Lake Agawam Health: A Balancing Act
During 2013, Lake Agawam showed some hopeful signs of improved water quality but also provided evidence that continued effort and vigilance is needed to restore the Lake to ideal conditions. Dissolved oxygen is required to sustain all aquatic life and The New York State of Environmental Conservation recommends that aquatic water bodies maintain dissolved oxygen levels above 5 mg L-1. Lake Agawam successfully attained this standard through the spring, summer, and fall, never falling below 5 mg of dissolved oxygen L-1 at all times for optimal health for fish populations and Agawam. In fact, Lake Agawam has sustained high levels of dissolved oxygen for nearly eight years, with the last low oxygen event occurring in 2006.
Chlorophyll a is a proxy for all of the algae in a water body. For many years, Lake Agawam was considered a hyper-eutrophic water body because it maintained chlorophyll a levels exceeding 25μg L-1. However, 2013 continued a hopeful trend of levels being below 25μg L-1 year — levels exceeded this standard on only 3 of 14 dates.
One continued aspect of concern in Lake Agawam is blue green algae or cyanobacteria. Blue-green algae can form harmful blooms that discolor the water and can produce toxins that can cause health risks to people and animals when they are exposed to them in excessive quantities. Blue-green algae continue to bloom in Lake Agawam.
The New York State of Environmental Conservation recommends that aquatic water bodies maintain levels of blue green algae below 20 μg L-1 this level for much of the year. Further, the World Health Organization states that recreational water bodies with levels of the cyanobacteria compound microcystin at levels between 4 – 20 μg microcystin L-1 pose a low risk whereas, above 20 μg L-1 criteria, during 2013, the lake was no risk on 3 of 14 dates, a low risk on 6 of 14 dates, and a moderate risk on 5 of 14 dates.
Hence, while the total amount of algae in the lake were moderate in 2013, the amount comprised of blue green algae or cyanobacteria was higher than would be ideal, to the point where there was some recreational threat during some times of the year.
Blue green algae have been shown to be promoted by excessive nutrient loading. As such, while there are great signs of hope for Lake Agawam (see decadal trends), continued efforts are needed to ameliorate nutrient loading into the lake in order to lessen the intensity of these blue green algal blooms.
The following data and analysis represents the work of Christopher J. Gobler, PhD and his students at the Stony Brook University School of Marine and Atmospheric Sciences.
- Chlorophyll and Cyanobacteria In Lake Agawam
- Dissolved Oxygen in Lake Agawam
- Blue Green Algae Blooms
- Nitrogen Budget for Lake Agawam
- Results of Experimental Decrease of Nutrients
Chlorophyll and Cyanobacteria In Lake Agawam
Chlorophyll and cyanobacteria values were at their highest in October, but remained at lower levels throughout the remainder of the sampling period. On most dates in 2013, the lake is no longer considered hypereutrophic by EPA standards (>25μg L-1 chlorophyll a) but rather has moved into the eutrophic range (8-25μg L-1 chlorophyll a). Updated: July 2014
Fig. 1: Chlorophyll concentrations between May and November, 2013.
Fig. 2: Cyanobacteria levels between May and November, 2013.
Fig. 3: Microcystin levels between May and November, 2013.
Chlorophyll and cyanobacteria levels are used as indicators of algae concentraions in lakes and oceans. Algae are also called phytoplankton or microalgae. They are microscopic plant cells which grow in all water bodies.
The US EPA defines the health of lakes based on their levels of chlorophyll because the overgrowth of algae can be problematic for aquatic ecosystems, leading to the loss of oxygen and fish. According to the US EPA, chlorophyll levels exceeding 25 micrograms per liter are considered hypereutrophic, meaning they have higher levels of nutrients and high levels of chlorophyll which can endanger aquatic ecosystems.
Dissolved Oxygen in Lake Agawam
Dissolved oxygen levels were at healthy levels during Spring, Summer and Fall.Updated: July 2014
Fig. 4: Dissolved oxygen levels between May and November 2013.
Dissolved oxygen is critical for the survival of all animals and levels above 5 milligrams per liter are required for robust health of fish. Although Lake Agawam has been in the hypereutrophic range with regard to chlorophyll, its oxygen levels have, on average, been good, partly due to day time photosynthesis by algae.
However, rapid declines in, or die-off of, algae can lead to a rapid reduction in oxygen levels. This was observed in the fall of 2006 when a "bloom" of algae died; oxygen levels rapidly decreased to less than 1 milligram per liter, and thousands of fish died in Lake Agawam. Reducing levels of nutrients entering Lake Agawam should reduce the levels of algae and decrease the likeihood of rapid declines in oxygen and fish kills in the future.
Blue Green Algae Bloom
The bright green coloration of the water and the accumulation of green material in surface waters of Lake Agawam are visable signs of a blue-green algae bloom. Such blooms are symptoms of too many nutrients entering a lake. At very high levels the algae are a health risk if consumed by animals and humans.
Nitrogen Budget For Lake Agawam
Lake Agawam's sources of nitrogen. (last updated April 11, 2009)
In 2007, Professor Chris Gobler and his graduate students Matt Harke and Tim Davis quantified the sources of nutrients entering Lake Agawam. They found that the largest sources of nitrogen entering the lake were from groundwater, sediments, and the storm drain at the north end of the lake. This finding is important because nitrogen stimulates blue-green algae in the lake. Future efforts to improve the water quality of Lake Agswam should focus on reducing levels of nitrogen and phosphorus entering the lake.
Reducing Nutrient Levels in Lake Agawam By Half: Cyanobacteria
This graphic depicts a series of experiments conducted by Professor Chris Gobler and his graduate students Matt Harke and Tim Davis. (last updated April 11, 2009)
It compares the levels of blue-green algae (as measured by phycocyanin) resulting from an experimental 50% decrease in the nutrients in Lake Agawam to doing nothing ("Business as usual"). The results suggest that a decrease in nutrients in Lake Agawam could decrease the abundance of blue-green algae in the lake, which would then boost the oxygen levels of the lake. This increase in oxygen levels could then improve the overall health of Lake Agawam.