For many years, improving agricultural production was the main goal of soil science. As part of this, a number of country-wide soil mapping programmes took place across Europe during the 20th Century, which also resulted in the creation of several national soil databases. Today, the importance of these data, complemented in some countries with irreplaceable archives, goes far beyond agriculture. They are proving to be an invaluable resource for a wide range of applications – from measuring the effects of climate change, monitoring environmental pollution and atmospheric deposition, to helping solve serious crimes.
Soil maps and databases
In the UK, truly national soil sampling programmes (with the goal of mapping soil distributions for agricultural purposes) started in England and Wales in 1939 and Scotland in 1948, although not until 1987 in Northern Ireland.
Published soil maps ranged in scale from 1:25,000 to 1:63,360, and included reports incorporating information about the soils and their associated landscapes and environments. Geographically, most of these are concentrated on the higher quality agricultural land, which reflects the early emphasis on agriculture and the desire to optimize the use of those soils for food production. In the late 1970s, the focus of attention for such mapping programmes moved to the production of soil maps which would provide national coverage (1:250,000 scale) for the whole of the Great Britain. These maps have subsequently been digitized greatly increasing their utility and applications.
As this mapping programme progressed, soil profiles were excavated in order to collect data that characterised the soils being mapped. Currently, approximately 13,000 profiles to a depth of a metre are held within the Macaulay Institute’s archive, comprising samples for approximately 40,000 soil horizons. The majority of these data were collected as being representative of different soil types across the country and not a strategy for the sampling of Scotland’s soils.
A core part of the database is the National Soils Inventory of Scotland (NSIS). These data were collected at every 5 km x 5 km grid intersection and offer several advantages over data gathered using subjective judgements. These include :
The NSIS provides a framework for a structured re-sampling of soils to determine trends of change, and to develop and test hypotheses on the drivers and pressures that have caused those changes.
The NSIS sites were first visited between 20 and 30 years ago, at a time of agricultural expansion and intensification, significant woodland expansion and when air pollution abatement strategies were being developed and implemented. Land use and environmental conditions (e.g. air pollution) have changed markedly since that programme of sampling. Re-sampling now provides a unique opportunity to quantify the impacts of those changes on the characteristics of soils, thus providing evidence from which to develop policies to protect our soils as we enter a further period of extensive change, both in land use and the environment.
A range of new techniques and methods are being considered; the NSIS provides the widest possible range of soils upon which to test them fully. Soils selected from the NSIS are therefore essential to carry out the most rigorous evaluation of these new methods.
It describes the soil environment of Scotland, and its relationship to above-ground plant communities, thus allowing examination of the biogeographical associations of microbes, vegetation and climate.
It is a well documented and consistent dataset, described, sampled and analysed using consistent techniques, guidelines and methods.
The 10 km x 10 km intersections of the National grid were sampled, producing approximately 3,000 samples from across the country. These samples have been analysed for their physical and chemical properties. This resource, forms part of Scotland’s National Soil Archive (which contains over 40,000 samples), and is held at the Macaulay Institute, in Aberdeen. In a sense, this archive can be considered to be a soil museum, and like all items housed in a museum they are irreplaceable.
As for all data, that for soils will age and a partial updating of the NSIS is currently under way, which will allow recently developed analytical techniques to be applied to fill gaps in the dataset and also help chart recent environmental changes.
Applications of soils data and maps
Although environmental data, including those on soils are invaluable in their own right, and represent a record of our natural capital, the application of these data to address a range of land use, environmental and ecological issues is probably what interests a wide and diverse range of stakeholders.
One of the first applications is that of the Land Capability for Agriculture (LCA), which was developed by the Macaulay Institute to describe the agricultural potential of land based on the degree of limitation imposed by its biophysical properties. It is a seven class system with Class 1 having the fewest limitations to agricultural exploitation, and Class 7 having little agricultural value. It is based, primarily, on climate, a number of soil properties, (for example depth and stoniness), wetness, erosion risk and slope. Also included is the overall pattern, i.e. variability, of the soil properties and, in one of the classes (Class 6), vegetation cover is also taken into account. The system therefore does not rely on soils data alone but they do form a key constituent.
A similar system has been developed for forestry but with different soil parameters reflecting the differences in growth requirements between agricultural crops and tree species. The LCA maps, although now in digital format, were produced by field based evaluation methods but can now be automated within a Geographic Information System, which will allow a range of scenarios of change in climate and soil properties to be explored.
A wide range of other applications have capitalised on this valuable map and database resource. Theses include :
The development of a hydrological classification of soils (Hydrology of Soil Types HOST). This in turn has been used in a wide range of applications, in particular those that seek to determine pollutant transport through soils and into water bodies.
A soil erosion risk classification which includes the integration of a few key soil attributes that are known to influence the physical movement of soil. Again there can be serious down-stream effects on water quality.
A model of native woodlands, which is a rule-based system that seeks to identify the best sites for new native woodlands based on soil conditions
The assessment of the capacity of different soils to bind pollutants and prevent their release to plants, water and air.
Many of these more recent applications have an ecological or environmental emphasis, reflecting the change in research focus from primary plant production to the wider multi-functional dimensions of soil.
The land and forestry sectors account for 20% of carbon dioxide emissions in Scotland, which is second only to that of power generation. This means that soils play a pivotal role in regulating, adapting and mitigating future climate change as they are a sink and a source of climate greenhouse gases.
Soils in different parts of the globe will respond differently to climate change. Climate may cause direct changes in soil properties that feedback to climate change such as, higher carbon turnover rates or nitrous oxide emissions when land-use is changed.
