Pollution is a word that gets used a lot in relation to environmental impacts. Most frequently people are referring to pollution of the air or water but the word actually covers any form of contaminant that enters the natural environment and causes unwanted effects.
So as well as covering chemical substances entering the water from sewers, or soot entering the air from car exhausts, it also covers light, noise and much more.
Wildlife and plant life have evolved over millions of years, but they are struggling to adapt to life on a polluted planet. The impact of humans is increasing all the time in line with a population set to reach over 10 billion by the end of this century.
In this article, I will cover a variety of different pollution types and look into how it is affecting biodiversity.
Air pollution is any substance suspended in the air that can have adverse effects on the health of humans and the wider ecosystem. This could be solid particles such as dust or soot from a coal-fired power station, or it could be gases that are invisible to the naked eye such as ammonia or carbon dioxide.
These pollutants can affect biodiversity in a direct way, i.e by impacting health due to inhalation or they can affect biodiversity indirectly by altering the wider environmental conditions.
One study looked at the direct impacts of air pollutants by placing birds in cages close to a working coal-fired power plant. The pollutants in the power plant emissions included nitrous oxide and sulphur dioxide and were shown to have negative effects in the bird’s respiratory system. (1)
Other studies dating back as far as the 1950s have found consistent adverse health effects on birds from air pollutants including a decrease in the success of egg-laying and changes in behavior. (2)
Air pollution has also been shown to have direct impacts on mammal species in cities where levels are high. A study in Sao Paulo, Brazil found that reproductive success of mice decreased when left in cages in polluted areas of the city. (3)
If these impacts are observed on these groups of animals it is reasonable to predict air pollution will have adverse effects on others too. This is likely to have consequences for biodiversity as a whole as food chain systems are disrupted.
Indirect impacts of air pollution on biodiversity are harder to measure accurately as they are harder to test under controlled conditions over a long period of time.
A number of air pollutants are known as ‘greenhouse gases’. This is because they contribute to the greenhouse effect forming a layer in the Earth’s atmosphere which traps in the suns heat which would usually escape. The most well known of these pollutants is carbon dioxide (CO2) which is produced by a variety of sources from power plants to airplane engines. CO2 occurs naturally in the atmosphere but human activities have caused a dramatic increase in the levels particularly since the industrial revolution just over 100 years ago.
Other air pollutants that are greenhouse gases include nitrous oxide (N2O) and methane (CH4) which although don’t occur in as higher quantity or last as long in the atmosphere as CO2, are much better at trapping in heat.
The earth’s climate has been changing since the dawn of time, with variations in solar activity and other events causing natural fluctuations in temperatures. However, this recent human-induced change is occurring much more rapidly and extremely. This means that plants and animals can’t adapt quickly enough and this is impacting biodiversity.
Animals are physically moving to cooler areas, a study in the UK from 275 out of 329 species had moved further north to areas with lower average temperatures. This could have many potential implications although studies are ongoing into the potential extent of the impacts.
Impacts of climate change on biodiversity are being studied closely. The ocean temperatures are rising and this is causing coral reefs to ‘bleach’. A coral bleaches by expelling algae from within it’s tissues. Although these corals aren’t dead at this stage they are much more likely to die. This impacts wider biodiversity because corals form the habitat for thousands of marine species from fish to crustaceans. Studies have shown links between these coral bleaching events and declines in fish diversity.
When two common air pollutants, sulphur dioxide and nitrogen oxide combine with water in the atmosphere it forms a weak acid. When it rains this rain is acidic and is referred to as ‘acid rain’.
The effects of acid rain on biodiversity are clearest to see in rivers, lakes and other aquatic habitats.
More acidic water has been linked to increased mucus build up in the gills of fish. This means they can’t absorb as much oxygen causing the fish to suffocate.
Other studies have found decreased microbial activity in soils which have been exposed to acid rain. (5)
If the smallest lifeforms are impacted, this is likely to have impacts all the way up the food chain.
Much of life on earth spends either all or some of its time in the water. Whether that is a small stream, a lake or the ocean. With humans being land-based animals you’d think the water would be a safe place to be….but unfortunately not. Humans have found several ways to pollute all types of natural water bodies, all of which are likely to have negative impacts on biodiversity.
Nitrogen and Phosphorus pollution
Nitrogen and phosphorus are common pollutants when they end up in rivers, lakes and other waterbodies. These pollutants originate primarily from chemical fertilizers and manure that are applied to fields to increase crop growth. Any of the nitrogen and phosphorus that isn’t absorbed by the crop plants ends up being washed away into various waterways or it finds it’s way into groundwater.
The livestock sector is responsible for the majority of this pollution, in Europe 73% of water pollution from these sources can be attributed to livestock production. (6)
It should come as no surprise that these nutrients not only make plants on land grow but they cause much more rapid growth of plants in the water. This, in turn, leads to a process known as ‘eutrophication‘, where this excessive aquatic plant growth starts to have adverse effects. 54% of all lakes in Asia are now eutrophic.
