Bottle with Sandy Lake water
Click on images for larger version. Viewed at max size, individual clumps of cells/colonies appear as small beads – approx 0.25 mm diameter, they can just be discriminated with the naked eye.
Circumstantial evidence suggests the appearance of “green aggregations” on the shoreline on the west side of the lake followed fall turnover of the water column, bringing up phosphorus-rich water from the hypolimnion which stimulated growth of a nitrogen-fixing BGA (Cyanobacterium), the ID confirmed by specialists to be Dolichospermum flos-aquae.
On Thursday, Nov 7th of 2024, D.S., a resident of Sandy Lake, arrived at my doorstep with a small bottle of Sandy Lake water he had collected along the shore on the west side of the lake in the late afternoon of Nov 6th.
It had a very distinctive layer of green near its top (pic at right).
“Green Aggregations” by the shore, west side of Sandy Lake
Nov 6, 2024
He showed me photos of where he had sampled. The next day, he said, it was gone.
I put some drops from the green layer under my Dissection Microscope and could just barely see the individual cells. That characteristic (very small cells) and the pattern of clumping of filaments of cells suggested to me it was a BGA (Blue Green Alga) aka “Cyanobacteria”.*
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*While the term BGA (Blue Green Algae) remains in common use today, these organisms are more correctly (scientifically) described not as algae but as a type of bacteria in the Phylum “Cyanobacteria“. These are photosynthetic bacteria, the light-capturing pigments sometimes giving them a blue-green colour, hence the common name.
On Friday I took the sample to Prof. Linda Campbell at Saint Mary’s University* and we examined a drop under a Light Microscope, allowing us see details needed for identification. She was fairly certain that it was a Cyanobacteria species in the genus Dolichospermum (older genus name: Anabaena), noting the “yellowish heterocysts and the tight coils in the photos which are quite indicative” and suspected it could be either D.lemmermannii or D. flos-aquae. We could see no other morphological types/species. She sent photos to a colleague, Dr. Michael Agbeti at Bio-Limno.com who identified it as Dolichospermum flos-aquae (often cited without the hyphen as “D. flosaquae”).
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*Beginning in July of this year, we (the volunteers conducting limnological observations at Sandy Lake) have been collaborating with Prof. Linda Campbell at Saint Mary’s University to facilitate their using Sandy Lake as a study site/topic for her class in Aquatic Environments. Margaret McNeil, Instructor for the class, accompanied us on our Aug 12 sampling; she took some class samples for chemical and biological analyses and in early October the class took samples along the shore of Sandy Lake Beach Park for examination/identification of zooplankton and algae (including BGA). So I suspected that Prof Campbell & Co. would be very interested in the ‘little bottle’ that D.S. had brought to me. Indeed they were, and we are collaborating on some followup sampling.
Photos from Dissection Microscope (left) and Light Microscope (right). At left, Individual clumps of cells readily visible, filaments are barely visible. At right, we can distinguish individual cells and filaments. The yellowish, empty-looking cells on the image at right are “heterocysts” which are sites of Nitrogen Fixation. They are stimulated to form at low levels of available N in the water and/or low N:P ratios.
About Dolichospermum species
Extracts From iNaturalist: Dolichospermum
Description
Dolichospermum (formerly Anabaena) is a cyanobacteria genus that is commonly found in freshwater phytoplankton assemblages. In nutrient-rich lakes it can form dense blooms…The cells are joined together end-to-end to form long, unbranched filaments that are surrounded by clear, often transparent mucilage. Depending on the species, the filaments can be straight, bent, coiled, or irregularly twisted, and may be solitary or aggregated into tangled clumps
In addition to ordinary (vegetative) cells, the filaments may contain pale blue heterocytes (also called heterocysts) and large, granular, thick-walled akinetes. Heterocytes are specialized cells that convert dissolved nitrogen gas into ammonium that can be used for cell growth. Akinetes are resting cells that are resistant to cold temperatures and other unfavorable environmental conditions, and can overwinter in lake sediments. Heterocytes, and especially akinetes, are used to identify Dolichospermum (and Anabaena) to species.
