Mosquito Creek, east from Joanna near the SA/Victorian border
2009 Aquatic Ecosystem Condition Report
- Dry in autumn and shallow, isolated pools in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation limited to a few gum trees over introduced grasses.
- Moderately eroded banks due to stock damage.
About the location
The Mosquito Creek is a large stream in the lower South East that rises east of Edenhope in south-western Victoria as two major branches, with the smaller northern branch called Yelloch Creek and the larger southern branch Mosquito Creek. Both flow in a westerly direction and join into the one channel about nine kilometres north-east of Struan. The main channel of Mosquito Creek has a large catchment that extends over 500 km2. The major land uses are grazing and cropping.
The monitoring site was located on Vincents Road, about nine kilometres upstream from the junction with Yelloch Creek and 22 kilometres south-east 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, bank erosion and a lack of vegetative cover in the riparian zone.
A sparse community of about 18 species of macroinvertebrates was collected from isolated pools, 5–6 metres wide and up to 25 centimetres deep, in spring 2009; the creek was dry in autumn. The community was dominated by generalists and species tolerant to poor water quality such as worms, chironomids and mosquito larvae. The site included an introduced snail (Physa) as well as a nuisance species of fish (Gambusia). No rare, sensitive or specialist species were recorded.
The water was moderately fresh (salinity of 1,030 mg/L), poorly oxygenated (25% saturation) and turbid, with high concentrations of nutrients such as nitrogen (4.49 mg/L) and phosphorus (0.99 mg/L).
The sediments were dominated by detritus, sand and silt, with smaller amounts of clay and gravel also present; samples taken from below the surface were blackened, sulfidic and anaerobic, or lacking in oxygen. Silt deposits over one centimetre thick were recorded in the channel and between 10–50 metres of the banks showed signs of erosion due to stock damage.
More than 10% of the channel was covered by several types of emergent aquatic plants (Bolboschoenus, Juncus, Triglochin and Typha). A moderate amount of phytoplankton was also recorded in 2009, which contributed to the cloudiness of water in the creek.
The narrow riparian zone consisted of a few gum trees over introduced grasses and included large areas of bare soil. The surrounding vegetation at the site was crop land.
Special environmental features
Pressures and management responses
|Drought||Through ground and surface water allocation planning and the South East Regional NRM Plan water affecting activity permit process the NRM Board seeks to manage water for environmental, social and economic purposes in a range of climatic scenarios.|
|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.|