This special issue "Rehabilitating large regulated rivers" of the Large Rivers supplement series of Archiv f#r Hydrobiologie comprehensively documents the presentations given at the International Conference "Lowland River Rehabilitation 2003", held in Wageningen (the Netherlands), September 29 to October 2, 2003. The Netherlands Centre for River Studies (NCR) and the Institute for Inland Water Management and Wastewater Treatment RIZA organized the conference. More than 50 oral contributions and over 40 posters were presented, 45 of which, from 14 different countries, are published as peer-reviewed high-quality papers in this issue.
The conference focused on large temperate lowland rivers and their floodplains in Europe and North America, with the aim of building upon advancements made in both continents. Although Europe and North America are equally faced by the logistical, socio-political, and economic challenges of rehabilitating their many environmentally degraded rivers, there has been insufficient exchange of information experiences and techniques in rehabilitation. The conference focused on large rivers because they share similar functions (navigation, flood protection, hydropower), which set boundary conditions to ecological rehabilitation. Our goal is to incorporate a general understanding of large river functioning into the practice of river rehabilitation by: (a) defining tangible and attainable endpoints deduced from ecologically intact or pristine references; (b) developing prognostic tools to link abiotic processes and patterns and biotic response at the appropriate spatial and temporal scales; and (c) optimizing rehabilitation within the multitude of functions large rivers fulfil and considering the heavily modified condition of most regulated large rivers.
The special issue is consequently divided into three sections, which we consider crucial to advance large river rehabilitation:
1. References and end-points for rivers and their floodplains: References and endpoints are the essential framework for rehabilitation. References are based on historical data or are obtained from other comparable, but (semi-)pristine river systems. End-points are our targets for rehabilitation derived from such references taking boundary conditions from other functions into consideration.
2. Assessing achievements of rehabilitation: The step from visionary plans to actual rehabilitation is often a long and winding road. For policy makers and managers is not self-evident that those projects should be properly documented and learned from. Our present expertise is insufficiently transferred to and applied by end users. Expressing costs and benefits is in its infancy especially at various spatial and temporal scales.
3. Integrating rehabilitation into river management: Rehabilitation interferes with other user functions. There are win-win options when other than technical solutions are considered. There seems little future for substantial rehabilitation without a solid socio-economic foundation.
The issue concludes with a synthesis paper that gives an overview of recent progress in Europe and North America structured along these three themes, addressing the management needs and making recommendations for a future research agenda on rehabilitation of large regulated rivers.