Timber Creek, d/s of Gauge
2013 Aquatic Ecosystem Condition Report
- Permanently flowing stream in autumn and spring 2013
- Sparse macroinvertebrate community with no rare, sensitive or flow-dependent species
- Water was saline, clear and high in nitrogen concentrations
- Riparian vegetation comprised native trees over weeds
About the location
Timber Creek is a moderately sized stream that drains the south-central part of Kangaroo Island. The creek rises over 4 km east from Parndana at an elevation of about 155 m and flows in a south-easterly direction for over 30 km before discharging into Murray Lagoon. The major land uses in the 12,732 hectare catchment upstream from the site sampled were grazing modified pasture (46%), cropping (28%) and other minimal uses (11%), with minor areas used for nature conservation, plantation forestry, roads, wetlands, irrigated perennial horticulture and dams. The site sampled was located in the lower catchment off the South Coast Road, about 20 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, the presence of introduced snails, and the dominance of weeds in the understorey of 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 9 in spring), 3.3-3.5 m wide and up to 35 cm deep, in autumn and spring 2013. The creek consisted of a still to slow-flowing channel in both seasons sampled. The community was dominated by moderate numbers of amphipods (Austrochiltonia) and chironomids (Procladius, Tanytarsus and Chironomus) and included smaller numbers of worms, introduced snails (Potamopyrgus), yabbies, beetles (Liodessus, Necterosoma, Platynectes, Lancetes and Limnoxenus), biting midges (Culicoides) and waterbugs (Anisops). All were tolerant generalists that are frequently found from other saline, nutrient enriched streams in South Australia. The site lacked any rare and sensitive species, and no flow-dependent species were recorded in 2013. Many groups and species of macroinvertebrates that commonly occur in other streams on the island and the wetter parts of the State were absent, including mites, shrimp, blackflies, mayflies, stoneflies, damselflies, dragonflies and caddisflies, and a wider range of chironomids and waterbugs.
The water was saline (salinity ranged from 6,022-7,577 mg/L), well oxygenated (80-92% saturation), clear but slightly coloured, and with low concentrations of phosphorus (0.02 mg/L) and high nitrogen concentrations (0.84-1.0 mg/L).
The sediments were dominated by detritus and sand, with smaller amounts of silt, clay, cobble and pebble also present; filamentous algae was present in spring. Samples taken from below the surface were black silts that tested positive for sulphide in autumn, indicating that the sediments were anaerobic and lacked oxygen. A 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 small amount of bank erosion extending over about 10% of the banks was recorded, which appeared to have been caused by past flood events and cattle accessing the creek. The only animal droppings seen in the vicinity of the creek were from cattle.
There was a small amount of phytoplankton recorded in autumn but a higher concentration was present in spring (chlorophyll a ranged from 1.2-11.1 μg/L). Filamentous algae was only seen in spring when it covered over 10% of the channel. No aquatic macrophytes were seen at the site during 2013. The narrow riparian zone was dominated by gums and wattles over introduced grasses and bridle-creeper. The surrounding vegetation near the creek comprised cleared cattle grazing land with a few scattered gums in the local landscape.
Special environmental features
Timber Creek provides a permanently wet, slow-flowing habitat on the southern end of the island and supports an aquatic community that is well adapted to live in saline, nutrient enriched streams.
Pressures and management responses
|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.|
|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.|
|Large nutrient and sediment inputs from diffuse sources in the catchment (leading to extensive growth of algae and aquatic weeds as well as increased turbidity and smothering of habitat).||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.|