Researchers from Denmark and the US have discovered that our planet's ecosystems are being overburdened with nitrogen generated by us. The burning of fossil fuels and a rise in industrial and agricultural activities are also boosting nitrogen levels. This excess nitrogen could have a serious impact on the climate, and is at the same time being compounded by the contamination of fresh waters and coastal zones through human activity. Published in the journal Science, the study has identified that greater use of sustainable, time-honoured practices would help curb any damaging impact on the environment. The researchers from the University of Southern Denmark, the University of California, Berkeley and Rutgers University in the US, say the billion-year-old nitrogen cycle converts non-biologically useful forms of nitrogen found in the atmosphere into a number of biologically useful forms of nitrogen that organisms need in order to create proteins, DNA and RNA (deoxyribonucleic and ribonucleic acids), and photosynthesis. 'Nitrogen fixation' is what experts call the conversion of atmospheric nitrogen into compounds, such as ammonia, by natural agencies or various industrial processes. . Nitrogen fixation, along with other nitrogen cycle components, move through the atmosphere, soil, plants and roots. This cycle fosters relationships between organisms, microorganisms and plants. The cycle has changed over time. Lightning, volcanic processes and biological activities controlled the cycle from its onset. Flash-forward 2.5 billion years, and microbial processes evolved to form the modern nitrogen cycle. From the 1900s, human activities started impacting the nitrogen cycle. 'In fact, no phenomenon has probably impacted the nitrogen cycle more than human inputs of nitrogen into the cycle in the last 2.5 billion years,' explains Professor Paul Falkowski from the Institute of Marine and Coastal Studies at Rutgers University, one of authors of the study. 'Altogether, human activities currently contribute twice as much terrestrial nitrogen fixation as natural sources, and provide around 45% of the total biological useful nitrogen produced annually on Earth. Their data show that a good majority of the nitrogen excess found in our ecosystems was triggered by an 800% jump in the use of nitrogen fertilisers in the period 1960-2000. Also responsible for this excess is the improper use of a lot of nitrogen fertiliser found across the globe. Some 60% of the nitrogen contained in applied fertiliser is never incorporated into plants and is thus freely washed out of root zones, only to contaminate rivers, lakes, aquifers and coastal areas through eutrophication (a process triggered by too many nutrients depleting oxygen in water bodies, which in turn leads to the death of animal life). In terms of what happens to the atmosphere, the researchers say nitrogen oxide is a greenhouse gas that has 300 times (per molecule) the warming potential of carbon dioxide. Nitrogen oxide basically wipes out the stratospheric ozone, which safeguards our planet from harmful ultraviolet rays. 'Natural feedbacks driven by microorganisms will likely produce a new steady-state over time scales of many decades,' Professor Falkowski points out. 'Through this steady state, excess nitrogen added from human sources will be removed at rates equivalent to rates of addition, without accumulating.' The team has identified three main intervention steps to curb the damage inflicted upon the nitrogen cycle: 1) use systematic crop rotations that would supply nitrogen; 2) optimise the timing and amounts of fertiliser applications, and adopt selected breeding techniques or develop genetically engineered plant varieties to boost nitrogen use efficiency; and 3) use traditional breeding techniques to enhance the potential of economically viable wheat, barley and rye varieties.
Denmark, United States