Chapman River, East from Woodleigh
2013 Aquatic Ecosystem Condition Report
- Permanently flowing stream in autumn and spring 2013
- Sparse macroinvertebrate community with no rare, sensitive or flow-dependent species
- Water was saline, clear and high in nitrogen concentrations
- Riparian vegetation comprised native trees over weeds and rushes
About the location
Chapman River is a small stream on Dudley Peninsula at the eastern end of Kangaroo Island. The river rises near Woodleigh north from Willson River Road and flows in an east to north-easterly direction for nearly 10 km, until it discharges into the Southern Ocean at Antechamber Bay. The major land uses in the 766 hectare catchment upstream from the site sampled included grazing modified pastures (74%) and unclassified other minimal uses (22%), and also included smaller areas of roads and dams. The site was located in the upper reaches off Moffat Road, about 11 km west-north-west from Cape Willoughby.
The river was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure and moderate changes to the way the ecosystem functions. There was evidence of human disturbance due to nitrogen enrichment, high salinity, the large deposit of fine sediment in the channel, the presence of introduced snails, and the large extent of weeds in the understorey of the riparian zone.
A sparse community of at least 17 species of macroinvertebrates was collected or seen from the river (13 species in autumn and 12 in spring), 2.2-2.6 m wide and up to 70 cm deep, in autumn and spring 2013. The river consisted of still to slow-flowing pools connected by tiny areas of faster-flowing, shallow riffle habitats in both seasons sampled. The community was dominated by low to moderate numbers of amphipods (Austrochiltonia), introduced snails (Potamopyrgus) and chironomids (Procladius, Tanytarsus and Dicrotendipes), and included low numbers of mites (Koenikea), beetles (Liodessus, Necterosoma penicillatus, Limnoxenus zealandicus and Scirtidae), mosquitoes (Culex), biting midges (Culicoides), soldierflies, waterbugs (Microvelia) and damselflies (Austrolestes annulosus and Ischnura). The presence of yabby holes at the site also indicated that freshwater crayfish were common inhabitants of this river. All species recorded in 2013 were tolerant generalists that are frequently found from other saline, nutrient enriched streams in South Australia. The site lacked any rare, sensitive species, or flow-dependent species, and many groups and species of macroinvertebrates that commonly occur in other streams on the island and the wetter parts of the State were also absent, including shrimp, blackflies, mayflies, stoneflies, dragonflies and caddisflies, and a wider range of beetles, waterbugs and chironomids.
The water was saline (salinity ranged 9,285-10,224 mg/L), well oxygenated (73-98% saturation), clear but slightly coloured, and with low concentrations of phosphorus (0.01 mg/L) and high nitrogen concentrations (0.66-0.81 mg/L).
The sediments were dominated by detritus with smaller amounts of silt, clay, gravel and sand also present; over 25% of the sediments were also covered by filamentous algae in autumn. Samples taken from below the surface were black silts that tested positive for sulfides, indicating that the sediments were anaerobic and lacked oxygen. A thick deposit of fine silt covered the bottom of the channel to a depth over 10 cm thick, which made the water highly turbid when disturbed. A moderate amount of bank erosion extending over 10% of the banks was noted, which appeared to have been caused by past flood damage of very soft banks. The only animal droppings seen in the vicinity of the river were from kangaroos.
There was a small amount of phytoplankton (chlorophyll a 0.9-1.2 μg/L) was recorded and, as noted above, a large growth of a type of filamentous algae (Cladophora) covered over 10% of the channel during autumn. A few patches of a submerged charophyte (Chara) and sea tassel (Ruppia) were the only plants seen at the site. The riparian zone was dominated by gums, paperbarks and wattles over yakkas, introduced grasses, bridle-creeper and patches of rushes. The surrounding vegetation near the river comprised a small area of cleared land among open woodland dominated by gums and wattles.
Special environmental features
Chapman River provides a permanently wet habitat on the eastern end of the island and supports an aquatic community that is well adapted to live in saline, nutrient enriched streams.
Pressures and management responses
|Widespread introduced weeds in the riparian zone at the site and upstream (reducing habitat quality).||This information is not available at the moment but it will be updated as soon as possible.|
|Saline groundwater inflows to the creek (reducing ecological integrity).||This information is not available at the moment but it will be updated as soon as possible.|
|Large nutrient and sediment inputs from diffuse sources in the catchment (leading to extensive growth of algae and aquatic weeds as well as increased turbidity and smothering of habitat).||The Kangaroo Island NRM Board has funded the fencing of significant areas of riparian vegetation in the catchment and continues to work with landowners to increase the fencing of watercourses.|