The turbulent properties of flow in rivers are of fundamental importance to aquatic organisms yet are rarely quantified during routine river habitat assessment surveys or the design of restoration schemes due to their complex nature. In this paper, we review the two-way interactions between aquatic biota and hydrodynamics in rivers, and key methodological approaches used in their quantification, to encourage more explicit consideration of the importance of turbulence in river science and management. We explore recent advances and issues relating to the study of these interactions in the field, laboratory and numerical modeling, the use of artificial and live biota, and different flow measurement technologies. We also review methods for the quantification of ecologically relevant turbulent flow properties, identifying key descriptors of the intensity, periodicity, orientation, and the scale of turbulent flow structures. Our analysis highlights not only the various ways in which plants and animals modify the flow field but also how this can deliver beneficial effects relating to solute exchange, food availability, oxygenation, waste removal, locomotion, and predator-prey interactions. It also demonstrates potential threats to growth and survival relating to turbulence, including injury, dislodgement, increased energy expenditure, mortality, and complex influences on predators and prey. We conclude by identifying some remaining barriers to the integration of turbulence into the science and practice of river assessment and restoration but also opportunities in the form of controlled laboratory experimentation, increasingly sophisticated flow sensors and imaging technologies, and numerical simulation of turbulence that could advance understanding in this complex field of research.There is considerable diversity in the research approaches applied to the study of interactions FIGURE 1 | Definition of Reynolds number and laminar and turbulent flow, with example Reynolds numbers for different types of organisms interacting with the flow. Advanced Reviewwires.wiley.com/water
Previous work suggests that ecohydraulics should consider the broad range of parameters that characterize turbulent flow combining Intensity, Periodicity, Orientation and Scale (IPOS;Lacey et al., 2012), but ecohydraulics research under field conditions in natural river systems remains rare, largely due to practical constraints. A novel combination of turbulence properties, computed from high frequency velocity time series, and underwater video of fish habitat use are presented here for two submerged large wood patches on a side channel of the Tagliamento River, Italy, providing insights into ecohydraulic interactions and the first known field application of the IPOS framework. Two adjacent wood patches of similar size reveal distinct differences in turbulence properties and fish habitat use, emphasizing the importance of considering the diverse properties of turbulent flow and reflecting the role of wood structural properties and position in determining the exact nature of hydraulic habitat. Key gradients in turbulence properties derived from multivariate analysis broadly align with IPOS categories, providing statistical validation for the IPOS framework. The application of IPOS to a habitat-focused study demonstrates its utility in understanding and deriving key trends from large and complex turbulence data sets. The results also provide a preliminary indication that IPOS-derived gradients may be helpful in explaining fish habitat selection but these findings need further validation through high spatial resolution studies with different species and bioenergetics models. These insights support previous calls for inclusion of diverse turbulence parameters in ecohydraulics research and, where possible, more explicit consideration of turbulence properties in river assessment, conservation and restoration.
Turbulent flow in natural river channels drives geophysical processes and exerts a fundamental influence on aquatic biota. An extensive range of turbulence properties have previously been synthesized into four categories or “dimensions” with ecological relevance: intensity, periodicity, orientation and scale (IPOS). We apply this framework across three rivers with differing morphologies in order to assess the statistical coherence of the four IPOS categories within turbulence field data and their utility in discriminating between fundamental units of river habitat. Intensity, periodicity‐scale and orientation were identified as the key gradients in the turbulence data set using multivariate analysis. These gradients all revealed statistically significant differences between rivers and/or geomorphic units. The intensity gradient accounted for the highest variance and most pronounced inter‐reach differences, but the periodicity‐scale and orientation gradients were also useful in distinguishing between certain combinations of rivers and/or geomorphic units. Different turbulence gradients, or combinations of gradients, were important in characterizing differences between rivers and geomorphic units (riffes, pools, steps). The gradients provided improved prediction of geomorphic units compared to standard hydraulic variables (mean velocity, depth), although the extent of improvement in prediction varied between river morphologies. The analysis reveals the statistical coherence of the four categories or “dimensions” of turbulence in multivariate space, connects the ecologically defined IPOS categories of turbulence properties with river types and fundamental units of river habitat (geomorphic units). Turbulence signatures of natural channel morphology are expressed across all four dimensions of turbulence, providing clear evidence that these four dimensions should be routinely considered in ecohydraulics and hydromorphology research to facilitate a full understanding hydraulic habitat.
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