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Sediment dynamics in flow-regulated streams and the impact on aquatic ecosystems

Sediment dynamics in flow-regulated streams and the impact on aquatic ecosystems. Nira L. Salant Dartmouth College 2005 Advisors: Carl Renshaw and Frank Magilligan. Impact of dams on ecosystems. - Limited recruitment of riparian species - Reduced access to floodplain habitat

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Sediment dynamics in flow-regulated streams and the impact on aquatic ecosystems

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  1. Sediment dynamics in flow-regulated streams and the impact on aquatic ecosystems Nira L. Salant Dartmouth College 2005 Advisors: Carl Renshaw and Frank Magilligan

  2. Impact of dams on ecosystems - Limited recruitment of riparian species - Reduced access to floodplain habitat - Reduced diversity and abundance of benthic fauna - Decreased productivity of algae and biofilm

  3. O2 N

  4. Purpose Link the ecological impacts of dams to the geomorphic response resulting from hydrologic changes Primary questions What are the geomorphic responses of the streambed? How can we effectively quantify these responses?

  5. Overview of methods Four metrics 1. Short-lived fallout radionuclides (7Be, 210Pb) 2. Embeddedness measurements 3. Long-term hydrologic and morphologic data 4. Benthic invertebrates Three rivers Regulated: Ompompanoosuc, Black Unregulated: White Year-long monitoring

  6. Three inter-connected parts **Use of fallout radionuclides to quantify sediment transport below dams** Timescales of stream bed stabilization due to altered flow and sediment regimes below dams The effect of substrate stability and sediment deposition on benthic ecology downstream of a flood-control/run-of-the-river dam

  7. water sediment DAM Deposition and aggradation Armoring and incision Ecological changes

  8. S* vs. T* From Grant et al. 2003

  9. DAM Changes in sediment residence time and transport velocity Deposition and aggradation Armoring and incision

  10. Short-lived fallout radionuclides Relative 7Be/210Pb activity High 7Be/210Pb = “New” Low 7Be/210Pb = “Old 7Be (t1/2 = 53.4 days) Erosion “New” “Old”

  11. Study sites

  12. Union Village Dam

  13. Level of flood-control gates compared to hydrograph

  14. Level of flood-control gates compared to hydrograph Highly regulated High flow

  15. Level of flood-control gates compared to hydrograph Partially regulated High flow

  16. Level of flood-control gates compared to hydrograph Unregulated Low flow

  17. Bed sediment sampling Monthly sampling February to July 2004

  18. Samples dried, sieved and counted for 7Be activity

  19. Highly regulated High flow

  20. Highly regulated flow: Early spring

  21. Highly regulated flow: Early spring

  22. Partially regulated High flow

  23. Study sites

  24. Partially regulated flow: Mid-spring

  25. Entire time period

  26. Measured transport velocities

  27. Comparisons to previous studiesSediment transport rates

  28. Effect of grain size interactions on transport

  29. Comparisons to previous studies Sediment transport models

  30. Timescales of stream bed stabilization due to altered flow and sediment regimes below dams Ompompanoosuc River - Sediment over-supply Black River - Sediment limitation

  31. Timescales of bed elevation stabilization Bed elevation variance

  32. Black RiverImmediate stabilization

  33. Ompompanoosuc RiverGradual stabilization

  34. Benthic ecology Lack of disturbance Sediment deposition

  35. Results

  36. Conclusions Radionuclides offer a simple and effective method for directly measuring transport rates Dams and their specific operation control the geomorphic response of the streambed Geomorphic changes to the streambed drive changes to benthic ecology

  37. Funding National Science Foundation Arthur D. Howard Award (GSA QG&G) Vermont Geological Society Dartmouth College Earth Sciences Hydrologic records/ dam information Greg Hanlon and Thomas Snow (U.S. Army Corps of Engineers) Ken Toppin (USGS) Biological assistance Jeffrey Veikko Ojala (USDA Forest Service) Scott Wixsom and Dan Mckinley (USFS Green Mountain National Forest) Craig Layne and Darren Ward (Dartmouth Department of Biology) Kaoru Itakura Rebecca Krystosek Julie Jo Walters Field assistance Kelly Sennatt and Alexandra Fleming (Dartmouth Department of Earth Sciences). Acknowledgements Thank you Frank and Carl! Also thanks to Jim Kaste, Keith Nislow, and Brian Dade for their advice and assistance

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