Climate Change Impacts on Freshwater Ecosystems E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 632

Veröffentlichungsjahr: 2011

Beschreibung

This text examines the impact of climate change on freshwater ecosystems, past, present and future. It especially considers the interactions between climate change and other drivers of change including hydromorphological modification, nutrient loading, acid deposition and contamination by toxic substances using evidence from palaeolimnology, time-series analysis, space-for-time substitution, laboratory and field experiments and process modelling. The book evaluates these processes in relation to extreme events, seasonal changes in ecosystems, trends over decadal-scale time periods, mitigation strategies and ecosystem recovery.

The book is also concerned with how aspects of hydrophysical, hydrochemical and ecological change can be used as early indicators of climate change in aquatic ecosystems and it addresses the implications of future climate change for freshwater ecosystem management at the catchment scale.

This is an ideal book for the scientific research community, but is also accessible to Masters and senior undergraduate students.

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Library of Congress Cataloging-in-Publication Data

Climate change impacts on freshwater ecosystems / edited by Martin Kernan, Rick Battarbee and Brian Moss.

p. cm.

Includes bibliographical references and index.

ISBN 978-1-4051-7913-3 (hardback)

1. Freshwater habitats. 2. Freshwater ecology. 3. Climatic changes–Environmental aspects. I. Kernan, M. R. II. Battarbee, R. W. III. Moss, Brian, 1943–

QH541.5.F7C65 2010

577.6′22–dc22

2010016420

A catalogue record for this book is available from the British Library.

Set in 10.5/12pt Classical Garamond by SPi Publisher Services, Pondicherry, India

Contents

Preface

Acknowledgements

Contributors

1 Introduction

Changing climate and a changing planet

Changing ideas on planetary function

Water and the freshwater biota

Euro-limpacs, European freshwater systems and approaches to investigation

Applications and the Water Framework Directive

2 Aquatic Ecosystem Variability and Climate Change – A Palaeoecological Perspective

Introduction

Climate over the Holocene

Multi-millennial scale change

Centennial to millennial scale

Seasonal, inter-annual and decadal change

Recent change

Conclusions

3 Direct Impacts of Climate Change on Freshwater Ecosystems

Introduction

Physical impacts

Chemical impacts

Conclusions

4 Climate Change and the Hydrology and Morphology of Freshwater Ecosystems

Introduction

Predicted changes in land use

Effects of climate change at the catchment scale

The effects of climate change on hydraulics and morphology at the reach scale

Effects of climate change on hydraulic conditions and channel morphology at the habitat scale

The effects of climate change on stream and river restoration success

Conclusions

5 Monitoring the Responses of Freshwater Ecosystems to Climate Change

Introduction

Climate change impacts on the biota of lakes

Climate change impacts on the biota of rivers

Climate change impacts on the biota of wetlands

Conclusions

6 Interaction of Climate Change and Eutrophication

Introduction

Changes in trophic structure

Mesocosm experiments

Stream and wetland experiments at paired sites

Palaeolimnology and modelling

Synthesis

Conclusion

7 Interaction of Climate Change and Acid Deposition

Introduction

Effects of climate change on nitrate leaching

Dissolved organic carbon (DOC)

Saharan dust

Effects of climate warming on soil chemical processes

Modelling the combined effects of climate change and acid deposition

Effects on aquatic biota

Conclusions

8 Distribution of Persistent Organic Pollutants and Mercury in Freshwater Ecosystems Under Changing Climate Conditions

Introduction

Organohalogen compounds

Polycyclic aromatic hydrocarbons

Mercury

The effects of temperature increases

The effects of changes in precipitation

Anthropogenic effects associated with water management

Conclusions

9 Climate Change: Defining Reference Conditions and Restoring Freshwater Ecosystems

Introduction

Detecting recovery with changing baseline conditions

Global change and restoration

Conclusions

10 Modelling Catchment-Scale Responses to Climate Change

Introduction

The Euro-limpacs modelling strategy

Dynamic models

Linking models

Uncertainty

Conclusions

11 Tools for Better Decision Making: Bridges from science to policy

Introduction – Decision making in the context of climate change

Tools for decision making and their bases

Transfer of science into policy

The role of Decision Support Systems

Conclusions

12 What of the Future?

Introduction

The Arctic/Boreal zone

The mid continental latitudes

Peninsulas and islands

The Mediterranean zone

High mountain zone

Index

Preface

The evidence that greenhouse gas emissions, primarily from fossil fuel combustion, is and will increasingly be a principal cause of climate change has been compelling for some time. Although uncertainties remain, the threat is sufficiently real for research now to focus not only on the climate system itself but also on how changes in the climate system in future might affect the functioning of natural ecosystems.

In this book, we are concerned with how climate change might affect freshwater ecosystems. The ideas and examples presented in the book stem largely from the ‘Euro-limpacs’ project, a major EU-funded project on ‘the impact of global change on European freshwater ecosystems’. Euro-limpacs brought together lake, river and wetland scientists from across Europe to assess not only the direct impacts of climate change on freshwaters but also its potential indirect impact through interactions with other stresses such as changes in hydromorphology, nutrient loading, acid deposition and toxic substance exposure.

A wide variety of approaches was used in the project ranging from the analysis of lake sediment and long-term instrumental records to identify past impacts of climate change, to the use of experiments, space-for-time substitution and modelling to assess what might happen in future under different climate scenarios.

The project also considered the implications of future climate change for the management of freshwater ecosystems in Europe, especially the extent to which current policies and practices designed to improve the ecological status of freshwater ecosystems need to be modified in light of projected future climate change.

This book brings together the key results from the project. Its structure follows the design of the Euro-limpacs project, first assessing the probable effects of climate change and then considering management issues.

