Cyanos Activity May 9, 2022

Water is clean for recreation.

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 May 9th, AER visited Bantam Lake to conduct monthly water quality monitoring and biweekly cyanobacteria monitoring as part of the ongoing lake management program. 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 plankton tow sample using a 10μm mesh plankton net was collected at the site. The concentrated plankton sample was transferred into a 25mL glass amber bottle and stored at 3°C. Approximately 500mL of the top three meters of water column was integrated and collected for algae counts at both the North Bay and Center Lake sites using a three-meter-long sampling tube. Those samples were preserved with Lugol’s solution shortly after collection and stored at 3C.

A portion of the live phytoplankton in the net sample was carefully examined with microscopy on the same day it was collected to identify and list all algal genera present prior to any treatment or preservation. Afterwards, the net sample was preserved with Lugol’s Solution and stored. The integrated whole water samples were prepared and analyzed as described in our April 15, 2022 memo.

Cyanobacteria and Algae Community

A total of 27 algae genera were observed among the net tow and concentrated whole water samples. Seven genera of Cyanophyta (aka cyanobacteria or blue-green algae) and seven genera of Bacillariophyta (aka diatoms) were identified; six genera of Chlorophyta (aka green algae) were identified; and three genera of Chrysophyta (aka golden algae) were also observed. Several other algae taxonomic groups were represented by one or two genera.

Total algae cell concentrations were 3,097 and 4,266 cells/mL at the North Bay and
Center Lake sites, respectively. Cyanobacteria were the most abundant with cell concentrations
of 2,458 and 3,502 cells/mL, or 79% and 82% of all cells counted at the respective
sites. The cyanobacteria cell concentrations were similar to those of April 26th
but the relative abundances were higher on May 9th due to the decrease in numbers of
golden algae cells.

The cyanobacteria concentrations were characteristic of Visual Rank Category 1 (or
good conditions) according to Connecticut’s guidance for municipalities (CT DPH & CT
DEEP 2019) and were consistent with our assessment of Secchi disk transparency (see
below). Aphanizomenon spp. (Fig. 1a) followed by Planktothrix spp. Fig. 1b) were the
most important cyanobacteria genera at both sites. Golden algae, e.g. Mallomonas
spp. (Fig. 1c), Uroglenopsis spp. (Fig. 1d) and diatoms, e.g. Aulocoseria sp. (Fig. 1e) and
Tabellaria sp. (Fig. 1f) were subdominant to the cyanobacteria.

Conditions

The skies were clear and sunny. Strong winds were out of the north to northeast with
highs of 20mph and gust of 26mph (White Memorial Conservation Center - KCTLITCH9).
Secchi disk transparencies (water clarity) continued to good (Table 1) as they
were in our April 26th visit.

The water columns at all four sites were thermally mixed. This differed slightly from
that observed on April 26th when a thermocline was detected between the 5- and 6-
meter strata of the North Bay site. The difference may be due to the strong wind conditions
of May 9th and the days preceding that date. The May 9th water temperatures
throughout the water columns were between 11.4 and 11.1°C (52.5 and 52.0°F). Oxygen
concentrations were high throughout the water columns of all four sites (Table 1).

Literature Cited

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