Mirror Lake 2018 Water Quality Report
Ausable River Association and Adirondack Watershed Institute
Brendan Wiltse, Corey Laxson, & Elizabeth Yerger
This is the third annual report on the water quality of Mirror Lake issued by the Ausable River Association and Paul Smith's College Adirondack Watershed Institute. Our ongoing work to study Mirror Lake, and threats to its water quality, continually yield new insights about the lake. As we move forward with this work, our goal is to provide stakeholders with the data and science necessary to make informed and effective decisions on how to best protect Mirror Lake. Road salt remains the top threat to the lake, and despite some steps towards salt reduction, there has not been a documented improvement in the water quality of Mirror Lake. As outlined in the 2017 report, collaboration between the state, town, village, local businesses, and residents is needed to achieve reductions in salt loading needed to protect Mirror Lake. Report highlights include:
Measures of the lake’s trophic status (total phosphorus, nitrate, chlorophyll-a, transparency, and trophic state index) continue to show no significant long-term trends. While many lakes across the state and country are facing threats related to eutrophication, this is not a immediate concern for Mirror Lake at this time. The lake is oligotrphic (low nutrients) and has remained that way over the period of record. Although, road salt pollution does put the lake at higher risk of algal blooms both through foodweb interactions and elevated internal phosphorus loading.
There is a significant long-term increase in calcium, this may be the result of soil cation exchange as a result of road salt and/or the maintenance of a crushed limestone beach on the lake. Increased calcium poses no specific threat to the water quality of the lake, other than an increased likelihood that zebra mussels could become established in the lake if they were introduced.
An invasive gastropod, the banded mystersnail, was confirmed in the lake and a limited survey documented quite high densities in the littoral area along the southwestern shore of the lake.
Significant long-term trends in conductivity, sodium, and chloride remain. Elevated bottom water chloride concentrations were documented and evidence exists that this impeding the natural turnover of the lake in the spring. The disruption of this important physical processes has the potential for the greatest negative effect on aquatic life.
A prolonged period of bottom water anoxia was documented throughout 2018. This condition
is likely natural for Mirror Lake, but is significantly worsened by the lack of spring turnover. If fall turnover were to also not occur, a significant die off of many aquatic organisms as a result of low dissolved oxygen would be likely. There is additional cause for concern related to climate change extending the length of the summer stratified period and delaying the replenishing of oxygen that occurs during fall turnover.
