Technosols in the World Reference Base for Soil Resources – history and definitions

ABSTRACT

The World Reference Base for Soil Resources (WRB) is an international soil classification system for naming soils and creating legends for soil maps. The currently valid version is the update 2015 of its third edition. WRB has two levels: first and second. The first level comprises 32 Reference Soil Groups (RSGs), identified using a Key. At the second level, the soil names are constructed by adding a set of qualifiers to the name of the RSG. In the WRB, diagnostic horizons, properties and materials are defined. Diagnostic materials are materials that significantly influence soil-forming processes. Diagnostic properties and horizons have a combination of attributes that mostly reflect results of soil-forming processes.

The RSG Technosols was introduced in the second edition of the WRB in 2006. In the current version of the WRB, two diagnostic materials are defined for Technosols: artefacts and technic hard material. Artefacts are substances that are created or substantially modified by humans or brought to the surface from a depth, where they were not influenced by surface processes. The technic hard material is a (relatively) continuous consolidated material resulting from an industrial process. The Technosols are at the third place in the Key after Histosols and Anthrosols. A soil is a Technosol if it has technic hard material within 5 cm or a geomembrane or a significant amount of artefacts within 100 cm. If a soil has no technic hard material and no geomembrane but a layer with artefacts that has undergone enough soil formation to develop a diagnostic horizon typical for advanced pedogenesis, the soil is excluded from the Technosols. There are specific qualifiers to further characterise the Technosols. They are also important to characterise soils other than Technosols that have artefacts or technic hard material. Human-transported natural soil material does not qualify as Technosol.

KEY WORDS:

• Artefacts
• parent material
• soil formation
• technic hard material
• technogenic soils

1. The WRB

The World Reference Base for Soil Resources (WRB) is an international soil classification system for naming soils and creating legends for soil maps. The currently valid version is the update 2015 of its third edition (IUSS Working Group WRB 2015). The WRB is edited by a Working Group of the International Union of Soil Sciences (IUSS) and published with the FAO World Soil Resources Reports. Previous editions of the WRB were the second edition (IUSS Working Group WRB 2006 – with an update in 2007) and the first edition (FAO 1998).

Figure 1. Spolic Technosol (Pantoandic, Pantoprotocalcic, Endofluvic, Katogypsic, Hyperartefactic, Pantoimmissic, Mollic, Siltic).

Figure 2. Reductic Garbic Technosol (Calcaric, Epigleyic, Hyperartefactic, Transportic).

Figure 3. Reductic Epispolic Ekranic Technosol (Katoprotocalcic, Katogleyic, Katosiltic, Episkeletic).

WRB has two levels of detail: the first level and the second level. The first level comprises 32 Reference Soil Groups (RSGs), which are identified using a Key. At the second level, the soil names are constructed by adding a set of qualifiers (which are adjectives) to the name of the RSG (which is a noun).

RSGs are groups of soils with similar morphologic, physical, and chemical characteristics. They may have formed by similar formation processes, stem from a certain parent material or represent major soil regions (Schad and Dondeyne 2017).

For the lower level, 184 qualifiers have been defined. Some can be combined with many RSGs, others with only a few or even with just one. The qualifiers available for use with a particular RSG are listed in the Key, along with the RSG. They are divided into principal and supplementary qualifiers. The principal qualifiers are ranked and given in an order of importance. The supplementary qualifiers are not ranked, but used in alphabetical order. Principal qualifiers are significant for a further subdivision of soils of the particular RSG. Supplementary qualifiers inform about the expression of some common soil characteristics.

In the WRB, diagnostic horizons, diagnostic properties and diagnostic materials (together called ‘diagnostics’) are defined. Their features can be observed or measured, either in the field or the laboratory, and require a minimum or maximum expression to qualify as diagnostic. Diagnostic materials are materials that significantly influence soil-forming processes or are indicative of them. Their features may stem from the parent material or may be the result of soil-forming processes. Diagnostic properties and horizons are characterised by a combination of attributes that reflect widespread, common results of the processes of soil formation. In addition, the diagnostic properties may indicate specific conditions of soil formation. Diagnostic horizons require a certain thickness, thus forming a recognisable layer in the soil. Many definitions in the Key and many definitions of the qualifiers refer to the presence or absence of diagnostic materials, diagnostic properties and diagnostic horizons in a certain depth. In addition, many definitions refer to individual features such as the base saturation or the clay content.

