B5. Pressure from pollution

B5a. Air pollution

i. Area affected by acidity

ii. Area affected by nitrogen

 

Type: Pressure Indicator

 

Indicator Description

The air pollutants – sulphur dioxide, nitrogen oxides and ammonia – can contribute to acidification, and nitrogen oxides and ammonia can contribute to terrestrial eutrophication.  Critical loads are thresholds above which significant harmful effects may occur on sensitive UK habitats.  The pollutants arise mainly from burning fossil fuels, industry, road transport, and emissions from livestock waste.  Around a third of UK land area is sensitive to acidification, and a third to eutrophication (with some areas sensitive to both).   A three-year average of deposition is used to calculate the exceedance of critical loads to give the figures for each year represented.

Summary

 

Areas of sensitive UK habitats that exceed critical loads for acidification and eutrophication have continued to decline since 1996.  The rate of decrease has slowed for both acidification and eutrophication in the short term (since 2009) with acid deposition exceeding critical load in 44% sensitive habitats in 2014 and nitrogen deposition exceeding critical loads in 63% of sensitive habitats in 2014.

 

Figure B5ai.  Area of sensitive UK habitats exceeding critical loads for acidification and eutrophication, 1996 to 2014.

Figure B5ai. Area of sensitive UK habitats exceeding critical loads for acidification and eutrophication, 1996 to 2014.

Notes:

  1. Each column represents critical load exceedances based on a three-year average of deposition data to reduce year-to-year variability.
  2. Since 2002, nitric acid has been included in the estimates of nitrogen deposition, and since 2003 aerosol deposition of sulphate, nitrate and ammonium have also been included.  This additional deposition led to some increases in critical load exceedance compared with earlier periods.
  3. There was a revision to the calculation of deposition data for the period 2004 to 2013 in 2015, which means the exceedance results for this period are not directly comparable to those previously published.

 

Source: Centre for Ecology & Hydrology.

 

Assessment of change in area of sensitive habitat exceeding critical loads

 

Long term

Short term

Latest year

Area affected by acidity

indicator improving
1996–2014

2010 indicator stable2009–2014

No change (2014)

Area affected by nitrogen

indicator improving
1996–2014

2010 indicator stable2009–2014

No change (2014)

 

 

Critical loads are thresholds for the deposition of pollutants causing acidification and/or eutrophication above which significant harmful effects on sensitive UK habitats may occur.  Approximately 78,000km2 of UK terrestrial habitats is sensitive to acid deposition.  About 73,000km2 is sensitive to eutrophication; much of this is sensitive to both.

In 1996, acid deposition exceeded critical loads in 73% of the area of sensitive habitats.  This declined to 44% in 2014.  There has been a slight decrease in the area affected over the short term, since 2009, when the figure was 45%.

In 2014, nitrogen deposition exceeded critical loads in 63% of sensitive habitats.  This was a decrease from a level of 75% in 1996.  However there was no change in the short term, since 2009 when the figure was also 63%.

Based on these figures the habitat areas at risk from acid and nitrogen deposition has declined over the long term (1996 to 2014), however, reducing deposition below the critical loads does not necessarily mean that ecosystems have recovered, as there can be a time-lag before both chemical and biological recovery occurs

 

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Last updated: August 2017

Latest data available: 2014 (2013 – 2015)