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GROUP 1 Atmospheric Deposition

Working group members and contributors

Atmospheric deposition

Outline of the issue

Introduction

2.1 Soil is a major sink for atmospheric pollutants that can protect both the water and air environments. It can buffer the release of pollutants into water courses or back into the atmosphere. Soil also has an important role in the biogeochemical cycles of carbon and nitrogen, and atmospheric deposition can influence this role. Some of the main threats to soil from atmospheric deposition lie in the processes of acidification and eutrophication of soils, and also soil contamination by heavy metals and Persistent Organic Pollutants ( POPs).

Sources

2.2 Combustion processes and agriculture are the main sources of widespread atmospheric pollutants.

Table 2.1 Sources of main pollutants

Fromwww.apis.ac.uk

2.3 Atmospheric pollution can be deposited at the local scale around a point (farm, factory) or linear (road) source. On a regional scale (<100km) pollutants are deposited in precipitation. Additionally some pollutants are emitted from high stacks, which can be transported over many 100s of kilometres and can in effect cross country boundaries. Transboundary effects are important as over 40% of the deposited oxidised sulphur comes from sources outside the UK, 60% of NOx comes from outside the UK while only 30% of reduced nitrogen is imported ( EMEP, 2007).

Current trends ( NAEI, 2007)

• Between 1970 and 2004 SO ₂ emissions have decreased by 87% (6 Mt of SO ₂ to less than 1 Mt)
• Between 1970 and 2004 NOx emissions have decreased by 47%, and
• Between 1990 and 2004 NH ₃ has decreased by only 12%. The current ratio between reduced N and oxidised N emissions in the UK is 2:1 (Fowler, 2001).

Issues

2.4 Atmospheric deposition to terrestrial and freshwater ecosystems can have a range of detrimental effects including loss of biodiversity and ecosystem functions, as well as the loss of valuable ecosystem services required for human wellbeing and health such as water purification and carbon sinks e.g. in peatlands. Some of the important issues include acidification, eutrophication and contamination from heavy metals and POPs.

Impact on soils

Introduction

2.5 Soil organisms undertake many key processes in ecosystems. Two of the most important are the breakdown and mixing of organic matter (including natural Carbon compounds in the form of litter as well as anthropogenic pollutant sources such as POPS, etc) and mineralisation (i.e. conversion of organic matter into more mobile, easily available inorganic nutrients).

2.6 Many of these processes produce important radiatively forcing greenhouse gases notably carbon dioxide (CO ₂), methane (CH ₄) and nitrous oxide (N ₂O) that can have damaging impacts on the environment. Release of CO ₂ from soils contributes around ten-times more carbon to the atmosphere than fossil fuel burning (Raich et al., 2002). Determining how atmospheric pollutants impact on soil organisms and the processes they undertake and regulate is of national and global relevance.

Acid Deposition and Soil Acidification

2.7 One of the most important chemical functions of the soil is to buffer acidity. This is achieved through cation-exchange sites, mostly provided by organic matter, to which cations (positively charged ions) attach. Leaching of 'mobile' acid anions such as nitrate and sulphate from the soil will deplete base cation stores within the soil, leading to soil and water acidification. Mineral weathering can replenish the base cations and hence slow down or completely buffer the effects of acidification.

Soil Acidification Impacts

• Species composition changes, and loss of species that are unable to function under more acidic conditions, can be a major issue for soil microbial processes e.g. nitrification, methanogenesis.
• Nutrient release and leaching due to acidification causes potential impacts for freshwater lakes and water courses via eutrophication.
• The existence of high levels of soluble Al ³⁺ at low pH values disrupts cell walls and membranes in plant roots and inhibits nutrient uptake especially P and Ca (Kennedy, 1992). Ecosystems on weakly buffered soils are at risk.
• High Al ³⁺ concentrations are toxic to earthworms in the soil and fish in freshwaters, and can affect drinking water quality (e.g. Battarbee, 1984).
• Increased solubility and mobility of heavy metals makes them more available for plant uptake and thus likely to enter the food chain.

