François De Vleeschouwer
email: fdevleeschouwer@student.ulg.ac.be

Laëtitia Gérard

Catherine Goormaghtigh

Nadine Mattielli

Gaël Le Roux

Nathalie Fagel

Atmospheric lead and heavy metal pollution records from a Belgian peat bog spanning the last two millenia: Human impact on a regional to global scale

Keywords: Peat, Geochemistry, Belgium, Pollution, Last two millennia

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Introduction

Centuries of atmospheric pollution caused by industrial activities, coal burning, and petroleum use has left an indelible mark in Europe's soils in the form of heavy metals. The fallout of these anthropogenic aerosols mix with natural aerosols, for example from rock weathering become incorporated into the soils where they are preserved. Over time the release of these heavy metals including lead, zinc, copper, and nickel, which well exceed natural levels [START_REF] Boyd | Ecology of metal hyperaccumulation[END_REF], can contaminate the soil and surrounding land.

Peat bogs are particularly sensitive archives of human activities and more specifically of atmospheric pollution (e.g. [START_REF] Shotyk | Two thousand years of atmospheric arsenic, antimony, and lead deposition recorded in an ombrotrophic peat profile, Jura Moutains, Switzerland[END_REF][START_REF] Shotyk | Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14C "bomb pulse curve[END_REF][START_REF] Weiss | The geochemistry of major and selected trace elements in a forested peat bog, Kalimantan, SE Asia, and its implications for past atmospheric dust deposition[END_REF][START_REF] Martinez-Cortizas | Atmospheric Pb deposition in Spain during the last 4600 years recorded by two ombrotrophic peat bogs and implications for the use of peat as archives[END_REF][START_REF] West | Heavy metals in Holocene peats from South West England: detecting mining impacts and atmospheric pollution[END_REF]Fig. 1. A. General map showing the Roman road system (redrawn after [START_REF] Corbiau | Les voies romaines: des performances techniques au service de la politique[END_REF]. The actual Ruhr-Eifel Region is also reported. Plain lines: Roman road system. Black circles: principal Roman cities and village (size of the circles gives an idea of the relative importance of each city). Grey lines: river system. B. Location map of the Hautes Fagnes Plateau and its surroundings. Dashed area: alluvial mounds remaining from gold prospecting, 14 the open-air gold mine (undated); 3. sites with roman graves; 4. site with Roman coins. Plain lines: Roman road system. Black circles: principal roman cities and village (size of the circles gives an idea of the relative importance of each city). Grey lines: river system. Pb-Zn ores: lead-zinc ore deposit (after [START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF]. C. Radar derived peat thickness of the Misten bog (modified after Wastiaux and Schumacker, 2003). Altitude lines are 5 m distant in altitude. The different dotted lines are forestry ways. Coring location is reported by the open circle. [START_REF] Mighall | Geochemical evidence of atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmystwyth, mid-Wales, UK[END_REF][START_REF] Novak | Origin of lead in eight Central European peat bogs determined from isotope ratios, strengths, and operation times of regional pollution sources[END_REF][START_REF] Roux | Identifying the sources and timing of ancient and medieval atmospheric lead pollution in England using a peat profile from Lindow bog, Manchester[END_REF]. Most importantly, peat is particularly effective at preserving atmospheric metal deposition in the form of lead (e.g. [START_REF] Shotyk | The chronology of anthropogenic, atmospheric Pb deposition recorded by peat cores in three minerogenic peat deposits from Switzerland[END_REF][START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14C yr BP from a peat bog, Jura mountains, Switzerland[END_REF][START_REF] Shotyk | Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14C "bomb pulse curve[END_REF][START_REF] Vile | Mobility of Pb in Sphagnum-derived peat[END_REF][START_REF] Weiss | Sphagnum mosses as archives of recent and past atmospheric lead deposition in Switzerland[END_REF], copper [START_REF] Rausch | Porewater evidence of metal (Cu, Ni, Co, Zn, Cd) mobilization in an acidified, ombrotrophic peat bog impacted by a smelter, Harjavalta, Finland[END_REF][START_REF] Mighall | Geochemical evidence of atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmystwyth, mid-Wales, UK[END_REF], nickel [START_REF] Krachler | Atmospheric deposition of V, Cr, and Ni since the Late Glacial: effects of climatic cycles, human impacts, and comparison with crustal abundances[END_REF] and zinc [START_REF] Rausch | Porewater evidence of metal (Cu, Ni, Co, Zn, Cd) mobilization in an acidified, ombrotrophic peat bog impacted by a smelter, Harjavalta, Finland[END_REF][START_REF] Twardowska | Adsorption of zinc onto peat from peatlands of Poland and Izrael[END_REF]. Recent research has shown that ancient Pb contamination in peat can be traced by Pb isotopes and fingerprinted to a local or regional origin (e.g. [START_REF] Kempter | The local nature of anthropogenic emission sources on the elemental content of nearby ombrotrophic peat bogs, Vulkaneifel, Germany[END_REF][START_REF] Monna | Pb isotopes as a reliable marker of early mining and smelting in the Northern Harz province (Lower Saxony, Germany)[END_REF][START_REF] Roux | Identifying the sources and timing of ancient and medieval atmospheric lead pollution in England using a peat profile from Lindow bog, Manchester[END_REF][START_REF] Kylander | Refining the pre-industrial atmospheric Pb isotope evolution curve in Europe using an 8000 year old peat core from NW Spain[END_REF]. The more recent atmospheric Pb pollution (i.e. coal burning and leaded gasoline) is shown to be more regional or even continental [START_REF] Dunlap | A synthesis of lead isotopes in two millennia of European air[END_REF][START_REF] Véron | Isotopic evidence of pollutant lead sources in Northwestern France[END_REF][START_REF] Roux | Recent atmospheric Pb deposition at a rural site in southern Germany assessed using a peat core and snowpack, and comparison with other archives[END_REF][START_REF] Shotyk | Accumulation rates and predominant atmospheric sources of natural and anthropogenic Hg and Pb on the Faroe Islands[END_REF].

The Hautes Fagnes Plateau (SE Belgium), the largest peatland area in Belgium, is located in an intermediate position in Western Europe (surrounded by France, U.K. and Germany). The Hautes Fagnes Plateau is also situated to the South of Pb-Zn ore deposits (extracted between the 19th and 20th centuries; [START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF] and nearby the German border which is 300 km from the Region of the Ruhr-Eifel industrial area. In more ancient times the Hautes Fagnes plateau was surrounded by several Roman sites. On the site several archaeological (Cauuet, 2005;[START_REF] Renson | Pourquoi une route pavée (via Mansuerisca ?) au travers des tourbières ? Enfin une hypothèse …qui tient la route[END_REF][START_REF] Renson | Early Pb-Zn mining and transport revealed by elemental and lead isotopes geochemistry nearby a Late Roman to Merovingian cobbled road (Belgium). A direct application of geochemistry to archaeology[END_REF][START_REF] Remy | Monographie archéologique[END_REF] and historical (Graillet, 1998) investigations support Roman occupation and ore mining in the area (see Sections 4.1 and 4.2).

