Naracoorte Creek, west from Naracoorte
2009 Aquatic Ecosystem Condition Report
- Isolated pools present in autumn and creek dry in spring.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation limited to introduced grasses, native rushes and lignum shrubs.
- Moderately eroded banks with silt deposits in the channel.
About the location
Naracoorte Creek is a large stream in the lower South East that has a catchment area over 750 km2. The creek rises as two branches in western Victoria to the south of Bringalbert that eventually join together to form the one channel about two kilometres west of Kybybolite in South Australia. The creek then flows in a westerly direction through Naracoorte and a series of ephemeral lakes, including Lake Ormerod, before discharging into the upper part of Drain E. The major land uses are grazing and cropping.
The monitoring site was located about 1.5 km downstream from the township of Naracoorte on Treatment Works Road, upstream from the treatment plant.
The drain 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, poor riparian habitat and bank erosion.
Macroinvertebrates were not collected from the isolated pools present in autumn 2009 because they were very fresh and thought to be rainwater puddles rather than part of a flowing stream habitat; the stream subsequently dried and no samples were taken in spring either.
One of the isolated pools was sampled and assessed as fresh (salinity of 156 mg/L), well oxygenated (76% saturation) and clear, with high concentrations of nutrients such as nitrogen (0.5 mg/L) and phosphorus (0.19 mg/L). These nutrient values were, however, generally much higher than would be expected from rainwater pools and it is likely that they were in fact remnants of more extensive in-stream pools that were drying out.
The sediments were dominated by detritus and fine sediments; samples taken from below the surface were blackened and anaerobic, or lacking in oxygen, in places. There was also some build-up of silt within the channel and between 10–50% of the banks showed evidence of erosion due to stock damage.
A few submerged (Chara) and emergent (Eleocharis and Juncus) plants were growing in the channel and on the water’s edge.
The narrow riparian zone consisted of introduced grasses with some patches of rushes and lignum bushes. The surrounding vegetation at the site was grazing land with little remnant native cover remaining in the landscape.
Special environmental features
Pressures and management responses
|Livestock have direct access at the site and upstream, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds)||The South East NRM Board supports targeted projects that provide opportunities for landholders to access grants for fencing for stock exclusion from time to time for priority catchments.|
|Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality)||The South East NRM Board assists landholders to access targeted grant opportunities for revegetation and ecosystem protection when funding is available. The Board also works closely with landholders consistent with the Board’s Regional Pest Management Plan to control weeds on their property and to assist in halting their spread to other properties.|