Environmental & Soil Microbiology

BIOGEOCHEMICAL CYCLING

Written by MicroDok

The phrase “biogeochemical” is derived from three words: bio (which involves living biological organisms like man, animals, plants and microbes found in the ecosystem), geo (which involves geological processes like the weathering of rocks and erosion occurring in the ecosystem), and chemical (which involves the formation of chemical elements in the ecosystem). Biogeochemical cycling is a pathway through which chemical substances including carbon, nitrogen, phosphorus, calcium, water, oxygen and sulphur are cycled through the biotic (living) and abiotic (non-living) components of the earth. It is any of the natural pathways by which essential elements of living matter are circulated in the environment. Biogeochemical cycle generally refers to the movement of elements and compounds moving continuously between the earth and the organisms found in it. Basically, these elements and compounds move among four (4) major systems of the earth in a controlled and circulatory manner.

The four spheres include: (1) the biosphere (comprising of the living organisms); (2) the lithosphere (comprising of the soil and land); (3) the hydrosphere (comprising of the ocean and other water bodies); and (4) the atmosphere (comprising of the air). The atmosphere, biosphere, lithosphere and the hydrosphere are four major components of the earth’s system – in which these chemical elements and compounds are reserved. And these elements can either be microelements (micronutrients) or macroelements (macronutrients) depending on how they are utilized or required by living organisms for the support of their growth and development. Macronutrients are those nutrients that are required in large amounts by all forms of life; and examples of macroelements include carbon (C), nitrogen (N), hydrogen (H), phosphorus (P), sulphur (S) and oxygen (O). Micronutrients are those nutrients that are required by all forms of life in small amounts or in moderate amounts by some forms of life; and typical examples of microelements include molybdenum, manganese and copper. These elements and compounds move through these four systems of the earth through biological processes (just as plants use the carbondioxide from the air for photosynthesis); through physical processes (just as carbondioxide is absorbed from the air to the ocean); and through human activities (just as the burning of fuels moves carbon from the ground to the atmosphere).

Biogeochemical cycles can be classified as either gaseous cycles or sedimentary cycles – in which the gaseous cycles have their elements reserved in the air or oceans while the sedimentary cycles have their elements reserved in the earth’s crust. Examples of the gaseous cycles include oxygen cycle, nitrogen cycle, carbon cycle, and water cycle. The sedimentary cycles include sulphur cycles, calcium cycles, phosphorus cycles, and iron cycles. Biogeochemical cycles involves biological, geochemical and chemical factors that help in the turnover or cycling of important chemical elements that are critical to the sustenance of life on planet earth. Biogeochemical cycling is the circulation of important chemical substances as aforementioned through the biological and physical aspect of the earth so that these substances could be replenished after being used up. In a biogeochemical cycle, chemical elements are moved in a defined and recycled manner through living organisms and the environment; and since these elements make up the cells of organisms, it is critical that they are being recycled from one organism to another and from one phase of the earth to another so that they can be utilized for desired results in the environment.

The chemical elements and/or substances recycled in nature including oxygen, nitrogen, phosphorus, sulphur, calcium and water are the currency of the ecosystem; and these elements are continuously utilized by living organisms in the environment to meet certain growth, metabolic and developmental requirements – which is why they must be circulated or cycled in optimal amounts. These elements are cycled from living things to non-living things, from the atmosphere to land and to sea, and from soils to plants and to microorganisms. Oxygen for example is an important element that supports virtually all forms of life on the planet; and if this important element is missing or in short supply, many forms of life will be affected. While green plants produce oxygen, animals consume oxygen to remain alive. Imagine what will happen to life if the consumption of oxygen is greater than its production. The amount of oxygen available in the atmosphere would drastically reduce and this will lead to the death of many living things. However, the concentration of oxygen in the atmosphere is maintained at an optimal level (about 20 %) that is essential for the support of life on the planet; and this also applies to other important elements and compounds found in the biosphere, atmosphere, lithosphere and hydrosphere.

The biogeochemical cycles ensures and even and optimal balance of these elements and compounds through their proper cycling and recycling across the different biological, geochemical, physical and chemical aspects of the earth. It is noteworthy that every biogeochemical cycles operate more like a closed system than an open system – since the products of every of the reactions occurring in these individual cycles act as substrates to other reactions in the ecosystem. The operation of the biogeochemical cycles is done in such a way that optimal balance of important chemical elements and compounds are always maintained at any given time in the ecosystem so that the existence of living things can be sustained overtime without much pressure on a particular element or compound. Some important biogeochemical cycles include the carbon cycle, phosphorus cycle, nitrogen cycle, water cycle, oxygen cycle and sulphur cycle.

One of the major limiting factors to the optimal operation of the biogeochemical cycles is in the limitation or unavailability of appropriate amounts of chemical elements required for chemical transformations in the biogeochemical cycles. When chemical elements and/or compounds are not available at the right times, in the right amounts, and in the right concentrations relative to each other, the biogeochemical cycles will not operate optimally, and the sustenance of life on earth will also be at risk. Human activities both in time past and now have greatly increased carbon dioxide levels in the atmosphere and nitrogen levels in the biosphere as well; and this alteration of the biogeochemical cycles occurs at a global scale – thus altering the normal functional of nutrient cycling and distribution in the ecosystem. For example, carbondioxide and/or carbon monoxide emissions from motor cars, industrial plants and indiscriminate bush burnings are the most significant driver of human-caused climate change. Altered biogeochemical cycles combined with climate change increase the vulnerability of biodiversity, food security, human health, and water quality to a changing climate and environment. It is important for us to study the biogeochemical cycles of life because altered biogeochemical cycles together with climate change increase the vulnerability of loss of biodiversity, food security, human health, and poor water quality due to eutrophication. However, natural and managed shifts in major biogeochemical cycles can help limit rates of climate change. Also, knowing how the biogeochemical cycles work, helps scientists to better understand and predict how climate change and human activities are related and how these can affect the environment.

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