Cyanos Activity September 13, 2021
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.
General Observations
Air temperatures were approximately 70°F and skies were mostly clear and sunny with
some passing clouds. A light breeze was detected coming out of the southwest. No
concentrated surface scums or streaks were observed at the State Launch at 8:45am
when we arrived, or anywhere on the lake, but the water clarity was visibly low.
Methods
AER visited Bantam Lake to conduct biweekly cyanobacteria monitoring and monthly
water quality 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, relative phycocyanin concentration,
oxidation reduction potential, and pH at one-meter intervals from the top to the bottom
of the water column, total depth, and Secchi disk transparency. 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. 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 from North Bay and Center Lake sites 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.
Secchi Disk Transparency and Relative Phycocyanin
Secchi disk transparencies at the four sites on September 13th were between 1.40m
and 1.52m (Table 1). Those measurements were the lowest of the season for each site;
the lake average of 1.44m was also the lowest of the season (Fig. 1, top).
Phycocyanin is the photosynthetic pigment unique to the cyanobacteria and is commonly used as a surrogate for cyanobacteria biomass. The average relative phycocyanin concentrations for the top three meters of the water column at the North Bay, Center Lake, and South Bay sites were similar to the August 16th averages at those sites.
The Folly Point average on September 13th was the highest reading of the season at
any site. The September 13th lake average was also the highest of the season (Fig. 1,
bottom).
Cyanobacteria Cell Concentrations and Algal Community Characteristics
Cyanobacteria cell concentrations at the North Bay and Center Lake sites were 94,873
and 134,006 cells/mL. The lake average based on those two sites was 114,439
cells/mL. Site concentrations and the lake average were similar to those determined
for samples collected on August 16th
, prior to the second copper sulfate treatment (Fig.
2).
The CT DPH and CT DEEP (2019) associates cyanobacteria cell concentrations of
>20,000 and <100,000 cells/mL with Visual Rank Category 2 conditions, and concentrations of >100,000 cells/mL with Visual Rank Category 3 conditions. The Center
Lake concentration and average for the lake were within the Visual Rank Category 3
range, and contact with the water should be avoided. Recommended interventions in
the interest of public health can be found in the State’s guidance document for municipal health departments for blue-green algae blooms in recreational freshwater (CT
DPH & CT DEEP 2019).
Similar to our last visit,the September 13th pelagic algae community species richness
was high with 34 genera observed from seven taxa observed. A season high of 16
were from the Chlorophyta (aka Green Algae). Also similar to our last visit, cells of
Chlorophyta were rare as compared to the abundance of cyanobacteria cells. The dominant cyanobacteria continued to be Aphanizomenon spp., followed by Dolichospermum spp.; Microcystis sp. was also important at the Center Lake site. Other cyanobacteria genera observed included Aphanocapsa spp., Gomphosphaeria spp., Pseudoanabaena spp., and Woronichinia spp. Most of these genera are considered toxigenic (CT DPH & CT DEEP 2019, Cheung et. al. 2013, USEPA 2020).
Water Column Temperatures and Oxygen Characteristics
Surface water temperatures were approximately 21°C (Table 1) and the lowest since
May 25th
. The water column at all sites was thermally mixed. Oxygen concentrations
decreased with depth at the North Bay site, Center Lake site, and particularly at the
Folly Point site. The oxygen concentration at the bottom of the South Bay site was
similar to the concentration at the surface (Table 1).
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
