Soil is a non-renewable, dynamic and living resource, which needs minimal and suitable conditions to carry out its indispensable functions for its conservation, to produce food and for supporting the environment quality (Doran et al., 1999). Soil is not only the support both for agriculture and different ecosystems, but also, all world depends on it. It is characterized by different properties which define its quality and which may vary depending on several factors such as climate, parent material, inhabitanting organisms and microrganisms, human agricultural practices. Soil health can be "measured" through indicators of physical, chemical and biological nature.
The concept of soil quality emerged in the early 1990s, and the first official definition of this term was proposed by the Soil Science Society of America Ad Hoc Committee on Soil Quality (S-581) in 1997 (Karlen et al., 1997).
Soil quality was defined as ‘‘the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation.’’ For the committee proposing this definition, the term soil quality is not synonymous with soil health, and they should not be used interchangeably. Soil quality is related to soil functions, whereas soil health presents the soil as a finite and dynamic living resource (Doran and Zeiss, 2000).
Soil health is defined as ‘‘the continued capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain biological productivity, maintain the quality of air and water environments, and promote plant, animal, and human health’’ (Doran et al., 1996).
These two definitions may appear similar, but soil health concept directly mentions plant health, which is not the case in the definition of soil quality of Karlen et al. (1997). In a simple manner, the Natural Resources Conservation Service of the United States Department of Agriculture proposes on its website (soils.usda.gov/sqi, 2005) the following definition: ‘‘soil quality is how well soil does what we want it to do.’’ Because of the numerous possible uses of soil, the meaning of the term soil quality heavily depends on the ecosystem considered. In agricultural soils, plant and animal productivity and health would be of the greatest importance, whereas it would not be the same in urban soils. Even in a given ecosystem, e.g. cultivated soils, their multifunctionality makes it difficult to define a healthy soil without first defining the targeted goal or aim. Such goals could be plant health, atmospheric balance, avoidance of erosion, etc.
- Karlen, D.L., Mausbach, M.J., Doran, J.W., Cline, R.G., Harris, R.F., Schuman, G.E., 1997. Soil quality: a concept, definition, and framework for evaluation. Soil Science Society of America Journal 61, 4–10.
- Doran, J.W., Sarrantonio, M., Liebig, M.A., 1996. Soil health and sustainability. Advances in Agronomy 56, 1–54.
- Doran, J.W., Zeiss, M.R., 2000. Soil health and sustainability: managing the biotic component of soil quality. Applied Soil Ecology 15, 3–11.
Soil degradation is a serious threat for an increasing number of areas all over the world. It is defined as a process that causes deterioration of soil productivity and low soil utility as a result of natural or anthropogenic factors which namely are displacement of soil material, and internal soil deterioration.
Globally, it has been estimated that nearly 2 billion hectares of land are affected by human-induced soil degradation. The main impact of agriculture on soil degradation is erosion, salinization, compaction, reduction of organic matter, and non-point source pollution. Loss of organic matter and soil biodiversity and consequently reducing soil fertility are often driven by unsustainable agricultural practices such as overgrazing of pasturelands, over intensive annual cropping, deep ploughing on fragile soils, cultivation of erosion-facilitating crops (e.g. maize), continuous use of heavy machinery destroying soil structure through compaction, unsustainable irrigation systems contributing to the salinisation and erosion of cultivated lands. In addition, intensification of agriculture, some of which is linked in the European Union to the implementation of the common agricultural policy, may accelerate loss of soil through erosion. The degree of soil degradation depends on soil's susceptibility to degradative processes, land use, and the duration of degradative land use.
Watch this video about desertification by GoodPlanet Foundation and produced by UNCCD (United Nations Convention to Combat Desertification) anf GEF (Global Environment Facility).
The processes of soil degradation have major implications on:
- Global carbon cycle, mainly due to the decrease in soil organic matter and the release of CO2 to the atmosphere
- Reduction in soil buffering capacity that is the capacity of soil to adsorb contaminants,
- Water and air quality,
- Food production, food and feed safety, and
- Human health.
Soil degradation involves physical loss and the reduction in quality of topsoil associated with nutrient decline and contamination.
In physical loss two main soil degradation processes are: soil erosion by water or wind; In the second category are chemical, physical, and biological degradation. The chemical degradation mainly consists of soil pollution and acidification and its consequences as mobilization of harmful elements/compounds, salinization and/or sodification, unfavourable changes in the nutrient regime, and decrease of natural buffering capacity.
Surface sealing or crusting of top soil, soil compaction, structure destruction, and extreme moisture regime comprise physical deterioration. Biological deterioration includes imbalance of biological activities via loss of soil organic matter and biodiversity. Biodiversity and organic matter can decline due to erosion or pollution, leading to a reduction in soil functions such as control of water and gas flows. Reduced above-ground plant diversity as a result of tillage, overgrazing, pollutants, and pesticides decreases the microbial diversity in the soil ecosystem and disturbs its normal functioning.
