Biogeochemical cycles

October 8, 2022

Written by: Caroline Kim

Earth’s functions as a very complex unit, but there are five fundamental biogeochemical cycles that allow our planet to contain life. A biogeochemical cycle is the movement of a particular chemical through the biologica, geological, or living and nonliving parts of an ecosystem (Science Safari). Of these five are: the hydrologic, oxygen, carbon, nitrogen, and phosphorous cycle.

Starting off with the most popular cycle: the hydrologic cycle, better known as the water cycle. In this cycle, condensation occurs in which water vapor turns into liquid, forming a cloud; after this, precipitation occurs in which it rains and water ends up in a body of water or runs off. Percolation may also occur in which water soaks into the ground and soil. Following this event, water changes form into water vapor (evaporation) or transpires when water evaporates from a leaf. From here, the cycle repeats, allowing for photosynthesis to occur and allowing water to be used as a source for all organisms on earth (Science Safari).

Next up is the oxygen cycle, in which plants can release up to 470 billion tons of oxygen during photosynthesis. This oxygen is stored in the ozone layer of the atmosphere as O3, earth’s crust, oceans, and is used by animals and humans for respiration. In the earth’s atmosphere, it acts as a buffer against ultraviolet rays and is key for survival (more can be found on the earth’s atmosphere post). Oxygen is also a necessary component of decomposition such as oxidation: the process by which metal rusts (Science Safari).

The carbon cycle is one that is relevant in environmental studies, as it contributes to the greenhouse effect. Carbon dioxide is take up by plants during the process of photosynthesis, but also released by humans and animals during respiration. The ocean is key in this cycle, as it dissolves CO2 easily and helps regulate the cycle. The part where carbon becomes a concern is when huge quantities are stored in decayed animals and plants, which are then burned as fossil fuels such as coal, oils, and natural gas. Too much carbon dioxide in the atmosphere can induce global warming, climate change, and ecological disaster (Science Safari).

Our atmosphere consists of 78% nitrogen gas and naturally plays a key role. Because this nitrogen in the atmosphere can not be directly utilized, a process known as nitrogen fixation occurs to make it more accessible. Nitrogen can be found in animal waste and is often used by higher organisms to make proteins. In addition, the nitrogen in the soil is denitrified by bacteria, so that it can be used again by plants. It is a resource for animals, plants, and cycles through our soil and atmosphere to support life on earth (Science Safari).

Last but not least is the only cycle without a gaseous phase: the phosphorus cycle. Most of the phosphorus on earth can be found in rocks and minerals and is essential for chemicals such as DNA. Phosphorus often cycles from soils and plants, to animals, then is returned to nature as waste. Phosphorus can be washed into basins or produced from man-made pollution, and can cause dangerous levels of plant overgrowth when too plentiful. In other words, too many phosphorus rich fertilizers can result in agricultural runoff known as eutrophication (Science Safari).

Sources:

Britannica, The Editors of Encyclopaedia. "biogeochemical cycle". Encyclopedia Britannica, 6 Oct. 2022, https://www.britannica.com/science/biogeochemical-cycle. Accessed 8 October 2022.

Britannica, “Nitrogen Fixation.” Encyclopedia Britannica, 8 Oct. 2022, https://www.britannica.com/science/nitrogen-fixation/images-videos#/media/1/416291/7

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