Currency Creek, near Mosquito Hill
2010 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, freshwater stream in autumn and spring.
- Moderately diverse macroinvertebrate community with at least two sensitive species.
- Obvious signs of moderate to gross nutrient enrichment.
- Riparian vegetation mostly introduced grasses with a few gum trees.
- Extensively eroded banks due to cattle damage.
About the location
Currency Creek is a moderately large stream in the southern Mount Lofty Ranges that rises west of Mosquito Hill and flows east where it ultimately discharges to the Lower Murray, north of Goolwa. The major land use is cattle grazing. The monitoring site was located on Mosquito Hill Road, about two kilometres southwest of Mosquito Hill.
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, poor riparian habitat, bank erosion caused by stock damage and fine sediment deposition in the channel.
A moderately diverse community of about 34 species of macroinvertebrates was collected from the creek, three metres wide and 60 centimetres deep, in autumn and spring 2010. The stream was slow-flowing in autumn but included areas of fast-flowing channel in spring. The community was dominated by species tolerant to poor water quality such as amphipods (Austrochiltonia australis) and blackfly larvae. It also included flatworms, snails (including the introduced Physa and Potamopyrgus), worms, mites, freshwater shrimp, springtails, beetles, mosquitoes, biting midges, chironomids, mayflies, waterbugs, dragonflies and caddisflies.
The community included at least two sensitive species of mayflies (Koorrnonga inconspicua and Atalophlebia australasica) and three flow-dependent species (blackfly Simulium ornatipes, dytiscid beetle Platynectes decempunctatus and chironomid Rheotanytarsus). The only fish collected was the introduced mosquitofish (Gambusia).
The water was fresh (salinity of 764 mg/L in autumn and 545 mg/L in spring), well oxygenated (77% saturation), slightly turbid and coloured, with moderate to high concentrations of nutrients such as nitrogen (0.72–2.85 mg/L) and phosphorus (0.08–0.59 mg/L).
The sediments were dominated by sand, detritus, silt and clay; samples taken from below the surface were blackened and sulfidic in autumn, indicating that too much organic matter had entered in the creek in the past. A deposit of 1–5 cm of silt covered the creekbed in autumn and more than 50 metres of bank erosion, caused by cattle damage, was observed in spring.
Filamentous algae (mostly Spirogyra) covered less than 10% of the site in both seasons sampled. Over 35% of the site was covered in aquatic emergent plants (Cotula, Polygonum, introduced Rorippa, Triglochin and Rumex) in autumn; plant cover subsequently declined to just over 10% of the channel in spring when flow in the creek was much higher. The narrow riparian zone and surrounding vegetation consisted of introduced grasses and a few scattered gum trees.
Special enironmental features
Currency Creek provides habitat for at least two sensitive species of mayfly and several flow-dependent species. The creek also supports at least two threatened fish species, the Mountain Galaxias 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.|