Other impacts are indirect. Freely drained soils may become droughtier leading to lower crop yields and increased vulnerability to wind erosion. In contrast, other soils may become wetter, resulting in shorter access periods for farm/forest operations and grazing.
Perhaps the most exciting (and high-profile) recent application of both the existing and new databases is within the field of soil forensics. Today there is general recognition that trace evidence (fibres/fluids/particles) found at a scene of crime can be instrumental in providing criminal intelligence to police investigations. Soil is a complex matrix composed of mineral grains, organic material, and living and decomposing organisms. The proportions and characteristics of the mineral, organic and biological components of soil vary, often in a unique manner. Underlying parent material, land-use/vegetation, and climate have important influences on soil composition.
Soil particles readily adhere to, and transfer from clothing, shoes, vehicles or tools, and can therefore be treated as trace evidence, potentially linking suspects to, or eliminating them from, a crime scene. Traditional methods applied to soil forensics have proven themselves in courts of law, through the judgment and testimony of an expert witness, and include visual comparison of colour, particle mineralogy and palynology (identification of pollen and spores).
With recent advances in analytical methodology, soil components can be separated and characterised at an increasing level of detail, and on an increasingly small size of sample. Recent years have seen significant analytical advances in profiling methods that can be applied to soil. For example Infa-Red radiation can be used to provide a general profile of soil chemistry; XRDP can provide a detailed fingerprint of the mineral components of soil, while advances in molecular microbial methods can be applied to fingerprint the biological component of soil. Research is currently underway to test such fingerprinting methods against conventional methods, to link the data to the available databases and to determine their likely applicability and use, depending upon the size, condition of sample and other case specific information.
An EPSRC-funded project entitled SoilFit (www.macaulay.ac.uk/forensics), run from the Macaulay Institute, in collaboration with NSRI and DARDNI, is using a suite of measurements to characterise soil samples from across the UK. The resulting database will include detailed information on a range of outputs including colour, particle size analysis, mineralogy, general chemical fingerprint, microbial community characterisation, wax biomarkers, pollen profiling, elemental analyses; major and trace minerals, and isotopes.
One crucial component of the SoilFit projects’ approach to soil as a forensic tool, is the development of a set of reference soils and databases. These databases will enable the estimation of the probability of obtaining accurate soil matches. Creating such a reference database offers great potential in effectively and efficiently applying soil forensic methods. Combining formal statistical analysis with highly specific, polyphasic soil fingerprinting methods will make soil analysis a more effective tool for routine forensic work, thus considerably extending its applicability.
Soil Forensics- reduction of search areas
Based upon the matching of soil properties from case evidence, with soil maps and spatial databases, potential target areas for search can be identified. The onus is then on the soil forensic research team to obtain the crucial link between the legal investigation area and the geo-morphological evidence. Non-invasive soil property monitoring, such as through airborne or terrestrial remote sensing, allows a potentially rapid search of areas of interest.
The use of Ground Penetrating Radar (GPR) can assist police and law enforcement investigation teams in forensic searches, enabling the rapid, non-destructive, searching of large areas for buried objects, hides and caches, and the detection of cavities both in the ground and in structures. This greatly improves search efficiency and reduces unnecessary excavation operations.
Linking descriptions of the soil characteristics of a field sample, from analytical and non-invasive sources, with the content of spatial databases of soils and vegetation enables areas of search to be geographically targeted. This can be done, for example, by identifying sites with a combination of soil and vegetation characteristics derived from analysis of evidence. Other geographic datasets (e.g. data on transport routes and population centres) can then be used in combination with those of soils and vegetation to explore hypotheses for the targeting of areas of search.
Urban surface soils
A coordinated network of related ‘projects is being developed, in partnership with the Robert Gordon University, Aberdeen, and based at a range of collaborating UK Universities. These projects are known as the Soil Forensics University Network (SoilFUN). The network draws together academics from a number of Universities in the UK who, through the use of student projects, will generate analytical data on a variety of soils in their urban areas. This coordinated approach uses a high degree of similarity in experimental design and quality control between the participating Universities.
Of particular forensic interest are the soil samples taken from surface layers in urban areas. The aim of SoilFUN is to broaden the knowledge of the urban soil environment. Specifically, it is hoped to address between city and within city discrimination of common urban land-use vegetation (LUV) classes. Each individual project targets four (LUV) types, each of which is represented at four sites across the urban area. Four replicate samples are taken at each site. The database will include replicate analytical information from the following urban location types: semi-natural deciduous wooded areas, managed flowerbeds, and man-made disturbed roadside lay-bys.
A number of parameters have been selected as having the potential to allow discrimination of surface layers of urban soils. These parameters have been selected as requiring chemical instrumentation that is readily available in university departments and is accessible to undergraduate and postgraduate students for use in project work. These include; visual inspection using a stereomicroscope, colour determination using spectrophotometer/Munsell colour charts, organic matter content using muffle furnace, biomarkers using GC-MS, and chemical profiling using ATR-FTIR.
The coordinated approach to the sampling and analysis will deliver a robust database of urban soils information from across the UK.
The agriculturally focused soil mapping and archiving programmes of the last 60 years are now finding a new lease of life combating some of today’s most pressing problems.
Advances on a number of fronts – through the merging and testing of the available national databases, and the spatial analysis of their characteristics; the development of soil analysis and protocols and their modification for applicability in court; coupled with various re-sampling initiatives – means that the UK should be an excellent place to test the application of soil to forensic investigations, in both criminal and environmental case work.
by Lorna Dawson, David Miller and Willie Towers – Macaulay Institute, Aberdeen, UK