Biodiversity and Human Impact on the Environment
Human Population Growth
The global human population is growing exponentially — it has increased dramatically in recent centuries due to advances in medicine, agriculture, sanitation, and technology. Currently over 8 billion people.
This rapid growth puts increasing pressure on the environment because more people need more:
- Resources — food, water, energy, raw materials
- Land — for housing, farming, and industry
- More waste is produced — pollution increases
Land Use Change
Humans reduce the land available for other organisms by building, quarrying, farming, and dumping waste. This destroys habitats and reduces biodiversity.
- Urbanisation — cities and infrastructure expand into natural areas
- Agriculture — clearing land for crops and livestock (especially through deforestation)
- Quarrying and mining — extracting resources destroys landscapes
Pollution
| Type | Sources | Effects |
|---|---|---|
| Air pollution | Burning fossil fuels → releases SO₂ (acid rain) and CO₂ (greenhouse gas) and particulates | Acid rain damages trees, lakes, and stone buildings; climate change; respiratory problems |
| Water pollution | Sewage, fertiliser run-off, industrial chemicals | Eutrophication (see below); kills aquatic organisms; unsafe drinking water |
| Land pollution | Pesticides, herbicides, landfill waste, industrial dumping | Toxins enter food chains; contaminates soil and groundwater |
Eutrophication
Eutrophication occurs when excess fertilisers (nitrates and phosphates) are washed into waterways:
1. Fertilisers enter rivers/lakes via surface run-off
2. Algae use the nutrients and grow rapidly → algal bloom (green layer on surface)
3. The algal bloom blocks sunlight from reaching underwater plants
4. Underwater plants cannot photosynthesise → they die
5. Decomposers (bacteria) break down the dead plants
6. Decomposers use up oxygen in the water through aerobic respiration
7. The water becomes deoxygenated (oxygen depleted)
8. Fish and other aquatic organisms suffocate and die
Deforestation
Large-scale deforestation (clearing forests) occurs to:
- Provide land for cattle farming and growing crops (e.g. soy, palm oil)
- Obtain timber for building and fuel
- Produce biofuels from plant crops
- Make space for roads and settlements
Consequences of deforestation:
- Loss of biodiversity — habitats destroyed
- Increased CO₂ in atmosphere — fewer trees to absorb CO₂ through photosynthesis; burning trees releases stored carbon
- Reduced rainfall — less transpiration from trees
- Soil erosion — tree roots no longer hold soil; heavy rain washes it away
- Flooding — less water absorbed by trees; increased surface run-off
Global Warming and Climate Change
The greenhouse effect is a natural process that keeps Earth warm enough for life. Greenhouse gases (CO₂, methane, water vapour) in the atmosphere absorb heat radiated from the Earth's surface and re-emit it, warming the planet.
Enhanced greenhouse effect: Human activities are increasing greenhouse gas concentrations:
- CO₂ — burning fossil fuels, deforestation
- Methane — cattle farming (digestive systems), rice paddies, landfill decomposition
This causes global warming — a rise in average global temperatures, leading to climate change.
Consequences of climate change:
- Rising sea levels — thermal expansion of water + melting ice caps → flooding of low-lying areas
- More extreme weather — hurricanes, droughts, flooding
- Changes to habitats — some species unable to adapt → migration or extinction
- Changes to species distribution — organisms move to cooler areas; tropical diseases may spread
- Reduced crop yields in some regions; changed growing seasons
- Coral bleaching — warmer seas cause corals to expel algae and die
Peat Bogs
Peat bogs are important carbon stores. Peat forms when plants in waterlogged, acidic conditions die but do not fully decompose (because decomposers need oxygen).
- Peat locks up carbon that would otherwise be released as CO₂
- Peat extraction (for compost and fuel) releases this stored carbon → increases CO₂ in the atmosphere
- Draining peat bogs for farming exposes peat to air → decomposition accelerates → CO₂ released
Conservation of peat bogs is important for reducing atmospheric CO₂.
Maintaining Biodiversity
Actions to maintain biodiversity include:
- Establishing nature reserves and marine protected areas
- Captive breeding programmes for endangered species
- Reducing deforestation and encouraging reforestation
- Controlling pollution through legislation
- Protecting hedgerows and creating wildlife corridors
- Reducing use of peat-based compost (using alternatives)
- Sustainable development — meeting present needs without compromising future generations
Exam Tips
- Eutrophication is a common 6-mark question — learn the full sequence of events in order
- Link deforestation to both habitat loss and increased CO₂
- Global warming questions often ask you to evaluate evidence — remember that correlation does not prove causation, but the scientific consensus strongly supports human-caused climate change
- Peat bogs are carbon stores — destroying them releases CO₂