Importance of Flood Flows to the Productivity of Dryland Rivers and Their Floodplains

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Final Report
Prof P.M. Davies, Prof S. E. Bunn and Ms F. Balcombe
Environment Australia, 2003

Floodplain Food Webs

Floodplain inundation was followed by a proliferation of aquatic invertebrates, especially small crustaceans. In addition ten species of fish, including larvae, juveniles and adults of several species, were recorded on the floodplain with an average biomass of over 1.0 tonne km-2. Samples of aquatic invertebrates, fish, terrestrial and aquatic detritus, algae and terrestrial invertebrates were collected for food web analysis (e.g. Figure 15). Analysis of stable isotope data indicated that much of the fish biomass is ultimately derived from algal sources .

A raft of ants

A raft of ants

Clam shrimp

Clam shrimp

Invertebrates being collected from the flood waters

A raft of ants and clam shrimp were amongst the invertebrates collected from the flood waters.

The diets of all fish species during the flood were dominated by aquatic sources but with a greater range of dietary items than that recorded during the dry (Figure 16). Some of this floodplain production undoubtedly returns to river waterholes as fish biomass once floodwaters recede. However, given the small area of permanent waterholes (3.2km2) compared with the inundated floodplain (several thousand km-2), much of the aquatic production must either be exported downstream, retained on the floodplain or immediately consumed (i.e. by birds).