In the past, soil protection had been addressed indirectly through measures aimed at the protection of air and water or developed within sectoral policies. Now soil protection refers not simply to the physical soil itself but to the soil as part of a functioning and living ecosystem that provides all the eco-services.
Soil is a non-renweable natural source and it performs manifold functions. In particular the major soil functions are:
- Production of food and other biomass filtering,
- Buffering and transformation capacity between the atmosphere, the ground water and the plant cover.
- Soil and water conservation function protecting people from off-site erosion damage and flooding against the contamination of ground water and the food chain,
- Soils are the main basis of biodiversity.
- Provides a platform for human activity.
- Soil is an element of geogenic and cultural heritage forming an essential part of the landscape,
- Soils are a source of raw materials as well as a source of geogenic energy and water.
An important advance has been the inclusion of plans for a thematic strategy on soil protection in the sixth environment action programme and the adoption of a Commission Communication on soil protection, endorsed by the European Council. European Union analyzed and described the threats being faced by the soils of Europe in document known as “Towards a Thematic Strategy of Soil Protection” or more simply the “Soil Communication”. EU proposed a series of environmental measures, designed to prevent soil degradation, including legislation related to mining, waste, sewage sludge and compost and integrating soil-protection concerns in major EU policies.The actual Thematic Strategy on soil protection was adopted by the EC in September 2006 (EC, COM 2006 231 final). In it, the EC has proposed to the Council and the European Parliament the adoption of a framework directive. The Strategy and the proposal have been sent to the other European Institutions for the further steps in the decision-making process. The adoption of Thematic Strategy by EC has given formal recognition of the severity of the soil and degradation processes in Europe. The main threats addressed in the European Thematic Strategy for Soil Protection, were sealing, compaction, erosion, contamination, loss of organic matter, loss of biodiversity, salinisation, flooding and landslides.
Deterioration of soils in Europe Soil degradation differs markedly across Europe due to the fact that the quality of Europe’s soils is a result of natural factors, (e.g. climate, soil type, vegetation, topography). In Europe, damage to soils from modern human activities is increasing and leads to irreversible losses mainly due to local and wide-spread contamination and soil erosion. Natural processes like emissions from volcanoes, forest fires, chemical composition of the parent material can be also important sources of pollutants to soils. The most common form of soil physical degradation is soil compaction. It was reported that of 32% of soils in Europe are highly vulnerable and 18% moderately affected. According to reports, more than a third of the soils in Europe are highly susceptible to compaction in the subsurface soil. Compared to topsoil, deep compaction of subsoil is persistent and cannot easily be reversed. Approximately the 36% of European subsoils face high or very high susceptibility to compaction. The thematic strategy (EC-COM 2006, EC-SEC 2006), emphasizes that soil degradation processes or threats or a combination of some of the threats will lead to desertification.
Desertification in Europe occurs everywhere, for example central and northern Europe and is not solely linked to poor land management or poverty. In arid arid or semi-arid areas with seasonal and unevenly distributed precipitations, fresh water scarcity and poor irrigation practices are linked to salinization. The most affected zones in dry land areas of Europe by zalinization are located in Hungary, Romania, Spain, Italy, Albania, FYROM and Greece, according to several authors. The Mediterranean area is identified as sensitive to desertification due to a combination of climate conditions, soil and terrain characteristics, agriculture and exploitation of water resources. In European Union most soils are out of equilibrium as regards soil organic matter contents. Almost half of European soils have low organic matter content, principally in southern Europe but also in areas of France, the United Kingdom and Germany. Land use and climate change have resulted in soil organic carbon loss at a rate equivalent to 10 % of the total fossil fuel emissions for Europe as a whole. It is calculated that 0.6% of soil carbon in European terrestrial ecosystems is lost annually. In the Mediterranean region the loss of organic matter during last decades is estimated at around 50% of the original content.
Moreover, decreased organic matter content and soil compaction result in reduced water retention capacity of the soil and therefore the capacity of the soil to store and retain water is decreased, which results in an increased risk to flooding. Northern and Western Europe is highly urbanized and soil sealing in particular at unsustainable rates is significant resulting in the loss or degradation of soil resources. Regarding surface seal formation, it is an important factor of soil structural degradation leading to reduction of infiltration and enhancement of surface runoff. Soil contamination in Westerner European countries still remains a problem despite several initiatives that have been taken the last years to reduce air emissions and to control and manage organic wastes (e.g. the application of sewage sludge and the use of landfill for waste disposal). Soil degradation problems in central and eastern European countries are similar to those in Western countries although soil sealing is less compared to Western Europe. Soil erosion is the most widespread form of soil deterioration which related to agricultural mismanagement and deforestation.
