Biogeochemistry verslag compleet

8/2/2019 Biogeochemistry verslag compleet

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BiogeochemistryAn essay on Earths most importantbiogeochemical cycles

Deadline: november 6 2011

Subject: geochemistry

Group:

Biere M.

Hirschfeld G.

Pahlad G.

Sewbarath Misser X.


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Index

Page.

Chapter 1: What is biogeochemistry? 4.

Chapter 2: Biogeochemical cycles 5.

Chapter 3: The carbon cycle 7.

Chapter 4: The Nitrogen cycle 11.

Chapter 5: The phosphorus cycle 14.

Chapter 6: The sulfur cycle 15.

Chapter 7:Other important biogeochemical cycles 17.

7.1: The water cycle 17.

7.2: The oxygen cycle 17.

7.3: The mercury cycle 18.

Conclusion 19.

Refernces 20.


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Chapter 1: What is biogeochemistry?

Biogeochemistry is a science closely related to systems ecology. Biogeochemistry is the study of the

chemical, physical, geological, and biological processes and reactions that govern the composition of the

natural environment, which include the biosphere, the hydrosphere, the pedosphere, the atmosphere andthe lithosphere. Biogeochemistry is also the study of the cycles of chemical elements and their

interactions with and incorporation into living things transported through earth scale biological systems in

space through time. The field focuses on chemical cycles which are either driven by or have an impact on

biological activity. The most important cycles within this field of study are those of carbon, nitrogen,

sulfur and phosphorus.

The founder of biogeochemistry was Vladamir Vernadsky, a Russian scientist. Vernadsky distinguished

three spheres in the universe domain. His observations led him to conclude that each sphere has its own

laws of evolution and that the higher spheres modify and dominate the lowers. These three spheres are:

Abiotic sphere = All non-living energy and material processes

Biosphere = The life processes that live within the abiotic sphere

Nsphere = the sphere of the cognitive process of man

Biogeochemistry is a highly inter-disciplinary field, which means it is part of many types of studies such

as atmospheric science, biology, geomicrobiology, ecology, geology, oceanography and environmental

chemistry.

Biogeochemistry has many important research fields. Some of which are:

Modeling of natural systems

Soil remediation

Global changeClimate change

Biogeochemical prospecting for ore deposits
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Chapter 2: Biogeochemical cycles

A biogeochemical cycle a pathway by which a chemical element or molecule moves through both biotic

and abiotic sections of the Earth.

A cycle is a series of change which comes back to the starting point and which can be repeated. The term

biogeochemical tells us that biological, geological and chemical factors are all involved.

The elements cycle in either a gas cycle or a sedimentary cycle; some cycle as both a gas and sediment

In a gas cycle elements move through the atmosphere. The main reservoirs are the oceans and the

atmosphere. In a sedimentary cycle elements move from land to water to sediment. The main reservoirs

are the soil and sedimentary rocks.

Ecological systems

Ecological systems have many biogeochemical cycles operating as a part of the system. All chemical

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

organisms the chemical elements also cycle through abiotic factors of ecosystems. These living organisms

make up the biosphere.

All the nutrients that are used by the living organisms like carbon, nitrogen, oxygen, phosphorus, and

sulfur are a part of a closed system; which means, these chemicals are recycled instead of being lost and

replenished constantly such as in an open system.

Energy flow in an ecosystem is an open system which means that the sun constantly gives the planet

energy in the form of light while it is eventually used and lost in the form of heat, but It is possible for an

ecosystem to obtain energy without sunlight.

Although the energy the Earth receives from the sun is constant, its 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.

Reservoirs and exchange pools

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

When chemicals are held for only short periods of time, they are being held in exchange pools. Generally,

reservoirs are abiotic factors and exchange pools are biotic factors. The amount of time that a chemical is

held in one place is called its residence.

Important cycles within the biogeochemistry

The most important biogeochemical cycles are the carbon cycle, the nitrogen cycle, the oxygen cycle, the

phosphorus cycle, the sulfur cycle and the water cycle. There are many biogeochemical cycles that are

currently being studied for the first time, because climate change and human influence have drastically

changing the speed, intensity, and balance of these lesser known cycles. These newly studied

biogeochemical cycles include the mercury cycle.
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The cycles themselves can be divided into:

The gas cycle, which include:- The Carbon cycle- The Nitrogen cycle- The Oxygen cycle

The sedimentary cycle, which include:- The Phosphorus cycle- The Sulfur cycle

The gas-sediment cycle, which include:- The Water cycle- The Mercury cycle


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Chapter 3: The carbon cycleThe carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere,

pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is a very important element, as

it makes up organic matter, which is a part of all life.

