William Rapuc
email: william.rapuc@univ-smb.fr

Julien Bouchez

Pierre Sabatier

Kim Genuite

Jérôme Poulenard

Jérôme Gaillardet

Fabien Arnaud

Quantitative evaluation of human and climate forcing on erosion in the Alpine Critical Zone over the last 2000 years

Keywords: Erosion, Human impact, Lake sediments, Source to sink method, isotopic mixing model

Soil erosion is one of the main environmental threats affecting the Critical Zone (CZ) and thus ecosystem services and human societies. Through time, physical erosion is linked to both climate variations and the landscape evolution under long-term human pressures. In mountainous areas where erosion is highest a combination of large spatial and temporal approaches allows to assess the effect of these forcing factors on erosion rates. Here, we apply a retrospective approach based on lake sediments to reconstruct the long-term evolution of erosion in alpine landscapes. Lake Iseo in the Italian Alps acts as a natural sink for all the erosion products from a large catchment (1777 km²). This catchment is representative of the southern Italian Alps, where Holocene human activity and climate fluctuations are well known. The approach combines a source-to-sink method, using isotopic geochemistry (εNd, 87 Sr/ 86 Sr) associated to a multiproxy study of a lacustrine sediment section covering the last 2000 years. The applied method allows us to disentangle the role of climate and land use as erosion forcing factors through their differential impact on the various rock types present in the catchment. Indeed, the high-altitude part of the Iseo catchment, where glacier advances and retreats drive the erosion, presents isotopic signature different from those of the sedimentary rocks located in the lower part of the catchment, where both human activities and precipitations impacted erosion through time. A chronicle of glacial erosion over the last 2000 years was produced. Once the climatic trend was highlighted, the signal of erosion of sedimentary rocks was investigated to understand the influence of humans. From the Roman Period to the Industrial Age several periods of deforestation and increased human pressure were documented. The past sediment yield inferred for sedimentary rocks exhibits the highest values (> 80 t.km -2 .yr -1 ) at periods of intense human practices. Hence, since the late Roman Period, human activities seem to be the dominant forcing factor of the physical erosion in mountainous environment of northern Italy. This study presents the first reconstruction through time of sediment yield derived from lake sediments associated with sediment sources identification and quantitative evaluation of the CZ erosion drivers.

Introduction

Erosion is a geological process that, on long timescales, impacts the Earth's topography, tectonics and climate (e.g. Gayer et al., 2019 and references therein). Currently, erosion is also the main process leading to the deterioration of the Critical Zone (CZ), defined as the thin active layer at the Earth's terrestrial surface, which host life forms. Among other impacts, by destroying soils, erosion alters food production, drinking water quality, ecosystems services, biodiversity, and soil carbon stocks (e.g. [START_REF] Bosco | Soil erosion risk assessment in the alpine area according to the IPCC scenarios[END_REF][START_REF] Panagos | The new assessment of soil loss by water erosion in Europe[END_REF]. Erosion also directly affects human societies [START_REF] Montgomery | Dirt -The Erosion of Civilizations[END_REF], especially in mountainous environments [START_REF] Bosco | Soil erosion risk assessment in the alpine area according to the IPCC scenarios[END_REF] and has thus become a scientific subject of prime importance worldwide [START_REF] Borrelli | Land use and climate change impacts on global soil erosion by water (2015-2070)[END_REF][START_REF] Fao | Status of the world's soil resources (SWSR)-main report[END_REF][START_REF] Panagos | The new assessment of soil loss by water erosion in Europe[END_REF][START_REF] Rusco | Soil Erosion: a main threats to the soil in Europe[END_REF]. Increasing concern about these deleterious effects has led Europe and the United Nations to rank soil erosion as one of the main threats to mankind, and to call for quantitative evaluation of soil loss over large spatial and long temporal scales (e.g. Panagos et al., 2015 and references therein). The objective of these evaluations is to better assess the relative effects of the main factors controlling erosion. In particular, climate (for example through the precipitation regimes or glaciers advances and retreats) and human activities (through land-use and vegetation cover management) have been identified as major controls on long-term changes in erosion rates (e.g. [START_REF] Panagos | The new assessment of soil loss by water erosion in Europe[END_REF].

Besides the use of modelling approaches (e.g. [START_REF] Angima | Soil erosion prediction using RUSLE for central Kenyan highland conditions[END_REF][START_REF] Borrelli | Land use and climate change impacts on global soil erosion by water (2015-2070)[END_REF][START_REF] Millward | Adapting the RUSLE to model soil erosion potential in a mountainous tropical watershed[END_REF][START_REF] Panagos | The new assessment of soil loss by water erosion in Europe[END_REF][START_REF] Renard | RUSLE: Revised universal soil loss equation[END_REF], this knowledge gap can be filled through the acquisition of empirical constraints provided by the study of lake sediment archives, in particular with the aim of evaluating erosion rates over the centennial to millennial time scales over which climatic and human forcing are the most likely drivers of erosion (e.g. [START_REF] Arnaud | Erosion under climate and human pressures: An alpine lake sediment perspective[END_REF]. Although regional syntheses of erosion rates over these time scales exist, in particular for the European Alps (e.g. Hinderer et al., 2013 and references therein), only a few studies have produced a quantitative assessment of erosion rates through time (e.g. [START_REF] Bajard | Pastoralism increased vulnerability of a subalpine catchment to flood hazard through changing soil properties[END_REF], but none on the quantitative impact of the various factors. The "source-to-sink" approach (e.g. [START_REF] Collins | Selecting fingerprint properties for discriminating potential suspended sediment sources in river basins[END_REF] offers the possibility to track the sources of sediment inputs (sub-catchments and/or rock types) to a sink (e.g., a lake) through time, making it in turn possible to disentangle the relative impacts of climate and human activities upon erosion rates, provided that each sediment source is sensitive to a given type of forcing.

For this study, we selected Lake Iseo, located in the Italian Alps, at the downstream end of the Val Camonica valley, an area where human activities since the beginning of the Neolithic period are well documented (e.g. Pini et al., 2016 and references therein). Lake Iseo drains a large catchment that can be split into three main sediment source areas, distinguishable through the means of geochemical tools, and coinciding with different relative roles of climatic and human forcings on erosion over the centennial to millennial scales:

(i)
The northernmost, high-altitude part of the catchment underlain by calco-alkaline rock series and where numerous glaciers have shaped the landscape [START_REF] Scotti | A regional inventory of rock glaciers and protalus ramparts in the central Italian Alps[END_REF];

(ii)

The mid-to high-altitude part of the catchment underlain by metamorphic Variscan basement rocks where both glaciers and human activities have impacted erosion [START_REF] Pini | Ecological changes and human interaction in Valcamonica, the rock art valley, since the last deglaciation[END_REF][START_REF] Scotti | A regional inventory of rock glaciers and protalus ramparts in the central Italian Alps[END_REF] (iii)

The southernmost, low-to mid-altitude part of the catchment underlain by Permian to Cretaceous sedimentary cover, and the locus of most human activities in the Val Camonica since the beginning of the late Holocene (Pini et al., 2016 and references therein).

To quantify the evolution of erosion in the catchment of Lake Iseo over the late Holocene, we selected a sediment sequence retrieved in the deep depositional basin of the lake, where most of the finegrained sediment inputs from the catchment have been captured. River samples were also collected from all the sub-catchments directly contributing to Lake Iseo. Neodymium (Nd) and Strontium (Sr) isotopic compositions and concentrations of river and lake sediments were used to constrain the results of a mixing model (for discussion of the model please refer to sub-section 4.3). Results from the model yielded quantitative contributions of each sediment source, allowing us to disentangle the effects of climate fluctuations and human activities on erosion in the Iseo catchment from the Roman Period to the present day.

Study sites

Lake Iseo (45°44.205′N; 10°4.340′E) lies in the Italian Alps, at the southern end of the Val Camonica valley at an altitude of 185 m a.s.l (above sea level). The lake is 25-km long and has a surface area of 60.9 km 2 .

Lake Iseo is fed water and sediment by the Oglio River, which originates in the Adamello Massif, and is the main lake tributary and unique outlet (Fig. 1). Upstream from Lake Iseo, the Oglio River drains a large catchment of 1777 km 2 with a maximum elevation of 3539 m a.s.l in the Adamello Massif and a mean altitude of 1400 m a.s.l [START_REF] Garibaldi | The trophic evolution of Lake Iseo as related to its holomixis[END_REF]. The Oglio catchment is limited to the North and East by the Insubric line, one of the main lineaments of the European Alpine [START_REF] Mittempergher | Fault reactivation and propagation in the northern Adamello pluton: The structure and kinematics of a kilometre-scale seismogenic source[END_REF], separating the Austroalpine domain (N) from the southern Alps (S). Rocks of high alpine metamorphic grade from the Austroalpine unit exist at the extreme northern limit of the catchment but constitute very small areas [START_REF] Chiesa | [END_REF][START_REF] Gosso | Note illustrative della Carta Geologica d'Italia alla scala[END_REF]. River and the SEB18 lake sediment coring site are also shown (grey circle). Lake Iseo bathymetry is modified from [START_REF] Pilotti | Data set for hydrodynamic lake model calibration: A deep prealpine case[END_REF] and is available at https://hydraulics.unibs.it/hydraulics/attivita-scientifica/laghi_pvbs/lake-iseo-data-set/.

The faulted Variscan basement of the southern Alps is made of low-to high-grade metamorphic rocks (pelites, schists, amphibolites, gneiss) visible in the North and West part of the Upper Oglio catchment.

To the South, the catchment is underlain by the sedimentary cover of the southern Alps, mainly composed of Triassic, Jurassic, and Cretaceous marlstones, limestones, and dolostones, associated with outcrops of Permian sandstones [START_REF] Bini | Foglio 078 Breno[END_REF].

The NE part of the catchment area is underlain by the famous Adamello batholith which is a plutonic series of calco-alkaline rocks of Cenozoic age (30 to 40 Ma) that intruded the old southern Alps Variscan basement [START_REF] Mittempergher | Fault reactivation and propagation in the northern Adamello pluton: The structure and kinematics of a kilometre-scale seismogenic source[END_REF]. The Adamello massif is mainly composed of felsic plutonic rocks such as tonalites, granites, granodiorites, and quartzodiorites, with some minor outcrops of mafic to ultramafic rocks [START_REF] Brack | Note illustrative della Carta Geologica d'Italia alla scala[END_REF]. Glaciers and rock glaciers are particularly numerous in this part of the catchment [START_REF] Scotti | A regional inventory of rock glaciers and protalus ramparts in the central Italian Alps[END_REF] and are suspected to have strongly impacted erosion in the area.

