Pollution's Impact On Aquatic Life: A Worrying Trend

Water pollution is a pressing global issue that has made its mark everywhere. It occurs when harmful substances contaminate a body of water, degrading water quality and rendering it toxic to both the environment and humans.

Water pollution has detrimental effects on aquatic life. For instance, contaminants like heavy metals, oil spills, and pesticides can directly harm fish and other aquatic organisms, causing deformities and even death. Pollution can also cause the destruction of habitats, as certain contaminants can promote the growth of fungus, bacteria, and algae, which can impede the growth of plants that marine life depends on.

In addition, water pollution can alter ocean temperature, pH, salinity, and oxygen levels, disrupting biological processes and physical environments essential to marine life. For example, algal blooms—which are often caused by nutrient pollution—can consume oxygen and block sunlight, resulting in environments with low levels of dissolved oxygen that can suffocate fish and other life, creating dead zones.

Furthermore, contaminants in wastewater can affect corals in various ways, impacting their reproduction, feeding, and growth. Pharmaceuticals, such as antidepressants and synthetic hormones, can also have behavioural and health impacts on fish.

The effects of water pollution on aquatic life are far-reaching and pose significant threats to the health and survival of marine ecosystems.

The destruction of habitats

Water pollution has a detrimental impact on marine life and their habitats. Wastewater carries solids, nutrients, contaminants, and pathogens into the ocean, causing coral bleaching and disease and threatening the lives of coral, fish, and shellfish.

Wastewater pollution can alter ocean temperature, pH, salinity, and oxygen levels, disrupting the biological processes and physical environments that marine life depends on. For example, wastewater pollution can lead to coral bleaching by reducing oxygen levels in the water, causing what is known as eutrophication, where waters become devoid of life.

Nutrients from agricultural runoff and wastewater cause algal blooms, which block sunlight from reaching underwater plants and consuming oxygen, leading to hypoxic environments that can trigger coral bleaching events and reduce the recovery capacity of corals.

In addition, suspended solid materials in wastewater, such as decomposing plant matter, algae, minerals, and silt, can block sunlight, decrease photosynthesis and coral growth, cause physical stress, and clog the filters of shellfish.

Contaminants in wastewater, such as herbicides, metals, and synthetic compounds, can also affect corals and other marine life at multiple life stages, disrupting reproduction, feeding, and growth. These contaminants accumulate through the food web and increase mortality rates in larger fish.

Pharmaceuticals, such as antidepressants, can impact fish behaviour and cause mortality, while synthetic hormones and endocrine disruptors can impair reproductivity and contribute to aggressive tendencies in fish.

The Impact on Human Health

Water pollution also has significant impacts on human health. According to a study published in The Lancet, water pollution caused 1.8 million deaths in 2015. Contaminated water can cause various illnesses, including cholera, giardia, typhoid, and hepatitis.

Pathogens, in the form of bacteria and viruses from human and animal waste, are a major cause of illness from contaminated drinking water. In addition, chemical and industrial pollutants in water supplies can cause a range of health issues, from cancer to hormone disruption to altered brain function.

Preventing Water Pollution

To address water pollution, it is essential to understand the sources of pollution and the types of water bodies affected. Point source pollution comes from a single source, such as a manufacturing facility or oil refinery, while nonpoint source pollution comes from diffuse sources like agricultural or stormwater runoff.

Reducing plastic consumption, properly disposing of chemicals and non-biodegradable items, maintaining vehicles to prevent leaks, and reducing the use of pesticides and herbicides can all help prevent water pollution.

