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Lake Anne Mirrors Nationwide Decrease in Lead Concentrations in Lakes and Reservoirs
Released: 9/2/1997

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192
Judy Fretwell 1-click interview
Phone: 703-648-6846 | FAX: 703-648-4460

Reston’s Lake Anne mirrors a significant decline in lead concentrations observed in the sediments at the bottom of several lakes and reservoirs across the nation. However, levels have not returned to the baseline levels of the 1950’s and 60’s according to a new U.S. Geological Survey (USGS) report.

USGS scientists said that the declines occurred despite significant increases in both population and the number of motor vehicles driven in the Lake Anne drainage basin. Although lead concentrations declined as much as 70 percent since the 1970’s and 80’s, they remain almost twice as high as the baseline levels of the 1950’s and 60’s. The article, "Reservoir Sediment Cores Show U.S. Lead Declines," by Edward Callender and Peter Van Metre, which is published in the September issue of Environmental Science and Technology, shows results of the study.

"We purposely picked lakes and reservoirs that were under urban pressure and likely to be affected by lead contamination," said Robert Hirsch, USGS Chief Hydrologist and a Reston resident. "The significant declines in lead in these urban lakes is encouraging. These declines are a good indication that the switch to unleaded gasoline in the late 1970’s, coupled with enactment of the Clean Air Act, have produced a positive effect on the Nation’s water resources."

Previous studies by the USGS show a significant downward trend in lead concentrations in the Nation’s streams. The newest sediment studies are particularly important because lake and reservoir sediments tend to be long-term "traps" that accumulate sediment and associated heavy-metal contaminants, such as lead. Lead in sediment accumulations can become sources of future water pollution.

Lake Anne, the oldest of the manmade lakes in the planned community of Reston, Virginia, was selected last year by the USGS to be part of a national study of lakes and reservoirs because of its nearly 30-year record of lake-bottom sediments and its suburban land-use setting. Also, there are no obvious point sources of contamination in the area, such as sewage outfalls or industrial waste discharges.

The overall lake study is part of the national synthesis effort of the USGS National Water Quality Assessment Program (NAWQA), which is the first comprehensive, ongoing study of trends in the quality of the Nation’s surface- and ground-water resources. Lake Anne is one of several sites studied.

Hydrologists used gravity-type coring devices and "grab baskets" to collect samples of the sediments at the bottom of the lake. From these samples, scientists can discern a "signature" of the quality of the water in the lake and its drainage basin over time. Because lakes and reservoirs efficiently trap sediments from rivers and streams, the accumulated sediments can provide a valuable historical record of what has been happening regarding the presence of lead in the Lake Anne drainage basin. Heavy metals like lead, for example, tend to accumulate in sediment. Scientists can look at the lead concentrations recorded in the core and determine the time frame when leaded gasoline was being used in the basin. Looking at lead concentrations in the older sediments in the core is like moving backward in time to see if there has been a change in the percent of lead present in sediments deposited in more recent times. In Lake Anne, there is a 90-percent decrease in lead in the more recent sediment deposits in the upper part of the core compared to the baseline concentrations in the oldest sediments at the bottom of the core. Radiochemical dating was used to determine the time represented by specific points along the length of the core.

Additional sediment sampling of Lake Anne and Lake Fairfax is planned to look at other contaminants and the effects of suburbanization on the lakes. Significant components of the NAWQA Program include consistent methods for sampling and the use of complex "clean" sampling protocols that ensure the validity and integrity of the data.

(Note to Editors: For further information on results of the study, please call Edward Callender, USGS, Reston, VA, 703-648-5826.)

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