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Acidity status and mobility of Al in podzols near SO2 emission sources on the Kola Peninsula, NW Russia
PII: S0883-2927(97)00071-1
Applied Geochemistry, Vol. 13, pp. 391±402, 1998 # 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0883-2927/98 $19.00 + 0.00
Acidity status and mobility of Al in podzols near SO2 emission sources on the Kola Peninsula, NW Russia G. Kashulina%, P. de Caritat and C. Reimann* Geological Survey of Norway, P.O. Box 3006-Lade, N-7002 Trondheim, Norway
M.-L. Raisanen Geological Survey of Finland, P.O. Box 1237, SF-70211 Kuopio, Finland
V. Chekushin Central Kola Expedition, Fersman St. 26, 184200 Apatity, Russia
I. V. Bogatyrev Kola Geological Information Laboratory Centre, Fersman St 26, 184200 Apatity, Russia
(Received 8 July 1996; accepted 30 June 1997) AbstractÐSoil acidity status and Al mobility in podzols was examined on a broad scale near the large emission sources of SO2 and heavy metals on the Kola Peninsula (the Severonikel and Pechenganikel smelter complexes) in NW Russia and in neighbouring parts of Norway and Finland. Acidi®cation of the upper podzol horizons and depletion of mobile base cations were only evident at sites where ecosystems are severely destroyed, in the immediate vicinity of the Severonikel smelter complex. The high content of base cations in the parent material (till) near the emission sources may mask the acidi®cation eect of pollution. Both strong anthropogenic (SO2) emissions and natural acidi®cation (in situ weathering of black schist) accelerate weathering and mobilize Al. However, drainage conditions seem to be the most important factor determining the content of mobile Al in the podzols. # 1998 Elsevier Science Ltd. All rights reserved
INTRODUCTION
Three of the largest sources of SO2 and heavy metal pollution in northern Europe are located in the western part of the Kola Peninsula. These are the Severonikel Ni±Cu ore smelter at Monchegorsk and the Pechenganikel complex consisting of the ore smelter at Nikel and the ore roasting plant at Zapoljarnij (Fig. 1). Together, they accounted in 1994 for about 300 000 t of SO2, 1900 t of Ni, 1100 t of Cu and 94 t of V2O5 emitted into the atmosphere (Reimann et al., 1997a). Cumulative SO2 emissions from the Severonikel smelter complex alone between 1960 and 1994 have been estimated at about 6.5 million tonnes (Caritat et al., 1997). In addition, there are several other sources of SO2 emissions in the area (coal-®red power plants and other industries). The long-term eect of such a high level of pollution is severe and there is widespread ecosystem *Corresponding author. %Present address: INEP, Kola Science Centre, Fersman St. 14, 184200 Apatity, Russia. 391
degradation in the region, and, in the close vicinity of Monchegorsk and Nikel, severely disturbed ecosystems, characterised by intensive soil erosion (Kryushkov, 1991; Hùgda et al., 1995; Solheim et al., 1995). Contamination of the various parts of the environment, including soil, by heavy metals near Monchegorsk and Nikel is well documented (Kozlov et al., 1993; AÈyraÈs et al., 1995; Niskavaara et al., 1996, 1997; de Caritat et al., 1996a,b, 1997; and Reimann et al., 1997a,b,c). Even though SO2 is the dominant component of the emissions, soil acidi®cation has not been investigated in detail in the area. Most studies are based on transect sampling with large distances between sampling points and pro®les. Laboratory experiments to study the direct interaction between precipitation and soil samples have shown that pollution from the Severonikel smelter complex may cause acidi®cation of podzols and base cation leaching (Kashulina et al., 1995; Koptsik and Muchina, 1995). In the ®eld, however, increased soil acidity has so far only been found in the organic horizon of podzols in severely damaged pine forests near Severonikel (Chertov et al., 1993) and Pechenganikel (Chertov et al., 1990, 1993; Koptsik
392
G. Kashulina et al
Fig. 1. Location of the survey area for the regional mapping project and the study catchments. Catchment C1: Zapoljarnij, C2: Monchegorsk, C3: Kirovsk, C4: Kurka, C5: Skjellbekken, C6: Kirakka, C7: Naruska, C8: Pallas.
and Nedbaev, 1992; Koptsik and Muchina, 1995) and within 4 km of the emission sources. Investigations in a pine forest near Monchegorsk did not reveal any trend of increasing acidi®cation over recent years (Chertov et al., 1990). The absence of any evidence for soil acidi®cation within 7±40 km of Nikel has been explained by the high buering capacity of the soil and a high anthropogenic input of base cations (Koptsik and Nedbaev, 1992). Transect investigations in pine forest ecosystems carried out during the Finnish Forest Damage Project (Tikkanen and NiemelaÈ, 1995) found no relationship between the level of pollution and the parameters that characterise soil acidity (pH in water, exchangeable H+ and Al3+) within 10± 70 km of Monchegorsk. However, Motova and Nikonov (1993) described an increase of amorphous
Al in the illuvial horizon of podzols near the source of pollution. During a detailed investigation of spruce forest ecosystems, lower acidity and higher contents of exchangeable base cations were found in the organic horizon of podzols located 7 and 20 km from the source of pollution, compared with control sites more than 100 km away (Kashulina et al., 1995). In addition, lysimeter studies revealed a sharp increase (about 10 times) in the leaching of Al at the sites 7 km from the pollution source (Jevtjugina, 1994). RaÈisaÈnen et al. (1994) investigated changes in soil mineralogy connected to Al-mobilisation at these sites and described a newly formed mixed-layer clay mineral (chlorite±aluminous montmorillonite) in the E horizon. They explained this as acidic deposition causing the mobilisation of Al-hydroxides, which enter the interlayer spaces of vermiculite.
N: 7 708 000; E: 422 605
N: 7 707 250; E: 422 950
N: 7 525 550; E: 495 100
N: 7 527 900; E: 495 600
N: 7 529 650; E: 494 400 N: 7 493 400; E: 533 700
N: 7 495 350; E: 531 750
N: 7 495 350; E: 532 650
N: 7 508 750; E: 493 050
N: 7 512 400; E: 493 550 N: 7 511 900; E: 491 100 N: 7 696 550; E: 597 200
N: 7 697 700; E: 597 000 N: 7 699 620; E: 597 550
N: 7 699 550; E: 596 390
N: 7 700 450; E: 600 100
N: 7 720 190; E: 454 380
N: 7 474 560; E: 602 500
N: 7 476 340; E: 606 040 N: 7 474 640; E: 605 100
N: 7 565 360; E: 370 180
N: 7 565 510; E: 368 520
N: 7 564 540; E: 371 020
1P28
1P38
2P36
2P37
2P38 3P15
3P51
3P52
4P06
4P38 4P39 5P37
5P38 5P39
5P40
5P41
6P12
7P05
7P18 7P19
8P13
8P15
8P18
Moraine plain, ¯at
Foot of moraine hill
Moraine plain, ¯at
Foot of moraine hill Moraine hill, gentle slope
Moraine plain
Foot of moraine hill
Moraine hill; gentle slope
Moraine hill; ¯at top
Glacio¯uvial delta; ¯at Moraine hill; ¯at top
Upper part of hill slope Valley, ¯at Moraine hill, upper slope
Foot of hill, ¯at
Mountain terrace
Mountain terrace, ¯at
Gentle mountain slope Mountain terrace, ¯at
Top of moraine hill
Top of moraine hill
Valley, ¯at
Top of moraine hill
Topography
b
From geological maps (Chekushin et al., 1995). Winter 1993±1994 deposition (Chekushin et al., 1995).
a
Location (m)
Quartzite
Quartzite
Quartzite
Granitoids Granitoids
Granitoids
Granite
Black schist
Andesitic laves, siltstone
Andesitic sandstone Mica schist
Gabbro, gabbro-norites Two-mica gneisses Amphibolitic gneiss
Amphibolites
Gneisses, nepheline syenite
Gabbro-norites
Pyroxenites Ma®c tus
Norites, gabbro-norites
Amphibole±biotite and granite gneisses Amphibole±biotite and granite gneisses Dacitic±andesitic tus
Bedrock typea Dwarf shrub±birch subarctic birch forest Dwarf shrub±sparse subarctic birch forest Empetrum±dead standing spruce forest Industrial desert with sparse birch shrubs Industrial desert Dwarf shrub±green mosses±birch forest with spruce Dwarf shrub±green mosses± subalpine birch forest Dwarf shrub±green mosses± subalpine birch forest Dwarf shrub±birch forest with spruce Dwarf shrub±sparse spruce forest Dwarf shrub±spruce forest Green moss±dwarf shrub±birch forest with pine White lichen±pine forest Green moss±dwarf shrub±pine forest with birch Green moss±dwarf shrub±birch forest with pine Green moss±dwarf shrub±pine forest Dwarf shrub±green moss±pine forest with birch Bilberry±green moss±sparse birch with spruce Bilberry±green moss±spruce forest Dwarf shrub±green moss forest with pine and birch Dwarf shrub±green moss spruce forest with birch and pine Grass±dwarf shrub±green moss± spruce forest Dwarf shrub±green moss±birch forest with spruce
Vegetation type
no
no
no
no no
no
slight
slight
slight
slight moderate
moderate moderate slight
moderate
slight
slight
severe slight
severe
strong
moderate
moderate
Degree of damage
60
60
70
80 100
70
33
45
45
30 40
125 125 30
80
190
200
250 215
260
310
460
440
S dep.b, kg kmÿ2
0.5
0.5
0.5
0.5 0.5
0.5
0.5
1.3
1.2
1.2 1.2
80 50 1
32
3.5
5
460 10
350
510
220
240
Ni + Cu dep.b, kg kmÿ2
Table 1. Location and main characteristics of the podzol pro®le sample sites. Information on the deposition of S and (Cu + Ni) from Chekushin et al. (1995)
Pro®le No.
