Cyanos Activity May 12, 2023

 

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 Friday, May 12th, Brawley Consulting Group visited Bantam Lake to conduct biweekly cyanobacteria monitoring as part of the 2023 lake management program. Water column profile data, total depth measurements, and Secchi transparency data were collected from the North Bay (NB) Site (N 41.71087° W -73.21155°), the Center Lake (CL) Site (N 41.70056° W -73.22102°), and the South Bay (SB) Site of the lake (N 41.69015 W -73.22728).

A plankton tow sample using a 10μm mesh plankton net was collected at the CL Site. The concentrated plankton sample was transferred into a 25mL glass amber bottle and stored at 3°C. Approximately 500 mL of the top three meters of water column was integrated and collected for algae counts at the North Bay, South Bay and Center Lake sites using a three-meter-long sampling tube. Those samples were preserved with Lugol’s solution shortly after collection and stored at 3C.

A portion of the live phytoplankton in the net sample was carefully examined with microscopy on the same day it was collected to identify and list all algal genera present prior to any treatment or preservation. Afterwards, the net sample was preserved with Lugol’s Solution and stored. The integrated whole water samples were using treated with hydrostatic pressure. Due to the visibly high algae concentration in the lake, samples were not concentrated and whole water samples were used for algae counts.

Cyanobacteria and Algae Community

Cyanobacteria continued to dominate the surface waters at Bantam Lake with high cell concentrations. Cyanobacteria cell concentrations at the NB and CL Sites were approximately 270,000 and 261,000 cells/mL; the concentration at the SB Site was modestly lower at approximately 142,000 cells/mL. All three concentrations were characteristic of Visual Rank Category 3 (having the greatest risk to public health) according to Connecticut’s guidance for municipalities (CT DPH & CT DEEP 2021). The State advises posting beach closure signage and reporting to the State at these concentrations.

The filamentous cyanobacteria Aphanizomenon spp. continued to dominate the phytoplankton accounting for >99% of all cells counted at each site (Fig. 1). Other cyanophytes observed included Woronichinia spp., Microcystis spp., and Aphanocapsa spp. Several golden algae genera (Chrysophyta) observed in the net or whole water samples included Dinobryon spp. and Uroglenopsis spp. Diatoms encountered included the centric Stephanodiscus spp. and filamentous Aulocoseria spp. All golden algae and diatoms were rare relative to the abundance of the cyanobacteria.

Water Quality

Secchi disk transparencies continued to be unseasonably low, lower than measurements from April 23rd, and between 1.06 meters and 1.34 meters (Table 1). The top three-meter average relative phycocyanin levels were also unseasonably high. Phycocyanin is the photosynthetic pigment contain in cyanobacteria and surrogate of cyanobacteria biovolume. For comparative purposes, the lake average Secchi transparency and relative phycocyanin concentration for April 23rd and May 12th of 2023 were overlaid onto the plots of measurements from 2022. The 2023 levels are more in line with historical August and September levels.

Site Conditions

The water columns the NB and CL Sites were stratified and relative resistance to mixing was high. Oxygen concentrations near the bottom had begun to decrease but were not at anoxic levels. At the SB Site, the water column was mixed and high oxygen concentrations were observed throughout. Surface water temperatures across the lake had increased by almost 5°C since April 23rd and were between 18.6 and 19.9°C (Table 1).

Conclusions

The cyanobacteria community observed in Bantam Lake on April 26th was more characteristic of mid- to late-season conditions. The warm winter and warm conditions this spring may have advanced the timing of germination of Aphanizomenon spp. or promoted its overwintering. Filaments were long and comprised of many cells, filaments had formed rafts, and heterocysts were visible.

Plans for earlier treatments this season should be considered.

Literature Cited

Connecticut Department of Public Health and Connecticut Department of Energy and Environmental Protection. 2019. Guidance to Local Health Departments for Blue–Green Algae Blooms in Recreational Freshwaters. See https://portal.ct.gov/-/media/Departments-and-Agencies/DPH/dph/environmental_health/BEACH/Blue-Green-AlgaeBlooms_June2019_FINAL.pdf?la=en

Analyses performed by Larry Marsicano, CLM, Brawley Consulting Group, LLC contracted by Bantam Lake Protective Association.