St. Regis Chain Limnology and Water Quality 2017 Report
Adirondack Watershed Institute
Corey Laxson, Elizabeth Yerger, Hunter Favreau, & Daniel Kelting
The purpose of this study is to provide a comprehensive analysis of the limnology and water quality of the St. Regis Lake Chain. The specific objectives are to: (1) synthesis and interpret the physical and chemical properties of the lakes during the 2017 ice free season, (2) create a functioning database that contains all of the available historical water quality data for the lakes, and (3) analyze the historical data for trends in key water quality parameters. The report can be summarized in the following main points.
Spitfire and Upper St. Regis Lakes are best classified as mesotrophic. Analysis of the available historical data reveals that the trophic state of these lakes has not experienced any major shift in trophic condition over the last 20 years.
Lower St. Regis Lake has experienced an ecological redemption since the late 1960’s. 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 perhaps more complex than described in previous reports. 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. The greatest increase was observed in Spitfire Lake (5x) followed by Upper St. Regis (4x) and Lower St. Regis (2x).
Examination of the historical data reveals that the annual average concentration of phosphorus has decreased in all of lakes since the 1970’s. Because of the small sampling frequency in the 1970’s and 1980’s, some restraint should be used wheninterpreting the downward trend in phosphorus concentration.
Cyanobacteria were detected in all of the lakes at relatively low densities, with the exception of Spitfire Lake, where a productive population of Planktothrix thrives near the bottom for most of the summer months. 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, prefer low oxygen, and require a high supply of phosphorus. During most of the summer the Planktothrixpopulation is not visible. When growth conditions along the bottom change, the species can constructs 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 ability, the lakes in the chain are circumneutral in terms of their pH and have not experienced noticeable degradation associated with acid deposition. All of the lakes have exhibited a significant downward trend in sulfate concentration, indicating that the acid deposition load to the watershed has decreased over time.
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 over the last 41 years. The greatest impact is in Lower St. Regis Lake, where the concertation of chloride is 90 times greater than the concentration observed in least impacted lakes. Spitfire and Upper St. Regis have similar salt concentration to each other, and are approximately 40 times greater than background values.
