Callawonga Creek, north of Taylors Road
2016 Aquatic Ecosystem Condition Report
Permanently fresh, flowing stream in autumn and spring 2016
Moderately diverse macroinvertebrate community with a number of rare, sensitive and flow-dependent species recorded
Water was fresh, clear and enriched with nutrients
Riparian vegetation consisted of native species and several aquatic plants grew in the creek
About the location
Callawonga Creek is a small stream in the Southern Mount Lofty Ranges that rises at an elevation of about 330 m near Parawa and flows southwards, before eventually discharging into the Southern Ocean at Callawonga Beach. The major land uses in the 1,264 hectare catchment upstream from the site were stock grazing (66%) and native vegetation (23%), with smaller areas used for plantation forestry, cropping, roads, dams and rural housing. The site was located just north from Taylors Road in the mid reaches of the catchment, about 19 km west from Encounter Bay on the southern Fleurieu Peninsula.
The creek was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was evidence of human disturbance due to the presence of elevated nutrient concentrations but the general lack of extensive plant and algal growths indicated the site was only showing the early signs of enrichment. The creek provided suitable habitat for a moderate number of rare, sensitive, flow-dependent, generalist and tolerant species of macroinvertebrates in 2016.
A moderately diverse community of at least 24 species of macroinvertebrates was collected from the creek (8 species in autumn and 21 in spring), 1.6-2 m wide and up to 41 cm deep, in autumn and spring 2016. The creek consisted of areas of fast-flowing and still pools in both seasons sampled but shallow riffle habitats were not present. The community was not numerically dominated by any species but included low to moderate numbers of mostly generalist and tolerant species of flatworms, snails, mites, amphipods, beetles, dixids, mosquitoes, blackflies, chironomids, mayflies, waterbugs, dragonflies and caddisflies. Several rare and sensitive species were also collected, including a blackfly (Austrosimulium furiosum), mayflies (Tasmanophlebia, Atalophlebia australasica and Thraulophlebia inconspicua) and caddisflies (Taschorema evansi and Triplectides similis).
The water was fresh (salinity ranged from 145-193 mg/L), well oxygenated (68-77% saturation), clear but strongly coloured in spring, and with generally high concentrations of nutrients such as phosphorus (0.04-0.09 mg/L) and nitrogen (1.11-3.01 mg/L).
The sediments were dominated by detritus, silt and sand; samples taken from below the surface were mostly grey clay and silt that did not release any sulfide when tested, indicating that the sediments were well oxygenated. There was no evidence of any significant bank erosion and the only animal droppings seen in the vicinity of the creek were from kangaroos. Over 10 cm of silt covered the streambed in spring, indicating that winter rains deposited large amounts of fine sediment, sourced from further upstream, throughout the centre of the channel.
Only a small amount of phytoplankton was recorded during the year (chlorophyll a ranged from 0.68-1.37 μg/L) but no filamentous algae was seen in 2016. Over 10% of the channel was covered by aquatic plants, including sedges (Baumea, Carex and Eleocharis), rushes (Juncus) and water ribbons (Triglochin). The narrow riparian zone comprised mostly bracken, rushes, sedges and a few gum trees. The surrounding vegetation was dense native eucalypt woodland.
Special environmental features
The creek provided flowing habitat in both seasons sampled and supported a regionally rare mayfly (Tasmanophlebia) and several other sensitive and flow-dependent macroinvertebrates.
Pressures and management responses
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.
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.