Soils from marsh: self-organization of biogeomorphological paludal patterns, their potential formation mechanisms and ecological interest

Within the Poitevin marsh, the second largest wetland in France, the ‘Michel Brosselin’ national natural reserve offers a unique conservation framework for the evolution of clayey soils of wet meadows that have almost disappeared with cultivation. The exceptional nature of this landscape is linked to the abundance of ‘mottureaux’, mounds with a diameter of several decimetres that can rise up to more than 40 cm above the ground surface. The mottureaux draw on the soil a great diversity of paludal patterns over dozens of hectares that were classified initially by Fernand Verger and that we complete and generalize in this work with drone measurements and image analysis supplemented by a spectral diagnosis. However, their morphogenesis remains unexplained: at the parcel scale, the mottureaux appear as a self-organized system whereas the hypothesis of morphogenesis by self-organization clashes with the usual hypothesis of the formation of mottureaux reported in the literature, which is mainly based on the filling of shrinkage cracks by surface aggregates during run-off, a mechanism that does not a priori induce any organization on the surface. This observation led us to formulate a new hypothesis on the driving mechanism of mottureaux formation which could have a solely physico-chemical origin.