Land: Soil
Background: threats to soils
Soils face a number of threats that will reduce their ability to perform their various functions.
The main threats to English soils include:
Climate change
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| Image courtesy of Tyndall Centre |
Climate change is likely to modify the key soil processes that underpin the capability of soil to perform its many functions.
Soil processes are influenced directly by temperature, rainfall and changes in atmospheric carbon dioxide, particularly as these affect soil ecology and organic matter. In turn this affects soil structure, water regimes, and plant growth. Additionally, rainfall intensity, duration, and amount, could alter soil erosion rates.
A project investigating the impacts of climate change on soil functions has been undertaken by the National Soil Resources Institute in collaboration with the UK Climate Change Impacts Programme. Full details including the final project report are available.
- The impacts of climate change on soil functions (on Defra science and research project database)
Compaction
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| Soil compaction Image courtesy of the Environment Agency |
Soil compaction reduces the pore space between soil particles, resulting in a reduced capacity to absorb water and air. It occurs when soils are subject to extensive pressure due to the use of heavy machinery, or dense stocking rates, and can be intensified when soil are wet.
The overall deterioration in soil structure due to compaction may result in an increased risk of soil erosion (see below) and accelerated run-off rates.
Contamination
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Soil contamination is the introduction to the soil environment of chemical compounds, biological organisms or other materials which negatively effect or alter soil function.
Common soil contaminants include heavy metals, hydrocarbons, biological pathogens and substances which can acidify and/or enrich the soil with nutrients.
Soil contamination can occur through deposition from the atmosphere (e.g. acid rain), deliberate application (e.g. fertiliser), spillage, leakage or illegal dumping.
A project investigating the sources and impacts of past, current and future contamination of soil is being undertaken to identify sources of soil contaminants, and to assess their potential impacts on soil functions.
The study will also summarise the regulatory and voluntary measures currently in place to control soil contamination, and assess their effectiveness in controlling contaminant inputs to soils. It is due to report during 2006.
- Sources and impacts of past, current and future contamination of soil (on Defra science and research project database)
For more information on land and soil contamination see the contaminated land pages.
Erosion
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Severe gully erosion, Bedfordshire.
Courtesy John Quinton, Lancaster University |
Soil erosion is a natural phenomenon. It normally occurs at a low level in this country but can become a problem when man's activities or severe weather events upset the ecological balance.
The loss of soil increases the need for soil conditioners and reduces the retention and filtering of water. The soil particles and their associated contaminants (that can include pesticides, nutrients, metals and pathogens) can enter watercourses and cause pollution.
Loss of biodiversity
Soil biodiversity is vitally important in maintaining soil functions as many of the key process underpinning these functions are mediated by the soil biota. Fungi, bacteria and larger organisms play a crucial role in the generation and stabilisation of soil structure which influences rooting, aeration and drainage; and mediates the balance of soil organic carbon and plant nutrients.
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Bacterial-feeding nematode visualised in a pore within an arable soil. Image width ≈ 180 µm. Courtesy: Karl Ritz, National Soil Resources Institute & Scottish Crop Research Institute |
The extent of this diversity is beginning to be described and quantified in detail (eg. the NERC Soil Biodiversity Programme) but provision of full inventories of soil biodiversity is not yet practical.
- NERC Soil Biodiversity Programme (on NERC website)
Our long-term aim is to maintain soil conditions which are favourable to diverse soil biota and functional soil systems. Initially, we need to gather the evidence to enable the development of robust indicators and soil management guidelines to monitor and maintain functional biodiversity in soils.
A Defra-funded R&D project, due to report in 2006, is looking to develop biological indicators of soil health:
- Soil quality indicators - developing biological indicators (on Defra science and research project database)
Loss of organic matter
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| Upland peat erosion |
Organic matter enters soils from plant, animal or microbial remains/products and is made up of carbon, nitrogen, phosphorus and potassium, as well as trace elements.
As an important ingredient of mineral-based soils, organic matter has an influence on its chemical, physical and biological characteristics. It also impacts plant growth through, for example:
- Altering soil pH
- Assisting with a good structure for root growth
- Easing trafficking and tillage
- Making soils more resistant to erosion
- Supplying nutrients
Soil Organic Matter (SOM) also increases the ability of the soil to bind chemicals and can buffer the release of pollutants into air or water.
Changes in SOM content can affect the potential of soils to perform the functions we require of them.
Sealing
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| Soil sealing |
Soil sealing is defined as the covering of the soil surface with a layer of impervious material or changing the nature of the soil so that it behaves as an impermeable medium.
Most sealed soils perform only the platform for construction function of soil, i.e. supporting buildings, as other functions such as food and fibre production or the ecological functions of soil are prevented.
The indirect impacts of soil sealing affect large areas due to fragmentation of habitats and disruption of ecological corridors.
For more on soil sealing see the soils in the built environment pages.
Page last modified: 23 June 2006
Page published: 1 September
2005