Changes in Streamflow and Water Quality 

in Selected Nontidal Sites in the 

Chesapeake Bay Basin, 1985-2003

by Michael J. Langland, Scott W. Phillips, Jeff P. Raffensperger, and Douglas L. 

Moyer

U.S. Department of the Interior 

U.S. Geological Survey

In cooperation with the U.S. Environmental Protection Agency, Chesapeake Bay Program;

the Maryland Department of Natural Resources; and the Virginia Department of Environmental Quality

Scientific Investigations Report 2004-5259
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services 

Box 25286, Denver Federal Center 

Denver, CO 80225

For more information about the USGS and its products: 

Telephone: 1-888-ASK-USGS 

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

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.

Suggested citation:

Langland, M.J., Phillips, S.W., Raffensperger, J.P., and Moyer, D.L., 2004, Changes in streamflow and water quality in 

selected nontidal sites in the Chesapeake Bay Basin, 1985-2003: U.S. Geological Survey Scientific Investigations 

Report 2004-5259, 50 p.
 iii

Contents

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

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

Purpose and Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Methods and Approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Data-Set Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Description and Evaluation of Methods and Techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Streamflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Load Computations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Concentrations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Observed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Flow-Weighted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Flow-Adjusted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Summary of Changes in Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Changes in Streamflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Annual Mean Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Quarterly Mean Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Changes in Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Observed Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Flow-Weighted Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Flow-Adjusted Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Summary and Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

References Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Appendix 1. Quarterly-mean streamflow for the Choptank, Patuxent , Appomattox, Rappahannock, 

Pamunkey, and Mattaponi Rivers, 1985-2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Appendix 2. Statistical summaries for water-quality concentration data for total nitrogen (A), 

total phosphorus (B), and sediment (C) for the Choptank, Patuxent, Rappahannock, Mattaponi,

Pamunkey, and Appomattox Rivers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Appendix 3. Trends in flow-adjusted concentration data for 9 River Input Monitoring Program sites 

and 24 Multi-Agency Nontidal Program Sites in the Chesapeake Bay Watershed, 1985-2003 . . . . . . 41

Figures

1. Map showing location and site number for the 33 sites used in this study, Chesapeake Bay 

watershed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2. Boxplot showing the percent change in magnitude using the revised equation

(linear and quadratic coefficients) to estimate trend as compared to the old method 

(linear coefficient) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

3. Graph showing variation in annual mean flow entering the Chesapeake Bay, 1935-2003, 

using computations as described in Bue (1968) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4. Graphs showing quarterly mean streamflow for the Susquehanna (1985-2003), Potomac 

(1985-2003), and James (1989-2003) Rivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
iv 

Figures—Continued

5. Boxplots showing range in observed concentrations for the nine River Input Monitoring sites,

Chesapeake Bay watershed, 1985-2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6. Boxplots showing annual distribution of observed total nitrogen, total phosphorus, and

sediment concentrations collected at the River Input Monitoring sites for the 

Susquehanna (A), Potomac (B), and James Rivers (C) in the Chesapeake Bay watershed, 

1984-2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

7. Graphs showing flow-weighted concentrations for the Susquehanna, Potomac, 

and James Rivers entering the Chesapeake Bay for 1988-2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

8-10. Maps showing:

8. Trends in flow-adjusted concentrations for total nitrogen, Chesapeake Bay watershed, 

1985-2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

9. Trends in flow-adjusted concentrations for total phosphorus, Chesapeake Bay watershed, 

1985-2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

10. Trends in flow-adjusted concentrations for sediment, Chesapeake Bay watershed, 

1985-2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

11-12. Graphs showing:

11. Significance and range in magnitude in trend for flow-adjusted concentrations from the 

ESTIMATOR model for the nine River Input Monitoring sites, Chesapeake Bay watershed, 

1985-2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

12. Combined annual flow and total nitrogen, total phosphorus, and sediment load for the

nine River Input Monitoring sites flowing into the Chesapeake Bay for 1990-2003. . . . . . . . . . . . . . . 26

Tables

1. Streamflow and water-quality station numbers for the 9 River Input Monitoring Program and

24 Multi-Agency Program sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2. Nitrogen, phosphorus, and sediment species tested for trend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3. Summary of trend tests, results of evaluations, and suggested approaches used in this report. . . . . . . 10

4. Minimum, mean, median, and maximum concentrations of total nitrogen, total phosphorus, and 

suspended sediment at the 9 River Input Monitoring sites and 25 Multi-Agency Nontidal

Program sites in the Chesapeake Bay watershed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5. Significant trend direction for the above-normal streamflow in 2003 (1985-2003 trends) and 

below-normal streamflow in 2002 (1985-2002 trends) calendar years. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
 v

Conversion Factors and Datum

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

(NAVD 88).

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

Concentrations of chemical constituents and sediment in water are given in milligrams per liter 

(mg/L).

Multiply By To obtain

Area

square mile (mi2) 2.590 square kilometer (km2)

Flow rate

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

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg)

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

Changes in Streamflow and Water Quality in Selected 

Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

by Michael J. Langland, Scott W. Phillips, Jeff P. Raffensperger, and Douglas L. Moyer

Abstract

Water-quality and streamflow data from 33 sites in nontidal portions of the Chesapeake Bay Basin were analyzed to 

document annual nutrient and sediment loads and trends for 

1985 through 2003 as part of an annual evaluation of waterquality conditions by the Chesapeake Bay Program. As part of 

this study, different trend tests and methodologies were evaluated for future use in assessment of the effectiveness of management actions in reducing nutrients and sediments to the 

Chesapeake Bay. Trends in streamflow were tested at multiple 

time scales (daily, monthly, seasonal, and annual), resulting in 

only one significant trend (annual flow for Choptank River near 

Greensboro, Md.). Data summaries for observed concentrations 

indicate higher ranges in total-nitrogen concentrations in the 

northern five major river basins in Pennsylvania, Maryland, and 

Virginia compared to the southern five basins in Virginia. Similar comparisons showed no distinct differences for total phosphorus. Flow-weighted concentration is useful in evaluating 

changes through time for the Susquehanna, Potomac, and James 

Rivers. Results indicate the Potomac River had the highest 

flow-weighted concentrations (2.5 milligrams per liter) for total 

nitrogen, and the Potomac and James Rivers averaged about the 

same (0.15 milligram per liter) for total-phosphorus concentrations. Flow-weighted concentrations were lowest in the Susquehanna River for phosphorus and sediment because of the trapping efficiency of three large reservoirs upstream from the 

sampling point. Annual loads were estimated by use of the U.S. 

Geological Survey’s ESTIMATOR model. Annual nutrient and 

sediment loads in 2003 were the second highest total nitrogen, 

total phosphorus, and sediment loads for the River Input Monitoring sites since 1990. Trends in concentrations, when adjusted 

for flow, can be used as an indicator of human activity and management actions. The flow-adjusted trends indicated significant 

decreasing trends at approximately 55, 75, and 48 percent of the 

sites for total nitrogen, total phosphorus, and sediment, respectively. This suggests management actions are having some 

effect in reducing nutrients and sediments. Sampling protocols 

for the river inputs to the bay have targeted high flows. Because 

this sampling strategy creates the potential for bias in estimated 

loads and trends, calculations are limited to flow-adjusted loads 

and trends in this report.

Introduction

The Chesapeake Bay has been adversely affected by nitrogen and phosphorus enrichment. The excess nutrients stimulate 

algal blooms that decay to consume dissolved oxygen and cause 

areas of low dissolved-oxygen concentrations in the bay. The 

algal blooms, along with sediment, also block sunlight needed 

by underwater grasses. In the mid-1980s, the Chesapeake Bay 

Program (CBP), a partnership between the Commonwealths of 

Pennsylvania and Virginia, the State of Maryland, the District 

of Columbia, the federal government, and the Chesapeake Bay 

Commission, began efforts to reduce nutrients and sediments in 

the bay. However, improvement in water-quality conditions in 

the bay has been slow, and the bay was listed as an “impaired” 

water body under the regulatory statues related to the Clean 

Water Act. The CBP has developed water-quality criteria (U.S. 

Environmental Protection Agency, 2003) and is implementing 

actions to reduce nutrients and sediments entering the bay in an 

attempt to meet these criteria by 2010. 

Progress toward the nutrient and sediment reduction goals 

has been evaluated by the CBP through the use of watershed 

and estuarine water-quality models. Additionally, water-quality 

and living-resource data are compiled annually and analyzed to 

assess the response of the watershed and the bay to nutrientreduction strategies and other factors affecting water quality 

and living resources. These results are used to update environmental indicators that are distributed to the public annually by 

the CBP and to help refine restoration strategies. 

The U.S. Geological Survey (USGS) has participated in 

the annual evaluation of water-quality trends since the early 

1990s. The USGS first reported trends from the River-Input 

Monitoring (RIM) sites using multivariate regression techniques developed by Cohn and others (1992), which are further 

explained in Darrell and others (1998). The trend technique 

attempts to adjust for the influences of river flow and season to 

help understand concentration trends related to management 
2 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

actions. Although this technique is useful in helping assess the 

water-quality change primarily resulting from management 

actions, the results could not be appropriately compared to 

trends in the tidal waters, because those trends were not 

adjusted for flow and season. Therefore, the USGS developed 

additional trend approaches to aid in the comparison of tidal and 

nontidal data (Langland and others, 1999). Some of the additional approaches included trends in streamflow, load, and 

flow-weighted concentrations (FWC). 

Annual updates of trends using these techniques have 

resulted in some further questions about the most appropriate 

techniques to use to (1) address changes in water quality that 

impact the ecosystem of the bay and its watershed, and 

(2) assess the influence of management actions to reduce nutrient and sediment concentrations. To evaluate the techniques 

needed to address these issues and to better explain the factors 

affecting the trends in the watershed, the USGS began a 3-year 

study in 2003 in partnership with the CBP and the Maryland 

Department of Natural Resources (MdDNR). The first year of 

the study focused on evaluation of existing trend techniques and 

assessment of approaches to determine trend in observed concentration and load. 

Purpose and Scope

This report presents results from the first year of the study. 

It presents changes in streamflow and in flow-adjusted concentrations (FAC) of nutrients and sediment from 33 sites from 

1985 to 2003. This report also presents an initial evaluation of 

techniques to describe changes in streamflow, concentrations, 

and loads in the Chesapeake Bay watershed.

Methods and Approach

This section includes (1) a discussion of how data sets used 

to assess water quality and streamflow were constructed and 

(2) a description and evaluation of the methods used to analyze 

the data sets. Additionally, the results of an evaluation of the 

trend techniques reported in Langland and others (1999) and 

trend in observed concentration are presented.

Data-Set Construction

The USGS maintains and annually updates a “nontidal 

database” containing selected water-quality and biological data 

from approximately 1,320 sites in nontidal areas of the Chesapeake Bay watershed. The data base is comprised of waterquality and flow data from sites with a minimum of 3 consecutive years of samples between 1972 and 2003. Although many 

sites have water-quality analyses programs that were collected 

on a routine (usually monthly) basis, many of these sites do not 

have a continuous flow record, which is necessary to compute 

annual loads. Water-quality data are updated annually at 30-35 

sites and are updated about every 3-4 years at as many additional sites in the database as possible. New sites are added to 

the database if the site has at least 12 samples collected over 

3 continuous years and at least 1 sample from each season in the 

3 years (spring, summer, fall, winter).

The sites have been organized into two programs for data 

analysis, the RIM and Multi-Agency Nontidal Programs, both 

providing information from the nontidal areas of the bay. As 

part of the RIM, water-quality and flow data are collected and 

analyzed by the USGS at nine sites near the most downstream 

limit of nontidal waters (fig. 1). Through the Multi-Agency 

Nontidal Programs, long-term, water-quality data are collected 

by several agencies at approximately 100 sites in the nontidal 

watershed. A subset of sites with long-term (10-15 years), 

water-quality and flow data are used to determine annual and 

seasonal changes in streamflow concentrations and to estimate 

loads. Trend calculations were completed at an additional 24 

sites (fig. 1) by the USGS in cooperation with the MdDNR, Virginia Department of Environmental Quality (VaDEQ), Washington D.C. Council of Governments (WashCOG), and the Susquehanna River Basin Commission (SRBC). Site information 

for the 33 sites analyzed as part of the 2003 annual CBP reevaluation is listed in table 1.

 A total of 42 physical, biological, and chemical waterquality constituents are available in the nontidal database. 

