The Lake in the Winter – Part 2
A frozen lake is just one more sign that winter has come to Roaming Shores. It presents a snapshot in time of the beauty of the lake. Of course the lake does not completely freeze (thanks to the properties of water), and one never knows if we will even see the surface of the lake freeze this year. But if we do, you may be surprised at what goes on under the ice.
A lake’s “winter” season is often identified based on the dates that the lake becomes fully ice covered. Once the lake is frozen, the entire ecosystem changes to cope with the colder temperatures.
Of most importance to many of our residents is the effect on the fish population. Fish seek the warmer waters under the ice and can survive as long as the oxygen levels in the water are adequate. Since they are not warm blooded, their metabolism slows, including respiration, digestion and activity level. This state, called torpor, allows them to survive until the ice melts and the water starts to warm up again. Some amphibians survive in this state by first burrowing into the sediment along the lake bottom before “hibernating”.
Macrophytes (aquatic plants) can actually handle the winter better than their terrestrial cousins if they are protected under the water. Some will form nodules, which can store energy while they wait for the sun to reappear. Some may go dormant. Some may die back, but their root systems may survive to grow again in the spring. While the lake drawdown can kill even the root systems if exposed long enough to the cold air, hopefully many beneficial aquatic plants will survive as they compete with the algae for the nutrients in the spring and summer.
As far as microscopic organisms are concerned, they also adapt. Phytoplankton (photosynthetic organisms) such as cyanobacteria (blue-green algae), produce thick-walled cells much like a cocoon that will protect them in a dormant state until conditions are more favorable. Some species can survive by becoming cannibals and consuming other algae species for food. Zooplankton (microscopic animal that also eat phytoplankton) may also form a cocoon for protection.
Like some of us, the lake’s many residents slow down their activity level during the cooler winter months and wait for the arrival of spring.
(Some information presented in this article was extracted in part from Lakeline Vol 34, #4 (2014))
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