Ecosystem engineers' contribution to soil structure formation in floodplains (FloodSTRESS)
Our main objectives are to understand how activities of ecosystem engineers, especially plants and earthworms, contribute to (re)create one of the main soil functions and ecosystem services, i.e. soil structural stability. Hence, we will study the building of burrows and macroaggregates through ecosystem engineers’ bioturbation activities in a context of a restored floodplain.
In this research project, several questions are raised: 1) Do soil engineers, i.e. plants and earthworms, contribute concomitantly and/or independently to burrows and aggregates building up? How discriminating plants and earthworm implication in soil aggregates and burrows network formation? 2) Are mineral textures and organic matter key factors in these processes? How long does it take to obtain stable aggregates that could improve significantly soil structure? The high-level hypothesis governing our research project is that, in a context of restored floodplains, ecosystem engineers initiate the first steps of soil structure formation and stabilization through their bioturbation activities. To reach our objectives and test our hypotheses, the research plan is divided into three sections built up at different scales, from field studies to microcosm’s experiments (15 cm diameter) then mesocosms (40 cm diameter) in the field. This triple approach will be helpful to have a holistic overview in order to better understand the structuring processes of a restored floodplain. At the field scale, we propose to identify and to describe the engineer communities and their habitat characteristics (soil, vegetation and water dynamics) in order to better understand their spatial distribution within a restored floodplain. At the microscosm scale, that constitutes the main part of the project, we will study fine processes involved in burrows and macroaggregates formation through ecosystem engineers’ bioturbation activities. Controlled conditions will allow testing the efficiency of each biological agent, independently and concomitantly (plants, earthworms separately, plants and earthworms mixed), as well as variables such as sediment texture (sand, silt), the superposition of different soil layers according to facies models (sand above silt, silt above silt; existence of a pre-existing soil layer), and time (5 and 10 weeks). The mesocosm scale will allow combining field work and laboratory experiments through an intermediate situation putting mesocosms directly in the field that will match semi-controlled variables, namely experimental designs in natural environmental conditions.
FiltresRéinitialiser les filtres
Outils d’évaluation de la diversité et de l’activité des vers de terre : de la science participative à la recherche fondamentale
2022-2-1, Le Bayon, Renée-Claire, Campiche, Sophie, Gerber, Valentine, Fietier, Amélie, Scherrer, Luc, Turberg, Pascal
La compréhension et le suivi du fonctionnement des écosystèmes requièrent l’utilisation d’indicateurs biologiques simples et efficaces. Les vers de terre en font partie et leur étude permet d’appréhender l’écosystème à différents niveaux, depuis les sciences participatives impliquant le grand public à la recherche de pointe nécessitant des compétences scientifiques de haut niveau. Cet article présente une synthèse et une comparaison des techniques et outils actuels pour l’étude des communautés de vers de terre et leurs activités de bioturbation en fonction des objectifs et des besoins des potentiels utilisateurs. Depuis le simple comptage d’animaux au séquençage d’ADN en passant par les techniques de tomographie, l’étude des vers de terre offre un large éventail d’outils et de techniques qui permettent de mieux comprendre leur implication essentielle dans les services écosystémiques.
Coupling X-ray computed tomography and freeze-coring for the analysis of fine-grained low-cohesive soils
2017-12-15, Liernur, Adrien, Schomburg, Andreas Cédric, Turberg, Pascal, Guenat, Claire, Le Bayon, Renée-Claire, Brunner, Philip
This paper presents the coupling of freeze-core sampling with X-ray CT scanning for the analysis of the soil structure of fine-grained, low-cohesive soils. We used a medical scanner to image the 3D soil structure of the frozen soil cores, providing X-ray CT data at a millimetric resolution over freeze-cores that are up to 62.5 cm long and 25 cm wide. The obtained data and the changes in gray level values could be successfully used to identify and characterize different soil units with distinctly different physical properties. Traditional measurements of soil bulk density, carbon and particle size analyses were conducted within each of the identified soil units. These observations were used to develop a 3D model of soil bulk density and organic matter distribution for five freeze-cores obtained at a restored floodplain in Switzerland. The millimetric X-ray CT scanning was applied to detect the impact of freeze-coring on the soil structural integrity. This allows identifying undisturbed zones, a critical precondition for any subsequent assessment of soil structure. The proposed coupling is thought to be applicable to a wide range of other low-cohesive soil types and has a large potential for applications in hydrogeology, biology or soil science.
Pioneer plant Phalaris arundinacea and earthworms promote initial soil structure formation despite strong alluvial dynamics in a semi-controlled field experiment
2019-9-11, Schomburg, Andreas Cédric, Brunner, Philip, Turberg, Pascal, Guenat, Claire, Riaz, M., Le Bayon, Renée-Claire, Luster, J.
