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BIOGEOCHEMICAL CYCLE-CARBON,SULPHUR AND PHOSPHORUS CYCLES1

BIOGEOCHEMICAL CYCLE

In ecology and Earth science, a biogeochemical cycle or substance turnover or cycling of substances is a

pathway by which a chemical element or molecule moves through both biotic (biosphere) and abiotic

(lithosphere, atmosphere, and hydrosphere) compartments of Earth. In effect, the element is recycled, although

in some cycles there may be places (called reservoirs) where the element is accumulated or held for a long period

of time (such as an ocean or lake for water). The water undergoes evaporation, condensation, and precipitation,

falling back to Earth clean and fresh. Elements, chemical compounds, and other forms of matter are passed from

one organism to another and from one part of the biosphere to another through the biogeochemical cycles.

Systems

All chemical elements occurring in organisms are part of biogeochemical cycles. In addition to being a part of

living organisms, these chemical elements also cycle through abiotic factors of ecosystems such as water

(hydrosphere), land (lithosphere), and the air (atmosphere). The living factors of the planet can be referred to

collectively as the biosphere. All the nutrients—such as carbon, nitrogen, oxygen, phosphorus, and sulfur—used

in ecosystems by living organisms operate on a closed system; therefore, these chemicals are recycled instead of

being lost and replenished constantly such as in an open system.

The flow of energy in an ecosystem is an open system; the sun constantly gives the planet energy in the form of

light while it is eventually used and lost in the form of heat throughout the trophic levels of a food web. Carbon is

used to make carbohydrates, fats, and proteins, the major sources of food energy. These compounds are

oxidized to release carbon dioxide, which can be captured by plants to make organic compounds. The chemical

reaction is powered by the light energy of the sun.

It is possible for an ecosystem to obtain energy without sunlight. Carbon must be combined with hydrogen and

oxygen in order to be utilized as an energy source, and this process depends on sunlight. Ecosystems in the deep

sea, where no sunlight can penetrate, use sulfur. Hydrogen sulfide near hydrothermal vents can be utilized by

organisms such as the giant tube worm. In the sulfur cycle, sulfur can be forever recycled as a source of energy.

Energy can be released through the oxidation and reduction of sulfur compounds (e.g., oxidizing elemental sulfur

to sulfite and then to sulfate).


Although the Earth constantly receives energy from the sun, it's chemical composition is essentially fixed, as

additional matter is only occasionally added by meteorites. Because this chemical composition is not replenished

like energy, all processes that depend on these chemicals must be recycled. These cycles include both the living

biosphere and the nonliving lithosphere, atmosphere, and hydrosphere.

Reservoirs

The chemicals are sometimes held for long periods of time in one place. This place is called a reservoir, which, for

example, includes such things as coal deposits that are storing carbon for a long period of time.When chemicals

are held for only short periods of time, they are being held in exchange pools. Examples of exchange pools

include plants and animals.Plants and animals utilize carbon to produce carbohydrates, fats, and proteins, which

can then be used to build their internal structures or to obtain energy. Plants and animals temporarily use carbon

in their systems and then release it back into the air or surrounding medium. Generally, reservoirs are abiotic

factors whereas exchange pools are biotic factors. Carbon is held for a relatively short time in plants and animals

in comparison to coal deposits. The amount of time that a chemical is held in one place is called its residence.

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THE CARBON CYCLE

When examining the biogeochemical cycling of an individual element, it is useful to consider the global reservoirs

of this element, the size of these reservoirs, and whether or not these reservoirs are being actively cycled. The

natural rates of carbon cycling in oceans and on land are close to a steady state; that is, the rates of movement of

carbon between the atmosphere and trees or between algae and the dissolved inorganic carbon of the oceans do

not change measurably from year to year and tend to balance each other. However, human activities have

recently introduced changes in the carbon cycle that are large enough to be measured. Today, the global carbon

cycling is a mixture of the natural steady-state rates and reservoirs and the changing rates and reservoirs affected

by human activities.

