IN-SITU FP-XRF SEDIMENT CORE ANALYSIS: IMPLICATIONS FOR ANTHROPOGENIC METAL LOADINGS LAKE WABAN MA

Lake Waban is a kettle lake with a maximum depth of 13 meters that formed during the last glaciation about 16,000 years ago. It is a suburban lake located in Wellesley, MA within the greater Boston area in New England. Lake Waban is hydrologically connected to Paintshop Pond, where a 20th century paint pigment manufacturing facility was located that has been a documented point source of legacy metals including Pb, Cr, and As. Peaks in the concentration of non-point source legacy metals Pb and V have been used as time stratigraphic markers, as they mark the peak usage of leaded gasoline for automobiles in 1979 and of high sulfur Venezuelan fuel in 1966, respectively. We collected geochemical data for four gravity cores collected from the two deepest basins in the lake using a handheld X-ray fluorescence (FP-XRF) analyzer. In an attempt to analyze the gravity cores in a reproducible manner, a ruler was aligned and fixed to the wrapped sediment core to control the depth intervals for each analysis. Elemental concentrations in the core were measured at every centimeter for 30 seconds for each of three wavelength filters installed on the FP-XRF. High atomic number elements, such as Pb, As, Cr, and Fe, which have much more energetic characteristic X-rays, are measured with the highest level of precision. In order to assess the reproducibility of single core scan a second scan was conducted in the same core revealing the maximum Pb concentration at exactly the same depth (24 cm) with only a 6% difference in measured concentration. In Lake Waban these in situ lead concentrations ranged from 1,000 ug/g near the surface to 16,000 ug/g at peak value. Despite this encouraging result, future work must address: analytical uncertainty that varies with atomic number, heterogeneity of the sediments relative the X-ray beam diameter, and variable water content which can absorb the fluorescence signal. This new method of analyzing elemental concentrations in sediment cores allows for quick scanning lake sediment cores that then inform how best to subsample the record for subsequent proxy analyses, leading to more targeting stratigraphic characterization.