Light River, west from Kapunda
2011 Aquatic Ecosystem Condition Report
- Permanently wet, flowing, saline stream in autumn and spring 2011
- Sparse macroinvertebrate community with no rare or sensitive species
- Obvious signs of moderate nutrient enrichment and salinisation
- Riparian vegetation dominated by gums over rushes and introduced grasses.
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 off the south-western end of Charles Hill Road, about 9 km west from Kapunda. The major land uses in the 105,008 hectare catchment are cereal cropping and stock grazing, with smaller areas used for legumes, remnant native vegetation, and various other agricultural and residential uses.
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, high salinity, degraded riparian vegetation and fine sediment deposition in the channel.
A sparse community of at least 23 species of macroinvertebrates was collected from the creek, 9.5 m wide and up to 20 cm deep, in autumn and spring 2011. The river consisted of large sections of still to slow-flowing pools connected by narrow areas of fast-flowing riffles. The community was dominated by generalists and species tolerant to high salinity and poor water quality such as leptocerid caddisflies (Notalina spira), amphipods and hydrobiid snails. It also included smaller numbers of nemerteans, introduced snails (Physa), freshwater shrimp, yabbies, beetles, blackflies, chironomids, mayflies (Cloeon), waterbugs, odonates and another leptocerid species (Triplectides australicus). No rare or sensitive species were collected but two flow-dependent species were recorded, including a beetle (Platynectes decempunctatus) and blackfly (Simulium ornatipes). The only fish seen at the site was an introduced pest called Mosquitofish (Gambusia).
The water was saline (salinity ranged from 3,838-4,481 mg/L), well oxygenated (83-99 % saturated), clear, and with moderate to high concentrations of nutrients such as nitrogen (0.78-0.87 mg/L) and phosphorus (0.03-0.04 mg/L).
The sediments were dominated by detritus, algae and cobble. Samples taken from below the surface were slightly blackened in colour and sulfidic on occasions, indicating that the sediments were anaerobic and represented a harsh environment for burrowing species to live in. Over 1 cm of fine sediment covered the channel in places and about 10 m of bank showed evidence of erosion in spring due to recent flood damage.
A moderate amount of phytoplankton was recorded and about 10% of the channel was covered by filamentous algae (mostly Cladophora) in spring. Aquatic plants covered more than 35% of the river, with reeds (Phragmites) particularly extensive and patches of emergent species also present (Bolboschoenus, Cotula, Cyperus, Juncus and Schoenoplectus). The riparian vegetation was dominated by River Red Gums over rushes and introduced grasses. The surrounding vegetation was cleared cereal cropping land with a few scattered gum trees in the local landscape.
Special environmental features
The Light River near Kapunda provides habitat for a few species of flow-dependent macroinvertebrates that are able to tolerate quite saline conditions.
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.