Atmospheric nitrogen (N) pollution is one of the main causes of biodiversity loss, but is often unrecognised as its effects are insidious and gradual. Nitrogen deposition causes acidification of soils, increases growth of tall and competitive plant species at the expense of smaller-growing wildflowers, and has direct damaging effects on many species. It has become increasingly apparent that many of the effects of N are long-term. Nitrogen tends to accumulate in soils, resulting in a drip-feeding of plant-available N over many years.
Sensitive species have already been lost over much of the UK, but the damage is progressive and there clear benefits of reducing N deposition rates for biodiversity conservation. However, current metrics for assessing the impacts of N deposition are rather insensitive to reductions in N deposition rates. The project will review research on the effects of cumulative and acute N deposition, and reductions in N load, and recommend a metric or metrics that are more responsive and reflect the benefits of marginal reductions in N deposition.
The effects of current N deposition are likely to be modified by the history of deposition of N onto the habitat in question. On chronically polluted sites, the mineralisation of plantavailable N from accumulated stocks in soil adds to the effects of current deposition. Together with limited rates of recolonisation of sensitive species, this means that habitats are unlikely to recover to a pristine condition quickly, even after a reduction in deposition. However, reducing deposition can rapidly reduce N availability in soil and leaching of nitrate, so some benefits are immediate. The challenge in policy terms is to characterise these benefits realistically whilst taking into account the effects of previous long-term N pollution.
The project will assess geographical variation in current and cumulative N deposition, allowing differences in pollution histories of England, Northern Ireland, Scotland and Wales to be taken into account.
The consortium, led by Centre for Ecology and Hydrology, includes UK experts on air pollution impacts from CEH, the James Hutton Institute, Lancaster University and Manchester Metropolitan University. The range of expertise is essential to fully assess current knowledge of cumulative impacts of N and recovery from N pollution, and to develop metrics that are readily applicable and capture the benefits of reductions in deposition on chronically polluted and more pristine sites. The work will help the UK meet international biodiversity conservation targets, by assisting with policy development aimed at placing sensible limits on N pollutant emissions.