Water Pollution, Deforestation and Global Warming

Question 1

Describe the process of eutrophication

Answer 1

• When mineral ions (like phosphates and nitrates) are leeched into still water sources they cause algae to reproduce rapidly, preventing sunlight from reaching plants in submerged in the water
• These plants that rely on photosynthesis to survie die, releasing their natural compounds into the water
• Mircroorganisms already present feed on the decomposing plant matter and reproduce rapidly
• As the mircroorganisms respire they use up all the oxygen, causing the water to become completely anoxic
• Water without oxygen cannot sustain life and so all remaining wild life (e.g. fish) dies out
  This is called eutrophication.

Question 2

What are the four effects of deforestation?

Answer 2

• Soil erosion
• Imbalance in water cycle
• Imbalance of carbon dioxide and oxygen
• Leaching

Question 3

Explain what is meant by leaching.

Answer 3

• Trees take up nutrients before they can be removed from the soil by leaching (i.e. washed away by rain water) but return them to the ground when they loose their leaves and their leaves decompose
• If trees are removed, the nutrients are washed away and there are no decomposing to replace them.
• This leaves infertile soil

Question 4

Explain what is meant by soil erosion.

Answer 4

• Tree roots are what holds soil in place, so when they are removed the soil is disrupted and washed away by the rain
• This leaves infertile ground

Question 5

Explain how deforestation can cause an imbalance in the water cycle.

Answer 5

• Trees stop rainwater reaching rivers too quickly, but when they are cut down rain water can run straight into the rivers. This can cause flooding.
• Transipiration from trees releases water into the atmosphere. When trees are cut down the local climate comes drier.

Question 6

Explain how deforestation can cause an imbalance in the levels of carbon dioxide and oxygen in the atmosphere.

Answer 6

• Trees take up CO2 by photosynthesis, store it in the wood, and slowly release it when they respire or decompose
• When trees are cut down and burnt carbon dioxide is released straight into the atmosphere and very quickly. This contributes to the global warming.
• Fewer trees also means less photosynthesis taking place, releasing less oxygen. This causes the oxygen level in the atmosphere to drop.

Question 7

What are the ways in which human activity produces greenhouse gases?

Answer 7

• We release carbon dioxide into the atmosphere through all aspects of our lives: in car exhausts, industrial processes, as we burn fossil fuels.
• Methane gas acts as a green house gas and is released naturally by from rotting plants in marshlands.
• Two man-made sources of methane are rice growing and cattle rearing (when the cows fart).
• CFCs are man-made chemicals that are really powerful greenhouse gases. They used to be used all the time in aerosol sprays and fridges but most countries have agreed not to produce them.

Question 8

Explain the effect of green house gases.

Answer 8

• Gases in the atmosphere absorb most of the heat from the sun that would normally be radiated into space and re-radiate back towards Earth.
• Green house gases are the ones that aborb the most heat, they include: water vapour, carbon dioxide and methane.
• As well as natural reasons, human activity increases the amount of green house gases in the atmosphere.
• As a result of all this the Earth is heating up, causing all kinds of climate change: changing rainfall patterns and crop growth patterns or flooding due to polar ice caps melting.