Cyanos Activity July 6, 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 and Methods
AER visited Bantam Lake to conduct biweekly Cyanobacteria monitoring as part of the
Bantam Lake Protective Association’s ongoing lake management efforts. Data collected in the field included measurements of temperature, dissolved oxygen, specific
conductance, and pH at one-meter intervals from the top to the bottom of the water
column, total depth, and Secchi disk transparency. These 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. Approximately 500 mL from the top three meters of the water column
were integrated and collected for algae counts at 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 3 C. Samples were also collected in a
similar fashion for analysis of microcystin toxins in 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.
Water Clarity
Secchi disk transparency readings in the lake on July 6th were between 2.27 and 2.55
meters (Table 1) and had decreased, on average, by 1.2 meters since June 26th (Fig. 1).
Between May 25th and June 23rd, and lake averages were between 2.89 and 3.75 meters, but the average was only 2.41 on July 6th
.
Algae Community and Cyanobacteria Cell Concentrations
Twenty-six algal genera were observed in the net tow and integrated whole water samples. The Cyanobacteria (aka Blue-green Algae) and Chlorophyta (aka Green Algae)
constituted 8 and 10 of the total genera observed, respectively. The remaining eight
genera were distributed among six other taxonomic groups.
The Cyanobacteria cell concentrations increased since June 23rd when concentrations
were between 15,000 and 16,000 cells/mL. July 6th concentrations were 38,568 and
40,840 cells/mL at the North Bay and Center Lake sites, respectively. These concentrations are characteristic of Visual Rank Category 2 conditions (CT DPH and CT
DEEP). In the State’s Guidance to Local Health Departments for Blue–Green Algae
Blooms in Recreational Freshwaters, the following interventions are recommended for
this category in the interest of public health and safety:
- Notify CT DPH, CT DEEP
- Increase regular visual surveillance until conditions change
- Consider cautionary postings at public access points (Examples are provided in the guidance document)
The dominant Cyanobacteria genus continued to be Aphanizomenon spp. (Fig. 1a). The
next most important Cyanobacteria genera were Dolichospermum spp. (Fig. 1b) and
Woronichinia spp. (Fig. 1c); these were not as abundant as Aphanizomenon spp. but important components of the pelagic algal community. These species are listed in the
literature as potentially toxigenic (Cheung et. al. 2013, CT DPH & CT DEEP 2019, EPA
2020).
Water Column Temperatures and Oxygen Characteristics
Surface water temperatures on July 6th between 22 and 23°C (Table 1) and very similar
to those recorded on June 23rd
. Some heat had transferred to the lower depths as temperatures there had slightly increased since June 23rd. Oxygen concentrations at the
bottom of the water column at the North Bay, Center Lake, and Point Folly sites were
all <0.05mg/L (Table 1). Oxidation-reduction potential (ORP) measured at the bottoms
of the North Bay and Center Lake sites were <50mV indicating that phosphates may
be loading from the sediments. At the mixed South Bay site, the oxygen concentration
at the bottom of the water column was 2.0mg/L and ORP at the bottom of the water
column was >250mV indicating that phosphorus was not loading from the bottom of
that site. A similar ORP was observed at the bottom of the Point Folly site.
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 [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
United States Environmental Protection Agency [US EPA]. 2020. Health Effects from
Cyanotoxins. https://www.epa.gov/cyanohabs/health-effects-cyanotoxins
