| Summary: | This thesis aims to assess the response of invertebrate assemblages to fine sediment in the River Isábena, a catchment generating unusually high sediment loads due to the presence of badland areas. First, a spatial approach was taken in order to assess evidence of sedimentrelated patterns in invertebrate assemblages across the catchment under stable flow conditions. This provided a “snap‐shot” of the spatial variability on the assemblages in relation to sediment stored in the channel, as well as the relative influence of physical habitat conditions of different spatial scales. Fine sediment proved to be driving invertebrate assemblages distribution, structure and trait composition, filtering‐out sensitive species and thus promoting nested patterns across the catchment. Strong interactions between spatial scales were found, emphasizing the existence of catchment scale controls (such as geology and rainfall) on reach physical habitat conditions and, in turn, on invertebrate assemblages distribution. This spatial approach was complemented with the study of the temporal dynamics, which focussed on understanding the dominant drivers in the catchment hydrosedimentary behaviour and the relationship between physical processes and the ecological response. Temporal distribution of rainfall (and thus the occurrence of floods), along with the sediment availability (both in the source and in the channel) were driving the intra‐annual suspended sediment dynamics. Turnover of invertebrate assemblages was jointly driven by taxon life cycles and the temporal dynamics in hydrosedimentary conditions (i.e. occurrence of floods and episodes of high sedimentation). Despite the intra‐annual variability, assemblages proved to be resilient, most likely as a result of the selection of pre‐adapted traits. Overall, these findings emphasize the importance of assessing the geomorphological and hydrological processes that control sediment production, delivery and permanence in the channel, in order to better understand the ecological impacts of excessive fine sediment loads.
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