Chapter 4: Affected Environment - Aitkin County Government

portion of the study area are listed for PCB’s. Mercury is introduced to most aquatichabitats in the study area via atmospheric precipitation rather than through immediatelyadjacent industrial or geological sources. The occurrence of mercury in its toxic methylmercuryform is generally associated with low dissolved oxygen and low Eh (redoxpotential) water in wetlands. PCB’s have been used extensively in industry and weretypically introduced into aquatic habitats via point sources. Therefore, aquatic habitatslisted as impaired for PCB’s in the study area typically are found in more industrialsettings.The MPCA has also developed a map of the Headwaters basin (Figure 4.4.9.b.) thatshows waters impaired for aquatic life and/or aquatic restoration. The factor contributingto the impairment is also given for each impaired water. In the northern half of the studyarea, the typical factors listed for impairment are either turbidity or low dissolved oxygen.In the southern half of the study area, fecal coliform, biota, low dissolved oxygen, andturbidity are typical listed factors.Changing the annual operating cycle could modify the volume and seasonal timing ofwater movement into and out of riparian wetlands. Such water exchange could be asignificant factor in assessing potential methyl-mercury loading and bioaccumulation infish. Scientific studies are needed to determine whether modifying the flow regime couldimprove fish habitat by eliminating stressful low dissolved oxygen conditions and reducemethyl-mercury loading.Headwaters ROPE Study 72