Nitrogen Pollution

This section looks at a nitrogen pollution definition, causes of nitrogen pollution, effects of nitrogen pollution, solutions to nitrogen pollution and nitrogen pollution facts. The latest nitrogen pollution news is included at the foot of the page.

Nitrogen pollution definition: the harmful release of excess nitrogen into the environment. It negatively impacts aquatic life in particular by decreasing oxygen levels in the water.

The nitrogen cycle: Nitrogen is essential for the formation of amino acids in proteins. The nitrogen cycle is a model that explains how nitrogen is recycled. Credit: BBC.

There's lot of nitrogen in air – about 78% of the air is nitrogen. Because nitrogen is so unreactive, it cannot be used directly by plants to make protein. Only nitrates are useful to plants, so we are dependent on other processes to convert nitrogen to nitrates in the soil.

  1. Nitrogen gas is converted to nitrate compounds by nitrogen-fixing bacteria in soil or root nodules. Lightning also converts nitrogen gas to nitrate compounds. The Haber process converts nitrogen gas into ammonia used in fertilisers. The Haber process combines nitrogen from the air with hydrogen derived mainly from natural gas (methane) into ammonia. The reaction is reversible. 
  2. Ammonia is converted to nitrates by nitrifying bacteria in the soil.
  3. Plants absorb nitrates from the soil and use these to build up proteins. The plant may be eaten by an animal, and its biomass used to produce animal protein.
  4. Urea and egested material is broken down by decomposers. This results in nitrogen being returned to the soil as ammonia.
  5. Decomposers also break down the bodies of dead organisms resulting in nitrogen being returned to the soil as ammonia.
  6. In some conditions denitrifying bacteria in the soil break down nitrates and return nitrogen to the air. This is usually in waterlogged soil. Improving drainage reduces this effect, making the soil more fertile.

Causes of nitrogen pollution

Nutrient pollution is a big problem. It's widespread and costly to rectify. Excess nitrogen can enter water and atmospheric systems from a variety of sources and cause great harm. Nitrogen is a natural component of water and air environments - in fact, Nitrogen is the biggest component of the air we breathe forming 78%. Oxygen forms 21% and other gases make up the remaining 1%. In water, nitrogen is essential for normal growth of algae and aquatic plants. Because water can travel great distances, pollution in one place can create adverse impacts thousands of miles away. Streams, rivers, estuaries, coastal waters, bays, seas and oceans are all vulnerable.


Credit: United States Environmental Protection Agency (EPA). 

Agricultural causes of nitrogen pollution

Animal manure, fertiliser applied to crops and field and soil erosion make agriculture one of the leading sources of nitrogen pollution.


Fertilisers make crops grow faster and bigger so that crop yields are increased. They are water-soluble minerals. They must be able to dissolve in water so that plants can absorb them through their roots.


Synthetic fertilisers are prepared in the lab by the reaction of an acid with an alkali.


Fertilisers provide plants with the essential chemical elements needed for growth particularly nitrogen, phosphorus and potassium.


Examples of fertilisers, their chemical formula [and the essential elements]:

  • ammonium nitrate > NH4NO3 [nitrogen]
  • ammonium sulfate > (NH4)2SO4 [nitrogen]
  • ammonium phosphate > (NH4)3PO4 [nitrogen and phosphorus]
  • potassium nitrate > KNO3 [potassium and nitrogen]
  • urea > (NH2)2CO [nitrogen]

The world population is increasing all the time, so more food has to be produced. Without fertilisers the yields of crops would be reduced. However, fertiliser has a tendency to run off into surrounding water supplies.


Fertilisers increase crop production by replacing essential elements used by a previous crop or by boosting levels of such elements. Nitrogen in particular is needed to build plant proteins, increasing growth.

Fossil fuels and nitrogen pollution

Airborne nitrogen pollution affects not only the quality of the air we breathe, but also the land and the water.


Nitrogen is the most abundant element in the air and is essential to plant and animal life. Sources of nitrogen from human activities, such as electric power generation, industry, transportation and agriculture, can upset the natural balance of nitrogen in the environment.


When fossil fuels are burned, they release nitrogen oxides into the atmosphere, which contribute to the formation of smog and acid rain.


The most common nitrogen-related compounds emitted into the air by human activities are collectively referred to as nitrogen oxides. Ammonia is another nitrogen compound emitted to the air, primarily from agricultural activities, but also from fossil fuels. 