Table: Major carbon reservoirs

Carbon is taken from the atmosphere in several

ways:

When the sun is shining, plants perform

photosynthesis to convert carbon dioxide into

carbohydrates, releasing oxygen in the process. This

process is most prolific in relatively new forests

where tree growth is still rapid. The effect is

strongest in deciduous forests during spring leafing

out. This is visible as an annual signal in the Keeling

curve of measured CO2 concentration. Northern

hemisphere spring predominates, as there is far

more land in temperate latitudes in that hemisphere

than in the southern.

Forests store 86% of the planet's above-ground carbon and 73% of the planet's soil carbon.

At the surface of the oceans towards the poles, seawater becomes cooler and more carbonic acid is

formed as CO2 becomes more soluble. This is coupled to the ocean's thermohaline circulation which

transports dense surface water into the ocean's interior (see the entry on the solubility pump).

Reservoir Amount (billions of metric

tons of carbon)

Atmosphere before 1850 560—610

Atmosphere in 1978 692

Oceans and fresh water

Inorganic 35,000

Dissolved organic 1,000

Land biota 600—900

Soil organic matter 1,500

Sediments 10,000,000

Fossil fuels 10,000


In upper ocean areas of high biological productivity, organisms convert reduced carbon to tissues, or

carbonates to hard body parts such as shells and tests. These are, respectively, oxidized (soft-tissue

pump) and redissolved (carbonate pump) at lower average levels of the ocean than those at which they

formed, resulting in a downward flow of carbon (see entry on the biological pump).

The weathering of silicate rock. Carbonic acid reacts with weathered rock to produce bicarbonate ions.

The bicarbonate ions produced are carried to the ocean, where they are used to make marine carbonates.

Unlike dissolved CO2 in equilibrium or tissues which decay, weathering does not move the carbon into a

reservoir from which it can readily return to the atmosphere.

Carbon can be released back into the atmosphere in many different ways:

Through the respiration performed by plants and animals. This is an exothermic reaction and it involves

the breaking down of glucose (or other organic molecules) into carbon dioxide and water.

Through the decay of animal and plant matter. Fungi and bacteria break down the carbon compounds in

dead animals and plants and convert the carbon to carbon dioxide if oxygen is present, or methane if not.

Through combustion of organic material which oxidizes the carbon it contains, producing carbon dioxide

(and other things, like water vapor). Burning fossil fuels such as coal, petroleum products, and natural gas

releases carbon that has been stored in the geosphere for millions of years. Burning agrofuels also

releases carbon dioxide.

Production of cement. Carbon dioxide is released when limestone (calcium carbonate) is heated to

produce lime (calcium oxide), a component of cement.

At the surface of the oceans where the water becomes warmer, dissolved carbon dioxide is released back

into the atmosphere.

Volcanic eruptions and metamorphism release gases into the atmosphere. Volcanic gases are primarily

water vapor, carbon dioxide and sulfur dioxide. The carbon dioxide released is roughly equal to the

amount removed by silicate weathering; so the two processes, which are the chemical reverse of each

other, sum to roughly zero, and do not affect the level of atmospheric carbon dioxide on time scales of

less than about 100,000 yr.

Forests and crops in the process of growing absorbs lots of carbon, while an old and stable forest

consumes as much CO2 during the day as they produce during the night.


In the biosphere

Around 1,900 gigatons of carbon are present in the biosphere. Carbon is an essential part of life on Earth. It plays

an important role in the structure, biochemistry, and nutrition of all living cells.

Autotrophs are organisms that produce their own organic compounds using carbon dioxide from the air

or water in which they live. To do this they require an external source of energy. Almost all autotrophs

use solar radiation to provide this, and their production process is called photosynthesis. A small number

of autotrophs exploit chemical energy sources in a process called chemosynthesis. The most important

autotrophs for the carbon cycle are trees in forests on land and phytoplankton in the Earth's oceans.