Naming a soil consists of three steps. Step 1 is detecting diagnostic horizons, properties and materials. Step 2 is allocating the soil to a Reference Soil Group (RSG) using the Key. Step 3 is allocating the qualifiers. The principal qualifiers are added before the name of the RSG without brackets and without commas. The sequence is from right to left, i.e., the uppermost qualifier in the list is placed closest to the name of the RSG. The supplementary qualifiers are added in brackets after the name of the RSG and are separated from each other by commas. The sequence is from left to right, i.e., the first qualifier according to the alphabet is placed closest to the name of the RSG. Qualifiers conveying redundant information are not added. For example, Eutric is not added if the Calcaric qualifier applies.

Qualifiers may be combined with specifiers (e.g., Epi-, Proto-) to form subqualifiers (e.g., Epiarenic, Protocalcic). Some subqualifiers can be constructed by the user according to certain rules. Other subqualifiers have a fixed definition given in the WRB document. Depending on the specifier, the subqualifier fulfils all the criteria of the respective qualifier, or it deviates in a defined way from its set of criteria. If a subqualifier applies that fulfils all the criteria of the qualifier, the subqualifier can – but does not have to – be used instead of its qualifier (optional subqualifiers). If a subqualifier applies that fulfils all the criteria of the qualifier except thickness and/or depth criteria, the subqualifier can – but does not have to – be used, but not the qualifier (additional subqualifiers). If a subqualifier applies that deviates in a defined way from the set of criteria of the qualifier, the subqualifier must be used instead of the qualifier that is listed as available for the respective RSG (mandatory subqualifiers). The alphabetical sequence of the supplementary qualifiers is according to the qualifier, not the subqualifier. The use of specifiers does not change the position of the qualifier in the soil name with the exception of the specifiers Bathy- (very deep), Thapto- (buried), and Proto- (weaker expressed): If they are used with a principal qualifier, the constructed subqualifier must shift to the supplementary qualifiers, with Bathy- and Thapto- even at the end of the list of the supplementary qualifiers.

Qualifiers that have depth requirements can be combined by the user with the specifiers Epi-, Endo-, Amphi-, Ano-, Kato-, Panto- and Bathy- to create subqualifiers (e.g., Epicalcic, Endocalcic) further expressing the depth of occurrence. If a diagnostic horizon or a layer with a diagnostic property belongs to a buried soil (see below) that does not meet the requirements of the related RSG, the Thapto- specifier can be used. For soils with technic hard material, a geomembrane, a continuous layer of artefacts, continuous rock or a cemented or indurated layer, subqualifiers with the Supra- specifier can be constructed to describe the soil material above, if the thickness or depth requirements of a qualifier or of its respective diagnostics are not fulfilled, but all other criteria are fulfilled throughout in the soil material above.

Where a soil is buried, the following rules apply:

1. The overlying material and the buried soil are classified as one soil if both together qualify as a Histosol, Anthrosol, Technosol, Cryosol, Leptosol, Vertisol, Gleysol, Andosol, Planosol, Stagnosol, Arenosol, Fluvisol or Regosol.

2. Otherwise, the overlying material is classified with preference if it is ≥ 50 cm thick or if the overlying material, if it stood alone, satisfies the requirements of a Folic Regosol or of a RSG other than a Regosol.

3. In all other cases, the buried soil is classified with preference.

4. If the overlying soil is classified with preference, the name of the buried soil is placed after the name of the overlying soil adding the word ‘over’ in between, e.g., Skeletic Umbrisol (Siltic) over Albic Podzol (Arenic). Alternatively, instead of the buried soil, a buried diagnostic horizon or a buried layer with a diagnostic property can be added with the Thapto- subqualifier to the name of the overlying soil (see subqualifiers, above).

5. If the buried soil is classified with preference, the overlying material is indicated with the Novic qualifier, and if applicable, with the qualifiers Aeolic, Akrofluvic, Colluvic or Transportic.

