Alisson Akerman

Priscia Oliva
email: priscia.oliva@get.omp.eu

Franck Poitrasson

Geraldo Resende Boaventura

Valmir Da

Silva Souza

Patrick Seyler

Impact of deforestation on soil iron chemistry and isotope signatures in Amazonia

Keywords: Iron isotopes, Soil degradation, Deforestation, Weathering, Pedogenetic processes. 56 57 1. Introduction 58

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

after leaching (Acrisol) and redox processes (Gleysol). Measurements performed by plasma 25 source mass spectrometry show a large range of iron isotope signature within the soil profiles 26 studied at the bottom of the slopes (i.e. foot slope and/or valley soils), under both forest and 27 pasture. Iron isotopic signature in foot slope soils under forest cover (δ 57 FeIRMM-14 +0.2 to 28 +0.6‰) and pasture (δ 57 FeIRMM-14 +0.3‰) are significantly heavier than both the continental 29 crust baseline and the reference ferralitic soils from the top of the hill (δ 57 FeIRMM-14 +0.1‰). 30

This enrichment in heavy isotopes is attributed to the preferential mobilisation and loss of light 31 iron during pedogenesis that involves redox processes in areas periodically flooded at the foot 32 slope and valley soils. Under forest, light iron depletion (where ~90% of the iron was leached 33 in the first metre of the soil) has greater influence on the soil isotopes signature, particularly in 34 foot slope sand-rich soils close to the river system with a remaining Fe having δ 57 Fe IRMM-14 35 +0.6‰. Under pasture where soils experience erosion processes, iron depletion in foot slope 36 and riverside soils is less important (where only a little more than half of the iron was leached 37 in the first metre of the soil) and the resulting δ 57 FeIRMM-14 +0.4‰ suggests an input of light 38 iron isotopes via colluvic material deposition. This difference indicates that geomorphological 39 changes due to erosion processes following deforestation (i.e. colluvic processes) lead to an 40 "isotopic rejuvenation" of the soils in the valley, mostly apparent within the riverside soils. 41

For comparison, we investigated isotopic changes in a recently deforested small watershed, 42 near Lake Balbina, Central Amazonia, focusing on riverside soils. Results confirm that the 43 isotopic rejuvenation effect appears within a few months following the first stage of 44 deforestation as a consequence of erosion processes following slash-and-burn practices. 45

Erosion can remove isotopically lighter (i.e. close to the continental crust value of ~0.1‰ in 46 δ 57 Fe) iron bearing soil material from the top of the hill. When such colluvial soil material 47 accumulates in the bottom of the hills on soils that were initially depleted in light iron isotopes, 48 again due to podzolisation as described in the previous site, it induces an "isotopic rejuvenation" 49 in understanding changes in biogeochemical cycles of iron but also carbon. The soil's iron cycle 99 is affected by drivers such as litterfall and soil moisture rates and it plays an important role in 100 organic matter decomposition [START_REF] Calabrese | Impact of ecohydrological fluctuations on iron-redox 788 cycling[END_REF]. Tropical soil cover is currently 101 undergoing important modifications due to natural chemical weathering, soil forming processes 102 (e.g. humic substances and iron eluviation, redox processes) and intensive agricultural practices 103 following deforestation. Thus, both natural and anthropogenic factors can affect iron speciation 104 and isotopic compositions in soils. Iron can be mobilised and transferred under dissolved or 105 particulate forms from soil bedrock to rivers as a result of numerous chemical and physical 106 processes (e.g. precipitation, complexation, adsorption, mineral dissolution, redox processes, 107 chemical weathering, leaching, erosion -see [START_REF] Olivié-Lauquet | Chemical distribution of 1005 trivalent iron in riverine matrial from a tropical ecosystem: a quantitative EPR study[END_REF][START_REF] Fritsch | Organic complexation and translocation of ferric iron in podzols of the Negro River 886 watershed. Separation of secondary Fe species from Al species[END_REF]. 108

The study of stable iron isotopes compositions in soils, rivers and lakes revealed that iron 109 isotope fractionation occurs following changes in iron speciation and can be a valuable tracer 110 of iron behaviour (e.g. [START_REF] Fantle | Iron isotopic fractionation during continental weathering. 851[END_REF][START_REF] Emmanuel | A preliminary mixing model for Fe 848 isotopes in soils[END_REF]Thompson et al., 111 al., 2014;[START_REF] Fekiacova | Can Fe isotope 868 fractionations trace the pedogenetic mechanisms involved in podzolization?[END_REF][START_REF] Li | Why was iron 954 lost without significant isotope fractionation during the lateritic process in tropical 955 environments?[END_REF]. On the other hand, tropical soil profiles known 124 to have evolved from lateritic soils following reductive mineral dissolution and/or ligand-125 controlled dissolution [START_REF] Thompson | Rayleigh ractionation 1072 of iron isotopes during pedogenesis along a climate sequence of Hawaiian basalt[END_REF][START_REF] Akerman | The Isotopic 766 fingerprint of Fe cycling in an equatorial soil-plant-water system: The Nsimi watershed, 767 South Cameroon[END_REF] display significantly 126 heavier Fe signature than both the continental crust baseline and the reference lateritic soils. 127 Different iron pools in soils frequently carry distinct iron isotope signatures. In particular, labile 128 iron pools (e.g. iron solubilised by ligand or reduced by bacteria and released into soil 129 porewater) have been found to be enriched in the lighter iron isotopes in the context of 130 podzolisation (e.g. Wiederhold et al., 2007b;[START_REF] Guelke | 915 Determining the stable Fe isotope signature of plant-available iron in soils[END_REF][START_REF] Akerman | The Isotopic 766 fingerprint of Fe cycling in an equatorial soil-plant-water system: The Nsimi watershed, 767 South Cameroon[END_REF]. As a 131 consequence, chemical weathering and pedogenesis under tropical environments could lead to 132 notable Fe isotope fractionation, in particular due to greater mobility of light Fe isotope forms. 133

However, the study of Fe isotopic composition of tropical soils affected by deforestation has 134 not been conducted so far, despite the potential insight Fe isotope may provide on the change 135 of iron cycling during soil evolution. Pasture establishment increases mean annual discharge 136 and runoff at the watershed scale compared with moist tropical forests (up to 40% of runoff 137 increase, [START_REF] Coe | The 803 Hydrology and Energy Balance of the Amazon Basin in Interactions Between Biosphere, 804 Atmosphere and Human Land Use in the Amazon Basin[END_REF]. This results in an increase of 1) the water table level and associated 138 hydromorphic processes (i.e. redox processes) in soils and 2) erosional processes as 139 pasturelands have a shallower rooting depth and a lower leaf area index. Such changes (i.e. 140 redox processes and erosion) can alter Fe cycling and thus Fe isotopes signature in soils at the 141 watershed level. 142

This study considers Fe isotope signatures in soil profiles representative of preserved 143 rainforest systems, recently deforested areas and long-term pasture environments in the 144 Brazilian Amazon Basin. For that purpose, soils profiles from Eastern Amazonia within the Rio 145 Capim watershed (Para State) were selected along catena under forest cover and in up to 50-146 year-old pasture. The Rio Capim watershed belongs to the "deforestation arc zone" where 147 deforestation has occurred at the fastest rate on the planet so far. For comparison, soil profiles 148 taken from both forest and recent slash-and-burn (<6 months) plots in the Cavernado Maroaga 149

Environmental Protection Area of central Amazonia (Presidente Figueiredo region, Amazonas 150 State) were also studied. 151

The aim of this work was therefore to 1) investigate the Fe isotopic composition of soil 152 profiles under forest, pasture and slash-and-burn agriculture, 2) link the differences in isotopic 153 composition to pedogenetic characteristics and processes, and 3) evaluate whether 154 environmental changes linked to deforestation (e.g. The study area is about 450 km south of the city of Belem, in Eastern Brazilian 160 Amazonia. This study was conducted in the Fazenda Rio Capim owned by the CIKEL-Brasil 161

Verde group and located in the district of Paragominas (from S3°18´ to 3°50´ -W48°28´ to 162 48°54´, WGS84; Fig. 1a andS.I. Fig. 1a). From a geological viewpoint, the study area is located 163 in the Northwest Paraiba Basin, on the southern portion of the tectonic plate 'Plataforma 164 Bragantina', which has been stable since the Cretaceous [START_REF] Urdinínea | Aspectos geoquímicos e ambientais dos calcários da Formação Pirabas 1079 -PA. Tese de Doutorado[END_REF]. The soils from the 165 catenas studied developed on detrital continental sedimentary bedrocks corresponding to 166 Cretaceous arkosic sandstone, pelites and mudstones (Itaperucu formation) and have been 167

strongly lateritised and bauxitised since the Late Tertiary [START_REF] Truckenbrodt | Composition and origin of the clay 1076 cover on north Brazilian laterites[END_REF]. Such soil 168 formations occur mainly at the top of the relief and thus partially govern geomorphology (Horbe 169 and da Costa, 2005). Flat to slightly undulated plateau (20 m above sea level) where lateritic 170 crust resists erosion is cut by U-shape valleys drained by the Rio Capim tributaries. 171 Geomorphology in deforested zones, mainly represented by old pasture areas, show distinct 172 features with denudation of the top flat plateau zones (i.e. total or partial dismantling of 173 ferralsols), widening and flattening of the valleys coupled with numerous colluvic and creeping 174 phenomenon visible at the catena level. 175

The current regional climate is equatorial and marked by two seasons, including a six-176 month wet season (from December to May) with mean annual rainfall of about 2100 mm 177 [START_REF] Crepani | Intensidade pluviométrica: uma maneira de 807 tratar dados pluviométricos para análise da vulnerabilidade de paisagens à perda de solo. 808 INPE[END_REF]) and a three-month dry season (from September to November). The mean 178 annual temperature is 26.3°C and relative air humidity 81% [START_REF] Embrapa | Normais climatológicas de Paragominas no período de 1980 a[END_REF]. 179

