Giles Creek, near Finniss
2010 Aquatic Ecosystem Condition Report
- Permanently wet, slow-flowing, freshwater creek in autumn and spring.
- Moderately diverse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation mostly consisting of River Red Gums, reeds and introduced grasses.
- Moderately eroded banks due to cattle damage.
About the location
Giles Creek is a small stream in the southern Mount Lofty Ranges that rises to the northeast of Ashbourne and flows in a southerly direction where it eventually discharges into the Finniss River. The major land uses are cattle grazing and cropping. The monitoring site was located on Signal Flat Road, about three kilometres northwest of Finniss.
The creek 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, bank erosion and fine sediment deposition.
A moderately diverse community of about 35 species of macroinvertebrates was collected from the slow-flowing creek, 2–5 metres wide and up to 23 cm deep, in autumn and spring 2010. The community was dominated by generalists and species tolerant to poor water quality such as amphipods (Austrochiltonia australis) and chironomids (eg Chironomus, Dicrotendipes and Cricotopus). It also included smaller numbers of mites, yabbies, springtails, beetles, dixid fly larvae, mosquitoes, biting midges, soldierflies, mayflies (Cloeon and Tasmanocoenis), waterbugs, odonates and caddisflies.
No sensitive or rare species were found and the only flow-dependent species collected was a dytiscid beetle (Platynectes decempunctatus). The only fish collected was the introduced mosquitofish (Gambusia).
The water was moderately fresh (salinity of 1,270 mg/L in autumn and 1,600 mg/L in spring), well oxygenated (70–94% saturation), slightly turbid and coloured, with moderate to high concentrations of nutrients such as nitrogen (0.65-0.76 mg/L) and phosphorus (0.02 mg/L).
The sediments were dominated by detritus, algae, clay and silt, with some bedrock and boulders also present; samples taken from below the surface showed no indications that the sediment was lacking in oxygen. A deposit of 1-5 centimetres of silt covered the creekbed and more than 10 metres of the bank showed signs of erosion due to cattle accessing and trampling the banks.
Filamentous algae (Cladophora) covered more than 10% of the site in spring and over 35% of the channel was covered by a range of emergent aquatic plants (Isolepis, Juncus, Mimulus, Typha, Phragmites, Cotula, Cyperus and Callitriche). The riparian zone consisted of introduced grasses, reeds and rushes under a canopy of River Red Gums. The surrounding vegetation at the site was cropping and grazing lands with a few scattered gums.
Special environmental features
None detected, although previous fish surveys in the catchment have collected a threatened fish called Mountain Galaxias from a site further downstream in 2004 (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.