Cox Creek, near Stirling
2008 Aquatic Ecosystem Condition Report
- Affected by nutrient enrichment and fine sediments.
- Macroinvertebrate community dominated by species tolerant of pollution.
- Excessive growths of algae and aquatic plants.
- Degraded riparian vegetation.
About the location
Cox Creek is a small perennial stream in the Piccadilly Valley of the Mount Lofty Ranges, which flows into the Onkaparinga River, downstream from Bridgewater. Small areas of native vegetation grow on the steeper slopes of its headwaters. Livestock grazing, viticulture and intensive horticulture are the major land uses on the gentler slopes and valley floor of the catchment which also includes the townships of Uraidla, Bridgewater and Aldgate.
The site selected for monitoring was located in the mid-reaches of the catchment, opposite the Mount Lofty Golf Course on Carey Gully Road, about two kilometres north of Stirling. A sedimentation basin and in-stream wetland had recently been installed just upstream from the site, providing some ability to trap excess nutrients and fine sediments from the catchment.
The creek was given a Poor rating at this site because the ecosystem showed evidence of major changes in the animal community and plant life, and moderate changes to the way the ecosystem functions due to excessive loads of nutrients and fine sediment.
Fast-flowing riffle habitats connected pools of variable depth at the site when it was sampled in October 2008.
A moderately diverse community of macroinvertebrates was collected, with 32 species recorded from the edges of the pools and 29 species from the riffles. Large numbers of species tolerant of pollution dominated the community, including small snails of an unidentified species, worms and chironomids (Cricotopus). Two introduced snails were also common at the site. Most of the community comprised species that feed on decaying plant matter, although a small number of species more sensitive to pollution were also collected.
The water was fresh (salinity of 276 mg/L), well oxygenated (98% saturation), and clear. It contained moderate to high concentrations of nutrients such as nitrogen (0.56 mg/L) and phosphorus (0.05 mg/L).
Large growths of green filamentous algae covered up to 65% of the bottom of the creek. A wide range of aquatic plants were growing in the stream and along its edges, including patches of introduced weeds such as mint (Mentha), Watercress (Rorippa nasturtium-aquaticum), buttercups (Ranunculus) and Alisma (Alisma lanceolatum); and native plants such as Pacific Azolla (Azolla filiculoides), duckweed (Spirodela), and Blunt Pondweed (Potamogeton ochreatus). Various sedges and rushes were found on the edges, including spikerush (Eleocharis), knotweed (Persicaria) and clubrush (Isolepis).
The sediments were mostly detritus, sand, silt and algae; in some areas the silt was blackened but not obviously anaerobic at the time of sampling. However, given the large amount of algae and detritus found in the creek, it is likely the sediments would turn anaerobic whenever water flows reduce to a trickle.
River Red Gums and exotic, deciduous trees grew over woody weeds such as broom and bamboo in the riparian zone. The understorey also comprised mainly introduced weeds and grasses such as Narrow-leafed Vetch (Vicia satira), mallow (Malva) and phalaris. The surrounding vegetation was mostly eucalypt woodland over introduced grasses.
Special environmental features
Cox Creek provides habitat for several notable species including a predatory caddisfly (Taschorema evansi), and two stoneflies(Austrocerca tasmanica and Illiesoperla mayi).
Pressures and management responses
|Extensive deciduous tree growth 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.|
|Large nutrient inputs from numerous diffuse sources in the catchment (leading to extensive growth of algae and aquatic weeds).||The Adelaide and Mount Lofty Ranges NRM Board's land management program encourages and promotes managing land to improve water quality. This includes working with industry and landholders to ensure efficient use of fertilisers and discuss ways to reduce runoff of nutrients into waterways.|
|Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||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.|
|Large decrease in natural water flows (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.|
This aquatic ecosystem condition report is based on monitoring data collected by the EPA and prepared in conjunction with the Adelaide and Mt Lofty Ranges NRM Board.