The
Centre forEcology &Hydrology
Centre forEcology & HydrologyNATURAL ENVIRONMENT RESEARCH COUNCIL
Formerly the Institutes of Hydrology,
Terrestrial Ecology. Freshwater Ecology,
and Virology and Environmental Microbiology
The Centre for Ecology and Hydrology has 600 staff, and well-equipped laboratories and fieldfacilities at nine sites throughout the United Kingdom.The Centre's administrative headquartersis at Monks Wood in Cambridgeshire.
This report is an official document prepared under contract between the
customer and the Natural Environment Research Council. It should not be
quoted without the permission of both the Centre for Ecology and Hydrology and
the customer.
CEH Sites
CEH DirectorateMonks Wood Abbots Ripton.
Huntingdon,
Cambridgeshire PE28 2LSTelephone +44 (0) 1487 772400Main Fax +44 (0) 1487 773590
CEH OxfordMansfield Road,
Oxford.
Oxfordshire OX I 3SR
Telephone +44 (0) 1865 281630Main Fax +44 (0) 1865 281696
CEH MerlewoodWindermere Road.
Grange-over-Sands,
Cumbria LAI I 6JUTelephone +44 (0) 15395 32264Main Fax +44 (0) 15395 34705
CEH WallingfordMaclean Building, Crowmarsh Gifford,
Wallingford,
Oxfordshire OXIO 888
Telephone •44 (0) 1491 838800Main Fax +44 (0) 1491 692421
CEH DorsetWinfrith Technology Centre.
Winfrith Newburgh, Dorchester,
Dorset 0T2 8ZD
Telephone +44 (0) 1305 213500Main Fax +44 (0) 1305 213600
CEH EdinburghBush Estate,
Penicuik.
Midlothian EH26 OQB
Telephone +44 (0) 131 4454343Main Fax +44 (0) 131 4453943
CEH WindermereThe Ferry House, Far Sawrey,
Ambleside.
Cumbria LA22 OLPTelephone +44 (0) 15394 42468Main Fax +44 (0) 15394 46914
CEH Monks WoodAbbots Ripton.
Huntingdon,
Cambridgeshire PE28 2LS
Telephone +44 (0) 1487 772400Main Fax +44 (0) 1487 773467
CEH BanchoryHill of Brathens,
Banchory.
Aberdeenshire AB3 I 4BYTelephone +44 (0) 1330 826300Main Fax +44 (0) 1330 823303
CEH BangorUniversity of Wales, Bangor,
Deiniol Road.
Bangor. Gwynedd LL57 2UPTelephone +44 (0) 1248 370045Main Fax +44 (0) 1248 355365
Further information about CEH is available on the World Wide Webat www.ceh.ac.uk
STATUS OF UK CRITICAL LOADS AND EXCEEDANCES
PART I —CRITICAL LOADS AND CRITICAL LOADS MAPS
UPDATE TO JANUARY 1998 REPORT: FEBRUARY 2001
Jane Hall', Jackie Ullyettl, Mike Hornung2,Fiona Kennedy3, Brian Reynolds°, Chris Curtis5,Simon Langan6,David Fowler2
1UK National Focal Centre, Centre for Ecology and Hydrology, Monks Wood, AbbotsRipton, Huntingdon, PE28 2LS2 Centre for Ecology and Hydrology, Merlewood, Windermerc Road, Grange-over-Sands,Cumbria, LAII 6JU3 Forestry Research, Alice Holt Lodge, Wrecclesham, Farnham, Surrey, GUIO 41-H
Centre for Ecology and Hydrology, Bangor Research Unit, University College NorthWales, Deiniol Road, Bangor, Gwynedd, LL57 2UW
Environmental Change Research Centre, Department of Geography, University CollegeLondon, 26 Bedford Way, London, WCIH OAP6 Macaulay Land Use Research Institute, Craigicbuckler, Aberdeen, AB9 2QJ7 Centre for Ecology and Hydrology, Bush Estate, Penicuik, Midlothian, EH26 OQB
á
I INTRODUCTION
The UK National Focal Centre (NFC) at CEH (previously ITE) Monks Wood isresponsible for co-ordinating critical loads mapping activities in the UK and compilingnational critical loads data sets and maps from data supplied by UK experts. In 1998 theUK NFC produced the report "Status of UK Critical Loads and Exceedances, Part 1 —Critical Loads and Critical Loads maps" (Hall et aL, 1998). This report documented themethods used to calculate national critical loads and the critical load values based onthese methods were submitted to the Coordination Centre for Effects (CCE) in theNetherlands in January 1998. The CCE arc responsible for compiling critical loads datasets and maps at the European scale from national contributions.
Since the 1998 report was published, research by UK experts has lead to changes in someof the data sets used to calculate critical loads. However, much of the information givenin the 1998 rcport (Hall et aL, 1998) remains relevant today. This document highlightsthe changes that have been made to national critical loads calculations since that time. Itshould be noted that the methods applied in the UK for calculating acidity and nutrientnitrogen critical loads continue to conform to the methods recommended by theInternational Cooperative Programme on Mapping and Modelling (UBA, 1996), underthe United Nations Economic Commission for Europe (UNECE) Convention on Long-Range Transboundary Air Pollution (CLRTAP).
Acidity critical loads for non-woodland ecosystems (ie, acid grassland, calcareousgrassland and hcathland) are still based on the empirical acidity critical loads map forsoils. The Simple Mass Balance (SMB) equation continues to be applied to woodland(coniferous and deciduous) ecosystems, though changes have been made to some of theinput parameters and a new criterion has been used to determine acidity critical loads fororganic forested soils. The methods for deriving empirical acidity critical loads forfreshwaters remain unchanged. However, new data on base cation deposition, basecation uptake and nitrogen uptake, have led to new values for the maximum critical loadsfor sulphur and nitrogen for all ecosystems; these critical loads are used in the calculationof critical load exccedances.
The methods and values used to define empirical critical loads for nutrient nitrogen forterrestrial ecosystems remain the same as in the 1998 report (Hall et aL, 1998). Thenutrient nitrogen mass balance equation for woodland ecosystems now includes revisedvalues for nitrogen uptake. However, the critical loads for woodland ecosystems arebased on the minimum of empirical and mass balance values.
National critical loads data, taking these revisions into account, were submitted to theCCE in February 2001.
A summary of the changes made to critical load calculations and the minimum andmaximum values across the UK are summarised (Appendix 3) and maps of the old (1998)versus ncw (2001) calculations presented (Appendix 4).
2 CRITICAL LOADS OF ACIDITY - TERRESTRIAL ECOSYSTEMS
Two methods are used in the UK for calculating acidity critical loads for terrestrialecosystems: the empirical approach is applied to non-woodland ecosystems and theSimple Mass Balance (SMB) equation to woodland ecosystems.
