Blue-Green Algae (Cyanobacteria) in Inland Waters Assessment and Control of Risks to Public Health

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Blue-Green Algae (Cyanobacteria) in Inland Waters: Assessment and Control of Risks to Public Health

Recognition and identification of blue-green algal blooms and methods for sampling Annex E

Recognising the presence of a bloom

Scottish waters can support numerous different species of algae which can "bloom", either as individual species or in combination, when suitable ecological conditions occur. Some ("planktonic") species exist as single cells or colonies of cells suspended in the water, whereas other ("benthic") species grow on the bed of a waterbody and occasionally form thick gelatinous mats.

When blooms of planktonic blue-green algae occur, it is often possible to see colonies of algal cells in the water column with the naked eye. These may resemble fine grass cuttings or take the form of small irregular clumps or pinhead-sized spheres. These colonies will concentrate on a downwind shore and sometimes accumulate to such an extent as to form a "scum" which is a thick (often many centimetres) layer of colonies. They may also be seen in rivers or streams downstream of lochs.

When the blue-green algal cells start to die and break up, any toxins that may be present are released into the surrounding water. Cell pigments are also released resulting in a scum resembling turquoise emulsion paint spilt along the shore. However, it is important to note that not all blue-green algae are this typical colour and can range from black through dark greens to blues, reds and pinks.

There are only a few other types of algae (e.g. E uglena, Botryococcus) that will occasionally form scums which can be confused with blue-green algal scums. Growths of some aquatic macrophytes, particularly duckweed ( Lemna), and filamentous algae are also commonly mistaken for blue-green algal scum by inexperienced observers.

Benthic blue-green algae can be found in both standing and running waters. The algal mats that these occasionally form can become a problem if the water level drops and exposes the mat, or in some cases, they may detach from the bed, rise to the surface and may then be washed up on the shore. These detached mats are often very different in appearance to planktonic forms. They are usually very dark in colour (black, dark brown or green) and are much more cohesive in nature than planktonic scums. For example, a planktonic scum will flow into a bottle as a liquid whereas benthic scum will be lumpy and often have to be scooped into a bottle or jar.

Sampling equipment

Blue-green algae can be sampled easily and cheaply using simple equipment comprising:

  • Sample bottles of suitable size e.g. 1 litre plastic bottle for planktonic forms; vials or jars minimum size 30 ml for benthic forms.
  • Plastic bucket tied to a rope (optional).
  • Wellington boots.
  • Rubber gloves.
  • Field data sheets or notebook.
  • Self-adhesive labels or waterproof marker.
  • Preservative (Lugol's iodine). Note that this is necessary only if it is likely that the samples will not be analysed within 24 hours. Lugol's iodine should not be added to samples if these are required for toxin analysis.

Sampling health and safety

BLUE-GREEN ALGAE MAY PRODUCE TOXINS HAZARDOUS TO HUMAN HEALTH. CARE SHOULD BE TAKEN TO AVOID INGESTING OR COMING INTO DIRECT SKIN CONTACT WITH BLUE-GREEN ALGAL SCUM. WEAR RUBBER GLOVES WHEN SAMPLING AND WASH HANDS BEFORE EATING OR DRINKING.

LUGOL'S IODINE IS A SKIN IRRITANT AND IS HARMFUL IF INGESTED IN QUANTITY. EYE PROTECTION AND RUBBER GLOVES MUST BE WORN WHEN HANDLING THIS CHEMICAL.

NORMAL HEALTH AND SAFETY PRECAUTIONS SHOULD BE TAKEN FOR WORKING IN OR NEAR WATER.

Sampling Procedure

Samples are normally collected from a point on the downwind shore of a waterbody where the concentration of blue-green algae is greatest. This may not be obvious to the naked eye, in which case any suitable site on the downwind shore can be selected. Bear in mind that blue-green algae will often collect in sheltered bays and inlets. If the downwind shore is inaccessible, then the waterbody should be sampled at the nearest accessible point to the downwind shore and this should be noted on the field data sheet or in a notebook.

In large lochs it is usually impractical to examine the whole downwind shore, in which case one or more samples should be taken at selected points.

Planktonic blue-green algae or floating benthic scums are sampled at or just below the water surface by directly immersing a pre-labelled bottle and filling it completely. Occasionally it may be difficult to reach open water, for example, because of dense emergent vegetation. In such cases a bucket on a rope may be a useful aid. Benthic blue-green algae may need to be scooped into a wide-mouthed jar.

The following information should be recorded on the sample bottle label:

  • Name of waterbody.
  • Sample identifier (site name or number).
  • National grid reference of sampling site.
  • Date of sampling.
  • Name or initials of sampler.

