Tod River, near Yallunda Flat
2015 Aquatic Ecosystem Condition Report
Permanently wet, non-flowing, saline river in autumn and spring
Moderately diverse macroinvertebrate community with no rare or sensitive species
Obvious signs of moderate nutrient enrichment
Riparian vegetation dominated by native trees over introduced grasses and weeds
Moderately eroded banks
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, cropping, with 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 from 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 and bank erosion of a river that has clearly been adversely affected by high salinity.
A moderately diverse community of about 25 species of macroinvertebrates (16 in autumn and 18 in spring) was collected from this slow non-flowing river, up to 4.5 metres wide and 38 centimetres deep, in autumn and spring 2015. The community was dominated large numbers of amphipods (Austrochiltonia), chironomids (Tanytarsus and Procladius) and waterbugs (Sigara, Agraptocorixa and Anisops). It also included smaller numbers of several other generalist and tolerant macroinvertebrates, including water mites (Recifella, Arrenurus and Koenikea), introduced snails (Potamopyrgus), yabbies (Cherax), beetles (including Sternopriscus and Necterosoma), mosquitoes (Culex and Aedes) and damselflies (Ischnura and Austrolestes). No sensitive or rare species were found.
The water was saline (salinity of 7,628 mg/L in autumn and 6,808 mg/L in spring), well oxygenated (56-73% saturation), clear and slightly coloured, and with moderate to high concentrations of nutrients such as nitrogen (1-1.06 mg/L) and phosphorus (0.04-0.05 mg/L).
The sediments were dominated by detritus, bedrock, sand, silt, clay and filamentous algae. Samples taken from below the surface were anaerobic smelling, grey clays and silts that released sulfide when tested, indicating that the sediments lacked oxygen and were a harsh environment for most benthic species to inhabit. Over 5 centimetres of fine silt covered the bed of the river and more than 10 metres of the bank showed evidence of erosion, probably due to past flood damage of the poorly vegetated banks.
A moderate to large growth of phytoplankton (chlorophyll a ranged from 3.8-24 µg/L) was recorded during the year and about 10% of the site was covered by a type of filamentous alga (Cladophora). Over 10% of the channel and edges of the river were covered by patches of sedges (Baumea) and samphire. The riparian zone consisted of tall gum trees and wattles over introduced grasses and weeds (including bridle creeper), with patches of rushes (Juncus), sedges (Baumea) and samphire also present. The surrounding vegetation was mostly cleared cropping and sheep grazing land with a few scattered gum trees in the local landscape.
Special environmental features
Common Galaxias (Galaxias maculatus) have 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.