Environ. Sci. Technol. 2005, 39, 5131-5140 Record of Metal Workshops in Peat Deposits: History and Environmental Impact on the Mont Lozère Massif, France S . B A R O N , * ,† M . L A V O I E , ‡,§ A . P L O Q U I N , † J. CARIGNAN,† M. PULIDO,‡ AND J.-L. DE BEAULIEU‡ Centre de Recherches Pétrographiques et Géochimiques, CNRS Nancy, 15 rue Notre Dame des Pauvres, BP 20, 54 501 Vandoeuvre les Nancy, France, and Institut Méditerranéen d’EÄ cologie et de Paléoécologie, Case 451, Faculté Saint-Jérôme, Université d’Aix-Marseille III, Marseille Cedex 20, France This study aims to document the history of the metallurgical activities on the Mont Lozère massif in the Cévennes Mountains in Southern France. Many medieval sites of metallurgical wastes (slags) have been reported on the massif. These sites are thought to represent ancient lead workshops. The impact of past metallurgical activity on the environment was studied using geochemical and palynological techniques on a core collected in the Narses Mortes peatland near medieval smelting area. Two main periods of smelting activities during the last 2200 years were revealed by the lead concentration and isotopic composition along the core profile: the first period corresponds to the Gallic period (∼ca. 300 B.C. to ca. 20 A.D.) and the second one to the Medieval period (∼ca. 1000-1300 A.D.). Forest disturbances are associated with lead anomalies for the two metallurgical activities described. The impact of the first metallurgy was moderate during the Gallic period, during which beech and birch were the tree species most affected. The second period corresponds to the observed slag present in the field. Along with agropastoral activities, the medieval smelting activities led to the definitive disappearance of all tree species on the summit zones of Mont Lozère. The abundance of ore resources and the earlier presence of wood on the massif justify the presence of workshops at this place. The relationship between mines and ores has been documented for the Medieval period. There is no archaeological proof concerning the Gallic activity. Nevertheless, 2500-2100 years ago, the borders of the Gallic Tribe territory, named the Gabales, were the same as the present-day borders of the Lozère department. Julius Caesar reported the existence of this tribe in 58 B.C. in “De Bello Gallico”, and in Strabon (Book IV, 2.2) the “Gabales silver” and a “treasure of Gabales” are mentioned, but to this day, they have not been found. Introduction Atmospheric deposition resulting from anthropogenic activity are recorded in natural archives such as ice cores (1, 2), * Corresponding author e-mail: sbaron@crpg.cnrs-nancy.fr. † Centre de Recherches Pétrographiques et Géochimiques. ‡ Université d’Aix-Marseille III. § Present address: Centre d’études nordique et Département de géographie, Université Laval, Québec G1K 7P4, Canada. 10.1021/es048165l CCC: $30.25 Published on Web 06/07/2005  2005 American Chemical Society peatlands (3-5), marine sediments (6), lake sediments (7, 8), and lichens (9-11). These archives record atmospheric pollution at regional or continental scale. Records at global scale have been reported (12, 13), but very few studies have been conducted at regional scale (14, 15). The knowledge of local history allows more accurate estimation of the sources of the heavy metals accumulated in the environment. In southern France, 60 metallurgical waste (slag) sites have been found on the Mont Lozère massif suggesting that metallurgical activities occurred in the past (16, 17). Fens are the most common peatlands in southern Europe. This type of peatland is not frequently used to reconstruct changes in past atmospheric deposition because of possible disturbances of the geochemical signal resulting from leaching and groundwaters (18). Although bogs are recognized to be a better geochemical archive, it has recently been shown that fens are also able to record successfully atmospheric deposition without significant distortion (19). This was deduced from the study of ombrotrophic peatlands where the underlying peat was minerotrophic (20, 21). Moreover, West et al. (20) demonstrated that high ash content in peat is not necessarily associated with high lead concentration, suggesting that variations in lead concentrations might not be the result of changes in the mineral fraction sedimentation. As a result, minerotrophic peatlands give the opportunity to establish local and regional environmental reconstructions in areas where bogs are absent. This study presents geochemical and pollen analyses of a core collected in a minerotrophic peatland on the Mont Lozère massif. Our aim is to document periods of local metallurgical activities during the last millennia and to examine their impact on the long-term forest dynamics. Elemental chemical analyses, lead isotopic compositions, and pollen analyses were used to reconstruct the history of the anthropogenic activities. The lead isotopic signature along the peat core allowed tracing the natural and anthropogenic origins of lead and constraining the role of human activities related to vegetation disturbance observed in the pollen records. Materials and Methods Studied Area and Site. Mont Lozère is located in the Cévennes National Park (French Massif Central) and is a part of an important mining district. It is a 300 million year old granitic massif, surrounded by various Pb mineralizations. Slag sites are found exclusively on the western part of the massif in an area of 8 km2, in the restricted altitude range of 1340-1430 m (Figure 1) where the plant cover is very poor, likely because of metal pollution. The silicate matrix of slag contains 25% Pb in average (17). All sites show the same slag typology: black slags are often vitreous and brittle, whereas white