Studies of the biogeochemistry of carbon on Earth must begin with a consideration of the origin of carbon

as an element. During the early development of Earth, the carbon cycle was decidedly non steady-state:

the carbon content of the planet grew with the receipt of planetesimals and meteorites, and the

atmospheric content increased as volcanoes released CO2.

The carbon cycle naturally consists of two parts, the terrestrial and the aquatic carbon cycle. The aquatic

carbon cycle is concerned with the movements of carbon through marine ecosystems and the terrestrial

carbon cycle is concerned with the movement of carbon through terrestrial ecosystems.

The following major reservoirs of carbon interconnected by pathways of exchange are:

The atmosphere The terrestrial biosphere, which is usually defined to include fresh water systems and non-living

organic material.

The oceans, including dissolved inorganic carbon and marine biota, The sediments. The Earth's interior, carbon from the Earth's mantle and crust is released to the atmosphere and

hydrosphere by volcanoeS.

The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various

chemical, physical, geological, and biological processes.

The global carbon budget is the balance of the exchanges of carbon between the carbon reservoirs or

between one specific loop of the carbon cycle. An examination of the carbon budget of a pool or reservoircan provide information about whether the pool or reservoir is functioning as a source or sink for carbon

dioxide. Since living tissue is composed primarily of carbon we can estimate that the global production

and destruction of organic carbon gives us an overall index of the health of the biosphere, both past and

present.

The carbon cycle is based on carbon dioxide (CO2), which can be found in air in the gaseous form, and in

water in dissolved form. Terrestrial plants use atmospheric carbon dioxide from the atmosphere, to

generate oxygen that sustains animal life. Aquatic plants also generate oxygen, but they use carbon

dioxide from water. The process of oxygen generation is called photosynthesis. During photosynthesis,

plants and other producers transfer carbon dioxide and water into complex carbohydrates, such as

glucose, under the influence of sunlight. Only plants and some bacteria have the ability to conduct this

process, because they possess chlorophyll; a pigment molecule in leaves that they can capture solarenergy with.

The overall reaction of photosynthesis is: carbon dioxide + water + solar energy -> glucose + oxygen

6 CO2 + 6 H2O + solar energy -> C6H12O6 + 6 O2
http://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Biospherehttp://en.wikipedia.org/wiki/Pedospherehttp://en.wikipedia.org/wiki/Geospherehttp://en.wikipedia.org/wiki/Hydrospherehttp://en.wikipedia.org/wiki/Earth%27s_atmospherehttp://www.lenntech.com/Periodic-chart-elements/C-en.htmhttp://en.wikipedia.org/wiki/Oceanhttp://en.wikipedia.org/wiki/Oceanhttp://en.wikipedia.org/wiki/Total_inorganic_carbonhttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Crust_(geology)http://www.lenntech.com/Periodic-chart-elements/O-en.htmhttp://www.lenntech.com/hazardous-substances/carbon-dioxide.htmhttp://www.lenntech.com/hazardous-substances/carbon-dioxide.htmhttp://www.lenntech.com/Periodic-chart-elements/O-en.htmhttp://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Total_inorganic_carbonhttp://en.wikipedia.org/wiki/Oceanhttp://www.lenntech.com/Periodic-chart-elements/C-en.htmhttp://en.wikipedia.org/wiki/Earth%27s_atmospherehttp://en.wikipedia.org/wiki/Hydrospherehttp://en.wikipedia.org/wiki/Geospherehttp://en.wikipedia.org/wiki/Pedospherehttp://en.wikipedia.org/wiki/Biospherehttp://en.wikipedia.org/wiki/Carbon


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Components of the carbon cycle

Carbon in the atmosphere

Carbon exists as a small percentage in the Earth's atmosphere primarily as the gas carbon dioxide (CO2).

Other gases containing carbon in the atmosphere are methane and chlorofluorocarbons.

Carbon is released into the atmosphere in several ways:

Through the respiration performed by plants and animals. This is an exothermic reaction and itinvolves the breaking down of glucose into carbon dioxide and water.

Through the decay of animal and plant matter. Fungi and bacteria break down the carbon compoundsin 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 carbondioxide.

Production ofcement. Carbon dioxide is released when limestone (calcium carbonate) is heated toproduce lime (calcium oxide) which is a component of cement.

