Chemosphere, Vol.16, Nos.lO-12, pp 2239-2248, 1987 0045-6535/87 $3.00 + .OO Printed in Great Britain Peraamon Journals Ltd.

CHANGES IN ACIDITY AND CATION POOLS OF SOUTH SWEDISH SOILS

BETWEEN 1949 AND 1985

Ursula Falkengren-Grerup*

Nils Linnermark

Germund Tyler*

D e p a r t m e n t of Plant Ecology

Soil Ecology Group

Univers i ty of Lund

i3stra Vallgatan 14

S-223 61 LUND, Sweden

ABSTRACT

The pH of south Swedish soils have decreased considerably during the last 15-35 years. The decrease has occurred throughout the soil profile, not only in the rhizosphere, and is particularly marked in the originally less acid soils. The pH decrease was accompanied by considerable losses of exchangeable Na, K, Mg and Ca, as wetl as of Zn and (in the originally less acid soils) of Mn. The changes can be prognosticated from the current relationship between soil pH and base saturation and from budget calculations based on lysimeter data.

INTRODUCTION

Increas ing ac id i ty of na tu ra l and s emina tu r a l soils was d e m o n s t r a t e d in r e c e n t s tudies f rom southern

Scandinavia and con t i nen t a l Europe. By r epea t ing pH m e a s u r e m e n t s or iginal ly pe r fo rmed in 1927 in an

e x p e r i m e n t a l fores t , p rovince of HaLland, sou thwes t Sweden, pH dec reases of 0.3-0.9 units were measured

(Hallb/~cken and T a m m 1986). The dec rease was s igni f icant as deep in the soils as 50-100 cm. At these

dep ths the pH dec rease was not r e l a t ed to s tand age or success ional s tage , whereas both acid deposi t ion

and s tand p rope r t i e s should have a c c o u n t e d for dec reases measured in the rh izosphere horizons.

in s tud ies f rom the province of SkAne, south Sweden (Fa lkengren -Ore rup 1986, 1987) pH dec reases of 0.5-

1.0 units were usuaUy demonstrated for various forest and heath]and sites, throughout the soil profile.

The original measurements were performed between 1949 and 1970 and were repeated in 1984-85.

Decreasing soil pH has also been reported from, e.g., Germany (Butzke 1981, yon Grenzius 1984) and Austria

(Glatzel et al 1984, Stdhr 1984).

However , t h e r e is s t i l l l i t t l e or no d o c u m e n t a t i o n of o t h e r c h e m i c a l changes resu l t ing f rom the ac id i f ica t ion .

2239

2240

From the current relationship between pH(KC1) and the base saturation in mug horizons of deciduous forests

(Fi E. 1) it might be prognosticated, that a pH decrease of ca 0.8 unit should be accompanied by a base

saturation decrease of ca 30 C.E.C. 96 units within a pH interval of 3.0-4.6. The negative balance of base

cations and certain other metals recorded in budget studies of south Swedish forest soils (Tyler 1981,

Bergkvist 1986) provides further evidence that the pH decline is accompanied by and partly the result

of decreasing pools of exchangeable base cations. A high AI solubility and low exchangeable Ca:A] molar

ratios (<0.05) nowadays characterize the B-horizon of most forest soils in this area. Silicate/base cation

buffering (L'lrich 1981) seems to prevail in few soils only. Aluminium is the dominating cation in the B-

horizon soil solution (Nilsson and Bergkvist 1983, Bergkvist 1986).

The aim of this paper is to provide further evidence o f the extent of current soil acidification in south

Sweden and, by reanatysing preserved soil samples, to compare the exchangeable pools of H, Na, K, \lg,

Ca, Zn, ,',In and A1 in soil profiles from ten sites sampled in 1949-54 and 1984-85.

4 ,6 "

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FiE. 1. Relationship between pH(0.2 ~1 KCL) and neutralization (base saturation) in neutral 9I NH4Ac rot mull soils (0-5 cm). The data refer to stands of Fagus sylvatica, (~.uercus robur and Carpinus betulus in southern Sweden, studied in 1981-1984.

