Thermodynamics and Ecological Modelling

Sven E. Jorgensen

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351990479
• Edition: 1
• Topic: Technik & Maschinenbau
• Subtopic: Umweltmanagement

Thermodynamics is used increasingly in ecology to understand the system properties of ecosystems because it is a basic science that describes energy transformation from a holistic view. In the last decade, many contributions to ecosystem theory based on thermodynamics have been published, therefore an important step toward integrating these theories and encouraging a more wide spread use of them is to present them in one volume.
An ecosystem consists of interdependent living organisms that are also interdependent with their environment, all of which are involved in a constant transfer of energy and mass within a general state of equilibrium or dis-equilibrium. Thermodynamics can quantify exactly how "organized" or "disorganized" a system is - an extremely useful to know when trying to understand how a dynamic ecosystem is behaving.
A part of the Environmental and Ecological (Math) Modeling series, Thermodynamics and Ecology is a book-length study - the first of its kind - of the current thinking on how an ecosystem can be explained and predicted in terms of its thermodynamical behavior. After the introductory chapters on the fundamentals of thermodynamics, the book explains how thermodynamic theory can be specifically applied to the "measurement" of an ecosystem, including the assessment of its state of entropy and enthalpy. Additionally, it will show economists how to put these theories to use when trying to quantify the movement of goods and services through another type of complex living system - a human society.

1 Introduction

Sven E. Jørgensen

CONTENTS

1.1 Energy and Ecology

1.2 A Short Overview of the Contents

1.1 Energy and Ecology

Energy became associated with ecology during the last years of the 1950s due to the brothers Odum, but not much interest for these approaches was shown by ecologists in the 1960s and 1970s with some few exceptions. During the last decade, an escalating interest for the use of thermodynamics in ecology has emerged with the result, that during the last 4 to 5 years, many papers on the application of thermodynamics to understand ecology have been published.

A number of theories based on thermodynamics of ecological systems have been proposed during the last decade. We felt it therefore timely to bring together these activities in one volume. We have asked the main proponents of each of these theories to present their work in this volume. The different theories are not completely consistent or even in some regard not necessarily compatible, but they represent different thermodynamic viewpoints on ecosystems, which on balance are complementary. We are of the opinion that a very complex system as an ecosystem requires plurality of perspectives to capture the richness of ecosystem dynamics. A simple physical phenomenon as light needs two descriptions: by waves and by particles. It is therefore not surprising that the very complex ecosystems need several complementary descriptions. We hope that this volume will contribute to the emergence of these complementary descriptions.

With this in mind we have chosen to let the authors speak for themselves, almost unfaded by the review process, which attempts to impose conformity. This way of presenting the various theories is well justified given the status of the selected authors. The readers will therefore have to judge for themselves on the applicability of the theories to achieve a better understanding of ecosystem behaviour. This implies, however, that the different authors may use different expressions to explain their ideas. It may even imply that different authors apply the same word to cover a different meaning. This has, however, often been the case with emergence of a new scientific field. To partly eliminate these ambiguities I decided to write a short introduction for each chapter to present the authors, the context for their work, the core ideas, and the terminology they use.

As already mentioned, we consider the different theoretical approaches as complementary. The final questions left for the readers to answer are: do we see consensus? Where do we see different perspectives, but not necessarily inconsistencies? Where do we see contradictions? Which theoretical approaches need further exploitation? Which theories need even further experimental testing?

We are also of the opinion that to a certain extent the different theories form a pattern of understanding, which we will attempt to reveal as far as it is possible in the introduction to each chapter.

1.2 A Short Overview of the Contents

Each chapter has an introduction with a short overview of the content. It is therefore not the intent of this section to repeat the introductions, but try to draw a short overview of the topic “Thermodynamics and Ecology” at the edge of the 21st century.

We have made energy balances for ecosystems for many decades, and it has certainly given us new knowledge about the ecosystems and the role energy plays in ecosystems. This approach can still bring new knowledge depending on the considered system, as it is demonstrated in Chapter 3. It is, however, very characteristic that this approach, although very important, still gives surprising results. We would like, however, to include a quality measure or index of the energy—not only a record of the flow pattern. Emergy and exergy are energy expressions and use energy units, the first of which is joule, but the energy is multiplied by a weighting factor taking the energy quality into account. Emergy uses a weighting factor based on how much solar radiation measured in joules (the ultimate energy source on earth) is used to make 1 joule of energy embodied in a specific object. In other words emergy is based on a quality factor which accounts for the total energy cost expressed in solar energy. Exergy, on the other hand, considers the information or organisation carried by a specific organism, but the energy quality is already included in the definition of exergy: the work content of a system compared with a reference state. We distinguish between energy which can do work and energy which cannot do work. Both approaches are valuable, giving “two different sides of the same coin.”

