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 water extraction from the Mitchell River, meaning that flows are largely unregulated. The catchment supports existing water users including Traditional Owners as well as significant ecological assets, including wetlands of national significance, threatened species, traditional harvests, and commercial and recreational fisheries. Information on the water needs of freshwater ecosystems and their associated biodiversity is required to guide decision-making around water planning and development.
This project examined the links between freshwater flows and floodplain inundation, aquatic plant biomass accumulation, floodplain subsidies to freshwater food webs, fish movement and fisheries production. The research had five major objectives.
The Mitchell River’s freshwater biodiversity – and the food and habitats that sustain it – depends on upstream flows and the connectivity they provide. Flows are important for all habitats, including rivers, floodplains and coasts. They inundate floodplains, and the nutrients they deliver fuel the growth of aquatic plants and algae which supports the entire food web. Flows also connect highly productive floodplains with their rivers. Flows and freshwater habitat availability support the abundance, age structure, biomass and population of barramundi in the coastal fishery in the Gulf of Carpentaria. Fish move more easily when rivers and floodplains are connected by flows. Given the importance of flows for the Mitchell’s freshwater biodiversity, these findings have direct relevance to environmental risk assessments for future water planning in the Mitchell catchment.
Key implications for water planning and river management:
The findings and implications have been summarised in three conceptual diagrams that depict the ecological processes in the dry season and wet season, and the predicted impacts of changes to the catchment.
Conceptual model of Mitchell River ecosystem function in the dry season. A pdf of this model is available here.
Conceptual model of Mitchell River ecosystem function in the wet season. A pdf of this conceptual model is available here.
Conceptual diagram of possible threats from water-resource development to Mitchell River ecosystem function. A pdf of this conceptual model is available here.
Possible threats from water-resource development to Mitchell River ecosystem function
Molinari, B., Stewart-Koster, B., Malthus, T.J. and Bunn, S.E. (2022), Impact of water resources development on connectivity and primary productivity across a tropical river floodplain. J Appl Ecol. Accepted Author Manuscript. https://doi.org/10.1111/1365-2664.14111
Molinari B, Stewart-Koster B, Malthus TJ, Bunn SE. Assessing Spatial Variation in Algal Productivity in a Tropical River Floodplain Using Satellite Remote Sensing. Remote Sensing. 2021; 13(9):1710. https://doi.org/10.3390/rs13091710
Venarsky, MP, Stewart‐Koster, B, Hunt, RJ, Jardine, TD, & Bunn, SE. (2020). Spatial and temporal variation of fish community biomass and energy flow throughout a tropical river network. Freshwater Biology. 2020; 00: 1– 11. https://doi.org/10.1111/fwb.13581
Martin Kainz presents how fatty acids can be used as biomarkers in analysing food webs and trophic flow.
Mike Venarsky presents at the December 2018 DES (Qld) Workshop about the community-level migration patterns of fish in the Mitchell River and some of its tributaries.
David Crook discusses how otolith chemistry can help explain and document fish life history.
Glenn McGregor presents on how environmental assessments contribute to the evaluation of Water Plans in Queensland at a DES Workshop from December 2018.
Jonathan Marshall explains how paleo-ecological tracers can help understand past ecosystem variability to predict and manage now and into the future.
The “Environmental water needs for the Mitchell River” project is supporting water planning and floodplain management in the Mitchell River catchment through increasing our understanding of the links between river flows, flooding and ecosystem assets such as fish and fisheries.
They were supported by researchers from Griffith University, CSIRO, Queensland Department of Science, Information Technology & Innovation, Queensland Department of Agriculture & Fisheries, and Charles Darwin University.