natural cycles

7/29/2019 Natural Cycles

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NATURAL CYCLES::::::::::::::

Natural Biochemical Cycles

The major natural biochemical cycles include thecarbon,nitrogen,

andphosphatecycles. They are presented in brief in this graphic.Plants such as trees and algae undergo the photosynthesis reaction where carbon

dioxide and water in the presence of sunlight are converted to organic materials and

oxygen.

An important reverse reaction occurs in the water: Fish use metabooilism where

oxygen and organic materials - other small fish or algae - as food is converted to

carbon dioxide, water, and energy.

Bacteria in water, as well as land, also undergometabolism and use oxygen and

decompose organic wastes as food to convert to carbon dioxide, water, and energy. Byproducts in the decomposition of organic waste are nitrates and phosphates.

The overall health of a body of water depends upon whether these factors are in

balance. Municipal sewage systems are now doing a better job of removing most of

the organic waste products in the discharge water, but some organic waste still enters

the streams and lakes. If an excess amount of organic waste is present in the water, the

bacteria use all of the available oxygen in the water in an attempt to decompose the

organic waste.

The amount of organic waste in water is represent by a chemical test called BOD -

Biological Oxygen Demand.The concentration of oxygen is measured in a watersample at the beginning of the test and again after five days. The difference between

the oxygen concentrations represents the amount of oxygen consumed by the bacteria

in the metabolism of the waste organics present.
http://www.elmhurst.edu/~chm/vchembook/306carbon.htmlhttp://www.elmhurst.edu/~chm/vchembook/306carbon.htmlhttp://www.elmhurst.edu/~chm/vchembook/307nitrogen.htmlhttp://www.elmhurst.edu/~chm/vchembook/307nitrogen.htmlhttp://www.elmhurst.edu/~chm/vchembook/307nitrogen.htmlhttp://www.elmhurst.edu/~chm/vchembook/308phosphate.htmlhttp://www.elmhurst.edu/~chm/vchembook/308phosphate.htmlhttp://www.elmhurst.edu/~chm/vchembook/308phosphate.htmlhttp://www.elmhurst.edu/~chm/vchembook/308phosphate.htmlhttp://www.elmhurst.edu/~chm/vchembook/307nitrogen.htmlhttp://www.elmhurst.edu/~chm/vchembook/306carbon.html


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Eutrophication:

In situations where eutrophication occurs, the natural cycles are overwhelmed by an

excess of one or more of the following: nutrients such as nitrate or phosphate, or

organic waste.

In the first case under aerobic conditions (presence of oxygen), the natural cycles

may be more or less in balance until an excess of nitrate and/or phosphate enters the

water. At this time the water plants and algae begin to grow more rapidly than normal.

As this happens there is also an excess die off of the plants and algae as sunlight is

blocked at lower levels. Bacteria try to decompose the organic waste, consuming the

oxygen, and releasing more phosphate and nitrate to begin the cycle anew. Some of

the phosphate may be precipitated as iron phosphate to remove the soluble form from

the water solution.

In the second case under anaerobic conditions (absence of oxygen), as conditionsworsen as more phosphates and nitrates may be added to the water, all of the oxygen

may be used up by bacteria in trying to decompose all of the waste. Different bacteria

continue to carry on decomposition reactions, however the products are drastically

different. The carbon is converted to methane gas instead of carbon dioxide, sulfur is

converted to hydrogen sulfide gas. Some of the sulfide may be precipitated as iron

sulfide. Under anaerobic conditions the iron phosphate in the sediments may be


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solubilized into solution to make it available as a nutrient for the algae which would

start the growth and decay cycle over again. The pond may gradually fill with

undecayed plant materials to make a swamp.

CARBON CYCLE::::::


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Carbon Cycle - Photosynthesis:

Photosynthesis is a complex series of reactions carried out by algae, phytoplankton,

and the leaves in plants, which utilize the energy from the sun. The simplified version

of this chemical reaction is to utilize carbon dioxide molecules from the air and water

molecules and the energy from the sun to produce a simple sugar such as glucose and

oxygen molecules as a by product. The simple sugars are then converted into other

molecules such as starch, fats, proteins, enzymes, and DNA/RNA i.e. all of the other

molecules in living plants. All of the "matter/stuff" of a plant ultimately is produced

as a result of this photosynthesis reaction.

An important summary statement is that during photosynthesis plants usecarbon

dioxide andproduceoxygen.


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Carbon Cycle - Combustion/Metabolism Reaction:

Combustion occurs when any organic material is reacted (burned) in the presence ofoxygen to give off the products of carbon dioxide and water and ENERGY. The

organic material can be any fossil fuel such as natural gas (methane), oil, or coal.

Other organic materials that combust are wood, paper, plastics, and cloth. Organic

materials contain at least carbon and hydrogen and may include oxygen. If other

elements are present they also ultimately combine with oxygen to form a variety of

pollutant molecules such as sulfur oxides and nitrogen oxides.

Metabolism occurs in animals and humans after the ingestion of organic plant or

animal foods. In the cells a series of complex reactions occurs with oxygen to convert

for example glucose sugar into the products of carbon dioxide and water andENERGY. This reaction is also carried out by bacteria in the decomposition/decay of

waste materials on land and in the water.

An important summary statement is that during

combustion/metabolism oxygen is used and carbon dioxide is a product. The whole

purpose of both processes is to convert chemical energy into other forms of energy

such as heat.


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Carbon Cycle - Sedimentation:

Carbon dioxide is slightly soluble and is absorbed into bodies of water such as the

ocean and lakes. It is not overly soluble as evidenced by what happens when a can of

carbonated soda such as Coke is opened. Some of the dissolved carbon dioxide

remains in the water, the warmer the water the less carbon dioxide remains in the

water.

Some carbon dioxide is used by algae and phytoplankton through the process of

photosynthesis.

In other marine ecosystems, some organisms such as coral and those with shells take

up carbon dioxide from the water and convert it into calcium carbonate. As the shelledorganisms die, bits and pieces of the shells fall to the bottom of the oceans and

accumulate as sediments. The carbonate sediments are constantly being formed and

redissolved in the depths of the oceans. Over long periods of time, the sediments may

be raised up as dry land or into mountains. This type of sedimentary rock is called

limestone. The carbonates can redissolve releasing carbon dioxide back to the air or

water.


