U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2011–5114

National Water-Quality Assessment Program

Nutrient Concentrations and Loads 

in the Northeastern United States—

Status and Trends, 1975–2003
Cover. The northeastern United States and southeastern Canada, from the Natural Earth physical map for the world, U.S. National 

Park Service; with state lines and study area boundary added.
Nutrient Concentrations and Loads 

in the Northeastern United States—

Status and Trends, 1975–2003

By Elaine C. Todd Trench, Richard B. Moore, Elizabeth A. Ahearn, 

John R. Mullaney, R. Edward Hickman, and Gregory E. Schwarz

National Water-Quality Assessment Program

Scientific Investigations Report 2011–5114

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:

Trench, E.C.T., Moore, R.B., Ahearn, E.A., Mullaney, J.R., Hickman, R.E., and Schwarz, G.E., 2012, Nutrient concentrations and loads in the northeastern United States—Status and trends, 1975–2003: U.S. Geological Survey Scientific 

Investigations Report 2011–5114, 169 p. (Also available at http://pubs.usgs.gov/sir/2011/5114.)
iii

Foreword

The U.S. Geological Survey (USGS) is committed to providing the Nation with reliable scientific information that helps to enhance and protect the overall quality of life and that facilitates effective management of water, biological, energy, and mineral resources (http://www.usgs.gov/). Information on the 

Nation’s water resources is critical to ensuring long-term availability of water that is safe for drinking and 

recreation and is suitable for industry, irrigation, and fish and wildlife. Population growth and increasing 

demands for water make the availability of that water, measured in terms of quantity and quality, even 

more essential to the long-term sustainability of our communities and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to support 

national, regional, State, and local information needs and decisions related to water-quality management and policy (http://water.usgs.gov/nawqa). The NAWQA Program is designed to answer: What 

is the quality of our Nation’s streams and groundwater? How are conditions changing over time? How 

do natural features and human activities affect the quality of streams and groundwater, and where are 

those effects most pronounced? By combining information on water chemistry, physical characteristics, 

stream habitat, and aquatic life, the NAWQA Program aims to provide science-based insights for current 

and emerging water issues and priorities. From 1991 to 2001, the NAWQA Program completed interdisciplinary assessments and established a baseline understanding of water-quality conditions in 51 of 

the Nation’s river basins and aquifers, referred to as Study Units (http://water.usgs.gov/nawqa/studies/

study_units.html ).

In the second decade of the Program (2001–2012), a major focus is on regional assessments of waterquality conditions and trends. These regional assessments are based on major river basins and principal 

aquifers, which encompass larger regions of the country than the Study Units. Regional assessments 

extend the findings in the Study Units by filling critical gaps in characterizing the quality of surface water 

and groundwater, and by determining water-quality status and trends at sites that have been consistently 

monitored for more than a decade. In addition, the regional assessments continue to build an understanding of how natural features and human activities affect water quality. Many of the regional assessments 

employ modeling and other scientific tools, developed on the basis of data collected at individual sites, 

to help extend knowledge of water quality to unmonitored, yet comparable areas within the regions. The 

models thereby enhance the value of our existing data and our understanding of the hydrologic system. 

In addition, the models are useful in evaluating various resource-management scenarios and in predicting 

how our actions, such as reducing or managing nonpoint and point sources of contamination, land conversion, and altering flow and (or) pumping regimes, are likely to affect water conditions within a region.

Other activities planned during the second decade include continuing national syntheses of information 

on pesticides, volatile organic compounds (VOCs), nutrients, trace elements, and aquatic ecology; and 

continuing national topical studies on the fate of agricultural chemicals, effects of urbanization on stream 

ecosystems, bioaccumulation of mercury in stream ecosystems, effects of nutrient enrichment on stream 

ecosystems, and transport of contaminants to production wells.

The USGS aims to disseminate credible, timely, and relevant science information to address practical and 

effective water-resource management and strategies that protect and restore water quality. We hope this 

NAWQA publication will provide you with insights and information to meet your needs, and will foster 

increased citizen awareness and involvement in the protection and restoration of our Nation’s waters. 

The USGS recognizes that a national assessment by a single program cannot address all water-resource 

issues of interest. External coordination at all levels is critical for cost-effective management, regulation, 

and conservation of our Nation’s water resources. The NAWQA Program, therefore, depends on advice 

and information from other agencies—Federal, State, regional, interstate, Tribal, and local—as well as 

nongovernmental organizations, industry, academia, and other stakeholder groups. Your assistance and 

suggestions are greatly appreciated.

William H. Werkheiser

USGS Associate Director for Water
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v

Contents

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

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

Regional Synthesis Studies of the U.S. Geological Survey National Water Quality 

Assessment..............................................................................................................................2

Purpose, Objectives, and Scope of Report.......................................................................................4

Previous Studies ...................................................................................................................................4

Environmental Setting of the Northeastern United States .....................................................................4

Population Density and Land Use ......................................................................................................4

Nutrients and Water Quality ...............................................................................................................5

Nutrient Sources...................................................................................................................................8

Management Context for Nutrient-Related Water-Quality Impairments .............................................8

Requirements of the Federal Clean Water Act................................................................................9

Water-Quality Criteria and Standards for Nutrients .......................................................................9

Data Selection and Screening...................................................................................................................12

Data from U.S. Geological Survey Monitoring Programs ............................................................12

Data from State Monitoring Programs............................................................................................19

Methods of Data Analysis ..........................................................................................................................19

Streamflow Analysis...........................................................................................................................20

Analysis of Trends in Nutrient Concentrations, Nutrient Loads, and Streamflow...................21

Flow-Adjusted Trend Analysis with Tobit Regression .........................................................21

Instream Trend Analysis with Coupled Statistical Streamflow and WaterQuality Model................................................................................................................21

Estimation of Nutrient Loads.............................................................................................................22

Analysis of Nutrient Sources............................................................................................................23

Land Use and Population Density ...........................................................................................23

Point Sources .............................................................................................................................24

Streamflow Conditions in the Northeastern United States ..................................................................26

Streamflow, 1993–2003.......................................................................................................................26

Low-Flow Years ..........................................................................................................................26

High-Flow Years .........................................................................................................................28

Annual Runoff.............................................................................................................................28

Streamflow During Sampling Years in National USGS Programs .....................................28

Comparison of 1993–2003 Period to Long-Term Streamflows .....................................................29

Long-Term Variability in Annual Mean Streamflow .............................................................29

Regional and Temporal Variability in Runoff .........................................................................31

Effects of Streamflow on Water-Quality Variability ......................................................................31

Effects of Streamflow Conditions on Trend Analysis...........................................................36

Effects of Streamflow Conditions on Load Estimation.........................................................37

Trends in Nutrient Concentrations, 1975–2003 and 1993–2003.............................................................37

Trends in Streamflow .........................................................................................................................37

Trends in Nutrient Concentrations...................................................................................................37

Trends in Flow-Adjusted Nutrient Concentrations...............................................................38

Total Nitrogen ....................................................................................................................38
vi

Dissolved Ammonia Nitrogen and Total Kjeldahl Nitrogen........................................38

Nitrite-plus-Nitrate Nitrogen ..........................................................................................41

Total Phosphorus ..............................................................................................................41

Suspended Sediment .......................................................................................................41

Trends in Flow-Adjusted Concentrations of Nutrients in Large Drainage 

Basins....................................................................................................................41

Trends in Modeled Instream Nutrient Concentrations........................................................46

Nutrient Concentrations in Undeveloped Drainage Basins ......................................46

Modeled Instream Nutrient Concentrations in Relation to Proposed 

Nutrient Criteria...................................................................................................50

Modeled Instream Nutrient Concentrations and Trends in Large Drainage 

Basins....................................................................................................................51

Comparing Trend Results from Different Periods of Record .......................................................56

Annual Nutrient Loads, 1975–2003............................................................................................................57

Relation of Nutrient Loads to Stream Discharge Conditions, 1975–2003 ..................................57

Effects of Calibration Period on Load Estimates ...........................................................................63

Effects of Storms on Annual Nutrient Loads..................................................................................63

Trends in Nutrient Loads, 1975–2003 and 1993–2003 ....................................................................64

Nutrient Loads in Large Drainage Basins.......................................................................................70

Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources...................................................77

Land Use and Population Density ....................................................................................................77

Forested Drainage Basins........................................................................................................88

Agricultural Drainage Basins ..................................................................................................91

Urbanized Drainage Basins .....................................................................................................93

Overall Effects of Urban and Agricultural Development.....................................................95

Large Drainage Basins that Integrate Numerous Land Uses and Nutrient Sources.....95

Effects of Variability in Streamflow Conditions.....................................................................96

Point-Source Discharges ................................................................................................................100

Quinebaug River Basin in Connecticut, Massachusetts, and Rhode Island .................105

Raritan River Basin in Northern New Jersey......................................................................109

Patuxent River Basin in Maryland ........................................................................................117

James River Basin in Central Virginia..................................................................................121

Summary, Conclusions, and Challenges for Management of Water Resources............................124

Regional Data Integration ...............................................................................................................124

Trends in Flow-Adjusted Nutrient Concentrations......................................................................124

Instream Concentration Trends in Relation to Proposed Nutrient Criteria.............................125

Annual Nutrient Loads and Trends in Loads ................................................................................125

Effects of Land Use and Population Density on Nutrient Yields ...............................................126

Effects of Point Sources ..................................................................................................................128

Challenges for Management of Nutrients in the Northeastern United States.......................129

Acknowledgments.....................................................................................................................................129

Selected References.................................................................................................................................130

Appendix 1. Methods—Data Retrieval, Screening, and Modification..........................................149

Appendix 2. Methods—Stations Used in Analysis of Discharge Conditions (CD–ROM)...........153

Appendix 3. Methods—Flow-Adjusted Trend Analysis with Tobit Regression in the 

S-ESTREND System .....................................................................................................................155
vii

Figures

1. Map showing major features of the northeastern region study area, including study 

area boundary, state lines, major coastal features, major cities, major rivers, and 

National Water Quality Assessment (NAWQA) study units ..................................................3

2. Map showing regional land-use and land-cover characteristics........................................6

3. Map showing nutrient ecoregions in the northeastern United States..............................11

4. Map showing locations of 130 U.S. Geological Survey water-quality monitoring 

stations evaluated in this study................................................................................................18

5. Bar graphs of long-term annual mean streamflows at selected stations, 1970–2004 ....30

6. Graphs showing characteristic plots of nutrient concentration as a function of 

discharge at selected stations, showing land-use and point-source effects..................32

7. Maps showing trends in flow-adjusted concentrations of total nitrogen, 

(A) 1975–2003 and (B) 1993–2003..............................................................................................39

8. Maps showing trends in flow-adjusted concentrations of nitrite-plus-nitrate 

nitrogen, (A) 1975–2003 and (B) 1993–2003.............................................................................42

9. Maps showing trends in flow-adjusted concentrations of total phosphorus, 

(A) 1975–2003 and (B) 1993–2003..............................................................................................44

10. Graph showing total phosphorus concentrations as a function of time, Patuxent 

River near Bowie, Md., 1979–2003 ...........................................................................................46

11. Graphs of nitrogen constituent concentrations as a function of time at selected 

stations .........................................................................................................................................52

12. Graphs of total phosphorus concentrations as a function of time at selected 

stations .........................................................................................................................................55

13. Graph of nitrite-plus-nitrate concentrations as a function of time, Potomac River at 

Chain Bridge, Washington, D.C ................................................................................................56

14. Bar graphs of annual mean discharges and annual nutrient loads for selected 

stations and constituents with no trend in load ....................................................................58

15. Bar graphs of long-term annual nutrient loads at selected stations with significant 

trends in load...............................................................................................................................66

16. Bar graphs of long-term annual nutrient loads in the five largest drainage basins 

of the region, 1975–2003 ............................................................................................................72

17. Graphs showing ranges for minimum, median, and maximum nutrient yields in 

relation to the percentage of developed land in a drainage basin ....................................85

18. Boxplots showing annual yields for (A) total nitrogen and (B) total phosphorus for 

46 stations during 1993–2003 ....................................................................................................89

19. Graphs showing annual nutrient yields in selected water years, including 2000 

(median flow year), 2002 (dry year), and 2003 (wet year), as a function of the 

percentage of developed land in a drainage basin ..............................................................98

Appendix 4. Methods—Trend Analysis Using Coupled Statistical Model of Streamflow 

and Water Quality.........................................................................................................................159

Appendix 5. Results—Trends in Streamflow, 1975–2003 and 1993–2003 (CD–ROM)..................163

Appendix 6. Results—Trend Analysis on Flow-Adjusted Nutrient Concentrations, 1975–2003 

and 1993–2003 (CD–ROM)...........................................................................................................165

Appendix 7. Results—Annual Load Estimates, 1975–2003, 1993–2003, and Varied Periods 

of Record (CD–ROM) ...................................................................................................................167

Appendix 8. Results—Trend Analysis on Nutrient Loads, 1975–2003 and 1993–2003 

(CD–ROM)......................................................................................................................................169
viii

Tables

1. Population density of states in the northeastern United States...........................................5

2. Land-use characteristics of the northeastern region of the United States........................7

3. Land-use characteristics of selected major drainage basins in the northeastern 

United States .................................................................................................................................7

4. Nutrient criteria proposed by the U.S. Environmental Protection Agency for 

ecoregions in the northeastern United States.......................................................................10

5. Characteristics of 130 U.S. Geological Survey (USGS) water-quality monitoring 

stations evaluated in this study................................................................................................13

6. Water-quality constituents retrieved for study, including constituent name, 

parameter code, and listing of parameter codes used in analyses in this report...........19

7. Land-use categories for 130 drainage basins evaluated for trends, loads, and 

yields in the northeastern United States ................................................................................24

8. Land-use and population characteristics for 130 monitored drainage basins in the 

northeastern United States.....................................................................................................136

9. Estimated numbers of point sources discharging nutrients in the northeastern 

United States study area ...........................................................................................................25

10. Summary of data sources and availability of point-source data for selected 

drainage basins...........................................................................................................................25

11. New minimum and maximum annual mean flows during 1993–2003 for selected 

stations with 60 or more years of record................................................................................27

12. Sampling years in NAWQA study units and ending water years at NASQAN 

stations in the Northeast...........................................................................................................29

13. Summary of trend results for flow-adjusted concentrations of nutrients and 

suspended sediment, 1975–2003 and 1993–2003...................................................................38

14. Trends in flow-adjusted nutrient concentrations and nutrient loads in large 

drainage basins, 1975–2003 and 1993–2003 ...........................................................................47

15. Trend results for modeled instream nutrient concentrations, proposed criteria for 

total nitrogen and total phosphorus, modeled reference concentrations for nutrients, 

and modeled changes in concentration for 47 streams in the northeastern region, 

1975–2003 and 1993–2003 ........................................................................................................142

20. Map showing drainage basins selected for analysis of point sources in relation to 

nutrient concentrations, loads, and yields ...........................................................................102

21. Map showing monitoring stations and point-source locations in the Quinebaug 

River Basin.................................................................................................................................106

22. Bar graphs showing annual stream loads of nutrients and point-source loads of 

total phosphorus in the Quinebaug River Basin..................................................................107

23. Map showing monitoring stations and point-source locations in the Raritan River 

Basin ...........................................................................................................................................110

24. Bar graphs showing annual stream loads and point-source loads of nutrients in 

the Raritan River Basin ............................................................................................................112

25. Map showing monitoring stations and point-source locations in the Patuxent and 

James River Basins..................................................................................................................118

26. Bar graphs showing annual stream loads and point-source loads of nutrients in 

the Patuxent River Basin .........................................................................................................119

27. Bar graphs showing annual stream loads and point source loads of nutrients in 

the James River Basin .............................................................................................................122
ix

16. Summary of trend results for modeled instream concentrations, 1975–2003 and 

1993–2003 .....................................................................................................................................48

17. Flow-weighted nutrient concentrations and nutrient yields in undeveloped basins 

evaluated in a national study....................................................................................................49

18. Summary of trends in nutrient and suspended sediment loads, 1975–2003 and 

1993–2003 .....................................................................................................................................64

19. Summary statistics for total nitrogen loads in the five largest drainage basins in 

the region, 1975–2003 and 1993–2003......................................................................................76

20. Summary statistics for total nitrogen yields by station, 1993–2003....................................78

21. Summary statistics for total phosphorus yields by station, 1993–2003 .............................81

22. Summary statistics for total nitrogen and total phosphorus yields for all stations 

and for four land-use categories, 1993–2003 .........................................................................84

23. Summary statistics for total nitrogen yields by water year, 1993–2003.............................96

24. Summary statistics for total phosphorus yields by water year, 1993–2003.......................97

25. Summary of point source information and basin characteristics in drainage basins 

selected for analysis ................................................................................................................101

26. Summary of trends in flow-adjusted nutrient concentrations in drainage basins 

selected for analysis of point sources ..................................................................................103

27. Summary of trends in nutrient loads in drainage basins selected for analysis of 

point sources.............................................................................................................................104
x

Conversion Factors, Datum, and Acronyms

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

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

Volume

gallon (gal) 3.785 liter (L)

gallon (gal) 0.003785 cubic meter (m3)

gallon (gal) 3.785 cubic decimeter (dm3)

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

cubic foot (ft3) 28.32 cubic decimeter (dm3)

cubic foot (ft3) 0.02832 cubic meter (m3)

Flow rate

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]

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

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

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg)

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

ton per year (ton/yr) 0.9072 megagram per year (Mg/yr)

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

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

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.

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

or micrograms per liter (μg/L).
xi

List of Acronyms

AG Agricultural

AMLE Adjusted Maximum Likelihood Estimation

AU Agricultural/Urban

BASINS Better Assessment Science Integrating point & Non-point Sources

BNR Biological Nitrogen Removal

CBP Chesapeake Bay Program

CTDEP Connecticut Department of Environmental Protection

CWA Clean Water Act

DMR Discharge Monitoring Report

ESTREND Estimate Trend

HBN Hydrologic Benchmark Network

HUC Hydrologic Unit Code, or Hydrologic Unit

LAD Least Absolute Deviation

LOADEST Load Estimator

LOESS Locally Weighted Scatterplot Smoothing

MCL Maximum Contaminant Level

MLE Maximum Likelihood Estimation

NASQAN National Stream Quality Accounting Network

NAWQA National Water Quality Assessment

NJDEP New Jersey Department of Environmental Protection

NLCDe 1992 National Land Cover Dataset, enhanced 2005

NOAA National Oceanic and Atmospheric Administration

NPDES National Pollutant Discharge Elimination System

NWIS National Water Information System

PCS Permit Compliance System

RIM River Input Monitoring

SIC Standard Industrial Classification

TMDL Total Maximum Daily Load

UA Urban/Agricultural

UN Undeveloped

UR Urban

USEPA United States Environmental Protection Agency

USGS U.S. Geological Survey

VOC Volatile organic compound
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Abstract

The U.S. Geological Survey (USGS) National Water 

Quality Assessment Program (NAWQA) began regional studies in 2003 to synthesize information on nutrient concentrations, trends, stream loads, and sources. In the northeastern 

United States, a study area that extends from Maine to central 

Virginia, nutrient data were evaluated for 130 USGS waterquality monitoring stations. 

Nutrient data were analyzed for trends in flow-adjusted 

concentrations, modeled instream (non-flow-adjusted) concentrations, and stream loads for 32 stations with 22 to 29 years of 

water-quality and daily mean streamflow record during 1975–

2003 (termed the long-term period), and for 46 stations during 

1993–2003 (termed the recent period), by using a coupled 

statistical model of streamflow and water quality developed 

by the USGS. Recent trends in flow-adjusted concentrations 

of one or more nutrients also were analyzed for 90 stations by 

using Tobit regression. 

Annual stream nutrient loads were estimated, and annual 

nutrient yields were calculated, for 47 stations for the longterm and recent periods, and for 37 additional stations that did 

not have a complete streamflow and water-quality record for 

1993–2003. Nutrient yield information was incorporated for 

9 drainage basins evaluated in a national NAWQA study, for a 

total of 93 stations evaluated for nutrient yields. 

Long-term downward trends in flow-adjusted concentrations of total nitrogen and total phosphorus (18 and 19 

of 32 stations, respectively) indicate regional improvements 

in nutrient-related water-quality conditions. Most of the 

recent trends detected for total phosphorus were upward 

(17 of 83 stations), indicating possible reversals to the longterm improvements. 

Concentrations of nutrients in many streams persist 

at levels that are likely to affect aquatic habitat adversely 

and promote freshwater or coastal eutrophication. Recent 

trends for modeled instream concentrations, and modeled 

reference concentrations, were evaluated relative to ecoregionbased nutrient criteria proposed by the U.S. Environmental 

Protection Agency. Instream concentrations of total 

nitrogen and total phosphorus persist at levels higher than 

proposed criteria at more than one-third and about one-half, 

respectively, of the 46 stations analyzed. 

Long-term trends in nutrient loads were primarily 

downward, with downward trends in total nitrogen and 

total phosphorus loads detected at 12 and 17 of 32 stations, 

respectively. Upward trends were rare, with one upward trend 

for total nitrogen loads and none for total phosphorus. Trends 

in loads of nitrite-plus-nitrate nitrogen included 7 upward and 

8 downward trends among 32 stations. Downward trends in 

loads of ammonia nitrogen and total Kjeldahl nitrogen were 

detected at all six stations evaluated. Long-term downward 

trends detected in four of the five largest drainage basins 

evaluated include: total nitrogen loads for the Connecticut, 

Delaware, and James Rivers; total Kjeldahl nitrogen and 

ammonia nitrogen loads for the Susquehanna River; ammonia 

nitrogen and nitrite-plus-nitrate nitrogen loads for the James 

River; and total phosphorus loads for the Connecticut and 

Delaware Rivers. No trends in load were detected for the 

Potomac River. 

Nutrient yields were evaluated relative to the extent of 

land development in 93 drainage basins. The undeveloped 

land-use category included forested drainage basins with 

undeveloped land ranging from 75 to 100 percent of basin 

area. Median total nitrogen yields for the 27 undeveloped 

drainage basins evaluated, including 9 basins evaluated in a 

national NAWQA study, ranged from 290 to 4,800 pounds per 

square mile per year (lb/mi2/yr). Total nitrogen yields even 

in the most pristine drainage basins may be elevated relative 

to natural conditions, because of high rates of atmospheric 

deposition of nitrogen in parts of the northeastern United 

States. Median total phosphorus yields ranged from 12 to 

330 lb/mi2/yr for the 26 undeveloped basins evaluated. The 

undeveloped category includes some large drainage basins 

with point-source discharges and small percentages of 

developed land; in these basins, streamflow from undeveloped 

headwater areas dilutes streamflow in more urbanized reaches, 

and dampens but does not eliminate the point-source “signal” 

of higher nutrient loads. Median total nitrogen yields generally 

do not exceed 1,700 lb/mi2/yr, and median total phosphorus 

yields generally do not exceed 100 lb/mi2/yr, in the drainage 

basins that are least affected by human land-use and wastedisposal practices. 

Nutrient Concentrations and Loads in the Northeastern 

United States—Status and Trends, 1975–2003

By Elaine C. Todd Trench, Richard B. Moore, Elizabeth A. Ahearn, John R. Mullaney, R. Edward Hickman, and 

Gregory E. Schwarz
2 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Agricultural and urban land use has increased nutrient 

yields substantially relative to undeveloped drainage basins. 

Median total nitrogen yields for 24 agricultural basins ranged 

from 1,700 to 26,000 lb/mi2/yr, and median total phosphorus yields ranged from 94 to 1,000 lb/mi2

/yr. The maximum 

estimated total nitrogen and total phosphorus yields, 32,000 

and 16,000 lb/mi2/yr, respectively, for all stations in the region 

were in small (less than 50 square miles (mi2)) agricultural 

drainage basins. Median total nitrogen yields ranged from 

1,400 to 17,000 lb/mi2/yr in 26 urbanized drainage basins, 

and median total phosphorus yields ranged from 43 to 

1,900 lb/mi2/yr. Urbanized drainage basins with the highest 

nutrient yields are generally small (less than 300 mi2) and are 

drained by streams that receive major point-source discharges. 

Instream nutrient loads were evaluated relative to loads 

from point-source discharges in four drainage basins: the 

Quinebaug River Basin in Connecticut, Massachusetts, and 

Rhode Island; the Raritan River Basin in New Jersey; the 

Patuxent River Basin in Maryland; and the James River Basin 

in Virginia. Long-term downward trends in nutrient loads, 

coupled with similar trends in flow-adjusted nutrient concentrations, indicate long-term reductions in the delivery of most 

nutrients to these streams. However, the absence of recent 

downward trends in load for most nutrients, coupled with 

instream concentrations that exceed proposed nutrient criteria in several of these waste-receiving streams, indicates that 

challenges remain in reducing delivery of nutrients to streams 

from point sources. During dry years, the total nutrient load 

from point sources in some of the drainage basins approached 

or equaled the nutrient load transported by the stream. 

Introduction

River basins of the northeastern United States, from 

Maine to central Virginia, encompassed 21 percent of the 

population of the United States in the year 2000, although 

constituting only about 5 percent of the land area (4.7 percent 

of the total land area, and 5.5 percent of the conterminous 

48 states). Despite large public expenditures for water-quality 

improvements, nutrient-related water-quality problems 

continue to cause substantial impairments in freshwater and 

estuarine areas. Estuarine areas adversely affected by nutrients 

include nationally prominent areas such as Chesapeake Bay 

and Long Island Sound, and many smaller estuaries. Estuaries 

that have historically had highly valued commercial fisheries, 

and aesthetic and recreational value, have been adversely 

affected by nutrients. With continued population growth and 

land development in the region, water-quality managers and 

public officials likely will continue to struggle with managing 

the effects of excess nutrients in rivers, lakes, and estuaries. 

The link between human presence and water-quality 

impairments is very strong in the northeastern United States. 

This link requires examination from multiple perspectives 

to understand and solve nutrient-related problems. Management decisions of increasing complexity require information 

suitable for protection and restoration of water quality, aquatic 

life, and habitat in rivers, lakes, and estuaries. Water-quality 

problems resulting from excessive nutrients in freshwater and 

estuaries are among the most widespread and complex issues 

currently facing water managers. 

Effective action to address nutrient-related water-quality 

problems in the northeastern United States requires scientific 

information on the sources, distribution, cycling, and transport 

of nutrients in the environment. Water-resources scientists 

and managers need to know the geographic and temporal 

distribution of nutrient concentrations and loads to evaluate 

the importance of various nutrient sources as factors causing 

water-quality impairments in the streams and estuaries of 

the region. Resource managers can use this information in 

designing programs to control nutrient sources and improve 

water quality. 

Regional Synthesis Studies of the 

U.S. Geological Survey National Water Quality 

Assessment

Nutrient conditions in the river basins of the northeastern 

United States (fig. 1) have been monitored and investigated 

by the U.S. Geological Survey (USGS), State agencies, and 

regional agencies since the early 1900s, and more intensively 

since the 1960s. The USGS began the National Water Quality 

Assessment (NAWQA) Program in 1991, with nutrients as a 

major focus. Seven NAWQA study units are in the regional 

study area of this report: New England Coastal Basins; 

Connecticut, Housatonic, and Thames River Basins; Hudson 

River Basin; Long Island–New Jersey Coastal Drainages; 

Delaware River Basin; Lower Susquehanna River Basin; and 

Potomac River Basin and Delmarva Peninsula (fig. 1). 

As part of the continuing effort to understand and 

improve water quality in the United States, the USGS 

NAWQA Program began regional studies in 2003 to synthesize information on nutrient concentrations, trends, loads, and 

sources. This study of nutrients in the northeastern United 

States is one of several regional synthesis studies nationwide. 
Introduction 3

Figure 1. Major features of the northeastern region study area, including study area boundary, state lines, major coastal 

features, major cities, major rivers, and National Water Quality Assessment (NAWQA) study units.

48°

36°

82° 66°

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

1990 Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

Chesapeake Bay

EXPLANATION

National Water Quality Assessment Study Units

 New England Coastal Basins

 Connecticut, Housatonic,

 and Thames River Basins

 Hudson River Basin

 Long Island - New Jersey

 Coastal Drainages

 Delaware River Basin

 Lower Susquehanna River Basin

 Potomac River Basin and

 Delmarva Peninsula

Boundary between hydrologic regions

Study area boundary

Washington, D.C.

State capital

City, over 250,000 population

James River

Shenandoah River

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Connecticut River

Merrimack River

Saint John River

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Lake

Champlain N e w E n g l a n d R e g i o n Augusta

Montpelier

Albany Boston

Concord

Richmond

Harrisburg Trenton

Dover

Annapolis

Hartford Providence

Washington, D.C.

Baltimore

Philadelphia

Newark

New York

City

M i d - A t l a n t i c R e g i o n

Long Island

Sound

Narragansett

Bay

Cape

Cod

Bay

Buzzards Bay

ATLANTIC OCEAN

Delaware

Bay

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUT

RHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

Penobscot River

Kennebec River
4 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Purpose, Objectives, and Scope of Report

The purpose of this report is to provide water managers, 

scientists, policymakers, and citizens with a regional 

perspective on nitrogen and phosphorus concentrations 

(nutrients) in streams, the changes (trends) in nutrient 

concentrations, the amounts of these nutrients (loads) 

transported by streams, and the sources of these nutrients 

in drainage basins. Specific objectives of the report are to 

present, evaluate, and synthesize: 

1. Information on recent (1993–2003) and long-term 

(1975–2003) trends in nutrient concentrations; 

2. Information on observed nutrient concentrations 

relative to water-quality criteria and benchmarks; 

3. Recent and long-term annual nutrient load estimates, 

and information on trends in annual loads; 

4. Selected information on nutrient sources, including 

regional land use and population density data, and 

point-source information for four selected drainage 

basins. 

The geographic scope of the report includes the drainage basins of rivers in the New England and the mid-Atlantic 

states that drain to the Atlantic Ocean and an area in Vermont 

and New York where rivers drain northward to Canada. The 

study area is coincident with, and includes all river basin 

units in, Hydrologic Region 01, the New England region, and 

Hydrologic Region 02, the mid-Atlantic region, as originally 

defined by the USGS and the U.S. Water Resources Council 

(Seaber and others, 1987), and refined for digital standards in 

the 1990s and 2000s under the Federal Geographic Data 

Committee (Natural Resources Conservation Service, 2009). 

The New England region includes most river basins in the 

New England states (fig. 1). The mid-Atlantic region includes 

drainage basins from eastern New York to central Virginia, 

including the Lake Champlain area along the Vermont–

New York border, from which rivers drain northward to 

Canada (fig. 1). 

Previous Studies

Nutrient conditions in many parts of the region have been 

studied over a period of several decades. Information from 

several of these studies is cited in this report, and additional 

relevant publications are listed in the references. 

Environmental Setting of the 

Northeastern United States

The area of the northeastern United States covered by 

this study includes river basins in the New England and midAtlantic hydrologic regions (fig. 1). The hydrologic landscape 

is composed of many small river basins drained by streams 

flowing generally southward or eastward toward estuaries of 

the Atlantic Ocean. An area along the Lake Champlain Valley 

in northern New York and Vermont drains northward toward 

Canada. The Susquehanna River is the largest river in the 

region, with a monitored drainage area of 27,100 square miles 

(mi2) and a total drainage area of 27,500 mi2 (Sprague and others, 2000, p. 13, 15). Most major streams have drainage areas 

of about 10,000 mi2 or less, and many have drainage areas less 

than 1,000 mi2. The study area encompasses 166,000 mi2 and a 

population of 59 million. 

Population Density and Land Use

The area of the northeastern United States covered by 

this study is one of the most densely populated regions of the 

country. Six of the seven most densely populated states in 

the nation are entirely, or almost entirely, in the study area, 

and the most densely populated areas of the seventh, New 

York, also are in the study area (table 1; U.S. Census Bureau, 

2001). The areas of highest population density are along the 

coast, in metropolitan areas from Boston, Massachusetts, to 

Washington, D.C. (figs. 1, 2). 

Despite the high population density of parts of the region, 

the region as a whole is largely forested (65 percent, table 2). 

In general, mountainous and hilly areas in the interior of the 

region are forested, and coastal areas are more highly urbanized (fig. 2). Major rivers in the region flow from interior 

highlands toward the coast, and consequently the land-use 

characteristics of major river basins are similar to the general 

landscape pattern of the region (table 3). Although most large 

river basins encompass densely populated areas near the coast, 

urbanized areas often constitute less than 10 percent of the 

monitored drainage area, and the large drainage basins as a 

whole are primarily forested. 

Agricultural areas constitute about 18 percent of the 

region, but are primarily in the central and southern parts of 

the study area. Agricultural land generally constitutes less than 

10 percent of the land in most of the large drainage basins of 

northern New England (table 3), with larger percentages in 

drainage basins from the Lake Champlain Valley and central 

New York south to Virginia. 

Changes in land use and population distribution over time 

have not been evaluated quantitatively for this study. However, 

some general patterns are evident, and may be major factors 

in future water-quality changes. During the second half of the 

20th century, the period of greatest percentage increases in 

population took place during the 1950s and 1960s in the eight 

most densely populated states of the region (table 1) (Hobbs 

and Stoops, 2002, Appendix A; Forstall, 1995). Population 

has continued to grow, at a slower rate, in most states of the 

region, and population growth rates have increased in the 

latter decades of the 20th century in some rural states, including New Hampshire. The distribution of population also has 

changed. Residential and commercial development pressure in 
Environmental Setting of the Northeastern United States 5

formerly rural or forested areas has increased in recent years, 

and the rate at which land is developed also has increased, in 

a process commonly called “suburban sprawl.” Development 

of vacation communities in coastal areas and mountain regions 

also has increased. All these factors are likely to affect future 

trends in nutrient-related water-quality conditions. 

Although the region as a whole is largely forested, a large 

proportion of the forested area has already been fragmented or 

otherwise affected by nearby development. A study of forest 

fragmentation in Connecticut found that about 59 percent 

of the state was forested in 2006, but only 46 percent of 

these forested lands were considered “core” forest, the least 

disturbed of the forested categories in the study (Center for 

Land Use Education and Research, 2009). 

Nutrients and Water Quality

Phosphorus and nitrogen are essential nutrients for plant 

growth. Free-floating aquatic plants such as algae depend on 

dissolved nitrogen and phosphorus compounds for nutrients 

(Hem, 1985, p. 128). Nitrogen availability rarely limits aquatic 

plant growth in freshwater, whereas phosphorus concentrations in natural or near-natural streams are generally low 

enough to limit plant growth. Excessive phosphorus concentrations in freshwater promote the growth of aquatic algae 

and resulting eutrophic conditions (Hem, 1985, p. 128; Litke, 

1999), whereas excessive nitrogen concentrations promote 

algal growth and eutrophication in estuarine environments 

(National Research Council, 2000, p. 63–112). 

Decomposition of aquatic plants contributes to a condition called hypoxia, or low dissolved oxygen, in freshwater 

and marine environments. As algal blooms die, organic 

decomposition releases nutrients to the water column, depletes 

oxygen from the water, and leaves nutrient-rich organic material that settles to the bottom of the stream, reservoir, or estuary. Freshwater algal blooms may be transported downstream 

to the estuarine environment, where algal decomposition 

depletes oxygen and contributes organic material and nutrients 

to the water column and sediments. 

Elevated concentrations of nitrogen and phosphorus have 

been reported historically and in recent years at water-quality 

monitoring stations operated cooperatively by the USGS and 

state agencies in the northeastern United States. Nuisance algal 

blooms develop annually during summer and autumn months 

in impoundments, streams, and estuarine areas in some parts 

of the region. Elevated instream phosphorus concentrations, in 

conjunction with other hydrologic and climatic factors, are the 

likely cause of freshwater algal blooms. Seasonal algal blooms 

and hypoxia are serious long-term problems in the Chesapeake 

Bay, Long Island Sound, and other estuaries. Elevated 

concentrations of nitrogen constituents from multiple sources 

are believed to promote estuarine algal blooms and contribute 

to high levels of biochemical oxygen demand, resulting in low 

dissolved oxygen concentrations in Narragansett Bay in Rhode 

Table 1. Population density of states in the northeastern United States.

[Sources for population data: U.S. Census Bureau, 2000, 2001; Hobbs and Stoops, 2002, appendix A; mi2, square mile; NA, not applicable]

State or district Area 

(mi2)

Population Population 

rank in 2000

Population density per 

square mile National density rank

1990 2000 1990 2000 1990 2000

New Jersey 7,419 7,730,188 8,414,350 9 1,042 1,134 1 1

Rhode Island 1,045 1,003,464 1,048,319 43 960 1,003 2 2

Massachusetts 7,838 6,016,425 6,349,097 13 768 810 3 3

Connecticut 4,845 3,287,116 3,405,565 29 678 703 4 4

Maryland 9,775 4,781,468 5,296,486 19 489 542 5 5

New York 47,224 17,990,455 18,976,457 3 381 402 6 6

Delaware 1,955 666,168 783,600 45 341 401 7 7

Pennsylvania 44,820 11,881,643 12,281,054 6 265 274 8 10

Virginia 39,598 6,187,358 7,078,515 12 156 179 15 14

New Hampshire 8,969 1,109,252 1,235,786 41 124 138 18 20

West Virginia 24,087 1,793,477 1,808,344 37 75 75 26 29

Vermont 9,249 562,758 608,827 49 61 66 30 30

Maine 30,865 1,227,928 1,274,923 40 40 41 36 38

District of Columbia 61 606,900 572,059 NA 9,883 9,317 NA NA
6 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Figure 2. Regional land-use and land-cover characteristics. [Source for land-use data: 1992 National Land Cover Dataset 

(NLCDe 92) (Vogelmann and others, 1998; enhanced as described by Nakagaki and Wolock, 2005)]

James River

Shenandoah River

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Connecticut River

Merrimack River

Saint John River

Penobscot River

Kennebec River

Chesapeake Bay

EXPLANATION

Land use and land cover

 Open water

 Forested land, wetlands, and 

 other undeveloped land

 Urbanized land and other developed land

 Agricultural land

Study area boundary

Washington, D.C.

State capital

City, over 250,000 population

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUT

RHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

48°

36°

82° 66°

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

1990 Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Lake

Champlain

Narragansett

Bay

Cape

Cod

Bay

Augusta Montpelier

Albany

Boston

Concord

Richmond

Harrisburg Trenton

Dover

Annapolis

Hartford

Providence

Washington, D.C.

Baltimore

Philadelphia

Newark

New York City

Buzzards Bay

Land use and Land cover from National Land Cover 

Dataset (NLCD) land-use data (Vogelmann and others, 2001) 

are aggregated to one-kilometer areas.

Delaware

Bay

Long Island Sound

ATLANTIC OCEAN

Lake Champlain Valley Central Valley

Great Valley
Environmental Setting of the Northeastern United States 7

Island, Long Island Sound in Connecticut and New York, and 

Chesapeake Bay in Maryland and Virginia, as well as in many 

smaller harbors, estuaries, and bays throughout the region 

(Ely, 2002, p. 6; Connecticut Department of Environmental 

Protection, 2001, p. 1; Chesapeake Bay Program, 2004, p. 13; 

Bricker and others, 2007, p. 40–54). 

The National Oceanic and Atmospheric Administration 

(NOAA) has evaluated eutrophic conditions, assessed changes 

in eutrophic conditions from the early 1990s to 2004, evaluated the effectiveness of management actions to reduce eutrophic conditions, and assessed the future outlook for eutrophic 

conditions in the Nation’s estuaries, through the National 

Estuarine Eutrophication Assessment (Bricker and others, 

2007). The North Atlantic region and the mid-Atlantic region 

of the NOAA assessment correspond closely to the geographic 

area encompassed by this study. 

The North Atlantic region defined by NOAA, 

encompassing the coasts of Maine, New Hampshire, and 

eastern Massachusetts (including Cape Cod), was the least 

eutrophic region in the nation, with most assessed systems 

having a low or moderate overall eutrophic condition (Bricker 

and others, 2007, p. 40–46). This condition is believed to 

be the result of low freshwater nitrogen loads relative to 

oceanic nitrogen inputs, generally sparse population, high 

tidal flushing, and moderate to good dilution capabilities of 

estuarine systems. Only one assessed system, the Merrimack 

River in New Hampshire and Massachusetts, was found to 

have high nitrogen loads relative to oceanic inputs. However, 

about one-third of the systems had insufficient monitoring 

data for assessment of eutrophic conditions. The NOAA 

assessment predicted worsening conditions in most systems 

that were evaluated in the North Atlantic region, as a result 

of anticipated increases in nutrient loads from treated 

wastewater, urban runoff, septic systems, combined sewer 

overflows, atmospheric deposition, increasing impervious 

surfaces, and fertilizer use in one or more of the estuarine 

systems, with increases in coastal population expected to 

increase nutrient loads from all these sources. NAWQA 

studies have found that concentrations of nutrients in streams 

and shallow groundwater generally increase with increasing 

amounts of agricultural and urban land in a drainage basin 

(U.S. Geological Survey, 1999, p. 15). A national NAWQA 

study of nutrient trends in streams and rivers from 1993 to 

2003 concluded that nutrient enrichment has increased in 

many streams that were among the least impaired by nutrients 

in 1993, and that the Nation’s least impaired streams are 

increasingly being affected by population growth (Sprague and 

others, 2009, p. 93, 101). These large-scale findings support 

the NOAA conclusion that coastal population increases are 

likely to result in increased nutrient loads to coastal areas. 

Table 2. Land-use characteristics of the northeastern region 

of the United States.

[Source: 1992 National Land Cover Dataset (NLCDe 92) (Vogelmann and 

others, 1998; enhanced as described by Nakagaki and Wolock, 2005). Other 

land uses constitute the remaining small percentage of the region]

Land use Percentage of region

Urban 8.3

Agricultural 18

Forested 65

Water 3.5

Wetland 4.0

Table 3. Land-use characteristics of selected major drainage basins in the northeastern United States.

[Source: 1992 National Land Cover Dataset (NLCDe 92) (Vogelmann and others, 1998; enhanced as described by Nakagaki and Wolock, 2005). Other 

lands uses constitute the remaining small percentage of each drainage area. Forested land includes wooded wetlands; water includes herbaceous wetlands; 

mi2, square miles]

River

Monitored 

drainage area 

(mi2)

Land-use percentages of monitored drainage area

Urban Agricultural Forested Water

Kennebec River at North Sidney, Maine 5,403 1.4 5.6 82.1 7.3

Merrimack River below Concord River at Lowell, Mass. 4,635 11.5 6.7 74.7 6.5

Connecticut River at Thompsonville, Conn. 9,660 5.0 8.3 81.0 3.5

Mohawk River at Cohoes, N.Y. 3,450 5.8 27.2 65.2 1.8

Delaware River at Trenton, N.J. 6,780 5.3 16.4 75.2 2.8

Susquehanna River at Conowingo, Md. 27,100 3.2 28.2 66.6 1.3

Potomac River at Chain Bridge, at Washington, D.C. 11,570 4.5 33.8 60.1 0.9

James River at Cartersville, Va. 6,252 3.5 15.0 79.6 0.8
8 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

The mid-Atlantic region of the NOAA assessment 

encompasses coastal areas from Buzzards Bay on the south 

side of Cape Cod in Massachusetts to the James River Basin 

at the southern end of Chesapeake Bay in Virginia. Nationally, 

the estuaries of the mid-Atlantic region were the most affected 

by eutrophication, with most assessed estuarine systems 

having a moderate-high or high overall eutrophic condition 

(Bricker and others, 2007, p. 47–54). Watershed nitrogen loads 

to these estuaries are high relative to oceanic inputs, major 

population centers are present, agriculture is a major source 

of nutrients, and many estuaries have low flushing capabilities. The future outlook described for this region is mixed, 

with improvements expected in some estuarine systems and 

worsening conditions predicted in others. Anticipated changes 

show a regional pattern, with predicted improvements more 

common in the northern part of the region and deterioration 

more likely in the southern part of the region. Coastal population increases are expected to result in increased nutrient 

loads. Details of the NOAA assessment for individual estuaries in the North Atlantic and mid-Atlantic regions are available 

(Bricker and others, 2007, p. 40–54). 

Nutrient Sources

Nitrogen and phosphorus constituents in streams of the 

northeastern United States are derived from natural sources 

and from many human uses of land and water resources. 

Sources of contamination that transmit nutrients or other contaminants through a pipe, such as effluent from a wastewatertreatment plant or an industrial facility, are referred to as point 

sources. By contrast, sources that are spread over large areas, 

such as fertilizer applications or septic systems, are referred 

to as nonpoint sources. Natural sources, including decaying 

plants and animal wastes, are the major nutrient sources in 

forested, undeveloped areas, and are also present in developed areas. Animal wastes, fertilizers, and decaying plants are 

major sources in agricultural areas. Nitrogen and phosphorus 

constituents from nonpoint sources are carried to streams by 

runoff during and after periods of rainfall or snowmelt, or are 

transported through groundwater and eventually discharged to 

streams. Municipal and industrial wastewater, residential and 

commercial fertilizers, local sources of atmospheric deposition, and urban runoff are major nutrient sources in urban 

areas. Historically, detergents have contributed large amounts 

of phosphorus to streams through municipal wastewater discharges (Litke, 1999). 

Atmospheric deposition contributes nitrogen constituents 

and minor amounts of phosphorus to the land surface. Some 

nutrients are deposited directly in streams and other water 

bodies from atmospheric deposition. Nitrogen deposited from 

the atmosphere is derived either naturally from chemical 

reactions or from the combustion of fossil fuels. The area of 

the northeastern United States covered by this report is in the 

air-shed of the larger industrialized northeast, and atmospheric 

deposition is a regionally important nonpoint source of 

nitrogen (Castro and others, 2001). Ammonia emissions to the 

atmosphere, primarily from animal agriculture, are considered 

to be a major source of nitrogen to land and water ecosystems 

in the Chesapeake Bay watershed (Chesapeake Bay Program, 

2002, p. 44). 

Groundwater inflow may contribute major or minor 

quantities of nutrients to streams, depending on hydrogeologic 

conditions and land-use effects. A study of base flow and 

groundwater nitrate loads in the Chesapeake Bay watershed 

determined that groundwater is a major source of water to total 

streamflow and a major source of nitrate to total stream nitrate 

loads (Bachman and others, 1998). Nitrogen constituents, 

which may infiltrate to groundwater from fertilizers, manure, 

septic systems, or other nonpoint sources, are generally 

unreactive in oxygenated groundwater, and consequently may 

reach streams with little attenuation. By contrast, some forms 

of phosphorus are chemically reactive, and may be filtered out 

of groundwater and retained by particulate materials. Minerals in rocks and soil are not major sources of nitrogen in the 

region, but phosphorus from rocks and soil is locally important 

in some areas. 

Point sources in urban areas are major nutrient sources 

in the northeast, where many of the Nation’s largest cities are 

located and where smaller urban areas are also numerous. 

Estimates made for this report indicate that more than 11,000 

point sources discharge effluent to rivers and streams of the 

region, and of these 11,000 sources, about 6,000 facilities 

discharge nutrients. 

Many of the largest municipal point discharges in the 

region are from large metropolitan areas on the coast, and 

the facilities discharge directly to estuarine or tidal areas. All 

water-quality data analyzed for this report come from monitoring stations on freshwater streams, upstream from the point 

of tidal influence. Consequently, the water-quality effects of 

many major point sources in the region are not encompassed 

by this analysis, as this report focuses on sources upstream 

from stream-quality monitoring stations. 

Surface-water and groundwater diversions and interbasin 

transfers of water are common in many drainage basins of the 

northeast. The use, transfer, and disposal of water affect nutrient concentrations and loads in many streams, and complicate 

the assessment of nutrient sources. 

Management Context for NutrientRelated Water-Quality Impairments

Nutrient-related water-quality impairments are among 

the water contamination problems regulated under Federal 

law. The U.S. Environmental Protection Agency (USEPA) 

is responsible for implementing the Clean Water Act, Safe 

Drinking Water Act, and parts of other statutes related 
Management Context for Nutrient-Related Water-Quality Impairments 9

to prevention, control, and abatement of pollution (U.S. 

Environmental Protection Agency, 2010). The USEPA 

delegates many water programs to State and tribal agencies, 

provides guidance, develops water-quality assessments and 

inventories, and develops strategies and criteria for waterquality restoration. 

Requirements of the Federal Clean Water Act

The Federal Water Pollution Control Act Amendments 

of 1972 (Clean Water Act, or CWA) established two 

complementary approaches to water pollution control: the 

existing interstate water-quality standards program was 

extended to intrastate waters, and technology-based discharge 

permits were required (U.S. Environmental Protection Agency, 

2006). The CWA, and subsequent amendments, requires 

States and Tribes to adopt water-quality standards and sets 

requirements for these standards. Water-quality standards, 

established under Section 303 (c) of the CWA, define goals for 

a water body by designating uses for the water body, setting 

water-quality criteria to protect those uses, and establishing 

an antidegradation policy (U.S. Environmental Protection 

Agency, 2006). The CWA established the National Pollutant 

Discharge Elimination System (NPDES), which requires a 

discharge permit for each point-source facility that discharges 

wastewater to waters of the United States. The NPDES 

process has been a critical factor supporting many waterquality improvements that have taken place during the 1970s 

and 1980s in the northeastern United States, a region with 

many urban areas, municipal discharges, and industries. 

Water-quality assessments are reported periodically by 

the States in a document referred to as the 305 (b) Report, 

or the Water Quality Report to Congress, as required under 

Section 305 (b) of the CWA. Water bodies that have been 

identified as not meeting designated uses are reported 

periodically in a document called the 303 (d) List, as required 

under Section 303 (d) of the CWA (U.S. Environmental 

Protection Agency, 2007). Despite substantial waterquality improvements in many areas of the region, some 

impoundments, stream reaches, and estuaries continue to 

be listed as not meeting standards of the CWA because of 

elevated nutrient and chlorophyll-a concentrations, excessive 

algal growth, and persistent organic enrichment that 

causes high levels of biochemical oxygen demand and low 

dissolved oxygen concentrations (Connecticut Department 

of Environmental Protection, 2008; Maryland Department 

of the Environment, 2008; Massachusetts Department of 

Environmental Protection, 2008; New Jersey Department of 

Environmental Protection, 2007; Pennsylvania Department of 

Environmental Protection, 2008; Rhode Island Department of 

Environmental Management, 2008; Virginia Department of 

Environmental Quality, 2008). 

The CWA requires that states, territories, and authorized 

tribes establish priority rankings for waters on the 303 (d) lists 

and develop Total Maximum Daily Load (TMDL) analyses for 

these water bodies (U.S. Environmental Protection Agency, 

2007). The TMDL process provides a framework to restore 

impaired waters by establishing the maximum amount of a 

contaminant that a water body can assimilate from all sources 

and still support uses designated by the water-quality standards. Water-quality restoration is an interstate concern in 

many areas of the northeastern United States, with major nutrient sources in multiple states contributing nutrients to streams 

with interstate watersheds. 

Water-Quality Criteria and Standards for 

Nutrients

National Water Quality Inventories produced periodically 

by the USEPA have repeatedly shown that nutrients are a 

major cause of water-quality use impairments, including 

failure to support aquatic life (U.S. Environmental Protection 

Agency, 2000d, 2002). To address this problem, the USEPA 

developed a National Strategy for the Development of 

Regional Nutrient Criteria (U.S. Environmental Protection 

Agency, 1998), under Section 304 (a) of the CWA (U.S. 

Environmental Protection Agency, 2000d, 2002). The National 

Strategy emphasizes development of guidance for specific 

water bodies and ecological regions, and the use of measured 

nutrient concentrations in pristine or minimally impaired 

waters as a basis for formulating nutrient criteria. Guidance 

has been or will be developed for four types of waters: lakes 

and reservoirs, rivers and streams, estuaries and coastal 

waters, and wetlands. 

This process has resulted in the development of proposed 

criteria for total nitrogen and total phosphorus for rivers and 

streams in 14 nutrient ecoregions in the United States (U.S. 

Environmental Protection Agency, 2002). Nutrient concentrations that exceed proposed criteria are likely to promote 

eutrophic conditions. These criteria provide benchmarks for 

evaluating the nutrient concentrations and trends presented in 

this report. Criteria for five ecoregions are applicable to the 

study area of this report (table 4, fig. 3) (U.S. Environmental 

Protection Agency, 2000a–d, 2001). 

The USEPA has established a Federal drinking-water 

standard, or Maximum Contaminant Level (MCL), of 

10 milligrams per liter (mg/L) for nitrate as nitrogen (U.S. 

Environmental Protection Agency, 2003). An MCL is a 

concentration above which adverse human health effects may 

occur. The USEPA also has established criteria for nonionic 

ammonia in surface water because of toxicity to fish (U.S. 

Geological Survey, 1999, p. 35). The chronic criteria for 

total ammonia (applicable to persistent rather than short-term 

conditions) vary from 0.07 to 2.1 mg/L, depending on the pH 

and temperature of the water (U.S. Environmental Protection 

Agency, 1986). 
10 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Table 4. Nutrient criteria proposed by the U.S. Environmental Protection Agency for ecoregions in the northeastern United States.

[Source for proposed ecoregional nutrient criteria: U.S. Environmental Protection Agency (2000a, 2000b, 2000c, 2000d, 2001; mg/L, milligrams per liter]

Nutrient 

ecoregion name

Ecoregion 

number

Proposed criteria

Ecoregion description States in study area Total 

nitrogen 

(mg/L)

Total 

phosphorus 

(mg/L)

Mostly glaciated 

dairy region

7 0.54 0.03300 Dominated by forests, dairy operations, pasture 

lands, and other agricultural operations. Mostly 

glaciated, with many wetlands and lakes, and a 

short growing season.

Vermont, New York, 

Pennsylvania

Nutrient-poor, 

largely glaciated 

upper Midwest 

and Northeast

8 0.38 0.01000 Sparsely populated, with extensive forests, nutrientpoor soils, a short growing season, limited 

cropland, and many marshes, swamps, lakes, and 

streams. High hills and low mountains.

Maine, New Hampshire, 

Vermont, Massachusetts, 

Connecticut, New York, New 

Jersey, Pennsylvania

Southeastern 

temperate 

forested plains 

and hills

9 0.69 0.03656 Irregular plains and hills with forests, cropland, and 

pasture. Urban development, coal mining, and 

livestock operations in some areas. Includes the 

Piedmont and Northern Piedmont physiographic 

provinces, transitional hilly areas between 

mountains to the west and plains to the east.

New Jersey, Pennsylvania, 

Delaware, Maryland, District 

of Columbia, Virginia

The central and 

eastern forested 

uplands

11 0.31 0.01000 Unglaciated, forested low mountains and upland 

plateaus. Characterized by forests, high relief 

terrain, steep slopes, and high gradient streams. 

Includes the Blue Ridge and Ridge and Valley 

physiographic provinces.

New York, New Jersey, 

Pennsylvania, Maryland, 

Virginia, West Virginia

Eastern coastal 

plain

14 0.71 0.03125 A lowland dominated by woodland, urban areas, 

or marshland. Low-gradient streams often are 

tidally influenced. Urban land uses, including 

some of the nation’s largest cities, occupy a large 

and growing percentage of the region.

Maine, New Hampshire, 

Massachusetts, Rhode Island, 

Connecticut, New York, New 

Jersey, Delaware, Maryland, 

Virginia
Management Context for Nutrient-Related Water-Quality Impairments 11

Figure 3. Nutrient ecoregions in the northeastern United States. (Source for ecoregions: Rohm and others, 2002)

James River

Shenandoah River

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Connecticut River

Merrimack River

Saint John River

Penobscot River

Kennebec River

48°

36°

82° 66°

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

1990 Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUT

RHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

Chesapeake Bay

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Lake

Champlain

Augusta

Montpelier

Albany Boston

Concord

Richmond

Harrisburg Trenton

Dover

Annapolis

Hartford

Providence

Washington, D.C.

Baltimore

Philadelphia

Newark

New York City

Narragansett

Bay

Cape

Cod

Bay

Buzzards Bay

ATLANTIC OCEAN

Delaware

Bay

Long Island Sound

EXPLANATION

Nutrient ecoregions—Number 

 and name

 Mostly glaciated dairy region

 Nutrient-poor, largely glaciated 

 upper midwest and northeast

 Southeastern temperate forested

 plains and hills

 The central and eastern forested uplands

 Eastern coastal plain

Study area boundary

Washington, D.C.

State capital

City, over 250,000 population

7

8

9

11

14
12 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Data Selection and Screening

Water-quality and streamflow data were investigated, 

retrieved, and evaluated for long-term and recent periods. 

Water-quality data were retrieved for a long-term period of 

analysis, 1975–2003. For some stations, the long-term period 

starts in 1979 or 1982. Nutrient data for the recent period, 

1993–2003, are used to describe and evaluate the most recent 

nutrient conditions in the region, within the longer-term period 

evaluated in this study. The 1993–2003 period was selected 

as a period of analysis for several regional NAWQA nutrient 

studies, to have a common basis for comparing trend results 

in different regions of the country. The 1993–2003 period also 

has been evaluated in a National synthesis of nutrient data by 

the NAWQA Program (Sprague and others, 2009). Stream 

discharge data were retrieved for the period 1970–2004, and 

for the full period of record for stations with discharge data 

prior to 1970. Unless otherwise specified, data were retrieved 

and analyzed by water year. A water year is defined as the 

12-month period from October 1 through September 30 and is 

designated by the calendar year in which the water year ends. 

Data from U.S. Geological Survey Monitoring 

Programs

Water-quality data and associated streamflow data for 

1975–2003 were retrieved from several USGS programs, 

including the NAWQA Program study units (fig. 1); the 

National Stream Quality Accounting Network (NASQAN); 

the Hydrologic Benchmark Network (HBN); State monitoring programs conducted by the USGS under the Federal–State 

cooperative program; and special projects conducted by USGS 

Water Science Centers in several states. 

Water-quality data for USGS National Stream WaterQuality Monitoring Networks, including NASQAN and 

HBN, were retrieved from a published CD–ROM (Alexander 

and others, 1996, 1997). Water-quality data for all USGS 

stations monitoring drainage areas greater than 1 mi2 were 

retrieved on a state-by-state basis from the USGS National 

Water Information System (NWIS), through the online source 

NWISWeb (U.S. Geological Survey, 2002; 2009b). Additional 

details of data retrievals and data screening are provided in 

appendix 1. 

Data were evaluated for more than 450 stations with at 

least 20 nutrient samples during the 1975–2003 period. These 

stations were screened to select stations with sufficient data 

and appropriate annual data distribution for trend analysis 

or load estimation during selected periods of interest. More 

than 200 stations have data sufficient for trend analysis during 

the 1993–2003 period or for load estimation during at least 

two years of the 1993–2003 period. Additional stations have 

long-term records in the period from the mid-1970s to the 

mid-1990s. Trend analyses for this report were restricted to 

stations with data for 8 to 11 years of the 1993–2003 period, 

and load estimation focused on stations with data for the 

entire 1993–2003 period and stations with longer-term records 

that included the entire 1993–2003 period. Annual loads 

were estimated for selected additional stations with less than 

the full 1993–2003 period of record to ensure geographic 

coverage of the region and representation of specific land 

uses in the results. One or more analyses were performed 

on nutrient data for 121 stations (table 5; fig. 4). In addition, 

nutrient concentration and yield information for nine drainage 

basins evaluated in a national NAWQA study of undeveloped 

drainage basins (Clark and others, 2000) is included in this 

study for comparison (table 5; fig. 4). Station sequence 

numbers have been assigned to the 130 stations included in 

this report (table 5; fig. 4), and sequence numbers are shown 

in parentheses when specific monitoring stations or drainage 

basins are discussed. 

Geographic coverage of the region by USGS waterquality monitoring programs is not complete, and the period 

of water-quality record available varies in different parts of 

the region. The NASQAN Program was established in 1973 to 

compile long-term, consistent, baseline water-chemistry data 

for major streams of the United States (Ficke and Hawkinson, 

1975). The NASQAN Program was redesigned in 1995, and 

water-quality monitoring was discontinued on several major 

streams in the Northeast during the early 1990s (Alexander 

and others, 1996). State monitoring programs are conducted 

by the USGS in some states, and by State regulatory agencies 

in other states. In some areas of the region, responsibility for 

water-quality monitoring has transferred between the USGS 

and State agencies at several points, and no single source 

provides continuous monitoring data. For these reasons, some 

major drainage areas of the region are not fully represented in 

the analyses in this report. 

Water-quality constituents evaluated in this report include 

several nitrogen constituents, total phosphorus, and suspended 

sediment (table 6). Analytical methods for determining nutrient concentrations have changed during the period of time 

covered in this report. Methods for calculating “total” constituent concentrations also have changed for some constituents. 

Consequently, long-term records evaluated in this study may 

combine data from more than one parameter code for a waterquality constituent (appendix 1). 

Changes in analytical methods may affect the 

interpretation of some reported concentrations and time trends. 

