Tributary of South Para River, W from Williamstown
2013 Aquatic Ecosystem Condition Report
- Permanently wet stream in autumn and spring 2013
- Diverse macroinvertebrate community with many generalist and tolerant species and two rare and sensitive species
- Water was fresh, clear and enriched with nutrients
- Riparian vegetation consisted of scattered gums over introduced grasses, rushes and sedges
About the location
Tributary of South Para River is a small stream that rises at an elevation of about 520 m near Wirra Wirra Peaks in the Southern Mount Lofty Ranges, and flows in a southerly direction for several kilometres before discharging into the South Para River, upstream from the Warren Reservoir. Major land uses in the 854 hectare catchment included stock grazing (55%) and plantation forestry (24%), with smaller areas also used for irrigated horticulture, residential living, roads, other minimal uses and dams. The site was located west from Portuguese Bridge on Springton Road, about 9 km east from Williamstown.
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 due to the extent of nutrient enrichment of the creek and some areas with minor bank erosion but the stream still provides habitat for a wide range of commonly occurring macroinvertebrates from the region.
A diverse community of at least 45 species of macroinvertebrates was collected or seen from the creek (17 species in autumn and 37 in spring), 5.8-6.2 m wide and 42 cm deep, in autumn and spring 2013. The creek consisted of a non-flowing, connected channel in autumn but had contracted to isolated pools in spring. The community was dominated by moderate numbers of hypogastrurid springtails and chironomids in autumn pools but also included lower numbers of snails, mites, amphipods, shrimp, yabbies, beetles, mosquitoes, biting midges, brineflies, mayflies, waterbugs, damselflies and caddisflies. The autumn assemblage comprised commonly occurring generalist, opportunistic and/or tolerant species, although one of the chironomids (Podonomopsis) is more typically found from newly wetted habitats, rather than streams that have ceased to flow and started to dry. In spring, a richer assemblage of mostly generalist and tolerant species was collected, which included 9 beetles, 6 chironomids, 5 waterbugs and 2 sensitive and flow-dependent mayflies (Offadens and Thraulophlebia inconspicua).
The water was fresh (salinity ranged from 765-2,235 mg/L), well oxygenated (102-121% saturation), clear but slightly coloured, and with generally high nutrient concentrations such as phosphorus (0.02-0.05 mg/L) and nitrogen (1.04-1.89 mg/L).
The sediments were dominated by detritus and pebbles, with smaller amounts of cobble, gravel, sand, silt and clay also present; samples taken from below the surface were grey silts, sands and clays that released sulfide when tested in spring, which indicates that the sediments were anaerobic and lacking oxygen for at least part of the year. A small amount of bank erosion was noted over about 10% of the site, which appeared to have been caused by cattle accessing and damaging the banks of the creek.
There was a small to moderate amount of phytoplankton was recorded (chlorophyll a ranged from 2.2-7.5 μg/L) and over 10% of the channel was covered by filamentous algae (Spirogyra) in spring. Another 35% of the creek was covered by several types of aquatic plants, which included sedges (Cyperus), rushes (Juncus), creeping monkey-flower (Mimulus), water ribbons (Triglochin) and water buttons (Cotula). The riparian zone consisted of scattered gums and wattles over introduced grasses, rushes and sedges. The surrounding vegetation near the creek comprised cattle grazing paddocks with scattered gums on one bank and pine forest on the other bank.
Special environmental features
The main environmental values of this creek are to provide habitat for a wide range of commonly found, generalist and tolerant aquatic species and support two of the more sensitive species of mayflies that occur in the region.
Pressures and 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.|
|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.