In this paper, we present the elemental records of Si, Ti, Sr, Pb, Cu, Zn and Ni for the top meter of a peat core from the Misten Bog from the Hautes Fagnes Plateau. Si and Ti were used as evidence for periods of enhanced atmospheric particle and Sr is used to demonstrate the ombrotrophic character of the bog. Ti is also used as a reference element for the calculation of enrichment factors. A Pb isotopic study is also presented in order to decipher from the possible lead pollution sources. The main aim of this study was to use the results of a high resolution investigation of heavy metal pollution in a peat core from Misten Bog to reconstruct the pollution history of the Hautes Fagnes and in turn, contribute to the pollution history of Europe.

Material and methods

Site description

The Misten bog is located in the Northern part of the Hautes Fagnes Plateau, 5 km from the German border (Fig. 1A). It is a law-protected raised bog accumulating more than 8 m of peat (Wastiaux and Schumacker, 2003), dating back to 9000 years ago [START_REF] Persh | Zur postglazialen Wald-und Moorentwicklung im Hohen Venn[END_REF][START_REF] Gérard | Suivi des apports atmosphériques en plomb au cours de l'Holocène[END_REF]. The first meter of the Misten bog is composed of young Sphagnum imbricatum peat with Eriophorum fragments. Between 30 and 20 cm, sphagnum species also include aquatic species like Sphagnum cuspidata [START_REF] Persh | Zur postglazialen Wald-und Moorentwicklung im Hohen Venn[END_REF].

Sampling and sample preparation

In summer 2003, a 1 m long, 10 cm diameter core was retrieved using a Belorussian-type stainless steel Dcorer [START_REF] Belokopytov | Giktorf's peat borers[END_REF][START_REF] Jowsey | An improved peat sampler[END_REF]. The inner parts of the corer are coated with Teflon® adhesive to avoid metal contamination by the coring device. Cores were bagged into PVC tubes and wrapped in plastic. The 1 m core was cut into 1 cm slices in the laboratory using clean plastic tools. Each sample was dried (105 °C, 12 h) and then ground twice: (1) manually using an agate mortar; (2) mechanically in agate jars pulverisette (400 rpm for 1 h). The mortar and jars were cleaned between each samples using tap and then mQ water, and finally air-dried.

XRF analyses

An average of 3.5 g of peat powder was pressed into pellets at 200 kN/cm 2 . Pellets were analyzed using ARL 9400 XP XRF spectrometer (University of Liège) for the following elements: Si, Ti, Sr, Ni, Zn, Cu and Pb. Calibrations were made using international standards: coals (CLB-1, NIST 1632b et NIST 1635), lichen (BCR-482), pond sediments (NIES-2), tea leaves (NIES-7), vehicle exhaust particulates (NIES-8) and sediments (JSD-2, JSD3, SGR). Reproducibility, accuracy and detection limits are summarized in Table 1. Sediments and vehicle exhaust particle standards were used in order to extend the concentration range to higher values often occurring in highly polluted recent peat Two samples from the bottom of the bog (660 and 678 cm depth, Table 2) were analyzed to establish natural background concentrations. As their elemental content could be expected to be very low and thus under XRF detection limits, these two samples were acid digested in clean air cabinets (University of Liège). Acid digestions consisted of a two-step dissolution in closed Savilex® beakers: (1) addition of H 2 O 2 30% p.a. and HNO 3 65% cc. sub. in a proportion of 3:1 for organic matrix dissolution, and (2) addition of HF suprapur (Merck) + HNO 3 65% cc. sub. of 1:6 for mineral matrix dissolution. The beakers were placed on a hot plate at 130 °C for 4 days. After drying, 0.5N HNO cc. sub. was added to obtain the solution. Analyses were performed on ICP-AES (IRIS Advantage) at the MRAC-Tervuren (Belgium). Calibrations were made with In-Ru-Re-Bi internal standards (10 and 20 ppb) and two international reference materials: CRM-100 beech leaves (EU certificated) and granite GA [START_REF] Govindaraju | Rapport (1966-1976) sur les éléments en trace dans trois roches standardes géochimiques du CRPG: basalte BR et granites GA et GH[END_REF]. Accuracy was between 1-11% for major elements and 1-2% for trace metals. Detection limits were lower than 1 ppm for major elements. Detection limits for trace metals and other trace elements were lower than 1 and 10 ppb, respectively.

Acid digestion for lead isotope analyses

All the samples were processed in clean air cabinets (University of Liège and University of Brussels, Belgium). 50 mg of original dry powder was aciddigested as previously described at Section 2.4, to which was added a further step. After drying, 6 N HCl was added and the perfectly pure solution obtained was slowly evaporated. The dried residues were dissolved in HBr 6% cc. sub. prior to the chromatographic separation.

Lead chemistry was performed by a single passage through anionic exchange micro-columns following the protocol of [START_REF] Weis | Highprecision Pb-Sr-Nd-Hf isotopic characterization of USGS BHVO-1 and BHVO-2 reference materials: comparison of first and second generation samples[END_REF]. Distilled (HNO 3 ) or subboiled (HCl, HBr) acids were used during the chemical treatment. Total procedural Pb blanks ranged from 0.1 ng to 0.4 ng and were negligible regarding Pb contents in 50 mg of sample (615 ng at 28.5 cm b Misten content b 4745 ng at 3.5 cm).

Lead isotopic ratios were measured on a Nu Instruments Multi-Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS) at University of Brussels during four analysis sessions of 5 days in total. Radionuclides ( 210 Pb, 214 Pb) were measured using low background Gamma Spectrometry (GCW4028, HPGe, Canberra) in Heidelberg. The maximum depth at which unsupported 210 Pb could be detected is 10 cm. The agedepth relationship was calculated using the CRS model [START_REF] Appleby | Chronostratigraphic techniques in recent sediments[END_REF]. Errors on 210 Pb age dating and peat accumulation rate were calculated by propagation of errors following the method of Appleby (op. cit.). These errors were rough estimations since the peat accumulation rate in the recent samples was very low. Results of these analyses are summarized in Table 4.

