Potential impacts of timber harvesting, climate, and conservation on sediment accumulation and dispersal in the South Slough National Estuarine Reserve, Oregon

Accurate sediment flux histories are critical data for deciphering the relative importance of climate and land use factors such as logging and road construction on sediment production and deposition. We use 210 Pb activities derived from sediment cores taken on the tidal flats of the South Slough of the Coos Bay estuary to establish temporal variations in sediment accumulation rates. We determined that average deposition varied between 0.4 and 0.81 cm/yr based on two ∼80 cm sediment cores. Sedimentation accumulation rates approached 2.1 cm/yr during the 1960s when a rainfall event of extreme intensity coincided with vigorous timber activity. Following this peak, a >40% reduction in peak lumber harvests in the latter part of the 20th century was accompanied by a decrease in sedimentation rates. Mean monthly rainfall during the same time period remained seasonably constant, indicating that land use is likely the key factor governing variations in sediment accumulation.