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Tuesday, December 30, 2008

Ecology 10

10. Discuss the impact of human activities on our ecosystem, highlighting issues on deforestation, over-fishing, eutrophication and biomagnification.

*Excuse my poor understanding in biology terms:
Main Entry: biomagnification
Part of Speech: n
Definition: the process by which the concentration of toxic substances increases in each successive link in the food chain; also called [biological magnification] which in my own words is smth similar to Bioaccumulation. Human beings are continually using and depleting/reducing Earth's natural resources, upsetting the balance of nature in many areas. The uncontrolled use of the world's natural resources, such as forests and wildlife, has caused lasting damage to the environment.

Deforestation
The clearing of forests is known as deforestation. Forests are cleared to meet the increasing demand for land and materials such as wood. [Population in S'pore increased from 150-4,000,000 from 1819-2008++] With modern technology, forests are being cleared at a much faster rate than they can be replaced. Deforestation leads to a loss in habitats!

Effects:
Soil Erosion
Deforestation causes soil erosion. With the trees removed, the soil is exposed directly to the force of the rain. The topsoil (the most fertile layer), gets washed away or eroded during the heavy rain and falls onto steep slopes.

Flooding
Eroded soil may be carried into rivers and streams and deposited in the water, blocking the flow of the water. The water level thus rises rapidly, causing floods.

Desertification
The sun shines directly on the soil, causing the water in soil to evapore thus leaving the soil hard. With the topsoil eroded, the land becomes barren and the plants can no longer grow in the soil. Other organisms depending on the plants eventually die off. The destruction of land causing desert-like conditions is known as desertification. Consequently, habitats are also lost and organisms become extinct.

(looks super disgusting...)

Climate Changes

Desertification also cause climate changes. The water absorbed and retained by the roots of the trees are lost as water vapour during transpiation thus causing rainfall. When the trees are cleared, the area dries up and annual rainfall decreases.

Overfishing

Some fishes have been caught in such large numbers that their population have decreased drastically, just to satisfy the growing population.

Most fishing gears catches marine life indiscrimnately; catching any marine life in its track. Other marine lifes are unintentionally caught during which. These 'accident' catches are then dumped back into the sea but often die:(

Methods of fishing destroy the seabed and marine habitat as well!:(

1. Shrimp/prawn trawlers drag large fishing nets along the seabed. Many unwanted species are trapped in the proccess.
2. Scallop dredges scrape the seabed, destorying the coral reefs and organisims living under teh seabed.
3. In cynaide fishing (cynaide a type of poison), stuns the fish and makes them lose the ability to swim properly. Explosives such as dynamites are used to stun fishes as well. These poisons kill corals and many other marine life.

Effects:

-Some species of fishes will be caught faster than they can be replaced, leading to a drop in their population.

-Marine lives caught unintentionally often die, endangering certain species of animals.

Eutrophication

Chemical fertilisers containing nitrates and phosphates are used to increase the yield of crops but overusing of these fertilisers causes water pollution!!!

Fertilisers not absorbed by the plants may be washed away into nearby rivers/streams. --->

Nitrates and phosphates in the fertilisers similary aid the growth of algae and water plants. The enrichment of nutrients would lead to a profuse growth and increase in number of these organisms in the stream. This is called Eutrophication. --->

Submerged algae and plants die due to the lack of sunlight and the dead bodies are decomposed by bacteria. Bacterial then grow and multiply rapidly, using the oxygen in the water. --->

Other organisms living in that habitat dies due to the lack of oxygen.

Biomagnification

Insectisides are used on plants to kill the insects but they inevitably end up affecting other organisms! DDT (a type of insectiside)is non-biodegradable. They remain in the soil for many years and the insecticides on the plants might we carried by rainwater to water bodies. In high concentrations, they may poison fishes/animal that take in the polluted water/feed on the contaminated fishes.

DDT is insoluble in water ans is stored in the fatty tissues of organisms. It cannot be excreted. Organisms cannot break down DDT. Therefore, DDT accumulates in bodies of the consumers, resluting in the DDT being passed along food chains, increasing in concentrations along each trophic levels. This = Bioamplification.

The top consumers suffer the toxic effects due to bioaccumulation.