Permanent, flowing stream in autumn and spring 2016
A diverse macroinvertebrate community with a few sensitive and flow-dependent species present
Water was fresh, clear but strongly coloured, and enriched with nutrients
Riparian vegetation consisted of willow and blackberries, over introduced grasses
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 area of 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 due to the extent of woody weeds in the riparian zone and evidence of nutrient enrichment, but the stream still provides habitat for a few sensitive and flow-dependent species of macroinvertebrates.
Findings
A diverse community of at least 55 species of macroinvertebrates was collected or seen from the creek (18 species in autumn and 45 in spring), 5.5 m wide and more than 65 cm deep, in autumn and spring 2016. The creek consisted of mostly still to slow-flowing pools connected by smaller areas of faster-flowing, shallow riffle habitats in both seasons sampled. The community was not dominated by any particular species instead comprising low to moderate numbers of flatworms, native and introduced snails, worms, mites, amphipods (including the Family Perthiidae), beetles, crane flies, biting midges, blackflies (Austrosimulium furiosum, Simulium melatum and Simulium ornatipes), chironomids (including Podonomopsis and the flow dependent Rheotanytarsus), waterbugs, dragonflies, stoneflies (Riekoperla naso and Austrocerca tasmanica) and caddisflies (including Ulmerochorema membrum). Most species recorded from this site were generalist, opportunistic and tolerant species, however, some rare, sensitive and/or flow-dependent species were also recorded including the above-listed amphipod, blackflies, stoneflies and caddisfly. The low number of taxa present in autumn was probably related to the timing of sampling, with flows only just starting at the site shortly before it was sampled in the middle of June and providing limited time for many species to establish in the creek.
The water was fresh (salinity ranged from 118-256 mg/L), well oxygenated (75-84% saturation), clear but strongly coloured in spring, and with moderate to high concentrations of nutrients such as phosphorus (0.04-0.09 mg/L) and nitrogen (0.62-1.30 mg/L). Froth was also present at the site in autumn.
The sediments were dominated by bedrock, detritus and sand, with smaller amounts of boulder, cobble, silt, and clay also present. Samples taken from below the surface were mostly grey silts and clays with no signs that the sediment was sulfidic or lacking oxygen. A small amount of bank erosion was noted, with less than 10% of the site showing damage caused by previous higher flows. No evidence of any stock accessing the creek were seen near the site during 2016.
There was only a small amount of phytoplankton present (chlorophyll a 0.32-1.23 μg/L) and no filamentous algae was seen during either sampling seasons. Less than 10% of the site was covered by aquatic plants with only Aponogeton and Isolepis being identified. The riparian zone consisted of extensive growths of woody weeds such as willow and blackberries, over introduced grasses. The surrounding vegetation near the creek comprised a park and school on one bank and cleared cattle grazing paddocks on the other bank.
Special environmental features
Aldgate Creek is a permanently flowing, freshwater stream that supports a diverse assemblage of generalist, tolerant, rare and sensitive macroinvertebrates.
Pressures and management responses
Pressures
Management responses
Widespread introduced weeds in the riparian zone at the site and upstream
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.
Nutrient inputs to the creek from numerous diffuse sources (potentially leading to excess growth of algae and aquatic weeds)
The Adelaide and Mount Lofty Ranges NRM Board 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.
Observed Condition
Expected Condition
