Salt Creek, near Rockleigh
2010 Aquatic Ecosystem Condition Report
- Dry in autumn and a saline, isolated pool present in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation was mostly introduced grasses, rushes and weeds.
About the location
Salt Creek is a moderately large stream in the eastern Mount Lofty Ranges. It rises about four kilometres east of Harrogate and flows in a south-easterly direction before disappearing underground on the plains of the River Murray, about four kilometres south of Caloote. The major land use is sheep grazing.
The monitoring site was located off Rockleigh Road, over two kilometres south-east of Rockleigh.
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, high salinity, fine sediment deposition and degraded riparian habitats.
A sparse community of about 12 species of macroinvertebrates was collected from an isolated pool, six metres wide and up to 35 centimetres deep, in spring 2010; the site was dry in autumn. The community was dominated by large numbers of species that are tolerant to high salinity and poor water quality such as chironomids (including Tanytarsus) and dytiscid beetles (Necterosoma). It also included smaller numbers of several other beetles (Antiporus, Rhantus and Berosus), soldierflies, waterbugs and odonates. No sensitive or rare species were found.
The water was saline (salinity of 16,772 mg/L), well oxygenated (120% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (2.89 mg/L) and phosphorus (0.08 mg/L).
The sediments were dominated by clay, silt, detritus and cobbles; samples taken from below the surface were black and sulfidic in spring, 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 and about 10 metres of bank showed evidence of erosion due to previous flood damage.
A large amount of phytoplankton was recorded from the isolated pool and over 10% of the surface was covered by filamentous algae (Cladophora). More than 10% of the site was also covered by aquatic plants, including a stonewort (Chara) growing in the water and rushes (Juncus) growing on the edges of the water.
The narrow riparian zone consisted of introduced grasses, rushes, weeds and a few paperbark trees. The surrounding vegetation was mostly grazing land with a few scattered gum trees and sheoaks.
Special environmental features
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.|
|Saline groundwater inflow (reducing ecological integrity).||Saline groundwater inflows may be exacerbated by two things; vegetation clearing and resultant increase in rainfall recharge, or the extraction of surface water reducing the dilution factor in natural saline discharge zones. The SA Murray–Darling Basin NRM Board’s Land Management Program strategically invests in salinity ‘hotspots’ by providing incentives to land managers to plant perennial pasture/fodder crops/ or revegetation to reduce recharge. The NRM Board works with various agencies to minimise any further vegetation clearing which may impact on the catchment’s water balance. The NRM Board seeks to manage and provide for environmental flows to allow natural dilution of saline waters through the development of Water Allocation Plans and Water Affecting Activity policies across the region.|