The environmental or polluting aspects of nitrogen in relation to livestock farms are gaseous losses to the atmosphere, nitrate leaching into water supplies and the eutrophication of surface waters. Gaseous losses of ammonia by volatilisation from organic materials and denitrification losses from soil as nitrogen and nitrous oxide have been at various times implicated in acid rain, photochemical smogs and effects on the ozone layer although the latter is now largely discounted. Nitrate leached from soil may pass rapidly into surface waters where it can affect quality for drinking or encourage algal blooms. Over porous strata nitrate may take many years to percolate downwards so as to pollute groundwater supplies. Restrictions may face livestock farmers in the arable areas of eastern England to restrict nitrate leaching from their land.