Photosynthesis follows the reaction 6CO2 + 6H2O → C6H12O6 + 6O2

Carbon is transferred within the biosphere as heterotrophs feed on other organisms or their parts (e.g.,

fruits). This includes the uptake of dead organic material (detritus) by fungi and bacteria for fermentation

or decay.

Most carbon leaves the biosphere through respiration. When oxygen is present, aerobic respiration

occurs, which releases carbon dioxide into the surrounding air or water, following the reaction C 6H12O6 +

6O2 → 6CO2 + 6H2O. Otherwise, anaerobic respiration occurs and releases methane into the surrounding

environment, which eventually makes its way into the atmosphere or hydrosphere (e.g., as marsh gas or

flatulence).

Burning of biomass (e.g. forest fires, wood used for heating, anything else organic) can also transfer

substantial amounts of carbon to the atmosphere

Carbon may also be circulated within the biosphere when dead organic matter (such as peat) becomes

incorporated in the geosphere. Animal shells of calcium carbonate, in particular, may eventually become

limestone through the process of sedimentation.

Much remains to be learned about the cycling of carbon in the deep ocean. For example, a recent

discovery is that larvacean mucus houses (commonly known as "sinkers") are created in such large

numbers that they can deliver as much carbon to the deep ocean as has been previously detected by


sediment traps. Because of their size and composition, these houses are rarely collected in such traps, so

most biogeochemical analyses have erroneously ignored them.

Carbon storage in the biosphere is influenced by a number of processes on different time-scales: while net

primary productivity follows a diurnal and seasonal cycle, carbon can be stored up to several hundreds of years in

trees and up to thousands of years in soils. Changes in those long term carbon pools (e.g. through de- or

afforestation or through temperature-related changes in soil respiration) may thus affect global climate change.

An idealized food web showing transfers

between trophic levels. Organic carbon

formed by primary producers is transferred to

grazers and predators. Decomposers and

respiration of grazers and predators return

CO2 to primary producers. The diagram shows

that the supportable biomass declines at

progressively higher trophic levels.

Carbon Transfer Through Food Webs

Every food web is based on primary producers. The net fixation of CO2 to form organic compounds is carried out

by autotrophic organisms. Among the microorganisms, this includes photosynthetic and chemolithotrophic

organisms. The most important groups of microorganisms, in terms of their abilities to convert CO 2 to organic

matter, are the algae, the cyanobacteria, and the green and purple photosynthetic bacteria. Chemoautotrophic

microorganisms contribute to a lesser extent. The principal metabolic pathway for photosynthetic CO2 fixation is

the Calvin cycle, in addition, microorganisms are capable of incorporating CO2 through the phosphoenol pyruvate

carboxylase system. In the case of heterotrophic microorganisms, exchange but no net CO2 fixation occurs, but

some chemolithotrophic microorganisms use this system either instead of or in addition to the pentose

phosphate cycle for net CO2 fixation. Methanogenic archaea play an important role in the anaerobic reduction of

CO2 .Only a limited number of microorganisms can utilize the resulting methane. These methylotrophs are

ecologically important in minimizing methane transfer to the atmosphere.


Carbon dioxide convened to organic carbon by primary producers represents the gross primary pro duction of

the community. This process is carried out predominantly by photosynthetic organisms that convert light energy

to chemical energy; the chemical energy is stored within the organic compounds that are formed. The conversion

of radiant energy to chemical energy in organic compounds is the essence of primary production.

A portion of the gross primary production is converted back to CO2 by the respiration of the primary

producers. The remaining organic carbon is the net primary production available to heterotrophic consumers;

the heterotrophs complete the carbon cycle, ultimately converting organic compounds formed by primary

producers back to CO2 during respiration.


