Tod River, downstream from Whites Flat
2015 Aquatic Ecosystem Condition Report
Permanently wet, saline, slow to non-flowing stream in autumn and spring
Moderately diverse macroinvertebrate community comprising only tolerant and generalist species
Obvious signs of moderate nutrient enrichment
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 stock grazing and cropping, with minor areas of native vegetation and urban settlement. The Tod Reservoir, located between Koppio and Whites Flat, 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 on Gawler Ponds Road, about one kilometre south from Whites 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, fine sediment in the channel and poor riparian habitat in what is clearly a salt affected river.
A moderately diverse community of about 21 species of macroinvertebrates (7 in autumn and 20 in spring) was collected from the slow to non-flowing channel, up to 9.4 metres wide and 73 centimetres deep, in autumn and spring 2015. The community was dominated by species that are tolerant to poor water quality, including amphipods (Austrochiltonia), waterbugs (Anisops and Sigara), hydrophilid beetle larvae and chironomids (Procladius, Paramerina and Chironomus). It also included smaller numbers of snails (Coxiella and introduced Potamopyrgus), water mites, dytiscid and hydrophilid beetles, mosquitoes (Culex), damselflies, dragonflies and caddisflies (Notalina). The presence of yabby hole also indicated that they were also a common inhabitant of the river. The community therefore comprised a range of generalist and tolerant species that are commonly found together in many saline streams in the region and State. The lack of mayflies and stoneflies coupled with the lack of any salt sensitive caddisflies, supports the role of high salinity in limiting the diversity of species that inhabits this stream.
The water was saline (salinity of 6,329 mg/L in autumn and 9,632 in spring mg/L), moderately well oxygenated (53-213% saturation), clear and slightly coloured, and with high to very high concentrations of nutrients such as nitrogen (0.89-2.95 mg/L) and phosphorus (0.07-0.13 mg/L).
The sediments were dominated by detritus, silt, clay and sand. Samples taken from below the surface were black silts that had an anaerobic odour and released sulfide when tested in spring, indicating that the sediments lacked oxygen and a harsh environment for most benthic species to be able to inhabit. Over 1 centimetre of silt covered the streambed but there was no evidence of any significant areas of bank erosion noted at the site.
A large amount of phytoplankton was recorded during in spring (chlorophyll a ranged from 2.6-11.8 µg/L) and no filamentous algae was recorded during either survey of the site. Over 10% of the channel was covered by submerged (Callitriche and Chara) and emergent aquatic plants (Baumea, Carex, Juncus and Schoenoplectus). The riparian zone extended over 40 metres from the edge of the stream and consisted of introduced grasses and swampy sedge land (mostly Baumea and Carex) but lacked an overstorey of trees and shrubs. The surrounding vegetation was cleared cropping and sheep grazing land with only a few scattered gums present in the local landscape.
Special environmental features
None detected at the site sampled in 2015. Previous sampling at the nearby Whites Flat site in 2010 recorded the presence of Climbing Galaxias (Galaxias brevipinnis), a threatened native fish in South Australia. It also supported a rare flow-obligate caddisfly (Cheumatopsyche) for the Eyre Peninsula and a commonly occurring flow-dependent macroinvertebrate (blackfly Simulium ornatipes).
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.