These constituents include 14 nutrient species, total suspended 

sediment (SED), and total suspended solids (TSS) (referred to 

as sediment). A time series of mean daily streamflow was 

retrieved from the USGS National Water Information System 

(NWIS) database. The updated water-quality database and the 

USGS streamflow database provided the input data files to estimate annual loads and trends. Concentration data were quality 

assured using a statistical program that identified suspect 

remark codes (such as less than detection), missing dates, and 

(or) missing times associated with the sample before they were 

added to the database. In addition, statistical tests and visual 

examination of the raw and residual data were made before and 

during their use in the various trend and load analysis programs.

The following species (forms) of nitrogen and phosphorus, 

SED, and TSS were evaluated for trends, and annual loads were 

estimated where applicable (table 2). Because of analytical differences between determinations of SED and TSS, concentrations of SED tend to be higher and more accurate than TSS 

(Kammerer and others, 1998). However, for the report, SED 

and TSS concentrations are grouped together as SED.

Records were missing for some water-quality constituents 

in some data sets. Where possible, missing values for these constituents were calculated from the reported species of the constituent. Missing constituents were estimated only for the input 

data files used to calculate loads and trends and generally were 

not populated in the original USGS nontidal database. If the 

concentration of more than one of the nitrogen species used in 

calculating total nitrogen was below the detection limit, then no 

estimate was made or was reported as less than the combined 

minimum reporting limit. In some data sets, total nitrogen and 

total phosphorus are calculated as the sum of the particulate and 

dissolved constituents.
Introduction 3

Figure 1. Location and site number for the 33 sites used in this study, Chesapeake Bay watershed.
4 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Table 1. Streamflow and water-quality station numbers for the 9 River Input Monitoring Program and 24 Multi-Agency Program sites.

[Site ID; figure 1 identification number; mi2, square miles]

Streamflow

station

Water-quality

station

Latitude 

(DDMMSS)

Longitude

(DDMMSS)

Site ID 

(fig. 1)

Drainage area 

(mi2

) Station name

River Input Program Sites

01491000 01491000 385950 754710 8 113 Choptank River near Greensboro, Md. 

01578310 01578310 393928 761029 7 27,100 Susquehanna River at Conowingo, Md.

01594440 01594440 385721 764136 11 348 Patuxent River near Bowie, Md.

01646580 PR01 385546 770701 23 11,600 Potomac River at Chain Bridge, Md.

01668000 01668000 381920 773105 25 1,596 Rappahannock River near Fredericksburg, Va. 

01673000 01673000 374603 771957 27 1,081 Pamunkey River near Hanover, Va.

01674500 01674500 375316 770948 28 601 Mattaponi River near Beulahville, Va.

02035000 02035000 374015 780510 32 6,257 James River at Cartersville, Va.

02041650 02041650 371330 772832 33 1,344 Appomattox River at Matoaca, Va. 

Multi-Agency Program Sites

01531500 01531500 414555 762628 1 7,797 Susquehanna River at Towanda, Pa.

01540500 01540500 405729 763710 2 11,220 Susquehanna River at Danvillle, Pa.

01553500 01553500 405803 765236 3 6,859 West Branch Susquehanna River at Lewisburg, Pa.

01567000 01567000 402842 770746 4 3,354 Juniata River at Newport, Pa.

01576000 01576000 400316 763152 5 25,990 Susquehanna River at Marietta, Pa.

01576754 01576754 395647 762205 6 470 Conestoga River at Conestoga, Pa.

01586000 NPA0165 393000 765300 9 56.6 Patapsco River at Hollofield, Md.

01592500 PXT0809 390700 765231 10 132 Patuxent River at Laurel, Md.

01599000 GEO0009 392936 790242 12 47 Georges Creek near Franklin, Md.

01601500 WIL0013 393941 784650 13 247 Wills Creek near Cumberland, Md.

01610000 POT2766 393218 782717 14 3,109 Potomac River at Paw Paw, WVa.

01613000 POT2386 394149 781036 15 4,073 Potomac River at Hancock, Md.

01614500 CON0180 394256 774931 16 501 Conococheague Creek at Fairview, Md.

01626000 1BSTH027.85 380326 785429 17 127 South River near Waynesboro, Va.

01631000 1BSSF003.56 385449 781240 18 1,642 S F Shenandoah River at Front Royal, Va.

01634000 1BNFS010.34 385836 782011 19 768 N F Shenandoah River near Strasburg, Va.

01638500 POT1595 391624 773238 20 9,651 Potomac River at Point of Rocks, Md.

01643000 MON0155 392313 772158 21 817 Monocacy River at Reels Mill, Rd., Md.

01646000 1ADIF000.86 385833 771446 22 58 Difficult Run near Great Falls, Va.

01666500 3-ROB001.90 381930 780545 24 179 Robinson Creek near Locast Dale, Va.

01671020 8-NAR005.42 375100 772541 26 463 North Anna at Hart Corner near Doswel, Va.

02013100 2JKS023.61 374719 800003 29 614 Jackson Creek below Dunlop Creek at Covington, Va.

02026000 2-JMS229.14 373211 784939 30 3,680 James River at Bent Creek, Va.

02029000 2-JMS189.31 374751 782747 31 4,584 James River at Scottsville, Va.
Introduction 5

The optimum period for reporting trend results in this 

study would begin in January 1985 and end in December 2003. 

Shorter time-series data are acceptable if they meet certain criteria. For the load model and any trend test, the data set must 

contain a minimum of 10 years and 100 samples representing 

“monthly” intervals, 10 years and 40 quarterly samples, or a 

mixture of both types with at least 10 years and 75 samples. Ideally, samples would represent the full range of the hydrograph 

during the estimation time period. Loads and trends were estimated on data sets for any period of 10 years or more starting 

between January 1985 and January 1989 and continuing 

through December 2002.

Description and Evaluation of Methods and 

Techniques

The following section provides descriptions of the tests 

used to evaluate current methods of load and trend estimations. 

Several types of techniques were evaluated to address changes 

in streamflow and water quality. These techniques included 

trends in streamflow, concentrations, and load. Based on the 

evaluation of techniques and statistical analysis, some trends 

procedures used in previous reports are now considered inappropriate because of the data-set structure. A summary of the 

trend methods, issues, and results of the evaluation discussed in 

more detail in the report are summarized at the end of this section.

Streamflow

Streamflow and streamflow variation have important consequences for water quality in the bay and watershed. The quantity of flow affects the salinity levels, freshwater/saltwater interface location, and stratification of water in the bay. Nutrient and 

sediment loads are a function of streamflow and may vary as 

streamflow changes from year to year. The concentration of a 

chemical in a stream or river will tend to exhibit some dependence on streamflow as dilution occurs or as the contributions 

from different flow paths or sources vary. It is important, therefore, to examine trends in streamflow because this information 

may help explain or understand trends in water quality.

Trends in streamflow may indicate changes in climatological or hydrological conditions over time. These changes can be 

caused by both natural and anthropogenic factors. Precipitation, 

evapotranspiration, and ground water are the primary natural 

factors determining streamflow; land-use change and other 

anthropogenic factors (diversions) also may affect streamflow.

A technique using linear regression to determine the trend 

in streamflow was presented in Langland and others (1999) and 

was evaluated for use in the present study. Linear regression 

(ordinary least squares) is a tool that can be used to describe the 

relation between some variable of interest and one or more 

other variables (Montgomery and Peck, 1982; Helsel and Hirsch, 1992). Application of the method is straightforward; a linear relation is obtained by regressing a response variable (such 

as streamflow) against one or more explanatory variables (such 

as time).

Evaluation of time series of daily-mean and monthly-mean 

streamflow for this study found the data residuals generally are 

autocorrelated so that trend estimation can be difficult. Autocorrelation problems may be overcome using a number of possible approaches. One approach used to overcome autocorrelation problems was to increase the averaging period. Time series 

of quarterly-mean streamflow were constructed based on four 

“seasons”—January-February-March, April-May-June, JulyAugust-September, and October-November-December. Time 

series of annual-mean streamflow for each site, as well as for 

the total freshwater flow to the bay, also were constructed. The 

Table 2. Nitrogen, phosphorus, and sediment species tested for trend.

[N, nitrogen; mg/L, milligrams per liter]

Constituent Species (Parameter code) Units Abbreviation

Nitrogen Total nitrogen (00600) mg/L TN

Dissolved Kjeldahl nitrogen (00623) mg/L DKN

Total Kjeldahl nitrogen (00625) mg/L TKN

Total ammonia (00608) as N mg/L TNH4

Dissolved ammonia (00610) as N mg/L DNH4

Total or dissolved nitrate, or, total or dissolved nitrite plus nitrate (00618, 00620, 00630, or 00631) 

as N

mg/L NO3+2

Phosphorus Total phosphorus (00665) mg/L TP

Dissolved phosphorus (00666) mg/L DP

Dissolved inorganic phosphorus (00671) mg/L DIP

Suspended sediment (80154) mg/L SED

Total suspended solids (00530) mg/L SED
6 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

annual-mean streamflow time series provide a basis for evaluating inter-annual variability; the quarterly-mean time series 

allow for examining trends for a particular season.

An approach that was not used in this study involves use 

of time-series models that include autoregressive (AR) and 

moving average (MA) terms, such as an autoregressive integrated moving average process model (ARIMA) or seasonal 

ARIMA (Box and Jenkins, 1976). Time-series models efficiently estimate model coefficients with autocorrelated errors, 

and provide meaningful inference of the coefficient estimates. 

Future work may pursue application of time-series process 

models to streamflow within the Chesapeake Bay watershed.

The time series were modeled by regressing the natural 

logarithm of streamflow against time:

(1)

where

ln is the natural logarithm function;

y is annual-mean streamflow or quarterly-mean streamflow for a particular season, in cubic feet per 

second;

β0 is a constant;

β1 is the coefficient on time and estimates the trend;

t is time, in years; and

ε is the unexplained noise or error in the data.

To evaluate trends, a null hypothesis of a zero coefficient 

on time (β1) was tested. If the coefficient was significantly different from zero in a two-tailed test, the null hypothesis was 

rejected, and it was concluded that a linear trend over time 

exists. A p-value of 0.05 or less was considered significant for 

this study.

In evaluating the application of linear regression to trend 

estimation for streamflow, a general observation is that very 

few statistically significant trends were found for quarterlymean and annual-mean streamflow for the sites listed in table 1 

over the study period. However, graphical depiction of the data 

and summary statistics can provide insights into variations in 

flow in the Chesapeake Bay watershed. For each time series, the 

25th, 50th (or median), and 75th percentiles of the data were calculated. The data were plotted as bars. The bars were colored 

blue if the mean flow for that time period was above the 75th

percentile, red if below the 25th percentile, and black if within 

the interquartile range (between the 25th and 75th percentiles).

Load Computations

The constituent load in a stream is highly related to and 

dependent on flow. The load represents the amount of a given 

constituent transported and delivered downstream, a part of 

which will eventually reach the tidal portions of the rivers 

draining into the bay. In previous reports, a trend in monthly 

load was estimated to aid in explaining changes in water quality 

and living resources in the bay and tidal estuaries and assessing 

the effectiveness of CBP Nutrient-Reduction Strategies. 

Loads of nutrients and suspended sediment were computed 

using the USGS 7-parameter, log-linear regression model 

(ESTIMATOR) developed by Cohn and others (1989). The 

ESTIMATOR computes loads in two steps. First, a center-estimate linear model is fit to the logarithms of the concentration 

using ordinary least squares (eqn. 2). The model uses the Minimum Variance Unbiased Estimator (MVUE) developed by 

Bradu and Mundlak (1970) to correct for bias when transforming data from “log” to “arithmetic” space. The Adjusted Maximum Likelihood Estimator (AMLE) (Cohn, 1988) is used to 

estimate the log-linear model for sites having censored observations, which are concentration values below a detectable limit. 

The model is of the form:

(2)

where

ln is the natural logarithm function;

C is measured concentration, in milligrams per liter;

Q is measured streamflow, in cubic feet per second;

T is time, measured in decimal years;

are centering variables for streamflow and time;

βx are parameters estimated by ordinary least squares

(non-censored data) and minimum variance

(censored data); and

β0 is a constant;

β1 and β2 describe the relation between concentration and

flow;

β3 and β4 describe the relation between concentration and time

apart from flow;

β5 and β6 describe seasonal variation in concentration data; 

and 

ε is combined independent random error, assumed to be 

normally distributed with zero mean and variance

.

Second, the model uses observed concentration data and 

streamflow to estimate a daily load (eqn. 3). 

Ld = Qd × Ce × K (3)

where, for any day (d)

Ld is daily mean load, in kilograms per day;

Qd is daily mean discharge, in cubic feet per second;

Ce is estimated (e) daily concentrations, in milligrams per

liter; and

K is 2.447, conversion factor for unit conversion.

