Charles James Lemckert

Natural or artificial? Habitat-use by the bull shark, Carcharhinus leucas.

Background Despite accelerated global population declines due to targeted and illegal fishing pressure for many top-level shark species, the impacts of coastal habitat modification have been largely overlooked. We present the first direct comparison of the use of natural versus artificial habitats for the bull shark, Carcharhinus leucas, an IUCN ‘Near-threatened’ species - one of the few truly euryhaline sharks that utilises natural rivers and estuaries as nursery grounds before migrating offshore as adults. Understanding the value of alternate artificial coastal habitats to the lifecycle of the bull shark is crucial for determining the impact of coastal development on this threatened but potentially dangerous species. Methodology/Findings We used longline surveys and long-term passive acoustic tracking of neonate and juvenile bull sharks to determine the ontogenetic value of natural and artificial habitats to bull sharks associated with the Nerang River and adjoining canals on the Gold Coast, Australia. Long-term movements of tagged sharks suggested a preference for the natural river over artificial habitat (canals). Neonates and juveniles spent the majority of their time in the upper tidal reaches of the Nerang River and undertook excursions into adjoining canals. Larger bull sharks ranged further and frequented the canals closer to the river mouth. Conclusions/Significance Our work suggests with increased destruction of natural habitats, artificial coastal habitat may become increasingly important to large juvenile bull sharks with associated risk of attack on humans. In this system, neonate and juvenile bull sharks utilised the natural and artificial habitats, but the latter was not the preferred habitat of neonates. The upper reaches of tidal rivers, often under significant modification pressure, serve as nursery sites for neonates. Analogous studies are needed in similar systems elsewhere to assess the spatial and temporal generality of this research.

Sediment resuspension within a microtidal estuary/embayment and the implication to channel management

ABSTRACT Sediment transport patterns within coastal environments continue to be of strong concern to the coastal engineer, scientist and manager. A study was conducted on Saltwater Creek, Gold Coast, Australia, which is a small microtidal estuary/embayment system that has no continual inflow of freshwater with inflows only resulting from direct catchment rainfall. Use was made of an Acoustic Doppler Current Profiler (ADCP) and a profiling transmissometer to determine the likelihood of tidal flow induced resuspension. Results showed that the apparently simple system was actually highly complex in nature. It was susceptible to significant sediment loadings as the result of catchment runoff and biological activity. Resuspension activity within the main channel was qualified and found to play only a minor role in the observed suspended sediment loadings. The results obtained have permitted the development of a conceptual model, from which some future management strategies can be proposed. Importantly, the techniques used in this study can be applied elsewhere to investigate sediment transport (including resuspension) properties when equipment resources are limited.

A conceptual model for integrating physical geography research and coastal wetland management, with an Australian example

We have developed a conceptual model to assist integration between physical geographical sciences, institutional frameworks and management in the context of coastal wetlands. Wetlands are key interconnected systems that will respond early to climate change and especially to associated sea-level changes. A major constraint on management of wetlands is the lack of congruence between the ecosystems and the institutional frameworks that govern their management: connectivity in coastal systems is overlain by institutional fragmentation. We introduce a model that facilitates integration of physical geographical (biophysical) information into the legislative, planning, policy and management process. It consists of interconnected parallel subprojects in science and in planning with strong cross-links with stakeholders at all levels, founded on long-term and trusting relationships. We also show progress that has been made in applying the model, with an Australian example. It is concluded that the approach has potential to move towards the goal of sustainable management but that it urgently needs to evolve, so as to meet the challenges of climate and associated changes.

Finite dispersal of a separative nepheloid plume by an internal hydraulic jump in a tropical mountainous river estuary

This paper investigates the dynamics of an internal hydraulic jump in a river plume and associated suspended sediment dispersal. Field investigations were undertaken into the river plume generated by the Herbert River, Australia, following a moderate flood event induced by Cyclone Fritz in 2004. The forced plume experiences an abrupt transition from supercritical to subcritical via an internal hydraulic jump, as defined by a mode-1 internal Froude number computed using the phase speeds from the Taylor-Goldstein equation. The hydraulic theory of a two-layer stratified flow was used to identify the plume shape and the mechanical energy loss within the jump. The hydraulic jump energy loss is primarily transferred to the buoyancy-driven potential energy, uplifting the river plume. Intense stratification decreases the bottom stress, damping the resuspension. Therefore, a separative nepheloid dispersal system occurs at the jump section. Both the upper and lower nepheloid flows are confined to the inner shelf, but have different dispersal behaviors and mechanisms. The upper nepheloid flow, which is primarily controlled by advection and settling, satisfies an exponential decay law of the total suspended sediment concentrations versus the offshore distance. The lower nepheloid flow dominated by deposition is detached seaward near the lift-off point of the river plume. A turbidity front associated with the jump may accumulate a large quantity of suspended sediments, enhancing sediment release from the river plume. These findings will promote in-depth understanding of both the cross-shelf sediment dispersal and muddy deposit on the shelf.

