Cyanos Activity May 23, 2022
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 May 23rd, AER visited Bantam Lake to conduct 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 Center Lake site. The concentrated plankton sample was transferred into a 25mL glass am-ber 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 Cen-ter 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 mi-croscopy on the same day it was collected to identify and list all algal genera present prior to any treatment or preservation The integrated whole water samples were pre-pared and analyzed as described in our April 15, 2022 memo.
Cyanobacteria and Algae Community
A total of 31 algae genera were observed between the net tow and concentrated whole water samples, which was the highest total thus far for the 2022 season. As is com-mon in lakes of the Northeast, Chlorophyta (aka green algae) had the greatest rich-ness (numbers of genera) with 11 genera observed. Cyanophyta (aka blue-green algae or cyanobacteria) and Bacillariophyta (aka diatoms) were represented by six and seven genera, respectively. Four genera of Chrysophyta (aka golden algae) were observed, and one genus from each of three other taxonomic groups were also observed.
Cyanobacteria cell concentrations increased by an order of magnitude since May 9th,
when AER last sampled the lake. May 23rd cyanobacteria cell concentrations at the
North Bay and Center Lake sites were 39,200 and 36,752 cells/mL, respectively.
Those concentrations constituted 90% and 92% of all cells counted at the respective
sites.
The cyanobacteria concentrations were characteristic of Visual Rank Category 2 conditions
according to Connecticut’s guidance for municipalities (CT DPH & CT DEEP
2021; Fig. 1). Connecticut’s Visual Rank Category system characterizes conditions
from Category 1 (good conditions) to Category 3 (conditions that present great enough
health risk to warrant beach closure signage). Recommended interventions for Category
2 conditions include notification of the CT DPH and CT DEEP, increased surveillance,
and posting cautionary signage.
Aphanizomenon spp. was the most abundant cyanobacteria based on cell concentration.
This genus alone constituted 86% and 89% of all cells counted in the North Bay
and Center Lake samples, respectively. Most Aphanizomenon spp. cells are very small
and linearly arranged into filaments, which group together forming rafts (Fig. 2). Rafts
disassemble into single filaments once the samples are preserved with Lugols. Other
cyanobacteria genera observed in the May 23rd samples included Planktothrix spp.,
Dolichospermum spp., Woronichinia spp., and Aphanocapsa spp.
Conditions
Temperatures at the time samples were collected were mild (mid 50s°F) with moderate
to strong winds out of the north (White Memorial Conservation Center - KCTLITCH9).
The preceding two days had much warmer temperatures that surpassed 90°F in some
parts of Connecticut. Surface water temperatures on May 23rd were 8 to 9°C warmer
than those observed on May 9th, measured between 19 and 20°C, and over 7°C greater
than temperatures at the bottom of the water column at all sites except the South Bay
site where the water column was still mixed (Table 1).
The temperature/density gradients at the North Bay, Center Lake, and Folly Point sites
resulted in a stratified water column at the those sites with high resistance to mixing at
the thermoclines. Those sites also exhibited decreasing oxygen concentrations below
the thermoclines, with a low of 1.8 mg/L of oxygen recorded at the bottom of the Folly
Point site (Table 1). At the mixed South Bay site, oxygen concentrations remained high
throughout the water column.
Data is collected and analyzed by Aquatic Ecosystem Research who is contracted by Bantam Lake Protective Association.
Literature Cited
Connecticut Department of Public Health and Connecticut Department of Energy and
Environmental Protection. 2021. Guidance to Local Health Departments for Blue–Green
Algae Blooms in Recreational Freshwaters. See https://portal.ct.gov/-/media/Departments-
