Cyanos Activity July 5, 2022
Treatment to control cyanobacteria (a.k.a. blue-green algae) is scheduled for
July 19, 2022; more details will be provided soon.
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 Tuesday, July 5th, 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 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
Little to no wind was encountered and skies were overcast and cloudy. Air tempera-tures during our time on the lake rose from approximately 17 to 21°C (approximately 63 to 70°F; White Memorial Conservation Center - KCTLITCH9). Surface scums were not observed at the State ramp at the time of launching, nor were they observed while on the water.
Based on measurements of relative phycocyanin concentrations throughout the water column, a second sample was collected for an algae count at the Center Lake site at 4 meters of depth where relative phycocyanin reached maximum concentrations (Fig. 1). Phycocyanin is the auxiliary photosynthetic pigment used as a surrogate for cyanobacteria biomass.
Cyanobacteria and Algae Community
A total of 31 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 10 genera observed. Cyanophyta
(aka blue-green algae or cyanobacteria) and Bacillariophyta (aka diatoms) were
represented by 7 and 5 genera, respectively. Four other taxonomic groups were represented
by three or less genera.
The most abundant taxon was the cyanobacteria. Cell concentrations of 83,672 and
73,442 cyanobacteria cells/mL were determined for the North Bay Site and Center
Lake Site, respectively, which represented approximately 99% and 94% of all cells
counted at the respective sites. Cyanobacteria concentrations at both sites were
within the range that characterizes Visual Rank Category 2 conditions. 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; (CT DPH & CT DEEP 2021). For Category 2 conditions, notification of
conditions to the CT DPH and CT DEEP, increased surveillance, and cautionary signage
at public beaches is advised.
Cell concentrations at the North Bay and Center Lake sites in recent weeks were characteristic
of the exponential growth phase for cyanobacteria (Fig. 2). These concentrations
were the samples integrated from the top three meters of the water column. Cyanobacteria
cell concentrations at the sample collected at the Center Lake site at 4 meters
– depth of highest relative phycocyanin concentration (Fig. 1) – was 94,358
cells/mL. Differences in the dominant cyanobacteria genus were observed between
the 1-to-3-meter integrated samples and the sample collected at 4 meters. The most
abundant genus in the integrated samples was Woronichinia spp., followed by Dolichospermum
spp. Woronichinia spp. comprised between 40 and 50% of all cells in the integrated
samples. At the 4-meter depth sample, collected at the Center Lake site,
Aphanizomenon spp. was the most abundant cyanobacteria, comprising 46% of all
cells counted, followed by Woronichinia spp. (25%).
Water Column Conditions
The water column at all sites was stratified, including at the South Bay site where the
thermocline separated the bottom meter from the rest of the water column. Oxygen
concentrations were <1 mg/L at the North Bay, Center Lake, and Folly Point sites. At
the South Bay site, the lowest oxygen concentration was 3.7 mg/L measured at 4 meters
of depth. Secchi disk transparencies were 2.15 and 2.71 meters (Table 1).
Data is collected and analyzed by Aquatic Ecosystem Research who is contracted by Bantam Lake Protective Association.
