Riparian vegetation consisted of weedy shrubs over introduced grasses and weeds
Area map
About the location
Inverbrackie Creek is a moderately sized stream that rises to the north and east of Woodside in the southern Mount Lofty Ranges, and flows west into the Onkaparinga River, to the south of Woodside. Grazing modified pastures (53%) was the main land use in the 2,589 hectare catchment upstream from the site sampled, with smaller areas used for irrigated pastures and horticulture, cropping, roads, residential housing, plantation forestry, dams, irrigated cropping and native vegetation. The site selected for monitoring was located in the lower reaches of the stream, off the Woodside–Nairne Road, over one kilometre south of Woodside, upstream from the bridge.
The creek was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and moderate changes to the way the ecosystem functions. There was clear evidence of human disturbance at the site due to nutrient enrichment, the mobilisation of fine sediment and the extent of weeds in the riparian zone.
Findings
A moderately diverse community of at least 29 species of macroinvertebrates was collected or seen from the creek (17 species in autumn and 22 in spring), 1-8-3.4 m wide and up to 42 cm deep, in autumn and spring 2013. The creek consisted of mostly still to slow-flowing pool habitats connected by tiny areas of faster-flowing, shallower riffle habitats in both seasons sampled. The community was dominated by moderate numbers of amphipods (Austrochiltonia australis), native (Glyptophysa concinna) and introduced snails (Potamopyrgus antipodarum and Physa acuta), and springtails (Family Hypogastruridae). If also included smaller numbers of turbellarians, worms, shrimp, yabbies, beetles, biting midges, chironomids, mosquitoes, waterbugs, damselflies and caddisflies. The riffles also supported blackfly larvae (probably Simulium ornatipes) that were seen clinging to rocks in spring. All macroinvertebrates collected were tolerant and generalist species that are well adapted to tolerate and thrive in organically polluted streams, and each has a wide distribution throughout the agricultural area of South Australia. No rare or sensitive species were recorded and the blackfly was the only flow-dependent species seen at the site. The only fish seen at the site was a threatened species called Mountain Galaxias (Galaxias olidus) in spring.
The water was moderately fresh (salinity ranged from 1,233-1,463 mg/L), well oxygenated (76-152% saturation), clear but slightly coloured, and with generally high concentrations of nutrients such as phosphorus (0.03-0.05 mg/L) and nitrogen (0.78-1.03 mg/L).
The sediments were dominated by detritus and silt, with smaller amounts of boulder, cobble, bedrock, pebble, filamentous algae, gravel, sand and clay also present; samples taken from below the surface were black silts that had a strong manure or anaerobic odour, and released sulphide when tested during each sampling period, indicating that the sediments lacked oxygen and were a harsh environment for most burrowing species to survive in. Over 10 cm of fine silt covered the bottom of the channel and a considerable amount of bank erosion (over 50%) occurred at the site, which appeared to have been caused by cattle accessing and trampling the banks and channel in autumn; stock appeared to have been excluded from accessing the stream in spring.
A large amount of phytoplankton was present in spring (chlorophyll a ranged from 1.6-10.7 μg/L) and filamentous algae (Cladophora and Spirogyra) was prominent because it covered over 10% of the channel in both seasons. A larger area (over 35%) of the creek was also covered by a range of aquatic plants, which included floating (Spirodella and Azolla), submerged (Callitriche) and emergent macrophytes (Typha, Cotula, Juncus, Eleocharis, Isolepis and introduced Rorippa and Rumex); the extent of algal and plant growths at the site support the nutrient enriched status of this creek. The riparian zone generally lacked any trees and consisted of weedy understorey shrubs (Gorse and Blackberries) over introduced grasses and herbaceous weeds. The surrounding vegetation near the creek comprised cropping and grazed paddocks with a few scattered gums.
Special environmental features
The only significant environmental values of the creek were the presence of a threatened native fish and a flow-dependent blackfly in spring; presumably these species moved into the catchment in response to high flows during the wetter, winter or early spring months of the year.
Pressures and management responses
Pressures
Management responses
Livestock having direct access at the site and upstream (causing sediment erosion and adding excessive nutrients).
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 waterway and wetland fencing to exclude or limit stock from entering riparian zones.
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.
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.
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.