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 - Reduced diversity and abundance of benthic fauna - Decreased productivity of algae and biofilm

O2O2 N

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?

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

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

watersediment Deposition and aggradationArmoring and incision Ecological changes DAM

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

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

Short-lived fallout radionuclides 7 Be (t 1/2 = 53.4 days) Relative 7 Be/ 210 Pb activity High 7Be/210Pb = “New” Low 7 Be/ 210 Pb = “Old Erosion “New” “Old”

Study sites

Union Village Dam

Level of flood-control gates compared to hydrograph

Highly regulated High flow

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

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

Bed sediment sampling Monthly sampling February to July 2004

Samples dried, sieved and counted for 7 Be activity

Highly regulated High flow

Highly regulated flow: Early spring

Partially regulated High flow

Study sites

Partially regulated flow: Mid-spring

Entire time period

Measured transport velocities Time period 7 Be velocity (m/d) Early spring: 31 March – 14 May40 – 60 Mid-spring: 31 March – 28 May40 – 60 Late spring: 28 May – 18 June below dam downstream 30 – – 80

Comparisons to previous studies Sediment transport rates MaterialVelocity (m/d)Source Bed load0.3 – 4.5 m/dBeechie (2001) Bed load30 – 80 m/dThis study Suspended load600 – 1500 m/dBonniwell (1999)

Effect of grain size interactions on transport

Dates 7 Be velocity One-fraction velocity Two-fraction velocity Sand | Gravel Sand fraction (F s ) 31 March – 14 May40 – – March – 28 May40 – – May – 18 June below dam downstream 30 – – – – – Comparisons to previous studies Sediment transport models

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

Timescales of bed elevation stabilization Bed elevation variance

Black River Immediate stabilization

Ompompanoosuc River Gradual stabilization

Benthic ecology Lack of disturbanceSediment deposition

FamilyDateRegulatedUnregulatedP HydropsychidaeJuly HydropsychidaeSeptember < EphemerellidaeJuly < EphemerellidaeSeptember < Results

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

Acknowledgements 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). Thank you Frank and Carl! Also thanks to Jim Kaste, Keith Nislow, and Brian Dade for their advice and assistance