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Salt is a natural component of the Australian landscape to which a number of biota inhabiting rivers and wetlands are adapted. Under natural flow conditions periods of low flow have resulted in the concentration of salts in wetlands and riverine pools. The organisms of these systems survive these salinities by tolerance or avoidance. Freshwater ecosystems in Australia are now becoming increasingly threatened by salinity because of rising saline groundwater and modification of the water regime reducing the frequency of high-flow (flushing) events, resulting in an accumulation of salt. Available data suggest that aquatic biota will be adversely affected as salinity exceeds 1000 mg L–1 (1500 EC) but there is limited information on how increasing salinity will affect the various life stages of the biota. Salinisation can lead to changes in the physical environment that will affect ecosystem processes. However, we know little about how salinity interacts with the way nutrients and carbon are processed within an ecosystem. This paper updates the knowledge base on how salinity affects the physical and biotic components of aquatic ecosystems and explores the needs for information on how structure and function of aquatic ecosystems change with increasing salinity.

Riparian ecosystems in the 21 st Century are likely to play a critical role in determining the vulnerability of natural and human systems to climate change, and in influencing the capacity of these systems to adapt. Some authors have suggested that riparian ecosystems are particularly vulnerable to climate change impacts due to their high levels of exposure and sensitivity to climatic stimuli, and their history of degradation. Others have highlighted the probable resilience of riparian ecosystems to climate change as a result of their evolution under high levels of climatic and environmental variability. We synthesize current knowledge of the vulnerability of riparian ecosystems to climate change by assessing the potential exposure, sensitivity and adaptive capacity of their key components and processes, as well as ecosystem functions, goods and services, to projected global climatic changes. We review key pathways for ecological and human adaptation for the maintenance, restoration and enhancement of riparian ecosystem functions, goods and services and present emerging principles for planned adaptation. Our synthesis suggests that, in the absence of adaptation, riparian ecosystems are likely to be highly vulnerable to climate change impacts. However, given the critical role of riparian ecosystem functions in landscapes, as well as the strong links between riparian ecosystems and human well-being, considerable means, motives and opportunities for strategically planned adaptation to climate change also exist. The need for planned adaptation of and for riparian ecosystems is likely to be strengthened as the importance of many riparian ecosystem functions, goods and services will grow under a changing climate. Consequently, riparian ecosystems are likely to become adaptation 'hotspots' as the century unfolds.

Terminal restriction fragment length polymorphism (T-RFLP) is increasingly being used to examine microbial community structure and accordingly, a range of approaches have been used to analyze data sets. A number of published reports have included data and results that were statistically flawed or lacked rigorous statistical testing. A range of simple, yet powerful techniques are available to examine community data, however their use is seldom, if ever, discussed in microbial literature. We describe an approach that overcomes some of the problems associated with analyzing community datasets and offer an approach that makes data interpretation simple and effective. The Bray-Curtis coefficient is suggested as an ideal coefficient to be used for the construction of similarity matrices. Its strengths include its ability to deal with data sets containing multiple blocks of zeros in a meaningful manner. Non-metric multi-dimensional scaling is described as a powerful, yet easily interpreted method to examine community patterns based on T-RFLP data. Importantly, we describe the use of significance testing of data sets to allow quantitative assessment of similarity, removing subjectivity in comparing complex data sets. Finally, we introduce a quantitative measure of sample dispersion and suggest its usefulness in describing site heterogeneity.

This paper reviews the abiotic processes that could lead to the stabilization of organic phosphorus in soils and the aquatic environment. The role of adsorption to soil minerals, complexation reactions, precipitation with polyvalent cations and the incorporation of organic phosphorus into humic substances in stabilizing organic phosphorus are examined in particular. The effects of soil solution chemistry on these reactions, as well as the effects of these reactions on the environment are also discussed.

Summary 1. This paper introduces, and summarises the key messages of, a series of papers that emanated from a symposium on the Role of Drought in the Ecology of Aquatic Systems, held in Australia in 2001.2. Defining drought hydrologically is problematic because the return times, intensity, duration and long‐term trends in low‐flow periods are specific to regions and times. Droughts may instead be referred to as ‘significant low‐flow periods’, many of which have been replaced by ‘anti‐drought’ conditions in rivers as they are used increasingly as irrigation conduits.3. Droughts can be divided into those that cause predictable, seasonal press disturbances and less predictable, protracted ‘ramp’ disturbances. However, while droughts may be ‘ramp’ disturbances, their effects on aquatic biota are most likely to be ‘stepped’ when geomorphological or hydrological thresholds are crossed, causing abrupt changes in biological community structure and ecosystem processes.4. Physical, morphological, physiological or behavioural refugia confer resistance or resilience to riverine populations and communities that experience drought conditions. The physical and chemical parameters associated with refugia habitats and their formation, influence population parameters within, and interactions among, species and can have protracted reproductive consequences, even well after the cessation of the drought.5. Fish, invertebrate and plant populations and assemblages seem to recover rapidly from drought. Most studies of the effects of drought, however, have arisen fortuitously and have involved relatively short temporal, and small spatial, scales. Innovative approaches, such as microsatellite DNA analyses, can reveal that the effects of drought may be profound and long‐lasting, resulting in population bottlenecks and altering the course of the evolution of species.6. During periods of drought, decreases in inputs of dissolved organic carbon, nitrogen and phosphorus may lead to carbon limitation to microbial metabolism, resulting in autotrophic production being favoured over heterotrophic production.7. Long‐term climate trends, as indicated by palaeoecological evidence, suggest that, at least for Australia, droughts are likely to occur more frequently in the future. Anthropogenic effects on climate are likely to exacerbate this.8. It is important that drought is seen for what it is: a natural extreme of the flow continuum, with flooding at the other extreme. Thus, despite the potential for dramatic impacts on aquatic biota and the negative social connotations associated with such events, drought must be incorporated into river management plans.

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This paper specifically focuses on the importance of organic phosphorus as a source of phosphorus for plant nutrition. In particular, the importance of rhizosphere phosphatase activity and its role in hydrolysing organic phosphorus in soil is considered. The bioavailability and utilization of organic phosphorus by plants as well as in the soil are also discussed.