Vegetation is representative of the dense and humid rainforest reaching more than 40 180 metres high and covering more than 70% of the Fazenda Cikel. Forested hills are built up by 181 deep Ferralsols and Acrisols that dominate soil types [START_REF] Morais Cruia | Caracterização dos sistemas de 976 produção da agricultura familiar de Paragominas-PA: a pecuária e propostas de 977 desenvolvimento[END_REF]. Riparian zones 182 are constituted by hydromorphic sandy rich soils with gleyic properties. The extensive 183 rainforest clearing permitted leaving more land available for introducing agro-pastoral 184 practices. Forest in the cleared basins is commonly converted to pasture by cutting, burning, 185 and planting grass pasture with Brachiaria brizantha [START_REF] Neill | Forest-and 986 pasture-derived carbon contributions to carbon stocks and microbial respiration of 987 tropical pasture soils[END_REF]. The soils from the Rio 186 Capim area are consistent with the nature of the dominant soils previously described in this area 187 [START_REF] Morais Cruia | Caracterização dos sistemas de 976 produção da agricultura familiar de Paragominas-PA: a pecuária e propostas de 977 desenvolvimento[END_REF][START_REF] Horbe | Lateritic crust and related soils in eastern Brazilian 923 Amazonia[END_REF]. Under forest cover, they show 188 morphological signs of plinthite formation and its hardening to pisoliths and petroplintic as a 189 consequence of repeated drying and wetting cycles at the top of the hill (plinthic Ferralsol). In After an initial evaluation of various sites, the soil study from the Rio Capim area was 206 conducted along two representative catenas from two small watersheds ( 5 km 2 ) belonging to 207 the Rio Surubiju catchment, a sub-watershed of the Rio Capim catchment (sampling points F 208 and P in s.I. Fig. 1a): one watershed under forest cover (Fig. 2A) and one watershed which has 209 been under grass pasture for approximately 50 years since deforestation (Fig. 2B). Both small 210 watersheds are about 30 km away and are drained by first order streams flowing from east to 211 west so that the two selected soil catenas are approximately oriented north-south on the right 212 bank. In April 2010, three soil profiles were sampled along the catena under forest: a Ferralsol-213 type soil profile at the top of the hill sampled to a depth of 400 cm through a recent track 214 excavation, an Acrisol-type soil profile located mid-slope and a Gleysol type soil profile at the 215 footslope near the sandy riverbank (both sampled with a soil corer at 90 and 150 cm 216 The study area is located within the Maroaga Cave Environmental Protection Area (Reis et al., 226 2008) belonging to the Presidente Figueiredo district (north of Manaus, Northeastern Amazonas 227

State) within the central Amazonian Craton (sites S1°42.916' to S1°50.012' and W60°00.574' 228 to W60°07.161'; WGS84; Fig. 1 andS.I. Fig. 1b). Soils from the area studied are developed on 229 Paleoproterozoic felsic to intermediate volcanic effusive and pyroclastic rocks from the 230 Iricoumé Group and A-type granites from the Mapuera Intrusive Suite. The Iricoumé-Mapuera 231 magmatic association has been linked genetically because both formations present geochemical 232 and geochronological similarities [START_REF] Souza | Seção geológica Manaus-Presidente Figueiredo (AM), 1064 borda norte da Bacia do Amazonas: Um guia para excursão de campo[END_REF][START_REF] Valério | The 1.90-1.87Ga magmatism in the 1082 centersouthernmost Guyana Shield, Brazil: geology, geochemistry, zircon 1083 geochronology, and tectonic implications[END_REF], 2012and 233 2018[START_REF] Marques | 962 Contributions to the petrography, geochemistry and geochronology (U-Pb and Sm-Nd) 963 of the Paleoproterozoic effusive rocks from Iricoumé Group, Amazonian Craton, Brazil[END_REF]. According to [START_REF] Horbe | Geochemical evolution of a lateritic Sn-Zr-Th-Nb-Y-919 REE-bearing ore body derived from apogranite: the case of Pitinga, Amazonas -Brazil. 920[END_REF], a lateritisation process 234 affected the area during the Early Tertiary and developed Al-Fe crust profiles. 235

This area has a hot humid tropical climate, with a mean annual temperature of 26°C, a 236 mean annual air humidity of 85%, and an average annual rainfall of about 2000 mm. The 237 months with maximum rainfall are from December to May [START_REF] Lesack | The deposition, composition, and potential sources of 946 major ionic solutes in rain of the central amazon basin[END_REF]238 Williams et al., 1997) and the dry season is from June to November. 239

The mature forest, known to have a particularly elevated biomass and biodiversity 240 [START_REF] Gehring | Resilience of secondary forest regrowth after 904 slash and burn agriculture in central Amazonia[END_REF], suffers from deforestation as a result of family farm activities along the 241 BR-174 road. Despite difficulties in accessing these remote areas and finding sites suitable for 242 our study, we had the opportunity to study two types of soils near the place known as the 243

Castanhal earth road: a deep Ferralsol-type soil profile (30 m in depth) under preserved tropical 244 rainforest through a stone quarry and a couple of adjacent riverine soils. The latter correspond 245 to two different streams flowing under forest or in a recently slashed and burned area (Figs. 2C 246 and D). They both occur within the Lake Balbina watershed. In the slash-and-burn zone, the 247 forest was cleared and burned in November 2010 and all soils samples were collected in April 248 2011. As mentioned, deforestation occurred along a small stream so that on both slopes 249 rainforest and riparian forest have largely been wiped out with important soil erosion features 250 (Fig. 2E). The strong perturbation of the site as a consequence of forest clear cutting and burning 251 (e.g. fallen tree trunks, important ash accumulations in some places, gully erosion features, see 252

Figs. 2D andE did not allow us to sample following a catena strategy. As riverine soils showed 253 the greatest pedological changes after pasture establishment in the Rio Capim area, we chose 254 to focus only on riverine soils in order to investigate any possible effect of recent slash-and-255 burn practice on soil chemical and Fe isotopic signatures. Therefore, we studied two soil 256 profiles in the riparian area: a Gleysol-type soil under tropical rainforest and a stagnic Acrisol 257 under a slash-and-burn area. 258 259 Working Group WRB, 2014). For each soil profile studied, the different soil horizons were 263 distinguished by identification of their matrix colour using the Munsell soil colour chart. Their 264 structure was also described and, when possible, also their texture and pedological features. 265

Materials and Methods

Soil descriptions are given in the Supplementary Information section (S.I. Fig. 2a and Fig. 2b 266

and associated text). The morphological descriptions of all soils in this study were carried out 267 on sections along the sides of car tracks or using an Edelman type auger (8 cm diameter). 268 269 270

In addition to in-situ description of their pedological characteristics, five soils profiles 271 sampled from the Rio Capim area (three under forest cover -hilltop, midslope and footslope -272 and two under pasture -footslope and valley), three soil profiles sampled from the Lake Balbina 273 area (Ferralsol and riverine Gleysol under forest and stagnic Acrisol under slash-and-burn) and 274 two parental rocks (granodiorite and granite taken from the Ferralsol rock quarry and the slash-275 and-burn riverbed respectively) were considered for further pedological, mineralogical, 276 chemical and isotopic analyses. All soil samples are listed in Table 1 and their sampling 277 locations are plotted in S.I. Fig. 1a and Fig. 1b. 278

Sampling was carried out according to the main horizons position (see Figs. 2a and2b 279 in S.I. section). For each horizon, between 1 and 2 kg were sampled and stored in plastic bags. 280

Back in the GET laboratory, the soil samples were dried at room temperature under laminar 281 flow hood, sieved to <2 mm, quartered, weighed and finely ground before mineralogical, 282 standard analysis using a Horiba EMIA-320V Carbon/Sulfur analyser. In this study, total 297 carbon contents of soil samples were found to derive from organic carbon or charcoal (no 298 contribution of carbonates). Cation exchange capacity (CEC) and pH measurements were 299 performed following the respective standardised method from AFNOR NF EN ISO 23470.2011 300 andNF ISO 10390.2005. This notably involved the determination of the effective CEC at the 301 soil pH using the hexamminecolbalt trichloride solution method. 302 303 Before chemical and isotopic analysis, each powdered and homogenised soil sample 304 (approximately 100 mg) was digested using a multistep dissolution procedure (H2O2, HNO3, 305 HF, HCl) with a microwave oven (MARS 5 system CEM, 150°C, 1600 W, 45 min). The main 306 decomposition step involved 9 ml of 15 M HNO3, 2 ml of 10 M HCl and 3 ml of Merck 307 Suprapur concentrated HF added together. Blank tests indicated that the level of contamination 308 induced by this acid digestion procedure was negligible and represented <2% of the sample 309 element of interest. 310

Iron and other major element compositions of soil samples were determined by ICP-311 OES (inductively coupled plasma optical emission spectrometry; Horiba Jobin Yvon Ultima2) 312 while Zr and other trace element compositions were measured on a quadrupole ICP-MS 313 (inductively coupled plasma mass spectrometry; Agilent 7500, Perkin Elmer) at the GET 314 laboratory (Toulouse, France). Indium and rhenium were used as internal standards for the ICP-315 MS measurements. The international SRM2709a geostandard (San Joaquin Soil, from NIST, 316 USA) for soils was used to check the validity and reproducibility of both acid digestion and 317 subsequent analyses. Typical uncertainties for the element analysed are <5%, 1SD. 318

