Nutrient Pollution

Eutrophication refers to the process by which bodies of water become over-enriched with nutrients such as nitrogen and phosphorus. This occurs when agricultural run-off carrying fertilizers and sewage end up in coastal marine ecosystems through rivers and streams.

Excess nutrients cause simple plant organisms (e.g. algae) to grow in abundance. Once the algae die, large populations of bacteria decompose the algae, depleting the water of oxygen needed to support other marine life.

Top Sources of Nutrient Pollution<br>
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Which Goals Does This Affect?

The Eutrophication Process<br>
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How Was It Measured?

Eutrophication was measured as country-level fertilizer use and then summed by watershed to estimate the likely amount of this pollution that reached river mouths. The raw data were derived from Halpern et al. (2008), which modeled plumes of land-based nitrogen pollution and produced intensity of pollution at 1km2 resolution.

What Are The Impacts?

Eutrophication often leads to the formation of dead zones, where the lack of oxygen limits the ability of many marine species to survive. Hypoxic zones in Mobile Bay, Alabama, for example, cause an annual “jubilee” in which bottom-dwelling fish, shrimp and crabs move towards the shore to avoid suffocation.

The incidence of dead zones worldwide has risen dramatically in the last 50 years, from 10 reported cases in 1960 to 405 cases in 2008 (Selman 2009)

While most marine species cannot survive in dead zones, some species thrive. Nomura’s jellyfish, for example, have plagued the Sea of Japan every summer since 2005. With few surviving predators and plenty of plankton for food, the jellyfish overpopulate the waters. They can grow up to 2 meters in width and become numerous enough to clog fishers' nets and compete with commercially valuable fish.
Between 1970 and 1990, more than 21,000 cases of serious waterborne infections were reported each year because of harmful algal blooms along the coast of the Black Sea (Merla 2008).  Exposure through the consumption of contaminated seafood can cause diarrhea, paralysis, memory loss, and other symptoms that can be fatal, or last for years after initial contamination.
Harmful algal blooms caused by eutrophication can lead to fishery closures, loss of tourism revenue, and high cleanup costs.

In the United States alone, harmful algal blooms are estimated to cost the economy at least US $82 million per year (Hoagland and Scatasta, 2006).

Between 1970 and 1990, an estimated US $2 billion worth of fish catch in the Black Sea was lost because of eutrophication, as well as US $500 million in tourism revenue (Merla 2008).

What Has Been Done?

Get More Information

World Resources Institute (WRI): World Hypoxic and Eutrophic Coastal Areas    
This WRI map identifies 415 eutrophic and hypoxic coastal systems worldwide.

WRI definition of the eutrophication process and its impacts.

National Oceanic and Atmospheric Administration (NOAA)
Overview of Harmful Algal Blooms (HABs). How to prevent and respond to the impacts of harmful algal blooms. 

Hypoxia: Dead Zone
Scientists Jack Barth and Francis Chan of Oregon Sate University conduct hypoxia research along Oregon's coast. 

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PHOTO(S): © Keith A. Ellenbogen
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