Changes in the surface water chemistry at low tide in drainage channels at East Trinity coastal wetland, Cairns (August 2013)

In this study surface water monitoring was undertaken at a number of locations at the East Trinity wetland site in August 2013 to gain an understanding of the flux of constituents from the drainage system. The monitoring period was set to co-inside with the extreme low-tide cycle to allow the best opportunity to measure flux

Application of a Multistressor Risk Framework to the Monitoring, Assessment, and Diagnosis of River Health

River health assessment and the science to support it have evolved and expanded over recent decades so that it is now a common component of water resource management throughout the world. The broad-scale application of such assessments began as audits of the current condition and trend (i.e., how condition changed over time) using general health indicators considered to be sensitive to a broad suite of anthropogenic stressors. These broad-scale audits provide an overall evaluation of the success of environmental management in protecting river health. However, water managers are increasingly interested in assessments that not only document health, but also go further by both diagnosing the causes of degradation and identifying the priorities for mitigation measures. We outline such an approach developed by the Queensland Government in Australia and provide a case study of its application. This approach identifies multiple stressors in river health within defined assessment regions, then quantifies both the likelihood of exposure to each and the impacts (consequences) to the ecosystem condition. This is done using cause-effect conceptual models that link human pressures to stressors and stressors to ecosystem responses. Specific regional information on the likelihood and consequence is derived from literature, interrogation of available data, and expert elicitation, along with associated estimates of confidence. Risk is calculated as the product of consequence and likelihood and used to rank stressors, with those posing high and moderate risks to the ecosystem condition selected for field measurement within resourcing constraints. Metrics of stressor intensity and relevant ecosystem responses are selected according to conceptual models and their operational efficacy, then applied to a spatially balanced statistical sampling design. The resulting assessments compare and combine results of the initial risk assessment with those from field samplings to give an overall picture of river health, and importantly along with the diagnosis of the stressors responsible for the degradation. Finally, recommendations are made for management priorities to restore river health or prevent further degradation. This approach has been successfully applied to many rivers in Queensland, Australia

Ecological impacts of invasive carp in Australian dryland rivers

Invasive carp are widely reported to harm ecosystems. In Australia, carp are a serious pest and, consequently, investigations of biocontrol options are under way. Best practice biocontrol requires cost/risk:benefit evaluation. To assist this, the impacts of carp on aquatic ecosystems have been summarized. To aid the evaluation of benefits, general predictions were tested by comparing dryland river ecosystems with and without carp, and ecosystem responses to a gradient in local carp density. Expectations were that in the presence of carp, and with increasing density, there would be increasing turbidity, decreasing densities of macrophytes and macroinvertebrates, and associated changes in assemblage composition, resulting in decreasing native fish density. Not all expected responses were found, indicating that the general understanding of carp impact requires modification for dryland rivers. Notably, carp did not increase turbidity or reduce macroinvertebrate density or composition, probably because of key attributes of dryland rivers. In contrast, there were large impacts on native fish biomass, not from the mechanisms expected, but from food resource monopolization by carp. Macrophyte occurrence was reduced, but macrophytes are naturally rare in these rivers. It is likely that the extirpation of an endangered river snail resulted from carp predation. Impacts on native fish may be reversible by carp control, but reversal of impacts on the snail may require carp elimination and snail reintroduction. Modelling is necessary to predict the probability of beneficial versus undesirable outcomes from carp control, and complementary measures to control other stressors may be needed. Benefits of carp control on dryland river ecosystems are fewer than generally predicted. This reinforces the point that ecological understanding cannot always be transferred between diverse settings and highlights the need to understand system characteristics relevant to causal impact pathways when applying generic carp impact models to specific settings. This has global relevance to future carp control efforts