Richard W. Battarbee

Acknowledgements

We are very grateful to Gene Likens and Curtis Richardson for encouraging us to write this book. We acknowledge European Union 6th Framework RTD programme which provided the funding for Euro-limpacs (EU Contract No. GOCE-CT-2003-505540). We would like to thank our EU project manager, Christos Fragakis, for his support throughout the 5 years of the project. We owe our considerable gratitude to the many participants involved in Euro-limpacs who provided the data and analyses underpinning much of this book. From UCL, we would like to thank Cath D’Alton for her efforts with the diagrams, and Catherine Rose and Katy Wilson for the invaluable help they provided the editorial team in putting the manuscripts together. We would also like to thank those colleagues who provided anonymous reviews for each of the chapters. We dedicate the volume to the very many scientists in Euro-limpacs who are not included as authors in the book but who contributed to the success of Euro-limpacs and whose work is drawn upon throughout the book.

Contributors

Julian Aherne

Environment & Resource Studies, Trent University, Peterborough, ON, Canada

Hans Estrup Andersen

NERI, Aarhus University, Silkeborg, Denmark

Tom Barker

Institute for Sustainable Water, Integrated Management, and Ecosystem Research, University of Liverpool, Liverpool, UK

Richard W. Battarbee

Environmental Change Research Centre, Department of Geography, University College London, London, UK

Helen Bennion

Environmental Change Research Centre, University College London, London, UK

Ekin Birol

International Food Policy Research Institute, Washington, DC, USA

Kevin Bishop

Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden

Karel Brabec

Faculty of Science, Masaryk University, Brno, Czech Republic

Laetitia Buisson

Laboratoire Evolution et Diversité Biologique, Université Paul Sabatier, Toulouse, France

Dan Butterfield

Department of Geography, University of Reading, Reading, UK

Laurence Carvalho

Centre for Ecology and Hydrology, Midlothian, UK

Jordi Catalan

CEAB-CSIC, Blanes, Spain

Luc DeMeester

Laboratory of Aquatic Ecology and Evolutionary Biology, KULeuven, Leuven, Belgium

Peter J. Dillon

Environment & Resource Studies, Trent University, Peterborough, ON, Canada

Martin Erlandsson

Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden

Chris D. Evans

Centre for Ecology and Hydrology, Environment Centre Wales,

Bangor, UK

Pilar Fernandez

Department of Environmental Chemistry, Institute of Environmental Assessment and Water Research, Barcelona, Spain

Heidrun Feuchtmayr

Centre for Ecology and Hydrology, Lancaster Environment Centre, Lancaster, UK

Martin Forsius

Ecosystem Change Unit, Natural Environment Centre, Finnish Environment Institute, Helsinki, Finland

Nikolai Friberg

Department of Freshwater Ecology, National Environmental Research Institute, Aarhus University, Silkeborg, Denmark

Mark O. Gessner

Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science & Technology, Dubendorf, Switzerland and Institute of Integrative Biology, ETH Zurich, Zurich, Switzerland

Wolfram Graf

Department Water-Atmosphere-Environment, Institute of Hydrobiology and Aquatic Ecosystem Management, BOKU–University of Natural Resources and Applied Life Sciences, Vienna, Austria

Gäel Grenouillet

Laboratoire Evolution et Diversité Biologique, Université Paul Sabatier, Toulouse, France

Joan O. Grimalt

Department of Environmental Chemistry, Institute of Environmental Assessment and Water Research, Barcelona, Spain

Alexandra Haidekker

Department of Applied Zoology/Hydrobiology, Institute of Biology, University of Duisburg–Essen, Essen, Germany

David W. Hardekopf

Institute of Environmental Studies, Charles University in Prague, Prague, Czech Republic

Mariet Hefting

Ecology and Biodiversity, Institute of Environmental Biology, Utrecht University, Utrecht, The Netherlands

Rachel C. Helliwell

Macaulay Instititute, Aberdeen, UK

Daniel Hering

Department of Applied Zoology/Hydrobiology, Institute of Biology, University of Duisburg–Essen, Essen, Germany

Thomas Horlitz

Entera, Hannover, Germany

Jakub Hruška

Czech Geolological Survey, Prague, Czech Republic

Mike Hutchins

Centre for Ecology and Hydrology, Wallingford, Oxon, UK

Sonja C. Jähnig

Limnology and Conservation Department, Natural History Museum Senckenberg, University of Duisburg-Essen, Gelnhausen, Germany

Ron Janssen

Department of Spatial Analysis and Decision Support, Institute for Environmental Studies, VU University Amsterdam, Amsterdam, The Netherlands

Erik Jeppesen

Department of Freshwater Ecology, National Environmental Research Institute, Aarhus University, Silkeborg, Denmark

Richard K. Johnson

Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden

Philip J. Jones

Centre for Agricultural Strategy, School of Agriculture, Policy and Development, The University of Reading, Reading, UK

Øyvind Kaste

Norwegian Institute for Water Research, Southern Branch, Grimstad, Norway

Martin Kernan

Environmental Change Research Centre, Department of Geography, University College London, London, UK

Jií Kopáek

Biological Centre ASCR, Institute of Hydrobiology, Ceske Budejovice, Czech Republic

Phoebe Koundouri

Department of International and European Economic Studies, Athens University of Economics and Business, Athens, Greece

Pavel Krám

Czech Geolological Survey, Prague, Czech Republic

Hjalmar Laudon

Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden

Torbden L. Lauridsen

Department of Freshwater Ecology, National Environmental Research Institute, Aarhus University, Silkeborg, Denmark

Lone Liboriussen

Department of Freshwater Ecology, National Environmental Research Institute, Aarhus University, Silkeborg, Denmark

Conor Linstead

Institute for Sustainable Water, Integrated Management, and Ecosystem Research, University of Liverpool, Liverpool, UK

David M. Livingstone

Department of Water Resources and Drinking Water, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland

Armin Lorenz

Department of Applied Zoology/Hydrobiology, Institute of Biology, University of Duisburg–Essen, Essen, Germany

Hilmar J. Malmquist

Natural History Museum of Kópavogur, Kópavogur, Iceland

Edward Maltby

Institute for Sustainable Water, Integrated Management, and Ecosystem Research, University of Liverpool, Liverpool, UK

