Small Lake, Big Picture
Say you’re a scientist who studies lakes. How do you choose which one to to study? Chances are you’ll pick one that’s a pretty good size…like Trout Lake, or Crystal Lake. You might pick one with a lot of species of fish, or one the public uses for recreation. But what about the tiny lakes…the backyard ones so small they may not even have names, or the ones that dry up completely when it doesn’t rain for a while? One researcher from the University of Wisconsin at Madison thinks those lakes are just as important as the big ones, and she’s doing a survey of small lakes in the Northwoods.
On a breezy July day Samantha Oliver and her research assistant Andy Muench are surveying the scene at a lake nestled off Oneida County Highway D. Oliver says according to a neighbor, this lake wasn’t even here last year, but re appeared in the wet weather.
“And that’s what we’re finding a lot this year is that the area’s been under a pretty severe drought for the past decade or so, and now it’s been a pretty wet season so a lot of these ephemeral systems are coming back. So a lot of them look like this.”
"Like this" - is small and oddly shaped, about the size of a football field, and ringed by maples and black spruces.
“And it looks like the water is maybe a couple feet deep at the most. And there’s sort of an island in the middle – of either grass or sedge growing.”
The lakes that Oliver studies aren’t boating destinations, or even of much interest to most scientists. But she says even though small lakes are…well…small…there are a lot of them. So taken together these lakes make up a big percentage of the water system.
“Small lakes outnumber large lakes by orders of magnitude. So there are a lot more small lakes in the region than say, your typical Trout Lake that’s big and clear, and has lots of nice fish in it. Those lakes are great – but these lakes are serving a completely different function in the landscape. And there are a heck of a lot of them.”
And they’re not very well studied. So Oliver says it’s hard to know what’s really going on in them. She explains small lakes like this one respond more quickly to changes in the environment. So they can serve as the equivalent to a canary in the coal mine.
“If you look at this lake right here, there’s not a lot of water there compared to the adjacent terrestrial system. And so if something changes, the lake will change because there’s simply not a lot of water there. These small systems are sort of good indicator systems of what might be going on in the region.”
Oliver and Muench hoist their canoe off their silver Ford Escape and carry it down to the water. Oliver says they never know what to expect when they first arrive at a new lake. They pick their sites based off satellite data. But that can be inaccurate, directing them to a lake that’s not actually there. Or a lake might be inaccessible, miles from the nearest road.
“And some days are really disappointing. Because you’ll visit five lakes, and you can’t get to a single one of them. And that’s really disappointing!”
Fortunately today’s entry is pretty easy, and they only have to carry the canoe a few feet. Oliver pushes off in a slightly wobbly canoe with two backpacks full of gear.
As dragonflies swoop by, Oliver begins with a measurement of tiny organisms called zooplankton, using a net that looks like a wizard’s hat.
She takes some other basic measurements, and then comes water filtering, to measure the amount of chlorophyll and other particles in the water. This is the slowest part of the data collection – sometimes it takes more than an hour. Today the filtering device is malfunctioning a little, and its motor starts to sound ironically like a ticking clock. The dragonflies get bold and land on the canoe.
The grind of data collection - in small, insignificant lakes - adds up to something Oliver hopes will be significant. She’ll spend this winter analyzing data from the fifty lakes she’ll survey this summer. And her project is part of a larger effort to create a database based on samples from over eight thousand lakes in the Midwest and northeast. Oliver says for this project, one surprising source of data has been private landowners.
“I would say 75 percent of our lakes are on private land. So much more interaction with the public than I originally thought. If it were mostly on public land, you wouldn’t get all these interesting details, like ‘oh yeah there are definitely fish in that lake, I’ve fished that lake for 20 years,’ or ‘that lake hasn’t been there for 10 years and it just showed up this year.’”
Asking landowners for permission, searching for tiny lakes that might not even exist - Oliver says all the unknowns can be challenging, but also make the project special.
“When you’re hiking through the forest, and you know you’re headed towards a lake. And then the forest kind of parts, and you just have this overwhelming sense that you’re the only person that’s seen that water body, or been on that water body, or taken a water sample.”
Those are the moments that she says make it worth it. And there’s that bigger picture to keep in mind.
“No, it’s not about visiting every one of these little systems – that will never happen. It’s just understanding the diversity of those systems that are out there”
That understanding comes one zooplankton tow, one small lake at a time.