To what extent is there excess sediment in the Middle Truckee River that impairs aquatic life use?

1. To what extent is there excess sediment in the Middle Truckee River that impairs aquatic life use? Application of benthic macroinvertebrate bioassessment to determine whether there is habitat degradation from deposited sediments David Herbst University of California Sierra Nevada Aquatic Research Laboratory

2. Goal: Biological Guidance for Sediment TMDLDefine deposited sediment guidelines for monitoring, protecting, and improving the biological health of the Middle Truckee River Objectives: Describe patch-scale distribution of fine + sand (FS) deposits along the river at representative reaches below tributary stream confluences Collect data to measure biotic responses and limiting effects of sediment at the patch-scale for both cover and volume of FS Compare biological health to other large rivers of eastern Sierra that are less developed than MTR

3. What we did and how and where we did it • 10 study sites along the river at locations below tributaries and over downstream changes in channel geomorphology • Sampled at baseflow (in late September of 2011) • Characterize the ambient distribution of FS sediment deposition cover using quadrat grid-frames • Associate the invertebrates within each quadrat (n=100) to define biological effects of sediment cover over a full range of FS from none to complete cover

4. SAMPLING Quadrats: D-net samples from 30 x 30 cm habitat patches at which %FS is recorded at 25 points: 10 sites x 10 patches = 100 samples over full range 0-100% FS %FS Cover What is the ambient level of sediment deposition over the Middle Truckee? Distribution of FS cover over these varied sites along the river: Random sampling of 100 quadrats at each of the 10 reaches to establish ambient FS levels (<50 cm depth, in depositional and erosional micro-habitat patches) = 25,000-point counts

5. Context for Results • Data analysis of quadrat FS: • Diversity, tolerance, and food web structure in relation to FS cover grouped in bins of - 0% 0-20% 20-40% 40-60% 60-80% 80-100% and cross-group statistical tests • Ordination and testing for differences between bin groups of FS cover • Indicator group analysis (preferences for low-high) • Ambient FS deposits downstream • How does the biological integrity of Middle Truckee compare to other large rivers of the eastern Sierra that can serve as references? Using different types of SWAMP-standard methods in mobile vs immobile reaches half of MT samples did not support standard. All regional reference large streams did.

6. How does the food web change over the FS cover gradient? Grazers Collector- Gatherers Collector- Filterers Shredders Predators • Changes w/ FS: • CG increase • G decrease • CF decrease • >More FPOM • >Less algae • >Less surface • for attached CF

7. How does density and body size of BMI community change over FS gradient? % EPT Density /m2 • Density reduced and body sizes smaller and this limits both food quantity and food quality to fish and riparian birds % Chironomidae midges With no or low FS cover, density is ~4,000/m2 At higher FS cover, reduced to ~3,000/m2 Percent of larger EPT declines, while the smaller midges increase with FS cover

8. How does community species composition change over the sediment gradient? Ordination Analysis Proximity of points means similarity, and distance signifies differences in species composition for the 100 quadrats across all sites MRPP Tests Show: Community types grouped by statistical differences -Low FS <20% -Mid FS 20-80% -High FS >80% a b bc c d MRPP Groups:

9. Indicator Organisms for FS Sediment Mostly EPT Mostly Midges p* significance values from indicator analysis

10. 60% 100% 20% 40% 80% Promote the objective of FS cover levels below 20% Greatest density of the EPT - most common food resources to fish, and are the most diverse and sensitive forms of benthic animal life. First significant community structure shift occurs above this FS level.

11. Distribution of FS sediment in vulnerable depositional zones along downstream river

12. Existing standard on MTR for turbidity states ≤25 mg/L in 90% of observations – use this approach? Deposited sediment within any river segment including both erosional and depositional habitats should have <80% FS cover in 90% or more of observations

13. Bottom-Line • Riverwide ambient conditions on the 1000 quadrats over 10 sites combining both erosional and depositional patches: 62.5% of habitat has <20%FS, the best conditions; in contrast 17.4% of habitat has >80%FS, poorest condition • Minimize >80% FS, maximize <20% FS • Management to achieve reduction in worst conditions of FS deposition in most vulnerable habitat zones (depositional patches) – e.g., flow management, erosion control • Promote increases in the best habitat conditions where FS deposition is low across all zones of geomorphology • Goal - beneficial effects for fish and wildlife, river function • Monitor FS patch distribution to evaluate if sediment reduction actions work, and verify with bioassessment trends