27 May 2024

Legacy of soil sealing studied in Strasbourg

A Strasburgo sono in atto da tempo inizitive di de-sealing del suolo. Foto: Ralph Hammann - Wikimedia Commons CC BY-SA 4.0 DEED Attribution-ShareAlike 4.0 International

The PerméaSol project will study the ecological trajectory of “liberated” urban soil over the next 3 years. Thus assessing the long-term effects of sealing

by Matteo Cavallito


Soil sealing is a critical phenomenon that impacts soil health by generating multiple effects. These include, in particular, the destruction of natural habitats, increased flooding and the heat island effect in urban areas. It is not surprising, therefore, that restoration interventions based on the removal of artificial cover are now finding an increasing place in environmental policies.

But what happens once this process is initiated? How does the once-sealed soil behave after its exposure to the open air? These are the fundamental questions now being attempted to be answered by the PerméaSol project, a research initiative launched in Strasbourg and presented last week at the IUSS (International Union of Soil Sciences) Centennial, the Florence-based mega-event that brought together more than 1,500 scientists from around the world.

The PerméaSol Project.

The French city has embarked on a program to reduce net sealing to zero. Any roofing work carried out in urban areas, in other words, must be offset by a desealing, or de-impermeabilization, initiative over an equivalent area. In this context, according to the website Strasbourg.eu, the PerméaSol project, launched in September last year, aims to “shed light on the capacity for spontaneous regeneration of soils under different conditions.” For this, “different types of surfaces – vegetated, stabilized and asphalted – and environments, such as urban and forested, are studied.”

Today, the researchers’ presentation says, “climate and biodiversity crisis led to question this type of land management with desealing of urban soils.”

However, “while sealing effects on soil are wellknown, desealing effects are less characterized. Using a holistic approach to characterize the evolutions of urban soil after desealing is thus crucial to understand the effect of such practice on water, soil and biodiversity, but also the underlying mechanisms and the required time to retrieve a functional soil.” The project therefore aims to study the ecological trajectory of a “liberated” urban soil over the next 3 years. Thus assessing the long-term effects of sealing that may continue to occur even after the cover is removed.

The investigation

The study involves three areas undergoing asphalt layer removal between September 2023 and January 2024. Two located in the urban area of Strasbourg, the third in a nearby forest. The survey also affects the still-sealed areas located next to each plot, which serve as a control group.

“Several analyses are regularly carried out to try and integratively capture the system dynamics,” the scientists explain. These include variables such as “water infiltration and storage, quantity and functional characteristics of vegetation and soil microorganisms, soil fertility and pollution, and soil chemical composition.” Next, they point out, the interactions and dynamics among the various observed processes will be studied.

Il fenomeno del soil sealing è ampiamente diffuso. La situazione si sta aggravando nella maggior parte delle regioni del Pianeta. IMMAGINE FAO http://www.fao.org/3/a-i6470e.pdf

The phenomenon of soil sealing is widespread. The situation is worsening in most regions of the Planet. Image: FAO

Early results

These, the authors continue, are the first phenomena observed: “At first, the desealed soils were characterized as a sand/gravel mix (~70% of soil particles >2mm) with little organic matter (~1%), low biological activity (~220mgC/kg) and no plants.” Then, “Water infiltration has significantly increased after desealing. Vegetation appeared within a month, with both pioneer and typical asphaltspecific species.”

Finally, soil heat “decreased following desealing, and is expected to maintain this pattern with vegetation growth. Both water storage and organic matter content are expected to increase in the next months.”