Tributary of Waitpinga Creek, 13 km south-west from Encounter Bay
2011 Aquatic Ecosystem Condition Report
- Permanently wet, saline, slow-flowing creek in autumn and spring 2011
- Sparse macroinvertebrate community with no rare or sensitive species
- Obvious signs of gross nutrient enrichment and salinisation
- Riparian vegetation limited in extent and dominated by emergent plants and weeds
- Some bank erosion and fine sediment deposited in the creek
About the location
Tributary of Waitpinga Creek is a small stream in the Southern Mount Lofty Ranges that rises east from ‘Coolawang’ and flows south-east into Waitpinga Creek, which ultimately flows onto Waitpinga Beach in the Southern Ocean. The monitoring site was located off Waitpinga Road, about 2 km north-west from Waitpinga Hill and 13 km south-west from Encounter Bay on the Fleurieu Peninsula. The major land use in the 187 hectare catchment is stock grazing, with smaller areas used for cereal cropping, roads and remnant native vegetation.
The creek was given a Very Poor rating because the site sampled showed evidence of major changes to both the animal and plant life inhabiting the stream, and a significant breakdown in the way the ecosystem functions. There was considerable evidence of human disturbance including nutrient enrichment, stream salinisation, degraded riparian habitats, silt deposition and bank erosion.
A sparse community of at least 19 species of macroinvertebrates was collected from the slow-flowing creek, 0.9-1.6 m wide and up to 11 cm deep, in autumn and spring 2011. The community was dominated by generalists and species tolerant to poor water quality such as chironomids, waterbugs (Micronecta) and amphipods (Austrochiltonia) in autumn but no species was abundant in spring. Other members of the community collected in low numbers included an introduced snail (Potamopyrgus), worms, marsh beetles, mosquitoes, biting midges, several types of waterbugs, damselflies and dragonflies. No sensitive, rare or flow-dependent species were collected and no fish were seen at the site in 2011.
The water was saline (salinity ranged from 4,522-4,701 mg/L), well oxygenated (101-125% saturated) and clear, with moderate to high concentrations of nutrients such as nitrogen (0.62-0.95 mg/L) and phosphorus (0.03-0.04 mg/L).
The sediments were dominated by detritus, algae and silt, with bedrock, boulder, cobble and sand also present. Samples taken from below the surface were blackened, sulfidic and anaerobic, indicating that the sediments lacked oxygen and were a harsh environment for burrowing animals to live in. A large deposit of fine silt, 5-10 cm deep, covered the channel in places and some minor bank erosion, covering less than 10 m of the site, was recorded in autumn when cattle had trampled the edges of the creek.
A large phytoplankton bloom was present in autumn and extensive growths of filamentous algae (mostly Cladophora and Enteromorpha) covered up to 65% of the channel in 2011. Over 10% of the creek was also covered by emergent aquatic plants (Cyperus, Juncus, introduced Rorippa, Rumex and Cotula). The riparian zone was limited in extent and included a few gum trees over an extensive understorey of sedges, rushes, introduced grasses and woody weeds such as gorse. The surrounding vegetation was grazing land with a few gum trees located towards the creekline.
Special environmental features
Pressures and management responses
|Insufficient natural water flows in the creek resulting from water extraction and climate variability (reducing ecological integrity.||Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.|
|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.|
|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.|
|Limited riparian zone vegetation at the creek and upstream (reducing habitat quality, increasing sediment erosion).||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 revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion.|
|Saline groundwater inflows to the creek (reducing ecological integrity).||The Adelaide and Mount Lofty Ranges NRM Board has installed telemetered groundwater monitoring stations at key locations within the region. These are monitored for level and salinity; unusual results (such as high salinity influxes) are investigated.|
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