McHargs Creek, near Ashborne
2008 Aquatic Ecosystem Condition Report
- Affected by nutrient enrichment and fine sediment.
- Moderately diverse macroinvertebrate community dominated by tolerant species.
- Provides habitat for rare and notable species.
- Efforts being made to restore the riparian zone.
About the location
McHargs Creek is part of a small network of streams west of Strathalbyn in the southern Mount Lofty Ranges, which drain into the Bull Creek–Finniss River catchment. The creek passes through mainly sheep and cattle grazing country; most of its tributaries have in-stream dams built to water livestock.
The site selected for monitoring was located off McHargs Creek Road, in the mid-reaches of the creek about three kilometres 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. Evidence showed nutrient enrichment was affecting the creek, however, some sensitive species were still found at the site, suggesting the potential for improvement if the appropriate action is taken to remediate the creek.
Shallow and deep pools of still-water and small areas of flowing riffles formed the creek at this location when it was sampled in spring 2008.
A moderately diverse community of 36 species of macroinvertebrates was collected. Species tolerant of high nutrient levels were the most common, including worms, native snails (Glyptophysa concinna), introduced snails (Physa acuta), and chironomids. Smaller numbers of sensitive species such as fly larvae from the Dixidae family, a stonefly and two types of mayflies were also found.
Despite only slight flows at the time of sampling, the water was fresh (salinity of 900 mg/L) and moderately well oxygenated (59% saturation). It was clear and only slight coloured, with moderate to high levels of nutrients such as nitrogen (0.55 mg/L) and phosphorus (0.02 mg/L).
The creekbed was made up mostly of clay, rotting plant material and large deposits of fine silt. Blackened rocks provided evidence the stream occasionally becomes anaerobic, which usually occurs when there is too much organic material present.
Small patches of green filamentous algae (Spirogyra) were found in the water. An introduced herb called Watercress (Rorippa nasturtium-aquaticum) grew in the channel with native plants such as rushes (Juncus), sedge (Cyperus) and clubrush (Isolepis).
River Red Gums grew over Sea Rush (Juncus kraussii) and introduced pasture grasses along the creek’s banks. Exotic trees, shrubs and weeds had been removed from the surrounding area and replaced with native plants, scattered among the remaining gums and paperbarks.
Special environmental features
The creek supports a range of notable macroinvertebrates, such as flies from the Dixidae family, a stonefly (Austrocerca tasmanica) and two species of mayflies (Koorrnonga inconspicua and Atalophlebia australasica). It also provides habitat for at least one threatened native fish called the Mountain Galaxias (Galaxias olidus).
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 zone 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.|