By Alanna Doughty

LEA Staff

I still recall peering through the hole cut in the ice floor of the shack. Squinting to see into the murky, cold water, I only perceived darkness with faint things floating. And then a bright fish meandered by. Several things popped into my six-year-old mind. One, the lake was not frozen all the way through. Two, could I fall in? Three, fish?! Cool!

Now, I work with students (and adults) to help them have those same “ah-ha” moments. Students routinely tell me “because it’s winter — everything is frozen and dead.” Not exactly. Not only are things alive, they are moving around and actively growing under the ice! And we are learning more all the time — Lakes Environmental Association (LEA) staff now monitors water quality in several of our ice-covered lakes.

To understand why the winter season might be important to lakes, let’s refresh what goes on the rest of the year. During the spring, the ice melts, and the lake “mixes.” Soon, the warming temperatures set the lake up into distinct layers (water has a different density at different temperatures). If you’ve ever been swimming and your toes drifted down to a colder section, you’ve felt how distinct these layers can be! Once “stratification” sets up, it remains throughout the summer — imagine a layered gelatin dessert, but more liquid-y. The deep water is cut off from oxygen at the surface because the layers do not mix (unless there is a major storm). With stratification in place, the clock starts ticking and oxygen at the bottom is slowly consumed by microbes in the sediment and water. When fall arrives, the cooling water temperature changes the water density again and the lake is able to mix. The mixing in the spring and fall are vital to redistributing oxygen and nutrients throughout the water column. As winter sets in, the coldest water becomes less dense and freezes at the surface (another unique property of water!). The ice insulates the water below, but also starts a new ticking clock, as it cuts off the entire water column from atmospheric oxygen replenishment. 

Both the lake stratification set-up in the summer and the ice cover in the winter are important to understand if we are to garner a better overall picture of lake health. Unusually short seasons will change the health of the water body, as will seasons that are too long. 

LEA’s Research Director Dr. Ben Peierls is gathering data to understand the implications of ice cover on the life underneath, and the health of the lake in the long-term, especially as we face a warming climate that reduces ice cover duration and thickness on our lakes. 

Join Dr. Peierls for a webinar presentation on Wednesday, Feb. 3 at 4 p.m. on his winter research and a multimedia look at life and water quality under the ice as part of Maine Lakes webinar series. For more information and to register for this virtual program, please visit www.lakes.meand look for their annual conference webinar series.