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Human Impacts on the Carbon Cycle - Fossil Fuels:

In the natural carbon cycle, there are two main processes which occur: photosynthesis

and metabolism.

During photosynthesis, plants usecarbon dioxide andproduceoxygen.

During metabolism oxygen is used and carbon dioxide is a product.

Humans impact the carbon cycle during the combustion of any type of fossil fuel,

which may include oil, coal, or natural gas. Fossil Fuels were formed very long ago

from plant or animal remains that were buried, compressed, and transformed into oil,

coal, or natural gas. The carbon is said to be "fixed" in place and is essentially locked

out of the natural carbon cycle. Humans intervene during by burning the fossil fuels.

During combustion in the presence of air (oxygen), carbon dioxide and water

molecules are released into the atmosphere.

The question becomes as to what happens to this extra carbon dioxide that is released

into the atmosphere. This is the subject of considerable debate and about it possible

effect in enhancing the greenhouse effect which may than result in global warming.


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The Carbon Cycle

All living things are made of carbon. Carbon is also a part of the ocean, air,

and even rocks. Because the Earth is a dynamic place, carbon does not

stay still. It is on the move!

In the atmosphere, carbon is attached to some oxygen in a gas called

carbon dioxide.

Plants use carbon dioxide and sunlight to make their own food and grow.

The carbon becomes part of the plant. Plants that die and are buried may

turn into fossil fuels made of carbon like coal and oil over millions of

years. When humans burn fossil fuels, most of the carbon quickly enters

the atmosphere as carbon dioxide.

Carbon dioxide is a greenhouse gas and traps heat in the atmosphere.

Without it and other greenhouse gases, Earth would be a frozen world.

But humans have burned so much fuel that there is about 30% more

carbon dioxide in the air today than there was about 150 years ago, and


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Earth is becoming a warmer place. In fact, ice cores show us that there is

now more carbon dioxide in the atmosphere than there has been in the

last 420,000 years.

NITROGEN CYCLE::::::::::::::::

The main component of the nitrogen cycle starts with the element nitrogen in the air.

Two nitrogen oxides are found in the air as a result of interactions with oxygen.

Nitrogen will only react with oxygen in the presence of high temperatures and

pressures found near lightning bolts and in combustion reactions in power plants or


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internal combustion engines. Nitric oxide, NO, and nitrogen dioxide, NO2, are formed

under these conditions. Eventually nitrogen dioxide may react with water in rain to

form nitric acid, HNO3. The nitrates thus formed may be utilized by plants as a

nutrient.

Nitrogen in the air becomes a part of biological matter mostly through the actions ofbacteria and algae in a process known as nitrogen fixation. Legume plants such as

clover, alfalfa, and soybeans form nodules on the roots where nitrogen fixing bacteria

take nitrogen from the air and convert it into ammonia, NH3. The ammonia is further

converted by other bacteria first into nitrite ions, NO2-, and then into nitrate ions, NO3

-.

Plants utilize the nitrate ions as a nutrient or fertilizer for growth. Nitrogen is

incorporate in many amino acids which are further reacted to make proteins.

Ammonia is also made through a synthetic process called the Haber Process. Nitrogen

and hydrogen are reacted under great pressure and temperature in the presence of a

catalyst to make ammonia. Ammonia may be directly applied to farm fields as

fertilizer. Ammonia may be further processed with oxygen to make nitric acid. The

reaction of ammonia and nitric acid produces ammonium nitrate which may then be

used as a fertilizer. Animal wastes when decomposed also return to the earth as

nitrates.

To complete the cycle other bacteria in the soil carry out a process known as

denitrification which converts nitrates back to nitrogen gas. A side product of this

reaction is the production of a gas known as nitrous oxide, N2O. Nitrous oxide, also

known as "laughing gas" - mild anesthetic, is also a greenhouse gas which contributesto global warming.


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Take a deep breath. Most of what you just inhaled is nitrogen. In fact,

80% of the air in our atmosphere is made of nitrogen. Your body does not

use the nitrogen that you inhale with each breath. But, like all living

things, your body needs nitrogen. Your body gets the nitrogen it needs to

grow from food.

Most plants get the nitrogen they need from soil. Many farmers use

fertilizers to add nitrogen to the soil to help plants grow larger and

faster. Both nitrogen fertilizers and forest fires add huge amounts of

nitrogen into the soil and nearby lakes and rivers. Water full of nitrogen

causes plants and algae to grow very fast and then die all at once when

there are too many for the environment to support.


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Phosphorus Cycle::::::::::::::

Phosphorus enters the environment from rocks or deposits laid down on the earth

many years ago. The phosphate rock is commercially available form is called apatite.Other deposits may be from fossilized bone or bird droppings called guano.

Weathering and erosion of rocks gradually releases phosphorus as phosphate ions

which are soluble in water. Land plants need phosphate as a fertilizer or nutrient.


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Phosphate is incorporated into many molecules essential for life such as ATP,

adenosine triphosphate, which is important in the storage and use of energy. It is also

in the backbone of DNA and RNA which is involved with coding for genetics.

When plant materials and waste products decay through bacterial action, the

phosphate is released and returned to the environment for reuse.

Much of the phosphate eventually is washed into the water from erosion and leaching.

Again water plants and algae utilize the phosphate as a nutrient. Studies have shown

that phosphate is the limiting agent in the growth of plants and algae. If not enough is

present, the plants are slow growing or stunted. If too much phosphate is present

excess growth may occur, particularly in algae.

A large percentage of the phosphate in water is precipitated from the water as iron

phosphate which is insoluble. If the phosphate is in shallow sediments, it may be

readily recycled back into the water for further reuse. In deeper sediments in water, it

is available for use only as part of a general uplifting of rock formations for the cycle

to repeat itself.

Human Inputs to the Phosphorus Cycle:

Human influences on the phosphate cycle come mainly from the introduction and use

of commercial synthetic fertilizers. The phosphate is obtained through mining of


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certain deposits of calcium phosphate called apatite. Huge quantities of sulfuric acid

are used in the conversion of the phosphate rock into a fertilizer product called "super

phosphate".

Plants may not be able to utilize all of the phosphate fertilizer applied, as aconsequence, much of it is lost form the land through the water run-off. The

phosphate in the water is eventually precipitated as sediments at the bottom of the

body of water. In certain lakes and ponds this may be redissolved and recyled as a

problem nutrient.

