Scott Creek, Scott Bottom
2013 Aquatic Ecosystem Condition Report
- Permanent flowing stream in autumn and spring 2013
- Diverse macroinvertebrate community with many rare, sensitive and flow-dependent species present
- Water was fresh, clear and showing signs of nutrient enrichment
- Riparian vegetation consisted of woody weeds and introduced grasses
About the location
Scott Creek is a small stream in the Southern Mount Lofty Ranges that rises south from Heathfield and flows in a SSW direction, where it eventually discharges into the Onkaparinga River near the Mount Bold Reservoir. The monitoring site was located off Scott Creek Road, about 1 km south-west from Scott Creek at Scott Bottom. The major land uses in the 2,570 hectare catchment are remnant native vegetation (47%), residential living (29%) and grazing modified pastures (16%), with smaller areas used for roads, irrigated pasture and horticulture, and dams.
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 due to nutrient enrichment and the extent of weeds in the riparian zone but the stream provides habitat for a significant number of rare, sensitive and flow-dependent species.
A diverse community of at least 47 species of macroinvertebrates was collected from the creek (27 species in autumn and 32 in spring), 0.8-5.6 m wide and up to 81 cm deep, in autumn and spring 2013. The creek consisted of deep pools connected by smaller areas of shallow, fast-flowing riffle habitats in both seasons sampled. The community was dominated by moderate numbers of amphipods (Austrochiltonia australis) in the pools and blackflies in the riffles. It also included smaller numbers of turbellarians, nematodes, mites, introduced (Physa and Potamopyrgus) and native snails (Glyptophysa and Angrobia), amphipods, shrimps, springtails, beetles, dixid flies, mosquitoes, biting midges, chironomids, waterbugs, mayflies, stoneflies and caddisflies. A number of rare and sensitive species were collected, including an amphipod (Family Perthiidae), mayflies (Atalophlebia australasica, Atalophlebia australis and Thraulophlebia inconspicua), blackflies (Austrosimulium furiosum, Simulium melatum and Paracnephia sp.), stoneflies (Illiesoperla mayi and Dinotoperla evansi) and caddisflies (Lingora aurata and Taschorema evansi). A range of species normally associated with flowing water were also collected, including the above- listed mayflies, stoneflies, caddisflies and blackflies, and another widely distributed blackfly (Simulium ornatipes) recorded from riffles in spring. The collection of such a rich assemblage of blackflies was particularly notable because few streams in the region support more than two different species in this group of insects.
The water was fresh (salinity ranged from 700-824 mg/L), well oxygenated (90-101% saturation), clear, and with variable nutrient levels that included low to moderate phosphorus (0.02-0.03 mg/L) and moderate to high nitrogen (0.35-0.7 mg/L) concentrations.
The sediments were dominated by detritus, filamentous algae (autumn) and cobble (spring), with smaller amounts of sand and silt also present. Samples taken from below the surface were grey to black silts and clays that released sulphide when tested in spring, indicating that the sediments were enriched with organic matter, anaerobic and lacking in oxygen for at least part of the year. There was no sign of any significant areas of bank erosion and no evidence that stock had recently accessed the creek near the site sampled.
There were extensive growths of filamentous algae recorded in autumn, when 10-35% of the channel was covered in Spirogyra. However, no filamentous algae was seen in spring, possibly due to the increased shading provided by new growth of deciduous trees; shading ranged from 30% in autumn to 70% in spring. Negligible amounts of phytoplankton were recorded during 2013 (chlorophyll a < 1 μg/L). Over 10% of the creek was covered by a range of aquatic plants, including submerged charophytes and emergent macrophytes (Cyperus, Phragmites, Triglochin and introduced Rorippa). The riparian zone consisted of introduced woody weeds (Willows and Blackberries) over a number of weedy grasses. The surrounding vegetation near the creek comprised areas of open tall woodland, planted gums and cleared paddocks that were not currently being cropped or grazed.
Special environmental features
Scott Creek provides a permanently flowing, freshwater stream that consistently supports a diverse range of aquatic biota, including many rare, sensitive and flow-dependent species. The creek provides an important refuge habitat for many of these species and is among the most significant biodiversity hotspots in the region and State.
Pressures and management responses
|Widespread introduced weeds in the riparian zone at the site and upstream (reducing habitat quality).||The Adelaide and Mount Lofty Ranges NRM Board has several pest plant (weed) mitigation and control programs. They work closely with landholders to control weeds on their property and to help stop the spread to other properties and waterways.|
|Moderate nutrient inputs to the creek from numerous diffuse sources (leading to extensive growth of algae and aquatic weeds)||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes working with industry and landholders to ensure efficient use of fertilisers and discuss ways to reduce runoff of nutrients into waterways.|
This aquatic ecosystem condition report is based on monitoring data collected by the EPA. It was prepared with and co-funded by the Adelaide and Mount Lofty Ranges NRM Board.