Anthroposols [AN]
Concept
These soils result from human activities which have caused a profound modification, mixing, truncation or burial of the original soil horizons, or the creation of new soil parent materials. Note that the concept of soil used in this classification of Australian soils (see Background) also applies to the Anthroposols, and hence sealed and semi-sealed surfaces such as streets, roads etc. are regarded as 'non-soil'. Also, in depositional situations, the anthropic material must be 0.3 m or more thick where it overlies buried soils. Anthropic materials < 0.3 m thick will identify an anthropic phase of the soil below.
To qualify as soil an Anthroposol needs to possess some pedogenic features, as noted below. Key criteria in the identification of an Anthroposol are the presence of artefacts in the profile or knowledge that the soils or their parent materials have been made or altered by human action.
Anthroposols differ from other soils in that we normally know their origin with a degree of certainty, and hence we can invoke a knowledge of process rather than defined pedogenic attributes to initially classify the soil. We can then subdivide at the higher levels on the basis of type of process and nature of the product which forms the parent material of the new soil. At lower levels in the classification, conventional soil properties could be used when available, although obviously these will be limited in very young soils.
Definition
Soils resulting from human activities which have led to a profound modification, truncation or burial of the original soil horizons, or the creation of new soil parent materials by a variety of mechanical means. Where burial of a pre-existing soil is involved, the anthropic materials must be 0.3 m or more thick. Pedogenic features may be the result of in situ processes (usually the minimal development of an A1 horizon, sometimes the stronger development of typical soil horizons) or the result of pedogenic processes prior to modification or placement (ie. the presence of identifiable pre-existing soil material).
Comment
It is difficult to quantify ‘profound modification, mixing and truncation’ but this would normally exclude the usual agricultural operations (including land planing) which may change a soil from say a Chromosol to a Dermosol by mixing or removal of the upper horizons. Similarly, soils that are artificially drained or flooded are not Anthroposols but may classify as different soil orders following a permanent change in water status (see also Comment in Hydrosols).
There will also be instances where the question is how much truncation results in ‘profound modification’ or merely a truncated phase. It is difficult to give guidelines that will cover all circumstances, and inevitably judgement is required. Similarly, there will be instances where land reclamation and restoration in the past have been so successful that little evidence of a prior disturbance remains, and soil development gives no clue to past history. A good example of this is Podosol development on restored and revegetated coastal dunes following sand mining.
Suborders
- Soils that have been formed by applications of human-deposited materials such as mill-mud, etc. or the accumulation of shells and organic materials to form middens. (Minimum depth of burial is 0.3 m). Cumulic [HR]
- Soils that have had additions of organic residues such as organic wastes, composts, mulches, etc. that have been incorporated into the soil and obliterated pre-existing pedological features. Hortic [HS]
- Mineral soil or regolithic materials that are underlain by land fill of manufactured origin and which is predominantly of an organic nature. These materials may be of domestic or industrial origin and usually occur as artificially elevated landforms. The intent is to designate refuse from human activity high enough in organic matter to generate significant quantities of methane when placed under anaerobic conditions. Garbic [HT]
- Mineral soil or regolithic materials that are underlain by land fill of predominantly a mineral nature. The fill may be wholly of manufactured origin (glass, plastics, concrete, etc.) or contain a mixture of manufactured materials and materials of pedogenic origin. The fill usually occurs as an artificially elevated landform. Urbic [HU]
- Soils that have formed or are forming on mineral materials that have been dredged through human action from the sea or other waterways, or deposited as a slurry resulting from mining operations; eg, tailings ponds, salt ponds, coal washing residues etc. The dredged materials commonly occur as a lithologically distinctive unit overlying (buried) flood plain surfaces. Such deposits frequently occur in coastal areas, common examples being airports, golf courses and other urban developments. Dredgic [HV]
- Soils that have formed or are forming on mineral materials that have been moved by earthmoving equipment in mining, highway construction, dam building etc. The materials contain too few manufactured artefacts to qualify as urbic soils. Landscapes are human-formed, and hence may present an 'unnatural' geomorphic expression. Spolic materials are increasingly being capped by pre-existing topsoil. Spolic [HW]
- Soils that have formed or are forming on land surfaces that have been created by humans by cutting away any previously existing soil by mechanical equipment such as bulldozers and graders. Common occurrences are found along highways where they are usually associated with fill areas with spolic materials. In some instances truncated remnants of the lower horizons of pre-existing soils may occur. Scalpic soil areas typically have peculiar geomorphic expressions, often with smooth and steep slopes. Scalpic [HX]
Comment
In the Garbic, Urbic and some Spolic soils it is common practice to cover the anthropic materials with a layer of soil materials as an aid to reclamation. This soil material is regarded as part of the suborder and can be used as a basis for lower category classification. In other situations sewage sludge is being used to rehabilitate mine spoil.
The Scalpic soils may also have material added to their new surface. If this is less than 0.3 m there would be, for example, a spolic phase of the Scalpic suborder; if 0.3 m or more thick the soil would classify as a Spolic suborder.
There will obviously be intergrade situations between some of the suborders. For example, it may sometimes be difficult to decide between Garbic and Urbic, Cumulic and Hortic. In these and similar situations judgement and/or knowledge of the process will be required. With the increasing emphasis on recycling, much of the garbic materials will be composted so the garbic group could become redundant.
Another likely difficult situation results when human-induced or human-accelerated erosion has removed upper soil horizons. On present thinking it would seem more appropriate for such soils to be regarded as an eroded phase of say a Sodosol, provided the original soil can be identified.
The question of soils contaminated by toxic wastes is also unresolved. They could be included in the Garbic suborder, but if the wastes are toxic to plant and animal life their host materials cannot strictly be regarded as soil. In some situations the problem could be overcome by referring to the site as a contaminated phase of the pre-existing soil.
Lower Categories
It is hoped that the seven suborders will provide a conceptual framework for the classification of most anthropic soils based on human-induced processes which provide particular kinds of soil parent materials. The suborders are a simplified relevant summary of an almost infinitely large range of anthropic processes and products. The need for subdivision below the suborder level is likely to be more desirable in some classes than others, but a major problem in creating lower category classes is the lack of data on the morphology and laboratory properties of anthropic soils. Most information seems to be available for the spolic soils created by mining operations. Here though it may be more appropriate to create a technical classification based on reclamation needs.
For some of the suborders, differentiae for lower categories could be based on appropriate traditional attributes used in classifying 'natural' soils, both morphologic and laboratory-determined. At present this is impractical due to the lack of an adequate representative profile data base. A related approach is to use at the great group level classes based on the other orders eg. Chromosolic, Sodosolic etc. as has been done for the Hydrosol great groups. In this approach Rudosolic Spolic Anthroposols would obviously be a very common class. A wide range of options is available for subgroup differentiae, but existing family criteria will probably be appropriate for most Anthroposols. A preliminary approach to classifying Australian minesoils based on proposed amendments to Soil Taxonomy has been made by Fitzpatrick and Hollingsworth (1994). A number of their proposed subgroups could be used in Spolic Anthroposols, and some examples are given in their paper.
Until more knowledge and experience is available, it is proposed not to formalise the classification of Anthroposols below the suborder level. Acknowledgment is due to Fanning and Fanning (1989) for a number of the concepts and terminology used in this preliminary classification of Anthroposols.