Urban Soils

Dublin City
Courtesy of Dept. of Environment, Heritage and Local Government

Urban soils are typically underrepresented in soil surveys and analysis, leading to information gaps. Urban soils are distinct from others, as they are formed from human construction and industrial activities along with fuel combustion, transport emissions and waste dumping, and therefore contain manufactured materials and wastes. With 62% of Irish citizens living in urban areas, it is important to consider the damage already done to urban soils, and ways to prevent damage or contamination in future.

‘Soil Sealing’ is defined as ‘covering of the soil surface with impervious materials as a result of urban development and infrastructure construction’ (EEA 2015). Pouring foundations for construction, building roads and footpaths, and clearing land for industrial activity all seal the soil in different ways, removing the natural interface between the soil and the atmosphere above. Different methods of soil sealing affect the permeability of the surface, for instance, pavements remain slightly permeable and can support vegetation in their cracks, while tree roots can grow beneath them and break down the concrete underneath. Think of an abandoned urban location and notice how vegetation takes over after just a few years of abandonment. 

As a result of urbanisation, many types of material can occur in urban soils, meaning urban soils are likely to include some of the following human-made substances:

1. Loose aeromorphic (wind-shaped) surface litter from plant leaves and other materials such as packaging, newspapers, cigarette filters, plastics, materials from roads such as tyre fragments.
2. Concrete, tarmac, bricks, stones from buildings.
3. Ceramics, concrete, stones, glass, metal and wood, sometimes containing artefacts from history, including coins made from precious metals.
4. Compacted subsoil (compacted due to the process of urbanisation)
5. Lime mortar from demolished structures.
6. Organic waste from food or food processing.
7. Ash, fused materials from burning processes.

Urban environments are the most economically valuable, with precious amounts of green space which are often managed by public authorities for public use. The process of converting urban areas back to green space is difficult, due to the likely contamination of soils as a result of urbanisation.