Animal wastes or manure may also be applied to the land as fertilizer. If misapplied

on frozen ground during the winter, much of it may lost as run-off during the spring

thaw. In certain area very large feed lots of animals, may result in excessive run-off of

phosphate and nitrate into streams.

Other human sources of phosphate are in the out flows from municipal sewage

treatment plants. Without an expensive tertiary treatment, the phosphate in sewage is

not removed during various treatment operations. Again an extra amount of phosphate

enters the water.


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The Rock Cycle

Over many thousands of years, energy from the Sun moves the wind and

water at the Earths surface with enough force to break rocks apart into

sand and other types of sediment. When sediment is buried and cemented

together, it becomes a sedimentary rock such as sandstone or shale.

If rocks are buried very deeply, they are in an environment that is very

hot and has high pressure. The crystals and texture of the rocks change

as they turn into metamorphic rocks like marble or slate. If, deep

underground, rocks are put under too much pressure and temperatures

that are too hot, they will melt, forming molten rock called magma.

Sometimes magma cools and forms igneous rock deep underground. Othertimes magma flows to the Earths surface and erupts from a volcano.

Rocks can affect the atmosphere! Erupting volcanoes send tiny particles

of ash and gases into the atmosphere. Tiny particles of ash help make

raindrops in the atmosphere as water condenses around them. The gases

released from volcanoes can become sulfuric acid droplets that screen

out sunlight. Large volcanic eruptions can even reduce Earths

temperature for months or several years.


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The Water Cycle

Water plays many different roles on the Earth. Some is at the poles in ice

caps, and some is in the snow and glaciers at the tops of high mountains.

Some is in lakes and streams, and some is underground. Some is vapor in

the atmosphere. But most of the water on Earth is in the oceans.


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Water is always on the move! The Suns energy causes water to evaporate

from oceans and lakes into the atmosphere. Plants and animals also

release water vapor into the atmosphere as they breathe. When the

atmosphere cools, water vapor condenses; making clouds that might

produce rain or snow. Water has been recycled in its different forms asice, liquid, or vapor --for more than 3.5 billion years.


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The Energy Balance

Earth gets all its energy from the Sun and loses energy into space If

more energy is lost into space than is received from the Sun, the planet

gets cooler. If it loses less energy than it receives, the planet will warm

up.

Have you noticed that it is often cooler when there are clouds in the sky?

Some types of clouds act like giant sun umbrellas, shading the Earth and

reflecting the sunlight that hits them. Other types of clouds act like a

jacket, holding the heat in and preventing it from leaving the atmosphere.

Today, most clouds act more like a sun umbrella and help keep our climate

cool. However, this could change if global warming affects the type ofclouds, their thickness, and how much water or ice they contain.

While it might be quite warm in the countryside on a summer day, it can

get unbearably hot in a nearby city! Thats because the buildings and

pavement in cities absorb oodles of sunlight, much more than the

countryside. These cities are called heat islands. The countryside is also

cooled by water evaporating from lakes and given off by the plants in

forests and fields. Cities have fewer plants and bodies of water and soare not cooled very much by evaporation.


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The Active Atmosphere

Has Earths atmosphere ruffled your hair, blown your homework down thestreet, or turned your umbrella inside out? The atmosphere, a thin

blanket of gases that surrounds Earth, transports heat and water and

filters out deadly ultraviolet radiation. Whether it is just a gentle breeze

or a hurricane-force gale, Earths atmosphere is constantly on the move.


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When the atmosphere moves, it evens out differences in temperature

between the chilly poles and the warm equator. Warm air from the

equator moves toward the poles and cold air from the poles moves towardthe equator. This circulation of air is disrupted a bit by the Earths

rotation. This makes counterclockwise winds around hurricanes, winterstorms, tornadoes, and other low-pressure areas north of the equator and

clockwise south of the equator.


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The Ocean in Motion

The ocean water is in motion because of differences in temperature and

saltiness. Water that is warmed at the sea surface near the equator

moves toward the chilly poles. Cold, salty currents flow into the deepest

parts of the sea.

Oceans can hold a large amount of heat energy much more than the

atmosphere. In the past few decades, Earths oceans have become

warmer. Even as far as 2 miles (3.2 kilometers) below the surface of the

sea, the ocean water has been warmed. Scientists estimate the oceans

may have absorbed up to half of the energy trapped by greenhouse gases

over the last century.


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Biogeochemical cycles:

InecologyandEarth science, a biogeochemical cycle orsubstance turnover orcycling of substances is a

pathway by which achemical elementormoleculemoves through both biotic (biosphere) and abiotic

(lithosphere,atmosphere, andhydrosphere) compartments ofEarth. A cycle is a series of change which comes back

to the starting point and which can be repeated.[1][2]

The term biogeochemical tells us that biological; geological and chemical factors are all involved. On the other hand

the circulation of chemical nutrients like carbon, oxygen, nitrogen, phosphorus, calcium, and water etc. through the

biological and physical world are known as biogeochemical cycle. 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).
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Nitrogen cycleThe nitrogen cycle is the process by whichnitrogenis 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 includefixation,mineralization,nitrification, anddenitrification. The majority ofEarth's

atmosphere(approximately 78%) isnitrogen,[1]

making it the largest pool of nitrogen. However, atmospheric nitrogen

has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems. The

nitrogen cycle is of particular interest toecologistsbecause nitrogen availability can affect the rate of key ecosystem

processes, includingprimary productionanddecomposition. Human activities such as fossil fuel combustion, use of

artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle.

A 2011 study has cast doubt on the traditional model of the nitrogen cycle described below; nitrogen from rocks may

also be a significant source not previously included.[2]

The processes of the nitrogen cycleNitrogen is present in the environment in a wide variety of chemical forms including organic

nitrogen,ammonium(NH4+),nitrite(NO2

-),nitrate(NO3

-),nitrous oxide(N2O),nitric oxide(NO) or inorganic nitrogen

gas (N2). Organic nitrogen may be in the form of a living organism,humusor in the intermediate products of organic

matter decomposition. The processes of the nitrogen cycle transform nitrogen from one form to another. Many of

those processes are carried out bymicrobes, either in their effort to harvest energy or to accumulate nitrogen in a

form needed for their growth. The diagram above shows how these processes fit together to form the nitrogen cycle.
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Nitrogen fixation

Atmospheric nitrogen must be processed, or "fixed" (see page onnitrogen fixation), to be used by plants. Some

fixation occurs inlightningstrikes, but most fixation is done by free-living orsymbioticbacteria. These bacteria have

thenitrogenaseenzymethat combines gaseous nitrogen withhydrogento produceammonia, which is then further

converted by the bacteria to make their ownorganic compounds. Most biological nitrogen fixation occurs by the

activity of Mo-nitrogenase, found in a wide variety of bacteria and someArchaea. Mo-nitrogenase is a complex twocomponentenzymethat has multiple metal-containing prosthetic groups.

