Overview of Soil Degradation Threats

​The United Nations and a number of global and regional institutions/entities have throughout the years recognised that growing soil degradation is not only a major threat to humanity, in that it compromises the continued tenure of food availability for a growing global population, but also since it mitigates against ongoing efforts to avert further species and ecosystem losses in all geographic regions (particularly in sensitive latitudes), reversal of landscape deterioration and to prevent negative implications resulting from climate change.
 
Primary causes behind soil quality deterioration
 
During its extensive technical analysis related to soil conservation, the European Commission identified the following overarching challenges impacting soil quality integrity:
 
Biodiversity decline (within all soil horizons)

There is an enormous variety of organisms, from bacteria to mammals, which shape the metabolic capacity of terrestrial ecosystems and many soil functions. All the other threats and degradation processes contribute to the loss of soil topsoil and subsoil biodiversity. A string of consequencies brought about by decline in  soil horizon biodiversity would be: reduced food web functioning and consequently crop yield losses, reduced soil formation,, nutrient recycling, nitrogen fixation, carbon sequestration, recycling of organic waste and litter, reduced resilience of soil to endure pressures, water infiltration rate and water holding capacity, hampered soil structure (by affecting the stabilization of organo-mineral complexes), increased plant pests and diseases, reduced bioremediation capacity, reduced genetic resources present in the soil  (including moral and ethical consequences) and negative impact on terrestrial/surface biodiversity outside of soil.
 
Compaction
 
Compaction is largely induced by the inappropriate use of heavy machinery in agriculture, that is, on the same piece of land, or to a lesser extent by the trampling of cattle when overstocked, in wet conditions or on wet soils. Subsoil compaction occurs when tractor wheels pass through the open furrow during ploughing, creating a persistent 'plough pan'. Severe subsoil compaction is also caused by heavy machinery used during harvest and the spreading of slurry with high capacity tankers having heavy axle loads. Soil compaction is potentially a major threat to agricultural productivity. It may occur at shallow soil depths as well as deeper in the subsoil. Shallow soil compaction occurs during seed bed preparation, spreading of fertilisers and pesticides.
 
But it is not confined solely to agricultural soils. Building sites and intensively used recreational areas, for instance, are also susceptible.
 
In all of the above examples, this form of degradation reduces the capacity of soil to store and conduct water, makes it less permeable for plant roots and increases the risk of soil loss by water erosion.
 
Contamination (diffuse and point source/ local pollution)
 
Due to more than 200 years of industrialization, contamination is widespread in Europe. The most frequent contaminants are heavy metals and mineral oil. Consequencies of contamination  (and untreated soil pollution) include primarily risk to human health  for people living in or around the contaminated site (through different exposure paths, e.g. consumption of food grown  in the contaminated area); contamination of surface and ground waters but also risk to soil’s resident flora and fauna through eco-toxicity process, reduction of soil fertility, land value depreciation impacting upon and restricting land use potential in that future redevelopment is compromised.
 
Erosion
 
Depletion of upper layers of this resources (and sometimes also of significant amounts of subsurface soil profiles) through wind and water action induced by natural and anthropogenic sources. Consequencies of soil erosion can occur on-site and off-site where event is taking place.
 
- On-site impacts include soil loss, loss of soil fertility due to disruption of nutrient cycles, restrictions on land use hindering future redevelopment and reducing the area of productive and valuable  soil available for other activities (agricultural and forestry production, recreation etc.) and land value depreciation.
 
- Off-site effects include: damage to infrastructures due to excessive sediment load, diffuse pollution of surface water, Negative effects on aquatic ecosystems and thereby biodiversity, reduced water retention capacity (hence ahigher flood risk potential), and human health problems due to dust and particles in the air.
 
Landslides (including soil mass displacement through torrential flooding)
 
Landslides will occur when the inherent resistance of the slope is exceeded by the forces acting on the slope such as excess rainfall or seismic activity, or as a consequence of human interference with the shape of the slope (e.g. constructing over-steepened slopes) or modifying the soil/bedrock conditions and groundwater flow, which affects slope stability. Landslides may be triggered by factors such as land abandonment and land use changes. 
 
