FLOW VARIABILITY AND THE ECOLOGY OF LARGE RIVERS

Ecological processes in large rivers are controlled by their flow vari ability. However, it is difficult to find measures of hydrological var iability that characterize groups of rivers and can also be used to ge nerate hypotheses about their ecology. Multivariate analyses of the hy drographs of 52 rivers worldwide revealed distinctive patterns of flow variability that were often correlated with climate. For example, the re were groups of rivers that corresponded broadly with 'tropical' and 'dryland' climates. However, some rivers from continental climates oc cupy both extremes of this range, illustrating the limitations of simp le classification. Individual rivers and groups of rivers may also hav e different hydrographic 'signatures', and attempts to combine measure s of hydrological variability into indices mask biologically significa nt information. This paper identifies 11 relatively independent measur es of hydrological variability that help categorize river types and ar e each associated with aspects of fish biology. Ways are suggested by which the Flood Pulse Concept can be expanded to encompass hydrologica l variability and accommodate differences among groups of rivers from different climatic regions. Such recognition of the complex role of hy drological variability enhances the value of the concept for river con servation, management and restoration.