[5]Some nitrogen fixing bacteria, such

asRhizobium, live in the root nodules oflegumes(such as peas or beans). Here they form amutualisticrelationship

with the plant, producing ammonia in exchange forcarbohydrates. Nutrient-poor soils can be planted with legumes to

enrich them with nitrogen. A few other plants can form suchsymbioses. Today, about 30% of the total fixed nitrogen is

manufactured inammoniachemical plants.[6]

[edit]Conversion of N2

The conversion of nitrogen (N2) from the atmosphere into a form readily available to plants and hence to animals and

humans is an important step in the nitrogen cycle, which distributes the supply of this essential nutrient. There are

four ways to convert N2 (atmospheric nitrogen gas) into more chemically reactive forms:[3]

1. Biological fixation: some symbiotic bacteria (most often associated with leguminous plants) and some free-living bacteria are able to fix nitrogen as organic nitrogen. An example of mutualistic nitrogen fixing bacteria

are theRhizobiumbacteria, which live inlegumeroot nodules. These species arediazotrophs. An example

of the free-living bacteria isAzotobacter.

2. Industrial N-fixation: Under great pressure, at a temperature of 600 C, and with the use of an iron catalyst,

hydrogen (usually derived from natural gas or petroleum) and atmospheric nitrogen can be combined to

form ammonia (NH3) in theHaber-Boschprocess which is used to make fertilizer and explosives.

3. Combustion of fossil fuels: automobile engines and thermal power plants, which release various nitrogen

oxides (NOx).

4. Other processes: In addition, the formation of NO from N2 and O2 due to photons and especially lightning,

can fix nitrogen.

[edit]Assimilation

Plants take nitrogen from the soil, by absorption through their roots in the form of

eithernitrateionsorammoniumions. All nitrogen obtained byanimalscan be traced back to the eating of plants at

some stage of thefood chain.

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.[3]

In plants

that have a mutualistic relationship with rhizobia, some nitrogen is assimilated in the form of ammonium ions directly

from the nodules. Animals, fungi, and otherheterotrophicorganisms obtain nitrogen by ingestion ofamino

acids,nucleotidesand other small organic molecules.

[edit]Ammonification

When a plant or animal dies, or an animal expels waste, the initial form of nitrogen isorganic. Bacteria, or fungi in

some cases, convert the organic nitrogen within the remains back intoammonium(NH4+), a process called

ammonification ormineralization. Enzymes Involved:

GS: Gln Synthetase (Cytosolic & PLastid)

GOGAT: Glu 2-oxoglutarate aminotransferase (Ferredoxin & NADH dependent)

GDH: Glu Dehydrogenase:

Minor Role in ammonium assimilation.
http://en.wikipedia.org/wiki/Nitrogen_fixationhttp://en.wikipedia.org/wiki/Nitrogen_fixationhttp://en.wikipedia.org/wiki/Nitrogen_fixationhttp://en.wikipedia.org/wiki/Lightninghttp://en.wikipedia.org/wiki/Lightninghttp://en.wikipedia.org/wiki/Lightninghttp://en.wikipedia.org/wiki/Symbiotichttp://en.wikipedia.org/wiki/Symbiotichttp://en.wikipedia.org/wiki/Symbiotichttp://en.wikipedia.org/wiki/Nitrogenasehttp://en.wikipedia.org/wiki/Nitrogenasehttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Organic_compoundhttp://en.wikipedia.org/wiki/Organic_compoundhttp://en.wikipedia.org/wiki/Organic_compoundhttp://en.wikipedia.org/wiki/Archaeahttp://en.wikipedia.org/wiki/Archaeahttp://en.wikipedia.org/wiki/Archaeahttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-MoirJWB-4http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-MoirJWB-4http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-MoirJWB-4http://en.wikipedia.org/wiki/Rhizobiumhttp://en.wikipedia.org/wiki/Rhizobiumhttp://en.wikipedia.org/wiki/Rhizobiumhttp://en.wikipedia.org/wiki/Legumeshttp://en.wikipedia.org/wiki/Legumeshttp://en.wikipedia.org/wiki/Legumeshttp://en.wikipedia.org/wiki/Mutualistichttp://en.wikipedia.org/wiki/Mutualistichttp://en.wikipedia.org/wiki/Mutualistichttp://en.wikipedia.org/wiki/Carbohydrateshttp://en.wikipedia.org/wiki/Carbohydrateshttp://en.wikipedia.org/wiki/Carbohydrateshttp://en.wikipedia.org/wiki/Symbiosishttp://en.wikipedia.org/wiki/Symbiosishttp://en.wikipedia.org/wiki/Symbiosishttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-5http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-5http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-5http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=4http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Rhizobiumhttp://en.wikipedia.org/wiki/Rhizobiumhttp://en.wikipedia.org/wiki/Rhizobiumhttp://en.wikipedia.org/wiki/Legumehttp://en.wikipedia.org/wiki/Legumehttp://en.wikipedia.org/wiki/Legumehttp://en.wikipedia.org/wiki/Diazotrophhttp://en.wikipedia.org/wiki/Diazotrophhttp://en.wikipedia.org/wiki/Diazotrophhttp://en.wikipedia.org/wiki/Azotobacterhttp://en.wikipedia.org/wiki/Azotobacterhttp://en.wikipedia.org/wiki/Azotobacterhttp://en.wikipedia.org/wiki/Haber-Boschhttp://en.wikipedia.org/wiki/Haber-Boschhttp://en.wikipedia.org/wiki/Haber-Boschhttp://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=5http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=5http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=5http://en.wikipedia.org/wiki/Nitratehttp://en.wikipedia.org/wiki/Nitratehttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Food_chainhttp://en.wikipedia.org/wiki/Food_chainhttp://en.wikipedia.org/wiki/Food_chainhttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Heterotrophichttp://en.wikipedia.org/wiki/Heterotrophichttp://en.wikipedia.org/wiki/Heterotrophichttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=6http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=6http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=6http://en.wikipedia.org/wiki/Organic_matterhttp://en.wikipedia.org/wiki/Organic_matterhttp://en.wikipedia.org/wiki/Organic_matterhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Mineralization_(soil)http://en.wikipedia.org/wiki/Mineralization_(soil)http://en.wikipedia.org/wiki/Mineralization_(soil)http://en.wikipedia.org/wiki/Mineralization_(soil)http://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Organic_matterhttp://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=6http://en.wikipedia.org/wiki/Nucleotidehttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Amino_acidhttp://en.wikipedia.org/wiki/Heterotrophichttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Food_chainhttp://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Ionhttp://en.wikipedia.org/wiki/Nitratehttp://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=5http://en.wikipedia.org/wiki/Haber-Boschhttp://en.wikipedia.org/wiki/Azotobacterhttp://en.wikipedia.org/wiki/Diazotrophhttp://en.wikipedia.org/wiki/Legumehttp://en.wikipedia.org/wiki/Rhizobiumhttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=4http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-5http://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Symbiosishttp://en.wikipedia.org/wiki/Carbohydrateshttp://en.wikipedia.org/wiki/Mutualistichttp://en.wikipedia.org/wiki/Legumeshttp://en.wikipedia.org/wiki/Rhizobiumhttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-MoirJWB-4http://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Archaeahttp://en.wikipedia.org/wiki/Organic_compoundhttp://en.wikipedia.org/wiki/Ammoniahttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Enzymehttp://en.wikipedia.org/wiki/Nitrogenasehttp://en.wikipedia.org/wiki/Symbiotichttp://en.wikipedia.org/wiki/Symbiotichttp://en.wikipedia.org/wiki/Lightninghttp://en.wikipedia.org/wiki/Nitrogen_fixation


