Outlook on the knowledge gaps to reduce soil sealing and increase the reuse of urban soil

The third specific objective of the Soil Mission is to achieve "no net soil sealing and increase the reuse of urban soil" (European Commission: Directorate-General for Research and Innovation 2022 p. 16). Soil sealing is considered as the main process that causes land degradation in urban areas (European Environment Agency et al. 2022). When soil is sealed, an impermeable layer interrupts the connection between the soil and the atmosphere, leading to the loss of soil resources, biodiversity, and ecosystem services. The process of soil sealing is strictly linked to land take, i.e. the conversion of natural and semi-natural land into artificial land (see definitions in Table 1). The Soil Mission implementation plan estimates that the area with poor soil health due to soil sealing is probably <1% of EU land, but can be as high as 2.5%. These figures are based on the assumption that sealed areas represent around 50% of artificial areas, which cover 4.2% of the EU. Locally, sealed surfaces can reach very high levels, with some areas exhibiting rates as high as 70% (Decoville and Feltgen 2023). Both soil sealing and land take have been steadily growing during the last decades (European Environment Agency et al. 2022). Between 2000 and 2018, artificial areas expanded by 7.1%, with net land take averaging 440 km²/year between 2012 and 2018, primarily at the expense of arable lands, pastures, and grasslands. Concerning the second part of the objective, soil reuse refers to the use of excavated soil from construction sites for other purposes (Reicosky and Wilts 2005). In many European countries, excavated soils are still classified as waste, contributing over 520 million tonnes to the total waste generated in the EU in 2018 (Scialpi and Perrotti 2022).