the primary farmland usage was cropland. Western and 

Great Plains river basins, including the Brazos, Missouri, and 

Arkansas Rivers, had high percentages of total farmland and 

in each case, more than one-half of the farmland was noncropland (fig. 4). However, several river basins located in the 

Midwestern United States had high percentages of the basin 

in farmland and almost all of this was cropland. These include 

the Des Moines, Maumee, Middle Illinois, Lower Illinois, and 

Upper Mississippi River basins (fig. 4). The Lower Mississippi 

River integrates inputs from many of the most heavily 

agricultural areas and had more than 60 percent of the basin 

in farmland, with the primary uses split between cropland and 

non-cropland (fig. 4). The remaining basins were all less than 

50 percent farmland in 2002. However, even among these 

basins, a similar pattern remains with rivers in the Western 

United States, particularly those in the Colorado River basin 

with non-cropland as the primary agricultural land use while 

the rivers in the Eastern United States have primarily cropland 

usage (fig. 4).

Non-Point Sources of Nitrogen and Phosphorus 

from Fertilizer and Livestock

Nonpoint sources of nitrogen (N) from fertilizer and 

animal livestock were highest in the Des Moines River basin 

averaging more than 8 grams of nitrogen per square meter 

per year (g (N/m2)/yr). These sources also contributed more 

than 5 g (N/m2)/yr in the Maumee, Middle Illinois, Lower 

Illinois, and Upper Mississippi (fig. 5A). In contrast, nonpoint 

sources from fertilizer and livestock contributed less than 

1 g (N/m2)/yr in the Connecticut, Delaware, Saint Lawrence, 

and all selected river reaches in the Colorado River basin 

over the same time period (fig. 5A). Fertilizer sources of N 

across all selected river basins ranged from less than 0.1 to 

almost 7 g (N/m2)/yr whereas animal sources ranged from 

about 0.2 to 2 g (N/ m2)/ yr. Fertilizer sources of N were about 

three times larger than animal sources of nitrogen in the 

river reaches with the highest inputs although animal sources 

dominated in the river reaches with the lowest sources of N 

(fig. 5A).

Phosphorus (P) sources followed largely the same 

geographic distribution with the Des Moines, Maumee, Upper 

Mississippi, Middle Illinois, and Lower Illinois all having 

greater than 1.0 g (P/m2)/yr inputs from animal livestock 

and fertilizer (fig. 5B). The river reaches with the lowest 

sources were the Saint Lawrence, Connecticut, and all river 

Figure 4. Agricultural land use in 2002 for all river basins included in this study.

tac12-0694_fig 04

Des Moines

Brazos

Maumee

Lower Illinois

Missouri

Arkansas

Middle Mississippi

Lower Mississippi

Upper Mississippi

Middle Illinois

Lower Ohio

Potomac

San Juan

Middle Ohio

James

Schuylkill

San Joaquin

Colorado at Lees Ferry

Green

Saint Lawrence

Gunnison

Willamette

Delaware

Colorado at Cisco

Connecticut

Santa Ana

Percentage of total area in specified land usage in the year 2002

River basin

Cropland

Non-cropland

0 20 40 60 88 100

EXPLANATION
18 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 5. Average nonpoint sources of (A) nitrogen and (B) phosphorus from fertilizer 

and animal livestock for all river basins included in this study, 1997–2001.

tac12-0694_fig 05

A.

B.

0 2 4 6 8 10

River Basin

Des Moines

Lower Illinois

Maumee

Middle Illinois

Upper Mississippi

Brazos River

Middle Mississippi

Lower Mississippi

Schulykill

Arkansas

Lower Ohio

Missouri

Potomac

San Joaquin

Santa Ana

Middle Ohio

Willamette

James

Delaware

Saint Lawrence

Gunnison

Connecticut

Colorado at Cisco

Green

Colorado at Lees Ferry

San Juan

Des Moines

Lower Illinois

Maumee

Middle Illinois

Upper Mississippi

Brazos River

Middle Mississippi

Lower Mississippi

Schulykill

Arkansas

Lower Ohio

Missouri

Potomac

San Joaquin

Santa Ana

Middle Ohio

Willamette

James

Delaware

Saint Lawrence

Gunnison

Connecticut

Colorado at Cisco

Green

Colorado at Lees Ferry

San Juan

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

River Basin

Areal nitrogen input, in grams of nitrogen per square meter per year (1997-2001)

Areal phosphorus input, in grams of phosphorus per square meter per year (1997-2001)

Fertilizer

Animal livestock

EXPLANATION

Fertilizer

Animal livestock

EXPLANATION
Recent Ancillary Data for all Basins 19

reaches of interest in the Colorado River basin, with less 

than 0.2 g (P/ m2)/yr (fig. 5B). Animal livestock accounted 

for a much larger share of the nonpoint phosphorus that was 

identified in these basins and exceeded fertilizer sources of 

phosphorus in 14 of the basins (fig. 5B). Overall, animal 

livestock and fertilizer contributions had similar ranges, from 

approximately 0 to 1.0 g (P/m2)/yr (fig. 5B).

The highest fertilizer application rates were in the basins 

with the greatest cropland coverage, which emphasized the 

importance of chemical fertilizers to agricultural production in 

these areas. The difference in agricultural production between 

Great Plains river basins, exemplified by the Arkansas River, 

and the central and Mid-Western streams, the Illinois and 

Maumee River basins, are especially apparent.

Corn Production

Corn production in the river basins of interest was also 

analyzed as a more direct indicator of agricultural intensity. 

Averaged over 2000–2010, corn harvest ranged from less than 

0.1 to more than 16,000 bushels/km2 of drainage area (fig. 6). 

The intensively cultivated river basins in the Midwestern 

United States had the highest corn production, the Illinois, Des 

Moines, Maumee, and main stem Mississippi River basins 

(fig. 6). River basins with the lowest corn production were 

mostly in the West including all five drainage basins of interest 

within the Colorado River basin, the Willamette, Santa Ana, 

and San Joaquin Rivers (fig. 6). The James River basin in 

Eastern United States also had notably low corn production 

(fig. 6).

Figure 6. Average corn harvested per square kilometer of drainage area for 2000–2010 for all 

river basins included in this study.

Corn harvest (2000–2010 average), in bushels per square kilometer of drainage area 

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000

River basin

Lower Illinois

Des Moines

Middle Illinois

Upper Mississippi

Maumee

Middle Mississippi

Lower Mississippi

Lower Ohio

Missouri

Saint Lawrence

Schuylkill

Middle Ohio

Arkansas

Potomac

Delaware

Brazos

Gunnison

James

San Joaquin

Colorado at Cisco

Colorado at Lees Ferry

Green

Santa Ana

San Juan

Willamette
20 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Specific Basins of Interest

The following discussion is organized geographically, 

with basins grouped together roughly by the USGS system of 

hydrologic units (Seaber and others, 1987).

Eastern Basins

The eastern basins include streams in New England and 

the Mid-Atlantic physiographic provinces: the Connecticut 

River, the Delaware River, Schuylkill River (major tributary 

of the Delaware River), the Potomac River, and the James 

River. The Schuylkill River basin, which includes parts of 

Philadelphia and its western suburbs, was one of the most 

densely populated basins in our study, with more than 

300 people/km2 (fig. 3). The Schuylkill River basin stands 

out due to the high population densities as far back as 1890. 

Because the City of Philadelphia has long been a population 

center, population density in this basin had surpassed 

100 people/km2 by 1900 and has been increasing steadily 

since then (fig. 7A). In contrast, population density is less than 

the national average in the James River basin, although it has 

been increasing in the past several decades, doubling from 14 

to 28 people/km2 during 1980–2000. This increase reflects the 

relatively high population growth rates that were observed in 

the Mid-Atlantic during that time period.

The eastern basins generally have low areal percentages 

in farmland and cropland usage at present (figs. 4 and 

7C–7D). These basins have steadily lost agricultural land 

throughout the 20th century (figs. 7C–7D). Most of these 

river basins were at least 70 percent agricultural land in 1900, 

but by 2002, none of exceeded 40 percent; the Connecticut 

and Delaware River basins were each less than 20 percent 

farmland (fig. 7C). This pattern reflects large-scale trends in 

agriculture throughout the 20th century, which was marked by 

specialization and consolidation resulting in a concentration 

of agricultural production in highly productive areas in the 

Central United States (Broussard and Turner, 2009). The 

loss of agricultural land in eastern basins also was reflected 

in the relatively low levels of fertilizer usage (fig. 5) and 

corn production, especially in the James River basin (fig. 6). 

Large increases in corn yields have caused corn production to 

increase in the Schuylkill River basin, despite the precipitous 

decrease in agricultural land in this basin (fig. 7D). However, 

the Schuylkill and Potomac Rivers also had fairly large 

inputs of nitrogen and phosphorus from animal livestock 

(figs. 5A–5B), which sets them apart from other basins in this 

region in terms of the amount of nitrogen and phosphorus 

from identified nonpoint sources (figs. 7E–7F).
Specific Basins of Interest 21

tac12-0694_fig 07

1860 1890 1920 1950 1980 2010

0

20

40

60

80

100

1860 1890 1920 1950 1980 2010

0

20

40

60

80

100

0

5,000

10,000

15,000

20,000

Percentage of the basin area in cropland

Percentage of the basin area in any farmland usage

1900 1920 1940 1960 1980 2000

Population density, in people per square kilometer 

A B

C D Corn harvest, in bushels per square kilometer of watershed area

1900 1920 1940 1960 1980 2000

0

50

100

150

200

250

300

350

Connecticut

River basin

Average National 

population 

density

Delaware

Schuylkill

Potomac

James

EXPLANATION

1900 1920 1940 1960 1980 2000

0

0.5

1.0

1.5

2.0

2.5

Year Year

Nonpoint nitrogen from fertilizer and animal livestock 

sources, in grams of nitrogen per square meter per year 

1900 1920 1940 1960 1980 2000

0

2

4

6

8

10

Nonpoint phosphorus from fertilizer and animal livestock 

sources, in grams of phosphorus per square meter per year

E F

Figure 7. Historical changes in (A) population density, (B) corn harvest, (C) percentage of basin area in any 

farmland usage, (D) percentage of basin area in cropland, and fertilizer and animal livestock sources of (E) nitrogen 

and (F) phosphorus in the Eastern basins.
22 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Connecticut River

The Connecticut River is the longest river in New 

England, originating in the Canadian Province of Quebec, 

and northern New Hampshire and flowing south along the 

border of Vermont, through central Massachusetts and coastal 

Connecticut into Long Island Sound (fig. 8). The river channel 

descends rapidly in the upper reaches, becoming relatively flat 

and meandering for the remainder of its course (Benke and 

Cushing, 2005). The mouth of the river includes a long estuary 

reach, with tidal influence extending approximately 90 km 

(60 mi) upstream to Windsor Locks, Connecticut, located 

approximately 5 miles downstream of the Thompsonville 

monitoring station (fig. 8). The drainage area is about 

25,000 km2 (9,660 mi2) at the USGS gage at Thompsonville 

(station No. 01184000), just 6 mi upstream of the head of tide. 

At this point, mean annual discharge (1928–2008) is just more 

than 485 m3/s (17,000 ft3/s) and basin runoff averages more 

than 600 mm/yr. The basin is entirely within the New England 

physiographic province (fig. 2) and is largely forested, 

encompassing the New England Forests ecoregion in the 

north and the Northeastern Coastal Forests ecoregion in the 

south (Benke and Cushing, 2005). Climate generally is humid 

and temperate in character, with annual precipitation ranging 

from 165 cm (65 in.) at high elevations to 86 cm (34 in.) 

in the lowlands (Garabedian and others, 1998). Streamflow 

in the Connecticut River shows a strong seasonal pattern 

characteristic of snowmelt, with highest flows during spring 

and critically low flow during the summer months (Garabedian 

and others, 1998). Flow is heavily regulated by at least 125 

reservoirs used for power generation and an additional 16 

reservoirs focused on flood control (Garabedian and others, 

1998).

The Connecticut River has likely been populated by 

humans since the retreat of the glaciers about 9,000 years ago 

(Benke and Cushing, 2005). Settlement by Europeans began 

when the Plymouth Colony was established in the lower river 

in 1633, with the river providing a key transportation corridor 

to the interior of the basin (Tetra Tech, 2000). Over the course 

of the next 200 years, about 75 percent of the forest in the 

basin was logged and converted to small-scale agricultural 

use, although most of the forest cover has been regained as 

agricultural usage has decreased (Tetra Tech, 2000). The 

northern part of the basin is currently mostly rural and relative 

wilderness with limited agriculture, although more urbanized 

areas occur farther downstream, especially focused in the tidal 

reach of the lower river. Some of these urban areas are among 

the oldest industrial areas in the Nation (Trench, 2000). 

Water-quality issues in the Connecticut River have been 

of concern throughout the 20th century, initially focused 

on decreasing oxygen conditions in the lower river (Tetra 

Tech, 2000). As early as 1897, the Connecticut General 

Assembly recognized the problem of pollution in the river 

and initiated an investigation of sewage-disposal practices 

(Hupfer, 1965). Despite this attention to the issue, however, 

by the 1930s, only about one-third of wastewater effluent 

received some form of primary treatment (Mullaney, 2004). 

In 1955, the New England Interstate Water Pollution Control 

Commission determined the reach of the river from Holyoke 

Dam in Massachusetts to Hartford, Connecticut (about 20 mi 

downstream of Thompsonville) was a Class D waterway, only 

suitable for transportation of sewage and industrial waste 

(Tetra Tech, 2000). The severe water pollution observed in this 

reach was due to effluent from industry and municipal sewage, 

much of which was not treated prior to the Clean Water Act of 

1972 (Tetra Tech, 2000). The primary industries responsible 

for water-quality degradation included paper mills, chemical, 

metal, plating, and dyeing (Mullaney, 2004). With the 

implementation of advanced wastewater treatment during the 

1970s and 1980s, dissolved oxygen conditions significantly 

improved, although combined sewer overflows continue to 

discharge untreated sewage to the river during storms (Tetra 

Tech, 2000). 

The population density in the basin upstream of the tidal 

reach was estimated to be about 52 people/km2 in the year 

2000 (fig. 3; U.S. Census Bureau, 2000). This value reflects 

the influence of the largely unpopulated region in the northern 

part of the basin. Nitrogen and phosphorus inputs from 

fertilizer and animal livestock averaged 0.5 and 0.1 (g/ m2)/ yr, 

respectively, and were split almost evenly between the two 

sources (fig. 5). Major nutrient sources to the Connecticut 

River also include municipal wastewater discharges and 

nonpoint runoff from urban areas and agricultural activities 

(Trench, 2000). Additionally, the widespread urban 

development across the Northeastern United States results in 

significant deposition of nitrogen to the landscape from fossil 

fuel deposition (Jaworski and others, 1997).

Data Sources

Data sources for the Connecticut River are summarized 

in table 4. Mean daily streamflow data are available for the 

reference stream gaging station at the Connecticut River at 

Thompsonville, Conn. (station No. 01184000) since 1928. 

USGS data for nitrogen are available for the Connecticut 

River at Warehouse Point, Conn., for 1890–1899; and for 

the Connecticut River below Springfield, Mass., from 1900. 

Nitrogen data from the Massachusetts State Department of 

Health also are available for the same site for 1914–1918. 

This collection site is downstream of the sewer outfall located 

near Westfield River in Springfield, Mass., and reflects the 

influence of this urban area. Works Progress Administration 

water-quality data are available for the Connecticut River 

below Thompsonville, Conn., for 1937. USGS data for the 

Connecticut River at Thompsonville, Conn., are available 

beginning in 1952.
Specific Basins of Interest 23

Figure 8. Connecticut River basin.

12-0694_fig08-Connecticut

74°W 73°W 72°W 71°W 70°W

45°N

44°N

43°N

42°N

Connecticut River

Providence

Albany

Worcester

Thompsonville Springfield

Boston

NEW YORK

MAINE

VERMONT

NEW HAMPSHIRE

MASSACHUSETTS

CONNECTICUT

RHODE

ISLAND

Base from U.S. National Park Service and ESRI

Landcover from U.S. Geological Survey National Land Cover Dataset 2006

Watershed boundary and flowlines from U.S. Environmental Protection Agency 

and U.S. Geological Survey NHDPlus 2005 

Albers Equal-Area Conic projection, North American Datum of 1983 0 25 50 KILOMETERS

0 25 50 MILES

EXPLANATION

Monitoring station

Watershed boundary

Developed/urban

Barren

Forest

Shrub/scrub

Grassland/pasture

Cropland

Wetland

No data

1

2,4

1

3

2,4

5

Long Island Sound

Windsor

Locks

Holyoke Dam

Hartford

Warehouse Point

CANADA
24 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Table 4. Connecticut River basin data sources.

[Monitoring station is shown in figure 8. Source: NWIS, National Water Information System; WPA, Works Progress Administration. Constituent: Alk, 

alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring

station Source Station Latitude Longitude Constituent Startyear

End

year

11 NWIS 01184000

Connecticut River at 

Thompsonville, Conn.

41o59'14′′ 72o36'19′′ Daily streamflow 1928 2008

TN 1969 2009

NH3 1969 2009

TON + NH3 1969 2009

NO3 1952 2009

Alk 1952 2009

TP 1968 2009

TDP 1966 2009

22 Leighton, 1903 Connecticut River below 

Springfield, Mass.

42o04′54′′ 72o34′58′′ NH3 1900 1900

NO3 1900 1900

23 Leighton, 1903 Connecticut River at 

Warehouse Point, 

Conn.

41o56′37′′ 72o36′50′′ NH3 1890 1899

NO3 1890 1899

24 Massachusetts State 

Department of 

Health, Fourth 

Annual Report

Connecticut River below 

Springfield, Mass.

42o04′54′′ 72o34′58′′ NH3 1914 1918

NO3 1914 1914

25 WPA, 1940 Connecticut River below 

Thompsonville, Conn.

41o58′30′′ 72o36′23′′ NH3 1937 1937

NO3 1937 1937

Alk 1937 1937

1

Reference stream gaging station.

2

Historical station, location approximate.
Specific Basins of Interest 25

Delaware River

The Delaware River basin has a long history of European 

settlement, dating back to the colonial period of the 17th

century (Patrick, 1992). The river originates in the Catskill 

Mountains and flows from north to south, draining parts 

of New York, Pennsylvania, New Jersey, and Delaware, 

before emptying into the Atlantic Ocean (fig. 9). The length 

of river of interest for this analysis is the non-tidal reach 

above the Delaware Estuary that heads at Trenton, New 

Jersey. The target drainage area encompasses 17,600 km2

(about 6,800 mi2), excluding the Schuylkill River basin 

that drains the city of Philadelphia farther downstream 

and is considered separately in this report. The river flows 

through complex terrain, incorporating five physiographic 

provinces: Appalachian Plateau, Valley and Ridge, New 

England, Piedmont Plateau, and Coastal Plain (fig. 2). The 

Lehigh River is a major tributary that drains important coal 

and steel producing areas of the Great Appalachian Valley. 

Climate is humid and continental, with little variation in 

precipitation across the drainage area (averaging about 

106 cm/yr or 42 in/ yr), although extreme precipitation occurs 

infrequently as hurricanes (Benke and Cushing, 2005). Mean 

annual discharge (1912–2008) is approximately 330 m3/s 

(11,800 ft3/s), so that average runoff is about 600 mm/yr.

When first discovered by Henry Hudson in 1609, the 

Delaware River basin was covered with forests, and timber 

harvest quickly became a major industry supplying wood 

for paper and building ships (Patrick, 1992). Abundant 

fishes in the river and the estuary supported important 

commercial fisheries during the 17th and 18th centuries, 

and the Delaware Valley grew to become a key center 

of trade. Cities were established along the lower river, 

especially after municipal water systems were developed to 

utilize river water for domestic and industrial use. Factories 

proliferated to utilize the availability of coal and iron, and 

glassblowing, silkweaving, pottery, and porcelain, as well as 

iron shipbuilding and munitions, became important industries 

during the 19th century (Patrick, 1992). The growth of 

factories in the lower Delaware Valley was associated with 

further increases in population during this time in the urban 

areas, especially in Philadelphia. Agriculture expanded 

throughout the middle reaches of the basin to meet the 

increasing demand for food. Numerous canals were built 

to provide a transportation network to support the growing 

population (Benke and Cushing, 2005). By the beginning of 

the 20th century, important water-quality issues were related to 

untreated sewage and industrial waste discharged from cities 

that simultaneously drew water from the river for their water 

supply.

Attempts at controlling pollution by sewage treatment 

during the first half of the 20th century were largely offset by 

ongoing growth of cities and industries (Patrick, 1992). The 

large quantities of waste material created significant oxygen 

demand, threatened industrial production, and contributed 

to abrupt decrease in commercial fishing (Patrick, 1992). 

Water quality in the lower river was further impacted by 

impoundment of headwater streams in the 1920s to augment 

the water supply for New York City, although water levels 

are now carefully regulated to maintain flow requirements 

to minimize detrimental downstream impacts (Fischer 

and others, 2004). In 1936, the Interstate Commission on 

the Delaware River Basin (INCODEL) was established to 

improve water-quality conditions (Kiry, 1974). INCODEL 

was incorporated with the newly formed Delaware River 

Basin Commission (DRBC) in 1955, which focused on a 

wide range of environmental problems in the basin, including 

flood control, water quality, and water supply (Kiry, 1974). 

As a result of these efforts during the 1950s, sewage treatment 

facilities began to be built and minimal treatment of industrial 

wastes became more common. By the end of that decade, the 

proportion of cities with “adequate” sewage treatment plants 

increased from 20 to 75 percent, most conducting secondary 

treatment (Albert, 1982). Substantial improvements in water 

quality ensued, especially as industrial loads were further 

reduced in response to passage of the Clean Water Act in 1972.

Contamination from fracking procedures associated 

with natural gas drilling is an important recent concern in 

the Delaware River basin. The Marcellus Shale is the largest 

shale basin in the continental United States (Kargbo and 

others, 2010), and underlies about 36 percent of the Delaware 

River basin (Delaware River Basin Commission, 2011). The 

Delaware River Basin Commission has been in the forefront 

of the development of regulations to limit the environmental 

impacts of fracking on water quality, especially because the 

Delaware River serves as a critical source for drinking water.

Presently, there exists a strong gradient from north to 

south in land use and population pressure in the Delaware 

River basin. Although, the northern part of the basin remains 

largely forested, only a small percentage of the basin 

population lives there (Fischer and others, 2004). Upstream of 

the Delaware Water Gap, two reaches of the river have been 

designated as Scenic and Recreational Rivers, which reflects 

the high quality of water and stringent protection provided 

(Albert, 1982). Farther downstream, agriculture remains an 

important influence in the basin, with corn and soybeans 

the most widely grown crops (Hickman, 2004). However, 

basinwide fertilizer and animal livestock sources of nitrogen 

and phosphorus are very low. Nitrogen inputs averaged less 

than 1.0 g (N/m2)/yr from 1997 to 2001 and phosphorus 
26 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

tac12-0694_fig09-Delaware

NEW YORK

PENNSYLVANIA

NEW JERSEY

MARYLAND

DE

Delaware River

Lehigh River

Schuylkill River

Allentown

Bethlehem

Trenton

Scranton

Philadelphia

77°W 76°W 75°W 74°WN

42°N

41°N

40°N

0 25 50 KILOMETERS

0 25 50 MILES Base from U.S. National Park Service and ESRI

Landcover from U.S. Geological Survey National Land Cover Dataset 2006

Watershed boundary and flowlines from U.S. Environmental Protection Agency 

and U.S. Geological Survey NHDPlus 2005 

Albers Equal-Area Conic projection, North American Datum of 1983

EXPLANATION

Monitoring station

Watershed boundary

Developed/urban

Barren

Forest

Shrub/scrub

Grassland/pasture

Cropland

Wetland

No data

9

7

10

8,9

7

6

Catskill Mountains

Delaware 

Estuary

New York 

City

Delaware Water Gap

Catskill Mountains

Delaware 

Estuary

New York 

City

Delaware Water Gap

Great Appalachian Valley

Figure 9. Delaware River basin.
Specific Basins of Interest 27

inputs were 0.2 g (P/m2)/yr in the same time period. Fertilizer 

sources of nitrogen and phosphorus were approximately 

twice as large as animal livestock sources (fig. 5). The most 

significant water-quality impact on the lower Delaware River 

basin is from urbanization and industrial activity, including 

the influence of the lower Lehigh River that drains the 

highly industrialized eastern Pennsylvania (Albert, 1982). 

Nonetheless, despite the significant urbanization in the lower 

basin, the population density for the entire basin upstream of 

Trenton is only moderately high compared to other basins in 

this study, estimated as 97 people/km2 in the year 2000 (fig. 3; 

U.S. Census Bureau, 2000).

Data Sources

Available data sources for the Delaware River are 

summarized in table 5. Daily streamflow data are available 

from the reference stream gaging station at Trenton since 1912 

(station No. 01463500). Water-quality data are available from 

the Delaware River at Trenton for 1900, 1923, and from 1944 

through 2009. Additional water-quality data are available from 

the Delaware River at Lambertville from 1906 and 1976–82; 

the overlap in time for data from this site and from Trenton 

allows an evaluation of comparability.

Table 5. Delaware River data sources.

[Monitoring station is shown in figure 9. Source: NWIS, National Water Information System. Constituent: Alk, alkalinity. See table 2 for definitions of all 

other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

16 NWIS 01463500

Delaware River at 

Trenton, N.J.

40o13′18′′ 74o46′41′′ Daily streamflow 1912 2008

TN 1969 2009

NH3 1970 2009

TON + NH3 1969 2009

NO3 1944 2009

Alk 1944 2009

TP 1969 2009

TDP 1964 2009

7 NWIS 01462000

Delaware River at 

Lambertville, N.J.

40o21′53′′ 74o56′56′′ Daily streamflow 1897 1906

TN 1976 1982

NH3 1976 1982

TON + NH3 1976 1982

NO3 1906 1982

Alk 1906 1982

TP 1976 1978

28 Leighton, 1903 Delaware River at 

Trenton, N.J.

40o12′28′′ 74o46′03′′ NH3 1900 1900

NO3 1900 1900

Alk 1900 1900

29 Collins and Howard, 

1928

Delaware River at 

Trenton, N.J.

40o12′28′′ 74o46′03′′ NO3 1923 1924

Alk 1923 1924

1

Reference stream gaging station.

2

Historical station, location approximate.
28 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Schuylkill River 

The Schuylkill River is the largest tributary to the 

Delaware River, and located entirely within the State of 

Pennsylvania (fig. 10). The river begins in the Blue Mountain 

part of the Valley and Ridge physiographic province of the 

Appalachian Mountains (fig. 2). From there it flows through 

the Piedmont Plateau and Coastal Plain provinces before 

bisecting the city of Philadelphia and emptying into the 

Delaware River Estuary (Stamer and others, 1985). The 

drainage area for the non-tidal river upstream of the Estuary, 

referenced at the USGS gage in Philadelphia, is about 

4,980 km2 (1,900 mi2). Climate in the basin generally is humid 

and precipitation is distributed evenly throughout the year, 

ranging from approximately 114–127 cm/yr (45–50 in/ yr) 

in the high elevation headwater regions to about 109 cm/yr 

(43 in/ yr) at the mouth (Schuylkill Watershed Conservation 

Plan, 2001). Mean annual discharge (1931–2008) for the 

gage at Philadelphia during the 20th century is approximately 

77 m3/s (2,700 ft3/s), which corresponds with mean annual 

runoff of nearly 500 mm/yr (19 in/yr).

