Agriculture Reference
In-Depth Information
that are often not mapped correctly or are not mapped at all. Anthropogenic soils are found on all
continents, but are most likely to be found in areas of long-term human habitation, where population
density is high, and in countries where large mechanical equipment is readily available. For example,
three major land types with anthropogenic soils are high-density residential, transportation corri-
dors, and mining areas. There are estimated to be about 150 Mha of urban land, about 1% of the
worldÔs land surface area (Grubler, 1994). The amount of urban land and urban population is
expected to increase rapidly (National Institute of Urban Affairs, 1994). Countries in Europe and
Asia that have long-term habitation have felt the need to distinguish urban soils from natural soils,
especially those with pollutants, garbage, and artifacts (Burghardt, 1994; Kimble et al., 1999). High-
density residential areas include less than 20% of natural soils (Smith, 1999) and include a high
percentage of impervious materials such as buildings and pavements that cover the soil (Hernandez
and Galbraith, 1997). These residential areas are also the home to several million metric tons of
municipal wastes each year. In addition, there are probably over 30 MKm of roads in the world,
and most of these have a corridor of 15 to 125 m where the soil has been highly altered. This
equates to anywhere from 28.1 to 233.5 Mha of anthropogenic soils in the world (United States
Central Intelligence Agency, 2000). Although the global geographical extent is difÝcult to estimate,
major and minor surface mining of soil, rocks, and minerals is by far the most extensive anthro-
pogenic process.
Anthropogenic processes often have profound and permanent effects on soils. For example,
human activity may lead to destruction or removal of soil horizons; burial of soil with pavements,
other soil, rock, garbage, or debris; contamination of the soil by air- or water-borne pollutants;
removal of the soil; or permanent alteration of the soil hydrology (Galbraith and Bryant, 1999;
Stroganova, 1999). Upland soils that contain garbage and other artifacts at depth are certain to have
been mixed or transported by humans. Human-altered upland soils frequently lack highly developed
genetic soil horizons, as compared to surrounding natural soils, and may be easily distinguished
from natural soils by virtue of their occurrence on anthropogenic landforms. Humans that live
around anthropogenic soils are usually aware of their history, and do not consider them to be natural
soils. Resource managers prefer that anthropogenic soils be classed separately from natural soils
because of the important management and interpretive differences (Craul, 1999). In particular,
Craul cites problems in sustainably vegetating urban soils because of improper respect paid to soil
properties and microclimates by planners. Urban soils are unique, thus the USDA-NRCS has
established an urban soils program (Scheyer, 1999), and urban soils are recognized and classiÝed
in numerous taxonomies around the world (Burghardt, 1994; Kimble et al., 1999).
Soil Taxonomy was designed to be a tool for making and interpreting soil surveys of agricultural
land and other areas where soils formed dominantly from natural soil-forming processes. Distur-
bances in the surface or plow layer were speciÝcally addressed by the system to prevent separation
of agricultural soils from their undisturbed equivalents. There are a few categories in Soil Taxonomy
that distinguish anthropogenic soils (Ahrens and Engel, 1999; Galbraith and Bryant, 1999), and
some mapping of urban landscapes in the United States has begun (Levin, 1999; Hernandez, 1999;
Smith, 1999). However, complete acceptance of these maps into the existing National Cooperative
Soil Survey system of mapping has not been achieved, and challenges to research (Pouyat and
EfÞand, 1999) and mapping of anthropogenic soils remain (Southard, 1999), especially with regard
to soils polluted with heavy metals (Russell-Anelli et al., 1999) and toxic organic compounds.
European countries have longer experience with industrial development and have developed several
categories of toxic or polluted urban soils (Gerasimova, 1999; Sobock, 1999; Tonkonogov and
Lebedeva, 1999).
The need for incorporating anthropogenic processes into soil classiÝcation systems may be
evaluated in terms of the purpose of existing classiÝcation schemes. All soil classiÝcation schemes
facilitate communications by organizing the tremendous number of individual soils (those soils
having similar characteristics that are signiÝcantly different from other soils) into groups that have
more similarity and less differentiation within the group than in comparison with other soils. A
