Northern branch of Brownhill Creek, near Eagle on the Hill
2013 Aquatic Ecosystem Condition Report
- Permanent flowing stream in autumn and spring 2013
- Diverse macroinvertebrate community with several rare, sensitive and flow-dependent species
- Water was fresh, clear and showing signs of nutrient enrichment
- Riparian vegetation dominated by introduced weeds and grasses
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 weedy riparian zone but the stream provides habitat for a number of rare, sensitive and flow-dependent species of macroinvertebrates.
A diverse community of at least 51 species of macroinvertebrates was collected from the creek (34 species in autumn and 33 in spring), 1.2-4.1 m wide and up to 41 cm deep, in autumn and spring 2013. The creek consisted of slow to moderately fast-flowing riffle habitats and areas of still or slow-flowing, deeper pools; riffles comprised 70% of the stream in autumn and 50% in spring. The community was dominated by moderate numbers of amphipods (Austrochiltonia), hydropsychid caddisflies (Cheumatopsyche modica), stoneflies (Dinotoperla evansi) and blackflies (Simulium ornatipes) in the riffles and waterbugs (Micronecta) and shrimps (Paratya) in the pools. It also included smaller numbers of nematodes, worms, introduced snails (Potamopyrgus), mites, yabbies, beetles, biting midges, blackflies, chironomids, mayflies, waterbugs, dragonflies, damselflies and caddisflies. While many of these macroinvertebrates were common, tolerant and/or generalist species, the community included a number of rare and sensitive species including the blackfly (Austrosimulium furiosum), mayflies (Offadens, Atalophlebia australasica, Atalophlebia australis and Thraulophlebia inconspicua), dragonflies (Hemigomphus gouldii and Austrogomphus) and caddisfly (Orphninotrichia maculata, Taschorema evansi and Ulmerochorema). A number of species normally associated with flowing water were also collected, including the dytiscid beetle (Platynectes), chironomid (Rheotanytarsus) and most of the above listed blackflies, mayflies, stoneflies and caddisflies. The only fish seen at the site were a few small galaxiid fish, which were probably juvenile Mountain Galaxiids (Galaxius olidus).
The water was fresh (salinity ranged from 382-423 mg/L), well oxygenated (93-133% saturation), clear and slightly coloured, and with variable concentrations of nutrients such as phosphorus (0.01-0.05 mg/L) and nitrogen (0.37-0.88 mg/L); lower nutrient concentrations were recorded in spring when flows were higher in the stream.
The sediments were dominated by detritus and silt, with smaller amounts of bedrock, boulder, cobble, pebble, gravel and sand also present; samples taken from below the surface were mostly grey silts that were sulphidic, indicating that the sediments were anaerobic due to the decomposition of the large amount of organic matter present at the site. Over 1 cm of fine silt covered the creekbed in places and a moderate amount of bank erosion extended over more than 10% of the site, which appeared to have been caused by past flow damage and cows accessing and damaging the banks. A considerable amount of cow droppings was also recorded from the banks and within the channel at the site sampled.
There was only a small amount of phytoplankton present (chlorophyll a ranged from 1-1.6 μg/L) and filamentous algae (Cladophora) was only seen in spring when it covered over 10% of the stream. A similar area was also covered by several different aquatic plants, including sedges (Cyperus), cumbungi (Typha), buttercups (Ranunculus), introduced watercress (Rorippa), and a few rushes (Juncus pallidus). The riparian zone consisted of introduced grasses, blackberries and other weeds, rushes and bracken. The surrounding vegetation near the creek comprised cropping and grazing land with a few gum trees, introduced broom and olives shrubs, and patches of bracken.
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, and at least one native fish species
Pressures and management responses
|Moderate 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.|
|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.