Naracoorte Creek, Naracoorte
2014 Aquatic Ecosystem Condition Report
- Permanently wet channel with isolated pools in autumn and spring 2014
- Moderately diverse macroinvertebrate community with no rare or sensitive species
- Obvious signs of gross nutrient enrichment
- Riparian vegetation comprised scattered gums over reeds and weeds
- 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 square kilometres. The creek rises as two branches in western Victoria to the south of Bringalbert, and they join 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 downstream from the caravan park and railway line off Park Terrace, in the middle of the township of Naracoorte.
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 fine sediment deposition.
A moderately diverse community of at least 24 species of macroinvertebrates (13 in autumn and 16 in spring) was collected from the isolated pools, up to 8.8 metres wide and 52 centimetres deep, during autumn and spring 2014. The community was dominated by moderate numbers of biting midges (Bezzia) in autumn and by waterbugs (Anisops) in spring. It also included lower numbers of flatworms, introduced snails (Physiella), water mites (Eylais), yabbies, springtails, beetles, waterbugs, mayflies (Tasmanocoenis tillyardi), chironomids, damselflies and caddisflies. All were common, widely distributed, generalist and tolerant species capable of surviving in poor quality water; no sensitive, rare or habitat specialists were found at the site sampled in 2014. The only fish seen inhabiting the creek was an introduced pest called mosquitofish (Gambusia).
The water was fresh to moderately fresh (salinity ranged from 713-1,361 mg/L), poor to moderately well oxygenated (27-53% saturation), clear and slightly coloured, and with high concentrations of nutrients such as nitrogen (1.76-3.82 mg/L) and phosphorus (0.05-0.15 mg/L).
The sediments were dominated by detritus, sand and silt, with a small amount of cobble and gravel also present; samples taken from below the surface were slightly blackened rocks and grey sands that released sulfide when tested in spring, indicating that the sediments were occasionally anaerobic or lacking in oxygen. Large deposits of silt and detritus over 10 centimetres deep were recorded from the middle of the channel. No significant areas of bank erosion or signs of stock accessing the stream were noted during either site visit in 2014.
The creek supported a large phytoplankton bloom, particularly in autumn (chlorophyll a ranged from 5-60 Âµg/L) but no growths of filamentous algae were seen at the site. Over 10% of the channel was covered by emergent aquatic plants such as reeds (Phragmites) and cumbungi (Typha).
The narrow (<5 metres wide) riparian zone consisted of a few scattered gums over reeds, dock and weeds. The surrounding vegetation at the site comprised urban parkland with planted grasses and other vegetation located in the middle of the town.
Special environmental features
None recorded. The creek has provided habitat for a commonly occurring native fish called the Flathead Gudgeon (Philypnodon grandiceps) in the past but only mosquitofish (Gambusia) were collected from the lower section of this creek in 2014.
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.|