In terms of human occupation, the southernmost area, closest to the lake, is located at low to mid altitude, and is where human activities are currently concentrated (Fig. 2). Archaeological and palynological studies also locate the main human settlements and agrarian activities within this area since the Neolithic (e.g. [START_REF] Marziani | The effects of human impact on the arboreal vegetation near ancient iron smelting sites in Val Gabbia, northern Italy[END_REF][START_REF] Pini | A high-resolution Late-Glacial -Holocene pollen diagram from Pian di Gembro (Central Alps, Northern Italy)[END_REF][START_REF] Pini | Ecological changes and human interaction in Valcamonica, the rock art valley, since the last deglaciation[END_REF]. Human activities in the rest of the catchment area are sparse, restricted to herd grazing and only minor urban areas, both for modern times (Fig. 2) and in the recent past [START_REF] Pini | Ecological changes and human interaction in Valcamonica, the rock art valley, since the last deglaciation[END_REF].

Materials and Methods

Lake sediment

In October 2018, a 15.5-m-long sediment sequence coded "SEB18" (45°43.536'N; 10°3.888'E) was retrieved from the deep basin of Lake Iseo, at 251 m below the lake surface (b.l.s). This site was selected as it is supposed (i) to be less influenced by event sedimentation [START_REF] Bini | Morphology and geological setting of Iseo Lake (Lombardy) through multibeam bathymetry and high-resolution seismic profiles[END_REF] and (ii) to have collected the sediment input from the Oglio River in a continuous way. For this survey, two UWITEC 90-mm diameter piston corers (Uwitec, Mondsee, Austria) were used, operated from an UWITEC platform (EDYTEM/LSCE/C2FN). Most of the sections were split, photographed at highresolution (20 pixels.mm -1 ), described and logged in detail. The identification of specific layers on the overlapping sections allowed the creation of the composite sediment sequence.

Thirty 1 cm-long sediment samples were collected from the background sedimentation (supplementary Table S1 & S2) using graduated syringes for geochemical analyses (sections 3.4 and 3.5). Due to the presence of multiple event-specific sediment layers, a continuous sampling step was impossible to apply. Sediment dry bulk density (DBD) was measured using sediment samples of an invariant 5 mL volume.

Loss-on-ignition measurements were conducted on all the sediment samples following the method of [START_REF] Heiri | Loss on ignition as a method for estimating organic and carbonate content in sediments: reproducibility and comparability of results[END_REF]. The proportion of detrital silicates in the sediment samples was evaluated from values of non-carbonate residue (NCIR) that is the sediment remaining after the last ignition step (950° for 2h; [START_REF] Bajard | Erosion record in Lake La Thuile sediments (Prealps, France): Evidence of montane landscape dynamics throughout the Holocene[END_REF].

To produce a precise age-depth model for the sediment sequence, we combined varve counting, shortlived radionuclides ( 210 Pb, 137 Cs, 241 Am), and 14 C. Varves were counted over the first 37 cm of the core, then 38 samples were collected over the first 48.1 cm of the sequence to measure short-lived radionuclide activities at the Laboratoire Souterrain de Modane using the well-type germanium detectors [START_REF] Reyss | Large, low background well-type detectors for measurements of environmental radioactivity[END_REF]. Short-lived radionuclide chronology was carried out using the R code package "serac" [START_REF] Bruel | serac: an R package for ShortlivEd RAdionuclide chronology of recent sediment cores[END_REF]. Thirteen samples of vegetal macro-organic remains were used to perform 14 C measurements at the LMC14 laboratory (CNRS) using AMS. Dates were calibrated at 2 sigma using the Intcal20 calibration curve [START_REF] Reimer | The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP)[END_REF], and the age-depth model was performed using R code packages "clam" [START_REF] Blaauw | Methods and code for 'classical'age-modelling of radiocarbon sequences[END_REF] and "bacon" [START_REF] Blaauw | rbacon: Age-Depth Modelling using Bayesian Statistics[END_REF]) in R software.

River sediment samples

To characterize the source of sediments accumulated in Lake Iseo deep basin, 14 river sediment samples were collected in May 2018 from flood deposits in all sub-catchments directly contributing to the Oglio River, close to the confluence with the main river (Fig. 1; Table S3). Eight samples were also collected from flood deposits in the Oglio main valley at several hundred meters downstream of each confluence to test for the mixing between sub-catchment and main river sediments (Fig. 1; Table S3).

Sub-catchments covered by this sampling set represent 52 % of the Iseo catchment total area. Samples were collected manually, an aliquot of each sample was sieved, and only the fraction finer than 63 µm was saved for later analysis, to account for the fact that the sedimentation in the studied lake sediment core is mostly of silty to clayey nature.

Sample preparation

Even in carbonate-dominated terrains, soil physical erosion occurs mostly through the removal of silicate phases, as carbonate minerals tend to be removed from soils through chemical dissolution. For this reason, our analysis focuses on siliciclastic material, and we removed the carbonate component of the lake and river sediments before geochemical analyses. Although the authigenic carbonate production is poorly preserved in the deep basin of peri-Alpine lakes [START_REF] Ramisch | Calcite dissolution in two deep eutrophic lakes[END_REF], this procedure also ensures that authigenic lake carbonates do not affect our interpretation. To that effect, after crushing in an agate mortar and drying at 60°C for 72 h in a laboratory oven, river and lake sediment samples were decarbonated by two successive 5 mL HCl 0.5N leaching steps to remove authigenic and detrital carbonate (supplementary S4). Major and trace elements of supernatants from each leaching step were measured by Q-ICP-MS (section 3.2) to evaluate the amount of calcium (Ca)

and Sr lost. As discussed below, this leaching procedure did not lead to complete removal of the carbonate component from the river sediment samples, which might be due to the presence of dolomite in the sediment.

A series of river sediment samples was kept unleached and measured as bulk powder for isotope and major and trace element concentration measurements. All samples (bulk or residue from the leaching steps), then underwent a digestion using concentrated acid mixtures of HF, HNO3, and HCl.

Major and trace elements

Major and trace element concentrations were measured using an Agilent 7900 quadrupole ICP-MS (Q-ICP-MS) at the High-Resolution Analytical Platform (PARI) of the Institut de physique du globe de Paris (IPGP). Liquid samples were sprayed through a micro-nebulizer in a Scott spray chamber prior to ionization. Magnesium (Mg), calcium (Ca), and iron (Fe) were measured using a collision-reaction cell with helium gas (5 mL.min -1 ) to remove polyatomic interferences. Nd and Sr were measured without collision gas. Signal drift and matrix effects were corrected by injection of scandium, indium, and rhenium as internal standards after inline mixing with the samples. Two sets of multi-element calibration standards (one for major and one for trace elements) were analysed to compute the calibration curves that were used to convert measured counts to concentrations. The reported uncertainties were calculated using the algebraic propagation of blank subtraction and sample count standard deviations (n=3). The NIST®SRM®2709a reference material (San Joaquin soil) was processed as samples and analysed repeatedly during the sequences to evaluate the accuracy of the measurements. The detection limit was between 0.2 and 0.5 ppt depending on the element, and the internal errors were 5% on average. The weight loss during carbonate leaching of lake (and river in some cases) sediments was considered in the estimate of major and trace element concentrations of the residue, such that the reported concentrations relate to the mass of residue (that is, carbonate-free, and referred to as "silicate" in the following) component of the sediment (see supplementary S4).

Isotopic composition

Isotope measurements were all performed at the PARI analytical platform of IPGP. After powder digestion, Sr and Nd were separated from the sample matrix by extraction chromatography. We used an Sr-SPEC resin (Eichrom) for Sr [START_REF] Hajj | Radiogenic and "stable" strontium isotopes in provenance studies: A review and first results on archaeological wood from shipwrecks[END_REF] and a combination of TRU-spec and Ln-spec resins for Nd [START_REF] Cogez | Constraints on the role of tectonic and climate on erosion revealed by two time series analysis of marine cores around New Zealand[END_REF].

Sr isotope ratios were measured by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS; Neptune, Thermo-Fisher Scientific) with an APEX-Q (ESI) desolvation system as a sample introduction system. Rubidium (Rb, that was observed in residual amounts in some samples, even after chromatographic purification) interference on mass 87 and krypton (Kr, present in the argon gas used to produce the plasma) interferences on masses 84 and 86 were corrected for using the 85 Rb and 83 Kr signals along with the Rb and Kr isotope ratios measured at the beginning of the sequence.

Instrumental and natural mass fractionation on the 87 Sr/ 86 Sr ratio were corrected using an exponential law, the measured 88 Sr/ 86 Sr ratio and the "natural" abundance 88 Sr/ 86 Sr ratio assumed to be equal to 8.3752. Measurement accuracy was checked through repeated measurements of the NIST pure-Sr, isotope reference material SRM 987 (2 S.D of 2.9 x 10-5), and the NIST soil reference material SRM 2709a ( 87 Sr/ 86 Sr = 0.70823 ± 0.00002; comparing well with the value provided by Brazier et al., 2020 of 0.70814 ± 0.00002). Each sample was measured up to three times during a session. For samples measured three times, the 95% confidence interval was obtained from Student's t-distribution and ranged from 3 x 10 -6 to 8 x 10 -3 . For other samples measured less than 3 times, the 2 S.D of 4.9 x 10 -5 estimated from the repeated measurements of the reference material NIST SRM 2709a (processed through powder digestion and separation as for samples) was used as an estimate of the 95% confidence interval.

Nd isotope analyses were performed by MC-ICP-MS Neptune using N2 addition and X-cones with an APEX-IR (ESI) desolvation system as the sample introduction system. Instrumental and natural mass fractionation on the 143 Nd/ 144 Nd ratio were corrected for using an exponential law, the measured 146 Nd/ 144 Nd ratio and its natural abundance ratio, taken as 0.7218. Accuracy was checked through repeated measurements of a NIST pure-Nd, isotope reference material ( ) 𝐶𝐻𝑈𝑅 (CHUR standing for "chondritic uniform reservoir") equal to 0.512638 [START_REF] Jacobsen | Sm-Nd isotopic evolution of chondrites[END_REF]. Each sample was measured twice during a session, and the 95% confidence interval of the measurement was estimated from the 2 S.D. at 0.4 εNd unit from repeated measurements of the NIST reference material SRM2709a at mass spectrometric signal levels similar to those of samples.

