WP2 focuses on hydromorphological and ecological processes and interactions within naturally functioning river systems. D2.1 proposes a hierarchical framework to support river managers in exploring the causes of river management problems and devising sustainable solutions. D2.2 builds on this framework by exploring published research and available data sets to more formally encompass the biota. This report (Part 2 of Deliverable 2.2) considers interactions between hydromorphology and macroinvertebrates and fish, and the role of floods and droughts as biota-shaping phenomena. Lastly, part 2 presents conclusions from the whole of Deliverable 2.2.

Summary of Deliverable 2.2 Part 2.

Research Objective.

The research developed in this report builds upon the Hierarchical Framework developed in Deliverable 2.1 to investigate links between ecology and hydromorphology at multiple scales considering its relevance for the better understanding of river fauna (macroinvertebrates and fish) functioning as well as incorporating extreme hydrological events as biota-shaping phenomena.

Methods and Results.

We have chosen the literature reviews in order to combine knowledge from multiple studies in a given topic, and to summarize the latest evidence. In sections 4.1, 4.2 and 5.1 we adopt a narrative form. In setions 5.2 we undertake a systematic review, using an explicit method to perform a comprehensive literature search and critical appraisal of the individual studies. As a result we are able to prove the usefulness and research gaps when employing the multi-scale framework as a basic tool for developing understanding of river ecosystem organization.

Conclusions and Recommendations.

The evidence extracted from the literature in relation to fish and macroinvertebrates in Chapter 4 demonstrates that their composition and functioning corresponds to the Hierarchical Framework of spatial scales. However, it is clear that some levels of this hierarchical structure are more relevant than others for understanding the mechanisms of biological response to environmental change. It is also evident from the literature review and data analysis presented in Chapter 5 that both floods and droughts are phenomena that shape the structure and composition of aquatic communities. To some extent the impact of these events is moderated by the morphological characteristics of the affected river channels and their floodplains, particularly reflecting the importance of the higher complexity of naturally-functioning rivers, especially multi-thread and floodplain river systems. There is a general pattern of biological response indicating that both types of events lead to changes in aquatic community structure, limiting the organisms that are less adapted to the disturbance and promoting those with better adaptations. However, responses to events of different type, magnitude, intensity and duration are highly variable.

Looking for the research gaps, we have found that the use of the Hierarchical Framework of spatial scales, linking macrobenthic structure and fish behaviour with functional Hydromorphology, is an important tool for understanding river ecosystem organization. However, a fuller understanding could be developed if purpose-specific data sets were collected, which incorporate the full range of scales and hydromorphological phenomena into investigations of the presence and dynamics of the fauna. A particularly profitable endeavour would be to align typical hydrological, hydraulic and geomorphic units along typical river types to analyse their correspondence with the fish-based river typology (FRI). Moreover, the literature review (section 5.1) and the meta-analysis (section 5.2) suggest that a key research area remains in developing a more robust and deeper understanding of the mechanisms of biological responses to environmental changes and extreme events across different, specific, time and space scales.

In terms of practical recommendations we have shown how interactions between plants and hydromorphology take on different characteristics in different biogeographical settings, leading to different spatial distributions and temporal dynamics. These long-overlooked dynamics need serious research and management attention. Riparian vegetation needs to be more formally incorporated into the Water Framework Directive and as a fundamental component of river management and restoration design.

We have also proved that moving beyond the reach scale to consider the broader spatial and temporal controls on hydromorphology, ecology and their interrelationships should be also a key component in the preparation of restoration plans.