Cyanos Activity September 12, 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, September 12th, 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).
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.
Copper sulfate treatment occurred at the lake on July 19th and August 30th.
General Conditions
Weather conditions were calm and overcast. Air temperatures were in the mid-60s °F (https://www.wunderground.com/dashboard/pws/KCTLITCH9/graph/2022-09-12/2022-09-12/daily). Surface scums were not observed along the shoreline at the State Boat Launch, nor were they observed while on the water. Notable amounts of cyanobacteria and algae were observed below the surface.
Cyanobacteria and Algae Community
A total of 31 algae genera were observed within the plankton net and whole water samples collected on September 12th. The taxonomic group with the greatest richness (most individual genera) was the Chlorophyta (aka green algae) with 14 genera identified, followed by the Cyanophyta (aka cyanobacteria or blue-green algae) which had a total of seven genera identified. Five other taxonomic groups were represented by three or fewer genera. Cyanobacteria genera counted or observed included Aphanizomenon spp., Aphanocapsa spp., Dolichospermum spp., Cylindrospermopsis spp., and
Pseudoanabaena spp., Snowella spp., and Woronichinia spp.
September 12th cyanobacteria cell concentrations were on average similar to the average since August 18th (Fig. 1). The concentrations at the North Bay and Center Lake sites were 69,414 and 67,260 cells/mL, respectively. Those concentrations accounted for 92% of all algae cells counted in the samples from both sites. At the North Bay Site, Dolichospermum spp., followed by Pseudanabaena spp., were the most abundant cyanobacteria on a cell count basis. At the Center Lake Site, Pseudanabaena spp., followed by Dolichospermum spp., were the most abundant. Woronichinia spp. was the third most abundant genus at both sites.
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 (a surrogate of cyanobacteria biomass).
Secchi disk transparencies measured on September 12th were between 1.65
and 1.85 meters (Table 1) and similar to those since August 18th (Fig. 2). September 12th
relative phycocyanin concentrations were also similar to concentrations measured
since August 18th with the exception of the August 31st South Bay average (Fig. 2).
Water Column Characteristics
The water column was mixed at all sites including Center Lake, which is the deepest
site. Water temperatures decreased from approximately 23°C (73°F) near the surface
to approximately 21°C (70°F) at the bottom of the Center Lake Site. Anoxic conditions
were observed at the bottom of the water column of each site with the exception of the
South Bay Site, where high oxygen concentrations were observed throughout the water
column (Table 1).
Data is collected and analyzed by Aquatic Ecosystem Research who is contracted by Bantam Lake Protective Association.
