iii

CONTENTS

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

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

Background....................................................................................................................................................................3

Purpose and scope .........................................................................................................................................................3

Previous studies .............................................................................................................................................................4

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

Description of study sites .......................................................................................................................................................4

Chesterville Branch near Crumpton, Maryland.............................................................................................................4

Conodoguinet Creek near Hogestown, Pennsylvania....................................................................................................8

North Fork Shenandoah River near Strasburg, Virginia................................................................................................8

South Fork Shenandoah River at Front Royal, Virginia................................................................................................8

Methods of study....................................................................................................................................................................9

Data collection...............................................................................................................................................................9

Measurement of streamflow ..........................................................................................................................................9

Water-quality samples....................................................................................................................................................9

Collection technique and equipment.....................................................................................................................9

Sample processing and analysis..........................................................................................................................11

Quality-assurance program .................................................................................................................................11

Data analysis................................................................................................................................................................13

Estimation of loads .............................................................................................................................................13

Calculation of trends ...........................................................................................................................................13

Concentrations, loads, and trends at study sites ...................................................................................................................14

Concentrations of nutrients and suspended sediment..................................................................................................14

Chesterville Branch.............................................................................................................................................14

Conodoguinet Creek ...........................................................................................................................................14

North Fork Shenandoah River ............................................................................................................................14

South Fork Shenandoah River ............................................................................................................................14

Loads of nutrients and suspended sediment ................................................................................................................14

Chesterville Branch.............................................................................................................................................21

Conodoguinet Creek ...........................................................................................................................................21

North Fork Shenandoah River ............................................................................................................................21

South Fork Shenandoah River ............................................................................................................................21

Trends of nutrients and suspended sediment ...............................................................................................................21

Chesterville Branch.............................................................................................................................................22

Conodoguinet Creek ...........................................................................................................................................22

North Fork Shenandoah River ............................................................................................................................22

South Fork Shenandoah River ............................................................................................................................22

Comparison of study sites ....................................................................................................................................................22

Summary and conclusions....................................................................................................................................................25

References cited ...................................................................................................................................................................26

Appendix A ..........................................................................................................................................................................28

Appendix B ..........................................................................................................................................................................30
iv

Figures

 1–3. Maps showing:

 1. Location of Chesapeake Bay watershed study area, study site basins, and Chesapeake Bay

River Input Monitoring Program site basins.............................................................................................2

 2. Location of Chesapeake Bay watershed study area showing land-use percentages of study

site basins..................................................................................................................................................5

 3. Hydrogeomorphic regions in the Chesapeake Bay watershed.....................................................................7

 4–5. Photographs showing:

 4. Stainless-steel weighted-bottle sampler and hand-reel with polyethylene rope ........................................12

 5. DH-95 isokinetic sampler with 1-liter Teflon bottle..................................................................................12

 6. Boxplots showing range of concentrations of (A) total nitrogen, (B) total phosphorus, and

 (C) suspended sediment at study sites................................................................................................................15

7–10. Graphs showing:

 7. Daily mean discharge and observed concentrations for (A) total nitrogen, (B) total phosphorus,

and (C) suspended sediment at Chesterville Branch near Crumpton, Maryland,

January 1997 through December 2001 ...................................................................................................16

 8. Daily mean discharge and observed concentrations for (A) total nitrogen, (B) total phosphorus,

and (C) suspended sediment at Conodoguinet Creek near Hogestown, Pennsylvania,

January 1997 through December 2001 ...................................................................................................17

 9. Daily mean discharge and observed concentrations for (A) total nitrogen, (B) total phosphorus,

and (C) suspended sediment at North Fork Shenandoah River near Strasburg, Virginia,

January 1997 through December 2001 ...................................................................................................18

10. Daily mean discharge and observed concentrations for (A) total nitrogen, (B) total phosphorus,

and (C) suspended sediment at South Fork Shenandoah River at Front Royal, Virginia,

January 1997 through December 2001 ...................................................................................................19

11–12: Bar charts showing:

11. Mean annual streamflow at study sites, 1997–2001 ...................................................................................21

12. Calculated yields for (A) total nitrogen, (B) total phosphorus, and (C) suspended sediment

 at study sites, 1997–2001........................................................................................................................23

13–15: Plots showing:

13. Comparison of average annual yields for (A) total nitrogen, (B) total phosphorus, and 

 (C) suspended sediment and percentage of agricultural land use at the study sites and 

 River Input Monitoring Program sites, 1997–2001 ...............................................................................23

14. Comparison of average annual yields for (A) total nitrogen, (B) total phosphorus, and 

 (C) suspended sediment and percentage of forested land use at the study sites and 

 River Input Monitoring Program sites, 1997–2001 ...............................................................................24

15. Comparison of average annual yields for (A) total nitrogen, (B) total phosphorus, and 

 (C) suspended sediment and percentage of developed land use at the study sites and

 River Input Monitoring Program sites, 1997–2001 ...............................................................................24

Tables

1. Study site locations and land-use characteristics in the study basins, Chesapeake Bay watershed..................6

2. Constituents and field parameters monitored at study sites in the Cheapeake Bay watershed, 

1997–2001.................................................................................................................................................10

3. Summary statistics for selected water-quality constituents monitored at the study sites in the

Chesapeake Bay watershed, 1997–2001...................................................................................................20
v

Appendixes

A. Annual load estimates and yield calculations for study sites: Chesterville Branch near Crumpton, Maryland;

Conodoguinet Creek near Hogestown, Pennsylvania; North Fork Shenandoah River near

Strasburg, Virginia; and South Fork Shenandoah River at Front Royal, Virginia.................................................28

B. Trends in streamflow, load, flow-weighted concentration, and flow-adjusted concentration data for study sites: 

Chesterville Branch near Crumpton, Maryland; Conodoguinet Creek near Hogestown, Pennsylvania;

North Fork Shenandoah River near Strasburg, Virginia; and South Fork Shenandoah River at

Front Royal, Virginia..............................................................................................................................................30

Conversion Factors, Datums, and Abbreviated Water-Quality Units 

_____________________________________________________________________________________________________________________________________

Multiply By To obtain

_____________________________________________________________________________________________________________________________________

Length

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

acre 4,047 square meter

acre 0.4047 hectare

square mile (mi2) 259.0 hectare

square mile (mi 2 ) 2.590 square kilometer

Flow Rate

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

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

Mass

pound, avoirdupois (lb) 0.4536 kilogram

ton per day per square mile [(ton/d)/mi2] 0.3503 megagram per day per square kilometer

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

Pressure

atmosphere, standard (atm) 101.3 kilopascal _____________________________________________________________________________________________________________________________________

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

°F = (1.8 x °C) + 32

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

°C = (°F - 32) / 1.8

Altitude, as used in this report, refers to distance above or below sea level.

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88) and horizontal 

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

Water year: Defined as the period beginning October 1 and ending September 30, designated by the calendar year 

in which it ends. Thus, the water year beginning on October 1, 2000 and ending on September 30, 2001,

is called the 2001 water year.

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

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

micrograms per liter (μg/L).
vi

Abbreviations and Acronyms

AMLE Adjusted Maximum Likelihood Estimate

BMPs Best Management Practices

BNR biological nutrient reduction

CBP Chesapeake Bay Program

DO dissolved oxygen

EDI equal-discharge increment

ETR equal-transit rate

EWI equal-width increment

GIS geographic information system

HSPF Hydrological Simulation Program- FORTRAN

MD DNR Maryland Department of Natural Resources

MVUE Minimum Variance Unbiased Estimate

MWCOG Metropolitan Washington Council of Governments

NAWQA National Water-Quality Assessment Program

NWIS National Water Information System

NWQL National Water-Quality Laboratory

PA DEP Pennsylvania Department of Environmental Protection

pH hydrogen potential

QA quality assurance

QAPP quality-assurance project plan

QC quality control

RIM River Input Monitoring

SEP standard error of prediction

SPARROW SPAtially Referenced Regressions On Watershed attributes

SRBC Susquehanna River Basin Commission

TMDL Total Maximum Daily Load

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VA DEQ Virginia Department of Environmental Quality

WSM Chesapeake Bay Watershed Model
Abstract 1

Nutrient and Sediment Concentrations, Loads, and Trends for Four 

Nontidal Tributaries in the Chesapeake Bay Watershed, 1997–2001

By Michael P. Senus, Michael J. Langland, and Douglas L. Moyer

Abstract

Excess nutrient and sediment loads in the 

Chesapeake Bay can cause unbalanced waterquality conditions that reduce the amount of 

oxygen and sunlight available to aquatic plants 

and organisms. Nutrient and sediment loads and 

trends were analyzed at four nontidal tributaries in 

the Chesapeake Bay watershed to collect additional data for the ongoing (since 1985) U.S. 

Geological Survey Chesapeake Bay River Input 

Monitoring Program. These sites were Chesterville Branch in Maryland, Conodoguinet Creek in 

Pennsylvania, North Fork Shenandoah River in 

Virginia, and South Fork Shenandoah River in 

Virginia. Monthly base-flow and stormflow 

water-quality samples were collected at each site, 

with a total of 90–120 samples collected at each 

site during the study period (1997–2001). These 

data were used to compute annual and monthly 

loads for selected nutrient and suspended-sediment constituents using a mass-load estimating 

model, ESTIMATOR, developed by the U.S. Geological Survey. Each of the four study sites in this 

report was characterized on the basis of land use 

and water-quality data. Basins with high percentages of agricultural land use had higher nitrogen 

and phosphorus loads and yields than basins with 

higher percentages of forested land and less agricultural land. No relation between land use and 

suspended-sediment loads and yields was evident. Study results also indicate that suspendedsediment loads were higher in years of high mean 

annual streamflow at Conodoguinet Creek, North 

Fork Shenandoah River, and South Fork 

Shenandoah River. The highest total suspendedsediment loads and yields at Chesterville Branch 

were caused by Hurricane Floyd in 1999, which 

was not a year with the highest annual total 

streamflow. Results of this study indicate that a 

5-year period of record is too short a timeframe to 

characterize factors affecting trends. Moreover, a 

combination of extreme variability in climate and 

lack of recent land-use data made characterizing 

basin nutrient and sediment relations problematic. Although the data and analysis established a 

baseline of water quality at the four tributaries, 

additional monitoring and tracking of loads would 

help identify long-term trends and factors affecting trends.