At the surface of the oceans where the water becomes warmer, dissolved carbon dioxide is releasedback into the atmosphere.

Volcanic eruptions andmetamorphismrelease gases into the atmosphere.Carbon in the biosphereCarbon 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 theair or water in which they live. This 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.

Carbon is transferred within the biosphere as heterotrophsfeed on other organisms or their parts.Most carbon leaves the biosphere through respiration. When oxygen is present, aerobic respiration

occurs, which releases carbon dioxide into the surrounding air or water. Otherwise, anaerobic

respiration occurs and releases methane into the surrounding environment.

Burning of biomass can also transfer substantial amounts of carbon to the atmosphere Carbon may also be circulated within the biosphere when dead organic matter becomes incorporated

in the geosphere.

Not all organic matter is immediately decomposed. Under certain conditions dead plant matter

accumulates faster than it is decomposed within an ecosystem. The remains are locked away inunderground deposits. When layers of sediment compress this matter fossil fuels will be formed, after

many centuries. 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 may thus affect global climate change. Long-term

geological processes may expose the carbon in these fuels to air after a long period of time, but usually

the carbon within the fossil fuels is released during humane combustion processes.

Carbon in the hydrosphere

In the aquatic ecosystem carbon dioxide can be stored in rocks and sediments. It will take a long timebefore this carbon dioxide will be released, through weathering of rocks or geologic processes that bring

sediment to the surface of water. Carbon dioxide that is stored in water will be present as either carbonate

or bicarbonate ions. These ions are an important part of natural buffers that prevent the water from

becoming too acidic or too basic.

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
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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:

CO2(atmospheric) CO2(dissolved)Conversion to carbonic acid:

CO2(dissolved) + H2O H2CO3First ionization:

H2CO3 H+ + HCO3

(bicarbonate ion)

Second ionization:

HCO3 H

++ CO3

2(carbonate ion)

In the oceans, dissolved carbonate can combine with dissolved calcium to precipitate solid calcium

carbonate, CaCO3, mostly as the shells of microscopic organisms. When these organisms die, their shells

sink and accumulate on the ocean floor. Over time these carbonate sediments form limestone which is the

largest reservoir of carbon in the carbon cycle. The dissolved calcium in the oceans comes from the

chemical weathering of calcium-silicate rocks, during which carbonic and other acids in groundwater

react with calcium-bearing minerals liberating calcium ions to solution and leaving behind a residue of

newly formed aluminum-rich clay minerals and insoluble minerals such as quartz.

Variations within the carbon cycle

Dissolved inorganic carbon in the ocean is the largest near-surface pool, which has an enormous capacity

to buffer changes in the atmosphere. At equilibrium, the sea contains about 56 times as much carbon as

the atmosphere. The largest pool of carbon on land is contained in soils. Surprisingly, at present time, the

atmosphere contains more carbon than the Earths living vegetation. The largest fluxes of the globalcarbon cycle are those that link atmospheric carbon dioxide to land vegetation and to the sea. Oscillations

in atmospheric content of CO2 by photosynthesis in each hemisphere and seasonal differences in the use

of fossil fuels and in the exchange of CO2 with the oceans. There is a small difference (about 4 ppm) in

the concentration of atmospheric CO2 between the northern and southern hemispheres, owing to thepredominant use of fossil fuel in the northern hemisphere.

Figure 1: The carbon cycle
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Figure 2: A schematic representation of the terrestrial carbon cycle

Figure 3: A schematic representation of the aquatic carbon cycle


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Chapter 4: The nitrogen cycleNitrogen is a part of vital organic compounds in microorganisms, such as amino acids, proteins and DNA.

The gaseous form of nitrogen (N2), makes up 78% of the troposphere. Nitrogen in the gaseous form

cannot be absorbed and used as a nutrient by plants and animals; it must first be converted by nitrifying

bacteria, so that it can enter food chains as a part of the nitrogen cycle.

The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. This

transformation can be carried out by both biological and non-biological processes. Important processes in

the nitrogen cycle include fixation, mineralization, nitrification, and denitrification.

History of the nitrogen cycle

The earliest atmosphere on Earth is thought to have been dominated by nitrogen, since nitrogen is

abundant in volcanic emissions and only sparingly soluble in seawater. Before the origin of life, nitrogen

was fixed by lightning and in the shock waves of meteors, which create local conditions of high

temperature and pressure in the atmosphere. The rate of N-fixation was very low, perhaps about 6% of

the present-day rate, because abiotic fixation in an atmosphere dominated by N2 and CO2 is much slower

than in an atmosphere of N2 and O2. The limited supply of fixed nitrogen in the primitive oceans is likely

to have led to the early evolution of N-fixation in marine biota.

