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1 May 2012 Elwha River Sediments: Phosphorus Characterization and Dynamics Under Diverse Environmental Conditions
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Abstract

Two large dams on the Elwha River, Olympic Peninsula, Washington, will be removed over a 2–3 year period starting in 2011. Sediments that have accumulated in reservoirs behind these dams will be exposed to new physical and chemical conditions that could affect P distribution and availability in the oligotrophic river system. Coarse sediments from a reservoir delta and fine sediments from a reservoir bottom were collected. The sediments were analyzed for physical and chemical characteristics relevant to P availability. The fine sediments had 20 to 200% greater concentrations of C, N, amorphous Fe, Fe-bound P, Ca-bound P and organic P than the coarse sediments. Both sediment types had relatively low P concentrations compared with published values for eutrophic systems. Both fine and coarse sediments immobilized large quantities of added P, but fine sediments maintained dissolved P concentrations at half the level of coarse sediments. A 300 h incubation of sediments under diverse environmental conditions indicated released P was not affected by short-term exposure to oxygen. For coarse sediments, P release was greater in freshwater than saltwater throughout the incubation, for fine sediments this occurred only initially. Results of sediment characterizations are important in understanding potential post-dam conditions. Release of P from eroded and resuspended sediments will likely be of sufficient magnitude to increase downriver P concentrations. The Ca-bound P in non-eroded dewatered sediments will likely be sufficient to meet the P demand of vascular vegetation that establishes in the new riparian zone.

© 2012 by the Northwest Scientific Association. All rights reserved.
Emily Cavaliere and Peter Homann "Elwha River Sediments: Phosphorus Characterization and Dynamics Under Diverse Environmental Conditions," Northwest Science 86(2), 95-107, (1 May 2012). https://doi.org/10.3955/046.086.0202
Received: 31 July 2011; Accepted: 29 January 2012; Published: 1 May 2012
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