Podzolized soils and paleoenvironmental implications of white-sand vegetation (Campinarana) in the Viruá National Park, Brazil

Geoderma Regional 2–3 (2014) 9–20

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Podzolized soils and paleoenvironmental implications of white-sand vegetation (Campinarana) in the Viruá National Park, Brazil Bruno Araujo Furtado de Mendonça a,⁎, Felipe Nogueira Bello Simas b, Carlos Ernesto Gonçalves Reynaud Schaefer c, Elpidio Inácio Fernandes Filho c, José Frutuoso do Vale Júnior d, Júlia Gaio Furtado de Mendonça e a

Institute of Forest, Rural Federal University of Rio de Janeiro, 23897-005 Seropédica, RJ, Brazil Department of Education, Federal University of Viçosa, 36570-900 Viçosa, MG, Brazil c Soil Department, Federal University of Viçosa, 36570-900 Viçosa, MG, Brazil d Soil and Agricultural Engineering Department, Federal University of Roraima, 69300-000 Boa Vista, RR, Brazil e Forestry Engineering Department, Federal University of Viçosa, 36570-900 Viçosa, MG, Brazil b

a r t i c l e

i n f o

Article history: Received 23 May 2014 Received in revised form 18 September 2014 Accepted 18 September 2014 Available online 22 September 2014 Keywords: Spodosol Entisol Podzol-like Podzolization Isotopic analyses White-sand vegetation

a b s t r a c t The vast and complex system of hydromorphic sandy soils in northern Brazilian Amazonia remains little studied. We investigated the broader soil–vegetation relationships in white-sand areas under Campinarana vegetation in the Viruá National Park, discussing pedogenetic processes as well as some paleoenvironmental implications. Our hypothesis was that white-sand areas were not covered with savanna grassland during dryer periods, and remained under arboreal vegetation. Seven soil profiles were studied along a typical forest–shrub–grassland gradient. All soils are acid, depleted in bases, with a fine-sandy texture. The vegetation gradient is associated with decreasing soil organic carbon contents. Imogolite is present in some soils as indicated by selective dissolution and microchemical analyses. Podzolization, indicated by illuvial organic and Al-rich coatings on quartz grains is clearly observed in thin sections. The mineralogy of the clay fraction indicates the occurrence of residual kaolinite, hydroxy-interlayered 2:1 mineral and traces of gibbsite, from alteration of sedimentary parent material. Carbon isotope analysis suggests a predominance of arboreal-shrubby vegetation (C3-type) during past drier periods of the Late Quaternary. We conclude that the local distribution of vegetation is primarily associated with edaphic factors. Poor drainage, impermeable subsurface layers, very sandy soils and intense leaching created subtle but contrasting pedo-environments, closely related to vegetation types. Overall, these Amazon Spodosols and Podzol-like soils are associated with C3-plant-dominated vegetation. © 2014 Elsevier B.V. All rights reserved.

1. Introduction The Viruá National Park (VNP) encompasses a vast and complex system of hydromorphic sandy soils, in the state of Roraima, northern Brazilian Amazonia. The Spodosols and Entisols are the main soils in this ecosystem with extensive flat surfaces (Mendonça et al., 2013) and occur under white-sand vegetation (Anderson, 1981), locally known as Campinarana, which can be subdivided into three phytophysiognomies: forest, arboreous and grassland (Brasil, 1975; Veloso et al., 1991). Campinaranas phytophysiognomies are characterized by a striking contrast with the surrounding rainforest landscape and are strongly influenced by the seasonal changes in the water table depths. Physiognomic gradients occur associated with different soil hydrological conditions (Mendonça et al., 2014).

⁎ Corresponding author. E-mail address: [email protected] (B.A.F. Mendonça).

http://dx.doi.org/10.1016/j.geodrs.2014.09.004 2352-0094/© 2014 Elsevier B.V. All rights reserved.

The literature on Amazon Campinaranas is scarce, with much discussion and controversy about the origin of this vegetation (Ducke and Black, 1954; Anderson et al., 1975; Anderson, 1978, 1981; Prance and Schubart, 1977; Ferreira, 1997). Some studies suggest a close soil–vegetation relationship in white-sand areas (Richards, 1952; Rodrigues, 1961). These environments with wet tropical climate and a dominance of quartz-rich soils with very low reserves of easily-weatherable primary minerals favor the podzolization process, with migration of organometallic complexes and accumulation of Fe, Al and organic materials in the spodic horizon (Lundström et al., 2000; Schaetzl and Anderson, 2005; Soil Survey Staff, 2014). The theories involving illuviation of organic compounds and aluminosilicates and their adsorption, precipitation and microbial degradation are partly contradictory, but some processes can act simultaneously (Malcolm and McCracken, 1968; Farmer et al., 1980; Petersen, 1976; Anderson et al., 1982; Buurman and van Reeuwijk, 1984; Little, 1986; Lundström et al., 2000). The biogeochemical interactions occurring in all processes are evident, and the formation of organic

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compounds has an important role in weathering and immobilization in the illuvial spodic horizon (Lundström et al., 2000). However, according to Ugolini and Dahlgren (1991) the presence of aluminosilicates (imogolite) in the Bs horizons of the Spodosol is best explained by in situ formation. The immobilized illuvial carbon in the spodic horizon, as well as charcoal fragments can be used in environmental studies through its isotopic composition to identify vegetation changes (Pessenda et al., 1996; Desjardins et al., 1996; Freitas et al., 2001; Vidotto et al., 2007). The C3 type species, such as trees, bushes and many grasses, have lower δ13C values, with average of −28‰, while the C4 species, typical of grasses, have higher values of δ13C (close to − 13‰). Since these values do not change during organic matter decomposition they can be used to indicate vegetation and climate dynamics (O'Leary, 1988; Boutton et al., 1998). Several authors suggested contractions and expansions of the Amazon forest, resulting from climatic fluctuations during the Quaternary period (Sarmiento and Monasterio, 1975; Prance, 1982), which can be detected by carbon isotopic composition of soil organic matter (Desjardins et al., 1996; Pessenda et al., 1996; Gouveia et al., 1997; Sanaiotti et al., 2002). Some studies detected a predominance of grasses in Amazon during dry phases in Pleistocene and Holocene (Van der Hammen, 1974; Absy and Van der Hammen, 1976; Ab'Saber, 1977; Bigarella and Andrade-Lima, 1982; Leyden, 1985; Markgraf, 1989; Bush and Colinvaux, 1990; Bush et al., 1990; Absy et al., 1991). However, in some areas, the forest vegetation was apparently not replaced by regional savanna expansion, raising questions about the relationship between climate change and non-uniform vegetation responses in the Amazon (Freitas et al., 2001). The vast and complex system of hydromorphic sandy soils in northern Brazilian Amazonia remains little studied, and is a key area for paleoenvironmental studies. We investigated the soil-vegetation relationship in white-sand areas, by means of chemical, mineralogical, micropedological and carbon isotope characterization of soils under Campinarana in the Viruá National Park, to discuss pedogenetic processes and paleoenvironmental implications. Our hypothesis was that white-sand areas, unlike other regions in Amazonia, have not been covered with savanna grassland during dryer periods, and remained under arboreal-shrubby vegetation. 2. Materials and methods 2.1. Study area and sampling The VNP (60°58′30″W and 1°18′7″N) is located in the State of Roraima, Brazil, and comprises 227,011 ha, covered mainly by the Campinarana (Mendonça et al., 2013). Local climate, according to Köppens classification, is defined Amw' (monsoon rain type) (Peel et al., 2007). According to data from the National Water Agency (ANA, 2011), obtained from the Caracaraí meteorological stations (Fig. 1), a series of 30 years shows annual rainfall variation of 1300–2350 mm, with an average of 1794 mm. The soils are developed mainly from Quaternary quartz-rich sedimentary cover of fluvial and eolian origin, both deeply weathered (Brasil, 1975; CPRM, 2000). The mean altitude of the National Park is 46 m. The main landform is an extensive plain, with scattered depressions, under periodic waterlogging by rainwater, separated by inactive dunes. Some depressions are flooded in the rainy season, whereas severe water deficit can occur in the dry season (Mendonça et al., 2013). The white-sand vegetation (Campinaranas) on sandy soils is divided into three vegetation types, according to Veloso et al. (1991): Forested (FC), Arboreous (AC) and Grassy–woody (GC). In the studied FC, the groundwater level does not reach the soil surface, which allows greater canopy height, with relatively thin trees, up to 15 m tall. The trees have straight, little twisted or untwisted stems and

