Essay on Geochemical Cycles | Geography

Here is an essay on ‘Geochemical Cycles’ for class 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Geochemical Cycles’ especially written for school and college students.

1. Essay on Gaseous Cycle:

The reservoir of gaseous cycle is the atmosphere or the hydrosphere.

Gaseous cycle move rapidly and adjust more readily to the changes in the biosphere because of the large atmospheric reservoir.

Any unusual or frequent disturbance affects the capacity for self-adjustment.

E.g. accumulations of carbon dioxide are scattered by winds and are absorbed by plants.

i. Water Cycle:

Water is one of the most important substances for life and on average water constitutes 70% of the body weight of an organism.

It is one of the important ecological factors, which determines the structure and function of the ecosystem.

Cycling of all other elements is dependent upon water as it provides their transportation during the various steps and acts as a solvent medium for their uptake by organisms.

Water covers about 75% of the earth’s surface, occurring in lakes, rivers, seas, and oceans. The oceans alone contain 97% of all the water on earth.

Much of the remainder is frozen in the polar ice and glaciers. Less than 1% water is present in the form of ice-free fresh water in rivers, lakes, and aquifers. Additionally there is underground supply of water. Soils near the surface also serve as reservoir for enormous quantities of water.

The hydrologic cycle is the movement of water from oceans to atmosphere by evaporation and from atmosphere to oceans and land by precipitation in the form of rain or snow, from land to oceans by runoff, from streams and rivers and subsurface ground water flow, and from land to atmosphere by evaporation again.

This cycle is driven by solar energy where nearly 0.004% of the total reserve of water is moving in the hydrological cycle all the time. The rest of the earth’s water is in cold storage in the form of glaciers and ice.

ii. Carbon Cycle:

Carbon is present in the atmosphere, mainly in the form of carbon dioxide. It is a minor constituent of the atmosphere as compared to oxygen and nitrogen.

Life cannot exist without CO₂ because carbon is vital for the production of carbohydrates through photosynthesis by plants and is the building block of life. It is carbon that anchors all organic substances from coal and oil to DNA.

The global carbon cycle consists of following steps:

1. Photosynthesis:

i. Green plants in the presence of sunlight utilize CO₂ through the process of photosynthesis and convert the inorganic carbon into organic matter (food) and release oxygen.

ii. Forests acts as reservoirs of CO₂ as carbon fixed by the trees remain stored in them for long due to their long life cycles. A very large amount of such CO₂ is released through forest fires.

2. Respiration:

All living organisms carry out respiration. It is a metabolic process where food is oxidized to liberate energy, CO₂ and water.

The energy released from respiration is used for carrying out life processes by living organism.

3. Decomposition

The food assimilated by animals or synthesized by plants is not metabolized completely. They retain a major part as their own biomass, which becomes available to decomposers on their death.

Microorganisms decompose the dead organic matter and C0₂ is released into the atmosphere by decomposers.

4. Combustion:

Fossil fuels such as coal, oil and natural gas etc., are part of the carbon cycle, which may release their carbon compounds after several years.

These fossil fuels are organic compounds that were buried before they could be decomposed and were subsequently transformed by time and geological processes into fossil fuels.

Burning of fossil fuels releases the carbon stored back into the atmosphere as carbon dioxide.

5. Impact of Human Activities:

Since the beginning of industrial era, large scale deforestation, ever growing consumption of fossil fuels by growing numbers of industries, power plants, urbanization and increasing use and number of automobiles are primarily responsible for increasing emission of carbon dioxide leading to global warming.

Carbon cycle basically involves a continuous exchange of carbon dioxide between the atmosphere and organism on one hand, and between the atmosphere and the sea, on the other.

The immediate source of carbon dioxide for exchange in the oceans is restricted to surface layers of water.

The carbon balance of the biosphere as a whole is moderated by exchange of carbon dioxide between the atmosphere and oceans (richest source of carbon).

The ocean contains about 50 times more carbon dioxide than the atmosphere.

This regulates atmospheric carbon dioxide level to 0.032%, despite photosynthesis uptake.

iii. Oxygen Cycle:

The oxygen cycle describes the movement of oxygen within the atmosphere, biosphere and the lithosphere.

Failures of occurrence of oxygen cycle in the hydrosphere may result in hypoxic zones.

Photosynthesis is the main factor for the oxygen cycle and is also responsible for the Earth’s atmosphere and life on earth.

iv. Nitrogen Cycle:

Nitrogen is the essential constituent of proteins (proteins and nucleic acids), which form the building blocks of all living tissues. It constitutes nearly 16% by weight of all the proteins.

There is an inexhaustible supply of nitrogen in the atmosphere but the elemental form cannot be used directly by most of the living organisms and cycling of nitrogen is vital for all living organisms.

There are five main processes which are essential for nitrogen cycle.

They are:

1. Nitrogen Fixation:

This process involves conversion of gaseous nitrogen into Ammonia, a form in which it can be used by plants.