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Important in amino acid catabolism.

[edit]Nitrification

Main article:Nitrification

The conversion of ammonium to nitrate is performed primarily by soil-living bacteria and other nitrifying bacteria. In

the primary stage of nitrification, the oxidation of ammonium (NH4+

) is performed by bacteria such astheNitrosomonasspecies, which converts ammonia to nitrites (NO2

-). Other bacterial species, such as

theNitrobacter, are responsible for the oxidation of the nitrites into nitrates (NO3-).

[3]It is important for the nitrites to be

converted to nitrates because accumulated nitrites are toxic to plant life.

Due to their very highsolubility, nitrates can entergroundwater. Elevated nitrate in groundwater is a concern for

drinking water use because nitrate can interfere with blood-oxygen levels in infants and causemethemoglobinemiaor

blue-baby syndrome.[7]

Where groundwater recharges stream flow, nitrate-enriched groundwater can contribute

toeutrophication, a process that leads to highalgal, especially blue-green algal populations and the death of aquatic

life due to the algae's excessive demand for oxygen. While not directly toxic to fish life, like ammonia, nitrate can

have indirect effects on fish if it contributes to this eutrophication. Nitrogen has contributed to severe eutrophication

problems in some water bodies. Since 2006, the application of nitrogenfertilizerhas been increasingly controlled in

Britain and the United States. This is occurring along the same lines as control of phosphorus fertilizer, restriction of

which is normally considered essential to the recovery of eutrophied waterbodies.

[edit]Denitrification

Main article:Denitrification

Denitrification is the reduction of nitrates back into the largely inert nitrogen gas (N2), completing the nitrogen cycle.

This process is performed by bacterial species such asPseudomonasandClostridiumin anaerobic conditions.[3]

They

use the nitrate as an electron acceptor in the place of oxygen during respiration. These facultatively anaerobic

bacteria can also live in aerobic conditions.

[edit]Anaerobic ammonium oxidation

Main article:Anammox

In this biological process,nitriteandammoniumare converted directly into elementalnitrogen(N2) gas. This process

makes up a major proportion of elemental nitrogen conversion in the oceans.

Marine nitrogen cycle

The nitrogen cycle is an important process in the ocean as well. While the overall cycle is similar, there are different

players and modes of transfer for nitrogen in the ocean. Nitrogen enters the water through precipitation, runoff, or as

N2 from the atmosphere. Nitrogen cannot be utilized byphytoplanktonas N2 so it must undergo nitrogen fixation

which is performed predominately bycyanobacteria.[8]

Without supplies of fixed nitrogen entering the marine cycle the

fixed nitrogen would be used up in about 2000 years.[9]

Phytoplankton need nitrogen in biologically available forms for

the initial synthesis of organic matter. Ammonia and urea are released into the water by excretion from plankton.

Nitrogen sources are removed from the euphotic zone by the downward movement of the organic matter. This can

occur from sinking of phytoplankton, vertical mixing, or sinking of waste of vertical migrators. The sinking results in

ammonia being introduced at lower depths below the euphotic zone. Bacteria are able to convert ammonia to nitrite

and nitrate but they are inhibited by light so this must occur below the euphotic zone.[10]

Ammonification

orMineralizationis performed by bacteria to convert the ammonia to ammonium.Nitrificationcan then occur to

convert the ammonium to nitrite and nitrate.[11]

