What is Soil Sealing?
Soil sealing can be defined as the destruction or covering of soils by buildings, constructions and layers of completely or partly impermeable artificial material (asphalt, concrete, etc.). It is the most intense form of land take and is essentially an irreversible process 1, 2.
The picture on the left below shows a typical suburban pattern, with houses, gardens, driveways and yards. This pattern corresponds to the term “settlement area” or “artificial surface”. On the right, the sealed soil of the same settlement area is shown in black. In this case, about 60% of the settlement area is actually sealed by buildings and streets.
Visualisation of the terms “settlement area” / “artificial surface” and “sealed soil” 2
Where does it occur?
Percentage of soil sealing according to EAA soil sealing layer, year 2012 5.
In 2012 the European Union’s territory was sealed by 2.43%. Compared to 2006 sealed surfaces increased by 6 360 km², which corresponds to an area that is 4 times larger than London.
The map shows the percentage of sealed area aggregated to NUTS 3 regions based on the European Environment Agency (EEA) soil sealing map. Metropolitan areas with more than 500 000 capita are hot spots of high sealing percentages with usually 30 % and more.
What causes it?
Driving forces of soil sealing relate to the need for new housing, business locations and road infrastructure for the socio-economic development of cities. Most social and economic activities of the population depend on the construction, maintenance and existence of sealed areas and developed land. However, the new housing or infrastructure developments usually take place at the edge of existing settlements creating pressures on previously agricultural lands and increasing areas of artificial surfaces and sealed soils.
Edge of Pulawy city, Poland
How can it be measured or assessed?
The table below lists indicators which were identified by the research projects ENVASSO and RECARE, which can directly or indirectly measure soil sealing.
|Soil Threat||Soil Threat||Threat 1|
The following table lists key indicators in more detail by providing their status (established/proposed), their purpose, the method they are based on and corresponding references.
|Sealed area (established at European level)||Determine imperviousness of artificially sealed areas||Copernicus Land Monitoring Services. The High Resolution Layer on imperviousness captures the spatial distribution of artificially sealed areas, including the level of sealing of the soil per area unit, available for EU and associated countries, 2006, 2009, 2012
Data: Copernicus land Monitoring Services 3, 5
|Artificial surface (established at European level) z||Land take changes, in particular increase of urbanization and urban sprawl, based on the CLC classes 1.1, 1.2 and 1.3||Corine Land Cover (CLC) inventory: high resolution satellite imagery which is visually interpreted, according to 44 land cover classes, available for EU and associated countries for 1990, 2000, 2006, 2012|
|Transition index (TI) (experimental, EU project URBAN SMS)||Determine loss of top soils within a defined region over time||Transition index (TI) 7,8 =
percent of soil class “n” in new built area
/ percent of soil class “n” in whole soil area
Data: local soil quality data
|Sealed to green areas ratio
|Determine availability of green areas in relation to sealed areas for a defined region||Sealed to green areas ratio =
sealed area of defined region [hectare]
/ green area of defined region [hectare]
Data: Corine Land Cover, Urban Atlas 5
How can it be prevented or remediated?
The European Commission recommends a three-tiered approach to limit (L), mitigate (M) and compensate (C) soil sealing6.
A range of different measures is available to prevent or influence soil sealing. However, only a limited number of measures are fixed in legal regulations. Some measures are largely focused on creating regional or city policies or strategies that take into consideration the valuable role or valorisation of soils and the need to protect them.
Permeable and permeable surfaces (Photo: G. Prokop): 1) Lawn, (2) Gravel Turf, (3) Plastic grass grids, (4) Concrete grass grids, (5) Water bound macadam, (6) Permeable pavers, (7) Porous asphalt, (8) Conventional asphalt
|Local measures||Regional Measures||National Measures|
Green roofs → M
Make small city centres more attractive → indirect L
Integrated spatial planning → L
Permeable surfaces, e.g. driveways → M
Improve the quality of life in large urban centres → indirect L
Land take targets at national and regional levels → L
Reuse of topsoil → M
Steer new developments to already developed land and provide financial incentives for the redevelopment of brownfield sites → L
Imposing development restrictions on top agricultural soils and valuable landscapes → L
|De-sealing → C||Integrate soil information into regional spatial development plans → L||Fees for converting most productive soils into non- agricultural purposes → L|
Case Study Experiment
How does it interact with other soil threats?