2241

MATERIALS AND METHODS

Measurements of pH(H20) in the A-horizon were repeated in 104 forest, heathland and pasture sites. The

original studies were made in 1949-70 and repeated in 1984-85 using the same extract ion and analytical

procedures as originally.

Air-dr ied samples of the <0.6 mm fract ion were preserved by one of the authors, who studied the soil

profi le in ten sites in 1949-54 (Linnermark 1960). These were resampled in 1984-85 with the original

methods. The 1949-54 samples were stored in air-dried condition in paper bags (top soil, 0-10 cm) or in

test-tubes. The sampling method is further described in Falkengren-Grerup (1987).

Simultaneously, using identical methods, corresponding samples from 1949-54 and 1984 were treated.

Samples of the top soil were extracted by M ammonium acetate solution pH 7.0 (5.0-8.0 g dry soil + I00

ml extractant) for 2 h. An aliquot of the filtrate was evaporated to dryness and treated with conc. HNO 3

+ HCIO 4 (4:1) for total destruction of organic matter. After dilution to 50 ml, the solutions were analysed

for Na, K, Mg, Ca, Mn and Zn by plasma emission spectroscopy (ICP).

Samples of the mineral soil horizons (below 10 cm) were extracted by M acid ammonium acetate, pH

4.8 (1.00 g dry soil + 10 ml extractant) for 2 h. Af ter appropriate dilutions the f i l t rates were analysed

for Na and Mn by ICP and for K, Ca, Mg, Zn and A1 by flame atomic absorption spectrophotometry (AAS)

against standards freshly prepared in similarly diluted pure extractant.

Samples of aU horizons were also extracted by M KCI solution and pH determined electrometr ical ly in

the supernatant liquid.

Concentrations of metals and hydrogen ions were calculated as eq dm °3, using reduced (<0.6 ram) bulk

density figures for the various depths. Total exchangeable pools in the entire soil profile were obtained

by summation.

The species are named according to Lid (1974).

SITE DESCRIPTIONS

The sites were thoroughly described by Linnermark (1960) as to the vegetation and chemical conditions

in 1949-54. The pH changes over 30-35 years down to 1 m are given for all profiles except no. ?b

(Falkengren-Grerup 1987), using the site numbers below, while the numbers in brackets are those of

Linnermark (op.c.). The main vegetational differences between the studies are given in table 1.

Site 1(22). Spruce forest, in 1949 a 60-year-old Picea abies stand, planted on former arable land. It was replanted by a second generation in about 1965. The ground was covered by mosses in both studies, mainly Pleurozium schreberi. The soil is a podsol with a mot layer of ca. 5 cm and an A 2 (mineral) horizon of the same thickness. The C-horizon is a moraine.

Site 2(10). Beech forest, almost clear-fel led a few months before the second study. Soil was sampled around a fresh and st i l l bleeding stump. The soil is a podsol with a thin mor layer and an A 2 (mineral) horizon of ca 10 cm. The C-horizon is a sandy moraine.

2242

Site 3(8). Beech forest. Coarse and scattered FaipLtS sylvat!ca in both studies. No shrub layer at either occasion; f ield layer composed almost exclusively of Deschampsia flexuosa. The soil is a well developed podsol with a mor layer of >5 cm and an A 2 (mineral) horizon o f ca 15 cm. The C-horizon is a local moraine formed by Cambrian sandstone.

Site 4(7). Heathland. A small area of old Calluna vulgaris heath, preserved for a long time without any marked changes in vegetation. Calluna prevailed in both studies, but scattered shrubs have started to colonize the area. The soil has a mot layer of ca 5 cm and a well developed A 2 (mineral) horizon down to ca. 30 cm. The C-horizon is a moraine on Cambrian sandstone.