The behaviour of Fe in the soil profiles can be evaluated through comparison with an 319 invariant element. Previous studies have shown that zirconium (Zr) can be taken as such an 320 invariant element [START_REF] Oliva | The effect of organic matter on chemical weathering: study of a small tropical 1001 watershed: nsimi-zoétélé site, Cameroon[END_REF][START_REF] Braun | Present weathering rates in a humid tropical watershed: Nsimi, SouthCameroon. 783[END_REF][START_REF] Viers | Evidence of Zn isotopic fractionation in a soil-plant system of a pristine tropical 1103 watershed (Nsimi, Cameroon)[END_REF]Poitrasson et al., 321 2008). Zirconium concentrations in continental crust and soils samples are also reported in 322

Table 2. In the absence of bulk density measurement, iron depletion factors relative to Zr in the 323 soil profiles (DFFe) were calculated using: 324

Eq. ( 1) 325 326 327

Iron isotope composition measurements 328

In order to measure the iron isotopic signature of the soil samples, the solutions obtained 329 after acid digestion were evaporated to dryness in the clean room and dissolved in 2 ml of 6 M 330 HCl. Iron was purified using anion exchange chromatography in an HCl medium as outlined in 331 [START_REF] Poitrasson | Iron isotope 1013 differences between Earth, Moon, Mars and Vesta as possible records of contrasted 1014 accretion mechanisms[END_REF]. We used 0.5 ml of Bio Rad AG1 X4 (200-400 mesh) anionic resins 332 loaded in thermo-retractable Teflon columns with an internal diameter of 4 mm. 333

Chromatography consisted in the preconditioning of the resin with 1 ml of 6 M HCl before 334 introduction of 0.5 ml of sample. The next step consisted in the addition of 3 ml of 6 M HCl to 335 elute the non-desired matrix elements. Finally, Fe was eluted with 2 ml of 0.05 M HCl. After 336 column chemistry and evaporation, the solutions were redissolved in 0.05 M HCl and stored 337 for iron isotope analyses. Blank tests were performed to estimate the level of contamination 338 induced by the overall dissolution and chemical procedure and it was found to be ~ <4 ng of 339

Fe. 340

Most of the iron isotope analyses were performed at the GET laboratory (Toulouse, 341

France), but some samples were analysed at the IFREMER laboratory (Brest, France) by high 342 and medium mass resolution, using a Neptune ThermoFischer MC-ICP-MS (Multi-Collector 343 Inductively Coupled Plasma Mass Spectrometer), following the procedure detailed in 344

DF Fe = C Fe C Zr ( ) sample C Fe C Zr ( ) continental crust
using a combination of the "standard-sample bracketing" approach with IRMM-014 as the Fe 346 standard, and Ni doping of the purified Fe samples using the daily regression method. 347

The Fe isotope compositions from all samples are reported following the standard delta 348 notation, relative to the European IRMM-014 reference material, and can be expressed in ‰ 349 for the 57 Fe/ 54 Fe ratio as: 350

Eq. ( 2) 351 Similar notations were also used for the 57 Fe/ 54 Fe and 56 Fe/ 54 Fe ratios. The literature values are 352 also reported as 56 Fe, but they may be recalculated to 57 Fe as ~1.5 * 56 Fe. 353

Our in-house hematite standard was measured every 6 samples in the analytical 354 sequence to assess data quality. The long-term external reproducibility of the method was 355 estimated from replicate analyses of this hematite in every session, whether using the Sensitive 356

Introduction System or the Apex desolvator as introduction systems to enhance instrument 357 sensitivity for samples with low Fe contents. The reproducibility and accuracy of these 358 measurements were checked with our in-house hematite standard [START_REF] Akerman | The Isotopic 766 fingerprint of Fe cycling in an equatorial soil-plant-water system: The Nsimi watershed, 767 South Cameroon[END_REF]. 359

Uncertainties on 57 Fe and 56 Fe values reported in this study are expressed as two standard 360 errors (2SE) calculated from the number of replicates and using the Student's correction factor 361 [START_REF] Platzner | Modern Isotope Ratio Mass Spectrometry[END_REF] The results for the mineralogical analyses by X-ray diffraction are presented in 367 Supplementary Table 2. All the soils studied present mineralogical composition in accordance 368 with typical Amazonian soils [START_REF] Horbe | Lateritic crust and related soils in eastern Brazilian 923 Amazonia[END_REF], with the dominance of inherited 369 quartz followed by secondary kaolinite, goethite and oxides such as hematite and gibbsite, and 370 poorly degradable residual phases such as zircon or rutile (S.I. Table 2). The mineralogical 371 composition of the <2µm clay fraction consists mainly of kaolinite. Gibbsite is also present in 372 the clay fraction of the forest plinthic Ferralsol and in the colluvic Gleysol from the pasture 373 catena. Illite is identified in the clay fraction of the forest haplic Gleysol. The very low CEC 374 values measured for the samples studied (below 5 cmol/kg, not shown) are in accordance with 375 the observed mineralogy. 376 Pedological analyses such as particle size, pH and carbon contents of the five soil 377 profiles studied are given in Supplementary Table 1. All soil profiles similarly have an acidic 378 pH between 4 and 5 0.02, which is consistent with these types of soil. For most soils studied, 379 except for the colluvic Gleysol under pasture for which a former surface horizon is buried under 380 colluvic material, the percentage of total carbon shows much higher values in the topmost 381 horizon and decreases with depth (S.I. Table 1). Grain size analysis showed different pattern 382 following soil types. Ferralsol soil samples granulometry is dominated by clay (49 to 77%) and 383 fine silt (10 to 27%) fractions. Plinthic Acrisol from the forest catena and colluvic Stagnosol 384 and colluvic Gleysol from the pasture catena showed similar particle size distributions 385 dominated by sand fractions (>50% with ~2/3 of coarse sand and ~1/3 of fine sand) and clay 386 fraction (26 to 47%), with the remaining silt fractions being <10%, except for the deepest 387 horizon. Lastly, the forest haplic Gleysol displays a sandy granulometry (total sand fraction 388 >73%) dominated by the coarse sand fraction, particularly within the 110-120 cm albic soil 389 material. 390 391 4.1.2. Soils from the Lake Balbina area 392

The results for the mineralogical analyses by X-ray diffraction are presented in 393 Supplementary Table 2. The Ferralsol is mainly composed of quartz, kaolinite, gibbsite, 394 goethite and hematite. Illite phases persist in the whole soil profile. Albic Gleysol and stagnic 395

Acrisol from the forested and slash-and-burn area riverbanks respectively show very simple 396 mineralogical features, essentially quartz, kaolinite and gibbsite. Primary phases such as K-397 feldspar and micas/illite are also present in trace amounts. It is important to note the decrease 398 of gibbsite and kaolinite in the surface horizon of the stagnic Acrisol and the absence of iron 399 bearing phases identified in the <2mm fraction of these soils. Such mineral disappearance can 400 be a consequence of severe soil heating by fire [START_REF] Certini | Effects of fire on properties of forest soils: a review[END_REF]. 401

Supplementary Table 1 presents classical soil parameters values such as particle size, 402 pH and carbon content for the samples from the three soil profiles. Given that the Ferralsol 403 studied was sampled at a depth of >3m, it would be inconsistent to interpret carbon content 404 results by comparison with stagnic Acrisol and albic Gleysol, which were only sampled down 405 to a depth of 1.2 m. All soil profiles have an acid pH between 4.6 and 6.3 0.02. Forest Ferralsol 406 and albic Gleysol soil profiles show similar pH values between 5.3 and 5.9, although the slash-407 and-burn stagnic Acrisol is more acidic (pH ~4.7) with the exception of the surface horizon 408 with a pH value of 6.3. Differences in pH values (about 1 pH unit) between the adjacent stagnic 409

Acrisol and albic Gleysol is substantial and several possible explanations exist (e.g. different 410 granitic parental rocks). However, an increase in surface soil pH during soil heating following 411 forest burning is commonly observed [START_REF] Certini | Effects of fire on properties of forest soils: a review[END_REF]. For all the soils studied, the percentage 412 of total carbon is relatively low and shows much higher contents in the topmost horizon and 413 decreases with depth (S.I. Table 1). A lower amount of soil carbon in slash-and-burn stagnic 414

Acrisol compared with the adjacent forest albic Gleysol may be a consequence of both erosion 415 processes and organic matter destruction by fire [START_REF] Certini | Effects of fire on properties of forest soils: a review[END_REF]. Ferralsol particle size analysis 416

shows an evolution of the soil granulometry from depth to surface with an increase of clay 417 fraction (17% in depth to 84% in surface) at the expense of the silt fraction (58% in depth to 418 7% in surface) due to chemical weathering. Like the riverine forest Gleysol in the Rio Capim 419 area, the riverine albic Gleysol from the Lake Babina area is dominated by a coarse sand 420 fraction (more than 90%). Lastly, particle size distribution for the stagnic Acrisol from the 421 slash-and-burn area displays variable results with depth. The observed variation in particle size 422 distribution is not a granulometric gradient as it corresponds to a superimposition of different 423 soil materials with sandiest texture at depth and at the surface compared with the rest of the soil 424 profile (S.I. Table 1). 425 426

Fe concentrations in soil samples

427

Iron and zirconium contents are given the Table 1 for the different soil samples collected 428 in the Rio Capim area and in the Lake Balbina area. Additional major and trace element 429 concentrations of these two sites are presented in Supplementary Table 3. 430

In the forest catena from the Rio Capim area, the samples from the plinthic Ferralsol 431 profile (i.e. top of the hill) showed large range of Fe concentrations from 5.55 wt.% in the 432 topmost mineral horizon to 8.31 wt.% in the deep ferruginous horizon below a depth of 390 433 cm. Iron concentrations in samples from the different soil horizons of the midslope plinthic 434

