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.
