Naracoorte Creek, western edge of Naracoorte
2009 Aquatic Ecosystem Condition Report
- Permanently wet channel in autumn and spring 2009.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation consisting of introduced willows over reeds and weeds
- Some silt deposited 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 at the downstream extent of the township of Naracoorte on the Riddoch Highway.
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, poor riparian habitat and silt deposited in the channel.
A sparse community of about 17 species of macroinvertebrates was collected from the channel that ranged up to five metres wide and 30 centimetres deep, in autumn and spring 2009. The community was dominated by species tolerant to poor water quality such as an introduced snail (Physa), isotomid springtails, and culicid mosquito larvae. The only uncommon, regionally endemic species collected was a type of fly larva from the family Dolichopodidae. However, no sensitive or rare species were found. The only fish species recorded at the site were introduced carp.
The water was fresh (salinity ranged from 171–213 mg/L), poorly oxygenated (34–35% saturation) and clear, with high concentrations of nutrients such as nitrogen (0.35–2.62 mg/L) and phosphorus (0.21–0.61 mg/L).
The sediments were dominated by detritus, clay, silt, sand, algae and cobble; samples taken from below the surface were blackened and anaerobic, or lacking in oxygen. Over one centimetre of silt was deposited in the channel in places.
Over 36% of the channel and water's edge was covered by several emergent plants (Typha, Phragmites, Schoenoplectus, Juncus and Bolboschoenus). A large amount of phytoplankton was also recorded during both seasons that were sampled.
The 5–10 metre wide riparian zone consisted of introduced willow trees over weeds, grasses, reeds (Phragmites) and Cumbungi (Typha). The surrounding vegetation at the site was mostly urban gardens.
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.|