slags are crystallized and crumbly. These represents the waste of smelting workshop sites for lead and silver making (17). However, silver extraction (used to coin) was not done on the massif as shown by the lack of cupellation wastes on the workshop sites. Nine radiocarbon ages obtained from charcoal (beech) found in archaeological excavations associated with slags gave ages suggesting that metallurgical activities occurred during the Medieval period (17). A recent lead isotope study clarified the relationship between the surrounding old mines and slags on the massif (22): the mines which provided the ores are not the ones close to slags but ones located on the south-southeastern part of the Mont Lozère massif. The “Narses Mortes Peatland” (44°26′ N, 3°36′ W; 1400 m asl) is located near two smelting slag sites (Figure 1) where VOL. 39, NO. 14, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 5131 FIGURE 1. Location of the Mont Lozère massif (Cévennes mountains) in southern France. The locations of the Narses Mortes Peatland and the granites samples are also indicated. an archaeological excavation was engaged (17, 23). It is a 21 ha treeless fen dominated by Sphagnum mosses and Molinia caerula (L.) Moench. A microtopographic pattern of hollows and hummocks characterizes the site. The organic sediment thickness reaches a maximum of 140 cm, and a radiocarbon date of 8150 14C yr B.P. was obtained for the onset of peat inception at the center of the peatland (24). The surrounding vegetation consists of a heatland dominated by Calluna vulgaris (L.) Hull, in association with Vaccinium myrtillus L., Cytisus scorparius (L.) Link, and Nardus stricta L. Scots pine (Pinus sylvestris L.) is the only tree species and was planted during the second half of the XIXth century. Sampling. According to palynological studies conducted at the studied site (24, 25), the marginal peat is more appropriate than the central part of the peatland to study in detail the anthropogenic period. In May 2002, a 140 cm-long peat profile was extracted at the western margin of the peatland i.e. out of the way of water draining the workshop 3-3′. The upper part of the profile consists of a 15 × 15 × 75 cm monolith, whereas the deeper sediments (76-140 cm) consist of a core collected using a modified Russian peat sampler. Sediments were wrapped in a plastic film and transported to the laboratory, where they were stored at 5 °C. Granite samples were also collected for an estimation of the local crustal composition. Peat Sample Treatment. The superficial part of the sediments as well as roots and living plant materials were discarded in order to remove potential contamination. The profile was divided into two longitudinal parts: one for the geochemical analysis and the other one for the palynological analysis and radiocarbon dating. The profile was sectioned into 2-cm thick slices. The upper part of the core (21-0 cm depth) has not been sampled for geochemistry because of the abundant roots and living plants. These last samples would have been inconsistent with routine analytical protocol 5132 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 14, 2005 applied here. Samples for geochemistry were dried at 30 °C during 5 days in a polypropylene box for conservation until the chemical analysis. Each sample was powdered in an agate mortar. After powdering, samples were sifted in an inorganic sieve (500 µm mesh) in order to obtain a homogeneous powder without roots or large components of flora. Ash Content. Ash content was determined by gravity using 1 g of sediment previously dried at 105 °C. Ashing was done by heating at 550 °C overnight in order to obtain a white color as indication that all the organic matter was burned. Elemental Chemical Analysis of Peat Samples. Elemental chemical composition was measured using a Thermo Elemental ICP-MS X7. Suprapure reagents were used for the preparation of samples, such as distilled-deionized water, distilled acids, and a homemade synthesized Li metaborate flux. All samples were digested using alkali fusion. After cooling, the fusion glass was dissolved with nitric acid and introduced in the mass spectrometer (26). Procedural blanks were carried out and were negligible (26). For the samples having predominant organic matter content, the accuracy and the reproducibility were verified by using the BCR-CRM 482 lichens reference material and are as reported by Doucet and Carignan (10). The accuracy and the reproducibility of high ash content samples were verified by using geological reference materials and are as reported by Carignan et al. (26). Lead Isotopic Measurements. Dried peat samples (30300 mg, according to lead concentration in each sample) were dissolved in a Teflon vessel using 2 mL of concentrated HNO3 and 0.5 mL of 30% H2O2. The Teflon vessels were sealed and left at room-temperature overnight. After evaporation at 110 °C, the residue was taken back with 1 mL of concentrated HNO3, 0.5 mL of H2O2, and 1 mL of concentrated HF (all Merck Suprapur quality) and set at 80 °C overnight. TABLE 1: Radiocarbon Ages of the Narses Mortes Peat Core depth, cm radiocarbon age 14C yr BP calibrated age (2σ) (calendar year) lab name 40-42 48-50 52-54 60-62 70-72 90-92 118-120 850+/-30 1330+/-35 1265+/-35 1460+/-35 1635+/-35 1950+/-40 2200+/-40 1156 A.D.-1264 A.D. 640 A.D.-780 A.D. 660 A.D.-870 A.D. 540 A.D.-660 A.D. 340 A.D.-540 A.D. 50 B.C.-140 A.D. 390 B.C.