Physical-Ecological Interactions in a Lowland River System: Large Wood, Hydraulic Complexity and Native Fish Associations in the River Murray, Australia

Interdisciplinary science involves the 'explicit joining of two or more areas of understanding into a single conceptual-empirical structure' (Pickett et al., 1999). Integration of disciplines in this way can be done along additive or extractive lines. The additive case is where two areas of study are combined, more or less intact, into a new composite understanding; in the extractive case, by contrast, different areas of study provide components that are fused to yield a new understanding. Both processes can be used in river science, depending on the nature of the problem at hand and the state of knowledge in the different disciplines. In the science of ecohydrology-hydroecology, where the investigator seeks to unravel mutual interactions between the hydrological cycle and ecosystems at different scales (Porporato and Rodriguez-Iturbe, 2002), additive studies have dominated (e.g., Statzner and Higler, 1986; Newson and Newson, 2000; Young, 1993). Such a science can be regarded as a subset of the broader field of ecogeomorphology in which three well-advanced disciplines are integrated: river ecology, hydrology, and fluvial geomorphology. Despite an acceleration in the number of research publications in ecohydrology-hydroecology since the 1980s, few have been extractive in nature (but see Poff and Alan, 1995; Parsons and Thoms, 2007, for exceptions). Thus, the case can be made that development of new paradigms within this emerging discipline has been restricted (Nuttle, 2002). With increasing pressures on the environment, there is a strong incentive to manage rivers as ecosystems (Palmer and Bernhardt, 2006). This provides a basis for extractive studies in ecohydrology-hydroecology, in this way potentially bridging the gap between the traditional subject boundaries of hydrology and ecology (Hannah et al., 2004). In this study we bring these general principles to bear and describe the hydraulic complexity of large wood in the main channel of the River Murray, a large lowland system in southeastern Australia. In particular, we examine hydraulic complexity by observing the use of these habitats by fish. We also provide hypotheses on which to base further investigations of large wood reinstatement in these types of river system.