Introduction

The Chesapeake Bay has been degraded by water-quality 

problems, loss of habitat, and over-harvesting of living 

resources. Since the early 1980s, scientists have been studying the bay and its 64,000-mi2 (square mile) watershed, 

which drains parts of Delaware, the District of Columbia, 

Maryland, New York, Pennsylvania, Virginia, and West Virginia (fig. 1). One important issue for bay resource managers is how the bay’s tributaries support a complex aquatic 

food web that is vulnerable to changes in water quality. The 

amount of nutrients and sediment delivered to the bay’s estuary affects water quality. Nutrients are needed to sustain 

life, but excess nutrient loads from human activities may 

cause unbalanced and unhealthy changes in water quality 

that are harmful to aquatic organisms. Nitrogen and phosphorus are two known nutrients of concern. Poor water 

quality caused by an abundance of these nutrients can stimulate the excessive growth of phytoplankton, promote algal 

blooms, reduce dissolved oxygen (DO) levels, and cause fish 

kills. Similarly, high sediment loads delivered to the bay 

degrade water quality. Sediment delivery from land surfaces to water bodies is a result of erosion. The erosion process also can be accelerated by certain land uses such as 

urban growth, or not using best management practices 

(BMPs) on agricultural land. If BMPs, such as conservation 

tillage and use of cover crops, planting buffer strips or grass 

waterways, establishing animal waste retention basins, or 

constructing streambank reinforcements are not utilized, 

then a greater load of excess nutrients and/or sediment is 

expected to be delivered to the bay. As a result, water clarity is reduced and sunlight needed to penetrate the water 
2 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001
Introduction 3

column for underwater bay grasses is diminished. Without 

sunlight, underwater plants die and remove life-supporting 

habitat and food for fish, shellfish, and other living 

resources. Hence, the Chesapeake Bay Program has determined that by reducing nutrient and sediment loads to the 

bay, water quality would improve by alleviating low DO 

conditions, reducing algal blooms, and improving water clarity (S.W. Phillips, U.S. Geological Survey, written commun., 

2003; U.S. Environmental Protection Agency, 1988, 2000, 

2003).

Background

Following a multi-year U.S. Geological Survey (USGS) 

study to assess water quality in the bay, the District of 

Columbia, Maryland, Pennsylvania, and Virginia signed a 

multi-jurisdictional agreement in 1983 with the U.S.

Environmental Protection Agency (USEPA) to form the 

Chesapeake Bay Program (CBP). The CBP is a voluntary 

partnership that works with citizen advisory groups to 

improve the quality of the bay and its tributaries. In 1999, 

the bay was listed formally under the Clean Water Act as an 

impaired water body because of excess nutrients and sediment (Phillips, 2001). The “Chesapeake 2000” agreement 

states that if improvements in water-quality conditions in 

the bay are not made by 2010, strict regulatory actions may 

be implemented (S.W. Phillips, U.S. Geological Survey, 

written commun., 2003; U.S. Environmental Protection 

Agency, 1988, 2000, 2003).

To help facilitate evaluation of the bay’s health on or 

before 2010, USGS monitoring, assessment, and prediction 

are used by the CBP to characterize past and present waterquality conditions. The Chesapeake Bay River Input Monitoring (RIM) Program provides long-term water-quality 

monitoring data and continuous streamflow data to quantify 

nutrient and sediment loads and trends in the nine major nontidal tributaries of the Chesapeake Bay watershed (fig. 1). 

In Maryland, the RIM Program was implemented in 1983 

between the USGS, the Maryland Department of Natural 

Resources (MD DNR), and the Metropolitan Washington 

Council of Governments (MWCOG). In 1988, the USGS 

began the RIM Program in Virginia in cooperation with the 

Virginia Department of Environmental Quality (VA DEQ). 

The Conodoguinet Creek site in Pennsylvania was a cooperative effort between the USGS and the Pennsylvania Department of Environmental Protection (PA DEP). To further 

characterize the bay, watershed-process modelers utilize 

these monitoring data to establish connections between 

watershed conditions (land-use type, agricultural management practices, anthropogenic nutrient inputs, and sediment 

erosion), hydrologic conditions (size, geology, and slope), 

changes in climate, and water quality in the bay. The CBP 

Watershed Model (WSM)1 and the USGS SPAtially Referenced Regressions On Watershed attributes (SPARROW) 

models help to identify factors affecting trends and are discussed further in Sprague and others (2000).

This study was undertaken in cooperation with the MD 

DNR, VA DEQ, and PA DEP, and is a supplement to the 

RIM studies that have been conducted since 1985. In the 

mid–1990s, the RIM Program was well established and studies were encouraged in order to advance scientific knowledge of the bay. To increase understanding of the nontidal 

part of the bay watershed, monitoring sites in addition to the 

RIM sites were needed to further describe the agricultural 

land-use part of the Eastern Shore, examine potential effects 

of emerging land-use changes in the lower Susquehanna 

River Basin, and focus study on two sub-basins of the 

Potomac River Basin. In 1996, four nontidal tributary sites 

within the Chesapeake Bay watershed were selected by the 

CBP Monitoring and Assessment subcommittee and associated workgroups for additional monitoring by the RIM 

Program. Balancing financial resources and the desire for 

greater understanding of the watershed, the subcommittee 

felt that four sites would meet this need (S.W. Phillips and 

J.P. Raffensperger, U.S. Geological Survey, oral commun., 

2003). These sites were Chesterville Branch in Maryland, 

Conodoguinet Creek in Pennsylvania, North Fork Shenandoah River in Virginia, and South Fork Shenandoah River in 

Virginia. These “add-on” sites will be referred to as the 

“study” sites.

In this report, the Chesapeake Bay watershed is defined 

as the area bounded by physical barriers that cause water to 

drain to the bay’s tributaries and estuary. Land area 

upstream of each USGS streamflow-gaging station is 

referred to as a “basin” for each study site. Collectively, 

these basins make up the bay watershed. Unless otherwise 

specified, the term “observed concentration” or “measured 

concentration” will be referred to simply as “concentration”.

Purpose and Scope

This report presents the nutrient and sediment concentrations, loads, and trends at the four study sites within the bay 

watershed for 5 full calendar years, 1997 through 2001. The 

purpose of this report, determined by the CBP, is to:

1. Provide watershed modelers with additional waterquality data for the SPARROW models and 

additional calibration data for the WSM to fill in the 

models’ spatial gaps;

2. Provide monthly and annual loads for nitrogen, 

phosphorus, and suspended sediment and relate 

them to various hydrogeomorphic regions in the 

watershed;

3. Provide information that can be used with other 

data to determine factors affecting trends in 

concentration and load; and

1. Model utilizes Hydrological Simulation Program-FORTRAN (HSPF).
4 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001

4. Provide information to resource managers 

formulating tributary strategies aimed at Total 

Maximum Daily Load (TMDL) development for 

nutrient and sediment control, and to the USEPA for 

nutrient- and sediment-reduction goals.

Criteria for selecting the new monitoring sites included 

limited capital costs, sites with a real-time streamflow gaging station already in operation, adequate site access under 

changing flow conditions, present and usable platforms for 

water-quality sampling near or at the streamflow-gaging 

station, and the need to further characterize specific basins 

because of land-use changes or data gaps.

Previous Studies

Initial studies in the Chesapeake Bay watershed focused 

on three major tributaries in Lang (1982). The RIM Program 

has over a decade of constituent and field parameter data for 

Virginia sites and almost two decades of data for the Maryland sites (James and others, 2003). Since 1994, reports on 

loads and trends for CBP RIM sites have been published 

periodically by the USGS in cooperation with the MD DNR 

and the VA DEQ. These data, values, and trends are available in publications and in electronic format through the 

USGS (Darrell and others, 1999; Lizarraga, 1999; Johnson 

and others, 1998; Langland and others, 1998, 2000, 2001). 

The regression model, ESTIMATOR, was developed by the 

USGS and is widely used for load estimation. The model is 

discussed in detail in Bradu and Mundlak (1970) and in 

Cohn and others (1989, 1992). Historical use of the ESTIMATOR model for Chesapeake Bay studies is described in 

Darrell and others (1999), and the revised load estimation 

procedure is described in Yochum (2000). Trends in nutrient 

and sediment delivery to the bay are discussed in Langland 

and others (2001) and Sprague and others (2000).

Acknowledgments

The authors wish to thank the following State cooperators: Bruce D. Michael, J. Shermer Garrison, and William 

Romano from the MD DNR, and Rick Hoffman from the 

VA DEQ. Also, the authors thank the following USGS 

personnel: Pennsylvania project chief and lead technician, 

Russell A. Ludlow; Maryland and Virginia lead hydrologic 

technicians, David P. Brower and Roger M. Moberg; hydrologic technicians, Joseph E. Beman, Karl M. Dydak, and 

Trisha L. Baldwin; Sarah K. Martucci and John W. Brakebill 

for GIS support in Baltimore; Lori A. Sprague, Daniel G. 

Galeone, Jeff P. Raffensperger, Frederick J. Tenbus, and 

Scott W. Phillips for technical reviews; and Timothy W. 

Auer, Valerie M. Gaine, Donna R. Knight, and Gloria J. 

Hyatt for publication support.

Description of Study Sites

The four study sites were carefully selected to meet the 

goals and objectives set forth by the CBP Monitoring and 

Assessment subcommittee. This section describes each of 

the four sites, and lists any characteristics unique to each site 

and its basin. The Chesterville Branch, Conodoguinet 

Creek, North Fork Shenandoah River, and South Fork 

Shenandoah River study sites were monitored for water 

quality and flow well above the point of tidal effects of the 

bay. Most RIM monitoring sites are located close to a point 

downstream not affected by tides, also known as the “Fall 

Line” boundary (fig. 1). The Fall Line refers to a distinct 

change in slope generally along a southwest to northeast 

trending line through the bay watershed, representing the 

boundary between the Piedmont and Coastal Plain hydrogeomorphic regions. The study sites’ basins include a wide 

range of land cover (fig. 2, table 1), geographic, and geologic 

regions, draining such diverse areas as the forested, agricultural, and developed land of the Appalachian Plateau of 

New York and Pennsylvania, the Valley and Ridge of the

Pennsylvania and West Virginia highlands, the Shenandoah 

Valley of Virginia, and the flat lowlands of Maryland’s Eastern Shore and Delaware. 

Chesterville Branch near Crumpton, Maryland

Streamflow and water quality are monitored on Chesterville Branch at the MD State Route 291 (also known as River 

Road) overpass, near Crumpton, MD. Chesterville Branch is 

a small tributary of the Chester River in the central part of 

the Eastern Shore in Kent County. The gaging station is 

located and water-quality samples are collected from the 

downstream side of the Route 291 overpass.

The Chesterville Branch Basin is 6.12 mi2, and is the 

smallest of the four study site basins and all nine RIM 

basins. Chesterville Branch originates in Kent County and 

flows south-southwest to the Chester River. The entire basin 

lies within the Atlantic Coastal Plain hydrogeomorphic 

region (fig. 3). Land use above the Chesterville gaging station is 3 percent forested, over 90 percent agricultural, and 

less than 1 percent developed (table 1). This basin is representative of a part of the Eastern Shore that is dominated by 

agricultural land use. The Chesterville gaging station is 

located in the Coastal Plain dissected upland hydrogeomorphic region (Brakebill and Kelley, 2000) that is underlain by 

permeable Tertiary sand and the marine glauconite Aquia 

Formation near land surface (Böhlke and Denver, 1995).

