Incorporating the interaction of flow into invertebrate responses to fine sediment deposition in temperate rivers

Fine sediment (particles <2 mm) is a natural and important component of riverine systems. However, excessive loads are one of the leading causes of ecological degradation globally. The flow regime is intrinsically linked to fine sediment dynamics (erosion, transport and deposition) and is further considered a ‘master’ variable in structuring the invertebrate community of lotic systems. To date, limited research has examined how the interaction of these variables affects the response of the ecological community, and how this varies temporally. Paired invertebrate, fine sediment and daily flow discharge data were acquired for 28 sites across England. Mixed effects models were used to determine the influence of fine sediment and flow, both individually and in interaction, on invertebrate indices and by season (spring and autumn). Our results indicate that some flow metrics were more influential in structuring the invertebrate community than others (including low pulse count and maximum annual monthly discharge), and flow metrics were more likely to have a significant effect on invertebrate indices in autumn than in spring. Flow was found to mitigate the negative effect of deposited fine sediment on invertebrate communities in some instances. This was particularly the case for high antecedent flow metrics (e.g. high flows in the seven days prior to sampling). However, overall, there was little evidence of an interaction between flow and fine sediment detected. Our study highlights the nuanced relationships between flow dynamics and deposited fine sediment, in influencing the composition of macroinvertebrate communities in lotic environments. Effective catchment management could integrate this knowledge, emphasising seasonality and site-specific hydrological characteristics to maximise ecological benefits.