Riparian vegetation consists of blackberries, bracken and sedges with exotic deciduous trees, gums and grasses beyond
Area map
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, about 1,855 hectares, is covered by urban development around the townships of Aldgate and Mylor (65%). Other land uses in the catchment include transport and communication, services, livestock grazing and nature conservation. The monitoring site was located in the lower reaches of the creek, upstream from Aldgate-Strathalbyn Road in Mylor.
The creek 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 including nutrient enrichment and fine sediment deposition and the presence of weeds in the riparian zones but the stream still provided habitat for a few sensitive macroinvertebrate species.
Findings
A moderately diverse community of at least 32 species of macroinvertebrates was collected from this flowing creek, approximately 3 m wide and 60 cm deep, in autumn and spring 2015. The creek consisted of a connected slow-flowing channel in autumn 2015 which had ceased to flow in spring. The site was dominated by amphipods, non-biting midges, small water striders and both purse-case caddisflies (hydroptilids) and longhorned caddisflies (leptocerids). A small riffle section was present in autumn but was too small to sample, however, non-biting midges, worms, black fly larvae (Simulium) and scirtid beetles were seen in the flowing water. Other species collected from the pools at this site included a range of generalist and pollution tolerant species, such as worms, snails, freshwater clams, beetles, mosquito larvae and waterbugs. Some rare species were also collected including the non-biting midge Podonomopsis and the flow-dependent caddisfly Triplectides similis. Introduced fauna such as the snails Potamopyrgus and Physiella were seen in the creek. Galaxias fish and yabbies were seen at the site and frogs were heard calling.
The water was fresh (salinity ranged from 216-270 mg/L), moderately well oxygenated (30-74% saturation) and clear but slightly coloured, with moderate concentrations of nutrients such as nitrogen (0.51-0.93 mg/L) and phosphorus (0.03-0.05 mg/L). Small patches of oils were noticed on the water’s edge in spring.
The sediments were dominated by sand with cobbles, pebbles, silt and detritus also present. Samples taken from below the surface were sandy. Small deposits of silt covered the streambed to a depth of between 1 and 5 cm in places and no significant areas of bank erosion were seen.
A small amount of phytoplankton (chlorophyll a ranged from <0.1-1.18 µg/L) but no filamentous algae was recorded from the site. Less than 10% of site was covered by aquatic plants, such as the emergent plants (Aponogeton, Isolepis, Juncus, Persicaria, Rorrippa, and Rumex). The riparian zone consisted of blackberries, bracken and sedges with scattered gums, exotic deciduous trees and grasses beyond.
Special environmental features
Aldgate Creek provides habitat for a species of non-biting midge (Podonomopsis), the caddisfly Triplectides similis and the native fish Galaxias sp.
Pressures and Management Responses
Pressures
Management responses
Stormwater runoff containing high nutrient and sediment loads discharging to the creek (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.
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.
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.