S07 - Session O4 - Desealing soils : an in-situ experimental device

Authors: Claire Vieillard *, Robin Dagois, Laure Vidal-Beaudet, Stéphanie Ouvrard

Urban soil sealing is one of the main causes of soil degradation in Europe. It increases the risk of flooding and has negative effects on biodiversity, quality of life, microclimate and the water cycle. In order to refresh the city, many unsealing operations are carried out in an empirical way without acquiring knowledge on the capacity of the uncovered soils to acquire a multifunctional state without environmental risk. The project developed in 3 French cities (Angers, Nancy, Cannes) with contrasting climates aims to study for two years the physico-chemical and biological characteristics of Technosols after unsealing to develop green spaces. Experimental designs have been installed on parking areas (Angers, Cannes) or an alley in an urban park (Nancy). In each site, four modalities with an increasing degree of desilting intervention were set up on four contiguous plots of 30 m² each. In all modalities, the surface tread (6 cm) was cut. Then, the aggregate of the underlying layer was (1) unmodified or (2) decompacted to 30 cm thickness or (3) decompacted and mixed with green waste compost to 30 cm or (4) replaced with a mixture of topsoil and green waste compost to 30 cm to mimic a control urban soil. All treatments were vegetated with a grass cover. Soil fertility, biological activity, infiltration properties and capacity to support vegetation were analysed by physical, chemical and biological soil indicators in spring. Soil temperature and moisture were monitored daily with sensors. The concentration of several traces of metals and polycyclic aromatic hydrocarbons was assessed in each modality. The results will help understanding the effect of the soil desealing processes and help urban planner to rely on more resilient methods of desealing.