Bull Creek, near Ashbourne
2008 Aquatic Ecosystem Condition Report
- Affected by nutrient enrichment and fine sediment.
- Riparian zone severely disrupted, with invasions of exotic trees, woody and herbaceous weeds.
- Extensive algal growths and weeds in the channel.
- Catchment provides habitat for rare fish species.
About the location
Bull Creek is a small network of streams rising on the eastern slopes of Bull Creek Range, about four kilometres south of Meadows in the southern Mount Lofty Ranges. Multiple dams capture water from every tributary in the network which flows south through Ashbourne before discharging into the Finniss River.
Livestock grazing (75%) is the main land use in the catchment, with minor areas of forestry, dairy farming, horticulture and urban development. There are also some protected areas of native vegetation. The site selected for monitoring was located off Chapel Hill Road, less than one kilometre west of Ashbourne.
The creek was given a Fair rating at this site because the ecosystem showed evidence of moderate changes to animal and plant life, and some changes to the way the ecosystem functions. Although the site contained too little water to sample, the large amount of algae present confirmed that the site was nutrient enriched. The sediment was also in poor condition, and human activity had severely disrupted the riparian zone.
Only small, disconnected puddles were found when the creek was inspected in December 2008. The water was slightly turbid (or cloudy), most likely due to blooms of single-celled algae, or phytoplankton. Up to 35% of the surface was covered with green filamentous algae (Cladophora). There was not enough water present to collect macroinvertebrate specimens, or take reliable samples to measure salinity levels, and concentrations of oxygen and nutrients.
Fine silt, sand and clay made up the creekbed, as well as organic debris and some cobbles. The sediments were blackened, anaerobic and sulfidic in places, indicating too much organic matter had entered the creek.
Patches of native Stiff Flat Sedge (Cyperus vaginatus) and knotweed (Persicaria) grew in the channel, as well as introduced plants such as Watercress (Rorippa) and dock (Rumex).
The riparian zone was narrow and in poor condition, with exotic trees, woody and herbaceous weeds and grasses such as Desert Ash, olives, blackberries, willows, ivy and periwinkle dominating the vegetation. A thin line of River Red Gums were also recorded along the creekbank. Cereal cropping occurred beyond the riparian zone.
Special environmental features
The creek provides habitat for a threatened native fish species called the Mountain Galaxias (Galaxias olidus) elsewhere in it's catchment.
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.|
|Drought (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.|