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Contaminants such as mercury, other heavy metals, and PCBs
(polychlorinated biphenyls) tend to accumulate in the sediments of
lakes and streams, and can be introduced to the aquatic food chain
by burrowing insects, plant uptake, and fish/wildlife foraging
behavior. In 1999, we were awarded a grant from EPA’s Great Lakes
National Program Office (GLNPO; http://www.epa.gov/grtlakes/) to do
a sediment quality assessment of twelve reservation lakes. In this
project, we looked at general lake sediment characteristics
(particle size, total organic carbon, percent solids), contaminants
(mercury, PCBs and lead), and performed
toxicity tests on half of the study lakes to see if
sediment-dwelling organisms (Chironomus tentans and
Hyalella azteca) were less able to survive and grow in our lake
sediments. The results of this study (link to Phase I Final Report)
indicated that PCBs are not a contaminant of concern in Fond du Lac
waters, but many of the mercury and lead concentrations in the
sediment samples were above a threshold level of concern for human
and aquatic life. In 2001 we received a second grant from GLNPO, in
order to specifically measure methylmercury in our previous samples,
plus add twelve new sampling sites from the St. Louis River. We then
looked for relationships between sediment contaminant levels and our
water quality and fish contaminant data (link to Phase II Final
Report). This type of information can also be useful for other water
quality protection and restoration efforts in the St. Louis River
watershed, as an example of “baseline” conditions for the river
upstream of the major point sources of contamination.
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