Authors: Lois Wolfson and Erick Elgin, Michigan State University Extension
This article was reprinted with permission and originally appeared in the Oakland Lakefront Lifestyle Magazine.
Did your lake freeze over this year? If yes, did it freeze the entire winter or was it intermittent, sometimes freezing, but sometimes thawing, giving way to open water? If it was the latter or your lake didn’t freeze at all, then you’ll not only have to forego some winter activities, but you may find changes in your lake for the remainder of the year.
In the Northern Hemisphere, if we look back over the past 165 years, scientists have determined that the length that ice remains on lakes has declined by 31 days on average(1). So, if you like to ice fish, ice skate, go snowmobiling or just play on the ice, you may have to forget about those activities. If there is ice, but it melts and then refreezes, you need to be extra careful because it won’t be as thick as it has been in the past and the risk of falling through increases substantially, particularly with heavy machinery like snowmobiles or trucks.
A recent study found that more than 15,000 lakes that froze over in the winter are now seeing some years with no ice forming(2). This lack of ice affects much more than our recreational activities. It has multiple effects on lakes including changing the timing and extent of important seasonal processes. These changes in turn can create disconnects in a lake’s food web having cascading impacts.
No ice or loss of ice early in the spring can result in an earlier start to a period in a lake called summer stratification. Summer stratification occurs when warm surface waters sit on top of the colder deep waters. You have likely experienced summer stratification if you have ever jumped off a boat and suddenly felt cold water as you went deeper. During summer stratification, oxygen can become depleted in the deep parts of lakes due to decomposition, especially in productive lakes. When summer stratification lengthens due to an earlier start, there is more time for oxygen to become depleted. As a result, fish that require cool, well oxygenated water become stressed as their habitat is lost.
Another example occurs in spring right after the ice melts when lakes begin to mix from top to bottom. This process is known as spring turnover. As ice disappears from lakes earlier and earlier in the season, spring turnover begins earlier as well. Spring turnover is very important since it puts in motion a beneficial algal bloom that fuels the food web in lakes. Under typical spring conditions, these algae, called diatoms, are eaten by Daphnia, a microscopic crustacean that proliferate during this time. The Daphnia are eaten by many species of fish. However, some recent studies show a disconnect between diatoms and Daphnia. Early spring mixing results in an early diatom bloom, but Daphnia do not emerge onto the scene until there is enough sunlight, and the waters become warmer. As a result, Daphnia are out of sync with their main food source, and an important linkage in the food web is broken. This event may impact fish higher up in the food chain(3).
We still have a lot to learn about how the loss of ice may impact the intricate web of connections in lakes. As the loss of ice continues, changes will cascade through lakes and some species will inevitably lose out, while others will thrive.
Ongoing research on thousands of lakes across the globe have shown that lakes are losing ice earlier in the season. How this loss impacts the physical, chemical, and biological components of lakes is still to be fully understood.
Citations:
1 – Woolway, RI., et al. 2020. Global lake responses to climate change. Nature Reviews Earth & Environment 1(8): 388-403.
2 – Sharma, S., et al. 2019. Widespread loss of lake ice around the Northern Hemisphere in a warming world. Nature Climate Change 9: 227-231.
3 – Winder and Schindler. 2004. Climate change uncouples trophic interactions in aquatic ecosystem. Ecology 85(8).