Tod River, Koppio
2015 Aquatic Ecosystem Condition Report
Permanently wet, saline, slow-flowing stream in autumn and spring
Moderately diverse macroinvertebrate community with a flow-dependent species present in small areas of fast-flowing riffle habitat
Obvious signs of moderate nutrient enrichment
Riparian vegetation included native and introduced species and appears to have largely recovered from the 2005 bushfire
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 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 Calderwood’s 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, fine sediment deposition and weeds in the riparian zone in what is clearly a salt affected river.
A moderately diverse community of about 25 species of macroinvertebrates (12 in autumn and 21 in spring) was collected or seen from the slow to fast-flowing river, 0.9-6.3 metres wide and up to 48 centimetres deep, in autumn and spring 2015. The community was dominated by moderate to large numbers of generalists and species tolerant to poor water quality, such as amphipods (Austrochiltonia) and chironomids (Paralimnophyes, Procladius, Tanytarsus, Chironomus and Dicrotendipes). It also included smaller numbers of introduced snails (Potamopyrgus), water mites (Arrenurus), yabbies, isopods (Haloniscus), several beetles, biting midges, mosquitoes (Aedes), soldierflies, small blackflies, waterbugs, damselflies and caddisflies (Hellyethira and Notalina). The only flow-dependent species recorded were the blackfly larvae, probably Simulium ornatipes, which commonly colonises flowing riffle habitats in saline streams in South Australia. The only fish noted from the site were a few introduced mosquitofish (Gambusia) that were collected during the spring survey.
The water was saline (salinity of 6,906 mg/L in autumn and 4,688 mg/L in spring), well oxygenated (74-81% saturation), clear, and with moderate to high concentrations of nutrients such as nitrogen (0.86-0.88 mg/L) and phosphorus (0.02-0.03 mg/L).
The sediments were dominated by detritus, silt, clay and boulder, and included smaller amounts of cobble and sand. Samples taken from below the surface were grey silts and clays that released sulfide when tested, indicating that the sediments were anaerobic and a harsh environment for most benthic species due to the absence of oxygen. Over 10 centimetres of silt covered the bottom of the stream in places during spring. There were no signs of any significant bank erosion or stock accessing the area during the year, indicating that any sediment in the river probably originated from further upstream.
A small to moderate amount of phytoplankton (chlorophyll a ranged from 2.84-5.37 µg/L) was recorded at the site and about 10% of the channel was covered by a filamentous alga (Enteromorpha and Cladophora). Over 65% of the channel was covered by aquatic plants, comprising emergent species such as sedges (Bolboschoenus and Baumea), rushes (Juncus) and dock (Rumex). The riparian zone extended over 40 m wide and consisted of gums and olive trees growing over introduced grasses, weeds, rushes and sedges (Baumea). The surrounding vegetation at the site was mostly cropping and horse grazing land with a few scattered gums remaining in the local landscape.
Special environmental values
The site was only notable due to the presence of a flow-dependent macroinvertebrate (blackfly larvae) in both seasons sampled 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.