Stéphane Audry - Academia.edu (original) (raw)

Papers by Stéphane Audry

The Moole Hole experimental watershed (4.3 km 2 ; South India) is located near the Western Ghâts ... more The Moole Hole experimental watershed (4.3 km 2 ; South India) is located near the Western Ghâts within a climatic transition zone (1100 mm/y rainfall). The chemical fluxes exported to the outlet through flash floods are strongly influenced by the variability of the SW monsoon intensity and occasionally by dissolution of ashes from forest fires, like in 2004. The aim of the present work was to quantify the chemical fluxes originating from ashes at the stream outlet and their temporal evolution. For this, we characterised the chemical signatures of the local ashes and their temporal evolution by using an experimental approach (420-min batch dissolution). Then, the quantification was performed by an inverse modelling.

This study reports the very first results on high-resolution sampling of sediments and their pore... more This study reports the very first results on high-resolution sampling of sediments and their porewaters from three thermokarst (thaw) lakes representing different stages of ecosystem development located within the Nadym-Pur in-terfluve of the Western Siberia plain. Up to present time, the lake sediments of this and other permafrost-affected regions remain unexplored regarding their biogeochemical behavior. The aim of this study was to (i) document the early diagenesic processes in order to assess their impact on the organic carbon stored in the underlying permafrost, and (ii) characterize the post-depositional redistribution of trace elements and their impact on the water column. The estimated organic carbon (OC) stock in thermokarst lake sediments of 14 ± 2 kg m −2 is low compared to that reported for peat soils from the same region and denotes intense organic matter (OM) mineralization. Mineralization of OM in the thermokarst lake sediments proceeds under anoxic conditions in all the three lakes. In the course of the lake development , a shift in mineralization pathways from nitrate and sulfate to Fe-and Mn-oxyhydroxides as the main terminal electron acceptors in the early diagenetic reactions was suggested. This shift was likely promoted by the diagenetic consumption of nitrate and sulfate and their gradual depletion in the water column due to progressively decreasing frozen peat lixiviation occurring at the lake's borders. Trace elements were mobilized from host phases (OM and Fe-and Mn-oxyhydroxides) and partly sequestered in the sediment in the form of authigenic Fe-sulfides. Arsenic and Sb cycling was also closely linked to that of OM and Fe-and Mn-oxyhydroxides. Shallow diagenetic enrichment of particulate Sb was observed in the less mature stages. As a result of au-Correspondence to: S. Audry (stephane.audry@get.obs-mip.fr) thigenic sulfide precipitation, the sediments of the early stage of ecosystem development were a sink for water column Cu, Zn, Cd, Pb and Sb. In contrast, at all stages of ecosystem development, the sediments were a source of dissolved Co, Ni and As to the water column. However, the concentrations of these trace elements remained low in the bottom waters, indicating that sorption processes on Fe-bounding particles and/or large-size organo-mineral colloids could mitigate the impact of post-depositional redistribution of toxic elements on the water column.

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Editorial handling by R. Fuge a b s t r a c t Mining/smelting wastes and reservoir sediment cores from the Lot River watershed were studied using mineralogical (XRD, SEM–EDS, EMPA) and geochemical (redox dynamics, selective extractions) approaches to characterize the main carrier phases of trace metals. These two approaches permitted determining the role of post-depositional redistribution processes in sediments and their effects on the fate and mobility of trace metals. The mining/smelting wastes showed heterogeneous mineral compositions with highly variable contents of trace metals. The main trace metal-bearing phases include spinels affected by secondary processes, silicates and sulfates. The results indicate a clear change in the chemical partitioning of trace metals between the reservoir sediments upstream and downstream of the mining/ smelting activities, with the downstream sediments showing a 2-fold to 5-fold greater contribution of the oxidizable fraction. This increase was ascribed to stronger post-depositional redistribution of trace metals related to intense early diagenetic processes, including dissolution of trace metal-bearing phases and precipitation of authigenic sulfide phases through organic matter (OM) mineralization. This redistribution is due to high inputs (derived from mining/smelting waste weathering) at the water–sediment interface of (i) dissolved SO 4 promoting more efficient OM mineralization, and (ii) highly reactive trace metal-bearing particles. As a result, the main trace metal-bearing phases in the downstream sediments are represented by Zn-and Fe-sulfides, with minor occurrence of detrital zincian spinels, sulfates and Fe-oxyhydroxides. Sequestration of trace metals in sulfides at depth in reservoir sediments does not represent long term sequestration owing to possible resuspension of anoxic sediments by natural (floods) and/or anthropo-genic (dredging, dam flush) events that might promote trace metal mobilization through sulfide oxidation. It is estimated that, during a major flood event, about 870 t of Zn, 18 t of Cd, 25 t of Pb and 17 t of Cu could be mobilized from the downstream reservoir sediments along the Lot River by resuspen-sion-induced oxidation of sulfide phases. These amounts are equivalent to 13-fold (Cd), $6-fold (Zn), 4-fold (Pb) the mean annual inputs of the respective dissolved trace metals into the Gironde estuary.

