Permanently flowing stream in autumn and spring 2016
Moderately diverse saline-tolerant macroinvertebrate community with no rare or sensitive species recorded
Water was saline, clear and enriched with nutrients
Riparian vegetation consisted of reeds and a few gum trees
No evidence that the 2015 Pinery fire caused any additional sediment or nutrient runoff to the river
Area map
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 lower reaches near Murphy’s Crossing on Murphy’s Crossing Road, about 4 km south-west from Hamley Bridge. The site was selected from the middle of the 2015 Pinery fire zone to 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 limited riparian zone. Only saline tolerant aquatic macroinvertebrates, fish and plants were recorded from the site.
Findings
A moderately diverse community of at least 26 species of macroinvertebrates was collected from the river (17 species in autumn and 16 in spring), 3-6.8 m wide and up to 32 cm deep, in autumn and spring 2016. The river consisted of a slow-flowing channel in autumn and comprised an equal area of fast-flowing riffles connecting slow-flowing to still pools in spring. The community was dominated by large numbers of amphipods from the Families Chiltoniidae and Eusiridae and snails from the Family Tataeidae. It also included smaller numbers of other tolerant and generalist species such as worms, mites, beetles, blackflies, soldierflies, brineflies, chironomids, damselflies, dragonflies and caddisflies. The site lacked any rare or sensitive species and the only flow-dependent species recorded was a blackfly (Simulium ornatipes). The community only included species normally found in saline waters. The only fish seen at the site were introduced mosquitofish (Gambusia), which is also commonly found in other saline agricultural streams in the region.
The water was saline (salinity ranged from 6,166-6,480 mg/L), well oxygenated (74-81% saturation), clear but slightly coloured, and with high concentrations of nutrients such as phosphorus (0.04-0.08 mg/L) and nitrogen (1.01-1.09 mg/L).
The sediments were dominated by detritus, sand, silt, algae, cobbles and pebbles; samples taken from below the surface were mostly grey sand that released sulfide when tested, indicating that the sediments were anaerobic and lacked oxygen. There was some minor evidence of bank erosion, which was probably caused by past flood damage. No stock droppings were 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 catchment affected by the 2015 Pinery Fire were noted during either autumn or spring 2016 survey period.
A large amount of phytoplankton was recorded during both surveys (chlorophyll a ranged from 16.5-23.6 μg/L), and large growths of filamentous algae (Cladophora, Spirogyra and Enteromorpha) extended over more than 10% of the river. More than 35% of the channel was also covered by aquatic plants, including extensive growths of reeds (Phragmites) and patches of submerged charophytes (Chara) and sedges (Bolboschoenus). The riparian zone was dominated by reeds with a few scattered gum trees and the surrounding landscape was mostly cleared grazing and cereal cropping land with a few isolated gums.
Special environmental features
None observed.
Pressures and management responses
Pressures
Management responses
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.
Nnutrient 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 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.