Light River, north from Freeling
2011 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, saline stream in autumn and spring 2011
- Moderately diverse macroinvertebrate community with only one sensitive species
- Obvious signs of moderate nutrient enrichment and salinisation effects
- Riparian vegetation dominated by introduced weeds and native emergent plants
- Fine sediment deposits cover the riverbed.
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 monitoring site was located near a track off the north-eastern end of Meaney Road, about 8.5 km north from Freeling. The major land uses in the 103,625 hectare catchment are cereal cropping and stock grazing, with smaller areas of remnant native vegetation, various agricultural activities, and rural and urban residential living.
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 riverbed.
A moderately diverse community of at least 34 species of macroinvertebrates was collected from the river, 0.7-15.5 m wide and up to 40 cm deep, in autumn and spring 2011. The river comprised still to slow-flowing pool habitats connected by smaller areas of faster-flowing riffle habitats. The community was dominated by generalists and species tolerant to high salinity and poor water quality such as hydrobiid snails, amphipods (Austrochiltonia and Eusiridae), blackflies and leptocerid caddisflies (Notalina spira). It also included smaller numbers of flatworms, bivalves, worms, beetles, soldierflies, chironomids, waterbugs, odonates and other types of caddisflies. No rare species was collected and the only sensitive species recorded was a flow-dependent blackfly (Austrosimulium furiosum). A few other species normally associated with flowing water were also collected, including a beetle (Platynectes decempunctatus), blackfly (Simulium ornatipes) and hydropsychid caddisfly (Cheumatopsyche sp. 2). No fish were seen at the site in 2011.
The water was saline (salinity ranged from 4,025-4,280 mg/L), well oxygenated (84-98% saturated), clear, and with moderate to high concentrations of nutrients such as nitrogen (0.69-0.71 mg/L) and phosphorus (0.02 mg/L).
The sediments were dominated by detritus and clay in the slower-flowing sections and cobble, algae and detritus in the riffles. Samples taken from below the surface were slightly blackened, anaerobic and sulfidic, indicating that the sediments lacked oxygen and were a harsh place for burrowing species to live in. A large deposit of fine silt, over 5 cm deep, covered the channel in places and more than 10 m of bank showed evidence of erosion in autumn due to recent flood damage.
A moderate amount of phytoplankton was recorded from the site and filamentous algae (mostly Cladophora) covered over 10% of the river. Aquatic plants extended over 35% of the site, with reeds (Phragmites) particularly extensive and smaller growths of a wide range of other species (Crassula, Juncus, Cyperus, Rumex and Schoenoplectus). The riparian vegetation was dominated by introduced grasses and weeds, sedges, rushes, lignum and a few scattered paperbark and gum trees. The surrounding vegetation was cleared sheep grazing and cereal cropping land with a few isolated gum trees in the local landscape.
Special environmental features
The Light River near Freeling provides habitat for a large number of saline tolerant macroinvertebrates, including several flow-dependent species.
Pressures and management responses
|Insufficient natural water flows in the creek resulting from water extraction and climate variability (reducing ecological integrity).||Through water allocation planning the Adelaide and Mount Lofty Ranges NRM Board seeks to manage a sustainable water supply for the region so that there is enough water available for everyone (including the environment) even in drought conditions.|
|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.