Riparian vegetation dominated by weeds and introduced grasses
Area map
About the location
Western Flat Creek is a moderately sized stream in the southern Mount Lofty Ranges that rises a few kilometres to the north from Macclesfield and flows in a north-north-easterly direction before discharging into Mount Barker Creek in the Mount Barker township. The major land uses are grazing cattle and sheep and cropping, with many rural properties scattered throughout the catchment. The monitoring site was located off Bollen Road on the south-westerly urban outskirts of Mount Barker.
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 gross nutrient enrichment, fine sediment deposition and degraded riparian and terrestrial habitats.
Findings
A sparse community of at least 25 species of macroinvertebrates (10 in autumn and 22 in spring) was collected from the slow to non-flowing creek, 4.1- 7.4 metres wide and up to 54 centimetres deep, in autumn and spring 2015. The community was dominated by generalists and species tolerant to poor water quality such as amphipods (Austrochiltonia), waterbugs (Anisops) and chironomids (Corynoneura, Tanytarsus, Chironomus and Dicrotendipes). It also included smaller numbers of worms, leeches, pea mussels, introduced snails (Physiella and Potamopyrgus), native snails (Glyptophysa), water mites, beetles, biting midges, damselflies, caddisflies (Hellyethira) and a few other waterbugs (Sigara and Enithares). No sensitive or rate species were recorded. The only fish seen and collected at the site were introduced mosquitofish (Gambusia) which occurred in large numbers in autumn in particular.
The water was fresh (salinity ranged from 712-1,476 mg/L), well oxygenated (47-72% saturated), clear, and with moderate to high concentrations of nutrients such as nitrogen (0.54-1.3 mg/L) and phosphorus (0.06-0.12 mg/L).
The sediments were dominated by detritus and silt. Samples taken from below the surface comprised anaerobic, rotting vegetation and silt that released sulfide when tested, indicating that the sediments lacked oxygen and were a harsh environment for most benthic species to be able to inhabit. Over 10 centimetres of silt covered the bottom of the stream, probably sourced from upstream agricultural lands because bank erosion was not seen at the site that was located opposite residential houses on the edge of Mount Barker township.
A small to large amount of phytoplankton (chlorophyll a ranged from 2.1-10.9 µg/L) was recorded but no filamentous algae was seen at the site during 2015. Over 90% of the channel and water’s edge was covered by dense growths of cumbungi (Typha) and smaller patches of sedges (Bolboschoenus), knotweed (Persicaria), water buttons (Cotula), and introduced watercress (Rorippa) and dock (Rumex). The narrow, <5 metres wide riparian zone was dominated by introduced grasses and weeds (including blackberries) with a few scattered gum trees. The surrounding vegetation at the site was associated with residential houses and a linear recreation park on opposite banks of the creek.
Special environmental values
None detected. However, Mountain Galaxias, a native fish species identified as vulnerable in the 2009 ‘Action plan for South Australian freshwater fishes’, has been found downstream of this site in Mount Barker within the last five years (Nick Whiterod, Aquasave Consultants, pers. comm.).
Pressures and management responses
Pressures
Management responses
Livestock have direct access to some creeks, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds).
Natural Resources SA Murray–Darling Basin 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 some creeks, providing minimal buffer protection from catchment landuses (reducing habitat quality).
Natural Resources SA Murray–Darling Basin recognises that the management of riparian vegetation requires a long-term, integrated approach to achieve ecosystem benefits. The NRM 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).
A water allocation plan that guides sustainable water use in the Eastern Mount Lofty Ranges has been developed by Natural Resources SA Murray–Darling Basin, working with the community and government (particularly the Department for Environment, Water and Natural Resources (DEWNR)). The plan aims to balance social, economic and environmental water needs and is implemented through a system of water licensing and permits for water affecting activities administered by DEWNR.
A key component of the water allocation plan is to provide water to sustain the environment at an acceptable level of risk. Securing low flows for the environment is a key environmental water provision in this area, and Natural Resources SA Murray–Darling Basin is working together with DEWNR, Natural Resources Adelaide and Mount Lofty Ranges and the community to develop a program to secure low flows across the Mount Lofty Ranges. For more information on water allocation planning and associated projects go to our Water Allocation Planning web page.
In addition, this site is located in an area where the total demand for water is higher than the sustainable limits set out in the water allocation plan. Natural Resources SA Murray–Darling Basin is monitoring the situation and will work with the community to develop solutions for managing high water demand where required.
Widespread introduced trees and weeds in riparian zones (reducing habitat quality).
Natural Resources SA Murray–Darling Basin recognises the limitations of available funds relative to the scale of the degradation caused by introduced trees and weeds. It 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. It actively seeks funding opportunities for weed control; most opportunities are for locations where biodiversity outcomes can be achieved.
Observed Condition
Expected Condition