Major sources of nitrogen oxide emissions include:

  • cars and trucks
  • coal-fired power plants
  • large industrial operations
  • ships and airplanes

The presence of excess nitrogen in the atmosphere in the form of nitrogen oxides or ammonia is deposited back onto land, where it washes into nearby water bodies.


These excess nutrients contribute to pollution, harmful algal blooms and oxygen-deprived aquatic zones. Excess ammonia and low pH* in these areas are toxic to aquatic organisms and affect their survival.


*pH: a figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral, lower values are more acid (0 the lowest value) and higher values more alkaline (14 the highest value). The pH is equal to −log10 c, where c is the hydrogen ion concentration in moles per litre. Moles measuring the concentration of a solute in solution.

Stormwater and wastewater nitrogen runoff


When precipitation occurs over urban areas, the water runs over surfaces which contain or harbour nitrogen and phosphorous pollution.



Sewer and sanitation infrastructure are tasked with processing significant volumes of waste. No system is 100% efficient and some nitrogen and phosphorous makes it through the filtration measures into waterways.


Nitrogen in wastewater mainly takes the form of ammonia, a chemical that is challenging to handle. Nitrogen is therefore normally removed in a biological process consisting of three steps – ammonification, nitrification and denitrification.


Ammonification. While traveling through sewer pipes, the majority of the nitrogen contained in raw sewage (urea and fecal material) is converted from organic-nitrogen to ammonia and ammonium through a process called hydrolysis (the chemical breakdown of a compound due to reaction with water). 


Nitrification. The biological conversion of ammonium to nitrate nitrogen is called Nitrification. Nitrification is a two-step process. Bacteria known as Nitrosomonas convert ammonia and ammonium to nitrite. Next, bacteria called Nitrobacter finish the conversion of nitrite to nitrate. 


Denitrification. The biological reduction of nitrate (NO3 ) to nitrogen gas (N2 ) by facultative heterotrophic bacteria is called Denitrification. “Heterotrophic” bacteria need a carbon source as food to live. “Facultative” bacteria can get their oxygen by taking dissolved oxygen out of the water or by taking it off of nitrate molecules. 

Domestic sources of nitrogen runoff

Nitrogen and phosphorous can be found in some household cleaning products, soaps and detergents.


Pet waste, human waste and garden waste also contains nitrogen.


Fertilisers for grass and plants make up the other major source of domestic nitrogen pollution.





Effects of nitrogen pollution

Environmental effects of nitrogen pollution


Eutrophication literally means "well-nourished" - with excess nutrients.

A major problem with the use of fertilisers occurs when they are washed off the land by rainwater into rivers and lakes. The increase of nitrate or phosphate in the water encourages the growth of algae which starts the eutrophication process.


The known consequences of man-made eutrophication include blooms of algae, tainted drinking water supplies, degradation of recreational opportunities, and hypoxia (oxygen deficiency in a biotic environment). A 2009 study put the estimated cost of damage caused by eutrophication in the U.S. at approximately $2.2 billion annually.


Harmful algal blooms sometimes create toxins (such as microcystins, a neurotoxin which destroys nerve tissue of mammals). After being consumed by small fish and shellfish, these toxins move up the food chain and hurt larger animals like sea lions, turtles, dolphins, birds, manatees, and fish.


Even if algal blooms are not toxic, they can hurt aquatic life by blocking out sunlight and clogging fish gills.


Ecosystem impact 

Eutrophication can cause shifts in the species composition of ecosystems. For instance, an increase in nitrogen might allow new, competitive species to invade and out-compete original inhabitant species. In most cases, eutrophication leads to a loss in local biodiversity.


Algal blooms limit the sunlight available to bottom-dwelling organisms and cause wide swings in the amount of dissolved oxygen in the water. Oxygen is required by all aerobically respiring plants and animals and it is replenished in daylight by photosynthesising plants and algae.


Under eutrophic conditions, dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae. When dissolved oxygen levels decline to hypoxic levels, fish and other marine animals suffocate. As a result, creatures such as fish, shrimp, and especially immobile bottom dwellers die off. Anaerobic conditions can promote growth of bacteria such as Clostridium botulinum that produces toxins deadly to birds and mammals.


Dead zones and hypoxia

Nutrient pollution can ultimately create dead zones, areas in water with little or no oxygen where aquatic life cannot survive. The algae form a bloom over the water surface. This prevents sunlight reaching other water plants, which then die. Bacteria break down the dead plants and as they respire these bacteria use up the oxygen in the water causing most other living organisms to die. Also known as hypoxia, these areas are not habitable.


