Lake McCarrons in Roseville, Minnesota, displays signs of anthropogenic eutrophication.
To increase its summer transparency, different approaches/actions have been considered.
A wetland system designed to remove phosphorus from the watershed surface runoff into
the lake was installed and went into operation in 1985. Its performance has been
described in reports by Oberts and Osgood (1988) and the Metropolitan Council
Environmental Services (MCES, 1997). Other reduction techniques for primary
productivity can be considered. There is also some question about the effect that the
wetland system has had on inflow water temperatures. By exposing the tributary water to
the atmosphere, a wetland may cause a warming of the tributary water, which is then
more likely to enter the surface mixed-layer of a stratified lake in summer. In the surface
mixed layer, light can be plentiful, and the phosphorus in the inflow may stimulate
'increased algae growth.
The Executive Summary of the MCES (1997) report ends with this statement:
"Because of the amount of polluting material discharged into the lake over
the past decades, lake improvement will be difficult and expensive. The
MWTS has been helpful over the past 12 years in reducing net inputs to
the lake, but this study has shown that the system is decreasing the
effectiveness and may be directing inflow to a limited volume of the lake
above the thermocline. Possible approaches to lake improvement include
chemical treatment of the lake andlor inflows; rerouting inflow below the
thennocline; whole or partial lake mlxmg; and attention to the
management changes noted above for the MWTS to improve
perfonnance. "In this report we shall address some of these issues.
Metropolitan Council Environmental Services, St. Paul, Minnesota
West-Mack, Deborah E.; Stefan, Heinz G..
Inflow Dynamics And Potential Water Quality Improvement in Lake McCarrons.
St. Anthony Falls Laboratory.
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