1. Water extraction from arid-zone rivers increases the time between floods across their floodplain wetlands. Less frequent flooding in Australian arid-zone rivers has impaired waterbird and fish breeding, killed riparian vegetation and diminished invertebrate and macrophyte communities. Restoration currently focuses on reinstating floods to rejuvenate floodplain wetlands, yet indicators to measure the success of this are poorly developed. 2. We explored the application of criteria for ecologically successful river restoration to potential restoration of floodplain wetlands on the Darling River, arid-zone Australia. Using emergence of micro-invertebrates from resting eggs as an indicator, we compared responses of taxa richness, densities and community composition in floodplain lakes with different inundation histories. 3. Increased drying of floodplain lakes reduced the number of micro-invertebrate taxa. Several key taxa were absent and faunal densities (particularly cladocerans) were reduced when the duration of drying increased from 6 to 20 years. 4. A conceptual model of the ecological mechanisms by which restoration of flooding regime could achieve the target of preserving micro-invertebrate community resilience predicts that reducing the dry period between floods will minimize losses of viable resting eggs. Protection of this 'egg bank' permits a boom in micro-invertebrates after flooding, promoting successful recruitment by native fish and waterbirds. 5. Synthesis and applications. In arid-zone rivers, micro-invertebrate densities and community composition are useful indicators of the impact of reduced flooding as a result of water extraction. Critical to successful native fish recruitment as their first feed and as prey for waterbirds, micro-invertebrates are a potential early indicator of responses by higher trophic levels. Taxon richness, density and key taxa present after flooding, all indicators of resilience, can be incorporated into targets for arid-zone river restoration. For example, one restoration target may be microcrustacean densities between 100 and 1000 L⁻¹ within 2–3 weeks after spring flooding. These criteria can be applied to measure the ecological success of restoration projects seeking to recover natural flood regimes. Given the high economic cost of water in arid zones, convincing demonstrations of the ecological success of environmental water allocations are crucial.

Floodplain wetlands in arid and tropical environments are intermittently or seasonally flooded, drying for months and up to years in arid wetlands between floods. Aquatic food webs in these systems are adapted to this variable water regime; pulsing in productivity and diversity after floods, yet dependent on nutrients generated during dry cycles. In floodplain wetlands, upstream dams and irrigated agriculture have reduced floods and extended drying, leading to changes to natural levels of productivity and diversity. Environmental flows can contribute to the sustainable management and restoration of degraded wetlands in agricultural landscapes. Decisions on the timing, frequency, duration and magnitude of environmental water allocations depend on sound knowledge of ecological thresholds, and indicators to measure success or failure of management interventions. Thresholds are discussed for concentrations of carbon, ecosystem metabolism and microinvertebrates in arid wetlands as indicators of key ecosystem functions. This approach is also relevant to floodplain wetlands in tropical climates where water managers must balance environmental and agricultural needs in the midst of the uncertainty of climate change.

Flowing waters in deserts vary from ephemeral rills that carry water only after irregular and episodic downpours to the lowland stretches of perennial rivers whose headwaters are fed by groundwater interflow, snowmelt, or monsoonal rains. Many deserts have uncoordinated (arheic) drainage patterns. Here, flow may depend as much on where in the desert rain fell as on the weak gradients of the poorly defined channels. In other desert areas, meandering endorheic channels end in internal basins that can contain water for long periods of time. For example, the Lake Eyre Basin is a large endorheic drainage system in Australia that fills irregularly in response to erratic incursions of moist tropical air from the north. Major floods can occur, associated with La Nina phases of the El Nino Southern Oscillation (Puckridge et al., 2000), triggering 'booms' in productivity of waterbirds, fish, and invertebrates (Kingsford et al., 1999; Timms, 1999; Chapters 2, 4, and 7, this volume).

Wetlands in arid and semi-arid areas face intensifying pressure for their water resources yet harbor unique biota and ecological processes that rely on the "boom and bust" regime of alternating flood and drought. Recent research in Australia has revealed that models of ecosystem processes derived from northern temperate zone wetlands are often inapplicable to arid zone wetlands, confounding efforts to manage or protect these threatened habitats. We review four case studies from inland Australia that demonstrate different degrees of successful management, aiming to draw out lessons learned that will improve our sustainable use of these delicate systems. Inappropriate extrapolation across scales that ignores the inherent spatial and temporal variability of arid-zone wetlands, "reactive" rather than "collaborative" research and management, and a reluctance to adopt functional indicators to complement state variable are several common themes. We are optimistic that managers and researchers are collaborating to tackle these issues but warn that a parched future faces some wetlands where jurisdictional boundaries hamper their effective management or entrenched beliefs and community distrust of managers threaten ecologically sustainable resource use. In arid areas where water is so precious, environmental allocations are costly and their long-term effects are difficult to identify against a backdrop of high inherent variability. Preservation of this variability is the key to successful management of these "boom and bust" systems but diametrically opposes the desire for regulated, reliable water supplies for human use. Social and institutional acceptance and change now appear to be greater barriers than limited ecological understanding to effective management of many "parched wetlands" in Australia.