Physical harm to fish

Rising pollution has a significant impact on aquatic life, and fish are particularly vulnerable to the physico-chemical changes in their environment. Here are some ways in which rising pollution causes physical harm to fish:

• Temperature changes: Fish are poikilothermic, meaning their body temperature is similar to the water they inhabit. Therefore, abrupt temperature changes can be harmful, even fatal, to fish. For example, transferring fish to water that is 8°C colder or warmer can cause paralysis of the respiratory and cardiac muscles, leading to death.
• Oxygen deficiency: Pollution by biodegradable organic substances, such as sewage and agricultural waste, can lead to oxygen deficiency in water bodies. This is because bacteria use oxygen to decompose these substances, reducing the oxygen available for fish. Fish affected by oxygen deficiency exhibit symptoms such as gasping for air, loss of balance, and ultimately death.
• Ammonia toxicity: Ammonia pollution, often from agricultural waste and industrial effluents, is highly toxic to fish. It affects their nervous system, causing increased respiration, restlessness, violent muscle spasms, and eventually death.
• Nitrite and Nitrate toxicity: Nitrite and nitrate pollution, commonly from sewage effluents and fertilizer use, can be toxic to fish. Nitrites, in particular, interfere with the oxygen-carrying capacity of fish blood, leading to reduced oxygen supply to tissues and possible death.
• Hydrogen Sulfide toxicity: Hydrogen sulfide, often found in organically polluted waters, is highly toxic to fish. It affects their nervous system and can cause respiratory failure and death.
• Carbon Dioxide toxicity: Both excess and deficiency of carbon dioxide in water can be harmful to fish. High levels of CO2 can cause acidosis, while low levels can lead to alkalosis, affecting the acid-base balance in fish blood and tissues.
• Metal toxicity: Metals, such as aluminium, chromium, iron, nickel, copper, zinc, arsenic, cadmium, mercury, and lead, can be toxic to fish, especially in their early developmental stages. These metals accumulate in sediments and aquatic organisms, leading to bioaccumulation and posing a significant threat to fish populations.
• Chemical toxicity: Various chemicals, including active chlorine, cyanides, phenols, pesticides, and oils, can cause physical harm to fish. For example, chlorine can cause increased respiration, nervous disorders, and death. Pesticides can lead to narcosis, respiratory issues, and even death.
• Physical damage: Oil spills and refined products can cause physical damage to fish, such as gill contamination, reduced respiratory capacity, and skin and eye damage.

Knock-on effects in the food chain

Rising pollution has a knock-on effect on the food chain, with toxins accumulating in larger fish and other marine life. This has a direct impact on humans, who are at the top of the food chain. Microplastics have been found in human bloodstreams due to the consumption of contaminated fish.

Water pollution can cause algal blooms, which can be toxic to people and wildlife. These blooms can also lead to oxygen depletion, creating 'dead zones' in the water where marine life cannot survive. This has a knock-on effect on the food chain, as the base of the chain is disrupted.

Nutrient pollution, caused by excess nitrogen and phosphorus, is the number-one threat to water quality worldwide. This type of pollution can cause algal blooms and harm marine life and ecosystems.

Herbicides, metals, and synthetic compounds such as polychlorinated biphenyls (PCBs) have toxic effects on marine life, including corals and fish. These contaminants can impact reproduction, feeding, and growth, reducing habitat options for other organisms. In fish, these toxins can accumulate through the food web and increase mortality rates.

Contaminants of Emerging Concern (CECs) are pollutants that are often unregulated and can build up in the tissues of marine life. These include agricultural chemicals, runoff from cities, household products, and pharmaceuticals. Endocrine disruptors, a type of CEC, can impair the reproductivity of fish and contribute to aggressive tendencies.

Eutrophication

Ecological Impacts

Increased Biomass of Phytoplankton Resulting in Algal Blooms

The increased availability of nutrients such as nitrates, phosphates, and sulfur leads to the growth and multiplication of phytoplankton, resulting in algal blooms. These blooms can occur in both freshwater and marine environments and are often characterised by a high density of pigmented cells that discolour the water. Enclosed and semi-enclosed water bodies are particularly sensitive to increased nutrient loads, especially nitrogen input from agricultural effluents, which can potentially lead to ecosystem collapse.

Toxic or Inedible Phytoplankton Species (Harmful Algal Blooms)

Harmful algal blooms (HABs) involve toxic or harmful phytoplankton that can produce toxins or accumulate biomass, affecting co-occurring organisms and altering food web dynamics. Impacts include mortality among fish, birds, and mammals following consumption or indirect exposure to HAB toxins, as well as substantial economic losses to coastal communities and commercial fisheries.