Another recent development in system ecology is the use of indicators or, as H. Bossel calls them, orientors. When we are using them in modelling context, we may call them goal functions. This development was initiated to assess the ecosystem health by use of indicators, or as it is called more frequently in Canada, ecosystem integrity. The environmental manager should consider himself a “doctor of the ecosystem” needing a diagnosis. As the doctor of medicine measures the blood pressure, makes biochemical analyses of the blood, listens to the heart and lungs, and analyses the urine, the doctor of ecosystem should have a list of ecosystem tests which could be used to assess the ecosystem health. Among the possible candidates as ecological health indicators, the thermodynamic-based orientors offer some advantages. Emergy, exergy, the energy flow pattern, entropy, and even ratios of these indicators (orientors) have been proposed and used to assess the ecosystem health. This application of thermodynamics in system ecology is mentioned and discussed in several chapters, particularly in Chapters 4, 8, 9, 12, and 13.

A third core topic in the application of thermodynamics in system ecology is the possibility to describe the ecosystem development by use of thermodynamic functions or, what would be even more beneficial, to set up rules or a theory on how an ecosystem will develop under given circumstances. Several propositions are presented in this volume and a more detailed discussion takes place in Chapters 6, 8, 9, 12, and 13. There seems to be general agreement that ecosystems use the available energy flow through the system to move away from thermodynamic equilibrium. The disagreement today in systems ecology is which of the possible thermodynamic functions are most appropriate to make this description. The discussion should not be repeated here; readers should make their own conclusions. There is, however, no doubt that this discussion will continue for several years, but also that a more complete theory for ecosystem development is around the corner and thermodynamics will play an important role in this theory.

Solutions close the possibilities Problems disclose them

CHAPTER 2

It is natural to start this volume with a contribution by Ramon Margalef. He has used energy considerations on ecosystems for almost 50 years, and has as professor emeritus produced this chapter. He recently (1997) published a book named: Our Biosphere in the series Excellence in Ecology. This book and this chapter give a clear message to the readers: there is a long way to go before we have the integrated but urgently needed ecological theory, which would make it possible to understand the nature and the reactions of ecosystems. However, Margalef has many ideas which can be used to develop the present ecosystem theories or maybe rather the fragments of ecosystem theories in the right direction.

Margalef emphasises the importance of information: information multiplies its value when the unified support for it grows larger—a phrase which is completely in accordance with the thermodynamic approach based on exergy presented by Svirezhev in Chapter 14. Margalef is also in accordance with both Chapter 11 by Johnson and Chapter 13 by Jprgensen and with Chapter 14, when he presents a tentative driving principle: go as fast as possible to a condition of high information content. It is a formulation which is very close to the tentative Fourth Law of Thermodynamics proposed in Chapter 13 as a hypothesis.

Margalef distinguishes between external energy (exosomatic energy), for instance, up-welling and internal energy (endosomatic energy), for instance, photosynthesis. He refers to emergy as the energy (endosomatic and exosomatic) that has been involved in any process leading to a presently given structure or situation. Evolution is a question of mastering (being able to properly utilise) exosomatic energy. With this in mind, he can distinguish five peaks in the evolution: the emergence of stromalites, of corals, of macrophytes, of eusocial insects, and of humankind, where the cultural transmission also plays a major role. The exosomatic energy is used to organise space and to build gradients (the same idea as presented in Chapter 13 by Jprgensen, who is using exergy to interpret the ecological observations). The complexity associated with spatial organisation and the irreversibility of ecological processes and their relations to exosomatic energy would for Margalef be the concepts which could be the basis for further progress in ecosystem theory.

It is recommended that this chapter be read carefully, because it contains many ideas—also between the lines—which may give the readers inspiration to further progress in ecosystem theory.

