What is the Nitrogen Cycle?
Nitrogen is one of the most important elements in our Earth’s ecosystem. It makes up 78% of our atmosphere, provides plants with nutrients, is part of DNA and RNA, and is in our water systems. Nitrogen strikes a balance within our world by the process of the nitrogen cycle.
Stage 1: Nitrogen Fixation
This is the stage in the nitrogen cycle where nitrogen is transferred from the atmosphere into soil. Nitrogen (N2) cannot be used by plants in its gaseous form; therefore, plants rely on a process called nitrogen fixation to retrieve its nutrients. Nitrogen fixation can happen in a couple ways. One is from lightning, which causes N to react with oxygen to form nitrogen oxide (NO). That then enters soil for plants to use. Another way plants may receive nitrogen is from man made fertilizers. The final and most common way nitrogen is transferred into soil is through bacteria. Legumes and this bacteria form a symbiotic relationship in which the bacteria attach to the roots, and then fix the nitrogen for plants to use.
Stage 2-3: Assimilation and Ammonification
Then, the nitrogen is assimilated, or incorporated into the tissues of these plants. When organic matter dies, it leaves its leftover nutrients in the soil. In doing so, it begins to mineralize and form ammonia (NH3). When ammonia reacts with water, it forms ammonium (NH4). Ammonium stays in soil and continues to provide plants with nutrients.
Stage 4: Nitrification
The ammonia then begins to mineralize, forming nitrates (NO3−) and nitrites (NO2−). These form an extra amount for plants to store away in their roots in the case of a nutrient deficient time.
Stage 5: Denitrification
In this final stage, nitrogen returns to the atmosphere as the nitrates are converted to atmospheric nitrogen once more. Denitrifying bacteria allows this to happen, and are usually more active in water-logged soils.
What is Eutrophication?
Eutrophication is a major issue in our large bodies of water, resulting in runoff of fertilizers and cities. It adds nitrogen and phosphorus into areas that spill into the ocean, resulting in large algae blooms. These plants mostly lie on the surface of the water, intruding upon plants that live on the ocean floor. These native plants then die, and organisms who rely on them also have to leave. Afterwards, the abundance of algae and plants eventually die off, producing a disproportionate amount of carbon dioxide as decomposers begin to break them down. This lowers the pH of ocean water (ocean acidification), and is known to kill off the remaining fish and organisms in the area. After an algae bloom often comes a dead zone, where almost all biodiversity in an aquatic ecosystem is destroyed due to the overabundance of carbon dioxide. This all resulted from the addition of nitrogen into the ecosystem.
Importance of the Nitrogen Cycle
Keeping the nitrogen cycle running properly is crucial for the health of both plants, animals, and humans alike. Humans contribute to the nitrogen cycle in many ways, many of them not beneficial to the environment. The burning of fossil fuels, and the application of nitrogen-based fertilizers heighten levels of nitrogen in terrestrial and aquatic ecosystems. A major imbalance in nitrogen can cause eutrophication, dead zones, nutrient imbalance, decrease in biodiversity, and can even be found in human tissue. It is of utmost importance that we regulate our additions of nitrogen into the environment, as it is so key to life on Earth.
Written by: Mackenzie P (@mprtchard)
References
Aczel, Miriam R. “What Is the Nitrogen Cycle and Why Is It Key to Life?” Frontiers for Young Minds, 12 Mar. 2019, https://kids.frontiersin.org/articles/10.3389/frym.2019.00041.
Bernhard, Anne. “The Nitrogen Cycle: Processes, Players, and Human Impact.” Nature News, Nature Publishing Group, https://www.nature.com/scitable/knowledge/library/the-nitrogen-cycle-processes-players-and-human-15644632/.
US Department of Commerce, National Oceanic and Atmospheric Administration. “What Is Eutrophication?” NOAA's National Ocean Service, 2 Apr. 2019, https://oceanservice.noaa.gov/facts/eutrophication.html.
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