Peter Creek is a small stream in the Southern Mount Lofty Ranges that rises west of the Kuitpo Forest and flows in a north-westerly direction, where it eventually discharges into the Onkaparinga River several kilometres downstream from Mount Bold Reservoir. The monitoring site was located in the Onkaparinga Gorge off Peters Creek Road, about 2 km south from Kangarilla. The major land uses in the 670 hectare catchment are stock grazing, remnant native vegetation and forestry, with smaller areas used for irrigated vines and rural residential living.
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, fine sediment deposition and weeds dominating the riparian vegetation. Despite this, the stream still provided habitat for rare and sensitive macroinvertebrate species.
Findings
A moderately diverse community of at least 38 species of macroinvertebrates was collected from the creek, 1-2 m wide and up to 18 cm deep, in autumn and spring 2011. The creek was slow-flowing in autumn but nearly 50% of the site comprised fast-flowing riffle habitat in spring. The community was dominated by generalists and species tolerant to poor water quality such as amphipods (Austrochiltonia australis), mosquitoes and chironomids. Large numbers of sensitive gripopterygid stoneflies were also collected from the riffles in spring. The community also included smaller numbers of native and introduced snails, mites, springtails, beetles, biting midges, blackflies, soldierflies, mayflies, waterbugs, odonates and caddisflies. At least six rare and sensitive species were collected, including a blackfly (Austrosimulium furiosum), mayfly (Thraulophlebiainconspicua), stoneflies (Dinotoperla evansi and Illiesoperla mayi) and caddisflies (Taschorema evansi and Ulmerochorema membrum). The site also provided habitat for a range of flow-dependent species, such as a beetle (Platynectes decempunctatus), chironomid (Rheotanytarsus) and the above-listed rare and sensitive species. No fish were seen at the site in 2011.
The water was fresh to moderately fresh (salinity ranged from 520-1,423 mg/L), generally well oxygenated (55-91% saturated), slightly turbid and coloured, and with moderate to high concentrations of nutrients such as nitrogen (0.66-0.96 mg/L) and phosphorus (0.02-0.06 mg/L).
The sediments were dominated by detritus, cobble and sand along the edges of the channel whereas the flowing riffles mostly comprised cobble, pebble and sand. Samples taken from below the surface were blackened and sulfidic in autumn, indicating that the sediments were anaerobic and lacked oxygen; in contrast, there was little evidence that the sediments were anaerobic in spring when the creek was flowing strongly. A deposit of 1-5 cm of silt covered the creekbed in places in autumn but was not as pronounced in spring. Less than 10 m of bank showed evidence of erosion in the spring survey, due to recent flood damage that presumably transported fine sediment further downstream.
Filamentous algae (mostly Cladophora) covered over 10% of the site in spring but none was detected earlier in the year in autumn. Several emergent aquatic plants (Cyperus, Juncus and Rumex) also covered over 10% of the channel. The narrow riparian zone consisted of willows and River Red Gums over a range of woody (blackberries and wild rose) and herbaceous weeds and grasses. The surrounding vegetation was sheep grazing country with a few scattered gum trees in the local landscape.
Special environmental features
The permanently wet, freshwater, flowing habitats of Peter Creek provide an important refuge for a range of aquatic species, including at least six sensitive species and another two flow-dependent macroinvertebrate species. These features indicate that this stream represents one of the most significant small (second order) watercourses in the region.
Pressures and management responses
Pressures
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.
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.
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.
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.
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Observed Condition
Expected Condition
