The global nitrogen challenge. Joining up the nitrogen cycle for a more sustainable world.
Nitrogen is everywhere in the world around us. In fact, 78% of every breath we take is di-nitrogen (N2). It is extremely unreactive and provides the stabilizing medium within which we live, ensuring that oxygen in the atmosphere is safely limited to 21%. In a dry atmosphere, this leaves just 1% of argon, while other trace constituents such as carbon dioxide make up only 0.04%.
We might call this N2 ‘dead nitrogen’. After all, this is the literal implication of its French word azote, meaning ‘without life’. The German word stickstoff is similar, meaning ‘suffocating material’. It refers to the fact that in an atmosphere of pure nitrogen we would all suffocate and die. It is a poignant reflection, for without nitrogen there would actually be no life on Earth.
Nitrogen compounds are actually the stuff of life. Proteins, amino acids, enzymes and even DNA all contain essential nitrogen. These eventually break down to form a diverse array of small nitrogen compounds such as ammonia (NH3), nitric oxide (NO) and laughing gas (nitrous oxide, N2O), as well as ions soluble in water such as ammonium (NH4) and nitrate (NO3). Each of these N forms may be recycled by biological systems, so contributing to the natural nitrogen cycle. Together they are commonly called ‘reactive nitrogen’ (Nr) because of the wealth of chemical and biological reactions where they play a key role.
Under natural conditions Nr compounds are mostly only available in limited supply. This is because conversion of atmospheric N2 into Nr needs substantial amounts of energy, while this is balanced by natural destruction of Nr back to N2, which releases substantial energy. For example, Nr is formed by bacteria though biological nitrogen fixation associated with the pea family (legumes). To do this, the plant invests part of the energy trapped by photosynthesis to get the precious Nr resource. As plants age and die, Nr is returned to the soil allowing other bacteria make their living by releasing this energy to form N2.
Human alternation of the system
While this illustrates a balanced system, humans have greatly altered the picture. Even in Roman times, the agricultural writer Columella reported the benefits of legume crops and manures to improve soil quality. Roman farmers were already benefiting by increasing nitrogen fixation. The 19th century was a turning point. With technological advancement in agriculture and industry, larger amounts of Nr started to be produced by humans. By the 1840s, mineral fertilizers started to be used, including ‘fossil nitrogen’ sources such as ammonium sulphate extracted from coal. At the same time, an increase in high temperature combustion processes, such as in transport and electricity generation, started to fix N2 into Nr unintentionally – with nitric oxide being liberated directly in exhaust fumes.
The result was a major shift as nitrogen started to change from a scarce resource to a form of pollution. With fast growing cities, import of food was reflected in increasing levels of nitrogen-rich sewage, leading to polluted rivers high in nitrate and a plethora of other organic nitrogen forms. In the air above the cities, horses and human excreta contributed to increase ammonia levels, while higher levels of nitric oxide emission also reacted to form toxic nitrogen dioxide (NO2) making the cocktail today known as NOx (=NO + NO2). Together, their products all react to produce fine particles, high in ammonium and nitrates, which reach deep into our lungs and damage human health.
The key tipping point came with the invention of an effective and relatively low-cost way of producing ammonia, from which other Nr compounds could be made. The process invented by Fritz Haber in 1908 and scaled up by Carl Bosch allowed cheap fertilizers to be produced, substantially increasing food production. At the same time, these Nr compounds were wanted to make explosives, providing the feedstock for two world wars. Overall, it has been estimated that in the 20th century there were 100 million deaths in armed conflict linked to Nr explosives while 3.5 billion births were allowed by the Nr-fuelled increase in food production. Since that time, humans have doubled global Nr flows.As the food benefits increased, so however did the adverse consequences. The result today is a web of nitrogen pollution of water, air and land that threatens health, climate and biodiversity.
Joining up nitrogen science
Until now, most attempts to address the environmental problems resulting from nitrogen have considered only parts of the problem. Following a tendency toward scientific specialisation through the 20th century, understanding of nitrogen impacts developed in a fragmented way. The same specialist perspective was reflected in testing of the solutions and ultimately in the policies to mitigate adverse effects. The result that both the science and policy communities became separated across the nitrogen cycle. Until recently, there has been little communication between experts and policy makers for rivers, lakes and the coastal zone with those addressing the problems of nitrogen air pollution. The same goes for those addressing nitrogen and climate change and others addressing nitrogen impacts on terrestrial biodiversity. There has also been a strong separation between those with knowledge of the source sectors, such as crop and livestock agriculture, waste water and fossil fuel combustion. This has severely hampered mutual understanding on the shared opportunities for better nitrogen management.
This is where there International Nitrogen Initiative (INI) comes in to the picture. Over the last decade or so, INI has been bringing scientists together across the nitrogen cycle and developing the links with the wide range of environmental, agriculture, energy and other policy areas. Together, through the INI network, the global science community has been quietly building the foundations needed to develop the next steps toward a more joined-up response to human alternation of the nitrogen cycle.
Towards an international approach
One of the key emerging messages is that there are substantial barriers to change in improving nitrogen management. Nitrogen is a valuable resource, but not sufficiently expensive to achieve instantly the improvements necessary to avoid damaging pollution. One of the reasons for the barriers is that stakeholders only see parts of the problem, and therefore do not grasp all the benefits that improved nitrogen management would bring.
This all points to the need to take the next step: to build the ‘gravity of common cause’ across the nitrogen cycle. As a science community, we need to be able to demonstrate the multiple benefits that this would bring – how a strategic approach to nitrogen and water, for example, would give quantified co-benefits, for air, climate, stratospheric ozone depletion and biodiversity. As part of this, there is a shift to include new aspirational indicators, where a reduction in pollution becomes reframed as a positive approach toward improving nitrogen use efficiency, with benefits for innovation and jobs in the circular economy.
Together these issues are now being addressed in a new process established in partnership between the United Nations Environment Program (UNEP) and INI, with funding through the Global Environment Facility. It is being termed “Towards INMS” – developing the International Nitrogen Management System – a process of science evidence gathering and synthesis that can support international policy development. It is a way of bringing issues together, of scientists working with governments, business and civil society to identify the options for change and to help overcome the barriers.
At its heart, however, this must be a process where the world learns to know nitrogen, and citizens realise why we should all care. It is amazing that nitrogen fertilizers sustain half the human population alive today, yet so few realise its importance across all aspects of our environment. Only once they do can we expect that governments and business will be empowered to make the changes necessary. From better water treatment to smart farming practices, this is exactly where the scientific guidance of INMS will help.
+ info: http://www.inms.international/