These new conditions are not good for thriving biodiversity. The new plants cause an increase in oxygen levels in the day but when night falls microorganisms in the water feast on the plant matter and cause a dramatic decrease in oxygen. This is not good news for fish and other animals such as shrimp which need this dissolved oxygen to breathe, many of which then die off in what are referred to as ‘dead zones’.
If not applied in the correct manner, pesticides can end up in watercourses via similar pathways to the fertilizers mentioned above.
Studies back in the mid-90s revealed that 90% of water and fish samples from waters in the USA contained one or more pesticides. Chlorpyrifos is a common contaminant in urban streams and is toxic to fish US. Other pesticides such as trifluralin and glyphosate which are common in everyday garden weedkillers might not directly kill fish but they can lessen the chance of survival which can impact population as a whole. (7)
The impacts of pesticides on biodiversity tend to be worse for non-flowing waterbodies such as ponds and lakes where the substances aren’t washed away and where wildlife can’t re-populate areas as easily.
Heavy metal pollution of water can originate from many sources, from mining, to cars, to cement production. Heavy metals include metals such as mercury, arsenic and cadmium which all have the characteristic of not breaking down easily once in the environment.
These metals have been found to have impacts on fish species impacting behavior and survival rates. (8)
Oil enters the water from many sources but it has the biggest impacts on wildlife during a large ‘oil spill’ event.
This is usually when oil is being transported in a ship across the ocean and somehow spills a large amount of the load, causing havoc on the impacted ecosystem.
Whilst it is the birds and larger animals that show the most visible effects of such an event, scientists suggest the greater impacts on biodiversity are caused by the adverse effects on life in the deeper oceans.
- suffocation caused by physical blockage of ar passages and gills.
- disrupting senses so animals are unable to find food or detect predators
- internal damage from the toxic effects of oil including damage to vital organs
- reduced growth rates and higher mortality of larvae.
Plastic pollution has become one of the most talked about forms of pollution in recent years, mainly due to the obvious visible impacts it has.
Plastic is an amazing product due to the fact it can be molded into virtually any shape and doesn’t break down for a very long time. But for this reason, once it gets into the environment as a form of pollution it persists for a very long time, impacting wildlife.
Although plastic originates on land it finds its way into rivers and eventually the ocean as it is blown into storm drains or washed away in flood events.
Groups of animals particularly vulnerable to plastics include turtles, particularly young individuals that consume the plastics and are then unable to regurgitate them leading to internal injuries and often death.
Seabirds are also particularly vulnerable. One study found 40% of Laysan albatross chicks were dying before fledging the nest. During the examination of the bodies after death, it was found the majority had consumed plastic waste.
Plastics do gradually break down, but these smaller fragments (known as microplastics) can be equally dangerous.
One study on sea urchins found that the toxic effects of microplastics was causing less larvae to survive. (9)
A variety of other studies have blamed microplastics for impacts on other species including decreased food consumption and weight loss. (10) (11)
Transport of invasive species
Finally, plastics that float through the oceans can act like ‘rafts’ for species to be transported vast distances.
This means that species that are not native to a particular area can be introduced to a habitat and outcompete the native species, impacting the local biodiversity. (12)
The impacts of plastics on biodiversity as a whole is an area of ongoing research. But we can imply from effects on certain species (as mentioned above) that this will eventually have consequences for global biodiversity.
Heavy metal pollution doesn’t just affect aquatic habitats and also gets into soils where it stays for a very long time.
These heavy metals can impact the health of microorganisms such as bacteria and fungi which are essential for life to thrive.
Plants do require some of these metals in low amounts but in high quantities, negative impacts are observed. The metals are absorbed from the soil and can’t be broken down by the plants. (13)
Fertilizers, pesticide and antibiotics from animal waste can end up in the soil particularly since agriculture has become industrialized and more intensive.
Excessive nitrogen from fertilizers can alter soil nutrient levels and pH. Soils where crops have been grown or adjacent become much more nutrient-rich and acidic. Higher nutrient levels encourage the growth of more robust grass species, which often stifles the growth of wildflowers, important for bees and other pollinating insects. This has impacts on biodiversity as a whole.
Pesticides, although heavily regulated in many areas of the world, are less well regulated in other areas.
‘Light’ might not be the first type of pollution that comes to mind when someone mentions the subject, but artificial light can have negative impacts on biodiversity.
A large number of animals have evolved to be nocturnal. Hunting or moving around under the cover of complete darkness, with only the light from the moon or stars. But humans have filled the night skies with artificial lights as they aim to extend their functional hours. This has lead to street lights on every highway, lights from office buildings glaring and car headlights beaming.
