Hamilton Creek, Ethawarra Waterhole
2012 Aquatic Ecosystem Condition Report
- Permanently wet, non-flowing, waterhole when sampled in autumn 2012
- Moderately diverse macroinvertebrate community with one sensitive but commonly found mayfly collected
- Water was very fresh, slightly turbid and enriched with nutrients
- Riparian vegetation consisted of native trees and shrubs but no aquatic plants were recorded from the edges of the waterhole
About the location
Hamilton Creek is a large arid zone stream in the Far North of the State that rises in the southern part of the Northern Territory near Umbeara, flows for over 300 km south-east into South Australia where it joins with Stevenson Creek and then joins with the Alberga River to form the Macumba River. This river then joins with Warburton Creek and discharges 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 to the north of Pedirka Desert off the Hamilton Station Track, about 45 km west from Hamilton and 60 km north-east from Lambina
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 possibly due in part to cattle occasionally accessing the banks but the stream provides an important refuge habitat for a range of aquatic macroinvertebrates.
A moderately diverse community of at least 15 species of macroinvertebrates was collected from the isolated waterhole, 80 m wide and over 1 m deep, in autumn 2012. The community was dominated by large numbers of mites (Limnesia), chironomids (Procladius, Ablabesmyia and Dicrotendipes) and waterbugs (Micronecta gracilis), and included smaller numbers of snails (Glyptophysa concinna), limpets (Ferrissia), baetid mayflies (Cloeon), dragonflies (Hemicordulia tau and Aeshidae), beetles (Hyphydrus and Necterosoma dispar), mosquitoes (Anopheles) and two types of caddisflies (Triplectides australis and Ecnomus). Most are generalist and tolerant species, found commonly throughout the arid parts of South Australia. The mite, however, has been rarely collected from the region in the past. The mayfly was the only sensitive macroinvertebrate collected that is often found in large numbers from among the freshest streams in the region. The presence of the mite, snail and limpet were notable because they lack strategies to cope with extended periods of drying, indicating that the waterhole probably provides a permanent refuge habitat in the creek. No fish were caught or seen at the site.
The water was fresh (salinity of 70 mg/L), well oxygenated (87% saturation) and slightly turbid, with moderate to high concentrations of nutrients such as nitrogen (1.25 mg/L) and phosphorus (0.05 mg/L).
The sediments were dominated by detritus, clay and algae, with smaller amounts of sand and silt also present; samples taken from below the surface were red sands and showed no signs that the sediments were anaerobic, or lacking in oxygen. No evidence of any significant bank erosion was noted but cattle faeces were noted on the edges of the waterhole.
A moderate amount of phytoplankton was present (chlorophyll a 3.9 Âµg/L) and over 10% of the shallow margins of the channel were covered by a type of filamentous alga (Spirogyra). No aquatic plants were recorded growing in or around the waterhole. The riparian vegetation was dominated by gum trees and acacias over native grasses on the well vegetated banks (>80% vegetative cover). The surrounding vegetation at the site comprised gum trees over acacias and other species of native shrubs.
Special environmental features
The waterhole was sampled in March 2012 as part of the Lake Eyre Basin Rivers Assessment when nearly 400 fish from three commonly occurring native species were collected, including Desert Rainbowfish, Spangled Perch and Bony Bream (Cockayne et al. 2013). This supports the view that the site is a significant refuge for aquatic life in the region.
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.|