Nitrate can be returned to the euphotic zone by vertical mixing and

upwelling where it can be taken up by phytoplankton to continue the cycle. N2 can be returned to the atmosphere

throughdenitrification.
http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=7http://en.wikipedia.org/wiki/Nitrificationhttp://en.wikipedia.org/wiki/Nitrificationhttp://en.wikipedia.org/wiki/Nitrificationhttp://en.wikipedia.org/wiki/Nitrosomonashttp://en.wikipedia.org/wiki/Nitrosomonashttp://en.wikipedia.org/wiki/Nitrosomonashttp://en.wikipedia.org/wiki/Nitrobacterhttp://en.wikipedia.org/wiki/Nitrobacterhttp://en.wikipedia.org/wiki/Nitrobacterhttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Solubilityhttp://en.wikipedia.org/wiki/Solubilityhttp://en.wikipedia.org/wiki/Solubilityhttp://en.wikipedia.org/wiki/Groundwaterhttp://en.wikipedia.org/wiki/Groundwaterhttp://en.wikipedia.org/wiki/Groundwaterhttp://en.wikipedia.org/wiki/Methemoglobinemiahttp://en.wikipedia.org/wiki/Methemoglobinemiahttp://en.wikipedia.org/wiki/Methemoglobinemiahttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Vitousek-6http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Vitousek-6http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Vitousek-6http://en.wikipedia.org/wiki/Eutrophicationhttp://en.wikipedia.org/wiki/Eutrophicationhttp://en.wikipedia.org/wiki/Eutrophicationhttp://en.wikipedia.org/wiki/Algalhttp://en.wikipedia.org/wiki/Algalhttp://en.wikipedia.org/wiki/Algalhttp://en.wikipedia.org/wiki/Fertilizerhttp://en.wikipedia.org/wiki/Fertilizerhttp://en.wikipedia.org/wiki/Fertilizerhttp://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=8http://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Pseudomonashttp://en.wikipedia.org/wiki/Pseudomonashttp://en.wikipedia.org/wiki/Pseudomonashttp://en.wikipedia.org/wiki/Clostridiumhttp://en.wikipedia.org/wiki/Clostridiumhttp://en.wikipedia.org/wiki/Clostridiumhttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Smil-2http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Nitrogen_cycle&action=edit&section=9http://en.wikipedia.org/wiki/Anammoxhttp://en.wikipedia.org/wiki/Anammoxhttp://en.wikipedia.org/wiki/Anammoxhttp://en.wikipedia.org/wiki/Nitritehttp://en.wikipedia.org/wiki/Nitritehttp://en.wikipedia.org/wiki/Nitritehttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Ammoniumhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Phytoplanktonhttp://en.wikipedia.org/wiki/Phytoplanktonhttp://en.wikipedia.org/wiki/Phytoplanktonhttp://en.wikipedia.org/wiki/Cyanobacteriahttp://en.wikipedia.org/wiki/Cyanobacteriahttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Miller_2008_60.E2.80.9362-7http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Miller_2008_60.E2.80.9362-7http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Miller_2008_60.E2.80.9362-7http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Gruber_2008_1.E2.80.9335-8http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Gruber_2008_1.E2.80.9335-8http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Gruber_2008_1.E2.80.9335-8http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-9http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-9http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-9http://en.wikipedia.org/wiki/Mineralization_(geology)http://en.wikipedia.org/wiki/Mineralization_(geology)http://en.wikipedia.org/wiki/Mineralization_(geology)http://en.wikipedia.org/wiki/Nitrificationhttp://en.wikipedia.org/wiki/Nitrificationhttp://en.wikipedia.org/wiki/Nitrificationhttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-10http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-10http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-10http://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Denitrificationhttp://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-10http://en.wikipedia.org/wiki/Nitrificationhttp://en.wikipedia.org/wiki/Mineralization_(geology)http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-9http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Gruber_2008_1.E2.80.9335-8http://en.wikipedia.org/wiki/Nitrogen_cycle#cite_note-Miller_2008_60.E2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NH4+

is thought to be the preferred source of fixed nitrogen for phytoplankton because its assimilation does not

involve a redox reaction and therefore requires little energy. However NO3 is more abundant so most phytoplankton

have adapted to have the enzymes necessary to undertake this reduction (nitrate reductase). There are a few notable

and well-known exceptions that includeProchlorococcusand someSynechococcus.[9]

These species can only take up

nitrogen as NH4+.

The nutrients in the ocean are not uniformly distributed. Areas of upwelling provide supplies of nitrogen from belowthe euphotic zone. Coastal zones provide nitrogen from runoff and upwelling occurs readily along the coast. However,

the rate at which nitrogen can be taken up by phytoplankton is decreased inoligotrophicwaters all year-round and

temperate water in the summer resulting in lower primary production.[12]

The distribution of the different forms of

nitrogen varies throughout the oceans as well.

Nitrate is depleted in near-surface water except in upwelling regions. Coastal upwelling regions usually have high

nitrate andchlorophylllevels as a result of the increased production. However, there are regions of high surface

nitrate but low chlorophyll that are referred to asHNLC(high nitrogen, low chlorophyll) regions. As of now the best

explanation for HNLC regions relates to iron limitation in the ocean. In recent years iron has become an important

player when discussing ocean dynamics and nutrient cycles. The input of iron varies by region and is delivered to the

ocean by dust (from dust storms) and is leached out of rocks. Iron is under consideration as the true limiting element

in the ocean.

NH4+

and NO2 show a maximum concentration at 5080 m (lower end of the euphotic zone) with decreasing

concentration below that depth. This distribution can be accounted for by the fact that NO2and NH4+

are intermediate

species. They are both rapidly produced and consumed through the water column.[9]

The amount of NH4+

in the

ocean is about 3 orders of magnitude less than nitrate.[9]

Between NH4+, NO2, and NO3, NO2 has the fastest turnover

rate. It can be produced during NO3 assimilation, nitrification, and denitrification; however, it is immediately consumed

again.

Water cycleThe water cycle, also known as the hydrologic cycle orH2O cycle, describes the continuous movement of water

on, above and below the surface of theEarth. Water can change states amongliquid,vapor, andsolidat various

places in the water cycle. Although the balance of water on Earth remains fairly constant over time, individual water

molecules can come and go, in and out of theatmosphere. The water moves from one reservoir to another, such as
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from river toocean, or from the ocean to the atmosphere, by the physical processes of evaporation, condensation,

precipitation, infiltration, runoff, and subsurface flow. In so doing, the water goes through different phases: liquid, solid ,

and gas.

The hydrologic cycle involves the exchange of heat energy, which leads to temperature changes. For instance, in the

process of evaporation, water takes up energy from the surroundings and cools the environment. Conversely, in the

process of condensation, water releases energy to its surroundings, warming the environment. The water cyclefigures significantly in the maintenance of life and ecosystems on Earth. Even as water in each reservoir plays an

important role, the water cycle brings added significance to the presence of water on our planet. By transferring water

from one reservoir to another, the water cycle purifies water, replenishes the land with freshwater, and transports

minerals to different parts of the globe. It is also involved in reshaping the geological features of the Earth, through

such processes as erosion and sedimentation. In addition, as the water cycle also involves heat exchange, it exerts

an influence on climate as well.

