Northern branch of Brownhill Creek, near Eagle on the Hill
2011 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, freshwater creek in autumn and spring 2011
- Diverse macroinvertebrate community with many rare, sensitive and flow-dependent species
- Obvious signs of moderate nutrient enrichment
- Riparian vegetation dominated by bracken and a range of woody and herbaceous weeds and introduced 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 1,497 hectare catchment are roads (including part of the South Eastern Freeway), remnant native vegetation and stock grazing, with smaller areas used for irrigated cropping and rural and urban residential living.
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 including nutrient enrichment, degraded riparian vegetation and sediment deposition in the channel. However, the stream provides habitat for many rare, sensitive and a wide range of generalist macroinvertebrate species which supported the high quality assessment for this site.
A diverse community of at least 50 species of macroinvertebrates was collected from the flowing creek, 1.1-2.2 m wide and up to 45 cm deep, in autumn and spring 2011. The creek consisted of large expanses of still to slow-flowing pool habitats connected by smaller areas of fast-flowing riffles. The community was dominated by a range of sensitive and tolerant types of macroinvertebrates, including chironomids, baetid mayflies, stoneflies, waterbugs and blackflies. It also included smaller numbers of nematodes, limpets, native and introduced snails, worms, amphipods, freshwater shrimp, yabbies, springtails, beetles, craneflies, biting midges, leptophlebiid mayflies, odonates and caddisflies. A number of rare and sensitive species were collected, including a chironomid (Riethia), dragonfly (Hemigomphus gouldii), blackflies (Austrosimulium furiosum and Paracnephia), mayflies (Offadens, Atalophlebia australasica and Thraulophlebia inconspicua), stoneflies (Dinotoperla evansi and Illiesoperla mayi) and caddisflies (Taschorema evansi and Ulmerochorema). Several species normally associated with flowing habitats were also collected, including a dytiscid beetle (Platynectes decempunctatus), blackfly (Simulium ornatipes), hydropsychid caddisfly (Cheumatopsyche sp. 2), and many of the above-listed rare and sensitive species. No fish was recorded from the site in 2011.
The water was fresh (salinity ranged from 334-418 mg/L), well oxygenated (95-141% saturated), clear, and with moderate concentrations of nutrients such as nitrogen (0.31-0.51 mg/L) and phosphorus (0.03-0.04 mg/L).
The sediments were dominated by algae, cobble, and gravel in the riffles and algae, detritus, silt and sand in the slower flowing sections. Samples taken from below the surface were slightly blackened under some rocks, indicating that the sediments had recently been anaerobic and lacked oxygen. A large amount of silt, 1-5 cm deep, covered the creekbed in places and about 10 m of bank showed evidence of erosion caused by cattle accessing the creek and previous flood damage.
Over 65% of the channel was covered by filamentous algae (mostly Cladophora) and about 35% of the site was covered by introduced watercress (Rorippa) and several other aquatic plants (Cyperus, Juncus, Persicaria, Phragmites, Ranunculus, Rumex and Typha). The riparian vegetation consisted of bracken, blackberries and other types of woody weed species and introduced grasses. The surrounding vegetation was a cleared rural property with a few scattered gum trees and olives.
Special environmental features
The Northern branch of Brownhill Creek provides permanently flowing, freshwater habitats that support a wide range of aquatic species, including many rare and sensitive macroinvertebrates.
Pressures and management responses
|Insufficient natural water flows in the creek resulting from water extraction and climate variability i.e. drought (reducing ecological integrity.||Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.|
|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 (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.|
|Limited riparian zone vegetation at the creek and upstream (reducing habitat quality, increasing sediment erosion).||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 revegetation programs around waterways and wetlands and stock exclusion as well as educating landholders about the importance of riparian vegetation in managing soil erosion.|
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