The Chesterville Branch near Crumpton, MD site was 

selected as a monitoring location in order to provide an additional Eastern Shore site in the Coastal Plain. The current 

(2004) RIM site on the Eastern Shore is at the Choptank 

River near Greensboro, MD (01491000). The Choptank 

River Basin is not entirely representative of the agriculturally dominated Eastern Shore (Sprague and others, 2000). 

Land use above the Choptank RIM site is approximately 

30 percent forested whereas the Chesterville Branch near 

Crumpton site is approximately 3 percent forested as narrow 

wooded riparian zones (U.S. Geological Survey, 2000). 

Agricultural land use in the Choptank River Basin is 50 percent, and agricultural land use in the Chesterville Branch 

Basin is over 90 percent (U.S. Geological Survey, 2000). 

The high percentage of agricultural to forested land use has 
Description of Study Sites 5
6 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001 Table 1. Study site locations and land-use characteristics in the study basins, Chesapeake Bay watershed [Modified from U.S. Geological Survey (USGS), 2000; ° , ' , '' , degree, minute, second] Percentage of Land Use USGS station name USGS station number Latitude ( ° ' '' ) Longitude ( ° ' '' ) Drainage (square miles) Forested Developed Agricultural Other Chesterville Branch near Crumpton, MD 01493112 39 15 00 75 53 00 6.12 3.4 0.5 92.0 4.1 Conodoguinet Creek near Hogestown, PA 01570000 40 15 08 77 01 17 470 32.6 3.7 62.2 1.5 North Fork Shenandoah River near Strasburg, VA 01634000 38 58 36 78 20 11 768 59.0 2.4 37.7 0.9 South Fork Shenandoah River 

 at Front Royal, VA

01631000 38 54 50 78 12 40 1,642 57.1 3.5 38.2 1.2
Description of Study Sites 7
8 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001

remained constant over the past 40–50 years (Böhlke and 

Denver, 1995). Much of the basin above the Choptank River 

gaging station has poorly drained soils and requires a network of ditches throughout the agricultural land. These 

ditches generally are devoid of vegetation to facilitate flow 

off the farmlands. Therefore, nutrient uptake by plants and 

denitrification are less likely to occur in comparison to other 

Eastern Shore basins.

Conodoguinet Creek near Hogestown, Pennsylvania

Streamflow and water quality are monitored on 

Conodoguinet Creek in Cumberland County, Pennsylvania. 

The Conodoguinet Creek Basin (470 mi2) originates in 

Cumberland County and flows northeast to the Susquehanna 

River (fig. 1). The Conodoguinet Creek Basin lies mostly 

within the Valley and Ridge Physiographic Province. The 

basin is composed geologically of a mix of 3 percent Blue 

Ridge Crystalline, 37 percent Valley and Ridge Carbonate, 

and 60 percent Valley and Ridge Siliciclastic hydrogeomorphic regions (Brakebill and Kelley, 2000). In 1997, land use 

above the Conodoguinet gaging station was 33 percent forested, 62 percent agricultural, and 4 percent developed 

(U.S. Geological Survey, 2000; table 1).

The Conodoguinet Creek near Hogestown, PA site was 

selected with input from the PA DEP because of rapid landuse changes from agriculture to developed lands within the 

basin. Much of this growth was caused by the development 

of residential communities along the flood plain on the banks 

of Conodoguinet Creek. Most of the land-use change has 

occurred downstream of the Conodoguinet gaging station; 

however, suburban growth is increasing at a rapid pace and 

moving upstream within the basin near the gaging station. In 

addition to the increase in residential areas, there has been a 

change from private individual septic systems to recently 

controlled or expanded public sewage-treatment plants, 

which have the potential to increase the nitrogen and phosphorus loads into Conodoguinet Creek.

North Fork Shenandoah River near Strasburg, Virginia

Streamflow and water quality are monitored on the North 

Fork Shenandoah River gaging station at the State Route 55 

bridge near Strasburg, VA. Streamflow has been measured 

continuously at this site since March 1925. A water-stage 

recorder (stilling well) is the recording device used at this 

gaging station. The North Fork Shenandoah River originates 

in Rockingham County, VA and flows northeast to the 

Shenandoah River. The 768-mi2 North Fork Shenandoah 

River Basin is a sub-basin of the Potomac River watershed. 

The North Fork Shenandoah flows southwest to northeast 

through long valleys and ridges where it converges with the 

South Fork Shenandoah River and continues on northward to 

empty into the Potomac River.

Land use above the North Fork site is 59 percent forested, 38 percent agricultural, and less than 3 percent developed (table 1). The percentage of agricultural land use has 

increased in this basin in the past decade, and the intensity 

of the agricultural practices also has increased. This basin 

lies in the Appalachian Mountain range in the Valley and 

Ridge Physiographic Province. It is composed of a mix of 

over 30 percent carbonate and over 60 percent siliciclastic 

Paleozoic sedimentary rock (Johnson and Belval, 1998).

The North Fork Shenandoah River site was selected for 

two reasons. The first was to study the shift in the major 

source of agricultural nitrogen from synthetic fertilizer to 

manure. The increase in manure use on agricultural lands 

primarily resulted from the growth of the poultry industry 

near the site in Rockingham, Shenandoah, and Page Counties, Virginia (U.S. Department of Agriculture, National 

Agricultural Statistics Service, 1997). As a result, there has 

been a considerable increase in manure production and distribution in the basin. Second, this site was chosen in conjunction with the South Fork Shenandoah River site to 

monitor the combined load of these two tributaries so that 

the Potomac River Basin could be partitioned between 

waters from Virginia and waters from West Virginia and 

Maryland.

An in-depth study of 35 sites in 5 major river basins in 

Virginia, including the North Fork and South Fork Shenandoah Rivers, was conducted from 1985 to 1996. The study is 

described in Johnson and Belval (1998) and presents a discussion of spatial distribution and temporal changes in concentrations, loads, and trends. This report represents a 

continuation of that study for 2 of the 35 sites that were 

monitored.

South Fork Shenandoah River at Front Royal, Virginia

Streamflow and water quality are monitored on the South 

Fork Shenandoah River at Front Royal, VA. Streamflow at 

this site has been measured continuously since September 

1930. The gaging station is located 0.7 mi (mile) downstream of the State Route 619 bridge at Front Royal, VA. 

Water-quality samples are collected from the bridge. The 

South Fork Shenandoah River Basin (1,642 mi2) is the largest of the four study sites. The South Fork Shenandoah 

River originates in Augusta County, VA and flows northeast 

to the Shenandoah River. The South Fork Shenandoah River 

Basin is a sub-basin of the Potomac River watershed. The 

South Fork Shenandoah River flows southwest-northeast 

through long valleys and ridges where it converges with the 

North Fork Shenandoah River and continues until it reaches 

the Potomac River.

Land use above the South Fork gaging station is 57 percent forested, 38 percent agricultural, and less than 4 percent 

developed (table 1). This sub-basin recently has been losing 

agricultural and forested land to increased urbanization and 

development in the area. The South Fork Basin is mainly in 

the Appalachian Mountain range, in the Valley and Ridge 

Physiographic Province, and is composed of a mix of over 

35 percent carbonate Paleozoic sedimentary rock, over 

40 percent Paleozoic sedimentary rock, and approximately 

20 percent Blue Ridge Crystalline region, metamorphicigneous rock (Johnson and Belval, 1998).

This site was chosen in conjunction with the North Fork 

Shenandoah River site to monitor the combined nutrient and 

sediment load of these two tributaries, and provide a separa-
Methods of Study 9

tion between Virginia’s contribution and the contributions of 

West Virginia and Maryland in the Potomac River Basin.

Methods of Study

As discussed earlier, this study was conducted to:

1. Collect water samples and continuously monitor 

water-quality parameters at four USGS gaging 

stations on a monthly basis under base-flow and 

stormflow conditions from 1997 through 2001;

2. Estimate monthly and annual loads for nitrogen, 

phosphorus, and suspended sediment from waterquality data; and

3. Utilize estimated loads to determine trends.

Concentrations were used to measure in-stream conditions at monitoring sites and are reported in mg/L (milligrams per liter). Loads were estimated as unit mass of 

nutrient or sediment transported by streamflow over unit 

time and are reported in tons/yr (tons per year). To compare 

loads between study basins, loads were normalized by 

calculating yields, load per unit area, and are reported in 

tons/yr/mi2 (tons per year per square mile). Temporal trends 

were determined by using either linear regression or by a 

non-parametric Kendall-Theil test (Langland and others, 

2001).

Data Collection

Streamflow and water-quality data were used in the estimation of annual loads and trends (Langland and others, 

2001). Daily streamflow was calculated and water-quality 

concentrations were checked visually and statistically for 

accuracy. Both data sets then were stored and entered into 

the USGS National Water Information System (NWIS) data 

base. As of 2002, water-quality and discharge monitoring 

was discontinued at Chesterville Branch. Conodoguinet 

Creek water-quality monitoring was discontinued, but the 

USGS still measures flow. VA DEQ conducts water-quality 

sampling at North Fork Shenandoah River and South Fork 

Shenandoah River every other month, and discharge is monitored daily by the USGS.

Measurement of Streamflow

Discharge measurements at each of the study sites were 

made using standard USGS streamflow-gaging procedures 

(Buchanan and Somers, 1982). Streamflow is the rate at 

which a volume of water passes a cross section in a stream 

channel per unit of time, such as ft3/s (cubic feet per second) 

(James and others, 2003). The relation between continuous 

gage-height measurements (stage) and periodic instantaneous discharge measurements, referred to as the “rating,” 

was used for calculation of either instantaneous or mean 

daily discharge (James and others, 2003). Monthly measurements were made at each gaging station to verify or adjust 

the rating at that gaging station (Carter and Davidian, 1968).

Water-Quality Samples

 Both base-flow and stormflow water-quality samples 

were collected at each of the four study sites for a targeted 

list of constituents (table 2). How each constituent is 

reported and the parameter numbers used in the USGS 

NWIS water-quality data base and, subsequently, in the load 

computation process are also described in table 2.

Three of these monitored constituents are of primary 

concern to the CBP and are discussed in detail: total nitrogen, total phosphorus, and suspended sediment. In addition, 

field parameters, such as air and water temperature, hydrogen potential (pH), barometric pressure, specific conductance, alkalinity, and DO, were measured when water-quality 

samples were taken in order to ensure that the data obtained 

represent the in-situ quality of water (James and others, 

2003) (table 2). Water-quality samples were collected, processed, and transported to their respective laboratories in 

accordance with USGS guidelines and protocol (Wilde and 

others, 1998) on the day of collection.

