Soil is often considered a purely natural resource, slowly forming over millennia through processes like weathering and decomposition. Yet, a vast portion of the planet’s terrestrial surface has been fundamentally altered by human activity, creating a distinct category of material known as anthropogenic soil. These human-altered soils are not merely disturbed natural ground; their properties, development, and composition are dominated by the historical and contemporary actions of people. Understanding the definition and impact of these human-made landscapes is becoming important as scientists recognize humanity’s lasting influence on the Earth’s surface. This article will define these soils and explain their significance to environmental function and the historical record.
Defining Anthropogenic Soil
Anthropogenic soil, or anthrosol, is any soil whose formation and characteristics have been fundamentally shaped or created by human action. This soil type contrasts with natural pedogenesis, which describes the slow, complex process of soil formation governed by five natural factors: parent material, climate, organisms, topography, and time. While natural soil formation can take thousands of years, human activities can create or drastically alter soil in decades or even less, often resetting the “pedogenic clock” entirely.
Human alteration of soil generally occurs through three distinct mechanisms that modify the natural soil-forming factors. Physical manipulation involves the mixing, moving, or burying of soil horizons through deep plowing, excavation, or construction. Chemical alteration changes the soil’s chemistry through the addition of substances, such as long-term fertilization, liming to adjust pH, or contamination from industrial pollutants. The third mechanism involves the introduction of foreign materials, where human-made artifacts, waste, or imported fill become incorporated into the soil matrix, effectively creating a new parent material. These foreign inclusions can include construction debris, municipal waste, or ancient settlement refuse.
Major Categories of Human-Altered Soils
Soil scientists classify anthropogenic soils based on the dominant human input that defines them. One prominent category is “Urbic” soils, which are characteristic of city environments and defined by the incorporation of human-made materials like concrete, brick, and glass fragments. These soils often suffer from significant compaction, which reduces water infiltration, and they frequently exhibit complex, highly disturbed layering due to construction and demolition activities.
Another major classification is the “Technosol,” reserved for soils formed predominantly from entirely new, human-deposited parent materials. Technosols can be found in areas of intensive waste disposal, such as landfills, or in landscapes heavily impacted by mining and industrial slag heaps. These are often the most heavily altered soils, exhibiting unique chemical properties, including high concentrations of contaminants or unusual mineral compositions not found in nature. Historical intensive farming also created distinct soil types, such as Plaggen soils, found across parts of Europe. These soils developed over centuries of continuously adding sod, manure, and organic waste to fields, resulting in a thick, dark, nutrient-rich top layer that fundamentally changed the soil profile depth and composition.
Environmental and Historical Importance
Anthropogenic soils hold a dual significance, serving as both functional components of the modern environment and records of human history. Environmentally, these modified landscapes play a growing role in global biogeochemical cycles. For instance, urban soils, despite their disturbed nature, impact the water cycle by influencing storm runoff and filtering pollutants, which affects the quality of groundwater and surface water.
Climate Dynamics and Carbon Storage
Human-altered soils directly influence climate change dynamics, particularly through their capacity for carbon storage. While practices like intensive tillage can deplete soil organic carbon, long-term historical additions of organic matter, such as in ancient agricultural fields or historic settlement layers, can create stable carbon reservoirs. Understanding the specific chemical and physical properties of these soils is necessary for accurately modeling global carbon budgets and planning effective climate mitigation strategies.
Archaeological Resources
Historically, anthropogenic soils are invaluable archaeological resources, acting as an archive of past human settlement and land use. The layers of these soils contain chemical signatures from ancient fires, refuse, and sustained cultivation, providing scientists with a chronological record of human-environment interactions over millennia. By studying the artifacts and chemical composition within these layers, researchers can reconstruct past settlement patterns, dietary habits, and the long-term environmental consequences of early human societies.
Managing and Utilizing These Landscapes
Dealing with widespread anthropogenic soils presents challenges that require specialized management techniques. A primary concern is contamination, particularly in urban and industrial Technosols, which may contain elevated levels of heavy metals like lead or various persistent organic pollutants. These contaminants pose risks to human health and local ecosystems, necessitating remediation efforts before the land can be safely used for housing or food production.
Despite these difficulties, anthropogenic landscapes offer opportunities for sustainable development. Many altered sites are being reclaimed and repurposed for urban green spaces, providing communities with parks and local recreational areas. Furthermore, with appropriate remediation and specific management practices, such as the importation of clean topsoil or the use of phytoremediation techniques, these soils can be used for urban agriculture. These efforts allow unproductive or contaminated land to be transformed into safe, productive areas that contribute to local food security and biodiversity within the urban matrix. The future of land use planning increasingly relies on understanding how to manage and utilize these human-made surfaces effectively for both safety and sustainability.