Acrisol and footslope haplic Gleysol exhibit lower values (Table 1). Within the plinthic Acrisol 435 soil profile, Fe concentration shows little variation with values ranging from 1.12 wt.% in the 436 topmost mineral horizon to 1.68 wt.% in the sandy clay horizon (75-90 cm). In the haplic 437

Gleysol with arenic and albic properties, the deep ferruginous nodular horizon shows four times 438 more Fe content (1.78 wt.%) than the shallow sandy eluvial horizon (0-15 cm), with values 439 ranging from 0.38 wt.% to 0.69 wt.%. 440

In the pasture landscape catena from the Rio Capim area, Fe concentrations in samples 441 from colluvic Stagnosol and colluvic Gleysol are 1) lower than those from forest plinthic 442

Ferralsol samples (Table 1) and 2) greater than Fe contents measured in samples from the forest 443 haplic Gleysol. In the colluvic Stagnosol profile, Fe concentration is 1.89 wt.% between 40 and 444 120 cm of depth in the redoxic clay horizon to a value of 1.20 wt.% at a depth of 0-10 cm in 445 the redoxic topmost mineral horizon. In the valley, soil samples from colluvic Gleysol exhibit 446 a ~30% increase of Fe concentrations from the bottom (1.74 wt.%) to the shallow topmost 447 mineral horizon (2.36 wt.% in Table 1). 448

The Ferralsol profile from the Lake Balbina area showed a large range of Fe 449 concentrations, from 9.36 wt.% in the micro-aggregated sandy clay horizon (3 m) to 12.44 wt.% 450 in the deep saprolite where the structure and volume are preserved down to 30 m in depth (Table 451 1). Iron concentrations in samples taken at a depth of 3 m are similar for both Ferralsols studied 452 (Ferralsols from Lake Balbina and Rio Capim areas with respectively 9.4 and 8.3 wt.%). Under 453 forest cover, in the albic Gleysol, the deep reductic sandy horizon shows six times more Fe 454 content (0.60 wt.%) than the topmost sandy horizon (0-30 cm; 0.10 wt.%). Within the stagnic 455

Acrisol soil profile from the slash-and-burn area, Fe concentration shows little variation with 456 values ranging from 0.48 wt.% in the surface stagnic sandy horizon to 0.72 wt.% in the massive 457 sandy clay horizon (i.e., 80-95 cm). Fe content is 0.96 wt.% between 50 and 65 cm of depth in 458 the nodular sandy horizon (Table 2). 459

Values of DFFe for all soil profiles from the Rio Capim area are shown in Table 1 and460 Fig. 3 for forest area and Fig. 4 for pasture landscape. All footslope soil profiles in forest and 461 pasture from this catchment exhibit between 45 and 90% depletion of Fe during weathering, 462 except the deep horizon of the forest haplic Gleysol which only shows 23% depletion. In the 463 pasture catena, colluvic Stagnosol is more Fe-depleted than the valley colluvic Gleysol, which 464 contrasts with the gradient observed in the forest catena. On the other hand, plinthic Ferralsol 465 samples do not exhibit Fe depletion with DFFe values close to 1 (from 0 to 390 cm in depth), 466 and a Fe enrichment of about 40% compared with the continental crust in the deep ferruginous 467

horizon. 468

Values of DFFe for the three soil profiles from the Lake Balbina area are shown in Table 469 1 and Fig. 5. Under forest cover, the albic Gleysol exhibits a high depletion with over 90% loss 470 of Fe in surface horizons (from 0 to 60 cm), and shows lower Fe depletion in the deep reductic 471 sandy horizon with 22% depletion of Fe with reference to the upper continental crust value. 472

Stagnic Acrisol from the slash-and-burn area appears to be less Fe-depleted than the forest albic 473

Gleysol with DFFe depletion between 55 and 75%. Only the deepest horizons of these two 474 profiles display an opposite relationship. Contrary to the albic Gleysol and the stagnic Acrisol, 475 the Ferralsol samples exhibit high Fe enrichments in both the deep micro-aggregated sandy clay 476 horizon and the saprolite (from 300 to 3000 cm in depth) compared with the continental crust 477 (more than 200%) or the parental granodiorite (up to 150% in the deep saprolite). However, 478 these results should be taken with caution, because the reference rock used for the DFe 479 calculation can have an impact on them. When using granite as the parental rock for both 480 riverine forest and slash-and-burn soils, it appears that the deep horizon of the albic Gleysol is 481 enriched in Fe while the overlying horizon is Fe-depleted. The upper part of the stagnic Acrisol 482

shows DFe close to 1 when compared with Fe from the granite, whereas the deepest horizon 483 shows 25% of Fe depletion. Given the complexity of the geological substratum in this area 484 described above, it is however unclear which granitoid can best be taken as a reference. Given 485 these uncertainties, the mean continental crust value should instead be used as a reference. 486 487

Fe isotope compositions in soil samples

488

Iron isotope compositions in the plinthic Ferralsol profiles from the Rio Capim area 489 (Table 1; Fig. 3 and Fig. 4) show a narrow range of δ 57 Fe values, ranging from 0.020‰ relative 490 to IRMM-14 in the deep horizon, down to -0.106‰ in the topmost mineral horizon. The δ 57 Fe 491 of all Ferralsol samples from the Lake Balbina area is isotopically similar with values ranging 492 from 0.155‰ to 0.190‰ (Table 1; Fig. 5). In fact, a large fraction of the values are analytically 493 indistinguishable from the mean iron isotope composition of the continental crust (~0.10‰; 494 Poitrasson, 2006), except for the topmost mineral horizon of the plinthic Ferralsol that presents 495 a lighter δ 57 Fe signature (Table 1). 496

Under forest cover from the Rio Capim area, the δ 57 Fe of all the samples from the 497 riverbank haplic Gleysol soil profile are isotopically similar and exhibit a heavy δ 57 Fe signature 498 with a value of ~0.66‰. For the plinthic Acrisol soil profile, an Fe isotopic composition of 499 about ~0.3‰ is observed from the bottom to the shallower mineral horizon with δ 57 Fe from 500 0.286‰ to 0.371‰ (Table 1 and Fig. 3). The albic Gleysol in forest from the Lake Balbina area 501 exhibits a heavy δ 57 Fe signature with values ranging from 0.608‰ to 0.863‰ from the topmost 502 mineral horizon to the bottom (Table 1; Fig. 5). Hence, whichever site studied (Rio Capim or 503 Lake Balbina), soils sampled in the midslope and footslope under forest cover display an 504 isotopically heavier Fe signature relative to the continental crust baseline and the reference 505 Ferralsol (Fig. 3 and Fig. 5). 506

In the pasture from the Rio Capim area, the Fe isotope compositions of samples from 507 the two soils studied (colluvic Stagnosol and colluvic Gleysol from footslope and valley) are 508 isotopically similar with a range of 0.304-0.384‰ for the colluvic Stagnosol and 0.236-0.479‰ 509 for the colluvic Gleysol, but remain heavier than the continental crust (Table 1; Fig. 4). The 510 stagnic Acrisol from the slash-and-burn area from the lake Balbina area shows a narrow range 511 of δ 57 Fe values, ranging from 0.211‰ relative to IRMM-14 in the topmost sandy horizon, up 512 to 0.334‰ in the deep horizon (Table 1). Iron isotope compositions in this soil profile are also 513 isotopically heavier than the reference Ferralsol and the continental crust baseline (Fig. 5). 514 515 5. Discussion 516

Similarity of Ferralsol and Acrisol systems within the Rio Capim catenas 517

Given that it is difficult to establish a genetic link among the soils from the two catenas 518 studied, it is important to ensure that the initial pedological cover before deforestation and 519 pasture setting up for the pasture catena is comparable with the one still occurring in the forest 520 catena. In the field, the choice of pasture and forest catenas was driven by the close vicinity of 521 the two sites, the presence of a nascent stream in each, ease of access and geomorphological 522 criteria (i.e. same orientation of the slopes that support both catenas, same flow direction). 523 However, it is necessary to characterise specific properties such as horizon particle size 524 distribution, geochemistry and mineralogy in order to test the comparability of the two catenas 525 investigated. This is particularly important given the heterogeneous lithology of the parent rock 526 consisting of sedimentary rocks of variable nature with a subhorizontal dip implying possible 527 differences in parental substrate along slopes [START_REF] Da Costa | The contribution of laterization processes 816 to the formation of the kaolin deposits from eastern Amazon[END_REF]. Clay fraction is strongly 528 affected by leaching processes or colluvic material deposition and therefore cannot be used to 529 infer any parental influence on soil granulometry. Soil particle size distributions reveal 530 disparate distributions of the coarsest fractions within the Ferralsol and between soils along a 531 given catena. The Ferralsol horizons display the most significant granulometric discrepancy 532 that can be linked to nodular formation and chemical weathering. However, midslope and 533 footslope soils which are sandier than the plinthic Ferralsol show similar granulometric 534 features, independently of the catena considered (see S.I. Table. 1). Hence, even if it is well 535 established that Acrisols result from pedogenetic differentiation through clay minerals and iron 536 oxides eluviation, the genetic link between the two Acrisols studied and plinthic Ferralsol 537 cannot be inferred using soil textures. However, even though significant differences are 538 observed with the particle size distributions along slopes, these differences are the same 539 whichever catena is considered, be it under forest or pasture cover. As a result, soils located at 540 comparable elevation (plinthic Acrisol vs colluvic Acrisol) not only display similar grain size 541 distributions for the >2µm fraction but also similar Fe contents and DFe values, thereby 542 allowing for their direct comparison. Indeed, the two watersheds studied (under forest cover 543 and under pasture cover) were selected as close as possible to each other to minimise lateral 544 lithology variations. This is confirmed by the triangular Fe-Si-Al chemical diagram that shows 545 a comparable chemical evolution for the different soil types among the different catenas (SI 546 Fig. 3). Hence, the initial Ferralsol-Acrisol system which has evolved following deforestation 547 and pasture establishment to the degraded soil cover within the pasture catena is assumed to be 548 very similar to the current Ferralsol-Acrisol system studied along the forest catena, changes in 549 particle size distribution for riverside soil profiles being attributed to land use changes. In this 550 context, the Fe isotopic signature can be an indication of such land use changes. Similar 57 Fe 551 values of about 0.3‰ for the surface horizon of the midslope forest plinthic Acrisol and for the 552 footslope colluvic Acrisol and colluvic Gleysol horizons under pasture can be considered as 553 markers for rejuvenation of soil profile after deforestation. 554 555

