Seasonal changes of principal anions con

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Pro

ﬁ

le distribution and temporal changes of sulphate and nitrate contents and

related soil properties under beech and spruce forests

Václav Tejnecký

a,

_⁎

_{, Monika Bradová}

a

_{, Lubo}

_š

_Bor

_ů

_vka

a

_{, Karel N}

_ě

_me

_č

_ek

a

_{, Ond}

_ř

_ej

_Š

_ebek

b

_,

Antonín Nikodem

a

_{, Jitka Zenáhlíková}

c

_{, Jan Rejzek}

c

_{, Ond}

_ř

_{ej Drábek}

a

a_{Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, 165 21 Prague 6, Czech Republic} b_{Laboratories of the Geological Institutes, Faculty of Science, Charles University in Prague, Albertov 6, 128 43 Prague 2, Czech Republic}

c_{Department of Silviculture, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Kamýcká 129, 165 21 Prague 6, Czech Republic}

H I G H L I G H T S

►Distribution of sulphate and nitrate in the soil proﬁle

►Sulphate and nitrate in acid forest soil under different vegetation covers ►Soil properties inﬂuencing the distribution of inorganic anions.

a b s t r a c t

a r t i c l e

i n f o

Article history:

Received 18 June 2012

Received in revised form 11 October 2012 Accepted 12 October 2012

Available online xxxx

Keywords:

Soil acidiﬁcation Vegetation cover Forest soils Anions Sulphate Nitrate

The behaviour of principal inorganic anions in forest soils, originating mainly from acid deposition, strongly influences the forest ecosystem response on acidification. The aim of this study was to describe seasonal and temporal changes of sulphate and nitrate contents and related soil properties under beech and spruce forests in a region heavily impacted by acidification. The Jizera Mountains area (Czech Republic) was chosen as such a representative mountainous soil ecosystem. Soil samples were collected at monthly intervals from April to October during the years 2008–2010 under both beech and spruce stands. Soil samples were collected from surface fermentation (F) and humified (H) organic horizons, humic (A) organo-mineral horizons and subsur-face mineral (B) horizons (cambic or spodic). A deionised water extract was applied to unsieved fresh samples and the content of anions in these extracts was determined by ion chromatography (IC).

In the studied soil profiles, the lowest amount of SO42−was found in the organo-mineral A horizons under both types of vegetation. Under spruce the highest amount of SO42−was determined in mineral spodic (B) horizons, where a strong sorption influence of Fe and Al oxy-hydroxides is expected. Under beech the highest amount was observed in the surface organic F horizons (forestfloor). The amount of NO3−is highest in the F horizons and de-creases with increasing soil profile depth under both types of vegetation. A significantly higher amount of NO3− was determined in soils under the beech stand compared to spruce. For both soil environments–under beech and also spruce stands–we have determined a general increase of water-extractable SO42−and NO3−during the whole monitoring period. The behaviour of SO42−and NO3−in the soils is strongly related to the dynamics of soil organic matter and particularly to the DOC.

1. Introduction

Principal inorganic anions (Cl−, SO 4

2−and NO 3

−) are introduced

into the environment mainly by dry and wet depositions. These anions have a major impact on soil chemical and biological processes, forest health status and quality of surface waters (DeHayes et al., 1999; Krug and Frink, 1983; Puhe and Ulrich, 2001).

Deposition of SO42−and NO 3−is signi

ﬁcantly affected by

anthropogen-ic emissions of SO2and NOx. Since 1985 there was a signiﬁcant decrease

in the deposition of SO2and NOxin the Czech and Slovak Republics. By

the year 2000 the deposition of SO2had decreased by about 87% and

de-position of NOxhad decreased by about 51% (Kopáček and Veselý, 2005).

The decrease of SO42−deposition has been observed since 1990.Prechtel et al. (2001)report the decrease by about 38_–82% on a European scale. However, pools of organically bound S (originating from the years of high S depositions) represent an internal source of SO42−in the soil

envi-ronment. Thus, this SO42−source can strongly affect the recovery of

an-thropogenically acidiﬁed soil environments (Mitchell et al., 2011). A faster degradation rate of soil organic matter (SOM) is attributed to the decreased deposition of SO42−and NO

3

−. In the same time, the amount

of dissolved organic carbon (DOC), observed in surface waters of North –

⁎ Corresponding author. Tel.: +420 224382759.