The lower region of the Schuylkill River was first 

settled by Europeans when Philadelphia was founded in 

the early 17th century. Population growth was slow until 

William Penn received the charter from King Charles II 

to establish the Commonwealth of Pennsylvania in 1680, 

after which population density began to increase rapidly in 

the Philadelphia area (Schuylkill Watershed Conservation 

Plan, 2001). By 1750, Philadelphia was the largest city in 

the colonies, serving as an important center of trade and 

government. Early land use in the basin during the colonial 

period focused on farming, timber harvest, and development 

of the iron industry, leading to the growth of Philadelphia 

into the most populous city during the Revolutionary War. 

Agriculture in the basin was a key element of the colonial 

economy, especially focused on wheat, and southeastern 

Pennsylvania was recognized as the largest producer of 

food in the Nation until the middle of the 19th century (U.S. 

Department of the Interior, 1987).

During the 19th century, the Schuylkill River became 

a critical industrial corridor, facilitating the transportation 

of anthracite coal from the upriver Appalachian mines to 

the factories and mills established in the cities of the lower 

river reaches (Schuylkill Watershed Conservation Plan, 

2001). The Schuylkill Navigation System was constructed, 

consisting of 32 dams and 103 locks, to facilitate the use of the 

river for transportation (Schuylkill Watershed Conservation 

Plan, 2001). At the same time, the river was dammed at the 

Fairmont Water Works in 1815 for use as municipal water 

supply by the city of Philadelphia and surrounding areas. 

Discharge of acidic wastes and fine sediment from coal 

mines caused clogging of the river channel and significant 

degradation of water quality, the effects of which peaked by 

the middle of the 20th century (Stamer and others, 1985). 

Water quality was further impacted by discharge of wastewater 

from the numerous cities located along the river. The decline 

in water quality was a subject of intense interest, resulting 

in passage of the Clean Streams Act and the Desilting Act in 

1945 by the State of Pennsylvania, which led to removal of 

unprecedented volumes of sediment from the river (Stamer 

and others, 1985). By this time, agriculture in the basin was 

dominated by dairy farming and egg production, although the 

number of farms was declining due to expanding urbanization 

(U.S. Department of the Interior, 1987).

The cleanup of the Schuylkill River in the last half of 

the 20th century has been remarkable. In 1979, the lower 

Schuylkill River was the first river segment to be added to 

the Pennsylvania Scenic Rivers System, emphasizing the 

increase in recreational use of the river as well as protection 

of anadromous fish populations (Stamer and others, 1985). 

Nonetheless, the Schuylkill River remains heavily affected by 

human land use, especially from the high population density 

(314 people/km2) (fig. 3). Agriculture also is still a significant 

influence (Jaworski and others, 1997) (figs. 5A–5B), although 

the Schuylkill River basin has experienced decreases in 

farmland and cropland similar to other Eastern basins 

(figs. 7C–7D). Nitrogen and phosphorus sources from 

fertilizer and animal livestock are low compared to other 

basins included in this study (fig. 5), but are among the highest 

in the Eastern basins (figs. 7E–7F).

Data Sources

Data sources for the Schuylkill River are summarized in 

table 6. Daily streamflow data are available for the reference 

stream gaging station at the Schuylkill River at Philadelphia 

(station No. 0147500) beginning in 1931. Water-quality 

data are available for the same location beginning in 1925, 

depending on constituent, and extending through the 20th 

century.
Specific Basins of Interest 29

tac12-0694_fig10-Schuylkill

75°W 76°W

40°N

DELAWARE

NEW JERSEY

PENNSYLVANIA

Trenton

Philadelphia

Reading

Pottstown

Norristown

Schuylkill River

Perkiomen

Creek

Ma

i

den

Creek

Tu l p

he ocken Creek

De al ware River

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

00 10 20 KILOMETERS

10 20 MILES

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

9

10

8,9

7

6

Appalachian Mountains

Fairmount Water Works

Figure 10. Schuylkill River basin.
30 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Table 6. Schuylkill River data sources.

[Monitoring station is shown in figure 10. Source: NWIS, National Water Information System. Constituent: Alk, alkalinity. See table 2 for definitions of all 

other constituent abbreviations]

Monitoring

station Source Station Latitude Longitude Constituent Startyear

End

year

110 NWIS 01474500

Schuylkill River at 

Phildelphia, Pa.

39o58′04′′ 75o11′20′′ Daily streamflow 1931 2008

TN 1954 2004

NH3 1970 2004

TON + NH3 1969 2004

NO3 1933 2004

Alk 1925 2004

TP 1969 2004

TDP 1969 2004

1

Reference stream gaging station.
Specific Basins of Interest 31

Potomac River

The Potomac River is located on the mid-Atlantic 

seaboard and drains parts of the Appalachian Mountains, 

piedmont, and coastal plain in Virginia, West Virginia, 

Maryland, and Pennsylvania (fig. 11). It is the second largest 

river flowing into Chesapeake Bay with a drainage area of 

37,800 km2 (14,600 mi2). For the purposes of this study, data 

were considered from the reference stream gaging station 

located just upstream of Washington, D.C. (station No. 

01646502). At this point, the drainage area is 29,900 km2

and mean annual discharge is 337 m3/s (11,888 ft3/s). Annual 

average discharge ranges from approximately 140 to 680 m3/s 

(5,000 to 24,000 ft3/s) throughout the period 1930–2009. 

Runoff averages 355 mm/yr throughout the same period but 

also is highly variable ranging from 140 to 730 mm/yr. This 

region is susceptible to large cyclonic storms originating in the 

Atlantic Ocean, partially accounting for the large interannual 

variability in river flow.

The Potomac River originates in the Appalachian 

Plateau physiographic province and runs through portions 

of the Valley and Ridge, Piedmont Plateau, and Blue Ridge 

physiographic provinces (fig. 2) before entering the Coastal 

Plain near Washington, D.C. More than 70 percent of the total 

river discharge originates in the mountainous regions upstream 

of the Piedmont Plateau. The North Branch Potomac, South 

Branch Potomac, and Shenandoah Rivers are major upland 

tributaries to the Potomac River and the Monocacy River is a 

major tributary that joins the Potomac River in the Piedmont 

Plateau.

Land use in the Potomac River has changed dramatically 

throughout the 20th century. In 1900, 80 percent of the basin 

was agricultural land with approximately 50 percent of the 

basin in cropland (figs. 7E–7F). However, as with many areas 

in the Eastern United States, agriculture became much less 

prominent as large-scale farming consolidated within the 

Midwestern United States throughout the 20th century. At 

the last Census of Agriculture in 2002 (U.S. Department of 

Agriculture, 2005), less than 40 percent of the Potomac River 

basin was in farmland usage with 20 percent of the basin 

area used as cropland (fig. 4). Corn harvest was relatively 

low, 660 bushels/km2 of drainage area (fig. 7B). Accordingly, 

fertilizer usage in the basin at the end of the 20th century 

is low compared with other basins of interest to this study. 

Nitrogen and phosphorus from fertilizer sources averaged 

only 1.1 and 0.2 (g/m2)/yr from 1997 to 2001, respectively 

(fig. 5). However, animal livestock sources of both N and P 

were larger than fertilizer sources, 1.7 and 0.5 (g/m2)/yr, 

respectively (fig. 5). Population density in the basin has 

increased during the 20th century from 17 people/km2 in 1900 

to more than 77 people/km2 in 2000, reflecting the growth of 

metropolitan Washington, D.C. and suburbs (fig. 7A).

Coal mining activity has long been a concern for water 

quality in the Potomac River basin. The economic viability 

of resource extraction was greatly aided by the construction 

of the Chesapeake and Ohio Canal in 1850, which ran from 

Washington, D.C. to Cumberland, Md. Coal mining began 

with small underground mines in the early 19th century, 

which gradually gave way to larger consolidated underground 

mines (Jaworski and others, 2007). Surface coal mining is 

the predominant type of coal mine operating in the basin 

today, but these types of mines did not begin until 1920 and 

increased significantly after World War II (Mills and Davis, 

2000).

By the late 19th century, concerns about pollution on the 

Potomac River were already being raised. The combination 

of population growth and the presence of heavy industry 

led to serious public health concerns. The Potomac River 

was one of the first basins studied by the U.S. Public Health 

Service in early 20th century because of its interstate nature, 

the predominance of pollution, and the fact that it served as 

the drinking water supply to Washington, D.C. (Cumming 

and others, 1916). In particular, there was a concern that the 

lethality of mining and industrial wastes inhibited the normal 

purification process in the river thus allowing pollution to 

persist far downstream from its source (Cumming and others, 

1916). Intensely degraded conditions were described in some 

of the headwater streams where mining was prevalent, such as 

Georges Creek in western Maryland, where the waters were 

said to be “lethal instead of life-giving in character. They 

destroy all vegetable and animal life in the channel, and stain 

the rocks on which they flow yellow...” (Parker and others, 

1907).

Environmental conditions in the Potomac River 

continued to deteriorate throughout most of the 20th century, 

eventually having a significant negative impact on the 

Chesapeake Bay. By mid-century, low oxygen in the river led 

to fish kills; silt pollution was considered a primary threat to 

the Chesapeake Bay; and much of the riverine and estuarine 

habitat was threatened (U.S. Department of the Interior, 

1968; Federal Water Pollution Control Administration, 1969; 

Maryland Department of Natural Resources, 2007).

State and multi-State efforts to remediate the Potomac 

River began in the 1930s and 1940s. Actions by individual 

States included limiting acid mine drainage pollution in 

Pennsylvania in 1945 and the creation of the Water Pollution 

Control Commission by Maryland in 1947. In 1940, the U.S. 

Congress also established the Interstate Commission on the 
32 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 11. Potomac River basin.

tac12-0694_fig11-Potomac

Chesapeake and

Ohio Canal

75°W 76°W 77°W 78°W 79°W

40°N39°N38°N

Chesapeake

Chesapeake and

Ohio Canal

N B. ar nch Po ot

mac R.

VIRGINIA

MARYLAND

PENNSYLVANIA

WEST

VIRGINIA

NEW JERSEY

DELAWARE

Washington, D.C.

Staunton

Frederick

Winchester

Hagerstown Cumberland

Martinsburg

Harrisonburg

. S

r B

na hc Po ot mac R.

Potomac Riv e r

Sh ne andoah R vi

er

N B. ar nch Po ot

mac R.

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

00 25 50 KILOMETERS

25 50 MILES

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

14

12 15

14 13

12

11

Georges Creek

Westernport

Bloomington Dam

Monocacy River Piedmont PlateauMonocacy River

Georges Creek

Alexandria

Westernport

Blue Plains WWP

Bloomington Dam

Dalecarlia Reservoir
Specific Basins of Interest 33

Potomac River Basin (ICPRB) to address pollution in the 

Potomac River. The commission consisted of members from 

Pennsylvania, Maryland, West Virginia, Virginia, and the 

District of Columbia. Other interstate efforts included the 

Potomac Enforcement Conference, which convened in 1957 

and the Potomac River Basin Advisory Committee, which 

was established in 1965. The first wastewater-treatment plant 

was built in 1938 downstream of Washington, D.C. to focus 

on reducing pollution in the lower river and the estuary. 

Other treatment plants were built in the 1950s and 1960s at 

Alexandria, Va., Cumberland, Md., and Westernport, Md. 

Improvements also were made to connect three suburban 

counties (Fairfax, Loudon, and Montgomery) to the Blue 

Plains wastewater-treatment plant. Thus, by 1968, about 

85 percent of all municipal and industrial effluent in the basin 

received “some degree of treatment” (U.S. Department of the 

Interior, 1968). By 1980, all wastewater-treatment plants in 

the basin had secondary treatment in operation (Jaworski et al. 

2007). 

Actions also have been taken to reduce acid mine 

drainage pollution in the basin. Bloomington Dam was 

constructed by U.S. Army Corps of Engineers on the North 

Branch Potomac River by 1981 partly with the goal of 

reducing downstream impacts of acid mine drainage. In 1993, 

Maryland and West Virginia entered an agreement with the 

ICPRB to restore water quality in the North Branch Potomac 

River by neutralizing acidic waters from mine drainage (Mills 

and Davis, 2000). Some estimates show that acid loading 

to the Potomac River had decreased by almost 90 percent 

between 1940 and 1988 (Mills and Davis, 2000).

Environmental conditions in the Chesapeake Bay came 

under scrutiny in the 1970s as pollution caused noticeable 

degradation of its fisheries and ecological health. In 1983, the 

Chesapeake Bay Program was formed to address pollution 

problems pertaining to the Chesapeake Bay. The Potomac 

River was among the basins targeted for pollution reductions. 

Principal objectives of the program included reductions in 

nitrogen and phosphorus pollution to the bay (Sprague and 

others, 2000). By 1998, the USGS estimated that landscape 

best-management practices had reduced the agricultural load 

of nitrogen to the Potomac River by 9 percent since 1985 

(Sprague and others, 2000).

Data Sources

Data sources for the Potomac River are summarized 

in table 7. Daily streamflow data are available beginning in 

1930 at the reference stream gaging station at the Potomac 

River near Washington, D.C. (station No. 01646502. As 

shown in table 7, the earliest known reliable data on nitrogen 

in Potomac River were collected by the USGS at this site 

in 1921. The U.S. Army Corps of Engineers also analyzed 

the water drawn from the Potomac River at Great Falls at 

Dalecarlia Reservoir water intake (monitoring station 15), 

which supplies Washington, D.C. Records of these analyses 

are available from 1922 through the mid-1960s (with some 

gaps, particularly in the 1940s). The USGS has been analyzing 

Potomac River waters at various intervals since 1973. 
34 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Table 7. Potomac River data sources.

[Monitoring station is shown in figure 11. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

111 NWIS; Clarke, 1924 01646502

Potomac River 

(adjusted) near 

Washington, D.C.

38o56′58′′ 77o07′40′′ Daily streamflow 1930 2009

NO3 1921 1921

Alk 1921 1921

12 NWIS 01645500

Potomac River at 

Great Falls, Md.

39o00′03′′ 77o14′55′′ TN 1980 1980

NH3 1973 1980

TON + NH3 1980 1980

NO3 1980 1980

Alk 1973 1973

TP 1980 1980

TDP 1980 1980

13 NWIS 01646580

Potomac River at 

Chain Bridge, at 

Washington, D.C.

38o55′46′′ 77o07′01′′ TN 1973 2009

NH3 1973 2009

TON + NH3 1973 2009

NO3 1973 2009

Alk 1973 2009

TP 1973 2009

TDP 1973 2009

14 STORET 100130

Potomac River at 

Washington, D.C.

38o53′14′′ 77o03′20′′ TN 1964 1969

NH3 1963 1965

TON + NH3 1964 1969

NO3 1964 1969

Alk 1963 1968

TP 1964 1969

TDP 1964 1969

15 District of Columbia 

water system

Potomac River at 

Dalecarlia water 

intake, near 

Washington, D.C.

38o55′57′′ 77o07′02′′ NH3 1922 1928

NO3 1922 1965

Alk 1922 1965

1

Reference stream gaging station.
Specific Basins of Interest 35

James River

The influence of European settlement in the James River 

basin began with establishment of Jamestown in the James 

River Estuary in 1607 (Benke and Cushing, 2005). It is the 

largest river contained entirely within the Commonwealth 

of Virginia, with the headwaters in the mountains along 

the western border and flowing through central Virginia to 

empty into the Chesapeake Bay (fig. 12). The target drainage 

area for this study is defined by the USGS reference stream 

gaging station at Cartersville, measured as approximately 

16,200 km2 (6,250 mi2), located about 40 mi upstream of 

the head of tide in Richmond (Belval and others, 1994). The 

river crosses three physiographic provinces as it flow from 

west to east: the Valley and Ridge, Blue Ridge, and Piedmont 

Plateau physiographic provinces. Climate is relatively mild, 

with hot, humid summers, and cool winters. Severe weather 

is a concern, including occasional heavy rain and high winds 

from hurricanes. Precipitation averages about 108 cm/yr 

(42 in/ yr) (Benke and Cushing, 2005). Mean annual discharge 

at Cartersville for the period 1899–2008 was approximately 

200 m3/s (7,100 ft3/s), which results in mean annual runoff of 

about 390 mm/yr. 

At the turn of the century, the dominant mode of 

agricultural activity in the Appalachian and Piedmont regions 

of the James River basin was subsistence farming (Pudup, 

1990). An important component of the human economy in 

this region during this time also was provided by the abundant 

chestnut forests in the Blue Ridge region of the upper basin. 

These areas served as an important source for timber as well 

as the trade in chestnuts, which were transported via the 

railroad to urban centers, such as Philadelphia and New York 

(Lutts, 2004). These activities declined rapidly by the 1930s 

coincident with the obliteration of the chestnut forests due to 

the invasion of the Chestnut fungus. 

Although the James River drainage basin contains large 

municipal areas in the lower reaches, the portion of the basin 

targeted by this study remains largely rural with only a few 

cities with population greater than 50,000 people. Population 

density is estimated at about 27 people/km2, based on the 

2000 census (fig. 3; U.S. Census Bureau, 2000). Most of the 

basin is forested, although agriculture is still recognized as 

an important influence on water quality (Benke and Cushing, 

2005). Over the course of the 20th century, farmland acreage 

and the total number of farms has decreased significantly 

in a pattern similar to that observed throughout the Eastern 

United States (Cohen, 2009) (figs. 7C–7D). Currently, 

agricultural lands comprise 15 percent of the basin upstream 

of Cartersville (Sprague and others, 2009) (fig. 4). Animal 

sources of nitrogen and phosphorus were more than double 

that of fertilizer on average from 1997 to 2001 (fig. 5). 

However, the sum of these sources of only 1.3 g (N/m2)/yr and 

0.3 g (P/m2)/yr (fig. 5), and has been steady or decreasing for 

most of the late 20th century (figs. 7E–7F). Since 1983, with 

the establishment of the Chesapeake Bay Program, there has 

been a strong emphasis on improving agricultural practices 

throughout the James River basin to reduce loads of nutrients 

and sediment to Chesapeake Bay (Virginia Department of 

Environmental Quality, 2005).

Data Sources

Data sources for the James River are summarized in 

table 8. Daily streamflow data are available from the reference 

stream gaging station, James River at Cartersville, Va., 

(station No. 02035000) beginning in 1899 and from gaging 

station No. 02037500 near Richmond, Va., beginning in 1934. 

Early water-quality data were collected from this station near 

Richmond, Va., in the early 20th century and published in the 

Clarke (1924) compilation. Sampling resumed at this station 

in the 1940s and continued intermittently until 2005. Waterquality data are available from the station at Cartersville 

beginning in 1929. Several years of water-quality data also 

are available from the 1940s and 1950s, although regular 

sampling did not begin until 1968 at this station. Comparing 

water-quality data from these two stations is complicated by 

the urban influence around the city of Richmond. However, 

limiting the use of water-quality data for trend analyses to 

the Cartersville station provides adequate data and avoids the 

potential influence of Richmond in the analysis. Comparing 

the data collected in 1906–07 near Richmond to the more 

recent data collected upstream of Richmond is expected to 

result in a conservative estimate of the changes in water 

quality because of the influence of the city of Richmond on 

water quality.
36 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 12. James River basin.

tac12-0694_fig12-James

77°W 78°W 79°W 80°W

38°N37°N

Co

utsap w

er R.

M rua R y .

Rivanna R.

l S a et R.

li W il Rs .

J ma

es R vi er

CHESAPEAKE

BAY

VIRGINIA

WEST VIRGINIA

Lynchburg

Charlottesville

Richmond

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

0 25 50 Kilometers

0 25 50 Miles

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

16

19

18 17 16

Jamestown

Blue Ridge
Specific Basins of Interest 37

Table 8. James River basin data sources.

[Monitoring station is shown in figure 12. Source: NWIS, National Water Information System. Constituent: Alk, alkalinity. See table 2 for definitions of all 

other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

116 NWIS 02035000

James River at Cartersville, Va.

37o40'15" 78o05'10" Daily streamflow 1899 2008

TN 1973 2008

NH3 1974 2008

TON + NH3 1973 1996

NO3 1929 2008

Alk 1929 2008

TP 1973 2008

TDP 1973 2008

17 NWIS 02037000

James River and Kanawha Canal 

near Richmond, Va.

37o33'52" 77o34'28" Daily streamflow 1936 2008

NO3 1952 1972

Alk 1952 1972

18 NWIS 02037500

James River near Richmond, Va.

37o33'47" 77o32'50" Daily streamflow 1934 2008

TN 2004 2005

NH3 2004 2005

NO3 1906 2005

Alk 1906 1969

TP 2004 2005

TDP 2004 2005

19 NWIS 02037700

James River at Richmond, Va.

37o31′55′′ 77o26′05′′ TN 1979 1981

TON + NH3 1979 1981

NO3 1979 1981

TP 1979 1981

1

Reference stream gaging station.
38 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Great Lakes Basins

The size and scope of the Laurentian Great Lakes is 

difficult to overstate. They cover 244,000 km2 (94,000 mi2) 

and hold 18 percent of the world’s freshwater. Theoretical 

water residence time within the entire basin is well over 

100 years. Residence times for individual lakes range from 

2.6 years in Lake Erie to almost 200 years in Lake Superior 

(Fuller and others, 1995). A shorter water residence time 

indicates higher water input relative to the size of the lake and 

therefore greater susceptibility of the lake to changes in the 

quality of the influent water.

The Laurentian Great Lakes system is geologically 

very young, only about 10,000 years old (Fuller and others, 

1995). It was formed by the combined action of a series 

of glacial advances and retreats associated with recent ice 

ages. The northern and western parts of the basin are highly 

influenced by the presence of the Canadian Shield including 

the Superior Uplands physiographic province (fig. 2), which 

is characterized by thin, acidic, poorly developed soils. The 

southern and eastern parts of the basin cover parts of the 

Central Lowlands physiographic province (fig. 2) and tend to 

have greater agricultural development and human population 

densities. The far eastern part of the basin covers parts of 

the Appalachian Highlands physiographic division, which is 

moderately developed. As a consequence, human development 

and its associated effects tend to be concentrated most heavily 

in the central and eastern parts of the basin. The western part 

of the basin, particularly around Lake Superior, is only lightly 

developed.

In this region, two highly contrasting river reaches were 

considered, the Maumee River at Waterville, Ohio, and the 

Saint Lawrence River at the outlet of the Great Lakes (fig. 1). 

The Maumee River is among the most highly agricultural 

drainage basins included in this study with more than 80 

percent of the basin in farmland in 2002 (fig. 4). Fertilizer 

and animal livestock sources of nitrogen and phosphorus are 

7.6 g (N/m2)/yr and 1.5 g (P/m2)/yr (figs. 5A–5B). In contrast, 

less than 20 percent of the Saint Lawrence River basin is 

in agricultural usage (fig. 4) and nitrogen and phosphorous 

loading have been low (figs. 5A–5B). Population density in the 

two basins has been remarkably similar throughout the 20th 

century (fig. 13A).
Specific Basins of Interest 39

tac12-0694_fig 13

1900 1920 1940 1960 1980 2000

0

0.5

1.0

1.5

2.0

2.5

1860 1890 1920 1950 1980

0

20

40

60

80

100

1860 1890 1920 1950 1980

0

20

40

60

80

100

0

20,000

Year

Percentage of the basin area in cropland

Percentage of the basin area in any farmland usage

1900 1920 1940 1960 1980 2000

Population density, in people per square kilometer 

A B

Year

Nonpoint nitrogen from fertilizer and animal livestock 

sources, in grams of nitrogen per square meter per year 

E F

C D Corn harvest, in bushels per square kilometer of watershed area Nonpoint phosphorus from fertilizer and animal livestock sources, in grams of phosphorus per square meter per year

1900 1920 1940 1960 1980 2000

0

50

100

150

200

250

300

350

1900 1920 1940 1960 1980 2000

0

2

4

6

8

10

Saint Lawrence

River basin

Average National 

population 

density

Maumee

EXPLANATION

2010 2010

5,000

10,000

15,000

Figure 13. Historical changes in (A) population density, (B) corn harvest, (C) percentage of basin area in any 

farmland usage, (D) percentage of basin area in cropland, and fertilizer and animal livestock sources of (E) nitrogen, 

and (F) phosphorus in the Great Lakes basins.
40 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Saint Lawrence River

The Saint Lawrence River has the second highest 

discharge of any river draining the conterminous United 

States. The main stem is less than 1,000 km long, but it 

derives an enormous proportion of its water and drainage area 

from the Laurentian Great Lakes, which cover over one-half 

of the basin (fig. 14). The USGS monitors discharge at the 

Lake Ontario water-level regulation point near Massena, N.Y 

(the reference stream gaging station, station No. 04264331). 

There is no stream gage at this location, but discharge is 

calculated as the sum of several water regulation structures 

in the area. Therefore, this site is best thought of as the outlet 

of the Laurentian Great Lakes. At this location, the drainage 

basin is 774,000 km2 (about 300,000 mi2), of which nearly 

450,000 km2 (173,000 mi2) is within the United States. 

Mean annual discharge from 1935 to 2009 at this station 

was approximately 7,100 m3/s (252,000 ft3/s) and mean 

annual runoff was approximately 291 mm/yr. This station 

has remarkable temporal stability in streamflow owing to the 

enormous hydrologic buffering capacity of the Great Lakes as 

well as the presence of the Lake Ontario water-level regulation 

structures. Between 1936 and 2008, the entire range of average 

annual discharges only deviated by about 25 percent from 

the mean annual discharge, approximately 5,400–8,750 m3/s 

(200,000–300,000 ft3/s).

The Great Lakes region has long been a focal point of 

industrial activity and a human population center. In 1990, 

the combined United States and Canadian human population 

in the basin was more than 33 million (Fuller and others, 

1995). Settlers were originally attracted to the Great Lakes 

region because of its abundant natural resources including 

fur-bearing animals, fertile soils, fisheries, mineable ores, 

and abundant desirable timber resources. More recently, the 

availability of fresh water and shipping access has encouraged 

the development of chemical, manufacturing, shipping, 

and steel industries in this region. Each of these activities 

has dramatically shaped this region both economically and 

ecologically. Despite the enormous size of the Laurentian 

Great Lakes, the combined effects of these human endeavors 

has substantially altered the Great Lakes ecosystem to the 

extent that it became severely degraded by the middle of the 

20th century.

