The timing of when ice forms on lakes in the winter can have big knock-on effects on life in the water the next spring and summer, according to a study that sheds light on how climate change will affect such ecosystems.
As the climate warms, lake ice is forming later and thawing earlier. But there hasn鈥檛 been much research done on lakes during the winter, partly because the ice-covered period has long been considered a dormant season for freshwater organisms, so how these changes might affect lake ecosystems is unclear.
鈥淭his is rather alarming given that we do not know much about under-ice lake ecology, so it is even harder to anticipate the consequences of ice loss and predict future changes,鈥� says , an aquatic scientist at McGill University in Montreal, Canada.
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To find out more, H茅bert and her colleagues conducted a unique experiment to manipulate the timing of ice onset in one lake in Canada. They constructed a floating platform with several deep containers extending below it, essentially turning columns of lake water into giant test tubes. Then, once the lake froze, they broke up and melted the ice in each container twice a day at dawn and dusk, delaying the onset of winter ice cover for 8, 15 or 21 days.
This delay had a profound effect on life in the water below. A later freeze meant that algae could continue photosynthesis for longer, which in turn allowed some of the tiny zooplankton that feed on the algae to fatten up more and so survive throughout the winter under the ice. Those surviving zooplankton then got a head start on eating the new batch of spring algae once the ice started to melt, leaving less food available for species that only become active once the ice is gone.
These changes in the population of algae and zooplankton could then cascade through the food web, says H茅bert, potentially disrupting the flow of energy through the lake over the summer and even affecting the populations of larger animals like fish.
, a freshwater ecologist at Mount Allison University in Sackville, Canada, says while this study was just a snapshot of one lake over one winter, it is an important step towards filling in gaps in knowledge of how climate change will affect freshwater ecosystems. 鈥淚t highlights the potential implications for food webs of changes in ice periods,鈥� he says.
PNAS
