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

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

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

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

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

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

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

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

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)

Metals IBI… generally increases over time in CF

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

Dissolved Cu highly correlated with discharge in CF…

but not in the tributaries Thus, catastrophic disturbance from high discharge likely had a negative impact on the benthos during 1995-97, and this confounded metals impacts in CF Metals IBI is not specific to metals

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

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

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

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

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

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.