A positive analytical bias of about 0.1 mg/L in total Kjeldahl 

nitrogen concentrations (as nitrogen), in samples analyzed by 

the USGS National Water Quality Laboratory from 1986 to 

the time of a method change in 1991, has been reported in a 

methods evaluation by Patton and Truitt (2000, p. 1, 29). The 

study further reports that nitrite-plus-nitrate concentrations 

greater than 1 mg/L (as nitrogen) may have caused either 

positive or negative interference in Kjeldahl nitrogen 

determinations during that period of time. The magnitude 

of the bias, however, is believed to be small relative to total 

nitrogen concentrations in most of the streams evaluated in 

this study. Additional discussion of the effects of changes in 

laboratory methods on historical nutrient data in the study area 

can be found in Zimmerman and others (1996, p. 29–30) and 

Trench (2000, p. 15). 
Data Selection and Screening 13

Table 5. Characteristics of 130 U.S. Geological Survey (USGS) water-quality monitoring stations evaluated in this study (with station sequence numbers keyed to fig. 4).—Continued[Source for station information: USGS National Water Information System (NWIS); mi2, square miles; x, analysis performed or available for that station; --, no analysis performed]

USGS 

station 

identification 

number

Station 

sequence 

number 

(fig. 4)

Station name

Drainage 

area 

(mi2)

Period 

analyzed in 

this report 

(water years)

Analyses

Trend analysis (Tobit 

regression, 

ESTREND), 

1993–2003

Trend 

analysis 

(statistical 

model), 

1975–2003

Trend 

analysis 

(statistical 

model), 

1993–2003

Load estimation 

(LOADEST)

Yields from 

national 

study (Clark 

and others, 

2000)

01036390 1 Penobscot River at Eddington, Maine 7,764 1980–94 -- -- -- x --01049265 2 Kennebec River at North Sidney, Maine 5,403 1979–93 -- -- -- x --01054200 3 Wild River at Gilead, Maine 69.6 1991–95 -- -- -- -- x01066000 4 Saco River at Cornish, Maine 1,293 1975–95 -- -- -- x --01095220 5 Stillwater River near Sterling, Mass. 31.6 1999–2003 -- -- -- x --01100000 6 Merrimack River below Concord River at Lowell, Mass. 4,635 1999–2003 -- -- -- x --01102500 7 Aberjona River at Winchester, Mass. 24.7 1999–2003 -- -- -- x --01104615 8 Charles River above Watertown Dam at Watertown, Mass. 271 2000 -- -- -- x --01111500 9 Branch River at Forestdale, R.I. 91.2 1993–2002 x -- -- -- --01116500 10 Pawtuxet River at Cranston, R.I. 200 1979–2002 x -- -- x --01118500 11 Pawcatuck River at Westerly, R.I. 295 1993–2002 x -- -- -- --01119375 12 Willimantic River at Merrow, Conn. 94.0 1993–2003 x -- -- -- --01122610 13 Shetucket River at South Windham, Conn. 408 1975–2003 x x x x --01124000 14 Quinebaug River at Quinebaug, Conn. 155 1982–2003 x x x x --01125100 15 French River at North Grosvenordale, Conn. 101 1993–2003 x -- -- -- --01125500 16 Quinebaug River at Putnam, Conn. 328 1999–2003 -- -- -- x --01125520 17 Quinebaug River at Cotton Bridge Road near Pomfret, Conn. 342 1995–2003 x -- -- -- --01127000 18 Quinebaug River at Jewett City, Conn. 713 1975–2003 x x x x --01137500 19 Ammonoosuc River at Bethlehem Junction, N.H. 87.6 1994–95 -- -- -- -- x01144000 20 White River at West Hartford, Vt. 690 1993–95 -- -- -- x --01170100 21 Green River near Colrain, Mass. 41.4 1994–95 -- -- -- -- x01184000 22 Connecticut River at Thompsonville, Conn. 9,660 1975–2003 x x x x --01184490 23 Broad Brook at Broad Brook, Conn. 15.5 1993–2003 x -- x x --01188000 24 Bunnell (Burlington) Brook near Burlington, Conn. 4.10 1975–2003 x x x x --01188090 25 Farmington River at Unionville, Conn. 378 1993–2003 x -- x x --01189030 26 Pequabuck River at Farmington, Conn. 57.2 1993–2003 x -- -- -- --01189995 27 Farmington River at Tariffville, Conn. 577 1975–2003 x x x x --01192500 28 Hockanum River near East Hartford, Conn. 73.4 1993–2003 x -- x x --01192704 29 Mattabesset River at Route 372 at East Berlin, Conn. 48.1 1995–2003 x -- -- -- --01193500 30 Salmon River near East Hampton, Conn. 100 1975–2003 x x x x --
14 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 Table 5. Characteristics of 130 U.S. Geological Survey (USGS) water-quality monitoring stations evaluated in this study (with station sequence numbers keyed to fig. 4). —Continued [Source for station information: USGS National Water Information System (NWIS); mi2, square miles; x, analysis performed or available for that station; --, no analysis performed] USGS station identi- fication number Station sequence number (fig. 4) Station name Drainage area (mi2

)

Period 

analyzed in 

this report 

(water years)

Analyses

Trend analysis (Tobit 

regression, 

ESTREND), 

1993–2003

Trend 

analysis 

(statistical 

model), 

1975–2003

Trend 

analysis 

(statistical 

model), 

1993–2003

Load estimation 

(LOADEST)

Yields from 

national 

study (Clark 

and others, 

2000)

01196222 31 Quinnipiac River near Meriden, Conn. 69.6 1993–2003 x -- -- -- --01196500 32 Quinnipiac River at Wallingford, Conn. 115 1975–2003 x x x x --01198125 33 Housatonic River near Ashley Falls, Mass. 465 1993–2003 x -- -- -- --01200600 34 Housatonic River near New Milford, Conn. 1,022 1993–2003 x -- -- -- --01201487 35 Still River at Route 7 at Brookfield Center, Conn. 62.3 1993–2003 x -- -- -- --01203000 36 Shepaug River near Roxbury, Conn. 132 1993–2003 x -- -- -- --01205500 37 Housatonic River at Stevenson, Conn. 1,544 1975–2003 x x x x --01208049 38 Naugatuck River near Waterville, Conn. 136 1993–2003 x -- -- -- --01208500 39 Naugatuck River at Beacon Falls, Conn. 260 1975–2003 x x x x --01208990 40 Saugatuck River near Redding, Conn. 21.0 1975–2003 x x x x --01209710 41 Norwalk River at Winnipauk, Conn. 33.0 1982–2003 x x x x --01309500 42 Massapequa Creek at Massapequa, N.Y. 38.0 1993–2001 x -- -- -- --01310500 43 East Meadow Brook at Freeport, N.Y. 31.0 1993–2001 x -- -- -- --01311000 44 Pines Brook at Malverne, N.Y. 10.0 1993–2001 x -- -- -- --01349150 45 Canajoharie Creek near Canajoharie, N.Y. 59.7 1994–2003 x -- -- x --01356190 46 Lisha Kill northwest of Niskayuna, N.Y. 15.6 1994–95, 

2001–03

-- -- -- x --

01357500 47 Mohawk River at Cohoes, N.Y. 3,450 1993–2003 x -- x x --01362200 48 Esopus Creek at Allaben, N.Y. 63.7 1994–95 -- -- -- -- x01367770 49 Wallkill River near Sussex, N.J. 60.8 1993–2003 x -- -- -- --01377000 50 Hackensack River at Rivervale, N.J. 58.0 1975–2003 x x x x --01381800 51 Whippany River near Pine Brook, N.J. 68.5 1993–2003 x -- -- -- --01382000 52 Passaic River at Two Bridges, N.J. 361 1993–2003 x -- -- -- --01382500 53 Pequannock River at Macopin Intake Dam, N.J. 63.7 1993–2003 x -- x x --01387500 54 Ramapo River near Mahwah, N.J. 120 1975–2003 x x x x --01389500 55 Passaic River at Little Falls, N.J. 762 1979–2003 x x x x --01391500 56 Saddle River at Lodi, N.J. 54.6 1975–2003 x x x x --01394500 57 Rahway River near Springfield, N.J. 25.5 1993–2003 x -- x x --01395000 58 Rahway River at Rahway, N.J. 40.9 1993–2003 x -- x x --01396660 59 Mulhockaway Creek at Van Syckel, N.J. 11.8 1993–2003 x -- x x --01397000 60 South Branch Raritan River at Stanton, N.J. 147 1992–97 -- -- -- x --
Data Selection and Screening 15

Table 5. Characteristics of 130 U.S. Geological Survey (USGS) water-quality monitoring stations evaluated in this study (with station sequence numbers keyed to fig. 4).—Continued[Source for station information: USGS National Water Information System (NWIS); mi2, square miles; x, analysis performed or available for that station; --, no analysis performed]

USGS 

station 

identification 

number

Station 

sequence 

number 

(fig. 4)

Station name

Drainage 

area 

(mi2)

Period 

analyzed in 

this report 

(water years)

Analyses

Trend analysis (Tobit 

regression, 

ESTREND), 

1993–2003

Trend 

analysis 

(statistical 

model), 

1975–2003

Trend 

analysis 

(statistical 

model), 

1993–2003

Load estimation 

(LOADEST)

Yields from 

national 

study (Clark 

and others, 

2000)

01398000 61 Neshanic River at Reaville, N.J. 25.7 1993–2003 x -- x x --01399500 62 Lamington (Black) River near Pottersville, N.J. 32.8 1984–97 -- -- -- x --01399780 63 Lamington River at Burnt Mills, N.J. 100 1993–2003 x -- -- -- --01400000 64 North Branch Raritan River near Raritan, N.J. 190 1998–2003 -- -- -- x --01400500 65 Raritan River at Manville, N.J. 490 1976–97 -- -- -- x --01401000 66 Stony Brook at Princeton, N.J. 44.5 1984–98 -- -- -- x --01402000 67 Millstone River at Blackwells Mills, N.J. 258 1993–2003 x -- x x --01403300 68 Raritan River at Queens Bridge at Bound Brook, N.J. 804 1982–2003 x x x x --01405340 69 Manalapan Brook at Federal Road near Manalapan, N.J. 20.9 1993–2003 x -- -- -- --01408000 70 Manasquan River at Squankum, N.J. 44.0 1993–2003 x -- x x --01408500 71 Toms River near Toms River, N.J. 123 1975–2003 x x x x --01409387 72 Mullica River at outlet of Atsion Lake at Atsion, N.J. 26.7 1993–2003 x -- -- -- --0140940950 73 Blue Anchor Brook at Elm, N.J. 4.86 1993–2003 x -- -- -- --01409416 74 Hammonton Creek at Wescoatville, N.J. 9.57 1993–2003 x -- -- -- --01409500 75 Batsto River at Batsto, N.J. 67.8 1993–2003 x -- x x --01410150 76 East Branch Bass River near New Gretna, N.J. 8.11 1993–2003 x -- -- -- --01411110 77 Great Egg Harbor River at Weymouth, N.J. 154 1993–2003 x -- -- -- --01411500 78 Maurice River at Norma, N.J. 112 1975–2003 x x x x --01412800 79 Cohansey River at Seeley, N.J. 28.0 1993–2003 x -- -- -- --01434000 80 Delaware River at Port Jervis, N.Y. 3,070 1999–2001 -- -- -- x --01434025 81 Biscuit Brook above Pigeon Brook at Frost Valley, N.Y. 3.72 1991–95 x -- -- -- x01438500 82 Delaware River at Montague, N.J. 3,480 1993–2003 x -- x x --01440000 83 Flat Brook near Flatbrookville, N.J. 64.0 1994–2003 x -- -- -- --01443000 84 Delaware River at Portland, Pa. 4,165 1993–2003 x -- -- -- --01443500 85 Paulins Kill at Blairstown, N.J. 126 1979–2003 x x x x --01451800 86 Jordan Creek near Schnecksville, Pa. 53.0 1999–2001 -- -- -- x --01457400 87 Musconetcong River at Riegelsville, N.J. 156 1993–2003 x -- -- -- --01457500 88 Delaware River at Riegelsville, N.J. 6,328 1993–2003 x -- -- -- --01461000 89 Delaware River at Lumberville, Pa. 6,598 1993–2003 x -- -- -- --01463500 90 Delaware River at Trenton, N.J. 6,780 1975–2003 x x x x --
16 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 Table 5. Characteristics of 130 U.S. Geological Survey (USGS) water-quality monitoring stations evaluated in this study (with station sequence numbers keyed to fig. 4). —Continued [Source for station information: USGS National Water Information System (NWIS); mi2, square miles; x, analysis performed or available for that station; --, no analysis performed] USGS station identi- fication number Station sequence number (fig. 4) Station name Drainage area (mi2

)

Period 

analyzed in 

this report 

(water years)

Analyses

Trend analysis (Tobit 

regression, 

ESTREND), 

1993–2003

Trend 

analysis 

(statistical 

model), 

1975–2003

Trend 

analysis 

(statistical 

model), 

1993–2003

Load estimation 

(LOADEST)

Yields from 

national 

study (Clark 

and others, 

2000)

01464515 91 Doctors Creek at Allentown, N.J. 17.4 1993–2003 x -- -- -- --01464907 92 Little Neshaminy Creek at Valley Road near Neshaminy, Pa. 26.8 2000–03 -- -- -- x --01466500 93 McDonalds Branch in Byrne State Forest, N.J. 2.35 1991–95 -- -- -- -- x01467000 94 North Branch Rancocas Creek at Pemberton, N.J. 118 1993–2001 x -- -- -- --01467150 95 Cooper River at Haddonfield, N.J. 17.0 1993–2003 x -- x x --01472157 96 French Creek near Phoenixville, Pa. 59.1 1999–2003 -- -- -- x --01474500 97 Schuylkill River at Philadelphia, Pa. 1,893 1975–94, 

1999–2003

x x -- x --

01477120 98 Raccoon Creek near Swedesboro, N.J. 26.9 1975–2003 x x x x --01482500 99 Salem River at Woodstown, N.J. 14.6 1993–2003 x -- -- -- --01487000 100 Nanticoke River near Bridgeville, Del. 75.4 1998–2001 -- -- -- x --01491000 101 Choptank River near Greensboro, Md. 113 1975–2003 x x x x --01493112 102 Chesterville Branch near Crumpton, Md. 6.12 1997–2002 -- -- -- x --01540500 103 Susquehanna River at Danville, Pa. 11,220 1975–95 -- -- -- x --01545600 104 Young Womans Creek near Renovo, Pa. 46.2 1991–95 -- -- -- -- x01553500 105 West Branch Susquehanna River at Lewisburg, Pa. 6,847 1975–95 -- -- -- x --01555400 106 East Mahantango Creek at Klingerstown, Pa. 44.7 1997–2000 -- -- -- x --01559795 107 Bobs Creek near Pavia, Pa. 16.6 1998–2000 -- -- -- x --01571490 108 Cedar Run at Eberlys Mill, Pa. 12.6 1994–95 -- -- -- x --01576521 109 Big Spring Run near Willow Street, Pa. 1.77 1993–2001 x -- -- -- --01576529 110 Unnamed Tributary to Big Spring Run near Lampeter, Pa. 1.42 1993–2001 x -- -- -- --

-- --

01578310 111 Susquehanna River at Conowingo, Md. 27,100 1979–2003 x x x x --01591000 112 Patuxent River near Unity, Md. 34.8 1986–2001 x -- -- x --01594000 113 Little Patuxent River at Savage, Md. 98.4 1986–2000 -- -- -- x --01594440 114 Patuxent River near Bowie, Md. 348 1979–2003 x x x x --01608000 115 South Fork South Branch Potomac River near Moorefield, 

W. Va.

277 1994–95 -- -- -- -- x
Data Selection and Screening 17

Table 5. Characteristics of 130 U.S. Geological Survey (USGS) water-quality monitoring stations evaluated in this study (with station sequence numbers keyed to fig. 4).—Continued[Source for station information: USGS National Water Information System (NWIS); mi2, square miles; x, analysis performed or available for that station; --, no analysis performed]

USGS 

station 

identification 

number

Station 

sequence 

number 

(fig. 4)

Station name

Drainage 

area 

(mi2)

Period 

analyzed in 

this report 

(water years)

Analyses

Trend analysis (Tobit 

regression, 

ESTREND), 

1993–2003

Trend 

analysis 

(statistical 

model), 

1975–2003

Trend 

analysis 

(statistical 

model), 

1993–2003

Load estimation 

(LOADEST)

Yields from 

national 

study (Clark 

and others, 

2000)

01614500 116 Conococheague Creek at Fairview, Md. 494 1993–2003 x -- x x --01618000 117 Potomac River at Shepherdstown, W. Va. 5,939 1979–93, 

2001–02

-- -- -- x --

01621050 118 Muddy Creek at Mount Clinton, Va. 14.3 1994–2001 x -- -- x --01631000 119 South Fork Shenandoah River at Front Royal, Va. 1,634 1996–2002 -- -- -- x --01634000 120 North Fork Shenandoah River near Strasburg, Va. 770 1996–2002 -- -- -- x --01636500 121 Shenandoah River at Millville, W. Va. 3,041 1979–95 -- -- -- x --01646580 122 Potomac River at Chain Bridge, at Washington, D.C. 11,570 1975–2003 x x x x --01654000 123 Accotink Creek near Annandale, Va. 23.9 1993–2001 x -- -- x --01668000 124 Rappahannock River near Fredericksburg, Va. 1,595 1979–2003 x x x x --01673000 125 Pamunkey River near Hanover, Va. 1,078 1975–2003 x x x x --01674500 126 Mattaponi River near Beulahville, Va. 603 1979–2003 x x x x --02035000 127 James River at Cartersville, Va. 6,252 1975–2003 x x x x --02038850 128 Holiday Creek near Andersonville, Va. 8.54 1991–95 -- -- -- -- x02041650 129 Appomattox River at Matoaca, Va. 1,342 1979–2003 x x x x --04296000 130 Black River at Coventry, Vt. 122 1978–94 -- -- -- x --

Number of stations analyzed 90 32 46 84 9
18 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Figure 4. Locations of 130 U.S. Geological Survey water-quality monitoring stations evaluated in this study (with station sequence 

numbers keyed to table 5).

48°

36°

82° 66°

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

1990 Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

9

10

11

12

13

14

15 16

17

18

22

23

24

25

26

27

28

29 30 31

32

33

34

35

36

37

38

39

40

41

48

49

50

5152

53 54

55 56

57

58 59

60 61

62

63 64

65

66

67

68

69

70

71

72

74 75 76

78 77 79

80

81

82

83

84 85

87 88

89

90

91 92

93

94 95

98

99

73

MASSACHUSETTS

CONNECTICUT

97

44 43 42

Philadelphia

Newark New York

City

Hartford

Providence

NEW YORK

PENNSYLVANIA

NEW JERSEY

MASSACHUSETTS

CONNECTICUT

RHODE

ISLAND

Trenton

Long Island

Inset Map

Long Island Sound

Narragansett

Bay

0 50 MILES

0 50 KILOMETERS

Delaware River

Hudson River

1

2

4

3

5 6

7

8

19

130

20

21 45 46 47

96

100

103

104

105

106

107

108 110

111

112

114 115

117

118

122

123

124

125

126

127 128

129

86

116

119

120 113

109

121

101

102

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUT RHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

Chesapeake Bay

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Augusta

Montpelier

Albany Boston

Concord

Richmond

Harrisburg Trenton

Dover

Annapolis

Hartford

Providence

Washington,

D.C.

Baltimore

Philadelphia

Newark

New York City

See Inset Map

Long Island Sound Narragansett

Bay

Cape

Cod

Bay

Buzzards Bay

ATLANTIC OCEAN

ATLANTIC OCEAN

Delaware

Bay

Shenandoah

R.

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Connecticut River

Merrimack River

Saint John River

Lake

Champlain

James River

Penobscot River

Kennebec River

EXPLANATION

Study area boundary

Washington, D.C.

State capital

City, over 250,000 population

USGS water-quality monitoring

 station, with sequence 

 number (table 5)

7
Methods of Data Analysis 19

Data from State Monitoring Programs

State nutrient data sets, and some municipal datasets for 

drinking water sources, were investigated during the initial 

phase of this study, but compilation, screening, and analysis of 

these data were beyond the scope of this report. These datasets 

represent a valuable resource for understanding nutrient conditions in the streams of the region, and provide coverage for 

some geographic areas that are not monitored through USGS 

programs. State nutrient datasets have been incorporated in a 

USGS NAWQA study that is modeling regional nutrient loads 

(R.M. Moore, U.S. Geological Survey, oral commun., 2008), 

and also are used in studies of the USGS Chesapeake Bay 

Program (CBP) (Langland and others, 2006). 

Methods of Data Analysis

USGS streamflow and water-quality data for the region 

were evaluated and analyzed by using several methods. 

Streamflow conditions were characterized for several time 

periods to evaluate streamflow during periods of water-quality 

analyses, and streamflow data were analyzed for trends. 

Streamgages used in the streamflow analysis, and a table 

of analyses performed, are shown in appendix 2. Nutrient 

data, and a small amount of suspended sediment data, were 

analyzed for flow-adjusted and non-flow-adjusted trends in 

concentrations. Annual constituent loads were estimated, and 

annual loads were analyzed for trends. All the methods for 

analysis of nutrient trends and loads involve relating nutrient 

concentrations to variables of streamflow, time, and season. 

The methods are described in more detail in the following sections and in appendixes 3 and 4. Results of trend analyses and 

other statistical tests were considered significant if the attained 

significance level of the test (p-value) was less than or equal to 

0.05, and were considered highly significant if the p-value was 

less than or equal to 0.01. Trend counts summarized in this 

report include both significant and highly significant trends, 

unless otherwise specified. 

Exploratory analyses for water-quality data included: 

tabular compilations of water-quality samples by year for each 

constituent of interest at each water-quality station; plots of 

concentration as a function of time; and plots of concentration 

Table 6. Water-quality constituents retrieved for study, including constituent name, parameter code, and listing of 

parameter codes used in analyses in this report.

[Water-quality constituents evaluated shown in bold. Parameter codes refer to laboratory methods for determining constituent concentrations. 

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

Water-quality constituent Parameter 

code

Parameter codes used in analyses 

(shown in order of priority for each constituent)

Nitrogen, total, as N, mg/L 00600, (00625 + 00631), (00623 + 49570 + 00631)

Nitrogen, total, as N, mg/L 00600

Ammonia, dissolved, as N, mg/L 00608 00608

Nitrate, dissolved, as N, mg/L 00618

Nitrate, total, as N, mg/L 00620

Ammonia-plus-organic nitrogen, dissolved, as N, mg/L 00623

Ammonia-plus-organic nitrogen, total, as N, mg/L 00625 00625

Nitrite-plus-nitrate, dissolved, as N, mg/L 00631, 00630, 00618, 00620

Nitrite-plus-nitrate, dissolved, as N, mg/L 00631

Nitrite-plus-nitrate, total, as N, mg/L 00630

Nitrogen, particulate, as N, mg/L 49570

Phosphorus, total, as P, mg/L 00665, (00667 + 00666)

Phosphorus, total, as P, mg/L 00665

Phosphorus, dissolved, as P, mg/L 00666

Phosphorus, particulate, as P, mg/L 00667

Suspended sediment, mg/L 80154 80154
20 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

as a function of stream discharge. A LOESS smoothing 

procedure in S-Plus (Insightful Corporation, 2002; TIBCO 

Software, Inc., 2008) has been used to identify generalized 

time trends, or other relations between variables, in the plots in 

this report. Outliers (values substantially outside the expected 

range) were identified and checked for validity by using several approaches. A small number of outliers were omitted from 

the analyses, on the basis of information that indicated the 

values were inaccurate. 

Selected ancillary datasets were analyzed to evaluate 

the effects of land use, population density, and point-source 

discharges on nutrient trends and loads. Compilation and 

analysis of point-source data for the whole region was beyond 

the scope of this report. Four drainage basins were selected 

for analysis of point-source information: the Quinebaug River 

Basin in Connecticut, the Raritan River Basin in New Jersey, 

the Patuxent River Basin in Maryland, and the James River 

Basin in Virginia. 

Streamflow Analysis

Streamflow data for 96 USGS streamgages in the region 

were analyzed to evaluate annual variability; to define low, 

average, and high flow years; to evaluate changes over time; to 

compare streamflow conditions during the recent period, 1993 

to 2003, to a reference period of 1970–2003; and to place 

the recent period in the context of longer-term data (records 

extending back to 1944 or earlier). Statistical analyses for 

selected streamgages included: (1) computing streamflow statistics such as the averages and percentiles of daily and annual 

mean flows, and (2) evaluating time-series plots of annual 

mean streamflow for the full period of record, with the annual 

median flow statistics computed for each of the three periods. 

Exploratory data analysis included review of flow-duration 

curves for each of the three periods for selected streamgages. 

The network of 96 streamgages used to summarize and evaluate streamflow represents a wide range of stream types and 

drainage basins—from steep, mountainous streams to lowgradient, meandering streams; from small streams to large 

rivers; and from mostly forested basins to urban environments 

(appendix 2, table 2–1). 

Daily-mean streamflow data were retrieved from the 

USGS National Water Information System (NWIS) and were 

used to generate annual mean and annual median flow statistics by water year (U.S. Geological Survey, 2009b; 2002). In 

general, annual mean flow is larger than the annual median 

flow because high flows often associated with storms affect 

the mean more than the median. Typically, high annual median 

flow results from an overall wet year. Percentiles calculated 

from the annual mean and annual median flows were used 

to identify low, average, and high annual mean and annual 

median flow years for selected streamgages. Annual mean 

and annual median flows from the 25th to the 75th percentiles were considered average (normal) flow years; flows less 

than the 25th percentile were considered low-flow years; 

and flows exceeding the 75th percentile were considered 

high-flow years. In addition, annual mean and annual median 

flows less than the 10th percentile were considered extremely 

low-flow years and flows greater than the 90th percentile were 

considered extremely high-flow years. Flow-duration curves 

constructed by using the daily-mean streamflow values were 

reviewed to compare how flow characteristics during the 

recent period differ from the reference period of 1970–2003 

and the long-term (60 years or more) full period of record. 

Flow-duration curves show the percentage of time during 

which a specified streamflow was equaled or exceeded in a 

given time period. 

Annual statistics of runoff from 1901 to 2003 were 

retrieved from the USGS WaterWatch web site for Hydrologic 

Region 01, the New England region, and Hydrologic Region 

02, the mid-Atlantic region (U.S. Geological Survey, 

2009c; Jian and others, 2008) and were used to summarize 

regional runoff. Hydrologic Regions are also referred to as 

Hydrologic Units, because all drainage areas in this system of 

classification are identified by Hydrologic Unit Codes (HUCs) 

on a scale from large regions to smaller local drainage basins 

(Natural Resources Conservation Service, 2009). The New 

England region is identified as HUC 01 and the mid-Atlantic 

region as HUC 02. 

Runoff is the amount of water running off a drainage 

area, measured in units that can be compared from one drainage area to another, and is expressed as the depth to which 

the drainage area would be covered by water (in inches), if 

all the water flowing from the basin were uniformly distributed over the drainage basin. Runoff for HUC 01 and HUC 

02 was determined by averaging the runoff from the basins in 

each HUC that had complete records of daily mean flow for 

the water year. The number of basins with daily mean flow 

data used to estimate annual runoff varies from year to year 

because certain time periods had fewer gaged basins. Annual 

runoff for each basin is determined for each water year by 

dividing the average daily flow for the water year by the basin 

drainage area. Annual runoff for each HUC is then determined 

by averaging the runoff from all the basins within each HUC, 

to provide a regional estimate of runoff. 

Streamflows also were compared regionally and over 

time by using the coefficient of variation. The coefficient of 

variation for annual runoff is defined as the standard deviation divided by the mean. The result is a ratio, or percentage. 

For comparison of streamflow conditions, the coefficient of 

variation equals the standard deviation divided by the mean 

of the annual runoff dataset for each period. The coefficient 

of variation was computed for the three periods of record for 

each group of streamgages evaluated. This statistic allows 

for direct comparisons in the variability of the annual runoff 

between periods of record for a given geographic area, and 

between regions with differences in annual runoff values during the same time period. Time periods or geographic areas 

with the lowest coefficient of variation have the least variability in the annual runoff. When comparing statistical results 

among different periods for a group of streamgages, a longer 
Methods of Data Analysis 21

time period generally includes more extreme climatic years 

and has a higher coefficient of variation. Other statistics used 

to characterize and compare streamflows include the mean and 

median of the annual runoff, and standard deviation. 

Streamflow data also were evaluated for trend, for the 

stations that were evaluated for trends in nutrient concentrations and loads. Long-term and recent records of daily mean 

streamflow for these streamgages were analyzed for trends 

by using methods described in the section entitled “Instream 

Trend Analysis with Coupled Statistical Streamflow and 

Water-Quality Model.”

Analysis of Trends in Nutrient Concentrations, 

Nutrient Loads, and Streamflow

Trends in nutrient concentrations, nutrient loads, and 

streamflow were identified by using two approaches described 

in the following sections. Tobit regression in the ESTREND 

system (Slack and others, 2003) was used to analyze flowadjusted trends in constituent concentrations during the 

1993–2003 period. A statistical modeling program has been 

developed by the USGS to analyze trends in streamflow, 

flow-adjusted constituent concentrations, non-flow-adjusted 

constituent concentrations, and stream constituent loads (G.E. 

Schwarz, U.S. Geological Survey, written commun., 2006). 

This statistical modeling program was used to analyze trends 

during the 1993–2003 and 1975–2003 periods. The two programs provide different capabilities that expanded the range of 

the analysis for this report. 

Flow-adjusted trends account for (or remove) the effects 

of natural fluctuations in streamflow on concentrations. 

Because the results are unaffected by these streamflow variations, flow-adjusted trend results provide an indication of 

water-quality changes resulting from changes in a watershed, 

such as implementation of management and pollution-control 

measures or changes in land use. Non-flow-adjusted trend 

results provide an indication of changes in the actual instream 

water-quality conditions that affect aquatic habitat and other 

resource uses. 

The parametric methods of trend analysis used in this 

study assume the presence of linear (monotonic) trends. A significant trend refers to a linear change between the beginning 

and the end of the period of record analyzed. During long periods of time, however, many constituent trends are nonmonotonic. The assumption that any trend is linear oversimplifies 

the reality of changes in streamflow, constituent concentration, 

flow-adjusted concentration, or constituent load over time. 

Although a nonlinear trend violates the linearity assumption 

of the trend methods, and may introduce some bias into the 

results, the presence of a nonlinear trend does not invalidate 

the trend results. Without knowledge of the true form of the 

trend, any trend function, including functions that incorporate 

nonlinearities, may overestimate or underestimate the trend 

(G.E. Schwarz, U.S. Geological Survey, written commun., 

2010). Trend results reported for this study, particularly trends 

for the long-term period, should be evaluated with the understanding that there may be some bias in the attained significance level of the trend tests (p-values) where the direction, or 

slope, of the trend has varied over time. Constituent concentrations or loads have changed substantially during the period 

of analysis at many stations, and simple plots of these values 

over time add strength to the argument that significant trends 

are, in fact, present. More detailed and intensive methods of 

analysis for individual stations and constituents could refine 

the identification of variable changes over time, but these 

methods are beyond the scope of this study, in which a large 

number of stations and constituents are evaluated to provide a 

broad picture of regional conditions. 

Flow-Adjusted Trend Analysis with Tobit 

Regression

USGS water-quality stations were selected for analysis 

of flow-adjusted trends in total nitrogen and total phosphorus 

based on the availability of nutrient concentration data during 

water years 1993–2003 and the availability of a streamflow 

measurement associated with each water-quality value. Trends 

in dissolved nitrite-plus-nitrate and dissolved ammonia were 

analyzed at stations in the four basins selected for analysis of 

point source information. 

Trends in flow-adjusted nutrient concentrations were 

identified with the S-PLUS version of the ESTREND system 

(Insightful Corporation, 2002; Slack and others, 2003; TIBCO 

Software, Inc., 2008). The Estimate Trend (ESTREND) 

Program (Schertz and others, 1991) was developed by the 

USGS to identify trends in water quality in streams. The 

ESTREND system provides three methods to identify trends, 

and Tobit regression was the method selected for this study. 

For each nutrient at each station, an equation was developed 

relating water quality to year, streamflow, and season. Aspects 

of the Tobit regression method are described by Helsel and 

Hirsch (2000, p. 372), and details of the application in this 

study are provided in appendix 3. 

Nutrient data for 90 stations were analyzed for trend, for 

periods ranging from 8 to 11 water years, depending on the 

amount and distribution of data. Trend tests for a station are 

reported if the dataset contained sufficient nutrient measurements to start the period of analysis during water years 1993, 

1994, or 1995 and end the period of analysis during water 

years 2001, 2002, or 2003. 

Instream Trend Analysis with Coupled Statistical 

Streamflow and Water-Quality Model

Determination of trends in instream water quality requires 

an approach that accommodates data with multiple changes in 

water-quality sampling intervals and in the types of streamflow conditions sampled. In many previous trend studies, trend 

analysis programs such as ESTREND have been applied to the 

reported instream concentrations during the period of interest, 
22 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

to understand water-quality changes that riverine habitats have 

actually experienced. Applying this type of trend analysis is an 

acceptable practice where monitoring programs collect waterquality samples at fixed intervals, without regard to streamflow, and the resulting samples represent a range of streamflow 

conditions during a period of several years. However, many 

monitoring programs have sampled streams intensively during 

high streamflow or low streamflow to evaluate specific conditions, and thus the range of constituent concentrations sampled 

during some parts of the period of record may be biased. 

Consequently, trend analyses on instream concentrations can 

be biased as well. 

A different approach for assessing instream waterquality changes is necessary because of the potential for 

biased trend results when trend programs are applied to data 

from sampling programs focused on specific hydrologic 

conditions. The approach developed for this study, and for 

similar nutrient studies in other regions of the country, uses a 

coupled streamflow model and water-quality model to derive a 

non-flow-adjusted trend in concentration (G.E. Schwarz, U.S. 

Geological Survey, written commun., 2006). The streamflow 

model and the water-quality model are estimated in natural 

logarithm space. The non-flow-adjusted trend in concentration 

derived from these models is referred to as the “modeled 

instream concentration trend” in this report. Because the 

water-quality model used to derive these trends includes 

streamflow as a predictor, the estimates of trend are immune 

to the bias arising from preferential water-quality sampling 

during extreme streamflow. 

This coupled statistical model provides trend results for 

streamflow, flow-adjusted constituent concentrations, nonflow-adjusted constituent concentrations (“modeled instream 

concentrations”), and constituent loads. A narrative explanation of this modeling approach is provided in appendix 4, 

and the detailed mathematical basis for the model has been 

presented by Sprague and others (2007, p. 10–12). In simplest 

terms, the streamflow model, which is estimated from all daily 

streamflow measurements during the period of analysis, relates 

the logarithm of daily streamflow to an intercept, a linear trend 

term (decimal time), sine and cosine functions of decimal time 

(to describe the seasonal component of flow), and a serially 

correlated error term; the streamflow residual is assumed to 

follow an autoregressive process of order 30 (AR(30)) (Fuller, 

1996). The streamflow model is estimated by using maximumlikelihood estimation methods as employed by the AUTOREG

procedure in SAS 9, version 1, release 2 (SAS Institute, Inc., 

2004). The high-order autoregressive process is necessary to 

remove as much serial correlation as possible from the flow 

residuals, thereby reducing bias in the estimated coefficient 

covariance matrix of the streamflow model. 

The water-quality model, estimated from constituent 

concentrations measured during the analysis period, relates 

the logarithm of constituent concentration to the terms in the 

streamflow model and also to functions of the logarithm of 

streamflow. Model results also include estimates of unit trends, 

that is, trends expressed in units of concentration or load per 

year, and also the reference concentrations and reference loads 

that are used to derive the unit trends. Reference flows, computed from streamflow model results, are essentially estimates 

of median daily streamflow for the period of analysis (G.E. 

Schwarz, U.S. Geological Survey, written commun., 2006). 

Estimation of Nutrient Loads

USGS water-quality stations were selected for estimation of annual nutrient loads on the basis of the availability of 

nutrient concentration data during water years 1975–2003 or 

1993–2003 and the availability of a complete record of daily 

mean stream discharge values for each year of interest. Annual 

stream nutrient loads were estimated for 32 water-quality 

monitoring stations for the period 1975–2003 and for 46 stations for the period 1993–2003 (table 5). Annual loads were 

estimated for 31 of these stations for both periods of record. 

One station, the Schuylkill River at Philadelphia, was included 

in the long-term period, but data for the station did not meet 

criteria for the recent period because of a four-year break in 

the water-quality record during water years 1995–98. For 

the recent period all stations had water-quality and discharge 

records beginning with the 1993 water year and ending with 

the 2003 water year. A few stations had one missing year of 

water-quality record during that period. For the long-term 

period, the beginning year of water-quality record varied 

among stations, and stations were grouped for load estimation with initial years of 1975, 1979, and 1982. All long-term 

annual load estimates ended with the 2003 water year. Annual 

loads were estimated for all years in the 1975–2003 period for 

the Schuylkill River at Philadelphia, including the four-year 

break in the water-quality record. 

Annual loads were estimated for 37 additional stations 

that had less than the full 1993–2003 period of record, to 

provide better geographic coverage of the region and representation of specific land uses in the results. Criteria for selection 

of additional stations were as follows: at least one integrator 

drainage basin (station monitoring a large drainage basin with 

varied land uses), one urban basin, one agricultural basin, and 

one forested basin in each of the NAWQA study units, where 

available; large drainage basins in under-represented areas 

of the region; small drainage basins with no point sources in 

under-represented areas of the region; and recommendations 

of NAWQA study unit staff. Water-quality records for these 

37 stations ranged in length from 1 to 10 years during the 

1993–2003 period and from 14 to 24 years during the 1975–

2003 period. Annual loads were estimated for all available 

years of record during the 1975–2003 period. 

Annual nutrient loads for all stations analyzed were 

normalized by drainage area and converted to annual yields 

in pounds per square mile for comparison among drainage 

basins. Mean annual nutrient yields for undeveloped drainage 

basins have been estimated in a national study by Clark and 

others (2000). Nine of the basins in the national study are in 

the northeastern region covered by this report. Mean annual 
Methods of Data Analysis 23

nutrient yields for these nine basins are presented in this report 

as a benchmark of conditions in relatively undeveloped and 

near-pristine watersheds of the region. 

Annual stream nutrient loads were estimated by using a 

multiple-linear-regression model contained in the computer 

program LOADEST, applied in the S-PLUS version of the 

program (Insightful Corporation, 2002; Runkel and others, 

2004; TIBCO Software, Inc., 2008). Given a time series of 

streamflow, additional data variables, and constituent concentration for a monitoring station, LOADEST assists the user 

in developing a regression model for estimating the stream 

load of a specific constituent at that location. This step is the 

calibration phase of the model. Explanatory variables in the 

regression model include various functions of streamflow, 

decimal time, and season, and can include additional userspecified data variables. The formulated regression model 

then is used in the estimation phase of the model, to estimate 

annual constituent loads during a user-specified time interval. 

Mean load estimates, standard errors, and 95-percent confidence intervals are developed on an annual basis. 

The calibration and estimation procedures in LOADEST are based on three statistical estimation methods. The 

first two methods, Adjusted Maximum Likelihood Estimation 

(AMLE) and Maximum Likelihood Estimation (MLE), are 

appropriate when the calibration model errors (residuals) are 

normally distributed. AMLE is the method of choice when 

the calibration dataset (time series of streamflow, additional 

data variables, and concentration) contains censored data. The 

third method, Least Absolute Deviation (LAD), is an alternative to maximum likelihood estimation when the residuals are 

not normally distributed and the dataset contains no censored 

data (Runkel and others, 2004). The AMLE method was used 

for all load estimates in this report because of censored data in 

most of the nutrient datasets. 

The LOADEST Program includes several predefined 

models that specify the form of the regression equation 

(Runkel and others, 2004, p. 12, table 7). A model may be 

selected by the user, on the basis of the user’s knowledge 

of the hydrologic and biogeochemical system of the stream. 

Alternatively, the software provides an automated model 

selection option to select the “best” model from the set of 

predefined models, on the basis of statistics computed for 

the full set of models (Runkel and others, 2004, p. 7). The 

“best” model option was used for most of the stations and 

constituents analyzed in this report. 

Analysis of Nutrient Sources

Nutrient sources in the region are numerous and complex, and a comprehensive evaluation of sources was beyond 

the scope of this report. Selected information on land use and 

population density for the region, and information on point 

sources in a small number of drainage basins, was compiled 

to provide an overview of some of the critical nutrient sources 

affecting stream nutrient conditions in the region. 

Land Use and Population Density

Land use and population data used in this report were 

developed by the USGS to support the analyses of surfacewater quality and aquatic ecological data by NAWQA 

regional studies (N. Nakagaki, U.S. Geological Survey, 

written commun., 2005). Population data were also obtained 

from the U.S. Census Bureau (Forstall, 1995; Hobbs and 

Stoops, 2002; U.S. Census Bureau, 2000, 2001). The land 

use dataset is the August 2005 enhanced version of the circa 

1992 National Land Cover Dataset, known as the “NLCDe 

92” dataset (Vogelmann and others, 1998; enhanced as 

described by Nakagaki and Wolock, 2005). The 25 detailed 

land-cover categories in this dataset have been aggregated 

into the following major categories for use in this report: 

total urban land, total agricultural land, total developed 

land (includes urban land, agricultural land, and other 

miscellaneous developed land uses), total forested land, and 

total undeveloped land (includes forested land). 

Monitored drainage basins have been assigned to the 

following five land-use categories on the basis of percentages of urban and agricultural land in the drainage basin 

upstream from each monitoring station: Undeveloped (UN), 

Urban (UR), Urban/Agricultural (UA), Agricultural (AG), and 

Agricultural/Urban (AU) (table 7). Effects on water quality 

from agricultural and urban land uses are generally much more 

pronounced than the effects of undeveloped land. Consequently, in this report, developed land uses covering less than 

half of a drainage basin are used to identify the predominant 

land use affecting water quality, even though the land use is 

not predominant in a spatial context. Most monitored drainage areas in the northeastern United States include mixed land 

uses, and consequently nutrient impairments are derived from 

multiple sources. 

Land-use categories defined for this report differ from the 

categories used by the NAWQA Program in national studies 

(described by Mueller and Spahr, 2006, p. 7–8), although both 

classification schemes are based on the land cover with the 

predominant effect on water quality in a drainage basin. For 

example, an Urban drainage basin as defined by the NAWQA 

Program is usually more than 25 percent urban and less than 

25 percent agricultural. In the northeastern United States, 

however, many streams with more than about 10 percent urban 

land in their watersheds also are receiving waters for one or 

more municipal point sources, and urbanized land is concentrated close to rivers and streams. The urban point-source 

signature is generally apparent in various measures of water 

quality in these streams, and consequently, the presence of 

10 percent urbanized land is considered a reasonable threshold 

for urban effects. Likewise, an Agricultural drainage basin 

as defined by the NAWQA Program is generally more than 

50 percent agricultural and less than 5 percent urban. Only a 

few of the stations for which nutrient loads were estimated 

in this report have drainage basins that meet this definition, 

and yet many other drainage basins in the region with lower 

percentages of agricultural land are affected by agricultural 
24 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

nutrient sources. Consequently, a lower threshold of 20 percent agricultural land (with urban land less than 10 percent) 

was used in this report to define a drainage basin as Agricultural. The threshold percentage for defining a drainage basin 

as urban is lower than the threshold percentage for defining a 

drainage basin as agricultural in both classification schemes. 

Likewise in both classification schemes, Undeveloped drainage basins have more than 70 percent undeveloped land. 

Undeveloped land is almost entirely forested land in the northeastern United States. The undeveloped land-use category in 

this report includes drainage basins with undeveloped land 

ranging from 74.1 to 100 percent of basin area. 

The NAWQA Program also defines a category of Large 

drainage basins, on the basis of a combination of drainage area 

(generally greater than about 600 mi2) and long-term mean 

annual streamflow, to account for the effects of a complex 

mixture of land cover, multiple point sources, and temporally variable sources of streamflow in these drainage basins. 

This category of size distinction has not been included in 

this report. Many large drainage basins, including some with 

multiple point sources, are classified as Undeveloped on the 

basis of land-use percentages. For example, the drainage area 

of the Connecticut River at Thompsonville, Conn., is 5 percent 

urban, 8.3 percent agricultural, and about 85 percent undeveloped, and is classified as Undeveloped, although there are 

major municipal point-source discharges in the basin (table 8, 

in back of report). Conversely, some large drainage basins are 

classified as Urban or Agricultural, even though more than half 

of their drainage areas are forested. For example, the drainage 

area of the Susquehanna River at Conowingo, Md., is largely 

undeveloped (about 68 percent) (table 8, in back of report). 

However, agricultural lands account for about 28 percent of 

the drainage area, most agricultural land is located in downstream areas of the drainage basin nearest the monitoring station, and agricultural land use provides the most pronounced 

effects on the observed water quality. Therefore, this basin 

is classified as Agricultural. The complex nature of nutrient 

sources in large drainage basins is discussed in this report. 

Land use and population characteristics have been summarized for 130 stations evaluated in this report (table 8, 

in back of report). The undeveloped category includes nine 

stations in the northeastern region that were evaluated in a 

national study of undeveloped drainage basins (Clark and others, 2000). These nine stations are identified in the “Undeveloped site” column in table 8 (in back of report).

Point Sources

Information used for the analysis of point sources was 

initially developed from the USEPA Permit Compliance 

System (PCS). Facility locations (coordinates for latitude 

and longitude) were obtained from the PCS data distributed 

with the USEPA “Better Assessment Science Integrating 

point & Non-point Sources” (BASINS) ArcView system 

(U.S. Environmental Protection Agency, 2005). The BASINS 

system includes information for 11,584 PCS sites in the study 

area of this report. Records for only 624 of these 11,584 PCS 

sites included annual estimates for total phosphorus loads 

(parameter code 00665) for any year from 1992 to 1999. 

Additionally, records for only 123 sites included annual 

estimates for total nitrogen loads (parameter code 00600). 

Many more sites must actually discharge nitrogen and 

phosphorus. By using the Standard Industrial Classification 

(SIC) Codes that are included with the PCS facility data, sites 

were identified that are likely to be discharging nutrient loads 

to streams in the region (table 9). A listing of these SIC codes 

and related criteria (McMahon and others, 2007, p. 5) were 

used in conjunction with PCS data to estimate the number 

of major and minor facilities discharging nutrients in each 

state of the study area (table 9). Major municipal facilities are 

defined by the U.S. Environmental Protection Agency (2008) 

as facilities that discharge at least 1 million gallons per day of 

effluent. Major non-municipal facilities are defined by a rating 

code formula. 

Table 7. Land-use categories for 130 drainage basins evaluated for trends, loads, and yields in the northeastern United States.

[Some stations were evaluated for trends only, some for loads only, and some for both. Counts include undeveloped basins from national study (Clark and 

others, 2000) (table 5). <, less than; >, greater than; %, percent; =, equal]

Category Land-use 

code Land-use percentages in drainage basin

Maximum number of stations evaluated Total 

number of 

stations Trend analysis Load and yield estimation

Undeveloped UN UR < 10% and AG < 20% 22 28 38

Urban UR UR > or = 10% and AG < 20% 37 26 43

Urban/agricultural UA UR > or = 10% and AG > or = 20% and < 50% 10 14 17

Agricultural AG AG > or = 20% and UR < 10% 19 25 30

Agricultural/urban AU UR > or = 10% and AG > or = 50% 2 0 2

Total: 90 93 130
Methods of Data Analysis 25

Additional state and regional programs were investigated 

for data on point-source nutrient loads because of the 

insufficient annual estimates for total nitrogen and total 

phosphorus loads provided with the PCS data. Sources of 

nutrient data for point sources in selected areas of the region 

include the Connecticut Department of Environmental 

Protection (CTDEP), the New Jersey Department of 

Environmental Protection (NJDEP), and the Chesapeake 

Bay Program (table 10). These data sources were analyzed to 

identify watersheds where the nutrient point-source data were 

adequate for detailed analysis. Analysis of all point sources in 

the region was beyond the scope of this project. Consequently, 

a small number of watersheds were selected for analysis, to 

represent major geographic areas in the region, and to take 

advantage of the extensive water-quality and point-source 

data available in some areas. Four watersheds were selected: 

the Quinebaug River Basin in Connecticut, Rhode Island, 

and Massachusetts; the Raritan River Basin in New Jersey; 

the Patuxent River Basin in Maryland; and the James River 

Basin in Virginia, which includes the Appomattox River Basin 

(table 10). 

Total nitrogen loads for point sources in the Quinebaug 

River Basin were provided by the CTDEP (Paul Stacey, 

Connecticut Department of Environmental Protection, written commun., 2006). Annual loads of total phosphorus for 

point sources in the Quinebaug River Basin (1990 through 

1999) were obtained directly from the PCS database accessed 

through the BASINS Program (Better Assessment Science 

Integrating point & Non-point Sources; U.S. Environmental 

Protection Agency, 2005). 

Annual loads for nitrogen constituents for point sources 

in the Raritan River Basin were obtained from TRC Omni 

Environmental Corporation for the period 1991–97 (James 

Cosgrove, TRC Omni Environmental Corporation, written 

commun., 2006). These data on point-source loads of nitrogen 

constituents were derived primarily from the discharge 

monitoring report (DMR) database of NJDEP, and were 

compiled in a point-source pollutant analysis (TRC Omni 

Environmental Corporation, 2001). Annual load compilations 

from this analysis were used subsequently to compute average 

point-source loads for the 1991–97 period (Reiser, 2004). 

Table 9. Estimated numbers of point sources discharging 

nutrients in the northeastern United States study area.

[Nutrient point-source locations were identified by using the reported Permit 

Compliance System (PCS) facility locations, in conjunction with Standard 

Industrial Classification (SIC) Codes. Sources: U.S. Environmental Protection Agency, 2005; McMahon and others, 2007, p. 5]

State or district

Nutrient point sources in the 

northeastern United States study area

Major facilities Minor facilities

Connecticut 78 40

Delaware 20 22

District of Columbia 3 2

Maine 82 154

Maryland 74 328

Massachusetts 117 235

New Hampshire 58 52

New Jersey 160 593

New York 152 623

Pennsylvania 201 1,973

Rhode Island 22 46

Vermont 31 45

Virginia 84 682

West Virginia 7 267

Total 1,089 5,062

Table 10. Summary of data sources and availability of point-source data for selected drainage basins.

[Sources: Stacey, Paul, Connecticut Department of Environmental Protection, written commun., 2006; U.S. Environmental Protection Agency, 2005; 

Cosgrove, James, TRC Omni Environmental Corporation, written commun., 2006; Reiser, 2004; Robinson and others, 1996; Chesapeake Bay Program 

Data Hub (http://www.chesapeakebay.net/data/index.htm); mi2, square miles; CTDEP, Connecticut Department of Environmental Protection; NJDEP, New 

Jersey Department of Environmental Protection; CBP, Chesapeake Bay Program]

Drainage basin

Monitored 

drainage area 

(mi2)

States Source for pointsource data

Time period for point-source data

Total nitrogen Total phosphorus

Quinebaug 713 Rhode Island, Massachusetts, Connecticut CTDEP 2002–2004 1990–1998*

Raritan 804 New Jersey NJDEP 1991–1997 1991–1997

Patuxent 348 Maryland CBP 1990–2003 1990–2003

James 6,252 Virginia CBP 1990–2003 1990–2003

Appomattox 1,342 Virginia CBP 1990–1999 1990–2003

*

No total phosphorus data for Quinebaug River at Jewett City, Conn.
26 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Total nitrogen loads for this report were calculated from the 

loads of nitrogen constituents, which were reported separately 

in the analysis by TRC Omni Environmental Corporation. 

Total nitrogen loads were calculated from annual loads 

of Kjeldahl nitrogen (ammonia, ammonium, and organic 

nitrogen), nitrate, and nitrite. Annual loads of total phosphorus 

for facilities in the Raritan River Basin were obtained directly 

from the PCS database. 

Nutrient loads for point sources in the Patuxent River and 

James River Basins were obtained from the Chesapeake Bay 

Program Data Hub (http://www.chesapeakebay.net/data/index.

htm, accessed February 16, 2006). Annual point-source loads 

for total nitrogen and total phosphorus (1990 to 2003) were 

provided from this source. 

Total point-source nutrient loads upstream from selected 

USGS water-quality monitoring stations were summed and 

plotted along with the total estimated stream nutrient loads for 

selected monitoring stations throughout the basins selected for 

analysis. Observations and inferences were then made regarding the role of point sources in the total annual stream loads. 

Point-source loads are reported for calendar years, whereas 

stream loads are reported by water year (October 1 through 

September 30). Although the comparison is for slightly different timeframes, with a three month offset, observations and 

inferences can be made. 

Additional information on point-source locations and 

return flows in the New England states is from Medalie 

(1996). Additional information for point-source locations in 

New Jersey is from Robinson and others (1996), and from 

Reiser (2004) for locations in the Raritan River Basin in 

New Jersey. 

Streamflow Conditions in the 

Northeastern United States

Nutrient concentrations and loads are often closely 

correlated with streamflow conditions, and consequently 

information on streamflow is necessary for interpreting and 

understanding these measures of stream nutrient conditions. 

Annual mean streamflows at most stations evaluated have 

varied substantially during the recent and long-term periods of 

record considered in this report. Substantial spatial variation in 

streamflow also is common in the region. 

Stream discharges were evaluated at 96 stations 

(appendix 2, table 2–1), for the period 1993–2003, the period 

1970–2003, if available, and the full period of record at 

stations with record prior to 1970. Several statistics were used 

to characterize streamflow, to compare the recent period to 

the reference period of 1970 to 2003, and to place the recent 

period in the context of longer-term data (records extending 

back to 1944 or earlier). Graphical methods also were used 

to evaluate and characterize streamflow for selected stations 

during the recent and long-term periods. 

Streamflow, 1993–2003

Annual mean flows and annual runoff during 1993–2003 

varied substantially from year to year, with extremely low 

annual mean flows and annual runoff in 2002 and high annual 

mean flows and annual runoff in 1996 and 2003, depending on 

the geographic area. New minimum or maximum annual mean 

flows were recorded at 18 of 51 stations with 60 or more years 

of record (appendix 2). Water-quality records were evaluated in this report for 13 of these 18 stations (table 11). Five 

water-quality stations with record lengths ranging from 62 to 

75 years experienced both new minimum and new maximum 

annual mean flows during 1993–2003: Ammonoosuc River, 

N.H.; Neshanic River, N.J.; Conococheague Creek, Md.; 

Shenandoah River, W. Va.; and Pamunkey River, Va. (station 

numbers 19, 61, 116, 121, and 125, respectively, in fig. 4 and 

table 5). 

Annual mean flow during 1993–2003 was fairly evenly 

distributed among high and low flows at all 51 stations, with 

about one-third of the annual mean flows greater than the 

75th percentile, one-third of the annual mean flows less than 

the 25th percentile, and one-third of the annual mean flows 

within the interquartile range (the 25th to 75th percentiles of 

flow). Across the region, only water year 2000 was near the 

long-term annual average. During 2002, annual mean flow 

was below normal (less than 25th percentile) at 90 percent 

(46 of 51) of the stations with long-term streamflow records 

(60+ years). During 1996 and 2003, annual mean flow was 

above normal (greater than 75th percentile) at 76 percent (39 

of 51) and 69 percent (35 of 51) of the stations, respectively. 

The five largest rivers in the region with long-term 

data for both stream discharge and water quality are the 

Connecticut River (9,660 mi2), Delaware River (6,780 mi2), 

Susquehanna River (24,100 mi2 at Harrisburg, Pa., for 

long-term streamflow; 27,100 mi2 at Conowingo, Md., for 

water quality), Potomac River (11,570 mi2), and James River 

(6,252 mi2) (numbers 22, 90, 111, 122, and 127 in fig. 4 and 

table 5). The combined annual median flow of these five rivers 

during 2002 (with streamflow for the Susquehanna based on 

the Harrisburg station) was 41 percent less than the long-term 

median flow. In contrast to the dry conditions of water year 

2002, the combined flow of these five rivers was 53 percent 

more than the long-term median flow during 1996 and 64 percent more than the long-term median flow during 2003, the 

two wettest water years in the recent period. 

Low-Flow Years

In water years 1995, 1999, and 2001, notable regional 

differences in the annual mean flow were observed among 

the 51 long-term surface-water stations. Conditions were 

drier in the northern part of the study area in 1995. During 

1995, annual mean flows were below normal (less than 25th 

percentile) or well below normal (less than 10th percentile) at 

82 percent of the stations in New England (14 of 17 stations) 

and at all 23 stations in the central part of the region (New 
Streamflow Conditions in the Northeastern United States 27

Table 11. New minimum and maximum annual mean flows during 1993–2003 for selected stations with 60 or more years of record.[USGS, U.S. Geological Survey; mi2, square miles; --, no new minimum or maximum in 1993–2003 period]

USGS streamflowgaging station 

number

Hydrologic 

Unit Code

Station 

sequence 

number 

(fig. 4)

Station name

Drainage 

area 

(mi2)

Begin date End date

Number 

of years of 

record

Year of new 

minimum 

annual 

mean flow

 Year of new 

maximum 

annual 

mean flow

01137500 01080101 19 Ammonoosuc River at Bethlehem Junction, N.H. 87.6 8/2/1939 9/30/2003 63 1995 199601184000 01080205 22 Connecticut River at Thompsonville, Conn. 9,660 8/1/1928 9/30/2003 75 -- 1996

01389500 02030103 55 Passaic River at Little Falls, N.J. 762 9/1/1897 9/30/2003 106 2002 --01398000 02030105 61 Neshanic River at Reaville, N.J. 25.7 10/1/1930 9/30/2003 73 2002 199401408500 02040301 71 Toms River near Toms River, N.J. 123 10/1/1928 9/30/2003 75 2002 --01608000 02070001 115 South Fork South Branch Potomac River near 

Moorefield, W. Va.

277 6/24/1928 9/30/2003 75 -- 2003

01614500 02070004 116 Conococheague Creek at Fairview, Md. 494 6/1/1928 9/30/2003 75 2002 199601618000 02070004 117 Potomac River at Shepherdstown, W. Va. 5,939 8/1/1928 9/30/2003 75 -- 200301636500 02070007 121 Shenandoah River at Millville, W. Va. 3,041 9/1/1928 9/30/2003 75 2002 199601668000 02080104 124 Rappahannock River near Fredericksburg, Va. 1,595 9/19/1907 9/30/2003 96 -- 200301673000 02080106 125 Pamunkey River near Hanover, Va. 1,078 10/1/1941 9/30/2003 62 2002 199801674500 02080105 126 Mattaponi River near Beulahville, Va. 603 9/19/1941 9/30/2003 62 2002 --02035000 02080205 127 James River at Cartersville, Va. 6,252 1/1/1899 9/30/2003 104 2002 --
28 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

York, New Jersey, and Pennsylvania). At one long-term 

surface-water and water-quality station in New Hampshire, 

a new minimum annual mean flow was recorded (table 11). 

By contrast, annual mean flows were normal (the 25th to 

75th percentiles) for 6 of 11 stations, and below normal (less 

than 25th percentile) for 5 of 11 stations, during 1995 in the 

southern part of the region (Virginia, West Virginia, 

and Maryland). 

A hydrologic drought characterized most of the southern 

part of the region, including areas of Virginia, West Virginia, 

and Maryland, from water year 1999 to 2002. Annual mean 

flows were well below normal (less than 10th percentile) 

during 1999, 2001, and 2002, and were below normal 

(between the 10th and 25th percentiles) at fewer stations 

in 2000 than in 1999, 2001, and 2002. Dry conditions also 

affected the central part of the region during 1999. Annual 

mean flows were below normal and well below normal for 

stations in New Jersey, New York, and Pennsylvania during 

water year 1999. Exceptionally dry conditions during 2002 

affected, in varying degrees, a broad area from Maine to 

Virginia. At stations in the central and southern parts of the 

region, including stations in New Jersey, Maryland, Virginia, 

and West Virginia, annual mean flows during 2002 were 

the lowest of record. New minimum annual mean flow was 

recorded during 2002 at 9 of 51 long-term streamflow stations 

evaluated, including 8 stations evaluated for water quality 

in this report. Two of these water-quality stations had more 

than 100 years of record, the Passaic River at Little Falls, N.J. 

(drainage area 762 mi2), and the James River at Cartersville, 

Va. (drainage area 6,252 mi2). The dry conditions of 2002, 

characterized by a substantial shortfall in precipitation and 

warmer than normal temperatures, affected annual mean flows 

in the northeastern part of the region less than in the southern 

part of the region. Annual mean flows were below normal 

(less than the 25th percentile) at 83 percent of the streamflow 

stations (19 of 23) in the northeastern part of the region (New 

York and the New England states); whereas annual mean flows 

were below normal at 96 percent of the streamflow stations 

(27 of 28) in the southern part of the region (New Jersey, 

Pennsylvania, West Virginia, Virginia, and Maryland). New 

minimum annual mean flows were recorded during 2002 at 

eight water-quality stations with long-term surface-water 

records in the southern part of the region, whereas no new 

minimum annual mean flow was recorded during 2002 in the 

northeastern part of the region (table 11). 

High-Flow Years

Generally, water years 1996 and 2003 were the wettest 

years in the period 1993–2003. New maximum annual mean 

flow was recorded at 14 of 51 long-term surface-water stations 

evaluated, with all but 2 of the 14 new maximums occurring 

in 1996 or 2003. An exceptionally wet pattern occurred across 

the region from 1996 through 1998. Annual mean flow was 

above normal (greater than 75th percentile) for 76 percent 

of the long-term stations during 1996 (39 of 51 stations), 

59 percent (30 of 51) during 1997, and 65 percent (33 of 51) 

during 1998. More stations in the northern part of the region 

experienced annual mean flows above normal during 1997 

than in the southern part of the region. New maximum annual 

mean flow was recorded during 2003 at three long-term 

stations evaluated for water quality in the southern part of 

the region (table 11). The Potomac River at Shepherdstown, 

W. Va. (number 117, fig. 4 and table 5) experienced the highest 

annual mean flow since 1928. Across the entire study area, 

annual mean flows were well above normal (greater than 

the 90th percentile) during 2003 for 35 percent of the longterm surface-water stations evaluated (18 of 51 stations). 

All streamflow stations in Pennsylvania, West Virginia, 

Virginia, and Maryland, with the exception of one station in 

Virginia, experienced annual mean flows well above normal 

during 2003. 

Annual Runoff

The 11 water years in the recent period were identified 

as low, average, or high runoff years by Hydrologic Unit. 

In the New England region (HUC 01, fig. 1), 6 of 11 water 

years (1993–94, 1999, 2000–01, 2003) were considered as 

average runoff years (in the 25th to 75th percentiles). The 

1996–98 water years were considered high runoff years 

(greater than the 75th percentile), whereas the 1995 and 2002 

water years were considered low runoff years (less than the 

25th percentile). 

In the mid-Atlantic region (HUC 02, fig. 1), records for 

most water years (10 of 11) indicate runoff in the upper and 

lower percentile ranges: either greater than the 75th percentile (high runoff, or wet conditions), or less than the 25th 

percentile (low runoff, or dry conditions). Only one water 

year (2000) was considered as an average runoff year. High 

runoff years include 1993–94, 1996–98, and 2003. Low runoff 

years include 1995, 1999, and 2001–2002. Water year 2002 

set a new all-time low record for annual runoff. Water year 

2002 was the driest year in more than 80 years of record and 

was followed by an extremely high runoff water year (2003). 

Water year 2003 ranked as the second highest runoff year on 

record, on the basis of records for groups of stations dating back to 1900. Overall, the median of the annual runoff 

(reported in units of inches per year) for the 11 water years of 

the 1993–2003 period was greater in the New England region 

(HUC 01, median of 25.05 inches per year (in/yr)) than in the 

mid-Atlantic region (HUC 02, median of 22.84 in/yr). 

Streamflow During Sampling Years in National 

USGS Programs

The duration of water-quality sampling at USGS monitoring stations in the region has varied considerably in both 

national programs and in programs and projects conducted in 

cooperation with individual states. Variation in the period of 
Streamflow Conditions in the Northeastern United States 29

record among stations complicates comparison of water-quality conditions among different drainage basins. 

The NAWQA Program is designed to have 3 years of 

high-intensity sampling at water-quality stations in each 

study unit, followed by 6 years of low-intensity sampling at a 

smaller number of stations, followed by 3 more years of highintensity sampling (Gilliom and others, 1995, p. 2). Nationally, 

the NAWQA study unit projects have been started in a phased 

approach, so that the high-intensity sampling period does not 

coincide for all study units (table 12). Funding constraints 

have played a role in the number of stations sampled or continued in the program. There has been no high-intensity sampling in the Lower Susquehanna River Basin Study Unit since 

the mid-1990s (M.J. Langland, U.S. Geological Survey, written commun., 2011). In the Hudson River Basin Study Unit, 

long-term sampling at a limited number of stations in the early 

2000s is not comparable to the 1993–95 high-intensity period, 

in terms of numbers of stations or duration of sampling (P.J. 

Phillips, U.S. Geological Survey, written commun., 2011). 

High-intensity sampling in 2002 and 2003 in the Connecticut, 

Housatonic, and Thames River Basins Study Unit is at a small 

number of stations, relative to the 1993–95 sampling period 

(C.J. Brown, U.S. Geological Survey, written commun., 2011). 

Program changes or periodic sampling may result in a 

situation where the sampling period misses extreme high- or 

low-flow years that help to define the range of expected stream 

nutrient loads, or misses more typical flow years that would 

help to define average stream nutrient loads. For example, 

the 1999–2001 high-intensity sampling period for the New 

England Coastal Basins NAWQA study unit misses the more 

extreme high and low flows of recent years, whereas the same 

period for the Potomac–Delmarva NAWQA study unit encompasses an extended dry period for some stations (tables 11, 

12). The 1996–98 sampling period for the Long Island–New 

Jersey NAWQA study unit is a period of generally high annual 

mean flows, and includes one of the highest flow years in the 

1993–2003 period. 

As noted in the section on Data Selection and Screening, water-quality monitoring through the NASQAN Program 

was discontinued on many major streams in the northeast in 

the early- to mid-1990s (tables 5, 12). Records for NASQAN 

stations that end in the early 1990s do not include several 

extreme flow years for the 1993–2003 period. 

Comparison of 1993–2003 Period to Long-Term 

Streamflows

Streamflows for the reference period of 1970–2003 were 

evaluated for 96 stations (appendix 2, table 2–1), and for longterm periods with initial dates ranging from 1890 to 1944 for 

51 of these stations. Long-term station records were evaluated 

in terms of annual mean streamflow, and regional patterns of 

annual runoff were identified. 

Long-Term Variability in Annual Mean 

Streamflow

Long-term annual mean streamflows for nine 

streamgages (fig. 5) provide an overview of long-term conditions in the region, with the understanding that streamflow 

at each location represents a unique combination of climate, 

geology, and geography. Streamgages from three subregions of 

the study area are shown: the northeastern part of the region, 

encompassing most of the New England states (figs. 5A, B, 

Table 12. Sampling years in NAWQA study units and ending water years at NASQAN stations in the Northeast.

[Shaded blocks show intensive sampling years for NAWQA stations or ending water years for NASQAN stations in the study area. NAWQA study units shown 

in figure 1. NAWQA, National Water Quality Assessment; NASQAN, National Stream Quality Accounting Network]

Study unit 

abbreviationStudy unit name 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

NAWQA Program

NECB New England Coastal Basins

CONN Connecticut, Housatonic, and Thames River Basins

HDSN Hudson River Basin

LINJ Long Island–New Jersey Coastal Drainages

DELR Delaware River Basin

LSUS Lower Susquehanna River Basin

PODL Potomac River Basin and Delmarva Peninsula

NASQAN Program

Final sampling years for selected stations in region
30 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 1970 1975 1980 1985 1990 1995 2000 2005 050 350 300 250 200 150 100

Annual mean flow, in cubic feet per second

Median annual mean 1993–2003 193 ft3/s

1970–2003 193 ft3/s1965–2003 192 ft3/s

A. Wild River at Gilead, Maine (station 3)

1970 1975 1980 1985 1990 1995 2000 2005 0

80604020

Median annual mean 1993–2003 34.6 ft3/s

1970–2003 33.8 ft3/s1965–2003 29.0 ft3/s

B. Aberjona River at Winchester, Massachusetts (station 7)

1970 1975 1980 1985 1990 1995 2000 2005

0

30,00020,00010,000

Median annual mean 1993–2003 17,100 ft3/s

1970–2003 17,900 ft3/s1929–2003 17,600 ft3/s

C. Connecticut River at Thomponsville, Connecticut (station 22)

1970 1975 1980 1985 1990 1995 2000 2005 0

300200100

Median annual mean 1993–2003 159 ft3/s

1970–2003 147 ft3/s1965–2003 144 ft3/s

D. Esopus Creek at Allaben, New York (station 48)

1970 1975 1980 1985 1990 1995 2000 2005

Water year

0

80604020

Median annual mean 1993–2003 42.4 ft3/s

1970–2003 42.8 ft3/s1931–2003 36.6 ft3/s

E. Neshanic River at Reaville, New Jersey (station 61)

1970 1975 1980 1985 1990 1995 2000 2005

0

5,000

20,00015,00010,000

Median annual mean1993–2003 12,600 ft3/s

1970–2003 12,400 ft3/s1913–2003 11,700 ft3/s

F. Delaware River at Trenton, New Jersey (station 90)

1970 1975 1980 1985 1990 1995 2000 2005

0

50

150100

Median annual mean1993–2003 83.8 ft3/s

1970–2003 74.6ft3/s

1966–2003 72.4 ft3/s

G. Young Womans Creek near Renovo, Pennsylvania (station 104)

1970 1975 1980 1985 1990 1995 2000 2005

0

604020

Median annual mean1993–2003 35.2 ft3/s

1970–2003 28.5 ft3/s1948–2003 28.5 ft3/s

H. Accotink Creek near Annandale, Virginia (station 123)

1970 1975 1980 1985 1990 1995 2000 2005

0

5,000

15,00010,000

Median annual mean1993–2003 7,970 ft3/s

1970–2003 7,780 ft3/s1900–2003 6,890 ft3/s

I. James River at Cartersville, Virginia (station 127)

75th percentile50th percentile (median)25th percentile

High flow year (annual mean flow greater than 75th percentile)Average flow year (annual mean flow from 25th to 75th percentile)Low flow year (annual mean flow less than 25th percentile)

Annual mean flow (percentiles for 1970–2003 period)(Annual mean flow for 2004 shown for context; data not included in percentiles.)

EXPLANATION

Percentiles for annual mean flows, 1970–2003

Figure 5. Long-term annual mean streamflows at selected stations, 1970–2004. (A) Wild River at Gilead, Maine, (B) Aberjona River at Winchester, Mass., (C) Connecticut River at Thompsonville, Conn., (D) Esopus Creek at Allaben, N.Y., (E) Neshanic River at Reaville, N.J., (F) Delaware River at Trenton, N.J., (G) Young Womans Creek near Renovo, Pa., 

(H) Accotink Creek near Annandale, Va., and (I) James River at Cartersville, Va.
Streamflow Conditions in the Northeastern United States 31

C); the central part of the region, including the Hudson and 

Delaware River Basins and adjacent coastal basins (figs. 5D, 

E, F); and the southwestern part of the region, including the 

Susquehanna and Potomac River Basins, and drainage basins 

in Maryland and Virginia (figs. 5G, H, I). The northern subregion is equivalent to Hydrologic Region 01, and the central 

and southwestern subregions constitute Hydrologic Region 02 

(fig. 1). Local and regional patterns of streamflow for the three 

subregions in the study area are illustrated by graphs of annual 

mean flows for small, undeveloped upland drainage basins 

(less than 100 mi2) (figs. 5A, D, G); small, developed coastal 

drainage basins (less than 50 mi2) (figs. 5B, E, H); and large 

drainage basins (greater than 5,000 mi2) (figs. 5C, F, I). 

Graphs of annual mean streamflow for the nine example 

basins illustrate some of the extreme hydrologic conditions 

during 1993–2003. Drier than normal conditions during 1999–

2002 affected streamflow for large drainage basins, particularly in the southwestern subregion, as illustrated by the James 

River (fig. 5I), where water years 1999–2002 represent the 

longest period of low annual mean flows from 1970 to 2003. 

For the Connecticut River (table 5; fig. 4, station 22), the 1996 

annual mean flow was the highest for the 1970 to 2003 period 

(fig. 5C). For the Delaware River at Trenton, N.J., (station 90), 

and James River (station 127), the 2003 annual mean flow 

almost equaled the annual mean flow of 1973, which was the 

highest annual mean flow as far back as 1970 (figs. 5F, I). 

For small, undeveloped upland drainage basins, the highest annual mean flows for the 1993–2003 period exceeded 

previous record high annual means for 1970–1992 (figs. 5A, 

D, G). The lowest annual mean flows during 1993–2003 

were lower than previous record low annual means for the 

Wild River at Gilead, Maine, and Young Womans Creek near 

Renovo, Pa. (figs. 5A, G). Similarly, among the three small, 

developed coastal drainage basins, the highest and lowest 

annual mean flows during the 1993–2003 period were higher 

and lower than annual mean flows from 1970 to 1992 for the 

Neshanic River at Reaville, N.J., and Accotink Creek near 

Annadale, Va. (figs. 5E, H). 

Although water year 2004 is not part of the period of 

analysis for streamflow and water quality in this report, water 

year 2004 is included in the graphs of annual mean flows 

(fig. 5), to provide another point of reference for evaluating 

streamflow in the 1993–2003 period. Water year 2003 

represents the highest, or one of the highest, annual mean 

flows for several stations in the study area, but annual mean 

flows in water year 2004 exceeded annual mean flows in 

water year 2003 at some stations, including Esopus Creek at 

Allaben, N.Y., the Delaware River at Trenton, N.J., and Young 

Womans Creek near Renovo, Pa. (figs. 5D, F, G). 

Regional and Temporal Variability in Runoff

The coefficient of variation for runoff, which equals the 

standard deviation divided by the mean of the annual runoff 

dataset, was used to compare the variability of the annual 

runoff between different periods of record for a hydrologic 

region, and between regions with differences in annual runoff 

values during the same time period. This statistic was computed for each of three periods for the two hydrologic regions 

in the study area, the New England region (HUC 01) and the 

mid-Atlantic region (HUC 02). 

The average annual runoff in the New England region 

(HUC 01), varied within a range of 1.5 inches (in.) for the 

three periods: an average of 24.4 in/yr from 1993 to 2003, 

25.5 in. from 1970 to 2003 (highest runoff period), and 

24.0 in. from 1930 to 2003. The coefficient of variation 

varied within a range of 1.1 percent for the three periods: 

21.8 percent (1993–2003); 22.9 percent (1970–2003); 

22.5 percent (1930–2003). The small range in the coefficients 

of variation for the New England region illustrates that the 

characteristics of annual runoff during 1993–2003 were very 

similar to the characteristics of annual runoff for 1970–2003 

and 1930–2003.