Carbon Cycling Within Habitats

The degradation and recycling of organic matter in habitats is accomplished by heterotrophic macro- and

microorganisms. Microbial activities are crucial in terms of not only the quantity but also the quality of their

contributions. Under aerobic conditions, macro- and microorganisms share the ability to biodegrade simple

organic nutrients and some biopolymers, such as starch pectin, proteins, and so on, but microorganisms are

unique in their capacity to carry out anaerobic (fermentative) degradation of organic matter. They are also

responsible for the recycling of most abundant but difficult-to-digest biopolymers, such as cellulose and lignin.

In the ocean

The oceans contain around 36,000 gigatonnes of carbon, mostly in the form of bicarbonate ion (over 90%, with

most of the remainder being carbonate). Extreme storms such as hurricanes and typhoons bury a lot of carbon,

because they wash away so much sediment. Inorganic carbon, that is carbon compounds with no carbon-carbon

or carbon-hydrogen bonds, is important in its reactions within water. This carbon exchange becomes important

in controlling pH in the ocean and can also vary as a source or sink for carbon. Carbon is readily exchanged

between the atmosphere and ocean. In regions of oceanic upwelling, carbon is released to the atmosphere.

Conversely, regions of downwelling transfer carbon (CO2) from the atmosphere to the ocean. When CO2 enters

the ocean, it participates in a series of reactions which are locally in equilibrium:

Solution:CO2(atmospheric) ⇌ CO2(dissolved)

Conversion to carbonic acid:

CO2(dissolved) + H2O ⇌ H2CO3

First ionization:

H2CO3 ⇌ H+ + HCO3− (bicarbonate ion)

Second ionization:

HCO3− ⇌ H+ + CO3

−− (carbonate ion)


This set of reactions, each of which has its own equilibrium coefficient determines the form that inorganic carbon

takes in the oceans[5]. The coefficients, which have been determined empirically for ocean water, are themselves

functions of temperature, pressure, and the presence of other ions (especially borate). In the ocean the equilibria

strongly favor bicarbonate. Since this ion is three steps removed from atmospheric CO2, the level of inorganic

carbon storage in the ocean does not have a proportion of unity to the atmospheric partial pressure of CO 2. The

factor for the ocean is about ten: that is, for a 10% increase in atmospheric CO 2, oceanic storage (in equilibrium)

increases by about 1%, with the exact factor dependent on local conditions. This buffer factor is often called the

"Revelle Factor", after Roger Revelle.

In the oceans, bicarbonate can combine with calcium to form limestone (calcium carbonate, CaCO3, with silica),

which precipitates to the ocean floor. Limestone is the largest reservoir of carbon in the carbon cycle. The

calcium comes from the weathering of calcium-silicate rocks, which causes the silicon in the rocks to combine

with oxygen to form sand or quartz (silicon dioxide), leaving calcium ions available to form limestone.

The greenhouse effect is the process in which the emission of infrared radiation by the atmosphere warms a

planet's surface.. The greenhouse effect was discovered by Joseph Fourier in 182

There is concern today that the continued in atmospheric C02 currently at a rate of about 1 per year, might

intensify the “greenhouse effect. C02 is transparent to visible radiation, but absorbs s in the infrared range.

Visible sunlight striking earth irradiated back as longer-wavelength infrared radiation. An increase in CO 2 in the

Earth’s atmospheric blanket would retain more of this radiation and thus would bring about a warming trend the

climate.

Contributing to the greenhouse effect is atmospheric methane released by human activities such as drilling for oil

and natural gas, land filling of solid waste and large scale cattle raising and wetland rice cultivation. Although

much lower in amount than CO2 the burning of fossil fuels, methane traps heat five times as effectively as CO 2 .

Thus even relatively small amounts, it can contribute to the green house effect significantly.

Global warming is the increase in the average measured temperature of the Earth's near-surface air and oceans

since the mid-20th century, and its projected continuation.

