What people lose: Ecosystem services are what a lake or sea does for us. Eutrophication damages four of them in particular.
Fisheries
- Fish and shellfish die or move away.
- Catches and incomes fall.
Recreation
- Swimming, boating and angling stop.
- Visitors stay away.
Aesthetics
- Green scum, murky water.
- Smell of rotting algae.
Health
- Toxins in drinking water and shellfish.
- Costly water treatment.
The points to remember
- Fisheries: less food and income from fish and shellfish.
- Recreation: swimming, boating and fishing for fun are spoiled or banned.
- Aesthetics: the water looks and smells unpleasant, so its beauty is lost.
- Health: toxins and germs harm people and pets; drinking water costs more to clean.
Remember it as: Fish, fun, view, health.
Example (SL): Lake Erie. The shallowest Great Lake supports walleye and perch fishing, beaches and boating, and gives drinking water to about 11 million people. Its summer blooms affect all four services at once.
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The first service to suffer is food. Fish and shellfish need oxygen, and dead zones and toxic blooms take it away.
The points to remember
- Dead zones kill animals on the sea bed and push fish away, so catches fall.
- Boats must travel further to find fish, so fishing costs more.
- Toxic blooms close shellfish harvests: eating them can poison people.
- Red tides kill fish in fish farms, which cannot swim away.
- Over time the species change: fewer valuable fish, more jellyfish.
Example (SL): Gulf of Mexico shrimp. Brown shrimp avoid the dead zone off Louisiana, so shrimp boats must sail further to find them. Studies show the dead zone also means fewer large shrimp, which sell for the highest price, so fishers earn less.
Link it to food: When a question asks about food production, describing the eutrophication chain is not enough: the last step must be fewer fish or shellfish to catch, sell or eat.
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Clear water and clean beaches bring visitors, and visitors bring jobs. A bloom turns that around in a few days.
The points to remember
- Swimming bans and beach closures when toxic algae are present.
- Scum, murky water and dead fish: the place looks ugly (aesthetic value lost).
- Rotting algae give off hydrogen sulphide: a smell of bad eggs.
- Fewer fish, so less angling; mats of weed stop boating.
- Fewer tourists, so hotels, cafes and boat hire lose income.
Example (SL): Florida, 2018. A red tide sat off Florida's Gulf coast for over a year. Tonnes of dead fish and a choking smell emptied the beaches, and the state declared an emergency to help the businesses that lost their visitors.
Some blooms are made of cyanobacteria that produce poisons. Then a lake that supplies drinking water becomes a health risk.
The points to remember
- Toxins from blooms in drinking water can damage the liver and cause sickness.
- Skin rashes and illness in swimmers; dogs can die after drinking the water.
- Shellfish poisoning in people who eat contaminated mussels or oysters.
- Water companies must spend more on treatment, or stop supply altogether.
Example (SL): Toledo, Ohio, 2014. A bloom on Lake Erie put microcystin, a liver toxin, into Toledo's tap water. For three days nearly half a million people could not drink or cook with it, and shops ran out of bottled water.
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How this comes up: Paper 2 Section A asks how eutrophication affects services from a named lake or sea [3-4]; Section B can ask you to explain the impacts on ecosystem services [7].
Blooms of algae now cover parts of western Lake Erie every summer.
Explain how eutrophication in Lake Erie can affect two ecosystem services that the lake provides.
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