At least one water-quality base-flow sample and as many 

as three stormflow samples were collected monthly. Stormevent sampling was emphasized because a major portion 

of runoff and associated nutrients and suspended-sediment 

loads is carried by storms (Johnson and Belval, 1998). 

Sampling began in June 1996 and ended in July 2002, however, the ESTIMATOR program traditionally has based its 

calculations on the calendar year (January 1 through 

December 31); therefore, concentrations, loads, and trends 

are presented in this report for a period of record beginning 

on January 1, 1997 and ending on December 31, 2001.

Collection Technique and Equipment Depth-integrated 

monthly samples were collected at this site using the equalwidth increment (EWI) method, or equal-transit rate (ETR) 

method, during low-flow and stormflow conditions at up to 

five sections along the sampling platform. This technique 

requires that the sampler(s) collect sample volumes proportional to the amount of flow at each of the approximately 6 

to 10 spaced verticals along the tributary’s cross section 

(Darrell and others, 1999).

The collection technique is determined by specific site 

characteristics and stage of water at the site. Water-quality 

samples were collected either as a composite sample at 

equal-width increments across a cross section of the tributary 

when possible, or collected as a discrete sample at a fixed 

point if depth and width of the tributary channel were too 

low under base-flow conditions (Maryland Department of 

Natural Resources, 2001). The platform above Chesterville 

Branch and the stream’s short cross-sectional distance did 

not allow for an operator to move freely across the width of 

the tributary above the water, so only a grab sample at the 

center of flow was collected.

A high flow or storm event at each of the monitoring 

sites is defined as a measurable increase in discharge based 

on the antecedent precipitation, the magnitude of discharge, 

and the season of the year. Efforts were made to sample a 

representative range of storm types and sizes throughout the 

year. Storms were selected for sampling on the basis of the 
10 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001

Table 2. Constituents and field parameters monitored at study sites in the 

 Chesapeake Bay watershed, 1997–2001

[USGS, U.S. Geological Survey; mg/L, milligrams per liter; n/a, not applicable; ° C, degrees Celsius; 

 mm Hg, millimeters of mercury; μS/cm, microsiemens per centimeter at 25 ° Celsius]

Constituent USGS parameter number Reported in Reported as

Total nitrogen (TN) P00600 mg/L Nitrogen (N)

Dissolved ammonia (NH3) P00608 mg/L Nitrogen (N)

Dissolved nitrite (NO2 ) P00613 mg/L Nitrogen (N)

Dissolved kjeldahl nitrogen (dissKN) P00623 mg/L Nitrogen (N)

Total kjeldahl nitrogen (TKN) P00625 mg/L Nitrogen (N)

Dissolved nitrite + nitrate (NO2+NO3) P00631 mg/L Nitrogen (N)

Total phosphorus (TP) P00665 mg/L Phosphorus (P)

Dissolved phosphorus (diss P) P00666 mg/L Phosphorus (P)

Orthophosphate (o-PO4) P00671 mg/L Phosphorus (P)

Total organic carbon (TOC) P00680 mg/L Carbon (C)

Dissolved silica (SiO2 ) P00955 mg/L Silicon dioxide (SiO2 )

Suspended-sediment concentration (SSC) P80154 mg/L n/a

Field parameters USGS parameter number Reported in

Water temperature P00010 °C

Air temperature P00020 °C

Barometric pressure P00025 mm Hg

Gage height P00065 feet

Specific conductance P00095 μS/cm

Dissolved oxygen (DO) P00300 mg/L

pH P00400 standard units

Alkalinity P39086 mg/L as calcium carbonate
Methods of Study 11

previous storm sampling history, such as frequency, size, and 

duration.

Various sample-collection devices, or samplers, used at 

the study sites are discussed in Wilde and others (1998). 

Geometry of the tributary’s cross section, access and sampling platform above the water, high- or low-flow conditions, and velocity of streamflow were factors in sampler 

selection. Selection of the type of sampler used was made at 

the discretion of the field personnel who assessed site and 

stream conditions in order to collect water-quality samples 

that are representative of tributary conditions at the time of 

sampling.

USGS field personnel used both isokinetic and non-isokinetic samplers to manually collect water samples (fig. 4). 

Isokinetic samplers are designed to accumulate representative, continuous, and depth-integrated water samples with 

ambient flow changes in actual stream velocities. Isokinetic 

samplers (fig. 5) with nozzles require a minimum stream 

velocity of 1.5 ft/s (feet per second) to function properly. 

The DH-95, D-96, and the D-952 samplers commonly were 

used during this study. These samplers are designed so that 

they are heavy enough to maintain a horizontal position 

under the water as they are lowered down to the streambed 

or riverbed and back up to the surface. They are designed 

to allow sample water to enter the sampler nozzle at the same 

velocity as the stream, allow the sampler nozzle to get as 

close to the streambed as possible without disturbing the 

bottom sediment, and minimize disturbance to the flow 

pattern of the stream (Guy and Norman, 1970).

For stream velocities less than 1.5 ft/s, non-isokinetic 

open-mouthed samplers were used at study sites. An operator raised and lowered these suspended samplers by using a 

hand reel and a polyethylene rope. Either a 1-L (liter) stainless-steel weighted-bottle sampler (fig. 4) or a WBH-96 was 

used.

The Isco 6700SR refrigerated autosampler (automatic 

sampler) was used at Chesterville Branch beginning in 2000. 

Because of the small size of this basin, the stream reacts 

quickly (within hours) to rainfall events, or is “flashy,” making the installation of a refrigerated automatic sampler a 

necessity. The sampler automatically drew a sample once a 

specific stage was reached. High-flow and stormflow samples were collected either by the automatic sampler or, if the 

storm duration was long enough, by a 1-L stainless-steel 

weighted-bottle sampler or the isokinetic DH-59 sampler. 

Using the larger sampling devices, such as the DH-95 or 

D-95, was not practical considering the small size of the 

Chesterville Branch cross-sectional width. Every effort was 

made to sample large stormflow events.

Sample Processing and Analysis Water-quality samples 

collected for this study were composited in a polypropylene 

churn splitter. When the churn splitter was used, the sample 

was composited into the pre-cleaned plastic vessel and subsamples for whole-water analysis were drawn while churning at a standard rate. The churn splitter was used to allow 

for subsamples to be drawn while maintaining a uniform distribution of suspended material in the composite sample 

(Darrell and others, 1999). The remaining samples were filtered on site for dissolved analysis using a 0.45-micrometer 

(average pore size, polycarbonate) capsule filter. After acid 

was added to the appropriate samples for preservation, 

the nutrient samples were placed immediately on ice and 

shipped within 24 hours to either the USGS National WaterQuality Laboratory in Denver, CO or to the Virginia Division of Consolidated Laboratory Services (VDCLS) in 

Richmond, VA. Samples collected on weekends or holidays 

were refrigerated and held until the next possible shipping 

day. Suspended-sediment samples, collected concurrently 

with the water-quality samples, were shipped to the USGS 

Sediment Laboratory in Louisville, KY for analysis. Chainof-custody procedures followed recommended USGS waterquality laboratory procedures.

Quality-Assurance Program Quality-assurance methods 

were documented in an annual Quality-Assurance Project 

Plan (QAPP) (Maryland Department of Natural Resources, 

2001). The monitoring for this study was consistent with 

previous RIM Program monitoring because the same personnel using the same equipment, procedures, and sampling 

techniques were involved. The quality-assurance effort 

included documentation of concentration variability within 

the cross section, sediment-transport analysis, sample-collection techniques and field personnel, and the variability 

within and among the analyzing laboratories. Discrete and 

composite samples, or samples collected by automatic sampler, were quality assured using a statistical program that 

identified suspect remark codes, missing dates, and/or missing times associated with the sample before they were added 

to the USGS data base (Langland and others, 2000). Quality-assurance results can be obtained from the USGS MDDE-DC, VA, and PA District offices. Laboratory quality 

control is discussed in detail in the USGS National WaterQuality Laboratory Quality Control manual (Pritt and Raese, 

1992). 

Blanks and duplicates were collected to evaluate bias and 

variability because of field sampling, processing, transportation, and analysis of environmental water-quality samples. 

Field blanks, trip blanks, and split-replicate samples were 

collected at each of the four study sites at a rate of no less 

than 1 quality-assurance sample per every 15 environmental 

samples, or greater than 5 percent. In addition, USGS personnel performed comparability studies between samples 

collected from an autosampler and those collected manually.

Blank water samples were collected using laboratorygrade inorganic-free deionized water. Trip blanks were collected as a solution that is processed with the same type of 

bottle used for an environmental sample and kept with the 

2. D- indicates “depth-integrated,” DH- indicates “depth-integrated, handheld,” and WBH- indicates “weighted-bottle holder, hand-held.”
12 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001
Methods of Study 13

set of sample bottles before and after environmental-sample 

collection, then transported to the analyzing laboratory with 

the environmental samples. Field-blank solutions were subjected to all aspects of sample collection, field-processing, 

preservation, transportation, and laboratory handling as environmental samples. These also were submitted to the analyzing laboratory along with the environmental samples.

Duplicate samples were collected to help evaluate laboratory precision. These split-replicate samples were processed from the same churn splitter as those processed as 

environmental samples. Results of the quality-assurance 

study showed that statistically similar nutrient-concentration 

data were repeated over a range of values reported by the 

laboratories.

Data Analysis

A brief description of the methods used to estimate loads 

and calculate trends is presented in the following section. 

The data-analysis approach and methods used for the four 

study sites were similar to those used for the RIM Program.

Estimation of Loads Load is the concentration of chemical constituents, such as nutrients and suspended sediment, 

in water multiplied by instantaneous volumetric discharge of 

water. Loads for nitrogen, phosphorus, and suspended sediment were estimated in a two-step process by using concentration values and calculated daily streamflow data and the 

USGS seven-parameter log-linear regression model ESTIMATOR.

In the first step, the relations among the variables of flow, 

concentration, and time are quantified in ESTIMATOR; 

therefore, concentrations are predicted for the days in the 

period of record in which discharge was measured but raw 

water-quality concentrations were not (Helsel and Hirsch, 

1992). In the second step, the model-predicted daily concentrations are multiplied by daily mean discharge values to 

estimate daily load values. These daily load values are 

summed to obtain both monthly and annual loads for each of 

the four study sites. An explanation of how streamflow, 

time, and seasonal terms are used in model simulation to predict daily constituent concentrations is presented in Cohn 

and others (1989).

To correct for a log-transformed bias associated with 

log-linear regression, a Minimum Variance Unbiased Estimator (MVUE) is used in ESTIMATOR—it is documented 

in Bradu and Mundlak (1970) and discussed in Gilroy and 

others (1990). The ESTIMATOR model incorporates a 

MVUE for correcting the bias when transforming data from 

“log space” to “real space.” An Adjusted Maximum Likelihood Estimator (AMLE) is used in the model to assign concentration values to censored data values—data below a 

detectable limit. The AMLE is discussed further in Cohn 

(1988) and Cohn and others (1992).

