Bull, K.

Campbell, G. W.

Chadwick, M. J.

Cresser, M. S.

Fowler, D.

Hall, J.

Hornung, M.

Irwin, J. G.

Jones, R. J. A.

Kuylenstierna, J. C. I.

Langan, S. J.

Loveland, P. J.

Wilson, M. J.

English

NERC Open Research Archive

CRITICAL LOADS MAPS FOR THE UNITED KINGDOM I. SOILS A report to the Department of the Environment by the UK Critical Loads Advisory Group CONTENTS Contributors to the soil and deposition maps MAP 1 Provisional map of critical loads for acidity of soils for Great Britain MAP 2 Critical loads for acidity for UK soils MAP 3 Estimated critical loads for sulphur for the UK MAP 4 Total non-marine sulpbur deposition in the UK MAP 5 Total non-marine sulphur and nitrogen deposition in the UK MAP 6 Non-marine calcium and magnesium deposition in h e  UK MAP 7 The ratio of total sulphur deposition to total sulphur plus nitrogen MAP 8 Areas of the UK where critical loads for acidity are exceeded MAP 9 Areas of h e  UK where critical loads far sulphur are exceeded MAP 10 The EMEP grid for the UK TABLE 1 The percentile distributions of the values of different cr i t id  loads for acidity of soils in EMEP squares of the UK REFERENCES CONTRIBUTORS TO THE SOILS AND DEPOSITION MAPS KRBdJ GW Campbell MJ Chadwick MS Cresser D Fowler JR Hall M Hornung JG Irwin RJA Jones JCI Kuylenstierna SJ Langan PJ Luveland MJ Wilson Institute of Terrestrial Ecology * Warren Spring Laboratory Stockholm Environment Institute, York University of Abcrdeen Institute of Terrestrial Ecology Institute of Terrestrial Ecology Institute of Terrestrial Ecology Warren Spring Laboratory Sail Survey and Land Research Centre Stockholm Environment Institute, York Heaning Cansultancy Soil Survey and Land Research Centre MacauIay Land Use Research Institute * UK Centre for Critical Loads Mapping PROVISIONAL MAP OF CRITICAL LOADS FOR ACIDITY OF SOIlS FOR GREAT BRITAIN The map is based on 1 km squares of the UK Ordnance Survey national grid and on 1 :250 000 sa le  soil maps, and supporting data bases. The soil maps for England and Wales were produced and published by the Soil Survey and Land Research Centre (SSLRC, 19831, and for Scotland by the Macaulay Land Use Research Institute (MLURI, 1981). Each 1 km square was assigned a critical load for total deposited acidity on the basis of the critical load of the soil map unit which occupied the largest proportion of the square. The map units were assigned a critical load fallowing their aiIocation to one of five soil classes, defined at the workshop held at Skokloster in 1988 (Nilsson and Grennfelt 1988), which were based on soil mineralogy (Table A). The soil classes proposed at the Skokloster workshop were equated with a band of critical load values, eg 20-50 keq H+ km-2year1. In the productionof this map the classes have been assigned a single critical load value, the upper limit of the band suggested at Skokloster; this has been done to facilitate the production of exceedance maps showing areas where the critical loads are ex- ceeded. On the soil maps covering Scotland, the map units, which are identified by number, comprise groups of soils, from a given soil association, occurring within a distinct landscapelgeamorphoIogica1 unit, The associations are assemblages of soil series formed on a given parent material. The map units were initialIy allocated to one of the five soil classes, defined at Skokloster, on the basis of available information on the mineralogy of the parent material of the relevant soit association. This initial allocation was then modified, where necessary, using modifiers basedon soil depth, texture and drainage, as suggested at Skokloster. Thus, where a map unit was dominated by shallow soils on slopes, the soil class based on mjncralogy was decreased by one class. Conversely, in units dominated by deep soils or soils inundated regularly the class was increased by one. The map units on the maps covering England and Wales are soil associations, which are groups of soil series occurring within defincd, distinct landscape/geomorphol- ogical units. The parent material can vary within the association, but only within narrow limits. The associations wi thin England and Wales are named after the most widespread soil series within the association. The map units were initially allocated to a soil class on the basis of the mineralogy of the most widespread soil series within the associalion. This initial allocation was modified, where necessary, after making allowance for variations in soil depth, texture and drainage conditions, as with the units on the maps covering Scotland. Organic soils cannot be allocated to one of the Skokloster classes on the basis of mineralogy. An approach developed in the Department of Plant and Soil Science, University of Aberdeen has, therefore, been used. Map units dominated by base p r  peats were allocated to one of the five soils classes on the basis of the H+ load (as W,SOS which would result in a pH reduction in the surface layers of the peats, in the given location, of >0.2; it is assumed that reductions of pH of ~ 0 . 