2.1 Empirical —soil-vegetation systems: acid grassland, calcareous grassland andheathland
The empirical acidity critical loads for soils continue to be used for the non-woodlandecosystcms (i.e. acid grassland, calcareous grassland and heathland). The methods usedto define the ecosystem areas and assign critical loads is unchanged from 1998 (Hall etat, 1998). The current form of the SMB equation is only suitable for woodlandecosystems; further work on parameterisation and testing of the equation would berequired to apply the SMB to non-woodland ecosystems in the UK.
2.2 Simple Mass Balance (SMB) equation
The SMB equation is the most commonly used model in Europe for the calculation ofacidity critical loads for forest ecosystems. In the UK we apply this method to coniferousand deciduous woodland ecosystems, except for wooded areas on peat soils, where theSMB is inappropriate; in such areas empirical critical loads of acidity are applied (Smithet. al., 1993). ). The SMB equations used are given in Appendices 1 and 2.
Chemical criteria and limitsIn 1998, the critical chemical criterion uscd in the SMB for all soil types (other thanpeats) was a critical molar Ca:Al ratio of one. However, recent work (Hall a at, 2001a& 2001b) has highlighted that the Ca:Al ratio is more appropriate for mineral soils thanorganic soils; for the latter a critical pH is considered to be more suitable. This findingwas confirmed at the recent UNECE Workshop on Chemical Criteria and Critical Limits,held in York 19-21 March 2001, where one of the recommendations was that critical pHwas the preferred criterion for organic soils. Therefore, in preparing critical loads for theFebruary 2001 data submission to the CCE, a Ca:Al ratio of one was applied to forestedmineral soils and a critical pH of 4.0 to forested organic soils, with the exception of peatsoils, where empirical critical loads continue to be used. The pH value of 4.0 isrccommended in the UNECE Mapping Manual (UBA, 1996).
Gibbsite equilibrium constantThe values for the gibbsite equilibrium constant (Kg,bo),which simulate the relationshipbetween aluminium and hydrogen ions in soil solution, have been set separately formineral and organic soils. The value now applied to mineral soils (950 m6/eq2)waspreviously applied to all soil types. For organic soils, a value of 9.5 m6/eq2has been
used. These values are based on the percentage of organic matter in the soil and arerecommended in the UNECE Mapping Manual (UBA, 1996).
Calcium deposition inputs to the SMBWhen using the Ca:Al criterion in the SMB, values for total (wet plus dry, marine plusnon-marine) calcium deposition to woodland need to be included in the critical loadcalculations (Appendix 1). Previously the 20km data for 1992-94 had been used. Thishas now been updated to the 5km resolution data for 1995-97, provided by CEHEdinburgh (Smith et al., 2000; Smith & Fowler, 2001).
Base cation, calcium and nitrogen uptakeThe methods used to estimatc base cation, calcium and nitrogen losses by the uptake andremoval through the harvesting of forests and woodlands, arc unchanged from thosegiven in the 1998 report (Hall et at, 1998). The uptake values used still represent thetheoretical maximum removal, which assume that potential timbcr yields are achieved, ie,no correction is made for the "best guess" of the actual timber yield. As this method canoverestimate timber removal, it represents a "worst case" for base cation removal and a"best case" for nitrogen removal (Hall et al., 1998).
Calcium uptake values are required for the SMB equation, when using the Ca:Alcriterion. Base cation uptake values for are needed in the calculation of the maximumcritical load of sulphur (CLmaxS), and nitrogen uptake values for deriving the minimumcritical load of nitrogen (CLminN) and mass balance critical loads of nutrient nitrogen.
Since 1998, further research has been carried out by Forest Research to improve theestimates of uptake values for coniferous and deciduous trees. They concluded that the1998 values were too low because: (a) they excluded biomass removal during forestthinning; (b) they used very low wood nitrogen concentrations due to measurements onlinear cores, which underestimate the contribution from sap wood. Therefore, ForestResearch investigated the effect of adding thinnings into the uptake estimates for theirForestry Level II sites. The new uptake values provided by Forest Research are given inTable 1; the values arc based on results for three Level 11 oak sites for deciduouswoodland and four Level II sitka spruce sites for coniferous woodland. The oak sites areall on calcium-rich soils, so uptake values for deciduous trees on calcium-poor soils werederived empirically. The average values for the coniferous and deciduous sites are usedin the national critical loads mapping exercise. However, it should be recognised thatthere are still uncertainties with this approach, since this provides only:
three default values for calcium and base cation uptake (coniferous on all soiltypes, deciduous on calcium-poor soils, deciduous on calcium-rich soils);two default values for nitrogen uptake (ie, no separation for calcium-rich andcalcium-poor soils necessary for nitrogen);
These default values are then applied to appropriate areas (see below) at the nationalscale. A range of uptake values for coniferous and deciduous woodland, for more sites ofdifferent soil types across the UK would improve the critical load calculations further.
Forest Research will recommend further revisions to these figures in the future when theyhave improved nutrient concentration data available for all IO Level II sites.
We have also changed the method used to identify areas of calcium-rich and calcium-poor soils. In 1998, we used a 1km map, which divided soils into three sensitivity classesdepending on their base saturation and pH (Hall et at, 1998). However, we wercconcerned that this did not accurately reflect the calcium richness of the soils across theUK, leading to uptake values being inappropriately assigned in some areas. Therefore,for the 2001 data submission, we used the 1km map of calcium weathering rates (alsoused in the SMB equation), assigning those grid squares with a low weathering rate (ie,
0.5 keq yean the calcium-poor uptake value, and squares with a higherweathcring rate the calcium-rich uptake value. We believe this gives ,a better representation of areas of calcium-rich and calcium-poor soils at the national scale.
Table I.Base cation, calcium and nitrogen uptake values for coniferous and deciduous woods.
Woodland Type Uptake Values (keq ha- yea( ) Uptake Values (keq ha- year- )
Conifers
0:7) , 0.5
0.33 0.5
Deciduous
DeciduousCa- oor soils
Januabasecations
1998calcium nitrogen
Februabasecations
0.253 0.117 0.279 0.25
0.613Ca-rich soils
0.516 0.278 0.85
0.171 0.076 0.278 0.4
2001
calcium nitrogen
0.12 0.5
3 CRITICAL LOADS OF ACIDITY —FRESHWATER ECOSYSTEMS
Two empirical models have been used in the UK to calculate sulphur and acidity criticalloads for freshwaters: the Diatom model and the Steady-State Water Chemistry (SSWC)model. In addition, to provide the critical loads needed for the calculation of exceedances(ie the minimum and maximum critical loads of sulphur and nitrogen) for work under theCLRTAP, the First-order Acidity Balance (FAB) model has been used.