2. Technosols in the WRB 2015

In the following, diagnostics will be written in italics.

For the classification of Technosols, WRB 2015 provides two diagnostic materials, the artefacts and the technic hard material (IUSS Working Group WRB 2015).

Artefacts :

Diagnostic criteria:

Artefacts are solid or liquid substances that are:

1. one or both of the following:

   1. created or substantially modified by humans as part of an industrial or artisanal manufacturing process; or

   2. brought to the surface by human activity from a depth, where they were not influenced by surface processes, and deposited in an environment, where they do not commonly occur, with properties substantially different from the environment where they are placed; and

2. have substantially the same chemical and mineralogical properties as when first manufactured, modified or excavated.

Examples of artefacts are bricks, pottery, glass, crushed or dressed stone, wooden boards, industrial waste, garbage, processed oil products, bitumen, mine spoil and crude oil. Technic hard material and geomembranes, intact, fractured or composed, also fulfil the diagnostic criteria of artefacts. Remark: WRB follows the British spelling. In the US spelling, it would be artifacts.

Technic hard material :

Diagnostic criteria:

Technic hard material:

1. is consolidated material resulting from an industrial process; and

2. has properties substantially different from those of natural materials; and

3. is continuous or has free space covering < 5% of its horizontal extension.

Examples of technic hard material are asphalt, concrete or a continuous layer of worked stones.

Related to Technosols is another diagnostic material:

Soil organic carbon :

Diagnostic criteria:

Soil organic carbon is organic carbon that does not meet the diagnostic criteria of artefacts.

With that, coal, lignite or oil as well as mine spoil and organic waste are excluded. Soil organic carbon is restricted to organic carbon accumulated through soil-forming processes without a previous manufacturing process and without a further diagenesis.

Technosols key out at the third place in the Key, after Histosols and Anthrosols. Histosols are soils having ≥ 20% soil organic carbon in the fine earth fraction over a specified depth. They may contain artefacts. Anthrosols are the result of long-term (agricultural) use and measures to improve soil fertility. These measures result in very specific diagnostic surface horizons. If these are ≥ 50 cm thick, the soils are Anthrosols. They may contain artefacts.

Three subtypes of Technosols are recognised: with artefacts, with a geomembrane and with technic hard material. Combinations are also possible. The criteria in the Key are (IUSS Working Group WRB 2015):

1. with all of the following:

   1. having ≥ 20% (by volume, weighted average) artefacts in the upper 100 cm from the soil surface or to continuous rock or technic hard material or a cemented or indurated layer; and

   2. not having a layer containing artefacts that qualifies as an argic, chernic, duric, ferralic, ferric, fragic, hydragric, natric, nitic, petrocalcic, petroduric, petrogypsic, petroplinthic, pisoplinthic, plinthic, spodic or vertic horizon starting ≤ 100 cm from the soil surface, unless buried; and

   3. not having continuous rock or a cemented or indurated layer starting ≤ 10 cm from the soil surface; or

2. having a continuous, very slowly permeable to impermeable, constructed geomembrane of any thickness starting ≤ 100 cm from the soil surface; or

3. having technic hard material starting ≤ 5 cm from the soil surface.

To criterion 1: These soils have a significant amount of artefacts. The layers, where these artefacts are found, have, after the deposition of the artefacts, not undergone an advanced soil formation and therefore do not qualify as one the diagnostic horizons listed under 1.b. In addition, a minimum thickness of fine earth of 10 cm is required. Depending on the type of artefacts, three qualifiers are provided. The Urbic qualifier stands for rubble and refuse of human settlements, the Spolic qualifier for industrial waste (mine spoil, dredgings, slag, ash, rubble, etc.) and the Garbic qualifier for organic waste. Required for every one of them is a layer ≥ 20 cm thick, with ≥ 20% artefacts and where ≥ 35% of the artefacts meet the above-mentioned characteristics. This includes the possibility that all three qualifiers apply to the same soil, up to two of them referring to the same layer.

