Queensland Lake Eyre and Bulloo

The Lake Eyre and Bulloo Freshwater Biogeographic Provinces (FBPs) comprises the Georgina, Diamantina, Cooper Creek, Hay and Bulloo drainage basins, and is located in the south-west of the State. The FBP covers the Channel Country, Mitchell Grass Downs, Northwest Highlands, Desert Uplands, and Mulga Lands vegetation bioregions, and a very small portion of the Brigalow Belt vegetation bioregion. This vast geographic area (greater than 550,000 km2), encompasses large variability in climate, geology and hydrology that produce and influence unique ecosystem features at local scales.

There are unique topographic and hydrologic features across the province. These large dryland river systems have extremely variable flows and their downstream transmission results in extensive floodplain inundation creating vast temporary wetlands. During dry times the riverine system exists as a series of waterholes with variable persistence (Bunn et al., 2006). The Lake Eyre Basin overlays the Great Artesian Basin, one of the world’s largest aquifer systems.

Lake Eyre and Bulloo FBP

Aquatic ecosystems in the LEB FBP include ecosystems dependent on surface and groundwater including; ephemeral rivers, waterholes, ephemeral wetlands, mound springs and subsurface habitats.

Key Ecosystem Drivers – Lake Eyre and Bulloo FBP

Rainfall

Annual mean precipitation ranges from dry to moderate along a LEB-west to north-east gradient. Driest Quarter Precipitation ranges from dry to moist along a west to east gradient. Summer monsoon rainfall in upper sections of catchments

Temperature

Temperatures tend to get cooler towards the south-east of the province. This is roughly influenced by the arid deserts to the west and dry grasslands to the east.

Water balance

Mean Annual Runoff in the province is negligible.

Geology

Soil is primarily clay and clay loams. These tend to be susceptible to poor water retention, low fertility, low organic matter reserves, low water penetration and contribute to turbidity.

Overlays much of the Great Artesian Basin

Terrain

The majority of the identifiable terrain in the province consists of valley bottom flat terrain. Small portions of the catchment contain ridge top flat and erosional classes.

Extensive system of braided channels associated with low relief floodplains

Base flow and flood flow

Most flow is related directly to the flood flow from rainfall events with little base flow contribution. Flow variability can be considered some of the greatest in the world (Puckridge et al., 1998).

Unregulated river flows

Most variable flow patterns on earth!!

Gauges

Modelled pre-development data from 5 gauges were used for these analyses.

Magnitude of spates

Spates generate very little run-off due to the size of the catchment areas and the bias towards extremes of flow.

No flow spells

Flow is intermittent in the province and no flow spells are an important feature of the hydrology.

Rise and fall of the hydrograph

The mean rate of rise for the province is approximately double the mean rate of fall.

Wet and dry seasons

The wet season is January-April and the dry season May-December.

Turbidity

In general turbidity in the province in high, though this may vary depending on site. In upland and headwaters turbidity can be low.

Photic Depth

Light penetration of the water column or photic zone depth is shallow, reflecting the high turbidity of the system.

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 (Bunn et al., 2006). Primary productivity in the region is mainly driven by littoral zone algae.

Bank shape and slope

Bank slopes are mainly of low-moderate incline, and predominantly of concave and convex shape classes. Undercut banks are rare in the province.

Riparian vegetation and macrophytes

The riparian zone is sparse and primarily dominated by grasses and medium/small trees. Macrophyte (aquatic plant) tend to be rare in the province.

Persistent habitat and refugia associated with waterholes

Low vegetation cover

Substrate composition and heterogeneity

Substrate heterogeneity is amongst the lowest in Queensland. Fine sediments (silt/clay and sand) dominate pool and edge habitats. Groundwater and mound spring ecosystems