Cyanos Activity September 29, 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.
General Observations and Summary
Air temperatures were approximately 50°F and skies were clear. Winds of approximately 5mph were out of the northwest. Concentrated surface scums or streaks were
not observed at the State Launch at 8:15am when we arrived, or anywhere on the lake.
The water clarity appeared to have improved since our last visit of September 13th
. Algae counts confirmed that observation with cyanobacteria cell concentrations at the
North Bay and Center Lake sites of 34,229 and 34,327 cell/mL, respectively.
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, 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 29th were between 1.67m
and 2.06m (Table 1). These data and the lake average of 1.82m were improvements
over conditions of September 13th (Fig. 1, top).
Phycocyanin is an auxiliary 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 all sites were
between 8.1 and 9.4 µg/L. The lake average of 8.6 µg/L was down from the 14.1 µg/L
lake average of September 13th (Fig. 1, bottom). This indicates that the relative biomass
of the cyanobacteria had decreased since the last sampling event on September 13th
.
Cyanobacteria Cell Concentrations and Algal Community Characteristics
Cyanobacteria cell concentrations at the North Bay and Center Lake sites were 34,229
and 34,327 cells/mL. The lake average based on those two site concentrations was
34,278 cells/mL. This represents an average decrease in cell concentration of approximately 80,000 cyanobacteria cells/mL since September 13th (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. Both the
North Bay and Center Lake site concentrations and average for the lake were within
the Visual Rank Category 2 range. Recommended interventions for this and other categories, 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).
The pelagic algae community species richness continues to be high with 35 genera
observed and distributed across seven taxa observed. Nine and thirteen were from the
Cyanophyta and Chlorophyta (aka Green Algae), respectively. Although the numbers
of genera observed for each tax were similar, cell concentrations for the two taxa were
very different. Cyanobacteria comprised 97 and 95% of all cells counted in the North Bay and Center Lake Site samples, respectively; Chlorophyta comprised, respectively, 1
and 3% of all cells counted.
Filamentous cyanobacteria, including Aphanizomenon spp., Dolichospermum spp., and
Pseudoanabaena spp. were three of the four most abundant genera. The other important genus was Aphanocapsa spp. These cyanobacteria forms colonies of very
small spherical cells (≤2µm in diameter) irregularly distributed within mucilage. Other
cyanobacteria genera observed included Chroococcus spp., Gomphosphaeria spp.,
Planktothrix spp., and Woronichinia spp. Most of these genera are considered toxigenic (CT DPH & CT DEEP 2019, Cheung et. al. 2013, USEPA 2020).
Water Column Temperature and Oxygen Characteristics
The water column at all four sites was isothermal, i.e. the same temperature was measured from the surface to the bottom. Temperatures varied modestly between sites (Table 1). Oxygen concentrations were also similar throughout the water column at each
site. The lowest oxygen concentration at the bottom was 6.4 mg/L measured at the
Folly Point Site. Oxygen concentrations at the bottom of the other three sites were
≥6.7 mg/L.
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