Iron isotope signatures of laterites (Ferralsols) as a baseline 556

In this study, it was possible to compare the Fe isotopic signatures of two Ferralsol soil 557 profiles from two different study sites under tropical rainforest (the Rio Capim and Lake 558

Balbina sites). Both Ferralsols studied display deep ferruginous horizons showing Fe 559

accumulation compared with the mean continental crust as expressed by the DFe using Zr as 560 an immobile element (Table 1 and Figs. 3 and5). Iron isotope analyses of these thicker lateritic 561 soils display similar δ 57 Fe signatures, close to the continental crust baseline (i.e., δ 57 Fe ~ 0.103 562 ‰ in δ 57 FeIRMM-14, Table 1 and SI Fig. 4). The upper sampled horizon of the Rio Capim 563

Ferralsol is lighter than this reference. Although the reason is unclear, this does not change the 564 observation that the deeper horizons are similar to the continental crust δ 57 Fe value, as are 565

Ferralsols from other locations whatever depth considered [START_REF] Poitrasson | Limited iron isotope variations in recent 1023 lateritic soils from Nsimi, Cameroon: Implications for the global Fe geochemical cycle[END_REF]Liu et al., 566 2014;[START_REF] Li | Why was iron 954 lost without significant isotope fractionation during the lateritic process in tropical 955 environments?[END_REF]. We thus consider this continental crust baseline as a robust reference for 567 comparing our other soil profiles for both the Rio Capim and Lake Balbina sites. The Ferralsol 568 from the Lake Balbina area is developed on volcanic-granitic parental rocks showing a light 569 iron isotope composition with a 57 Fe value of -0.003 0.05‰ (Table 1). Crustal rocks tend to 570 show a homogeneous Fe isotope composition, although some volumetrically minor, strongly 571 differentiated granites or some sedimentary rocks may show notable deviation from the 572 continental crust baseline (e.g. [START_REF] Matthews | 968 Controls on iron-isotope fractionation in organic-rich sediments (Kimmeridge Clay, 969 Upper Jurassic, southern England)[END_REF]Poitrasson, 2006;Schoenberg and von 573 Blanckenburg, 2006;[START_REF] Yamaguchi | 1134 Isotopic evidence for iron mobilization during Paleoproterozoic lateritization of the 1135 Hekpoort paleosol profile from Gaborone, Botswana[END_REF]. Nevertheless, the expanding databases of Fe 574 isotope study of laterites confirm their homogeneous δ 57 Fe values, very close to the continental 575 crust baseline [START_REF] Poitrasson | Limited iron isotope variations in recent 1023 lateritic soils from Nsimi, Cameroon: Implications for the global Fe geochemical cycle[END_REF][START_REF] Liu | Copper and iron isotope 958 fractionation during weathering and pedogenesis: Insights from saprolite profiles[END_REF][START_REF] Li | Why was iron 954 lost without significant isotope fractionation during the lateritic process in tropical 955 environments?[END_REF] whatever the parental 576 rock. As a result, the Fe isotope composition of laterites may be used as a baseline with a δ 57 Fe 577 composition of 0.1‰ similar to that of the continental crust (~0.10‰ in δ 57 FeIRMM-14 ) (SI Fig. 578 4). 579 580

Iron mobility in Ferralsol-Acrisol systems under forest cover 581

As can be seen in Table 1 and Figs. 3 and5, DFFe values mean that Fe loss with reference 582 to the continental crust occurred for all horizons studied from soils profiles along slopes under 583 forest cover (i.e., Acrisols and riverine Gleysols). Relative Fe loss in surface horizons is also 584 apparent for the Rio Capim Ferralsol soil profile but it did not induce large Fe isotopes 585 fractionation. Accordingly, iron isotope signatures for both Ferralsols show a very limited range 586 (-0.106 to +0.190‰) with δ 57 Fe close to the continental crust mean value (see section 5.2). 587

These results contrast clearly with previous modern soil studies in various areas (Fantle and 588 DePaolo, 2004;[START_REF] Emmanuel | A preliminary mixing model for Fe 848 isotopes in soils[END_REF][START_REF] Thompson | Rayleigh ractionation 1072 of iron isotopes during pedogenesis along a climate sequence of Hawaiian basalt[END_REF]Wiederhold et al., 2007a;589 Yesavage et al., 2012;[START_REF] Fekiacova | Inferences from the vertical 865 distribution of Fe isotopic compositions on pedogenetic processes in soils[END_REF] which show a wider range of δ 57 Fe. This implies 590 that lateritic soil formation (i.e. primary silicate phases weathering and secondary Fe oxides 591 and oxyhydroxides formation) does not generate large Fe isotopic fractionations because of 592 quantitative iron transfer without separation of isotopically distinct pools (Poitrasson et al., 593 2008;[START_REF] Liu | Copper and iron isotope 958 fractionation during weathering and pedogenesis: Insights from saprolite profiles[END_REF][START_REF] Li | Why was iron 954 lost without significant isotope fractionation during the lateritic process in tropical 955 environments?[END_REF]. On the other hand, samples from soils resulting from the 594 pedogenetic evolution/degradation of Ferralsol soil-type material leading to Fe mobilisation 595 through Fe 3+ reduction by bacteria (mainly Stagnosols and Gleysols), leaching (Acrisols), 596 acidolysis and/or complexolysis with organic acids (riverine Gleysols) show strong Fe 597 depletion (between 45 and 90% of Fe depletion estimated on the basis of a constant Zr 598 concentration relative to the continental crust; see Fig. 3 and Fig. 5). The Fe isotope 599 compositions of these samples reveal that the δ 57 Fe of the evolved soils from midslope and 600 footslope are isotopically heavier than the continental crust baseline and the upslope Ferralsol. 601

Our data on Fe depletion and Fe isotopic compositions suggest that the relative heavy Fe 602 enrichment compared with Ferralsols signature is linked to a weathering gradient inducing loss 603 of light Fe isotopes along slopes (see Fig. 3 and SI Fig. 2a) consistent with soil description. In 604 response to the tropical climate, topsoil exposure to the land surface involved chemical 605 weathering of lateritic soils. In the Paragominas-Rio Capim region, it has been proven that the 606 hot and humid climates act intensively on the lateritic crust causing their weathering and 607 transformation into degraded soils [START_REF] Horbe | Lateritic crust and related soils in eastern Brazilian 923 Amazonia[END_REF]. The plinthic Acrisol is a 608 strongly weathered acid soil and it is still undergoing further degradation [START_REF] Quesada | 1032 Soils of Amazonia with particular reference to the RAINFOR sites[END_REF]. 609

Several authors explain that Ferralsols and Acrisols can undergo transformations to form 610 podzolic soils under water saturation, by selective clay removal, accumulation of surface 611 organic compounds and lateral mobility of organo-metallic chelates [START_REF] Chauvel | On the genesis of the soil mantle of the region of 800 Manaus, Central Amazonia, Brazil[END_REF]Do 612 Nascimento et al., 2004;[START_REF] Quesada | 1032 Soils of Amazonia with particular reference to the RAINFOR sites[END_REF]. Moreover, previous studies [START_REF] Oliva | The effect of organic matter on chemical weathering: study of a small tropical 1001 watershed: nsimi-zoétélé site, Cameroon[END_REF]613 Braun et al., 2005;[START_REF] Akerman | The Isotopic 766 fingerprint of Fe cycling in an equatorial soil-plant-water system: The Nsimi watershed, 767 South Cameroon[END_REF] have shown that redox processes coupled with 614 podzolisation-like mechanisms occurring in tropical soils from bottomlands under forest can 615 induce strong Fe depletions. The footslope riverine sand-rich haplic Gleysol from the Rio 616 Capim area and albic Gleysol from the Lake Balbina area are temporarily water saturated (i.e. 617

Fe 3+ mottling and reductive features) but the settlement of podzolisation processes is not 618 morphologically visible. Iron depletion in soils from the current forested watersheds undergo 619 redox processes coupled with other pedogenic processes such as leaching (e.g. Fe leaching in 620 Acrisols) and/or organic acid mediated chemical weathering (e.g. Fe-OM complexation in 621 riverine Gleysols). Such processes lead to the loss of isotopically light Fe and imply 622 mobilisation of lighter Fe isotopes by lateral drainage when considering natural degradation of 623 an initial Ferralsol soil cover. These results concur with those of a previous study (Thompson 624 et al., 2007) showing a large range of Fe isotopic signatures in specific montane rainforest soils 625 and high rainfall gradient inducing pedogenic processes associated with redox mechanisms. 626

More recently, the study of iron isotope composition in tropical soils of a small experimental 627 watershed in Cameroon [START_REF] Akerman | The Isotopic 766 fingerprint of Fe cycling in an equatorial soil-plant-water system: The Nsimi watershed, 767 South Cameroon[END_REF] showed similar results. Pedogenetic processes 628 along a catena associated with redox mechanisms and lateral Fe leaching significantly 629 fractionate iron isotopes during weathering and soil evolution, particularly within riverine 630