Vertical distributions of dissolved major redox parameters, Mo and U from the water to the sedime... more Vertical distributions of dissolved major redox parameters, Mo and U from the water to the sediment were sampled in the salinity gradient of the Gironde estuary. In the water, sulfate and Mo are conservatively transported throughout the salinity gradient. In contrast, U shows a significant removal rate of 85 μmol m − 2 a − 1 related to reductive sequestration of U in the anoxic sediment. Early diagenesis is highly transient and characterized by a three-zone regime related to three density layers functioning at different timescales. Excess of sulfate (up to 1 mM) is observed in the soft mud layer and is assigned to sulfide oxidation by both abiotic Mn-and Fe-oxide reduction and bacterial nitrate reduction. During early diagenesis, Mo and U are released in the sediment porewater from Mn-and Fe-oxides. In not-dredged anoxic sediments, authigenic precipitation of Mo and U with iron sulfides is proposed to explain their removal from solution. In contrast, in dredged sediments, authigenic precipitation of U is inhibited probably owing to the less effective reduction of soluble U(VI) to insoluble U(IV) due to oxidizing transient conditions. Mixing of anoxic sediment porewater with oxygenated water, due to (i) cyclical resuspension of the soft mud layer and (ii) dredging operations in the navigation channel, induces addition of dissolved sulfate (produced from diagenetic sulfide oxidation), Mo and U to the water. This addition is equivalent to 2% (sulfate), 5.5% (Mo) and 0.5% (U) of the dissolved fluvial inputs into the estuary for the natural resuspension, and 0.4% (Mo), less than 0.2% (sulfate, U) for dredge-induced resuspension. Addition of dissolved Mo and U, produced by oxidation of sulfide phases in the dredged sediments redeposited in dynamic environments, are equivalent to 12% (Mo) and 0.8% (U) of their respective fluvial inputs. Additional Mo and U inputs into the water originate from diffusive outflow from muddy sediments and are equivalent to 2% (Mo) and 0.3% (U) of their respective fluvial inputs. However, we show that all these dissolved inputs are scavenged by solid phases.

The behavior and budget of Mn, Cd and Cu in the Gironde estuary were investigated through data fr... more The behavior and budget of Mn, Cd and Cu in the Gironde estuary were investigated through data from both the water column (WC) and sediment depth profiles. In the estuarine freshwater reaches, Mn and Cd removal from and Cu addition to the dissolved phase occurs with a magnitude equivalent to 10%, 30% and 25% of their respective annual fluvial gross dissolved input, respectively. In the saline estuary, diffusive benthic outflow is the main source of dissolved Mn (74% of the total gross dissolved input within the estuary) to the WC. In contrast, Cd (96%) and Cu (89%) are mainly released into the dissolved phase of the WC from fluvial, estuarine and dredging-related particles through complexation (Cd) and organic carbon mineralization (Cu). Anthropogenic activities (sediment dredging) induce pore water inputs, particulate sulfide oxidation and sediment resuspension, significantly contributing to the metal budget of the WC. The related amounts of metals released could be equivalent to 20–50% (Cd) and up to 70% (Cu) of their respective net dissolved addition. Mass balances suggest that a large part of the metals previously released into the dissolved phase from processes within the estuary are removed by suspended particles due to (co-)precipitation of Fe/Mn (oxy)hydroxides and scavenging on autochthonous organic matter. On an annual basis, the Gironde estuary acts as a net sink of dissolved Mn, removing 60% of the dissolved fluvial inputs, and as a net source of dissolved Cd and Cu, contributing ∼ 85% and 20–45% to the dissolved Cd and Cu fluxes to the ocean.