3.1 Empirical models
The methods for calculating empirical acidity critical loads for freshwaters (ie, theDiatom model and the SSWC model) remain unchanged. However, the number of sitesto which the models have been applied has increased, with an extra 25 sites in GreatBritain, bringing the total to 1470, plus 140 sites in Northern Ireland, giving a total of1610 sites in the UK.
3.2 First-order Acidity Balance model
FAB is a catchment-based model and therefore takes into account catchment specific datasuch as deposition, forest areas and lake to catchment ratios. To derive these parametersthe catchment boundaries and areas are required. The boundaries for the additional 25sites in Great Britain have been defined on Ordnance Survey maps and digitised underthe DETR Freshwater Umbrella contract at University College London (UCL). The gridreferences for the 140 sites in Northern Ireland were provided to the Department of theEnvironment in Northern Ireland (DOE NI), whose GIS staff used an Ordnance SurveyNorthern Ireland digital elevation model (DEM) to define the catchment boundaries andcalculate the catchment areas. However, for 36 of these sites it was not possible todetermine the catchment boundaries from the DEM, so these were defined and digitisedmanually at UCL.
Many of the input parameters to FAB (eg, catchment-weighted estimates of nitrogenimmobilisation and denitrification) remain the same as those used in 1988. Thecatchment-weighted runoff values for Great Britain are still based on the 1941-60 dataset. However, for the sites in Northern Ireland catchment-weighted values based on1961-90 runoff data were provided by DOE NI. The areas of forestry in the catchmentsin Northern Ireland were determined from the CORINE land cover map (CORINE,1994).
4 Critical Loads of Nutrient Nitrogen
Critical loads for nutrient nitrogen (CL.N) can be calculated using two differentmethods, empirical and mass balance (UBA, 1996). In the UK the empirical, massbalance, or both of these approaches, have been used to calculate nutrient nitrogen criticalloads for the same terrestrial ecosystems for which acidity critical loads are determined.Nutrient nitrogen critical loads have not been calculated for UK freshwaters. The small,upland catchments selected for the calculation of acidity critical loads arc not consideredto be at risk from eutrophication (ie excess nitrogen as a nutrient), since they are morelikely to be phosphorous, rather than nitrogen limited systems.
4.1 Empirical critical loads of nutrient nitrogen
The empirical critical loads of nutrient nitrogen applied to terrestrial in the UK (Hall etaL, 1998), have not changed since 1998. In addition to the values previously agreed uponin the UK for acid grassland, calcareous grassland, heathland and deciduous woodland,an empirical value (13 kg N ha4 yean has now been assigned to coniferous woodlandecosystems, on the basis of changes in ground flora. This value has been assigned toareas of coniferous woodland by selecting those 1km squares where the coniferouswoodland class (ic, class 16) on the combined CEH Land Cover Map of Great Britain andthe CORINE land cover map covering Northern Ireland (Hall et aL, 1998), occupies >5%of a grid square.
However, following the UNECE Workshop on Chemical Criteria and Critical Limits(York, March 2001), it has been agreed that there will be a UNECE Workshop inAutumn 2002 (probably November) to review the empirical critical loads for nutrientnitrogen. This will incorporate the results of recent research on the effects of excessnitrogen deposition on plants and habitats, to review and revise the values wherenecessary. Following this workshop the UK will revise its empirical nutrient nitrogenvalues accordingly.
4.2 Mass balance critical loads for nutrient nitrogen
The mass balance approach has been used to calculate critical loads for coniferous anddeciduous woodland ecosystems. In 1998, for deciduous woodland, the minimum valuefrom the empirical or mass balance approaches was used to set the critical load for each1km square of this woodland ecosystem. In 2001, it was agreed that the same approachshould be applied to coniferous woodland ecosystems, hence, the assignment of anempirical critical load as described above. This means that national maps of nutrientnitrogen critical loads for woodland ecosystems are set to protect either changes inground flora or excess nitrogen leaching, depending on which method gives the lowestcritical load value in any grid square.
The mass balance equation for CLmaN is:CLnwN = Nu+Ns+Nte(aco+Nde
Where N. = nitrogen uptake= nitrogen immobilisation
Nle(acc) = acceptable level of nitrogen leaching Nde = denitrification
The derivation of, and values for N, Nde and Nieo„d remain unchanged from the 1998report (Hall et al., 1998). 'The nitrogen uptake values for the woodland ecosystems havebeen revised as described in Section 2.2 above, while the values for other ecosystemshave not been changed.
5 Critical Loads Function
The Executive Body of the CLRTAP adopted the Protocol to Abate Acidification,Eutrophication and Ground-level Ozone in Gothenburg (Sweden) on 30 November 1999.The Protocol sets emission ceilings for 2010 for four pollutants: sulphur, oxidisednitrogen, ammonia and Volatile Organic Compounds (VOCs). Consequently, in additionto examining the impact of excess nitrogen as a nutrient (ie, eutrophication), it becamenecessary to consider the combined acidifying effects of both sulphur and nitrogendeposition. To examine these effects, the so-called "Critical Loads Function" (CLF) wasdeveloped in Europe (Posch a aL, 1999; Posch & Hettelingh, 1997; Posch a aL, 1995;Hettelingh et 1995). The CLF defines separate acidity critical loads in terms ofsulphur and nitrogen, referred to as the "minimum" and "maximum" critical loads ofsulphur and nitrogen. These "new" acidity critical loads can be compared with sulphurand nitrogen deposition using the CLF (Hall et aL 1998, Hall et aL, 2001c). The effectsof excess nitrogen as a nutrient are considered separately. The sections below describeany changes made to the calculations of these "new" acidity critical loads in preparationfor the data submission in February 2001.
5.1 Maximum Critical Load of Sulphur (CL„,..„S)
For terrestrial ecosystems, CL...2.,Sis based on the acidity critical load values but alsotakes into account the net base cation deposition to the soil system and base cationremoval from the system:
CL„„uS= CL(A) + BC&T-BC.Where CL(A) =acidity critical load (empirical or SMB)
BCdep = non-marine base cation less non-marine chloride depositionBC„ = base cation uptake by vegetation
The acidity critical loads used in this calculation are those described in Section 2 above.
