Sixth Creek, near Montacute Heights
2011 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, freshwater creek in autumn and spring 2011
- Diverse macroinvertebrate community with many rare and sensitive species
- Obvious signs of moderate nutrient enrichment
- Riparian vegetation dominated by wattles, gums and willows over introduced weeds and grasses.
About the location
Sixth Creek is a moderately sized stream in the Southern Mount Lofty Ranges that rises in Carey Gully and flows northwards where it discharges into the Torrens River at Castambul, about 2 km west from Kangaroo Creek Reservoir. The monitoring site was located in the lower reaches of the creek on Sixth Creek Road, west from Montacute Heights. The major land uses in the 3,005 hectare catchment are remnant native vegetation, irrigated cropping and stock grazing, with smaller areas used for rural and urban residential living, roads and conservation.
The creek was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was evidence of human disturbance including nutrient enrichment, degraded riparian vegetation and some fine sediment deposition into the creek. Despite this, the creek provides habitat for many rare and sensitive species of macroinvertebrates.
A diverse community of at least 51 species of macroinvertebrates was collected from the flowing creek, 3.3-4.4 m wide and up to 60 cm deep, in autumn and spring 2011. The creek comprised slow-flowing pools connected by faster-flowing riffle habitats in both seasons, with flow slightly higher during the autumn period. The community was dominated by a range of generalists, tolerant and more sensitive species, including waterbugs (Micronecta), amphipods (Austrochiltonia), baetid mayflies, coenoscucid caddisflies (Lingora) and chironomids. It also included smaller numbers of flatworms, limpets, bivalves, introduced snails (Physa and Potamopyrgus), worms, mites, isopods, beetles, craneflies, dixids, biting midges, blackflies, leptophlebiid and caenid mayflies, other types of waterbugs, stoneflies and several types of caddisflies. Numerous rare and sensitive species were collected, including a mite (Limnesia), beetle (Sclerocyphon), chironomid (Riethia), blackflies (Paracnephia and Austrosimulium furiosum), mayflies (Offadens, Atalophlebia australasica and Thraulophlebia inconspicua), stoneflies (Dinotoperla evansi, Illiesoperla mayi and Austrocerca tasmanica) and caddisflies (Taschorema evansi and Lingora). A number of species normally associated with flowing habitats were also recorded, including a dytiscid beetle (Platynectes decempunctatus), chironomid (Rheotanytarsus), caddisfly (Cheumatopsyche sp. 2), and many of the above-listed rare and sensitive species. The only fish seen at the site was a school of introduced Brown Trout.
The water was fresh (salinity ranged from 228-289 mg/L), well oxygenated (81-139% saturated), clear, and with low to moderate concentrations of nutrients such as nitrogen (0.35-0.47 mg/L) and phosphorus (0.013-0.016 mg/L).
The sediments were dominated by detritus, silt and algae in the slow-flowing pools and algae, boulders, cobbles, gravel and pebble in the fast-flowing riffles. Samples taken from below the surface were grey in colour and showed no evidence that the sediments were anaerobic or lacked oxygen. Over 1 cm of silt covered the creekbed and more than 10 m of bank showed evidence of erosion in spring, due to some bank slumping at the site presumably caused by recent winter flooding.
A large amount of filamentous green algae (mostly Cladophora) covered over 35% of the creekbed, and a similar area was covered by several species of aquatic plants (Persicaria, Bolboschoenus, Cyperus, Juncus, Phragmites, Ranunculus, Rumex, Typha, Isolepis and introduced Rorippa). The narrow riparian zone consisted of wattles, River Red Gums and willows over rushes, blackberries and introduced grasses that included bamboo and wild oats. The surrounding vegetation consisted of a citrus orchard on one bank and eucalypt woodland in the other.
Special environmental features
Sixth Creek is one of the most biodiverse streams in the region in terms of aquatic macroinvertebrates, providing habitat for a large number of rare, sensitive and flow-dependent species. Further upstream, this stream also supports at least one state-listed threatened species of native fish called the Mountain Galaxias.
Pressures and management responses
|Livestock having direct access at the site and upstream (causing sediment erosion and adding excessive nutrients).||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes incentives for waterway and wetland fencing to exclude or limit stock from entering riparian zones.|
|Widespread introduced weeds in the riparian zone at the site and upstream (reducing habitat quality).||The Adelaide and Mount Lofty Ranges NRM Board has several pest plant (weed) mitigation and control programs. They work closely with landholders to control weeds on their property and to help stop the spread to other properties and waterways.|
|Limited riparian zone vegetation at the creek and upstream (reducing habitat quality, increasing sediment erosion).||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes incentives for revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion.|
This aquatic ecosystem condition report is based on monitoring data collected by the EPA. It was prepared with and co-funded by the Adelaide and Mount Lofty Ranges NRM Board.