Answering the Question: Why?Factors Affecting Change in Water Quality• Exceptional challenge to explain “why”

• Poor quality of pollution source information• Ex. Ag source sector has poor information on BMP implementation (due

in part to Farm Bill privacy issues and technical limitations of NRCS.) • Many assumptions (with errors associated with them) are required to

generate a time series of source information• Lag time issue of pollutants in surface and ground water • Expectation for change is not realistic given degree of management practice

implementation• Explaining change is hard in large rivers given multiple pollutants however,

explaining change in the point sources is possible• Ex. Point source controls are the explanation for most decreases in

nutrients in large CBW rivers since 1980s• Smaller systems allow for understanding of factors affecting change

• Monitoring is moving to from large river focus to monitoring some small watersheds where large amounts of practice implementation is planned or ongoing in order to better describe factors affection change.

• Point source easier to explain than non point source

Flow-Adjusted Concentration Trends

1985-2008:Total Phosphorus

22 downward trends

4 upward trends

8 non-significant trends

Flow-Adjusted Concentration Trends

1985-2008:Total Nitrogen

25 downward trends

2 upward trends

7 non-significant trends

Flow-Adjusted Concentration Trends 1985-2008:Total Sediment13 downward trends

2 upward trends

19 non-significant trends

Wastewater Discharge Locations: Patuxent River WatershedData Source:

Chesapeake Bay Program:

Point Source Database

20 Locations upstream from USGS Patuxent River Gage

Significant Investment(s) in treatment technology

Phosphorus Detergent Ban

Watershed Changes:

Urban/Suburban devt.

Land Conversion

Population increase

NPS management

SWM management

Large Point-Source Reductions Yield Measurable Improvements in Phosphorus Concentrations

Annual Point source Discharges Upstream from Patuxent River Monitoring Station

Observed Concentrations atPatuxent River Monitoring Station

44 years of Nitrate concentration data show long-term increases in an agricultural setting:Choptank River at Greensboro, MD

Groundwater Models Develop Nutrient Loading Forecasts

Eastern Shore of Virginia

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