Cyanos Activity June 6, 2022
Water is clean for recreation.
On Monday June 6th, AER visited Bantam Lake to conduct monthly water quality moni-toring and biweekly cyanobacteria monitoring as part of the ongoing lake manage-ment program. Water column profile data, total depth measurements, 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 Folly Point (N 41.70773 W -73.22638), and at a site in the South Bay region of the lake (N 41.69015 W -73.22728).
A plankton tow sample using a 10μm mesh plankton net was collected at the Center Lake site. The concentrated plankton sample was transferred into a 25mL glass am-ber bottle and stored at 3°C. Approximately 500mL of the top three meters of water column was integrated and collected for algae counts at both the North 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 3°C.
A portion of the live phytoplankton in the net sample was carefully examined with mi-croscopy on the same day it was collected to identify and list all algal genera present prior to any treatment or preservation. The integrated whole water samples were pre-pared and analyzed as described in our April 15, 2022 memo
General Conditions
Little to no wind was encountered and skies were mostly clear with occasional passing clouds. Air temperatures during our time on the lake rose from approximately 15.6 to 21.1°C (approximately 60 to 70°C; White Memorial Conservation Center - KCTLITCH9). Bloom-like conditions were not observed at the State ramp at the time of launching. However, patches of what appeared to be algae bloom were regularly observed on the open water (Fig. 1). A cyanobacteria bloom had formed at the State ramp by the end of the trip (Fig. 2).
The open water bloom-like material had a grainy appearance. That, and the time of
year, raised the question of whether this was cyanobacteria algae forming a bloom or
pollen that regularly collects on the surface of lakes in the late spring / early summer.
Despite the floating matter at the surface, water clarity was very good. Secchi transparencies
at the North Bay, Center Lake, and Folly Point sites were between 3.5 and
3.9 meters. This indicates that algal concentration below the surface were relatively
low. The South Bay site was more turbid (Table 1).
Cyanobacteria and Algae Community
A total of 35 algae genera were observed between the net tow and concentrated whole
water samples, which was the highest total thus far for the 2022 season. As is common
in lakes of the Northeast, Chlorophyta (aka green algae) had the greatest richness
(numbers of genera) with 14 genera observed. Cyanophyta (aka blue-green algae
or cyanobacteria) and Bacillariophyta (aka diatoms) were both represented by seven
genera. Four other taxonomic groups were represented by three or less genera.
The most abundant taxon was the cyanobacteria. Cell concentrations of 12,390 and
6,700 cyanobacteria cells/mL were determined for the North Bay Site and Center Lake
Site, respectively, which represented approximately 92% and 87% of all cells counted at
the respective sites. Cyanobacteria concentrations at both sites were within the range
that characterizes Visual Rank Category 1 conditions. Connecticut’s Visual Rank Category
system characterizes conditions from Category 1 (good conditions) to Category 3 (conditions that present great enough health risk to warrant beach closure signage;
(CT DPH & CT DEEP 2021). There are no recommended interventions for Category 1
conditions.
Aphanizomenon spp. (Fig. 4) was the most abundant cyanobacteria based on cell concentration.
This genus alone constituted 62% and 36% of all cells counted in the North
Bay and Center Lake samples, respectively. Most Aphanizomenon spp. cells are very
small and linearly arranged into filaments, which group together forming rafts (Fig. 2).
Rafts disassemble into single filaments once the samples are preserved with Lugols.
Other cyanobacteria genera observed in the May 23rd samples included Planktothrix
spp., Dolichospermum spp., Woronichinia spp., and Aphanocapsa spp.
This genus alone constituted 62% and 36% of all cells counted in the North
Bay and Center Lake samples, respectively. Most Aphanizomenon spp. cells are very
small and linearly arranged into filaments, which group together forming rafts (Fig. 2).
Rafts disassemble into single filaments once the samples are preserved with Lugols.
Other cyanobacteria genera observed in the May 23rd samples included Planktothrix
spp., Dolichospermum spp., Woronichinia spp., and Aphanocapsa spp.
A sample of the bloom at the State Launch was collected and also examined with microscopy
and photographed. Cell concentrations were estimated to be above the Visual
Rank Category 3 levels of 100,000 cyanobacteria cells/mL. The sample was dominated
by Dolichospermum spp. (Fig. 4). Other cyanobacteria genera observed in the
bloom included Woronichinia spp. and Microcystis spp. Tree pollen was also observed
(Fig. 5).
and photographed. Cell concentrations were estimated to be above the Visual
Rank Category 3 levels of 100,000 cyanobacteria cells/mL. The sample was dominated
by Dolichospermum spp. (Fig. 4). Other cyanobacteria genera observed in the
bloom included Woronichinia spp. and Microcystis spp. Tree pollen was also observed
(Fig. 5).
Water Column Conditions
Surface water temperatures increased by several degrees since May 23rd and were all
between 21.8 and 22.1°C (Table 1). The water column at all four sites was stratified with
a thermocline observed between 4 and 5 meters of depth at the North Bay, Center
Lake, and Folly Point sites. Resistance to mixing (RTRM value) at the thermocline was
high at these three sites. At the South Bay site, the thermocline was detected between
3 and 4 meters of depth and resistance to mixing was moderate.
Oxygen concentrations below the thermocline rapidly decreased to <1mg/L by the bottom
of all sites except at the South Bay site where bottom oxygen was 3.4mg/L.
Literature Cited
Connecticut Department of Public Health and Connecticut Department of Energy and
Environmental Protection. 2021. Guidance to Local Health Departments for Blue–Green
Algae Blooms in Recreational Freshwaters. See https://portal.ct.gov/-/media/Departments-
Data is collected and analyzed by Aquatic Ecosystem Research who is contracted by Bantam Lake Protective Association.
