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Planet Earth's nine lives: Our planet's limits

Too much of a good thing

Nitrogen gas on its own is inertInformationNitrogenThe nitrogen gas we all breathe is inert. It doesn't react with anything and just stays as ordinary nitrogen gas. Did you know that 78 per cent of the air is made of nitrogen and only 21 per cent is oxygen? If there was much more oxygen, there would be many more serious fires. About 300 million years ago during a period geologists call the Carboniferous, oxygen levels soared to as much as 35 per cent. As well as wildfires, the extra oxygen meant that enormous insects and amphibians could evolve. . It makes up most of the air we breathe and is vital for life. But there's a big problem because humans are using enormous amounts of artificial nitrogen fertilisers for growing crops. People can do this because clever chemistry means that nitrogen gas can be 'fixed'Information'Fixing' nitrogen: why it's so importantNitrogen gas is ‘fixed’ by combining it with hydrogen gas to make ammonia which is then turned into solid nitrogen compounds. These will dissolve in water and can be used by plants. They can also be used to make explosives. So the N is no longer inert like the gas in our atmosphere. It is reactive. ‘Fixing’ N artificially is called the Haber process and it uses a lot of energy from fossil fuel (natural gas) from the air and made into a form which plants can use to grow big and fast. A good thing, you might think, because it means more people can be fed.

But all this extra nitrogen is beginning to cause major pollution problems, damaging the natural nitrogen (N) cycle by massive overload. NatureInformationFixing nitrogenCertain types of plants have the ability to ‘fix’ nitrogen from the air. They have formed a special relationship with a type of bacteria which actually does the ‘fixing’. In return for nitrogen compounds it needs to grow, the plant gives the bacteria both a home in its roots and the sugars the bacteria need to live. This cooperation is an example of symbiosis and is quite common in the natural world has always 'fixed' N too but the natural nitrogen cycle is now overwhelmed by all the artificial N fertilisers farmers use.

Scientists reckon that people can safely make around 35 million tons of nitrogen fertilisers each year and not overload the system. At present, people are making four times that amount and nature can't cope with it. Farmers use so much N fertiliser, often unnecessarily, that it makes the soil acid and kills wildlife. Because it’s soluble, it dissolves in rain and runs off into rivers, lakes and the sea where it causes havoc by making 'dead zones'InformationToo much foodThis is called eutrophication and is caused by algae which have so much fertiliser ‘food’ that they use more oxygen than they produce. This means that all oxygen-breathing creatures - like fish - die where all the oxygen in the water gets used up and nothing can live. Fish and coral reefs die. The best known ‘dead zone’ is in the Gulf of Mexico though there are many othersInformationOver 400 at the last count in 2008 around the planet caused by this over-fertilisation.

Find out your nitrogen 'footprint' at n-print.org

Phosphorus is another element which plants need to grow and once again, humans are overdoing it and this adds to the problems of dead zones. People are using twice as muchInformationGreedy peopleIsn't it funny that humans always use more than their fair share, comments Amy, my junior editor. So long as they get lots of what they want, they don't seem to realise that this is affecting the planet... and penguins too! as they can safely use, say the scientists.



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