THE ROLE OF INTERTIDAL SEAGRASS ZOSTERA SPP. IN SEDIMENT DEPOSITION AND COASTAL STABILITY IN THE TAY ESTUARY, SCOTLAND Lorna Wilkie A Thesis Submitted for the Degree of PhD at the University of St. Andrews YEAR Full metadata for this item is available in Research@StAndrews:FullText at: http://research-repository.st-andrews.ac.uk/ Please use this identifier to cite or link to this item: http://hdl.handle.net/10023/3180 This item is protected by original copyright This item is licensed under a Creative Commons License The role of intertidal seagrass Zostera spp. in sediment deposition and coastal stability in the Tay Estuary, Scotland Lorna Wilkie A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at the University of St Andrews School of Biology University of St Andrews December 2011 1 1. Candidate’s declarations: I, Lorna Wilkie, hereby certify that this thesis, which is approximately 40,000 words in length, has been written by me, that it is the record of work carried out by me and that it has not been submitted in any previous application for a higher degree. I was admitted as a research student in November 2007 and as a candidate for the degree of Doctor of Philosophy in November 2008; the higher study for which this is a record was carried out in the University of St Andrews between 2007 and 2011. 2. Supervisor’s declaration: I hereby certify that the candidate has fulfilled the conditions of the Resolution and Regulations appropriate for the degree of Doctor of Philosophy in the University of St Andrews and that the candidate is qualified to submit this thesis in application for that degree. 3. Permission for electronic publication: In submitting this thesis to the University of St Andrews I understand that I am giving permission for it to be made available for use in accordance with the regulations of the University Library for the time being in force, subject to any copyright vested in the work not being affected thereby. I also understand that the title and the abstract will be published, and that a copy of the work may be made and supplied to any bona fide library or research worker, that my thesis will be electronically accessible for personal or research use unless exempt by award of an embargo as requested below, and that the library has the right to migrate my thesis into new electronic forms as required to ensure continued access to the thesis. I have obtained any third-party copyright permissions that may be required in order to allow such access and migration, or have requested the appropriate embargo below. The following is an agreed request by candidate and supervisor regarding the electronic publication of this thesis: Access to printed copy and electronic publication of thesis through the University of St Andrews. i Acknowledgements I would like to thank the following people and organisations for their input into this Ph.D. project: my supervisors, Prof. Dave Paterson, Dr Mattie O‟Hare and Dr Bernard Dudley; the Sediment Ecology Research Group at the University of St Andrews; staff and students at the Centre for Ecology and Hydrology; Scottish Natural Heritage; Fife Coast and Countryside Trust; the people of Tayport, and to Tayport Caravan Park for letting me use their “facilities” on many occasions. Thank you to NERC (Ph.D. award NE/F009300/1) for funding this project, and to the Spragge Conservation Scholarship. Thanks also to Prof. David Raffaelli and Dr Iain Matthews for an enjoyable viva, and for their constructive comments. Special thanks go to Irvine Davidson and Clare Maynard for spending many cold days out on the shore with me, for their suggestions, good humour and support. Also thank you Dr Beccy Aspden for being the most patient lab manager. Most of all I would like to thank my mum and Innes for their continual encouragement and support throughout the last four years. i Abstract The Tay estuary is situated on the east coast of Scotland. The estuary is dominated by sediment biotopes, including mudflats which support sparse beds of two nationally scarce seagrass species, Zostera marina var. angustfolia (Hornem.) and Z. noltii (Hornem.). Seagrasses have been described as ecosystem engineers, shaping their sediment environment, and this may increase sediment deposition and stability. In this thesis the ecosystem engineering characteristics of seagrass habitats are explored. In 2008, the distribution of Zostera spp. in the Tay estuary was surveyed and mapped for the first time. Sediments within beds of Z. marina and Z. noltii were compared to investigate the influence of seagrasses on sediment characteristics. To