The average annual runoff in the mid-Atlantic region 

(HUC 02) varied within a range of 1.3 in. for the 3 periods: 

20.0 in/yr for 1993–2003, 20.1 in/yr for 1970–2003 (highest runoff period), and 18.8 in/yr for 1930–2003. The coefficient of variation varied within a range of 6.7 percent among 

the three periods: 31.2 percent (1993–2003); 25.9 percent 

(1970–2003); 24.5 percent (1930–2003). The coefficient 

of variation was highest for the stations in the mid-Atlantic 

region during 1993–2003, indicating that variability in annual 

runoff was greater during 1993–2003 than during 1970–2003 

or 1930–2003. This result is consistent with the finding of 

new record maximum and minimum annual mean flows at a 

substantial number of stations in the mid-Atlantic region during the 1993–2003 period (table 11). This variability during 

the 1993–2003 period also can be seen in plots of annual mean 

flows for several stations in the mid-Atlantic region, where 

few annual mean flows are near the long-term median 

(figs. 5D, F, G, H, I). 

Effects of Streamflow on Water-Quality 

Variability

The concentrations of many water-quality constituents 

are correlated with streamflow (fig. 6), and consequently a 

large part of the variability in constituent concentration over 

time may be caused by variability in streamflow, both seasonally and from year to year. A LOESS smoothing procedure, 

referenced in the section on Methods of Data Analysis, has 

been used to identify generalized relations between constituent 

concentration and daily mean streamflow (fig. 6), and also has 

been used to show relations between concentration and time in 

plots in subsequent sections of this report. 

The correlation between concentration and streamflow 

may be more pronounced in streams that are influenced by 

developed land uses or waste-disposal practices. Streams 

in small drainage basins (less than about 1,000 mi2) with 

point-source discharges often have high nutrient concentrations at low flows, when point-source effluent constitutes a 
32 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

10 100 1,000 10,000

0.1

1

10

100

Nitrite-plus-nitrate nitrogen concentration, 

in milligrams per liter

Nitrite-plus-nitrate nitrogen concentration, 

in milligrams per liter

A. Pawtuxet River at Cranston, Rhode Island, 1979–2002 

 (station 10)

C. Pawtuxet River at Cranston, Rhode Island, 1979–2002 

 (station 10)

10 100 1,000 10,000

0.1

1

10

B. Patuxent River near Bowie, Maryland, 1979–2003 

 (station 114)

10 100 1,000 10,000

0.01

0.1

1

10

Total phosphorus concentration, 

in milligrams per liter

10 100 1,000 10,000

0.01

0.1

1

10

Total phosphorus concentration, 

in milligrams per liter

D. Naugatuck River at Beacon Falls, Connecticut, 1975–2003 

 (station 39)

Daily mean streamflow, in cubic feet per second Daily mean streamflow, in cubic feet per second

EXPLANATION

LOESS smooth line

Constituent concentration

Figure 6. Characteristic plots of nutrient concentration as a function of discharge at selected stations, showing land-use and point-source 

effects. (A) Pawtuxet River at Cranston, R.I., nitrite-plus-nitrate concentrations, 1979–2002, (B) Patuxent River near Bowie, Md., nitriteplus-nitrate concentrations, 1979–2003, (C) Pawtuxet River at Cranston, R.I., total phosphorus concentrations, 1979–2002, (D) Naugatuck 

River at Beacon Falls, Conn., total phosphorus concentrations, 1975–2003, (E) Canajoharie Creek near Canajoharie, N.Y., total nitrogen 

concentrations, 1994–2003, (F) Canajoharie Creek near Canajoharie, N.Y., nitrite-plus-nitrate concentrations, 1994–2003, (G) Choptank 

River near Greensboro, Md., nitrite-plus-nitrate concentrations, 1975–2003, (H) Canajoharie Creek near Canajoharie, N.Y., total phosphorus 

concentrations, 1994–2003, (I) Connecticut River at Thompsonville, Conn., total nitrogen concentrations, 1975–2003, (J) Connecticut River at 

Thompsonville, Conn., total phosphorus concentrations, 1975–2003, (K) Susquehanna River at Conowingo, Md., total nitrogen concentrations, 

1979–2003, (L) James River at Cartersville, Va., total nitrogen concentrations, 1975–2003, (M) Susquehanna River at Conowingo, Md., total 

phosphorus concentrations, 1979–2003, and (N) James River at Cartersville, Va., total phosphorus concentrations, 1975–2003.
Streamflow Conditions in the Northeastern United States 33

0.1 1 10 100 1,000 10,000

0.1

1

10

Total nitrogen concentration, 

in milligrams per liter

E. Canajoharie Creek near Canajoharie, New York, 1994–2003 

 (station 45) 

100 1,000 10,000

0.1

1

10

F. Canajoharie Creek near Canajoharie, New York, 1994–2003 

 (station 45)

0.1 1 10

0.01

1 10 100 1,000 10,000

Daily mean streamflow, in cubic feet per second

0.1

1

10

G. Choptank River near Greensboro, Maryland, 1975–2003 

 (station 101)

0.1 1 10 100 1,000 10,000

Daily mean streamflow, in cubic feet per second

0.001

0.01

0.1

1

10

Total phosphorus concentration, 

in milligrams per liter

H. Canajoharie Creek near Canajoharie, New York, 1994–2003

 (station 45) 

Nitrite-plus-nitrate nitrogen concentration, 

in milligrams per liter

Nitrite-plus-nitrate nitrogen concentration, 

in milligrams per liter

EXPLANATION

LOESS smooth line

Constituent concentration

Figure 6. Characteristic plots of nutrient concentration as a function of discharge at selected stations, showing land-use and point-source 

effects. (A) Pawtuxet River at Cranston, R.I., nitrite-plus-nitrate concentrations, 1979–2002, (B) Patuxent River near Bowie, Md., nitriteplus-nitrate concentrations, 1979–2003, (C) Pawtuxet River at Cranston, R.I., total phosphorus concentrations, 1979–2002, (D) Naugatuck 

River at Beacon Falls, Conn., total phosphorus concentrations, 1975–2003, (E) Canajoharie Creek near Canajoharie, N.Y., total nitrogen 

concentrations, 1994–2003, (F) Canajoharie Creek near Canajoharie, N.Y., nitrite-plus-nitrate concentrations, 1994–2003, (G) Choptank 

River near Greensboro, Md., nitrite-plus-nitrate concentrations, 1975–2003, (H) Canajoharie Creek near Canajoharie, N.Y., total phosphorus 

concentrations, 1994–2003, (I) Connecticut River at Thompsonville, Conn., total nitrogen concentrations, 1975–2003, (J) Connecticut River at 

Thompsonville, Conn., total phosphorus concentrations, 1975–2003, (K) Susquehanna River at Conowingo, Md., total nitrogen concentrations, 

1979–2003, (L) James River at Cartersville, Va., total nitrogen concentrations, 1975–2003, (M) Susquehanna River at Conowingo, Md., total 

phosphorus concentrations, 1979–2003, and (N) James River at Cartersville, Va., total phosphorus concentrations, 1975–2003.—Continued
34 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

1,000 10,000 100,000

Daily mean streamflow, in cubic feet per second

0.1

1

10

Total nitrogen concentration, 

in milligrams per liter

1,000 10,000 100,000

Daily mean streamflow, in cubic feet per second

0.001

0.01

0.1

1

10

Total phosphorus concentration, 

in milligrams per liter

I. Connecticut River at Thompsonville, Connecticut, 1975–2003 

 (station 22)

J. Connecticut River at Thompsonville, Connecticut, 1975–2003 

 (station 22)

EXPLANATION

LOESS smooth line

Constituent concentration

Figure 6. Characteristic plots of nutrient concentration as a function of discharge at selected stations, showing land-use and point-source 

effects. (A) Pawtuxet River at Cranston, R.I., nitrite-plus-nitrate concentrations, 1979–2002, (B) Patuxent River near Bowie, Md., nitriteplus-nitrate concentrations, 1979–2003, (C) Pawtuxet River at Cranston, R.I., total phosphorus concentrations, 1979–2002, (D) Naugatuck 

River at Beacon Falls, Conn., total phosphorus concentrations, 1975–2003, (E) Canajoharie Creek near Canajoharie, N.Y., total nitrogen 

concentrations, 1994–2003, (F) Canajoharie Creek near Canajoharie, N.Y., nitrite-plus-nitrate concentrations, 1994–2003, (G) Choptank 

River near Greensboro, Md., nitrite-plus-nitrate concentrations, 1975–2003, (H) Canajoharie Creek near Canajoharie, N.Y., total phosphorus 

concentrations, 1994–2003, (I) Connecticut River at Thompsonville, Conn., total nitrogen concentrations, 1975–2003, (J) Connecticut River at 

Thompsonville, Conn., total phosphorus concentrations, 1975–2003, (K) Susquehanna River at Conowingo, Md., total nitrogen concentrations, 

1979–2003, (L) James River at Cartersville, Va., total nitrogen concentrations, 1975–2003, (M) Susquehanna River at Conowingo, Md., total 

phosphorus concentrations, 1979–2003, and (N) James River at Cartersville, Va., total phosphorus concentrations, 1975–2003.—Continued
Streamflow Conditions in the Northeastern United States 35

N. James River at Cartersville, Virginia, 1975–2003 

 (station 127)

K. Susquehanna River at Conowingo, Maryland, 1979–2003 

 (station 111)

L. James River at Cartersville, Virginia, 1975–2003 

 (station 127)

M. Susquehanna River at Conowingo, Maryland, 1979–2003 

 (station 111)

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

0.1

1

10

Total nitrogen concentration, 

in milligrams per liter

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

0.1

1

10

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

Daily mean streamflow, in cubic feet per second

0.001

0.01

0.1

1

Total phosphorus concentration, 

in milligrams per liter

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

Daily mean streamflow, in cubic feet per second

0.001

0.01

0.1

1

10

Total nitrogen concentration, 

in milligrams per liter

Total phosphorus concentration, 

in milligrams per liter

EXPLANATION

LOESS smooth line

Constituent concentration

Figure 6. Characteristic plots of nutrient concentration as a function of discharge at selected stations, showing land-use and point-source 

effects. (A) Pawtuxet River at Cranston, R.I., nitrite-plus-nitrate concentrations, 1979–2002, (B) Patuxent River near Bowie, Md., nitriteplus-nitrate concentrations, 1979–2003, (C) Pawtuxet River at Cranston, R.I., total phosphorus concentrations, 1979–2002, (D) Naugatuck 

River at Beacon Falls, Conn., total phosphorus concentrations, 1975–2003, (E) Canajoharie Creek near Canajoharie, N.Y., total nitrogen 

concentrations, 1994–2003, (F) Canajoharie Creek near Canajoharie, N.Y., nitrite-plus-nitrate concentrations, 1994–2003, (G) Choptank 

River near Greensboro, Md., nitrite-plus-nitrate concentrations, 1975–2003, (H) Canajoharie Creek near Canajoharie, N.Y., total phosphorus 

concentrations, 1994–2003, (I) Connecticut River at Thompsonville, Conn., total nitrogen concentrations, 1975–2003, (J) Connecticut River at 

Thompsonville, Conn., total phosphorus concentrations, 1975–2003, (K) Susquehanna River at Conowingo, Md., total nitrogen concentrations, 

1979–2003, (L) James River at Cartersville, Va., total nitrogen concentrations, 1975–2003, (M) Susquehanna River at Conowingo, Md., total 

phosphorus concentrations, 1979–2003, and (N) James River at Cartersville, Va., total phosphorus concentrations, 1975–2003.—Continued
36 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

large percentage of streamflow, and often have lower nutrient 

concentrations at high streamflows, when point-source effluent 

is diluted by storm runoff. Water-quality data for the Pawtuxet 

River in Rhode Island, the Patuxent River in Maryland, and 

the Naugatuck River in Connecticut demonstrate the relationship of nitrite-plus-nitrate and total phosphorus concentrations 

to streamflow under these conditions (stations 10, 114, 39) 

(figs. 6A–D). 

Nutrient concentrations in small agricultural drainage 

basins may have a variety of responses to increases in stream 

discharge. In Canajoharie Creek in New York, total nitrogen 

and nitrite-plus-nitrate concentrations increase with moderate 

increases in stream discharge, as storm runoff transports 

nutrients from agricultural areas to streams (station 45, 

figs. 6E–F). Total nitrogen concentrations continue to increase 

at high discharges, whereas nitrite-plus-nitrate concentrations 

level off. This difference in response indicates that particulate 

forms of nitrogen predominate at high discharges on 

Canajoharie Creek. In the Choptank River in Maryland 

(station 101, fig. 6G), nitrite-plus-nitrate concentrations remain 

within a similar range at low to moderate stream discharges, 

and concentrations decrease at high discharges. Decreasing 

nitrite-plus-nitrate concentrations at high streamflows may 

indicate the effects of dilution, or may indicate that available 

nonpoint sources of the constituent have been depleted during 

earlier stages of increasing discharge. Concentrations of 

total phosphorus may decrease with moderate increases in 

streamflow as a result of dilution, as in the case of Canajoharie 

Creek (fig. 6H). By contrast, total phosphorus concentrations 

increase gradually with moderate increases in stream discharge 

in the Choptank River (not shown in fig. 6). Total phosphorus 

concentrations increase steeply at very high rates of 

streamflow in Canajoharie Creek (fig. 6H) and the Choptank 

River, probably as a result of sediment-borne phosphorus at 

very high flows. 

The relation between nutrient concentrations and streamflow is affected by multiple factors in the large drainage basins 

of the region, most of which have numerous point sources, 

urban and agricultural areas, and large forested areas. No consistent patterns were evident among the large drainage basins 

evaluated (figs. 6I–N). Total nitrogen and total phosphorus 

concentrations increase with moderate increases in discharges 

in the Connecticut River in Connecticut (station 22, figs. 6I, 

J). At higher discharges, concentrations of both constituents 

decrease, with increases in total phosphorus concentrations at 

very high discharges. The Connecticut River has the largest 

percentage of undeveloped land (about 85 percent, table 8, in 

back of report) and the least agricultural land (about 8 percent) of the three large basins shown in figure 6. The largest 

drainage basin evaluated in this study, the Susquehanna River 

at Conowingo, Md. (station 111), is about 28 percent agricultural, with much of the agricultural land concentrated in the 

downstream parts of the basin. Plots of nutrient concentration 

as a function of streamflow for the Susquehanna River and the 

James River (station 127, 15 percent agricultural) show some 

similarities to smaller agricultural drainage basins. Overall, 

total nitrogen concentrations on the Susquehanna increase 

gradually over a range from low to high stream discharges 

(fig. 6K). Total nitrogen concentrations in the James River 

(fig. 6L) increase steeply with increases in stream discharge. 

Nitrite-plus-nitrate concentrations in the James River (not 

shown in fig. 6) increase with increasing discharges and then 

level off at high discharges, in a similar pattern to Canajoharie 

Creek (fig. 6F). Increasing concentrations of total nitrogen at 

high stream discharges on the Susquehanna and James Rivers 

probably indicate the predominance of particulate forms of 

nitrogen in the total nitrogen concentration at very high discharges. Total phosphorus concentrations in the Susquehanna 

increase gradually from low to moderate stream discharges 

(fig. 6M), and then increase steeply at very high discharges. 

Total phosphorus concentrations on the James River 

(fig. 6N) decrease as streamflow increases from low to moderate streamflows, and concentrations increase steeply at very 

high streamflows, in a pattern similar to that of Canajoharie 

Creek (fig. 6H). 

In small, primarily forested drainage basins, such as the 

Stillwater River in Massachusetts, Bunnell (Burlington) Brook 

in Connecticut, and Bobs Creek in Pennsylvania (not shown 

in fig. 6), nutrient concentrations may not be clearly correlated 

with streamflow. Drainage basins that are undeveloped or 

relatively undeveloped also may not be sampled as frequently 

as impaired streams, and consequently the relation of concentration to streamflow may not be as well defined. 

Effects of Streamflow Conditions on Trend 

Analysis

In trend analysis, flow-adjustment procedures may be 

used to remove that part of concentration variability that is 

caused by variability in streamflow. Trend analysis is often 

performed on flow-adjusted concentrations, because the trend 

results show changes in constituent concentration that are 

independent of streamflow conditions during the period of 

interest. Some cause other than streamflow has produced the 

trend. Consequently, flow-adjusted trend results are useful in 

evaluating changes in water quality that arise from changes in 

contamination sources or management activities in a watershed. For example, downward trends in flow-adjusted nutrient 

concentrations may indicate a decrease in the delivery of nutrients to streams from various sources, whereas upward trends 

may indicate an increase. 

Water managers and scientists also want to understand 

what trends are taking place in the instream concentrations of 

constituents, the actual concentrations that affect the habitat and life processes of aquatic organisms. These instream 

concentrations or values, reported from field or laboratory 

analyses of the water-quality samples collected, represent the 

real environmental conditions. The modeled instream concentration trends in this report provide an indication of changes in 

the actual water quality in streams of the region, and provide a 

measure of whether aquatic habitat conditions are improving, 

deteriorating, or not changing significantly over time. 
Trends in Nutrient Concentrations, 1975–2003 and 1993–2003 37

In the absence of a trend in streamflow, results for the 

analyses of flow-adjusted and modeled instream concentration 

trends should be about the same. However, even a small trend 

in streamflow that is not statistically significant may be sufficient to cause different trend results for the flow-adjusted and 

instream trend analyses. Consequently, the results for these 

two forms of analysis are not identical in all cases. 

Effects of Streamflow Conditions on Load 

Estimation

Annual nutrient load estimates typically vary according 

to the stream discharge conditions during each year, in the 

absence of a trend in constituent load. Larger loads are transported in years of high annual mean streamflow and smaller 

loads in years of low annual mean streamflow. In this report, 

most of the discussion of the effects of streamflow on load 

estimates refers to annual mean streamflow. 

Extreme high flows may transport a large part of the total 

annual stream load, even if concentrations are low during high 

flows. The load estimation procedure relates concentration 

values for a small number of water-quality sampling days to 

a large series of daily mean streamflow values, and predicts 

loads on unsampled days based on this relation. Consequently, 

the accuracy of annual load estimates for a stream depends 

on availability of water-quality data over a wide range of 

streamflows. Although water-quality monitoring during high 

flows has received increased emphasis in recent years, waterquality data for extreme high flows are often lacking for a 

variety of logistical reasons, including cost, unpredictability, 

planned deployment of resources, and safety. Constituent 

concentrations during streamflows on the rising limb of a 

storm hydrograph are often very different from concentrations 

during equivalent streamflows on the falling limb of the storm 

hydrograph, a phenomenon termed “hysteresis.” This phenomenon further complicates load estimation if concentrations are 

not known for the streamflows immediately preceding and following flood peaks. Estimated loads that include streamflows 

exceeding the range for which constituent concentrations 

have been measured will have larger measures of uncertainty 

(error bars) than loads based on known conditions. Additional 

information on the effects of stormflow samples on constituent 

load estimation can be found in Robertson and Roerish (1999) 

and Sprague (2001). 

Trends in Nutrient Concentrations, 

1975–2003 and 1993–2003

Water-quality data for selected USGS monitoring stations 

were analyzed for trends in flow-adjusted nutrient concentrations and modeled instream (non-flow-adjusted) concentrations during long-term (1975–2003) and recent (1993–2003) 

periods. Stream discharges also were analyzed for trends 

during these two periods. Results of trend tests, and results of 

associated statistical tests, were considered significant if the 

attained significance level of the test (p-value) was less than 

or equal to 0.05, and were considered highly significant if the 

p-value was less than or equal to 0.01. 

The trend analysis techniques used in this study are all 

parametric techniques, which assume a linear trend during the 

period of analysis. In many cases, the trends discussed here 

have not been linear, particularly during the long-term period. 

Consideration of nonlinear trends as part of the evaluation of 

trend results is discussed in more detail in the “Methods” section of this report. 

Trends in Streamflow

Trends in stream discharge were analyzed by the streamflow model component of the statistical modeling approach 

described in the “Methods” section (results in appendix 5). 

The streamflow trend evaluated by the model is the trend in 

daily median flow. Trends in streamflow were detected at only 

two stations during the periods of analysis. Downward trends 

in streamflow were detected for the Quinebaug River at Jewett 

City, Conn., for the long-term period, and for the Cooper River 

at Haddonfield, N.J., during the recent period (stations 18 and 

95, fig. 4, table 5). 

About half of the stations analyzed (15 of 32) for the 

long-term period had significant serial correlation in the flow 

residuals, and 10 of the 15 stations had highly significant serial 

correlation. About one-fourth of the stations analyzed (12 of 

46) for the recent period had significant serial correlation, 

with highly significant serial correlation at 6 of the 12 stations 

(appendix 5, table 5–1). This finding in the streamflow trend 

results means that some additional serial correlation in the 

residuals was not removed by the autoregressive component 

of the streamflow model. The practical importance of this 

circumstance for the statistical significance of water-quality 

trend estimates is likely to be small (G.E. Schwarz, U.S. 

Geological Survey, written commun., 2006). Serial correlation 

in the streamflow residuals is likely to decrease the p-value 

associated with the trend coefficient in the streamflow model, 

thus increasing the likelihood of observing a significant 

trend in streamflow. However, this possible outcome was not 

observed in the analyses included in this report. Among the 

stations with significant serial correlation in the flow residuals, 

only one station, the Quinebaug River at Jewett City, Conn., 

also had a significant trend in streamflow. 

Trends in Nutrient Concentrations

Trends in flow-adjusted nutrient concentrations and 

modeled instream (non-flow-adjusted) concentrations were 

analyzed for 32 stations during 1975–2003 and for 46 stations during 1993–2003 by using the coupled statistical model 

of streamflow and water quality; 31 stations were analyzed 

for both periods. Flow-adjusted trends in one or more nutrient concentrations also were analyzed for 90 stations during 

1993–2003 by using Tobit regression in ESTREND. The 
38 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

statistical model requires a continuous record of daily mean 

streamflow, whereas ESTREND requires only instantaneous 

streamflow measurements at the time of water-quality sampling. Consequently, use of ESTREND enabled evaluation of 

a larger group of stations. Some water-quality stations were 

evaluated with both programs. Altogether, 90 stations were 

analyzed for trends in flow-adjusted concentrations of one or 

more nutrients during the two periods (appendix 6, table 6–1). 

Stations analyzed for trend during the long-term period 

have varied initial dates for water-quality data. The longterm period selected for analysis started in 1975 for 22 of 

the 32 stations analyzed, in 1979 for 7 stations, and in 1982 

for 3 stations (22 to 29 water years). All stations evaluated 

with the coupled statistical model during the recent period of 

1993–2003 had records beginning in 1993 and ending in 2003 

(11 water years). Stations evaluated with Tobit regression had 

records of 8 to 11 years in the 1993–2003 period. 

Trends in Flow-Adjusted Nutrient Concentrations

Significant trends in flow-adjusted nutrient concentrations 

were more frequent during the long-term period than during 

the recent period (table 13). About two-thirds of the 32 stations analyzed for trends in total nitrogen, nitrite-plus-nitrate, 

and total phosphorus during 1975–2003 had significant trends 

in one or more of these nutrients. By contrast, significant 

trends in these nutrients were detected in about one-quarter to 

one-third of the 52 to 83 stations analyzed for trends in these 

three constituents during 1993–2003. In some cases, findings 

of no trend during the recent period may result from decreased 

sensitivity of the trend test to detect subtle trends during a 

shorter period with fewer samples. 

In general, downward trends in flow-adjusted nutrient 

concentrations were more frequently detected than upward 

trends during both periods of analysis, with two major exceptions that are discussed in the following sections. Numerous 

downward trends in flow-adjusted concentrations of nitrogen 

and phosphorus constituents are an indication of regional 

improvements in nutrient-related water-quality conditions. 

Total Nitrogen

Significant long-term downward trends in flow-adjusted 

concentrations of total nitrogen were detected at about half 

(18) of the 32 stations analyzed; 4 stations had upward trends. 

By contrast, during the recent period, about two-thirds of the 

81 stations analyzed had no significant trend, and the remaining stations were about equally divided between upward and 

downward trends (fig. 7, table 13). 

Numerous nonlinear trends in flow-adjusted concentrations of total nitrogen were identified. Of the 31 stations that 

were analyzed during both the long-term and recent periods, 

11 had downward trends during 1975–2003 and no significant 

trend during 1993–2003, and 4 had downward trends during 1975–2003 and upward trends during 1993–2003. These 

results may indicate that at a little less than half of the stations 

evaluated, the major decreases in flow-adjusted total nitrogen 

concentrations took place prior to 1993, with flow-adjusted 

concentrations remaining stable, or in some cases increasing, 

in the more recent period. 

Downward trends in flow-adjusted concentrations of 

total nitrogen were detected during both periods of analysis at 

three stations: the Naugatuck River at Beacon Falls, Conn., 

the Passaic River at Little Falls, N.J., and the Delaware River 

at Trenton, N.J. (stations 39, 55, and 90). Upward trends in 

total nitrogen were detected during both periods of analysis at 

four stations: the Saddle River at Lodi, N.J., Toms River near 

Toms River, N.J., the Choptank River near Greensboro, Md., 

and the Pamunkey River near Hanover, Va. (stations 56, 71, 

101, 125). 

Dissolved Ammonia Nitrogen and Total Kjeldahl Nitrogen

Trends in ammonia nitrogen and total Kjeldahl nitrogen 

(total-ammonia-plus-organic nitrogen in unfiltered or whole 

Table 13. Summary of trend results for flow-adjusted concentrations of nutrients and suspended sediment, 1975–2003 and 1993–2003.

[Long-term period for trend analysis spans 22–29 water years at different stations, all ending in 2003; recent period for trend analysis spans 8 to 11 water years 

within the 1993–2003 period at different stations. Significant trend: p-value less than or equal to 0.05; highly significant trend: p-value less than or equal to 

0.01; --, not analyzed]

Water-quality constituent

1975–2003, 1979–2003, or 1982–2003 1993–2003

Number of 

stations 

analyzed

Upward 

trend

Downward 

trend

No significant 

trend

Number of 

stations 

analyzed

Upward 

trend

Downward 

trend

No significant 

trend

Total nitrogen 32 4 18 10 81 12 15 54

Ammonia nitrogen 6 0 6 0 15 2 6 7

Total Kjeldahl nitrogen 6 0 6 0 0 -- -- --

Nitrite-plus-nitrate nitrogen 32 11 10 11 52 1 12 39

Total phosphorus 32 3 19 10 83 17 6 60

Suspended sediment 4 0 4 0 8 1 2 5
Trends in Nutrient Concentrations, 1975–2003 and 1993–2003 39

Figure 7. Trends in flow-adjusted concentrations of total nitrogen, (A) 1975–2003 and (B) 1993–2003.

48°

36°

82° 66°

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

1990 Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

MASSACHUSETTS

CONNECTICUT

Philadelphia

Newark New York City

Hartford

Providence

NEW YORK

PENNSYLVANIA

NEW JERSEY

MASSACHUSETTS

CONNECTICUT RHODE

ISLAND

Trenton

Long Island

Inset Map

0 50 MILES

0 50 KILOMETERS

Delaware River

Hudson River

Long Island Sound

Narragansett

Bay

13

14

18

27 22

30

37 39

40

41

50

55

85

90

24

32

54

68

78

97

98

56

71

CONNECTICUT RHODE

ISLAND

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUT RHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

Chesapeake Bay

Philadelphia

Providence

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Augusta

Montpelier

Albany

Boston

Concord

Richmond

Harrisburg Trenton

Dover

Annapolis

Hartford

Providence

Washington, 

D.C.

Baltimore

Philadelphia

Newark New York 

City

See Inset Map

Narragansett

Bay

Cape

Cod

Bay

Buzzards Bay

ATLANTIC OCEAN

ATLANTIC OCEAN

Delaware

Bay

Long Island Sound

Schuylkill R.

De al ware River

Hudson River

Penobscot River

Kennebec River

Shenandoah River

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Connecticut River

Merrimack River

Saint John River

Lake

Champlain

James River

EXPLANATION

Study area boundary

Trends in flow-adjusted concentrations

 of total nitrogen, 1975–2003, with 

 station sequence number (table 5)

 Upward

 No significant trend

 Downward

Washington, D.C.

State capital

City, over 250,000 population

101

55

111

114

124

127

101

125

122

122

126

129

A
40 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Figure 7. Trends in flow-adjusted concentrations of total nitrogen, (A) 1975–2003 and (B) 1993–2003.—Continued

48°

36°

82° 66°

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

1990 Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

Philadelphia

MASSACHUSETTS

CONNECTICUT

Philadelphia

Newark New

York City

Hartford

Providence

NEW YORK

PENNSYLVANIA

NEW JERSEY

MASSACHUSETTS

CONNECTICUT RHODE

ISLAND

Trenton

Long Island

Inset Map

0 50 MILES

0 50 KILOMETERS

Delaware River

Hudson River

Long Island Sound

Narragansett

Bay

14

35

41

56

71

78

11

12

13

17

18

22

23

24 25 26

27

28

29

30 31

32

33

34 36

37

40

49

50 53

54

57 59 58

61 67

68

69

70

75

77 79

85

87

88 89

91

94 97 95

98

99

9

10

38

39

42

51

52 55

72

74

82

83

90

,

MASSACHUSETTS

CONNECTICUT RHODE

ISLAND

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUT RHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

Chesapeake Bay

Philadelphia

Providence

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Augusta

Montpelier

Albany Boston

Concord

Richmond

Harrisburg Trenton

Dover

Annapolis

Hartford

Providence

Washington, 

D.C.

Baltimore

Philadelphia

Newark

New York City

See Inset Map

Narragansett

Bay

Cape

Cod

Bay

Buzzards Bay

ATLANTIC OCEAN

ATLANTIC OCEAN

Delaware

Bay

Long Island Sound

De al ware River

Hudson River

Schuylkill R.

De al ware River

Hudson River

Penobscot River

Kennebec River

Shenandoah River

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Connecticut River

Merrimack River

Saint John River

Lake

Champlain

James River

EXPLANATION

Study area boundary

Trends in flow-adjusted concentrations

 of total nitrogen, 1993–2003, with 

 station sequence number (table 5)

 Upward

 No significant trend

 Downward

Washington, D.C.

State capital

City, over 250,000 population

56

55

47

101

124

125 126

127

129

109

110

47

111

112

114

118

122

123

B

116
Trends in Nutrient Concentrations, 1975–2003 and 1993–2003 41

water samples) were analyzed at a small number of stations, 

primarily in drainage basins where point sources have 

been evaluated for this report. The long-term record for the 

Susquehanna River at Conowingo, Md., also was analyzed 

for trends in these constituents, because of the regional 

importance of this drainage basin. 

Downward trends in flow-adjusted concentrations of 

ammonia nitrogen and total Kjeldahl nitrogen were detected 

at the six stations analyzed for the long-term period (table 13). 

During the recent period, downward trends in ammonia 

nitrogen were detected at 6 of the 15 stations evaluated, and 

2 stations, both in the Raritan River Basin in New Jersey, had 

upward trends. 

Nitrite-plus-Nitrate Nitrogen

Long-term flow-adjusted concentrations of nitrite-plusnitrate nitrogen increased at about one-third of the 32 stations 

analyzed, decreased at about one-third of the stations, and 

had no significant trend at about one-third of the stations 

(table 13, fig. 8A). During the recent period, three-quarters 

of the stations had no trend in nitrite-plus-nitrate, and only 

one station had an upward trend (table 13, fig. 8B). The 

Saddle River at Lodi, N.J. (station 56), was the only station 

with upward trends detected during both periods of analysis. 

Downward trends in flow-adjusted concentrations of nitriteplus-nitrate were detected at four stations during both the 

long-term and recent periods: the Naugatuck River at Beacon 

Falls, Conn.; the Delaware River at Trenton, N.J.; the Patuxent 

River near Bowie, Md.; and the Appomattox River at Matoaca, 

Va. (stations 39, 90, 114, 129). 

Total Phosphorus

Downward trends in flow-adjusted concentrations of 

total phosphorus were detected at more than half the stations 

analyzed (19 of 32) during the long-term period (table 13, 

fig. 9A). During the recent period, however, most of the 

significant trends detected (17 of 83 stations) were upward 

trends (table 13, fig. 9B), indicating possible reversals to the 

overall long-term water-quality improvements relative to total 

phosphorus concentrations. Seven stations where downward 

trends in flow-adjusted concentrations of total phosphorus 

were detected during 1975–2003 had upward trends during 

1993–2003. These results indicate that the long-term trends 

at these stations were not monotonic; that is, flow-adjusted 

concentrations generally decreased from the late 1970s to 

the early 1990s, and then increased from the early 1990s 

to 2003, although flow-adjusted concentrations in the early 

2000s were still lower than in the late 1970s. This general 

pattern is apparent in a plot of unadjusted total phosphorus 

concentrations for the Patuxent River near Bowie, Md. 

(station 114, fig. 10), a station with a highly significant longterm downward trend in flow-adjusted concentrations of total 

phosphorus, and a highly significant upward trend in the more 

recent part of the period of record. 

Most of the 17 stations with upward trends in flowadjusted concentrations of total phosphorus during 1993–2003 

monitor streams that receive municipal wastewater effluent, 

but a few monitor streams in basins with agricultural or urban 

land use and no point sources. The Pamunkey River near 

Hanover, Va., was the only station with upward trends detected 

for both periods of analysis (station 125). 

Suspended Sediment

All four stations analyzed for trends in flow-adjusted 

concentrations of suspended sediment during 1975–2003 

had downward trends (table 13). The Susquehanna River at 

Conowingo, Md., had downward trends during both the longterm and recent periods (station 111). Sediment carried by 

the Susquehanna River tends to settle behind the Conowingo 

Dam and in other reservoirs on the lower reaches of the river 

(Langland and Hainly, 1997). Of eight stations analyzed for 

the recent period, the only station with an upward trend in 

flow-adjusted concentrations of suspended sediment was 

Conococheague Creek at Fairview, Md. (station 116); two 

stations had downward trends. 

Trends in Flow-Adjusted Concentrations of Nutrients in 

Large Drainage Basins

Flow-adjusted trend results for the 11 largest drainage 

basins evaluated in the study, with drainage areas greater 

than 1,000 mi2, showed many long-term improvements in 

nutrient conditions, and also some indications of long-term 

or recent deterioration in water quality (table 14). Monitored 

drainage areas for these 11 basins encompass 72,275 mi2, or 

about 44 percent of the region. The six largest drainage basins, 

with drainage areas greater than 3,000 mi2, encompass about 

39 percent of the region. 

Long-term downward trends in flow-adjusted concentrations of nutrients predominated at 7 of the 10 stations with 

long-term records; 20 downward trends were detected out of 

35 analyses for these 10 stations (table 14). During the recent 

period, 19 of 36 trend analyses for 10 stations showed no 

significant trend; the remaining analyses were about equally 

divided between upward and downward trends. Four upward 

trends in total nitrogen and four upward trends in total phosphorus were detected during the recent period. Four downward 

trends in nitrite-plus-nitrate were detected during the recent 

period, and no upward trends were detected. 

Trend results indicate that progress has been made in 

reducing flow-adjusted nutrient concentrations in the largest drainage basins of the region. Downward trends in flowadjusted concentrations also may indicate progress in reducing nutrient delivery to streams from various sources. The 

1993–2003 results, however, also indicate increases in nutrient 

concentrations in some drainage basins during the most recent 

part of the period analyzed in this study. The preponderance of 

downward trends during the long-term period, viewed in conjunction with the absence of significant trends for about half 

of the analyses in these large basins for the recent period, may 

indicate that the largest reductions in flow-adjusted nutrient 

concentrations took place prior to the 1990s. 
42 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

48°

36°

82° 66°

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

1990 Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

0 50 100 MILES

0 50 100 KILOMETERS

Philadelphia

Newark New York

City

Hartford

Providence

NEW YORK

PENNSYLVANIA

NEW JERSEY

MASSACHUSETTS

CONNECTICUT

RHODE

ISLAND

Trenton

Long Island

Inset Map

Narragansett

Bay

0 50 MILES

0 50 KILOMETERS

Delaware River

Hudson River

Long Island Sound

27

32

54

55 56

68

71 97

13

30

39

41

50

90

14

18

22

24

37

40

78

85

98

101 122

125

111

126

114

124

127

129

RHODE

ISLAND

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUT RHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

Chesapeake Bay

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Augusta

Montpelier

Albany

Boston

Concord

Richmond

Harrisburg Trenton

Dover

Annapolis

Hartford Providence

Washington, D.C.

Baltimore

Philadelphia

Newark New York City

See Inset Map

Narragansett

Bay

Cape

Cod

Bay

Buzzards Bay

Delaware

Bay

ATLANTIC OCEAN

ATLANTIC OCEAN

Long Island Sound

Schuylkill R.

De al ware River

Hudson River

Penobscot River

Kennebec River

Shenandoah River

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Connecticut River

Merrimack River

Saint John River

Lake

Champlain

James River

EXPLANATION

Study area boundary

Trends in flow-adjusted concentrations

 of nitrite-plus-nitrate, 1975–2003, with 

 station sequence number (table 5)

 Upward

 No significant trend

 Downward

Washington, D.C.

State capital

City, over 250,000 population

122

124

24

A

Figure 8. Trends in flow-adjusted concentrations of nitrite-plus-nitrate nitrogen, (A) 1975–2003 and (B) 1993–2003.
Trends in Nutrient Concentrations, 1975–2003 and 1993–2003 43

48°

36°

82° 66°

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

1990 Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

13

14

15 17

18

22

23

24

27

28

30 31

37

40

41

50 53 54

57 59 58

61

63

67

68

69

71

78

85

95

98

56

25

32

39

55

70

75

82

90

Philadelphia

Newark

New York

City

Hartford

Providence

NEW YORK

PENNSYLVANIA

NEW JERSEY

MASSACHUSETTS

CONNECTICUT

RHODE

ISLAND

Trenton

Long Island

Inset Map

Long Island Sound

Narragansett

Bay

0 50 MILES

0 50 KILOMETERS

Delaware River

Hudson River

Penobscot River

Kennebec River

James River

Shenandoah River

Connecticut River

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Merrimack River

Saint John River

Lake

Champlain

EXPLANATION

Study area boundary

Trends in flow-adjusted concentrations

 of nitrite-plus-nitrate, 1993–2003, with 

 station sequence number (table 5)

 Upward

 No significant trend

 Downward

Washington, D.C.

State capital

City, over 250,000 population

56

55

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUT RHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

47

47

101

112

124

116

125 126

127

111

114

122

129

B

Chesapeake Bay

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Augusta

Montpelier

Albany Boston

Concord

Richmond

Harrisburg Trenton

Dover

Annapolis

Hartford

Providence

Washington, 

D.C.

Baltimore

Philadelphia

Newark New York

City

See Inset Map

Narragansett

Bay

Cape

Cod

Bay

Buzzards Bay

Delaware

Bay

ATLANTIC OCEAN

ATLANTIC OCEAN

Long Island Sound

Figure 8. Trends in flow-adjusted concentrations of nitrite-plus-nitrate nitrogen, (A) 1975–2003 and (B) 1993–2003.—Continued
44 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

48°

36°

82° 66°

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

1990 Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

13

14

18

22

24

27

30

32

37

40

41

55

71

78

85

90

39

54 50

56

68

97

98

RHODE

ISLAND

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUT RHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

125

129

101

124

126

127

111

114

122

A

Schuylkill R.

Hudson River

Penobscot River

Kennebec River

James River

Shenandoah River

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Connecticut River

Merrimack River

Saint John River

Lake

Champlain

Chesapeake Bay

Providence

Philadelphia

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Augusta

Montpelier

Albany

Boston

Concord

Richmond

Harrisburg Trenton

Dover

Annapolis

Hartford

Providence

Washington, D.C.

Baltimore

Philadelphia

Newark

New York City

See Inset Map

Narragansett

Bay

Cape

Cod

Bay

Buzzards Bay

Delaware

Bay

ATLANTIC OCEAN

ATLANTIC OCEAN

Long Island Sound

Philadelphia

Newark New York City

Hartford

Providence

NEW YORK

PENNSYLVANIA

NEW JERSEY

MASSACHUSETTS

CONNECTICUT

RHODE

ISLAND

Trenton

Long Island

Inset Map

0 50 MILES

0 50 KILOMETERS

Delaware River

Hudson River

Long Island Sound

Narragansett

Bay

EXPLANATION

Study area boundary

Trends in flow-adjusted concentrations

 of total phosphorus, 1975–2003, with 

 station sequence number (table 5)

 Upward

 No significant trend

 Downward

Washington, D.C.

State capital

City, over 250,000 population

125

124

114

Figure 9. Trends in flow-adjusted concentrations of total phosphorus, (A) 1975–2003 and (B) 1993–2003.
Trends in Nutrient Concentrations, 1975–2003 and 1993–2003 45

48°

36°

82° 66°

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

1990 Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

10

38

51

72

74 76

9

14

15 22

23

26 28

31

32

33

34

35

36

40 37

43 42 44

49

50 52

53

54

55

57 58

61

63

67

68

69

70

71

77 78

81

82

83

84 85

87

88

89

90

91

94 95 97

98 73

11

13

17

18

27

29

39

41

56

99

Philadelphia

Newark

New York 

City

Hartford

Providence

NEW YORK

PENNSYLVANIA

NEW JERSEY

MASSACHUSETTS

CONNECTICUT

RHODE

ISLAND

Trenton

Long Island

Inset Map

0 50 MILES

0 50 KILOMETERS

Delaware River

Hudson River

Long Island Sound

Narragansett

Bay

RHODE

ISLAND

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUTRHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

Schuylkill R.

Hudson River

Penobscot River

Kennebec River

James River

Shenandoah River

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Connecticut River

Merrimack River

Saint John River

Lake

Champlain

Chesapeake Bay

Providence

Philadelphia

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Augusta

Montpelier

Albany

Boston

Concord

Richmond

Harrisburg Trenton

Dover

Annapolis

Hartford

Providence

Washington, D.C.

Baltimore

Philadelphia

Newark

New York City

See Inset Map

Narragansett

Bay

Cape

Cod

Bay

Buzzards Bay

Delaware

Bay

ATLANTIC OCEAN

ATLANTIC OCEAN

Long Island Sound

EXPLANATION

Study area boundary

Trends in flow-adjusted concentrations

 of total phosphorus, 1993–2003, with 

 station sequence number (table 5)

 Upward

 No significant trend

 Downward

Washington, D.C.

State capital

City, over 250,000 population

51

101

109

111

114

114

122

124

125

110

45 47

116

118

118

123

126

127

129

B

Figure 9. Trends in flow-adjusted concentrations of total phosphorus, (A) 1975–2003 and (B) 1993–2003.—Continued
46 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Trends in Modeled Instream Nutrient 

Concentrations

Trends in modeled instream nutrient concentrations for 

the long-term and recent periods were analyzed by using 

the coupled statistical model of streamflow and water quality (table 15, in back of report, and table 16). This method of 

analysis provides a modeled “reference concentration” for a 

constituent at the beginning of a period of analysis, that is, a 

central tendency in the concentration data for the initial year 

of the analysis that is not affected by seasonal variability or 

by fluctuations in annual streamflow (G.E. Schwarz, U.S. 

Geological Survey, written commun., 2006). These reference concentrations, in conjunction with trend results for the 

periods of analysis, provide a useful indicator for assessing the 

status of instream water quality, in terms of habitat conditions 

for aquatic life and in terms of conditions that may promote 

freshwater eutrophication or downstream eutrophication in 

estuarine areas. 

Trends in modeled instream concentrations (non-flowadjusted concentrations) are likely to be the same as or similar 

to trends in flow-adjusted concentrations, in the absence of 

trends in streamflow. This is the case for the trend results 

reported in this study, where the direction of change, upward 

or downward, was similar for instream (non-flow-adjusted) 

and flow-adjusted trends in concentration at most monitoring 

stations (table 15, in back of report; appendix 6, table 6–1). 

Nutrient Concentrations in Undeveloped Drainage Basins

Flow-weighted nutrient concentrations for undeveloped 

drainage basins have been evaluated in a national study by 

Clark and others (2000). Nine drainage basins evaluated in the 

national study are in the northeastern region encompassed by 

this study. Information for these nine streams and their drainage basins provides another useful reference point for evaluating nutrient concentrations and trends in the northeastern 

United States (table 17). 

Figure 10. Total phosphorus concentrations as a function of time, Patuxent River near Bowie, Md., 1979–2003.

1979–2003: Downward trend

1993–2003: Upward trend

19781980198219841986198819901992199419961998200020022004

0.01

0.1

1

Total phosphorus concentration, in milligrams per liter

Patuxent River near Bowie, Maryland, total phosphorus concentrations, 

 1979–2003 (station 114)

0.002

3

Year

EXPLANATION

LOESS smooth line

Constituent concentration
Trends in Nutrient Concentrations, 1975–2003 and 1993–2003 47

Table 14. Trends in flow-adjusted nutrient concentrations and nutrient loads in large drainage basins, 1975–2003 and 

1993–2003.—Continued

[No long-term record for Mohawk River at Cohoes, N.Y. Schuylkill River at Philadelphia not analyzed for 1993–2003 period because of gap in waterquality record. Significant trend: p-value less than or equal to 0.05; highly significant trend: p-value less than or equal to 0.01; mi2

, square miles; 

*, highly significant trend; N, no significant trend; --, data unavailable for period or not analyzed]

Station 

sequence number 

(fig. 4)

Water-quality constituent Initial 

water year

Flow-adjusted concentration trend Trend in load

1975–2003 1993–2003 1975–2003 1993–2003

Susquehanna River at Conowingo, Md. (27,100 mi2)

111 Total nitrogen 1979 *Down N N N

111 Ammonia nitrogen 1979 *Down -- *Down --

111 Total Kjeldahl nitrogen 1979 *Down -- Down --

111 Nitrite-plus-nitrate nitrogen 1979 N *Down N N

111 Total phosphorus 1979 *Down *Up N N

111 Suspended sediment 1979 *Down *Down N N

Potomac River at Chain Bridge, at Washington, D.C. (11,570 mi2)

122 Total nitrogen 1975 N N N N

122 Nitrite-plus-nitrate nitrogen 1975 *Up *Down N N

122 Total phosphorus 1975 Down *Up N N

122 Suspended sediment 1993 -- N -- N

Connecticut River at Thompsonville, Conn. (9,660 mi2)

22 Total nitrogen 1975 *Down N *Down N

22 Nitrite-plus-nitrate nitrogen 1975 N N N N

22 Total phosphorus 1975 *Down N *Down N

22 Suspended sediment 1993 -- N -- N

Delaware River at Trenton, N.J. (6,780 mi2)

90 Total nitrogen 1975 *Down Down Down N

90 Nitrite-plus-nitrate nitrogen 1975 *Down *Down N N

90 Total phosphorus 1975 *Down N *Down N

James River at Cartersville, Va. (6,252 mi2)

127 Total nitrogen 1975 *Down *Up Down N

127 Ammonia nitrogen 1979 *Down *Down *Down Down

127 Nitrite-plus-nitrate nitrogen 1975 *Down N *Down N

127 Total phosphorus 1975 N N N N

Mohawk River at Cohoes, N.Y. (3,450 mi2)

47 Total nitrogen 1993 -- N -- N

47 Nitrite-plus-nitrate nitrogen 1993 -- N -- N

47 Total phosphorus 1993 -- N -- N

47 Suspended sediment 1993 -- *Down -- N

Schuylkill River at Philadelphia, Pa. (1,893 mi2)

97 Total nitrogen 1975 N -- N --

97 Nitrite-plus-nitrate nitrogen 1975 *Up -- N --

97 Total phosphorus 1975 N -- N --

Rappahannock River near Fredericksburg, Va. (1,595 mi2)

124 Total nitrogen 1979 Down *Up N N

124 Nitrite-plus-nitrate nitrogen 1979 *Down N N N

124 Total phosphorus 1979 N *Up N N
48 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Flow-weighted concentrations are not identical to timeweighted concentrations, and comparisons should be made 

with caution. These measures may differ because of short periods of high streamflow, where dilution or runoff enrichment 

may have a strong effect on flow-weighted concentrations. 

However, flow-weighted and time-weighted concentrations are 

likely to be much more similar in streams with undeveloped 

watersheds than in streams with substantial development and 

nutrient inputs (J.D. Blomquist, U.S. Geological Survey, written commun., 2010). 

In the national study, flow-weighted concentration, in 

milligrams per liter (mg/L), was estimated as the total stream 

load of a constituent during the entire estimation period 

divided by the total stream discharge during the estimation 

period (Clark and others, 2000). Flow-weighted concentration 

can be thought of as the concentration of a constituent that 

would be present in a giant storage tank holding all the 

discharge from the stream (G.E. Schwarz, U.S. Geological 

Survey, written commun., 2007). A day with more streamflow 

has more weight in determining the flow-weighted 

Table 14. Trends in flow-adjusted nutrient concentrations and nutrient loads in large drainage basins, 1975–2003 and 

1993–2003.—Continued

[No long-term record for Mohawk River at Cohoes, N.Y. Schuylkill River at Philadelphia not analyzed for 1993–2003 period because of gap in waterquality record. Significant trend: p-value less than or equal to 0.05; highly significant trend: p-value less than or equal to 0.01; mi2

, square miles; 

*, highly significant trend; N, no significant trend; --, data unavailable for period or not analyzed]

Station 

sequence number 

(fig. 4)

Water-quality constituent Initial 

water year

Flow-adjusted concentration trend Trend in load

1975–2003 1993–2003 1975–2003 1993–2003

Housatonic River at Stevenson, Conn. (1,544 mi2)

37 Total nitrogen 1975 *Down N N N

37 Nitrite-plus-nitrate nitrogen 1975 N N N N

37 Total phosphorus 1975 *Down N *Down N

Appomattox River at Matoaca, Va. (1,342 mi2)

129 Total nitrogen 1979 N *Up N N

129 Ammonia nitrogen 1980 *Down *Down *Down N

129 Nitrite-plus-nitrate nitrogen 1979 Down Down Down N

129 Total phosphorus 1979 Up N N N

Pamunkey River near Hanover, Va. (1,078 mi2)

125 Total nitrogen 1975 *Up *Up N N

125 Nitrite-plus-nitrate nitrogen 1975 *Up N N N

125 Total phosphorus 1975 *Up *Up N N

Table 16. Summary of trend results for modeled instream concentrations, 1975–2003 and 1993–2003.

[Long-term period for trend analysis spans 22–29 water years at different stations, all ending in 2003; recent period for trend analysis spans 11 water years 

at all stations. Significant trend: p-value less than or equal to 0.05; highly significant trend: p-value less than or equal to 0.01; --, not analyzed]

Water-quality constituent

1975–2003, 1979–2003, or 1982–2003 1993–2003

Number of 

stations 

analyzed

Upward 

trend

Downward 

trend

No significant trend

Number of 

stations 

analyzed

Upward 

trend

Downward 

trend

No significant trend

Total nitrogen 32 4 16 12 46 6 4 36

Ammonia nitrogen 6 0 5 1 9 1 4 4

Total Kjeldahl nitrogen 6 0 6 0 0 -- -- --

Nitrite-plus-nitrate nitrogen 32 11 7 14 46 0 8 38

Total phosphorus 32 2 18 12 46 11 0 35

Suspended sediment 4 0 4 0 8 0 2 6
Trends in Nutrient Concentrations, 1975–2003 and 1993–2003 49

Table 17. Flow-weighted nutrient concentrations and nutrient yields in undeveloped basins evaluated in a national study (Clark and others, 2000).[Source for flow-weighted mean concentrations and associated remark codes: Clark and others, 2000. Source for mean streamflow and mean annual yields: D.K. Mueller, U.S. Geological Survey, written commun., 2007. Mean annual yields have been converted from kilograms per square kilometer per year to pounds per square mile per year, and have been rounded. Drainage areas shown in this table are from the national study, and differ slightly from those shown in table 5. mi2, square miles; ft3/s, cubic feet per second; mg/L, milligrams per liter; e, flag indicating a lower level of confidence in the reported concentration; lb/mi2/yr, pounds per square mile per year; <, less than]

Station 

sequence 

number 

(fig. 4)

Station name

Ecoregion 

(table 4)

Drainage 

area 

(mi2)

Estimation 

years

Mean 

streamflow 

(ft3/s)

Ammonia 

nitrogen 

(as nitrogen)

Nitrite-plusnitrate 

(as nitrogen)

Total 

nitrogen

Phosphate 

(as phosphorus)

Total 

phosphorus

Flow-weighted mean concentration (mg/L)

3 Wild River at Gilead, Maine 8 69.48 1991–95 168.27 0.015e 0.029e 0.12e 0.007e < 0.030

19 Ammonoosuc River at Bethlehem Junction, N.H. 8 88.39 1994–95 157.35 0.020 0.130 < 0.20 < 0.010 < 0.03021 Green River near Colrain, Mass. 8 41.3 1994–95 64.92 0.020 0.130 < 0.20 < 0.010 < 0.03048 Esopus Creek at Allaben, N.Y. 8 65.23 1994–95 127.63 0.020 0.250 0.35 0.010 0.037e81 Biscuit Brook above Pigeon Brook at Frost Valley, N.Y. 8 4.01 1991–95 9.77 0.024 0.456 0.46 0.003e < 0.03093 McDonalds Branch in Byrne State Forest, N.J. 14 2.35 1991–95 1.47 0.023 0.025e 0.19e 0.006e < 0.030

104 Young Womans Creek near Renovo, Pa. 8 46.32 1991–95 80.81 0.017e 0.335 0.50 0.005e < 0.030

115 South Fork South Branch Potomac River near 

Moorefield, W. Va.

11 279.46 1994–95 274.10 0.020 0.770 1.11 < 0.010 0.037e

128 Holiday Creek near Andersonville, Va. 9 8.49 1991–95 9.16 0.023 0.036e 0.21 0.008e 0.031e

Mean annual yield (lb/mi2/yr)

3 Wild River at Gilead, Maine 8 69.48 1991–95 168.27 77.0 109 503 32.1 43.2

19 Ammonoosuc River at Bethlehem Junction, N.H. 8 88.39 1994–95 157.35 61.6 450 701 35.0 35.021 Green River near Colrain, Mass. 8 41.3 1994–95 64.92 46.9 389 619 30.9 45.848 Esopus Creek at Allaben, N.Y. 8 65.23 1994–95 127.63 60.2 959 1,350 32.4 14381 Biscuit Brook above Pigeon Brook at Frost Valley, N.Y. 8 4.01 1991–95 9.77 107 2,260 2,230 15.7 47.993 McDonalds Branch in Byrne State Forest, N.J. 14 2.35 1991–95 1.47 29.0 30.7 295 7.37 11.7

104 Young Womans Creek near Renovo, Pa. 8 46.32 1991–95 80.81 58.3 1,260 1,740 18.0 34.0

115 South Fork South Branch Potomac River near 

Moorefield, W. Va.

11 279.46 1994–95 274.10 41.5 1,480 2,140 19.3 71.8

128 Holiday Creek near Andersonville, Va. 9 8.49 1991–95 9.16 49.5 72.5 433 16.1 44.8
50 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

concentration than a day with less streamflow. By contrast, 

time-weighted concentration puts equal weight on each 

water-quality observation, or more specifically, puts equal 

weight on the time span between samples. Sampling schemes 

with some kind of regularity are acceptable for determining 

time-weighted concentration, with sample concentrations 

representing an average over time (D.L. Lorenz, U.S. 

Geological Survey, written commun., 2009). Time-weighted 

concentrations are commonly the basis of regulatory standards, 

because regulations address the issue of whether water-quality 

conditions are adverse on a daily basis. A flow-weighted 

concentration may be less than regulatory limits over time, 

but on a given day, a standard or criterion may be exceeded, 

creating adverse conditions for aquatic life. The difference 

between flow-weighted and time-weighted concentrations 

depends on the relation between the constituent concentration 

and streamflow (D.L. Lorenz, U.S. Geological Survey, written 

commun., 2009). For example, if concentration increases as 

streamflow increases, then the flow-weighted concentration 

could exceed regulatory limits, but on a typical day (during 

lower streamflow), the concentration could be less than the 

limit. Conversely, if concentration decreases as streamflow 

increases, then the flow-weighted concentration could be less 

than regulatory limits, but concentrations could exceed limits 

on days of lower streamflow. 

Modeled Instream Nutrient Concentrations in Relation to 

Proposed Nutrient Criteria

Trend results for modeled instream concentrations, along 

with modeled reference concentrations for streams, can be 

evaluated relative to nutrient criteria proposed for rivers and 

streams by the USEPA (table 4) and relative to flow-weighted 

concentrations from the national study for streams with relatively undeveloped or near-pristine drainage areas (table 15, 

in back of report, and table 17), as a means of assessing the 

status of nutrient conditions in the study area. Nutrient criteria 

have been proposed by the USEPA for total nitrogen and total 

phosphorus for 14 ecoregions in the United States (table 4). 

Several cautionary notes should be considered when 

making comparisons between modeled instream concentrations and proposed nutrient criteria. The coupled statistical 

model of streamflow and water quality does not provide a 

measure of uncertainty for the modeled instream concentrations, and consequently, comparisons with proposed nutrient 

criteria are considered qualitative rather than quantitative. 

Additionally, the USEPA has stated that nutrient criteria recommendations “serve as a starting point for States and Tribes 

to develop more refined criteria, as appropriate, to reflect local 

conditions,” and also states that the values presented in nutrient criteria documents “generally represent nutrient levels that 

protect against the adverse effects of nutrient overenrichment” 

(U.S. Environmental Protection Agency, 2001, p. iv). Nutrient 

criteria adopted in the future for specific streams in the region 

may differ from the proposed criteria shown here (tables 4, 15, 

in back of report). Finally, many drainage basins, particularly 

the larger drainage basins, encompass parts of more than one 

nutrient ecoregion, and consequently the nutrient criteria proposed for a single ecoregion may not represent all conditions 

in a given drainage basin. For drainage basins that encompass 

parts of more than one ecoregion, the nutrient criteria shown 

in table 15 (in back of report) either reflect ecoregional assignments made in the NAWQA Program (D.K. Mueller, U.S. 

Geological Survey, written commun., 2003), or represent the 

ecoregion with the highest criterion (highest concentration) 

in that drainage basin. The overall range in proposed criteria 

is small enough that these comparisons, although qualitative, 

provide a useful indicator of water-quality status. 

The national study of nutrients in undeveloped drainage 

basins presents flow-weighted concentrations for total nitrogen, ammonia nitrogen, nitrite-plus-nitrate nitrogen (referred 

to as nitrate in the national report), phosphate, and total 

phosphorus (table 17; Clark and others, 2000). This national 

study found that “concentrations and yields of nitrate tended to 

be highest in northeastern and mid-Atlantic coastal states and 

correlated well with areas of high atmospheric nitrogen deposition” (Clark and others, 2000, p. 1). Nitrate constitutes from 

at least 65 percent to almost 100 percent of the flow-weighted 

mean concentration of total nitrogen in six of the nine streams 

evaluated in the national study, and only 13 to 24 percent 

in three of the streams (table 17). The streams where nitrate 

constitutes a high proportion of total nitrogen are generally 

in upland areas with high concentrations of nitrate in precipitation (Clark and others, 2000, p. 14, fig. 2). Total nitrogen 

concentrations exceed proposed criteria in three of the nine 

drainage basins, including Biscuit Brook in New York, Young 

Womans Creek in Pennsylvania, and the South Fork South 

Branch of the Potomac River in West Virginia (tables 4, 17). 

Elevated concentrations of nutrients persist in many 

of the streams evaluated in this study. Modeled reference 

concentrations for total nitrogen at the start of the 1993–2003 

period exceeded proposed criteria for total nitrogen by a factor 

of two or more at 21 of the 46 stations analyzed (table 15, in 

back of report). Concentrations exceeded proposed criteria 

by a factor of five or more at 4 of the 21 stations. No trend in 

modeled instream concentration of total nitrogen was detected 

for 1993–2003 at 17 of these 21 stations, downward trends 

were detected at 3 stations, and an upward trend was detected 

at 1 station, indicating persistence of elevated concentrations 

during the period of analysis at more than one-third of the stations analyzed. Although criteria have not been proposed for 

nitrite-plus-nitrate, elevated concentrations of this constituent 

are indicated at several stations where modeled reference concentrations for the 1993–2003 period exceed proposed criteria 

for total nitrogen (table 15, in back of report).

Modeled reference concentrations for total phosphorus at 

the start of the 1993–2003 period exceeded proposed criteria 

for total phosphorus by a factor of two or more at 24 of the 

46 stations analyzed for trends (table 15, in back of report). 

At 4 of the 24 stations, modeled reference concentrations 

exceeded proposed criteria by an order of magnitude. No 

significant trends in the modeled instream concentration of 
Trends in Nutrient Concentrations, 1975–2003 and 1993–2003 51

total phosphorus were detected for 1993–2003 at 19 of these 

24 stations, and upward trends were detected at 5 stations, 

indicating persistence of elevated instream total phosphorus 

concentrations during the period of analysis at about one-half 

of the stations analyzed. 

Modeled reference concentrations for total nitrogen 

and total phosphorus at the start of the long-term period 

provide a useful indication of historical instream nutrient 

conditions, and the starting point for long-term trends. Graphs 

of nutrient concentrations as a function of time at selected 

stations show some of these long-term changes (figs. 11, 12). 

Numerous long-term downward trends in flow-adjusted and 

modeled instream nutrient concentrations indicate that at 

many stations, the reference concentrations for the late 1970s 

are no longer representative of conditions in the mid-2000s. 

For example, long-term downward trends in concentrations 

of total nitrogen were detected for the Naugatuck River in 

Connecticut (station 39) and the Delaware River at Trenton, 

N.J. (station 90) (figs. 11A, B). The trends in total nitrogen 

for the Naugatuck and Delaware Rivers are nonlinear, with 

an increase in concentration from the mid-1970s to the mid1980s, and a decrease in concentration from the mid-1980s 

to the mid-2000s; overall, concentrations in the mid-2000s 

are lower than in the mid-1970s. Long-term downward 

trends in all nitrogen constituents evaluated, including total 

nitrogen, nitrite-plus-nitrate nitrogen, ammonia nitrogen, 

and total Kjeldahl nitrogen, were detected for the Patuxent 

River in Maryland (station 114) (figs. 11C–F), with the largest 

decreases in instream concentration taking place prior to the 

early 1990s. Elevated total nitrogen concentrations in the late 

1980s in these and other streams may be affected to some 

extent by a positive analytical bias in total Kjeldahl nitrogen 

concentrations (Patton and Truitt, 2000), as discussed in the 

“Methods” section of this report. The magnitude of the bias is 

believed to be small relative to total nitrogen concentrations 

in streams with substantial urban and agricultural influences. 

In some rivers, such as the Naugatuck and Patuxent, recent 

instream concentrations of total nitrogen substantially exceed 

proposed criteria, despite significant long-term downward 

trends in total nitrogen (figs. 11A, C), and in some rivers, 

recent instream concentrations of nitrite-plus-nitrate nitrogen 

also exceed proposed criteria for total nitrogen (figs. 11D, H). 

At stations with no long-term trend in a constituent, 

reference concentrations modeled for the beginning of the 

long-term period also may be indicative of more recent conditions. No significant long-term trend in instream concentrations of total nitrogen was detected for the Raritan River in 

New Jersey, although short-term changes are apparent during 

the period of record, with concentrations generally decreasing 

from 1982 to 1995, and then increasing from the mid-1990s to 

the early 2000s (fig. 11G). Although no trend in total nitrogen 

was detected for the 1993–2003 period at the significance 

level selected for this study (p-value = 0.05), possible upward 

trends in flow-adjusted and instream concentrations of total 

nitrogen are indicated by trend test results for the 1993–2003 

period, with p-values of 0.125 and 0.116, respectively. A 

long-term upward trend in nitrite-plus-nitrate nitrogen was 

detected for the Raritan River (fig. 11H). Many recent concentrations of total nitrogen and nitrite-plus-nitrate nitrogen 

exceed the proposed criterion for total nitrogen at this location 

(figs. 11G, H). By contrast, long-term downward trends in 

instream concentrations of ammonia nitrogen and total 

Kjeldahl nitrogen were detected, indicating overall improvement in the quality of water in the Raritan River (figs. 11I, J). 

Long-term upward trends in instream concentrations of 

total nitrogen and nitrite-plus-nitrate nitrogen were detected 

for some rivers, including the Saddle River in New Jersey 

and the Choptank River in Maryland (figs. 11K–N). Many 

of the most recent concentrations of both total nitrogen and 

nitrite-plus-nitrate nitrogen in the Choptank River exceed 

the proposed criterion for total nitrogen, and all recent 

concentrations of these constituents in the Saddle River 

exceed the proposed criterion. 

Instream concentrations of total phosphorus decreased 

during the long-term period in several rivers, including the 

Connecticut River in Connecticut and the Delaware River in 

New Jersey (figs. 12A, B); no trends were detected during 

the recent period at these stations. At six locations, including 

the Patuxent River (fig. 10), instream concentrations of total 

phosphorus decreased during the long term, but increased during the recent period. Long-term increases in total phosphorus 

were detected at only two locations, on Raccoon Creek in New 

Jersey and the Pamunkey River in Virginia (figs. 12C, D). 

Despite the number of long-term downward trends detected, 

many of the most recent concentrations of total phosphorus 

substantially exceed proposed criteria in a number of streams. 

Modeled Instream Nutrient Concentrations and Trends in 

Large Drainage Basins

Evaluation of the 11 largest drainage basins analyzed 

for trends shows mixed results in terms of proposed nutrient criteria. Modeled reference concentrations for either total 

nitrogen or total phosphorus or both constituents exceed 

proposed nutrient criteria by a factor of at least two at the start 

of the recent period in the Connecticut, Housatonic, Delaware, 

Potomac, and James Rivers (table 15, in back of report). The 

Schuylkill River was not analyzed for the 1993–2003 period, 

but modeled reference concentrations for both constituents at 

the start of the 1975–2003 period exceed proposed criteria, 

and no long-term trend was detected in either constituent. 

