NITROGEN CYCLE INRELATION TO GEOLOGY

Nitrogen Cycle
Presentation on the topic
DEPARTMENT OF GEOLOGICAL SCIENCES
GAUHATI UNIVERSITY
 Ajanta Deka
 Angshumi Khaund
 Aseng Mili
 Arnab Bordoloi
 Chinmoy Saikia
 Himangshu Barman
 Kaijirsong Rongpi
 PragyaTamuli
 Sharika Boruah
 Sudipta Anurag Borah
GROUP A (M.SC. 2ND SEMESTER)

2
1. Introduction on the Geochemical Cycle
2. Nitrogen Element
3. The Nitrogen Cycle
(i) Geological Nitrogen Cycle
(ii) Components of Nitrogen Cycle
(iii)Nitrogen in the crust
(iv) Nitrogen in the mantle
(v) Nitrogen in the core
(vi)Evolution of the Nitrogen Cycle
4. Conclusion
5. Bibliography/References
CONTENTS

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 In Earth Science ,a geochemical cycle is the pathway that chemical elements take in the surface
and crust of the earth. The term "geochemical" tells us that geological and chemical factors are all
included.
 The migration of heated and compressed chemical elements and compounds such
as silicon, aluminium, and general alkali metals through the means of subduction and volcanism is
known in the geological world as geochemical cycles.
 The geochemical cycle encompasses the natural separation and concentration of elements and heat-
assisted recombination processes. Changes may not be apparent over a short term, such as
with biogeochemical cycles, but over a long term changes of great magnitude occur, including the
evolution of continents and oceans.
 Some of the major biogeochemical cycles are as follows:
1. Water Cycle or Hydrologic Cycle
2. Carbon-Cycle
3. Nitrogen Cycle
4. Oxygen Cycle
GEOCHEMICAL CYCLE

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 The Earth system is an assemblage of atoms of the 92 natural elements. Almost all of these atoms have
been present in the Earth system since 4.5 billion years ago by gravitational accretion of a cloud of gases
and dust.
 The atoms, in the form of various molecules, migrate continually between the different reservoirs of the
Earth system. Most of the mass of the Earth system is present in the deep Earth, but this material is
largely isolated from the surface reservoirs: atmosphere, hydrosphere, biosphere and lithosphere.
 Communication between the deep Earth and the surface reservoirs takes place by volcanism and by
subduction of tectonic plates, processes that are extremely slow compared to those cycling elements
between the surface reservoirs.
 Nitrogen makes up about 78% of our atmosphere which is mostly in the form of N₂, which is a compound
that plants and animals cannot use. The process of converting nitrogen into compounds that can be used
by plants and animals is called the Nitrogen Cycle
 Nitrogen has an atomic number of 7 and an atomic weight of 14, nitrogen has five valence electrons and
occurs in oxidation states ranging from –3 to +5. Nitrogen occurs in nature in six of its eight possible
oxidation states, and the odd oxidation states are most common, except for the ground state N2 with an
oxidation state of zero.
WHAT IS NITROGEN ?

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 Nitrogen is an incredibly versatile element,
existing in both inorganic and organic forms as
well as many different oxidation states.
 The movement of nitrogen between
the atmosphere, biosphere, and geosphere in
different forms is called the nitrogen cycle one
of the major biogeochemical cycles.
 Similar to the carbon cycle, the nitrogen cycle
consists of various reservoirs of nitrogen and
processes by which those reservoirs exchange
nitrogen
 The nitrogen cycle processes that undergo
through biosphere, atmosphere, geosphere;
Nitrogen fixation, nitrogen uptake through
organismal growth, nitrogen mineralization
through decay, nitrification, and
denitrification.
THE NITROGEN CYCLE
Fig 1:The Nitrogen cycle showing us the major cycle processes

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Microorganisms, particularly bacteria, play major roles in all of the principal nitrogen transformations. Because these
processes are microbially mediated, or controlled by microorganisms, these nitrogen transformations tend to occur
faster than geological processes like plate motion, a very slow, purely physical process that is a part of the carbon
cycle. Instead, rates are affected by environmental factors that influence microbial activity, such as temperature,
moisture, and resource availability.
1. Nitrogen Mineralization
2. Nitrogen Fixation
3. Nitrogen Assimilation
4. Ammonification
5. Nitrification
6. Denitrification
 Nitrogen Mineralization: After nitrogen is incorporated into organic matter, it is often converted back
into inorganic nitrogen by a process called nitrogen mineralization, otherwise known as decay.
Organic N → NH4
+