form an almost continuous canopy, sometimes with open areas. The main species on FC area are Licania heteromorpha Benth., Sacoglottis guianensis Benth., Andira micrantha Ducke, Ferdinandusa goudotiana K. Schum. and Ouratea sp. This forest vegetation occurs at slightly higher positions above the plain, about 0.4 to 1.0 m above the lowlands which is enough to prevent flooding. Soils from the AC and GC experience annual flooding to varying degrees. In AC, the vegetation is shorter and thinner and the general presence of termite mounds associated with shrubs is notable. These mounds, despite the high acidity, have greater levels of phosphorus, sum of bases, CEC, and OM compared with the surface mineral horizons of the surrounding soils (Mendonça et al., 2013). The main species on AC study area is Ilex sp., Humiria balsamifera (Aubl.) J.St.-Hil., Tibouchina aspera Aubl., Blepharandra sp. and Barcella odora (Trail) Drude. The Grassy–woody Campinarana (GC) is the longest innundated environment, with open vegetation, dominated by Cyperaceae and Poaceae species and with sparse shrubs, also associated with termite mounds. We collected soil samples from seven pedons in the VNP and surroundings (Fig. 1), representing different vegetation types (Fig. 2), according to the Campinarana phytophysiognomies (Forest, Arboreous and Grassy–woody Campinarana). Inside of VPN we found many areas with very difficult access, due to the large extent of waterlogged lowlands (about 130,000 ha), which are also prevalent in the surrounding region (Mendonça et al., 2013), and therefore some representative soils were studied near the boundaries of the Park (Fig. 1). Some general characteristics of the studied soils are presented in Table 1. Flooding in this area is caused by intense rainfall except for P4, which was collected at the Anauá river floodplain and is influenced by the river innundation. Soil pits were dug, followed by a morphological description (Santos et al., 2005). Undisturbed samples of soil horizons and important horizon boundaries were collected and submitted to chemical, physical, mineralogical and micropedological analysis. The soils were classified according to the Soil Taxonomy (Soil Survey Staff, 2014). 2.2. Methods Soil samples were air-dried and passed through a 2 mm sieve. The percentage of gravels, when present, was calculated. Soil colors were obtained using the Munsell color chart (Münsell, 1994). The assessment of particle size was based on wet sieving, dispersion and sedimentation, followed by siphoning of the b0.002 mm fraction (Ruiz, 2005). Soil chemical properties were determined by the following procedures: pH in water and in 1 M KCl pH was measured using a potentiometer, and a soil:solution ratio of 1:2.5 with an hour of contact and shaking of the suspension during reading; available P, exchangeable Na and K were extracted with Mehlich-1, P was determined spectrophotometrically and Na and K by flame emission photometry; Ca and Mg by atomic absorption spectroscopy and exchangeable Al by titration after extraction with 1 M KCl in the ratio 1:10; and potential acidity (H + Al) by titration after extraction with 0.5 mol l− 1 Ca acetate, pH 7.0. P-rem is a quantity of phosphate in equilibrium solution for a phosphate concentration added to soil (Donagemma et al., 2008), and was determined using CaCl2 10 mmol l− 1 solution, containing P 60 mg l− 1 (Novais and Smyth, 1999). The total organic carbon (TOC) in the b2 mm fraction was determined by titration of residual K2Cr2O7 with 0.2 mol l− 1 Fe (NH4)2(SO4)2·6H2O after wet oxidation treatment (Yeomans and Bremner, 1988). The mineralogy of the clay fraction was determinated by X-ray diffraction analysis (XRD), using monochromated CuKα radiation on basally oriented samples. The diffractograms were interpreted according to Chen (1977). Low crystalline phases of iron and aluminum were extracted with ammonium oxalate (McKeague and Day, 1966) and the free iron with dithionite–citrate–bicarbonate (Mehra and Jackson,

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Fig. 1. Location of the Viruá National Park, with soil samples and meteorological stations.

1960). To extract the organic-bounds forms of Al and Fe we used sodium pyrophosphate, pH 10.0 (SSIR No.42, 2004). Fe, Al and Si were determined using atomic absorption spectrometry. As an indicator of poorly crystalline minerals, we measured the pH in NaF of the b2 mm fraction, according to the Soil Taxonomy (SSIR No.42, 2004). Values of NaF pH greater than 9.4 indicate the presence of such minerals (SSIR No.42, 2004). Undisturbed samples were collected only from the cemented spodic horizons (Bhsm and Bsm) in P4. These samples were investigated in thin sections, following the recommendations of Stoops et al. (2010), using scanning eletronic microscopy with Wavelength Dispersive Spectrometry (WDS) analysis system (JEOL 8200 SEM). Semi-quantitative elementary analysis and microchemical maps were obtained after stoichiometric normalization by ZAF procedures (“Z” to the atomic number, “A” for absorption and “F” for X-ray fluorescence), which nearly eliminate shadowing effects. Soil humic substances were chemically fractionated based on the alkali and acid solubility according to Swift (1996) adapted by Mendonça and Matos (2005). The δ13C isotopic ratios of the humic acid fraction from the A and spodic horizons of each soil profile were determined by mass spectrometry. The sample was frozen, lyophilized and dried in an oven at 45 °C for analysis in the mass spectrometer to obtain a continuous flow isotope ratio (EMRI) (20–20, ANCA GSL, SERCON, Crewe, UK). The δ13CPDB value represents the 13 C/12C ratio proportion of a sample in relation to the international standard PDB (Belemnitella Americana at Pee Dee Formation) (Boutton et al., 1998).

3. Results 3.1. Morphological, chemical and physical attributes Table 2 shows the color for all soil horizons, which do not meet the criteria for spodic materials (Soil Survey Staff, 2014), due to the pale color of most B horizons. Although these soils cannot be classified as Spodosols or Podzols, except for P1, many other morphological and chemical attributes are similar to Spodosols, so we adopted the Podzol-like term. This common situation is in boreal and tropical regions alike, where Podzol-like soils form on quartz sands despite lacking formal criteria to be classified as Spodosols (Jien et al., 2010; Álvarez Arteaga et al., 2008). Hardened subsurface horizons, with extremely hard consistency when dry and extremely firm when moist, only occurred in P4. Overall, soils showed a weak structural development, or single grain, for most soil horizons, due to their sandy texture. In open areas, dominated by Grassy–woody Campinarana, fossil dune fields occur, associated with Spodic Quartzipsamments (P6), showing clear evidences of lateral podzolization, and exhibiting very irregular and wavy boundaries (Table 2). Oxyaquic Quartzipsamments (P7) occurs mainly under Grassy–woody and sparsely vegetated sites, associated with lower organic matter contents (Mendonça et al., 2013). This soil has similar chemical and physical characteristics to closely related Aquodic Quartzipsamments (P3 and P5) (Table 3) that follow along the gradient. However, the organic matter content (OM) is lower than 18.5 g kg− 1 (Table 3). P1 and P2 occur under FC and have the highest levels of organic carbon at the surface. The O horizon

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Fig. 2. Toposequences of soils (P1 to P7) with their landscape position and vegetation types in the National Park of Viruá, Roraima state, Brazil. (A) Mosaic of Campinaranas phytophysiognomies. (B) Inactive dune field, where P36 was collected. (C) Arboreous Campinarana and Anauá river floodplain, where P4 was collected.

only occurs in P1 and P2, being 10 cm thick and rich in fine roots. In P3, P4 and P5 the E horizons are thicker (more than 25 cm) and albic (whitish). All studied soils are sandy, with a predominance of fine sand, followed by coarse sand, silt and clay (Table 3). P1 and P2 (forested) differ from the others by having lower coarse sand and higher silt and clay contents (Table 3). In general, all soils are acidic, nutrient-poor and dystrophic, with pH varying from 3.52 to 5.65, sum of bases (SB) lower than 0.8 cmolc dm−3 and Base saturation (BS) lower than 20% (Table 3). In all soils the B horizon has lower values of P-rem than the overlying horizons, indicating greater P adsorption by amorphous OM-mineral phases.

