Access to nutrients provides the foundation for many marine ecosystems and food webs worldwide. These nutrients are the materials that primary producers synthesise into organic matter that is ingested by primary consumers and subsequently, passed through the trophic levels of food chains as biomass. Nutrient pollution concerns the contamination of water bodies or the atmosphere by releasing an excess of unwanted nutrients. Nitrogen and phosphorus are the most significant contributors to global nutrient pollution,
- Here, we’ll discuss nutrient pollution, focusing on aquatic ecosystems.
- First, we’ll define what nutrient pollution is.
- Then, we’ll briefly describe an algal bloom as an example of nutrient pollution.
- We’ll continue with the causes of nutrient pollution.
- We’ll also analyze the consequences of nutrient pollution.
- To finish, we’ll suggest some strategies for the prevention of nutrient pollution.
Nutrient Pollution Description
Nutrient pollution is the excessive release of nutrients into nearby watercourses that has damaging consequences for the functionality of local aquatic ecosystems.
Natural pollution can occur, often from chemical / physical weathering and mixing from ocean action, but these processes are uncontrollable (discounting mining of phosphate rocks). Atmospheric pollution can occur from ammonia volatilisation, but the effects on the atmosphere are much less than the impacts on bodies of water, so, for now, we shall focus on marine pollution.
Phosphate rock mining is the most prominent method of industrial phosphorus acquisition for fertilizers. Excessive mining can lead to uneven distribution of phosphorus among land spheres and can also disturb the landscape.
Marine species have evolved over millions of years to be best adapted to dealing with natural pollution, so these factors are not a problem. However, recent anthropogenic pollution surges are disconcerting, with many aquatic communities under threat around the world.
Ammonia volatilisation is the reduction of nitrogen content in the soil via the release of ammonia gas into the atmosphere.
The adjective anthropogenic simply means caused by humans. You will come across this term a lot in environmental science, so make sure you are familiar with it!
You should know two types of nutrient pollution: point source nutrient pollution and non-point source nutrient pollution.
Point source nutrient pollution refers to pollution that can be attributed to a certain point and is easily quantifiable. Examples are discharge pipes and drainage from coastal factories and powerplants.
Non point source nutrient pollution concerns pollution, making it more difficult to pinpoint where it originates. Land runoff from urban areas, precipitation and consequent sedimentation, and agricultural runoff are examples of pollution from widespread sources.
Example of Nutrient Pollution
An example of nutrient pollution are algal blooms. Nitrogen and phosphorus application to soils causes plants to grow faster, larger, and produce greater yields. Therefore, the same will happen when these nutrients runoff into nearby watercourses (leaching); this excess of nutrients will cause algal colonies to increase rapidly and often from 'algal blooms' near the surface.
Figure 1: photograph of an algal bloom in Russia, via Wikimedia Commons
Algal blooms can have detrimental consequences for aquatic ecosystems (which we will cover later) as they restrict the availability of sunlight for producers occupying deeper spaces, which can lead to severe reductions in oxygen availability.
Causes of Nutrient Pollution
Here we shall cover some of the significant causes of nutrient pollution, which are often a result of human activity.
Fig. 2: Causes of nutrient pollution that can result in eutrophication, a common consequence of this kind of pollution.
Agricultural Runoff
Agricultural practices have intensified in the last century, along with using nitrogen and phosphorus fertilisers. Overuse of these fertilisers can lead to an excess of nutrients in the soils. Rainfall will lead to nutrient-rich soils leaching into nearby watercourses, eventually running into the sea. A surplus of nitrogen and phosphorus stimulates rapid growth of algal colonies resulting in algal blooms and consequent eutrophication. Nitrogen lost to the atmosphere in ammonia volatilisation can pollute water bodies via atmospheric deposition.
Aquaculture causes nutrient pollution, with excess fertiliser, waste, and leftover food causing masses of nitrogen and phosphorus to be released into coastal waters.
Although the application of manure is a more sustainable way to fertilise soils, over-application will result in the leaching of nutrients.
Atmospheric deposition is the process by which particles (often pollutants) in the form of dust or precipitation enter water systems.
Elemental phosphorus is one of the rarest substances on the planet! This is because the phosphorus cycle is extremely slow, with phosphorus being trapped in rocks and sediment for hundreds of years. So reducing the amount of phosphorus-containing fertilisers we use in agriculture will minimise nutrient pollution and conserve the limited supply of phosphorus available to us.
Wastewater Treatment
Sewage treatment plants and septic tanks treat vast amounts of waste every day. However, these systems are focused on removing dangerous and poisonous particulates rather than nutrients like nitrogen and phosphorus, so nutrient-rich water will often be discharged. This is especially a problem in highly urbanised areas where an abundance of waste is produced and treated.
Urban Run off and Litter
Heavy rainfall in urbanised areas can overwhelm sewage and waste systems. Fertiliser usage in lawns, pet and wildlife waste, and industrial discharge contribute to urban runoff. This runoff will contain large amounts of nutrients, so aquatic ecosystems can be devastated when storms occur. Littering from civilians can be a problem, too, with nitrogen and phosphorous being released from littered food.
Fig. 3: photo of urban runoff into coastal waters, via Wikimedia Commons.
Fossil Fuels
Fossil fuels are combusted to release energy for electricity, transportation, and industrial processes. This combustion releases nitrogen oxides into the atmosphere, which can then be atmospherically deposited as nitrogen ions directly into waterways, or onto terrestrial land masses and subsequently leached off into water.