The daily load estimates are summed to produce monthly and 

annual loads. The standard errors are estimated using formulas 

in Gilroy and others (1990) and Cohn and others (1992). The 

ln( ) y β0 β1 = + +t ε ln[] β C o β1ln[ ] Q ⁄ Q β2{ } ln[ ] Q ⁄ Q 2

β3[ ]β T – T 4[ ] T – T 2

β5 [ ]β 2πT 6 sin + cos[ ]ε 2πT + ,

+ +

+ +

+

=

Q and T

σε

2
Introduction 7

standard error of prediction (SEP) predicts how close the regression model is to the “true” regression model; in other words, 

how close the predicted load values are to the “true” load values 

(Darrell and others, 1998). The results from any linear-regression model can be subject to residual non-normality and lack of 

residual homogeneity. This could indicate a bias in model coefficients, or bias the restransformation adjustment. To aid in the 

“inspection” of output from ESTIMATOR, the following guidelines are utilized:

1. The probability plot correlations coefficient (measure of 

normality) must be greater than 0.96.

2. There should be “constant variance” (random variation) 

shown in the residual plots, indicating no bias with any 

individual predictor variable.

3. Outliers—ideally the range for residuals should be 

within 2 standard deviations (Y-axis).

If any of the above cannot be adequately resolved, the 

trend results from ESTIMATOR probably should not be 

reported and an alternative method for trend determination considered.

As part of a “reevaluation” of current trend methodology, 

trends based on estimated loads in any time series (monthly, 

annual, or using the loads in flow-weighted concentrations) 

from the ESTIMATOR model are not reported because of concerns that the load estimates in the time series are not independent of each other and are not representative of the true variability in the data. These deficiencies may result in a biased 

assessment of trend leading to the detection of spurious significant results. In addition, the potential bias introduced from the 

targeted sampling protocols used at the RIM sites is a concern. 

Targeting higher flow events to reduce error due to the log-linear relation between concentration and flow is appropriate for 

load estimation using ESTIMATOR. However, targeting could 

possibly bias linear-trend results for non-flow adjusted tests. 

For this report, changes in loads are described, but a statistical 

approach to determine significance was not reported.

Concentrations

Previous reports have discussed techniques to estimate 

trends in FWC and FAC (Langland and others, 1999; Darrell 

and others, 1998). Trends in observed and FWC were not 

reported this year because of technical concerns with the data 

sets. Trends in FAC were estimated using a revised approach to 

estimate significance and magnitude of trend.

Observed

Observed TN, TP, and SED concentrations are presented 

in tabular and graphical form. Observed TN, TP, and SED are 

presented for the 24 multi-agency sites and 9 RIM sites. These 

data are presented as the sample minimum, mean, median, and 

maximum for the period of record. Additionally, boxplots of 

annual TN, TP, and SED are presented later in the report for 

each of the nine RIM sites. These boxplots provide information 

on the annual distribution of TN, TP, and SED concentrations 

observed at each RIM site. 

Data from the RIM sites were used to evaluate changes in 

water quality with time using linear regression. This technique 

was attempted to better compare the nontidal trends to the 

trends in tidal data. The results indicate a significant change 

over time in observed concentration could not be detected for 

TN, TP, and SED in the majority of the RIM sites and the trend 

results that were calculated are not valid. The primary reason 

for this result can be directly linked to the observed variability 

of TN, TP, and SED concentrations in these rivers. The RIM 

sampling protocol has been developed in a manner that will provide greater accuracy in predicted load estimates. At the same 

time, the RIM sampling protocol is not designed to accurately 

quantify trends in observed concentration. RIM samples are 

collected over a range of flow conditions; higher flow events 

are given added importance. At each site, 20-30 samples are 

collected each year; at least 1 sample is collected routinely each 

month and the remaining 10-20 samples are collected from 

storm events. The range of concentrations, along with the number of samples collected, varies during different flow and seasonal events and therefore contributes to the inability to detect 

a significant trend. As a result, trends in observed TN, TP, and 

SED concentration are not presented in this report. 

The representation of targeted storm samples at the nine 

RIM sites results in a positive 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 TN, TP, and SED concentration. However, the mean and median for TN, TP, and SED presented in this report do accurately represent the sample mean 

and sample median.

The USGS is evaluating other techniques used to provide 

trends in observed data. These techniques include conducting a 

trend test just on the routine monthly samples collected from the 

RIM and other nontidal sites or selecting samples for trend testing to represent the flow distribution at each site.

Flow-Weighted 

A trend in FWC represents a trend not adjusted for flow 

and may be useful in comparing to trends in the bay and tidal 

portions of the rivers. It is important to account for flow variability because the volume of flow occurring in short time periods between sample intervals is likely to have a more pronounced and longer effect on average concentrations in the tidal 

waters. Because ESTIMATOR uses daily flow to predict a daily 

concentration, which is summed to a monthly load, the resultant 

FWC should provide a more accurate estimate of the concentration than the single monthly sample. In previous reports (Langland and others, 1999), a monthly FWC was calculated by 

dividing the monthly load (from ESTIMATOR) by the monthly 

streamflow. However, as discussed in the “Load Computations” 

section, there are concerns about conducting trend analyses on 

estimated loads because of the potential for biased and unreli-
8 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

able trend statistics. Therefore, trends in monthly FWC are not 

reported. Instead, annual FWC results are summarized and presented. The FWC data are useful to help evaluate changes over 

time within a river basin, make comparisons among different 

river basins, and make comparisons to tidal data.

Flow-Adjusted

Concentrations of water-quality constituents commonly 

are correlated with streamflow and season. The cause of this 

relation varies by the constituent and the individual river basin. 

For example, in point-source dominated basins, the input of 

constituent sources is relatively constant. An increase in streamflow will most likely result in decreased concentrations as a 

result of dilution. In nonpoint-source dominated basins, constituent concentrations entering the stream from overland flow 

most likely will increase as flow increases (Shertz and others, 

1991). This flow-related variability must be reduced or 

removed to obtain water-quality concentrations independent of 

flow. The USGS has developed techniques to compensate for 

the influence of flow variability to better understand changes in 

concentrations that may be the result of human activities (Helsel 

and Hirsch, 1992).

In previous reports, flow-adjusted trends were estimated 

using the coefficient from the “linear time” parameter (β3) from 

the ESTIMATOR load model as follows:

%C = 100{e β3*t - 1} (4)

where 

%C is percent change in flow-adjusted concentration,

e is exponential function,

β3 is coefficient (slope) of the linear time parameter,

and

t is number of years of trend estimation.

A trend was considered significant if the p-value was less 

than or equal to 0.05, with a 95-percent confidence interval.

A comparison of the magnitude of change for FAC using 

three different trend tests, ESTIMATOR, the Seasonal Kendall 

(SK), and the Kendall Theil (KT), was reported in Langland and 

others (1999). The report indicated the trend magnitude results 

generally were comparable, and more significant trends were 

detected using the parametric test (ESTIMATOR) than the nonparametric tests (SK and KT). Further testing of the model was 

performed to access magnitude and significance of trend based 

on the model “centering” dates and using both the linear and 

quadratic time parameters (β3 and β4, in equation 2). 

As constructed, the ESTIMATOR uses orthogonal properties to center the predictor variables and remove covariance 

between model predictors. However, this approach may result 

in a different center date in the model than the center date for 

the period of record of the actual data set. This center date is 

used to estimate the slope, as well as estimate the magnitude of 

change in concentration. Currently, equation 4, containing only 

the linear time parameter (β3), is used to compute the magnitude of change in FAC. As the length of the trend estimation 

time period increases, use of a linear trend model may be less 

useful to detect a significant trend because of the possibility of 

non-linear variability that results from changes in land use, climate, and hydrology. Generally, the power and efficiency of a 

statistical trend test for detecting and estimating magnitude of 

change is improved if the variance of the data is improved. 

Therefore, the nonlinear quadratic (β4) term was incorporated 

to estimate a flow-adjusted trend. Both the difference in a 

change in the centering date and addition of quadratic term are 

included in the revised equation to estimate a flow-adjusted 

trend (eqn. 5).

%C = 100{e (β3*(T1-T0)+2β4(T1-T0)(Tr-Tc)) - 1} (5)

where 

%C is percent change in concentration adjusted for flow,

e is exponential function,

β3 is coefficient (slope) of the linear time parameter,

β4 is coefficient (slope) of the quadratic time parameter,

T0 is the beginning date for period of trend estimation,

T1 is the end date for period of trend estimation,

Tr is the center date of the actual data set,

and 

Tc is the center date of the data from ESTIMATOR.

The significance was then determined by forming a 

2-tailed t-test where the numerator is the exponential portion in 

equation 5 divided by the model standard error. A trend was 

considered significant if the p-value was less than or equal to 

0.05, with a 95-percent confidence interval. The revised equation was used for all 232 trends adjusted for flow in this report. 

The results indicate three trends reported as significant using 

the previous method are nonsignificant.

The resulting change in magnitude using equation 5 indicates a slight increase in median percent change for DP, KJD, 

NH4, NO3, NO3+2, and SED (fig. 2). Slight decreases resulted 

from using equation 5 for DIP, TN, and TP. The variability 

between the 25th and 75th percentile was within 10-percent difference of the mean for all constituents except for DIP. The 

largest decrease in median (-8 percent) and range in variability 

in magnitude difference was for DIP (fig. 2). The greater difference in percent magnitude for DIP may be related to the fact that 

DIP has the largest number of samples that are at or below the 

detection level. Therefore, it should be noted that a large percentage change for DIP does not reflect a large change in concentration.

Summary of Changes in Methods

A summary of the changes resulting from the evaluation of 

methods and techniques in estimating loads and trends is presented. In previous reports, tests for trend were reported for the 

following:

• monthly trend in streamflow

• monthly trend in load
Changes in Streamflow 9

• monthly trend in FWC

• a concentration adjusted for flow and season

In addition, as part of this year’s update and evaluation, 

trends also were proposed for the following, using parametric 

and nonparametric tests:

• daily, seasonal, and annual streamflow

• instantaneous and annual load

• observed concentration

The evaluation of methods raised several concerns with 

(1) sample data sets used to represent concentrations in a river, 

and (2) the statistical tests used to estimate a trend, which are 

summarized in table 3. Water-quality data sample collection 

can be classified into two groups, which are ambient and targeted sampling. Ambient sampling involves a routine sample 

collected at approximately the same interval, usually monthly, 

but targeted sampling contains a combination of ambient and 

higher-flow storm samples. Although this targeting protocol is 

necessary to compute loads using ESTIMATOR-type load 

models, a biased assessment could result when estimating a 

trend in observed concentration and loads. This potential bias is 

the result of the water-quality observations, which may not be 

representative of the true variability in the data. Therefore, 

observed concentrations, FWC, and loads are presented, but a 

statistical test of trend was not performed. In addition, serial 

correlation was a problem for many of the streamflow results, 

and a new approach for estimating a trend in FAC was developed. Therefore, the reevaluation of methods resulted in the 

decisions presented in table 3.

Changes in Streamflow

Changes in streamflow are one of the primary factors 

affecting water quality in the Chesapeake Bay and its watershed. These changes in streamflow can be caused by both natural and anthropogenic factors. Precipitation is the primary natural factor affecting streamflow; however, land-use changes and 

other anthropogenic factors in the watershed also may affect 

streamflow. Variability in flow affects the observed concentrations and the average load and concentration of chemical constituents and sediments delivered to the bay and tidal portions 

of the rivers.

Annual Mean Flow

More than twice the amount of streamflow entered the bay 

in 2003 than in 2002 (fig. 3). This was the third highest amount 

since 1937 when the USGS began keeping records to compute 

estimates of the total streamflow to the bay. These computation 

methods are described in Bue (1968). Between 1940 and 1959, 

15 of the 20 years had annual total streamflow values within the 

interquartile range (between the 25th and 75th percentiles). 

A dry period occurred in the 1960s (6 of the 10 years were 

below the 25th percentile), and wetter conditions occurred in the 

1970s (5 of the 10 years were above the 75th percentile). The 

most variable flows were in the last 10 years, between 1994 and 

2003; only 2 years were within the interquartile range. The wetter conditions observed from 1970 to the present (11 of 34 years

Figure 2. The percent change in magnitude using the revised equation (linear and quadratic coefficients) 

to estimate trend as compared to the old method (linear coefficient).
10 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Table 3. Summary of trend tests, results of evaluations, and suggested approaches used in this report.

