Negative Human Impacts On Ecosystems (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Revision Note

Human Impacts on Ecosystems

• Many human activities, or consequences for human activities, are reducing biodiversity in individual ecosystems and on a global level. These include:

  • Land use e.g. building, quarrying, farming and clearing woodland

  • Deforestation

  • Destruction of peat bogs and other peat areas

  • Pollution of streams, rivers and lakes

Land Use

• The increasing human population of the planet means an increasing amount of land is required for activities such as building, quarrying, farming and dumping waste

• This is causing the destruction of many habitats, such as rainforests and woodlands

• This reduces the biodiversity of these areas and interrupts food chains and webs, meaning that more species may die because their prey is gone

• The main reasons for habitat destruction include:

Deforestation

• Deforestation is the large-scale removal of trees. If trees are replanted at the same rate they are removed, deforestation can be sustainable

• However, in many areas deforestation is unsustainable, as trees are cut down faster than they can regenerate

• Unsustainable deforestation is occurring on a large scale in tropical rainforests, mainly to:

  • clear land for farming (e.g. cattle grazing and rice fields)

  • grow crops used to produce ethanol-based biofuels

• The reduction in tree cover causes serious environmental damage and is a major example of habitat destruction

• The main issues resulting from deforestation include:

Destruction of peat bogs

• Peat bogs are waterlogged, acidic areas where dead plant material does not fully decompose due to a lack of oxygen

• Over long periods of time, this partially decomposed material builds up to form peat

• Carbon that would otherwise be released as carbon dioxide is stored in peat, making peat bogs important carbon stores

• Peat bogs also provide habitats for many species, including migrating birds

Why peat bogs are being destroyed?

• drained to provide land for farming

• peat is dried and used as a fuel

• peat is used to make compost to increase food production

Negative impacts

• burning peat releases carbon dioxide, contributing to global warming

• peat forms so slowly that it is effectively a non-renewable resource

• destruction of peat bogs reduces habitat area and biodiversity

• peat bogs are being destroyed faster than they can form, so their use is unsustainable

Water pollution

• Many human activities cause water pollution by releasing harmful substances into rivers, lakes and seas, leading to damage to aquatic ecosystems and loss of biodiversity

• The main causes of water pollution and the effect on biodiversity are as follows:

Global Warming

• An example of a global impact of human activity is global warming leading to climate change, which reduces biodiversity through flooding of coastal habitats, coral bleaching and an increased frequency of extreme weather events caused by rising global temperatures

Greenhouse gases

• A greenhouse gas is a gas that absorbs infrared radiation from the Sun so it remains trapped in the Earth’s atmosphere

• This is important to ensure Earth is warm enough for life, however if levels of these gases in the atmosphere increase it leads to an increase in the greenhouse effect which causes the Earth’s average temperature to rise

• There are many greenhouse gases, the most important are:

  • Water vapour

  • Carbon dioxide

  • Methane

  • Nitrous oxides

  • CFCs

• Human activities have led to increasing levels of carbon dioxide and methane in the atmosphere:

  • Carbon dioxide is produced during the combustion of fossil fuel

  • Methane is produced by cattle as they digest grass and released by rice paddy fields

The greenhouse effect

• The Sun emits rays that enter the Earth’s atmosphere

• The heat bounces back from the Earth’s surface

• Some heat is reflected back out into space

• Some heat is absorbed by greenhouse gases and is trapped within the Earth’s atmosphere – this is normal

• However, as the levels of greenhouse gases in the atmosphere rise due to human activities the Earth’s average temperature rises beyond normal (an enhanced greenhouse effect), causing global warming

How the greenhouse effect works

The consequences of global warming

• The consequences of global warming due to an enhanced greenhouse effect include:

  • Ocean temperatures increasing, causing melting of polar ice caps / rising sea levels / flooding / coral bleaching

  • Increasing temperatures causing extreme weather like super storms, flooding, droughts

  • Changes in or loss of habitats due to these extreme weather events

  • Decreases in biodiversity as food chains are disrupted and extinction rates increase

  • Increases in migration of species to new places, including increased spread of pests and disease

The evidence for global warming

• There is scientific consensus (almost all scientists agree) that global warming is happening and that human activities are largely responsible for the most recent warming

• This scientific consensus is based on systematic reviews of thousands of scientific research papers that have been ‘peer reviewed’ by other scientists (the method used by scientists to check each other’s work in order to ensure that research findings are valid)

• Although they can make good predictions, it is difficult for scientists to say for certain what the consequences of global warming will be