The distribution of particulate organic carbon and sediment in the Elwha River dispersal system during the dam removal process
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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.