Klement Tockner

When the river runs dry: human and ecological values of dry riverbeds

Temporary rivers and streams that naturally cease to flow and dry up can be found on every continent. Many other water courses that were once perennial now also have temporary flow regimes due to the effects of water extraction for human use or as a result of changes in land use and climate. The dry beds of these temporary rivers are an integral part of river landscapes. We discuss their importance in human culture and their unique diversity of aquatic, amphibious, and terrestrial biota. We also describe their role as seed and egg banks for aquatic biota, as dispersal corridors and temporal ecotones linking wet and dry phases, and as sites for the storage and processing of organic matter and nutrients. In light of these valuable functions, dry riverbeds need to be fully integrated into river management policies and monitoring programs. We also identify key knowledge gaps and suggest research questions concerning the values of dry riverbeds.

Why Should We Care About Temporary Waterways

Intermittently flowing streams and rivers should be recognized, afforded protection, and better managed. A proposed ruling by the U.S. Environmental Protection Agency (EPA), aimed at clarifying which bodies of water that flow intermittently are protected under law (1), has provoked conflict between developers and environmental advocates. Some argue that temporary streams and rivers, defined as waterways that cease to flow at some points in space and time along their course (see the figure, left) ( Fig. 1) (2), are essential to the integrity of entire river networks. Others argue that full protection will be too costly. Similar concerns extend far beyond the United States. Debate over how to treat temporary waterways in water-policy frameworks is ongoing (3), particularly because some large permanent rivers are shifting to temporary because of climate change and extraction of water (4). Even without human-induced changes, flow intermittency is part of the natural hydrology for streams and rivers globally.

Effects of Hydrologic Alterations on the Ecological Quality of River Ecosystems

In most of the world’s watercourses, dramatic modifications have occurred as a consequence of intensive use by human societies. The simplification of the channel network and the alteration of water fluxes have an impact upon the capacity of fluvial systems to recover from disturbances, because of their irreversible consequences. However, human impacts on river hydrology, such as those that derive from regulating their flow or by affecting their channel geomorphology, affect the functional organisation of streams, as well as the ecosystem services that derive from them, and lead to the simplification and impoverishment of these ecosystems.

Contraction, fragmentation and expansion dynamics determine nutrient availability in a Mediterranean forest stream

Temporary streams are a dominant surface water type in the Mediterranean region. As a consequence of their hydrologic regime, these ecosystems contract and fragment as they dry, and expand after rewetting. Global change leads to a rapid increase in the extent of temporary streams, and more and more permanent streams are turning temporary. Consequently, there is an urgent need to better understand the effects of flow intermittency on the biogeochemistry and ecology of stream ecosystems. Our aim was to investigate how stream nutrient availability varied in relation to ecosystem contraction, fragmentation and expansion due to hydrologic drying and rewetting. We quantified the temporal and spatial changes in dissolved nitrogen (N) and phosphorus (P) concentrations along a reach of a temporary Mediterranean forest stream during an entire contraction–fragmentation–expansion hydrologic cycle. We observed marked temporal changes in N and P concentrations, in the proportion of organic and inorganic forms as well as in stoichiometric ratios, reflecting shifts in the relative importance of in-stream nutrient processing and external nutrient sources. In addition, the spatial heterogeneity of N and P concentrations and their ratios increased substantially with ecosystem fragmentation, reflecting the high relevance of in-stream processes when advective transport was lost. Overall, changes were more pronounced for N than for P. This study emphasizes the significance of flow intermittency in regulating stream nutrient availability and its implications for temporary stream management. Moreover, our results point to potential biogeochemical responses of these ecosystems in more temperate regions under future water scarcity scenarios.

Non-perennial Mediterranean rivers in Europe: Status, pressures, and challenges for research and management

Non-perennial rivers and streams (NPRS) cover >50% of the global river network. They are particularly predominant in Mediterranean Europe as a result of dry climate conditions, climate change and land use development. Historically, both scientists and policy makers underestimated the importance of NRPS for nature and humans alike, mainly because they have been considered as systems of low ecological and economic value. During the past decades, diminishing water resources have increased the spatial and temporal extent of artificial NPRS as well as their exposure to multiple stressors, which threatening their ecological integrity, biodiversity and ecosystem services. In this paper, we provide a comprehensive overview of the structural and functional characteristics of NPRS in the European Mediterranean, and discuss gaps and problems in their management, concerning their typology, ecological assessment, legislative and policy protection, and incorporation in River Basin Management Plans. Because NPRS comprise highly unstable ecosystems, with strong and often unpredictable temporal and spatial variability - at least as far as it is possible to assess - we outline the future research needs required to better understand, manage and conserve them as highly valuable and sensitive ecosystems. Efficient collaborative activities among multidisciplinary research groups aiming to create innovative knowledge, water managers and policy makers are urgently needed in order to establish an appropriate methodological and legislative background. The incorporation of NPRS in EU-Med River Basin Management Plans in combination with the application of ecological flows is a first step towards enhancing NPRS management and conservation in order to effectively safeguard these highly valuable albeit threatened ecosystems.

Chapter 1 – Introduction to European Rivers

Publisher Summary nRivers recognize no political boundaries. This is particularly true for Europe, which has over 150 transboundary rivers. For example, the Danube is the 29th longest river globally and it drains parts of 19 countries and 10 ecoregions. Further, 8 of the 10 largest catchments in Europe are in the eastern plains of Russia and the Ukraine and information on their present status is highly limited. Europe also has a long history in river training with most rivers being severely fragmented, channelized, and polluted. The European Union launched an ambitious program called the Water Framework Directive (WFD), which requires a catchment management plan for all major European rivers for achieving “good ecological status” by 2015. This chapter provides a comprehensive overview of all major European catchments included in the book, starting with the bio-geographic setting, with an emphasis on physiography, hydrology, ecology/biodiversity, and human impacts.

Biodiversity research: data without theory—theory without data

1 Plant Ecology, Institute of Biology, Freie Universitat Berlin, Berlin, Germany, 2 Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), Berlin, Germany, GeoZentrum Nordbayern, Friedrich-Alexander Universitat Erlangen-Nurnberg, Erlangen, Germany, Museum fur Naturkunde, Leibniz Institute for Research on Evolution and Biodiversity, Berlin, Germany, 5 Botanischer Garten und Botanisches Museum Berlin-Dahlem, Freie Universitat Berlin, Berlin, Germany, 6 Forest Dynamics, Swiss Federal Research Institute WSL, Birmensdorf, Switzerland, 7 Leibniz Center for Agricultural Landscape Research (ZALF), Muncheberg, Germany, 8 Leibniz Institute for Zoo and Wildlife Research (IZW), Berlin, Germany, 9 Biodiversity Research/Systematic Botany, University of Potsdam, Potsdam, Germany, 10 Institute of Geoecology, Technische Universitat Braunschweig, Braunschweig, Germany, 11 Potsdam Institute for Climate Impact Research (PIK), Potsdam, Germany, 12 Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany, 13 Plant Ecology and Conservation Biology, University of Potsdam, Potsdam, Germany

Protecting U.S. temporary waterways

Protecting the ecological health of rivers relies on maintaining intact flows from source areas to downstream navigable waters (1). Yet the U.S. Environmental Protection Agency (EPA) intends to rescind legal protection of tributary rivers, streams, and wetlands that do not have year-round flows (temporary waterways) and whose surface waters contribute flow to permanent navigable waters (2). This decision would severely damage the condition and uses of many U.S. waters, both temporary and navigable.