Site 5(25). Mixed oak forest. A small stand surrounded by Picea abies. In 1949 the tree layer consisted of scarce Quercus robur with five species of shrubs, none of them with more than 10% cover: a remnant of a former coppiced forest meadow. In 1984 Quercus had somewhat higher cover and the shrub layer, consisting of ten species~ was quite dense. The oaks were young in the first study. A large number of species were found in the field layer at both occasions, ranging from those usually found in acid soils to more demanding species. The mull soil is developed on a sandy moraine.

Site 6(170). Mixed deciduous forest. Changed from a dominance of Quercus robur and Corylu s avellana to a much lower cover of these species and a colonization of several shrubs, e.g., Sambucus sp., Sorbus

and Rubus idaeus. The change is partly due to felling of trees, but some influence of the fertilization of ~ s~-"~'~='~ing arable land cannot be excluded. The pH changes were as large as in the other sites. The soil is developed from a sandy moraine, the humus layer being a mull.

Site 7(23). Spruce forest. The history is the same as for site no. I. Picea abies was planted on former arable land and replanted with a second generation in about 1965. The field layer in 1949 was considerably richer than in 1984, including, e.g., Oxalis acetosella, Lamium galeobdolon and Mercurialis perennis. These species were not found in the second study, when the nitrophilous species Rubus idaeus and Chamaenerion an_.~ustifolium had increased in cover and the acidophilous Deschampsia flexuosa had colonized. The soil is developed from a sandy moraine, the humus layer being a mull.

Site 7b(190). Pasture (not recorded in Falkeng1"en-Grerup 1987). In 1949 this site was characterized as a dry meadow with Calluna vulgaris. Cattle have grazed the land continuously, but probably with a lower intensity during the last years, as Juniperus communis has spread and grown taller, while Canuna has decreased and not rejuvenated. The site is bounded to arable land but the influence of farmland fertilization has probably been small. The profile was reanalysed down to 80 cm. In the first study, the pH(H20) of the upper and lower samples ranged from 6.0 to 6.8 and the pH(KCI) from 5.3 to 5.7, respectively. The corresponding values in 1985 were 4.6 to 5.6 in pH(H20) and 3.6 to 4.5 in pH(KCI).

Site 8(200). Hornbeam forest. Carpinus betulus dominated in 1949. The trees are large and thinning of the stand has reduced the cover of Carpinus to less than half. TiUa cordata has colonized, but is still of minor importance. In 1949 there was a rich field layer with Anemone ranunculoides, Hepatica nobilis and Galium odoratum. These species were found with a lower cover in the second study. The soil is developed from a fine-sandy moraine, the humus layer being a mull.

Site 9(37). Hornbeam(-lime)forest. The least acid soil of all studied. Carpinus betulus dominated in both studies, but Tilia cordata had colonized and attained the same cover as ~ in 1984. The field layer consisted of ca 35 species in both studies including such demanding species as Dentaria bulbifera, Polygonatum odoratum, Pulmonaria officinalis and Sanicula europaea. The site is situated on a steep slope With mobile ground water. The mull was very weU aggregated, developed from sandy moraine.

RESULTS

I. pH chanKes in the A horizon

The pH decrease measured in 1984-85 was most pronounced in forest soils originally studied in the 1950's

(Pig. 2; cf. Falkengren-Grerup 1986). As might be expected the greatest decreases were found in soils

with an originally high pH, whereas small or no changes have occurred in the originally very acid rnor

horizons with pH(H20) around 4.0. The few spruce (Picea abies) sites studied do not diverge from this

general pattern. The same is true for the two heathland sites without tree canopy, where biological

acidification should play a minor role.

2243

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o heathl~niper o pasture O 0 0

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o

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oa o

CD 0

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Fig. 2. pH changes f rom or iginal pH(H20) in the A-horizon of 104 s i tes s tud ied in 1949-70 and reana lysed in 1984-85. The number s in the f igure r e f e r to the s i tes descr ibed in this paper .

