Negative Human Impacts On Ecosystems

Section 1 of 7Main ways humans harm ecosystems

Loss of biodiversity

Land use

• Land use Building, quarrying, farming and dumping waste take over natural habitats.

Deforestation

• Deforestation Large-scale clearing of trees for timber, farmland and settlements.

Peat destruction

• Peat destruction Peat bogs are drained and dug up for compost or fuel.

Pollution

• Pollution Chemicals and waste contaminate rivers, lakes and streams, as well as air and soil.

Section 2 of 7Land use and habitat loss

1Growing population

• Growing population More people need housing, food and resources, and living standards are rising.

2Habitats cleared

• Habitats cleared Rainforest, grassland and woodland are destroyed or broken into small fragments.

3Food webs disrupted

• Food webs disrupted Species lose food and shelter, and populations fall.

4Biodiversity drops

• Biodiversity drops Some species become extinct, so the ecosystem is less stable and less able to recover.

Section 3 of 7Deforestation

Sustainable or not

• Sustainable or not It is sustainable only if trees are replanted as fast as they are cut.
  • In many areas they are removed faster than they regrow.

Why it happens in the tropics

• Why it happens in the tropics Land is cleared for cattle and rice fields and for crops used to make biofuel, as well as for timber.

Consequences

• Consequences Habitat and species loss, less CO₂ absorbed by photosynthesis, more CO₂ from burning, soil erosion and altered rainfall.

Section 4 of 7Peat bogs and pollution

Impact	Cause	Effect
Peat destruction	Digging for garden compost and fuel	Habitat lost; stored carbon is released as CO2 when peat decays or burns
Water pollution	Fertilisers, sewage and toxic waste entering waterways	Plants and animals die; oxygen in the water falls
Waste dumping	Landfill takes up land	Habitat loss and release of methane
Air pollution	Smoke and gases from burning fossil fuels	Acid rain damages trees and lakes

Section 5 of 7Worked example: how fertiliser run-off kills fish

1

Rain washes excess fertiliser from farmland into a nearby lake.

2

The extra nutrients make algae grow rapidly and form a thick layer on the surface.

3

The algae block light, so plants below the surface cannot photosynthesise and die.

4

Bacteria decompose the dead plants and use up oxygen in the water.

5

Fish and other animals suffocate, so biodiversity in the lake falls.

Section 6 of 7Key terms

Term	Meaning
Biodiversity	The variety of living organisms in an ecosystem or on Earth.
Deforestation	The large-scale removal of trees.
Peat	Partly decayed plant material that builds up in waterlogged bogs and stores carbon.
Sustainable	Used in a way that does not stop future generations meeting their needs.
Habitat	The place where an organism lives.
Extinction	The permanent loss of a species when the last individual dies.

Section 7 of 7Exam technique

1

Saying all deforestation is unsustainable. It can be sustainable if trees are replanted at the same rate.

2

Forgetting peat bogs store carbon, so draining them adds to carbon dioxide levels.

3

Naming only farming as a reason for tropical deforestation. Biofuel crops are another main one.

4

Writing 'animals die' without linking to loss of food chains and habitats.

5

Saying fertiliser kills fish directly. The oxygen shortage after algae decay is the cause.