This paper critically reviews developments in the conceptualization and elaboration of the River Ecosystem Health (REH) concept. Analysis of literature shows there is still no consistent meaning of the central concept Ecosystem Health, resulting in models (i.e. elaborations) that have unclear and insufficient conceptual grounds. Furthermore, a diverse terminology is associated with describing REH, resulting in confusion with other concepts. However, if the concept is to have merit and longevity in the field of river research and management, unambiguous definition of the conceptual meaning and operational domain are required. Therefore a redefinition is proposed, based on identified characteristics of health and derived from considering semantic and conceptual definitions. Based on this definition, REH has merit in a broader context of river system health that considers societal functioning next to ecological functioning. Assessment of health needs integration of measures of multiple, complementary attributes and analysis in a synthesized way. An assessment framework is proposed that assesses REH top-down as well as bottom up by combining indicators of system stress responses (i.e. condition) with indicators identifying the causative stress (i.e. stressor). The scope of REH is covered by using indicators of system activity, metabolism (vigour), resilience, structure and interactions between system components (organization). The variety of stress effects that the system may endure are covered by using biotic, chemical as well as physical stressors. Besides having a unique meaning, the REH metaphor has added value to river management by being able to mobilize scientists, practitioners and publics and seeing relationships at the level of values. It places humans at the centre of the river ecosystem, while seeking to ensure the durability of the ecosystem of which they are an integral part. Optimization of the indicator set, development of aggregation and classification methodologies, and implementation of the concept within differing international frames are considered main aims for future research.

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Bioenergy expansion can signifi cantly impact water resources in the region in which it occurs.Investment, policy, and resource management decisions related to bioenergy should therefore take this critical consideration into account. Water resource impacts can defy easy quantifi cation because water consumption varies spatially and temporally, different water sources are not necessarily commensurable, and impact depends on the state of the resource base that is drawn upon. This perspective offers an assessment framework that operators and policy-makers can use in evaluating projects to avoid or mitigate detrimental effects.We adapt water footprint (WF) and life cycle assessment (LCA) techniques to the bioenergy context, describing comprehensive life cycle inventory (LCI) approaches that account for blue and green water use as well as for pollution effects, varying sources, coproduct allocation, and spatial heterogeneity. Impact assessment requires that characterization (weighting) factors be derived so that consumption values can be summed and compared across resources and locations. We recommend that characterization draw on metrics of water stress, accounting for environmental fl ow requirements, climatic variability, and non-linearity of water stress effects. Finally, we describe some location-specifi c impacts of concern that may not be revealed through common analytical approaches and may warrant closer consideration.

Interdisciplinarity results from dynamics at two levels. Firstly, research questions are approached using inputs from a variety of disciplinary fields. Secondly, the results of this multidisciplinary research feed back into the various research fields. This may either contribute to the further development of these fields, or may lead to disciplinary reconfiguration. If the latter is the case, a new interdisciplinary field may emerge. Following this perspective, the scientific landscape of river research and river science is mapped to assess to which current river research is a multi-disciplinary endeavor, and to which extent it results in a new emerging (inter)disciplinary field of river science. The paper suggests that this two level approach is a useful method to study interdisciplinary research and, more generally, disciplinary dynamics.With respect to river research, we show that it is mainly performed in several fields (limnology, fisheries & fish research, hydrology & water resources, and geomorphology) that hardly exchange knowledge. The different river research topics are multidisciplinary in nature, as they are shared by different fields. However, river science does not emerge as an interdisciplinary field, and often-mentioned new interdisciplinary fields such as hydroecology or hydromorphology are not (yet) visible. There is hardly any involvement of social within river research. Finally, the field of ecology occupies a central position within river research, whereas an expected engineering field is shown absent. This together may signal the acceptance of the ecosystem-based paradigm in river management, replacing the traditional engineering paradigm.