Drawing together multiple lines of evidence from assessment studies of hydropeaking pressures in impacted rivers

Hydropeaking has negative effects on aquatic biota, but the causal relationships have not been studied extensively, especially when hydropeaking occurs in combination with other environmental pressures. The available evidence comes mainly from case studies demonstrating river-specific effects of hydropeaking that result in modified microhabitat conditions and lead to declines in fish populations. We used multiple lines of evidence to attempt to strengthen the evidence base for models of ecological response to flow alteration from hydropeaking. First, we synthesized evidence of ecological responses from relevant studies published in the scientific literature. We found considerable evidence of the ecological effects of hydropeaking, but many causal pathways are poorly understood, and we found very little research on the interactive effects of hydropeaking and other pressures. As a 2nd line of evidence, we used results from analyses of large-scale data sets. These results demonstrated the extent to which hydropeaking occurs with other pressures, but did not elucidate individual or interactive effects further. Thus, the multiple lines of evidence complemented each other, but the main result was to identify knowledge gaps regarding hydropeaking and a consequent pressing need for novel approaches, new questions, and new ways of thinking that can fill them.© 2017 by The Society for Freshwater Science.publishedVersio

Harmonisation of international conceptual cause-effect tools, based on ecological evidence data for multiple stressor impacts on riverine ecosystems

European rivers are impacted by multiple stressors, which alone and in combination cause changes in riverine ecosystems. The cause-effect chains leading to ecological impairments should be critically diagnosed in order to plan effective restoration measures to improve the biological condition. Methods for ecological causal assessment, as well as associated tools have been developed simultaneously in different parts of the world. These methods use scientific evidence in ecological literature to support causal assessments in environmental investigations. The objective of this thesis is to support the development of diagnostic and predictive tools in the EU-funded project MARS (Managing Aquatic ecosystems and water Resources under Multiple Stress), by studying existing methods and creating conceptual ecological models with their assistance. The results of this work contain literature-based evidence on causes and ecological effects of excess fine sediment and nutrients in rivers. The results are visualised in conceptual diagrams, which organise and combine the evidence on cause-effect associations. The diagrams demonstrate how fine sediment and nutrients affect the ecological functioning of rivers by changing benthic invertebrate and fish community structures. The combined effects of the stressors are mainly additive multi-stressor relationships, but the reference literature also evidenced synergistic and antagonistic effects between the stressors. Additionally the study revealed a research gap concerning joint effects of the stressors on fish indicators. The main challenges for the future development of cause-effect tools are effective extraction of cause-effect associations from the primary studies and visualisation of complex multi-stress relationships in conceptual models.Nona HumerUniversität für Bodenkultur Wien, Masterarbeit, 2016(VLID)193571