Results and interpretations

All the results of lake (sink) and river (source) sediment geochemistry, dating and sedimentology are presented in Figs. 3 and4 and in supplementary Table S1, S2, S3 & S5.

Lake sediments

In the SEB18 sediment section, background sedimentation accounts for 39 % of the total sediment accumulation and is composed mainly of grey clay, visually distinguishable from homogenite or turbidite-type graded layers interpreted as event layers. Over the 15.5 m of sediment, 146 event layers (≥ 1 mm) have been identified and represent 61 % of the sediment. The material making the background sedimentation of the lake Iseo deep basin mainly consists of detrital silicates. Indeed, most of the lake authigenic carbonate is dissolved within the water column whereas the organic matter content is under 8 %, and detrital carbonates account for less than 18 %. NCIR mean value in the background sedimentation is 82.5 % and increase progressively towards the bottom of the sequence (see supplementary S1).

The age depth-model of the SEB18 sequence was constrained by a combination of short-lived radionuclides, varve counting, and 14 C ages, detailed information is presented in supplementary S5.

To constrain the upper part (0 -48 cm) of the sediment section, we used 137 Cs and 241 Am profiles, that present two peaks (16.7 -19.7 and 42.5 -43.5 cm) that are widely attributed to the 1986 CE Chernobyl accident (e.g., Appleby et al., 1991) and to the maximum nuclear weapon tests at 1963 CE (Appleby et al., 1991b). These peaks, in good agreement with the varve counting model and the 210 Pb excess profile ( 210 Pbex), are used as chronological markers to construct the age-depth model of the entire SEB18 sediment section. Thirteen samples of terrestrial macro-remains were analyzed to provide radiocarbon ages for the rest of the sediment section. Once calibrated, 4 of these 13 dates were not used because they presented ages older than the best-fit age-depth curve of the SEB18 sequence. The thickness of each event layer was subtracted from the SEB18 sediment sequence depth to create an event-free depth and to obtain the best age-depth model. The obtained SR was calculated from the event-free depth and is not influenced by the variation of the event layer occurrence (Fig. 3). To reduce the SR uncertainty linked to the first radiocarbon age, we decided to use only the uncertainty of the shortlived radionuclides and the other radiocarbon ages.

The SEB18 sequence covers the last 2000 yrs (21 -2018 CE) with a continuous SR that varies between 5.1 and 2.1 mm.yr -1 , with a mean of 3.1 mm.yr -1 . Three periods of gradual increase of SR are identified in the sequence: (i) between 500 and 800 CE (SR max = 3.2 mm.yr -1 ), (ii) between 1000 and 1400 CE (SR max = 3.06 mm.yr -1 ) and (iii) from 1500 CE towards the top (SR max = 5 mm.yr -1 ).

In the siliciclastic fraction of Iseo Lake sediments, the 87 Sr/ 86 Sr ratio ranges between 0.730 and 0.722 with a significant increase from 97 to 1033 CE followed by a decrease until 1265 CE, and then relatively high values with successive high and lows until the present day (Fig. 3). Values of εNd are relatively invariant and range between -11.8 and -10.4 (Fig. 3), with only two notable excursions towards higher values from 907 to 1185 CE and from 1551 to 1872 CE.

River samples

River sediments taken in Oglio sub-catchments are characterized by εNd values ranging from -5.5 to -13.4 (Fig. 4). Sediment samples from the northern, high-altitude basins, thus reflective of the calcoalkaline-type rock sources present the most radiogenic values: -5.5 to -6.3 for sub-catchments essentially underlain of tonalites (6.A and 5.A1) and -8.4 to -9.7 for granite dominated sub-catchments. Southern sub-catchments draining sedimentary rocks present 87 Sr/ 86 Sr ratios from 0.725 to 0.726. At face value, none of the 87 Sr/ 86 Sr ratios from the sampled sub-catchments can explain the most radiogenic ratios observed in lake sediments (Fig. 4). Bulk values are presented in Table S3 and Fig.

S6

.1 and display systematically lower 87 Sr/ 86 Sr values for sub-catchments where limestones and dolostones crop out.

Oglio River samples εNd values range between -7.5 and -11.8, whereas their 87 Sr/ 86 Sr ratios range from 0.716 to 0.721 (Fig. 4).

Interpreting Sr and Nd isotope ratios in term of sediment source fingerprinting

Two main assumptions are made here for the interpretation of the Sr and Nd isotope data from Lake

Iseo and Oglio River in terms of the contribution of each rock source to the detrital sediment input to the lake:

-All the major sediment sources contributing to detrital inputs to the lake were sampled.

-

The isotopic signatures of the various potential rock sources have remained constant over the period considered.

Because we removed the carbonate component of the lake and river sediments, the Sr-Nd isotope signatures of lake samples can be interpreted as a mixture of the identified silicate sources. In order to quantitatively deconvolve the contributions of the dominant rock sources through time, end members need to be identified, and their signatures need to be constrained. To that effect, we selected sediment samples from sub-catchments presenting a homogeneous lithology (Fig. 5A). Indeed, samples from the Oglio River and sub-catchments with heterogeneous lithology (Fig. 1) result from a mixture of several rock sources on their own, such that considering them would not provide independent constraints on the composition of the end members. River sediment samples for which only one out of the two isotope signatures was available were not considered either.

Out of the remaining 8 samples, three main sources can be identified and summarized into: i) calcoalkaline rocks ("A"), ii) metamorphic ("B") and iii) sedimentary ("C") rock sources.

Sub-catchments draining mainly rocks from the calco-alkaline rock series (6.A, 5.A 1 , 2.A 1 ) were gathered into a single "calco-alkaline rocks" source. Minor marlstone and limestone outcrops are also present in these areas, especially in 2.A 1 sub-catchment (Fig. 1) which may explain the lower εNd values measured for some sub-catchment samples compared to the values reported for the rocks themselves (+3.8 to -4.9; [START_REF] Kagami | Nd-Sr isotopic and geochemical characteristics of the southern Adamello (northern Italy) intrusives: Implications for crustal versus mantle origin[END_REF]. This end member is sourced from the high-altitude

Adamello massif (Fig. 1). Several glaciers and rock glaciers are currently present in this area [START_REF] Scotti | A regional inventory of rock glaciers and protalus ramparts in the central Italian Alps[END_REF]. Sr-Nd isotope signatures of the sample 6.A (Fig. 4) were selected as a fingerprint of the contribution of the calco-alkaline rocks source, as this sample is the closest to the Adamello massif outcrops signature [START_REF] Kagami | Nd-Sr isotopic and geochemical characteristics of the southern Adamello (northern Italy) intrusives: Implications for crustal versus mantle origin[END_REF].

Sub-catchments draining mostly metamorphic rocks were combined into the "metamorphic" source.

We note that these catchments are also partially underlain by sedimentary rock outcrops and Quaternary deposits. Samples from this source (2.B, 3.A and 4.A) present contrasted Sr-Nd isotope signatures, linked to their heterogeneous composition (Fig. 4). The sub-catchment of sample 4.A presents the highest proportion of metamorphic rocks (Fig.

1;

https://www.cartografia.servizirl.it/cargviewer/), which constitutes the only rock source that can explain the lowest εNd values observed in lake sediment samples (Fig. 4). As a consequence, the isotope signatures of sample 4.A are used as a fingerprint for the contribution of metamorphic rocks in the Lake Iseo catchment. Due to the significant heterogeneity of the metamorphic source, the fractional input from this end member to Lake Iseo sediments over time are discussed with great caution hereafter.

The remaining samples 7.A and 8.A originate from sub-catchments dominated by sedimentary rocks and were thus gathered into the "sedimentary rock" source. This source shows εNd values between -10.5 and -9.7, associated to the highest 87 Sr/ 86 Sr ratios (> 0.725). However, these 87 Sr/ 86 Sr values are not high enough to explain the highest 87 Sr/ 86 Sr ratios observed in lake sediment samples. This is because the sub-catchments dominated by sedimentary rocks are actually underlain by marlstones and limestones/dolostones. Although our decarbonation protocol has likely removed a large fraction of the carbonate component present in the river sediment, we expect that relatively refractory carbonate minerals such as dolomite remain in the "silicate" residue of the leaching procedure. As a consequence, this residue hosts a non-silicate component, most likely characterized by relatively low 87 Sr/ 86 Sr ratios [START_REF] Faure | Strontium isotope composition of marine carbonates of Middle Triassic to Early Jurassic age, Lombardic Alps, Italy*[END_REF], and the contribution of which needs to be corrected for. Details about this correction are provided in supplementary S6. After correction, the Sr signature of river sediments from sub-catchments draining sedimentary rocks is sufficiently 87 Sr-enriched to explain the highest 87 Sr/ 86 Sr ratios observed in Lake Iseo sediments (Fig. 4). Areas corresponding to the "sedimentary rock" source are located at low to mid altitude, in the southern part of the Iseo catchment, and correspond to places of current intense human activities (Fig. 2).

𝜀𝑁𝑑 𝑀 × [𝑁𝑑] 𝑀 = 𝜀𝑁𝑑 𝐴 × [𝑁𝑑] 𝐴 × 𝑓 𝐴 + 𝜀𝑁𝑑 𝐵 × [𝑁𝑑] 𝐵 × 𝑓 𝐵 + 𝜀𝑁𝑑 𝐶 × [𝑁𝑑] 𝐶 × 𝑓 𝐶 (5)
with the superscript M standing for lake sediment ("mixture") values, and the superscripts A, B and C stand for the three rock sources values (calco-alkaline rocks, metamorphic, and sedimentary rocks, respectively); fx represents the fractional contribution of each rock source.

Solving this equation system leads to estimates of the relative contributions of sources A, B and C.

