Cyanos Activity October 7, 2019
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 October 7th
, AER visited Bantam Lake to perform biweekly cyanobacteria
and monthly water quality monitoring as part of the ongoing lake management
program. Samples collected for algal identifications and enumerations were
from the North Bay site (N 41.71087° W -73.21155°) and Center Lake site (N
41.70056° W -73.22102°). A plankton net tow sample, using a 10µm mesh
plankton net, was also collected at the Center Lake site. Samples were treated,
stored, and analyzed following methods discussed in previous memos.
Water column profile and Secchi transparency data were also collected at the
North Bay Site, the Center Lake Site, a site west of Folly Point (N 41.70773 W -
73.22638), and in the South Bay region of the lake (N 41.69015 W -73.22728).
Five of the fifteen algal genera identified in the plankton net sample were cyanobacteria genera. Cyanobacteria cell concentrations were 169,466 cells/mL at
the North Bay site but only 51,419 at the Center Lake site. The difference was
due to one large colony (over 1,000 cells) of Aphanocapsa spp. in the North Bay
sample.
Aphanocapsa spp. cells are very small (>3µm in diameter) compared to other
cyanobacteria cells. Dolichospermum spp. for example, which has a diameter of
approximately 10µm. Using those approximate diameters (3 and 10µm), the
corresponding cellular volumes of an Aphanocapsa spp. cell and a Dolichospermum spp. cell are 14µm3 and 524µm3
, respectively. Using that ratio, 96,000
cells of Aphanocapsa spp. has the equivalent volume of approximately 2,565
cells of Dolichospermum spp. This suggests that the differences between the
two sites may not be as great when compared on a cellular volume basis.
The balance of the North Bay site cyanobacteria community was composed of
Aphanizomenon spp., Dolichospermum spp., and Woronichinia spp. Those
three genera collectively accounted for 73,894cells/mL. At the Center Lake site, those three genera collectively accounted for 51,419cells/mL and all of the
cyanobacteria cells observed that that site.
The recent cyanobacteria cell concentration at the North Bay site, including the
Aphanocapsa spp. cells, was very similar to that observed on September 23rd
.
The recent cyanobacteria cell concentrations at the Center Lake site was considerably lower than the 190,387cells/mL counted in the September 23rd sample. Cyanobacteria cell concentrations ranged from Visual Rank Category 2 at
Center Lake to Visual Rank Category 3 at North Bay. Recommended interventions for both categories can be found CT DPH & CT DEEP (2019).
Aphanizomenon spp. and Dolichospermum spp. are identified as toxigenic by
the CT DPH and CT DEEP (2019). A species of Woronichinia spp. has been documented as capable of producing toxins (iNaturalist 2019). Aphanocapsa spp.
has also been identified as toxigenic (Cheung et al. 2013).
Secchi transparencies on October 7th (Table 1) were modestly higher than those
recorded on September 23rd. The lake average on October 7th was 1.37m; the
lake average on September 23rd was 1.01m.
The water column was thermally mixed at all sites on October 7th (Table 1). Oxygen levels at all depths and at all sites were ≥6.3mg/L with the exception of the
very bottom of the Center Lake site. At the Center Lake site, anoxic conditions
were recorded at the 7.5m strata, but 6.1mg/L of oxygen at the 7m strata.
Literature Cited
Data is collected and analyzed by Aquatic Ecosystem Research, who is contracted by Bantam Lake Protective Association.