Acidity status and mobility of Al in podzols 393
394
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The aim of the present paper is to provide data on the state of soil acidity and Al mobility in podzols in the western part of the Kola Peninsula and neighbouring parts of Finland and Norway, where the Geological Surveys of Finland (GTK) and Norway (NGU) and the Central Kola Expedition (CKE) in Russia are carrying out a major geochemical mapping project (World Wide Web site http:// www.ngu.no/Kola) in a 188 000 km2 area between 248 and 35.58 E and N of the Arctic Circle to the Barents Sea (Fig. 1). As part of this project, 8 widely distributed catchments (hereafter abbreviated C1±C8, with C1±C4 in Russia, C5 in Norway and C6±C8 in Finland) were investigated in detail in 1994. Snow (meltwater and ®lter residue), rainwater, stream water, organic stream sediments, terrestrial moss, topsoil (0±5 cm), complete podzol pro®les, Quaternary deposits and bedrock were all sampled and analysed.
METHODOLOGY
Field procedures Criteria for the selection of sample sites within the catchments, as well as methods used for sampling, are detailed in AÈyraÈs and Reimann (1995). Between one and 5 pro®les were dug in each catchment (Table 1) and all major horizons were sampled. The depth of the soil pits varied from 50 to 100 cm depending on local conditions. Most of the pro®les investigated were free-draining haplic or ferric podzols. Pro®les 1P38, 2P36 and 7P18 (the ®rst ®gure gives the catchment number Ð see Table 1) were close to the water table. Two pro®les (7P05 and 8P18) showed morphological evidence of temporary excess of water (gleyic podzols). Pro®le 2P38 was strongly eroded and had neither humus nor an E horizon. The other 2 pro®les in catchment C2 showed some evidence of erosion. The parent material at most sites was sandy till with a variable stone content. The soil at site 5P38, however, was developed on ¯uvioglacial sand, and in the E horizon of site 5P41, an ablation till was mixed with weathered black schist. Additional information about sample sites is listed in Table 1. Generally, the Finnish catchments are underlain by more acidic lithologies (granite, gneiss and quartzite) than the Norwegian and Russian catchments, with C2 (Monchegorsk) having the most basic lithology (including gabbro and pyroxenite). The sampling sites had dierent types of vegetation and the degree of ecosystem damage varied. Almost total vegetation damage is characteristic of C2, quite serious vegetation damage was observed in C1 and C4, and slight damage in C3 and C5. C6 is in¯uenced by reindeer grazing and tree felling. Although C7 and C8 in Finland gener-
ally show no traces of damage to vegetation or soil cover, site 8P18 has a number of dead spruce trees and slightly damaged ground vegetation. Yearly airborne input of S and Ni + Cu in the dierent sample sites was estimated from the chemistry of snow and rain samples (Chekushin et al., 1995, 1997). These data are summarised in Table 1, which shows that deposition levels in catchments close to the industry (C1 and C2) are 5±10 times higher for S and up to 1000 times higher for Ni + Cu compared to the Finnish catchments. Pollution deposition values determined for the Finnish catchments (C6±C8) are similar to remote background sites worldwide (Galloway et al., 1982).
Analytical methods All samples were air dried at temperatures R408C. The O horizon samples were homogenised by milling in a domestic blender with blades made of non-contaminating material. The samples were then sieved to <2 mm. For the determination of total element content, 0.5 g of humus was digested with 10 ml of concentrated HNO3 in a microwave oven and diluted to 50 ml with deionised water. The clear solutions were analysed by Thermo Jarrell Ash Polyscan 61E ICP-AES for 30 elements and by Sciex Elan ICP-MS for 29 elements. For the mineral soil horizons, 2 g of the <2 mm fraction was mixed with 9 ml concentrated HCl and 3 ml concentrated HNO3 (aqua regia) in borosilicate tubes. The mixture was left at room temperature overnight and then heated to 908C for 2 h on an Al block. The digest was diluted to 60 ml with deionised water, thoroughly mixed, decanted into polystyrene tubes and centrifuged. In addition, an ammonium acetate extraction buered at pH 4.5 (shaking time 2 h) was carried out on all samples. After centrifugation both solutions were analysed by ICP-AES for 30 elements. Arsenic and Cd were determined by graphite furnace-AAS. All the above analyses were carried out at the GTK laboratory. In addition, the total content of major elements in the mineral soil horizons was determined by XRF on fused beads. pH and electrical conductivity (EC) was determined in water extracts (2 g of soil in 20 ml deionised water for the mineral soils, 2 g of sample in 40 ml deionised water for the O horizon samples), and anion concentration in these water extracts was determined by ion chromatography after ®ltration (0.45 mm) and removal of humic acids in the O horizon samples using Waters2 Sep-Pak Plus C18 cartridges, at the NGU laboratory. Fr more details on analytical techniques and quality control procedures see Niskavaara (1995). The GTK and NGU laboratories are both accredited according to ISO 9001 and ISO-Guide 25.
Acidity status and mobility of Al in podzols
395
Table 2. Total element content (XRF analysis) of the C horizon samples from all pro®les (LOI-corrected values) Pro®le 1P28 1P38 2P36 2P37 2P38 3P15 3P51 3P52 4P06 4P38 4P39 5P37 5P38 5P39 5P40 5P41 6P12 7P05 7P18 7P19 8P13 8P15 8P18
LOI %
SiO2 %
Al2O3 %
Fe2O3 %
MgO %
CaO %
Na2O %
K2O %
TiO2 %
1.5 4.3 2.7 1.9 2.0 1.3 1.8 3.0 2.3 1.3 1.8 1.9 1.2 1.2 2.0 2.6 0.8 1.6 4.2 3.7 0.9 2.4 1.1
67.4 63.2 62.2 60.6 60.2 69.7 65.4 64.8 60.2 67.0 63.7 62.7 66.8 65.4 62.8 68.3 73.1 73.3 66.0 68.2 72.7 72.1 73.4
13.7 14.3 15.1 14.3 15.6 13.9 13.7 14.8 13.6 14.0 13.9 14.8 14.8 14.5 15.2 13.1 13.3 13.2 17.3 15.9 12.4 12.6 12.0
5.7 8.3 7.3 8.2 7.6 4.2 6.6 6.2 9.5 5.7 7.6 8.6 5.5 6.8 9.0 8.6 2.2 2.9 5.1 4.5 3.3 4.2 3.4
2.4 3.4 4.2 5.7 5.7 2.1 2.8 2.6 5.1 2.5 3.5 3.0 2.5 2.5 3.5 1.7 0.8 1.6 2.5 2.2 1.5 1.8 1.6
4.2 4.6 5.3 5.9 5.9 4.1 4.4 4.1 5.0 4.6 5.0 4.9 3.9 4.4 4.3 3.2 1.8 2.7 2.9 2.8 2.7 2.7 2.5
3.5 3.1 3.1 2.7 2.7 3.7 3.4 3.8 3.1 3.6 3.2 3.1 3.3 3.3 3.1 3.1 3.6 3.6 3.6 3.6 3.4 3.0 3.0
1.8 1.5 1.3 1.2 1.1 1.6 1.6 2.2 1.9 1.6 1.7 1.1 1.8 1.4 1.4 1.1 3.5 1.6 2.0 1.7 2.6 2.5 2.6
0.72 0.92 0.67 0.74 0.63 0.46 0.87 0.86 0.76 0.66 0.82 0.87 0.55 0.74 1.01 0.66 0.32 0.41 0.48 0.54 0.43 0.48 0.46
RESULTS AND DISCUSSION
C horizon, total element content Table 2 summarises the analytical results (XRF) for the major element content of the C horizon. Dierences in lithology (Table 1) result in signi®cant dierences in the chemical composition of the parent material (till) between, and sometimes within, catchments (Table 2). The greatest dierences between catchments and sites were found for Fe2O3, MgO, CaO and K2O content. The mean sum of CaO and MgO in C2
(11.2%) is at least twice as high as in the Finnish catchments (C6±C8). The other Russian catchments (C1, C3, C4) and the Norwegian catchment (C5) are intermediate in terms of (CaO + MgO) content (4.9±8.5%). Although the alkali elements only show slight variation between catchments and sites, K2O concentrations are elevated in the 3 Finnish catchments compared to the others. Dierences in the Al2O3 content are signi®cant, varying from 12% (C8) to 17.3% (C7). Surprisingly, the soil pro®les in C3, which is partly underlain by alkaline rocks, show no unusual chemical composition of the C horizon (or till).
Fig. 2. pH in water extracts from all major soil horizons.
396
G. Kashulina et al
Only the weathered sediments of the Hibiny alkaline rocks, which are located in the upper part of C3, are enriched in Na and Al (Chekushin et al., 1995). The question of whether or not the C horizons represent the natural geochemical background of the area is unclear. When comparing the chemical composition of 2P37, 2P38 and 5P41 with other pro®les from the same catchments (Table 2) and with samples of Quaternary deposits (Pavlov et al., 1996), it can be concluded that the low alkali content of the C horizon of 2P37 and 2P38 is related to anthropogenic factors, while the low K, Na, Ca, Mg and Al content in 5P41 is related to intensive weathering and leaching due to natural factors (sulphides in the E horizon). An extremely high natural content of base cations in C2 due to its bedrock composition may mask element leaching from the C horizon in 2P37 and 2P38. Thus, both natural soil-forming processes and anthropogenic eects can alter the composition of the C horizon substantially.
Soil pH Figure 2 shows the pH values (water extracts) of all pro®les in the main soil horizons. For most of the pro®les investigated, both pH and its variation throughout the pro®le are typical of podzolic soils.
The pH measured in the C horizon is weakly acidic in most pro®les and varies from 5.7 to 6.4. The exceptions are 3P52, which has a near neutral pH (7.3), and 1P38, 2P36 and 5P40, which are the most acidic (pH 5.4, 5.6 and 5.5, respectively). This can be explained by the C horizon being unrelated to the upper horizons (3P52, 1P38 and 2P36), or by the unusual geochemistry of the whole pro®le (5P40). Generally, the parent material in the 3 Finnish catchments (C6: granite, C7: gneiss, C8: quartzite) can be regarded as the most acidic. In contrast, the Russian catchments are characterised by very basic lithologies (Table 1). These major lithological dierences are not re¯ected in the pH values of the C horizon. Apparently in this case, the base cation content plays no signi®cant role in determining soil pH. Correlation analysis does show, however, a positive correlation between H+ concentration and base cation content in the B horizon (Table 3). The only cation showing a negative correlation with H+ throughout the whole pro®les is Na+. Sulphur deposition rates are positively correlated with H+ concentration in the C horizon (Table 3). There are also good correlations between H+ concentration in soils and the concentration of 4 major pollutants (Cr, Co, Cu, Ni) determined in the ammonium acetate extracts from the C horizon.
