USING GEOCHEMICAL AND SEDIMENTOLOGICAL TRENDS TO CHARACTERIZE PRE- AND POST- SETTLEMENT OVERBANK FLOODPLAIN DEPOSITS IN A NORTH CAROLINA PIEDMONT WATERSHED

The environmental history of a watershed is generally preserved in vertically-accreted floodplain deposits, offering the potential to reconstruct major disturbances to a river system. Human settlement and land clearing tend to increase sedimentation rates on valley floors, particularly during forest to agriculture land conversion. While mining pollution tracers are commonly used to study and date historical floodplain units, the response of watersheds during pre-mining periods is largely unknown due to the lack of a discriminating fingerprint. The Dutch Buffalo watershed (253 km2) in the North Carolina Piedmont is the site of the nation's first gold mining district with major mining activities beginning in 1842. The use of mercury (Hg) during gold ore-processing and a well-documented mining history enables the dating of overbank units during the mining period (1842-1915). The geochemical and sedimentological response of the basin during pre- and post- European settlement, however, is largely unknown.

This study uses geochemical and physical properties of overbank floodplain deposits to characterize pre- and post-settlement floodplain units. Floodplain sediment cores collected along cross-valley transects downstream of the mining district were assessed for geochemical and physical properties including extractable and total elemental geochemical trends, grain size, pH, organic matter content, and color. The geochemical and sedimentological profiles of floodplain deposits are sensitive to subtle changes in land use and mining history. The pre-settlement/post-settlement boundary is indicated by the presence of a buried A-horizon and/or shift in elemental ratios and grain size distribution. This study provides a context for understanding the history of channel and floodplain changes caused by anthropogenic processes during early American settlement of North Carolina Piedmont watersheds.