Table I. Cover of dominating species in 1949 and 1984, respectively, having cover classes of 3 (40-~0%), 4 (60-80%) or S (80-100%).

Site no. T ree / sh rub layer 1949 1984 Field layer 1949 1984

1 Picea abies 4 4* Deschampsia flexuosa 4 4 Vaccinium myrtiUus 3 0

2 Fagus sylvatica S 0"* Deschampsia flexuosa 1 4 Vaccinium myrtillus 5 l

3 Fagus sylvatica 4 4 Deschampsia flexuosa 5 .~ 4 - none - Calluna vulgaris 5 5 5 Quercus robur 2 3 Convallaria majalis 4 i

Festuca rubra 3 l Melampyrum pratense 3 1

6 Quercus robur 5 2 Galium aparine 0 3 Corylus avellana 4 2 Rubus idaeus 0 3

7 Picea abies 4 3" Oxalis acetosella 5 0 7b Juniperus communis I 3 Calluna vulgaris 3 I 8 Carpinus betulus 5 2 Melica uniflora I 3 9 Carpinus betulus 4 3 Aegopodium podagraria 4 3

Tilia cordata 0 3 Allium ursinum 3 2 Mercurialis perennis . . I 3

*) replanted in about 1963 **) clear felled in 1984

2244

There are a few beech (Fagus sylvatica) sites with a high pH, where pH increases since the 1950's have

actually been recorded. They are all located in slopes influenced by oozing groundwater, in areas with

calcareous sedimentary bedrock and therefore continuously fed by water rich in calcium and bicarbonate

from below.

As an average, only a minor pH decrease has occurred since the 1960's in meadow sites managed by grazing

or hay-making. No lime or fertilizers have been applied since the time of the original study.

2. Changes of cation pools

The exchangeable pools of base cations, Zn and Mn decreased significantly during the period 1949-1985

in most or all of the ten forest sites, where the entire soil profile was studied (Fig. 3, table 2). Exchangeable

hydrogen usually increased its pools. There was no consistent trend as to the relative change with soil

depth.

Table 2. Sum of exchangeable pooLs of cations (keq ha -I) in ten profiles extracted in neutral (top soil) and acid ammonium acetate. Note the different profile depths among sites and for Al, compared to other elements.

Site no. Year Depth (cm) H AI Na Ca Mg K Zn Mn Ca:AI AI other

I 1949 14 167 8 7 3 4 0.I 0.1 0.01 10-35 0-35 1984 12 223 2 4 2 2 0.1 0.i 0.01

2 1949 30 777 16 31 9 12 1.2 4.3 0.02 20-100 0-I00 1984 65 709 6 12 5 6 0.4 3.2 0.01

3 1949 18 671 12 16 7 6 0.8 1.8 0.02 I0-100 0-I00 1984 32 685 6 9 6 5 0.3 1.9 0.02

4 1949 5 537 20 12 3 7 0.4 1.2 0.03 15-100 15-100 1984 II 500 3 5 I 3 0.I 1.0 0.02

5 1949 1 529 20 15 4 4 0 .7 2 .1 0 . 0 4 10-100 0 -100 1984 4 569 5 17 2 3 0 .4 3 .9 0 .05

6 1949 4 459 22 48 18 12 0.5 15.7 0.06 15-100 0-100 1984 19 590 7 20 6 I0 0.3 5.6 0.03

7 1949 3 273 23 i03 16 I0 3.6 34.6 0.46 10-100 0-I00 1984 20 357 6 68 13 11 0.6 7.0 0.24

7b 1949 2 290 17 13 3 6 0 .3 2 .2 0 .07 10-90 10-90 1984 7 253 3 15 5 3 0 .2 1.7 0 . 0 9

8 1949 I 384 23 78 24 12 0.7 21.6 0.30 5-100 0-I00 1984 7 422 7 43 13 7 0,6 14.3 0.15

9 1949 <1 53 29 455 34 12 0 .6 37 .9 12 .80 0-100 0-100 1984 2 119 12 363 26 9 0 .5 9 .9 4 .59