E-mail address:[email protected](V. Tejnecký).

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Science of the Total Environment

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America and Europe, exhibited an increasing trend (De Wit et al., 2007; Monteith et al., 2007). Nowadays, the deposition of N compounds re-mains on a constant level. Nevertheless, a decrease of dissolved inorganic nitrogen forms (DIN) in surface waters has been reported. It was shown that the distribution and movement of DIN are signiﬁcantly inﬂuenced by S deposition, depth of surface organic horizons and C/N ratios in forest

ﬂoors (Oulehle et al., 2008).

The type of vegetation cover strongly affects not only soil characteris-tics but also the amount of deposited S and N compounds. The difference between deposition caused by coniferous and broad-leaved species is ap-parent in basic soil characteristics, mainly in soil pH (De Schrijver et al., 2007; Rothe et al., 2002). Whilst studying clear-cut areas,Drábek et al. (2007)observed changes in Al speciation and pH in soils under different vegetation covers. Generally, it is coniferous vegetation cover that catches more of the dry deposition as opposed to broad leaved vegetation cover or clear cut-areas. The difference is caused by the higher speciﬁc surface of needles compared to leaves or grass and by the fact that needles are present the whole year, unlike leaves of deciduous species. Thus, the coniferous forests have higher interception of dust and gases. These deposits are consequently washed by precipitation into the soil environ-ment (Augusto et al., 2002; Berger et al., 2008; Rothe et al., 2002; Vannier et al., 1993).

Mayer et al. (1995)andZhang et al. (1998)concluded that the mineralization of carbon-bound S was a considerable source of SO42−

in soil solutions of acidic forest soils.Alewell et al. (1999)also identi_ﬁed that the organic S was determined as the main S pool in forest soils; moreover, they claimed that adsorption/desoption of SO42−plays an

im-portant role in the retention of S in forest watershed ecosystems.

Ukonmaanaho and Starr (2002)studied an acidiﬁed watershed and they found that organic soil layers are particularly important for N retention and in contrast, deeper soil mineral layers (containing S sorbents_—Al and Fe hydroxide) are crucial for S retention.

Seasonal trends of SO42−and NO

3−contents in stream waters have

been reported (Likens et al., 2002; Oulehle et al., 2008). The accumulation of snow and its subsequent melting plays a major role in the dynamic of SO42−output from soils and their input into stream_ﬂows during the year

(Likens et al., 2002). Tree uptake was identiﬁed as the main mechanism that controls the amount of NO3−in watershed ecosystems during the

year (low values in midsummer and high values in winter) (Oulehle et al., 2008).

The aim of this work is to i) monitor the amount of water-extractable anions, namely SO42−and NO

3−, in soils under beech and spruce forests

af-fected by anthropogenic acidiﬁcation and ii) assess seasonal and annual trends in the distribution and behaviour of these anions.

2. Materials and methods

2.1. Site description

The principal part of the study was carried out on the locality Paličník in the Jizera Mountains located in the north of the Czech Republic (Fig. 1). The altitude of both studied plots ranges from 635 (bottom edge) to 680 (upper edge) m a.s.l. Annual precipitation is approximately 1200 mm and the annual mean temperature 4–7°°C (Balcar et al., 2012; Remrova and Císlerová, 2010). The climate is strictly identical between sites. Veg-etation cover is formed mainly by acidophilic beechwood (forest domi-nated byFagus sylvatica L.) and spruce monoculture (forest dominated byPicea abies[L.]Karst.) with a dominance ofCalamagrostis arundinacea

(L.) Roth andCalamagrostis villosa(Chaix ex Vill.) J. F. Gmel. in the herbal layer; the clear-cut area is predominantly covered byC. villosa(Chaix ex Vill.) J. F. Gmel. (Tejnecký et al., 2010). The average stand height is 28.6 m in the spruce forest and 32.4 m in the beech forest. Average crown area is 14.7 m2_{(spruce forest) and 32.4 m}2_{(beech forest). Soils are developed}

from medium-grained porphyric granite to granodiorite of the Upper Carboniferous age (Cháb et al., 2007). The soils were classi_ﬁed according to the World Reference Base for Soil Resources (WRB, 2006). The prevail-ing soil types are Entic and Haplic Podzols (et PZ, ha PZ) under spruce for-est and Aluminic Cambisols (au CM) under beech forfor-est.

