• Mckenzie Bagayas

Water Pollution and its effect on Aquatic Biodiversity

“Living species variations from sources that include terrestrial, marine, different aquatic ecosystems and also ecological groups to which they belong: including diversity among species and also ecosystems.” This is the well-accepted definition of biodiversity that was made by the United Nations Convention on Biological Diversity.

Biodiversity could also refer to the variety of life on Earth. Variety of life and living things can come in the form of genetic diversity among species within an ecosystem and diversity of ecological systems. Biodiversity may also include evolutionary, ecological, and cultural processes that sustain life. Biodiversity is not solely about rare, threatened, and endangered species. Instead, biodiversity is about the interconnectedness of all living things.

Although we, humans, are just a single species amidst all of the living things present on this Earth, we are the only species whose actions can have a huge impact on biodiversity. With that said, we have the obligation to try our best to practice biodiversity conservation.

Biodiversity - Why is it important

People value biodiversity differently, some through a utilitarian lens while others value their intrinsic value.

Biodiversity in some form or way is capable of providing for our basic needs like food, fuel, shelter, and even medicine. This is where the utilitarian perspective of the value of biodiversity comes in. Being conscious of the utilitarian value of biodiversity leads to the appreciation of ecosystems. With the appreciation and care of ecosystems natural and beneficial processes such as pollination, seed dispersal, climate regulation, water purification, nutrient cycling, and control of agricultural pests are improved. The utilitarian value of biodiversity could also come in the form of possible unknown services and the possibility of discovering new medicines. Moreover, people also value biodiversity for their cultural, spiritual, and religious value.

Biodiversity also holds intrinsic value. In other words, people value biodiversity for its inherent worth regardless of its value to anyone or anything else. The intrinsic value of biodiversity is more of a philosophical concept that can stem from an individual’s belief in the right to exist regardless of species.

People may also value biodiversity for its relational value. We find value in the intricate relationships we form with nature. These relationships impart a sense of wellbeing, responsibility, and connection.

The various ways people value biodiversity are important because this can be leveraged to influence conservation decisions people make every day.

Water pollution and its effect on Biodiversity

For aquatic environments, pollution poses a serious issue as it can cause variations in the environmental conditions to which aquatic organisms are sensitive. Aquatic organisms respond to drastic changes in their environment by migrating to any other suitable habitat or in extreme cases they just die off. In less extreme cases only the reproductive capacity and metabolism of the aquatic organisms are affected negatively. However, this can have a negative consequence on their population in the long run.

Every species present in various trophic levels are important for freshwater ecosystems. Zooplanktons and macrobenthic organisms modulate the aquatic productivity of aquatic ecosystems by occupying the intermediate level in the food chain. The aforementioned aquatic organisms are also capable of indicating changes in the aquatic environment. Recent studies have demonstrated that some species of zooplankton and macrobenthic organisms can be used as an indicator of deteriorating water quality resulting from eutrophication and or pollution.

The intricate relationships between species in a food web are important. Fish numbers may start to dip as a result of food chain disruption and diversity loss or degradation. The relationship between biodiversity decline and food chain disruption was demonstrated when data from two separate studies about the Egyptian Nile waters conducted several years apart were compared side by side. In 1907 the first study reported that there are a total of 85 fish species in the Egyptian Nile waters. However, the second study, which was conducted in 1997, reported that there are a total of 71 fish species. This significant reduction in fish species has been attributed to several pollution sources generated by industrial activities, agricultural sources, and sewage drains. These findings showed evidence that pollution can reduce species diversity and affect the fish population.

Studies have also shown that pollution can make rivers more susceptible to drastic changes. In one study, researchers investigated the effects of rising water temperature and low oxygen levels brought about by pollution on the common mayfly species. Mayfly species are considered cool water insects and they are used as bioindicators that help determine ecologically important features of freshwater ecosystems. During warmer seasons, they have trouble thriving in polluted waters due to elevated temperatures and reduced dissolved oxygen; conditions that the mayfly species are not accustomed to.

In a controlled laboratory setting, mayfly species such as the green drake and blue-winged olive, or Ephemera danica and Serratella ignita respectively, are capable of tolerating higher temperatures where dissolved oxygen levels are sufficient. Lowered oxygen levels, near depletion, can lower the mayflies’ ability to tolerate temperature extremes. These laboratory findings were substantiated by field study data. Analysis of data collected by the Environment Agency and Natural Resources Wales demonstrated that mayflies populations dropped when the freshwater oxygen concentration decreased and temperature increased.