Impairment of the Great Lakes arguably began in the 

late 19th century, but culminated in the second half of the 

20th century as Lake Erie began to experience frequent 

hypoxia and noxious algal blooms (Litke, 1999). Problems 

with water quality were identified as early as 1849 when 

Chicago began experiencing recurring typhoid fever and 

cholera outbreaks, which were later linked to contamination 

of its drinking water source, Lake Michigan (Hill, 2000). In 

response, Chicago reversed the flow of its primary sanitary 

sewer, the Chicago River, such that waste from the city would 

flow into the Des Plaines River and eventually the Illinois 

River. Ecological disruptions to the Great Lakes continued and 

worsened throughout the 20th century. The Great Lakes have 

been the setting for several disastrous ecological invasions 

that dramatically altered the entire ecosystem and severely 

damaged native fisheries. The first documented invasion 

was that of the sea lamprey. Although the lamprey had been 

observed in Lake Ontario as early as 1830, it only began 

spreading to the other Great Lakes after improvements to the 

Welland Canal in 1919, which allowed the lamprey to enter 

Lake Erie (Great Lakes Fishery Commission, 2000). By the 

1950s, the lamprey had spread to all of the Great Lakes and 

greatly reduced populations of several valuable native species, 

such as lake trout, whitefish, and chub (Great Lakes Fishery 

Commission, 2000). The alewife was the next important 

invasion. The alewife arrived in the Great Lakes by the late 

1940s. This fish is native to the Atlantic Ocean, but is able to 

survive in the Great Lakes and has grown large populations 

in Lake Michigan and Lake Huron. The alewife primarily 

feeds on zooplankton placing it in direct competition with 

native lake herring, whitefish, chub, and perch (University of 

Wisconsin Sea Grant, 2002), further stressing these native fish. 

More recently, zebra mussel invasions of the Great Lakes also 

have had complex and far-ranging effects on the ecosystem. 

Zebra mussels are filter feeders and have greatly increased 

water clarity. Some native species benefit, such as northern 

pike and yellow perch, but zebra mussels displaced the 

native unionid clams in Lake Erie and Lake Saint Clair ( U.S. 

Geological Survey, 2011).

Pollution inputs to the Great Lakes also increased 

throughout the first half of the 20th century and resulted in 

water-quality degradation of the lakes and many of the lake 

tributaries. Eutrophication was a severe problem in the Great 

Lakes by the mid-20th century, particularly in Lake Erie 

(Conference on Water Pollution and the Great Lakes, 1961). 

Industrial pollutants are a continuing concern in the Great 

Lakes, including mercury, legacy DDT, and polychlorinated 

biphenyls. Although the input of these pollutants has greatly 

decreased in recent decades, fish consumption advisories are 

still in place for many fish species (Great Lakes Information 

Network, 2012). In 1969, a fire on the Cuyahoga River, 

which had burned repeatedly throughout the 20th century, 

crystallized national discontent over the rapidly deteriorating 

quality of waters throughout the Nation and helped provide the 

necessary impetus for passage of the Clean Water Act (Melosi, 

2000).
Specific Basins of Interest 41 Figure 14. Saint Lawrence River basin. tac12-0694_fig14-SaintLawrence

64°W 66°W 68°W 70°W 72°W 74°W 76°W 78°W 80°W 82°W 84°W 86°W 88°W 90°W 92°W 94°W

52°N50°N48°N46°N44°N42°N40°N

C A N A D I A N S H I E L D

Ogdensburg

Flint

Toledo

Detroit

Lansing

Buffalo

Rochester Grand Rapids

Sa ni t Lawrence River

A T L A N T I C

O C E A N

Sa

ni t L

wa

er nce Seaway

MINNESOTA

OHIO

WISCONSIN

MICHIGAN

ILLINOIS PENNSYLVANIA

INDIANA

NEW YORK

VT

NH

MA

CT RI

MAINE

IOWA

C A N A D A

kaL

M

e

hci

gi

na

Lake Huron

Lake Erie

Lake Ontario

Lake Superior

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

0 100 200 MILES

0 100 200 KILOMETERS

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

23

24

22,23

21

20

RisonRiver

Robert MosesRobert H. Saunders power dam

Welland Canal

Long Sault Dam

Massena Diversion

Wiley-Dondero navigation canal

Oswegatchie River

Long Sault Dam

Massena Diversion

Wiley-Dondero navigation canal Cornwall navigation canal

Oswegatchie River

RaisonRiver

Grass River

Robert MosesRobert H. Saunders power dam
42 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Additional attention has been focused on remediation and 

protection of the Great Lakes through the Great Lakes Water 

Quality Agreement, which is a lake management agreement 

between entities in the United States and Canada. The 

agreement was signed in 1978 and emphasizes an ecosystembased approach to address the problems confronting the Great 

Lakes (Fuller and others, 1995). Implementation of the Clean 

Water Act and the Great Lakes Water Quality Agreement 

resulted in major reductions in pollution including reductions 

in toxic pollutant inputs, phosphorus inputs, and floating 

debris (Fuller and others, 1995). In 1987, updates to the Great 

Lakes Water Quality Agreement also included designations 

for areas of concern with special remedial action plans to be 

implemented to restore beneficial uses to the Great Lakes.

In the United States part of the basin, human population 

density was 48 people/km2 in 2000, which was greater than 

the national average of 31 people/km2 and placed this basin 

approximately in the middle of basins considered in this study 

(fig. 3). Fuller and others (1995) reported a similar population 

density for the entire basin, approximately 43 people/km2

(including the Canadian portion of the basin). In 2002, 

farmland covered 22 percent of the entire basin and cropland 

covered 17 percent (fig. 4), but there are strong gradients in 

farmland coverage such that agricultural land use varies from 

6 percent surrounding Lake Superior to 60 percent around 

Lake Erie (Fuller and others, 1995). In the United States 

portion of the basin, farmland area peaked early in the 20th 

century with nearly 40 percent of the basin in agricultural 

land usage. However, the total amount of farmland has 

decreased steadily since the 1940s. In the parts of the basin 

downstream of the Great Lakes, forest cover increased from 

37 to 60 percent over the latter half of the 20th century 

(Benke and Cushing, 2005). Fertilizer and animal livestock 

sources of nitrogen are relatively low with animal livestock 

comprising a very small portion of total inputs. On average 

from 1997 to 2001, fertilizer and animal livestock sources of 

nitrogen were 0.6 and 0.3 g (N/m2)/yr (fig. 5A). Phosphorus 

sources from fertilizers and animal livestock were similar, 

each averaging approximately 0.1 g (P/m2)/yr between 1997 

and 2001 (fig. 5B). It is important to recognize that point 

sources of phosphorus were a severe problem in the Great 

Lakes in the middle and late 20th century and were a major 

focus of an intense effort to clean up the Great Lakes (Litke, 

1999). Average corn harvest for the United States part of the 

basin during 2000–2010 was 1,464 bushels/km2 of basin area 

(fig. 6), the eighth highest for all basins considered in this 

study. 

Data Sources

Data sources for the Saint Lawrence River are 

summarized in table 9. The USGS has monitored discharge 

from Lake Ontario at Cornwall, Ontario near Massena, N.Y., 

since 1935 (reference stream gaging station, station No. 

04264331). However, there is no stream gage at this location. 

Instead, discharge is determined from summation of discharge 

through the Robert Moses-Robert H. Saunders power dam, 

the Long Sault Dam, the Massena Diversion, the Raisin 

River Diversion, the Cornwall and Massena municipal water 

supply, and the Cornwall and the Wiley-Dondero navigation 

canals. Nitrate and alkalinity are available at the reference 

stream gaging station near Massena, N.Y. since 1955 although 

regular sampling did not begin until 1974 (table 9). The 

Saint Lawrence River also was included in the Clarke (1924) 

publication with 11 discrete samples having been taken in 

1906 and 1907 at Ogdensburg, N.Y. Ogdensburg is upstream 

of Cornwall and misses inputs from several tributaries 

including the Oswegatchie and Grass Rivers. However, the 

basin area is reported to be 765,000 km2 (295,000 mi2) and 

Clarke (1924) reports that discharge at this location was 

248,000 ft3/s (7,000 m3/s). Both of these properties are within 

2 percent of the calculation for the reference stream gaging 

station and so data from the Ogendsburg and Cornwall stations 

are presumed to be adequately representative of water quality 

in this part of the Saint Lawrence River. Additional waterquality sampling was performed at the Saint Lawrence River 

at Cornwall, Ontario, by the Canada Department of Mines 

and Resources, and published in a series called “Industrial 

Water of Canada” (Leverin, 1947). These include annual 

nitrate, alkalinity, and major ion observations from 1935 to 

1940, which were reported in USGS Water Supply Paper 2400 

along with a series of discrete samples taken from 1947 to 

1948 (table 9; U.S. Geological Survey, 1993). The New York 

State Department of Health also reported several water-quality 

observations taken from Ogdensburg, N.Y., in 1914 (table 9).
Specific Basins of Interest 43

Table 9. Saint Lawrence River basin data sources.

[Monitoring station is shown in figure 14. Source: NWIS, National Water Information System; USGS, U.S. Geological Survey; WSP, Water-Supply Paper. 

Constituent: Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring

station Source Station Latitude Longitude Constituent Startyear

End

year

120 NWIS 04264331

Saint Lawrence River at 

Cornwall, Ontario, near 

Massena, N.Y.

45o00′22′′ 74o47′42′′ Daily streamflow 1935 2009

TN 1974 2009

NH3 1977 2009

TON+NH3 1974 2009

NO3 1955 2009

Alk 1955 2009

TP 1974 2009

TDP 1977 2009

21 NWIS 04264000

Saint Lawrence River at 

Ogdensburg, N.Y.

44o41′20′′ 75o30′45′′ TN 1968 1971

NH3 1968 1971

TON+NH3 1968 1971

NO3 1906 1971

Alk 1906 1971

TP 1966 1971

222 USGS WSP 2400 Saint Lawrence River at 

Cornwall, Ontario

45o00′22′′ 74o47′42′′ NO3 1935 1940

Alk 1935 1940

223 Canada Department 

of Mines and 

Resources

Saint Lawrence River at 

Cornwall, Ontario

45o00′22′′ 74o47′42′′ NO3 1947 1948

Alk 1947 1948

224 New York State 

Department of 

Health 

Saint Lawrence River at 

Ogdensburg, N.Y.

44o41′20′′ 75o30′45′′ NH3 1914 1914

NO3 1914 1914

Alk 1914 1914

1

Reference stream gaging station.

2

Historical station, location approximate.
44 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Maumee River

The Maumee River is located in the Great Lakes 

basin and covers portions of Michigan, Ohio, and Indiana 

(fig. 15). It is the largest river basin draining to the Great 

Lakes, about 17,000 km2 (6,600 mi2). The Maumee River 

is the largest single source of sediment to the Great Lakes 

(Myers and others, 2000). Mean annual discharge at the 

reference stream gaging station (station No. 04193500) for 

the period 1898–2008 is 150 m3/s (5,300 ft3/s) and runoff is 

280 mm/ yr. The Maumee River is formed by the confluence 

of the Saint Joseph and Saint Mary Rivers in Fort Wayne, Ind., 

and flows approximately 130 mi before emptying into Lake 

Erie at Toledo, Ohio. The entire basin is located within the 

Central Lowlands physiographic province (fig. 2), which was 

originally covered with temperate deciduous forest, but has 

been extensively cultivated. 

More than 90 percent of the soils in the basin are poorly 

to very poorly drained. The central basin was originally 

covered with a large wetland called the Black Swamp. 

Agricultural development of this area required draining the 

wetland through a network of ditches and tile drains (Myers 

and others, 2000). Poor water retention and the presence of 

these drainage structures in the basin contribute to runoff and 

carry sediments from drained agricultural areas to stream 

channels and other water bodies.

Water-quality problems in the Maumee River basin 

relating to agricultural nonpoint pollution and other pollution 

sources prompted the Environmental Protection Agency 

to list the basin as one of its “Areas of Concern” for the 

Great Lakes region (U.S. Environmental Protection Agency, 

2006). The increase in suspended solid load by the river is of 

particular concern. Soil erosion in the Maumee River basin 

increases sediment transport from the upper parts of the basin 

toward the mouth. The increased sediment load has negative 

economic, ecological, and human health effects. Fish and 

aquatic invertebrate communities often suffer from significant 

changes in sediment load. Accordingly, some of the most 

highly altered fish and aquatic invertebrate communities 

in Ohio reside within the Maumee River basin (Myers and 

others, 2000). High sediment loads also require increased 

dredging to maintain waterways including the port of Toledo, 

Maumee Bay, and Federal waterways along the lower river 

channel. Efforts to control sedimentation in this basin include 

adoption of conservation tillage practices by farms in the 

basin. By the late 1990s, nearly one-half of all farm acres were 

in conservation tillage (Myers and others, 2000).

The Port of Toledo is an important shipping node in 

the Laurentian Great Lakes, which greatly contributed to 

the Maumee River basin becoming an important regional 

manufacturing hub. Pollution associated with manufacturing 

is a continuing concern in the Maumee River, including PCB 

(polychlorinated biphenyl) and mercury contamination in 

the lower river segments (Benke and Cushing, 2005). The 

presence of these contaminants exacerbates the sediment 

pollution problem because it complicates disposal of the 

dredge material (Myers and others, 2000).

The largest population centers in the basin are Toledo, 

Ohio, located at the mouth of the river, and Fort Wayne, Ind., 

at the headwaters. Overall population density in the basin in 

2000 was 53 people/km2, which is higher than the national 

average of 31 people/km2 and makes the Maumee River basin 

the eighth most populous basin included in this study (fig. 3; 

U.S. Census Bureau, 2000). The city of Toledo built its first 

coordinated sewerage system, called the Bay View facility, 

located near the mouth of the Maumee River, in 1922 although 

primary wastewater treatment did not begin until 1932 (City 

of Toledo, 2010). Secondary treatment of wastewater began 

in 1959 along with grit and grease removal. Capacity of the 

wastewater-treatment facility was increased several times 

in the second half of the 20th century. Combined sewer 

overflows remain a concern in older parts of the system and in 

1983, the city built a facility to provide settling treatment to 

storm water overflows. 

The basin has a very high degree of agricultural 

development with 75 percent of the basin in cropland 

and another 8 percent in other agricultural uses (fig. 4). 

Agricultural development occurred later in this drainage basin 

than several other Midwestern streams included in this study. 

Maximum cropland area, more than 78 percent, was recorded 

in the 1920 Census of Agriculture (fig. 13; M. Haines, Colgate 

University, written commun., 2004) whereas other heavily 

agricultural basins, such as the Des Moines and Illinois River, 

reached maximum cropland area prior to 1900. Nevertheless, 

the Maumee River basin remains among with most highly 

developed agricultural basins in this study. Nitrogen fertilizer 

application rates averaged 6.5 g (N/m2)/yr between 1997 

and 2001 and were comparable to the Illinois River basin 

(fig. 5). Animal livestock sources accounted for another 

1.1 g (N/m2)/ yr (fig. 5). Similarly, fertilizer and animal 

livestock sources of phosphorus were among the highest in 

this study, averaging more than 1.5 g (P/m2)/yr from 1997 

to 2001 (fig. 5). This basin also has the highest output of 

corn outside of the upper Mississippi River basin, averaging 

more than 8,000 bushels/km2 of drainage area between 2000 

and 2010 (fig. 6). The Maumee River basin exemplifies the 

tremendous increases in fertilizer usage and corn production 

that occurred in the second half of the 20th century. Fertilizer 

and animal livestock sources of nitrogen were around 2 g 

(N/ m2)/yr and then increased dramatically in the latter decades 

of the 20th century (fig. 13E). Phosphorus sources show a 

similar pattern, but there is a notable decrease from about 2.3 

to 1.7 g (P/ m2)/ yr between 1980 and 2000 (fig. 13E). 
Specific Basins of Interest 45 Figure 15. Maumee River basin. tac12-0694_fig15-Maumee

84°W 85°W 86°W

42°N41°N

OHIO

INDIANA

MICHIGAN

Maumee River Auglaize R.

St.

Jo

es

hp

. R

St. Mary’s R.

Tiff ni R.

Fort Wayne

Waterville

Defiance

Lima

Findlay

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

0 10 20 MILES0 10 20 KILOMETERS

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

25

35

34

33

32

31 30 29

28 27

26

25

Toledo

Maumee Bay

LAKE ERIE
46 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Data Sources

Data sources for the Maumee River are summarized 

in table 10. Daily stream gage data began to be collected in 

1898 at the reference stream gaging station at Waterville, 

Ohio, (station No. 04193500) with a gap from January 1936 

to March 1939. The basin area at this gage, is 16,400 km2 

(6,330 mi2) or about 10 percent less than at the mouth of the 

river. However, this station has the longest stream-gaging 

record on this segment of the river. Substantial amounts 

of water-quality data are available at Waterville from the 

USGS and the Ohio Environmental Protection Agency for 

the second half of the 20th century. Additional water-quality 

data, including samples collected in 1906–07, are available 

from sampling stations located in Toledo, Ohio. Notably, 

these stations are downstream of the Bay View wastewatertreatment facility and so water quality will be affected by its 

effluent. During 1950–66, water-quality data are available 

only from near the mouth of the Maumee River and so provide 

the only frame of reference. Since 1965, data have become 

available at Waterville, Ohio. Inferences drawn from waterquality trends in this basin must take these considerations into 

account. It is presumed that the water-quality data collected 

near the mouth of the Maumee River during 1950–66 were 

affected by the effluent of the wastewater-treatment plant, 

including elevated nutrient concentrations. More recent data 

collected at Waterville, Ohio, about 15 mi upstream of Toledo, 

was not influenced by wastewater from Toledo and so the 

inferred trends from the data could be conservative.
Specific Basins of Interest 47

Table 10. Maumee River basin data sources.

[Monitoring station is shown in figure 15. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

25 NWIS 04193490

Maumee River near 

Waterville, Ohio

41o28′34′′ 83o44′20′′ TN 1979 1989

NH3 1979 1980

TON + NH3 1979 1989

NO3 1979 1989

TP 1979 1989

126 NWIS 04193500

Maumee River at 

Waterville, Ohio

41o30′00′′ 83o42′46′′ Daily streamflow 1898 2008

TN 1974 2007

NH3 1977 2007

TON + NH3 1974 2007

NO3 1966 2007

Alk 1965 2007

TP 1968 2007

TDP 1977 2007

27 NWIS 04194010

Maumee River at Craig 

Bridge, at Toledo, Ohio

41o39′46′′ 83o30′29′′ NO3 1962 1966

Alk 1962 1966

TP 1962 1966

28 NWIS 04194022

Maumee River at Toledo 

OSEAS Terminal Dock, 

Ohio

41o41′06′′ 83o28′35′′ NO3 1962 1974

Alk 1962 1974

TP 1962 1974

29 NWIS; Clarke, 1924 04194023

Maumee River at mouth, 

at Toledo, Ohio

41o41′36′′ 83o28′20′′ NH3 1974 1975

NO3 1906 1975

Alk 1906 1975

TP 1974 1975

30 NWIS 04194030

Maumee River at C & O 

Dock, at Toledo, Ohio

41o41′46′′ 83o27′39′′ NO3 1962 1974

Alk 1962 1974

TP 1962 1974

31 NWIS 04194050

Maumee River at Buoy 

39, at Toledo, Ohio

41o42′22′′ 83o24′0′′ NO3 1962 1966

Alk 1962 1966

TP 1962 1966

32 STORET 500080

Maumee River at 

Waterville, Ohio

41o30′00′′ 83o42′46′′ TN 1973 1998

NH3 1973 1998

TON + NH3 1973 1998

NO3 1973 1998

Alk 1973 1998

TP 1968 1998

TDP 1974 1996

33 Heidelberg University USGS04193500

Maumee River at 

Waterville, Ohio

41o29′12′′ 83o42′46′′ TN 1976 1998

NH3 1975 1998

TON + NH3 1976 1998

NO3 1975 1998

Alk 1993 1997

TP 1975 1998

234 Love, 1954, 1955, 

1956a

Maumee River at 

Waterville, Ohio

41o29′12′′ 83o42′46′′ NO3 1950 1952

Alk 1950 1952

235 Love, 1954, 1955, 

1956a

Maumee River at Toledo 

OSEAS Dock, Ohio

41o41′06′′ 83o27′39′′ NO3 1950 1952

Alk 1950 1952

1

Reference stream gaging station.

2

Historical station, location approximate.
48 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Central Basins

Central basins include the Mississippi River basin, which 

incorporates the Ohio River basin in the east, the Missouri 

River basin in the west, as well as the upper, middle, and 

lower Mississippi River. The Illinois River, Des Moines River, 

and Arkansas River are other major tributaries included in 

this study (fig. 1). The Brazos River also was included in this 

category because of its similarity and geographic proximity to 

the other river basins west of the Mississippi River main stem, 

such as the Arkansas and the Missouri. The Brazos River basin 

is part of the Texas Gulf Hydrologic region. 

The Mississippi River is the largest river in North 

America with a drainage basin covering 3.2 million km2 

(1.2 million mi2), about 40 percent of the continental 

United States. The Mississippi River, together with its 

main distributary, the Atchafalaya River, discharges about 

800,000 ft3/s into the northern Gulf of Mexico. This is 

almost 40 percent of the total river flow from the continental 

United States to the coastal ocean. Substantial hydrologic 

modification of the basin has occurred throughout the main 

stem Mississippi through the construction of wing-dams, 

levees, and lock-and-dam structures designed to maintain a 

navigable channel. Major tributaries of the Mississippi River 

including the Ohio, Illinois, Missouri, and Arkansas Rivers 

also have been extensively dammed for navigation, municipal 

water supply, irrigation, and flood control projects.

All or part of 31 States and two Canadian Provinces 

reside within the Mississippi River basin, making a broad 

description of the basin difficult. Accordingly, the factors 

influencing the water quality in the main stem Mississippi 

River are certainly diverse. Intense agriculture occurs 

throughout much of the basin, particularly in the Upper 

Midwestern United States and along the alluvial floodplain 

of the lower Mississippi River. Major population centers, 

such as Chicago, Ill., Nashville, Tenn., St. Louis, Mo., 

Minneapolis-St. Paul, Minn., and Denver, Colo., are located 

within the drainage basin boundaries. Because of the large 

geographic extent of this region and the number of river 

reaches of interest, the discussion of ancillary data is focused 

into three geographic regions: basins east of the main stem 

of the Mississippi River, basins west of the main stem of the 

Mississippi River, and the Mississippi River main stem itself.

River reaches of interest to this study in the eastern part 

of the Central region include the Middle and Lower Illinois 

River and the Middle and Lower Ohio River (fig. 1). The 

Illinois River is among the most densely populated, and 

most highly agricultural basins in this study (figs. 3 and 4). 

In contrast, the Ohio River has much lower population 

density and a much lower percentage of the basin in farmland 

(figs. 3 and 4). The Illinois River basin is most affected by 

large urban centers, encompassing densely populated areas 

of northern and central Illinois. This basin has been subject 

to relatively high population density for most of the 20th 

century, with population density reaching 100 people/km2 by 

1920 (fig. 16A). By contrast, population density within the 

Ohio River basin was less than 100 people/km2 by the end of 

the 20th century (fig. 16A). Middle and Lower Illinois River 

basins are 70 and 80 percent farmland, respectively, and major 

agricultural development occurred before 1900 (fig. 16C). 

The Ohio River basin reached 80 percent farmland by 1900 

and has steadily decreased throughout the 20th century to 

around 40 percent in 2002 (fig. 16C). The Lower and Middle 

Illinois River reaches also had among the highest average 

corn harvest rates from 2000 to 2010 (fig. 6), and among the 

highest intensity of nitrogen sources from fertilizer and animal 

livestock (figs. 5A–5B). 

River reaches west of the Mississippi River include the 

Missouri, Arkansas, and Brazos Rivers, which are very large 

basins in the more arid Great Plains (fig. 1). The Des Moines 

River also is west of the Mississippi main stem, but it contrasts 

strongly with the other basins. All basins have low population 

density, less than 21 people/km2 in the year 2000 (fig. 3), and 

a large proportion of the basin in farmland (fig. 4). However, 

the Des Moines River basin is more than 75 percent cropland 

while the Missouri, Arkansas, and Brazos River basins each 

have less than 40 percent of the basin in cropland (fig. 4). 

Of all the basins considered in this study, the Des Moines 

River has the highest identified sources of nitrogen and 

phosphorus from fertilizer and animal livestock (figs. 5A–5B). 

It also averaged the second highest corn harvest rate from 

2000 to 2010 (fig. 6). In contrast, the Missouri, Arkansas, 

and Brazos Rivers have much lower corn harvests and only 

a small fraction of the nitrogen and phosphorus sources 

from fertilizer and animal livestock (figs. 5A–5B). Farmland 
Specific Basins of Interest 49

Figure 16. Historical changes in (A) population density, (B) corn harvest, (C) percentage of basin area in any 

farmland usage, (D) percentage of basin area in cropland, and fertilizer and animal livestock sources of (E) nitrogen 

and (F) phosphorus in the Central basins east of the main stem of the Mississippi River.

tac12-0694_fig 16

1900 1920 1940 1960 1980 2000

0

0.5

1.0

1.5

2.0

2.5

1860 1890 1920 1950 1980

0

20

40

60

80

100

1860 1890 1920 1950 1980

0

20

40

60

80

100

0

20,000

Year

Percentage of the basin area in cropland

Percentage of the basin area in any farmland usage

1900 1920 1940 1960 1980 2000

Population density, in people per square kilometer 

A B

Year

Nonpoint nitrogen from fertilizer and animal livestock 

sources, in grams of nitrogen per square meter per year 

E F

C D Corn harvest, in bushels per square kilometer of watershed area

1900 1920 1940 1960 1980 2000

0

50

100

150

200

250

300

350

1900 1920 1940 1960 1980 2000

0

2

4

6

8

10

Nonpoint phosphorus from fertilizer and animal livestock 

sources, in grams of phosphorus per square meter per year

Middle Ohio

River basin

Average National 

population 

density

Lower Ohio

Middle Illinois

Lower Illinois

EXPLANATION

2010 2010

5,000

10,000

15,000
50 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

development in all of these basins west of the Mississippi 

River proceeded along a similar timeline and trajectory with 

the basins becoming heavily agricultural by the early 20th 

century (fig. 17C). However, the Des Moines River basin had 

approximately double the amount of cropland in the basin 

as the other basins as early as 1900 (fig. 17D). These data 

emphasize the contrasting nature of agricultural development 

and the implications on the identified sources of nitrogen 

and phosphorus in heavily cultivated river basins, such as 

the Maumee (figs.13B–13D), Illinois (figs. 16B–16D), and 

Des Moines Rivers (figs. 17B–17D) as compared with those 

of the Great Plains (Missouri, Arkansas, and Brazos Rivers) 

(figs. 17B–17D).

The river reaches of interest along the main stem of 

the Mississippi River largely reflect regional influences of 

the basin. Accordingly, the Upper Mississippi River, which 

includes the Illinois and Des Moines Rivers as well as other 

parts of eastern Iowa, southern Minnesota, and western 

Illinois, has a higher population density, corn harvest rate, 

farmland and cropland percentage, and identified sources 

of nitrogen and phosphorus in the basin (figs. 18A–18F). In 

contrast, the Middle and Lower parts of the main stem of 

the Mississippi River are similar and reflect the influences 

of several large tributaries including the Missouri, Ohio, 

and Arkansas Rivers. Although the percentage of basin area 

in farmland acreage in these basins is similar to that of the 

Upper Mississippi (fig. 18C), these basins have much lower 

cropland percentages (fig. 18D). Corn harvest rates also 

are much lower (fig. 18B) as are the identified sources of 

nitrogen and phosphorus from fertilizer and animal livestock 

(figs. 18E–18F).

