Middle River, N from Bangor
2013 Aquatic Ecosystem Condition Report
- Permanently wet river comprising a slow-flowing channel in autumn and areas of faster-flowing water in spring
- Sparse macroinvertebrate community with two sensitive, flow-dependent species collected in spring
- Water was fresh, clear and high in nitrogen
- Riparian vegetation comprised native trees and understorey species
About the location
Middle River is one of the largest streams on Kangaroo Island, located from around the middle to the northern part of the island. It rises at an elevation of about 275 m north from the Playford Highway near Gosse and flows in a north-easterly direction for over 33 km before discharging into Investigator Strait at Snelling Beach. The major land uses in the 3,936 hectare catchment upstream from the site sampled were grazing modified pasture (35%), plantation forestry (31%), other minimal uses (15%) and nature conservation (12.5%), with minor areas also used for wetlands, roads, cropping, residential living and dams. The site sampled was located in the middle of the catchment off Coopers Road, north from ‘Bangor’ and about 5 km north-east from Gosse.
The river 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 presence of introduced marron in 2013.
A sparse community of at least 19 species of macroinvertebrates was collected or seen from the river (11 species in autumn and 15 in spring), 4-4.4 m wide and over 1 m deep, in autumn and spring 2013. The river consisted of a slow-flowing channel in autumn but was deeper and more extensive in spring when large pools where connected by small areas of faster flowing riffle habitats. The community was dominated by moderate numbers of amphipods (Austrochiltonia) and included low numbers of mites, yabbies, beetles, mosquitoes, craneflies, biting midges, blackflies, chironomids, mayflies, waterbugs and caddisflies. Introduced marron were also present at the site and were being caught by fishermen during the autumn survey. Most species collected were tolerant, generalist species that have a wide distribution throughout the island and wetter parts of the State. Two sensitive flow-dependent species were collected when the river was flowing in spring, including the blackfly (Austrosimulium furiosum) and mayfly (Thraulophlebia inconspicua).
The water was fresh (salinity ranged from 129-794 mg/L), well oxygenated (90-91% saturation), acidic (pH 6.59-6.95), clear and slightly coloured, and with moderate to high nutrient concentrations for phosphorus (0.01-0.03 mg/L) and nitrogen (0.66-0.88 mg/L).
The sediments were dominated by detritus and sand, with smaller amounts of silt, clay, and algae in spring, also present. Samples taken from below the surface were grey silts and clays that were anaerobic in spring, indicating that the sediments were lacking in oxygen. A small amount of bank erosion extending over nearly 10% of the site was noted in spring, presumably caused by recent winter flood damage. The only animal droppings seen in the vicinity of the site were from kangaroos.
There was a small amount of phytoplankton (chlorophyll a 2.1-2.7 μg/L) recorded from the river in 2013 but filamentous algae (Spirogyra) was only seen in spring, when it covered over 10% of the channel. Over 10% of the channel was covered by aquatic plants such as rushes (Juncus) and tall-spike rush (Eleocharis) in autumn but these plants were not evident in the subsequent spring survey. The riparian zone extended 5-10 m wide and was dominated by gums and wattles over bracken, sedges and rushes. The surrounding vegetation near the river comprised dense eucalypt woodland.
Special environmental features
Middle River provides a permanently wet, freshwater habitat and supports a sparse assemblage of mostly commonly occurring aquatic macroinvertebrates in the middle reaches. It does, however, provide habitat for two sensitive, flow-dependent species when the river flows in spring.
Pressures and management responses
|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.|