Processes of the nitrogen cycle

Nitrogen is present in the environment in a variety of chemical forms which include organic nitrogen,

ammonium (NH4+), nitrite (NO2

-), nitrate (NO3-), nitrous oxide (N2O), nitric oxide (NO) or inorganic

nitrogen gas (N2). The processes of the nitrogen cycle transform nitrogen from one form to another. Many

of those processes are carried out by microbes.

Nitrogen fixationNitrogen fixation is the natural process, which is either biological or abiotic, by which nitrogen (N2) in the

atmosphere is converted into ammonia (NH3).This process is essential for life because fixed nitrogen is

required to biosynthesize the components of life.

Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by an

enzyme called nitrogenase. The reaction for BNF is:

N2 + 8 H+ + 8 e

2 NH3 + H2

There are four ways to convert N2 (atmospheric nitrogen gas) into more chemically reactive forms:

- Biological fixation: some symbiotic bacteria and some free-living bacteria are able to fix nitrogenas organic nitrogen. Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is

converted to ammonia by an enzyme called nitrogenase. The reaction for BNF is:

N2 + 8 H+ + 8 e

2 NH3 + H2

Microorganisms which fix nitrogen are:

1. Cyanobacteria (cyanobacteria are able to utilize a variety of inorganic and organic sources ofcombined nitrogen, like nitrate, nitrite, ammonium, urea, or some amino acids).
http://www.lenntech.com/Periodic-chart-elements/N-en.htmhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Nitrogen_fixationhttp://en.wikipedia.org/wiki/Mineralization_(biology)http://en.wikipedia.org/wiki/Nitrificationhttp://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Nitritehttp://en.wikipedia.org/wiki/Nitratehttp://en.wikipedia.org/wiki/Nitrous_oxidehttp://en.wikipedia.org/wiki/Nitric_oxidehttp://en.wikipedia.org/wiki/Microbeshttp://c/wiki/Nitrogenhttp://c/wiki/Earth's_atmospherehttp://c/wiki/Ammoniahttp://c/wiki/Biosynthesishttp://c/wiki/Nitrogenasehttp://c/wiki/Nitrogenasehttp://c/wiki/Cyanobacteriahttp://c/wiki/Nitratehttp://c/wiki/Nitritehttp://c/wiki/Ammoniumhttp://c/wiki/Ureahttp://c/wiki/Amino_acidshttp://c/wiki/Amino_acidshttp://c/wiki/Ureahttp://c/wiki/Ammoniumhttp://c/wiki/Nitritehttp://c/wiki/Nitratehttp://c/wiki/Cyanobacteriahttp://c/wiki/Nitrogenasehttp://c/wiki/Nitrogenasehttp://c/wiki/Biosynthesishttp://c/wiki/Ammoniahttp://c/wiki/Earth's_atmospherehttp://c/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Microbeshttp://en.wikipedia.org/wiki/Nitric_oxidehttp://en.wikipedia.org/wiki/Nitrous_oxidehttp://en.wikipedia.org/wiki/Nitratehttp://en.wikipedia.org/wiki/Nitritehttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Nitrificationhttp://en.wikipedia.org/wiki/Mineralization_(biology)http://en.wikipedia.org/wiki/Nitrogen_fixationhttp://en.wikipedia.org/wiki/Nitrogenhttp://www.lenntech.com/Periodic-chart-elements/N-en.htm


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2. Azotobacteraceace3. Rhizobia4. Frankia- Industrial N-fixation: Under great pressure and with the use of an iron catalyst, hydrogen and

atmospheric nitrogen can be combined to form ammonia (NH3) in the Haber-Bosch process

which is used to make fertilizer and explosives.- Combustion of fossil fuels: automobile engines and thermal power plants, which release variousnitrogen oxides (NOx).

- In addition, the formation of NO from N2 and O2 due tophotons and especially lightning, can fixnitrogen.

Assimilation

Plants can absorb nitrate or ammonium ions from the soil via their root hairs. If nitrate is absorbed, it is

first reduced to nitrite ions and then ammonium ions for incorporation into amino acids, nucleic acids, and

chlorophyll. Animals cannot absorb nitrates directly. They receive their nutrient supplies by consuming

plants or plant-consuming animals. When nitrogen nutrients have served their purpose in plants and

animals, specialized decomposing bacteria will start a process called ammonification, to convert them

back into ammonia and water-soluble ammonium salts.