If a soil is not a Technosol, but contains a certain amount of artefacts, the Technic qualifier is provided. A soil with the Technic qualifier has ≥ 10% (by volume, weighted average) artefacts in the upper 100 cm from the soil surface or to continuous rock or a cemented or indurated layer, whichever is shallower; or it has a layer ≥ 10 cm thick, and starting ≤ 90 cm from the soil surface, with ≥ 50% (by volume, weighted average) of artefacts. The Hypertechnic subqualifier requires ≥ 20% (by volume, weighted average) artefacts in the upper 100 cm from the soil surface or to continuous rock or a cemented or indurated layer, whichever is shallower. The Prototechnic subqualifier has ≥ 5% (by volume, weighted average) artefacts in the upper 100 cm from the soil surface or to continuous rock or a cemented or indurated layer, whichever is shallower; or has a layer ≥ 10 cm thick, and starting ≤ 90 cm from the soil surface, with ≥ 25% (by volume, weighted average) artefacts.

To criterion 2: These are the soils with a geomembrane within 100 cm from the soil surface, which completely separates the soil material into two soils isolated from each other. For these soils, the Linic qualifier is provided.

To criterion 3: These soils have technic hard material like asphalt or concrete within ≤ 5 cm from the soil surface (often exactly at the soil surface). For these soils, the Ekranic qualifier is provided.

If a soil has technic hard material that starts > 5 cm and ≤ 10 cm from the soil surface, the Technolithic subqualifier applies. If the technic hard material starts > 10 and ≤ 100 cm from the soil surface, the Technoleptic subqualifier applies. It can be further specified as Epitechnoleptic (technic hard material starting > 10 cm and ≤ 50 cm) or Endotechnoleptic (technic hard material starting > 50 cm and ≤ 100 cm).

The fourth RSG in the Key, after the Technosols, are the Cryosols, followed by the Leptosols, so the sequence of the first five soils in the Key is Histosols – Anthrosols – Technosols – Cryosols – Leptosols. Histosols may have technic hard material starting ≥ 10 cm, and Cryosols may also have technic hard material, both with the Technoleptic subqualifier. However, most soils with technic hard material starting > 5 cm and ≤ 25 cm will be Leptosols, either with the Technolithic or with the Technoleptic subqualifier.

Besides Ekranic, Linic, Urbic, Spolic and Garbic, the following principal qualifiers are listed for the Technosols: Cryic, Isolatic, Leptic, Subaquatic, Tidalic, Reductic, Hyperskeletic (IUSS Working Group WRB 2015). For its importance, the definition of the Isolatic qualifier is given here:

Isolatic: having, above technic hard material, above a geomembrane or above a continuous layer of artefacts starting ≤ 100 cm from the soil surface, soil material containing fine earth without any contact to other soil material containing fine earth (e.g., soils on roofs or in pots).

Some supplementary qualifiers important for Technosols are: Archaic, Carbonic, Hyperartefactic, Immissic, Lignic, Technoskeletic (subqualifier of the Skeletic qualifier), Toxic, Transportic (IUSS Working Group WRB 2015). For the Toxic and the Transportic qualifiers, the full definitions are given here:

Toxic: having in some layer within ≤ 50 cm of the soil surface, toxic concentrations of organic or inorganic substances other than ions of Al, Fe, Na, Ca and Mg, or having radioactivity dangerous to humans. Remark: WRB does not provide threshold values, because this is a legal issue, not a soil classification issue.

Transportic: having at the soil surface a layer ≥ 20 cm thick, or with a thickness of ≥ 50% of the entire soil if continuous rock, technic hard material or a cemented or indurated layer is starting ≤ 40 cm from the soil surface, with soil material that does not meet the criteria of artefacts; and that has been moved from a source area outside the immediate vicinity of the soil by intentional human activity, usually with the aid of machinery, and without substantial reworking or displacement by natural forces.

3. The history of Technosols in WRB

In the first edition of the WRB (FAO 1998) the technogenic soils were allocated to the Regosols. The RSG of Technosols was introduced in the second edition of the WRB in 2006 (IUSS Working Group WRB 2006). Valuable contributions to the definition of the Technosols were provided by the IUSS Working Group ‘Soils of Urban, Industrial, Traffic, Mining and Military Areas’ (SUITMA), which was founded in 1998 (see the history of SUITMA in Burghardt et al. (2017)). Lehmann (2005) summarised suggestions leading to the introduction of the Technosols. The history of the introduction of the Technosols was reflected by Rossiter (2007).

