Cyanos Activity August 18, 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 Thursday, August 18th, 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).
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 thirty days after the July 19th copper sulfate treatment.
General Conditions
Winds were light and variable for much of the morning. Skies were bright with few passing clouds. Air temperatures were in the mid-60s to low 70s°F (https://www.wunderground.com/dashboard/pws/KCTLITCH9/graph/2022-08-18/2022-08-18/daily). Surface scums were not observed along the shoreline at the State Boat Launch, nor were they observed while on the water. Lake water appeared turbid.
Cyanobacteria and Algae Community
A total of 21 algae genera were observed in the plankton net and whole water samples collected on August 18th. 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), with each represented by seven genera. Cyanobacteria genera counted or observed in the plankton net sample included Aphanizomenon spp., Aphanocapsa spp., Dolichospermum spp., Microcystis spp., Planktothrix spp. Pseudoanabaena spp., and Woronichinia spp.
August 18th cyanobacteria cell concentrations had increased exponentially since August 1st (Fig. 1). Concentrations at the North Bay and Center Lake sites were 62,812 and 90,966 cells/mL. Those concentrations accounted for 94% and 96% of all algae cells counted in the samples from the respective sites. Cyanobacteria cell growth over the last two weeks, was similar to that observed in the four weeks prior to the July 19th treatment.
Woronichinia spp. was replaced as the dominant cyanobacteria genus by the filamentous
Dolichospermum spp. and Aphanizomenon spp. (Fig. 2).
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 18th were between 1.56 and
1.98 meters (Table 1) and on average 1 meter less than those measured on August 1st
(Fig. 3). Relative phycocyanin concentrations correspondingly increased since August
1st and were the highest of the season (Fig. 3). The relatively large cell size of Dolichospermum
spp. may have contributed to the increase in relative cyanobacteria biomass,
as well as the increase in cyanobacteria cell concentration.
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 only observed at the Center Lake Site below the thermocline
(Table 1).
Data is collected and analyzed by Aquatic Ecosystem Research who is contracted by Bantam Lake Protective Association.
