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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.

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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.

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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?

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References

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

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ninjadapaul
20/(×-6^2)
Salomon
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ninjadapaul
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ninjadapaul
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ninjadapaul
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ninjadapaul
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ninjadapaul
Commplementary angles
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The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
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Kristine 2*2*2=8
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Differences Between Laspeyres and Paasche Indices
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Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
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. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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Cied
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I start with an easy one. carbon nanotubes woven into a long filament like a string
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AMJAD
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Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
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AMJAD
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AMJAD
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Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
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Prasenjit
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Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
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not now but maybe in future only AgNP maybe any other nanomaterials
Azam
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Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
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how did you get the value of 2000N.What calculations are needed to arrive at it
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Source:  OpenStax, Sustainability: a comprehensive foundation. OpenStax CNX. Nov 11, 2013 Download for free at http://legacy.cnx.org/content/col11325/1.43
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