2.8 There is mounting evidence of a link between recovery from acidification and rising dissolved organic carbon ( DOC) export to surface waters, indicative of a change in soil function (either a change in capacity to retain carbon, or a shift in the form of carbon loss from gaseous CO ₂ to DOC). These changes should be borne in mind in protection of surface waters (in addition to climate-change and land-management issues). However it is worth noting that higher DOC concentrations in surface waters cannot be viewed as uniformly detrimental (although they present significant challenges for water supply); the link to recovery from acidification may imply that waters are in the process of returning to their more highly-coloured natural (i.e. pre-industrial) state.

Nitrogen Deposition, Eutrophication and Biogeochemical Cycling

2.9 In the soil, nitrogen can impact microorganisms both directly and indirectly. Direct effects result from nitrogen toxicity and from stimulation of metabolic activity, while indirect effects occur via plants. Direct toxic effects are only likely to be observed under very high deposition loads such as occur near point sources of atmospheric nitrogen emissions (e.g. intensive livestock units). Indirect pathways in contrast are more diffuse, and include effects caused by changes in plant litter type, quality and quantity, changes in the flux of carbon from roots to microbes via bulk soil, and direct flux of carbon to microorganisms colonising roots (i.e. mycorrhizal fungi and pathogens).

Figure 2.1 The Nitrogen Cascade (From UNEP, 2004).

2.10 In the semi-natural ecosystems, including the soil, atmospheric N deposition provides a substantial increase in mineral N input, which can be taken up by the plant and microbial biomass, stored as soil N or nitrified and denitrified to gaseous products of NO and the greenhouse gas N ₂O, and the inert gas N ₂ in the same manner as for agricultural fertilized soils (Skiba et al., 2000, 1997). In agricultural N fertilised systems the impact of relatively small additional N inputs by atmospheric deposition cannot be separated from the much larger impact N fertilisation has on NO ₃ leaching and NO and N ₂O emissions. When soils are exposed to large rates of N deposition, ecosystem N sinks become less effective, and NO ₃ leaching and N trace gas emission rates increase (Skiba et al., 1998 a&b Rennenberg et al., 1998). This process of 'nitrogen saturation' typically occurs more rapidly in thin soils with a low organic matter content, which are less able to store additional N (Evans et al., 2006a)

2.11 The chemical reactions of anthropogenic nitrogen as it cycles through various environmental reservoirs in the atmosphere, terrestrial ecosystems, and aquatic ecosystems, is magnified with time as reactive N moves along this biogeochemical pathway. This has been described as a 'nitrogen cascade' (Galloway et al., 2003) and is represented in Figure 2.1.

EutrophicationImpacts

• An increase in the availability of N to the nitrifying and denitrifying microbial community, thereby potentially increasing the rate of greenhouse gas emissions e.g. N ₂O, and the O ₃ precursor NO.
• Alterations to soil capacity to sequester carbon. This is difficult to predict with certainty, but in more organic soils, increases in above-ground productivity and decreases in long-term litter degradability with elevated N have been shown to increase ecosystem Carbon stocks (e.g. Magnani et al., 2007; Evans et al., 2006b). Pollution of ground water and drinking water due to nitrate leaching;
• Losses of both inorganic and organic N from terrestrial systems may contribute to freshwater, coastal and marine eutrophication (Hornung et al., 1995).
• N deposition can be detrimental to the mycorrhizal symbioses, which facilitate access to and the uptake of nutrients that are otherwise unavailable to plants in semi-natural (e.g. forest, moorland and species-rich grassland) and organic agricultural systems.
• Changes in species composition with the loss of high conservation value species, which can also impact on ecosystem function. Bogs are particularly at risk if they lose Sphagnum mosses, which may severely damage their capability to act as a Carbon sink, counteracting the impact of N on Carbon sequestration noted above.
• Competition from invasive species - often grasses pose a threat for many communities.
• Plant and microbial uptake removes a varying proportion of N deposition, the excess can potentially acidify the soil. N uptake is potentially acidifying depending on the form of N and the amount of growth stimulation will also deplete the base cation resource.

