Currency Creek, Goolwa North
2011 Aquatic Ecosystem Condition Report
- Nutrient enriched and salinity higher than expected for a freshwater stream.
- Sparse macroinvertebrate community consisting of generalists and species tolerant to moderate salinity levels.
- Large amount of phytoplankton algae and dense stands of emergent aquatic plants.
- Removing the regulating bank will re-instate the connection to the lower lakes and improve the ecology and water quality of the creek .
About the location
Currency Creek rises in the southern Mount Lofty Ranges about seven kilometres south of Mount Compass. It flows southeast through land predominantly used for livestock grazing (70%) and irrigated cropping (20%) to the Lower Murray, just north of Goolwa North. The catchment also includes small areas of wine grapes, horticulture and remnant native vegetation in the Scott Conservation Park.
The site selected for monitoring was located in the lowest reach of the creek off Fiddock Road on the outskirts of Goolwa North, a few hundred metres upstream from the low-level regulating bank installed in September 2009 to keep acid sulfate soils saturated in the lower Currency Creek.
The site was given a Poor rating because the ecosystem showed evidence of major changes in the animal community and plant life, and moderate changes to the way the ecosystem functions.
In the 2010 report for this site, it was noted that the creek had undergone a catastrophic change from a freshwater to a saline environment, as a result of drought and prolonged low water levels in Lake Alexandrina in the late 2000s. Salinity levels were around 7,000 mg/L which was too high for most freshwater species to persist. Evidence also suggested there was increasing likelihood the effects of nutrient enrichment (eg nuisance algal growths) would become more apparent over time as a result of the limited opportunity to flush the system out, due to the placement of the bank and lack of flows in the Currency Creek catchment.
The results for 2011 show some reduction in salinity but significant ecological improvement does not appear to have occurred so far.
The creek was sampled from the well vegetated edges of the 800-metre wide channel. A sparse community of about 16 macroinvertebrate species was collected from among the reeds and other aquatic plants along the edge of the stream. The community was dominated by moderate numbers of amphipod crustaceans called water scuds (Families Eusiridae and Chiltoniidae) and included low numbers of nematodes, syllid polychaete worms, isopod crustaceans, eight species of chironomids, water striders, damselflies and caddisflies. They represent a range of generalist species that are able to tolerate moderately fresh to brackish salinity levels and typically occur in well vegetated habitats. The community included several species found a year earlier but it lacked any characteristic freshwater species, and no rare or sensitive species were recorded.
The water was moderately fresh to saline (salinity of 2,825 mg/L), well oxygenated (81% saturation) and alkaline (pH 7.56). It was also turbid and strongly coloured, and contained moderate to high concentrations of nutrients such as nitrogen (1.57 mg/L) and phosphorus (0.07 mg/L).
The sediments were characterised by detritus and silt; below the surface they were blackened, sulphidic and anaerobic, which means that the sediments were a harsh place for burrowing species to be able to tolerate.
Large stands of Common Reed (Phragmites australis) and Cumbungi (Typha) lined the edge of the stream and extended into the water. Large growths of what appeared to be dead Sago Pondweed (Stuckenia pectinata) were also noted at the site sampled. A large bloom of small, free-floating algae called phytoplankton was present and probably contributed to the turbid appearance of the water.
The riparian vegetation was dominated by Common Reed and Cumbungi growing over introduced kikuyu grass and patches of wattles, lignum, saltbush and thistles. Low samphire and other salt-tolerant shrubs grew over the surrounding area, where there were also rural dwellings with associated garden plantings.
Special environmental features
The site sampled lies within the Coorong and Lakes Alexandrina and Albert Wetland which is listed as a Ramsar Wetland of international importance due to the wide range of wetland habitats present, its importance for waders and waterfowl, and the presence of many nationally threatened species. In 2010, Currency Creek provided habitat to at least three common species of native fish (Australian Smelt, hardyheads and Blue-spot Gobies), however, only introduced mosquitofish were collected in 2011. Consequently, no special features were noted at the site sampled.
Pressures and management responses
|The extended drought conditions prior to 2010 caused severe salinity related impacts. The salinity has decreased but it has not returned to its normal level, despite freshwater inflows (reducing ecological integrity).||The SA Government is negotiating through the Basin Planning process to secure water to achieve water quality and ecosystem health objectives for the region. South Australia has determined the environmental water requirements for the CLLMM site, this report can be obtained from the Goyder Institute. For further information follow the link to the DENR website on environmental water requirements.|
|Livestock have direct access to many creeks in the catchment, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds).|
|Limited riparian vegetation throughout the catchment, which means there is minimal buffer protection from agricultural runoff carrying sediments and nutrients (causing habitat disturbance and algal growth).|