The water regime of the studied area was previously described by (Batysta et al., 2010).

2.2. Soil sampling and sample treatment

Soil samples were collected on two adjacent areas; one covered with beech forest and one with spruce forest (Tejnecký et al., 2010). Sampling was carried out monthly in the period from April to October 2008–2010 (from April to November in 2009). Each time, three new soil pits were dug on each area, with two pits closer to the opposite edges and one close to the centre of the area. Following this rule, the particular place for each pit was selected randomly. The distance between pits was

Prague

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at least 20 m. Soil samples were collected from all horizons with sufﬁ -cient thickness. In all cases, samples were collected from surface fer-mentation (F) and humiﬁed (H) organic horizons and subsurface B horizons (cambic or spodic). Where possible, samples from the surface organo-mineral (humic, A) horizon were also collected. In total, 132 soil pits were described and sampled during the sampling period and 492 samples were collected.

Two permanent research plots (PRP) in the spruce stand (60×55 m) and in the beech stand (65×45 m) have been created in the investigated area since 2010 (Fig. 1).

Collected samples were immediately treated and analysed in the laboratory. Each sample was thoroughly mixed and then divided into two parts. Theﬁrst part was analysed in a“fresh”state representing actual soil moisture. The moisture was determined gravimetrically. The second part of each soil sample was air dried and sieved through a 2 mm sieve.

2.3. Sample analyses

2.3.1. Analysed soil characteristics

Fresh samples were subjected to a deionised water extracting agent (ratio soil/water 1:10 w/v, 24 h extraction on a reciprocal shaker at a stable laboratory temperature). The suspension was then centrifuged at 4000 rpm for 15 min;ﬁnally, extracts wereﬁltrated through a 0.45μm

nylon membrane_ﬁlter (Cronus Membrane Filter Nylon, GB). In aqueous extracts the following chemical parameters were analysed: selected inorganic anions (F−, SO

4 2−, NO

3

−and Cl−) with ion chromatography

(IC) with suppressed conductivity, Al content with inductively coupled plasma_–optical emission spectrometer (see details below). Dissolved or-ganic carbon (DOC) content was determined by a modiﬁed wet dichro-mate oxidation method according toYakovchenko and Sikora (1998)

and Zbíral (2004). Results were compared for selected soil samples with results of TOC Analyser (Apollo 9000HS, Central Laboratory of the Czech Geological Survey) (Tejnecký et al., in preparation). A signiﬁcant correlation between results by the two methods was obtained (data not shown). All results were recalculated to soil dry weight.

Active and exchangeable pH (pHH2Oand pHKCl) were determined

on dried and sieved soil samples potentiometrically (pH metre inoLab pH level 1 WTW, Germany); ratio soil/water or 0.2 M KCl was 1:10 w/v.

2.3.2. Analytical equipment

The IC method for determination of inorganic anions was performed by means of the ion chromatograph ICS 90 (Dionex, USA) equipped with IonPac AS14A (Dionex, USA) guard and analytical columns were used. The eluent composition was 8.0 mM Na2CO3/1.0 mM NaHCO3

andﬂow rate was set to 1 mL min−1. To suppress eluent conductivity

an AMMS 300—4 mm suppressor (Dionex, USA) and 25 mM H2SO4

re-agent was used. The eluent conductivity was even further suppressed by the carbon removal device CRD 300—4 mm (Dionex, USA) and 0.2 M NaOH solution. Samples were introduced by the autosampler AS-DV (Dionex, USA). Chromatograms were processed and evaluated using the software Chromeleon 6.80 (Dionex, USA). The methodology

of the anion determination was based on the application manual of the IC instrument producer (Dionex, 2000; Dionex, 2003) and the US EPA methodology for water analysis (US EPA, 1993). Standards were prepared by dilution from 1 g L−1anion concentrates (Analytika, CZ)

and deionised water (conductivityb0.055μS cm−1; Millipore, USA) in

the range of 0.1_–50 mg L−1. The following determination limits were

calculated according toCerjan Stefanovićet al. (2001): Cl−0.19, SO 4 2−

0.56, NO3−0.56 mg L−1.

