Cyanos Activity August 31, 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 31, 2021, and results of analyses of samples collected that day. These findings come seven days following the copper sulfate treatment of August 24th.
General Observations
Air temperatures were approximately 70°F and skies were partly clear and sunny. A
light breeze was detected coming out of the west. No concentrated surface scums or
streaks were observed at the State Launch at 7:45am when we arrived, or later at the
North Bay, Center Lake, and Folly Point sites, but the water clarity was generally low.
We did observe an uncommon presence of bubbles, often in swaths, in the vicinity of
the Center Lake Site. We can not be sure
of the cause of the surface bubbles, but it
may be related to high concentrations of
cyanobacteria cells (viable and senesced
from the treatment) and agitation by motorboats.
The South Bay Site is the last we visit during each visit. By the time we arrived at
this site on August 31st (approximately
9:30am), streaks of cyanobacteria were
visible (Fig. 1). An additional sample was
collected here, but not by integrating the
top three meters of the water column, but
rather by lowering the sample bottle to collect the very surface of the water column,
where the streaks were visible.
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. An additional sample was collected at the
South Bay site but only from the very surface of the water column as noted above.
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 August 31st were between 1.90m and
1.92m (Table 1). The measurements and lake average were approximately 30cm
greater than corresponding August 16
th data, but still in the same range observed since
July 19th (Fig. 2).
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 each site were between 9 and 12µg/L; the lake average was 10.6µg/L. These relative concentrations
were modestly lower than those measured on August 16th (Fig. 2).
Cyanobacteria Cell Concentrations and Algal Community Characteristics
Cyanobacteria cell concentrations on August 31st at the North Bay and Center Lake
sites, were 76,999 and 99,235 cells/mL; the average of the two sites was 88,117
cells/mL and lower than the August 16th average (Fig. 3). The decrease in cell concentrations between August 16th and August 31st was similar to the decrease observed between July 19th and August 3rd (Fig. 3). It was between those two sets of dates when
the copper sulfate treatments occurred.
Concentrations measured on August 31st spanned Visual Rank Category 2 and 3 in the
State of Connecticut’s guidance for Health Departments (CT DPH & CT DEEP 2019).
Visual Rank Category 2 cell concentration are >20,000 and <100,000 cells/mL. Visual Rank Category 3 cell concentrations are >100,000 cells/mL. Recommended interventions for both categories can be found in the State’s guidance document (CT DPH
& CT DEEP 2019). It should be noted that the cell concentration at the South Bay Site,
where streaking was observed (Fig. 1), was within the Visual Rank Category 3 range.
Contact with the water when conditions are similar to these should be avoided
The algal community was very diverse with 31 different genera from seven taxonomic
groups identified. A season high of 14 different Chlorophyta (aka Green Algae) were
identified. However, cells of species from the Chlorophyta were rare as compared to
the abundance of cyanobacteria cells. The dominant cyanobacteria continued to be
the filamentous Aphanizomenon spp., followed by Dolichospermum spp. Other cyanobacteria genus observed included Aphanocapsa spp., Gomphosphaeria spp., Microcystis 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 Temperature and Oxygen Characteristics
Surface water temperatures are slowly decreasing. The August 31st surface water temperature at all sites was 24.2°C and lower than those of August 16th which were between 25 and 26°C. Most recent temperatures at the bottom of the water column are
approximately one degree warmer than they were on August 16th indicative of mixing
of the water column. The water column at the South Bay Site was thermally mixed. At
the Center Lake Site, resistance to mix at the thermocline was still strong (RTRM >80)
but the thermocline was a meter lower than observed on August 16th
. The thermoclines at the North Bay and Folly Point Sites were also lower in the water column and
less resistant to mixing than observed on August 16th
. Oxygen concentrations below
the thermocline were ≤0.2mg/L (Table 1). At the mixed South Bay Site, the oxygen concentration near the bottom was 5.5mg/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
