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

Dry season Research on Dryland River Ecosystems

Primary sources of organic carbon and consumers were collected for stable isotope analysis in several river waterholes at four locations in the Cooper Creek system in central Australia. A conspicuous band of filamentous algae was observed along the shallow littoral zone of the larger waterholes (Figure 11). Despite the high turbidity, benthic gross primary production in this narrow zone was very high (1.7 - 3.6 g C m-2 day-1), about two orders of magnitude greater than that measured in the main channel (Figure 12). Stable carbon isotope analysis confirmed that this 'bath-tub ring' of algae was the major source of energy for aquatic consumers, ultimately supporting large populations of crustaceans and fish.

Figure 11 The bath-tub ring of algae in the shallow littoral zone

Figure 11 The bath-tub ring of algae in the shallow littoral zone

Figure 12 The main channel of Cooper Creek near Windorah

Figure 12 The main channel of Cooper Creek near Windorah

Variation in the stable carbon and nitrogen isotope signatures of consumers suggests that zooplankton was the other major primary source. Existing ecosystem models of large rivers often emphasize the importance of longitudinal or lateral inputs of terrestrial organic matter as a source of organic carbon for aquatic consumers. Our data suggest that, despite the presence of large amounts of terrestrial carbon, there was no evidence of it being a significant contributor to the aquatic food web in this floodplain river system. SOURCE: Bunn, Davies & Winning (2003)