Gleysol. This view is also supported by results from [START_REF] Schuth | Redox-dependent fractionation of iron 1055 isotopes in suspensions of a groundwater-influenced soil[END_REF] on the Fe isotope 631 composition of horizons of a Gleysol from north-west Germany. They found δ 57 Fe values 632 ranging from + 0.3‰ in the organic horizon to -0.2‰ in the reductic horizon. A recent article 633 reviewing Fe isotopes in soils [START_REF] Wu | Iron cycling and 1131 isotope fractionation in terrestrial ecosystems[END_REF] The Fe isotope compositions of the two soil profiles studied in the pasture catena from 640 the Rio Capim area (see Table 2 and Fig. 4) show that these degraded soils (colluvic Stagnosol 641 and valley colluvic Gleysol, see Fig. 4) are isotopically similar but remain heavier than the 642 forest plinthic Ferralsol and the continental crust mean value (~0.10‰ in δ 57 FeIRMM-14). The 643 stagnic Acrisol collected in the slash-and-burn area from the Lake Balbina site also exhibits an 644 iron isotope signature heavier than the Ferralsol from this district (see Table 1 and Fig. 5) and 645 the continental crust mean value (~0.10‰ in δ 57 FeIRMM-14). These results reinforce the idea that 646 the Fe lost during soil formation and evolution is isotopically light. 647

As in the footslope and valley profiles covered by the forest for both sites studied, these 648 soil profiles under pasture show Fe depletion (see DFFe values in Table 1 andFigs. 3, 4 and5). 649

Compared with the weathering gradient observed along the forest catena from the Rio Capim 650 area, the DFFe values show that the Fe depletion in pasture footslope colluvic Stagnosol is 651 comparable to that of forest plinthic Acrisol (more than 60% of Fe lost). The pasture valley 652 colluvic Gleysol appears to be less iron-depleted than both Acrisols, with 40 to 60% of iron 653 depletion (see Table 1), the deepest horizon (110 to 120 cm in depth) being the more Fe 654 depleted. Thus, the previously shown weathering gradient for forest soils along the catena is 655 not reproduced in pasture catena from the Rio Capim area. Deforestation involves 656 geomorphological modifications by erosion processes and pedogenesis (Fig. 6 and SI Fig. 5). 657

After deforestation, a flattening of the hill morphology is observed, due to erosion processes. 658

These processes take place from the first moments of deforestation, as observed in the riverbank 659 stagnic Acrisol in the slash-and-burn area from the Lake Balbina site (see Fig. 2e). In the pasture 660 landscape catena from the Rio Capim area, the erosion and accumulation of eroded material 661 downslope induce modifications in local drainage. Flattening of the interfluve by accumulation 662 of fine-grained material rich in clay and iron oxide is responsible for the settlement of 663 hydromorphic conditions involving enhanced redox processes in footslope soils (see Fig. 2f). 664 Pedological functioning of footslope soils is thus modified with the prevalence of redox 665 processes relative to others, visible in the Rio Capim area as redoximorphic features in the 666 footslope colluvic Stagnosol, and both redoximorphic and reductimorphic patterns in the valley 667 colluvic Gleysol. Such reductimorphic colours also occur in the Lake Balbina gleyic Acrisol 668 from the slash-and-burn area. 669

In a deforestation context, our Fe isotope results indicate that, besides morphological 670 changes leading to a flattening of the relief, erosion, transport of particles from hill top and 671 accumulation in the valley are coupled with redox processes and are responsible for pedological 672 modification such as rejuvenation of valley soil profiles (Fig. 6 and SI Fig. 5). These processes 673 lead to isotopically heavier Fe signatures than reference Ferralsols (plinthic Ferralsol from the 674 Rio Capim area and Ferralsol from the Lake Balbina area) and the continental crust, but lighter 675 Fe signatures than riverine Gleysol type soils under forest cover (haplic Gleysol from the Rio 676 Capim area and albic Gleysol from the Lake Balbina area) (SI Fig. 5). These results are 677 concordant with the previous study of [START_REF] Fantle | Iron isotopic fractionation during continental weathering. 851[END_REF] suggesting that the net effect 678 of continental weathering processes is to mobilise small amounts of isotopically light Fe in an 679 exchangeable or dissolved form. As redox reactions induce the largest isotopic fractionation 680 [START_REF] Jarzecki | DFT analysis of Fe(H2O)6 3+ and Fe(H2O)6 2+ 942 structure and vibrations: implications for isotope fractionation[END_REF], stable iron isotopes can help to study Fe transfer following redox 681 processes in soils during pedogenesis and soil degradation, not only under forest cover but also 682 after deforestation (e.g. slash-and-burn followed by pasture establishment) (see Fig. 5). The 683 observed chemical and isotopic soil rejuvenation of footslope soils (changes in riverine soils δ 684 57 Fe from 0.7 to 0.3‰) is a direct consequence of soil erosion processes taking place along 685 29 slopes after deforestation. Thus, it is obvious that biogeochemical cycles of iron in riverine 686 environments is significantly altered following deforestation. Colluviation brings iron-bearing 687 phases that are less depleted in light Fe isotopes than the original riverine soils developed under 688 forest cover. Changes in soil hydraulic properties following deforestation (decrease of soil 689 surface permeability, runoff increase) and the likely rise of the water table level (Coe et al, 690 2016) enhance temporary hydromorphic conditions and thus activate redox processes involving 691 iron on the biogeochemistry of riverine soils. Such changes appear to be already active after the 692 first stage of erosion following slash-and-burn. 693 [START_REF] Neill | Deforestation alters the hydraulic and biogeochemical 991 characteristics of small lowland Amazonian streams[END_REF] studied how clearing of the tropical rainforest for pasture in the 694 Brazilian Amazon can influence stream hydraulic characteristics, solute concentrations and 695 uptake of dissolved inorganic nitrogen and phosphorus. They found that deforestation alters 696 stream hydrology and biogeochemistry. The pasture streams had lower concentrations of 697 dissolved oxygen and higher concentrations of dissolved Fe 2+ . It is therefore important to study 698 the exchanges of Fe at the soil/surface water interface. This raises the question of the Fe isotope 699 composition of the iron carried by stream waters (dissolved and particulate phases) during and 700 after deforestation, and the use of iron isotope signatures of stream water as tracers of 701 deforestation. This requires long-term monitoring of watersheds undergoing deforestation. It is 702 also likely that the effect will be less obvious for large watersheds because they will more likely 703 have tributaries draining lands with different forest management histories. A scale effect has 704 also to be considered in the Amazon watershed for particulate phase since some tributaries have 705 a strong signature inherited from erosion of the Andes. Hence, in a context of increasing 706 deforestation, changes in Fe isotopic signatures in the dissolved and particulate fractions of the 707 Amazon and its tributaries should be further explored. 708 709

Conclusion and perspectives 710

This study demonstrates that Fe isotope compositions in soils under forest cover can 711 show a δ 57 FeIRMM-14 fractionation of up to 0.8‰ between the hill top Ferralsol and the footslope 712 haplic Gleysol and albic Gleysol of, respectively, the Rio Capim and the Lake Balbina areas. 713

This likely results from redox, leaching and/or podzolisation processes occurring in these types 714 of soils, which in turn leads to mobilisation and loss of the lighter Fe. Relative to the starting 715 continental crust composition (δ 57 Fe ~0.1‰), this leads to heavy isotope compositions in the 716 stagnic Acrisol (with δ 57 Fe ranging from 0.21 to 0.33‰), colluvic Stagnosol (δ 57 Fe from 0.3 to 717 0.38‰) and colluvic Gleysol (δ 57 Fe from 0.24 to 0.48‰). The slash-and-burn area from Lake 718

Balbina and pasture catena from the Rio Capim area exhibit a similar Fe signature (δ 57 Fe 719 ~0.3‰), again heavier than the reference Ferralsols studied (δ 57 Fe ~0.1‰) but lighter than the 720 forest riverine Gleysols (δ 57 Fe ~0.7‰). The relative enrichment in heavy Fe isotopes in soils 721 as a consequence of light Fe isotope mobilisation (total Fe depletion >50%) is attributed to the 722 redox processes highlighted in these soils which caused the reduction of iron and its subsequent 723 leaching (occurrence of white iron-depleted gleyic horizons). Hence, our results confirm that 724 redox processes can significantly fractionate iron isotopes under tropical environments, as 725 previously shown by [START_REF] Thompson | Rayleigh ractionation 1072 of iron isotopes during pedogenesis along a climate sequence of Hawaiian basalt[END_REF] in a different context, and more recently by 726 [START_REF] Akerman | The Isotopic 766 fingerprint of Fe cycling in an equatorial soil-plant-water system: The Nsimi watershed, 767 South Cameroon[END_REF] in a more similar environment. 727

Moreover, this study illustrates that Fe isotopes can be used to identify erosion, even 728 when soil textures make it challenging to unravel. The similar 57 Fe values between the 729 footslope soil and the valley soil may result from geomorphological modifications by erosion 730 coupled with redox processes and accumulation of eroded material downslope. Such a process 731 would induce a chemical and isotopic rejuvenation of riverine soils in connection with the 732 stream draining the system. Following deforestation, riverine soils receive colluvic material 733 from upslope which is less depleted in Fe and has lighter Fe signatures than the former riverine 734 soil. This addition of new Fe-bearing material would induce changes in the features of redox 735 processes occurring in these soils. Our different site study shows that this rejuvenation takes 736 place from the first months of deforestation and will last for several decades as long as the 737 pastures are maintained. 738

Hence, this study demonstrates that anthropic activities such as deforestation may 739 modify the environment and lead to different Fe isotopic compositions in soils. Iron isotopes 740 can therefore be used as a new geochemical tool to quantify and qualify possible impacts of 741 anthropogenic pressure, and in particular the effect of deforestation on soil degradation in 742 tropical environments. The δ 57 Fe of the suspended and particulate fractions of the rivers 743 draining those deforested areas are also likely to be less strongly fractionated compared with 744 those draining the pristine rainforest. Considering the difference between the Fe isotopic 745 signatures of forest soils and pasture soils, the dissolved Fe transported by streams in deforested 746 areas should be isotopically lighter than in unaffected tropical forest streams and rivers where 747 it is heavy (dos Santos Pinheiro et al., 2013;[START_REF] Akerman | The Isotopic 766 fingerprint of Fe cycling in an equatorial soil-plant-water system: The Nsimi watershed, 767 South Cameroon[END_REF]. On the other hand, a change 748 in Fe isotope signatures is also expected for the particulate phase in stream waters draining such 749 a system. In undisturbed systems where sandy rich Gleysols or Podzosols are drained by the 750 river, Fe isotopes of the suspended load currently show a light signature (Rio Negro;dos Santos 751 Pinheiro et al., 2013). Regarding both the early and long-term physical degradation of soil cover 752 after deforestation, it is likely that river particulate phase becomes heavier with deforestation. (Poitrasson, 2006). Data are from Table 1. (Poitrasson, 2006). Data are from Table 1. Fe depletion factor relative to Zr) as a function of depth for the three soil profiles from the Lake Balbina area under forest cover (Ferralsol and albic Gleysol) and slash-and-burn area (stagnic Acrisol). The purple line denotes the continental crust mean value (Poitrasson, 2006). (Poitrasson, 2006). Data are from Table 1.