Analytical solutions for 𝑓 𝐴 , 𝑓 𝐵 and 𝑓 𝐶 were obtained from Maple software (see supplementary S7). A Monte Carlo method was used to compute uncertainties on the fractional contributions. Random sampling within the analytical uncertainties of each parameter was executed using a Box-Muller transform (Box and Muller, 1958) for each of the 5000 iterations of the Monte Carlo procedure. From the simulated parameter distributions, D84, D16, median and standard deviation were obtained for each proportion 𝑓 𝑥 (Table S8). The "sedimentary rocks" source contributes on average to 79.6 -5.7 +4.8 % of the total siliciclastic sedimentation in Lake Iseo deep basin, whereas the calco-alkaline rocks source is the smallest contributor with a mean contribution of 3.5 -1.5 +1.8 % and the metamorphic source contribute to 16.7 -5.0 +6.1 % on average (Fig. 5B). Through the last 2000 years, the "sedimentary rock" inputs to Lake Iseo remain predominant and increase progressively towards the Middle Ages and the Industrial Age.

Beyond accounting for analytical uncertainties, an additional sensitivity test was run to evaluate the impact of the Sr-Nd isotope signatures selected for each rock end member. "Geological" uncertainties of 0.005 on the 87 Sr/ 86 Sr ratio and of 0.8 epsilon-units on εNd, together with a 50 % relative uncertainty on Nd and Sr concentrations were attributed to each end member, and a Monte Carlo procedure was performed in the same manner as that laid out above (Table S9 and Fig. 5B). Regardless of the exact composition of the three end members within the ranges given above, the "sedimentary rocks" source remains the predominant contributor to the continuous accumulation of siliciclastic material over time in Lake Iseo deep basin. Therefore, results from our mixing model can be reliably used to discuss the evolution of the contribution of each source in terms of temporal variations in erosion processes in the catchment.

Evaluation of the sediment yield

Once the proportion of each sediment source to lake sediments has been calculated, river loads, and corresponding sediment yields can be estimated to obtain a quantitative assessment of catchmentscale erosion rates, for each area in the catchment. Sediment accumulated in a sinking basin, such as natural lakes, is partly composed of river silt-sized material and of authigenic deposits; sand-sized material such as river bedload being in general deposited along the sides of the river channel or in the delta [START_REF] Hinderer | River loads and modern denudation of the Alps -A review[END_REF]. Few or none of the authigenic carbonates produced in Lake Iseo are preserved in the deep basin of the lake, as demonstrated in other deep peri-Alpine lakes [START_REF] Ramisch | Calcite dissolution in two deep eutrophic lakes[END_REF], making this lake the ideal candidate to reconstruct the evolution of river suspended load through time, and thus of erosion rates in the contributing catchment. The time-dependent erosion flux from the catchment was determined as follows by using the calculation of a siliciclastic flux (SCF; g.cm -2 .yr -1 ) from the lake sediment samples:

𝑆𝐶𝐹 = 𝑁𝐶𝐼𝑅 × 𝑆𝑅 × 𝐷𝐵𝐷 (6)
Here NCIR is the fraction of non-carbonate ignition residue of the lake sediments; SR is the sedimentation rate (cm.yr -1 ) derived from the age-depth-model; and DBD is the dry bulk density of the samples (g.cm -3 ). The DBD used in the SCF calculation was smoothed using a weighted arithmetic mean to reduce the impact of measurement bias in successive samples.

The sediment yield is defined as the mass of sediment that, over a given time span, leaves a boundary, such as the outlet of a catchment. SY is expressed in units of mass per unit of area and time (Hinderer et al., 2013 and reference therein). This parameter is used here to enable comparison with previous studies on erosion in the Alps. To calculate SY for the Iseo catchment, the total amount of sediment stored in Lake Iseo per amount of time (Stocksed) needs to be estimated:

𝑆𝑡𝑜𝑐𝑘 𝑠𝑒𝑑 = 𝑆𝐶𝐹 × 𝐿𝑎𝑘𝑒 𝑎𝑟𝑒𝑎 (7)
SR may vary spatially over the surface of a lake. To calculate a consistent 𝑆𝑡𝑜𝑐𝑘 𝑠𝑒𝑑 for the entire lake we consider only the fraction of the total lake area where SR should be commensurate with that measured at the coring site. We assume here that this area corresponds to the flat part of the deep basin as suggested by the seismic survey [START_REF] Bini | Morphology and geological setting of Iseo Lake (Lombardy) through multibeam bathymetry and high-resolution seismic profiles[END_REF], which lies below the slope discontinuity.

Based on the lake bathymetry, we consider that the lake area with water depth below 210 m b.l.s should be taken into account in the calculation of 𝑆𝑡𝑜𝑐𝑘 𝑠𝑒𝑑 , corresponding to a total of 18 km² (supplementary S10). The sediment stock is then multiplied by the contribution of each source to the lake sediment, in order to calculate changes in the source-specific sediment loads (SL, in t.yr -1 ) through time:

𝑆𝐿 = 𝑆𝑡𝑜𝑐𝑘 𝑠𝑒𝑑 × 𝑠𝑜𝑢𝑟𝑐𝑒 𝑝𝑟𝑜𝑝𝑜𝑟𝑡𝑖𝑜𝑛 (8)
To obtain an area-normalized sediment yield value for each source (𝑆𝑌 𝑖 ), SL is normalized to the drainage area of each rock type. A value for total sediment yield (𝑆𝑌 𝑇𝑜𝑡𝑎𝑙 ) was also computed from the total 𝑆𝐿:

𝑆𝑌 𝑖 = 𝑆𝐿 𝑆𝑜𝑢𝑟𝑐𝑒 𝑎𝑟𝑒𝑎 (9)
𝑆𝑌 𝑇𝑜𝑡𝑎𝑙 = 𝑆𝐿 𝑊𝑎𝑡𝑒𝑟𝑠ℎ𝑒𝑑 𝑎𝑟𝑒𝑎 [START_REF] Gayer | Storm-induced precipitation variability control of long-term erosion[END_REF] with 𝑆𝑌 𝑖 and 𝑆𝑌 𝑇𝑜𝑡𝑎𝑙 expressed in t.km -2 .yr -1 . For the computation of 𝑆𝑌 𝑖 and 𝑆𝑌 𝑇𝑜𝑡𝑎𝑙 , only the parts of the catchment area likely to be subjected to physical erosion are considered. For more detail on these calculations, see supplementary S11.

During the Industrial Age, SYSedimentary rocks and SYCalco-alkaline, representing area-specific erosion rates of the sedimentary and the calco-alkaline rocks areas in the Iseo catchment, show values around 100 and 10 t.km -2 .yr -1 , respectively (Fig. 6). SYSedimentary rocks values for the recent times are coherent with estimates derived from the RUSLE model for similar contexts [START_REF] Panagos | The new assessment of soil loss by water erosion in Europe[END_REF]; supplementary S12). Calculated SYSedimentary rocks values for the twentieth century are also close to present-day sediment yield measurements on Alpine rivers (30 -671 t.km -2 .yr -1 ; [START_REF] Hinderer | River loads and modern denudation of the Alps -A review[END_REF]. Deviations between our calculations and previously reported values can be explained by storage of sediment in the lake delta [START_REF] Hinderer | River loads and modern denudation of the Alps -A review[END_REF] and by the absence of consideration of the bed load in our calculation.

However, [START_REF] Hinderer | River loads and modern denudation of the Alps -A review[END_REF] showed that in the southern crystalline Alps, where Lake Iseo is located, suspended load generally dominates over bed load. Altogether the present-day sediment yield estimated here for the Lake Iseo catchment is consistent with previously reported figures, lending support to our estimates of erosion rates through time.

Discussion

The record of erosion in Val Camonica

The calculated SYTotal is about 20 t.km -2 .yr -1 during the Roman Period (Fig. 6A). From then on, SYTotal values increase nearly two-fold until the Medieval Period, when it reaches values between 30 and 40 t.km -2 .yr -1 . Then, SYTotal values decrease slightly until 1661 CE, prior to a sharp increase again during the Industrial Age and until the present.

Over centennial to millennial time scales, erosion is mainly a result of climate, vegetation, and land use changes (e.g. [START_REF] Bosco | Soil erosion risk assessment in the alpine area according to the IPCC scenarios[END_REF][START_REF] Panagos | The new assessment of soil loss by water erosion in Europe[END_REF], the last two parameters being associated with human activities. To disentangle the impact of climate and human practices on erosion in the Lake Iseo catchment, we investigate separately the reconstructed sediment yields of the "sedimentary rock" and calco-alkaline rocks areas. Indeed, no or very few human activities are reported in the high-altitude part of the catchment (e.g. [START_REF] Biagi | Human settlement and environmental exploitation of Valcamonica-Valtrompia watershed from the beginning of the Holocene to the Middle Ages[END_REF]. Conversely, a great number of glaciers and rock glaciers are present in this area [START_REF] Scotti | A regional inventory of rock glaciers and protalus ramparts in the central Italian Alps[END_REF], making erosion there highly sensitive to climate induced glacial fluctuations. In contrast, human activities are widely developed at low-to mid-altitude levels in the Val Camonica, meaning that human and climate have an unquestioned influence on erosion rates in the "sedimentary rock" area. No further investigation was conducted here on the sediment yields of the metamorphic area because of the lack of information about land use over time in this area, which was in addition certainly affected by a combination of glacier fluctuations and human activities such as grazing and deforestation (Fig. 6B). [START_REF] Marziani | The effects of human impact on the arboreal vegetation near ancient iron smelting sites in Val Gabbia, northern Italy[END_REF]brown shades); (F) the evolution of the Italian population modified from [START_REF] Cascio | Cycles and Stability. Italian Population before the Demographic Transition[END_REF]

Climate impact on erosion of high-altitude areas

Erosion in the high-altitude area of the Adamello massif is influenced by glacier advances and retreats and by extreme precipitation events. Glacier volumes depend on summer temperature and winter precipitation amounts (e.g. [START_REF] Fouinat | One thousand seven hundred years of interaction between glacial activity and flood frequency in proglacial Lake Muzelle (western French Alps)[END_REF][START_REF] Holzhauser | Glacier and lake-level variations in west-central Europe over the last 3500 years[END_REF][START_REF] Roy | Calendar-dated glacier variations in the western European Alps during the Neoglacial: the Mer de Glace record, Mont Blanc massif[END_REF], all linked to Mediterranean climate. Therefore, in order to discuss the impact of climate fluctuations on erosion in Lake Iseo catchment, we focus on the SYCalco-alkaline reconstruction. Currently, glaciers present in the calco-alkaline rocks area of Lake Iseo catchment correspond to a small glacial tongue (0.

