Scott Creek, Scott Bottom
2016 Aquatic Ecosystem Condition Report
Permanent flowing stream in autumn and spring 2016
Diverse macroinvertebrate community with many rare, sensitive and flow-dependent species present
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 Scotts 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 53 species of macroinvertebrates was collected from the creek (35 species in autumn and 35 in spring), 5.5 m wide and more than 1 m deep, in autumn and spring 2016. The creek consisted of deep pools connected by smaller areas of shallow, fast-flowing riffle habitats in both sampling seasons. The community was dominated by large numbers of amphipods (Austrochiltonia australis), blackflies and leptophlebiid mayflies. It also included smaller numbers of turbellarians, introduced snails (Physiella and Potamopyrgus), springtails, beetles, biting midges, chironomids, waterbugs, stoneflies and caddisflies. A number of rare and sensitive species were collected, including an amphipod (Family Perthiidae), mayflies (Atalophlebia australasica and Thraulophlebia inconspicua), blackflies (Austrosimulium furiosum and Simulium melatum), stoneflies (Illiesoperla mayi and Dinotoperla evansi) and caddisflies (Triplectides similis 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). Yabby holes were also seen along the wet banks of the stream.
The water was fresh (salinity ranged from 360-600 mg/L), well oxygenated (66-80% saturation), slightly turbid and slightly coloured, and with variable nutrient levels that included low to high phosphorus (0.02-0.12 mg/L) and high nitrogen (0.36-1 mg/L) concentrations. Froth was also present at the site in autumn.
The sediments were dominated by detritus, with smaller amounts of sand, silt and clay present in the pools and cobbles and pebbles in the riffle sections. Some filamentous algae was noticed in the riffles in spring. Samples taken from below the surface were grey silts and clays that released sulfide, indicating that the sediments were enriched with organic matter, anaerobic and lacking in oxygen. There was some sign of bank erosion (<10 m) due to high flows down the channel in the past but no evidence of stock accessing and damaging the creek.
Filamentous algae (Cladophora) covered 10-35% of the channel in spring. However, no algae was seen in autumn. Small amounts of phytoplankton were recorded during 2016 (chlorophyll a ranged from 0.46-2.45 μg/L). Over 10% of the creek was covered by a range of aquatic plants, including Cyperus, Isolepis, Juncus and Ranunculus. The riparian zone consisted of willows and blackberry bushes over weedy grasses. The surrounding vegetation near the creek comprised areas of dense woodland, with a weedy understorey.
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 State.
Pressures and management responses
Widespread introduced weeds in the riparian zone at the site and upstream
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.
Limited riparian zone vegetation at the creek and upstream (reducing habitat quality, increasing sediment erosion)
The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes incentives for revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion. The Board also partner with local government to deliver a number of watercourse revegetation projects across the region.
Nutrient inputs to the creek from numerous diffuse sources (potentially leading to excess growth of algae and aquatic weeds)
The Adelaide and Mount Lofty Ranges NRM Board 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.