Human Impacts on the Nitrogen Cycle (HL) (DP IB Environmental Systems & Societies (ESS))

Human Impacts on the Nitrogen Cycle

Human activities altering the nitrogen cycle

Deforestation

• Removing forests reduces the amount of vegetation that can absorb nitrogen from the soil (for plant growth)

• This leads to an increase in nitrogen leaching into water bodies, where it can cause pollution

  • For example, deforestation in the Amazon has increased nitrogen runoff into rivers due to exposed soil and soil erosion

  • This has led to eutrophication (nutrient over-enrichment) and harmful algal blooms

  • These blooms deplete oxygen levels in the water, creating hypoxic or dead zones where aquatic life cannot survive

  • Studies have shown that deforestation in the Amazon basin has increased nitrogen concentrations in the rivers by 20–50%

    • Disrupting these freshwater ecosystems

    • Contributing to biodiversity loss

Agriculture

• The heavy use of nitrogen-based fertilisers on agricultural land to increase crop growth leads to excess nitrate being washed into rivers and oceans

• This contributes to eutrophication and causes dead zones in surrounding aquatic environments

  • For example, excessive fertiliser runoff in the Mississippi River basin causes a very large dead zone in the Gulf of Mexico every year

Aquaculture

• Fish farms often use large quantities of feed that introduce excess nitrogen into water systems

• Uneaten feed and fish waste add nitrates and ammonia to the water, causing algal blooms and oxygen depletion

  • For example, salmon farming in Norway contributes to nitrogen pollution in coastal waters

Urbanisation

• Cities and towns contribute to nitrogen pollution through:

  • Sewage:

    • Wastewater contains nitrogen from human waste, detergents, and food, which can enter rivers and oceans, increasing nitrogen levels

  • Stormwater runoff:

    • Rainwater picks up nitrogen from fertilisers, pet waste, and other pollutants on roads and carries it into water bodies

  • Vehicle emissions:

    • Cars release nitrogen oxides (NOx) into the air, which can contribute to nitrogen pollution when it settles onto land or water

    • These emissions can also react with water vapour to form nitric acid, leading to acid rain

The Haber process and its impact

• The Haber process is an industrial method for synthesising ammonia (NH₃) from nitrogen (N₂) in the atmosphere and hydrogen (H₂)

  • This ammonia can be used to produce fertilisers that enhance crop yields

• Advantages:

  • Increases global food production by improving crop yields

  • Provides a reliable and large-scale source of nitrogen fertiliser for agriculture

• Disadvantages:

  • Excess nitrogen from fertilisers contributes to pollution and environmental issues like eutrophication and reduced biodiversity in aquatic ecosystems

  • The Haber process requires large amounts of energy, typically from fossil fuels, contributing to greenhouse gas emissions

Crossing the nitrogen planetary boundary

• Nitrogen is one of the boundaries used in the planetary boundaries model

  • The planetary boundaries model outlines nine critical processes and systems that regulate the stability and resilience of our Earth system

• Human activities, especially the extensive use of nitrogen fertilisers, have resulted in excessive nitrogen in ecosystems

• This has pushed the nitrogen cycle beyond its safe limits, leading to potentially irreversible changes in the environment

  • Excess nitrogen disrupts natural cycles, causing water pollution and loss of biodiversity

  • Evidence shows that the nitrogen cycle is beyond its safe operating space

Global collaboration to restore balance

• Global dependence on fertilisers:

  • Most of the world’s food production relies on inorganic nitrogen fertilisers

  • This has created an unsustainable cycle of nitrogen pollution

    • Global fertiliser use continues to increase, especially in rapidly industrialising countries like China and India

• Collaborative solutions:

  • To address the nitrogen crisis, countries must cooperate to:

    • Reduce nitrogen emissions

    • Improve nitrogen use efficiency in agriculture

• Measures to restore balance:

  • Use more sustainable farming techniques, such as crop rotation and precision farming, to reduce fertiliser use

  • Improve sewage treatment plants to reduce nitrogen pollution from urban areas

  • A key way to combat nitrogen pollution is to transition away from cars that emit nitrogen-based pollutants, such as those that run on petrol and diesel

    • For instance, EVs reduce emissions that contribute to nitrogen pollution and acid rain