The concentration of extracted Al was determined on an iCAP 6500 Radial ICP Emission spectrometer (Thermo Scientiﬁc, UK) equipped with a concentric nebulizer and cyclonic spray chamber. The radial plas-ma instrument was chosen to reduce plas-matrix interference. Standard ref-erence materials NIST 1640 and NIST 1643d were used to check the quality of the element determination in the aqueous extract. Aluminium concentration was determined at the wavelength 167.079 nm, determi-nation limit=0.05 mg Al L−1.

2.4. Statistical analyses

Stratigraphics XVI.I Centurion was used for statistical analyses. Basic statistical analyses such as simple and multiple regression and correlation and multivariate analysis of variance (MANOVA) were used.

3. Results and discussion

3.1. Basic soil characteristics

Tables 1 and 2summarise the basic soil properties and their statis-tical parameters for soils under beech and spruce vegetation cover. All sampled forest soils were strongly acidic. Under beech, active pH (pHH2O) ranged from 3.45 to 5.00, and exchangeable pH (pHKCl) values

ranged from 2.80 to 4.07 (Table 1). Under spruce, pHH2Oranged from

3.17 to 4.64, and pHKClvalues ranged from 2.55 to 4.17 (Table 2). In

comparison, soils under spruce forest were more acidic (3.82±0.29) than beech forest (4.08±0.27).

3.2. Water extractable anions in soil

The period under consideration was 3 years–22 months of sam-pling. Sampling month, vegetation cover, and soil horizons were con-sidered by means of MANOVA as the main factors inﬂuencing SO42−

and NO3−content in soil. The main factors in_ﬂuencing SO

42−were

de-termined to be the sampled horizon (F-ratio=12.33, pb0.001) and

month of sampling (F-ratio=3.52, pb0.001). The least important factor

for all samples was soil vegetation cover (F-ratio=0.01, p=0.906). The amount of water extractable NO3−was also mainly inﬂuenced by the

sampled horizon (F-ratio=30.97, pb0.001) and month of sampling

(F-ratio=12.05, pb0.001). However, the inﬂuence of soil vegetation

cover was also signiﬁcant in the case of nitrates (F-ratio=9.57, p= 0.002). The various in_ﬂuences on the amount of SO42−and NO

3 −are

discussed separately in the following section.

Table 1

Basic statistical parameters of soil properties for the total set of soil beech samples.

Cl− NO

3

− SO

4

2− DOC Al pH

H2O pHKCl Moisture

mg kg−1 _– _– g.g−1

Count 232 232 232 232 231 224 224 232

Average 10.2 108 33.7 135 12.5 4.08 3.54 0.42

Median 6.72 22.2 24.0 73.6 9.02 4.08 3.57 0.39

Standard deviation 14.4 203 42.9 164 13.6 0.27 0.25 0.15

Coeff. of variation 141% 189% 127% 121% 109% 6.60% 7.16% 34.9%

Minimum b0.19a b0.56a b0.56a b0.5a b0.05a 3.45 2.8 0.17

Maximum 156 1204 526 910 105 5 4.07 0.76

Recalculations to dry sample weight.

a_{Determination limits of the used analytical methods (mg L}−1).

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3.3. Distribution of anions in the soil proﬁle

We have observed signiﬁcant differences in anion distribution within soil proﬁles during the investigated period of time. The largest amount of SO42−under beech stands was identi

ﬁed in the organic F

horizon (55.5±4.84 mg kg−1). The determined amount subsequently

decreases with depth to the lowest average value which was observed in the A organo-mineral horizon (17.2±7.59 mg kg−1). The deepest B

horizons exhibit a signiﬁcantly higher amount of SO42−, compared to A

horizons (Table 3). In the case of the spruce stand, we have observed that the amount of SO42−follows the pattern: F>H>A

bB. Thus, a high

amount was found in F, less in H and the lowest amount was determined in the A horizons. However, the largest amount of SO42− (40.2±

2.11 mg kg−1) was determined for the mineral B horizon (Table 3).

