Polluted Water

What is Water Pollution?

Water pollution is the alteration of the natural composition of a body of water. This can be by the addition of chemicals, metal particulates, radioactivity, or even heat. Some natural causes can result in water pollution however human activity is the major driver behind the contamination of global waters.

There are two types of pollution: point-source pollution and non-point source pollution:

Governments will find non-point source pollution difficult to attribute and control directly, so strict laws and legislations must be put into place to reduce the general release of pollutants.

Fig. 2. Wetlands. Source: Unsplash.

Examples of water pollution

Let's have a look at some examples of water pollution:

• Fertilisers: agricultural fertilisers normally contain large amounts of nitrogen and phosphorus and can runoff into nearby rivers, lakes, and oceans if by the coast. These elements are beneficial in small amounts but will harm aquatic ecosystems when waters become inundated with them.
• Pesticides: other agrochemicals farmers use to deter natural pests may also runoff into nearby waters after rainfall. These chemicals can often be poisonous to many different species.
• Sewage: poorly managed sewage can seep into nearby waters and often contains large amounts of nitrogen and phosphorus.
• Industrial waste: discharge from industrial areas can contain a variety of toxic and radioactive chemicals like crude oils, metal particulates, acids, alkalis, solvents, and PCBs (polychlorinated biphenyls).
• Pathogens: the addition of disease-carrying microorganisms and viruses can also pollute waters.
• Heat: waste heat from industrial plants and global warming can cause dangerous increases in water temperature.

In theory, you can consider the introduction of non-native species to an aquatic environment as water pollution. This can occur by humans physically carrying alternative species into the habitat, or climate change forcing species to migrate to more suitable habitats. These species will take up space, compete for resources, and potentially become novel predators, which can seriously disrupt an ecosystem's balance.

Causes of Water Pollution

So now we know the different types of water pollution; what causes the addition of these substances to the water? There are six main causes for water pollution:

• Wrong wastewater treatment
• Agricultural runoff
• Industrial discharge
• Urban runoff
• Acid rain
• Global warming

We'll have a look at each of these causes in more detail in the sections below.

Wastewater treatment

In highly populated areas, massive amounts of human and animal sewage are treated daily. This sewage will contain animal faeces and detritus, so will contain lots of organic nutrients and lots of bacteria. The disease-carrying pathogens will pose a threat to human health, while the decomposing bacteria will suffocate the waters of their oxygen and release lots of nutrients. Sewage treatment facilities are often focused on eliminating some of the dangerous chemicals that can be released into the water like oils, metals, acids and alkalis, rather than the seemingly less dangerous bacteria and organic nutrients. However, the combination of decomposing bacteria and nutrients is harmful to entire ecosystems and the quality of drinking water.

Agricultural runoff

Farmers need to produce enough food to feed the population and earn money to make a living, so the environmental implications of their methods are not always considered. The overuse of artificial fertilisers and pesticides is endangering nearby aquatic ecosystems. Agricultural fertilisers contain nitrogen and phosphorus for plant growth, so you can imagine how much is needed for a field of crops (then think about entire agricultural regions!). After rainfall, the water (containing nitrogen and phosphorus ions not taken up by plants) will run off into nearby aquatic waters, which can cause oxygen depletion. Pesticides will also be present in the runoff and will contain poisonous chemicals as their purpose is to kill and deter species.

Fig. 4. Can you imagine the amount of artificial fertilisers and pesticides that is needed to optimise the production of this field? And this is only one farmland! Source: Unsplash.

Industrial Discharge

Industrial processes involve the use of chemicals and particulates which are poisonous, radioactive, or carcinogenic in water. Runoff from industrial areas and poorly treated industrial waste will contain large amounts of dangerous metal compounds (mercury, aluminium, chromium), radioactive chemicals (uranium, plutonium), and acidic compounds. The discharge of cooling water from power plants can cause heat pollution as well. Despite being called 'cooling water', it is much warmer than the water in lakes, rivers, and oceans, and can cause drastic changes in temperature which can have a knock-on effect on ecosystems.

Urban Runoff

In densely populated urban areas, dumped litter and waste can make their way into nearby waters. Improperly disposed waste from cities and general public litter in the form of plastics, food, metals, and electronics can contain all sorts of toxic and radioactive chemicals (metal compounds, hydrocarbons, solvents). The degradation of waste only releases more of these chemicals.

Acid Rain

Nitrous oxides and sulphur dioxide emissions from power plants can cause acid rain. These gaseous particles will react with water vapour molecules in clouds to form nitric acid and sulfuric acid and then fall as acidic precipitation (pH < 5.2). Acid rain can pour directly into waters and increase pH or runoff from soils and carry harmful chemicals with them.

Global Warming

Anthropogenic global warming is causing heat pollution of waters. Many marine species become stressed in warmer environments and require more oxygen to match their increasing metabolic rates. Carbon dioxide (CO₂) emissions are causing ocean acidification as well, which reduces carbonate availability. Organisms with calcareous shells and exoskeletons require carbonates to survive.

Fig. 6. Crabs are one of the species that have an exoskeleton and can be affected by a reduction in carbonate availability. Molluscs and other bivalves also suffer from a lack of carbonate.

Effects of Polluted Water

As you can imagine, with water being such a crucial part of human and wildlife life, polluted water causes severe problems for the ecosystems and for the human species. Check out our Impacts of Polluted Water article for more detail, but here are some of the consequences of polluted water:

• Algal blooms can affect entire aquatic ecosystems and can even result in anoxic 'dead zones' where no life can survive.
• The breakdown of algal blooms can release poisonous toxins that harm wildlife and can spoil drinking water.
• Sedimentation fluxes from agricultural and industrial runoff can severely affect coastal ecosystems by smothering producer populations and adding an excess of nutrients.
• Water polluted from fertilisers and sewage can contain nitrate ions, which form acid rain after evaporation and condensation.
• Debris from litter can physically disrupt and trap organisms.
• Dangerous microorganisms can spread disease in aquatic ecosystems.
• Rising temperatures increase stress on aquatic organisms and cause disease to spread quicker.
• Many metal compounds are toxic and can poison wildlife.
• Carcinogenic and radioactive chemicals can lead to the rise of mutations and the breakdown of populations.

Solutions for water pollution

There are many solutions to prevent water pollution, this can be by introducing widespread regulations or by stopping a point of serious pollution. Here are some examples:

• Daily water conservation: water is a limited resource and essential for everyday life, so conserving water by turning off taps and limiting showers will save money and reduce pollution.
• Sewage treatment: the appropriate treatment of liquid waste is necessary to reduce water pollution. Many sewage treatment systems focus on the removal of toxic chemicals and particulates, but implementing methods to remove nutrients and microorganisms could limit pollution massively.
• Agriculture: limiting the use of pesticides and fertilisers in agriculture is needed to reduce water pollution of nearby waterways. Transitioning to sustainable and regenerative agricultural methods will help lessen the need for agrochemicals.
• Renewable energy: changing to renewable energy sources will reduce the amount of waste released from factories and power plants.
• Stormwater management: powerful storms can increase the rate and unpredictability at which water runs off. Reverse osmosis, sand filtration, and simple blockades can help limit the runoff of polluted waters.

Hopefully, you now know more about water pollution. Remember that water pollution is the alteration of the natural composition of a body of water and can be caused by humans but also by natural causes.