Soil contamination is mainly a result of inefficient technologies and uncontrolled emissions. High content of heavy metals in soils is reported in Central-Eastern Europe. Many of the soil contamination problems derived from past activities and poor management practices leading to reduction of the capacity of soil to remove contaminates from the environment by filtration and adsorption. Furthermore large areas in the Former USSR have experienced salinisation due to unsustainable irrigation schemes and cultivation practices (e.g. drying-up of the Aral Sea). Past agricultural policies favored high productivity via incorrect use of mineral fertilisers, pesticides and heavy machinery results in increased rates of soil loss by erosion, pollution of surface and groundwater and soil fertility problems.
Contamination of soil is by natural and artificial radionuclides is also important. Land contaminated with naturally occurring radioactivity is considered for uranium and other mining tails, phosphogypsum dumps, metal industry, etc. Furthermore, it was shown that due to nuclear weapons tests sites, improper radioactive waste disposal and after the Chernobyl incident that nuclear fallout especially 137Cs, causing widespread contamination that seriously affected some European countries and several other parts of the world., is retained in the soil, causing potential pollution hazards. Soil contamination
Soil pollution as one important parameter to estimate in order to determine soil quality and soil sustainability. Soil contamination can be divided in point source contamination and diffuse contamination. Soil contamination from diffuse and localized sources can result in the damage of several soil functions (mainly buffering, filtering and transforming capacities) and the contamination of surface water and groundwater. Diffuse Sources Diffuse pollution is contamination that comes from many individually minor, dispersed sources. Diffuse soil contamination is in general associated with atmospheric deposition, certain agricultural practices (Soil amendment with sewage sludge, application of manure, mineral fertilizers, pesticides, fumigation) and inadequate waste and wastewater recycling and treatment.
Pollutants can be washed by rainfall both into the soil and from soil into surface and groundwaters. Currently, the most important soil contamination problems from diffuse sources are atmospheric deposition of acidifying and eutrophying compounds or potentially harmful chemicals, deposition of contaminants from flowing water or eroded soil itself, and the direct application of substances such as pesticides, sewage sludge, fertilisers and manure which may contain heavy metals. The diffuse pollution of European soils is not widespread, except for acidification and eutrophication. Pollution is localised mainly urban areas and industrial compounds, Acidification is the most widespread type of soil contamination in western and central Europe where vast areas have been affected, especially in Poland (10 million ha including natural acidification) and Ukraine (about 11 million ha of agricultural land). Atmospheric deposition releases into soils acidifying contaminants (e.g. SO2, NOx), heavy metals (e.g. cadmium, lead arsenic, mercury), and several organic compounds (e.g. dioxins, PCBs, PAHs). Acidification favours the leaching out of nutrients leading to loss of soil fertility and possible eutrophication problems in water and may decrease biological activity. In addition, acidifying components reduce the buffer capacity of the soil and the pH will gradually decrease. Acidification in Mediterranean soils, although not frequent, is caused by land use through the removal of base cations from the soil by harvesting, careless use of nitrogen fertilizers and soil drainage. Major effect of acidification is the mobilization of aluminum from clay minerals which the soil might have accumulated. Heavy metal input in agriculture may be caused by human activities, such as fertilisation and amendment practices, used to increase soil productivity. Heavy metals together with excessive nitrogen inputs are regarded as the main sources of contamination in agricultural soils. Metals like Hg, Cd, As, Pb can contaminate the soil gradually and damage soil and ecosystem functioning. These contaminating elements will become part of the nutrient cycling resulting in biodiversity decline, water pollution and consequently a potential danger for human health.
