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