Little Para River, One Tree Hill Crossing
2016 Aquatic Ecosystem Condition Report
Permanent to nearly permanent flowing stream in autumn and spring 2016
Moderately diverse macroinvertebrate community with several rare, sensitive and flow-dependent species recorded
Water was fresh, clear and moderately enriched with nutrients
- Riparian vegetation mostly consisted of native trees over reeds and a weedy understorey
About the location
The Little Para River is a large stream in the Southern Mount Lofty Ranges that rises south from Inglewood and drains northwards into the Little Para Reservoir; downstream flows head westwards where it eventually discharges into the Port River estuarine environment at Swan Alley Creek. The major land uses in the catchment are stock grazing, water supply (Little Para Reservoir), rural residential living and remnant native vegetation, with smaller areas used for a range of irrigated crops and other agricultural activities, quarries and recreation. The monitoring site was located about 1.5 km upstream from reservoir off One Tree Hill Road, 3 km south from One Tree Hill.
The river was given a Good rating because the site sampled showed evidence of minor changes in ecosystem structure and function. There was evidence of human disturbance due to the presence of a weedy riparian zone and moderately enriched nutrient concentrations recorded from the river. The site still supported several sensitive taxa and a number of generalist and tolerant species.
A moderately diverse community of at least 36 species of macroinvertebrates was collected from the river (23 species in autumn and 24 in spring), 1.6-7.5 m wide and well over 1 m deep in places, in autumn and spring 2016. The river consisted of a slow-flowing channel in autumn and large pools connected by faster flowing riffles in spring. The community was dominated by amphipods and baetid mayflies (Offadens) and included smaller numbers of nematodes, limpets, worms, shrimp, yabbies, beetles, blackflies, mothflies, chironomids, leptophlebiid mayflies (Atalophlebia australasica, Atalophlebia australis and Thraulophlebia inconspicua), caenid mayflies, waterbugs, dragonflies, stoneflies and caddisflies. Several rare, sensitive and flow-dependent species were collected, including the above-listed baetid and leptophlebiid mayflies, dragonfly (Hemigomphus), and caddisflies (Taschorema evansi, Ulmerochorema membrum and Cheumatopsyche sp.2), blackfly (Austrosimulium) and stonefly (Dinotoperla evansi).
The water was fresh (salinity ranged from 265-514 mg/L), well oxygenated (83-86% saturation), clear but slightly coloured in spring, and with generally moderate concentrations of nutrients such as phosphorus (0.02 mg/L) and nitrogen (0.47-0.55 mg/L).
The sediments were dominated by detritus, boulder and cobble; samples taken from below the surface were mostly grey silts, clays and sands that did not release any sulfide when tested, indicating that the sediments were well oxygenated. There was some minor evidence of bank erosion seen in spring, which was attributed to recent flood damage. No stock or other animal droppings were seen in the vicinity of the river.
Only a small amount of phytoplankton was recorded during the year (chlorophyll a 0.61 μg/L) and filamentous algae (Cladophora) was only seen in spring, when it extended over nearly 10% of the river. Over 35% of the stream was covered by aquatic plants in autumn but after winter floods scoured the channel only about 10% of the channel was covered with vegetation during the spring survey. Aquatic plants recorded from the site included reeds (Phragmites), cumbungi (Typha) and knotweed (Persicaria). The riparian zone comprised native gum trees, wattles and reeds, and a range of woody and herbaceous weeds (e.g. blackberries, gorse, ash trees, willows, introduced grasses). The surrounding terrestrial vegetation comprised an open woodland with an understorey dominated by introduced grasses and weeds.
Special environmental features
The site supported a number of rare, sensitive and flow-dependent species as well as a wide range of generalist and tolerant macroinvertebrates.
Pressures and management responses
Widespread introduced weeds in the riparian zone at the site and upstream
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.
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.