Last But Not Least

The third and final boundary considered already ‘breached’ by the Stockholm Resilience Centre is that of Nitrogen and Phosphorus cycle loading.  That is, the rate at which both are removed from the natural environment (the atmosphere in the case of N) and converted to reactive forms for human use respectively. Industrial processes (including agricultural practices) account for an overwhelming proportion of this.

Prior to global human influence, N was only available in limited supply to most of the biological world and thus acted as “one of the major limiting factors controlling the dynamics, biodiversity and functionality of many ecosystems” (Vitousek et al). For plants to be able to utilise N, they must extract it from the atmosphere (which is 78% N) and ‘fixed’, i.e. bonded to hydrogen or oxygen to form inorganic compounds such as NH₄ and NO₃.

This diagram shows a simplified Nitrogen cycle, importantly illustrating the importance of the atmosphere as an essential store and the integral role of industrial fixation.

Sources

• Fertilisers
• Fossil fuel combustion
• Deforestation
• Cultivation of certain crops

Modern agriculture is a major cause of environmental pollution in general, but especially large-scale N- and P- induced environmental change. Primarily, the manufacture and use of fertiliser along with the cultivation of leguminous crops convert more N₂ to reactive forms per year than all of Earth’s terrestrial processes (Rockström et al). Furthermore, human activity is also speeding up the release of N from long-term storage in soils and organic matter, amplifying the effect.

The above diagram shows the rate of increase in various sources of N, most notably is the incredible rate of industrial fertiliser since the mid-1970s, this very effectively illustrates in responsibility of industries in tackling the scale of alteration.

Similarly, P is utilised in a vast array of ways from fertiliser to toothpaste, however around half of all mined P finds its way into the oceans which is estimated to be in the region of 8 times the natural rate of influx.

Consequences

• Increased global N₂O
• Alteration of ecosystem functionality
• Biodiversity loss

A considerable proportion of N involved in agriculture ends up either polluting water courses, in the coastal zone, accumulating in land systems or enhancing processes that add a number of gases to the atmosphere (Rockstrom et al). Altered levels of N in circulation have been proved to have caused changes in composition and functioning of estuarine and near-shore ecosystems, contributing to long-term declines in coastal marine fisheries (Vitousek et al). Historical climatic data has shown that the P that finds its way to the ocean could quite realistically cause large-scale ocean anoxic events, and even lead to marine extinctions.  

Management Options

• Increase fertiliser efficiency
• Alternative energies

Often, half of fertiliser used is lost to air and water, yet practices have been identified and practised which can increase efficiency and reduce wastage. A further enhancement on this is to contain fertilising practices to farmland, and prevent nutrients reaching nearby water courses.

In order to reduce the level of fossil fuel burning, alternative energies are required – this of course is not exclusive to N and P cycle restoration, but to almost all of the boundaries in Rockström’s model.