6C

, [START_REF] Roy | Calendar-dated glacier variations in the western European Alps during the Neoglacial: the Mer de Glace record, Mont Blanc massif[END_REF], or smaller glacial bodies (e.g. [START_REF] Fouinat | One thousand seven hundred years of interaction between glacial activity and flood frequency in proglacial Lake Muzelle (western French Alps)[END_REF][START_REF] Glur | Alpine lacustrine varved record reveals summer temperature as main control of glacier fluctuations over the past 2250 years[END_REF] presents similarities. Except for the Roman Period, SYCalco-alkaline increases during periods of major glacier advances and decreases during retreat periods (Fig. 7D). During the Roman Period, SYCalco-alkaline present high values that are not consistent with the relatively low volume of great glaciers in the European Alps [START_REF] Holzhauser | Glacier and lake-level variations in west-central Europe over the last 3500 years[END_REF][START_REF] Roy | Calendar-dated glacier variations in the western European Alps during the Neoglacial: the Mer de Glace record, Mont Blanc massif[END_REF]. However, erosion signals from small glacial bodies in the western French Alps [START_REF] Fouinat | One thousand seven hundred years of interaction between glacial activity and flood frequency in proglacial Lake Muzelle (western French Alps)[END_REF] or in the Central Alps [START_REF] Glur | Alpine lacustrine varved record reveals summer temperature as main control of glacier fluctuations over the past 2250 years[END_REF], present several peaks of enhanced erosion between 0 to 600 CE in relation to short term temperature variation, but the sampling resolution presented here do not allow the comparison.

From ~500 to 1000 CE, SYCalco-alkaline decreases in agreement with the volume of major great Alpine glaciers [START_REF] Holzhauser | Glacier and lake-level variations in west-central Europe over the last 3500 years[END_REF][START_REF] Roy | Calendar-dated glacier variations in the western European Alps during the Neoglacial: the Mer de Glace record, Mont Blanc massif[END_REF]. At that period, climate is warm and dry in the southern Alps, favouring glacier retreats [START_REF] Büntgen | Years of European Climate Variability and Human Susceptibility[END_REF]. From 1000 to 1200 CE, erosion in highaltitude areas of Lake Iseo catchment increases sharply and remains high until 1300 CE. This period known as the High Medieval Advance (HMA) corresponds to a general episode of glacier advance in the Alps (Le Roy et al., 2015 and references therein) despite temperature increase in Europe [START_REF] Büntgen | Years of European Climate Variability and Human Susceptibility[END_REF]. After the HMA, SYCalco-alkaline decreases again until 1450 CE before another increase, observable in every alpine glacier chronicle, and corresponding to the onset of the Little Ice Age (LIA;

Figs. 6C).

This period is characterized by a globally cold and wet climate, inducing significant glacier advances that caused intense erosion throughout the alpine area (e.g. [START_REF] Fouinat | One thousand seven hundred years of interaction between glacial activity and flood frequency in proglacial Lake Muzelle (western French Alps)[END_REF][START_REF] Glur | Alpine lacustrine varved record reveals summer temperature as main control of glacier fluctuations over the past 2250 years[END_REF][START_REF] Holzhauser | Glacier and lake-level variations in west-central Europe over the last 3500 years[END_REF][START_REF] Roy | Calendar-dated glacier variations in the western European Alps during the Neoglacial: the Mer de Glace record, Mont Blanc massif[END_REF]. The LIA is known to last approximately until the middle of the nineteenth century, which correspond to the penultimate observed peak in SYCalco-alkaline.

Collectively, these observations suggest, as demonstrated elsewhere in the Alps (e.g. [START_REF] Fouinat | One thousand seven hundred years of interaction between glacial activity and flood frequency in proglacial Lake Muzelle (western French Alps)[END_REF][START_REF] Glur | Alpine lacustrine varved record reveals summer temperature as main control of glacier fluctuations over the past 2250 years[END_REF], that even over short time scales, colder periods induced higher erosion rates in the mountainous parts of the Lake Iseo catchment, implying a strong link between climate and erosion in high-altitude areas.

Human impact on erosion of low-altitude areas

At lower altitudes, climate fluctuations are not the only factors responsible for changes in erosion rates. Indeed, with land use and vegetation cover management, humans play a key role on erosion (e.g. [START_REF] Bosco | Soil erosion risk assessment in the alpine area according to the IPCC scenarios[END_REF][START_REF] Panagos | The new assessment of soil loss by water erosion in Europe[END_REF]. However, during periods of high SYCalco-alkaline, climatic forcing of the erosion in the low-altitude such as the sedimentary area need to be considered together with the human forcing as a possible driver of erosion.

The SYSedimentary rocks values increase two-fold from the Roman Period until the High Middle Ages. This increase occurs during dry and warm climate conditions across Europe [START_REF] Bini | Hydrological changes during the Roman Climatic Optimum in northern Tuscany (Central Italy) as evidenced by speleothem records and archaeological data[END_REF][START_REF] Büntgen | Years of European Climate Variability and Human Susceptibility[END_REF], and is associated with a gradual decrease of the SYCalco-alkaline signal (Fig. 6D), suggesting that human practices become the main driver of erosion in the Lake Iseo catchment at that time.

Abandonment of forest management plans until the Migration Period (300 -570 CE) has been attributed to a declining influence of the Roman Empire in the Lake Iseo catchment [START_REF] Comiti | How natural are Alpine mountain rivers? Evidence from the Italian Alps[END_REF]. The period from the Roman Period until the High Middle Ages is interpreted as a period of enhanced human pressure on the environment due to:

(i) Deforestation to allow for instance for increased mining activity, as observable elsewhere in Europe [START_REF] Büntgen | Years of European Climate Variability and Human Susceptibility[END_REF] and at low-to mid-altitude sites in the Val Camonica (Fig. 6E, [START_REF] Marziani | The effects of human impact on the arboreal vegetation near ancient iron smelting sites in Val Gabbia, northern Italy[END_REF][START_REF] Pini | A high-resolution Late-Glacial -Holocene pollen diagram from Pian di Gembro (Central Alps, Northern Italy)[END_REF][START_REF] Pini | Ecological changes and human interaction in Valcamonica, the rock art valley, since the last deglaciation[END_REF];

(ii) A general population increase in Italy towards the Middle Ages (Fig. 6F, [START_REF] Cascio | Cycles and Stability. Italian Population before the Demographic Transition[END_REF];

(iii) An intensification of land use and human practices, coupled with replacement of preexistent buildings [START_REF] Büntgen | Years of European Climate Variability and Human Susceptibility[END_REF].

In the Iseo catchment, the collapse of the forest management system of the Roman Empire should be at the origin of an enhancement of erosion. During the High Middle Ages and until the Late Middle Ages, SYSedimentary rocks remains relatively high (Fig. 6G). At that time, regional climate is wet [START_REF] Bini | Hydrological changes during the Roman Climatic Optimum in northern Tuscany (Central Italy) as evidenced by speleothem records and archaeological data[END_REF][START_REF] Büntgen | Years of European Climate Variability and Human Susceptibility[END_REF], extreme precipitations are frequent locally until 1300 CE [START_REF] Wirth | A 2000 year long seasonal record of floods in the southern European Alps[END_REF], and the human pressure remains important, with (i) attested periods of deforestation in the catchment [START_REF] Marziani | The effects of human impact on the arboreal vegetation near ancient iron smelting sites in Val Gabbia, northern Italy[END_REF] and (ii) intense land use and pastoralism in the Italian Alps [START_REF] Büntgen | Years of European Climate Variability and Human Susceptibility[END_REF][START_REF] Comiti | How natural are Alpine mountain rivers? Evidence from the Italian Alps[END_REF][START_REF] Joannin | Climate and land-use change during the late Holocene at Lake Ledro (southern Alps, Italy)[END_REF][START_REF] Pini | A high-resolution Late-Glacial -Holocene pollen diagram from Pian di Gembro (Central Alps, Northern Italy)[END_REF]. Therefore, disentangling human and climate forcing over this period is not possible, and it is likely that the combination of the two factors induced intense erosion in the entire Lake Iseo catchment until the Great Famine (1315 -1317 CE) and the Black Death (1347 -1351 CE). A slight decrease in SYSedimentary rocks is observed just after these two (Fig. 7G,F). These events are known to have deeply impacted European populations, resulting in particular in agricultural decline in the Southern Alps (e.g. [START_REF] Büntgen | Years of European Climate Variability and Human Susceptibility[END_REF][START_REF] Joannin | Climate and land-use change during the late Holocene at Lake Ledro (southern Alps, Italy)[END_REF][START_REF] Ruddiman | The early anthropogenic hypothesis: Challenges and responses[END_REF].

After this trough, SYSedimentary rocks increases progressively until 1800 CE and then strongly until 1872 CE and the onset of the Industrial Age (Fig. 6G). Two hypotheses can be invoked to explain this pattern:

the effect of the Little Ice Age (LIA) following an increase of human activity. Indeed, maximal glacier advances in the Alps are reported at around 1850 CE [START_REF] Holzhauser | Glacier and lake-level variations in west-central Europe over the last 3500 years[END_REF][START_REF] Roy | Calendar-dated glacier variations in the western European Alps during the Neoglacial: the Mer de Glace record, Mont Blanc massif[END_REF], before the current period of general retreat. The LIA is also characterized by more frequent extreme precipitation events in the Southern Alps [START_REF] Wirth | A 2000 year long seasonal record of floods in the southern European Alps[END_REF]. The effect of LIA climate change on erosion, through precipitation events and plausible glacier advances, are well visible on SYCalco-alkaline at that time and thus cannot be ignored for the interpretation of the low and mid-altitude part erosion signal of the Lake Iseo catchment, even if the LIA starts before the increase in SYCalco-alkaline.

Synchronously, human pressure on the environment grows sharply in the Italian Alps generally, and in the Lake Iseo catchment in particular, with an increase of the population [START_REF] Cascio | Cycles and Stability. Italian Population before the Demographic Transition[END_REF] associated to a surge in agricultural practices and a transition towards intensive farming [START_REF] Federico | Progress, decline, growth: product and productivity in Italian agriculture, 1000-2000[END_REF].

Between 1872 and 1926 CE, SYSedimentary rocks decreases sharply, most likely due to the onset of outward migration, with more than 11 million people leaving Italy for the New World [START_REF] Moretti | Social Networks and Migrations: Italy 1876-1913[END_REF]. SYSedimentary rocks finally increases until 1938 CE (last sample).