Heavy Metals

2.12 The heavy metal content of soils is a result of the naturally occurring soil forming mineralogy and anthropogenic inputs. Potential consequences of elevated soil heavy metal levels are perturbation of the Carbon and N cycle and soil respiration, and reduction in functional diversity (Scottish Executive, 2006). Soil microbial biomass, which plays an important role in nutrient cycling and ecosystem sustainability, has been found to be sensitive to increased heavy metal concentrations in soils (Giller et al., 1998). Research has shown a decrease in the soil microbial biomass Carbon and N as a result of long-term exposure to heavy metal contamination (Knight et al, 1997).

2.13 Soil properties such as pH, bulk density and organic matter influence the availability of heavy metals and as such their uptake by plants (Environment Agency UK Soil and Herbage Pollutant Survey, Report No. 7, 2007).

Heavy metal impacts

• Heavy metals accumulate in organisms as a result of direct uptake from the surroundings across the body wall, from the air and from food. Uptake via food is most important in terrestrial organisms and it may also be important in the aquatic environment.
• Metals exert toxic effects if they enter into biochemical reactions in the organism and typical responses are inhibition of growth, suppression of oxygen consumption and impairment of reproduction and tissue repair.

Persistent Organic Pollutants ( POPs)

2.14 In the soil PolyChlorinated Biphenyls ( PCB) and other POPS may be either degraded by soil micro-organisms, adsorbed by soil organic matter or re-emitted by volatilisation (Environment Agency UK Soil and Herbage Pollutant Survey, Report No. 9, 2007). Adsorption by soil organic matter is an important retention mechanism for POPs in soil. Calculations suggest that soils in the UK may now be net sources of the lower PCB congeners but still net sinks for the heavier congeners (Cousins and Jones, 1998). However, a more recent study concluded that UK soils are still net sinks of PCBs 28, 153 and 180 (Dalla Valle et al., 2005).

2.15 Polycyclic Aromatic Hydrocarbons ( PAHs) movement from soil to plants via root uptake is not believed to be a major pathway for transferring PAHs to vegetation (Wild and Jones, 1995) because PAHs are strongly retained by soil organic matter.

2.16 Vegetation differs from soil in that it responds more quickly to changes in atmospheric burdens and deposition. Concentrations in soil of POPs such as PAHs, PCBs and dioxins show a marked time lag in their response. Thus, vegetation is a more sensitive indicator of changes (both increases and decreases) in atmospheric levels of such compounds (Environment Agency UK Soil and Herbage Pollutant Survey, Report No. 9, 2007). However, the majority of POPs partition into the soil phase as opposed to vegetation.

Persistent organic Pollutants Impacts

• POPs are toxic, persistent and tend to bioaccumulate.
• PAHs in some lake sediments is high enough that sediment-dwelling organisms (midge larvae, oligochaetes, crustacea) may be affected (Sanders et al., 1996; Rippey, 1990).
• The tendency of POPs to bioaccumulate means that it is predators at the top of the food chain, that are affected, in particular, birds (raptors and piscivors) (Pearse et al., 1979; Bosveld & van den Berg, 1994; Munroe et al., 1994) and marine mammals (seals and whales).
• More recently, organochlorines and PCBs are now though to be responsible for endocrine disruption in freshwater fish.

The impact in Scotland

Acidification

2.17 Sulphates, from sulphur deposition, are readily acidifying, but their role has diminished with the decline in S deposition The role of N pollutants which are drawn into the nitrogen cycle is more complex.

Figure 2.2 Empirical acidity critical loads for soils 2004

Figure 2.3 Total Acidity Deposition 2002-04

2.18 Critical loads for acidity are based on soil type, including weathering processes and rainfall pH. From 2.2 it can be seen that the sensitive soils in Scotland (red) occur over much of Scotland but particularly in the upland areas of the north and north west and the Southern Uplands and Dumfries and Galloway. The most sensitive soils are the montane areas (black).

