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A Changing Pattern
Thu February 13, 2014
Great Lakes and Little Lakes: Rise and Fall Are Linked Together
A new study from the University of Wisconsin’s Trout Lake Station links the rise and fall of Northwoods lakes with the rise and fall of the Great Lakes.
It also shows some troubling signs of falling water levels in the past twenty years - that break the cycle of the last seventy. And it’s not clear what’s driving these changes.
“So here’s one with a lid that’s coming off relatively easily. And so now with the lid off and our well open..."
Tim Meinke is showing how he measures groundwater levels, down the road from the UW Trout Lake Station near Boulder Junction. He uses a simple tool involving a hollow lead weight attached to a tape measure. He listens for the sound of the weight hitting the water, and checks the tape measure to get the depth.
"I can drop this tape along with the popper, and in this case we’re at eight meters right now. And there we’ve just finally reached the level. So I heard a little bit of a pop there."
Repeated measurements like these are part of what led to a paper published last month by Carl Watras, research scientist at the Trout Lake station.
“Our study showed that the changes in water levels in our small lakes and aquifers here – those changes were basically the same as the changes that have been observed in Lake Michigan Huron over the last 70 years or so.”
Watras put together datasets of local groundwater, inland lake levels, Lake Superior and the connected Lakes Michigan-Huron. He found that they all followed the same pattern. Over the past 70 years all these different water levels have gone up and down by similar amounts, according to a pretty regular 13-year cycle.
“And that was surprising. There was no a priori reason to expect these little lakes to go up and down at the same frequency as a huge lake, the largest lake in the world.”
We think of bodies of water as subject to many influences: different amounts of withdrawals, dredging around some of the great lakes. But Watras says this research indicates larger factors are at play: namely, the balance of precipitation, or rainfall, and evaporation, or how much water is absorbed back into the atmosphere. In sense this news could ease the minds of some lakeshore property owners.
"Yes, there are differences between your lake and my lake but over all they’re all going to be behaving the same way. And it’s not because Fred ran his sprinkler for a lot longer than I did, it’s because of the climate.”
And for years that climate factor has had a regular pattern. But just because you can’t blame your neighbor for low lake levels doesn’t mean there’s nothing to worry about. Water levels across the board seem to be dropping and breaking their consistent cycle. Watras points to the graph that shows the oscillation of water levels.
“And you can see that there’s a pretty strong cycle here. And then the bottom drops out. And in 2010 we had the lowest that we’d seen for 70 years, and then it started to come up.”
Instead of going up and down within a 13-year period, levels just went down – by more than a meter. Lower than normal lake levels may not be news to many Northwoods residents observing exposed shorelines during the recent drought. Lakes have rebounded somewhat in the past few years, but it’s too early to say for sure what that means for the future. Watras says the decade-long decline could be an anomaly, and things could return to normal. Or a new pattern could emerge, with longer cycles and bigger changes.
“The third alternative which is a little disconcerting that we may now start oscillating around a new low. That water levels may reach an equilibrium that is lower than it has been in the past."
It's not clear what could be causing the cycle to re-calibrate - but if that’s the case, it could mean less water for all of us here in the Northwoods.
End of an Era