J. Angus Webb

Ecological risk to aquatic systems from salinity increases

Salinity is a major problem in many regions of Australia, and is predicted to get considerably worse over the next 30-50 years. Most effort has focused on the terrestrial environment, and specifically on the loss of productive agricultural land. Increased salinity can also result in unwanted changes to aquatic ecosystems in rivers, streams and particularly wetlands. This paper first reviews the importance of assessing risks from salinity increases in a catchment context, and then introduces a disturbance-response conceptual model to assist with the understanding of such situations. Two factors are shown to be particularly important in assessing which freshwater systems will be most susceptible to increases in salinity—the location of the systems in the landscape, and the current ecological condition of the system. The resilience of an ecosystem to salinity disturbances is shown to be a useful concept which with further knowledge may be incorporated into risk-assessment approaches. The development of a new ecological risk assessment approach for assessing risks to aquatic systems in the Goulburn-Broken catchment from increases in salinity over the medium (20 years) and long (100 years) term is reported. The risks to the biota in Hughes Creek, a tributary of the Goulburn River, are assessed by using a probabilistic approach. Current salinity levels in the creek present a low risk to the biota. Finally, the paper addresses the challenge of making the ecological risk assessment method more quantitative by discussing the following two key aspects: how to better quantify the linkages between the key stressors and the biotic components, and how to better handle uncertainties. BT02 Eco t om ty B. T. H

Measurement of environmental trace-metal levels with transplanted mussels and diffusive gradients in thin films (DGT): a comparison of techniques

Transplanted mussels and diffusive gradients in thin films (DGT) were used to assess levels of cadmium, copper, lead and zinc at four sites situated inside and outside of two enclosed marinas, near Melbourne, Australia. Mussels accumulated all metals except cadmium. Over one year, there were large temporal differences in tissue metal levels in mussels, but differences between sites were only apparent for copper and lead. DGT showed temporal differences of the same kind as those seen in the mussels, but appeared to have more power to discriminate between sites. DGT found higher copper levels inside marinas than outside, and high levels of zinc were found inside one marina. Levels of copper and zinc were high enough to be of environmental concern for one site. The effect of fouling on DGT measurements will have to be quantified, or avoided by the use of multiple short-term exposures, if the technique is to become a widespread in situ monitoring tool.

Risk-Based Approaches to Managing Contaminants in Catchments

ABSTRACT Risk-based methods promise improved decision-making for managing of contaminants, such as salinity, sediments, nutrients, and toxicants, that can adversely affect the ecological condition of aquatic ecosystems. Two aspects of ecological risk assessment (ERA) and management—stakeholder involvement and more quantitative approaches to risk analysis—are particularly challenging. Stakeholder involvement is crucial both in the risk assessment process and the development, acceptance, and implementation of a risk management plan. Additionally, a number of quantitative approaches (particularly Bayesian approaches and multi-criteria decision-making) have been identified as having the potential to include expert-based inputs into risk-based decision-making. These offer promise for better inclusion of stakeholder knowledge and preferences into the decision-making process, and for improving the links between stakeholder inputs and potential risks to the ecological condition of the system. A major challenge for ecologists and natural resource managers is to make the ERA process more quantitative. Most ERAs conducted to date have been qualitative assessments that suffer from a number of deficiencies, the most serious being the lack of transparency and a reliance on subjective judgments. This article argues that the most productive way forward may be to use Bayesian methods to couple existing process-based models, empirical relationships based on good data, and expert opinion, to make the analysis of ecological risks more robust, consistent, and repeatable.

Negotiating the turbulent boundary: the challenges of building a science–management collaboration for landscape-scale monitoring of environmental flows

With drought and climate change leading to increased water scarcity at a time of increasing consumptive demand, the provision of environmental flows is a potentially divisive issue. Demonstrating the ecological effects of environmental flows is thus important for supporting policy and management decisions. We describe the development of a multi-basin monitoring and assessment program for environmental flows in Victoria, Australia. We examine the challenges associated with negotiating the turbulent boundary between water science and water management when building a partnership between multiple partners with differing priorities, expectations and responsibilities. We describe the mistakes made and corrective actions taken, and present a critical analysis of the lessons learned. Strong science-management collaboration will be aided by: explicit recognition of the importance of the engagement process, establishing the partnership at the outset, assessing and understanding the disparate needs of individual partners, frequent articulation of the shared vision that motivated the collaboration, and providing sufficient opportunities for information exchange among partners. Cullen first described the challenges to science-management collaboration twenty years ago, but to some extent, the same mistakes continue to be made. Our real-world example shows that it is possible to develop a strong partnership, even when such mistakes are made at the outset.

