Cyanos Activity July 1, 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, July 1st , AER visited Bantam Lake to perform 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 composite sample of the top three meters of water column were collected for algae counts at the North Bay and Center Lake sites using a threemeter long sampling tube. These samples were preserved with Lugol’s solution shortly after collection and stored at 3°C. Sample preparations and counting methods were undertaken as described in earlier memos. A concentrated plankton tow sample using a 10µm mesh plankton net was also 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 on July 1st were between 2.50 and 2.83 meters (m) at the North Bay, Center Lake, and Folly Point Sites (Table 1). At the South Bay Site Secchi transparency was 2.15m. All measurements were consistent with transparency measurements taken since June 17th (Fig. 1). Average relative phycocyanin concentrations in the top 3m of the July 1st water column had modestly increased from levels from the previous two weeks (Fig. 2). Phycocyanin is the signature photosynthetic pigment of freshwater Cyanobacteria and was measured in situ with a fluorimeter. 

Cyanobacteria cell concentrations of 61,344 and 71,390 cells/mL at the North Bay and Center Lake sites, respectively, indicated an increase over levels from the last two weeks (Fig. 3). These concentrations, however, were still 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 for this category 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)

Cells of the Cyanobacteria Aphanizomenon spp. (Fig. 4) continued to be the most abundant as they have since late April and particularly during the bloom of June 1st when that genus comprised >99% of the algae community. Several other Cyanobacteria genera in the July 1st samples, including Dolichospermum spp. (Fig. 5) and Coelosphaerium spp., were also important. A total of eight Cyanobacteria genera were observed in samples (Table 2). A number of those have been associated with toxin production (Cheung et.al. 2013, CT DPH & CT DEEP 2019, iNaturalist 2020).

Surface water temperatures at all sites on July 1st had, on average, decreased by 1 to 2°C since July 24th, while temperatures at the bottom of each site increased by approximately 0.25 to 0.75°C at all sites with the exception of the South Bay Site. There the bottom temperature increased by 2.3°C (Table 1). 

The water column was stratified at all sites with the exception of the South Bay Site. Where the water column was stratified, the resistance to mixing was strong (i.e. RTRM >80) with the thermocline observed between 4 and 5 meters of depth and oxygen concentrations below that depth measured at <1mg/L (Table 1). 

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.