Understanding the nutrient dynamics on the main stem 

Mississippi River is particularly important because of the 

contribution to the hypoxia that develops annually in the 

northern Gulf of Mexico. On average, the hypoxic area covers 

about 16,500 km2 (6,400 mi2) and is the second largest coastal 

hypoxic zone in the world (U.S. Environmental Protection 

Agency Science Advisory Board, 2007). Coastal hypoxia is a 

growing problem worldwide and is caused by excess nutrient 

inputs that foster algal blooms. The death and decomposition 

of algae following blooms consumes oxygen and causes 

hypoxic conditions, depending on the stability of the water 

column and the rate of oxygen consumption. Although there 

is some evidence for hypoxic events in the northern Gulf 

of Mexico occurring more than 100 years ago, the intensity 

and magnitude of these events has increased greatly in the 

past several decades (U.S. Environmental Protection Agency 

Science Advisory Board, 2007). It is clearly of interest to 

investigate long-term patterns in nutrient dynamics in the 

Mississippi River.
Specific Basins of Interest 51

Figure 17. Historical changes in (A) population density, (B) corn harvest, (C) percentage of basin area in any 

farmland usage, (D) percentage of basin area in cropland, and fertilizer and animal livestock sources of (E) nitrogen 

and (F) phosphorus in the Central basins west of the main stem of the Mississippi River.

tac12-0694_fig 17

1900 1920 1940 1960 1980 2000

0

0.5

1.0

1.5

2.0

2.5

1860 1890 1920 1950 1980

0

20

40

60

80

100

1860 1890 1920 1950 1980

0

20

40

60

80

100

0

20,000

Year

Percentage of the basin area in cropland

Percentage of the basin area in any farmland usage

1900 1920 1940 1960 1980 2000

Population density, in people per square kilometer 

A B

Year

Nonpoint nitrogen from fertilizer and animal livestock 

sources, in grams of nitrogen per square meter per year 

E F

C D Corn harvest, in bushels per square kilometer of watershed area

1900 1920 1940 1960 1980 2000

0

50

100

150

200

250

300

350

1900 1920 1940 1960 1980 2000

0

2

4

6

8

10

Nonpoint phosphorus from fertilizer and animal livestock 

sources, in grams of phosphorus per square meter per year

Des Moines

River basin

Average National 

population 

density

Missouri

Arkansas

Brazos

EXPLANATION

2010 2010

5,000

10,000

15,000
52 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 18. Historical changes in (A) population density, (B) corn harvest, (C) percentage of basin area in any 

farmland usage, (D) percentage of basin area in cropland, and fertilizer and animal livestock sources of (E) nitrogen, 

and (F) phosphorus in the basins of interest on the main stem of the Mississippi River.

tac12-0694_fig 18

1900 1920 1940 1960 1980 2000

0

0.5

1.0

1.5

2.0

2.5

1860 1890 1920 1950 1980

0

20

40

60

80

100

1860 1890 1920 1950 1980

0

20

40

60

80

100

0

20,000

Year

Percentage of the basin area in cropland

Percentage of the basin area in any farmland usage

1900 1920 1940 1960 1980 2000

Population density, in people per square kilometer 

A B

Year

Nonpoint nitrogen from fertilizer and animal livestock 

sources, in grams of nitrogen per square meter per year 

E F

C D Corn harvest, in bushels per square kilometer of watershed area

1900 1920 1940 1960 1980 2000

0

50

100

150

200

250

300

350

1900 1920 1940 1960 1980 2000

0

2

4

6

8

10

Nonpoint phosphorus from fertilizer and animal livestock 

sources, in grams of phosphorus per square meter per year

Upper Mississippi

River basin

Average National 

population 

density

Middle Mississippi

Lower Mississippi

EXPLANATION

2010 2010

5,000

10,000

15,000
Specific Basins of Interest 53

Ohio River 

The Ohio River is the third largest river in terms of 

discharge in the United States. Measured at the reference 

stream gaging station for the lower river at Metropolis, Ill. 

(station No. 03611500), mean annual discharge (1928–2008) 

is 7,900 m3/s (278,000 ft3/s) and runoff is 472 mm/yr. The 

Ohio River basin has the highest runoff of any major tributary 

to the Mississippi River and contributes 40 percent of the 

total discharge of the Mississippi River while making up only 

16 percent of the total basin area, approximately 526,000 km2

(203,000 mi2). The Ohio River is formed in Pittsburgh, Pa., 

by the confluence of the Allegheny and Monongahela Rivers 

(fig. 19). Flow at the confluence of these rivers is about 

960 m3/s (34,000 ft3/s) and runoff is nearly 600 mm/yr. The 

river then flows almost 1,600 km to its confluence with the 

Mississippi at Cairo, Ill. Benke and Cushing (2005) identify 

12 major tributaries to the Ohio River, which account for 

84 percent of the total basin area. They include the Allegheny, 

Monongahela, Scioto, Little Miami, Great Miami, Licking, 

Kentucky, Green, Kanawha, Wabash, Cumberland, and 

Tennessee Rivers. The major tributaries encompass a wide 

range of physiographic conditions including steep, rocky 

streams draining the Appalachian Mountains to gently 

sloping streams draining deep till plains. The Tennessee 

and Cumberland River basins also are noted for their high 

diversity of fishes and aquatic invertebrates (Benke and 

Cushing, 2005). Flow on the river is tightly controlled for 

river navigation, with the first dam built on the river almost 

200 years ago at Henderson, Ky. (Benke and Cushing, 2005). 

The Ohio River Valley is highly industrialized and has been 

at the center of the American industrial economy for over a 

century. Consequently, the river has a long history of waterquality problems arising from mining, industrial activities, and 

population centers.

The first coordinated water quality study of the Ohio 

River was conducted in 1914–1915 by the U.S. Public 

Health Service. Passage of the Public Health Service Act of 

1912 paved the way for Federal studies of water pollution 

in the United States (Scarpino, 1985). The Ohio River 

was the first river to be studied by the U.S. Public Health 

Service. Early in the 20th century, interacting problems of 

untreated sewage disposal, industrial pollution, and acidic 

mine drainage resulted in degradation of water quality in the 

river. Major metropolitan areas of Pittsburgh, Cincinnati, 

and Louisville discharged considerable amounts of untreated 

sewage into the river. However, the presence of industrial 

waste and acidic waters inhibited “self-purification,” the 

usual process of biological remediation of pollution in the 

river (Hoskins and others, 1927). In the early 20th century, 

38 low-head navigational dams were constructed along the 

Ohio River (Hoskins and others, 1927). The dams created a 

series of slackwater pools that trapped particulate matter and 

interrupted downstream transport of polluted material. Flood 

events often scoured sediments behind the navigational dams 

and resulted in a pulse of polluted material being transported 

downstream, which led to undesirable conditions and 

complicated drinking water treatment (Cleary, 1967).

In the early 1920s, phenol pollution became a prominent 

issue on the Ohio River. Even in minute amounts, phenols 

impart a medicinal aroma to drinking water, a quality 

that is exacerbated by chlorination (Cleary, 1967). State 

and municipal officials came to an informal agreement 

with industry leaders to minimize phenol discharges into 

the Ohio River and its tributaries, although there was no 

legal mechanism to enforce this agreement (Cleary, 1967). 

The nature of this agreement exemplifies the difficulties 

encountered by public health officials trying to coordinate 

water-quality improvements in the Ohio River.

As previously discussed, efforts to strengthen the 

Federal role in guaranteeing water quality in the Nation’s 

rivers proceeded very slowly throughout the 20th century. 

Although the preferred model was one in which the States 

took lead responsibility for cleaning up their own waters, the 

Ohio River provided a counter example of a region in urgent 

need of water-quality improvement that no single State could 

achieve on its own. As a result, by the middle of the century 

eight States bordering the main stem Ohio River joined 

together to form a regional compact known as the Ohio River 

Valley Water Sanitation Commission (ORSANCO). Water 

sanitation officials and industry leaders began discussing the 

idea in 1935, but the final commission did not form until 1948 

(Cleary, 1967).

The objective of ORSANCO was to control existing and 

future pollution in rivers and streams in the Ohio River basin 

(Cleary, 1967). ORSANCO relied upon the cooperative nature 

of the commission in setting out to achieve these goals. By the 

mid-1960s, almost $1 billion had been spent on cleanup and 

wastewater treatment in the Ohio River basin (Cleary, 1967). 
54 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 19. Ohio River basin, Ohio.

tac12-0694_fig19-Ohio

78°W 80°W 82°W 84°W 86°W 88°W 90°W 92°W 94°W 96°W

42°N40°N38°N36°N34°N

Green

R.

Tennessee R. h O oi R vi

er

Kentucky R.

Licking R.

Columbus

Knoxville

Huntsville

Louisville

Charleston

Cincinnati

Pittsburgh

Indianapolis

Nashville

IOWA

OHIO

MISSOURI

ILLINOIS

ARKANSAS

INDIANA

KANSAS

TENNESSEE

KENTUCKY

OKLAHOMA

VIRGINIA

GEORGIA

ALABAMA

MICHIGAN

SOUTH CAROLINA

WEST VIRGINIA

MISSISSIPPI

WISCONSIN

PENNSYLVANIA

NORTH CAROLINA

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

0 50 100 MILES0 50 100 KILOMETERS

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

43

46,48

45,47

44

42

40,41

39

38

37

36

46,47,48

45,49

44

43

42

40,41

39

38

37

36

Monongahela River

Allegheny River

Cairo

Scioto River

Little Miami River

Great Miami River

Kanawha River

Cumberland River

Appalachian Mountains

Henderson

Monongahela River

Allegheny River

Cairo

Scioto River

Little Miami River

Great Miami River

Kanawha River

Wabash River

Cumberland River

Appalachian Mountains

Henderson
Specific Basins of Interest 55

This achievement occurred at a time when water quality was 

deteriorating dramatically in many other parts of the country. 

At the time of formation, ORSANCO relied heavily upon a 

massive survey of pollution in the Ohio River basin conducted 

by the U.S. Public Health Service in 1940–42. The published 

report was nearly 1,400 pages long and detailed water quality, 

pollution sources, recommendations for remediation, and cost 

estimates for the entire basin (U.S. Public Health Service, 

1942). The principal pollution issues identified by the Ohio 

River Pollution Survey are familiar, but instructive. The 

report included recommended standards for coliform bacteria, 

dissolved oxygen, biochemical oxygen demand, pH, and 

phenol content (Cleary, 1967). In the 1940s, the main driving 

forces of pollution in this basin were identified as deriving 

from industry, population centers, and mining. 

In contrast to many heavily farmed basins included in 

this study, the Ohio River basin is approximately 47 percent 

forested land and 47 percent agricultural land (Benke and 

Cushing, 2005). Meanwhile population density for the entire 

basin (referenced as the lower Ohio River) is 53 people/km2, 

and comparable for the middle basin upstream of Louisville 

at 62 people/km2 (fig. 3). These values reflect a mix of large 

population centers with more sparsely populated agricultural 

and forest land. Agricultural intensity differs between the 

upper and lower part of the Ohio River basin with the 

percentage of the basin in agricultural land usage ranging 

from less than 20 percent in Pennsylvania in to more than 70 

percent in Illinois and Indiana, near the confluence with the 

Mississippi (Benke and Cushing, 2005). Slightly more than 45 

percent of the entire Ohio River basin is agricultural land with 

30 percent in cropland (fig. 4). Upstream of Louisville, Ky., 

the basin is 37 percent farmland with 22 percent in cropland 

(fig. 4). The basin has steadily lost farmland throughout the 

20th century with nearly 80 percent of the basin in farmland 

and 55 percent of the basin in cropland in 1900 (figs. 16C–

16D). Industrial and urban sources are likely to be the 

principal driving forces of pollution upstream of Louisville, 

Ky., while agricultural influences may be more significant in 

the lower part of the Ohio River basin.

Data Sources

For the purposes of our study, two reaches of the Ohio 

River were considered. The middle Ohio River was assessed 

at stations around Louisville, Ky. and Evansville, Ind. The 

lower Ohio River includes data from stations around Cairo and 

Metropolis, Ill. Data sources for the lower and middle Ohio 

River are summarized in table 11.

For the middle Ohio River, daily streamflow is available 

from 1928 to 2010 at the reference stream gaging station 

at Louisville, Ky. (station No. 03294500) and from the 

1970s to 2007 from Cannelton Dam. The drainage area at 

Louisville, Ky., is about 236,000 km2 (91,000 mi2), mean 

annual discharge for the period 1970–2007 is 3,300 m3/s 

(116,000 ft3/s), and runoff is about 440 mm/yr. In 1968, USGS 

water-quality sampling began at the reference stream gaging 

station at Louisville. Water-quality data also are available 

from the USGS stream-gaging station farther downstream 

at Cannelton Dam and from the STORET database from 

Evansville. Predating the USGS data on the middle Ohio 

River are data collected by the U.S. Public Health Service in 

1939–40 as part of the Ohio River Pollution Survey and in 

1929–30 (monitoring station 42) as part of a follow-up study 

to the groundbreaking work done in 1914–15 on the Ohio 

River. The earliest water–quality data on the Middle Ohio 

River comes from State and local sources. The Indiana State 

Board of Health conducted a longitudinal survey on the Ohio 

River in 1911 that contains water–quality data for a number of 

stations. The Louisville Water Company also published waterquality data collected from the Ohio River at Louisville, Ky., 

in 1895–1897.

For the lower Ohio River, daily streamflow data began 

to be collected at the reference stream gaging station at 

Metropolis, Ill. (station No. 03611500), in 1928. The USGS 

began collecting water-quality data at Dam 53 near Grand 

Chain, Ill., in the mid-1950s. The Illinois State Water Survey 

also collected water-quality data at Cairo, Ill., from 1958 to 

1976 and at Metropolis, Ill., from 1950 to 1956. These data 

were published in the Illinois State Water Survey Bulletin. The 

oldest data on the lower Ohio River also were collected by 

the Illinois State Water Survey as part of the work begun by 

Arthur Palmer in the late 19th century. Data collected at Cairo 

and Metropolis, Ill., exist for a few years between 1898 and 

1908.
56 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Table 11. Ohio River basin data sources.

[Monitoring station is shown in figure 19. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring

station Source Station Latitude Longitude Constituent Startyear

End

year

Middle Ohio River

36 NWIS 03277200

Ohio River at Markland Dam, 

near Warsaw, Ky.

38o46′29′′ 84o57′52′′ Daily streamflow 1970 2007

TN 1974 1986

NH3 1977 1986

TON + NH3 1974 1986

NO3 1959 1986

Alk 1959 1986

TP 1967 1986

TDP 1978 1986

37 NWIS 03303280

Ohio River at Cannelton Dam, 

at Cannelton, Ind.

37o53′58′′ 86o42′20′′ Daily streamflow 1975 2007

TN 1974 2009

NH3 1977 2009

TON + NH3 1974 2009

NO3 1974 2009

Alk 1974 2009

TP 1974 2009

TDP 1978 2009

138 NWIS 03294500

Ohio River at Louisville, Ky.

38o16'49′′ 85o47′57′′ Daily streamflow 1928 2010

NO3 1968 1995

Alk 1968 1995

TP 1968 1995

39 STORET 170036

Ohio River at Evansville, Ind.

37o57'28′′ 87o 4′28′′ TN 1960 1974

NH3 1958 1974

TON + NH3 1960 1974

NO3 1960 1974

Alk 1958 1974

TP 1960 1974

TDP 1964 1974

240 Fuller, 1898 Ohio River at Louisville, Ky. 38o16′49′′ 85o47′57′′ NH3 1895 1897

NO3 1895 1897

Alk 1895 1897

241 State Board of 

Health of 

Indiana, 1911

Ohio River at Louisville, Ky. 38o16′ 49′′ 85o47′57′′ NH3 1911 1911

NO3 1911 1911

Alk 1911 1911

242 Crohurst, 1933 Ohio River at Louisville, Ky. 38o15′ 49′′ 85o45′06′′ Alk 1929 1930
Specific Basins of Interest 57

Monitoring

station Source Station Latitude Longitude Constituent Startyear

End

year

Lower Ohio River

143 NWIS 03611500

Ohio River at Metropolis, Ill.

37o08′51′′ 88o44′27′′ Daily streamflow 1928 2008

TN 1978 1995

NH3 1978 1995

TON + NH3 1978 1995

NO3 1978 1995

Alk 1978 1995

TP 1978 1995

TDP 1978 1995

44 NWIS 03612500

Ohio River at Dam 53, near 

Grand Chain, Ill.

37o12'11′′ 89o02′30′′ TN 1972 2009

NH3 1972 2009

TON + NH3 1972 2009

NO3 1954 2009

Alk 1954 2009

TP 1967 2009

TDP 1972 2009

245 Larson and 

Larson, 1957

Ohio River at Metropolis, Ill. 37o08′51′′ 88o44′27′′ NH3 1950 1956

NO3 1950 1956

Alk 1950 1956

246 Larson and 

Larson, 1957; 

Harmeson and 

Larson, 1969; 

Harmeson and 

others, 1973

Ohio River at Cairo, Ill. 37o12′11′′ 89o10′30′′ NH3 1958 1976

NO3 1958 1976

Alk 1958 1976

TDP 1960 1976

247 Long, 1889 Ohio River at Cairo, Ill. 37o01′23′′ 89o10′30′′ NO3 1888 1888

NH3 1888 1888

248 Bartow, 1907, 1909 Ohio River at Cairo, Ill. 37o01′23′′ 89o10′30′′ NH3 1898 1908

NO3 1898 1908

Alk 1898 1908

249 Bartow, 1907, 1909 Ohio River at Metropolis, Ill. 37o08′41′′ 88o44′32′′ NH3 1898 1908

NO3 1898 1908

Alk 1898 1908

1

Reference stream gaging station.

2

Historical station, location approximate.

Table 11. Ohio River basin data sources.—Continued

[Monitoring station is shown in figure 19. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]
58 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Illinois River

The Illinois River is a major tributary to the upper 

Mississippi River with the confluence of the two rivers located 

at Grafton, Ill. (fig. 20). The Illinois River basin covers more 

than 75,000 km2 (29,000 mi2) and lies almost entirely within 

Illinois with small portions in Indiana and Wisconsin. 

The main stem is approximately 440 km long and 

contributes nearly 20 percent of the total water discharge in 

the upper Mississippi at Alton, Ill. The farthest downstream 

gaging station is at Valley City, Ill., almost 100 km upstream 

of the confluence because river stage downstream from 

there can be affected by flooding on the Mississippi River 

(Groschen and others, 2000). Mean annual discharge is 

approximately 650 m3/s (23,000 ft3/s) and runoff is 300 mm/ yr 

at the reference stream gaging station for the lower basin at 

Valley City (station No. 05560000) for the period 1938–2010. 

The river is formed by the convergence of the Des Plaines 

and Kankakee Rivers southwest of Chicago, Ill. Other 

tributaries include the Fox, Vermillion, Mackinaw, Spoon, 

Sangamon, and La Moine Rivers. The Illinois River basin lies 

almost entirely within the Till Plains section of the Central 

Lowlands physiographic province. The lower Illinois basin 

is heavily cultivated with farmland making up more than 

80 percent of the land area (fig. 4). In addition, five urban 

areas with populations greater than 100,000 are within the 

basin and population density of the lower Illinois basin is 

155 people/ km2 (fig. 3). Both of these metrics indicate very 

intense human activity, including agricultural production and 

urbanization in this drainage basin. Therefore, both urban and 

agricultural pressures are expected to influence water quality 

in this basin.

The environmental history of the Illinois River is 

exceptionally well-documented and encompasses several 

serious environmental challenges faced by this ecosystem. A 

survey of water pollution on the Illinois River was conducted 

in 1888 and published in 1889 by the Illinois State Board of 

Health (Long, 1889) and contains the oldest water chemistry 

data available for this study. Biological surveys of the aquatic 

ecosystems of Illinois began in 1894 by Stephen Forbes of 

the Illinois Natural History Survey (Benke and Cushing, 

2005). Around this time, the Illinois State Water Survey also 

began methodically categorizing the quality of drinking-water 

sources for municipalities throughout the State under the 

direction of Arthur Palmer. The first “Chemical Survey of the 

Water Supplies of Illinois” (Palmer, 1897) was published in 

1897 and included water-quality data for groundwater and 

surface waters throughout the State. These sources contribute 

greatly to our knowledge of the Illinois River in the late 19th 

and early 20th centuries.

Perhaps the most significant environmental alteration 

to the river was the reversal of the Chicago and Calumet 

Rivers in the late 19th century. These rivers formerly flowed 

into Lake Michigan and were used extensively at this time as 

sanitary sewers to transport wastewater away from Chicago. 

However, Lake Michigan also was the drinking water source 

for Chicago, so legitimate concerns were raised about the 

wisdom of dumping wastewater in close proximity to the 

location of city drinking water intakes. City managers decided 

to reverse the flow of the Chicago River to direct wastewater 

into the Illinois River rather than Lake Michigan. Part of the 

plan also included diluting the wastewater with water pumped 

from Lake Michigan as a way of ameliorating some of the 

negative effects of diverting sewage into the Illinois River. 

The Chicago Sanitary and Shipping Canal opened in 1900 and 

is still in operation. The alteration added around 2,000 km2

(770 mi2) to the river basin and in some years more than 25 

percent of the total flow in the Illinois River originated from 

the canal as either wastewater or water from Lake Michigan 

meant to dilute the waste (Murphy, 1961).

Although the Illinois River was hardly in pristine 

condition at the opening of the Chicago Sanitary and Ship 

Canal, the influx of polluted wastewater accelerated waterquality degradation in the river. Other pressures on the 

river ecosystem included overfishing, urban and industrial 

development within the basin, and the development of levee 

and drainage districts, which disconnected the river from 

its riparian ecosystem and allowed its extensive bottomland 

floodplain to be converted into agricultural land (Thompson, 

2002). Additionally, the Illinois River once supported diverse 

and extremely productive fisheries. The low hydrologic 

gradient and wide floodplain in the lower basin allow 

long water residence time in the river basin and probably 

contributed to the magnitude and diversity of its fisheries 

production under pristine conditions (Benke and Cushing, 

2005). Overfishing, low oxygen resulting from pollution 

inputs, and silt deposition all contributed to the demise of the 

fisheries on the Illinois River. The mussel fishery collapsed 

in the early 20th century and the fin fishery collapsed by the 

1920s (Thompson, 2002). By 1922 “animal life [had been] 

almost excluded from the upper river...due to increase of 

sewage incident to the growth of the city of Chicago” (Purdy, 

1930, p. 9).

A great deal of effort has gone into cleaning up the 

Illinois River, but pressures on the ecosystem are still 

tremendous. Currently (2012), 196 wastewater-treatment 

plants exist in the upper drainage basin (Benke and Cushing, 

2005) although the influx of municipal wastes has decreased 

substantially. Nonetheless, nutrient (N and P) concentrations 

within the river are still very high (Groschen and others, 

2000). The lower Illinois River had the highest corn harvest, 

more than 16,000 bushels/km2 of drainage area (fig. 6), 

and among the highest identified sources of nitrogen and 

phosphorus of the basins included in this study (figs. 5A–5B). 
Specific Basins of Interest 59 Figure 20. Illinois River basin. tac12-0694_fig20-Illinois

86°W 87°W 88°W 89°W 90°W 91°W 92°W 93°W 94°W 95°W

43°N42°N41°N40°N39°N

Havana

Peoria

Havana

Springfield

Bloomington

Chicago

Grafton

LAKE

MICHIGAN

IOWA

ILLINOIS

MISSOURI

INDIANA

WISCONSIN

MICHIGAN

Ill ni o si R vi er

Mack ni aw R.

Vermilion R.

pS oon R.

La Moine R.

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

00 50 100 KILOMETERS

50 100 MILES

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

63

Creve Coeur Lock and Dam

Hardin

Pekin

Meredosia

Averyville

Kampsville 62

61

59

57

56

53

52

51,54 50

49,55

67

66

64,65

62

61,63

60

58,59

55

54

53,56 51,52

50,57

Kampsville

Averyville

Meredosia

Pekin

Hardin

Creve Coeur Lock and Dam

Valley City

Kingston Mines

Beardstown

River

Alton

Des Plaines River Kankakee Fox River

Sangamon River

Chicago River

Calumet River

Chicago Sanitary and Ship Canal

Alton

Des Plaines River Kankakee Fox River

Sangamon River

Chicago River

Calumet River

Chicago Sanitary and Ship Canal

River

Beardstown

Kingston Mines

Valley City
60 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Data Sources

For the purposes of this study, water quality and 

streamflow data will be considered from two reaches of the 

Illinois River based on the location of USGS stream gages. 

The middle Illinois River is defined by streamflow data from 

around Kingston Mines and the reference stream gaging 

station at Peoria, Ill. (station No. 05560000), while the lower 

Illinois River is described by streamflow data from around 

Beardstown and the reference stream gaging station at Valley 

City, Ill (station No. 05586100). Data sources for the lower 

and middle Illinois River are summarized in table 12. 

Partial daily streamflow data are available for the 

middle Illinois River at Peoria beginning in 1903 and 

complete data are available beginning in 1910 through 1938. 

Beginning in 1939, the stream-gaging station was relocated 

approximately 15 mi downstream to Kingston Mines and 

is still in operation. The drainage area at Kingston Mines 

incorporates the Mackinaw River drainage basin and is about 

41,000 km2 (15,800 mi2), about 10 percent larger than Peoria 

at 36,500 km2 (13,700 mi2). For the lower Illinois River, daily 

streamflow data exist beginning in 1920 at Beardstown, Ill. 

Since 1938, daily streamflow data have been collected about 

30 mi downstream at Valley City, Ill. The drainage area at 

Valley City is 69,264 km2 (26,740 mi2), about 9 percent larger 

than Beardstown at 62,753 km2 (24,230 mi2).

As mentioned above, water-quality data exist as far back 

as 1888 for both the middle and lower Illinois River. Data 

also exists for these river reaches as part of volumes 1 and 2 

of the Illinois State Water Survey Bulletin around Kampsville 

in the lower reach and Peoria in the middle reach. Notably, 

these samples contain Kjeldahl N data, which is still in use 

today and provides a basis for comparing long-term changes in 

total N in the Illinois River. Data from 1906 to 1907 at Peoria 

and Kampsville, Ill. also were included in the Clarke (1924) 

compilation. A survey of the Illinois River was conducted in 

1921–22 and included 23 stations between Lockport (in the 

Chicago area) and Kampsville, Ill. This study also includes 

Kjeldahl N measurements and provides critical insight into 

the total N status of the river before substantial wastewater 

treatment had begun. For the purposes of this compilation, 

data from stations at Peoria and Averyville, Ill., were identified 

as describing conditions for the middle reach, and three 

stations between Hardin and Beardstown, Ill. (combined and 

designated as monitoring station 63; table 12) for the lower 

reach. The Illinois State Water Survey resumed collecting and 

publishing water-quality data from surface and groundwater 

in 1945, including the Illinois River at Peoria, which was 

sampled regularly by the Illinois State Water Survey until 

1971. Beginning in 1955, the Illinois River also was sampled 

at Meredosia, which is between Beardstown and Valley City, 

Ill. in the lower Illinois River. The Illinois Environmental 

Protection Agency began collecting data throughout the 

State in 1958 and continuing through 1977. These data were 

published by the U.S. Geological Survey and include data 

from both the lower and middle Illinois River (Healy and 

Toler, 1978; Grason and Healy, 1979). The USGS began 

collecting water-quality data at Pekin, Ill., in 1977 and at 

Valley City, Ill., in 1974. Sampling continued at Valley City, 

Ill. (2008), but sampling at Pekin was discontinued in 1998, 

although data from the Illinois EPA Ambient Water Quality 

Monitoring Network were collected at Pekin, Ill., between 

1999 and 2005.

