Tributary of Middle River, N from Bangor
2013 Aquatic Ecosystem Condition Report
- Permanently wet, slow-flowing stream in autumn and spring 2013
- Moderately diverse macroinvertebrate community with one rare and one sensitive flow-dependent species recorded
- Water was fresh, clear and high in nutrients
- Riparian vegetation comprised native trees and understorey species
About the location
The Tributary of Middle River is a small third order creek that rises at an elevation of about 225 m and flows in an easterly direction for nearly 4 km, before discharging into the upper reaches of the Middle River near ‘Bent Valley’. The major land-use in the 454 hectare catchment upstream from the site sampled was grazing modified pastures (81%), with minor areas also used for cropping, other minimal uses, roads, nature conservation, plantation forestry and dams. The site sampled was located off Coopers Road, north from ‘Bangor’ and about 6 km north-east from Gosse.
The creek was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure and some changes to the way the ecosystem functions. There was evidence of human disturbance due to nutrient enrichment and the deposition of large amounts of fine sediment in the stream.
A moderately diverse community of at least 26 species of macroinvertebrates was collected or seen from the creek (16 species in autumn and 19 in spring), 5.3-8 m wide and over 1 m deep, in autumn and spring 2013. The creek consisted of a slow-flowing channel in both seasons sampled. The community was not dominated by any species but comprised low numbers of worms, mites (Koenikea), amphipods, yabbies, springtails, beetles, craneflies, mosquitoes (Aedes and Culex), chironomids, mayflies, waterbugs and caddisflies. Most species were tolerant generalists that are frequently found from similar pool and channel habitats elsewhere on the island and from the wetter parts of the State. The only sensitive, flow-dependent species collected was the mayfly (Thraulophlebia inconspicua), and the only rarely collected species recorded was the caddisfly (Leptorussa darlingtoni).
The water was generally fresh (salinity ranged from 248-1,043 mg/L), well oxygenated (100% saturation), alkaline in autumn but acidic in spring (pH 6.79-7.07), clear and slightly coloured, and with moderate to high nutrient concentrations such as phosphorus (0.03-0.08 mg/L) and nitrogen (0.83-1.6 mg/L).
The sediments were dominated by sand and detritus, with smaller amounts of silt, clay and gravel also present. Samples taken from below the surface were grey sands and showed no evidence that the sediments were anaerobic and lacked oxygen. Over 5 cm of fine sediment covered the creekbed in places but there was no evidence of any significant bank erosion at the site sampled in 2013. The only sign of any animal droppings recorded in the vicinity of the stream were from kangaroos.
There was a small to moderate amount of phytoplankton (chlorophyll a 1.8-4.3 μg/L) present but no sign of any significant growths of filamentous algae in 2013. Over 10% of the channel was covered by aquatic plants such as rushes (Juncus) and sedges (Carex). The riparian zone extended over 10 m wide in places and was dominated by gums and wattles over proteas, sedges and rushes. The surrounding vegetation near the creek comprised dense eucalypt woodland.
Special environmental features
Tributary of Middle River provides a permanently wet, freshwater habitat and supports a moderately diverse assemblage of commonly occurring aquatic macroinvertebrates. The presence of at least one rare and one sensitive, flow-dependent species highlights the significance of this tributary in the upper catchment of the Middle River.
Pressures and management responses
|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.