Type of trend

Streamflow Concentrations

(observed, flow-weighted, flow-adjusted) Loads 

Time step Quarterly, annual Instantaneous, monthly, annual Instantaneous, monthly, annual

Reason for test Variability of streamflow helps to assess 

changes in water quality in nontidal and 

tidal waters.

Observed concentration gives most direct 

measure of water-quality change. 

Flow-weighted approximates the monthly 

concentration to help explain changes in the 

tidal waters. 

Flow-adjustment compensates for the 

influence of streamflow and seasonality and 

accesses change due to human activities.

Changes in load over time help 

explain changes in tidal waters.

Trend test 

evaluated

Linear regression ESTIMATOR, linear regression Linear regression

Result of 

evaluation

Autocorrelation within daily-mean and 

monthly-mean streamflow time series 

makes trend estimation difficult. 

Very few statistically significant trends 

in quarterly-mean and annual-mean 

streamflow.

Potential for bias in trend assessment due 

to sampling protocols that target higher 

flows. 

Therefore, did not perform trend tests for 

observed or flow-weighted concentration. 

Flow-adjusted concentrations estimated 

using a revised approach.

A trend test for load is based on estimated loads that already have uncertainty. Therefore, a trend in load was 

discontinued. 

Potential for bias in trend assessment 

due to sampling protocols that target 

higher flows.

Suggested 

approach

Continue using linear regression for 

quarterly-mean and annual-mean streamflow. 

Consider use of time-series process 

models for trend estimation.

Develop additional statistical methods to 

“remove bias” and improve an approach 

for trends on observed and flow-weighted 

concentrations.

Develop additional statistical 

methods to incorporate load uncertainty and improve an approach for 

trends on loads.

Figure 3. Variation in annual mean flow entering the Chesapeake Bay, 1935-2003, using computations as described in Bue (1968).
Changes in Water Quality 11

were above the 75th percentile), along with the effects of 

increased nutrients and sediment from human activities, have 

been cited as one possible cause for the declines in dissolved 

oxygen and water clarity in the bay that were documented in the 

1970s and that remain today (Phillips, 2002).

Linear regression models of annual mean streamflow were 

developed for all 33 sites in this study. Only one site (Choptank 

River) yielded a statistically significant trend (eqn. 6).

(6)

where

ln is the natural logarithm function;

y is annual-mean streamflow for a particular season, 

in cubic feet per second;

-78.5 is a constant;

0.04 is the coefficient on time and estimates the trend;

t is time, in years; and

ε is the unexplained noise or error in the data.

with R2 = 0.3 and p-value = 0.01. This model indicates a statistically significant increase in annual-mean streamflow, estimated to be approximately 4 percent per year.

Quarterly Mean Flow

Changes in quarterly-mean streamflow can provide insight 

into hydrological changes within a watershed for a particular 

season and help explain changes in the bay and tidal rivers. Linear regression models were developed for four “seasons” (January-February-March, April-May-June, July-August-September, and October-November-December) for all 33 sites in this 

study. As is the case for daily-mean and monthly-mean streamflow, autocorrelation within the quarterly-mean streamflow 

time series for each season makes trend estimation difficult. 

However, graphical depiction of the seasonal data and some 

summary statistics can provide insights into variations in flow 

in the Chesapeake Bay watershed (fig. 4 and Appendix 1).

A number of observations are common to all RIM sites. 

The drought of 1999-2002 is evident for all nine RIM sites, as 

is the relatively wet 2003. For the three largest rivers (Susquehanna, Potomac, and James, fig. 4), all 12 quarters for 1999 

through 2001 were normal (between the 25th and 75th percentiles) or dry (below the 25th percentile). For all nine RIM sites, 

all four quarters of 2003 exhibited normal or above-normal 

(above the 75th percentile) flows (fig. 4 and Appendix 1).

Changes in Water Quality 

Changes in water quality in terms of concentrations and 

loads are presented for 1985-2003 for most of the sites. Some 

sites have shorter data-collection periods. Results include summary statistics and trends. Not all trends tests previously used 

(Langland and others, 1999) are presented based on the evaluation of trend procedures. Reasons for omitting specific trends 

tests are presented and discussed in the section “Study Methods.”

Observed Concentrations

The most direct measure of change in water quality is 

observed-concentration data. The range of observed concentrations of TN, TP, and SED for the 33 water-quality monitoring 

sites are listed in table 4. TN concentrations were elevated in the 

northern five river basins (Susquehanna, Choptank, Western 

Shore, Patuxent, and Potomac Rivers) compared to TN concentrations in the southern five river basins (Rappahannock, Mattaponi, Pamunkey, James, and Appomattox Rivers). The 

median TN concentrations in the northern five basins ranged 

from 0.90 to 7.50 mg/L, compared to the median TN concentrations in the southern five basins that ranged from 0.43 to 

0.93 mg/L. TP concentrations generally were lower in the five 

northern basins; the median concentrations ranged from 0.017 

to 0.283 mg/L, compared to the median concentrations in the 

southern five basins that ranged from 0.030 to 0.500 mg/L. SED 

concentrations in the Susquehanna River Basin were elevated 

(median range = 13 to 43 mg/L) compared to the remaining nine 

river basins (median range = 3 to 36).

The RIM sites have been established in 9 of the 10 major 

river basins (in this report) within the Chesapeake Bay watershed. The Western Shore River Basin is the only major basin 

not represented by the RIM program. The distribution (10th and 

90th percentiles) of TN, TP, and SED collected at the nine RIM 

sites during 1985-2003 is shown in figure 5. TN concentrations 

generally were elevated at the Susquehanna, Potomac, Patuxent, and Choptank RIM sites, compared to the concentrations 

observed at the Rappahannock, Mattaponi, Pamunkey, James, 

and Appomattox RIM sites. The James and Rappahannock 

River RIM sites exhibited the greatest variability in observed 

TN concentration. TP concentrations at each of the nine RIM 

sites typically ranged from 0.06 to 0.07 mg/L. The greatest variability in TP concentration was observed at the Patuxent, Rappahannock, and James RIM sites. Sediment concentrations also 

were similar at each of the nine RIM sites and typically ranged 

from 4 to 100 mg/L. The Rappahannock and James RIM sites 

exhibited the greatest variability in observed sediment concentration.

Annual distribution of observed TN, TP, and SED concentrations collected at the RIM stations for the three largest basins 

(Susquehanna, Potomac, and James Rivers) in the Chesapeake 

Bay watershed is shown in figures 6A, B, and C. These figures 

include the 10th and 90th data percentiles with “outliers” (data 

points 1.5 times outside the interquartile range) to provide a full 

distribution of the data by site. Annual distribution for each of 

these three constituents collected at the remaining six RIM sites 

are presented in Appendix 2. The primary concern regarding 

water quality within the Chesapeake Bay watershed over the 

past 5 years is to what extent water quality was influenced by 

the extreme variability in flow conditions. The 4-year period, 

1999-2003, was dominated by drought conditions; 2003 was 

one of the wettest years on record (fig. 3). TN concentrations at 

ln( ) y = – 78.5 + + 0.04t ε
12 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 4. Quarterly mean streamflow for the Susquehanna (1985-2003), Potomac (1985-2003), and James (1989-2003) Rivers. For 

each season, 25th, 50th, and 75th percentiles were calculated. Bars representing the quarterly mean flow are red if the value for 

that quarter is below the 25th percentile, blue if above the 75th percentile, and black if between the 25th and 75th percentiles.
Table 4. Minimum, mean, median, and maximum concentrations of total nitrogen, total phosphorus, and suspended sediment at the 9 River Input Monito

Agency Nontidal Program sites in the Chesapeake Bay watershed.

[Station: Map site number, location on figure 1; Flow, USGS streamflow-gaging station number; WQ, water-quality site alphanumeric identity; POR: Sample period of record fo

tics: mg/L, milligrams per liter; Number of samples, samples used in the statistical determination; Min, minimum; Med, median; Max, maximum]

Station Statistics

Flow WQ

Map 

site

number

Drainage 

area

POR

Total nitrogen as N (mg/L) Total phosphorus as P (mg/L) Suspen

Number 

of 

samples

Min Med Mean Max

Number

of

samples

Min Med Mean Max

Number

of 

samples

Susquehanna River Basin

01531500 01531500 1 7,797 1988-2003 472 0.00 1.12 1.19 4.30 519 0.013 0.068 0.093 0.700 1 519 

01540500 01540500 2 11,220 1984-2003 585 .21 1.24 1.34 6.20 656 .010 .070 .099 .730 1 650 01553500 01553500 3 6,850 1984-2003 538 .00 1.04 1.12 6.73 610 .009 .040 .061 .880 1 604 01567000 01567000 4 3,354 1984-2003 461 .44 1.80 1.87 11.46 524 .003 .079 .109 6.300 1 518 01576000 01576000 5 25,990 1986-2003 548 .73 1.60 1.71 7.92 622 .006 .080 .106 .520 1 618 01576754 01576754 6 470 1984-2003 539 1.23 7.50 7.73 30.00 590 .030 .283 .364 4.200 1 608 01578310 01578310 7 27,100 1984-2003 563 .81 1.70 1.75 6.60 586 .010 .045 .055 .320 1 575 

Choptank River Basin

01491000 01491000 8 113 1984-2003 425 .64 1.70 1.69 3.58 435 .007 .065 .078 .330 1 423 

Western Shore River Basin

01586000 NPA0165 9 56.6 1985-2003 217 1.66 4.25 4.22 6.30 217 .010 .028 .048 .503 2 223 

Patuxent River Basin

01592500 PXT0809 10 132 1985-2003 217 .02 1.64 1.67 3.70 220 .010 .033 .044 .950 2 222 

01594440 01594440 11 348 1984-2003 554 1.13 2.20 2.63 8.40 631 .004 .140 .183 1.200 1 551 

Potomac River Basin

01599000 GEO0009 12 72.4 1985-2003 206 .49 1.50 1.52 4.43 214 .010 .047 .079 1.100 2 216 

01601500 WIL0013 13 247 1985-2002 184 .20 1.07 1.15 2.55 190 .010 .017 .033 .382 2 189 01610000 POT2766 14 3,109 1985-2003 197 .40 1.06 1.10 2.25 195 .010 .036 .050 .730 2 193 01613000 POT2386 15 4,073 1985-2003 210 .40 1.01 1.09 4.60 213 .010 .035 .053 .397 2 220 01614500 CON0180 16 501 1985-2003 208 .87 4.65 4.67 7.60 214 .010 .125 .154 .741 2 220 01626000 1BSTH027.85 17 127 1984-2003 181 .36 .90 .93 3.49 184 .010 .100 .099 .400 2 189 01631000 1BSSF003.56 18 1,642 1984-2003 182 .37 1.42 1.54 22.70 184 .010 .100 .163 4.000 2 188 01634000 1BNFS010.34 19 768 1984-2003 178 .35 1.95 2.09 32.60 180 .060 .100 .155 .720 2 180 01638500 POT1595 20 9,651 1985-2003 216 .82 2.05 2.07 4.96 215 .010 .060 .088 2.900 2 225 01643000 MON0155 21 817 1985-2003 211 1.28 3.62 3.63 7.60 214 .015 .166 .218 1.200 2 223 01646000 1ADIF000.86 22 57.9 1984-2003 171 .24 1.44 2.59 20.40 174 .010 .100 .146 9.400 2 178 01646580 PR01 23 11,570 1984-2003 913 .35 1.72 1.79 5.09 931 .010 .070 .096 1.390 2 199 
Rappahannock River Basin 01666500 3ROB0001.90 24 179 1984-2003 166 0.24 0.81 0.83 1.81 168 0.200 0.100 0.102 0.700 2 172 

01668000 01668000 25 1,596 1988-2003 512 .12 .93 1.07 4.21 521 .006 .055 .138 1.500 2 521 

Mattaponi River Basin 01647500 01674500 28 601 1989-2003 549 .22 .57 .59 1.88 557 .010 .050 .057 .392 2 573 

Pamunkey River Basin 01671020 8-NAR005.42 26 463 1984-2003 190 .15 .43 .43 .94 193 .010 .030 .055 .220 2 193 

01673000 01673000 27 1,081 1989-2003 566 .31 .69 .74 2.58 568 .020 .071 .088 .802 2 585 

James River Basin 02013100 2-JKS023.61 29 614 1984-2003 205 .24 .75 .79 1.81 207 .040 .500 .887 6.500 2 207 

