River to landscape connections and biodiversity

This project delivered new understanding of the contributions of floodplains to the maintenance of biodiversity and fish biomass in river-floodplain systems, meeting both pure and applied scientific objectives. The outputs of the project can feed directly into wetland management and conservation planning processes, providing end users with methods and tools to quantify the importance of different landscape elements towards overall system biodiversity.

Linkages among habitats and movements of materials across ecosystem boundaries often have major implications for the production of animal and plant biomass and resultant biodiversity.  Fully-aquatic species which typically inhabit the river channel, floodplain billabongs and estuarine waters in the dry season move onto floodplains during the wet season.  As these floodwaters recede, aquatic production that has been assimilated by consumers such as fish is often transferred back into the river systems and exported offshore. These types of subsidies can therefore represent a significant transfer of aquatic carbon and nutrients from floodplains to other parts of the river system and indeed to other aquatic systems over hundreds or thousands of kilometers. Yet it is very difficult to quantify the importance of these linkages and movements.  By measuring sources of energy and trophic level of predators along with underlying sources of production such as algae, and the movement patterns of key fauna species, this project generated ecosystem-level science needed for management.

Project activities involved the following:

Food webs

• Used stable isotope techniques to trace the chemical signatures of food through the food web.

Remote sensing

• Mapped long-term seasonal connectivity of flooding and vegetation patterns using remote sensing techniques.

Algal productivity

• Measured and mapped the sources of algal abundance which support aquatic food webs.

Fish movement

• Tracked the movement and connectivity of large predators across the aquatic landscape using radio tracking techniques.

For the floodplains of the Alligator Rivers region within Kakadu National Park the project delivered:

• clarification of the food web implications of water resource development by quantification of the importance of different habitats in sustaining fish and other consumers in river-floodplain systems;
• remote sensing methods to map, monitor and asses the seasonal connectivity between catchments, floodplains and coastal receiving waters;
• methods to identify and map seasonally available ‘hotspots’ of floodplain primary productivity that are critical to the maintenance of  food webs, and implications of the loss of such habitats;
• understanding of the movement patterns of key fauna that use floodplains and the freshwater-saltwater interface in estuaries; and
• a global context on how the predictability of flood magnitude and timing drives ecosystem responses in tropical floodplain riverscapes.

The project study area comprised the Alligator Rivers Region within Kakadu National Park in the wet-dry tropics along the coastal zone of northern Australia. This region includes the iconic Kakadu National Park which has been designated as internationally important under criteria established by the Ramsar Convention on Wetlands.