The largest drainage basin, the Susquehanna, incorporates 

several ecoregions, with proposed nutrient criteria at low concentrations in upland headwater areas and at somewhat higher 

concentrations downstream where the monitoring station is 

located. If the highest concentration criteria for ecoregions 

within its drainage area are applied to the Susquehanna River 

at Conowingo, Md. (station 111), the modeled reference concentration for total nitrogen exceeds the proposed criterion by 

a factor of two, and the modeled reference concentration for 

total phosphorus is slightly higher than the proposed criterion 

(table 15, in back of report). A downward trend in the modeled 
52 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

EXPLANATION

LOESS smooth line

Proposed criterion

Constituent concentration

Modeled reference concentration

1975–2003: Downward trend

1993–2003: Downward trend

1975–2003: Downward trend

1993–2003: Downward trend

1979–2003: Downward trend

1993–2003: No trend

1979–2003: Downward trend

1993–2003: No trend

1975 1980 1985 1990 1995 2000 2005

0

1

2

3

4

Total nitrogen concentration, 

in milligrams per liter

B. Delaware River at Trenton, New Jersey, 1975–2003 (station 90)

Proposed criterion: 0.38 mg/L

1975 1980 1985 1990 1995 2000 2005

0

1

2

3

4

5

6

7

8

9

10

11

12

Total nitrogen concentration,

in milligrams per liter

Proposed criterion: 0.71 mg/L

A. Naugatuck River at Beacon Falls, Connecticut, 1975–2003 (station 39)

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 1978 2004

0

1

2

3

4

5

6

7

8

9

10

Total nitrogen concentration, 

in milligrams per liter

C. Patuxent River near Bowie, Maryland, 1979–2003 (station 114)

Proposed criterion: 0.69 mg/L

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

D. Patuxent River near Bowie, Maryland, 1979–2003 (station 114)

0

1

2

3

4

5

6

7

8

Nitrite-plus-nitrate concentration, 

in milligrams per liter

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

0.01

0.1

1

10

Dissolved ammonia concentration,

in milligrams per liter

E. Patuxent River near Bowie, Maryland, 1980–2003 (station 114)

Year

0.001 0

1

2

3

4

5

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

F. Patuxent River near Bowie, Maryland, 1979–2003 (station 114)

Year

Total Kjeldahl nitrogen concentration,

in milligrams per liter

1980–2003: Downward trend

1993–2003: Downward trend

1979–2003: Downward trend

1993–2003: Not analyzed

Figure 11. Nitrogen constituent concentrations as a function of time at selected stations. (See facing page for explanations of (A–F))
Trends in Nutrient Concentrations, 1975–2003 and 1993–2003 53

EXPLANATION

LOESS smooth line

Proposed criterion

Constituent concentration

Modeled reference concentration

1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2004

2004 2004

0

1

2

3

4

5

6

Total nitrogen concentration,

in milligrams per liter

proposed criterion: 0.69 mg/L

1982–2003: No trend

1993–2003: No trend

G. Raritan River at Queens Bridge at Bound Brook New Jersey,

 1982–2003 (station 68)

Year Year

1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

0

1

2

3

4

5

Nitrite-plus-nitrate concentration, 

in milligrams per liter

1982–2003: Upward trend

1993–2003: No trend

H. Raritan River at Queens Bridge at Bound Brook New Jersey,

 1982–2003 (station 68)

0.01

0.1

1

10

Dissolved ammonia concentration,

in milligrams per liter

1982–2003: Downward trend

1993–2003: No trend

I. Raritan River at Queens Bridge at Bound Brook New Jersey,

 1982–2003 (station 68)

0

1

2

3

Total Kjeldahl nitrogen concentration,

in milligrams per liter

1982–2003: Downward trend

1993–2003: Not analyzed

J. Raritan River at Queens Bridge at Bound Brook New Jersey,

 1982–2003 (station 68)

Figure 11. Nitrogen constituent concentrations as a function of time at selected stations. (A) Naugatuck River at Beacon Falls, Conn., 

total nitrogen concentrations, 1975–2003, (B) Delaware River at Trenton, N.J., total nitrogen concentrations, 1975–2003, (C) Patuxent 

River near Bowie, Md., total nitrogen concentrations, 1979–2003, (D) Patuxent River near Bowie, Md., nitrite-plus-nitrate concentrations, 

1979–2003, (E) Patuxent River near Bowie, Md., dissolved ammonia concentrations, 1980–2003, (F) Patuxent River near Bowie, Md., total 

Kjeldahl nitrogen concentrations, 1979–2003, (G) Raritan River at Queens Bridge at Bound Brook, N.J., total nitrogen concentrations, 

1982–2003, (H) Raritan River at Queens Bridge at Bound Brook, N.J., nitrite-plus-nitrate concentrations, 1982–2003, (I) Raritan River 

at Queens Bridge at Bound Brook, N.J., dissolved ammonia concentrations, 1982–2003, (J) Raritan River at Queens Bridge at Bound 

Brook, N.J., total Kjeldahl nitrogen concentrations, 1982–2003, (K) Saddle River at Lodi, N.J., total nitrogen concentrations, 1975–2003, 

(L) Saddle River at Lodi, N.J., nitrite-plus-nitrate concentrations, 1975–2003, (M) Choptank River near Greensboro, Md., total nitrogen 

concentrations, 1975–2003, and (N) Choptank River near Greensboro, Md., nitrite-plus-nitrate concentrations, 1975–2003.—Continued
54 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

1975 1980 1985 1990 1995 2000 2005 2005

2005 2005

0

5

10

15

Total nitrogen concentration,

in milligrams per liter

Proposed criterion: 0.71 mg/L

1975–2003: Upward trend

1993–2003: No trend

K. Saddle River at Lodi New Jersey, 1975–2003 (station 56)

EXPLANATION

LOESS smooth line

Proposed criterion

Constituent concentration

Modeled reference concentration

1975 1980 1985 1990 1995 2000

0

2

4

6

8

10

Nitrite-plus-nitrate concentration, 

in milligrams per liter

1975–2003: Upward trend

1993–2003: No trend

L. Saddle River at Lodi, New Jersey, 1975–2003 (station 56)

1975 1980 1985 1990 1995 2000

0

1

2

3

4

Total nitrogen concentration,

in milligrams per liter

1975–2003: Upward trend

1993–2003: Upward trend

Proposed criterion: 0.71 mg/L

M. Choptank River near Greensboro, Maryland, 1975–2003

 (station 101)

Year

1975 1980 1985 1990 1995 2000

0

0.5

1.0

1.5

2.0

2.5

Nitrite-plus-nitrate concentration, 

in milligrams per liter

1975–2003: Upward trend

1993–2003: No trend

N. Choptank River near Greensboro, Maryland, 1975–2003 

 (station 101) 

Year

Figure 11. Nitrogen constituent concentrations as a function of time at selected stations. (A) Naugatuck River at Beacon Falls, Conn., 

total nitrogen concentrations, 1975–2003, (B) Delaware River at Trenton, N.J., total nitrogen concentrations, 1975–2003, (C) Patuxent 

River near Bowie, Md., total nitrogen concentrations, 1979–2003, (D) Patuxent River near Bowie, Md., nitrite-plus-nitrate concentrations, 

1979–2003, (E) Patuxent River near Bowie, Md., dissolved ammonia concentrations, 1980–2003, (F) Patuxent River near Bowie, Md., total 

Kjeldahl nitrogen concentrations, 1979–2003, (G) Raritan River at Queens Bridge at Bound Brook, N.J., total nitrogen concentrations, 

1982–2003, (H) Raritan River at Queens Bridge at Bound Brook, N.J., nitrite-plus-nitrate concentrations, 1982–2003, (I) Raritan River 

at Queens Bridge at Bound Brook, N.J., dissolved ammonia concentrations, 1982–2003, (J) Raritan River at Queens Bridge at Bound 

Brook, N.J., total Kjeldahl nitrogen concentrations, 1982–2003, (K) Saddle River at Lodi, N.J., total nitrogen concentrations, 1975–2003, 

(L) Saddle River at Lodi, N.J., nitrite-plus-nitrate concentrations, 1975–2003, (M) Choptank River near Greensboro, Md., total nitrogen 

concentrations, 1975–2003, and (N) Choptank River near Greensboro, Md., nitrite-plus-nitrate concentrations, 1975–2003.—Continued
Trends in Nutrient Concentrations, 1975–2003 and 1993–2003 55

Figure 12. Total phosphorus concentrations as a function of time at selected stations. (A) Connecticut River at Thompsonville, Conn., 

1975–2003, (B) Delaware River at Trenton, N.J., 1975–2003, (C) Raccoon Creek near Swedesboro, N.J., 1975–2003, and (D) Pamunkey 

River near Hanover, Va., 1975–2003.

EXPLANATION

LOESS smooth line

Proposed criterion

Constituent concentration

Modeled reference concentration

1975–2003: Downward trend

1993–2003: No trend

1975–2003: Downward trend

1993–2003: No trend

1975–2003: Upward trend

1993–2003: No trend

1975–2003: Upward trend

1993–2003: Upward trend

1975 1980 1985 1990 1995 2000 2005

0.01

0.1

1

10

Total phosphorus concentration, 

in milligrams per liter

A. Connecticut River at Thompsonville, Connecticut, (station 22), 

 1975–2003 

Proposed criterion: 0.01 mg/L

1975 1980 1985 1990 1995 2000

0.01

0.1

1

Total phosphorus concentration, 

in milligrams per liter

Proposed criterion: 0.01 mg/L

0.007

B. Delaware River at Trenton, New Jersey, (station 90), 

1975–2003

1975 1980 1985 1990 1995 2000 0.01

0.1

1

Total phosphorus concentration, 

in milligrams per liter

C. Raccoon Creek near Swedesboro, New Jersey, (station 98), 

1975–2003

Proposed criterion: 0.03125 mg/L

Year

1975 1980 1985 1990 1995 2000

0.001

0.01

0.1

1

Proposed criterion: 0.03656 mg/L

D. Pamunkey River near Hanover, Virginia, (station 125), 

1975–2003

Year

0.001

Total phosphorus concentration, 

in milligrams per liter

2005

2005 2005
56 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

instream concentration of total nitrogen, indicating improvement relative to reference conditions, and an upward trend in 

total phosphorus, indicating deterioration, were detected for 

the recent period for the Susquehanna River. 

Large drainage basins in the region generally have 

sparsely developed headwater basins in upland or mountainous areas, with highly developed and densely populated areas 

near the coast, where monitoring stations are located. Nutrient 

criteria for some large basins are based on forested headwater 

areas that constitute most of the drainage area, and are generally more stringent than criteria for smaller nearby coastal 

basins, even though the downstream reaches share the dense 

population and urban land use characteristics of the coastal 

area. The criteria exceedances reported here may appear to 

contradict the positive results shown by the many long-term 

downward trends in flow-adjusted nutrient concentrations 

in large drainage basins (table 14). However, both analyses 

contain useful information. Progress has been made in reducing nutrient delivery to large streams in the region, as shown 

by numerous long-term downward trends in flow-adjusted 

concentrations of nutrients. The starting point for these trends 

was high, however, and instream concentrations still exceed 

proposed criteria in several major streams. 

Comparing Trend Results from Different Periods 

of Record

Trend results in this report, and in many trend studies, 

refer to linear trends, sometimes called monotonic trends. That 

is, a significant trend refers to a linear change in concentration 

or flow-adjusted concentration between the beginning and the 

end of the period of record analyzed. During long periods of 

time, however, many constituent trends are nonmonotonic, 

with increases, plateaus, and decreases in concentration during 

different periods of time. Typically, the longer the period of 

record, the more likely it is that nonmonotonic trends will be 

present. 

Considering the period of record is always critical when 

evaluating and comparing any trend results. Because longterm trends are often nonmonotonic, different studies might 

report trend results that may appear contradictory, whereas 

the different results are actually attributable to differences in 

the period of record analyzed. Results for different periods of 

record may even appear contradictory in the same study. For 

example, trend analyses for this study determined that flowadjusted and modeled instream concentrations of nitrite-plusnitrate nitrogen in the Potomac River at Washington, D.C., 

increased during the 1975–2003 period and decreased during 

the 1993–2003 period. A study of nutrient trends and loads 

in the Chesapeake Bay watershed found that flow-adjusted 

concentrations of nitrite-plus-nitrate nitrogen at this station 

decreased during the 1985–2004 period, and that modeled 

instream concentrations had no trend (Langland and others, 

2006). A plot of nitrite-plus-nitrate concentrations over time 

clarifies why all these results can be accurate representations 

of water-quality changes in the Potomac River (fig. 13). A 

smooth line through the plot shows the general tendency of 

concentration over time. Concentrations are generally higher 

at the end of the period of record (2003) than at the beginning (1975), supporting the finding of a long-term increase in 

flow-adjusted and modeled instream concentrations. No trend 

in streamflow was detected during either period. The steepest 

increase in nitrite-plus-nitrate concentrations occurred from 

about 1975 to 1985, after which the smooth line is closer to 

horizontal. The position of the smooth line is consistent with 

the finding of no trend in modeled instream concentration for 

1985–2004 (Langland and others, 2006). The downward trend 

in flow-adjusted concentrations detected for the 1985–2004 

period may reflect streamflow variability over time, although 

no trend in streamflow was detected. The smooth line (fig. 13) 

shows a gradual decline during the 1990s and early 2000s, 

consistent with the finding in this study of downward trends in 

flow-adjusted and modeled instream concentrations during the 

1993–2003 period. 

1975 1980 1985 1990 1995 2000 2005

0

1

2

3

Nitrite-plus-nitrate concentration, 

in milligrams per liter

Year

EXPLANATION

LOESS smooth line

Modeled reference

 concentration

Constituent concentration

Potomac River at Chain Bridge, at Washington, D.C. (station 122)

1975–2003: Upward trend

1993–2003: Downward trend

Figure 13. Nitrite-plus-nitrate concentrations as 

a function of time, Potomac River at Chain Bridge, 

Washington, D.C.
Annual Nutrient Loads, 1975–2003 57

Annual Nutrient Loads, 1975–2003

Annual stream loads of total nitrogen, nitrite-plus-nitrate 

nitrogen, and total phosphorus were estimated for 32 stations 

for the period 1975–2003 and for 46 stations for the period 

1993–2003 (table 5); 31 of these stations were evaluated during both periods. Long-term and recent trends in nutrient loads 

were evaluated for these stations by using the coupled statistical model of streamflow and water quality. Load estimation 

and analysis of trends in load were performed for a smaller 

number of stations for ammonia nitrogen, total Kjeldahl 

nitrogen, and suspended sediment. Results of tests for trends 

in load were considered significant if the attained significance 

level of the test (p-value) was less than or equal to 0.05, and 

were considered highly significant if the p-value was less than 

or equal to 0.01. 

Annual loads of total nitrogen and total phosphorus were 

estimated for 37 additional stations that did not have a complete streamflow or water-quality record during the 1993–2003 

period (table 5), to provide better geographic coverage of the 

region and representation of specific land uses in the results. 

Trends in load were not evaluated for these stations because 

of the short and varied periods of record available. Altogether, 

annual loads were estimated for 84 stations. Annual nutrient 

loads, confidence intervals, and annual yields have been compiled for all stations analyzed (appendix 7, table 7–1). 

Relation of Nutrient Loads to Stream Discharge 

Conditions, 1975–2003

Stream discharge has varied substantially from year 

to year during the period of record evaluated in this report, 

and annual nutrient loads have varied accordingly (fig. 14). 

Stations with no long-term or recent trends in annual loads 

have been selected to illustrate the relation of annual loads 

to annual streamflow variability; in one case, the Kennebec 

River at North Sidney, Maine (figs. 14A, B), trends in annual 

loads were not analyzed because of the incomplete record 

for 1993–2003. Stations also have been included to illustrate 

annual loads in years of new minimum or maximum annual 

mean flows in the recent period (table 11). The absence of a 

trend in constituent load means that for similar annual mean 

discharges in different years, the annual constituent load also 

would be similar. 

In many parts of the region, water years 1981, 1985, 

1992, 1995, and 2002 were extremely dry years, and water 

years 1978, 1979, 1984, 1994, 1996, and 2003 were extremely 

wet years (fig. 5). These years represent the minimum and 

maximum ranges for annual nutrient loads estimated for many 

stations in the region during the 1993–2003 or 1975–2003 

periods (fig. 14). Maximum annual loads are often three to 

five times the minimum annual loads during the period of 

record. For example, on the Schuylkill River at Philadelphia, 

Pa. (figs. 14E, F), water years 1984 and 2003 are the first and 

second highest annual mean flows; the first and second highest 

annual loads of total nitrogen and total phosphorus also were 

estimated for those years. Water years 2002 and 1981 are the 

first and second lowest annual mean flows; the first and second 

lowest annual loads of total nitrogen and total phosphorus on 

the Schuylkill River also were estimated for those years. The 

annual load of total nitrogen in 1984 was 3.2 times the annual 

load in 2002 on the Schuylkill River, and the annual load of 

total phosphorus in 1984 was 2.7 times the annual load in 

2002. The interannual difference in loads was much greater on 

Conococheague Creek in Maryland (figs. 14G, H), where the 

maximum annual load of total nitrogen in 2003 was 7.0 times 

the minimum load in 2002, and the maximum total phosphorus 

load in 1996 was 11.5 times the minimum load in 2002. Water 

year 1996 represented a new maximum annual mean flow on 

Conococheague Creek in 75 years of record, and water year 

2002 represented a new minimum (table 11), and this large 

difference in streamflow contributed to the order-of-magnitude 

difference in total phosphorus loads between the two years. 

Annual loads of total nitrogen are typically several times 

greater than annual loads of total phosphorus at a given station. For example, on the Schuylkill River, the maximum total 

nitrogen load is 15.7 times the maximum total phosphorus 

load, and the minimum total nitrogen load is 13.5 times the 

minimum total phosphorus load. Error ranges for annual total 

phosphorus loads are often much larger than error ranges for 

total nitrogen at many stations. Phosphorus concentrations 

vary over orders of magnitude relative to nitrogen concentrations; therefore, phosphorus loads can be expected to have 

larger error ranges. The larger variability in the concentration 

data for total phosphorus may be affected by several factors, 

including the transport of particulate phosphorus during high 

streamflows. Error ranges for nutrient loads are typically larger 

in high flow years with major storms than in low flow years 

characterized by a higher proportion of base flow in the total 

streamflow, and this difference is more pronounced for total 

phosphorus than for total nitrogen, as illustrated by annual 

loads for the Rappahannock River in Virginia (figs. 14I, J). 

Error ranges for total phosphorus may be smaller on streams 

that receive large or numerous point-source discharges, such 

as the Schuylkill River (fig. 14F), because the relatively 

uniform point-source contribution of nutrients throughout the 

year results in a relatively narrow concentration range (less 

scatter in the data). Error ranges for total phosphorus may 

be much larger in drainage basins that have few or no point 

sources and large percentages of agricultural land, such as the 

Choptank, Rappahannock (fig. 14J), and Pamunkey Rivers, 

because of the more varied amounts of nutrients in runoff during extreme storms. 

Annual loads of total nitrogen and total phosphorus 

in the recent period were generally substantially greater 

in 2003 than in 2002, particularly in southern parts of the 

region (figs. 14G–J). Annual loads of total nitrogen or total 

phosphorus or both differ by an order of magnitude for 

those two years in some locations, including the Choptank 

River (not shown), Conococheague Creek (figs. 14G, H), the 

Rappahannock River (figs. 14I, J), and the Pamunkey River 
58 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Total nitrogen load

Annual mean

 discharge

EXPLANATION

EXPLANATION

197819791980198119821983198419851986198719881989199019911992199319941995199619971998199920002001200220032004

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

Annual total nitrogen load, in pounds

0

5,000

10,000

A. Kennebec River at North Sidney, Maine (station 2)

15,000

Annual mean discharge, in cubic feet per second

0

5,000

10,000

15,000

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

Water Year

0

500,000

1,000,000

Annual total phosphorus load, in pounds

B. Kennebec River at North Sidney, Maine (station 2) 

Total phosphorus load

Annual mean

 discharge

Annual mean discharge, in cubic feet per second

1,500,000

Not analyzed for trend

19782004

Not analyzed for trend

Annual stream loads of total nitrogen, 1979–1993

Annual stream loads of total phosphorus, 

1979–1993

Figure 14. Annual mean discharges and annual nutrient loads for selected stations and constituents with no trend in load. 

(A) Kennebec River at North Sidney, Maine, total nitrogen loads, 1979–1993, (B) Kennebec River at North Sidney, Maine, total 

phosphorus loads, 1979–1993, (C) Neshanic River at Reaville, N.J., total nitrogen loads, 1993–2003, (D) Neshanic River at Reaville, 

N.J., total phosphorus loads, 1993–2003, (E) Schuylkill River at Philadelphia, Pa., total nitrogen loads, 1975–2003, (F) Schuylkill River at 

Philadelphia, Pa., total phosphorus loads, 1975–2003, (G) Conococheague Creek at Fairview, Md., total nitrogen loads, 1993–2003, 

(H) Conococheague Creek at Fairview, Md., total phosphorus loads, 1993–2003, (I) Rappahannock River near Fredericksburg, Va., total 

nitrogen loads, 1979–2003, and (J) Rappahannock River near Fredericksburg, Va., total phosphorus loads, 1979–2003.
Annual Nutrient Loads, 1975–2003 59

Total nitrogen load

Annual mean 

 discharge

95-percent confidence

 interval of load estimate

EXPLANATION

EXPLANATION

Total phosphorus load

Annual mean

 discharge

Annual mean discharge, in cubic feet per second

Water Year

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

0

100,000

200,000

300,000

400,000

Annual total nitrogen load, in pounds

C. Neshanic River at Reaville, New Jersey (station 61)

0

20

40

60

450,000 80

Annual stream loads of total nitrogen, 1993–2003

No trend

Annual stream loads of total phosphorus, 1993–2003

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

0

100,000

200,000

300,000

400,000

Annual total phosphorus load, in pounds

D. Neshanic River at Reaville, New Jersey (station 61)

No trend

0

20

40

60

Annual mean discharge, in cubic feet per second

450,000 80

Figure 14. Annual mean discharges and annual nutrient loads for selected stations and constituents with no trend in load. 

(A) Kennebec River at North Sidney, Maine, total nitrogen loads, 1979–1993, (B) Kennebec River at North Sidney, Maine, total 

phosphorus loads, 1979–1993, (C) Neshanic River at Reaville, N.J., total nitrogen loads, 1993–2003, (D) Neshanic River at Reaville, 

N.J., total phosphorus loads, 1993–2003, (E) Schuylkill River at Philadelphia, Pa., total nitrogen loads, 1975–2003, (F) Schuylkill River at 

Philadelphia, Pa., total phosphorus loads, 1975–2003, (G) Conococheague Creek at Fairview, Md., total nitrogen loads, 1993–2003, 

(H) Conococheague Creek at Fairview, Md., total phosphorus loads, 1993–2003, (I) Rappahannock River near Fredericksburg, Va., total 

nitrogen loads, 1979–2003, and (J) Rappahannock River near Fredericksburg, Va., total phosphorus loads, 1979–2003.—Continued
60 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

0

10,000,000

20,000,000

30,000,000

Annual total nitrogen load, in pounds

0

1,000

2,000

3,000

4,000

5,000

Annual mean discharge, in cubic feet per second

E. Schuylkill River at Philadelphia, Pennsylvania (station 97)

Annual stream loads of total nitrogen, 1975–2003

1975–2003

No trend

1993–2003

Not analyzed for trend

35,000,000 5,500 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Water Year

0

500,000

1,000,000

1,500,000

2,000,000

Annual total phosphorus load, in pounds

0

1,000

2,000

3,000

4,000

5,000

Annual mean discharge, in cubic feet per second

F. Schuylkill River at Philadelphia, Pennsylvania (station 97)

Annual stream loads of total phosphorus, 1975–2003

1975–2003

No trend

1993–2003

Not analyzed for trend

2,500,000 5,500

Total nitrogen load

Annual mean 

 discharge

95-percent confidence

 interval of load estimate

EXPLANATION

EXPLANATION

Total phosphorus load

Annual mean

 discharge

95-percent confidence

 interval of load estimate

Figure 14. Annual mean discharges and annual nutrient loads for selected stations and constituents with no trend in load. 

(A) Kennebec River at North Sidney, Maine, total nitrogen loads, 1979–1993, (B) Kennebec River at North Sidney, Maine, total 

phosphorus loads, 1979–1993, (C) Neshanic River at Reaville, N.J., total nitrogen loads, 1993–2003, (D) Neshanic River at Reaville, 

N.J., total phosphorus loads, 1993–2003, (E) Schuylkill River at Philadelphia, Pa., total nitrogen loads, 1975–2003, (F) Schuylkill River at 

Philadelphia, Pa., total phosphorus loads, 1975–2003, (G) Conococheague Creek at Fairview, Md., total nitrogen loads, 1993–2003, 

(H) Conococheague Creek at Fairview, Md., total phosphorus loads, 1993–2003, (I) Rappahannock River near Fredericksburg, Va., total 

nitrogen loads, 1979–2003, and (J) Rappahannock River near Fredericksburg, Va., total phosphorus loads, 1979–2003.—Continued
Annual Nutrient Loads, 1975–2003 61

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

0

5,000,000

10,000,000

Annual total nitrogen load, in pounds

0

500

1,000

Annual mean discharge, in cubic feet per second

G. Conococheague Creek at Fairview, Maryland (station 116)

Annual stream loads of total nitrogen, 1993–2003

No trend

12,000,000 1,500

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Water Year

0

200,000

400,000

600,000

800,000

Annual total phosphorus load, in pounds

H. Conococheague Creek at Fairview, Maryland (station 116)

Annual stream loads of total phosphorus, 1993–2003

No trend

0

500

1,000

900,000 1,500

Annual mean discharge, in cubic feet per second

Total nitrogen load

Annual mean 

 discharge

95-percent confidence

 interval of load estimate

EXPLANATION

EXPLANATION

Total phosphorus load

Annual mean

 discharge

95-percent confidence

 interval of load estimate

Figure 14. Annual mean discharges and annual nutrient loads for selected stations and constituents with no trend in load. 

(A) Kennebec River at North Sidney, Maine, total nitrogen loads, 1979–1993, (B) Kennebec River at North Sidney, Maine, total 

phosphorus loads, 1979–1993, (C) Neshanic River at Reaville, N.J., total nitrogen loads, 1993–2003, (D) Neshanic River at Reaville, 

N.J., total phosphorus loads, 1993–2003, (E) Schuylkill River at Philadelphia, Pa., total nitrogen loads, 1975–2003, (F) Schuylkill River at 

Philadelphia, Pa., total phosphorus loads, 1975–2003, (G) Conococheague Creek at Fairview, Md., total nitrogen loads, 1993–2003, 

(H) Conococheague Creek at Fairview, Md., total phosphorus loads, 1993–2003, (I) Rappahannock River near Fredericksburg, Va., total 

nitrogen loads, 1979–2003, and (J) Rappahannock River near Fredericksburg, Va., total phosphorus loads, 1979–2003.—Continued
62 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

9,000,000

10,000,000

11,000,000

12,000,000

Annual total nitrogen load, in pounds

I. Rappahannock River near Fredericksburg, Virginia (station 124)

Annual stream loads of total nitrogen, 1979–2003

1979–2003

No trend

1993–2003

No trend

0

1,000

2,000

3,000

Annual mean discharge, in cubic feet per second

13,000,000 3,500 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Water Year

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

Annual total phosphorus load, in pounds

J. Rappahannock River near Fredericksburg, Virginia (station 124)

Annual stream loads of total phosphorus, 1979–2003

0

1,000

2,000

3,000

Annual mean discharge, in cubic feet per second

1979–2003

 No trend

1993–2003

No trend

5,500,000 3,500

Total nitrogen load

Annual mean 

 discharge

95-percent confidence

 interval of load estimate

EXPLANATION

EXPLANATION

Total phosphorus load

Annual mean

 discharge

95-percent confidence

 interval of load estimate

Figure 14. Annual mean discharges and annual nutrient loads for selected stations and constituents with no trend in load. 

(A) Kennebec River at North Sidney, Maine, total nitrogen loads, 1979–1993, (B) Kennebec River at North Sidney, Maine, total 

phosphorus loads, 1979–1993, (C) Neshanic River at Reaville, N.J., total nitrogen loads, 1993–2003, (D) Neshanic River at Reaville, 

N.J., total phosphorus loads, 1993–2003, (E) Schuylkill River at Philadelphia, Pa., total nitrogen loads, 1975–2003, (F) Schuylkill River at 

Philadelphia, Pa., total phosphorus loads, 1975–2003, (G) Conococheague Creek at Fairview, Md., total nitrogen loads, 1993–2003, 

(H) Conococheague Creek at Fairview, Md., total phosphorus loads, 1993–2003, (I) Rappahannock River near Fredericksburg, Va., total 

nitrogen loads, 1979–2003, and (J) Rappahannock River near Fredericksburg, Va., total phosphorus loads, 1979–2003.—Continued
Annual Nutrient Loads, 1975–2003 63

(not shown). Differences in annual loads between the two 

years were generally more pronounced for total phosphorus 

than for total nitrogen at some stations. The total phosphorus 

load estimated for the Rappahannock River for 2003 was 

48 times the load estimated for 2002. The 2003 load, however, 

was not the maximum for the period of record at this station; 

the total phosphorus load for 1996 was 70 times the 2002 

load (fig. 14J). In some drainage basins, exceptionally dry 

antecedent conditions in 2002 may have resulted in retention 

of nutrients that would have been transported to streams under 

normal conditions, thus creating a reservoir or backlog of 

nutrients that contributed to the exceptionally high nutrient 

loads in 2003. 

The drought of 2002 persisted into 2003 in parts of northern New England, and consequently water year 2003 does not 

represent an extreme high flow year for the Kennebec River 

in Maine (fig. 14A), the Connecticut River in Connecticut 

(fig. 5C), and other streams in the northern part of the region. 

In fact, the annual mean flow for 2002 on the Kennebec River 

exceeded the annual mean flow for 2003. Consequently, water 

year 2003 is typically not the peak nutrient load year for the 

more northerly drainage basins in the region. 

Annual mean flows during 1993–2003 varied substantially from year to year, with extremely low annual mean 

flows in 1995 and 2002, and high annual mean flows in 1996 

and 2003, depending on the geographic area (fig. 5). Consequently this period of record provides a good indication of 

recent annual nutrient loads under a wide range of conditions. 

In some parts of the region, particularly drainage basins in the 

southernmost areas, few annual mean flows near long-term 

median flows occurred during this period of record (fig. 5I), 

and consequently annual nutrient loads that represent more 

typical conditions are less readily identified. Annual nutrient 

loads for years with typical annual mean streamflows earlier in 

the period of record may not be representative of more recent 

conditions in drainage basins where long-term trends in nutrient loads have taken place. 

Effects of Calibration Period on Load Estimates

Annual load estimates often must be considered provisional, because load estimation programs are sensitive to data 

at the ends of the period of record, particularly the final year in 

the load estimation period. The USGS Chesapeake Bay River 

Input Monitoring (RIM) Program has used a nine-year “moving window” approach to evaluate changes in annual load 

estimates related to changes in the calibration period. Results 

from this evaluation showed that annual load estimates for the 

years at the center of each nine-year load estimation period 

were typically more accurate than the estimates for years at 

either end of the period (Yochum, 2000). The final (ninth) 

year of estimation showed the most change when that year 

became the eighth year in the next nine-year “window,” and 

this change approached a minimum when that year became the 

fifth, or center, year of a subsequent calibration period. Based 

on this information from the RIM evaluation, and the extreme 

hydrologic conditions in 2002 and 2003 at some locations, the 

annual load estimates in this report for those years are considered provisional. Accurate annual load estimates generally can 

be considered a “moving target” that requires repeated analyses in future years to verify or modify existing estimates. 

Annual loads for 31 stations have been estimated for both 

the long term period (1975–2003, 1979–2003, or 1982–2003) 

and recent period (1993–2003). Annual loads estimated for 

years in the 1993–2003 period may differ depending on the 

calibration period used, and the years of maximum or minimum loads also may differ. Where annual loads for the longterm period are shown (for example, fig. 14), the calibration 

period used is the long-term period. 

Effects of Storms on Annual Nutrient Loads

Although the magnitude of annual nutrient loads often 

follows the magnitude of annual mean discharge fairly closely, 

individual floods may contribute to peak annual loads in years 

that are otherwise unremarkable in terms of annual mean 

streamflow, and multiple storms may result in a year with 

higher than average annual mean flow. Storms can contribute 

to peak loads in any season, and short-term peak seasonal 

loads can result in high annual constituent load estimates. 

The effects of major storms on constituent loads may differ 

for different constituents, depending on a number of factors. 

For example, on the Kennebec River in Maine, the peak total 

nitrogen load occurred in 1984, which was also the peak year 

for annual mean flow for the 1979–1993 period (fig. 14A). 

By contrast, the peak total phosphorus load was estimated 

for 1987, a year in which the annual mean discharge is close 

to median conditions (fig. 14B). A major flood in April 1987, 

with associated transport of sediment and particulate materials, 

is a likely cause for the unusually high estimated annual load 

of total phosphorus. According to a study of this storm, “snowmelt and precipitation from two storms caused record flooding 

in April 1987 in central and southwestern Maine” (Fontaine 

and Nielsen, 1994, p. 1). The flood flow for the Kennebec 

River at North Sidney had a greater than 100-year recurrence 

interval (Fontaine and Nielsen, 1994, p. 24, table 11). 

Three major floods occurred in the Potomac River Basin 

in 1996 (Ator and others, 1998, p. 14). Intense rainfall and 

rapid snowmelt in January resulted in a record high flow for a 

single day on the Potomac River at Washington, D.C.; intense 

rainfall during a five-day period in June caused flooding in 

drainage basins in Maryland, including Conococheague Creek 

(figs. 14G, H); and a tropical storm in September caused 

flooding in the Shenandoah River Basin (Ator and others, 

1998, p. 14). These floods were regional in nature, and annual 

mean flows and annual nutrient loads for 1996 are among the 

highest for the 1993–2003 period at many monitoring stations 

(figs. 5, 14). 
64 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

A new maximum annual mean flow for a 73-year period 

occurred in 1994 on the Neshanic River at Reaville, N.J. 

(table 11). The second highest total nitrogen load for the 

1993–2003 period was estimated for 1994 (fig. 14C). However, the peak total phosphorus load for this station was in 

1999, a year in which the annual mean flow was near the longterm median (fig. 14D). The annual load of total phosphorus 

estimated for 1999 is more than an order of magnitude higher 

than annual loads estimated for other years with annual mean 

flows similar to 1999. The total phosphorus load estimated for 

1999 was 3.5 times the second highest load, which occurred in 

1994, and was 130 times the minimum load, which occurred 

in 1995. The peak phosphorus load estimated for 1999 is 

likely the result of heavy rainfall from Tropical Storm Floyd, 

which, combined with a western storm system, produced as 

much as 14 in. of rain in New Jersey during September 15–17, 

1999, resulting in flooding of historical proportions in many 

areas of the state (Reed and others, 2000, p. 2, 4). Maximum 

annual peak streamflows were measured for several long-term 

streamgages in the Raritan River Basin on September 16 or 

17, 1999, including the Neshanic River at Reaville, where 

the peak streamflow on September 16 was the maximum 

annual peak for the period 1931–2007 (U.S. Geological 

Survey, 2009a). 

Trends in Nutrient Loads, 1975–2003 and 

1993–2003

Trends in nutrient loads were detected much more 

frequently during the long-term period than during the recent 

period (table 18). Detected trends in nutrient loads were 

primarily downward during 1975–2003, and few statistically 

significant trends in nutrient loads were detected during the 

recent period (table 18). Results of trend analyses for nutrient loads for all stations and constituents analyzed, including p-values (significance level of trend tests), are shown in 

appendix 8 (table 8–1). Total phosphorus data for five stations 

monitoring undeveloped drainage basins were considered 

insufficient for evaluating trends in load during the recent 

period (appendix 8, table 8–1). 

Some of the long-term trends in nutrient loads that illustrate changing conditions in the region are shown in figure 15. 

Long-term trends in nutrient loads, coupled with similar 

trends in flow-adjusted concentrations, are likely to indicate 

long-term changes in the delivery of nutrients to some streams 

in the region, and are not likely to be caused by changes in 

streamflow, because trends in streamflow were detected at 

only two stations, one in each of the two periods analyzed. 

Many of the long-term records available for load estimation and trend analysis are for drainage basins with large 

percentages of urban or agricultural land, and most of these 

drainage basins receive point-source discharges. Most of 

the significant trends in load have been detected in the more 

developed drainage basins of the region, where changes in 

land use and point-source loadings have a major effect on 

nitrogen and phosphorus delivery to streams. 

Comparison of trends in load among different forms 

of nitrogen often provides some insight into long-term 

effects of wastewater-treatment improvements. Long-term 

trends of nitrogen constituent loads in the Quinnipiac River 

in Connecticut (fig. 15A) illustrate a pattern that could be 

typical for streams where improvements in wastewater 

treatment have taken place. Previous analyses for this river 

have shown that over the long term, stream loads of total 

Kjeldahl nitrogen have decreased, nitrite-plus-nitrate loads 

have increased, and total nitrogen loads have shown no trend 

(J.R. Mullaney, U.S. Geological Survey, written commun., 

Table 18. Summary of trends in nutrient and suspended sediment loads, 1975–2003 and 1993–2003.

[Long-term period for trend analysis spans 22–29 water years at different stations, all ending in 2003; recent period for trend analysis spans 11 water years 

at all stations. Significant trend: p-value less than or equal to 0.05; highly significant trend: p-value less than or equal to 0.01; --, not analyzed]

Water-quality constituent

1975–2003, 1979–2003, or 1982–2003 1993–2003

Number of 

stations 

analyzed

Upward 

trend

Downward 

trend

No significant trend

Number of 

stations 

analyzed

Upward 

trend

Downward 

trend

No significant trend

Total nitrogen 32 1 12 19 46 0 1 45

Ammonia nitrogen 6 0 6 0 9 0 3 6

Total Kjeldahl nitrogen 6 0 6 0 0 -- -- --

Nitrite-plus-nitrate nitrogen 32 7 8 17 46 0 4 42

Total phosphorus 32 0 17 15 41 2 1 38

Suspended sediment 4 0 1 3 8 0 0 8
Annual Nutrient Loads, 1975–2003 65

2006). These trend results for nitrogen constituent loads in 

the Quinnipiac River have persisted in the period analyzed in 

this study (fig. 15A), with total Kjeldahl nitrogen representing 

a decreasing proportion of the total nitrogen load over time, 

and nitrite-plus-nitrate nitrogen representing an increasing 

proportion. This pattern of trends in load is consistent with 

implementation of wastewater-treatment improvements that 

remove organic material and convert ammonia nitrogen 

to nitrite and nitrate. Based on this information for the 

Quinnipiac River, a working hypothesis for this study was that 

a similar pattern of nitrogen constituent loads would be likely 

in other streams that receive municipal wastewater effluent. 

No consistent pattern was found, however, among other rivers 

with similar land use or point-source discharge conditions. 

Trends and loads for ammonia nitrogen and total Kjeldahl 

nitrogen were only evaluated for a small number of stations. 

Downward trends in total nitrogen loads were detected 

at more than one-third of the stations analyzed (12 of 32) 

during the long-term period (table 18), and 10 of these trends 

were highly significant (appendix 8). Of the 12 stations with 

downward trends, nine stations monitor streams that receive 

major point-source discharges, including the Naugatuck River 

in Connecticut (fig. 15C) and the Passaic River in New Jersey 

(fig. 15E), both of which had highly significant downward 

trends. The Naugatuck River also had a highly significant 

downward trend in total nitrogen load for the recent period. 

Only one long-term upward trend in total nitrogen load was 

detected, at Toms River near Toms River, N.J. (fig. 15G), a 

stream that receives small amounts of nitrogen from minor 

point-source discharges. 

Long-term trends in loads of nitrite-plus-nitrate nitrogen 

were detected at almost half the stations analyzed (15 of 32), 

with results about evenly divided between upward (7) and 

downward (8) trends (table 18). Of the seven rivers with longterm upward trends in loads of nitrite-plus-nitrate nitrogen, 

five receive major municipal point-source discharges, including the Quinnipiac River in Connecticut (fig. 15A) and the 

Passaic River in New Jersey (fig. 15E); Toms River in New 

Jersey (fig. 15G) receives minor point-source discharges. The 

seventh station with an upward trend, the Choptank River in 

Maryland, drains an agricultural drainage basin (48 percent 

agricultural land) with no major or minor point sources. Of 

the eight rivers with long-term downward trends in loads of 

nitrite-plus-nitrate nitrogen, five receive major point-source 

discharges, including the Naugatuck River in Connecticut 

(fig. 15C), the Patuxent River in Maryland, and the James 

River in Virginia. Stations with downward trends in load 

and no major point discharges include the Hackensack River 

(67 percent urbanized) and Raccoon Creek (66 percent agricultural; fig. 15I), both in New Jersey, and the Salmon River 

in Connecticut (about 24 percent developed land) (table 8, in 

back of report). In some streams that are receiving waters for 

major point-source discharges, downward trends in nitriteplus-nitrate nitrogen loads, and also total nitrogen loads, may 

result in part from advanced wastewater-treatment practices 

such as Biological Nitrogen Removal (BNR), which has been 

implemented in treatment plants in the Patuxent River Basin 

(Maryland Department of Natural Resources, 2009). 

Long-term downward trends in loads of ammonia 

nitrogen and total Kjeldahl nitrogen were detected at the six 

stations evaluated for these constituents (table 18; appendix 

8), and most of the downward trends were highly significant. 

Three downward trends in loads of ammonia nitrogen were 

detected for the recent period, and no upward trends were 

detected. Nine of the 10 streams evaluated for ammonia 

nitrogen or total Kjeldahl nitrogen receive major pointsource discharges. 

Downward trends in total phosphorus loads were detected 

at slightly more than half of the stations analyzed (17 of 32) 

during the long-term period (table 18). Of the 17 stations 

with downward trends, 14 stations monitor streams that 

receive major or minor point-source discharges, including the 

Quinnipiac River in Connecticut (fig. 15B) and the Passaic 

River and Toms River in New Jersey (figs. 15F, H). 

Several long-term trends in nutrient loads were detected 

at stations in drainage basins evaluated for point-source loads. 

These trends are discussed in the “Point Sources” section. 

Long-term downward trends in loads of one or more 

nutrients were detected for three streams with relatively 

undeveloped drainage basins and no major or minor point 

discharges: Bunnell (Burlington) Brook, the Salmon River, 

and the Saugatuck River in Connecticut. The drainage basins 

for these streams are largely undeveloped (75, 76, and 74 

percent, respectively), although the Salmon and Saugatuck 

River Basins have been classified as urban (table 8, in back 

of report). Highly significant long-term downward trends in 

total nitrogen loads and nitrite-plus-nitrate nitrogen loads were 

detected for the Salmon River. Downward trends in nitrogen 

constituents in undeveloped areas could be related to changes 

in atmospheric deposition of nitrogen. Long-term downward 

trends in total phosphorus loads also were detected for all 

three streams. Additional investigation would be necessary to 

evaluate possible causes for downward trends in nutrient loads 

in these drainage basins. 

A small number of stations were evaluated for trends in 

suspended sediment load, four in the long-term period and 

eight in the recent period (table 18). The only significant trend 

was a downward trend in load for the Raritan River at Bound 

Brook in New Jersey. 
66 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

0

500,000

1,000,000

1,500,000

Annual nitrogen constituent loads, in pounds

A. Quinnipiac River at Wallingford, Connecticut (station 32)

2,000,000

0

100

200

300

400

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

Water Year

0

50,000

100,000

150,000

200,000

B. Quinnipiac River at Wallingford, Connecticut (station 32)

250,000

0

100

200

300

400

Annual mean discharge, in cubic feet per second Annual mean discharge, in cubic feet per second

Annual total phosphorus load, in pounds

Trends in load 1975–2003 1993–2003

Total nitrogen

Nitrite-plus-nitrate nitrogen

Total Kjeldahl nitrogen

No trend

Upward trend

Downward trend

No trend

No trend

Not analyzed

Downward trend No trend

Trends in load 1975–2003 1993–2003 

Total phosphorus

EXPLANATION

Total nitrogen load

Nitrite-plus-nitrate 

 nitrogen load

Total Kjeldahl nitrogen load 

Annual mean discharge

EXPLANATION

Total phosphorus load

Annual mean discharge

Figure 15. Long-term annual nutrient loads at selected stations with significant trends in load. (A) Quinnipiac River at Wallingford, 

Conn., total nitrogen, nitrite-plus-nitrate nitrogen, and total Kjeldahl nitrogen, 1975–2003, (B) Quinnipiac River at Wallingford, Conn., 

total phosphorus, 1975–2003, (C) Naugatuck River at Beacon Falls, Conn., total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003, 

(D) Naugatuck River at Beacon Falls, Conn., total phosphorus, 1975–2003, (E) Passaic River at Little Falls, N.J., total nitrogen and nitriteplus-nitrate nitrogen, 1979–2003, (F) Passaic River at Little Falls, N.J., total phosphorus, 1979–2003, (G) Toms River near Toms River, N.J., 

total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003, (H) Toms River near Toms River, N.J., total phosphorus, 1975–2003, and 

(I) Raccoon Creek near Swedesboro, N.J., total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003.
Annual Nutrient Loads, 1975–2003 67 Annual mean discharge, in cubic feet per second Annual mean discharge, in cubic feet per second

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

Water Year

0

100,000

200,000

300,000

400,000

Annual total phosphorus load, in pounds

D. Naugatuck River at Beacon Falls, Connecticut (station 39)

500,000

0

200

400

600

800

900

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

0

1,000,000

2,000,000

3,000,000

4,000,000

Annual total nitrogen and nitrite-plus-nitrate 

nitrogen loads, in pounds

C. Naugatuck River at Beacon Falls, Connecticut (station 39)

4,500,000

0

200

400

600

800

900

Trends in load 1975–2003 1993–2003

Total nitrogen

Nitrite-plus-nitrate nitrogen

Downward trend

Downward trend

Downward trend

Downward trend

Trends in load

Total nitrogen load 

Nitrite-plus-nitrate 

 nitrogen load

Annual mean discharge

EXPLANATION

EXPLANATION

Total phosphorus load

Annual mean discharge

1975–2003

No trend

1993–2003

Total phosphorus Upward trend

Figure 15. Long-term annual nutrient loads at selected stations with significant trends in load. (A) Quinnipiac River at Wallingford, 

Conn., total nitrogen, nitrite-plus-nitrate nitrogen, and total Kjeldahl nitrogen, 1975–2003, (B) Quinnipiac River at Wallingford, Conn., 

total phosphorus, 1975–2003, (C) Naugatuck River at Beacon Falls, Conn., total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003, 

(D) Naugatuck River at Beacon Falls, Conn., total phosphorus, 1975–2003, (E) Passaic River at Little Falls, N.J., total nitrogen and nitriteplus-nitrate nitrogen, 1979–2003, (F) Passaic River at Little Falls, N.J., total phosphorus, 1979–2003, (G) Toms River near Toms River, N.J., 

total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003, (H) Toms River near Toms River, N.J., total phosphorus, 1975–2003, and 

(I) Raccoon Creek near Swedesboro, N.J., total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003.—Continued
68 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Total nitrogen load 

Nitrite-plus-nitrate 

 nitrogen load

Annual mean discharge

EXPLANATION

EXPLANATION

Total phosphorus load

Annual mean discharge

Downward trend

Upward trend

No trend

No trend

Trends in load 1979–2003 1993–2003

Total nitrogen

Nitrite-plus-nitrate nitrogen

Trends in load

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

Water Year

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

F. Passaic River at Little Falls, New Jersey (station 55)

0

500

1,000

1,500

Annual mean discharge, in cubic feet per second

800,000 2,000

Annual total phosphorus load, in pounds

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

0

2,000,000

4,000,000

6,000,000

Annual total nitrogen and nitrite-plus-nitrate nitrogen 

loads, in pounds

E. Passaic River at Little Falls, New Jersey (station 55)

0

500

1,000

1,500

Annual mean discharge, in cubic feet per second

7,000,000 2,000

1979–2003 1993–2003

Total phosphorus Downward trend No trend

Figure 15. Long-term annual nutrient loads at selected stations with significant trends in load. (A) Quinnipiac River at Wallingford, 

Conn., total nitrogen, nitrite-plus-nitrate nitrogen, and total Kjeldahl nitrogen, 1975–2003, (B) Quinnipiac River at Wallingford, Conn., 

total phosphorus, 1975–2003, (C) Naugatuck River at Beacon Falls, Conn., total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003, 

(D) Naugatuck River at Beacon Falls, Conn., total phosphorus, 1975–2003, (E) Passaic River at Little Falls, N.J., total nitrogen and nitriteplus-nitrate nitrogen, 1979–2003, (F) Passaic River at Little Falls, N.J., total phosphorus, 1979–2003, (G) Toms River near Toms River, N.J., 

total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003, (H) Toms River near Toms River, N.J., total phosphorus, 1975–2003, and 

(I) Raccoon Creek near Swedesboro, N.J., total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003.—Continued
Annual Nutrient Loads, 1975–2003 69

Trends in load 1975–2003 1993–2003

Total nitrogen

Nitrite-plus-nitrate nitrogen

Upward trend

Upward trend 

No trend

No trend 

Downward trend No trend

Trends in load 1975–2003 1993–2003 

Total phosphorus

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

0

100,000

200,000

300,000

400,000

Annual total nitrogen and nitrite-plus-nitrate 

nitrogen loads, in pounds

G. Toms River near Toms River, New Jersey (station 71)

0

100

200

300

Annual mean discharge, in cubic feet per second

500,000 350 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Water Year

0

5,000

10,000

15,000

20,000

Annual total phosphorus load, in pounds

0

100

200

300

Annual mean discharge, in cubic feet per second

25,000 350

H. Toms River near Toms River, New Jersey (station 71)

EXPLANATION

Total nitrogen load 

Nitrite-plus-nitrate 

 nitrogen load

Annual mean 

 discharge

EXPLANATION

Total phosphorus load

Annual mean 

 discharge

Figure 15. Long-term annual nutrient loads at selected stations with significant trends in load. (A) Quinnipiac River at Wallingford, 

Conn., total nitrogen, nitrite-plus-nitrate nitrogen, and total Kjeldahl nitrogen, 1975–2003, (B) Quinnipiac River at Wallingford, Conn., 

total phosphorus, 1975–2003, (C) Naugatuck River at Beacon Falls, Conn., total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003, 

(D) Naugatuck River at Beacon Falls, Conn., total phosphorus, 1975–2003, (E) Passaic River at Little Falls, N.J., total nitrogen and nitriteplus-nitrate nitrogen, 1979–2003, (F) Passaic River at Little Falls, N.J., total phosphorus, 1979–2003, (G) Toms River near Toms River, N.J., 

total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003, (H) Toms River near Toms River, N.J., total phosphorus, 1975–2003, and 

(I) Raccoon Creek near Swedesboro, N.J., total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003.—Continued
70 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Nutrient Loads in Large Drainage Basins

No upward trends in nutrient loads were detected in 

the 11 largest drainage basins during either the long-term or 

recent periods, although some upward trends in flow-adjusted 

concentrations were detected during both periods (table 14). 

The 10 drainage basins with nutrient data for the long-term 

period either had downward trends in load or no trends in 

load (table 14). Some of the long-term downward trends were 

highly significant (p-value less than or equal to 0.01). 

Collectively and individually, the 11 largest rivers 

evaluated in this study deliver the largest freshwater inflows 

and nutrient loads to major estuaries on the northeast coast, 

including Long Island Sound, the Hudson River Estuary, 

Delaware Bay, and Chesapeake Bay. Consequently, long-term 

downward trends in nutrient loads represent major regional 

water-quality improvements. 

The Susquehanna, Potomac, Connecticut, Delaware, 

and James River Basins (in descending order of size) are the 

largest monitored basins for which long-term water-quality 

records were available for evaluation of trends in nutrient 

loads. The Susquehanna, Potomac, and James Rivers are 

the three largest sources of streamflow and nutrients to 

Chesapeake Bay from the nontidal part of the Chesapeake Bay 

drainage basin (Belval and Sprague, 1999, p. 3–4). Nutrient 

trends and loads for these and numerous other streams in the 

Chesapeake Bay drainage basin are evaluated annually by the 

USGS in cooperation with federal, state, and regional agencies 

of the Chesapeake Bay Program (Langland and others, 2006). 

The Susquehanna River, with a monitored drainage area 

Total nitrogen load 

Nitrite-plus-nitrate 

 nitrogen load

Annual mean discharge

Trends in load 1975–2003 1993–2003 EXPLANATION

Total nitrogen

Nitrite-plus-nitrate nitrogen

No trend

Downward trend 

No trend

No trend 

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

Water Year

0

50,000

100,000

150,000

200,000

250,000

Annual total nitrogen and nitrite-plus-nitrate nitrogen 

loads, in pounds

0

10

20

30

40

50

Annual mean discharge, in cubic feet per second

300,000 60

I. Raccoon Creek near Swedesboro, New Jersey (station 98)

Figure 15. Long-term annual nutrient loads at selected stations with significant trends in load. (A) Quinnipiac River at Wallingford, 

Conn., total nitrogen, nitrite-plus-nitrate nitrogen, and total Kjeldahl nitrogen, 1975–2003, (B) Quinnipiac River at Wallingford, Conn., 

total phosphorus, 1975–2003, (C) Naugatuck River at Beacon Falls, Conn., total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003, 

(D) Naugatuck River at Beacon Falls, Conn., total phosphorus, 1975–2003, (E) Passaic River at Little Falls, N.J., total nitrogen and nitriteplus-nitrate nitrogen, 1979–2003, (F) Passaic River at Little Falls, N.J., total phosphorus, 1979–2003, (G) Toms River near Toms River, N.J., 

total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003, (H) Toms River near Toms River, N.J., total phosphorus, 1975–2003, and 

(I) Raccoon Creek near Swedesboro, N.J., total nitrogen and nitrite-plus-nitrate nitrogen, 1975–2003.—Continued
Annual Nutrient Loads, 1975–2003 71

encompassing 42 percent of the 64,000 mi2 drainage basin 

for Chesapeake Bay, contributes about 60 percent of the 

total streamflow, 62 percent of the total nitrogen load, and 

34 percent of the total phosphorus load from the nontidal 

part of the Chesapeake Bay drainage basin. The Potomac 

River Basin, encompassing 18 percent of the Bay drainage 

area, contributes about 20 percent of the total streamflow, 

28 percent of the total nitrogen load, and 33 percent of the 

total phosphorus load, and the James River, encompassing 

9.8 percent of the Bay drainage area, contributes about 

12 percent of the streamflow, 5 percent of the total nitrogen 

load, and 20 percent of the total phosphorus load (Belval and 

Sprague, 1999, p. 4–5). The Connecticut River is the largest 

source of freshwater inflow and a major nutrient source to 

Long Island Sound, and the Delaware River is the major 

freshwater inflow to Delaware Bay. 

Long-term downward trends in total nitrogen loads were 

detected for the Connecticut, Delaware, and James Rivers, 

and no trends in total nitrogen loads were detected for the 

Susquehanna or Potomac Rivers (figs. 16A, C, E, G, H). 

The downward trends are more apparent in graphs of annual 

loads for the Connecticut and Delaware Rivers than for the 

James River, where the extended dry period from 1999 to 

2002 represents a long-term anomaly (figs. 16A, C, H). Mean, 

median, and maximum total nitrogen loads were lower during 

the recent period than during the long-term period for all three 

rivers (table 19). Although no trend in total nitrogen load was 

detected for the Potomac for either the long-term period or the 

recent period, the 1993–2003 period contains both extreme 

high and extreme low annual loads, and five of the six highest 

annual loads are in the 1993–2003 period (fig. 16G). Mean 

and median total nitrogen loads for the Potomac River were 

higher during the recent period than during the long-term 

period (table 19). 

Although no long-term or recent trend in total nitrogen 

load was detected for the Susquehanna River, a downward 

trend in total Kjeldahl nitrogen load and a highly significant 

downward trend in ammonia nitrogen load were detected for 

the long-term (1979–2003) period (fig. 16F; table 14). No 

long-term or recent trend in nitrite-plus-nitrate nitrogen load 

was identified for the Susquehanna at the 0.05 significance 

level used in this study, but a likely downward trend in this 

constituent for the recent period is present (p-value = 0.07) 

(fig. 16F). 

Highly significant long-term downward trends in total 

phosphorus loads were detected for the Connecticut and 

Delaware Rivers (table 14, figs. 16B, D). No long-term trends 

in total phosphorus loads were detected for the Susquehanna, 

Potomac, and James Rivers (table 14; not shown in fig. 16). A 

downward trend in ammonia nitrogen load for the James River 

was the only trend in load detected for any of the nutrients 

analyzed for the five largest drainage basins during the 

1993–2003 period (table 14). 

Four of the 11 largest drainage basins were evaluated for 

trends in suspended sediment load during the recent period: 

the Susquehanna, Potomac, Connecticut, and Mohawk Rivers 

(table 14). No trends in load were detected. Although not 

significant at the level selected for this study, data for the 

Susquehanna River showed a possible downward trend in 

suspended sediment load for the 1993–2003 period 

(p-value = 0.100). 

The Susquehanna River, as the largest freshwater inflow 

to the Chesapeake Bay, transports a large amount of the 

suspended sediment and nutrient load that enters the Bay. 

Suspended sediment loads, total phosphorus loads, and to 

a lesser extent, total nitrogen loads entering Chesapeake 

Bay from the Susquehanna River are affected by three 

hydroelectric dams, and associated reservoirs, on the lower 

reaches of the Susquehanna in Pennsylvania and Maryland. 

The three reservoirs trap a large amount of the sediment 

transported by the river, and some associated nutrients 

(Langland, 2009). The Conowingo Reservoir is the largest 

and farthest downstream of the three reservoirs. The USGS 

conducted bathymetric surveys in 2008 to estimate the 

remaining sediment storage capacity in the three reservoirs 

(Langland, 2009, p. 1). Although it is difficult to estimate the 

length of time until the remaining sediment storage capacity of 

the Conowingo Reservoir is reached, the remaining capacity 

may be filled in 15 to 20 years, depending on sediment 

transport rates, sediment deposition rates, and the absence 

of major sediment scours resulting from floods. When the 

remaining sediment storage capacity is reached, then the 

sediment loads and associated phosphorus loads transported 

by the Susquehanna River into the Chesapeake Bay are 

expected to increase (Langland, 2009, p. 1, 19). 

Large drainage basins of the region integrate streamflow 

and nutrient sources from many smaller basins that experience 

a wide range of conditions in any one year. Although streamflow has not been uniform across the region, high annual 

streamflows, and consequently high nutrient loads, have been 

measured in many parts of the region in the late 1970s, 1984, 

1993–94, 1996, and 2003. Low annual streamflows, and 

consequently low nutrient loads, have been measured in many 

parts of the region in 1981, 1985, 1988, 1992, 1995, 1999, and 

2001–2002. Maximum total nitrogen loads for the 1993–2003 

period (with estimation based on the 1975–2003 calibration period) were transported by the Connecticut, Delaware, 

and Potomac Rivers in 1996; by the Susquehanna River in 

1994; and by the James River in 2003 (figs. 16A, C, G, E, 

H). Minimum total nitrogen loads for the 1993–2003 period 

were transported by the Connecticut, Delaware, Potomac, and 

James Rivers in 2002, and by the Susquehanna River in 2001. 
72 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Annual total nitrogen loads, 1975–2003

1975–2003 

Downward trend

1993–2003

No trend

Annual total phosphorus loads, 1975–2003

1975–2003

Downward trend

1993–2003

No trend 

Total nitrogen load

Annual mean discharge

95-percent confidence

 interval of load estimate

 

EXPLANATION

EXPLANATION

Total phosphorus load

Annual mean discharge

95-percent confidence

 interval of load estimate

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

0

10,000,000

20,000,000

30,000,000

40,000,000

A. Connecticut River at Thompsonville, Connecticut (station 22)

0

5,000

10,000

15,000

20,000

25,000

Annual mean discharge, in cubic feet per second

45,000,000 30,000 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

Annual total phosphorus load, in pounds

B. Connecticut River at Thompsonville, Connecticut (station 22)

0

5,000

10,000

15,000

20,000

25,000

6,500,000 30,000

Annual mean discharge, in cubic feet per second

Annual total nitrogen load, in pounds

Water Year

Figure 16. Long-term annual nutrient loads in the five largest drainage basins of the region, 1975–2003. (A) Total nitrogen, Connecticut 

River at Thompsonville, Conn., 1975–2003, (B) total phosphorus, Connecticut River at Thompsonville, Conn., 1975–2003, (C) total nitrogen, 

Delaware River at Trenton, N.J., 1975–2003, (D) total phosphorus, Delaware River at Trenton, N.J., 1975–2003, (E) total nitrogen, 

Susquehanna River at Conowingo, Md., 1979–2003, (F) nitrite-plus-nitrate nitrogen, total Kjeldahl nitrogen, and ammonia nitrogen, 

Susquehanna River at Conowingo, Md., 1979–2003, (G) total nitrogen, Potomac River at Chain Bridge, at Washington, D.C., 1975–2003, 

and (H) total nitrogen, James River at Cartersville, Va., 1975–2003.
Annual Nutrient Loads, 1975–2003 73

Annual total nitrogen loads, 1975–2003

1975–2003 

Downward trend

1993–2003 

No trend

Annual total phosphorus loads, 1975–2003

1975–2003

Downward trend

1993–2003

No trend

Total nitrogen load

Annual mean discharge

95-percent confidence

 interval of load estimate

EXPLANATION

EXPLANATION

Total phosphorus load

Annual mean discharge

95-percent confidence

 interval of load estimate

197519761977197819791980

1981

1982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

0

10,000,000

20,000,000

30,000,000

40,000,000

50,000,000

Annual total nitrogen load, in pounds

0

5,000

10,000

15,000

Annual mean discharge, in cubic feet per second

60,000,000 18,000

C. Delaware River at Trenton, New Jersey (station 90) 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993

1994199519961997199819992000200120022003

Water Year

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

Annual total phosphorus load, in pounds

D. Delaware River at Trenton, New Jersey (station 90)

0

5,000

10,000

15,000

Annual mean discharge, in cubic feet per second

18,000

Figure 16. Long-term annual nutrient loads in the five largest drainage basins of the region, 1975–2003. (A) Total nitrogen, Connecticut 

River at Thompsonville, Conn., 1975–2003, (B) total phosphorus, Connecticut River at Thompsonville, Conn., 1975–2003, (C) total nitrogen, 

Delaware River at Trenton, N.J., 1975–2003, (D) total phosphorus, Delaware River at Trenton, N.J., 1975–2003, (E) total nitrogen, 

Susquehanna River at Conowingo, Md., 1979–2003, (F) nitrite-plus-nitrate nitrogen, total Kjeldahl nitrogen, and ammonia nitrogen, 

Susquehanna River at Conowingo, Md., 1979–2003, (G) total nitrogen, Potomac River at Chain Bridge, at Washington, D.C., 1975–2003, 

and (H) total nitrogen, James River at Cartersville, Va., 1975–2003.—Continued
74 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Total nitrogen load

Annual mean discharge

95-percent confidence

 interval of load estimate

EXPLANATION

EXPLANATION

Trends in load 1979–2003 1993–2003

Nitrite-plus-nitrate nitrogen

Total Kjeldahl nitrogen

Ammonia nitrogen

No trend

Downward trend

Downward trend

No trend

Not analyzed

Not analyzed

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

0

50,000,000

100,000,000

150,000,000

200,000,000

Annual total nitrogen load, in pounds

E. Susquehanna River at Conowingo, Maryland (station 111)

Annual total nitrogen loads, 1979–2003

0

10,000

20,000

30,000

40,000

50,000

Annual mean discharge, in cubic feet per second

250,000,000 60,000

1979–2003

No trend

1993–2003 

No trend

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

Water Year

0

50,000,000

100,000,000

Annual nitrogen constituent loads, in pounds

F. Susquehanna River at Conowingo, Maryland (station 111)

0

10,000

20,000

30,000

40,000

50,000

Annual mean discharge, in cubic feet per second

150,000,000 60,000

Nitrite-plus-nitrate nitrogen load

Total Kjeldahl nitrogen load

Ammonia nitrogen load

Annual mean discharge

Figure 16. Long-term annual nutrient loads in the five largest drainage basins of the region, 1975–2003. (A) Total nitrogen, Connecticut 

River at Thompsonville, Conn., 1975–2003, (B) total phosphorus, Connecticut River at Thompsonville, Conn., 1975–2003, (C) total nitrogen, 

Delaware River at Trenton, N.J., 1975–2003, (D) total phosphorus, Delaware River at Trenton, N.J., 1975–2003, (E) total nitrogen, 

Susquehanna River at Conowingo, Md., 1979–2003, (F) nitrite-plus-nitrate nitrogen, total Kjeldahl nitrogen, and ammonia nitrogen, 

Susquehanna River at Conowingo, Md., 1979–2003, (G) total nitrogen, Potomac River at Chain Bridge, at Washington, D.C., 1975–2003, 

and (H) total nitrogen, James River at Cartersville, Va., 1975–2003.—Continued
Annual Nutrient Loads, 1975–2003 75

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

0

50,000,000

100,000,000

Annual total nitrogen load, in pounds

G. Potomac River at Chain Bridge, at Washington, D.C. (station 122)

Annual total nitrogen loads, 1975–2003

0

5,000

10,000

15,000

20,000

Annual mean discharge, in cubic feet per second

140,000,000 25,000

1975–2003

No trend

1993–2003

No trend

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

Water Year

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

Annual total nitrogen load, in pounds

H. James River at Cartersville, Virginia (station 127)

Annual total nitrogen loads, 1975–2003

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

12,000

Annual mean discharge, in cubic feet per second

13,000

1975–2003

Downward trend

1993–2003

No trend

Total nitrogen load

Annual mean discharge

95-percent confidence

 interval of load estimate

EXPLANATION

Figure 16. Long-term annual nutrient loads in the five largest drainage basins of the region, 1975–2003. (A) Total nitrogen, Connecticut 

River at Thompsonville, Conn., 1975–2003, (B) total phosphorus, Connecticut River at Thompsonville, Conn., 1975–2003, (C) total 

nitrogen, Delaware River at Trenton, N.J., 1975–2003, (D) total phosphorus, Delaware River at Trenton, N.J., 1975–2003, (E) total 

nitrogen, Susquehanna River at Conowingo, Md., 1979–2003, (F) nitrite-plus-nitrate nitrogen, total Kjeldahl nitrogen, and ammonia 

nitrogen, Susquehanna River at Conowingo, Md., 1979–2003, (G) total nitrogen, Potomac River at Chain Bridge, at Washington, D.C., 

1975–2003, and (H) total nitrogen, James River at Cartersville, Va., 1975–2003.—Continued
76 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 Table 19. Summary statistics for total nitrogen loads in the five largest drainage basins in the region, 1975–2003 and 1993–2003. [Source for land-use data: 1992 National Land Cover Dataset (NLCDe 92) (Vogelmann and others, 1998; enhanced as described by Nakagaki and Wolock, 2005). Definitions for land-use codes are in table 7. lb, pound; mi2, square miles; UN, undeveloped; AG, agricultural] Station sequence number (fig. 4) Station name Drainage area (mi2

)

Land-use percentages (table 8) Landuse 

code

Annual total nitrogen load (lb)

Urban 

land

Agricultural land Forested land Minimum Mean Median Maximum

1975–2003 or 1979–2003

22 Connecticut River at Thompsonville, Conn. 9,660 5.0 8.3 81.0 UN 16,200,000 26,100,000 26,500,000 38,000,000

90 Delaware River at Trenton, N.J. 6,780 5.3 16.4 75.2 UN 15,600,000 33,500,000 35,400,000 51,800,000

111 Susquehanna River at Conowingo, Md. 27,100 3.2 28.2 66.6 AG 71,900,000 132,000,000 136,000,000 194,000,000

122 Potomac River at Chain Bridge, at Washington, D.C. 11,570 4.5 33.8 60.1 AG 11,700,000 52,600,000 48,100,000 113,000,000127 James River at Cartersville, Va. 6,252 3.5 15.0 79.6 UN 1,900,000 12,600,000 13,200,000 21,300,000

1993–2003

22 Connecticut River at Thompsonville, Conn. 9,660 5.0 8.3 81.0 UN 16,200,000 22,300,000 23,900,000 30,400,000

90 Delaware River at Trenton, N.J. 6,780 5.3 16.4 75.2 UN 15,600,000 30,800,000 32,500,000 44,200,000

111 Susquehanna River at Conowingo, Md. 27,100 3.2 28.2 66.6 AG 71,900,000 131,000,000 137,000,000 194,000,000

122 Potomac River at Chain Bridge, at Washington, D.C. 11,570 4.5 33.8 60.1 AG 11,700,000 59,500,000 68,300,000 113,000,000127 James River at Cartersville, Va. 6,252 3.5 15.0 79.6 UN 1,900,000 11,400,000 11,600,000 20,100,000
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 77

Relation of Nutrient Trends, Loads, and 

Yields to Nutrient Sources

Land use and land cover in many drainage basins of the 

northeastern United States constitute a complex and changing mosaic, often with many nutrient sources contributing to 

the nutrient concentrations and loads measured or estimated 

for a stream. A full evaluation of the effects of these sources 

on nutrient trends, loads, and yields is beyond the scope of 

this report. Some general relations observed between nutrient 

conditions and basin land use, population density, and hydrologic conditions are discussed, and effects of point sources are 

evaluated for selected drainage basins. 

