Intermittent rivers and ephemeral streams: what water managers need to know. CHP.3 Water Physicochemistry in IRES

Intermittent rivers and ephemeral streams (IRES) drain over half the world's land surface and are common water bodies throughout Europe. Often 'hotspots' of regional biodiversity and pivotal for the functional integrity of river networks, many IRES are exploited to achieve growing human demands for water and other ecosystem services. However, suffering from negative perceptions and historically overlooked by researcher compared to perennial rivers and streams, IRES are degraded at alarming rates, and attempts to exclude them from legislations are growing. In the last two decades, research into the ecohydrology of these prevalent and unique ecosystems has bloomed and management issues have intensified because all climate change scenarios predict expansion in the global extent of IRES. Also, many perennial rivers are gradually becoming intermittent and IRES will become the dominant type of water bodies in the future. Therefore, supported by COST (European Cooperation in Science and Technology, www.cost.eu), we have gathered a dense network of European academics and managers from different disciplines spanning hydrology, ecology, biogeochemistry, and social sciences. This consortium, SMIRES (Science and Management of Intermittent Rivers and Ephemeral Streams, www.smires.eu) aims to compile the scattered knowledge on IRES across Europe for a better understanding of these ecosystems. Although important research gaps remain, our aim was to translate the current level of knowledge to manage, protect, and restore the diverse types of IRES across Europe. This effort resulted in the present handbook, which is the first, to our knowledge, to provide recommendations and guidelines for most aspects related to IRES management issues. Our effort will continue in the near future, notably within the ECOSTAT working group that will integrate IRES into the current management efforts driven by the Water Framework Directive. Rivers or streams are defined by flowing waters confined within river channels (except during floods) and moving into one direction: rivers are usually larger and deeper than streams, but this is a loose distinction of common usage. The same applies to describing different types of non-perennial flow regimes: "ephemeral" implies a shorter flow duration and lower predictability than "intermittent", but no fixed boundaries exist. Whereas the scientific literature is peppered with attempts to assign names to classes of streams and rivers whose flows cease for varying periods with varying predictability, a global consensus remains elusive and probably will continue to do so. Therefore, rather than opening this semantic minefield, we refer to "intermittent rivers and ephemeral streams" and adopt the acronym "IRES" in this consortium and handbook as a shorthand term for all flowing waters that cease flow and/or dry completely at some point along their course. We are indebted to the core team, which supervised this handbook preparation, to the many contributors of the different chapters, ant to all the contributors of the working groups of SMIRES, who have done a magnificent job throughout the 4-year timeframe of the action. Last, if this handbook is the first to focus entirely on the management of IRES, there is still much to learn about these dynamic ecosystems and how best to protect their beauty, ecological integrity, and other social values.