North Para River, Gawler Park Rd, Angaston
2013 Aquatic Ecosystem Condition Report

The river 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 due to the extent of nutrient enrichment of the stream and the limited, weedy riparian zone. The aquatic life comprised mostly tolerant and generalist species but also included two sensitive species of mayfly.

A moderately diverse community of at least 34 species of macroinvertebrates was collected from the river (28 species in autumn and 22 in spring), 4.5-5.4 m wide and up to 70 cm deep, in autumn and spring 2013. The river consisted of isolated pool habitats in both seasons sampled. The community was dominated by moderate numbers of amphipods (Austrochiltonia), with smaller numbers of native and introduced snails (including Physa and Potamopyrgus), worms, mites, yabbies, shrimp, beetles, mosquitoes, biting midges, chironomids, mayflies, waterbugs,  damselflies, dragonflies and caddisflies. Most were generalists, opportunists or tolerant species that are capable of surviving in organically polluted waters, or avoiding poor water quality by burrowing into the sediments or flying away. The only sensitive species collected were two mayflies (Atalophlebia australasica and Atalophlebia australis) which generally occur together in permanently flowing, freshwater habitats from the wetter parts of the region; their presence near Angaston may indicate they occasionally colonise this section of river from further upstream after the river flows, or the site has some unseen features (eg small seeps or riffles) present that sustain these species at the site sampled in 2013. Two species of fish were caught at the site in low numbers, including a native species called Big-headed Gudgeon (Philypnodon grandiceps) and an introduced pest called mosquitofish (Gambusia); both are typically found in deep, in-stream pools and lake environments and they are among the most pollution tolerant species found in the region.

The water was fresh to moderately fresh (salinity ranged from 796-1,446 mg/L), moderately well to well oxygenated (59-88% saturation), clear, and with very high concentrations of nutrients such as phosphorus (0.24-0.32 mg/L) and nitrogen (2.03-2.35 mg/L).

The sediments were dominated by detritus, with smaller amounts of silt, clay, sand and gravel also present; samples taken from below the surface were black silts with a manure odour and tested positive for the release of sulfides, indicating that the sediments were anaerobic and lacking in oxygen. A small amount of bank erosion was noted over about 10% of the site, which appeared to have been caused by cattle accessing and damaging the bed and banks of the river. The only animal droppings seen in the vicinity of the river were from cattle.

There was a large amount of phytoplankton recorded during the year (chlorophyll a ranged from 54-62 μg/L) but no filamentous algae was seen during either sampling period. Over 35% of the channel were covered by different types of aquatic plants, including dense growths of reeds (Phragmites) and cumbungi (Typha), and smaller patches of sedges (Cyperus) and water ribbons (Triglochin). The narrow riparian zone extended less than 5 m wide in places and comprised a few large River Red Gums, willows and wattles over an understorey dominated by introduced grasses and reeds. The surrounding vegetation near the creek comprised cleared sheep grazing paddocks with a few remnant gums and vineyards.

The most significant environmental features for this site were the unexpected presence of the two sensitive species of mayflies that are normally found together in flowing streams from the region, not isolated pools that lack any apparent flow.

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