Impact of urbanization on sediment chemistry in small-scale watersheds, southeast Virginia.

The state of Virginia contains only two natural bodies of water with the rest being comprised of mill ponds, farm ponds and impoundment lakes. These man made water bodies are ubiquitous along the eastern seaboard. Southeast Virginia (Williamsburg, Jamestown and surrounding counties) was the locus of early European settlement and many of the local ponds date back to the early colonial period. As such, the sediment record in these ponds provides a unique historical record of the impact human activity can have on small watersheds. Two small man-made ponds (Lake Matoaka and Jolly Pond) were studied. Both ponds lie within the James River basin, a major feeder to the Chesapeake Bay. Both drainage basins cover ~600 ha but differ significantly in the level of development. Lake Matoaka was originally dammed ca. 1720. The Matoaka drainage is currently experiencing rapid development (~22% high population residential/commercial) and includes the College of William & Mary's campus. Jolly Pond and the two dams that created it first appear on maps dating back to 1863. The Jolly Pond basin is largely dominated by forests and agricultural land. Sediment cores were taken from both ponds using a Russian peat corer, Matoaka to 1.5m depth and Jolly Pond to 0.9m dpeth. Sediment splits were analyzed for total exchangeable lead concentration and lead isotopes (207Pb/206Pb & 208Pb/206Pb), as well total carbon and nitrogen. Carbon/Nitrogen ratios were used to indicate changes in water level and dam height increases. Lead concentrations in both cores show a peak associated with leaded gasoline use. [Pb] in Matoaka are significant (~320 ppm) and show a clear anthropogenic isotopic signature. Jolly Pond [Pb] are surprisingly low and are close to background values. These data indicate that even minimal development has significant impact on sediment chemistry. Likely lead sources for Lake Matoaka include road and building runoff and lead aerosols.