2  would not have significant ecological consequences. The boundaries between classes have been set using the results of laboratory equilibration studies, and data on the relationship between changes in surface horizon pH of peats in Scotland over the last 20 years and inputs of acidic deposition over that period. The input of acidity over the last 20 years has included both nitric and sulphuric acid. In order to assign the peats to one of the five classes based on sulphur alone, it has been assumed that 70% of the input of acidity was as sulphuric acid and 30% as nitric acid. Where 30% of recent input, ie the nitric acid portion of the input, has produced a reduction in pH of >0.2, the peat unit is allocated to the most sensitive class, class 5. Where 30% of recent input would produce a reduction in surface pH of ~ 0 . 2 ,  then the critical load has been based on the 'acceptable load' of sulphuric acid, over and above the existing nitric acid load. Finally, a land use modifier was applied to the complete map using a database developed by the Institute of Terrestrial Ecology (Bunce & Heal, 1984). For each lkm square, the critical load class of the dominant soil was decreased by one unit if ihe dominant land use for that area was arable or improved pasture. It was assumed that in these areas lime would be added to the wiI, where necessary, to maintain the pH within the optimal range far arable crops or high yielding grass varieties. This would clearly increase the "effective critical load". A number of points must be stressed about the map produced using the above procedures: 1. The map units prtraycd on the It250 000 soil base maps can encompass considerable variation in soil type, although the soils within any one map unit are usually related to each other by one or more important factors. However, not all soil types within a geographical area may have been recorded at this mapping scale, and not all of the ones recorded occupy a sufficiently large area to be delineated. Thus, the most sensitive sail may have bccn omitted because it occupies only a very small area of land. 2. The soil properties assessed as the basis for producing the critical loads map were those of the most widespread mi1 (the 'dominanr' soiI) wifhin the soii map unii on the 1:250 000 soil map. This may not be the most sensitive of the soils forming the association which corresponds b that map unit. 3. The 1 km squares are assigned a critical load on the basis of the most widespread soil map unit within the square - in practice, the most widespread soil type within the map unit. 4. The critical loads assigned to the soil mapping units have not k e n  calculated using a mass balance approach, dynamic modelling or determinations of weather- ing rates for specific UK sites. It is a "level 0" map (UNECE, 1990). 5. The critical loads assigned to the soil mapping units are still being validated. The resultant map is best seen as providing an indication of the regional distribution patterns of soils ranked in terms of a series of critical loadlsensitivity classes. Mineralogical classification of soil material and critical loads of soils:- Class Minerals controlling Critical load weathering keq H' kinm2 year1 5 Quartz K- feldspar 4 Muscovite Plagiaclu Biotite (< 5%) Biotite Amphibole (< 5%) Pyroxene Epidote Olivine (< 5%) 1 Carbonates (After Nilsson & Grennfelt, 1988) Provisional Map of the Critical Loads for Acidity of Soils of Great Britain The map is drawn by allocating each 1 km square of the national grid of Great Britain to a critical load class on ihe basis of mineralogy of the dominant soil unit but with modification to allow for current agricultural management. Critical load classes for acidification (Nilsson and GremfeH, 1988*), c x p d  as keq H+ ha-' Nitson. I. andChmafclt. P., (d), Critical Loads br Sdphur mdNitrop Report ha^ 4 wortsbop beldrSbkJon!er, Suedm 19-24 March. 1988 by UN-ECEd the Nordic C a d  ofMinisters. Saildatadoitid loadsd~erionbySoil Sm*cJaadLradRcsearhChm, Sum mdMrmlrJL.ndUaeRed lnst ih l l t ,hdCCt l .  Lsndm data- h t i h u e  ofTmatddEabgy (Merlmmd), Qrange---Sd. Map mnpil.tionbyUIC Centre for C r i l i u l b d a h h p p i ~ .  