Threat to biodiversity

A STUDY that has proven the damage that nitrogen pollution inflicts on grassland biodiversity in the UK is now providing evidence that the effect is Europe-wide.

Scientists have been investigating 70 grasslands in nine countries for the past year and the first field results seem to corroborate the pattern found in the UK: a direct link between species loss and long-term deposition of nitrogen.

"The loss in Great Britain is much larger than people had imagined," says Professor Nancy Dise of MMU’s Department of Environmental and Geographical Sciences.

"It is almost 25% of species at the average deposition rate. If this is occurring across Europe, it will be an important find, with implications for government policy on ecosystem protection."

Wildflower threat

Hardest hit are wildflowers and other plant species with broad leaves. Grasses, on the other hand, do not appear to be affected to the same extent.

Agriculture and fossil fuel emissions are the principal human activities that create nitrogen. In the UK, for instance, the rate of deposition per year may range from five to 35 kg per hectare, with the highest rates occurring in densely-populated areas. The initial study showed that one plant species was lost for each additional 2.5 kg of nitrogen deposited per hectare and year.

The aim now is to gather similar data for other parts of Europe and also to find a way to maintain species richness in spite of nitrogen deposition.

Professor Dise's collaborator David Gowing from the Open University, said: "If we find a way, we can offer a management strategy for nature conservation."

Biomass stripping

One possible approach could be extra mowing and grazing, so called 'biomass stripping'.

The researchers also hope to be able to predict future developments: "Nitrogen deposition in Europe probably peaked in the 1990s, and is coming down now, in many places," Dr Gowing added. "Having been accumulating nitrogen for 40 years, we might be near the edge of a cliff where communities will suddenly change. Perhaps we will be able to say: you have another five years of accumulating at this rate, so now is the time to act."

The project started out as an Open University PhD study by Carly Stevens, now a post-doctoral researcher at MMU.

The study is part of the project 'Biodiversity of European grasslands - the impact of atmospheric nitrogen deposition (BEGIN)' funded under European Science Foundation's EuroDIVERSITY Programme.

For more information, contact Professor Nancy Dise on 0161 247 1593 or go to www.egs.mmu.ac.uk.