Cyanos Activity July 6, 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 Monday, July 6 th , AER visited Bantam Lake to perform Cyanobacteria monitoring. Water column profile data, total depth measurements, and Secchi transparency data 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). 

An 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. 

Based on relative phycocyanin concentrations profiled at the four sites, two additional samples were collected at 5 meters of depth at the North Bay and Center Lake Sites (Fig. 1). These were analyzed using the same methods as were used for the surface to 3-meter composite samples. 

Secchi transparency measurements at all sites on July 6 th were between 2.5 and 3.0 meters (Table 1). These were consistent with transparency measurements taken since June 17th (Fig. 2). One difference noted in the recent measurements was that the South Bay transparency was similar to transparencies at the other sites. In the prior four weeks, Secchi transparency at South Bay was up to 0.5m less than transparency at the other sites (Fig. 2). 

The lake average relative phycocyanin concentration in the top 3m of the July 6 th water column exhibited a small decrease from the July 1st average; individual site averages were within the range observed since June 17th (Fig. 3). Phycocyanin is the signature photosynthetic pigment of freshwater Cyanobacteria and was measured in situ with a fluorimeter. 

Cyanobacteria cell concentrations of 32,819 and 31,503 cells/mL at the North Bay and Center Lake sites, respectively, represented a decrease over levels from the prior week (Fig. 4). 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) 

Aphanizomenon spp. continued to be the most abundant Cyanobacteria genus, as it has all season, particularly after it reached bloom conditions on June 1st. That genus comprised 54 and 64% of all algae cells on July 6th. Since June 9th , Dolichospermum spp. has continued to increase in abundance. In the recent sample it comprised 28 and 27% of all cells counted, which are the highest relative abundances for that genus this season. A total of nine Cyanobacteria genera were observed in the July 6th samples (Table 2). A number of those have been associated with toxin production (Cheung et.al. 2013, CT DPH & CT DEEP 2019, iNaturalist 2020).

Samples collected at 5m of depth had fewer cell than was anticipated given the higher relative phycocyanin concentration measured with the fluorimeter at that depth (Fig. 1). This suggest that the higher phycocyanin levels were due to Blue-green picoplankton (very small algae with cell diameters of 0.2 to 2µm) or the deep-water collections were not at the exact depth of the phycocyanin maximum concentrations in the water column. 

Cyanobacteria concentrations at 5m of depth were 14,737 and 9,880 at the North Bay and Folly Point Sites, respectively. At North Bay, Aphanizomenon spp. accounted for 46% of the Cyanobacteria cells; at the Folly Point Site, Aphanizomenon spp. and Oscillatoria spp. (aka Planktothrix spp.) were codominant genera comprising 32 and 29% of all cells. 

Surface water temperatures at all sites on July 6 th had, on average, increased by 1 to 2°C since July 1 st, while increases in temperatures at the bottom of the North Bay, Center Lake, and South Bay Sites were <1°C. The bottom of the Folly Point Site increased by nearly 2°C (Table 1). 

The water column was stratified at all sites. The thermocline was located between 4 and 5m of depth at the North Bay and Folly Point Sites, between 5 and 6m of depth at the Center Lake Sites, and between 3 and 4m of depth at the South Bay Site. Resistance to mixing was strong (RTRM >80) and oxygen concentrations were <1mg/L at all sites except South Bay (Table 2). Oxidation-reduction potential values indicated conditions for loading of phosphorus from the sediments could occur at the Center Lake Site.

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.