2 Exosomatic Structures and Captive Energies Relevant in Succession and Evolution

Ramon Margalef

CONTENTS

2.1 Present Ecological Theory Needs to be Improved

2.2 Constraints of the Physical World

2.3 What is Life and How the Biosphere Becomes Organized

2.4 Ecological Succession

2.5 The Asymmetry of Change—Difficulties Concerning Prediction

2.6 Do We Need Just Plain Physics?

2.7 Back to Everyday Work

2.8 Properties of the Space Required for Obtaining Work from Exosomatic Energy Opens New Evolutionary Scenarios

2.9 Use of Exosomatic Energy Goes with the Capacity to Organize Space

References

2.1 Present Ecological Theory Needs to be Improved

The proper study of the biosphere requires a converging effort from many sciences. A balanced synthesis may be impossible to achieve, or at least has not been achieved, as, in function of intellectual fashion and of eventual breakthroughs being made in definite fields, separate aspects become emphasized in a nonsimultaneous way. Today, to speak of ecological theory is out of fashion, although there are many concepts and particular models. For example, theoretical ecology has continued the study of interaction among individuals of different species, perhaps in the continued hope to develop some kind of statistical mechanism, taking into account the eventual peculiarities of ecological relations. But creative insights into the working of large segments of the biosphere, in what concerns use of energy and capacity for organizations, are not being produced in the measure of the need for them, as it appears in relation with the pressing problems concerning global cycles and changes.

The bits and pieces of theory that have been proposed, even if some of them seem to be validated by experiments and observations, do not fit together easily and do not provide a general satisfying picture of how the biosphere has worked and evolved in the past and works and is evolving now. Attempts to find inspiration in more abstruse fields, like chaos, I consider as reactions taken in desperation when they come from ecologists. As ecology deals with physical systems, it seems reasonable that ecologists refrain from accepting theories that have not passed the proof of being of consequence in the field of physics.

I have often voiced these and other complaints (Margalef, 1980, 1991), being worried about the way the Lotka-Volterra approach has gone. Populations are treated as continuous variables and not enough attention was given to space and thermodynamics. The low reputation in which succession theory has fallen might show the lack of feeling for historical processes.

One of the subliminal reasons for the success of the word ecosystem may have been in the magic involved in the suffix “-system.” Without going more formally into the concept, system implies a relatively close frame of reference for elements and events that play against each other and are bound together in a flexible way. Systems extend over space and time and can be mentally dissected into subsystems of different degrees of coherence, persistence, and flexibility. To set boundaries to any systems is a job for the observer, usually motivated by the convenience of the moment.

Concepts like matter and energy historical change need to be used in a consistent way. Others like ecosystem or succession are less precise or can be redefined by any “qualified” ecologist. It seems it would be easier to accept individuals as the smallest units to work with, but it is not so, because of the existence of such proteiform systems unified by common secretions as mucilages and sheats (stromatolithes), wood (vascular plants, in general, best exemplified by trees), materials like wax or the materials that build the constructions of termites, and even mortar and concrete in humans. This adds pungency to the task of defining boundaries.

2.2 Constraints of the Physical World

Passage of time is associated with the irreversible changes studied in thermodynamics. Entropy is a concept that has to be used with care: the increase of its value, measured in a conventional way, becomes an index of total physical change, but does not anticipate ho...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents
• preface
• Chapter 1 Introduction
• Chapter 2 Exosomatic Structures and Captive Energies Relevant in Succession and Evolution
• Chapter 3 How Light and Nutrients Affect Life in a Closed Bottle
• Chapter 4 Emergy Accounting of Human-Dominated, Large-Scale Ecosystems
• Chapter 5 Thermodynamics and Theory of Stability
• Chapter 6 Application of Thermodynamic Concepts to Real Ecosystems: Anthropogenic Impact and Agriculture
• Chapter 7 The Thermodynamic Concept: Exergy
• Chapter 8 Entropy and Exergy Principles in Living Systems
• Chapter 9 Exergy and the Emergence of Multidimensional System Orientation
• Chapter 10 Thermodynamics and Ecology: Far from Thermodynamic Equilibrium
• Chapter 11 Imperfect Symmetry: Action Principles in Ecology and Evolution
• Chapter 12 The Third Law of Thermodynamics Applied in Ecosystem Theory
• Chapter 13 A Tentative Fourth Law of Thermodynamics
• Chapter 14 Thermodynamics of the Biosphere
• Index