Cyanos Activity July 27, 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 27th , AER visited Bantam Lake to monitor Cyanobacteria concentrations. In addition, 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). 

A 500mL composite sample of the top three meters of water column was 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 3°C. Sample preparations did not include concentration of whole water samples since those samples appeared to have sufficient cell concentrations to count without any processing. Counting methods were undertaken as described in earlier memos. 

Additionally, a concentrated plankton tow sample, which was obtained using a 10µm mesh 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 transparency measurements on July 27th ranged from a high of 2.23 meters (m) at the North Bay Site, to a low of 1.47m at the South Bay Site (Table 1). Average Lake Secchi transparency has decreased by 0.75m since July 6th; and, the July 27th lake average was the second lowest of the season (Fig. 1). Only the average Secchi transparency during the June 1st bloom was lower. 

Relative phycocyanin, which is the signature photosynthetic pigment of Cyanobacteria was measured in situ with a fluorimeter; those data suggest that concentrations have increased since July 13th at each individual site and lake wide to the highest of the season with the exception of those during the June 1st bloom (Fig. 2). 

Cyanobacteria cell concentrations at the North Bay and Center Lake Sites that were 15,561 and 12,845 cells/mL, respectively on July 13th and increased to 38,221 and 62,109 cells/mL, respectively by July 27th (Fig. 3). The recent cell concentrations were within the Visual Rank Category 2 range (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) 

Dolichospermum spp. continued to be the most abundant Cyanobacteria genus observed. Aphanizomenon spp. still remained an important component of the community but was superseded by Dolichospermum spp. in cell concentrations on July 13th . A total of nine different Cyanobacteria genera were observed in the examination of the plankton net sample or in the samples used for counts (Table 2). A number of these genera have been described as having toxigenic properties (CT DPH & CT DEEP 2019, Cheung et.al. 2013, iNaturalist 2019). 

Cyanobacteria comprised >95% of all cells counted in both samples. Chlorophyta (aka Green Algae) and Bacillariophyta (diatoms) were the next most abundant genera but each comprised <2% of the total at either site. 

Data for several of the variables collected at the North Bay and Center Lake Sites during each visit were regressed against each other to understand the nature of any relationships between those variable and the consistency in the analyses. The related variables were Cyanobacteria cell concentration, relative phycocyanin concentration, and Secchi transparency. Results of those analyses are presented in Figure 4. 

All relationships were highly significant. Data points from the June 1st bloom and the July 27th conditions are noted on the regression plots (Fig. 4). Based on any combination of three variables, July 27th conditions were the closest to the conditions encountered on June 1st (Fig. 4). 

Over the weekend of July 25th and 26th, several samples were collected by Peter Longo and Kris Trutta from the community who expressed concerned about possible bloom conditions. Those samples were provided to James Fischer of the White Memorial Foundation who also collected a sample and provided them all to AER for examination. 

Based on a visual examination, samples contained accumulations of what appeared to be algae (Fig. 5). Upon further examination with microscopy, it was determined that several of the samples contained the filamentous Cyanobacteria Oscillatoria spp., aka Planktothrix spp. (Baker et.al. 2012). Concentrations of Oscillatoria spp. in these samples, presumably collected without a plankton net to concentrate cells, were high and consistent with bloom conditions (Fig. 6 and 7). 

It was reported that the bloom-like conditions dissipated that weekend. Oscillatoria spp. was not observed in the July 27th sample collections by AER. Like a number of the Cyanobacteria genera observed at Bantam Lake, Oscillatoria spp. can regulate its buoyancy and presumably became negatively buoyant after some time at the surface. High concentrations of Oscillatoria spp. can be observed in other lakes near or below the thermocline. 

On July 27th, the highest concentrations of Cyanobacteria based on measures of relative phycocyanin concentrations were below 5 meters of depth at the North Basin, Center Lake, and Folly Point Sites. Concentrations were similar throughout the water column at the South Bay Site. 

Literature Cited 

Baker, A.L. et al. 2012. Phycokey -- An image based key to Algae (PS Protista), Cyanobacteria, and other aquatic objects. University of New Hampshire Center for Freshwater Biology. http://cfb.unh.edu/phycokey/phycokey.htm 28 Jul 2020. 

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.