Mirror Lake Long-Term Monitoring Pays Off
Long-term environmental monitoring is notoriously difficult to fund and challenging to keep going. Yet, the return on investment is significant, and we know that to protect and manage our natural resources, we need good data. Mirror Lake is a prime example of how long-term monitoring can improve water quality and lake health.
Eight years ago, the Adirondack Watershed Institute issued the 2014 Adirondack Lake Assessment Program reports around this time of the year. At that time, I was less than a year into a new job with the Ausable River Association, charged with starting a water quality monitoring and assessment program within the watershed. I eagerly thumbed through the reports for the lakes in the Ausable watershed: Lake Placid, Mirror Lake, Upper Cascade Lake, Mill Pond, and Eaton Pond. 2014 was their first time being sampled through ALAP for all these lakes except Upper Cascade. One finding jumped out at me; Mirror Lake had higher sodium and chloride concentrations than 97% of the lakes in the program.
I spent the next several weeks planning the start of a lake monitoring program within the watershed, and Mirror Lake was at the top of the list. I'll never forget my first trip out on the lake; it was May 18th, 2015, and it was one of the most memorable days of my scientific career. I put my Hornbeck canoe in the lake near the public beach along the southern shore and paddled north toward the deepest part of the lake. I occasionally stopped to use a hand sounder to check the water depth, slowly homing in on my target of 18 meters. Once over the deep hole, I dropped an anchor and started collecting water samples for analysis at the AWI lab. Before leaving, I lowered a sonde through the water column. A sonde is a piece of equipment that can measure water quality parameters in real-time; this one measured temperature, dissolved oxygen, conductivity (salt content), and pH.
AWI Research Associate Corey Laxson sampling Mirror Lake.
Before working for the Ausable River Association, I studied how lakes in northwestern Ontario responded to climate change as part of my Ph.D. thesis work at Queen's University. Over the preceding six years, I had been thinking a lot about how lakes mix in the spring and fall, stratify in the summer, and are covered in ice in the winter. Climate change impacts all these processes in our lakes, and the ramifications of those changes reverberate throughout the lake ecosystem, affecting everything from the physics to the fish.
As the sonde lowered through the water of Mirror Lake, meter by meter, I observed an unexpected pattern in the data. The ice had gone out three weeks prior, which means the lake should have gone through the period of spring mixing and begun to thermally stratify. There should be warmer water at the top of the lake and cool water below, which there was. The spring mixing should have also distributed oxygen to the bottom water of the lake, but there wasn't any down there. And the conductivity was much higher toward the bottom of the lake. If the lake had mixed that spring, the oxygen should have been high from top to bottom, and the conductivity should be the same throughout the water column. But they weren't; why?
I had a hypothesis for what was going on. In all my reading and studying of lake mixing, I had learned of lakes impacted by road salt runoff that had their natural mixing regime interrupted. The high conductivity at the lake bottom suggested a lot of salt was accumulated there. The additional salt results in an increase in the density of water, making it harder for the lake to mix. It all lined up, but we needed data during the winter and through the period of spring mixing to determine if my hypothesis was true. And so we started intensely monitoring the lake every two weeks, all year long.
After several years, we collected enough data to confirm my hypothesis that road salt was reducing Mirror Lake's mixing. Our study was published in the Journal of Lake and Reservoir Management in early 2020 and was recognized as one of the best papers published that year. The paper distinguished Mirror Lake as one of a small handful of lakes in the country to have this phenomenon documented. Mirror Lake could be considered one of the most road salt-affected lakes in the country. Though there are very likely many lakes like Mirror Lake that haven't been studied, and therefore, no one knows how road salt is affecting them.
Heatmap plot showing chloride concentrations in Mirror Lake from May 2015 through November 2022. The color corresponds to the concentration of chloride at a particular lake depth and sampling time. The yellow at the bottom of the figure represents the accumulation of chloride at the lake bottom in the winter. In recent years, there has been much less salt accumulation at the lake bottom.
AWI and AsRA are interested in more than just publishing scientific papers; both organizations focus on ensuring the science is communicated to stakeholders so that they can make informed decisions about protecting our lakes, rivers, and streams. From 2015 on, we worked hard to share what we learned about Mirror Lake with everyone in the Lake Placid area. Slowly, everyone from the town and village highway departments to local businesses started taking steps to reduce their salt use. By the winter of 2019-2020, the Town of North Elba had bought a new Live Edge plow and altered their sanding practices on Mirror Lake Drive, the Village of Lake Placid was reducing their salt application on the sidewalks and focusing more on sweeping, and businesses like the Golden Arrow Lakeside Resort were trying alternative de-icing products. AsRA was coordinating these activities as part of their Salt Use Reduction Initiative (SURI) and bringing in experts from WIT Advisers to consult with the local highway departments and businesses to reduce their salt use further.
The benefits of these efforts were almost immediately seen in Mirror Lake. Less salt accumulated in Mirror Lake over the 2019-2020 winter than any prior winter except 2015-2016, which was extremely mild. Most importantly, Mirror Lake completely mixed in the spring of 2020. As an environmental scientist, it's rare to see your work go from documenting a problem to implementing solutions so quickly, especially when it involves a community-scale effort to make that happen.
The news gets even better. Our work on Mirror Lake helped guide the Village of Lake Placid as they sought funds to fix critical infrastructure under Main Street, including the stormwater system. During the summer of 2020, work began on a multi-year project to completely rebuild Main St, including the water, sewer, and stormwater lines beneath it. Before this work, stormwater from Main St was fed directly to Mirror Lake, allowing for a direct injection of salt-laden runoff from the street into the lake. The new system routes the stormwater into underground infiltration basins, and only when those overtop does water flow directly to the lake. This design prevents high concentrations of salt water from directly entering the lake, though it may create other challenges in the future as the saltwater accumulates underground.
This figure shows the total mass of chloride retained in Mirror Lake. The red line indicates a period when the chloride in the lake was increase, blue indicates the period when it was decreasing. The horizontal orange and yellow lines represent the points at which the lake will meet water quality targets (40 mg/L & 10 mg/L). The green line represents how much chloride would naturally be in Mirror Lake.
The improvements in Mirror Lake are just the beginning; more work is needed to help the lake reach water quality targets for sodium and chloride. But we're on the right path, and it's important to remember that we wouldn't be on this path at all if it weren't for long-term monitoring. More importantly, had intensive lake monitoring been started decades ago, Mirror Lake may have never ended up in this situation. Road salt affected the lake for decades before we began monitoring, but no one knew.
There is an old saying, 'What gets measured gets improved.' And if we aren't monitoring our lakes and streams, not only may they not improve, they may be getting worse without us even knowing. Long-term monitoring of our lakes is an intelligent investment ensuring they remain healthy and problems are addressed quickly. There are many ways to support long-term monitoring, whether volunteering for ALAP, donating to AWI, joining your local lake association, or talking with your elected officials. We can each make a difference, and together we'll ensure our lakes remain clean and healthy.