Soil structure formation is among the most important processes in river floodplains which are strongly influenced by alluvial dynamics. In the context of river restoration projects, a better understanding of soil structure formation in habitats adjacent to the river can help to prevent damages caused by riverbank erosion. Ecosystem engineers such as pioneer herbaceous plants and earthworms likely contribute to soil structure formation even despite less favourable environmental conditions. This study aims to assess the capacity of the herbaceous perennial and native species Phalaris arundinacea and earthworm communities to promote a stable soil structure in alluvial sediments, in particular fresh alluvial deposits, in the short term. Delimited plots were set-up in a restored floodplain adjacent to the Thur River in NE Switzerland and exposed to natural alluvial dynamics for 19 months. Four treatments were replicated in a randomised complete block design: (i) plots with Phalaris arundinacea as only vegetation, (ii) plots with all vegetation constantly removed, (iii) and (iv) the earthworm community reduced by mustard treatment, otherwise as (i) and (ii), respectively. Soil structure formation was analysed at the end of the experiment using different indicators: aggregate stability, field-saturated hydraulic conductivity and the porosity calculated from X-ray CT reconstructions of freeze cores. Phalaris arundinacea was capable of improving the porosity and aggregate stability of both alluvial sediments present at the beginning of the experiment but also of sediments freshly deposited during the observation period. The latter indicates a structuring effect within only one vegetation period. Earthworm abundance was as a whole very low, most likely due to the large proportion of sand. There was a small earthworm effect on soil structure formation, and only in combination with Phalaris.arundinacea. Our findings highlight the ability of Phalaris arundinacea in efficiently structuring sandy alluvial sediments in the short term even under strong alluvial dynamics. Phalaris arundinacea can therefore play a key role in the early stage of river restoration projects. Thus, facilitating the colonisation by such native pioneer herbaceous plants is a suitable step to improve the success of river restoration projects.
Use of X-ray microcomputed tomography for characterizing earthworm-derived belowground soil aggregates
2020-3-21, Le Bayon, Renée-Claire, Guenat, Claire, Schlaepfer, Rodolphe, Fischer, Franziska, Luiset, Alexandre, Schomburg, Andreas Cédric, Turberg, Pascal
Soil structure is closely linked to biological activities. However, identifying, describing and quantifying soil aggregates remain challenging. X-ray microcomputed tomography (X-ray μCT) provides a detailed view of the physicalstructure at a spatial resolution of a few microns. It could be a useful tool todiscriminate soil aggregates, their origin and their formation processes for a better comprehension of soil structure properties and genesis. Our study aims to (a) determine different X-ray μCT-based aggregate parameters for differentiating earthworm casts belowground (earthworm aggregates) from aggregates that are not formed by earthworms (non-earthworm aggregates), and (b) to evaluate if these parameters can also serve as specific “tomographic signatures” for the studied earthworm species. For this purpose, we set up a microcosm experiment under controlled conditions during 8 weeks, including three species of earthworms tested separately: the epigeic Lumbricus rubellus, the anecic Lumbricus terrestris and the endogeic Allolobophora chlorotica. Our results show that X-ray μCT analysis helps distinguish earthworm aggregates from non-earthworm ones using (a) the relative volume of the components within aggregates and (b) the volumetric mass of aggregates and their global volume. In particular, the volume ratio of mineral grains within the aggregates is significantly different according to earthworm species. So, X-ray μCT is a powerful and promising tool for studying the composition of earthworm casts and their formation. However, future research is needed to take into account the shapes and spatial distribution of the aggregates' components, in particular the different states of organic matter decomposition.
Topsoil structure stability in a restored floodplain: Impacts of fluctuating water levels, soil parameters and ecosystem engineers
2018-6-1, Schomburg, Andreas Cédric, Schilling, Oliver, Guenat, Claire, Schrimer, Mario, Le Bayon, Renée-Claire, Brunner, Philip
Ecosystem services provided by floodplains are strongly controlled by the structural stability of soils. The development of a stable structure in floodplain soils is affected by a complex and poorly understood interplay of hydrological, physico-chemical and biological processes. This paper aims at analysing relations between fluctuating groundwater levels, soil physico-chemical and biological parameters on soil structure stability in a restored floodplain.Water level fluctuations in the soil are modelled using a numerical surface-water–groundwater flow model and correlated to soil physico-chemical parameters and abundances of plants and earthworms. Causal relations andmultiple interactions between the investigated parameters are tested through structural equation modelling (SEM). Fluctuatingwater levels in the soil did not directly affect the topsoil structure stability, but indirectly through affecting plant roots and soil parameters that in turn determine topsoil structure stability. These relations remain significant for mean annual days of complete and partial (N25%)water saturation. Ecosystemfunctioning of a restored floodplainmight already be affected by the fluctuation of groundwater levels alone, and not only through complete flooding by surface water during a flood period. Surprisingly, abundances of earthworms did not showany relation to other variables in the SEM. These findings emphasise that earthworms have efficiently adapted to periodic stress and harsh environmental conditions. Variability of the topsoil structure stability is thus stronger driven by the influence of fluctuatingwater levels on plants than by the abundance of earthworms. This knowledge about the functional network of soil engineering organisms, soil parameters and fluctuating water levels and how they affect soil structural stability is of fundamental importance to define management strategies of near-natural or restored floodplains in the future