To summarize, each episode of SYSedimentary rocks increase in the Lake Iseo catchment can be associated to a period of intense human pressure on the environment (Fig. 6). Between 1030 and 1300 CE and during the LIA, wetter and colder climate favoured erosion not only at high altitudes but also at intermediate and low altitudes, making it hard to disentangle climate versus human influences.

However, from the Roman Period to the Middle Ages and up to the present, erosion at low altitudes shows a clear increase, asynchronous and decorrelated from the regional climate trend. Therefore, only human pressure on the environment can be responsible for this trend (Fig. 6H). Human activities, through the development of agricultural practices and deforestation at low-and mid-altitude have induced a three-fold increase in erosion rates in a large catchment of the Italian Alps. Hence, even in large mountainous catchments, human activities affect the CZ by increasing erosion, resulting in damages on ecosystems and in soil and biomass carbon shrinkage. The CZ is deteriorated by human practices for 2000 years in the Alps, making it highly sensitive to the current anthropization pressure.

Long term erosion chronicles, such as those produced from lake sediments, are critical to quantify the influence of the different forcing factors impacting CZ erosion through time.

Conclusion

Contributions of glacial variability and human activities to erosion were reconstructed from a sediment core with a stable isotope mixing model. The absolute value of sediment yields signal is highly coherent with previous work and annual average erosion models, making it possible to interpret its variations reported in the three mains sources. The erosion signal from high-altitude areas, synchronous with the three main episodes of European glacier advances and retreats, is interpreted to be driven by climatic fluctuations. From the comparison between the erosion signals of high-and low-altitude areas, we were able to disentangle the main triggers of the erosion at low-altitude areas in the study area.

Human activities, through deforestation, agricultural practices and grazing become the main forcing factors affecting erosion between the Roman Period and the Middle Ages, and from the Late Middle Ages to the present. A three-fold increase, from 36 to 118 t.km -2 .yr -1 is observed in anthropized areas. This is the first time that the impact of human activity on catchment-scale erosion is quantitatively assessed over time, based on lake sediments. These findings should contribute to enhance modelling of human impacts on Critical Zone erosion and on carbon shrinkage in soils.

Figure 1 -

 1 Figure 1 -Geological map of the study area, superimposed on a shaded relief map, and location of sampling sites. The geological information is modified from the geological map of Lombardy (CARG project; https://www.cartografia.servizirl.it/cargviewer/). The tributaries (blue) and sub-catchments (boundaries in black) of the Oglio

Figure 2 -

 2 Figure 2 -Land-use map of the study area, superimposed on a shaded relief map, and location of sampling sites. Land use information is derived from the CORINE land cover map for Lombardia, available here: http://www.geoportale.regione.lombardia.it/. Locations of glaciers, relicts, and intact rock glaciers are derived from Scotti et al. (2013).

Figure 3 -

 3 Figure 3 -Silicate detrital flux (SCF, for siliciclastic flux), sedimentation rate (SR) and Sr and Nd isotope ratios of Lake Iseo over the last 2000 years obtained from lake sediment SEB18 sediment sequence. The siliciclastic flux was obtained from loss on ignition analyses, age-depth modelling and density measurements (supplementary S1). The sedimentation rate was obtained from the age-depth model (supplementary S5). Error bars on the 87 Sr/ 86 Sr and εNd curves represent the 95% confidence intervals corresponding to analytical uncertainty.

Figure 4 -

 4 Figure 4 -Nd and Sr isotope composition of Lake Iseo siliciclastic sediment samples (small grey circles), and of river sediment samples from the Oglio sub-catchments upstream from Lake Iseo (diamonds) and from the Oglio main valley (large blue circles). Oglio sub-catchments symbols (diamonds) are coloured as a function of the dominant rock types underlying the catchment. Oglio main valley sediment samples (blue circles) are numbered as in Figs 2 and 3. Dotted arrows represent the

Figure 5 -

 5 Figure 5 -Results from the mixing model. (A) Nd-Sr isotope signatures of the three identified rock sources, used as end members for explaining the composition of lake sediments. Samples 6.A, 8.A and 4.A are used to constrain the composition of the rock end members. Lake sediments are shown as grey circles within an array described by mixing hyperbolae. The pink, red, and purple symbols correspond to the composition of each Monte Carlo iteration used for the sensitivity test. (B) Fractional contributions of each rock source to Lake Iseo sediment against time (yr CE). The propagation of analytical uncertainties are represented as error bars and by dark shaded areas, corresponding to the D84 and D16 of the distribution of the parameters obtained from Monte Carlo simulations. The light shaded areas represent the propagation of the uncertainty associated to

Figure 6 -

 6 Figure 6 -Erosion in the Lake Iseo catchment and forcing factors evolution over the last 2000 years. From top to bottom: (A) total sediment yield obtained from the SEB18 sediment core (black curve); (B) the sediment yield originating from the erosion

  7 km²) of the great Adamello glacier (21.6 km²) and small glacier bodies (< 0.5 km²) south and north of it. By their sizes, these glacier bodies are thought to be more sensitive to local climate change and present a lower inertia during glacier retreat than great Alpine glaciers. SYCalco-alkaline first decreases from 100 to 1000 CE before increasing sharply until 1200 CE. The erosion from calco-alkaline rocks area remains high (> 6 t.km -2 .yr -1 ) until 1300 CE before decreasing again until 1450 CE. Another increase is observed until 1550 CE. SYCalco-alkaline values remain high until the present days, with two peaks at 1845 CE and 1940 CE. The comparison of SYCalco-alkaline evolution over the last 2000 years with other alpine glaciers advances and retreats such as that of the Mont Blanc valley (Fig.

  143 Nd/ 144 Nd = 0.511418;[START_REF] Caro | High-precision 142Nd/144Nd measurements in terrestrial rocks: Constraints on the early differentiation of the Earth's mantle[END_REF], with a measured 2 S.D of 2.7 x 10 -6 , and the NIST soil reference material SRM2709a (0.512381 ± 0.000028). For convenience we report Nd isotope ratios as εNd values:

		εNd = (	( Nd 143 ( Nd / Nd 144 ) 𝑠𝑎𝑚𝑝𝑙𝑒𝑠 143 / Nd 144 ) 𝐶𝐻𝑈𝑅	-1) × 10 000
	with ( Nd 143	/ Nd 144

  Sr/ 86 Sr ratios for leached river sediment samples range from 0.708 to 0.726. Northern Oglio subcatchments dominated by calco-alkaline series display low 87 Sr/ 86 Sr values, from 0.708 for tonalitedominated catchments to 0.712 for granite-dominated catchments. Sub-catchments underlain mostly by Variscan metamorphic rocks are characterized by 87 Sr/ 86 Sr ratios ranging from 0.718 to 0.723.

	Southern sub-catchments draining sedimentary rocks display εNd values ranging from -8.3 to -10.5,

while sub-catchments dominated by Variscan metamorphic rocks present the highest variability in εNd values, from -10.1 to -13.4.

Acknowledgments

This work was financed by CRITLAKE project co-funded by EC2CO and AAP Université Savoie Mont Blanc. Parts of this work were also supported by IPGP multidisciplinary programme PARI and by Paris-IdF region SESAME Grant No. 12015903. We wish to thank the support of the entire staff of the C2FN-DT-INSU associated to the CLIMCORE project. 14 C analyses were acquired thanks to the CNRS-INSU ARTEMIS national radiocarbon AMS measurement programme at Laboratoire de Mesure 14 C (LMC14) in the CEA Institute at Saclay (French Atomic Energy Commission).

We are grateful to Pierre Burckel for help with Q-ICP-MS measurements; to Laëticia Faure for her valuable help and assistance with lab work; to Pascale Louvat, Thibaud Sondag, and Barthélémy Julien for assistance with MC-ICP-MS measurements; and to Ana Brancelj for the help on the field during river samples collection. We wish to thank Damien Guinoiseau for helpful conversations about the interpretation of isotope data. The authors are grateful to the editors P. Rioual and G. Zanchetta for their comments and help during the review processing and to the two anonymous reviewers.


MD, PhD Nicolas Bertheuil
email: nbertheuil@gmail.com

MD Damien Bergeat

MD Yanis Berkane

MD Raphael Carloni

MD Silvia Gandolfi

MD, PhD Jérôme Duisit

Lipo-Bodylift Reconstruction Following Massive Weight Loss: Our Experience with 100 Consecutive Cases

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Introduction

Massive weight loss caused by hygienic-dietetic rebalancing or bariatric surgery is associated with two types of major cutaneous sequelae. First, excess skin may be present in all dimensions; reconstruction affords only a partial response at the cost of significant scarring.

Second, the skin may exhibit loss of elasticity and (potentially) extensive skin laxity attributable to metabolic and/or nutritional disorders [START_REF] Manzoni | Skin changes after bariatric surgery[END_REF] . The latter compromise(s) the outcomes of plastic surgery, which are often difficult to predict and potentially disappointing. No current treatment is available. The goal of plastic surgical management after massive weight loss is reconstruction of a skin envelope that considers the patient's body mass index (BMI); an acceptably reconstructed bodily image improves the quality-of-life. Truncal skin redundancy can be corrected via abdominoplasty; however, excess skin and fat on the flanks, hips, buttocks, and gluteal ptosis cannot thus be corrected. The circular deformation caused by massive weight loss can be fully corrected only via a circular technique termed a lower circumferential body lift. Such major surgery is associated with significant complications [START_REF] Carloni | Are There Factors Predictive of Postoperative Complications in Circumferential Contouring of the Lower Trunk? A Meta-Analysis[END_REF] , explaining the growing interest in less-invasive techniques that reduce postoperative morbidity and the hospital stay.

Here, we describe a procedure that assists patients suffering from weight loss sequelae: the "Lipo-Bodylift". This combines extensive circular liposuction with circular skin resection immediately below the dermis, as previously described [START_REF] Bertheuil | Reply: The Lipo-Body Lift: A New Circumferential Body-Contouring Technique Useful after Bariatric Surgery[END_REF][START_REF] Bertheuil | The Lipo-Body Lift: A New Circumferential Body-Contouring Technique Useful after Bariatric Surgery[END_REF][START_REF] Bertheuil | The Lipo-Bodylift: An ideal technique for type I and II massive weight loss patients (reply to Dast et al.)[END_REF][START_REF] Bertheuil | Lower Body Lift after Massive Weight Loss: Autoaugmentation versus No Augmentation[END_REF][START_REF] Bertheuil | The Lipo-Body Lift: Operative Technique[END_REF] . We detail our experience with 100 patients.