Table 3. Correlation coecients (r) between soil acidity (expressed as H+ concentration) and the deposition of major pollutants, and element concentrations in the podzol pro®les Deposition Horizon (No. of samples)
Soil variables
S
Ni + Cu
Water extraction
NH4 Ac (pH 4.5) extraction
Aqua regia extraction
O (n = 25) E (n = 23)
ÿ0.32 ÿ0.01
ÿ0.32 0.17
none EC (0.53*)
none S (0.61*)
B1 (n = 24)
0.19
0.67*
EC (0.93*) Anion sum (0.90*) SO4 (0.89*) Cl (0.82*) F (0.57*)
S (0.90*), Cu (0.84*) Pb (0.81*) As (0.77*) Co (0.71*) Ni (0.69*)
B2 (n = 22)
0.43
0.87*
EC (0.95*) Anion sum (0.90*) SO4 (0.89*) Cl (0.82*) F (0.57*)
Cu (0.88*) Ni (0.56*)
BC1 (n = 23) BC2 (n = 21) C (n = 46)
0.42 0.13 0.32*
0.64* 0.30 0.19
F (0.59*)EC (0.43*) none none
none none Cr (0.45*) Co (0.35*) Cu (0.33*) Ni (0.30*)
none S (0.64*) Fe (0.61*) P (0.53*) S (0.5*) Ca (0.46*) Ni (0.86*) Te (0.85*) Cu (0.84*) Co (0.78*) Ag (0.78*) Cd (0.66*) Na (0.81*) Ni (0.78*) Cu (0.71*) S (0.72*) Cd (0.67*) Ca (0.66*) Pb (ÿ0.62*) none none Te (0.40*) Cu (0.31*) Na (ÿ0.24)
*Signi®cant correlation (p < 0.05). none: no signi®cant correlations found. EC: electrical conductivity.
XRF no data Na (ÿ0.50*) Ca (0.43*) Mg (0.68*) Na (ÿ0.64*)
Ca (0.65*) Mg (0.75*) Na (ÿ0.59*) Si (ÿ0.50*)
none none Na (ÿ0.26)
Acidity status and mobility of Al in podzols
The variation in pH values in the O horizon in the 8 catchments is low: for 14 out of 22 pro®les investigated, pH ranges from 4.3 to 4.5. The lowest pH of all the O horizon samples was found in 2P37 (pH 3.9). Although this appears to be related to pollution, there is no signi®cant correlation between H+ concentration and the degree of pollution (Table 3). For 18 out of 22 pro®les, the pH of the E horizon varies from 4.8 to 5.1. The lowest pH value (4.5) was found in the E horizon of 5P41. This can be explained by in situ weathering of S-rich black schist, a natural acidi®cation factor. Although the pH of the E horizons at the polluted Monchegorsk catchment (C2) is low, the correlation between H+ concentration in the E horizon and degree of pollution is not signi®cant (Table 3). Deposition of Ni + Cu appears to in¯uence the pH of the B1 horizon strongly, with all the lowest pH values occurring in C2 near Monchegorsk (Fig. 2), despite it containing the most basic bedrock lithology of all the catchments. However, lithology still has an in¯uence on the pH values observed in the BC1 horizon; 2 of the 3 pro®les from C2 showing high pH values. There are good correlations between soil H+ concentration and
397
Ni + Cu deposition, and between the soil H+ concentration and the concentrations of the mobile forms of most pollutants (S, Ni, Cu, Co, As, Cd, Pb) within the B1 and B2 horizons (Table 3).
Mobility of Al Figure 3 shows the mobile (available) Al contents measured by ammonium acetate extraction in mg kgÿ1 and expressed as a percentage of total (nitric acid extractable) Al. Up to 1% of total Al is available in the C horizon, up to 2.5% in the BC1 horizon. In the B1 horizon, this proportion reaches 4%, in the E horizon just over 0.4%, and in the O horizon it can exceed 10% (Fig. 3). There is generally a good correlation between total and mobile Al content in the soil horizons (Table 4). Most of the elements which display a signi®cant positive correlation with mobile Al concentration have a natural, geogenic origin. However, with the exception of the B1 horizon, pollution level and soil acidity are not correlated with mobile Al (Table 4). In the most polluted catchment (C2, Monchegorsk), only pro®le 2P36 shows a high level of Al mobility in the O, E
Table 4. Correlation coecients (r) between mobile Al concentration and (1) deposition of major pollutants, (2) soil acidity and (3) element concentrations in dierent extractants in the podzol pro®les Deposition
Soil variables
S
Ni + Cu
H+ in water extraction
O (n = 25)
ÿ0.02
0.06
E (n = 23)
0.14
B1 (n = 24)
Horizon (No. of samples)
Water extraction
NH4 Ac(pH 4.5) extraction
Aqua regia extraction
ÿ0.18
PO4 (ÿ0.59*) Anion sum(ÿ0.52*)
Fe (0.58*) Zn (ÿ0.52*)
0.19
0.08
PO4 (ÿ0.51*) NO3 (0.48*)
Cr (0.65*) Fe (0.50*) Zn (ÿ0.47*)
0.45*
0.11
ÿ0.14
NO3 (0.47*)
Cr (0.75*) Sr (0.47*) Mg (ÿ0.53*)
B2 (n = 22)
0.06
ÿ0.10
ÿ0.07
NO3 (0.51*)
BC1 (n = 23)
0.03
0.00
0.13
NO3 (0.83*)
BC2 (n = 21)
ÿ0.16
ÿ0.20
0.25
none
0.19
0.12
0.17
none
Cr (0.70*) Fe (0.54*) Cr (0.80*) Fe (0.79*) Co (0.48*) Cr (0.64*) Fe (0.54*) Co (0.50*) Cd (0.47*) S (0.74*) Fe (0.57*) K (0.55*) Cr (0.54*)
Al (0.86*) Li (0.75*) Sc (0.75*) P (0.46*) Zn (ÿ0.61*) Al (0.61*) Hg (0.54*) Na (0.51*) Fe (0.50*) Al (0.84*) Sr (0.63*) Y (0.57*) Hg (0.43*) none
C (n = 46)
* Signi®cant correlation (p < 0.05). none: no signi®cant correlations found.
XRF no data
Na (0.44*)
Al (0.80*)
none
none
none
Hg (0.50*) Al (0.47*) Li (0.43*)
Al (0.54*)
Al (0.77*) Li (0.71*) Hg (0.64*) B (0.63*) Bi (0.44*) Ba (0.43*) Mg (0.32*)
Al (0.56*)
398
G. Kashulina et al
Fig. 3. Content of mobile Al (ammonium acetate extraction) in mg kgÿ1 (left scale, bars) in all major horizons of the podzol pro®les, and proportion in % (right scale, black dots connected with lines) of mobile Al to total Al content measured by conc. HNO3 extraction (O horizon) or by XRF (mineral soil horizons).
and BC1 horizons. In contrast, the other 2 pro®les from this catchment show some of the lowest contents of mobile Al, especially in their upper horizons. Parent material and the degree of pollution are very similar at these sites. It is suggested that the dierences observed here in the proportions of mobile Al are caused by varying drainage con-
ditions. Free surface and vertical drainage, in the case of 2P37 and 2P38, promote the leaching of mobile Al from the pro®les. In pro®le 2P36, the drainage is hindered by ¯at ground and close proximity to the water table. Drainage conditions can also help to explain the high content of mobile Al in several horizons of pro®les from other catch-
Acidity status and mobility of Al in podzols
ments (1P38, 7P05, 8P13 and 8P18) (Fig. 3); all these pro®les are developed on ¯at ground with a high water table. In pro®le 8P18, which has one of the highest contents and proportions of mobile Al in most of its horizons, poor drainage conditions are not only related to relief and proximity to the water table, but also to the formation of an organo-mineral horizon (Ah) with a high clay content. In combination with low contents of base cations, the high content of mobile Al may also help explain the damage to spruce trees observed at this site. Indirect evidence for the importance of surface drainage in the removal of mobile Al from the upper part of the soil may come from the chemistry of surface water during snowmelt. Despite the diluting eect of peak discharge related to snowmelt, a sharp increase in Al content was observed at this time in both polluted and unpolluted catchments (Caritat et al., 1996b). Seasonal soil investigations have shown a sharp decrease in all mobile elements in upper soil horizons after snowmelt (Levina, 1969; Niskavaara et al., 1997). Pro®les from C3, especially 3P51 and 3P52, display the highest content of mobile (and total) Al in the illuvial horizon (B1). This is because of the proximity of an alkaline nepheline syenite intrusion. In addition, dierences in pH between eluvial and illuvial horizons were large in this catchment (Fig. 2), creating a favourable situation for the accumulation of Al in the B1 horizon. Catchment 5 generally has the lowest content and proportion of mobile Al in its soils; this is also re¯ected in the low Al concentration of stream water (Caritat et al., 1996a). Strong natural acidi®cation related to in situ weathering of S-rich black schist in the eluvial horizon of 5P41 is likely to intensify weathering throughout the pro®le and result in the removal of Al under free drainage conditions.
