Turvey’s Drain, near Milang
2010 Aquatic Ecosystem Condition Report
- Permanently wet drain in autumn and spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation limited to introduced grasses.
- Moderately eroded banks and large silt deposit in the channel.
About the location
Turvey’s Drain is a very small, 500-metre long drain in the southern Mount Lofty Ranges that discharges water from a small catchment to the east of Milang into Lake Alexandrina. The major land use is cattle grazing.
The monitoring site was located off Lake Road, over three kilometres east of Milang.
The drain 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, heavy sedimentation and a degraded riparian zone.
A sparse community of about 21 species of macroinvertebrates was collected from the drain, up to seven metres wide and 70 centimetres deep, in autumn and spring 2010. The community was dominated by species tolerant to poor water quality such as chironomids (including Dicrotendipes, Chironomus, Tanytarsus and Polypedilum), amphipods (Austrochiltonia australis) and corixid waterbugs (Micronecta). It also included an introduced hydrobiid snail (Potamopyrgus), dytiscid beetles, mosquitoes, biting midges, corixid and notonectid waterbugs, odonates and leptocerid caddisflies. No sensitive or rare species were found. The only fish recorded was the introduced mosquitofish (Gambusia).
The water was moderately fresh to saline (salinity of 3,056 mg/L in autumn and 2,638 mg/L in spring), moderately well oxygenated (42–58% saturation), turbid and strongly coloured, with high concentrations of nutrients such as nitrogen (1.52–2.38 mg/L) and phosphorus (0.1–0.19 mg/L).
The sediments were dominated by detritus, silt, clay and algae; samples taken from below the surface were black, sulfidic and anaerobic, indicating that too much organic matter had entered the drain in the past. Large deposits of silt, over 10 centimetres thick, were recorded from the channel in places. Over 10 metres of bank showed signs of erosion due to cattle damage.
A large amount of phytoplankton was recorded in autumn and less than 10% of the site was covered by filamentous algae (Spirogyra and Cladophora). Over 65% of the channel was covered by a range of emergent aquatic plants (e.g. Typha, Phragmites, Cotula, Juncus and Myriophyllum).
The riparian zone consisted of introduced grasses and reeds, and lacked any trees. The surrounding vegetation was grazing land.
Special environmental features
None detected in 2010, however, recent fish surveys of the drain in 2004–09 have collected two threatened species (Southern Pygmy Perch and Murray Hardyhead) and several other common native species (M. Hammer, Aquasave Consultants, 2009). A threatened frog called the Southern Bell-frog has also been collected from the drain in recent years (M. Hammer, personal communication).
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.|