Geomorphology of Upland Peat: Erosion, Form and Landscape Change Martin Evans and Jeff Warburton Geomorphology of Upland Peat RGS-IBG Book Series The Royal Geographical Society (with the Institute of British Geographers) Book Series provides a forum for scholarly monographs and edited collections of academic papers at the leading edge of research in human and physical geography. The volumes are intended to make signifi cant contributions to the field in which they lie, and to be written in a manner acces- sible to the wider community of academic geographers. Some volumes will disseminate current geographical research reported at conferences or sessions convened by Research Groups of the Society. Some will be edited or authored by scholars from beyond the UK. All are designed to have an international readership and to both refl ect and stimulate the best current research within geography. The books will stand out in terms of: • the quality of research • their contribution to their research field • their likelihood to stimulate other research • being scholarly but accessible. For series guides go to www.blackwellpublishing.com/pdf/rgsibg.pdf Published Forthcoming Geomorphology of Upland Peat: Erosion, Form and Landscape Politicizing Consumption: Making the Global Self in an Unequal Change World Martin Evans and Jeff Warburton Clive Barnett, Nick Clarke, Paul Cloke and Spaces of Colonialism: Delhi’s Urban Governmentalities Alice Malpass Stephen Legg Living Through Decline: Surviving in the Places of the Post- Industrial Economy People/States/Territories Huw Beynon and Ray Hudson Rhys Jones Swept up Lives? Re-envisaging ‘the Homeless City’ Publics and the City Paul Cloke, Sarah Johnsen and Jon May Kurt Iveson Badlands of the Republic: Space, Politics and Urban Policy After the Three Italies: Wealth, Inequality and Industrial Change Mustafa Dikeç Mick Dunford and Lidia Greco Climate and Society in Colonial Mexico: A Study in Vulnerability Putting Workfare in Place Georgina H. Endfield Peter Sunley, Ron Martin and Corinne Nativel Resistance, Space and Political Identities Domicile and Diaspora David Featherstone Alison Blunt Complex Locations: Women’s Geographical Work and the Canon 1850–1970 Geographies and Moralities Avril Maddrell Edited by Roger Lee and David M. Smith Driving Spaces Military Geographies Peter Merriman Rachel Woodward Geochemical Sediments and Landscapes A New Deal for Transport? Edited by David J. Nash and Sue J. McLaren Edited by Iain Docherty and Jon Shaw Mental Health and Social Space: Toward Inclusionary Geographies? Geographies of British Modernity Hester Parr Edited by David Gilbert, David Matless and Brian Short Domesticating Neo-Liberalism: Social Exclusion and Spaces of Economic Practice in Post Socialism Lost Geographies of Power Adrian Smith, Alison Stenning, Alena John Allen Rochovská and Dariusz S´wia˛tek Globalizing South China Value Chain Struggles: Compliance and Defi ance in Carolyn L. Cartier the Plantation Districts of South India Geomorphological Processes and Landscape Change: Britain in Jeffrey Neilson and Bill Pritchard the Last 1000 Years Edited by David L. Higgitt and E. Mark Lee Geomorphology of Upland Peat: Erosion, Form and Landscape Change Martin Evans and Jeff Warburton © 2007 by Martin Evans and Jeff Warburton BLACKWELL PUBLISHING 350 Main Street, Malden, MA 02148-5020, USA 9600 Garsington Road, Oxford OX4 2DQ, UK 550 Swanston Street, Carlton, Victoria 3053, Australia The right of Martin Evans and Jeff Warburton to be identifi ed as the Authors of this Work has been asserted in accordance with the UK Copyright, Designs, and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs, and Patents Act 1988, without the prior permission of the publisher. First published 2007 by Blackwell Publishing Ltd 1 2007 Library of Congress Cataloging-in-Publication Data Evans, Martin (Martin Grant), 1970– Geomorphology of upland peat : erosion, form, and landscape change / Martin Evans and Jeff Warburton. p. cm. – (RGS-IBG book series) Includes bibliographical references and index. ISBN-13: 978-1-4051-1507-0 (hardcover : alk. paper) 1. Peatlands. 2. Peatland ecology. 