Nitrogen poses global pollution threat

Posted: 5 April 2006

Nitrogen from human activities - such as fossil fuel burning and livestock farming - has become a potential threat to a high proportion of the world's valuable plant species according to researchers at the Universities of Sheffield and York. The gases released into the atmosphere fall back down to earth as atmospheric nitrogen deposition. This can harm ecosystems and has resulted in the loss of species from sensitive ecosystems in Europe.

An international research team led by scientists at the Stockholm Environment Institute (SEI), the University of York, and the Department of Animal and Plant Sciences at the University of Sheffield, has looked at atmospheric nitrogen inputs to 34 plant biodiversity hotspots identified by Conservation International, to which half of the world's plant species are restricted (they are "endemic" and occur no where else in the world).

They used a combination of emissions predictions and atmospheric chemistry models to estimate current nitrogen deposition and likely changes over the next half-century. Using computer modelling, the researchers discovered that some of the global hotspots already receive potentially damaging amounts of nitrogen deposition. With the anticipated global increase in nitrogen emissions by 2050, all but one of the 34 will see an increase in their deposition, with the average total more than doubling. Half the hotspots will receive more nitrogen deposition than amounts that can typically damage sensitive ecosystems in Europe. The most polluted location - the tropical Western Ghats and Sri Lanka - is predicted to receive an average pollution load that is double the current average for the UK.

Spreading danger

The Mountains of Southwest China and Indo-Burma are also among the areas predicted to receive significantly elevated levels of nitrogen pollution by 2050, along with three areas of the world with some of the highest numbers of species as endemics, the Tropical Andes, the Atlantic Forest and the Mediterranean Basin. Dr Gareth Phoenix, of the Department of Animal and Plant Sciences at the University of Sheffield, said: "Until recently, scientists have focused on the threat of atmospheric nitrogen deposition in Europe and North America - partially since these were the first areas of the world to receive high levels of this pollutant. However, our work shows that atmospheric nitrogen deposition is becoming a global threat." This coincidence of high levels of atmospheric nitrogen deposition with areas of particularly high plant diversity may significantly increase the threat to plant biodiversity over the coming century.

Dr Kevin Hicks, at the Stockholm Environment Institute at the University of York, said: "Scientists know very little about the sensitivity of the hotspot ecosystems to nitrogen deposition, so accurate estimates of the amount of likely species loss are not possible. Understanding the impacts of N deposition in hotspots is, therefore, a priority for future research."