Little Para River, NW Little Para Reservoir
2013 Aquatic Ecosystem Condition Report
- Permanently flowing stream in autumn and spring 2013
- Diverse macroinvertebrate community with several rare, sensitive and flow-dependent species present
- Water was fresh, clear and high in nitrogen
- Riparian vegetation consisted of willows and pines over reeds
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 across several urban suburbs, where it eventually discharges into the Port River estuarine environment at Swan Alley Creek. The major land uses in the 4,172 hectare catchment upstream from the reservoir were stock grazing of modified pastures (56%) and residential living (23%), with smaller areas used for irrigated horticulture, other minimal uses, roads, services, managed resource protection, plantation forestry, cropping, mining and dams. The site sampled was located at the end of a fire track off Snake Gully Road and One Tree Road.
The river was given a Good rating because the site sampled showed evidence of relatively minor changes in ecosystem structure and function. There was evidence of human disturbance due to the dominance of woody weeds lining the river, presence of filamentous algae in spring and the moderate nitrogen concentrations recorded from river. Despite this, the stream provides significant habitat for a number of rare, sensitive and flow-dependent species of macroinvertebrates.
A diverse community of at least 41 species of macroinvertebrates was collected or seen from the river (24 species in autumn and 33 in spring), 1.8-4.1 m wide and up to 24 cm deep, in autumn and spring 2013. The river consisted of similar areas of fast-flowing, shallow riffle habitats and still to slow-flowing pools in both seasons sampled. The community was dominated by moderate numbers of sensitive groups such as mayflies and blackflies, and also included smaller numbers of flatworms, introduced snails (Potamopyrgus), limpets, worms, mites, amphipods (including eusirids), shrimp, yabbies, springtails, beetles, dixid flies, mosquitoes, biting midges, chironomids, waterbugs, stoneflies and caddisflies. Several rare and sensitive species were collected, including mayflies (Offadens sp.5, Atalophlebia australasica, Atalophlebia australis and Thraulophlebia inconspicua), blackflies (Austrosimulium furiosum and Simulium melatum), and a stonefly (Dinotoperla evansi) and caddisfly (Taschorema). A range of species normally associated with flowing water were also collected, including a caddisfly (Cheumatopsyche sp. 2), blackfly (Simulium ornatipes), chironomid (Rheotanytarsus) and the above-mentioned sensitive and rare species. In autumn, the site also provided habitat for a chironomid (Podonomopsis) that is normally associated with newly wetted habitats; the presence of larvae and pupae indicated that it had colonised the site several weeks prior to sampling. The remaining macroinvertebrates comprised a range of generalist, opportunistic and tolerant species that have a widespread distribution across the region.
The water was fresh (salinity ranged from 615-751 mg/L), well oxygenated (117-134% saturation), clear, and with generally low to moderate concentrations of nutrients such as phosphorus (0.01 mg/L) and nitrogen (0.37-0.59 mg/L).
The sediments were dominated by detritus, sand, boulder and cobble, with smaller amounts of clay, pebble, gravel and silt present. Samples taken from below the surface were sandy grey in appearance and tested positive for the presence of sulfides, indicating that the sediments were anaerobic and lacked oxygen. This was probably due to the decomposition of the large amount of organic detritus that is being deposited into the river from the many introduced trees that line the banks. There was no evidence of any bank erosion and the only animal droppings seen near the stream were from kangaroos.
There were no significant growths of phytoplankton detected during the year (chlorophyll a ranged from 0.2-1.1 μg/L) but large amounts of filamentous algae (Cladophora) covered more than 10% of the stream in spring. A similar area was also covered by several types of aquatic plants, including reeds (Phragmites), cumbungi (Typha) and sedges (Cyperus). The narrow riparian zone was dominated by introduced woody weeds (willows and pines) over reeds and a few sedges. The surrounding vegetation near the creek comprised open woodland dominated by gums and wattles.
Special environmental features
Little Para River is a significant freshwater stream in the Mount Lofty Ranges that supports a number of rare, sensitive and flow-dependent species in the upper and middle parts of its catchment.
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.|
|Nutrient inputs to the creek from numerous diffuse sources (leading to extensive growth of algae and aquatic weeds)||The Adelaide and Mount Lofty Ranges NRM Board’s land management program encourages and promotes managing land to improve water quality. This includes working with industry and landholders to ensure efficient use of fertilisers and discuss ways to reduce runoff of nutrients into 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.