The pool of the base cations (Na + K ÷ ~Ig + Ca) decreased in all sites, on average by ca 50% of the pool

of 1949/54 (Fig. 3). The base cation loss was not related to the original acidity state of the soiLs. However,

it is interesting that the decrease was particularly great in site 4, a heathland without marked changes

in the vegetation ducing the studied time interval. Only a minor decrease of the base cations (ca 25%)

was measured in site 9, a hornbeam (Car~) forest originally with a very high soil pH.

Sodium usually decreased more than the three other base cations. The pools of Ca and Mn actually increased

to some extent in site 7b, a semi-natural pasture bordering arable land. The increase is partly due to a

couple of aberrant values from the lower horizons, probably due to sampling inaccuracy.

2245

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Na

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4

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Fig. 3. Relative change of cation pools between 1949-54 and 1984-85. The sites are ordered from the originally most acid to the least acid soil. The broken line represents the pool in 1949-54 (100%).

The exchangeable pool of Zn decreased considerably, though in a highly variable way, but was unrelated to

the original acidity. Great losses (50-80%) of Mn were measured in the least acid sites (nos. 6-9), originally

characterized by large extractable pools. Otherwise the changes in Mn were small or, in one case (site 5),

distinctly positive.

The pool of H ions exchangeable with M KCI increased quite substantially and was closely (inversely) related

to the original acidity of the soils. It was almost unchanged in site i, a spruce forest on mor podzol, but

20 times the original pool in site 9, a hornbeam stand with mull of a good aggregation. The relationship

to the original acidity is, however, less evident when the absolute change of the H pool is considered

(table 2).

2 2 4 7

In all but one site (no. 9), Al dominates the exchange complex in the mineral soil horizons (table 2). Increases

were recorded in sites no. 5-9, whereas the changes were less dist inct in the more acid sites, except for

site no. l . The relat ive differences are usually quite small (Fig. 3) and exchangeable AI (calculated as

A13+) dominated the equivalent sum of cations already in t949154 in sites no. 1-8, though it played an

even greater role in 1984-85.

DISCUSSION

All available information clearly indicates that the weathering rate of soil minerals has been far from

sufficient in recent decades to compensate for leaching losses and biomass immobilization/cropping output

of base cations, Zn and (often) Mn in southern Sweden. The pools of exchangeable H and Al ions have usually

increased, particularly in the previously less acid soils.

It may be argued, however, to what extent natural biological acidification, e.g., due to excess uptake

and immobilization of base cations by the vegetation, is responsible for these changes. It is well known

that top soils are acidified to some extent during the rotation of a forest stand and that, e.g., spruce

(characterized by a high aerosol capturing capacity and a high growth rate under optimum conditions)

is more acidifying than deciduous trees in the climate of and under the prevailing state of atmospheric

pollution in northern and central Europe. It is, however, difficult to explain by biological acidification

why sub-rhizosphere soil horizons, at least down to a depth of l m, have become increasingly acid and

lost part of the exchangeable pool of base cations during recent decades. An increased transport of strong

mineral acids from the upper horizons, mainly derived from the atmospheric deposition, is the most probable

reason.

Another circumstance, which points towards atmospheric deposition as highly decisive of the reported

soil changes, is that these changes seem to have occurred or occur in almost all types of non-arable soils

more or less irrespective of ecosystem characterist ics. Though only few heathland sites have been restudied,

data obtained do not support the opinion that internal biological processes should be decisive. On the

contrary, the changes have been at least equally great in these soils as in the majori ty of soils under various

deciduous and coniferous tree canopies. Immobil izat ion or removal of mineral nutrients in biomass has

been almost negligible and cannot possibly account for the great base cation losses, nor the considerable

pH decreases recorded.