Vertical profiles from the water column, including the maximum turbidity zone (MTZ) to the consol... more Vertical profiles from the water column, including the maximum turbidity zone (MTZ) to the consolidated sediment were sampled in September 2000 in the freshwater reaches of the Gironde Estuary during a complete neap tide-spring tide cycle. The vertical distributions of dissolved major redox parameters and metals (Mn, Fe, Cd, Cu, V, Co, Ni, Mo, and U) were determined. Reactive particulate metal fractions were also determined from selective leaching. The studied system is characterized by density layers functioning at different timescales , consisting of two mobile layers, i.e., the liquid (LM) and the soft mud (SM), overlying consolidated sediments (CS). This results in a three-zone diagenetic regime where (1) O 2 dynamics are fast enough to show depletion in the rapidly mixed LM sequence (tidal timescale), (2) denitrification occurs on the weekly timescale mixing SM sequence, and (3) the Mn, Fe, and sulfate cycling occurs in the CS layer (annual timescale). The studied trace metals show differential behavior during early diagenesis: (1) Cd, Cu, and V are released into pore water preferentially from organic matter in the SM, (2) Co, Ni, and U are released in the CS from Mn and Fe oxides during reduc-tive dissolution, and (3) Mo from both processes. Transient conditions (i.e., oscillations of redox fronts and reoxidation processes), due to the dynamics of the mobile layers, strongly influence the trace metal distributions as inducing resolubilization (Cd, Cu, and Mo). In the CS, authigenic metal phases accumulate, either by direct precipitation with sulfides (Cu, Cd) or co-precipitation with Fe-sulfides (Mo). Microbially mediated reduction of Fe oxides is proposed to control U removal from pore water by reduction of U(VI) to U(IV) at depth. However, a significant fraction of the trace metals is trapped in the sediment in exchangeable forms, and therefore is susceptible to be mobilized due to resuspension of estuarine sediment during strong river flood periods and/or dredging activities.

The partitioning of particulate trace metals was investigated during one year of monthly sampling... more The partitioning of particulate trace metals was investigated during one year of monthly sampling of suspended particulate matter (SPM) at eight sites along the Lot–Garonne fluvial system, known for its polymetallic pollution. The chemical partitioning in five operationally defined fractions (exchangeable/carbonate, Fe/Mn oxides, organic matter/sulfides, acid soluble, residual) was determined using a multiple single extraction approach. This approach showed that Cd, Zn, Pb and Cu were mainly associated with acid soluble phases (84–95%, 65–88%, 61–82% and 55–80% of the respective total metal content), and therefore showed a high mean potential of mobilization and bioavailability. In the Riou-Mort River, draining the smelting-wastes, Zn, Cd and Mn showed high mobility as they were little associated with the residual fraction (1–2%) and mainly bound to the dexchangeableT fraction of SPM (60–80%), probably weakly adsorbed on amorphous freshly-precipitated sulfide and/or oxide phases. Upstream and downstream of the anthropogenic source of metallic pollution, Mn and Cd, and Zn to a lesser extent, remained highly reactive. The other trace metals were mainly associated with the residual fraction and thus less mobile. However, the multiple single extraction scheme revealed that the most reactive transport phases were non-selectively extracted by the conventional extractants used here. These selectivity problems could not have been observed if sequential extraction was used.

