Tod River, near Yallunda Flat
2010 Aquatic Ecosystem Condition Report
- Permanent saline river with flowing water in autumn and non-flowing habitats present in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation consisted of native trees and introduced grasses.
- Moderately eroded banks and large silt deposits in the channel.
About the location
Tod River is the major surface water supply catchment in Eyre Peninsula. It rises north of Yallunda Flat and flows in a southerly direction before discharging into Spencer Gulf at the southern end of Louth Bay. The major land uses are sheep grazing, cropping, and minor areas of native vegetation and urban settlement. The Tod Reservoir, located about 15 kilometres downstream from Yallunda Flat, is a large off-stream dam that receives water via concrete aqueducts from Pillaworta Creek and the Tod River.
The monitoring site was located in the upper reaches of the river off Yallunda Flat Road, about one kilometre south of Yallunda Flat.
The river 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, bank erosion and fine sediment deposition.
A sparse community of about 20 species of macroinvertebrates was collected from the still to slow-flowing river, 5–7 metres wide and more than 70 centimetres deep, in autumn and spring 2010. The community was dominated by species tolerant to poor water quality and high salinity such as amphipods, chironomids (including the salt tolerant Tanytarsus barbitarsis), mosquitoes and notonectid waterbugs (Anisops). It also included an introduced snail (Potamopyrgus), worms, yabbies, several types of beetles (including dytiscids, hydrophilids and hydraenids), soldierflies, corixid waterbugs and three odonates. No sensitive or rare species were found.
The water was saline (salinity of 9,000 mg/L in autumn and 5,998 mg/L in spring), well oxygenated (62–79% saturation) and clear but strongly coloured, with moderate to high concentrations of nutrients such as nitrogen (1–1.37 mg/L) and phosphorus (0.02–0.05 mg/L.
The sediments were dominated by detritus, sand, silt and clay; samples taken from below the surface were blackened, sulfidic and anaerobic, or lacking in oxygen. Heavy sedimentation was recorded during both seasons sampled, with more than 10 centimetres of silt deposited in the channel in places. Over 10 metres of the bank showed evidence of erosion, possibly due to stock access in the past or flood damage due to the poor vegetative cover on the banks.
Several types of aquatic plants were recorded growing in the channel or on the banks, including both submerged (Chara and Stuckenia) and emergent species (Juncus, Eleocharis and Rumex). Moderate amounts of phytoplankton were recorded but no filamentous algae was noted during either survey of the site.
The riparian zone consisted of gum trees over introduced grasses and weeds, with smaller growths of rushes (Juncus) and samphire also present. The surrounding vegetation was mostly cropping and grazed grasslands with a few scattered gum trees.
Special environmental features
Pressures and management responses
|Livestock have direct access at the site and upstream in the catchment, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds).||
The Eyre Peninsula NRM Board promotes managing land to improve water quality. This includes incentives for:
|Limited natural riparian vegetation at the site and upstream in the catchment, providing minimal buffer protection from catchment landuses (reducing habitat quality).|
|Saline groundwater inflow (reducing ecological integrity).||The Eyre Peninsula NRM Board promotes the revegetation of recharge areas known to contribute to dryland salinity and encourages the adoption of perennial pastures as an alternative to annual cropping in these areas.|