Chapman River, d/s Lashmar Lagoon
2013 Aquatic Ecosystem Condition Report
- Dry in autumn and non-flowing pools present in spring 2013
- Sparse macroinvertebrate community with no rare, significant or flow-dependent species
- Water was saline, clear and high in nutrients
- Riparian vegetation comprised native trees over rushes and bracken
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 9,863 hectare catchment upstream from the site sampled included grazing modified pastures (60%) and nature conservation (18%), with smaller areas also used for roads, cropping, wetlands, and irrigated horticulture. The site was located on a track off Main Road downstream from Lashmar Lagoon in the lower reaches, about 7 km 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 the extent of nutrient enrichment and salinization of the stream.
A sparse community of at least 12 species of macroinvertebrates was collected or seen from the non-flowing river, 7.4 m wide and up to 58 cm deep, in spring 2013; the river was dry in autumn. The community was not dominated by any species but included low numbers of introduced snails (Potamopyrgus antipodarum), amphipods (Austrochiltonia), beetles (Megaporus, Rhantus, Lancetes and Limnoxenus), soldierflies, and chironomids (Tanytarsus, Chironomus, Dictrotendipes and Parachironomus). Crayfish claws were also seen on the edges of the stream which indicated that yabbies occurred at the site. All of these macroinvertebrates are tolerant, generalist species that frequent fresh to brackish, nutrient enriched streams elsewhere on the island and in South Australia. No rare, sensitive or flow-dependent species were collected. The site lacked many groups that commonly occur in fresher streams, including mites, native snails, shrimp, mayflies, stoneflies, waterbugs, odonates and caddisflies. Several small native fish called Western Blue-spotted Gobies were also collected from the site; this species frequents estuarine and lowland stream habitats throughout the southern part of the State.
The water was saline (salinity of 5,779 mg/L), moderately well oxygenated (53% saturation), clear and slightly coloured, and with high concentrations of phosphorus (0.14 mg/L) and nitrogen (2.88 mg/L).
The sediments were dominated by detritus with smaller amounts of silt, sand and clay also present. Samples taken from below the surface were black and grey silts that released sulphide when tested in spring, indicating that the sediments were anaerobic or lacked oxygen for at least part of the year. Over 1 cm of fine silt covered the channel in places, presumably deposited during recent winter flows in the river. There was no evidence of any significant areas of bank erosion noted and the only animal droppings seen in the vicinity of the stream were from kangaroos.
There was a large phytoplankton bloom when the river was wet (chlorophyll a 77 μg/L) but there was no evidence of any filamentous algae at the site during 2013. The only aquatic plants seen in the river were a sedge (Bolboschoenus) and Waterbuttons (Cotula) which extended over more than 35% of the channel. The riparian zone extended over 30m wide in places and was well shaded (70% shading) by paperbarks over samphire and sedges. The surrounding vegetation near the river comprised dense paperbark woodland.
Special environmental features
None identified in 2013.
Pressures and management responses
|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.|