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 Nitrogen Uptake: The ammonium (NH4
+) produced by nitrogen-fixing bacteria is usually quickly taken up by a host plant, the
bacteria itself, or another soil organism and incorporated into proteins and other organic nitrogen compounds, like DNA.
NH4
+ → Organic N
 Nitrogen fixation: It is the process wherein N2 is converted to ammonium, or NH4
+. This is the only way that organisms can
attain nitrogen directly from the atmosphere.
 Nitrogen assimilation: It is the process by which NH3 /NH4 is transfer to organic nitrogen containing compound since NH3
/NH4 is toxic for several organism.
 Assimilation: It is the process by which the primary nitrogen input of many microorganism
 Ammonification: It refers breakdown of organic nitrogen into ammonium (NH4). The resulting ammonium can be
assimilated or microbially oxidized in the nitrification process.
 Nitrification: It is the process by which ammonium is oxidized to nitrite and further to nitrate. The 1st stage of nitrification is
NH4
+ + O2 ------ NO2
- + H2O
Some representative bacteria are Nitrosomomas and Nitrocystic species and the 2nd stage of nitrification is
NO2
- + O2 ------ NO3
-
 Denitrification: It is the biologically facilitated reduction of nitrate (NO3
-) to N₂ and other gaseous intermediates mostly
N2O, which may return to atmosphere.
 NO3
- → N2+ N2O

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Fig 2: Simplified schematic representation of integrated geologic and biologic recycling schemes of nitrogen in the Earth’s crust.
https://media.springernature.com/lw685/springer-static/image/art%3A10.1186%2Fs40645-019-0286-
x/MediaObjects/40645_2019_286_Fig1_HTML.png?as=webp
GEOLOGICAL NITROGENCYCLE
 The Nitrogen may be transported through the Earth
interion either as a minor component in mineral or in
solution in magnetic liquid.
 After nitrogen fixation process, all ammonium are not
involved in nitrification process, some Nitrogen also
remain as NH4 and dissolved clay mineral and carbonate.
 Sedimentation and diagenesis release of fluid or melting
to yield felsic element in deep crust as upper mantle.
 During the process of prograde metamorphism N2 gas
released and it return to the ocean and atmosphere and
releases typically occur at the depth of 100 km
associating with dehydration and melting of hydrous
mineral.
 These N2 reached the ocean surface with the help of
some ocean ridge or fractures. and some of the nitrogen
may be brought deep mantle and may not return to the
earth surface.

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 Although only 16% of total atmospheric emissions were
estimated to derive from human activities in 1860, changes
in land use (deforestation, annual biomass burning) and
concentrated food production had already made indelible
marks on the global N cycle by that time. Human-induced
changes in the N cycle are :
 N fertilizer: Organic fertilizers have been used since the
beginning of agriculture. Most industrial fixed N (86%) is
used to make fertilizer; at least half of global fertilizer
applications are now in the developing countries of Asia.
COMPONENTSOFTHE NITROGEN CYCLE
Fig 3: Oxidation states of biogeochemically important
N compounds
Fundamentals of Geobiology,Page-40

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• Fossil fuel combustion continues to liberate N from the long-term geological reservoirs. Even though the N
content of coal and oil is low and variable, the immense net transfer of old organic matter via combustion to the
atmosphere now accounts for 24.5 Tg N yr−1, or about a quarter of the total atmospheric emissions.
• Nitrogen-fixing crops: Cultivation of naturally N-fixing crops has replaced mixed vegetation in natural systems,
substantially increasing the total biological N fixation by 32–53 Tg N yr−1 from agriculture (Galloway et al., 2004).
Thus total biological N fixation has increased, even though the natural rate has declined.
• N-mobilization: The various human activities liberates Nitrogen from biological storage reservoirs:
deforestation/biomass burning, conversion of forest and savannahs to croplands, drainage of wetlands and peat
burning, erosion, all increase biologically available N. By 1993, human activities in total had increased the
production of fixed N to 156Tg yr−1 more than doubling the natural rate of new nitrogen production.
• Modern emissions of fixed N (NH3, NO3) to the atmosphere are dominated by anthropogenic sources, whereas in
early industrial times, 1860, natural sources such as lightning and emissions from soil and vegetation dominated.