The average global air temperature near the Earth's surface increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the

100 years ending in 2005. The Intergovernmental Panel on Climate Change (IPCC) concludes "most of the

http://en.wikipedia.org/wiki/Fahrenheit

http://en.wikipedia.org/wiki/Celsius

http://en.wikipedia.org/wiki/Plus-minus_sign


observed increase in globally averaged temperatures since the mid-twentieth century is very likely due to the

observed increase in anthropogenic (man-made) greenhouse gas concentrations" via an enhanced greenhouse

effect. Natural phenomena such as solar variation combined with volcanoes probably had a small warming effect

from pre-industrial times to 1950 and a small cooling effect from 1950 onward.

On Earth, the major greenhouse gases are water vapor, which causes about 36–70 percent of the greenhouse

effect (not including clouds); carbon dioxide (CO2), which causes 9–26 percent; methane (CH4), which causes 4–9

percent; and ozone, which causes 3–7 percent. The issue is how the strength of the greenhouse effect changes

when human activity increases the atmospheric concentrations of some greenhouse gases.

Human activity since the industrial revolution has increased the concentration of various greenhouse gases,

leading to increased radiative forcing from CO2, methane, tropospheric ozone, CFCs and nitrous oxide.

Fossil fuel burning has produced approximately three-quarters of the increase in CO2 from human activity over

the past 20 years. Most of the rest is due to land-use change, in particular deforestation.

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Phosphorus cycle

A phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movements of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth.

Phosphorus is an essential nutrient for plants and animals in the form of ions PO43- and HPO4

2- . 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 normally occurs in nature as part of a phosphate ion, consisting of a phosphorus atom and some number of oxygen atoms, the most abundant form (called orthophosphate) having four oxygens: PO4

3-. Most phosphates are found as salts in ocean sediments or in rocks. Over time, geologic processes can bring ocean sediments to land, and weathering will carry terrestrial . Plants absorb phosphates from the soil. The plants may then be consumed by herbivores who in turn may be consumed by carnivores. After death, the animal or plant decays, and the phosphates are returned to the soil. Runoff may carry them back to the ocean or they may be reincorporated into rock.

The primary biological importance of phosphates is as a component of nucleotides, which serve as energy storage within cells (ATP) or when linked together, form the nucleic acids DNA and RNA. Phosphorus is also found in bones, whose strength is

derived from calcium phosphate, and in phospholipids (found in all biological membranes).

Phosphates move quickly through plants and animals; however, the processes that move them through the soil or ocean are very slow, making the phosphorus cycle overall one of the slowest biogeochemical cycles.

However, recent findings suggest that phosphorus is cycled through the ocean on the timescale of 10,000yr, suggesting that the phosphorus cycle may play a role in global warming.

Unlike other cycles of matter compounds, phosphorus cannot be found in air as a gas. This is because at normal temperature and circumstances, it is a liquid. It usually cycles through water, soil and sediments. In the atmosphere phosphorus is mainly small dust particles.

Phosphorus is one of the longest cycles, and takes a long time to move from sediments to living organisms and back to sediments.

Eutrophication is an increase in chemical nutrients -- typically compounds containing nitrogen or phosphorus -- in an ecosystem. It may occur on land or in water. The term is however often used to mean the resultant increase in the ecosystem's primary productivity (excessive plant growth and decay), and further effects including lack of oxygen and severe reductions in water quality, fish, and other animal populations.


Eutrophication is frequently a result of nutrient pollution such as the release of sewage effluent and run-off from lawn fertilizers into natural waters (rivers or coasts) although it may also occur naturally in situations where nutrients accumulate (e.g. depositional environments) or where they flow into systems on an ephemeral basis (e.g. intermittent upwelling in coastal systems). Eutrophication generally promotes excessive plant growth and decay, favors certain weedy species over others, and is likely to cause severe reductions in water quality . In aquatic environments, enhanced growth of choking aquatic vegetation or phytoplankton (that is, an algal bloom) disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen in the water, needed for fish and shellfish to survive. The water then becomes cloudy, colored a shade of green, yellow, brown, or red. Human society is impacted as well: eutrophication decreases the resource value of rivers, lakes, and estuaries such that recreation, fishing, hunting, and aesthetic enjoyment are hindered. Health-related problems can occur where eutrophic conditions interfere with drinking water treatment.

