Modelling Blanket Peat Erosion Under Environmental Change
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Modelling blanket peat erosion under environmental change Pengfei Li Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Geography September 2014 The candidate confirms that the work submitted is his own and that appropriate credit has been given where reference has been made to the work of others. This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. The right of Pengfei Li to be identified as Author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988. © 2014 The University of Leeds and Pengfei Li i Acknowledgements I would like firstly to thank my PhD supervisors Prof. Joseph Holden and Dr. Brian Irvine for their support, guidance and encouragement throughout the course of this research. Their enthusiasm inspired me a lot, especially when times were dark. I have learnt a lot from them; not only professional knowledge on peat erosion and modelling but also a passionate attitude to scientific research. This work was funded by a School of Geography, University of Leeds studentship and the China Scholarship Council. I am extremely grateful for the funding which provided the opportunity for me to undertake this PhD. Many people have helped with this research whose assistance I would like to acknowledge. Prof. Mike Kirkby at the School of Geography, University of Leeds helped me understand the principles of the PESERA model and TOPMODEL. Thanks to Prof. Martin Evans at the University of Manchester who supplied measured suspended sediment concentration and water discharge data from Rough Sike catchment. My RSG panel members are thanked; Dr. Jonathan Carrivick and Dr. Richard Grayson reviewed the work every half year, and gave helpful comments and suggestions about this research. Dr. Richard Grayson also supplied sediment data from Stean Moor for model testing. Dr. Fei Wang at the Institute of Soil and Water Conservation, Chinese Academy of Science helped with general issues on erosion processes through emails and QQ. Prof. Andy Baird at the School of Geography, University of Leeds introduced me to understanding peat hydrology from the viewpoint of modelling. Rob Rose at the UK Environmental Change Network supplied climate, water table, runoff, and suspended sediment concentration data for the Trout Beck catchment for which I am grateful. These data were used for establishment of the sediment production regressions. Dr. Pippa Chapman at the School of Geography, University of Leeds kindly helped to check the potential evapotranspiration calculations for the Trout Beck catchment. Dr. Matthew Shepherd at Natural England kindly provided maps of peat status in England and the distribution of ditches in the North Pennines. Dr. Xiang Qin at the Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Science often discussed statistics questions with me when he visited the ii School of Geography, University of Leeds in 2013. Simon Desmit, my PhD colleague at the School of Geography, University of Leeds, kindly drove me to the Trout Beck catchment for field visits. I would also like to thank David Appleyard, Qamir Zia and Ben Broadbent for their valuable assistance in installing software to my office computer and making the computer powerful for the modelling work. Many people have helped with personal support, mainly in the form of dinner, cups of tea and beer. I would like to thank in alphabetical order: Brenda Chan, Chengchao Zuo, Faith Chan, Joo Kheong, Rong Wang, Sally Jobs, Sorain Ramchunder, Wintry Zhou, Yanpeng Jiang and Ying Nan. Special thanks also go to the colleagues (in alphabetical order) in my office for keeping such a friendly atmosphere, which is important for us to complete the research task: Adriane Esquivel Muelbert, Federico Venturini, Freddie Draper, Greta Dargie, James Bell, Jeannie Beadle, Kathryn Smith, Lawrence Akanyang, Magaly Valencia Avellan, Thomas Doherty-Bone, Thomas Kelly and William James. Finally I would like to thank my family. It was really important for me to have their strong support during my PhD. It was not possible to complete this thesis without their support. iii Abstract Many peatlands across the world are suffering from degradation and erosion exacerbated by human influences. Blanket peat erosion has adverse impacts on terrestrial and aquatic habitats, reservoir capacity and water quality. It also leads to accelerated carbon release. Bioclimatic modelling suggests that some areas, which are suitable for active peat growth currently, may be no longer under a climate supporting the accumulation of peat by the end of the century. Erosion in these marginal regions is thus more likely. However, there have been no attempts to date, to model blanket peat erosion mechanisms and rates and how they might respond to different climate scenarios and land management drivers. The PESERA-GRID model was chosen as a basis for modelling blanket peat erosion as it had a number of suitable properties such as its applicability in various spatial scales, and hydrological module is theoretically suitable for blanket peatlands. The model was modified to incorporate freeze-thaw and desiccation processes and typical land management practices (artificial drainage and burning) in blanket peatlands. This resulted in a modified model called PESERA-PEAT. In PESERA- PEAT, blanket peat erosion is determined by both sediment supply through weathering and the transport capacity of overland flow. A novel sediment supply index was defined and employed to parameterize the sediment supply from blanket peatlands. Land management practices were parameterized for their influence on vegetation cover and biomass and soil moisture condition. Potential wildfire severity was estimated with a previously developed ignition model. The PESERA- PEAT model was calibrated and validated with field data from previous publications and data from three blanket peat-covered catchments. Model testing suggested that PESERA-PEAT was robust for modelling blanket peat vegetation, runoff and erosion. Climate change scenarios were established and climate data were compiled to 2100. The PESERA-PEAT model was applied at a regional scale for the blanket peatlands of the North Pennines and at a smaller scale for ten sites across Great Britain to examine the response of blanket peat erosion to possible changes in climate and land management practices. Modelling results suggested that the response of blanket peat iv erosion to climate change was highly variable across space both within regions and across Great Britain with some sites experiencing reduced erosion under some climate scenarios with most experiencing increased erosion. The model suggested that peat erosion change would be generally higher in southern and eastern areas than in western and northern parts of Great Britain. Predicted erosion change was particularly high in the North York Moors where lower rainfall and higher temperatures suppressed the water table, and led the predicted future erosion to be usually transport limited. It was suggested that summer desiccation may become a more important sediment source for British blanket peat erosion in the future, leading to more sediment erosion released from blanket peatlands during subsequent rainstorms. Erosion change with climate change to 2100 was predicted to be smaller in wetter and colder locations. As climate changes, rainfall was shown to be more important than temperature in shaping long-term changes in runoff production while temperature was generally more dominant than rainfall in controlling long-term erosion change. However, in the North York Moors rainfall appeared to be more dominant in long-term erosion change. Overall, the modelling work suggested that land management may have a greater impact on blanket peat erosion than on runoff, while climate plays a more important role in runoff production rather than in blanket peat erosion. It was suggested that adjusting land management practices may be appropriate in order to buffer the impacts of future climate change on blanket peat erosion. However, when blanket peatlands were managed to protect them from soil erosion through ensuring a thriving vegetation biomass cover, then wildfire- awareness and precautionary fire measures would be required as the wildfire risk increased substantially with climate change and may also increase with such land management strategies. v Table of Contents Acknowledgements ..................................................................................................... i Abstract ..................................................................................................................... iii Table of Contents ...................................................................................................... v List of Tables ............................................................................................................ ix List of Figures .......................................................................................................... xii Chapter 1 Introduction ............................................................................................. 1 1.1 Background .................................................................................................. 1 1.2 Research aim and objectives .......................................................................