For the calculations of CL„,„,r,S'for the 1998 data submission we used 20km non-marinebase cation values for 1992-94 minus a modelled estimate of non-marine chloride for2010 (Hall et at, 1998). However, since other countries in Europe use present day valuesonly, this was discussed with UK experts and we agreed to compare longer-term meanvalues of BCdep, with those for 2-3 years and the values previously used. The latestavailable deposition data are for 1995-97 at 5km resolution; however, problems wereidentified in thc non-marine deposition values in this data set, which have been reportedback to NETCEN (via Cal Edinburgh) for clarification, hence these data have not beenused. Comparisons of B'Cdepvalues for 1986-91 (5km resolution data) with thosepreviously used (ie, based on non-marine base cations for 1992-94 and modelled non-marine chloride for 2010) showed that although the maximum values for 1986-91 werehigher, the mean values across the country were lower than those previously used.However, we decided to use the 1986-91 5km data as longer-term mean values, ratherthan continuc to include a modelled estimate of non-marine chloride for 2010.
Values for BC„ remain unchanged for acid grassland, calcareous grassland and heathland.For the woodland ecosystems the new BC„ values described in Section 2.2 and listed inTable 1, were used.
The calculation of CL„,„,,,Sfor freshwater ecosystems remains unchanged since 1998 (Hallet al., 1998).
5.2 Minimum Critical Load of Nitrogen (CL„,b,IV)
The calculation of CL„,I„Nfor terrestrial ecosystems has been changed since that used inthe UK in 1998 (which excluded denitrification), so it is now consistent with the UNECEMapping Manual (UBA, 1996):
CL,,„„N= Nu+Nri-NdeWhere N„ = nitrogen uptake
N, = nitrogen immobilisationNde = denitrification
N, data are thc same as in 1998, based on soil type. Uptake values for woodlandecosystems have been modified according to Section 2.2 and Table I of this report.Uptake values for other ecosystems remain unchanged. Values for Nth,are based on soiltype (Hall et at, 1998). The inclusion of Aide in the equation and revised nitrogen uptakevalues for woodland ecosystems have lcd to increased CLm,„NI values
The calculations of CL„,,„Nfor freshwater ecosystems remain unchanged since 1998 (Hallet al., 1998).
5.3 Maximum Critical Load of Nitrogen (CL„,aN)
CLN is calculated for terrestrial ecosystems as:CL„,„,,N= CL„„„N+ CL„,arS
Changes to the input data used in the calculations of CL„,,„Nand CL„„uS have led tochanges in the values of CL„,a,N. However, for most ecosystems the changes are verysmall (less than 0.1 keq ha1 year.' for mean values).
The calculation of CL„,„„N for freshwater ecosystems remains unchanged since 1998(Hall et at, 1998).
REFERENCES
CORINE. 1994. CORINE Land Cover Technical Guide. European Commission.Directorate-General Environment, Nuclear Safety and Civil Protection.
Fuller, R.M., Groom, G.B. & Jones, A.R. 1994. The Land Cover Map of Great Britain:an automated classififcation of Landsat Thematic Mapper data. PhotogrammetricEngineering and Remote Sensing, 60, 553-562.
Hall, J., Bull, K., Bradley, I., Curtis, C., Freer-Smith, P., Hornung, M., Howard, D.,Langan, S., Loveland, P., Reynolds, B., Ullyett, J. & Warr, T. 1998. Status of UKCritical Loads and Exceedances, January 1998. Part 1 — Critical Loads and CriticalLoads Maps. Report prepared under DETR/NERC Contract EPG1/3/116. Also on theUK NFC web site at: http://critloads.ceh.ac.uk
Hall, J., Broughton, R., Bull, K., Curtis, C., Fowler, D., Heywood, E., Hornung, M.,Metcalfe, S., Reynolds, B., Ullyett, J. & Whyatt, D. 2001. Status of UK Critical Loadsand Exceedances, January 1998. Part 2 —Exceedances. In preparation.
Flail, J., Reynolds, B., Aheme, J. & Hornung, M. 2001a. The importance of selectingappropriate criteria for calculating acidity critical loads for terrestrial ecosystems usingthe simple mass balance equation. Water, Air and Soil Pollution: Focus 1: 29-41.
Hall, J., Reynolds, B., Langan, S., Hornung, M., Kennedy, F. & Aherne, J. 2001b.Investigating uncertainties in the simple mass balance equation for acidity critical loadsfor terrestrial ecosystems in the United Kingdom. Water, Air and Soil Pollution: Focus 1:43-56.
Hettelingh, J.-P., Posch, M., de Smet, P.A.M. & Downing, R.J. 1995. The use of criticalloads in emission reduction agreements in Europe. Water, Air and Soil Pollution, 85,2381-2388.
Posch, M. & Hettelingh, J.-P. 1997. Remarks on critical load calculations. In: Posch,M., de Smet, P.A.M., Hettelingh, J.-P. & Downing, R.J. (Eds.), Calculation and Mappingof Critical Thresholds in Europe: Status Report 1997. Coordination Centre for Effects,National Institute of Public Health and the Environment (RIVM), Bilthoven, TheNetherlands. pp 25-28.
Posch, M., de Smet, P.A.M. & Hettelingh, J.-P. 1999. Critical loads and theirexceedances in Europe: an overview. In: Posch, M., de Smet, P.A.M., Hettelingh, J.-P. &Downing, R.J. (Eds.), Calculation and Mapping of Critical Thresholds in Europe: StatusReport 1999. Coordination Centre for Effects, National Institute of Public Health and theEnvironment (RIVM), Bilthoven, The Netherlands. pp 3-11.
Posch, M., de Vries, W., & Hettelingh, J.-P. 1995. Critical loads of sulphur and nitrogen. In: Posch, M., de Smet, P.A.M., Hettelingh, J.-P. & Downing, R.J. (Eds.),
Calculation and Mapping of Critical Thresholds in Europe: Status Report 1995.Coordination Centre for Effects, National Institute of Public Health and the Environment(RIVM), Bilthoven, The Netherlands. pp 31-41.
Smith, C.S.S., Cresser, M.S. & Mitchell, R.D.J. 1993. Sensitivity to acid deposition ofdystrophic peat in Great Britain. Ambio. 22, 22.
Smith,R.I. & Fowler,D. 2001. Uncertainty in estimation of wet deposition of sulphur.Water, Air, and Soil Pollution (in press).
Smith,R.I., Fowler,D., Sutton,M.A., Flechard,C.R. & Coyle,M. 2000. Regionalestimation of pollutant gas dry deposition in the UK: model description, sensitivityanalyses and outputs. Atmospheric Environment, 34, 3757-3777.
UBA. 1996. UNECE Manual on methodologies and criteria for mapping criticallevels/loads and geographical areas where they are exceeded. Federal EnvironmentalAgency (Umweltbundesamt), Berlin.
.
Appendix 1
SMB equation using Ca:Al ratio as chemical criterion (mineral soils).NB. Base cation (BC) terms here only relate to calcium.