Results are presented from observation of dissolved metal concentrations and fluxes at 5 sites in... more Results are presented from observation of dissolved metal concentrations and fluxes at 5 sites in the Lot–Garonne fluvial system known for its historic metal contamination. The contamination originates from the upstream Lot River where a small tributary (Riou-Mort River) drains a smelting-waste area. Unlike non-neutralised acid mine drainage systems, the Riou-Mort waters were not acidic (6.8 < pH < 8.0) due to application of alkaline reagents for neutralisa-tion. Relatively high dissolved U concentrations (up to 1.1 lg L À1) were attributed to these reagents. High metal concentrations (e.g., up to 23 and 1190 lg L À1 , for Cd and Zn, respectively) in the Riou-Mort water resulted from the oxidation of the sulphide phases within the smelting-wastes. Pyrite oxidation rate was estimated (5530 t a À1 ; 35.7 t km À2 a À1) from the total amount of SO 2À 4 discharged in the river water. The related dissolved metal inputs into the Lot River were, e.g., 0.55 and 35 t a À1 for Cd and Zn, respectively. The dissolved Cd fluxes in the Lot River corresponded to 65% of those in the downstream Garonne River. The dissolved Zn fluxes were even similar to those in the Garonne River. Mass balance calculations showed that, downstream the Riou-Mort/Lot River confluence, the exchange between dissolved and particulate phases accounted for the removal of 15% of Zn and 50% of Cd from the dissolved phase. The calculated annual dissolved metal fluxes at the outlet of the Lot–Garonne River system are significant at the global scale, as they represent 0.02–0.25% of the global river budget.

''Capsule'': Reservoir sediments provide fine-scale information on the historical record of metal... more ''Capsule'': Reservoir sediments provide fine-scale information on the historical record of metal pollution in a watershed. Abstract The Lot–Garonne fluvial system is known for its historic heavy metal pollution resulting from mining and smelting activities since the late 19th century. Here, we report 137 Cs activities and heavy metal (Cd, Zn, Cu, Pb and V) concentration–depth profiles from sediment cores retrieved in 2001 from three reservoirs in the Lot River. High mean sedimentation rates of 2.4–2.8 cm a ÿ1 are indicated by 137 Cs dating. The reservoir sediments have recorded the heavy metal deposition and thus allow establishing a connection between the temporal evolution of the heavy metal pollution and historical changes in smelting and waste-treatment proceedings. Based on heavy metal concentrations in sediments upstream of the anthropogenic inputs and bottom-sediments of the furthest downstream core (interpreted as old soil or riverbed), concentrations of w17, w82, w0.33 and w28 mg kg ÿ1 for Cu, Zn, Cd and Pb, respectively, are proposed as natural background values for the Lot fluvial system. The geoaccumulation index (

Heavy metal (Zn, Cd, Cu and Pb) mass balances in the Lot-Garonne fluvial system have been establi... more Heavy metal (Zn, Cd, Cu and Pb) mass balances in the Lot-Garonne fluvial system have been established for 1999 and 2000. The mean annual discharges of these years are close to the mean discharge of the previous decade. The estimated annual dissolved and particulate fluxes in this model watershed integrate daily input from diffuse and point sources, diffusive fluxes at the water/sediment interface, changes in the dissolved-particulate partition and changes in sediment stock. Cadmium, Zn, Cu and Pb entering the Gironde estuary via the Garonne River (11–14 t a À1 of Cd; 1330–1450 t a À1 of Zn; 126–214 t a À1 of Cu and 127–155 t a À1 of Pb) are mainly transported in the particulate phase and the major part (i.e. $ 74 to 96% for Cd, $ 60% for Zn, $ 50 to 60% for Cu and $ 80% for Pb) is transported by the Lot River. The main anthropogenic heavy metal point source is located in a small upstream watershed (Riou-Mort River) accounting for at least 47% (Cd), 2020% (Zn), 20 4% (Cu) and $ 7 to 9% (Pb) of the total heavy metal inputs into the Garonne River, although it contributes only 1% of the discharge. Mass balances for 1999 suggest that under mean annual hydrologic conditions on the basin scale, the heavy metal budget of the Lot-Garonne fluvial system is balanced and that the stocks of Cd [200 t; Environ. Tech. 16 (1995) 1145] and Zn in the Lot River sediment are constant under mean discharge conditions. Heavy metal input by molecular diffusion at the sediment surface represents an important component of dissolved metal inputs into the system (e.g. 30% for Cu). Except for Cu, these dissolved inputs are totally removed from solution by SPM. Based on the generally constant Zn/Cd ($50) concentration ratio in sediment cores from the polluted Lot River reaches and the sediment stock of Cd [200 t; Environ. Tech. 16 (1995) 1145], the present day Zn stock in the Lot River sediments has been estimated at about 10,000 t. In addition to the mobilization of riverbed sediment and associated heavy metals by intense floods, local human activities, including riverbed dredging, may strongly modify the heavy metal budget of the river system. In 2000, the dredging-related remobilization of polluted Lot River sediment released 2–6 t Cd. This additional Cd point source was estimated to account for 15–43% of the gross inputs into the Gironde Estuary.

