Management of toxic algae in Danish lakes

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Management of toxic algae in Danish lakes

• 2. LakePromo Seminar - April 2022 2005
• Bad Saarow - Germany

Mette Bramm - County of North Jutland
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Massive algae blooms

• recurring problem every summer in lakes
• aesthetic problem
• inconvenient for recreational activities

More serious some algae produce toxins which may
present a health risk!
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Cyanobacteria - main producers of toxins in lakes

• type cyanotoxins (liver toxins)
• 2/3 of Danish lakes contain cyanotoxins
• responsible genera mostly Anabaena and
  Microcystis
• LD50 lt 50 µg/l (mice)

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Effects of cyanotoxins

• If consumed, inhaled or by direct contact
  symptoms can be.
• skin irritations, stomach ache/cramps,
  diarrhoea, fever, headache etc.
• pneumonia, liver cancer, hepatitis, gastric
  catarrh etc.
• - depending on the degree of exposure
• Symptoms first recognized in 1833
• Fauna death

Less serious
Very serious
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Management of massive algae blooms - a
co-operation between municipalities and counties
supervision of lakes used for recreational
purposes
national and regional surveillance of lakes
sometimes the same
fulfilling the obligations of The National
Action Plan of Water Environment and The Water
Framework Directive
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Action programme at critical blooms
Weather forecasts
Reports of blooms
Risk assessment by municipalities
national and regional surveillance of lakes
Supervision of lake bath water
Increased occurrence of toxic algae
Risk assessment by counties
No or few toxic algae
Advises against bathing or prohibition
Routine supervision continued
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Risk assessment - signs of potential toxic algae
In the field. coloring of the water, low
transparency, accumulation of algae, dead animals
(e.g. fish, birds) In the laboratory chlorophyll
-a levels gt 50 ug/l, dominance of cyanobacteria
especially genera like Microcystis and
Anabaena Toxicity tests an exception to the
rule, as cyanotoxins are always present
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Informing the public - an important task
General information - about algae, health risks,
signs of blooms, good bathing advises,
recommendations etc. - done through brochures,
internet, libraries etc Boards at the lake
site - all year round general information -
when potential toxic algae blooms are detected
warning/prohibition boards
Warning!
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Lake Hornum
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Algae blooms - bathing forbidden
Reduction in diffuse loading
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Algae blooms - bathing forbidden
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Thank you