UK smog: Nitrogen doesn't just cause air pollution - it is a huge threat to Britain's wildlife too, experts warn

The amount of nitrogen stored in the soil as a result of soaring emissions from agriculture, power stations and cars is now so great it has reached critical levels (Getty Images)

The nitrogen pollution contributing to Britain’s smog poses the biggest threat to wildlife that the public has never heard of – with the potential to wipe out everything from clover to butterflies in eco-systems across the country – experts have warned.

The amount of nitrogen stored in the soil as a result of soaring emissions from agriculture, power stations and cars is now so great it has reached critical levels in the majority of non-agricultural land, according to Clare Whitfield, air pollution consultant at the government’s statutory conservation adviser.

Nitrogen-rich soil reduces biodiversity because it causes species which thrive on nitrates to flourish at the expense of those that don’t.

“Nitrogen represents a major threat to biodiversity in the UK and across Europe. It is an under-acknowledged and very big issue that has slowly crept up on us,” said Ms Whitfield.

The rapid accumulation of nitrogen in the soil has already damaged eco-systems across the country as thick outcrops of beneficiaries such as grass, heather, thistles and nettles “swamp out” a wide range of species such as flowers, bees, beetles, lizards, snakes and spiders by depriving them of water, space, light and the other conditions they need.

High levels of nitrogen also cause problems by leaching into groundwater which can impair the blood’s oxygen-carrying capacity in small infants causing “blue baby syndrome” and can be toxic for ruminants such as cattle and sheep.

The problem has got worse in recent years and, with the majority of eco-systems outside agriculture above the ‘critical load’ for nitrogen, that trend is set to continue, Ms Whitfield said. The critical load is the point beyond which the rate of nitrogen deposited from the air to the ground poses an increasing risk of habitat damage.

Once in the ground, nitrogen can remain for hundreds, even thousands of years while the level of accumulation is not measured and its potential impact not fully understood, experts said.

“The nitrogen level is building up all the time as we continue to add to the pot and increase the cumulative impact,” Ms Whitfield added.

Her comments will increase pressure on the government to get nitrogen levels under control two months after the European Commission launched legal proceedings against it for failing to reduce “excessive” levels of nitrogen dioxide air pollution from traffic, despite 15 years of warnings and several extensions and postponements granted to the government.

Other European countries have also failed to meet the air quality directive – that should have been adopted in 2008 – but the EU environment commissioner, Janez Potocnik, has singled out Britain for its “persistent” breaches of the air quality directive. The government has been sent a letter of the formal notice of the intention to take Britain to court the government has until next Friday (April 18th) to respond.

Unlike so-called natural and semi-natural habitats, which are generally harmed by rising nitrogen levels, farmland is benefitting from the increase – and fuelling it - because crops benefit enormously from nitrogen-rich fertilisers. Ammonia, a pungent colourless compound of nitrogen and hydrogen released by livestock exacerbates the problem.

“This is the biggest threat to biodiversity that the public is not aware of. For wildlife it really is a pernicious and pertinent cause of decline in very many species as the burning of fossil fuels turns the volume of nitrate falling onto habitats from a drizzle to a downpour,” said Matt Shardlow, head of the Buglife insect charity.

“The longer we keep pouring this into natural habitats, the more it accumulates and unless we can reverse the situation we can expect many of these declines to continue,” he added.

Getting nitrates out of the ground is a “real challenge”, Mr Shadlow said. Methods include a sustained programme of “cropping off” – or burning – and removing vegetation, or deep ploughing, when a tractor turns over the top metre of soil to bury the nitrates further underground.

Nitrogen emissions also need to come down, Mr Shardlow said. “There is no obvious sign of that happening at the moment but that could start to come down with hybrid and electric cars,” he said – but adds that even if that does happen, the accumulation of nitrates in the soil will be so high that it will still need to be dealt with.

A spokesman for the Department for Environment, Food and Agriculture (Defra) said: “Air quality has improved significantly in recent decades. Just like for other [EU] member states, meeting the NO2 (nitrogen dioxide) limit alongside busy roads has been a challenge.”

“That is why we’re investing heavily in transport measures to improve the air quality around busy roads and we are working with the Commission to ensure this happens as soon as possible,” he added.

The species being edged out by rising nitrogen levels in the soil

Wildflowers such as Bird’s Foot Trefoil and Clover which don’t thrive on nitrogen and get shaded out by the plants, which also consume the water

Bees and other pollinators suffer because fewer flowers mean less nectar

Grasshoppers may eat grass but they still suffer when too much of it takes over their environments, because they like to lay their eggs in the bare ground so they can be exposed to the sunlight and grow.

Cirl buntings are hindered because they eat grasshoppers, which are in decline

Capercaillie and black grouse suffer because their chicks get trapped in the cold, dense, wet heather

Caterpillars suffer because the increase in plants makes the ground colder

Reptiles such as lizards and snakes are hurt by the loss of the bare ground they need to bask in

Butterflies such as the Large Blue and Silver spotted Skipper suffer because they need large, bare habitats to survive

Insects such as beetles and ants, which require warm chalky or sandy ground on which to nest, suffer from dense vegetation