-160 B.C. POZ-7045 POZ-2012 POZ-2014 POZ-2015 POZ-2016 POZ-1957 POZ-1958 H2O2 was added to the Teflon vessel step by step in order to ovoid effervescence of the organic matter. Samples were digested in a clean room laboratory under a laminar flow hood to avoid any contamination. After the last evaporation, the residue was taken up in 1 mL of 0.9 M HBr and stayed at the room-temperature overnight in order to homogenize the solution with the residue. The samples were then ultrasonized for 1 h. After centrifugation, Pb was separated from the other elements by ion exchange using the AG1X8 resin (27). After separation, the solution was evaporated at 80 °C, and the residue was taken back in 3 mL of 0.3 M HNO3. The lead isotopic composition was measured with a MC-ICP-MS (Isoprobe, Micromass, now GV Instruments) equipped with 9 Faraday cups allowing the measurement of all the Pb isotopes, Tl isotopes, and 200Hg simultaneously. The reference materials, NIST 981 Pb and NIST 997 Tl, were used to correct for instrumental mass bias, according to the empirical technique used by Maréchal et al. (28) and reported by White et al. (29) for lead applications. This technique is based on the relationship measured between Pb and Tl mass bias. Reference values used for both reference materials were taken from Thirlwall (30). A Pb/Tl ratio of 10 was used for both the reference solution and samples. Repeated measurements of the NIST NBS 981 Pb reference material yielded accurate recalculated values (using the Pb-Tl relationship) with a reproducibility (2*standard deviations) better than 150 ppm for all the reported Pb isotope ratios. The uncertainties are better than 180 ppm (2*standard deviations) for all the reported Pb isotope ratios. Pollen Analysis. Subsamples were collected at 2 cm (074 cm) and 4 cm (74-138 cm) intervals for pollen analysis. They were processed following standard methods. Pollen counting was done at 500× magnification and at 1000× for critical determinations. At least 300 grains of terrestrial vascular plants (pollen sum) were counted for every pollen spectrum. Results are expressed in pollen percentages. Only some selected species are presented in the pollen diagram. Whole data will be published elsewhere by M. Pulido (25). Radiocarbon Ages. Eight 2-cm thick samples were dated by acceleration mass spectrometry (AMS) at the Poznan Radiocarbon Laboratory, Poland (Table 1). For the choice of dated levels, special attention was paid to lead anomalies and signs of forest disturbance in the pollen diagram. Radiocarbon ages (14C yr B.P.) were calibrated (yr B.C.-A.D.) using the OxCal3 program (31, 32). A contemporary age of 2002 A.D. was attributed to the top of the profile (0 cm). Net peat accumulation rates (cm‚yr-1) were calculated by linear interpolation. Results and Interpretations Net Peat Accumulation Rates. The matrix of the peat mainly consists of herbaceous plant remains. The onset of peat accumulation (139 cm) was not dated, and the oldest age obtained for the profile (118-120 cm) was 390-160 B.C. (Table 1). Net “sediment” accumulation rates varied throughout the profile, ranging from 0.024 to 0.096 cm yr-1 (Figure 2). FIGURE 2. Age-depth model for the lateral core of Narses Mortes Peatlands. The error bars are given at 95% confidence level. Ash Content. The ash content varied from 8 to 85% (Figure 3a). The deepest part of the profile (133-139 cm) presents the highest ash content (saprolite), whereas samples from 23 to 27 cm have the lowest values. There is a general decrease with depth with some fluctuations. The total measured mineral elements have the same pattern with depth suggesting that the peat bog is minerotrophic. The Al concentration will be used for crustal normalization of metals. Heavy Metals. The elemental concentrations of As, Cd, Pb, Sb, Zn, and Al measured in peat samples and surrounding granites are summarized in Table 2. Systematic variations along the profile are mostly found for Pb concentrations which present two “rich-zones”, a large one from ∼120 to 80 cm depth, the peak concentration being at 113 cm, and another one from about 45 cm depth to the subsurface (23 cm), the peak concentration being at 35 cm. Arsenic concentrations present a pattern similar to Pb but with the first peak being slightly displaced toward a deeper position, centered around 120 cm. The other metals (Cd, Sb, and Zn) present a systematic increase in concentration only in the upper part of the profile (35-23 cm), the remaining samples having similar or lower concentrations erratically distributed from 35 cm to the bottom of the profile. The mean concentrations in As, Cd, Pb, Sb, Zn, and Al of the Mont Lozère granite were calculated from the three samples C, F, and G (Table 2). They are 7.1 ppm, <0.30 ppm, 34.2 ppm, 0.2 ppm, 39.6 ppm, and 7.87%, respectively. The Al, Sb, and Pb concentrations are similar to those of the upper continental crust (UCC) (33, 34) (Table 2), while the Cd and Zn concentrations are less than the UCC and the As concentrations are higher than the UCC. Heavy metal concentrations normalized to Al (crustal inputs) are used to calculate the enrichment factors (EF) as defined by ([metal]/[Al]sample)/([metal]/[Al]saprolite) the composition of the saprolite being the average of the four deepest samples (called saprolite) which best represent the detritic silicates feeding the system (T 139, T 137, T 135, and T 133). VOL. 39, NO. 14, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 5133 FIGURE 3. (a) Ash concentration (%) versus depth of the Narses Mortes Peatland, (b) EF Pb and EF As versus depth (cm), (c) EF Zn, Sb, and Cd versus depth (cm), (d) excess Pb and total Pb (ppm) versus depth (cm), (e) 206Pb/207Pb ratio versus depth (cm), and (f) Pb/Al ratio versus depth (cm). EF for Pb and As are presented in Figure 3b and for Sb, Cd, and Zn in Figure 3c. Enrichment factors for all the metals increase systematically from the ∼35 cm sample to the subsurface (23 cm) sample with significant EF values ranging from 3 to 65 depending on the element. Along this section of the profile, Pb, As, and Cd increase by a factor of 4, whereas Sb and Zn increase by a