Land Use and Population Density

Land use in drainage basins evaluated for this report 

ranges from 96 percent developed land (urban or agricultural 

land) to 100 percent undeveloped land (primarily forested) 

(table 8, in back of report). Although the region as a whole is 

65 percent forested, urban nutrient sources dominate water 

quality in many areas, particularly near the coast, and agricultural nutrient sources predominate in some areas, particularly 

in central and southern parts of the region. 

Annual nutrient yields have been used to compare the 

effects of major land uses in the region on stream nutrient 

transport. Annual nutrient yields (annual loads divided by 

drainage basin area) are a convenient measure for comparing the relative nutrient contributions from drainage basins 

with a wide range in total basin size and a wide range in basin 

characteristics. Nutrient yields vary seasonally, annually, and 

regionally, on the basis of hydrologic conditions, natural drainage basin characteristics, and nutrient sources associated with 

various land uses and waste-disposal practices. 

Annual yields have been evaluated and summary 

statistics have been calculated for 93 stations for total nitrogen 

(table 20) and for 92 stations for total phosphorus (table 21). 

The White River at West Hartford, Vt. (station 20, table 20), 

had sufficient data for estimation of total nitrogen loads, 

but had insufficient uncensored data for estimation of total 

phosphorus loads. Annual yields of total nitrogen and total 

phosphorus were evaluated for stations with annual load 

estimates for all or some of the 11 water years in the 1993–

2003 period, including: 46 stations with annual load estimates 

for the full 11-year period; one station, the Schuylkill River 

at Philadelphia, Pa., with annual load estimates for the 

1993–2003 period based on the 1975–2003 load estimation; 

and 37 additional stations that had from 1 to 10 years of 

annual load estimates in the 1993–2003 period (table 5, load 

estimation column). In addition, mean annual yields for nine 

basins evaluated in a national study of undeveloped basins 

were included (Clark and others, 2000; D.K. Mueller, U.S. 

Geological Survey, written commun., 2007). 

Summary statistics for the individual stations have been 

further summarized into statistics for minimum, median, and 

maximum yields for all stations and for four land use categories (table 22). Stations with annual yield estimates for three 

or fewer years generally do not have records that cover a full 

range of annual mean streamflows. Consequently, these stations have been included only in selected summary statistics 

for all stations or for the four land use categories (table 22), 

on the basis of an evaluation of annual mean flows during the 

years of available yield estimates. Ranges in annual yields for 

stations with 1 to 10 years of yield estimates in the 1993–2003 

period are not exactly comparable to yield ranges for stations 

with estimates for the full 11-year period, because of differences in hydrologic conditions during different calibration 

periods. Additional years of data would be required to define 

the yield ranges more accurately for these stations with short 

periods of record. However, the analyses for these stations 

provide information on yields for geographic areas and land 

uses that are not fully covered by the stations with more complete records, and thus extend the understanding of nutrient 

yields in the region. Mean annual yields for the nine basins 

evaluated in a national study of undeveloped basins (Clark and 

others, 2000; D.K. Mueller, U.S. Geological Survey, written 

commun., 2007) are included only in the summary statistics 

for median yields for all basins and median yields for undeveloped basins (table 22). 

Estimated total nitrogen yields for all drainage basins 

and all years evaluated during the recent period ranged over 

four orders of magnitude, from 41 pounds per square mile per 

year (lb/mi2/yr) to 32,000 lb/mi2/yr (table 22, fig. 17). Minimum yields ranged from 41 to 15,000 lb/mi2

/yr, median yields 

ranged from 290 to 26,000 lb/mi2/yr, and maximum yields 

ranged from 1,300 to 32,000 lb/mi2/yr. 

Estimated total phosphorus yields for all drainage basins 

and years evaluated ranged over five orders of magnitude, 

from 1.4 to 16,000 lb/mi2/yr (table 22, fig. 17). Minimum 

yields ranged from 1.4 to 900 lb/mi2/yr, median yields ranged 

from 12 to 1,900 lb/mi2/yr, and maximum yields ranged from 

less than 100 to 16,000 lb/mi2/yr. A maximum total phosphorus yield of more than 100,000 lb/mi2

/yr was estimated 

for water year 1996, a year of extremely high streamflow, 

for Muddy Creek at Mount Clinton, Va., (table 21). This 

maximum has not been included in the summary statistics 

(table 22) and graph (fig. 17F) for reasons described in the section on Effects of Variability in Streamflow Conditions. 
78 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Table 20. Summary statistics for total nitrogen yields by station, 1993–2003.—Continued

[Definitions for land-use codes are in table 7. Stations with drainage areas greater than or equal to 1,000 mi2 are shaded. Annual loads and yields for the Schuylkill 

River at Philadelphia, Pa. (station 97) based on load estimation for 1975–2003 period. mi2, square miles; lb/mi2/yr, pounds per square mile per year; NA, not available; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural]

Station 

sequence 

number

Station name

Drainage 

area 

(mi2)

Number of 

years of 

record in 

1993–2003

Total nitrogen yields 

(lb/mi2/yr) Landuse 

code Minimum

Mean Median Maximum

1 Penobscot River at Eddington, Maine 7,764 2 NA 1,600 1,600 NA UN

2 Kennebec River at North Sidney, Maine 5,403 1 NA 1,100 1,100 NA UN

3 Wild River at Gilead, Maine 69.6 3 NA 500 500 NA UN

4 Saco River at Cornish, Maine 1,293 3 330 500 580 NA UN

5 Stillwater River near Sterling, Mass. 31.6 5 620 1,100 1,200 1,600 UN

6 Merrimack River below Concord River at 

Lowell, Mass.

4,635 5 1,700 2,400 2,400 2,900 UR

7 Aberjona River at Winchester, Mass. 24.7 5 4,400 7,000 7,600 9,100 UR

8 Charles River above Watertown Dam at 

Watertown, Mass.

271 1 NA 4,900 4,900 NA UR

10 Pawtuxet River at Cranston, R.I. 200 10 2,900 5,100 5,100 7,100 UR

13 Shetucket River at South Windham, Conn. 408 11 1,200 2,200 2,400 2,800 UR

14 Quinebaug River at Quinebaug, Conn. 155 11 1,200 1,800 2,000 2,300 UR

16 Quinebaug River at Putnam, Conn. 328 5 1,700 2,400 2,400 3,300 UR

18 Quinebaug River at Jewett City, Conn. 713 11 1,600 3,000 3,200 3,700 UN

19 Ammonoosuc River at Bethlehem Junction, N.H. 87.6 2 NA 700 700 NA UN

20 White River at West Hartford, Vt. 690 3 800 1,100 1,200 NA UN

21 Green River near Colrain, Mass. 41.4 2 NA 620 620 NA UN

22 Connecticut River at Thompsonville, Conn. 9,660 11 1,700 2,200 2,200 2,900 UN

23 Broad Brook at Broad Brook, Conn. 15.5 11 7,500 14,000 15,000 17,000 UA

24 Bunnell (Burlington) Brook near Burlington, Conn. 4.10 11 730 1,300 1,400 1,700 UN

25 Farmington River at Unionville, Conn. 378 11 610 1,100 1,100 1,400 UN

27 Farmington River at Tariffville, Conn. 577 11 2,200 3,300 3,500 4,000 UR

28 Hockanum River near East Hartford, Conn. 73.4 11 7,200 11,000 11,000 12,000 UR

30 Salmon River near East Hampton, Conn. 100 11 780 1,500 1,500 2,400 UR

32 Quinnipiac River at Wallingford, Conn. 115 11 6,600 10,000 11,000 12,000 UR

37 Housatonic River at Stevenson, Conn. 1,544 11 1,200 2,500 2,600 3,600 UR

39 Naugatuck River at Beacon Falls, Conn. 260 11 3,700 7,300 7,700 9,900 UR

40 Saugatuck River near Redding, Conn. 21.0 11 810 1,400 1,400 2,000 UR

41 Norwalk River at Winnipauk, Conn. 33.0 11 1,500 2,600 2,400 3,700 UR

45 Canajoharie Creek near Canajoharie, N.Y. 59.7 10 1,900 5,700 5,800 9,400 AG

46 Lisha Kill northwest of Niskayuna, N.Y. 15.6 5 770 1,600 1,500 2,900 UR

47 Mohawk River at Cohoes, N.Y. 3,450 11 2,200 4,200 4,600 5,400 AG

48 Esopus Creek at Allaben, N.Y. 63.7 2 NA 1,300 1,300 NA UN

50 Hackensack River at Rivervale, N.J. 58.0 11 1,400 2,900 3,100 3,800 UR

53 Pequannock River at Macopin Intake Dam, N.J. 63.7 11 41 700 820 1,300 UN

54 Ramapo River near Mahwah, N.J. 120 11 2,200 4,100 4,200 5,700 UR
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 79

Table 20. Summary statistics for total nitrogen yields by station, 1993–2003.—Continued

[Definitions for land-use codes are in table 7. Stations with drainage areas greater than or equal to 1,000 mi2 are shaded. Annual loads and yields for the Schuylkill 

River at Philadelphia, Pa. (station 97) based on load estimation for 1975–2003 period. mi2, square miles; lb/mi2/yr, pounds per square mile per year; NA, not available; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural]

Station 

sequence 

number

Station name

Drainage 

area 

(mi2)

Number of 

years of 

record in 

1993–2003

Total nitrogen yields 

(lb/mi2/yr) Landuse 

code Minimum

Mean Median Maximum

55 Passaic River at Little Falls, N.J. 762 11 1,500 4,400 5,000 5,900 UR

56 Saddle River at Lodi, N.J. 54.6 11 12,000 16,000 17,000 22,000 UR

57 Rahway River near Springfield, N.J. 25.5 11 2,700 5,700 5,700 8,200 UR

58 Rahway River at Rahway, N.J. 40.9 11 2,000 4,800 5,000 7,800 UR

59 Mulhockaway Creek at Van Syckel, N.J. 11.8 11 1,500 3,300 3,100 5,500 AG

60 South Branch Raritan River at Stanton, N.J. 147 5 3,300 6,500 7,200 7,600 UA

61 Neshanic River at Reaville, N.J. 25.7 11 2,400 7,600 7,900 12,000 AG

62 Lamington (Black) River near Pottersville, N.J. 32.8 5 2,600 4,300 4,700 4,800 UR

64 North Branch Raritan River near Raritan, N.J. 190 6 2,100 3,500 3,400 4,700 UA

65 Raritan River at Manville, N.J. 490 5 3,300 7,500 8,500 9,300 UA

66 Stony Brook at Princeton, N.J. 44.5 6 1,900 6,000 6,400 8,600 UA

67 Millstone River at Blackwells Mills, N.J. 258 11 4,200 7,700 8,000 10,000 UA

68 Raritan River at Queens Bridge at Bound Brook, N.J. 804 11 3,000 6,500 6,700 9,000 UA

70 Manasquan River at Squankum, N.J. 44.0 11 930 2,900 3,500 5,100 UA

71 Toms River near Toms River, N.J. 123 11 2,100 2,800 2,900 3,600 UR

75 Batsto River at Batsto, N.J. 67.8 11 460 1,300 1,600 1,900 UN

78 Maurice River at Norma, N.J. 112 11 2,700 4,700 4,800 6,500 UA

80 Delaware River at Port Jervis, N.Y. 3,070 3 900 1,400 1,400 NA UN

81 Biscuit Brook above Pigeon Brook at Frost Valley, N.Y. 3.72 3 NA 2,200 2,200 NA UN

82 Delaware River at Montague, N.J. 3,480 11 990 2,400 2,400 4,500 UN

85 Paulins Kill at Blairstown, N.J. 126 11 1,100 3,400 3,200 5,000 AG

86 Jordan Creek near Schnecksville, Pa. 53.0 3 9,400 12,000 12,000 NA AG

90 Delaware River at Trenton, N.J. 6,780 11 2,400 4,600 4,800 6,400 UN

92 Little Neshaminy Creek at Valley Road near 

Neshaminy, Pa.

26.8 4 2,300 6,000 6,600 8,300 UA

93 McDonalds Branch in Byrne State Forest, N.J. 2.35 3 NA 290 290 NA UN

95 Cooper River at Haddonfield, N.J. 17.0 11 2,100 3,900 3,800 6,400 UR

96 French Creek near Phoenixville, Pa. 59.1 5 1,500 4,400 4,100 8,300 AG

97 Schuylkill River at Philadelphia, Pa. 1,893 11 5,300 11,000 11,000 16,000 UA

98 Raccoon Creek near Swedesboro, N.J. 26.9 11 2,500 5,200 5,100 7,300 AG

100 Nanticoke River near Bridgeville, Del. 75.4 4 8,400 13,000 13,000 15,000 AG

101 Choptank River near Greensboro, Md. 113 11 1,400 4,600 4,900 9,300 AG

102 Chesterville Branch near Crumpton, Md. 6.12 6 9,800 14,000 15,000 17,000 AG

103 Susquehanna River at Danville, Pa. 11,220 3 2,500 4,500 NA 5,600 AG

104 Young Womans Creek near Renovo, Pa. 46.2 3 NA 1,700 1,700 NA UN

105 West Branch Susquehanna River at Lewisburg, Pa. 6,847 3 2,000 3,500 NA 4,300 UN
80 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Table 20. Summary statistics for total nitrogen yields by station, 1993–2003.—Continued

[Definitions for land-use codes are in table 7. Stations with drainage areas greater than or equal to 1,000 mi2 are shaded. Annual loads and yields for the Schuylkill 

River at Philadelphia, Pa. (station 97) based on load estimation for 1975–2003 period. mi2, square miles; lb/mi2/yr, pounds per square mile per year; NA, not available; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural]

Station 

sequence 

number

Station name

Drainage 

area 

(mi2)

Number of 

years of 

record in 

1993–2003

Total nitrogen yields 

(lb/mi2/yr) Landuse 

code Minimum

Mean Median Maximum

106 East Mahantango Creek at Klingerstown, Pa. 44.7 4 15,000 25,000 26,000 32,000 AG

107 Bobs Creek near Pavia, Pa. 16.6 3 2,200 3,000 2,700 3,900 UN

108 Cedar Run at Eberlys Mill, Pa. 12.6 2 7,000 11,000 11,000 14,000 UA

111 Susquehanna River at Conowingo, Md. 27,100 11 2,600 4,600 5,200 6,500 AG

112 Patuxent River near Unity, Md. 34.8 9 2,800 6,800 7,100 11,000 AG

113 Little Patuxent River at Savage, Md. 98.4 8 3,300 6,600 7,300 9,400 UA

114 Patuxent River near Bowie, Md. 348 11 2,000 4,300 4,700 6,700 UA

115 South Fork South Branch Potomac River near 

Moorefield, W. Va.

277 2 NA 2,100 2,100 NA UN

116 Conococheague Creek at Fairview, Md. 494 11 3,100 13,000 13,000 22,000 AG

117 Potomac River at Shepherdstown, W. Va. 5,939 3 1,300 3,400 2,200 6,700 AG

118 Muddy Creek at Mount Clinton, Va. 14.3 8 2,100 9,200 8,500 19,000 AG

119 South Fork Shenandoah River at Front Royal, Va. 1,634 7 530 3,300 2,000 7,500 AG

120 North Fork Shenandoah River near Strasburg, Va. 770 7 1,200 3,600 2,700 7,100 AG

121 Shenandoah River at Millville, W. Va. 3,041 3 2,200 4,100 4,900 5,100 AG

122 Potomac River at Chain Bridge, at Washington, D.C. 11,570 11 1,000 4,700 5,100 8,400 AG

123 Accotink Creek near Annandale, Va. 23.9 9 2,700 6,100 6,400 8,900 UR

124 Rappahannock River near Fredericksburg, Va. 1,595 11 410 3,300 2,700 7,400 AG

125 Pamunkey River near Hanover, Va. 1,078 11 200 1,500 1,700 3,000 AG

126 Mattaponi River near Beulahville, Va. 603 11 150 1,000 1,200 2,000 UN

127 James River at Cartersville, Va. 6,252 11 310 1,900 1,800 4,200 UN

128 Holiday Creek near Andersonville, Va. 8.54 3 NA 430 430 NA UN

129 Appomattox River at Matoaca, Va. 1,342 11 220 1,200 1,200 3,200 UN

130 Black River at Coventry, Vt. 122 2 1,500 1,700 1,700 NA AG
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 81

Table 21. Summary statistics for total phosphorus yields by station, 1993–2003.—Continued

[Definitions for land-use codes are in table 7. Stations with drainage areas greater than or equal to 1,000 mi2 are shaded. Annual loads and yields for the Schuylkill 

River at Philadelphia, Pa. (station 97) based on load estimation for 1975–2003 period. mi2, square miles; lb/mi2/yr, pounds per square mile per year; NA, not available; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural]

Station 

sequence 

number

Station name

Drainage 

area 

(mi2)

Number of 

years of 

record in 

1993–2003

Total phosphorus yields 

(lb/mi2/yr) Landuse 

code Minimum

Mean Median Maximum

1 Penobscot River at Eddington, Maine 7,764 2 NA 91 91 NA UN

2 Kennebec River at North Sidney, Maine 5,403 1 NA 130 130 NA UN

3 Wild River at Gilead, Maine 69.6 3 NA 43 43 NA UN

4 Saco River at Cornish, Maine 1,293 3 48 62 63 NA UN

5 Stillwater River near Sterling, Mass. 31.6 5 27 52 56 74 UN

6 Merrimack River below Concord River at 

Lowell, Mass.

4,635 5 140 210 220 280 UR

7 Aberjona River at Winchester, Mass. 24.7 5 69 140 140 230 UR

8 Charles River above Watertown Dam at 

Watertown, Mass.

271 1 NA 210 210 NA UR

10 Pawtuxet River at Cranston, R.I. 200 10 370 550 550 720 UR

13 Shetucket River at South Windham, Conn. 408 11 68 110 110 150 UR

14 Quinebaug River at Quinebaug, Conn. 155 11 64 100 100 170 UR

16 Quinebaug River at Putnam, Conn. 328 5 89 130 120 200 UR

18 Quinebaug River at Jewett City, Conn. 713 11 100 180 180 350 UN

19 Ammonoosuc River at Bethlehem Junction, N.H. 87.6 2 NA 35 35 NA UN

21 Green River near Colrain, Mass. 41.4 2 NA 46 46 NA UN

22 Connecticut River at Thompsonville, Conn. 9,660 11 120 190 190 280 UN

23 Broad Brook at Broad Brook, Conn. 15.5 11 150 490 510 820 UA

24 Bunnell (Burlington) Brook near Burlington, Conn. 4.10 11 25 62 63 83 UN

25 Farmington River at Unionville, Conn. 378 11 26 51 53 67 UN

27 Farmington River at Tariffville, Conn. 577 11 230 310 310 450 UR

28 Hockanum River near East Hartford, Conn. 73.4 11 730 1,000 1,000 1,200 UR

30 Salmon River near East Hampton, Conn. 100 11 23 54 43 110 UR

32 Quinnipiac River at Wallingford, Conn. 115 11 550 1,000 1,100 1,500 UR

37 Housatonic River at Stevenson, Conn. 1,544 11 50 110 110 150 UR

39 Naugatuck River at Beacon Falls, Conn. 260 11 720 1,200 1,300 1,600 UR

40 Saugatuck River near Redding, Conn. 21.0 11 30 55 55 75 UR

41 Norwalk River at Winnipauk, Conn. 33.0 11 64 130 120 220 UR

45 Canajoharie Creek near Canajoharie, N.Y. 59.7 10 75 580 540 1,100 AG

46 Lisha Kill northwest of Niskayuna, N.Y. 15.6 5 32 86 68 190 UR

47 Mohawk River at Cohoes, N.Y. 3,450 11 110 380 420 540 AG

48 Esopus Creek at Allaben, N.Y. 63.7 2 NA 140 140 NA UN

50 Hackensack River at Rivervale, N.J. 58.0 11 90 140 120 260 UR

53 Pequannock River at Macopin Intake Dam, N.J. 63.7 11 1.4 38 32 77 UN

54 Ramapo River near Mahwah, N.J. 120 11 190 340 350 480 UR

55 Passaic River at Little Falls, N.J. 762 11 210 520 530 690 UR
82 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Table 21. Summary statistics for total phosphorus yields by station, 1993–2003.—Continued

[Definitions for land-use codes are in table 7. Stations with drainage areas greater than or equal to 1,000 mi2 are shaded. Annual loads and yields for the Schuylkill 

River at Philadelphia, Pa. (station 97) based on load estimation for 1975–2003 period. mi2, square miles; lb/mi2/yr, pounds per square mile per year; NA, not available; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural]

Station 

sequence 

number

Station name

Drainage 

area 

(mi2)

Number of 

years of 

record in 

1993–2003

Total phosphorus yields 

(lb/mi2/yr) Landuse 

code Minimum

Mean Median Maximum

56 Saddle River at Lodi, N.J. 54.6 11 900 1,800 1,900 2,600 UR

57 Rahway River near Springfield, N.J. 25.5 11 200 1,500 800 6,300 UR

58 Rahway River at Rahway, N.J. 40.9 11 160 490 380 1,100 UR

59 Mulhockaway Creek at Van Syckel, N.J. 11.8 11 40 110 94 180 AG

60 South Branch Raritan River at Stanton, N.J. 147 5 82 190 140 400 UA

61 Neshanic River at Reaville, N.J. 25.7 11 120 2,600 1,000 16,000 AG

62 Lamington (Black) River near Pottersville, N.J. 32.8 5 76 140 160 180 UR

64 North Branch Raritan River near Raritan, N.J. 190 6 150 320 260 700 UA

65 Raritan River at Manville, N.J. 490 5 130 320 350 420 UA

66 Stony Brook at Princeton, N.J. 44.5 6 120 590 580 980 UA

67 Millstone River at Blackwells Mills, N.J. 258 11 410 840 860 1,300 UA

68 Raritan River at Queens Bridge at Bound Brook, N.J. 804 11 290 710 610 1,900 UA

70 Manasquan River at Squankum, N.J. 44.0 11 89 290 250 670 UA

71 Toms River near Toms River, N.J. 123 11 38 75 71 170 UR

75 Batsto River at Batsto, N.J. 67.8 11 14 39 23 120 UN

78 Maurice River at Norma, N.J. 112 11 23 55 54 91 UA

80 Delaware River at Port Jervis, N.Y. 3,070 3 48 89 100 NA UN

81 Biscuit Brook above Pigeon Brook at Frost Valley, N.Y. 3.72 3 NA 48 48 NA UN

82 Delaware River at Montague, N.J. 3,480 11 37 130 97 290 UN

85 Paulins Kill at Blairstown, N.J. 126 11 44 120 120 230 AG

86 Jordan Creek near Schnecksville, Pa. 53.0 3 150 200 200 NA AG

90 Delaware River at Trenton, N.J. 6,780 11 160 340 330 580 UN

92 Little Neshaminy Creek at Valley Road near 

Neshaminy, Pa.

26.8 4 170 680 690 1,200 UA

93 McDonalds Branch in Byrne State Forest, N.J. 2.35 3 NA 12 12 NA UN

95 Cooper River at Haddonfield, N.J. 17.0 11 560 1,200 1,100 2,100 UR

96 French Creek near Phoenixville, Pa. 59.1 5 43 260 200 590 AG

97 Schuylkill River at Philadelphia, Pa. 1,893 11 390 710 680 1,000 UA

98 Raccoon Creek near Swedesboro, N.J. 26.9 11 190 580 610 1,000 AG

100 Nanticoke River near Bridgeville, Del. 75.4 4 280 520 570 640 AG

101 Choptank River near Greensboro, Md. 113 11 67 330 290 1,000 AG

102 Chesterville Branch near Crumpton, Md. 6.12 6 98 480 510 860 AG

103 Susquehanna River at Danville, Pa. 11,220 3 120 320 NA 460 AG

104 Young Womans Creek near Renovo, Pa. 46.2 3 NA 34 34 NA UN

105 West Branch Susquehanna River at Lewisburg, Pa. 6,847 3 110 250 NA 320 UN

106 East Mahantango Creek at Klingerstown, Pa. 44.7 4 170 220 220 270 AG
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 83

Table 21. Summary statistics for total phosphorus yields by station, 1993–2003.—Continued

[Definitions for land-use codes are in table 7. Stations with drainage areas greater than or equal to 1,000 mi2 are shaded. Annual loads and yields for the Schuylkill 

River at Philadelphia, Pa. (station 97) based on load estimation for 1975–2003 period. mi2, square miles; lb/mi2/yr, pounds per square mile per year; NA, not available; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural]

Station 

sequence 

number

Station name

Drainage 

area 

(mi2)

Number of 

years of 

record in 

1993–2003

Total phosphorus yields 

(lb/mi2/yr) Landuse 

code Minimum

Mean Median Maximum

107 Bobs Creek near Pavia, Pa. 16.6 3 39 58 52 84 UN

108 Cedar Run at Eberlys Mill, Pa. 12.6 2 68 130 130 190 UA

111 Susquehanna River at Conowingo, Md. 27,100 11 71 160 190 270 AG

112 Patuxent River near Unity, Md. 34.8 9 60 320 200 1,100 AG

113 Little Patuxent River at Savage, Md. 98.4 8 180 1,400 1,300 3,000 UA

114 Patuxent River near Bowie, Md. 348 11 130 330 280 890 UA

115 South Fork South Branch Potomac River near 

Moorefield, W. Va.

277 2 NA 72 72 NA UN

116 Conococheague Creek at Fairview, Md. 494 11 110 630 590 1,300 AG

117 Potomac River at Shepherdstown, W. Va. 5,939 3 92 200 100 420 AG

118 Muddy Creek at Mount Clinton, Va. 14.3 8 68 14,000 500 110,000 AG

119 South Fork Shenandoah River at Front Royal, Va. 1,634 7 85 280 220 550 AG

120 North Fork Shenandoah River near Strasburg, Va. 770 7 130 340 280 630 AG

121 Shenandoah River at Millville, W. Va. 3,041 3 130 250 310 320 AG

122 Potomac River at Chain Bridge, at Washington, D.C. 11,570 11 61 330 280 870 AG

123 Accotink Creek near Annandale, Va. 23.9 9 160 880 980 1,800 UR

124 Rappahannock River near Fredericksburg, Va. 1,595 11 24 610 630 1,500 AG

125 Pamunkey River near Hanover, Va. 1,078 11 29 180 190 440 AG

126 Mattaponi River near Beulahville, Va. 603 11 12 99 120 180 UN

127 James River at Cartersville, Va. 6,252 11 61 380 320 860 UN

128 Holiday Creek near Andersonville, Va. 8.54 3 NA 45 45 NA UN

129 Appomattox River at Matoaca, Va. 1,342 11 16 130 120 350 UN

130 Black River at Coventry, Vt. 122 2 140 220 220 NA AG
84 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Table 22. Summary statistics for total nitrogen and total phosphorus yields for all stations 

and for four land-use categories, 1993–2003.

[Definitions for land-use categories are in table 7. lb/mi2/yr, pounds per square mile per year]

Number of 

stations

Yield 

(lb/mi2/yr)

Minimum Median Maximum

All basins

Minimum total nitrogen yields 81 41 2,000 15,000

Median total nitrogen yields 91 290 3,400 26,000

Maximum total nitrogen yields 76 1,300 6,400 32,000

Minimum total phosphorus yields 80 1.4 91 900

Median total phosphorus yields 90 12 200 1,900

Maximum total phosphorus yields 75 67 460 16,000

Undeveloped basins

Minimum total nitrogen yields 17 41 730 2,400

Median total nitrogen yields 27 290 1,300 4,800

Maximum total nitrogen yields 14 1,300 3,100 6,400

Minimum total phosphorus yields 16 1.4 38 160

Median total phosphorus yields 26 12 63 330

Maximum total phosphorus yields 14 67 230 860

Urban basins

Minimum total nitrogen yields 25 770 2,100 12,000

Median total nitrogen yields 26 1,400 4,000 17,000

Maximum total nitrogen yields 25 2,000 4,800 22,000

Minimum total phosphorus yields 25 23 140 900

Median total phosphorus yields 26 43 210 1,900

Maximum total phosphorus yields 25 75 280 6,300

Urban/agricultural basins

Minimum total nitrogen yields 14 930 3,100 7,500

Median total nitrogen yields 14 3,400 7,000 15,000

Maximum total nitrogen yields 14 4,700 8,800 17,000

Minimum total phosphorus yields 14 23 140 410

Median total phosphorus yields 14 54 430 1,300

Maximum total phosphorus yields 14 91 850 3,000

Agricultural basins

Minimum total nitrogen yields 25 200 2,100 15,000

Median total nitrogen yields 24 1,700 5,000 26,000

Maximum total nitrogen yields 23 3,000 7,500 32,000

Minimum total phosphorus yields 25 24 92 280

Median total phosphorus yields 24 94 280 1,000

Maximum total phosphorus yields 22 180 610 16,000
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 85

32

Agricultural basin

Urban/agricultural basin

Undeveloped basin

Urban basin

Station sequence number

EXPLANATION

EXPLANATION

10

100

1,000

10,000

Minimum total nitrogen yield,

in pounds per square mile per year

A. Minimum yields of total nitrogen, 1993–2003

25th percentile

Median

75th percentile

30,000

100

1,000

10,000

Median total nitrogen yield,

in pounds per square mile per year

B. Median yields of total nitrogen, 1993–2003

19

25th percentile

Median

75th

percentile

40,000

Northeastern region study site

Undeveloped basin (mean from 

 national study)

Agricultural basin

Urban/agricultural basin

Undeveloped basin

Urban basin

Station sequence number

Total developed land, as percentage of drainage basin

56

106

102

108

86 100 23 28

32

7 67

97

107

22

105

90

18

4

126

125 129

127

124

119

46

75

25 5

20 80

82

24

40 30

70 122

111 113 116

112

57 123 10

6

85

14

13 37

11759 16 130

27 71

54103

62 47

39 60

64

121

55 96

120

66

101

41

50

45

114

65 68

78 61

92

98

118

95 58

53

18

90

93

128 3

106

23

97 28 32

100 116 86

56

102

108

4

21 19 53 25

2 20

5 126 129

30 40

127

24

75 80 1 48

104

81 115 22

82 107

46

123 7 118

92

61 112 113 67 68

65

66 60 39

122

50

95

58 10 57

54 27

98 45

114 78 101

64 70

8 121

47

55

96 62

71 59 85 120 124 119

6 13 37

16 117

125

130

111

41

14

0 10 20 30 40 50 60 70 80 90 100

0 10 20 30 40 50 60 70 80 90 100

Figure 17. Ranges for minimum, median, and maximum nutrient yields in relation to the percentage of developed land in a drainage 

basin. (A) Minimum yields of total nitrogen for 81 stations, 1993–2003, (B) median yields of total nitrogen for 91 stations, 1993–2003, 

(C) maximum yields of total nitrogen for 76 stations, 1993–2003, (D) minimum yields of total phosphorus for 80 stations, 1993–2003, 

(E) median yields of total phosphorus for 90 stations, 1993–2003, and (F) maximum yields of total phosphorus for 75 stations, 

1993–2003.
86 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

EXPLANATION

EXPLANATION

Total developed land, as percentage of drainage basin

1,000

10,000

Maximum total nitrogen yield,

in pounds per square mile per year

C. Maximum yields of total nitrogen, 1993–2003

75th percentile

Median

25th percentile

50,000

Agricultural basin

Urban/agricultural basin

Undeveloped basin

Urban basin

46 Station sequence number

10

1

100

1,000

Minimum total phosphorus yield,

in pounds per square mile per year

D. Minimum yields for total phosphorus, 1993–2003

75th percentile

Median

Agricultural basin

Urban/agricultural basin

Undeveloped basin

Urban basin

46 Station sequence number

2,000

25th percentile

106

23

97

28 32

100

67

116

112 61

118

56

102

108

46

41

53

25 5

75 24

126 40

14 30

13 6 22 125 129 16

71 37

90

50

70

78 95

18

127

27 105

82

107

113 7

45

65 101 39

122 68

98

57 58

123

114

66 96

124 120119

60

121

64

54

10 117

59

103

62 8547

55

111 92

53

90

127

126

129

78

46

108 118 7

112

45

101 41

54 27

10

55

39

106

68

97

100

67

32

28

113 92 98 57

95

56

122

22 123

102

50

61 86

116 114

23

65 66

70

64

121

120

119 60

124

96

85

62

47

103

130

117 16 14

13 105 18

6

37

59

125

71

40

24 30

75

5 25

82

80

107

4

111

58

0 10 20 30 40 50 60 70 80 90 100

0 10 20 30 40 50 60 70 80 90 100

Figure 17. Ranges for minimum, median, and maximum nutrient yields in relation to the percentage of developed land in a 

drainage basin. (A) Minimum yields of total nitrogen for 81 stations, 1993–2003, (B) median yields of total nitrogen for 91 stations, 

1993–2003, (C) maximum yields of total nitrogen for 76 stations, 1993–2003, (D) minimum yields of total phosphorus for 80 stations, 

1993–2003, (E) median yields of total phosphorus for 90 stations, 1993–2003, and (F) maximum yields of total phosphorus for 

75 stations, 1993–2003.—Continued
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 87

Northeastern region study site

Undeveloped basin (mean from

 national study)

Agricultural basin

Urban/agricultural basin

Undeveloped basin

Urban basin

39 Station sequence number

Agricultural basin

Undeveloped basin

Urban basin

61 Station sequence number

Urban/agricultural basin

EXPLANATION

EXPLANATION

30

40

71 46

10

39

55

124 66

23

102 98

45 116 100 68

97 67

28 32

92

61

113

57

123 95

56

127

90

118

7

41 50

78

93

48

122

22

27

54 47 121 65

101 114

106 86

112

120 70 64

119 8 96

60

85

62 125

130 6

18

129 16

13

59 117

37 14

24

75

2 80

1 82

115

5 25

4

107

128

21 81

3

104 19

53

126 108

111

58

61

56

123

92

124

39 101

116

67

28 97

112

45

40

30

14

127

90

25th percentile 7

46

50 106

41

78

122

22

37 71

16

62

6

100

102 23

70

66

64

119

47 120 55

96

103 60 65

121 85

59

10

27 54

105 18

129

117

125

126

82

75

53 107

25

5 24

57

113

95

58 98

68

32

108

111

13

114

10 20 30 40 50 60 70 80 90 100

10

100

1,000

Median total phosphorus yield,

in pounds per square mile per year

E. Median yields for total phosphorus, 1993–2003

75th percentile

Median

25th percentile

3,000

0

0 10 20 30 40 50 60 70 80 90 100

Total developed land, as percentage of drainage basin

10

100

1,000

10,000

Maximum total phosphorus yield,

in pounds per square mile per year

F. Maximum yields for total phosphorus, 1993–2003

Median

75th percentile

20,000

Figure 17. Ranges for minimum, median, and maximum nutrient yields in relation to the percentage of developed land in a 

drainage basin. (A) Minimum yields of total nitrogen for 81 stations, 1993–2003, (B) median yields of total nitrogen for 91 stations, 

1993–2003, (C) maximum yields of total nitrogen for 76 stations, 1993–2003, (D) minimum yields of total phosphorus for 80 stations, 

1993–2003, (E) median yields of total phosphorus for 90 stations, 1993–2003, and (F) maximum yields of total phosphorus for 

75 stations, 1993–2003.—Continued
88 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Annual nutrient yields for total nitrogen and total phosphorus have been summarized in boxplots for the 46 stations 

with annual load estimates for all years in the 1993–2003 

period, to show the distribution of yields in individual basins 

in more detail (fig. 18). In addition to the large station-tostation variations in nutrient yields, large total ranges and 

large interquartile ranges for some stations also demonstrate 

that large variations in yield take place from year to year at 

some locations. Yield estimates are generally low for drainage basins with large percentages of undeveloped land (more 

than 70 percent of the basin) and few or no point sources; the 

total range is compact, with minimal interannual variation. For 

example, total nitrogen yields for Bunnell (Burlington) Brook 

in Connecticut (station 24, about 75 percent undeveloped), 

the Pequannock River at Macopin Intake Dam in New Jersey 

(station 53, about 94 percent undeveloped), and the Batsto 

River in New Jersey (station 75, about 86 percent undeveloped) are all low (less than 2,000 lb/mi2

/yr), with narrow total 

ranges and narrow interquartile ranges (table 5, and fig. 18A). 

By contrast, drainage basins with large percentages of developed land, or major point-source influences, generally have 

high nutrient yields, large total ranges, and large interquartile 

ranges. The large interquartile ranges indicate substantial 

variation in yields, and consequently large variations in 

water quality, from year to year. Examples of stations with 

high total nitrogen yields (medians from 11,000 to 

17,000 lb/mi2/yr), large total ranges, and large interquartile 

ranges include: Broad Brook in Connecticut, an urbanagricultural basin (station 23, about 48 percent undeveloped); 

the Hockanum River in Connecticut, an urbanized basin with 

major point sources (station 28, about 46 percent undeveloped); the Saddle River in New Jersey, an urbanized basin 

with point sources (station 56, 10 percent undeveloped), and 

Conococheague Creek in Maryland, an agricultural basin with 

point sources (station 116, about 39 percent undeveloped) 

(table 5, and fig. 18A). Differences in yield related to land-use 

characteristics are discussed in more detail in the sections on 

Forested, Agricultural, and Urbanized Drainage Basins. 

Forested Drainage Basins

Headwater tributaries have a profound influence on 

downstream water quality, water quantity, and habitat, as noted 

in a series of papers on the hydrologic connections between 

headwater streams and downstream waters (Nadeau and 

Rains, 2007; Alexander and others, 2007). As one researcher 

observes, “Every important aspect of the river ecosystem, 

the river geomorphic system, and the river chemical system 

begins in headwater streams” (Freeman and others, 2007). 

These findings have major implications for future water quality in the river basins of the northeastern United States, where 

most of the land is still forested, where major river basins have 

relatively pristine headwater areas and impaired downstream 

reaches, and where development pressures in the late 20th and 

early 21st centuries have increased in previously undeveloped 

areas of many drainage basins. 

A study of the influence of headwater streams on downstream water quality (Alexander and others, 2007) emphasizes 

that the hydrologic modifications accompanying urbanization 

in headwater streams accelerate and increase the delivery of 

nutrients to downstream reaches, independent of increases in 

the nutrient sources. Based on the understanding of nitrogen 

transport processes, 

“Land-use changes or modifications to stream channels that increase the rates of flow in headwater 

streams may heighten their influence on the chemical quality of downstream receiving waters. For 

example, increases in the peak discharge and flashiness of flows that are often associated with urbanization would be likely to reduce the natural processing 

of nitrogen in low-order streams, increasing the 

distance over which nitrogen is transported downstream. In addition, stream channelization projects 

that straighten channels and remove natural pools 

and riffles are likely to shorten the water travel time 

in stream reaches; this would also be likely to reduce 

nitrogen losses and increase downstream transport” 

(Alexander and others, 2007, p. 46).

These conclusions underscore the importance of understanding baseline nutrient concentrations, trends, and loads in 

the relatively pristine headwater drainage basins of the region, 

and the changes that may be occurring in sparsely developed 

basins that are undergoing increased urbanization. 

Nutrient yields have been evaluated for 28 drainage 

basins classified as undeveloped in this report (table 20), ranging in size from slightly more than 2 mi2

 to almost 10,000 mi2, 

and with undeveloped land ranging from 75 to 100 percent of 

basin area. Undeveloped drainage basins include small, largely 

forested and sparsely populated basins, and large basins that 

meet the land-use criteria for undeveloped basins as applied in 

this study (table 7, and table 8, in back of report), but nevertheless include large urban areas and major point-source discharges. Nine undeveloped basins from a national study (Clark 

and others, 2000; D.K. Mueller, U.S. Geological Survey, written commun., 2007) are included in the summary statistics for 

median yields for undeveloped basins and all basins, but are 

excluded from the summary statistics for minimum and maximum yields (table 22). The yields calculated for undeveloped 

basins in the national study (table 17) are mean annual yields 

based on estimates for years in the early 1990s, made by using 

a different methodology from the load estimation procedure 

used in this report. Although the mean annual yields for these 

nine basins are not equivalent to the median yields estimated 

for other undeveloped basins analyzed in this report, these 

basins represent a useful comparison, and an additional 

source of information for understanding likely nutrient 

yields in undeveloped drainage areas of the region. One 

undeveloped drainage basin, the West Branch Susquehanna in 

Pennsylvania (station 105, table 20), has been excluded from 

median yield statistics, because the available years of load 
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 89

0

5,000

10,000

15,000

20,000

Station sequence number (table 5)

(With percent of undeveloped land, land-use classification (table 7), and presence of major point sources (P))

13 14 18 22 23 24 25 27 28 30 32 37 39 40 41 47 50 53 54 55 56 57 58 59 61 67 68 70 71 75 78 82 85 90 95 98 101 111 114 116122 124 125126 127 129

25,000

79%, P 81%, P 79%, P 85%, P 48%75%90%, P80%, P 46%, P 76% 44%, P 75%, P 65%, P 74% 47%, P 67%, P 33% 94% 78%, P 65%, P 10%, P 20% 16% 71% 32% 45%, P 48%, P 50% 76% 86% 49% 88%, P 66%, P 78%, P 21% 27% 49% 68%, P 41%, P 39%, P 61%, P 60%, P 72%, P 76% 80%, P 76%, P 

13 14 18 22 23 24 25 27 28 30 32 37 39 40 41 47 50 53 54 55 56 57 58 59 61 67 68 70 71 75 78 82 85 90 95 98 101 111 114 116122 124125126127 129 1

10

100

1,000

10,000

30,000

79%, P 81%, P 79%, P 85%, P 48%75%90%, P80%, P 46%, P 76% 44%, P 75%, P 65%, P 74% 47%, P 67%, P 33% 94% 78%, P 65%, P 10%, P 20% 16% 71% 32% 45%, P 48%, P 50% 76% 86% 49% 88%, P 66%, P 78%, P 21% 27% 49% 68%, P 41%, P 39%, P 61%, P 60%, P 72%, P 76% 80%, P 76%, P 

Annual total nitrogen yields, in pounds per square mile Annual total phosphorus yields, in pounds per square mile

Schematic boxplot

Undeveloped

Urban

Agricultural

Urban/agricultural

P Point source

EXPLANATION 

Median

75th percentile

25th percentile

Outlier within 1.5 times

 the interquartile range

Outlier within 1.5 times

 the interquartile range

Outlier

A

B

Figure 18. Annual yields for (A) total nitrogen and (B) total phosphorus for 46 stations during 1993–2003.
90 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

estimation in the 1993–2003 period include 1 year of very low 

annual mean flow, and 2 years of high annual mean flow. 

Median total nitrogen yields for 27 undeveloped (generally forested) drainage basins in the region during the 1993–

2003 period range from 290 to 4,800 lb/mi2/yr, with a median 

of 1,300 lb/mi2/yr (table 22). Mean annual total nitrogen yields 

for the nine undeveloped basins evaluated in the national 

study (Clark and others, 2000; D.K. Mueller, U.S. Geological 

Survey, written commun., 2007; table 17) range from about 

300 to 2,200 lb/mi2/yr (shown as green triangular symbols in 

fig. 17B). The lowest median (or mean) annual total nitrogen 

yields, less than 1,000 lb/mi2/yr, are found in drainage basins 

with more than 90 percent undeveloped land, including the 

Wild and Saco Rivers in Maine, the Ammonoosuc River 

in New Hampshire, the Green River in Massachusetts, the 

Pequannock River and McDonalds Branch in New Jersey, and 

Holiday Creek in Virginia (table 20; fig. 17B, stations 3, 4, 19, 

21, 53, 93, and 128). 

The national study of nutrients in undeveloped basins 

found that concentrations and yields of nitrate were generally 

highest in northeastern and mid-Atlantic coastal states, and 

that these high concentrations and yields correlated well with 

areas of high atmospheric nitrogen deposition (Clark and 

others, 2000, p. 1). Total nitrogen concentrations and yields 

for several stations evaluated in the national study (table 17) 

are composed largely of nitrate, and these basins are in the 

areas with high rates of atmospheric deposition of inorganic 

nitrogen (Clark and others, 2000, p. 14, fig. 2). Thus it is likely 

that even the most pristine drainage basins in the study area of 

this report have total nitrogen yields that are elevated relative 

to natural conditions. Undeveloped basins from the national 

study with mean annual total nitrogen yields that exceed 

1,000 lb/mi2/yr include Esopus Creek and Biscuit Brook 

in New York, Young Womans Creek in Pennsylvania, and 

the South Fork South Branch of the Potomac River in West 

Virginia (table 20; fig. 17B, stations 48, 81, 104, and 115). 

These four drainage basins, and the drainage basins of the 

Pequannock River and McDonalds Branch in New Jersey, are 

in the area of highest total atmospheric deposition of inorganic 

nitrogen, based on data for 1994 (Clark and others, 2000, 

p. 14, fig. 2). The national analyses for these drainage basins 

are based on data for 1991–95, and trends in the atmospheric 

deposition of nitrogen would affect expectable current yields 

in these and other drainage basins. All streams in the region 

are affected by the atmospheric deposition of nitrogen to 

some extent. 

Drainage basins are classified as undeveloped for 11 

of the 46 monitoring stations with annual load estimates 

for all years in the 1993–2003 period. Undeveloped land 

encompasses about 75 to 94 percent of the drainage basin 

areas of these streams. Among these 11 stations, 7 monitor 

streams that receive major point-source discharges, including 

the Quinebaug River at Jewett City, the Connecticut River at 

Thompsonville, and the Farmington River at Unionville in 

Connecticut; the Delaware River at Montague and at Trenton 

in New Jersey, and the James and Appomattox Rivers in 

Virginia (table 8, in back of report; figs. 17, 18A, stations 18, 

22, 25, 82, 90, 127, 129). The four streams without major 

point-source discharges are Bunnell (Burlington) Brook in 

Connecticut, the Pequannock and Batsto Rivers in New Jersey, 

and the Mattaponi River in Virginia (table 8, in back of report; 

figs. 17, 18A, stations 24, 53, 75, 126). 

Boxplots of annual total nitrogen yields for the recent 

period show that median yields are less than or equal to about 

4,800 lb/mi2/yr for all 11 undeveloped drainage basins, and are 

less than 2,000 lb/mi2/yr for 7 of these basins (fig. 18A; undeveloped basins shown in green). Interquartile ranges for yields 

in the undeveloped drainage basins evaluated in this report 

are generally narrow, less than 1,000 lb/mi2/yr for 8 of the 11 

undeveloped basins; that is, the yield at the 75th percentile 

exceeds the yield at the 25th percentile by less than 1,000 lb 

(fig. 18A). Total range in yield generally is narrow, with a difference between minimum and maximum yields ranging from 

about 800 to 2,100 lb/mi2/yr in 7 of the 11 basins. The range 

in total nitrogen yields equals or exceeds 3,000 lb/mi2/yr in the 

drainage basins of the Delaware River at Montague (range of 

about 3,500 lb/mi2/yr) and at Trenton (4,000 lb/mi2/yr), New 

Jersey, and the James (3,900 lb/mi2/yr) and Appomattox 

(3,000 lb/mi2/yr) Rivers in Virginia (fig. 18A), all of which 

receive major point-source discharges. The Delaware River at 

Trenton, N.J., has the highest median (4,800 lb/mi2/yr), largest interquartile range (2,600 lb/mi2

/yr), largest range in total 

nitrogen yields (4,000 lb/mi2/yr), and highest maximum yield 

(6,400 lb/mi2/yr) of these 11 undeveloped drainage basins 

(figs. 17, 18A, table 20; station 90). The Pequannock River in 

New Jersey (no major point-source discharges) has the lowest 

median total nitrogen yield (820 lb/mi2/yr), and the Farmington River at Unionville, Conn. (one major point-source discharge), has the narrowest interquartile range (350 lb/mi2

/yr) 

and the narrowest total range in yields (790 lb/mi2/yr) among 

these 11 undeveloped drainage basins (figs. 17, 18A, table 20; 

stations 53, 25). 

Minimum total nitrogen yields for 17 undeveloped drainage basins range from less than 100 to 2,400 lb/mi2

/yr, with a 

median value for minimum yields of 730 lb/mi2/yr (table 22, 

fig. 17A). Minimum yields of total nitrogen are less than about 

1,600 lb/mi2/yr in 75 percent of the undeveloped drainage 

basins. Maximum total nitrogen yields for 14 undeveloped 

drainage basins range from 1,300 to 6,400 lb/mi2/yr, with a 

median value for maximum yields of 3,100 lb/mi2/yr (table 22, 

fig. 17C). 

Median total phosphorus yields range from 12 to 

330 lb/mi2/yr for the 26 undeveloped basins evaluated, with 

a median of 63 lb/mi2/yr (table 22). Mean annual total phosphorus yields for undeveloped basins evaluated in the national 

study (Clark and others, 2000; D.K. Mueller, U.S. Geological Survey, written commun., 2007) range from about 12 to 

140 lb/mi2/yr (table 17), and were generally less than 

75 lb/mi2/yr (shown as green triangular symbols in fig. 17E). 

Boxplots of annual total phosphorus yields for the recent 

period show that median yields are less than or equal to about 

330 lb/mi2/yr for the 11 undeveloped drainage basins with 
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 91

annual load estimates for all years in the 1993–2003 period 

(fig. 18B, undeveloped basins shown in green; table 21). 

Median total phosphorus yields are less than 200 lb/mi2/yr for 

9 of the 11 undeveloped basins, and less than 100 lb/mi2/yr 

for 5 of the 11 basins. The five undeveloped drainage basins 

with median total phosphorus yields less than 100 lb/mi2/yr 

are Bunnell (Burlington) Brook and the Farmington River at 

Unionville in Connecticut, and the Pequannock, Batsto, and 

Delaware (at Montague) Rivers in New Jersey (figs. 17, 18B, 

table 21; stations 24, 25, 53, 75, 82). Undeveloped basins with 

medians greater than 100 lb/mi2/yr are generally larger drainage basins that receive at least some point source discharges. 

As in the case of total nitrogen, interquartile ranges for total 

phosphorus yields in the undeveloped drainage basins are generally narrow, relative to the more developed drainage basins, 

although this narrow range is less obvious on the logarithmic 

scale used for total phosphorus (fig. 18B) than on the linear 

scale used for total nitrogen (fig. 18A). 

Minimum total phosphorus yields for 16 undeveloped 

basins range from 1.4 to 160 lb/mi2/yr, with a median of 

38 lb/mi2/yr (table 22, fig. 17D). Maximum total phosphorus 

yields range from 67 to 860 lb/mi2/yr for 14 undeveloped 

basins, with a median of 230 lb/mi2/yr (table 22, fig. 17F). 

Undeveloped drainage basins with maximum total phosphorus 

yields that exceed about 200 lb/mi2/yr are generally drained by 

streams that receive point-source discharges (table 8, in back 

of report, and table 21). 

Total nitrogen and total phosphorus yields for drainage 

basins with 90 percent or more undeveloped land and no point 

sources provide an indication of nutrient yields under the least 

developed conditions in the study area, although this information is incomplete, in terms of both geographic distribution 

and years of record. The drainage basins that are least affected 

by human land-use and waste-disposal practices (although not 

totally unaffected) generally have median total nitrogen yields 

in the range of 300 to 1,700 lb/mi2/yr (fig. 17B) and median 

total phosphorus yields in the range of 30 to 100 lb/mi2/yr 

(fig. 17E). In the large drainage basins that receive pointsource discharges and have large percentages of undeveloped 

land, streamflow with low nutrient loads from relatively undeveloped headwater areas dilutes streamflow in the more urbanized downstream reaches, and dampens but does not eliminate 

the point-source “signal” of higher nutrient loads. 

Agricultural Drainage Basins

Drainage basins with substantial agricultural influences 

on water quality are concentrated primarily in the mid-Atlantic 

hydrologic region, that is, the central and southern parts of the 

study area, largely because of favorable climatic, geologic, and 

geomorphic conditions, although monitoring priorities also 

may play a part in the distribution of monitored basins. Agricultural and urban/agricultural drainage basins are common 

in the Delaware River Basin, the lower Susquehanna River 

Basin, coastal basins of Maryland, Delaware, and Virginia, 

and the Potomac River Basin (fig. 2, table 8, in back of report; 

fig. 18). 

The most extensive areas of agricultural land are in 

three ecoregions of the study area (figs. 2, 3): the Eastern 

Coastal Plain (ecoregion 14), in the Delmarva Peninsula and 

southern New Jersey; parts of the Southeastern Temperate 

Forested Plains and Hills (ecoregion 9), in areas extending 

from northeastern Virginia through central Maryland and 

southeastern Pennsylvania and into north-central New 

Jersey; and the Great Valley in the Central and Eastern 

Forested Uplands (ecoregion 11). The Great Valley, underlain 

by fractured carbonate bedrock in many areas, is a major 

physiographic feature in the study area, extending along the 

southeastern edge of the Central and Eastern Forested Uplands 

from the Shenandoah River valley in west-central Virginia 

through western Maryland and southeastern Pennsylvania 

and into northern New Jersey (visible as a distinct band of 

agricultural land that passes through Harrisburg, Pa., in fig. 2). 

Agricultural drainage basins have some of the highest 

total nitrogen yields in the region (table 22). Several 

agricultural and urban/agricultural basins in the study area 

have median total nitrogen yields that equal or exceed 

10,000 lb/mi2/yr (substantially more than the 75th percentile 

of about 6,400 lb/mi2/yr for all drainage basins evaluated), 

including Broad Brook in the Connecticut River Basin, Jordan 

Creek and the Schuylkill River in the Delaware River Basin, 

the Nanticoke River and Chesterville Branch in the Eastern 

Coastal Plain of Delaware and Maryland, East Mahantango 

Creek and Cedar Run in the lower Susquehanna River Basin, 

and Conococheague Creek in the Potomac River Basin 

(table 20; fig. 17B, stations 23, 86, 97, 100, 102, 106, 108, 

116; agricultural basins shown in blue, urban/agricultural 

basins in purple). Broad Brook is in an area known as 

the Central Valley (in central Connecticut and western 

Massachusetts), a former agricultural region that has become 

progressively more urbanized since the mid-20th century. 

Jordan Creek, parts of the Schuylkill River Basin, and Cedar 

Run in Pennsylvania, and Conococheague Creek in Maryland, 

are in the Great Valley. High median total nitrogen yields 

for these drainage basins, as well as high minimum yields 

(figs. 17A, B), indicate that high total nitrogen yields are 

common on an annual basis in these basins. Periods of record 

are short for some of these stations, however, and additional 

years of record would be necessary to identify yield ranges 

and typical conditions. 

Median total nitrogen yields for 24 agricultural basins 

range from 1,700 to 26,000 lb/mi2/yr (table 22), with a median 

for all 24 basins of 5,000 lb/mi2/yr. Median total phosphorus 

yields range from 94 to 1,000 lb/mi2/yr for the 24 agricultural basins evaluated, with a median yield of 280 lb/mi2

/yr 

(table 22). 

The maximum total nitrogen yield and maximum total 

phosphorus yield estimated for all stations in the region are 

both in small (less than 50 mi2) agricultural drainage basins 

that do not receive any major point-source discharges. The 

maximum total nitrogen yield, 32,000 lb/mi2/yr, was estimated 
92 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

for East Mahantango Creek, in the lower Susquehanna River 

Basin in Pennsylvania (about 55 percent agricultural land; 

table 8, in back of report, and table 20; fig. 17C, station 106). 

The maximum total phosphorus yield included in the summary 

statistics, 16,000 lb/mi2/yr, was estimated for the Neshanic 

River Basin, a subbasin of the Raritan River Basin in New 

Jersey (about 60 percent agricultural land; table 8, in back of 

report, and table 21; fig. 17F, station 61). 

Among the 46 stations with records for the full 1993–

2003 period, agricultural land is a major source of nutrients 

in two of the five basins with median total nitrogen yields 

exceeding 10,000 lb/mi2/yr. (The other three are small urban 

basins with major point-source discharges and high population densities, discussed in the section on Urbanized Drainage 

Basins). Among these 46 stations, the second highest total 

nitrogen yield, 22,000 lb/mi2/yr, and the largest range in total 

nitrogen yields, were estimated for an agricultural basin that 

also receives point-source discharges, Conococheague Creek 

in Maryland (about 57 percent agricultural land, table 8, in 

back of report) (fig. 18A, table 20; station 116). The maximum total phosphorus yield was estimated for the agricultural 

Neshanic River Basin in New Jersey (fig. 18B, table 21; station 61). Annual variability in nutrient yields can be large, as 

indicated by relatively large interquartile ranges and large total 

ranges in yield for several agricultural and urban/agricultural 

basins (fig. 18; agricultural basins shown in yellow, urban/

agricultural basins in orange). 

Nutrient yields in agricultural and urban/agricultural 

drainage basins generally increase with increasing percentages 

of developed land in a drainage basin, although there is a wide 

range in yields at most levels of development (fig. 17), and 

point-source effects in some basins complicate interpretations. 

Nutrient yields for the Raritan River Basin (804 mi2) and its 

agricultural and urban/agricultural subbasins (11.8 to 490 mi2) 

show a somewhat varied but steady increase with increasing 

percentages of developed land, particularly in the median 

and maximum yields of total nitrogen (figs. 17B, C; 

stations 59–61, 64–68). Five of these eight Raritan basins 

receive major point-source discharges; the Stony Brook 

Basin receives minor point-source discharges (fig. 17; station 66), and Mulhockaway Creek and the Neshanic River are 

nonpoint-source basins (fig. 17; stations 59, 61). The Potomac 

River Basin (11,570 mi2) and most of its agricultural subbasins 

(770 to 5,939 mi2), have large percentages of undeveloped 

land. Yields for these streams generally are between the 25th 

and 75th percentiles for all drainage basins, with no clear 

relation to increases in developed land (fig. 17; stations 117, 

119–122); all these streams receive major point-source discharges (table 8, in back of report). However, the median total 

nitrogen yield for the small Muddy Creek Basin (14.3 mi2, 

about 68 percent agricultural), located in the Great Valley in 

the headwaters of the Potomac River Basin, exceeds the 75th 

percentile for all stations, and the maximum total nitrogen 

yield in this basin of nonpoint sources is one of the highest in the study area (station 118, figs. 17B, C). Median and 

maximum yields for total nitrogen and total phosphorus in the 

Conococheague Creek Basin (about 57 percent agricultural), 

which receives major point-source discharges, exceed the 75th 

percentile for all drainage basins (figs. 17B, C, E, F; station 

116). The high total nitrogen yields estimated for the Muddy 

and Conococheague Creek basins support findings from the 

1992–96 NAWQA study in the Potomac River Basin (fig. 1), 

which concluded that elevated concentrations of nitrogen were 

common in streams and groundwater in the northeastern part 

of the drainage basin (ecoregion 9) and areas underlain by carbonate bedrock, such as the Great Valley (ecoregion 11, figs. 

2, 3) (Ator and others, 1998, p. 2, 8). 

The Susquehanna and the Potomac River Basins are the 

largest monitored drainage basins in the region with complete 

records for the 1993–2003 period (stations 111 and 122, 

figs. 17 and 18), and provide the largest freshwater inflows 

to the Chesapeake Bay. Although both drainage basins are 

more than 60 percent undeveloped, stream quality in both 

basins is affected by agricultural influences. A NAWQA study 

of the Lower Susquehanna River Basin concluded that the 

main source of nitrogen in the study unit is animal manure 

used as agricultural fertilizer (Lindsey and others, 1998, p. 2, 

9). Similarly, a NAWQA study of the Potomac River Basin 

concluded that commercial fertilizers and manure were major 

sources of nitrogen and phosphorus to the basin in 1990, and 

that tributary streams draining agricultural areas yielded the 

greatest quantities of nitrogen to the Potomac River (Ator 

and others, 1998, p. 2, 6–9). The Susquehanna and Potomac 

River Basins are classified as agricultural drainage basins in 

this report, with about 28 and 34 percent agricultural land, 

respectively, and less than 10 percent urbanized land 

(table 8, in back of report). Median total nitrogen yields 

for the Susquehanna (5,200 lb/mi2/yr) and Potomac 

(5,100 lb/mi2/yr) are close to the median (of all medians) 

for total nitrogen yields for all agricultural drainage basins 

(5,000 lb/mi2/yr) (tables 20, 22). The median total phosphorus 

yield for the Potomac (280 lb/mi2/yr) is similar to the median 

(of all medians) for all agricultural basins (tables 21, 22). The 

median for the Susquehanna, by contrast, is somewhat lower 

(190 lb/mi2/yr), possibly because phosphorus tends to bind 

to sediment particles that settle and are retained behind the 

Conowingo Dam (Belval and Sprague, 1999, p. 5). Maximum 

total nitrogen yields for the Susquehanna and Potomac, 

and maximum total phosphorus yields for the Potomac, 

are near the median (of the maximums) for all agricultural 

basins, whereas the maximum total phosphorus yield for the 

Susquehanna is substantially lower than the median (of the 

maximums) for all agricultural basins (tables 20, 21, 22). 

Although the northeastern United States is one of the 

most highly urbanized areas in the nation, agricultural land is a 

major source of nutrients. Nutrients derived from agricultural 

land contribute to some of the highest total nitrogen yields 

in the study area. High nutrient yields related to agricultural 

land are most common in smaller drainage basins of the midAtlantic hydrologic region. Overall, maximum total nitrogen 

yields show a pronounced increase when the agricultural land 

in a drainage basin exceeds 50 percent (fig. 17C; agricultural 
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 93

basins shown in blue; urban/agricultural basins in purple). 

Agricultural and urban/agricultural drainage basins dominate 

the highest maximum yields for total nitrogen (greater than the 

75th percentile for all stations), whereas urban drainage basins 

are more numerous among the highest yields for total phosphorus (figs. 17C, F). 

Land-use percentages and generalized land-use categories for this report are based on the 1992 National Land Cover 

Dataset. Agricultural land has been converted to residential 

developments and other forms of urbanized land in some parts 

of the study area during the 1993–2003 period for which nutrient yields have been analyzed. Consequently, annual nutrient 

yields are likely to have been affected by changing sources of 

nutrients in some drainage basins. 

Urbanized Drainage Basins

Drainage basins with substantial urban influences on 

water quality are concentrated in the Eastern Coastal Plain 

(ecoregion 14) in New England and southern New Jersey, 

and in parts of the Southeastern Temperate Forested Plains 

and Hills (ecoregion 9) in northern New Jersey, southeastern 

Pennsylvania, and central Maryland (figs. 2, 3; table 8, in back 

of report). Urbanized drainage basins encompass a wide range 

of total developed land, and a wide range in the predominant 

type of urban development. Consequently, nutrient yields vary 

over a wide range in drainage basins classified as urbanized in 

this report. Differences among urbanized drainage basins have 

not been evaluated quantitatively in this study, but qualitative observations of nutrient yields in urbanized drainage 

basins provide an indication of the conditions that have the 

greatest effect on these yields. Conditions affecting nutrient 

yields in urbanized drainage basins include the presence or 

absence of point sources, the size of the drainage basin relative to the magnitude of the point sources, population density, percentages of urbanized versus undeveloped land, and 

nonpoint source water-quality effects related to the intensity 

of the urbanized land development. Point sources have not 

been evaluated quantitatively for most drainage basins in the 

region, and the magnitude of point-source effluents relative to 

drainage basin size or measures of streamflow in the receiving 

water have not been evaluated. Consequently, the discussion 

of the effects of point sources is qualitative. As noted in the 

section on Agricultural Drainage Basins, some drainage basins 

are affected by both urban and agricultural nutrient sources, 

further complicating the evaluation of nutrient yields. 

Median total nitrogen yields range from 1,400 to 

17,000 lb/mi2/yr in 26 urbanized drainage basins, with a 

median (of all medians) of 4,000 lb/mi2/yr (table 22). Median 

total nitrogen yields in agricultural basins (5,000 lb/mi2/yr) 

and urban/agricultural basins (7,000 lb/mi2/yr) exceed median 

total nitrogen yields in urban basins (4,000 lb/mi2/yr) 

(table 22). Among the 46 stations with records for the full 

1993–2003 period, three of the five basins with median total 

nitrogen yields exceeding 10,000 lb/mi2/yr are small urban 

basins with major point-source discharges and high population 

densities: the Hockanum (station 28, 73.4 mi2, 1,331 people/

mi2) and Quinnipiac (station 32, 115 mi2, 1,396 people/mi2) 

River Basins in Connecticut, and the Saddle River Basin 

(station 56, 54.6 mi2, 2,624 people/mi2) in New Jersey 

(figs. 17B, urban basins shown in orange; fig. 18A, urban 

basins shown in red; table 8, in back of report). 

Median total phosphorus yields in 26 urbanized drainage 

basins range from 43 to 1,900 lb/mi2/yr, with a median of 

210 lb/mi2/yr (table 22). As in the case of total nitrogen, 

median total phosphorus yields (median of all medians) in 

agricultural basins (280 lb/mi2/yr) and urban/agricultural 

basins (430 lb/mi2/yr) exceed median total phosphorus 

yields of urban basins (210 lb/mi2/yr) (table 22). However, 

the highest median total phosphorus yield, 1,900 lb/mi2/yr, 

was estimated for an urban drainage basin, the Saddle River 

at Lodi, N.J. (figs. 17E, 18B, station 56; table 8, in back of 

report, about 89 percent urbanized land). Among stations with 

records for the full 1993–2003 period, five of the six basins 

with median total phosphorus yields equaling or exceeding 

1,000 lb/mi2/yr are small urban basins with major or minor 

point-source discharges: the Hockanum, Quinnipiac, and 

Naugatuck River Basins in Connecticut, and the Saddle and 

Cooper River Basins in New Jersey (figs. 17E, urban drainage 

basins shown in orange; 18B, urban basins in red; stations 28, 

32, 39, 56, 95). 

Total nitrogen yields are consistently high in several 

small drainage basins that have major urban influences on 

water quality in the form of large percentages of urbanized 

land, high population densities, or major point-source 

discharges. Minimum total nitrogen yields in eight urbanized 

drainage basins exceed or are about equal to the 75th 

percentile for all minimum yields (2,700 lb/mi2/yr) (fig. 17A). 

Total developed land exceeds 50 percent of the drainage basin 

in six of the eight basins, major point sources discharge to 

streams in five of the eight basins, and population densities 

exceed 1,000/mi2 in six of the eight basins. The drainage 

basins range in size from about 24 to 260 mi2, and five are 

less than 100 mi2. The Pawtuxet River in Rhode Island, the 

Hockanum, Quinnipiac, and Naugatuck Rivers in Connecticut, 

and the Saddle River in New Jersey all receive major pointsource discharges (table 8, in back of report; fig. 17A, stations 

10, 28, 32, 39, 56; urban basins shown in orange). In the three 

drainage basins where nonpoint sources determine water 

quality, population densities are high and the percentage of 

urbanized land is high: the Aberjona River in Massachusetts 

(station 7, 2,955/mi2, about 79 percent urbanized land), the 

Rahway River near Springfield, N.J. (station 57, 4,372/mi2, 

about 80 percent urbanized land), and Accotink Creek in 

Virginia (station 123, 4,170/mi2, about 85 percent urbanized 

land) (table 8, in back of report; fig. 17A). 

