Piseco Lake, in southern Hamilton County, is one of the 21 lakes featured in a new report on water quality by the Adirondack Watershed Institute and the Hamilton County Soil and Water District. (Provided photo — Jamie Parslow, AWI)

The Paul Smith’s College Adirondack Watershed Institute has released a report on the water quality of lakes in Hamilton County after studying the waterbodies for two-and-a-half decades.

“The State of Hamilton County Lakes: A 25 Year Perspective 1993-2017” was developed with the Hamilton County Soil and Water District, and has been funded over the years by the state’s Environmental Protection Fund and the Finger Lakes-Lake Ontario Watershed Protection Alliance.

The report looks at 21 lakes in the central Adirondack county, including notable ones such as Blue Mountain Lake, Indian Lake, Piseco Lake and Lake Eaton.

“It is widely acknowledged that long-term monitoring programs are incredibly important for understanding lake ecology and detecting ecosystem change,” the report says. “Many of the lakes are exhibiting a clear signal of recovery from acid deposition, including elevated pH and acid neutralizing ability. This study has also identified areas of concern, most notably, a trend toward depressed transparency and increased salinity.”

The studies looked at a number of water quality measurements, including pH, dissolved oxygen, phosphorous and transparency. Chloride, which can signal road salt infiltration, was also measured.

“Nineteen of the study lakes (91 percent) exhibited a clear signal of road salt influence. We found that 93 percent of the variation in chloride concentration across HC study lakes could be explained by state road density,” the report says. “Routine monitoring of chloride and sodium began in 2013, so we were limited in our ability to analyze historical trends. Despite the lack of historical data, we know that HC lakes with paved roads in their watershed have experienced substantial salt enrichment because concentrations of chloride range from 4 to 70 times greater than background values for Adirondack lakes.

“Lakes in the Adirondack region have naturally low concentrations of both chloride and sodium, with median background concentrations of 0.3 mg/L and 0.5 mg/L respectively. Wide spread use of road salt (primarily sodium chloride) over the last several decades has significantly increased the concentration of these ions in the environment. Many lakes in the Adirondacks now contain anywhere from 10 to 170 times the background concentration of chloride. Adirondack roads receive approximately 208,000 metric tons of road deicers each year, with an annual average of 23 tons of salt applied to each lane kilometer of state roads.”

Ten of the 21 lakes were found to be marginal or depleted of dissolved oxygen, and 17 of the lakes had lower visibility over the last 25 years.

“Transparency data is used most often to assess the productivity of a lake. In general, lakes that have low productivity and low algal abundance have greater transparency,” the report says. “As algal productivity increases the transparency of the water body tends to decrease. Many other factors can affect transparency, such as turbidity, suspended sediment, and dissolved chemicals.

“Analysis of the 25-year dataset revealed that 17 of the HC study lakes (81 percent) have experienced a significant downward trend in transparency. As an example, during the first three years of the study (1993-1995) the average transparency of Seventh Lake ranged from 5.6 to 7.0 meters, while more recently (2015-2017) it has ranged from 3.3 to 5.3 meters.

“Reduction in water transparency appears to be a regional phenomenon. The Adirondack Watershed Institute has observed statistically significant downward trends in several lakes in the Adirondack region, including Upper Saranac Lake, the Rainbow Lake Chain, Litchfield Park Lakes, as well as 15 percent of the lakes participating in the Adirondack Lake Assessment Program.

“Current research suggests that increased dissolved organic carbon concentration is responsible for the observed downward trend in transparency. Two popular hypothesis that attempt to explain increased concentrations of DOC in lakes are the reduction in acidic deposition, and increased precipitation from climate change. It is clear that both of these interacting environmental stressors are at work in the Adirondack Region and may be influencing the transparency of lakes in Hamilton County.”

The report goes on to break down the parameters of each lake, as well as look at the overall trends across all the lakes.

The full report can be downloaded from www.adkwatershed.org/sites/default/files/the_state_of_hamilton_county_lakes_a_25yr_perspective_2_0.pdf.