Gomes et al., 1998; Buurman and Jongmans, 2005; de Oliveira et al., 2010). Al extracted with sodium pyrophosphate (AlP) was higher in most horizons than that extracted by DCB. In the studied soils, the FeO/FeDCB ratio is higher in B horizons, and only P1 has a gradual reduction in depth indicating more crystalline phases (Table 5). The FeP/FeO ratio was greater than 1.0 in P1, P2, P3, P4 and P6. Values of pHNaF are higher than 9.63 in Bs and Bhs horizons of all profiles (Table 4). In the P1 and P2, pHNaF N 9.4 occurs in the A/E and BC transitional horizons. P3, P4 and P5 shows high pHNaF values only in the lower layers of the B horizons.

3.3. Clay mineralogy 3.2. Soil chemistry: selective dissolution and pHNaF The Al, Fe, Si and P extracted with ammonium oxalate, sodium dithionite–citrate–bicarbonate (DCB) and sodium pyrophosphate indicate an accumulation of these elements in the B horizons (Table 4). In all extracts, Al was higher than Fe, Si and P, which is consistent with the literature of Spodosols (Holzhey et al., 1975; Anderson et al., 1982;

The X-ray diffractograms of diagnostic horizons indicate that all soils, except P7, have a predominantly kaolinitic mineralogy in the clay fraction (major diffraction peaks at 7.22 Å and 3.58 Å — Fig. 3), and traces of quartz (3.34 Å — Fig. 3). XRD of B horizons of P1, P2, P3, and P5 shows traces of gibbsite with diffraction peaks at 4.82–4.86 Å (Table 6). In P1, we identified traces of hydroxyl-Al interlayered 2:1 clay mineral, with spacing ranging from 14.2 Å to 14.6 Å (Fig. 3).

Table 1 General characteristics of the studied soils. Profiles

Soil Class

Altitude

White-sand vegetation types

Geomorphic Features

Flood regimea

P1 P2 P3 P4 P5 P6 P7

Typic Haplorthods Spodic Quartzipsamments Aquodic Quartzipsamments Aquodic Quartzipsamments Aquodic Quartzipsamments Spodic Quartzipsamments Oxyaquic Quartzipsamments

66 66 65 45 65 52 65

Forest Forest edge Arboreous Arboreous Arboreous Grassy–woody Grassy–woody

Pediplain Pediplain Pediplain Fluvial plain Pediplain Inactive dune Pediplain

Absent Absent Moderate High Moderate Absent High

a

m m m m m m m

Classification based on the period of the inundation in the rainy season.

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Table 2 Morphological properties of the soil profile. Horizon and depth (cm)

Boundaries(1)

Structure(2)

Consistency(3)

Cementation(4)

Dry

Moist

Wet

dl dl ds ds ds

ml ml mvfr mvfr mvfr

wpo/wso wpo/wso wpo/wso wpo/wso wpo/wso

P2 Spodic Quartzipsamments — Forest Campinarana (edge) A (0–4) g, f sg A/E (4–16) g, f sg Bh (16–62) g, f wk f sbk; sg BC (62–76) c, f wk f sbk; sg C (76–90) mc

dl dl ds ds dvh

ml ml mvfr mvfr mvfi

P3 Aquodic Quartzipsamments — Arboreous Campinarana A (0–10) g, f sg E (10–60) g, w sg Bh (60–80) c, f wk m sbk; sg Bhs (80–100) g, f wk m sbk; sg C1 (100–140) – mc

dl dl ds ds dvh

P4 Aquodic Quartzipsamments — Arboreous Campinarana E (0-20/25) a, f sg Bhm (20–25) g, w st, mc Bhsm (25–115) g, w st, mc Bsm (115–170) – st, mc

Color (Munsell) Moist

Dry

nc nc nc nc nc

10YR 2/1 10YR 4/1 10YR 2/1 10YR 3/2 10YR 6/6

10YR 3/1 10YR 5/1 10YR 3/2 10YR 5/2 10YR 8/6

wpo/wso wpo/wso wpo/wso wpo/wso wpo/wso

nc nc nc nc nc

10YR 2/1 10YR 3/2 10YR 3/1 10YR 4/1 10YR 5/2

10YR 3/1 10YR 5/2 10YR 4/2 10YR 6/2 10YR 7/2

ml ml mvfr mvfr mvfi

wpo/wso wpo/wso wpo/wso wpo/wso wpo/wso

nc nc nc nc wc

10YR 4/1 10YR 7/1 10YR 4/4 10YR 5/4 10YR 7/6

10YR 5/1 10YR 8/1 10YR 5/3 10YR 6/3 10YR 8/3

dl deh deh deh

ml mefi mefi mefi

wpo/wso wpo/wso wpo/wso wpo/wso

nc sc sc sc

10YR 6/1 10YR 3/2 10YR 4/2 10YR 5/4

10YR 7/1 10YR 4/2 10YR 5/3 10YR 6/3

P5 Aquodic Quartzipsamments — Arboreous Campinarana A1 (0–8) g, f sg A2 (8–19) g, f sg E (19–49) g, f sg EC (49–70) g, f sg Bh1 (70–81) d, f wk m sbk; sg Bh2 (81–92) d, f wk m sbk; sg – wk m sbk; sg Bhs (92–104+)

dl dl dl dl ds ds ds

ml ml ml ml mvfr mvfr mvfr

wpo/wso wpo/wso wpo/wso wpo/wso wpo/wso wpo/wso wpo/wso

nc nc nc nc nc nc nc

10YR 5/1 10YR 6/2 10YR 8/1 10YR 6/3 10YR 6/3 10YR 5/3 10YR 4/3

10YR 6/1 10YR 7/1 10YR 9/1 10YR 8/2 10YR 6/2 10YR 6/3 10YR 6/4

P6 Spodic Quartzipsamments — Grassy–woody Campinarana (dune) E1 (0–9) c, f sg E2 (9–21) c, w sg E3 (21–31/126) a, w/i sg Bh (31–36/131) a, w/i wk m sbk; sg Bs (36–136) – wk m sbk; sg

dl dl dl ds ds

ml ml ml mvfr mvfr

wpo/wso wpo/wso wpo/wso wpo/wso wpo/wso

nc nc nc nc nc

10YR 6/2 10YR 6/2 10YR 8/1 10YR 5/2 10YR 6/3

10YR 8/1 10YR 7/1 10YR 9/1 10YR 6/1 10YR 7/3

P7 Oxyaquic Quartzipsamments — Grassy–woody Campinarana EC (0–15) g, f sg C1 (15–85) g, f sg C2 (85–100) – sg

