Industrialization and urbanization around San Francisco Bay as well as mining and agriculture in the watersheds of the Sacramento and San Joaquin rivers have profoundly modified sedimentation patterns throughout the estuary. We provide some constraints on the onset of these erosional disturbances with Be-10 data for three sediment cores: two from Richardson Bay, a small embayment near the mouth of San Francisco Bay, and one from San Pablo Bay, mid-way between the river delta and the mouth. Comparison of pre-disturbance sediment accumulation determined from three C-14-dated mollusk shells in one Richardson Bay core with more recent conditions determined from the distribution of Pb-210, and Th-234 [Fuller, C.C., van Geen, A., Baskaran, M., Anima, R.J., 1999. Sediment chronology in San Francisco Bay, California, defined by Pb-210, Th-234, Cs-137, and Pu-239,Pu-240] shows that the accumulation rate increased by an order of magnitude at this particular site. All three cores from San Francisco Bay show subsurface maxima in Be-10 concentrations ranging in magnitude from 170 to 520 x 10(6) atoms/g. The transient nature of the increased Be-10 input suggests that deforestation and agricultural development caused basin-wide erosion of surface soils enriched in Be-10, probably before the turn of the century. (C) 1999 Elsevier Science B.V. All rights reserved.
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