The size of the basin is the primary factor in determining 

the volume of captured precipitation in that basin. The 

amount of rainfall and snowmelt directly affects surfacewater runoff and ground-water recharge, and, subsequently, 

streamflow. As a result, increased discharge increases 

loads, and therefore affects water quality. In addition to 

visual comparison of loads between basins, annual loads 

were “normalized” by using basin area to calculate yields, 

which can be used to make meaningful comparisons among 

basins of different sizes. Taking the mean-annual discharge 

or annual load and dividing by the drainage area of the study 

site basin determined annual yields.

Annual nutrient and sediment loads were calculated 

based on a calendar year. The quality of the data set greatly 

affects the accuracy of the regression produced by the

ESTIMATOR model. If the regression is not performed on 

different flow conditions, the slope of the regression line will 

adversely affect the extrapolation of concentration values. In 

other words, the relation developed between concentration 

and flow will not be representative of the undersampled flow 

conditions. The model simulates actual conditions with at 

least 21 observations above detectable limits for at least each 

of the 2 consecutive years (Baire and others, 2000). Every 

effort was made to meet this guideline at each study site. 

Monthly base-flow and stormflow water-quality samples 

were collected for each site, totaling 90–120 samples at each 

site during the study period of 5 calendar years, from 1997 

through 2001.

A standard error of prediction (SEP) within a 95-percent 

confidence interval is used in ESTIMATOR to calculate 

loads. A SEP is generated to indicate how well the estimated 

regression model fits a “true” regression model (Darrell and 

others, 1999). SEP is a function of the variability between 

the estimated and predicted loads on the days of measurement. SEPs are presented along with their respective study 

site loads in appendix A.

Calculation of Trends Trends are the statistically significant, measurable tendencies for streamflow, concentration, 

or load to change over time. Trends can be used to quantify 

improving, degrading, or unchanged water-quality conditions over time. For this study, trends in (1) streamflow, (2) 

load, (3) flow-weighted concentration, and (4) flow-adjusted 

concentration were calculated for the four study sites. Each 

trend analysis was used to characterize changes within the 

study basins during the 5-year study period.

Trends were calculated for each of the three selected constituents for which loads were determined. These trends are 

expressed as a percent change during the period of record. A 

positive percent change, or upward trend, indicates a degrading trend in concentration or load. A negative percent 

change, or downward trend, indicates an improving trend 

either in concentration or load. The probability that a computed trend is real and not caused by random variations in 

the data is measured by the probability value (p-value) of 

the time coefficient (Johnson and Belval, 1998). A lower 

p-value indicates greater confidence in a trend. For this 

study, a p-value that was less than 0.05 was considered 

significant. In other words, a trend with a p-value of 0.05 

has a 95-percent chance that the computed trend truly is 

present in the data, and is not a result of random variation.

Trend in streamflow (also referred to as flow or discharge) helps to indicate natural hydrologic changes. Natural fluctuations in flow affect water-quality concentrations, 
14 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001

loads, and trends. Trend in flow was calculated using parametric log regression with time. Trend in load represents the 

temporal change of a particular water-quality constituent 

delivered downstream to a particular point—in this case, the 

point of sample collection.

Flow-weighted concentration was calculated by dividing 

the average monthly load by the average monthly streamflow (Langland and others, 2001). The resulting flowweighted concentration provides a more representative, or 

truer, monthly concentration than is represented by a point in 

time (sample value). This trend in flow-weighted concentration is not adjusted for flow, and therefore may be useful in 

comparing trends in nontidal areas to those in the tidal estuaries.

Concentrations and loads can fluctuate over time as flow 

conditions change. This fluctuation makes the characterization of trends by use of only time-series plots of raw concentration data difficult. Additionally, the effectiveness of 

BMPs are difficult to assess. To characterize trends over 

time under uniform flow conditions for the period of record, 

trend in flow-adjusted concentration was used. Trend in 

flow-adjusted concentration was calculated by predicting 

daily concentration values using only season and streamflow 

terms (not time) in the ESTIMATOR model. A non-parametric Kendall-Theil test (Helsel and Hirsch, 1992) was 

used on residual concentrations, the difference between predicted and observed concentrations, thereby removing the 

effect of flow. When flow is removed, other factors, such as 

land use and BMPs within the basin, may become apparent.

Concentrations, Loads, and Trends at Study 

Sites

Concentrations of Nutrients and Suspended Sediment

The distribution of selected water-quality constituents

for each of the four study sites is shown in boxplots of 

the data (fig. 6). Concentrations are presented in timeseries plots (figs. 7–10), and summary statistics for the 

concentrations measured from January 1, 1997 through 

December 31, 2001, are shown in table 3. These data provide the basis for analysis of loads and yields for this study. 

Concentrations for phosphorus and suspended sediment 

increased with increased streamflow at all four sites, and the 

rate of increase in concentration was amplified during 

extreme high-flow conditions. 

The representation of targeted storm samples at the four 

study sites results in a bias in the distribution of each year’s 

data. As a result, the mean and the median presented in the 

table and boxplots are not representative of the true mean 

and median for the population of total nitrogen, total phosphorus, and suspended-sediment concentrations. Percentiles 

for total nitrogen, total phosphorus, and suspended-sediment 

concentrations presented in this report do accurately represent the sample mean and sample median, however.

Chesterville Branch Streamflow and total nitrogen, 

phosphorus, and suspended-sediment concentrations (fig. 7) 

were measured at the Chesterville Branch gaging station 

from 1997 through 2001. Total nitrogen concentrations 

ranged from 1.20 to 8.70 mg/L, with a median of 6.1 mg/L 

(table 3). Total nitrogen concentrations were correlated 

poorly with discharge. Total phosphorus and suspendedsediment concentrations were correlated positively with 

discharge. Total phosphorus and suspended-sediment 

concentrations were at their highest levels during Hurricane 

Floyd (September 1999) and other high-flow events (fig. 7). 

Total phosphorus concentrations ranged from less than 

(<) 0.001 to 1.280 mg/L, with a median of 0.076 mg/L. 

Suspended-sediment concentrations ranged from 3.1 to 

608 mg/L, with a median of 15.0 mg/L.

Conodoguinet Creek Streamflow was measured and 

water samples were collected and analyzed for total nitrogen, total phosphorus, and suspended-sediment concentration at the Conodoguinet Creek gaging station from 1997 

through 2001 (fig. 8). Total nitrogen concentrations ranged 

from 2.4 to 5.1 mg/L, with a median of 3.8 mg/L. Total 

nitrogen concentrations were correlated poorly with discharge. Total phosphorus concentrations ranged from 

<0.005 to 0.50 mg/L, with a median of 0.03 mg/L. Total 

phosphorus concentrations were correlated poorly with discharge. Suspended-sediment concentrations ranged from 

1.0 to 490 mg/L, with a median of 8.0 mg/L. Suspendedsediment concentrations were correlated positively with 

discharge.

North Fork Shenandoah River Streamflow and total 

nitrogen, phosphorus, and suspended-sediment concentrations were measured at the North Fork Shenandoah River 

gaging station from 1997 through 2001 (fig. 9). Total 

nitrogen concentrations ranged from 0.59 to 4.10 mg/L, 

with a median of 2.10 mg/L, and concentrations were correlated poorly with discharge. Total phosphorus concentrations ranged from <0.01 to 0.94 mg/L, with a median of 

0.193 mg/L, and concentrations were correlated poorly with 

discharge. Suspended-sediment concentrations ranged from 

0.5 to 652 mg/L, with a median of 8.1 mg/L, and concentrations were correlated positively with discharge.

South Fork Shenandoah River Streamflow and total 

nitrogen, phosphorus, and suspended-sediment concentrations were measured at the South Fork Shenandoah River 

from 1997 through 2001 (fig. 10). Total nitrogen concentrations ranged from 0.40 to 3.40 mg/L, with a median of 

1.40 mg/L, and were correlated poorly with discharge. Total 

phosphorus concentrations ranged from <0.01 to 0.77 mg/L, 

with a median of 0.131 mg/L, and were correlated poorly 

with discharge. Suspended-sediment concentrations ranged 

from 0.3 to 755 mg/L, with a median of 7.3 mg/L, and were 

correlated positively with discharge.

Loads of Nutrients and Suspended Sediment 

Selected loads for each of the four study sites are tabulated by site, parameter, and year in appendix A. Annual 

load estimates are discussed in the following respective site 
Concentrations, Loads, and Trends at Study Sites 15
16 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001
Concentrations, Loads, and Trends at Study Sites 17
18 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001
Concentrations, Loads, and Trends at Study Sites 19
20 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001

 

 Table 3. Summary statistics for selected water-quality constituents monitored

 at the study sites in the Chesapeake Bay watershed, 1997–2001

[All values are in milligrams per liter; <, less than; mean was calculated with all values less than the

 reporting limit set at the reporting limit, possibly giving a slight positive bias to the estimate of the mean]

Statistic

Total 

nitrogen

Total 

phosphorus

Suspended

sediment

Chesterville Branch near Crumpton, MD

Number of observations 122 126 85

Minimum 1.20 <0.001 3.1

Mean 5.89 0.203 45.9

Median 6.10 0.076 15.0

Maximum 8.70 1.28 608

Conodoguinet Creek near Hogestown, PA

Number of observations 81 86 86

Minimum 2.40 <0.005 1.0

Mean 3.74 0.0622 36.7

Median 3.80 0.03 8.0

Maximum 5.10 0.50 490

North Fork Shenandoah River near Strasburg, VA

Number of observations 113 110 106

Minimum 0.59 <0.01 0.5

Mean 2.12 0.228 44.4

Median 2.10 0.193 8.1

Maximum 4.10 0.94 652

South Fork Shenandoah River at Front Royal, VA

Number of observations 102 111 110

Minimum 0.40 <0.01 0.3

Mean 1.45 0.157 42.9

Median 1.40 0.131 7.3

Maximum 3.40 0.77 755
Concentrations, Loads, and Trends at Study Sites 21

 

sections. These estimates provide the basis for analysis of 

yields and trends for this study.