Ecological Responses to Flow Alteration: Assessing Causal Relationships with Eco Evidence

The environment is being increasingly recognized as a legitimate user of water. However, tension between environmental and consumptive uses remains and environmental water allocations may be subject to legal challenge. Current predictions of ecological response to altered flow regimes are not sufficiently transparent or robust to withstand such challenges. We review the use of causal criteria analysis to systematically review ecological responses to changes in flow regimes. Causal criteria analysis provides a method to assess the evidence for and against cause-effect hypotheses. Relationships supported by sufficient evidence can inform transparent and robust environmental flow recommendations. The use of causal criteria analysis in environmental science has been facilitated by the development of the Eco Evidence method and software—a standardized approach for synthesizing evidence from the scientific literature. Eco Evidence has thus far been used to assess the evidence concerning responses of vegetation, fish, macroinvertebrates, and floodplain geomorphology to changes in flow regime, and provides a robust and transparent assessment of this evidence. There is a growing movement internationally to shift from experience-based to evidence-based methods in environmental science and management. The research presented here is at the leading edge of a fundamental change in the way environmental scientists use evidence.

Uncertainty in Nutrient Spiraling: Sensitivity of Spiraling Indices to Small Errors in Measured Nutrient Concentration

A bstractProper assessment of ecological data must consider uncertainty. However, reported estimation of uncertainty in calculated values of nutrient spiraling indices is rare. Interpretations based on single values of spiraling indices, may therefore be unwittingly flawed. We investigated the sources of analytical uncertainty in the nutrient concentrations used to calculate two spiraling indices, uptake length (Sw) and uptake velocity (Vf), and used Monte Carlo Simulation (MCS) to estimate the resultant uncertainty in index values. We also examined the effect of the level of nutrient enrichment on the magnitude of index uncertainty. Outcomes under high and low nutrient uptake capacity were compared by performing nutrient addition experiments in two streams with contrasting ambient nutrient concentrations. We found that small differences (or uncertainties) in the average plateau nutrient concentration resulted in large uncertainties in spiraling indices. The uncertainty resulted from a combination of small differences in nutrient concentrations between upstream and downstream stations (particularly for the low uptake case), the low nutrient concentration added into the stream, and the sample matrix and storage. The stream with low nutrient uptake capacity had larger relative uncertainties in Sw than when the nutrient uptake capacity was high. The presence of such errors demands that Sw and Vf values should be reported with uncertainty, rather than the normal practice of a single calculated value.

Interactive effects of urban stormwater drainage, land clearance, and flow regime on stream macroinvertebrate assemblages across a large metropolitan region

Urban impacts on streams are mediated by alteration of land cover and subsurface drainage. Understanding interactions of these 2 effects is critical for urban land and water management. We used boosted regression trees to analyze relationships between environmental predictors, including land-cover measures that indicate urban impacts, and Stream Invertebrate Grade Number Average Level (SIGNAL) or the occurrence of 60 macroinvertebrate families across the Melbourne (Australia) region. SIGNAL and 51 families were negatively correlated with attenuated imperviousness (AI). Twenty-four families exhibited a steep decline in probability of occurrence between 0 and ≤3% AI, consistent across the range of natural discharge (Q). Responses to attenuated forest cover (AF) were more variable among families (39 positive, 15 negative). AF had a less positive influence on SIGNAL at high than at low AI because the many (high SIGNAL-grade) families that were strongly negatively correlated with AI were likely to be absent at high AI. Interactions that suggested a modification of response to AI or AF as a result of the influence of another variable were restricted to 19 families. For 4 families with occurrences that were positively correlated with AF, the negative effect of AI was reduced in streams with high AF. For 14 families, responses of occurrence to AI or AF varied with Q or antecedent discharge in multiple ways. A reduced effect of AI was observed in low-Q streams or after very dry antecedent conditions for 10 families. Despite strong effects of the regional gradient in rainfall and vegetation across our study area, catchment-scale urban stormwater drainage was consistently associated with reduced occurrence of most families. The relative number of families predicted to be lost at low levels of AI underestimated relative loss of genera or species. Urban stormwater runoff probably is a strong driver of species loss in streams, but riparian forest can increase the probability of occurrence of a small number of tolerant families.