The sampling station at Peoria, Ill., is located near the 

center of the city and upstream of the major sewer outfall. 

Therefore, data collected more recently from Pekin, Ill., may 

include some effect of this point source. However, data are 

available from the sampling station at Peoria, Ill., beginning 

in the early 20th century through 1977, so this station offers 

more than 70 years of data collected from the same site thus 

allowing for interpretation of long-term trends.
Specific Basins of Interest 61

Table 12. Illinois River basin data sources. 

[Monitoring station is shown in figure 20. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

Middle Illinois River

150 NWIS; 

Clarke, 1924

05560000

Illinois River at Peoria, Ill.

40o42′08′′ 89o33′52′′ Daily streamflow 1903 1938

NO3 1906 1907

Alk 1906 1907

51 NWIS 05568500

Illinois River at Kingston 

Mines, Ill.

40o33′11′′ 89o46′38′′ Daily streamflow 1939 2010

252 Long, 1889 Illinois River at Pekin, Ill. 40o42′08′′ 89o33′52′′ NO3 1888 1888

NH3 1888 1888

53 NWIS 05563800

Illinois River at Pekin, Ill.

40o34′23′′ 89o38′17′′ TN 1977 1998

NH3 1977 1998

TON + NH3 1977 1998

NO3 1977 1998

Alk 1978 1998

TP 1980 1998

TDP 1981 1998

54 STORET 48367

Illinois River at Creve Coeur 

Lock and Dam, Ill.

40o37′57′′ 89o37′28′′ TN 1989 1990

NH3 1974 1990

TON + NH3 1989 1990

NO3 1972 1990

Alk 1989 1990

TP 1972 1990

TDP 1989 1990

55 Larson and 

Larson, 1957; 

Harmeson and 

Larson, 1969; 

Harmeson and 

others, 1973

48809

Illinois River at Peoria, Ill.

40o40′55′′ 80o36′04′′ NH3 1945 1971

NO3 1945 1971

Alk 1945 1971

TDP 1959 1971

256 Hoskins and 

others, 1927

Illinois River at Pekin, Ill. 40o34′23′′ 89o38′17′′ TN 1921 1922

NH3 1921 1922

TON + NH3 1921 1922

NO3 1921 1922

257 Palmer, 1897, 

1903

Illinois River at Peoria, Ill. 40o41′57′′ 89o34′11′′ TN 1896 1901

NH3 1895 1901

TON + NH3 1896 1901

NO3 1895 1901
62 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Table 12. Illinois River basin data sources.—Continued

[Monitoring station is shown in figure 20. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

Lower Illinois River

258 Long, 1889 Illinois River at Beardstown, Ill. 40o01′23′′ 90o26′12′′ NO3 1888 1889

NH3 1888 1889

59 NWIS 05584000

Illinois River at Beardstown, Ill.

40o01′23′′ 90o26′12′′ Daily streamflow 1920 1938

160 NWIS 05586100

Illinois River at Valley City, Ill.

39o42′12′′ 90o38′43′′ Daily Streamflow 1938 2010

TN 1974 2008

NH3 1975 2008

TON + NH3 1974 2008

NO3 1974 2008

Alk 1974 2008

TP 1974 2008

TDP 1977 2008

61 NWIS 05587060

Illinois River at Hardin, Ill.

39o09′37′′ 90o36′55′′ TN 1978 1995

NH3 1977 1998

TON + NH3 1978 1995

NO3 1977 1998

Alk 1977 1995

TP 1978 1998

TDP 1984 1998

62 Harmeson and 

Larson, 1969; 

Harmeson and 

others, 1973

Illinois River at Meredosia, Ill. 39o49′24′′ 90o34′05′′ NH3 1955 1971

NO3 1955 1971

Alk 1955 1971

263 Hoskins, 1927 Illinois River at Hardin, Ill. 39o09′37′′ 90o36′55′′ TN 1921 1922

NH3 1921 1922

TON + NH3 1921 1922

NO3 1921 1922

264 Palmer, 1897, 

1903

Illinois River at Havana, Ill. 40o17′40′′ 90o04′12′′ TN 1896 1900

NH3 1895 1900

TON + NH3 1896 1900

NO3 1895 1900

265 Clarke, 1924 Illinois River at Kampsville, Ill. 39o17′59′′ 90o36′22′′ NO3 1906 1907

Alk 1906 1907

266 Palmer, 

1897, 1903

Illinois River at Kampsville, Ill. 39o17′59′′ 90o36′22′′ TN 1896 1901

NH3 1896 1902

TON + NH3 1896 1901

NO3 1896 1902

267 Palmer, 1903 Illinois River at Grafton, Ill. 38o58′04′′ 90o26′04′′ TN 1899 1901

NH3 1899 1902

TON + NH3 1899 1901

NO3 1899 1902

1

Reference stream gaging station.

2

Historical station, location approximate.
Specific Basins of Interest 63

Des Moines River

The Des Moines River is a tributary to the upper 

Mississippi River located primarily in Iowa. It is the largest 

river basin in Iowa, covering nearly 37,500 km2 (14,500 mi2). 

The headwaters are located in southern Minnesota and the 

farthest southern reaches of the basin are in Missouri (fig. 21). 

The Des Moines River runs primarily from northwest 

to southeast and enters the upper Mississippi River just 

downstream of Keokuk, Iowa. Measured at the reference 

stream gaging station at Keosauqua, Iowa (USGS station 

No. 05490500), mean annual discharge on the Des Moines 

River was approximately 257 m3/s (9,100 ft3/s) between 1970 

and 2010 but was extremely variable, ranging from 37 m3/s 

(1,300 ft3/s) in 1977 to 763 m3/s (almost 27,000 ft3/s) in 1993. 

Mean annual runoff during this period was 220 mm/yr, but 

annual runoff also ranged widely from 32 to 660 mm/yr.

The entire basin lies within the Central Lowlands 

physiographic province and is heavily agricultural, but there 

are important differences between the northern and southern 

portions of the basin, basically upstream and downstream of 

Des Moines, Iowa. The northern part of the basin is located 

within the Des Moines Lobe landform region and was 

glaciated 12,000–15,000 years ago. The topography in this 

region is flat with poorly developed soil drainage networks. 

Wetlands and prairie potholes covered this area before 

European settlement and the development of agriculture 

depended upon building artificial drainages such as ditches 

and tiles. The relatively young soil is erodible resulting in 

significant down cutting along the main stem Des Moines 

River, which causes the channel to be relatively narrow 

with a constricted alluvial plain. The soils in this area also 

are highly productive and cultivated for crops, such as corn 

and soybeans. Downstream of Des Moines, the river flows 

through the Southern Iowa Drift Plain, which is characterized 

by older surface soils and highly developed surface drainage 

networks, including numerous stream channels and steep 

hill slopes (Keeney and DeLuca, 1993). The main channel 

of the Des Moines River runs through a wide alluvial plain. 

Outside of the alluvial plain, older upland soils are not as 

productive as in the northern part of the basin and so are not as 

heavily cultivated (Heusinkveld, 1989). The wide, flat alluvial 

plain in this area also is subject to heavy flooding, which 

was a constant danger to communities located near the Des 

Moines River until the construction of upstream flood-control 

structures (Heusinkveld, 1989).

Many of the oldest communities in southern Iowa are 

located adjacent to the Des Moines River because it was 

a critical means of transportation during settlement of this 

area. However, many of these communities experienced 

periodic and sometimes devastating flooding. In the latter 

half of the 20th century, the Saylorville and Red Rock Dams 

were constructed to help control flooding on the Des Moines 

River. The Red Rock Dam is located downstream of Des 

Moines. Construction began in 1960 and was completed 

in 1969. The Saylorville Dam is upstream of Des Moines. 

Construction began in 1965 and the reservoir was filled by 

1977 (Heusinkveld, 1989). The presence of the Red Rock 

and Saylorville Dams has helped to curtail the floods that 

periodically struck communities adjacent to the river.

Among the river basins considered in this analysis, 

the Des Moines River basin is one of the most intensively 

cultivated and the population density is relatively low. In 

2002, almost 90 percent of the entire basin was in some form 

of agricultural usage and almost 77 percent was in cropland 

(fig. 4). Corn and soybeans are the major crops grown in 

this basin (Keeney and DeLuca, 1993; Benke and Cushing, 

2005) and the annual harvest of corn averaged nearly 15,000 

bushels/km2 of drainage area between 2000 and 2010 (fig. 

6). The average annual nitrogen sources from fertilizer and 

animal livestock between 1997 and 2001 were 8.1 g (N/m2)/yr 

of drainage area, about 75 percent of which was from fertilizer 

application (fig. 5A). Phosphorus sources over the same period 

were nearly 1.6 g (P/m2)/yr and nearly evenly split between 

animal livestock and fertilizer sources (fig. 5B). In the year 

2000 Population Census (U.S. Census Bureau, 2000), human 

population density in this drainage basin was 21 people/km2, 

less than the national average of 31 (fig. 3). The City of Des 

Moines, Iowa, is the only large urban area in the basin.

Data Sources

Data sources for the Des Moines River are summarized 

in table 13. The USGS began stream gaging on the Des 

Moines River in 1903 at the reference stream gaging station 

at Keosauqua (station No. 05490500) and at Ottumwa in 

1917 (station No. 05489500). The earliest water-quality 

samples come from Keosauqua in 1906 and were published 

in the Clarke (1924) national water-quality compilation. 

Water-quality data also were collected at Keosauqua in 1967 

and then resumed in 2004. The Iowa Department of Public 

Health Engineering published water-quality data collected 

along the Des Moines River from 1928 to 1934 and the Iowa 

Department of Natural Resources has data from 16 stations 

for several years between 1935 and 1955. These same stations 

were sampled again from 1968 to 1979. The USGS collected 

water-quality samples regularly at Ottumwa beginning in 

1949, continued through 1968, and then intermittently since 

then. The Des Moines River at St. Francisville, Mo. (station 

No. 05490600) is the station farthest downstream and was 

sampled regularly between 1967 and 1993. Because of the 

shape of the Des Moines River basin, very little additional 

basin area is gained per river mile in the southernmost part of 

the basin (fig. 21). For example, even though Ottumwa, Iowa, 

and St. Francisville, Mo. are relatively far apart in terms of 

river miles, only 7 percent of the river basin is gained when 

moving from Ottumwa downstream to St. Francisville, Mo. 

Therefore, minimal differences in water quality are expected 

between Ottumwa and St. Francisville.
64 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 21. Des Moines River basin.

tac12-0694_fig21-DesMoines

90°W 91°W 92°W 93°W 94°W 95°W 96°W 97°W 98°W

44°N43°N42°N41°N

Des Moines River

Raccoon River

Des Moines River

IOWA

NEBRASKA

MINNESOTA

WISCONSIN

SOUTH DAKOTA

ILLINOIS

MISSOURI

Des Moines

Keosauqua

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

0 50 100 KILOMETERS0 50 100 MILES

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

68

70

69,71,72

68

Keokuk

Southern Iowa Drift Plain

Saylorville dam

Red Rock dam
Specific Basins of Interest 65

Table 13. Des Moines River data sources.

[Monitoring station is shown in figure 21. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

68 NWIS 05489500

Des Moines River at 

Ottumwa, Iowa

41o0′39′′ 92o24'41" Daily streamflow 1917 2008

TN 2008 2008

NH3 1955 2008

TON + NH3 2008 2008

NO3 1949 2008

Alk 1940 2008

TP 2008 2008

TDP 2008 2008

169 NWIS 05490500

Des Moines River at 

Keosauqua, Iowa

40o43′40′′ 91o57'35" Daily streamflow 1903 2008

TN 2004 2008

NH3 1967 2008

TON + NH3 2004 2008

NO3 1906 2008

Alk 1906 2008

TP 2004 2008

TDP 1967 2008

70 NWIS 05490600

Des Moines River at 

St. Francisville, Mo.

40o27′45′′ 91o03'41" TN 1967 1993

NH3 1968 1993

TON + NH3 1967 1993

NO3 1967 1993

Alk 1967 1993

TP 1967 1993

TDP 1968 1993

2,371 STORET 410360

Des Moines River at 

Keosauqua, Iowa

40 ̊43′40′′ 91 ̊57′35′′ TN 1934 21979

NH3 1934 21979

TON + NH3 1934 21979

NO3 1934 21979

Alk 1969 21979

TP 1968 21979

272 Iowa Division of 

Public Health 

Engineering, 1934

Des Moines River at 

Keosauqua, Iowa

40 ̊43′42′′ 91 ̊57′39′′ NH3

NO3

1928

1928

1934

1934

1Reference stream gaging station.

2

Historical station, location approximate.

3

Overall time series length contains many missing years.
66 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Missouri River 

The Missouri River is a major tributary to the 

Mississippi River accounting for approximately 20 percent 

of the Mississippi River total discharge. The Missouri River 

drainage basin covers about 1.37 million km2 (529,000 mi2) 

of the north-central Great Plains and the Eastern Slope of 

the Rocky Mountains (fig. 22). Parts of 10 states, Canada, 

and 7 physiographic provinces are within the Missouri River 

drainage basin (fig. 2). Accordingly, climatic conditions 

vary widely from cold and moist in the Rocky Mountains 

to semiarid in the Great Plains to humid continental in the 

Central Lowlands. Mean annual discharge near the confluence 

with the Mississippi River nearly doubles the mainstem 

streamflow at that point, measured at the reference stream 

gaging station at Hermann Mo. (station No. 06934500) for 

the period 1928–2008 as 80,000 ft3/s. This translates to 

annual runoff for the entire basin as 52 mm/yr and reflects the 

prominence of the dry Great Plains located within the basin. 

Historically, the Missouri River was shallow and 

sediment-laden with frequently shifting channels, riparian 

sloughs, and backwaters (Sprague and others, 2007). 

Historically the river experienced large interannual variation 

in discharge because of the contribution of melting snow in the 

northern Rocky Mountains to overall river flow. Management 

of the Missouri River, including snag removal and bank 

stabilization dates back to the 19th century. However, the 

most intensive management steps began with the initiation 

of the Pick-Sloan Missouri Basin Project in 1944 and the 

Missouri River Bank Stabilization and Navigation Project of 

1945. These projects were officially completed in 1981 with 

a large portion of the activity occurring in the 1950s (U.S. 

Geological Survey, 1998). The projects aimed to provide 

flood and erosion protection to infrastructure, communities, 

and agricultural lands in the Missouri River basin as well as 

a navigable channel along the lower 1,180 km of the river 

from St. Louis, Missouri to Sioux City, Iowa. Additionally, 

reservoirs and dams were constructed throughout the basin for 

flood control and to provide irrigation water. The total storage 

capacity of this network is more than 9 × 1010 m3 (more than 

73 million acre-ft), making it the largest reservoir network 

in North America (Sprague and others, 2007). Engineering 

the Missouri River has dramatically altered the annual 

hydrograph and has greatly reduced the amount of sediment 

delivered to the Mississippi River (Meade and Moody, 2010). 

Bank stabilization projects also greatly curtailed the periodic 

inundation of wetlands and backwaters, which originally 

promoted ecosystem productivity and supported diverse native 

fish and migratory bird populations (U.S. Geological Survey, 

1998). 

Prior to the 1950s, the Missouri River delivered an 

estimated 300 million tons of sediment to the Mississippi 

River, approximately 75 percent of the total sediment load 

carried to coastal Louisiana (Meade and Moody, 2010). 

However, by 1980, the Missouri River carried less than 100 

million tons of sediment and the entire Mississippi River basin 

delivered approximately 150 million tons of sediment to the 

Louisiana coast (Meade and Moody, 2010).

Population density throughout the entire basin was very 

low according to the 2000 census (U.S. Census Bureau, 2000), 

8.7 people/km2 (fig. 3), but several large metropolitan areas 

are within the basin including Denver, Colo., Omaha, Nebr., 

Kansas City and St. Louis, Mo. In 2002, almost 80 percent 

of the basin was farmland and this was split nearly evenly 

between cropland and other uses (fig. 4). Agricultural land 

development occurred late in this basin with less than 40 

percent of the basin in farmland usage in 1900, increasing 

to 70 percent by 1940 (fig. 17C). The most highly cultivated 

land occurs adjacent to the main river channel or in the eastern 

parts of the drainage basin in eastern Kansas, eastern South 

Dakota, western Iowa, and western Missouri. Average nitrogen 

sources from fertilizer and animal livestock were moderate 

compared with other basins in this study, 2.8 g (N/m2)/yr on 

average from 1997 to 2001 (fig. 5A). Phosphorus sources were 

moderate as well over the same period, 0.5 g (P/m2)/yr with 

slightly more phosphorus arising from animal livestock than 

fertilizer (fig. 5B). 

Data Sources

Data sources for the Missouri River are summarized in 

table 14. The USGS maintains reference stream gaging and 

water-quality station on the Missouri River at river mile 97.9 

near Hermann, Mo. (station No. 06934500, table 14). Nutrient 

concentration samples have been collected from this site 

regularly since 1967 and daily streamflow has been collected 

since 1928 (table 14). This station also was included in the 

Clarke (1924) publication with nitrate and alkalinity values 

reported in 1906–07. Monthly average NO3 and alkalinity 

concentration data also are available from 1930 to 2008 at 

the Howard Bend Drinking Water Intake Facility located at 

river mile 37 near Chesterfield, Mo. (table 14). Because these 

sites are close along the main stem of the Missouri River and 

because the drainage area at both sites is nearly identical, 1.35 

versus 1.37 million km2 at the Hermann and Howard Bend 

sites, respectively, these sites can be considered equivalent in 

an assessment of water quality on the Missouri River.
Specific Basins of Interest 67 Figure 22. Missouri River basin. tac12-0694_fig22-Missouri

90°W 95°W 100°W 105°W 110°W 115°W

45°N40°N

Yellows ot ne River

Platte River

Yellows ot ne R vi er

Missouri R.

North Platte R.

Missouri River

Ja

mes R

.

Mississippi River

Omaha

Denver

Lincoln

Cheyenne

Billings

St. Joseph

Sioux City

Rapid City

Kansas 

City

Sioux Falls

Great Falls

UTAH

MONTANA

IDAHO

KANSAS

IOWA

WYOMING

COLORADO

NEVADA

NEBRASKA

MINNESOTA

MISSOURI

SOUTH DAKOTA WISCONSIN

NORTH DAKOTA

ILLINOIS

ARIZONA

OKLAHOMA

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

00 100 200 KILOMETERS

100 200 MILES

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

73

75

73 74

Great Plains

Rocky Mountains

Central Lowlands

St. Louis

Chesterfield
68 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Table 14. Missouri River basin data sources.

[Monitoring station is shown in figure 22. Source: NWIS, National Water Information System. Constituent: Alk, alkalinity. See table 2 for definitions of all 

other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

173 NWIS 06934500

Missouri River at 

Hermann, Mo.

38o42′35′′ 91o26′19′′ Daily streamflow 1928 2010

TN 1967 2008

NH3 1970 2008

TON + NH3 1967 2008

NO3 1967 2008

Alk 1967 2008

TP 1967 2008

TDP 1969 2008

274 Clarke, 1924 06934500

Missouri River at St. 

Charles (Ruegg), Mo.

38 ̊47′48′′ 90 ̊27′57′′ NO3 1906 1907

Alk 1906 1907

75 City of St. Louis 

Water Division

(written 

commun., 

Microsoft®

Excel file)

Missouri River at 

Howard Bend Intake, 

Chesterfield, Mo.

38o40′51′′ 90o32′40′′ NO3 1930 2008

Alk 1930 2008

1

Reference stream gaging station.

2

Historical station, location approximate.
Specific Basins of Interest 69

Arkansas River

The Arkansas River flows primarily east-southeasterly 

through the south-central plains of the United States and 

is a major tributary of the Mississippi River (fig. 23). The 

Arkansas River drainage basin covers more than 154,400 mi2

(400,000 km2) and includes parts of six physiographic 

provinces and seven States (fig. 2). At the reference stream 

gaging station at Little Rock, Ark. (station No. 07263500), 

which is near the confluence with the Mississippi River, 

mean annual discharge (1928–1970) is more than 1,100 m3/s 

(38,800 ft3/s) and runoff for the entire basin is 87 mm/yr. 

Major tributaries include the Neosho, Verdigris, Cimarron, 

and Canadian Rivers. The headwaters of the Arkansas River 

are located in the southern Rocky Mountains near Leadville, 

Colo., at approximately 3,000 m (10,000 ft) above sea level. 

The climate at the headwaters is cold and wet, and annual 

runoff can reach 90 mm/yr as it emerges from the mountains 

near Pueblo, Colo. However, evaporation and extensive 

withdrawals for irrigation reduce the overall flow such that 

runoff out of the John Martin Reservoir in southeastern 

Colorado averages only 5 mm/yr and the river becomes 

ephemeral in western Kansas upstream of Great Bend, Kans. 

(Benke and Cushing, 2005). At Great Bend, the Pawnee River 

joins the Arkansas River and increases overall flow. The river 

gains water through central Kansas and Oklahoma, and after 

the Cimarron River joins the Arkansas River upstream of 

Tulsa, Okla., mean annual discharge (USGS station 07164500, 

1965–2011) is just under 250 m3/s. Runoff for the entire basin 

is low because part of the basin is located in arid parts of 

eastern Colorado, western Kansas, and northern Oklahoma. 

At the gaging station near Little Rock, approximately 15 

percent of the basin (57 km2 or 22,000 mi2) is probably 

non-contributing. 

The lower portion of the river has been extensively 

modified by the locks, dams, and canals making up the 

McClellan-Kerr Arkansas River Navigation System, 

which allows commercial traffic on the river and provides 

recreational opportunities through the creation of reservoirs 

(Benke and Cushing, 2005). The navigation system begins at 

the confluence of the White River and the Mississippi River 

and then joins the Arkansas River near Gillett, Ark., by means 

of the man-made Arkansas Post Canal. Fourteen lock and dam 

structures are located along the main stem of the Arkansas 

River and an additional three extend the system approximately 

72 km (45 mi) upstream on the Verdigris River to the Port of 

Catoosa, Okla. (near Tulsa, Okla.). In all, the system covers 

more than 400 river miles. Construction began on this project 

in 1963 and continued into 1970.

Agriculture is a major land use in the river basin with 

grazing and rangeland uses dominating in arid parts of the 

western basin; row-cropping becomes more common and 

more intense in the eastern parts of the drainage basin. In the 

1930s, tremendous damage was done to agricultural lands in 

the basin from the Dust Bowl, including severe wind erosion 

in eastern Colorado and Kansas as well as moderate to severe 

sheet and gully erosion in Oklahoma (Hansen and Libecap, 

2004). In 2002, even though total farmland was very high in 

the Arkansas River basin (fig. 4), the intensity of fertilizer 

use in the basin during a comparable time period was low 

(figs. 5A–5B) because of the predominance of rangeland and 

dryland wheat agriculture in the western and central parts of 

the basin. In the year 2000, population density in the river 

basin was 15 people/km2, about one-half the national average 

of 31 people/km2 (fig. 3).

Data Sources

Data sources for the Arkansas River are summarized in 

table 15. Long-term data are available around Little Rock, 

Ark. Daily streamflow data were collected since 1927 at 

Little Rock (station No. 07263500). After construction of 

the Murray Dam in 1969 as part of the McClellan-Kerr 

Arkansas River Navigation System, the gaging station was 

moved approximately 7 river miles upstream to the outlet 

of the Murray Dam (considered the reference stream gaging 

station), renumbered as USGS station No. 07263450, and 

daily streamflow continued to be collected. Therefore, a good 

daily streamflow record exists for this river reach dating back 

to 1927 (table 15). The earliest water-quality samples from 

this river reach were collected in 1906 and included in the 

Clarke (1924) compilation of water-quality data collected 

across the country (table 15). Water-quality sampling by the 

USGS resumed in 1945 and was collected routinely until 1969 

at the Little Rock gaging station (07263500). Beginning in 

1969 and continuing through 2009, water-quality data have 

been collected several river miles downstream at the outlet of 

the David D. Terry Lock and Dam (07263620). Water-quality 

data also have been collected from the outlet of Murray Dam. 

Two sewer outfalls are located in this river reach, which 

could influence interpretation of water-quality data. The first 

is upstream of the USGS gaging station at Little Rock and 

the second is between the Little Rock and David D. Terry 

gaging stations. The presence of these point sources must be 

considered when interpreting trends in water quality. Some 

water-quality data also have been collected around Little 

Rock, Ark., by the EPA and the Arkansas Pollution Control 

and Ecology Commission and published in the EPA STORET 

database (table 15). 
70 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 23. Arkansas River basin.

12-0694_fig23-Arkansas

90°W 91°W 92°W 93°W 94°W 95°W 96°W 97°W 98°W 99°W 100°W 101°W 102°W 103°W 104°W 105°W 106°W 107°W

40°N39°N38°N37°N36°N35°N34°N33°N32°N

Canadian

River

Arkansas River

reV vi Rsir gi d

re

Cimarron

River

Canadian

River

Ne so

vi R oh er

vi Ri ppississi M

re

White River Tulsa

Pueblo

Wichita

Fort Smith

OklahomaCity

Colorado Springs

Little  Rock

TEXAS

KANSAS

COLORADO

OKLAHOMA

MISSOURI

NEW MEXICO

ARKANSAS

NEBRASKA

LOUISIANA

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

0 50 100 MILES0 50 100 KILOMETERS

77

80

81

78

76

77,79

Rocky Mountains

Leadville

John Martin Reservoir Great Bend

Pawnee River

Gillett

Arkansas Post Canal

Catoosa

Rocky Mountains

Leadville

John Martin Reservoir Great Bend

Pawnee River

Gillett

Arkansas Post Canal location

Catoosa
Specific Basins of Interest 71

Table 15. Arkansas River basin data sources.

[Monitoring station is shown in figure 23. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

76 NWIS 07263450

Arkansas River at 

Murray Dam, near 

Little Rock, Ark.

34o47′27′′ 92o21′33′′ Daily streamflow 1970 2010

TN 1977 1994

NH3 1977 1994

TON + NH3 1977 1994

NO3 1975 1994

Alk 1975 1980

TP 1975 1994

177 NWIS 07263500

Arkansas River at 

Little Rock, Ark.

