THE FLOOD PULSE CONCEPT: NEW ASPECTS, APPROACHES AND APPLICATIONS - AN UPDATE Junk W.J. Wantzen K.M. Max-Planck-Institute for Limnology, Working Group Tropical Ecology, P.O. Box 165 , 24302 Pln, Germany E-mail: wjj@mpil-ploen.mpg.de ABSTRACT The flood pulse concept (FPC), published in 1989, was based on the scientific ex perience of the authors and published data worldwide. Since then, knowledge on floodplains has increased considerably, creating a large database for testing the predictions of the concept. The FPC has proved to be an integrative approach for studying highly diverse and complex ecological processes in river-floodplain sys tems; however, the concept has been modified, extended and restricted by several authors. Major advances ha ve been achieved through detailed studies on the effects of hydrology and hydrochemistry, climate, paleoc limate, biogeography, biodiversity and landscape ecology and also through wetland restoration and sustainable manag ement of floodplains in different latitudes and continents. Discussions on floodplain ecology and man agement are greatly influenced by data obtained on flow pulses and connectivity, the Riverine Produc tivity Model and the Multiple Use Concept. This paper summarizes the predictions of the FPC, evaluates their v alue in the light of recent data and new concepts and discusses further developments in floodplain theory.

The flood pulse concept: New aspects, INTRODUCTION Rivers and floodplain wetlands are among the most threatened ecosystems. For example, 77 percent of the water discharge of the 139 largest river systems in North America and Europe is affected by fragmentation of the river channels by dams and river regulation (Dynesius and Nilsson 1994). In recent reviews on wetlands, demographic trends, economic and political development, demand for hydroelectric energy and water, agriculture and animal ranching, eutrophication and pollution, fisheries, logging, recreation and ecotourism and invasion by exotic species have been identified as the most important current determinants for the development of rivers and floodplain wetlands (Tockner and Stanford 2002; Junk 2002). The global water crisis and the threat to aquatic organisms, especially riverine biota (Dudgeon 2000; Pringle 2001), increase the necessity to develop models that serve both science and policy. The flood pulse concept (FPC) (Junk, Bayley and Sparks 1989) was primarily designed as a scientific concept, but it also outlined some strategies for use, recently specified in Junk et al. (2000). Here, the impact of advances in river ecology on this and other contemporary concepts is critically analyzed. THEORETICAL BACKGROUND HISTORICAL DEVELOPMENT Limnologists classify inland waters as standing waters (lakes, ponds) and running waters (streams and rivers). Both system types receive allochthonous substances and produce autochthonous organic matter, both of which are metabolized and recycled. Standing waters, however, are closed systems that store inorganic and organic matter, circulate organic matter and dissolved inorganic substances in characteristic internal cycles in the lake basin and eventually deposit them in the sediments. These systems are characterized mainly by thermal and/or chemical stratification. Running waters are open systems that transport water and dissolved and suspended matter from the continents to the sea or to endorheic basins. This transport includes intermediate deposition and re-suspension of sediments in the river channel or in the connected flood plain, where production and degradation of organic matter also takes place. These characteristics are reflected for lakes in the Seentypenlehre (Lake typology), elaborated by Thienemann and Naumann between 1915 and 1935 (e.g. Thienemann 1925; Naumann 1932) and for streams and rivers in articles by Illies (1961a) and

Illies and Botosaneanu (1963) on the differentiation into different zones. These zones, described in these early studies as rhithron and potamon with epi-, metaand hypo-subzones, were mainly characterized by abiotic patterns (current, temperature) and by the occurrence of distinct animal and plant communities that depend on a given set of these abiotic patterns. For example, epirithral communities are those typical of glacier outflows and that depend on low temperatures, high oxygen concentrations and fast current. In latitudinal comparisons, Illies (1961b) found evidence for a generality of this zonation in mountain streams worldwide - high-elevation streams in the tropics have communities similar to those of low-latitude coldwater streams. Later, Vannote et al. (1980) substituted this rather static view of river classification with the River Continuum Concept (RCC), which introduced a dynamic concept of continuously changing physical conditions and biological components along the river channel, especially regarding the allochthonous and autochthonous inputs and the processing of organic matter in the flowing water along the river continuum. The RCC predicts major changes in the load and quality of organic matter and the biota in the stream/river channel from the headwaters to the lower river courses. The high allochthonous input from riparian vegetation in the headwaters decreases with increasing channel width (increasing stream order). Autochthonous primary production in the headwaters is low because of shading by trees (P/R 1) and decreases again in the lower reaches because of high water depth and increased turbidity and turbulence (P/R