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Southeastern Australia is presently experiencing one of the worst droughts observed in the region in the last 200 years. The consequences of drought have been far reaching both for human consumptive uses and for aquatic ecosystems, and serve to highlight several important aspects of the nature of droughts, their ecological impacts, and how humans respond to them. Running water ecosystems are the dominant form of freshwater ecosystem in Australia, yet, despite the high frequency of drought we lack a basic understanding of the consequences of long-term droughts (as distinct from seasonal droughts) as an ecosystem disturbance, and more is known about drought effects on flowing than on standing waters. Drought is well defined and characterised meteorologically, but hydrologically its characterisation is equivocal. While drought severely impacts natural aquatic ecosystems, its effects have been and are exacerbated by direct and indirect anthropogenic modifications to streams and their catchments. In streams the major impacts are the loss of water and habitat availability, and the reduction, if not severing, of connectivity (lateral, longitudinal and vertical). Despite the relative frequency of drought in Australia we have failed to develop long-term management strategies capable of contending with droughts and their impacts, particularly in catchments where human disturbances have reduced the natural resistance and resilience of aquatic ecosystems, and where the demand for consumptive water use is high and rising. Here, we provide a commentary on drought and its implications for the management of freshwater ecosystems. We begin with a general discussion of drought and its impacts on streams and rivers before discussing some of the more specific management issues and response strategies that have arisen in response to the current drought in Australia. Throughout we consider global as well as local examples. We conclude by highlighting important knowledge gaps and by providing some general principles for better incorporating droughts and their impacts into river management strategies. [ABSTRACT FROM AUTHOR]

Diatoms and macroinvertebrates are both commonly used for biological assessment of stream condition. As the use of biological assessment techniques increases, resource managers will need to make decisions on which biological tool to use for a particular study. In a study of the Kiewa River, Victoria, Australia we assessed these two components of the biota—macroinvertebrates and diatoms—using indices and pattern analysis, and comparing them with an a priori landscape classification. We also assessed the relationship exhibited between the biological results and environmental variables which are usually significant in stream ecosystems. To make the data comparable we used categorical abundances for both data sets. The pattern analyses showed complementary results, with diatoms more closely related to water quality variables, whereas macroinvertebrates were primarily related to catchment and habitat features. An analysis of a combined data set (diatoms plus macroinvertebrates) showed no extra information was gained. Using categorisation to create consistency between data sets was shown to reduce the information and affect results from the diatom analyses. The results suggested that the locally derived bioassessment models and indices provided a more accurate assessment of the sites than the overseas-derived diatom index. The outcomes are complicated by issues of data weighting, whereby a presence/absence diatom index may have performed better than abundance-weighted indices due to strong dominance of one or two species at a site. Future comparisons will benefit from an increase in the knowledge of regional diatom taxonomy and autecology. [ABSTRACT FROM AUTHOR]

This paper presents the approach and methods used, and the outputs generated, in the derivation of numeric biological objectives for the protection of rivers and streams across Victoria, Australia. Biological objectives have been designed for inclusion in State government legislation for the protection of the State’s waterways. The objectives were developed using data from extensive macroinvertebrate sampling of multiple reference sites across the State. Regional variations are incorporated into the objective-setting process by using an a priori, macroinvertebrate-based regionalisation of the State. The objectives consist of four separate components, including a measure of diversity, two biotic indices and a measure of community composition. The objectives are designed for use across broad regions and any attempt to extend the system to subregional levels would require a careful consideration of the influence of scale upon the grouping of reference sites. [ABSTRACT FROM AUTHOR]

Urbanization is acknowledged as one of the most severe threats to stream health, spawning recent research efforts into methods to ameliorate these negative impacts. Attention has focused on streams in densely-populated cities but less populous regional urban centres can be equally prone to some of the same threats yet might not meet the conventional definitions of urban. Several recent reviews have identified the changes to streams that occur during urbanization but they note that few ecological studies have explored ecosystem-level responses, typically focusing instead on state variables such as invertebrate abundance. In many regional urban streams, changes to the extent of impervious drainage have implications for their hydrology and channel morphology but the influence of these changes on fundamental ecosystem processes of leaf litter breakdown and transport compared with those in nearby rural streams are poorly known. The widespread practice of planting exotic trees along riparian zones and street margins draining into urban streams further exacerbates the disruption of natural organic matter dynamics. The combination of seasonal leaf fall by exotic species and the altered drainage patterns through urbanization in Armidale, a regional town in New South Wales, Australia, resulted in contrasting patterns of benthic organic matter storage over 18 months compared to nearby reference and rural streams. Macroinvertebrate detritivore densities were low in the urban stream, implying disruption of the usual biological pathways of leaf breakdown. Understanding the interactions of hydrology, drainage pattern, leaf input and biological attributes of a stream is crucial for managers trying to restore stream ecosystem services without incurring public concern about the appearance of regional urban streams. [ABSTRACT FROM AUTHOR]