Light River, Kapunda Bridge
2016 Aquatic Ecosystem Condition Report
Permanently flowing stream in autumn and spring 2016
Moderately diverse saline tolerant macroinvertebrate community with only one flow-dependent species but no rare or sensitive species recorded
Riparian vegetation consisted of native trees over a weedy understorey
No evidence that the 2015 Pinery fire caused any additional sediment or nutrient runoff to the river
About the location
The Light River is a large river in the Northern Mount Lofty Ranges that rises south from Waterloo in the Mid North and flows in a southerly direction past Kapunda, and then heads south-west, where it eventually discharges into Gulf St Vincent near Middle Beach. The major land uses in the catchment include cereal cropping and grazing, with smaller areas used for legumes, remnant native vegetation, and various other agricultural and residential uses. The monitoring site was located in the mid reaches downstream from Kapunda Bridge on Kapunda Road, about 2 km south from Kapunda. The site was selected from the eastern edge of the 2015 Pinery fire zone to help determine if any subsequent runoff caused additional sediment and nutrient enrichment of the Light River.
The river was given a Poor rating because the site sampled showed evidence of major changes in ecosystem structure, and moderate changes to the way the ecosystem functions. There was considerable evidence of human disturbance including nutrient enrichment, salinization and a weedy riparian zone. Only saline tolerant aquatic macroinvertebrates, fish and plants were recorded from the site.
A moderately diverse community of at least 38 species of macroinvertebrates was collected from the river (27 species in autumn and 23 in spring), 4.2-8.2 m wide and up to 30 cm deep, in autumn and spring 2016. The river consisted of similar areas of fast-flowing riffles connecting slow-flowing and still pools in both seasons sampled. The community was dominated by large numbers of salt-tolerant amphipods (Austrochiltonia and Eusiridae), blackflies, hydrobiid snails (mostly introduced Potamopyrgus) and chironomids. It also included smaller numbers of worms, other snails (including introduced Physiella), mites, beetles, craneflies, gall midges, biting midges, mosquitoes, soldierflies, waterbugs, damselflies, dragonflies and caddisflies. No rare or sensitive species were collected, and the only flow-dependent species recorded was a blackfly (Simulium ornatipes). All species collected were typical of saline, nutrient enriched streams draining agricultural catchments in South Australia. The only fish seen at the site was the introduced mosquitofish (Gambusia), which also commonly occurs in saline streams in the region.
The water was saline (salinity ranged from 5,266-5,741 mg/L), well oxygenated (83-97% saturation), clear, and with generally moderate to high concentrations of nutrients such as phosphorus (0.023-0.024 mg/L) and nitrogen (0.69-0.81 mg/L).
The sediments comprised a wide range of coarse and fine sediment types, with filamentous algae dominating the pools in autumn; samples taken from below the surface were mostly grey clay and silt that released sulfide when tested in autumn, indicating that the sediments were occasionally anaerobic and lacked oxygen. There was no evidence of any significant bank erosion or any signs of animal droppings seen in the vicinity of the river.
No evidence of any significant additional loads of ash, fine sediment and nutrients entering the site from the burnt parts of the nearby catchment affected by the 2015 Pinery Fire were noted during either autumn or spring 2016 survey period.
A moderate amount of phytoplankton was recorded (chlorophyll a ranged from 4.2-8.6 μg/L), and filamentous algae (Cladophora, Spirogyra and Enteromorpha) covered more than 10% of the river during both survey periods. Over 35% of the channel was also covered by aquatic plants, including reeds (Phragmites), sedges (Schoenoplectus and Bolboschoenus), rushes (Juncus), monkey-flower (Mimulus) and submerged charophytes (Chara).
The riparian zone extended over 30 m wide in places and was dominated by River Red Gums over various weeds that included Sharp Rush (Juncus acuta), olives, and fennel and introduced grasses. The surrounding landscape was cleared grazing and cropping land with a few isolated gums.
Special environmental features
Pressures and management responses
Nutrient inputs to the creek from numerous diffuse sources (potentially leading to excess growth of algae and aquatic weeds)
The Adelaide and Mount Lofty Ranges NRM Board 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.
Saline groundwater inflows to the creek
The Adelaide and Mount Lofty Ranges NRM Board has installed telemetered groundwater monitoring stations at key locations within the region. These are monitored for level and salinity; unusual results (such as high salinity influxes) are investigated.
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.