River catchments, particularly the Mitchell River catchment, of the Gulf of Carpentaria are home to many important freshwater assets, such as significant commercial and recreational fisheries, threatened species, and wetlands of national significance. With considerable interest in agricultural expansion in the Gulf, there’s concern these assets may be impacted by intensive development.
These assets depend greatly on the linkages between rivers, floodplains and estuaries. However, our current ability to predict the consequences of future development on these linkages is limited. There are also significant gaps in our understanding of environment flow requirements, such as the quantity and timing of water flows needed to trigger the migration of key aquatic species
This research is improving our understanding of the critical flow needs to sustain freshwater ecosystems in the Mitchell River catchment. In particular, the project aims to predict the impacts of future development on important ecosystem linkages between the river and its floodplain wetlands, and to better understand other potential risks associated with changes to flow regimes. This information is vital to help inform decision makers about water allocation that both enables agricultural development and protects environmental assets.
This project is:
Component 1: Threat assessment of ecological assets in the Mitchell River
An initial desktop threat assessment is generating information about key ecological assets, their critical links to flow, and the likely consequences of development in the Mitchell River.
Component 2: Implications of water resource development on flood flows and ecosystem productivity in the Mitchell River
Researchers are using river models to predict the effect of development scenarios on floods, and combine modelled floodplain inundation patterns with inundation patterns captured from satellite images to analyse the ‘connectivity’ of the floodplain. This understanding of how rising floodwaters connect low areas across the floodplain, and of how long these connections last and waterholes persist in different places, is helping highlight the effects of changes in flow on floodplain wetlands. Without such connectivity, floodplains can’t provide important resources such as food back to the river, even if particular wetlands produce abundant resources. The timing, duration and frequency of floodplain connections will likely change with changes in river flow and therefore potentially impact habitat, food and/or access for fish, birds and other species.
Component 3: Critical flow needs for ecological assets in the Mitchell River
Researchers are mapping important aquatic refugia, floodplain wetland vegetation and algal production using remote sensing and field surveys to determine the impacts of changes to flows on the distributions and quality of habitat and food sources. The team is sampling important species to determine how much each depends on river, floodplain and estuarine sources of food production. Otoliths (fish ear bones) have been extracted from multiple species and the team are using these to determine how flood flows influence their movement and growth. Researchers are subsequently using this understanding of species food, habitat and movement needs to identify their river and floodplain flow needs. They are combining this with the threat assessment (C1) and floodplain connectivity modelling (C2) to assess the impact of potential developments that alter flows and disrupt connectivity through water extraction and infrastructure in channels or across floodplains.
The research is being undertaken within the Mitchell River catchment, with a focus on the floodplain and other key ecological assets in-stream.
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 are being supported by researchers from Griffith University, CSIRO, Queensland Department of Science, Information Technology & Innovation, Queensland Department of Agriculture & Fisheries, and Charles Darwin University.
This project is due for completion in June 2021.