Calculation of enrichment factor

Lead Enrichment factor (Pb E.F.) was calculated in order to decipher anthropogenic lead inputs from lead of natural (i.e. crustal) origin. In line with previous similar geochemical investigations in peat (e.g. [START_REF] Shotyk | Geochemistry of the peat bog at Etang de la Gruère, Jura Mountains, Switzerland, and its record of atmospheric Pb and lithogenic trace metals (Sc, Ti, Y, Zr, and REE) since 12,370 14C yr BP[END_REF][START_REF] Kempter | Der Verlauf des anthropogenen elementeintrags in Regenwassermoore des westlichen Mitteleuropas während des jüngeren Holozäns[END_REF], Ti was used as a reference element, because its mineral phases (e.g. titanite, ilmenite or titano-magnetite) are resistant to alteration [START_REF] Wedepohl | Handbook of geochemistry[END_REF][START_REF] Nesbitt | Weathering of granodioritic crust, longterm storage of elements in weathering profiles, and petrogenesis of siliciclastic sediments[END_REF]. Lead enrichment factor was obtained as follows: Pb E.

Results

Elemental content

Elemental concentrations and lead E.F. of Misten bog are represented along depth in Fig. 2. For graphical presentation purposes, samples from levels 660 cm and 678 cm are not shown.

Sr

Low Sr concentrations ([Sr] b 20 ppm) were expected and are typical of peat from ombrotrophic bog (e.g. [START_REF] Shotyk | The chronology of anthropogenic, atmospheric Pb deposition recorded by peat cores in three minerogenic peat deposits from Switzerland[END_REF]. The two samples (660 and 678 cm depth) analyzed for natural background Sr gave a mean concentration of 46 ppm, a doubling concentration from the samples above the top meter. This higher concentration reflects the minerotrophic character of the peat, starting to accumulate just above the bottom sediment (loess and quartzite fragments). (Graillet, 1998;[START_REF] Remy | Monographie archéologique[END_REF]. These people were the first important farmers and land clearers in the area, but their agricultural activities remained small compared to those of the following Roman period [START_REF] Ferdière | Les campagnes en Gaule romaine.T.1. Les hommes et l'environnement en Gaule rurale[END_REF]. They were however known their mining activities. They developed gold extraction from, river overbank, river sediments, and arkose mines for making grinds (Cauuet, 2005;[START_REF] Remy | Monographie archéologique[END_REF]Graillet, 1998). Archeological evidence of early gold mining in Southeast Belgium are attested by more than 1000 mining waste mounds (fluvial deposits) dumped near the source, mainly rivers and streams (Cauuet, 2005 and reference therein). Two of these mounds are found overlying peat. These provide respective radiocarbon age ranges of 120 B.C.-140 A.D. [START_REF] Dumont | Première datation d'un tertre d'orpaillage en Ardenne[END_REF][START_REF] Gilot | Index général des dates Lv. Laboratoire du carbone 14 de[END_REF]400 B.C.-200 B.C. (Dumont, 1980;[START_REF] Gilot | Index général des dates Lv. Laboratoire du carbone 14 de[END_REF]. Though it would be beneficial to confirm these data with further dates and field investigations, there are in good agreement with the Second Iron age and the Early Roman Empire.

Romans then extended land clearance for pasture and cultivation. Further evidence for pasture are shown in several pollen diagrams from peat sequences from the Hautes Fagnes. Indeed, Plantago lanceolata (considered as the best indication for pasture) made a first occurence during the Neolithic, becoming more abundant during the Gallo-Roman period [START_REF] Damblon | Les dépôts tourbeux et l'histoire de la végétation sur le plateau des Hautes-Fagnes (Belgique)[END_REF]. Cereal pollens indicative of increase anthropogenic activities were also found in significant amounts in the Hautes Fagnes representative of the Roman period [START_REF] Damblon | Les dépôts tourbeux et l'histoire de la végétation sur le plateau des Hautes-Fagnes (Belgique)[END_REF][START_REF] Gotjé | A palynological study of a Holocene deposit from Gran Bongard (Hautes-Fagnes, Belgium)[END_REF]. Additional archaeological remnants from the Roman period are prolific in Belgium (Fig. 1B). Evidence of early mining activities include an open-air gold and arkose mine with grind remnants (Fig. 1B.2), and a mine gallery (Fig. 1B.3). (Cauuet, 2005;[START_REF] Remy | Monographie archéologique[END_REF]. The open air mine is still not well dated and requires further archaeological investigation. Actually, the only link to the Roman period is made by field comparison with similar sites in France (Cauuet, 2005). In the mine gallery, a piece of wood used once used for propping up the mine shaft was dated to an age interval of 240 A.D.-440 A.D. (Cauuet, 2005) which corresponds to the Late Roman Empire period. However, as no evident archaeological artifacts of Roman facture have been found in this gallery, the age of gold extraction should be taken with caution. However, this piece of wood could represent later re-occupation of the mine. No further archaeological artifact of Roman age have been found to support this. Therefore the exact age of the extraction is still uncertain. There is no further evidence for metal mining or smelting Romans in the area. Moreover, from the 4th century A.D., a decline of the agricultural activities is observed in Belgium [START_REF] Brulet | La gaule septentrionale au Bas-Empire: occupation du sol et défense du territoire dans l'arrière pays du limes aux IVè et Vè siècles[END_REF]. The Early Middle Ages were characterized by a more extended extractive industry and Pb-Zn ore extraction occurred [START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF][START_REF] Renson | Pourquoi une route pavée (via Mansuerisca ?) au travers des tourbières ? Enfin une hypothèse …qui tient la route[END_REF]; see also Section 4.2.1). Further Si and Ti inputs to the bog are due to the extensive clearance and mining exploitation of sedimentary rocks, associated with the second industrial revolution.

