Upper Saranac Lake State of the Lake Report
Adirondack Watershed Institute
Corey Laxson, Elizabeth Yerger, Sean Regalado, & Daniel Kelting
Upper Saranac Lake is one of the most intensively studied lakes in the Adirondacks. The lake has been the subject of numerous scientific research projects, a 28-year water quality monitoring initiative, and an invasive plant management program that has served as a model for lakes around the world. The goal of this report is to provide a synthesis of the historical and current monitoring data for Upper Saranac Lake and to provide interpretations of the findings where possible. The report can be summarized in the following key points:
2017 was the inaugural year for the Upper Saranac Lake Environmental Monitoring Platform, an autonomous in-lake monitoring station that collects high frequency data on physio-chemical, biological, and meteorological characteristics of the lake. This station is a valuable tool that will enhance our understanding of the lake, foster collaboration, and engage citizen involvement in lake issues.
The phosphorus concentration of the surface water has exhibited a significant downward trend since the early 1990’s in both the north and the south basins of the lake. Currently the total phosphorus concentration is below the target range identified in the Upper Saranac Lake Management Plan (12 μg/L). The phosphorus concentration in the bottom strata of the lake remains elevated, particularly in the late summer, when hypoxic conditions positively influence internal phosphorus loading to the lake.
Chlorophyll-a concentration (a surrogate measure of algal productivity) has exhibited a significant downward trend in the north basin and this may be related to ef- forts to reduce nutrient loading into the lake. Chlorophyll concentration has also exhibited a decline in the south basin, but this trend is not statistically significant.
Although substantial reductions in phosphorus and chlorophyll-a have been observed, the water clarity has exhibited a statistically significant reduction. The average transparency across the summer is nearly a meter less than it was in the early 1990’s. Evidence from published research as well as our regional observations suggests that decreases in transparency may be related to recovery from acid deposition as well as shifts to our regional climate.
Historical analysis of nitrogen to phosphorus ratios confirms that Upper Saranac tends to be a phosphorus limited system; however, the TN:TP ratio is within the range where we should expect cyanobacteria dominance to occur from time to time.
Oxygen depletion occurs rapidly in the shallow north basin of the lake and this pattern has shown no signs of improvement. By early September of 2017, nearly half the water column was hypoxic at the deep hole of the north basin. Oxygen depletion in the deep- er south basin has improved and the basin has experienced a reduction in overall oxygen depletion rate.
The chemistry of Upper Saranac Lake is influenced by the 27 km of salted roads in the watershed. The concentration of chloride in the lake (a surrogate for road salt impact) is approximately 40 times higher than baseline levels for least impacted Adirondack Lakes. This observation may not be entirely related to roads. Some of the chloride in the lake may be attributed to septic input and permitted discharge. For example, analysis of the EPA discharge monitoring report re- veals that the hatchery has discharged an average of 1.3 million kilograms of chloride/year to the Little Clear Outlet over the last decade (1,400 tons/year). There is currently some debate over the validity of the chloride export data described in the EPA report.
The watershed monitoring program initiated in 2007 covers 75% of the Upper Saranac Watershed and captures 63% of the hydrologic budget of the lake. Con- tinuous discharge observations at the lake outlet indicate that the water retention time of the lake was 0.7 years in 2017. Retention time calculated by the surface runoff model suggests a retention time of 0.9 years.
Phosphorus loading rates are within the range we would expect for low to moderately developed watersheds in the Adirondack Region. The tributary with the greatest phosphorus load in 2017 was Mill Brook, followed by Fish Creek and Black Swamp. Approximately 31% of the phosphorus content in Mill Brook can be attributed to the Little Clear Outlet, the receiving water for the permitted discharge of the Adirondack Fish Culture Station. The Hatchery continues to operate well below its permitted discharge rate.
Greatest nitrogen export was observed at Mill Brook (34 kg/day), which was double the next highest load found at Fish Creek. Our limited analysis suggests that approximately 21% of the nitrogen load of Mill Brook can be attributed to the Little Clear Outlet. The Adirondack Fish Culture Station is also permitted to discharge ammonium (an important nitrogen bearing molecule), and typically exports the nutrient at an average rate of 363 kg/year.
In general, the rates at which tributaries export chloride to Upper Saranac Lake are related to the density of salted roads within the sub-watersheds. When normalized for watershed area, Cranberry Brook contributed the most amounts of sodium and chloride to the lake, with a median loading coefficient of 245 and 448 grams/ha/day respectively, followed by Mill Brook, and Indian Carry. In addition to salted state roads, Mill Brook also receives salt from the Little Clear Outlet, the receiving water for the hatcheries permitted discharge.
Eurasian water-milfoil was only detected at 5 of the 16 monitoring locations in 2017. The greatest encounter rate was at Fish Creek Pond, followed by Little Square Bay and Saginaw Bay. The average milfoil density across all Upper Saranac locations was 15 stems/acre, substantially lower than the 600 stems per acre observed in 2004. Eurasian water-milfoil would best be classified as a rare plant in Upper Saranac Lake.
The average Eurasian water-milfoil density at the Fish Creek Pond location in July was estimated at 474 stems/acre. The density of the species has been relatively stable over the past three years.
Variable-leaf milfoil was first detected at the Fish Creek Pond location in 2009. In 2017, the species was encountered on 46% of the study segments, an increase of about 4%/year.