A total of 26 sites were sampled from streams in the Adelaide Plains and Western Mount Lofty Ranges that drain into the Gulf St Vincent and Southern Ocean. Sites were selected from stream reaches that had not been assessed for 10–20 years, and included sampling from both the lower and upper reaches of target streams (Inman, Gawler, South Para, Sturt and Onkaparinga River catchments) to provide an understanding of changes that occur with changes in elevation. Sites were also sampled from the urbanised part of the Little Para River and a few coastal streams on the Fleurieu Peninsula that are dominated by agricultural and urban land uses.
Sites monitored in 2021 were considered to be in a Good to Very Poor condition. No sites were assigned Excellent or Very Good condition, and given the scale of vegetation clearance in the region, it is unlikely that any stream remains unaffected by human activities.
Of the sites assessed, 10 sites (38%) were in Good condition, with little change to animal and plant life; 13 sites (50%) were in Fair condition, with moderate changes to animal and plant life and some changes to the way the ecosystems functioned; 2 sites (8%) were in Poor condition with major change to biotic life and the way the ecosystems functioned; and 1 site (4%) was in Very Poor condition with severe changes to aquatic species and ecosystem functioning.
The better sites were located in higher rainfall catchments (>600 mm annual rainfall) from the coastal creeks on the Fleurieu Peninsula (eg Congeratinga River, and Wirra and Waterfall Creeks) and from the Adelaide Plains and Southern Mount Lofty Ranges (eg mid- to upper elevation sites on the Little Para River, and in the Sturt and Onkaparinga River catchments). These sites were characterised by their moderately diverse to diverse macroinvertebrate communities that included several rare, sensitive and flow dependent species, presence of well vegetated riparian zones, waters with low salinity and low to moderate nutrient concentrations.
In contrast, the poorer sites were from cleared or urbanised catchments and were characterised by macroinvertebrate communities dominated by tolerant and generalist species, lacked rare or sensitive species, had riparian habitats that were limited in extent and highly degraded, and their waters were enriched with nutrients and sometimes by fine sediment and high salinity.
The aquatic macroinvertebrate communities of most streams in the region were dominated by a small number of generalist and tolerant species, with low numbers of rare and sensitive species present at the better sites.
Macroinvertebrates commonly present in sampled streams included the amphipod crustacean (Austrochiltonia), introduced snails (Potamopyrgus and Physa), native snails (Glyptophysa), worms, chironomids (including Procladius, Paramerina, Cricotopus, Paratanytarsus, Chironomus, Dicrotendipes and Polypedilum), waterbugs (Micronecta, Agraptocorixa, Microvelia and Anisops), mayflies (Tasmanocoenis), damselflies (Ischnura), dragonflies (Hemicordulia) and caddisflies (Triplectides).
The rare and sensitive species collected from the better sites with flowing riffle habitat included snails (Angrobia), mites (Oxus and Piona), blackfly larvae (Austrosimulium and Simulium), chironomid larvae (Stictocladius, Stempellina, Riethia, Cardiocladius, Thienemaniella and Rheotanytarsus), meniscus midge larvae (Dixidae), biting midge larvae (Ceratopogon), riffle beetles (Simsonia), mayflies (Offadens confluens, Atalophlebia australasica and Thraulophlebia), dragonflies (Hemigomphus), stoneflies (Illiesoperla mayii, Dinotoperla evansi and Austrocerca tasmanica) and caddisflies (Taschorema evansi, Ulmerochorema membrum, Lingora aurata,Triplectides similis, Cheumatopsyche and Lectrides varians).
Other rare and sensitive species collected from the better streams in the region in recent years but were not detected in 2021 included water penny beetles (Sclerocyphon), dipterans (Aphroteniella, Alluauodomyia, Paracnephia and Simulium melatum), mayflies (Centroptilum, Nousia fuscula and Tasmanophlebia), stonefly (Newmanoperla thoreyi) and caddisflies (Tasimia, Atriplectides, Apsilochorema, Orthotrichia, Orphninotrichia, Oxyethira, Anisocentropus and Leptorussa).
Most streams in the region had a narrow 5–10 m wide riparian zone, comprising River Red Gums and often introduced Ash or Willow trees, over an understorey dominated by introduced grasses and weeds.
Sites in better condition, located in the Adelaide Hills and Fleurieu Peninsula, were fresh (salinity mostly <1,000 mg/L), and well oxygenated (>8 mg/L), with nitrogen concentrations ranging from 0.25–0.9 mg/L and phosphorus concentrations ranging from 0.01–0.08 mg/L. These sites were often well shaded and usually had low amounts of phytoplankton and filamentous algae present but aquatic plants sometimes extended over 35% of the stream channel.
Sites in poorer condition in the more urbanised and cleared agricultural areas were fresh to slightly saline (470–1,500 mg/L), sometimes poorly oxygenated, and typically had elevated nitrogen concentrations ranging up to 1.48 mg/L and phosphorus concentrations around 0.07 mg/L. These sites generally had less shade provided by degraded riparian zones lining each stream, and typically supported extensive growths of phytoplankton, filamentous algae and aquatic plants.
Several rare and sensitive macroinvertebrates were recorded in 2021, including several mites, stoneflies, mayflies, dragonflies, caddisflies, beetles and some significant species of dipterans. They were typically found from the better streams in the Adelaide Hills and Fleurieu Peninsula, which were characterised by the presence of large areas of native vegetation in their catchments, flowing freshwater habitats and good water quality.
The most notable species collected included the odonate Hemigomphus from a riffle at the Little Para River at One Tree Hill, adult and larvae elmid beetles Simsonia from Wirra Creek in Willunga, and stonefly nymphs Illiesoperla mayi from riffles in Waitpinga Creek and the Onkaparinga River upstream from Baker’s Gully.
Only a few fishes were recorded in spring 2021, mostly of the introduced mosquitofish from degraded streams but the sampling methods used for invertebrate sampling are not very effective at surveying fish communities. Recent comprehensive fish surveys have shown that a rich assemblage of rare, threatened and significant species occurs in the more permanently flowing freshwater streams in the Western Mount Lofty Ranges, including Mountain Galaxias, Climbing Galaxias, Southern Pygmy Perch, Congolli, Freshwater Catfish and various eels and lampreys (Hammer et al 2009, Schmarr et al 2018).
