Aldgate Creek, Aldgate
2008 Aquatic Ecosystem Condition Report
- Affected by nutrient enrichment.
- Diverse macroinvertebrate community with small number of species sensitive to pollution
- Riparian zone dominated by exotic trees and weeds.
- Creek provides important habitat for notable insect species.
About the location
Aldgate Creek is a small, permanently-flowing stream that empties into the Onkaparinga River near Mylor in the southern Mount Lofty Ranges. Most of its catchment area is covered by urban development around the township of Aldgate (78%), however there is also some livestock grazing (11%). About 8% of the area is classified as protected land, with some native vegetation. The monitoring site was located off Churinga Road within Aldgate.
The creek was given a Good rating at this site because the ecosystem showed evidenceof relatively minor changes to its animal and plant life. However, there were some clear, emerging signs of occasional high nutrient loads degrading the creek, which could lead to further decline.
At the time of inspection in October 2008 the creek was only one to two metres wide and almost entirely composed of rapidly-flowing riffle habitats, with very small areas of pooled water at the edges.
A total of 45 species of macroinvertebrates were found in the riffles, including species tolerant of pollution but there were also smaller numbers of more sensitive species. The community was dominated by worms, introduced and native snails, non-biting midges, and fly larvae (Austrosimulium furiosum) which depend on flowing water.
The water was fresh (salinity of 120 mg/L), well oxygenated (greater than 96% saturation) and clear of fine, suspended sediments. However, it was strongly coloured by tannins and had high concentrations of nutrients such as nitrogen (1.2 mg/L), phosphorus (0.1 mg/L), and oxidised nitrogen (0.26 mg/L).
The sediments were mostly large cobbles, boulders, pebbles and gravel with small amounts of finer sands and detritus. Below the surface, they were well oxygenated and provided a suitable refuge for burrowing species during floods or occasional non-flowing periods.
Aquatic weeds such as Creeping Yellow Cress (Rorippa sylvestris), buttercups (Ranunculus) and Cape Pond Lily (Aponogeton distachyos), and several species of native rush (Juncus) covered most of the creek’s edges.
A large number of introduced and native trees grew along the banks (mostly oaks, elms and gums), over a weedy understorey that included blackberry, ivy, onion grass, Blue Periwinkle and various thistles. The dense tree cover shaded the creek which limited the ability for algae to thrive in the stream.
Special environmental features
The creek provides habitat for small numbers of sensitive macroinvertebrates such as stoneflies (Dinotoperla evansi and Austrocerca tasmanica), caddisflies (Taschorema) and fly larvae from the Empididae family.
Pressures and management responses
|Limited riparian zone vegetation at the site and upstream, providing minimal buffer protection from catchment landuses (reducing habitat quality).||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.|
|Excessive introduced trees and weed growth 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.|
|Stormwater runoff causing high water velocities, containing nutrients and sediments (causing habitat disturbance, algal growth and aquatic weeds).||The Adelaide and Mount Lofty Ranges NRM Board has a well developed stormwater quality improvement, harvesting and reuse program which has installed (and maintains) gross pollutant (and silt) traps in several watercourses across the region to catch litter, debris and silt in order to minimise impacts and damage to seagrass in the receiving marine environment. Stormwater captured is also treated through artificial wetlands across the region which act as suspended solid and nutrient filters; these wetlands also provide important habitat for many native species.|
|Failing onsite wastewater treatment systems in the catchment, adding nutrients through shallow subsurface flows or overland flows to creeks (leading to algal growth).||Failing onsite wastewater treatment systems in the Mount Lofty Ranges Watershed are being addressed by improving maintenance of existing systems, upgrading to a more effective system, or via connection to a local government Community Wastewater Management Systems or to an SA Water sewer network, where these are available. The Mount Lofty Ranges Waste Control Program is addressing failing onsite systems by identifying and facilitating upgrades. This effective program is being delivered by the Adelaide Hills Council in partnership with the AMLR NRM Board, SA Water, Department of Health and the EPA.|
This aquatic ecosystem condition report is based on monitoring data collected by the EPA and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.