Non-silicate Al and Fe forms and soil organic matter are very important soil constituents which signiﬁcantly inﬂuence SO42−sorption (Sokolova and Alekseeva, 2008). The proportional share of Fe oxy-hydroxides can be roughly estimated from the soil colour determined by means of Munsell's colour scale (Scheinost and Schwertmann, 1999). We have ob-served differences in colour between cambic and spodic horizons for the studied soil environment. The cambic horizons have generally darker colours: brown–dark brown (7.5 YR, 4/4 value/chroma). The spodic ho-rizons are brighter in colour: light brown (7.5–10 YR, 5/6 value/chroma) and it can be expected that they have a higher content of Fe and Al oxy-hydroxides. It suggests that there is a higher amount of positive-ly charged sorption sites in spodic horizons leading to a stronger ability to bind sulphate anions. Another factor contributing to the release of SO42−can be the decomposition of S containing organic

matter (Mitchell et al., 2011).Kaiser et al. (2002)reported that in acidic soils only about 40–50% of organic carbon (OC) is contained in subsurface horizons, so the rest of the OC is located in mineral horizons—such as B horizons. The amount of soil water extractable OC was found to be signiﬁcantly (p=0.005) higher for the spruce stand (62.8±7.32 mg kg−1) compared to the value determined for the beech

stand (32.1±7.72 mg kg−1), which could imply a stronger organic S

pool in soils under spruce.

The amount of NO3−(Table 4) determined in F and H horizons of

the beech forest stand was the highest and it was decreasing with in-creasing depth. The lowest NO3−content (26.1±18.4 mg kg−1) was

determined in the B horizons. A similar trend of NO3− was also

noted for the spruce stand. The highest NO3−amount was observed

in the F horizon, a signi_ﬁcantly decreasing amount was further deter-mined for H, A and B horizons. The lowest amounts were deterdeter-mined in organo-mineral (15.0±11.8 mg kg−1) and mineral B (15.4±

9.61 mg kg−1) (Table 4) horizons. The distribution of NO 3 −in the

soil profile is significantly influenced by i) the continuous supply of NO3−by means of dry and wet deposition (Aber et al., 1989) and

ii) decomposition of soil organic matter and litter fall (Prescott, 2002). Albers et al. (2004)describe faster decomposition of litter fall in the environment under beech stands in comparison to that under spruce stands. Moreover, they claim that beech litter is a more favourable source of N for microorganisms, compared to spruce litter (Albers et al., 2004).

A signiﬁcantly higher amount of NO3−was determined in the

sur-face horizons of the beech stand compared to the spruce stand (Table 4).Christiansen et al. (2006)also described higher soil satura-tion by NO3−and elevated NO3−leaching under beech stands

com-pared to spruce stands. The principal source of NO3−, utilised by

microorganisms and vegetation in the environment of the beech stand, seems to be from the decomposition of soil organic matter. According toChristiansen et al. (2006), this phenomenon is caused by the fact that the soils under beech stands have a higher nutrient content and a more favourable C:N ratio, in comparison to the condi-tions under spruce stands.

3.4. The relationship of water extractable sulphates and nitrates with other soil characteristics

Table 5shows correlations of SO42−and NO

3−contents with other

soil characteristics in the F and B horizons under spruce and beech forests. A fairly close and signiﬁcant correlation between the content of SO42−and NO

3

−was found in the F horizons under both forest types

(r=0.444, at pb0.001 for F horizon under beech forest and r=0.579,

at pb0.001 for F horizon under spruce forest). A similar correlation

was also reported in stream waters e.g., byLikens et al. (2002). The content of SO42−in the F horizon is not signiﬁcantly related to pH.

Sul-phates in the F horizons show positive correlations with DOC content. The release of SO42−from decomposed soil organic matter was

recent-ly reported byMitchell et al. (2011). Soil organic matter mineraliza-tion thus yields not only S, but also DOC (Kalbitz et al., 2000). Under

Table 3

Mean and 95% LSD interval of water extractable SO42−in beech and spruce forests (mg kg−1).

Horizon Beech SO42−(mg kg−1) Spruce SO 4

2−(mg kg−1)

Count LS mean LS sigma H.G. Count LS mean LS sigma H.G.

F 66 55.5 4.84 b 63 37.7 2.33 b

H 66 28.4 4.84 a 66 30.8 2.28 b

A 29 17.2 7.59 a 53 17.6 2.59 a

B 72 25.8 4.68 a 79 40.2 2.11 c

H.G. homogeneous groups.

Table 4

Mean and 95% LSD interval of water extractable NO3−in beech and spruce forests (mg kg−1).

Horizon Beech NO3−(mg kg−1) Spruce NO 3

−(mg kg−1)

Count LS mean LS sigma H.G. Count LS mean LS sigma H.G.

