Quantifying the response of macroinvertebrates to gradients of fine sediment pollution

  • Morwenna McKenzie

    Student thesis: Doctoral ThesisDoctor of Philosophy


    Erosion, transportation and deposition of fine sediment (organic and inorganic particles < 2mm in diameter) are fundamental processes in the hydrogeomorphic cycle and river systems require a constant supply in order to function. However, excessive fine sediment delivery can cause serious deleterious effects to aquatic systems and is one of the leading causes for failure to meet Good Ecological Status as set out by the EU Water Framework Directive (2000/60/EC). Given the need for effective management of fine sediment, this thesis examines how fine sediment is driving macroinvertebrate responses in order to help improve biomonitoring, i.e. the practice of using biological communities to track environmental change. A systematic style review was undertaken to assess the weight of evidence for macroinvertebrate responses to fine sediment, which identified several correlative relationships. However, a global imbalance of evidence is apparent and there is a distinct knowledge gap of the mechanisms driving macroinvertebrate responses to fine sediment. The review outcomes helped inform the design of a controlled laboratory experiment which investigated the direct physical effects of fine sediment (e.g. clogging and abrasion of gills) on three different species of macroinvertebrates. The results showed that gill surfaces were covered in fine sediment debris to varying extents and responded differently to treatments in a way that suggested gill morphology and behavioural responses (such as avoidance) as key factors.

    The last decade has seen a development in sediment-specific biomonitoring tools globally. Through a national (England) fieldwork sampling regime, existing sediment-specific biomonitoring indices were tested against varying gradients of fine sediment (deposited and suspended) alongside indices for general ecological health. Further insights into the response of macroinvertebrates (both taxonomic and trait-based) to fine sediment were explored using a variety of statistical techniques. The results reinforced several outcomes of the earlier systematic style review and also supported the use of sediment-specific biomonitoring indices. However, the majority of variation in sediment-specific index scores at each site were related to habitat and flow variables. Finally, the results obtained within this thesis were linked with emerging ecological theory and the factors which may influence the success of biomonitoring indices globally (e.g. invasive non-native species and climate change). This thesis ends by making recommendations for monitoring approaches and future research directions.
    Date of AwardJan 2020
    Original languageEnglish
    Awarding Institution
    • Coventry University
    SupervisorMartin Wilkes (Supervisor), Ian D.L. Foster (Supervisor), Damian Lawler (Supervisor) & Judy England (Supervisor)

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