Tunkalilla Creek rises near Parawa on the bottom of the Fleurieu Peninsula and flows in a southerly direction to the Southern Ocean. The swamps in the upper part of the Tunkalilla catchment have been included in a group of wetland habitats 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 1,616 hectare catchment are grazing pastures (64%), native vegetation (12%) and softwood production (7.5%). The monitoring site was located between Eric Bonython Conservation Park and Rymill Road, about 4 kilometres south from Parawa.
In summary
The creek was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure, and some changes to the way the ecosystem functions. There was evidence of human disturbance including nutrient enrichment, fine sediment deposition and weeds dominating the understorey vegetation on the banks but the stream still provided habitat for some rare and sensitive macroinvertebrate species.
Findings
A diverse community of at least 48 species of macroinvertebrates was collected from this flowing creek, 2.5 m wide and up to 70 cm deep in spring 2011 and autumn 2012. While the creek was flowing well in autumn 2012, only a small amount of flowing habitat (riffle) was present in spring 2011 when no animals typically found in riffle habitat were seen. The community consisted of a range of generalist and pollution tolerant taxa as well as some sensitive species. Amphipods (scuds) and non-biting midges dominated the edge habitat of the pools at this site, while worms and the non-biting midge Rheotanytarsus dominated the fast-flowing habitat. Other species collected in smaller numbers included three different types of mites, five beetles, dance fly larvae, 13 different types of non-biting midges, waterbugs and four types of dragonflies. Many sensitive and rare species were also found including the non-biting midge Stictocladius, two species of flow-dependent blackfly larvae (Austrosimulium and Simulium), mayflies (Offadens, Atalophlebia and Thraulophlebia), a stonefly (Austrocerca) and caddisflies (Taschorema, Oxyethira, and Triplectides similis). Yabbies and stonefly adults were also seen in and around the creek and the frog Crinia was heard. The threatened native fish Climbing Galaxias (Galaxias brevipinnis), and a rare mayfly (Nousia fuscula) and caddisfly (Atriplectides dubius) have been collected from this creek in the past.
The water was fresh (salinity ranged from 164-241 mg/L), well oxygenated (80-89% saturation) and clear, with high concentrations of nutrients such as nitrogen (0.7-1.02 mg/L) and phosphorus (0.02-0.04 mg/L).
The sediments were dominated by silt with some detritus also present. Samples taken from below the surface were grey/brown and showed no evidence of being anaerobic, or lacking oxygen. Large deposits of silt covered the streambed to a depth greater than 10 cm in places and a small amount of bank erosion was evident due to cattle trampling.
A small amount of phytoplankton (chlorophyll a ranged from 1.4-2.28 µg/L) was recorded but no filamentous algae was seen. More than 90% of the site was covered by aquatic plants, with extensive amounts of knotweed (Polygonum) at the site. Other emergent plants such as Eleocharis, Juncus, Rorrippa, Schoenoplectus and Triglochin were also present. The riparian zone comprised mainly grasses, Juncus, blackberries, Melaleuca and knotweed. The surrounding vegetation at the site was native vegetation with eucalypts, bracken, yaccas, Acacia and Melaleuca present, as well as some blackberry bushes.
Special environmental values
Tunkalilla Creek provides important habitat for a number of rare, sensitive and flow-dependent aquatic macroinvertebrates.