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Schomburg, Andreas Cédric

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Schomburg, Andreas Cédric
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Ancien.ne collaborateur.trice
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https://libra.unine.ch/handle/123456789/1000

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  • Publication
    Accès libre
    Composition and superposition of alluvial deposits drive macro-biological soil engineering and organic matter dynamics in floodplains
    (2019-8)
    Schomburg, Andreas Cédric 
    ;
    Sebag, D.
    ;
    Turberg, P.
    ;
    Verrecchia, Eric 
    ;
    Guenat, C.
    ;
    Brunner, Philip 
    ;
    Adatte, T.
    ;
    Schlaepfer, R.
    ;
    Le Bayon, Renée-Claire 
    Soil structure formation in alluvial soils is a fundamental process in near-natural floodplains. A stable soil structure is essential for many ecosystem services and helps to prevent river bank erosion. Plants and earthworms are successful soil engineering organisms that improve the soil structural stability through the incorporation of mineral and organic matter into soil aggregates. However, the heterogeneous succession of different textured mineral and buried organic matter layers could impede the development of a stable soil structure. Our study aims at improving the current understanding of soil structure formation and organic matter dynamics in near natural alluvial soils. We investigate the effects of soil engineering organisms, the composition, and the superimposition of different alluvial deposits on the structuration patterns, the aggregate stability, and organic matter dynamics in in vitro soil columns, representing sediment deposition processes in alluvial soils. Two successions of three different deposits, silt–buried litter–sand, and the inverse, were set up in mesocosms and allocated to four different treatments, i.e. plants, earthworms, plants+earthworms, and a control. X-ray computed tomography was used to identify structuration patterns generated by ecosystem engineers, i.e. plant root galleries and earthworm tunnels. Organic matter dynamics in macro-aggregates were investigated by Rock- Eval pyrolysis. Plant roots only extended in the top layers, whereas earthworms preferentially selected the buried litter and the silt layers. Soil structural stability measured via water stable aggregates (%WSA) increased in the presence of plants and in aggregates recovered from the buried litter layer. Organic matter dynamics were controlled by a complex interplay between the type of engineer, the composition (silt, sand, buried litter) and the succession of the deposits in the mesocosm. Our results indicate that the progress and efficiency of soil structure formation in alluvial soils strongly depends on the textural sequences of alluvial deposits.
  • Publication
    Accès libre
    Rock-Eval pyrolysis discriminates soil macro-aggregates formed by plants and earthworms
    (2018)
    Schomburg, Andreas Cédric 
    ;
    Verrecchia, Eric 
    ;
    Guenat, C.
    ;
    Brunner, Philip 
    ;
    Sebag, D.
    ;
    Le Bayon, Renée-Claire 
    Plants and earthworms, as soil ecosystem engineers, play a crucial role during stabilisation of organic matter in soil through its incorporation into soil aggregates. It is therefore essential to better understand the mechanisms and interactions of soil engineering organisms regarding soil organic matter stabilisation. Several methods have already been successfully applied to differentiate soil aggregates by their origin, but they cannot specify the degree of organic matter stability within soil aggregates. Rock-Eval pyrolysis has already been proved to be pertinent for analyses of soil organic matter bulk chemistry and thermal stability, but it has not yet been directly applied to identify biogenic organic matter signatures within soil aggregates. In this study, Rock-Eval pyrolysis was used for the identification of the soil aggregate origin as well as for the determination of the soil organic matter bulk chemistry and thermal stability in a controlled experiment. Mesocosms were set up, containing treatments with a plant, an earthworm species, or both. Water stable soil macro-aggregates > 250 μm were sampled and tested with Rock-Eval pyrolysis after a two-month incubation period. Rock-Eval pyrolysis was able to differentiate soil macro-aggregates by their origin, and to identify a specific signature for each treatment. Macro-aggregates from the plant and earthworm treatment were characterized by a mixed signature incoming from the two soil engineers, indicating that both engineers contribute concomitantly to soil aggregate formation. Organic matter thermal stability was not positively affected by earthworms and even tends to decrease for the plant treatment, emphasising that organic matter was mainly physically protected during the incubation period, but not stabilised. However, future research is required to test if signatures for the tested organisms are species-specific or generally assignable to other plant and earthworm species.
  • Publication
    Accès libre
    Topsoil structure stability in a restored floodplain: Impacts of fluctuatingwater levels, soil parameters and ecosystem engineers
    (2017-6)
    Schomburg, Andreas Cédric 
    ;
    Schilling, Oliver 
    ;
    Guenat, C.
    ;
    Schirmer, Mario 
    ;
    Le Bayon, Renée-Claire 
    ;
    Brunner, Philip 
    Ecosystem services provided byfloodplains are strongly controlled by the structural stability of soils. The developmentof a stable structure infloodplain soils is affected by a complex and poorly understood interplay of hydrological,physico-chemical and biological processes. This paper aims at analysing relations betweenfluctuating groundwaterlevels, soil physico-chemical and biological parameters on soil structure stability in a restoredfloodplain. Water levelfluctuations in the soil are modelled using a numerical surface-water–groundwaterflow model and correlated tosoil physico-chemical parameters and abundances of plants and earthworms. Causal relations and multiple interactionsbetween the investigated parameters are tested through structural equation modelling (SEM). Fluctuating water levelsin the soil did not directly affect the topsoil structure stability, but indirectly through affecting plant roots and soil pa-rameters that in turn determine topsoil structure stability. These relations remain significant for mean annual days ofcomplete and partial (N25%) water saturation. Ecosystem functioning of a restoredfloodplain might already be affectedby thefluctuation of groundwater levels alone, and not only through completeflooding by surface water during afloodperiod. Surprisingly, abundances of earthworms did notshow any relation to other variables in the SEM. Thesefindingsemphasise that earthworms have efficiently adapted to periodic stress and harsh environmental conditions. Variabilityof the topsoil structure stability is thus stronger driven by the influence offluctuating water levels on plants than by theabundance of earthworms. This knowledge about the functional network of soil engineering organisms, soil parametersandfluctuating water levels and how they affect soil structural stability is of fundamental importance to define man-agement strategies of near-natural or restoredfloodplains in the future.