Cyanos Activity June 20, 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 June 20th, 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 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 3°C.
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. The integrated whole water samples were pre-pared and analyzed as described in our April 15, 2022 memo.
General Conditions
Air temperatures that morning were in low to mid-60°F (White Memorial Conservation Center - KCTLITCH9). There was a breeze out of the north but wind speeds had declined from those occurring on June 18th and 19th. Surface blooms were not observed, but waters did appear moderately turbid.
Cyanobacteria and Algae Community
A total of 26 algae genera were observed between the net tow and concentrated whole
water samples. As is common in lakes of the Northeast, Chlorophyta (aka green algae)
had the greatest richness (numbers of genera) with 8 genera observed. Cyanophyta
(aka blue-green algae or cyanobacteria) closely followed with 6 genera observed. Bacillariophyta
(aka diatoms) and Chrysophyta (aka golden algae) were represented by 5 and
4 genera, respectively. Three other taxa were represented by one genus.
The cyanobacteria continue to be the most abundant taxon. Cell concentrations of
24,989 and 37,440 cyanobacteria cells/mL were determined for the North Bay Site and
Center Lake Site, respectively, which represented approximately 98% of all cells counted
at both sites. Cyanobacteria concentrations at both sites were within the range of Visual
Rank Category 2 conditions (CT DPH & CT DEEP 2021). 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. Recommended
interventions for Category 2 conditions included reporting to the State and consideration
of posting cautionary signage.
Aphanizomenon spp. was the most abundant cyanobacteria based on cell concentration,
constituting 33% and 49% of all cells counted in the North Bay and Center Lake samples,
respectively. Planktothrix spp. and Gomphosphaeria spp. were also important at both
sites. Other cyanobacteria genera observed in the June 20th samples included Dolichospermum
spp., Aphanocapsa spp., and Pseudoanabaena spp.
Other Indicators
Several other water quality parameters measured on June 20th, and each time the lake is
visited, corroborated the increased cyanobacteria cell concentrations. Secchi disk transparencies
on June 20th were the lowest of season to date (Fig. 2). Average relative phycocyanin
concentration, which is a surrogate measure of cyanobacteria biovolume, was
the highest of the season to date (Fig. 2).
Water Column Conditions
Surface water temperatures decreased by several degrees since June 20th and were all
between 20.0 and 20.5°C (Table 1). The water columns at the North Bay and South Bay
sites were thermally mixed and exhibited oxygen concentrations of >7.0mg/L throughout.
This differs from conditions observed on June 6th when the water column at those
sites were stratified and oxygen levels at the bottom of the North Bay site were <1mg/L.
As observed on June 6th, the water columns at the Center Lake and Folly Point sites were
stratified. On June 20th, the thermoclines were observed between 5 and 6 meters of
depth. Resistance to mixing (RTRM value) at the thermocline was moderate. Oxygen
concentrations at the bottom strata of the Center Lake site were <1mg/L and were
3.0mg/L at the bottom of the Folly Point site.
Data is collected and analyzed by Aquatic Ecosystem Research who is contracted by Bantam Lake Protective Association.
Literature Cited
