19. Pollution: air and marine

Question 1

Introduction

Accepted Answer

The first part of this indicator shows changes in pressures on biodiversity from air pollution in England. The air pollutants sulphur dioxide, nitrogen oxides and ammonia can contribute to acidification; nitrogen oxides and ammonia can also contribute to terrestrial eutrophication. These pollutants arise mainly from emissions from livestock waste, burning fossil fuels in industry, and road transport.

Approximately 23,000 km² of terrestrial habitat areas in England are sensitive to acidification and about 26,000 km² are sensitive to nutrient nitrogen deposition (eutrophication); many areas (almost 14,000 km²) are sensitive to both. Critical loads are thresholds for pollutant load above which significant harmful effects may occur on sensitive habitats; statistics on critical load exceedance indicate the risk of damage. To reduce the effects of variation in meteorology, exceedance statistics are reported as the mean of three years of data and time periods are referred to using the middle year of the three. For example, “2020” means the period 2019 to 2021.

The second part of this indicator shows changes in pressures on marine biodiversity from waterborne pollution in the UK (separate England figures are not currently available). It provides the combined input of 6 of the most hazardous substances to the UK marine environment: 5 heavy metals (cadmium, mercury, copper, lead and zinc); and one organic compound (lindane). Pollution in the marine environment from these 6 substances should decrease to levels that are non-detrimental by 2020. For this indicator, the most recent data is from 2019.

Due to recent data availability it has not been possible to update this indicator beyond 2019. This indicator uses annual averages so to be representative of the real life conditions it is important to capture seasonal patterns in the monitoring otherwise the averages would be skewed. The coronavirus pandemic severely impacted monitoring efforts during 2020. In England, no riverine monitoring was carried out during the months of April through to September and sampling from October to December was extremely limited compared to previous years. Similarly in Northern Ireland, no monitoring was carried out in April and May and in Wales monitoring was not possible between from April to July. This is expected to have a significant impact on the 2020 data, and it has therefore not been included in the indicator.

There was also reduced monitoring in 2021 compared to previous (pre-pandemic years). This was due to a number of factors including prioritisation of resources within the UK Administrations. The incompleteness of the data due to this reduction in monitoring affected the data quality and made 2021 inputs appear artificially low compared to previous years. The 2021 data has therefore not been included in the indicator.

Due to a complex cyber-attack that took place in December 2020, it is not possible to report 2020 or 2021 monitoring data for Scotland.

Type of indicator

Pressure indicator

Question 2

Assessment of change

Accepted Answer

(a) i. Area affected by acidity:

Long term (2003 to 2020): Improving
Short term (2015 to 2020): Improving
Latest year (2019 to 2020): Decreased

(a) ii. Area affected by nutrient nitrogen:

Long term (2003 to 2020): Little or no change
Short term (2015 to 2020): Little or no change
Latest year (2019 to 2020): Little or no change

(b) Combined input of hazardous substances to the UK marine environment:

Long term (1990 to 2019): Improving
Short term (2014 to 2019): Improving
Latest year (2018 to 2019): Increased

Notes on indicator assessment

Short-term assessments are based on a direct comparison of the 2 relevant data points using a 3% rule of thumb. See Assessing Indicators.

Question 3

19a.  Air pollution

Accepted Answer

Trend description for Figure 19.1

There have been two changes to the methods used to prepare the 2023 update of this indicator (see the ‘Background’ section and the technical background document for details of these changes).

There was a 14% decrease in the percentage of sensitive terrestrial habitat areas in England exceeding the critical load for acidification between 2003 and 2020, whereas there was little or no change in the percentage of areas exceeding the critical load for nutrient nitrogen deposition (eutrophication). In 2020, acid deposition exceeded critical load for acidification in 67% of sensitive terrestrial habitats and nitrogen deposition exceeded critical load for eutrophication in 100% of sensitive habitats.