I ~ t i h l l c o f T d B o o b m  (hhbwood). Hunringdw. CRITICAL LOADS FOR ACIDITY FOR UK SOILS This map is based on 10h squares of the UK Ordnance Survey national $rid of Great Britain. The map of critical loads for acidity of soils draws on 2 datasets. For Grcat Britain, the lkm map of critical loads for acidity (map 1) is summarized on the lOkm grid, using the calculated dominant (modal) critical load class for each grid square. For Northern Ireland and the lsle of Man, where comparable soil map data are not yet available, the 1: 1 000 000 Soil Map of the European Communities (CEC, 1984) has been used to identify the dominant soil in each 1Ox10km grid square. The approach used for allocating soils for these areas to critical loads classes was analogous to that used for the lkm critical loads for acidity map (see notes for Map 1). The land use modifier applied to these data was taken from the 1:4 000 000 Europcan Community farming map (CEC, 1987). Critical loads for acidity of UK soils - - - - - - - -  - - - -- - = =  - -  - - I I Critical loads for acidity (keq H+ ha-l year1) 0.2 0.5 1.0 2.0 4.0 4 b January 1991 ESTIMATED CRITICAL LOADS FOR SULPHUR FOR THE UK Critical loads for sulphur have been estimated from the critical loads for acidity, using a methodology recommended by the UNECE Task Force on Mapping. The method partitions each critical load far acidity into a critical load for sulphur and a critical load for nitrogen on the basis of the "current" regional deposition of the 2 elements. For the UK, the l O k m  critical loads for acidity map (Map 2) has been partitioned using the calculated ratio of the total sulphur deposition to total (sulphur+niirogen) deposition (Map 7). Such maps of critical loads for sulphur can only be considered simple estimates, since partitioning critical loads on the basis of deposition assumes sulphur and nitrogen are identical environmentally and economically. The approach, there- fore, ignores any chemical interactions of deposited nitrogen with the terrestrial environment. Also, it lakes no account of the different abatement strategies for reducing the deposition of the two elements, or of lhe relative costs of abatement of any of the components of the two pollubnts. Critical loads for sulphur (keq H+ ha-l year1) Estimated critical loads for sulphur for UK soils -- -- ~ TOTAL NON-MARINE SULPHUR DEPOSITION IN THE UK Sulphur deposition for the UK has been calculated from the surn of:- 1. data interpolated from measured wet deposited sulphur, including es- timated seeder-feeder scavenging; 2. dry deposited sulphur modelled from measurements of the gaseous con- centration of SO,, allowing for different deposition rates to different vege- tation types; 3. estimated deposition of sulphur from cloud and mist (occult deposition). These data for Great Britain have been described elsewhere (UKRGAR, 1990). For Northern Ireland simple estimates of dry deposited sulphur have been used in conjunction with the total wet deposited sulphur. The data are mapped on 20km squares of the Ordnance Survey national grid of Great Britain. This level of resolution is considered appropriate for mapping the interpolated pollutant data. Consequently, when the data are considered for lOxlOkrn squares, the 4 squares within each 20x20km square are given the same pollutant value. The pollutant ranges used for the map are those recommended by the UNECE Task Form on Mapping (UNECE, 1990). Sulphur deposition (keq H+ ha-l year-') Total non-marine sulphur deposition January 1991 TOTAL N O N - W N E  SUtPHUR AND NITROGEN DEPOSITION IN THE UK The sum of the total non-marine sulphur (map 4) and nitrogen provides a coaven- ient estimate of deposited acidity. This may be used for comparison with the critical Ioads for acidity maps. Pollutant data is mapped on a 20km grid as for the sulphur deposition map (Map 4) using the same colour coding and ranges. The methods used for measuring and interpolating the data are described elsewhere (UKRGAR, 1990). Inputs of NHf to managed land were not considered previously (UKRGAR, 1990) so only estimates for unmanaged land are included here. Sulphur+ nitrogen deposition (keq H+ ha-l year1) L Total non-marine sulphur and nitrogen deposition II : I I - 9  1 -  L 2 * v NON-MARINE CALCIUM AND MAGNESIUM DEPOSITION IN 'CHE UK These elements neutralize the acidity of deposited sulphur and nitrogen. Their deposition values are therefore subtracted from the values of deposited pollutants before these are compared with the maps of critical loads. The grids, colours and ranges used for the map are the same as those used for the poHutant maps. Non-marine calcium and magnesium deposition 7 Calcium + magnesium deposition (keq H+ ha-' year1) < 0.2 0.2 - 0.5 1 0.5 - 1.0 1.0 - 2.0 > 2.0 b THE RATIO OF TOTAL SULPHUR DEPOSITION TO TOTAL SULPHUR PLUS NITROGEN This ratio is used for deriving a critical loads map for sulphur (map 3) from the critical loads map for acidity (map 2) according to the methodoIogy recommended by the UNECE Task Force on