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NITROGEN RESERVOIR
Table 1: Terrestrial nitrogen reservoirs (modified after Goldblatt et al. 2009; Palya et al. 2011)

12
• In high energy environments, clays and organic matter do not
accumulate and the coarser grained sands do not acquire
ammonium and Nitrogen is returned to the atmosphere during
metamorphism.
• All of the ammonium in the Earth’s crust has been derived
ultimately from the atmosphere through nitrogen fixation and
this constitutes trapping of about a quarter of the original
atmospheric inventory. Although primary rocks contain
essentially no nitrogen, organic N is a relatively large reservoir
in the global N inventory.
Fig 4: N content of geological reservoirs
Fundamentals of Geobiology,Page-38

13
Fig 5: Distribution of nitrogen concentrations in various continental sedimentary rocks modified after Johnson
and Goldblatt (2015)
NITROGEN INTHE CRUST
• The oceanic sedimentary crust is
dominated by shale, sandstone, and
carbonate.
• Most of the nitrogen is found in
sandstone (260 ± 10 ppm) and shale
and silt with 860 ± 64 ppm nitrogen

14
Fig 6: Distribution of nitrogen concentrations in various continental sedimentary rocks modified after Johnson and Goldblatt (2015)
• In biogenic continental sediments, the
nitrogen content averages at
1930 ± 1540 ppm.
• Clastic sediments from continental
environments can be quite nitrogen-rich
with an average abundance of
670 ± 56 ppm.

15
Fig 7: Nitrogen content of bulk rock and of its biotite in metamorphic rocks from Western Maine (USA) as a function of
temperature (metamorphic grade) (data from Plessen et al. 2010.
• Mica minerals are the primary carriers of nitrogen.
• The Nitrogen concentration in the igneous rocks
varies widely.
• For example, granite formed by partial melting of
biomass precursors typically is ammonium-rich
with up to more than 100 ppm N held in mica and
feldspar minerals, whereas granite formed by
fractional crystallization or melting of mafic rocks
is nitrogen poor with only several ppm N.
• Other igneous rocks such as gabbro and tonalite
contain on average 10 ppm or less N.

16
• The Nitrogen solubility in garnet is the highest among
upper mantle silicate minerals (olivine, pyroxenes, and
garnet).
• The Nitrogen solubility in these upper mantle minerals is,
therefore, higher than the suggested upper mantle
nitrogen concentration (≤ 1 ppm N). This means that the
upper mantle is undersaturated with respect to nitrogen.
• The Nitrogen abundance in the modern mantle
commonly is considered near 1 ppm.
• Nitrogen solubility as high as nearly 25 ppm in forsterite,
pyroxene, and garnet which might be of the range 1.5–
3.0 Gpa.
• The highest nitrogen content in upper mantle minerals is
found in diamonds with an average N concentration of
235 ppm in diamonds from the lithosphere (≤ 200 km
crystallization depth).
NITROGEN INTHE MANTLE
Fig 8 Distribution of nitrogen concentrations in mantle rocks modified after Johnson and Goldblatt (2015)

17
• Nitrogen is one of the light elements
proposed for the Earth’s core.
• Nitrogen also is an attractive core
component because such a core
might contain the so-called missing
nitrogen of the silicate Earth
• Iron nitrides are possible candidates
for the Earth’s core.
NITROGEN INTHE CORE
Fig 9: Chondrite-normalized noble gas, carbon, and nitrogen content of the silicate earth (modified from Marty 2012

18
• The emergence and evolution of Nitrogen cycles over earth
history is not clear yet. An early deep biosphere. Abiotic N2
reduction to ammonium within hydrothermal system could
have been supplied fixed Nitrogen
• An Archean time abiotic N₂ formed fixation by lightning to
the surface of the ocean from the atmosphere. However it
is estimate that the very limited supply of N2 fixation. Once
the N₂ fixation was established it is generally assumed that
the input of nitrogen to the biosphere could keep pace with
primary productivity as long other nutrient
• Nitrogen cycle are highly redox-dependent s0 it changed
significantly with the progressive oxygenation of earth
environment.
• During Archean times have very significant amount of
oxygen therefore the process of modern N cycle where
nitrification, i.e. oxidation of NH3+ (ammonium) to nitrite
(NO2
-) and nitrate (NO3
-) would have been absent
• Thus in the Archean and Early Proterozoic, the nitrogen
cycle would likely have consist of N₂ fixation followed by
burial and regeneration of NH4
+ in sediment. During GOE
between 2.4 - 2.3 Ga redox stratified, ocean develop which
causes nitrification of NH3+ rich deep water with
denitrification.
EVOLUTION OF BIOGEOCHEMICAL NITROGEN CYCLE
Fig 10: Estimated evolution of nitrogen through time,
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5412885/bi
n/GBI-15-343-g003.jpg

