Bull Creek, 3.5km north of Ashbourne
2010 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, freshwater creek in autumn and spring.
- Highly diverse macroinvertebrate community with many rare and sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation was mostly deciduous trees and introduced grasses.
- Some bank erosion and large silt deposits in the channel.
About the location
Bull Creek is a small stream in southern Mount Lofty Ranges. It rises south of Meadows and flows in a southerly direction where it eventually discharges into the Finniss River. The major land uses are sheep and cattle grazing. The monitoring site was located off McHarg Creek Road, about three kilometres north of Ashbourne.
The creek 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, silt deposition and a degraded riparian zone. Given the extent of vegetation clearance and grazing in the catchment, it is possible that excessive levels of nutrients and/or fine sediments could eventually lead to the loss of sensitive species and the creek being assigned a poorer rating in the future. However, the creek currently supports many rare and sensitive species of macroinvertebrates and fish, which contributed to its Good condition rating in 2010.
A diverse community of about 45 species of macroinvertebrates was collected from the flowing creek, four metres wide and up to 40 cm deep, in autumn and spring 2010. The creek consisted of a still to slow-flowing channel and small areas of fast-flowing riffle habitats. The community was dominated by large numbers of amphipods (Austrochiltonia australis), hydrobiid snails (including introduced Potamopyrgus), chironomids (including Cricotopus, Chironomus and Dicrotendipes), and leptophlebiid mayflies.
It also included flatworms, introduced snails (Physa), leeches, freshwater limpets, worms, freshwater shrimps, yabbies, beetles, craneflies, biting midges, blackflies, mayflies, waterbugs, odonates, stoneflies and caddisflies. A large number of rare and sensitive species were collected including mayflies (Atalophlebia australasica and Koorrnonga inconspicua), stoneflies (Illiesoperla mayi and Austrocerca tasmanica) and caddisflies (Ethochorema hesperium, Taschorema and Triplectides volda).
Most of these were recorded from riffle habitats, particularly in spring. The community also included several other flow-dependent species, including blackflies (Austrosimulium furiosum and Simulium ornatipes) and a dytiscid beetle (Platynectes decempunctatus). The only fish recorded was a threatened native species called Mountain Galaxias (Galaxias olidus) that was collected from the slow-flowing channel in spring.
The water was fresh (salinity of 715 mg/L in autumn and 617 mg/L in spring), well oxygenated (84-85% saturation) and clear, with low to moderate concentrations of nutrients such as nitrogen (0.36-0.75 mg/L) and phosphorus (0.02-0.03 mg/L).
The sediments in the riffle habitat were dominated by cobbles and pebbles with some algae and gravel, while the still and slow-flowing sections were mostly dominated by detritus with some clay, silt, cobbles, pebbles and algae also present. Samples taken from below the surface were black, sulfidic and anaerobic, indicating that too much organic matter had entered the creek in the past. Heavy sedimentation was recorded in autumn when more than 10 cm of silt covered the creekbed and a small amount of bank erosion was also recorded during the same survey as a result of the combined effects from flood and stock damage in the past.
A small amount of phytoplankton was recorded from water in the creek and over 10% of the site was covered by filamentous algae (Cladophora and Spirogyra). More than 10% of the channel was also covered by a range of emergent aquatic plants (Cyperus, Isolepis, introduced Rorippa, Rumex and Callitriche). The narrow riparian zone consisted mainly of introduced grasses and deciduous trees (including willows and ash). The surrounding vegetation was grazing land with large growths of blackberries present in places.
Special environmental features
Bull Creek provides habitat for several rare and sensitive species of mayflies, stoneflies and caddisflies, and a threatened fish species (Mountain Galaxias).
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.|
|Extensive weed growth in the riparian zone at the site and upstream in the catchment (causing habitat disturbance).||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.|