So with all the findings of the studies combined, there is strong evidence that water pollution can reduce dissolved oxygen in freshwater environments and increase temperature. Moreover, reductions in dissolved oxygen compromised the mayflies’ ability to survive temperature extremes. Their ability to increase in numbers was also severely restricted even at temperatures below the lethal limits.

Improving dissolved oxygen levels in freshwater environments is one method of improving their resilience against rising temperatures. By reducing the amount of pollution, especially those of agricultural origins, the freshwater environment can absorb oxygen better. This is supported by a review published in Global Change Biology, which mentioned that there is growing evidence that freshwater ecosystems that contain minimal pollution are resilient against changes brought about by climate change. Pollution reduction may also help improve biodiversity in the freshwater ecosystem.

What are the main threats to biodiversity?

We live in an unofficial unit of geologic time called “anthropocene”. In this geologic time, humans have developed the capacity to cause impactful changes to our environment. Unfortunately, most of these impactful changes cause harm to our environment. What’s even more worrying is that these changes are happening at an alarming rate. Before the anthropocene period, environmental changes and extinctions occurred at a natural and slow pace. However, during the anthropocene period species are going extinct faster than they should. Some major direct threats to an environment’s biodiversity include global climate change, pollution, the introduction of invasive species, unsustainable use of resources, and habitat destruction and loss. The steady increase in our population and the subsequent increase in demand for resources are the primary causes of widespread biodiversity loss. These are hard to tackle because they stem from many interrelated and complex factors.

Major threats to Global Aquatic Biodiversity can be categorized into the following categories:

Climate change

Erratic atmospheric, biogeochemical, and hydrological cycles are the result of climate change. These fluctuations include changing temperatures, changes in the start and end of seasons, irregularities in the carbon cycle, and solar radiation. These changes are evidenced by rising temperatures which increased by 0.6 degrees Celsius in the past centuries. Researchers were able to determine this temperature increase by studying tree rings and ice cores. This temperature change caused a significant decline in oceanic coral reef ecosystems. The temperature increase also caused sea levels to rise which led to coastal regions quickly being submerged. It is estimated that sea levels rose by 0.1 to 0.2 meters in the last century. These changes may damage habitats and even species directly leading to loss of biodiversity.

Water pollution

Contaminants that can pollute water can be categorized into physical, biological, chemical, and radioactive. These contaminants may originate from various sources such as agricultural runoff, mining activities, industrial effluents, and domestic sewage.

It is estimated that water pollution, which leads to drinking water contamination, caused 485,000 diarrhoeal deaths each year. Most of these deaths happen in Asia and Africa. Pathogenic microorganisms may enter drinking water sources through the improper disposal of untreated wastewater.

Nuclear power plants can produce nuclear waste and end up in water bodies as well.

Point sources or non-point sources are two major categories of pollutants. Point source pollution comes from a single easily identifiable place. Non-point source pollution originates from several locations. This category of pollutants is harder to address because their origin is hard to pinpoint.

According to the United States Environmental Protection Agency, point source pollution is defined as “any contaminant that enters the environment from an easily identified and confined place”. Some common producers of point source pollutants include oil refineries, paper mills, and auto plants, specifically those ones that use water as part of the manufacturing process. They would discharge the water used for the manufacturing process as wastewater and are often dumped into water bodies. This wastewater contains some harmful chemical pollutants that can cause damage to the water bodies’ ecosystem. Another common producer of point source pollutants is the municipal wastewater treatment plants. Effluents from the municipal wastewater treatment plants are often dumped into waterways which leads to the introduction of nutrients and microbes into the water. If this waterway connects to a drinking water source, the drinking water source would become contaminated. Once they are contaminated, people who live in the households that draw water from this drinking water source are at risk of acquiring water-borne diseases. The nutrients from the effluent can encourage the growth of algae in the water and may lead to algal blooms which may damage water quality.

Non-point source pollution is hard to address because it’s difficult to pinpoint its exact origin. Consider this situation, there are several large plots of land that are made available for grazing to the public. A huge number of grazing animals may hang around in these plots of land to graze and even defecate in. When it rains, the rain would generate runoff from these plots of lands which may carry microbial pathogen and nutrients. The runoff could enter nearby water bodies that may connect to drinking water sources. This drinking water source would now be contaminated with microbial pathogens. Aside from that the drinking water source would also be contaminated with nutrients like phosphorus and nitrates. These nutrients could encourage algae growth and cause algae blooms in the drinking water source. When concerned individuals would find out that the drinking water source has a problem, they would have a hard time figuring out what went wrong. Primarily because it is hard to determine where the pollutants came from.

