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Research activities

Research activities on badlands

A recent review on badlands (i.e. severely degraded surfaces highly dissected by rills and gullies) around Mediterranean area, has stated that these surfaces expand over a large climatic conditions (semi-arid to humid) and are characterised by some non-consolidated material mainly marls and clay rocks (Nadal-Romero et al., 2011). Caused by this particular lithology, badlands present the highest erosion rates in Mediterranean area (de Vente and Poesen, 2005). Another recent finding from badlands study concerns the recycling of geologic organic carbon (GOC) in continental surfaces. Indeed marls and clay rocks contain a significant amount of GOC (between 0.5 to 1.0 wt. %, Ronov and Yaroshevski, 1976), which can be release in drainage network after the weathering and the erosion of badlands. High erodability and high GOC content features imply that badlands can be viewed as a source of GOC for the Critical Zone. Therefore, our recent study claims that 20-25% of the particulate OC exported to the Rhône delta is originate from the badlands area (Terres Noires in local name) covering less than 0.25% of the Rhône catchment (Graz et al., 2012).
To resume, badlands is and will be a significant source of sediments and OC in Mediterranean environments ; and with the risk of an increase in erosion intensity in the future decades, these surfaces would strongly modify the biogeochemical cycles and the sediment yield within a catchment. This research interest on badlands currently concerns three current projects :

DEMON project (Devenir des Matières Organiques fossiles à l’affleurement : exemples des terres Noires des Alpes de Haute Provence, coord. : Y. Copard)
Funding agency : INSU EC2CO-BIOHEFECT (2013-2014).
This project deals with the fate of the GOC after erosion and weathering processes of the Terres Noires (Alpes de Haute Provence).
One of the main interests and originalities of this project is to couple the method used to investigate regolith production rates or residence times in a regolith (disequilibrium in the Uranium- series isotopes from fresh rocks to weathered rocks, Ma et al., 2010) with the conventional study of OM (optical and RE6 pyrolysis). This coupling would provide a weathering rate of the GOC within the regolith. For this purpose, a series of regolith profiles was selected regarding the variation of land-cover, slope, aspect and precipitation in the Bléone catchment, as sub-catchment of the Durance River. Other point is the spatial extension (900km2) of these GOC fluxes within this catchment by using GIS methodology and modelling.
Collaborations : ISTO, LHyGes, GéHCO.

OMO project (Origine des Matières Organiques particulaires des sédiments du Rhône et de la Durance, coord. : Y. Copard)
Funding agency : INEE OHM Vallée du Rhone (2013).
This project deals with the contribution of the GOC originate from these Terres Noires in the suspended load and fluvial / flood deposits of the Durance and Rhone Rivers.
Here we have to analyse (i) a large set of suspended sediments from the Durance and from the Rhone (before and after the confluence with the Rhône River) and (ii) some riverine deposits (coring) from the Durance River (Cabannes) and from the Rhône River (Avignon and Arles). We plan to use of OM properties to track this GOC in these materials by the use their specific optical and geochemical properties. Indeed, geological OM, bearing GOC, was subjected to a series of irreversible thermal transformations during burial prior to their exhumation. Accordingly, the ensuing chemical composition and physical structure of geological OM strongly contrast with those of soil OM or aquatic OM, the main other common OC sources in riverine sediments. With these techniques, additional information as soil types, soil horizons and rocks types can be distinguished (Copard et al., 2006). It is therefore possible to track any OC sources and to estimate their respective contribution to the total particulate OC of river sediments.
Collaborations : ISTO, GéHCO, CEREGE, MIO ENTPE, IRSN.

RESOBAM network (RESeau d’Observations des BAdlands en zone Méditerranéenne, coord. : Y. Copard)
Funding agency : MISTRAL – ENVIMed (2013-2014).
One of the consequences of the Global Change is the increase of extreme events frequency as heavy precipitations which, in turn, leading to an increase of erosion. Such process is expressed by dramatic floods provoking some deleterious effects both for Human activities, communities and individuals than for environment. In particular, it is expected that countries from the south shore of the Mediterranean Sea would be the most stressed and impacted by these environmental changes. In this respect, RESOBAM addresses two important issues related to the sedimentary and GOC transfers within instrumented badlands catchments and would help to propose the instrumentation of a future badlands pilot site in NE Algeria.
Instrumented sites on badlands : Draix (France), Vallcebre, Arnas/Arraguas, Tabernas (Spain), Soumam river sub-catchment (Algeria).
Collaborations : Irstea, CSIC-IPE, CSIC-IDAEA, CSIC-EEZA, U. Zaragoza, 3BS-Univ. Bejaia.

Research activities on analytical developments for the study of OM

In sediments, the main scientific challenge remains to develop some new technics leading to well identify, and if possible, quantify each OM sources at high resolution. Among these potential methods, spectrocolorimetry, hyperspectral camera and Rock-Eval 6 pyrolysis are promising.
Spectrocolorimeter proves to be powerful tool for the determination of sedimentological structures, facies as this instrument is non destructive, easy to use and maintain, portable for use in the field, fast to implement and is capable of high resolution. This technique helps to identify the different pigments linked to the degradation and/or nature of the OM (Debret et al, 2011). Some evidences indicate the usefulness of spectrophotometry to track recalcitrant OM as combustion residue and geological OM (Debret et al., submitted). In this respect, ongoing developments concern the hyperspectral camera, which provides the same signals than spectrophotometry but at a higher spatial resolution (65 um pixel size) and at a higher spectral resolution (3 nm).
Collaborations : Chrono-Environnement, Edytem, IFPEN and Berne University. At M2C, M. Debret is the leader of this research activity.

Rock-Eval 6 pyrolysis is a routine technique used for bulk characterisation of natural OM. Further details on OM signatures were evidenced by some treatments on the S2 signals (Disnar et al., 2003). Such a development was further used to track geological orgC in suspended load within a catchment (Copard et al., 2006). Ongoing activities concern the exploration of other signals in order to extract the BCM signature from a OM mélange and the coupling RE6 pyrolysis with ATR-FTIR spectroscopy (Delarue et al., 2013).
Collaborations : ISTO.

These methodological developments are supported by a task named PAF (hyPerspectral Analyzes of organic Fraction) included in the federative and regional project TEQQ (Transfert Eau Qualité Quantité).
Funding agency : general council of the region Haute-Normandie via the SCALE federation and own lab resources (2013).
Studied sites are regional (Basse-Normandie : darse des docks along the Seine River and fluvial sediments from the Eure River) and national (lake Bresson, Esterel range ; badlands of the Durance catchment).