Tributary of Cygnet River, NW from Kerribee Park
2013 Aquatic Ecosystem Condition Report
- Permanently flowing stream in autumn and spring 2013
- Moderately diverse 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 introduced grasses and weeds
About the location
Tributary of Cygnet River is a small stream on the north-central part of Kangaroo Island. It rises at an elevation of about 110 m and flows in a southerly direction for about 7 km before discharging into the mid-reaches of the Cygnet River. The major land uses in the 687 hectares catchment upstream from the site sampled included grazing modified pastures (87%) and other minimal uses (12%), with smaller areas also used for roads, cropping and dams. The site was located off Miller Road, about 2 km north-west from Kerribee Park and nearly 12 km north-east from Parndana.
The creek 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 and poor riparian habitat.
A moderately diverse community of at least 22 species of macroinvertebrates was collected or seen from the creek (14 species in autumn and 15 in spring), 2.5-3.4 m wide and up to 32 cm deep, in autumn and spring 2013. The creek consisted of a still to slow-flowing channel in both seasons sampled. The community was not dominated by any species but comprised low to moderate numbers of amphipods (Austrochiltonia), hypogastrurid springtails, beetles (Necterosoma, Allodessus, Sternopriscus, Eretes and Lancetes), mosquitoes (Anopheles, Aedes and Culex), biting midges (including Dasyhelea), soldierflies, danceflies, chironomids (Procladius, Cricotopus, Tanytarsus and Chironomus), waterbugs (Microvelia and Micronecta) and coenagrionid damselflies. Yabby holes were also seen in the banks of the creek. These species were all tolerant, generalist types of macroinvertebrates that are frequently found from other saline, nutrient enriched streams in the State. Most were highly mobile insect groups capable of colonising newly wetted pools in ephemeral and more permanent streams and all can tolerate extended periods of poor quality water. The site lacked any rare and sensitive species, and no flow-dependent species were recorded in 2013. Many macroinvertebrates that commonly occur in other streams on the island and from the wetter parts of South Australia were absent from this site, including worms, mites, shrimp, blackflies, mayflies, stoneflies, dragonflies and caddisflies; high salinity probably prevents many of these groups from inhabiting this small tributary within the Cygnet River catchment.
The water was saline (salinity ranged from 3,971-9,478 mg/L), well oxygenated (119-124% saturation), clear and slightly coloured, and with low to moderate concentrations of phosphorus (0.01-0.04 mg/L) and high nitrogen concentrations (0.76-2.71 mg/L); the high amount of oxidised nitrogen (1.6 mg/L) recorded in autumn indicates that groundwater inflows probably occur near the site sampled. The surface of the water was also covered by an oily sheen in spring, presumably due to road runoff from the nearby sealed road following recent rains in the area.
The sediments were dominated by boulder, sand and detritus, with smaller amounts of cobble, gravel, silt and filamentous algae also present on occasion. Samples taken from below the surface were sulphide generating grey and black silts and clays, indicating that the sediments were anaerobic and lacked oxygen. A small amount of bank erosion was noted over nearly 10% of the banks, possibly caused by past stock and/or flood damage. The only animal droppings seen in the vicinity of the creek were from kangaroos.
There was a low to moderate amount of phytoplankton present during the year (chlorophyll a ranged from 0.9-9 μg/L) and filamentous algae (Enteromorpha) covered less than 10% of the stream in spring. No rooted aquatic plants were observed at the site in 2013. The narrow riparian zone was dominated by patches of gums and wattles and paperbarks over introduced grasses and weeds (e.g. boxthorn). The surrounding vegetation near the creek comprised cleared cattle grazing land, with only a few scattered gum trees and yakka shrubs present in the local landscape.
Special environmental features
None were recorded from the site in 2013. The creek supports a range of commonly occurring, saline tolerant aquatic macroinvertebrates but lacks any significant species and provides poor in-stream and riparian habitat features.
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.|
|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.|
|Large nutrient inputs from diffuse sources in the catchment (leading to some growth of algae and aquatic weeds)||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.|