Linda May

Centre for Ecology and Hydrology, Midlothian, UK

Mariana Meerhoff

Department of Freshwater Ecology, National Environmental Research Institute, Aarhus University, Silkeborg, Denmark and Grupo de Ecología y Rehabilitación de Sistemas Acuáticos, Departamento de Ecología, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay

Filip Moldan

Swedish Environmental Research Institute IVL, Gothenburg, Sweden

Don Monteith

Centre for Ecology & Hydrology, Lancaster Environment Centre, Lancaster, Lancashire, UK

Brian Moss

Institute for Sustainable Water, Integrated Management and Ecosystem Research, University of Liverpool, Liverpool, UK

John Munthe

IVL Swedish Environmental Research Institute, Gothenburg, Sweden

John Murphy

FBA River Laboratory, The School of Biological and Chemical Sciences, Queen Mary, University of London, Wareham, Dorset, UK

Ulrike Nickus

Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria

Jon S. Olafsson

Institute of Freshwater Fisheries, Reykjavik, Iceland

Helle Ørsted Nielsen

Department of Policy Analysis, National Environmental Research Institute, University of Aarhus, Roende, Denmark

Benjami Piña

Department of Environmental Chemistry, Institute of Environmental Assessment and Water Research, Barcelona, Spain

Katri Rankinen

Finnish Environment Institute, Helsinki, Finland

Kyriaki Remoundou

Department of International and European Economic Studies, Athens University of Economics and Business, Athens, Greece

Michela Rogora

Institute of Ecosystem Study, CNR, Verbania, Italy

Neil L. Rose

Environmental Change Research Centre, University College London, London, UK

Leonard Sandin

Department of Aquatic Sciences & Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden

Astrid Schmidt-Kloiber

Department Water-Atmosphere-Environment, Institute of Hydrobiology and Aquatic Ecosystem Management, BOKU–University of Natural Resources and Applied Life Sciences, Vienna, Austria

Anne Merete S. Sjøeng

Norwegian Institute for Water Research, Oslo, Norway

Richard A. Skeffington

Department of Geography, University of Reading, Reading, UK

Merel B. Soons

Ecology and Biodiversity Group, Institute of Environmental Biology, Utrecht University, Utrecht, The Netherlands

Sonja Stendera

Department of Aquatic Sciences & Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden

Hansjörg Thies

Institute of Ecology, University of Innsbruck, Innsbruck, Austria

Piet F.M. Verdonschot

Freshwater Ecology, Alterra, Centre for Ecosystem Studies, Wageningen, The Netherlands

Jos T.A. Verhoeven

Ecology and Biodiversity Group, Institute of Environmental Biology, Utrecht University, Utrecht, The Netherlands andrew J. Wade

Department of Geography, School of Human and Environmental Sciences, The University of Reading, Reading, UK

Paul G. Whitehead

Department of Geography, School of Human and Environmental Sciences, The University of Reading, Reading, UK

Heleen A. de Wit

Norwegian Institute for Water Research, Oslo, Norway

Richard F. Wright

Norwegian Institute for Water Research, Oslo, Norway

1

Introduction

Brian Moss, Richard W. Battarbee and Martin Kernan

Changing climate and a changing planet

In June 2008, one of us chanced upon a shepherd repairing his five-ft high (he didn’t deal in metres) dry limestone walls on the uplands near Asby Scar in Cumbria, north-west England. We exchanged pleasantries that inevitably, this was Britain after all, embraced the weather. It was a bright warm day. But ‘Bleak in winter up here’ I said. ‘Not so much in the past fifteen years’ he replied, ‘Before that the snow lay in drifts hiding the walls, but not any more’. It was yet another anecdotal sliver of evidence to complement the mass of information assembled by the Intergovernmental Panel on Climate Change (IPCC 2007) on the reality of global warming.

That Fourth Report of the IPCC summarized changes to date (Fig 1.1) that included an almost 1°C increase in the northern hemisphere mean air temperature, over the years since the industrial revolution accelerated the yet unabated burning of fossil fuels. It presented evidence that these processes were related and that we could have high confidence that the temperature rise was largely human-induced. Linked with it have been changes in the distribution of rainfall, with generally more falling in winter or wet seasons and less in the summer and dry seasons. There has been an increase in sea level of about 20 cm, largely due to thermal expansion of the huge mass of oceanic water, to which the melting of the mountain and polar glaciers is now making a contribution. And there has been an increase in the frequency of extreme weather events, such as cyclones, droughts and floods. In turn, there have been numerous records of changes in the phenology of species (Sparks & Carey 1995; Roy & Sparks 2000; Parmesan & Yohe 2003; Hays et al. 2005; Adrian et al. 2006) and a steady migration polewards of a variety of the more mobile species (Walther et al. 2002; Root et al. 2003).

Figure 1.1 Summary of climate and sea-level change to date. (a) Global average temperature. (b) Global average sea level. (c) Northern hemisphere snow cover. (From Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (eds S. Solomon, M. Manning, Z. Chen, et al.). Cambridge University Press, Cambridge and New York.)

Climate is a master variable, and all activity on this planet eventually depends upon it. It determines the overall structure of natural biomes, be they deserts, grasslands or deciduous or evergreen forests. It has driven the evolution of life histories, the dynamics of food webs and the development of homeostases. It fixes the circulation of the oceans, the availability of nutrients to the plankton community, the onset of rain and ripening for crops and the reflectance of radiation from the Poles. It manifests itself in the day-to-day weather, a preoccupation of everyone, not just the British. It is the greatest determinant of leisure travel, and, in its extremes, a source of extreme misery to match its delights of balmy summer days, exciting ski runs and the fresh spring rain. A major change in climate is a very considerable issue.

