What is water pollution?
Water pollution occurs when organisations, industry, agriculture or individuals extract water or discharge substances into water bodies in ways that affect the hydrological cycle and cause negative effects on humans or wildlife. This could be by affecting drinking water, dirtying water that humans come into contact with, or causing toxicity to animals and vegetation.
What are the causes and effects of water pollution?
Industrial processes
An obvious cause of a reduction in water quality is from industrial processes. Often the waste discharged has high levels of organic matter that begins to biodegrade (break down) in the water. This biodegradation needs oxygen and so causes the de-oxygenation of rivers and lakes. When materials are non-biodegradable; for example those used in industrial cleaning processes, it can form a foam layer on the water and reduce oxygen levels in the water.
Although in developed nations water discharges are regulated to some extent or other, there is always the risk of incidents, accidents and emergencies that create infrequent but highly damaging effects. For example, toxic chemicals leak into a river or the sea. Also; even when regulated, industry is often permitted to discharge a certain amount of effluent into water courses, often in the form or organic matter.
A less obvious form of industrial water pollution is thermal pollution – when the discharge is of a different temperature to the water body it is entering into. Warm water from sources such as large industrial plants and coastal power stations has lower oxygen content and so will cause a reduction in the overall oxygen content of any cooler water it is being added to.
You will notice that this pollution is generally related to causing a depletion of oxygen or too much toxicity. Both can cause the death of wildlife (or at least the damage of aquatic ecosystems) or make water unfit for human contact or consumption.
Agricultural processes
Agricultural pollution from farming is also important. Modern processes often include the use of artificial fertilisers and pesticides that the rain can wash into rivers, lakes and especially groundwater, meaning an increase in the concentration of harmful phosphates and nitrates in water. These nitrates have been linked to causing serious diseases like cancer and together with phosphates also help form blue-green algae in lakes and rivers which unfortunately can kill the native aquatic wildlife. Farming is also a source of biodegradable organic matter from silage and cow slurry that leads a reduction in oxygen levels in water courses.
Domestic Use
All of the waste water that we use in our homes and workplaces has to be disposed of. Whilst some of it is cleansed at water or sewage treatment works to some extent, it rarely returns to the water cycle in a pure state. So all of the waste that we flush down our toilets becomes biodegradable organic matter that uses oxygen when discharged to water courses. Also consider the various detergents we use to clean things with in the home that gets thrown down the sink or an outside drain. It all ends up in the water cycle at some stage!
Oil pollution
A big issue that rears its head all too frequently is that of oil pollution. I remember reading that it accounts for about a quarter of all water pollution incidents. One of the main problems is the thin layer of oil that forms on the water surface. It excludes oxygen from the water, meaning asphyxiation of the wildlife beneath. More obvious is the fact that large animals like seabirds or otters become coated in the oil. This affects their mobility and also the maintenance of their body coats that are important to survival. Unsurprisingly this can lead to widespread deaths and environmental disasters. Oil pollution even indirectly affects large mammals such as whales because the toxic oil kills plankton and other basic organisms that are an important food source in the food chain of the aquatic ecosystem. Although people tend to think of high profile incidents as being the main source of oil pollution, the truth is that the main sources of oil into the water cycle are the everyday operations of refineries, tankers and oil drills as well as poor storage and careless disposal of waste engine oil.
Water extraction
Although we tend to think of water pollution being principally caused by discharges into the hydrological cycle, the extraction of water is also important. If water is taken out of the cycle during the warmer summer months, it can cause a reduction in groundwater and river levels so that any pollution already existing becomes even more concentrated. Both the lower water levels and reduced water quality can cause serious damage to aquatic ecosystems and subsequent disruption or death of wildlife.
Conclusion
For much of the 20th Century and beforehand, a blind eye was turned to the issue of water pollution as water bodies were an easy, cheap and almost invisible way of disposing of waste. These days; at least in more economically developed countries, there is thankfully more regulation to help reduce or prevent much of the everyday causes of water contamination. Unfortunately, this does not prevent the inevitable major disasters such as those caused by accidents with oil tankers. As population, consumption and the resultant waste continues to grow globally, the issue of how to reduce water pollution will only become more prominent, especially in an increasingly inter-connected world where there is virtually no hiding place for pollution perpetrators from pressure groups.