Ecology
Dolichospermum blooms often form during warm, calm weather in lakes and ponds with relatively high nutrient concentrations (nitrogen or phosphorus) or low nitrogen to phosphorus ratios (N:P<15)…Because Dolichospermum is capable of converting dissolved nitrogen gas ammonium, it can dominate blooms when inorganic nitrogen (ammonium, nitrate, and nitrite) is limiting to other types of algae.Toxicity
Dolichospermum cells may produce microcystins (liver toxin), cylindrospermopsin (liver toxin), anatoxins (nerve toxin), saxitoxins (nerve toxin – paralytic shellfish toxin group), lipopolysaccharides (skin irritants), and BMAA (beta-Methylamino-L-alanine; nerve toxin). These toxins are released into the ambient environment when the cell wall is disrupted (cell lysis)…Higher water temperatures and light appear to be associated with increased toxin production. Not all Dolichospermum blooms result in the release of toxins.
Dolichospermum flos-aquae is known to form blooms in Canadian fresh waters along with associated toxins.*
*See Table 1 in Blooming algae: a Canadian perspective on the rise of toxic cyanobacteria
FR Pick, 2016 in Can. J. Fish. Aquat. Sci. 73: 1149–1158
What caused the bloom?
Nitrogen-fixing aquatic cyanobacteria such as Dolichospermum flos-aquae are commonly “phosphorus limited” and so are stimulated by elevated P (phosphorus) levels. Pick 2016 comments that “According to the model of Downing et al. (2001), the risk of
cyanobacterial blooms rises rapidly when TP is between 20 and 30 ug·L−1″. (TP: Total Phosphorous). Historically, Sandy Lake has had TP levels well below 20 ug/L (AECOM 2014) and it does not have a history of BGA blooms; while there have been warnings issued, there have been no confirmed cases to date (Post Mar 21, 2023), so this occurrence, assuming it is accepted as legitimate, will be the first confirmed case.
In NS, we generally associate BGA blooms with the ‘hot days of summer’, not with the cool days of November! In 2024, the number of “reports” of BGA in NS were highest in June and July:
Number of “Reports” of BGA in NS by month for 2024*
| Month | No. Reports |
| May | 3 |
| June | 13 |
| July | 15 |
| Aug | 9 |
| Sep. | 10 |
*From stats in section on “Blue-green algae reported in 2024” on Blue-green algae, a page on the Government of Nova Scotia website. These reports from citizens are followed up with formal testing only if drinking water is affected, so some of them could have been blooms of photosynthetic organisms other than BGA. No reports are cited for October. The final report listed for Sep 2024 is for “Sandy Lake, nearest Community: Hammonds Plains” – this appears to refer to the “other Sandy Lake” in the area, which lies approx 6 km to the northwest of Sandy Lake (Bedford).
Nov 6th, 2024 was an unusually warm day, air temperatures reaching 20 degrees in the Halifax area, so perhaps that was a factor, the shallower areas of the lake warming up. D.S. noted “green aggregations” in the water along a limited length of the shoreline and only close to the shore (approx 0 to 1 meter or less out) but his observations were made on foot and he did not look further out in the lake or further along the shoreline. He said the wind was blowing from the NW. The following day the temperature fell to about 7 degrees air temperature, and D.S. said that he did not see blooms along the shore on that day.
Temperature Profile for Aug 12, 2024 with inserts for subsequent nearshore surface temperatures, and the TP values for samples of surface and deeo water on Aug 12, 2024
Volunteer Bruce S has been monitoring lakeside temperature at Sandy Lake at a site nearby to where D.S collected the sample monthly since 2019. The latest values:
Oct 2, 2024: 18.9 deg C
Nov 3, 2024: 10.5 deg C
That’s a big drop within one month.