Mobile cations The toxic eect of mobile Al on the vegetation depends upon its relationship to base cation concentrations (Sverdrup et al., 1992). Figure 4a shows the relationship between Al and base cation content in the main soil horizons of each pro®le. To better illustrate the dierences between catchments and pro®les, contents of Al, Ca, Mg, K and Na are calculated as a % of their total equivalent sum for the O and E horizon (Fig. 4b). At most sites the principal mobile cation in the O horizon is Ca, followed by Mg, K and Al, Na being negligible (Fig. 4b). Large changes in the mobile cation composition as a result of pollution were found in the organic horizons of pro®les 2P36 and 2P37. In 2P36, a high Al content and a reduction in
399
the content of base cations cause Al to become the dominant cation, accounting for 50% of the total. In 2P37, although the content of all the mobile cations is very low (Fig. 4a), there is also a comparatively high content of mobile Al. A high proportion of mobile Al was, however, also observed at a number of signi®cantly less polluted sites. For example, in the organic horizon of 5P38, formed on ¯uvioglacial deposits, mobile Al accounts for about 40% of the total sum. In the organic horizon of pro®le 8P18, the mobile Al content is 32% in the upper part (O1, Fig. 4b) and 66% of the total cations in the lower part. Catchment 1 (Zapoljarnij), which receives the highest S deposition of all sites studied (Table 1), is characterised by a low content of mobile Al and the highest content of mobile Mg in the organic horizon. For this site Reimann et al. (1997a,c) described a signi®cant input of Mg from local dust sources due to anthropogenic activities (open pit mining of basic rocks). In addition, C1 is closest to the Barents Sea coast and Mg may be deposited onto the O horizon by a signi®cant seaspray input. Pro®le 8P15 is an interesting and unusual one. The pro®le is developed on quartzite (Table 1), a very acidic, nutrient-poor lithology. It shows, however, surprisingly high contents of mobile Ca and K and one of the highest contents of Mg in the O horizon. Possible explanations may be topographic (base of slope, input of cations from runo) or intensive biological turnover. The E horizons of all pro®les contain considerably lower amounts of mobile cations than the O horizons (Fig. 4a). The principal mobile cation in the E horizon is Al, followed by Ca and Mg (Fig. 4b). In the C and illuvial (B1) horizons the content of mobile base cations is usually negligible with only Al remaining mobile. Correlation analysis shows that the proportion of mobile Al (or the absolute Al concentration) are unrelated to either the deposition of heavy metals, or to soil acidity throughout the major horizons of the podzolic soils.
CONCLUSIONS
The importance of natural conditions (bedrock lithology and relief) on soil acidity and Al mobility in podzols has been investigated by studying soil pro®les from 8 catchments characterised by dierent lithologies and situated at dierent distances from some of Europe's largest point sources of SO2. The total element content (XRF) of the C horizon varies considerably between, but also in some cases within, catchments. The data show that the chemical composition of the C horizon can be aected by pollution (for example in C2) or by
400
G. Kashulina et al
natural acidi®cation and subsequent leaching of cations due to sulphide-rich saprolite (5P41). In general, the base cation content of the parent material is naturally high in the catchments close to the pollution sources, and low in the remote catchments. The natural geochemical conditions of the area thus tend to mask or mitigate acidi®cation eects near pollution sources. Not even relatively long lasting and high inputs of S and heavy metals (C1 and C2) have led to detectable signs of soil acidi®cation in the podzol pro®les developed on till overlying basic lithologies.
Moreover, strong degradation of the ecosystem, including soil erosion, seems to be necessary to give measurable eects in the O, E and B horizons, as is the case in C2. Even here, however, the O horizon, which has a very high buering capacity, shows only slight acidi®cation, and the E horizon is naturally leached. Of the upper horizons of the podzol pro®le, the illuvial horizon (B1) appears to be most sensitive to soil acidi®cation. Strong natural acidi®cation, as observed in pro®le 5P41, aects only the pH of the E horizon containing the sulphide-rich material, and not that of any
Fig. 4(a).
Acidity status and mobility of Al in podzols
401
Fig. 4. (a) Ammonium acetate extractable cation concentrations (expressed in meq/100 g) in the major soil horizons. (b) Relative proportions of mobile cations (calculated as % of SAl + Ca + Mg + K + Na) in the O and E horizon of all pro®les.
other horizon. Weathering of the lower soil horizons, however, is clearly aected. Vegetation is undamaged at this site. In general, the content of mobile Al varied signi®cantly between and within catchments. In the area studied, contamination plays a minor role in the regional variation of mobile Al. Comparison of pro®les 2P37 with 2P36, and 1P33 with 1P38, shows that even under very high inputs of anthropogenic S, high contents of mobile Al can only be found in poorly drained soils. Although acidi®cation will mobilize Al and base cations, these will be leached out of the pro®le under free-drainage conditions. Geogenic factors (as observed for all pro®les in C3, and at 7P18, 7P19 and 5P40) and drainage conditions (8P18, 2P36, 1P38), and not soil acidi®cation, are therefore the key factors governing the availability of mobile Al in podzol pro®les. It is consequently not surprising that the highest content of mobile Al in all pro®les was measured at an unpolluted site in C8 (8P18), where drainage conditions are especially poor. Here, the vegetation is clearly aected by Al toxicity, the natural content of base cations (and all other nutrients) also being low. Mobile Al generally makes up a large proportion of the total mobile cation pool in the E horizon and can become the dominant mobile cation, independent of pollution levels. In the deeper soil horizons (B and C), Al is always the dominant
mobile cation and pollution inputs appear to be relatively unimportant. AcknowledgementsÐThe authors would like to thank the Geological Surveys of Finland and Norway, the Norwegian Ministry of the Environment and the Central Kola Expedition for their support of the project. We are grateful to the whole project team in all 3 countries and to the guest scientists from Lithuania and Austria who participated in the ®eld work and in many stimulating discussions. The suggestions by 2 anonymous referees were greatly appreciated, and the dedicated editorial assistance of Mike Billett was highly valued. Editorial handling: M. Billett
REFERENCES AÈyraÈs M. and Reimann C. (1995) Joint ecogeochemical mapping and monitoring in the scale of 1:1 million in the west Murmansk region and contiguous areas of Finland and Norway-Field Handbook. Nor. Geol. Unders. Rep. 95.111, 33p. AÈyraÈs M., Caritat P. de, Chekushin V. A., Niskavaara H. and Reimann C. (1995) Ecogeochemical investigation, Kola Peninsula: sulphur and heavy metal content in snow. Water, Air Soil Pollut. 85, 749±754. Caritat P. de, Reimann C., AÈyraÈs M., Niskavaara H., Chekushin V. A. and Pavlov V. A. (1996a) Stream water geochemistry from selected catchments on the Kola Peninsula (NW Russia) and in neighbouring areas of Finland and Norway: 1. Element levels and sources. Aquatic Geochem. 2, 149±168.
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Caritat P. de, Reimann C., AÈyraÈs M., Niskavaara H., Chekushin V. A. and Pavlov V. A. (1996b) Stream water geochemistry from selected catchments on the Kola Peninsula (NW Russia) and in neighbouring areas of Finland and Norway: 2. Time series. Aquatic Geochem. 2, 169±184. Caritat P. de, Krouse H. R. and Hutcheon I. (1997) Sulphur isotope composition of stream water, moss and humus from eight Arctic catchments in the Kola Peninsula region (NW Russia, N Finland, NE Norway). Water, Air Soil Pollut. 94, 191±208. Chekushin V. A., Bogatyrev I. V., Pavlov V. A. and Danilova S. I. (1995) Report on Joint Ecogeochemical Mapping and Monitoring in the scale 1:1 mill. in the West Murmansk Region and the contiguous areas of Finland and Norway (Catchment Study, 1994±95). Central Kola Expedition (CKE) and Kola Geological Information Laboratory Centre (KGILC) Report. Monchegorsk, Apatity, Russia. Chekushin V. A., Bogatyrev I. V., Caritat P. de, Niskavaara H. and Reimann C. (in press) Annual deposition of 16 elements in eight catchments of the central Barents region. Manuscript submitted. Chertov O. G., Languzova I. V., Druzina V. D. and Menshikova G. P. (1990) In¯uence of sulphur and heavy metals pollution on forest soils. In Forest Ecosystems and Air Pollution, ed. V. A. Alexeev, pp. 65±73, Nauka, Leningrad (in Russian). Chertov O. G., Nadporozshkaya M., Lapshina I. and Grigorieva O. (1993) Soil degradation in surrounding of ``Pechenganikel'' smelter complex. In Aerial Pollution on Kola Peninsula, eds. M. V. Kozlov, E. Haukioja and V. T. Yarmishko, Proceeding of the International Workshop, April 14±16, St. Petersburg. Apatity, 1993, pp. 159±162. Galloway J. N., Thornton J. D., Norton S. A., Volchok H. L. and McLean R. A. N. (1982) Trace metals in atmospheric deposition: a review and assessment. Atmos. Environ. 16, 1677±1700. Hùgda K. A., Tùmmervik H., Solheim I. and Marhaug O. (1995) Use of multitemporal Landsat image data for mapping the eects from Air Pollution in the Kirkenes± Pechenga Area in the period 1973±1994. NORUT Information Technology Ltd. report IT2039/1-95, Tromsù, Norway, 66 p. Jevtjugina Z. A. (1994) Peculiarities of water migration of chemical elements in the landscapes under air±technogenic pollution. Pre-print, Kola Scienti®c Centre of Russian Academy of Science, Apatity, 48 p. (in Russian). Kashulina G., Jevtjugina Z. and de Caritat P. (1995) Soil acidity status in the vicinity of the Severonikel Smelter complex (Kola Peninsula, Russia). In Abstracts of the 5th International Conference on Acidic Deposition. Gothenburg, Sweden, 26±30 June 1995. Koptsik G. and Muchina I. (1995) Eect of acid deposition on acidity and exchangeable cations in the podzols of Kola peninsula. Water, Air Soil Pollut. 85, 1209± 1214. Koptsik G. and Nedbaev N. (1992) Eect of atmospheric deposition on the forest soil in the north±westmost of Kola Peninsula. In Eect of Air Pollution on the Terrestrial Ecosystems in the Border Area between Russia and Norway, eds. V. Kismul and J. Jerre. Eects of air pollution on terrestial ecosystems in the border area between Russia and Norway. Proceedings from the First Symposium, Svanvik, Norway, 18±20 March 1992, pp. 48±55. Kozlov M. V., Haukioja E. and Yarmishko V. T. (eds.) (1993) Aerial pollution in Kola Peninsula. Proceeding of the International Workshop, April 14±16, 1993, St. Petersburg. Apatity, 417 p.
