Salt Creek, near Mangalo
2010 Aquatic Ecosystem Condition Report
- Dry in autumn and slightly flowing, very saline stream in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of gross nutrient enrichment.
- Riparian vegetation dominated by samphire and introduced grasses.
- Moderately eroded banks due to unstable soils and extensive vegetation clearance.
About the location
Salt Creek is the largest stream in Eyre Peninsula, rising about 20 kilometres west of Mangalo and flowing in an easterly direction before eventually draining onto the Uteralitera Plain to the north of Franklin Harbour. The major land uses are cropping and grazing.
The monitoring site was located off Mangalo Road in Mangalo.
The creek was given a Very Poor rating because the site sampled showed the ecosystem was in a severely degraded condition with major changes to both the animal and plant life, and a significant breakdown in the way the ecosystem functions because of human impact. There was considerable evidence of nutrient enrichment, bank erosion, lack of riparian vegetation and high salinity affecting the biological condition of this creek.
A very low diversity of about eight species of macroinvertebrates was collected from the slightly flowing channel, eight metres wide and less than 10 centimetres deep, in spring 2010; the site was dry in autumn. The community was dominated by large numbers of species tolerant to high salinity and poor water quality including amphipods, mosquitoes and one species of chironomid (Tanytarsus barbitarsis). There was also an unusually large number of zooplankton or micro-crustaceans (seed shrimps and copepods) specimens present in the stream. Three species of beetles and two types of fly larvae that frequently occur in saline waters were also present. No sensitive or rare species were found.
The water was saline (salinity of 21,865 mg/L), well oxygenated (100% saturation), slightly turbid and coloured, with moderate to high concentrations of nutrients such as nitrogen (2.28 mg/L) and phosphorus (0.02 mg/L).
The sediments were dominated by sand with some pebbles, gravel, clay and algae also present. There were no indications that the sediment was lacking in oxygen, presumably due to the high sand content and general lack of organic matter. More than 10 metres of the site was affected by bank erosion, presumably due to the unstable sandy soils and extent of vegetation clearance in the catchment.
Filamentous algae (Cladophora) covered more than 35% of the site in spring. No aquatic plants were found growing in the channel because the high salinity would limit the types of plants that could colonise and grow in this ephemeral stream.
The riparian zone was mainly samphire and introduced grasses, and the surrounding vegetation consisted of crops and saltbush with a few scattered gums and pine trees.
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.|