Industrialized nations have accepted that the pollution problem has reached pandemic proportions. The worse thing about them is that they are damaging to both people’s health and to entire ecosystems which leads to biodiversity loss. That is why a lot of countries are trying to resolve the pollution problem.


This goes back to the definition of biodiversity, there is a delicate relationship between various species in an ecosystem. When specific aquatic species are overexploited or overfished, their dwindling numbers may negatively affect other species that are dependent on them. Sadly, a lot of aquatic species are being overfished, fish species such as tuna, cod, salmon, bass, grouper, shark, and swordfish. Destruction of ecosystems due to overfishing of specific aquatic species has been observed in several studies. One study regarding sand eel and cod overfishing revealed that their dwindling numbers increased copepod populations which led to ecological imbalance.

Invasion by exotic species

Human activities like travel unintentionally carried and transported certain species to environments that they are not native to. When this happens, sometimes the invading species dominate the new environment causing ecological damage. This damage can lead to increased susceptibility to chemical and physical insults brought about by pollution and or climate change.

Habitat degradation

A habitat is a place an organism considers its home, as it has the right environmental conditions to support the said organism. The main components of a habitat include shelter, water, food, and space. Some human activities such as dredging, bottom trawling, shrimp farming, dynamiting, and poison fishing caused widespread destruction in aquatic habitats. These activities physically damaged the habitat, made food unavailable, and destroyed shelters making it difficult for organisms to breed.

Aside from the aforementioned activities, the usage of boats and ships for transportation has caused habitat damage through their hulls, propellers, and anchors. Although divers and snorkelers are taught to respect delicate aquatic habitats, their direct contact with them, deliberate or not, is unavoidable. Oftentimes, this contact can damage aquatic habitats. Even the infrastructure that supports our internet, a giant web of submarine fibre optic cables, can damage marine habitats. Especially when new ones are installed or old ones are undergoing maintenance.

When habitat destruction occurs, species reliant on that habitat would either move to a different place or die off. Either way, it would have a huge impact on biodiversity as species richness, abundance, distribution, genetic variation, and inter-population dynamics would be negatively affected.

Flow modification

Altering the flow of moving water bodies, such as rivers, can have drastic changes to the physical habitat, habitat access, food supplies, behaviour of aquatic organisms, community composition, energy expenditure, and population dynamics in a given aquatic ecosystem. More and more studies have concluded that altered flow regimes can have negative consequences on a water bodies’ biodiversity.

Modifications in water follow are quite common in running water bodies. They are more frequent and severe in places with high demand for water storage and food protection.

Flow modification may have caused low water levels in several large rivers around the world. This reduction in water levels can affect the aquatic ecosystem of the river leading to biodiversity loss.

Effects of Biodiversity loss on species that are not threatened

Concerns regarding biodiversity loss shouldn’t be focused on species that are threatened or on the verge of extinction, it should be on all species. Specifically, the focus should be directed towards the population of every species, and shifts in domination patterns. Common species, or species whose conservation status is “LC” or “Least Concern”, are the major drivers of most ecosystem processes. Any alterations in their population lead to harmful changes in the ecosystem. This is especially true for fishes. Within the aquatic food chain, common fish species generally feed on the benthic fauna and most of the pelagic fauna feed on the fish. Thus, fish is important for controlling benthic populations and is a vital food source for pelagic fauna. When the population of dominant fishes would decrease, other fish species that are functionally equivalent to the dominant fish species cannot act as a substitute for them. This is due to the fact that dominant fishes tend to cover more trophic levels. Severe reductions in fish populations are especially problematic when the fish species is a long-distance migratory fish. Migratory fishes are capable of carrying materials like nutrients through long distances. When their population would dwindle, this process of carrying materials through long distances would be compromised.

Final Thoughts

Biodiversity is the sum of all species within an ecosystem and the important roles that they play within it. Each species in an ecosystem has a complex relationship with each other. To say that one is less important than the rest is gravely flawed. This is why each species should be given importance and not just those species that are threatened.

To maintain biodiversity in aquatic ecosystems we need to identify the activities that can harm it. Once we’ve identified them, we need to find ways to mitigate the impact that these activities have on the ecosystem. Aside from that, we need to promote the sustainable usage of resources that are derived from the aquatic ecosystems. We need to keep in mind that the activities that lead to biodiversity loss are driven by complex factors such as demographics, economics, socio-political, cultural, religious, scientific, and technological. These need to be addressed as well so that majority of the population will be onboard with the idea of improving aquatic biodiversity.