Landslides occur more frequently in areas with steep slopes and highly erodible soils, clayey sub-soil, weathered and jointed bedrock, following intense and prolonged precipitation, earthquakes – in southern Europe, or rapid snowmelt.  Locally, man-made slope cutting and loading can also cause landslides.
 
Landslides threaten soil functioning in two ways:

i) removal of soil from its in situ position, and
ii) covering the soil downslope from the area where the slope has ‘failed’.
 
Where a landslide removes all soil material, all soil functions will be lost and weathering processes of the hard rock, or sediment, now exposed at the surface, need to operate for hundreds if not thousands of years to produce enough soil material for soil functioning to resume. When only a part of the soil profile (e.g. the A horizon) is removed by a landslide, some soil functions may remain, although most functions are likely to be impaired. Further information about the various impacts can be found here.
 
Various types of landslides may result as a result of either rock, debris or earth failure to retain soil and/or earth cohesion:
 
 
Organic Matter Depletion (OMD)
 
 
A well-replenished organic matter level in soils is a key component of the resource's top layer which in turn facilitates and controls the viability of its many vital functions (unique soil ecosystem services). Organic material in the soil is essentially derived from residual plant and animal material, synthesised by microbes and decomposed under the influence of temperature, moisture and ambient soil conditions. The annual rate of loss of organic matter can vary greatly, depending on cultivation practices, the type of plant/crop cover, drainage status of the soil and weather conditions. There are two groups of factors that influence inherent organic matter content: natural factors (climate, soil parent material, land cover and/or vegetation and topography), and human-induced factors (land use, management and degradation).
 
Salinisation (including sodification and acidification)

Soil quality may be threatened as a result of salt, sodium accumulation and other substances likely to be generated when field stewardship draws support from irrigation water and fertilizers all of which negatively impact plant growth. Soil salinisation causes harm to many elements of the environment, including:
  • plant life (soil fertility, agricultural productivity, cultivated crops and their biomass yield);
  • natural vegetation (ecosystems); 
  • life and function of soil biota (biodiversity); 
  • soil  functions  (increased  erosion  potential,  desertification,  soil  structure,  aggregate  failure, compaction); 
  • the hydrological  cycle  (moisture  regime,  increasing hazard  –  frequency, duration,  severity  – of extreme moisture events as flood, water logging, and drought); and
  • biogeochemical cycles of elements (plant nutrients, pollutants, potentially harmful elements and compounds).

In view of the above, a distinction can be made between primary and secondary salinisation processes. Primary salinisation involves accumulation of salts through natural processes such as physical or chemical weathering and transport from saline geological deposits or groundwater. Secondary salinisation is caused by human interventions such as inappropriate irrigation practices, use of salt-rich irrigation water and/or poor drainage conditions. 

 
Sealing (including land take)
 
Soil quality deterioration from a spatial perspective occurs when agricultural and non-developed land is lost to unregulated urban sprawl, projects designated through strategic and local land use planning processes, industrial development, landscaping and aesthetic upgrading or transport and utilities infrastructure. Normally it includes the removal of topsoil layers and leads to the loss of important soil functions, such as food production, water storage or temperature regulation through management of urban heat island effects.
 
Desertification (including land degradation and drought)

Desertification is a global phenomenon, often characterized by significant human-induced pressures as it is largely caused by unsustainable use of scarce resources occurring alongside a not-to-be discarded desertification induced through natural processes. It is the persistent degradation of dryland ecosystems.  Desertification has environmental impacts that go beyond the areas directly affected. For instance, loss of vegetation can increase the formation of large dust clouds that can cause health problems in more densely populated areas, thousands of kilometers away. Moreover, the social and political impacts of desertification also reach non-dryland areas. For example, human migrations from drylands to cities and other countries can harm political and economic stability.
 
Legislative action by the United Nations has resulted in the drawing up of a specific Convention for Combating Desertification. Further information about this Convention can be found here.
 
This initiative spurred later action where various reports synthesising the situation, established in terms of the so-called Millenium Ecosystem Assessment were prepared by various stakeholders for specific global audiences. The specific report, prepared in relation to this global degradation theme, provides a state-of-the-art scientific appraisal of the condition and trends as well as a scientific basis for action to use natural resources in a sustainable manner.
 
