Cyanos Activity October 12, 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 and Summary

Air temperature was approximately 55°F when we first arrived at 9am and warmed to 61°F by the time we completed data and sample collections. Skies were a mix of sun and clouds; winds were very light to calm, and out of the northeast. 

Concentrated surface scums or streaks were not observed at the State Launch upon arrival. However, once on the water away from the marina, surface scums were visible across much of the lake. The scums were not thick, but some streaking and clumping were observed. Towards late morning, scums appeared to diminish some in portions of the middle of the lake. However, the thickest and most extensive scums were observed in late morning at the South Bay site. We did observe a small surface scum along the shoreline of the State launch at the conclusion of our visit. 

The conditions we observed would meet Visual Rank Category 3 standards based on State guidance (CT DPH & CT DEEP 2019). Cell concentrations, as described below however, were characteristic of Visual Rank Category 2 conditions. Our cell concentrations are based on analyses of 3-meter integrated samples. Concentrations directly at the surface are likely higher than those from the integrated samples.

Secchi Disk Transparency and Relative Phycocyanin

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

Average Secchi disk transparency on October 12th was nearly identical to the September 29th average (Fig. 1). The North Bay Secchi transparency did improve to 2.32 meters (m) but the South Bay Secchi transparency was only 1.50m (Table 1). Measurements at the other two sites on October 12th were between the North Bay and South Bay measurements and similar to those at corresponding sites on September 29th . 

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 increases in one generally accompanies an increase in the other, while decreases in one is normally associated with decreases in the other. 

The average relative phycocyanin concentrations in the top three meters of the water column increased modestly since September 29th with the exception of the North Bay concentration which on both dates was between 9 and 10µg/L (Fig 1). The lake average of 11.7µg/L was up from the 8.6µg/L calculated for September 29th. This indicated that the average biomass of the cyanobacteria in the top three meters of the water column had increased since the last sampling event on September 29th . 

Cyanobacteria Concentrations and Algae Community Characteristics

Cyanobacteria cell concentrations at the North Bay and Center Lake sites were 24,189 and 57,969 cells/mL, respectively; the former was a decrease and the latter an increase over concentrations at the respective sites on September 29th (Fig. 2). The lake average based on those two concentrations was 41,079 cells/mL, and was similar to the September 29th average (Fig. 2).

The CT DPH and 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. However, based on the visible surface scum, a Visual Rank Category 3 designation is appropriate. Interventions for these conditions and others, in the best interest of public health, 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 in samples was 26 and down from the 35 observed on September 29th . Nine cyanobacteria genera were observed, which was only one down from total cyanobacteria genera observed on September 29th . Cyanobacteria comprised 90 and 97% of all cells counted in the North Bay and Center Lake Site samples, respectively; Chlorophyta (aka green algae) and Bacillariophyta (aka diatoms) each comprised approximately 4% of the algal cells in the North Basin sample. Relative cell abundances for all other taxa, other than those mentioned above, were <2% in both samples.

Filamentous cyanobacteria continue to provide the majority of cyanobacteria cells counted in samples, as it has for much of the season. Different from past cyanobacteria compositions, the filamentous cyanobacteria Planktothrix spp. (formerly Oscillatoria spp.) was an important constituent of the community reaching relative abundances of 22 and 10% of all cells counted in the North Bay and Center Lake site samples, respectively. 

Aphanizomenon spp., Dolichospermum spp., and, to a lesser degree, Pseudoanabaena spp. were other important filamentous cyanobacteria genera counted in October 12th samples. The other important non-filamentous but colonial genera included Woronichinia spp., Aphanocapsa spp., and Microcystis spp. Most of these genera are considered toxigenic (CT DPH & CT DEEP 2019, Cheung et. al. 2013, USEPA 2020). 

Water Column Temperature and Oxygen Characteristics

The water column at all four sites was mixed, i.e., not thermally stratified on October 12th , nor has it been since September 13th . Differences in surface and bottom temperatures at each site were <1°C (Table 1). Oxygen concentrations were generally high at all depths except the very bottom where oxygen consumption exceeded replenishment. A concentration of 0.5 mg/L was measured at the Center Lake Site. Oxygen concentrations at the bottom of the other three sites were ≥3.9 mg/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