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The Nitrogen Cycle
The Nitrogen Cycle. Figure illustrates the nitrogen cycle on, above, and below the Earth's surface. Source: Physical Geography Fundamentals eBook .

Human interactions with the nitrogen cycle

Humans are primarily dependent on the nitrogen cycle as a supporting ecosystem service for crop and forest productivity. Nitrogen fertilizers are added to enhance the growth of many crops and plantations. The enhanced use of fertilizers in agriculture was a key feature of the green revolution that boosted global crop yields in the 1970s. The industrial production of nitrogen-rich fertilizers has increased substantially over time and now matches more than half of the input to the land from biological nitrogen fixation (90 MtN each year). If the nitrogen fixation from leguminous crops (e.g. beans, alfalfa) is included, then the anthropogenic flux of nitrogen from the atmosphere to the land exceeds natural fluxes to the land. As described above, most ecosystems naturally retain and recycle almost all of their nitrogen. The relatively little nitrogen that is being gained or lost by fluxes to the atmosphere and water cycle is also nearly being balanced. When humans make large additions of nitrogen to ecosystems leakage often results, with negative environmental consequences. When the amount of nitrate in the soil exceeds plant uptake, the excess nitrate is either leached in drainage water to streams, rivers, and the ocean or denitrified by bacteria and lost to the atmosphere. One of the main gases produced by denitrifying bacteria (nitrous oxide) is an important greenhouse gas that is contributing to human-induced global warming. Other gases released to the atmosphere by denitrifying bacteria, as well as ammonia released from livestock and sewage sludge, are later deposited from the atmosphere onto ecosystems. The additional nitrogen from this deposition, along with the nitrogen leaching into waterways, causes eutrophication. Eutrophication occurs when plant growth and then decay is accelerated by an unusually high supply of nitrogen, and it has knock-on effects, including the following: certain plant species out-competing other species, leading to biodiversity loss and altered ecosystem function; algal blooms that block light and therefore kill aquatic plants in rivers, lakes, and seas; exhaustion of oxygen supplies in water caused by rapid microbial decomposition at the end of algal blooms, which kills many aquatic organisms. Excess nitrates in water supplies have also been linked to human health problems. Efforts to reduce nitrogen pollution focus on increasing the efficiency of synthetic fertilizer use, altering feeding of animals to reduce nitrogen content in their excreta, and better processing of livestock waste and sewage sludge to reduce ammonia release. At the same time, increasing demand for food production from a growing global population with a greater appetite for meat is driving greater total fertilizer use, so there is no guarantee that better practices will lead to a reduction in the overall amount of nitrogen pollution.

Review questions

There is approximately 2,000 cubic kilometers of water stored in rivers around the world. Using the terms  water cycle flux  and  pool , describe under what conditions removing 1000 cubic kilometers per year from rivers for human use could be sustainable.

Each year, around a quarter of the carbon dioxide found in the atmosphere is turned into plant matter via photosynthesis. Does this mean that, in the absence of human activity, all carbon dioxide would be removed from the atmosphere in around four years? Explain your answer.

The water, carbon, and nitrogen cycles are all influenced by human activity. Can you describe a human activity that impacts all three cycles? In your example, which of the cycles is most significantly altered?


Le Quere, C., Raupach, M. R., Canadell, J. G., Marland, G., Bopp, L., Ciais, P., et al. (2009, December). Trends in the sources and sinks of carbon dioxide. Nature Geoscience, 2 , 831-836. doi: 10.1038/ngeo689

Millennium Ecosystem Assessment (2005). Ecosystems and Human Well-Being: Synthesis. Washington DC. Retrieved from (External Link)

Questions & Answers

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
in a comparison of the stages of meiosis to the stage of mitosis, which stages are unique to meiosis and which stages have the same event in botg meiosis and mitosis
Leah Reply
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