34o44′59′′ 92o16′09′′ Daily streamflow 1927 1970

TN 1968 1969

TON + NH3 1967 1969

NO3 1945 1969

Alk 1945 1969

TP 1965 1969

TDP 1964 1969

78 NWIS 07263620

Arkansas River at 

David D. Terry Lock and 

Dam below Little Rock, 

Ark.

34o40′52′′ 92o09′05′′ TN 1969 2009

NH3 1970 2009

TON + NH3 1969 2009

NO3 1969 2009

Alk 1969 2009

TP 1969 2009

TDP 1977 2009

279 Clarke, 1924 Arkansas River near Little 

Rock, Ark.

34o44′59′′ 92o16′09′′ NO3 1906 1907

Alk 1906 1907

80 STORET 040131 Arkansas River at 

Little Rock, Ark.

34o46′17′′ 92o17′49′′ TN 1964 1968

TON + NH3 1964 1968

NO3 1964 1968

Alk 1963 1969

TP 1964 1969

81 STORET 050056 Arkansas River at 

David D. Terry Lock and 

Dam

34o40′07′′ 92o09′18′′ TN 1986 1998

NH3 1986 1998

TON + NH3 1986 1998

NO3 1986 1998

TP 1986 1998

1

Reference stream gaging station.

2

Historical station, location approximate.
72 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Brazos River

The Brazos River is a relatively low-gradient stream 

for most of its length, extending across central Texas from 

southeastern New Mexico to the Gulf of Mexico (fig. 24). The 

basin is the second largest in Texas, more than 116,800 km2

(45,100 mi2) at the reference stream gaging at Richmond, 

Tex. (station No. 08114000). Numerous intermittent and 

relatively saline streams exist in the upper basin and much of 

this area, approximately 25,000 km2 (9,500 mi2), probably 

is non-contributing to downstream flow in the main stem 

Brazos River (Vogl and Lopes, 2009). The Brazos River flows 

through the Great Plains, Central Lowlands, and Coastal Plain 

physiographic provinces, which are largely characterized 

by grasslands and prairies (Benke and Cushing, 2005). 

Precipitation in the basin ranges from about 41 cm (16 in/ yr) 

in the upper basin to more than 127 cm (50 in.) near the river 

mouth (Wurbs and others, 1993). Mean annual discharge 

at the reference stream gaging station at Richmond (station 

No. 08114000) for the period 1903–2010 is approximately 

210 m3/s (7,500 ft3/s), which coincides with mean annual 

runoff of 56 mm/yr from the entire drainage area. Runoff 

is approximately 5 percent of precipitation in this basin, 

emphasizing the magnitude of evapotranspiration (Benke and 

Cushing, 2005). Recurring drought conditions and population 

growth have been identified as the most important issues for 

water management in the basin, resulting in the development 

of a large network of reservoirs located primarily in the middle 

and upper basin (Vogel and Lopes, 2009).

Rangeland accounted for 42 percent of land cover in 

2002 (data not shown), and the primary land-use activities 

included grazing, cropland, and urban development (fig. 24). 

The oil and gas industries also are important components of 

the economy, especially in the upper regions of the basin (Vogl 

and Lopes, 2009). Agricultural production includes cattle, 

cotton, grain sorghum, wheat, peanuts, dairy products, and 

rice (Benke and Cushing, 2005). Forest, pasture, and cropland 

predominate in the upper basin while grassland and row 

crops are important farther downstream, sometimes abutting 

directly on the river’s edge with no riparian buffer (Zeng and 

others, 2011). Nitrogen fertilizer application rates and animal 

livestock sources of nitrogen both averaged approximately 2 g 

(N/m2)/yr for 1997–2001 (fig. 5A). However, animal livestock 

sources of phosphorus were approximately double that of 

fertilizer sources over the same period (fig. 5B).

Population density in the Brazos River basin was about 

18 people/km2, based on the 2000 census (fig. 3). Several 

large cities (population greater than 100,000) are located in 

the basin (Lubbock, Abilene, and Waco). Urban sprawl in 

the Houston area also is an important influence near the river 

mouth, although the center of Houston is located outside 

the basin. Water use has been dominated by agriculture for 

most of the century, especially in the middle basin, although 

population growth since 1970 has been associated with 

increasing water use for industrial and domestic use (Vogl and 

Lopes, 2009). 

Data Sources

Data sources for the Brazos River are summarized 

in table 16. Daily streamflow data are available from the 

reference stream gaging station at Richmond, Tex. (station No. 

08114000), beginning in 1903. Water-quality data from 3- to 

10-day composite samples are available from selected USGS 

Water Supply Papers for 1946–58 (Paulsen, 1950; Paulsen, 

1952a; Paulsen, 1952b; Paulsen, 1953; U.S. Geological 

Survey, 1955; Love, 1956; U.S. Geological Survey, 1958; 

Love, 1959a; Love, 1959b; Love, 1960; Love, 1961; Love, 

1963). Water-quality data from point samples are available 

from NWIS beginning in 1959.
Specific Basins of Interest 73 Figure 24. Brazos River basin. 12-0694_fig24-Brazos

94°W 95°W 96°W 97°W 98°W 99°W 100°W 101°W 102°W 103°W 104°W

34°N33°N32°N31°N30°N29°N

TEXAS

OKLAHOMA

NEW MEXICO

Waco

Bryan

Killeen

Lubbock

Richmond

White River

Leon River

White River

Brazos River

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

00 50 100 KILOMETERS

50 100 MILES

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

82

84 83 82

GULF OF MEXICO

Abilene

Houston

Amarillo
74 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Table 16. Brazos River basin data sources.

[Monitoring station is shown in figure 24. Source: NWIS, National Water Information System. Constituent: Alk, alkalinity. See table 2 for definitions of all 

other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

182 NWIS 08114000

Brazos River at Richmond, Tex.

29o34′56′′ 95o45′27′′ Daily streamflow 1903 2010

TN 1971 1995

NH3 1970 2002

TON + NH3 1970 1995

NO3 1959 2002

Alk 1959 2002

TP 1969 1995

TDP 1980 2002

283 (3) 08114000

Brazos River at Richmond, Tex.

29o34′56′′ 95o45′27′′ NO3 1946 1958

Alk 1946 1958

84 NWIS 08116650

Brazos River at Rosharon, Tex.

29o20′58′′ 95o34′56′′ Daily streamflow 2006 2010

TN 1970 2008

NH3 1970 2008

TON + NH3 1970 2008

NO3 1968 2008

Alk 1968 2008

TP 1969 2008

TDP 1977 2008

1

Reference stream gaging station.

2

Historical station, location approximate.

3

Paulsen, 1950, 1952a, 1952b, 1953a, 1953b, 1953c; U.S. Geological Survey, 1955, 1958; Love, 1959a, 1959b,1960, 1961, 1963.
Specific Basins of Interest 75

Upper Mississippi River

The upper Mississippi River is defined as the part of 

the Mississippi River upstream of the confluence with the 

Missouri River near St. Louis, Mo. (fig. 25). The main stem 

Mississippi River begins at the outlet of Lake Itasca, Minn., 

and flows approximately 2,000 km to the confluence with the 

Missouri River in St. Louis, Mo. At Alton, Ill., just upstream 

of the confluence of the Mississippi and Missouri Rivers, the 

basin area is 0.44 million km2 (170,000 mi2) and incorporates 

parts of the States of Minnesota, Wisconsin, Iowa, Illinois, 

and Indiana. Long-term mean annual discharge (1933–1987) 

at the reference stream gaging station 24 km upstream from 

this site (station No. 05587450) is approximately 3,100 m3/s 

(110,000 ft3/s) and runoff is 220 mm/yr.

Most of the basin is located within the Central Lowlands 

physiographic province, and land use in this basin is 

characterized by the presence of several large population 

centers mixed with extensive cultivated agricultural areas 

(Benke and Cushing, 2005). Large population centers in 

the upper Mississippi River basin include Chicago, Ill., 

Minneapolis-St. Paul, Minn., Des Moines, Iowa, and the 

Quad Cities Metro Area (Bettendorf and Davenport, Ia., 

and Moline and Rock Island, Ill.) in Iowa and Illinois. 

Nevertheless, population density throughout the entire 

basin was only 48 people/km2 in 2000, or about 50 percent 

greater than the national average (fig. 3). This indicates that 

outside of the major metropolitan areas, population densities 

were low. Several of the most highly agricultural drainage 

basins included in this study, the Des Moines River and the 

Illinois River (figs. 20 and 21), are located within the upper 

Mississippi River basin. Accordingly, nearly 70 percent of 

the total area in the upper Mississippi River basin was used 

for agriculture by the end of the 20th century and the primary 

use of this land was cropland (fig. 4). Fertilizer and animal 

livestock sources of nitrogen and phosphorus are relatively 

high in this basin and reflect the influence of the highly 

agricultural regions of the basin (figs. 5A–5B). Fertilizer inputs 

of N and P averaged 4.4 and 0.7 (g/m2)/yr during the period 

1997–2001, respectively (fig. 5A). Animal livestock sources of 

N and P averaged 1.5 and 0.5 (g/m2)/yr, respectively (fig. 5B). 

Corn harvested in this drainage basin averaged over 10,000 

bushels/km2 during the period 2000–2010 and indicates fairly 

intense agricultural production throughout the entire basin 

(fig. 6). 

There also has been extensive hydrologic modification 

along the main stem of the upper Mississippi River. The 1930 

Flood Control Act mandated that the U.S. Army Corps of 

Engineers build and maintain a 9-ft navigational channel from 

St. Louis, Ill., to Minneapolis, Minn. This was accomplished 

primarily through the construction of a series of low-head 

navigational dams that alter the low-flow conditions, decrease 

contact between main channel and backwater habitats, and 

increase sedimentation rates behind the dams (Benke and 

Cushing, 2005).

Data Sources

Data sources for the main stem Upper Mississippi 

River are summarized in table 17. U.S. Geological Survey 

streamflow data are available from the reference stream gaging 

station at Grafton Ill., beginning in 1933. Water-quality data 

are available primarily from the Illinois State Water Survey 

and the U.S. Geological Survey. The Illinois State Water 

Survey began collecting data on rivers bordering or contained 

within Illinois beginning in 1895 and published these results 

regularly through 1908. Several sites included in this survey 

are on the upper Mississippi River including Alton, Ill., and 

Golden Eagle, Mo. Data from this survey are particularly 

notable because they include total nitrogen measurements, 

which are the most useful way to consider changes in nitrogen 

concentrations. The Illinois State Water Survey also collected 

water-quality data at several sites in the upper and middle 

Mississippi River from 1950 to 1975. U.S. Geological Survey 

data collection resumed in 1975 and between Grafton and 

Alton, Ill., water-quality data are available through 2009.

Middle Mississippi River

The middle Mississippi River is defined as the part of the 

river downstream of the confluence with the Missouri River 

and upstream of the confluence with the Ohio River (fig. 25). 

Although this stretch of river is only 300 km, it is important 

to consider separately because it integrates the influence 

of the upper Mississippi River with the Missouri River. 

Hydrologic differences between Alton and Thebes, Ill., reflect 

the influence of the Missouri River on the middle Mississippi 

River. For example, the total drainage area at the reference 

stream gaging station at Thebes, Ill. (station No. 07022000), 

is 1.85 million km2 (714,000 mi2), mean annual discharge 

(1933–2008) is 5,900 m3/s (209,000 ft3/s), and runoff is 

101 mm/yr. The Missouri River also is a major source of 

suspended sediments to the middle Mississippi River. More 

information about the Missouri River are provided in the 

Missouri River section.
76 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 25. Mississippi River basin.

tac12-0694_fig25-Mississippi

95°W 80°W 85°W 90°W 100°W 105°W 110°W 115°W 120°W

45°N40°N35°N30°N

nagi hci MekaL

Lake Huron

Lake Erie

Lake Ontari o

Lake Superior

Gulf of

Mexico 106

103,104,

107,108

102

101

100

99

98

87

85

83

82

75 74 73

72

84

106

111

103,104,

107,108

102

101

100

99

98

87

85

83

82

75 74 73

72

84

nagi hci MekaL

Lake Huron

Lake Erie

Lake Ontari o

Lake Superior

Gulf of

Mexico

Platte River

Missouri River

Mississippi River

Missouri River

Tennessee R.

Arkansas River

h O

oi

River

White R.

ssi M is

revi R i ppis

Tulsa

Omaha

Denver

Memphis

Columbus

Chicago

St. Paul

Knoxville

St. Louis

Louisville

Cincinnati Kansas City

Sioux Falls

Minneapolis

Indianapolis

Des Moines

Wichita

Madison

Belle 

Chase

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

0

0 250 500 KILOMETERS

250 500 MILES

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

87

85,86,95

112

111

109,110,

113,114

108

107

106

105

104

100,101

98,99,103

102

97

92

91

90

88

87

96

85,86,95

94 93

89

Des Moines River

Quad CitiesMetro Area

Meramac River

Illinois River

Yazoo River

Lake Itasca

Quad CitiesMetro Area

Des Moines River

Illinois River

Meramac River

Red River

Yazoo River

Atchafalaya River

Old River Control Structure
Specific Basins of Interest 77

Human alteration of the middle Mississippi River channel 

dates back almost 200 years. After the passage of the Rivers 

and Harbors Act of 1824, the U.S. Army Corps of Engineers 

began to maintain a navigable 8-ft channel on the main stem 

Mississippi River to St. Louis. At first, this was achieved 

primarily through revetment and wing-dam construction but 

dredging became more prominent by the early 20th century. 

Levee construction to protect communities and farmland 

adjacent to the river also has been intense along this stretch 

of the river. Flood protection became a central focus after a 

large flood in 1903; most of the levee construction around St. 

Louis was completed by 1908 (Criss and Wilson, 2003). Since 

1945, additional engineering has occurred in this region as 

flood-control levees were heightened and the entire main stem 

channel was restricted to 1,500 ft width (Criss and Wilson, 

2003). Additionally, the Pick-Sloan Flood Control Act of 1944 

authorized the construction of dozens of dams and reservoirs 

in the Missouri River basin, fundamentally altering streamflow 

in the Missouri River and dramatically reducing sediment 

loading to the middle Mississippi (Meade and Moody, 2010).

The middle Mississippi River also is distinguished from 

the upper Mississippi because of the proximity to St. Louis. 

To a large degree, the proximity to the Mississippi River has 

enabled St. Louis to remain a pivotal commercial center, so 

there has always been a close connection between the city 

and the river. St. Louis grew rapidly in the 19th century and 

by 1900 St. Louis was the fourth largest city in the country 

with a population approaching 600,000 (Criss and Wilson, 

2003). Currently, almost 3 million people live in the 16 county 

metropolitan area making it the 18th largest in the United 

States (Criss and Wilson, 2003). St. Louis grew quickly before 

the advent of drinking water treatment or sewerage systems. 

The city has always drawn its drinking water from easily 

contaminated surface waters including the Missouri, Meramec, 

and Mississippi Rivers. Several early epidemics of waterborne 

illness resulted including a cholera outbreak in 1849, which 

claimed 5,000 lives (Criss and Wilson, 2003). Outbreaks of 

typhoid fever continued and in 1900 the city of St. Louis filed 

suit against the city of Chicago for discharging untreated 

sewage into the Illinois River, which resulted in degraded 

water quality in the Mississippi River downstream of the 

confluence with the Illinois River (Leighton, 1907). St. Louis 

slowly developed a sewer system, beginning in 1916; by 1956, 

only 5 percent of the population had wastewater treatment 

service (Criss and Wilson, 2003). In 1933, the city applied for 

a permit from the U.S. Army Corps of Engineers to dispose 

of solid waste garbage in the Mississippi River. Although 

the Bureau of Fisheries opposed the idea on the grounds 

that it would be detrimental to fish populations, the permit 

was issued in 1937 allowing the disposal of several hundred 

tons of solid waste garbage daily into the Mississippi River 

(Ellis, 1943; Scarpino, 1985). Concerns about water quality 

grew throughout the middle 20th century and such practices 

became less common. By 1965, 95 percent of the St. Louis 

metropolitan area residents had wastewater treatment service 

and by 1972, the city became known as a leader in solutions to 

water-quality problems (Criss and Wilson, 2003).

Land use and population characteristics of the middle 

Mississippi River reflect the influence of its two primary 

tributaries – the upper Mississippi River and the Missouri 

River. Population density was 19 people/km2 according to the 

2000 U.S. Census (fig. 3). Almost 77 percent of the total basin 

area is in some agricultural use, with 40 percent in cropland 

(fig. 4). Other indicators of agricultural intensity were 

moderately high in this basin and reflect the joint influence 

of the intensively cultivated upper Mississippi River basin 

and Missouri River basin, which has less overall percentage 

of cropland area (fig. 4). Nitrogen from fertilizer and animal 

livestock sources averaged 3.5 g (N/m2)/yr from 1997 to 

2001 (fig. 5A). Phosphorus sources were approximately 

0.7 g (P/ m2)/ yr (fig. 5B). Corn harvest rates also were 

moderate at 4,100 bushels/km2 of drainage area (fig. 6).

Data Sources

Data sources for the main stem Mississippi River are 

summarized in table 17. For the middle Mississippi River, 

intermittent streamflow data are available beginning in 1861 

at St. Louis, Mo., with daily data available after 1928; daily 

streamflow data also are available beginning in 1933 at the 

reference stream gaging station at Thebes, Ill. (prior to 1941, 

published as “at Cape Girardeau, Mo.), and beginning in 1942 

at Chester, Ill. (table 17). The Mississippi River at Chester, 

Ill., also was included in the Clarke (1924) compilation and 

sampled in 1906–07. Several sites on the middle Mississippi 

River were included as part of the Illinois State Water Survey 

water-quality sampling, including Thebes (1950–56), Chester, 

Ill. (1955–76), and East St. Louis, Ill. (1958–76). Regular 

water-quality sampling by the U.S. Geological Survey began 

in 1973 at Thebes, Ill.

Lower Mississippi River

The lower Mississippi River is defined as the 

approximately 1,500 km-long part of the river downstream 

of the confluence with the Ohio River at Cairo, Ill. (fig. 25). 

The Ohio River discharges 7,900 m3/s (278,000 ft3/s) annually 

(reference stream gaging station for lower Ohio, period 

1928–2008) and approximately doubles the streamflow of 

the Mississippi River. Measured near Arkansas City, Ark., 

(USGS station 07265450; years 1928–1980) the mean 

annual discharge of the Mississippi River is 15,300 m3/s 
78 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

(540,000 ft3/s), the drainage area is 2.9 million km2

(1.1 million mi2), and mean annual runoff is 170 mm/yr. Other 

significant tributaries to the lower Mississippi River include 

the White, Arkansas, Red, and Yazoo Rivers, which deliver 

another 5,700 m3/s (200,000 ft3/s) to the main stem river. The 

Atchafalaya River is the main distributary of the Mississippi 

River, which diverges from the main channel at river mile 

315. Since 1963, the U.S. Army Corps of Engineers has 

regulated the amount of water flowing into the Atchafalaya 

River through the Old River Control Structure in Louisiana. 

The purpose of this structure is to ensure that no more than 

30 percent of the total flow of the Mississippi River enters the 

Atchafalaya (Benke and Cushing, 2005).

The lower Mississippi River channel is located entirely 

within the deep alluvial deposits of the Coastal Plain 

physiographic province (fig. 2). The largest tributaries, 

the Ohio, Arkansas, and Red Rivers, encompass many 

physiographic provinces and land uses, and others originate 

in the Ozark and Ouachita Plateaus (further details about the 

Ohio and Arkansas Rivers are provided in respective sections 

in this report). 

Most of the entire length of the lower Mississippi River 

channel is surrounded by levees. The floodplain inside the 

levees is less than 10 percent of the total natural floodplain 

area for this part of the river (Benke and Cushing, 2005). The 

river channel itself has been extensively modified for flood 

control including armoring shorelines, artificially installing 

channel cutoffs, and building revetments to prevent channel 

meandering. Therefore, the ecological integrity of this riverfloodplain ecosystem has been highly challenged.

Because the Mississippi River basin includes a large 

portion of the continental United States, data to describe 

population, land use, and agricultural activity encompass 

many of the river basins included in this study. According to 

the year 2000 census, population density was 25 people/km2

in the river basin considered as a whole, which was slightly 

less than the national average of 31 people/km2 (fig. 3). Just 

more than 70 percent of the basin was agricultural land with 

38 percent of the basin in cropland (fig. 4). Nitrogen from 

fertilizer and animal livestock averaged 3.5 g (N/m2)/yr 

from 1997 to 2001 with fertilizer sources being about twice 

as large as animal livestock sources (fig. 5A). This amount 

was virtually unchanged for several decades at the end of 

the 20th century (fig. 18E). Phosphorus from these sources 

totaled 0.6 g (P/m2)/yr and was split almost evenly between 

fertilizer and animal livestock (fig. 5B). Corn harvest averaged 

approximately 3,300 bushels/km2 of drainage area (fig. 6). 

Data Sources

Data sources for the main stem Mississippi River are 

summarized in table 17. Daily streamflow data are available 

for the reference stream gaging station at Tarbert’s Landing, 

Miss. beginning in 1930 (table 17). The earliest water-quality 

data were collected by the Sewerage and Water Board of New 

Orleans, La. in 1900–1901. The Mississippi River also was 

sampled at New Orleans in 1906–07 and included as part of 

the Clarke (1924) compilation. U.S. Geological Survey waterquality sampling began in the 1950s at St. Francisville, Luling, 

and New Orleans, La. The most current water-quality data, 

beginning in the 1970s, are available at Belle Chasse, Baton 

Rouge, and St. Francisville, La. 

All water-quality and streamflow data for the lower 

Mississippi River reach are located downstream of the 

Atchafalaya River diversion and so only reflect water 

quality and water discharge in that part of the stream, which 

represents about 70 percent of the original water volume. 

Therefore, analysis of these data should not be interpreted as 

equivalent to estimates developed for the entire MississippiAtchafalaya River basin. Furthermore, many different 

water-quality and stream-gaging stations are included in our 

summary of available data. The distance between some of 

these stations is quite large. However, it is presumed that the 

overall scale of the Mississippi River basin and the magnitude 

of water carried by the main stream channel causes local 

influences to be minimal and water-quality data between the 

stations should be comparable.
Specific Basins of Interest 79

Table 17. Mississippi River basin data sources.

[Monitoring station is shown in figure 25. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse; USACE, 

U.S. Army Corps of Engineers. Constituent: Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

Upper Mississippi River

185 Long, 1889 Mississippi River at Alton, Ill. 38o53′06′′ 90o10′51′′ NO3 1888 1888

NH3 1888 1889

186 Palmer, 1897, 

1903; Bartow, 

1907

Mississippi River at Alton, Ill. 38o52′55′′ 90o10′44′′ TN 1896 1900

NH3 1896 1906

TON + NH3 1896 1900

NO3 1896 1906

Alk 1904 1906

187 Bartow, 1907, 

1909

Mississippi River at 

Rock Island, Ill.

41o31′08′′ 90o34′01′′ NH3 1896 1908

NO3 1896 1908

Alk 1896 1908

188 Palmer, 1897, 

1903; Bartow, 

1907, 1909

Mississippi River at 

Qunicy, Ill.

39o56′30′′ 91o25′51′′ TN 1895 1900

NH3 1895 1906

TON + NH3 1895 1900

NO3 1905 1908

Alk 1905 1908

189 Bartow, 1907, 

1909

Mississippi River at 

Moline, Ill.

41o30′38′′ 90o31′06′′ NH3 1905 1907

NO3 1905 1907

Alk 1905 1907

190 Larson and 

Larson, 1957

Mississippi River at Keokuk, 

Iowa

40o23′27′′ 91o22′23′′ NH3 1950 1955

NO3 1950 1955

Alk 1950 1955

191 Palmer, 1897 Mississippi River at Golden 

Eagle, Mo.

38o52′18′′ 90o33′59′′ TN 1896 1896

NH3 1896 1896

TON + NH3 1896 1896

192 Wiebe, 1931 Mississippi River at Fairport, 

Iowa

41o26′07′′ 90o54′06′ NH3 1929 1930

NO3 1929 1930

TDP 1929 1930

293 NWIS 05587450

Mississippi River at Grafton, Ill.

38o58′05′′ 90o25′04′′ Daily streamflow 1933 2008

94 NWIS 05587455

Mississippi River below 

Grafton, Ill.

38o57′04′′ 90o22′16′′ TN 1989 2009

NH3 1989 2009

TON + NH3 1989 2009

NO3 1989 2009

Alk 1989 2009

TP 1989 2009

TDP 1989 2009

95 NWIS 05587500

Mississippi River at Alton, Ill.

38o53′06′′ 90o10′51′′ Daily streamflow 1933 1987

96 NWIS 05587550

Mississippi River below Alton, 

Ill.

38o51′41′′ 90o08′15′′ TN 1975 1989

NH3 1975 1989

TON + NH3 1975 1989

NO3 1975 1989

Alk 1974 1989

TP 1975 1989

TDP 1975 1989
80 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Table 17. Mississippi River basin data sources.—Continued

[Monitoring station is shown in figure 25. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse; USACE, 

U.S. Army Corps of Engineers. Constituent: Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

Middle Mississippi RIver

97 NWIS 07010000

Mississippi River at 

St Louis, Mo.

38o37′44′′ 90o10′47′′ Daily streamflow 1861 2008

198 Long, 1889 Mississippi River at Chester, Ill. 37o54′14′′ 89o50′08′′ NO3 1888 1888

NH3 1888 1888

199 NWIS; Clarke, 

1924

07020500

Mississippi River near 

Chester, Ill.

37o54′14′′ 89o50′08′′ Daily streamflow 1942 2008

NO3 1906 1907

Alk 1906 1907

2100 NWIS 07022000

Mississippi River at 

Thebes, Ill.

37o12′59′′ 89o28′03′′ Daily streamflow 1933 2008

TN 1973 2008

NH3 1973 2008

TON + NH3 1973 2008

NO3 1973 2008

Alk 1973 2008

TP 1973 2008

TDP 1973 2008

101 Larson and 

Larson, 1957

Mississippi River at 

Thebes, Ill.

37o12′59′′ 89o28′03′′ NH3 1950 1956

NO3 1950 1956

Alk 1950 1956

102 Harmeson and 

Larson, 1969; 

Harmeson and 

others, 1973

Mississippi River at East St. 

Louis, Ill.

38o46′33′′ 90o09′35′′ NH3 1958 1976

NO3 1958 1976

Alk 1958 1976

TDP 1960 1976

103 Larson and 

Larson, 1957; 

Harmeson and 

Larson, 1969; 

Harmeson and 

others, 1973

Mississippi River at 

Chester, Ill.

37o54′14′′ 89o50′08′′ NH3 1955 1976

NO3 1955 1976

Alk 1955 1976

TDP 1960 1976

Lower Mississippi RIver

2104 USACE 01100

Mississippi River at Tarbert’s 

Landing, Miss.

31o00′30′′ 91o37′25′′ Daily streamflow 1930 2009

105 NWIS 07289000

Mississippi River at 

Vicksburg, Miss.