02026000 2-JMS229.14 30 3,683 1984-2003 185 .15 .59 .64 1.77 188 .030 .100 .186 .960 2 190 02029000 2-JMS189.31 31 4,584 1984-2003 171 .14 .52 .54 1.50 174 .020 .100 .140 .600 2 179 02035000 02035000 32 6,257 1988-2003 569 .05 .64 .78 3.30 571 .009 .114 .168 1.400 2 575 

Appomattox River Basin 02041650 02041650 33 1,344 1989-2003 549 .15 .57 .60 1.35 554 .010 .047 .053 .200 2 557 

1Suspended-sediment concentration was determined through the suspended sediment concentration analysis. 2Suspended-sediment concentration was determined through the suspended solid concentration analysis. Table 4. Minimum, mean, median, and maximum concentrations of total nitrogen, total phosphorus, and suspended sediment at the 9 River Input Monito

Agency Nontidal Program sites in the Chesapeake Bay watershed.—Continued [Station: Map site number, location on figure 1; Flow, USGS streamflow-gaging station number; WQ, water-quality site alphanumeric identity; POR: Sample period of record fo

tics: mg/L, milligrams per liter; Number of samples, samples used in the statistical determination; Min, minimum; Med, median; Max, maximum] Station Statistics Flow WQ Map site num- ber Drainage area POR Total nitrogen as N (mg/L) Total phosphorus as P (mg/L) Suspen

Num- ber of sam- ples Min Med Mean Max Num- ber of sam- ples Min Med Mean Max Num- ber of sam- ples 
Changes in Water Quality 15

Figure 5. Range in observed concentrations 

for the nine River Monitoring Input sites, 

Chesapeake Bay watershed, 1985-2003. 
16 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 6A. Annual distribution of observed total nitrogen, total phosphorus, and sediment concentrations collected at the 

River Input Monitoring sites for the Susquehanna River in the Chesapeake Bay watershed, 1984-2003.
Changes in Water Quality 17

Figure 6B. Annual distribution of observed total nitrogen, total phosphorus, and sediment concentrations collected at 

the River Input Monitoring sites for the Potomac River in the Chesapeake Bay watershed, 1984-2003.—Continued
18 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 6C. Annual distribution of observed total nitrogen, total phosphorus, and sediment concentrations collected at the 

River Input Monitoring sites for the James River in the Chesapeake Bay watershed, 1984-2003.—Continued
Changes in Water Quality 19

the three major RIM sites generally exhibited decreased concentrations during the 1999-2002 drought period. Conversely, 

TN concentration increased markedly in 2003 as a result of the 

prolonged high-flow conditions. TP concentrations at the Susquehanna RIM site exhibited a similar pattern to what was 

observed for TN concentration (fig. 6A) with decreased concentrations during the drought and markedly elevated concentrations during the prolonged high-flow period. The Potomac and 

James River RIM sites (figs. 6B and 6C) did not exhibit any distinguishing patterns during the drought and prolonged highflow periods. The sediment concentrations at the Potomac and 

James River RIM sites had drastically different concentrations 

when comparing the last year of the drought (2002) to the 

extended high-flow period (2003). SED concentrations 

observed during 2002 at both of these RIM sites were collectively one of the lowest on record; 2003 yielded considerably 

elevated concentrations. The Susquehanna RIM site exhibited a 

similar, but less variable, pattern as what was observed at the 

Potomac and James RIM sites with respect to SED concentration. This attenuated pattern observed at the Susquehanna RIM 

site was related to sediment settling in the three reservoirs above 

the monitoring site. The prolonged high-flow conditions and 

elevated concentrations of TN, TP, and SED, in 2003, resulted 

in one of the largest annual loads of TN, TP, and SED delivered 

to the Chesapeake Bay since monitoring began in the late 

1980s.

Flow-Weighted Concentration

An approach to evaluating the changing relation between 

streamflow and load is a FWC. It approximates the annual concentration. Changes over time can be illustrated within a basin 

and comparisons made among different basins.

The Potomac River consistently had higher annual TN 

FWC averaging about 2.25 mg/L (fig. 7). This exceeded the 

FWC in the Susquehanna (1.71 mg/L) and was about three 

times the annual FWC of TN in the James River (0.75 mg/L). 

The FWC for TN in the Susquehanna River decreased from 

1988 to 1998, with a more pronounced decline in the drought 

years of 1999-2002, and then increased in 2003. In general, the 

TN FWC for the Potomac and James Rivers exhibited little 

change from 1988 through 2003 except during the past 5 years, 

first dropping from 1999 through 2002 because of drought conditions over most of the bay watershed, then increasing in 2003 

because of above-normal precipitation over the bay watershed. 

FWC for TP and SED exhibited much more variability 

than TN because of different mechanisms of transport (fig. 7). 

Most of the TN is transported in the dissolved phase as nitratenitrogen; TP and SED are transported in the particulate phase. 

From 1988 to 2003, the TP FWC averaged about 0.15 mg/L for 

the Potomac and James Rivers, and the Susquehanna River 

averaged about 0.05 mg/L. The lower value in the Susquehanna 

River was most likely because of the phosphorus and sediment 

trapping behind three large reservoirs in the lower reaches of 

the river. Figure 7 suggests an increase in TP FWC even 

through the drought period of 1999-2002 for all three major rivers.

As with TP, the average SED FWC during 1988-2003 was 

similar at the Potomac and James Rivers (120 mg/L and 

85 mg/L, respectively) and lowest for the Susquehanna River 

(25 mg/L), likely because of the settling and trapping of sediment behind the three reservoirs. The variability in FWC was 

consistent among the major rivers (fig. 7), with the exception of 

the Potomac River in 2002. The FWC increased by a factor of 

10 from 2001 to 2002 with little change in flow, then was 

reduced by half in 2003 when flow increased by a factor of 4.

Flow-Adjusted Concentration

The observed and FWC data are highly influenced by 

changes in streamflow. Therefore, the USGS attempted to compensate for the influence of streamflow to improve understanding of changes in water quality that result from human influences. Results from ESTIMATOR are used to determine a 

flow-adjusted trend for concentration, by partitioning variability in observed concentration data due to season and flow, so 

that the coefficient from the “time” parameter is an estimate of 

the amount of change over time. An important point to mention 

is that the results of “flow adjustment” do not necessarily represent all the changes in water quality that result from human 

influence and management actions, only those apart from flow. 

For example, a change in farming practices that reduces surface 

runoff but increases ground-water recharge and a change in 

atmospheric deposition will not be captured using flow adjustment. Therefore, while FAC trends are an indicator of human 

activities affecting water quality within a watershed, the relative 

magnitude must be considered in terms of the hydrologic variability.

For the period 1985-2003, results from ESTIMATOR 

indicated about 55 percent of the sites (17 of 33 sites) had 

decreasing flow-adjusted trends for TN (fig. 8 and Appendix 3). 

Four sites indicated increasing trends; the remaining 12 sites did 

not have any significantly detectable trend. All seven sites in the 

Susquehanna River Basin had decreasing trends in TN. In the 

Potomac River Basin, there were nine decreasing trends, two 

increasing trends, and one site with no detectable trend. Sites in 

the James River Basin indicated no significantly detectable 

trends. Trends in nitrate concentration adjusted for flow were 

decreasing at 18 sites, occurring in nearly all major Chesapeake 

Bay drainage basins, and increasing at 5 of the 33 sites (Appendix 3). Decreasing trends for TN and nitrate coincided at 

14 sites; increasing trends coincided at 2 sites.

Flow-adjusted trends for TP concentrations were significantly decreasing at 25 of the 33 sites (fig. 9 and Appendix 3) 

and increasing at 4 sites; the remaining 4 sites did not have any 

significantly detectable trends. Trends were decreasing at 

4 RIM sites with decreasing trends in TP occurring in 8 of the 

10 major bay drainage basins. Increasing trends in TP were 

identified at four sites, three of which are RIM sites.
20 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 7. Flow-weighted concentrations for the Susquehanna, Potomac, and James Rivers entering the Chesapeake Bay for 1988-2003. 
Changes in Water Quality 21

Figure 8. Trends in flow-adjusted concentrations for total nitrogen, Chesapeake Bay watershed, 1985-2003.
22 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 9. Trends in flow-adjusted concentrations for total phosphorus, Chesapeake Bay watershed, 1985-2003.
Changes in Water Quality 23

Significant downward flow-adjusted trends for SED concentration were detected at 15 sites. Four RIM sites indicted 

downward trends. An upward trend was reported at two sites 

(sites 26 and 27) (fig. 10 and Appendix 3). The RIM sites had 

four increasing and one decreasing trend in SED. The Susquehanna River Basin indicted decreasing trends at all seven sites. 

Results for the Potomac Basin indicate about an equal number 

of decreasing (7) trends and no significantly detectable trends 

(8). In the James River Basin (including the Appomattox 

Basin), there was one decreasing trend, and four sites had no 

significantly detectable trends.

The significance and range in magnitude for TN, TP, and 

SED for concentrations adjusted for flow for the nine RIM sites 

are shown in figure 11. Five sites did not have significant FAC 

trends for TN. The Susquehanna, Potomac, and Patuxent Rivers 

had decreasing trends (improvement) of -28, -13, and -56 percent, respectively; the Pamunkey River increased 23 percent 

(fig. 11 and Appendix 3). TP trends adjusted for flow decreased 

at four rivers, ranging from -62 to -25 percent, and increased at 

three sites, ranging from 26 to 65 percent. Four RIM sites had 

decreasing FAC trends for SED, ranging from -65 to -27 percent, and a 53 percent increasing FAC trend for SED at one site. 

In summary, for the nine RIM sites, there were 16 significant 

trends and 13 no significantly detectable trend results for TN, 

TP, and SED. Thirteen of the 16 had significant trends greater 

than a 25-percent change in magnitude. 

As previously mentioned, streamflows for the years 1999-

2002 were below normal; streamflow for most of 2003 was well 

above normal throughout most areas of the Chesapeake Bay 

watershed. Trends at the nine RIM sites for TN, TP, and SED 

ending in calendar years 2002 and 2003 were examined to 

determine if the extreme change in hydrology affected the FAC 

trends. The extreme variability in hydrology did not affect the 

significance or direction of trend at four of the nine RIM sites 

(Susquehanna, Patuxent, Potomac, and Pamunkey Rivers) 

(fig. 1 and table 5). Three sites were consistently decreasing for 

TN, TP, and SED; one site (Pamunkey River) was consistently 

increasing for TN, TP, and SED. A significant change occurred 

at five RIM sites; Choptank and James Rivers for TN, Rappahannock River for TP, and Mattaponi and Appomattox Rivers for 

SED (table 5). 

Loads

Nutrient and sediment loads have a large impact on the 

health of the Chesapeake Bay Ecosystem and habitat in the rivers of the watershed. In 2003, nutrient and sediment loads at the 

RIM sites were the second highest since 1990. The estimated 

loads at the nine RIM sites for 2003 were 350 million pounds 

(Mlbs) of nitrogen, 30 Mlbs of phosphorus, and 18,200 Mlbs of 

sediment. The loads at the RIM sites represented about 60 percent of the total load that entered the tidal waters of the bay 

watershed (Gary Shenk, U.S. Environmental Protection 

Agency, written commun., 2004). The increased nutrient and 

sediment loads probably resulted in less light penetration in the 

bay waters, which may have contributed to a decline of submerged aquatic vegetation (SAV). The increased nutrient loads 

also may have contributed to large areas of low dissolved oxygen levels in the bay during the summer of 2003.

The prolonged high-flow conditions and elevated concentrations of TN, TP, and SED, in 2003, resulted in one of the 

greatest annual loads of TN, TP, and SED delivered to the Chesapeake Bay since monitoring began in the late 1980s. In 2003, 

more than twice the amount of river flow entered the bay than 

in 2002 (fig 12). This was the third highest amount of river flow 

to enter the bay since 1937 (fig. 3), when the USGS began keeping records to compute estimates of the total flow to the bay. 

The large increase in river flow was one factor that contributed 

to the loads in 2003 being much higher than 2002. At the RIM 

sites, about 3 times the amount of TN, 5 times the amount of TP, 

and 11 times the amount of SED entered the bay in 2003 compared to 2002.

In addition to higher streamflow, the loads also were influenced by higher nutrient and sediment concentrations at the 

RIM sites in 2003 than in 2002. The increased TN concentrations were the result of higher amounts of nitrogen being 

flushed from the land and ground water. Increased SED and TP 

concentrations were caused by the substantial erosion of sediment from the land and streams. A more detailed description of 

the concentrations in each river is shown in figure 5 and in 

table 4. The large variability of loads since 1985 contributed to 

the difficulty in attempting to detect significant trends over 

time. 