Chesterville Branch The annual loads of total nitrogen 

entering the Chesapeake Bay from Chesterville Branch measured near Crumpton, MD ranged from 38 tons/yr in 1999 to 

56 tons/yr in 1997 (appendix A). The annual load of total 

phosphorus ranged from 0.6 tons/yr in 1997 to 3.4 tons/yr in 

1999, and the annual load for suspended sediment ranged 

from 220 tons/yr in 2001 to 1,349 tons/yr in 1999. Total 

annual loads for total phosphorus and suspended sediment 

were much higher in 1999 than during the other 4 years of 

the study period. Outlier data may be attributed to Hurricane 

Floyd and could have positively biased phosphorus and 

suspended-sediment load estimates for the month of 

September 1999 as well as the annual loads for 1999. The 

SEP is especially high for phosphorus (79 percent) and suspended sediment (71 percent) for 1999, while for other 

years, the SEP was below 25 percent (appendix A). The SEP 

affected the yield calculations for those two constituents 

(discussed later in the Comparison of Study Sites section), 

where mean annual discharge showed that 1999 was not 

apparently a distinctly wet year during the study period 

(fig. 11). During Hurricane Floyd, a total of over 12 inches 

of rainfall fell between September 15–17, 1999, and peak 

(instantaneous) discharge3 was recorded at 3,220 ft3/s 

(Tallman and Fisher, 2001). The flood recurrence interval on 

Chesterville Branch was not computed because the streamflow-gaging station had not been in operation long enough to 

provide the data needed to produce meaningful statistics 

(Tallman and Fisher, 2001). However, the estimated recurrence intervals for flooding from Hurricane Floyd in the 

nearby Morgan Creek and Unicorn Branch sub-basins in the 

Chester River Basin were 85 and 200 years, respectively 

(Doheny and Dillow, 2002).

Conodoguinet Creek The annual load of total nitrogen 

entering the Chesapeake Bay from Conodoguinet Creek 

measured near Hogestown, PA ranged from 1,189 tons/yr in 

2001 to 3,029 tons/yr in 1998. The annual load for total 

phosphorus ranged from 27 tons/yr in 2001 to 90 tons/yr in 

1998, and the annual load for suspended sediment ranged 

from 12,950 tons/yr in 2001 to 71,353 tons/yr in 1998. Total 

annual loads for all three constituents were higher in 1998 

than during the other 4 years in the study period, because 

1998 was a relatively wet year compared to other recent 

years. There was no apparent effect on annual loads from 

Hurricane Floyd in 1999, a relatively dry year.

North Fork Shenandoah River The annual load of total 

nitrogen entering the Chesapeake Bay from the North Fork 

Shenandoah River measured near Strasburg, VA ranged from 

714 tons/yr in 2000 to 2,205 tons/yr in 1998. The annual 

load for total phosphorus ranged from 32 tons/yr in 1997 to 

181 tons/yr in 2001, and the annual load for suspended sediment ranged from 4,828 tons/yr in 2000 to 174,536 tons/yr in 

1998. Total annual loads for all three constituents at the 

North Fork Shenandoah River gaging station were significantly higher during 1998 than during the other 4 years in the 

study period (with the exception of 2001, during which relatively high phosphorus loads also occurred). These high 

loads can be attributed to 1998 having been a wet year.

The SEP is high (greater than 16 percent) at all study 

sites for suspended-sediment loads, but is highest for the 

North Fork Shenandoah River Basin (29–98 percent). This 

high SEP indicates that there is a lower confidence level in 

the corresponding load values. Further analysis of the relation between larger basin size and higher SEP may be helpful in explaining this SEP.

South Fork Shenandoah River The annual load of total 

nitrogen entering the Chesapeake Bay from the South Fork 

Shenandoah River measured at Front Royal, VA ranged 

from 1,136 tons/yr in 2001 to 4,813 tons/yr in 1998. The 

annual load for total phosphorus ranged from 121 in 1997 to 

471 tons/yr in 1998, and the annual load for suspended sediment ranged from 17,051 tons/yr in 1999 to 347,315 tons/yr 

in 1998. As with the North Fork Shenandoah River Basin, 

the total annual loads for all three constituents at the South 

Fork Shenandoah River were significantly higher during 

1998 than during the other 4 years in the study period 

(appendix A). This result can be attributed to 1998 being a 

wet year.

Trends of Nutrients and Suspended Sediment

Selected trends for each of the four study sites are tabulated by site, parameter, and type of trend in appendix B. 

Trend results are discussed in the following sections on 

study sites.

3. Mean daily discharge for September 16, 1999, was 722 ft3/s.
22 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001

Chesterville Branch A significant upward (degrading) 

trend in flow-adjusted concentration and flow-weighted concentration for total phosphorus during the study period was 

evident, but no significant trends in load and flow-weighted 

concentration were observed for total nitrogen or suspended 

sediment (appendix B).

Factors affecting trends or relations between streamflow 

and constituent loading at Chesterville Branch are difficult to 

assess because of the small size of the basin and the flashy 

response to precipitation, runoff, and snowmelt. In addition, 

there was no significant trend in flow during the study period 

(appendix B), so determining whether BMPs had any effect 

is problematic. This basin would have been ideal to study 

the effects of BMPs because there historically has not been 

any large change in land use for tens of years.

Conodoguinet Creek There was a downward trend in 

flow during the study period. There was a significant downward (improving) trend in load for total nitrogen, and a 

significant upward (degrading) trend in flow-adjusted concentration for total phosphorus and suspended sediment during the study period (appendix B).

North Fork Shenandoah River Phosphorus and sediment 

generally are transported by runoff (Brooks and others, 

1991). As a result, there usually is a corresponding upward 

trend in phosphorus and suspended-sediment concentrations 

if there is an upward trend in flow. Although there was an 

upward trend in load, in flow-adjusted concentration, and in 

flow-weighted concentration for phosphorus (appendix B) at 

the North Fork Shenandoah River, there was no corresponding trend in flow or suspended sediment as might be 

expected. Further evaluation at this site would help determine why runoff apparently was not a factor in the increase 

of phosphorus concentration.

Although there was an upward trend in flow-adjusted 

concentration for nitrogen during a 1985–96 study (Johnson 

and Belval, 1998), there was no significant trend either in 

load, flow-adjusted concentration, or flow-weighted concentration for total nitrogen during the current study. The reason for this result is not known at this time.

South Fork Shenandoah River There was a downward 

trend in flow during the study period. There was a significant downward (improving) trend in load and flow-weighted 

concentration for total nitrogen, and there was a significant 

upward (degrading) trend in flow-adjusted concentration for 

total phosphorus (appendix B).

A downward trend in flow-adjusted concentration for 

phosphorus was documented in a 1985–96 study and discussed in Johnson and Belval (1998). The reason for the 

change in trend direction is not known at this time.

Comparison of Study Sites

Part of this study included analysis of the basins encompassing the study sites to provide information to resource 

managers formulating tributary strategies aimed at TMDLs. 

To highlight individual basin characteristics, all four study 

basins were compared by yields to each other and to the nine 

RIM site basins. Annual loads were normalized by using 

basin area to calculate yields, which can be used to make 

meaningful comparisons between annual and/or monthly 

loads and basins of different sizes (fig. 12). As discussed in 

the Data Analysis section, annual yield was determined by 

taking the mean-annual discharge or annual load and dividing by the drainage area of the study site basin. The results 

of this analysis showed higher nitrogen yields in basins with 

higher percentages of agricultural land, whereas lower values of nitrogen loads and yields were indicated for areas with 

higher percentages of forested land and less agriculture. 

There was no apparent relation between land use and phosphorus or suspended-sediment yields. 

Hurricane Floyd positively biased monthly (September 

1999) and annual load estimates (1999) for Chesterville 

Branch. This bias subsequently affected the yield calculations, especially for phosphorus and suspended sediment, 

where mean annual discharge in 1999 was not unusually 

high during the study period (fig. 11).

High annual yields for total nitrogen, total phosphorus, 

and suspended sediment (figs. 12 a–c) at Conodoguinet 

Creek were positively associated with higher annual streamflow. Annual yields for all three constituents had the highest 

values in 1998, the year with the highest streamflow.

High annual yields for total nitrogen and suspended sediment (figs. 12a and 12c) at North Fork Shenandoah River 

were positively associated with higher annual streamflow 

(appendix A). Annual yields for nitrogen and suspended 

sediment were highest in 1998, the year with the highest 

mean annual streamflow. Annual yields for phosphorus also 

were high in 1998 and 2001.

High annual yields for total nitrogen, total phosphorus, 

and suspended sediment (figs. 12a–c) at the South Fork 

Shenandoah River were associated with higher annual 

streamflow. Annual yields for all three constituents had the 

highest values in 1998, the year with the highest streamflow.

The South Fork Shenandoah River Basin (1,642 mi2) is 

more than twice the size of the North Fork Shenandoah 

River Basin (768 mi2). Both basins have nearly identical 

mean annual yields (appendix A) of nitrogen and nearly 

identical percentages of primary land-use types (fig. 2), with 

the exception of yield in 2001. Similar observations were 

noted during the 1985–96 study described in Johnson and 

Belval (1998).

Study site yields in relation to percentages of agricultural, forested, and developed land use are shown in figures 

13–15. The three land uses are used for comparison because 

they show the greatest differences from other common landuse types. 

A series of linear regressions was performed for the 

four study sites, as well as the nine RIM sites to compare 

the relation between nutrient and suspended-sediment yields 

and land-use type (figs. 13–15). The RIM sites were used 

for additional data points for comparison and regression 

analysis. Mean annual yields of nitrogen, phosphorus, and 
Comparison of Study Sites 23
24 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001
Summary and Conclusions 25

suspended sediment were plotted and regressed against 

percentages of three major land uses in the Chesapeake Bay 

watershed: agricultural, forested, and developed lands. 

Plots showed a strong, positive linear correlation (positive 

slope) between the percentage of agricultural land within a 

basin and the nitrogen yield. This sub-plot (fig. 13a) had the 

largest coefficient of determination (R2= 0.93) of any of the 

relations indicating that this is the best relation of those presented. Phosphorus yields (fig. 13b) showed the same relation to the percentage of agricultural land as that of nitrogen, 

but contained more outliers and had a lower R2 value (0.66). 

There was a strong, negative linear correlation (R2= 0.79) 

between nitrogen and forested land (fig. 14a). This correlation indicated that yields of nitrogen decrease with an 

increasing percentage of forested lands in a basin. A lower 

negative correlation (R2= 0.58) was calculated between 

phosphorus yield and the percentage of forested lands (fig. 

14b). There was no significant correlation between suspended sediment and any of the three major land uses (figs. 

13c, 14c, and 15c). There was no apparent relation between 

nitrogen, phosphorus, and suspended-sediment yields and 

percentage of developed land (figs. 15 a–c).

Summary and Conclusions

The Chesapeake Bay Program has determined that 

excess nitrogen, phosphorus, and suspended sediment can 

trigger unbalanced algae growth and poor water-quality conditions that deprive living resources of oxygen and sunlight. 

By reducing nutrient and sediment loads to the bay, scientists 

predict water quality would improve by relieving low dissolved-oxygen conditions, reducing algal blooms, and 

improving water clarity. Since 1985, the River Input Monitoring Program has estimated the load of nutrient and sediment constituents in the nine major tributaries draining the 

Chesapeake Bay watershed.