factor of more than 10. As observed for concentrations, EF Sb, Cd, and Zn decrease progressively but erratically from 35 to 130 cm by a factor of 2 or 3 before entering the saprolite zone at the bottom of the profile. EF As defines a different pattern than Sb, Cd, and Zn. Indeed, from sample 33-85 cm, EF As shows a relative constant value of 4.5 ( 1.5, then progressively rises to 10 ( 2 for samples 95-119 cm, and then progressively drops down to EF of 1 in the saprolite zone. Lead presents the most contrasted EFs along the profile. From sample 33 to 49 cm, EF Pb systematically drops from 5 to 1 and stays at 1.5 ( 0.5 down to sample 75 cm. It then progressively rises to 9 ( 1 for samples 93-113 cm and rapidly drops down to a value of 1 at sample 121 cm to the bottom of the profile (Table 2). Excess Pb in Peat Core. The excess Pb is calculated by the following formula excess Pb: Pb totalpeat - (Pb/Al)saprolite*Alpeat where Pb total is the total Pb concentration in a given peat sample, Pb/Al saprolite is represented by the four samples at the bottom of the profile, and Al peat is the total Al concentration in a given peat sample. Figure 3d shows the 5134 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 14, 2005 excess Pb profile of the peat core from 20 to 140 cm depth. The excess Pb is considered as total anthropogenic Pb input in the system from both the atmosphere and the surface draining. In the two sections where the EF Pb are the highest, the calculated Pb excess is similar to the total Pb suggesting that the Pb content comes from anthropogenic sources. This is not the case in the two background sections suggesting that no anthropogenic activities occur and that the total Pb is mainly supplied by natural sources. There is no correlation between the excess Pb and the ash content. Pb Isotopes in Granite and Slag Samples. Three samples of the surrounding granite present typical crustal values but heterogeneous isotopic compositions, with, for example, 206 Pb/204Pb ratios varying between 19.339 and 19.644 and 206 Pb/207Pb ratios varying from 1.2298 to 1.2486 (Table 3). On the other hand, the composition of slag materials found in the area of the Narses Mortes peat land seems less heterogeneous with much lower 206Pb/204Pb ratios of 18.472 ( 0.008 and 206Pb/207Pb ratios of 1.1789 ( 0.0001 (Table 3). The later composition is totally within the range measured for many other slag sites on the Mont Lozère (22). Pb Isotopes in Peat Samples. The Pb isotopic compositions along the profile are listed in Table 3. Ratios range from 1.9325 to 2.0981 (208Pb/206Pb), 1.1675 to 1.2712 (206Pb/207Pb), 38.043 to 38.701 (208Pb/204Pb), 15.630 to 15.751 (207Pb/204Pb), and 18.249 to 20.023 (206Pb/204Pb). Sharp gradients of the lead isotopic composition may be observed along the profile but with a coherent distribution (Figure 3e). Indeed, lower 206 Pb/207Pb ratios are related to higher Pb concentrations TABLE 2: Elementary Chemical Analysis of Narses Mortes Peatlands (with Their Corresponding EF), Mont Lozère Granite, and UCCa depth, cm As, ppm Cd, ppm Pb, ppm Sb, ppm Zn, ppm Al, % Pb/Al EF Pb EF As EF Cd EF Sb EF Zn 57.8 64.5 36.8 24.5 12.1 6.0 5.7 5.7 8.0 6.1 6.7 6.6 7.4 5.9 9.3 9.9 5.7 5.8 4.2 5.5 6.2 6.6 2.9 3.6 4.9 7.5 6.9 5.6 4.2 2.9 3.3 3.3 3.4 5.1 4.4 3.6 4.4 5.4 6.4 5.3 4.0 3.2 2.9 3.3 5.5 5.4 5.4 4.1 2.0 2.0 2.2 1.6 2.0 0.8 39.1 33.0 14.0 7.0 3.4 3.1 3.0 2.6 4.7 6.4 4.0 3.0 0.9 0.9 0.9 1.3 1.0 0.8 1.0 1.2 T 23 T 25 T 27 T 29 T 31 T 33 T 35 T 37 T 39 T 41 T 43 T 45 T 47 T 49 T 51 T 53 T 55 T 57 T 59 T 61 T 63 T 65 T 67 T 69 T 71 T 73 T 75 T 79 T 81 T 83 T 85 T 87 T 89 T 91 T 93 T 95 T 97 T 99 T 101 T 103 T 105 T 107 T 109 T 111 T 113 T 115 T 117 T 119 T 121 T 123 T 125 T 127 T 129 T 131 1.9 2.5 2.9 2.1 2.5 3.4 3.9 3.1 3.2 3.0 3.5 2.8 3.3 2.8 2.1 2.5 2.1 2.2 2.6 2.7 3.1 4.1 3.7 3.5 3.5 2.9 3.7 2.9 3.9 4.2 4.7 4.2 4.9 6.1 5.1 4.9 5.6 6.3 7.6 7.2 7.6 6.1 7.8 7.4 8.6 9.2 7.5 9.1 8.5 8.6 8.9 8.4 7.5 6.0 1.0 1.6 2.3 2.0 1.9 1.5 1.2 0.9 0.8 0.9 0.9 1.0 0.9 1.2 1.0 1.2 0.8 0.7 0.6 0.6 0.5 0.8 0.4 0.4 0.4 0.5 0.5 0.4 0.7 0.7 0.5 2.1 < ld < ld < ld < ld < ld < ld < ld < ld 0.3 0.5 0.4 0.4 < ld 0.3 0.4 0.5 0.6 0.8 1.1 1.2 3.8 < ld 19.5 27.2 28.1 27.8 31.7 33.7 36.2 27.4 27.2 15.0 12.6 12.3 9.3 5.5 4.8 6.7 5.3 5.0 5.6 5.5 5.5 6.5 6.2 6.2 6.0 5.7 8.2 28.6 19.9 19.8 20.4 25.1 28.1 25.8 29.3 33.7 31.7 29.0 35.9 34.4 43.8 47.1 42.1 40.7 52.0 29.6 16.7 12.7 14.4 14.5 19.4 16.8 20.5 22.1 1.0 1.4 1.2 1.0 0.9 0.7 0.7 0.6 0.7 0.5 0.5 0.5 0.6 0.4 0.6 0.6 0.3 0.4 0.3 0.4 0.4 0.6 0.3 0.3 0.3 0.4 0.5 0.5 0.4 0.4 0.3 0.3 0.4 0.5 0.3 0.3 0.3 0.4 0.5 0.4 0.4 0.3 0.3 0.3 0.4 0.4 0.5 0.5 0.4 0.5 0.5 0.4 0.6 0.4 Peat 19.3 19.8 12.4 7.8 6.6 9.5 10.1 7.8 11.8 15.1 8.6 6.6 <ld <ld 6.2 10.5 8.9 <6.00 <6.00 <6.00 <6.00 6.7 <ld <ld <ld <ld <ld <ld <ld <ld 6.3 <ld <ld 13.6 <ld <ld <ld <ld <ld <ld <ld <ld <ld <ld <ld <ld <ld <ld <ld 7.7 8.8 9.4 10.7 14.1 0.20 0.24 0.35 0.44 0.78 1.22 1.36 1.18 1.00 0.94 0.87 0.87 0.88 0.81 0.66 0.70 0.62 0.83 0.88 0.77 0.77 0.94 1.01 0.82 0.65 0.57 0.86 1.06 1.15 1.32 1.07 1.06 1.21 1.02 0.83 0.77 0.72 0.76 0.77 0.85 1.02 1.07 1.08 0.97 0.88 0.85 1.08 1.29 2.18 2.55 2.67 2.79 3.32 4.69 9.8E-03 1.1E-02 8.0E-03 6.3E-03 4.0E-03 2.8E-03 2.7E-03 2.3E-03 2.7E-03 1.6E-03 1.4E-03 1.4E-03 1.1E-03 6.8E-04 7.3E-04 9.6E-04 8.5E-04 6.1E-04 6.3E-04 7.2E-04 7.1E-04 6.9E-04 6.2E-04 7.5E-04 9.2E-04 9.9E-04 9.5E-04 2.7E-03 1.7E-03 1.5E-03 1.9E-03 2.4E-03 2.3E-03 2.5E-03 3.6E-03 4.4E-03 4.4E-03 3.8E-03 4.7E-03 4.0E-03 4.3E-03 4.4E-03 3.9E-03 4.2E-03 5.9E-03 3.5E-03 1.5E-03 9.9E-04 6.6E-04 5.7E-04 7.3E-04 6.0E-04 6.2E-04 4.7E-04 19.8 22.7 16.0 12.6 8.1 5.5 5.4 4.7 5.5 3.2 2.9 2.8 2.1 1.4 1.5 1.9 1.7 1.2 1.3 1.4 1.4 1.4 1.2 1.5 1.9 2.0 1.9 5.4 3.5 3.0 3.9 4.8 4.7 5.1 7.1 8.8 8.8 7.7 9.4 8.1 8.6 8.9 7.9 8.4 11.9 7.0 3.1 2.0 1.3 1.1 1.5 1.2 1.2 1.0 