Atmospheric nitrogen can be fixed by the following three methods:

(a) Atmospheric Fixation:

Lightening, combustion and volcanic activity fixes nitrogen in the atmosphere

(b) Industrial Fixation:

At high temperature (400°C) and high pressure (200 psi.), molecular nitrogen is broken into atomic nitrogen which then combines with hydrogen to form ammonia.

(c) Bacterial Fixation:

There are two types of bacteria:

i. Symbiotic bacteria:

Rhizobium in the root nodules of leguminous plants.

ii. Free-Living/ Symbiotic:

Nostoc, Azobacter and Cyanobacteria can combine atmospheric or dissolved nitrogen with hydrogen to form ammonia.

2. Nitrification:

It is a process by which ammonia is converted into nitrates or nitrites by Nitrosomonas and Nitrococcus bacteria respectively. Another soil bacterium Nitrobacter that covert nitrate into nitrite.

3. Assimilation:

In this process nitrogen fixed by plants is converted into organic molecules such as proteins, DNA, RNA etc. These molecules make up for the plant and animal tissue.

4. Ammonification:

Living organisms produce nitrogenous waste products such as urea and uric acid. These waste products as well as dead remains of organisms are converted back into inorganic ammonia by the bacteria through ammonification with the help of Ammonifying bacteria.

5. Denitrification:

Conversion of nitrates back into gaseous nitrogen is called Denitrification. Denitrifying bacteria lives deep in the soil near the water table as they like to live in oxygen free medium. Denitrification is reverse of nitrogen fixation.

2. Essay on Sedimentary Cycle:

The reservoir of the sedimentary cycle is the earth’s crust. The phosphorous, calcium and magnesium circulate by means of the sedimentary cycle.

The elements involved in the sedimentary cycle normally does not cycle through the atmosphere but follows a basic pattern of flow through erosion, sedimentation, mountain building, volcanic activity and biological transport through the excreta of marine birds.

i. Sulphur Cycle:

Sulphur cycle is mostly sedimentary except two of its compounds hydrogen sulphide (H₂S) and sulphur dioxide (SO₂), which add a short gaseous phase to its normally sedimentary cycle.

The sulphur cycle illustrates the linkage between air, water and the earth’s crust.

The large sulphur reservoir is the soil and sediments where it is locked in organic (coal, oil and peat) and inorganic deposits (pyrite rock and sulphur rock) in the form of sulphates, sulphides and organic sulphur.

It is released by weathering of rocks, erosional runoff and decomposition by bacteria and fungi of organic matter and is carried to terrestrial and aquatic ecosystems in salt solution.

Sulphur is found in gaseous forms like hydrogen sulphide and sulphur dioxide in small quantities in the atmosphere.

Sulphur enters the atmosphere from several sources like volcanic eruptions, combustion of fossil fuels, from surface of ocean and from gases released by decomposition.

Atmospheric hydrogen sulphide gets oxidized into sulphur dioxide (SO₂) and is carried back to the earth after being dissolved in rainwater as weak Sulphurous acid and sulphuric acid (H₂SO₄).

Sulphur in the form of sulphates (SO₄^-2) is taken up by the plants and is incorporated through a series of metabolic processes into sulphur bearing amino acid which in turn is incorporated into the protein structure of autotroph tissues.

Passing through the grazing food chain and through excretion and decomposition of dead organic matter, Sulphur bound in living organism is carried back to the soil and to the bottom of ponds, lakes and seas.

Under aerobic conditions fungi like Aspergillus and Neurospora and under anaerobic conditions, bacteria like Escherichia and Proteus are largely responsible for the decomposition of proteins.

ii. Phosphorus Cycle:

Phosphorus is an essential nutrient for plants and animals in the form of ions PO₄^3- and HPO₄².

It is a part of DNA-molecules, of molecules that store energy (ATP and ADP) and of fats of cell membranes. Phosphorus is also a building block of certain parts of the human and animal body, such as the bones and teeth. Phosphorus can be found on earth in water, soil and sediments. Unlike the compounds of other matter cycles, phosphorus cannot be found in air in the gaseous state. This is because phosphorus is usually liquid at normal temperatures and pressures. In the atmosphere phosphorus can mainly be found as very small dust particles.

Phosphorus moves slowly from deposits on land and in sediments, to living organisms, and then much more slowly back into the soil and water sediment. The phosphorus cycle is the slowest one of the matter cycles.

Phosphorus is most commonly found in rock formations and ocean sediments as phosphate salts. Phosphate salts that are released from rocks through weathering usually dissolve in soil water and will be absorbed by plants.

Because the quantities of phosphorus in soil are generally small, it is often the limiting factor for plant growth. That is why humans often apply phosphate fertilizers on farmland. Phosphates are also limiting factors for plant-growth in marine ecosystems, because they are not very water-soluble. Animals absorb phosphates by eating plants or plant-eating animals.

Phosphorus cycles through plants and animals much faster than it does through rocks and sediments. When animals and plants die, phosphates will return to the soils or oceans during decay. After that, phosphorus will end up in sediments or rock formations remaining there for millions of years.