Tod River, Koppio
2010 Aquatic Ecosystem Condition Report
- Permanently wet, saline, flowing stream in autumn and spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation included native and introduced species that were still in the process.of regenerating following the 2005 bushfire.
- Ash from the 2005 bushfire was still present in the creek.
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 cattle grazing and cropping, with minor areas of native vegetation and urban settlement.
The Tod Reservoir, located downstream from Koppio, is a large off-stream dam that receives water via concrete aqueducts from Pillaworta Creek and the Tod River. The reservoir has not been used to supply water to the region for over a decade due to the high salinity of water in the river and reservoir.
The monitoring site was located at the Calderwoods Road ford on the northern edge of Koppio.
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 and fine sediment deposition as a result of a recent fire in the catchment in 2005.
A sparse community of about 20 species of macroinvertebrates was collected from the slow to fast-flowing channel, 3–5 metres wide and 50 centimetres deep, in autumn and spring 2010. The community was dominated by generalists and species tolerant to poor water quality including large numbers of amphipods, chironomids and blackfly larvae and lower numbers of snails (including the introduced Potamopyrgus), mites, beetles, velvet waterbugs, damselflies, dragonflies and the introduced mosquitofish.
No sensitive or rare species were seen but the site was unusual because it included a rich assemblage of mites (families Eylaidae, Unionicolidae and Arrenuridae) and two flow-dependent species (blackfly Simulium ornatipes and dytiscid beetle Platynectes decempunctatus).
The water was saline (salinity of 6,382 mg/L in autumn and 5,931 mg/L in spring), well oxygenated (78% saturation), slightly turbid and strongly coloured, with moderate to high concentrations of nutrients such as nitrogen (0.98–1.23 mg/L) and phosphorus (0.04–0.06 mg/L).
The sediments were dominated by cobbles, detritus, silt and algae. There were no indications that the sediments were lacking in oxygen, although heavy siltation was noticed at the site in spring when more than 10 centimetres of silt covered the riverbed. Some ash from a recent bushfire in 2005 was still present in parts of the channel and may contribute to occasional declines in oxygen levels when flows in the stream are very low or cease entirely for weeks to months at a time over summer.
Moderate amounts of phytoplankton were present in both seasons sampled and more than 10% of the site was covered by filamentous algae (Enteromorpha) in spring. Emergent plants (Bolboschoenus, Eleocharis, Juncus, Schoenoplectus, Typha and Isolepis) were recorded growing over more than 10% of the channel and water’s edge.
The riparian zone consisted of gums and olive trees growing over introduced grasses, thistles, rushes and cumbungi (Typha). The surrounding vegetation at the site was mostly crops and grazed grassland.
Special environmental features
The site was notable due to the presence of at least two flow-dependent macroinvertebrate species and three families of aquatic mites.
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.|