Coonta Creek, near Tumby Bay
2010 Aquatic Ecosystem Condition Report
- Dry in autumn and flowing, freshwater stream in 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
Coonta Creek is a small stream in Eyre Peninsula that rises near Pillaworta and flows in an easterly direction before discharging into an intermittent swamp south of Tumby Bay, about four kilometres from Spencer Gulf. The major land uses are sheep grazing and cropping, and a disused mine occurs in the upper reaches. The monitoring site was located downstream from Foothills Road, about nine kilometres 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, bank erosion and a lack of vegetative cover in the riparian zone.
A sparse community of about 16 species of macroinvertebrates was collected from this flowing creek, two metres wide and 45 cm deep, in spring 2010; the site was dry in autumn. The community was dominated by species tolerant to poor water quality such as dytiscid beetles and dragonfly nymphs in the edge habitats and blackfly larvae (Simulium ornatipes) in the flowing riffle habitats. Several species of dytiscid and hydrophilid beetles were collected at the site, along with low numbers of chironomids, waterbugs, damselflies and caddisflies. No sensitive or rare species were found.
The sediments were dominated by cobbles and algae, with some pebbles and detritus also present. The sediment was not blackened and showed no signs of lacking oxygen. More than 10 metres of the bank showed evidence of erosion, due to stock damage.
Sedges (Cyperus), rushes (Juncus) and small amounts of clubrush (Isolepis) were growing in the channel and on the water’s edge and filamentous algae (Cladophora and Spirogyra) covered more than 65% of the site in spring.
The riparian zone consisted mainly of introduced grasses and weeds with cropping land and sheep grazing occurring on the surrounding landscape.
Special environmental features
Coonta Creek was noteworthy because it was a flowing freshwater stream that supported at least two flow-dependent species (blackfly Simulium ornatipes and dytiscid beetle Platynectes) in spring 2010. Only two other streams had salinities less than 3,000 mg/L when the region was sampled in 2010 and only six streams had sufficient flowing water present to sample during the spring survey period. Previous work in the catchment has also collected several other rare species for the region (eg caddisflies Ecnomus cygnitus and Hellyethira simplex), so the creek has supported a richer range of species in the past.
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).|