CL(A) = ANC, —ANCufrnoWhere:
= critical loads of acidity (calculated in eq had yean[using units given here divide CL(A) by 1000 to give keq hi' yeaf ']
= Acid Neutralising Capacity produced by weathering (eq had yeard)
= critical leaching of ANC (eq hi' yea(d)= -Airekrio —fitercrio
= critical leaching of Aluminium (eq hi' yea(')= ((I.5 • BC,,)/ Ca:AI) " 1000
= calcium leaching (keq hi' year')= BC„ - BC
= net uptake of calcium (keq had yeard)= minimum (u, BC„)
= calcium uptake (keq had year' ), see values in Table 2.
= calcium availability (keq had year.) = maximum (Co,.. + Caag, —BC„„„, 0)
= calcium weathering (keq had year )
= total (marine plus non-marine) calcium deposition for woodland1995-97 (keq had year. 1)
= minimum calcium leaching (keq had year')Q • [BC] • 0.01
= runoff (metres year")
= limiting concentration for uptake of calcium (2peq 11)
= critical leaching of hydrogen ions (eq had yeard)= (1.5 ((BCk * 1000)/ (Kgtho * CO:A0))113 (Q 10000)213
= gibbsite equilibrium constant (mineral soils: 950 [m6/eq2])
= Calcium:Aluminium ratio = 1
CL(A)
ANC.
ANCemo
Aluuno
BC
BCa
Ca,,
Cadet,
[BC1]
Hk(ert0
Kgibb
Co:Al
Appendix 2SMB equation using critical pH as chemical criterion (organic soils).
CL(A) = ANC. —ANCIeknoWhere:
CL(A) = critical loads of acidity (calculated in eq hal yearl)[using units given here divide CL(A) by 1000 to give keq hal yearl]
ANC. = Acid Neutralising Capacity produced by weathering (eq hal yearl)
ANCtefrno = critical leaching of ANC (eq hal yearl)= Q (IN + LAU)
= runoff (m3 hal = mm runoff * 10)
[11] = hydrogen ion concentration (eq m-3)= lo(.pH)* woo
pH = critical pH (4.0)
[AI] = aluminium concentration (eq n13)Kgibb* H3
Kgsbb = gibbsite equilibrium constant (organic soils: 9.5 [n.16/eq2])
App
endi
x3.
Sum
mar
yof
UK
criti
cal
load
valu
esan
dth
eju
stifi
catio
nfo
rth
eir
use
Crit
ical
load
sar
amet
erE
cosy
stem
code
Min
imum
valu
eM
axim
umva
lue
Dat
aso
urce
s/m
etho
dsus
ed
CL(
S)
AG
130
5030
=C
LA+
(BC
dcp•
--
BC
uE
q/ha
/yea
rC
G59
847
98C
LA=
empi
rical
soil
criti
cal
load
s(b
ased
on
H13
050
10w
eath
erin
gra
te&
min
eral
olog
yof
dom
inan
tso
ilty
pe)
C10
1173
2fo
rA
G,
CG
&H
,an
dS
MB
equa
tion
for
C&
D.
D4
1110
8S
eeB
Cde
p,C
ldep
and
BC
uco
mm
ents
belo
w.
W0
3690
0=
L/
1-
•C
L„,,,
,(N
)A
G21
357
0=
N,
+N
, s-N
d,E
q/ha
/yea
rC
G85
712
14S
eeN
u,N
i,&
Nde
com
men
tsbe
low
.
H43
379
0
C64
310
00
D64
310
00
W15
638
-fly
„+
(1-1
9(7v
, +N
dc)
CL„
,„(N
)A
G36
355
50=
CL„
„a(S
)+
CLu
„,,(
N)
Eq/
ha/y
ear
CG
1455
5972
583
5466
733
1265
1
647
1175
1
143
2015
00=
CL„
,„/V
+L
,/
I—
NC
L„,u
(N)
AG
714
1786
Em
piric
alva
lues
appl
ied:
Ey/
ha/y
ear
Aci
dgr
assl
and:
10,
12.5
,25
kgN
/ha/
ycar
depe
ndin
gon
sci
esre
sent
.
CG
3571
3571
Em
irica
lva
lue
alie
d:50
kN
ib./
ear
714
1214
Em
piric
alva
lues
appl
ied:
10,
15,
17kg
N/h
a/ye
arde
pend
ing
onsp
ecie
spr
esen
t.
Just
ifica
tion
Map
ping
Man
ual
(UB
A,
1996
)
Map
ping
Man
ual.
Map
ping
Man
ual.
Ne,
.valu
esca
tclu
nent
-wci
ghte
dac
cord
ing
toar
eaof
diffe
rent
soils
rcsc
ntin
catc
hmen
t.M
appi
ngM
anua
l
Map
ping
Man
ual.
Map
ping
Man
ual.
Em
piric
alva
lues
reco
mm
ende
dby
UK
expe
rts
(Hal
let
at19
98).
How
ever
,th
cU
Kw
illre
view
thes
eaf
ter
the
UN
EC
Ew
orks
hop
in20
02to
revi
ewem
piric
alcr
itica
llo
ads
for
nutr
ient
nitr
ogen
.
928
928
Min
imum
ofem
piri
cal v
alue
(13
kgN
/ha/
year
) or
mas
sba
lanc
eva
lue
(whe
reC
L„
„,(
N)=
N„
+N
,+
Ndd
.N
,&
Nd
eva
lues
betw
een
1&
4kg
N
/ha/
year
depe
ndin
gon
soil
typc
.Pr
evio
usly
only
mas
sba
lanc
eus
edfo
r con
ifer
s.
1071
1214
Min
imum
ofem
piri
cal v
alue
(17k
gN
/ha/
year
) or
mas
sba
lanc
eva
lue
(whc
rcC
L„
,(N
)-
144,+
N, +
N
,k).
N, &
Nth
. valu
esbe
twee
n1
&4
kgN
/ha/
ycar
dend
inon
soil
N
otca
lcul
ated
.-
AG
1150
BC
dep•
and
C/d
ep•=
chan
ged
tom
easu
red
mca
nda
taE
q/ha
/yea
rC
G
1150
1986
-91
for
low
vege
tatio
n.
11
50
18
50B
Cd,
./,'a
ndC
Idep
•=ch
angc
dto
mea
sure
dm
ean
data
I)
1850
1986
-91
for
woo
dlan
dm
osst
ems.
N
otus
ed.
AG
00
Sct t
oze
ro-
upta
kene
glig
ible
for a
cid
gras
slan
d.E
q/ha
/yea
r
CG
222
222
Incl
udes
rem
oval
via
shee
.
II0
0N
ou
take
for h
eath
land
.
250
250
New
valu
es.
