Cyanos Activity June 24, 2020

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.

On Wednesday, June 24th , AER visited Bantam Lake to conduct cyanobacteria monitoring. Water column profile data, total depth measurements, and Secchi transparencies were collected from the North Bay Site (N 41.71087° W -73.21155°), the Center Lake Site (N 41.70056° W -73.22102°), a site west of Folly Point (N 41.70773 W -73.22638), and at a site in the South Bay region of the lake (N 41.69015 W -73.22728). 

Approximately 500mL of a composite of the top three meters of lake water were collected for algae counts at the North Bay and Center Lake sites using a three-meter long sampling tube. These samples were preserved with Lugol’s solution shortly after collection and stored at 3C. Sample preparations and counting methods were undertaken as described in earlier memos. A concentrated plankton tow sample using a 10µm mesh plankton net was collected at the Center Lake site. The concentrated plankton sample was transferred into a 25mL glass amber bottle, stored at 3°C, and preserved with Lugols after an examination with microscopy. 

Secchi transparencies were between 2.73 and 2.80 meters (m) at the North Bay, Center Lake, and Folly Point Sites. At the South Bay Site Secchi transparency was 2.25m. All measurements were consistent with transparency measurements from June 17th (Fig. 1). Relative phycocyanin concentrations in the top 3m of the water column on June 24th were similar to those measured on June 17th (Fig. 2). Phycocyanin is the signature photosynthetic pigment of freshwater cyanobacteria and was measured with a fluorimeter in situ throughout the water column. 

Cyanobacteria cell concentrations of 32,721 and 44,439 cells/mL at the North Bay and Center Lake sites, respectively, were similar to corresponding concentrations on June 17 th (Fig. 3). These concentrations were within the range that is characteristic of Visual Rank Category 2 conditions (CT DPH & CT DEEP 2019). In the State’s Guidance to Local Health Departments for Blue–Green Algae Blooms in Recreational Freshwaters, the following interventions are recommended in the interest of public health and safety:

• Notify CT DPH, CT DEEP 
• Increase regular visual surveillance until conditions change 
• Consider cautionary postings at public access points (Examples are provided in the guidance document)

The most abundant cyanobacteria genus observed with microscopy was Aphanizomenon spp. which comprised 63 and 88% of all algal cells at the North Bay and Center Lake Sites, respectively. This genus is found prior to preservation as rafts of filaments. Each filament is comprised of many small, cylindrical or barrel-shaped cells. After preservation with Lugols, the rafts fall apart into separate filaments, but cells in each filament stay intact. 

Aphanothece spp. and Woronichinia spp. were the second most abundant genera at the North Bay Site. Woronichinia spp. was also the second most abundant cyanobacteria genus at Center Lake. A total of seven cyanobacteria genera were observed in either the plankton net sample, or in samples collected for counts (Table 1). Several of the genera have been associated with toxin production (Cheung et.al. 2013, CT DPH & CT DEEP 2019, iNaturalist 2020). 

It is worth noting that the highest concentrations of cyanobacteria were located at 4m of depth based relative phycocyanin concentration data. Our sampling focused on conditions from the surface to 3m of depth to be consistent with EPA sampling protocols and because most of the public contact with the water occurs at those depths. 

Surface water temperatures on June 24th increased, on average, by 3.9°C since June 17 th. Temperatures at the bottom of the water column increased, on average, by 0.9°C during that period (Table 2). The differences in change was due to the stratification of the water column. On June 24th, there was strong resistance to mixing at the thermocline located between 5 and 6m of depth at all sites except South Bay where the total depth was <5m (Table 2). Oxygen concentrations from the surface to a depth of 4m were between 7 and 8.5mg/L at the North Bay, Center Lake and Folly Point Sites. Below the thermocline, oxygen concentrations decreased to <1mg/L. At the South Bay Site, concentrations were between 8 and 9mg/L in the top 3m of the water column before decreasing to 5mg/L at 4m of depth.

Literature Cited 

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 

[CT DPH & CT DEEP] Connecticut Department of Public Health and Connecticut Department of Energy and Environmental Protection. 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 

iNaturalist. 2019. Woronichinia. See https://www.inaturalist.org/guide_taxa/700578

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