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Halsteds
Bay
pictures 1,
panorama
(800K)
Halsteds Bay is located at the far west end of Lake Minnetonka.
This 544-acre bay is relatively shallow (maximum depth is 36 ft,
average depth is 13 ft) and hypereutrophic-meaning that it is a
very fertile and productive water body (it grows a lot of algae).
The bay received raw and partially treated sewage inputs until sewage
discharge into the lake was outlawed in 1969.
Development
along the shoreline consists of 143 homes, all of which are sewered.
A great deal of the shoreline consists of wetlands and the Lake
Minnetonka Regional Park takes up a portion of the southern shore.
Halsteds Bay
experiences intense algal blooms in the summer. Algae are single-celled
plants that need sunlight, carbon dioxide and nutrients to grow.
Usually, the fertility of the lake is controlled by the concentration
of nutrients in the water-most often phosphorus in the metro lakes.
In historically polluted lakes, phosphorus is delivered to the lake
in runoff from the watershed (via erosion, lawn fertilizer runoff
and sheet runoff), but also from "below"-from the phosphorus that
has accumulated in the sediments and is released when the oxygen
is depleted.
We were interested
in the potential for intermittent wind mixing to cause temporary
breakdowns in thermal stratification in Halsteds Bay. This mixing
can inject high phosphorus/low oxygen bottom water up into the sunlit
euphotic zone, which can trigger algal blooms.
The RUSS unit
is key in determining when these mixing events occur because it
can sample the entire water column every few hours, even during
storms when it would be dangerous for limnologists to sample.
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