The State of Hamilton County Lakes: A 25-Year Perspective, 1993-2017
Hamilton County Soil & Water Conservation District and Adirondack Watershed Institute
Corey Laxson, Leonard Croote, Caitlin Stewart, Sean Regalado, & Daniel Kelting
It is widely acknowledged that long-term monitoring programs are incredibly important for understanding lake ecology and detecting ecosystem change. Twen- ty-five years of limnological monitoring on Hamilton County lakes has informed us that the lakes support relatively low algal productivity and stable trophic characteristics. Many of the lakes are exhibiting a clear signal of recovery from acid deposition, including ele- vated pH and acid neutralizing ability. This study has also identified areas of concern, most notably, a trend toward depressed transparency and increased salini- ty. This report synthesizes the current and historical water quality data for these 21 lakes and provides in- terpretations of the findings where possible. The re- port can be summarized in the following key points:
We observed a wide variety of oxygen content in the bottom water of the study lakes. Eleven of the study lakes (51%) had adequate oxygen during the month of August, while seven lakes (33%) exhibited a propensity for either hypoxic or anoxic conditions. Lake depth, and thereby hypolimnion volume, like- ly drives the rapid depletion in many of the lakes.
The pH of the study lakes were all within the circum- neutral range, indicating that they were not partic- ularly impacted by acid deposition. The observed circumneutral condition may partially be due to the sampling regime, which only examines the surface water condition during the summer months. Anal- ysis of the historical data indicated the majority of the lakes (86%) experienced stable pH values and two of the lakes (10%) experienced an increas- ing pH trend. Although the lakes were variable in their acid neutralizing ability, the majority of lakes (81%) exhibited a trend toward increasing alkalinity.
The concentrations of total phosphorus in the surface water tended to be quite low, and ranged from less than 4 μg/L in Blue Mountain Lake to as high 14 μg/L in Adirondack Lake. We observed that 19 of the lakes (90%) exhibited a significantdownward trend in total phosphorus concentra- tion. We believe that significant method changes over the past 25-years influenced the observed decrease in phosphorus, and therefore recom- mend cautious interpretation of these trends.
The photosynthetic pigment chlorophyll-a was vari- able between and within lakes. Generally, concen- tration was lowest in Blue Mountain Lake, and greatest in Oxbow Lake. Historically, the concentration of chlorophyll in the HC lakes had been stable, with 19 lakes (90%) exhibiting no discernable trend over time.
The transparency of the lakes ranged from a low of 2.4 meters in Oxbow Lake to a maximum of 7.8 me- ters in Blue Mountain Lake. Analysis of the 25-year dataset revealed that 17 of the lakes (81%) expe- rienced a significant downward trend in transpar-ency. Evidence from published research as well as regional observation by the AWI suggests that de- creased transparency relates to changes in regional climate variables and/or acid deposition recovery.
We classified five lakes as oligotrophic (24%), 14 lakes as mesotrophic (67%), and two lakes (9%) as eutro- phic. Assessment of trophic state using Carlson’s TSI supports the opinion that the majority of lakes in the HC dataset are limited by phosphorus availability.
Nineteen of the study lakes (91%) exhibited a clear signal of road salt influence. We found that 93% of the variation in chloride concentration across HC study lakes could be explained by state road density. Routine monitoring of chloride and sodi- um began in 2013, so we were limited in our abil- ity 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 concentra- tions of chloride range from 4 to 70 times great- er than background values for Adirondack lakes.
The calcium concentration of the study lakes was generally low, with the majority of lakes having a concentration less than 4 mg/L of chloride. Calcium concentration in all of the study lakes was below the threshold needed to support a viable zebra mussel population.
The average total aluminum concentration for the HC lakes was low, and ranged from below detection values in Adirondack Lake to 54 μg/L in Limekiln Lake. Morehouse Lake was the only exception to this range, where the average aluminum concentra-tion over the past three years averaged 123 μg/L. In general, HC lakes with lower alkalinity and great- er acidity tended to have greater concentrations of aluminum, supporting the observations made by numerous researchers over the last three decades.