19
• During Mid-Proterozoic time most of the primary
productivity (Process by which organism make their own
food from to inorganic source) occurring via oxygenic
photosynthesis in the surface of ocean and the nitrogen
fixation could not keep place with fixed Nitrogen loss to
fuel this primary productivity. Primary producer in that
time had direct access to upwelling nutrients, including
NH3, before reached redox interface and was last to
nitrification and denitrification.
• As the delivery of nitrogen to the sediment is intimately
linked to the biosphere and dependent on redox and other
environment parameter, the burial nitrogen over
geological time would have changes in response to these
changes in the biogeochemical Nitrogen cycle.
• Now, researcher assumed 25% of modern denitrification
levels early in the GOE and increases to 30% with the build
up of nitrate reservoir. At present day, calculate N2 fixation
rate with enhance Molybdenum during Neoproterozoic
oxygenation event as switch from Mo-limited state to
modern N₂ fixation. The changes of Nitrogen burial over
time period a progressive increase in the delivery of
Nitrogen to deep earth via subduction following an even
increasingly efficient biosphere.

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• The Geochemical cycle is the pathway that chemical elements take in the surface and crust of the earth. The term "geochemical" tells us
that geological and chemical factors are all included.
• Nitrogen makes up about 78% of our atmosphere which is mostly in the form of N₂, which is a compound that plants and animals cannot
use. The process of converting nitrogen into compounds that can be used by plants and animals is called the Nitrogen Cycle. Nitrogen has
an atomic number of 7 and an atomic weight of 14, nitrogen has five valence electrons and occurs in oxidation states ranging from –3 to
+5..
• The five processes in the nitrogen cycle – fixation, uptake, mineralization, nitrification, and denitrification – are all driven by
microorganisms.
• The global nitrogen cycle includes important geological and biological components, in which relatively small biological fluxes control the
availability of nitrogen between large reservoirs. The versatile redox chemistry of nitrogen means that it occurs in a wide range of
compounds, whose concentrations are mostly controlled by microbial transformations. The inventory of fixed nitrogen on Earth is
controlled by the balance between nitrogen fixation and denitrification/anammox.
• Nitrous oxide is produced and consumed in both nitrification and denitrification, and although the pathways are fairly well known in
cultivated organisms, it is still not clear to what degree the two processes are involved in N2O production in nature. In the ocean, for
example, highest N2O concentrations are found in oxygen-limited environments. These are the same locations where coupled
nitrification/denitrification occurs, so it is not obvious whether both or one of the processes is responsible for net N2O production.
• If excess N loading to the coastal or even open ocean were to lead to increased production of organic matter, which subsequently resulted
in increased oxygen demand and the expansion of anoxic environments, would this lead to an increase in N2O release to the atmosphere.
NO2 compounds are highly reactive and short lived, N2O has very long residence time in the atmosphere. Because it is the source of some
of the NO2 compounds via its photochemistry, the long-term increase in N2O already documented has probably already affected the
concentration of trace NOy compounds in the atmosphere, and thus their reaction rates.
CONCLUSION

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• Fundamentals of Geobiology, Chapter-4, Andrew H. Knoll, Donald E. Canfield and Kurt O. Konhauser
• An article on Biochemical Cycles, Puja Mondal, https://www.yourarticlelibrary.com/environment/ecosystem/4-common-
biogeochemical-cycles-explained-with-diagram/28229
• Chapter 6- Geochemical Cycles, Introduction to Atmospheric Chemistry, by Daniel J. Jacob, Princeton University Press,
1999.
• Geochemical Cycle - https://en.wikipedia.org/wiki/Geochemical_cycle
• The Geobiological Nitrogen Cycle: From microbes to the mantle, A.L Zerkle & S. Mikhail
• Nitrogen Cycle, Sayeed Ahmad; https://www.slideshare.net/xsayeed/nitrogen-cycle-31670520
• The Nitrogen Cycle: Of Microbes and Men, John Arthur Harrison; https://www.visionlearning.com/en/library/Earth-
Science/6/The-Nitrogen-Cycle/98/reading
• An article on the Nitrogen in the Earth: abundance and transport, Bjorn Mysen;
https://progearthplanetsci.springeropen.com/articles/10.1186/s40645-019-0286-x?hcb=1
BIBLIOGRAPHY

NITROGEN CYCLE INRELATION TO GEOLOGY

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