Cyanos Activity October 28, 2021

 

Reconsider activities and limit exposure to the water.

Disclaimer: The information presented below reflects conditions throughout the lake and may differ from conditions on specific shorelines. For information regarding beach closings please contact the Torrington Area Health District or local town officials.

General Observations

Air temperature was approximately 43°F upon arrival at approximately 8:30am and increased to only 45°F by the time we completed data and sample collections. Skies were a mix of sun and clouds; winds were very light to calm out of the northeast. A light cyanobacteria surface film with streaking was observed across much of the lake. 

Over two inches of rain had fallen in the three days prior to our visit.  Average site depths had increased by 23cm since our last visit on October 12th. The volume of water that would increase the 916ac surface area of Bantam Lake is approximately 2.25x108 gallons.

Secchi Disk Transparency and Relative Phycocyanin

Secchi disk transparency is a surrogate measurement of algal cell concentration. The correlation is a negative one where greater Secchi disk transparency indicates fewer algae cells in the water; lower Secchi disk transparency indicates greater numbers of cells in the water. 

Average Secchi disk transparency on October 28th was nearly identical to the October 12th and September 29th averages (Fig. 1). Secchi transparencies were similar at the four sites; they varied by 21cm among the sites (Table 1). Since July 18th, average Secchi transparency has been <2 meters.

Phycocyanin is an auxiliary photosynthetic pigment unique to the cyanobacteria and is commonly used as a surrogate for cyanobacteria biomass. The relationship is positive in that an increase in one is generally accompanied by an increase in the other; ergo, a decrease in one is normally associated with a decrease in the other. 

The average relative phycocyanin concentrations in the top three meters of the water column was nearly identical to the October 12th average (Fig 1). The lake average on October 28th was 12.0µg/L; and on October 12th , it was 11.7µg/L. Since July 19th, average relative phycocyanin concentrations were >8µg/L on seven of the eight days measurements were taken. The one instance that the lake average was <8µg/L during that timeframe was on August 3rd , which was five days after the first copper sulfate treatment at the lake this season. Prior to July 19th , all averages were <6µg/L and were <4µg/L from April 27th to June 23rd (Fig. 1).

Cyanobacteria Cell Concentrations and Algal Community Characteristics

Cyanobacteria cell concentrations at the North Bay and Center Lake sites were 31,658 and 54,549 cells/mL, respectively. The average of the two concentrations was 38,014 cells/mL and only ±4,000 cells/mL different from the October 12th and September 29th averages (Fig. 2). The consistency of average cell concentrations over the last month is concordant with the consistency of average Secchi transparency and relative phycocyanin concentrations over that same period of time. 

The CT DPH and CT DEEP guidance documentation for local health departments (CT DPH & CT DEEP 2019) associates cyanobacteria cell concentrations of >20,000 and <100,000 cells/mL with Visual Rank Category 2 conditions. Both the North Bay and Center Lake site concentrations and average for the lake were within the Visual Rank Category 2 range. Based on our visual assessment and the State guidance, conditions may be at the Visual Rank Category 3. Interventions for these conditions and others can be found in the State’s guidance document for municipal health departments for blue-green algae blooms in recreational freshwater (CT DPH & CT DEEP 2019).

The total number of individual genera observed from all samples was 29. Six of those were cyanobacteria genera and those constituted between 98 and 99% of all cells counted at both sites; eleven Chlorophyta (aka green algae) genera and five Bacillariophyta (aka diatoms) genera were identified in samples; but, neither were >1% of the algal cells in the whole water samples. Other taxa were represented by three or less genera and were also <1% of cells counted. 

Filamentous cyanobacteria continue to constitute the majority of cyanobacteria cells counted in samples as it has for much of the season. Of those, Planktothrix spp. (formerly Oscillatoria spp.; Fig 3a) was the most numerous at both sites comprising 59 and 31% of all cells counted at the North Bay and Center Lake sites, respectively. Aphanocapsa spp. (Fig. 3b) was the most abundance cyanobacteria genus at the Center Lake site with a relative abundance of 40%. This genus is comprised of picoplankton size (≤2µm diameter) spherical cells irregularly distributed within mucilage. 

Aphanizomenon spp. (Fig. 3c) and to a lesser degree Dolichospermum spp. (Fig. 3d), continued to be important filamentous cyanobacteria at Bantam Lake. The other important non-filamentous but colonial genera included Woronichinia spp. and Microcystis spp. All of these genera are considered toxigenic (CT DPH & CT DEEP 2019, Cheung et. al. 2013, USEPA 2020).

Water Column Temperatures and Oxygen Characteristics

The water column at all four sites was mixed, i.e., not thermally stratified, on October 28th. That condition has persisted since September 13th 2021. Differences in surface and bottom temperatures at each site were <1°C at the Center Lake, Folly Point, and South Bay sites; at North Bay the difference was 1.3°C (Table 1). The minimum oxygen concentrations regardless of site or depth was 7.8mg/L.

Data is collected and analyzed by Aquatic Ecosystem Research who is contracted by Bantam Lake Protective Association.

Literature Cited

Connecticut Department of Public Health and Connecticut Department of Energy and Environmental Protection [CT DPH & CT DEEP]. 2019. Guidance to Local Health Departments for Blue–Green Algae Blooms in Recreational Freshwaters. See https://portal.ct.gov/-/media/Departments-and-Agencies/DPH/dph/environmental_health/BEACH/Blue-Green-AlgaeBlooms_June2019_FINAL.pdf?la=en 

Cheung MY, S Liang, and J Lee. 2013. Toxin-producing Cyanobacteria in Freshwater: A Review of the Problems, Impact on Drinking Water Safety, and Efforts for Protecting Public Health. Journal of Microbiology (2013) Vol. 51, No. 1, pp. 1–10. See http://www.jlakes.org/ch/web/s12275-013-2549-3.pdf 

United States Environmental Protection Agency [US EPA]. 2020. Health Effects from Cyanotoxins. https://www.epa.gov/cyanohabs/health-effects-cyanotoxins