Australasian Science: Australia's authority on science since 1938

Your Nitrogen Footprint Has Far-Reaching Consequences

By Xia Liang

Australia’s reliance on coal and taste for beef is contributing to nitrogen pollution as far away from our population centres as the Great Barrier Reef.

Nitrogen is an essential component of the nucleic acids and enzyme proteins found in the living cells of plants, animals and humans. Life can only exist because of the availability of reactive nitrogen, which encompasses all forms of nitrogen other than the inert nitrogen gas that makes up 80% of the air we breathe.

However, only a tiny fraction of the reactive nitrogen we produce goes into building up our muscles. Instead, most of it gets released into the environment, costing of billions of dollars worldwide in human health and ecosystem damages.

Once reactive nitrogen has escaped into environ­mental reservoirs, it cascades through atmospheric, terrestrial, aquatic and marine pools, and has a range of effects during its lifetime. These include smog, climate change, stratospheric ozone depletion, soil acidification, forest dieback, biodiversity loss, groundwater pollution, ocean acidification and eutrophication.

For example, reactive nitrogen loss in Australia poses a major pollution risk to the Great Barrier Reef, leading to algal blooms and outbreaks of crown-of-thorns starfish. In 2016 and 2017, more than 40% of coral was lost.

Reactive nitrogen pollutants are derived from a range of diffuse and point sources, including agriculture, manufacturing and industry, mining, rural and urban residential sources, transport, waste treatment and disposal.

In order to assess the contribution of anthropogenic activities to reactive nitrogen pollution and their environmental impacts, we quantified the contribution of reactive nitrogen pollution sources. Our earlier research showed that Australia has a larger nitrogen footprint – up to 47 kg of nitrogen per person each year – than the USA (39 kg), Japan (28 kg), Europe (25 kg) and Tanzania (15 kg). Australia’s large nitrogen footprint is driven largely by our love of beef and the heavy dependence on coal for electricity.

Our new research, published in the Journal of Cleaner Production (https://goo.gl/opi76w), took this concept further by measuring the nitrogen footprint of an entire institution, the University of Melbourne, to set clear goals to improve its sustainability. We found that in 2015 the university’s total nitrogen footprint was 139 tonnes. The major contributors were food production (37%), utilities (32%) and transport (28%).

Our research shows that institutions can have a large contribution to nitrogen pollution, but also that they have significant potential and capacity to reduce this contribution. We found that the nitrogen footprint of the university could be reduced by 60% if it implements changes to food purchases and energy use. Universities are leading the way in sustainable development, and the calculation of the nitrogen footprint for the University of Melbourne can be the starting point for future work on sustainable institutional nitrogen management in Australia.

Australia has the largest measured nitrogen footprint but is generally perceived as a “green and clean” country. To explore this discrepancy, we proposed a new indicator – “reactive nitrogen spatial intensity” – that estimates the intensity of the reactive nitrogen loss on a per area basis.

We demonstrated that a nation with a high nitrogen footprint per capita , such as Australia, could have a low reactive nitrogen spatial intensity and vice versa. Of the seven countries we sampled, Australia had the lowest reactive nitrogen spatial intensity (6 kg/ha/year) while The Netherlands had the highest (217 kg/ha/year).

Since a measure of reactive nitrogen spatial intensity connects reactive nitrogen loss with the land area over which it is lost, it can better identify reactive nitrogen emission hotspots. This identifies the potential for environmental impacts and leads to recommendations that can help manage those impacts.

The combined nitrogen footprint and reactive nitrogen spatial intensity could be used as a benchmark for assessing the reactive nitrogen loss and its environmental pressure in Australia. It will also help to set priorities of mitigating reactive nitrogen pollution to achieve the United Nations Sustainable Development Goals by 2030.

Given the pressures from our growing global population and the world’s increasing food and energy consumption, research like this is critical to identifying, and ultimately combating, our nitrogen pollution hotspots.


Xia Liang is a Research Fellow in The University of Melbourne’s Faculty of Veterinary and Agricultural Sciences.