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Human Influence


Farming

The human population is increasing by more and more each year (estimated to be over 7 billion at present), the majority of resources on earth are used for the single species: Homo sapiens. In order to feed the billions of people, far more intensive methods of farming have been used. Every year the efficiency of crop production increases because of progress in crop science, these increases however aren't keeping up with the population increases.

Traditionally farms would have a variety of crops and animals. The modern farm specializes in one type of crop: a monoculture. This makes the farmers money, but because exactly the same species inhabits large areas, nutrients are depleted quickly; so industrial fertilisers have to be used. Traditionally a field would have been rotated so that, over several years, it grows a variety of crops, and the soil is naturally fertilised.

Another issue in farming is hedgerows, these have been removed to provide more space for farming and prevents pests for example. On the other hand, this increases erosion by wind when crop hasn't yet grown, and removes an important ecosystem for birds and rodents.

Farming Pollution

Farming produces huge amounts of waste, both from inorganic sources such as fertiliser and organic sources such as cattle effluent. Generally, effluent is well managed, but if it seeps in to bodies of water, the nitrates and phosphates can cause eutrophication.

To begin with, large amounts of mineral and certain favourable conditions can cause an algal bloom, where the phytoplankton population leaps. This blocks light to aquatic plants so they can't photosynthesize and so they die. These decay at the bottom of the water and large amounts of aerobic bacteria feed on them - using up the oxygen. This lack of oxygen in the water means that fish will die.

an outline of eutrophication

The effects of eutrophication are monitored by the authorities, they keep track of the biochemical oxygen demand. This is measured by collecting water samples and measuring the oxygen concentration before and after it is incubated, the difference gives an indication of the aerobic bacteria in the water.

The rise of monoculture means chemcals that prevent unwanted organisms -pesticides - are used. However, pesticides can cause problems by bioaccumulation, this is where pesticides do not break down so remain in organisms. As they come in to contact with more pesticide, it builds up.

diagram of biomagnification of pesticides

Biomagnification (see diagram above) is the increase in pesticide as you move up a food chain. If the organism at the bottom has small amounts of pesticide, the predator that eats 100 of these will get 100 times the amount of pesticide in the individual organisms. The same will happen to the next predator so that the final consumer (often humans) will have huge amounts of pesticide.

A way of preventing bioaccumulation and biomagnification is to have pesticides that degrade and so they will not get stored in organisms. Modern pesticides are tested extensively and these rarely tend to be a problem, although there is always a chance of some slipping through the net.

Biodiversity loss is important in the use of pesticides, so if you have something to kill insects that might eat your crops it is also likely to have an affect on other insects in the environment. So pesticides must be developed to take this in to account.

Extensive use of a pesticide can lead to the rapid development of resistance to it. If 1 in 100 insects are resistant to an insecticide and this is sprayed it will kill the 99 in 100 that are affected, but now the entire population will be founded by individuals that have resistance and soon the insecticide is useless. I way of addressing this is to have a refuge near the crop where the pest can live without any selection for resistance.

Reaching a Balance

Although modern farming has many negative impacts, reverting to traditional and less harmful methods would not provide enough for our ever expanding population, so we need to strike a balance between meeting the demand for food and conserving the environment.

In Europe, farmers generate surplus crop as a result of more efficient practises, so they can now afford to become more sustainable. With the encouragement of governments, some of the following are being done to improve sustainability.

MethodExplained
Organic FertiliserRetains more water. When it decays, nutrients are slowly released so they are less likely to be washed away.
Soil ErosionLeaving crop stubble over winter protects the soil; building furrows on slopes stops water running down them quickly and washing away topsoil.
Set asideThis is leaving areas of land to develop naturally. In order to receive subsidies, European farmers must set aside around 10% of their land.
HedgerowsMaintaining and developing hedgerows improves biodiversity.