Chronological control

The chronology of the core is based on dates obtained from radiocarbon dating, palynology and 210 Pb. Only one sample at 53.5 cm has been 14 Cdated. This gave an age of 326 ± 76 cal A.D. (Late Roman Empire). The results of pollen profiles from previous studies in the same bog were used to delineate critical periods of human activities [START_REF] Hindryckx | Evolution régressive récente de la végétation des tourbières hautes à sphaignes en Haute Ardenne (Hautes-Fagnes[END_REF][START_REF] Hindryckx | L'altération des bords de la tourbière active du Misten par l'exploitation de la tourbe pourrait dater du début du 14e siècle[END_REF][START_REF] Gérard | Suivi des apports atmosphériques en plomb au cours de l'Holocène[END_REF][START_REF] Goormaghtigh | Suivi des apports atmosphériques en métaux lourds durant la période Subatlantique (depuis 850 ans), dans un milieu continental pollué: enregistrement de deux tourboères des Hautes Fagnes[END_REF]. All cores used for palynology were retrieved within 100 m of the core site used in this study, where peat thickness extended more than 6.5 m (see Fig. 1). In all pollen diagrams used, the top meter is representative of the young Subatlanticum Zone XI (as defined by [START_REF] Firbas | Vegetationsentwicklung unnd Klimawandel in der mitteleuropäischen Spät-und Nacheiszeit[END_REF], covering roughly the last 2000 years. This zone is characterized by abundant pollen maxima of Fagus (beech tree) and significant presence of Carpinus (hornbeam) (N 1-2%). These palynological characteristics have been controlled in the present core by [START_REF] Gérard | Suivi des apports atmosphériques en plomb au cours de l'Holocène[END_REF] and [START_REF] Goormaghtigh | Suivi des apports atmosphériques en métaux lourds durant la période Subatlantique (depuis 850 ans), dans un milieu continental pollué: enregistrement de deux tourboères des Hautes Fagnes[END_REF]. Coincidence of abundant Fagus and start of Carpinus has been recently dated at 150 A.D. by [START_REF] Streel | Palynological and geochemical data in peat sediments at the side of an old (Roman to/or Merovingian) paved road in the Hautes-Fagnes[END_REF] in a peat bog a few kilometers to the South-East of the Misten bog. In the Misten bog, [START_REF] Hindryckx | L'altération des bords de la tourbière active du Misten par l'exploitation de la tourbe pourrait dater du début du 14e siècle[END_REF] dated the third peak of Fagus at around 1140 ± 125 A.D. This third maximum of Fagus is found at 30 cm depth in the present core [START_REF] Goormaghtigh | Suivi des apports atmosphériques en métaux lourds durant la période Subatlantique (depuis 850 ans), dans un milieu continental pollué: enregistrement de deux tourboères des Hautes Fagnes[END_REF], providing a chronological indicator for the Middle Ages.

With the date of 150 A.D. around 95 cm depth [START_REF] Streel | Palynological and geochemical data in peat sediments at the side of an old (Roman to/or Merovingian) paved road in the Hautes-Fagnes[END_REF], our new date of 326 ± 76 A.D. at 53.5 cm, the date of 1140 ± 125 A.D. [START_REF] Hindryckx | L'altération des bords de la tourbière active du Misten par l'exploitation de la tourbe pourrait dater du début du 14e siècle[END_REF] around 30 cm depth, and finally our 210 Pb age model for the subsurface, a rather accurate age-depth relationship can be accepted. (2002). Belgian ore data from [START_REF] Cauet | Genetic study of Belgian lead zinc mineralizations in carbonate environments through lead isotope geochemistry[END_REF] and [START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF]. Data from archeological site from [START_REF] Renson | Early Pb-Zn mining and transport revealed by elemental and lead isotopes geochemistry nearby a Late Roman to Merovingian cobbled road (Belgium). A direct application of geochemistry to archaeology[END_REF] are also reported. Belgian pre-industrial sediment from Sonke et al. (op. cit.). Upper continental crust field from [START_REF] Millot | Lead isotopic systematics of major river sediments: a new estimate of the Pb isotopic composition of the Upper Continental Crust[END_REF], [START_REF] Hemming | Pb isotope compositions of modern deep sea turbidites[END_REF], [START_REF] Grousset | Transient Pb isotopic signatures in the Western-European atmosphere[END_REF] and [START_REF] Asmeron | The Pb isotopic evolution of the Earth: inferences from river water suspended loads[END_REF]. Gasoline from The Netherlands from [START_REF] Hopper | Regional source discrimination of atmospheric aerosols in Europe using the isotopic composition of lead[END_REF].

Can Si and Ti measurements provide evidence for Roman activities?

Si and Ti increase significantly between 90 and 55 cm depth. It has already been shown that land clearance, farming, and following erosion could play a role in Si and Ti inputs to a peat bog [START_REF] Holynska | Characterisation of 210Pb dated peat core by various X-ray fluorescence techniques[END_REF][START_REF] Hölzer | Silicon and titanium in peat profiles as indicators of human impacts[END_REF][START_REF] Görres | The Pb, Br, and Ti content in peat bogs as indicator for recent and past depositions[END_REF]. An increase in Si and Ti often reflects an increase in soil dust inputs (e.g. [START_REF] Holynska | Characterisation of 210Pb dated peat core by various X-ray fluorescence techniques[END_REF][START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14C yr BP from a peat bog, Jura mountains, Switzerland[END_REF][START_REF] Görres | The Pb, Br, and Ti content in peat bogs as indicator for recent and past depositions[END_REF]. In support for this in our core, the cereal pollen content increase between 80 and 60 cm [START_REF] Goormaghtigh | Suivi des apports atmosphériques en métaux lourds durant la période Subatlantique (depuis 850 ans), dans un milieu continental pollué: enregistrement de deux tourboères des Hautes Fagnes[END_REF], favoring the hypothesis of cultivation. Arkose mining and gold prospecting could also have played a role. However, with little known about the age of these mines, we conclude that it is most likely that the primary input of Si and Ti-bearing particle are due to extensive Roman agricultural activities.

Origin of heavy metals through the last 2000 years

The origin of lead and associated heavy metals can be established both by 208 Pb/ 207 Pb vs. 206 Pb/ 207 Pb diagram and Pb E.F. coupled with 206 Pb/ 207 Pb isotopic ratio (Fig. 5). The principle being the isotopic signature changes with origin of particles form the upper continental crust, through Belgian ores and toward a signature of modern Benelux aerosols (see Fig. 4 for references). The lowermost samples (660 cm and 678 cm) show good agreement with upper continental crust values [START_REF] Millot | Lead isotopic systematics of major river sediments: a new estimate of the Pb isotopic composition of the Upper Continental Crust[END_REF][START_REF] Hemming | Pb isotope compositions of modern deep sea turbidites[END_REF][START_REF] Grousset | Transient Pb isotopic signatures in the Western-European atmosphere[END_REF][START_REF] Asmeron | The Pb isotopic evolution of the Earth: inferences from river water suspended loads[END_REF] and Belgian pre-industrial background sediments from [START_REF] Sonke | A chemical and mineralogical reconstruction of Zn-smelter emissions in the Kempen region (Belgium), based on organic pool sediment cores[END_REF]. However, the least radiogenic values of 208 Pb/ 207 Pb and 206 Pb/ 207 Pb ratios are still far from The Netherlands gasoline (similar to Belgian gasoline) values ( 208 Pb/ 206 Pb = 2.28 ± 0.013, 206 Pb/ 207 Pb = 1.062 ± 0.019) reported by [START_REF] Hopper | Regional source discrimination of atmospheric aerosols in Europe using the isotopic composition of lead[END_REF]. It is known that Romans mined and extracted a wide range of ores all over NW Europe and around the Mediterranean Sea, increasing significantly the amount of aerosol which has a wide range of Pb-isotopic composition particles in the air. However, in the Misten bog, it seems that a more local influence has been recorded. Indeed, the isotopic values of samples from 98.5 cm to 50 cm depth show good agreement with the isotopic field of the Belgian Pb-Zn ores (Fig. 4).