dl dl dl

ml ml ml

wpo/wso wpo/wso wpo/wso

nc nc nc

10YR 6/1 10YR 7/2 10YR 8/2

10YR 7/1 10YR 8/1 10YR 9/1

P1 Typic Haplorthods — Forest Campinarana A (0–5) g, f A/E (5–13) g, f Bh (13–70) g, f Bhs (70–110) c, f Bs (110-170+) -

sg sg wk m sbk; sg wk m sbk; sg wk m sbk; sg

(1) Boundaries: c: clear, a: abrupt, g: gradual, d: diffuse, f: flat, w: wavy, i: irregular, d: discontinuous. (2)Structure: Development level: wk: weak, md: moderate, st: strong. Size: vf: very fine, f: fine, m: medium, g: large, mg: extra large. Form: sg: single grain, gr: granular, sbk: subangular blocky, lm: laminar, mc: massive. (3)Consistency: Dry: dl: loose, ds: soft, dsh: slightly hard, dh: hard, dvh: very hard, deh: extremely hard, nod.: nodules. Moist: ml: loose, mvfr: very friable, mfr: friable, mfi: firm, mvfi: very firm, mefi: extremely firm. Wet: wpo: nonplastic, wps: slightly plastic, wp: plastic; wso: nonsticky, wss: slightly sticky, ws: sticky. (4)Cementation: nc: no cemented, wc: weakly cemented, sc: strongly cemented.

3.4. Microscopic studies We used SEM and WDS microprobe analysis to study the strong cementation of soil layers diagnostic horizons (Bhsm and Bsm) in P4 (Table 2). P4 is an Aquodic Quartzipsamments with a massive structure, extremely firm when moist, exhibiting a single grain microstructure and a low proportion of ferruginous concretions, linked with the coarse texture and the low iron content in the parent material. The groundmass is basically formed by mineral grains (quartz, mainly) with a pellicular or bridged grain structure, with c/f related distribution of chitonic type. In P4 we identified illuvial features rich in organic matter and Al compounds (Al rich organs), coating quartz grains (Figs. 4 and 5). High values of H2O in Table 6 indicate that C-values have not been established and Al is largely present in the form of organo-metal complexes; however, other results probably indicate the presence of imogolite coating on quartz grains, and traces of kaolinite, Al(OH)3 and ilmenite (Table 6 and Fig. 4). According to Parfitt et al. (1980), the chemical analysis of an ideal imogolite in acid–oxalate extracts is 27.2% of Al and 14.1% of Si.

Fig. 5 shows two analytical transects in the Bs horizon of P4. We highlight the amounts of Al, Fe, Si and C in the soil matrix, which are associated with: ferruginous/aluminous cement, formed by OM–Fe–Al complexes, accumulated at the Bsm horizon. Also on the edge of quartz grains we found an increase of the C content, indicating illuvial organic carbon covering these features. Al compounds occur in cracks in the quartz grains (Fig. 5B). 3.5. Organic carbon and humic substances The phytophysiognomic gradient of the Campinarana is associated with decreasing Total Organic Carbon (TOC) in soils from forest to grassland (Table 7). Higher values of TOC in O, A and B horizons (Bh, Bhs or Bs) are highlighted in P1 and P2. In these soils the TOC in humic substances decreases in the subsurface horizons and has a systematic with accompanying increase in the FA, HA and Humin fractions. In P1 and P2 the surface horizons (A and A/E) have the highest contents of OC and the B horizon occurs near the soil surface, differing from the other studied soils. In P1 and P7 the HUM fraction decreases with

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Table 3 Chemical and physical characteristics of the b2 mm fraction of the studied soils. Horizon and depth

pH

(cm)

H2O

P KCl

K

Na

mg dm−3

P1 Typic Haplorthods — Forest Campinarana O (10–0) 3.8 3.0 0.6 33 A (0–5) 4.5 3.5 2.2 15 A/E (5–13) 4.9 4.2 2.1 3 Bh (13–70) 5.3 4.4 0.6 0 Bhs (70–110) 5.0 4.6 0.6 0 4.7 4.4 0.4 0 Bs (110-170+)

Ca2+

Mg2+

Al3+

H + Al

SBa

CEC

cmolc kg−1

%

OM

Prem

GRd

CSe

FSf

g kg−1

mg l−1

%

g kg−1

Silt

Clay

3.7 3.2 1.4 0.7 0.3 0.2

26.7 21.1 11.9 9.3 3.8 1.6

0.76 0.54 0.43 0.43 0.42 0.41

27.5 21.6 12.3 9.73 4.22 2.01

2.8 2.5 3.5 4.4 10 20

83 85.7 76.9 60.9 40.8 31.7

404.3 87.9 34.2 34.2 36.2 6.0

59.9 24.8 18.6 12.1 22.5 46.6

0 0 0 0 0 0

190 230 180 160 170 200

260 400 510 470 470 450

290 260 230 270 270 200

260 110 80 100 90 150

P2 Spodic Quartzipsamments — Forest Campinarana (edge) A (0–4) 3.3 3.0 2.1 43 16.1 0 A/E (4–16) 4.0 3.0 3.2 10 5.1 0 Bh (16–62) 5.5 4.4 1.5 9 0.0 0 BC (62–76) 5.1 4.0 1.2 7 0.0 0 C (76–90) 5.3 5.0 1.7 3 0.0 0

0.09 0.01 0.01 0 0

4.2 1.95 0.92 0.41 0.1

27.2 11.3 8.3 5.1 2.5

0.27 0.06 0.03 0.02 0.01

27.5 11.4 8.33 5.12 2.51

1.0 0.5 0.4 0.4 0.4

94.0 97.0 96.8 95.3 90.9

211.4 28.3 30.6 22.2 5.2

47.2 26 14.3 18.6 31.4

0 0 0 0 0

270 240 250 270 250

430 520 500 480 500

200 190 200 210 220

100 50 50 40 30

P3 Aquodic Quartzipsamments — Arboreous Campinarana A (0–10) 4.2 3.0 4.9 30 8.3 0.08 E (10–60) 4.0 4.0 1.0 0 0.0 0.03 Bh (60–80) 4.3 3.1 4.1 4 0.0 0.01 Bhs (80–100) 4.2 4.1 1.0 0 0.0 0 C1 (100–140) 4.7 4.3 0.5 1 0.0 0.17

0.09 0.04 0.04 0.04 0.04

1.33 0.31 1.54 1.33 0.51

9.8 1.5 9.3 2.5 2.2

0.29 0.07 0.06 0.04 0.21

10.1 1.57 9.36 2.54 2.41

2.9 4.5 0.6 1.6 8.7

82.1 81.6 96.3 97.1 70.8

47.4 3.8 22.5 27.8 4.9

59.9 60 36.2 7.1 44.4

0 0 0 0 0

200 300 250 220 180

530 490 480 460 480

230 200 240 240 200

40 10 30 80 140

P4 Aquodic Quartzipsamments — Arboreous Campinarana E (0–20/25) 5.4 4.1 1.9 7 8.3 0.06 Bhm (20–25) 4.5 3.1 0.6 0 0.0 0.12 Bhsm (25–115) 4.3 3.5 15.0 0 0.0 0 Bsm (115–170) 4.9 4.4 4.6 0 0.0 0.03

0.05 0.06 0.04 0.07

0.72 5.33 3.18 1.43

3.2 22.8 16.4 10.1

0.17 0.18 0.04 0.10

3.37 23 16.4 10.2

5.0 0.8 0.2 1.0

80.9 96.7 98.8 93.5

4.7 53.0 34.4 27.9

59.9 28.3 15.2 20.9

4.7 1.2 0 2.3

560 710 600 550

340 190 300 360

70 30 20 10

30 70 80 80

P5 Aquodic Quartzipsamments — Arboreous Campinarana A1 (0–8) 4.6 3.3 1.2 8 12.7 0 A2 (8–19) 5.1 3.7 0.7 2 1.8 0 E (19–49) 5.5 4.3 0.5 0 0.0 0 EC (49–70) 5.5 4.0 0.8 0 0.0 0 Bh1 (70–81) 5.6 4.6 0.5 0 0.0 0 Bh2 (81–92) 5.4 4.1 0.7 0 0.0 0 Bhs (92–104+) 5.5 4.6 1.4 0 0.0 0