explore the role of seagrass in sediment deposition and erosion, and coastal stability, sediment depth measurements were made in patches of Z. noltii, Z. marina and bare sediment over one year. The role of the root/rhizome system on sediment retention over winter was also considered. Sediment deposition in Z. noltii beds, and the influence of the plants on near- bed flow dynamics was further explored in the laboratory, using an 8 m seawater flume. In the field the retention of particles over 2 and 14 tides was measured, and the results of this experiment led to a study of the influence of leaf and sediment biofilms on particle retention, using the novel method of magnetic particle induction (MagPI). The efficacy of artificial seagrass beds and Z. noltii transplantation as habitat restoration techniques were compared over one year. During the trial, sediment deposition and changes in sediment chacteristics were determined, and the protection given to saltmarsh cliffs fringing the study plots was assessed. Mechanisms underlying the results are suggested and the findings discussed. This study provides an insight into the ecology of seagrass in the Tay estuary and its role as an ecosystem manager. It may offer valuable data which could be utilised for future conservation policies, habitat restoration schemes and management planning of the area. ii Contents Declarations Acknowledgements i Abstract ii Contents iii List of Figures viii List of tables xii Chapter 1 – General Introduction 1 1.1 The River Tay and the Tay estuary 1 1.1.1 The physical environment 1 1.1.2 Habitats, flora and fauna of the Tay estuary 4 1.1.3 Human influences on the physical and chemical environment 6 1.1.4 Conservation status of the Tay estuary 9 1.2 Seagrass 9 1.2.1 Ecological and economic significance of seagrass 9 1.2.2 Seagrass species in Scotland 13 1.2.3 Seagrass in the Tay estuary 18 1.2.4 Causes of decline in seagrass species 19 1.3 Aims of the thesis 23 1.4 Study site 25 References 27 Chapter 2 – The status of Zostera spp. in the Tay estuary 36 Abstract 36 2.1 Introduction 38 2.1.1 The distribution of seagrass in the Tay estuary 38 2.1.2 Physical effects of intertidal seagrass on sediments 39 2.1.3 Aims 41 2.2 Materials and methods 41 2.2.1 Full survey of intertidal Zostera and mapping of Zostera beds 41 2.2.2 Sediment sampling 42 2.2.3 Statistical analysis 47 iii 2.3 Results 47 2.3.1 Full survey of intertidal Zostera and mapping of Zostera beds 47 2.3.2 Comparison between the sediments of Z. marina and Z. noltii 51 beds within the Tay estuary 2.4 Discussion 57 2.4.1 Distribution of intertidal Zostera spp. 57 2.4.2 Comparison between the sediments of Z. marina and Z. noltii 59 beds within the Tay estuary 2.5 Conclusions 61 References 63 Chapter 3 – The influence of Zostera spp. on sediment deposition and stability 70 in the Tay estuary Abstract 70 3.1 Introduction 72 3.1.1 Processes influencing sedimentation at Tayport 72 3.1.2 The influence of intertidal seagrasses on sediment composition, 75 deposition and retention 3.1.3 Aims 77 3.2 Materials and methods 77 3.2.1 Sediment deposition/erosion measurements 77 3.2.2 Statistical analysis 81 3.3 Results 82 3.4 Discussion 88 3.5 Conclusions 92 References 94 Chapter 4 – Particle trapping and retention by Zostera noltii: a flume and field study 100 Abstract 100 4.1 Introduction 101 4.1.1 Seagrass as an ecosystem engineer 101 4.1.2 The effect of seagrass on water flow 102 4.1.3 The use of flume and tracer particles 104 iv 4.1.4 Relevance of the study 104 4.1.5 Aims 105 4.2 Materials and methods 105 4.2.1 Flume study 105 4.2.2 Field study 110 4.2.3 Statistical analysis 112 4.3 Results 113 4.3.1 Flume study 113 4.3.2 Field study 122 4.4 Discussion 123 4.4.1 Particle trapping and flow reduction 123 4.4.2 Sediment retaining capacity of Z. noltii in the field 127 4.5 Conclusions 128 References 130 Chapter 5 – Measurement of particle adhesion to sediment and leaf biofilms using 135 magnetic particle induction (MagPI) Abstract 135 5.1 Introduction 136 5.1.1 Adhesion of sediment particles to aquatic biofilms 136 5.1.2 Aims 138 5.2 Materials and methods 138 5.2.1 MagPI – sediment and leaf biofilms 138 5.2.2 Flume study – leaf biofilms 142 5.2.3 Statistical analysis 143 5.3 Results 144 5.3.1 MagPI – sediment and leaf biofilms 144 5.3.2 Flume study – leaf biofilms 146 5.4 Discussion 150 5.5 Conclusions 152 References 154 v Chapter 6 – Can artificial segrass be used to restore sediment habitats? 159 A comparison of restoration techniques Abstract 159 6.1 Introduction 161 6.1.1 The decline of saltmarsh habitat in the U.K.