Nitrogen Cycle

Objectifs

Understanding the nitrogen cycle and its impact in nature.

Introduction

Summary

Introduction
Natural nitrogen cycle
Anthropogenic nitrogen cycle
Outflows and nitrogen cascade
Environmental Impacts

Introduction

Atmosphere's composition :

Dinitrogen N₂ 78%

Oxygen O₂ 20%

Argon Ar 9%

Carbon dioxyde CO₂ 0,40% *

Water vapor H₂O 0-3%

Cox, Arthur N., éd. 2002. Allen’s Astrophysical Quantities. 4^eéd. New York : Springer-Verlag. https://doi.org/10.1007/978-1-4612-1186-0.

* "Vital signs: Carbon Dioxide". NASA Climate. May 2020. Retrieved 5 June 2020

Dinitrogen molecule

N₂, the large amount of energy required to break the nitrogen-nitrogen triple bond makes this structure stable, which is why N₂ is the most abundant in air.

Nitrogen reservoirs

Canfield, Donald E., Alexander N. Glazer, et Paul G. Falkowski. 2010. « The Evolution and Future of Earth’s Nitrogen Cycle ». Science 330 (6001): 192‐96.

https://doi.org/10.1126/science.1186120.

Nitrogen compounds

Zoom	Ammonium NH₄⁺ Nitrite NO₂^- Nitrate NO₃^-

Why nitrogen is important to life ?

Hint : DNA

Medias

Natural nitrogen cycle

Biological fixation

Zoom	Actinomycetes

Zoom	Cyanophyceae

Mineralization

Zoom	Aerobic and anaerobic conditions.

Assimilation by plants

Nitrification

Takes place under aerobic conditions.

The activity of the microflora is optimal for pH 6.9 to 9 and temperatures between 20 and 36 °C.

Denitrification

The role of lightning

Zoom	Energy from lighting breaks apart N₂ into N and O₂ into O. They bond to form nitrogen oxides (NOx). They react with rain water to form nitrates.

QCM

1) What is the name of the process that oxidizes ammonium (NH₄⁺) to produce nitrite (NO₂^-) and then forms nitrate (NO₃^-)?

Denitrification
Biological fixation
Nitrification

2) Thanks to their roots, plants are able to absorb atmospheric nitrogen (N􏰂).

True
False

3) What are the functions of nitrogen on the planet ?

Participate in photosynthesis
Produce the nitrogenous bases of DNA
Doing cellular respiration
Transporting Oxygen (O₂) molecules
Making proteins

Medias

Anthropogenic nitrogen cycle

Nitrogen use in manufacturing & processing

Zoom	Blanketing : Nitrogen gas can be used to flush wine bottles both before and after filling. https://www.generon.com/nitrogen-for-wine-sparging-bottling-blanketing/

Zoom	Nitrogen generator in Beverage processing & packaging On the picture : Juice cartons on packaging production line https://www.peakgas.com/Articles-and-News/article/basic-nitr ogen-facts-uses-and-onsite-gas-generation

The most important use is for fertilizer

Zoom	Starter fertilizer can enhance growth and yield by improving access of immobile nutrients https://www.mississippi-crops.com/2020/03/20/top-five-management-strategies-to-improve-corn-profitability/

Nitrogen and fertilizer

Zoom	The natural process of fixation of atmospheric nitrogen has been amplified by man through an increasing use of industrial fixation of atmospheric nitrogen.

The Haber-Bosch process

Video to watch :

https://www.youtube.com/watch?v=o1_D4FscMnU

The modern nitrogen cycle

Zoom	NH4+ production : 9,5 x 10^12 mol Fossil fuel combustion : 1.8 x 10^12mol Anthropogenic sources contribute double the natural rate of terrestrial nitrogen fixation.

Nitrogen and the agro-food system

Why does livestock farming produce large quantities of nitrogen-rich effluents ?

Conclusion

QCM

1) What is the Haber-Bosh process?

A process that transforms air into fertilizer.
A process to fix atmospheric dinitrogen in the form of ammonia.
A process that converts ammonia into nitrate.
A process that permit to have available nitrogen in sufficient quantity to allow its industrialization.