Additional information useful to the analyst should be recorded on a field data sheet or in a notebook. This should include:

  • Sampling location. For waterbodies which are sampled regularly, it may be more convenient to include an outline map on the field sheet so that the position of the sampling site can be marked on.
  • The presence and extent of any blue-green algal scum. For small easily surveyed waterbodies an estimate of percentage cover of the surface could be made or the position of any scum could be drawn on an outline map.
  • The presence of any visible blue-green algal colonies in the water column.
  • The direction and strength of the wind.

Sample Handling

Samples should be kept in a cool, dark place and transported to the laboratory as quickly as possible. If this cannot be achieved within 24 hours then the samples should be preserved for microscopy by adding Lugol's iodine solution. Sufficient should be added to turn the sample a dark straw colour.

Samples for toxin analysis should be stored in a cool box after collection and transferred to a refrigerator at about 4 oc, but not frozen, if analysis is possible within 48 hours. If not possible within this period, samples for toxin analysis should be deep-frozen.

Sample analyses

Where appropriate capability exists, samples can be analysed locally. Alternatively, (as indicated in Section 5) SEPA or Scottish Water can provide an analytical service to identify and quantify algal blooms in samples taken by others.

The general analytical procedure is as follows. The water/algal sample is thoroughly mixed in the sample bottle and a small quantity is pipetted into a calibrated Lund counting chamber or Sedgewick Rafter cell. This sub-sample is then scanned for blue-green algae which are identified and colonies and filaments counted. The count is then multiplied up to give the number of cells or units per ml of original sample. The identification of dominant algae will be to species level wherever possible.

Having identified the dominant blue-green algal species, Table E1 identifies the "units" (colonies, filaments or gyres) that the different species typically form and the concentrations of these units that equate approximately to the lower WHO guidance level (Table 7.1) of 10 g chlorophyll-a per litre.

Toxicity assessment and toxin analysis testing may be carried out as a further aid to the management of algal blooms or scum on waterbodies with high recreational amenity value or on waterbodies used to supply potable water.

Further Information

Further information and advice can be obtained from Ecology staff at SEPA Regional and Divisional offices. Contact details are given here in Annex C.

Table E1:
The nature and size of the units typically formed by different blue-green algal species and the concentration of these typically equivalent to the lower WHO guidance level for chlorophyll-a. (Derived from; "Environment Agency Policy on Blue Green Algal Monitoring and Management of Incidents including Technical Guidance. National Centre for Ecotoxicology and Hazardous Substances". March 2000).

Taxon

Assume "Units" are

Concentration (units per ml) equivalent to 10 (g of chlorophyll-a per litre.

Anabaena circinalis
Anabaena spiroides
f. spiroides

18 cells/gyre

1,000 - 1,400 gyres

Anabaena flos - aquae

26 cells/gyre

760 - 2,300 gyres

Anabaena solitaria

50 cells/filament

40 - 160 filaments

Anabaena spiroides
f. crassa

50 cells/filament

70 - 80 filaments

Aphanizomenon flos - aquae

60 cells, single filaments
60 - 70 filaments

1,200 - 4,200 filaments
20 - 60 flakes

Aphanothece/Aphanocapsa

40m colonies (= 100 cells)
80m colonies (= 1,000 cells)

4,000 colonies
240 colonies

Coelosphaerium kutzingianum

50m colonies (= 300 cells)
80m colonies (= 1,000 cells)

350 colonies
60 colonies

Gloeotrichia echinulata

500 m filaments

120 - 200 filaments
or 1 - 2 colonies

Gomphosphaeria naegeliana

50m colonies (= 300 cells)
80m colonies (= 1,000 cells)

160 colonies
40 colonies

Merismopedia sp. (tentative)

30m 2 'plates' (= 64 cells)

2,000 - 42,000 plates

Microcystis aeruginosa

90m colonies (= 1,000 cells)
200m colonies (= 10,000 cells)

40 colonies
3 colonies

Nodularia spumigena

15 cells/filament

2,000 - 8,000 filaments

Oscillatoria agardhii

300 m filaments

250 - 600 filaments

Oscillatoria isothrix

1,000 m filaments

60 - 160 filaments

Oscillatoria redekei

300 m filaments

1,300 - 3,500 filaments

Oscillatoria rubescens

1,000 m filaments

120 - 360 filaments

Pseudanabaena sp

300 m filaments

600 - 700 filaments

Synechococcus sp

Unicellular

0.5 - 25 x 106 cells