Changing ideas on planetary function

Ecologists have long sought to explain the huge variation of natural systems: the tapestry of weather and soil-related detail on land and physical and chemical detail in water that fits into a grand pattern of climate zones. G.E. Hutchinson (1965) (Fig 1.2) linked the ways that organisms evolve, as both grand and local patterns change, in his metaphor of the ecological (or environmental) theatre and the evolutionary play. His concept, in the 1960s, was very much one of the players adjusting to the nature of the theatre and then to each other. The generally accepted paradigm was that the physicochemical setting, the geology and climate, determined the biology and ecology of living organisms. Twenty years later, James Lovelock (1988) (Fig 1.2) began an overturning of this by a spectroscopic examination of the chemistry of the atmospheres of Earth and its sister planets and a study of Earth’s oceans. He calculated that the chemical state of Earth was very far from that expected by a simple chemical equilibrium of the available elements, and inferred that it was determined, and maintained, by the activities of living organisms rather than physicochemically imposed upon them for their response. Moreover, the state was regulated within the limits between which our particular biochemical system could persist. There is still controversy about the underlying mechanism of the regulation, but not about its existence. Such a change in paradigm is key to our understanding of the mutual interactions of climate and living organisms that this book is about. By altering our atmosphere, we challenge the entire biosphere system, and although we can predict some immediate physical effects, we have little idea about what the ultimate biological consequences might be.

Figure 1.2 (a) G.E. Hutchinson and (b) James Lovelock.

The IPCC has made a range of predictions about how climate will change over the regions of the Earth, based on a range of assumptions about how human societies will react as the first of the changes are experienced. There is a problem, however, in these predictions. They all hold to the former model of living systems responding to imposed conditions. They are models of simple physicochemical control. They do not allow for the likelihood of positive ecological feedbacks. Temperature influences many biological processes, but not in a linear way. More usual is some sort of exponential relationship in which the process accelerates or decelerates to a point of death as temperature changes linearly. A key process in regulating the carbon dioxide content of the atmosphere is the storage of carbon as organic matter in soils and peat deposits or as calcite in the ocean sediments, derived from the scales of planktonic coccolithophorids or the matrices of corals (Lovelock 1988). If the temperature change induces more carbon dioxide or methane release, through increases of respiration using organic matter stored in soils and sediments, for example, or through inhibition of calcite formation in the walls of marine organisms, a positive feedback on further temperature increase may be induced and the greenhouse effect may be reinforced. Temperature changes predicted for the future may thus have been underestimated, and climate modellers are now attempting to rectify this.

The system that maintains the non-equilibrium, equable state of the planet is the biosphere. The biosphere has, for convenience, been divided up into atmosphere, hydrosphere and lithosphere: air, ocean and land. And the lithosphere is thought of in terms of biomes: tundra, coniferous forest, deciduous forest, tropical forest, scrub savannah, grassland and desert. In turn, these may be divided into constituent ecosystems, which Arthur Tansley (1935) defined as more or less self-contained systems of living organisms, and their biologically produced debris, in their physicochemical setting. In truth, this idea was an artefact of working in the greatly subdivided landscape of the British Isles, where several thousand years of human activity have entirely compartmented the landscape. Our upland shepherd, with his walls, in a sense influences our ecological as well as climatic thinking. For convenience we nonetheless talk of woodland, heath, saltmarsh, river and lake ecosystems. But the pristine biosphere was ultimately a continuum that adjusted mutually, gradually and in many dimensions to changing climatic and geological conditions, and in considering freshwaters in particular, the greatest understanding comes from seeing them as intimately linked with the land and atmosphere. It is sometimes convenient, however, for the process of accounting for change to see the parts rather than the whole.

A report as authoritative as that of the IPCC, the Millennium Ecosystem Assessment, appeared in 2005. It received much less publicity, for though weather is immediately noticeable to people everywhere, the fate of distant oceans, tundras and savannahs is not, unless you are a deep sea mariner, Inuit hunter or Masai herder. But major changes (Fig 1.3) have happened to most natural ecosystems, and are continuing to happen to most of them, as a result of climate change and also because of many other, independent drivers that depend on the workings of global economics and the needs of a rising population. It is expected that we will have lost over half of the world’s land ecosystems to agriculture or development by 2050. The urbanites may not be noticing this but the consequences will nonetheless be huge, for it is these natural ecosystems that regulate the nature of the biosphere. We have absolutely no idea how much of them can be damaged without serious consequences for human survival. All we know is that such systems, honed by the utterly ruthless mechanisms of natural selection to be as near fit for purpose as possible, are just as crucial to us, indeed much more fundamentally so, than the local grocer, filling station or hospital. The chemistry of the biosphere is the ultimate sine qua non of our existence. Damaged ecosystems, including all agricultural ones, do not store as much carbon as intact ones. James Lovelock’s contribution was to point this out.

Figure 1.3 Projected losses of major ecosystems and biomesa. (From Millennium Ecosystem Assessment 2005.)

We have responded rather oddly to the increasing damage we have caused by attempting to value in classical economic terms the goods and services we draw from ecosystems, to demonstrate their importance (Costanza et al. 1997; Balmford et al. 2002). This has been influential in drawing attention to their very great apparent value and in helping communicate with economists and politicians. But perhaps we have completely missed the point. They are not items that can be used, misused, repaired, ignored or traded at will. They are outside the current economic system. What they do in maintaining the equable state of the planet for all living organisms, including us, is so fundamental as to be priceless. It would be inconceivable, as William Shakespeare (1623) well knew 400 years ago, through the wonderful speech of Portia in The Merchant of Venice, to value the blood as a separate component of the body. What is sine qua non supersedes evaluation. Yet we damage the biosphere as casually as we throw away our rubbish, and in contemplating the hitherto effects of climate change, we fail to realize that the loss of ecosystems and the changing climate are mutually linked. Indeed, we blithely cost the damage of climate change (Stern 2006) as we cost the goods and services we are losing through application of the same approach of classical economics. We have failed to see the interaction of climate, ecology and equability. Our attempts to mitigate climate change, in a desperate bid to avoid disruption of our societies, may inevitably be doomed to failure unless we begin to see the whole picture and not just the components we find most convenient to our cash economy.