Drivers of soil degradation

Drivers of soil degradation refers to a wide range of indirect or direct factors likely to trigger a loss in soil quality and the wider land degradation over the short, medium and long-term timescales. Soil degradation is but one important negative implication behind land deterioration which can then cause the intensification of natural phenomena whilst accentuating other human-induced impacts upon these natural resources which are fundamental building blocks of life and human societies as we know them.

An extensive report, published in January 2016 with reference to RECARE project deliverables, amply evaluates the various forms of soil degradation from a pan-European perspective.
 
According to the Rural Development Plan for Malta, soil quality deterioration is compounded by the spatial pattern of soil resources, both in the case of semi-natural areas and also within agricultural land as different soil types often occur even within a single field or within a distance of few metres. The movement of excavated soil material from sites of construction, in accordance  to  the Fertile Soil Act, and  the creation of ‘made ground’ or replenishment of eroded or shallow soils, and the associated impacts  of  progressive  urbanisation,  have  contributed  to  increase  the heterogeneity of the soils, and have rendered the characterisation of soils more complex.
 
Examples of direct drivers of soil degradation usually triggered by human-induced activity:
  • changes in land use (land conversion, sealing and land take) and habitat fragmentation (when natural habitats are divided into smaller fragments);
  • desertification spread and intensification (development of desert-like conditions, as a result of inappropriate land-use practices that lead to soil erosion and loss of water-holding capacity in the soil (for further details refer to activities connected to implementation of thematic priorities established under the United Nations Convention to Combat Desertification);
  • abandonment of farming practices in cultivated land, where human intervention would be necessary to prevent ensuing degrading activities and for maintaining the various species that are connected with soil biodiversity (e.g. maintainance of rubble walls which serve as a shelter to various species);
  • illegal water abstraction, causing decline of water tables, which hence leads to impacts on water-reliant habitats and species;

  • tree cover decimation (deforestation); 
  • intentional/illegal and naturally-induced fires;
  • unbridled unsustainable development on virgin land. Soil sealing is the permanent covering of soil with hard surfaces such as roads and buildings. The impacts that the sealing of soils can have are: loss of all soil functions, loss of high quality agricultural land, loss of natural habitat, increased flood risk by making run-off more rapid and peak discharge greater, and habitat fragmentation; 
  • climate change is an overarching driver affecting numerous soil quality issues such as: loss of organic matter because of higher decomposition rates (e.g. increased temperature, drying of wetlands), erosion as a result of more frequent extreme rainfall events, reduced trafficability as a result of periods of increased soil wetness, a reduction in soil fertility, increased and changing pest loads, and a change of vegetation type and an increase in plant growth (both crops and natural vegetation;
  • atmospheric deposition - The burning of fossil fuels by industry, households and vehicles releases gaseous emissions of sulphur dioxide and oxides of nitrogen that can travel hundreds of miles in the atmosphere. These gases can be dissolved in rainwater to form sulphuric and nitric acids. These will subsequently be deposited on soil and result in soil acidification which can cause reduced drainage water quality due to increased leakage of acidic compounds and toxic elements, a loss of above and below ground biodiversity, as certain species are unable to survive in acidic soils, and structural damage to soil minerals. In addition, excess nitrogen deposition can result in soil eutrophication. Intensive agriculture can release high concentrations of ammonia which tends to be deposited close to the source. Soil eutrophication can result in: loss of biodiversity and changes to vegetation and ecosystems, the potential for increased microbial activity resulting in more rapid organic matter decomposition and greenhouse gas emission, and the potential for an increase of nutrients in surface water and groundwater.
  • waste-to-land contamination.

Examples of indirect drivers of soil degradation resulting from the human activity footprint:

  • demography (rise in population growth coupled with increasing consumer demands) in economy-generating activities;
  • rural to urban population shift resulting in rapid/ sustained settlement growth;
  • land-based biodiversity loss;
  • outcome of land-intensive uncontrolled recreation activities which result in littering.

Further detailed information about how to detect and mitigate soil degradation can be viewed from here and by evaluating way forward established in this 2009 document on the wider issues of land degradation and desertification. The latter contribution was formulated by expert representatives acting on behalf of the Economic and Scientific Policy Department of the European Parliament.