Callawonga Creek, downstream of Gold Diggings Swamp
2012 Aquatic Ecosystem Condition Report
Permanently wet freshwater creek with slow flowing water in spring 2011 and autumn 2012
Diverse macroinvertebrate community with many rare and sensitive species
Emerging signs of nutrient enrichment
Riparian vegetation was mostly native species but included weeds and grasses
About the location
Callawonga Creek rises near Parawa and flows in a southerly direction towards the Southern Ocean. The swamps in the upper part of its catchment are some of the most intact natural swamps still existing on the Fleurieu Peninsula. The Gold Diggings Swamp (part of the Callawonga Creek system) is considered to be one of the most environmentally significant swamps in the region and included in the group known as the Fleurieu Peninsula Swamps, which have been listed as ‘critically endangered’ under the Environment Protection and Biodiversity Conservation Act 1999. The major land uses in the 1,264 hectare catchment are grazing pastures (66%), native vegetation (23%) and softwood production (5.5%). The monitoring site was located just upstream of Taylor Road, about 3 kilometres south from Parawa.
The creek was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was evidence of human disturbance including emerging signs of nutrient enrichment and weedy riparian zones but the stream provides habitat for several rare and sensitive species of macroinvertebrates.
A diverse community of at least 44 species of macroinvertebrates was collected from the pools of this slow-flowing, 1.5 m wide and up to 43 cm deep creek in spring 2011 and autumn 2012. The community was dominated by amphipods (scuds) and the non-biting midge Tanytarsus with other pollution tolerant species present in smaller numbers, including three types of snail, four different mites, at least 9 species of non-biting midge and two species of dragonfly. Many sensitive and rare species were also found including the non-biting midges Aphroteniella and Stenochironomus, the mayflies Atalophlebia and Thraulophlebia, the dragonfly Synthemis austalacta, the stoneflies Illiesoperla and Austrocerca and the caddisflies Taschorema, Oxyethira, Atriplectides, and Triplectides similis. The frog Crinia was also heard calling at the site. The snail Potamopyrgus was the only introduced species found at the site.
The water was fresh (salinity ranged from 250-367 mg/L), well oxygenated (81-83% saturation) and clear, with high concentrations of nutrients such as nitrogen (0.47-1.06 mg/L) and phosphorus (0.02-0.04 mg/L).
The sediments were dominated by clay and detritus. Samples taken from below the surface were brown clays and showed no evidence of being anaerobic or lacking oxygen. Only small deposits of silt covered the streambed to a depth of about 1 cm in places and only small areas of bank erosion were seen due to undercutting of the banks.
A small amount of phytoplankton (chlorophyll a ranged from 0.55-1.13 µg/L) was recorded but no filamentous algae was seen. More than 10% of the site was covered by aquatic plants, including the emergent plants Carex, Eleocharis, Isolepis, Schoenoplectus, Triglochin and Gahnia. The riparian zone comprised bracken, Gahnia, Juncus, Carex and introduced grasses and weeds. The surrounding vegetation was mainly native scrubland with bracken, eucalypts, and wattles present.
Special environmental values
Callawonga Creek provides important habitat for a number of rare, sensitive and flow-dependent aquatic macroinvertebrates and a wide range of aquatic plants for the region.
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