Kryushkov V. V. (1991) Heavy metal accumulation in spruce needles and changes of northern taiga ecosystems. In Environmental Geochemistry in North Europe, ed. E. Pulkkinen, Geological Survey of Finland, Special Paper 9, pp. 177±184. Levina V. I. (1969) Seasonal dynamic of moisture and chemical properties of podzolic, mountain±podzolic and mountain±tundra soils in Murmansk region. In Soil Regimes on the Polar North, pp. 5±58, Nauka, Leningrad (in Russian). Motova A. D. and Nikonov V. V. (1993). Aluminium compounds in podzolic Al±Fe-humus soils in the surroundings of the ``Severonikel'' smelter complex. In Aerial Pollution in Kola Peninsula, eds. M. V. Kozlov, E. Haukioja and V. T. Yarmishko, Proceeding of the International Workshop, April 14±16, 1993, St. Petersburg. Apatity, pp. 178±183. Niskavaara H. (1995) A comprehensive scheme of analysis for soils, sediments, humus and plant samples using inductively coupled plasma atomic emission spectrometry. Geological Survey of Finland, Current Research 1993±1994. Geological Survey of Finland Special Paper 20, pp. 167±176. Niskavaara H., Reimann C. and Chekushin V. (1996) Distribution and pathways of heavy metals and sulphur in the vicinity of the copper±nickel smelters in Nikel and Zapoljarnij, Kola Peninsula, Russia, as revealed by dierent sample media. Appl. Geochem. 11, 25±34. Niskavaara H., Reimann C., Chekushin V. and Kashulina G. (1997) Seasonal variability of total and easily leachable element contents in topsoil (0±5 cm) from eight catchments in the European Arctic (Finland, Norway and Russia). Environ. Pollut., 96 261±274. Pavlov V. A., RaÈisaÈnen M. L., Melezhik V, and Caritat P. de (1996) Composition of bedrock and Quaternary deposits in eight catchments subjected to detailed ecogeochemical investigation in the Barents region. In Kola Project Ð International Report, Catchment Study 1994, eds. C. Reimann, V. A. Chekushin and M. AÈyraÈs, Nor. Geol. Unders. Rep. 96.088, pp. 18±37. RaÈisaÈnen M. L., Pulkkinen E. and Kontio M. (1994) Alteration of podzolized till by acid load near Ni±Cu smelters at Monchegorsk, Kola Peninsula, Russia. Bull. Geol. Soc. Finland 66, 19±38. Reimann C., Caritat P. de, Halleraker J. H., Volden T., AÈyraÈs M., Niskavaara H., Chekushin V. A. and Pavlov V. A. (1997a) Rainwater composition in eight arctic catchments of Northern Europe (Finland, Norway and Russia). Atmos. Environ. 31, 159±170. Reimann C., Caritat P. de, Finne T. E., Kashulina G., Niskavaara H. and Pavlov V. A. (1997b) Comparison of heavy metal contents in O- and C horizon soils from the surroundings of Nikel, Kola Peninsula, using dierent grain size fractions and extractions. Geoderma, in press. Reimann C., Boyd R., Caritat P. de, Halleraker J. H., Kashulina G., Niskavaara H. and Bogatyrev I. (1997c) Topsoil (0±5 cm) composition in eight arctic catchments in northern Europe (Finland, Norway and Russia). Environ. Pollut. 95, 45±56. Solheim I., Tùmmervik H. and Hùgda K. A. (1995) A time study of the vegetation in Monchegorsk, Russia, NORUT Information Technology Ltd. report IT2039/295, Tromsù, Norway, November 2, 1995, 42 p. Sverdrup H., Warfvinge P., Frogner T., HaÊùya A. O., Johansson M. and Andersen B. (1992) Critical load for forest soil in the Nordic Countries. Ambio 21, 348±355. Tikkanen E. and NiemelaÈ I. (1995) Kola Peninsula pollutants and forest ecosystems in Lapland. Finland's Ministry of Agriculture and Forestry, The Finnish forest research Institute. Print: Gummerus Kirjapaino Oy JyvaÈskylaÈ. 82 p.
Applied Geochemistry, Vol. 13, pp. 391±402, 1998 # 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0883-2927/98 $19.00 + 0.00
Acidity status and mobility of Al in podzols near SO2 emission sources on the Kola Peninsula, NW Russia G. Kashulina%, P. de Caritat and C. Reimann* Geological Survey of Norway, P.O. Box 3006-Lade, N-7002 Trondheim, Norway
M.-L. Raisanen Geological Survey of Finland, P.O. Box 1237, SF-70211 Kuopio, Finland
V. Chekushin Central Kola Expedition, Fersman St. 26, 184200 Apatity, Russia
I. V. Bogatyrev Kola Geological Information Laboratory Centre, Fersman St 26, 184200 Apatity, Russia
(Received 8 July 1996; accepted 30 June 1997) AbstractÐSoil acidity status and Al mobility in podzols was examined on a broad scale near the large emission sources of SO2 and heavy metals on the Kola Peninsula (the Severonikel and Pechenganikel smelter complexes) in NW Russia and in neighbouring parts of Norway and Finland. Acidi®cation of the upper podzol horizons and depletion of mobile base cations were only evident at sites where ecosystems are severely destroyed, in the immediate vicinity of the Severonikel smelter complex. The high content of base cations in the parent material (till) near the emission sources may mask the acidi®cation eect of pollution. Both strong anthropogenic (SO2) emissions and natural acidi®cation (in situ weathering of black schist) accelerate weathering and mobilize Al. However, drainage conditions seem to be the most important factor determining the content of mobile Al in the podzols. # 1998 Elsevier Science Ltd. All rights reserved
INTRODUCTION
Three of the largest sources of SO2 and heavy metal pollution in northern Europe are located in the western part of the Kola Peninsula. These are the Severonikel Ni±Cu ore smelter at Monchegorsk and the Pechenganikel complex consisting of the ore smelter at Nikel and the ore roasting plant at Zapoljarnij (Fig. 1). Together, they accounted in 1994 for about 300 000 t of SO2, 1900 t of Ni, 1100 t of Cu and 94 t of V2O5 emitted into the atmosphere (Reimann et al., 1997a). Cumulative SO2 emissions from the Severonikel smelter complex alone between 1960 and 1994 have been estimated at about 6.5 million tonnes (Caritat et al., 1997). In addition, there are several other sources of SO2 emissions in the area (coal-®red power plants and other industries). The long-term eect of such a high level of pollution is severe and there is widespread ecosystem *Corresponding author. %Present address: INEP, Kola Science Centre, Fersman St. 14, 184200 Apatity, Russia. 391
degradation in the region, and, in the close vicinity of Monchegorsk and Nikel, severely disturbed ecosystems, characterised by intensive soil erosion (Kryushkov, 1991; Hùgda et al., 1995; Solheim et al., 1995). Contamination of the various parts of the environment, including soil, by heavy metals near Monchegorsk and Nikel is well documented (Kozlov et al., 1993; AÈyraÈs et al., 1995; Niskavaara et al., 1996, 1997; de Caritat et al., 1996a,b, 1997; and Reimann et al., 1997a,b,c). Even though SO2 is the dominant component of the emissions, soil acidi®cation has not been investigated in detail in the area. Most studies are based on transect sampling with large distances between sampling points and pro®les. Laboratory experiments to study the direct interaction between precipitation and soil samples have shown that pollution from the Severonikel smelter complex may cause acidi®cation of podzols and base cation leaching (Kashulina et al., 1995; Koptsik and Muchina, 1995). In the ®eld, however, increased soil acidity has so far only been found in the organic horizon of podzols in severely damaged pine forests near Severonikel (Chertov et al., 1993) and Pechenganikel (Chertov et al., 1990, 1993; Koptsik
392
G. Kashulina et al
Fig. 1. Location of the survey area for the regional mapping project and the study catchments. Catchment C1: Zapoljarnij, C2: Monchegorsk, C3: Kirovsk, C4: Kurka, C5: Skjellbekken, C6: Kirakka, C7: Naruska, C8: Pallas.
and Nedbaev, 1992; Koptsik and Muchina, 1995) and within 4 km of the emission sources. Investigations in a pine forest near Monchegorsk did not reveal any trend of increasing acidi®cation over recent years (Chertov et al., 1990). The absence of any evidence for soil acidi®cation within 7±40 km of Nikel has been explained by the high buering capacity of the soil and a high anthropogenic input of base cations (Koptsik and Nedbaev, 1992). Transect investigations in pine forest ecosystems carried out during the Finnish Forest Damage Project (Tikkanen and NiemelaÈ, 1995) found no relationship between the level of pollution and the parameters that characterise soil acidity (pH in water, exchangeable H+ and Al3+) within 10± 70 km of Monchegorsk. However, Motova and Nikonov (1993) described an increase of amorphous
Al in the illuvial horizon of podzols near the source of pollution. During a detailed investigation of spruce forest ecosystems, lower acidity and higher contents of exchangeable base cations were found in the organic horizon of podzols located 7 and 20 km from the source of pollution, compared with control sites more than 100 km away (Kashulina et al., 1995). In addition, lysimeter studies revealed a sharp increase (about 10 times) in the leaching of Al at the sites 7 km from the pollution source (Jevtjugina, 1994). RaÈisaÈnen et al. (1994) investigated changes in soil mineralogy connected to Al-mobilisation at these sites and described a newly formed mixed-layer clay mineral (chlorite±aluminous montmorillonite) in the E horizon. They explained this as acidic deposition causing the mobilisation of Al-hydroxides, which enter the interlayer spaces of vermiculite.
