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

Project Objectives

The aims of this project were to assess rates of primary production on floodplains of rivers of the Channel Country and compare these with known terrestrial rates of production in the surrounding landscape. This, together with the use of stable isotope techniques, were used to determine how important this aquatic production is to both aquatic and terrestrial food webs and to estimate the overall importance of significant floodplain inundation for landscape-scale productivity. Data were produced for rates of metabolism with different inundation durations. The project also identified key ecological processes and, based on this, parameters that would 'drive' a quantitative model on the likely consequences of changing patterns of floodplain inundation, occurring through water harvesting and other forms of flow regulation. These data and parameters are to be incorporated into a predictive model of flow regulation produced by the ARIDFLO project.

Background

Many Australian dryland rivers are characterised by extensive floodplains and a network of anastomosing channels and distributaries. The river water in many systems in the Lake Eyre basin is highly turbid and remains so, even during the long periods between episodic flood flows when rivers are reduced to a series of permanent waterholes. Given these features, we predicted that riverine food webs would be supported by energy sources derived from extensive floodplain exchange which occurs during episodic floods, and by continual input from fringing vegetation along the vast network of channels during the dry (see Figure 1). We also predicted that aquatic plant production would be limited by low light penetration due to the turbid water and thus make a minor contribution to the aquatic food web.

 Flood runners in Cooper Creek Windorah following a flood coming down the Thomson River.

Figure 1: Flood runners in Cooper Creek Windorah following a flood coming down the Thomson River.

Study Approach

The approach of the study was focused on gaining an understanding of the important ecological processes in arid zone rivers and how these may be influenced by flow regulation. In the dry, rates of carbon metabolism were measured in different habitats and stable isotope analyses was used to determine how this carbon was distributed through the aquatic food web. Dry floodplain soils were experimentally inundated to simulate flooding; measuring rates of algal production and species present. Finally, measurements of ecological processes (carbon sources and fate) were made during a flood. Based on these results, parameters for model development have been suggested which would predict the relationship between productivity and flows. This information will be utilised by ARIDFLO for their predictive model.

During late summer 2000, a significant flood in Cooper Creek resulted in substantial floodplain inundation near Windorah, western Queensland. This flood event was extensively sampled at ten sites on two occasions (early flood; 1-8 March 2000 and late flood 18-21 March 2000).

A satellite image of Cooper Creek in western Queensland.

A satellite image of Cooper Creek in western Queensland.

The Cooper Creek Catchment in western Queensland.

The Cooper Creek Catchment in western Queensland.

Study site locations
TC1 S 25° 25.597'
E 142° 38.713'
TC2 S 25° 25.541'
E 142° 38.808'
TC3 S 25° 25.582'
E 142° 39.042'
W1 S 25° 21.688'
E 142° 30.641'
W2 S 25° 21.606'
E 142° 31.121'
W3 S 25° 21.596'
E 142° 31.393'
RL1
S 25° 22.895'
E 142° 31.863'
RL2
S 25° 22.791'
E 142° 31.874'
RL3 S 25° 22.438'
E 142° 31.897'
CL1 S 25° 21.814'
E 142° 31.531'
CL2
S 25° 21.734'
E 142° 31.587'
CL3
S 25° 21.661'
E 142° 31.509'
WD1
S 25° 26.157'
E 142° 43.458'
WD2
S 25° 26.159'
E 142° 43.360'
WP1
S 25° 25.436'
E 142° 43.745'
TP
S 25° 25.977'
E 142° 43.528'
JY1
S 25° 20. 807'
E 142° 42.494'
JY2
S 25° 20. 612'
E 142° 41.230'
BGC
S 25° 23.642'
E 142° 46.192'
RTQ
S 25° 25.886'
E 142° 47.761'
CC3 S25° 26.271'
E142° 48.002'
CC5 S25° 25.542'
E142° 43.975'
BGC
plain
S 25° 23.642'
E 142° 46.192'
BGC
channel
S 25° 23.642'
E 142° 46.192'
RTQ
S 25° 25.886'
E 142° 47.761'