Figure 2.4 Exceedance of Acid Grassland critical loads by deposition for 2002-2004

Figure 2.5 Exceedance of Bogs critical loads by deposition for 2002-2004

Figure 2.6 Exceedance of Freshwater critical loads by deposition for2002-2004

Figure 2.7 Exceedance of Montane critical loads by deposition for 2002-2004

2.19 Figures 2.4 to 2.7 show exceedance of critical loads for deposition from the year 2002-2004 (Figure 2.3) for a number of habitats. There is exceedance in many parts of Scotland including areas around Argyll, the central Highlands (especially the Cairngorm area) and the Southern Uplands.

2.20 Table 2.2 shows the trend over the years of the percentage of Scotland exceeded for acidity with on average over 40% of all habitats exceeded for acidity of the critical loads for soils. Caution should be taken in comparing years as changes in methodologies of both critical loads and deposition have occurred especially between 1995-97 and other years.

Table 2.2 Percentage area of Scotland exceeded for Acidity

Acidification - status recovery and future predictions

• Long-term soil solution data are relatively sparse, but the Glensaugh and Sourhope ECN datasets (both acid grassland sites) show clear evidence of pH recovery since 1993. A more extensive basis for assessing long-term recovery will become available following completion of the current Countryside Survey (providing a large spatial dataset extending from 1978-2007). Recent simple dynamic model simulations for soils generally predict recovery from acidification under current emissions legislation, However, there is still a persistence of acidified conditions in some peatland, acid grassland, heathland and woodland areas of Southern and Eastern Scotland; montane areas of the Eastern Grampians; and more extensive and severe acidic conditions under conifer forestry outside the northwest Highlands (Evans et al., 2007).
• Surface water data provide greater spatial coverage and are probably largely indicative of soil trends; observations from the UK Acid Waters Monitoring Network AWMN (Davies et al., 2005) show that surface water sulphate concentrations are decreasing most in areas previously subject to the highest deposition - within the Scottish AWMN dataset these areas include Galloway and the Eastern Grampians (Lochnagar). These areas typically do show recovery in pH and/or Acid Neutralising Capacity, but it is not uniform; the forested Loch Grannoch in Galloway remains highly acidic and is showing little or no recovery.
• MAGIC and other models predict long-term future recovery from acidification, but with uncertainty associated with a possible future decrease in soil capacity to retain atmospheric nitrogen. If this capacity decreases, increased nitrate leaching to surface waters could lead to (potentially major) re-acidification (e.g. Curtis et al., 2005). The magnitude and timing of nitrogen 'saturation' is however highly uncertain. It is also linked to issues of soil carbon sequestration - if more atmospheric nitrogen goes into accumulating soil organic matter, less will be leached to surface waters (e.g. Evans et al., 2006b). Typically, soils containing less organic matter are least able to retain nitrogen at present deposition levels, and may be at greatest risk of increased nitrate leaching in future.

Eutrophication (from atmospheric deposition of nutrient nitrogen)

2.21 Empirical nitrogen critical loads (some examples in Table 2.3) are based on observed changes in the structure and function of ecosystems, field addition experiments, mesocosm studies, and in some cases dynamic ecosystem modelling ( UNECE, 2003). Soil processes are taken into account when calculating empirical critical loads and are intrinsically linked to the health and viability of the ecosystem.

Table 2.2 Empirical critical loads of nutrient nitrogen (kg N ha ^-1 yr ^-1) for some typical Scottish habitats:

2.22 Exceedance of the critical loads are shown for some key habitats in Figures 9-13 based on deposition for the years 2002-04 (Figure 2.8). Montane areas and woodlands/forest have high exceedance of their critical loads for nutrient nitrogen, while large areas of bog and dwarf shrub habitats are also exceeding their critical loads. Montane habitats have a low critical load (5-10 kg N ha ^-1 yr ^-1) while forests are very good at capturing pollutants and tend to have higher deposition to their aerodynamically rougher surfaces

Figure 2.8 Total N deposition 2002-04

Figure 2.9 Exceedance of Montane critical loads by deposition for 2002-2004

Figure 2.10 Exceedance of Unmanaged Woodland critical loads by deposition for 2002-2004

Figure 2.11 Exceedance of Bog critical loads by deposition for 2002-2004

Table 2.4 below shows the percentage area of Scotland exceeded for nutrient nitrogen. On average around 38% of habitats are exceeded for their critical load, but over 90% of sensitive montane habitats are exceeded.

