Cyanos Activity September 21, 2020

 

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.







On Wednesday, September 21st , 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. Our methods of preparing and counting algae cells have been discussed in earlier memos. 

A surface algae bloom was observed across much of the lake at the time of our arrival at 8:30am (Figs. 1 and 2). The surface film was still visible at the time of our departure at 10am. The surface film was not thick, but clearly visible, with the most visible areas located in the South Basin and in the center portion of the lake in the vicinity of the Center Lake Site. These types of visible conditions are considered Visual Rank Category 3 conditions and the following interventions are recommended (CT DPH & CT DEEP 2019):
  • Update/inform CT DPH & CT DEEP and expand risk communication efforts.
  • Collect samples for analysis and/or increase frequency of visual assessment.
  • POSTED BEACH CLOSURE: If public has beach access, alert water users that a blue-green algae bloom is present.
Secchi transparencies at the individual sites and the lake average were the lowest of the season (Fig. 2). The lowest transparency on September 21st of 0.99m was measured at the South Bay Site and the highest of 1.20m was measured at the North Bay Site. Secchi transparencies at the other two sites were similar (Table 1). 

Cyanobacteria cell concentrations were not >100,000 cells/mL, which is characteristic of Visual Rank Category 3 conditions, but instead were 49,169 and 82,844 cells/mL at the North Bay and Center Lake Sites, respectively. It is important to remember that these numbers reflected concentrations of samples that were integrations of the top three meters of the water column. Concentrations of just the surface film were most likely higher. The recent cell concentrations and average for the lake were similar to those in samples collected on September 9th (Fig. 3).

Relative concentration of phycocyanin, which is the signature photosynthetic pigment of Cyanobacteria, was measured on September 21st in situ with the fluorimeter that is part of the sensor array in AER’s field instrumentation. Measurements from the top three meters of the water column were averaged for each site and presented in Fig. 4. Individual site concentrations and the lake average concentration were the highest of the 2020 season. 

The Cyanobacteria Dolichospermum spp. comprised nearly 50% of all cells counted at both the North Bay and Center Lake Sites. Cells of this genus are relatively large which may explain the relatively higher phycocyanin concentrations. Cyanobacteria collectively comprised 93 and 95% of all cells counted at the North Bay and Center Lake Sites, respectively. Aphanizomenon spp., Coelosphaerium spp., and Woronichinia spp. were the other Cyanobacteria genera observed or counted in the September 21st samples. 

The Cyanobacteria genera observed in the September 21st samples have been described as having toxigenic properties (CT DPH & CT DEEP 2019, Cheung et.al. 2013, iNaturalist 2019).

Profile data revealed that the lake was thermally mixed with temperatures nearly uniform from top to bottom (Table 1). Anoxic conditions still prevailed at the very bottoms of the North Basin and Center Lake Sites. At the Folly Point and South Bay Sites, oxygen concentrations at the bottom were very similar to those measured at 1m of depth. 

In summary, the on-the-water assessment were clearly indicative of Visual Rank Category 3 conditions. These conditions were supported by the lowest Secchi transparencies and highest relative phycocyanin concentration of the season measured at all sites. Cell concentrations in the 3-meter integrated samples collected at the North Bay and Center Lake Sites were indicative of Category 2 conditions (CT DPH and CT DEEP 2019) but were still high, particularly in the Center Lake Site. A water sample of just the top several centimeters of the water column, where the surface bloom was observed, would most likely had higher cell concentrations that may have exceeded 100,000 cells/mL. Contact with the types of conditions observed on the morning of September 21st should be avoided by both people and pets. 

Literature Cited 

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 

[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 

iNaturalist. 2019. Woronichinia. See https://www.inaturalist.org/guide_taxa/700578

Data is collected and analyzed by Aquatic Ecosystem Research, who is contracted by Bantam Lake Protective Association.

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