Waterfall Creek, near Wadella Falls
2010 Aquatic Ecosystem Condition Report
- Permanently wet, saline stream with slow-flowing riffle habitats present in both autumn and spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation limited to introduced grasses and weeds.
About the location
Waterfall Creek is a small stream in Eyre Peninsula that rises east of Yallunda Flat and flows in an easterly direction before discharging into Mine Creek. The major land uses are cropping and grazing (sheep and cattle), with some areas of native vegetation present in the upper reaches.
The monitoring site was located in the lower reaches of the creek off Wadella Falls Road, about 10 kilometres north-west of Tumby Bay.
The creek was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and moderate changes to the way the ecosystem functions. There was considerable evidence of human disturbance, including nutrient enrichment, fine sediment deposition and a lack of vegetative cover in the riparian zone.
A sparse community of about 16 species of macroinvertebrates was collected from the slow-flowing creek, 5–9 metres wide and up to 30 centimetres deep, in autumn and spring 2010. The community was dominated by species tolerant to high salinity and poor water quality such as amphipods (Austrochiltonia), hypogastrurid springtails, chironomids (Procladius, Tanytarsus and Chironomus) and small snails (including Coxiella). It also included small numbers of isopods, beetles, mosquitoes, soldierflies, waterbugs and odonates. No sensitive or rare species were found and no flow-dependent species were collected, despite the presence of small areas of riffles in both autumn and spring.
The water was saline (salinity of 10,584 mg/L in autumn and 7,889 mg/L in spring), moderately well oxygenated (42–47% saturation), slightly turbid and coloured, with moderate to high concentrations of nutrients such as nitrogen (0.68–1.34 mg/L) and phosphorus (0.03–0.11 mg/L).
The sediments were dominated by detritus but also included silt, clay, algae and boulders; samples taken from below the surface were sulfidic and black in some places, which indicates that too much organic matter had entered the creek in the past. A moderately thick deposit of 1–5 centimetres of silt was recorded in the creekbed in spring.
Filamentous algae (Cladophora) covered more than 10% of the channel and over 35% of the site was covered by aquatic plants such as a stonewort (Chara) growing in the water and a sedge (Baumea) and rush (Juncus) growing on the water’s edge and banks.
The riparian zone consisted of introduced grasses, thistles and sedges, with a few gum trees also present. The surrounding vegetation at the site was cropping land and grazed grassland.
Special environmental features
Pressures and management responses
|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:
|Limited natural riparian vegetation at the site and upstream in the catchment, providing minimal buffer protection from catchment landuses (reducing habitat quality).|
|Saline groundwater inflow (reducing ecological integrity)||The Eyre Peninsula NRM Board promotes the revegetation of recharge areas known to contribute to dryland salinity and encourages the adoption of perennial pastures as an alternative to annual cropping in these areas.|