Cyanos Activity October 5, 2020
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.
On Monday, October 5th
, AER visited Bantam Lake to conduct biweekly Cyanobacteria
monitoring. Water column profile data, total depth measurements, and Secchi transparency data were collected from 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 500mL composite sample of the top three meters of water column was collected for
algae counts at the North Bay and Center Lake Sites using a three-meter long sampling tube. Additionally, a concentrated plankton tow sample, was collected at the
Center Lake Site using a 10µm mesh net. The concentrated plankton sample was
transferred into a 25mL glass amber bottle, stored at 3°C, and preserved with Lugols
after an examination with microscopy. Methods of preparing samples and performing
algae counts have been discussed in earlier memos.
Conditions appeared modestly improved since our last visit on September 21st when a
distinct surface film was present. No surface film was visible on October 5th but algal
concentrations in the water did appear high.
Secchi transparencies at the individual sites and the lake average increased from
those measured on September 21st (Fig. 1). The lowest transparency on October 5th of
1.38m was measured at the South Bay Site and the highest of 1.68m measured at the
Center Lake Site. Secchi transparencies at the other two sites were similar (Table 1).
Cyanobacteria cell concentrations were 46,044 and 39,415 cells/mL at the North Bay
and Center Lake Sites, respectively. Site concentrations and the lake average were
lower than those on September 21st (Fig. 2). Concentrations were characteristic of Visual Rank Category 2 conditions (CT DPH & CT DEEP 2019). The recommended response for this category are:
- 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)
As we have done all season, the average relative phycocyanin1
levels at each site were
determined fluorimetrically from the top three meters of the water column and compared between sites and dates (Fig. 3). The October 5th levels were on average lower
than September 21st levels. The reduced levels were consistent with the lower cell concentrations and increased Secchi transparencies.
The October 5th algae community at the North Bay Site was dominated by the Cyanobacteria (98% of all cells), with the genera Dolichospermum spp. and Aphanizomenon
spp. comprising 73% and 19% of all cells, respectively. At the Center Lake Site, Cyanobacteria comprised 82% of all cells with Aphanizomenon spp. and Dolichospermum
spp. the co-dominant genera at 40% and 35% of the total, respectively. Other less important Cyanobacteria genera observed in the counts or in the net sample included
Coelosphaerium spp., Microcystis spp., and Woronichinia spp.
Akinetes were commonly observed on the filaments of Dolichospermum spp. (Fig. 4).
Formation of akinetes occurs within the life cycle of nitrogen-fixing Cyanobacteria like
Dolichospermum spp. after the exponential growth phase when filaments begin to senesce (Kortmann 2015). This may explain the decrease in cell concentrations and relative phycocyanin concentration, and the modest increase in Secchi disk transparency.
Profile data collected at the four sites indicated that the lake was completely mixed
(Table 1). Oxygen concentrations exceeded 5mg/L at all sites and depths.
1Phycocyanin is the signature photosynthetic pigment of Cyanobacteria.
Data is collected and analyzed by Aquatic Ecosystem Research who is contracted by Bantam Lake Protective Association.
Literature Cited
[CT DPH & CT DEEP] Connecticut Department of Public Health and Connecticut Department of Energy and Environmental Protection. 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/BlueGreen-AlgaeBlooms_June2019_FINAL.pdf?la=en
Kortmann, RW. 2015. Cyanobacteria in Reservoirs: Causes, Consequences, Controls.
Journal of the New England Water Works Association. 129:73-90.