Figure 2.12 Exceedance of Dwarf Shrub Heath critical loads by deposition for 2002-2004

Figure 2.13 Exceedance of Managed Woodland critical loads by deposition for 2002-2004

Table 2.3: Percentage area of Scotland exceeded for Nutrient Nitrogen

2.23 Semi-natural ecosystems that have evolved under conditions of low nutrient availability are most at risk from N eutrophication in Scotland. Although the at risk area for organic soils supporting heaths and bogs is relatively modest, the implications for soil sustainability and carbon sequestration are among the highest. However because the links between acidity and N and Carbon cycling are complex and also strongly influenced by drying and rising temperatures, we presently have insufficient data to predict the consequences for these organic soils.

Soil contamination by Heavy Metals

2.24 Atmospheric deposition of heavy metals is generally low over Scotland and is predicted to decline (MacDonald et al., 2001; Scottish Executive, 2006). However, average concentrations of heavy metals have been found to be elevated in both urban and industrial soils when compared with the rural soil (Environment Agency UK Soil and Herbage Pollutant Survey, Report No. 7, 2007). However, atmospheric deposition can become more of an issue in relatively pristine habitats such as most of the Highlands. Deposition onto ombotrophic peats through long distance transport has led to significant elevation in peat metal burdens, though this again is decreasing for the reasons mentioned above and with the ban of lead in petrol (Farmer et al. 1997; Meharg et al., 2006). The importance of this peat loading is not well understood. Its ecotoxicological impact is probably minimal. However, with peat oxidation caused by climate change the peat heavy metal pool may be mobilised into catchments, affecting water quality (Heal, 2001; Rothwell et al., 2005).

Soil contamination and POPs

2.25 The situation for POPs in many ways is similar to heavy metals with declining industry, increased regulation and better technologies decreasing atmospheric inputs and causing a decline in deposition. POPs differ from most heavy metals in that they biomagnify, and thus ecotoxicological concerns persist with endangered and highly valued top predators such as ospreys, golden and sea eagles. Also, there is evidence that POP deposition is driven by temperature and therefore altitude, suggesting that deposition will be greater at higher altitudes (Weiss et al., 1998; Demers et al. 2007; Rimal et al., 2004).

2.26 POPs have been detected in rural, urban and industrial soils, and the concentration were found to be greatest in urban, then industrial, then rural soils ( UK Soil and Herbage Pollutant Survey Reports 8, 9, 10; 2007). As the Highland region of Scotland is relatively pristine, large industrial installations in the Highlands (oil refining, oil rig refurbishment, timber bleaching) have the potential to greatly elevate background levels of heavy meals and POPs as illustrated by fluoride atmospheric deposition surrounding the now closed aluminium plant at Invergordon (Gilbert, 1985). Aluminium installations have also led to POP pollution such as PAH contamination observed in marine lochs impacted by this activity (McIntosh et al., 2004). The atmospheric impact of these large-scale industries still has to be ascertained in any detail. Recent reviews have indicated that current emissions of POPs are now dominated by a wide range of smaller diffuse sources and that further work is required to accurately quantify these sources.

Gaps in Research and Data

The need for an Integrated Approach

2.27 We must also remember that soil microorganisms are primarily energy limited. Plants are the main source of labile Carbon flux into soils and so it is essential to take an integrated approach when studying the effects of deposition of atmospheric pollutants on soils. Future research must consider how changes to plant community composition and biomass indirectly affect the functioning of microbes. The impacts of nitrogen may also be exaggerated by other pollutant pressures, in particular climate change (changes in temperature and rainfall patterns) and elevated atmospheric CO ₂ concentrations, and so it is essential that future research programmes take an integrated approach rather than addressing the effects of nitrogen deposition in isolation. A better and more integrated approach to monitoring change is required e.g. monitoring plants, diversity, soils and waters in the same catchments (currently limited to a very few ECN sites). There is also a need for experimental data showing how climate change and atmospheric deposition interact to effect soils.

