Water Pollution: Killing Animals, Destroying Ecosystems

Water pollution is a pressing issue that poses a significant threat to aquatic ecosystems and the animals that inhabit them. It refers to the contamination of water bodies, such as rivers, lakes, and oceans, due to various human activities and industries, including agriculture, industrial discharges, and improper waste disposal. This pollution has far-reaching consequences, affecting not only marine life but also birds, mammals, and ultimately, humans. The delicate balance of aquatic ecosystems is disrupted, leading to a decline in biodiversity and the health of both animal and human life.

Plastic waste

Similarly, it is estimated that 60% of all seabird species have consumed plastic, with predictions of this figure rising to 99% by 2050. Seabirds often mistake plastic for food, leading to fatal intestinal blockages and starvation. Plastic waste kills approximately one million seabirds annually.

The durability of plastic, which can take hundreds to thousands of years to degrade, poses a long-term threat to wildlife. Microplastics, resulting from the breakdown of larger plastic waste, are spread throughout the water column and have been found in various environments, including drinking water systems. These microplastics are then consumed by smaller organisms, transferring plastic up the food chain to larger predators and humans.

To address the detrimental impacts of plastic waste, it is crucial to focus on prevention and proper waste management. This includes minimizing plastic leakage into the environment, reducing toxicity, and promoting reuse, repurposing, and recycling.

Pesticides and heavy metals

Pesticides are toxic to aquatic life, even at low concentrations. They can directly harm fish and other aquatic organisms, causing gill damage, reproductive issues, and even death. When too much pesticide is used, it can be carried by rainwater and enter waterways. These chemicals do not decompose and remain dangerous for a long time, and can be absorbed into the tissue or organs of plants. When aquatic animals eat these plants, they ingest the pesticides, and when other animals eat these contaminated animals, the pesticides move up through the food chain. The higher in the food chain, the higher the concentration of pesticides.

Pesticides can also be carried into waterways by agricultural runoff. This runoff leads to nutrient pollution, a major contaminant in freshwater sources, causing issues like eutrophication and harmful algal blooms. Excessive amounts of nitrogen and phosphorus from fertilizers and sewage can cause eutrophication, an overgrowth of algae that depletes oxygen levels, suffocating aquatic life. When these algae die, the process of decomposition uses up the oxygen dissolved in the water, creating hypoxic (low-oxygen) or anoxic (no-oxygen) "dead zones" where fish and other aquatic life cannot survive.

Heavy metals are also toxic to aquatic life and can accumulate in the tissues of organisms over time through bioaccumulation. When a predator consumes contaminated prey, these heavy metals become more concentrated within their bodies through a process called biomagnification. Top predators, such as large fish, marine mammals, and predatory birds, can accumulate very high levels of heavy metals, leading to severe health problems and reproductive issues. Heavy metals can be released into the atmosphere by the combustion of fossil fuels and eventually find their way into bodies of water. They can also enter water sources through industrial discharge, mining activities, and agricultural runoff.

Oxygen depletion

Oxygen is essential for all aquatic life. Aquatic animals absorb oxygen into their blood through their gills or directly through their body surface. Oxygen enters a water body through diffusion from the surrounding air, aeration, and as a by-product of photosynthesis by algae and aquatic plants.

Nutrient pollution, such as excess nitrogen and phosphorus from fertilizers, dog waste, and other sources, can enter water bodies through runoff or direct discharge. This promotes the growth of algae and aquatic plants, which can lead to oxygen depletion when they decay. Pesticides and heavy metals can also enter waterways, harming or killing fish and impairing their ability to locate food and protect themselves.

The increase in water temperature also impacts oxygen levels. Warmer water has lower oxygen content, and higher temperatures increase biological activity and oxygen consumption by aquatic organisms. Deoxygenation is further exacerbated by warming temperatures, leading to a reduction in the quality and quantity of suitable habitats, growth rates, visual function, reproductive capacity, and an increase in disease susceptibility.

Marine debris, such as plastic waste, can also contribute to oxygen depletion. Debris can smother and damage sensitive habitats like coral reefs, reducing oxygen production and increasing the risk of hypoxia. Additionally, animals may become entangled in marine debris, restricting their movement and, in the case of air-breathing fauna, preventing them from reaching the surface to breathe.

Marine debris entanglement

Smaller animals, such as dolphins, seals, sea lions, and smaller sea turtles, are particularly vulnerable to entanglement. They may drown immediately if entangled in large or heavy gear. Even if they do not drown, their movement can be restricted, leading to starvation as they are unable to feed. Entanglement can also cause abrasions and dangerous infections, further reducing the animal's chances of survival.

Larger animals, such as whales, can typically pull themselves free from entanglement but still face significant risks. Whales may suffer from exhaustion and infection, and entanglement is considered a primary cause of human-induced mortality in many whale species, including right whales, humpback whales, and gray whales. The restrictions caused by entanglement can also make it difficult for animals to avoid vessels, increasing the risk of vessel strikes.

The impact of marine debris entanglement is not limited to the animals themselves. It can also affect the ecosystem as a whole. For example, derelict fishing gear can continue to trap and kill marine animals long after it has been lost or discarded, in a process known as "ghost fishing." Additionally, non-native species may hitchhike on marine debris, invading new regions and potentially becoming invasive, which can wreak havoc on ecosystems by depleting food sources or destroying habitats.

Responding to marine debris entanglement is crucial but challenging. Trained responders use specialized tools and techniques to safely disentangle animals, often from small inflatable rescue boats. They may employ historic whaling techniques, such as "kegging," where grapples or hooks are thrown to attach to the entangling gear, and buoys are used to control the animal's movement. These rescue efforts are dangerous for both the animals and the rescuers, and each successful disentanglement provides valuable information to guide future prevention strategies.

Habitat damage

Water pollution has a devastating impact on animal life, and one of the most significant ways it does this is through habitat damage. Marine debris, such as plastic, fishing lines, nets, and even derelict lobster traps, can smother and damage sensitive habitats like coral reefs and seagrass. This, in turn, affects the animals that rely on these habitats for survival.

Coral reefs, for example, are incredibly diverse ecosystems, often referred to as the "rainforests of the sea". They provide a home for numerous species of marine life, from small invertebrates to larger fish and sharks. When debris smothers and damages these reefs, the animals lose their shelter and breeding grounds, and the complex web of life that depends on these habitats is disrupted.

Seagrass meadows are another vital habitat that suffers from water pollution. These underwater grass beds provide food and shelter for a variety of marine species, including sea turtles, manatees, and juvenile fish. They also play a crucial role in stabilizing sediment, improving water quality, and protecting coastlines from erosion. When heavy or large debris falls onto seagrass beds, it can smother and damage the grass, leading to a loss of habitat for these animals and a decline in their populations.

The impact of habitat damage from water pollution extends beyond the immediate area. For instance, when native grasses and populations of animals that birds prey on die off due to pollution, bird populations are affected as their food sources diminish. This can lead to a decline in bird numbers and even the disappearance of certain bird species from the affected areas.

Furthermore, water pollution can create 'dead zones' where aquatic life cannot survive due to oxygen depletion caused by excessive algae growth. These dead zones are a result of agricultural runoff containing nitrogen and phosphorus, which promote algae growth. When the algae die, their decomposition consumes oxygen, leading to oxygen depletion in the water. This, in turn, affects the survival of fish and other aquatic organisms, creating a ripple effect up the food chain.

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