Shallow, non-flowing stream in autumn and spring 2016
Few macroinvertebrates were recorded and no rare, sensitive or flow-dependent species were present
Water was saline, slightly coloured and highly enriched with nutrients
Riparian vegetation consisted of a few scattered gums over introduced grasses and weeds
Area map
About the location
Walkers Creek is a moderately sized stream in the Southern Mount Lofty Ranges that rises near Belvidere in the Nain Range and flows in a south-westerly direction, before discharging into the North Para River near Rosedale. The monitoring site was located near Dee Road, about 4.5 km south-east from Freeling. The major land uses in the 6,574 hectare catchment upstream from the site were cereal cropping (75%) and grazing modified pastures (14%), with smaller areas of roads, other minimal uses, residential living, irrigated horticulture, mining, manufacturing and industry also present.
The creek was given a Very Poor rating because the site sampled showed evidence of major changes to both the animal and plant life inhabiting the stream, and a significant breakdown in the way the ecosystem functions. There was considerable evidence of human disturbance due to high salinity, nutrient enrichment and degraded riparian and buffer zones associated with this creek. The only aquatic life recorded were a few of the most saline tolerant and generalist species of aquatic macroinvertebrates that frequently occur together in organically enriched streams.
Findings
A very sparse community of only 14 species of macroinvertebrates was collected or seen from the creek (8 species in autumn and 11 in spring), 3.5 m wide and up to 22 cm deep, in autumn and spring 2016. The creek consisted of a connected, non-flowing channel in both sampling seasons. The community was dominated by large numbers of chironomids with low to moderate numbers of beetles, mosquitoes, brineflies, water boatmen and backswimmers also present. All were tolerant species capable of surviving in saline, nutrient enriched waters. No rare, sensitive or flow-dependent species were recorded and the site lacked many freshwater macroinvertebrates commonly found in the region, including mites, amphipods, yabbies, mayflies, stoneflies, caddisflies, damselflies, dragonflies and a richer assemblage of beetles and chironomids.
The water was saline (salinity ranged from 3,996-7,002 mg/L), well oxygenated (83-180% saturation), slightly coloured, and with very high concentrations of nutrients such as phosphorus (0.27-3.42 mg/L) and nitrogen (1.56-3.76 mg/L). Froth was also present at the site in autumn.
The sediments consisted of silt, clay, detritus and algae. Samples taken from below the surface were grey silts and clays that had a strong anaerobic odour and released sulfide when tested in spring, indicating that the sediments lacked oxygen and were a harsh environment for most burrowing species to survive in. There was a small amount of bank erosion present, covering less than 10% of the site, which appeared to have been caused by recent high flows, or stock accessing the site in previous years.
There was a moderate amount of phytoplankton present at the site (chlorophyll a ranged from 9.3-16.4 μg/L) and filamentous algae (Cladophora and Enteromorpha) extended over more than 10% of the channel in spring. A similar area of the creek was covered by aquatic plants (Bolboschoenus and Juncus articulatus). The narrow riparian zone comprised of a few scattered gum trees over introduced grasses and thistles. The surrounding vegetation consisted of cropping lands, with only a few scattered gums in the general landscape.
Special environmental features
None identified.
Pressures and management responses
Pressures
Management responses
Saline groundwater inflows to the creek
The Adelaide and Mount Lofty Ranges NRM Board has installed telemetered groundwater monitoring stations at key locations within the region. These are monitored for level and salinity; unusual results (such as high salinity influxes) are investigated.
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.
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 (e.g., stream and creek) and wetland fencing to exclude or limit stock from entering riparian zones.
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.