Cyanos Activity September 24, 2018

Water is clean for recreation.

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, September 24, 2018, AER visited Bantam Lake to conduct biweekly cyanobacteria and monthly water quality monitoring as part of the ongoing lake management program. Water column profile data and Secchi transparencies 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 Point Folly (N 41.70773 W -73.22638), and at a site in the South Bay region of the lake (N 41.69015 W -73.22728). Algae samples and other water samples were collected at the North Bay and Center Lake sites. An additional algae sample was collected at the South Bay site. Algae samples were analyzed by methods described in an earlier memo. 

Cyanobacteria cell concentrations on September 24th were approximately one-third of those observed on September 11th (Fig. 1) and within the Visual Rank Category 1 threshold of 20,000 cells/mL. The lowest concentration was observed at the North Bay Site and the highest at the Center Lake Site (Table 1). Cyanobacteria cell concentrations on September 11th were similar to those observed in the weeks following the late July copper sulfate treatment, and to those prior to late June when cyanobacteria concentrations began increasing. Dominant cyanobacteria genera were Aphanizomenon spp. followed in importance by Dolichospermum spp. 

Despite the lower cyanobacteria cell concentrations, Secchi transparencies did not improve from September 11th readings. The September 24th lake average was 1.53m with the greatest measured at the Point Folly and North Bay sites, and the lowest Secchi transparency observed at the South Bay sit (Table 1). On September 11th Secchi transparency ranged from a high of 1.57m at the North Bay Site to 1.34 at the South Bay Site and averaged 1.44m. 

Since September 11th, considerable amounts of rain have fallen within the Bantam watershed. The White Memorial Conservation Center Weather Station reported over 4 inches of rain on September 12th alone. It is conceivable that the volume of water flowing through the lake during this time has flushed out much of the cyanobacteria in the water column. Low Secchi transparencies may be due to elevated levels of detritus and inorganic particulate matter in the water column from runoff from the watershed. These were noted while performing the algal analyses. 

The water column was completely mixed at three of the four sites and almost completely mixed at the fourth site. Surface water temperatures ranged from 19 to 19.6°C and bottom temperatures ranging from 19.4 to 18.9°C (Table 1). Oxygen levels between 7.9 and 6.7mg/L were observed everywhere in the water column at the Center Lake, Point Folly, and South Bay sites. At the very bottom of the North Bay site an oxygen reading of 0.2mg/L was recorded. 

In an effort to better understand the life stages of cyanobacteria in Bantam Lake, efforts were given in noting the presence of akinetes. Akinetes are specialized cells of some genera of cyanobacteria (e.g. Dolichospermum spp. and Aphanizomenon spp.) that will over winter in the sediments in depths down to 3 to 4m. Akinetes are formed before the rest of the cells senesces. Akinetes were readily observed in the net samples and whole water samples concentrated for cell counts (see Fig. 2).

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

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