Bruce C. Chessman

New sensitivity grades for Australian river macroinvertebrates

The SIGNAL biotic index for river macroinvertebrates, originally developed and tested in eastern Australia, was revised for application to the entire continent. Macroinvertebrate survey data from the National River Health Program were used to set grade numbers between 1 and 10 to represent the water-quality sensitivities of 210 taxa. Grades were assigned at the taxonomic levels customarily used by government agencies (predomi- nantly family level) and by community groups (mainly order). A new index version using these grades, SIGNAL2, was correlated with water temperature, turbidity, electrical conductivity, alkalinity, pH, dissolved oxygen, total nitrogen and total phosphorus. Because of natural spatial variation in water quality, index scores need to be inter- preted in a local context or against site-specific predictions generated by the Australian River Assessment System (AUSRIVAS).

Bioassessment without reference sites: use of environmental filters to predict natural assemblages of river macroinvertebrates

Abstract Sets of reference sites often are used to create a benchmark for biological assessment of river condition. Unfortunately, human modification of river systems is now so widespread and complex that this practice can result in comparisons against a reference condition that embodies an appreciable and poorly defined degree of human impact. Our paper describes an alternative means of deriving reference conditions that does not require the use of reference sites. Instead, the tolerances and preferences of each taxon in the regional taxon pool are established for various environmental factors. These factors can be regarded as filters that exclude members of the regional pool from sites where environmental conditions are incompatible with their tolerances and preferences. The suite of taxa that can occupy an assessment site under natural conditions can be estimated if the natural values of the environmental filters at that site can be determined. A comparison between this suite of potential taxa and the taxa actually collected at an assessment site provides an indication of human impact on taxonomic richness. This approach is illustrated for aquatic macroinvertebrate families in rivers in northeastern New South Wales, Australia, and the environmental filters of annual water temperature range, flow regime, and river bed type. An assessment based on this approach showed substantial correlation with several independent measures of human influence, in contrast to very little correlation for a previous macroinvertebrate bioassessment based on reference sites. The performance of the filters approach probably could be improved with further development of the underlying techniques and data.

Rapid assessment of Australian rivers using macroinvertebrates: cost and efficiency of 6 methods of sample processing

The cost and efficiency of different techniques for processing rapid-assessment samples of lotic macroinvertebrates were evaluated. Subsamples of 50, 100, and 150 selectively picked individuals were compared to determine the optimal subsample size for selective picks. Selective subsampling of a set number of animals was then compared with subsampling by picking for a set time (30 min), exhaustive picking of a sample, and randomly subsampling 100 animals. Identification was to family level. Efficiency was assessed by comparing the ability of data generated by each technique to discriminate between unpolluted reference sites and sites with mild to severe pollution by municipal effluent and urban stormwater runoff. This discrimination was tested using both univariate metrics (SIGNAL biotic index, family richness, and EPT [Ephemeroptera, Plecoptera, Trichoptera] family richness) and multivariate tests (analysis of similarity--ANOSIM). Cost was assessed as the amount of time each method required for picking and identification. The selective 100-animal subsample is recommended as the most cost-effective method for assessing sites affected by municipal sewage-treatment-plant discharges and urban stormwater runoff. SIGNAL was the best of the 3 metrics, having the most highly significant differences between reference and polluted sites and being most robust to variations in processing method. ANOSIM could distinguish between the reference and polluted sites using any of the sample processing methods, but the degree of the distinction varied with sample processing method.

