Pollution detectors

Lichen

Usefulness of lichens as

bio-indicators

• They are found almost everywhere and at all seasons

• They absorb nutrients and pollutants from the air, often to high concentrations

• Different species show different sensitivities and accumulation abilities

• They are symbiotic organisms. The fungus cannot survive if the algae is killed by pollution

Indicator

species

Pollution

Level

Mayfly nymph Clean

Caddis fly larva Low

Water louse High

Sludgeworm Very high

(a) What can you conclude from the results

about the level of pollution in the stream?

Give your reasons. [3 marks]

The level of pollution is

decreasing / the stream has

become cleaner. [1]

The species that live in cleaner

water have increased or specific

examples. [1]

The species that live in polluted

water have decreased or specific

examples.[1]

(b) Nona said that these samples should be taken at the same time

each year but Rhys said it doesn’t matter. State who you think is right,

giving a reason. [1 mark]

(c) State one other non-biological factor that could be measured and

used as an indicator of the level of pollution in the stream. [1 mark]

(b) (Nona because) water conditions such as temperature must

be the same to be a valid comparison. [1]

(c) Oxygen/pH/heavy metals/nitrate/phosphate/pesticide

(Any 1) [1]

Fresh water shrimp

Bloodworm

StoneflySludge worm