Bungala River, Yankalilla
2013 Aquatic Ecosystem Condition Report

The creek was given a Poor rating because the site sampled showed evidence of evidence of major changes in ecosystem structure and function. There was evidence of human disturbance due to poor water quality, nutrient enrichment, the build-up of fine silt on the bottom of the channel, and the dominance of weeds in the riparian zone.

A sparse community of only 15 species of macroinvertebrates was collected or seen from the river (3 species in autumn and 13 in spring), 3.7-5 m wide and up to 125 cm deep, in autumn and spring 2013. The river consisted of a deep, connected channel that was only flowing in autumn. The community was not dominated any species but comprised low numbers of native and introduced snails (Glyptophysa, Potamopyrgus and Physa), limpets, worms, mites, amphipods (Austrochiltonia), chironomids, baetid mayflies (Cloeon) and caddisflies (Lectrides and Notalina spira). The presence of yabby holes in the banks indicated that this species also occurs in the river. These macroinvertebrates are all common generalists that can tolerate poor water quality and limited in-stream habitats, features that are always associated with urban stream environments. The mayfly and caddisflies recorded were among the most tolerant members of each of these insect orders. The community lacked any rare, sensitive or flow-dependent macroinvertebrates, and many groups that commonly occur in the region were similarly missing, including beetles, waterbugs, stoneflies, damselflies, dragonflies and a richer range of flies, mayflies and caddisflies. Three species of fish were caught or seen at the site, including native Flat-headed Gudgeon (Philypnodon grandiceps) and a galaxiid (Galaxias species), and introduced mosquitofish (Gambusia); possible predation by the many fish that occurred at the site, may have contributed towards the limited number of macroinvertebrates recorded in 2013.

The water was moderately fresh to saline (salinity ranged from 2,554-3,683 mg/L), poor to well oxygenated (40-94% saturation), clear and slightly coloured, and with high concentrations of nutrients such as phosphorus (0.07-0.1 mg/L) and nitrogen (0.94-1.01 mg/L).

The sediments were dominated by silt and clay, with smaller amounts of detritus, sand and algae in spring also present; samples taken from below the surface were anaerobic, black silts that released sulfides when tested, indicating that the sediments were lacking oxygen and represented a harsh environment for most burrowing species to be able to survive in. A large amount of silt (over 10 cm deep) was deposited throughout the middle of the river’s channel. About 50% of the banks showed evidence of significant erosion on occasion, which was presumably caused by past flood damage and the disturbance caused by the many houses that abut the river (e.g. stormwater pipes and retaining walls constructed on the banks). No animal droppings were seen in the vicinity of the river during 2013.

There was a small to moderate amount of phytoplankton present (chlorophyll a ranged from 1.4-3.8 μg/L), and filamentous algae (Spirogyra) was only seen in spring when it covered less than 10% of the channel. Aquatic plants covered over 35% of the site and included extensive growths of Common Reeds (Phragmites australis) and patches of cumbungi (Typha). The riparian zone generally only extended up to 5m wide on each bank and was dominated by patches of gums over woody and herbaceous weeds, introduced grasses and reeds. The surrounding vegetation near the creek comprised urban gardens on one side and cleared grazing land with a few scattered gum trees, wattles and regenerating native plants on the other bank.

None identified.

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