Vermont’s cleanest lakes are showing alarming signs of increasing phosphorus pollution — the nutrient that feeds algae blooms — according to a research study published by state scientists.
Phosphorus levels over the last few decades have roughly doubled in clear, cold waterbodies like Maidstone, Caspian and Shadow lakes.
You can't find a lake much cleaner and clearer than Shadow Lake in Glover. It's prized by anglers, swimmers and camp owners. And for 20 years, Sara Gluckman has been its volunteer lake monitor.
She’s gathered water samples and measured the water clarity of the 210 acre lake using a Secchi disk – a plate-sized disk painted black and white – which, on most days, she can see as far down as 20 to 30 feet below the surface.
Yet the water samples Gluckman has pulled from the depths over two decades also show an alarming trend. Phosphorus, the nutrient pollution that plagues parts of Lake Champlain, is increasing.
“It’s almost doubled," Gluckman said. "It’s a small increase, but it’s statistically significant."
Shadow and most of the state’s other cold water lakes have not seen the toxic algae blooms that have fouled areas of Lake Champlain this summer, although a blue green algae bloom was reported on Bald Hill Pond in Westmore.
But the phosphorus trend still concerns the scientists who recently pored over the data.
“Most people are going to go to these lakes and still be really impressed with how good the water quality is,” said Kellie Merrell, an aquatic ecologist at the Department of Environmental Conservation.
“But for us, we’ve been able to see this increasing phosphorus trend over 40 years now,” she said. “This is a trend that we would expect to see over centuries or over geologic time, and we’re seeing it in decades now.”
"We've been able to see this increasing phosphorus trend over 40 years now. This is a trend that we would expect to see over centuries or over geologic time, and we're seeing it in decades now." — Kellie Merrell, state aquatic ecologist
Indeed, Shadow Lake and Vermont’s other two dozen cold water lakes, like Caspian, Willoughby and Seymour, are monuments to geologic time. They date back to the glaciers, when the ice carved these deep chasms that then filled in with water.
To understand what’s happening with the lakes, here’s a quick primer on lake terminology.
Scientists classify lakes in terms of their nutrient levels. Low-nutrient lakes are called oligotrophic and are characterized by cold water that support trout and other cold-loving species. Mesotrophic lakes are weedier, warmer and sustain warm water fish like pickerel and small mouth bass. Eutrophic lakes are shallow, warm, high in nutrients, and full of plant growth. The state tracks the health of Vermont lakes with an on-line scorecard.
Throughout the country, cold-water, oligotrophic lakes are in trouble. Merrell said Vermont scientists reviewed 40 years of lake data after a 2016 paper that looked at trends in U.S. lakes had some alarming news.
"Our long-term monitoring has revealed that Vermont's oligotrophic lakes could be starting down a path to extinction." — Lake assessment paper published by state scientists
“We are losing our oligotrophic lakes on a continental scale,” Merrell said.
The paper Merrell and her colleagues published cautions that the same thing is happening in Vermont. It includes this stark warning: “Our long-term monitoring has revealed that Vermont’s oligotrophic lakes could be starting down a path to extinction.”
Their study was published last summer. Merrell's now trying to get the word out to the public and to the citizen-volunteers who work on lake quality. The outreach included a meeting earlier this month with the Federation of Vermont Lakes and Ponds.
"While we're not going to be alarmist ... we may be the last generation to actually get to experience these waters in this condition, and why wouldn't we try to make it so future generations can also enjoy this?" she said.
Vermont has two dozen lakes that were considered oligotrophic by measurements collected during the 1980s. Scientist Leslie Matthews, who co-authored the study with Kellie Merrell, said many of the state’s oligotrophic lakes are slipping into the more nutrient-rich category because of the increasing phosphorus.
“They’re creeping up and they’re creeping up into what we would call a different trophic state,” Matthews said.
So why is this happening? Where is the phosphorus coming from?
The study doesn’t pinpoint a cause. But it does round up the usual suspects.
Stormwater, road run-off, stream bank erosion, and agriculture are all likely sources, although the exact culprit no doubt varies from lake to lake. Phosphorus may even be entering the lakes in airborne dust. And climate change – which has brought increased precipitation to the region – has exacerbated the run-off that carries organic matter with phosphorus into the lakes.
The good news, said Matthews, is that the data offers a valuable warning that now can be heeded.
“If it turns out that some of the trend we’re seeing is due to forces that are more beyond our control such as climate change, it’s still important to address the run-off into the lake because that’s something we have tools to remedy,” she said. “And it may be even more important to apply those tools in light of the other pressures on these lake from climate change.”
The paper also looked at data for similar lakes in Maine, and found that those waterbodies have not seen an increase in phosphorus. One factor, the scientists said, may be that Maine passed a strict shoreline protection law in 1971. The law requires 100 foot setbacks for lakeside construction, and buffer zones to control runoff.
Controlling run-off is a challenge. But Merrell and Matthews point to a success story in Vermont, on Lake Seymour in Morgan, after the volunteer lake monitor documented an increase in phosphorus levels. The state gave a presentation to Vermont lake stewards recently on some of the techniques that could be used to control phosphorus.
“The community took it very seriously, and they did a lot of projects in this watershed over the last 10 years,” she said. “And now that trend is flat. It is no longer statistically increasing in phosphorus.”
Mindy Morales, an assistant professor and lake scientist at the University of Vermont, said it’s important to maintain perspective about the health of Vermont’s cold water lakes.
“It’s very important to pay attention to these trends because phosphorus has doubled in many of our oligotrophic or low nutrient lakes,” she said. “But when you put that in context to the rest of the world, we’re still at oligotrophic status relative to most lakes.”
"Shadow Lake is a jewel. It's a beautiful, clear, deep, cold... and we want it to stay that way." - Sara Gluckman, lake monitor
On Shadow Lake, volunteer Sara Gluckman demonstrates how she reads the Secchi disk for water clarity. While she knows the lake is still clean, she’s concerned about the trend.
“Shadow Lake is a jewel. It’s a beautiful, clear, deep cold – you feel that water, it’s cold – and we want it to stay that way,” she said.
Gluckman said road runoff and shoreline disturbances have no doubt contributed phosphorus to the lake. She notes that the delta on an inlet stream is expanding, as material is carried into the lake – a phenomenon observed on Caspian and other lakes.
Asked why she dedicates so much time as a volunteer lake monitor, Gluckman has a ready answer.
“Because I love Shadow Lake," she said. "That’s important to me. I’ve been coming here since I was a kid. My dad grew up in West Glover. It’s sort of part of me, Shadow Lake is."
While Gluckman pointed out that Shadow is public water; it belongs to everyone, and deserves protection. She and the state’s scientists hope that the new research will motivate people to do more to protect these jewels of Vermont.
