Global threats to soil
The term global environmental change refers to environmental changes that have an impact at a global scale.
We will be focusing on human-induced global change - environmental change bought about by man. This term encompasses a whole range of different environmental problems, including air pollution from pollutants like ozone, sulphur and nitrogen, increasing ultra violet (UV) radiation caused by degradation of the ozone layer, land use change, loss of biodiversity, invasive species and of course, climate change.
All of these changes have the potential to impact on soils. Some of these impacts are described below and are examined in more detail throughout the week.
Climate change or global warming refers to the long-term change in the global average temperature caused by increasing concentrations of greenhouse gases such as carbon dioxide in the atmosphere.
Climate change is expected to bring about changes in temperature and rainfall patterns, both of which have important implications for soils. These changes are caused by an increase in carbon dioxide in the atmosphere, so we also have to consider this as a factor.
Higher concentrations of carbon dioxide could lead to increased plant growth and result in more organic matter being added to the soils. A change in temperature will change the rate of microbial processes such as the decomposition of organic matter. Changes in rainfall will have a similar effect. These changes may also alter the species composition found in the soil and the chemical processes. One potentially important effect of climate change is melting permafrost in soil. This could lead to the release of stored greenhouse gases, in particular methane.
Read about melting permafrost.
We will look at climate change in more detail in Steps 4.3 and 4.4
We have already learned about causes of localised contamination of soils. Air pollution can lead to widespread contamination. This can be with toxic pollutants such as persistent organic pollutants from a range of sources such as pesticide use but it can also be with pollutants like nitrogen and sulphur emitted from fossil fuel combustion and other sources which are not actually toxic but still have an impact on soil.
Nitrogen and sulphur form acids in rain water so can be deposited as acid rain changing soil chemistry and impacting organisms living in the soil. We will look more at the impact of nitrogen deposition on soils in section 4.5.
Ozone is also a pollutant in the lower levels of the atmosphere and high levels of ozone are caused by chemical reactions in the atmosphere as a result of emission of nitrogen oxides and volatile organic compounds emitted from fossil fuel combustion. When these chemicals react in the presence of sunlight ozone can be produced. Ozone can also impact on soil microbial communities leading to changes in carbon cycling.
In the upper atmosphere ozone plays an important role in screening us from harmful ultra-violet radiation but the production of certain chemicals such as chlorofluorocarbons (CFCs) causes chemical breakdown of ozone and has led to ozone depletion and holes in the ozone layer. This leads to increased levels of UVB ultraviolet light reaching the earth’s surface. In the polar regions, where this effect is most apparent, scientists have demonstrated the potential for changes in UVB radiation levels to cause changes in the soil microbial community potentially impacting on the species composition and the processes they perform in the soil.
Loss of biodiversity
Worldwide biodiversity is being lost at an incredible rate, so much so that some have argued that we are now in the midst of the 6th mass extinction that the planet has experienced. As you saw in the second week of this course, there is actually a limit to how much we know about life in the soil, and as a consequence of human activities we may be losing biodiversity without even knowing what species existed to start with.
We will look at how these and other types of global change affect soils as the week goes on.
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