N: 7 708 000; E: 422 605
N: 7 707 250; E: 422 950
N: 7 525 550; E: 495 100
N: 7 527 900; E: 495 600
N: 7 529 650; E: 494 400 N: 7 493 400; E: 533 700
N: 7 495 350; E: 531 750
N: 7 495 350; E: 532 650
N: 7 508 750; E: 493 050
N: 7 512 400; E: 493 550 N: 7 511 900; E: 491 100 N: 7 696 550; E: 597 200
N: 7 697 700; E: 597 000 N: 7 699 620; E: 597 550
N: 7 699 550; E: 596 390
N: 7 700 450; E: 600 100
N: 7 720 190; E: 454 380
N: 7 474 560; E: 602 500
N: 7 476 340; E: 606 040 N: 7 474 640; E: 605 100
N: 7 565 360; E: 370 180
N: 7 565 510; E: 368 520
N: 7 564 540; E: 371 020
1P28
1P38
2P36
2P37
2P38 3P15
3P51
3P52
4P06
4P38 4P39 5P37
5P38 5P39
5P40
5P41
6P12
7P05
7P18 7P19
8P13
8P15
8P18
Moraine plain, ¯at
Foot of moraine hill
Moraine plain, ¯at
Foot of moraine hill Moraine hill, gentle slope
Moraine plain
Foot of moraine hill
Moraine hill; gentle slope
Moraine hill; ¯at top
Glacio¯uvial delta; ¯at Moraine hill; ¯at top
Upper part of hill slope Valley, ¯at Moraine hill, upper slope
Foot of hill, ¯at
Mountain terrace
Mountain terrace, ¯at
Gentle mountain slope Mountain terrace, ¯at
Top of moraine hill
Top of moraine hill
Valley, ¯at
Top of moraine hill
Topography
b
From geological maps (Chekushin et al., 1995). Winter 1993±1994 deposition (Chekushin et al., 1995).
a
Location (m)
Quartzite
Quartzite
Quartzite
Granitoids Granitoids
Granitoids
Granite
Black schist
Andesitic laves, siltstone
Andesitic sandstone Mica schist
Gabbro, gabbro-norites Two-mica gneisses Amphibolitic gneiss
Amphibolites
Gneisses, nepheline syenite
Gabbro-norites
Pyroxenites Ma®c tus
Norites, gabbro-norites
Amphibole±biotite and granite gneisses Amphibole±biotite and granite gneisses Dacitic±andesitic tus
Bedrock typea Dwarf shrub±birch subarctic birch forest Dwarf shrub±sparse subarctic birch forest Empetrum±dead standing spruce forest Industrial desert with sparse birch shrubs Industrial desert Dwarf shrub±green mosses±birch forest with spruce Dwarf shrub±green mosses± subalpine birch forest Dwarf shrub±green mosses± subalpine birch forest Dwarf shrub±birch forest with spruce Dwarf shrub±sparse spruce forest Dwarf shrub±spruce forest Green moss±dwarf shrub±birch forest with pine White lichen±pine forest Green moss±dwarf shrub±pine forest with birch Green moss±dwarf shrub±birch forest with pine Green moss±dwarf shrub±pine forest Dwarf shrub±green moss±pine forest with birch Bilberry±green moss±sparse birch with spruce Bilberry±green moss±spruce forest Dwarf shrub±green moss forest with pine and birch Dwarf shrub±green moss spruce forest with birch and pine Grass±dwarf shrub±green moss± spruce forest Dwarf shrub±green moss±birch forest with spruce
Vegetation type
no
no
no
no no
no
slight
slight
slight
slight moderate
moderate moderate slight
moderate
slight
slight
severe slight
severe
strong
moderate
moderate
Degree of damage
60
60
70
80 100
70
33
45
45
30 40
125 125 30
80
190
200
250 215
260
310
460
440
S dep.b, kg kmÿ2
0.5
0.5
0.5
0.5 0.5
0.5
0.5
1.3
1.2
1.2 1.2
80 50 1
32
3.5
5
460 10
350
510
220
240
Ni + Cu dep.b, kg kmÿ2
Table 1. Location and main characteristics of the podzol pro®le sample sites. Information on the deposition of S and (Cu + Ni) from Chekushin et al. (1995)
Pro®le No.
Acidity status and mobility of Al in podzols 393
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The aim of the present paper is to provide data on the state of soil acidity and Al mobility in podzols in the western part of the Kola Peninsula and neighbouring parts of Finland and Norway, where the Geological Surveys of Finland (GTK) and Norway (NGU) and the Central Kola Expedition (CKE) in Russia are carrying out a major geochemical mapping project (World Wide Web site http:// www.ngu.no/Kola) in a 188 000 km2 area between 248 and 35.58 E and N of the Arctic Circle to the Barents Sea (Fig. 1). As part of this project, 8 widely distributed catchments (hereafter abbreviated C1±C8, with C1±C4 in Russia, C5 in Norway and C6±C8 in Finland) were investigated in detail in 1994. Snow (meltwater and ®lter residue), rainwater, stream water, organic stream sediments, terrestrial moss, topsoil (0±5 cm), complete podzol pro®les, Quaternary deposits and bedrock were all sampled and analysed.
METHODOLOGY
Field procedures Criteria for the selection of sample sites within the catchments, as well as methods used for sampling, are detailed in AÈyraÈs and Reimann (1995). Between one and 5 pro®les were dug in each catchment (Table 1) and all major horizons were sampled. The depth of the soil pits varied from 50 to 100 cm depending on local conditions. Most of the pro®les investigated were free-draining haplic or ferric podzols. Pro®les 1P38, 2P36 and 7P18 (the ®rst ®gure gives the catchment number Ð see Table 1) were close to the water table. Two pro®les (7P05 and 8P18) showed morphological evidence of temporary excess of water (gleyic podzols). Pro®le 2P38 was strongly eroded and had neither humus nor an E horizon. The other 2 pro®les in catchment C2 showed some evidence of erosion. The parent material at most sites was sandy till with a variable stone content. The soil at site 5P38, however, was developed on ¯uvioglacial sand, and in the E horizon of site 5P41, an ablation till was mixed with weathered black schist. Additional information about sample sites is listed in Table 1. Generally, the Finnish catchments are underlain by more acidic lithologies (granite, gneiss and quartzite) than the Norwegian and Russian catchments, with C2 (Monchegorsk) having the most basic lithology (including gabbro and pyroxenite). The sampling sites had dierent types of vegetation and the degree of ecosystem damage varied. Almost total vegetation damage is characteristic of C2, quite serious vegetation damage was observed in C1 and C4, and slight damage in C3 and C5. C6 is in¯uenced by reindeer grazing and tree felling. Although C7 and C8 in Finland gener-
ally show no traces of damage to vegetation or soil cover, site 8P18 has a number of dead spruce trees and slightly damaged ground vegetation. Yearly airborne input of S and Ni + Cu in the dierent sample sites was estimated from the chemistry of snow and rain samples (Chekushin et al., 1995, 1997). These data are summarised in Table 1, which shows that deposition levels in catchments close to the industry (C1 and C2) are 5±10 times higher for S and up to 1000 times higher for Ni + Cu compared to the Finnish catchments. Pollution deposition values determined for the Finnish catchments (C6±C8) are similar to remote background sites worldwide (Galloway et al., 1982).
Analytical methods All samples were air dried at temperatures R408C. The O horizon samples were homogenised by milling in a domestic blender with blades made of non-contaminating material. The samples were then sieved to <2 mm. For the determination of total element content, 0.5 g of humus was digested with 10 ml of concentrated HNO3 in a microwave oven and diluted to 50 ml with deionised water. The clear solutions were analysed by Thermo Jarrell Ash Polyscan 61E ICP-AES for 30 elements and by Sciex Elan ICP-MS for 29 elements. For the mineral soil horizons, 2 g of the <2 mm fraction was mixed with 9 ml concentrated HCl and 3 ml concentrated HNO3 (aqua regia) in borosilicate tubes. The mixture was left at room temperature overnight and then heated to 908C for 2 h on an Al block. The digest was diluted to 60 ml with deionised water, thoroughly mixed, decanted into polystyrene tubes and centrifuged. In addition, an ammonium acetate extraction buered at pH 4.5 (shaking time 2 h) was carried out on all samples. After centrifugation both solutions were analysed by ICP-AES for 30 elements. Arsenic and Cd were determined by graphite furnace-AAS. All the above analyses were carried out at the GTK laboratory. In addition, the total content of major elements in the mineral soil horizons was determined by XRF on fused beads. pH and electrical conductivity (EC) was determined in water extracts (2 g of soil in 20 ml deionised water for the mineral soils, 2 g of sample in 40 ml deionised water for the O horizon samples), and anion concentration in these water extracts was determined by ion chromatography after ®ltration (0.45 mm) and removal of humic acids in the O horizon samples using Waters2 Sep-Pak Plus C18 cartridges, at the NGU laboratory. Fr more details on analytical techniques and quality control procedures see Niskavaara (1995). The GTK and NGU laboratories are both accredited according to ISO 9001 and ISO-Guide 25.
