First Creek, off Tunkalilla Road
2016 Aquatic Ecosystem Condition Report
Permanently wet freshwater stream that flowed in autumn but comprised a non-flowing channel in spring
Diverse macroinvertebrate community with several rare, sensitive and flow-dependent species recorded
Water was fresh, clear and enriched with nutrients
Riparian vegetation consisted of native vegetation over bracken, sedges and weeds
About the location
First Creek is a small stream in the Southern Mount Lofty Ranges that rises near ‘Tunkalilla’ and flows southwards, where it discharges onto Tunkalilla Beach in the Southern Ocean. The creek is located about 2 km east from Deep Creek Conservation Park on the Fleurieu Peninsula. The monitoring site was located in the mid-reaches off Tunkalilla Road, about 1.9 km from the junction with Erik Road, and was accessed by walking approximately 600 m to the stream. The major land uses in the 186 hectare catchment are stock grazing (87%), remnant native vegetation (17%) and roads (8%).
The creek was given a Fair rating because the site sampled showed evidence of relatively moderate changes in ecosystem structure and function. There was evidence of human disturbance due to the presence of high nutrient concentrations and weeds in the riparian zone. The stream provides habitat for a few rare, sensitive and flow-dependent species of macroinvertebrates and many generalist and tolerant species.
A moderately diverse community of at least 43 species of macroinvertebrates was collected from the creek (37 species in autumn and 20 in spring), 1.1-1.5 m wide and up to 25 cm deep, in autumn and spring 2016. The creek consisted of equal areas of slow-flowing pools and faster-flowing riffles in autumn but only a non-flowing channel was present in spring. The community was dominated by amphipods and chironomids, with blackflies abundant in riffles in autumn. Low numbers of snails, worms, springtails, beetles, craneflies, dixids, biting midges, soldierflies, mayflies, waterbugs, damselflies, dragonflies, stoneflies and caddisflies were also collected. Several rare, sensitive and/or flow-dependent species were recorded, including blackflies (Austrosimulium furiosum and Simulium ornatipes), a chironomid (Rheotanytarsus), leptophlebiid mayflies (Atalophlebia australasica and Atalophlebia australis), a stonefly (Austrocerca tasmanica) and caddisflies (Oxyethira columba and Taschorema evansi). The only fish seen at the site was a juvenile galaxiid that was collected in the riffle sample in autumn.
The water was fresh (salinity ranged from 256-382 mg/L), well oxygenated (53-76% saturation), clear but slightly coloured, and with high concentrations of nutrients such as phosphorus (0.08-0.11 mg/L) and nitrogen (1.32-1.5 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 sulfide when tested, indicating that the sediments were well oxygenated. No evidence of any significant bank erosion was noted but cattle, sheep and kangaroos droppings were seen in the channel and on the banks, particularly in autumn.
A moderate to large amount of phytoplankton was recorded during the year (chlorophyll a ranged from 2.11-12.8 μg/L) but no filamentous algae was recorded from the site. A dense cover of aquatic plants extended over more than 90% of the channel in spring, comprising floating duckweed (Spirodella), various submerged and emergent herbaceous species (Callitriche, Crassula, Cotula, Hydrocotyle, Ranunculus and Triglochin), knotweed (Persicaria), sedges (Isolepis and Carex), rushes (Juncus), cumbungi (Typha), and weedy watercress (Rorippa). The riparian zone merged with the surrounding vegetation and consisted of native vegetation that was dominated by gums and a few wattles over correas, yaccas, bracken and ferns.
Special environmental features
The site sampled indicated that the creek provides a significant habitat for a wide range of rare, sensitive, flow-dependent, generalist and tolerant macroinvertebrates, a rich aquatic plant assemblage and at least one species of native fish.
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.