10.8 11.9 9.5 5.4 3.7 3.3 3.4 3.1 3.8 3.6 4.6 3.8 4.3 4.0 3.8 4.1 3.9 3.1 3.4 4.1 4.7 5.1 4.2 5.0 6.3 6.0 5.0 3.2 3.9 3.7 5.2 4.7 4.7 6.9 7.2 7.4 8.9 9.5 11.5 9.9 8.6 6.6 8.4 8.9 11.3 12.6 8.1 8.2 4.5 3.9 3.9 3.5 2.6 1.5 33.4 43.2 40.6 28.1 15.0 7.7 5.7 4.9 5.1 5.8 6.3 7.0 6.7 9.2 9.6 10.6 8.0 5.1 4.2 5.3 4.4 5.5 2.6 3.4 3.9 5.1 4.0 2.4 3.6 3.4 3.2 12.4 T 133 T 135 T 137 T 139 4.6 4.5 3.5 3.6 1.3 0.7 0.4 0.5 23.6 27.6 22.8 24.4 0.4 0.4 0.4 0.6 Saprolite 11.2 10.4 11.5 13.8 4.45 4.98 4.67 4.70 5.3E-04 5.5E-04 4.9E-04 5.2E-04 1.1 1.1 1.0 1.0 1.2 1.1 0.9 0.9 1.8 0.9 0.6 0.7 C F G mean 7.8 6.8 6.6 7.1 < 0.30 < 0.30 < 0.30 - 31.5 35.2 35.8 34.2 0.1 0.1 0.3 0.2 Granites 45.0 37.8 35.9 39.6 7.83 7.94 7.82 7.87 4.0E-04 4.4E-04 4.6E-04 4.3E-04 Wedepohlb Taylor and McLennanb 2.0 1.5 17.0 20.0 0.31 0.2 UCC 52.0 71.0 7.74 8.04 0.102 0.98 2.0 2.7 2.2 2.5 2.4 2.2 2.3 1.7 2.1 2.7 2.8 7.2 3.8 6.0 5.8 2.8 2.4 5.3 1.2 1.3 1.4 1.3 1.2 a The limits of determination for peat and granite samples (ld) are 0.70 ppm for As, 0.30 ppm for Cd, 0.90 for Pb, 0.10 for Sb, 6 ppm for Zn, and 0.1% for Al. The analytical uncertainties depend of the sample concentration; all the details are reported in ref 26. b 1995. VOL. 39, NO. 14, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 5135 206 TABLE 3: Lead Isotopic Composition of Peat, Slags, and Granite Samples depth cm 208Pb/ 206Pb 206Pb/ 207Pb 2sda 0.0003 208Pb/ 204Pb 207Pb/ 204Pb 206Pb/ 204Pb 0.0001 0.009 0.003 0.003 Peat 38.289 38.372 38.667 38.530 38.589 38.617 38.625 38.636 38.655 38.648 38.657 38.648 38.701 38.695 38.694 38.672 38.678 38.688 38.690 38.676 38.671 38.662 38.545 38.553 38.575 38.578 38.608 38.600 38.591 38.573 38.618 38.631 38.633 38.598 38.628 38.635 38.566 38.621 38.557 38.492 38.588 38.544 38.513 38.600 38.607 38.466 38.487 38.502 38.475 15.631 15.641 15.669 15.654 15.665 15.670 15.673 15.678 15.686 15.697 15.699 15.706 15.751 15.751 15.751 15.740 15.741 15.742 15.737 15.732 15.731 15.725 15.702 15.679 15.680 15.673 15.679 15.675 15.672 15.670 15.673 15.674 15.675 15.664 15.672 15.672 15.669 15.685 15.695 15.703 15.715 15.698 15.700 15.717 15.723 15.698 15.702 15.704 15.702 18.249 18.316 18.463 18.511 18.577 18.611 18.644 18.715 18.818 19.042 19.069 19.241 19.992 20.023 20.000 19.751 19.777 19.761 19.709 19.645 19.639 19.540 19.250 18.838 18.783 18.754 18.728 18.644 18.613 18.594 18.608 18.612 18.621 18.620 18.631 18.617 18.605 18.877 19.050 19.180 19.264 19.219 19.152 19.327 19.356 18.888 18.833 18.882 18.876 15.733 15.725 15.728 15.669 0.008 19.644 19.339 19.453 18.472 0.008 23 25 27 29 31 33 35 37 39 41 43 45 49 51 53 57 59 63 65 67 69 73 75 85 87 89 91 93 95 99 101 103 107 109 111 113 115 117 119 121 123 125 127 129 131 133 135 137 139 2.0981 2.0950 2.0944 2.0815 2.0772 2.0749 2.0718 2.0644 2.0541 2.0296 2.0272 2.0087 1.9358 1.9325 1.9348 1.9580 1.9557 1.9578 1.9631 1.9687 1.9691 1.9786 2.0023 2.0466 2.0537 2.0571 2.0615 2.0704 2.0733 2.0745 2.0753 2.0756 2.0748 2.0729 2.0733 2.0752 2.0729 2.0459 2.0240 2.0069 2.0031 2.0055 2.0109 1.9973 1.9946 2.0365 2.0436 2.0391 2.0383 1.1675 1.1710 1.1783 1.1825 1.1859 1.1877 1.1895 1.1938 1.1997 1.2132 1.2147 1.2251 1.2693 1.2713 1.2698 1.2548 1.2564 1.2553 1.2524 1.2487 1.2484 1.2426 1.2260 1.2014 1.1979 1.1966 1.1945 1.1894 1.1876 1.1866 1.1873 1.1875 1.1879 1.1888 1.1888 1.1880 1.1874 1.2035 1.2137 1.2214 1.2258 1.2243 1.2199 1.2297 1.2310 1.2032 1.1994 1.2024 1.2021 C F G slags 2sdb 1.9622 1.9911 1.9783 2.0933 0.0004 Granites 1.2486 38.544 1.2298 38.506 1.2368 38.483 1.1789 38.668 0.0001 0.020 a External analytical uncertainty (n)10). (n)3). b Total external uncertainty and EF. The composition of the four saprolite samples (139133 cm) have a homogeneous 206Pb/207Pb of 1.2015 ( 0.0020, slightly lower than the granite composition. The 206Pb/207Pb ratio rises to ca. 1.22 in samples 131-117 cm and then drops to a constant 206Pb/207Pb of 1.1878 ( 0.0015 for samples 11595 cm. This section of the profile corresponds to a EF Pb comprised between 10 and 12. The 206Pb/207Pb ratios raise again systematically from the 93 cm sample to the 75 cm sample and stays at high values (1.24-1.27) to sample 47 cm. This section also shows the lowest EF Pb of 1 and 2. Finally, the 45-23 cm samples show a systematic decrease of the 5136 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 14, 2005 Pb/207Pb ratios from 1.225 to 1.165. This section of the profile corresponds to the highest EF Pb measured. Pollen Analysis. The pollen diagram of the lateral core of the Narses Mortes peatland is presented in Figure 4. In the diagram, only selected taxa (pollen percentages and concentrations) are illustrated with the lead anomalies (ppm). At the bottom of the profile (> ca. 390-160 B.C.; 138-119 cm), a forested environment at the time of the peat inception is indicated from high pollen percentages and concentrations of birch (Betula; 10-20%), deciduous oak (deciduous Quercus; 10-15%), and beech (Fagus; 15-20%). Certain grasses (Poaceae) were also strongly represented during this period (10-20%) probably due to local pollen inputs from Molinia caerula growing on the peatland. A gradual reduction in the abundance of Betula and Fagus began after 390-160 B.C. (119 cm) indicating a fragmentation of the forest cover. This opening of the forest cover is associated with an abrupt and rapid increase in Pb anomalies reaching a maximum at 113 cm. The increase in the pollen representation of Quercus (20-30%) probably reflects long-distance pollen transport from oak trees located at lower altitudes on the Mont Lozère. The decline in pollen concentrations affecting all species undoubtedly results from an acceleration of the net peat accumulation rate compared to the previous period. Subsequently, lead anomalies began to drop progressively at the same time of a new