Linking water-resource models to ecosystem-response models to guide water-resource planning -- an example from the Murray--Darling Basin, Australia

Objectively assessing ecological benefits of competing watering strategies is difficult. We present a framework of coupled models to compare scenarios, using the Coorong, the estuary for the MurrayDarling River system in South Australia, as a case study. The framework links outputs from recent modelling of the effects of climate change on water availability across the MurrayDarling Basin to a hydrodynamic model for the Coorong, and then an ecosystem-response model. The approach has significant advantages, including the following: (1) evaluating management actions is straightforward because of relatively tight coupling between impacts on hydrology and ecology; (2) scenarios of 111 years reveal the impacts of realistic climatic and flow variability on Coorong ecology; and (3) ecological impact is represented in the model by a series of ecosystem states, integrating across many organisms, not just iconic species. We applied the approach to four flow scenarios, comparing conditions without development, current water-use levels, and two predicted future climate scenarios. Simulation produced a range of hydrodynamic conditions and consequent distributions of ecosystem states, allowing managers to compare scenarios. This approach could be used with many climates and/or management actions for optimisation of flow delivery to environmental assets.

Multiple dispersal vectors drive range expansion in an invasive marine species

The establishment and subsequent spread of invasive species is widely recognised as one of the most threatening processes contributing to global biodiversity loss. This is especially true for marine and estuarine ecosystems, which have experienced significant increases in the number of invasive species with the increase in global maritime trade. Understanding the rate and mechanisms of range expansion is therefore of significant interest to ecologists and conservation managers alike. Using a combination of population genetic surveys, eDNA plankton sampling and hydrodynamic modelling we examined the patterns of introduction of the predatory Northern Pacific seastar (Asterias amurensis) and pathways of secondary spread within southeast Australia. Genetic surveys across the invasive range reveal some genetic divergence between the two main invasive regions and no evidence of ongoing gene flow; a pattern that is consistent with the establishment of the second invasive region via a human-mediated translocation event. In contrast hydrodynamic modelling combined with eDNA plankton sampling demonstrated that the establishment of range expansion populations within a region is consistent with natural larval dispersal and recruitment. Our results suggest that both anthropogenic and natural dispersal vectors have played an important role in the range expansion of this species in Australia. The multiple modes of spread combined with high levels of fecundity and a long larval duration in A. amurensis suggests it is likely to continue its range expansion and significantly impact Australian marine ecosystems.

Decadal decline in demersal fish biomass coincident with a prolonged drought and the introduction of an exotic starfish

Between 1990 and 2011, Port Phillip Bay in southern Australia experienced 2 major ecological disturbances: a prolonged drought from 1997 to 2010, and the introduction of the invasive starfish, Asterias amurensis. The drought reduced land-based nitrogen inputs by 64%, and the biomass of A. amurensis in the deep centre of the bay peaked at 56% of the resident fish biomass in 2000. The impacts of these disturbances on fish were assessed using a demersal trawl time-series spanning 2 decades (1990 to 2011). The timing and spatial extent of changes to fish biomass were analysed using ANCOVA and change point analysis. During the drought, fish biomass declined by 69% in the deep centre of the bay, by 50% at intermediate depths, and showed no significant change around the shallow fringes. This spatial pattern is consistent with hydrodynamic modelling, which suggests that during the drought a greater proportion of the (lower) nitrogen input was retained near the coastal fringe. Most of the decline in fish biomass was attributed to the cumulative effects of reduced productivity during the 12 yr drought. However, declines in 3 species in the deep region were attributed to competition with A. amurensis. Each of these species exhibited high dietary overlap with A. amurensis and displayed sharp declines in biomass coinciding with the peak abundance of A. amurensis in 2000.

Coupled modelling of hydrodynamics and mass transfer in membrane filtration

This research produced a novel predictive computational model for the water treatment processes of nanofiltration and reverse osmosis. This model combined commercial computational fluid dynamics codes with numerical mass transfer models developed by the candidate to provide a rigorous description of these processes’ hydrodynamic and pollutant removal behaviour.