Rocky River, eastern branch Flinders Chase NP
2013 Aquatic Ecosystem Condition Report
- Permanently flowing river in autumn and spring 2013
- Moderately diverse macroinvertebrate community with several rare, sensitive and/or flow-dependent species present
- Water was fresh, clear and generally low in nutrients
- Riparian vegetation consisted of native trees and shrubs
About the location
Rocky River is a moderately sized stream within Flinders Chase National Park on the western end of Kangaroo Island. The eastern branch of the river rises at an elevation of nearly 300 m south from the Playford Highway, and flows in a south-easterly direction for about 30 km, until it discharges into the Southern Ocean in Maupertuis Bay. The major land use in the 8,658 hectare catchment upstream from the site sampled was nature conservation (97%), with small areas also used for plantation forestry, roads and grazing modified pastures. The site was located within the mid catchment of the eastern branch, accessed via Melrose East Track from the West End Highway, about 7 km north-east from the Flinders Chase Visitor Centre.
The river was given a Very Good rating because the site sampled showed no evidence of any significant changes in ecosystem structure and function. The only degrading features that could affect the environmental condition of the mid-reaches of this river include sediment runoff from the unsealed track that crosses the stream and the presence of introduced marron.
A moderately diverse community of at least 23 species of macroinvertebrates (at least 16 species in autumn and 14 species in spring) was collected from the river, 2.1-4.4 m wide and up to 62 cm deep, in 2013. The river consisted of mostly still to slow-flowing pools connected by smaller areas slow to faster-flowing riffle habitats in both seasons sampled. The community was not dominated by any species but included low to moderate numbers of worms, water mites (Coaustraliobates, Australiobates and Koenikea), amphipods (Austrochiltonia), introduced marron (Cherax tenuimanus), beetles (Sternopriscus tarsalis), craneflies (Tipulidae sp. 8), chironomids (Paramerina, Parakiefferiella, Tanytarsus and Rheotanytarsus), mayflies (Centroptilum elongatum, Atalophlebia sp. and Thraulophlebia inconspicua), waterbugs (Micronecta, Microvelia and Anisops), dragonflies from the Family Telephlebiidae and caddisflies (Lectrides). The riffles also supported blackflies, stoneflies (Family Gripopterygidae) and marsh beetles. The presence of crayfish holes in the banks also indicated that marron commonly occurred at the site. Many of the species collected were tolerant or generalist macroinvertebrates capable of persisting in a wide range of habitats and conditions. However, the site was notable due to the presence of several rare, sensitive and/or flow dependent species, including the mayflies, stonefly, blackfly, and one of the chironomids (Rheotanytarsus).
The water was fresh (salinity 197-250 mg/L), well oxygenated (71-86% saturation), clear and slightly coloured, and with generally low to moderate concentrations of nutrients such as phosphorus (0.01-0.03 mg/L) and nitrogen (0.48-0.57 mg/L).
The sediments were dominated by detritus and sand, with smaller amounts of bedrock, silt and clay also present. Samples taken from below the surface were grey sands and showed no evidence to indicate that the sediments had recently been anaerobic or lacking in oxygen. Over 1 cm of fine sediment covered the streambed in places in spring. There was a small amount of bank erosion noted over nearly 10% of the site, which appeared to have been caused by past flood damage. The only animal droppings seen in the vicinity of the river were from kangaroos.
There was a very small amount of phytoplankton recorded (chlorophyll a <0.1-0.34 μg/L) but no evidence of any filamentous algae was made during 2013. Aquatic plants covered over 10% of the channel and included water ribbons (Triglochin) in the deeper water and water pennywort (Hydrocotyle) on the margins. The riparian zone extended over 5 m wide and was dominated gums and wattles over bracken and banksias. The surrounding vegetation near the river comprised dense native eucalypt woodland within the national park.
Special environmental features
The most significant feature of Rocky River, including the eastern branch sampled at this site, is the limited extent of human disturbance throughout the catchment, due to its location within a national park. As a result, the river represents a near natural reference stream for the island and the wetter parts of the State, dominated by natural vegetation, habitats and biota. The results from sampling in 2013 showed that the river supports several rare, sensitive and/or flow-dependent macroinvertebrates and at least two aquatic plants. The presence of the mayfly Centroptilum in particular, emphasises the significance of this stream because it only occurs in a limited number of streams on the western end of Kangaroo Island and the freshest streams on the Fleurieu Peninsula and the Southern Mt Lofty Ranges.
Pressures and management responses
|Runoff from unsealed roads during high rainfall periods leading to fine sediments discharging into the creek (increasing turbidity and smothering habitat)||This information is not available at the moment but it will be updated as soon as possible.|