2) What are the anthropogenic sources of the nitrogen cycle?

Fossil fuel combustion
Industrial fixation
Deforestation
Crops and livestock
Building construction

Medias

Outflows and nitrogen cascade

Introduction

What is on of the main difference between phosphorus, potassium and nitrogen ?

Nitrate goes from the biosphere to the environment by nitrate leaching, gaseous emissions.

Nitrate leaching

Nitrate leaching is highly dependent on rainfall, soil type and soil nitrogen content.

Video to watch

https://www.youtube.com/watch?v=-6e_iF9d2F0

Ammonia volatilization

The presence of ammoniacal nitrogen in a solution in contact with air systematically leads to the volatilization of ammonia.

Volatilization depends very strongly on the physical and chemical conditions of the environment.

the nitrogen content of the substrate in contact with the air ;
the proportion of nitrogen present in the form of ammonia ;
the contact surface between the solution containing ammoniacal nitrogen and the atmosphere ;
the dispersion of the air in contact with the emission zone.

Nitrogen oxides and nitrous oxide emissions

Zoom	The parameters which are likely to intervene to regulate the proportion of nitrous oxide formed during denitrification are : the pH of the environment ; the nitrate concentration ; the soil aeration, often characterized by the water saturation rate ; the availability of reducing agents.

In addition to nitrous oxide emissions, there are nitric oxide emissions, rather observed in dry environments, and associated with nitrification situations.

Nitrogen oxides, mainly NOx (NO₂ and NO) and nitrous oxide (N₂O) are emitted during nitrification and/or denitrification reactions, both in the field and in livestock buildings (bedding, effluent storage areas).

The nitrogen cascade

Simplified view of the nitrogen cascade, highlighting the major anthropogenic sources of reactive nitrogen (Nr) from atmospheric dinitrogen (N₂), the main pollutant forms of Nr (orange boxes) and nine main environmental concerns (blue boxes). Estimates of anthropogenic N fixation for the world (Tg /yr for 2005, in black) are compared with estimates for Europe (Tg /yr for 2000, in blue italic). Blue arrows represent intended anthropogenic Nr flows; all the other arrows are unintended flows.

QCM

1) Nitrogen is characterized by a great ability to leave the soil-plant-animal cycle

True
False

2) Nitrate leaching losses increase when fertilizer applications are in excess of the crop need.

True
False

3) What is the physical and chemical condition of the environment on which the volatilization of ammonia depends?

the nitrogen content of the substrate in contact with the air.
the proportion of nitrogen present in the form of ammonia.
the proportion of nitrogen present in the form of nitrate.
the contact surface between the solution containing ammoniacal nitrogen and the atmosphere.
the soil aeration.
the dispersion of the air in contact with the emission zone.

Medias

Environmental Impacts

Video to watch : The impact of nitrogen pollution

https://www.youtube.com/watch?v=ZvKXHQM6soo

The nitrogen cascade

Small reminder :

This cascade of unintentional flows of reactive nitrogen is accompanied by a cascade of harmful consequences for the environment, the climate and human health.

When reactive nitrogen returns in the form of inert atmospheric nitrogen dioxide, it has potentially crossed several compartments in several forms in excessive quantities, and thus contributed to different environmental impacts on all of our planet.

Air pollution

Zoom	Regulations : Air quality standards The Convention on Long-Range Transboundary Air Pollution (LRTAP Convention)

1. Health impacts

Ammonia

NH₃ - Health effects of ammonia are indirect through contribution of NH₄⁺ to particulate matter (PM).

Ammonia emissions significantly contribute to the formation of secondary particulate matter in the atmosphere (~ 20% by mass).

The main source of ammonia in the atmosphere is agriculture.

Nitrogen dioxide (NO2)

It is a toxic gas that has adverse health effects both in the long term (chronic) and short term (acute).

Data from Europe suggested that long-term concentrations of nitrogen dioxide or nitrogen oxides (NO) were associated with an increased risk of all-cause mortality.

