Brownhill Creek, d/s caravan park
2016 Aquatic Ecosystem Condition Report
Permanent flowing stream in autumn and spring 2016
Diverse macroinvertebrate community with several sensitive and flow-dependent species present
Water was fresh, clear and showing signs of nutrient enrichment
- Riparian vegetation consisted of ash trees, gums and introduced grasses
About the location
Brownhill Creek is made up of a network of three small streams flowing through steeply-sided, well-vegetated valleys in the foothills of the southern Mount Lofty Ranges at Mitcham. Much of the native vegetation in the flatter areas of the non-urbanised catchment has been removed for cropping, sheep grazing and rural living. The site selected for monitoring was located on the main channel, downstream from the junction of the tributary streams and near the Brownhill Creek Caravan Park, off Brownhill Creek Road. The major land use in the 1,754 hectare catchment upstream from the site is native vegetation (47%), and grazing modified pastures (23%), with small areas also used for roads, rural living and residential areas.
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 weeds in the riparian zone, nutrient enrichment and fine sediment deposits in the channel but the creek still provides a significant habitat for a diverse number of aquatic species.
A diverse community of at least 38 species of macroinvertebrates was collected from the creek (18 species in autumn and 30 in spring), 4.4 m wide and up to 70 cm deep, in autumn and spring 2016. The creek consisted of mostly still or slow-flowing pools connected by shallow, faster flowing riffles in both sampling seasons. The community was not dominated by any particular species but comprised low to moderate numbers of flatworms, native and introduced snails, worms, mites, amphipods, beetles, mosquitoes, blackflies (Austrosimulium furiosum and Simulium ornatipes), chironomids, mayflies (Offadens, Atalophlebia australasica and Thraulophlebia inconspicua), waterbugs, stoneflies (Dinotoperla evansi and Illiesoperla mayi) and caddisflies (including Taschorema evansi). Most of the macroinvertebrates were tolerant, opportunistic or generalist species that have a wide distribution across the region, however some more sensitive species found at this site included a blackfly, and the above mentioned mayflies, stoneflies and caddisfly; these species are also normally associated with flowing freshwater habitats.
The water was fresh (salinity ranged from 360-588 mg/L), well oxygenated (83-85% saturation), clear and with low concentrations of nutrients such as phosphorus (0.02 mg/L) and nitrogen (0.13--0.25 mg/L).
The sediments were dominated by detritus, sand and silt with smaller amounts of other rocky and fine substrates, as well as some algae in spring. Samples taken from below the surface were mostly grey silts and clays that showed no signs of being anaerobic, or lacking in oxygen. More than 1 cm of silt covered the bottom of the creek in autumn. There was no evidence of bank erosion.
There was a small amount of phytoplankton recorded from the creek (chlorophyll a ranged from 0.14-1.23 μg/L) and a large amount of filamentous algae (Cladophora and Enteromorpha) was recorded in spring, when it covered over 35% of the channel. About 10% of the creek was also covered by several types of aquatic plants, including cumbungi (Typha), knotweed (Persicaria) and introduced dock (Rumex). The riparian zone and consisted of ash trees, gums and introduced grasses and the surrounding vegetation beyond included lawn and garden areas of the caravan park on one side and residential properties on the other.
Special environmental features
The site supported a diverse range of tolerant, generalist, and a few sensitive and flow-dependent species of macroinvertebrates.
Pressures and 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.
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.