Pillaworta Creek, near Koppio
2010 Aquatic Ecosystem Condition Report
- Permanently wet saline stream with small areas of flowing habitat only present in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Large deposit of ash in the channel from the 2005 bushfire.
- Riparian vegetation comprises mostly native species, regenerating after the fire.
About the location
Pillaworta Creek is a small stream in Eyre Peninsula that rises north of Pillaworta Hill and flows in a south-westerly direction into the Tod River. Flow from the creek can also be diverted into the Tod Reservoir via an open, concrete-lined aqueduct at a weir located near the downstream extent of the stream. The major land uses are sheep grazing and cropping, with small areas of native vegetation remaining along the creekline.
The monitoring site was located at the diversion weir that was accessed from a track off Pillaworta Road, about three kilometres east of Koppio.
The creek was given a Fair rating because the site sampled showed moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance, including nutrient enrichment, heavy siltation and ash deposited in the stream from a recent fire in the catchment in 2005.
A sparse community of about 23 species of macroinvertebrates was collected from the creek, eight metres wide and 60 centimetres deep, in autumn and spring 2010. Small areas of slow-flowing riffle habitats were only present in spring but were too small to sample. The community was dominated by species that are tolerant to poor water quality such as amphipod crustaceans and chironomids. Mites, beetles, soldierfly larvae, waterbugs, damselflies and leptocerid caddisflies were also present. No sensitive or rare species were found.
The water was saline (salinity of 7,043 mg/L in autumn and 3,860 mg/L in spring), well oxygenated (86–103% saturation) and clear, with moderate to high concentrations of nutrients such as nitrogen (0.6–0.9 mg/L) and phosphorus (0.03–0.06 mg/L).
The sediments were dominated by silt, detritus and algae. Heavy sedimentation was evident at the site due to the presence of a layer of silt and ash more than 10 centimetres deep over the bottom of the creek. The sediments were blackened and anaerobic below the surface, indicating that too much organic matter had entered the creek in the past.
More than 10% of the site was covered by filamentous algae (Spirogyra and Cladophora), and emergent plants (Juncus, Bolboschoenus, Isolepis and Cotula) covered a similar area in both autumn and spring.
The riparian zone consisted of patches of native trees (acacias and eucalypts) with some native shrubs, rushes and samphire. Many young gum trees had germinated in the riparian zone as a result of the 2005 bushfire but weeds and grasses dominated the understorey. The surrounding vegetation was cropping land.
Special environmental features
Pressures and management responses
|Bushfire in the catchment (2005), causing sediment erosion (habitat disturbance).||Bushfires are disturbances that can occur naturally. The affected area can take approximately five years or more to naturally recover.|
|Livestock have direct access at the site and upstream in the catchment, causing sediment erosion and adding excessive nutrients (which leads to habitat disturbance, algal growth and aquatic weeds).||The Eyre Peninsula NRM Board promotes managing land to improve water quality. This includes incentives for waterway and wetland fencing to exclude or limit stock from entering riparian zones and the best practice managements of springs, soaks and waterholes as stock water supplies.|
|Extensive weed growth in the riparian zone at the site and upstream in the catchment (causing habitat disturbance).||The Eyre Peninsula NRM Board has several pest plant (weed) mitigation and control programs. We work closely with landholders to control weeds on their property and to help stop the spread to other properties and waterways.|