Cyanos Activity July 30, 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 July 30, 2018, AER visited Bantam Lake to collect profile data and algae samples as part of the ongoing lake monitoring initiative. This sampling event came four days following treatments for aquatic invasive plants and algae on July 26th. Copper sulfate was used to treat the cyanobacteria populations. 

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 were collected at the North Bay and Center Lake sites. Algae samples were analyzed by methods described in a prior memo. 

Cyanobacteria cell concentrations were down markedly from those observed on July 16th. The cyanobacteria cells concentrations at the North Bay and Center Lake Sites were 4,883 and 3,063 cells/mL and represented 75 and 76% of all algal cells counted in those samples, respectively. July 30th cyanobacteria cell concentrations at the North Bay and Center Lake sites were approximately 71% and 87%, respectively less than those observed in samples collected on July 16th . 

Bantam Lake waters appeared visually clearer than observed on July 16th . July 30th Secchi transparencies ranged from 2.40m to 3.00m and averaged 2.77m. As has been the case all season, the South Bay site had the lowest Secchi transparency; Secchi transparency at the other sites ranged from 2.76m to 3m. 

The cyanobacteria genera Aphanizomenon spp., Dolichospermum spp., and Woronichinia spp. continued to be the most abundant genera at both sites. Although treatment preceded sampling by four days, most of the algal cells, including cyanobacteria, were viable suggesting that the remnants of the treated algae had settled out of much of the water column and new living cells were filling in the niche. As noted in earlier memos, the three dominant cyanobacteria genera can form blooms and produce toxins.  

The relative abundances of the cyanobacteria were down from July 16th while abundances of green algae (Chlorophyta), golden algae (Chrysophyta), and diatoms (Bacillariophyta) were up. This suggests that the copper sulfate treatment may have, at least temporarily, improved the competitiveness of non-cyanobacteria algae. 

Surface water temperatures cooled modestly at all sites. Surface temperatures that ranged from 27.3 to 27.9°C on July 16th ranged from 25.6 to 26.0°C on July 30th. Bottom water temperatures at the North Bay and Point Folly sites, where maximum depth is between 6 and 7m, were elevated compared to July 16th. Bottom temperature at the Center Lake site where the depth was just over 8m did not change from July 16th; while bottom temperatures at the South Bay site were just over 1°C cooler. 

The water temperature data indicated that the thermocline is between 6 and 7 meters. Mixing of the water column transferred heat to those depths, thereby increasing temperature at the North Bay and Point Folly sites. Since the lake is still stratified, bottom temperatures at the deep site (i.e. the Center Lake site) have not appreciably changed. At the South Bay site, a more thorough mixing of the water column because of the shallower depth lowered water temperatures at the bottom compared to July 16th temperatures. 

At the North Bay, Center Lake and Point Folly sites, oxygen levels were between 3 and 5mg/L at 5m depth but <1mg/L from 6m to the bottom. However, at the South Bay site, oxygen levels were 6.7 at 4m depth but >1.0mg/L at 4.5m depth, despite a thermally mixed water column. 

Overall, the water quality has improved in regards to the algal community; however, the community is still dominated by the cyanophyta, which suggests that the algal community should still be monitored with vigilance because the genera dominating the community can quickly cause bloom conditions.

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

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