Southern Sweden is situated just outside (north and northeast of) the main source area of atmospheric

pollutants in Europe, Since at least ten years the pH of rainfal l averages ca. 4.2 af ter a decrease in the

1950's - 1960's. The wet deposition of sulphur and nitrogen in southern Sweden at the end of the 1970's

was estimated at ca. 10 kg ha "1 yr -1, respectively, or 4-5 times the amounts in northern Sweden (Nilsson

1986). In a spruce forest in south Sweden the dry deposition is equally as high as the wet deposition. The

low pH of the precipi tat ion indicates that the deposition of unneutralized acid is considerable, part ly due

to a comparat ively low level of alealine particles. A rough approximation indicates that a total of at

least 20 keq . ha - l of unneutralized hydrogen ions have been supplied by wet deposition alone over south

Sweden over the last 35 years, the maximum interval of this study. This equalizes or exceeds the

exchangeable soil pool of hydrogen (1949-54) in the most acid sites studied. It is by far in excess of this

pool in the less acid sites, where the changes have been part icular ly pronounced.

2248

It must be concluded that atmospheric acidification is a major (though not the only) reason for the reported

soil changes in southern Sweden. The excess deposition of strong mineral acids has contributed greatly

to the losses of base cations, Zn and Mn from the whole soil profile and inabil i ty of the natural I~uffering

systems to keep pace with the acid input has resulted in decreasing pH of the soils.

REFERENCES

Bergkvist, B. 1986. Metal fluxes in spruce and beech fores t ecosys tems of south Sweden. Diss., Univ. of Lund, Sweden.

Butzke, H. von. 1981. Versauern unsere W~lder? Erste Ergebnisse der tiberprdfung 20 Jahre alter pH-Wert- Messungen in Waldb~den Nordrhein-Westfalens. Forst-und Holzwirt. 21,542-548.

Faikengren-Grerup, U. 1986. Soil acidification and vegetation changes in deciduous forest in southern Sweden. Oecologia 70, 339-347.

Falkengren-Grerup, U. 1987. Long-term changes in pH of forest soils in southern Sweden. Environ. Pollut. 43, 79-90.

Grenzius, R. von. 1984. Starke Versauerung der Waldl~bden Berlins. Forstw. Cbl. 103, 131-139.

Hallb~cken, L. and Tamm, C.O. 1986. Changes in soil acidity from 1927 to 1982-1984 in a forest area of South-west Sweden. Scan. J. For. Res. 1, 219-232.

Lid, J. 1974. Norsk off svtnsk flora. Det norske samlaget, Oslo.

Linnermark, N. 1960. Podsol och brunjord l-II. Summary in English. Publications from the institutes of mineralotFy, paleontology, and quarternary geology, Univ. of Lurid, Sweden, No. ?5, pp 1-233 and diagrams.

Nilsson, J. (ed.) 1986. Cri t ical loads for nitrogen and sulphur. Nordisk ministerrAd, Stockholm, miljSrapport 1986:11.

Nilsson, S.i. and Be~kvist, B. 1983. Aluminium chemistry and acidification processes in a shallow podzoI on the Swedish west coast. Water, Air, and Soil Pollut. 20, 311-329.

St6hr, D. (ed.). 1984. Waldbodenversauerung in Osterreich. Ver~nderungen der pH-Werte von Waldb6den w~hrend der letzten Dezennien. iDsterreichischer Fortsverein Forschungsinitiative gegen das Waldsterben, Institut f(Jr Forst6kologie, Wien.

Tyler, G. 1981. Leaching of metals from the A-horizon of a spruce forest soil. Water, Air, and Soil Pollution 15, 353-369.

Ulrich, B. 1981. Okologische Gruppierung von BSden nach ihrem chemischen Bodenzustand. Z. Pflanzen- ernaehr. Bodenk. 144, 289-305.

(Received in Germany 23 A~,ril 1987: accepted 13 May 1987)

The project was financed by the National Swedish Environment Protection Board.