Truro Creek, near Accomodation Hill
2010 Aquatic Ecosystem Condition Report
- Isolated, saline pools present in both autumn and spring.
- Sparse macroinvertebrate community with one rare species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation was mostly rushes and a few trees.
About the location
Truro Creek is a small stream in the northern Mount Lofty Ranges that rises around Truro, drains in an easterly direction through a series of gorges, and eventually disappears underground in the Murray mallee towards the west of Twelve Mile Plain. The major land use is sheep grazing.
The monitoring site was located on Wild Dog Track Road, off the Sturt Highway, about eight kilometres east-south-east of Truro.
The creek was given a Fair rating because the site sampled showed moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance, including nutrient enrichment, poor riparian habitat and heavy sediment deposition in the channel.
A sparse community of about 26 species of macroinvertebrates was collected from the isolated pools, seven metres wide and over one metre deep, in autumn and spring 2010. The community was dominated by species tolerant to poor water quality such as mites, amphipods (Austrochiltonia australis), waterbugs (Micronecta) and chironomids (Chironomus). It also included smaller numbers of freshwater shrimps, yabbies, beetles, mosquitoes, biting midges, soldierflies, odonates, caddisflies and several types of waterbugs and chironomids. The site was unusually rich in mites, with at least three families collected (Unionicolidae, Hydryphantidae and Limnesiidae). The only uncommonly collected species was a type of waterbug called the water measurer (Hydrometra).
The water was saline (salinity of 5,968 mg/L in autumn and 7,680 mg/L in spring), well oxygenated (75–142% saturation), clear in autumn but turbid in spring, with moderate to high concentrations of nutrients such as nitrogen (1.37–1.57 mg/L) and phosphorus (0.05–0.08 mg/L).
The sediments were dominated by silt, detritus, bedrock, cobbles and algae; samples taken from below the surface were blackened and sulfidic in spring, indicating that too much organic matter had entered the creek in the past. Thick deposits of silt over 10 centimetres deep were recorded from the channel in places.
Large growths of phytoplankton were present in the creek in both seasons sampled but filamentous algal growths (mostly Cladophora) were only significant in spring, when they covered more than 10% of the channel. Over 35% of the site was covered in aquatic plants, including the Common Reed (Phragmites australis) and an introduced weed called Sharp Rush (Juncus acutus).
The narrow riparian zone consisted of Sharp Rush, reeds, weeds and a few gums and wattles. The surrounding vegetation was grazed grassland and chenopod shrubland.
Special environmental features
Truro Creek provides habitat for a rarely collected waterbug (Hydrometra) which typically occurs among aquatic vegetation along the edges of permanent waterholes and lakes.
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.
|Insufficient natural water flows resulting from water extraction and climate variability (reducing ecological integrity.
|The SA Murray–Darling Basin NRM Board’s Regional NRM Plan sets limits for new dam construction through the water affecting activity permits section. The dam capacity limits aim to keep new dam development within sustainable limits.
|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.