Rodwell Creek, west from Woodchester
2015 Aquatic Ecosystem Condition Report
Permanently wet, saline, slightly flowing 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 dominated by rushes and reeds
About the location
Rodwell Creek is a small stream in the southern Mount Lofty Ranges. It rises east from Macclesfield and 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 off Tinpot Road, about two kilometres west from Woodchester.
The creek was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure, and some changes to the way the ecosystem functions. There was evidence of human disturbance including nutrient enrichment, salinization and fine sediment deposition.
A sparse community of about 22 species of macroinvertebrates (8 in autumn and 18 in spring) was collected or seen from the slow-flowing creek, 2.1-8.3 metres wide and up to 73 centimetres deep, in autumn and spring 2015. The community was dominated by mosquitoes (Aedes and Culex) in autumn and waterbugs (Anisops) in spring. It also included low numbers of several other tolerant macroinvertebrates such as hydrozoans (Hydra), water mites (Koenikea and Arrenurus), amphipods (Austrochiltonia), yabbies, dytiscid beetles, chironomids (Parachironomus, Procladius, Tanytarsus and Chironomus), damselflies, dragonflies, and caddisflies (Triplectides australicus). No sensitive or rare species were recorded.
The water was saline (salinity of 3,686 mg/L in autumn and 3,665 mg/L in spring), moderately well to well oxygenated (52-60% saturation), clear and slightly turbid, and with high to very high concentrations of nutrients such as nitrogen (1.49-1.65 mg/L) and phosphorus (0.07-0.13 mg/L).
The sediments were dominated by detritus and clay, with smaller amounts of sand, silt, boulder, bedrock, cobble, pebble, filamentous algae and gravel also present. Samples taken from below the surface were grey clays and silts that released sulfide and lacked oxygen in spring, indicating that the sediments were a harsh environment for benthic species to inhabit for at least part of the year. A small amount of clay partly covered rocks on the bottom of the stream and about 10 metres of the bank showed evidence of erosion due to cattle accessing the stream in the past. The only droppings seen near the stream were from kangaroos.
A large amount of phytoplankton was recorded during the year (chlorophyll a 18-24 µg/L) and nearly 10% of the channel was covered by a filamentous alga (Spirogyra) in autumn; no filamentous algae was seen in spring. Over 35% of the creek was covered by a range of submerged (Callitriche) and emergent aquatic plants (Juncus, Typha, Phragmites, Eleocharis and Triglochin). The riparian zone extended 5-10 metres from the edge of the stream and was dominated by rushes and reeds under a few scattered gum trees and acacias. The surrounding vegetation at the site comprised a 10-15 metre fenced buffer zone that was dominated by regenerating native sedges (Cyperus) and understorey plants. Beyond the fenced area, dryland cropping and grazing lands with a few scattered gum trees dominated the local landscape.
Special environmental values
None detected at the site sampled but refuge pools further upstream provide a significant habitat for a threatened fish called River Blackfish (M. Hammer, Aquasave Consultants, 2009).
Pressures and 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.
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.