New techniques

2.28 It is only very recently that significant in-roads into quantifying microbial diversity been made, primarily by the advent of molecular techniques. While these techniques provide unparalleled assessment of microbial diversity, they are not without limitations and have in many cases not been applied to particular ecosystems, especially natural ecosystems. Whilst descriptive information of previously unknown groups of microbes is crucial, we need to link this information to key functions. This can be achieved by application of novel techniques, for example stable isotope probing of Phospholipid Fatty-acid Analysis ( PLFA) and nucleic acids, combining secondary ion mass spectrometry with fluorescence in-situ hybridisation.

Relevant Policies

2.29 There are no overarching soil protection policies for combating atmospheric pollution impacts. However, there are a raft of EU directives, protocols, and local planning instruments are primarily associated with reducing emissions of atmosphere pollutants and preventing potentially damaging industrial installations. PPC regulations also provide emission controls measures through BAT (Best Available Techniques).

• IPPC and PPC - provides an integrated approach to establish pollution prevention from stationary "installations".
• Large Combustion Plant Directive ( LCPD) - aims to reduce acidification, ground level ozone and particles throughout Europe.
• National Emissions Ceiling Directive ( NECD) - seeks to reduce emissions of those pollutants that cause acidification, eutrophication and ground-level ozone in order to protect the environment and human health.

2.30 There are some directives and conventions which are indirectly relevant to soils through protecting habitats and species, by establishing a network of protected sites (Natura 2000 network). They include the EC Habitats Directive, the EC Birds Directive, and the Ramsar Convention on Wetlands. The Habitats Directive and the Ramsar Convention also address the conservation of habitats more widely. In Scotland the policy for achieving favourable condition for Sites of Special Scientific Interest ( SSSI) is similarly relevant. For nitrogen there is the Nitrates Directive to protect water quality.

References

Cape, J.N., Sheppard, L.J., Binnie, J., Arkle, P. and Woods, C.: 1995, Water, Air and Soil Pollut., 2247 - 2252.

Cousins I T and Jones K.C. (1998). Air-soil exchange of semi-volatile organic compounds ( SOCs) in the UK. Environmental Pollution, 102, 105-118.

Curtis, C.J., Evans C.D., Helliwell, R.C., Monteith, D.T. (2005). Nitrate leaching as a confounding factor in chemical recovery from acidification in UK upland waters. Environmental Pollution, 137, 73-82.

Dalla Valle M, Jurado E, Dachs J, Sweetman A J and Jones K.C. (2005). The maximum reservoir capacity for soils for persistent organic pollutants: implications for global cycling. Environmental Pollution, 134, 153 - 164.

Davies, J.J.L, Jenkins, A., Monteith, D.T., Evans, C.D. and Cooper, D.M. (2005). Trends in surface water chemistry of acidified UK freshwaters, 1988-2002. Environmental Pollution, 137, 27-39.

Demers MJ, Kelly EN, Blais JM, et al. (2007). Organochlorine compounds in trout from lakes over a 1600 meter elevation gradient in the Canadian Rocky Mountains. Environmental Science & Technology 41 (8): 2723-2729.

EMEP (2007). Transboundary air pollution by main pollutants (S, N, O ₃) and PM. Meteorologisk Institutt, Norway.

Environment Agency - UK Soil and Herbage Pollutant Survey ( UKSHS Report No. 7) - Environmental concentrations of heavy metals in UK soil and herbage. June 2007.

Environment Agency - UK Soil and Herbage Pollutant Survey ( UKSHS Report No. 8) - Environmental concentrations of polychlorinated biphenyls ( PCBs) in UK soil and herbage. June 2007.

