Cyanos Activity August 3, 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.
Below we have provided a summary of findings from our visit on Tuesday, August 3,
2021 and of analyses of samples collected that day. These findings come five days following the copper sulfate treatment of July 29th. Copper sulfate is an algaecide and
used historically at Bantam when cyanobacteria (aka Blue-green algae) concentrations
are high.
General Observations
For the second consecutive visit, skies were overcast and air temperatures were unseasonably low (~70°F). No concentrated surface blooms were observed but the water
clarity appeared low, and pockets of the lake appeared to have more floating material
(dead insects, leaves, and some algae) than others.
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, 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 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 on August 3rd were between 1.72m and 1.89m at the four
sites (Table 1) and very similar to those recorded on July 19th when Secchi transparencies were between 1.68m and 1.94m (Fig. 1, top).
Phycocyanin is a photosynthetic pigment found in cyanobacteria and a surrogate for
cyanobacteria biomass. Since a primary standard is not used in instrument calibration,
the values across sites and dates are relative. Measurements were made at 0.5 meter
from the surface and at one-meter intervals down to 0.5 meters above the bottom. The
average of readings from the top three meters of the water column at each site were
calculated. Those site averages were used to determine a lake average. Those data
have been plotted along with the corresponding data from the earlier sampling dates
(Fig. 1, middle).
The site average relative phycocyanin concentrations of August 3rd were notably lower
than those observed on July 19th, with the exception of North Bay average. The lake average was also down from that on July 19th and similar to that of July 6th (Fig. 1, middle).
This suggests that the July 29th treatment reduced the average biomass of cyanobacteria in the lake.
Cyanobacteria Cell Concentrations and Algal Community Characteristics
Cyanobacteria cell concentrations on August 3rd were lower than concentrations on
July 19th (Fig. 1, bottom). The August 3rd lake average of 46,593 cells/mL was approximately half of the July 19th average. Cell concentrations at both the North Bay and Center Lake sites on August 3rd were within the Visual Rank Category 2 levels. Recommended interventions for that category can be found in the State’s guidance document (CT DPH & CT DEEP 2019).
Most of the cyanobacteria cells counted were Dolichospermum spp. or Aphanizomenon spp., two filamentous genera that are frequently found at Bantam Lake.
Other Cyanobacteria genera encountered in samples included Aphanocapsa spp.,
Gomphosphaeria spp., Microcystis spp., Planktothrix spp., Pseudoanabaena spp., and
Woronichinia spp. Most of these genera are considered toxigenic (CT DPH & CT DEEP
2019, Cheung et. al. 2013, USEPA 2020).
Ten different genera of Chlorophyta (Green Algae), and three different genera of both
Chrysophyta (Golden Algae) and Pyrrhophyta (Dinoflagellates) were observed. A total
of five other genera from three different taxa were also observed. Cell concentration of
genera other than Cyanobacteria were a minor contributor to the algal community. Cyanobacteria comprised 97% and 89% of all cells counted at the North Bay and Center
Lake sites, respectively.
Water Column Temperatures and Oxygen Characteristics
Water temperatures near the surface on August 3rd, which were between 23 and 23.2°C
(Table 1), had decreased by approximately 2°C since July 19th; temperatures at the bottom of the water column were similar to those measured on July 19th
. The water at all
sites was mixed down to 5m of depth (the entire South Bay site water column was
mixed). A thermocline with strong resistance to mixing was located between 5 and 6m
of depth. Oxygen concentrations at the bottom of the water column at all sites but the
South Bay site were <1mg/L (Table 1). At the South Bay site, the oxygen concentration
at the bottom of the water column was 6.8mg/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