Total phosphorus yields are consistently high in many 

urbanized drainage basins, as indicated by high minimum 

yields (fig. 17D, urban basins shown in orange). Minimum 

total phosphorus yields exceeding 200 lb/mi2/yr were estimated for 13 stations during 1993–2003 (fig. 17D). Of these 

13 stations, all but 1 monitor streams that drain urban basins 
94 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

(9 stations) or urban/agricultural basins (3 stations). Twelve of 

the 13 drainage basins, including the agricultural Nanticoke 

River Basin in Delaware (fig. 17D, station 100), receive major 

or minor municipal point discharges. These 12 basins are 

typical of the older urbanized drainage basins of the northeast: 

the Pawtuxet River Basin in Rhode Island; the Farmington (at 

Tariffville), Hockanum, Quinnipiac, and Naugatuck Rivers 

in Connecticut; the Passaic, Saddle, Rahway (at Springfield), 

Millstone, Raritan, and Cooper River Basins in New Jersey; 

and the Schuylkill River Basin in Pennsylvania (fig. 17D, 

stations 10, 27, 28, 32, 39, 55, 56, 57, 67, 68, 95, 97). All 

but the Schuylkill Basin are less than 1,000 mi2 in area, and 

several are less than 100 mi2. Consequently, for most of these 

streams, wastewater discharges constitute a substantial part of 

the stream nutrient loads under most conditions, and minimum 

total phosphorus yields are high relative to other land-use categories. The maximum values for minimum and median total 

phosphorus yields are in urbanized drainage basins (table 22). 

Among these 12 drainage basins, the Millstone, Raritan, and 

Schuylkill are classified as urban/agricultural basins, and nutrient yields reflect agricultural and urban nutrient sources. 

Maximum total nitrogen yields for urbanized basins 

range from 2,000 to 22,000 lb/mi2/yr, with a median of 

4,800 lb/mi2/yr (table 22). Urbanized drainage basins with 

maximum total nitrogen yields near or less than the 

25th percentile for maximum yields for all stations (about 

3,700 lb/mi2/yr) include larger drainage basins with major 

point sources and a high percentage of undeveloped land, such 

as the Merrimack River in Massachusetts and the Shetucket, 

Quinebaug, and Farmington Rivers in Connecticut (fig. 17C, 

stations 6, 13, 16, 27; urban basins shown in orange; table 8, 

in back of report); small drainage basins with minor point 

sources and a large percentage of undeveloped land, such as 

Toms River in New Jersey (station 71); and small drainage 

basins with low-density development, no point sources, and a 

large percentage of undeveloped land, such as the Salmon and 

Saugatuck Rivers in Connecticut (stations 30, 40). However, 

three urbanized basins with large percentages of developed 

land, moderate to high population densities, and in one case, 

point sources, also have maximum total nitrogen yields at 

or less than the 25th percentile for all stations: the Norwalk 

River in Connecticut (about 47 percent undeveloped, with a 

major point source), Lisha Kill in New York (about 31 percent 

undeveloped), and the Hackensack River in New Jersey 

(about 33 percent undeveloped) (fig. 17C, stations 41, 46, 

50). Detailed land-use classifications show that low-intensity 

residential development and forested residential development 

dominate the urbanized land in these drainage basins, constituting 79 percent of the urbanized land in the Norwalk River 

Basin, 55 percent in the Lisha Kill Basin, and 78 percent in the 

Hackensack River Basin. These results indicate the complexities of factors affecting nutrient yields in urbanized drainage 

basins, including the type and intensity of development, 

and possibly the location and level of treatment of point 

source discharges. 

Maximum total nitrogen yields in six urbanized drainage 

basins exceed or are about equal to the 75th percentile for 

maximum yields for all stations (about 9,100 lb/mi2/yr; 

fig. 17C; urban basins shown in orange). Five of these 

drainage basins are small (about 100 mi2 or less), and all six 

are located in or encompass older highly urbanized areas 

of the region: the Aberjona River in Massachusetts; the 

Hockanum, Quinnipiac, and Naugatuck Rivers in Connecticut; 

the Saddle River in New Jersey; and Accotink Creek in 

Virginia (fig. 17C, stations 7, 28, 32, 39, 56, 123; urban basins 

shown in orange). The Hockanum, Quinnipiac, Naugatuck, 

and Saddle Rivers are all receiving waters for major pointsource discharges. The maximum total nitrogen yield among 

25 urbanized drainage basins, 22,000 lb/mi2/yr, was estimated 

for the Saddle River in New Jersey (tables 20, 22). The 

routinely high annual total nitrogen yields in these drainage 

basins (figs. 17A–C) illustrate the challenges of managing 

nutrients in the older urbanized drainage basins of the region. 

Maximum total phosphorus yields for urbanized basins 

encompass a wide range, from less than 100 to more than 

6,000 lb/mi2/yr (table 22). As in the case of total nitrogen, the 

lower maximum total phosphorus yields in urbanized basins 

(less than about 200 lb/mi2/yr) are generally in larger drainage basins with major point sources and a high percentage of 

undeveloped land, or in smaller drainage basins with minor or 

no point sources and a high percentage of undeveloped land 

(fig. 18B, urban basins shown in red; table 8, in back of report, 

and table 21). Maximum yields exceed 1,000 lb/mi2/yr in 

eight urban basins, including the Hockanum, Quinnipiac, and 

Naugatuck Rivers in Connecticut; the Saddle, Rahway (near 

Springfield and at Rahway), and Cooper Rivers in New Jersey; 

and Accotink Creek in Virginia (fig. 17F, stations 28, 32, 39, 

56, 57, 58, 95, 123; urban basins shown in orange). Although 

the monitored areas of the Rahway River, the Cooper River, 

and Accotink Creek do not receive major point-source discharges, the drainage areas have some of the highest population densities in the study area (table 8, in back of report). 

Nine of the 26 drainage basins classified as urban have 

median total nitrogen yields ranging from about 5,000 to 

17,000 lb/mi2/yr and maximum total nitrogen yields ranging 

from about 7,000 to 22,000 lb/mi2/yr (figs. 17B, C, table 20). 

The drainage areas for these nine basins are small, less than 

300 mi2; drainage areas for six of the nine basins are less 

than 100 mi2. Nine urban basins have median total phosphorus yields ranging from about 500 to 1,900 lb/mi2

/yr, 

and maximum yields ranging from about 700 to 

6,300 lb/mi2/yr (table 21, figs. 17E, F). Drainage areas for 

these nine basins are less than 800 mi2, and drainage areas 

for seven of the nine are 200 mi2 or less. Most of the urban 

drainage basins with these very high nutrient yields are 

drained by streams that are receiving waters for major pointsource discharges. 

Ten of the 26 drainage basins classified as urban have 

no major point-source discharges: the Aberjona River in 

Massachusetts (fig. 17, station 7); the Salmon and Saugatuck 

Rivers in Connecticut (stations 30, 40); Lisha Kill in New 
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 95

York (station 46); the Hackensack, Rahway (near Springfield, 

and at Rahway), Toms, and Cooper Rivers in New Jersey 

(stations 50, 57, 58, 71, 95); and Accotink Creek in Virginia 

(station 123) (table 8, in back of report). The drainage basins 

of Toms River and Cooper River receive minor point-source 

discharges. These 10 basins range in size from 15.6 to 123 mi2, 

and 7 of these basins are less than 50 mi2. Nutrient yields 

generally increase with increasing percentages of developed 

land in urbanized drainage basins where water quality is 

influenced primarily by nonpoint sources (fig. 17; urban 

basins shown in orange). This relation differs for total nitrogen 

and total phosphorus. Median and maximum total nitrogen 

yields for the Rahway and Cooper Rivers and Accotink 

Creek, which are among the most highly developed drainage 

basins evaluated, fall approximately between the median and 

75th percentile for all stations (figs. 17B, C; stations 57, 58, 

95, 123), whereas median total phosphorus yields for three 

of these drainage basins exceed the 75th percentile for all 

stations, and maximum total phosphorus yields for all four 

basins exceed the 75th percentile for all stations (figs. 17E, 

F). This relation indicates that high total phosphorus yields 

are likely in small, highly urbanized drainage basins. Nutrient 

yields for Lisha Kill (station 46) are generally low relative to 

the extent of development in the drainage basin (fig. 17). 

Total nitrogen yields for Toms River (figs. 17A, B, C; 

station 71) are somewhat high, relative to the large percentage 

of undeveloped land in the drainage basin; this relatively 

high yield may be caused by minor point-source discharges. 

Total nitrogen yields for the Aberjona River Basin are at or 

above the 75th percentile for all drainage basins, and are in a 

range similar to that of the other highly developed nonpoint 

urban basins (figs. 17A, B, C; station 7). By contrast, total 

phosphorus yields for the Aberjona are relatively low, between 

the 25th percentile and the median for all stations (figs. 17D, 

E, F). These nutrient yield variations among small urbanized 

basins indicate that identification of specific urban nonpoint 

sources and land-use conditions may be necessary to address 

nutrient management in urbanized drainage basins, particularly 

in the older urbanized areas of the northeastern United States. 

Nutrient yields for urbanized drainage basins demonstrate 

that streams draining highly urbanized areas of the region are 

major nutrient sources, delivering nutrient loads to the main 

stems of major rivers and in some cases directly to estuaries 

and coastal areas. Smaller urbanized drainage basins (less than 

about 300 mi2), including drainage basins with and without 

point sources, have some of the highest nutrient yields in the 

study area (fig. 17). 

Overall Effects of Urban and Agricultural 

Development

The extent of developed land in a drainage basin has 

a profound effect on the magnitude of nutrient yields. Most 

drainage basins with more than 30 percent developed land 

have maximum total nitrogen yields that equal or exceed 

5,000 lb/mi2/yr, and 14 of 31 basins with more than 50 percent 

developed land have maximum total nitrogen yields that equal 

or exceed 10,000 lb/mi2/yr (fig. 17C). Of these 14 drainage 

basins, 3 are classified as urban, 4 as urban/agricultural, and 

7 as agricultural. Most drainage basins with more than 

50 percent developed land (23 of 31 basins) have maximum 

total phosphorus yields that exceed 600 lb/mi2/yr, and in 18 

of these basins, maximum total phosphorus yields equal or 

exceed 1,000 lb/mi2/yr (fig. 17F). Of these 18 basins, 7 are 

classified as urban, 5 as urban/agricultural, and 6 as agricultural. Where more than about 50 percent of a drainage area is 

developed, in either agricultural or urban land or both, 

the potential for very high maximum yields is present 

(figs. 17C, F). 

Summary statistics for total nitrogen and total phosphorus 

yields for drainage basins in the northeastern United States 

indicate that urban and agricultural land use (more than 

20 to 30 percent of a drainage basin) has increased median 

total nitrogen yields by factors of three to five and has 

increased median total phosphorus yields by factors of three to 

six, relative to undeveloped drainage basins, although the yield 

ranges for both constituents are large for all land use categories (table 22, figs. 17B, E). Median yields increase as the percentage of developed land in a drainage basin increases, and 

the increase in yield is notable in the range of 20 to 40 percent 

developed land (figs. 17B, E). Major point-source discharges 

contribute to elevated nutrient yields throughout the study area 

(fig. 18, table 8, in back of report), in agricultural, urban/agricultural, and forested basins, as well as in urban basins. 

The type of development, the extent of developed land, 

and the intensity of urban or agricultural development varies in the region. Percentages of agricultural land are higher 

in the central and southern drainage basins of the region (the 

mid-Atlantic hydrologic region), and most developed drainage basins in these areas are classified as agricultural or 

urban/agricultural. Only one drainage basin south and west of 

southern New Jersey is classified as urban, among the basins 

evaluated in this study (Accotink Creek in Virginia, station 

123, table 8, in back of report). Consequently, conclusions and 

generalizations about the contributions of agricultural or urban 

land to nutrient yields may be applicable to subregions in the 

study area, but not applicable to the entire region. 

Large Drainage Basins that Integrate Numerous 

Land Uses and Nutrient Sources

Water quality in large drainage basins of the northeastern 

United States integrates the effects of numerous and varied 

land uses and nutrient sources. Nutrient yields in 21 of the 

22 large drainage basins evaluated (about 1,000 mi2 or larger; 

highlighted in gray, tables 20, 21) are affected by major pointsource discharges. Nutrient yields in large drainage basins 

with point sources are generally substantially lower than 

nutrient yields in smaller drainage basins with point sources. 

Ranges for nutrient yields in some large drainage basins with 
96 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

point sources are similar to ranges for yields in undeveloped 

basins with no point sources (fig. 18). For example, the 

Connecticut River in Connecticut, the Delaware River (at 

Montague) in New Jersey, and the James and Appomattox 

Rivers in Virginia (table 8, in back of report; numbers 22, 82, 

127, and 129), are all classified as undeveloped on the basis of 

land use percentages (less than 10 percent urban and less than 

20 percent agricultural). These drainage basins are about 76 to 

88 percent undeveloped, and all these streams receive major 

point-source discharges. Drainage basin size for these four 

rivers ranges from about 1,300 to almost 10,000 mi2. Median 

total nitrogen yields for these four rivers range from 1,200 

to 2,400 lb/mi2/yr, and 75 percent of the annual yields for 

these rivers are less than 3,000 lb/mi2/yr (fig. 18A, table 20). 

By contrast, total nitrogen yields for the Delaware River 

at Trenton (table 8, in back of report; fig. 18A; station 90), 

also classified as undeveloped, are substantially higher than 

for these four basins, possibly because of higher population 

density or the size and distribution of point sources. Median 

total phosphorus yields are less than 200 lb/mi2/yr for the 

Connecticut, Delaware (at Montague), and Appomattox 

Rivers, and more than 300 lb/mi2/yr for the Delaware (at 

Trenton) and James Rivers (table 21). 

The Susquehanna, Potomac, Connecticut, Delaware (at 

Trenton), and James Rivers are the five largest monitored 

drainage basins with complete records for the 1993–2003 

period (stations 111, 122, 22, 90, and 127, figs. 17 and 18). 

Total nitrogen and total phosphorus yields for these drainage 

basins generally fall in the interquartile range for all stations 

(fig. 17). Median total nitrogen yields for the Susquehanna, 

Potomac, and Delaware River Basins are more than two 

times the median yields for the Connecticut and James River 

Basins (fig. 17B, table 20). In the case of the Susquehanna and 

Potomac River Basins, this difference may be attributable to 

the much larger percentage of developed (agricultural) land. 

Median total phosphorus yields for the Potomac, Delaware, 

and James River Basins exceed median yields for the 

Susquehanna and Connecticut River Basins, but only by about 

50 percent (fig. 17E, table 21). Total phosphorus yields in the 

James River Basin are relatively higher than total nitrogen 

yields, compared to the other four basins, possibly because 

of natural phosphorus sources in the drainage basin (Belval 

and Sprague, 1999). The very low minimum total nitrogen 

yield for the James River Basin (fig. 17A) occurred during the 

drought conditions of 2002. 

Forested land constitutes 65 percent or more of the 

drainage area in 17 of the 22 large drainage basins evaluated 

for nutrient yields (table 8, in back of report). Cleaner streamflow from forested areas is a source of dilution for the more 

impaired waters downstream. The relation of upstream nutrient contributions to main stem rivers is complex, however, as 

described in the evaluation of headwater streams and transport processes (Alexander and others, 2007). Development 

in forested areas of large drainage basins may contribute to 

future increases in nutrient yields, both through the increases 

in nutrient sources and the changes in hydrologic processes in 

headwater streams. 

Effects of Variability in Streamflow Conditions

Annual nutrient yields vary considerably from year to 

year in response to changing hydrologic conditions, as shown 

in the previous discussion of nutrient loads. These effects are 

more pronounced in small drainage basins, and also may be 

related to basin land use. For the period analyzed, maximum 

total nitrogen yields in wet years, such as 1996 and 2003, are 

generally about two times larger than maximum yields in dry 

years, such as 1995 and 2002 (table 23). Maximum total phosphorus yields in wet years, such as 1994, 1996, and 2003, are 

generally two to four times larger than maximum yields in dry 

years, such as 1995 and 2002 (table 24). Differences between 

wet and dry years in individual drainage basins may be much 

greater. Maximum nutrient yields in any one year may be 

affected by one or more localized storms that do not affect the 

entire region. Regional variations in the same year also may 

be pronounced. 

None of the water years in the 1993–2003 period represents a truly median streamflow year (on the basis of annual 

mean streamflows) for the entire region (fig. 5). In particular, 

drainage basins in the southern part of the study area generally experienced annual precipitation and streamflows during 1993–2003 that were either substantially more than or 

substantially less than median conditions. Drought conditions 

prevailed in the southern part of the study area during much 

of the 1999–2002 period. Nutrient yields for water year 2000 

are presented as the year most closely representing median 

Table 23. Summary statistics for total nitrogen yields by water 

year, 1993–2003.

[Undeveloped stations from Clark and others (2000) not included in statistics. lb/mi2

/yr, pounds per square mile per year]

Water 

year

Number of 

stations

Total nitrogen yield 

(lb/mi2/yr)

Minimum Mean Median Maximum

1993 64 580 5,000 4,400 19,000

1994 66 590 5,600 4,800 19,000

1995 64 330 3,100 2,400 12,000

1996 59 1,300 6,500 5,700 21,000

1997 61 1,200 6,500 5,100 31,000

1998 61 960 6,200 4,800 32,000

1999 67 220 3,700 2,600 15,000

2000 69 550 4,900 3,700 20,000

2001 67 480 4,300 3,000 17,000

2002 61 41 2,300 1,700 12,000

2003 56 840 6,100 4,800 22,000
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 97

conditions in large parts of the region, particularly central and 

northern areas (figs. 19A, B). 

In water year 2000, a year with fairly typical hydrologic 

conditions, nutrient yields are high in all types of highly 

developed drainage basins: small urbanized drainage basins 

that receive point sources, small highly urbanized nonpoint 

source basins, agricultural basins with large percentages of 

agricultural land, and agricultural and urban/agricultural 

basins that receive point sources (figs. 19A, B). As in the 

case for minimum, median, and maximum nutrient yields 

(fig. 17), the range in yields in water year 2000 is large, with 

a more compact range for total nitrogen yields (fig. 19A) 

and greater scatter in total phosphorus yields (fig. 19B). The 

high total phosphorus yield for the agricultural Canajoharie 

Creek Basin in New York (fig. 19B; station 45) illustrates 

regional variability in conditions. The total phosphorus yield 

for Canajoharie Creek in 2000 is the maximum yield for that 

station for the 1994–2003 period; the median total phosphorus 

yield is 540 lb/mi2/yr (table 21). Annual mean streamflows in 

water year 2000 exceeded the 75th percentile in some drainage 

basins in this part of the study area (fig. 5D). 

Streamflows and nutrient yields in water year 2000 

varied considerably among the five largest drainage basins 

with records for the complete 1993–2003 period. Total 

nitrogen yields in 2000 generally follow a gradient from 

higher streamflow in the northern part of the study area to 

lower streamflow in the southern part of the study area 

(figs. 5C, F, I). The total nitrogen yield in 2000 for the 

Connecticut River Basin (fig. 19A, station 22; 2,500 lb/mi2/yr) 

was relatively high, about equal to the 75th percentile for that 

station. The yield for the Delaware River at Trenton in 2000 

(station 90; 4,300 lb/mi2/yr) was close to the station median 

(4,800 lb/mi2/yr, table 20), whereas the yield in 2000 for the 

Susquehanna River Basin (station 111; 3,900 lb/mi2/yr) was 

75 percent of the median for that station (5,200 lb/mi2/yr). The 

yield for the Potomac River Basin in 2000 (station 122; 

2,500 lb/mi2/yr) was about half of the median (5,100 lb/mi2/yr) 

and slightly greater than the 25th percentile (2,300 lb/mi2/yr) 

for that station. Similarly, the total nitrogen yield for the James 

River Basin in 2000 (station 127; 1,100 lb/mi2/yr) was less 

than two-thirds of the median (1,800 lb/mi2/yr) and slightly 

greater than the 25th percentile (890 lb/mi2/yr) for that station. 

Water years 2002, a very dry year throughout the region, 

and 2003, a very wet year in many parts of the region, represent extreme streamflow conditions for many drainage basins, 

with large differences in maximum yields for both total nitrogen and total phosphorus between the two years (figs. 19C, D). 

Differences in yield were less pronounced in the northern part 

of the study area, where the dry conditions of 2002 persisted 

into 2003 in some areas (figs. 5A, C). Regional hydrologic 

differences are the likely cause of regional differences in the 

extent of variation in yield between the two years, with more 

extreme streamflow conditions prevailing during both 2002 

and 2003 in the southern part of the study area. However, 

predominant land use also may be a factor in the regional differences. Agricultural basins, more prevalent in the southern 

part of the study area, have large differences in yield between 

the two years, presumably because nonpoint sources are the 

predominant nutrient sources in these basins, and yields are 

largely dependent on varying hydrologic conditions. In the 

northeastern part of the study area, by contrast, urbanized 

drainage basins are more prevalent, and nutrient yields generally have less year-to-year variability because point-source 

discharges in many of these basins contribute to relatively 

constant annual nutrient yields. 

Total nitrogen yields in 2003 generally exceeded yields in 

2002 by a factor of 2.0 or less in most drainage basins in New 

England and New York, including large drainage basins such 

as the Merrimack and Connecticut (fig. 19C, stations 6, 22), 

and small drainage basins with point sources, (stations 28, 32). 

Differences in yield between the two years were greater in the 

central and southern parts of the study area. The Pequannock 

River Basin in New Jersey (station 53) had the greatest difference in yields among the 56 stations with estimates for both 

years, with a 2003 total nitrogen yield that was 20 times the 

yield estimated for 2002. All stations in Virginia had an orderof-magnitude difference in total nitrogen yields between the 

two years (2003 yields ranging from 13 to 18 times the 2002 

yields), including the Rappahannock, Pamunkey, Mattaponi, 

James, and Appomattox River Basins (fig. 19C; stations 124, 

125, 126, 127, and 129). The large differences in yield for 

the Virginia drainage basins may be caused in large part by 

differences in hydrologic conditions between the two years 

(figs. 5H, I), and to the nonpoint nutrient contributions from 

agricultural land related to the hydrologic conditions in each 

year. Antecedent conditions also may be a factor in the large 

Table 24. Summary statistics for total phosphorus yields by 

water year, 1993–2003.

[Undeveloped stations from Clark and others (2000) not included in statistics. lb/mi2

/yr, pounds per square mile per year]

Water 

year

Number of 

stations

Total phosphorus yield 

(lb/mi2/yr)

Minimum Mean Median Maximum

1993 63 48 390 320 1,300

1994 65 60 520 330 4,500

1995 63 22 210 110 1,100

1996 59 32 2,400 440 110,000

1997 61 29 580 300 4,500

1998 61 23 470 330 2,300

1999 67 8.5 660 140 16,000

2000 69 16 340 200 2,600

2001 67 19 340 200 2,200

2002 61 1.4 180 99 1,700

2003 56 32 550 420 2,400
98 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

1,000

100

10,000

Total nitrogen yield, in pounds per square mile per year

A. Total nitrogen yields, water year 2000

25th percentile

2000 median

75th percentile

40,000

Total developed land, as percentage of drainage basin

10

100

1,000

Total phosphorus yield, in pounds per square mile per year

B. Total phosphorus yields, water year 2000

2000 median

25th percentile

75th percentile

56

95

102

45

98

57

58

7

92

118

32

39

55 97

67

68

47 10

113

116

100

114

61

86

50

112

106

41 70

101

8

119

64

96

85 111

59

78

30

40

71

75

53

107

5

82

80

14

13 16 37

18

6 90

54

3,000

56

86 102

106

7 45

67 116

23

97

28

32

100

57 123

118 95 58

98 61 92 112

113

50 114

78 101

68 8

41

64

70 119

124

122 120

85

111 96

55

39

47

59 37

16

71

18 6

27

54

90

126

129

125

40

24

30

127 75

5

53

13 14

25

80

82

22 107

10

123

28

23

120

25

22

27

124

122

24

126

129

125

127

0 10 20 30 40 50 60 70 80 90 100

0 10 20 30 40 50 60 70 80 90 100

23

Agricultural basin

Urban/agricultural basin

Undeveloped basin

Urban basin 

Station sequence number

EXPLANATION

Figure 19. Annual nutrient yields in selected water years, including 2000 (median flow year), 2002 (dry year), and 2003 (wet 

year), as a function of the percentage of developed land in a drainage basin. (A) Total nitrogen yields for 69 stations, water year 

2000, (B) total phosphorus yields for 69 stations, water year 2000, (C) total nitrogen yields for 56 stations, water years 2002 and 

2003, and (D) total phosphorus yields for 56 stations, water years 2002 and 2003.
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 99

61

53

53

125

125

127

127

124

124

122

122

111

111

129

129

126

39

39

28

28

32

32 56

56

22

22 6

6

27

70

70

61

61

85

85

96

96 101

101

116

116

90

90

75

5

25

82

25

82

75 5 18

14 13 37

30 24

40

54

59 16 24

40

47

7

57 58

58

95

7

57

95

98

98

92

50

46

92

50

46

45

45

114

114

67

67

41

41

68

78

97 78

23

23

97

64

64

55

55

47

59

27 18

37

71

71

16

54

30 13

126

14

68

61

127

127

22

22

124

124

101

75

75

53

53

125

125

126

126

129

129

96

96

56

56

28

28

32

32

39

39

64

64

6

6

97

97

122

122

111

111

57

57

85

85

92

92

98

98

70

70

114

114

116

116

90

90

25

25

82

5

5

14

30 24

40

71 37

59

13 24

40 16 30

37 18

47 59 16

71

55

18

78

78 41

46 7

7

58 46

50

50

23

41

68 45

95 58

95

45

67

68

23

55

47 54

27

27

14

82

13

54

101

67

2002

Agricultural basin

Urban/agricultural basin

Undeveloped basin

Urban basin

90 Station sequence number

2003

Agricultural basin

Urban/agricultural basin

Undeveloped basin

Urban basin

90 Station sequence number

EXPLANATION

10

100

1,000

10,000

Total nitrogen yield, in pounds per square mile per year

C. Total nitrogen yields in 2002 and 2003

2002 median

2003 median

30,000

Total developed land, as percentage of drainage basin

1

10

100

1,000

Total phosphorus yield, in pounds per square mile per year

D. Total phosphorus yields in 2002 and 2003

2002 median

2003 median

3,000

0 10 20 30 40 50 60 70 80 90 100

0 10 20 30 40 50 60 70 80 90 100

Figure 19. Annual nutrient yields in selected water years, including 2000 (median flow year), 2002 (dry year), and 2003 (wet 

year), as a function of the percentage of developed land in a drainage basin. (A) Total nitrogen yields for 69 stations, water year 

2000, (B) total phosphorus yields for 69 stations, water year 2000, (C) total nitrogen yields for 56 stations, water years 2002 and 

2003, and (D) total phosphorus yields for 56 stations, water years 2002 and 2003.—Continued
100 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

differences between the two years. Wet conditions and high 

streamflow during 2003 may have removed and transported 

nutrients delivered to drainage basins in 2002, nutrients which 

might have been transported out of the basins if normal hydrologic conditions had prevailed during 2002, but which were 

retained in the basins because of extremely dry conditions. 

Differences in total phosphorus yields between 2002 

and 2003 followed a similar regional pattern to that of total 

nitrogen, with even greater differences observed for total 

phosphorus in some parts of the study area. The maximum 

differences in total phosphorus yields between the two years 

were observed in the Rappahannock River Basin in Virginia 

(fig. 19D, station 124; 2003 yield 54 times greater than the 

2002 yield), the Pequannock River Basin in New Jersey 

(station 53; 2003:2002 ratio of 23), the Appomattox River 

Basin in Virginia (station 129; ratio of 22), the Choptank 

River Basin in Maryland (station 101; ratio of 15.5), and the 

Pamunkey River in Virginia (station 125; ratio of 14.9). In 

general, differences in total phosphorus yields between the 

two years were greatest in drainage basins from New Jersey to 

Virginia, particularly in small agricultural drainage basins and 

in some larger drainage basins with agricultural influences in 

Maryland and Virginia. Ratios of total phosphorus yields for 

the five largest drainage basins varied widely along a general 

north–south gradient in the study area: the Connecticut River 

Basin (fig. 19D, station 22; ratio of 1.3), the Delaware River 

Basin (station 90; ratio of 3.2), the Susquehanna River Basin 

(station 111; ratio of 2.5), the Potomac River Basin (station 

122; ratio of 12), and the James River Basin (station 127; 

ratio of 14). 

Evaluation of nutrient yields in high, low, and “typical” 

streamflow years indicates that substantial annual variations in 

nutrient yields are the norm in the study area, particularly in 

smaller drainage basins and drainage basins in which nonpoint 

sources of nutrients predominate. This large interannual variability has implications for management of nutrients to restore 

receiving waters, in both freshwater reaches and estuarine 

areas. Management strategies targeted to address average 

nutrient yield conditions may not be adequate to address more 

extreme, but nevertheless moderately frequent, conditions. 

A maximum total phosphorus yield of more than 

100,000 lb/mi2/yr is shown for water year 1996 (table 24), 

a wet year. This estimate is included as an example of 

conditions in small agricultural basins and also as an example 

of uncertainties in load estimation beyond the range of known 

hydrologic and water-quality conditions. This maximum yield 

is based on the annual load estimated for 1996 for Muddy 

Creek at Mount Clinton, Va., a drainage basin of about 14 

mi2 with about 68 percent agricultural land (table 8, in back 

of report, station 118; table 21). Annual loads were estimated 

for the period 1994–2001; however, no water-quality data 

were collected during 1996, which included several peak 

streamflows for the period. The highest daily mean streamflow 

value paired with water-quality data during 1994–2001 

is 92 cubic feet per second (ft3/s), and most daily mean 

streamflow values are less than 100 ft3/s. Water year 1996 

included the five highest daily mean stream discharge values 

in the 1994–2001 period, ranging from 290 to 1,760 ft3/s. 

Consequently, the load estimate for 1996 is based on extreme 

streamflows that are well beyond the range of the known 

concentration-discharge relation. The 1996 yield estimate 

for Muddy Creek is not included in the graph of maximum 

total phosphorus yields (fig. 17F) or the summary statistics 

for total phosphorus yields (table 22) because of the high 

degree of uncertainty associated with the estimate, and also 

because the range of yields for all stations is illustrated more 

clearly without the distortion introduced by this extreme 

outlier. Additional monitoring of high streamflows would be 

necessary to determine how high maximum total phosphorus 

yields might be in this and other small agricultural 

drainage basins. 

Point-Source Discharges

Numerous regional improvements in municipal 

wastewater treatment took place during the time period 

covered by this study, including upgrades of primary treatment 

facilities to secondary treatment after passage of the Clean 

Water Act in 1972, and implementation of subsequent 

regulations. Some secondary treatment processes are designed 

to remove biodegradable organic material and material that 

contains organic nitrogen prior to discharge, by converting 

ammonia nitrogen to nitrate in a process called nitrification 

(U.S. Environmental Protection Agency, 2004, p. 12). During 

the same period, implementation of phosphate detergent 

bans reduced the discharge of phosphorus in treatment plant 

effluent (Litke, 1999). Implementation of phosphate detergent 

bans in the northeastern United States took place during a 

period ranging from 1972 to 1995 (Litke, 1999, p. 6, table 1). 

Nationally, the detergent industry phased out the use of 

phosphorus in domestic laundry detergent by about 1994. 

Detergent bans, however, typically limited phosphorus only in 

household laundry detergent during the time period covered 

by this study; phosphate was still allowed in dishwashing 

detergents and commercial cleaning products (Litke, 1999, 

p. 5–6). Implementation of secondary treatment, and in 

some cases tertiary treatment, has also reduced phosphorus 

concentrations in the effluent from wastewater-treatment 

plants during the period of this study (Litke, 1999, p. 8–9). 

Four drainage basins were evaluated for nutrient 

loads from point source discharges: the Quinebaug River 

Basin in Connecticut, Massachusetts, and Rhode Island; 

the Raritan River Basin in New Jersey; the Patuxent River 

Basin in Maryland; and the James River Basin (including the 

Appomattox River Basin) in Virginia (table 25, fig. 20). In 

these four drainage basins, trends in flow-adjusted nutrient 

concentrations were analyzed for 14 stations during the recent 

period and 6 stations during the long-term period (table 26). 

Trends in nutrient loads were analyzed and annual loads of 

nutrients were estimated for nine stations during the recent 

period and six stations during the long-term period (table 27). 
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 101

Table 25. Summary of point source information and basin characteristics in drainage basins selected for analysis.[Source for land-use data: 1992 National Land Cover Dataset (NLCDe 92) (Vogelmann and others, 1998; enhanced as described by Nakagaki and Wolock, 2005); mi2, square miles; CTDEP, Connecticut Department of Environmental Protection; NJDEP, New Jersey Department of Environmental Protection; CBP, Chesapeake Bay Program; Incomplete, data not available for point sources in Massachusetts]

Station 

sequence 

number 

(table 5, 

fig. 4)

Drainage 

basin

Monitored 

drainage 

area 

(mi2)

States

Source 

for point 

source 

data

Time periods for point 

source data

Nitrogen point 

sources in 

monitored 

drainage area

Phosphorus 

point sources 

in monitored 

drainage area

Land-use percentages in drainage basin 

(table 8)

Total 

nitrogen

Total 

phosphorus Major Minor Major Minor Urban Agricul- tural For- ested

Total 

undeveloped 

land

Population 

per square 

mile in 

2000 

18 Quinebaug 713 Rhode Island, 

Massachusetts, Connecticut

CTDEP 2002–2004 1990–1998* Incomplete Incom- plete 8 3 9.2 11.4 73.5 78.9 264

68 Raritan 804 New Jersey NJDEP 1991–1997 1991–1997 10 54 10 27 17.5 34.2 46.6 48.3 653

114 Patuxent 348 Maryland CBP 1990–2003 1990–2003 7 7 7 7 19.1 37.5 38.9 40.5 1,023

127 James 6,252 Virginia CBP 1990–2003 1990–2003 10 0 10 0 3.5 15.0 79.6 80.4 65129 Appomattox 1,342 Virginia CBP 1990–1999 1990–2003 1 1 1 1 1.9 19.9 74.4 75.7 49

*No phosphorus data for Quinebaug River at Jewett City, Conn.
102 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

MAINE

VIRGINIA

DELAWARE

MARYLAND

NEW

YORK

PENNSYLVANIA

MASSACHUSETTS

CONNECTICUT RHODE

ISLAND

VERMONT

NEW

HAMPSHIRE

NEW

JERSEY

WEST

VIRGINIA

Schuylkill R.

Hudson River

Penobscot River

Kennebec River

James River

Shenandoah River

Potomac River

West Branch

Susquehanna River

Susquehanna River

Schuylkill R.

De al ware River

Hudson River

Mohawk River

Connecticut River

Merrimack River

Saint John River

Lake

Champlain

Chesapeake Bay

Providence

Philadelphia

Delmarva

Peninsula

Cape Cod

Long Island

CANADA

Augusta

Montpelier

Albany

Boston

Concord

Richmond

Harrisburg

Trenton

Dover

Annapolis

Hartford Providence

Washington, 

D.C.

Baltimore

Philadelphia

Newark

New York

City

Quinebaug River Basin

James and Appomattox 

River Basins 

Patuxent River Basin

Raritan River Basin

Narragansett

Bay

Cape

Cod

Bay

Buzzards Bay

Delaware

Bay ATLANTIC OCEAN

Long Island Sound

48°

36°

82° 66°

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

Albers Equal-Area Projection

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

EXPLANATION

Quinebaug River Basin

Raritan River Basin

Patuxent River Basin

James and Appomattox River Basins

Study area boundary

Washington, D.C.

State capital

City, over 250,000 population

Figure 20. Drainage basins selected for analysis of point sources in relation to nutrient concentrations, loads, and yields.
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 103

Initial 

water quality date, 

1975–2003

Water-quality constituent

Flow-adjusted 

concentration trend

Water 

years 

1975–2003

Water 

years 

1993–2003

Quinebaug River Basin

Quinebaug River at Quinebaug, Conn. (station 14) (155 mi2)

10/26/1981 Total nitrogen *Down *Up

2/10/1993 Ammonia nitrogen -- Down

10/26/1981 Total Kjeldahl nitrogen *Down --

10/26/1981 Nitrite-plus-nitrate nitrogen N N

10/26/1981 Total phosphorus *Down N

French River at North Grosvenordale, Conn. (station 15) (101 mi2)

2/10/1993 Ammonia nitrogen -- N

10/20/1992 Nitrite-plus-nitrate nitrogen -- N

10/20/1992 Total phosphorus -- N

Quinebaug River at Cotton Bridge Road near Pomfret, Conn. 

(station 17) (342 mi2)

3/8/1995 Total nitrogen -- N

3/8/1995 Ammonia nitrogen -- N

3/8/1995 Nitrite-plus-nitrate nitrogen -- N

3/8/1995 Total phosphorus -- *Up

Quinebaug River at Jewett City, Conn. (station 18) (713 mi2)

10/22/1974 Total nitrogen *Down N

10/22/1974 Ammonia nitrogen Down N

10/22/1974 Total Kjeldahl nitrogen *Down --

10/22/1974 Nitrite-plus-nitrate nitrogen N N

10/22/1974 Total phosphorus *Down *Up

Raritan River Basin

Mulhockaway Creek at Van Syckel, N.J. (station 59) (11.8 mi2)

11/5/1992 Total nitrogen -- N

11/5/1992 Nitrite-plus-nitrate nitrogen -- N

Neshanic River at Reaville, N.J. (station 61) (25.7 mi2)

11/5/1992 Total nitrogen -- N

11/5/1992 Ammonia nitrogen -- N

11/5/1992 Nitrite-plus-nitrate nitrogen -- N

11/5/1992 Total phosphorus -- N

Lamington River at Burnt Mills, N.J. (station 63) (100 mi2)

11/18/1992 Ammonia nitrogen -- Down

11/18/1992 Nitrite-plus-nitrate nitrogen -- N

11/18/1992 Total phosphorus -- N

Millstone River at Blackwells Mills, N.J. (station 67) (258 mi2)

11/19/1992 Total nitrogen -- N

11/19/1992 Ammonia nitrogen -- Up

2/17/1993 Nitrite-plus-nitrate nitrogen -- N

2/17/1993 Total phosphorus -- N

Initial 

water quality date, 

1975–2003

Water-quality constituent

Flow-adjusted 

concentration trend

Water 

years 

1975–2003

Water 

years 

1993–2003

Raritan River Basin—Continued

Raritan River at Queens Bridge at Bound Brook, N.J. 

(station 68) (804 mi2)

11/23/1981 Total nitrogen N N

11/23/1981 Ammonia nitrogen *Down N

11/23/1981 Total Kjeldahl nitrogen *Down --

11/23/1981 Nitrite-plus-nitrate nitrogen *Up N

11/23/1981 Total phosphorus N N

11/23/1981 Suspended sediment *Down N

Manalapan Brook at Federal Road near Manalapan, N.J. 

(station 69) (20.9 mi2)

11/10/1992 Total nitrogen -- N

11/10/1992 Ammonia nitrogen -- Up

11/10/1992 Nitrite-plus-nitrate nitrogen -- N

11/10/1992 Total phosphorus -- N

Patuxent River Basin

Patuxent River near Unity, Md. (station 112) (34.8 mi2)

10/5/1992 Total nitrogen -- N

10/6/1992 Ammonia nitrogen -- N

10/5/1992 Nitrite-plus-nitrate nitrogen -- N

10/5/1992 Total phosphorus -- N

Patuxent River near Bowie, Md. (station 114) (348 mi2)

10/10/1978 Total nitrogen *Down N

10/17/1979 Ammonia nitrogen *Down *Down

10/10/1978 Total Kjeldahl nitrogen *Down --

10/10/1978 Nitrite-plus-nitrate nitrogen *Down Down

10/10/1978 Total phosphorus *Down *Up

10/10/1978 Suspended sediment *Down N

James River Basin

James River at Cartersville, Va. (station 127) (6,252 mi2)

10/7/1974 Total nitrogen *Down *Up

8/21/1979 Ammonia nitrogen *Down *Down

10/1/1974 Nitrite-plus-nitrate nitrogen *Down N

10/7/1974 Total phosphorus N N

Appomattox River at Matoaca, Va. (station 129) (1,342 mi2)

10/11/1978 Total nitrogen N *Up

10/10/1979 Ammonia nitrogen *Down *Down

10/11/1978 Nitrite-plus-nitrate nitrogen Down Down

10/11/1978 Total phosphorus Up N

Table 26. Summary of trends in flow-adjusted nutrient concentrations in drainage basins selected for analysis of point sources.

[Station sequence numbers shown in table 5. Significant trend: p-value less than or equal to 0.05; highly significant trend: p-value less than or equal to 0.01. 

mi2, square miles; *, highly significant trend; N, no significant trend; --, data not available or not analyzed]
104 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Table 27. Summary of trends in nutrient loads in drainage basins selected for analysis of point sources.

[Significant trend: p-value less than or equal to 0.05; highly significant trend: p-value less than or equal to 0.01. N, no significant trend; *, highly significant 

trend; --, data not available or not analyzed]

Station 

sequence 

number

(table 5)

Station name Water-quality constituent

Initial 

waterquality date, 

1975–2003

Trend 

in load, 

water years 

1975–2003

Trend 

in load, 

water years 

1993–2003

Quinebaug River Basin, Conn.

14 Quinebaug River at Quinebaug, Conn. Total nitrogen 10/26/1981 *Down N

14 Quinebaug River at Quinebaug, Conn. Ammonia nitrogen 2/10/1993 -- *Down

14 Quinebaug River at Quinebaug, Conn. Total Kjeldahl nitrogen 10/26/1981 *Down --

14 Quinebaug River at Quinebaug, Conn. Nitrite-plus-nitrate nitrogen 10/26/1981 N N

14 Quinebaug River at Quinebaug, Conn. Total phosphorus 10/26/1981 *Down N

18 Quinebaug River at Jewett City, Conn. Total nitrogen 10/22/1974 *Down N

18 Quinebaug River at Jewett City, Conn. Ammonia nitrogen 10/22/1974 *Down N

18 Quinebaug River at Jewett City, Conn. Total Kjeldahl nitrogen 10/22/1974 *Down --

18 Quinebaug River at Jewett City, Conn. Nitrite-plus-nitrate nitrogen 10/22/1974 N N

18 Quinebaug River at Jewett City, Conn. Total phosphorus 10/22/1974 *Down N

Raritan River Basin, N.J.

59 Mulhockaway Creek at Van Syckel, N.J. Total nitrogen 11/5/1992 -- N

59 Mulhockaway Creek at Van Syckel, N.J. Nitrite-plus-nitrate nitrogen 11/5/1992 -- N

59 Mulhockaway Creek at Van Syckel, N.J. Total phosphorus 11/5/1992 -- N

61 Neshanic River at Reaville, N.J. Total nitrogen 11/5/1992 -- N

61 Neshanic River at Reaville, N.J. Ammonia nitrogen 11/5/1992 -- N

61 Neshanic River at Reaville, N.J. Nitrite-plus-nitrate nitrogen 11/5/1992 -- N

61 Neshanic River at Reaville, N.J. Total phosphorus 11/5/1992 -- N

67 Millstone River at Blackwells Mills, N.J. Total nitrogen 11/19/1992 -- N

67 Millstone River at Blackwells Mills, N.J. Ammonia nitrogen 11/19/1992 -- N

67 Millstone River at Blackwells Mills, N.J. Nitrite-plus-nitrate nitrogen 2/17/1993 -- N

67 Millstone River at Blackwells Mills, N.J. Total phosphorus 2/17/1993 -- N

68 Raritan River at Queens Bridge at Bound Brook, N.J. Total nitrogen 11/23/1981 N N

68 Raritan River at Queens Bridge at Bound Brook, N.J. Ammonia nitrogen 11/23/1981 *Down N

68 Raritan River at Queens Bridge at Bound Brook, N.J. Total Kjeldahl nitrogen 11/23/1981 *Down --

68 Raritan River at Queens Bridge at Bound Brook, N.J. Nitrite-plus-nitrate nitrogen 11/23/1981 N N

68 Raritan River at Queens Bridge at Bound Brook, N.J. Total phosphorus 11/23/1981 N N

68 Raritan River at Queens Bridge at Bound Brook, N.J. Suspended sediment 11/23/1981 Down N

Patuxent River Basin, Md.

114 Patuxent River near Bowie, Md. Total nitrogen 10/10/1978 *Down N

114 Patuxent River near Bowie, Md. Ammonia nitrogen 10/17/1979 *Down Down

114 Patuxent River near Bowie, Md. Total Kjeldahl nitrogen 10/10/1978 *Down --

114 Patuxent River near Bowie, Md. Nitrite-plus-nitrate nitrogen 10/10/1978 *Down N

114 Patuxent River near Bowie, Md. Total phosphorus 10/10/1978 *Down N

114 Patuxent River near Bowie, Md. Suspended sediment 10/10/1978 N N

James River Basin, Va.

127 James River at Cartersville, Va. Total nitrogen 10/7/1974 Down N

127 James River at Cartersville, Va. Ammonia nitrogen 8/21/1979 *Down Down

127 James River at Cartersville, Va. Nitrite-plus-nitrate nitrogen 10/1/1974 *Down N

127 James River at Cartersville, Va. Total phosphorus 10/7/1974 N N

129 Appomattox River at Matoaca, Va. Total nitrogen 10/11/1978 N N

129 Appomattox River at Matoaca, Va. Ammonia nitrogen 10/10/1979 *Down N

129 Appomattox River at Matoaca, Va. Nitrite-plus-nitrate nitrogen 10/11/1978 Down N

129 Appomattox River at Matoaca, Va. Total phosphorus 10/11/1978 N N
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 105

During the long-term period, numerous downward trends 

in nutrient loads were detected (table 27). Long-term downward trends in total nitrogen loads were detected at four stations, with no significant trend at two stations. Highly significant long-term downward trends in ammonia nitrogen loads 

were detected at the five stations analyzed for this constituent. 

Highly significant downward trends in loads of total Kjeldahl 

nitrogen were detected at the four stations with long-term data 

for this constituent. Long-term downward trends in nitriteplus-nitrate nitrogen were detected at three stations, and three 

stations had no significant trend. Highly significant long-term 

downward trends in total phosphorus loads were detected at 

three stations, and three stations had no significant trend. The 

only significant trends in nutrient loads detected during the 

recent period were downward trends in dissolved ammonia at 

three stations. 

No consistent pattern was found in terms of trends in 

load among different forms of nitrogen, in streams that receive 

point-source discharges. The long-term effects of wastewatertreatment improvements have varied in different drainage 

basins, including the small number of basins evaluated for the 

effects of point sources. 

The prevalence of long-term downward trends in nutrient 

loads in the drainage basins evaluated for point-source influences indicates substantial improvements in nutrient-related 

water-quality conditions. The finding of long-term downward 

trends in ammonia or total Kjeldahl nitrogen loads is consistent with wastewater-treatment processes that have reduced 

aquatic toxicity problems by converting ammonia to nitrate 

prior to discharge, and by removing organic material from 

wastewater. Long-term downward trends in total phosphorus 

loads in some drainage basins are consistent with implementation of phosphate detergent bans (Litke, 1999, p. 6, table 1). 

The absence of trends in load for most nutrients during the 

recent period (table 27), coupled with modeled instream concentrations for the early 1990s that exceed proposed nutrient 

criteria in many streams that receive wastewater effluent 

(table 15, in back of report), indicates that additional challenges remain in reducing the delivery of nutrients to streams 

from point sources. 

Long-term downward trends in flow-adjusted concentrations of most nutrients (table 26) indicate reductions in the 

delivery of nutrients to streams, in the absence of trends in 

streamflow. Comparison of long-term and recent trends in 

flow-adjusted nutrient concentrations and trends in nutrient 

loads indicates that in the basins evaluated, the major reductions in delivery of nutrients to streams, whether from point 

sources or other sources, may have taken place prior to the 

1993–2003 period of analysis. The reduction in delivery of 

nutrients is consistent with the history of improvements in 

wastewater-treatment facilities in the region, although this 

relation has not been documented quantitatively or in historical detail. Trends in nutrient loads, for most stations, coupled 

with similar trends in flow-adjusted concentrations of nutrients, appear to indicate changes in the delivery of nutrients to 

streams, with long-term reductions in nutrients detected for 

most nutrients evaluated. During the recent period, however, 

upward trends in flow-adjusted concentrations of some nutrients at a few locations indicate processes or changes that have 

increased nutrient delivery to some streams since 1993 

(table 26). 

Quinebaug River Basin in Connecticut, 

Massachusetts, and Rhode Island

The Quinebaug River Basin is in eastern Connecticut 

and adjoining areas of Massachusetts and Rhode Island, a 

relatively undeveloped area of the Boston-to-Washington 

urban corridor (fig. 21). Annual stream nutrient loads were 

estimated, trends in nutrient loads were evaluated, and pointsource loads of total phosphorus were estimated for two 

monitoring stations in the Quinebaug River Basin, both in 

Connecticut: the Quinebaug River at Quinebaug (155 mi2), 

near the state line with Massachusetts, and the Quinebaug 

River at Jewett City (713 mi2), near the mouth of the river 

(fig. 21; stations 14, 18). The Quinebaug River Basin at the 

Jewett City monitoring station is largely forested, with about 

9 percent urbanized land, about 11 percent agricultural land, 

and about 79 percent undeveloped land (table 8, in back of 

report). Comparisons between point-source loads and stream 

loads of total nitrogen could not be made because nitrogen 

data were unavailable for point sources in Massachusetts that 

discharge to the Quinebaug River Basin. Nitrogen pointsource data for the Quinebaug River Basin are limited to data 

from the State of Connecticut (table 25). 

Highly significant long-term downward trends in stream 

loads of total nitrogen and total Kjeldahl nitrogen were 

detected for the Quinebaug River at Quinebaug (fig. 22A, 

table 27). No trends in loads of nitrite-plus-nitrate nitrogen 

were detected for either the long-term (1982–2003) or recent 

period (fig. 22A). A highly significant downward trend in 

ammonia nitrogen load was detected for the recent period; 

data for ammonia nitrogen were not available for the longterm period (fig. 22A). 

The drainage area of the Quinebaug River at Quinebaug 

(table 8, in back of report, station 14) includes three major 

point-source discharges in Massachusetts with phosphorus 

loads identified in the PCS database. Comparison of total 

phosphorus point-source loads with estimated annual stream 

loads for the Quinebaug River at Quinebaug (fig. 22B) shows 

that the total point-source load was substantially less than the 

total stream load for all years from 1993 to 1999, with pointsource loads generally representing 9 to 34 percent of the 

stream load. A substantial decrease in phosphorus point-source 

loads appears to have taken place between 1990 and 1993, 

and this decrease is reflected in a decrease in estimated stream 

loads during the mid- to late-1990s. In 1999, a dry year, the 

total point-source load of phosphorus represented 53 percent 

of the estimated stream phosphorus load. Point-source loads 

of total phosphorus as a percentage of stream phosphorus 

loads have decreased during the mid- to late-1990s. Stream 
106 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Quinebaug River

French River

Quinebaug

River

Shetucket River

Thames River

72°15' 71°15'

42°15'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS

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

Albers Equal-Area Projection

North American Datum of 1983

Fishers Island, NY

Narragansett Bay

Long Island Sound

9

10

12

23

28

13

14

15

16

17

18

30 Connecticut

River

Providence

EXPLANATION

Quinebaug River Basin

USGS water-quality monitoring station,

 with station sequence number (table 5)

Point sources that discharge nutrients

State capital

17

11

RHODE ISLAND RHODE ISLAND

CONNECTICUT

CONNECTICUT

MASSACHUSETTS MASSACHUSETTS

Figure 21. Monitoring stations and point-source locations in the Quinebaug River Basin.
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 107

EXPLANATION

Total nitrogen load

Total Kjeldahl nitrogen 

 load

Nitrite-plus-nitrate 

 nitrogen load

Ammonia nitrogen load

Annual mean discharge

EXPLANATION

Stream phosphorus load

Point source load 

 (1990–1999)

Annual mean discharge

1982

19831984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

19981999

2000

2001

2002

2003

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

Annual loads of nitrogen constituents, in pounds

0

100

200

300

400

Annual mean discharge, in cubic feet per second

900,000 500

A. Quinebaug River at Quinebaug, Connecticut (station 14) 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

19981999

2000

2001

2002

2003

0

20,000

40,000

60,000

80,000

100,000

120,000

Annual total phosphorus load, in pounds

0

Annual mean discharge, in cubic feet per second

Water Year

B. Quinebaug River at Quinebaug, Connecticut (station 14)

140,000 500

400

300

200

100

Trends in load 1982–2003 1993–2003

Total nitrogen

Total Kjeldahl nitrogen

Nitrite-plus-nitrate nitrogen

Downward trend

Downward trend

No trend 

No trend

Not analyzed

No trend 

Ammonia nitrogen Data not available Downward trend

Trends in load 1982–2003 1993–2003

Total phosphorus Downward trend No trend

Figure 22. Annual stream loads of nutrients and point-source loads of total phosphorus in the Quinebaug River Basin. (A) Nitrogen 

constituents, Quinebaug River at Quinebaug, Conn., 1982–2003, (B) total phosphorus, Quinebaug River at Quinebaug, Conn., 1982–2003, 

(C) nitrogen constituents, Quinebaug River at Jewett City, Conn., 1975–2003, and (D) total phosphorus, Quinebaug River at Jewett City, 

Conn., 1975–2003.
108 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Trends in load 1975–2003 1993–2003

Total nitrogen

Total Kjeldahl nitrogen

Nitrite-plus-nitrate nitrogen

Ammonia nitrogen

Downward trend

Downward trend

No trend

Downward trend

No trend

Not analyzed

No trend 

No trend 

1975–2003

Downward trend

1993–2003

No trend

Trends in load

Total phosphorus

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

4,000,000

Annual loads of nitrogen constituents, in pounds

0

500

1,000

1,500

2,000

Annual mean discharge, in cubic feet per second

C. Quinebaug River at Jewett City, Connecticut (station 18)

4,500,000 2,200 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Water Year

0

100,000

200,000

300,000

400,000

Annual total phosphorus load, in pounds

0

500

1,000

1,500

2,000

Annual mean discharge, in cubic feet per second

D. Quinebaug River at Jewett City, Connecticut (station 18) 450,000 2,200 EXPLANATION

Total nitrogen load

Total Kjeldahl nitrogen 

 load

Nitrite-plus-nitrate 

 nitrogen load

Ammonia nitrogen load

Annual mean discharge

EXPLANATION

Stream phosphorus load

Point source load 

 (1990–98)

Annual mean discharge

Figure 22. Annual stream loads of nutrients and point-source loads of total phosphorus in the Quinebaug River Basin. (A) Nitrogen 

constituents, Quinebaug River at Quinebaug, Conn., 1982–2003, (B) total phosphorus, Quinebaug River at Quinebaug, Conn., 1982–2003, 

(C) nitrogen constituents, Quinebaug River at Jewett City, Conn., 1975–2003, and (D) total phosphorus, Quinebaug River at Jewett City, 

Conn., 1975–2003.—Continued
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 109

loads of total phosphorus have a highly significant downward 

trend for the 1982–2003 period, and no trend for the 1993–

2003 period (table 27, fig. 22B). 

A long-term downward trend in stream discharge was 

detected for the Quinebaug River at Jewett City (appendix 5, 

table 5–1). Consequently, the highly significant long-term 

downward trends in loads of total nitrogen, ammonia nitrogen, 

total Kjeldahl nitrogen, and total phosphorus detected 

for this station (table 27, figs. 22C, D) may be caused in 

part by decreases in streamflow. However, plots of annual 

mean discharge and annual loads of total nitrogen and total 

phosphorus (figs. 22C, D) indicate that for a given annual 

mean discharge, annual loads of these two constituents were 

lower in the 1990s and early 2000s than in the 1970s and 

1980s. This decrease in loads can be attributed in part to the 

long-term downward trends in flow-adjusted concentrations of 

these constituents (table 26), which indicate that a reduction 

in the delivery of nutrients to the Quinebaug River has taken 

place, in addition to the likely effects of the downward trend 

in streamflow. 

The drainage area of the Quinebaug River at Jewett 

City (table 8, in back of report, station 18; table 25), has 

11 upstream point sources with phosphorus loads identified 

in the PCS database. Eight of these point sources are identified as major point-source discharges. The borough of Jewett 

City, which discharges effluent directly upstream from the 

monitoring station, does not have reported phosphorus loads 

for the 1990s in the PCS database; consequently, data for this 

municipality are not included in the point-source load estimate. Jewett City has a population of 3,053 (in 2000) and is 

not identified in PCS as a major point-source facility. Total 

phosphorus point-source loads were highest in 1990 and 1991 

(fig. 22D), and represented the largest percentage of stream 

loads in those years, 43 and 60 percent, respectively. Annual 

point-source loads were substantially less than annual stream 

loads estimated for the Jewett City monitoring station from 

1992 to 1998, representing 16 to 33 percent of the stream 

loads for that period (fig. 22D). 

Decreases in point-source loads of total phosphorus may 

have contributed to the large decreases in stream loads prior 

to the 1990s (figs. 22B, D), but point-source data for this early 

period were not readily available. Long-term downward trends 

in total phosphorus loads for the Quinebaug River Basin are 

consistent with implementation of phosphate detergent bans in 

Connecticut in 1972 (Litke, 1999, p. 6, table 1). 

A few trends in flow-adjusted nutrient concentrations 

for the 1993–2003 period may indicate processes or changes 

that are increasing nutrient delivery to the Quinebaug River in 

recent years (table 26). An upward trend in flow-adjusted total 

nitrogen concentrations was detected for the Quinebaug River 

at Quinebaug, and upward trends in flow-adjusted concentrations of total phosphorus were detected for Quinebaug River 

stations near Pomfret and at Jewett City. 

Raritan River Basin in Northern New Jersey

The Raritan River Basin encompasses a highly developed 

area of northern New Jersey (fig. 23). Stream quality in the 

Raritan River Basin has been studied extensively by the 

USGS in cooperation with the New Jersey Department of 

Environmental Protection and the New Jersey Water Supply 

Authority (Reiser, 2004, p. 3, 9–10). Streamflow, water 

quality, and permitted (point source) and nonpermitted 

(nonpoint source) loads and yields were evaluated for water 

years 1991–98 (Reiser, 2004). Water-quality constituents 

evaluated included the following nutrients: total Kjeldahl 

nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus. 

Concentrations, loads, and yields were evaluated at low, 

median, and high streamflows. In evaluating the effects of 

point-source loads on stream loads, adjustments were made 

to point-source loads for time-of-travel from point discharges 

to monitoring locations and for constituent attenuation rates 

(Reiser, 2004, p. 20–21, p. 127–133). Readers are referred 

to the New Jersey study for detailed information. This study 

evaluates point-source nutrient loads in the Raritan Basin in 

the long-term context of stream nutrient loads and trends in 

load, and provides regional comparisons. 

Annual stream nutrient loads were estimated for nine 

monitoring stations in the Raritan River Basin, all in New 

Jersey: the Raritan River at Queens Bridge at Bound Brook, 

N.J., and eight subbasins, including Mulhockaway Creek at 

Van Syckel, South Branch Raritan River at Stanton, Neshanic 

River at Reaville, Lamington (Black) River near Pottersville, 

North Branch Raritan River near Raritan, Raritan River at 

Manville, Stony Brook at Princeton, and Millstone River at 

Blackwells Mills (stations 59–62 and 64–68, table 5; fig. 23). 

Trends in nutrient loads were evaluated for four of these stations (table 27), and point-source nutrient loads were estimated for eight of the nine stations. 

The drainage area of the Raritan River at Queens Bridge 

at Bound Brook (804 mi2), includes 64 point sources with 

nitrogen loads reported in the New Jersey Department of 

Environmental Protection database and 37 point sources 

with phosphorus loads reported in the PCS database. Ten of 

these point sources (nitrogen and phosphorus) are identified 

as major point sources (table 25). The Raritan River Basin, 

measured at the Bound Brook monitoring station, is one of the 

most highly developed of the watersheds selected for analysis 

of point sources, with about 17 percent of the drainage area 

in urbanized land, about 34 percent in agricultural land, and 

about 48 percent in undeveloped land (table 8, in back of 

report, station 68). 

Total point-source loads of nitrogen for the Raritan 

River at Bound Brook ranged from 32 to 79 percent of the 

estimated annual stream loads from 1991 to 1997 (fig. 24A). 

During years with annual mean flows that were above average, including 1994, 1996, and 1997, the point-source load of 

total nitrogen constituted 32 to 42 percent of the stream load. 

In 1993, an average flow year, the point-source load was about 
110 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

75°15' 74°15'

41°

40°15'

0 5 10 MILES

0 5 10 KILOMETERS

Base from U.S. Geological Survey Digital Data 1:100,000

Albers Equal-Area Projection 

North American Datum of 1983

PENNSYLVANIA

Staten Island

New York

NEW JERSEY

Delaware River

Newark

Trenton

51

52 55 56

57

58

59

59

60

61

62

63

64

65

66

67

68

69

70

84

85

87

88

89

90

91

92

Raritan Bay

South Branch Raritan River

Lam ni gton River

North

Branch

Raritan

River

Raritan River

Millston e River

Neshanic River

Stony Brook

Millstone River

EXPLANATION

Raritan River Basin

USGS water-quality monitoring station,

 with station sequence number (table 5)

Point sources that discharge nutrients

State capital

City, over 250,000 population

Figure 23. Monitoring stations and point-source locations in the Raritan River Basin.
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 111

41 percent of the stream load. During dry years, including 

1992 and 1995, point-source loads of total nitrogen constituted 

more than 75 percent of the estimated annual stream loads 

(fig. 24A). 

These estimates of point-source loads of total nitrogen as 

a percentage of total stream loads are similar to percentages 

for nitrogen constituents analyzed in the New Jersey study, 

which determined that attenuated contributions from permitted 

(point) sources accounted for 36 percent of the instream 

loads of total Kjeldahl nitrogen at the Raritan (Bound Brook) 

monitoring station during median streamflow, 100 percent 

during base flow, and 18 percent during high flow, during 

the growing season for the 1991–97 water years (Reiser, 

2004, p. 100, table 25). The New Jersey study reported that 

permitted sources accounted for 59 percent of the instream 

loads of nitrite-plus-nitrate nitrogen at this location during 

median streamflow, 100 percent during base flow, and 

38 percent during high flow for the same period (Reiser, 2004, 

p. 107, table 29). 

Trend results for the Raritan River at Bound Brook were 

generally similar for flow-adjusted concentrations of nitrogen 

constituents and for nitrogen constituent loads (tables 26, 

27). No long-term or recent trends in either flow-adjusted 

concentrations of total nitrogen or loads of total nitrogen 

(fig. 24A) were detected. Long-term downward trends in 

flow-adjusted concentrations and loads of ammonia nitrogen 

and total Kjeldahl nitrogen were detected (fig. 24B). No 

recent trends in flow-adjusted concentrations or loads of 

ammonia nitrogen were detected (fig. 24B); trends in total 

Kjeldahl nitrogen were not evaluated for the recent period. A 

long-term upward trend in the flow-adjusted concentration of 

nitrite-plus-nitrate nitrogen was detected (table 26); however, 

no long-term or recent trends in load were detected for this 

constituent (table 27, fig. 24B). 

Total point-source loads of phosphorus in the drainage 

area of the Raritan River at Bound Brook ranged from 16 to 

99 percent of the estimated annual stream loads from 1990 to 

1998 (fig. 24C). During years with above average annual mean 

streamflows, including 1994, 1996, and 1997, the point-source 

load of total phosphorus ranged from 16 to 34 percent of 

the stream load. In 1993 and 1998, when annual mean flows 

were near the long-term average, the point-source loads of 

total phosphorus constituted 40 and 29 percent, respectively, 

of the stream loads. During 1992, a dry year, the total pointsource load equaled the estimated total phosphorus load of 

the river (fig. 24C). Point-source data for total phosphorus 

were unavailable for 1995, also a dry year. These percentages are similar to percentages in the New Jersey study, 

which determined that attenuated contributions from permitted (point) sources accounted for 46 percent of the instream 

load of total phosphorus at the Raritan River at Bound Brook 

during median streamflow, 78 percent during base flow, and 

31 percent during high flow, during the growing season for the 

1991–97 water years (Reiser, 2004, p. 110, table 31). No longterm or recent trends in either flow-adjusted concentrations or 

stream loads of total phosphorus were detected for the Raritan 

River at Bound Brook (tables 26, 27; fig. 24C). 

Annual loads for subbasins in the Raritan River Basin 

illustrate differences based on land use, population density, 

and numbers of point sources, and also illustrate the complexity of evaluating nutrient sources in drainage basins with 

multiple land uses. Comparisons among subbasins are complicated to some extent by differences in years and sources for 

data on population density and land use. Population density 

data for this report are from the 2000 census, and land-use 

data are from the 1992 NLCDe dataset (table 8, in back of 

report); consequently, the population density figures for areas 

that were undergoing increased urbanization during the 1990s 

may represent a more highly developed land-use condition 

than is indicated by the land-use percentages. In the report on 

stream quality and point sources in the Raritan River Basin, 

population density figures are from the 1990 census, and landuse percentages are based on 1996 data from NJDEP (Reiser, 

2004, p. 6, table 1). Consequently, population densities presented in this report are generally higher than population densities in the Reiser report, whereas total developed land-use 

percentages are generally higher in the Reiser report, which 

also shows relatively higher percentages of urban land and 

lower percentages of agricultural land for several subbasins. 

Although the Raritan River Basin is in one of the most 

highly urbanized areas in the nation, one-third of the land in 

the drainage area was in agricultural uses in 1992 (table 8, 

in back of report), and most of the subbasins evaluated for 

nutrient loads had one-quarter to one-third of their land in 

agricultural uses. The overall population density for the 

Raritan River Basin in 2000 was about 650 people per square 

mile (table 8, in back of report). Population densities for 

subbasins evaluated in this report range from about 200 per 

square mile in the Mulhockaway Creek drainage basin 

to about 800 per square mile in the drainage basin of the 

Millstone River at Blackwells Mills. Population densities 

for most subbasins are in the range of 450 to 600 per square 

mile. Point sources discharge to streams in many subbasins, 

including three with drainage areas that are less than 50 mi2. 

The Neshanic River at Reaville is the only subbasin without 

point discharges evaluated in this report. 

Point-source loads of nutrients, as a percentage of total 

stream load, are lowest in the Mulhockaway Creek Basin 

(station 59), which has no major municipal discharges (table 8, 

in back of report). The Mulhockaway Creek Basin has the 

lowest population density (about 200 per square mile) and the 

highest percentage of undeveloped land (about 71 percent) of 

the Raritan subbasins evaluated in this report (table 8, in back 

of report). Annual point-source loads of total nitrogen and total 

phosphorus in this drainage basin represent an extremely small 

proportion of stream nutrient loads, less than 1 percent of the 

total stream load in each year for which point-source data 

are available. 