Patients and Methods

One hundred patients requiring abdominal body-contouring reconstruction following massive weight loss underwent the Lipo-Bodylift procedure performed by the senior author (NB) in the Department of Plastic and Reconstructive Surgery of Rennes University Hospital between January 2015 and January 2020. Patient data were prospectively recorded in a secure database; we noted age, sex, weight, height, pre-bariatric surgery BMI, pre-bodylift BMI, the type and number of bariatric procedure(s), and any medical history. Before performing Lipo-Bodylift, all patients exhibited stable weight for least 6 months after massive weight loss.

Smoking cessation 1 month before surgery was strongly advised but not mandatory. We collected the following peroperative data: The anterior and posterior liposuction volumes; the weight of resected skin; the operative duration (min); the American Society of Anesthesiologists (ASA) score; postoperative complications (major and minor); and the duration of hospital stay. Major complications were events occurring within 30 days after surgery that required either surgical revision, hospital re-admission, or a visit to an emergency room. Minor complications were those that could be treated in an outpatient clinic; among these, delayed wound-healing was defined as any scar that required dressing for longer than 15 days postoperatively, without wound dehiscence, which was considered present when an initially closed wound required resumption of dressing care, even if the wound was less than 0.5 cm 2 in area. The study was approved by the Institutional Review Board of Rennes University Hospital and adhered to all relevant tenets of the Declaration of Helsinki (1964) and the French bioethics laws that came into force on 7 July, 2011.

Patient selection

Patients with certain weight loss sequelae (deformities of the lower trunk) can be classified by reference to three parameters: (1) excess skin (in either the horizontal direction or in both the horizontal and vertical directions); (2) the BMI; and, (3) skin quality (skin hyperlaxity or skin of normal tone). Such patients can be divided into four groups depending on the extent of the lower trunk deformities. Patients of Type I exhibit only excessive, very deflated skin of poor tone (thus high-level skin laxity). The BMI is normal, thus <25 kg/m 2 (Figures 1 and2). Type II patients exhibit both significant skin laxity (as do Type I patients) and moderate lipodystrophy. The BMI ranges from that characteristic of overweight to that of type 1 obesity (<35 kg/m 2 ) (Figures 3 and4). Type III patients exhibit moderate-to-poor skin laxity and moderate-to-major fat excess; the BMI generally ranges up to 35 kg/m 2 . Type IV patients include those with a transverse skin excess requiring a "fleur-de-lys" body lift, irrespective of skin laxity status and the BMI. We considered that the optimal Lipo-Bodylift candidates were those of Types I and II; Type III patients required lower body lifts with traditional undermining [START_REF] Meal | Impact of Lipo-Body Lift Compared to Classical Lower Body Lift on Postoperative Outcome and Patient's Satisfaction: A Retrospective Study[END_REF] ; and Type IV patients "inverted T" body lifts [START_REF] Mendes | Fleur-de-lis Abdominoplasty and Neoumbilicus[END_REF] .

Patients with any history of prior abdominal surgery (other than bariatric surgery) were treated very cautiously during the Lipo-Bodylift procedure, because of the extensive liposuction required. Preoperative imaging was performed to exclude hernias of the linea alba and flank, [START_REF] Delliere | Multiple bowel perforation and necrotising fasciitis secondary to abdominal liposuction in a patient with bilateral lumbar hernia[END_REF] and any parietal anomaly. Patients with rectus diastasis were not favored for surgery even if rectus plication was feasible [START_REF] Saldanha | Lipoabdominoplasty without undermining[END_REF] . A follow-up by a nutritionist was requested in the preoperative period; all biological deficiencies were systematically recorded and remedied (if necessary).

Operative procedure

Patients were preoperatively marked-up in both the standing and supine positions, as previously described [START_REF] Bertheuil | The Lipo-Body Lift: A New Circumferential Body-Contouring Technique Useful after Bariatric Surgery[END_REF][START_REF] Bertheuil | Lower Body Lift after Massive Weight Loss: Autoaugmentation versus No Augmentation[END_REF][START_REF] Bertheuil | The Lipo-Body Lift: Operative Technique[END_REF] . All were placed under general anesthesia. Antibioprophylaxis featured administration of 4 g Cefazolin prior to surgery. A urinary catheter was out in place. Adipose tissue was infiltrated with an adrenaline solution in saline (1:1,000 [w/v]; mean 1-1.2 L/patient) to reduce bleeding during surgery and to facilitate liposuction. We initiated the procedure in the posterior region, with the patient prone. Liposuction was performed (using 4 mm-diameter cannulae) between the superior and inferior marks from the dermis to the muscular fascia.

Commencing with the 25 th patient, we used a power-assisted liposuction device (PAL; Microaire, Charlottesville, VA, USA). The trochanteric areas were suctioned under the superficialis fascia to facilitate lifting of the lateral thigh. Thereafter, the required skin excisions were checked by pinching, and skin resections were performed immediately below the dermis to preserve all connective tissue [START_REF] Bertheuil | Liposuction Preserves the Morphological Integrity of the Microvascular Network: Flow Cytometry and Confocal Microscopy Evidence in a Controlled Study[END_REF] (Figure 5 and Supplemental Digital Content Video 1). We next performed flapless gluteal autoaugmentation, as previously described [START_REF] Bertheuil | Lower Body Lift after Massive Weight Loss: Autoaugmentation versus No Augmentation[END_REF] ; we lifted the buttock from the outside inwards. This suturing tip moderately increases the buttock projection, or at least ensures that it is not entirely flat, which is normally the case after a body lift. Posterior wound closure was performed without drain placement using absorbable stitches (Polysorb 2;

Covidien, Dublin, Ireland) placed between the two superficial fascial layers and the use of additional absorbable stitches (Monocryl 3/0; Ethicon, Somerville, NJ, USA) to secure the subdermal plane. A running suture (Monocryl 4/0) was employed for wound closure.

Thereafter, the patient was placed in the supine position and the anterior procedure commenced.

We performed highly modified lipoabdominoplasty; only areas under the skin resection were subjected to liposuction, as in the previous step. Very limited (traditional) undermining was performed in the area below the region running from above the umbilicus to the xiphoid.

Monsplasty (using three non-absorbable stitches; [Premicron 1; B. Braun, Melsungen, Germany]) was performed from the region between the Camper adipose layer to the muscular fascia. This smoothly elevated the mons pubis and corrected any ptosis. [START_REF] Patoue | Safe monsplasty technique[END_REF] Next, high-tension suturing was performed at the top of the umbilicus to facilitate wound closure (by reducing the tension on the scar) and to remodel the subumbilical abdomen. [START_REF] Louarn | High superior tension abdominoplasty[END_REF] Tension-free closure was achieved using absorbable Polysorb 2/0 and 3/0, and Monocryl 4/0, stitches. All patients wore compression garments (Lipo-Panty S005; Medical Z, San Antonio, TX, USA) for 2 months postoperatively.

Postoperative care

Deep venous thrombosis (DVT) prophylaxis required mandatory wearing of compression stockings and low-molecular weight heparin injections for 15 postoperative days (PODs). The dressings were changed every two days. Walking was authorized on POD 1 and the urinary catheter removed the next day. Physiotherapy (scar massage, LPG therapy, and lymphatic drainage) was initiated no earlier than 6 weeks after surgery.

Statistical analysis

Statistical analyses were performed using R statistical software (http://www.r-project.org/). Continuous data are expressed as medians with interquartile ranges (IQRs) and were compared with the aid of the Mann-Whitney U-test. Categorical data are expressed as percentages and were compared employing the Chi-squared test or the two-sided Fisher's exact test when the Chi-squared test was inappropriate. Exploratory univariate analyses were performed to define risk factors for postoperative complications. We calculated the Spearman correlation between operative time and patient sequence (from the earliest to the latest). The threshold for statistical significance was set at P < 0.05.

Results

During the study period, 100 post-massive weight loss patients underwent the Lipo-Bodylift procedure. The patient and procedural characteristics are summarized in Tables 1 and2. The median patient age was 41 years. The median pre-body lift BMI was 26.3 kg/m 2 and the average weight loss prior to body lift 50 kg, with a mean delta-BMI loss of 18.5 kg/m 2 . Of all patients, 94% had histories of bariatric surgery (either gastric bypass [75%] or sleeve gastrectomy [26%]). The pre-operative ASA scores were 1 in 36% and 2 in 64% of all patients. The median operative time was 153.5 min; the median liposuction volume 2,800 mL; and the mean mass of resected skin 904.5 g. Notably, the operative time fell with increasing experience; a learning curve was in play (Figure 6). The median hospital stay was 3 days and the median drainage duration 3 days. Of all patients, 30% experienced at least one complication; 2% developed hematomas and/or phlebitis (major complications). Minor complications predominated (28%), including a 27% incidence of wound dehiscence treated via healing with secondary intention, a 3% incidence of wound infections, and a 4% occurrence of fat necrosis. The wound dehiscence was isolated in six patients but not so in others; the mean defect area was 3.7±2.6 cm 2 . We encountered no seroma. We performed seven revision surgeries for esthetic purposes (secondary liposuction because of initial undercorrection). Complications were significantly associated with smoking status (Table 4) (p<0.001).

Discussion

We report one of the most extensive series of circumferential body contouring of the lower trunk; we performed extensive liposuction and skin resection immediately under the dermis.

