Yankalilla Creek, near Normanville
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.
- Limited riparian vegetation.
- Despite the impact of human activities provides habitat to notable species.
About the location
Yankalilla Creek is a coastal stream which rises about four kilometres east of Yankalilla on the Fleurieu Peninsula, and flows west through Yankalilla and Normanville before discharging into Yankalilla Bay in Gulf St Vincent. Most of the upstream catchment is devoted to livestock grazing (47%) and dairying (29%), with smaller areas of forestry, protected vegetation, horticulture and urban living.
The site selected for monitoring was located off Hay Flat Road, south of Normanville, in the lower reaches of the creek.
The creek was given a Fair rating at this site because the ecosystem showed moderate changes to animal and plant life, and some changes to the way the ecosystem functions. Nutrient levels were moderately high, and the riparian zone was limited and dominated by weeds.
At the time of sampling in December 2008 the creek was made up of a series of pools ranging in width from one to over four metres, connected by small areas of slow-flowing riffles. The pools were more than 50 cm deep in places.
A diverse community of 44 macroinvertebrate species was found in the pools, including 10 species of flies and seven species of caddisflies, as well as beetles, bugs and molluscs. The community was dominated by large numbers of species tolerant to pollution, including small crustaceans or water scuds (Austrochiltonia australis), chironomids (Procladius) and worms. There were only low numbers of more sensitive and rare species collected. No mites, roundworms and stoneflies were collected despite the presence of suitable habitat.
The water was moderately fresh (salinity of 1,399 mg/L) and moderately well oxygenated (43% saturation). However, it was strongly coloured and cloudy or turbid, with high concentrations of nutrients such as nitrogen (1.2 mg/L), phosphorus (0.11 mg/L) and organic carbon (20.3 mg/L). Algal growths in the creek were significant with moderate amounts of phytoplankton, and up to 35% of the water’s surface was covered in green filamentous algae (Cladophora and Spirogyra).
Aquatic plants covered up to 65% of the creek, including Narrow-leafed Cumbungi (Typha domingensis), Common Reed (Phragmites australis), Jointed Rush (Juncus articulatus), Water Ribbons (Triglochin procerum), Waterbuttons (Cotula coronopifolia), Pacific Azolla (Azolla filiculoides) and duckweed (Spirodela).
A narrow strip of River Red Gums, introduced grasses, gorse bushes and daisies formed the riparian zone. Cereal crops grew over most of the surrounding area which had only a few remnant native gum trees.
Special environmental features
The creek provides habitat for at least two notable species of mayflies (Atalophlebia and Koorrnonga inconspicua) and five different caddisflies (Hellyethira, Lectrides varians, Oecetis, Triplectides australis and Triplectides similis). A single shrub of the once common native tea-tree (Leptospermum) remained in the riparian zone.
Pressures and management responses
|Livestock have direct access at the site and upstream, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth 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 incentives for waterway and wetland fencing to exclude or limit stock from entering riparian zones.|
|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.|
|Extensive weed 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.|
This aquatic ecosystem condition report is based on monitoring data collected by the EPA and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.