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Critical water needs to sustain freshwater ecosystems and aquatic biodiversity in Queensland’s Mitchell River The Australian Government has identified water-resource development in the north of Australia as a priority for the coming years and Queensland’s Mitchell River is a focus of this interest. The Queensland Government currently regulates small amounts of extraction from the Mitchell River meaning that the flow regime is largely unregulated. In its current condition, the catchment supports existing water users, including Traditional Owners, and significant ecological assets, including wetlands of national significance, threatened species, traditional harvests, and commercial and recreational fisheries. Information is needed on the water needs of freshwater ecosystems and their associated biodiversity to guide decision-making around water planning and development. This project examined the links between freshwater flow and floodplain inundation, aquatic plant biomass accumulation, floodplain subsidies to freshwater food webs, fish movement and fisheries production. This project had five major objectives to understand the flow requirements of freshwater assets: 1. Identify the dependence of floodplain inundation and aquatic plant biomass accumulation on river flow 2. Map key ‘hotspots’ of freshwater primary productivity within the floodplain 3. Quantify riverine and floodplain connectivity to assess the likely impact of varying wet seasons and water-resource development on aquatic food webs, and the movement of fish between river channels and floodplain wetlands 4. Quantify the importance of river flows to estuaries by examining the flow dependence of barramundi growth, population dynamics and habitat use 5. Assess the implications of flow alteration on freshwater ecological communities, including movement of fish throughout the catchment.

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Floods are extreme events that can rapidly alter water and habitat quality in receiving estuaries. Because floods are unpredictable, they are more difficult to study, so have received less research attention than freshwater flow studies, resulting in a paucity of information on their ecological effects in the coastal zone. Previous studies have shown correlations between high flow periods and increased fisheries catches, which suggests that floods stimulate productivity in receiving waters. However, there have been no studies providing direct links between floods and increased productivity responses in fisheries species. In addition, the long-term effects of deposited flood sediment on food webs in estuaries are poorly understood. Floodwaters can carry high loads of fine sediment, which settles at the most offshore portion of the estuary delta, known as a prodelta. Nutrients, trace elements and other substances are also exported from the catchment dissolved in floodwater or attached to fine sediment particles and are deposited in estuaries. However, the processes of nutrient release from suspended sediments and settled sediments, and uptake of nutrients and trace elements into the food web in receiving estuaries are not well understood. Therefore, this thesis used laboratory experiments (Chapter 2 & 3) to study these processes with the aim of gaining a better understanding of the mechanisms underpinning measured ecological flood responses using field studies (Chapter 4 & 5). This study used catchment soils formed from three distinct rock types (granite, basalt and sandstone) from the Brisbane River (Queensland, Australia) catchment in a flood simulation experiment to quantify the rates of nutrient release during flooding (Chapter 2). In the laboratory, the fine fraction (<63 µm) of the soils was tumbled in freshwater for three days and left to settle in seawater for four weeks, and filtered water samples were taken throughout. A thin layer of the fine soils was also

Estuaries are critical aquatic environments that are used by many fish during their life cycle. However, estuaries often suffer from poor water quality as a result of anthropogenic activities. Fish diversity studies in estuaries are common, although few have examined whether correlations exist between water quality, metal contamination and fish assemblages. In the present study we investigated the effect of abiotic conditions, heavy metals and estuary characteristics on the abundance, diversity and composition of fish in four intermittently open estuaries along the Illawarra coast of south-eastern Australia. The heterogeneity of environmental conditions was reflected in the fish assemblages in each estuary. Environmental variables predicted fish species composition, and estuaries in particularly poor condition contained few species (estuarine residents) in high abundance, indicating their ability to acclimatise and survive in conditions that are hostile to other species. Overall, these findings demonstrate that estuarine fish assemblages may be useful indicators of estuary condition and reveal the importance of managing anthropogenic activities in the surrounding catchment to improve water quality so that biodiversity of fish can be restored in these estuarine environments.

Anthropogenic climate change is expected to result in dramatic shifts in the abiotic conditions within estuaries, including an elevation of temperature and salinity levels. Even so, few studies have addressed the impacts of multiple abiotic stressors on the behaviour and life history of key estuarine species, such as those of biological and commercial importance. Here we used a cross-factored experimental design to tease apart the effects of temperature and salinity on intraspecific aggression and growth rates of a native estuarine fish species, the Australian bass (Macquaria novemaculeata). Juvenile bass were exposed to one of four treatment conditions: 1) baseline temperature and salinity, 2) elevated temperature, 3) elevated salinity, and 4) elevated temperature and salinity. Elevated salinity increased rates of aggression, and elevated temperature decreased rates of growth, although the effects of both factors were mediated by the body size of individual bass. These results therefore highlight complex and variable effects of abiotic stressors and body size, emphasising the importance of considering individual-level attributes when evaluating the impacts of climate change on estuarine fishes.

This study was commissioned by the Hawkesbury-Nepean (HNCMA), Sydney Metropolitan (SMCMA) and Southern Rivers (SRCMA) Catchment Management Authorities and undertaken by the University of Wollongong to collate existing data and to provide a preliminary assessment of the potential impacts of coal seam gas (CSG) and coal mining activities on environmental assets within the three CMA regions, where environmental assets were defined under three broad themes; water, land and biodiversity. This study formed part of the Australian Federal Government’s Department of Sustainability, Environment, Water, Population and Communities (SEWPaC) Bioregional Assessment initiative within regions potentially affected by CSG and coal mining activities. The key components of this study included: Creating a database (using on the SEWPaC supplied template) identifying key environmental assets (groundwater, surface water, wetlands, land use, soils, vegetation and threatened species) within each of the three CMA regions. Providing a list of the key GIS datasets used to compile the database and their sources. Providing this report which outlines findings in relation to potential impacts and hazards of coal seam gas and mining activity on these environmental assets. Identifying knowledge and data gaps, and providing recommendations for future research.