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 morpho- and 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 inter- and 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 non-native 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 Vörösmarty 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 highly threatened or at risk of extinction. For example, all sturgeon species are on the IUCN Red List of Threatened Species and 16 of the 25 species are critically endangered (IUCN 2018; Version 2017-3). Risks to water security and ecology, as well as rapid declines, threatened status, or extinctions of aquatic species is compelling worldwide research on impacts, mitigation, restoration and conservation efforts. With such complex interactions between physical and ecological processes, clearly there is tremendous potential, as well as necessity for pioneering ecohydraulic research and applications to continue making significant contributions in addressing such issues effectively over a broad range of environments and scales, from river segments, to watersheds, to large geographic regions.

Harmful alteration, disruption, degradation or destruction of ecosystems and habitat has prompted worldwide efforts to recover ecologically important morphodynamic features and restore rivers, lakes and deltas. Such efforts include (Hart et al. 2002; Palmer et al. 2005; Roni et al. 2005; Katopodis and Aadland 2006; Paola et al. 2006; Elosegi et al. 2010; Brown et al. 2011; Wohl et al. 2015):

1. improving ecological status and environmental conditions;

2. increasing recreational and aesthetic values;

3. upgrading affected ecosystems;

4. restoring wetlands;

5. controlling streambank erosion through various hard and soft methods, such as using vegetation;

6. rehabilitating degraded aquatic habitats;

7. replacing destroyed habitats;

8. re-establishing near natural ecosystem functions;

9. re-naturalising channelized rivers and streams;

10. relaxing or eliminating human constraints on natural diversity;

11. controlling and eradicating aquatic invasive species;

12. re-flooding with pulse-flow releases (e.g. Colorado River; Mueller et al. 2017);

13. removing infrastructure such as levees, weirs and dams;

14. designing and managing new projects using natural analogues for morphologies and key characteristics of hydrographs, sediment regimes and ice conditions;

15. gaining knowledge and enhancing winter habitats in circumpolar countries, especially during the dynamic periods of freeze-up and ice break-up;

16. protecting natural or well-functioning managed ecosystems;

17. monitoring based on science and developing standard methods to measure effectiveness of measures undertaken.

The quantitative and transdisciplinary information and knowledge needed for the morphodynamic, ecological and biological dimensions to ensure successful implementation of even a few of this long list of efforts, requires remarkable ecohydraulic studies.

Re-establishing robust geomorphic and ecological processes that auto-generate conditions for biodiversity to flourish, building artificial waterbodies to substitute for natural or semi-natural ecosystems, or compensating in other ways for harmful consequences or loss of freshwater ecosystems and river deltas, are increasingly important for most countries. For example, river restoration efforts may involve a variety of measures, including infrastructure designed to repair damaged ecosystems, artificial channels built with features which may mimic natural habitats or removal of dams and other river works (Hart et al. 2002; Katopodis and Aadland 2006). Such measures are now common in many countries, though frequently their design and construction fall short of expectations. Reasons for underperformance may include: (1) limited understanding of the morphodynamic and ecological interactions; (2) inadequate initial studies; (3) lack of understanding of how much morphological change it takes to affect ecologically important functions and biodiversity; (4) short-term or no follow-up monitoring; (5) or failure simply because of poor maintenance. Often appropriate maintenance from an ecosystem recovery perspective may take decades and is as important for effectiveness as sound design and accurate construction. For restoration measures it is important of course to consider the time scale of morphodynamic changes: rivers may adjust their depths and widths over short geomorphic time (e.g. tens to hundreds of years), while river valley slope adjustments may require long geomorphic time (tens of thousands of years or more). Long-term scientific evaluations are usually needed to establish degree of effectiveness, allow adaptability for improved performance, as well as increase learning opportunities from well-functioning measures, partial solutions or failures. Science-based monitoring is also indispensable for validating assessments, mathematical models, and assumptions, identifying knowledge and data gaps, as well as providing insights for many needed breakthroughs. All aspects of river restoration could benefit from research and long-term monitoring based on an ecohydraulic framework to develop durable and effective solutions. Such research has delivered and will continue to afford opportunities to fill knowledge gaps in science and engineering, especially in the complex interactions between ecological and physical processes and advance Ecohydraulics.

Publishing interdisciplinary articles such as those most suitable for this journal (TJoE), was challenging in decades past. It was much more straightforward for high quality manuscripts to be published in single discipline scientific and engineering journals. Depending on the journal, interdisciplinary researchers emphasized the physical or the ecological/biological aspects, and not necessarily integrated the two well. For example, there is a large volume of publications spread over many journals with morphological topics almost completely isolated from ecology, and on ecological topics almost completely isolated from morphology. Synthesis through comprehensive reviews to integrate knowledge may offer significant benefits and would be welcome in TJoE. Naturally many journals have adapted their policy on content to address the need and include interdisciplinary articles. In addition, numerous new interdisciplinary journals have appeared over many years now. With a plethora of journals, interdisciplinary knowledge is rather fragmented and spread over many sources and thousands of articles. We posit that TJoE is designed to be an excellent publication vehicle for topics covered by the ecohydraulic trilogy: (1) movements and passage of aquatic biota; (2) environmental flows and (3) ecological restoration. So, we are pleased to welcome in this issue Czuba et al. (2018), the first article integrating morphodynamics and ecology. TJoE has now reached a milestone, i.e. in its first four issues it has published articles in all areas of the ecohydraulic trilogy.

The Journal of Ecohydraulics welcomes critical and comprehensive interdisciplinary reviews, meta-analyses of large data sets, articles integrating hydraulics/hydrology/morphology with ecology/biology, items that strive to achieve symmetrical treatment of physics and ecology, abiotic and biotic data, and analyses. Furthermore, perspectives and critiques on ecohydraulic themes and ways to advance the science and practice, are most welcome. It is time for the worldwide Ecohydraulic Community to adopt TJoE as the main publication vehicle.

Acknowledgments

We would like to take this opportunity to thank all those who contributed to the Journal of Ecohydraulics since the inaugural double issue appeared in November 2016, especially all the Associate Editors and all the reviewers for their diligence.

Disclosure statement

No potential conflict of interest was reported by the authors.