Nutrient pollution is due to many sources. This article focuses on NPK nutrient runnoff from farming of both plant and animal sources because in both instances overuse of fertilizer is the major culprit. A brief history of nutrient development is included with results of dead zones. When algae grows it takes the oxygen from the water to suffocate and prohibit other life making it a dead zone.

There is currently much debate about sources of pollution, particularly nutrient pollution of surface and ground waters. It frequently appears that everyone is quite confident everyone else is contributing far more than they are. The reality, particularly for nutrient pollution, is that we all are part of the problem and must be part of the solution.

Lake Erie algae bloom

Lake Erie algae bloom

Nutrient pollution is one of America’s most widespread, costly and challenging environmental problems, and is caused by excess nitrogen, phosphorus and potassium in the air and water.  Nitrogen and phosphorus (NPK) are nutrients that are natural parts of aquatic ecosystems. Nitrogen is also the most abundant element in the air we breathe. Nitrogen and phosphorus support the growth of algae and aquatic plants, which provide food and habitat for fish, shellfish and smaller organisms that live in water.  But when too much nitrogen and phosphorus enter the environment – usually from a wide range of human activities – the air and water becomes polluted. Nutrient pollution has impacted many streams, rivers, lakes, bays and coastal waters for the past several decades, resulting in serious environmental and human health issues, and impacting the economy.


Nitrogen is one of the nutrient elements plants need to grow. Every apple or ear of corn plucked represents nutrients pulled from soil, and for land to remain productive, those nutrients must be replenished. Nitrogen is extremely plentiful—it makes up nearly 80 percent of the air we breathe. But atmospheric nitrogen (N2) is joined together in an extremely tight bond that makes it unusable by plants. Plant-available nitrogen, known as nitrate, is actually scarce, and for most of agriculture’s 10,000-year-old history, the main challenge was figuring out how to cycle usable nitrogen back into the soil. Farmers of yore might not have known the chemistry, but they knew that composting crop waste, animal manure, and even human waste led to better harvests.

In the 19th century German scientist Justus Von Liebig was responsible for the theory that Nitrogen, Phosphorous, and Potassium levels are the basis for determining healthy plant growth. He figured out the science behind nitrogen’s central role in plant growth, just as the industrial revolution was pushing more people off of farms and into cities. European elites realized that feeding a growing urban population from a shrinking rural labor base would be a problem—and that cheap and easy nitrate would be part of the solution. So the “fixation” of nitrogen—the ability pull it from the air and transform it into something that plants could use—became a fixation. In 1909, a German chemist named Fritz Haber developed a high-temperature, energy-intensive process to synthesize plant-available nitrate from air. And so agriculture’s millennia-old nitrogen-cycling problem was solved. Today’s industrial-scale farms would not be possible without it.


It was not until well after World War II that nutrient pollution was considered a major water quality issue. Nutrient pollution, and its consequences (low dissolved oxygen and poor water clarity) are now deemed the leading cause of degradation of lakes, rivers, streams, and coastal waters (US EPA, 1999). Nutrient pollution of surface waters causes excessive growth of algae and is commonly termed eutrophication, or “overenrichment.” The most common problem is low or no dissolved oxygen as a result of the oxygen demand generated by decaying algae. The algae can also reduce water clarity thus making it difficult for underwater grasses to grow in the shallows. Nutrient pollution manifests itself in slow-flowing coastal areas, lakes and reservoirs and portions of some rivers.

Nutrients can run off of land in urban areas where lawn fertilizers are used

Nutrients can run off of land in urban areas where lawn fertilizers are used. Pet and wildlife wastes are also sources of nutrients since they eat the fertilized plant life. To see how this happens, consider this visualization of the Chesapeake Bay, part of the largest watershed in the Northeast. This illustration shows the amount of suspended matter (e.g, silt, mud, debris) in waterways before (left) and after (right) areas in this region received exceptionally heavy rainfall in 2011. All of this rain and runoff eventually made its way into the Chesapeake Bay

The rapid growth in nutrient pollution that began after World War II was largely the result of major changes in science and technology, and lifestyles, particularly in the United States. New technologies meant we were able to create large quantities of readily available fertilizers from previously inert materials. It also meant we could generate new materials such as nylon that use nitrogen rich amino acids as a primary building block. New cleansers and detergents made shirts and dishes cleaner than ever, but contained large amounts of phosphorus. The ability to convert “inert” nutrient compounds into bioavailable forms for many uses began to grow exponentially.

Agriculture also began a change that has accelerated in the last two decades. Specialization, intensification, and concentration increased dramatically. In animal agriculture, particularly poultry, production concentrated into major production centers or regions.

The lifestyle change was no less significant. The combination of new fertilizers, improved genetics and rapid mechanization meant that more food could be grown with fewer people.

Today’s Focus

Excessive nitrogen and phosphorus that washes into water bodies and is released into the air are often the direct result of human activities. The primary sources of nutrient pollution are:

  • Agriculture: Animal manure, excess fertilizer applied to crops and fields, and soil erosion make agriculture one of the largest sources of nitrogen and phosphorus pollution in the country
  • Stormwater: When precipitation falls on our cities and towns, it runs across hard surfaces – like rooftops, sidewalks and roads – and carries pollutants, including nitrogen and phosphorus, into local waterways.
  • Wastewater: Our sewer and septic systems are responsible for treating large quantities of waste, and these systems do not always operate properly or remove enough nitrogen and phosphorus before discharging into waterways.
  • Fossil Fuels: Electric power generation, industry, transportation and agriculture have increased the amount of nitrogen in the air through use of fossil fuels.
  • In and Around the Home: Fertilizers, yard and pet waste, and certain soaps and detergents contain nitrogen and phosphorus, and can contribute to nutrient pollution if not properly used or disposed of. The amount of hard surfaces and type of landscaping can also increase the runoff of nitrogen and phosphorus during wet weather.


where the Mississippi River meets the Gulf of Mexico

Gulf of Mexico Dead Zone


Waste and drainage water runs off the land completely unfiltered into storm drains flowing to lakes, streams and rivers, finally making its way into the ocean. This pollution runoff results in dead zones due to algae growth using all available oxygen needed for all other life forms.  Dead zones are low-oxygen, or hypoxic, areas in the world’s oceans and lakes. Because most organisms need oxygen to live, few organisms can survive in hypoxic conditions. That is why these areas are called dead zones.