F 66 191 19.0 b 63 142 10.7 c

H 66 147 19.0 b 66 91.5 10.4 b

A 29 37.2 29.8 a 53 15.0 11.8 a

B 71 26.1 18.4 a 79 15.4 9.61 a

H.G. homogeneous groups.

Table 2

Basic statistical parameters of soil properties for the total set of soil spruce samples.

Cl− NO

3− SO

4

2− DOC Al pH

H2O pHKCl Moisture

mg kg−1 _– _– g.g−1

Count 260 260 260 262 261 260 260 262

Average 9.98 66.8 32.6 200 9.45 3.82 3.22 0.37

Median 6.26 25.3 27.0 134 7.58 3.79 3.05 0.32

Standard deviation 15.4 115 22.0 192 7.94 0.29 0.45 0.15

Coeff. of variation 154% 172% 67.5% 96.1% 84.0% 7.7% 14.0% 38.8%

Minimum b0.19a b0.56a b0.56a b0.5a b0.05a 3.17 2.55 0.05

Maximum 196 867 155 792 64.9 4.64 4.17 0.69

Recalculations to dry sample weight.

a_{Determination limits of the used analytical methods (mg L}−1).

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beech forest, the content of SO42−and NO 3

−in the F horizons is

posi-tively correlated with water extractable Al. In contrast, under spruce forest the correlation between NO3−and Al is negative, and the

corre-lation between SO42−and Al is not signi

ﬁcant. It suggests that

sul-phate anions play a more important role as ligands complexing Al under beech than under spruce, where the Al complexing role is played more by DOC (Tejnecký et al., 2010). This difference between soils under spruce and beech forests is supported by a closer correla-tion between Al and DOC in the F horizons under spruce (r=0.694, at pb0.001) than under beech (r=0.270, at p=0.03). The fact that DOC,

SO42−and NO

3−are important factors of Al mobility and speciation has

been reported by numerous authors (e.g.Drábek et al., 2005; Norton and Veselý, 2003).

Little to no effect of other determined soil characteristics on the content of SO42−and NO

3−could be determined in the B horizons

(Table 5).

3.5. Temporal variations of the content of water extractable anions

Short-term temporal and also seasonal variations in the forest ecosystem inﬂuence the soil vegetation cover, soil fauna and soil chemical and biological processes. The seasonality itself is pronounced in a scale of weeks or months. The main seasonal changes are the vege-tation growth, and the composition and activity of populations of organ-isms. All of these changes also strongly in_ﬂuence the soil environment (Puhe and Ulrich, 2001). During three years (2008_–2010) the changes in the amount of water extractable SO42−and NO

3−were recorded. The

seasonal changes in organic F and mineral B horizons are shown in

Figs. 2 and 3. It is apparent that for the time period of concern, the amount of SO42−is increasing in F and B soil horizons under both

beech and spruce stands, though the rate of S deposition in Central Europe is decreasing or at least constant (CHMI, 2009; Kopáček and Veselý, 2005). We can easily explain this slight increasing trend of SO42−. Generally, the majority–around 95%–of total soil S is bound in

the structure of soil organic matter (Scherer, 2009), which seems to be increasingly decomposing and transforming. These changes of organic matter were reported e.g., byHruška et al. (2009). These authors have found an increasing release of DOC to surface water streams in the mountainous regions of the Czech Republic. The close correlation of the amount of aqueous extractable DOC and SO42−in soil F horizons was

discussed inSection 3.3.

The temporal variation of anion content under the beech stand is wider in F horizons compared to B horizons. A similar phenomenon was also observed in soils under spruce stands. However, the variability of SO42−in the B horizons was still quite strong under spruce. This is

A M J J A S O N A M J J A S O N A M J J A S O N A M J J A S O N A M J J A S O N A M J J A S O N

Fig. 2.Seasonal variation of water extractable SO42−in organic F (top) and mineral B (bottom) soil horizons under beech (left) and spruce (right) forests (mg kg−1; mean and 95% LSD interval).

Table 5

Correlation coefﬁcients of the relationships between SO42−, NO 3

−and other soil charac-teristics in F and B horizons under spruce and beech forests.

