Urban soil protection
WHY SOIL PROTECTION IS IMPORTANT FOR URBAN ECOSYSTEMS
Traditional understanding of soil role in the ecosystem has been reduced to its production function, strictly related to agricultural and forestry sectors. Thus, until now soil protection has been aimed mostly at minimizing the risk of soil degradation and preventing transformation of most productive agricultural land for non-agricultural purposes. Reduction of soil role just to production causes that little attention is paid to a soil role in functioning of urban ecosystems including soil effects on microclimate and life conditions. For these reasons, treating urban soils just as a ground with certain geotechnical properties, which determine the types of buildings to be constructed does not correspond to complex needs of urban ecosystems management that is crucial for life quality of human population.
Protection of the most valuable urban soil habitats, characterized by high water and heat capacity, high fertility and biological activity is motivated by the role of these surfaces in controlling many important functions of urban ecosystem. Maintaining open spaces with high quality undisturbed soils in urbanization process has a direct impact on biodiversity, quality of urban landscape and health conditions of urban population. One of measurable effects of loss of best quality soil habitats in urbanization process is degradation of green areas and reduction of variability and quantity of flora and fauna. Species living on poor quality soils are sensitive to drought and have limited capacity to absorb pollution. Furthermore, poor vegetation occupying low quality soils produce limited amount of oxygen and has weak ability to prevent soil surface against wind erosion.
Lack of protection of the best quality soils leads to a loss of urban ecosystem's retention abilities, i.e. ability to hold water, which influences the microclimatic conditions (low quality soils retain small amounts of precipitation water hence they are not able to effectively absorb heat). In summer period the inhabitants of densely built-up areas are exposed to higher temperature than in zones where high quality soils were saved for green areas and recreation purposes. Such vegetated areas with high biodiversity have ability to absorb the heat and therefore to alleviate the thermal extremes in their surroundings. However, in residential areas where the unsealed areas are occupied by poor soils the capability to absorb the heat and to alleviate the thermal extremes is much smaller.
Buffering function of soils with high water retention capacity is also important for preventing abrupt surface runoff of the precipitation water. This ability prevents flooding, but its main role is to form the conditions essential to maintain green areas with high species diversity, biomass abundance and capability to prevent excessive dusting of the air. Buffering functions of soils are also related to accumulation of pollutants emitted in urban environment and, thus, preventing their migration to surface and groundwater (low quality soils with poor sorption capacity are ineffective in filtration of pollutants).
An important rationale for protection of soils in urban areas is keeping aesthetic functions of space, directly related to biodiversity – perception of surrounding landscape is an integral factor contributing to quality of our life. Monotonous urban landscape devoid of areas rich in water and biological activity constitutes human-unfriendly “urban deserts”, which cause discomfort, disturbance of social relationships and also restrict availability of recreation activities. Interactions of these factors may influence general health level of population.
Summarizing, consumption of high quality soils in urbanization process and leaving low quality soils for recreation and green surfaces have the following consequences: low biological productivity of habitats and limited amounts of oxygen emitted by plants, poor protection against erosion and atmosphere dusting, poor development of vegetation which intensifies adverse thermal effects, weak protection against migration of pollutants, degradation of aesthetic functions of space. It is beyond of all doubts that the loss of valuable soil habitats, which are vital for quality of life in the city, is an irreversible process. Therefore, protection of valuable soils within newly urbanized areas will have an important effect on quality of life and the environment. A need for such protection refers not only to intensively urbanized areas that have already lost their agricultural character, but first of all, to suburban zones, which are recently undergoing the urbanization.