Figure 8: Iron isotope composition (in ‰) relative to IRMM-014 and evolution of DFFe as a function of depth for the three soil profiles from the Lake Balbina area under forest cover and slash-and-burn area. The purple line denotes the continental crust mean value (Poitrasson, 2006). Data are from Table 3. 1. b) Range of 57 Fe relative to IRMM-014 found in bulk Ferralsol samples from this study compared to comparable lateritic soils from the literature (from Cameroon, [START_REF] Poitrasson | Limited iron isotope variations in recent 1023 lateritic soils from Nsimi, Cameroon: Implications for the global Fe geochemical cycle[END_REF]China, Liu et al., 2014 andThe Philippines, Li et al., 2017). The purple line denotes the continental crust mean value (Poitrasson, 2006).

Number of analyses

Lake Balbina slash and burn area d The iron isotope composition and two standard error uncertainties quoted are calculated from the number of analyses indicated and using the Student's t-correcting factors [START_REF] Platzner | Modern Isotope Ratio Mass Spectrometry[END_REF].

Sample Origin

  190 the slope zones, this results from natural evolution by clay and iron leaching (plinthic Acrisol) 191 and by redox processes coupled with organometallic complexes formation in the riverine zone 192 inducing strong element-depleted sandy soils (haplic Gleysol). Under pasture, the soil profiles 193 studied display features associated with physical degradation linked with deforestation, such as 194 important loss of surface material in the highest zone of the hills and its accumulation at the 195 bottom of the hills. Thus, upslope soils are characterised by the outcropping of petroplinthic 196 horizons from initial plinthic Ferralsol and by strong colluvic deposition that influence 197 pedogenesis evolution for soils downslope becoming buried soils where processes of clay 198 leaching and organometallic complexes formation are no longer relevant. Therefore, the top of 199 the hill and foot slope are formed by chemically and physically degraded lateritic soils and 200 stagnosol type soils showing both stagnic and gleyic properties (i.e. seasonal water saturation 201 in surface and permanent waterlogging in depth). The flattening of the valley by erosion 202 processes coupled with soil physical compaction by grazing animals are responsible for the 203 widening of the valley area at the catena level. Thus, colluvic materials intensely affect valley 204 soil cover in pasture areas. 205

  respectively). Similarly, three soils profiles were considered along the catena under pasture: a 217 truncated Ferralsol-type soil profile at the top of the hill and two soil profiles deeply affected 218 by colluvic deposition respectively in footslope and river valley positions. Contrary to the 219 others soil profiles, we could only conduct a soil description of the truncated Ferralsol as it 220 consisted mainly of a thick hard plinthite horizon, visible along track banks and physically 221 impossible to sample properly. Differences observed concerning the pedology of soils from the 222 two catenas were especially marked in footslope positions.

  following the World Reference Base for Soil Resources (IUSS 262

  X-ray diffraction (INEL X-ray diffraction system with high 286 resolution curved X-ray detector, cobalt or copper anticathode and graphite monochromator) 287 were performed on bulk soil samples and on clay fractions of each horizon of three of the soils 288 studied from the Rio Capim area (top and bottom of the hill soil profiles along the forest catena 289 and valley soil profile in pasture). The X-ray diffraction analyses of the clay fraction were 290 performed on oriented thin sections after separation of the <2µm fraction by sedimentation in 291 water following Stokes law. 292 Grain size analysis (5 size fractions) considering clay (<2 µm), fine silt (2-20 µm), 293 coarse silt (20-50 µm), fine sand (50-200 µm) and coarse sand (200-2000 µm) was performed 294 at the Laboratoire d'Analyses des Sols (LAS) in Arras. Total carbon contents of approximately 295 13 200 mg of each powdered and homogenised soil samples were determined after blank and 296

  put forward Fe fractionation in δ 57 Fe of +3‰ 634 during oxidation and -3‰ during dissimilatory Fe reduction in soils. Hence, pedogenetic 635 processes can therefore easily account for the heavy δ 57 Fe signature of ~0.6‰ measured in 636 forest Gleysols in the two sites presented in this work. 637 638 5.4. Iron mobility in Ferralsol-Acrisol systems following deforestation 639

  Figure 1: (A) Location of the studied zones within the general geological map of North Brazil; (B) Geological map of the study area in the Amazonas State near Presidente Figuereido; (C) Geological Map of the study area in the Para State near Goianesia do Para. The figure 1C is adapted from Vasquez et al., 2008.

Figure

  Figure

Figure 2 :

 2 Figure 2: Pictures showing a typical non-disturbed riverine ecosystem within the Rio Capim watershed (A), modified riverine ecosystem under a 50 years old pasture within the Rio Capim watershed (B). Slash and burn area a few days (C) and 6 months (D) after burning in the lake Balbina are. Pictures (E) and (F) showing details of high rate of erosion 6 month after fire in the slash-and-burn zone and of Fe remobilization.

Figure

  Figure

Figure 3 :

 3 Figure 3: Iron isotope composition (in ‰) relative to IRMM-014 and evolution of DFFe (Fe depletion factor relative to Zr) as a function of depth for the three soil profiles from the Rio Capim area along the forest catena. The purple line denotes the continental crust mean value(Poitrasson, 2006). Data are from Table1.

Figure

  Figure

Figure 4 :

 4 Figure 4: Iron isotope composition (in ‰) relative to IRMM-014 and evolution of DFFe (Fe depletion factor relative to Zr) as a function of depth for the soil profiles from the Rio Capim area in the pasture catena (colluvic Stagnosol and colluvic Gleysol). The reference ferralsol from the forest catena is given for comparison. The purple line denotes the continental crust mean value(Poitrasson, 2006). Data are from Table1.

Figure

  Figure

Figure 5 :

 5 Figure5: Iron isotope composition (in ‰) relative to IRMM-014 and evolution of DFFe (Fe depletion factor relative to Zr) as a function of depth for the three soil profiles from the Lake Balbina area under forest cover (Ferralsol and albic Gleysol) and slash-and-burn area (stagnic Acrisol). The purple line denotes the continental crust mean value(Poitrasson, 2006).

  Figure5: Iron isotope composition (in ‰) relative to IRMM-014 and evolution of DFFe (Fe depletion factor relative to Zr) as a function of depth for the three soil profiles from the Lake Balbina area under forest cover (Ferralsol and albic Gleysol) and slash-and-burn area (stagnic Acrisol). The purple line denotes the continental crust mean value(Poitrasson, 2006).

Figure

  Figure

Figure 7 :

 7 Figure 7: Iron isotope composition (in ‰) relative to IRMM-014 and evolution of DFFe as a function of depth for the three soil profiles from the Rio Capim area in the pasture landscape catena. The purple line denotes the continental crust mean value(Poitrasson, 2006). Data are from Table1.

Figure 6 :

 6 Figure6: Synthetic sketches of the pedological processes and behavior of the Fe isotopic variation occurring with natural degradation under forest cover along slopes and after deforestation from slash-and-burn to old pastures systems. The Rio Negro water ( RN ) is reported as an example of black waters carrying dissolved heavy Fe and particulate light Fe inherited from soils of the evergreen Amazonian tropical forest.

FigureFigure

  Figure

Figure SI 2a :

 2a Figure SI 2a: Synthetic soil description along the two catenae from the Rio Capim forest farm: Left, under pasture and right, under forest. Soils experiencing erosion processes (colluvic processes) are marked with an asterisk. Colors are only indicatives in the figures. Following the Munsell color chart for soils red colors (matrix and nodules) from the plinthic Ferralsol are 2.5YR4/6 to 2.5YR4/8, ochre colors (matric) from both the plinthic Acrisol, the Stagnosol colluvic and the deep horizon of the haplic Gleysol are 10YR5/6 and the colors from the Gleysol colluvic are mainly 2.5Y4/2 in the surface horizons and 2.5Y6/2 in depth.

Figure SI 2b :

 2b Figure SI 2b: Synthetic soil description from reference Ferralsol and for riverine soils in slash and burn and forest zones within the Lake Balbina area. Soil experiencing erosion processes is marked with an asterisk. Colors are only indicative in the figure. Following the Munsell color chart for soils red colors are 10YR4/6 to 10YR5/8 (Ferralsol), ochre colors are 5YR5/6 (Ferralsol) and 10YR6/6 (stagnic Acrisol) and colors for the albic Gleysol are 10YR3/2 (surface) and 10YR5/8 to 8/1.