Ammonification

When a plant or animal dies, or expels waste, the initial form of nitrogen is organic. Bacteria or

sometimes fungi convert the organic nitrogen within the remains back into ammonium (NH4+), a process

called ammonification or mineralization.

Nitrification

Nitrification is the biological oxidation ofammonia with oxygen into nitrite followed by the oxidation of

these nitrites into nitrates. Nitrification is an important step in the nitrogen cycle in soil. The oxidation of

ammonia into nitrite is performed by two groups of organisms, ammonia-oxidizing bacteria (AOB) andammonia-oxidizing archaea (AOA). The second step (oxidation of nitrite into nitrate) is mostly done by

bacteria of the genus Nitrobacter. Nitrification is carried out according to the following reactions:

2NH3+ 3O2-> 2NO2+ 2H

++ 2H2O

2 NO2-+ O2 -> 2 NO3

-

Together with ammonification, nitrification forms a mineralization process that refers to the complete

decomposition of organic material, with the release of available nitrogen compounds. This replenishes the

nitrogen cycle.

Denitrification

Denitrification is a microbially facilitated process of nitrate reduction that produces molecular nitrogen

(N2) through a series of intermediate gaseous nitrogen oxide products. The process is performed primarily

by heterotrophic bacteria, although autotrophic denitrifiers have also been identified. Denitrification takes

place under special conditions in both terrestrial and marine ecosystems. It occurs where oxygen is

depleted, and bacteria respire nitrate as a substitute. Due to the high concentration of oxygen in our

atmosphere denitrification only takes place in anaerobic environments where oxygen consumption

exceeds the oxygen supply and where sufficient quantities of nitrate are present. These environments may
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include certain soils and groundwater, wetlands, oil reservoirs, poorly ventilated corners of the ocean, and

in seafloor sediments. Denitrification is carried out according to the following reaction:

NO3-+ CH2O + H

+-> N2O + CO2 + 1 H2O

The annamox reaction

In 1999 researchers at the Gist-Brocades in Delft, The Netherlands, discovered a new reaction to be addedto the nitrogen cycle; the so-called annamox reaction. Anammox, an abbreviation for ANaerobic

AMMonium OXidation, is a biological process where nitrite and ammonium are converted directly into

dinitrogen gas. This process contributes up to 50% of the dinitrogen gas produced in the oceans. It is thus

a major sink for fixed nitrogen and so limits oceanic primary productivity. The reaction is:NH4

+ + NO2 N2 + 2H2O.

The bacteria that perform the anammox process belong to the bacterial phylum Planctomycetes, of which

Planctomyces and Pirellula are the best known genera. Currently four genera of anammox bacteria have

been defined: Brocadia, Kuenenia, Anammoxoglobus, Jettenia (fresh water species), and Scalindua

(marine species). The anammox process was originally found to occur only from 20 C to 43 C[but more

recently, anammox has been observed at temperatures from 36 C to 52 C in hot springs and 60 C to 85

C at hydrothermal vents located along the Mid-Atlantic Ridge.

Figure 4: A schematic representation of the nitrogen cycle
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Chapter 5: The phosphorus cycleThe phosphorus cycle is the biogeochemical cycle that describes the movement ofphosphorus through the

lithosphere, hydrosphere, and biosphere.

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

and HPO42-

. It is a partof DNA-molecules, of molecules that store energy and of fats of cell membranes. Phosphorus is also a

building block of certain parts of the human and animal body.

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, it only occurs under highly reducing

conditions as the gas Phosphine PH3. This is because phosphorus is usually liquid at normal temperatures

and pressures. It is mainly cycling through water, soil and sediments.

Phosphorus normally occurs in nature as part of a phosphate ion, the most abundant form is

orthophosphate. 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 these phosphates to terrestrialhabitats. Plants absorb phosphates from the soil, then bind the phosphate into organic compounds. The

plants may then be consumed by herbivores who in turn are consumed by carnivores. After death, the

animal or plant decays, and the phosphates are returned to the soil. Runoffmay carry them back to the

ocean or they may be reincorporated into rock. The primary mineral with significant phosphorus content,

apatite [Ca5(PO4)3OH] undergoes carbonation weathering releasing phosphorus contained different forms.

