Tributary of Scott Creek, SE from Cherry Gardens
2013 Aquatic Ecosystem Condition Report
- Permanently wet stream in autumn and spring 2013
- Moderately diverse macroinvertebrate community with a few sensitive and flow-dependent species present
- Water was fresh, clear and showing signs of nitrogen enrichment
- Riparian vegetation consisted of woody weeds and introduced grasses
About the location
Tributary of Scott Creek is a small second order stream in the Southern Mount Lofty Ranges that rises at an elevation of about 360 m and flows south for about 1.5 km before entering the main channel of Scott Creek. This creek then continues flowing in a southerly direction and eventually discharges into the Onkaparinga River a few kilometres downstream from Mount Bold Reservoir. The major land use in the 107 hectare catchment upstream from the site sampled was residential (77%), associated with Cherry Gardens, with minor areas also used for other minimal uses, roads and stock grazing. The site was located off a track to ‘Chellaston Park from Dorset Vale Road, about 1.5 km south-east from Cherry Gardens.
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 due to the extent of weeds in the riparian zone and nutrient enrichment but the stream still provides habitat for a few sensitive and flow-dependent macroinvertebrates.
A moderately diverse community of at least 21 species of macroinvertebrates was collected from the creek (9 species in autumn and 17 in spring), 0.9-5.5 m wide and up to 15 cm deep, in autumn and spring 2013. The creek consisted of a shallow flowing channel in both seasons sampled. The community was not dominated by any species but comprised low to moderate numbers of introduced and native snails, worms, mites, springtails, beetles, craneflies, mosquitoes, blackflies, chironomids, mayflies, stoneflies and caddisflies. Four sensitive species that commonly occur in flowing riffle habitats were recorded, including a blackfly (Austrosimulium furiosum), mayfly (Thraulophlebia inconspicua) and two stoneflies (Riekoperla naso and Austrocerca tasmanica). The other macroinvertebrates were generalist, opportunistic and tolerant species that have a widespread distribution, from both clean and polluted streams, in the region.
The water was fresh (salinity ranged from 494-655 mg/L), moderately well oxygenated (50-63% saturation), slightly acidic (pH 6.85-6.95), clear, and with low phosphorus (0.01 mg/L) but high nitrogen (0.61-0.65 mg/L) concentrations.
The sediments were dominated by detritus and silt. Samples taken from below the surface comprised leaves, iron bacterial growths and grey silt but showed no evidence to indicate that the sediments were anaerobic or lacking in oxygen (e.g. odours were unremarkable and no sulfide was released from the sediments when tested); despite this, the sediments probably turn anaerobic on occasion in response to the decomposition of the organically enriched detrital material and silt in the channel. There was no evidence of any bank erosion and no stock had recently accessed the creek near the site sampled.
There was only a small amount of phytoplankton present in the creek (chlorophyll a ranged from 0.1-0.5 μg/L) and no filamentous algae was seen at the site in 2013. Over 35% of the channel was covered by aquatic plants, including floating duckweed (Spirodela) and emergent species of sedges (Carex and Bolboschoenus), rushes (Juncus) and dock (Rumex). The narrow riparian zone was mostly less than 5 m wide in extent and consisted of introduced woody weeds (Willows and Blackberries) and native acacias over sedges, rushes and dock; these riparian plants provided between 70-80% shading to the creek. The surrounding vegetation near the creek comprised dense native woodland.
Special environmental features
Tributary of Scott Creek provides a permanently flowing, freshwater stream that supports a small number of sensitive and flow-dependent macroinvertebrates.
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.|
|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.|
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.