Timber Creek, SE Parndana
2013 Aquatic Ecosystem Condition Report
- Permanently flowing stream in autumn and spring 2013
- Sparse macroinvertebrate community that provides habitat for two flow-dependent species in spring
- Water was saline, clear and high in nitrogen concentrations
- Riparian vegetation comprised native trees over sedges, rushes and weeds
About the location
Timber Creek is a moderately sized stream on the south-central part of Kangaroo Island. It rises in the middle of the island about 5 km east from Parndana and flows in a south-easterly direction for over 30 km before discharging into Murray Lagoon in Cape Gantheaume Conservation Park. The major land uses in the 5,396 hectares catchment upstream from the site sampled included grazing modified pastures (66%), cropping (11%) and other minimal uses (11%), with smaller areas also used for nature conservation, transport and communication, plantation forestry, irrigated cropping, dams and residential living. The site was located in the upper catchment off Timber Creek Road, about 11 km south-east from Parndana.
The creek was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and moderate changes to the way the ecosystem functions. There was evidence of human disturbance due to nitrogen enrichment, high salinity and weeds in the riparian zone.
A sparse community of at least 14 species of macroinvertebrates was collected or seen from the creek (7 species in autumn and 11 in spring), 2.6-2.7 m wide and up to 25 cm deep, in autumn and spring 2013. The creek consisted of a still to slow-flowing channel in both seasons sampled; small areas of faster-flowing riffle habitat were also present during the spring survey. The community was dominated by moderate numbers of amphipods (Austrochiltonia), and included smaller numbers of worms, beetles (Ochthebius and Scirtidae), mosquitoes (Anopheles), biting midges, chironomids (Cladotanytarsus, Tanytarsus and Paramerina) and caddisflies (Notalina spira). Yabby holes were also seen in the banks of the creek and the riffles provided habitat for blackfly larvae and dytiscid beetles (Platynectes larvae and Sternopriscus). The community mostly comprised tolerant, generalist macroinvertebrates that are frequently found from other saline, nutrient enriched streams in South Australia. The site lacked any rare and sensitive species, and the only flow-dependent species recorded were the blackfly larvae and dytiscid beetle (Platynectes). Many groups and species of macroinvertebrates that commonly occur in other streams on the island and the wetter parts of the State were absent from this site, including mites, shrimp, mayflies, stoneflies, waterbugs, damselflies and dragonflies, and a wider range of beetles and caddisflies; the high salinity throughout the catchment is likely to prevent many of these types of macroinvertebrates from inhabiting this stream.
The water was saline (salinity ranged from 5,186-6,741 mg/L), well oxygenated (61-87% saturation), clear and slightly coloured, and with low concentrations of phosphorus (0.01-0.02 mg/L) but high nitrogen concentrations (0.72-0.85 mg/L); the high amount of oxidised nitrogen (0.17 mg/L) recorded in autumn indicates that groundwater inflow probably occurs near the site.
The sediments were dominated by detritus with smaller amounts of silt, sand and clay also present. Samples taken from below the surface were anaerobic grey sands and clays that released sulphide when tested in spring; these observations indicate that the sediments lacked oxygen and were probably a harsh environment for many burrowing species to be able to inhabit. A small deposit of over 1 cm of fine silt was present on the bottom of the channel, which made the water highly turbid when disturbed. A moderate amount of bank erosion extended over more than 10% of the banks, which appeared to have been caused by past flood events. No animal droppings were seen in the vicinity of the creek during either sampling period.
There was a small to moderate amount of phytoplankton recorded (chlorophyll a 1.6-3 μg/L) but no filamentous algae was seen at the site during 2013. About 10% of the edges of the creek were covered by two emergent aquatic plants (Juncus and Carex). The riparian zone extended over 5 m wide on each bank and was dominated by gums and patches of wattles and paperbarks over sedges, rushes, yakka’s and various weeds. The surrounding vegetation near the creek comprised dense woodland with a largely native understorey.
Special environmental features
Timber Creek provides a permanently wet habitat on the southern end of the island and supports an aquatic community that is well adapted to live in saline, nutrient enriched streams. The most notable feature of the aquatic biota present in 2013 was the colonisation of riffle habitats by two commonly occurring salt-tolerant, flow-dependent species.
Pressures and management responses
|Saline groundwater inflows to the creek (reducing ecological integrity).||This information is not available at the moment but it will be updated as soon as possible.|
|Widespread introduced weeds in the riparian zone at the site and upstream (reducing habitat quality).||This information is not available at the moment but it will be updated as soon as possible.|
|Moderate to large nutrient inputs from diffuse sources in the catchment (leading to algal growth).||The Kangaroo Island NRM Board has funded the fencing of significant areas of riparian vegetation in the catchment and continues to work with landowners to increase the fencing of watercourses.|