Millalee Creek, near Peake Bay
2010 Aquatic Ecosystem Condition Report
- Permanent slow-flowing saline creek with riffle habitat present in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation consisted of introduced grasses and samphire.
- Moderately eroded banks and silt deposited in the channel.
About the location
Millalee Creek is a small stream in Eyre Peninsula that rises south of Pillaworta Hill and flows south-east before discharging into an intermittent swamp to the north of Peake Bay. The major land use is cropping, with minor areas of native vegetation near the sampled site.
The monitoring site was located off the Lincoln Highway, about 12 kilometres south-west of Tumby Bay.
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 considerable evidence of human disturbance, including nutrient enrichment, bank erosion, fine sediment deposition and a lack of vegetative cover in the riparian zone.
A sparse community of about 21 species of macroinvertebrates was collected from this slow-flowing stream, four metres wide and 10 centimetres deep, in autumn and spring 2010. Riffle habitat was only present in spring. The community was dominated by species tolerant to high salinity and poor water quality such as amphipods (Austrochiltonia australis), chironomids (includes Procladius, Tanytarsus and Chironomus) and dytiscid beetles (Necterosoma penicillatus). It also included smaller numbers of springtails, mosquitoes, soldierflies, several other beetles (including Hydrophilidae and Hydraenidae), notonectid waterbugs, lestid damselflies and leptocerid caddisflies. No sensitive or rare species were found and the only flow-dependent species collected was a single dytiscid beetle (Platynectes decempunctatus) from the riffle habitat.
The water was saline (salinity of 10,190 mg/L in autumn and 9,833 mg/L in spring), well oxygenated (69–133% saturation) and clear, with moderate and high concentrations of nutrients such as nitrogen (1.03–1.13 mg/L) and phosphorus (0.02–0.02 mg/L).
The sediments were dominated by pebbles, gravel, cobbles and sand in the faster flowingriffles and detritus, silt, clay, algae and sand in the still and slow-flowing habitats. Samples taken from below the surface were well aerated in autumn but sulphidic and slightly anaerobic in spring, presumably in response to the decomposition of organic matter in the sediments with increasing temperature. A deposit of 1-5 centimetres of silt covered the creekbed and more than 10 metres of the bank showed signs of erosion due to past flood damage.
Filamentous algae (Cladophora and Enteromorpha) covered more than 35% of the site in autumn but only a 10% cover was noted in spring when greater flows occurred in the stream. The only aquatic plants recorded growing in the water and on the water’s edge were the Sea Tassel (Ruppia) and rush (Juncus); they covered more than 10% of the site.
The narrow riparian zone consisted of introduced grasses, samphire and rushes. The surrounding vegetation at the site included patches of mallee scrub and saltbush among cropping land.
Special environmental features
The only notable feature of Millalee Creek was the presence of one flow-dependent species from the riffle habitat in spring.
Pressures and management responses
|Livestock have direct access at the site and upstream in the catchment, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds).||The Eyre Peninsula NRM Board promotes managing land to improve water quality. This includes incentives for revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion.|
|Saline groundwater inflow (reducing ecological integrity).||The Eyre Peninsula NRM Board promotes the revegetation of recharge areas known to contribute to dryland salinity and encourages the adoption of perennial pastures as an alternative to annual cropping in these areas.|
|Insufficient natural water flows (reducing ecological integrity).||The Eyre Peninsula NRM Board's water resources program regulates the diversion of water from priority catchments on Eyre Peninsula.|