Water and the freshwater biota

Though the ultimate driver of climate change effects will be temperature, the immediate executive will be the availability of freshwater. Freshwater systems stitch together the biosphere through the hydrological cycle. The stitching, however, can become undone, and the surface freshwater component is perhaps the most vulnerable part of the hydrosphere. Living organisms absolutely need liquid water. The ability of liquid water to persist is a fundamental characteristic of a planet capable of supporting life based on carbon compounds. The creation of conditions allowing its existence is the ultimate triumph of the biosphere. The Earth in chemical equilibrium would be so hot as to bear only water vapour. Moreover, human history is, at bottom, an account of the availability of water for drinking, crop growing and sanitation. It follows from the effects of climate change through floods and droughts that the next century, even the next few decades, will likely see more disruption of human activities than has been experienced in the evolution of our species.

For the freshwater systems and organisms with which this book is concerned, the detailed effects of moderate climate change could vary from being disastrous to locally positive. In the absolute scale of temperature, water has its boiling and freezing points very close to the mean surface temperature of the Earth. In its evaporation and condensation, water is the operative liquid of the earth’s refrigerator. It follows that the denizens of freshwaters have had an evolutionary history in which their habitats have rather frequently frozen solid or evaporated to mud flats or rocky beds. Freshwater animals and plants are comparatively young in evolutionary terms for they have had repeatedly to recolonize newly constituted freshwaters from the land and the ocean following prolonged glaciation, volcanic disruption or periods of great aridity. They are creatures of continual disturbance (Milner 1996).

Some manifestations of this are that many aquatic insects and vascular plants retain land characteristics as adults or where they flower, respectively; the diversity of freshwaters is much lower, for example, lacking whole phyla, than that of the oceans; freshwater organisms may have particularly high rates of evolutionary change; resting spores and eggs to tide over inimical conditions are common (Pennak 1985). Marine organisms, in contrast, almost universally lack resting stages, for their medium, though changing in shape and depth, has persisted as a body of water for nearly 4 billion years. The longevity of freshwaters may sometimes be only weeks. The retention of adult flight allows movement for insects that cannot persist as resting eggs, and apart from fish, almost all the vertebrates associated with freshwaters are highly motile over land. Fish are vulnerable for few can survive drought, though they are adept at migration through river systems, using even the ocean as part of their life history in some cases. Some crustaceans, however, may respond genetically and very rapidly to thermal stress (van Doorslaer et al. 2007).

As climate changes, marine communities will have a continuity of habitat that will accommodate major changes in distribution, though for sedentary organisms like corals, the speed of change may cause severe difficulties. In contrast, land communities, subjected to more frequent drought and without the buffering medium of water, with its high specific heat, will be more vulnerable to extreme temperatures. But the freshwater biota might adjust most readily to climate change because of its preadaptation to disturbance. For them, however, there is a further complication. Freshwaters most immediately and most graphically reflect the many abuses an increasing human population, with its increasing demands for resources, increasing production of waste and rapidly accelerating ability to make changes through its technology, can impose. Freshwaters reflect all the activities that go on in their catchments, which means the entire land surface. Chemical and agricultural wastes, both dissolved and suspended, run into them or rain onto them. Rivers have been repeatedly used as cheap pipes to remove urban wastes. Floodplain wetlands have been embanked and drained so that their fertile soils might be cultivated. Fish communities, the main source of animal protein for many peoples, have been severely overfished. And the very ability of freshwater communities to accommodate change has led to the persistence of many introduced species that have sometimes become dominant and simplified the communities that they have invaded. Not surprisingly, the Millennium Ecosystem Assessment listed freshwaters as one of the most vulnerable of the ecosystems it considered (Fig 1.4). Exactly how freshwater habitats will change, how the adjustments of their communities will occur and what will be the detailed consequences of the changes for particular places and individual species are thus much more difficult to predict than if climate change were the only threat to them. Current attempts rest largely on expert opinion (Mooij et al. 2005). It is one role of this book to add to the factual basis for predictions.

Figure 1.4 Summary of effects of major drivers on major biomes. (From Millennium Ecosystem Assessment 2005.)

Euro-limpacs, European freshwater systems and approaches to investigation

Europe provides a huge range of inland waters, from the Greenland, Icelandic and mountain glaciers to the streams and lakes of the arider parts of Spain, from the small crater lakes of the Azores to the expanses of Lakes Ladoga, Mälaren and Maggiore and from the tiny headwater streams of the hills to the large, if not Amazonic, rivers of the Rhine and Danube. Of course, other continents contain an equal or greater variety, but Europe also offers the complication of major biological barriers to animal and plant movements in the Mediterranean, the Alps, the Baltic and the North Sea, the benefits of a long and sophisticated tradition of research in freshwater ecology, and a large concentration of freshwater scientists. Euro-limpacs, on which this book is based, has been a European-Union-funded, continent-wide research programme to further our understanding of the potential effects of climate change on freshwaters. It has contributed to our understanding of the direct physical and hydrological effects of warming in the past (Chapter 2) and present day (Chapters 3 and 4) and on the interactions with climate of nutrients (Chapter 6), acidity (Chapter 7) and toxic pollution (Chapter 7). It has looked at the implications for monitoring and restoration (Chapters 5 and 9) and the definition of reference conditions under the Water Framework Directive. Moreover, it has sought to use the results of these studies in modelling the future (Chapter 10) and in helping political organizations to make decisions on management (Chapter 11).

Euro-limpacs has been far from the last word, but it has contributed important advances, and its strength has been the wide range of approaches it has used. There is a nexus of stages in investigating any general phenomenon and climate change effects on freshwater systems are no exception. The first stage is simply in establishing their existence. There can be no doubt now that climate change is occurring and virtually no doubt that it has largely been caused by human activity. There is then a plethora of studies showing consequent effects (e.g. Carvalho & Kirika 2003; Berger et al. 2007), though, strictly speaking, it is rare for the consequence to be rigorously demonstrated. We are dealing with an unreplicated grand experiment with no control.

