Lowland rivers: an Australian introduction

An evident trend in river ecosystem research over the last 10 years has been the increased emphasis on larger systems and, in particular, on the importance of interconnections between river channels and their floodplains. The trend has been reflected in a rapidly expanding literature describing the character of large rivers. The 1989 special issue of Canadian Journal of Fisheries and Aquatic Sciences was one of the first publications to deal with these systems. These papers from the symposium on large rivers (Dodge, 1989) had a multidisciplined focus but only 11 of the 49 papers dealt with large floodplain rivers. The geomorphological character of lowland rivers was presented in Lowland Floodplain Ri6ers: Geomorphological Perspecti6es (Carling and Petts, 1992). There the aim was to describe the holistic nature of the river valley, shifting attention away from the river bed per se and considering, instead, the data that are required for a better understanding of channel–floodplain relationships over a range of time scales. More recently, selected papers from the International Conference, Sustaining the Ecological Integrity of Large Floodplain Ri6ers were presented in an issue of this journal. The common theme of the papers was the highly variable physical, chemical and biological natures of large river systems. Large rivers were portrayed as ‘moving targets’ or highly dynamic systems, with the general synthesis that research should focus on the trajectories of these systems rather than their status at points in time and space. Despite the lack of a detailed definition of lowland rivers there are a number of ecosystem models that conceptualize their structure and function. The River Continuum Concept (RCC; Vannote et al., 1980) was initially applied but later criticized (Sedell et al., 1989) because of its inability to evaluate biotic assemblages in large rivers and metabolic interactions in ecosystems and its emphasis on longitudinal linkages rather than lateral transfers between the channel and floodplain. The Flood Pulse Concept (FPC; Junk et al., 1989) addresses this problem and concerns itself with the ecological significance of temporal patterns of flow in lowland rivers. It recognizes the importance of floods in the dynamics of river–floodplain systems. However, this concept may be less applicable to confined lowland systems. The Riverine Productivity Model of Thorp and Delong (1994) concentrated on confined lowland systems and highlighted the significance of instream production and floodplain inputs of carbon in periods not just related to floods. Recently, Walker et al. (1995) have called for the development of a more generic model for dryland–lowland rivers. They suggest a more flexible approach that recognizes the importance of all energy transfers, and propose that a hybrid model could be formulated from the models and concepts already outlined. In a review of the ecology of Australian lotic systems, Lake (1994) notes that contemporary ecosystem theories, developed from research on temperate perennial streams to explain river system functioning, do not apply to Australian river systems. This observation has been echoed by many, including Walker et al. (1995). Moreover, water policies and legislation (Johnson, 1993), and river management and restoration strategies, e.g. Petts and Calow (1996), also share similar origins. Boulton et al. (2000) suggest that the uncritical extrapolation of these theories to any system can prove perilous and even misleading, as observed for Australian systems (Williams, 1988).