Acidity status and mobility of Al in podzols
395
Table 2. Total element content (XRF analysis) of the C horizon samples from all pro®les (LOI-corrected values) Pro®le 1P28 1P38 2P36 2P37 2P38 3P15 3P51 3P52 4P06 4P38 4P39 5P37 5P38 5P39 5P40 5P41 6P12 7P05 7P18 7P19 8P13 8P15 8P18
LOI %
SiO2 %
Al2O3 %
Fe2O3 %
MgO %
CaO %
Na2O %
K2O %
TiO2 %
1.5 4.3 2.7 1.9 2.0 1.3 1.8 3.0 2.3 1.3 1.8 1.9 1.2 1.2 2.0 2.6 0.8 1.6 4.2 3.7 0.9 2.4 1.1
67.4 63.2 62.2 60.6 60.2 69.7 65.4 64.8 60.2 67.0 63.7 62.7 66.8 65.4 62.8 68.3 73.1 73.3 66.0 68.2 72.7 72.1 73.4
13.7 14.3 15.1 14.3 15.6 13.9 13.7 14.8 13.6 14.0 13.9 14.8 14.8 14.5 15.2 13.1 13.3 13.2 17.3 15.9 12.4 12.6 12.0
5.7 8.3 7.3 8.2 7.6 4.2 6.6 6.2 9.5 5.7 7.6 8.6 5.5 6.8 9.0 8.6 2.2 2.9 5.1 4.5 3.3 4.2 3.4
2.4 3.4 4.2 5.7 5.7 2.1 2.8 2.6 5.1 2.5 3.5 3.0 2.5 2.5 3.5 1.7 0.8 1.6 2.5 2.2 1.5 1.8 1.6
4.2 4.6 5.3 5.9 5.9 4.1 4.4 4.1 5.0 4.6 5.0 4.9 3.9 4.4 4.3 3.2 1.8 2.7 2.9 2.8 2.7 2.7 2.5
3.5 3.1 3.1 2.7 2.7 3.7 3.4 3.8 3.1 3.6 3.2 3.1 3.3 3.3 3.1 3.1 3.6 3.6 3.6 3.6 3.4 3.0 3.0
1.8 1.5 1.3 1.2 1.1 1.6 1.6 2.2 1.9 1.6 1.7 1.1 1.8 1.4 1.4 1.1 3.5 1.6 2.0 1.7 2.6 2.5 2.6
0.72 0.92 0.67 0.74 0.63 0.46 0.87 0.86 0.76 0.66 0.82 0.87 0.55 0.74 1.01 0.66 0.32 0.41 0.48 0.54 0.43 0.48 0.46
RESULTS AND DISCUSSION
C horizon, total element content Table 2 summarises the analytical results (XRF) for the major element content of the C horizon. Dierences in lithology (Table 1) result in signi®cant dierences in the chemical composition of the parent material (till) between, and sometimes within, catchments (Table 2). The greatest dierences between catchments and sites were found for Fe2O3, MgO, CaO and K2O content. The mean sum of CaO and MgO in C2
(11.2%) is at least twice as high as in the Finnish catchments (C6±C8). The other Russian catchments (C1, C3, C4) and the Norwegian catchment (C5) are intermediate in terms of (CaO + MgO) content (4.9±8.5%). Although the alkali elements only show slight variation between catchments and sites, K2O concentrations are elevated in the 3 Finnish catchments compared to the others. Dierences in the Al2O3 content are signi®cant, varying from 12% (C8) to 17.3% (C7). Surprisingly, the soil pro®les in C3, which is partly underlain by alkaline rocks, show no unusual chemical composition of the C horizon (or till).
Fig. 2. pH in water extracts from all major soil horizons.
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Only the weathered sediments of the Hibiny alkaline rocks, which are located in the upper part of C3, are enriched in Na and Al (Chekushin et al., 1995). The question of whether or not the C horizons represent the natural geochemical background of the area is unclear. When comparing the chemical composition of 2P37, 2P38 and 5P41 with other pro®les from the same catchments (Table 2) and with samples of Quaternary deposits (Pavlov et al., 1996), it can be concluded that the low alkali content of the C horizon of 2P37 and 2P38 is related to anthropogenic factors, while the low K, Na, Ca, Mg and Al content in 5P41 is related to intensive weathering and leaching due to natural factors (sulphides in the E horizon). An extremely high natural content of base cations in C2 due to its bedrock composition may mask element leaching from the C horizon in 2P37 and 2P38. Thus, both natural soil-forming processes and anthropogenic eects can alter the composition of the C horizon substantially.
Soil pH Figure 2 shows the pH values (water extracts) of all pro®les in the main soil horizons. For most of the pro®les investigated, both pH and its variation throughout the pro®le are typical of podzolic soils.
The pH measured in the C horizon is weakly acidic in most pro®les and varies from 5.7 to 6.4. The exceptions are 3P52, which has a near neutral pH (7.3), and 1P38, 2P36 and 5P40, which are the most acidic (pH 5.4, 5.6 and 5.5, respectively). This can be explained by the C horizon being unrelated to the upper horizons (3P52, 1P38 and 2P36), or by the unusual geochemistry of the whole pro®le (5P40). Generally, the parent material in the 3 Finnish catchments (C6: granite, C7: gneiss, C8: quartzite) can be regarded as the most acidic. In contrast, the Russian catchments are characterised by very basic lithologies (Table 1). These major lithological dierences are not re¯ected in the pH values of the C horizon. Apparently in this case, the base cation content plays no signi®cant role in determining soil pH. Correlation analysis does show, however, a positive correlation between H+ concentration and base cation content in the B horizon (Table 3). The only cation showing a negative correlation with H+ throughout the whole pro®les is Na+. Sulphur deposition rates are positively correlated with H+ concentration in the C horizon (Table 3). There are also good correlations between H+ concentration in soils and the concentration of 4 major pollutants (Cr, Co, Cu, Ni) determined in the ammonium acetate extracts from the C horizon.
Table 3. Correlation coecients (r) between soil acidity (expressed as H+ concentration) and the deposition of major pollutants, and element concentrations in the podzol pro®les Deposition Horizon (No. of samples)
Soil variables
S
Ni + Cu
Water extraction
NH4 Ac (pH 4.5) extraction
Aqua regia extraction
O (n = 25) E (n = 23)
ÿ0.32 ÿ0.01
ÿ0.32 0.17
none EC (0.53*)
none S (0.61*)
B1 (n = 24)
0.19
0.67*
EC (0.93*) Anion sum (0.90*) SO4 (0.89*) Cl (0.82*) F (0.57*)
S (0.90*), Cu (0.84*) Pb (0.81*) As (0.77*) Co (0.71*) Ni (0.69*)
B2 (n = 22)
0.43
0.87*
EC (0.95*) Anion sum (0.90*) SO4 (0.89*) Cl (0.82*) F (0.57*)
Cu (0.88*) Ni (0.56*)
BC1 (n = 23) BC2 (n = 21) C (n = 46)
0.42 0.13 0.32*
0.64* 0.30 0.19
F (0.59*)EC (0.43*) none none
none none Cr (0.45*) Co (0.35*) Cu (0.33*) Ni (0.30*)
none S (0.64*) Fe (0.61*) P (0.53*) S (0.5*) Ca (0.46*) Ni (0.86*) Te (0.85*) Cu (0.84*) Co (0.78*) Ag (0.78*) Cd (0.66*) Na (0.81*) Ni (0.78*) Cu (0.71*) S (0.72*) Cd (0.67*) Ca (0.66*) Pb (ÿ0.62*) none none Te (0.40*) Cu (0.31*) Na (ÿ0.24)
*Signi®cant correlation (p < 0.05). none: no signi®cant correlations found. EC: electrical conductivity.
XRF no data Na (ÿ0.50*) Ca (0.43*) Mg (0.68*) Na (ÿ0.64*)
Ca (0.65*) Mg (0.75*) Na (ÿ0.59*) Si (ÿ0.50*)
none none Na (ÿ0.26)
Acidity status and mobility of Al in podzols
The variation in pH values in the O horizon in the 8 catchments is low: for 14 out of 22 pro®les investigated, pH ranges from 4.3 to 4.5. The lowest pH of all the O horizon samples was found in 2P37 (pH 3.9). Although this appears to be related to pollution, there is no signi®cant correlation between H+ concentration and the degree of pollution (Table 3). For 18 out of 22 pro®les, the pH of the E horizon varies from 4.8 to 5.1. The lowest pH value (4.5) was found in the E horizon of 5P41. This can be explained by in situ weathering of S-rich black schist, a natural acidi®cation factor. Although the pH of the E horizons at the polluted Monchegorsk catchment (C2) is low, the correlation between H+ concentration in the E horizon and degree of pollution is not signi®cant (Table 3). Deposition of Ni + Cu appears to in¯uence the pH of the B1 horizon strongly, with all the lowest pH values occurring in C2 near Monchegorsk (Fig. 2), despite it containing the most basic bedrock lithology of all the catchments. However, lithology still has an in¯uence on the pH values observed in the BC1 horizon; 2 of the 3 pro®les from C2 showing high pH values. There are good correlations between soil H+ concentration and
397
Ni + Cu deposition, and between the soil H+ concentration and the concentrations of the mobile forms of most pollutants (S, Ni, Cu, Co, As, Cd, Pb) within the B1 and B2 horizons (Table 3).
Mobility of Al Figure 3 shows the mobile (available) Al contents measured by ammonium acetate extraction in mg kgÿ1 and expressed as a percentage of total (nitric acid extractable) Al. Up to 1% of total Al is available in the C horizon, up to 2.5% in the BC1 horizon. In the B1 horizon, this proportion reaches 4%, in the E horizon just over 0.4%, and in the O horizon it can exceed 10% (Fig. 3). There is generally a good correlation between total and mobile Al content in the soil horizons (Table 4). Most of the elements which display a signi®cant positive correlation with mobile Al concentration have a natural, geogenic origin. However, with the exception of the B1 horizon, pollution level and soil acidity are not correlated with mobile Al (Table 4). In the most polluted catchment (C2, Monchegorsk), only pro®le 2P36 shows a high level of Al mobility in the O, E
Table 4. Correlation coecients (r) between mobile Al concentration and (1) deposition of major pollutants, (2) soil acidity and (3) element concentrations in dierent extractants in the podzol pro®les Deposition
Soil variables
S
Ni + Cu
H+ in water extraction
O (n = 25)
ÿ0.02
0.06
E (n = 23)
0.14
B1 (n = 24)
Horizon (No. of samples)
Water extraction
NH4 Ac(pH 4.5) extraction
Aqua regia extraction
ÿ0.18
PO4 (ÿ0.59*) Anion sum(ÿ0.52*)
Fe (0.58*) Zn (ÿ0.52*)
0.19
0.08
PO4 (ÿ0.51*) NO3 (0.48*)
Cr (0.65*) Fe (0.50*) Zn (ÿ0.47*)
0.45*
0.11
ÿ0.14
NO3 (0.47*)
Cr (0.75*) Sr (0.47*) Mg (ÿ0.53*)
B2 (n = 22)
0.06
ÿ0.10
ÿ0.07
NO3 (0.51*)
BC1 (n = 23)
0.03
0.00
0.13
NO3 (0.83*)
BC2 (n = 21)
ÿ0.16
ÿ0.20
0.25
none
0.19
0.12
0.17
none
Cr (0.70*) Fe (0.54*) Cr (0.80*) Fe (0.79*) Co (0.48*) Cr (0.64*) Fe (0.54*) Co (0.50*) Cd (0.47*) S (0.74*) Fe (0.57*) K (0.55*) Cr (0.54*)
Al (0.86*) Li (0.75*) Sc (0.75*) P (0.46*) Zn (ÿ0.61*) Al (0.61*) Hg (0.54*) Na (0.51*) Fe (0.50*) Al (0.84*) Sr (0.63*) Y (0.57*) Hg (0.43*) none
C (n = 46)
* Signi®cant correlation (p < 0.05). none: no signi®cant correlations found.
