Riparian vegetation dominated by exotic trees and weeds
Area map
About the location
Aldgate Creek is a small stream in the Southern Mount Lofty Ranges that rises west from Stirling and flows in an easterly direction, where it joins with Cox Creek and eventually discharges into the Onkaparinga River to the south of Bridgewater. The monitoring site was located off Cricklewood Road, between Stirling and Heathfield. The major land uses in the 294 hectare catchment are urban and rural residential living, roads and remnant native vegetation.
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 considerable evidence of human disturbance including degraded riparian habitats and nutrient enrichment.
Findings
A sparse community of at least 12 species of macroinvertebrates was collected from the flowing creek, 2 m wide and up to 15 cm deep, in autumn 2011; the creek was not sampled in spring due to the dense growth of blackberries and shallowness of the water. The community was dominated by leptocerid caddisflies, amphipods and chironomids. It also included smaller numbers of snails, worms, beetles and waterbugs. The site was notable due to the absence of mayflies, stoneflies, odonates and many types of flies, despite the presence of what appeared to be suitable habitats. The only rare species collected included an amphipod from the Family Perthiidae and a leptocerid caddisfly (Leptorussa). A single chironomid from the genus Rheotanytarsus was the only flow-dependent species recorded. The only fish present at the site was an introduced pest species called mosquitofish (Gambusia).
The water was fresh (salinity of 183 mg/L), well oxygenated (88% saturated), clear, and with high concentrations of nutrients such as nitrogen (0.91 mg/L) and phosphorus (0.1 mg/L).
The sediments were dominated by cobble, bedrock and detritus, with pebble, gravel, sand and silt also present. Samples taken from below the surface were grey in colour and showed no evidence that the sediments were anaerobic or lacked oxygen. A small amount of silt, 1 cm deep, was recorded from the deeper pool habitats at the site. No significant areas of bank erosion were noted during 2011.
Nearly 10% of the channel was covered by filamentous algae in spring but was not seen during the autumn survey. Aquatic plants covered over 10% of the creek and included patches of pondweed (Potamogeton tricarinatus) and sedge (Isolepis). The riparian vegetation included a few scattered gum trees among a thick growth of exotic trees (willows, pine and ash), blackberries and other weeds. The surrounding vegetation comprised urban gardens.
Special environmental features
The permanently wet creek provided habitat for a few rare and flow-dependent species.
Pressures and management responses
Pressures
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.
Large nutrient inputs to the creek from numerous diffuse sources (leading to extensive growth of algae and aquatic weeds)
The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes working with industry and landholders to ensure efficient use of fertilisers and discuss ways to reduce runoff of nutrients into waterways.
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.
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Observed Condition
Expected Condition