The discussions before the introduction of the Technosols were focused on three questions:

1. Do we need Technosols (or can these soils be well allocated within the existing RSGs, just with the introduction of some new qualifiers)?

2. If we introduce Technosols, should they include soils developed on human-transported natural soil material (or should they be restricted to soils from human-made material)?

3. If the human-made material has undergone soil formation and common diagnostic horizons (like mollic, duric, argic, cambic) or common diagnostic properties (like gleyic, stagnic, vitric, andic) have developed, is it then still a Technosol (or should it belong to other RSGs like Phaeozems, Durisols, Luvisols, Cambisols, Gleysols, Stagnosols, Andosols etc.)?

The following decisions were made:

1. Yes. Their properties are so specific and different from those of all other RSGs that we need the Technosols.

2. No. We introduce the Transportic qualifier and allocate these soils to other RSGs according to other characteristics.

3. Yes and no. Some results of advanced soil formation should exclude a soil from the Technosols but some results of soil formation should be allowed in Technosols. The differentiation between the first and the latter was handled in a different way in the second (2006/07) and the third (2014/15) edition of the WRB.

In 2006, two new diagnostic materials were introduced to characterise human-made materials: artefacts and technic hard rock.

In 2014, only little changes were made to the definition of the artefacts (see above). In point 1.b., ‘deposited in an environment, where they do not commonly occur’ was added. In point 2., ‘properties’ were changed into ‘chemical and mineralogical properties’.

In 2014, the technic hard rock was renamed technic hard material (see above), because it is substantially different from natural rock. To the two points of the definition, a third was added: ‘is continuous or has free space covering < 5% of its horizontal extension’. For the Technosols, this was not a change, because in 2006 this criterion was part of the definition of the Technosols in the Key. But shifting this criterion to the definition of the technic hard material allowed using the technic hard material for soils other than the Technosols. Many definitions, especially of qualifiers, previously referred to a certain ‘depth from the (mineral) soil surface or to continuous rock, whichever is shallower’. Now, they refer to a certain ‘depth from the (mineral) soil surface or to continuous rock or technic hard material, whichever is shallower’. Very important was the addition of the technic hard material to the definition of the Leptosols. Criterion 1.a. of the Leptosols reads now ‘having continuous rock or technic hard material starting ≤ 25 cm from the soil surface’. This allows that soils with technic hard material starting > 5 cm from the soil surface and therefore (unless having a geomembrane or enough artefacts) failing the definition of the Technosols are now allocated within the Leptosols. They have the Technolithic or the Technoleptic subqualifier.

Qualifiers indicating an advanced soil formation were not included in the list of qualifiers of the Technosols in 2006. But the definition of the Technosols in the Key did not exclude the diagnostics resulting from an advanced soil formation. This was an inconsistency, which was corrected in 2014. In the WRB 2014, only in those soils that are Technosols because of a geomembrane or of technic hard material, every diagnostic may be present. But soils that have enough artefacts to qualify as Technosols are not Technosols, if layers with artefacts have developed into one of the following diagnostic horizons: argic, chernic, duric, ferralic, ferric, fragic, hydragric, natric, nitic, petrocalcic, petroduric, petrogypsic, petroplinthic, pisoplinthic, plinthic, spodic or vertic. On the other hand, none of the diagnostic properties is excluded. Especially important in Technosols may be the gleyic, stagnic, vitric and andic properties. And if layers with artefacts developed into one of the following diagnostic horizons, the soils are also not excluded from the Technosols:

1. the organic horizons folic and histic;

2. the mineral surface horizons mollic and umbric;

3. the anthropogenic horizons anthraquic, hortic, irragric, plaggic, pretic, terric (Note: If these horizons are ≥ 50 cm thick, the soil keys out as Anthrosol, and the artefacts are indicated with the Technic qualifier.);

4. the horizons specific for Andosols: fulvic and melanic;

5. horizons of relatively rapid formation: calcic, cambic, cryic, gypsic, protovertic, salic, sombric, thionic.