I suspect/suggest the cooling of surface waters down to circa 10 degrees was sufficient for the water column to turn over, as the temperature of the bottom of the thermocline back on Aug 12, 2024 was circa 10 degrees, and hypolimnion temperature not much lower – i.e., the gradient in density associated with temperature differences had declined to the point that some wind disturbance would probably mix the water top to bottom.
Such mixing would bring the TP-rich deep waters (40 ug/L on Aug 12), with the lower TP surface waters (5.2 ug/L on Aug 12), stimulating a bloom, perhaps only in the shallower, warmer waters – but that we don’t know.
While we tend to associate BGA blooms with warmer temperatures and there has been some scientific evidence in support of such trends, a recent paper which reviewed studies covering a large geographic scale concluded that ” There were no clear latitudinal or climatic trends in cyanobacterial biomass” and that “Phosphorus was the main driver of cyanobacterial biomass throughout the Americas”*
*Nutrients and not temperature are the key drivers for cyanobacterial biomass in the Americas by Sylvia Bonill et al., 2023 in Harmful Algae
Bathymetric Map of Sandy Lake with approx location of the “Green Aggregations” and wind direction at circa 4 pm on Nov 6,2024. Bathymetric Map by Ed Glover, 2006.
The green aggregations by the shore may have developed on the shore, or became concentrated there by wind action after a bloom on the lake more broadly or over the area of deeper water – the site where the green aggregations were sighted lies adjacent to deep areas of Sandy Lake and the wind direction on that day, from the NW, was onshore for that section of the shoreline.
It’s not a far fetched explanation for the bloom:
“In lake systems, nutrient loading is still an important risk factor. Additional research in Nova Scotia has highlighted the importance of surrounding land-use on cyanobacteria proliferations. Road salt run-off in highly urbanized areas can lead to prolonged stratification (occurring earlier and lasting longer), resulting in anoxic conditions at the bottom of the lake and subsequent phosphorous (P) release from the sediment. Following lake turnover, the internal P load is mixed and available for cyanobacteria. As such, lakes that may have unfavourable conditions for cyanobacteria in upper levels of their water column, may show favourable conditions after lake turnover.” – Under “Lessons Learned” in A. Hiscock et al., 2022. A Workshop on Monitoring, Mitigation, and Management of Cyanobacteria in Atlantic Canada, Final Report. http://hdl.handle.net/10222/82236
While this explanation for the bloom is based on circumstantial evidence, it is consistent with and adds to accumulating evidence that the health of Sandy Lake is currently highly precarious, and would likely be seriously affected by a major development to the southwest of the lake in an area of major headwaters and associated wetlands.
Many thanks to Sandy Lake limnology volunteers, to Linda Campbell and colleagues at Saint Mary’s University in Halifax, and to Dr. Michael Agbeti at Bio-Limno.com for their collaboration on this project. – David P
RELATED
– Dolichospermum flosaquae
Post on iNaturalist reporting on the “green aggregations” at Sandy Lake, with more photos.
– In Conclusion…
Page on this website, posted Sep 20, 2024 “The latest limnological profile (Aug 12, 2024) confirms a long term trend of decline in the health of Sandy Lake (Bedford, NS); a major new development on its headwaters could do it in. The evidence and rationale for this assertion is provided in detail in many separate pages on this website. This page provides a concise overview of the key facts and arguments.
– HRM LakeWatchers State of the Lakes Report 2022-23 Sampling Years
It’s Included as “Attachment A, for Item No. 13.1.2, Environment & Sustainability Standing Committee October 03, 2024: Subject: LakeWatchers Water Quality Monitoring Program Report 2022-2023. 38 pages _ appendices. There are several references to Cyanobacteria blooms. e.g., “Earlier ice-out in the spring allows for an elongated growing season for plants and algae, including potentially harmful cyanobacteria. Warmer overall surface water temperatures can strengthen and prolong a lake’s summer stratification period, which could disrupt ecological processes and contribute to eutrophication risk.”
– Algae Identifcation Lab Guide
Agriculture and Agri-Food Canada. Agri-Environment Services Branch, 2011. 46 pages.