Finniss River, near Clayton
2011 Aquatic Ecosystem Condition Report
- Prolonged drought in the mid to late 2000s and high salinity degraded the lower reaches of the river.
- Recent flooding and freshening inflows in late 2010 to early 2011 have not yet resulted in significant environmental improvements.
- Sparse macroinvertebrate community consisting of low numbers of a few generalist species.
- Nutrient enriched with excessive growths of algae and aquatic plants.
- Condition expected to improve if water levels and salinity in Lake Alexandrina return to pre-drought levels and if normal average flow patterns returns to the Finniss River.
About the location
The Finniss River rises about 30 km southeast of Adelaide near Meadows in the southern Mount Lofty Ranges. Meadows, Blackfellows, Bull, Tookayerta and Nangkita creeks all flow into the river, which ultimately drains into the Lower Murray about five kilometres west of Clayton. Livestock grazing and dairying are the main land uses in the catchment, with smaller areas of vines, plantation forestry, olives and urban development.
The site selected for monitoring was located in the lower reaches off Glengrove Road, about eight kilometres northwest of Clayton.
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.
Salinity levels remain slightly higher than many freshwater animal and plant species normally tolerate and will probably continue to prevent the colonisation by a wider range of species unless concentrations drop down to the 500–1000 mg/L range for the majority of the time. The site also continues to show several lines of evidence that the lower Finniss River is significantly nutrient enriched.
Given the extent of disturbance caused by the prolonged drought in the region during the 2000s, it will probably take several months to years for a wider suite of freshwater species to recolonise the lower reaches of the Finniss River. This will require a return to pre-drought water levels in a freshwater Lake Alexandrina and regular, near average flows down the Finniss River for the most downstream section of this stream to again provide a significant refuge area for freshwater plants and animals as it did in the lead up to the drought.
A sparse community of about 13 macroinvertebrate species was collected from the slow-flowing channel in February 2011. The community was dominated by low numbers of worms and included a few colonial cnidarians, oribatid mites, two types of amphipods crustaceans, freshwater shrimp, two beetles, four chironomids and a waterbug. The site lacked many groups that would be expected to occur in the available habitats, including snails, bivalves, a range of other flies and waterbugs, mayflies, odonates and caddisflies.
There were also no rare or sensitive species and no habitat specialists collected. Consequently, the community comprised tolerant and generalist species and included many of the same species recorded a year earlier when the salinity was about 4,500 mg/L. This shows that the lower Finniss River has not significantly improved in biological condition despite the recent freshening that occurred in late 2010–early 2011. Presumably it will take many months to years for a wider range of animals and plants to recolonise this section of the river.
The water was moderately fresh (salinity of about 1,340 mg/L), well oxygenated (74% saturation), alkaline (pH 7.8), strongly coloured and turbid, and contained high concentrations of nutrients such as nitrogen (2.34 mg/L) and phosphorus (0.3 mg/L).
The edges of the water were densely vegetated with Common Reed (Phragmites australis) and clubrush (Schoenoplectus litoralis), and included a few patches of Water Ribbons (Triglochin procerum). A large bloom of small, free-floating algae called phytoplankton was present and probably contributed to the turbid appearance of water in the channel. A green filamentous alga (Cladophora) was also quite extensive because it covered nearly 10% of the channel.
The riparian vegetation was dominated by Common Reed growing over introduced grasses and thistles, with patches of Lignum (Muehlenbeckia cunninghamii), rushes (Juncus) and samphire.
The surrounding area was covered mostly with low acacia woodland growing over introduced grasses.
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. 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).|