Many new qualifiers have been introduced in 2014. Relevant for soils with technic hard material or a geomembrane or a continuous layer of artefacts is, e.g., the Isolatic qualifier that applies to soils on buildings or roofs. If these soils are deposited artificially, in addition the Transportic qualifier is needed.

In 2014, the concept of specifiers and subqualifiers was introduced. For soils with technic hard material, the qualifiers Technolithic and Technoleptic are important. Also relevant is the possibility to construct subqualifiers with the Supra- specifier to characterise thin soil layers established on technic hard material or on a geomembrane or on a continuous layer of artefacts.

4. The reception of the Technosols RSG by the scientific community

The introduction of the Technosols was well received by the scientific community (Rossiter 2007). Case studies of technogenic soils now include a classification according to WRB (e.g., Charzynski et al. 2013a). Soon, suggestions for improvements were published. Charzynski et al. (2013b) summarised the experiences gathered in Poland. Many of them were considered in the third edition of the WRB, maybe with other wordings or with different combinations of properties – but considered.

In the 12^th edition of the Keys to Soil Taxonomy (Soil Survey Staff 2014), ‘characteristics diagnostic for human-altered and human-transported soils’ were defined. Furthermore, to recognise human-altered and human-transported materials, one of seven specific subgroups is now available for any existing great group, and a new family class was introduced.

Of course, the discussion goes on after the publication of the third edition of WRB. A milestone is the book ‘Soils within cities’ (Levin et al. 2017). It provides a chapter on classification of urban soils in the WRB, the Soil Taxonomy, the Russian and the German systems (Charzynski et al. 2017).

5. Conclusions

The introduction of the Technosols as a Reference Soil Group in the WRB in 2006 was an important step forward in soil classification. After the revision in 2014/15, it seems that the Update 2015 of the third edition provides a satisfactory scheme for classifying technogenic soils giving sufficient information about soil characteristics, genesis and functions. It also seems that the current version of the WRB caused a boost in soil classification work. An increasing number of soil scientists dedicates itself to soil classification. This helps understand soils. And it will lead to numerous suggestions for further improving soil classification systems.

6. Example soils

In the following, three example soils are presented. The first two are Technosols because of having many artefacts. The first soil has artefacts from industrial waste (Figure 1) and the second from household waste (Figure 2). The deposition of the artefacts has taken place only some decades ago but many soil-forming processes are already going on leading to the presence of some diagnostic properties or even diagnostic horizons. The third soil is a Technosol because of having technic hard material (Figure 3). In addition, it has a layer of artefacts that, if alone, would not have been sufficient for a Technosol but has to be recognised with a qualifier. These three soils should give an overview of the most important subtypes of the Technosols RSG.

Example 1

Location: Halle-Trotha, Germany;

Authors of the profile: Reinhold Jahn and Klaus Kaiser, University of Halle-Wittenberg;

Photo: Peter Schad, 2016;

Further reading: Lehmann and Schad (2007);

Parent material: lignite ash from a power plant, deposited in an artificial lake, later dried out;

Horizonation (according to FAO 2006): see photo;

Diagnostic materials:

artefacts: throughout (mined lignite and its ash are artefacts; some are weathered, but there are still enough for a Technosol);

fluvic material: from 70 cm downwards (the sedimentation of the artefacts in the lake forms stratification that is still visible from 70 cm downwards);

Diagnostic properties: andic properties: throughout (the ash contains glasses, the weathering of which causes andic properties);

protocalcic properties: throughout (the ash contains carbonates, which are dissolved, and secondary carbonates are formed);

Diagnostic horizons:

mollic horizon: 0–20 cm (after drying out, pioneer species have been planted; the accumulation of organic matter leads to the formation of a mollic horizon);

gypsic horizon: 20–120 cm (the lignite contains calcium and sulfur that forms secondary gypsum);

Classification: Spolic Technosol (Pantoandic, Pantoprotocalcic, Endofluvic, Katogypsic, Hyperartefactic, Pantoimmissic, Mollic, Siltic);

Explanation of the qualifiers:

Spolic: the artefacts consist of ash from mined lignite;

Pantoandic: andic properties, throughout;

Pantoprotocalcic: protocalcic properties, throughout;

Endofluvic: fluvic properties, starting at 70 cm;

Katogypsic: gypsic horizon, 20–120 cm;

Hyperartefactic: ≥ 50% (by volume, weighted average) artefacts within 100 cm of the soil surface;

Pantoimmissic: a layer, starting at the soil surface, with ≥ 20% (by mass) recently sedimented dust, soot or ash that meets the criteria of artefacts, throughout;

Mollic: mollic horizon;

Siltic: silt or silt loam in most parts of the soil.