0.05 0.01 0 0 0 0 0

0.92 0.31 0.1 0.21 0.41 0.41 0.51

4.1 2 0.8 1 1.4 2.4 3.2

0.13 0.03 0.00 0.00 0.00 0.00 0.00

4.23 2.03 0.8 1 1.4 2.4 3.2

3.1 1.5 0.0 0.0 0.0 0.0 0.0

87.6 91.2 100 100 100 100 100

27.5 14.1 4.3 5.7 7.5 9.5 11.0

56.4 56.6 57.1 55.1 45.1 36.5 22.7

0 0 0 0 0 0 0

310 330 390 390 390 330 280

520 480 470 490 460 530 520

130 170 120 110 140 120 180

40 20 20 10 10 20 20

P6 Spodic Quartzipsamments — Grassy–woody Campinarana (dune) E1 (0–9) 4.2 3.3 2.6 7 0.4 0 0.05 E2 (9–21) 4.8 3.3 1.4 0 0.0 0 0.04 E3 (21–31/126) 5.4 4.2 0.6 0 0.0 0 0.03 Bh (31–36/131) 5.4 4.3 44.0 0 0.0 0 0.03 Bs (36–136) 5.4 4.0 5.1 0 0.0 0 0.03

0.31 0.31 0.51 0.41 0.21

2.7 3.4 1.4 4.1 2.7

0.07 0.04 0.03 0.03 0.03

2.77 3.44 1.43 4.13 2.73

2.5 1.2 2.1 0.7 1.1

81.6 88.6 94.4 93.2 87.5

8.4 7.7 2.9 9.4 3.6

59.9 60 60 46.5 46

0 0 0 0 0

230 210 330 310 310

690 720 620 640 640

60 50 30 20 20

20 20 20 30 30

P7 Oxyaquic Quartzipsamments — Grassy–woody Campinarana 5.3 3.7 1.2 1 0.0 0.01 EC (0–15) C1 (15–85) 5.0 4.4 1.1 0 0.0 0 C2 (85–100) 5.4 4.8 1.2 0 0.0 0

0.41 0.1 0.1

1.7 0.7 1.9

0.02 0.00 0.00

1.72 0.70 1.90

1.2 0.0 0.0

95.3 100 100

18.5 8.4 4.1

56.6 55.4 27.3

0 0 0

230 370 230

570 500 500

190 120 240

10 10 30

b c d e f

0 0 0 0 0 0

mc

0.5 0.5 0.4 0.4 0.4 0.4

a

38.1 11.9 0.9 0.0 0.0 0.0

BSb

0.01 0 0

SB — sum of bases. BS — base saturation. m = (Al3+/Na+ + K+ + Ca2+ + Mg2+ + Al3+) × 100. GR — gravel. CS — coarse sand. FC — fine sand.

depth, as found by Gomes et al. (1998) in quartz-rich soils, which is in agreement with the low solubility of this fraction. The other studied soils have small increments of all fractions in the B horizon. In the majority soils we found a higher HA content in relation to FA (Table 7).

C3-type species, particulary in P1 with −28.1‰ to −30.1‰, which indicates a predominance of C3-type species, without any C4-type contribution. In P2, at the edge of these forested formations, the δ13C value in subsurface soil has a higher value (−24.5‰) and may reflect a mixture of C3 and C4-type species.

3.6. Isotopic analysis (δ13C) The isotopic composition (δ13C) of the HA fraction for selected soil horizons is in Table 7. The B horizons have higher δ13C values (−24.3‰ to −28.1‰) than the overlying surface horizons (− 26.4‰ to −30.1‰), showing an isotopic enrichment of δ13C with depth in all soils (Table 7). These data indicate a predominance of C3-type species, which is in agreement with the dominant tree species in Campinarana. Except for P1, the other soils show a higher δ13C value in subsurface which may indicate a slight contribution of illuvial carbon derived from C4-type species which occur in surrounding areas, often species of the Cyperaceae and Poaceae families. P1 and P2 have an isotopic δ13C value typical of

4. Discussion The soils occur in a gradient in the three vegetation types (Forested, Arboreous and Grassy–woody) (Fig. 2). However they show some morphological, chemical and physical variations, according to landform and biomass. The extremely hard consistencies when dry and extremely firm when moist, of the hardened horizon, are common features of Spodosols in Amazonia (Dubroeucq and Volkoff, 1998; Horbe et al., 2004). In P4 it was associated with the inundating exposure by the erosion promoted by the Anauá river floodplain.

B.A.F. Mendonça et al. / Geoderma Regional 2–3 (2014) 9–20

15

Table 4 Results for pHNaF, and the Al, Fe, P and Si extracted with ammonium oxalate, sodium dithionite–citrate–bicarbonate (DCB) and sodium pyrophosphate for the studied soils. Horizon and depth (cm)

pH NaF

Oxalate AlO

DCB

Pyrophosphate

FeO

PO

SiO

AlDCB

FeDCB

PDCB

SiDCB

AlP

FeP

SiP

0.49 0.45 0.18 0.09

0.03 0.00 0.03 0.00

0.88 0.56 0.00 0.86

0.94 1.89 1.85 1.44

0.28 0.50 0.68 1.06

0.19 0.09 0.07 0.06

3.09 1.16 0.69 1.03

1.09 3.56 5.48 1.18

0.02 0.46 0.47 0.08

1.96 2.17 3.10 0.72

P2 Spodic Quartzipsamments — Forest Campinarana (edge) A (0–4) 6.46 0.72 0.01 Bh (16–62) 11.00 1.01 0.00 BC (62–76) 11.11 1.30 0.03

0.05 0.01 0.01

0.27 0.43 0.48

0.86 1.14 1.46

0.07 0.00 0.13

0.09 0.06 0.07

0.95 0.57 0.56

1.07 2.08 2.52

0.01 0.04 0.13

0.66 0.85 0.97

P3 Aquodic Quartzipsamments — Arboreous Campinarana A (0–10) 7.15 0.15 0.01 Bh (60–80) 9.87 0.63 0.00 Bhs (80–100) 11.93 6.60 0.19

0.00 0.00 0.02

0.28 0.41 1.55

0.19 0.65 5.94

0.05 0.00 0.25

0.10 0.06 0.05

0.95 0.57 1.27

0.26 1.17 4.22

0.01 0.00 0.16

0.56 0.63 0.18

P4 Aquodic Quartzipsamments — Arboreous Campinarana E (0–20/25) 7.50 0.00 0.00 Bhm (20–25) 6.45 0.62 0.01 Bsm (115–170) 10.65 0.90 0.00

0.02 0.02 0.02

0.20 0.32 0.51

0.00 0.87 0.96

0.00 0.02 0.00

0.08 0.04 0.08

0.76 0.67 0.63

0.03 1.09 2.13

0.00 0.05 0.05

0.74 0.47 1.34

P5 Aquodic Quartzipsamments — Arboreous Campinarana A1 (0–8) 7.34 0.00 0.00 E (19–49) 7.47 0.00 0.05 EC (49–70) 7.54 0.00 0.00 Bh2 (81–92) 9.20 0.16 0.00 Bhs (92–104+) 10.73 0.75 0.00

