The process of making synthetic fertilizers for use in agriculture by causing N 2 to react with H 2 , known as the Haber-Bosch process, has increased significantly over the past several decades. Much of the nitrogen applied to agricultural and urban areas ultimately enters rivers and nearshore coastal systems. In nearshore marine systems, increases in nitrogen can often lead to anoxia no oxygen or hypoxia low oxygen , altered biodiversity, changes in food-web structure, and general habitat degradation.
One common consequence of increased nitrogen is an increase in harmful algal blooms Howarth Toxic blooms of certain types of dinoflagellates have been associated with high fish and shellfish mortality in some areas.
Even without such economically catastrophic effects, the addition of nitrogen can lead to changes in biodiversity and species composition that may lead to changes in overall ecosystem function.
Some have even suggested that alterations to the nitrogen cycle may lead to an increased risk of parasitic and infectious diseases among humans and wildlife Johnson et al. Additionally, increases in nitrogen in aquatic systems can lead to increased acidification in freshwater ecosystems. Nitrogen is arguably the most important nutrient in regulating primary productivity and species diversity in both aquatic and terrestrial ecosystems Vitousek et al. Microbially-driven processes such as nitrogen fixation, nitrification, and denitrification, constitute the bulk of nitrogen transformations, and play a critical role in the fate of nitrogen in the Earth's ecosystems.
However, as human populations continue to increase, the consequences of human activities continue to threaten our resources and have already significantly altered the global nitrogen cycle. Galloway, J.
Year Consequences of population growth and development on deposition of oxidized nitrogen. Ambio 23 , — Howarth, R. Coastal nitrogen pollution: a review of sources and trends globally and regionally.
Harmful Algae 8 , 14— Johnson, P. Linking environmental nutrient enrichment and disease emergence in humans and wildlife. Ecological Applications 20 , 16—29 Koenneke, M.
Isolation of an autotrophic ammonia-oxidizing marine archaeon. Nature , — Kuypers, M. Massive nitrogen loss from the Benguela upwelling system through anaerobic ammonium oxidation. Risgaard-Petersen, N. Evidence for complete denitrification in a benthic foraminifer. Nature , 93—96 Strous, M. Missing lithotroph identified as new planctomycete.
Vitousek, P. Human alteration of the global nitrogen cycle: sources and consequences. Ecological Applications 7 , — Towards an ecological understanding of biological nitrogen fixation. Biogeochemistry 57 , 1—45 Ward, B. Denitrification as the dominant nitrogen loss process in the Arabian Sea. Nature , 78—81 Introduction to the Basic Drivers of Climate.
Terrestrial Biomes. Coral Reefs. Energy Economics in Ecosystems. Biodiversity and Ecosystem Stability. Biological Nitrogen Fixation.
Ecosystems Ecology Introduction. Factors Affecting Global Climate. Rivers and Streams: Life in Flowing Water. The Conservation of Mass. The Ecology of Carrion Decomposition. Causes and Consequences of Biodiversity Declines. Earth's Ferrous Wheel. Learning Objectives Describe the nitrogen cycle and how it is affected by human activity.
Key Points Nitrogen is converted from atmospheric nitrogen N2 into usable forms, such as NO2-, in a process known as fixation. The majority of nitrogen is fixed by bacteria, most of which are symbiotic with plants. Recently fixed ammonia is then converted to biologically useful forms by specialized bacteria.
This occurs in two steps: first, bacteria convert ammonia in to nitrites NO2-, and then other bacteria species convert it to NO3- nitrate.
Nitriates are a form of nitrogen that is usable by plants. Take a closer look at dairy farming and the nitrogen cycle with this article and interactive. See how nitrogen leaching due to agriculture has increased over time in New Zealand. Add to collection. Nature of science Scientists make observations and develop their explanations using inference, imagination and creativity.
Activity idea Students may enjoy experimenting with components of the nitrogen cycle in the student activity, Nitrification and denitrification. Related content Take a closer look at dairy farming and the nitrogen cycle with this article and interactive. Useful link See how nitrogen leaching due to agriculture has increased over time in New Zealand.
Go to full glossary Add 0 items to collection. Download 0 items. Twitter Pinterest Facebook Instagram. Email Us. This ammonium is held in the soils and is available for use by plants that do not get nitrogen through the symbiotic nitrogen fixing relationship described above. The third stage, nitrification, also occurs in soils. Nitrates can be used by plants and animals that consume the plants.
Some bacteria in the soil can turn ammonia into nitrites. Although nitrite is not usable by plants and animals directly, other bacteria can change nitrites into nitrates—a form that is usable by plants and animals. This reaction provides energy for the bacteria engaged in this process. The bacteria that we are talking about are called nitrosomonas and nitrobacter.
Nitrobacter turns nitrites into nitrates; nitrosomonas transform ammonia to nitrites. Both kinds of bacteria can act only in the presence of oxygen, O 2 [ 7 ]. The process of nitrification is important to plants, as it produces an extra stash of available nitrogen that can be absorbed by the plants through their root systems.
The fourth stage of the nitrogen cycle is immobilization, sometimes described as the reverse of mineralization. These two processes together control the amount of nitrogen in soils.
Just like plants, microorganisms living in the soil require nitrogen as an energy source. These soil microorganisms pull nitrogen from the soil when the residues of decomposing plants do not contain enough nitrogen.
Immobilization, therefore, ties up nitrogen in microorganisms. However, immobilization is important because it helps control and balance the amount of nitrogen in the soils by tying it up, or immobilizing the nitrogen, in microorganisms. In the fifth stage of the nitrogen cycle, nitrogen returns to the air as nitrates are converted to atmospheric nitrogen N 2 by bacteria through the process we call denitrification. This results in an overall loss of nitrogen from soils, as the gaseous form of nitrogen moves into the atmosphere, back where we began our story.
The cycling of nitrogen through the ecosystem is crucial for maintaining productive and healthy ecosystems with neither too much nor too little nitrogen. Plant production and biomass living material are limited by the availability of nitrogen. Understanding how the plant-soil nitrogen cycle works can help us make better decisions about what crops to grow and where to grow them, so we have an adequate supply of food.
Knowledge of the nitrogen cycle can also help us reduce pollution caused by adding too much fertilizer to soils. As you have seen, not enough nitrogen in the soils leaves plants hungry, while too much of a good thing can be bad: excess nitrogen can poison plants and even livestock!
Pollution of our water sources by surplus nitrogen and other nutrients is a huge problem, as marine life is being suffocated from decomposition of dead algae blooms. Farmers and communities need to work to improve the uptake of added nutrients by crops and treat animal manure waste properly. We also need to protect the natural plant buffer zones that can take up nitrogen runoff before it reaches water bodies.
But, our current patterns of clearing trees to build roads and other construction worsen this problem, because there are fewer plants left to uptake excess nutrients.
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