Cyanos Activity September 11, 2018

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 Tuesday, September 11, 2018, AER visited Bantam Lake to conduct biweekly cyanobacteria monitoring as part of the ongoing lake management program. Water column profile data 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 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 were collected at the North Bay and Center Lake sites as contracted. An additional sample was also collected at the South Bay site since Secchi transparencies there have, at times, been lower than transparencies at the other three sites suggesting that there could be greater algal productivity. Algae samples were analyzed by methods described in an earlier memo. 

The cyanobacteria cell concentrations of September 11th continued to be elevated and similar to concentrations determined for samples collected on August 27th (Fig. 1). The highest concentration on September 11th was at the Center Lake Site, followed by the South Bay Site, and the North Bay Site (Table 1). Cyanobacteria dominated the plankton comprising 90% of the all algae at the North Bay Site, 98% at the South Bay Site, and 99% at the Center Lake Site. 

The most abundant genera were Aphanizomenon spp. followed by Dolichospermum spp. Both grow as linear colonies or filaments; both can regulate buoyancy, fix atmospheric nitrogen, and produce cyanotoxins. Aphanizomenon cells are small but filaments can form rafts which can be visible to the naked eye. 

Upon arrival at 10am on September 11th conditions were very calm such that no ripples were observed on the lake. Cyanobacteria (Aphanizomenon rafts, etc.) were visible in the water but no surface scums were detected in the area of the State Boat Launch. By 11am when we reached the fourth sampling site, the South Bay Site, a very light breeze and ripples were observed. A definitive surface scum was encountered at the State Boat Launch at approximately 11:45am and due likely to the light breeze “packing” the cyanobacteria floating on the surface along the shoreline. A sample of the scum was collected at the State Boat Ramp and will be analyzed to determine cell concentrations in the very near future. 

The cyanobacteria cell concentrations at the Center Lake and South Bay Sites were within the 20,000 – 100,000 cells/mL range for Visual Rank Category 2 designation. Increased regular visual assessments and cautionary postings at public access points are advised by the State under these conditions. Bloom conditions observed at the State Boat Ramp were characteristic of Visual Rank Category 3 and under these conditions posting of beach closure is advise by the State. Examples of cautionary and beach closure signage are available in https://www.ct.gov/deep/lib/deep/water/water_quality_management/monitoringpubs/bluegreenalgaeblooms_guidanceforlhds_2017version.pdf). 

 Secchi transparencies on September 11th were the lowest observed this season, ranging from a high of 1.57m at the North Bay Site to 1.34 at the South Bay Site. The average for all four sites was 1.44m. It is worth noting that there was little to no sunshine and considerable cloud cover during our time on the water which also contributed to the reduce transparency. 

Surface water temperatures had dropped by approximately 4°C since August 27th . Bottom water temperatures at each site were within 1.6°C of surface water temperatures indicating that the water column had mixed from top to bottom. These mixed conditions were also reflected in oxygen concentrations which ranged from 8.7 to 6.8mg/L anywhere in the water column at the Center Lake, Point Folly, and South Bay Sites. At the North Bay Site, oxygen concentrations of >6mg/L were measured throughout the water column except at the very bottom (6 meters) where anoxic conditions were observed.

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