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The distribution of particulate organic carbon and sediment in the Elwha River dispersal system during the dam removal process
Abstract
The delivery and deposition of particulate organic carbon (POC) into the marine
environment via rivers impacts local biological and geological processes as well as the
global carbon cycle. This is especially the case in small mountainous rivers, such as the
Elwha River, Washington, which delivers a significant fraction of particulate organic
carbon to the Strait of Juan de Fuca annually. Recently, the Elwha has begun undergoing
dam deconstruction. To study the resulting fluctuations of POC in response to dam
removal, water and seabed samples were collected and analyzed using loss on ignition to
estimate levels of POC. The concentrations of suspended sediments in the water column
and compositions of grain size in the marine seabed sediments were also examined.
Seabed samples were found to contain higher concentrations of POC compared to surface
water samples. POC levels increased when more suspended material was present in the
river, and also when seabed samples consisted primarily of mud. Overall, the major
concentrations of POC occurred below the Glines Canyon and Elwha Dams, where
sediment is being released and eroded due to dam removal processes, and also in the river
mouth, which is an area of high turbidity.