Cal
cula
ted
from
: ave
rage
volu
me
incr
emen
t•
basi
cw
ood
dens
ity•
conc
entr
atio
nin
woo
dan
das
sum
ing
pote
ntia
l yie
lds
achi
eved
.V
alue
sba
sed
onda
tafo
r Sitk
aS
ruce
.
400
850
New
valu
es.
Cal
cula
ted
from
: ave
rage
volu
me
incr
emen
t •ba
sic
woo
dde
nsity
•co
ncen
trat
ion
inw
ood
and
assu
min
gpo
tent
ial y
ield
sac
hiev
ed.
Val
ues
base
don
data
for O
ak.
Min
imum
valu
efo
rC
a-po
orso
ilsan
dm
axim
umva
lue
for
Ca-
rich
soils
.
Not
used
.A
NC
,E
q/ha
/yea
rA
G
CG
SMB
not u
sed:
empi
rica
l cri
tical
load
sof
acid
ityfo
rso
ilsap
plie
d,th
eref
ore
AN
Cw
not a
ssig
ned.
040
00Se
t to
zero
for
peat
soils
Mas
sba
lanc
eeq
uatio
nan
dem
piri
cal v
alue
asre
com
men
ded
inM
appi
ngM
anua
l.In
put v
alue
sre
com
men
ded
byU
Kex
pert
s(H
all e
taL
1998
).E
mpi
rica
l val
uelo
wer
ever
ywhe
re.
Map
ping
Man
ual.
Em
piri
cal v
alue
sre
com
men
ded
byU
Kex
pert
s.In
put v
alue
sto
mas
sba
lanc
eeq
uatio
nre
com
mcn
dcd
byU
Kex
pert
s(H
all e
tat
1998
).
Map
ping
Man
ual.
Bas
edon
publ
ishe
dda
taby
UK
expe
rts.
Bas
edon
ublis
hed
data
bU
Kex
ens.
Bas
edon
publ
ishe
dda
ta.
Sing
leva
lue
for
UK
for
each
ofth
efo
llow
ing:
coni
fero
usw
oodl
and
(all
soils
),de
cidu
ous
woo
dlan
d(C
a-po
orso
ils),
deci
duou
sw
oodl
and
(Ca-
rich
soils
).R
egio
nal a
ndsp
ecie
ssp
ecif
icvo
lum
ein
crem
ent a
ndco
ncen
trat
ion
inw
ood
tobe
inco
rpor
ated
infu
ture
.N
B.
The
seus
edin
CL
max
Sca
lcul
atio
nson
ly,
estim
ates
ofca
lciu
mup
take
only
used
inSM
Bfo
rm
iner
also
ils.
Met
hods
agre
edby
UK
expe
rts
(Ila
net
aL19
98).
(SM
Bon
lyap
plie
dto
woo
dlan
dcc
osys
tem
sin
UK
).
Rec
omm
ende
din
Map
ping
Man
ual.
See
Hor
nung
etaL
,19
95.
Ass
igne
dva
lues
chec
ked
agai
nst
appl
icat
ion
ofPR
OFI
LE
for
limite
dnu
mbe
rof
site
s.
040
00
N
otus
ed.
AN
Cto
c,„)
AG
SM
Bno
tus
ed:
empi
rical
criti
cal
load
sof
acid
ityfo
rM
etho
dsag
reed
byU
Kex
pert
s(H
all
etat
1998
).E
q/ha
/yea
rC
G
soils
appl
ied,
ther
efor
eA
NC
le(c
rit)
not
calc
ulat
ed.
(SM
Bon
lyap
plie
dto
woo
dlan
dec
osys
tem
sin
UK
).
0.1
7734
Cal
cula
ted
via
SM
Beq
uatio
nw
ithra
tioof
Ca:
Al
=1
SM
Bw
ithB
C:A
lra
tioan
dba
seca
tion
depo
sitio
n
070
67as
chem
ical
crite
rion
for
min
eral
soils
and
criti
cal
pH4.
0fo
ror
gani
cso
ils.
Em
piric
alac
idity
criti
cal
load
sa
lied
tot
soils
.
prod
uccd
unre
alis
tical
lyhi
ghcr
itica
llo
ads.
Ca:
Al
ratio
rcco
mm
endc
din
pape
rby
Cro
nan
&G
rigel
1995
.
F
orfr
eshw
ater
sth
eA
NC
li„,„
isse
tat
zero
Req
/1.
Val
uese
lect
edfo
r50
%pr
obab
ility
ofda
mag
eto
brow
ntr
out
oul
atio
ns.
NA
G70
70E
quiv
alen
tto
lkg
N/h
a/ye
arB
ased
onpu
blis
hed
data
byU
Kex
pert
sE
q/ha
/yea
rC
G71
471
4E
uiva
lent
to10
kN
/ha/
ear
29
029
0E
uiva
lent
to4k
N/h
a/ea
r
50
050
0N
ewva
lues
.M
etho
dsas
for
BC
a.B
ased
onpu
blis
hed
data
—on
eva
lue
for
who
leof
UK
:
500
500
reio
nal
row
thva
lues
tobe
inco
rate
din
futu
rc.
027
9=
No.
Use
sN
ava
lue
of27
9eq
/ha/
year
for
all
coni
fero
usfo
rest
mul
tiplie
dby
perc
enta
gefo
rest
inca
tchm
ent.
Bas
edon
publ
ishe
dda
ta.
Cur
tiset
al(1
998)
.
N,
AG
7121
4V
alue
sde
pend
ant
onso
ilty
pe.
Bas
edon
publ
ishe
dda
tafo
rlo
ngte
rmsu
stai
nabi
lity.
Eq/
ha/y
ear
CG
7121
4E
quiv
alen
tto
1or
3kg
N/h
a/ye
ar
7121
4
7121
4
I)71
214
721
4N
, val
ues
catc
hmen
t-w
eigh
ted
acco
rdin
gto
arca
ofdi
ffere
ntso
ilsre
sent
inca
tchm
ent.
Eq/
ha/y
ear
AG
CG
Em
piric
alnu
trie
ntni
trog
encr
itica
llo
ads
used
.th
eref
ore
Nle
(acc
)no
tas
sign
ed.
428
428
Equ
ival
ent
to6k
gM
ita/y
ear.
Val
ues
base
don
data
from
alim
ited
num
ber
of
428
428
deta
iled
site
stud
ies
for
GB
lant
atio
ns.
Not
used
.
Nat
,E
q/ha
/yea
rA
G71
286
Use
din
CLm
inN
only
.(E
mpi
rical
criti
cal
load
sof
nutr
ient
nitr
ogen
used
).V
alue
sas
sign
edac
cord
ing
toso
ilty
pe.
Equ
ival
ent
to1,
2or
4kg
N/h
a/ye
ar.
CG
H71
71
286
286
C
7128
6U
sed
inC
Lm
inN
and
mas
sba
lanc
eof
CL
nutN
.