Over 166 dead zones have been documented in th U.S. alone, affecting waterbodies like the Chesapeake Bay and the Gulf of Mexico. The Gulf of Mexico dead zone is the largest in the United States, measured to be 5,840 square miles in 2013. It occurs every summer because of nutrient pollution from the Mississippi River Basin, an area that drains 31 upstream states. 


Acid rain

Acid rain, caused by nutrient pollution in the air, damages lakes, streams, estuaries, forests and grasslands across the country. The main cause is the industrial burning of coal and other fossil fuels, the waste gases from which contain sulphur and nitrogen oxides which combine with atmospheric water to form acids.


Air pollution

Airborne nitrogen compounds like nitrogen oxides contribute to the formation of other air pollutants such as ground-level ozone, a component of smog which can restrict visibility. Wind and weather can carry ozone many miles from urban to rural areas. Ozone pollution can damage trees and harm the appearance of vegetation and scenic areas.

Human health effects of nitrogen runoff

Nutrient pollution and harmful algal blooms create toxins and compounds that are dangerous for your health. There are several ways that people (and pets) can be exposed to these compounds.


Direct exposure to toxic algae

Drinking water can be a source of exposure to chemicals caused by nutrient pollution. Drinking, accidentally swallowing or swimming in water affected by a harmful algal bloom can cause serious health problems including:

  • rashes
  • stomach or liver illness
  • respiratory problems
  • neurological affects

Nitrates in drinking water

Nitrate, a compound found in fertiliser, often contaminates drinking water in agricultural areas. Infants who drink water too high in nitrates can become seriously ill and even die. Symptoms include shortness of breath and blue-tinted skin, a condition known as blue baby syndrome.


A 2010 report on nutrients in ground and surface water by the U.S. Geological Survey found that nitrates were too high in 64 percent of shallow monitoring wells in agricultural and urban areas.


Byproducts of water treatment

Stormwater runoff carries nutrients directly into rivers, lakes and reservoirs which serve as sources of drinking water for many people. When disinfectants used to treat drinking water react with toxic algae, harmful chemicals called dioxins can be created. These byproducts have been linked to reproductive and developmental health risks and even cancer.

Economic effects of nitrogen runoff

Nutrient pollution has diverse and far-reaching effects on national economies, impacting tourism, property values, commercial fishing, recreational businesses and many other sectors that depend on clean water.


Drinking water costs

Nitrates and algal blooms in drinking water sources can drastically increase treatment costs. It can also cost billions of pounds/dollars to clean up polluted water bodies. 


Tourism losses

In the U.S. the tourism industry loses approximately $1 billion each year, mostly through losses in fishing and boating activities, as a result of water bodies that have been affected by nutrient pollution and harmful algal blooms.


Airborne nutrient pollution forming smog and acid rain can also affect visibility at popular outdoor destinations. Acid rain can also damage buildings and other structures, especially those made of marble and limestone.


Commercial fishing and shellfish losses

Fishing and shellfish industries are hurt by harmful algal blooms that kill fish and contaminate shellfish. In the U.S. shellfish is big business. Annual losses to these industries from nutrient pollution are estimated to be in the tens of millions of dollars.

Eutrophication made simple

Solutions to nitrogen pollution

Personal actions to reduce nitrogen runoff

Credit: United States Environmental Protection Agency.

We can all take action to reduce nutrient pollution through the choices we make around the house, with our pets, in lawn maintenance, and in transportation. 


Actions around the home to reduce nitrogen runoff

Cleaning Supplies-Detergents and Soaps

Choose phosphate-free detergents, soaps, and household cleaners. Select the proper load size for your washing machine.
Only run your clothes or dish washer when you have a full load. Use the appropriate amount of detergent; more is not better.


Pet Waste

Always pick up after your pet. Avoid walking your pet near streams and other waterways. Instead, walk them in grassy areas, parks or undeveloped areas.

Inform other pet owners of why picking up pet waste is important and encourage them to do so.

Take part in a storm drain marking program in your area to help make others aware of where pet waste and other runoff goes when not disposed of properly.


Water Efficiency

Devices like low-flow showerheads can reduce the volume of wastewater discharged to home septic systems and sewage treatment plants. Choose water efficient appliances.


Use low-flow taps, shower heads, reduced-flow toilet flushing equipment, and water-saving appliances such as dish and clothes washers. Repair leaking taps, toilets and pumps. Take short showers instead of baths and avoid letting taps run unnecessarily.


