Sixth Creek, near Castambul
2011 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, freshwater stream in autumn and spring 2011
- Diverse macroinvertebrate community with many rare, sensitive and flow-dependent species
- Obvious signs of moderate to gross nutrient enrichment
- Riparian vegetation dominated by woody and herbaceous 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 lowest reach of the creek on Corkscrew Road near Castambul. The major land uses in the 4,435 hectare catchment are remnant native vegetation and stock grazing, with smaller areas used for forestry, rural residential living and irrigated cropping.
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 and degraded riparian vegetation but the stream still provides habitat for many rare and sensitive species of macroinvertebrates.
A diverse community of at least 43 species of macroinvertebrates was collected from the flowing creek, 3.1-6.2 m wide and up to 35 cm deep, in autumn and spring 2011. The creek comprised similarly sized areas of fast-flowing riffle habitats and still to slow-flowing pools. The community was dominated by generalists and species tolerant to poor water quality such as waterbugs, chironomids, baetid mayflies and blackflies. It also included smaller numbers of flatworms, limpets, introduced snails (Physa and Potamopyrgus), worms, mites, amphipods, yabbies, springtails, beetles, biting midges, other types of mayflies, dragonflies, stoneflies and caddisflies. Numerous rare or sensitive species were collected, including a mite (Limnesia), elmid beetle (Simsonia leai), blackfly (Austrosimulium furiosum), chironomids (Podonomopsis, Ablabesmyia and Riethia), mayflies (Offadens, Atalophlebia australasica, Atalophlebia australis and Thraulophlebia inconspicua), stoneflies (Dinotoperla evansi and Illiesoperla mayi) and caddisflies (Taschorema evansi, Ulmerochorema membrum and Lingora). Several flow-dependent species were also recorded, including a dytiscid beetle (Platynectes decempunctatus), caddisfly (Cheumatopsyche sp. 2) and many of the above-listed rare and sensitive species. The only fish seen at the site in 2011 were several introduced Brown Trout.
The water was fresh (salinity ranged from 259-333 mg/L), well oxygenated (85-138% saturated), clear, and with low concentrations of nutrients such as nitrogen (0.18-0.24 mg/L) and phosphorus (0.012-0.018 mg/L).
The sediments were dominated by pebble, gravel, cobble and algae in the riffles and algae, cobble, pebble and detritus in the pools. Samples taken from below the surface were sandy grey in appearance and showed no evidence that the sediments were anaerobic or lacked oxygen. No significant deposits of silt or signs of bank erosion were noted at the site in 2011.
Extensive growths of filamentous algae (mostly Cladophora) covered over 65% of the creek. A range of emergent plants covered most of the remaining surface, including sedges (Bolboschoenus, Cyperus and Isolepis), rushes (Juncus), knotweed (Persicaria), dock (Rumex), and introduced watercress (Rorippa). The riparian vegetation only extended over about 5 m and consisted of woody weeds (willows and ash) over introduced grasses, weeds and some native sedges. The surrounding landscape included cleared sheep grazing paddocks and hills covered with native vegetation.
Special environmental features
Sixth Creek is one of the most significant streams in the region because it supports a wide range of rare, sensitive and flow-dependent species.
Pressures and management responses
|Insufficient natural water flows in the creek resulting from water extraction and climate variability (reducing ecological integrity).||Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.|
|Widespread introduced trees and 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.|
|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.|
|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.