U.S. Geological Survey, Water Resources of Pennsylvania

U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2004-5259

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

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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 water-quality 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.

Table of Contents

Abstract
Introduction
     Purpose and Scope
     Methods and Approach
     Data-Set Construction
     Description and Evaluation of Methods and Techniques
          Streamflow
          Load Computations
          Concentrations
               Observed
               Flow-Weighted
               Flow-Adjusted
     Summary of Changes in Methods
Changes in Streamflow
     Annual Mean Flow
     Quarterly Mean Flow
Changes in Water Quality
     Observed Concentrations
     Flow-Weighted Concentration
     Flow-Adjusted Concentration
     Loads
Summary and Conclusions
References Cited
Appendix 1. Quarterly-mean streamflow for the Choptank, Patuxent, Appomattox, Rappahannock, Pamunkey, and Mattaponi Rivers, 1985-2003
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
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

Figures

1. Map showing location and site number for the 33 sites used in this study , Chesapeake Bay watershed
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)
3. Graph showing variation in annual mean flow entering the Chesapeake Bay, 1935-2003, using computations as described in Bue (1968)
4. Graphs showing quarterly mean streamflow for the Susquehanna (1985-2003), Potomac (1985-2003), and James (1989-2003) Rivers
5. Boxplots showing range in observed concentrations for the nine River Input Monitoring sites, Chesapeake Bay watershed, 1985-2003
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
7. Graphs showing flow-weighted concentrations for the Susquehanna, Potomac, and James Rivers entering the Chesapeake Bay for 1988-2003
8-10. Maps showing:
     8. Trends in flow-adjusted concentrations for total nitrogen, Chesapeake Bay watershed, 1985-2003
     9. Trends in flow-adjusted concentrations for total phosphorus, Chesapeake Bay watershed, 1985-2003
     10. Trends in flow-adjusted concentrations for sediment, Chesapeake Bay watershed, 1985-2003
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
     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

Tables

1. Streamflow and water-quality station numbers for the 9 River Input Monitoring Program and 24 Multi-Agency Program sites
2. Nitrogen, phosphorus, and sediment species tested for trend
3. Summary of trend tests, results of evaluations, and suggested approaches used in this report
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
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

This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.

View the full report in PDF 3.27 MB

For more information about USGS activities in Pennsylvania contact:
District Chief
U.S. Geological Survey
Water Resources Discipline
215 Limekiln Road
New Cumberland, Pennsylvania 17070
Telephone: (717) 730-6960
Fax: (717) 730-6997
or access the USGS Water Resources of Pennsylvania home page at:
http://pa.water.usgs.gov/.




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