Example 2

Location: Stuttgart, Germany;

Authors of the profile: Andreas Lehmann and Karl Stahr, University of Hohenheim;

Photo: Peter Schad, 2007, also published in Zech et al. (2014);

Further reading: Lehmann and Schad (2007);

Parent material: artificially deposited natural soil from loess over household and industrial waste;

Horizonation (according to FAO 2006): see photo;

Diagnostic materials:

artefacts: from 25 cm downwards (household and industrial waste);

calcaric material: throughout (both the natural soil from loess and the waste contain carbonates);

Diagnostic properties:

reducing conditions: starting at some cm depth (the decomposition of large amounts of organic matter, mostly in plastic bags and buried by transported soil material, leads to the formation of methane; the methane moves upwards and causes reducing conditions even in the topsoil);

gleyic properties: in the artificially deposited topsoil, Fe is reduced and re-oxidised at the walls of the coarse pores;

Diagnostic horizons: none;

Classification: Reductic Garbic Technosol (Calcaric, Epigleyic, Hyperartefactic, Transportic);

Explanation of the qualifiers:

Garbic: the artefacts contain ≥ 35% organic waste;

Reductic: reducing conditions caused by something other than water, starting some cm from the soil surface;

Calcaric: carbonates in the waste and in the artificially deposited topsoil;

Epigleyic: gleyic properties and reducing conditions in the artificially deposited topsoil;

Hyperartefactic: ≥ 50% (by volume, weighted average) artefacts within 100 cm of the soil surface;

Transportic: artificially deposited natural soil from loess, 0–25 cm.

Example 3

Location: Essen, Germany;

Author of the profile: Wolfgang Burghardt, University of Duisburg-Essen;

Photo: Peter Schad, 2007, also published in Zech et al. (2014);

Further reading: Lehmann and Schad (2007);

Parent material: tar over artificially deposited natural gravel over slag over loess;

Horizonation (according to FAO 2006): see photo;

Diagnostic materials:

technic hard material: 0–8 cm (tar);

artefacts: 32–40 cm (slag; close to 100% of the soil volume);

Diagnostic properties:

reducing conditions: from 40 cm downwards (a leaking gas pipeline caused strongly reducing conditions; but even in the absence of methane, the sealing lowers the gas diffusion between atmosphere and soil and may cause low redox potentials);

gleyic properties: from 40 cm downwards (Fe is reduced in most parts of the soil matrix; only at some coarse pores enough oxygen from the atmosphere moves in and re-oxidises some Fe);

protocalcic properties: from 40 cm downwards (the gravel and the slag contain carbonates, which are dissolved; the ions move downwards, and secondary carbonates precipitate);

Diagnostic horizons: none;

Classification: Reductic Epispolic Ekranic Technosol (Katoprotocalcic, Katogleyic, Katosiltic, Episkeletic);

Explanation of the qualifiers:

Ekranic: technic hard material at the soil surface;

Epispolic: 32–40 cm: 100% artefacts consisting of slag; calculating the weighted average for a layer of 20 cm thickness results in ≥ 20% (by volume) of artefacts;

Reductic: reducing conditions caused by something other than water, from 40 cm downwards;

Katoprotocalcic: protocalcic properties, from 40 cm downwards;

Katogleyic: gleyic properties and reducing conditions, from 40 cm downwards;

Katosiltic: silt or silt loam, from 40 cm downwards;

Episkeletic: ≥ 40% (by volume) coarse fragments averaged over the first 50 cm and < 40% averaged over the first 100 cm.

Acknowledgments

Reinhold Jahn, University of Halle-Wittenberg, Wolfgang Burghardt, University of Duisburg-Essen, and Andreas Lehmann, University of Hohenheim, for allowing to use their profiles as example soils.