Derwent Creek, Mungeranie Waterhole
2012 Aquatic Ecosystem Condition Report
- Permanently wet, non-flowing, creek site when sampled in spring 2012
- Moderately diverse macroinvertebrate community with three rare or sensitive species collected
- Water was very fresh, turbid and enriched with nutrients
- Riparian vegetation consisted of native trees and shrubs over weeds, and several native aquatic plants occurred in the river
About the location
Diamantina River is a large stream that rises at an altitude of nearly 500m in central west Queensland and flows south-westerly for about 900 km through central Queensland and the ‘channel country’ to form the Warburton River at its confluence with the Georgina River, downstream from Goyder Lagoon in South Australia. For much of its length, the Diamantina River has no main channel but consists of a series of wide, relatively shallow channels and associated floodplain habitats. Soils in the catchment are dominated by grey and brown clays that are generally low in phosphate but rich enough to support abundant growths of grasses whenever rains occur.
Flow patterns in the unregulated Diamantina River are highly variable and driven by monsoonal summer rainfall in the upper catchment area of Queensland. The Diamantina River and Cooper Creek are the world’s most variable major rivers in the world, characterised by ‘boom’ (major floods) and ‘bust’ (major dry periods and drought). In extremely wet years when rainfall reaches around 500mm year across much of its catchment, water flows down the Warburton River and reaches as far downstream as Lake Eyre. Large stretches of the Diamantina and Georgina rivers have little reliable water but a small number of widely-spaced permanent and semi-permanent waterholes occur throughout each river system (for more details see Silcock 2009).
The major land uses in the 157,000 square kilometre catchment are sheep (Qld only) and cattle grazing on native grasslands, with smaller areas used for rural towns and settlements, mining, tourism and the Diamantina National Park near Winton.
The monitoring site was located on the northern bank near gauge station 002101 at Birdsville, in south-western Queensland.
The creek was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was evidence of human disturbance including nutrient enrichment and weedy riparian zones but the stream provides habitat for a diverse community of aquatic macroinvertebrates which includes a few rare and sensitive species. Note that the high nutrient concentrations recorded from the waterhole were similar to other sites sampled from the Diamantina River and were assumed to have originated from upstream grazing and cropping practices. Similarly, the high turbidity was presumably sourced by floods naturally mobilising clays from the channels and flood-out areas in Queensland and was not obviously exacerbated by local land use practices.
A moderately diverse community of at least 16 species of macroinvertebrates was collected from the 35 m wide, non-flowing, arid-zone channel in spring 2012. The community was dominated by large numbers of waterbugs (Anisops) but included smaller numbers of 4 types of beetle (Enochrus, Sternopriscus multimaculatus, Eretes australis and Ochthebius), 4 waterbugs (Microvelia, Micronecta, Agraptocorixa and Enithares woodwardi), 2 mayflies (Cloeon and Wundacaenis), 2 chironomids (Tanytarsus and Paratanytarsus) and a freshwater prawn (Macrobrachium), dragonfly (Austrogomphus cornatus) and caddisfly (Triplectides). The total number of species is likely to be closer to 20 since yabby holes were recorded in the banks and numerous empty mussel shells were noted on the exposed streambed in places. The rich assemblage of tolerant, aerially dispersed insect groups such as beetles, waterbugs and chironomids were similar to those found in other waterholes in the region. The prawn was the only species recorded that is normally associated with stream environments. The only rarely collected macroinvertebrates recorded from the region were the caenid mayfly (Wundacaenis) and odonate (Austrogomphus). The baetid mayfly also represents a sensitive but widely distributed group that is typically found in the more permanent freshwater habitats in the northern parts of South Australia. No fish were caught or seen at the site when it was sampled in October 2012.
The water was fresh (salinity of about 143 mg/L), well oxygenated (81% saturated) and very turbid (secchi depth 3 cm), with high concentrations of nutrients such as nitrogen (2.7 mg/L) and phosphorus (0.79 mg/L).
The sediments were dominated by detritus and clay, with smaller amounts of silt, sand and cobble; samples taken from below the surface were grey clays and silts and showed no signs that the sediments were anaerobic, or lacking in oxygen. No evidence of erosion was recorded but horse faeces were deposited along the banks and edge of the river.
A moderate amount of phytoplankton was present (chlorophyll a 9.9 Âµg/L) and included some blue-green algae or cyanobacteria (chlorophyll b 1.3 Âµg/L). No filamentous alga was recorded when the site was assessed. Over 10% of the channel was covered by several types of emergent, native aquatic plants, including Water Primrose (Ludwigia peploides), sedge (Cyperus) and Water Buttons (Cotula). The riparian vegetation was dominated by coolabah gums and lignum over various weeds on the moderately vegetated banks (50-79% vegetative cover). The surrounding vegetation comprised scattered gum trees and lignum over weeds and grasses.
Special environmental features
Diamantina River at Birdsville provides habitat for a diverse range of aquatic macroinvertebrates and plants and probably also supports a wide range of native fish from the Diamantina catchment.
Pressures and management responses
|High nutrient concentrations causing excessive algal growth although the source(s) of all the nutrients is not known with certainty.||The EPA in collaboration with the Department for Environment, Water and Natural Resources is anticipating a study program to investigate the source(s) of nitrogen and phosphorus. This will provide a better understanding of nutrient dynamics with the aim of developing a management strategy (if appropriate).|
|Livestock have direct access at the site and upstream in the catchment exerting excessive grazing pressure on vegetation, causing sediment erosion.||The SA Arid Lands Natural Resources Management Board recognizes that both direct and diffuse impacts on aquatic ecosystem condition can occur through direct stock access and excessive grazing pressure from stock and feral herbivores. Technical advice and incentives are offered to land managers in the region, as funding permits, to address these impacts through appropriate activities suitable for the context. In addition, projects are underway across the region to identify, prioritise and address impacts at key aquatic sites.|
|Introduced weeds in the riparian zone.||The SA Arid Lands Natural Resources Management Board provides technical advice and incentives for the management of introduced weeds and feral pest animals, as funding permits. Pest management efforts are guided by a region-wide strategy, based on risk assessment, to determine priority locations and species. Funding is actively sought from a number of sources to support region-wide integrated management.|
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- Silcock, J. (2009). “Identification of Permanent Refuge Waterbodies in the Cooper Creek and Georgina-Diamantina River Catchments for Queensland and South Australia.” Final report to South Australia Arid Lands Natural Resource Management Board.