It is the objective of this volume to demonstrate that we do have an ecosystem theory, mainly based on thermodynamics for ecosystems. The theory should be applied as any other theory to explain our observations. The fundament of any ecosystem theory will inevitably be the basic thermodynamics laws: the First, the Second and the Third Law of Thermodynamics. The introduction of the concept of exergy will later enable us to apply these three fundamental laws more directly in an ecological context, because exergy is a thermodynamic variable that can be applied far from thermodynamic equilibrium. However, after presentation of the three basic laws of classic thermodynamics, we can already glimpse the enormous importance the laws have for ecology.
The conservation laws are widely applied in all ecological models, which are based on a "book-keeping" of matter and energy, i.e. the use of Eq. (2.1). The holistic description of the ecosystem embodied in the model thereby becomes the consequence of the thermodynamic laws or, expressed slightly differently: the description of an ecosystem by a model reflects the constraints of the thermodynamic laws on the ecosystem.
The concept of an ecosystem, widely used in ecology, makes it possible to distinguish the system and the environment in a thermodynamic sense. System ecology is concerned with the exchange of mass and energy between the system and the environment, and the influence of these exchange processes on the ecosystem and its processes.
Thermodynamics is furthermore applied in biochemistry to understand the relationships between chains of biochemical processes and the corresponding energy budget. The catabolic processes are important as the supplier of energy for maintenance of the life processes. When the energy demand is covered by the catabolic processes, additional energy may be used to build up biomass—to cover the anabolism. The organisms need, in other words, to transport energy between cells—from cells where the energy is produced to cells where the energy is needed. The organisms use small packages of ATP, which are easily transported and are able to release 41.8 kJ/mol by the following process:
to solve that problem. All these considerations are in accordance with the thermodynamic laws.
Also, the Second Law gives us a deep insight into the function of ecosystems. The function is based on entirely irreversible processes. Energy that can do work is lost as heat to the environment. It is the cost of keeping the ecological machine cycling and repeatedly recycling the matter, so it can be used to build continuously new biomass, which in the long run contains more and more information. The energy for maintenance of the cycling and recycling is provided by solar radiation that supplies the work to the ecosystem needed for recycling the matter. Heat is produced due to "friction" in this process caused by the life processes. Ecosystems therefore require an input source of useful energy to drive the life processes.
We cannot understand ecosystems by Newton's Laws, because the processes are irreversible and the time arrow is governing. The process is one way: solar radiation ! plant biomass is built according to the photosynthesis ! the biochemical energy in the plant biomass is utilised throughout the entire food web ! new biomass is formed continuously, which implies that new "solutions" to life under the continuously changing conditions are formed. The result is the evolution, a distinct one-way process—no symmetry. The consequence is that we cannot describe ecosystems by Newton's Laws. Ecological models cannot be developed from Newton's mechanics but they must be based on the thermodynamics.
The calculations of the equilibrium constants for the decomposition of high molecular weight proteins show that the decomposition processes are spontaneous and provide a considerable amount of energy (that can do work). It is only possible to avoid the decomposition process by feeding energy to the living organisms to compensate for the inexorable production of entropy inexorable reducing gradients to obtain a more probable situation. Living systems require an energy source that can provide the energy needed to maintain the system far from thermodynamic equilibrium. Without the energy source, the system will inevitably move toward thermodynamic equilibrium, where there are no gradients in space or time—the system is therefore dull and has no life. An energy source is a necessary prerequisite for living systems. Is it also a sufficient condition for creation of life? We will turn back to this question a few times in the coming chapters.
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