Tag Archives: Nitrogen Cycle

What is the Nitrogen Cycle?

Different parts of our ocean ecosystems, from the shallow water reefs we snorkel in, to the open ocean systems we travel across, to the deepest unknown depths, are connected by biogeochemical cycles. This includes the water cycle that transports water between our oceans, lakes, streams, and atmosphere, as well as the carbon cycle that transports organic matter through earth’s atmosphere, oceans, soils, and crust. It also includes the lesser-known, but equally important, nitrogen cycle.

Nitrogen Cycle

An example of how the nitrogen cycle functions in terrestrial (land) environments.

Nitrogen is one of the most basic and necessary elements of life along with carbon, hydrogen and oxygen. Although it makes up around 80% of our atmosphere it is not always very easy to come by. That is because nitrogen exists in many forms like nitrogen gas (N2), ammonium (NH4+), nitrite (NO2-), and nitrate (NO3-), only some of which are directly usable to the organism that need them to function.

Nitrogen Cycle 1

Ammonium is the form of nitrogen that is most easily consumed by microorganisms. For this reason, ammonium is consumed almost as fast as it is produced, a process called “assimilation.” The result is that the nitrogen becomes incorporated into the cells of living organisms. Ammonium also happens to be very easy to find around the island. You only have to look for a white rock!

Nitrogen Cycle 2

Guano, or bird poop, is loaded with ammonium! When this guano is washed off the rocks, it fertilizes the algae in the water. The algae, in turn, is eaten by fish, which are then eaten by bird! When the birds return to the rocks to rest and poop, the cycle starts all over again.

The Nitrogen Cycle

The Nitrogen Cycle is an essential building block of life. Living organisms need nitrogen to develop the proteins that form the structures of their cells. Nitrogen is also all around us, with nitrogen gas making up nearly 80% of the Earth’s atmosphere. However, most organisms are unable to directly use nitrogen in its pure, gaseous form, so other processes must come into play that help convert the nitrogen in the air into a form that organisms are able to use.


In the ocean, nitrogen gas is dissolved and taken up by nitrogen-fixing microbes, which convert the nitrogen into compounds that allow other organisms to consume it and incorporate it into their cells. Algae is one of these organisms, using the nitrogen to help build chlorophyll-binding proteins that help the algae harvest light.

IMG_6573Ammonia is a nitrogen compound found in the feces and urine of animals that algae is able to readily absorb. Bird poop in particular has high levels of ammonia in it. Rocks that are surrounded by water, like Ship Rock, are favorite resting grounds for birds because their isolation protects the birds from predators. As dense numbers of birds congregate on the rocks, they become covered in poop. Algae then starts to grow around the rock to take advantage of the consistent supply of nitrogen the poop supplies. This in turn brings lots of fish towards the rock who want to live off of the algae. And what do the birds eat? Fish! So the birds continue to stay and poop on the rock because they have a nearby food source readily available to them. This cycle continues, with every organism contributing something important to their ecosystem. And the unlikely powerhouse that keeps this cycle moving is the underrated (and often even despised) substance we call poop.



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