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Definition of Soil Biodiversity

European Convention on Biological Diversity (CBD) defined the soil biodiversity as “the variation in soil life, from genes to communities, and the ecological complexes of which they are part, that is from soil micro-habitats to landscapes”.

In other words, the soil biodiversity represents the variety of life belowground. The term biodiversity denotes the number of distinct species (richness) and their proportional abundance (evenness) present in a system, but may be extended to encompass phenotypic (expressed), functional, structural or trophic diversity. The total biomass belowground generally equals or exceeds that aboveground. At the same time, especially in regards with the microbial scale, the biodiversity in the soil always exceeds that on the associated surface by orders of magnitude.

Biodiversity underpins sustainable development and is central food production, the provision of clean water and achieving environmental goals. There is growing concern about the unprecedented rate of global biodiversity loss. Direct drivers of biodiversity loss include pollution and nutrient overload, overexploitation of resources, land fragmentation and soil erosion, climate change and biological invasions. Socio-cultural factors, such as lifestyle and consumer choices, can be indirect drivers of biodiversity loss and the disruption of ecosystems.

Biodiversity decline (within all soil horizons)

Decline in soil biodiversity is the reduction of forms of life living in soils, both in terms of quantity and variety. Soil biodiversity is under increasing pressure because of threats to soil, such as erosion, contamination, salinization and sealing. These events threaten soil biodiversity by compromising or destroying the habitat of the soil biota.

 

Management practices that reduce the deposition or persistence of organic matter in soils, or bypass biologically-mediated nutrient cycling also tend to reduce the size and complexity of soil communities. It is however notable that even polluted or severely disturbed soils still support relatively high levels of microbial diversity at least. It has been observed that specific groups may be more susceptible to certain pollutants or stresses than others (e.g., nitrogen-fixing bacteria that are symbiotic to legumes are particularly sensitive to copper). Additional studies on the negative effects of direct and indirect soil threats on specific organisms are required.

Malta and soil biodiversity

In order to tackle the aforementioned issues Malta’s National Biodiversity Strategy and Action Plan (NBSAP) has already been adopted and applied.

Through the NBSAP, national targets have been set to be reached by 2020 in support of Malta’s natural heritage. Some of the targets address both direct pressures and underlying causes of biodiversity loss. A number of other targets are aimed at improving the status of Malta’s biodiversity and enhancing the benefits from biodiversity and associated life supporting services. The finalisation of the NBSAP fulfils one of the requirements for the National Environment Policy by providing the comprehensive strategic framework to protect Malta’s biodiversity. The conservation and sustainable use of biodiversity has a positive impact on the standard of living and on sectors such as tourism that are central for generating commercial activity and employment. On the other hand, such sectors must continue to develop in a sustainable manner and in ways that respect biodiversity and enrich our environment. It is therefore important that biodiversity is integrated in the relevant policies that directly or indirectly affect biodiversity.

Protecting Malta’s biodiversity presents a big challenge. Malta has a very small land mass, coupled with the highest population density in Europe. As a small island state, Malta faces the challenge of meeting the future demands of a growing population for land, water, food and energy, while at the same time halting the loss of biodiversity and the degradation of ecosystem services. This challenge is exacerbated by other environmental concerns, which are inherent to our isolated and insular ecosystems. The status of Malta’s biodiversity is still not understood well enough. The status of 36% of Maltese species and 29% of Maltese habitats listed in the EC Habitats Directive is still unknown; a significant number of these relate to the marine environment. These knowledge gaps hinder the development and implementation of effective protection and conservation. In addition, 44% of species and 64% of habitats do not have a favourable conservation status and hence require enhanced conservation action.

Several goals are set regarding biodiversity and soil, especially through sustainable use of the natural resources, Soil, Water and Land:

• High Nature Value Farmland (HNVF) in Malta is mapped according to defined criteria, and good agricultural and low-intensive practices, including organic farming, are applied to preserve such land and associated agrobiodiversity.
• Land uses are commensurate with the management of soil and by inference, water resources across the Maltese Islands. This is required in order to promote: the build-up of soil organic matter; the enhancement of soil biodiversity; the reduction (and reversal, where possible) of soil erosion, contamination and compaction; the minimisation of salinization/sodification levels (where applicable); the mitigation of flood-induced soil mass displacement/ land sliding; and the increase in infiltration and moisture retention in the soil. Measures incorporated in a soil action plan are formulated to address these goals in terms of how to mitigate the threats to Maltese soils and adopt measures aimed at soil conservation. The soil action plan and other national relevant policies shall contribute towards the requirements of the Convention to Combat Desertification (UNCCD) to develop desertification national action programmes.
• Transposition and implementation of the Pesticides Framework Directive, which advocates the sustainable use of pesticides and integrated pest management, assists in reducing the potential damage on biological and water resources caused by pesticides. This is supported by the development of a national action plan
• Effective measures are in place and implemented to address the over-abstraction and pollution of groundwaters, namely by nitrates and chlorides, in line with the Groundwater Directive, the Nitrates Directive, the Dangerous Substances Directive, transposing national legislation, the National Water Policy for the Future, and the Water Catchment Management Plan for Malta.
• Appropriate and cost-effective rainwater harvest technologies are adopted, where feasible, in urban and rural areas as an environmentally sound approach to address imbalances between water supply and demand, and thus ensure long term water security in Malta (links with NR4).
• Integrated water resources management, based on the ecosystem approach, is achieved via the full implementation of the Water Framework Directive and its programme of measures as well as the Marine Strategy Framework Directive. Such implementation shall be in a mutually supporting manner in the case of coastal waters. The successful implementation of measures in the Water Catchment Management Plan for Malta results in the attainment of “Good Ecological Status” in surface waters, “Good Chemical Status” for groundwater and surface waters, and “Good Quantitative Status” for groundwater bodies, all by 2015 (and if this is not possible, by 2021 or 2027). “Good Environmental Status” in the marine environment is achieved by 2020, at the latest, via drawing up a national marine strategy by 2016, and, where possible supported by other policies in line with relevant Regional Seas Conventions. Implementation of the MSFD on a national level also contributes to the goals of the EU’s Integrated Maritime Policy.

Soil Degradation Threats

The United Nations and a number of global and regional entities have recognised that soil degradation is a major threat to humanity. Soil degradation compromises the continued tenure of food availability for a growing global population and harms ongoing efforts to avert the loss of species and ecosystem losses, and the prevention of negative implications resulting from climate change.

Primary causes behind soil quality deterioration

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

Due to more than 200 years of industrialization, contamination is widespread in Europe. The most frequent contaminants are heavy metals and mineral oil. Consequences 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 a higher flood risk potential), and human health problems due to dust and particles in the air.

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.