Cyanos Activity August 31, 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 Wednesday, August 31st, AER visited Bantam Lake to conduct biweekly cyanobacteria monitoring as part of the ongoing lake management program. Water column pro-file 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).
Water samples were collected at the North Bay Site and Center Lake Site for algal analyses. These samples included whole water samples and a plankton net tow sample. These were prepared and analyzed as described in our April 15, 2022 memo. Samples were collected one day after the second copper sulfate treatment of the season on August 30th.
General Conditions
Winds were light and mostly out of the northwest. Skies were bright with few passing clouds. Air temperatures were in the mid-60s to low 70s°F (https://www.wunder-ground.com/dashboard/pws/KCTLITCH9/graph/2022-08-31/2022-08-31/daily). Sur-face scums were not observed along the shoreline at the State Boat Launch, nor were they observed while on the water. Lake water appeared somewhat turbid.
Cyanobacteria and Algae Community
A total of 20 algae genera were observed in the plankton net and whole water samples collected on August 31st. The taxonomic groups with the greatest richness (most individual genera) were the Chlorophyta (aka green algae) and Cyanophyta (aka cyano-bacteria or blue-green algae), which were represented by 7 and 5 genera, respectively.
A total of three Bacillariophyta (aka diatom) genera were observed; all other taxa were
represented by two or less genera. Cyanobacteria genera counted or observed in the
plankton net sample included Aphanizomenon spp., Aphanocapsa spp., Dolichospermum
spp., Coelosphaerium spp., and Pseudoanabaena spp.
August 31st cyanobacteria cell concentrations were on average modestly lower than
those from August 18th (Fig. 1). The Center Lake Site cell concentration notably decreased,
while North Bay concentrations were nearly identical to the August 18th concentration.
August 31st concentrations at the North Bay and Center Lake sites were
65,769 and 49,220 cells/mL, respectively. Those concentrations accounted for 97%
and 95% of all algae cells counted in the samples from the respective sites. Dolichospermum
spp. and followed by Aphanizomenon spp. were the most abundant cyanobacteria
on a cell count basis.
The cyanobacteria cell concentrations at both sites were characteristic of Visual Rank
Category 2 conditions. Connecticut’s Visual Rank system, which is based on visual assessments,
characterizes conditions from Category 1 (safe conditions) to Category 3 (conditions that present great enough health risk from cyanobacteria to warrant beach closure signage; (CT DPH & CT DEEP 2021). The State guidance document also provides ranges of cyanobacteria cell concentrations that correspond with each Visual Rank category (Fig. 1), and recommendations to municipal health departments on public interventions for Category 2 and 3 conditions.
Secchi Disk Transparency and Relative Phycocyanin Concentrations
Two other related indicators of cyanobacteria productivity routinely measured at Bantam
Lake are Secchi disk transparency (surrogate of water clarity) and the surface-to-3
meters averaged relative phycocyanin concentration (surrogate of cyanobacteria biomass).
Secchi disk transparencies measured on August 31st were between 1.60 and
1.73 meters (Table 1) and similar to those from August 18th (Fig. 2). August 31st relative
phycocyanin concentrations were also similar to August 18th levels with the exception
of the average concentration at the South Bay Site which was lower than the others
(Fig. 2).
Water Column Conditions
The water column was mixed at all sites except Center Lake. At Center Lake, the thermocline
was located near the bottom of the water column between 6 and 7 meters of
depth. Anoxic conditions were observed at the Center Lake Site below the thermocline,
as well as at the bottom of the Folly Point site (Table 1).
Data is collected and analyzed by Aquatic Ecosystem Research who is contracted by Bantam Lake Protective Association.