Nutrient Pollution Consequences
Nutrient pollution consequences in waterways can have catastrophic ramifications for marine ecosystems, fishing industries, and the aquatic environment. Let's go over some of these consequences:
Eutrophication
We covered algal blooms earlier; they occur when excess nutrients are released into bodies of water resulting in the exponential growth of algal colonies, causing large green patches to form near the surface. Algal blooms can block sunlight penetration to deeper layers of the ocean, leading to the decline of producer populations. These producer populations often form the foundation of aquatic ecosystems and provide oxygen and a stable food source at the base of the food chains. Therefore declining producer populations will not only result in limited oxygen availability (eutrophication) but also cause a reduction in food resources at many trophic levels. Predators will also be affected by algal blooms as they cannot locate their prey efficiently.
Fig. 4: The process of eutrophication.
'Dead zones' occur in areas where oxygen availability is so low that aquatic life cannot exist.
Further Effects on Ecosystems
Poisonous toxins from algal blooms will harm fish assemblages, and invasive species will be better adapted to high-nutrient environments and drive out the original species, which may lead to a loss in ecosystem functionality. Acid rain and atmospheric deposition will decrease the water's pH, which will negatively impact marine organisms requiring calcium carbonates for their calcareous exoskeletons.
Modern industrialisation and commercialisation of coastal communities have resulted in reef ecosystems being subject to pollution in the form of agricultural runoff and industrial discharge, which increase nutrient availability and siltation (water pollution with sand or soil) rates in coastal areas. Coral-building polyps form the foundation of the ecosystem, providing shelter and feeding grounds for countless organisms, so any impairment to them will have consequences for the sustained biodiversity of the ecosystem. Since corals thrive in low-nutrient environments, limited exposure to nutrient-rich sediments can impact corals' ability to grow and reproduce.
Consequences for Human Populations
The toxins released by algal blooms are poisonous and can ruin drinking water for entire communities. Declining aquatic ecosystems will negatively affect the livelihoods of people working in coastal areas. For example, declining fish assemblages will limit the available catch to fishermen and seriously impact the output of commercial fishing businesses if popular fish are affected. Coral and mangrove ecosystems will also be degraded by nutrient pollution, and these habitats provide revenue for coastal communities in the form of materials and tourism.
Excessive nitrogen levels of drinking water especially poses a risk for infants and children under the age of six months. However, using chemicals to treat the water is also risky as chlorine could react with algae to form by products that are damaging to reproductive and developmental health problems.
Environmental Implications
Algal blooms resulting from nutrient pollution will decrease water quality from the toxins released, and these toxins can travel to other waterbodies and affect these areas too. The weakening of ecosystems will affect aquatic habitats worldwide, ranging from riverbeds to tropical mangroves and seagrass. Acid rain produced from polluted waters precipitating will devastate terrestrial habitats as well.
Prevention of Nutrient Pollution
The prevention of nutrient pollution is highly important, as it threatens aquatic ecosystems worldwide, especially in densely populated areas. Therefore, we must be careful with what we allow to wash away into nearby waterways. Here are some ways humans can reduce nutrient pollution:
Agricultural Practices
There must be a change in agricultural practices which cause excess nutrients to runoff into waterbodies:
- Only using fertiliser when completely necessary and use environmentally friendly fertilisers which release nutrients slowly.
- Implementing efficient drainage systems to deal with unpredictable weather.
- Management of animal waste must also improve, so that nutrients are not so easily released from manure. This could mean exclusively using manure as fertiliser and restricting livestock from wandering near waterways.
- Similar changes must be made in aquaculture, with a greater stress on reforming practices as soon as possible because aquatic farms can so easily damage water bodies.
Sewage Treatment
There must be changes in how sewage treatment is conducted to limit the discharge of waste rich in polluting nutrients:
- The nitrogen and phosphorus content of waste must be considered, new methods must be implemented to remove these chemicals before releasing waste into water bodies.
- More comprehensive sewage treatment structures must be built that are able to deal with the pressures of severe weather and which can resist overflowing.
- There must be in-depth research into potential discharging locations to make sure there is minimal impact on aquatic ecosystems.
Results from the reformation of potentially polluting practices will take time to observe because algal blooms have not been shown to reduce in nutritive content straight after limiting nutrient sources.
Renewable Energy
Switching to renewable energy sources which do not produce pollutants (such as nitrogen oxides from fossil fuels) will have a considerable impact on reducing nutrient pollution. Solar, geothermal, and tidal power are just a few of the alternatives to fossil fuels.
Hopefully you are now more aware of nutrient pollution now. A top tip for preventing nutrient pollution is remembering to always pick up dog poo!
Nutrient pollution - Key takeaways
- Nutrient pollution is the release of excess nutrients into waterways of the atmosphere.
- Ammonia volatilisation is the reduction of nitrogen content in the soil via the release of ammonia gas into the atmosphere.
- Nutrient runoff into waterbodies can result in algal blooms, which limit sunlight penetration and consequently oxygen and food availability as producer populations dwindle.
- Overuse of fertilisers, inefficient sewage treatment, and urban runoff are the major causes of nutrient pollution.
- Limiting fertiliser use in agriculture is essential in reducing nitrogen/phosphorus runoff.
References
- Fig. 1: (https://commons.wikimedia.org/wiki/File:%D0%A8%D0%B8%D1%84%D0%B0%D0%BB%D1%8B_%D0%B1%D0%B0%D1%82%D2%A1%D0%B0%D2%A1.jpg) by Рәшиҙә Ғизәтуллина (no author page), under CC BY-SA 4.0 License .
- Fig. 2: Eutrophication (https://commons.wikimedia.org/wiki/File:Eutrophication.png) by Zhang mz6ws (no user page), under License CC BY-SA 4.0
- Fig. 3: View of urban runoff discharging to coastal waters (https://commons.wikimedia.org/wiki/File:View_of_urban_runoff_discharging_to_coastal_waters.jpg) by Monterey Bay National Marine Sanctuary, California, USA.Mattisse at English Wikipedia, Public domain.
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