Figure 19.1: Percentage area of sensitive terrestrial habitats in England where critical loads for acidity and nutrient nitrogen were exceeded, 2003 to 2020

Source: UK Centre for Ecology & Hydrology

Download the data for Figures 19.1 in ods format

Notes about Figure 19.1:

Each bar represents a rolling 3-year average of deposition data to reduce the effects of year-to-year variation in meteorology; each period is referred to by the middle year of the 3, for example, ‘2020’ refers to the period 2019 to 2021.
Changes to the methodology mean that the time-series could be extended back to 2003, rather than to 1996 as in previous publications (see ‘Background’ section). These changes also mean that the chart presented here cannot be directly compared to those presented in previous publications of this indicator.

Critical loads are thresholds for the deposition of pollutants causing acidification and/or eutrophication above which significant harmful effects on sensitive habitats may occur. Approximately 23,000 km² of terrestrial habitats in England are sensitive to acid deposition. About 26,000 km² is sensitive to eutrophication; many areas (around 14,000 km²) are sensitive to both.

In 2003, acid deposition exceeded critical loads in 77.3% of the area of sensitive terrestrial habitats in England. This declined to 66.5% in 2020. The short-term trend between 2015 and 2020 was a 6% decrease in the area affected by acidity. In 2020, nitrogen deposition exceeded the critical load for eutrophication in 100% of sensitive habitats in England. This percentage was the same in 2003. In the short term, the area where nitrogen deposition exceeded critical load showed little or no change between 2015 and 2020.

Question 4

19b.  Marine pollution

Accepted Answer

Trend description for Figure 19.2

The combined inputs of all 6 of the hazardous materials included within this indicator have shown a long-term decrease of 78% since 1990 (Figure 19.2). In the short term (since 2014), inputs of 5 out of 6 of these substances show decreases; one heavy metal (zinc) has increased.

Figure 19.2: Combined input of hazardous substances to the UK marine environment, as an index of estimated weight of substances per year, 1990 to 2019

Download the data for Figure 19.2 in ods format

Source: Defra Marine Strategy and Evidence Division, using data provided by: Environment Agency, Northern Ireland Environment Agency and the Scottish Environment Protection Agency.

Levels of all 6 substances declined over the period 1990 to 2019. The heavy metals, mercury, cadmium, lead, copper and zinc decreased by 91%, 88%, 59%, 59% and 55%, respectively. The organic compound lindane decreased by 86% (Figure 19.3).

In the short-term, the combined inputs of all 6 hazardous substances decreased by 18% from 2014 to 2019 (using a 3-year average for 2014). Inputs for 5 out of the 6 of the hazardous substances declined in the short-term: lindane had the highest percentage decrease (-44%), cadmium decreased by 31%, mercury by 26%, copper by 8% and lead by 6%. By contrast, zinc increased by 17%.

Figure 19.3: Inputs of hazardous substances to the UK marine environment, as an index of weight of substance per year, 1990 to 2019

Download the data for Figure 19.3 in ods format

Source: Defra Marine Strategy and Evidence Division, using data provided by: Environment Agency, Scottish Environment Protection Agency, and Northern Ireland Environment Agency

The detection limits for analysis have gradually decreased over the period of 1990 to 2023. This is likely to have caused an overestimation in the input levels for early years compared to more recent years, leading to the reported decreases being overestimates.

Question 5

Relevance

Accepted Answer

The indicator shows progress with commitments to reduce pressure from a range of sources as set out in Annex A of Biodiversity 2020: A strategy for England’s wildlife and ecosystem services. The indicator is also relevant to international goals and targets (see Annex B of the aforementioned publication).

The UK and England Biodiversity Indicators are currently being assessed alongside the Environment Improvement Plan Targets,and the new Kunming-Montreal Global Biodiveristy Framework Targets, when this work has been completed the references to Biodiversity 2020 and the Aichi Global Biodiversity Framework Targets will be updated.

Question 6

Background

Accepted Answer

Air pollution

Critical loads are thresholds above which significant harmful effects on sensitive habitats may occur, according to current levels of scientific understanding. Critical loads have been established separately for acidification and nutrient nitrogen (eutrophication effects). The pollutants causing acidification and eutrophication mainly arise as a result of emissions from livestock waste, burning fossil fuels in industry, and road transport.

