Spring Creek, near Wilmington
2012 Aquatic Ecosystem Condition Report

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, bank erosion and weeds dominating the understorey vegetation on the banks but the stream still provided habitat for some rare and sensitive macroinvertebrate species.

A moderately diverse community of at least 22 species of macroinvertebrates was collected from the isolated waterholes in the creek, 4.2 m wide and up to 22 cm deep, in autumn; a shallow, 2 m long puddle was present in spring 2012 but it was too small to sample for aquatic life. The community in autumn was dominated by moderate numbers of baetid mayflies (Cloeon) and chironomids (Paramerina, Larsia, Tanytarsus and Chironomus). It also included smaller numbers of flatworms, molluscs (snail Angrobia and limpet Ferrissia), worms, amphipod crustaceans (Austrochiltonia), beetles (Necterosoma, Macrogyrus and Hydrochus), mosquitoes (Anopheles), leptophlebiid mayflies (Thraulophlebia), waterbugs (Microvelia, Micronecta, Enithares and Anisops), dragonflies (Hemianax papuensis and Hemicordulia tau) and caddisflies (Hellyethira simplex). The most notable features of the community were the collection of a few regionally rare and sensitive species, including the mayfly (Thraulophlebia inconspicua) and beetle (Hydrochus), and large numbers of sensitive but widely distributed baetid mayflies that dominated the pool habitats. Tadpoles, waterbugs and beetles were the only aquatic species seen in the puddle in spring.

The water was fresh (salinity ranged from 544 mg/L in autumn to 718 mg/L when the stream was drying in spring), generally well oxygenated (38-86% saturation), clear to slightly coloured, and with low concentrations of nutrients such as phosphorus (0.02 mg/L) and nitrogen (0.1-0.34 mg/L).

The sediments were dominated by cobble, filamentous algae and detritus, with smaller amounts of pebble, gravel and boulder also present; samples taken from below the surface were grey silts and sands and showed no evidence that the sediments were anaerobic, or lacking in oxygen. About 10 m of the banks at the site showed evidence of erosion caused by sheep accessing the stream; sheep and kangaroo faeces were also deposited throughout edges and banks of the creek.

Only a small amount of phytoplankton was present in autumn but a moderate amount was recorded from the drying puddle in spring (chlorophyll a ranged from 0.14-3.1 µg/L). A type of filamentous alga (Spirogyra) covered over 10% of the site and a similar area was also covered by an aquatic plant (sedge Cyperus gymnocaulos). The extent of algal growth was unexpected given the very low nutrient levels recorded, and indicates that the early signs of nutrient enrichment are starting to cause the build-up of potentially nuisance amounts of algae in this normally rock covered stream. The riparian vegetation was dominated by River Red Gums over sedges, introduced weeds (wild rose) and grasses on the poorly vegetated banks (25-49% vegetative cover). The surrounding vegetation at the site was cleared sheep grazing land with a few scattered wattles and gum trees among introduced grassland.

Spring Creek is a largely natural, autumn-winter flowing, ephemeral stream in the Southern Flinders Ranges that provides habitat for a wide range of aquatic macroinvertebrates, including a few regionally significant and rare species. The upper reaches in the park are likely to provide the best habitat but the lower reaches among agricultural grazing land around the site sampled, still retains sufficient value to support an important component of the aquatic life from the region when it holds water.

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