As previously mentioned, because of the concerns of using 

any estimated load to access a trend, no trends in loads are 

reported this year. Alternative methods of expressing a change 

in load with time (trend) are being explored. Trends in load may 

be reinstated in the future, pending the development of additional statistical methods.
24 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 10. Trends in flow-adjusted concentrations for sediment, Chesapeake Bay watershed, 1985-2003.
Changes in Water Quality 25

Figure 11. Significance and range in magnitude in trend for flow-adjusted concentrations from the ESTIMATOR model for the nine 

River Input Monitoring sites, Chesapeake Bay watershed, 1985-2003.
26 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 12. Combined annual flow and total nitrogen, total phosphorus, and sediment load for the nine 

River Input Monitoring sites flowing into the Chesapeake Bay for 1990-2003.
Summary and Conclusions 27

Summary and Conclusions

Nutrient and suspended sediment data from 33 sites in 

nontidal parts of the Chesapeake Bay Basin were analyzed to 

document changes in streamflow, concentrations, and loads 

from 1985 through 2003, as part of an annual update of waterquality conditions for the Chesapeake Bay Program. Annual 

loads and flow-adjusted concentration (FAC) trends were estimated by use of the U.S. Geological Survey (USGS) ESTIMATOR model. Changes in seasonal and annual flow, annual nutrient and sediment concentrations and loads, and flow-weighted 

concentration (FWC) were evaluated to help assess impacts on 

the bay ecosystem. FAC trends were evaluated to help assess 

changes that result from human activities and management 

actions. As part of this report, several different trend techniques 

were evaluated to improve statistical analysis to help address 

changes in water quality and assess the influence of management actions in reducing nutrient and sediment concentrations. 

Streamflow in 2003 was more than double that of 2002 and 

was the third highest since 1937. However, the results for 

streamflow data for 1985 through 2003 revealed a significant 

increase in annual flow for only one site, Choptank River in 

Maryland. Streamflow changes for the remaining 32 sites were 

not statistically significant because of serial correlation for 

daily, monthly, seasonal, and annual trends. 

Observed concentration samples collected for 10 major 

river basins indicate higher ranges in total-nitrogen concentrations in the five “northern” basins in Pennsylvania and Maryland compared to the five “southern” basins in Virginia. Totalphosphorus concentrations showed no distinct difference 

among the 10 basins. The median range of sediment concentrations was highest in the Susquehanna. Median concentrations 

increased at all nine River Input Monitoring (RIM) sites for 

total nitrogen, total phosphorus, and sediment in 2003 compared to 2002. A test for trend in observed concentration was 

not performed because of concerns that sampling protocols may 

have biased the trend because a disproportionate number of 

samples were collected during high-flow conditions.

The Potomac River consistently had higher FWC for 

annual total nitrogen averaging about 2.25 mg/L, nearly double 

that of the Susquehanna River and three times that of the James 

River. The Potomac generally exhibited little change except 

during the past 5 years, as a result of drought conditions from 

1999 through 2002 and well above-normal streamflow conditions in 2003. FWC values for total phosphorus averaged about 

0.15 mg/L for the Potomac and James Rivers and 0.05 mg/L for 

the Susquehanna River. The lower FWC value in the Susquehanna River is likely because of the sediment- and phosphorustrapping capability of three large reservoirs in the lower reaches 

of the river. An increase in total phosphorus FWC was observed 

for all three major rivers through the drought period of 1999-

2002. FWC for sediment was similar at the Potomac and James 

Rivers (120 and 85 mg/L, respectively) and lowest for the Susquehanna River (25 mg/L) because of the settling and trapping 

of sediment behind the three reservoirs. The variability in 

annual FWC for sediment is consistent among the major rivers 

with the exception of the Potomac River in 2002 when the FWC 

increased by a factor of 10 with little change in flow, then was 

reduced by half in 2003 when flow increased. 

In 2003, nutrient and sediment loads at the RIM sites were 

the second highest since 1990. In 2003, the loads at the nine 

RIM sites were 350 million pounds (Mlbs) of nitrogen, 30 Mlbs 

of phosphorus, and 18,200 Mlbs of sediment. The loads at the 

RIM sites represented about 60 percent of the total load that 

entered the tidal waters of the bay watershed. The nutrient and 

sediment loads in 2003 were influenced by near-record river 

flow to the bay in 2003 when more than twice the amount of 

river flow entered the bay than in 2002. This was the third-highest amount of river flow to enter the bay since 1937 when the 

USGS began keeping records to compute estimates of the total 

flow to the bay. The large increase in river flow contributed 

about 3 times the amount of nitrogen, 5 times the amount of 

phosphorus, and 11 times the amount of sediment entering the 

bay in 2003 compared to 2002 at the RIM sites. The nutrient and 

sediment loads in 2003 contributed to low dissolved oxygen and 

loss of submerged aquatic vegetation (SAV) in 2003.

Table 5. Significant (flow-adjusted concentration) trend direction for the above-normal streamflow in 2003 (1985-2003 trends) and belownormal streamflow in 2002 (1985-2002 trends) calendar years.

[ns; no significant trend detected]

Basin Site number Site ID

(fig. 1)

Total nitrogen Total phosphorus Sediment

2003 2002 2003 2002 2003 2002

Choptank 01491000 8 ns decrease increase increase decrease decrease

Susquehanna 01578310 7 decrease decrease decrease decrease decrease decrease

Patuxent 01594440 11 decrease decrease decrease decrease decrease decrease

Potomac 01646580 23 decrease decrease increase increase decrease decrease

Rappahannock 01668000 25 ns ns decrease ns ns ns

Pamunkey 01673000 27 increase increase increase increase increase increase

Mattaponi 01674500 28 ns ns ns ns ns increase

James 02035000 32 ns decrease decrease decrease ns ns

Appomattox 02041650 33 ns ns ns ns ns increase
28 Changes in Streamflow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

When the influences of flow and seasonality are removed, 

results for trends adjusted for flow (FAC) suggest improvement 

in water quality due to management actions. Results indicated 

about 55 percent of the sites (18 sites) had decreasing FAC for 

total nitrogen. Four sites indicated increasing FAC trends, with 

no significantly detectable trends at the remaining 11 sites. 

Trends were deceasing at four and increasing at one of the nine 

RIM sites. All seven sites in the Susquehanna River Basin had 

decreasing FAC trends in total nitrogen. In the Potomac River 

Basin, there were nine sites with decreasing trends and two sites 

with increasing FAC trends; the James River Basin had one site 

with a decreasing trend and four sites showed no significantly 

detectable FAC trends. FAC trends in nitrate concentration 

were decreasing at 18 sites in nearly all major Chesapeake Bay 

drainage basins and increasing at 5 of the 33 sites.

FAC trends in total phosphorus were significantly decreasing at 25 of the 33 sites, increasing at 4 sites, with no significantly detectable trends at the remaining 4 sites. Trends were 

decreasing at 4 RIM sites with decreasing trends in total phosphorus in 8 of the 10 major bay drainage basins. Increasing 

trends in total phosphorus were identified at four sites, three of 

which are RIM sites. 

Significant downward FAC trends for suspended sediment 

were detected at 15 sites. Four RIM sites indicated downward 

FAC trends. An upward trend was reported at three sites. For 

FAC trends in sediments, four of the RIM sites showed an 

increasing trend and one showed a decreasing trend. All seven 

sites in the Susquehanna River Basin indicated a decreasing 

trend. Results for the sites in the Potomac River Basin indicate 

about an equal number of decreasing (7) trends and no significantly detectable trends (8). At the James River Basin sites, 

there was one decreasing trend and four no significantly detectable FAC trends.

As part of an evaluation of current trend methodology, 

trends in estimated loads in any time series (annual, monthly, or 

using the loads in the flow weighted concentrations) from the 

ESTIMATOR model are not reported because of concerns the 

load estimates in the time series are not independent, are estimates rather than measurements, and may not be representative 

of the variability of the natural system. Estimating trend on the 

estimates of load may produce biased results. In addition, there 

is concern over the potential bias introduced from the targeted 

sampling protocols used at the RIM sites. Although targeting 

higher flow events to estimate loads is appropriate for load estimation using models similar to ESTIMATOR, this targeting 

could possibly bias a simple linear regression analysis trend. 

The reporting of these trends may be reinstated in the future 

pending the development of additional statistical methods.

Acknowledgments

The authors wish to thank all who participated in the writing, reviewing, and revisions made to this report. In particular, 

a special thanks goes to Greg Schwarz and Jurate Landwehr for 

their insightful statistical reviews and suggestions. In addition, 

thanks to the USGS reports section staff for their prompt revisions, editorial, and publishing assistance.

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Appendix 1

Figure 1.1. Quarterly-mean streamflow for the Choptank River and Patuxent River, 1985-2003. 

Figure 1.2. Quarterly-mean streamflow for the Appomattox, Rappahannock, Pamunkey, and Mattaponi 

Rivers, 1990-2003.
30 Changes in Flow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 1.1. Quarterly mean streamflow for the Choptank River and Patuxent River, 1985-2003. For each season, 25th, 50th, and 75th

percentiles were calculated. Bars representing the quarterly mean flow are red if the value for that quarter is below the 25th percentile, blue if above the 75th percentile, and black if between the 25th and 75th percentiles.
Appendix 1 31

Figure 1.2. Quarterly mean streamflow for the Appomattox, Rappahannock, Pamunkey, and Mattaponi Rivers, 1990-

2003. For each season, 25th, 50th, and 75th percentiles were calculated. Bars representing the quarterly mean flow are 

red if the value for that quarter is below the 25th percentile, blue if above the 75th percentile, and black if 

between the 25th and 75th percentiles.

Appendix 2

Figure 2.1 - Statistical summaries for water-quality concentration data for total nitrogen (A), total 

phosphorus (B), and sediment (C) for the Choptank River.

Figure 2.2 - Statistical summaries for water-quality concentration data for total nitrogen (A), total 

phosphorus (B), and sediment (C) for the Patuxent River.

Figure 2.3 - Statistical summaries for water-quality concentration data for total nitrogen (A), total 

phosphorus (B), and sediment (C) for the Rappahanock River.

Figure 2.4 - Statistical summaries for water-quality concentration data for total nitrogen (A), total 

phosphorus (B), and sediment (C) for the Mattaponi River.

Figure 2.5 - Statistical summaries for water-quality concentration data for total nitrogen (A), total 

phosphorus (B), and sediment (C) for the Pamunkey River.

Figure 2.6 - Statistical summaries for water-quality concentration data for total nitrogen (A), total 

phosphorus (B), and sediment (C) for the Appomattox River.
34 Changes in Flow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 2.1. Statistical summaries for waterquality concentration data for total nitrogen 

(A), total phosphorus (B), and sediment (C) 

for the Choptank River. 
Appendix 2 35

Figure 2.2. Statistical summaries for waterquality concentration data for total nitrogen 

(A), total phosphorus (B), and sediment (C) 

for the Patuxent River.
36 Changes in Flow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 2.3. Statistical summaries for waterquality concentration data for total nitrogen 

(A), total phosphorus (B), and sediment (C) 

for the Rappahannock River.
Appendix 2 37

Figure 2.4. Statistical summaries for waterquality concentration data for total nitrogen 

(A), total phosphorus (B), and sediment (C) 

for the Mattiponi River.
38 Changes in Flow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 2.5. Statistical summaries for waterquality concentration data for total nitrogen (A)

total phosphorus (B), and sediment (C) for the 

Pamunkey River.
Appendix 2 39

Figure 2.6. Statistical summaries for waterquality concentration data for total nitrogen 

(A), total phosphorus (B), and sediment (C) for 

the Appomattox River.

Appendix 3

Figure 3.1. Location and site number for the 33 sites used in this study, Chesapeake Bay Basin.

Station: Site number, location on figure 1; Flow, USGS streamflow gage number; 

WQ, water-quality site alphanumeric identity.

POR: BegDate, begin date; End Date, end date.

Parameter: Flow, streamflow; TN, total nitrogen; DN, dissolved nitrogen; DNH4, dissolved 

ammonia; TNH4, total ammonia; TNO3, DNO3, total or dissolved nitrate; TNO3+2, DNO3+2, total or 

dissolved nitrite plus nitrate; DKJD, dissolved ammonia plus organic nitrogen; TKJD, total 

ammonia plus organic nitrogen; TP, total phosphorus; DP, dissolved phosphorus; DIP, dissolved 

inorganic phosphorus; TSS, total suspended solids; SED, suspended sediment.

