Finniss River, near Mount Observation
2010 Aquatic Ecosystem Condition Report
- Permanently wet freshwater river with isolated pools in autumn and flowing channel and riffle habitats present in spring.
- Highly diverse macroinvertebrate community with many rare and sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation includes native species and woody weeds and grasses.
About the location
Finniss River is a large stream in the southern Mount Lofty Ranges that rises east of Yundi and flows in an easterly direction where it eventually discharges into the Lower Murray, north-east of Goolwa. It receives flow from Meadows, Blackfellows and Bull creeks in the upper reaches and Tookayerta Creek in the lower reach, several kilometres south of Finniss. The major land uses are cattle grazing with minor areas of rural residential living and native vegetation. The monitoring site was located on Braeside Road, over two kilometres west of Mount Observation.
The river was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was evidence of human disturbance, including nutrient enrichment and a weedy riparian zone but the river provides habitat for many rare and sensitive species of macroinvertebrates and fish.
A diverse community of about 40 species of macroinvertebrates was collected from the river, up to five metres wide and 70 cm deep, in autumn and spring 2010. The river consisted of isolated pools in autumn and a slow-flowing channel with fast-flowing riffle habitats in spring. The pools and slow-flowing channel were dominated by large numbers of amphipods, chironomids and leptophlebiid mayflies whereas the riffles were dominated by thousands of blackfly larvae.
The community also included smaller numbers of freshwater limpets, snails (including the introduced Physa), leeches, worms, mites, beetles (including Macrogyrus and Aulonogyrus), and fly larvae from the family Dixidae, biting midges, baetid mayflies, waterbugs, dragonflies, stoneflies and caddisflies.
The general composition of the community consisted of generalist species that are tolerant of poor water quality such as amphipods, snails and waterbugs, and a range of sensitive and rare species that are normally found in flowing freshwater streams with good water quality and habitats, such as chironomids (Thienemanniella, Parametriocnemus, Eukiefferiella, Riethia, Rheotanytarsus and Cryptochironomus), a mayfly (Koorrnonga inconspicua), stonefly (Riekoperla naso) and caddisfly (Taschorema evansi).
Several species were recorded from the site that are normally associated with flowing habitats, including two species of blackflies (Austrosimulium furiosum and Simulium ornatipes), a dytiscid beetle (Platynectes decempunctatus), chironomid (Rheotanytarsus) and two caddisflies (Cheumatopsyche AV2 and Taschorema evansi). The site also provided habitat for two threatened native fish, the Climbing Galaxias (Galaxias brevipinnis) and Mountain Galaxias (Galaxias olidus).
The water was fresh to moderately fresh (salinity of 871 mg/L in autumn and 1,522 mg/L in spring), poorly oxygenated (26% saturation) in autumn but well oxygenated (89 % saturation) in spring, clear and slightly coloured, with moderate to high concentrations of nutrients such as nitrogen (1.16–1.25 mg/L) and phosphorus (0.04–0.14 mg/L).
The sediments were dominated by boulders, cobbles and pebbles in the riffle habitat and detritus, cobbles, sand and boulders in the still to slow-flowing channel. A deposit of 1–5 cm covered the riverbed in autumn and samples taken from below the surface were blackened and sulphidic, indicating that too much organic matter had entered the river in the past. Subsequent sampling in spring indicated much smaller silt deposits were present and the sediments were well aerated, presumably as a result of the high flows that passed down the river during winter and early spring.
Moderate amounts of phytoplankton were recorded from the river and over 10% of the channel was covered with green filamentous algae in spring (Spirogyra). More than 35% of the site was covered in aquatic plants, including both floating (Spirodela) and emergent species (Typha, Juncus, Phragmites, Cyperus, Isolepis, Rumex and Triglochin). The riparian zone consisted of gum trees, acacias, introduced deciduous trees such as elms over an understorey of rushes, reeds and weedy grasses. The surrounding vegetation at the site was grazed grassland.
Special environmental features
Finniss River provides habitat for a diverse macroinvertebrate community that includes many tolerant and sensitive species. The more notable species recorded from the site in 2010 included a mayfly (Koorrnonga inconspicua), stonefly (Riekoperla naso) and caddisfly (Taschorema evansi) and several uncommonly collected chironomids. The river also supports at least two threatened species of native fish (Mountain Galaxias and Climbing Galaxias).
Recent fish surveys in the catchment have also recorded another three threatened species from the main channel of the river, namely the Southern Pygmy Perch, Murray Hardyhead and Congolli (M Hammer, Aquasave Consultants, 2009).
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 SA Murray–Darling Basin NRM Board acknowledges the significant impacts that livestock have on aquatic environments and seeks to provide free technical advice and incentives to land managers for fencing and other works as funding permits. Funding incentives are limited in value and extent and require land managers to volunteer to be involved.|
|Limited riparian vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||The SA Murray–Darling Basin NRM Board recognises that the management of riparian vegetation requires a long-term, integrated approach to achieve ecosystem benefits. The board therefore provides free technical advice on a range of topics for land managers and various incentives for works as funding permits.|
|Insufficient natural water flows resulting from water extraction and climate variability (reducing ecological integrity.||The SA Murray–Darling Basin NRM Board is working with the Department for Water and the community to develop a water allocation plan and licensing system which aim to balance social, economic and environmental needs for water. The objective for providing water to the environment is to maintain and/or restore self-sustaining water-dependent ecosystems which are resilient in times of drought.|
|Widespread introduced trees and weeds in the riparian zone at the site and upstream in the catchment (reducing habitat quality).||The SA Murray–Darling Basin NRM Board recognises the limitations of available funds relative to the scale of the degradation caused by introduced trees and weeds. The NRM Board provides free technical advice and community education to assist land managers in dealing with the integrated management of aquatic weeds. The NRM Board also has a targeted process, as directed by State Government, to strictly prioritise its investment in weed control activities as funds are limited. The NRM Board actively seeks funding opportunities for weed control; most opportunities are for locations where biodiversity outcomes can be achieved.|