World’s Soil Resources

Although poorly explored, diversity changes in soil are likely to impact soil physical properties, with
consequences for ecosystem services related to soil formation and water regulation. Diversity effects on soil
physical properties have not been explicitly studied, but they are likely to be important given the potential for
different groups of soil organisms to differentially impact soil structure through different routes. For example,
fungi promote soil aggregate stability through the physical enmeshment of soil particles by their extensive
networks of mycelia, whereas bacteria produce metabolic products, mainly polysaccharides, which bind
soil particles together (Hallett et al., 2009). Mycorrhizal infection can also influence soil aggregate stability
through physical enmeshment of soil particles by their extensive networks of mycelium, but also through the
binding of soil particles via the production of extracellular polysaccharides and proteins, including the protein
glomalin, which alters the wetting behaviour of soil (Rillig and Mulley, 2006). Finally, soil animals, especially
ecosystem engineers such as earthworms and termites, impact soil structure by creating macropores and
channels, thereby improving water movement through soil (Bardgett, 2005).
While evidence is mounting that shifts in soil biodiversity resulting from human activities have significant
consequences for ecosystem functions and the services that they underpin, there is still much to be learned.
The mechanisms by which soil biodiversity change can impact ecosystem are enormous, involving a range of
ecological and evolutionary processes at different spatial and temporal scales, and links between aboveground
and soil communities. Moreover, impacts of soil biodiversity change on soil functions are likely to be context
dependent, varying with soil abiotic properties and vegetation type. Unravelling this complexity in order to
make better predictions about the consequences of soil biodiversity change for the services that ecosystems
provide is a major challenge.
7.9 | Soils and human health regulation
The linkage between soils and human health is increasingly being recognized (Abrahams, 2006, 2013;
Baumgardner, 2012; Brevik and Burgess, 2013; Jeffrey and van der Putten, 2011; Oliver, 1997). A central
understanding is that soils form an integral link in a holistic view of human health that includes physical,
mental and social dimensions. The soil acts as a natural filter, it can kill off pathogens, it can biodegrade
organics and, in general, it does a wonderful job of protecting us from human health threats. However, soil is
not able to protect itself against all the insults it is subject to on a regular basis.
Soils aid in the regulation of human health. They do this by keeping in check, or balancing, the beneficial
versus deleterious concentrations of elements and moderating disease-causing organisms. For example, soils
regulate human health by impacting the nutrient quality or nutrient density of foods. Too little of an essential
nutrient in soil can lead to human diseases such as Keshan disease caused by selenium deficiencies in the
human diet (Chen, 2012). Conversely, health problems can be caused by an excess amount of organics or trace
elements such as the arsenic released by soils into the drinking and irrigation waters of Bangladesh (Khan,
Hamra and Mu, 2009) (Section 7.3).
Soil is a natural source of radiation that can adversely affect human health, and soil can also affect human
health by directly interacting with people. One example is the disease of podoconiosis or Mossy Foot disease
(Mossy Foot Project, 2014). Mossy Foot disease affects about 5 percent of the population in highland tropical
areas with volcanic soils and lots of rainfall. These soils are rich in silicates that can penetrate the skin of
susceptible people as they go barefoot about their daily business. Soils can also act as a reservoir of all kinds
of introduced materials that can impact human health. The dioxin at Love Canal in New York, United States
is a classic example (Silkworth, Culter and Sack, 1989). There are large quantities of industrial and agricultural
products and by-products added to soil every year that have the potential to impact human health.
Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services
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