St. Regis: State of Lake Report 2021
Adirondack Watershed Institute
Corey Laxson, Elizabeth Yerger, Lija Treibergs, Brendan Wiltse, & Daniel Kelting
The purpose of this study is to provide an update to the comprehensive State of the Lake Report issued in 2018. The specific objectives are to: (1) Update the lake users on the physical and chemical properties of the lakes during the 2018-2020 field seasons, (2) maintain a functioning database that contains all of the available historical water quality data for the lakes, and (3) analyze the last 20 years of data to detect recent trends in key water quality parameters. The report can be summarized in the following main points.
Lower St. Regis Lake has experienced an ecological redemption since the late 1960’s, one that has continued to improve since 2000. The primary trophic indicators (phosphorus, chlorophyll, and transparency) have exhibited statistically significant improvements, shifting the lake from a eutrophic to a mesotrophic condition.
All three of the lakes experience rapid oxygen depletion in the bottom strata. Although this information is not news to the SRPOA, the cause of the anoxia is probably a result of several factors. We hypothesize that some degree of bottom water anoxia is natural in the Regis lakes, and has probably always occurred. Ultimately, the controlling factor for anoxia is the ratio of the lakes sediment surface area to hypolimnion volume (SSA:HV). For the relatively shallow lakes in the St. Regis chain this ratio is large, indicating that oxygen depletion should be anticipated. Current and historical nutrient pollution from the watershed has certainly augmented the oxygen depletion by providing a store of organic material for decomposition.
Anoxia in the bottom water of the lakes creates a reducing environment that allows dissolved reactive phosphate to move out of the sediments. All of the lakes experience a significant increase in phosphorus concentration in the bottom strata, typically ranging from 6 to 10 times higher then the surface.
Over the last 20 years (2000-2020) the surface water concentration of phosphorus has decreased in Lower St. Regis Lake and remained stable in Spitfire and Upper St. Regis.
We detected low densities of cyanobacteria in Lower and Upper St. Regis; however, a productive population of Planktothrix thrives near the bottom of Spitfire Lake during the warmest weeks of the summer. The low light intensity, anoxia, and nutrient supply at the bottom of the lake provide a perfect environment for Planktothrix, a species that can photosynthesis in suppressed light, prefers low oxygen, and requires a high supply of phosphorus. During most of the summer the cyanobacteria population is not visible. When growth conditions along the bottom change, the species can construct gas vacuoles and float to the surface. It is only at this point that they become noticeable to lake users.
Due to their inherent acid neutralizing capacity, the lakes in the chain are circumneutral in terms of their pH, and have not experienced noticeable degradation associated with acid deposition.
The chemistry of the St. Regis chain is influenced by salted roads in the watershed. The concentrations of sodium and chloride have increased in all the lakes. The greatest impact is in Lower St. Regis Lake, where the concentration of chloride is 135 times greater than the concentration observed in least impacted lakes around the Adirondacks. Spitfire and Upper St. Regis have similar salt concentration to each other, and are approximately 42 times greater than background values.