increase in the pollen representation of Fagus, Abies, and Betula. This increase is an indication of a densification of the forest cover and a response of a cessation of metallurgical activities in the immediate vicinity of the peatland. Percentages of Fagus remained high (10-30%) until around 50 cm but were also characterized by some fluctuations. Agropastoral activities are deduced from the abundance of ruderal species (Rumex, Cerealia, Chenopodiaceae) at depth 60 cm. A second episode of deforestation is deduced from a significant decrease and/or a definitive disappearance of Betula, Abies, Fagus, and Quercus from the summital zones of the Mont Lozère, corresponding to a peak in lead anomalies between 48 and 30 cm. The pollen percentages of Poaceae are maximum for all the profile, but a part of the Poaceae pollen likely reflects local pollen inputs. Asylvatic vegetation characterizes the past decades (<20 cm). Pollen assemblages are dominated by grasses, except for pine (likely Pinus sylvestris), a high pollen producer, which was reintroduced during the 19th century. Discussion It is clear from the chemical, isotopic, and pollen data that the core of the Narses Mortes peatland recorded at least two different episodes of metal enrichments related to anthropogenic activities. Origin of Mineral Materials and Assessment of Anthropogenic Contribution. Ash content along the profile is very variable (Figure 3a). The four bottom samples have the highest ash content (73.4-85.3%) and represent the saprolite of the granitic basement which formed during the early stage of the peat formation. The chemical compositions of these four samples are thought to represent those of detrical sediments reaching the sedimentary basin during the whole history of peat formation. The Pb/Al ratio of the saprolite samples is slightly shifted toward higher values compared to the granite (5.2 × 10-4 ( 0.3 × 10-4 vs 4.3 × 10-4 ( 0.3 × 10-4) probably because of a change in mineralogy. The Pb/Al ratios of the saprolite, the 131-121 and 75-45 cm background section, are similar if we can consider Al analytical uncertainties of about 10% (Figure 3f), while their lead isotopic compositions are wide (Figure 3e). A mineral sorting might explain these observations. These small changes may effectively occur along the profile but seem insignificant regarding the EF calculations. Indeed, although the six samples above the saprolite (131-121 cm) show a significant decrease in their ash content FIGURE 4. Pollen and lead concentration versus depth diagram with the corresponding radiocarbon dates. Only selected taxa are presented. Results are expressed as pollen percentages (curves) and pollen concentrations (histograms). Shaded areas correspond to periods of metallurgical activities. from 45 to 21%, their corresponding Pb EF stayed at 1, suggesting no anthropogenic input during that period. A second period free of anthropogenic input is recorded in samples 75-49 cm with Pb EF varying between 1 and 2 for ash contents of 47 ( 10%. If only samples having Pb EF of 1 or 2 are considered, a significant variation in Pb isotopic composition is observed. This variation results from a change in crustal source materials which may be external to the hydrologic system (aerosols) or simply reflect mineralogical sorting. This last hypothesis is supported by the fact that all these low Pb EF samples plot along a reference 300 Ma PbPb isochron passing through the composition of the granite and the saprolite (Figure 5). This suggests that most of the detrical sediments feeding the peat bog along the whole profile originate from the surrounding granitic catchment. A mixing involving silicate aerosols with a composition averaging larger segments of the upper continental crust (UCC) would define a much steeper slope in the Pb-Pb isochron diagram, as shown by different estimated compositions of the UCC (35) (Figure 5). The Possible Mobility of Lead through the Profile. The 113-95 cm section presents a sharp contrast in lead anomalies with the surrounding sections representing the background lead content (Figure 3d). Moreover, this section presents a constant lead isotopic composition (Figure 3e). Thus, a postdepositional Pb migration is not probable. In that case, one would observe a tail shaped profile. Sources of Pb through Time (Figure 3e). The 139-117 cm section is the onset of the formation of the Narses Mortes peat bog. All the metals show no or low EF, and the Pb isotopic composition of these samples suggests a typical local crustal origin. Hence, no anthropogenic activity is recorded in this section of the profile. The age of deposition is older than ca. 390-160 B.C., that of the -119 cm depth sample (Table 1). In this area, the Narses Mortes peat bog started to develop before the middle of LaTène period, the second Iron Age. FIGURE 5. 207Pb/204Pb versus 206Pb/204Pb diagram showing all the low EF Pb aligned along the 300 Ma reference isochron. The lead isotopic compositions of the average UCC, reported by Millot et al. (2004) (35). The 115-95 cm section presents an important increase in its Pb EF with a significant change in its lead isotopic composition. At 115 cm (∼ ca. 200 B.C., Iron Age), the 206 Pb/207Pb ratios decrease significantly and reached values down to 1.1874. This is interpreted as the result of a major change in the source of Pb, which lasted over a very large period of time, about 200 years. Indeed, the 206Pb/207Pb ratios remained relatively constant to the 95 cm sample, which has a deposition age of approximately 20 A.D. Because the lead isotopic composition of peat samples is very close to that of slags present in the surrounding archaeological sites (206Pb/207Pb of 1.17891 ( 0.0022) (35), we suggest that this section of the profile recorded the trace of