PARA QUÉ SUELES USAR INTERNET?

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Within the mature ecosystem, cyclic processes move and renew supply of energy, water, chemical elements, sediments and air. These cyclic processes enable the constant transfer of essential nutrients in a cyclical pathway in the ecosystem. The cyclic process is referred to as biogeochemical cycle or nutrient cycle.

The Collins Dictionary of Environmental science defines biogeochemical or nutrient cycle as the "the constant transfer of essential nutrients from the living organisms to the physical environment and back to the organisms in a cyclical pathway". This sequence is achieved by physical processes such as weathering and/or by biological processes such as decomposition. Therefore for organic life to continue the nutrients, which are finite in nature, must constantly be re-used.

SELF-ASSESSMENT EXERCISE 1

• Flip back to Unit l, Figure 1.3 and compare with Figure 4.1. Do you observe any differences or similarities in the two figures?

3.1.1 Functions

The major function of biogeochemical cycles is that it is responsible for the movement and renewal of energy, water, chemical elements sediments and air supplies in a mature ecosystem. Biogeochemical cycles control the movement of nutrients between the non-living environments and living organisms. 3.1.2

3.1.2 Classification and Characteristics

Biogeochemical cycles according to Chadwick and Goodman 1975:4 in Barrow (1993:23) could be classified as:

1) Natural -Barring occasional catastrophic events.

Biogeochemical cycles are always in a state of dynamic stability.

2) Upset by humans -Where biogeochemical cycles are upset by human activity, the result is runaway positive feedback i.e. upset to one process may affect others; problems could become magnified and uncontrollable.

3) Recycling managed by humans and sustainable.

3.2 Types of Biogeochemical Cycles:

There are two basic types of biogeochemical cycles. They are

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a) Gaseous cycles and

b) Sedimentary cycles (Miller 1991) 3.2.1 Gaseous Cycles:

Gaseous cycles are responsible primarily for the movement of nutrients back and forth between reservoirs in the atmosphere and hydrosphere and living organisms. Recycling of elements occurs within a short span of hours or days. Examples of gaseous cycles are oxygen, carbon, hydrogen and nitrogen cycles.

3.2.2 Sedimentary Cycles:

Just as the name implies biogeochemical cycles involve sediments, with a cycle so slow perhaps authors of years. Materials in the sedimentary cycle are non renewable as far as human are concerned. Specifically, sedimentary cycles are responsible for the movement of nutrients front and backward between reservoirs in the earth crust, hydrosphere and living organisms (Miller, 1991).

3.3 Human Interventions in Matters Recycling in Ecosystem All the chemical elements are subject to some degree of biogeochemical cycling, but these cycles, which are crucial for the nutrition of organisms or for the maintenance of atmospheric gas and global temperature within acceptable limits. The cycles are water, oxygen, carbon, and nitrogen, phosphorous. And they're over 30 known biogeochemical cycles.

Now let us study of the cycles to understand what we (humans) have done to them.

3.3.1 Carbon Cycle

Carbon is very important to life; it mixes with other organic compounds necessary for life to form the basic building block. Plants get their carbon by absorbing carbon dioxide from the atmosphere through pores in their leaves (photosynthesis).

How have we intervened?

Our interventions in this cycle are two fold.

i) Deforestation and devegetation of land which today has destroyed the trees, which serve as the carbon-dioxide bank.

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ii) Our continued dependence on burning fossil fuel and woods, which have led to increase in atmospheric carbon dioxide. The resultant effect is the global warming problems.

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3.2.2 Water Cycle

This cycled collects, purifies and distributes the earth's fixed supply of water. Human interventions in this cycle are:

1) Damming and irrigation projects have led to the withdrawal of freshwater quantities from lakes, rivers etc.

2) Deforestation - this has reduced seepages that recharges ground water supplier. What therefore result is that there is increase in flood risks.

4.0 CONCLUSION

In this unit you have learned how nutrients move in the ecosystem.

Specifically, this unit focused on biogeochemical cycles, its functions classification and characteristics as well as the types. You are aware that upset by humans is the most potent danger that can face the biogeochemical cycles.

5.0 SUMMARY

This unit concerns functions, classification and characteristics of biogeochemical cycles. It has served to introduce you to matters recycling in the ecosystems.

6.0 REFERENCES/FURTHER READING

Barrow, C.J. (1993). Developing the Environment: Problems and Management. London: Longman Scientific and Technical.

Chadwick, M.J. & Goodman G.T. (Eds) (1975). The Ecology of

Resource Degradation and Renewal. Oxford: Blackwell Scientific.

Earlich, P.R. (1986): The Machinery of Life: The Living World Around us and How it Works. New York: Simon & Schuster.

Other Resources

Park, C D (1980) Ecology and Environmental Management.

Folkstone: Dawson.

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UNIT 5 SPECIES INTERACTION IN ECOSYSTEM