Phosphates move quickly through plants and animals; however, there movement through the soil or

ocean are very slow, making the phosphorus cycle overall one of the slowest biogeochemical cycles. The

turnover of P through the organic pools in the surface ocean is only a few days. Nearly 90% of the

phosphorus taken up by marine biota is regenerated in the surface ocean, and most of the rest is

mineralized in the deep sea. Eventually, phosphorus is deposited in ocean sediments, which contain thelargest phosphorus pool near the surface of the Earth.

Figure 5: A schematic representation of the phosphorus cycle
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Chapter 6: The sulfur cycleThe sulfur cycle is the collection of processes by which sulfur moves to and from minerals and living

systems. Episodic events, including volcanic eruptions and dust storms, contribute to the global

biogeochemical cycle of sulfur.

Steps of the sulfur cycle are:

Mineralization of organic sulfur into inorganic forms, such as hydrogen sulfide (H2S), elementalsulfur, as well as sulfide minerals.

Oxidation of hydrogen sulfide, sulfide, and elemental sulfur (S) to sulfate (SO42). Reduction of sulfate to sulfide. Incorporation sulfide into organic compounds (including metal-containing derivatives).The terms often associated with these steps are:

- Assimilative sulfate reduction is a process in which sulfate (SO42) is reduced by plants, fungi andvarious prokaryotes.

-

Desulfurization is a process in which organic molecules containing sulfur can be desulfurized,producing hydrogen sulfide gas.

- Oxidation of hydrogen sulfide produces elemental sulfur (S8). This reaction occurs in thephotosynthetic green and purple sulfur bacteria and some chemolithotrophs. Often the elemental

sulfur is stored as polysulfides.

- oxidation of elemental sulfurby sulfur oxidizers produces sulfate.- Dissimilative sulfur reductioninwhich elemental sulfur can be reduced to hydrogen sulfide.- Dissimilative sulfate reduction in which sulfate reducers generate hydrogen sulfide from sulfate.

Igneous rocks such as pyrite (FeS2) comprised the original pool of sulfur on earth. Within the sulfur cycle,

the amount of mobile sulfur has been continuously increasing through volcanic activity as well asweathering of the crust in an oxygenated atmosphere and when SO4 is assimilated by organisms, it is

reduced and converted to organic sulfur, which is an important component of proteins. However, the

biosphere does not act as a major sink for sulfur, instead the majority of sulfur is found in seawater or

sedimentary rocks especially pyrite rich shale and evaporite rocks. The amount ofsulfate in the oceans is

controlled by three major processes:

1. input from rivers

2. sulfate reduction and sulfide reoxidation on continental shelves and slopes

3. burial of anhydrite and pyrite in the oceanic crust.

Dimethylsulfide [(CH3)2S or DMS] is produced by the decomposition of dimethylsulfoniopropionateDMSP from dying phytoplankton cells in the shallow levels of the ocean, and is the major biogenic gas

emitted from the sea, where it is responsible for the distinctive smell of the sea along the coastlines.DMS is the largest natural source of sulfur gas, but still only has a residence time of about one day in the

atmosphere and a majority of it is redeposited in the oceans rather than making it to land. However, it is a

significant factor in the climate system, as it is involved in the formation of clouds.
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Figure 6: A schematic representation of the sulfur cycle


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Chapter 7: Other important biogeochemical cycles

7.1: The water cycle

The water cycle, also known as the hydrologic cycle describes the continuous movement of water on,

above and below the surface of the Earth. Water can change states among liquid, vapor, and solid at

various places in the water cycle. The annual circulation of water is the largest movement of a chemical

substance at the surface of the Earth. Movements of water through the atmosphere determine the

distribution of rainfall on Earth. Where precipitation exceeds evapotranspiration on land, there is runoff.

Runoff carries the products of mechanical and chemical weathering to the sea.

Processes of the water cycle

- Precipitation: Condensed water vapor that falls to the Earth's surface .- Canopy interception: The precipitation that is intercepted by plant foliage and eventually

evaporates back to the atmosphere rather than falling to the ground.

- Snowmelt: The runoff produced by melting snow.- Runoff: The variety of ways by which water moves across the land. This includes both surface

runoff and channel runoff.

- Infiltration: The flow of water from the ground surface into the ground. Once infiltrated, thewater becomes soil moisture or groundwater.

- Subsurface flow: The flow of water underground, in the vadose zone and aquifers. Subsurfacewater may return to the surface or eventually seep into the oceans.

- Evaporation: The transformation of water from liquid to gas phases as it moves from the groundor bodies of water into the overlying atmosphere. The source of energy for evaporation is

primarily solar radiation. Evaporation often implicitly includes transpiration from plants, though

together they are specifically referred to as evapotranspiration.

