The Deep Creek, Deep Creek Conservation Park
2013 Aquatic Ecosystem Condition Report

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 due to recreational use around the banks and evidence of nutrient enrichment but the stream provides habitat for many rare, sensitive and flow-dependent species of macroinvertebrates.

A diverse community of at least 34 species of macroinvertebrates was collected from the creek (13 species in autumn and 27 in spring), 2.3-5.2 m wide and up to 70 cm deep, in autumn and spring 2013. The creek consisted of still to slow-flowing deep pools that were connected by shallow, fast-flowing riffle habitats in both seasons sampled; in autumn, riffles comprised tiny areas of the channel whereas in spring, riffles were more extensive and covered about 65% of the stream. The community was dominated by moderate numbers of amphipods (Austrochiltonia australis), with blackflies (Austrosimulium furiosum and Simulium melatum), leptophlebiid mayflies (Atalophlebia australasica and Thraulophlebia inconspicua) and hydropyschid caddisflies (Cheumatopsyche sp. 2) comprising the most abundant members of the riffle community in spring. Lower numbers of a range of macroinvertebrates were also recorded at the site including cnidarians, introduced snails (Potamopyrgus), limpets, worms, introduced marron, beetles, dixid flies, biting midges, chironomids, mayflies, waterbugs, dragonflies, stoneflies and caddisflies. The riffles were too small to sample in autumn but provided habitat for an additional species of blackfly (Simulium ornatipes). Numerous crayfish holes were seen in the wet banks of the creek, which were assumed to be marron burrows. A wide range of rare, sensitive and/or flow-dependent species were recorded, including the stoneflies (Illiesoperla mayii, Newmanoperla thoreyi and Riekoperla naso), caddisflies (Taschorema and Cheumatopsyche) and the above-listed blackflies and leptophlebiid mayflies.

The water was fresh (salinity ranged from 639-885 mg/L), well oxygenated (83-113% saturation), clear and occasionally strongly coloured, and with moderate to high concentrations of nutrients such as phosphorus (0.04-0.05 mg/L) and nitrogen (1.03-1.21 mg/L).

The sediments were dominated by clay, detritus, cobble and silt, with smaller amounts of boulder, sand and filamentous algae also present; samples taken from below the surface were mostly grey clays and silts and showed no signs that the sediments were anaerobic or sulfidic. There was some evidence of bank erosion extending over about 10m due to recent flows undercutting the bank in places; this may be due to the clay-dominated banks drying out during the recent drought and making them vulnerable to erosion when the creeks subsequently flows. There was no evidence of any animal access of damage of the banks but the area has been subject to considerable camping pressure on both sides of the creek.

There was only a small amount of phytoplankton present (chlorophyll a ranged from 0.034-1.9 μg/L) and filamentous algae (Cladophora) was only seen in autumn when it extended over about 5% of the channel. Aquatic plants covered over 10% of the creek and included submerged water ribbons (Triglochin) and several emergent species such as reeds (Phragmites), sedges (Carex and Isolepis), buttercups (Ranunculus), rushes (Juncus) and cumbungi (Typha). The riparian zone consisted of native vegetation that was dominated by gums and wattles over tea-tree shrubs and bracken, with a few weedy broom bushes also present. The surrounding vegetation near the creek comprised dense native woodland within The Deep Creek National Park.

The Deep Creek consists of a permanently flowing, freshwater, riffle-pool sequence stream that supports a wide range of rare, sensitive and flow-dependent species, particularly in spring when riffle habitats were most extensive.  

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