D71
286
Val
ues
assi
edac
cord
into
soil
.
W7
285
Use
sca
tchm
ent-
wei
ghte
dN
d,va
lues
(bas
edon
soil
type
)in
stea
dof
fd,..
Use
offd
,(0
.1-0
.8)
asin
Map
ping
Man
ual g
ives
Ack
valu
esup
to25
kgN
/ha/
year
—m
uch
too
high
for U
K
C
urtis
etal
1998
. Pr
ecip
itatio
nsu
rplu
sQ
(m)
AG
C
G
SMB
not u
sed,
ther
efor
eQ
not a
ssig
ned.
H
C
0.05
73.
876
Ikm
runo
ffda
taba
sed
on30
-yea
r (19
41-1
970)
mea
nU
sed
inSM
Beq
uatio
nfo
r aci
dity
criti
cal
load
s.
D0.
057
3.87
6ra
infa
llda
ta.
kOD
(m6/
eq2)
W AG
C
G
0.09
73.
364
lkm
catc
hmen
t-w
eigh
ted
runo
ffba
sed
onm
ean
Use
din
FAB
.ra
infa
llda
tafo
r19
41-7
0fo
r GB
and
1961
-90
for N
I.SM
Bno
t use
d(e
mpi
rica
l aci
dity
criti
cal
load
sap
plie
d).
H
C9.
595
0M
inim
umva
lue
appl
ied
toor
gani
cso
ilsan
dm
axim
umM
appi
ngM
anua
l.
D9.
595
0va
lue
alie
dto
min
eral
soils
.
W
Not
used
.
a- Eco
syst
emC
odes
:A
G=
acid
gras
slan
dC
G=
calc
areo
usgr
assl
and
H=
heat
hlan
dC
=co
nife
rous
fore
stD
=de
cidu
ous
fore
stW
=w
ater
s
Ref
eren
ces
Cro
nan,
C.S
.&
Grig
al,
D.F
.19
95.
Use
ofca
lciu
m/a
lum
iniu
mra
tios
asin
dica
tors
ofst
ress
info
rest
ecos
yste
ms.
Jour
nal
ofE
nviro
nmen
tal
Qua
lity,
24:2
09-2
26.
Cur
tis,
C.J
.,A
llott,
T.E
.H.,
Bird
,D
.,H
all,
J.,
Har
riman
,R
.,H
elliw
ell,
R.,
Ker
nan,
M.,
Rey
nold
s,B
.&
Ully
ett,
J.19
98.
Crit
ical
load
sof
sulp
hur
and
nitr
ogen
for
fres
hwat
ers
inG
reat
Brit
ain
and
asse
ssm
ent
ofde
posi
tion
redu
ctio
nre
quire
men
tsw
ithth
eF
irst-
orde
rA
cidi
tyB
alan
ce(F
AB
)m
odel
.R
esea
rch
Pap
erN
o.16
.E
nviro
nmen
tal
Cha
nge
Res
earc
hC
entr
e,U
nive
rsity
Col
lege
Lond
on.
Hal
l,J.
,B
ull,
K.,
Bra
dley
,I.,
Cur
tis,
C.,
Fre
er-S
mith
,P
.,H
ornu
ng,
M.,
How
ard,
D.,
Lang
an,
S.,
Love
land
,P
.,R
eyno
lds,
B.,
Ully
ett,
J.&
War
r,T
.19
98.
Sta
tus
ofU
Kcr
itica
llo
ads
and
exce
edan
ces,
Janu
ary
1998
.P
art
1—
Crit
ical
load
san
dcr
itica
llo
ads
map
s.R
epor
tpr
epar
edun
der
DE
TR
/NE
RC
Con
trac
tE
PG
1/3/
116.
Als
oon
the
UK
NF
Cw
ebsi
te:
http
://cr
itloa
ds.c
eh.a
c.uk
Hor
nung
,M
.,B
ull,
K.R
.,C
ress
er,
M.,
Hal
l,J.
,La
ngan
,S
t,Lo
vela
nd,
P.
&S
mith
,C
.19
95.
An
empi
rical
map
ofcr
itica
llo
ads
ofac
idity
for
soils
inG
reat
Brit
ain.
Env
ironm
enta
lP
ollu
tion,
90:3
01-3
10.
Pos
ch,
M.,
Het
telin
gh,
J.-P
.,de
Sm
et,
P.A
.M.
&D
owni
ng,
R.J
.(e
ds.)
1997
.C
alcu
latio
nan
dm
appi
ngof
criti
cal
thre
shol
dsin
Eur
ope:
CC
ES
tatu
sR
epor
t19
97.
Nat
iona
lIn
stitu
teof
Pub
licH
ealth
and
the
Env
ironm
ent,
Rep
ort
2591
0100
7,B
iltho
ven,
Net
herla
nds.
UB
A,
1996
.M
anua
lon
met
hodo
logi
esan
dcr
iteria
for
map
ping
criti
cal
leve
ls/lo
ads
and
geog
raph
ical
area
sw
herc
they
are
exce
eded
.U
NE
CE
Con
vent
ion
onLo
ng-R
ange
Tra
nsbo
unda
ryA
irP
ollu
tion.
Fed
eral
Env
ironm
enta
lA
genc
y(U
mw
eltb
udes
amt)
,B
erlin
.
Appendix 4: Maps of critical loads based on the old (1998) versus the new (2001)calculations.
The following pages contain ecosystem maps of:The maximum critical loads of sulphur (CLma/S))The minimum critical loads of nitrogen (CL,,,,,,,(N))The maximum critical loads of nitrogen (CL,,a(N))Critical loads of nutrient nitrogen (anaN))
The text in the main body of the report describes the derivation of these critical loadsand should be read in conjunction with viewing these maps.
2001
1998
Max
imum
criti
cal
load
sof
Sulp
hur
for
acid
gras
slan
d
keg
11ha
''ea
r'
111
0.2
-0.
5
0.5
-1.
0
1.0
-2.
0
>2.
0
Max
imum
crit
ical
load
sof
Sulp
hur
for
calc
areo
usgr
assl
and
1998
412
2001
keq
1-1+
had
year
'
<=
0.2
0.2
-0.
5
ri0.
5-
1.0
1.0
-2.
0
>2.
0
4
Max
imum
crit
ical
load
sof
Sulp
hur
for
heat
hlan
d
2001
keq
H+
ha-'
ear'
<=
0.2
0.2
-0.
5
0.5
-1.
0
1.0
-2.
0
>2.
0
1998
Max
imum
crit
ical
load
sof
Sulp
hur
for
coni
fero
usw
oodl
and
keq
Hha
-Iye
ar'
<=
0.2
1111
0.2
-0.