metallurgical activities at that time. Besides As, the other metals do not VOL. 39, NO. 14, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 5137 show a significant increase in this section of the profile suggesting that either they were not emitted in the environment during smelting or they have a mobile behavior in peat sediments so that anthropogenic traces were erased with time. The later hypothesis is the most probable because the slags are also Sb, Cd, and Zn-rich (Baron et al. manuscript in preparation). Furthermore, it was shown that Zn is mobile with time in peat sediments (36). The 93-45 cm section is characterized by a return to the crustal background values with Pb EF systematically decreasing from 7 (93 cm) to less than 2 (75-45 cm) and 206 Pb/207Pb moving up to a natural crustal composition. This suggests the end of important metallurgical activities at around ca. 20 A.D. The fact that it takes close to 300 years for the signal to reach crustal values may be interpreted in two ways. The first one would be that the metallurgical activities did not completely stop but diminished progressively as the Roman Period ended. Another interpretation would be that activities really ended at ca. 20 A.D. and that the progressive return to natural crustal values is a simple relaxation of the geochemical/hydrological system. This last hypothesis would imply that a significant input of Pb to the peat came from the washout of metallurgical wastes during rain events and not directly from the atmosphere. The Narses Mortes peat did not recorded Pb anthropogenic input for the following 300-400 years (ca. 700-800 A.D.). Again, during this whole period, Sb, Cd, Zn, and As concentrations in the profile do not show any systematic behavior like Pb, having enrichment factors varying erratically between 3 and 10 depending on the element. This again suggests that these metals might not have a conservative behavior in peat samples through time. The 45-23 cm depth section is characterized by a second increase in Pb EF and a decrease in 206Pb/207Pb ratios. According to chemical and isotopic data, this section recorded two different anthropogenic events. The first one occurs between samples 45 and 35 cm, for which only Pb EF increased and not the other metals EF. Sample 41 cm yielded a radiocarbon Medieval age of ca. 1156-1264 A.D. which is in total agreement with the ca. 1120 ( 30 A.D. 14C age found for coal samples related to paleometallurgical activities around the Narses Mortes peatland and with the age of other similar coal samples elsewhere on the Mont Lozère (ref 22 and unpublished data). Furthermore, the Pb isotopic ratios measured in this section of the peat profile change progressively from typical crustal composition toward that of slag found in the different paleometallurgical sites. This first anthropogenic event recorded in that section of the profile is then interpreted as reflecting the impact of Medieval metallurgical activities in the area. Although many sites were found to be of the Medieval age, the Pb EF recorded by the 45-35 cm peat samples are lesser than the ones recorded in the 115-95 cm section (Iron Age - Roman Period). This may result from proximity of the earlier event or the process by which Pb reached the peat: atmospheric only or atmospheric and washout of slag. A second anthropogenic event is recorded in the 35-23 cm samples for which all metals EF increase systematically. In these uppermost samples, the Pb isotope ratios progressively changed from “Medieval slag” composition toward those of less radiogenic compositions (206Pb/ 207Pb of 1.1675 in sample at 23 cm depth). The 207Pb/204Pb vs 206Pb/204Pb diagram of Figure 6 presents all the data obtained in this study. A synthesis of the different isotopic evolution steps through time is shown. First, a saprolite formed at the base of the peat formation, with an isotopic composition different from that of the granitic basement, probably because of mineral sorting. The following “true” peat samples show a rapid decrease in their mineral content, and the isotopic ratios progressively reach that of the granite. Samples recording the two paleometallurgical 5138 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 14, 2005 FIGURE 6. 207Pb/204Pb versus 206Pb/204Pb diagram illustrating the historical reconstruction following the corresponding number. The historical reconstruction starts with the granite (i.e. 1). During the peat land formation, granite undergoes an in situ alteration in order to lead to the saprolite (i.e. 2) presenting a wide range of lead isotope (i.e. 3). Some metallurgical activities occur on the massif; Pb arrives in the peat (i.e. 4) and reaches the slag composition (i.e. 5). This first smelting activity is strictly Gallic. Indeed, the -119 cm depth is dated at ca. 390-160 B.C., and it corresponds to the beginning of Pb increase. These activities might have lasted until 20 A.D. After the Roman invasion (ca. 52 B.C.), metallurgical activities decreased, thus, lead isotopes became more radiogenic (i.e. 6) and reached and exceeded the local granite (i.e. 7). This metallurgical diminution begins in the 1st century A.D. until ca. 900 A.D. Then, during the Roman period until the end of the Carolingians reign, no anthropogenic activities are reported on the massif except pastoral ones as indicating by pollen analysis. At ca. 1000 A.D., Pb concentration increases again, thus, lead isotopes reach fewer radiogenic values (i.e. 8); it is the beginning of the second metallurgical activity. Lead isotopes present some values close to those of slags (i.e. 9). These metallurgical activities (beginning at ca. 900 A. D. in the peat record) are ones shown in slags (ca. 985-1277 A.D.) collected during the fieldwork. At 35 cm depth, the medieval signal