In Belgium, there is no historical, archaeological or field evidence for Roman Pb-Zn mining. However, [START_REF] Renson | Apport de la géochimie élémentaire et des isotopes du plomb à l'étude d'un site d'intérêt archéologique situé dans une tourbière des Hautes Fagnes[END_REF] and [START_REF] Renson | Early Pb-Zn mining and transport revealed by elemental and lead isotopes geochemistry nearby a Late Roman to Merovingian cobbled road (Belgium). A direct application of geochemistry to archaeology[END_REF], in their study on a peat column taken nearby an archaeological site constituted by a Roman to Merovingian road in the Hautes Fagnes, found and dated very high Zn concentrations (up to 1000 ppm) associated with peaks in lead concentration (up to 80 ppm). Such high concentration clearly reflect a local pollution linked to the road (Renson, 2005). Moreover, the lead isotopic composition ( 208 Pb/ 207 Pb ∼ 1.17-1.18, 208 Pb/ 206 Pb ∼ 2.08-2.10) of the Pb and Zn-contaminated levels found by [START_REF] Renson | Apport de la géochimie élémentaire et des isotopes du plomb à l'étude d'un site d'intérêt archéologique situé dans une tourbière des Hautes Fagnes[END_REF] and [START_REF] Renson | Early Pb-Zn mining and transport revealed by elemental and lead isotopes geochemistry nearby a Late Roman to Merovingian cobbled road (Belgium). A direct application of geochemistry to archaeology[END_REF] are in very good agreement with isotopic composition of Pb-Zn ores located 15 km northwards to the Hautes Fagnes Plateau. These new data suggests that local Pb-Zn ores from the Verviers area (for location see Fig. 1.) were extracted and transported through the Hautes Fagnes Plateau from around A.D. 150 [START_REF] Renson | Apport de la géochimie élémentaire et des isotopes du plomb à l'étude d'un site d'intérêt archéologique situé dans une tourbière des Hautes Fagnes[END_REF].

In conclusion, although there is no field archaeological evidence for Roman lead-zinc ore mining in Belgium, this study from this study and from [START_REF] Renson | Apport de la géochimie élémentaire et des isotopes du plomb à l'étude d'un site d'intérêt archéologique situé dans une tourbière des Hautes Fagnes[END_REF] and [START_REF] Renson | Early Pb-Zn mining and transport revealed by elemental and lead isotopes geochemistry nearby a Late Roman to Merovingian cobbled road (Belgium). A direct application of geochemistry to archaeology[END_REF] show significant support for mining of Pb-Zn ores in Belgium during the Roman Empire.

Late Roman Empire and Early Middle Ages

Following the Roman Empire, the next phase of change is characterized by a decrease in Pb enrichment factors (∼ 40 cm-25 cm depth), reflecting the decline of the Roman mining activities. Minimum Pb E.F. values (less than 20) are observed between depth of 35 cm and 25 cm. This Early Middle Ages period has already been well documented in other European peat bogs (e.g. Le [START_REF] Roux | Identifying the sources and timing of ancient and medieval atmospheric lead pollution in England using a peat profile from Lindow bog, Manchester[END_REF]. Its main geochemical characteristic in peat bogs is a wide range of Pb isotopic composition, but low Pb E.F., as various ores were mined across Europe, but in smaller quantities, as suggested in the estimation from [START_REF] Settle | Lead in Albacore: guide to lead pollution in Americans[END_REF] and the data from [START_REF] Hong | Greenland ice evidence of hemispheric lead pollution two millenia ago by greek and Romand civilizations[END_REF]. Here however, although mining industries were growing up across Europe, the most probable source of anthropogenic dust is the Belgian ore bodies (Fig. 4

above).

This period is followed by the Classic and Late Middle Ages (i.e. 900 A.D. to 1450 A.D.), and the Early modern period (i.e. 1450A.D. to 1700A.D.). This time period is represented by Pb isotopic signatures which also match well with Belgian ores. The extraction of these ores are well documented in historical texts back to Middle Ages [START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF], adding a new source for Pb inputs to Belgian bogs.

Industrial revolution

Between 10 cm (1835 A.D.) and 2.5 cm (1964 A.D.), Pb E.F. increase in parallel with a small decrease of 206 Pb/ 207 Pb ratio. During this period enhanced local Pb-Zn ore processing (∼ 1840 A.D., [START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF] together with coal mining and burning [START_REF] Gaier | Huit siècles de houillerie liégeoise. Histoire des hommes et du charbon à Liège[END_REF], and the introduction of leaded gasoline, allow the addition of tremendous amounts of anthropogenic aerosols in the atmosphere. Around 1975, the estimated anthropogenic Pb was about 4240 metric tons per annum (p.a.) in Belgium, 2263 metric tons p.a. in The Netherlands, 18,860 metric tons p.a. in France, and 16,500 metric tons p.a. in nearby Germany (cumulated FDR and DDR, von Storch et al., 2003). This strong increase in atmospheric pollution is recorded in the Misten bog by a marked increase in Pb from 89.1 ppm at 10.5 cm to 949 ppm at 3.5 cm depth. This is followed by related heavy metals concentrations (from 10.5 cm to 3.5 cm depth, Cu from 1.8 ppm to 18.7 ppm, Ni from bD.L. to 22.8 ppm, Zn from 91.6 ppm to 214 ppm), together with an increase of Pb E.F. (from 39 to 218) and shifts in lead isotopic ratios ( 206 Pb/ 207 Pb 15 cm = 1.1666, then 206 Pb/ 207 Pb 2 cm = 1.1532). Reduced radiogenic 206 Pb/ 207 Pb values do not, however, predate the maximum Pb concentrations and Pb E.F. as previously reported in peat cores from Denmark, Greenland [START_REF] Shotyk | Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14C "bomb pulse curve[END_REF] and the Faeroe Islands [START_REF] Shotyk | Accumulation rates and predominant atmospheric sources of natural and anthropogenic Hg and Pb on the Faroe Islands[END_REF]. [START_REF] Shotyk | Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14C "bomb pulse curve[END_REF] argued that in Denmark or Greenland, this shift is linked to the predominance of coal burning more than the total Pb pollution. It is therefore likely that, in the Hautes Fagnes, leaded gasoline accounts at least as much as the other Pb sources (industries and coal burning) for the Pb input in this area. This is further corroborated by observations from von [START_REF] Von Storch | Four decades of gasoline lead emissions and control policies in Europe: a retrospective assessment[END_REF], who reported that among the diverse anthropogenic Pb sources, leaded gasoline is the main one, increasing from its introduction (1931 A.D.) and reaching a maximum in the early 1970's. During this period, leaded gasoline accounted for 75% of the total atmospheric lead emission across Europe. In the same study, decadal estimations of anthropogenic Pb emissions over the last 50 years show a maximum around 1965, which also agrees with our findings.

