Scott Creek, 1 km south-west from Scott Creek
2011 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, freshwater creek in autumn and spring 2011
- Sparse macroinvertebrate community with several rare, sensitive and flow-dependent species
- Obvious signs of moderate nutrient enrichment
- Riparian vegetation dominated by introduced grasses and a range of native trees and shrubs.
About the location
Scott Creek is a small stream in the Southern Mount Lofty Ranges that rises south from Heathfield and flows in a SSW direction, where it eventually discharges into the Onkaparinga River near the Mount Bold Reservoir. The monitoring site was located off Scott Creek Road, about 1 km south-west from Scott Creek. The major land uses in the 949 hectare catchment are rural residential living, remnant native vegetation and stock grazing.
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, degraded riparian habitats and fine sediment deposits in the creek. Despite this, the site still provided habitat for some rare and sensitive macroinvertebrate species.
A sparse community of at least 28 species of macroinvertebrates was collected from the flowing creek, 2.5-2.6 m wide and up to 42 cm deep, in autumn and spring 2011. The majority of the creek consisted of a non-flowing channel but also included small areas of fast-flowing riffles connecting pool habitats, in both seasons sampled. The community was dominated by generalists and species tolerant to poor water quality such as amphipods (Austrochiltonia), freshwater shrimp (Paratya) and waterbugs (Micronecta and Microvelia). It also includes smaller numbers of introduced snails, worms, yabbies, springtails, beetles, dixids, biting midges, chironomids, mayflies, odonates, stoneflies and caddisflies. Several rare and sensitive species that are frequently associated with flowing water were collected or seen at the site, including a blackfly (Austrosimulium furiosum), mayfly (Thraulophlebia inconspicua), stoneflies (Dinotoperla evansi and Illiesoperla mayi) and caddisflies (Ulmerochorema membrum and Triplectides similis). The only fish recorded from the site was a European Carp in autumn.
The water was fresh (salinity ranged from 436-488 mg/L), well oxygenated (72-103% saturated), clear, and with moderate to high concentrations of nutrients such as nitrogen (0.4-1.23 mg/L) and phosphorus (0.03-0.04 mg/L).
The sediments were dominated by detritus and sand, with boulder, cobble, pebble, silt and algae also present. Samples taken from below the surface were anaerobic and sulphidic in autumn, indicating the sediments lacked oxygen but they appeared unremarkable and well-aerated in spring. A large deposit of fine silt, 1-5 cm deep, covered the creekbed in autumn but only 1 cm was recorded in spring following winter high flow periods. No significant erosion was noted at the site in 2011.
About 10% of the channel was covered by filamentous algae (including Cladophora) and another 35% of the site was covered by aquatic plants in spring. A range of submerged (Callitriche and Potamogeton crispus) and emergent species (Cotula, Juncus, Rumex, Isolepis, Persicaria and introduced Rorippa) were recorded at the site. The 5-10 m wide riparian zone consisted of introduced grasses, bracken and rushes under various types of gums, wattles and tea tree shrubs. The surrounding vegetation included areas of remnant native vegetation on the steeper hills and cleared stock grazing land on the flatter parts of the landscape.
Special environmental features
Scott Creek provides perennial flowing habitats that support a range of rare, sensitive and flow-dependent species.
Pressures and management responses
|Insufficient natural water flows in the creek resulting from water extraction and climate variability (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.