The proportion of an estimated annual stream nutrient 

load derived from point-source discharges is generally, 

although not always, related to annual mean streamflow 
112 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

EXPLANATION

Total nitrogen load

Total Kjeldahl nitrogen load

Nitrite-plus-nitrate 

 nitrogen load

Ammonia nitrogen load

Annual mean discharge

EXPLANATION

Stream nitrogen load

Point source load 

 (1991–97)

Annual mean discharge

1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

9,000,000

10,000,000

Annual total nitrogen load, in pounds

0

0

500

1,000

1,500

Annual mean discharge, in cubic feet per second

A. Raritan River at Queens Bridge at Bound Brook, New Jersey (station 68)

11,000,000 2,000

1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Water Year

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

9,000,000

10,000,000

Annual load of nitrogen constituents, in pounds

500

1,000

1,500

Annual mean discharge, in cubic feet per second

11,000,000 2,000

B. Raritan River at Queens Bridge at Bound Brook, New Jersey (station 68)

Trends in load 1982–2003 1993–2003

Total nitrogen

Total Kjeldahl nitrogen

Nitrite-plus-nitrate 

 nitrogen

No trend

Downward trend

No trend 

No trend

Not analyzed

No trend 

Ammonia nitrogen Downward trend No trend

Trends in load 1982–2003 1993–2003

Total nitrogen No trend No trend

Figure 24. Annual stream loads and point-source loads of nutrients in the Raritan River Basin. (A) Total nitrogen, Raritan River at 

Queens Bridge at Bound Brook, N.J., 1982–2003, (B) nitrogen constituents, Raritan River at Queens Bridge at Bound Brook, N.J., 1982–

2003, (C) total phosphorus, Raritan River at Queens Bridge at Bound Brook, N.J., 1982–2003. Point source data unavailable for 1995, (D)

total nitrogen, Lamington (Black) River near Pottersville, N.J., 1984–97, (E) total phosphorus, Lamington (Black) River near Pottersville, 

N.J., 1984–97, (F) total nitrogen, Millstone River at Blackwells Mills, N.J., 1991–2003, (G) total phosphorus, Millstone River at Blackwells 

Mills, N.J., 1993–2003, and (H) suspended sediment, Raritan River at Queens Bridge at Bound Brook , N.J., 1982–2003.
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 113

EXPLANATION

S

Stream nitrogen load

Point source load (1991–97)

Annual mean discharge

Stream load, where less 

 than estimated point 

 source load

EXPLANATION

Stream phosphorus load

Point source load 

 (1990–94, 1996–98)

Annual mean discharge

95-percent confidence

 interval of load estimate

1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 0

500,000

1,000,000

1,500,000

2,000,000

Annual total phosphorus load, in pounds

0

500

1,000

1,500

2,500,000 2,000

Annual mean discharge, in cubic feet per second

C. Raritan River at Queens Bridge at Bound Brook, New Jersey (station 68)

1984 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 0

100,000

150,000

200,000

250,000

D. Lamington (Black) River near Pottersville, New Jersey (station 62)

Annual total nitrogen load, in pounds

0

10

20

30

40

50

60

70

80

90

Annual mean discharge, in cubic feet per second

S

S

S

300,000 100

50,000

1985

Water Year

Trends in load 1982–2003 1993–2003

Total phosphorus No trend No trend

Stream loads not analyzed for trend

Figure 24. Annual stream loads and point-source loads of nutrients in the Raritan River Basin. (A) Total nitrogen, Raritan River at 

Queens Bridge at Bound Brook, N.J., 1982–2003, (B) nitrogen constituents, Raritan River at Queens Bridge at Bound Brook, N.J., 1982–

2003, (C) total phosphorus, Raritan River at Queens Bridge at Bound Brook, N.J., 1982–2003. Point source data unavailable for 1995, (D)

total nitrogen, Lamington (Black) River near Pottersville, N.J., 1984–97, (E) total phosphorus, Lamington (Black) River near Pottersville, 

N.J., 1984–97, (F) total nitrogen, Millstone River at Blackwells Mills, N.J., 1991–2003, (G) total phosphorus, Millstone River at Blackwells 

Mills, N.J., 1993–2003, and (H) suspended sediment, Raritan River at Queens Bridge at Bound Brook , N.J., 1982–2003.—Continued
114 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

EXPLANATION

S

Stream phosphorus load

Point source load (1990–97)

Annual mean discharge

Stream load, where less 

 than estimated point 

 source load

EXPLANATION

Stream nitrogen load

 (1993–2003)

Point source load 

 (1991–97)

Annual mean discharge

Trends in load 1993–2003

Total nitrogen No trend

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 0

5,000

10,000

15,000

20,000

25,000

E. Lamington (Black) River near Pottersville, New Jersey (station 62)

Annual total phosphorus load, in pounds

0

10

20

30

40

50

60

70

80

90

100

Annual mean discharge, in cubic feet per second

S

30,000

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

Annual total nitrogen load, in pounds

F. Millstone River at Blackwells Mills, New Jersey (station 67)

0

100

200

300

400

500

600

Annual mean discharge, in cubic feet per second

Water Year

3,000,000

Stream loads not analyzed for trend

Figure 24. Annual stream loads and point-source loads of nutrients in the Raritan River Basin. (A) Total nitrogen, Raritan River at 

Queens Bridge at Bound Brook, N.J., 1982–2003, (B) nitrogen constituents, Raritan River at Queens Bridge at Bound Brook, N.J., 1982–

2003, (C) total phosphorus, Raritan River at Queens Bridge at Bound Brook, N.J., 1982–2003. Point source data unavailable for 1995, (D)

total nitrogen, Lamington (Black) River near Pottersville, N.J., 1984–97, (E) total phosphorus, Lamington (Black) River near Pottersville, 

N.J., 1984–97, (F) total nitrogen, Millstone River at Blackwells Mills, N.J., 1991–2003, (G) total phosphorus, Millstone River at Blackwells 

Mills, N.J., 1993–2003, and (H) suspended sediment, Raritan River at Queens Bridge at Bound Brook , N.J., 1982–2003.—Continued
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 115

EXPLANATION

Stream phosphorus load

Point source load 

 (1993–94, 1996–98)

Annual mean discharge

Suspended sediment load

Annual mean discharge

EXPLANATION

Trends in load 1993–2003

Total phosphorus No trend

Trends in load 1982–2003 

Suspended

 sediment

1993–2003

Downward trend No trend

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

Annual total phosphorus load, in pounds

G. Millstone River at Blackwells Mills, New Jersey (station 67)

0

100

200

300

400

500

600

Annual mean discharge, in cubic feet per second

1982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

Water Year

0

1,000,000,000

2,000,000,000

3,000,000,000

Annual suspended sediment load, in pounds

H. Raritan River at Queens Bridge at Bound Brook, New Jersey (station 68)

0

500

1,000

1,500

Annual mean discharge, in cubic feet per second

3,500,000,000 2,000

Figure 24. Annual stream loads and point-source loads of nutrients in the Raritan River Basin. (A) Total nitrogen, Raritan River at 

Queens Bridge at Bound Brook, N.J., 1982–2003, (B) nitrogen constituents, Raritan River at Queens Bridge at Bound Brook, N.J., 1982–

2003, (C) total phosphorus, Raritan River at Queens Bridge at Bound Brook, N.J., 1982–2003. Point source data unavailable for 1995, (D)

total nitrogen, Lamington (Black) River near Pottersville, N.J., 1984–97, (E) total phosphorus, Lamington (Black) River near Pottersville, 

N.J., 1984–97, (F) total nitrogen, Millstone River at Blackwells Mills, N.J., 1991–2003, (G) total phosphorus, Millstone River at Blackwells 

Mills, N.J., 1993–2003, and (H) suspended sediment, Raritan River at Queens Bridge at Bound Brook , N.J., 1982–2003.—Continued
116 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

(figs. 24A, C). In several subbasins, point-source loads 

of nutrients generally constitute 10 to 20 percent of total 

stream nutrient loads in years with above average annual 

mean streamflows, and constitute 25 to 50 percent or more 

of stream nutrient loads in dry years. Annual point-source 

loads of nutrients were fairly constant during the 1990s in 

some subbasins, including the South Branch Raritan River at 

Stanton, the Raritan River at Manville, and Stony Brook at 

Princeton (not shown in fig. 24), whereas annual point-source 

loads varied considerably in other subbasins, including the 

Lamington River near Pottersville, and the Millstone River at 

Blackwells Mills (figs. 24D–G). 

Point-source nutrient loads generally constitute a large 

percentage of annual stream loads for the Lamington River 

near Pottersville (station 62), a small drainage basin (almost 

33 mi2) with a high population density (about 600 per square 

mile; table 8, in back of report). Point-source nitrogen loads 

represented 57 to 100 percent of stream nitrogen loads 

during the 1990s (fig. 24D). Point-source phosphorus loads 

represented 15 to 100 percent of stream phosphorus loads, 

and in most years constituted one-third to three-quarters of the 

stream load (fig. 24E). Estimated annual point-source nitrogen 

loads for the Lamington River exceeded estimated stream 

loads by a large amount in 1992 (a dry year) and 1996 (a wet 

year) (fig. 24D). Large interannual changes in point-source 

discharges of total nitrogen are caused primarily by changes at 

a single facility in the Lamington River Basin (R.M. Moore, 

U.S. Geological Survey, written commun., 2011). 

Instream attenuation of nutrients may in part account 

for instances in which estimated point-source loads exceed 

estimated stream loads in the Lamington River Basin. Substantial attenuation of nutrients is likely in streams of the 

Raritan River Basin, more so than in some of the other basins 

evaluated for point sources, because many point sources are 

discharged into small streams where attenuation is likely to 

occur. Attenuation of nutrients discharged from point sources 

is likely for all years evaluated in the Lamington River Basin, 

because of the small size of the stream and because the three 

point sources are located in the headwaters of the drainage 

basin (fig. 23). Uncertainties in the estimation process or 

inadequacy of data also may contribute to the unusually large 

differences between stream loads and point-source loads for 

water years 1992 and 1996 in the Lamington River Basin. 

Agricultural land as a percentage of total basin area 

exceeds urban land in seven of the eight subbasins for which 

nutrient loads were estimated (table 8, in back of report). 

Agricultural land is a major nutrient source in most subbasins, despite the urbanized nature of many subbasins and the 

numerous point sources that discharge nutrients to streams in 

the Raritan River Basin. A comparison of the Neshanic and 

Lamington River Basins, which are similar in size, illustrates 

this point (table 8, in back of report, stations 61, 62). The 

Neshanic River at Reaville (about 26 mi2) is a predominantly 

agricultural drainage basin (about 60 percent agricultural land) 

with no point-source discharges and a low population density (about 340 per square mile) relative to other subbasins. 

The Neshanic is the most highly agricultural and most highly 

developed of the subbasins (about 68 percent developed land). 

The Lamington River near Pottersville (almost 33 mi2), an 

urbanized drainage basin with point-source discharges, has 

only half as much developed land (about 34 percent of the 

basin) as the Neshanic River, but the population density is 

higher (about 600 per square mile). Annual total nitrogen 

loads for the Neshanic River range from 130,000 pounds (lb) 

to 275,000 lb for most years in the 1993–2003 period, with 

peak loads of about 300,000 pounds per year (lb/yr) in 1994 

and 1996 (fig. 14C). By contrast, annual total nitrogen loads 

for the Lamington River are lower, generally ranging from 

100,000 to 165,000 lb for the 1984–1997 period, with a peak 

load of 270,000 lb in 1984 (fig. 24D). Annual total phosphorus 

loads for the Neshanic River range from 3,000 to 65,000 lb 

in most years, with peak loads of 115,000 lb in 1994 and 

400,000 lb in 1999 (fig. 14D). Annual total phosphorus loads 

for the Lamington River are much lower, generally ranging 

from 4,000 to 11,000 lb, with a peak load of 25,000 lb in 1984 

(fig. 24E). Comparison of summary statistics for total phosphorus yields for these two similarly-sized basins shows that 

median and maximum yields for the Neshanic are an order 

of magnitude greater than those yields for the Lamington 

(table 21). 

The Raritan River at Manville (490 mi2) and the 

Millstone River at Blackwells Mills (258 mi2) are the 

largest tributary subbasins of the Raritan at Bound Brook, 

together constituting 93 percent of the 804 mi2 drainage 

basin. Comparison of point-source effects in these two major 

tributary subbasins is limited by the small number of years 

of readily available point-source data for nutrients, and the 

fact that the available years of water-quality data for stream 

load estimates, and the available years of point-source data, 

differ for the two stations. The Millstone River has the highest 

population density (about 800 per square mile), the highest 

percentage of urbanized land (about 19 percent), the second 

highest percentage of agricultural land (about 36 percent), 

and the second highest percentage of total developed land 

(about 55 percent) of the subbasins evaluated (table 8, in 

back of report, station 67). The drainage basin of the Raritan 

River at Manville (station 65) has a population density of 

526 per square mile, and about 49 percent of the drainage 

basin is developed, values that are similar to, though less than, 

those for the Millstone River Basin. Point-source loads of 

total nitrogen in the Millstone River Basin range from 32 to 

73 percent of the stream nitrogen load, depending on annual 

mean streamflow, and point-source loads of total phosphorus 

range from 24 to 47 percent of stream loads (figs. 24F, G). 

No point-source data for total phosphorus are available for 

the Millstone River for 1995, a low flow year in which the 

point-source load is likely to represent a high percentage of 

the stream load. Point-source nutrient loads as a percentage 

of total stream loads are generally lower for the Raritan River 

at Manville (not shown in fig. 24). Point-source loads of total 

nitrogen generally range from 12 to 38 percent of stream 

loads, and point-source loads of total phosphorus generally 
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 117

range from 14 to 50 percent of stream loads. Comparison 

of total nitrogen and total phosphorus yields for these two 

subbasins shows that total nitrogen yields are similar, whereas 

total phosphorus yields in the Millstone River Basin are 

substantially larger than total phosphorus yields for the Raritan 

River at Manville (tables 20, 21). 

Unusually high annual total phosphorus loads were 

estimated for 1999 for the Raritan River and several subbasins 

(figs. 24C, G). Annual mean streamflow for water year 1999 

for the Raritan River at Bound Brook was slightly below average (less than the 25th percentile). Precipitation during water 

year 1999 had begun with a record dry period that extended 

from July to December 1998; extremely dry conditions prevailed again from April through July 1999, and streamflow 

declined to below normal levels during both of these periods 

(Reed and others, 2000, p. 2–3). Drought conditions ended in 

mid-September when Tropical Storm Floyd combined with a 

western storm system to produce as much as 14 in. of rain in 

New Jersey from September 15 to 17 (Reed and others, 2000, 

p. 2, 4). Record high streamflows were documented at several 

locations in the Raritan River Basin on September 16–17, 

1999, resulting in unusually high estimated annual total phosphorus loads and suspended sediment loads, relative to annual 

mean streamflow (figs. 14D, 24C, G, H). September 16, 1999, 

was the maximum annual peak flow recorded for the Neshanic 

River at Reaville (for the period 1931–2007), the North 

Branch Raritan River (1896–2007), and the Raritan River at 

Manville (1904–2007), and was the second highest annual 

peak for Mulhockaway Creek (1978–2007), the South Branch 

Raritan River at Stanton (1904–2007), and Stony Brook 

(1954–2007) (U.S. Geological Survey, 2009a). September 17, 

1999, was the peak daily mean flow for the Raritan River at 

Bound Brook for the period 1982–2003. 

The Raritan River at Bound Brook was the only station where a trend in suspended sediment load was detected, 

among four stations in the region evaluated for trends in 

suspended sediment load in the long-term period and eight 

stations evaluated for the recent period (tables 18, 27). A 

long-term downward trend in suspended sediment load was 

detected, and a long-term downward trend in flow-adjusted 

concentration of suspended sediment also was detected for this 

station (tables 26, 27). However, as can be observed in the plot 

of estimated annual suspended sediment loads for this station 

(fig. 24H), an extremely high estimated annual load (1999) 

can be produced by peak streamflow during a small number of 

days in any year, even when changes in a drainage basin may 

be contributing to an overall downward trend in load. 

Patuxent River Basin in Maryland

The Patuxent River Basin, on the western shore of 

Chesapeake Bay, is in an urbanizing area of central Maryland, 

between Baltimore and Washington, D.C. (fig. 25). Of the 

watersheds selected for evaluation of point sources, the 

Patuxent River Basin has the highest percentage of urban land 

(about 19 percent, table 8, in back of report, station 114), and 

the highest percentage of agricultural land (about 38 percent), 

and the highest population density (about 1,000 per square 

mile). About 40 percent of the basin is undeveloped. 

Annual stream nutrient loads were estimated for three 

monitoring stations in the Patuxent River Basin, all in 

Maryland. Trends in nutrient loads were evaluated and pointsource loads were estimated for one station, the Patuxent River 

near Bowie (table 8, in back of report, station 114, 348 mi2). 

The Chesapeake Bay Program has identified 14 point sources 

with nutrient loads in the drainage area of the Patuxent River 

near Bowie. Seven of these point sources are identified as 

major (table 25). 

Total point-source loads of nitrogen in the drainage basin 

of the Patuxent River near Bowie ranged from 25 to 82 percent of the estimated annual stream loads from 1990 to 2003 

(fig. 26A). During years with annual mean flows that were 

above average, including 1996, 1997, and 2003, the pointsource load constituted 25 to 35 percent of the annual stream 

load. In 1998, a median flow year for the recent period, the 

point-source load of total nitrogen was about 34 percent of the 

stream load. During dry years and drought periods, including 

1990–92, 1995, and 1999–2002, point-source loads of nitrogen 

constituted 45 to 82 percent of the estimated annual stream 

loads (fig. 26A). 

Point-source loads of total nitrogen decreased during the 

early 1990s (fig. 26A), and then remained fairly constant from 

1994 to 2003, at about 500,000 to 600,000 lb/yr. The decrease 

in the early 1990s is probably the result of wastewater-treatment improvements. Seasonal biological removal of nitrogen 

was implemented at major wastewater-treatment plants in the 

Patuxent Basin between 1991 and 1993 (Darrell and others, 

1999). 

Highly significant downward trends in stream loads of 

total nitrogen, ammonia nitrogen, total Kjeldahl nitrogen, 

and nitrite-plus-nitrate nitrogen were detected for the 

Patuxent River near Bowie for the long-term period (table 27; 

figs. 26A, B); a downward trend in the stream load of ammonia nitrogen was the only trend in load detected during the 

recent period (table 27). Long-term trends in flow-adjusted 

nitrogen constituent concentrations were similar to trends in 

load, with downward trends detected for these four constituents (table 26). During the recent period, downward trends 

were detected in flow-adjusted concentrations of ammonia 

and nitrite-plus-nitrate nitrogen; total Kjeldahl nitrogen was 

not evaluated (table 26). The Maryland Department of Natural 

Resources has attributed large decreases in total nitrogen 

concentrations in the Patuxent River between the late 1980s 

and the mid-2000s primarily to the addition of an advanced 

treatment practice, biological removal of nitrogen, at wastewater-treatment plants (Maryland Department of Natural 

Resources, 2009). 

Phosphorus load data are reported by the Chesapeake 

Bay Program for all seven major point sources. Phosphorus 

load data are not reported for four of the seven minor point 

sources, however, and the lack of data for these minor sources 

may affect this analysis. From 1990 to 2003, total point-source 
118 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

102

111

112

113

114 115

116

117

118

119

120

121

122

123

124

125

126

127

127

128

129

Washington ,

D.C.

Baltimore

Annapolis

Richmond

Appomattox River

PamunkeyRiver

Mattaponi River Shenandoah River

Potomac River

Patuxent River

Rappahannock River

Chesapeake

B

ay

James River

VIRGINIA

MARYLAND

PENNSYLVANIA

PENNSYLVANIA

WEST VIRGINIA

VIRGINIA

NORTH CAROLINA

WEST VIRGINIA

0 25 50 MILES

0 25 50 KILOMETERS

80° 76°

39°

37°

Base from U.S. Geological Survey Digital Data 1:100,000

Albers Equal-Area Projection

North American Datum of 1983

EXPLANATION

Patuxent River Basin

James and Appomattox River Basins

Study area boundary

Point sources that discharge nutrients

USGS water-quality monitoring station,

 with station sequence number (table 5) 

Washington, D.C.

State capital

City, over 250,000 population

Susquehanna R.

Figure 25. Monitoring stations and point-source locations in the Patuxent and James River Basins.
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 119

EXPLANATION

Stream nitrogen load

Point source load

 (1990–2003)

Annual mean discharge

95-percent confidence interval

 of load estimate

Total nitrogen load

Total Kjeldahl nitrogen load

Nitrite-plus-nitrate 

 nitrogen load

Ammonia nitrogen load

Annual mean discharge

EXPLANATION

1979–2003

Downward trend

1993–2003

No trend

Trends in load

Total nitrogen

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

Annual total nitrogen load, in pounds

0

100

200

300

400

500

600

700

Annual mean discharge, in cubic feet per second

A. Patuxent River near Bowie, Maryland (station 114) 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994

199519961997199819992000200120022003

Water Year

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

Annual loads of nitrogen constituents, in pounds

B. Patuxent River near Bowie, Maryland (station 114)

0

100

200

300

400

500

600

700

Annual mean discharge, in cubic feet per second

Trends in load 1979–2003 1993–2003

Total nitrogen

Total Kjeldahl nitrogen

Nitrite-plus-nitrate nitrogen

Ammonia nitrogen

Downward trend

Downward trend

Downward trend

No trend

Not analyzed

No trend

Downward trend

1980–2003 

Downward trend

Figure 26. Annual stream loads and point-source loads of nutrients in the Patuxent River Basin. (A) Total nitrogen, Patuxent River near 

Bowie, Md., 1979–2003, (B) nitrogen constituents, Patuxent River near Bowie, Md., 1979–2003, and (C) total phosphorus, Patuxent River 

near Bowie, Md., 1979–2003.
120 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

loads of phosphorus in the drainage area of the Patuxent River 

near Bowie ranged from 21 to 100 percent of the estimated 

annual stream loads (fig. 26C). During years with annual mean 

flows that were above average, including 1996, 1997, and 

2003, the point source load of total phosphorus constituted 21 

to 30 percent of the stream load. In 1998, a median flow year, 

the point source load of total phosphorus was about 40 percent 

of the stream load. During dry years and drought periods, 

including 1990–92, 1995, and 1999–2002, point-source loads 

of total phosphorus constituted 38 to 100 percent of the annual 

stream loads, exceeding 50 percent of the stream load in six of 

the eight dry years (fig. 26C). The point-source load calculated 

for 2002, an extreme low-flow year, exceeded the estimated 

stream load, but was within the upper confidence limit for the 

stream load. Point-source loads of total phosphorus ranged 

from 36,000 to 53,000 lb/yr during the 1990–2003 period, 

with a mean of 46,000 lb/yr. Point-source loads were slightly 

higher in the early 1990s, but a pronounced change during the 

period is not apparent. 

A highly significant downward trend in the stream load 

of total phosphorus was detected for the Patuxent River near 

Bowie for the long-term period (table 27; fig. 26C). During 

the recent period, however, an upward trend in flow-adjusted 

concentrations of total phosphorus for the Patuxent River 

may indicate processes or changes that are increasing nutrient 

delivery to the Patuxent River in recent years (table 26). 

Long-term downward trends in flow-adjusted 

concentrations and loads of nutrients indicate progress in 

improving nutrient-related water-quality conditions in the 

Patuxent River. A substantial amount of this progress may 

be attributable to wastewater-treatment improvements, 

including biological removal of nitrogen, and implementation 

of phosphate detergent bans in Maryland in 1985 (Litke, 

1999, p. 6, table 1). Based on the stream loads estimated for 

total nitrogen and total phosphorus for the period 1979–1989 

(figs. 26A, C), it seems likely that some of the reductions in 

nutrients from wastewater-treatment plants took place prior to 

the period for which point-source data were available for 

this analysis. 

Challenges to improving nutrient-related water-quality 

conditions remain. Stream load estimates and point-source 

estimates for nitrogen and phosphorus during the recent period 

indicate that most of the nutrients transported by the Patuxent 

River during dry years are from wastewater-treatment plants. 

As noted in the section on Modeled Instream Concentrations, 

recent total nitrogen and total phosphorus concentrations 

typically exceed proposed criteria in the highly developed 

Patuxent River Basin (table 15, in back of report). 

EXPLANATION

1979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

Water Year

0

500,000

1,000,000

1,500,000

Annual total phosphorus load, in pounds

Stream phosphorus load

Point source load

 (1990–2003)

Annual mean discharge

0

100

200

300

400

500

600

700

Annual mean discharge, in cubic feet per second

C. Patuxent River near Bowie, Maryland (station 114)

1,700,000

1979–2003

Downward trend

1993–2003

No trend

Trends in load

Total phosphorus

Figure 26. Annual stream loads and point-source loads of nutrients in the Patuxent River Basin. (A) Total nitrogen, Patuxent River near 

Bowie, Md., 1979–2003, (B) nitrogen constituents, Patuxent River near Bowie, Md., 1979–2003, and (C) total phosphorus, Patuxent River 

near Bowie, Md., 1979–2003.—Continued
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 121

James River Basin in Central Virginia

The James River Basin in central Virginia, with a 

monitored drainage area of 6,252 mi2, is the third largest 

streamflow and nutrient source to Chesapeake Bay, after 

the Susquehanna and Potomac Rivers (fig. 25) (Belval and 

Sprague, 1999, p. 5). Annual stream nutrient loads were 

estimated, trends in nutrient loads were evaluated, and pointsource nutrient loads were estimated for two monitoring 

stations in the James River Basin, both in Virginia: the James 

River at Cartersville and the Appomattox River at Matoaca 

(fig. 25, stations 127, 129). The Appomattox River is a 

tributary to the James River, but the confluence with the James 

is downstream from the monitored part of the James River 

(fig. 25). Consequently, nutrient conditions on the Appomattox 

River are not encompassed by the data for the James River, 

and the two are essentially separate drainage basins for the 

purposes of this discussion. 

The Chesapeake Bay Program has identified 10 point 

sources, all of them major point sources, that contribute 

nutrient loads in the drainage area of the James River at 

Cartersville (table 8, in back of report, station 127; table 25). 

Of the watersheds selected for analysis of point sources, 

the James River watershed upstream from Cartersville is 

among the least developed and the most forested, with only 

3.5 percent of the basin in urbanized land, 15 percent in 

agricultural land, and about 80 percent undeveloped (table 25). 

The total point-source load of nitrogen upstream from the 

Cartersville monitoring station represents a small percentage 

of the estimated stream load during many years (fig. 27A). 

During wet years such as 1996, 1998, and 2003, when the 

annual mean flows were substantially greater than recent and 

long-term medians, the point-source load of total nitrogen 

was only about 10 to 15 percent of the annual stream load. 

However, the total point-source nitrogen load constituted from 

33 to 100 percent of the estimated annual stream load during 

the prolonged dry period from 1999 to 2002. In 1997, a year in 

which the annual mean flow was close to long-term and recent 

median streamflow, point-source loads of total nitrogen were 

about 22 percent of the annual stream load. Annual pointsource loads of total nitrogen were fairly constant during the 

1990–2003 period, ranging from 2.1 to 2.6 million pounds per 

year, with a peak annual load of 2.9 million pounds in 1994 

(fig. 27A). 

Long-term downward trends in stream loads of total 

nitrogen, ammonia nitrogen, and nitrite-plus-nitrate nitrogen were detected for the James River; a downward trend in 

ammonia nitrogen load also was detected for the recent period 

(table 27; fig. 27B). Trends in flow-adjusted concentrations of 

nitrogen constituents were similar, with long-term downward 

trends detected for total nitrogen, ammonia nitrogen, and 

nitrite-plus-nitrate nitrogen, and a downward trend in ammonia nitrogen detected for the recent period (table 26). However, an upward trend in the flow-adjusted concentration of 

total nitrogen was detected for the recent period (table 26). 

No long-term or recent trends in flow-adjusted 

concentrations or stream loads of total phosphorus were 

detected for the James River (tables 26, 27; fig. 27C). The total 

point-source load of phosphorus is substantially less than the 

estimated stream load for the James River during most years 

(fig. 27C). During the wet years of 1996, 1998, and 2003, the 

point-source load of total phosphorus constituted about 10 to 

18 percent of the annual stream load. During dry years from 

1999 to 2002, however, the point-source load approached or 

equaled the estimated stream load (fig. 27C). Point-source 

loads of phosphorus increased during the 1990–2003 period, 

with annual loads ranging from 325,000 to 480,000 lb from 

1990 to 1997, and annual loads ranging from 450,000 to 

700,000 lb from 1998 to 2003 (fig. 27C). 

The calculated point source load of phosphorus for 

2002 exceeded the estimated stream load for the James River 

and also exceeded the upper confidence limit for the stream 

load. Instream attenuation processes may account in part for 

this difference, but uncertainties in the estimation process 

or inadequacy of data also may be involved. The point 

sources in this drainage basin are in the upstream part of the 

watershed (fig. 25). Instream biogeochemical processes affect 

the forms of nutrients transported, and may remove nutrients 

from streams. Nutrient processing and attenuation, and the 

differences in processes that affect nitrogen and phosphorus, 

may play a role in the observed differences between total 

point-source loads of nutrients and estimated stream loads of 

nitrogen and phosphorus. Phosphorus appears to undergo more 

in-stream decay (attenuation) than nitrogen. Concentrations 

of phosphorus are naturally high in some soils and rocks 

of the James River Basin (Belval and Sprague, 1999). The 

importance of this natural source relative to total stream loads 

has not been evaluated in this study. 

The Chesapeake Bay Program has identified two point 

sources with nutrient loads in the drainage basin of the 

Appomattox River at Matoaca (table 8, in back of report, 

station 129; table 25). Both point sources are near the 

headwaters of the drainage basin, and one is identified as 

major, although total wastewater discharges are small relative 

to the other drainage basins evaluated. Instream nutrient 

processing may affect comparisons between total nutrient 

point-source loads and estimated stream loads, because of the 

distance between the point sources and the stream monitoring 

location. Of the drainage basins selected for analysis of 

point sources, the Appomattox River at Matoaca is among 

the least urbanized and the most forested (about 74 percent), 

with only about 2 percent of the basin in urbanized land, 

about 20 percent in agricultural land, and about 76 percent 

undeveloped (table 25). 

Annual point-source loads of total nitrogen contribute 

only a small fraction of the estimated stream loads of total 

nitrogen for the Appomattox River, representing about 2 

to 6 percent of the annual stream load from 1990 to 1999. 

Annual point-source loads of phosphorus contribute only 

a small fraction of stream phosphorus loads during most 

years, representing only 2 to 11 percent of the stream load 
122 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

EXPLANATION

EXPLANATION

Stream nitrogen load

Point source load

 (1990-2003)

Annual mean discharge

Total nitrogen load

Nitrite-plus-nitrate

 nitrogen load

Ammonia nitrogen load

Annual mean discharge

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

Annual total nitrogen load, in pounds

0

5,000

10,000

15,000

Annual mean discharge, in cubic feet per second Annual mean discharge, in cubic feet per second

A. James River at Cartersville, Virginia (station 127)

1975–2003

Downward trend

1993–2003

No trend

19751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003

Water Year

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

Annual loads of nitrogen constituents, in pounds

B. James River at Cartersville, Virginia (station 127)

0

5,000

10,000

15,000

Trends in load

Total nitrogen

Nitrite-plus-nitrate nitrogen

Ammonia nitrogen

1975–2003

Downward trend

Downward trend

1993–2003

No trend

No trend

Downward trend

1979–2003

Downward trend

Trends in load

Total nitrogen

Figure 27. Annual stream loads and point source loads of nutrients in the James River Basin. (A) Total nitrogen, James River at 

Cartersville, Va., 1975–2003, (B) nitrogen constituents, James River at Cartersville, Va., 1975–2003, and (C) total phosphorus, James River 

at Cartersville, Va., 1975–2003.
Relation of Nutrient Trends, Loads, and Yields to Nutrient Sources 123

in 13 of the 14 years from 1990 to 2003. In 2002, however, 

an extremely dry year in this part of the study area, pointsource loads of phosphorus represented about 45 percent of 

the stream load. This large percentage represents the low 

streamflow in 2002 rather than an increase in the annual point 

source load, which was similar to previous years. Point-source 

loads of total phosphorus did, however, approximately double 

during the period of analysis, from 4,000 to 5,000 lb/yr in the 

early 1990s to 7,000 to 11,000 lb/yr in the late 1990s and 

early 2000s. 

Few trends in stream nutrient loads were detected for the 

Appomattox River (table 27). No recent trends in any nutrient 

loads were detected, and no long-term trends in total nitrogen 

or total phosphorus loads were detected. Long-term downward 

trends in loads of ammonia nitrogen and nitrite-plus-nitrate 

nitrogen were the only significant trends in stream nutrient 

loads (table 27). Long-term and recent downward trends in 

flow-adjusted concentrations of ammonia nitrogen and nitriteplus-nitrate nitrogen were detected for the Appomattox River 

(table 26). No long-term trend in flow-adjusted concentrations of total nitrogen was detected; however, a recent upward 

trend was detected. A long-term upward trend in flow-adjusted 

concentrations of total phosphorus was detected, but no recent 

trend was detected (table 26). Increases in point-source loads 

of total phosphorus may be a factor contributing to the upward 

trend in total phosphorus concentrations. 

Nutrient transport measured on the Appomattox River 

is affected by an impoundment on the river less than 3 mi 

upstream from the monitoring station (Belval and Sprague, 

1999, p. 6). Sedimentation of particles containing nutrients 

in the impoundment contributes to the relatively low nutrient 

yields on the Appomattox River compared to other major rivers flowing into Chesapeake Bay. 

EXPLANATION

Stream phosphorus load

Point source load

 (1990-2003)

Annual mean discharge

C. James River at Cartersville, Virginia (station 127) 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991

199219931994199519961997199819992000200120022003

Water Year

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

Annual total phosphorus load, in pounds

0

5,000

10,000

15,000

Annual mean discharge, in cubic feet per second

1975–2003

No trend

Trends in load

Total phosphorus

1993–2003

No trend

Figure 27. Annual stream loads and point source loads of nutrients in the James River Basin. (A) Total nitrogen, James River at 

Cartersville, Va., 1975–2003, (B) nitrogen constituents, James River at Cartersville, Va., 1975–2003, and (C) total phosphorus, James 

River at Cartersville, Va., 1975–2003.—Continued
124 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Summary, Conclusions, and Challenges 

for Management of Water Resources

Water-quality problems resulting from excessive nutrients 

in freshwater and estuaries are among the most widespread 

and complex issues facing water managers in the northeastern United States. Effective action to address nutrient-related 

water-quality problems requires scientific information on the 

sources, distribution, cycling, and transport of nutrients in 

the environment. 

The National Water Quality Assessment (NAWQA) 

Program of the U.S. Geological Survey (USGS) began 

regional studies in 2003 to synthesize information on nutrient 

concentrations, trends, stream loads, and sources. This report 

presents results of the nutrients study for river basins in the 

northeastern United States. The region extends from Maine to 

central Virginia, encompassing 166,000 square miles (mi2) and 

a population of 59 million. 

This report provides water managers, scientists, policymakers, and citizens with a regional perspective on the 

changes (trends) in nitrogen and phosphorus concentrations in 

streams of the northeastern United States; the nutrient concentrations observed in streams; the amounts of these nutrients 

(loads) transported by streams; and the sources of these nutrients in drainage basins. Specific objectives of the report were 

to present, evaluate, and synthesize (1) information on recent 

(1993–2003) and long-term (1975–2003) trends in nutrient 

concentrations; (2) observed and modeled instream nutrient 

concentrations relative to water-quality criteria and benchmarks; (3) recent and long-term annual nutrient load estimates, 

and information on trends in annual loads; and (4) selected 

information on nutrient sources, including regional land use 

and population density data, and point source information for 

a small number of drainage basins. 

Nutrient data were evaluated for 130 USGS water-quality 

monitoring stations. Nutrient data were analyzed for trends in 

flow-adjusted concentrations, modeled instream (non-flowadjusted) concentrations, and stream loads for 32 stations with 

22 to 29 years of water-quality and daily mean streamflow 

record during 1975–2003 (termed the long-term period), and 

for 46 stations during 1993–2003 (termed the recent period), 

by using a coupled statistical model of streamflow and water 

quality developed by the USGS. Recent trends in flowadjusted concentrations of one or more nutrients also were 

analyzed for 90 stations by using Tobit regression, which does 

not require a record of daily mean streamflow. Data for some 

stations were analyzed with both programs. 

Annual stream nutrient loads were estimated, and annual 

nutrient yields were calculated, for 47 stations for the longterm and recent periods, and for 37 additional stations that did 

not have a complete streamflow and water-quality record for 

1993–2003. Nutrient yield information was incorporated for 

9 drainage basins evaluated in a national NAWQA study, for a 

total of 93 stations evaluated for nutrient yields. 

Trends were analyzed and annual loads were estimated 

for total nitrogen, nitrite-plus-nitrate nitrogen, and total phosphorus for stations with sufficient data. Trend analysis and 

load estimation were performed for ammonia nitrogen, total 

Kjeldahl nitrogen, and suspended sediment for a small number 

of stations. 

Regional Data Integration

A full regional synthesis of information on nutrient 

concentrations, trends, loads, and sources represents an unattained goal, in terms of continuity and consistency of waterquality data. Geographic coverage of the region by USGS 

water-quality monitoring programs is not complete, and 

consequently some major drainage areas of the region are not 

included in the analyses presented in this report. Many of the 

water-quality monitoring stations with the longest and most 

complete records were established in response to the Clean 

Water Act, and consequently many of these stations monitor 

waste-receiving streams. Comparable long-term monitoring is 

often lacking in drainage basins without point sources. 

Trends in Flow-Adjusted Nutrient 

Concentrations

Numerous downward trends in flow-adjusted concentrations of nitrogen and phosphorus constituents during the 

period analyzed in this study indicate noteworthy regional 

improvements in nutrient-related water-quality conditions. 

Trends in streamflow were detected at only two stations, one 

in the 1993–2003 period, and one in the 1975–2003 period. 

Consequently, statistically significant trends in flow-adjusted 

concentrations are believed to represent changes in the delivery of nutrients to streams for most of the streams evaluated. 

Flow-adjusted concentrations of total nitrogen decreased 

at about half the stations analyzed during the long-term period 

(18 of 32 stations), and 4 upward trends were detected. During 

the recent period, 12 upward trends and 15 downward trends 

in total nitrogen concentrations were detected, among 81 stations analyzed. During the long-term period, downward trends 

in flow-adjusted concentrations of ammonia nitrogen and total 

Kjeldahl nitrogen were detected at all six of the stations evaluated for these constituents. During the recent period, upward 

trends in ammonia nitrogen were detected at 2 stations and 

downward trends at 6 stations, among 15 stations analyzed. 

Downward trends in flow-adjusted nutrient concentrations were more frequently detected than upward trends during 

both the recent and long-term periods, with two exceptions: 

nitrite-plus-nitrate concentrations during 1975–2003, and total 

phosphorus concentrations during 1993–2003. Flow-adjusted 

concentrations of nitrite-plus-nitrate nitrogen increased at 

one-third of the stations analyzed during the long-term period 

(11 of 32 stations), decreased at one-third of the stations 

(10 of 32), and had no significant trend at one-third of the 

stations. During the recent period, by contrast, only 1 upward 
Summary, Conclusions, and Challenges for Management of Water Resources 125

trend in nitrite-plus-nitrate concentrations was detected, 

and 12 downward trends were detected, among 52 stations 

analyzed. Downward trends in flow-adjusted concentrations 

of total phosphorus were detected at more than half the stations analyzed (19 of 32 stations) during the long-term period; 

3 upward trends were detected. During the recent period, 

however, most of the significant trends detected for total phosphorus concentrations were upward (17 upward and 6 downward trends among 83 stations analyzed), indicating possible 

reversals to the long-term water-quality improvements. 

Progress has been made in reducing nutrient 

concentrations in the largest drainage basins of the region. 

Monitored drainage areas for the 11 largest drainage basins 

evaluated for trends (drainage areas greater than 1,000 mi2) 

encompass 72,275 mi2, or about 44 percent of the region. One 

of these 11 large drainage basins was evaluated for the recent 

period only, and one for the long-term period only. Long-term 

downward trends in flow-adjusted concentrations of nutrients 

predominated at 7 of the 10 stations with long-term records; 

20 downward trends were detected out of 35 analyses for these 

10 stations. The 1993–2003 results, however, indicate recent 

increases in nutrient concentrations in some drainage basins. 

The preponderance of downward trends during the long-term 

period, viewed in conjunction with the absence of significant 

trends for about half of the analyses in these large basins for 

the recent period, may indicate that the largest reductions in 

nutrient concentrations took place prior to the 1990s. 

Instream Concentration Trends in Relation to 

Proposed Nutrient Criteria

Trends in modeled instream nutrient concentrations for 

the long-term and recent periods were analyzed by using a 

coupled statistical model of streamflow and water quality. 

This method provides a modeled “reference concentration” 

for a constituent, that is, a typical concentration for the 

initial year of analysis that is not affected by seasonal 

variability or by fluctuations in annual streamflow conditions. 

Modeled reference concentrations, in conjunction with trend 

results, provide a useful indicator for assessing the status of 

instream water quality. Trend results for modeled instream 

concentrations and associated reference concentrations were 

evaluated relative to ecoregion-based criteria proposed by 

the U.S. Environmental Protection Agency (USEPA) for total 

nitrogen and total phosphorus. 

Concentrations of nutrients in many of the streams 

evaluated in this study persist at levels that are likely to 

affect aquatic habitat adversely and promote freshwater or 

coastal eutrophication. Modeled reference concentrations for 

total nitrogen at the start of the 1993–2003 period exceeded 

proposed criteria by a factor of two or more at 21 of the 

46 stations analyzed. Concentrations at 4 of these 21 stations 

exceeded proposed criteria by a factor of five or more. No 

trends in modeled instream concentrations of total nitrogen 

were detected during 1993–2003 at 17 of these 21 stations, 

indicating persistent elevated concentrations throughout 

the period of analysis at more than one-third of the 

46 stations analyzed. 

Modeled reference concentrations for total phosphorus at 

the start of the 1993–2003 period exceeded proposed criteria 

by a factor of two or more at 24 of the 46 stations analyzed for 

trends. At 4 of the 24 stations, modeled reference concentrations exceeded proposed criteria by an order of magnitude. No 

trends in modeled instream concentrations of total phosphorus 

were detected for 1993–2003 at 19 of these 24 stations, and 

upward trends were detected at 5 stations, indicating persistence of elevated instream total phosphorus concentrations 

throughout the period of analysis at about one-half of the 

46 stations analyzed. 

Evaluation of trend results and reference concentrations 

demonstrated mixed results in terms of instream nutrient conditions in the 11 largest drainage basins analyzed. Reference 

concentrations for total nitrogen or total phosphorus exceeded 

proposed criteria for several large rivers for the recent period, 

which may appear to contradict the water-quality improvements indicated by the many long-term downward trends 

detected for nutrient concentrations in large drainage basins. 

However, both analyses contain useful information. Substantial progress has been made in reduction of nutrient delivery 

to large streams in the region, as indicated by the long-term 

downward trends in flow-adjusted nutrient concentrations. 

The starting point of nutrient concentrations for these longterm downward trends was high, however, and modeled 

instream concentrations for the start of the 1993–2003 period, 

in conjunction with trend results for that period, indicate that 

instream concentrations still exceed proposed criteria for total 

nitrogen and total phosphorus in several major streams. 

Annual Nutrient Loads and Trends in Loads

Stream discharge has varied substantially from year to 

year during the period of record evaluated, and annual nutrient loads have varied accordingly. During the recent period, 

annual mean flows varied substantially, with extremely low 

annual mean flows in 1995 and 2002, and high annual mean 

flows in 1996 and 2003, depending on the geographic area. In 

some parts of the region, particularly drainage basins in the 

southernmost areas, few annual mean flows near long-term 

median flow conditions were present in the 1993–2003 period, 

and consequently annual nutrient loads that represent typical 

conditions are less readily identified than annual loads during 

more extreme hydrologic conditions. 

Annual loads of total nitrogen and total phosphorus in the 

recent period were generally substantially greater in 2003 than 

in 2002, particularly in southern parts of the region. Water 

years 2002 and 2003 represent the minimum and maximum 

annual nutrient loads, respectively, estimated during the recent 

period for some streams. Annual loads of total nitrogen or total 

phosphorus or both differ by an order of magnitude for those 

two years in some locations. 
126 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Most of the long-term records available for load estimation and trend analysis are for streams with drainage basins 

that have large percentages of urban or agricultural land, and 

most of these drainage basins receive point-source discharges. 

Most of the significant trends in load have been detected in 

the more developed drainage basins of the region, where 

changes in land use and point-source loadings have a major 

effect on nitrogen and phosphorus delivery to streams. Trends 

in nutrient loads, coupled with similar trends in flow-adjusted 

concentrations, are likely to indicate long-term changes in the 

delivery of nutrients to streams in the region, because trends in 

streamflow were detected at only two stations. 

Trends in nutrient loads were primarily downward 

during 1975–2003. Few statistically significant trends in 

nutrient loads were detected during the 1993–2003 period. 

Downward trends in total nitrogen loads were detected at more 

than one-third of the stations analyzed (12 of 32) during the 

long-term period; 1 upward trend was detected. Long-term 

trends in loads of nitrite-plus-nitrate nitrogen were detected 

at almost half the stations analyzed (15 of 32), with results 

about evenly divided between upward (7) and downward (8) 

trends. Long-term downward trends in ammonia nitrogen and 

total Kjeldahl nitrogen loads were detected at the six stations 

evaluated for these constituents. Three downward trends in 

loads of ammonia nitrogen were detected among nine stations 

evaluated for the recent period, and no upward trends were 

detected. All the streams evaluated for ammonia nitrogen 

and total Kjeldahl nitrogen receive point-source discharges. 

Downward trends in total phosphorus loads were detected 

at slightly more than half of the stations analyzed (17 of 

32) during the long-term period; no upward trends in total 

phosphorus loads were detected. 

The 10 largest drainage basins with long-term records 

(drainage areas greater than 1,000 mi2) had either downward 

trends in nutrient loads or no trends in load during the 1975–

2003 period. No upward trends in nutrient loads were detected 

in these 10 drainage basins during either period of analysis. 

The 10 largest rivers with long-term records deliver the largest 

freshwater inflows and nutrient loads to major estuaries on 

the northeast coast, including Long Island Sound, Delaware 

Bay, and Chesapeake Bay. Consequently, long-term downward 

trends in nutrient loads represent critical regional waterquality improvements. 

The Susquehanna, Potomac, Connecticut, Delaware, 

and James River Basins (in descending order of size) are the 

largest monitored basins for which long-term records were 

available for evaluation of trends in nutrient loads. Longterm downward trends in total nitrogen loads were detected 

for the Connecticut, Delaware, and James Rivers. No trend 

in total nitrogen load was detected for the Potomac River for 

either the long-term period or the recent period; however, the 

1993–2003 period contains both extreme high and extreme 

low annual loads, and five of the six highest annual loads are 

in the 1993–2003 period. Although no trend in total nitrogen 

load was detected for the Susquehanna River for either period 

of analysis, a downward trend in total Kjeldahl nitrogen load 

and a highly significant (p-value less than or equal to 0.01) 

downward trend in ammonia nitrogen load were detected for 

the long-term (1979–2003) period. Highly significant longterm downward trends in total phosphorus loads were detected 

for the Connecticut and Delaware Rivers. A downward trend 

in ammonia nitrogen load for the James River was the only 

trend in load detected for any nutrients for these five rivers 

during the recent period. 

Effects of Land Use and Population Density on 

Nutrient Yields

Annual nutrient yields were used to compare the effects 

of major land uses in the region on stream nutrient transport. 

Annual yields were evaluated and summary statistics were 

calculated for 93 stations for total nitrogen and for 92 stations for total phosphorus, including stations with annual load 

estimates for all or some of the water years in the 1993–2003 

period. Summary statistics for individual stations were further 

summarized into statistics for minimum, mean, median, and 

maximum yields for all stations and for four land-use categories (undeveloped, urban, urban/agricultural, and agricultural), 

on the basis of percentages of land uses in each drainage 

basin. Mean annual yields for nine basins in the region that 

were evaluated in a national study of undeveloped basins are 

included in the summary statistics for median yields for all 

basins and median yields for undeveloped basins. 

Estimated yields for all drainage basins and years 

evaluated ranged over four orders of magnitude for total 

nitrogen and five orders of magnitude for total phosphorus. 

Estimated total nitrogen yields for the 1993–2003 period 

ranged from 41 to 32,000 pounds per square mile per year 

(lb/mi2/yr). Minimum total nitrogen yields ranged from 41 

to 15,000 lb/mi2/yr, median yields ranged from 290 to 

26,000 lb/mi2/yr, and maximum yields ranged from 

1,300 to 32,000 lb/mi2/yr. Estimated total phosphorus yields 

ranged from less than 10 to 16,000 lb/mi2/yr. Minimum total 

phosphorus yields ranged from 1.4 to 900 lb/mi2/yr, median 

yields ranged from 12 to 1,900 lb/mi2/yr, and maximum yields 

ranged from less than 100 to 16,000 lb/mi2/yr. 

Drainage basins classified as undeveloped in this report 

include small, largely forested and sparsely populated drainage 

basins, and also large drainage basins that meet the land-use 

criteria for undeveloped basins, but include urban areas and 

major point-source discharges. In 27 undeveloped (generally 

forested) drainage basins in the region, with undeveloped 

land ranging from 75 to 100 percent of basin area, median 

total nitrogen yields range from 290 to 4,800 lb/mi2/yr, with 

a median of 1,300 lb/mi2/yr, for the 1993–2003 period. It is 

likely that even the most pristine drainage basins in the region 

have total nitrogen yields that are elevated relative to natural 

conditions, because of high rates of atmospheric deposition of 

nitrogen in parts of the northeastern United States. Maximum 

total nitrogen yields for 14 undeveloped drainage basins range 

from 1,300 to 6,400 lb/mi2/yr. 
Summary, Conclusions, and Challenges for Management of Water Resources 127

Median total phosphorus yields range from 12 to 

330 lb/mi2/yr for the 26 undeveloped basins evaluated, with 

a median of 63 lb/mi2/yr. Maximum total phosphorus yields 

range from 67 to 860 lb/mi2/yr for 14 undeveloped basins, 

with a median of 230 lb/mi2/yr. Undeveloped drainage basins 

with maximum total phosphorus yields that exceed about 

200 lb/mi2/yr are generally drained by streams that receive 

point-source discharges. 

Total nitrogen and total phosphorus yields for drainage 

basins with 90 percent or more undeveloped land and no point 

sources provide an indication of nutrient yields under the least 

developed conditions in the study area, although this information is incomplete, in terms of both geographic distribution 

and years of record. Among the drainage basins evaluated in 

this study, the drainage basins that are least affected by human 

land-use and waste-disposal practices (although not totally 

unaffected) generally have median total nitrogen yields in the 

range of 300 to 1,700 lb/mi2/yr and median total phosphorus 

yields in the range of 30 to 100 lb/mi2/yr. In large drainage 

basins that receive point-source discharges and have large 

percentages of undeveloped land, streamflow with low nutrient loads from relatively undeveloped headwater areas dilutes 

streamflow in the more urbanized downstream reaches, and 

dampens but does not eliminate the point-source “signal” of 

higher nutrient loads. 

Although the northeastern United States is one of the 

most highly urbanized areas in the nation, agricultural land is a 

major source of nutrients. Nutrients derived from agricultural 

land contribute to some of the highest total nitrogen yields in 

the study area. Drainage basins with substantial agricultural 

influences on water quality are concentrated primarily in the 

central and southern parts of the study area. Total nitrogen 

yields are high on an annual basis in many agricultural basins. 

Several agricultural basins in the southern part of the study 

area have median total nitrogen yields that equal or exceed 

10,000 lb/mi2/yr. In some cases, periods of record are short, 

and additional years of record would be necessary to verify 

yield ranges and typical conditions. Median total nitrogen 

yields for 24 agricultural basins range from 1,700 to 

26,000 lb/mi2/yr, with a median for all 24 basins of 

5,000 lb/mi2/yr. Median total phosphorus yields range from 

94 to 1,000 lb/mi2/yr for the 24 agricultural basins evaluated, 

with a median yield of 280 lb/mi2/yr. 

The maximum total nitrogen yield and maximum total 

phosphorus yield estimated for all stations in the region were 

both in small (less than 50 mi2) agricultural drainage basins 

with no major point sources. The maximum total nitrogen 

yield, 32,000 lb/mi2/yr, was estimated for East Mahantango 

Creek in Pennsylvania (about 55 percent agricultural land). 

The maximum total phosphorus yield, 16,000 lb/mi2/yr, was 

estimated for the Neshanic River in New Jersey (about 

60 percent agricultural land). 

Nutrient yields in agricultural and urban/agricultural 

drainage basins generally increase with increasing percentages of developed land in a drainage basin, although there 

is a wide range in yields at most levels of development, and 

point-source effects in some basins complicate interpretations. 

Agricultural and urban/agricultural drainage basins dominate 

the highest maximum yields for total nitrogen (greater than the 

75th percentile for all stations), whereas urban drainage basins 

are more numerous among the highest yields for total phosphorus. Agricultural land has been converted to residential 

developments and other forms of urbanized land in some parts 

of the study area during the 1993–2003 period for which nutrient yields have been analyzed. Consequently, annual nutrient 

yields are likely to have been affected by changing sources of 

nutrients in some drainage basins. 

The Susquehanna and the Potomac River Basins are the 

largest monitored drainage basins in the region with complete 

records for the 1993–2003 period, and provide the largest 

freshwater inflows to the Chesapeake Bay. Although both 

drainage basins are more than 60 percent undeveloped, stream 

quality in both basins is affected by agricultural influences. 

The Susquehanna and Potomac River Basins are classified 

as agricultural drainage basins in this report, with about 

28 and 34 percent agricultural land, respectively, and less than 

10 percent urbanized land. Median total nitrogen yields 

for the Susquehanna (5,200 lb/mi2/yr) and Potomac 

(5,100 lb/mi2/yr) are close to the median (of all medians) 

for total nitrogen yields for all agricultural drainage basins 

(5,000 lb/mi2/yr). The median total phosphorus yield for 

the Potomac (280 lb/mi2/yr) is similar to the median (of all 

medians) for all agricultural basins. The median for 

the Susquehanna, by contrast, is somewhat lower 

(190 lb/mi2/yr), possibly because phosphorus tends to bind 

to sediment particles that settle and are retained in 

impoundments upstream from the monitoring station. 

Urbanized drainage basins encompass a wide range of 

total developed land, and a wide range in the predominant type 

of urban development. Consequently, nutrient yields vary over 

a wide range in drainage basins classified as urbanized in this 

report. Conditions affecting nutrient yields in urbanized drainage basins include population density, percentages of urbanized versus undeveloped land, the presence or absence of point 

sources, the magnitude of point-source discharges relative to 

streamflow, and nonpoint source water-quality effects related 

to the intensity of the urbanized land development. Point 

sources have not been evaluated quantitatively for most drainage basins in the region; however, some general conclusions 

can be drawn. Urban drainage basins with the highest total 

nitrogen and total phosphorus yields are generally drained by 

streams that are receiving waters for major point discharges, 

and drainage areas for these streams are generally small, usually less than 300 mi2

 and in many cases less than 100 mi2. 

Urbanized drainage basins with low total nitrogen and total 

phosphorus yields are generally larger drainage basins with 

point sources and a high percentage of undeveloped land; 

small drainage basins with presumed small point sources and 

a large percentage of undeveloped land; and small drainage 

basins with low-density development, no point sources, and a 

large percentage of undeveloped land. 
128 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Median total nitrogen yields range from 1,400 to 

17,000 lb/mi2/yr in 26 urbanized drainage basins, with a 

median (of all medians) of 4,000 lb/mi2/yr. Maximum total 

nitrogen yields for urbanized basins range from 2,000 to 

22,000 lb/mi2/yr, with a median of 4,800 lb/mi2/yr. 

Median total phosphorus yields in 26 urbanized drainage basins range from 43 to 1,900 lb/mi2

/yr, with a median of 

210 lb/mi2/yr. Maximum total phosphorus yields for urbanized basins encompass a wide range, from less than 100 to 

more than 6,000 lb/mi2/yr. Maximum total phosphorus yields 

exceeded 1,000 lb/mi2/yr in several urban basins. 

The urbanized drainage basins with the highest nutrient yields are generally drained by streams that are receiving 

waters for major point-source discharges. For many small 

streams in the older urbanized areas of the northeastern U.S., 

wastewater discharges contribute a substantial part of the 

stream nutrient loads under most conditions. Total nitrogen 

yields are consistently high in several small drainage basins 

(300 mi2 or less) that have major urban influences on water 

quality in the form of large percentages of urbanized land, 

high population densities, or major point-source discharges. 

Minimum total phosphorus yields in urbanized drainage basins 

are high relative to other land-use categories. The maximum 

values for minimum and median total phosphorus yields are 

in urbanized drainage basins. Routinely high annual nutrient 

yields in urban drainage basins illustrate the challenges of 

managing nutrients in the older urbanized areas of the region. 

Nutrient yields generally increase with increasing percentages of developed land in urbanized drainage basins where 

no major point sources are present, and where water quality is 

influenced primarily by nonpoint sources. This relation differs 

for total nitrogen and total phosphorus. High total phosphorus 

yields are common in small, highly urbanized drainage basins. 

Identification of specific urban nonpoint sources and land-use 

conditions may be necessary to address nutrient management 

in older urbanized areas. 

Streams draining highly urbanized areas of the region are 

major nutrient sources, delivering nutrient loads to the main 

stems of major rivers and in some cases directly to estuaries 

and coastal areas. Smaller urbanized drainage basins (less than 

about 300 mi2), including drainage basins with and without 

point sources, have some of the highest nutrient yields in the 

study area. 

Urban and agricultural land use (more than 20 to 30 percent of a drainage basin) has increased median total nitrogen 

yields by factors of three to five and has increased median 

total phosphorus yields by factors of three to six, relative to 

undeveloped drainage basins in the northeastern United States, 

although the yield ranges for both constituents are large for 

all land use categories. The amount of developed land has a 

pronounced effect on the magnitude of nutrient yields. Where 

more than about 50 percent of a drainage area is developed, 

in either agricultural or urban land or both, the potential for 

very high yields is present. In 14 of 31 basins with more than 

50 percent developed land, maximum total nitrogen yields 

equaled or exceeded 10,000 lb/mi2/yr. Most drainage basins 

with more than 50 percent developed land (23 of 31 basins) 

had maximum total phosphorus yields that exceeded 

600 lb/mi2/yr, and in 18 of these basins, maximum total 

phosphorus yields equaled or exceeded 1,000 lb/mi2/yr. Major 

point-source discharges contribute to elevated nutrient yields 

throughout the study area, in agricultural, urban/agricultural, 

and forested basins, as well as in urban basins. 

Annual nutrient yields varied considerably from year to 

year in response to changing hydrologic conditions. Large 

differences in maximum yields for total nitrogen and total 

phosphorus were observed between 2002, a very dry year 

throughout the region, and 2003, a very wet year in many parts 

of the region. Order-of-magnitude differences in yield between 

the two years were observed in several drainage basins in New 

Jersey, Pennsylvania, and Maryland; the Potomac River Basin; 

and all drainage basins in Virginia. 

Effects of Point Sources

Four drainage basins were evaluated for the effects of 

point-source discharges: the Quinebaug River Basin in eastern 

Connecticut and adjacent areas of Massachusetts and Rhode 

Island, the Raritan River Basin in New Jersey, the Patuxent 

River Basin in Maryland, and the James River Basin in 

Virginia. Comparison of long-term and recent trends in flowadjusted nutrient concentrations, and trends in nutrient loads, 

indicates that in the basins evaluated, the major reductions in 

delivery of nutrients to streams, whether from point sources 

or other sources, may have taken place prior to the 1993–2003 

period of analysis. The reduction in delivery of nutrients is 

consistent with the history of improvements in wastewatertreatment facilities in the region, although this relationship 

has not been documented quantitatively or in historical detail. 

A trend in stream discharge, for the 1975–2003 period, was 

detected at only one of the stations analyzed. Consequently, 

the trends in nutrient loads, for most stations, coupled with 

similar trends in flow-adjusted concentrations of nutrients, 

appear to indicate changes in the delivery of nutrients to 

streams, with long-term reductions detected for most 

nutrients evaluated. 

The prevalence of long-term downward trends in nutrient 

loads in these four drainage basins indicates substantial 

improvements in nutrient-related water-quality conditions. 

Long-term downward trends in loads of ammonia nitrogen 

or total Kjeldahl (total-ammonia-plus-organic) nitrogen are 

consistent with wastewater-treatment processes that have 

reduced aquatic toxicity problems by converting ammonia 

to nitrate prior to discharge, and by removing organic 

material from wastewater. Long-term downward trends 

in total phosphorus loads are consistent with wastewatertreatment improvements and with the implementation of 

phosphate detergent bans in states of the region. The absence 

of downward trends in load for most constituents during 

the 1993–2003 period, coupled with modeled instream 

concentrations for the early 1990s that exceed proposed 
Acknowledgments 129

nutrient criteria in several of these waste-receiving streams, 

indicates that additional challenges remain in reducing the 

delivery of nutrients to streams from point sources. 

At most of the monitoring stations evaluated in these 

drainage basins, long-term downward trends in nutrient loads 

were paired with long-term downward trends in flow-adjusted 

concentrations of nutrients, indicating reductions in the delivery of nutrients to streams. During the recent period, however, 

the following upward trends in flow-adjusted nutrient concentrations may indicate processes or changes that are increasing nutrient delivery to some streams in recent years: three 

upward trends in total nitrogen concentrations, two upward 

trends in ammonia nitrogen concentrations, and three upward 

trends in total phosphorus concentrations. 

The interannual variation in stream nutrient loads was 

much greater than the interannual variation in the contribution of point-source loads to the stream, for most years at 

most monitoring stations evaluated in the Quinebaug, Raritan, 

Patuxent, and James River Basins; that is, the point source 

load was fairly constant from year to year. During dry years, 

however, nutrient loads contributed by nonpoint sources were 

minimal, and the total nutrient load from all point sources in 

the drainage area approached the level of the nutrient load 

transported by the stream. This general pattern was observed 

in all four drainage basins. The pattern was more pronounced 

in the more highly developed drainage basins, but was noticeable in less developed drainage basins in extremely dry years. 

The implication of this finding is that point-source loads are 

likely to be the predominant source of the nutrients in many 

rivers of the region during critical times. At times of low flow, 

the nutrient load from nonpoint sources is small, and less 

streamflow is available to dilute the point-source nutrients. 

Consequently, high nutrient concentrations, derived from point 

sources, are observed during times of low flow. 

Challenges for Management of Nutrients in the 

Northeastern United States

Forested land cover generally constitutes 65 percent or 

more of the drainage area in the large drainage basins of the 

region, and cleaner streamflow from forested areas is a source 

of dilution for the more impaired waters in downstream urbanized reaches of major rivers. Development pressures in previously undeveloped forested areas of large drainage basins may 

contribute to future increases in nutrient yields, both through 

the increases in nutrient sources and the changes in hydrologic 

processes in headwater streams. Changes in land use have the 

potential to alter flow regimes substantially and to increase the 

delivery of nutrients to downstream reaches. These headwater changes may threaten long-term gains resulting from 

improved wastewater treatment along historically impaired 

main-stem reaches of major streams in the region. 

Trend results for flow-adjusted nutrient concentrations, 

modeled instream nutrient concentrations, and nutrient loads 

show that over three decades, major gains have been made 

in controlling nutrient-related water-quality problems that 

result from point-source effluent in many streams of the 

region. Although nutrient concentrations are substantially 

reduced in many drainage basins, concentrations in many 

waste-receiving streams, including some of the major streams 

in the region, persist at levels that may promote freshwater 

or estuarine eutrophication and may adversely affect aquatic 

habitat conditions. 

Small, heavily developed drainage basins (either urban or 

agricultural) have extremely high nutrient yields during high 

streamflows. Many small drainage basins with major pointsource discharges have consistently high nutrient yields during 

all streamflow conditions. These small drainage basins contribute large nutrient loads to major streams, and sometimes 

directly to estuarine areas. 

Long-term nutrient data are sparse in many areas of the 

region for small, nonpoint drainage basins with a variety of 

land uses and a range of development intensity. Additional 

long-term monitoring, and regional modeling, will help to 

identify expectable nutrient yields from various land uses 

more accurately. 

Acknowledgments

Information and assistance from the following U.S. 

Geological Survey (USGS) staff is appreciated: Jacob Gibs, 

New Jersey; Michael Langland, Pennsylvania; Doug Moyer, 

Virginia; Jeff Raffensperger, Maryland; Jonathan Kennen, 

New Jersey; Virginia de Lima, Jon Morrison, Craig Brown, 

and Karen Beaulieu, Connecticut; James M. Caldwell, Maine; 

Craig Johnston and Sarah Flanagan, New Hampshire; Laura 

Medalie, Vermont; Pat Phillips, New York; Robert Breault, 

Rhode Island; David K. Mueller and Lori Sprague, Colorado; 

Naomi Nakagaki, California; Michael Yurewicz, Office of 

Water Quality; Charles Crawford, NAWQA National Support. 

Thomas Trombley, Connecticut, provided spatial data analyses for maps in this report. Colleague review was provided 

by: David Lorenz, Minnesota, and Joel Blomquist, Maryland. 

Editorial review was provided by Lyn Osburn. 

Paul Stacey, Connecticut Department of Environmental 

Protection, provided information on point-sources discharges 

in Connecticut. Kelly Streich, Connecticut Department of 

Environmental Protection, provided helpful comments on 

the report. 

Information and interpretations in this report rely on 

streamflow measurements and water-quality data compiled 

during several decades by USGS hydrologic technicians and 

hydrologists in 13 states and 7 NAWQA study units, and on 

water-quality analyses by scientists at the USGS National 

Water Quality Laboratory in Denver, Colorado. Interpretations in this report would not have been possible without 

their efforts. 
130 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

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Tables 8, 15
136 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 Table 8. Land-use and population characteristics for 130 monitored drainage basins in the northeastern United States.—Continued [Source for land-use data: 1992 National Land Cover Dataset (NLCDe 92) (Vogelmann and others, 1998; enhanced as described by Nakagaki and Wolock, 2005). Source for population data: Nakagaki, N., U.S. Geological Survey, written commun., 2005. Sources for information on point sources: U.S. Environmental Protection Agency, 2005, McMahon and others, 2007, p. 5. Sequence numbers and station locations shown in figure 4. Land-use codes defined in table 7. Total forested land includes wooded wetlands. Total undeveloped land includes herbaceous wetlands and open water. mi2, square miles; Mgal/d, million gallons per day; N, No; Y, yes; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural; AU, agricultural/urban; >, greater than] Station sequence number (fig. 4) Station name Drainage area (mi2

)

Population 

per square 

mile, 

2000

Major municipal point 

discharge 

(>1 Mgal/d) 

in basin

Undeveloped site 

(Clark 

and others, 2000)

Landuse 

code

Land-use percentages

Total 

urban 

land

Total 

agricultural 

land

Total 

developed 

land

Total 

forested 

land

Total 

undeveloped 

land

1 Penobscot River at Eddington, Maine 7,764 10 Yes

N UN 0.7 1.4 4.7 88.0 95.3

2 Kennebec River at North Sidney, Maine 5,403 28 Yes

N UN 1.4 5.6 10.1 82.1 89.8

3 Wild River at Gilead, Maine 69.6 8 No

Y UN 0.1 0.0 0.2 99.4 99.9

4 Saco River at Cornish, Maine 1,293 34 No

N UN 2.0 3.5 6.4 88.8 93.6

5 Stillwater River near Sterling, Mass. 31.6 163 No

N UN 6.0 8.8 15.6 80.7 84.4

6 Merrimack River below Concord River at 

Lowell, Mass.

4,635 324 Yes

N UR 11.5 6.7 18.7 74.7 81.3

7 Aberjona River at Winchester, Mass. 24.7 2,955 No

N UR 79.3 0.0 79.7 16.1 20.3

8 Charles River above Watertown Dam at 

Watertown, Mass.

271 1,479 Yes

N UR 40.4 4.3 45.0 49.3 55.0

9 Branch River at Forestdale, R.I. 91.2 275 Yes

N UN 8.8 5.1 14.1 81.8 85.9

10 Pawtuxet River at Cranston, R.I. 200 565 Yes

N UR 13.8 4.4 19.0 75.1 81.0

11 Pawcatuck River at Westerly, R.I. 295 231 No

N UN 9.7 4.6 14.7 82.4 85.0

12 Willimantic River at Merrow, Conn. 94.0 202 Unknown

N UN 8.6 8.3 17.3 78.3 82.7

13 Shetucket River at South Windham, Conn. 408 256 Yes

N UR 10.0 11.0 21.3 73.8 78.7

14 Quinebaug River at Quinebaug, Conn. 155 262 Yes

N UR 10.9 7.4 18.7 75.5 81.3

15 French River at North Grosvenordale, Conn. 101 559 Yes

N UR 17.2 8.5 26.3 64.6 73.8

16 Quinebaug River at Putnam, Conn. 328 347 Yes

N UR 12.5 10.7 23.6 69.8 76.4

17 Quinebaug River at Cotton Bridge Road near 

Pomfret, Conn.

