A growth in population, global or local, typically has a negative effect on the waterways, lakes and oceans. As more people move to an area and more people are born, more waste is generated in the form of sewage, refuse and carbon emissions. In many areas sewage is simply piped into the ocean or nearby rivers. Some rivers, such as the Yangtze in China, have become notorious for their pollution levels, and sewage is a significant cause of this. Refuse is rarely disposed of directly into water, but litter often fills rivers and therefore causes pollution. Carbon emissions rise into the atmosphere and can lead to acid rain, much like industrial plants leaking harmful gasses.
Gradual increases in population can be easily managed, with new infrastructure being built to cope with the influx of waste, but when population growth is rapid this is more difficult and the negative effects of a high population begin to show.
When substances, natural or artificial, are released into a body of water – nitrates or phosphates for example – a process called eutrophication occurs. This is a natural response often involving a "bloom" of phytoplankton when more nutrients are present. This creates the effect of almost opaque, bright green water, and leads to hypoxia – the depletion of oxygen in the water. This lack of oxygen kills fish and damages the underwater ecosystem.
There are a number of factors that contribute to the pollution of water.
Gases released by industry into the atmosphere cause rain-clouds to become acidic. When the rain falls, it has a pH below 7. This causes rocks to be eroded quicker than normal and also causes the acidification of streams, rivers and lakes.
Chemicals from farming, particularly of arable land, can easily wash with the rain out of the farm soil and into nearby waterways. Some consider it a responsibility of farmers to ensure that the fertilisers and other chemicals that they use are not particularly damaging to the environment.
Fertilisers are not the only damaging chemical released by many farms. Pesticides also have a negative effect, and have been found in the tissue of shell fish. This suggests that the chemicals poisoned the wildlife.
One of the most prominent forms of pollution is from sewage and other waste that is readily disposed of in waterways, lakes and oceans. The bacteria present in the water then causes algae to grow.
Power plants and research facilities may release radioactive waste, knowingly or not. This can build up in waters that aren't flowing, and can damage the environment and create pollution.
Via many different sources, metals including lead, copper and mercury have been found in the marine food chain. These are naturally found in waters, but not in the concentrations that industry and littering cause.
Oil being leaked has greatly damaging effects on the environment. Some include:
The oil industry has led to a great deal of pollution over the years, in a series of disasters. Some of the worst in history include:
The worlds population is growing at a very fast rate. It has soared from under two-billion, as it has been throughout most of history, to over seven-billion in little more than two-hundred years. This is mainly due to modern methods of farming and medicine which have increased life expectancy in many countries around the globe. However, while this may be a predominantly positive phenomenon, it does create some issues...
Because we, as a species, are now widespread across this planet, our actions no longer have small, localised effects but instead often affect the whole planet in rather unpleasant ways. As the world's population grows, resources are used up so that the race can survive. This can be forests, land, stone, coal, gas or oil, among other possibilities. Most of these resources are non-renewable, meaning that if we rely on these for the survival of the human race (which we do) and they get used up (which they almost are), we would face serious challenges in the future regarding how to support a much larger human population with fewer resources.
Using some of these resources to generate energy, which we currently do, is having an adverse affect on the atmosphere of our planet. This is, in turn, leading to extreme weather conditions and rising sea levels across the planet. Meaning that we have engineered a huge threat to humanity ourselves.
One of the main problems of the large human population, however, is space. Humans take up a lot of land and it is often destroyed at our hands. We build cities, which are not suitable habitats for most species but humans, meaning that space for animal habitats is taken away from them. Farming is a good example of humans manipulating nature to suit themselves and giving little back. Dumping waste and quarrying also take up space and make land unusable, not just for humans but all animal life. Fortunately, nature is sometimes able to reclaim quarries after they have been fully exhausted.