0.02 0.03 0.03 0.05 0.02

0.50 0.43 0.30 0.43 0.56

0.00 0.00 0.00 0.15 0.64

0.00 0.06 0.00 0.00 0.00

0.04 0.03 0.03 0.04 0.04

0.71 0.62 0.54 0.46 0.47

0.00 0.00 0.03 0.37 0.95

0.01 0.03 0.00 0.00 0.00

0.76 0.88 0.46 0.40 0.30

P6 Spodic Quartzipsamments — Grassy–woody Campinarana (dune) E2 (9–21) 7.46 0.00 0.00 0.00 Bh (31–36/131) 9.21 0.09 0.16 0.03

0.50 0.22

0.00 0.18

0.01 0.23

0.02 0.09

0.61 0.66

0.02 0.43

0.00 0.26

0.56 0.51

P7 Oxyaquic Quartzipsamments — Grassy–woody Campinarana EC (0–15) 7.39 0.00 0.00 C1 (15–85) 7.44 0.00 0.00 C2 (85–100) 7.43 0.00 0.00

0.35 0.31 0.26

0.00 0.00 0.00

0.00 0.00 0.00

0.06 0.03 0.04

0.56 0.64 0.58

0.00 0.00 0.00

0.00 0.00 0.00

0.71 0.52 0.57

g kg−1 P1 Typic Haplorthods — Forest Campinarana O (10–0) 6.12 1.09 A/E (5–13) 10.30 1.53 Bhs (70–110) 10.97 0.48 9.63 1.43 Bs (110–170+)

0.04 0.03 0.06

P6 occur at an inactive dune field, highly exposed to wind, and possible active during dry paleoclimates, being currently stable and partially vegetated (Santos and Nelson, 1995; Carneiro Filho et al., 2003). The presence of lamellae in P6 is a strong evidence of the lateral podzolization (Sommer et al., 2001; Jankowski, 2014) of the waterlogged sandy plain. Boundaries between the B and the overlying horizon ranged from flat to undulating and abrupt to clear, suggesting a variation in soil water flow (Mokma et al., 2004; de Oliveira et al., 2010). Due to the very low clay content, OM accounts for most CEC in all horizons, and is key for nutrient cycling. It represents a typical oligotrophic environment, where vegetation is open and of reduced stature (Fig. 2), because of the severe shortage of nutrients (Grime, 2001), comparing with forest developed on clayey soils at the same region (Mendonça et al., 2013). In all soils the B horizon has lower values of P-rem than the overlying horizons, indicating a higher affinity for phosphate due to the presence of illuvial organometallic materials and poorly crystalline Al and Fe phases. In the selective dissolution of soils, the predominance of Al is also related to the high Al affinity for complexing organic compounds. Sodium pyrophosphate is a poor extractant of allophane, imogolite, amorphous aluminosilicate and non-crystalline Fe and Al hydrated oxides, but extracts Fe and Al bound to organic compounds (SSIR No.42, 2004). AlP of the majority soils (P1 to P6) is strongly indicative of the Al-OM illuviation. Except for P1, all soils show lower amounts of FeDCB, probably because most free iron was reduced and leached out under seasonal inundation. However, AlDCB was not affected in this way, because it is not mobilized under reducing conditions (Stützer, 1998). Schwertmann et al. (1986) reported that Fe precipitates in C rich soils as ferrihidrite

instead of forming goethite, hematite or lepidocrocite. FeO/FeDCB ratios close to 1.0 may indicate ferrihidrite in soils. However, ammonium oxalate can also extract Fe bound to organic compounds (Schwertmann et al., 1986). FeP/FeO in P1, P2, P3, P4 and P6 show the dominance of Fe–humus complexes in relation to poorly crystalline Fe forms. Gomes et al. (1998) found similar results for flooded sandy soils. With reducing conditions prevailing during flooding periods, Fe present as ferric iron in secondary iron containing minerals and in ferric iron–organic matter complexes, may be reduced and be leached as Fe2+ (Brinkman, 1970; Anderson et al., 1982; Andrade, 1990), and further accumulated in subsurface horizons. Values of pHNaF higher in B horizons indicate the dominance of poorly crystalline Al–Si phases (SSIR No.42, 2004) and also high Al activity. There is no indication of these forms in surface horizons, except for the A/E horizon in P1. In the P1 and P2, pHNaF N 9.4 indicates an advanced stage of the podzolization process, with the accumulation of poorly crystalline aluminosilicates in surface and/or subsurface. The high pHNaF values in P3, P4 and P5 soils indicate a lower abundance of amorphous aluminosilicates and, possibly, a less advanced stage of the podzolization process, leading to a severe loss of alumino-silicates from the topsoil. Inorganic Al–Si precipitates in the B horizons, possibly imogolitetype materials, may have formed from organic materials derived from O and E horizons, further translocated in the soil profile and immobilized in B horizons (Lundström et al., 2000). Imogolite was first described by Yoshinaga and Aomine (1926, cited by Wada, 1989) in soils derived from volcanic ash (Andisols), having chemical properties similar to allophane, but it was also found in Spodosols (Wada, 1989; Ugolini and Dahlgren, 1991; Dahlgren and Ugolini, 1991).

16

B.A.F. Mendonça et al. / Geoderma Regional 2–3 (2014) 9–20

Table 5 Relationships of the chemical dissolution and mineralogical identification by the X-ray diffractogram of the studied soils. AlO–AlP

FeO/FeDCB

AlP/AlO

FeP/FeO

AlO + 1/2 FeO

Mineralogya (clay fraction)

0.00 −2.02 −5.00 0.24

1.76 0.89 0.27 0.09

1.00 2.32 11.53 0.83

0.03 1.02 2.58 0.83

0.13 0.18 0.06 0.15

Kt N Qz N Gb Kt N Hiv = Gb N Qz Kt N Hiv = Gb N Qz

P2 Spodic Quartzipsamments — Forest Campinarana (edge) A (0–4) −1.26 −0.35 Bh (16–62) −2.49 −1.07 BC (62–76) −2.52 −1.22

0.08 – 0.20

1.48 2.06 1.93

1.20 – 5.08

0.07 0.10 0.13

Kt N Qz N Gb Kt N Qz N Gb

P3 Aquodic Quartzipsamments — Arboreous Campinarana A (0–10) −0.39 −0.11 Bh (60–80) −1.32 −0.53 Bhs (80–100) 1.54 2.38

0.15 – 0.76

1.73 1.84 0.64

2.00 – 0.80

0.02 0.06 0.67

Kt N Qz N Gb

P4 Aquodic Quartzipsamments — Arboreous Campinarana E (0–20/25) −0.15 −0.03 Bhm (20–25) −1.47 −0.48 Bsm (115–170) −2.44 −1.23

– 0.42 –

– 1.77 2.37

– 6.75 –

0.00 0.06 0.09

Kt N Qz Kt N Qz

P5 Aquodic Quartzipsamments — Arboreous Campinarana A1 (0–8) 0.00 0.00 E (19–49) 0.00 0.00 EC (49–70) −0.10 −0.03 Bh2 (81–92) −0.47 −0.20 Bhs (92–104+) −0.36 −0.21

– 0.75 – – –

– – – 2.23 1.27

– 0.60 – – –

0.00 0.00 0.00 0.02 0.08

Kt N Qz N Gb Kt N Qz N Gb

P6 Spodic Quartzipsamments — Grassy–woody Campinarana (dune) E2 (13–25) −0.03 −0.02 Bh (35–40/135) −1.58 −0.34

0.00 0.68

– 4.81

– 1.66

0.00 0.02

Kt N Qz

P7 Oxyaquic Quartzipsamments — Grassy–woody Campinarana EC (0–15) 0.00 0.00 C1 (15–85) 0.00 0.00 C2 (85–100) 0.00 0.00

– – –

– – –

– – –

– – –

(AlO–AlP)/SiO

Horizon and depth (cm)

P1 Typic Haplorthods — Forest Campinarana O (0–10) 0.01 A/E (15–23) −3.59 Bhs (80–120) – + 0.28 Bs (120–180 )

a

Kt — kaolinite; Qz — quartz; Gb — gibbsite; Hiv — hydroxyl-Al interlayered vermiculite.