32o18′54′′ 90o54′21′′ Daily streamflow 2008 2009

TN 1973 1999

NH3 1975 1999

TON + NH3 1973 1999

NO3 1961 1999

Alk 1961 1999

TP 1973 1999

TDP 1973 1999

106 NWIS 07374000

Mississippi River at 

Baton Rouge, La.

30o26′44′′ 91o11′30′′ Daily streamflow 2004 2009

TN 1975 2009

NH3 1975 2009

TON + NH3 1975 2009

NO3 1975 2009

Alk 1975 2009

TP 1975 2009

TDP 1991 2009
Specific Basins of Interest 81

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

Lower Mississippi RIver—Continued

107 NWIS 07373420

Mississippi River near 

St. Francisville, La.

30o45′30′′ 91o23′45′′ TN 1974 2009

NH3 1969 2009

TON + NH3 1974 2009

NO3 1954 2009

Alk 1954 2009

TP 1974 2009

TDP 1973 2009

108 NWIS 07374400

Mississippi River at 

Luling, La.

29o56′19′′ 90o21′49′′ TN 1974 1999

NH3 1991 1999

TON + NH3 1974 1999

NO3 1957 1999

Alk 1957 1999

TP 1973 1999

TDP 1973 1999

109 NWIS 07374500

Mississippi River near 

New Orleans, La.

29o58′28′′ 90o10′14′′ NO3 1905 1955

Alk 1905 1955

110 NWIS 07374508

Mississippi River at 

New Orleans, La.

29o57′03′′ 90o08′17′′ TN 1973 1988

NH3 1974 1976

TON + NH3 1973 1988

NO3 1954 1988

Alk 1954 1988

TP 1973 1988

TDP 1972 1984

111 NWIS 07374522

Mississippi River at 

Violet, La.

29o52′52′′ 89o54′02′′ TN 1974 1976

TON + NH3 1974 1974

NO3 1973 1978

Alk 1973 1973

TP 1973 1978

TDP 1973 1974

112 NWIS 07374525

Mississippi River at 

Belle Chasse, La.

29o51′25′′ 89o58′40′′ Daily streamflow 2008 2009

TN 1977 2009

NH3 1978 2009

TON + NH3 1977 2009

NO3 1977 2009

Alk 1977 2009

TP 1977 2009

TDP 1978 2009

1113 STORET 210020

Mississippi River at 

New Orleans, La.

29o56′38′′ 90o10′07′′ TN 1964 1971

NH3 1958 1969

TON + NH3 1964 1968

NO3 1964 1976

Alk 1958 1976

TP 1964 1976

TDP 1964 1968

1114 Weston, 1903 Mississippi River at 

New Orleans, La.

29o56′40′′ 90o10′10′′ NH3 1900 1901

NO3 1900 1901

Alk 1900 1901

NH3 1900 1901

1

Historical station, location approximate.

2

Reference stream gaging station.

Table 17. Mississippi River basin data sources.—Continued

[Monitoring station is shown in figure 25. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse; USACE, 

U.S. Army Corps of Engineers. Constituent: Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]
82 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Upper Colorado River Basins

The Colorado River is the largest river in the 

Southwestern United States, and drains a complex landscape 

ranging from high mountains to desert lowlands (fig. 26). The 

Colorado River supplies water for municipal and industrial use 

to about 27 million people, and water for irrigation of nearly 

4 million acres of land (U.S. Department of the Interior, 2003). 

Water management in the Colorado River basin is intense and 

subject to the terms of the 1922 Colorado River Compact, 

which serves to divide the basin into upper and lower to 

facilitate the complex allocation of its water among seven 

Western States and Mexico. The division between the two 

basins is legally defined at the confluence of the Paria River, 

downstream of Glen Canyon Dam near Lees Ferry, Arizona. 

The total area for the basin upstream of Lees Ferry is about 

290,000 km2 (111,800 mi2). The upper Colorado region is the 

area of interest for this study, where the three major drainage 

basins include the main stem Colorado River, the Green River, 

and the San Juan River basins. Two sampling sites on the 

Colorado River were selected for this analysis: the Colorado 

River at Cisco, Utah, located just upstream of the confluence 

with the Green River; and the Colorado River at Lees Ferry, 

Ariz., representing the output from the upper basin. The 

Gunnison River also was included because it is the largest 

tributary to the upper Colorado River upstream of Cisco. 

The upper Colorado River basin lies within the Colorado 

Plateau physiographic province (fig. 2) and is bounded by the 

Wyoming Basin to the north, the Middle and Southern Rocky 

Mountains to the east and south, and the Basin and Range to 

the west. As a consequence of the highly erodible character 

of much of the basin, the river has continually deepened its 

bed to create massive canyons in many areas through which 

the rivers flow (Bishop and Porcella, 1980). Climate patterns 

include short and warm summers and long, cold winters with 

deep snow in the mountains. Precipitation ranges widely, 

exceeding 125 cm (50 in.) at high elevations and reaching a 

minimum of about 15 cm (6 in.) in the high desert areas at 

lower elevation (Bishop and Porcella, 1980). Mean annual 

discharge (1921–2008) at the lowermost reference stream 

gaging station at Lees Ferry (station No. 09380000) is about 

400 m3/s (14,000 ft3/s), indicating average runoff of about 

43 mm/yr (among the lowest of streams in this study). 

Because of the range of precipitation and topography, 

one of the key characteristics of the upper Colorado River 

basin is that the primary source of water is snowfall high in 

the mountains while the major course of the river itself and its 

tributaries runs through arid land. The area is subject to largescale wet and dry climate cycles, which are associated with 

extreme variability in annual flow conditions that can range 

over an order of magnitude. Natural streamflow patterns were 

historically highly seasonal, with most of the runoff provided 

during the spring snowmelt period. To provide regulation of 

flow variability to meet downstream needs during summer 

low-flow periods, an extensive network of large dams was 

developed over the course of the 20th century. By 1980, 

more than 117 storage reservoirs had been constructed in the 

basin, primarily located in the mountainous areas of the upper 

reaches, supplying hydropower as well as supporting the 

export of pristine water out of the basin (Bishop and Porcella, 

1980). Dozens of trans-mountain canals and tunnels transport 

water from these headwater regions to the South Platte, 

Arkansas, and Rio Grande basins (Bishop and Porcella, 1980). 

The upper Colorado River basin is largely rural, having 

few population centers with more than 50,000 people. 

Population density for the entire upper basin is about 

3 people/ km2, as determined by the 2000 census (fig. 3). 

Irrigated agriculture is the largest water use, although irrigated 

agricultural lands represent a small proportion of the total area 

(less than 5 percent in 1990) (U.S. Department of the Interior, 

2003). Total agricultural area is low, just over 20 percent of the 

entire basin, and the primary agricultural land use is grazing. 

Irrigation water primarily is used to support livestock rather 

than crops (Benke and Cushing, 2005). Geology of the basin 

is dominated by calcium, sulfate, and bicarbonate dissolution 

ions (Stanford and Ward, 1991). As a result, although waterquality issues in the upper basin range from the impact of 

mining to reservoir effects, the most significant water-quality 

issue relates to the increasingly high levels of salinity that 

result from natural geologic sources concentrated by climatic 

factors and coincident evaporation from the many reservoirs, 

and anthropogenic water use.

The five basins considered in the Colorado River basin 

had the lowest population densities among all basins in 

this study, ranging from approximately 2 to 6 people/km2

(fig. 3). These basins lack significant metropolitan areas so 

population growth was slow throughout the 20th century 

(fig. 27A). Agriculture, and especially cropland, is not a major 

land use in these basins, with less than 40 percent of their 

area in agricultural land and less than 7 percent in cropland 

in 2002 (fig. 4). In the mid-20th century, almost 60 percent 

of the San Juan River basin was reported as farmland in the 

Census of Agriculture (fig. 27C). However, among the other 

basins, agricultural land never surpassed 30 percent of basin 

area (fig. 27C). Nitrogen and phosphorus from fertilizer 

and animal livestock sources were among the lowest in this 

study averaging less than 0.6 g (N/m2)/yr and less than 0.15 g 

(P/m2)/yr, respectively, in these basins from 1997 to 2001 

(figs. 5A–5B). Animal sources of nitrogen and phosphorus 

surpassed fertilizer sources in all basins over the same 

time period (figs. 5A–5B). Corn harvest averaged less than 

100 bushels/km2 in all basins of interest in the Colorado River 

with less than 1 bushel of corn/km2 harvested on average 

between 2000 and 2010 in the San Juan basin (fig. 6). The 

relative magnitude of corn harvest intensity in these basins 

is emphasized by the fact that the lines are barely visible in 

figure 27B.
Specific Basins of Interest 83

Figure 26. Upper Colorado River basins.

12-0694_fig26-Colorado

UTAH

NEVADA

WYOMING

COLORADO

ARIZONA

NEW MEXICO

Gunnison

Green

River

Colorado

River

San Juan River

Lake

Powell

Farmington

Grand Junction

Lee’s Ferry

115°W 114°W 113°W 112°W 111°W 110°W 109°W 108°W 107°W 106°W 105°W

43°N

42°N

41°N

40°N

39°N

38°N

37°N

36°N

Base from U.S. National Park Service and ESRI

Landcover from U.S. Geological Survey National Land Cover Dataset 2006

Watershed boundary and flowlines from U.S. Environmental Protection Agency 

and U.S. Geological Survey NHDPlus 2005 

Albers Equal-Area Conic projection, North American Datum of 1983 0 50 100 KILOMETERS

0 50 100 MILES

EXPLANATION

Monitoring station

Watershed boundary

Developed/urban

Barren

Forest

Shrub/scrub

Grassland/pasture

Cropland

Wetland

No data

111

109

110

111 115

116

117

118

119

Paria River

Glen Canyon Dam

Colorado 

Plateau

Wyoming Basin

Rocky Mountains

Wasatch 

Mountains

Uinta Mountains

Wind 

 River 

 Range

Fontenelle Dam

Flaming Gorge Dam

Uncompahgre 

Project

Uncompahgre River

Four Corners area

Paria River

Glen Canyon Dam

Colorado 

Plateau

Wyoming Basin

Rocky Mountains

Wasatch 

Mountains

Uinta Mountains

Wind 

 River 

 Range

Fontenelle Dam

Flaming Gorge Dam

Uncompahgre 

Project

Uncompahgre River

Four Corners area B A S I N A N D R A N G E
84 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 27. Historical changes in (A) population, (B) corn harvest, (C) percentage of basin in any farmland usage, (D) 

percentage of basin in cropland, and fertilizer and animal livestock sources of (E) nitrogen and (F) phosphorus in the 

basins of interest in the Upper Colorado River.

tac12-0694_fig 27

1900 1920 1940 1960 1980 2000

0

0.5

1.0

1.5

2.0

2.5

1860 1890 1920 1950 1980

0

20

40

60

80

100

1860 1890 1920 1950 1980

0

20

40

60

80

100

0

20,000

Year

Percentage of the basin area in cropland

Percentage of the basin area in any farmland usage

1900 1920 1940 1960 1980 2000

Population density, in people per square kilometer 

A B

Year

Nonpoint nitrogen from fertilizer and animal livestock 

sources, in grams of nitrogen per square meter per year 

E F

C D Corn harvest, in bushels per square kilometer of watershed area

1900 1920 1940 1960 1980 2000

0

50

100

150

200

250

300

350

1900 1920 1940 1960 1980 2000

0

2

4

6

8

10

Nonpoint phosphorus from fertilizer and animal livestock 

sources, in grams of phosphorus per square meter per year

Colorado at Cisco

River basin

Gunnison

Green

San Juan

Colorado at Lees Ferry

EXPLANATION

2010 2010

5,000

10,000

15,000
Specific Basins of Interest 85

Green River

The Green River drains the northernmost region of 

the upper Colorado basin, including areas in southwestern 

Wyoming, northeastern Utah, and northwestern Colorado 

(fig. 26). It is the largest tributary to the Colorado River, with 

a drainage area of approximately 116,000 km2 (44,850 mi2) 

referenced to the USGS gage at Green River, Utah. Although 

the Green River originates in the Wind River Range in 

Wyoming, most of the river drains high desert dominated by 

dryland vegetation. Annual precipitation ranges from more 

than 100 cm (nearly 40 in.) in the mountains, falling mostly 

as snow, to less than 25 cm (about 10 in.) at low elevations 

(Benke and Cushing, 2005). Streamflow is regulated by a 

large number of dams, with the largest being the Fontanelle 

Dam in southwestern Wyoming and Flaming Gorge Dam in 

northeastern Utah. Mean annual discharge at the reference 

stream gaging station at Green River (station No. 09315000) 

(1894–2008) is about 175 m3/s (6,200 ft3/s), and runoff is 

48 mm/yr.

The largest towns in the Green River basin are small 

(population less than 20,000) so urbanization is not a major 

factor for water quality. Population density was the lowest of 

all streams in this study, estimated as less than 2 people/km2 in 

the 2000 U.S. Census (fig. 3). Although the major industry is 

mineral production focused on oil and natural gas (Bureau of 

Reclamation, 2010), agriculture is the most important land use 

in the basin (Benke and Cushing, 2005), with approximately 

20 percent of the total basin area in some form of agricultural 

use in 2002 (fig. 4). Agriculture in the Green River basin is 

focused primarily on livestock production of beef, cattle, and 

sheep (Bureau of Reclamation, 2010), so that most water 

use in the basin is for irrigation of feed for livestock. Little 

fertilizer application is associated with these crops and so 

animal livestock was a much larger source of nitrogen and 

phosphorus in this basin (figs. 5A–5B), although these sources 

are among the lowest in this study.

Colorado River at Cisco

The part of the Colorado River basin upstream of the 

confluence with the Green River covers about 62,400 km2

(24,000 mi2), as referenced by the USGS gage at Cisco, 

Utah (fig. 26). The gradient in topography and precipitation 

is similar to the Green River basin, with most precipitation 

falling in the eastern and southern mountains as snow and 

very little precipitation associated with the lower elevations 

farther west (Apodaca and others, 1996). Despite the smaller 

area of this subbasin compared to the Green River basin, mean 

annual discharge for the reference stream gaging station at 

Cisco (station No. 09180500) (1913–2008) is higher at about 

210 m3/s (7,400 ft3/s), and runoff is correspondingly higher as 

well (106 mm/yr).

The largest town in the sub-basin is Grand Junction, 

Colo., which has a population of about 60,000 (U.S. Census 

Bureau, 2000), although most towns have populations 

less than 10,000 (Apodaca and others, 1996). Population 

density was correspondingly low at the end of the 20th 

century, approximately 5.5 people/km2 according to the 

2000 census (fig. 3). Mineral production is the predominant 

industry, including gold in the past and currently focused on 

molybdenum (Bureau of Reclamation, 2010). Most land use 

is designated as rangeland or forest, with large areas set aside 

as National and State parks, wilderness areas, and ski areas; 

irrigated agricultural lands are limited to river valleys and low 

altitude areas. Irrigation accounts for about one-half of water 

use, generally devoted to livestock feed but also including 

crops, such as corn, beans, vegetables, and fruit (Bureau of 

Reclamation, 2010). As with the other basins of interest in this 

region, nitrogen and phosphorus sources from fertilizer and 

animal livestock were extremely low (figs. 5A–5B). 

Gunnison River 

The Gunnison River is the largest tributary to the 

upper Colorado River, draining an area of about 20,000 km2

(nearly 8,000 mi2) in western Colorado (fig. 26) with a mean 

annual discharge at the reference stream gaging station near 

Grand Junction (station No. 09152500) (1896–2008) of 

about 72 m3/s (2,500 ft3/s). Elevation ranges from more than 

4,000 m (about 13,800 ft) to approximately 1,400 m (4,500 ft) 

(Williams and others, 2009). Population density was very 

low, about 4 people/km2 in the 2000 census (fig. 3). The basin 

encompasses two physiographic provinces: the Southern 

Rocky Mountains in the headwaters and Canyonlands 

subprovince of the Colorado Plateau in the lower reaches 

(fig. 2; Apodaca and others, 1996). Mean annual runoff (1896–

2008) is relatively high at 110 mm, reflecting the largely 

mountainous character of the drainage basin. One of the first 

Federal reclamation projects in the Western United States 

was in the Gunnison basin: the Uncompahgre Project, which 

has provided irrigation water to lands in the Uncompahgre 

River valley since 1909 (Butler and others, 1991). Like other 

basins in the upper Colorado River, agricultural land primarily 

was non-cropland and comprised around 20 percent of total 

basin area in 2002 (fig. 4). Nonetheless, irrigation has been 

implicated in increased levels of dissolved solids and nitrate in 

the Gunnison River (Butler and others, 1991).
86 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

San Juan River

The San Juan River at Bluff, Utah, drains an area of 

nearly 60,000 km2 (23,000 mi2) in the Four Corners area of 

Arizona, Colorado, Utah, and New Mexico (fig. 26). It is the 

second largest tributary to the Colorado River and empties 

into the middle of Lake Powell, which is the reservoir behind 

Glen Canyon Dam. Climate and topography are similar 

to that of the upper basin as a whole, ranging from alpine 

mountains dominated by snowmelt to desert lowlands that 

contribute little runoff to the river. Mean annual discharge for 

the reference stream gaging station at Bluff, Ut. (station No. 

09379500) for the period 1914–2008 is 71 m3/s (2,500 ft3/s); 

annual runoff is estimated as 36 mm/yr, the lowest of all 

streams considered in this study.

Land ownership is dominated by Native American 

reservations, which cover approximately 60 percent of the 

San Juan River basin (Kirkpatrick, 2000). National forests and 

parks also represent a significant component, with only about 

13 percent of the basin held in private ownership (Kirkpatrick, 

2000). Energy and mineral extraction are important industries 

in the San Juan River basin, especially natural gas, crude oil, 

and coal (Kirkpatrick, 2000). Agriculture is equally important 

as a component of the local economy, with most cropland 

focused on feed for livestock although corn, dry beans, truck 

gardens, and orchards are cultivated in low-elevation areas 

close to the river (Bureau of Reclamation, 2010). Irrigation 

accounts for more than 90 percent of water usage (Bureau of 

Reclamation, 2010). 

Colorado River at Lees Ferry

The Colorado River at Lees Ferry represents outflow 

from Lake Powell, a large hydroelectric and storage reservoir 

that fills the canyon behind Glen Canyon Dam. Glen Canyon 

Dam was closed in 1963 and the reservoir reached full pool 

20 years later in 1983 (Stanford and Ward, 1991). As a result, 

water quality in the Colorado River at this site since that time 

primarily reflects the limnological processes occurring in the 

reservoir, interacting with the operation of the dam. Lake 

Powell is the second largest reservoir in the United States, 

with a maximum depth of 171 m and volume exceeding 

33 km3 (Stanford and Ward, 1991). The water budget of the 

reservoir is largely determined by the legal allocation of water 

between the upper and lower basins, based on the Colorado 

River Compact of 1922. Inflow primarily is from the Colorado 

and San Juan Rivers and occurs during snowmelt in late spring 

and early summer. Because the average residence time for 

water is about 1.2 years, the reservoir acts as a critical buffer 

between the upper and lower basins when inflow is reduced 

(Gloss and others, 1981). The reservoir has a significant effect 

on downstream water quality. 

Streamflow patterns have significantly changed in 

the Colorado River downstream of Lake Powell, and are 

now essentially determined by the needs of hydropower 

production (Stanford and Ward, 1991). Water chemistry 

in the river at Lees Ferry reflects the intensity of seasonal 

stratification occurring in the reservoir, which is driven largely 

by interaction of inflowing water with cold and saline water 

on the bottom of the reservoir, resulting in overflowing or 

interflowing density currents (Stanford and Ward, 1991). 

Stratification is further enhanced by the reduction of winddriven circulation due to the preponderance of vertical 

cliffs along the shoreline, so that the reservoir never fully 

mixes to the bottom (Johnson and Merritt, 1979). Nutrient 

concentrations in the mixed water near the surface are strongly 

determined by phytoplankton production, being more uniform 

during the winter and early spring and declining during the 

summer growing season (Stanford and Ward, 1991). Water 

delivered during the spring flood tends to remain near the 

surface of the reservoir, so that inflowing nutrients are readily 

taken up by phytoplankton and removed from the system 

(Gloss and others, 1981). Water withdrawal is focused in 

the metalimnion. The reservoir essentially functions as a 

nutrient sink and retains more than 80 percent of the incoming 

nutrient load (Stanford and Ward, 1991). Phosphorus removal 

is especially significant, mediated by calcite precipitation as 

primary production increases over the summer, and reflected 

in near total retention of phosphorus in the reservoir (Stanford 

and Ward, 1991).

Data Sources

Data sources for the upper Colorado River basins are 

summarized in table 18. Daily streamflow data have been 

collected by USGS at all sites for all or most of the 20th 

century (Green River at Green River, Utah, 09315000, since 

1894; Colorado River at Cisco, 09180500, since 1913; 

Gunnison River near Grand Junction, Colo., 09152500, since 

1896; San Juan River near Bluff, Utah, 09379500, since 1914; 

Colorado River at Lees Ferry, Ariz., 09380000, since 1921. 

Water-quality data, including major ions and nitrate, from 

USGS are available beginning in the 1920s (table 18).
Specific Basins of Interest 87

Table 18. Upper Colorado River basin data sources.

[Monitoring station is shown in figure 26. Source: NWIS, National Water Information System. Constituent: Alk, alkalinity. See table 2 for definitions of all 

other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

1115 NWIS 09152500

Gunnison River near 

Grand Junction, Colo.

38o59′00′′ 108o27′00′′ Daily streamflow 1896 2008

TN 1975 1998

NH3 1977 2002

TON + NH3 1975 1998

NO3 1931 2002

Alk 1931 2009

TP 1975 2002

TDP 1967 2002

1116 NWIS 09180500

Colorado River at Cisco, 

Utah

38o48′38′′ 109o17′34′′ Daily streamflow 1913 2008

TN 1974 2000

NH3 1977 2000

TON + NH3 1974 2000

NO3 1928 2000

Alk 1928 2008

TP 1974 2000

TDP 1969 2000

1117 NWIS 09315000

Green River at 

Green River, Utah

38o59′10′′ 110o09′04′′ Daily streamflow 1894 2008

TN 1974 2000

NH3 1977 2000

TON + NH3 1974 2000

NO3 1928 2000

Alk 1928 2000

TP 1974 2000

TDP 1968 2000

1118 NWIS 09379500

San Juan River at 

Bluff, Utah

37o08′49′′ 109o51′53′′ Daily streamflow 1914 2008

TN 1974 2000

NH3 1977 2000

TON + NH3 1974 2000

NO3 1928 2000

Alk 1928 2009

TP 1974 2000

TDP 1968 2000

1119 NWIS 09380000

Colorado River at 

Lee’s Ferry, Ariz.

36o51′53′′ 111o35′15′′ Daily streamflow 1921 2008

TN 1974 2008

NH3 1977 2008

TON + NH3 1974 2008

NO3 1926 2008

Alk 1926 2008

TP 1974 2008

TDP 1971 2000

1

Reference stream gaging station.
88 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Western Basins 

Western basins include the Willamette River in the 

Pacific Northwest region, and the San Joaquin River and the 

Santa Ana River in the California region (fig. 1). The Santa 

Ana River basin was the most densely populated basin in this 

study, with almost 330 people/km2 (fig. 3). In contrast to other 

densely populated basins in the east, population densities were 

low or moderate in the Santa Ana River basin until the 1940s 

(fig. 28A). After then, population has grown tremendously, 

surpassing the Schuylkill River basin by the year 2000 (fig. 3). 

Population growth in the Santa Ana River basin was greatly 

augmented by importation of water from the Colorado River 

beginning in 1928 and by the presence of a large military 

training facility used during World War II, which catalyzed 

population growth after cessation of hostilities (further details 

provided in the Santa Ana River section).
Specific Basins of Interest 89

Figure 28. Historical changes in (A) population, (B) corn harvest, (C) percentage of basin in any farmland usage, (D) 

percentage of basin in cropland, and fertilizer and animal livestock sources of (E) nitrogen and (F) phosphorus in the 

basins of interest in the Western United States.

tac12-0694_fig 28

1900 1920 1940 1960 1980 2000

0

0.5

1.0

1.5

2.0

2.5

1860 1890 1920 1950 1980

0

20

40

60

80

100

1860 1890 1920 1950 1980

0

20

40

60

80

100

0

20,000

Year

Percentage of the basin area in cropland

Percentage of the basin area in any farmland usage

1900 1920 1940 1960 1980 2000

Population density, in people per square kilometer 

A B

Year

Nonpoint nitrogen from fertilizer and animal livestock 

sources, in grams of nitrogen per square meter per year 

E F

C D Corn harvest, in bushels per square kilometer of watershed area

1900 1920 1940 1960 1980 2000

0

50

100

150

200

250

300

350

1900 1920 1940 1960 1980 2000

0

2

4

6

8

10

Nonpoint phosphorus from fertilizer and animal livestock 

sources, in grams of phosphorus per square meter per year

Santa Ana

River basin

Average National 

population 

density

San Joaquin

Willamette

EXPLANATION

2010 2010

5,000

10,000

15,000
90 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Santa Ana River

The Santa Ana River is one of the largest rivers in the 

Los Angeles region of southern California, although it drains 

a relatively small basin (fig. 29). The river’s headwaters arise 

high in the San Bernardino Mountains, from which it flows 

roughly west through the Santa Ana Mountains down onto 

the Orange County coastal plain before discharging into the 

Pacific Ocean (California Regional Water Quality Control 

Board, 1995). The topography of the basin is diverse despite 

the small size, including mountain peaks up to 3,500 m 

(11,500 ft) above sea level, broad inland alluvial valleys, 

and the coastal plain in the west. The basin includes two 

ecoregions: the California Montane Chaparral and Woodlands 

and the California Coastal Chaparral and Woodlands (Benke 

and Cushing, 2005) of the Lower Californian physiographic 

province (fig. 2). The area of interest for this study is the 

upper part of the drainage area, located upstream of the Chino 

Hills and the Santa Ana Mountains, with a drainage area of 

about 5,800 km2 (2,260 mi2) as referenced by the USGS gage 

below Prado Dam. Located within the basin is the closed San 

Jacinto River/Lake Elsinore drainage, which covers 3,860 km2

(1,500 mi2) and very rarely provides discharge to the Santa 

Ana River—only several times during the 20th century. This 

area is thus considered non-contributing to downstream flow 

(Burton and others, 1998). This area of southern California is 

currently highly urbanized and densely populated. The Santa 

Ana River basin is the most densely populated basin included 

in this study, 330 people/km2, according to the 2000 census 

(fig. 3). 

Climate in the Santa Ana River basin is arid to semi-arid; 

summer is warm and dry while most precipitation falls during 

the relatively mild winter (November–March). Average annual 

precipitation is about 38 cm (15 in.) (California Regional 

Water Quality Control Board, 1995), with a slight gradient that 

ranges from lower near the coast to higher in the inland valleys 

and in the mountains (Izbicki and others, 2000). Mean annual 

discharge (USGS station 11074000; 1940–2008) is about 

5 m3/s (187 ft3/s), indicating runoff of about 26 mm/yr if the 

entire basin, including the non-contributing area, is considered 

in the calculation. Active exchange between surface water and 

large reservoirs of groundwater were characteristic of the river 

prior to significant development and use of water resources 

in the basin. Streamflow in the river has ebbed and flowed 

with a complementary pattern of groundwater recharge and 

discharge, responding to the presence of large geologic faults 

that forced water to the surface (California Regional Water 

Quality Control Board, 1995). Downstream of Prado Dam, the 

Santa Ana River is now routed to infiltration ponds in order 

to recharge the underlying aquifers of the coastal plain. Water 

quality in the river is of great interest because these aquifers 

provide the primary source of supply for about 2 million 

people in Orange County, California (Izbicki and others, 

2000).