Environment Agency - UK Soil and Herbage Pollutant Survey ( UKSHS Report No. 9) - Environmental concentrations of polycyclic aromatic hydrocarbons in UK soil and herbage. June 2007.

Evans, C., Hall, J., Rowe, E., Aherne, J, Helliwell, R, Jenkins, A., Cosby, J., Smart, S., Howard, D., Norris, D., Coull, M., Bonjean, M., Broughton, R., O'Hanlon, S., Heywood, E., and Ullyett, J. (2007). Critical Loads and Dynamic Modelling, Final Report. Report to the Department of the Environment, Food and Rural Affairs under Contract No. CPEA 19. 53 pp.

Evans, C.D., Caporn, S.J.M., Carroll, J.A, Pilkington, M.G. Wilson, D.B., Ray, N., Cresswell, N. (2006b) Modelling nitrogen saturation and carbon accumulation in heathland soils under elevated nitrogen deposition. Environmental Pollution, 143, 468-478.

Evans, C.D., Reynolds, B., Jenkins, A., Helliwell, R.C., Curtis, C.J., Goodale, C.L., Ferrier, R.C., Emmett, B.A., Pilkington, M.G., Caporn, S.J.M., Carroll, J.A., Norris, D., Davies, J., Coull, M.C. (2006) Evidence that soil carbon pool determines susceptibility of semi-natural ecosystems to elevated nitrogen leaching. Ecosystems, 9, 453-462.

Farmer JG, Mackenzie AB, Sugden CL, et al. (1997). A comparison of the historical lead pollution records in peat and freshwater lake sediments from central Scotland. Water Air and Soil Pollution. 100 (3-4): 253-270.

Fowler, D. 2001, Transboundary Air Pollution: Acidification, Eutrophication and Ground-Level Ozone in the UK, Report to DEFRA by the National Expert Group on Transboundary Air Pollution ( NEGTAP), CEH Edinburgh.

Galloway, J. N., et al. 2003. The nitrogen cascade. BioScience 53: 341-356.

Gilbert O.L. (1985). Environmental-effects of airborne fluorides from aluminum smelting at Invergordon, Scotland 1971-1983. Environmental Pollution Series A - Ecological and Biological 39 (4): 293-302.

Giller K.E., Witter E. and McGrath S.P. (1998). Toxicity of heavy metals to microorganisms and microbial processes in agricultural soils: a review, Soil Biol. Biochem. 30, 1389-1414.

Grimalt JO, Borghini F, Sanchez-Hernandez JC, et al. (2004). Temperature dependence of the distribution of organochlorine compounds in the mosses of the Andean mountains. Environmental Science & Technology 38 (20): 5386-5392.

Heal K.V. 2001. Manganese and land-use in upland catchments in Scotland. Science of the Total Environment. 265 (1-3): 169-179.

Knight B., McGrath S.P. and Chaudri A.M. (1997). Biomass carbon measurements and substrate utilization patterns of microbial populations from soils amended with cadmium, copper, or zinc, Appl. Environ. Microbiol. 63, 39-43.

Magnani, F., Mencuccini, M., Borghetti, M., Berbigier, P., Berninger, F., Delzon, S., Grelle, A., Hari, P., Jarvis, P.G., Kolari, P., Kowalski, A.S., Lankreijer, H., Law, B.E., Lindroth, A., Loustau, D., Manca, G., Moncrieff, J.B., Rayment, M., Tedeschi, V., Valentini, R., Grace, J., 2007. The human footprint in the carbon cycle of temperate and boreal forests. Nature 447, 848-850.

Meharg AA, Deacon C, Edwards KJ, Donaldson M, Davidson DA, Spring C, Schrimshaw C, Feldmann J, Raab A & Ellam R (2006). Ancient manuring practices pollutes arable soil at the St Kilda World Heritage Site, Scottish North Atlantic. Chemosphere, 64, 1818-1828.

McDonald, A.G.; Nemitz, E.; Dragosits, U.; Sutton, M.A.; Fowler, D. (2002): Modelling Heavy Metal Deposition Across Scotland In: M.B. Usher, E.C. Mackey, J.C. Curran (eds.) The State of Scotland's Environment and Natural Heritage, The Stationary Office, Edinburgh, ISBN 0 11 497306 7, pp 111-116.