Unleaded gasoline

The phasing out of lead in gasoline began in 1972 in Europe. Indeed, during the European oil crisis, Germany began to adopt policies to reduce lead content of gasoline. This was followed by the first EU regulation (1981). Between 1984 and 1989, unleaded gasoline was progressively introduced across Europe. As a result, atmospheric Pb emissions began to decrease slightly in the second half of the 1960's, then suddenly by the mid-1970mid- 's (von Storch et al., 2003)). Although there are slight discrepancies of age in our peat core due to sampling intervals (1 cm representing a mean of 20 years above 3 cm depth, see Table 2), this decrease in Pb concentration and Pb E.F. is marked in the upper samples from above 3.5 cm depth, and is therefore representative for post-A.D. 1950. These records also correspond with diverse records from Belgium [START_REF] Petit | Stable lead isotopes in pond sediments as tracer of past and present atmospheric lead pollution in Belgium[END_REF], France [START_REF] Rosman | A two century record of lead isotopes in high altitude Alpine snow and ice[END_REF][START_REF] Arnaud | A 300 year history of lead contamination in Northern French Alps reconstructed from distant lake sediment records[END_REF], and Switzerland [START_REF] Kober | Pb isotopes in sediments of Lake Constance, Central Europe constrain the heavy metal pathways and the pollution history of the catchment, the lake and the regional atmosphere[END_REF][START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14C yr BP from a peat bog, Jura mountains, Switzerland[END_REF].

Conclusions

Geochemical and lead isotopic derived from the top meter of peat from the Misten peat bog (Fig. 5) record four major periods of pollution. Firstly the Roman Empire (P-I), represented between 100 cm and ∼57 cm, is characterized by local pollution sources from Pb-Zn ores mining and agriculture activities. Between ∼57 cm and ∼30 cm, the geochemical profiles show a decline in the Roman activities and the transition to Early Middle Ages (P-II). The Middle Ages and Early modern period (∼30 cm to ∼10 4cm, P-III) rapidly give way to the modern industrial Revolution (from ∼10 cm to the actual surface, P-IV) in which lead gasoline accounts for at least 50% of the lead pollution.

This study provides the opportunity to complete the European datasets for pollution reconstruction in continental environments.

  Fig. 1. A. General map showing the Roman road system (redrawn after Corbiau, 1998). The actual Ruhr-Eifel Region is also reported. Plain lines: Roman road system. Black circles: principal Roman cities and village (size of the circles gives an idea of the relative importance of each city). Grey lines: river system. B. Location map of the Hautes Fagnes Plateau and its surroundings. Dashed area: alluvial mounds remaining from gold prospecting, 14 C-dated at A: 120 B.C.-140 A.D. and B: 400 B.C.-200 B.C. Diamonds: 1. the gold mine gallery with dated wooden piece; 2. the open-air gold mine (undated); 3. sites with roman graves; 4. site with Roman coins. Plain lines: Roman road system. Black circles: principal roman cities and village (size of the circles gives an idea of the relative importance of each city). Grey lines: river system. Pb-Zn ores: lead-zinc ore deposit (after Dejonghe, 1998). C. Radar derived peat thickness of the Misten bog (modified after Wastiaux and Schumacker, 2003). Altitude lines are 5 m distant in altitude. The different dotted lines are forestry ways. Coring location is reported by the open circle.

  F. = ([Pb] sample / [Ti] sample ) / ([Pb] Upper crust / [Ti] Upper crust ). Upper crust reference values (17 and 4100 ppm for Pb and Ti, respectively) were taken from Mc Lennan (2001).

Fig. 2 .

 2 Fig. 2. Concentration variations along depth for Misten bog (in % for Si and in ppm for other elements, respectively). 14 C mean age for 53.5 cm sample (325 A.D.) and last 210 Pb (10.5 cm; 1835 A.D.) sedimentation model derived-date are reported. Dotted lines represent the separation between five major intervals (see Sections 4 and 5 for further details). The x-scale of Pb profile is changed at 15 cm depth for visual commodity.

  3.1.1. Si, Ti Both Si and Ti display a similar pattern of change with depth. Concentrations are low below 90 cm depth ([Si] b ∼0.4%, [Ti] b ∼120 ppm), and increase to moderately between 90 and 55 cm depth (∼0.4%b [Si] b ∼1.5%, ∼300b [Ti] b ∼1300 ppm). These values are followed by a zone of minimum concentrations between 55 cm and 40 cm depth (∼0.28%b [Si]b ∼0.62%, ∼150 ppmb [Ti]b ∼500 ppm). Between 40 cm and 20 cm depth, a slight increase in concentrations can be detected ( ∼ 0 . 3 0 % b [ S i ] b ∼ 0 . 7 0 % , ∼ 2 5 0 p p m b [ Ti ] b ∼850 ppm). Finally, the concentrations increase significantly towards the surface of the bog (∼ 0.6% b [Si]b ∼5%, ∼50b [Ti] b ∼500 ppm).

  3.1.3. Cu, Ni, Pb, Zn Between 100 cm and 50 cm, Cu and Zn concentration profiles are partially under detection limits (D.L.), and Ni concentrations are low. Pb concentrations do however show relatively high values (32.3 ppm to 139 ppm). For the top 50 cm of the core, values of Ni, Cu and Pb display similar trends, with minimum concentrations ([Pb] ∼ 13 ppm, [Zn] ∼ 50 ppm, [Cu] ∼ 1.5 ppm and [Ni] b D.L.) at around 30 cm depth, with increased values ([Pb] up to 949 ppm, [Zn] up to 214 ppm, [Cu] up to 18.7 ppm and [Ni] up to 22.8 ppm) toward the surface. 3.2. Lead isotopic ratios Profiles of lead isotopic ratios vs. depth are shown in Fig. 3. 208 Pb/ 204 Pb, 207 Pb/ 204 Pb, 206 Pb/ 204 Pb isotopic ratios exhibit similar trends: poorly radiogenic values ( 208 Pb/ 204 Pb N 38.200, 207 Pb/ 204 Pb around 15.615, 206 Pb/ 204 Pb N 18.250) between 100 and 90 cm, and comparatively unradiogenic values (37.931 b 208 Pb/ 204 Pb b 38.120, 15.594 b 207 Pb/ 204 Pb b 15.608, 17.990 b 206 Pb/ 204 Pb b 18.165) between 60 cm and 30 cm. Then ratios shift toward more radiogenic values between 30 cm and 10 cm (38.150 b 208 Pb/ 204 Pb b 38.200, 15.605 b 207 Pb/ 204 Pb b 15.615, 18.200 b 206 Pb/ 204 Pbb 18.300) and in the top 10 cm show a sudden shift towards low isotopic values ( 208 Pb/ 204 Pb b 37.950, 207 Pb/ 204 Pb b 15.600, 206 Pb/ 204 Pb b 18.015).

