Rodwell Creek, near Wheal Ellen mine
2010 Aquatic Ecosystem Condition Report
- Permanently flowing, moderately freshwater creek in autumn and spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate to gross nutrient enrichment.
- Riparian vegetation was mostly introduced grasses and weeds.
About the location
Rodwell Creek is a small stream in the southern Mount Lofty Ranges. It rises east of the Bugle Ranges and flows in a south-easterly direction where it ultimately discharges into the Bremer River. The major land uses are cattle grazing and cropping.
The monitoring site was located on a track off Highland Valley Road, about four kilometres west of Woodchester.
The creek 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, fine sediment deposition and a degraded riparian zone.
A sparse community of about 21 species of macroinvertebrates was collected from the slow-flowing creek, 4–7 metres wide and up to 45 centimetres deep, in autumn and spring 2010. Faster-flowing riffle habitats were present in both seasons but were too small to sample. The community consisted of low abundances of 12 species in autumn but was dominated by large numbers of very tolerant anopheline mosquitoes and amphipods (Austrochiltonia australis) in spring. Low numbers of worms, mites, freshwater shrimps, beetles, chironomids, waterbugs, damselflies and leptocerid caddisflies were also recorded. No sensitive or rare species were found. The only fish recorded was the introduced mosquitofish (Gambusia) in autumn.
The water was moderately fresh (salinity of 2,997 mg/L in autumn and 2,013 mg/L in spring), moderately well to well oxygenated (50–100% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (0.71–0.9 mg/L) and phosphorus (0.02–0.03 mg/L).
The sediments were dominated by detritus, clay and silt; samples taken from below the surface were black, sulfidic and anaerobic, indicating that too much organic matter had entered the creek in the past. A deposit of 1–5 centimetres of silt covered the creekbed in autumn.
Only a small amount of phytoplankton was recorded in autumn and spring, and no filamentous algae was seen at the site. Over 10% of the channel was covered in a range of emergent aquatic plants (Juncus, Typha, Cyperus, Phragmites and Triglochin).
The narrow riparian zone consisted of introduced grasses, sedges, rushes, weeds (e.g. soursobs and Salvation Jane) and a few scattered gum trees and acacias. The surrounding vegetation was cropping and grazing lands, with only a few scattered gum trees and native shrubs.
Special environmental features
None detected at the site sampled but refuge pools further upstream provide a significant habitat for a threatened fish called the River Blackfish (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.|
|Widespread introduced trees and weeds in the riparian zone at the site and upstream in the catchment (reducing habitat quality).||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.|