Tod River, near North Shields
2015 Aquatic Ecosystem Condition Report
Permanently wet, slow to non-flowing, saline stream in autumn and spring
Sparse macroinvertebrate community with no rare or sensitive species
Obvious signs of gross nutrient enrichment
Riparian vegetation consisting of native trees, rushes and introduced grasses
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 and cattle grazing, 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 in the lower reaches of the river near the Lincoln Highway, about four kilometres north from North Shields.
The river was given a poor rating because the site sampled showed evidence of major changes in ecosystem structure and moderate changes to the way the ecosystem functions. There was considerable evidence of human disturbance, including nutrient enrichment and weedy vegetation in the riparian zone of this salt-affected river in the region.
A sparse community of about 13 species of macroinvertebrates (7 in autumn and 8 in spring) was collected or seen from the slow to non-flowing river, up to 5.8 metres wide and 80 centimetres deep, in autumn and spring 2015. The community was dominated by moderate numbers of species tolerant to poor water quality such as snails (Angrobia) and hypogastrurid springtails in autumn and amphipods (Austrochiltonia and Corophiidae) and chironomids (Procladius, Chironomus and Tanytarsus) in spring. It also included lower numbers of a few other generalist and tolerant invertebrates such as water mites (Oxus), yabbies (Cherax), waterbugs (Microvelia) and mosquitoes. No rare, sensitive or flow-dependent species were recorded during the year. Three species of fish commonly found in the estuarine and lower section of coastal streams were also recorded at the site, including small galaxiids, Western Blue-spot Gobies and introduced mosquitofish.
The water was saline (salinity of 7,064 mg/L in autumn and 5,626 mg/L in spring), well oxygenated (75-85% saturation), clear and slightly coloured, and with high concentrations of nutrients such as nitrogen (0.83-1.26 mg/L) and phosphorus (0.04-0.06 mg/L).
The sediments were dominated by detritus and included smaller amounts of sand, cobble, pebble, gravel, clay and silt. Samples taken from below the surface were grey sands and the only evidence that the sediments may become anaerobic or lacking in oxygen was the slightly blackened underside of rocks in contact with the sediments; normally they would be expected to have a similar appearance to the surface when sediments are continually well aerated. There was no evidence of any bank erosion and no signs of any stock accessing the stream in recent times.
A moderate to large growth of phytoplankton (chlorophyll a ranged from 3.6-10.9 µg/L) was recorded but no filamentous algae was seen at the site during 2015. Over 65% of the channel and water’s edge was covered by extensive growths of introduced grasses (Paspalum) and sedges (Schoenoplectus).
The 5-10 m wide riparian zone consisted of gum trees and paper barks over an understorey of introduced grasses, rushes, dock and samphire. The surrounding vegetation at the site was cleared cropping land with a few scattered gum trees remaining in the local landscape.
Special environmental features
The lower Tod River is a significant reach for estuarine and native freshwater fish for the region as shown by the presence of at least two species in 2015; note that both Common Galaxias (Galaxias maculatus) and threatened Climbing Galaxias (Galaxias brevipinnis) have also been recorded from further upstream over the past 10 years.
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 landuses.