The effect of sediment characteristics and a fine sediment pulse on invertebrate distributional patterns

The amount of fine sediment entering river systems has increased dramatically in the last century and this has been recognised as a leading cause of ecological degradation and water quality impairment. In order to monitor and manage this problem more effectively further research is needed in to the quantitative, mechanistic relationships between the amount of fine sediment delivery in to river systems and the response of the lotic freshwater community. At present, this lack of information is problematic for environmental managers and regulators as they attempt to meet the challenges posed by this issue. This thesis aimed to address this research gap by using stream mesocosms to investigate the response of invertebrates to a fine sediment pulse. It was unique in considering the effect of prior exposure to increased fine sediment deposition, whilst examining the response of benthic, hyporheic and drifting invertebrates concurrently. The research also set out to assess the effectiveness of fine sediment biomonitoring approaches, comparing them with more traditional metrics, it also investigated the power of a functional trait approach to discriminate fine sediment stress. The results detailed in this thesis demonstrate that biomonitoring approaches have the ability to identify fine sediment stress more effectively than traditional taxonomic metrics (e.g. abundance and taxonomic richness), particularly when applied to invertebrate communities which are relatively tolerant of fine sediment stress. This was one of the first studies to identify the effects of prior fine sediment deposition on the response of invertebrates to a fine sediment pulse, finding that this factor plays an important role in their response, providing important evidence which may be used to better tailor our fine sediment management strategies. Examining, in tandem, the effects of a fine sediment pulse on invertebrate drifting behavior and their use of the hyporheic zone identified taxa-specific responses to fine sediment which will be useful to further refine our understanding of the mechanistic relationship between increased amounts of fine sediment and invertebrate communities. This information will help to inform the refinement of functional trait databases, which has been identified by the work in this thesis as one of the major factors limiting their effective use