Patterns of recent sediment accumulation in Chesapeake Bay (Virginia—Maryland, U.S.A.) tributaries

Abstract

Sediment accumulation rates obtained from 39 cores in 10 tributaries of the western shore of Chesapeake Bay average 0.30 cm yr. −1 since European settlement, compared with pre-settlement rates in three tributaries of 0.14 cm yr. −1. Drainage areas of six of the tributaries extend from the Coastal Plain into the Piedmont and four are restricted to the Coastal Plain. Rates are highly variable, but higher in the upper parts of the tributaries and lower at the mouths. During the period of early agriculture, when <20% of the land was under cultivation, the average rate was 0.19 cm yr. −1. Later, when land under cultivation reached 40–50%, rates almost doubled averaging 0.34 cm yr. −1. There are no differences in post-settlement mass accumulation rates (g cm −2yr. −1 during periods of different land use or in different stretches of the tributaries. Pre-settlement rates are based on unpublished reports of 14C dates, ranging from 670 to 5330 yr. B.P., of peat layers from three western shore tributaries where sediment deposition is believed to have been continuous. Post-settlement rates are average rates calculated between a maximum of five pollen horizons. The pollen horizons represent historically documented changes in the regional vegetation and include initial land clearance (1634, 1650, 1720 and 1730, depending on the tributary), shift to intensive agriculture (1780 and 1840), beginning of the chestnut blight (1910), demise of chestnut (1930) and the beginning of large-scale urbanization (1960).