Sediment source variations and lead-210 inventories in recent Potomac Estuary sediment cores

Oldfield, Frank and Maher, Barbara and Appleby, Peter (1989) Sediment source variations and lead-210 inventories in recent Potomac Estuary sediment cores. Journal of Quaternary Science, 4 (3). pp. 189-200. ISSN 0267-8179

Abstract

We present the results of magnetic measurements (low field susceptibility, anhysteretic and isothermal remanences) on samples of sediment from 11 cores from the Potomac River between Washington DC and its mouth. The magnetic properties indicate that at sites in the upstream reaches especially, there has been a shift to surface-soil-derived sediments in recent times. No such shift is indicated at the mouth of the Estuary. Comparison with pollen, 210Pb and trace metal analyses, where available, suggests that the shift to soil-derived material dates from the early to mid-19th century and coincides with a major land use change previously documented by Brush et al. (1982). Inventories of unsupported (excess) 210Pb activity in the cores increase upstream, are positively correlated with total sedimentation rates, and, in the upper reaches where the magnetic properties indicate soil inwash, greatly exceed values expected from direct atmospheric deposition alone. We infer that in these cores, most of the unsupported 210Pb is deposited from the surfaces of the catchment as a result of soil erosion.