Statistics: Slope, regression slope; P-value, measure of significance of regressor at 0.05; 

direction, improving (improvement in WQ), degrading (degrading of WQ); ns (no significantly 

detectable trend); magnitude, LowCI (lower confidence interval), trend (actual estimated trend), 

UpCI (upper confidence interval); remarks, not normally distributed residuals (nn); >50% BDL, 

greater than 50 percent below detection limit.
42 Changes in Flow and Water Quality in Selected Nontidal Sites in the Chesapeake Bay Basin, 1985-2003

Figure 3.1. Location and site number for the 33 sites used in this study, Chesapeake Bay Basin.
Appendix 3. Trends in flow-adjusted concentration data for 9 River Input Monitoring Program sites and 24 Multi-Agency Nontidal Program sites in the shed, 1985-2003.[<, less than]

Statistics

Station POR 

Map site 

number Flow WQ BegDate EndDate Parameter Slope p-value Direction Low

River Input Monitoring Sites

7 1578310 1578310 1985 2003 TN -0.0173 <0.0001 IMPROVING -37 1578310 1578310 1985 2003 DNO3+2 -.0075 .0003 IMPROVING -22 

7 1578310 1578310 1985 2003 TP -.0181 <.0001 IMPROVING -35 7 1578310 1578310 1985 2003 DIP .0125 .115 ns -2 7 1578310 1578310 1985 2003 SSED -.0154 <.0001 IMPROVING -38 1491000 1491000 1985 2003 TN -.0013 .4826 ns -8 1491000 1491000 1985 2003 DNO3+2 .0111 .0001 degrading 10 

8 1491000 1491000 1985 2003 TP .0104 .0252 degrading 5 8 1491000 1491000 1985 2003 DIP .0128 .0472 degrading 8 1491000 1491000 1985 2003 SSED -.0418 <.0001 IMPROVING -64 

11 1594440 1594440 1985 2003 TN -.0474 <.0001 IMPROVING -59 11 1594440 1594440 1985 2003 DNO3+2 -.0459 <.0001 IMPROVING -5

11 1594440 1594440 1985 2003 TP -.0TKJD <.0001 IMPROVING -611 1594440 1594440 1985 2003 DIP -.0574 <.0001 IMPROVING -611 1594440 1594440 1985 2003 SSED -.0499 <.0001 IMPROVING -623 1646580 1646580 1985 2003 TN -.0066 <.0001 IMPROVING -123 1646580 1646580 1985 2003 DNO3+2 .0014 .5669 ns -52 

23 1646580 1646580 1985 2003 TP .0095 .0119 degrading 22 23 1646580 1646580 1985 2003 DIP .0113 .0223 degrading 123 1646580 1646580 1985 2003 SSED -.0521 <.0001 IMPROVING -75 25 1668000 1668000 1988 2003 TSS -.0077 .4732 ns -325 1668000 1668000 1988 2003 TN -.0004 .919 ns -12 25 1668000 1668000 1988 2003 DNO3+2 -.0069 .4048 ns -3

25 1668000 1668000 1988 2003 TP -.0174 .0104 IMPROVING -325 1668000 1668000 1988 2003 DIP .0011 .8527 ns -127 1673000 1673000 1989 2003 TSS .0292 .0018 degrading 127 1673000 1673000 1989 2003 TN .0141 <.0001 degrading 12 27 1673000 1673000 1989 2003 DNO3+2 .0122 .006 degrading 9 

27 1673000 1673000 1989 2003 TP .0344 <.0001 degrading 40 27 1673000 1673000 1989 2003 DIP .059 <.0001 degrading 12
28 1674500 1674500 1990 2003 TSS 0.009 0.2777 ns -28 1674500 1674500 1990 2003 TN .0006 .8085 ns -2 28 1674500 1674500 1990 2003 DNO3+2 -.0069 .2278 ns -1

28 1674500 1674500 1990 2003 TP -.0071 .0759 ns -17 28 1674500 1674500 1990 2003 DIP -.0052 .2972 ns -24 32 2035000 2035000 1988 2003 TSS -.0135 .0782 ns -332 2035000 2035000 1988 2003 TN -.0077 .0916 ns -232 2035000 2035000 1988 2003 DNO3+2 -.0262 <.0001 IMPROVING -45 32 2035000 2035000 1988 2003 TP -.0346 <.0001 IMPROVING -50 32 2035000 2035000 1988 2003 DIP -.0578 <.0001 IMPROVING -633 2041650 2041650 1989 2003 TSS .0048 .4169 ns -33 2041650 2041650 1989 2003 TN .0036 .1968 ns -7 33 2041650 2041650 1989 2003 DNO3+2 -.0127 .0614 ns -333 2041650 2041650 1989 2003 TP -.0008 .8669 ns -15 33 2041650 2041650 1989 2003 DIP -.0185 .0009 IMPROVING -35 

Multi-Agency Program Sites 1 1531500 Towanda 1989 2003 TN -.0284 <.0001 IMPROVING -39 

1 1531500 Towanda 1989 2003 DNH4 -.0194 .0014 IMPROVING -39 

1 1531500 Towanda 1989 2003 TNH4 -.0437 <.0001 IMPROVING -51 1531500 Towanda 1989 2003 DKJD -.0233 <.0001 IMPROVING -31 1531500 Towanda 1989 2003 TKJD -.0343 <.0001 IMPROVING -47 1 1531500 Towanda 1989 2003 TNO3+2 -.0242 <.0001 IMPROVING -37 1 1531500 Towanda 1989 2003 DNO3+2 -.0243 <.0001 IMPROVING -37 1 1531500 Towanda 1989 2003 TP -.0195 .0003 IMPROVING -31 1531500 Towanda 1989 2003 TP -.0303 <.0001 IMPROVING -41 1531500 Towanda 1989 2003 DIP .0978 <.0001 degrading 211 1531500 Towanda 1989 2003 SSED -.0302 .0005 IMPROVING -42 1540500 Danville 1985 2003 TN -.0259 <.0001 IMPROVING -42 2 1540500 Danville 1985 2003 DNH4 -.0357 <.0001 IMPROVING -65 2 1540500 Danville 1985 2003 TNH4 -.0524 <.0001 IMPROVING -72 1540500 Danville 1985 2003 DKJD -.0302 <.0001 IMPROVING -52 2 1540500 Danville 1985 2003 TKJD -.0361 <.0001 IMPROVING -5

Appendix 3. Trends in flow-adjusted concentration data for 9 River Input Monitoring Program sites and 24 Multi-Agency Nontidal Program sites in the shed, 1985-2003.—Continued[<, less than]

Statistics

Station POR 

Map site 

number Flow WQ BegDate EndDate Parameter Slope p-value Direction Low
2 1540500 Danville 1985 2003 TNO3+2 -0.0175 <0.0001 IMPROVING -32 

2 1540500 Danville 1985 2003 DNO3+2 -.0179 <.0001 IMPROVING -32 1540500 Danville 1985 2003 TP -.0312 <.0001 IMPROVING -54 2 1540500 Danville 1985 2003 TP -.0323 <.0001 IMPROVING -57 2 1540500 Danville 1985 2003 DIP .0762 <.0001 degrading 127 2 1540500 Danville 1985 2003 SSED -.0518 <.0001 IMPROVING -69 3 1553500 Lewisburg 1985 2003 TN -.0173 <.0001 IMPROVING -34 3 1553500 Lewisburg 1985 2003 DNH4 -.0112 .0193 IMPROVING -33 1553500 Lewisburg 1985 2003 TNH4 -.0334 <.0001 IMPROVING -53 1553500 Lewisburg 1985 2003 DKJD -.0283 <.0001 IMPROVING -52 3 1553500 Lewisburg 1985 2003 TKJD -.026 <.0001 IMPROVING -52 3 1553500 Lewisburg 1985 2003 TNO3+2 -.0078 .0001 IMPROVING -19 3 1553500 Lewisburg 1985 2003 DNO3+2 -.0076 .0001 IMPROVING -19 3 1553500 Lewisburg 1985 2003 TP -.0284 <.0001 IMPROVING -52 3 1553500 Lewisburg 1985 2003 TP -.0438 <.0001 IMPROVING -65 3 1553500 Lewisburg 1985 2003 DIP .0636 <.0001 degrading 85 3 1553500 Lewisburg 1985 2003 SSED -.0496 <.0001 IMPROVING -64 4 1567000 Newport 1985 2003 TN -.0068 <.0001 IMPROVING -19 4 1567000 Newport 1985 2003 DNH4 -.0231 <.0001 IMPROVING -50 4 1567000 Newport 1985 2003 TNH4 -.0402 <.0001 IMPROVING -64 4 1567000 Newport 1985 2003 DKJD -.0285 <.0001 IMPROVING -54 1567000 Newport 1985 2003 TKJD -.0198 <.0001 IMPROVING -44 1567000 Newport 1985 2003 TNO3+2 -.0024 .1788 ns -14 1567000 Newport 1985 2003 DNO3+2 -.0013 .4611 ns -14 1567000 Newport 1985 2003 TP -.013 .0014 IMPROVING -34 1567000 Newport 1985 2003 TP -.0087 .0261 IMPROVING -34 1567000 Newport 1985 2003 DIP .0702 <.0001 degrading 132 4 1567000 Newport 1985 2003 SSED -.0154 .0198 IMPROVING -45 5 1576000 Marietta 1987 2003 TN -.0156 <.0001 IMPROVING -30 5 1576000 Marietta 1987 2003 DNH4 -.0189 .0002 IMPROVING -42 5 1576000 Marietta 1987 2003 TNH4 -.0333 <.0001 IMPROVING -54 5 1576000 Marietta 1987 2003 DKJD -.017 .0002 IMPROVING -37 5 1576000 Marietta 1987 2003 TKJD -.026 <.0001 IMPROVING -4

Appendix 3. Trends in flow-adjusted concentration data for 9 River Input Monitoring Program sites and 24 Multi-Agency Nontidal Program sites in the shed, 1985-2003.—Continued[<, less than]

Statistics

Station POR 

Map site 

number Flow WQ BegDate EndDate Parameter Slope p-value Direction Low
5 1576000 Marietta 1987 2003 TNO3+2 -0.0086 0.0006 IMPROVING -2

5 1576000 Marietta 1987 2003 DNO3+2 -.0084 .0008 IMPROVING -25 1576000 Marietta 1987 2003 TP -.001 .8228 ns -19 5 1576000 Marietta 1987 2003 TP .0029 .4869 ns -15 1576000 Marietta 1987 2003 DIP .152 <.0001 degrading 815 1576000 Marietta 1987 2003 SSED -.0178 .0078 IMPROVING -42 6 1576754 Conestoga 1985 2003 TN -.0104 <.0001 IMPROVING -22 6 1576754 Conestoga 1985 2003 DNH4 -.0658 <.0001 IMPROVING -77 6 1576754 Conestoga 1985 2003 TNH4 -.0709 <.0001 IMPROVING -79 6 1576754 Conestoga 1985 2003 DKJD -.0165 <.0001 IMPROVING -37 6 1576754 Conestoga 1985 2003 TKJD -.0324 <.0001 IMPROVING -54 6 1576754 Conestoga 1985 2003 TNO3+2 .0009 .5475 ns -4 

6 1576754 Conestoga 1985 2003 DNO3+2 .0019 .2352 ns -2 6 1576754 Conestoga 1985 2003 TP -.0175 <.0001 IMPROVING -36 1576754 Conestoga 1985 2003 TP -.0191 <.0001 IMPROVING -39 6 1576754 Conestoga 1985 2003 DIP -.0048 .1193 ns -16 1576754 Conestoga 1985 2003 SSED -.0347 <.0001 IMPROVING -59 1586000 NPA0165 1985 2003 TSS -.0424 .0012 IMPROVING -79 1586000 NPA0165 1985 2003 TN .0036 .0841 ns -9 1586000 NPA0165 1985 2003 TNH4 -.0342 <.0001 IMPROVING -6

9 1586000 NPA0165 1985 2003 DNO3 .0096 .0001 degrading 9 

9 1586000 NPA0165 1985 2003 TKJD -.0334 <.0001 IMPROVING -69 1586000 NPA0165 1985 2003 TNO3+2 .0083 .0003 degrading 7 9 1586000 NPA0165 1985 2003 TP -.0501 <.0001 IMPROVING -7

10 1592500 PXT0809 1985 2003 TSS .0114 .2541 ns -25 10 1592500 PXT0809 1985 2003 TN -.0033 .1621 ns -10 10 1592500 PXT0809 1985 2003 TNH4 .0159 .1093 ns -10 1592500 PXT0809 1985 2003 DNO3 -.0075 .0918 ns -27 