342 344 Yes

N UR 12.3 11.3 24.1 69.3 75.9

18 Quinebaug River at Jewett City, Conn. 713 264 Yes

N UN 9.2 11.4 21.1 73.5 78.9

19 Ammonoosuc River at Bethlehem Junction, N.H. 87.6 10 No

Y UN 1.0 0.4 2.6 92.3 97.4

20 White River at West Hartford, Vt. 690 34 No

N UN 0.8 12.5 13.8 84.8 86.2

21 Green River near Colrain, Mass. 41.4 31 No

Y UN 0.3 6.1 6.4 92.5 93.6

22 Connecticut River at Thompsonville, Conn. 9,660 122 Yes

N UN 5.0 8.3 14.0 81.0 84.9

23 Broad Brook at Broad Brook, Conn. 15.5 381 No

N UA 13.1 39.0 52.4 45.9 47.6

24 Bunnell (Burlington) Brook near Burlington, Conn. 4.10 181 No

N UN 5.6 18.8 24.9 71.1 75.1

25 Farmington River at Unionville, Conn. 378 130 Yes

N UN 5.2 4.8 10.2 84.0 89.8
Table 8 137

Table 8. Land-use and population characteristics for 130 monitored drainage basins in the northeastern United States.—Continued[Source for land-use data: 1992 National Land Cover Dataset (NLCDe 92) (Vogelmann and others, 1998; enhanced as described by Nakagaki and Wolock, 2005). Source for population data: Nakagaki, N., U.S. Geological Survey, written commun., 2005. Sources for information on point sources: U.S. Environmental Protection Agency, 2005, McMahon and others, 2007, p. 5. Sequence numbers and station locations shown in figure 4. Land-use codes defined in table 7. Total forested land includes wooded wetlands. Total undeveloped land includes herbaceous wetlands and open water. mi2, square miles; Mgal/d, million gallons per day; N, No; Y, yes; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural; AU, agricultural/urban; >, greater than]

Station 

sequence 

number 

(fig. 4)

Station name

Drainage 

area 

(mi2)

Population 

per square 

mile, 

2000

Major municipal point 

discharge 

(>1 Mgal/d) 

in basin

Undeveloped site 

(Clark 

and others, 2000)

Landuse 

code

Land-use percentages

Total 

urban 

land

Total 

agricultural 

land

Total 

developed 

land

Total 

forested 

land

Total 

undeveloped 

land

26 Pequabuck River at Farmington, Conn. 57.2 1,316 Unknown N UR 38.6 7.8 47.0 49.7 53.027 Farmington River at Tariffville, Conn. 577 329 Yes N UR 13.0 6.7 20.0 75.1 80.028 Hockanum River near East Hartford, Conn. 73.4 1,331 Yes N UR 42.7 11.2 54.4 42.2 45.729 Mattabesset River at Route 372 at East Berlin, Conn. 48.1 1,285 No N UR 41.5 12.7 54.7 41.0 45.330 Salmon River near East Hampton, Conn. 100 272 No N UR 10.8 12.5 23.6 71.8 76.431 Quinnipiac River near Meriden, Conn. 69.6 1,109 Unknown N UR 48.7 1.1 50.7 46.9 49.332 Quinnipiac River at Wallingford, Conn. 115 1,396 Yes N UR 54.2 1.1 56.0 41.1 44.133 Housatonic River near Ashley Falls, Mass. 465 192 Yes N UR 12.8 10.4 23.5 72.8 76.534 Housatonic River near New Milford, Conn. 1,022 130 Yes N UN 8.2 13.9 22.3 74.4 77.735 Still River at Route 7 at Brookfield Center, Conn. 62.3 1,474 Yes N UR 50.0 3.6 53.6 43.6 46.436 Shepaug River near Roxbury, Conn. 132 122 No N UN 6.7 18.9 25.9 67.8 74.137 Housatonic River at Stevenson, Conn. 1,544 236 Yes N UR 11.3 13.7 25.2 70.6 74.838 Naugatuck River near Waterville, Conn. 136 373 Unknown N UR 13.0 12.8 26.0 69.2 74.139 Naugatuck River at Beacon Falls, Conn. 260 935 Yes N UR 25.0 10.1 35.5 60.2 64.640 Saugatuck River near Redding, Conn. 21.0 347 No N UR 21.4 4.4 25.9 70.7 74.141 Norwalk River at Winnipauk, Conn. 33.0 728 Yes N UR 50.2 2.8 53.1 44.8 46.942 Massapequa Creek at Massapequa, N.Y. 38.0 3,269 No N UR 84.0 0.7 85.1 14.6 15.043 East Meadow Brook at Freeport, N.Y. 31.0 3,595 No N UR 90.2 0.0 90.2 9.2 9.844 Pines Brook at Malverne, N.Y. 10.0 5,991 No N UR 93.1 0.1 93.1 6.5 6.945 Canajoharie Creek near Canajoharie, N.Y. 59.7 47 No N AG 1.0 61.1 62.1 37.7 37.946 Lisha Kill northwest of Niskayuna, N.Y. 15.6 1,422 No N UR 62.6 6.5 69.4 29.2 30.747 Mohawk River at Cohoes, N.Y. 3,450 171 Yes N AG 5.8 27.2 33.1 65.2 66.948 Esopus Creek at Allaben, N.Y. 63.7 13 No Y UN 0.4 0.9 1.3 98.7 98.749 Wallkill River near Sussex, N.J. 60.8 515 Unknown N UR 14.2 16.3 30.9 64.3 69.150 Hackensack River at Rivervale, N.J. 58.0 1,989 No N UR 66.8 0.5 67.4 25.0 32.6
138 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 Table 8. Land-use and population characteristics for 130 monitored drainage basins in the northeastern United States.—Continued [Source for land-use data: 1992 National Land Cover Dataset (NLCDe 92) (Vogelmann and others, 1998; enhanced as described by Nakagaki and Wolock, 2005). Source for population data: Nakagaki, N., U.S. Geological Survey, written commun., 2005. Sources for information on point sources: U.S. Environmental Protection Agency, 2005, McMahon and others, 2007, p. 5. Sequence numbers and station locations shown in figure 4. Land-use codes defined in table 7. Total forested land includes wooded wetlands. Total undeveloped land includes herbaceous wetlands and open water. mi2, square miles; Mgal/d, million gallons per day; N, No; Y, yes; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural; AU, agricultural/urban; >, greater than] Station sequence number (fig. 4) Station name Drainage area (mi2

)

Population 

per square 

mile, 

2000

Major municipal point 

discharge 

(>1 Mgal/d) 

in basin

Undeveloped site 

(Clark 

and others, 2000)

Landuse 

code

Land-use percentages

Total 

urban 

land

Total 

agricultural 

land

Total 

developed 

land

Total 

forested 

land

Total 

undeveloped 

land

51 Whippany River near Pine Brook, N.J. 68.5 1,655 Yes

N UR 54.4 3.3 57.7 39.1 42.3

52 Passaic River at Two Bridges, N.J. 361 1,300 Yes

N UR 41.0 4.5 45.6 51.0 54.4

53 Pequannock River at Macopin Intake Dam, N.J. 63.7 197 No

N UN 5.6 0.8 6.4 87.8 93.6

54 Ramapo River near Mahwah, N.J. 120 635 Yes

N UR 20.7 1.5 22.3 74.2 77.7

55 Passaic River at Little Falls, N.J. 762 1,018 Yes

N UR 32.5 2.9 35.5 60.1 64.5

56 Saddle River at Lodi, N.J. 54.6 2,624 Yes

N UR 88.9 1.0 90.0 9.5 10.0

57 Rahway River near Springfield, N.J. 25.5 4,372 No

N UR 79.7 0.4 80.1 19.3 19.9

58 Rahway River at Rahway, N.J. 40.9 4,227 No

N UR 83.5 0.4 83.9 15.5 16.1

59 Mulhockaway Creek at Van Syckel, N.J. 11.8 212 No

N AG 3.1 25.4 28.6 71.2 71.4

60 South Branch Raritan River at Stanton, N.J. 147 515 Yes

N UA 11.7 28.6 40.3 57.4 59.7

61 Neshanic River at Reaville, N.J. 25.7 342 No

N AG 8.5 59.9 68.3 31.5 31.7

62 Lamington (Black) River near Pottersville, N.J. 32.8 616 Yes

N UR 17.5 15.8 33.8 63.9 66.2

63 Lamington River at Burnt Mills, N.J. 100 355 Unknown

N UA 11.5 27.7 39.4 59.7 60.6

64 North Branch Raritan River near Raritan, N.J. 190 464 Yes

N UA 15.7 27.3 43.1 56.2 56.9

65 Raritan River at Manville, N.J. 490 526 Yes

N UA 14.7 34.4 49.2 48.9 50.8

66 Stony Brook at Princeton, N.J. 44.5 544 No

N UA 13.3 33.5 47.0 52.5 53.0

67 Millstone River at Blackwells Mills, N.J. 258 803 Yes

N UA 19.1 36.1 55.3 43.5 44.7

68 Raritan River at Queens Bridge at Bound Brook, N.J. 804 653 Yes

N UA 17.5 34.2 51.7 46.6 48.3

69 Manalapan Brook at Federal Road near 

Manalapan, N.J.

20.9 373 Unknown

N AG 4.4 48.7 53.1 46.2 46.9

70 Manasquan River at Squankum, N.J. 44.0 891 No

N UA 22.1 27.8 49.9 47.0 50.1

71 Toms River near Toms River, N.J. 123 464 No

N UR 13.3 5.5 23.5 74.9 76.5

72 Mullica River at outlet of Atsion Lake at Atsion, N.J. 26.7 342 Unknown

N UR 11.5 5.2 17.5 78.2 82.5

73 Blue Anchor Brook at Elm, N.J. 4.86 231 Unknown

N UA 13.0 43.7 57.8 40.5 42.2

74 Hammonton Creek at Wescoatville, N.J. 9.57 435 Unknown

N AU 20.3 50.3 70.6 27.9 29.4

75 Batsto River at Batsto, N.J. 67.8 96 No

N UN 2.3 12.1 14.4 82.8 85.6
Table 8 139

Table 8. Land-use and population characteristics for 130 monitored drainage basins in the northeastern United States.—Continued[Source for land-use data: 1992 National Land Cover Dataset (NLCDe 92) (Vogelmann and others, 1998; enhanced as described by Nakagaki and Wolock, 2005). Source for population data: Nakagaki, N., U.S. Geological Survey, written commun., 2005. Sources for information on point sources: U.S. Environmental Protection Agency, 2005, McMahon and others, 2007, p. 5. Sequence numbers and station locations shown in figure 4. Land-use codes defined in table 7. Total forested land includes wooded wetlands. Total undeveloped land includes herbaceous wetlands and open water. mi2, square miles; Mgal/d, million gallons per day; N, No; Y, yes; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural; AU, agricultural/urban; >, greater than]

Station 

sequence 

number 

(fig. 4)

Station name

Drainage 

area 

(mi2)

Population 

per square 

mile, 

2000

Major municipal point 

discharge 

(>1 Mgal/d) 

in basin

Undeveloped site 

(Clark 

and others, 2000)

Landuse 

code

Land-use percentages

Total 

urban 

land

Total 

agricultural 

land

Total 

developed 

land

Total 

forested 

land

Total 

undeveloped 

land

76 East Branch Bass River near New Gretna, N.J. 8.11 21 No N UN 2.1 0.2 2.4 96.6 97.677 Great Egg Harbor River at Weymouth, N.J. 154 500 Unknown N UR 17.6 17.9 37.3 61.5 62.778 Maurice River at Norma, N.J. 112 484 No N UA 22.3 28.3 50.9 48.1 49.179 Cohansey River at Seeley, N.J. 28.0 174 No N AG 3.4 78.4 81.8 17.6 18.280 Delaware River at Port Jervis, N.Y. 3,070 49 Yes N UN 2.0 10.6 12.6 84.7 87.481 Biscuit Brook above Pigeon Brook at Frost 

Valley, N.Y.

3.72 8 No Y UN 0.0 0.0 0.0 100.0 100.0

82 Delaware River at Montague, N.J. 3,480 57 Yes N UN 2.4 9.8 12.2 85.0 87.883 Flat Brook near Flatbrookville, N.J. 64.0 39 No N UN 1.5 6.9 8.5 90.1 91.684 Delaware River at Portland, Pa. 4,165 78 Yes N UN 3.0 9.1 12.1 85.0 87.985 Paulins Kill at Blairstown, N.J. 126 249 Yes N AG 8.2 25.6 34.2 61.9 65.886 Jordan Creek near Schnecksville, Pa. 53.0 192 No N AG 1.9 65.0 66.9 32.7 33.187 Musconetcong River at Riegelsville, N.J. 156 606 Unknown N UA 11.6 21.6 33.7 61.4 66.388 Delaware River at Riegelsville, N.J. 6,328 197 Yes N UN 5.2 14.9 20.6 76.7 79.489 Delaware River at Lumberville, Pa. 6,598 199 Yes N UN 5.2 15.7 21.3 75.9 78.790 Delaware River at Trenton, N.J. 6,780 207 Yes N UN 5.3 16.4 22.1 75.2 78.091 Doctors Creek at Allentown, N.J. 17.4 186 Unknown N AG 5.3 56.7 62.0 36.5 38.092 Little Neshaminy Creek at Valley Road near 

Neshaminy, Pa.

26.8 1,344 Yes N UA 37.3 31.2 68.9 30.3 31.1

93 McDonalds Branch in Byrne State Forest, N.J. 2.35 10 No Y UN 0.0 0.0 9.1 90.9 90.994 North Branch Rancocas Creek at Pemberton, N.J. 118 293 No N UR 12.2 3.8 19.1 77.8 80.995 Cooper River at Haddonfield, N.J. 17.0 2,546 No N UR 69.4 6.5 78.8 20.5 21.296 French Creek near Phoenixville, Pa. 59.1 166 No N AG 1.8 34.2 36.0 63.3 64.097 Schuylkill River at Philadelphia, Pa. 1,893 689 Yes N UA 13.9 37.3 52.6 45.9 47.498 Raccoon Creek near Swedesboro, N.J. 26.9 344 No N AG 6.9 65.7 72.6 27.0 27.499 Salem River at Woodstown, N.J. 14.6 122 No N AG 5.2 75.3 80.5 18.1 19.5

100 Nanticoke River near Bridgeville, Del. 75.4 85 Yes N AG 4.4 54.7 59.1 40.7 40.9
140 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 Table 8. Land-use and population characteristics for 130 monitored drainage basins in the northeastern United States.—Continued [Source for land-use data: 1992 National Land Cover Dataset (NLCDe 92) (Vogelmann and others, 1998; enhanced as described by Nakagaki and Wolock, 2005). Source for population data: Nakagaki, N., U.S. Geological Survey, written commun., 2005. Sources for information on point sources: U.S. Environmental Protection Agency, 2005, McMahon and others, 2007, p. 5. Sequence numbers and station locations shown in figure 4. Land-use codes defined in table 7. Total forested land includes wooded wetlands. Total undeveloped land includes herbaceous wetlands and open water. mi2, square miles; Mgal/d, million gallons per day; N, No; Y, yes; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural; AU, agricultural/urban; >, greater than] Station sequence number (fig. 4) Station name Drainage area (mi2

)

Population 

per square 

mile, 

2000

Major municipal point 

discharge 

(>1 Mgal/d) 

in basin

Undeveloped site 

(Clark 

and others, 2000)

Landuse 

code

Land-use percentages

Total 

urban 

land

Total 

agricultural 

land

Total 

developed 

land

Total 

forested 

land

Total 

undeveloped 

land

101 Choptank River near Greensboro, Md. 113 98 No

N AG 2.9 48.5 51.4 48.0 48.6

102 Chesterville Branch near Crumpton, Md. 6.12 31 No

N AG 0.4 90.8 91.2 7.9 8.8

103 Susquehanna River at Danville, Pa. 11,220 127 Yes

N AG 3.5 26.9 30.7 68.1 69.3

104 Young Womans Creek near Renovo, Pa. 46.2 8 No

Y UN 0.0 0.3 0.4 99.6 99.6

105 West Branch Susquehanna River at Lewisburg, Pa. 6,847 67 Yes

N UN 1.5 13.7 16.9 82.6 83.1

106 East Mahantango Creek at Klingerstown, Pa. 44.7 36 No

N AG 0.6 54.9 56.1 43.6 43.9

107 Bobs Creek near Pavia, Pa. 16.6 39 No

N UN 0.1 9.1 9.3 90.6 90.7

108 Cedar Run at Eberlys Mill, Pa. 12.6 1,966 No

N UA 59.0 30.8 93.5 6.2 6.5

109 Big Spring Run near Willow Street, Pa. 1.77 1,282 No

N AU 12.5 81.3 93.9 5.6 6.2

110 Unnamed Tributary to Big Spring Run near 

Lampeter, Pa.

1.42 477 No

N AG 8.2 88.0 96.3 3.4 3.7

111 Susquehanna River at Conowingo, Md. 27,100 145 Yes

N AG 3.2 28.2 32.2 66.6 67.8

112 Patuxent River near Unity, Md. 34.8 153 No

N AG 1.1 62.5 63.6 35.6 36.4

113 Little Patuxent River at Savage, Md. 98.4 1,362 No

N UA 24.1 42.8 67.1 32.1 32.9

114 Patuxent River near Bowie, Md. 348 1,023 Yes

N UA 19.1 37.5 59.5 38.9 40.5

115 South Fork South Branch Potomac River near 

Moorefield, W. Va.

277 10 No

Y UN 0.2 10.0 10.8 88.9 89.2

116 Conococheague Creek at Fairview, Md. 494 168 Yes

N AG 3.5 56.9 60.9 38.3 39.1

117 Potomac River at Shepherdstown, W. Va. 5,939 83 Yes

N AG 1.8 23.6 26.4 72.9 73.6

118 Muddy Creek at Mount Clinton, Va. 14.3 75 No

N AG 5.0 68.3 73.4 26.5 26.7

119 South Fork Shenandoah River at Front Royal, Va. 1,634 132 Yes

N AG 7.8 35.5 43.7 55.6 56.3

120 North Fork Shenandoah River near Strasburg, Va. 770 70 Yes

N AG 5.8 35.5 41.6 57.8 58.4

121 Shenandoah River at Millville, W. Va. 3,041 114 Yes

N AG 6.7 35.8 42.9 56.4 57.1

122 Potomac River at Chain Bridge, at Washington, D.C. 11,570 179 Yes

N AG 4.5 33.8 39.1 60.1 60.9

123 Accotink Creek near Annandale, Va. 23.9 4,170 No

N UR 85.2 2.5 88.7 11.0 11.2

124 Rappahannock River near Fredericksburg, Va. 1,595 70 Yes

N AG 4.5 34.7 39.9 59.6 60.1

125 Pamunkey River near Hanover, Va. 1,078 60 Yes

N AG 2.7 23.0 27.9 69.1 72.1
Table 8 141

Table 8. Land-use and population characteristics for 130 monitored drainage basins in the northeastern United States.—Continued[Source for land-use data: 1992 National Land Cover Dataset (NLCDe 92) (Vogelmann and others, 1998; enhanced as described by Nakagaki and Wolock, 2005). Source for population data: Nakagaki, N., U.S. Geological Survey, written commun., 2005. Sources for information on point sources: U.S. Environmental Protection Agency, 2005, McMahon and others, 2007, p. 5. Sequence numbers and station locations shown in figure 4. Land-use codes defined in table 7. Total forested land includes wooded wetlands. Total undeveloped land includes herbaceous wetlands and open water. mi2, square miles; Mgal/d, million gallons per day; N, No; Y, yes; UN, undeveloped; UR, urban; UA, urban/agricultural; AG, agricultural; AU, agricultural/urban; >, greater than]

Station 

sequence 

number 

(fig. 4)

Station name

Drainage 

area 

(mi2)

Population 

per square 

mile, 

2000

Major municipal point 

discharge 

(>1 Mgal/d) 

in basin

Undeveloped site 

(Clark 

and others, 2000)

Landuse 

code

Land-use percentages

Total 

urban 

land

Total 

agricultural 

land

Total 

developed 

land

Total 

forested 

land

Total 

undeveloped 

land

126 Mattaponi River near Beulahville, Va. 603 78 No N UN 2.2 18.6 24.0 73.8 76.0127 James River at Cartersville, Va. 6,252 65 Yes N UN 3.5 15.0 19.6 79.6 80.4128 Holiday Creek near Andersonville, Va. 8.54 16 No Y UN 0.2 0.6 6.6 93.2 93.5129 Appomattox River at Matoaca, Va. 1,342 49 Yes N UN 1.9 19.9 24.3 74.4 75.7130 Black River at Coventry, Vt. 122 23 No N AG 3.0 22.0 25.8 71.1 74.2

Number of undeveloped basins (UN): 38Number of urban basins (UR): 43Number of urban/agricultural basins (UA): 17Number of agricultural basins (AG): 30Number of agricultural/urban basins (AU): 2

Total number of basins: 130
142 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 Table 15. Trend results for modeled instream nutrient concentrations, proposed criteria for total nitrogen and total phosphorus, modeled reference concentrations for nutrients, and modeled changes in concentration for 47 streams in the northeastern region, 1975–2003 and 1993–2003.—Continued [Source for proposed ecoregional criteria for total nitrogen and total phosphorus: U.S. Environmental Protection Agency (2000a, 2000b, 2000c, 2000d, 2001). Columns for Modeled reference concentration and Modeled change in concentration show program output from statistical model. Significant trend: 

p-value less than or equal to 0.05; highly significant trend: 

p-value less than or equal to 0.01. USEPA, U.S. 

Environmental Protection Agency; mg/L, milligrams per liter; *, highly significant trend; N, no significant trend; --, data unavailable for period or not analyzed]

Station 

sequence 

number 

(table 5)

Station name

Proposed 

USEPA nutrient ecoregion 

criteria 

(mg/L)

Modeled reference 

concentration 

(mg/L)

Trend result for modeled 

instream concentration

Modeled change in concentration 

(mg/L)

1975, 1979, 

or 1982 1993 1975–2003, 1979– 2003, or 1982–2003 1993–2003 1975–2003, 1979– 2003, or 1982–2003 1993–2003

Total nitrogen

13 Shetucket River at South Windham, Conn. 0.71 0.797 0.603 *Down

N -0.2155 0.0626

14 Quinebaug River at Quinebaug, Conn. 0.71 1.183 0.530 *Down *Up -0.4781 0.234418 Quinebaug River at Jewett City, Conn. 0.71 1.036 0.913 *Down

N -0.2100 -0.0361

22 Connecticut River at Thompsonville, Conn. 0.38 0.864 0.624 *Down

N -0.2778 0.0303

23 Broad Brook at Broad Brook, Conn. 0.71 -- 4.259 --

N -- 0.0030

24 Bunnell (Burlington) Brook near Burlington, Conn. 0.71 0.444 0.371

N

N -0.0064 0.0456

25 Farmington River at Unionville, Conn. 0.71 -- 0.270 --

N -- 0.1125

27 Farmington River at Tariffville, Conn. 0.71 0.995 1.018

N

N -0.0920 0.2343

28 Hockanum River near East Hartford, Conn. 0.71 -- 3.480 --

N -- 0.1902

30 Salmon River near East Hampton, Conn. 0.71 0.469 0.436 *Down

N -0.2105 0.0599

32 Quinnipiac River at Wallingford, Conn. 0.71 3.034 3.208

N

N 0.1441 -0.0425

37 Housatonic River at Stevenson, Conn. 0.38 0.780 0.661 *Down

N -0.2332 0.0798

39 Naugatuck River at Beacon Falls, Conn. 0.71 2.581 2.492 *Down *Down -1.1524 -1.228440 Saugatuck River near Redding, Conn. 0.71 0.428 0.307 Down

N -0.1431 0.1236

41 Norwalk River at Winnipauk, Conn. 0.71 1.293 0.642 *Down Up -0.5090 0.155947 Mohawk River at Cohoes, N.Y. 0.54 -- 1.048 --

N -- -0.0951

50 Hackensack River at Rivervale, N.J. 0.71 1.497 1.032 *Down

N -0.4399 0.1393

53 Pequannock River at Macopin Intake Dam, N.J. 0.38 -- 0.500 --

N -- 0.1075

54 Ramapo River near Mahwah, N.J. 0.71 1.162 1.537

N

N 0.2829 -0.0818

55 Passaic River at Little Falls, N.J. 0.69 3.785 3.357 Down

N -0.9749 -0.4089

56 Saddle River at Lodi, N.J. 0.71 4.767 5.794 Up

N 1.4482 1.4165

57 Rahway River near Springfield, N.J. 0.69 -- 1.727 --

N -- 0.0159

58 Rahway River at Rahway, N.J. 0.69 -- 1.407 --

N -- -0.0014

59 Mulhockaway Creek at Van Syckel, N.J. 0.69 -- 1.090 --

N -- -0.1480

61 Neshanic River at Reaville, N.J. 0.69 -- 1.753 --

N -- -0.2486
Table 15 143

Table 15. Trend results for modeled instream nutrient concentrations, proposed criteria for total nitrogen and total phosphorus, modeled reference concentrations for nutrients, and modeled changes in concentration for 47 streams in the northeastern region, 1975–2003 and 1993–2003.—Continued[Source for proposed ecoregional criteria for total nitrogen and total phosphorus: U.S. Environmental Protection Agency (2000a, 2000b, 2000c, 2000d, 2001). Columns for Modeled reference concentration and Modeled change in concentration show program output from statistical model. Significant trend: p-value less than or equal to 0.05; highly significant trend: p-value less than or equal to 0.01. USEPA, U.S. Environmental Protection Agency; mg/L, milligrams per liter; *, highly significant trend; N, no significant trend; --, data unavailable for period or not analyzed]

Station 

sequence 

number 

(table 5)

Station name

Proposed 

USEPA nutrient ecoregion 

criteria 

(mg/L)

Modeled reference 

concentration 

(mg/L)

Trend result for modeled 

instream concentration

Modeled change in concentration 

(mg/L)

1975, 1979, 

or 1982 1993 1975–2003, 1979– 2003, or 1982–2003 1993–2003 1975–2003, 1979– 2003, or 1982–2003 1993–2003

Total nitrogen—Continued

67 Millstone River at Blackwells Mills, N.J. 0.69 -- 2.902 -- N -- 0.339068 Raritan River at Queens Bridge at Bound Brook, N.J. 0.69 2.858 2.316 N N -0.1397 0.378870 Manasquan River at Squankum, N.J. 0.71 -- 0.647 -- N -- -0.034071 Toms River near Toms River, N.J. 0.71 0.739 0.854 *Up *Up 0.3640 0.273575 Batsto River at Batsto, N.J. 0.71 -- 0.386 -- N -- -0.085478 Maurice River at Norma, N.J. 0.71 1.830 1.695 N N 0.0704 0.257882 Delaware River at Montague, N.J. 0.38 -- 0.487 -- Down -- -0.112885 Paulins Kill at Blairstown, N.J. 0.31 1.173 0.958 Down N -0.2279 0.044690 Delaware River at Trenton, N.J. 0.38 1.255 1.277 *Down Down -0.2762 -0.233295 Cooper River at Haddonfield, N.J. 0.71 -- 0.921 -- N -- 0.008097 Schuylkill River at Philadelphia, Pa. 0.69 3.701 -- N -- -0.0500 --98 Raccoon Creek near Swedesboro, N.J. 0.71 1.682 1.658 N N -0.1132 0.1472

101 Choptank River near Greensboro, Md. 0.71 1.427 1.457 *Up *Up 0.2279 0.3257

111 Susquehanna River at Conowingo, Md. -- 1.523 1.526 *Down Down -0.2565 -0.1428

114 Patuxent River near Bowie, Md. 0.69 4.641 2.078 *Down N -2.9237 0.0105116 Conococheague Creek at Fairview, Md. 0.31 -- 5.429 -- N -- -0.2000

122 Potomac River at Chain Bridge, at Washington, D.C. 0.31 1.341 2.010 N N 0.0732 -0.3766124 Rappahannock River near Fredericksburg, Va. 0.69 0.747 0.577 N N -0.1075 0.1010125 Pamunkey River near Hanover, Va. 0.69 0.614 0.653 *Up *Up 0.1323 0.1764126 Mattaponi River near Beulahville, Va. 0.69 0.553 0.623 N N 0.0060 0.0632127 James River at Cartersville, Va. 0.69 0.659 0.478 *Down N -0.2084 0.0086129 Appomattox River at Matoaca, Va. 0.69 0.546 0.587 N Up -0.0217 0.0698
144 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 Table 15. Trend results for modeled instream nutrient concentrations, proposed criteria for total nitrogen and total phosphorus, modeled reference concentrations for nutrients, and modeled changes in concentration for 47 streams in the northeastern region, 1975–2003 and 1993–2003.—Continued [Source for proposed ecoregional criteria for total nitrogen and total phosphorus: U.S. Environmental Protection Agency (2000a, 2000b, 2000c, 2000d, 2001). Columns for Modeled reference concentration and Modeled change in concentration show program output from statistical model. Significant trend: 

p-value less than or equal to 0.05; highly significant trend: 

p-value less than or equal to 0.01. USEPA, U.S. 

Environmental Protection Agency; mg/L, milligrams per liter; *, highly significant trend; N, no significant trend; --, data unavailable for period or not analyzed]

Station 

sequence 

number 

(table 5)

Station name

Proposed 

USEPA nutrient ecoregion 

criteria 

(mg/L)

Modeled reference 

concentration 

(mg/L)

Trend result for modeled 

instream concentration

Modeled change in concentration 

(mg/L)

1975, 1979, 

or 1982 1993 1975–2003, 1979– 2003, or 1982–2003 1993–2003 1975–2003, 1979– 2003, or 1982–2003 1993–2003

Ammonia nitrogen

14 Quinebaug River at Quinebaug, Conn. -- -- 0.042 -- Down -- -0.020718 Quinebaug River at Jewett City, Conn. -- 0.076 0.069

N

N -0.0206 -0.0231

32 Quinnipiac River at Wallingford, Conn. -- -- 0.208 --

N -- -0.0911

61 Neshanic River at Reaville, N.J. -- -- 0.013 --

N -- -0.0000

67 Millstone River at Blackwells Mills, N.J. -- -- 0.035 -- Up -- 0.069268 Raritan River at Queens Bridge at Bound Brook, N.J. -- 0.525 0.047 *Down

N -0.4850 -0.0074

111 Susquehanna River at Conowingo, Md. -- 0.073 -- *Down -- -0.0324 --

114 Patuxent River near Bowie, Md. -- 1.097 0.170 *Down *Down -1.0115 -0.0771

127 James River at Cartersville, Va. -- 0.023 0.016 *Down *Down -0.0168 -0.0100129 Appomattox River at Matoaca, Va. -- 0.039 0.054 *Down Down -0.0217 -0.0238

Total Kjeldahl nitrogen

14 Quinebaug River at Quinebaug, Conn. -- 0.839 -- *Down -- -0.4474 --18 Quinebaug River at Jewett City, Conn. -- 0.580 -- *Down -- -0.1669 --32 Quinnipiac River at Wallingford, Conn. -- 2.043 -- *Down -- -1.4193 --68 Raritan River at Queens Bridge at Bound Brook, N.J. -- 1.264 -- *Down -- -0.7411 --

111 Susquehanna River at Conowingo, Md. -- 0.494 -- *Down -- -0.2099 --

114 Patuxent River near Bowie, Md. -- 1.805 -- *Down -- -1.2688 --

Nitrite-plus-nitrate nitrogen

13 Shetucket River at South Windham, Conn. -- 0.356 0.393 *Down

N -0.0682 -0.0485

14 Quinebaug River at Quinebaug, Conn. -- 0.282 0.260

N

N 0.0073 0.0518

18 Quinebaug River at Jewett City, Conn. -- 0.374 0.481

N

N 0.0502 -0.0929

22 Connecticut River at Thompsonville, Conn. -- 0.359 0.327

N

N -0.0015 0.0277

23 Broad Brook at Broad Brook, Conn. -- -- 3.743 --

N -- 0.1465

24 Bunnell (Burlington) Brook near Burlington, Conn. -- 0.164 0.149

N

N -0.0187 -0.0003

25 Farmington River at Unionville, Conn. -- -- 0.183 --

N -- -0.0417

27 Farmington River at Tariffville, Conn. -- 0.524 0.641 *Up

N 0.2110 0.1158

28 Hockanum River near East Hartford, Conn. -- -- 2.545 --

N -- 0.2524

30 Salmon River near East Hampton, Conn. -- 0.201 0.297 *Down

N -0.0691 -0.0775
Table 15 145

Table 15. Trend results for modeled instream nutrient concentrations, proposed criteria for total nitrogen and total phosphorus, modeled reference concentrations for nutrients, and modeled changes in concentration for 47 streams in the northeastern region, 1975–2003 and 1993–2003.—Continued[Source for proposed ecoregional criteria for total nitrogen and total phosphorus: U.S. Environmental Protection Agency (2000a, 2000b, 2000c, 2000d, 2001). Columns for Modeled reference concentration and Modeled change in concentration show program output from statistical model. Significant trend: p-value less than or equal to 0.05; highly significant trend: p-value less than or equal to 0.01. USEPA, U.S. Environmental Protection Agency; mg/L, milligrams per liter; *, highly significant trend; N, no significant trend; --, data unavailable for period or not analyzed]

Station 

sequence 

number 

(table 5)

Station name

Proposed 

USEPA nutrient ecoregion 

criteria 

(mg/L)

Modeled reference 

concentration 

(mg/L)

Trend result for modeled 

instream concentration

Modeled change in concentration 

(mg/L)

1975, 1979, 

or 1982 1993 1975–2003, 1979– 2003, or 1982–2003 1993–2003 1975–2003, 1979– 2003, or 1982–2003 1993–2003

Nitrite-plus-nitrate nitrogen—Continued

32 Quinnipiac River at Wallingford, Conn. -- 1.403 2.625 *Up N 1.5353 -0.307437 Housatonic River at Stevenson, Conn. -- 0.347 0.342 N N 0.0179 0.043439 Naugatuck River at Beacon Falls, Conn. -- 1.022 1.055 Down N -0.1827 -0.140940 Saugatuck River near Redding, Conn. -- 0.138 0.120 N N -0.0216 -0.007641 Norwalk River at Winnipauk, Conn. -- 0.562 0.392 Down N -0.1444 -0.005247 Mohawk River at Cohoes, N.Y. -- -- 0.689 -- N -- -0.069750 Hackensack River at Rivervale, N.J. -- 0.523 0.461 N N -0.1356 -0.096353 Pequannock River at Macopin Intake Dam, N.J. -- -- 0.184 -- N -- 0.055354 Ramapo River near Mahwah, N.J. -- 0.541 1.292 *Up N 0.7029 -0.082255 Passaic River at Little Falls, N.J. -- 1.126 2.719 *Up N 1.0667 -0.545956 Saddle River at Lodi, N.J. -- 2.292 4.463 *Up N 3.0125 1.279857 Rahway River near Springfield, N.J. -- -- 1.356 -- N -- 0.040458 Rahway River at Rahway, N.J. -- -- 0.867 -- N -- 0.083759 Mulhockaway Creek at Van Syckel, N.J. -- -- 0.931 -- N -- -0.193661 Neshanic River at Reaville, N.J. -- -- 1.430 -- N -- -0.217967 Millstone River at Blackwells Mills, N.J. -- -- 2.410 -- N -- 0.074968 Raritan River at Queens Bridge at Bound Brook, N.J. -- 1.610 1.878 *Up N 0.5762 0.293870 Manasquan River at Squankum, N.J. -- -- 0.563 -- *Down -- -0.216271 Toms River near Toms River, N.J. -- 0.315 0.454 *Up N 0.2375 0.068275 Batsto River at Batsto, N.J. -- -- 0.168 -- *Down -- -0.101978 Maurice River at Norma, N.J. -- 1.326 1.387 N N 0.1474 0.065782 Delaware River at Montague, N.J. -- -- 0.295 -- *Down -- -0.129785 Paulins Kill at Blairstown, N.J. -- 0.550 0.795 N N 0.0096 -0.008790 Delaware River at Trenton, N.J. -- 0.877 1.003 *Down *Down -0.1215 -0.243095 Cooper River at Haddonfield, N.J. -- -- 0.349 -- Down -- -0.1124
146 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 Table 15. Trend results for modeled instream nutrient concentrations, proposed criteria for total nitrogen and total phosphorus, modeled reference concentrations for nutrients, and modeled changes in concentration for 47 streams in the northeastern region, 1975–2003 and 1993–2003.—Continued [Source for proposed ecoregional criteria for total nitrogen and total phosphorus: U.S. Environmental Protection Agency (2000a, 2000b, 2000c, 2000d, 2001). Columns for Modeled reference concentration and Modeled change in concentration show program output from statistical model. Significant trend: 

p-value less than or equal to 0.05; highly significant trend: 

p-value less than or equal to 0.01. USEPA, U.S. 

Environmental Protection Agency; mg/L, milligrams per liter; *, highly significant trend; N, no significant trend; --, data unavailable for period or not analyzed]

Station 

sequence 

number 

(table 5)

Station name

Proposed 

USEPA nutrient ecoregion 

criteria 

(mg/L)

Modeled reference 

concentration 

(mg/L)

Trend result for modeled 

instream concentration

Modeled change in concentration 

(mg/L)

1975, 1979, 

or 1982 1993 1975–2003, 1979– 2003, or 1982–2003 1993–2003 1975–2003, 1979– 2003, or 1982–2003 1993–2003

Nitrite-plus-nitrate nitrogen—Continued

97 Schuylkill River at Philadelphia, Pa. -- 2.488 -- *Up -- 0.5650 --98 Raccoon Creek near Swedesboro, N.J. -- 1.112 1.398

N

N -0.2091 -0.3642

101 Choptank River near Greensboro, Md. -- 0.937 1.291 *Up

N 0.4117 0.0410

111 Susquehanna River at Conowingo, Md. -- 0.973 1.299

N *Down -0.0117 -0.3039

114 Patuxent River near Bowie, Md. -- 2.668 1.434 *Down

N -1.5857 -0.1483

116 Conococheague Creek at Fairview, Md. -- -- 4.995 -- Down -- -0.4722

122 Potomac River at Chain Bridge, at Washington, D.C. -- 0.548 1.807 *Up Down 0.4984 -0.7537124 Rappahannock River near Fredericksburg, Va. -- 0.539 0.312

N

N -0.2666 -0.0925

125 Pamunkey River near Hanover, Va. -- 0.246 0.282 *Up

N 0.0701 0.0190

126 Mattaponi River near Beulahville, Va. -- 0.138 0.155

N

N -0.0065 0.0358

127 James River at Cartersville, Va. -- 0.295 0.219 *Down

N -0.1766 -0.0953

129 Appomattox River at Matoaca, Va. -- 0.143 0.142

N

N -0.0233 -0.0196

Total phosphorus

13 Shetucket River at South Windham, Conn. 0.03125 0.095 0.021 *Down Up -0.0606 0.013914 Quinebaug River at Quinebaug, Conn. 0.03125 0.246 0.036 *Down

N -0.2157 0.0086

18 Quinebaug River at Jewett City, Conn. 0.03125 0.130 0.046 *Down *Up -0.0806 0.037322 Connecticut River at Thompsonville, Conn. 0.01000 0.088 0.033 *Down

N -0.0468 0.0091

23 Broad Brook at Broad Brook, Conn. 0.03125 -- 0.092 --

N -- -0.0157

24 Bunnell (Burlington) Brook near Burlington, Conn. 0.03125 0.020 0.010 *Down

N -0.0120 -0.0011

25 Farmington River at Unionville, Conn. 0.03125 -- 0.018 --

N -- 0.0085

27 Farmington River at Tariffville, Conn. 0.03125 0.148 0.087 *Down *Up -0.0719 0.048728 Hockanum River near East Hartford, Conn. 0.03125 -- 0.364 --

N -- -0.0293

30 Salmon River near East Hampton, Conn. 0.03125 0.018 0.017 *Down

N -0.0110 0.0046

32 Quinnipiac River at Wallingford, Conn. 0.03125 0.504 0.241 *Down

N -0.2237 -0.0436

37 Housatonic River at Stevenson, Conn. 0.01000 0.052 0.021 *Down

N -0.0342 0.0021

39 Naugatuck River at Beacon Falls, Conn. 0.03125 0.364 0.227

N *Up 0.0645 0.1696

40 Saugatuck River near Redding, Conn. 0.03125 0.022 0.012 *Down

N -0.0102 0.0033

41 Norwalk River at Winnipauk, Conn. 0.03125 0.082 0.030 *Down Up -0.0365 0.0133
Table 15 147

Table 15. Trend results for modeled instream nutrient concentrations, proposed criteria for total nitrogen and total phosphorus, modeled reference concentrations for nutrients, and modeled changes in concentration for 47 streams in the northeastern region, 1975–2003 and 1993–2003.—Continued[Source for proposed ecoregional criteria for total nitrogen and total phosphorus: U.S. Environmental Protection Agency (2000a, 2000b, 2000c, 2000d, 2001). Columns for Modeled reference concentration and Modeled change in concentration show program output from statistical model. Significant trend: p-value less than or equal to 0.05; highly significant trend: p-value less than or equal to 0.01. USEPA, U.S. Environmental Protection Agency; mg/L, milligrams per liter; *, highly significant trend; N, no significant trend; --, data unavailable for period or not analyzed]

Station 

sequence 

number 

(table 5)

Station name

Proposed 

USEPA nutrient ecoregion 

criteria 

(mg/L)

Modeled reference 

concentration 

(mg/L)

Trend result for modeled 

instream concentration

Modeled change in concentration 

(mg/L)

1975, 1979, 

or 1982 1993 1975–2003, 1979– 2003, or 1982–2003 1993–2003 1975–2003, 1979– 2003, or 1982–2003 1993–2003

Total phosphorus—Continued

47 Mohawk River at Cohoes, N.Y. 0.03300 -- 0.034 -- N -- 0.004850 Hackensack River at Rivervale, N.J. 0.03125 0.058 0.065 N N -0.0096 0.013553 Pequannock River at Macopin Intake Dam, N.J. 0.01000 -- 0.025 -- N -- -0.013254 Ramapo River near Mahwah, N.J. 0.03125 0.131 0.120 N N 0.0089 -0.008355 Passaic River at Little Falls, N.J. 0.03656 0.445 0.372 N N -0.0472 0.071756 Saddle River at Lodi, N.J. 0.03125 0.975 0.369 N *Up -0.2135 0.424457 Rahway River near Springfield, N.J. 0.03656 -- 0.054 -- N -- 0.005158 Rahway River at Rahway, N.J. 0.03656 -- 0.071 -- N -- 0.025559 Mulhockaway Creek at Van Syckel, N.J. 0.03656 -- 0.018 -- N -- -0.005861 Neshanic River at Reaville, N.J. 0.03656 -- 0.042 -- N -- 0.009967 Millstone River at Blackwells Mills, N.J. 0.03656 -- 0.195 -- N -- 0.066968 Raritan River at Queens Bridge at Bound Brook, N.J. 0.03656 0.169 0.160 N N 0.0156 0.034270 Manasquan River at Squankum, N.J. 0.03125 -- 0.099 -- N -- -0.004771 Toms River near Toms River, N.J. 0.03125 0.048 0.024 *Down N -0.0296 0.006975 Batsto River at Batsto, N.J. 0.03125 -- 0.033 -- N -- 0.062678 Maurice River at Norma, N.J. 0.03125 0.083 0.014 *Down N -0.0640 -0.002082 Delaware River at Montague, N.J. 0.01000 -- 0.041 -- N -- -0.017985 Paulins Kill at Blairstown, N.J. 0.01000 0.065 0.025 *Down N -0.0404 0.001190 Delaware River at Trenton, N.J. 0.01000 0.081 0.057 *Down N -0.0246 -0.006295 Cooper River at Haddonfield, N.J. 0.03125 -- 0.198 -- N -- -0.007397 Schuylkill River at Philadelphia, Pa. 0.03656 0.229 -- N -- -0.0161 --98 Raccoon Creek near Swedesboro, N.J. 0.03125 0.118 0.117 Up N 0.0409 0.0326

101 Choptank River near Greensboro, Md. 0.03125 0.070 0.045 N *Up -0.0022 0.0510

111 Susquehanna River at Conowingo, Md. -- 0.046 0.021 *Down *Up -0.0127 0.0137

114 Patuxent River near Bowie, Md. 0.03656 0.971 0.116 *Down Up -0.8548 0.0476
148 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003 Table 15. Trend results for modeled instream nutrient concentrations, proposed criteria for total nitrogen and total phosphorus, modeled reference concentrations for nutrients, and modeled changes in concentration for 47 streams in the northeastern region, 1975–2003 and 1993–2003.—Continued [Source for proposed ecoregional criteria for total nitrogen and total phosphorus: U.S. Environmental Protection Agency (2000a, 2000b, 2000c, 2000d, 2001). Columns for Modeled reference concentration and Modeled change in concentration show program output from statistical model. Significant trend: 

p-value less than or equal to 0.05; highly significant trend: 

p-value less than or equal to 0.01. USEPA, U.S. 

Environmental Protection Agency; mg/L, milligrams per liter; *, highly significant trend; N, no significant trend; --, data unavailable for period or not analyzed]

Station 

sequence 

number 

(table 5)

Station name

Proposed 

USEPA nutrient ecoregion 

criteria 

(mg/L)

Modeled reference 

concentration 

(mg/L)

Trend result for modeled 

instream concentration

Modeled change in concentration 

(mg/L)

1975, 1979, 

or 1982 1993 1975–2003, 1979– 2003, or 1982–2003 1993–2003 1975–2003, 1979– 2003, or 1982–2003 1993–2003

Total phosphorus—Continued

116 Conococheague Creek at Fairview, Md. 0.01000 -- 0.114 --

N -- 0.0166

122 Potomac River at Chain Bridge, at Washington, D.C. 0.01000 0.078 0.030 Down Up -0.0206 0.0230124 Rappahannock River near Fredericksburg, Va. 0.03656 0.039 0.033

N

N -0.0038 0.0022

125 Pamunkey River near Hanover, Va. 0.03656 0.042 0.066 *Up *Up 0.0494 0.0542126 Mattaponi River near Beulahville, Va. 0.03656 0.051 0.059

N

N -0.0022 -0.0041

127 James River at Cartersville, Va. 0.03656 0.064 0.100

N

N -0.0086 -0.0110

129 Appomattox River at Matoaca, Va. 0.03656 0.032 0.047

N

N 0.0039 -0.0063

Suspended sediment

22 Connecticut River at Thompsonville, Conn. -- -- 6.345 --

N -- -2.3477

47 Mohawk River at Cohoes, N.Y. -- -- 7.595 -- *Down -- -3.989368 Raritan River at Queens Bridge at Bound Brook, N.J. -- 13.276 8.989 *Down

N -7.4157 -3.4364

101 Choptank River near Greensboro, Md. -- 5.689 5.535 *Down

N -2.5506 -0.4262

111 Susquehanna River at Conowingo, Md. -- 9.468 6.345 *Down Down -3.6231 -2.3601

114 Patuxent River near Bowie, Md. -- 34.451 24.526 Down

N -14.3559 2.9439

116 Conococheague Creek at Fairview, Md. -- -- 10.428 --

N -- 9.7100

122 Potomac River at Chain Bridge, at Washington, D.C. -- -- 9.588 --

N -- -2.4078
Appendix 1 149

Appendix 1. Methods—Data Retrieval, 

Screening, and Modification

Contents

USGS Water-Quality Data Retrieval and Screening ...................................................................150

National Stream Water-Quality Monitoring Networks (WQN) Data ...............................150

National Water Information System (NWISWeb) ..............................................................150

Data Modifications ...........................................................................................................................150

Recensoring..............................................................................................................................150

Parameter Codes, Calculated Values, and Order of Precedence for Use 

in Analyses ..................................................................................................................150

Reference...........................................................................................................................................151
150 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Water-quality constituent and parameter code

Date when 

NWQL started 

reporting values 

with laboratoryreporting levels

Dissolved ammonia (00608) 10/1/1999

Dissolved nitrite (00613) 10/4/2000

Dissolved organic nitrogen plus ammonia (00623) 10/1/1998

Total organic nitrogen plus ammonia (00625) 10/1/1998

Dissolved nitrite plus nitrate (00631) 10/1/1999

Total phosphorus (00665) 10/1/1998

Dissolved phosphorus (00666) 10/1/1998

Appendix 1. Methods—Data Retrieval, Screening, and Modification

By R. Edward Hickman

USGS Water-Quality Data Retrieval and 

Screening

U.S. Geological Survey (USGS) water-quality data were 

obtained from National Stream Quality Accounting Network 

(NASQAN) and Hydrologic Benchmark Network (HBN) files, 

referred to collectively as the National Stream Water-Quality 

Monitoring Networks (WQN) (Alexander and others, 1997), 

and from online retrievals from the USGS National Water 

Information System (NWISWeb). These two datasets 

were merged. 

National Stream Water-Quality Monitoring 

Networks (WQN) Data

Water-quality data were obtained from CD–ROMs containing data from NASQAN and HBN (Alexander and others, 

1997). Data were retrieved from files for nutrients, major ions, 

and physical properties, and then merged. 

National Water Information System (NWISWeb)

Stream water-quality stations were identified and 

retrieved on a state-by-state basis. A list of all surface-waterquality stations was retrieved for each state. Those stations 

in the study area (Hydrologic Regions 01 and 02) that had 

a drainage area of one square mile or more were identified. 

Water-quality data for these stations were retrieved. Data from 

all states were merged and duplicates records were removed. 

Data Modifications

Recensoring

Water-quality constituents with recent values reported 

with laboratory-reporting limits (LRLs) were identified from 

the Laboratory Information Management System (LIMS) of 

the USGS National Water Quality Laboratory (NWQL). For 

each constituent, the value of each censored concentration 

was set to half the original value if the sample was collected 

after the date the NWQL started using LRLs for at least one 

method of analysis; these dates were available through LIMS. 

This procedure follows the recommendation of Helsel (2005). 

Censored values of dissolved ammonia (parameter code 

00608) prior to October 1, 1997, were reset to 0.02 milligrams 

per liter (mg/L) (as nitrogen), following NAWQA Program 

recommendations (D.K. Mueller, U.S. Geological Survey, 

written commun., 2004).

Parameter Codes, Calculated Values, and Order 

of Precedence for Use in Analyses

Total nitrogen was set equal to parameter code 00600 

(see next table). If 00600 was unavailable, total nitrogen was 

calculated by combining parameters: 00625 + nitrite-plusnitrate, or nitrite-plus-nitrate + 49570 + 00623. In either case, 

total nitrogen was calculated by summing estimated or uncensored values; if the sum was less than 0.2 mg/L the value was 

set to <0.2 mg/L.

Ammonia nitrogen was set equal to 00608.

Nitrite-plus-nitrate was set equal to one of the following 

parameters, if available, listed in order of precedence: 00631, 

00630, 00618, or 00620. 

Total ammonia-plus-organic nitrogen (total Kjeldahl 

nitrogen) was set equal to 00625. 

Total phosphorus was either set equal to 00665 or calculated from 00666 and 00667 by use of the following method 

(where “r” is the remark code and “p” is the constituent concentration value for that parameter code):
Appendix 1 151

If r00667 and r00666 are both not equal to “<”, 

then p00665=p00666+p00667

If r00667 equals “<” and r00666 is not equal to “<”, 

then p00665=p00666

If r00667 is not equal to “<” and r00666 equals “<”, 

then p00665=p00667

If r00667 equals “<” and r00666 equals “<”, 

then p00665=p00667

Suspended sediment was set equal to 80154. 

Reference

Alexander, R.B., Slack, J.R., Ludtke, A.S., Fitzgerald, K.K., 

and Schertz, T.L., 1997, Data from selected U.S. Geological 

Survey National Stream Water-Quality Monitoring Networks (WQN) on CD–ROM: U.S. Geological Survey Fact 

Sheet FS–013–97, 2 p.

Water-quality constituents 

and parameter codes Description of water-quality constituent Calculated from or set equal to (in order of precedence for use in analyses)

(Remarks and values for the following)

PHOSPHORUS Phosphorus, total mg/L 00665, (00667 + 00666)

00665 Phosphorus, total mg/L

00667 Phosphorus, particulate, mg/L

00666 Phosphorus, diss, mg/L

NITROGEN Total nitrogen, in mg/L as N 00600, (00625 + 00631), (49570 + 00623 + 00631)

00600 Total nitrogen, in mg/L as N

49570 Particulate-N, mg/L

TOT.ORG.N NH3+orgN, wu mg/L as N 00625

00625 NH3+orgN, Total mg/L as N

00623 NH3+orgN, Diss mg/L as N

DISS.AMMONIA Ammonia, Diss mg/L as N 00608

00608 Ammonia, Diss mg/L as N

NITRATE Dissolved nitrate plus nitrite, in mg/L as N 00631, 00630, 00618, 00620

00631 Dissolved nitrate plus nitrite, in mg/L as N

00630 Total nitrate plus nitrite

00618 Dissolved nitrate

00620 Total nitrate

00613 Dissolved nitrite

00615 Total nitrite

SUSPSED Suspended sediment 80154

80154 Suspended sediment
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Appendix 2 153

Appendix 2. Methods—Stations Used in 

Analysis of Discharge Conditions (CD–ROM)

[In pocket]

Table

2–1. List of U.S. Geological Survey streamgages used in analysis of streamflow conditions, 

and summary of analyses performed
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Appendix 3 155

Appendix 3. Methods—Flow-Adjusted 

Trend Analysis with Tobit Regression in the 

S-ESTREND System

Contents

Flow-Adjusted Trend Analysis ........................................................................................................156

References.........................................................................................................................................157
156 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Appendix 3. Methods—Flow-Adjusted Trend Analysis with Tobit Regression in 

the S-ESTREND System

By R. Edward Hickman

Flow-Adjusted Trend Analysis

U.S. Geological Survey (USGS) water-quality stations 

were selected for analysis of flow-adjusted trends in total 

nitrogen and total phosphorus based on the availability of 

nutrient concentration data during water years 1993–2003 and 

the availability of a streamflow measurement associated with 

each water-quality value. Trends in dissolved nitrite-plusnitrate and dissolved ammonia were analyzed at stations in 

four basins selected for analysis of point source information, if 

sufficient water-quality data were available.

Trends were identified with the S-PLUS version of the 

ESTREND system (Slack and others, 2003). The ESTREND 

program (Schertz and others, 1991) was developed by the 

USGS to identify trends in water quality in streams. The 

program provides three methods to identify trends, and Tobit 

regression was the method selected to identify trends in this 

study.

Schertz and others (1991) recommend the amount of 

data required by the Tobit regression method to determine 

trends for periods longer than 5 years. First, a minimum of 

10 detected observations are needed. Second, a minimum 

user-specified percentage of the total number of observations 

in the record must be detected observations; for this study, this 

minimum value was set to 20 percent. Third, a minimum of 

one observation per year had to be present in the beginning 

and ending fifths of the period. Additional requirements of (A) 

at least one measurement during water years 1996–2000, and 

(B) no more than four continuous water years with no observations, were used to screen out datasets with observations only 

at the beginning and end of the period.

Trend tests were conducted for periods ranging from 8 to 

11 water years, depending on the availability and distribution 

of data. Trend test results for a nutrient at a station are reported 

where sufficient numbers of measurements were available to 

start the period of the trend test during either water years 1993, 

1994, or 1995 and end the period of the test during either 

water years 2001, 2002, or 2003.

Relations between nutrient concentrations, year, streamflow, and season were developed with Tobit regression for 

each nutrient at each station with sufficient measurements. The 

general equation relating water quality to year, streamflow, 

and season is: 

where

C = concentration of nitrogen or phosphorus 

compound,

B0 = intercept,

B1 = coefficient for year,

Year = year,

B2 = coefficient for streamflow,

log = base-10 logarithm,

Q = streamflow, in cubic feet per second,

B3 = first season coefficient,

sin = sine,

t

 = fraction of water year prior to month and 

day of measurement,

B4 = second season coefficient, and

cos = cosine

The term for streamflow was included in each test. The 

seasonal terms were included only if (A) seasonality appeared 

to be important based on an examination of a plot of residuals as a function of season, and (B) if the coefficients for the 

seasonal terms were significant at the 0.05 level.

Trends were identified if the coefficient for year (B1) was 

different than zero at the 0.05 level of significance. If B1 was 

greater than zero, concentrations increased over time; if B1

was less than zero, concentrations decreased over time. For 

each nutrient at each station, the magnitude of the change in 

concentration is reported in percent of mean per year. 

Changes in the variance of the residuals over the years 

were considered as part of each trend test. The level of significance reported for the coefficient for year (B1

) is accurate only 

if the variance of the residuals is constant over time. Results 

of a few tests were not reported if the level of significance of 

coefficient for year was close to 0.05 and if the variance of the 

residuals did not appear to be constant during the period of the 

test.

The effects of outlying measurements (outliers) on the 

results of the trend tests also were considered. For some tests, 

outliers were removed from the dataset and the dataset was 

then retested. In some cases, therefore, results presented do 

not include outliers. 

log( ) * * log( ) sin(2 ) cos(2 ) 0 1 2 3 4 C = B + B Year + B Q + B t + B t (1)
Appendix 3 157

References

Schertz, T.L., Alexander, R.B., and Ohe, D.J., 1991, The computer program Estimate Trend (ESTREND), a system for 

the detection of trends in water-quality data: U.S. Geological Survey Water-Resources Investigations Report 91–4040, 

72 p. 

Slack, J.R., Lorenz, D.L., and others, 2003, USGS library for 

S-PLUS for Windows–Release 2.1: U.S. Geological Survey 

Open-File Report 2003–357. 
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Appendix 4 159

Appendix 4. Methods—Trend Analysis Using 

Coupled Statistical Model of Streamflow and 

Water Quality

Contents

Definition of Non-Flow-Adjusted Trend.........................................................................................160

Flow-Adjusted Trend in Concentration..........................................................................................160

Unit Trends and Reference Values.................................................................................................160

Additional Interpretive Notes .........................................................................................................161

Reference...........................................................................................................................................161
160 Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003

Appendix 4. Methods—Trend Analysis Using Coupled Statistical Model of 

Streamflow and Water Quality

By Gregory E. Schwarz

This appendix describes the use of coupled statistical 

models of streamflow and water quality to determine “flowadjusted concentration trends,” “modeled instream concentration trends,” and “trends in load” in support of the analysis of 

nutrient concentrations, trends, and loads in the northeastern 

United States. The modeled instream concentration trend, 

or non-flow-adjusted trend in concentration, is referred to as 

“total trend in concentration” in this appendix. Many other 

alternative descriptive titles are used for trend results of this 

nature, including: non-flow-adjusted trend, unadjusted trend, 

full trend, total parametric trend, and modeled instream concentration trend. The phrase “modeled instream concentration 

trend” has been used in this report to refer to the non-flowadjusted trend in concentration. The non-flow-adjusted trend 

in load is referred to as simply “trend in load” in this appendix 

and in this report. 

Definition of Non-Flow-Adjusted Trend

Trend in load and total trend in concentration are defined 

as the percent changes in model-estimated, smoothed trend 

in load and concentration over the period of the water-quality 

record, divided by the length of the record. The modelestimated trend in load and concentration is determined by 

fitting separate trend models for streamflow and water-quality 

concentration. The streamflow model, estimated from all daily 

streamflow measurements available over the analysis period 

(water years 1993–2003, 1982–2003, 1979–2003, or 1975–

2003 in this report), relates the logarithm of daily streamflow to an intercept, a linear trend term (measured by time 

expressed as a decimal), and sine and cosine seasonal factors 

(also functions of decimal time). The water-quality model, 

estimated from all water-quality measurements collected during the analysis period, relates the logarithm of constituent 

concentration to an intercept, possibly nonlinear functions of 

the logarithm of streamflow and decimal time, and to seasonal 

factors consisting of sine and cosine functions of decimal 

time. The smoothed trend in the logarithm of water-quality 

concentration is determined by the streamflow and time trend 

components of the water-quality model, where the smoothed 

trend in the logarithm of streamflow is substituted for the 

actual logarithm of streamflow in the streamflow component. 

Smoothed trend in the logarithm of streamflow is a simple 

linear function of decimal time, computed over the waterquality period of record, the function value being given by the 

average logarithm of streamflow over the water-quality period 

of record plus the product of the streamflow model trend coefficient and the deviation of decimal time from the mid-point 

of decimal time for the water-quality period of record. Total 

trend in concentration is obtained by transforming the modelestimated, smoothed water-quality trend from logarithm space 

to real space, computing the percent change corresponding to 

the first and last dates of the water-quality record period, and 

normalizing by the decimal time length of this period. Trend 

in load is computed similarly, except the smoothed trend in 

the logarithm of streamflow is added to the smoothed trend 

in the logarithm of water-quality prior to retransformation to 

real space. A formal mathematical description of this method 

is presented in Sprague and others (2007, p. 10–12), with 

additional discussion of the estimation of the streamflow and 

water-quality models, and an explanation of the associated 

statistical tests for trend. 

Flow-Adjusted Trend in Concentration

The estimation of flow-adjusted trend in concentration is 

similar to total trend, the only difference being that the streamflow component of the water-quality model is not included in 

the determination of the smoothed water-quality trend; otherwise, the estimation methods are the same. The estimation of 

the trend in streamflow is based on the smoothed streamflow 

trend corresponding to the simple linear function of decimal 

time described in the previous section. The conversion of this 

smoothed trend to a trend estimate follows the same procedure described for total parametric trend, the only difference 

being that the period of the trend is defined by the beginning 

and ending dates for the flow record in the analysis period, 

rather than the beginning and ending dates of the water-quality 

record. 

Unit Trends and Reference Values

The results also report estimates of unit trends—trends 

expressed in the units of load or concentration (for example, 

kilograms per year per year or milligrams per liter per year). 

The unit trends in load and concentrations are determined by 

multiplying the load and concentration trend estimates (either 

flow adjusted or total—depending on the trend concept being 

described, expressed as rates rather than in percentage) by 

appropriate reference values of load and concentration. The 

reference value for the logarithm of concentration is obtained 

by evaluating the water-quality model at reference conditions 
Appendix 4 161

consistent with the trend in water quality at the beginning of 

the water-quality period of record. These conditions include 

setting the logarithm of streamflow to its smoothed trend value 

corresponding to the first day of the water-quality period, setting the trend term to the decimal equivalent of the first day of 

the water-quality period, and setting the sine and cosine seasonal factors to their average values over the full water-quality 

period. The logarithm value of the reference concentration is 

transformed to real space and a multiplicative retransformation factor is applied to correct for statistical bias arising from 

sample error in the water-quality model coefficients (Sprague 

and others, 2007). The reference load is computed similarly, 

except the logarithm of streamflow trend, as determined by 

the linear streamflow equation evaluated at the starting date of 

the water-quality period, is added to the logarithm value of the 

reference concentration prior to transformation to real space; 

also, a multiplicative constant is applied to convert the result 

to appropriate load units. The same reference concentration is 

used to derive total unit trend and flow-adjusted unit trend in 

concentration; the same reference load is used in the evaluation of unit trend in load and flow-adjusted unit trend in load.

Additional Interpretive Notes

Flow-adjusted trend, being independent of streamflow 

conditions, is best used to evaluate changes in water quality 

arising from changes in contamination sources or management 

activities in a watershed; conversely, total trend is indicative of 

the water-quality changes that riverine habitats have actually 

experienced. If no trend in streamflow is observed over time, 

the two estimates of trend will be equivalent. Because the 

water-quality model used to derive these trends includes 

streamflow as a predictor, the estimates of trend are immune 

to bias arising from preferential water-quality sampling during 

high-streamflow events. Care should be taken, however, in 

interpolating or extrapolating these trend estimates within or 

beyond the period of record for a site, or in making comparisons of trend across sites that have different periods of record. 

Because of the possible nonlinearity of trend, as arising from 

nonlinear specifications of the water-quality model streamflow 

or trend components, trends within the water-quality period, 

or trends experienced outside this period could be quite different from the trends reported here. The methodology used 

to evaluate trend is insensitive to changes in the variability 

of streamflow or to changes in the unexplained variability of 

water-quality, both changes potentially resulting in trends in 

water-quality arising from nonlinearity in the specification of 

the water-quality model. Accommodation of these uncertainty 

effects awaits future research. 

Reference

Sprague, L.A., Clark, M.L., Rus, D.L., Zelt, R.B., Flynn, J.L., 

and Davis, J.V., 2007, Nutrient and suspended-sediment 

trends in the Missouri River Basin, 1993–2003: U.S. Geological Survey Scientific Investigations Report 2006–5231, 

80 p. 
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Appendix 5 163

Appendix 5. Results—Trends in Streamflow, 

1975–2003 and 1993–2003 (CD–ROM)

[In pocket]

Table

5–1. Trends in streamflow, and serial correlation of residuals, 1975–2003 and 1993–2003
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Appendix 6 165

Appendix 6. Results—Trend Analysis on 

Flow-Adjusted Nutrient Concentrations, 

1975–2003 and 1993–2003 (CD–ROM)

[In pocket]

Table

6–1. Results of trend analysis on flow-adjusted nutrient concentrations, using Tobit 

regression and coupled statistical model of streamflow and water quality, 1975–2003 

and 1993–2003
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Appendix 7 167

Appendix 7. Results—Annual Load Estimates, 

1975–2003, 1993–2003, and Varied Periods of 

Record (CD–ROM)

[In pocket]

Tables

7–1. Annual load estimates, confidence intervals, and yields, 1975–2003, 1993–2003, and 

varied periods of record

7–1A. Annual load estimates, confidence intervals, and yields for total nitrogen, 1975–2003

7–1B. Annual load estimates, confidence intervals, and yields for total nitrogen, 1993–2003

7–1C. Annual load estimates, confidence intervals, and yields for ammonia nitrogen, 

1975–2003

7–1D. Annual load estimates, confidence intervals, and yields for ammonia nitrogen, 

1993–2003

7–1E. Annual load estimates, confidence intervals, and yields for total Kjeldahl nitrogen, 

1975–2003

7–1F. Annual load estimates, confidence intervals, and yields for nitrite-plus-nitrate nitrogen, 

1975–2003

7–1G. Annual load estimates, confidence intervals, and yields for nitrite-plus-nitrate nitrogen, 

1993–2003

7–1H. Annual load estimates, confidence intervals, and yields for total phosphorus, 

1975–2003

7–1I. Annual load estimates, confidence intervals, and yields for total phosphorus, 1993–2003

7–1J. Annual load estimates, confidence intervals, and yields for suspended sediment, 

1975–2003

7–1K. Annual load estimates, confidence intervals, and yields for suspended sediment, 

1993–2003

7–1L. Annual load estimates, confidence intervals, and yields for total nitrogen, varied 

periods of record

7–1M. Annual load estimates, confidence intervals, and yields for nitrite-plus-nitrate 

nitrogen, varied periods of record

7–1N. Annual load estimates, confidence intervals, and yields for total phosphorus, varied 

periods of record
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Appendix 8 169

Appendix 8. Results—Trend Analysis on 

Nutrient Loads, 1975–2003 and 1993–2003 

(CD–ROM)

[In pocket]

Table

8–1. Results of trend analysis on nutrient loads, calculated by using coupled statistical 

model of streamflow and water quality, 1975–2003 and 1993–2003
Prepared by the Pembroke Publishing Service Center.

For more information concerning this report, contact:

Director

U.S. Geological Survey

Connecticut Water Science Center

101 Pitkin Street

East Hartford, CT 06108

dc_ct@usgs.gov

or visit our Web site at:

http://ct.water.usgs.gov
Trench and others—Nutrient Concentrations and Loads in the Northeastern United States—Status and Trends, 1975–2003—Scientific Investigations Report 2011–5114

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