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, fine sediment deposition, 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 9 species of macroinvertebrates was collected or seen from the creek (2 species in autumn and 8 in spring), 2.4-2.8 m wide and up to 34 cm deep, in autumn and spring 2013. The creek consisted of isolated shallow pools in both seasons sampled. The community was not dominated by any species but comprised low numbers of worms, beetles (including Necterosoma penicillatus), biting midges (Culicoides), soldierflies, brineflies, chironomids (Procladius and Tanytarsus) and damselflies (Austrolestes). All were tolerant species capable of surviving in highly 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, waterbugs, caddisflies, dragonflies and a richer assemblage of beetles and chironomids.
The water was very saline (salinity ranged from 15,298-28,464 mg/L), well oxygenated (67-114% saturation), clear but slightly coloured, and with very high concentrations of nutrients such as phosphorus (0.21-0.38 mg/L) and nitrogen (3.06--8.13 mg/L).
The sediments were dominated by detritus, silt, and clay with a smaller amounts of boulder, sand and algae also present on occasion; samples taken from below the surface were black silts that had a strong anaerobic odour and released sulphide when tested, indicating that the sediments lacked oxygen and were a harsh environment for most burrowing species to survive in. There was a moderate amount of bank erosion present, covering over 10% of the site, which appeared to have been caused by sheep occasionally accessing the edges of the stream.
There was a large amount of phytoplankton present in spring (chlorophyll a ranged from 1.4-87 μg/L) at a time when a filamentous alga (Spirogyra) extended over more than 10% of the channel. Similarly, small patches of sedge (Bolboschoenus) were noted in autumn and much larger growths, covering over 35% of the creek, were recorded during the active growing season in spring. The narrow riparian zone comprised of a few scattered gum trees over introduced grasses and areas of bare soil. The surrounding vegetation near the creek consisted of cleared sheep grazing and cereal cropping lands, with only a few scattered gums in the general landscape.
Special environmental features
None identified.
Pressures and management responses
Pressures
Management responses
Large 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’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.
Saline groundwater inflows to the creek (reducing ecological integrity).
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.
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.