This thesis is formatted as a series of journal articles and book chapters. Thus it comprises three peer-reviewed book chapters (one first-author) that have been accepted for publication (Chapters 2.2; 3.3; 3.4), one published journal article (Chapter 2.1) and four manuscript-style chapters (Chapters 4-8), essentially articles for imminent submission to international, peer-reviewed journals. The published paper is a detailed review of the prospects and challenges to lacustrine palaeoflood investigations. One of the book chapters is a co-authored review of mining and industrial activities and impacts on the sediment records in lakes. The other two book
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chapters address important methodological issues related to the collection, processing and use of micro-scale X-ray fluorescence spectrometry (µXRF) scanning technology and the development of calibration tools to rigorous data quality in µXRF scanning, which underpins aspects of the PhD research.
Chapter 2:
Section 2.1: Flood stratigraphies in lake sediments: a review (Earth-Science Reviews 135, pp 17-37, August 2014). This paper provides a comprehensive review of the sequence of considerations vital to successfully extracting palaeoflood information from lake sediments. It outlines physical controls on the behaviour and characteristics of depositing material, evaluates the proxies and dating techniques employed to date in palaeoflood research, presents two conceptual models to guide further research and presents five case studies where different interpretational protocols have been applied to reconstruct palaeofloods.
Section 2.2: Lacustrine archives of metals from mining and other industrial activities- a geochemical approach. (Boyle, JF., Chiverrell, RC., Schillereff, D. (2014, In press) Lacustrine archives of metals from mining and other industrial activities- a geochemical approach. In: Blais, JM, Rosen, MR and Smol, JP (eds). Environmental Contaminants: Using Natural Archives to Track Sources and Long-term Trends of Pollution. Dordrecht, Springer). The chapter reviews research on the recent stratigraphic changes of heavy metal concentrations in lake sediments, examining the recent methodological advances, placing them in the context of the historical development of the discipline, and exploring the various purposes to which such methods have been applied. The processes controlling natural variations in metal flux in lake sediments are introduced and techniques for measuring concentrations in sediments and calculating enrichment or fluxes from concentration data are reviewed. Applications of metal stratigraphies in lakes are explored focusing on: i) their use as geochronological markers in sediments; ii) quantifying pollution loading histories, or to identify pollutant sources and iii) assessing pre- and post-mining baseline conditions, and pollutant pathways or environmental processes regulating heavy metals.
Chapter 3: Methodological context and data quality evaluation. Detailed descriptions of the study sites as well as an overview of the field sampling and laboratory techniques employed in this thesis are provided, alongside guidance to the relevant Chapters in which these methods are described in greater detail where applicable.
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Section 3.3: The prevalence of µXRF in contemporary palaeoenvironment research necessitates addressing imperfections in the scan data that arise because of its acquisition from wet sediments. This chapter outlines two calibration approaches to convert wet sediment concentrations or count rate collected by µXRF scanning to dry- mass equivalent output. Both approaches are applied to two lakes of differing sediment composition and their respective suitability is evaluated.
Section 3.4: A number of different µXRF core scanning instruments are currently in use in palaeolimnological research around the world. This chapter presents the results of a first inter-comparison of µXRF measurements made by an Olympus/Geotek and an ITRAX instrument on a sediment core extracted from Loch of the Lowes, Scotland. Chapter 4: Lake sediments have been demonstrated to be effective tools for evaluating historical trends in anthropogenic-derived trace metal contamination within catchments. Here, geochemical data are presented from high-resolution analyses of multiple sediment cores extracted from Brotherswater, English Lake District. The development of a robust chronology for the Brotherswater sediment sequence is outlined, including the chronological markers that were employed, and uncertainties associated with the resultant age-depth model. High-resolution estimates of late- Holocene sediment flux to the lake, in particular mineral supply and mining-derived metal contamination, were calculated using the chronological data, and these are presented alongside proposed drivers of the highly variable accumulation rates. Insights into catchment-lake sediment dynamics, spatial patterns of sediment deposition across the basin and the persistent negative impacts of mining on the aquatic ecosystems evident in the sedimentary record are also highlighted. In terms of the mining history, sedimentary Pb concentrations in the sediment closely reflect the known record of historical mining at the now-closed Hartsop Hall Mine. Issues including whether Pb levels in the aquatic ecosystem have recovered or remain higher than pre-mining period are explored.
Chapter 5: This chapter explores the construction of a late-Holocene palaeoflood record from Brotherswater. The laboratory methods are detailed and multiple lines of evidence are presented that illustrate the detectable imprints of historical floods preserved in the sediment sequence. Trends in flood frequency and potential links to climatic and/or anthropogenic drivers are discussed. The temporal consistency between the Brotherswater record and regional, independent instrumental and
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documentary palaeoflood data is assessed and some comments on reconstructing flood magnitude are made.
Chapter 6: The results from the 18 month sediment trapping programme at Brotherswater are presented in this chapter. Particle size measurements are used to assess whether the presumption that a hydrodynamic relationship exists between river discharge and the calibre of material delivered to the lake water column is valid at Brotherswater. The sediment trap data also yield insights into seasonal variability of within-lake depositional mechanisms and sediment provenance. A comparison of the particle size distributions between trapped material and adjacent sediment cores is performed and a particle size distribution representing total sedimentation that will be preserved in the abyssal sediments is presented.
Chapter 7: Results from the second study site, Loch of the Lowes, are presented in this chapter, as an opportunitity for testing the methodology developed at Brotherswater. The rationale for site selection is provided, the sediment sequence and depositional mechanisms are described in detail and the proposed palaeoflood signature is outlined. Some comments on trends in flood occurrence are offered in the context of the solely relative chronology currently available.
Chapter 8: This chapter presents an extended discussion that ties the findings together from the two reviews (Chapter 2.2 and 2.3), the methodological papers (Chapters 3.3 and 3.4) and the four results sections (Chapters 4-8) and explicitly addresses the key scientific questions outlined in Chapter 1. Finally, key limitations to the research and several avenues of future work are highlighted.