Blue-Green Algae

Methods

Initial Screening:  The first stage of monitoring is designed to locate developing cyanobacteria populations.  In this stage, vertical plankton net tows (63µm net, upper 3 m of the water column) are used to concentrate surface waters for microscopic analysis of the cyanobacteria present.  Samples should be screened within 48 hours to determine if potential toxin-producing cyanobacteria are present.  Samples should be collected monthly in the spring and early summer, and twice a month from mid-summer through the fall, when cyanobacteria blooms are most likely.  Once potential toxin-producing species have been identified, progress to the next level.

Quantitative Monitoring:  At this stage, sampling at sites should continue at a frequency of twice a month.  Sampling method continues to be a vertical plankton net tow (63µm net, upper 3 m of the water column), but samples should be fully enumerated.  Detection of cyanobacteria at densities of  500 - 2000 cells per mL in the upper 3 m of the water column will trigger the progression to the next level.

Vigilance Level:  At this stage, net samples for both phytoplankton and chlorophyll a should be collected once a week at mid-day from locations where potential toxin-producing cyanobacteria have reached densities of 500 - 2000 cells per mL in the upper 3 m of the water column.  Chlorophyll a is useful because it provides a means of standardizing data reports.  Because warm calm conditions can result in rapid accumulation of cyanobacteria at the surface, weather conditions should influence the specific sampling days.   Public health officials should also be notified at this stage that cyanobacteria are abundant and, under certain conditions, could accumulate at the surface.

Samples should be enumerated within 48 hrs.  Cyanobacteria densities of more than 2000 cells per mL or 1 µg chlorophyll a per L with greater than 80% of the cells represented by cyanobacteria will trigger the progression to the next level.

Alert Level 1:  At this stage, there is a large amount of accumulated algal biomass in the upper water column and toxin production could pose a risk to people and animals.  Whole water samples should be collected on a weekly basis at mid-day to determine algal density, chlorophyll a concentration and toxin concentration, more frequently if conditions warrant.  Whole water samples at this stage replace net sampling in order to order to reduce the loss of colony fragments through the net.

Subsamples for toxin analysis should be screened immediately for microcystin by enzyme-linked immunosorbant assays (ELISA).  The turnaround for the ELISA method is a few hours.  If potential anatoxin-producing species are found, then an additional subsample should be submitted for these analyses, which take several days.

ELISA results should be communicated to public health officials, along with appropriate level of concern.  Ambient toxin concentrations above the World Health Organization’s guideline of 1 µg per L microcystin represent a potential threat to human health and will trigger progression to the next level.

By relying on the results of the ELISA for action, we may miss anatoxin-producing blooms, but technology offers no rapid screening method for anatoxin at this time.   If anatoxin-producing species predominate in a bloom, this information should factor into the appropriate communication to public health officials.

Alert Level 2:  Significant toxin concentrations have been documented in the water at this level.  Sampling should continue as described for Alert Level 1.  Public health officials should be notified of the toxin concentrations and advisories may be issued concerning recreational activities and consumption of water.  Frequent sampling to track toxin and chlorophyll concentrations should continue until the bloom subsides and toxin concentrations fall below 1 µg per L microcystin.

Routine sampling for the Burlington Bay project occurred once a month in May, June and October, and twice a month during July, August and September.  Samples for cyanobacteria analyses were collected at this time.  Additional samples were collected during August, September and October when it appeared that a bloom might be developing.  Two types of algal samples were collected – whole water and concentrated plankton samples obtained by filtering lake water through a 63 micrometer mesh net.

In addition to microscope counts, plankton samples were periodically analyzed for the presence of two toxins, microcystin LR and anatoxin-a, utilizing four different methodologies:  1) ELISA; 2) high pressure liquid chromatography (HPLC); 3) protein phosphatase inhibition assay (PPIA); and 4) gas chromatography/mass spectrometry (GC/MS).   Surface water samples taken over the water treatment intakes and at beach areas documented the distribution of algae and toxins in portions of the lake routinely used for recreational activities such as boating and swimming.  Drinking water exposures were evaluated by periodically collecting intake (“raw”) water and treated (“finish”) water at the two drinking water facilities.

In addition to the algal and toxin samples collected as part of the monitoring system, water samples were collected for total nitrogen and total phosphorus analysis.  Phytoplankton population dynamics are linked closely to these nutrients, and these data may provide important predictive capability with respect to algal blooms in Burlington Bay.