F horizon

Moisture 0.228 0.216 −0.210 0.207

B horizon

Al 0.114 0.082 ₋0.010 0.110

Moisture 0.283⁎ 0.205 −0.163 −0.019

⁎ Signiﬁcant at the probability level of 0.05.

⁎⁎Signiﬁcant at the probability level of 0.01.

⁎⁎⁎Signiﬁcant at the probability level of 0.001.

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caused by larger amounts of SO42−in the B horizon under the spruce

stand compared to the beech forest (Fig. 2).

The amount of water extractable NO3−had increased slightly during

the investigated time period (Fig. 3). This fact cannot be attributed to the increased deposition of NO3−and NH

4+. Nitrate deposition in Central

Europe and in the Czech Republic remains constant or exhibits a slightly decreasing trend (CHMI, 2009; Kopáček and Veselý, 2005). The slightly increasing annual temperature might be a possible explanation for the increase of water extractable NO3−(Veselý et al., 2003) and thus

accel-erated nitriﬁcation processes. Moreover, nitriﬁcation processes are pos-itively affected by increasing pH (Ste-Marie and Paré, 1999). In the studied environment we have observed pH increases on both stands (Fig. 4). A higher variability for the water extractable NO3−content can

be seen in organic F horizons compared to the mineral B horizons. The inﬂuence of biota is apparent here and also a larger vulnerability of F horizons to external factors (precipitation, temperature, etc.) can be

observed (e.g.Attiwill and Adams, 1993). The increased amount of avail-able NO3−can in

ﬂuence the vegetation cover, accelerate the environmen-tal acidi_ﬁcation and indirectly increase Al toxicity (Bowman et al., 2008).

4. Conclusions

In soil proﬁles, the lowest amount of SO42−was found in the

organo-mineral A horizons under both types of vegetation. However, while under spruce stands the highest amount of SO42−was determined in

the mineral spodic (B) horizons (where a strong influence of Fe and Al oxy-hydroxides is expected), under beech stands the highest amount was observed in the surface organic F horizons (forestfloor). The amount of NO3−is highest in the F horizons and decreases with increasing soil pro-file depth under both types of vegetation. A significantly higher amount of NO3−was determined in soils under the beech stand compared to spruce.

F horizon pH

H20

Years (months) Years (months)

5.0

4.5

4.0

3.5

30

pH

H20

5.0

4.5

4.0

3.5

30

Fig. 4.Seasonal variation of active soil pH in organic F horizons under beech (left) and spruce (right) forests (mean and 95% LSD interval). Years (months)

A M J J A S O N A M J J A S O N A M J J A S O N

2009 2010 2008

Years (months)

2009 2010 2008

Years (months)

2009 2010 2008

NO

3

- (mg kg -1)

F horizon

NO

3

- (mg kg -1)

B horizon

Spruce forest

Beech forest

0 200 400 600 800 1000

NO

3

- (mg kg -1)

0 200 400 600 800 1000

0 20 40 60 80

NO

3

- (mg kg -1)

0 20 40 60 80

Fig. 3.Seasonal variation of water extractable NO3−in organic F (top) and mineral B (bottom) soil horizons under beech (left) and spruce (right) forests (mg kg−1; mean and 95% LSD interval).

(7)

Higher temporal variability in the investigated characteristics was proven for organic horizons compared to mineral horizons. The be-haviour of sulphates and nitrates in the soils is strongly related to the dynamics of soil organic matter and particularly to the DOC. An im-portant role of SO42−in Al behaviour was shown in organic horizons

under beech forest, while under spruce forest the effect of DOC is more prominent.

For both soil environments–under beech and also spruce stands–

we have determined a general increase of water-extractable SO42−

and NO3−contents during the whole monitoring period. It indicates

a long-lasting impact of these acidiﬁcants accumulated in soils, even though the rate of acid deposition has decreased signi_ﬁcantly in the last decades.

Acknowledgements

This study was supported by the Czech University of Life Sciences Prague (project no. CIGA 1313/213106), the Ministry of Agriculture of the Czech Republic (project no. QI92A216) and the Ministry of Educa-tion, Youth and Sports (project no. MSM 6046070901 and project no. MSM 0021620855). We would like to express our gratitude to Chris Ash for editing the manuscript. The authors thank the associate editor Dr. Charlotte Poschenrieder and anonymous reviewers for their valu-able comments and suggestions to the manuscript.

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