The acceleration of the nitrogen cycle as a result of the production and industrial use of artificial nitrogen fertilizers worldwide has enabled human kind to increase food production. However there are unforeseen environmental problems.
Studies on these alterations in the nitrogen cycle have led to a much improved understanding of the scope of the problem and possible strategies for managing it. These alterations in the nitrogen cycle affect other major biogeochemical cycles, particularly that of carbon.
The release of carbon dioxide (CO2) from the burning of fossil fuels has major consequences for the functioning of the global carbon cycle, and as nitrogen has a crucial role in controlling key aspects of this cycle, the nitrogen-carbon-climate interactions are becoming increasingly pressing.
Does the availability of nitrogen affect the capacity of Earth’s biosphere to continue absorbing carbon from the atmosphere, and hence continue to help in mitigating climate change. The dynamics of the nitrogen cycle are important in the context of a changing carbon cycle, a changing climate and changes in human actions.
Nitrogen is a fundamental component of living organisms; but is in short supply in forms that can be assimilated by plants in both marine and land ecosystems. Nitrogen has a critical role in controlling primary production in the biosphere. Nitrogen is also a limiting factor for the plants grown by humans for food. Without the availability of nitrogenous fertilizer produced by the Haber-Bosch process, the enormous increase in food production over the past century, which in turn has sustained the increase in global population, would not have been possible. All the nitrogen used in food production is added to the environment, as is the nitrogen emitted to the atmosphere during fossil-fuel combustion.
In the 1990s, these two sources of anthropogenic nitrogen to the environment amounted to more than 160 teragrams (Tg) N per year On a global basis, this is more than that supplied by natural biological nitrogen fixation on land (HOTg N per year) or in the ocean (UOTgN per year}.
Given expected trends in population, demand for food, agricultural practices and energy use, anthropogenic nitrogen fluxes will increase; that is, humans are likely to be responsible for doubling the turnover rates not only of the terrestrial nitrogen cycle but also of the nitrogen cycle of the entire Earth.
The negative consequences of these nitrogen additions include excessive growth of plant and microorganisms in terrestrial and aquatic systems to global acidification and stratospheric ozone loss
Also chemical transformations of nitrogen along its transport pathway in the environment is important. Nitrogen oxide can first cause photochemical smog and then, after it has been oxidized in the atmosphere to nitric acid and deposited on the ground, can lead to soil and water acidification and excessive growth of plant and microorganisms
The human acceleration of the nitrogen cycle did not occur, alone as the phosphorus, sulphur and carbon cycles are are affected. The burning of fossil fuels and carbon emissions from land-use change, atmospheric CO, has increased to levels that are more than 30% above those of pre-in Industrial times and the observed warming over the past century, particularly that of the past 30 years.
The perturbations of the global nitrogen and carbon cycles caused by human activity are in part linked to each other. This is mostly a result of the atmosphere’s being very efficient in spreading the nitrogen oxides and ammonia emitted as a result of energy and food production, and also because this nitrogen is deposited on the ground in a form that is readily available to plants, thereby stimulating productivity and enhancing the uptake of CO, from the atmosphere
The deposition of both nitrogen products and carbon in the oceans has unknown effects.
Gruber and Galloway 2008 An earth-system perspective of the global nitrogen cycle . Nature vol 451, 293-296

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