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  • Meteorological and climatic impacts on

    the phytoplankton community of a

    small meso-eutrophic lake

    Emma Gray BSc, MSc

    This thesis is submitted for the degree of Doctor of Philosophy

    November 2019

    Lancaster Environment Centre

  • Declaration

    I declare that this thesis has not been submitted in support of an application for another

    degree at this or any other university. It is the result of my own work and includes nothing

    that is the outcome of work done in collaboration except where specifically indicated.

    Many of the ideas in this thesis were the product of discussion with my supervisors; Ian

    Jones, Eleanor Mackay, Alex Elliott and Andrew Folkard.

    Signed: Date:

    Emma Gray BSc, MSc

    Lancaster University, UK

  • Statement of authorship

    Chapters 4-7 are presented in the style of papers, two of which have been published and

    are presented as the final copy before journal editing. The papers have multiple authors

    and their contributions are identified below.

    Chapter 4 has been published in Water Research:

    Gray, E., Mackay, E. B., Elliott, J. A., Folkard, A. M., & Jones, I. D. (2020). Wide-spread

    inconsistency in estimation of lake mixed depth impacts interpretation of limnological

    processes. Water Research, 168, 115136;

    doi: https://doi.org/10.1016/j.watres.2019.115136.

    EG: designed study, completed data collection, developed the statistical methods of

    mixed depth estimation, completed the data analysis, led manuscript preparation

    EBM: conceived the idea, designed study, advised data collection, developed the

    statistical methods of mixed depth estimation, advised data analysis and contributed to

    manuscript revisions.

    JAE: advised data collection, advised data analysis and contributed to manuscript

    revisions.

    AMF: advised data collection, advised data analysis and contributed to manuscript

    revisions.

    IDJ: conceived the idea, designed study, advised data collection, developed the statistical

    methods of mixed depth estimation, advised data analysis and contributed to manuscript

    revisions.

    https://doi.org/10.1016/j.watres.2019.115136

  • Chapter 5 has been published in Freshwater Biology:

    Gray, E., Elliott, J. A., Mackay, E. B., Folkard, A. M., Keenan, P. O., & Jones, I. D.

    (2019). Modelling lake cyanobacterial blooms: Disentangling the climate‐driven impacts

    of changing mixed depth and water temperature. Freshwater Biology.

    doi: https://doi.org/10.1111/fwb.13402

    EG: designed study, completed modelling experiment, completed the data analysis and

    led manuscript preparation.

    JAE: conceived the idea, advised modelling experiment, advised data analysis and

    contributed to manuscript revisions.

    EBM: advised modelling experiment, advised data analysis and contributed to manuscript

    revisions.

    AMF: advised data analysis and contributed to manuscript revisions.

    PK: completed nutrient analysis.

    IDJ: conceived the idea, advised modelling experiment, advised data analysis and

    contributed to manuscript revisions.

    Chapter 6 is in preparation for submission:

    Gray, E., Mackay, E.B., Folkard, A.M, Elliott, J.A., and Jones, I.D. (2019) From one

    extreme to another: the impact of a storm event on physical and chemical lake processes

    at a time of atypical heightened stratification strength.

    EG: designed study, completed the data analysis, led manuscript preparation

    EBM: designed study, advised data analysis and contributed to manuscript revisions.

    https://doi.org/10.1111/fwb.13402

  • AMF: advised data analysis and contributed to manuscript revisions.

    AE: advised data analysis and contributed to manuscript revisions.

    IDJ: designed study, advised data analysis and contributed to manuscript revisions.

    Chapter 7 is in preparation for submission:

    Gray, E., Mackay, E.B., Elliott, J.A., Folkard, A.M, and Jones, I.D. (2019) The impact

    and recovery of a phytoplankton community in response to storm event in a small meso-

    eutrophic lake.

    EG: designed study, completed data collection and phytoplankton counts, completed the

    data analysis, led manuscript preparation

    EBM: conceived the idea, designed study, advised data collection, advised data analysis

    and contributed to manuscript revisions.

