1. Physiological and ecological approaches to assess metal-specific impacts on stream benthos
Cain, DJ, Carter, JL, Buchwalter, DB, and Luoma, SN
U.S. Geological Survey, Menlo Park, CA 94025

2. Environmental indicators:
Water
Sediment
Environmental indicators:
Photo: Ed Moon
Biota
Measures of ecosystem response…
Floodplains
Stream banks
Tailing Deposits
Sources:
Photo: John Lambing
Toxicological risk
Exposure
Bioaccumulation
Photo: Ed Moon

3. X X X Measures of ecosystem response… Sources:
Water
Sediment
Environmental indicators:
Photo: Ed Moon
Biota
Measures of ecosystem response…
Floodplains
Stream banks
Tailing Deposits
Sources:
Photo: John Lambing X X
Toxicological risk
Exposure X
Bioaccumulation
Photo: Ed Moon

4. Conceptual understanding
Metals eliminate some species from assemblages.
Reference condition
Metal
Impaired condition

5. Conceptual understanding
The absence of other species may be caused by other factors.
Metal
Substrate,
Current , etc
Reference condition
Impaired condition

6. Mechanistic understanding of species-specific vulnerability to metals can reduce ambiguity
Substrate,
Current , etc
Reference condition
Impaired condition

7. Mechanistic understanding of species-specific vulnerability to metals can reduce ambiguity
Highly vulnerable
Metal
Tolerant
Substrate,
Current , etc
Reference condition
Impaired condition

8. Assessment of metal effects: types and sources of data
Bioassessment (State)
Annual surveys of benthic macroinvertebrates
Characterize exposures (USGS/USEPA)
Water
Sediments
Macroinvertebrate species (aquatic insects)
Comparative physiology of metal bioaccumulation (USGS, NRP)
Infer species-specific vulnerability based on metal bioaccumulation patterns

9. Response of macroinvertebrates and relation to metal exposure
Reach A
Highest levels of contamination
Area where greatest impacts have occurred in the past
Area where remediation is focused
Evaluated by a metals-specific IBI composed of three metrics (i.e. tolerance index, EPT, density) (McGuire 1993)

10. Metals IBI… generally increases over time in CF

11. Metals IBI… decreases at CF and reference sites in 1995-97

12. Dissolved Cu highly correlated with discharge in CF…

13. but not in the tributaries
Thus, catastrophic disturbance from high discharge likely had a negative impact on the benthos during , and this confounded metals impacts in CF
Metals IBI is not specific to metals

14. Comparative physiological studies
Understand mechanisms affecting metal bioaccumulation.
Infer species-specific differences in metal tolerance.
Are field observations consistent with understanding of mechanisms?

15. Hydropsyche
Tolerant
Whereas tolerant taxa e.g. Hydropsyche are abundant throughout the river, and dominant in contaminated sections.

16. Sensitive Epeorus Scraper
Sensitive taxa e.g. Epeorus are not present in contaminated sections of the river

17. Vulnerability to metal is related to
Accumulated body concentration
Intracellular dose associated with sites vulnerable to metal toxicity (metabolically active e.g. enzyme)
Mayfly
Metal Sensitive
Detoxified / Stored
Caddisfly 1 2 3 4 5 6
Cu in µmol/g

18. Cu accumulation at intracellular sites vulnerable to toxicity (average for sites in the CF)
Bioaccumulation patterns suggest…
Epeorus and Serratella are more vulnerable than
Hydropsyche, Arctopsyche, and Baetis

19. Summary
Understanding community-level responses to metals requires information from a variety of sources.
Bioassessment data indicate improving ecological conditions in the upper CF.
The response generally corresponds to lower Cu exposures.
However, isolating the influences of Cu and discharge is problematic.
The Metals IBI appears to be sensitive to both Cu exposure and discharge.
Species-specific Cu bioaccumulation patterns are consistent with observed distribution patterns.
Absence of species that bioaccumulate high concentrations of Cu at intracellular sites vulnerable to toxicity is indicative of where metals effects were most likely occurring.