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Mercury in Sediment. The highest sediment concentrations were observed at site 1775 (St. 

 Louis River at Hwy 2), 1780 (St. Louis River at Hwy 31), 2280 (mouth of Midway River at 

 the Thomson Reservoir), 2720 (mouth of Anichoke River). These results indicate that 1) the 

 Midway River may be draining an area that is significantly contaminated with mercury, 2) 

 there may be several mercury source areas in the upper StLR contributing to the observed 

 levels in fish, and 3) additional sediment samples above the Scanlon impoundment are needed 

 to better identify potential upstream mercury sources. 



Table VII. Statistical Summary of Data Relating to Water, Plankton, and Sediment Samples 

 parameter n min max mean median 



Hg in water (ng/L) 



Hg in plankton (ppb) 



plankton density in water (mg/m^) 



Hg in sediment (ppb)^ 



% moisture in sediment 



^Analyzed as a wet sample. 



Summary and Conclusions 



Mercury in Fish and Consumption Advisories. Mercury concentrations in fish show that most 

 fish from the sites sampled can be categorized by MDH criteria as being restricted to one 

 meal per week for the general population (Minnesota). For our sample group it appears that 

 the channel catfish, redhorse sucker, and walleye are the highest in mercury while the black 

 crappie and bluegill sunfish may be the lowest, though more data is necessary to confirm the 

 latter. 



Mercury Concentration in Fish vs Fish Length. The mercury concentrations in channel 

 catfish, northern pike, white sucker, rock bass, smallmouth bass, and walleye taken from these 

 St. Louis River sites follow a power relationship with fish length. More data is needed to 

 define the mathematical relationship for black crappie, bluegill sunfish, and redhorse sucker. 



Channel catfish taken from the Scartlon Dam were significantly higher in mercury than fish 

 from all other sampling sites. Sites above the Scanlon impoundment have a mixture of fish 

 with both high mercury levels, approaching those at the Scanlon dam, and levels that are 

 significantly lower This data suggests that one or more mercury source(s) exist somewhere 

 within or upstnjam that stretch of the river. 



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