Human impact on ecosystems

Human population growth and rising standards of living put increasing pressure on ecosystems.

Pollution

Type	Source	Effect
Air	Burning fossil fuels (CO_2, SO_2, NO_x)	Greenhouse effect, acid rain, smog
Water	Sewage, fertiliser run-off, oil spills	Eutrophication, kills aquatic life
Land	Landfill, pesticides, plastics	Soil contamination, biomagnification

Eutrophication sequence: fertiliser runs into a lake, algae bloom, light is blocked, plants die, decomposing bacteria use up oxygen, fish suffocate.

Deforestation

Trees are cleared for timber, cattle grazing, rice fields and biofuel crops. Consequences:

• Loss of habitat / biodiversity.
• Less photosynthesis, so less CO_2 removed from the atmosphere.
• Soil erosion as roots no longer hold the soil.
• Disruption of the water cycle.

Biodiversity and why it matters

Biodiversity is the variety of species in an ecosystem. High biodiversity:

• Stabilises food webs (loss of one species has alternatives).
• Provides genetic resources for medicine and crops.
• Supports tourism and human well-being.

Conservation methods

• Protected areas (nature reserves, SSSIs).
• Captive breeding programmes for endangered species.
• Seed banks to preserve plant genetic material.
• Reforestation and rewilding.
• Sustainable fisheries (quotas, mesh size limits).

Climate change link

Burning fossil fuels and deforestation both raise atmospheric CO_2, enhancing the greenhouse effect. Consequences include rising sea levels, ocean acidification (harming coral reefs), shifting habitats and more extreme weather.

WJEC exam tip

If the question asks you to evaluate a conservation action, give one benefit AND one cost (e.g. "captive breeding saves species from extinction B1 but is expensive and may reduce genetic diversity B1"). Examiners reward balance.