Bats are one group of species that are known to be adversely affected by light pollution. Bats are very nocturnal, very rarely emerging in the light. Bat feeding activity was found to dramatically decrease and the emergence from roosts was delayed when artificial lighting was nearby. This reduces the amount of time the bats have to forage for food and pushes the bats into smaller areas of habitat where they have increased competition from other individuals. (14)
Streetlights were also found to impact moth behavior. Moths are not only important prey for other species but they are important pollinators of many plant species too. (15)
In one study of nocturnal insects in alpine meadows, abundance of species fell by 62%. (16)
As light pollution has increased with human numbers and increased urbanization so has noise pollution from various sources.
One study found traffic noise from a motorway was having a negative effect on the success of birds in noisier areas where females began laying less eggs as it masks the important territorial calls birds make. (17)
A collation of various studies into the impacts of noise on animals found that negative impacts start at noise levels as low as 50dBA, which is the equivalent volume of an everyday conversation! (18)
The sound from machinery at a mining site in Brazil was found to impact wildlife. Species numbers declined at sites nearer the mine and were higher further away. (19)
Pollution thanks to humans occurs virtually everywhere around the world and in many different forms as mentioned here. Studies are ongoing into the true scale of the impacts on biodiversity of many of these pollutants but with the dramatic decreases in numbers we have seen in recent decades, it does not look good.
We can argue over the full impact of some of these pollutants on biodiversity as a whole, some species might recover once pollutants are removed for example. But that is a risky strategy to rely on. The reality is that just removing or reducing the numbers of a single species or tiny group of microorganisms can affect an entire ecosystem and send everything out of balance.
‘Biodiversity’ refers to the importance of the diversity of creatures on planet earth and how vital every interaction is. We must work to clean up our act before it is too late.
- Llacuna, S., et al. “Effects of air pollution on passerine birds and small mammals.” Archives of Environmental Contamination and Toxicology 24.1 (1993): 59-66.
- Sanderfoot, Olivia V., and Tracey Holloway. “Air pollution impacts on avian species via inhalation exposure and associated outcomes.” Environmental Research Letters 12.8 (2017): 083002.
- Mohallem, Soraya Vecci, et al. “Decreased fertility in mice exposed to environmental air pollution in the city of Sao Paulo.” Environmental research 98.2 (2005): 196-202.
- Pecl, Gretta T., et al. “Biodiversity redistribution under climate change: Impacts on ecosystems and human well-being.” Science 355.6332 (2017): eaai9214.
- Bååth, Erland, B. Lundgren, and Bengt Söderström. “Effects of artificial acid rain on microbial activity and biomass.” Bulletin of environmental contamination and toxicology 23.1 (1979): 737-740.
- eip, Adrian, et al. “Impacts of European livestock production: nitrogen, sulphur, phosphorus and greenhouse gas emissions, land-use, water eutrophication and biodiversity.” Environmental Research Letters 10.11 (2015): 115004.
- Liong PC, Hamzah WP and Murugan V. (1988). Toxicity of some pesticides towards freshwater fi shes. Malaysian Agric J 54(3): 147–156.
- Afshan, Sehar, et al. “Effect of different heavy metal pollution on fish.” Research Journal of Chemical and Environmental Sciences 2.1 (2014): 74-79.
- Nobre, C. R., et al. “Assessment of microplastic toxicity to embryonic development of the sea urchin Lytechinus variegatus (Echinodermata: Echinoidea).” Marine pollution bulletin 92.1-2 (2015): 99-104.
- (5) Besseling, Ellen, et al. “Effects of microplastic on fitness and PCB bioaccumulation by the lugworm Arenicola marina (L.).” Environmental science & technology 47.1 (2012): 593-600
- Wright, Stephanie L., et al. “Microplastic ingestion decreases energy reserves in marine worms.” Current Biology 23.23 (2013): R1031-R1033.
- Garcia-Vazquez, Eva, et al. “Leave no traces–Beached marine litter shelters both invasive and native species.” Marine pollution bulletin 131 (2018): 314-322.
- Chibuike, Grace U., and Smart C. Obiora. “Heavy metal polluted soils: effect on plants and bioremediation methods.” Applied and environmental soil science 2014 (2014).
- Stone, Emma Louise, Stephen Harris, and Gareth Jones. “Impacts of artificial lighting on bats: a review of challenges and solutions.” Mammalian Biology 80.3 (2015): 213-219.
- Macgregor, Callum J., et al. “The dark side of street lighting: impacts on moths and evidence for the disruption of nocturnal pollen transport.” Global Change Biology 23.2 (2017): 697-707.
- Knop, Eva, et al. “Artificial light at night as a new threat to pollination.” Nature 548.7666 (2017): 206.
- Halfwerk, Wouter, et al. “Negative impact of traffic noise on avian reproductive success.” Journal of applied Ecology 48.1 (2011): 210-219.
- Shannon, Graeme, et al. “A synthesis of two decades of research documenting the effects of noise on wildlife.” Biological Reviews 91.4 (2016): 982-100
- Duarte, M. H. L., et al. “The impact of noise from open-cast mining on Atlantic forest biophony.” Biological Conservation191 (2015): 623-631.