Riparian vegetation consists of a mixture of native and exotic trees with mostly introduced trees and grasses beyond
Area map
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 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 the presence of weeds in the riparian zones but the stream still provided habitat for some rare and sensitive macroinvertebrate species.
Findings
A highly diverse community of at least 41 species of macroinvertebrates was collected from this flowing creek, approximately 4 m wide and 55 cm deep, in autumn and spring 2015. The creek consisted of slow-flowing pools with fast-flowing riffle sections between the pools in autumn 2015 but only had slower flowing water in spring 2015. The site was dominated by Hydrobiid snails, mites, non-biting midge larvae, blackfly larvae (Austrosimulium and Simulium) and the stoneflies Dinotoperla and Illiesoperla. Other species collected in smaller numbers included a range of generalist and pollution tolerant species, such as worms, snails, mites, isopods, amphipods, beetles, fly larvae from the family Dixidae, mayflies, waterbugs, and caddisflies. Some sensitive and rare species, as well as flow-dependent species, were also collected, including the uncommon non-biting midge larvae Podonomopsis and Ablabesmyia, mayflies (Offadens and Atalophlebia), and the caddisfly Cheumatopsyche. Introduced fauna such as the snails Potamopyrgus and Physiella the native fish Galaxias olidus (Mountain Galaxias) were also seen in the creek.
The water was fresh (salinity ranged from 416-557 mg/L), moderately well oxygenated (31-67% saturation) and clear but slightly coloured, with moderate concentrations of nutrients such as nitrogen (0.35-0.38 mg/L) and phosphorus (0.02-0.06 mg/L). Small patches of oil on the water’s surface were noticed in spring.
The sediments were dominated by detritus and fine sediment with some cobbles and pebbles also present. Samples taken from below the surface were grey sand and showed no evidence of being anaerobic, or lacking oxygen. Only small deposits of silt covered the streambed to a depth of about 1 cm in places and no significant areas of bank erosion were seen.
A small amount of phytoplankton (chlorophyll a ranged from <0.1-0.23 µg/L) and no filamentous algae was recorded from the site. More than 65% of site was covered by a range of aquatic plants in spring, including the emergent plants (Polygonum, Rorrippa, Rumex and Typha). The riparian zone consisted of mostly gums and exotic trees with some tea trees also present over a weedy understorey. The surrounding vegetation was mainly lawn from nearby houses, exotic grasses, scattered gums and English oaks.
Special environmental features
Brownhill Creek provides important habitat for many species sensitive to pollution and dependent on the near permanent flows that occur in this creek, such as blackfly larvae, the stoneflies Dinotoperla and Illiesoperla, the mayflies Offadens and Atalophlebia, the caddisfly Cheumatopsyche and Mountain Galaxias fish.
Pressures and management responses
Pressures
Management responses
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.
Large 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 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.