Beyond QMRA: Modelling microbial health risk as a complex system using Bayesian networks

BACKGROUND Quantitative microbial risk assessment (QMRA) is the current method of choice for determining the risk to human health from exposure to microorganisms of concern. However, current approaches are often constrained by the availability of required data, and may not be able to incorporate the many varied factors that influence this risk. Systems models, based on Bayesian networks (BNs), are emerging as an effective complementary approach that overcomes these limitations. OBJECTIVES This article aims to provide a comparative evaluation of the capabilities and challenges of current QMRA methods and BN models, and a scoping review of recent published articles that adopt the latter for microbial risk assessment. Pros and cons of systems approaches in this context are distilled and discussed. METHODS A search of the peer-reviewed literature revealed 15 articles describing BNs used in the context of QMRAs for foodborne and waterborne pathogens. These studies were analysed in terms of their application, uses and benefits in QMRA. DISCUSSION The applications were notable in their diversity. BNs were used to make predictions, for scenario assessment, risk minimisation, to reduce uncertainty and to separate uncertainty and variability. Most studies focused on a segment of the exposure pathway, indicating the broad potential for the method in other QMRA steps. BNs offer a number of useful features to enhance QMRA, including transparency, and the ability to deal with poor quality data and support causal reasoning. CONCLUSION The method has significant untapped potential to describe the complex relationships between microbial environmental exposures and health.

Salt Fluxes within a Very Shallow Subtropical Estuary

Abstract This article describes the transport processes and net salt flux within a shallow estuarine system, with particular reference to the Coombabah Lake–Creek system in Queensland, Australia. Observations of currents and salinity at two locations within Coombabah Lake provided a basis for assessing the relative importance of various transport processes within a very shallow (water depth <1 m) subtropical estuary. The instantaneous velocity and salinity data were decomposed into time-averaged means and time-varying components and were used to quantify the salt flux components attributed to various physical processes. In this study, advection by residual flow, which contributed 65% of the total salt flux, was identified as the dominant process in transporting salt. The advective flux also determined the direction of the net salt flux within this shallow estuarine system. This study concludes that the net salt flux varies spatially and temporarily with hydromorphological and meteorological conditions.

Modelling microbial health risk of wastewater reuse: A systems perspective.

There is a widespread need for the use of quantitative microbial risk assessment (QMRA) to determine reclaimed water quality for specific uses, however neither faecal indicator levels nor pathogen concentrations alone are adequate for assessing exposure health risk. The aim of this study was to build a conceptual model representing factors contributing to the microbiological health risks of reusing water treated in maturation ponds. This paper describes the development of an unparameterised model that provides a visual representation of theoretical constructs and variables of interest. Information was collected from the peer-reviewed literature and through consultation with experts from regulatory authorities and academic disciplines. In this paper we explore how, considering microbial risk as a modular system, following the QMRA framework enables incorporation of the many factors influencing human exposure and dose response, to better characterise likely human health impacts. By using and expanding upon the QMRA framework we deliver new insights into this important field of environmental exposures. We present a conceptual model of health risk of microbial exposure which can be used for maturation ponds and, more importantly, as a generic tool to assess health risk in diverse wastewater reuse scenarios.

Turbulence within inertia‐buoyancy balanced axisymmetric intrusions

Data from two detailed field experiments were used to investigate the turbulence within inertia-buoyancy balanced, axisymmetric intrusive gravity currents entering nearly quiescent stratified water bodies. The intrusions were generated by energetic point source bubble plume systems installed within different freshwater reservoirs, and the mixing activity was recorded with microstructure profilers. Close to the bubble plume, the intrusions were found to be very turbulent. The turbulent activity within the intrusions was observed to decay most rapidly in the intrusion core, but the shear at the upper and lower boundaries of the intrusions maintained the turbulence in these regions for a long distance. The results showed that the turbulence began with a length scale equal to the maximum sustainable overturn length for internally generated shear and hence a turbulent Froude number near unity. As the intrusions moved away from the generation region, the Froude number remained near unity, but the Reynolds number decreased with distance; the shear generated by the intrusion thus sustained an active turbulence field, albeit with ever decreasing length scales.

Sediment Dynamics of a Very Shallow Subtropical Estuarine Lake

ABSTRACT Ali, A.; Lemckert, C.J.; Zhang, H., and Dunn, R.J.K., 2014. Sediment dynamics of a very shallow subtropical estuarine lake. Estuaries are of immense importance to many communities. The characteristics of estuarine flow and sediment conditions are important, since they play a critical role in the functionality and health of these systems. This study investigated sediment dynamics of a very shallow subtropical estuarine system: Coombabah Lake, southern Moreton Bay (Australia). Total suspended solid concentrations, turbidity, salinity, and tide levels were measured at eight stations within the lake. In situ current velocity and meteorological data were also collected during the study period, and data were analysed to determine the dominant sediment dynamic processes within the lake. Sediment transport was simulated using a three-dimensional numerical model to better understand the influence of various physical processes. Influence of sea-level rise on the sedimentary dynamic processes was also examined. Results of the study identified that sediment dynamics were dominated by advection processes driven by the influence of tides, with wind and wave forcing playing minor roles during the study period. Model simulations agreed well with the collected field data. The influence of sea-level rise within the system was predicted to reduce the turbidity of the system, and presumably increase primary productivity.

Fiber Optic Pressure Sensing Arrays for Monitoring Horizontal and Vertical Pressures Generated by Traveling Water Waves

Distributed pressure sensing arrays fabricated from fiber Bragg gratings have been demonstrated for real-time monitoring of the dynamic subsurface pressures beneath water waves in a wave tank. Two sensing arrays were used to monitor horizontal and vertical pressures in the tank as periodic wave trains passed overhead. The horizontal and vertical arrays contained 90 and 35 sensing elements, respectively, spaced at 1-cm intervals allowing highly accurate spatial resolution to be achieved in both orientations. The wave tank paddle was programmed to generate wave-trains varying from ~5 to 30-cm peak-to-trough and the pressures measured using the fiber optic array were validated using commercial piezo-electric pressure sensors and video image analysis. The length and sensor separation of the fiber optic sensing array can be varied to suit the location under test, and the fiber optic elements make the devices inherently resistant to corrosion and electromagnetic interference.