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Sulphur Cycle

Sulfur cycle is one of the constituents of many proteins, vitamins and hormones. It recycles as in other biogeochemical cycles.Sulphur like nitrogen, is an essential element for all living systems but because of its inert nature is not utilized by plants. To be used, sulphur has to be first oxidized or reduced. In the soil it occurs both in organic (sulphur amino acids, vitamins etc.) as well as in the inorganic form (sulphur, sulphates etc.) and is readily metabolized.Sulphur .

Pools in Nature

Ocean

air to ocean 180 (mainly sea salt)

sea salt to air 144

biogenic activity to air 16 (DMS)

marine volcanoes to air 5 (H2S )

marine volcanoes to air 5

Land

amount, 1018 g S yr-1

industry to air 90 (as SO2)

desert dust to air 8 (as sulphate salts)

volcanoes to air 5 (H2S > SO2)

biogenic activity to air 4 (H2S)

air to land 90

human extraction 160

Pools

amounts, 1018 g sulphur

Sedimentary rocks: ....

evaporites

2470

...... shales 4970

seawater 1280

land plants 0.0085

soil organic matter

0.0155

atmosphere 0.0000025

TOTAL 8270


pyrite deposition 39

hydrothermal sulphides 96

The essential steps of the sulfur cycle are:

Mineralization of organic sulfur to the inorganic form, hydrogen sulfide: (H2S). Oxidation of sulfide and elemental sulfur (S) and related compounds to sulfate (SO4

2–). Reduction of sulfate to sulfide. Microbial immobilization of the sulfur compounds and subsequent incorporation into the organic form of

sulfur.

These are often termed as follows:

Assimilative sulfate reduction in which sulfate (SO42–) is reduced to organic sulfhydryl (otherwise known

as thiol) groups (R–SH) by plants, fungi and various prokaryotes. The oxidation states of sulfur are +6 in sulfate and –2 in R–SH.

Desulfuration in which organic molecules containing sulfur can be desulfurated, producing hydrogen sulfide gas (H2S), oxidation state = –2. Note the similarity to deamination.

Oxidation of hydrogen sulfide produces elemental sulfur (So), oxidation state = 0. This reaction is done by the photosynthetic green and purple sulfur bacteria and some chemolithotrophs.

Further oxidation of elemental sulfur by sulfur oxidizers produces sulfate.

Land - Ocean

air transport to sea 20 (pollution)

air transport to land 4 (cyclic salts)

weathering to rivers 72

rivers to ocean 130


Dissimilative sulfur reduction in which elemental sulfur can be reduced to hydrogen sulfide. Dissimilative sulfate reduction in which sulfate reducers generate hydrogen sulfide from sulfate.

Bacteria carry out various transformations of sulphur:

1. Sulphate reduction in anaerobic environments2CH2O + 2H+ + SO4

2- --> H2S + 2CO2 + 2H2O This reaction is analagous to aerobic respiration but with SO4

2-. rather than oxygen, acting as the terminal electron acceptor in the oxidation reaction. The H2S produced may form reduced sulphur compounds such as pyrite or undergo either of the reactions that follow;

2. Sulphur-based (anaerobic) photosynthesis 2H2S + CO2 --> CH2O + 2S + 2H2O This reaction is probably the earliest form of photosynthesis using H2S, rather than water H2O, as the hydrogen donor in the reduction of CO2. It (or something similar) is employed by green and purple suphur-bacteria today;

Chemoautotrophy in aerobic conditions:4H2S + CO2 + O2 --> CH2O + 4S + 3H2O


This reaction is performed by species of Thiobacilli in environments with free elemental sulphur or with H2S, for example in the vicinity of deep sea hydrothermal vents.

