Human Effect on the Enviroment


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Atmosphere Pollution

The air is always around us but we pay it little attention. It contains 78% nitrogen, 20% oxygen and 0.04% carbon dioxide and is essential for our lives.

Yet we do not seem to be too bothered about it and go on pumping all sorts of nasty things into it.

The atmosphere is a complex thing, which we do not realise is important to us. Recently we have begun to realise just how important one part of it is to us, the ozone layer.

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The ozone layer

Ozone is a molecule made up of three oxygen atoms:

The oxygen molecules present in air has only 2 oxygen atoms in it. So what is so different about ozone?

If you go up to 12-30 miles above the Earth's surface you find a layer of air which contains small amounts of ozone gas. The ozone molecules absorb the ultraviolet (UV) rays that are emitted from the Sun and which are dangerous to all living things. UV rays can increase the risk of cancers forming, such as skin cancer.

So ozone gives us a protective blanket high above us that reduces the amount of UV rays that get through to the Earth's surface. Therefore ozone helps protect us.

However the atmosphere's protective effect is under threat from things we do.

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CFC's are "Chloro-fluoro-carbons" to their friends. Although nowadays they don't have many friends.

We thought that they were great molecules at one time. They used to do useful things like running cool machines such as 'fridges' and air-conditioning units. They were in aerosols and polystyrene foam.

However, we now know that they break up ozone molecules and so destroy the layer that protects us from UV rays from the Sun. Not a good idea!

In the last few years we have realised that there are huge holes in the ozone layer near the North and South poles - and they have grown! As more nasty UV rays flood through more people are developing skin cancer.

CFC's have been banned in many countries and alternatives are used instead, but these can be expensive. 

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Burning fossil fuels

We all burn fossil fuels. We do it directly by burning coal or driving cars. We also indirectly burn fossil fuels when we use electricity generated using them.

Our cars and power stations are responsible for most of the fossil fuel burning. The gases released include carbon dioxide, sulphur dioxide and oxides of nitrogen (NO2, NO3, etc.). Up in the atmosphere these gases are dissolved in water and cause acid rain.

The gases also mess up the atmosphere. The extra carbon dioxide causes the greenhouse effect.

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Leaded petrol

Not only do our cars burn a fossil fuel but the older "4 star" petrol contains the element lead.

This leaded petrol was used because it made engines run smoothly. But when it was burned it released the lead into the air. When breathed in it could damage our nervous system. Not nice.

Thankfully, more modern engines can burn "lead-free" petrol and so there will be less lead in the air.

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Greenhouse Effect

It seems like everyone blames bad weather on the greenhouse effect. But...

What is it?

The greenhouse effect is where the temperature of the Earth increases. This happens as less heat is radiated back from the Earth than is received from the Sun.

The atmosphere becomes clogged up with "greenhouse gases" such as carbon dioxide from burning fossil fuels and methane. This lets the heat from the Sun in but stops some of it from be radiated back out again.

This is just how the glass on a greenhouse works. So the inside of the greenhouse gets warmer and warmer over time.

In the case of the Earth the warming up has happened very slowly over decades and centuries. However the levels of greenhouse gases have risen sharply recently.

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What might be the effects?

As the temperature of the Earth increases it is predicted that we will see changes in weather patterns, including drought and flooding.

The Polar ice caps may melt and so produce raised sea levels. Low-lying areas will be flooded including many major cities.

What may cause it?

Carbon dioxide and methane are thought to be "greenhouse gases". But how are they produced?

Carbon dioxide

Normally there is a balance in the amount of carbon dioxide in the atmosphere. It is produced by respiration and used up in photosynthesis. So across the whole planet there is a beautiful balance as part of the "carbon cycle".

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However, as we have cut down trees for farming land, fuel and timber we reduce the number of plants that can carry out photosynthesis. This 'deforestation' results in less carbon dioxide being cleared from the atmosphere.

At the same time we have burned a huge amount of fossil fuels in the last two centuries, ever since the start of the 'industrial revolution'.

All this burning results in even more carbon dioxide being produced. Levels have risen by about 20% already and are still increasing - and doing so even more quickly!

More carbon dioxide is being produced and less cleared away.

We are slowly suffocating ourselves!

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The other common greenhouse gas is methane. Its molecules have one carbon and four hydrogen atoms.

Marshland and bogs produce methane naturally. It bubbles up from decaying plant material.

However, increasing amounts are produced through agriculture. The two main ways are in rice production (paddy fields) and cattle rearing. It seems that cows pass wind each day, just like us, but in greater volume.

Anyone want to volunteer to find out how many litres a cow farts each day?

No, I thought not.

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Acid Rain

During the 1970's people first began to notice the effects of acid rain and to think about how it might be caused.

The causes

It is down to us again. Whenever we burn fossil fuels we release waste gases such as carbon dioxide, sulphur dioxide and various oxides of nitrogen. The main sources of these are cars and power stations

Carbon dioxide is the main cause of the greenhouse effect.

Sulphur dioxide and the oxides of nitrogen will mix with rainwater in clouds and form acidic solutions. These then fall as acid rain.

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The effects

Acid rain has severe effects on the environment and individual ecosystems within it.

The acid rain will kill trees and damage buildings made from limestone.

The water will also make lakes and rivers more acidic. This will kill fish and other aquatic life.

The increased acidity of the water also allows aluminium salts to dissolve more easily. The aluminium ions are very poisonous to fish and birds.

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The solution

The solution is to basically produce less greenhouse gases.

To do this we well need to use less fossil fuel. This includes our use of materials and power that rely on them.

In addition to this we can reduce the amount released from source, that is to remove the gases before they are released.

To do this, we can build power stations that have acid gas "scrubbers" to remove them from the chimneys. We can also use catalytic converters in our car exhausts which break up the greenhouse gases as they leave our cars.

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There are about 6 billion of us at the moment with an estimated 90 million more born each year.

That is a lot of people in a fixed amount of space!

What is it?

Overpopulation occurs when there are more people than the land can sustain.

A lower death rate is a good thing. Modern medicine and farming techniques have allowed us to reduce deaths through starvation and disease.

However the birth rate has increased alarmingly. It has resulted in population rises that are out of control, many of these are in so-called 'under-developed' countries.

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The results

As the population of a country rises so there more people to feed and support.

As the poorer, under-developed countries become more industrialised they use more of their limited resources for their growing populations. They want to provide all the essentials such as health care and education.

These growing economies demand more energy from fossil fuels, adding to the pollution problems.

Deforestation is increased to provide building land, timber and farmland. This includes the essential rainforests. Areas the size of Wales are lost each year.

Mining and other extraction techniques lead to reduced mineral reserves.

But these effects include us too. Our demand for materials and energy is much greater than under-developed countries. They just want what we want. They have that right, don't they?We want new things and to run all our equipment - including computers!Overpopulation is a global problem- but it is also personal.

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The solution

At this present rate there will be many billions of people trying to live in smaller and smaller areas, fighting for fewer and fewer resources.

Not a great vision of the future is it!

We must do something. But what?

Encouragingly, a lot of time has been spent over recent years into examining what might be done. Some countries have introduced strict birth control laws. China has even made it illegal to have more than one child!

Education, including about contraception and birth control is another key measure. This has been shown to help to reduce the birth rate in a population.

However, this can be an expensive and difficult measure to introduce.

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Intensive Farming

Farming is often under-rated nowadays. Modern farming practices have radically increased the efficiency of farming, producing more food from the available land. In a lifetime we have moved from not having enough to eat to having tons of food.Despite this "intensive farming" providing us with masses of cheap food there are a number of problems.

Effects on animals

Strain can be placed upon domestic animals so that they produce the best possible food yield for us. Examples include the confinement of battery hens and veal calves.

Food chains are damaged by the use of pesticides to kill insects and animals that could damage crops. The chemicals used are indiscriminate, they kill any insect. So the links in food chains are wiped out and whole communities of animals can suffer.Fields that are intensively farmed contain only single crop species, and the crowd of plants, insects, animals and birds that used to exist there are gone. Some face extinction.

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Deforestation is the loss of trees due to demand for timber, land and so on.It doesn't just occur in rainforests, the deforestation happens here too. We have virtually deforested our whole country over centuries, including our hedgerows.The rainforests are the lungs of the Earth. The rapid rate of deforestation there has critical importance.

What are the effects of deforestation?

There are 4 main effects:

  1. Decrease in rainfall:less trees means less transpiration and photosynthesis.
  2. Soil erosion: the exposed soil dries out under the Sun.
  3. Serious flooding: rainwater runs off the exposed soil rather than soaking in as before.
  4. More carbon dioxide: the trees that used to remove the gas are gone.

The problem gets worse and worse.

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Pesticides are used to kill animal pests, and herbicides are used to kill weeds.

Both can be useful types of chemicals. However, their use has problems.

One problem is "bioaccumulation". These chemicals are poisonous to other animal life. If the animals at the start of a food chain take up small amounts it becomes more and more concentrated higher up until it can kill the animals at the top - including humans.

One example was the use of a pesticide called DDT used in the 1960's. It was used to kill insects (an insecticide) that were damaging crops but it leaked into rivers and contaminated plants. The small animals and fish further up the food chain collected more and more because it wasn't lost (not excreted) from their bodies. Eventually, otters ate the fish and were killed. Otters were virtually made extinct in Southern England.

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Eutrophicationis what happens when too much chemical fertiliser is used on crops and it washes into rivers and streams.The nitrates in the fertilisers are essential to get crops to grow well and increase yields.

However, if too much is used, or it rains soon after it is added to fields, the fertiliser gets washed away. The nitrates then help plants in the rivers and streams to grow very quickly, especially algae.But after the initial massive growth in algae there isn't enough light and for them all and a lot of the algae die.

All those dead plant start to decay. You are left with a green and slimy mess. This removes oxygen from the water and kills fish and other animals. Then even more algae and animals die.

So farmers have to be very careful using fertilisers so not to wipe out all river life. The bottom line with all these problems with modern, intensive farming is that to change will be very expensive.

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Managing the Enviroment

Farming and the environment often seem to clash. But it is possible to produce our food without destroying the Earth.

We have to realise that "traditional farming" techniques will work but will give us poorer yields. Food will therefore be more expensive.

But it will mean that we can treat animals better and recreate a "balanced ecosystem", which will continue to produce our food year after year - that is be sustainable.

Surely it must be worth spending that bit more money?

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Organic farming

Organic farming is a phrase often used to describe traditional farming practices.

It is becoming increasingly used and with scientific knowledge it is more efficient that it used to be but without being intensive.

There are three main areas included in organic techniques:

1. Using organic fertilisers The faeces of farm animals such as cows contain lots of useful nitrates. Spreading this useful 'muck' back onto fields saves using chemical fertilisers. 2. "set-aside" By replanting trees (reforestation) and allowing the ground to lie uncultivated, erosion of the soil is prevented and the amount of mineral ions in it can recover after each crop. 3. Using biological pest control Using natural predators to kill pest animals. You can even buy or rent hedgehogs to use now!

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Fish farming

Many fish farms have been set up in Scotland and Norway as an attempt to stop relying on North Sea oil too heavily.

Their basic design is the same. A large cage or net is floated in a sea-loch or fjord, that is a narrow sea-inlet.

Salmon are grown from artificially fertilised eggs kept in aquarium tanks. When they are large enough they are released into the nets in the sea-loch.

The salmon can swim around inside the cages but cannot escape outside. This together with the large number of fish =restricts their movement. This smaller movement maximises the energy transfer from their food into putting on weight.

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The fish are fed a carefully controlled diet of food pellets. If too much is given it falls through the net and is wasted on the floor of the loch. This wasted food and their faeces can pollute the water, so the nets are sometimes moved around within the loch.

In the nets the salmon are protected from their natural predators - seals and seabirds. However, they can suffer from parasites called "fish lice". One way to treat these is to use an insecticide called Dichlorvos. Another, is to put another type of fish called wrasse in with the salmon. The wrasse feed on the salmon's fish lice and keep them clean. This is a good example of biological pest control.

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Biological pest control

Biological pest control includes any example where an animal is chosen which will eat the pest species.

Advantages over using chemical pesticides:

  1. It can be cheaper.
  2. There are no concerns about using too much and damaging the environment.
  3. You can be specific about which things you kill, rather than just killing every insect including the useful ones.
  4. You can sell edible plants and crops without having to worry about pesticide residues inside them.

The only disadvantage is that you never get rid of all the pests but instead after a couple of years the number of pests will have fallen to an acceptable, lower level.

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The following diagram illustrates what happens when a pest is controlled by using a predator against it:

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Notice that in the end, a gentle, undulating pattern develops between the numbers of pests and predators with far fewer pests around.

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Greenhouses are great. They let plants grow in nice, warm, sheltered conditions.

As the Sun's rays shine in they warm up because the heat cannot get out as quickly as it comes in. Closing the windows during the day helps to raise the temperature, humidity and carbon dioxide levels. You can change the light at night time too.

All of this helps to speed up photosynthesis and the growth of the plants.However, there are many pests, which affect greenhouses and just love those nice conditions.

The four main pests are:

  1. Aphids.
  2. Whitefly.
  3. Mealy bugs.
  4. Red spider mites.
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What could we do about them?

We could just blast them with chemical pesticides. But that would kill all the useful worms, ladybirds and bees. It would also stay around in the soil and our crop.

A better way is to use specific predators against each one, that is, use biological pest control.

Pest: Biological control: What the predator does: Aphids Aphidoletes The larvae eat the aphids. Yum! Mealy bugs Ladybird One type of ladybird attacks and eats them. Whitefly Encarsia This tiny wasp lays its eggs inside the whitefly so that the larvae can eat their way out. Nice! Red spider mites Phytoseiulus These tiny red mites attack the red spider mites.

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