Queensland Lake Eyre and Bulloo Freshwater Biogeographic Province

Queensland Lake Eyre and Bulloo Freshwater Biogeographic Province – Water quality

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• Introduced fauna—riparian
• Introduced flora—riparian

Turbidity

Turbidity within the Lake Eyre and Bulloo FBP is generally high, but can be low at upland or headwater sites.  At lowland sites, turbidity remains high even during the sometimes long periods between flows[2][1].  Average visibility measurements (secchi disc depths) from the Lake Eyre Basin rivers show visibility to be variable between catchments and over time, although there is a slight gradient of decreasing variability and turbidity moving westwards[1].  For more eastern rivers (e.g. Thomson and Barcoo Rivers) the average visibility depth is around 6 cm, ranging between 0.1 - 28cm. Western rivers have an average visibility depth of 4cm in the mid reaches and lower reaches have 6cm with a range of 1 - 12cm[1].  Dispersive soil types and run-off patterns are contributing factors to turbidity in this FBP[1].

Information about primary productivity and light climate

Information about methods

Photic depth

Light penetration of the water column or photic zone depth is shallow, reflecting the high turbidity of the system.  Light is one factor governing rates of in-stream primary production because the growth of most aquatic plants is limited by light availability.  Photic depth has been determined for 15 waterholes in the Cooper Creek catchment, shown below, and these results show that incident light can be measured at slightly deeper depths in this system compared with the Murray-Darling FBP[3].

Benthic metabolism

Arid zone streams and rivers are more metabolically active than temperate systems, with gross primary production one to two orders of magnitude greater[3].  Rates of benthic metabolism in the Lake Eyre and Bulloo FBP have been recorded for dry season habitats and on the inundated floodplains of the Cooper Creek system.  During the dry season, a prominent band of epipelic algae in the littoral zone of waterholes has been found to be highly productive.  The productivity of littoral zone algae is so prolific that despite low productivity in the deeper water column due to light extinction and only a limited area of littoral zone habitat (< 10%), these waterholes have been found to be net producers of carbon[2].  Rates of primary production associated with phytoplankton can also occasionally be high in the surface waters of these turbid systems, rates ranging from 1.5 mg C L^-1 day^-1 to 500 mg C L^-1 day^-1, have been measured during extended periods of no-flow[3].  During inundation of the vast floodplains of the Cooper Creek system warm, slow-flowing waters transform the terrestrial landscape into a shallow ‘lake’ with productivity increasing with inundation time[4].

References

1. ^ a b c d Bailey, V (2001), Western streams water quality monitoring project, p. 42, Department of Natural Resources and Mines, Queensland, ed. Q L D Department of Natural Resources and Mines.
2. ^ a b Bunn, SE, Davies, PM & Winning, M (2003), 'Sources of organic carbon supporting the food web of an arid zone floodplain river', Freshwater Biology. [online], vol. 48, no. 4, pp. 619-635. Available at: Scopus.
3. ^ a b c d Bunn, SE, Balcombe, SR, Davies, PM, Fellows, CS & McKenzie-Smith, FJ (2006), 'Aquatic productivity and food webs of desert river ecosystems', Ecology of desert rivers, Cambridge University Press, Sydney, NSW, ed. R T Kingsford.
4. ^ Davies, PM, Bunn, SE & Balcombe, F (2003), Importance of flood flows to the productivity of dryland rivers and their floodplains. [online], Environment Australia, ed. D E W Resources. Available at: http://www.environment.gov.au/water/publications/environmental/rivers/nrhp/flood/.

Last updated: 22 March 2013