Fig. 3 .

 3 Fig. 3. 208 Pb/ 204 Pb, 207 Pb/ 204 Pb, 206 Pb/ 204 Pb isotopic ratio vs. depth. Open circles are replicates. 14 C mean age for 53.5 cm sample (325 A.D.) and last

Fig. 4 .

 4 Fig. 4. 206 Pb/ 207 Pb vs. 208 Pb/ 206 Pb isotopic ratios, and 206 Pb/ 207 Pb vs. Pb E.F. Modern industrial Belgian aerosols from[START_REF] Bollhöfer | Isotopic source signatures for atmospheric lead: the Northern Hemisphere[END_REF][START_REF] Bollhöfer | Isotopic source signatures for atmospheric lead: the Northern Hemisphere[END_REF][START_REF] Sonke | A chemical and mineralogical reconstruction of Zn-smelter emissions in the Kempen region (Belgium), based on organic pool sediment cores[END_REF]. Belgian ore data from[START_REF] Cauet | Genetic study of Belgian lead zinc mineralizations in carbonate environments through lead isotope geochemistry[END_REF] and[START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF]. Data from archeological site from[START_REF] Renson | Early Pb-Zn mining and transport revealed by elemental and lead isotopes geochemistry nearby a Late Roman to Merovingian cobbled road (Belgium). A direct application of geochemistry to archaeology[END_REF] are also reported. Belgian pre-industrial sediment fromSonke et al. (op. cit.). Upper continental crust field from[START_REF] Millot | Lead isotopic systematics of major river sediments: a new estimate of the Pb isotopic composition of the Upper Continental Crust[END_REF],[START_REF] Hemming | Pb isotope compositions of modern deep sea turbidites[END_REF],[START_REF] Grousset | Transient Pb isotopic signatures in the Western-European atmosphere[END_REF] and[START_REF] Asmeron | The Pb isotopic evolution of the Earth: inferences from river water suspended loads[END_REF]. Gasoline from The Netherlands from[START_REF] Hopper | Regional source discrimination of atmospheric aerosols in Europe using the isotopic composition of lead[END_REF].

  4.2.1. Roman EmpireIn the core Pb enrichment factors display a wide range of variation during the Early Roman Empire with isotopic ratios being very low (see Fig.5, samples at 98.5 cm and 88.5 cm depth). During the Roman Empire, and particularly towards the upper end (60 cm-40 cm) Pb E.F. are quite high (up to 110) and 206 Pb/ 207 Pb ratio shows lower radiogenic values ( 206 Pb/ 207 Pb up to 1.154).

Fig. 5 .

 5 Fig. 5. Summary of major Pb, Pb E.F. and 206 Pb/ 207 Pb in the first meter Misten bog and interpretation of historical intervals. The x-scale of Pb profile has been changed at 15 cm depth for visual clarity.

Table 2

 2 Elemental content along the top meter of a peat core from the Misten Bog

	Depth Si	Ti	Sr	Cu	Ni	Pb	Zn	Pb E.F.
	0.5	4.32 1187 14.1 8.40	14.2	537 106
	1.5	4.34 1206 17.2 12.3	18.3	647 133
	2.5	3.41 1223 16.4 13.2	14.5	766 153
	3.5	3.40 1048 19.1 18.7	22.8	949 214
	4.5	3.67 1056 16.1 10.6	9.4	617 133
	5.5	4,93 1066 16.7 8.71	7.2	413 117
	6.5	3,60 785 14.5 5.60	3.9	299 106
	7.5	2,60 677 15.7 4.63	4.9	265 135
	8.5	1,98 585 13.6 2.70	bD.L. 207 120
	9.5	1,97 576 12.7 2.08	bD.L. 139 105
	10.5	1,48 549 10.4 1.80	bD.L. 89.1 91.6
	12.5	1,53 592 12.6 1.80	bD.L. 61.6 105
	14.5	0,58 272 10.5 1.70	bD.L. 32.3 97.3
	16.5	0,53 232 13.5 2.40	bD.L. 40.6 135
	18.5	0,61 259 10.2 2.70	bD.L. 31.9 91.8
	20.5	0.44 174 12.9 2.50	bD.L. 32.1 107
	22.5	0.31 153 17.0 2.20	bD.L. 28.7 123
	24.5	0.46 200 15.3 2.20	bD.L. 25.0 102
	26.5	0.42 191 12.9 2.00	bD.L. 19.0 70.5
	28.5	0.66 302 10.3 bD.L. bD.L. 12.3 47.1
	30.5	0.63 272 13.6 1.60	bD.L. 13.5 52.1
	32.5	0.47 236 13.4 2.50	bD.L. 22.4 50.6
	34.5	0.38 197 13.2 2.10	bD.L. 20.7 42.8
	36.5	0.59 259 12.4 2.40	bD.L. 21.3 34.2
	38.5	0.33 138 12.9 2.90	bD.L. 24.9 33.8
	40.5	0.28 154 14.9 3.00	3.70	28.9 28.8
	42.5	0.33 165 15.6 2.50	bD.L. 22.2 23.0
	44.5	0.37 159 16.8 2.00	bD.L. 19.4 18.3
	46.5	0.39 145 18.0 3.90	4.00	35.0 17.7
	48.5	0.37 146 16.0 3.30	3.50	30.9 14.5
	49.5	0.41 159 18.1 4.47	6.69	39.5 16.7
	50.5	0.61 223 17.0 5.70	13.1	84.6 34.2
	51.5	0.41 154 16.4 6.08	10.9	58.6 16.7
	52.5	0.30 116 14.1 4.70	7.30	45.2 12.5
	54.5	0.32 136 13.4 4.10	6.40	43.2 9.20
	56.5	0.48 138 13.8 4.10	6.50	43.8 8.80
	58.5	0.63 195 12.9 4.40	7.80	47.4 8.60
	60.5	1.25 318 9.30 bD.L. bD.L. 32.3 bD.L.
	64.5	0.67 233 7.50 bD.L. 6.43	57.9 bD.L.
	68.5	0.79 228 6.99 bD.L. 3.85	60.4 bD.L.
	72.5	1.54 468 7.91 bD.L. 4.28	82.9 bD.L.
	76.5	0.52 193 7.80 bD.L. 4.25	81.8 bD.L.
	80.5	0.70 252 10.6 bD.L. bD.L. 139 bD.L.
	86.5	0.65 254 6.97 bD.L. bD.L. 95.1 bD.L.
	88.5	1.07 335 6.96 bD.L. 6.19	98.7 bD.L.
	96.5	0.36 98	8.53 3.06	7.26	60.9 bD.L.
	98.5	0.44 144 9.11 10.2	12.4	69.1 bD.L.
	660	-	2081 28.3 bD.L. 51.4	7.66 20.8
	678	-	4215 63.9 11.38 50.4	16.1 18.1
	bD.L. : under detection limits. Values in italic are semi-quantitative
	(3σ b N 6σ). bis-samples are replicates. Si concentrations are not
	measured for 660 and 678 cm samples because of SiF 4 volatilization
	during HF digestion.

