As spring moves to summer, an unprecedented scientific collaboration is sending researchers around the globe scrambling into their boats and simultaneously heading out onto the world’s lakes. It’s called “Spring Blitz,” and, from Wisconsin to Florida to Switzerland, scientists are out monitoring everything from water temperature to dissolved oxygen to plankton communities as lakes in the northern hemisphere warm up and settle in to their stratified summer conditions.
Most lakes in temperate climates undergo stratification during the warmer months. As the surface water warms, it becomes less dense and “floats” on the cold water below it and, eventually ,the water column of the lake is divided into distinct sections, the warm upper layer (epilimnion to science-minded folks) and the cold bottom layer (hypolimnion).
This is the first year of the project, which is organized by the Global Lake Ecological Observatory Network, a grass-roots collection of limnologists, ecologists, engineers and IT professionals collaborating to build a better understanding of the world’s freshwater ecosystems. Paul Hanson, co-chair of the GLEON steering committee and faculty member at the Center for Limnology, says this late spring is pushing researchers to their limits.
“The real mile marker for this study is [lake] stratification and we know we have to sample for a certain period of time after that occurs. But the onset of stratification is going to depend very much upon the weather and the warm up seems to be delayed this year, so everyone’s out there sampling, putting all this effort in, but things aren’t moving [to stratification quickly] so everyone’s getting fatigued.”
For example, a recent query about how Spring Blitz was going in Canada yielded this response from Jim Rusak, group leader of water chemistry on Harp Lake in Ontario. “Spring – what spring? We had snow halfway through the blitz!” Though now, he concedes, things are warming up “nicely.”
Cayelan Carey, a Center for Limnology post doctoral researcher, says the overworked teams are trying to answer a question posed by ecologist, G.E. Hutchinson way back in 1961 – if a lake is a fairly homogenous ecosystem, with similar features throughout and fierce competition for limited resources, then what’s up with the amazing diversity of plankton?
According to Carey, between 1995 and 2010, scientists identified nearly 250 different species of tiny bacteria, protists and plants called phytoplankton in Lake Mendota alone. That doesn’t even include the microscopic animals called zooplankton. Considering that plankton are the base of a lake’s food web, getting to the bottom of what’s driving plankton diversity is important work.
Many researchers think the stratification process is what lets so many different species of plankton co-exist in lakes. During spring, before a lake stratifies, the water column is “unstable,” which means it’s continually mixing, and that means plankton “growing conditions” – things like temperature, dissolved oxygen, and available nutrients are fairly consistent through the entire lake. Then, as a lake settles into its summer state, distinct habitats arise in its warm upper half, cold bottom half and even the area of the water column between those two halves.
Carey says that, currently, Lake Mendota is close to being stratified, but not there. “When we started this on April 30th, the lake was completely mixed and then when we went out on Monday (May 13th) the lake was really beginning to stratify, showing a differential of about 4 degrees and right now, if you go from zero to 20 meters, there’s a differential of about 5 degrees C, so that’s a sign that we’re really getting there.”
It will be interesting to see what researchers learn as they examine lakes across the globe.
“Lakes are sentinels for the landscape,” Carey says. What we do on land is reflected in the health of our lakes. And Spring Blitz is important, because “phytoplankton are sentinels for the lakes.”
To see what the spring plankton community in Lake Mendota looked like, see below: