Lessons
Learned from Viewing Seasonal Mixing Pattern
Ice
Grindstone
Independence
West
Upper-Minnetonka
Halsteds
Bay-Minnetonka
northern,
urban
mid-state,
forested
Minneapolis
metro area
Minneapolis
metro area
Minneapolis
metro
area
small,
deep, good water quality
mid-size
lake, deep,
very good water quality
small
lake, deep,
moderate water quality
large
lake basin, deep, moderate water quality
small
embayment, shallower,
poor water quality
1. The WOW lakes
all thermally stratified in the ice-free season; that is, they separated
into layers of warmer water overlying colder water.
2. In spring, summer, and fall, the upper warmer layer was relatively
uniform in temperature,oxygen and also other RUSS parameters, indicating
that the wind was mixing this layer thoroughly.
3. Deeper water below the sharp temperature dropoff at about 4 to
6 meter depth (the thermocline) shows a steady decline in oxygen throughout
the ice-free season. This hypolimnetic water is cut-off from atmospheric
oxygen until the water column cools off enough in the fall for the
wind to completely mix the lake.
4. Because of a lack of oxygen below the thermocline, cool and cold
water fish habitat is greatly reduced or absent for most of the ice-free
season in Halseds and West Upper Bays, Lake Independence, and Ice
Lake. Grindstone however, maintains adequate dissolved oxygen thoughout
most of its hypolimnion in summer.
