Nutrient Cycle
Nutrients
Nutrients are chemicals required for plant and animal growth and other life processes. They are constantly recycled within Earth’s biosphere. Nutrients spend different amounts of time in stores within the atmosphere, oceans and land. Nutrients are stored for short periods of time in short-term stores, such as living organisms and the atmosphere. Nutrients can also be incorporated into longer-term stores, such as Earth’s crust.
Nutrient cycles describe the flow of nutrients in and out of stores as a result of biotic and abiotic processes. Without human interference, nutrient cycles are almost perfectly balanced. There are three main cycles that move nutrients through terrestrial and aquatic ecosystems.
- The carbon cycle
- The nitrogen cycle
- The phosphorus cycle
The Carbon Cycle
Carbon is an essential component of cells and life sustaining chemical reactions. Carbon is cycled through living and decaying organisms, the atmosphere, bodies of water, and soil and rock. Carbon moves between stores via six main processes.
- Photosynthesis
- Cellular Respiration
- Decomposition
- Ocean processes
- Volcanic eruptions
- Forest fires
Fossil fuel combustion and land clearance can deeply affect the carbon cycle by introducing carbon into the atmosphere from longer term stores.
The Nitrogen Cycle
Nitrogen is an important component of DNA and proteins.
The nitrogen cycle involves four processes, three of which make nitrogen available to plants and animals.
- Nitrogen fixation
- Nitrification
- Uptake
- Denitrification
Fossil fuel combustion and burning organic matter can release nitrogen into the atmosphere, where it then can form acid rain. As well as chemical fertilizers which too contain nitrogen, which then can escape into the atmosphere or leaches into lakes and streams. High levels of nitrogen can cause eutrophication (too many nutrients), and increased algal growth in aquatic ecosystems, depriving aquatic organisms of sunlight and oxygen.
# The Phosphorus Cycle
Phosphorus carries energy to cells. It is found in phosphate rocks and sediments on the ocean floor. Weathering through chemical or physical means break down rock, releasing phosphate into the soil from longer term stores. Organisms take up phosphorus. When they die, decomposers return phosphorus to the soil. Excess phosphorus settles on floors of lakes and oceans, eventually forming sedimentary rock. It remains trapped for millions of years until it is exposed through geologic uplift or mountain building.
- Commercial fertilizers and phosphate containing detergents enter waterways and contribute additional phosphate to the phosphorus cycle. Forest clearance reduces phosphate levels, as phosphate in trees enters soil as ash. It leaches out of the soil and settles on lake and ocean bottoms, unavailable to organisms.