Towards diagnostic biotic indices for river macroinvertebrates

The construction of biotic indices that use macroinvertebratesto assess pollution and other anthropogenic disturbances ofrivers and streams often requires that each taxon be assigned anumber indicating its level of sensitivity. A problem inconstructing such indices is that individual taxa may varyquite widely in sensivity, depending on the nature of theparticular disturbance. One possible means of overcoming thisproblem is to construct a suite of indices, each assembledusing sensitivity numbers targeted to a particular impact.In order to test this idea, we sampled macroinvertebrates fromrivers in south-eastern Australia subjected to three differenttypes of anthropogenic disturbance: operation of large dams,discharge of effluent from municipal sewage treatment plants,and contamination by metals originating from historical mining.Using macroinvertebrate data from sampling sites with varyinglevels of exposure to disturbance, we developed sensitivitynumbers for macroinvertebrate families for individual riversand combinations of rivers with the same disturbance type.Sensitivity numbers calculated for individual families differedsignificantly according to disturbance type in several cases.Gastropod molluscs (family Thiaridae) were tolerant of dameffects but sensitive to sewage and metals, whereascoenagrionid damselfly nymphs, elmid beetles and ostracods weremost tolerant of sewage. Corydalid alderfly larvae,leptophlebiid mayfly nymphs, lestid damselfly nymphs,libellulid dragonfly nymphs and scirtid beetle larvae weremost tolerant of metals. Indices constructed using sensitivitynumbers for a particular disturbance were generally mostresponsive to that disturbance, but there was considerablegenerality in responses as well as substantial variabilitybetween different rivers with the same disturbance type. Inparticular, macroinvertebrate communities at sites downstreamof dams responded quite variably, probably because ofsubstantial differences in release regimes. We conclude thatthe approach has merit but requires considerable furtherdevelopment and testing, as well as consideration of the levelsof specificity and diagnostic strength that are appropriate orachievable.

Rapid assessment of rivers using macroinvertebrates: the role of experience, and comparisons with quantitative methods

We assessed rapid biological assessment (RBA) of macroinvertebrate communities in comparison with quantitative sampling at 18 pairs of river sites in south-eastern Australia. One member of each pair served as a reference site and the other was affected by mild to moderate human disturbance from a point or diffuse source (fish farm effluents, small municipal sewage discharges, a dam, agriculture and grazing). Samples were taken from riffles, stream edges and rocks in pools, mostly using hand nets (RBA) and Hess samplers (quantitative). Macroinvertebrates in RBA samples were always subsampled by live-picking by eye on site for 30 min. Comparisons were made between novice operators (university undergraduates) and experienced river biologists in the application of RBA, including sample identification. Quantitative samples were collected only by experienced river biologists, preserved and picked under stereomicroscopes in the laboratory, either in their entirety or after mechanical subsampling. Specimens were identified to family level for both methods. Novices recorded slightly fewer families than experts and misidentified some specimens, and expert data for the same site and habitat were on average more consistent than novice data. Nevertheless, Procrustes analysis of ordinations showed that differences between RBA and quantitative data did not depend on the type of RBA operator. And regardless of the operator, RBA data were better than quantitative data at discriminating between reference and disturbed sites for all three habitat types. We conclude that this type of RBA is sensitive and cost-effective, and we recommend improvements to inter-operator consistency.

Regime shifts, thresholds and multiple stable states in freshwater ecosystems; a critical appraisal of the evidence

The concepts of ecosystem regime shifts, thresholds and alternative or multiple stable states are used extensively in the ecological and environmental management literature. When applied to aquatic ecosystems, these terms are used inconsistently reflecting differing levels of supporting evidence among ecosystem types. Although many aquatic ecosystems around the world have become degraded, the magnitude and causes of changes, relative to the range of historical variability, are poorly known. A working group supported by the Australian Centre for Ecological Analysis and Synthesis (ACEAS) reviewed 135 papers on freshwater ecosystems to assess the evidence for pressure-induced non-linear changes in freshwater ecosystems; these papers used terms indicating sudden and non-linear change in their titles and key words, and so was a positively biased sample. We scrutinized papers for study context and methods, ecosystem characteristics and focus, types of pressures and ecological responses considered, and the type of change reported (i.e., gradual, non-linear, hysteretic or irreversible change). There was little empirical evidence for regime shifts and changes between multiple or alternative stable states in these studies although some shifts between turbid phytoplankton-dominated states and clear-water, macrophyte-dominated states were reported in shallow lakes in temperate climates. We found limited understanding of the subtleties of the relevant theoretical concepts and encountered few mechanistic studies that investigated or identified cause-and-effect relationships between ecological responses and nominal pressures. Our results mirror those of reviews for estuarine, nearshore and marine aquatic ecosystems, demonstrating that although the concepts of regime shifts and alternative stable states have become prominent in the scientific and management literature, their empirical underpinning is weak outside of a specific environmental setting. The application of these concepts in future research and management applications should include evidence on the mechanistic links between pressures and consequent ecological change. Explicit consideration should also be given to whether observed temporal dynamics represent variation along a continuum rather than categorically different states.

