Rock Valley Creek, near Koppio
2015 Aquatic Ecosystem Condition Report
Slow to non-flowing saline stream in autumn and dry in spring
Sparse macroinvertebrate community with no rare or sensitive species
Obvious signs of moderate to gross nutrient enrichment
Riparian vegetation limited to introduced grasses, rushes and sedges
About the location
Rock Valley Creek is a small stream in Eyre Peninsula that rises near Pillaworta Hill and flows in a south-westerly direction, where it discharges into the Tod River upstream from the reservoir. The major land uses are sheep grazing and cropping. The monitoring site was located downstream from the disused Koppio Mine off Rock Valley Road, about five kilometres south-east from Koppio.
The creek was given a very poor rating because the site sampled showed evidence of major changes in ecosystem structure and a significant breakdown to the way the ecosystem functions. There was considerable evidence of human disturbance, including nutrient enrichment, high salinity and a lack of vegetative cover in the riparian zone.
A sparse community of about 11 species of macroinvertebrates was collected or seen from the creek, up to 3.2 metres wide and 38 centimetres deep, in autumn; the creek was dry in spring 2015. The community was dominated by large numbers chironomids (Chironomus and Tanytarsus) and included smaller numbers of a few other generalist and tolerant macroinvertebrates, such as yabbies (Cherax), waterbugs (Anisops), mosquitoes (Culex and Aedes) and beetles (including Berosus, Necterosoma and Lancetes). No sensitive or rare species were recorded.
The water was saline (salinity of 8,399 mg/L), well oxygenated (88% saturation), clear and slightly coloured, and with high concentrations of nutrients such as nitrogen (1.13 mg/L) and phosphorus (0.08 mg/L).
The sediments were dominated by detritus, gravel, clay and sand but also included cobble, pebble and silt. Samples taken from below the surface were grey clays and silts that released sulfide when tested in autumn, indicating that the sediments lacked oxygen and were a harsh environment for most benthic species to inhabit. About 10% of the site showed signed of bank erosion, presumably caused by a lack of vegetative cover, past flood damage and both sheep and kangaroo grazing activity on the banks.
A moderate growth of phytoplankton (chlorophyll a 4.8-µg/L) was recorded at the site but there was no sign of any filamentous algae during the year. Over 10% of the channel and edges of the creek were covered by a type of submerged plant (Ruppia). The riparian zone was very limited in extent (<5 metres wide), lacked any trees or shrubs and was only vegetated with introduced grasses and a few rushes (Juncus) and sedges (Isolepis). The surrounding vegetation consisted of extensively cleared cropping and grazing land (sheep and cattle) with only a few scattered gums remaining in the local landscape.
Special environmental features
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. The Eyre Peninsula NRM Board continues to promote managing land to improve water quality. This includes incentives for:
|Limited natural riparian vegetation at the site and upstream in the catchment, providing minimal buffer protection from catchment land uses.|