Paper No. 14-9
Presentation Time: 1:00 PM-5:00 PM
A SEDIMENTARY RECORD OF ENVIRONMENTAL CHANGE SINCE 1720 FROM LAKE MATOAKA, WILLIAMSBURG, VIRGINIA
Sediments archived in mill ponds constructed during Colonial times record landscape developments driven by human activity as well as natural environmental changes. Mill ponds also provide important local and regional environmental records for the Coastal Plain, where few natural lakes exist. This study reconstructs the history of environmental changes in the catchment of Lake Matoaka, a former mill pond on the Virginia Coastal Plain. Lake Matoaka was formed c. 1720 from the damming of College Creek, and its catchment has been impacted by various historic anthropogenic activities, including developments associated with agriculture, military encampments, the progressive expansion of the College of William & Mary, and increased urbanization of Williamsburg. To assess how the lake was impacted, sediment cores were recovered and a 1.54-m core from the deepest basin was analyzed for magnetic susceptibility, bulk density, bulk organic matter properties, and diatom assemblages. Relative elemental abundances, primarily Pb, Ti, and Ca, were also acquired by scanning X-ray fluorescence. A chronology for the record has been developed using the onset of lacustrine sedimentation at 118 cm (AD 1720) and the analysis of 210Pb and 137Cs profiles across the upper 80 cm. Average sedimentation rates are ~4 mm/yr and total organic carbon values range from 3-13%, mostly from algal sources. The record contains six lithostratigraphic units marked by distinct changes in magnetic susceptibility, Ca, and Ti values attributed to periods of enhanced runoff and aquatic productivity, which we correlate with historic land-use changes. Significant fluctuations in the Pb content of the upper 30-cm of the core record changes in regional pollution loads to the lake’s watershed from the use of leaded gasoline and subsequent air quality legislation. Two of the most significant period of sedimentation correspond to the raising of the lake level in 1920 and the progressive eutrophication of the lake over the last fifty years due to nutrient inputs from the campus and surrounding urban landscapes. Overall the sedimentary record from Lake Matoaka provides perspectives on how a colonial mill pond has been impacted by environmental changes as its catchment transitioned from primarily agricultural to a more urbanized landscape.