Modification of Biogeochemical Flows
Boundary Breached
The disruption of the natural nutrient cycles of key elements like nitrogen, and phosphorus through the environment and organisms, which are crucial for supporting life and maintaining ecosystems. Both the global phosphorus flow into the ocean and the industrial fixation of nitrogen (extracting nitrogen from the atmosphere), are disrupting the corresponding nutrient cycles beyond the safe level.
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Importance
Nitrogen (N) and phosphorus (P) are two essential elements that help animals and plants to live and grow. But human activity has interfered with the natural flows of these elements between living organisms and the environment in which they live. This negatively affects soil health, water quality and biodiversity, and triggers dead zones in freshwater and marine systems. For example, fertilizers used in industrial agriculture enter waterways and cause the excessive growth of algae. As the algae dies, it releases CO2 and consumes oxygen from the water - meaning these ecosystems are unable to support many forms of life, becoming “dead zones”.
Impacts
Transgressing the safe boundaries for phosphorus and nitrogen has profound and widespread impacts on aquatic and terrestrial ecosystems, human health, and economic sectors like agriculture, fisheries, and tourism.
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For example, excessive phosphorus promotes rapid algae growth, causing harmful algal blooms that produce toxins harmful to aquatic life and humans (eutrophication).
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Furthermore, oxygen-depleted dead zones caused by excess nutrients result in the death of fish, invertebrates, and other aquatic organisms, reducing biodiversity and altering ecosystem structures.
Control Variables
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Phosphorus (P)
Phosphorus is a critical nutrient applied to agricultural soils through fertilization. This causes leaching of phosphorus through soil erosion and run-off (regional boundary), and flows from freshwater systems into the ocean (global boundary). Excessive runoff and phosphorus leaching from agriculture can lead to eutrophication, causing harmful algal blooms and oxygen depletion in water bodies. The rise in phosphorus use in agriculture is driving harmful algal and cyanobacteria blooms in freshwater systems, highlighting the urgent need for sustainable phosphorus management.
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Nitrogen (N)
Nitrogen is a key nutrient for plant growth and productivity. Human activities have significantly altered the global nitrogen cycle, primarily through industrial and intentional biological nitrogen fixation. Industrial nitrogen fixation converts nitrogen gas from the atmosphere into ammonia, which is used to produce synthetic fertilizers.
Global Map of Changes in Phosphorus Use Rate for Agriculture
Strong increases in phosphorus use rates are observed, particularly in parts of South America, India, China, and Southeast Asia. In contrast, parts of Europe show a notable reduction in phosphorus use over the same period, likely due to improved agricultural practices and regulations. This map highlights the growing use of phosphorus in developing regions, raising concerns about nutrient runoff and its environmental impacts, especially in coastal and freshwater systems.
Global Map of Change in Nitrogen Use Rate for Agriculture
The map highlights a global increase in nitrogen use, particularly in developing regions, raising concerns about environmental impacts and the need for sustainable agricultural practices.
Global Risk Map of the Biogeochemical Cycles Boundary Transgression - Nitrogen Cycle
Global Risk Map of the Biogeochemical Cycles Boundary Transgression - Phosphorus Cycle
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Key Drivers - Nitrogen
Human activities disrupt the global nitrogen (N) and phosphorus (P) cycles, similar to how they affect the carbon cycle. Key drivers include extensive fertilizer use and the cultivation of nitrogen-fixing crops in agriculture. The invention of the Haber-Bosch process in the early 20th century led to exponential growth in synthetic nitrogen fertilizer production, which has increased more than tenfold since 1960. Today, the amount of human-generated nitrogen entering the biosphere equals all natural sources combined.
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Key Drivers - Phosphorus
Agriculture similarly disrupts the phosphorus cycle, historically through manure and now significantly through mined rock phosphate, accelerating phosphorus cycles two to three times beyond natural rates. Agriculture accounts for over 90% of phosphorus boundary transgressions.
Connected Tipping Points
If the status of this Planetary Boundary continues to deteriorate, it will push many tipping elements toward tipping, including:
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The death of warm-water coral reefs
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Death of kelp forests, seagrass and mangrove ecosystems
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Deoxygenation of marine environments
Read more about other Boundaries
Planetary Boundary process inside Earth's safe operating space
Planetary Boundary process outside Earth's safe operating space
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