Adirondack Watershed Institute Research Associate Lija Treibergs collects water data in a canoe on Mirror Lake Friday, April 9, the same day the ice officially went out. (Provided photo — Brendan Wiltse/Adirondack Watershed Institute)

LAKE PLACID — Brendan Wiltse and Lija Treibergs bundled up with cold-water gear and packed their canoe with scientific equipment. As soon as the ice went out on Mirror Lake Friday morning, April 9, they began to paddle to collect their water data.

There was a bluebird sky and calm water; the lake lived up to its name, reflecting the buildings, trees and snow-capped high peaks on the glassy surface. And it was warm, reaching 70 degrees by mid-afternoon.

This duo from the Adirondack Watershed Institute at Paul Smith’s College was on a mission. Their data will eventually tell them whether the road salt accumulating over the winter will prevent the lake from turning over this spring. It’s a crucial time of the year, according to Wiltse, the AWI’s water quality director.

“We watch the lake very closely to make sure that we get on the water the day the ice goes out and start our monitoring of the spring turnover process,” Wiltse said Tuesday, April 13. “This is really important to redistribute oxygen and nutrients throughout the water column.”

The AWI and Ausable River Association have been monitoring Mirror Lake’s water year-round since May 2015. In the winter, they send monitoring equipment through a hole in the ice every other week. When the ice is out, they collect data and water samples from a canoe once a week.

A construction crew works on the new stormwater drainage system on Tuesday, April 13, at One Main Street Park. (News photo — Lou Reuter)

Since 2015, they’ve documented some years when this turnover process has been interrupted by road salt building up at the bottom of the lake throughout the winter. And that’s not good for the ecosystem, especially fish such as lake and rainbow trout, which try to find cooler, oxygen-rich water during the summer.

“Without the mixing, we have really low oxygen at the bottom of the lake, and that’s obviously not suitable for fish if it’s too low,” Wiltse said. “But it also causes chemical changes in the water column so that a prolonged period of low oxygen causes phosphorus and other nutrients to leach and metals to leach out of the sediments into the water above. If that gets mixed up to the surface in the fall when there’s turnover, it can cause an algal bloom and other impacts to the lake.”

For the first time, a harmful algal bloom was recorded on Mirror Lake last fall. It was found on Nov. 9 at the south end of the lake, where the public beach is located, but Wiltse said he doesn’t believe it was associated with road salt.

“That bloom corresponded with several other blooms in other lakes across New York state,” he said, adding that Mirror Lake cooled down and turned over in the fall, which was followed by a warm, calm, sunny period that likely triggered the algal bloom.

With road salt-reduction efforts — on roadways, parking lots and sidewalks — the goal is to have Mirror Lake turn over every spring and fall. That actually happened last year, but Wiltse said it’s too early to say whether it was due to salt reduction or a mild winter.

A Lake Champlain Basin Program grant to the Ausable River Association may help answer this question in the future. It’s funding data collection, in part, by monitoring stormwater systems and town and village snowplows, measuring the amount of salt being spread on the roadways.

“All of those pieces put together, once we have all of the data, will allow us to figure that out, but at this point we just don’t have the information necessary to say definitively whether or not it’s the salt-reduction efforts or its the mild winter,” Wiltse said.

The village’s Main Street upgrades will also help with salt reduction. Crews began installing a new stormwater drainage system this week in the business district, which follows the shoreline of the lake.

“Instead of having these really high concentrations of salt flow directly into the lake in the wintertime the way they do now, that stormwater is going to go underground and filter through … the groundwater before making it to Mirror Lake,” Wiltse said. “So the concentrations that reach the lake are going to be lower.”

That should have an immediate effect on restoring turnover in the lake, he said. That’s good news for the lake’s turnover, but it may be bad news in the long run if salt-reduction efforts don’t continue.

“If we continue to use the amounts of salt we’re using, we’re going to contaminate the groundwater around the lake, which could in several decades be a whole other problem that we’re facing with Mirror Lake that’s going to be harder to solve,” Wiltse said.

In the meantime, the AWI team will be out on Mirror Lake once a week collecting data. They paddle to a buoy that was set up with the help of the Ausable River Association, based in Wilmington, and the Troy-based Rensselaer Polytechnic Institute, which operates the Darrin Fresh Water Institute on the shore of Lake George in Bolton Landing.

“And that has a bunch of sensors that are dangling below it that are recording data every 15 minutes, so it’s sort of carrying some of the weight for us in terms of data collection during this time of year,” Wiltse said.

While on the lake, the team collects a profile of the water column with an instrument called a sonde, which also has sensors on it.

“We use that to measure the temperature, the oxygen, the pH, the electrical conductivity, which is the measure of the amount of salt in the water, as well as the amount of chlorophyll and the amount of phycocyanin,” Wiltse said.

They also collect water samples from the surface and from 1 meter off the bottom of the lake. Mirror Lake is deep enough to stratify, meaning it has a warm layer at the top and a cold layer at the bottom in the summer. Trout need the colder, oxygen-rich water during the warmer months to survive. As the ice goes off the lake, Wiltse said the water warms from about 0 to 4 degrees Celsius, which is when water is most dense.

“So that warming actually causes the water at the surface to become more dense and settle through the water column, displacing the water below it and basically pushing the water from the bottom of the lake back up to the surface,” he said.

That’s the turnover process, and it can also be helped along by wind events and storms that mix the water even more.

There’s some good news here. Not only did Mirror Lake turn over twice in 2020, Wiltse said they’ve recorded the lowest amount of salt at the bottom of the lake this winter since monitoring began on 2015.

“So that bodes well for the lake turning over this spring,” he said. And with the ice going out sooner than usual, there’s a longer period of time in which the lake can turn over.