Tod River, near the Tod Reservoir
2015 Aquatic Ecosystem Condition Report
Moderately diverse macroinvertebrate community with no rare or sensitive species and one flow-dependent species
Obvious signs of nutrient enrichment in spring
Riparian vegetation was mostly introduced grasses and weeds among rushes and sedges
Silt deposits in the channel
About the location
Tod River is the only permanent flowing stream on the 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 and cropping, with minor areas of native vegetation and urban settlement further upstream. The Tod Reservoir, located just downstream from the site, is a large off-stream dam that receives water via concrete aqueducts from Pillaworta Creek and the Tod River. The monitoring site was located off Growdens Road, about two kilometres north of the reservoir.
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 poor riparian habitat, nutrient enrichment in spring and fine sediment deposition in a salt-affected watercourse in the region.
A moderately diverse community of about 26 species of macroinvertebrates (17 in autumn and 14 in spring) was collected or seen from the river, 0.7-3.4 metres wide and up to 55 centimetres deep, in autumn and spring 2015. About 80% of the stream comprised slow to non-flowing pool or channel habitats connected by 20% of faster-flowing, shallow riffles in both seasons sampled. The community was dominated by species tolerant to poor water quality and high salinity such as amphipods (Austrochiltonia), blackflies (Simulium), hypogastrurid springtails and chironomids (Tanytarsus, Chironomus, Procladius and Cardiocladius). It also included smaller numbers of worms, water mites (Arrenurus and Piona), snails (Angrobia), yabbies (Cherax), beetles, biting midges, waterbugs, damselflies, dragonflies and caddisflies (Triplectides australis and Notalina). The only flow-dependent species detected in the riffles were a few blackfly larvae (Simulium ornatipes) in autumn but they were the most numerous species recorded from the riffle habitats in spring. No rare, sensitive or freshwater species were seen. The only fish recorded from the site was an introduced pest called mosquitofish (Gambusia); a juvenile fish was collected in the autumn survey.
The water was saline (salinity of 6,600 mg/L in autumn and 5,705 mg/L in spring), well oxygenated (89-117% saturation), clear and slightly coloured, and with remarkably low concentrations of nutrients such as nitrogen (0.12-0.91 mg/L) and phosphorus (0.013-0.055 mg/L) in autumn compared to spring.
The sediments were dominated by clay, detritus and silt in the pools and by sand, detritus and gravel in the riffles; filamentous algae was only recorded in spring when it covered 20-30% of the in-stream habitats. Samples taken from below the surface were grey clays and silts that appeared to be well aerated, and showed no evidence to indicate the sediments occasionally turned anaerobic (e.g. blackened underside of rocks embedded in the sediments and no strong odours). Over 1 centimetre of silt covered the riverbed and there was no sign of any significant bank erosion at the site sampled, despite the presence of sheep droppings on the bank.
A large amount of phytoplankton was recorded in spring (chlorophyll a ranged from 1.6-39.8 µg/L) at a time when over 35% of the river was covered by filamentous algae (Cladophora and Spirogyra). A similar area was also covered by aquatic plants, including sedges (Schoenoplectus), rushes (Juncus) and samphire. The riparian zone consisted of introduced grasses, weeds, and patches of sedges (Baumea and Carex), rushes (Juncus), samphire and a few paperbark trees. The surrounding vegetation at the site was cleared cropping and sheep grazing land.
Special environmental features
The presence of a flow-dependent blackfly was the only notable feature recorded at the site in 2015.
Common Galaxias (Galaxias maculatus) have also been previously observed at this site.
Pressures and management responses
Livestock have direct access at the site and upstream in the catchment, causing sediment erosion and adding excessive nutrients.
The Eyre Peninsula NRM Board administer the Water Affecting Activities permits and polices for the region. This process allows the Board to grant or refuse permits to undertake certain activities affecting water resources. The process is the region’s primary means of preventing any potential impact on the environmental integrity of surface water catchments.
In 2012 the Eyre Peninsula NRM Board delivered a project titled Delivering the Requirements of the Tod River Management Plan. This project implemented recommendations outlined in the River Management Plan for the Tod Catchment, as well as the Freshwater Fish Survey of Southern Eyre Peninsula baseline report. In doing so, the project protected and enhanced over 380ha of native habitat identified as having high conservation value. This was achieved primarily by reducing pressures on degraded areas through removal of livestock, enhancing remnant vegetation, re-establishing native vegetation, and control of invasive Weeds of National Signifiance (WoNS). In addition, two fish-friendly watercourse crossings were constructed which has helped improve the hydrology of two highly significant sections of the Tod River, while greatly improving the ability for native fish and other aquatic biota to migrate unimpeded.
The Eyre Peninsula NRM Board continues to promote managing land to improve water quality. This includes incentives for:
The Eyre Peninsula NRM Board also undertakes a native freshwater fish monitoring program throughout this catchment.
Limited natural riparian vegetation at the site and upstream in the catchment, providing minimal buffer protection from catchment land uses.