Inverbrackie Creek, near Woodside
2016 Aquatic Ecosystem Condition Report
Permanent flowing stream in autumn and spring 2016
Sparse macroinvertebrate community lacking any rare or sensitive species
Water was moderately fresh, turbid and slightly coloured, and enriched with nutrients
Riparian vegetation consisted of weedy shrubs over introduced grasses
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.
Adelaide and Mount Lofty Ranges NRM Regional Summary 2016
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.
A sparse community of at least 21 species of macroinvertebrates was collected or seen from the creek (13 species in autumn and 15 in spring), 3.5 m wide and up to 50 cm deep, in autumn and spring 2016. 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 large numbers of mites, amphipods (Austrochiltonia australis) and water boatmen. Smaller numbers of native and introduced snails, shrimp, beetles, chironomids, mosquitoes, waterbugs, and dragonflies were also found. No flow-dependent species were seen in the small riffles that were present at the site. 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 areas of South Australia. No rare or sensitive species were recorded. Yabby holes were seen along the wet banks of the stream.
The water was moderately fresh (salinity ranged from 510-1,460 mg/L), well oxygenated (66-116% saturation), turbid and slightly coloured, and with moderately high concentrations of nutrients such as phosphorus (0.04-0.08 mg/L) and nitrogen (0.63-0.76 mg/L). Froth was also present at the site in autumn.
The sediments were dominated by detritus and silt, with smaller amounts of boulder, bedrock, cobble, pebble, filamentous algae, sand and clay also present; samples taken from below the surface were black clays and silts that were anaerobic, and released sulfide 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 silt covered the bottom of the channel and a considerable amount of bank erosion (up to 50%) occurred at the site, which appeared to have been caused by cattle accessing and trampling the banks and channel.
A large amount of phytoplankton was present in spring (chlorophyll a ranged from 1.27-6.58 g/L). Filamentous algae (Cladophora) covered over 10% of the channel in both seasons. The same area of the creek was also covered by a range of aquatic plants, which included floating (Azolla), submerged (Callitriche and Crassula) and emergent macrophytes (Typha, Persicaria, Juncus, Phragmites, Mimulus, Isolepis and the introduced Rorippa and Rumex). The riparian zone generally lacked any trees and consisted mainly of weedy shrubs and introduced grasses. The surrounding vegetation comprised grazing paddocks.
Special environmental features
No significant environmental values of the creek were apparently in 2016, however this site has provided habitat for a threatened native fish in previous years.
Pressures and management responses
|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 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.|
|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. The Board also partner with local government to deliver a number of watercourse revegetation projects across the region.|
|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.|
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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.