Variability in riverine ecosystems

Riverine ecosystems are complex features of the landscape displaying structures and processes that reflect the influence of many variables at a range of scales. Thus, the physical, chemical and ecological character of riverine ecosystems differs between them and may change over time, often at different rates and in different ways. In addition, the structure and function of riverine ecosystems also varies downstream. Rivers are process-response systems whereby changes to discharge and sediment load induce a range of ecosystem responses. Those river systems subject to highly variable process regimes may be expected to exhibit enhanced levels of complexity and display processform relationships commensurate of this variability, where both equilibrium and non-equilibrium conditions can exist. The process-form relationships and interactions between the physical, chemical and ecological templates of highly variable riverine ecosystems challenge some of the accepted wisdoms of river system functioning. This paper introduces some of these challenges and the general theme of the ten papers of this special issue of River Research and Applications. As a collective they apply an interdisciplinary approach to the study and management of variability in riverine ecosystems and in doing so advance our knowledge of these systems. Copyright (C) 2006 John Wiley & Sons, Ltd.