Water Pollution: Impacting Life Below The Surface

Water pollution is a pressing issue that poses a significant threat to aquatic life and ecosystems. It occurs when harmful substances, such as chemicals and microorganisms, contaminate bodies of water, degrading water quality and rendering it toxic to humans and the environment. This issue is exacerbated by the fact that water is a 'universal solvent,' easily mixing with and dissolving toxic substances.

One of the main sources of water pollution is the agricultural sector, which is the largest consumer of global freshwater resources. Agricultural activities contribute to water pollution through the use of fertilizers, pesticides, and animal waste, which wash into waterways during rainfall. This leads to eutrophication, where excessive nutrients deplete oxygen levels in the water, creating dead zones where aquatic life cannot survive.

Additionally, sewage and wastewater, including domestic and industrial waste, contribute to water pollution. Oil spills, both accidental and from regular operations in the shipping industry, also play a significant role in polluting marine environments.

The effects of water pollution are devastating, with unsafe water causing approximately 1.8 million deaths in 2015, according to a study published in The Lancet. It also has negative impacts on human health, leading to various infections and health problems, including cancer and cardiovascular conditions.

Oil spills

The impact of oil spills on wildlife varies depending on the amount of exposure, the pathway of exposure (ingestion, absorption, or inhalation), the age and health of the animal, and the type of synthetic chemicals used in the cleanup process.

Sewage and wastewater

Untreated or partially treated sewage and wastewater can contaminate water bodies and harm aquatic life. For example, in September, a sewage leak in Staffordshire, UK, killed over 15,000 fish in the River Trent. This incident highlights the detrimental impact of sewage on aquatic ecosystems.

One of the significant effects of sewage and wastewater pollution is the introduction of harmful bacteria and chemicals that can make people and animals sick. For instance, sewage contamination in water sources can lead to the spread of diseases such as E. coli, typhoid fever, salmonella, cholera, and hepatitis A.

Another consequence of sewage and wastewater pollution is eutrophication, which occurs due to the presence of nutrient-rich materials such as fertilizers (nitrogen and phosphorus) and waste products. Eutrophication leads to excessive growth of algae, reducing light transmission in the water and decreasing oxygen levels, ultimately creating "dead zones" where aquatic life cannot survive.

In addition to the direct impact on aquatic life, sewage and wastewater pollution also affect the food chain. Fish and other aquatic organisms accumulate heavy metals and toxins as they consume contaminated prey. This process, known as biomagnification, can result in the poisoning of humans and other creatures higher up the food chain who consume these fish.

Furthermore, industrial wastes, which are often treated in the same wastewater treatment plants as domestic wastes, introduce a range of chemicals and heavy metals into water bodies. These pollutants can have toxic effects on aquatic life, reducing their lifespan and reproductive abilities.

While most wastewater treatment facilities aim to remove these contaminants, it is important to recognize that they are not always fully effective, and some pollutants may still find their way into sensitive ecosystems. Therefore, it is crucial to properly manage and treat sewage and wastewater to minimize their impact on life below water.

Eutrophication

The effects of eutrophication on life below water include:

• Dense blooms of noxious, foul-smelling phytoplankton that reduce water clarity and harm water quality.
• Increased growth of filamentous and short-lived nuisance macroalgae at the cost of long-lived species, leading to a change in the structure of macroalgae communities with reduced diversity.
• Oxygen depletion in lower water layers, creating "dead zones" where waters are devoid of life.
• Production of toxins by some algal blooms, which can be harmful to people and wildlife.
• Changes in aquatic community structure, with small-bodied zooplankton tending to dominate plankton communities during cyanobacterial blooms.
• Increased carbon dioxide levels and ocean acidification, which can impact the growth of fish and shellfish and prevent shell formation in bivalve mollusks.

Microplastics

The effects of microplastics on marine life vary. They can cause blockages in the gastrointestinal system, reduced food intake, developmental disorders, and behavioural changes. In some cases, microplastics can even be fatal.

Climate change

Ocean Warming

The ocean absorbs much of the sun's energy trapped by greenhouse gases in the atmosphere, causing ocean waters to warm. Warmer waters also contribute to sea level rise. This warming has already had dramatic impacts on marine animals, plants, and microbes. Warmer water can also increase oxygen demand and alter organisms' metabolisms.

Ocean Acidification

The ocean absorbs carbon dioxide from the atmosphere, which changes the pH of the seawater, making it more acidic. This increased acidity makes it more difficult for organisms such as corals, molluscs, and some plankton to build and maintain their structural integrity, such as shells and skeletons.

Ocean Deoxygenation

Warmer water cannot hold as much oxygen as cold water. This loss of oxygen in seawater is further exacerbated by increased oxygen consumption by various organisms and increased stratification and changes in ventilation. Deoxygenation, or hypoxia, will be lethal to many species, especially sessile (non-mobile) marine organisms.

Coral Bleaching

Coral reefs host a wide variety of marine life and are important for tropical fisheries. They are vulnerable to even small increases in water temperature, suffering high mortalities when temperatures rise as little as 1-2°C above the normal range. This results in coral bleaching, where the coral animal ejects the algal partners it depends on. After mass coral mortalities due to bleaching, reef recovery can take at least 10-15 years.

Impact on Fisheries

Mobile species, such as fish, may respond to warming waters by moving to more favourable regions, with populations shifting poleward or to deeper waters. As a result, fisheries in tropical regions could lose up to half of their current catch levels by the end of the century.

Impact on Polar Regions

In polar seas, species adapted to life on or under sea ice are directly threatened by habitat loss due to climate change. The complex interactions between the rich diversity of life in these regions may be altered if new warmer-water species extend their ranges as sea temperatures rise.

Extreme Weather Events

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