Nitrogen dioxide is strongly related to particulate matter.

https://www.epa.vic.gov.au/for-community/environmental-information/air-quality/nitrogen-dioxide-in-the-air

Particulate matter (PM)

Zoom	NO₂ and NH₃ - Reactive nitrogen contributes to particle mass and to the adverse health effects caused by the PM.

Ozone

Zoom	NO₂ and NH₃ - Reactive nitrogen contributes to particle mass and to the adverse health effects caused by the PM. https://www.lung.org/research/sota/health-risks

Ecosystems

Ammonia

Atmospheric ammonium is absorbed by the leaves of plants. More precisely through the stomata, where gas exchanges take place.

Before reaching the leaf, the pollutant will first have to pass through the “boundary layer”.

Zoom	Lichens are very affected by atmospheric pollution because they not have a impermeable cuticle. Lichens and bryophytes are an important part of the ecosystem integrity. https://www.irishtimes.com/news/science/the-trouble-with-ammonia-1.3721098

Ammonia acts as a macro-nutrient and at low exposure levels plants respond by increasing their biomass production.

Because plant growth is often limited by the supply of nutrient nitrogen, and so any increases in growth may lead to negative effects on community composition.

The fertilisation effect can at higher exposure levels lead to secondary long-term adverse effects including increased susceptibility to abiotic (drought, frost) and biotic stresses.

Oxides of nitrogen

Oxides of nitrogen can have a fertiliser effect, but can also be toxic to plants, depending on concentrations.

At low concentrations typical of ambient conditions, nitrogen oxides is more phytotoxic than nitrogen dioxide.

As for ammonia, the growth stimulation was also considered as potentially adverse for (semi-) natural vegetation owing to potential negative effects on community composition.

Today ozone is considered to be the most important gaseous pollutant causing effects on vegetation.

Besides visible injuries on leafs and needles, ozone also causes premature leaf loss, reduced photosynthesis and reduced leaf, root, and total dry weights in sensitive plant species.

https://extension.umd.edu/learn/air-pollution-effects-vegetables

Today ozone is considered to be the most important gaseous pollutant causing effects on vegetation.

Besides visible injuries on leafs and needles, ozone also causes premature leaf loss, reduced photosynthesis and reduced leaf, root, and total dry weights in sensitive plant species.

This leads to significant decrease in productivity of some agricultural crops and to reduced forest production.

Effects of ozone on vegetation: from plant cells to ecosystems. [Source: © J.P. Garrec]

Effects on materials

Corrosion of materials was originally mostly associated with air pollution by sulphur dioxide; however know that nitric acid (HNO3), ozone and particulate matter also contribute significantly to the negative effect of air pollution on materials.

The lifetime of technological products is shortened because of air pollution.

Water Pollution

How does nitrogen get into drinking water?

https://www.dvgw.de/english-pages/topics/water/nitrates-and-drinking-water/

The regulatory level is usually met for public water supplies, which are routinely monitored.

In the EU, noncompliance to the nitrate or nitrite standards in large public supplies is reported regularly but rarely exceeds 􏰃% of the sample population.

Bryan, Nathan S., et Hans van Grinsven. « The Role of Nitrate in Human Health ». In Advances in Agronomy, 119:153‐82. Elsevier, 2013.https://www.sciencedirect.com/science/article/abs/pii/B9780124072473000032?via%3Dihub

Effects of nitrogen rich drinking water on human health

Zoom	Nitrate itself is generally considered to be harmless at low concentrations. Nitrite, on the other hand, is reactive especially in the acid environment of the stomach where it can nitrosate other molecules including proteins, amines and amides.

Eutrophication

Zoom	Is one of the most common alterations of continental and marine waters. Result in an exacerbated productivity of aquatic ecosystems due to an excessive nutrient inputs.

Factors controlling eutrophication can be summed up as a combination of some or all of the following interacting factors:

An excess of nutrients
A long water residence time
A sufficient amount of light
A favourable temperature

Fig. Functional linkages between hydrology, anthropogenic nutrient inputs, eutrophication (phytoplankton blooms), and hypoxia/anoxia

in estuarine and coastal aquatic ecosystems.

