Tributary of the South Para River, west from Portuguese Bridge
2011 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, freshwater creek in autumn and spring 2011
- Diverse macroinvertebrate community with a few sensitive species that frequent flowing habitats
- Obvious signs of moderate nutrient enrichment
- Riparian vegetation dominated by introduced grasses and weeds, sedges and rushes.
About the location
This creek is a small stream in the Southern Mount Lofty Ranges that rises north-east from Williamstown and flows in a southerly direction where it discharges into the South Para River about 3 km east from the Warren Reservoir. The monitoring site was located west from Portuguese Bridge on the Williamstown-Springton Road, about 7.5 km south-east from Williamstown. The major land uses in the 852 hectare catchment are stock grazing and forestry, with smaller areas used for irrigated vines, residential living and remnant native vegetation.
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, a degraded riparian zone and lack of surrounding vegetated buffer to protect the stream from adjacent land uses. Despite this, the stream still provided habitat for a wide range of macroinvertebrate species.
A diverse community of at least 45 species of macroinvertebrates was collected from the flowing creek, 2.2-6.8 m wide and up to 70 cm deep, in autumn and spring 2011. The creek was only just flowing in autumn when water levels were low but small areas of fast-flowing riffle habitats were present in spring. The community was dominated by generalists and species tolerant to poor water quality such as amphipods (Austrochiltonia), chironomids, waterbugs (Anisops) and springtails. It also included smaller numbers of native and introduced snails, worms, mites, freshwater shrimp, yabbies, beetles, mosquitoes, biting midges, soldierflies, sciomyzids, mayflies, other waterbugs, odonates and caddisflies. The only sensitive species collected was a single leptophlebiid mayfly (Thraulophlebia inconspicua) in spring, and some small gripopterygid stoneflies were seen in the riffle habitats in the same season. The riffles also supported at least two other species normally associated with flowing waters, including small blackfly larvae and a dytiscid beetle (Platynectes decempunctatus). No fish were seen at the site in 2011.
The water was fresh to moderately fresh (salinity ranged from 1,618 mg/L in autumn to 812 mg/L in spring), well oxygenated (62-89% saturated), clear but strongly coloured in autumn, and with moderate to high concentrations of nutrients such as nitrogen (0.84-1.43 mg/L) and phosphorus (0.04-0.05 mg/L).
The sediments were dominated by sand, pebble, cobble and detritus, with silt, gravel and clay also present. Samples taken from below the surface were generally indicative of well-aerated sediments (e.g. grey in colour, unremarkable odour) but the undersides of rocks were slightly blackened in spring, indicating that they occasionally become low in oxygen. Only small deposits of silt, 1 cm deep, were recorded from the channel in places and about 10 m of bank showed evidence of erosion in spring due to recent flood damage.
No extensive growths of filamentous algae were seen at the site and only low levels of phytoplankton were recorded during both survey periods. Aquatic plants covered more than 35% of the creek in spring and included a range of submerged (Crassula) and emergent species (Cotula, Cyperus, Eleocharis, Isolepis, Juncus, Mimulus, Persicaria, Ranunculus, Lythrum, Rumex and Triglochin). The riparian vegetation consisted of a few River Red Gums over an extensive growth of introduced grasses, weeds, rushes and sedges. The surrounding vegetation consisted of a pine forest on one bank and a grazed eucalypt woodland with introduced grasses dominating the understorey of the other bank..
Special environmental features
The permanently wet, flowing, freshwater habitats support a wide range of aquatic species, including a few 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.|
|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.