- Sublimation: The state change directly from solid water to water vapor.- Advection: The movement of water in solid, liquid, or vapor states through the atmosphere.

Without advection, water that evaporated over the oceans could not precipitate over land.- Condensation: The transformation of water vapor to liquid water droplets in the air, creating

clouds and fog.

- Transpiration: The release of water vapor from plants and soil into the air.7.2: The oxygen cycle

The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within its three

main reservoirs: the atmosphere, the biosphere and the lithosphere. The main driving factor of the oxygen

cycle is photosynthesis, which is responsible for the modern Earth's atmosphere and life.

Reservoirs

The largest reservoir of Earth's oxygen is within the silicate and oxide minerals of the crust and mantle

(99.5%). Only a small portion has been released as free oxygen to the biosphere (0.01%) and atmosphere

(0.36%). The main source of atmospheric oxygen is photosynthesis.

An additional source of atmospheric oxygen comes from photolysis, whereby high energy ultraviolet

radiation breaks down atmospheric water and nitrous oxide into component atoms.
http://c/wiki/Earthhttp://c/wiki/Liquidhttp://c/wiki/Water_vaporhttp://c/wiki/Solidhttp://c/wiki/Precipitation_(meteorology)http://c/wiki/Precipitation_(meteorology)http://c/wiki/Interception_(water)http://c/wiki/Interception_(water)http://c/wiki/Snowmelthttp://c/wiki/Snowmelthttp://c/wiki/Runoff_(hydrology)http://c/wiki/Channel_runoffhttp://c/wiki/Infiltration_(hydrology)http://c/wiki/Infiltration_(hydrology)http://c/wiki/Soil_moisturehttp://c/wiki/Subsurface_flowhttp://c/wiki/Subsurface_flowhttp://c/wiki/Vadose_zonehttp://c/wiki/Evaporationhttp://c/wiki/Evaporationhttp://c/wiki/Solar_radiationhttp://c/wiki/Planthttp://c/wiki/Sublimation_(chemistry)http://c/wiki/Sublimation_(chemistry)http://c/wiki/Advectionhttp://c/wiki/Condensationhttp://c/wiki/Condensationhttp://c/wiki/Cloudhttp://c/wiki/Transpirationhttp://c/wiki/Transpirationhttp://en.wikipedia.org/wiki/Biogeochemical_cyclehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Biospherehttp://en.wikipedia.org/wiki/Lithospherehttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Photolysishttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Photolysishttp://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Photosynthesishttp://en.wikipedia.org/wiki/Lithospherehttp://en.wikipedia.org/wiki/Biospherehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Biogeochemical_cyclehttp://c/wiki/Transpirationhttp://c/wiki/Cloudhttp://c/wiki/Condensationhttp://c/wiki/Advectionhttp://c/wiki/Sublimation_(chemistry)http://c/wiki/Planthttp://c/wiki/Solar_radiationhttp://c/wiki/Evaporationhttp://c/wiki/Vadose_zonehttp://c/wiki/Subsurface_flowhttp://c/wiki/Soil_moisturehttp://c/wiki/Infiltration_(hydrology)http://c/wiki/Channel_runoffhttp://c/wiki/Runoff_(hydrology)http://c/wiki/Snowmelthttp://c/wiki/Interception_(water)http://c/wiki/Precipitation_(meteorology)http://c/wiki/Solidhttp://c/wiki/Water_vaporhttp://c/wiki/Liquidhttp://c/wiki/Earth


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Oxygen is also cycled between the biosphere and lithosphere. Marine organisms in the biosphere create

calcium carbonate shells (CaCO3) that are rich in oxygen. When the organism dies its shell is deposited

on the shallow sea floor and buried over time to create the limestone rock of the lithosphere. Weathering

processes initiated by organisms can also free oxygen from the lithosphere.

7.3: The mercury cycleMercury in the environment is constantly cycled and recycled through a biogeochemical cycle.The cycle has six major steps:

1. Degassing of mercury from rock, soils, and surface waters, or emissions from volcanoes and fromhuman activities.

2. Movement in gaseous form through the atmosphere.3. Deposition of mercury on land and surface waters.4. Conversion of the element into insoluble mercury sulfide.5. Precipitation or bioconversion into more volatile or soluble forms such as methyl mercury.6. Reentry into the atmosphere or bioaccumulation in food chains.

