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While good progress has been made in understanding freshwater ecosystems in northern Australia, there is still much to learn about biodiversity and the key factors that sustain aquatic species.
Floodplains are very important to aquatic food webs, because it is here that small fish feed on microscopic plants and animals, later providing sustenance for larger species when they move to connected waterways and the coast.
However some key questions remain:
• Are there ‘hotspots’ of floodplain productivity and how do these compare with productivity in main river channels?
• Do longer periods of flooding and higher productivity sustain higher biodiversity?
• How dependent are large animals, like predatory fish, on floodplains?
• How much do these animals move around?
Understanding the importance of linkages between rivers, floodplains and estuaries will allow us to predict how natural and man-made changes to connectivity or flows could affect aquatic biodiversity.
The project will provide a detailed understanding of the importance of floodplains to freshwater biodiversity in northern Australian river systems, and inform water resource management.
Researchers are identifying which areas flood, how deep, and for how long, and developing landscape-scale models to show connectivity and flows between floodplains, river channels and coasts.
They are also measuring the amount of microscopic aquatic plants produced in different floodplain habitats, identifying where fish and other animals get their food for growth and reproduction, and measuring the movement of large predators, such as sawfish, between habitats.
Where is the water on the floodplain?
Satellite images taken at different times of year are being used to work out which floodplain areas are inundated, how much water they are holding and for how long. This will help to predict which floodplain areas are ’hotspots’ for supporting food webs.
How much microscopic plant material is growing on floodplains?
Experiments measuring primary production, light availability and plant mass are being used to work out how much food is being produced in different floodplains habitats while they are flooded.
Are animals eating then moving?
Plants, algae, leaf litter, plankton, insects, prawns, and fish are being collected at a variety of sites. The chemical signatures of animal tissues will be used to show where animals are feeding and how important these food resources are for growth and reproduction.
How much are fish moving?
Acoustic tags are being implanted in large-bodied fishes including bull sharks and sawfish in Kakadu National Park. A fixed array of receivers in the lower reaches of these rivers is being used to monitor their daily movements from fresh to salt water.
• Tools and techniques to map and monitor water movement between floodplains, river channels and coasts using satellite images.
• A quantified understanding of the importance of floodplains in supporting the food webs of adjoining waterways.
• An understanding of how key fish species move between floodplains, rivers, and the freshwater-saltwater interface in estuaries.
• An understanding of the relationship between floodplain flows, biodiversity and biomass which will help guide water resource management.
On the rivers and floodplains of Kakadu National Park (Alligator Rivers Region), Daly River and the southern Gulf of Carpentaria (Norman, Gilbert, Leichhardt).