The ground water moving to streams in the Bay watershed has an average age of 10 years. The relatively slow movement of ground water to streams and into the Bay will impact the "lag time" between implementation of management practices and improvement of water quality in the Bay. The Chesapeake Bay Program, a multi-agency watershed partnership, is implementing nutrient-reduction strategies in an attempt to improve water-quality conditions in the Bay by 2010.

"Over the past dozen years we have seen more than 3 million acres in the Bay watershed put under nutrient management plans," said Chesapeake Bay Program Director Rebecca Hanmer. "This improved scientific understanding provided by the USGS will help us better estimate when we'll see the benefits from these efforts and how much more is needed to bring back the Bay."

The age of ground water in shallow aquifers underlying most of the Chesapeake Bay watershed ranges from less than 1 year to more than 50 years. The majority of the ground water (75 percent) is less than 13 years old, which is younger than previously thought.

The USGS study found that just over 50 percent of the water in a stream is from ground water with a range of 16 to 92 percent. Surface-water runoff and soil water supply the rest of the water to a stream; both have very young ages (hours to months).

Nitrogen in streams that drain to the Bay comes from both runoff and ground water. Nitrogen enters ground water from rainfall or through application of fertilizers and other practices associated with agricultural, suburban and urban areas. The USGS study estimated that on aver
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Contact: Kathleen Gohn
kgohn@usgs.gov
703-648-4242
United States Geological Survey
18-Feb-2004