8/10/2019 Biogeochemical Cycle Reviewer
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BIOGEOCHEMICAL CYCLE
Nitrogen Cycle
Water Cycle
Phosphorus Cycle
Carbon-Oxygen Cycle
BIOGEOCHEMICAL CYCLE
IngeographyandEarth science,
a biogeochemical cycleor substance
turnoveror cycling of substancesis 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.
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
nitrogen cycle..
is the process by whichnitrogenis converted
between its various chemical forms.
the Important processes in the nitrogen cycle
includefixation,mineralization,nitrification,anddenitrification.
The majority ofEarth's atmosphere
(approximately 78%) isnitrogen
Ecological function
Nitrogen is essential for many processes;it is
crucial for any life on Earth.
It is a component in allamino acids,as
incorporated intoproteins,and is present in the
bases that make upnucleic acids,such
asDNAandRNA.
Inplants,much of the nitrogen is used
inchlorophyllmolecules, which are essential for
photosynthesisand further growth.
nitrogen cycle process
Nitrogen is present in the environment in a
wide variety of chemical forms :organic
nitrogen,ammonium,nitrite,nitrate,nitrous
oxide,nitric oxideor inorganic nitrogen gas.
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.
Conversion of N2 ..
The conversion of nitrogen (N2) from the
atmosphere into a form readily available to
plants and hence to animals is an important
step in the nitrogen cycle, which distributes the
supply of this essential nutrient.
There are 4 ways to convert N2(atmospheric
nitrogen gas) into more chemically reactive
forms.
four(4) ways ..
Biological fixation: some symbiotic bacteria
(most often associated with leguminous plants)
and some free-living bacteria are able to fixnitrogen as organic
nitrogen.
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).
Combustion of fossil fuels : automobile engines
and thermal power plants, which release
various nitrogen oxides (NOx).
Other processes : In addition, the formation ofNO from N2and
O2due to photons and
especially lightning, can fix nitrogen.
Nitrogen fixation ..
Atmospheric nitrogen must be processed, or
"fixed" to be used by plants. Some fixation
occurs inlightningstrikes, but most fixation is
done by free-living orsymbioticbacteria.
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.
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
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8/10/2019 Biogeochemical Cycle Reviewer
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Sulfur Cycle
The 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.
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(SO4
2).
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 and 2
in RSH.
Desulfurization in 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.
Oxidation of hydrogen sulfide produces
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 sulfur by sulfur
oxidizers produces sulfate.
Dissimilative sulfur reduction in which
elemental sulfur can be reduced to
hydrogen sulfide.
Dissimilative sulfate reduction in
whichsulfate reducersgenerate
hydrogen sulfide from sulfate.
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