Threats to soil biodiversity

Biodiversity loss and climate change are two of the most pressing challenges of our time, and soil biodiversity is part of the solution to both. Yet it is under constant threat, largely from human activities that we can control.

To better understand the threats we need to analyse 2 sides of a medal: the pressures placed on soil biodiversity on the one hand, and the vulnerability of the various soil organism communities on the other hand. The latter can be gained from monitoring as described in the section before. But what is the state of knowledge regarding the pressure side?

Probably the main anthropogenic disturbance factor is land use change. Remember how the linkage between above- and belowground diversity has been shown above. As agricultural intensification proceeds, above-ground biodiversity is reduced. As a consequence, the biological regulation of soil processes is altered and often needs to be substituted by the use of mechanical tillage, chemical fertilizers and pesticides. This in turn is assumed to reduce below-ground diversity, which may cause losses of function and reduce the ability of agricultural systems to withstand unexpected periods of stress.

The following is a list of pressures that arise from the driving force of land use change:

  • Organic matter depletion
    Depleting the level of organic matter in soil means starving the soil organisms that depend on it as source of food and energy. Converting a natural ecosystem such as a forest to farmland, for example, cuts the soil carbon pool by 50-75%. In nearly half of Europe’s soils organic matter levels are below 2%, seen by some as critically low.
  • Chemicals
    can affect soil organisms directly, with toxic effects on their reproductive ability and survival, or indirectly, by contaminating their food supply or habitat. The most common chemicals involved are pesticides, fertilisers, petroleum-derived hydrocarbons, solvents, and heavy metals. Some contaminants, such as pharmaceuticals, steroids, hormones or nanoparticles, may have detrimental effects on soil organisms, but research into these potential hazards is just at the beginning.
  • Compaction
    is caused by both natural and human activities, particularly the use of heavy machinery in farming on wet soils. It causes air to be squeezed out of the soil, preventing water infiltration and destroying networks of tunnels and pores created and used by ‘soil architects’ such as earthworms. Especially in connection with organic matter depletion it leads to both a reduction in soil biodiversity and a modification of community composition.
  • Sealing
    describes any impermeable layer between the above-ground and below-ground environment as the result of urbanisation and the widespread use of asphalt and concrete. It instantly affects the diversity and abundance of soil organisms, but can also cause ‘off-site’ damage, as displaced water runs off to other areas where it may cause erosion and flooding.

Other relevant drivers besides land use/land use change are the use and release of Genetically Modified Organisms (GMO), that may impact on soil biodiversity and promote genetic resistance in the pest species they are designed to target. And finally climate change which is expected to impact on soil organisms directly, by altering their habitat and food web, or indirectly, through increased erosion, droughts, wildfires and so on.

Based on consultations of 20 international experts, a series of Europe-wide maps of potential threats to soil biodiversity has been published in 2013. It shows high scores (high potential threats) in several parts of the UK and central Europe which are determined by the combined effect of a high intensity agriculture with a high number of invasive species and by the risk of soil organic matter depletion.

On the positive side, scientists all over the world have begun to quantify the causal relationships between

  1. the composition, diversity and abundance of soil organisms
  2. sustained soil fertility, and
  3. environmental effects such as greenhouse gas emission and soil carbon sequestration.

In the field of applied sciences, a major EU research project called RECARE is looking into developing effective prevention, remediation and restoration measures for a large range of soil threats. One of the outcomes of RECARE will be policy messages to stimulate renewed care for soils in Europe, and the wider world.

Driver-Pressure-State-Impact-Responses (DPSIR) framework applied to soil biodiversity. ‘Driving forces’ are the socio-economic and socio-cultural forces driving human activities, which can either increase or mitigate pressures on the environment. ‘Pressures’ are the stresses that human activities place on the environment. ‘State’ refers to the state or condition of the environment.  ‘Impacts’ are the effects of environmental degradation, and ‘Responses’  refers to the responses by society to the environmental situation.
Source: Jeffery et al. (2010)

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