    JAE: designed study, advised data collection, advised data analysis and contributed to

    manuscript revisions.

    AMF: advised data collection, advised data analysis and contributed to manuscript

    revisions.

    IDJ: conceived the idea, designed study, advised data collection, advised data analysis

    and contributed to manuscript revisions.

  • Data Statement

    Original data collected during this thesis is stored in NERC’s Environmental Information

    Data Centre (EIDC) hosted by the Centre for Ecology & Hydrology under the title

    Blelham Tarn: Ecological and chemical lake profiles, and inflow and outflow chemistry

    2016-17.

    The dataset can be cited: Gray, E.; Jones, I.D.; Mackay, E.B.; Elliott, J.A.; Folkard, A.M.

    (2019). Blelham Tarn: Ecological and chemical lake profiles, and inflow and outflow

    chemistry 2016-17. NERC Environmental Information Data Centre.

    doi: https://doi.org/10.5285/791f7613-c7a4-44e0-b197-53f92757f875

    https://doi.org/10.5285/791f7613-c7a4-44e0-b197-53f92757f875

  • Abstract

    Climate change is having long term impacts on the physical structure of lakes including

    potential shallower surface mixing, increases in stratification strength and increases in

    surface water temperature. It is therefore vital that lake thermal dynamic properties, like

    the depth of surface mixing, are quantified in a robust way. Comparing methods of mixed

    depth estimation in this thesis, however, found that values were highly inconsistent

    leading to disparate interpretations of ecological and chemical water quality parameters.

    Future limnological studies using the mixed depth should be vigilant to this issue and test

    multiple methods to ensure that findings are not dependant on the choice of method.

    Long term changes in lake water temperature and surface mixing as a result of climate

    change occur concurrently, but they have separate consequences for phytoplankton

    growth. Using a phytoplankton model, water temperature and mixed depth were changed

    independently. Increases in water temperature led to an increase in phytoplankton growth

    at most mixed depths. Contrary to previous research, mixed depth shallowing did not

    always lead to increases in cyanobacteria biomass, with shallowing from deep to

    intermediate depths resulting in a reduction in cyanobacteria.

    The magnitude and frequency of episodic weather events such as storms are also expected

    to increase as a result of climate change. It is therefore becoming increasingly likely that

    extreme events will occur at a time of heightened stratification strength, but the

    interaction of these two extremes have not yet been explored in detail. Despite concerns

    that episodic weather events will push lakes into more extreme states, evidence here

    suggests that in some cases storms can return the thermal stability and seasonal

    phytoplankton community succession to conditions more typical for the time of year. This

    highlights the importance of setting the responses of episodic weather events in the

    context of long term averages.

  • Acknowledgements

    First and foremost, I would like to thank my supervisors Ian Jones, Eleanor Mackay, Alex

    Elliott and Andrew Folkard for all of their patience, guidance, motivation and endless

    support over the last four years. I have learnt a great deal from each of them and I am

    very grateful for all of the time and effort they have invested in me and this project.

    This project would not have been possible without the financial input from the NERC

    Envision Doctoral Training Partnership.

    I am also grateful to all of the members of the Lake Ecosystems Group at the Centre for

    Ecology & Hydrology (CEH) for all of their support and for making me feel like part of

    the team. A special thank you goes to Steve Thackeray for all of his advice and

    encouragement and for putting up with sharing an office with me. I would also like to

    thank Mitzi De Ville for all of her phytoplankton and laboratory expertise and Mike

    Clarke for all of his help installing, maintaining and calibrating sensors. I would also like

    to thank the CEH Chemistry group for processing samples for nutrient analysis.

    This project involved lots of trips to the often wet and windy Lake District I therefore

    have lots of volunteers to thank for all of their help and hard work in the field, thank you

    to: Katy, Rob, Stella, Ellie G, Ellie M, Tom, Alex, Joe, Jonathan, Andrew, Ceri, Laura,

    Callum, Steve, Emma, Liam Q, Liam R, Nye, Ethan, Merryn, Anna, Matt and Elizabeth.

    I would like to thank all of my family and friends for supporting and encouraging

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