5
ri0.
5-
1.0
1.0
-2.
0
>2.
0
2001 eg
.'I'
"CIA
1998
Max
imum
crit
ical
load
sof
Sulp
hur
for
deci
duou
sw
oodl
and
1998
2001
keg
H±
ha-'
year
'
<=
0.2
0.2
-0.
5
n0.
5-
1.0
1.0
-2.
0
>2.
0
Max
imum
crit
ical
load
sof
Sulp
hur
for
fres
hwat
ers
1998
2001
keq
H+
had
year
'
<=
0.2
1.1
0.2
-0.
5
n0.
5-
1.0
1.0
-2.
0
>2.
0
epa.
I...11
..r•
....
S.
!,-.
2.1ei
ts-C
:1-;
'
Ia
I14
%14
•a
%I.L
.J.1
11-"
sh-r-
N
-....
I%
1-
.. ..
...la
..4.
......
•tp,
zi .
..-4
..
lair
d.a
.J
.•
1
e ,.re. _
..1
r11
:zc
atlialt
r,-
-i-g
-IC
is'•
1..
.,-
---4
,-,,,
crcl
-
Min
imum
crit
ical
load
sof
Nit
roge
nfo
rac
idgr
assl
and
2001
key
H+
had
year
'
<=
0.2
IIII
0.2
-0.
5
n0.
5-
1.0
1.0-
2.0
>2.
0
1998
•
Min
imum
crit
ical
load
sof
Nit
roge
nfo
rca
lcar
eous
gras
slan
d
1998
2001
keq
Ht
ha-I
year
'
<=
0.2
0.2
-0.
5
n0.
5-
1.0
1.0
-2.
0
>2.
0
,•A
Cr1
7.
k1
)cr
e-r
•e
,
Min
imum
crit
ical
load
sof
Nit
roge
nfo
rhe
athl
and
keq
ha-1
year
t
<=
0.2
0.2
-0.
5
ni0.
5-
1.0
1.0
-2.
0
>2.
0
2001
1998
44-
fre-
'719
'SQ
L-1
Min
imum
crit
ical
load
sof
Nit
roge
nfo
rco
nife
rous
woo
dlan
d
1998
41
<rs
,
keq
H+
ha-1
year
'
1111
<=
0.2
II0.
2-
0.5
n0.
5-
1.0
1.0
-2.
0
>2.
0
2001 ce
a.
Min
imum
crit
ical
load
sof
Nit
roge
nfo
rde
cidu
ous
woo
dlan
d
1998
cr2
S.
keq
H+
lia-'
year
'
<=
0.2
0.2
-0.
5
ri0.
5-
1.0
1.0
-2.
0
>2.
0
2001
Min
imum
crit
ical
load
sof
Nit
roge
nfo
rfr
eshw
ater
s
1998
2001
keq
H+
had
year
'
<=
0.2
0.2
-0.
5
n0.
5-
1.0
1.0
-2.
0
>2.
0
a••
•°
I'
Max
imum
criti
cal
load
sof
Nitr
ogen
for
acid
gras
slan
d
2001
keg
IIII:
II
{
-0.
2
11.1
-0.
5
0.5
1.0
1.0
-2.
0
2.0
.11
Max
imum
crit
ical
load
sof
Nit
roge
nfo
rca
lcar
eous
gras
slan
d
1998
2001
4"77
•‘
Stf
Yr(
••
40
•%
ye
ci
keq
IVha
dye
ard
<=
0.2
0.2
-0.
5
pi0.
5-
1.0
1.0
-2.
0
>2.
0
\
41.•
FaC
Y-
I
e•I 4
Max
imum
crit
ical
load
sof
Nit
roge
nfo
rhe
athl
and
1998
2001
keq
1-1+
ha-1
year
'
<=
0.2
0.2
-0.
5
n0.5
-1.
0
II1.
0-
2.0
>2.
0
Max
imum
crit
ical
load
sof
Nit
roge
nfo
rco
nife
rous
woo
dlan
d
1998
2001
keq
H÷
ha-1
year
'
<=
0.2
El
0.2
-0.
5
0.5
-1.
0
1.0
-2.
0
>2.
0
Max
imum
crit
ical
load
sof
Nit
roge
nfo
rde
cidu
ous
woo
dlan
d
2001
keq
Hha
-1ye
ari
<=
0.2
0.2
-0.
5
ri0.
5-
1.0
1.0
-2.
0
>2.
0
1998
Cri
tica
llo
ads
ofN
utri
ent
Nit
roge
nfo
rhe
athl
and
1998
f20
01
keq
H+
hal
year
'
<=
0.2
0.2
-0.
5
1110.5
-1.
0
1.0
-2.
0
>2.
0
•
Cri
tica
llo
ads
ofN
utri
ent
Nit
roge
nfo
rco
nife
rous
woo
dlan
d
2001
1998
keqH
+hr'
year
'
<=
0.2
NI
0.2-
0.5
ri0.
5-1.
0E
l1.
0-2.
0>
2.0
Cri
tica
llo
ads
ofN
utri
ent
Nit
roge
nfo
rde
cidu
ous
woo
dlan
d
Ic
1998
2001
keq
Wha
-'ye
ar'
<=
0.2
0.2
-0.
5
n0.
5-
1.0
1.1
1.0
-2.
0
>2.
0
Max
imum
crit
ical
load
sof
Nit
roge
nfo
rfr
eshw
ater
s
1998
2001
key
H+
hal
year
l
<=
0.2
El
0.2
-0.
5
0.5
-1.
0
El
1.0
-2.
0
>2.
0
iY. 1
.raly
14)
Iic
ei
I
ma
ma
%jib
aas
ar•.
•I
II
an%
I.1••
,r:j
ci‘
or
r-s
I
I•
it-
\
• r
.••
ou
t;t•
—•
L%S
. 1.I
11kl
me
a. ni
a&
cak;
rr.;„e
jihrj
r•la
•tr-
_an
.
Li
Cri
tica
llo
ads
ofN
utri
ent
Nit
roge
nfo
rac
idgr
assl
and
2001
keq
Wha
-'ye
ar'
<=
0.2
0.2
-0.
5
n0.
5-
1.0
1.0
-2.
0
>2.
0
1998
Cri
tica
llo
ads
ofN
utri
ent
Nit
roge
nfo
rca
lcar
eous
gras
slan
d
1998
2001
keq
1-1*
hai
year
'
<=
0.2
0.2
-0.
5
ri0.
5-
1.0
1.0
-2.
0
>2.
0
ea
erf
4Pe.
Edinburgh
mere od
ksWood/ctorate
n ord
4011.NATURALtow ENVIRONMENT
RESEARCH COUNCIL
•