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Management of toxic algae in Danish lakes
2. LakePromo Seminar - April 20–22 2005
Bad Saarow - Germany
Mette Bramm - County of North Jutland
Massive algae blooms
• recurring problem every summer in lakes
• aestheticaesthetic problem• inconvenient for
recreational recreational activitiesactivities
More serious…
some algae produce toxins which may present a health risk!
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 < 50 µg/l (mice)
Relative toxicity
1 : 122
Amanita muscaria
Anabaena circinalis
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 deathFauna death
LessLessseriousserious
VeryVeryseriousserious
Management of massive algae blooms
- a co-operation between municipalitiesmunicipalities and countiescounties
supervision of lakessupervision of lakesused for recreationalused for recreational
purposes purposes
municipalitiesmunicipalities countiescounties
national* and regionalnational* and regional surveillance of lakessurveillance of lakes
*fulfilling the obligations of The National Action Plan of Water Environment and The Water Framework Directive
sometimes the same
Action programme at critical blooms
Supervision oflake bath water
Reports of blooms
Weatherforecasts
Advises against bathing or prohibition
Routine supervision continued
Risk assessmentRisk assessmentby by countiescounties
Risk assessmentRisk assessmentby by municipalitiesmunicipalities
national and regional surveillance of lakes
Increased occurrence Increased occurrence of toxic algaeof toxic algae
No or few No or few toxic algaetoxic algae
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 > 50 ug/l, dominance of cyanobacteria especially genera like Microcystis and Anabaena
Toxicity tests…
an exception to the rule, as cyanotoxins are always present
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!Warning!Warning!Warning!
Lake HornumLake Hornum
Algae blooms - bathing forbidden
Reduction in diffuse loading
Algae blooms - bathing forbidden
Thank you