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 monitoring site was located near a track off Rock Brook Road, about 5 km east from Kapunda. The major land uses in the 82,777 hectare catchment are cereal cropping and stock grazing, with smaller areas used for a range of other agricultural activities, residential living and remnant native vegetation.
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, salinisation, degraded riparian vegetation and fine sediment deposition in the channel.
Findings
A sparse community of at least 22 species of macroinvertebrates was collected from the river, 9.2-10.9 m wide and up to 51 cm deep, in autumn and spring 2011. The river consisted of a still channel in autumn but was slightly flowing when the site was re-sampled again in spring. The community was dominated by saline tolerant generalists, such as ceinid (Austrochiltonia) and eusirid amphipods. It also included smaller numbers of native snails (Glyptophysa), freshwater shrimp, freshwater prawns (Macrobrachium), yabbies, beetles, biting midges, chironomids, waterbugs, odonates, mayflies (Cloeon) and caddisflies. No sensitive or rare species were collected, and no flow-dependent species were seen when the river was flowing in spring. Similarly, no fish were seen at the site in 2011.
The water was saline (salinity ranged from 4,112-4,518 mg/L), well oxygenated (71-90% saturated), clear, and with moderate to high concentrations of nutrients such as nitrogen (0.42-0.77 mg/L) and phosphorus (0.02 mg/L).
The sediments were dominated by detritus, algae and silt. Samples taken from below the surface were blackened, anaerobic and sulphidic, indicating that the sediments lacked oxygen and represented a harsh environment for burrowing species to live in. A large deposit of fine silt, over 10 cm deep, covered the riverbed and more than 10 m of bank showed evidence of erosion due to sheep and flood damage.
A large growth of filamentous algae (Cladophora and Spirogyra) covered over 35% of the channel, and a similar area was also covered by a range of aquatic plants (Phragmites, Typha, Juncus and Schoenoplectus). The narrow riparian zone was dominated by introduced grasses and weeds, with only a few scattered gum trees present. The surrounding vegetation was cleared sheep grazing land with a few areas of planted trees in the local landscape.
Special environmental features
The Light River near Mingays Waterhole provides habitat for a range of saline tolerant macroinvertebrates, including freshwater prawns (Macrobrachium) and mayflies (Cloeon) that are more typically found in fresher environments; their occurrence in the Light River may be at or around their upper salinity tolerance levels.
Pressures and management responses
Pressures
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.
Saline groundwater inflows to the creek (reducing ecological integrity).
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.
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.
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Observed Condition
Expected Condition
