Cyanos Activity June 17, 2020

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, June 17, 2020, AER visited Bantam Lake to conduct monthly water quality monitoring and biweekly Cyanobacteria monitoring as part of the community’s ongoing lake management program. Water column profile data and Secchi transparencies 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 Center Lake site. The concentrated plankton sample was transferred into a 25mL glass amber bottle and stored at 3°C. Approximately 500mL of the top three meters of lake water were integrated and collected for algae counts at both the North Bay and Center Lake sites using a three-meter long sampling tube. These samples were preserved with Lugol’s solution shortly after collection and stored at 3C. Sample preparations and counting methods were undertaken as described in earlier memos. 

Water clarity measured as Secchi transparency decreased by approximately 0.5 meters since our last visit on June 9th (Fig. 1). Relative concentrations of phycocyanin (the photosynthetic pigments of cyanobacteria) were slightly higher than June 9th levels, but not at the levels measured on June 1st when a bloom of the cyanobacteria Aphanizomenon spp. was encountered (Fig. 2). 

Twenty-eight algae genera were identified in either the plankton net tow or whole water samples. Eight of those were cyanobacteria and seven were from the Chlorophyta (Green Algae). One of the Green Algae genera was Mougeotia spp., which often grows among aquatic vegetation but can break loose and be observed in the plankton.

Cyanobacteria cell concentrations on June 17th were higher than those determined from samples collected on June 9th , but were not as high as those determined in samples collected on June 1st when the bloom was observed. Cyanobacteria cell concentrations on June 17th at the North Bay and Center Lake Sites were 37,724 and 36,301 cells/mL, respectively. Both concentrations were above the intervention threshold of 20,000 cells/mL, and indicative of Visual Rank Category 2 (CT DPH & CT DEEP 2019). Additional information on Cyanobacteria and recommended public interventions are available at https://portal.ct.gov/DPH/Environmental-Health/Environmental-HealthSection/Blue-Green-Algae-Blooms. 

The most dominant cyanobacteria genus continued to be Aphanizomenon spp. which comprised 61 and 75% of all cells counted at the North Bay and Center Lake Sites, respectively. As discussed in earlier memos, the small cells of Aphanizomenon spp. are arranged in filaments which form rafts comprised of multiple filaments (Fig. 3). The second most abundant cyanobacteria genera was Aphanocapsa spp. which have even smaller cells that are irregularly arranged in a mucilage (Fig. 3). 

Diatoms were the second most abundant taxonomic group comprising 6 to 7% of the total cells. Tabellaria spp. was the most abundant diatom observed in the June 17th sample. Cells of this alga are much larger, rectangular in shape and connect with each other at the corners (Figs. 3 and 4). On a cell volume basis, Tabellaria spp. was an important component of the algae community on June 17th . 

Surface water temperatures increased by approximately 1°C since June 9th. A thermocline with strong resistance to mixing was observed between 5 and 6 meters of depth at the North Bay, Center Lake, and Folly Point Sites. At the South Bay Site, the thermocline was between 3 and 4 meters (bottom) of depth, but did not exhibit strong resistance to mixing. Oxygen concentrations below 5 meters of depth were <1mg/L at all sites except the South Bay Site where it was 1.4mg/L (Table 1).

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

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