Mercury cycles in the environment as a result of natural and anthropogenic (human) activities. The

primary anthropogenic sources are: fossil fuel combustion and smelting activities. Both these natural and

human activities release elemental mercury vapor (Hg0) into the atmosphere. Once in the atmosphere, the

mercury vapor can circulate for up to a year, and hence become widely dispersed. The elemental mercury

vapor can then undergo a photochemical oxidation to become inorganic mercury that can combine with

water vapors and travel back to the Earths surface as rain. This mercury-water is deposited in soils and

bodies of water. Once in soil, the mercury accumulates until a physical event causes it to be released

again. In water, inorganic mercury can be converted into insoluble mercury sulfide which settles out of

the water and into the sediment, or it can be converted by bacteria that process sulfate into methyl

mercury. The conversion of inorganic mercury to methyl mercury is important for two reasons:

Methyl mercury is much more toxic than inorganic mercury.

Organisms require a long time to eliminate methyl mercury, which leads to bioaccumulation.

Now the methyl mercury-processing bacteria may be consumed by the next higher organism up the food

chain, or the bacteria may release the methyl mercury into the water where it can adsorb (stick) to

plankton, which can also be consumed by the next higher organism up the food chain. Alternatively, both

elemental mercury and organic (methyl) mercury can vaporize and re-enter the atmosphere and cycle

through the environment.

Figure 7: The mercury cycle
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Conclusion

With this essay we now have a better understanding about the biogeochemistry and the biogeochemical

cycles. The cycles are very important processes of this planet, because we would not be here without

them. The existence of the cycles is primarily thanks to microorganisms, and as we have seen, the cycles

themselves can be influenced by global warming and human activity.


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References

www.lenntech.com

Biogeochemistry: An analysis of global change

Autor: William H. Schlesinger

ISBN: 0-12-625155-X

Phanerozoic Cycles of Sedimentary Carbon and Sulfur

Author(s): Robert M. Garrels and Abraham Lerman

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Source: Proceedings of the National Academy of Sciences of the United States of America,Vol. 78, No. 8,

[Part 1: Physical Sciences] (Aug., 1981), pp. 4652-4656

The Oxygen Cycle

Author(s): LaMont C. ColeReviewed work(s):

Source: BioScience, Vol. 19, No. 2 (Feb., 1969), p. 108

Global Environmental Change: The Causes and Consequences of Disruption to BiogeochemicalCycles

Author(s): A.M. Mannion

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Source: The Geographical Journal, Vol. 164, No. 2 (Jul., 1998), pp. 168-182

Atmospheric Influence of Earth's Earliest Sulfur Cycle

Author(s): James Farquhar, Huiming Bao, Mark Thiemens

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Source: Science, New Series, Vol. 289, No. 5480 (Aug. 4, 2000), pp. 756-758

The Global Carbon Cycle: A Test of Our Knowledge of Earth as a System

Author(s): P. Falkowski, R. J. Scholes, E. Boyle, J. Canadell, D. Canfield, J. Elser, N. Gruber,K. Hibbard,

P. Hgberg, S. Linder, F. T. Mackenzie, B. Moore III, T. Pedersen, Y. Rosenthal, S.Seitzinger, V.

Smetacek, W. Steffen

Reviewed work(s):

Source: Science, New Series, Vol. 290, No. 5490 (Oct. 13, 2000), pp. 291-296

Nitrogen Cycles: Past, Present, and FutureAuthor(s): J. N. Galloway, F. J. Dentener, D. G. Capone, E. W. Boyer, R. W. Howarth, S. P.Seitzinger, G.

P. Asner, C. C. Cleveland, P. A. Green, E. A. Holland, D. M. Karl, A. F. Michaels,J. H. Porter, A. R.

Townsend, C. J. Vrsmarty

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Source: Biogeochemistry, Vol. 70, No. 2 (Sep., 2004), pp. 153-226


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The Global Phosphorus Cycle

Author(s): U. Pierrou

Reviewed work(s):

Source: Ecological Bulletins, No. 22, Nitrogen, Phosphorus and Sulphur: Global Cycles: ScopeReport 7

(1976), pp. 75-88

The Hydrologic Cycle: an Open or a Closed System?

Author(s): Francisco de Assis Matos de Abreu, Andr Montenegro Duarte, Mrio RamosRibeiro, Ana

Rosa Carrio de Lima, Wellington de Jesus Sousa

Reviewed work(s):

Source: Revista Geogrfica, No. 137 (ENERO-JUNIO 2005), pp. 109-122

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