EVALUATING RECORDS OF NITROGEN AND HEAVY METALS IN SMALL, UPLAND WATERSHEDS AFFECTED BY 17TH CENTURY TO PRESENT LAND USE CHANGE, SOUTHERN NEW ENGLAND

Land use activity such as deforestation and agriculture is often linked with increased sediment erosion and transport due to lowered soil stability and/or increased runoff. Eroded material from human impacts, often referred to as legacy sediment, may be stored within watersheds on its way downstream. Identifying and mapping out legacy sediment, therefore, offers clues to the timing, intensity and extent of past land use practices. Historic land use change following European settlement in the 17^th century was rapid and widespread throughout southern New England. Intensive land use practices during this time were eventually abandoned in the late 19^th century, which initiated forest recovery. Today, high resolution topographic data (LiDAR) allows identification of remnant features such as stonewalls (which indicate pasture-style agriculture) and charcoal hearths (which indicate deforestation to produce charcoal) beneath the canopy of new growth forests. This study uses GIS and geospatial analysis to reconstruct the aerial extent of past land use practices that were vulnerable to erosion and potential sediment transport during the time of clearance, and sediment cores to evaluate the geochemical signatures of past land use in small upland watersheds upstream of wetlands in the region. We focus on the use of isotopic nitrogen values to indicate a shift from natural nitrogen cycles to agricultural waste input, and Pb concentrations to indicate atmospheric deposition resulting from the combustion of fossil fuels. Preliminary data indicate that changes in nitrogen isotope systematics precede peak shifts in Pb, highlighting a two-stage record of human impact due to historic agriculture. Further study will produce similar records across the range of land use histories and intensity inferred by the LiDAR mapping, allowing for identification and comparison of geochemical markers applying to each land use type, and overall comparison with background, natural conditions.