Family- and species-level biotic indices for macroinvertebrates of wetlands on the Swan Coastal Plain, Western Australia

SWAMPS (Swan Wetlands Aquatic Macroinvertebrate Pollution Sensitivity) was developed as a biotic index for wetlands near Perth, Western Australia. Numerical grades between 1 and 100 were assigned to wetland macroinvertebrate taxa, generally at the family and species levels, to reflect the sensitivities of these taxa to anthropogenic disturbance, primarily nutrient enrichment. Index scores for individual wetlands were calculated as abundance-weighted or unweighted means of the grades of all taxa present in standard samples. Scores calculated at both the family and species levels showed a strong correlation with independent measures of cultural eutrophication and other anthropogenic disturbances, but such correlations were generally higher for the species-level index. The species index also discriminated more between individual wetlands. SWAMPS should be useful in routine and rapid assessment and monitoring of wetland condition in the Perth region and could be easily adapted to other regions and continents.

Development of diatom-based tools for assessing stream water quality in south-eastern Australia: assessment of environmental transfer functions

Models were developed of relationships among water quality, geospatial and species-level diatom data for 465 samples collected from stream sites across south-eastern Australia. Transfer functions were derived from weighted averaging and artificial neural network approaches. Analysis of spatial variations in species assemblages was used to divide the sites into two groups according to site elevation. The strongest predictive models for the upland group associated diatom assemblages with conductivity, longitude, altitude, and to a lesser extent pH, NOx and TKN. The strongest predictors for the lowland group were longitude and conductivity, but artificial neural network models performed well for NOx and temperature. The importance of the geospatial variables suggests that there may be a capacity to develop diatom sub-regions within which robust models for other water quality variables important to management can be generated.

Macroinvertebrate traits distinguish unregulated rivers subject to water abstraction

Abstract The biological effect of water abstraction from unregulated streams in New South Wales, Australia, was assessed with data on macroinvertebrate assemblages in riffles (445 samples) and pool edges (718 samples) obtained from a national assessment of river condition in 1995 to 2000. We used limiting environmental difference (LED) modeling to predict the macroinvertebrate assemblage expected for each sample in the absence of water abstraction and estimated effect by comparing predicted and observed assemblages for sites with upstream abstraction. We found a high likelihood of effect on macroinvertebrates in 30% of riffles with upstream abstraction and 22% of edges. Complex combinations of biological traits appeared to determine the sensitivities and tolerances of individual taxa to water abstraction. For example, rheophilous families generally were rarer than predicted in apparently affected riffles, where thermophilic families seemed tolerant of the effects of water abstraction, and free-swimming families were less common than predicted in apparently affected edges, where families with tegument respiration appeared unaffected by water withdrawals. The trait response was clearer for the riffle fauna than for the edge fauna, perhaps because the physical and chemical effects of abstraction are more consistent for riffles than for edges. Our approach can support management planning by identifying taxa that are most at risk from water abstraction and sites where apparent effects are most evident.

Progress, problems and prospects in Australian river repair

Effective river restoration requires an integrative approach among researchers, managers and stakeholders, grounded in sound science. Using Australia as a case study, we examined contemporary responses to the following three global challenges for river management: first, to base management practice on ‘best available science’ (BAS); second, to integrate diverse, discipline-bound knowledge within cross-disciplinary and trans-disciplinary approaches; and third, to achieve adaptive management based on monitoring and evaluation. Analysis of 562 papers from the six Australian national stream-management conferences held since 1996 provided insight into the rapidly growing area of management, and the degree to which these three challenges are being met. The review showed that discipline-bound abiotic or biotic science was the focus of 46% of papers. Cross-disciplinary science, defined as the integration of biophysical sciences, was presented in 36% of papers, and trans-disciplinary science, defined as the merging of biophysical science with social and economic perspectives, in 17%. Monitoring and evaluation results were presented in only 12% of papers, whereas applications of adaptive management were reported in a mere 2%. Although river management has been transformed in recent decades, much remains to be done to create a holistic foundation for river restoration that links biophysical science to social science and economics.