Inverbrackie Creek, near Woodside
2008 Aquatic Ecosystem Condition Report
- Significantly affected by nutrient enrichment and fine sediment.
- Sparse macroinvertebrate community dominated by species tolerant of pollution.
- Streambanks extensively eroded by livestock and flood events.
- Limited riparian zone invaded by exotic plants and weeds.
About the location
Inverbrackie Creek 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. Livestock grazing (44%), dairying (24%) and horticulture (18%) are the main land uses in this small catchment, as well as some vineyards, urban living, forests and areas of remnant 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 Very Poor rating at this site because the ecosystem showed evidence of major changes to both the animal and plant life, and a significant breakdown in the way the ecosystem functions because of human impact. The stream had been severely affected by nutrient enrichment, and the riparian zone was significantly disrupted, with limited native vegetation.
A series of shallow, connected pools formed the creek at the time of inspection in spring 2008.
A sparse community of 18 macroinvertebrate species was collected. The community was dominated by moderate to large numbers of organic-feeding species such as tiny crustaceans called water scuds (Austrochiltonia australis), freshwater isopods (Heterias pusilla) and chironomids (Corynoneura and Paralimnophyes). The absence of insects such as mayflies, stoneflies, caddisflies and dragonflies highlighted the poor condition of the stream.
The water was moderately fresh (salinity of 1,600 mg/L), moderately well oxygenated (42% saturation) and clear. It contained high levels of nutrients such as nitrogen (0.8 mg/L) and phosphorus (0.11 mg/L).
The water was covered with aquatic plants such as the fern Pacific Azolla (Azolla filiculoides) and duckweed (Spirodela); large amounts of introduced Watercress (Rorippa nasturtium-aquaticum) grew along the edges.
The streambanks had been heavily eroded by livestock accessing the stream, and from occasional flooding.
Small patches of River Red Gums and exotic willow trees grew in the riparian zone, which had also been invaded by introduced grasses and woody weeds such as blackberries and gorse.
Cereal cropping and grazing occurred over the surrounding area, and there was little or no native vegetation remaining, apart from along the roadsides.
Special environmental features
Pressures and management responses
|Livestock have direct access at the site and upstream, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth 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 incentives for waterway and wetland fencing to exclude or limit stock from entering riparian zones.|
|Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||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.|
|Large decrease in natural water flows (reducing ecological integrity).||Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.|
|Extensive weed growth 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.|
|Large nutrient inputs from numerous diffuse sources in the catchment (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 and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.