XRF no data
Na (0.44*)
Al (0.80*)
none
none
none
Hg (0.50*) Al (0.47*) Li (0.43*)
Al (0.54*)
Al (0.77*) Li (0.71*) Hg (0.64*) B (0.63*) Bi (0.44*) Ba (0.43*) Mg (0.32*)
Al (0.56*)
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G. Kashulina et al
Fig. 3. Content of mobile Al (ammonium acetate extraction) in mg kgÿ1 (left scale, bars) in all major horizons of the podzol pro®les, and proportion in % (right scale, black dots connected with lines) of mobile Al to total Al content measured by conc. HNO3 extraction (O horizon) or by XRF (mineral soil horizons).
and BC1 horizons. In contrast, the other 2 pro®les from this catchment show some of the lowest contents of mobile Al, especially in their upper horizons. Parent material and the degree of pollution are very similar at these sites. It is suggested that the dierences observed here in the proportions of mobile Al are caused by varying drainage con-
ditions. Free surface and vertical drainage, in the case of 2P37 and 2P38, promote the leaching of mobile Al from the pro®les. In pro®le 2P36, the drainage is hindered by ¯at ground and close proximity to the water table. Drainage conditions can also help to explain the high content of mobile Al in several horizons of pro®les from other catch-
Acidity status and mobility of Al in podzols
ments (1P38, 7P05, 8P13 and 8P18) (Fig. 3); all these pro®les are developed on ¯at ground with a high water table. In pro®le 8P18, which has one of the highest contents and proportions of mobile Al in most of its horizons, poor drainage conditions are not only related to relief and proximity to the water table, but also to the formation of an organo-mineral horizon (Ah) with a high clay content. In combination with low contents of base cations, the high content of mobile Al may also help explain the damage to spruce trees observed at this site. Indirect evidence for the importance of surface drainage in the removal of mobile Al from the upper part of the soil may come from the chemistry of surface water during snowmelt. Despite the diluting eect of peak discharge related to snowmelt, a sharp increase in Al content was observed at this time in both polluted and unpolluted catchments (Caritat et al., 1996b). Seasonal soil investigations have shown a sharp decrease in all mobile elements in upper soil horizons after snowmelt (Levina, 1969; Niskavaara et al., 1997). Pro®les from C3, especially 3P51 and 3P52, display the highest content of mobile (and total) Al in the illuvial horizon (B1). This is because of the proximity of an alkaline nepheline syenite intrusion. In addition, dierences in pH between eluvial and illuvial horizons were large in this catchment (Fig. 2), creating a favourable situation for the accumulation of Al in the B1 horizon. Catchment 5 generally has the lowest content and proportion of mobile Al in its soils; this is also re¯ected in the low Al concentration of stream water (Caritat et al., 1996a). Strong natural acidi®cation related to in situ weathering of S-rich black schist in the eluvial horizon of 5P41 is likely to intensify weathering throughout the pro®le and result in the removal of Al under free drainage conditions.
Mobile cations The toxic eect of mobile Al on the vegetation depends upon its relationship to base cation concentrations (Sverdrup et al., 1992). Figure 4a shows the relationship between Al and base cation content in the main soil horizons of each pro®le. To better illustrate the dierences between catchments and pro®les, contents of Al, Ca, Mg, K and Na are calculated as a % of their total equivalent sum for the O and E horizon (Fig. 4b). At most sites the principal mobile cation in the O horizon is Ca, followed by Mg, K and Al, Na being negligible (Fig. 4b). Large changes in the mobile cation composition as a result of pollution were found in the organic horizons of pro®les 2P36 and 2P37. In 2P36, a high Al content and a reduction in
399
the content of base cations cause Al to become the dominant cation, accounting for 50% of the total. In 2P37, although the content of all the mobile cations is very low (Fig. 4a), there is also a comparatively high content of mobile Al. A high proportion of mobile Al was, however, also observed at a number of signi®cantly less polluted sites. For example, in the organic horizon of 5P38, formed on ¯uvioglacial deposits, mobile Al accounts for about 40% of the total sum. In the organic horizon of pro®le 8P18, the mobile Al content is 32% in the upper part (O1, Fig. 4b) and 66% of the total cations in the lower part. Catchment 1 (Zapoljarnij), which receives the highest S deposition of all sites studied (Table 1), is characterised by a low content of mobile Al and the highest content of mobile Mg in the organic horizon. For this site Reimann et al. (1997a,c) described a signi®cant input of Mg from local dust sources due to anthropogenic activities (open pit mining of basic rocks). In addition, C1 is closest to the Barents Sea coast and Mg may be deposited onto the O horizon by a signi®cant seaspray input. Pro®le 8P15 is an interesting and unusual one. The pro®le is developed on quartzite (Table 1), a very acidic, nutrient-poor lithology. It shows, however, surprisingly high contents of mobile Ca and K and one of the highest contents of Mg in the O horizon. Possible explanations may be topographic (base of slope, input of cations from runo) or intensive biological turnover. The E horizons of all pro®les contain considerably lower amounts of mobile cations than the O horizons (Fig. 4a). The principal mobile cation in the E horizon is Al, followed by Ca and Mg (Fig. 4b). In the C and illuvial (B1) horizons the content of mobile base cations is usually negligible with only Al remaining mobile. Correlation analysis shows that the proportion of mobile Al (or the absolute Al concentration) are unrelated to either the deposition of heavy metals, or to soil acidity throughout the major horizons of the podzolic soils.
CONCLUSIONS
The importance of natural conditions (bedrock lithology and relief) on soil acidity and Al mobility in podzols has been investigated by studying soil pro®les from 8 catchments characterised by dierent lithologies and situated at dierent distances from some of Europe's largest point sources of SO2. The total element content (XRF) of the C horizon varies considerably between, but also in some cases within, catchments. The data show that the chemical composition of the C horizon can be aected by pollution (for example in C2) or by
400
G. Kashulina et al
natural acidi®cation and subsequent leaching of cations due to sulphide-rich saprolite (5P41). In general, the base cation content of the parent material is naturally high in the catchments close to the pollution sources, and low in the remote catchments. The natural geochemical conditions of the area thus tend to mask or mitigate acidi®cation eects near pollution sources. Not even relatively long lasting and high inputs of S and heavy metals (C1 and C2) have led to detectable signs of soil acidi®cation in the podzol pro®les developed on till overlying basic lithologies.
Moreover, strong degradation of the ecosystem, including soil erosion, seems to be necessary to give measurable eects in the O, E and B horizons, as is the case in C2. Even here, however, the O horizon, which has a very high buering capacity, shows only slight acidi®cation, and the E horizon is naturally leached. Of the upper horizons of the podzol pro®le, the illuvial horizon (B1) appears to be most sensitive to soil acidi®cation. Strong natural acidi®cation, as observed in pro®le 5P41, aects only the pH of the E horizon containing the sulphide-rich material, and not that of any
Fig. 4(a).
Acidity status and mobility of Al in podzols
401
Fig. 4. (a) Ammonium acetate extractable cation concentrations (expressed in meq/100 g) in the major soil horizons. (b) Relative proportions of mobile cations (calculated as % of SAl + Ca + Mg + K + Na) in the O and E horizon of all pro®les.
other horizon. Weathering of the lower soil horizons, however, is clearly aected. Vegetation is undamaged at this site. In general, the content of mobile Al varied signi®cantly between and within catchments. In the area studied, contamination plays a minor role in the regional variation of mobile Al. Comparison of pro®les 2P37 with 2P36, and 1P33 with 1P38, shows that even under very high inputs of anthropogenic S, high contents of mobile Al can only be found in poorly drained soils. Although acidi®cation will mobilize Al and base cations, these will be leached out of the pro®le under free-drainage conditions. Geogenic factors (as observed for all pro®les in C3, and at 7P18, 7P19 and 5P40) and drainage conditions (8P18, 2P36, 1P38), and not soil acidi®cation, are therefore the key factors governing the availability of mobile Al in podzol pro®les. It is consequently not surprising that the highest content of mobile Al in all pro®les was measured at an unpolluted site in C8 (8P18), where drainage conditions are especially poor. Here, the vegetation is clearly aected by Al toxicity, the natural content of base cations (and all other nutrients) also being low. Mobile Al generally makes up a large proportion of the total mobile cation pool in the E horizon and can become the dominant mobile cation, independent of pollution levels. In the deeper soil horizons (B and C), Al is always the dominant
mobile cation and pollution inputs appear to be relatively unimportant. AcknowledgementsÐThe authors would like to thank the Geological Surveys of Finland and Norway, the Norwegian Ministry of the Environment and the Central Kola Expedition for their support of the project. We are grateful to the whole project team in all 3 countries and to the guest scientists from Lithuania and Austria who participated in the ®eld work and in many stimulating discussions. The suggestions by 2 anonymous referees were greatly appreciated, and the dedicated editorial assistance of Mike Billett was highly valued. Editorial handling: M. Billett
REFERENCES AÈyraÈs M. and Reimann C. (1995) Joint ecogeochemical mapping and monitoring in the scale of 1:1 million in the west Murmansk region and contiguous areas of Finland and Norway-Field Handbook. Nor. Geol. Unders. Rep. 95.111, 33p. AÈyraÈs M., Caritat P. de, Chekushin V. A., Niskavaara H. and Reimann C. (1995) Ecogeochemical investigation, Kola Peninsula: sulphur and heavy metal content in snow. Water, Air Soil Pollut. 85, 749±754. Caritat P. de, Reimann C., AÈyraÈs M., Niskavaara H., Chekushin V. A. and Pavlov V. A. (1996a) Stream water geochemistry from selected catchments on the Kola Peninsula (NW Russia) and in neighbouring areas of Finland and Norway: 1. Element levels and sources. Aquatic Geochem. 2, 149±168.
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