Ecology of Desert Rivers

by Richard Kingsford

Overview

Almost half the world is comprised of desert or dryland regions. Life in these harsh environments depends upon spectacular rivers that are constantly changing between states of flood and drought, but compared to the other rivers of the world, our knowledge of their ecology is limited. Ecology of Desert Rivers provides a comprehensive account of the variable ecology of these areas and how they determine the behaviour and composition of the organisms that survive in this 'boom and bust' environment. It also covers how human interventions such as the creation of dams affect desert rivers and the animals and plants that depend on them for survival. This book provides an up-to-date synthesis of all aspects of desert river ecology and will appeal to researchers and students in ecology, hydrology and geomorphology as well as conservation managers and policy-makers.

Product Details

ISBN-13:	9780521818254
Publisher:	Cambridge University Press
Publication date:	06/01/2006
Pages:	368
Product dimensions:	6.26(w) x 9.25(h) x 0.87(d)

About the Author

Dr Richard Kingsford is a Principal Research Scientist with the Department of Environment and Conservation in NSW, with wide experience in conservation biology. Born in East Africa in Kenya, his interest in wildlife began in childhood. His research over about the last 20 years has focussed on the waterbirds, wetlands and rivers of arid Australia, which cover about 70% of the continent. These magnificent systems define the ecology of the Australian continent with their boom and bust periods, times of droughts and floods. Research has focussed on the wetlands of Cooper Creek, one of the world's most magnificent desert rivers, and the Paroo River, the last free-flowing river in the Murray-Darling Basin. His research has demonstrated the ecological values of many rivers in arid Australia and impacts of water resource development on desert rivers. In 2001, he was awarded a national science prize (Eureka) for environmental research for his work on Australian rivers. He has also received three national Banksia awards for work on rivers and environmental leadership.

Read an Excerpt

Cambridge University Press
0521818257 - Ecology of Desert Rivers - by Richard Kingsford
Excerpt

Desert or dryland rivers of the world: an introduction

Rivers channel the world's rainfall into floodplains, lakes or groundwater basins, or out to sea. They provide habitats for diverse biota that often climax in floodplain wetlands, areas of incredible biodiversity. River flows are integral to many coastal and marine environments, processes and organisms (Gillanders & Kingsford, 2002). Their fresh water allows humans to penetrate and flourish in the most inhospitable parts of this planet. They are the arteries that define ecological landscapes and processes for many biota. Climate and the nature of land surfaces primarily govern the size, hydrology, geomorphology and ecology of rivers. For example, the Amazon River, which accounts for about 20% of the world's river flow, is a massive river system originating in areas of extremely high rainfall. Contrast this with rivers from the desert regions of the world (Fig. 1.1) where rainfall is less than 500 mm per year and is usually exceeded by evaporation. In these regions rivers often stop flowing for long periods, sometimes even years.

What makes desert rivers any different from other rivers or aquatic systems around the world? This book uses ‘desert’ and ‘dryland’ interchangeably to describe land areas and their rivers where there is less than 500 mm of annual rainfall: the arid and semi-arid regions of the world (Fig. 1.1). This encompasses about47% of the global land surface, including hyperarid, arid, semi-arid and dry humid regions (Table 1.1) (Middleton & Thomas, 1997). Why do we need a book about the ecology and management of these desert or dryland rivers? Intrinsic properties of scarcity and variability of these rivers and their associated floodplain habitats, combined with poor knowledge and increasing human pressures, demand attention. The story of desert or dryland rivers is one of changeable, changing and changed ecosystems, as humans progressively apply control.

Desert rivers do not have unique landforms (Nanson et al., 2002) but their hydrology is much more variable than that of mesic rivers (McMahon et al., 1992; Puckridge et al., 1998; Peel et al., 2001). We are only just beginning to understand the implications of such variability for the ecology of these rivers, the effects of river regulation and future management. Rivers in dry regions of the world are the poor cousins in the knowledge base of river and wetland ecology. Their ecology is probably the least known of our freshwater resources (Williams, 1988; Nanson et al., 2002), despite recent advances in understanding (see Bull & Kirkby, 2002), because relatively few people live in such inhospitable parts of the world. Scientific effort is often strongly biased towards humid regions, with most of our knowledge of aquatic ecology from temperate freshwater science (Ward et al., 2001). Even in a relatively affluent country such as Australia, where arid regions dominate (75% of the land area), freshwater scientific effort can be biased towards the mesic regions where most people live (Kingsford, 1995). Desert rivers and their ecology are often out of sight and out of mind, so it is important to consolidate our knowledge and provide a basic framework for ecological understanding of desert or dryland rivers.

Desert or dryland rivers of the world

Almost 50% of the world's land surface is either arid or semi-arid (Middleton & Thomas, 1997), occupying most continents (Comín & Williams, 1994). Many thousands of streams and large rivers flow wholly or partly through such areas (Fig. 1.1). Rivers and their dependent ecosystems form a continuum of variability, seldom adequately captured by pigeonhole classifications. This variability is characteristically higher in dryland rivers. Rivers challenge us even more because their longitudinal dimensions seldom respect climatic regions; worse, for managers and policy makers, they do not respect jurisdictional or national borders (Postel, 1996; Kingsford et al., 1998). Many large rivers that flow through desert regions (e.g. the Nile, Okavango and Murray) originate in mesic areas. This book adopts a broad definition of what constitutes a desert river because it is impossible to divorce a river from its catchment: desert rivers flow wholly or partly through desert or dryland regions of the world (annual rainfall < 500 mm).

