Impacts of hydromorphological degradation and disturbed sediment dynamics on ecological status. Deliverable 3.1 of REFORM (REstoring rivers FOR effective catchment Management), a collaborative project (large-scale integrating project) funded by the European Commission within the 7th Framework Programme under Grant Agreement 282656.

There is an acknowledged need among stakeholders that new hydromorphological metrics are required to facilitate site remediation and for reporting at national and European levels. Pressure/ impact data were assembled from across Europe. The task was challenging, but useful information was gathered. For each major hydromorphological pressure, the physical response gradients of rivers was summarised as diagnostic diagrams. For the first time we provide evidence that metrics indicating HYMO impact could be developed from monitoring data on fish and macrophytes. For the first time we demonstrate the potential to derive metrics sensitive to fine sediment. We provide evidence that phytobenthos (diatoms), invertebrates and macrophytes have the potential to be used in combined metrics. We found that many existing macroinvertebrate metrics lack specificity and can provide false positive responses to HYMO pressure, suggesting that disentanglement of multi-stressor responses is critical to good diagnosis. There is evidence that aquatic habitats protected under the Habitats Directive will be increasingly vulnerable to hydrological pressures with the changing climate. Frequently, overlooked topics such as sediment quality and groundwater issues ought to supplement or be included in HYMO assessments due to their potential for explaining variance in biological datasets. Land-use data on a spatial scale beyond the reach scale (corridor and catchment) relates to site-specific macroinvertebrate metrics and could be a more robust way of assessing impacts.