Cyanos Activity July 22, 2022

 

Water is clean for recreation.

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 Friday, July 22nd, AER and the BLPA collaboratively collected water quality data and samples from Bantam Lake to determine cyanobacteria cell concentrations. Samples were collected three days after a copper sulfate treatment, which occurred within hours following AER’s last cyanobacteria sample collections of July 19th.

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). Samples collected for cyanobacteria counts were prepared and analyzed as described in our April 15, 2022 memo.

General Conditions

Winds were light and out of the south. Skies were bright with passing clouds. Air temperatures during our time on the lake were in the 80s °F (https://www.wunder-ground.com/dashboard/pws/KCTLITCH9/graph/2022-07-22/2022-07-22/daily). Surface scums were not observed along the shoreline at the start of the sampling event, nor were they observed while on the water. Lake water appeared clearer than what was observed on July 19th prior to the copper sulfate treatment.

Cyanobacteria and Algae Community

A total of 19 algae genera were observed in the water samples collected on July 22nd. Four genera of cyanobacteria were observed: Aphanizomenon spp., Aphanocapsa spp., Dolichospermum spp., and Woronichinia spp. The Chlorophyta (aka green algae) were represented by eight different genera, but none were a major factor in algal cell concentrations. Cyanobacteria continued to constitute most of the cells counted. Percent abundances for cyanobacteria at the North Bay Site and Center Lake Site were 97%and 98%, respectively, and similar to levels from July 19th. However, respective cell concentrations of 22,868 and 16,053 cells/mL were much lower than cell concentrations of July 19th (Fig. 1). The most abundant cyanobacteria genus at both sites was Woronichinia spp.

The cyanobacteria cell concentration at the North Bay Site was just over the recommended
threshold delineating Visual Rank Category 1 and Category 2 conditions, while
the Center Lake Site concentration and lake average were just below that threshold.
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 categories of
cyanobacteria cell concentrations that correspond with each Visual Rank category
(Fig. 1), and recommends actions by municipalities for Category 2 and 3 conditions.

Water Column Conditions

The water column was stratified at all sites with the exception of the South Bay Site. The thermoclines at the stratified sites were observed between 3 and 4 meters of depth. Relative phycocyanin concentrations measured at one-meter intervals throughout the water column at each site indicated that the highest cyanobacteria concentrations were at 4 meters of depth (Fig. 2). That is one meter below the range of depths (surface to 3 meters) integrated and collected for cyanobacteria cell concentration

analyses. 

Oxygen concentration at the bottom of the South Bay site was 3.6 mg/L; at the North Bay and Center Lake sites, levels were <1 mg/L from 5 or 6 meters of depth to the bottom (Table 1). Oxygen was not measured at the bottom of the Folly Point site.

Secchi Disk Transparency and Relative Phycocyanin Concentrations

Two other indicators of cyanobacteria productivity regularly measured at Bantam Lake

are Secchi disk transparency (surrogate of water clarity) and the surface-to-3 meters

average relative phycocyanin concentration (surrogate of cyanobacteria biomass).

Secchi disk transparencies increased since July 19th, while relative cyanobacteria biomass

in the top three meters decreased (Fig. 3).

Data is collected and analyzed by Aquatic Ecosystem Research who is contracted by Bantam Lake Protective Association.

Literature Cited

Connecticut Department of Public Health and Connecticut Department of Energy and

Environmental Protection. 2021. 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/2021/Guidance-to-

LHD-for-Blue-Green-AlgaeBlooms_June2021_FINAL.pdf