Issue 3: Farming

 

Methane is released along with nitrous oxide in farming. Methane is produced by cattle and rice fields. Nitrous Oxide is released from fertilisers and animal waste. As the human population increases, as we need to feed more people we need more farms. This is causing the release of more greenhouse gases.

 

Nitrate fertilisers used to increase crop growth and make crops stronger can be washed by rain from the soil in the fields into rivers, ponds, lakes etc, causing water pollution (the discharge of harmful substances into water). Due to nitrates being easily dissolved in water, it is very difficult to remove them. They can cause a process called eutrophication which will be discussed further on. Farmers may also use pesticides, and these can also be washed into nearby water sources. Pesticides include insecticides (chemicals that kill insects that may damage crops), herbicides (chemicals that kill plants such as weeds which may affect crop growth) or fungicides (chemicals which kill fungi which may damage crops). These chemicals may also have a negative effect on surrounding land wildlife as some herbicides may kill other plants and some insecticides may kill insects that aren’t harmful to their crops, or the chemicals may enter the food chain and effect other living organisms who eat the insects. A famous case of this will also be discussed below.

 

The case of DDT

DDT was a widely used pesticide just after world war two. It was highly useful at the time and was widely used, particularly on agriculture crops. However it became apparent that it was starting to have a negative effect on the environment. When herbivores consumed plants which contained DDT the DDT was stored in them because body cells can’t break the chemical down. Many carnivores would come along and eat these herbivores and the DDT would be passed into them. The chemical was passed along the food chain and the further along the food chain it is, the higher the level of DDT in the animal. It can reach a toxic level. Sometimes it would reach humans and it was believed that DDT could cause cancer in some people. The concerns were first highlighted in a book by scientist Rachel Carson. Her disastrous claims made the people in the pesticide industry furious. In order to prove her observation was correct it was important to collect scientific data as evidence. It was found that DDT had a very bad effect on birds. The chemical induced a hormonal change that affected the production of calcium in the birds. These birds ended up laying eggs with very thin shells, resulting in a high loss of eggs through breakage and some produced infertile offspring.

 

Eutrophication

Eutrophication starts when nutrients such as nitrogen are washed from farmland into rivers/ponds/lakes etc. This is called leaching. The increase in nutrients causes plants, algae and other photosynthesisers to grow rapidly.   As the algae blooms, it covers the surface of the water and prevents sunlight reaching the plants and other photosynthesisers underneath. As a result of this these plants and photosynthesisers die. When things die, they are broken down by microbes. As more things are dying, these microbes increase in number. Microbes carry out aerobic respiration and so use up oxygen in the water. When there are more microbes more oxygen is being used up by them and there is not enough oxygen for all the other living organisms to use for respiration in the water so they die. And as all the oxygen is used up the microbes die too. Eventually there is no life left in the water.

When sewage is left untreated it can also cause eutrophication. This is because the microorganisms in the water source where the untreated sewage is decompose it, using up oxygen as they do so, leaving less oxygen for other living organisms so they die.

Fish farming can lead to eutrophication in surrounding waters because the waste from the fish kept in the tanks must be removed and exposed of regularly, and can be disposed of into surrounding waters or be washed into surrounding waters. The microorganisms there decompose it, using up all the oxygen and causing other living organisms in the water to die.

You may not necessarily have to use the term eutrophication in your exam, but it is important you understand how to explain it.