For more detailed explanation, dead zones occur because of a process called eutrophication, which happens when a body of water gets too many nutrients, such as phosphorus and nitrogen. At normal levels, these nutrients feed the growth of an organism called cyanobacteria, or blue-green algae. With too many nutrients, however, cyanobacteria grows out of control, which can be harmful. Since human activities are the main cause of these excess nutrients being washed into the ocean, dead zones are often located near inhabited coastlines.  Understanding the eutrophication process provides the clearest picture of how and why dead zones develop.


Eutrophic events due to intensive agricultural practices, industrial activities, and population growth.

Eutrophic events due to intensive agricultural practices, industrial activities, and population growth.

Causes of Eutrophication

Eutrophic events have increased because of the rapid rise in intensive agricultural practices, industrial activities, and population growth. These three processes emit large amounts of nitrogen and phosphorous. These nutrients enter our air, soil, and water and runoff increases significantly with heavy rainfall. Human activities have emitted nearly twice as much nitrogen and three times as much phosphorus as natural emissions.

Different regions of the world emit different levels of these nutrients. In developed countries, such as the United States and nations in the European Union, heavy use of animal manure and commercial fertilizers in agriculture are the main contributors to eutrophication. Runoff from large agricultural fields enters creeks and bays because of rain or irrigation practices.



To reduce nutrient pollution, consider reducing the amount of pollution that can run off your property: install a rain garden or rain barrel to capture and absorb rainfall; use porous gravel or pavers in place of asphalt or concrete; and redirect downspouts onto grass or gravel rather than paved driveways or sidewalks. If you have a lawn to take care of, use fertilizers properly: do not use more than needed, and do not apply to dormant lawns or frozen ground. You can also reduce air pollution by walking, biking or taking public transportation, or using electric or manual lawn mowers and yard tools instead of gas-powered machines.

NPK nitrogen phosphorus and potassium nutrientChemical fertilizers and organic fertilizers show their nutrient content with three bold numbers on the package. These numbers represent three different compounds: Nitrogen, Phosphorous, and Potash (Potassium), which we can also describe with the letters N-P-K.

Understanding NPK ratings on lawn and plant fertilizers is an important part of deciding whether or not fertilizers are appropriate or even necessary for your garden and landscaping.





There are other ways of looking at how plants utilize nutrients that have largely been ignored, especially by those companies who produce the chemical fertilizers commonly on the market today. For example,

  • Properly aerated soil encourages the life of earthworms, beneficial microbes, and other critters found underneath your garden and lawn who will have better access to the oxygen they need to thrive. As they live and digest organic matter, they help to create soil that is healthy and fertile. Healthy soil is the basis for healthy plants.
  • Compost in the form of organic humus is ever present in natural plant communities, providing lots of the nutrients that plants need to grow and thrive. Compost contains Nitrogen, Phosphorous, Potassium, and a great abundance of other trace elements that will benefit your plants.

It is clear that Nitrogen, Phosphorous, and Potassium are not necessarily the most important elements you need for your plants to grow well. In fact, elements such as carbon, hydrogen, oxygen, sulfur, magnesium, copper, cobalt, sodium, boron, molybdenum, and zinc are just as important to plant development as N-P-K. (Source:

Over the years, Justus Von Liebig’s theory developed into the dominant paradigm for how we grow our ornamental and edible plants. The bad news is that this has lead to a vast amount excess nutrients building up in our streams, lakes, and rivers, because chemical fertilizers are under utilized and often over-applied.  It is our responsibility to limit the number of nutrients to keep our planet earth’s ecosystem in balance.




Article Credits

Thomas W. Simpson, PhD

United States Environmental Protection Agency
Nutrient Pollution

Mother Jones
A Brief History of Our Deadly Addiction to Nitrogen Fertilizer

A Brief History of Our Deadly Addiction to Nitrogen Fertilizer

National Geographic
What Are Dead Zones

Chesapeake Bay Program

Clean Air Gardening


Photo credits

An algae bloom caused by fertilizer runoff in Lake Erie in 2014, whicvh was so toxic the ity of Toledo, Ohio, shut down its tap water system (Haraz N. Chanbari/Associated Press)

Dead Zones

Mississippi River Gulf of Mexico
Gulf of Mexico dead zone in July 2017
At 8,776 square miles, this year’s dead zone in the Gulf of Mexico is the largest ever measured. (Courtesy of N. Rabalais, LSU/LUMCON)


The Mississippi River and the Gulf of Mexico dead zone


Donna Ebeling About Donna Ebeling
Gardening had always been my passion, until I learned about organic gardening. That's a whole new ballgame. So when I was asked to write for this blog, I jumped at the opportunity to research, to learn more about organic gardening and to write about that and other plant-related topics. Thank you for being here, I hope you enjoy these articles at least half as much as I do writing them!