Imperilled rivers of Australia: Challenges for assessment and conservation

In Australia, riverine biodiversity (as judged by species diversity) is threatened by an array of anthropogenic effects common in industrialised countries (e.g. in-stream barriers, mining and sewage effluents, increased nutrient inputs, introduced species) as well as more diffuse, widespread phenomena characteristic of most of the arid and semi-arid areas of the world (e.g. salinisation and alteration of flows). Although much has been learned from specific case studies in the more populated areas, the nationally systematic efforts at quantifying these threats rely mostly on measures of river "condition" or "health" because measuring species diversity across areas as large as Australia is too expensive. However, these measures are incomplete representations of biodiversity, and some of the auditing processes compound other human values into their summaries of river condition or health. Furthermore, public perceptions of what rivers in Australia can deliver in terms of "ecosystem services" may not be feasible in many areas owing to the way that the Australian landscape has evolved. To avoid making the mistake of assuming that "good river health" automatically means "all biodiversity is conserved," three advances are needed: appropriate conceptual frameworks of how a given river system functions, more research that clarifies the links between processes and biodiversity, and an understanding of the historical biogeography of the river biota so that we can provide a clear context for the first two items. Substantial progress has been made in developing and adapting conceptual models of river systems, research into processes is being initiated even in some remote, sparsely populated catchments, and much has been learned about the history and distribution of the flora and fauna. Key challenges remain in consolidating reliable empirical relationships between biodiversity and the surrogate variables used to measure it, estimating the rates of biodiversity change likely to accrue from climate change over the next millennium, and identifying biodiversity "hot spots" particularly for less than charismatic species