Human Influence on Ecosystems
Natural ecosystems everywhere have been affected by humans, either directly or indirectly. The serious implications of this have become increasingly apparent, and considerable action is required. The new generation will feel the consequences more strongly than anyone previous.
A lot of rubbish is dropped as litter... Crisp packets, Big Mac cartons, aluminum cans, glass bottles, plastic bags, bus tickets. Most litter is from food and drink containers. Because it decomposes only very slowly, or not at all, it will remain in the environment for a long time.
Household rubbish is sometimes burned, which puts a lot of smoke and poisonous gases into the air, causing air pollution.
Pollution is contamination by poisonous or harmful substances. Air can become polluted by smoke or harmful gases, e.g. from factories and (mainly) car exhausts. Water can become polluted by the dumping of waste from households and factories at sea or in rivers, and by the spread of chemicals used on farms, e.g. pesticides and chemical fertilizers.
Breathing polluted air can make animals, plants and humans ill. It also causes the "Greenhouse effect," whereby Earth's atmosphere cannot get rid of enough of the Sun's heat, and so gets hotter and hotter [global warming]. The immense masses of ice at the North and South Poles could melt, releasing a massive amount of water into the oceans. Sea levels will rise all over the world, leaving a lot of land underwater. Global negative effects of air pollution include the enhanced greenhouse effect and the ozone hole.
Smog and acid rain are the best known local effects. The word "smog" is the combination of the words smoke and fog.
There are two kinds of smog:
- London-type smog.Burning coal leads to emissions of sulphur dioxide and dust. When these pollutants mix with fog, droplets of highly corrosive sulphuric acid (H2SO4) are produced in the air. In London in 1952, concentrations of SO2 during a smog event exceeded 3.5 mg m-3 (3500 µg m-3) and many people died.
- Los Angeles-type or photochemical smog. This type of smog forms on sunny days and is the result of emissions from traffic. Nitrogen oxides from car exhausts and hydrocarbons from various anthropogenic and biogenic sources react in the presence of sunlight to produce a harmful mixture of aerosols and gases. The substances in these smogs are irritating to our eyes and can damage our respiratory system. They also affect vegetation. This type of smog is rather common now in large cities in the summer and has generally replaced the London-type smog.
Air pollution is a threat to our health and can also cause economic losses.
Air pollution has an impact on both local and global scales. Harmful substances which are emitted into the atmosphere in one country, are transported by the wind and cross over national borders. International co-operation is, therefore, necessary to improve overall air quality.
3. Comprehension: