Assessing soil ecosystem services in urban and peri-urban areas: From urban soils survey to providing support tool for urban planning

The current practice of urban planning does not pay proper attention to the quality of urban soils, to their multiple functions and to the supply of ecosystem services to the urban population. The purpose of this paper is to contribute to raising awareness about the role of soil in the built-up environment, to provide tools to assess and map urban soils ecosystem services and to highlight the possibility of integrating soil knowledge into urban planning. Within the framework of the EU funded project SOS4LIFE - Save Our Soils for LIFE, we surveyed, sampled, analyzed and mapped the soil of the city of Carpi (NE Italy), integrating the existing knowledge about soils and land use with the urban plan, and providing the basis for the production of a 1:5,000 map of urban soils. Soil data interpolated over the entire case study area provided the inputs for locally calibrated pedotransfer functions whose outputs were used to assess a set of six indicators of ecosystem services supply: soil biodiversity, buffer capacity, carbon storage, agricultural production, water regulation, and water storage. Maps of the six ecosystem services are presented along with an overall urban soil quality map based upon the number of service hotspots per unit area of unsealed soil. Results show that for a number of services, hotspots occur not only in the peri-urban agricultural areas but also in unsealed soils within the urban fabric, and that different soils provide high quality services in diverse constellation depending on soil characteristics and degree of sealing. We estimated that the unsealed soils of the green areas within the city (193 ha) store within the first 30 cm of depth 15,067 Mg of organic carbon (55,246 Mg CO eq.) corresponding to an average carbon density of 78.0 Mg ha, which is significantly higher than the corresponding average of the agricultural soils of the area (43.4 Mg ha). Furthermore, thanks to their high available water capacity they store up to 58,682 m of water, corresponding to 304 m ha. Our approach can contribute to making soils and their ecosystem services an integral part of the urban planning process, and an example of its application is provided in order to highlight the impact of planning decisions of the joint provision of soil ecosystem services.