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Relationships between Watershed Alterations and Sediment Accretion Rates in Willapa Bay Washington and Yaquina Bay, Oregon
Citation:
YOUNG, D. R., P. J. CLINTON, AND R. J. OZRETICH. Relationships between Watershed Alterations and Sediment Accretion Rates in Willapa Bay Washington and Yaquina Bay, Oregon. Presented at Pacific Estuarine Research Society Annual Meeting, Anacortes, WA, April 12 - 14, 2012.
Impact/Purpose:
The Pacific Northwest (PNW) is one of the leading regions of timber production in the United States.
Description:
The Pacific Northwest (PNW) is one of the leading regions of timber production in the United States. It also undergoes aperiodic episodes of catastrophic forest fires, and systematic slash burns following logging activities. Such conditions raise concerns regarding increased releases of sediment to the coastal streams and rivers leading to coastal estuaries of the PNW. This study was conducted to investigate the rates of sediment accumulation since the late 1800’s in two major estuaries of the PNW, Willapa and Yaquina bay. Five cores from low marshes or adjacent mudflats from each site were collected and 1-cm layers dated using traditional Pb-2100 geochronology methods. Polynuclear aromatic hydrocarbons, along with total organic carbon and grain size distribution, also were measured in some of the cores. The histories of forest fires, and of logging and other human activities, in the watersheds of these two estuaries also have been researched and evaluated, and relationships sought between these events and changes in the rates of sediment accretion in the estuaries. Despite intense logging activities and major reductions in old-growth forest stands during the 1900’s, generally there was no indication that sediment accretion rates had increased during or following such events. Average accretion rates in most lower marsh cores ranged from 0.1 to 0.4 cm/yr, although a higher rate (1.15 cm/yr) was measured in one mudflat core from lower Yaquina estuary. Only one of the ten cores collected showed a clear increase in accretion rate, beginning around 1976.