Pokalalie Creek, near Mangalo
2010 Aquatic Ecosystem Condition Report
- Dry in autumn and saline isolated pools present in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate nutrient enrichment.
- Riparian vegetation limited to grasses, sedges and saltbush.
About the location
Pokalalie Creek is a small stream in Eyre Peninsula that rises west of Pootitnie Hill and drains northwards before discharging into Salt Creek. The major land uses are cropping and grazing, with areas of native vegetation in the upper catchment.
The monitoring site was located off the Cowell–Mangalo Road, about two kilometres south-east of Mangalo.
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, poor riparian habitat and fine sediment deposition.
A sparse community of about 14 species of macroinvertebrates was collected from isolated pools in the nine metre wide, 40 centimetre deep channel in spring 2010; the site was dry in autumn. The community was dominated by species tolerant to high salinity and poor water quality such as amphipods (Austrochiltonia australis) and chironomids (including Procladius, Tanytarsus and Chironomus). It also included smaller numbers of several other saline tolerant macroinvertebrates such as beetles, mosquitoes, craneflies, soldierflies, a notonectid waterbug, and a damselfly and dragonfly. No sensitive or rare species were found.
The water was saline (salinity of 11,618 mg/L), well oxygenated (91% saturation), slightly turbid and coloured, with moderate to high concentrations of nutrients such as nitrogen (0.86 mg/L) and phosphorus (0.02 mg/L).
The sediments were dominated by detritus, gravel, clay and sand; samples taken from below the surface were blackened, sulfidic and anaerobic, indicating that too much organic material had entered the creek in the past. A moderately thick deposit of 1-5 centimetres of silt covered the creekbed in places.
Filamentous algae (Cladophora) covered less than 10% of the site in spring and dried algal deposits were not noted when the site was inspected in autumn. More than 10% of the channel was covered in aquatic plants, with a submerged stonewort (Chara) growing in the channel and an emergent rush (Juncus) growing on the water’s edge and banks.
The riparian zone was very limited on one bank and only slightly more extensive on the other. It consisted of introduced grasses, saltbush, samphire, rushes and native shrubs under a patchy canopy of blue gums and pines. The surrounding vegetation at the site was a cereal crop with no remnant vegetation evident near the stream.
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.|