Geoscience Reference
In-Depth Information
21
As well as being distinctive assemblages of plants and
animals, ecosystems also carry out work. Solar energy is
converted by plants and some micro-organisms through
photosynthesis into organic matter, which can then be
passed on to other organisms. In addition, ecosystems
circulate nutrients sufficient to maintain healthy vegetative
growth. Nutrients enter ecosystems from the atmosphere
and from rock weathering, and can exit the ecosystem
into the atmosphere and by drainage water. Nutrient
cycles thus link the air, the rocks and the soils (abiotic
environment) with organisms (biotic component).
Although each nutrient element has its own unique
biogeochemical cycle, different nutrient cycles can be
classified into general types. Processes involved in energy
flow and nutrient cycling are analysed in the present
chapter.
The role of the element carbon in the environment is
currently receiving enormous attention. This stems from
the debate on climate change, and the position of carbon
compounds in the atmosphere, vegetation, soils, fresh
waters and the oceans. There are also clear links with many
human activities such as energy production, economic
development, waste management, and issues of 'carbon
footprints', 'carbon credits' and 'carbon management' in
society as a whole. The fluxes in the carbon cycle are
therefore discussed in this chapter.
ENERGY FLOW AND TROPHIC
CYCLES
Central to research into ecological systems is the need to
understand their structure and function at various scales,
ranging from small, local communities to the global
biosphere as a whole. In the 1960s the US ecologist E. P.
Odum suggested that ecology could best be defined as 'the
study of the relationships between structure and function
in nature'.
Table 21.1
simplifies the major items which are
studied under the two fundamental headings of structure
and function.
Structure
1
Composition of the
Species, numbers,
biological community
biomass, etc.
2
Quantity of abiotic
Nutrients, water,
materials
etc.
3
Environmental
Temperature, light,
gradients
etc.
Function
1
Rates of energy flow
2
Rates of nutrient cycling
3
Regulation by the
physical environment
