Riparian vegetation dominated by introduced weeds and bracken
Area map
About the location
The Northern branch of Brownhill Creek is a small stream in the Southern Mount Lofty Ranges that rises near Eagle-on-the-Hill and flows in a westerly direction, where it eventually becomes channelised as it passes through the south-eastern suburbs and discharges into the Patawalonga. The monitoring site was located off Tilleys Hill Road in Brown Hill. The major land uses in the 1,491 hectare catchment are minimal uses (53%), stock grazing (22%) and residential living (15%), with smaller areas used for conservation, roads, mining and irrigated horticulture.
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 due to nutrient enrichment and the presence of a weedy riparian zone but the stream provides habitat for a number of rare, sensitive and flow-dependent species of macroinvertebrates.
Findings
A diverse community of at least 47 species of macroinvertebrates was collected from the creek (31 species in autumn and 30 in spring), 3 m wide and up to 25 cm deep, in autumn and spring 2016. The creek consisted of moderately fast-flowing rifflehabitats and areas of still or slow-flowing, deeper pools; riffles comprised 70% of the stream. The community was dominated by large numbers of amphipods (Austrochiltonia), and non-biting midges. It also included smaller numbers of hydrobiid snails (including the introduced Potamopyrgus), shrimp, beetles, crane flies, blackflies, chironomids, mayflies, waterbugs, damselflies, dragonflies, stoneflies and caddisflies. The community included a number of rare, sensitive or flow-dependent species including the blackfly Austrosimulium furiosum, mayflies (Offadens and Thraulophlebia inconspicua), the dragonfly Hemigomphus gouldii, stoneflies (Dinotoperla evansi, Illiesoperla mayi and Newmanoperla thoreyi), and the caddisfly Taschorema evansi.
The water was fresh (salinity ranged from 300-464 mg/L), well oxygenated (90-101% saturation), clear, and with low to moderate concentrations of nutrients such as phosphorus (0.01-0.04 mg/L) and nitrogen (0.26-0.30 mg/L).
The sediments were highly variable with a mixed amount of rocks and finer sediments present. Detritus and algae were also present at the site. Samples taken from below the surface were mostly grey clay and silts that were sulfidic, indicating that the sediments were lacking in oxygen due to the decomposition of organic matter. Up to 5 cm of fine silt covered the creekbed in places and a small amount of bank erosion (<10 m) was noticeable, which appeared to have been caused by past flow damage and cows accessing and damaging the banks. Cow manure was also noticed on the banks.
There was a small amount of phytoplankton present (chlorophyll a ranged from 1.6-2.8 μg/L) and filamentous algae (Spirogyra and Cladophora) was also present with more growth noticed in spring (>35% of the stream covered). 10-35% of the site was also covered by aquatic plants, including Cyperus, Juncus, Phragmites, Rumex, Typha, and the introduced watercress (Rorrippa). The riparian zone consisted of bracken and weeds such as blackberries and the surrounding vegetation comprised grazing land with a few gum trees.
Special environmental features
The Northern Branch of Brownhill Creek provides a permanently flowing, freshwater stream that supports a number of rare, sensitive and flow-dependent species of blackflies, stoneflies, caddisflies and mayflies.
Pressures and management responses
Pressures
Management responses
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.
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.
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