Threshold values for soils are difficult to evaluate since heavy metals toxicity and metal bioavailability is not only dependent on the total content in soils but also in other environmental factors. At European level only threshold values related to the application of sewage sludge in agricultural soils have been defined (EU Directive 86/278/EC). The determination of natural background values is very difficult since the geochemistry of most of the European ecosystems is greatly influenced by human activities. The excessive application of fertilizers or manures usually exceeds the functional ability of the soil to retain and transform the nutrients and influence the capability of the soil to provide nutrients for plant growth and its buffering and filtering capacity. The saturation of the soil with nitrogen or phosphate, have led to losses of nitrates and saturation of the soil with phosphate, which move into groundwater waterways and coastal systems, causing eutrophication. The main soil functions that degraded due to extensive use of pesticides are the food web support, the retention and transformation of toxicants and nutrients, soil resilience, and the ability of soil to protect surface and ground water. Uncontrolled use of pesticides is linked to alteration of soil properties, the degradation of soil’s toxicant retention and transformation function, the destruction of part of the soil flora and fauna, leaching and drainage of pesticides into the surface and ground water, According to the estimated degree of contamination in central eastern European countries is is light to moderate In Ukraine more than 5 million ha are a 20 % of the investigated agricultural lands are polluted by DDT and its degradation products, about 4 % are polluted by hexachlorine-cyclohexane. In Romania more than 4 million ha are affected as well. New management practices, such as integrated crop management (ICM), have evolved as a response to the need to reduce dependence on pesticides and fertilizer consumption. Localized sources Point source contamination is often linked to no operational industrial plants, power generation, past industrial accidents, uncontrolled industrial municipal and agricultural waste disposals, and mining activities. The major source of contamination in Europe is inadequate waste management which has lead to a large number of contaminated sites. Sites contaminated in these ways can pose serious threats to health and to the local environment as a result of releases of harmful substances to water resources, uptake by plants and direct contact by people. Major pollutants include heavy metals, organic contaminants such as chlorinated hydrocarbons, and mineral oil. Soil contamination from local sources is widespread across Europe. Estimates of the number of contaminated sites in the EU-15 (before the enlargement with the Central and Eastern European Countries) range from 300.000 to 1.500.000. The largest and probably most heavily affected areas are concentrated around the most industrialized regions in northwest Europe, from Nord-Pas de Calais in France to the Rhein-Ruhr region in Germany, across Belgium and the Netherlands and the south of the United Kingdom. There are approximately 3,000 problem areas including former military sites, abandoned industrial facilities and storage sites which may still be releasing pollutants to the environment leading to groundwater contamination and related health problems. The contaminated sites in Ukraine there are about 5 million ha, mostly in human settlements and around the industrial factories and in Lithuania nearly 3 million ha. In the mining industry, which is a major driver of soil degradation in central and eastern European countries, the risk of contamination is associated with sulfur and heavy metal-bearing tailings stored on mining sites, and the use of certain chemical reagents such as cyanide in the refining process. Waste landfilling is an important potentially contaminating activity as well. On average, 57 % of municipal waste generated in the EU is landfilled. Application of farm manures, sewage sludge, and composted green wastes lead to air pollution (odour and ammonia) and to diffuse water (nitrate and phosphate) pollution, Moreover the potential soil contamination is greatly increased in landfills that that do not comply with the minimum requirements set by the landfill directive (Directive 1999/31/EC).
Wastewater reclamation and reuse is increasingly being integrated in the planning and development of water resources in in arid and semi arid regions particularly for irrigation.
For Mediterranean countries disposal of Olive Mill Wastes (OMW) are considered a major environmental problem. OMW contain oil compounds that may result in increased soil hydrophobicity and decrease water retention and infiltration rate. The use of OMW in agriculture may also affect acidity, salinity, N immobilization, microbial activity, nutrient leaching, lipids concentration, organic acids and phenols. These compounds may cause alterations in N cycle, changes in soil microbial activity as well as contamination of surface- and groundwater.
Regarding the remediation techniques of soil contamination, the most commonly used technologies (in-situ and non-in-situ methods) include:
- Soil leaching/washing/flushing; soil with water or surfactant,
- Soil extraction; the contaminated soil is exposed to chemical extraction and/or thermal treatment,
- Solidification/stabilization/immobilization – soil amendments with materials having a high capacity to bind metals in possible slightly mobile fractions and/or immobilize,
- Microbial/fungal –remediation,
- Excavation the contaminated soil is removed and disposed elsewhere,
A Report of the task group, regarding the status of soil contamination, established under the Thematic Strategy for Soil Protection drawn the following conclusions:
- The whole soil-water-sediment system has to consider for the protection against the threat of contamination and the definition of appropriate measures have to be linked with all kinds of land use and Land use planning in particular in urban areas
- The fluxes and the bioavailability of contaminants will be affected by climate changes via its impact on water flow and organic matter status of soils
- Guidelines and regulations for materials applied to agroforestry and incentives for reducing input of pollutants are further needed
- A world-wide co-ordination regarding large-scale diffuse contamination should be initiated
- Raising awareness on soil issues is key factor on soil protection
- Soil data getting of public interest due to risk of damage to the environment have to publicly available
Since that there is no EU legislation dealing with soil protection on its own right, there is need for a comprehensive regulatory framework approach for soil protection. This framework should not replace current regulations which already contribute to soil protection but act as an umbrella aiming at the coordination of the implementation of regulations already exist or amendments concerning soil contamination as well as improving current regulations if soil is not addressed sufficiently. A proposal for a Soil Frame Directive is under discussion among member Stares where a framework for the protection of soil, its sustainable use and the preservation of soil function is subject to the co-decision procedure.
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