Human impact on the sulfur cycle is primarily in the production of sulfur dioxide (SO2) from industry (e.g. burning coal) and the internal combustion engine. Sulfur dioxide can precipitate onto surfaces where it can be oxidized to sulfate in the soil (it is also toxic to some plants), reduced to sulfide in the atmosphere, or oxidized to sulfate in the atmosphere as sulfuric acid, a principal component of acid rain.In these systems sulphur is found mostly as a component of sulphur containing amino acids such as methionine and cysteine and to a small extent in some vitamins. When plant and animal proteins are degraded, the sulphur is released from the amino acids and accumulates in the soil which is then oxidized in the presence of oxygen while under anaerobic conditions H2S may accumulate.

H2S can also accumulate during the reduction of sulphates under anaerobic conditions which can be oxidized to sulphate under aerobic conditions. Plants utilize sulphur in the form of sulphates and then reduce it within the cells to H2S before it is utilized mainly in the synthesis of sulphur amino acids and vitamins (biotin, thiamine, lipoic acid). The assimilation of sulphur therefore, in many ways resembles the assimilation of nitrates.

The inorganic sulphur compounds which are transformed biologically represent various oxidation states from 2 of sulphide to +6 of sulphate. Not all the stages involved are biological. The biological oxidation of elemental sulphur' and inorganic sulphur compounds such as H2S, sulphite and thiosulphate is brought about by chemoautotrophic and photosynthetic bacteria. The oxidation of H2S is characteristic of certain pigmented sulphur bacteria which use this compound as an electron donor in photosynthesis.

Members of the genus Thiobacillus are the main organisms involved in the oxidation of elemental sulphur.The ability to oxidize sulphur is not restricted to only the genus Thiobacillus. Heterotrophic bacteria, actinomycetes and fungi are also reported to oxidize sulphur compounds. For example species of Bacillus, Pseudomonas,


Arthrobacter and Flavobacterium are known to oxidize elemental sulphur or thiosulphate to sulphate.sulhur is first converted enzymatically to sulphite which is then oxidized to sulphate.

It is believed that some of the sulphite from the first reaction reacts with sulphur to yield thiosulphate which is then either cleaved to sulphur and sulphite or converted into tetrathionite. The latter is then metabolized to sulphur or sulphite which are then oxidized to sulphate.under anaerobic conditions, sulphate is first reduced to H2S by sulphate reducing microorganisms, mostly the bacteria. Many bacteria including species of Bacillus and Pseudomonas are known to reduce sulphur or sulphate to H2S but among these, Desulfovibrio desulfuricans seems to be the most important.

The mechanism by which sulphate is reduced involves the conversion of sulphate to sulphite, a reaction that needs A TP. The sulphite is then reduced to H2S.The dissimilation of sulphur as sulphide and its release into the atmosphere has been recognized in recent years as a pollution problem. In fact, it is believed that the microbial volatilization of sulphur as H2S far exceeds the total amount of H2S produced from all other pollution sources. The sulphur reducers have therefore become a recognized source of atmospheric sulphur.

Acid rain is rain or any other form of precipitation that is unusually acidic. It has harmful effects on the environment and on structures. Acid rain is mostly caused by emissions due to human activity of sulfur and nitrogen compounds which react in the atmosphere to produce acids. In recent years, many governments have introduced laws to reduce these emissions.

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PASS WORD : biogeocycle

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BIOGEOCHEMICAL CYCLE-CARBON,SULPHUR AND …€¦ · Web viewbiochemistry, and . nutrition. of all living . cells. ... such as the bones and teeth. ... PASS WORD : biogeocycle. Author: