The challenges and opportunities of addressing particle size effects in sediment source fingerprinting: A review

publisher: Elsevier articletitle: The challenges and opportunities of addressing particle size effects in sediment source fingerprinting: A review journaltitle: Earth-Science Reviews articlelink: http://dx.doi.org/10.1016/j.earscirev.2017.04.009 content_type: article copyright: © 2017 Elsevier B.V. All rights reserved

Quantification de la cinétique des transferts verticaux de matière solide dans les sols par une approche multi-isotopique

Le lessivage du lutum (0-2 µm) est un de processus majeurs de la pédogenèse, qui a néanmoins été peu quantifié et modélisé. Ce processus ainsi que la bioturbation ont été quantifiés ici en couplant des différents systèmes isotopiques (137Cs, 210Pb (xs), 10Be atmosphérique, 206/207Pb, δ13C, 14C) à une modélisation numérique par une équation de diffusion-convection à paramètres variables avec la profondeur. Cette méthode originale a été appliquée sur des anthroposéquences de Luvisols développées sur du loess et différantes de par leur utilisation (culture, prairie ou forêt) et leurs pratiques agricoles (travail du sol, apport du fumier). Nos résultats montrent que 91 ± 9 % du 137Cs et 80 ± 9 % du 10Be sont associés au lutum et ainsi peuvent effectivement tracer des transferts verticaux de matière solide dans les sols à pH > 5 et à teneur en carbone organique faible. Le partage du plomb entre les différentes phases solides est plus complexe. En considérant deux compartiments pour les isotopes (macropores ou la matrice de sol), nous avons conçu un modèle multi-isotopique permettant de quantifier la contribution des transferts de matière solide à la distribution verticale de la fraction 0-2 µm actuelle. Le lessivage est responsable de 9 à 66 % de l'accumulation de lutum dans l'horizon Bt. Le coefficient de diffusion permet de quantifier le taux de mélange par la bioturbation. La modélisation multi-isotopique est une méthode de prédilection pour les études modernes de la pédogenèse et des processus de la zone critique.Clay translocation is one of the major soil forming processes, howeverit is poorly quantified and modeled. We propose to quantify it togetherwith bioturbation by combining different isotopic systems (137Cs , 210Pb (xs),meteoric 10Be, 206/207Pb, δ13C, 14C) with numerical modeling based on a nonlineardiffusion-convection equation with depth dependent parameters. Thisnovel method has been applied on Luvisol anthroposequences developed onloess, differing by their land use (cropping versus grassland or forest) andtheir agricultural practices (reduced tillage, no tillage and manure input).Our results show that as much as 91 ± 9 % and 80 ± 9 % of 137Cs and10Be, respectively, are associated to the clay size fraction (0-2 µm) and canthus effectively trace vertical solid matter transfers in soils with pH > 5 andlow organic carbon. Lead partitioning between different solid phases is morecomplex. Considering two spatial distributions of isotopes (macropores or soilmatrix), we built up a multi-isotopic modelling approach that simulates theexperimental data with the common set of transfer parameters and allowedus to quantify the relative contributions of vertical solid matter transfers topresent-day 0-2 µm vertical distributions. Clay translocation is responsiblefor 9 to 66 % of the clay accumulations in the Bt-horizon. The diffusion coefficientalso quantifies the rate of soil mixing by bioturbation. Modeling of thekinetics of solid matter transfer at multiple spatio-temporal scales should becomea method of predilection in modern pedogenic and critical zone studies

Vertical distributions of Cs-137 in soils: a meta-analysis

International audienceThe vertical distribution of Cs-137-an artificial fallout radionuclide-is controlled by soil characteristics and processes that may differ among soil groups. The application of a single modelling approach to large number of soil profiles provides an original contribution to the literature and allows for comparison between these different soil groups. In order to quantify Cs-137 migration in soils, we compiled and modelled depth-distributed data documented in the literature published before 2013. The resulting database comprised ninety-nine Cs-137 profiles sampled in 14 soil groups of the World Reference Base (WRB) classification (FAO 1998) under different land uses or covers and collected at various geographical locations in the Northern hemisphere between 1992 and 2007. The Cs-137 profiles were classified in seven different categories according to the shape and location of radiocaesium peak. Depth of the latter ranged between 0 and 12 cm (median of 2 cm) and maximal penetration of cesium reached from 12 to 60 cm. The Cs-137 depth distributions in these soils were fitted using a diffusion-convection equation to allow comparison between different soil groups. Diffusion coefficients ranged from 0.02 to 4.44 cm(2) years(-1) in soils (median of 0.64 cm(2) year(-1)), and convection velocities varied from 0 to 0.74 cm year(-1) (median of 0.1 cm year(-1)). The model underestimated Cs-137 concentrations by a median value of 1.9 % of the total inventory in soil samples collected below a 13-cm depth. Global Cs-137 penetration velocities ranged from 0.05 to 0.76 cm year(-1) (median of 0.28 cm year(-1)) over a 25-year period. Our results showed that modelling Cs-137 depth profile with a diffusion-convection equation allowed estimating the bioturbation and clay translocation velocity in a certain number of soil groups. This quantification is crucial as these processes partially control the development of soil surface characteristics and several soil services

Quantification of vertical solid matter transfers in soils during pedogenesis by a multi-tracer approach

International audiencePurpose: Vertical transfer of solid matter in soils (bioturbation and translocation) is responsible for changes in soil properties over time through the redistribution of most of the soil constituents with depth. Such transfers are, however, still poorly quantified.Materials and methods: In this study, we examine matter transfer in four eutric Luvisols through an isotopic approach based on 137Cs, 210Pb(xs), and meteoric 10Be. These isotopes differ with respect to chemical behavior, input histories, and half-lives, which allows us to explore a large time range. Their vertical distributions were modeled by a diffusion-advection equation with depth-dependent parameters. We estimated a set of advection and diffusion coefficients able to simulate all isotope depth distributions and validated the resulting model by comparing the depth distribution of organic carbon (including 12/13C and 14C isotopes) and of the 0–2-μm particles with the data.Results and discussion: We showed that (i) the model satisfactorily reproduces the organic carbon, 13C, and 14C depth distributions, indicating that organic carbon content and age can be explained by transport without invoking depth-dependent decay rates; (ii) translocation partly explains the 0–2-μm particle accumulation in the Bt horizon; and (iii) estimates of diffusion coefficients that quantify the soil mixing rate by bioturbation are significantly higher for the studied plots than those obtained by ecological studies.Conclusions: This study presents a model capable of satisfactorily reproducing the isotopic profiles of several tracers and simulating the distribution of organic carbon and the translocation of 0–2-μm particles

Modeling the migration of fallout radionuclides to quantify the contemporary transfer of fine particles in Luvisol profiles under different land uses and farming practices

International audienceSoil mixing and the downward movement of solid matter in soils are dynamic pedological processes that strongly affect the vertical distribution of all soil properties across the soil profile. These processes are affected by land use and the implementation of various farming practices, but their kinetics have rarely been quantified. Our objective was to investigate the vertical transfer of matter in Luvisols at long-term experimental sites under different land uses (cropland, grassland and forest) and different farming practices (conventional tillage, reduced tillage and no tillage). To investigate these processes, the vertical radionuclide distributions of Cs-137 and Pb-210 (xs) were analyzed in 9 soil profiles. The mass balance calculations showed that as much as 91 +/- 9% of the Cs-137 was linked to the fine particles (<= 2 mu m). To assess the kinetics of radionuclide redistribution in soil, we modeled their depth profiles using a convection-diffusion equation. The diffusion coefficient represented the rate of bioturbation, and the convection velocity provided a proxy for fine particle leaching. Both parameters were modeled as either constant or variable with depth. The tillage was simulated using an empirical formula that considered the tillage depth and a variable mixing ratio depending on the type of tillage used. A loss of isotopes due to soil erosion was introduced into the model to account for the total radionuclide inventory. All of these parameters were optimized based on the Cs-137 data and were then subsequently applied to the Pb-210 (xs) data. Our results show that the Cs-137 isotopes migrate deeper under grasslands than under forests or croplands. Additionally, our results suggest that the diffusion coefficient decreased with depth and that it remained negligible below the tillage depth at the cropland sites, below 20 cm in the forest sites, and below 80 cm in the grassland sites. (C) 2014 Elsevier B.V. All rights reserved

Découverte et étude de remplissages karstiques allochtones d’âge miocène dans l’Obiou (Dévoluy, Alpes françaises) Implications géomorphologiques et paléogéographiques

International audienceAt the mountainside of Obiou (2 789 m) located in the Dévoluy massif (Southwestern Alps) a fortunate discovery has revealed the presence of allochthonous crystalline pebbles excavated from marmot holes. Successive prospecting in the surrounding caves have permitted to identifycrystalline allochthonous sediments such as conglomerates, sands and clays, which formed endokarstic deposits. According to petrographic diversity with presence of granite, orthogneiss, varia gneiss, migmatites, amphibolic gneiss, volcanic basic rocks, sandstones and even limestone with nummulites, these alluvions originate from the SW of the Ecrins massif (Champsaur and Valgaudemar), the localities which are nowadays drained by the Drac River, situated some 1 600 m below the studied caves. These alluvions were analyzed using cosmogenic nuclides (10Be, 26Al, 21Ne), in order to determine their burial ages. However, the dating was compromised due to 26Al concentrations being bellow the limit of quantification (very old burial ages, probably more than 5 Ma). Nevertheless, one sample was analyzed for 10Be/21Ne indicating 15,6 ± 3,8 Ma burial age, which corresponds to Miocene. Even though, our burial dating is quite large due to analytical limitations, the caves in Obiou should be considered as important geomorphological marker of the ancient Drac River drainage (called “paleo-Drac”), during the middle Miocene. Furthercosmogenic nuclide analyses are conducted, in order to precise the burial age of the alluvions and thus frame the incision and uplift rates of this part of the French Alps.Sur les flancs de l’Obiou (2 789 m) dans le massif du Dévoluy (Hautes-Alpes et Isère, France), une découverte fortuite a été réalisée : celle de galets cristallins affleurant, depuis un terrier de marmottes, au beau milieu d’un éboulis calcaire. La prospection de plusieurs cavités environnantes a mis au jour la présence d’alluvions cristallins allochtones sous forme de conglomérats, sables et argiles constituant une série de remplissages endokarstiques. Du point de vue pétrographique, le spectre compte notamment des granites, orthogneiss, gneiss divers, migmatites, gneiss amphiboliques, roches volcaniques basiques, mais aussi des grès, et même des calcaires gréseux à nummulites. D’après cette pétrographie, laprovenance de ces alluvions se situe dans le S-O du massif des Écrins (Champsaur et Valgaudemar), une zone des massifs cristallins externes actuellement drainée par le Drac, lequel s’écoule à environ 1 600 m en contrebas des cavités étudiées. Nous avons tenté de déterminer la durée del’enfouissement de ces alluvions en utilisant des nucléides cosmogéniques produits in situ (10Be, 26Al, 21Ne). Du fait de la faible teneur en 26Al en deçà de la limite de détection, les âges d’enfouissement seraient supérieurs à 5 Ma. Pour un échantillon dont la teneur en 21Ne a été mesurée, le rapport 10Be/21Ne permet une estimation de la durée d’enfouissement aux alentours de 15,6 ± 3,8 Ma, donnant un âge miocène.Au regard de ces âges, les cavités de l’Obiou doivent être considérées comme un niveau repère traduisant la position d’un ancien réseau hydrographique du « paléo-Drac » au Miocène moyen. Des analyses complémentaires de 21Ne couplées au 10Be sont actuellement entreprises pour préciser l’âge d’enfouissement de ces alluvions afin de parvenir à mieux contraindre les taux d’incision et de soulèvement de ce secteur des Alpes françaises

Understanding long-term soil processes using meteoric Be-10: A first attempt on loessic deposits

International audienceMeteoric Be-10, due to its high affinity with soil and sediment particles, is widely used in geomorphologic and environmental studies attempting to evaluate the soil production/denudation rates or soil ages up to 10(7) years. However, the evolution of the Be-10 distribution as a function of depth is poorly known in soils as revealed by recent reviews (Graly et al., 2010; Willenbring and von Blanckenburg, 2010). In this study, Be-10 concentrations in the bulk and the 0-2 mu m (lutum) granulometric fraction of samples along Luvisols profiles developed from loess in Northern France have been measured. The bulk Be-10 concentrations are significantly higher in one of the three sites, likely reflecting differences in the inherited Be-10 concentrations of the loess parent material as well as in the accumulation rates of the later. However, the bulk Be-10 concentrations along all profiles are significantly correlated with the lutum (0-2 mu m fraction) content, the maximum Be-10 concentrations being evidenced in the Bt-horizon. Dominant adsorption of Be-10 to the lutum has been furthermore corroborated by the mass-balance calculations with as much as 79.8 +/- 9.0% of Be-10 being associated with the lutum. Contrary to the bulk Be-10 concentrations, the lutum Be-10 concentrations showed several maxima coinciding with shifts in the coarse to fine silt ratio. This was interpreted as a change in the loess deposit dynamic. Finally, using numerical modeling approach based on the advection-diffusion equation, an average downward migration of Be-10 by clay translocation was estimated. It ranges from 0.01 to 0.08 cm yr(-1). Inherited Be-10 in the loess parent material represented from 64 to 71% of the total Be-10 content in the simulated soils. Vertical Be-10 distributions and their maximum concentrations in the Bt-horizon thus mainly result from redistribution of the inherited Be-10 by clay translocation and bioturbation. (C) 2014 Elsevier B.V. All rights reserved