Mapping. It is also used to calculate a "sulphur component" of the calcium and magnesium deposition for deriving the map showing areas where the critical loads for sulphur are exceded (Map 9). - Total sulphur/(total sulphur+nitrogen) - " '. r Sulphur/(sulphur+nitrogen) + I I -. c I 1 II I I I L AREAS OF THE UK WHERE CRITICAL LOADS FOR ACIDITY ARE EXCEEDED The amounts by which critical loads are exceeded are calculated as the difference between the 10km critical loads map for acidity (map 2) and the total sulphur and nitrogen deposition (map 5). As the deposition data are for 20km squares, all four lOkm squares within each 20km area are assumed to have the same pollutant value. The pollutant deposition is reduced by the neutralizing non-marine calcium and magnesium deposition (map 6). The ranges displayed on the map are those recom- mended by the UNECE Task Force on Mapping (UNECE, 1990). b Areas where critical loads for acidity of soils are exceeded I Exceedance of acidity A 4 ,( (keq H+ ha-l year1) Not exceeded 0.0 - 0.2 , 0.2 - 0.5 0.5 - 1.0 > 1.0 L AREAS OF THE UK WHERE THE CRITICAL LOADS FOR SULPHUR ARE EXCEEDED The amounts by which critical loads for sulphur are exceeded are calculated by subtracting the critical load displayed on the lOkm critical loads map for sulphur (map 3) from the total sulphur deposition (map 4). As for map 8, the calcium and magnesium deposition is subtracted from the pollutant load. However, these elements neutralize the deposition of both sulpbur and nitrogen, and only sulphur is considered here, Therefore, the calcium and magnesium deposition values for this calculation (for sulphur) are estimated using the sulphur:(sulphur + nitrogen) ratio (map 7) in an analogous fashion to the calculation of the critical loads for sulphur. The ranges displayed on the map are those recommended by the UNECE Task Force on Mapping (UNECE, 1990). Areas where critical loads for sulphur of soils are exceeded Not exceeded 0.0 - 0.2 0.2 - 0.5 0.5 - 1.0 > 1.0 Exceedance of sulphur (keq H+ ha-l year1) 2 b MAP 10 THE EMEP GRID FOR THE UK The EMEP (European Monitoring and Evaluation Programme) grid is to be used for abatement strategy modelling within the UNECE Convention on Long Range Transboundary Air Pollution. The 15Ox150km grid squares (red) are shown in relation to the UK coastline, the national grid of Great Britain (yellow) and lines of longitude and latitude (blue). The EMEP grid for the area of the UK TABLE 1 THE PERCENTILE DISTRIBUTIONS OF THE VALUES OF CRITICAL LOADS FOR ACIDITY OF SOILS IN EMEP SQUARES OF THE UK The base data for the Great Britain and Northern Ireland maps of critical loads for acidity of soils (Maps 1 & 2) have been used to derive the areas covered by each critical loads class. These are expressed in terns of percentage area cover within each EMEP square. It should be noted that some squares are the summation of areas in Northern Ireland and parts of Great Britain, they are therefore based on 2 different data sets. Further, some EMEP squares indude the national boundary between Northern Ireland and Eire. For these, only the Northern Ireland areas have been measured. In compiling the European map of critical loads, the additional areas from Eire must be added to this table. TABLE 1 a + Critical loads values are in keq H+ ha-' yeara1 For same areas nsea" includes areas of bcland (Eire) REFERENCES Buncc, R,G,H. & Heal, O.W. 1984. Landscape evaluation and the impact of changing land-use on the rural environment: the problem and an approach. In: Planning and Ecology, edited by R.D. Roberts and T.M. Roberts. 164-188. Chapman and Hall: London, CEC 1984. 1: 1 000 000 soil map of the European Communities. Office for the Official Publications of the European Cummunities: Luxembourg. CEC 1987. 1:4 000 000 European Community farming map. Office for the Official Publications of the European Communities: Luxembourg* Nilsson, J. & Grennfelt, P. 1988. Eds, Critical loads for Sulphur and Nitrogen. UNECE/Nordic Council workshop report, Skokloster, Sweden. March 1988. Nordic Council of Ministers: Copenhagen. UKRGAR 1990. Aciddeposition in the United Kingdom 1986-1988. Third report of the United Kingdom Review Group on Acid Rain. Warren Spring Laboratory: Stevenage, U K  UNECE 1990. Draft manual on methodologies and criteria for mapping of critical levelsfloads and geographical areas where they are exceeded. Report prepared by the Task Force on Mapping under tbe Convention on hng-Range Transboundary Air Pollution of the United Nations Economic Commission for Europe. 

Critical loads maps for the United Kingdom I. Soils

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Critical loads maps for the United Kingdom I. Soils

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