SUMMARY1. Human-induced changes in river flow regimes are ubiquitous worldwide. Although numerous case studies have identified negative ecological impacts of changes in different aspects of flow regimes (e.g. magnitude, timing), there have been few attempts to systematically review this literature to derive general relationships regarding ecological responses to changes in flow regimes. 2. Systematic literature reviews can inform science and management in ecologically complex systems not amenable to experimentation. However, such analysis of existing literature is often limited by inconsistent study design and data reporting. To attempt to overcome these difficulties, we used the recently developed Eco Evidence method and software to analyse 165 studies of ecological responses to changes in river flow regimes. 3. Eco Evidence provides a rule set and standardised list of terms to assist reviewers to interpret consistently the results of disparate studies. The companion software assists with the synthesis of this information to reach transparent and repeatable conclusions regarding cause-effect hypotheses of ecological responses to environmental drivers. 4. We compared our results to those of a recent, informal systematic review of the same studies, which is proving extremely influential. Stronger conclusions are reached when evidence is weighted, classified and combined according to the rules in Eco Evidence. Compared to the original review, we reached informative conclusions for a larger number of flow-response hypotheses, found that hypotheses for which the most evidence was available returned inconsistent results, addressed hypotheses at levels of conceptual resolution relevant to management and identified where insufficient evidence exists to reach a conclusion. 5. Analyses conducted at several levels of conceptual resolution found strong support for many hypotheses regarding ecological impacts. We found a consistent sensitivity to changes in flow regime for both fish and riparian vegetation across a variety of performance metrics. While macroinvertebrate responses varied among performance metrics (e.g. abundance was negatively affected by increases or decreases in flows, diversity was only negatively affected by flow decreases, and assemblage structure was affected by neither), they were largely consistent within these metrics. 6. We thus conclude that the Eco Evidence approach allowed us to extract more knowledge from the data set than was possible in the original review. Eco Evidence can improve synthesis of the burgeoning ecological literature and improve our general understanding in ecology. Amid widespread 2439This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.Freshwater Biology (2013Biology ( ) 58, 2439Biology ( -2451Biology ( doi:10.1111 calls for 'evidence-based' environ...

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Floods and droughts are key driving forces shaping aquatic ecosystems. Climate change may alter key attributes of these events and consequently health and distribution of aquatic species. Improved knowledge of biological responses to different types of floods and droughts in rivers should allow the better prediction of the ecological consequences of climate change‐induced flow alterations. This review highlights that in unmodified ecosystems, the intensity and direction of biological impacts of floods and droughts vary, but the overall consequence is an increase in biological diversity and ecosystem health. To predict the impact of climate change, metrics that allow the quantitative linking of physical disturbance attributes to the directions and intensities of biological impacts are needed. The link between habitat change and the character of biological response is provided by the frequency of occurrence of the river wave characteristic—that is the event's predictability. The severity of impacts of floods is largely related to the river wave amplitude (flood magnitude), while the impact of droughts is related to river wavelength (drought duration).

Knowledge of temporal change in ecological condition is important for the understanding and management of ecosystems. However, analyses of trends in biological condition have been rare, as there are usually too few data points at any single site to use many trend analysis techniques. We used a Bayesian hierarchical model to analyse temporal trends in stream ecological condition (as measured by the invertebrate-based index SIGNAL) across Melbourne, Australia. The Bayesian hierarchical approach assumes dependency amongst the sampling sites. Results for each site ''borrow strength'' from the other data because model parameter values are assumed to be drawn from a larger common distribution. This leads to robust inference despite the few data that exist at each site. Utilising the flexibility of the Bayesian approach, we also modelled change over time as a function of catchment urbanisation, allowed for potential temporal and spatial autocorrelation of the data and trend estimates, and used prior information to improve the estimate of data uncertainty. We found strong evidence of a widespread decline in SIGNAL scores for edge habitats (areas of little or no flow). The rate of decline was positively associated with catchment urbanisation. There was no evidence of such declines for riffle habitats (areas with rapid and turbulent flow). Melbourne has experienced a decline in rainfall, indicative of either drought and/or longer-term climate change. The results are consistent with the expected coupled effects of these rainfall changes and increasing urbanisation, but more research is needed to isolate a causal mechanism. More immediately, however, the Bayesian hierarchical approach has allowed us to identify a pattern in a biological monitoring data set that might otherwise have gone un-noticed, and to demonstrate a large-scale temporal decline in biological condition.

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