The gorge's species-rich grassland is vulnerable to global air pollution. (Grasslands page on this website)
Starter's Guide to Air Pollution link
Primary pollutants are gases and very small particles directly
emitted from sources such as power stations, incinerators, motor
vehicles and industrial farming.
Primary pollutants, mostly
sulphur and nitrogen compounds, are deposited eventually, by wet or
dry deposition, before or after chemical reactions forming secondary
pollutants. At ground level, photochemical reactions cause some primary
pollutants to form ground-level ozone, which is toxic to plants. Primary pollutants react with oxygen to form secondary
pollutant aerosols which travel in high air streams around the
world, and cause acid rain or background ground-level ozone far away from the primary source.
Despite recent reductions in UK air pollution, background levels of ozone
and nitrogen pollution in the UK continue to threaten biodiversity.
"There is strong evidence that
nitrogen deposition has reduced
(the number of different species)
in a range of
of high conservation value
over large areas of the UK."
"Ground level ozone
remains a threat
Some of the worst pollutants are the nitrous oxides, known as NOx (NO and NO2), which can fall as acid rain, and which are precursors for ground-level ozone. NOx pollution causes changes which make plants more susceptible to pests and weather extremes. link
Calcareous grasslands are sensitive to nutrient nitrogen, which causes increase in tall grasses and decline in diversity. Taller grasses increase the chance of thin soils drying out. link (Then if plants die from drought and footfall, the soils are more likely to blow away).
Air pollution causes changes in soil chemistry, including acidity, which may be toxic to plants and mycorrhiza (soil fungi). link
Ground level ozone may visibly injure foliage, or reduce plant growth rate. It may alter the species mix, by increasing the plants which tolerate ozone, and reducing plants susceptible to it. There is also a changed reaction to water stress. link
Page updated 11 Feb 2013