Merintha Creek, near Wangary
2010 Aquatic Ecosystem Condition Report
- Dry in autumn and saline, isolated pool habitats present in spring.
- Sparse macroinvertebrate community with no rare or sensitive species.
- Obvious signs of moderate to gross nutrient enrichment.
- Riparian vegetation consisted of native trees and introduced grasses.
About the location
Merintha Creek is a small stream in Eyre Peninsula that rises near Wanilla and drains in a south-westerly direction as a discontinuous series of channels and shallow wetland areas, before eventually disappearing as a surface feature in Kellidie Bay Conservation Park. The major land uses are sheep grazing, cropping and minor areas of native vegetation.
The monitoring site was located off Flinders Highway, about eight kilometres south-east of Wangary.
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 relating to the widespread clearance of native vegetation in the catchment, including the nutrient enrichment of the stream. The prolonged drought also contributed to the poor condition of the creek because the normally dry channel had been invaded by terrestrial salt tolerant plants.
A sparse community of about 17 species of macroinvertebrates was collected from isolated pools, up to 65 centimetres deep within the seven metre wide channel, in spring 2010; the stream was dry in autumn. The community was dominated by species tolerant to high salinity and poor water quality, including amphipods (Austrochiltonia australis) and notonectid waterbugs (Anisops). It also included low numbers of turbellarians, snails (Coxiella), dytiscid beetles, mosquitoes, soldierflies, chironomids, odonates and leptocerid caddisflies. No sensitive or rare species were found.
The water was saline (salinity of 6,822 mg/L), well oxygenated (61% saturation), clear and slightly coloured, with moderate to high concentrations of nutrients such as nitrogen (1.98 mg/L) and phosphorus (0.06 mg/L).
The sediments were dominated by detritus, clay and sand; samples taken from below the surface showed no signs of being anaerobic and lacking in oxygen.
Filamentous algae (Enteromorpha) covered more than 10% of the site in spring. No aquatic plants were growing in the channel but a salt tolerant, terrestrial plant called samphire was present on the edges of the water and on the banks.
The riparian zone consisted of native paperbark and gum trees over a groundcover of introduced grasses. The surrounding vegetation was cereal cropping land with a few patches of native woodland that were dominated by paperbarks and gums.
Special environmental features
None detected apart from the presence of one adult dytiscid beetle (Platynectes decempunctatus) that is normally found in flowing stream habitats. This beetle may have been using the pool habitats in Merintha Creek as a temporary refuge because it is capable of flying to other more suitable habitats when the stream dries over summer.
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.|