The AuSable River Association released its annual report on the water quality of Mirror Lake, which says that increasing amounts of salt in the water is interfering with the lake’s natural processes. (Photo provided)

LAKE PLACID — The AuSable River Association has released its annual report on the water quality of Mirror Lake, and warns that increasing salt and chloride levels could have major impacts on the overall health of the lake.

“Significant long-term trends in conductivity, sodium, and chloride remain a concern,” the report says. “Elevated bottom water chloride concentrations were documented and evidence exists that these concentrations are impeding the natural turnover of the lake in the spring. The disruption of this important physical process has the potential for a significant negative effect on aquatic life.”

Lake turnover is the natural process — usually in spring and fall — where the upper portions of lake water sink to the bottom, forcing the water on the bottom of a lake to rise to the top.

The report says that due to increased chloride levels in the lake, the water on the bottom of the lake is more dense than normal, preventing a spring turnover.

“Chloride builds in the bottom waters of the lake during the winter because stormwater runoff has concentrations as high as 2,400mg/L,” the report explains. “The high concentration of salt in the stormwater makes it denser than the lake water, it appears that the dense salt-laden water flows along the lake bottom and accumulates in the deep waters.

“These density differences result in an increased amount of energy needed to completely mix the water column during spring turnover.”

While much of the salt comes from winter treatment of roads, the village of Lake Placid has taken note and reduced the use of road salt within the village. These steps — which include diversion of stormwater runoff and alternatives to salt — have had a positive impact.

“In 2016, a combination of a mild winter and use of alternative deicing practices by the village resulted in much less salt building at the bottom of the lake,” the report says. The reports explains that if salt concentrations were evenly distributed throughout the water column, less energy would be required for turnover to occur. The report says that 2016’s light salt year required about 2.8-times more energy than if the salt was spread evenly. In 2017, when salt concentrations were higher, the lake required 75.5-times more energy to turnover.

Although AsRA has determined that salt concentrations in the lake are causing issues with natural cycles, the group says that it needs to determine how much salt is being spread during the winter before it can estimate the reduction required to maintain the lake’s health.

“AsRA is currently seeking funding to estimate the load of salt applied to each of these sources on an annual basis, conduct stormwater monitoring to understand how the salt moves to Mirror Lake and expand our continuous monitoring stations in the Chubb River watershed to better understand the water and chloride mass balance for Mirror Lake,” the report says. “All of these components together will allow us to estimate the reduction in salt necessary to restore turnover to Mirror Lake and set the lake on a path of recovery.

“Additionally, we will be able to determine target salt reductions and which best management practices will allow us to achieve the reductions necessary to protect the lake. Without this work being completed, we are left guessing as to how much of a reduction in salt is necessary to protect Mirror Lake and how effective particular efforts are at achieving those reductions.

“The lack of spring turnover in Mirror Lake is a significant threat to the long-term health of the lake. If fall turnover is interrupted as well, there would be significant negative impacts to much of the life in the lake.

“Mirror Lake is central to the identity of Lake Placid. Many people, both residents, and visitors have meaningful connections to the lake. Protecting the lake requires the entire community to serve as its stewards, understanding its value and the essential components of its health, and recognizing the actions necessary to preserve it.”

To read the full report, go to www.ausableriver.org/watershed/lakes/mirror-lake.