Although the Santa Ana River basin has been home 

to people for many centuries, settlement by Europeans 

began during the 18th century when the Spanish arrived. 

Development of the floodplain began during the 19th century 

when settlers started diverting water from the river for 

irrigation of their gardens. Large-scale agriculture became 

more prominent as the population grew, and irrigation was 

a key factor supporting the growth of citrus orchards and 

vineyards. By 1928, surface waters were at risk throughout 

the region and the Metropolitan Water District of Southern 

California was formed to import water from the Colorado 

River to southern California, including the Santa Ana River. 

Initially, little water was imported because most demand 

was being met by widespread pumping of groundwater. 

Nonetheless, increased demand for water in the Los Angeles 

area in the middle of the century was an important impetus 

for the development of the California State Water Project, 

which was approved in 1960 to transport water from northern 

to southern California, further augmenting streamflow in the 

Santa Ana River. Groundwater pumping has remained the 

largest source of water to the basin, providing about twothirds of the total water demand by the end of the 20th century 

while imported water provided about one-quarter (Kratzer and 

others, 2010). 

During World War II, the U.S. Army Air Corps 

established a training center in Santa Ana, which contributed 

to the large population growth that occurred in the basin after 

the war ended. This population growth was further stimulated 

by the proliferation of the entertainment, tourism, and aircraft 

industries in the Los Angeles area through the second half of 

the 20th century. During this time, population in the Santa Ana 

River basin increased significantly (California Regional Water 

Quality Control Board, 1990). Accordingly, the balance of 

land use has shifted over the course of the 20th century from 

primarily agricultural to urban. About 75 percent of water use 

was estimated as urban in the basin by the end of the century, 

with the remaining 25 percent estimated for agricultural use 

(Kratzer and others, 2010). As a consequence of this intense 

urban water use, by late in the 20th century, base flow in 

the river had become dominated by treated effluent from 

wastewater-treatment plants (Izbicki and others, 2000). 

Among river basins considered in this study, the Santa 

Ana River basin had the lowest proportion used for farmland 

at 4 percent, with only 1 percent in cropland, in 2002 (fig. 4). 

Nonetheless, extensive dairy operations are concentrated in 

the Chino Valley and may affect nutrient inputs to the Santa 

Ana River. The Chino basin provides rising groundwater 

discharge to the Santa Ana River near Prado Dam, estimated 

as accounting for 5 to 10 percent of base flow (California 
Specific Basins of Interest 91 Figure 29. Santa Ana River basin. tac12-0694_fig29-SantaAna

117°W 117°30'W 118°W

34°N

Prado Dam

Ontario

Riverside

San Bernardino Rancho Cucamonga

Santa Ana

Long Beach

CALIFORNIA

PACIFIC OCEAN

aS n

at Ana R vi er

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

00 10 20 KILOMETERS

10 20 MILES

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

125

122,123

121,124,

125

120

Chino Valley

Los Angeles

San Bernardino Mountains

Santa Ana Mountains

ORANGE COUNTY

Chino Hills

Chino

San Jacinto River Lake 

Elsinore

Los Angeles

San Bernardino Mountains

Santa Ana Mountains

ORANGE COUNTY

Chino Hills

Chino

San Jacinto River Lake 

Elsinore

Chino Valley
92 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Table 19. Santa Ana River basin data sources.

[Monitoring station is shown in figure 29. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring

station Source Station Latitude Longitude Constituent Startyear

End

year

120 NWIS 11074500

Santa Ana River at 

County Line below 

Prado Dam, Calif.

33o52′24′′ 117o40′17′′ Daily streamflow 1919 1960

1121 NWIS 11074000

Santa Ana River below 

Prado Dam, Calif.

33o53′00′′ 117o38′40′′ Daily streamflow 1940 2008

TN 1970 2008

NH3 1971 2008

TON+NH3 1970 2008

NO3 1966 2008

Alk 1966 2008

TP 1971 2008

TDP 1970 2008

122 NWIS 11068000

Santa Ana River at 

River Road near 

Corona, Calif.

33o55′21′′ 117o35′46′′ NH3 1997 1997

NO3 1966 1997

Alk 1968 1997

TDP 1997 1997

2123 Clarke, 

1924

Santa Ana River near 

Corona, Calif.

33o55′21′′ 117o35′46′′ NO3 1906 1907

Alk 1906 1907

124 STORET Y1155000

Santa Ana River below 

Prado Dam, Calif.

33o53′03′′ 117o35′42′′ TN 1975 1978

NH3 1973 1979

TON+NH3 1975 1978

NO3 1950 1988

Alk 1950 1988

TP 1973 1979

TDP 1974 1974

125 STORET WB08Y1155000

Santa Ana River below 

Prado Dam, Calif.

33o53′03′′ 117o38′42′′ TN 1975 1978

NH3 1973 1978

TON+NH3 1975 1978

NO3 1950 1978

Alk 1950 1978

TP 1973 1978

TDP 1974 1974

1

Reference stream gaging station.

2

Historical station, location approximate.

Regional Water Quality Control Board, 1990). This 

groundwater contains significant loads of nitrogen, calculated 

to be about 30–40 percent of the nitrate measured in the river 

at the Prado Dam. These nitrogen loads originate largely from 

the discharge of wastewater from the high density of dairies 

located in the Chino Valley (California Regional Water Quality 

Control Board, 1990). Dairies began to be concentrated in this 

area during the 1970s; approximately 300 dairies supporting 

nearly 300,000 dairy cows were reported in 1995 (Burton and 

others, 1998). The Chino basin represents an area of about 

650 km2 (250 mi2), and this density is considered among the 

highest concentration of dairy cows in the world (California 

Regional Water Quality Control Board, 1990). 

Data Sources

Data sources for the Santa Ana River basin are 

summarized in table 19. USGS streamflow data are available 

for the reference stream gaging station below Prado Dam 

(station No. 11074500) beginning in 1919, and through the 

20th century including data from a second station below Prado 

Dam (station No. 11074000). Water-quality data for the Santa 

Ana River near Corona, California, from 1906 to 1907 are 

available from the Clarke (1924) report, including major ions 

and nitrate. Inorganic carbon and nitrate data were collected 

by the California Department of Water Resources below 

Prado Dam beginning in 1950. The USGS began sampling for 

nitrate and alkalinity below Prado Dam in 1966 and continued 

through 2008.
Specific Basins of Interest 93

San Joaquin River

The San Joaquin River is the second longest river in 

California, extending for a total length of 560 km (about 

350 mi) to drain the southern two-thirds of the Central Valley 

(fig. 30). The major area of the basin includes parts of three 

physiographic regions: the Coast Ranges, San Joaquin Valley, 

and the Sierra Nevada (Kratzer and others, 2011) of the 

Cascade-Sierra Mountains and Pacific Border physiographic 

provinces (fig. 2). The broad and flat expanse of the San 

Joaquin Valley is bounded on the east by the Sierra Nevada 

Mountains, the south by the Tehachapi Mountains, which are 

located approximately 190 miles south of Merced, CA, and 

on the west by the Coast Ranges, while the Sacramento–San 

Joaquin Delta defines the northern boundary. The southern 

part of the basin is essentially hydrologically separate from 

the northern part and characterized by the closed or endorheic 

Tulare basin, which is located approximately 170 miles 

southeast of the Sacramento-San Joaquin Delta, that flows 

into the San Joaquin River only under exceptionally wet 

conditions. For this study, the basin area is defined as the 

northern perennial region with the river mouth at Vernalis, 

and equals 19,150 km2 (about 7,400 mi2) (Kratzer and others, 

2011). Major tributaries include the Stanislaus, Tuolumne, 

and Merced Rivers, which originate in the Sierra Nevada. 

Streams draining the Coast Ranges in the west are smaller and 

generally intermittent.

Climate in the San Joaquin basin is considered arid to 

semi-arid, with hot summers and relatively mild winters. A 

strong gradient of precipitation occurs across the basin from 

east to west, with little precipitation falling in the western 

region because of the rain shadow of the Coast Ranges. 

In contrast, the eastern part of the basin receives heavy 

precipitation on the western slopes of the Sierra Nevada that 

occurs as both rainfall and snow, and provides essentially 

all runoff to the river. Mean annual discharge (1923–2008) 

leaving the basin at the reference stream gaging station at 

Vernalis (station No. 11303500) is about 127 m3/s (4,500 ft3/s) 

(Kratzer and others, 2011), which indicates annual water yield 

of 210 mm. Seasonal patterns of streamflow were originally 

heavily influenced by snowmelt peaks in the spring and 

early summer, with lowest flow magnitudes occurring late 

in the summer and early autumn. These patterns have been 

significantly altered by reservoir storage in the second half of 

the 20th century, which generally acts to equalize flow volume 

throughout the year.

Over the course of the 19th and 20th centuries, an 

extensive network of channels and diversions has been built 

throughout the basin to divert surface water for irrigation. 

Originally, these channels were hand-dug and therefore 

agriculture was restricted to land close to the surface water 

supply. After the discovery of gold in the Serra Nevada in 

the mid-19th century, the development of water resources 

greatly expanded to meet the needs of the miners and the 

growing population. This development included construction 

of thousands of miles of diversion ditches and flumes for 

sluicing gold, which were later converted to irrigation use after 

mining ceased. By early in the 20th century, nearly all surfacewater supply in the San Joaquin Valley had been diverted to 

support irrigation of agriculture (Gronberg and others, 1998). 

Subsequent development in the mid-20th century included 

large-scale Federal and State projects that import water to the 

basin from the Sacramento River and Trinity River, which is 

located approximately 200 miles north of the Sacramento-San 

Joaquin Delta, in the north via the Delta–Mendota Canal and 

the California Aqueduct. Additionally, streamflow in most of 

the major streams in the Sierra Nevada is currently controlled 

by reservoirs, which are largely managed for irrigation and 

hydropower production. Most water use in the basin is focused 

on agriculture, although surface water also is supplied to 

municipal users in southern California and the San Francisco 

area (Gronberg and other, 1998).

Because most of the water in the San Joaquin River 

originates in the Sierra Nevada, logging and mining land use 

there has important influences on water quality. Additionally, 

several cities, and other wastewater sources in the valley, 

discharge directly to the river (Kratzer and Shelton, 1998). 

Nonetheless, the greatest source of water-quality degradation 

in the river is agricultural water use, either due to direct return 

flow of runoff from irrigated fields or inflow from subsurface 

tile drain systems. Because irrigation water serves as a primary 

source of recharge to the groundwater system, irrigation return 

flow also can be routed to the river as groundwater discharge. 

Major crops grown include fruit and nuts, cotton, vegetables, 

and some grains, and livestock also is an important component 

of agricultural land use in the basin (Gronberg and others, 

1998). 

In 2002, although only 25 percent of the San Joaquin 

basin was agricultural (fig. 4), virtually the entire valley 

floor was in cropland or rangeland (fig. 30). Therefore, 

agricultural influence on water quality in this basin may not 

be most accurately described using basin-wide estimates of 

ancillary data. Also, in contrast to the intensively cultivated 

corn belt river basins such as the Maumee, Illinois, and 

Des Moines Rivers (figs. 4, 5A–5B, and 6), the focus of 

agricultural production in the San Joaquin Valley is not on 

corn agriculture. Thus, the corn harvest rate in this basin was 

very low, averaging 52 bushels/km2 from 2000 to 2010, which 

was less than 1 percent as large as in the corn belt river basins 

(fig. 6). Fertilizer and animal livestock sources of nitrogen 

and phosphorus were the highest of the Western river basins 

(figs. 5A–5B). Population density was low, 21 people/km2

(fig. 3).
94 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Figure 30. San Joaquin River basin.

tac12-0694_fig30-SanJoaquin

120°W 121°W 122°W

38°N37°N

Oakland

San Francisco

Merced

Modesto

Vernalis

CALIFORNIA

NEVADA

Merced River

Bear Creek

Stanislau s i R ev r

Tuolumne River

PACIFIC OCEAN

Base from U.S. National Park Service and ESRILandcover from U.S. Geological Survey National Land Cover Dataset 2006Watershed boundary and flowlines from U.S. Environmental Protection Agency and U.S. Geological Survey NHDPlus 2005 Albers Equal-Area Conic projection, North American Datum of 1983

0 25 50 KILOMETERS0 25 50 MILES

EXPLANATION

Watershed boundaryMonitoring station

Developed/urbanBarrenForest

Shrub/scrubGrassland/pasture

CroplandWetlandNo data

127

130

129

128

127

126

San

Joaquin River

Sacramento 

 River

Central Valley

Sierra Nevada Mountains

Coastal Range

SacramentoSan Joaquin 

Delta

Delta-Mendota Canal

California Aqueduct

Central Valley

Sierra Nevada Mountains

Coastal Range

SacramentoSan Joaquin 

Delta

Delta-Mendota Canal

California Aqueduct
Specific Basins of Interest 95

Data Sources

Data sources for the San Joaquin River basin are 

summarized in table 20. Daily streamflow data have been 

collected by USGS at the reference stream gaging station at 

Vernalis since 1923, except for 1925–28. Water–quality data 

for the San Joaquin River at Lathrop, California, from 1907 to 

1908, are available from Clarke (1924), including major ions 

and nitrate. Inorganic carbon data were collected at Vernalis 

by the Bureau of Reclamation beginning in the 1930s through 

the 1980s. Additional data were collected by USGS and the 

California Department of Water Resources beginning briefly in 

the 1930s, and continuing in the 1950s through the second half 

of the 20th century.

Table 20. San Joaquin River basin data sources.

[Monitoring station is shown in figure 30. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

1126 NWIS 11303500

San Joaquin River near 

Vernalis, Calif.

37o40'34" 121o15'55" Daily streamflow 1923 2008

TN 1973 2008

NH3 1977 2008

TON+NH3 1973 2008

NO3 1950 2008

Alk 1950 2008

TP 1960 2008

TDP 1977 2008

2127 Clarke, 1924 San Joaquin River near 

Lathrop, Calif.

37o50′29′′ 121o19′06′′ NO3 1907 1908

Alk 1907 1908

128 STORET RSAN112

San Joaquin River at 

Airport Way Bridge, 

Vernalis, Calif.

37o40'18" 121o23'02" TN 1955 1977

NH3 1955 1977

TON + NH3 1955 1977

NO3 1942 1977

Alk 1938 1990

TP 1955 1977

129 STORET WB05B0704000

San Joaquin River at 

Maze Bridge Road, 

Calif.

37o38'24" 121o13'37" TN 1962 1968

NH3 1962 1978

TON + NH3 1962 1978

NO3 1934 1978

Alk 1934 1978

TP 1962 1978

130 STORET WB05B0708000

San Joaquin River near 

Grayson, Calif.

37o33'48" 121o09'07" TN 1961 1978

NH3 1961 1978

TON+NH3 1961 1978

NO3 1932 1978

Alk 1932 1978

TP 1962 1978

1

Reference stream gaging station.

2

Historical station, locatoin approximate.
96 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Willamette River

The Willamette River is the largest river in Oregon, 

flowing north through the Willamette Valley for approximately 

480 km (300 mi) to join the Columbia River at Portland, Oreg. 

(fig. 31). The sampling site referenced in this study is located 

in Salem, Oreg., near the center of the basin. The basin is 

located in the Pacific Border and Cascad-Sierra Mountains 

physiographic provinces (fig. 2). It is roughly rectangular in 

shape and drains about 18,900 km2 (7,280 mi2) at the reference 

stream gaging station at Salem (station No. 14191000). The 

Coastal Mountains are the western boundary of the basin and 

the Cascades Mountains delimit the east and south (fig. 31). 

The Willamette Valley Plains are in the center of the river 

valley with the Willamette Valley Foothills surrounding 

(fig. 31) (Uhrich and Wentz, 1999). Major tributaries include 

the McKenzie River in the south, and the Santiam River in the 

central part of the basin. 

The climate in this region of western Oregon is tempered 

by proximity to the Pacific Ocean, giving rise to temperate 

rain forest conditions that are characterized by two major 

seasons: relatively cool and wet winters, and warm and dry 

summers. With a mean annual discharge (1909–2009) at 

Salem of about 660 m3/s (23,000 ft3/s), runoff is about 1,100 

mm/yr. Considering the basin as a whole, the Willamette 

River basin produces more runoff per unit of drainage area 

than any other large river in the conterminous United States 

(Kammerer, 1990). Precipitation falls primarily during 

October–March, as snow at high elevations and rainfall on the 

valley floor. The seasonal distribution of streamflow reflects 

the precipitation patterns, with about 60–85 percent of runoff 

occurring during the winter season (Uhrich and Wentz, 1999). 

Very low discharge during the summer months has been a 

major factor affecting water quality in the basin.

The most important land-use activity in the basin 

upstream of Salem is timber production, which became 

a major industry in the early 20th century. Effluent from 

the associated pulp and paper industry was a major water 

quality concern in the 1930s and 1940s (Gleeson, 1972). 

Additionally, because the river served historically as the 

primary transportation link within the valley, numerous 

settlements were established in close proximity to the main 

stem river, including the three largest cities in the State 

(Portland, Salem, and Eugene). Population density in the basin 

was 29 people/ km2 according to the year 2000 census (fig. 3). 

Because of the accessibility of the river to these towns and 

cities, one of the most important water-quality issues in the 

early 20th century was discharge of untreated sewage wastes 

to the river (Gleeson, 1972). 

As a result of public concerns about pollution and 

coincident oxygen depletion from municipal and industrial 

wastes, a major effort to clean up the Willamette River 

occurred during the middle of the 20th century. This effort 

was focused primarily on improving treatment of wastewater 

and effluent from the paper industry (Gleeson, 1972). Another 

major component was construction of 13 flood control 

reservoirs by the U.S. Army Corps of Engineers in the upper 

reaches of the basin that allowed streamflow augmentation 

during the critical low-flow months in late summer. These 

reservoirs exert an important control on the flow in the 

Willamette River, with storage capacity equal to nearly 1.9 

million acre-ft (Shearman, 1976). By 1972, the restoration of 

the Willamette River had become a national success story after 

achieving the desired goals for dissolved oxygen during lowflow conditions (Gleeson, 1972). 

Agriculture has been an important component of land use 

on the valley floor since the first settlers arrived on the Oregon 

Trail in the mid-19th century. The fertility of the Willamette 

Valley soils was a major draw to early pioneers, who grew 

wheat, oats, potatoes and other vegetables, as well as fruit 

orchards; limited livestock raised included beef and dairy 

cattle. Major crops today include grass seed, Christmas trees, 

berries, filberts, and peppermint (Uhrich and Wentz, 1999). In 

2002, 20 percent of the basin was in agricultural land usage 

(fig. 4). Nitrogen and phosphorus from fertilizer and animal 

livestock generally are low with fertilizer inputs being a larger 

proportion of these inputs (figs. 5A–5B). These sources were 

less than one-quarter of the largest mean annual sources in 

the corn belt of the Midwestern United States (figs. 5A–5B), 

and have been consistently low throughout the 20th century 

(figs. 28E–28F). Nonetheless, nitrogen fertilizer use in the 

Willamette River basin was an order of magnitude greater 

than in other western basins like the Colorado that generally 

are associated with application rates less than 0.2 g (N/m2)/ yr 

(figs. 5A–5B) During 2000–2010, the corn harvest rate in 

the Willamette River basin was the lowest of any river basin 

considered in this study, 0.06 bushels/km2 of drainage area 

(fig. 6).
Specific Basins of Interest 97

Figure 31. Willamette River basin.

tac12-0694_fig31-Willamette

124°W 123°W 122°W 121°W

46°N

45°N

44°N

Salem

Eugene

OREGON

WASHINGTON

McKenzie R.

Calapooia R.

Santiam R.

Coast Fork Willamette R.

Fall Creek

Middle Fork

Willame t te

P A C I F I C O C E A N

134

131

135

Salem

Eugene

OREGON

WASHINGTON

McKenzie R.

Calapooia R.

Santiam R.

Coast Fork Willamette R.

Fall Creek

Middle Fork

Willame t te

P A C I F I C O C E A N

Willamette River

Base from U.S. National Park Service and ESRI

Landcover from U.S. Geological Survey National Land Cover Dataset 2006

Watershed boundary and flowlines from U.S. Environmental Protection Agency 

and U.S. Geological Survey NHDPlus 2005 

Albers Equal-Area Conic projection, North American Datum of 1983

0 25 50 KILOMETERS

0 25 50 MILES

EXPLANATION

Monitoring station

Watershed boundary

Developed/urban

Barren

Forest

Shrub/scrub

Grassland/pasture

Cropland

Wetland

No data

126

127 131

132

133,134

Coastal Mountains

Cascade Mountains

Willamette Valley 

Plains and Foothills

Portland

Columbia River
98 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States

Data Sources

Data sources for the Willamette River basin are 

summarized in table 21. Daily streamflow data have been 

collected by USGS at Salem, Oreg., since October 1909 

(table 21). Water-quality data from 1911 to 1912 are available 

for the Willamette River at Salem from Clarke (1924), 

including major ions and nitrate. Additional data are available 

from the USGS and the Oregon Department of Environmental 

Quality, beginning in 1951 through the second half of the 20th 

century.

Table 21. Willamette River basin data sources.

[Monitoring station is shown in figure 31. Source: NWIS, National Water Information System; STORET, Storage and Retrieval Data Warehouse. Constituent: 

Alk, alkalinity. See table 2 for definitions of all other constituent abbreviations]

Monitoring 

station Source Station Latitude Longitude Constituent Startyear

End

year

1131 NWIS 14191000

Willamette River at Salem, 

Oreg.

44o56′40′′ 123o02′30′′ Daily streamflow 1909 2009

TN 1971 1972

TON+NH3 1971 1972

NO3 1951 1979

Alk 1951 1979

TDP 1970 1979

2132 Clarke, 1924 Willamette River at Salem, 

Oreg.

44 ̊56′40′′ 123 ̊02′30′′ NO3 1911 1912

Alk 1911 1912

133 STORET 402014

Willamette River at

Salem Railroad Bridge, 

Oreg.

44o56′52′′ 123o02′42′′ TN 1982 1991

NH3 1959 1995

TON+NH3 1982 1991

NO3 1965 1995

Alk 1959 1995

TP 1965 1971

134 STORET 402226

Willamette River at Marion 

Street, Salem, Oreg.

44o56′46′′ 123o02′31′′ TN 1991 1998

NH3 1991 1998

TON+NH3 1991 1998

NO3 1991 1998

Alk 1991 1998

TP 1991 1998

1

Reference stream gaging station.

2

Historical station, location approximate.
References Cited 99

Summary

 The issue of excess nutrients in streams and rivers of the 

Nation has been a critical one throughout the 20th century. 

Nutrient pollution has resulted in eutrophication of receiving 

waters and the coincident loss of biodiversity and development 

of hypoxia in coastal areas, especially the Gulf of Mexico. 

Adequately describing the origins and severity of nutrient 

pollution requires a large amount of data accumulated over a 

long period of time. In this study, we have provided evidence 

that long-term data exist for 26 drainage basins of interest 

including some of the largest rivers in the Nation. Utilizing 

these data will provide greater insight into the causes and 

trends in nutrient pollution.

The uneven geographic distribution of nutrient pollution 

over the past century is reflected in the unique history of 

water-quality issues in each of the drainage basins included 

in this study. On a national scale, water-quality problems can 

be considered to have begun in the middle 19th century as 

municipal water usage experienced its first wave of growth. 

An intense and largely successful effort to improve water 

sanitation for public health purposes occurred during the early 

and middle part of the 20th century. This effort focused on 

ensuring the safety of drinking water supplies, but in most 

areas wastewater was not treated. Even as water sanitation 

improved, other water-quality problems arose including 

increased pollution loads from industry, municipalities, and 

agriculture. In some cases, hydrologic development also 

created or exacerbated water-quality problems. Growth in 

population and affluence during the middle part of the 20th 

century also placed increasing pressures on water supplies and 

caused further water-quality degradation. Degraded in-stream 

conditions led to periods of anoxia, fish kills, and reduced 

utility of water resources.

Dramatic changes in agricultural practices occurred 

in the middle part of the 20th century and had important 

consequences for quality of water resources. Chemical 

fertilizer usage increased dramatically beginning in the 

late 1940s and led to tremendous increases in agricultural 

productivity, but has also been connected with increased 

nutrient pollution in rivers. In the 1950s, the usage of confined 

animal feeding operations (CAFOs) in livestock production 

became more common. By the end of the 20th century, most 

of the animals raised for human consumption are produced in 

CAFOs. Concentrating livestock population and concentrates 

livestock waste such that CAFOs can also be a source of 

nutrient pollution to aquatic ecosystems.

Local efforts to address water-quality concerns have been 

ongoing since the late 19th century. National-scale efforts 

developed more slowly with the first attempt at controlling 

water pollution nationwide being passed in the mid-20th 

century. The 1948 Water Pollution Control Act was a relatively 

ineffective law, but it laid the foundation for subsequent 

improvements, culminating in the passage of the Clean Water 

Act in 1972.

The Clean Water Act was passed with the stated goal of 

restoring and maintaining the integrity of the Nation’s waters. 

This legislation was significant because it required dischargers 

to obtain a permit for their effluent, thereby defining a limit 

to the pollution load that could be discharged. As a result, 

treatment of effluent wastewater was greatly enhanced, 

especially focused on municipal and industrial point sources. 

Additionally, land-use planning was initiated to limit runoff 

from nonpoint sources in an attempt to solve the full range of 

pollution problems in the country. More recently, a range of 

research programs have been implemented to investigate the 

relation between land use and nonpoint pollution, evaluating 

soil conservation practices and runoff from farm fields and 

urban areas.

This study is focused on compiling data from selected 

river basins that will be useful to evaluate how these long-term 

changes in land use and policy have coincided with changes in 

nutrient concentrations. Sources for long-term streamflow and 

nutrient data are presented for 26 river basins, ranging across 

the continental United States. Brief histories are provided for 

each basin to describe the important events that are presumed 

to influence nutrient concentration patterns throughout the 

20th century. Various issues of data assembly and management 

are discussed, including algorithms used to synthesize relevant 

data from disparate collecting agencies. Ancillary data 

documenting streamflow, population density, and selected 

land-use characteristics provide context for comparing these 

rivers with one another. The perspective provided by these 

data is unprecedented, although challenging to develop over 

such a lengthy period. Regardless, a long-term view of nutrient 

concentrations is essential for correctly understanding the 

impact of policies and legislation in controlling the delivery of 

excess nutrients to streams and rivers of the Nation.

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108 Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States
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Stets and others— Century-Scale Perspective on Water Quality in Selected River Basins of the Conterminous United States—Scientific Investigations Report 2012–5225