However, where changes occur in many different glaciers, rivers and lakes and where these correlate closely with changing temperatures or precipitation (Gerten & Adrian 2000; Straile 2002; Winder & Schindler 2004), there can be some confidence in the link. Such correlation, however, is made difficult because many other changes have occurred in freshwater systems over the same period as climate change, and most changes are ultimately caused by the increasing size, aspirations and technological development of human societies in the past 200 years or so.

The correlations of recent history can be placed in context by the reconstructions of the more distant past through analysis of lake and wetland sediments. The record is patchy and selective, and interpretations usually lack experimental validation, but where sediment and direct records have been compared over the past few decades, there is often a close relationship (Haworth 1980), and sophisticated statistical approaches (Birks 1998; Battarbee 2000) have been used to quantify the palaeoecological record.

For periods before the last few decades, or occasionally the last two centuries, where diary and documentary evidence exists, the sediment record is the only record and we must use it as efficiently as we can. The range of chemical and biological remains that can now be counted and calibrated against contemporary observations and sediments is very wide. It can be increasingly elaborated by the techniques of resurrection ecology where resting stages of invertebrates can be hatched and their changing characteristics and genome traced through a period of environmental change (Mergeay et al. 2004).

A parallel approach to palaeoecological studies is to use space-for-time investigation, where existing climate gradients provide different systems for examination. The gradient from Greenland to Greece in Europe provides a wide range of systems in which processes and food webs can be compared to predict how they might change as temperatures increase (Moss et al. 2004; Meerhof et al. 2007). There are, as with every approach, problems with this otherwise attractive endeavour. Not only does climate change along the gradient, but so do relief, geology and the intensity of human activity. Good design of observational schemes can correct for these by stratified random sampling, but one major source of variation, accidents of history, cannot. Glaciation and the nuances of biogeography impose differences that can only be judged. A formerly glaciated lake in Finland, with an Ice-Age-depleted, still recolonizing biota, may not respond to temperature increase in the same way as a long-established Mediterranean lake that may have been affected but not obliterated by the ice of the glacial period, 20,000 years ago, even if the Finnish lake eventually becomes as warm as the Mediterranean one now.

The next stage of investigation is to attempt to reproduce alleged effects through experimentation. Experiments can reveal mechanisms because the drivers of change can be controlled, and experimental designs and adequate replication allow the study of several simultaneous drivers. Experiments are thus potentially more powerful than comparative observations. They also compel the creation of mechanistic hypotheses that force the experimenter to think through the processes that are going on. But the scale of the experiment is important in ecology. Whole-system experiments (Carpenter et al. 2001) (clear-felled versus undisturbed sub-catchments of a forested river system, lakes subdivided by curtains and parallel-engineered river channels) are ideal but liable to pseudoreplication because the experiments are so expensive, and the subjects so individual, that generally only one system can be handled at a time. In contrast, experimental laboratory microcosms (Petchey et al. 1999) can be replicated extensively but lack reality. The fashion of using micro-organism communities to mimic large-scale systems (Benton et al. 2007) is attractive but perhaps mostly to theoreticians.

The compromise is to use subsystems of real communities: mesocosms in lakes, artificial river channels or plots in wetlands, or mesocosm tanks big enough to contain all or almost all of the structures and food-web levels of a system (McKee et al. 2000, 2002, 2003; Liboriussen et al. 2005). Usually ‘almost all’ is apposite, for the top predators of a fish community need much more space than is possible in replicable mesocosms, and the complete complexity of a natural system, which, in rivers, for example, might involve interactions with large land mammals (Terborgh 1988; Ripple & Beschta 2004) and tonnages of dead timber, is beyond contemplation.

Another compromise is to do the experiments on simulated systems or models using computer technology. This is, of course, the approach taken by the IPCC in modelling future climate change. Per se it is relatively inexpensive, but the models are reflections of the data input to them. If there are unsuspected factors involved, these cannot be included and the output of the model is a reflection of the perceptions of its perpetrators. The same is true of observational techniques and practical experiments. Through choice of variables or of initial experimental conditions, the conclusions are partly predetermined. Nonetheless, the failures of both models and experiments to replicate reality are valuable indicators of what might be missing from their designs. Such gaps are inexpensive to plug in modelling, if not in repeated large-scale experiments, and the behaviour of whole river systems, regions or the biosphere can ultimately be only the province of modelling.

The organization of Euro-limpacs reflected these advantages and uncertainties by using a range of approaches. It had to build on existing experience and facilities for the most part and could not achieve the ideal of using all the approaches on a single habitat and a single aspect of climate change, even if such singularity exists. Understanding increases nonetheless, even if tidy systems of operating are inevitably confounded by the realities of funding and personal preferences. In the end, opinion will depend on expert judgement based on all lines of evidence, for precise prediction is only possible for simple systems, and nothing in earth system science, with its underpinning of living organisms, not least the human ones, is remotely simple.

Applications and the Water Framework Directive

Euro-limpacs included substantial components concerning the application of the emerging scientific understanding. In Europe at present, water management is very much focussed on the Water Framework Directive (EC/2000/60). The Directive changes the previous approach to monitoring waters in Europe by emphasising a whole-basin approach and by requiring determination and restoration of ecological quality, as opposed simply to chemical water quality. This must be done with respect to reference systems, which are defined in the Directive as those unaltered or only negligibly altered by human activity. There are few, if any, such systems left in Europe, so great has been the impact of large population densities over several centuries, so determination of the schemes to determine ecological quality is problematic. Nonetheless, tools for determining the status of phytoplankton, aquatic plants, macroinvertebrates and fish are being developed (UKTAG 2007), often using particular indicator species or families. Climate change will inevitably upset these schemes as species become eliminated or new ones move into previous cooler habitats.

