The overabundance of nutrients is a major element of ecological disruption, primarily due to human activity’s impact on the nitrogen and phosphorus biogeochemical cycles. One example is the recent decades’ high dependence on synthetic fertilizers, feed, and intensive farming methods.

As human populations grow, so does the burden placed on global food systems, which drives massive nitrogen and phosphorus use. While these substances are crucial in improving the productivity of crops, grass, and feed, their high use has exacerbated or created new problems worldwide. Moreover, poor management of waste products from cattle, fish, and other farmed organisms worsens the situation.

Understanding the role of nitrogen and phosphorus overabundance is critical to addressing ecological security.

N- and P-compounds Essential to Plant Life

Nitrogen (N) and phosphorus (P) compounds are used in plant fertilizers because these elements play crucial roles in plant growth and development. The nitrogen in fertilizer compounds such as urea, ammonium nitrate, and ammonium sulfate is vital for producing amino acids, which make up proteins, and for synthesizing chlorophyll, the pigment that allows photosynthesis to take place.

Moreover, nitrogen is a central component of DNA and RNA, which store and transmit genetic information. Phosphorus, typically found in fertilizers as phosphate salts, is essential for energy storage and transfer within plant cells as adenosine triphosphate (ATP). Furthermore, phosphorus promotes healthy root development and enhances flowering and fruiting.

… But Also Promote Other Life Forms

The growth, development, and energy transfer within each of life’s kingdoms also require proteins, nucleic acids, ATP, and other biomolecules. Even though sectors may use nutrients to target the growth of a specific set of organisms (such as crops, fish, etc.), they nonetheless also promote the development of other life forms.

Microorganisms such as bacteria, algae, and fungi are often very adept at uptaking extra nutrients due to their rapid growth rates and metabolic versatility, enabling them to swiftly adapt and thrive in nutrient-rich environments.

Too Many Nutrients!

Nutrient overabundance, particularly in nitrogen and phosphorus, has become a significant concern arising mainly from the widespread availability of synthetic fertilizers since the mid-20th century. While these substances have revolutionized modern farming and benefited global food security, their often excessive and improper application has contributed to excessively high levels of nutrients in soils and water bodies.

In addition, intensive aquaculture, particularly prawn farming, contributes heavily to eutrophication. This sector uses large amounts of nitrogen and phosphorus feed for farmed fish and seafood, much left unconsumed. Further, the water exchange systems that circulate freshwater into farm ponds discharge considerable amounts of nutrient pollution into the receiving bodies.

The livestock and animal husbandry sectors also employ fertilizers to improve the productivity and quality of pastures and grasslands. However, in addition to being significant fertilizer consumers, these sectors re-generate large amounts of nitrogen and phosphorus through manure and waste. Thus, improper waste management is an additional pathway of nutrient overabundance.

Beyond food production, other industries contribute to nutrient overabundance when inputs are not appropriately managed. These include horticulture, landscaping, turf management, wastewater treatment, paper production, detergent manufacturing, mining, and resource extraction.

Nutrient Pollution in Soils

When soil becomes overly nutrient-rich, several consequences can affect the soil ecosystem and the surrounding environment. For example, ammonium compounds contribute substantially to soil acidification, a form of soil degradation.

In addition, high nutrient levels can alter soil microbial activities, potentially impacting ecosystem services like decomposition, organic matter breakdown, and nutrient cycling. However, most nutrients in the soil will be carried away as surface runoff into nearby water bodies, contributing to substantial problems in marine and freshwater systems.

A Global Eutrophication Crisis

Eutrophication is an ecological regime shift in aquatic ecosystems that occurs when nitrogen and phosphorus enrichment spurs the rapid growth of algae and aquatic plants. As a result, many organisms die from over-competition for resources and dissolved oxygen; respiration from microbial decomposition further consumes oxygen, rapidly leading to hypoxic conditions—and often dead zones. Mass mortality events (mass die-offs) are a particularly ghoulish outcome of some hypoxic events. Further, eutrophication can trigger harmful algal blooms, which carry numerous additional ecological burdens.

source: R. Schoonover

Eutrophication, particularly in extreme cases, poses significant risks to people and nations through a variety of pathways:

Declines in Fisheries

• Dead zones substantially affect the productivity and sustainability of fisheries, which has downstream impacts on food security and livelihoods.
• Habitat and biodiversity loss fueled by eutrophication can disrupt aquatic food webs, dampening the availability of commercially valuable species.

Decreased Tourism

• Eutrophied waters, particularly when unsightly, malodorous, or toxic, deter visitors and diminish the appeal of recreational activities.
• Declines in tourism revenue affect local businesses and economies that predominantly rely on tourist spending.

Direct Impacts on Human Health

• Harmful algal blooms produce toxins that, when ingested, can cause paralytic or diarrhetic poisoning.
• Skin irritation and respiratory issues are common symptoms of close contact with eutrophied waters.
• Eutrophication has been linked to an increased risk of waterborne diseases caused by pathogens that thrive in nutrient-rich waters.

Increased Water Treatment Costs

• Municipalities must often invest in additional water treatment resources and processes to address excess nutrients.
• Increased treatment expenses are typically passed to citizens via higher water bills or increased public expenditure on water infrastructure.

Loss in Property Values

• Unpleasant or dangerous aquatic conditions diminish the appeal of nearby properties, which is amplified further when harmful algal blooms are recurrent.

Hotspots for Antimicrobial Resistance

• Nutrient-rich aquatic environments promote rapid microbial growth and biofilms that have been identified as hotspots for the emergence of antibiotic resistance genes
• Eutrophication is also suspected as a heavy contributor to antifungal resistance emergence in the environment

The Eutrophic Footprint of Food Items

Looking narrowly at nutrient overabundance from food production, a few charts from the wizards at Our World in Data bring insights into which sectors produce the most excess nutrients that can participate in eutrophication. Of course, each chart employs a different metric, conveying another part of the story. But a general theme courses through all three: Farming animals is accompanied by more eutrophying emissions than farming plants, with a few exceptions (namely, coffee and chocolate).

The Comparative Importance of Nutrient Overabundance

The Planetary Boundaries Framework project seeks to identify and assess critical thresholds for sustaining a stable Earth system. Thus far, the project has identified nine such boundaries:

• climate change
• ocean acidification
• stratospheric ozone depletion
• atmospheric aerosol loading (microscopic particles in the atmosphere)
• freshwater use
• land-system change
• biodiversity loss
• novel entities (such as synthetic chemicals and plastics)
• biogeochemical flows (primarily nutrient overabundance)

If the Planetary Boundaries research is any indication, humanity is well beyond the safe operating level for biogeochemical flows (explicitly expressed here as nitrogen and phosphorus overabundance).

Designed by Azote for Stockholm Resilience Centre, source: Persson et all 2022, Stefan et al 2015

An important conclusion is that if we assess the security implications of only climate change or resource scarcity, we overlook, perhaps fatally, the danger from other forms of ecological disruption.

As we can see, nitrogen and phosphorus overabundance are critically important drivers of ecological disruption and, thus, crucial to analyzing and addressing ecological security.