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Nutrient Cycles

Nutrient cycles act as nature’s recycling systems by exchanging inorganic and organic materials within ecosystems. Nutrients cycle through ecosystems in different forms, following the movement of energy.  The carbon, nitrogen and phosphorus cycles are three important nutrient cycles in ecology since these three chemical elements are essential nutrients required by organisms and the environment.

Carbon is a fundamental element required by all living matter. Carbon is essential for both photosynthesis and respiration and thus, the carbon cycle is critical for distributing carbon. Globally, the major flows of carbon are between: 1) land and the atmosphere, 2) the lake and atmosphere and 3) the ocean and the atmosphere.  Throughout this cycle, carbon is not created nor destroyed. However, anthropogenic forces such as the burning of fossil fuels, are causing an increase in the amount of carbon in the atmosphere.

Nitrogen is a majorly important element for ecosystem functioning and is fundamental for plants. Plant growth is limited by the inability to acquire nitrogen. It is through the nitrogen cycle that nitrogen becomes available for plants in the proper chemical form. In the air, nitrogen exists in the form N2, but at the point in which nitrogen is taken up by plants, it has transformed into nitrate (NO3). The nitrogen cycle involves many transformations including:

  • The decomposition of organic matter into dissolved organic nitrogen  
  • Mineralization, which involves converting organic nitrogen to ammonium nitrogen (plants cannot not use organic nitrogen)
  • Nitrification, the conversion of ammonium nitrogen to nitrite

The phosphorus cycle is a third nutrient cycle, although it differs from both the carbon and nitrogen cycle in the way that the atmosphere does not play a large role in the nutrient cycling. The largest amounts of phosphorus are found typically in marine sediments and in mineral deposits. Unfortunately, phosphorus is not an evenly distributed mineral, with three countries possessing about 85% of the global phosphorus available. Similar to carbon and nitrogen, phosphorus is another critical element required by all living things.



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