Riparian vegetation dominated by a River Red Gum corridor over weeds and introduced grasses
Area map
About the location
Marne River is a large stream in the eastern Mount Lofty Ranges that rises west from Springton and flows in an easterly direction where it eventually discharges into the River Murray to the north of Walker Flat. The major land uses are cereal cropping and sheep grazing. The monitoring site was located on a track off the Mannum–Sedan Road, about two kilometres south from Cambrai.
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 habitats.
Findings
A sparse community of at least 14 species of macroinvertebrates was collected from the isolated pools in the shallow creek, up to 5.7 metres wide and 21 centimetres deep, in autumn; the creek was dry in spring 2015. The community was dominated by generalists and species tolerant to poor water quality such as worms, waterbugs (Anisops and Enithares) and aquatic sowbugs (Heterias pusilla). It also included smaller numbers of introduced snails (Potamopyrgus), mites, amphipods, yabbies, freshwater shrimps, beetles, biting midges and chironomids. The site lacked any sensitive and rare species, and no mayflies, stoneflies, caddisflies or odonates were recorded.
The water was saline (salinity was 3,666 mg/L), well oxygenated (60% saturated), slightly turbid and coloured, and with high concentrations of nutrients such as nitrogen (1.44 mg/L) and phosphorus (0.08 mg/L).
The sediments were dominated by silt and dead detritus, and included smaller amounts of boulder, cobble and sand. Samples taken from below the surface were anaerobic, black clays and silts 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 1 cm of silt covered the bottom of the pools in places and more than 10% of the banks showed signs of erosion due to past flood damage.
A large phytoplankton bloom was recorded in autumn (chlorophyll a 80.4 µg/L) but filamentous algae was not seen at the site during the year. Over 35% of the channel and water’s edge was covered by cumbungi (Typha) and sedges (Bolboschoenus). The riparian zone extended over 5-10m from the edges of the stream and comprised a River Red Gum corridor over sedges (Cyperus) and various weeds and introduced grasses. The surrounding vegetation at the site was cleared cropping land with a few scattered large gum trees remaining in the local landscape.
Special environmental values
None detected.
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 Marne Saunders catchments 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.
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
