Angas River, near Strathalbyn
2010 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, freshwater stream in autumn and spring.
- Highly diverse macroinvertebrate community with many rare and sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation was mostly introduced grasses and weeds.
About the location
Angas River is a large stream in the southern Mount Lofty Ranges that rises northwest of Macclesfield and flows in a southerly direction through Strathalbyn before discharging into Lake Alexandrina. The major land uses are cattle grazing and cropping, with minor areas of orchards. The monitoring site was located on a track off Paris Creek Road, about three kilometres northwest of Strathalbyn.
The river was given a Fair rating because the site sampled showed moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance, including nutrient enrichment, poor riparian habitat and fine sediment deposition.
A highly diverse community of about 41 species of macroinvertebrates was collected from the flowing river, up to 3-6 metres wide and 45 cm deep, in autumn and spring 2010. The river was largely a slow-flowing stream with small areas of riffles present in autumn but included much larger areas of fast-flowing riffles in spring.
The community was dominated by species tolerant to poor water quality such as blackfly larvae, amphipods and chironomids. It also included flatworms, snails (including the introduced Physa), worms, mites, freshwater shrimp, springtails, beetles, mosquitoes, biting midges, soldierflies, mayflies, waterbugs, odonates, stoneflies and caddisflies. The species collected included several rare and sensitive species such as a mayfly (Koorrnonga inconspicua), stoneflies (Dinotoperla evansi and Illiesoperla mayi) and a caddisfly (Ulmerochorema membrum). The community included several uncommonly collected species for the region (eg chironomids Larsia and Eukiefferiella and blackflies Austrosimulium furiosum and Simulium melatum) and a range of flow-dependent species (eg blackfly larvae, dytiscid beetle Platynectes decempunctatus, caddisfly Cheumatopsyche AV2). The riffle habitat in spring, in particular, supported many of the flow specialists and the rare, sensitive and uncommon species.
The water was moderately fresh (salinity of 1,025 mg/L in autumn and 1,396 mg/L in spring), well oxygenated (63-72% saturation) and clear, with low concentrations of nutrients such as nitrogen (0.21-0.49 mg/L) and phosphorus (0.01-0.02 mg/L).
The sediments were dominated by boulders, cobbles, pebbles, algae and silt in the riffle habitat and cobbles, pebbles, sand, silt and detritus in the non-flowing areas. Samples taken from below the surface were blackened and sulphidic in spring, indicating that too much organic matter had entered in the river in the past. A deposit of 1-5 cm of silt covered the riverbed in the slower-flowing sections and a small area of bank erosion (<10% of the site) caused by water damage was recorded in both seasons sampled in 2010.
Filamentous algae (Spirogyra) covered more than 35% of the site in spring whereas over 35% of the channel was covered by aquatic plants in autumn. The emergent plants included sedges (Cyperus), cumbungi (Typha) and dock (Rumex). The riparian zone consisted of gum trees and acacias with a groundcover of thistles, introduced grasses, weeds and sedges. The surrounding vegetation at the site was mostly organic vegetable gardens.
Special environmental features
Angas River provides habitat for diverse community of macroinvertebrates that include several rare, sensitive and flow specialist species. The river also supports a wide range of threatened fish species, including Mountain Galaxias, River Blackfish and Southern Pygmy Perch (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.|