Soil restoration for urban areas: Exploring water-related ecosystem services and hydrological functionality 

The challenge of restoring degraded landscapes or ecosystems and recultivating them in a way that maximizes the multifunctionality of the artificial soil depends on the extent of soil degradation and its causes. The process of land restoration is expensive, time-consuming and requires careful planning and collaboration between different stakeholders and sectors. In densely populated regions such as Central Europe, there are two major types of artificial soil ecosystems: restoration of landfills or mining pits and urban green infrastructure (e.g. urban tree sites, stormwater retention areas). To compensate for the increasing scarcity of arable land, soils with unfavorable properties must be improved and degraded land must be rehabilitated in order to fulfill soil functions and promote agricultural production. Engineered soils offer a solution for construction the top layer that allows the restored ecosystem to function. Such soils are made from excavated material and other mineral or organic waste and are composed to provide suitable conditions for plant growth and other ecosystem services provided by the soil. As the need for green spaces in urban areas is also increasing, e.g. to adapt and mitigate the urban heat island effect, soil is needed as a habitat for plants and engineered soil mixtures are required depending on the target location and purpose. Soil mixtures with suitable chemical, physical, biological and geotechnical properties (i.e. physical structure) are needed, which are suitable for the restoration of topsoil for various purposes (e.g. mining reclamation, urban greening) and can be used for the near-natural composition of functional soil layers suitable for reclamation and plant growth. Soil structural properties such as infiltration rate, pore volume and water retention capacity are crucial for the functionality of restored soils in the water cycle, especially in view of the increasing challenges posed by ongoing climate change. The aim of this study is to provide a comprehensive overview of the experiences made at research sites in Slovenia and Austria with the application of engineered soils for the restoration of degraded areas. The focus of the contribution is set on different regulatory requirements and methods to ensure the proposed soil hydrological functionality. This research has been financed by ARIS BI-AT-22-23-019, LIFE20 IPE/SI/000021 ReStart and OEAD WTZ SI 01/2023.