- Soil biodiversity. Sealing of soil also causes a near complete loss of soil biodiversity.
- Flooding and landslides. Soil sealing drastically increases the risk of flooding. A high proportion of impermeable surfaces leads to enhanced runoff during rainstorms, which significantly contributes to flooding. Risk of landslides might also be enhanced by human settlements due to loss of natural vegetation and disturbance of slope stability or increased runoff and related soil erosion.
- Soil compaction. construction work can cause soil compaction due to heavy machinery. This effect is increased when soil is excessively saturated with water.
- Soil contamination. Urbanization also usually elevates the contents of pollutants in the soil (e.g. trace elements or polycyclic aromatic hydrocarbons).
How does it affect soil functions?
- Biomass production – land found in suburban areas is often agriculturally productive and therefore sealing these areas results in less availability of fertile soil for food and other biomass production.
- Storing/filtering/transforming – soil sealing reduces the soil’s function as a sink and diluter for pollutants and reduces its capacity to store water.
- Gene pool - Soil sealing results in habitat loss for soil organisms, plant species and animals and such pressures lead to local extinction processes. Decreases in soil biodiversity lead to the inhibition or slowdown of organic matter and nutrient cycles.
- Physical basis - Major functions provided by sealing and urbanisation as a whole are housing and workplace provision (industry, services, commerce) and transport infrastructure.
- Raw material - soil sealing is a driving force for extraction of raw materials for construction work (sand, clay, limestone).
- Cultural heritage - The cultural heritage function of soil, measured as an archaeological value, is generally negatively affected by urbanization and soil sealing, despite the fact that some construction work might help to discover buried records of natural or human history.
Below are two presentations explaining some of the impacts of sealing and potential measures to reduce its impact.
1 Huber, S., Prokop, G., Arrouays, D., Banko, G., Bispo, A., Jones, R., Kibblewhite, M., Lexer, W.,Möller, A., Rickson, J., Shishkov, T., Stephens, M., Van den Akker, J., Varallyay, G., Verheijen, F., 2008. Indicators and Criteria report. ENVASSO Project (Contract 022713) coordinated by Cranfield University, UK, for Scientific Support to Policy, European Commission 6th Framework Research Programme.
2 Prokop G, Jobstmann H., A. Schonbauer. 2011. Report on best practices for limiting soil sealing and mitigating its effects. Publisher: European Commission, Brussels, Technical Report - 2011 – 050, ISBN: 978-92-79-20669-6
3 EEA Website. Imperviousness and imperviousness change http://www.eea.europa.eu/data-and-maps/indicators/imperviousness-change/assessment
4 EEA Website. Land Take http://www.eea.europa.eu/data-and-maps/indicators/land-take-2/assessment-2
5 Copernicus land Monitoring Services; http://land.copernicus.eu/
6 European Commission (2012): Guidelines on best practice to limit, mitigate or compensate soil sealing, SWD(2012) 101 final/2
7 Siebielec G., A. Lopatka, T. Stuczyński, M. Kozak, M. Gluszynska, J. Koza, A. Zurek, R. Korzeniowska-Puculek. 2010. Assessment of soil protection efficiency and land use change. Urban SMS project: Deliverable number: 6.1.2, pp.42
8 Stuczynski T. (2007). Assessment and modeling of land use change in Europe in the context of soil protection. IUNG Pulawy, ISBN: 978-83-89576-19-8
9 Piotrowska-Długosz, A. & Charzyński, P. (2015) The impact of the soil sealing degree on microbial biomass, enzymatic activity, and physicochemical properties in the Ekranic Technosols of Toruń (Poland); Journal Soils Sediments Vol. 15: Issue 1 47-49.
- FAO UN - Soil sealing leaflet - World Soil Day (2016)
- FAO UN - Soil crusting and sealing: Ch.5 in 'Soil tillage in Africa: needs and challenges' (1993)
- European Commission - Overview of best practices for limiting soil sealing or mitigating its effects in EU-27 (2011)