Nitrogen processes and cycle

The conceptual models were compiled by researchers in collaboration with a wide range of stakeholders from Natural Resource Management groups, universities and government agencies and based on available scientific information[1].

Click on elements of the model or select from the tabs below

• Overview
• Chemical forms
• Processes

The nitrogen cycle

The nitrogen cycle, in which atmospheric nitrogen is converted into different nitrogenous compounds, is one the most crucial natural processes to sustain living organisms. During the cycle, certain bacteria ‘fix’ atmospheric nitrogen into ammonia, which plants need in order to grow. Other bacteria convert the ammonia into amino acids and proteins. Animals eat the plants and consume the protein. Nitrogen compounds return to the soil through animal and plant waste. Bacteria convert the waste nitrogen back to nitrogen gas, which returns to the atmosphere.

In an effort to make crops grow faster, people use nitrogen in fertilisers. However, excessive use of those fertilisers, as well as urban stormwater and wastewater discharges, can adversely affect the environment and human health, as it can contribute to the pollution of groundwater and surface waters.

Nitrogen processes in the landscape

Excess nitrogen (N) is one of the most prevalent and serious pollutants affecting waterways. Agricultural, urban and industrial activities have increased the amount of reactive N globally by a factor of nine from pre-industrial times[2][5][1]. The N generated from land use and erosion in catchments may be transported by surface water runoff and groundwater flows to waterways and coastal and marine ecosystems, causing eutrophication and the degradation of these ecosystems[3].

As manufactured nitrogen production exceeds what is cycled naturally, the excess nitrogen in its different forms can harm natural ecosystems[7]. The amount and type of nitrogen and its effects, vary across ecosystems as it travels from its source to the sea[6].

Nitrogen is transported in water and can also be stored in sediments and plants, including algae. Algal blooms (both macroalgae and microalgae) and increased plant growth occur in areas with increased nutrients and high light availability.

Different parts of the landscape process dissolved and particulate nitrogen differently depending on the soils, vegetation, hydrology, and sources of nitrogen and carbon. Some land units and land uses contribute nitrogen to waterways, others, like wetlands, remove it.

Additional information

• NESP Tropical Water Quality Hub Research Theme - Nutrients. Supports the Reef 2050 Water Quality Improvement Plan to reduce the delivery of nutrients from the catchment to the Great Barrier Reef (with a particular focus on nitrogen).
• The Paddock to Reef Integrated Monitoring, Modelling and Reporting Program (Paddock to Reef program) collects and integrates data and information on agricultural management practices, catchment indicators, catchment loads and the health of the Great Barrier Reef.
• The Healthy Land and Water Report Card provides an annual assessment of the environmental condition of South East Queensland catchments, bays and broadwaters.
• Reef Water Quality Report Cards
• The Queensland Water Modelling Network (QWMN) page includes a strategic review of models suite with documents on an assessment framework and model classification.
• Terrain NRM have released this video on how constructed wetlands and vegetated farm drains treat water high in nitrate, through denitrification.

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References

1. ^ a b Adame, MF, Vilas, MP, Franklin, H, Garzon-Garcia, A, Hamilton, D, Ronan, M & Griffiths, M (2021), 'A conceptual model of nitrogen dynamics for the Great Barrier Reef catchments', Marine Pollution Bulletin. [online], vol. 173PA. Available at: https://www.sciencedirect.com/science/article/pii/S0025326X21009437.
2. ^ Galloway, JN & Cowling, EB (2002), 'Reactive nitrogen and the world: 200 years of change', AMBIO: A Journal of the Human Environment. [online], vol. 31, no. 2, pp. 64-71. Available at: http://www.bioone.org/doi/abs/10.1579/0044-7447-31.2.64.
3. ^ Galloway, JN, Aber, JD, Erisman, JW, Seitzinger, SP, Howarth, RW, Cowlilng, EB & Cosby, BJ (2003), 'The Nitrogen Cascade', BioScience. [online], vol. 53, no. 4, pp. 341-341. Available at: https://academic.oup.com/bioscience/article/53/4/341-356/250178.
4. ^ Kotz, JC, Treichel, P, Townsend, JR & Treichel, DA (2019), Chemistry & chemical reactivity, p. 1187, Cengage Learning, Boston, MA.
5. ^ Kulkarni, MV, Groffman, PM & Yavitt, JB (2008), 'Solving the global nitrogen problem: It's a gas!', Frontiers in Ecology and the Environment, vol. 6, no. 4, pp. 199-206.
6. ^ Seitzinger, S, Harrison, JA, Bohlke, JK, Bouwman, AF, Lowrance, R, Peterson, B, Tobias, C & Vand, D (2006), 'Denitrification across landscapes and waterscapes: A synthesis', Ecological Applications, vol. 16, no. 6, pp. 2064-2090.
7. ^ Verhoeven, JTA, Arheimer, B, Yin, C & Hefting, MM (2006), 'Regional and global concerns over wetlands and water quality', Trends in Ecology and Evolution, vol. 21, no. 2, pp. 96-103.

Last updated: 28 September 2021