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Fresh Water Ecosystems

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Destroying the Dam
Teacher Contributed

Destroying the Dam

Topic

Restoring the Elwha

Student Exploration

How will the removal of the Elwha dam affect the freshwater ecosystem upstream?

For over a hundred years in the Pacific Northwest, the Elwha freshwater ecosystem was being disturbed by the Elwha dam. Salmon that typically spawn upstream were not able to do so. Check it out: Restoring the Elwha

How were the salmon being affected by the dam? By simply removing the dam, will the ecosystem improve? What will change?

Extension Investigation

  1. Hydoelectric power, a renewable energy source with no pollution, is an excellent alternative to fossil fuels. Removing the dam means removing a good source of power. How was the dam threatening the survival of salmon? Pacific Salmonids: Major Threats and Impacts Are there other threats to the survival of the salmon in the Pacific Northwest?
  2. As mentioned in the video clip, scientists are paying close attention to the number of salmon present in the Upper Elwha River to assess how the ecosystem is improving. How are they measuring the population growth? If the salmon population increases in the ecosystem, how will that impact other organisms? Create a “before” food web and an “after” food web showing the other players that would be affected.
  3. How will the shape of the river change as the dam is removed? How will incorporating log jams improve areas for salmon to spawn? Build a model or use a stream table to simulate the Elwha river with the dam and without the dam. Add log jams. Observe the velocity of stream flow and locations of sediment deposition.

Resources Cited

NOAA. http://www.nmfs.noaa.gov/stories/2012/07/07_20_2012_elwha_restoration_video.html

http://www.nmfs.noaa.gov/pr/species/fish/salmon.htm

http://www.nmfs.noaa.gov/pr/pdfs/criticalhabitat/cohosalmon.pdf

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