Table 6 Results of the microchemical analyses of the spodic horizons in P4 (Bhsm). Bhsma (7 points)

Element

Bhsm (1 point)

Bhsm (1 point)

0.00 0.03 0.00 62.43 37.54 Al(OH)3

12.95 7.06 0.92 10.25 67.63 Ti oxide + kaolinite

% TiO2 SiO2 FeO Al2O3 H2O Probable mineral a

0.48 ± 0.2 12.30 ± 2.2 0.57 ± 0.1 22.89 ± 8.6 63.76 ± 7.0 Imogolite

Mean and standard deviation.

The AlO–AlP value is an estimate of the Al in imogolite type materials (SSIR No. 42, 2004). Our chemical results suggest that these materials are present only in P1 and P3 (Table 5), indicating a patchy occurrence. However, this relationship may be inadequate in some soils, because AlP in Spodosols is higher than AlO (Gomes et al., 1998). Typically, imogolite occurs in the Bs and C horizons in Spodosols (Wada, 1989; Ugolini and Dahlgren, 1991), which is in good agreement with our results. According to Dahlgren and Ugolini (1989), the soil solution in the Bs and C horizon appeared to be simultaneous equilibrium with the hydroxy-Al interlayer of 2:1 layer silicates and imogolite, which suggest that the interlayer Al(OH)3 regulates Al activities while imogolite buffers H4SiO4 activities and also this simultaneous equilibrium

Fig. 3. X-ray diffractograms of the clay fraction of spodic horizons (Kt — Kaolinite; Qz — quartz; Gb — gibbsite; 2:1 — Hydroxy-Al interlayered 2:1 clay mineral).

B.A.F. Mendonça et al. / Geoderma Regional 2–3 (2014) 9–20

Fig. 4. The superposed illuvial features forming layered, coatings on quartz grains (Qz) in the Bhsm horizon of P4. The arrows indicate a morphologic feature with all P4 points in Table 5.

suggests that imogolite formation may be limited by the availability of H4SiO4, which in P1 may originate from leaching of the upper soil horizons and corroborate with the imogolite presence. Hydroxy-Al interlayer 2:1 clay mineral appear in P1 and is related to some mica presented in the parent material, which would correspond to a quartz-rich sediments and deeply weathered (sandy mantle). These deep sandy mantles are formed by in situ pedogenesis of Late Tertiary/Quaternary sediments (Lucas et al., 1984; Bravard and Righi, 1990; Andrade et al., 1997). Several studies point out that Spododols in French Guiana and Brazil are formed by the transformation of Oxisols, from sandy materials related to geological deposits and poor in clay minerals, representing a final stage on the soil formation of the tropical landscapes (Lucas et al., 1984; Boulet et al., 1984; Andrade, 1990; Dubroeucq et al., 1991; Dubroeucq and Volkoff, 1998; Mafra et al., 2002). Kaolinite and gibbsite with

17

aluminous goethite are the mainly clay minerals reported in these Oxisols (Dubroeucq and Volkoff, 1998; Mafra et al., 2002; Horbe et al., 2004), which support a detrital origin (residual) for the gibbsite and kaolinite detected. However, gibbsite progressively disappears in the Spodosols with high flooding regime, by dissolution (P4). Also, no gibbsite is found in soils developed on paleodunes of Late Holocene age (P6) (CPRM, 2000; Carneiro Filho et al., 2003). The presence of imogolite coatings on quartz grains, and traces of kaolinite, Al(OH)3 and ilmenite indicates that podzolization was preceded by clay translocation, so that cutans represent different illuviation phases, as commonly observed in Podzols with incipient clay translocation (Bravard and Righi, 1990; Dias et al., 2003). According to Van Breemen and Buurman (2002) kaolinite is dominant in the clay fraction of the tropical and subtropical Spodosols. Kaolinite coatings (micropans) on quartz grains (Table 6 and Fig. 4) and associated with other ferruginous/aluminous and illuvial features in subsurface horizons indicate the occurrence of translocation and podzolization in these cement horizons. These secondary materials act as cementing agents in the Bsm horizon forming a bridged grain structure (Fig. 5). High OC levels in P1 and P2 indicate a more developed soil, with greater degree of podzolization. Some studies point out that early stages of podzolization are characterized by a lightening in color and increase in thickness of the eluvial horizon, indicating the beginning of Fe and Al translocation and infiltration of organic substances into the subsoil (Stützer, 1998). Thus P3, P4, P5 and P6 exhibits thicker and more whitish E horizons than P1 and P2 soils, indicating earlier stages of podzolization for non-forest soils (AC and GC). In that sense, the close relationship between soils and Campinarana vegetation types (FC, AC, GC) suggests a clear separation of soil degree, where P1 and P2 exhibit a more advanced stage of podzolization due to more stable landform, greater OM inputs and better drainage conditions. Some studies (De Coninck, 1980; Anderson et al., 1982; Skjemstad et al., 1992) have also reported higher levels of the HA fraction in the upper part of the spodic horizon, while the FA fraction dominates the lower part. However, De Coninck (1980) conclude that the loose spodic horizon with many roots have mostly polymorphic organic matter,

Fig. 5. Two analytical transects in thin sections of the Bsm horizon in P4, and the main elements analyzed.

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B.A.F. Mendonça et al. / Geoderma Regional 2–3 (2014) 9–20

Table 7 Organic matter fractions (FA — fulvic acid; HA — humic acid; HUM — humin), total organic carbon (TOC), isotope analysis for the studied soils. HA

HUM

TOC

HA/FA

(HA + FA)/HUM

δ13C V-PDB

27.9 13.4 4.0 7.1 0.5 0.8

163.5 37.1 13.8 7.8 5.8 3.3

234.5 51.0 19.8 19.9 21.1 3.5

2.51 4.29 1.22 3.29 0.97 0.47

0.24 0.44 0.53 1.20 0.19 0.77

−30.09 −28.79 n.d. −28.10 n.d. n.d.

P2 Spodic Quartzipsamments — Forest Campinarana (edge) A (0–4) 5.9 14.8 A/E (4–16) 1.7 4.8 Bh (16–62) 2.4 4.1 BC (62–76) 1.3 2.8 C (76–90) 1.1 1.7

56.7 11.9 3.4 5.7 2.4

122.6 16.4 17.7 12.9 3.0

2.53 2.82 1.70 2.13 1.51

0.36 0.55 1.90 0.71 1.20

−26.43 n.d. −24.46 n.d. n.d.

P3 Aquodic Quartzipsamments — Arboreous Campinarana A (0–10) 1.6 2.3 E (10–60) 0.8 0.5 Bh (60–80) 1.4 1.8 Bhs (80–100) 8.0 3.1 C1 (100–140) 0.3 1.1

6.4 2.1 3.3 8.3 3.5

27.5 2.2 13.1 16.1 2.8

1.46 0.63 1.29 0.38 4.23

0.61 0.61 0.96 1.34 0.39

−30.02 n.d. −25.24 n.d. n.d.

P4 Aquodic Quartzipsamments — Arboreous Campinarana E (0–20/25) 0.7 0.8 Bhm (20–25) 2.7 26.3 Bhsm (25–115) 8.3 4.3 Bsm (115–170) 8.8 0.8

2.6 5.8 2.8 6.4

2.7 30.7 19.9 16.2

1.16 9.59 0.52 0.09

0.58 4.97 4.47 1.51

n.d. −25.50 n.d. n.d.

