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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

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)

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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])

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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

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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

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k1

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e-r

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,

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

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ye

ci

keq

IVha

dye

ard

<=

0.2

0.2

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0

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0

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Y-

I

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Max

imum

crit

ical

load

sof

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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

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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

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0

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0

1998

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tica

llo

ads

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utri

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Nit

roge

nfo

rhe

athl

and

1998

f20

01

keq

H+

hal

year

'

<=

0.2

0.2

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5

1110.5

-1.

0

1.0

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0

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0

•

Cri

tica

llo

ads

ofN

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rous

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d

2001

1998

keqH

+hr'

year

'

<=

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2.0

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tica

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ads

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woo

dlan

d

Ic

1998

2001

keq

Wha

-'ye

ar'

<=

0.2

0.2

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5

n0.

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1.0

1.1

1.0

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0

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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

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5

0.5

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1998

2001

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Edinburgh

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4011.NATURALtow ENVIRONMENT

RESEARCH COUNCIL

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