Cyanos Activity June 8, 2021

 

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.

Introduction, Methods, and General Observations

AER visited Bantam Lake to conduct the regular biweekly Cyanobacteria monitoring, which is part of the Bantam Lake Protective Association’s ongoing lake management program. Data collected in the field included temperature, dissolved oxygen, specific conductance, and pH at one-meter intervals from the top to the bottom of the water column. We also assessed water clarity. Those data were collected at four sites: 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 net tow sample using a 10µm mesh plankton net was collected at the Center Lake site. Additionally, the top three meters of the water column were integrated and concentrated to a sample of ~500mL for algae analysis at the North Bay and Center Lake sites. Those samples were preserved with Lugol’s solution after collection and stored at 3C. Samples were also collected in a similar fashion for the analysis of microcystin toxins at the laboratory of Dr. Edwin Wong at Western Connecticut State University. Methods for analyses of the phytoplankton net sample and the integrated samples discussed in our April 30th memo were followed. 

A surface film was detected in the waters near the State boat launch; similar conditions were also observed at the North Bay and Folly Point sites; but, not at the Center Lake and South Bay sites. A sample was collected from the surface of the North Bay site by carefully dipping the rim of a sampling vial just below the surface and allowing only the very top of the water column to enter. This sample was also analyzed with microscopy.

Water Clarity

June 8th water clarity on was good; readings at the four sites measured between 2.82 and 2.98 meters (Table 1). However, those measures represent a loss of between 70 cm to 1 meter in clarity since May 25th when readings were between 3.5 and 4 meters.

Algae Community and Cyanobacteria Cell Concentrations

Twenty-eight algal genera were observed in the net tow and integrated whole water samples. The Cyanobacteria (aka Blue-green Algae) and Chlorophyta (aka Green Algae) each comprised approximately one-third of the total genera observed. The remaining third were divided between the Bacillariophyta (aka Diatoms) and Chrysophyta (aka Golden Algae). 

The Cyanobacteria cell concentrations substantially increased since May 25th when between 7,000 and 9,000 cells/mL were determined. In the June 8th samples collected from the North Bay and Center Lake sites; concentrations were between 24,000 and 29,000 cells/mL (Table 1) and reflective of Visual Rank Category 2 conditions (CT DPH and CT DEEP).  

The dominant Cyanobacteria genus was Aphanizomenon spp. (Fig. 1a). Other important Cyanobacteria genera included Dolichospermum spp., Aphanocapsa spp. and Woronichinia spp. (Figs. 1b, c, d). Microcystis spp. was also present (Fig. 1e). These species are listed in the literature as toxigenic (Cheung et. al. 2013, CT DPH & CT DEEP 2019, EPA 2020). Aphanizomenon spp. was the genus responsible for the bloom conditions experienced for much of last year.

Examination of Surface Film at the North Bay Site

Constituents of the surface film sampled at the North Bay site included both Cyanobacteria and tree pollen (Fig 2). Much of the Cyanobacteria appeared to be Dolichospermum lemmermannii (St. Amand 2021). The pollen appeared to be from pine trees (Baker et. al. 2021). It is not uncommon for tree pollen concentrated in a cove or bay to be mistaken for an algae bloom.

Water Column Temperature and Oxygen Characteristics

Water temperatures near the surface were warm; between 23 and 24.5°C, and nearly 10°C warmer than those at the bottom of three of the four sites (Table 1). At the Center Lake and South Bay sites, the thermocline – and strong resistance to mixing – was observed between 3 and 4 meters of depth. At the North Bay and Folly Point sites, the thermocline with strong resistance to mixing was located between 2 and 3 meters of depth. Oxygen concentrations near the bottom were lower than those measured near the surface as a result of the stratification, but still >2 mg/L at all sites (Table 2). 

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

Literature Cited 

Baker, A.L. et al. 2012. Phycokey -- an image-based key to Algae (PS Protista), Cyanobacteria, and other aquatic objects. University of New Hampshire Center for Freshwater Biology. http://cfb.unh.edu/phycokey/phycokey.htm 

Connecticut Department of Public Health and Connecticut Department of Energy and Environmental Protection [CT DPH & CT DEEP]. 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 

Cheung MY, S Liang, and J Lee. 2013. Toxin-producing Cyanobacteria in Freshwater: A Review of the Problems, Impact on Drinking Water Safety, and Efforts for Protecting Public Health. Journal of Microbiology (2013) Vol. 51, No. 1, pp. 1– 10. See http://www.jlakes.org/ch/web/s12275-013-2549-3.pdf 

St. Amand, Ann. 2021. Identification, Ecology, and Control of Freshwater Algae. Cyanobacteria Monitoring Collaborative 2021 Mini-Conference. 

United States Environmental Protection Agency [US EPA]. 2020. Health Effects from Cyanotoxins. https://www.epa.gov/cyanohabs/health-effects-cyanotoxins