Fluvial cadmium (Cd) inputs into the Gironde estuary via the Lot–Garonne River system were evalua... more Fluvial cadmium (Cd) inputs into the Gironde estuary via the Lot–Garonne River system were evaluated using nine years of daily measurements of water discharge and total suspended sediment content (TSS) combined with monthly analyses of dissolved and particulate Cd concentrations. This study demonstrates that dissolved and particulate Cd concentrations in the Lot River have strongly decreased in the early 1990s. However, dissolved and particulate Cd concentrations in the Lot River are still higher than those in the Garonne River. In 1992–1998 mean annual Cd concentrations are more or less constant and thus, annual Cd fluxes mainly depend on hydrology. Daily total Cd fluxes range from 0.26 to 966 kg day in the Lot River and from 0.31 to 1360 kg day in the Garonne River, y1 y1 downstream their confluence. During dry years, Cd fluxes at La Reole are dominated by inputs from the upstream´Garonne River, whereas during wet years they are controlled by inputs from the polluted Lot River watershed. The relation between particulate and dissolved Cd fluxes depends on TSS concentrations, which appear to be mainly controlled by the succession of floods and low waters reflecting short-term basin-scale climate variability. Cadmium concentrations, fluxes and the ratio between the particulate and dissolved Cd fluxes depends on the absolute value and instantaneous evolution (strong relative increase or decrease) of discharge. An empiric model permits deducing intervals of daily dissolved Cd fluxes from discharge, hydrological key situation and related intervals of 'typical' dissolved Cd concentrations. In 1992–1998 the Lot–Garonne River system shows close relations between annual dissolved and particulate Cd fluxes. These relations allow deducing annual particulate Cd fluxes using annual dissolved Cd fluxes obtained from the model. The validation a posteriori shows that our empiric model accurately reproduces the annual Cd fluxes estimated from the field data with uncertainty lower than 25% for dissolved fluxes and lower than 30% for the particulate fluxes. Consequently, the empiric model permits estimating annual dissolved and particulate Cd fluxes in the Lot–Garonne River system, from daily discharge data, without Cd analysis. Cadmium fluxes obtained from the model may be used as approximate values for gross fluvial Cd inputs into the Gironde estuary.

Chemical Geology, 2014

The current understanding of wildfire effects on water chemistry is limited by the quantification... more The current understanding of wildfire effects on water chemistry is limited by the quantification of the elemental dissolution rates from ash and element release rate from the plant litter, as well as quantification of the specific ash contribution to stream water chemistry. The main objective of the study was to provide such knowledge through combination of experimental modelling, field data and end-member mixing analysis (EMMA) of wildfire impact on a watershed scale. The study concerns watershed effects of fire in the Indian subcontinent, a region that is typically not well represented in the fire science literature. In plant litter ash, major elements are either hosted in readily-soluble phases (K, Mg) such as salts, carbonates and oxides or in less-soluble carrier-phases (Si, Ca) such as amorphous silica, quartz and calcite. Accordingly, elemental release rates, inferred from ash leaching experiments in batch reactor, indicated that the element release into solution followed the order K N Mg N Na N Si N Ca. Experiments on plant litter leaching in mixed-flow reactor indicated two dissolution regimes: rapid, over the week and slower over the month. The mean dissolution rates at steady-state (R ss ) indicated that the release of major elements from plant litter followed the order Ca N Si N Cl N Mg N K N Na. R ss for Si and Ca for tree leaves and herbaceous species are similar to those reported for boreal and European tree species and are higher than that from the dissolution of soil clay minerals. This identifies tropical plant litters as important source of Si and Ca for tropical surface waters. In the wildfire-impacted year 2004, the EMMA indicated that the streamflow composition (Ca, K, Mg, Na, Si, Cl) was controlled by four main sources: rainwater, throughfall, ash leaching and soil solution. The influence of the ash end-member was maximal early in the rainy season (the two first storm events) and decreased later in the rainy season, when the stream was dominated by the throughfall end-member. The contribution of plant litter decay to the streamwater composition for a year not impacted by wildfire is significant with estimated solute fluxes originating from this decay greatly exceed, for most major elements, the annual elemental dissolved fluxes at the Mule Hole watershed outlet. This highlighted the importance of solute retention and vegetation back uptake processes within the soil profile. Overall, the fire increased the mobility and export of major elements from the soils to the stream. It also shifted the vegetationrelated contribution to the elemental fluxes at the watershed outlet from long-term (seasonal) to short-term (daily to monthly).

