A6: Exceedance of damaging levels of nutrient nitrogen deposition on ecosystems
Short Description
This indicator shows changes in the percentage of sensitive habitats exceeding the internationally agreed thresholds for harmful effects (critical load) of nutrient nitrogen deposition. The damaging nutrient nitrogen comes predominantly from UK emissions of ammonia (NH3), but partly from UK emissions of nitrogen oxides (NOx) and long-range transport of these air pollutants.
This indicator is an assessment of clean air (reporting the condition of the atmosphere as an asset). Nutrient nitrogen deposition can also be considered as a pressure on thriving plants and wildlife. The first component of this indicator is determined by calculating the area of sensitive habitat exceeding the internationally agreed thresholds for likely damaging effects from reactive nitrogen deposition in both oxidised and reduced forms, termed the critical load. It uses modelled interpolations of atmospheric concentrations of NOx and NH3 and models deposition processes based on internationally agreed methodology. The second component of this indicator measures the magnitude of the nutrient-nitrogen exceedance.
Readiness and links to data
Assessments of nutrient nitrogen deposition are undertaken and published annually using 3-year moving average data at UK Air Information Resource: Trends in critical load and critical level exceedances in the UK. Component A6i shows the percentage area of sensitive habitats in England where nutrient nitrogen deposition exceeded the internationally agreed thresholds for likely damaging effects from reactive nitrogen deposition in both oxidised and reduced forms, termed the critical load. In the 2025 update of this indicator, component A6ii was introduced to show the magnitude of the nutrient-nitrogen exceedance (expressed as average accumulated exceedance, or excess nitrogen) across England.
Notes on indicator
The 13 nitrogen-sensitive habitat types included in this indicator are acid grassland, calcareous grassland, dwarf shrub heath, montane, bog, Scots pine woodland, managed coniferous woodland, beech woodland, acidophilous oak woodland, other broadleaved woodland, mixed woodland, dune grassland, and saltmarsh. In total, these habitats amount to approximately 26,000 square kilometres (almost 20% of the land area of England).
Indicator components
Figure A6i: Exceedance of damaging levels of nutrient nitrogen deposition in England, 2002-2004 to 2020-2022
Table A6i: Exceedance of damaging levels of nutrient nitrogen deposition in England, 2002-2004 to 2020-2022
| Year | Value |
|---|---|
| 2002-2004 | 100.00 |
| 2003-2005 | 100.00 |
| 2004-2006 | 100.00 |
| 2005-2007 | 100.00 |
| 2006-2008 | 99.90 |
| 2007-2009 | 99.90 |
| 2008-2010 | 100.00 |
| 2009-2011 | 100.00 |
| 2010-2012 | 100.00 |
| 2011-2013 | 100.00 |
| 2012-2014 | 100.00 |
| 2013-2015 | 100.00 |
| 2014-2016 | 100.00 |
| 2015-2017 | 99.90 |
| 2016-2018 | 100.00 |
| 2017-2019 | 100.00 |
| 2018-2020 | 100.00 |
| 2019-2021 | 99.90 |
| 2020-2022 | 99.30 |
Trend description for A6i
The percentage area of sensitive habitats in England where nutrient nitrogen deposition exceeded critical load remained between 99.9% and 100.0% from 2002-2004 to 2019-2021 (3-year moving average time periods). In the most recent time period, 2020-2022, the percentage area fell to 99.3% - the lowest value in the time series so far. Nutrient nitrogen deposition has fallen, but still exceeds the thresholds of harm. See component A6ii for more information on the magnitude of the nutrient-nitrogen exceedance.
Assessment of change
There has been little or no change observed in exceedance of damaging levels of nutrient nitrogen deposition on ecosystems over the short-, medium- and long-term assessment periods.
There has also been little or no change observed in exceedance of damaging levels of nutrient nitrogen deposition on ecosystems since the 2016-2018 period. However, this result is based on only 5 data points so should be considered as indicative and not evidence of a clear trend.
Further information on this assessment, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results pages.
Table A6i: Assessment of change
| Component | Period | Date range | Percentage change | Smoothing function | Assessment of change |
|---|---|---|---|---|---|
| A6i | Short term | 2015-2017 to 2020-2022 | -0.60 | Moving average data | Little or no change |
| A6i | Medium term | 2010-2012 to 2020-2022 | -0.70 | Moving average data | Little or no change |
| A6i | Long term | 2002-2004 to 2020-2022 | -0.70 | Moving average data | Little or no change |
Note that percentage change refers to the difference seen from the first to last 3-year moving average in the specified date range.
Figure A6ii: Excess deposition of nutrient nitrogen in England, 2002-2004 to 2020-2022
Table A6ii: Excess deposition of nutrient nitrogen in England, 2002-2004 to 2020-2022
| Year | Value |
|---|---|
| 2002-2004 | 19.20 |
| 2003-2005 | 18.90 |
| 2004-2006 | 18.80 |
| 2005-2007 | 18.60 |
| 2006-2008 | 18.10 |
| 2007-2009 | 17.40 |
| 2008-2010 | 17.10 |
| 2009-2011 | 17.90 |
| 2010-2012 | 17.60 |
| 2011-2013 | 17.80 |
| 2012-2014 | 17.10 |
| 2013-2015 | 17.30 |
| 2014-2016 | 17.00 |
| 2015-2017 | 16.00 |
| 2016-2018 | 16.40 |
| 2017-2019 | 16.90 |
| 2018-2020 | 16.80 |
| 2019-2021 | 14.50 |
| 2020-2022 | 14.30 |
Trend description for A6ii
The magnitude of the nutrient-nitrogen exceedance (expressed as average accumulated exceedance, or excess nitrogen) across England has fluctuated over the last 2 decades, but overall it has decreased by 26%, from 19.2 kg per hectare per year (kg/ha/year) in the 3-year moving average time period 2002-2004 to 14.3 kg/ha/year in 2020-2022. However, it still exceeds the thresholds of harm.
Assessment of change
There has been a decrease (improvement) in the deposition of excess nutrient nitrogen over the short-, medium- and long-term assessment periods.
There has also been an improvement in the deposition of excess nutrient nitrogen since 2016-2018. However, this result is based on only 5 data points so should be considered as indicative and not evidence of a clear trend.
Further information on this assessment, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results pages.
Table A6ii: Assessment of change
| Component | Period | Date range | Percentage change | Smoothing function | Assessment of change |
|---|---|---|---|---|---|
| A6ii | Short term | 2015-2017 to 2020-2022 | -10.62 | Moving average data | Improvement |
| A6ii | Medium term | 2010-2012 to 2020-2022 | -18.75 | Moving average data | Improvement |
| A6ii | Long term | 2002-2004 to 2020-2022 | -25.52 | Moving average data | Improvement |
Note that percentage change refers to the difference seen from the first to last 3-year moving average in the specified date range.