Riparian vegetation consists of mostly introduced weedy species and gum trees with cattle grazing beyond
Area map
About the location
Congeratinga Creek is a small network of streams which rises in the Second Valley Forest on Fleurieu Peninsula. It flows through land used mainly for pine plantations (46%) and grazing livestock (37%), into the Wirrina Reservoir. The site selected for monitoring was located off Main South Road, just over one kilometre northeast of Second Valley.
The creek was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure, and some changes to the way the ecosystem functions. There was evidence of human disturbance including emerging signs of nutrient enrichment and the presence of weeds in the riparian zones. The stream provided habitat for few rare and sensitive macroinvertebrate species.
Findings
A sparse community of at least 16 species of macroinvertebrates was collected from this connected flowing creek, approximately 4.3 m wide and 22 cm deep, in autumn 2015 but the creek was dry in spring. The site was dominated by non-biting midges. Other species collected in smaller numbers included a range of generalist and pollution tolerant species, such as snails, beetles, and backswimmers. Some sensitive and rare species, as well as flow-dependent species, were also collected, including the blackfly larvae (Simulium), the non-biting midge Podonomopsis and the stonefly Riekoperla. The introduced snail Physiella and yabbies were also seen in the creek.
The water was brackish (salinity was 1186 mg/L), well oxygenated (87% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (0.74 mg/L) and phosphorus (0.034 mg/L). Some froth was seen on the water’s surface in autumn.
The sediments were dominated by boulders and cobbles and pebbles with some detritus also present. Samples taken from below the surface were grey clay with silt present and showed no evidence of being anaerobic, or lacking oxygen. Only small deposits of silt covered the streambed to a depth of about 1 cm in places and less than 10% of the bank was effected by erosion, likely due to cattle and sheep trampling the banks, which was evident by the faeces deposited on the banks of the creek and within the channel.
A small amount of phytoplankton (chlorophyll a 0.88 µg/L) but no filamentous algae was noticed at the site. Less than 10% of the site was covered by aquatic plants with Cyperus and Rumex only sparsely present. The riparian zone consisted of gum trees with an understorey of sedges, blackberries and other weeds. The surrounding vegetation was pasture grass for cattle grazing.
Special environmental features
Congeratinga Creek provides habitat for the flow-dependent blackfly larvae, the non-biting midge Podonomopsis and the stonefly Riekoperla.
Pressures and Management Responses
Pressures
Management responses
Widespread introduced weeds in the riparian zone at the site and upstream (reducing habitat quality).
The Adelaide and Mount Lofty Ranges NRM Board has several pest plant (weed) mitigation and control programs. They work closely with landholders to control weeds on their property and to help stop the spread to other properties and waterways.
Livestock having direct access at the site and upstream (causing sediment erosion and adding excessive nutrients).
The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes incentives for waterway and wetland fencing to exclude or limit stock from entering riparian zones.
This aquatic ecosystem condition report is based on monitoring data collected by the EPA. It was prepared with and co-funded by the Adelaide and Mount Lofty Ranges NRM Board.
Observed Condition
Expected Condition
