Fishing for data: Research may help predict impact of diminishing ice, snow on lake ecosystems
ON SIDE LAKE, Minn. — They had ice augers and pop-up shelters and even depth finders, but not a single fishing rod between them. And no minnows, either.
From a distance the research team looked like any other group of northern Minnesota ice anglers. Until they took out their secchi discs and zooplankton trap nets and algae-trapping canisters.
They pulled sleds loaded with big jugs and small beakers, water pumps, filters, ice chisels and shovels, snow and ice measuring devices and a host of other gadgets and tools.
"We have a lot of stuff to deploy," said Andy Bramburger, a researcher with the University of Minnesota Duluth's Natural Resources Research Institute, as he stripped to his T-shirt and pulled a sled across the snow.
Bramburger was part of a team of six researchers out this day looking at how the very base of the food chain is acting when the lake is covered by ice. He has hypothesized that there's a lot more going on under the ice than most people — even most scientists — believed.
"They've been studying lakes for decades, but almost always in the summer. We really have very little data on what's going on in these lakes for almost half the year," Bramburger said.
So far, the project is proving him right.
On a sunny, early March morning on this lake north of Chisholm, scientists were pulling up scoops of algae, tiny plants and zooplankton — tiny animals — by the hundreds, maybe thousands.
For some tests, researchers remained in the shelters, in the dark, so as not to alter the natural photosynthesis going on. They used radioactive carbon tracers that the living, active algae would suck up to measure how much activity was really going on under the ice. It's that photosynthesis that allows tiny plants to turn carbon dioxide into the energy that starts the food chain, with the algae in turn devoured by zooplankton, which are eaten by tiny minnows which are eaten by bigger fish which are eaten by otters, eagles and people.
On Side Lake, researchers found what appeared to be a winter algae bloom. On Lake Minnetonka near Minneapolis, they found a huge population of winter-active zooplankton.
"We're surprised by how much biomass there is under the ice," said Greg Silsbe, a researcher based at the University of Maryland's Center for Environmental Science and part of Bramburger's team on the ice project. "There's clearly a lot going on down there."
Less ice, less snow, more light?
But the project may have even more ominous importance. Scientists have been watching for decades as winters have been getting warmer and shorter, as the amount of time northern lakes are ice-covered decreases — in some cases with weeks less ice than the mid-1900s. While there are still some cold winters, like this one with average ice and snow, the trend has been toward less of both.
"We don't know what impact that will have. If there's less snow and less ice, will there be more photosynthesis? What will that do to the system?" Bramburger said. "We don't know if that will speed up biomass too much. We don't know how much lakes need the winter slowdown to keep their balance."
What happens if there is little or no winter slowdown? Ted Ozersky, a biologist with UMD's Large Lakes Observatory and also part of the team, wonders if lakes have more-active winter ecosystems with more light penetrating, if that will "rip" the system into overdrive by summer.
"We already have longer summers changing" lake ecosystems, Ozerksy said. "Nobody's really taken winter into account. We just don't have enough data yet to make that prediction."
But that data is starting to come in.
Farther out on the frozen lake, Christopher Crawford, a satellite data expert with the U.S. Geological Survey, was walking across the ice by himself, measuring snow and ice just as an Earth-orbiting satellite was flying over. Crawford and Leif Olmanson, of the University of Minnesota's Department of Forest Resources, are comparing real-time data on the ground with readings from two kinds of satellites — radar and photo imaging — to see if they match. If the measurements match on the six lakes in the study, it might help the satellite experts measure ice and snow thickness on lakes across the region, the state, even across the continent, without having to physically go to each lake.
"We're ground-truthing to see how accurately we can read the snow surface and ice thickness using satellites," Crawford said.
Last winter Bramburger tried to look at water under the ice of the St. Louis River near Duluth. But the winter of 2016-17 was too short, and they didn't get much data. This year there's been plenty of old-fashioned winter: About two feet of ice and 15 inches of snow covered Side Lake.
This winter the "pilot" study is looking at two lakes north of Chisholm, two north of Duluth and two near the Twin Cities. In each region they are picking one clearwater lake and one darker-water or stained lake to get a better cross-sample of light penetration and biomass.
The researchers scraped together their own funding from "pockets" at their research agencies and departments. If all goes well, the team hopes to land National Science Foundation money to keep the project going.
"We hope to get enough information this winter so we can convince people that there is interesting stuff going on in lakes under the ice in winter," Bramburger said. "It's looking pretty interesting to us."