Pulse disturbances to the colonization of hard-substrates and in situ determination of copper using diffusive gradients in thin-films (DGT): quantifying dose and response in the field.

Studies conducted in Port Philip Bay, Victoria, Australia are described that examined the effect of experimentally elevated copper concentrations on the recruitment of epifauna to settlement plates. Simultaneous measurement of the copper concentration using diffusive gradients in thin films (DGT) allowed direct comparisons to be made between the labile copper concentration measured at the settlement surface, and the biological effects observed. Copper concentrations created by the field dosing technique were between 20 – 30 μg l−1 for the first 2 d, but then dropped considerably for the following 4 d (3 μg l−1), and were indistinguishable from background for the final 7 d. The first 2 d of a copper pulse reduced the recruitment of barnacles, ascidians, serpulid worms, an encrusting bryozoan, and didemnid ascidians. The impacts occurred despite the copper pulse being much less than published LC50 values for similar species. The impacts were no longer obvious by day 7 or 14, having been obscured by either high mortality of early settlers, or large settlement events that took place after day 2. Thus the greatest impact of the pollution event occurred during the period of highest toxicant concentration. The value of this study lies in the correlation of toxicity effects with bio-available metal concentrations under realistic (natural, in situ) conditions.

Improving the predictive power of spatial statistical models of stream macroinvertebrates using weighted autocovariance functions

Spatial statistical stream-network models are useful for modelling physicochemical data, but to-date have not been fit to macroinvertebrate data. Spatial stream-network models were fit to three macroinvertebrate indices: percent pollution-tolerant taxa, taxa richness and the number of taxalacking out-of-network movement (in-stream dispersers). We explored patterns of spatial autocorrelation in the indices and found that the 1) relative strength of in-stream and Euclidean spatial autocorrelation varied between indices; 2) spatial models outperformed non-spatial models; and 3) the spatial-weighting scheme used to weight tributaries had a substantial impact on model performance for the in-stream dispersers; with weights based on percent stream slope, used as a surrogate for velocity because of its potential effect on dispersal and habitat heterogeneity, producing more accurate predictions than other spatial-weighting schemes. These results demonstrate the flexibility of the modelling approach and its ability to account for multi-scale patterns and processes within the aquatic and terrestrial landscape.

High and Dry: Comparing Literature Review Approaches to Reveal the Data that Informs the Geomorphic Management of Regulated River Floodplains

While the impacts of regulation on river systems have been investigated, the main focus of the research has been on ecological and in-channel impacts. An understanding of the impacts of regulation on floodplain geomorphology is needed in order to inform management actions, in particular environmental flows. Concurrently with a traditional literature review on the effects of river regulation on floodplain geomorphology, we undertook a systematic review of the evidence using causal criteria analysis. The causal criteria approach tested evidence from multiple studies against a ‘checklist’ of criteria, constructing an argument for causality by combining a number of pieces of evidence into a single coherent argument. The causal criteria analysis only found support for one hypothesized cause-effect linkage in the conceptual model. In contrast, after discussing many of the conceptual model linkages, the traditional review provided a series of eight hypothesised scenarios to highlight the different possibilities for floodplain geomorphic change resulting from regulation. The difference was partly as a result of the time taken to enter studies into the Eco Evidence Database, but mainly because of the quality of evidence from geomorphic studies. Low statistical rigour in study designs meant that many papers were inadmissible as evidence. Thus, the causal criteria analysis made transparent the quality of data used in a traditional literature review that might subsequently be used to justify costly management recommendations.