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Copper toxicity to Bristol Bay sockeye salmon larvae under field-relevant water quality conditions

Investigators

Benjamin BarstWater and Environmental Research Center
Institute of Northern Engineering
Matthew WoollerWater and Environmental Research Center
Institute of Northern Engineering
Jeffrey MorrisHealth and Environment
Todd RadenbaughBristol Bay Environmental Science Laboratory

Student

Synopsis

Potential mining activities within the Bristol Bay watershed (BBW) have raised concerns over the possible impacts that releases of copper (Cu) and other elements may have on the health of the valuable salmonids occupying the region’s freshwater habitats.
Copper bioavailability and toxicity are highly depends upon local water quality; Cu
bioavailability and toxicity decrease with increasing hardness and dissolved organic matter
(DOM). Notably, freshwaters within the BBW are low in both hardness and DOM, suggesting
that there would be little protection against potential releases of Cu for local salmonids. In our
previous research, we showed that the model endorsed by USEPA under-predicts Cu toxicity to
fathead minnows (a model test species) exposed in water collected from the BBW. In addition to
the variation brought about by local water chemistry, Cu toxicity also varies among life stages
and species of fish; salmonids are more sensitive than fathead minnows, and larvae are more
sensitive than embryos and adult fish. While our previous work with fathead minnows indicates
that the current model under estimates Cu toxicity, more testing is needed with a species of fish
(i.e., sockeye salmon) that is relevant to the BBW. In addition to determining toxic levels of Cu
to local sockeye salmon, it is necessary to both characterize baseline levels of Cu and other trace
elements in freshwater environments of the BBW and understand their historical variation.

Overview

The issue

Potential mining activities within the Bristol Bay watershed (BBW)
have raised concerns over the possible impacts that releases of copper (Cu) and other elements
may have on the health of the valuable salmonids occupying the region’s freshwater habitats.
Copper bioavailability and toxicity are highly dependent upon local water quality; Cu
bioavailability and toxicity decrease with increasing hardness and dissolved organic matter
(DOM). Notably, freshwaters within the BBW are low in both hardness and DOM, suggesting
that there would be little protection against potential releases of Cu for local salmonids. In our
previous research, we showed that the model endorsed by USEPA under-predicts Cu toxicity to
fathead minnows (a model test species) exposed in water collected from the BBW. In addition to
the variation brought about by local water chemistry, Cu toxicity also varies among life stages
and species of fish; salmonids are more sensitive than fathead minnows, and larvae are more
sensitive than embryos and adult fish. While our previous work with fathead minnows indicates
that the current model under estimates Cu toxicity, more testing is needed with a species of fish
(i.e., sockeye salmon) that is relevant to the BBW. In addition to determining toxic levels of Cu
to local sockeye salmon, it is necessary to both characterize baseline levels of Cu and other trace
elements in freshwater environments of the BBW and understand their historical variation.

Why is this an Alaska Sea Grant project?

This research aligns with Alaska Sea Grant’s
mission, vision, and core values and is relevant to the “Healthy Coastal Ecosystems” focus area.
The project will promote the conservation of salmon resources through research, education, and
extension and will increase the shared body of knowledge about the BBW through consultation
and engagement of stakeholders. Specifically, with help from project partners we will fill
existing knowledge gaps about the potential risks posed to the valuable sockeye salmon within
the BBW. The new information generated from this research will help to address stakeholder
concerns and inform the policies of state and federal agencies as they seek to protect salmonids.

How will researchers conduct their study?

We will conduct bioassays with larval sockeye salmon using water from the
BBW as a test medium. These bioassays will provide us with the concentrations of Cu that result
in acute toxicity, as well as those that cause olfactory responses by larval sockeye salmon. Next,
we will capitalize on the traditional knowledge of locals to identify freshwater habitats of the
BBW that are used by sockeye salmon and important for subsistence fishing. We will measure
baseline water quality and trace element concentrations in water and sediments of these habitats.
By comparing pre-mining levels of Cu in waters from the various sites in the BBW to the data
generated from Objectives 1 and 2, we will understand the magnitude of increase in aqueous Cu
concentrations needed to result in effects to sockeye salmon. Lastly, we will analyze dated
sediment cores for Cu and other trace elements to reconstruct their historical delivery to Iliamna
Lake. This will allow us to understand the pre-mining variability in trace element inputs so that
any future increases due to mining activities can be placed in historical context.