This report presents the results of a study in cooperation 

with the Maryland Department of Natural Resources, the 

Virginia Department of Environmental Quality, and the

Pennsylvania Department of Environmental Protection that 

was conducted in four basins of the Chesapeake Bay 

watershed. The watershed drains 64,000 square miles in 

Delaware, the District of Columbia, Maryland, New York, 

Pennsylvania, Virginia, and West Virginia. The study 

included (1) base-flow and stormflow water-quality sampling on a monthly basis from 1997 through 2001, (2) estimation of monthly and annual nutrient and sediment loads 

using the U.S. Geological Survey ESTIMATOR model, and 

(3) calculation of trends in streamflow, load, flow-adjusted 

concentration, and flow-weighted concentration. This study 

provided supplemental information to the River Input Monitoring Program by presenting short-term water-quality data 

and estimated loads at four sites from 1997 through 2001.

The four study sites (Chesterville Branch, Conodoguinet 

Creek, North Fork Shenandoah River, and South Fork 

Shenandoah River) were selected to meet the goals and 

objectives set forth by the Chesapeake Bay Program Monitoring and Assessment subcommittee. The basins encompassing the study sites include a wide range of land use, 

geographic, and geologic regions, draining such diverse 

areas as the forested, agricultural, and developed land of the 

Appalachian Plateau of New York and Pennsylvania, the 

Valley and Ridge of the Pennsylvania and West Virginia 

highlands, the Shenandoah Valley of Virginia, and the flat 

lowlands of Maryland’s Eastern Shore and Delaware.

The Chesterville Branch Basin is the smallest (6.12 

square miles) of the four study site basins, and is located in 

a predominantly agricultural region of Maryland’s Eastern 

Shore. The site was chosen to supplement the River Input 

Monitoring Program location on the Choptank River, which 

is more forested and developed than the Chesterville Branch. 

The Conodoguinet Creek Basin lies mostly within the Valley 

and Ridge Physiographic Province in Pennsylvania. This 

site was selected because land use is changing rapidly from 

agriculture to developed lands within the basin.

The North Fork Shenandoah River in Virginia was chosen for study because of recent increases in agricultural 

intensity and a shift in nitrogen source from fertilizer to 

poultry manure. This site was monitored in conjunction with 

the South Fork Shenandoah River in Virginia to allow the 

separation of Virginia’s contribution and the contributions of 

West Virginia and Maryland to nutrient and sediment loads 

in the Potomac River Basin. The South Fork Shenandoah 

River is the largest of the study basins, and recently has been 

losing agricultural and forested land to increased urbanization and development.

The results of the study showed higher nitrogen and 

phosphorus loads and yields in basins with higher percentages of agricultural land, whereas lower values of nitrogen 

loads and yields were indicated for areas with higher percentages of forested land and less agriculture. There was no 

apparent relation between land use and suspended-sediment 

loads or yields.

Land-use characteristics are important in the determination of factors affecting trends. Basins that predominantly 

are agricultural tend to have applied a proportionally greater 

amount of fertilizers than forested or developed areas. In 

this study, determining relations between nutrient loads and 

factors, such as fertilizers sales, fertilizer application rates, 

manure loads, or animal densities within basins, was problematic because of the lack of agricultural census data that 

corresponded with the study period (1997–2001). The connection between nutrient loads and land development also 

could not be established. The period of record, which 

included 2 drought years (1997 and 2001) and Hurricane 

Floyd (1999), was probably too short to differentiate the 

effect of increased development from climatic variability in 

any of the study basins and draw meaningful conclusions.

Both Conodoguinet Creek and South Fork Shenandoah 

River had the highest nitrogen, phosphorus, and suspendedsediment loads and yields in the years of highest annual total 

streamflow. Similarly, loads and yields of total nitrogen and 
26 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001

suspended sediment were related to annual total streamflow 

in the North Fork Shenandoah River. Total phosphorus, 

however, did not show the same pattern. Chesterville 

Branch had the highest phosphorus and suspended-sediment 

loads and yields as a result of Hurricane Floyd in 1999, 

which was not the year with the highest annual total streamflow.

Chesterville Branch, Conodoguinet Creek, and the North 

and South Fork Shenandoah River Basins represent various 

and unique land-use, geologic, hydrologic, and hydrogeomorphic characteristics. Activities within a basin, such as 

the use of combined sewer overflows, may affect water quality. The Chesapeake Bay Program may benefit from additional studies that consider specific basin characteristics and 

how they affect nutrient and sediment loads and yields. 

Although the data and analysis from this study established a 

baseline of water quality at these four sites, additional monitoring and tracking of loads in selected basins would help 

identify long-term trends and factors affecting those trends.

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28 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001

 

Appendix A. Annual load estimates and yield calculations for study sites: Chesterville Branch near 

Crumpton, Maryland; Conodoguinet Creek near Hogestown, Pennsylvania; 

North Fork Shenandoah River near Strasburg, Virginia; and South Fork Shenandoah 

River at Front Royal, Virginia

[mi 2 , square mile; kg/yr, kilogram per year; kg/mi 2/yr, kilogram per square mile per year; ton/yr, ton per year; ton/mi 2/yr, ton per 

square mile per year. The standard errors of prediction also are provided. The standard error of prediction is a measure of the 

expected difference between an individual estimate and the estimated daily load. Station: U.S. Geological Survey streamflowgaging and water-quality station number. Parameters: TN, total nitrogen; TP, total phosphorus; and SSC, suspended-sediment 

concentration]

Standard Error of

Prediction

Standard Error of

Prediction

Station

number

Basin

area

(mi 2)

USGS

parameter

code Parameter Year

 Annual

 Load

 (kg/yr)

 + / -

 (kg/yr)

 + / -

(Percent)

Annual

 Yield

(kg/mi2/yr)

Annual

 Load

(ton/yr)

 + / - 

(ton/yr)

 + / -

(Percent)

 Annual

 Yield

 (ton/mi2/yr)

Chesterville Branch near Crumpton, MD 

01493112 6.12 P00600 TN 1997 50,882 2,629 5 8,314 56.1 2.9 5 9.16

01493112 6.12 P00600 TN 1998 44,124 1,234 3 7,210 48.6 1.4 3 7.95

01493112 6.12 P00600 TN 1999 34,433 1,222 4 5,626 38.0 1.3 4 6.20

01493112 6.12 P00600 TN 2000 39,044 1,029 3 6,380 43.0 1.1 3 7.03

01493112 6.12 P00600 TN 2001 41,376 1,465 4 6,761 45.6 1.6 4 7.45

01493112 6.12 P00665 TP 1997 504 118 23 82 0.6 0.1 23 0.09

01493112 6.12 P00665 TP 1998 1,423 288 20 233 1.6 0.3 20 0.26

01493112 6.12 P00665 TP 1999 3,091 2,447 79 505 3.4 2.7 79 0.56

01493112 6.12 P00665 TP 2000 1,658 343 21 271 1.8 0.4 21 0.30

01493112 6.12 P00665 TP 2001 1,121 266 24 183 1.2 0.3 24 0.20

01493112 6.12 P80154 SSC 1997 123,372 22,382 18 20,159 136.0 24.7 18 22.22

01493112 6.12 P80154 SSC 1998 323,534 52,834 16 52,865 356.6 58.2 16 58.27

01493112 6.12 P80154 SSC 1999 1,224,140 871,692 71 200,023 1,349.4 960.9 71 220.48

01493112 6.12 P80154 SSC 2000 313,667 54,374 17 51,253 345.8 59.9 17 56.50

01493112 6.12 P80154 SSC 2001 199,932 37,680 19 32,669 220.4 41.5 19 36.01

Conodoguinet Creek near Hogestown, PA 

01570000 470 P00600 TN 1997 1,930,059 75,992 4 4,107 2,127.5 83.8 4 4.53

01570000 470 P00600 TN 1998 2,747,494 72,431 3 5,846 3,028.5 79.8 3 6.44

01570000 470 P00600 TN 1999 1,531,903 35,378 2 3,259 1,688.6 39.0 2 3.59

01570000 470 P00600 TN 2000 1,512,403 35,946 2 3,218 1,667.1 39.6 2 3.55

01570000 470 P00600 TN 2001 1,079,020 35,814 3 2,296 1,189.4 39.5 3 2.53

01570000 470 P00665 TP 1997 31,019 12,144 39 66 34.2 13.4 39 0.07

01570000 470 P00665 TP 1998 81,697 18,980 23 174 90.1 20.9 23 0.19

01570000 470 P00665 TP 1999 33,207 7,633 23 71 36.6 8.4 23 0.08

01570000 470 P00665 TP 2000 32,584 5,667 17 69 35.9 6.2 17 0.08

01570000 470 P00665 TP 2001 24,841 7,729 31 53 27.4 8.5 31 0.06

01570000 470 P80154 SSC 1997 38,611,053 19,428,930 50 82,151 42,560.7 21,416.4 50 90.55

01570000 470 P80154 SSC 1998 64,731,394 18,118,683 28 137,726 71,352.9 19,972.1 28 151.81

01570000 470 P80154 SSC 1999 17,330,905 5,197,019 30 36,874 19,103.7 5,728.6 30 40.65

01570000 470 P80154 SSC 2000 12,455,660 2,526,287 20 26,501 13,729.8 2,784.7 20 29.21

01570000 470 P80154 SSC 2001 11,748,262 4,413,563 38 24,996 12,950.0 4,865.0 38 27.55
Appendixes 29

 

Appendix A. Annual load estimates and yield calculations for study sites: Chesterville Branch near 

Crumpton, Maryland; Conodoguinet Creek near Hogestown, Pennsylvania; 

North Fork Shenandoah River near Strasburg, Virginia; and South Fork Shenandoah 

River at Front Royal, Virginia—Continued

Standard Error of

Prediction

Standard Error of

Prediction

Station

number

Basin

area

(mi 2)

USGS

parameter

code Parameter Year

 Annual

 Load

 (kg/yr)

 + / -

 (kg/yr)

 + / -

(Percent)

Annual

 Yield

(kg/mi2/yr)

Annual

 Load

(ton/yr)

 + / - 

(ton/yr)

 + / -

(Percent)

 Annual

 Yield

 (ton/mi2/yr)