Processes

Precipitation

Condensed water vapor that falls to the Earth's surface . Most precipitation occurs asrain, but also includes

snow,hail,fog drip,graupel, andsleet.[1]

Approximately 505,000 km3

(121,000 cu mi) of water falls as

precipitation each year, 398,000 km3

(95,000 cu mi) of it over the oceans.[2]

Canopy interception

The precipitation that is intercepted by plant foliage and eventually evaporates back to the atmosphere

rather than falling to the ground.

Snowmelt
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The runoff produced by melting snow.

Runoff

The variety of ways by which water moves across the land. This includes both surface runoff andchannel

runoff. As it flows, the water may seep into the ground, evaporate into the air, become stored in lakes or

reservoirs, or be extracted for agricultural or other human uses.

Infiltration

The flow of water from the ground surface into the ground. Once infiltrated, the water becomessoil

moistureor groundwater.[3]

Subsurface flow

The flow of water underground, in thevadose zoneand aquifers. Subsurface water may return to the

surface (e.g. as a spring or by being pumped) or eventually seep into the oceans. Water returns to the land

surface at lower elevation than where it infiltrated, under the force ofgravityor gravity induced pressures.

Groundwater tends to move slowly, and is replenished slowly, so it can remain in aquifers for thousands of

years.

Evaporation

The transformation of water from liquid to gas phases as it moves from the ground or bodies of water into

the overlying atmosphere.[4]

The source of energy for evaporation is primarilysolar radiation. Evaporation

often implicitly includestranspirationfromplants, though together they are specifically referred to

asevapotranspiration. Total annual evapotranspiration amounts to approximately 505,000 km3

(121,000

cu mi) of water, 434,000 km3

(104,000 cu mi) of which evaporates from the oceans.[2]

Sublimation

The state change directly from solid water (snow or ice) to water vapor.[5]

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.[6]

Condensation

The transformation of water vapor to liquid water droplets in the air, creatingcloudsand fog.[7]

Transpiration

The release of water vapor from plants and soil into the air. Water vapor is a gas that cannot be seen
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Carbon cycleThe carbon cycle is the biogeochemical cycle by whichcarbonis exchanged among

thebiosphere,pedosphere,geosphere,hydrosphere, andatmosphereof the Earth. It is one of the most important

cycles of the earth and allows for carbon to be recycled and reused throughout the biosphere and all of its

organisms.[citation needed]

The carbon cycle was initially discovered byJoseph PriestleyandAntoine Lavoisier, and popularized byHumphry

Davy.[1]

It is now usually thought of as including the following major reservoirs of carbon interconnected by pathways

of exchange:

The atmosphere

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

such assoil carbon.

Theoceans, includingdissolved inorganic carbonand living and non-living marine biota,

Thesedimentsincludingfossil fuels.

The Earth's interior, carbon from the Earth'smantleandcrustis released to the atmosphere and hydrosphere by

volcanoes and geothermal systems.

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

physical, geological, and biological processes. The ocean contains the largest active pool of carbon near the surface

of the Earth, but thedeep oceanpart of this pool does not rapidly exchange with the atmosphere in the absence of an

external influence, such as ablack smokeror an uncontrolled deep-water oil well leak.
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The global carbon budget is the balance of the exchanges (incomes and losses) of carbon between the carbon

reservoirs or between one specific loop (e.g., atmosphere biosphere) of the carbon cycle. An examination of the

carbon budget of a pool or reservoir can provide information about whether the pool or reservoir is functioning as a

source or sink for carbon dioxide.

Oxygen cycle:::::

The Oxygen cycle is thebio-geochemical cyclethat describes the movement ofoxygenwithin its threemain reservoirs: theatmosphere(air), the total content of biological matter within thebiosphere(the global

sum of all ecosystems), and thelithosphere(Earth's crust). Failures in the oxygen cycle within

thehydrosphere(the combined mass of water found on, under, and over the surface of a planet) can result

in the development ofhypoxia zones. The main driving factor of the oxygen cycle isphotosynthesis, which is

responsible for the modern Earth's atmosphere and life.

Reservoirs

By far the largest reservoir of Earth's oxygen is within the silicate and oxidemineralsof thecrustandmantle(99.5%).

Only a small portion has been released as free oxygen to the biosphere (0.01%) and atmosphere (0.36%). The mainsource of atmospheric oxygen is photosynthesis, which produces sugars and oxygen from carbon dioxide and water: -

6CO2 + 6H2O + energy C6H12O6 + 6O2

Photosynthesizing organisms include the plant life of the land areas as well as thephytoplanktonof the oceans.

The tiny marinecyanobacteriumProchlorococcuswas discovered in 1986 and accounts for more than half of the

photosynthesis of the open ocean.[1]
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An additional source of atmospheric oxygen comes fromphotolysis, whereby high energyultravioletradiation

breaks down atmospheric water and nitrous oxide into component atoms. The free H and N atoms escape into

space leaving O2 in the atmosphere:

2H2O + energy 4H + O2

2N2O + energy 4N + O2The main way oxygen is lost from the atmosphere is viarespirationanddecay, mechanisms in

whichanimallife andbacteriaconsume oxygen and release carbon dioxide.

Because the lithosphere consumes oxygen. An example of surface weathering chemistry is formation

ofiron-oxides(rust):

4FeO + O2 2Fe2O3

Main article:Mineral redox buffer

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

biosphere createcalcium carbonateshell material (Ca CO3) that is rich in oxygen. When the

organism dies its shell is deposited on the shallow sea floor and buried over time to create

thelimestonerock of the lithosphere. Weathering processes initiated by organisms can also

free oxygen from the lithosphere. Plants and animals extract nutrient minerals from rocks and

release oxygen in the process.

Ozone

The presence of atmospheric oxygen has led to the formation ofozone(O3) and theozone layerwithin

thestratosphere. The ozone layer is extremely important to modern life as it absorbs harmfulultravioletradiation:

O2+ uv energy 2O

O + O2 O3

Phosphorus cycle

The phosphorus cycle is thebiogeochemical cyclethat describes the movement ofphosphorusthrough

thelithosphere,hydrosphere, andbiosphere. Unlike many other biogeochemical cycles, theatmospheredoes not play

a significant role in the movement of phosphorus, because phosphorus and phosphorus-based compounds are

usually solids at the typical ranges of temperature and pressure found on Earth. The production ofphosphinegas

occurs only in specialized, local conditions.