P5 Aquodic Quartzipsamments — Arboreous Campinarana A1 (0–8) 1.0 1.8 A2 (8–19) 0.3 1.3 E (19–49) 0.6 0.5 0.1 1.0 EC (49–70) Bh1 (70–81) 0.7 1.3 Bh2 (81–92) 0.7 1.5 Bhs (92–104+) 1.0 0.5

10.1 1.6 2.9 3.7 1.4 4.1 0.6

16.0 8.2 2.5 3.3 4.3 5.5 6.4

1.80 5.10 0.83 10.98 1.97 2.17 0.48

0.27 1.00 0.37 0.29 1.44 0.53 2.53

−26.54 n.d. n.d. n.d. n.d. −25.83 n.d.

P6 Spodic Quartzipsamments — Grassy–woody Campinarana (dune) E1 (0–9) 0.5 2.4 E2 (9–21) 0.6 1.3 E3 (21–31/126) 0.7 0.5 Bh (31–36/131) 1.1 1.9 Bs (36–136) 1.5 0.6

2.2 4.8 4.4 4.8 1.0

4.9 4.4 1.7 5.5 2.1

4.62 2.15 0.70 1.76 0.40

1.31 0.39 0.28 0.61 2.19

n.d. n.d. n.d. −24.36 n.d.

P7 Oxyaquic Quartzipsamments — Grassy–woody Campinarana EC (0–15) 1.0 0.9 C1 (15–85) 0.0 0.8 C2 (85–100) 0.2 0.7

6.8 4.1 3.2

10.7 4.9 2.4

0.88 – 3.00

0.27 0.19 0.30

n.d. n.d. n.d.

Horizon and depth (cm)

FA g kg−1

P1 Typic Haplorthods — Forest Campinarana O (10–0) 11.1 A (0–5) 3.1 A/E (5–13) 3.3 Bh (13–70) 2.2 Bhs (70–110) 0.6 Bs (110–170+) 1.7

n.d. — not determined.

typically present as the mesofauna excrements and linked to decomposing root remains, and also a higher content of humin composed of directly transformed plant remains and more humic acids in the extractable fraction. These statements corroborate the high level of the HA fraction and HUM mostly in upper horizons of all studied soils. According to Fontana et al. (2008, 2010), (FA + HA)/HUM ratios higher than 2.0, are diagnostic of spodic horizons. Benites et al. (2001, 2003) suggest that the high values of this relationship indicates the migration and accumulation of alkali-soluble compounds in the spodic horizons. In the studied soils this ratio is highest in the spodic horizons, with values higher than 2.0 in P4, P5 and P6 (Table 7). According to Boutton et al. (1998), the older organic matter located at 20 cm depth has δ13C values that are generally 1–3‰ greater than organic carbon in the surface soil. This may reflect small but cumulative isotope effects attributable to respiration by invertebrate and microbial decomposers, or to differential decomposition of isotopically distinct biochemical components of litter, and/or the 1.5‰ decrease in the δ13C value of atmospheric CO2 during the past 200 years.

During drier climate phases during the Late Quaternary, large areas of forest and grassland in the Amazon basin were affected by fire, which produced fragmentation and vegetation mosaics, as indicated by the charcoal present in all subsurface soils (Sanford et al., 1985). The edge of Forested Campinarana experiences natural fires and the isotopic analysis indicate a C4-type contribution. In the National Park of Viruá, Late Quaternary dry events were associated with active dunes (Ab'Saber, 1977; Absy, 1985; Prance, 1985), and we should expect little vegetation, and a possible dominance of the C4-type grasses, which are more resistant to decomposition in soils of low moisture content (Pearcy et al., 1987; Ehleringer and Monson, 1993; Nordt et al., 1994). However, the δ13C values of the HA fraction, especially at Forest Campinarana soils, suggest C3 species predominant in these Late Quaternary dry spells. These data are consistent with result of Martinelli et al. (1996), who indicated that C4 grasses were not dominant during dry periods in the Holocene of Amazonia. Thus, we postulated that during drier periods, the vegetation was dominated by seasonal woody vegetation or other C3-plants.

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The dominance of forest-arboreous vegetation type (FC and AC) at the early Holocene is consistent with some reconstructions of past vegetation in the Amazon region (Colinvaux et al., 1996; Haberle and Maslin, 1999). 5. Conclusions The soils of the flat plains of Viruá National Park along a Campinarana vegetation gradient are very sandy and chemically poor, dominated by fine sand, and with evidences of podzolization process, although most soils do not meet all criteria for Spodosols. The Campinarana phytophysiognonies show a decreasing contents of organic carbon and humic substances in soils with decreasing plant biomass. In the study area, the flat relief with sandy quartz-rich soil provides favorable conditions for organic matter mobility; organic carbon losses are greater in Grassy–woody Campinaranas. The landform variability is closely related with the particular occurrence of clay minerals in these Spodosols. Imogolite is present in some soils, as indicated by soil chemistry (P1) and microchemical analysis (P4). The studied soils show different levels of podzolization. The deposition of a two-phase illuvial coating (organic matter-rich and Al-rich) is clearly shown by microchemical analysis. The isotopic analysis suggests that there are no indications of a past dominance of C4-vegetation during the Late Quaternary. We conclude that the local distribution of these vegetation types is primarily associated with edaphic factors. Ill drainage, subsurface impermeable layers, very sandy soils and intense leaching created subtle and contrasting pedo-environments, closely related to vegetation types. Overall, these Amazon Spodosols and Podzol-like are associated with C3-plantdominated vegetation. Acknowledgements We thank the Protected Areas of Amazon Program (ARPA) (2007.0611.1231.3114), Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) of Roraima (2007.0611.1231.3114), and the National Park of Viruá team (2007.0611.1231.3114), for financing and logistics supports during the expeditions. Thanks are due to Conselho Nacional de Desenvolvimento Científico e Tecnológico CNPq for the scholarship, and Prof. Bob Gilkes for a manuscript review. Appendix A. Supplementary data Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.geodrs.2014.09.004. These data include Google map of the most important areas described in this article. References Ab'Saber, A.N., 1977. Espaços ocupados pela expansão dos climas secos na América do Sul, por ocasiçao dos períodos glaciais quaternários. Paleoclimas 3. Instituto de Geografia, USP, São Paulo. Absy, M.L., 1985. Palinology of Amazonia: the history of the forests as revealed by the palynological record. In: Prance, G.T., Lovejoy, T.E. (Eds.), Amazonia. Pergamon Press, Oxford, Reino Unido (442 pp.). Absy, M.L., Van der Hammen, T., 1976. Some paleoecological data from Rondonia, southern part of the Amazon Basin. Acta Amazon. 6, 293–299. Absy, M.L., Cleef, A., Fournier, M., Martin, L., Servant, M., Sifeddine, A., Da Silva, M.F., Soubiès, F., Suguio, K., Turcq, B., Van der Hammen, T., 1991. Mise en évidence de quatre phases d'ouverture de la forêt dense dans le sud-est de l'Amazonie au cours des 60000 dernières années. Premières comparaisons avec d'autres forêts tropicales. C. R. Acad. Sci. Paris II 312, 673–678. Álvarez Arteaga, G., García Calderón, N.E., Krasilnikov, P.V., Sedov, S.N., Targulian, V.O., Velázquez Rosas, N., 2008. Soil altitudinal sequence on base-poor parent material in a montane cloud forest in Sierra Juárez, Southern Mexico. Geoderma 144, 593–612. ANA, 2011. Agência Nacional de Águas, Sistemas de Informações Hidrológicas, Estação meteorológica de CaracaraíAvailable, http://www.ana.gov.br (Accessed 20 Oct 2011).

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