There is also the underlying issue that since climate is now strongly influenced by people, the establishment of reference pristine standards has become conceptually impossible (Moss 2007, 2008). These issues are discussed in Chapter 9. The Directive also requires restoration of aquatic systems to good ecological status, defined as only slightly different from the high ecological status of the reference standards. At this stage, the uncertainties become so great that schemes are needed to help the appraisal of the available scientific information by agencies and governments, and this issue is considered in Chapter 11.

Several reports have pointed out the economic consequences of climate change. The Stern Report (2006) concluded that climate change could be mitigated at the cost of a substantial but affordable sum, if there were reaction now, but much greater sums if there were delays. Governments have attempted to put in place mechanisms to generate energy by means other than burning fossil fuels, devices to encourage energy conservation and schemes to offset carbon usage by paying for trees to be planted. By and large none of these schemes has yet reduced fossil fuel consumption (Monbiot 2007) and it seems very likely that temperatures will rise later this century by several degrees. A 2°C rise may be held at a concentration of greenhouse gases equivalent to about 480 ppm carbon dioxide compared with the current value of 380 ppm carbon dioxide. It seems, however, more likely that concentrations will rise to at least 550 ppm, denoting a temperature rise of 3°C–4°C, which will bring many problems (Fig 1.5). The possibilities of biological feedback mechanisms have not, of course, been factored into any of these targets.

Figure 1.5 Projected effects of increasing temperatures on natural and human systems. (From Stern 2006.)

A glance through any daily newspaper will reveal several pages of business and sports news that change in detail but not overall content. Pages of other news will change in scope more than business and sport and increasingly a consistent though still very small element of these will concern environmental issues. We might anticipate a time, however, when this formula will change. Sport will undoubtedly retain its hegemony, but the unfolding impacts of resource depletion, waste accumulation, ecosystem destruction, population increase and climate change must eventually displace the multi-page minutiae of stocks, shares, executive salaries and the fate of companies. A new economics will need to be in place or we may be in our final human throes. But for the moment, this book essentially takes the emerging evidence from the physical to the sociological and applies expert judgement to it to assess the interplay between freshwaters and human societies as the climate drama, now just past the Prologue, enfolds. It brings together the major concepts of Hutchinson, Lovelock and Tansley in a crucial act of the evolutionary play as the theatre itself begins to change somewhat ominously.

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2

Aquatic Ecosystem Variability and Climate Change – A Palaeoecological Perspective

Richard W. Battarbee

Introduction

Over the last decade it has become increasingly clear that there is a strong human contribution to global warming (IPCC 2007). Antarctic ice-core records (e.g. Petit et al. 1999; EPICA 2004) show that greenhouse gas concentrations are already higher than at any time in the last 750,000 years, temperatures in the northern hemisphere are now on average probably higher than the previous 1000 years (Mann et al. 1998) and climate models can only simulate temperatures accurately over the last 150 years if greenhouse gases are included as a forcing mechanism (Stott et al. 2001).

Evidence is also accumulating to suggest that changes in natural systems that can be unambiguously attributed to rising temperatures are also occurring. In particular, most mountain glaciers across the world are receding (Oerlemans 2005), there is evidence that the collapse of Antarctic ice shelves in the Antarctic is unprecedented in the Holocene (Domack et al. 2005) and ecological changes are taking place in remote Arctic lakes that appear to be outside the range of their natural variability (Douglas et al. 1994).

The evidence for human impact on the climate system is thought now to be so compelling that Crutzen has argued that the recent period of earth history dating from the late 18th century and associated with a significant rise in atmospheric CO2 manifested in Antarctic ice cores (Petit et al. 1999) should be given a new geological name, the Anthropocene (Crutzen & Stoermer 2000). Indeed Ruddiman (2003) has argued that human activity may have affected atmospheric greenhouse gas concentrations even earlier as a result of deforestation and land-cover change associated with early agriculture in the early to middle Holocene, approximately 5–8000 years ago.

Yet, despite the strength of the evidence for human-induced change, climate-change sceptics still remain, arguing that the role of natural variability is being underestimated. It can indeed be maintained that changes in aquatic ecosystems described in this book, as shown by long-term records (e.g. ice-cover loss on lakes over the last two centuries (Magnuson et al. 2000) or the observed increase in river and lake temperatures over recent decades (Hari et al. 2006) ), are still within the long-term natural range of the climate system, if viewed on centennial timescales. Despite their quality, even these multi-decadal long-term data sets cover too short a time span to differentiate a recent global warming component from changes that might be caused by natural variability.

In this chapter, I examine evidence for changes in aquatic ecosystems from the palaeoecological record in an attempt to define the natural variability of aquatic systems as a baseline against which the impact of recent and projected future climate changes can be assessed. I also examine the impact of past warmer periods on surface waters as a guide to what might happen in future, although once global mean temperatures exceed +2°C, the past is unlikely to hold useful analogues as temperatures greater than about +2°C have not occurred previously for at least 100,000 years.

I describe briefly how climate has changed over the Holocene and then summarize palaeoecological evidence for the response of freshwater ecosystems, principally lakes, to climate change over different timescales, from multi-millennial to seasonal. Two principal effects of climate change are described: those that are driven by changes in temperature and those that are driven by changes in effective moisture (precipitation minus evaporation). These are considered in both high- and low-latitude settings. The chapter ends by setting evidence for greenhouse-gas-forced climate change against other causes of ecological change, specifically those associated with human activity. Note, however, that the evidence presented here for the effects of past climate change on freshwater ecosystems is entirely inferential, as inevitably is the case for all palaeoecological interpretations. Moreover, in some cases, it is difficult to avoid problems of circular reasoning as changes in the biological history of lakes revealed from sediment records are often used to reconstruct past climate changes rather than the response of lake ecosystems to climate change.