ABSTRACT River Nethravati is a small west flowing river originating in the Western Ghatsand falli... more ABSTRACT River Nethravati is a small west flowing river originating in the Western Ghatsand falling into the Arabian Sea after traversing for 147km. The river flows through a densely vegetated forest with steep gradient in the youthful stages of the river which rapidly decreases in the plains. The catchment of the river is spread out in an area of 3657km2 with a discharge of 388m3/sec. The watershed receives frequent and intense southwest monsoonal rainfall with an annual avearage of 4300mm. During the monitoring period, the surface waters from the river Nethravati were collected on a monthly basis for a period of three years, groundwater were collected once in three months for a year and rain waters were collected during the monsoon for a year from the study area and subsequently analysed for major ions. Multivariate statistical techniques like ANOVA, PCA/FA and CA are applied to understand the temporal variability, sources of major ions and to explain the hydrogeochemical process which could explain the water chemistry.The statistical results shows very less heterogeniety in water chemistry temporally and spatially. The anthropogenic source of major ions are negligible during the study period and silicate mineral weathering are the dominant source of major ions in the catchment. In this study, an attempt is also made to explain the interacton between surface water and ground water. The results suggests homogeneity of chemical composition between these compartments which could be explained by shallow ground water table, steep gradients and local recharge. Recent studies on small watersheds highlighted the significance of deep ground water in estimation of chemical outputs (Marechal et al., 2011). In this study, the chloride mass balance approach is used to estimate the annual groundwater recharge to this shallow unconfined aquifer. Natural concentrations of chloride, dissolved in precipitation and groundwater are used to quantify the rate of ground water recharge which is accomplished by using a mass balance of the conservative chloride ion. It is found that the mean chloride concentration in ground water is 4.8mg/L and mean chloride concentration in precipitation is 1.3mg/L. The calculated ground water recharge is >15% of the total precipitation. The ground water discharge is estimated by balancing the mass of chloride in surface runoff, precipitation and groundwater.

Environ Earth Sci, 2014

Systematic monitoring of subsurface hydrogeochemistry has been carried out for a period of one ye... more Systematic monitoring of subsurface hydrogeochemistry has been carried out for a period of one year in a humid tropical region along the Nethravati-Gurupur River. The major ion and stable isotope (d 18 O and d 2 H) compositions are used to understand the hydrogeochemistry of groundwater and its interaction with surface water. In the study, it is observed that intense weathering of source rocks is the major source of chemical elements to the surface and subsurface waters. In addition, agricultural activities and atmospheric contributions also control the major ion chemistry of water in the study area. There is a clear seasonality in the groundwater chemistry, which is related to the recharge and discharge of the hydrological system. On a temporal scale, there is a decrease in major cation concentrations during the monsoon which is a result of dilution of sources from the weathering of rock minerals, and an increase in anion concentrations which is contributed by the atmosphere, accompanied by an increase in water level during the monsoon. The stable isotope composition indicates that groundwater in the basin is of meteoric origin and recharged directly from the local precipitation during the monsoonal season. Soon after the monsoon, groundwater and surface water mix in the subsurface region. The groundwater feeds the surface water during the lean river flow season.

Geochimica et Cosmochimica Acta, 2012

The comparison between contemporary and long-term weathering has been carried out in the Small Ex... more The comparison between contemporary and long-term weathering has been carried out in the Small Experimental Watershed (SEW) of Nsimi, South Cameroon in order to quantify the export fluxes of major and trace elements and the residence time of the lateritic weathering cover. We focus on the hillside system composed of a thick lateritic weathering cover topped by a soil layer. This study is built on the recent improvements of the hillside hydrological functioning and on the analyses of major and trace elements.

Chemical Geology, 2014

Environ Earth Sci, 2014

Geochimica et Cosmochimica Acta, 2012