3. Soil erosion. I. Warburton, J. (Jeff) II. Title. GB622.E93 2007 551.41–dc22 2006032840 A catalogue record for this title is available from the British Library. Set in 10 on 12 pt Plantin by SNP Best-set Typesetter Ltd, Hong Kong Printed and bound in Singapore by Markono Print Media Pte The publisher’s policy is to use permanent paper from mills that operate a sustainable for- estry policy, and which has been manufactured from pulp processed using acid-free and elementary chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. For Juliet, Daniel and Anna and for Christine, Isobel and Katie Contents Series Editors’ Preface xi Acknowledgements xii Figure and Table Acknowledgements xiv 1 Introduction 1 1.1 The Aims of this Volume 1 1.1.1 Thematic coverage 1 1.1.2 Geographical context 2 1.2 Terminology, Defi nitions and Peatland Geomorphology 3 1.2.1 Defi nitions of peat 3 1.2.2 The physical and geotechnical properties of peat 6 1.2.3 Peatland classifi cation 6 1.3 The Geography of Blanket Mire Complexes 11 1.4 Patterns of Peat Erosion in Space and Time 15 1.4.1 The onset of peat erosion 18 1.4.2 Direct observation of the onset of erosion 20 1.5 Causes of Peat Erosion 21 1.6 A Brief History of the Evolution of Peatland Geomorphology 22 1.6.1 Accounts of erosion in the natural science tradition 23 1.6.2 Descriptive accounts of widespread peat erosion 23 1.6.3 Quantitative observations of blanket peatlands 24 1.7 Structure of this Volume and the Peat Landsystem Model 26 2 The Hydrology of Upland Peatlands 28 2.1 Introduction 28 2.2 Controls on Water Movement in Peat Landsystems 28 2.2.1 Hydraulic conductivity of upland peat soils 28 viii CONTENTS 2.2.2 The diplotelmic mire hypothesis 30 2.2.3 Groundwater fl ow in upland peatlands 34 2.2.4 Evaporation 37 2.2.5 Runoff generation 38 2.2.6 The water balance of ombrotrophic mires 47 2.3 Geomorphology and the Hydrology of Upland Peatlands 49 3 Sediment Production 54 3.1 Introduction 54 3.1.1 Monitoring sediment production using erosion pins 54 3.1.2 Sediment trap data 56 3.2 Sediment Production as a Control on Catchment Sediment Flux 61 3.3 Evidence from Field Observation 65 3.3.1 Climate correlations with trap data 65 3.3.2 Direct observations of surface change 67 3.4 Evidence from Controlled Experiments 69 3.5 Timescales of Sediment Supply 73 3.6 Conclusion 74 4 Fluvial Processes and Peat Erosion 76 4.1 Introduction 76 4.2 Gully Erosion of Blanket Peat 76 4.2.1 Gully morphology and topology 77 4.2.2 Fluvial erosion in ephemeral hillslope gullies 81 4.2.3 Sediment delivery from hillslope gullies 85 4.3 Erosion and Transport of Peat in Perennial Stream Channels 87 4.3.1 Production of peat blocks by fl uvial erosion 87 4.3.2 Transport of peat blocks in stream channels 91 4.3.3 The fate of fine peat sediment in channels 93 4.4 Sediment Yield 94 4.4.1 Bedload yields 94 4.4.2 Suspended sediment yields 94 4.4.3 Dissolved load 97 4.4.4 A conceptual model of sediment dynamics in eroding blanket peatlands 99 4.4.5 Sediment yield, sediment supply and assessing catchment erosion status 101 4.5 Conclusions 103 5 Slope Processes and Mass Movements 104 5.1 Introduction 104 CONTENTS ix 5.2 Peat-Covered Hillslopes 108 5.2.1 Limits to the stability of peat on slopes 108 5.2.2 Creep on peat hillslopes 111 5.3 Morphology of Rapid Peat Mass Movements 112 5.3.1 Source zone 115 5.3.2 Rafted peat debris 116 5.3.3 Runout track 116 5.3.4 Secondary tension and compression features 118 5.3.5 Bog burst and peat slides – are they different? 120 5.4 Mechanism of Peat Failure 123 5.4.1 Speed of failure and movement 125 5.5 Signifi cance of Surface Hydrology in Peat Failures 125 5.5.1 Water content, pore pressures, and volume changes 127 5.5.2 Rainfall 128 5.5.3 Slope drainage 128 5.6 Stability Analysis and Modelling of Peat Mass Movements 129 5.7 The Changing Frequency of Peat Mass Movements Over Time 131 5.8 Summary and Overall Framework 133 6 Wind Erosion Processes 136 6.1 Introduction 136 6.2 The General Signifi cance of Wind Erosion in Upland Peatlands 137 6.3 Mechanisms and Processes of Wind Erosion 140 6.4 Direct Measurements of Wind Erosion of Peat 146 6.5 Signifi cance of Dry Conditions and Drought for Wind Erosion 150 6.6 Conclusions 153 7 Peat Erosion Forms – From Landscape to Micro-Relief 155 7.1 Rationale and Introduction 155 7.2 Macroscale – Region/Catchment Scale 158 7.3 Mesoscale – Slope Catena Scale 162 7.4 Microscale – Material Structure Scale 165 7.5 Linking the Geomorphological and the Ecohydrological 167 7.6 Conclusions 169 8 Sediment Dynamics, Vegetation and Landscape Change 171 8.1 Introduction 171 8.2 The Effect of Peatland Dynamics on Long-Term Sediment Budgets 172 x CONTENTS 8.3 Re-Vegetation of Eroding Peatlands 174 8.3.1 Artifi cial re-vegetation of bare peat surfaces 174 8.3.2 Natural re-vegetation of eroded landscapes 175 8.4 Controls and Mechanisms of Natural Re-Vegetation 178 8.4.1 Extrinsic controls on re-vegetation 178 8.4.2 Intrinsic controls on re-vegetation 181 8.4.3 Eriophorum spp.