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Harmful Algal Bloom (red tide) -- This ‘red tide’ in August 2014 covered more than 10,000 square kilometers of ocean off the west coast of Florida.
Harmful Algal Bloom (red tide) -- This ‘red tide’ in August 2014 covered more than 10,000 square kilometers of ocean off the west coast of Florida. Photo by Kai Schumman.

Sponsored article from Jeb Berman of Nutrient Guru, a gold sponsor of the Ganjier Spring Kickoff!

Even though we can’t easily see nutrient pollution at work in our day-to-day lives, the basics are pretty simple. While some of the nutrients we apply to our gardens get absorbed by plants, some of them wash off and into rivers and streams that eventually make their way to the ocean. When our waterways and coastline get dosed with more nutrients than what they’re used to, that’s nutrient pollution (also called eutrophication).

An Explanation of Eutrophication -- These conceptual diagrams compare a healthy ecosystem with one experiencing nutrient pollution.
An Explanation of Eutrophication — These conceptual diagrams compare a healthy ecosystem with one experiencing nutrient pollution. Source.

Where do these nutrients come from?

Although nitrogen and phosphorus are normally found at base levels in our soils (and nitrogen in our air), humans are the major source of nutrients added to the natural environment – and we just can’t stop using more and more fertilizer to help increase agricultural yields. From 1960 to 1995, the amount of nitrogen fertilizer used globally increased by 700%, while worldwide use of phosphorous increased by 350%.[i] Billions of pounds of these nutrients are applied to agricultural lands each year, but not all of them stay put.

So where do they go?

We know that plants don’t absorb all of the nutrients that we apply because we can track the nitrogen in our fertilizers all the way downstream from farms to rivers to the ocean.[ii]

In both fresh- and salt- water ecosystems, too many nutrients cause algae to grow way faster than normal, resulting in huge blooms of algae that can block sunlight from reaching underwater plants. When those big algae blooms run out of nutrients and the algae die – along with the plants that were cut off from sunlight – bacteria in the decomposition process will start to use up oxygen in the water. A total lack of oxygen (anoxia) or even lower amounts of oxygen in the water (hypoxia) will kill off most organisms that cannot escape these “dead zones.”

Coastal Eutrophic and Hypoxic Areas of North America and the Caribbean -- This map identifies 131 eutrophic and hypoxic coast zones in North America and the Caribbean. Sixty-two have documented hypoxia, 59 are areas of concern, and 10 are systems in recovery.
Coastal Eutrophic and Hypoxic Areas of North America and the Caribbean — This map identifies 131 eutrophic and hypoxic coast zones in North America and the Caribbean. Sixty-two have documented hypoxia, 59 are areas of concern, and 10 are systems in recovery. Photo from WRI.org

Why should we care?

Algal blooms and dead zones are really bad news for ocean and coastal ecosystems. To start, some kinds of algae produce dangerous compounds like domoic acid or paralytic shellfish toxins. When the algae get eaten or tossed around and broken open by waves, the toxins spill out and start to affect the entire ecosystem, all the way up to sea lions[iii] and humans.[iv]

Even without the toxins, the low oxygen levels caused by algae overgrowth will either kill marine organisms outright (fish need oxygen to breathe, just like we do) or force them to swim away. And what about crabs, sea stars, sponges, or other less-mobile critters? You guessed it: if they can’t move, they die. So, hypoxia can be seriously detrimental to fisheries, and to opportunities for coastal tourism and recreation.

And now for the really bad news: the occurrence of dead zones has been steadily increasing over time, and we’re pretty confident that climate changes like increasing temperatures and ocean acidification are only going to make things worse.[v], [vi]

What can I do?

There are a lot of simple steps you can take to do your part in preventing nutrient pollution.

In the Garden

  • Plant cover crops in the winter
  • Don’t over-apply fertilizer
  • Match your application timing to your plants’ needs. For example, applying nutrients before windy or rainy days, or when the plant isn’t at the right life-cycle stage to use them, is a great way to ensure that lots of fertilizer will wash away.
  • Don’t apply close to streams.
  • Make use of rain gardens, vegetated swales, buffer strips, and other techniques to manage stormwater runoff and keep nutrients on your land and out of our waters.

In the Home

  • Watch what goes down the drain.
  • Don’t let pet waste or sewage end up in waterways.
  • Choose phosphate-free laundry detergents.
  • Make sure that you’re using water efficiently.
Additional Resources

California Coastkeeper Alliance

EPA Nutrient Pollution

National Rivers and Streams Assessment

National Estuarine Eutrophication Assessment

World Resources Institute: Mapping Eutrophication and Hypoxia

EPIC Best Management Practices Guide

Citations

[i] Tilman, D, et al. (2002). “Agricultural sustainability and intensive production practices.” Nature 418: 671-677.

[ii] Heikoop, JM, et al. (2000). “Nitrogen-15 Signals of Anthropogenic Nutrient Loading in Reef Corals.” Marine Pollution Bulletin 40.7: 628-636.

[iii] Silvagni, PA, et al. (2005). “Pathology of Domoic Acid Toxicity in California Sea Lions (Zalophus californianus).” Veterinary Pathology 42: 184-191.

[iv] Backer, LC, et al. (2005). “Occupational exposure to aerosolized brevetoxins during Florida red tide events: effects on a healthy worker population.” Environmental Health Perspectives 115(5): 644-649.

[v] Diaz, RJ and R Rosenberg. (2008). “Spreading Dead Zones and Consequences for Marine Ecosystems.” Science 321: 926-929.

[vi] Altieri, AH and KB Gedan. (2014). “Climate change and dead zones.” Global Change Biology.

 

Photo caption: Harmful Algal Bloom (red tide) — This ‘red tide’ in August 2014 covered more than 10,000 square kilometers of ocean off the west coast of Florida. Photo by Kai Schumman.

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