Relief and paleoenvironmental conditions during the mid-late Miocene in the French Western Alps (Dévoluy Massif) revealed by Obiou cave deposits

International audienceCave levels at high elevations (2250-2370 m), hosting allochthonous sediments with clear provenance from the Pelvoux External Crystalline Massif were identified in the Obiou mountain, Dévoluy Massif (French Western Alps). These deposits result from burial of alluvial sediments of the paleo-Drac River in Miocene times (burial ages of ca. 10-15 Ma). The Drac River is currently situated 1600 m below the caves, indicating significant post-middle Miocene fluvial incision. The pollen analysis on clay cave infill indicates a humid and warm climate, typical for Western Europe in the mid-late Miocene. It also reveals the presence of dinoflagellate cysts from coastal and lagoon environments suggesting deposition of the clays in the caves when they were close to sea level. These findings indicate uplift of the caves of at least 2000 m since the mid-late Miocene. Furthermore, the pollen assemblage originated from different vegetation belts, in agreement with existing data for mid-late Miocene deposits in the western Alps. The pollen flora includes cool-temperate and boreal trees, suggesting high-elevated source areas for the deposits within the Pelvoux catchment. These data confirm the exceptional character of the Obiou cave deposits that provide new geomorphologic constraints for the evolution of the French Western Alps

Relief and paleoenvironmental conditions during the mid-late Miocene in the French Western Alps (Dévoluy Massif) revealed by Obiou cave deposits

International audienceCave levels at high elevations (2250-2370 m), hosting allochthonous sediments with clear provenance from the Pelvoux External Crystalline Massif were identified in the Obiou mountain, Dévoluy Massif (French Western Alps). These deposits result from burial of alluvial sediments of the paleo-Drac River in Miocene times (burial ages of ca. 10-15 Ma). The Drac River is currently situated 1600 m below the caves, indicating significant post-middle Miocene fluvial incision. The pollen analysis on clay cave infill indicates a humid and warm climate, typical for Western Europe in the mid-late Miocene. It also reveals the presence of dinoflagellate cysts from coastal and lagoon environments suggesting deposition of the clays in the caves when they were close to sea level. These findings indicate uplift of the caves of at least 2000 m since the mid-late Miocene. Furthermore, the pollen assemblage originated from different vegetation belts, in agreement with existing data for mid-late Miocene deposits in the western Alps. The pollen flora includes cool-temperate and boreal trees, suggesting high-elevated source areas for the deposits within the Pelvoux catchment. These data confirm the exceptional character of the Obiou cave deposits that provide new geomorphologic constraints for the evolution of the French Western Alps

Relief and paleoenvironmental conditions during the mid-late Miocene in the French Western Alps (Dévoluy Massif) revealed by Obiou cave deposits

International audienceCave levels at high elevations (2250-2370 m), hosting allochthonous sediments with clear provenance from the Pelvoux External Crystalline Massif were identified in the Obiou mountain, Dévoluy Massif (French Western Alps). These deposits result from burial of alluvial sediments of the paleo-Drac River in Miocene times (burial ages of ca. 10-15 Ma). The Drac River is currently situated 1600 m below the caves, indicating significant post-middle Miocene fluvial incision. The pollen analysis on clay cave infill indicates a humid and warm climate, typical for Western Europe in the mid-late Miocene. It also reveals the presence of dinoflagellate cysts from coastal and lagoon environments suggesting deposition of the clays in the caves when they were close to sea level. These findings indicate uplift of the caves of at least 2000 m since the mid-late Miocene. Furthermore, the pollen assemblage originated from different vegetation belts, in agreement with existing data for mid-late Miocene deposits in the western Alps. The pollen flora includes cool-temperate and boreal trees, suggesting high-elevated source areas for the deposits within the Pelvoux catchment. These data confirm the exceptional character of the Obiou cave deposits that provide new geomorphologic constraints for the evolution of the French Western Alps