Woolridge Creek, Murdarinna Waterhole
2012 Aquatic Ecosystem Condition Report
- Semi-permanent, non-flowing, waterhole when sampled in autumn 2012
- Moderately diverse macroinvertebrate community with one rare species collected
- Water was very fresh, turbid and enriched with nutrients
- Riparian vegetation consisted of native trees and shrubs and one species of aquatic plant was recorded
About the location
Woolridge Creek is a medium sized stream in the Far North of the State that rises 50 km east from Welbourn Hill and flows in an easterly direction before discharging into the lower reaches of Alberga River. This river then joins with Hamilton Creek to form the Macumba River, which eventually drains into the northern part of Lake Eyre North during exceptionally wet years. The major land use in the catchment is cattle grazing. The monitoring site was located on a track off the Oodnadatta Track, about 48 kilometres north-west from Oodnadatta.
The creek was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure, and some changes to the way the ecosystem functions. There was evidence of human disturbance including nutrient enrichment, fine sediment deposition and cattle faeces on the banks but the stream still provided habitat for a rare chironomid.
A sparse to moderately diverse community of at least 10 species of macroinvertebrates was collected from the isolated, 30 m wide and 50 m long, waterhole in autumn 2012. The community was dominated by moderate numbers of caddisflies (Triplectides australis) and waterbugs (Micronecta), and included smaller numbers of chironomids (Coelopynia, Ablabesmyia and Cryptochironomus), dytiscid beetles (Allodessus and Sternopriscus), waterbugs (Anisops stali), prawns (Macrobrachium) and flatworms (Turbellaria). Most were generalist and tolerant species, found commonly throughout the arid parts of South Australia. The chironomid Coelopynia was the only rare species collected that has a limited distribution in the Lake Eyre Basin. The only riverine species collected was the prawn which has typically been recorded from stream channel habitats in the Cooper and Diamantina catchments, River Murray and a few coastal streams from the wetter parts of the State. The lack of snails, yabbies, mayflies and the limited range of beetles and waterbugs collected indicates that the site is frequently wet but probably is not a permanent refuge habitat for aquatic species in all years. Large numbers of zooplankton were recorded from the site but comprised only ostracod species. Fish were seen jumping out of the water at the site but were not able to be caught and subsequently identified.
The water was fresh (salinity of 268 mg/L), saturated with oxygen (167% saturation), strongly coloured and turbid (secchi depth 22 cm), with high concentrations of nutrients such as nitrogen (2.7 mg/L) and phosphorus (0.24 mg/L).
The sediments were dominated by sand, with smaller amounts of silt, gravel, detritus, clay and algae also present; samples taken from below the surface were sulfidic grey sands that smelt of manure, indicating that the sediments were organically enriched and lacked oxygen. Over 1 cm of sand was deposited in the waterhole but no evidence of any significant bank erosion was present despite cattle faeces being recorded from the banks and along the edges of the waterhole.
A large amount of phytoplankton was present (chlorophyll a 82 Âµg/L) which included some blue-green algae or cyanobacteria (chlorophyll b 7.6 Âµg/L). Less than 10% of the shallow margins of the waterhole were covered by a type of filamentous alga (Cladophora), and a similar area was covered by a submerged aquatic plant (Myriophyllum). The riparian vegetation was dominated by sheoaks, coolibahs and black box trees on the poorly vegetated banks (<25% vegetative cover). The surrounding vegetation at the site comprised similar native floodplain species.
Special environmental features
The creek provides habitat for a moderate diversity of aquatic macroinvertebrates and at least one species of fish inhabits this stream on occasions.
Pressures and management responses
|Livestock have direct access at the site and upstream in the catchment exerting excessive grazing pressure on vegetation, causing sediment erosion and adding nutrients to the watercourse.||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.|