Climate drives river flows and dependent ecological responses. Within desert regions rainfall is low and is often highly variable in both space and time (Peel et al., 2001). Hydrology holds primacy in any treatment of rivers, their behaviour and their understanding. By way of introduction, we take the monthly flows of six unregulated desert rivers from different regions of the world: North America, South America, northeast Africa, South Africa, Asia and Australia (Fig. 1.2). Even a simple inspection of monthly flow regimes illustrates considerable differences among rivers from these different regions. Seasonal regularity, particularly in relation to wet and dry seasons in the tropics (Atbara River, northeast Africa) and snowmelt in temperate regions (Huanghe River, Asia) is translated into a clear seasonal signal in river flows (Fig. 1.2), which has considerable implications for ecology and management. Interannual variability is relatively small compared with that of rivers in other desert regions of the world such as South Africa, North and South America and Australia (Fig. 1.2). In these regions annual variability in the timing and volume of flows is also high. Some dryland rivers have periods of no flow or low flow. In some, such as the Atbara River in Northeast Africa (Fig. 1.2), these periods coincide with the marked dry season and their timing and duration are relatively uniform. Others, such as Australia's Darling River and the Gila River of North America (Fig. 1.2), exhibit less predictable periods of low or no flow. Such regions generally have highly stochastic rainfall that results in extremely variable river flows, a pattern particularly well known for Australian and South African rivers (McMahon et al., 1992; Puckridge et al., 1998; Peel et al., 2001; Nanson et al., 2002). Chapter 2 of this book extends this introduction into river ecology by examining in considerably more detail some of the differences in the hydrology of desert rivers and their implications for river ecology and water resource development.

It follows that hydrological disturbance patterns exert a dominant influence on the ecology of desert rivers, through the drying and flooding of river habitats: channels, waterholes, floodplains and estuaries. Hydrology affects geomorphological processes of rivers, which in turn drive the distribution of dependent vegetation (Chapter 3, this volume). The next section of the book has a series of chapters that examine ecological responses to variable flows in desert rivers. This begins with food webs and productivity (Chapter 4) and moves to higher levels of biota: plants (Chapter 5), invertebrates (Chapter 6) and vertebrates (Chapter 7). A new force, almost as important as climate, now governs the hydrology and ecology of many rivers: human control.

The human responses to water scarcity around the world are driving major changes to dryland rivers. Part II of this book concentrates on how humans have altered the behaviour of dryland rivers, affecting their ecology. Despite our lack of knowledge, we are busily exploiting dryland rivers, wreaking immeasurable ecological damage (Lemly et al., 2000; Gillanders & Kingsford, 2002). Are we changing these unique systems forever? This part of the book begins with an examination of how we change desert river flows and the impact these changes have had on some of the more spectacular and biodiverse habitats in the world (Chapter 8). The next chapter shows the long-lasting and extensive hydrological and ecological effects of even relatively minor river regulatory structures, such as weirs, on the Lower River Murray (Chapter 9). Deserts are naturally salty places, but human land and river management is increasing the salinity of desert rivers with severe ecological consequences (Chapter 10). Expanding human populations represent the greatest pressure on the world's water resources (Postel, 2000), at their most extreme in desert regions (Chapter 11). Finally, a synthesis chapter (Chapter 12) examines the competing demands of the ecology of desert rivers and their changeable nature against our ever-increasing needs for water, imposing simplicity on incredibly complex ecosystems. Hopefully, this book will encourage an interest in the magnificent systems that are desert rivers, will raise awareness of the challenges that they face, and will in turn promote their future conservation.

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© Cambridge University Press

Table of Contents

Part I. Natural Disturbance in Desert River Systems: 1. Desert or dryland rivers of the world - an introduction R. T. Kingsford and J. Thompson; 2. Flow variability in large unregulated dryland rivers W. J. Young and R. T. Kingsford; 3. Variability, complexity and diversity - the geomorphology of river ecosystems in dryland regions M. C. Thoms, P. H. Beyer and K. H. Rogers; 4. Aquatic productivity and food webs of desert river ecosystems S. E. Bunn, S. R. Balcombe, P. M. Davies, C. S. Fellows and F. J. McKenzie-Smith; 5. Disturbance of plant communities dependent on desert rivers M. A. Brock, S. J. Capon and J. L. Porter; 6. Natural disturbance and aquatic invertebrates in desert rivers A. J. Boulton, F. Sheldon and K. M. Jenkins; 7. Vertebrates of desert rivers - meeting the challenges of temporal and spatial unpredictability R. T. Kingsford, A. Georges and P. J. Unmack; Part II. Human Disturbance in Desert River Systems: 8. Impacts of dams, river management and diversions on desert rivers R. T. Kingsford, A. D. Lemly and J. R. Thompson; 9. Serial weirs, cumulative effects: the Lower River Murray, Australia K. F. Walker; 10. Salinisation as an ecological perturbation to rivers, streams and wetlands of arid and semi-arid zones P. C. E. Bailey, P. I. Boon, D. W. Blinn and W. D. Williams; 11. Water scarcity: politics, populations and the ecology of desert rivers M. Wishart; 12. Changing desert rivers R. T. Kingsford; Index.

Editorial Reviews

"I enjoyed reading this book and it has opened my eyes to what is clearly an important freshwater topic that I had previously tended to ignore.... I shall use some of the examples in my teaching and the insights that I gained will be useful even in my own work on rivers..."
Mark Young, Bulletin of the British Ecological Society

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