An invisible threat could change Britain’s landscapes

Feb 12, 2005

People and farm animals are helping an invisible pollutant to change the types of plants that grow in Britain, particularly in remote and rural regions such as the Lake District.
Nitrogen deposits are the cause of the problem. The dung from farm animals produces vast quantities of ammonia. Since the industrial revolution, burning fuels (coal, gas, petrol) has lead to massive emissions of nitrogen oxides into the atmosphere. These practices lead to ammonia and nitrates being deposited back onto the land, acting as fertilisers and acidifying soils.

Scientists working on the NERC-funded GANE (Global Atmospheric Nitrogen Enrichment) research initiative will be presenting the results of their investigations into this unseen and largely unnoticed problem at a conference in London next week.

Professor Alan Davison, Co-ordinator of the research programme, said, “What most people don’t realise is that they are helping to change areas like the Pennines or the Lake District, which are considered to be unspoilt. Their cars are small ‘fertiliser factories’ so every time they start the engine nitrate is released and can be carried over long distances before falling on plants and soils.”

He added, “The chicken and pork that we eat has played a part in contributing to the ammonia that is changing the biodiversity in our countryside. I wonder if farmers, including organic growers, understand that their land is receiving a significant amount of ‘free’ fertiliser.”

Nitrogen cascades through the environment like no other pollutant and at the right level is good – plants depend on the use of nitrogenous fertilisers. But this extra nitrogen is providing an environment for ‘takeover bids’ on the land from more aggressive plant species. The winners are the plants that can mop up nitrogen – grasses, brambles and nettles. They will move in on slower growing plants that live in habitats where low levels of nitrogen are more usual - heather moorland will become grassland, for example. These are often the species in our countryside that we try to conserve.

Land is not the only element affected. It has always been thought that freshwater lakes are immune to the effects of additional nitrogen but GANE researchers have shown that this is not the case. There are nitrogen-sensitive lakes and their plant life may well be at risk from nitrogen deposition.

The extra nitrogen is not just acting on a local scale. It increases the emission from soil and water of the potent greenhouse gas, nitrous oxide.

Findings from the research are not all gloomy – there is good news to be reported as well. GANE scientists have produced a clearer picture of the sources and rates of emission of this gas that will help the UK fulfil its International obligations for reductions. To estimate emissions on a large scale it is necessary to use an ‘emission factor’. The GANE scientists have shown that the UN’s Intergovernmental Panel on Climate Change’s emission factor for ground and drainage waters overestimates nitrous oxide emissions. Only 0.2% of the nitrate in water, not 1.5%, is emitted as nitrous oxide.

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