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

Comparison of Aquatic and Terrestrial Rates of Production

The rates of production (as estimated Net Primary Productivity) in the river waters were compared to known terrestrial rates. Table 4 shows steady-state net terrestrial primary productivity per unit area (NPP), spatially averaged across major drainage divisions (Australian Agriculture Assessment, 2001) as compared to estimated benthic NPP measured from Cooper Creek. For aquatic systems, NPP estimated from GPP by the methodology of Bott et al. (1985).

Table 4: Terrestrial primary productivity
  Drainage NPP
(t Carbon/ha/yr)
Rates of estimated terrestrial NPP across a range on catchments in Australia. Indian Ocean 0.2
Western Plateau 0.3
Murray-Darling 2.3
Lake Eyre Basin 0.1
South Western WA 2.1
South East coast 5.5
Timor Sea 1.0
Rates of aquatic NPP have been scaled to the hectare (shaded). Cooper Creek “dry” littoral 5.5
Cooper Creek “dry” channel 0.03
Experiment (after 8 days) 1.0
Floodplain (> 2 weeks) 2.5

Rates of terrestrial NPP for the Lake Eyre Basin (based on current land-use practices and average rainfall) are about 0.1 t C/ha/year. In contrast, estimated NPP for the littoral areas of the pools (the 'bath-tub ring' sensu Bunn, Davies and Winning 2003) is over 50x this value. Rates of NPP in the bathtub ring are similar to primary rainforest or highly irrigated areas of the south east coast of Australia (Australian Agriculture 2001).

Aquatic primary production accounts for a substantial biomass of highly palatable carbon in the Cooper Creek system, particularly associated with wide scale flooding. This is undoubtedly important to the aquatic food web, but also likely to make a significant contribution to terrestrial ecosystems.

Algal growth on floodplain soils.

Algal growth on floodplain soils.

Algae formed into floating mats in the floodwaters.

Algae formed into floating mats in the floodwaters.

Cooper Creek floodwaters 2000.

Cooper Creek floodwaters 2000.