10 1592500 PXT0809 1985 2003 TKJD -.0042 .395 ns -210 1592500 PXT0809 1985 2003 TNO3+2 -.0061 .1397 ns -24 10 1592500 PXT0809 1985 2003 TP -.0165 .0299 IMPROVING -45 12 1599000 GEO0009 1985 2003 TSS -.0305 .0128 IMPROVING -70 12 1599000 GEO0009 1985 2003 TN -.0283 <.0001 IMPROVING -50 

Appendix 3. Trends in flow-adjusted concentration data for 9 River Input Monitoring Program sites and 24 Multi-Agency Nontidal Program sites in the shed, 1985-2003.—Continued[<, less than]

Statistics

Station POR 

Map site 

number Flow WQ BegDate EndDate Parameter Slope p-value Direction Low
12 1599000 GEO0009 1985 2003 TNH4 -0.0824 <0.0001 IMPROVING -85 

12 1599000 GEO0009 1985 2003 DNO3 -.009 .3458 ns -39 12 1599000 GEO0009 1985 2003 TKJD -.0288 <.0001 IMPROVING -57 12 1599000 GEO0009 1985 2003 TNO3+2 -.0261 <.0001 IMPROVING -412 1599000 GEO0009 1985 2003 TP -.0448 <.0001 IMPROVING -713 1601500 WIL0013 1985 2003 TSS -.0222 .1359 ns -613 1601500 WIL0013 1985 2003 TN -.0257 <.0001 IMPROVING -49 13 1601500 WIL0013 1985 2003 TNH4 -.0418 <.0001 IMPROVING -67 13 1601500 WIL0013 1985 2003 DNO3 -.0253 .1048 ns -913 1601500 WIL0013 1985 2003 TKJD -.0295 .0003 IMPROVING -513 1601500 WIL0013 1985 2003 TNO3+2 -.0245 .0001 IMPROVING -47 13 1601500 WIL0013 1985 2003 TP -.0333 .0074 IMPROVING -69 14 1610000 POT2766 1985 2003 TSS -.0297 .0244 IMPROVING -614 1610000 POT2766 1985 2003 TN -.0162 <.0001 IMPROVING -314 1610000 POT2766 1985 2003 TNH4 -.0416 <.0001 IMPROVING -65 14 1610000 POT2766 1985 2003 TKJD -.0244 <.0001 IMPROVING -514 1610000 POT2766 1985 2003 TNO3+2 -.012 .0092 IMPROVING -34 14 1610000 POT2766 1985 2003 TP -.0168 .033 IMPROVING -415 1613000 POT2386 1985 2003 TSS .0164 .1705 ns -15 15 1613000 POT2386 1985 2003 TN -.0199 <.0001 IMPROVING -42 15 1613000 POT2386 1985 2003 TNH4 -.0201 .0047 IMPROVING -415 1613000 POT2386 1985 2003 DNO3 -.0189 .0012 IMPROVING -44 15 1613000 POT2386 1985 2003 TKJD -.0173 .0009 IMPROVING -47 15 1613000 POT2386 1985 2003 TNO3+2 -.022 .001 IMPROVING -49 15 1613000 POT2386 1985 2003 TP -.0251 .0075 IMPROVING -516 1614500 CONO180 1985 2003 TSS .0161 .1744 ns -5 16 1614500 CONO180 1985 2003 TN -.0143 <.0001 IMPROVING -32 16 1614500 CONO180 1985 2003 TNH4 -.0375 .0001 IMPROVING -65 16 1614500 CONO180 1985 2003 DNO3 -.0083 .0142 IMPROVING -25 16 1614500 CONO180 1985 2003 TKJD -.0219 .0003 IMPROVING -516 1614500 CONO180 1985 2003 TNO3+2 -.0113 <.0001 IMPROVING -27 16 1614500 CONO180 1985 2003 TP -.0527 <.0001 IMPROVING -717 1626000 1BSTH027.85 1985 2003 TSS -.0166 .1078 ns -52 

Appendix 3. Trends in flow-adjusted concentration data for 9 River Input Monitoring Program sites and 24 Multi-Agency Nontidal Program sites in the shed, 1985-2003.—Continued[<, less than]

Statistics

Station POR 

Map site 

number Flow WQ BegDate EndDate Parameter Slope p-value Direction Low
17 1626000 1BSTH027.85 1985 2003 TN 0.0047 0.3965 ns -117 1626000 1BSTH027.85 1985 2003 TNH4 -.0482 .0022 IMPROVING -72 

17 1626000 1BSTH027.85 1985 2003 TNO3 -.0015 .7541 ns -217 1626000 1BSTH027.85 1985 2003 TKJD -.0003 .9645 ns -217 1626000 1BSTH027.85 1985 2003 TNO3+2 -.0012 .8648 ns -32 17 1626000 1BSTH027.85 1985 2003 TP -.0509 <.0001 IMPROVING -718 1631000 1BSSF003.56 1985 2003 TSS -.0367 .0025 IMPROVING -64 18 1631000 1BSSF003.56 1985 2003 TN -.0168 .0162 IMPROVING -44 18 1631000 1BSSF003.56 1985 2003 TNH4 -.05 .0002 IMPROVING -74 18 1631000 1BSSF003.56 1985 2003 TNO3 -.0258 .0024 IMPROVING -62 18 1631000 1BSSF003.56 1985 2003 TKJD -.0291 .0001 IMPROVING -55 18 1631000 1BSSF003.56 1985 2003 TNO3+2 -.0231 .0148 IMPROVING -618 1631000 1BSSF003.56 1985 2003 TP -.0342 .0001 IMPROVING -62 19 1634000 1BNFS010.34 1985 2003 TSS -.0057 .7255 ns -47 19 1634000 1BNFS010.34 1985 2003 TN .034 <.0001 degrading 45 19 1634000 1BNFS010.34 1985 2003 TNH4 -.0369 .0893 ns -79 19 1634000 1BNFS010.34 1985 2003 TNO3 .0486 <.0001 degrading 72 

19 1634000 1BNFS010.34 1985 2003 TKJD .0057 .4735 ns -17 19 1634000 1BNFS010.34 1985 2003 TNO3+2 .0483 <.0001 degrading 69 19 1634000 1BNFS010.34 1985 2003 TP .0554 <.0001 degrading 119 20 1638500 POT1595 1985 2003 TSS -.0293 .0075 IMPROVING -65 20 1638500 POT1595 1985 2003 TN -.0209 <.0001 IMPROVING -39 20 1638500 POT1595 1985 2003 TNH4 -.043 <.0001 IMPROVING -67 

20 1638500 POT1595 1985 2003 DNO3 -.0163 <.0001 IMPROVING -320 1638500 POT1595 1985 2003 TKJD -.0214 .0004 IMPROVING -50 20 1638500 POT1595 1985 2003 TNO3+2 -.0154 <.0001 IMPROVING -35 20 1638500 POT1595 1985 2003 TP -.0332 <.0001 IMPROVING -57 21 1643000 MON0155 1985 2003 TSS -.0057 .4042 ns -47 21 1643000 MON0155 1985 2003 TN -.0079 .0052 IMPROVING -221 1643000 MON0155 1985 2003 TNH4 -.0931 <.0001 IMPROVING -90 21 1643000 MON0155 1985 2003 DNO3 .0149 .0015 degrading 1

21 1643000 MON0155 1985 2003 TKJD -.0216 .0004 IMPROVING -52 21 1643000 MON0155 1985 2003 TNO3+2 .0113 .0057 degrading 

Appendix 3. Trends in flow-adjusted concentration data for 9 River Input Monitoring Program sites and 24 Multi-Agency Nontidal Program sites in the shed, 1985-2003.—Continued[<, less than]

Statistics

Station POR 

Map site 

number Flow WQ BegDate EndDate Parameter Slope p-value Direction Low
21 1643000 MON0155 1985 2003 TP -0.0085 0.1252 ns -322 1646000 1ADIF000.86 1985 2003 TSS -.0002 .9933 ns -422 1646000 1ADIF000.86 1985 2003 TN .0248 <.0001 degrading 24 22 1646000 1ADIF000.86 1985 2003 TNH4 -.0123 .4729 ns -45 

22 1646000 1ADIF000.86 1985 2003 TNO3 .0122 .0652 ns -1

22 1646000 1ADIF000.86 1985 2003 TKJD .0236 .0023 degrading 27 22 1646000 1ADIF000.86 1985 2003 TNO3+2 .0108 .3879 ns -322 1646000 1ADIF000.86 1985 2003 TP -.0577 <.0001 IMPROVING -824 1666500 3-ROB001.90 1985 2003 TSS .0133 .2745 ns -24 24 1666500 3-ROB001.90 1985 2003 TN .0007 .9108 ns -224 1666500 3-ROB001.90 1985 2003 TNH4 -.0143 .3653 ns -424 1666500 3-ROB001.90 1985 2003 TNO3 -.0514 <.0001 IMPROVING -77 24 1666500 3-ROB001.90 1985 2003 TKJD .0249 .0045 degrading 24 24 1666500 3-ROB001.90 1985 2003 TNO3+2 -.0348 .0032 IMPROVING -7

24 1666500 3-ROB001.90 1985 2003 TP -.0419 .0001 IMPROVING -726 1671020 8-NAR005.42 1985 2003 TSS .0442 .003 degrading 426 1671020 8-NAR005.42 1985 2003 TN .036 <.0001 degrading 54 26 1671020 8-NAR005.42 1985 2003 TNH4 -.0157 .4122 ns -54 26 1671020 8-NAR005.42 1985 2003 TNO3 -.0026 .6949 ns -24 26 1671020 8-NAR005.42 1985 2003 TKJD .0082 .0992 ns -9 26 1671020 8-NAR005.42 1985 2003 TNO3+2 .0229 .0476 IMPROVING 

26 1671020 8-NAR005.42 1985 2003 TP -.0977 <.0001 IMPROVING -829 2013100 2-JKS023.61 1985 2003 TSS -.0137 .0463 IMPROVING -42 29 2013100 2-JKS023.61 1985 2003 TN .0026 .5692 ns -129 2013100 2-JKS023.61 1985 2003 TNH4 -.0346 .0029 IMPROVING -6

29 2013100 2-JKS023.61 1985 2003 TNO3 -.0081 .1728 ns -34 29 2013100 2-JKS023.61 1985 2003 TKJD -.0007 .8655 ns -19 29 2013100 2-JKS023.61 1985 2003 TNO3+2 -.0111 .1446 ns -42 29 2013100 2-JKS023.61 1985 2003 TP -.1419 <.0001 IMPROVING -95 30 2026000 2-JMS229.14 1985 2003 TSS .0181 .1506 ns -30 30 2026000 2-JMS229.14 1985 2003 TN -.0031 .2671 ns -37 30 2026000 2-JMS229.14 1985 2003 TNH4 -.0375 .0002 IMPROVING -65 30 2026000 2-JMS229.14 1985 2003 TNO3 -.0605 <.0001 IMPROVING -82 

Appendix 3. Trends in flow-adjusted concentration data for 9 River Input Monitoring Program sites and 24 Multi-Agency Nontidal Program sites in the shed, 1985-2003.—Continued[<, less than]

Statistics

Station POR 

Map site 

number Flow WQ BegDate EndDate Parameter Slope p-value Direction Low
30 2026000 2-JMS229.14 1985 2003 TKJD 0.0225 0.0002 degrading 130 2026000 2-JMS229.14 1985 2003 TNO3+2 -.056 <.0001 IMPROVING -84 

30 2026000 2-JMS229.14 1985 2003 TP -.0756 <.0001 IMPROVING -84 31 2029000 2-JMS189.31 1985 2003 TSS .0182 .1201 ns -131 2029000 2-JMS189.31 1985 2003 TN .0082 .3447 ns -17 31 2029000 2-JMS189.31 1985 2003 TNH4 -.0532 <.0001 IMPROVING -72 31 2029000 2-JMS189.31 1985 2003 TNO3 -.0389 <.0001 IMPROVING -631 2029000 2-JMS189.31 1985 2003 TKJD .0069 .2994 ns -15 31 2029000 2-JMS189.31 1985 2003 TNO3+2 -.0263 .1108 ns -631 2029000 2-JMS189.31 1985 2003 TP -.0569 <.0001 IMPROVING -75 

Appendix 3. Trends in flow-adjusted concentration data for 9 River Input Monitoring Program sites and 24 Multi-Agency Nontidal Program sites in the shed, 1985-2003.—Continued [<, less than] Statistics Station POR 

Map site number Flow WQ BegDate EndDate Parameter Slope p-value Direction Low