Configuration of the collector array enabled simultaneous collection of Pb (for masses

208, 207, 206, 204)

together with

Tl (205, 203)

and Hg (202). Hg was used to correct interferences on mass 204 (because of 204 Hg). Tl is added to all samples and standards to monitor and correct instrumental mass fractionation. All standard and sample solutions were prepared to obtain a Pb/Tl ratio of ∼ 5, a signal of ∼ 100 mV on the axial collector ( 204 Pb), and to match the Pb, Tl concentrations

Table 3 208

 3 Pb/ 204 Pb, 207 Pb/ 204 Pb, 206 Pb/ 204 Pb, 207 Pb/ 206 Pb, 208 Pb/ 207 Pb, 208 Pb/ 206 Pb isotopic ratios

	Depth	208 Pb/ 204 Pb	2se	207 Pb/ 204 Pb	2se	206 Pb/ 204 Pb	2se	208 Pb/ 206 Pb	2se	207 Pb/ 206 Pb	2se
	0.5	37.9300	0.0030	15.5947	0.0011	17.9864	0.0012	2.1088	0.00180	0.8670	0.00010
	0.5bis	37.9300	0.0040	15.5947	0.0015	17.9856	0.0017	2.1089	0.0023	0.8671	0.00020
	2.5	37.9350	0.0020	15.5962	0.0008	17.9857	0.0009	2.1092	0.00110	0.8671	0.00010
	5.5	37.8979	0.0031	15.5829	0.0013	17.9701	0.0017	2.1089	0.00009	0.8672	0.00002
	5.5bis	37.9221	0.0034	15.5931	0.0014	17.9806	0.0016	2.1090	0.0001	0.8672	0.00003
	8.5	37.9540	0.0020	15.5969	0.0007	18.0042	0.0009	2.1081	0.00110	0.8663	0.00020
	10.5	37.9465	0.0041	15.5867	0.0015	18.0102	0.0017	2.1069	0.00008	0.8655	0.00002
	15.5	38.1640	0.0030	15.6117	0.0011	18.2119	0.0014	2.0956	0.00160	0.8572	0.00030
	20.5	38.1903	0.0032	15.6087	0.0013	18.2464	0.0014	2.0930	0.00009	0.8554	0.00003
	24.5	38.1417	0.0038	15.6030	0.0013	18.1881	0.0016	2.0969	0.00007	0.8578	0.00001
	30.5	37.9950	0.0060	15.5971	0.0023	18.0678	0.0025	2.1029	0.00350	0.8633	0.00020
	40.5	38.1196	0.0027	15.6078	0.0011	18.1652	0.0015	2.0985	0.00011	0.8592	0.00004
	50.5	37.9310	0.0060	15.5935	0.0024	17.9881	0.0029	2.1087	0.00310	0.8669	0.00050
	50.5bis	37.9400	0.0040	15.5985	0.0014	17.9964	0.0016	2.1082	0.0024	0.8668	0.00020
	52.5	37.9844	0.0043	15.5943	0.0015	18.0424	0.0017	2.1052	0.00010	0.8643	0.00003
	52.5bis	37.9789	0.0079	15.5930	0.0030	18.0415	0.0022	2.1051	0.0001	0.8643	0.00003
	56.5	38.1012	0.0094	15.5985	0.0038	18.1486	0.0049	2.1319	0.00007	0.8594	0.00003
	88.5	38.3310	0.0040	15.6191	0.0015	18.3631	0.0020	2.0874	0.00200	0.8506	0.00050
	98.5	38.2245	0.0041	15.6088	0.0015	18.2656	0.0018	2.0926	0.00008	0.8545	0.00003
	660	39.0227	0.0065	15.6770	0.0056	19.0430	0.0029	2.0491	0.00006	0.8233	0.00002
	678	38.9966	0.0033	15.6878	0.0009	19.2016	0.0013	2.0309	0.00004	0.8170	0.00001
	se refers to standard error, i.e. derived from standard deviation.
						Table 4
						210 Pb age depth relationship in the 10.5 cm depth sample
						Laboratory	Mean depth	210 Pb corrected date	Uncertainty
						no.		(cm)	(year)		(year)
						1		0.5	2003		0
						2		1.5	1984		2
						3		2.5	1964		5
						4		3.5	1950		8
						5		4.5	1938		10
						6		5.5	1935		10
						7		6.5	1920		16
						8		7.5	1874		44
						9		8.5	1835		28
						10		9.5	1835		28
						11		10.5	1813		57

Pb (10.5 cm; 1835 A.D.) sedimentation model derived-date are reported. Dotted lines represent the separation between five major intervals (see Sections 4 and 5 for more details). Background samples (660 cm and 678 cm) are not represented.

Acknowledgements

We are very grateful to Guy Bologne and Sophie Leclercq for the XRF analysis, M. Streel and L. Leclercq their advice and knowledge of the Hautes Fagnes Plateau. Claude Maershalk is thanked for assistance in the clean lab at ULB and for the MC-ICP-MS measurements. Xavier Boës was of great help during the coring. We are especially grateful to Maurice Streel for fruitful discussions and reference searching concerning pollen diagrams, and to Béatrice Cauuet (C.N.R.S., Univ. Toulouse Le Mirail, France) and Muriel van Ruymbeke (European Center for Archeometry, Univ. Liège, Belgium) for having accurately commented and improved the archeological background. Pascal Mertes (DNF-Belgian Forest and Nature Ministry) is also warmly thanked for providing us the official authorization for coring the Misten bog. We finally thank Maria Gehrels (Univ. Plymouth, U.K.) and one anonymous reviewer for English smoothing. This work was funded by NSRF (Belgian Scientific Research Foundation) credits. François De Vleeschouwer is FRIA fellowship.