Challenges of integrating habitat for aquatic life and morphodynamics offer a plethora of opportunities for advances in Ecohydraulics

Morphodynamics and aquatic biota (i.e. plants and animals) interact through complex processes, to generate suitable, diverse and resilient habitats. We define morphodynamics in broad terms as the discipline of Earth surface characteristics and evolution which integrates hydrological, geomorphological and geological aspects. This definition is similar, although narrower to that offered by Paola et al. (2006), since we include ecological and biological aspects in Ecohydraulics. Complex physical processes are linked to planforms, longitudinal profiles and cross-sectional geometries in rivers, lakes and deltas and involve the cycling of water, sediment, ice, nutrients, solutes and organic materials in watersheds. Through surface, subsurface or groundwater flow, erosion, transport, deposition and ice conditions, morphodynamics shapes bars, pools, riffles, islands, side channels and other features in waterbodies (Paola et al. 2006; Wohl et al. 2015). Ecological dynamics, commonly understood less clearly, represent the even more complex life processes and food webs, responses by aquatic species and vegetation, populations and communities, as well as suitable habitats characterized by spatial complexity, connectivity and dynamism which meet biota life cycle requirements, enable ecosystem functionality and support biodiversity (Elosegi et al. 2010). Large differences in genetic flow, dispersal and mobility strategies or abilities of aquatic biota populations add another layer to this complexity and needs for more in-depth knowledge and understanding. With such complexities, it is not surprising that large knowledge gaps exist in morphodynamics and ecology, and particularly in the interaction between the two. Although often it is thought that geomorphology sets the template for biological processes (e.g. Vannote et al. 1980), recent studies indicate direct and indirect effects on physical processes from aquatic and riparian vegetation, particularly in the riparian zone (e.g. Gurnell et al. 2012), or even from fish through nutrient enrichment or potential effects on gravel substrates (e.g. DeVries 2012). Such interactions create numerous feedback mechanisms between biotic and abiotic processes, ecology and morphodynamics, generate further knowledge gaps and offer potentially great insights if elucidated though comprehensive studies. Since Ecohydraulics is at the interface between morphoand eco-dynamics and explores biota and physical interactions, breakthroughs in this interdisciplinary field become very challenging. At the same time, such challenges offer a plethora of opportunities for pioneering research and practical applications for interand trans-disciplinary advances in Ecohydraulics. River systems have influenced people and their settlements since the dawn of civilization, while humans continue to alter, regulate and manage them to: (1) suppress floods and control water levels; (2) supply water for domestic use, agriculture, recreation and many industries; (3) enable navigation and hydroelectric power production; (4) inter-basin water transfers from wet regions to dry regions; (5) control sediment, erosion and mine waste; (6) convert wetlands and river deltas to agricultural or other use; (7) support waste dilution, waste disposal, logging activities and paper mills; (8) intentionally or accidentally introduce nonnative exotic species. Control and management of rivers change the dynamic nature of aquatic ecosystems which are characterized by ecological dynamism, habitat connectivity and species biodiversity. Dams, pumping stations, canals, hydroelectric facilities, other infrastructure, as well as biological invasions, may: impair natural functions; render living conditions for biota unsuitable; fragment free-flowing rivers; alter the timing and magnitude of river and stream flows; disrupt sediment transport, nutrient cycling, biota movements, as well as connections to floodplain and groundwater; impact long-term river morphology, water quality and ice conditions; add pressures on biodiversity (Katopodis and Aadland 2006; Elosegi et al. 2010). Minimizing negative impacts, understanding biota responses to changed abiotic environments, developing and implementing mitigation measures and evaluating their effectiveness with a focus on dynamic interactions between aquatic life and morphodynamics calls for innovative ecohydraulic solutions and presents challenging research questions. Over millennia, anthropogenic influences have left morphological signatures which have been increasingly prevalent. It seems that natural rivers, lakes and deltas or even segments are rare, if not non-existent, particularly if pollution by air transport and climate change are considered. This is despite wide recognition that freshwater is essential for human and aquatic life, economic development, as well as robust ecosystem functions. Such river modifications throughout the planet, have made and continue to make changes to biodiversity and biota redistribution, as well as provide large risks to water security for humanity. A global analysis by V€ or€ osmarty et al. (2010) found that nearly 80% of humanity lives with a major threat to water security, while the increasing rates of degradation to freshwater aquatic habitats means that hundreds of biota are