The 3 main steps in the assessment of the area of sensitive habitat exceeding critical loads are:

calculation of critical loads for each of the sensitive habitats
mapping of the habitats; and
identification of the area of habitat where deposition exceeds the critical load

While these 3 main steps remain valid, there have been two changes to the underlying methodology for the 2023 update of this indicator:

Critical loads for nutrient N were reviewed and revised in 2022, and the new values have been applied in 2023.
A calibration step has been introduced to ensure that outputs from the atmospheric chemistry and transport model used to estimate ammonia concentration are closely matched to measured concentrations from the UK Ammonia Monitoring Network.

Values have been recalculated for previous years back to 2003 (2002 to 2004) using the revised methods, to allow time series to be reported with consistent methodology.

The values of the metrics reported in the 2023 update of this indicator have changed, in some cases considerably, from those reported in the 2022 update, but the trends in air pollution pressure over time are similar using the old and new methods. For example, in the UK as a whole, exceedance statistics for acidification reported under the new methodology are approximately 4% lower than those reported under the old methodology. Exceedance statistics for eutrophication in the UK overall are approximately 20% higher, due the more precautionary values for empirical critical loads agreed in the 2022 review.

Table 19.1: The 14 habitats considered sensitive to acidification and /or eutrophication for which critical loads are calculated

Habitat	Critical loads calculated for acidification	Critical loads calculated for eutrophication
Acid grassland	Yes	Yes
Calcareous grassland	Yes	Yes
Dwarf shrub heath	Yes	Yes
Bog	Yes	Yes
Montane	Yes	Yes
Coniferous woodland	Yes	Yes
Beech woodland	No	Yes
Oak woodland on acid soil	No	Yes
Scots pine	No	Yes
Dune grassland	No	Yes
Saltmarsh	No	Yes
Mixed woodland	No	Yes
Freshwaters	Yes	No
Broadleaved and mixed woodland	Yes	No

Further information on how critical loads are calculated and detailed critical load exceedance maps are available in the technical background document and on the Critical Loads and Dynamic Modelling website.

Critical loads for acidification and nutrient nitrogen have also been applied to interest features of protected sites (Special Areas of Conservation, Special Protection Areas and Areas/Sites of Special Scientific Interest). Further information on critical load exceedance on protected sites is available in the Trends Report 2022 and on the Air Pollution Information System (APIS) website.

Marine pollution

Inputs into the marine environment are estimated from concentrations and flow rates in rivers entering the sea and those from estuarine and coastal point sources. Riverine inputs reflect both point and diffuse sources upstream of the sampling point and tend to be strongly influenced by flow rates. Flow rates are heavily affected by rainfall patterns so year to year fluctuations in pollutant loads are likely. A detailed illustration of changing levels of each input is seen in Figure 19.3. The low point in 2003 is thought to be a consequence of reduced river flows during an exceptionally dry year. Conversely, levels increased in 2012 and again in 2014 corresponding with years of heavy rainfall. In 2012, England had the wettest year since records began in 1910; the summer was the wettest since 1912. Increased rainfall in November and December contributed to extensive flooding. In 2014, the winter period (January to February) was the wettest since records began.

The data presented relate to the UK as a whole; separate data are not readily available for England. Although data for total UK (direct plus riverine) inputs to the marine environment are available as lower and upper estimates, for ease of interpretation only upper (that is, maximum) values have been used in this assessment, rather than presentation of the data range for each substance.

Web links for further information

Defra: Trends Report 2023
Defra: Clean Seas: hazardous substances
Defra: Marine Strategy Framework Directive
Defra: Technical Background Document - air pollution
OSPAR: Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR)
UK Centre for Ecology & Hydrology: Critical Loads and Dynamic Modelling
United Nations Economic Commission for Europe: Convention on Long Range Transboundary Air Pollution

19. Pollution: air and marine

Applies to England