Energy Efficiency

Using less electricity at home can reduce emissions of nitrogen pollution from energy production. Turn things off or unplug them when you're not using them. Adjust the thermostat by a few degrees to be slightly warmer in the summer and cooler in the winter.


Replace old light bulbs with new energy efficient bulbs. Use a power strip to turn on and off electronic devices. Open shades to utilise daylight instead of turning on lights; on cool days this helps to keep rooms warmer. In the summer, close shades when not in the room to keep rooms cooler and use less electricity.

Hang-dry clothes instead of using the dryer. Find out if it is possible to switch to wind or solar-generated energy.

Vehicle actions to reduce nitrogen runoff
Washing Your Car

Use a commercial car wash; commercial car washes are required to properly dispose of wastewater and many filter and recycle their water.

If washing your car at home consider the following actions:

Wash your car on a pervious surface such as grass or gravel (not concrete or asphalt) so water is filtered before reaching a water body. Use nontoxic, phosphate-free soaps. Use soap sparingly.

Minimise runoff by reducing water use, using a spray nozzle to restrict water flow. Wring out sponges and rags over the bucket or in a sink, not the ground. Empty wash water into the sink or toilet, or the grass if you wish to dispose of it outside.


Plan out your errands for one trip so you can reduce the amount of time you have to drive. Carpool with friends or co-workers. Take public transportation. Consider alternative means of travel, such as biking or walking whenever practical. Telecommute from home. Choose for flex fuel, diesel, hybrid, compact, or other fuel-efficient vehicles.

Get better gas mileage:

Routinely checking tire pressure.
Avoid using the air conditioning during city driving.
Be light on the gas by using smooth acceleration and deceleration and maintain a constant speed.
Regularly service and perform maintenance on your car.
Avoid driving with extra weight in the car; transport only necessary items.


Lawn care

Apply fertilisers only when necessary and at the recommended amount. Don't apply fertiliser before windy or rainy days. Apply fertiliser as close as possible to the period of maximum uptake and growth for grass and other plants, which is usually spring and fall in cool climate, and early and late summer in warm climates.
Avoid applying fertiliser close to waterways.

Do not overwater lawns and garden; use a soaker hose, a porous hose that releases water directly to the ground, which can reduce overwatering that carries away fertilisers that would otherwise enrich lawns and gardens.

Fill fertiliser spreaders on a hard surface so that any spills can be easily cleaned up. Properly store unused fertilisers and properly dispose of empty containers.

Maintain your lawn mowers, snow blowers, chain saws, leaf vacuums and similar outdoor power equipment to reduce nitrogen oxide emissions.


Garden care

Plant a rain garden of native plants, shrubs and trees that reduce the amount of fertiliser needed and provide a way for water to soak into the ground.


Install a rain barrel to collect rainwater; the rainwater can later be used to wash your car or water your plants and lawn.
Adopt techniques that utilise natural processes to manage stormwater runoff and reduce the impact of impervious surfaces on water quality.
Use pervious pavers for walkways and low traffic areas to allow water to soak into the ground.

Install a green roof on your home or business.
Incorporate best management practices, such as grassed swales, filter strips, or buffer strips on your property to control and temporarily store stormwater runoff.

Use garden waste, which includes grass clippings and leaves, in mulch or compost for your garden. If this is not an option, prepare all clippings and leaves for community composting, or in barrels or secured papers bags for disposal, which keeps them from washing into streams.

Nitrogen pollution facts

Eutrophication impact and prevalence

Recent surveys have showed that 54% of lakes in Asia are eutrophic; in Europe, 53%; in North America, 48%; in South America, 41%; and in Africa, 28%.

375 Hypoxic coastal zones

The World Resources Institute has identified 375 hypoxic coastal zones in the world, concentrated in coastal areas in Western Europe, the Eastern and Southern coasts of the US, and East Asia, particularly Japan.

Over 100,000 miles of waterways impaired by nitrogen and phosphorous pollution in the U.S. alone

4 billion litres a day

Scientists estimate that globally, dysfunctional sewage works produce more than 4 billion litres a day of untreated, or at best partially treated, sewage effluent that discharges into rivers and dams.

Nitrogen Pollution Search Results

More precise nitrogen recommendations for corn to help farmers, cut pollution (Tue, 20 Oct 2020)
… in reductions in nutrient pollution and sedimentation, the … have a lot of nitrogen pollution from agriculture coming from … nitrogen recommendations for corn to help farmers, cut pollution … 2020-10-precise-nitrogen-corn-farmers-pollution.html This document …
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