Paerl, Hans W. « Assessing and Managing Nutrient-Enhanced Eutrophication in Estuarine and Coastal Waters: Interactive Effects of Human and Climatic Perturbations ». Ecological Engineering 26, no 1 (janvier 2006): 40‐54.

The increase in nutrients leads to a strong increase in primary productivity.
The new limiting factor becomes light.
The light penetration decreasing by self-shading as the biomass produced increases.
Development of more competitive species, which affects a change in primary producer communities, which changes the ecosystem and affects biodiversity.

https://www.unenvironment.org/nowpap/what-we-do/prevent-and-reduce-pollution/eutrophication

Video to watch

Eutrophication and dead zones | Ecology | Khan Academy

https://www.youtube.com/watch?v=AxaWXWd2pw4

Zoom	A natural eutrophication phenomenon. The difference between natural and anthropogenic eutrophication is time.

Soil pollution

Soil quality and functions

Effect of soil degradation on nitrogen

Zoom	the effects of soil compaction. https://civilblog.org/

the effects of erosion.
1. Loss of productivity and sediment accumulating due to erosion sometimes can be seen in the same field as showing in this photo.
2. Rain enhances the translocation of soil through the process of splashing. Individual raindrops detach soil aggregates and redeposit particles. The dispersed particles may then plug soil pores, reducing water intake. Once the soil dries, these particles develop into a crust at the soil surface and runoff is further increased.
https://wiki.ubc.ca/

Zoom	the effects of salinisation. High salt concentrations inhibit biological nitrogen transformations in soil, as well as nitrogen fixing capacity by legumes. https://www.quora.com/

Zoom	the effects of soils contamination. https://www.worldatlas.com/

Zoom	the effect of organic matter decline. Figure. The vicious cycle of depletion in soil organic matter-decline in crop yield-food insecurity-soil Vicente Vicente, José. « Soil organic carbon sequestration in Andalusian olive groves: effect of the managements on soil organic carbon dynamics », 2017.

Effect of nitrogen on soil

Nitrogen as a threat to biodiversity

What is biodiversity ?

Video to watch :

https://www.youtube.com/watch?v=GK_vRtHJZu4&t=36s

Ecosystems can be defined by both their sensitivity and their

vulnerability to a stress such as enhanced nitrogen deposition.

The major impacts of nitrate deposition on terrestrial ecosystem

diversity are through :

eutrophication,
Fig. 1. Process-based impact pathway for eutrophication. Black arrows indicate process-based links, grey arrows show links to ecosystem services, where + and – indicate the nature of relationship and examples are given in small type. Solid arrows represent positive relationships and dashed arrows negative relationships. The dotted line box encompasses processes linked to C and N cycling (=Supporting Services). Impacts on species composition are generalised to increases in graminoids and decreases in forbs, but in reality are much more complex.

Zoom	acidification, Fig. 2. Process-based impact pathway for acidification.

direct foliar impacts,
Fig. 3. Process-based impact pathway for direct toxicity (incorporating NOx and NH₃ effects).
exacerbation of other stresses.

Jones, L., A. Provins, M. Holland, G. Mills, F. Hayes, B. Emmett, J. Hall, et al. « A Review and Application of the Evidence for Nitrogen Impacts on Ecosystem Services ». Ecosystem Services 7 (1 mars 2014): 76‐88. https://doi.org/10.1016/j.ecoser.2013.09.001.

Figure. Schematic of the main impacts of enhanced N deposition on ecosystem processes and species richness. Stress is considered to occur when external constraints limit the rate of production of vegetation; disturbance consists of mechanisms that affect plant biomass by causing its partial or total destruction.

Sutton, Mark A., éd. The European Nitrogen Assessment: Sources, Effects and Policy Perspectives. Cambridge: Cambridge Univ. Press, 2011.

Example : Red-backed shrike

Medias

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« European Nitrogen Assessement - Summary for Policy Makers ». Consulté le 3 octobre 2020. https://www.researchgate.net/publication/254838099_European_Nitrogen_Assessement_- _Summary_for_policy_makers.