TECHNICAL
Fig 3: Atomic structure of inorganic C-12
The decomposition
process that occurs in a functioning soil is fundamental for achieving equilibrium in the C cycle
To start our journey, let’s take a closer look at the molecular properties that make C special. C-12 is the most abundant form of inorganic C. It has an atomic number of 6 (6 protons in the nucleus) and an atomic mass of 12 (6 neutrons and 6 electrons), this accounting for the C-12 categorisation (Fig 3). A unique feature of C is its ability to bond with itself, leading to the term ‘pattern maker’. This ability allows it to create exceptionally long and resilient chains known as polymers, seen everyday in natural and synthetic forms, including proteins, nylon and plastics. It is capable of making covalent bonds with other organic molecules such as oxygen and nitrogen. These exceptionally strong single, double and treble bonds enable the production of the organic compounds that are present in all living things.
On a global context, evolution over millennia has enabled processes, fl uxes and exchanges to achieve regulation and equilibrium of the levels of C currently present in soils, oceans and the atmosphere. These providing the foundation for the multitude of life supporting services that humans are dependent on. The production
and decomposition of all living material and the subsequent production of OM are a constant addition and subtraction to these C rich reservoirs. Advances in technology and a changing climate has made previously secure stores of C now accessible. OM newly exposed to its nemesis oxygen, resulting in accelerated rates of decomposition. The greatest depths of the oceans are a resting place for huge accumulations of carbonates, these now threatened by warming waters. Onset of the industrial age and the growth of the human population has placed pressure on the natural world’s C equilibrium. Anthropogenic inputs from industry, as well as land change driven by agriculture and urbanisation, has had a destabilising impact. Simply put, more C is being produced than the planet’s buff ering mechanisms can absorb (Fig 4). Why should increased levels of atmospheric C be of concern? A term that I am sure you will be familiar with is that
of greenhouse gases (GHG). C plays a prevalent role in two of these, carbon dioxide (CO2
) and methane (CH4 ), with the other
perhaps less well known, but equally potent, GHG being nitrous oxide (N2
O) (Fig 5). The
presence of these gases at increasing levels in the atmosphere has an insulating aff ect on the planet, preventing heat rebounding from the Earth’s surface from escaping. Think of the stratosphere layer of the atmosphere as a large porous umbrella covering the planet, with the permeability of the umbrella reducing as concentrations of GHG increase. This subsequently leading to a warming of atmospheric temperature, hence the term ‘global warming’. The scale of this issue emphasised by the fact that estimated atmospheric CO2
levels in 1860 were
260ppm, while in 2018 they were 407ppm[2] An increase of 64%.
.
Lets now concentrate on an area that I hope is of particular relevance to the majority of readers, the relationship between C
Evolving technology is
providing land managers with an increasing armoury at their disposal for monitoring soil moisture
Fig 4: Global carbon cycle 128 PC April/May 2021
levels, providing the greater transparency that comes with the collation of data
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