Human Influences on Ecosystems
Summary: Human activities significantly impact ecosystems through deforestation, pollution, and climate change. Deforestation causes habitat loss, soil erosion, flooding, and increased atmospheric CO2. Pollution includes air pollution (SO2 causing acid rain, CO2/greenhouse gases), water pollution (eutrophication from fertilisers/sewage, bioaccumulation of pesticides like DDT), and land pollution. The enhanced greenhouse effect leads to global warming and climate change. Conservation efforts aim to protect biodiversity through sustainable development, captive breeding, habitat protection, and international agreements. Tags: igcse biology human-influences deforestation pollution eutrophication greenhouse-effect conservation Created: 2026-07-16 Last Updated: 2026-07-16
1. Deforestation
Deforestation is the large-scale removal of trees from forests, usually to clear land for agriculture, timber, or urban development.
Effects of deforestation:
| Effect | Explanation |
|---|---|
| Habitat loss and biodiversity decline | Forests are home to ~80% of terrestrial biodiversity. Removing trees destroys habitats → species become endangered or extinct |
| Soil erosion | Tree roots bind soil particles together. Without trees, topsoil is washed away by rain (leaching) and carried off by wind — land becomes infertile |
| Flooding | Trees absorb water through roots and release it slowly. Without trees, rainwater runs off rapidly into rivers, increasing flood risk. Silt from soil erosion can block river channels |
| Increased atmospheric CO2 | Forests act as carbon sinks — they absorb CO2 during photosynthesis. Burning forests releases stored carbon as CO2. Less photosynthesis means less CO2 removal. Both contribute to the enhanced greenhouse effect |
| Disruption of the water cycle | Less transpiration from trees → less cloud formation → reduced rainfall → desertification of previously forested areas |
| Loss of potential medicines | Many pharmaceutical compounds come from rainforest plants — deforestation destroys undiscovered potential treatments |
2. Pollution
Air Pollution
| Pollutant | Source | Effects |
|---|---|---|
| Sulfur dioxide (SO2) | Burning fossil fuels (coal, oil) in power stations and factories, especially coal containing sulfur impurities | Dissolves in atmospheric water vapour → forms acid rain (sulfuric acid). Acid rain: damages plant leaves, acidifies lakes and rivers (kills fish), corrodes buildings and statues (limestone), leaches minerals from soil |
| Carbon monoxide (CO) | Incomplete combustion of fossil fuels, especially in vehicle engines | Binds permanently to haemoglobin (forms carboxyhaemoglobin) — reduces the blood’s capacity to carry oxygen. Can be fatal at high concentrations |
| Nitrogen oxides (NOx) | Car engines (nitrogen and oxygen combine at high temperatures in engines) | Contributes to acid rain (nitric acid); irritates lungs, worsening asthma |
| Particulates (soot, PM2.5/PM10) | Burning of diesel, coal, wood; industrial processes | Inhaled into lungs → respiratory diseases, asthma, lung cancer. PM2.5 can enter the bloodstream |
| CFCs (chlorofluorocarbons) | Old refrigerants, aerosol propellants, foam-blowing agents (now banned) | Destroy the ozone layer in the stratosphere — ozone protects Earth from harmful UV radiation. UV causes skin cancer, cataracts, crop damage |
Greenhouse Gases and Climate Change
The greenhouse effect is a natural process where certain gases in the atmosphere trap heat, keeping Earth warm enough for life.
Enhanced (anthropogenic) greenhouse effect: Human activities have increased greenhouse gas concentrations, trapping more heat and causing global warming.
| Greenhouse Gas | Sources | Contribution |
|---|---|---|
| Carbon dioxide (CO2) | Burning fossil fuels, deforestation, cement production | Main anthropogenic greenhouse gas |
| Methane (CH4) | Cattle (enteric fermentation), rice paddies, landfill sites, natural gas leaks | ~25x more potent than CO2 per molecule |
| Nitrous oxide (N2O) | Fertilisers, industrial processes, vehicle exhausts | ~300x more potent than CO2 per molecule |
| Water vapour | Natural evaporation | Most abundant greenhouse gas but not directly anthropogenic — its concentration increases as the atmosphere warms (positive feedback) |
Effects of climate change:
- Rising global temperatures — more frequent and intense heatwaves
- Melting ice caps and glaciers — sea level rise → coastal flooding and loss of coastal habitats
- More extreme weather — storms, floods, droughts, wildfires
- Changes in species distribution — species migrate towards poles or to higher altitudes as temperatures rise. Some cannot adapt/migrate fast enough → extinction
- Coral bleaching — warmer oceans cause coral to expel their symbiotic algae, killing the coral → loss of marine biodiversity
- Effects on agriculture — some regions become too dry for crops; others become newly farmable
Water Pollution
| Type | Source | Effects |
|---|---|---|
| Eutrophication | Excess nitrates (from fertilisers) and phosphates (from detergents, sewage) washed into rivers and lakes | Algae bloom (rapid growth) blocks sunlight → underwater plants die → decomposers (bacteria) break down dead plants/algae, using up oxygen in the water (increase in BOD — biochemical oxygen demand) → fish and other aquatic organisms die from lack of oxygen |
| Sewage | Untreated or partially treated human sewage released into water | Contains pathogens (cholera, typhoid); decomposers break down organic matter, depleting oxygen → eutrophication-like effect |
| Oil spills | Accidental release of oil from tankers, pipelines, or drilling | Oil coats feathers (birds cannot fly/insulate), fur (mammals), gills (fish) → death. Blocks sunlight → kills phytoplankton |
| Heavy metals (e.g. lead, mercury) | Industrial discharge, mining | Toxic — accumulate in food chains (bioaccumulation), damaging nervous systems of top predators and humans |
| Pesticides / Insecticides (e.g. DDT) | Agricultural run-off | Toxic to aquatic life; bioaccumulation and biomagnification — concentration increases at each trophic level. DDT caused thinning of bird eggshells (top predators like eagles) → population crashes |
Bioaccumulation
Bioaccumulation is the build-up of a toxic substance (e.g. DDT, mercury) in the tissues of an organism over its lifetime — the organism absorbs the substance faster than it can excrete it.