Our technique was inspired by that of Saldanha,[START_REF] Saldanha | Lipoabdominoplasty without undermining[END_REF] but differs in some respects. We incorporated several new adaptations to deal with the major skin laxities of Type I and II patients with massive weight loss. After such loss, the skin and the subcutaneous adipose layer are particularly affected. Obesity induces chronic inflammation of both adipose tissue and skin, triggering skin reshaping via differential expression of certain proteins involved in maintenance of biomechanical properties and extracellular matrix organization. [START_REF] Shipman | Obesity and the skin[END_REF][START_REF] Light | Effect of weight loss after bariatric surgery on skin and the extracellular matrix[END_REF][START_REF] Halawi | Bariatric surgery and its effects on the skin and skin diseases[END_REF] Skin inflammation is always present after massive weight loss, but is more significant after bariatric surgery than after dieting. [START_REF] Gallo | Skin Protein Profile after Major Weight Loss and Its Role in Body Contouring Surgery[END_REF] The mechanical properties of the subcutaneous fat also change. The subcutaneous adipose tissue is divided into two layers (superficial and deep) by the superficialis (Scarpa) fascia that parallels the skin, and into multiple compartments separated by connective septa that run from the dermis to the muscular fascia. [START_REF] Markman | Anatomy of the subcutaneous tissue of the trunk and lower extremity[END_REF] Lockwood, in 1991, described this entire conjunctival structure, and termed it the "superficial fascial system" (SFS). [START_REF] Lockwood | Superficial fascial system (SFS) of the trunk and extremities: a new concept[END_REF] The system divides adipose tissue into multiple compartments that support the skin surfaces overlying musculoskeletal structures. The SFS is more dense in some locations than others, creating deepseated skin adhesions. The SFS is of great importance in terms of the sequelae of obesity in patients experiencing massive weight loss. In obese patients, the SFS becomes progressively looser ("relaxes") as the adipose content increases. On palpation, the skin and subcutaneous fat appear tense (thus not very mobile). During massive weight loss, the SFS that became highly relaxed during obesity does not retract and the septae perpendicular to the skin do not restore the "traditional" tension. This creates extreme laxity on palpation, and marked skin mobilization (which is often greater than suggested clinically). These SFS changes explain the typical deformations encountered after massive weight loss; an analysis of the SFS greatly assists selection of an appropriate technique. We developed our "Lipo-Bodylift" technique after careful consideration of SFS hyperlaxity and the related skin changes [START_REF] Bertheuil | The Lipo-Body Lift: A New Circumferential Body-Contouring Technique Useful after Bariatric Surgery[END_REF] . The key principles are: The Lipo-Bodylift differs greatly from the lipoabdominoplasty of Saldanha. [START_REF] Saldanha | Lipoabdominoplasty without undermining[END_REF] The latter surgery is performed on patients of normal weight who lack skin and SFS abnormalities; liposuction is performed above and below the umbilicus. The skin below the umbilicus and the superficial adipose layer (above the Scarpa fascia) are then removed with preservation of the superficialis fascia and the deep fat (to avoid lymphatic damage). Liposuction is performed under the abdominal flap to increase flap mobility, and the flap is then pulled down.

We incorporated extensive circumferential liposuction into our Lipo-Bodylift procedure to reduce the complication rate, particularly seroma (we encountered no seroma). We then extended the principle (mostly to arm lifts) and achieved results as good as those afforded by medial thighplasty [START_REF] Louarn | The concentric medial thigh lift[END_REF][START_REF] Bertheuil | Quality-of-Life assessment after medial thighplasty in patients following massive weight loss[END_REF][START_REF] Bertheuil | Reply: The Lipo-Body Lift: A New Circumferential Body-Contouring Technique Useful after Bariatric Surgery[END_REF] and brachioplasty [START_REF] Pascal | Brachioplasty[END_REF][START_REF] Hunstad | Avulsion Thighplasty: Technique Overview and 6-Year Experience[END_REF][START_REF] Knotts | Avulsion brachioplasty: technique overview and 5-year experience[END_REF] . We consider that the absence of seroma is probably attributable to the preservation of connective tissue in the resected areas. Indeed, it has been previously reported that the tissue remaining after liposuction exhibits a morphologically preserved microvascular network, suggestive of functional preservation. [START_REF] Bertheuil | Liposuction Preserves the Morphological Integrity of the Microvascular Network: Flow Cytometry and Confocal Microscopy Evidence in a Controlled Study[END_REF] Our present data support this suggestion.

The Lipo-Bodylift is as reproducible and safe as traditional abdominal flap undermining, with a lower complication rate than that described in a recent meta-analysis (36.55% [IQR: 26.63-45.65%]). [START_REF] Carloni | A higher excision pattern does not only reduce gluteal cleft elongation but also reduces overall complications in circumferential contouring of the lower trunk. Results of a meta-analysis[END_REF] Notably, our major complication rate was only 2% in a relatively large series, possibly attributable to connective tissue preservation in the subumbilical area, the very limited subumbilical undermining, and that the fact that abdominal flap mobilization exploited the mechanical properties of tissue (we did not engage in wide undermining). This avoids complications attributable to large dead spaces and abdominal flap problems that appear following undermining and the sacrifice of some vascularization.

The principal postoperative complication of the present study was wound dehiscence. Notably, our prospective database showed that the dehiscence rate was less than that of the only prior prospective study (that of Kitzinger) (60%). [START_REF] Kitzinger | Prospective study on complications following a lower body lift after massive weight loss[END_REF] Indeed, our rate was higher than those of the retrospective studies of Rohrich 30 , Koller [START_REF] Koller | Circumferential superficial fascia lift of the lower trunk: surgical technique and retrospective review of 50 cases[END_REF] , Vico [START_REF] Vico | Circumferential body contouring in bariatric and non-bariatric patient[END_REF] , and Nemerofsky [START_REF] Nemerofsky | Body lift: an account of 200 consecutive cases in the massive weight loss patient[END_REF] (1, 16, 23, and 32.5% respectively). This shows that prospective studies/databases reflect clinical reality more accurately than do retrospective studies/databases. Also, no consensus definition of wound dehiscence yet exists; we used a broad definition. This may have enhanced the apparent complication rate.

ACCEPTED MANUSCRIPT 10

Smoking status was the only factor that increased the rate of postoperative complications. Peri-operative tobacco use was previously shown to be a risk factor for postoperative complications after circumferential lowering of the trunk contours, [START_REF] Nemerofsky | Body lift: an account of 200 consecutive cases in the massive weight loss patient[END_REF][START_REF] De Runz | Satisfaction and complications after lower body lift with autologous gluteal augmentation by island fat flap: 55 case series over 3 years[END_REF][START_REF] Van Huizum | Circular belt lipectomy: a retrospective followup study on perioperative complications and cosmetic outcome[END_REF] and also in a recent meta-analysis of plastic surgery outcomes. [START_REF] Pluvy | Smoking and plastic surgery, part II. Clinical implications: a systematic review with meta-analysis[END_REF] The suggested association between tobacco use and complications is not obvious in all reported series, probably because of a lack of true self-reporting and because increasing numbers of surgeons refuse to operate on smokers.

Our technique has certain limitations. A learning curve is in play. The technique usefully treats Type I and II deformities, but not those of Type III, given the absence of tissue flaccidity (poor skin tone) in the latter patients, who may thus require liposuction of the umbilical abdominal flap (as described by Saldanha) [START_REF] Saldanha | Lipoabdominoplasty without undermining[END_REF] prior to flap lowering. We did not perform rectus plication, although this could be performed by removing the "tissue connectives" between the inner edges of the rectus abdominis muscles. Indeed, after massive weight loss, all patients exhibit a certain parietal "hypotonia/laxity" that includes the muscles, without necessarily evidencing a real diastasis of the abdominal rectus. Intraoperatively, we commonly observe a 2-cm gap between the rectus abdominis muscles; this does not require correction. Indeed, correction would be painful and increase the risk of postoperative bleeding. However, the lack of rectus plication may be associated with incomplete correction of parietal laxity.

Conclusion

The Lipo-Bodylift seems to be less invasive than the traditional undermining that usually accompanies circumferential reconstruction of the lower trunk. The rate of major complications is low. We developed the Lipo-Bodylift technique after analyzing the changes in skin and subcutaneous fat induced by massive weight loss. The technique deals particularly well with the sequelae developing in Type I and II patients after massive weight loss.

Legends to Figures

Figure 1: A Lipo-Bodylift patient of Type I.

Top: Preoperative view. Bottom: After the Lipo-Body lift. The BMI of a 37-year-old female fell from 39.7 to 25.9 kg/m 2 after BYPASS. The operative time fell as the number of procedures performed increased.

Supplemental Digital Content Video 1: Skin resection.

The video shows the skin resection performed immediately below the dermis; this conserved all connective tissue.

( 1 )

 1 the different structures affected by massive weight loss are treated differently; excess fat is removed via liposuction and excess skin by resection immediately below the dermis, allowing preservation of the entire connective framework and thus better conservation of tissue structure and (probably) tissue physiology; (2) no undermining is performed outside the areas of skin resection; (3) abdominal flap descent is possible given the hyperlaxity induced by changes to the skin and the SFS; and, (4) only limited subumbilical undermining is required to transpose the umbilicus.

Figure 2 :

 2 Figure 2: Lipo-Bodylift patient of Type I.

Figure 3 :

 3 Figure 3: Lipo-Bodylift patient of Type II.

Figure 4 :

 4 Figure 4: Lipo-Bodylift patient of Type II.

Figure 5 :

 5 Figure 5: Dissection level of skin resection.

Figure 6 :

 6 Figure 6: The learning curve.

Fig

  Fig. 1A Type I Lipo-Bodyliftpatient. Top: Preoperative view.Bottom: After the Lipo-Bodylift. The BMI of a 37-year-oldfemale fell from 39.7 to 25.9 kg/m2after BYPASS

Table 4 -

 4 Risk factors analysis for postoperative complications

		Overall complication
		Yes	No	P value
		n=30	n=70
	Age	38.5[32.5-44.75]	41[31.0-47.0]	0.81
	ASA score			0.30
	1	8 (26.67)	28 (40.00)
	2	22 (73.33)	42 (60.00)
	Pre plastic surgery BMI 26.80[25.75-28.10]	25.85[24.22-28.09]	0.25
	Delta BMI	18.51[13.82-22.55]	18.54[16.72-21.66]	0.68
	Hypertension	3 (10.00)	3 (4.29)	0.36
	Diabetes	1 (3.33)	1 (1.43)	0.51
	Smoking	18 (60.00)	13 (18.57)	<0.001
	Liposuction volume (mL) 3325[1925-3812]	2625[2100-3475]	0.25
			101.00[85.59-
	Liposuction volume/BMI 124.27[78.46-138.47]	122.43]	0.20
	Weight of skin resection
	(gram)	914.0[775.5-1074.5]	904.5[819.2-999.2]	0.95
	Operative time (min)	164.0[142.5-235.2]	150.0[138.2-180.8]	0.08
	Consecutive cases			0.56
	First 10 patients	4 (13.33)	6 (8.57)
	From 11 to 50 patients	13 (43.33)	27 (38.57)
	After 50 patients	13 (43.33)	37 (52.86)
	Categorical variables are presented with numbers and (%) ; Continuous variables are expressed with
	median and [interquartile range]

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funding support for the research of this article and declared no potential conflicts of interest with the respect to the research, authorship and/or publication.