Scientists eye winter ecosystems in ice-covered lakes
A team of international scientists who studied more than 100 lakes during the winter said there’s more going on beneath the ice than we realized. Their findings stand to complicate the understanding of freshwater systems just as climate change is warming lakes around the planet, and shortening the ice season on many lakes. Other parts of the planet’s cryosphere are also melting under the thickening layer of heat-trapping greenhouse gas pollution.
“As ice seasons are getting shorter around the world, we are losing ice without a deep understanding of what we are losing,” said Stephanie Hampton, a Washington State University professor and lead author of a new study published in the journal Ecology Letters. “Food for fish, the chemical processes that affect their oxygen and greenhouse gas emissions will shift as ice recedes.”
Even when it’s cold, algae and zooplankton are still abundant beneath the frozen surface, according to Liz Blood, program director in the National Science Foundation’s Division of Environmental Biology, which funded the research. “What will happen if lake ice cover decreases in warming temperatures?” she said. “These results are a significant step in understanding what may be far-reaching changes for lake ecosystems.”
The researchers concluded that the seasonal rhythms of lakes freezing and thawing has a big effect on what happens in the winter can have a substantial effect on what happens during the rest of the year. This is especially true for lakes that let in a lot of sunlight, stimulating the growth of algae and zooplankton on the underside of the ice. These in turn serve as food sources for fish at the start of their growing season.
“In some lakes where the ice is really clear and there’s not very much snow cover, there can be a lot of photosynthesis and a lot of productivity,” said Hampton, who has extensive experience studying Lake Baikal in Russia, the world’s deepest lake. “So there were some lakes in this study where the productivity in winter actually exceeded the productivity you would see in summer.”
The research includes documenting ecosystems hanging from the ice, including algae that helps sustain a food chain that’s important to fish at the start of the spring growing season.
“It’s interesting to think about these lakes that get a lot of light through the ice,” Hampton said. “Russian researchers who spend a lot of time on Baikal remind us that when you get ice, now you’ve got a new habitat. It can be a vast habitat extending across the entire lake.”
The scientists posted a request for data on a listserv of professional colleagues, expecting maybe 30 responses. They got 140 responses from researchers with measurements of various winter conditions, like plankton and nutrient levels, that could be compared to summer values.
The findings varied a lot, often depending on whether a lake was covered with clear ice or covered with snow that blocked most light.
“In some cases, we know that zooplankton under ice are really important for seeding the populations that will take off in the summer and grow to be more abundant,” said Hampton. In other cases, there may be algae consuming large amounts of nutrients under the ice so the summer algae have less for their own growth.
Climate change stands to introduce another set of considerations.
“A number of things are changing, with climate change, that actually affect the characteristics of the ice itself,” Hampton said. The ice season can be shorter. There can be less snow, which will let in more light. Or there can be more rain during ice formation, making the ice cloudy.
“Overall, this study tells us that limnologists no longer have any off-season,” Hampton said. “No more down time, especially as we’re losing ice so rapidly.”