Low phosphorus (chemical symbol, P) availability slows down microbial growth, which has been shown in studies of

soilmicrobialbiomass. Soil microorganisms act as sinks and sources of available P in the biogeochemical

cycle.[1]

Locally, transformations of PO4 are microbially driven; however, the major transfers in the global cycle of P

are not driven by microbial reactions, but bytectonicmovements ingeologic time.

[2]

Further studies need to beperformed for integrating different processes and factors related to grossphosphorusmineralizationand microbial

phosphorusturnoverin general.
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Process of the cycle

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.

Unlike other cycles of matter compounds, phosphorus cannot usually be found in air as a gas, it only occurs under

highly reducing conditions as the gas Phosphine PH3. This is because at normal temperature and circumstances, it is

a solid in the form of red and white phosphorus. It usually cycles through water, soil and sediments. Phosphorus is

typically the limiting nutrient found in streams, lakes and fresh water environments. As rocks and sediments graduallywear down, phosphate is released. In the atmosphere phosphorus is mainly small dust particles.

Initially, phosphate weathers from rocks. The small losses in a terrestrial system caused by leaching through the

action of rain are balanced in the gains from weathering rocks. In soil, phosphate is absorbed on clay surfaces and

organic matter particles and becomes incorporated (immobilized). Plants dissolve ionized forms of phosphate.

Herbivores obtain phosphorus by eating plants, and carnivores by eating herbivores. Herbivores and carnivores

excrete phosphorus as a waste product in urine and feces. Phosphorus is released back to the soil when plants or

animal matter decomposes and the cycle repeats.

Sulfur cycleThe sulfur cycle is the collection of processes by which sulfur moves to and from minerals (including the waterways)

and living systems. Suchbiogeochemical cyclesare important ingeologybecause they affect many minerals.

Biogeochemical cycles are also important for life becausesulfuris anessential element, being a constituent of

manyproteinsandcofactors.[1]

Steps of the sulfur cycle are:

Mineralization oforganic sulfurinto inorganic forms, such ashydrogen sulfide(H2S), elemental sulfur, as well

assulfide minerals.

Oxidationof hydrogen sulfide,sulfide, and elemental sulfur (S) tosulfate(SO42

).

Reduction of sulfate to sulfide.

Incorporation sulfide into organic compounds (including metal-containing derivatives).

These are often termed as follows:

Assimilative sulfate reduction(see alsosulfur assimilation) in which sulfate (SO42

) is reduced

byplants,fungiand variousprokaryotes. The oxidation states of sulfur are +6 in sulfate and2 in RSH.

Desulfurizationin which organic molecules containing sulfur can be desulfurized, producing hydrogen sulfide

gas (H2S, oxidation state =2). An analogous process for organic nitrogen compounds is deamination.
http://en.wikipedia.org/wiki/Biogeochemical_cyclehttp://en.wikipedia.org/wiki/Biogeochemical_cyclehttp://en.wikipedia.org/wiki/Biogeochemical_cyclehttp://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Essential_elementhttp://en.wikipedia.org/wiki/Essential_elementhttp://en.wikipedia.org/wiki/Essential_elementhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Cofactorhttp://en.wikipedia.org/wiki/Cofactorhttp://en.wikipedia.org/wiki/Sulfur_cycle#cite_note-Brock-0http://en.wikipedia.org/wiki/Sulfur_cycle#cite_note-Brock-0http://en.wikipedia.org/wiki/Sulfur_cycle#cite_note-Brock-0http://en.wikipedia.org/wiki/Organosulfur_compoundshttp://en.wikipedia.org/wiki/Organosulfur_compoundshttp://en.wikipedia.org/wiki/Organosulfur_compoundshttp://en.wikipedia.org/wiki/Hydrogen_sulfidehttp://en.wikipedia.org/wiki/Hydrogen_sulfidehttp://en.wikipedia.org/wiki/Hydrogen_sulfidehttp://en.wikipedia.org/wiki/Sulfide_mineralshttp://en.wikipedia.org/wiki/Sulfide_mineralshttp://en.wikipedia.org/wiki/Sulfide_mineralshttp://en.wikipedia.org/wiki/Oxidationhttp://en.wikipedia.org/wiki/Oxidationhttp://en.wikipedia.org/wiki/Sulfidehttp://en.wikipedia.org/wiki/Sulfidehttp://en.wikipedia.org/wiki/Sulfidehttp://en.wikipedia.org/wiki/Sulfatehttp://en.wikipedia.org/wiki/Sulfatehttp://en.wikipedia.org/wiki/Sulfatehttp://en.wikipedia.org/wiki/Sulfur_assimilationhttp://en.wikipedia.org/wiki/Sulfur_assimilationhttp://en.wikipedia.org/wiki/Sulfur_assimilationhttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Prokaryotehttp://en.wikipedia.org/wiki/Prokaryotehttp://en.wikipedia.org/wiki/Prokaryotehttp://en.wikipedia.org/wiki/Prokaryotehttp://en.wikipedia.org/wiki/Fungihttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Sulfur_assimilationhttp://en.wikipedia.org/wiki/Sulfatehttp://en.wikipedia.org/wiki/Sulfidehttp://en.wikipedia.org/wiki/Oxidationhttp://en.wikipedia.org/wiki/Sulfide_mineralshttp://en.wikipedia.org/wiki/Hydrogen_sulfidehttp://en.wikipedia.org/wiki/Organosulfur_compoundshttp://en.wikipedia.org/wiki/Sulfur_cycle#cite_note-Brock-0http://en.wikipedia.org/wiki/Cofactorhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Essential_elementhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Geologyhttp://en.wikipedia.org/wiki/Biogeochemical_cycle


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Oxidation of hydrogen sulfideproduces elemental sulfur (S8), oxidation state = 0. This reaction occurs in

thephotosyntheticgreen and purple sulfurbacteriaand somechemolithotrophs. Often the elemental sulfur is

stored aspolysulfides.

oxidation of elemental sulfurby sulfur oxidizers produces sulfate.

Dissimilative sulfur reductionin which elemental sulfur can be reduced to hydrogen

natural cycles

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