Biomagnification is the increase in concentration of a substance as it moves up the food chain — top predators have the highest concentrations because they consume many prey organisms, each containing the toxin.
Example — DDT in a food chain: Water (traces of DDT) → Phytoplankton (low concentration) → Zooplankton (higher) → Small fish (higher still) → Large fish (high) → Bird of prey (eagle, osprey) (very high — enough to cause thin eggshells and reproductive failure).
3. Conservation
Conservation is the protection and management of ecosystems, habitats, and species to maintain biodiversity and ensure natural resources are used sustainably.
Why conservation is important:
- Maintains biodiversity — the variety of living organisms on Earth
- Preserves genetic diversity for future crop breeding and medicines
- Maintains ecosystem services (pollination, nutrient cycling, water purification, climate regulation)
- Ethical and aesthetic reasons — preventing human-caused extinction
Conservation Strategies
| Strategy | Description | Examples |
|---|---|---|
| Protected areas | National parks, nature reserves, marine protected areas — restrict human activity | Yellowstone National Park, Serengeti National Park |
| Captive breeding programmes | Breeding endangered species in zoos with the aim of reintroducing them to the wild | California condor, Arabian oryx, Przewalski’s horse |
| Habitat restoration | Restoring damaged ecosystems (replanting forests, cleaning up polluted rivers, restoring wetlands) | Reforestation projects, wetland restoration |
| Seed banks | Storing seeds from many plant species to preserve genetic diversity — can be used to restore extinct plant populations | Svalbard Global Seed Vault, Millennium Seed Bank (Kew) |
| Sustainable development | Meeting the needs of the present without compromising the ability of future generations to meet their needs | Sustainable forestry (replanting after logging), sustainable fishing (quotas, net size regulations) |
| International agreements | Global treaties and laws to protect species and habitats | CITES (trade in endangered species), Paris Agreement (climate change), Montreal Protocol (CFC ban) |
| Education | Raising awareness about conservation and encouraging sustainable behaviour | Public campaigns, school programmes |
Sustainable Development Examples
| Practice | How It Promotes Sustainability |
|---|---|
| Sustainable forestry | Trees are replanted after logging; selective logging (only certain trees removed, not clear-cutting); maintaining buffer zones around rivers |
| Sustainable fishing | Fishing quotas (limits on how many fish can be caught), minimum net mesh sizes (allows young fish to escape and reproduce), closed seasons (no fishing during breeding periods) |
| Renewable energy | Solar, wind, hydroelectric, and tidal power reduce dependence on fossil fuels, decreasing CO2 emissions |
| Recycling | Reduces demand for raw materials, reduces landfill waste, saves energy compared to manufacturing from new materials |
Related Notes
- Organisms and their Environment — Food chains, energy transfer, carbon cycle, water cycle, population dynamics
- Diseases and Immunity — Waterborne diseases from sewage pollution (cholera)
- Variation and Selection — How environmental changes drive natural selection
- Plant Nutrition — Nitrates from fertilisers; photosynthesis and CO2
- Respiration — CO2 production from respiration of decomposers in eutrophication
- IGCSE-Bio-Index — Full IGCSE Biology index
Sources
- BBC Bitesize GCSE Biology — Human impact on the environment / Pollution, BBC (free educational resource)
- OpenStax Biology 2e — Chapter 47: Conservation Biology and Global Change, Rice University (free, CC BY 4.0)
- Cambridge IGCSE Biology 0610 — Topic 20: Human Influences on Ecosystems, Cambridge Assessment International Education
- CK-12 Biology for High School — Human Impacts on the Environment chapter, CK-12 Foundation (free, CC BY-NC 3.0)
Common Misconceptions
| Misconception | Reality |
|---|---|
| ”The greenhouse effect is bad and should be eliminated” | The natural greenhouse effect is essential for life on Earth — without it, Earth’s average temperature would be about -18 degrees C instead of +15 degrees C. The problem is the enhanced greenhouse effect from human activities |
| ”The ozone hole causes global warming” | Ozone depletion and global warming are separate issues. Ozone depletion is caused by CFCs allowing UV through. Global warming is caused by greenhouse gases trapping heat. They are linked only in that CFCs are also greenhouse gases |
| ”Acid rain immediately kills trees” | Acid rain damages trees slowly by: leaching minerals from soil, damaging leaves (reducing photosynthesis), and releasing toxic aluminium ions from soil into water. Fish die when lake pH drops below ~5 |
| ”Eutrophication is caused by toxic chemicals in the water” | Eutrophication is caused by excess nutrients (nitrates, phosphates) — not directly toxic chemicals. The problem is the depletion of oxygen when algae and plants die and decompose |
| ”Biodiversity just means ‘lots of different species‘“ | Biodiversity includes genetic diversity (within species), species diversity (number of species), and ecosystem diversity (variety of habitats). All three levels are important |
| ”All pollution has immediate, visible effects” | Many pollutants have gradual, cumulative, and long-term effects — e.g. bioaccumulation of DDT took years to affect bird populations, and CO2 accumulates in the atmosphere over decades |