is rapidly disturbed by a more recent one, and then lead isotopes continue toward a less radiogenic signal that not corresponding to regional ores sources (22). activities on the Mont Lozère form a linear array between crustal and slag compositions suggesting anthropogenic Pb inputs. Indeed, both Pb EF and Pb isotopes mass balance suggest that 90% of total Pb in these samples has an anthropogenic origin. Between these two events, peat samples recorded no Pb EF with typical crustal isotopic values. The four uppermost peat samples define a linear array suggesting less radiogenic inputs where sources are unknown. Forest Cover Reconstruction on the Mont Lozère Massif. The pollen diagram of the Narses Mortes Peatland indicates that past metallurgical activities played a significant role on the long-term vegetation dynamics of Mont Lozère and were a disturbed factor. Two main periods of fragmentation of the vegetation cover occurred during the last 2200 years and are related to peaks in lead concentrations (Figure 4). Before the onset of the oldest period (> ca. 390-160 B.C.), the summital zones of Mont Lozère were characterized by a forest cover, as indicated by high pollen percentages and concentrations of birch (Betula), deciduous oak (deciduous Quercus), and beech (Fagus). During the first period of mining activities, an opening of the forest cover is deduced from a significant decrease in the abundance of Fagus and Betula. Despite a synchronous increase in pollen percentages of deciduous Quercus at the same time, this species was probably also affected by metallurgical activities. This increase in pollen percentages likely reflects long-distance pollen transport from oaks located at lower altitudes, in the Tarn valley. The radiocarbon date obtained at depth 119 cm (ca. 390-160 B.C.) indicating an Antique age for these first activities is supported by the presence of pollen of planted tree species such as chestnut (Castanea) and walnut (Juglans). A subsequent increase in the abundance of the abovementioned arborescent species, especially Fagus, occurred at the same time of a gradual decrease in lead concentrations (Figure 4). These are an indication of a lower pressure of mining activities on the vegetation cover and/or a cessation of mining activities in the vicinity of the peatland. A densification of the forest cover is indicated by higher pollen percentages and/or concentrations of Fagus, Betula, deciduous Quercus, and Abies. The second episode of forest clearance, also associated with a peak in lead concentrations, happened more recently during Medieval times. The representation of all tree species declined abruptly leading to the disappearance, among others, of beech and oak in the area where smelting slag sites are located. The current asylvatic character of the summital zones of the Mont Lozere is a response of human activities during this period. If metallurgical activities exercised strong pressure on the forest cover during the Medieval period, the deforestation is also likely the result of agropastoral activities. An abrupt increase in the representation of ruderal species (Chenopodiaceae, Rumex, Cerealia) occurred at 60 cm depth (ca. 540-660 A.D.) indicating an intensification of agropastoral activities. For the moment, it is not possible to indicate what was the exact contribution of mining versus agropastoral activities on the fragmentation of the forest cover. However, the high pollen representation of ruderal species until the top of the record indicates that agriculture and pastoralism inhibited the reforestation of Mont Lozère after the cessation of medieval metallurgical activities, with the exception of Scots pine (Pinus sylvestris) planted during the second half of the XIX century. The Silver of the Gabales Tribe. The Gallic metallurgical activity occurring at 390-160 B.C. corresponds to the period where the Lozère “département” was the territory of the Gabales tribe (Gaballum). Caesar (100-44 B.C.) in his book “De Bello Gallico” (58 B.C.) mentions that the Gabales tribe (37) lived in the present-day Lozère department. Furthermore, Strabon (58 B.C.-25 A.D.), in his book IV, 2.2, talked about “Gabales Silver” and Gallic metallurgy (38) in the same region. Actually, the settlement of “Javols” corresponds to the ancient city of the Gabales tribe (Anderitum during the Roman period) as reported by the numerous excavations of the Gallo-Roman city. However, actually, there are no archaeological proofs about metallurgical activities in this region This geochemical record represents the first signs of local metallurgy for this period. Furthermore, the pollen analyses complete and support the record. The geochemical and paleobotanical data combined with the archaeological knowledge of the area allowed a comprehensive interpretation and a better understanding of ancestral activities. Then, mining heritage should be taken account in order to not overestimate the impact of modern pollutions (39) and to better understand the origin of the old sources (40). The study of interactions between early societies and their environment is essential in order to better manage our present-day environment. Acknowledgments The grant was founded by ADEME (the French Environmental Agency) and by Languedoc-Roussillon Region. All the analyses have been supported by CRPG and SARM (CNRS), in Nancy. We thank the CERL of Mende and the National Park of Cévennes for their assistance. Thanks to the “SaintEtienne du Valdonnez” commune and its mayor, Claude Feybesse, for his technical support during fieldwork and his good reception. Special thanks to Jean Peytavin. 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Received for review November 22, 2004. Revised manuscript received April 15, 2005. Accepted May 4, 2005. ES048165L