North Fork Shenandoah River near Strasburg, VA 

01634000 768 P00600 TN 1997 986,641 74,478 8 1,285 1,087.6 82.1 8 1.42

01634000 768 P00600 TN 1998 2,000,322 105,482 5 2,605 2,204.9 116.3 5 2.87

01634000 768 P00600 TN 1999 696,065 34,968 5 906 767.3 38.5 5 1.00

01634000 768 P00600 TN 2000 647,467 28,822 4 843 713.7 31.8 4 0.93

01634000 768 P00600 TN 2001 881,471 54,762 6 1,148 971.6 60.4 6 1.27

01634000 768 P00665 TP 1997 28,574 4,461 16 37 31.5 4.9 16 0.04

01634000 768 P00665 TP 1998 148,257 21,086 14 193 163.4 23.2 14 0.21

01634000 768 P00665 TP 1999 70,406 7,618 11 92 77.6 8.4 11 0.10

01634000 768 P00665 TP 2000 86,963 8,073 9 113 95.9 8.9 9 0.12

01634000 768 P00665 TP 2001 164,420 27,818 17 214 181.2 30.7 17 0.24

01634000 768 P80154 SSC 1997 36,179,427 29,886,661 83 47,109 39,880.3 32,943.9 83 51.93

01634000 768 P80154 SSC 1998 158,339,439 82,095,939 52 206,171 174,536.4 90,493.8 52 227.26

01634000 768 P80154 SSC 1999 5,743,956 2,494,897 43 7,479 6,331.5 2,750.1 43 8.24

01634000 768 P80154 SSC 2000 4,379,962 1,265,568 29 5,703 4,828.0 1,395.0 29 6.29

01634000 768 P80154 SSC 2001 36,602,503 35,789,211 98 47,660 40,346.7 3,9450.2 98 52.53

South Fork Shenandoah River at Front Royal, VA 

01631000 1,642 P00600 TN 1997 1,912,439 172,132 9 1,165 2,108.1 189.7 9 1.28

01631000 1.642 P00600 TN 1998 4,366,077 260,124 6 2,659 4,812.7 286.7 6 2.93

01631000 1.642 P00600 TN 1999 1,218,784 61,886 5 742 1,343.5 68.2 5 0.82

01631000 1,642 P00600 TN 2000 1,349,342 62,126 5 822 1,487.4 68.5 5 0.91

01631000 1,642 P00600 TN 2001 1,030,299 76,383 7 627 1,135.7 84.2 7 0.69

01631000 1,642 P00665 TP 1997 109,464 14,500 13 67 120.7 16.0 13 0.07

01631000 1,642 P00665 TP 1998 427,365 53,288 12 260 471.1 58.7 12 0.29

01631000 1,642 P00665 TP 1999 137,239 12,730 9 84 151.3 14.0 9 0.09

01631000 1,642 P00665 TP 2000 170,210 14,655 9 104 187.6 16.2 9 0.11

01631000 1,642 P00665 TP 2001 112,337 14,110 13 68 123.8 15.6 13 0.08

01631000 1,642 P80154 SSC 1997 29,054,829 9,784,497 34 17,695 32,026.9 10,785.4 34 19.50

01631000 1,642 P80154 SSC 1998 315,084,158 122,424,059 39 191,890 347,315.0 134,947.2 39 211.52

01631000 1,642 P80154 SSC 1999 15,468,601 4,185,743 27 9,421 17,050.9 4,613.9 27 10.38

01631000 1,642 P80154 SSC 2000 18,043,287 3,414,841 19 10,989 19,889.0 3,764.2 19 12.11

01631000 1,642 P80154 SSC 2001 17,245,857 5,777,642 34 10,503 19,010.0 6,368.7 34 11.58
30 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001 Appendix B. Trends in streamflow, load, flow-weighted concentration, and flow-adjusted concentration data for study sites: Chesterville Branch near Crumpton, Maryland; Conodoguinet Creek near Hogestown, Pennsylvania; North Fork Shenandoah River near Strasburg, Virginia; and South Fork Shenandoah River at Front Royal, Virginia

[Station: U.S. Geological Survey streamflow-gaging and water-quality station number. Trend: Q, streamflow; FWC, flow-weighted concentration; FAC, flow-adjusted concentration; 

Parameters: Q, streamflow; TN, total nitrogen; TP, total phosphorus; and SSC, suspended-sediment concentration. Statistics: test, regression (Reg), Kendall Theil (KT); 

p-value, measure of significance of regressor at 0.05; trend direction, upward (up), downward (down), bold “up” or “down” are significant at 95-percent confidence level,

residuals are not significant (ns); Magnitude: minimum, and maximum percentage change in trend indicated for period of record; --, not applicable or insufficient data]

Statistics

Magnitude

Stationnumber

Period of record Trend Parameter Test

Logtransform

Regression

slope

p-value Normality

Trend

direction Trend Minimum Maximum

Chesterville Branch near Crumpton, Maryland01493112 1997–2001 Q Q Reg yes -0.02637 0.4143 0.86819 ns -10.0115 -29.979 15.64901493112 1997–2001 load TN Reg yes -0.03759 0.1144 0.96027 ns -13.9595 -28.381 3.36601493112 1997–2001 FWC TN Reg yes -0.0112 0.4102 0.8349 ns -4 -14 601493112 1997–2001 FAC TN KT yes -0.0018 0.8914 -- ns -1 -13 1301493112 1997–2001 load TP Reg yes 0.131593 0.1335 0.92352 ns 69.278 -14.016 233.25801493112 1997–2001 FWC TP Reg yes 0.1580 0.0106 0.9622 up 88 18 200

01493112 1997–2001 FAC TP KT yes 0.1237 0.0244 -- up 85 7 221

01493112 1997–2001 load SSC Reg yes 0.05422 0.5463 0.85642 ns 24.2195 -38.321 150.17501493112 1997–2001 FWC SSC Reg yes 0.0806 0.1987 0.8868 ns 38 -15 12401493112 1997–2001 FAC SSC KT yes 0.0547 0.2303 -- ns 31 -17 109
Appendixes 31

 Appendix B. Trends in streamflow, load, flow-weighted concentration, and flow-adjusted concentration data for study sites: 

 Chesterville Branch near Crumpton, Maryland; Conodoguinet Creek near Hogestown, Pennsylvania; North Fork Shenandoah River near Strasburg, Virginia; and South Fork Shenandoah River at Front Royal, Virginia—Continued

Statistics

Magnitude

Stationnumber

Periodof record Trend Parameter Test

Logtransform

Regression

slope p-value Normality

Trend

direction Trend Minimum Maximum

Conodoguinet Creek near Hogestown, Pennsylvania01570000 1997–2001 Q Q Reg yes -0.18118 0.0014 0.98247 down -51.5532 -68.275 -26.0177

01570000 1997–2001 load TN Reg yes -0.17787 0.0011 0.98526 down -50.9081 -67.2676 -26.372201570000 1997–2001 FWC TN Reg yes 0.0033 0.3845 0.9722 ns 1 -2 401570000 1997–2001 FAC TN KT yes 0.0050 0.6892 -- ns 3 -10 1701570000 1997–2001 load TP Reg yes -0.09046 0.4871 0.96683 ns -30.3612 -74.73 91.91101570000 1997–2001 FWC TP Reg yes 0.0907 0.2438 0.9521 ns 44 -21 16301570000 1997–2001 FAC TP KT yes 0.2760 0.0000 -- up 296 103 67501570000 1997–2001 load SSC Reg yes -0.29324 0.0611 0.96713 ns -69.0549 -90.704 3.01501570000 1997–2001 FWC SSC Reg yes -0.1121 0.2760 0.9510 ns -36 -71 4201570000 1997–2001 FAC SSC KT yes 0.1435 0.0205 -- up 105 10 281
32 Nutrient and Sediment Concentrations, Loads, and Trends, Chesapeake Bay Watershed, 1997–2001 Appendix B. Trends in streamflow, load, flow-weighted concentration, and flow-adjusted concentration data for study sites: Chesterville Branch near Crumpton, Maryland; Conodoguinet Creek near Hogestown, Pennsylvania; North Fork Shenandoah River near Strasburg, Virginia; and South Fork Shenandoah River at Front Royal, Virginia—Continued Statistics Magnitude Station number Period of record Trend Parameter Test Log transform Regression slope

p-value Normality

Trend

direction Trend Minimum Maximum

North Fork Shenandoah River near Strasburg, Virginia01634000 1997–2001 Q Q Reg yes -0.07965 0.2394 0.97231 ns -27.284 -56.963 22.86201634000 1997–2001 load TN Reg yes -0.06508 0.4193 0.97249 ns -22.92 -58.8 44.20901634000 1997–2001 FWC TN Reg yes 0.0146 0.3294 0.9757 ns 6 -6 1901634000 1997–2001 FAC TN KT yes 0.0223 0.2769 -- ns 12 -9 3701634000 1997–2001 load TP Reg yes 0.349258 0.0001 0.93501 up 304.318 124.221 629.0701634000 1997–2001 FWC TP Reg yes 0.4289 0.0001 0.9758 up 456 339 60501634000 1997–2001 FAC TP KT yes 0.4477 0.0000 -- up 834 514 1,321

01634000 1997–2001 load SSC Reg yes -0.21732 0.1924 0.93435 ns -58.075 -88.474 52.49401634000 1997–2001 FWC SSC Reg yes -0.1377 0.1824 0.9032 ns -42 -74 2801634000 1997–2001 FAC SSC KT yes -0.0845 0.2788 -- ns -34 -70 44
Appendixes 33

 Appendix B. Trends in streamflow, load, flow-weighted concentration, and flow-adjusted concentration data for study sites:

 Chesterville Branh near Crumpton, Maryland; Conodoguinet Creek near Hogestown, Pennsylvania; North Fork Shenandoah River near Strasburg, Virginia; and South Fork Shenandoah River at Front Royal, Virginia—Continued

Statistics

Magnitude

Stationnumber

Periodof record Trend Parameter Test

Logtransform

Regression

slope p-value Normality

Trend

direction Trend Minimum Maximum

South Fork Shenandoah River at Front Royal, Virginia01631000 1997–2001 Q Q Reg yes -0.13965 0.0132 0.95862 down -42.7986 -62.689 -12.3056

01631000 1997–2001 load TN Reg yes -0.20862 0.0064 0.96462 down -56.5895 -75.622 -22.6975

01631000 1997–2001 FWC TN Reg yes -0.0690 0.0020 0.9827 down -24 -36 -10

01631000 1997–2001 FAC TN KT yes -0.0215 0.3924 -- ns -10 -30 1601631000 1997–2001 load TP Reg yes -0.08366 0.2703 0.93641 ns -28.4393 -60.284 28.937801631000 1997–2001 FWC TP Reg yes 0.0560 0.0708 0.9621 ns 25 -1 5901631000 1997–2001 FAC TP KT yes 0.1058 0.0095 -- up 70 13 154

01631000 1997–2001 load SSC Reg yes -0.29182 0.0649 0.92159 ns -68.8783 -90.76 4.828101631000 1997–2001 FWC SSC Reg yes -0.1522 0.1442 0.9140 ns -46 -76 2201631000 1997–2001 FAC SSC KT yes 0.0697 0.2567 -- ns 42 -24 163