Nilpena Creek, Nilpena
2012 Aquatic Ecosystem Condition Report
- Permanent stream comprising pools connected by smaller flowing riffle habitats in autumn and spring 2012
- Moderately diverse macroinvertebrate community with a few sensitive and flow-dependent species present
- Water was saline, clear and low in nutrients but showing evidence of enrichment due to the extent of algal growth in spring
- Riparian vegetation consisted of a few native trees and shrubs over saltbush
About the location
Nilpena Creek rises as Deadman and Breakfast Time creeks near the Red Range in the Northern Flinders Ranges and they flow in a south-westerly direction where they merge at Nilpena, and the creek then flows westwards and eventually disappears underground on the plains on the eastern side of Lake Torrens. The major land use in the 80,185 hectare catchment, upstream from the site sampled, is grazing natural vegetation (99%) with minor areas also used for transport and communications, nature conservation, residential living and mining. The monitoring site was located off the road to Nilpena from Leigh Creek Road, about 20 km north-west from Parachilna.
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 bank erosion but the stream still provided habitat for a wide range of saline tolerant aquatic macroinvertebrates and two aquatic plants
A moderately diverse community of at least 29 species of macroinvertebrates was collected from the creek, 0.5-5.4 m wide and up to 51 cm deep, in autumn and spring 2012. The creek consisted of a series of shallow pools connected by small areas of flowing riffles in autumn but was more extensive in spring when larger pools were connected by substantial riffle habitats. The community was dominated by large numbers of biting midges (Bezzia, Culicoides and Nilobezzia) and chironomids (Procladius, Cricotopus, Tanytarsus and Chironomus) in autumn and moderate numbers of blackflies (Simulium ornatipes) in spring. It also included smaller numbers of yabbies (Cherax), beetles (Hyphydrus, Antiporus andSternopriscus maedfooti), mosquitoes (Anopheles and Culex), soldierflies, chironomids (Larsia and Polypedilum), baetid mayflies (Cloeon), waterbugs (Agraptocorixa, Micronecta and Anisops), dragonflies (Hemianax, Orthetrum and Hemicordulia) and caddisflies (Hydroptila, Cheumatopsyche, Ecnomus, Oecetis and Triplectides australis). The only sensitive macroinvertebrate collected was the mayfly, although it is widely distributed from permanent freshwater habitats in the region and is among the most tolerant mayflies found in South Australia; its occurrence in Nilpena Creek is probably around its upper salinity tolerance range (Corbin & Goonan 2010). The site also supported two flow-dependent species (blackfly S. ornatipes and caddisfly Cheumatopsyche sp.2) in both seasons sampled, although none of the rare and more sensitive species associated with flowing habitats were collected. The community was dominated by saline tolerant insects and the only non-insect collected were a few yabbies, which are capable of surviving prolonged drying by sheltering deep in their burrows.
The water was saline (salinity ranged from 4,652-5,556 mg/L), well oxygenated (127-139% saturation), clear, and with low concentrations of nutrients such as phosphorus (0.01-0.03 mg/L) and nitrogen (0.12-0.45 mg/L).
The sediments were dominated by sand and filamentous algae in the pools and pebble, cobble and sand in the riffles; samples taken from below the surface were well-aerated grey sands in autumn but in spring the sediments were mostly slightly blackened and sulphidic sands, indicating that they were anaerobic, or lacking in oxygen. Over 1 cm of silt covered the streambed in spring, which would have contributed to the poor condition of the underlying sediments. About 10 m of bank showed evidence of erosion caused by flood damage and cattle accessing the creek; cattle and kangaroo droppings were seen on the banks during the spring survey.
A small amount of phytoplankton was present (chlorophyll a 0.3-0.5 Âµg/L) but large growths of filamentous algae (Cladophora, Spirogyra and Enteromorpha) were recorded during the year, particularly in spring when over 35% of the site was covered by algae; the large amount of algae was probably responsible for the low concentrations of nutrients recorded from the water samples, due to regular uptake by the algal species throughout the year. More than 10% of the creek was also covered by two types of aquatic plants, including cumbungi (Typha) and club-rush (Schoenoplectus) growing in the channel, which would have also helped remove nutrients from the water column. The riparian vegetation was dominated by a few acacias and gums over saltbush on poorly vegetated banks (<25% vegetative cover). The surrounding vegetation at the site comprised a few scattered gums and acacias among grazed saltbush country.
Special environmental features
Nilpena Creek drains a large section of the eastern run-off from the Northern Flinders Ranges and maintains habitat for a number of saline tolerant generalists and flow-dependent macroinvertebrates. The site also supports patches of club-rush which has a limited distribution in the region. The presence of the mayfly Cloeon in this stream may be towards the extreme salinity tolerance for the genus because it normally occurs in waters with much lower salinity.
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 excessive 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.|