Cyanos Activity April 26, 2023

 

Do not expose yourself or your pets 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, April 26th, Brawley Consulting Group visited Bantam Lake to conduct biweekly cyanobacteria monitoring as part of the 2023 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 site. The concentrated plankton sample was transferred into a 25mL glass amber bottle and stored at 3°C. Approximately 500 mL of the top three meters of water column was integrated and collected for algae counts at the North Bay, South 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 3C.

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. Afterwards, the net sample was preserved with Lugol’s Solution and stored. The integrated whole water samples were prepared and analyzed as described in earlier reports.

Cyanobacteria and Algae Community

A total of 18 algae genera were observed among the net tow and concentrated whole water samples. These included genera from Cyanophyta (aka cyanobacteria or blue-green algae), the Chlorophyta (aka green algae), the Bacillariophyta (aka diatoms), Chrysophyta (aka golden algae), and Dinophyceae (aka dinoflagellates). Total algae cell concentrations were 6,891 and 6,855 at the

Cell concentrations were only determined in the Center Lake and South Bay sites due laboratory glassware containing the North Bay Site sample breaking during preparations.

Cyanobacteria cell concentrations were unseasonably high and greater than 300,000 cells/mL in both samples. The vast majority of the cells were from Aphanizomenon spp. Other cyanobacteria genera observed included Microcystis spp., Woronichinia spp., Dolichospermum spp. and Aphanocapsa spp. Filaments of Aphanizomenon spp. are comprised of longer rectangular cells near the filament ends and very small in the middle of the filament (Fig. 1). Filaments group together forming rafts of multiple filaments.

The cyanobacteria concentrations in the two samples were characteristic of Visual Rank Category 3 (having the greatest risk to public health) according to Connecticut’s guidance for municipalities (CT DPH & CT DEEP 2021). The State advises posting beach closure signage and reporting to the State at these concentrations.

Conditions

Secchi disk transparencies were unseasonably low, and between 1.88 meters and 1.97 meters (Table 1). For comparison, on the same date in 2022 Secchi disk transparencies were >3.5 meters at all sites. On both dates, skies were overcast. Rain did fall during the 2023 visit.

The water columns at all four sites were thermally mixed. Surface water temperatures were between 13.6 and 13.3°C (56 and 56.5°F). Temperatures at the bottom were only 2 to 2.5°C lower (Table 1). Oxygen concentrations were high throughout the water columns of all four sites except at Folly Point where concentrations were 1.7 mg/L (Table 1).

Conclusions

The cyanobacteria community observed in Bantam Lake on April 26th was more characteristic of mid- to late-season conditions. The warm winter and warm conditions this spring may have advanced the timing of germination of Aphanizomenon spp. or promoted its overwintering. Filaments were long and comprised of many cells, filaments had formed rafts, and heterocysts were visible.

Plans for earlier treatments this season should be considered.

Literature Cited

Connecticut Department of Public Health and Connecticut Department of Energy and Environmental Protection. 2019. Guidance to Local Health Departments for Blue–Green Algae Blooms in Recreational Freshwaters. See https://portal.ct.gov/-/media/Departments-and-Agencies/DPH/dph/environmental_health/BEACH/Blue-Green-AlgaeBlooms_June2019_FINAL.pdf?la=en

Analyses performed by Larry Marsicano, CLM, Brawley Consulting Group, LLC contracted by Bantam Lake Protective Association.