Figure SI 3 :

 3 Figure SI 3: Triangular Fe-Si-Al chemical diagram showing a comparable chemical evolution towards the silicon end-member for the studied soils along the toposequences under forest cover (plinthic Ferralsol, plinthic Acrisol and haplic Gleysol) and pasture (colluvic Stagnosol, colluvic Gleysol) from the Rio Capim area.

Figure SI 4

 4 Figure SI 4: a) Iron isotope composition (in ‰) relative to IRMM-014 as a function of depth for the Ferralsol profiles from the Rio Capim (RC) and the Lake Balbina (LB) studied sites. Data are from Table1. b) Range of 57 Fe relative to IRMM-014 found in bulk Ferralsol samples from this study compared to comparable lateritic soils from the literature (from Cameroon,[START_REF] Poitrasson | Limited iron isotope variations in recent 1023 lateritic soils from Nsimi, Cameroon: Implications for the global Fe geochemical cycle[END_REF] China, Liu et al., 2014 and The Philippines, Li et al., 2017). The purple line denotes the continental crust mean value(Poitrasson, 2006).

Figure SI 5 :

 5 Figure SI 5: Range of 57 Fe relative to IRMM-014 found in bulk soil samples from Rio Capim area and lake Balbina area

Site description and sampling strategy 158 2.1 Soils from the Rio Capim area 159

	155	erosion, waterlogging) can leave an imprint
	156	on soil Fe isotopic compositions.
	157
		2.

Soils from the Rio Capim forest farm 366

	364	4. Results
	365	4.1. Mineralogical and pedological analyses
		4.1.1.
		57 Fe	57 Fe 54 Fe sample 57 Fe 54 Fe IRMM 014	1 1000
	362	.
	363

Table 1 :

 1 Iron and Zr concentrations and Fe isotopic compositions (d 57 Fe) for the soil samples from the Rio Capim and Balbina Lake area under forest and pasture.

	DF Fe

a Data from

[START_REF] Wedepohl | The composition of the continental crust[END_REF]

for Fe and Zr concentrations and

Poitrasson (2006)

for isotopic composition.

b Field description. c DF Fe is the Fe depletion factor relative to Zr in the soil profiles computed according to Eq. (

2

) in the text. δ 57 Fe (‰) 2SE d

Table

  Click here to access/download;Table;Akerman_et_al_revised_version_table1.xlsx

Table 2 :

 2 Classical soil parameters values for soil profiles from the Rio Capim and Balbina Lake sites Rio Capim forest Top of the hill soil profile forest (plinthic Ferralsol) Footslope soil profile slash and burn area (Stagnic Acrisol)

	Sample Origin	Depth (cm)	sample type b	[Corg.] (wt.%)	pH(H 2 O)	Clay (<2mm)	Fine silt (2-20µm)	Coarse silt (20-50µm)	Fine sand (50-200µm)	Coarse sand (200-2000µm)
		0-20	sombric A horizon	5.07	4.6	49	27.3	2.7	8.3	12.7
		100-170	plinthic Bv horizon	0.44	4.85	76.6	10.8	0.8	4.4	7.4
		170-350	plinthic Bv horizon	0.08	4.8	73.9	19.1	1.7	2.4	2.9
		350-400	ferric B horizon	0.07	5	72.4	23.7	1.6	1.2	1.1
		Downhill soil profile forest (plinthic Acrisol)
		0-15	sombric A horizon	0.99	4.52	25.9	5.7	2.4	25.9	40.1
		15-30	ferralic Bto horizon	0.8	4.82	30.9	5.1	3.8	24.5	35.7
		45-60	plinthic Bvo horizon	0.35	4.74	35.6	4.7	4.3	22.6	32.8
		75-90	ferric Bo horizon	0.35	4.54	43.7	4.7	3.6	19.3	28.7
		Footslope soil profile forest (haplic Gleysol)
		0-15	sandy material Ah horizon	0.76	3.99	9.3	1.6	0.8	21.2	67.1
		75-90	sandy material/El horizon with gleyic properties	0.36	4.8	10.3	1.8	1.5	18.3	68.1
		110-120	albic material/Er horizon with gleyic properties	0.13	4.81	4.9	1.7	0.4	8	85
		120-155	plinthic Bv horizon	0.18	4.5	18.3	5.3	3	11.5	61.9
	Rio Capim pasture	Downhill soil profile pasture (colluvic Stagnosol)
		0-10	Ag horizon with stagnic properties	1.29	4.24	31.2	6.5	4.8	22.7	34.8
		40-120	Bg horizon with stagnic properties	0.35	4.16	40.5	6	6.1	23.8	23.6
		Valley soil profile pasture (colluvic Gleysol)
		0-15	Ag horizon with stagnic properties	1.35	4.92	35.3	7.3	2.8	22	32.6
		30-45	Bl horizon with capillary fringe molting	1.16	4.31	31.1	9.5	4	23.5	31.9
		45-75	Br horizon with gleyic properties	1.95	4.3	30.6	9.8	3.9	22.7	33
		110-120	Br horizon with gleyic properties	0.69	4.23	47.1	6.4	7.2	19.4	19.9
	Lake Balbina forest	Top of the hill soil profile forest (Ferralsol)
		300	ferralic Bo horizon	0.39	5.41	83.9	6.9	1.9	4.2	3.1
		800	alloterite	0.08	5.89	32	47	9.4	5.5	6.1
		3000	isalterite	0.08	5.93	17.3	58.5	15	7.6	1.6
		Footslope soil profile forest (albic Gleysol)
		0-30	sandy Ah horizon	1.46	5.32	1.6	2.5	2.5	19	74.4
		30-60	sandy material/El horizon with gleyic properties	1.32	5.65	1.1	2.5	1.7	22.7	72
		60-85	albic material/Er horizon with gleyic properties	0.26	5.9	0.3	2.2	1.7	14.4	81.4
	Lake Balbina slash and burn area
		0-10	A/E horizon with coal artifact	1.11	6.35	12.3	4.4	1.7	24.4	57.2
		50-65	plinthic Bv horizon	0.53	4.86	24.9	7.3	3.8	28.2	35.8
		80-95	Bg horizon with stagnic properties	0.27	4.61	24.7	7.3	2.8	26	39.2
		110-120	albic material with gleyic properties	0.08	4.62	13.7	10.9	9.9	17.8	47.7

Table

  Click here to access/download;Table;Akerman_et_al_revised_tables_supplementary_information.x

	Supplementary

Table 1 :

 1 Mineralogical composition of the studied soil samples from the Rio Capim and Lake Balbina sites determined by X-Ray diffraction analysis. , goet=goethite, ferr= ferrhydrite, hem=hematite, gibb=gibbsite, fd= feldspath, ill= illite. The main mineral phases are reported in boldface, trace minerals are within brackets.

	Rio Capim forest Rio Capim pasture Lake Balbina forest Lake Balbina slash and burn area qz=quartz, kaol=kaoliniteSample Origin	Top of the hill soil profile forest (plinthic Ferralsol) 0-20 qz -kaol 100-170 qz -kaol -hem -gibb -goet -magh or ferr 170-350 (qz) -kaol -hem -gibb -goet -magh or ferr -(Fd) 350-400 (qz) -kaol -hem -gibb -goet -magh or ferr -(Fd) Downhill soil profile forest (plinthic Acrisol) 0-15 qz -kaol -goet 15-30 qz -kaol -hem -goet -ferr 45-60 qz -kaol -hem -goet 75-90 qz -kaol -hem -goet -ferr Footslope soil profile forest (haplic Gleysol) 0-15 qz -kaol 75-90 qz -kaol 110-120 qz -kaol 120-155 qz -kaol -hem -goet -gibb -ferr -(ill) -(fd) Downhill soil profile pasture (colluvic Stagnosol) 0-10 qz -kaol -goet 40-120 qz -kaol -hem -goet -gibb -ferr Valley soil profile pasture (colluvic Gleysol) 0-15 qz -kaol -hem -goet -ferr 30-45 qz -kaol -hem -goet -ferr 45-75 qz -kaol -hem -goet -ferr 110-120 qz -kaol -hem -gibb -goet -ferr Top of the hill soil profile forest (Ferralsol) 300 qz -kaol -gibb -goet -hem -(ill) 800 qz -kaol -gibb -goet -hem -ill 3000 qz -kaol -goet -hem -ill Footslope soil profile forest (albic Gleysol) 0-30 qz -kaol -(gibb) -(fd) 30-60 qz -kaol -(gibb) -(fd) 60-85 qz -kaol -(gibb) -(fd) Footslope soil profile slash and burn area (Stagnic Acrisol) 0-10 qz -(kaol) -(gibb) -(fd) 50-65 qz -kaol -gibb -(fd) 80-95 qz -kaol -gibb -(fd) -(ill) 110-120 qz -(kaol) -(gibb) -fd -(ill) Depth (cm) mineralogy < 2mm bulk fraction	kaolinite -gibbsite kaolinite -gibbsite kaolinite -gibbsite kaolinite -gibbsite not analyzed not analyzed not analyzed not analyzed kaolinite kaolinite kaolinite kaolinite -illite not analyzed not analyzed Kaolinite -gibbsite Kaolinite -gibbsite Kaolinite -gibbsite Kaolinite -gibbsite not analyzed not analyzed not analyzed not analyzed not analyzed not analyzed not analyzed not analyzed not analyzed not analyzed mineralogy < 2µm clay fraction

Acknowledgements 755

The CIKEL-Brasil Verde group and the IFT (Instituto Floresta Tropical) are thanked 756

for their permission to work on their Rio Capim watershed and their help during the sampling 757 campaigns. We thank Plinio Sist, from CIRAD, for initial guidance and advice in the Cikel 758

Supplementary information Figures