McIntosh AD, Moffat CF, Packer G, et al. (2004). Polycyclic aromatic hydrocarbon ( PAH) concentration and composition determined in farmed blue mussels (Mytilus edulis) in a sea loch pre- and post-closure of an aluminium smelter. Journal of Environmental Monitoring 6 (3): 209-218.

Nasholm T, Ekblad A, Nordin A, Giesler R, Hogberg M, Hogberg P (1998). Boreal forest plants take up organic nitrogen. Nature 392: 914-916.

Pilegaard K., Skiba U., Ambus P., Beier C., Bruggemann N., Butterbach-Bahl K., Dick J., Dorsey J., Duyzer J., Gallagher M., Gasche R., Horvath L., Kitzler B., Leip A., Pihlatie M. Rosenkranz K., Seufert P., Vesala G., T., Westrate H., and Zechmeister-Boltenstern S. (2006) Nitrogen load and forest type determine the soil emission of nitrogen oxides (NO and N2O) Biogeosciences, 3, 651-661

Pitcairn, C. E. R., Leith, I. D., Sheppard, L. J., Sutton, M. A., Fowler, D., Munro, R. C., Tang, S., and Wilson, D.: The relationship between nitrogen deposition, species composition and foliar nitrogen concentrations in woodland flora, Environ. Pollution,102, 41-48, 1998.

Raich, J.W., Potter, C.S., Bhagawati, D. (2002). Interannual variability in global soil respiration, 1980-94. Global Change Biology 8, 800-812.

Rennenberg, H., Kreutzer, K., Papen, H., and Weber, P.: 1998, New Phytol. 139, 71-86.

Rothwell JJ, Robinson SG, Evans MG, et al. (2005). Heavy metal release by peat erosion in the Peak District, southern Pennines, UK. Hydrological Processes 19 (15): 2973-2989.

Scottish Executive, (2006). Scotland's Soil Resource - Current State and Threats. Environmental Research Report 2006/01.

Sheppard, L.J., A. Crossley, J.N. Cape, F. Harvey, J. Parrington and C. White: 1999, Phyton, 39, 1-25.

Skiba, U., Sheppard, L.J., MacDonald, J. and Fowler, D. 1998a, Atmos. Environ. 32, 3311 - 3320.

Skiba, U., Sheppard, L.J., Pitcairn, C.E.R., Leith, L., Crossley, A., van Dijk, S., Kennedy, V.H., and Fowler, D. 1998b, Environ. Poll, 102, 457 - 461.

Skiba, U. and Smith, K.A.: 2000. The control of nitrous oxide emissions from agricultural and natural soils Chemosphere, 2, 379-386.

Skiba, U., Fowler, D. and Smith, K.A. 1997. Nitric oxide emissions from agricultural soils in temperate and tropical climates: sources, control and mitigation options. Nutrient Cycling in Agroecosystems 48, 75 - 90.

Taylor AFS, Martin F, Read DJ. (2000). Fungal diversity in ectomycorrhizal communities of Norway spruce (Picea abies (L.) Karst.) and Beech (Fagus sylvatica L.) in forests along north-south transects in Europe. In: Carbon and Nitrogen Cycling in European Forest Ecosystems. E-D. Schulze (ed) Ecological Studies Vol.142. pp 343-365. Springer-Verlag, Heidelberg.

UNEP 2004, GeoYear Book. United Nations Environment Programme.

Wallenda T, Kottke I (1998). Nitrogen deposition and ectomycorrhizas New Phytologist 139: 169-187.

Weiss P, Lorbeer G, Scharf S. (1998). Persistent organic pollutants in remote Austrian forests - Altitude-related results. Environmental Science and Pollution Research : 46-52.

Wild S and Jones K.C. (1995). Polynuclear aromatic hydrocarbons in the United Kingdom environment: a preliminary source inventory and budget. Environmental Pollution, 88, 91-108.

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