Climate over the Holocene

How far back should we go in considering past climate change and its impacts? Although most lakes in high latitudes are relatively young, formed after the recession of the last ice sheets approximately 15,000–10,000 years ago, lakes outside the glacial margin, mainly but not exclusively at lower latitudes, have survived repeated switches from glacial to interglacial conditions and contain sediment records spanning many hundreds of thousand years. A few (e.g. Lake Baikal) span the entire Pleistocene period and are of considerable interest amongst palaeoclimatologists as well as palaeoecologists as rare archives of environmental change, comparable to those found in deep oceans, and as in situ centres of evolution. Here I restrict the time span under consideration to the Holocene period, approximately the last 11,500 years. The onset of the Holocene is marked very clearly in Europe by a very rapid increase in air temperature and a rapid recession of land ice, clearly seen in the sediments of most lakes in Northern Europe by a switch from clays to organic lake muds. Adjustments in the ‘earth system’ to post-glacial warming were more gradual: global ice cover shrank, the land surface, previously depressed by the weight of ice, rose, sea level rose as a result of global ice melting, the ocean circulation pattern established a new equilibrium, new soils developed and plants and animals returned from glacial refugia to occupy land areas similar to those occupied in the previous interglacial period (cf. Roberts 1998). By approximately 8000 years ago, new ‘boundary conditions’ for the natural world, not significantly different from those of the present day, were established (Fig 2.1).

Figure 2.1 Schematic diagram of major changes since 18,000 years before present of external forcing (solar radiation (S)) and internal boundary conditions (land ice, sea-surface temperature (SST), atmospheric carbon dioxide concentration and excess glacial aerosol) used for climate simulations. (Modified from Kutzbach & Street-Perrott 1985.)

Overall, the Holocene period is a warm stage, contrasting to the previous cold (or glacial) period but similar in many respects to preceding warm (or interglacial) periods, the last of which is referred to in Europe as the Eemian, approximately 130–105,000 years ago (cf. Drysdale et al. 2005). The Holocene, therefore, is considered to be yet another interglacial period, differing from previous ones principally because of the impact of people in practising agriculture (causing land-cover change) and in developing industrial processes (causing pollution), which together have significantly and progressively, over approximately the last 5000 years, strongly modified both terrestrial and aquatic ecosystems. It is now also entirely possible that human activity has modified or is modifying the climate system itself, even to an extent that a return to glacial conditions, as considered inevitable only a decade ago, may be prevented by the current and projected rise in greenhouse gas concentrations (Crucifix 2008).

Although the Holocene is a warm period, on average 7°C–8°C higher than the mean for the last glacial period (cf. Lowe & Walker 1997), there have been significant changes in climate within it, driven by a range of different natural forcing mechanisms. These have operated on different timescales and have affected, and will continue to affect, both temperature and precipitation patterns across the world. The principal external forcings are (i) orbital change, mainly related to changes in precessional changes of the earth’s axis as it orbits the sun; (ii) solar variability, related to cyclical variations in solar activity through time; and (iii) volcanic activity, related to the scattering and absorption of incoming radiation caused by changes in volcanic dust concentrations in the stratosphere. Climate also varies in a quasi-cyclical way on a range of timescales purely in response to the internal dynamics of the climate system itself. The best known and important of these modes of internal variability is the Southern Ocean Oscillation, ENSO, although in higher latitudes of the northern hemisphere, the Arctic Oscillation (AO) and the associated North Atlantic Oscillation (NAO) can be equally or more important. Changes in these modes can also occur and can be influenced by changes in external forcing (e.g. Shindell et al. 2004). In addition to these natural forcings, there is now very good evidence (cf. IPCC 2007) that anthropogenically produced greenhouse gases are playing an important role in altering the climate system and are beginning to warm the planet, potentially to higher temperatures than have hitherto been caused by natural factors. However, such is the complexity and variability of the climate system that attributing changes in natural ecosystems at the present time solely to a rise in greenhouse gas concentrations is not easy (cf. Battarbee & Binney 2008).

Multi-millennial scale change

Temperate latitudes

Palaeoclimate reconstructions of sea-surface temperatures provide evidence of warmer conditions than at present prevailing in the northern hemisphere in the early Holocene (e.g. Jansen et al. 2008). The early warming followed by a progressive cooling to the present day agrees closely with the expected decrease in northern hemisphere insolation based on known precessional changes in the orbit of the earth around the sun. Perihelion (when the earth’s orbit takes it closest to the sun) now occurs in January, whereas it occurred in July 11,000 years ago. Although proxy records vary, the cooling experienced in medium to high latitudes suggests a decrease in mean annual temperature over the Holocene of approximately 2°C (e.g. Seppä et al. 2005) sufficient to cause major southwards shift in the northern limit of plants and animals, including a depression of the northern timber line (Birks & Birks 2003). However, demonstrating the response of aquatic organisms to this long-term cooling is not easy, partly because human activity, in clearing forests and developing agricultural practices since the beginning of the Neolithic period, has masked the impact of climate change, and partly because changes in plant and animal records in lake sediments, especially sediments from shallow lakes, are also influenced by hydroseral processes that take place naturally.

For example, the contraction of the northern boundary of the water chestnut (Trapa natans), a thermophilous floating leaved aquatic macrophyte, during the Holocene, was thought to be the result of, and provide good evidence for, Holocene cooling (cf. Alhonen 1964). Korhola and Tikkanen (1997), however, have suggested from a detailed study of shallow lake sediments in Finland that the loss of Trapa natans may have been caused by changes in lake habitat as lakes gradually filled in and were transformed into peatland. Similar arguments can be made for the apparent decline in the abundance of other aquatic macrophytes such as Cladium mariscus (Conway 1942). The one aquatic fossil record that seems unambiguous in indicating a range response to Holocene cooling in Europe is the European pond turtle (Emys orbicularis, Fig 2.2). At the present day, the breeding range of this species centres on the Mediterranean, and its northern limit coincides closely with the 20°C isotherm. By contrast, its fossil record from the mid-Holocene indicates a distribution in Europe that included eastern England, Denmark and southern Sweden, where mean July temperatures today are close to 18°C (Stuart 1979), providing good evidence for the potential impact of the c. 2°C cooling over the last 5000 years suggested by climate models.

Figure 2.2 The European pond turtle (Emys orbicularis). (Photograph from Biopix.dk.)

Low latitudes