Increased Blooms of Gelatinous Zooplankton

Phytoplankton serve as a food source for zooplankton, which are primarily transported by ambient water currents. Gelatinous zooplankton, such as jellyfish, tend to increase in relative importance compared to crustacean zooplankton in areas affected by pollution, over-fishing, and climate change.

Decreases in Water Transparency (Increased Turbidity)

The growth of phytoplankton and subsequent algal blooms cause increased turbidity or decreased penetration of light into the lower depths of the water column. This can inhibit the growth of submerged aquatic plants and negatively affect species that depend on them, such as fish and shellfish.

Dissolved Oxygen Depletion or Hypoxia

Algal blooms can cause strong fluctuations in dissolved oxygen levels. As algae populations grow rapidly, they can block sunlight from reaching other organisms, leading to a decrease in dissolved oxygen levels. When the algae die, their decomposition by bacteria further consumes oxygen, creating hypoxic or anoxic "dead zones" that lack sufficient oxygen to support most organisms. These dead zones are commonly found in freshwater lakes and coastal marine environments, posing a significant threat to lucrative commercial and recreational fisheries worldwide.

The decomposition of dead algae by bacteria not only consumes oxygen but also produces carbon dioxide, leading to an increase in the carbonic acid content of the water. This results in acidification, which poses a serious threat to calcifying benthic organisms such as scallops and other bivalves. Eutrophication-driven acidification exacerbates ocean acidification due to the uptake of atmospheric carbon dioxide.

Species Biodiversity Decreases and the Dominant Biota Changes

Human Health Impacts

Harmful algal blooms can produce toxins dangerous to humans, which can accumulate in shellfish and other seafood, posing risks to human health. These toxins can cause various illnesses, including paralytic, neurotoxic, and diarrhoeic shellfish poisoning.

Socio-Economic Impacts

Impact on Recreation and Tourism

Aesthetic Impacts

The presence of dense algal growth and the associated unpleasant smells can affect the aesthetic value of water bodies and surrounding areas.

Economic Impacts

Commercial fish and shellfish may become unsuitable for consumption due to contamination by harmful algal blooms, resulting in economic losses for the fishing industry. Eutrophication can also lead to the collapse of ecosystems, impacting fisheries and aquaculture. The annual economic costs related to illness and death caused by consuming poisoned fish products are significant globally.

Oil spills

Impact on Aquatic Life

Marine Mammals

Marine mammals, such as bottlenose dolphins, spend a lot of time near the surface of the water, where oil floats, putting them at high risk during oil spills. They can be exposed through inhalation, ingestion of oiled food, or swimming through it, leading to devastating health issues. Physical contact with oil affects furred mammals like sea otters as they rely on their outer coats for buoyancy and warmth. These animals often succumb to hypothermia, drowning, and smothering when oil flattens and adheres to their outer layer.

Birds

Once oiled, birds cannot regulate their body temperature or use their feathers for insulation against water and cold weather, which can lead to death by hypothermia. Oiled birds can also die from dehydration and exhaustion.

Fish

Fish important to recreational and commercial fishers are impacted by oil spills. Oily water damages the gills of fish and makes it harder for them to get enough oxygen. Oil can also kill fish eggs and impair growth in young fish.

Coral Reefs

Coral reefs are important components of marine ecosystems as they serve as nurseries for shrimp, fish, and other animals. They are rapidly degrading due to a variety of environmental and anthropogenic pressures, leading to significant changes in species diversity, abundance, and habitat structure worldwide. Oil dispersants and dispersed oil are harmful to soft and hard coral species at early life stages.

Preventive Measures

Some preventive measures to reduce water contamination and protect aquatic ecosystems include:

• Following recycling practices and proper waste disposal
• Using eco-friendly products
• Implementing and enforcing water quality laws and regulations
• Using detergents with low or no phosphate to prevent eutrophication
• Controlling stormwater runoff
• Avoiding the use of non-degradable products

Frequently asked questions