LAUSR

River systems are among the world's most threatened ecosystems, facing multiple and often interlinked pressures across different spatial and temporal scales (Best, 2019; Tockner, Pusch, Borchardt, & Lorang, 2010; Vörösmarty et al., 2010). With increasing population growth, industrialization, and the intensification of land use during the last century, both the variety of demands and the intensity of uses have increased, while ecological integrity, functioning, and biodiversity of riverine landscapes have declined (Ferreira, Globevnik, & Schinegger, 2019). The subordination of multiple ecosystem services provided by pristine river-floodplain systems to a few dominant anthropic uses has reduced the multifunctionality of these ecosystems severely (Parsons et al., 2017). Today, river managers face the challenge of considering a variety of social, economic, and ecological demands simultaneously and objectively, where policy and human attitudes and perceptions may hamper the acceptance of management measures (Dunham et al., 2018; Jähnig et al., 2011). Thus, future management and restoration need to recognize river landscapes as socio-ecological entities, which provide ecosystem services for humans based on their ecological integrity. The 6th Biennial Symposium of the International Society for River Science (ISRS) was hosted by the Institute of Hydrobiology and Aquatic Ecosystem Management at the University of Natural Resources and Life Sciences, Vienna (BOKU), Austria, from September 8–13, 2019. According to the conference theme “Riverine landscapes as coupled socio-ecological systems,” the symposium emphasized integrative research on the sustainable use, management, and protection of aquatic ecosystems. Particular attention was given to the complex interactions between society and the ecological functioning of highly modified riverine landscapes. This special issue of River Research and Applications includes 16 articles from this meeting, which address various challenges and solutions relating to the management and restoration of river-floodplain systems in the face of changing environmental and climatic conditions and increasing complexity of ecological and socio-economic demands. The articles span a wide range of topics, from the hydro-morphological development of river systems to the consideration of social aspects and complex abiotic–biotic interactions in river management, thus highlighting the need for process-based, dynamic, and integrated approaches in river management. 2 | THEMES OF THIS SPECIAL ISSUE