Little Para River, Salisbury Downs
2011 Aquatic Ecosystem Condition Report
- Permanently wet, shallow, freshwater pools present in autumn and spring 2011
- Sparse macroinvertebrate community with no rare or sensitive species
- Obvious signs of gross nutrient enrichment
- Riparian vegetation dominated by introduced grasses and weeds
- Fine sediment deposits and areas with severe bank erosion.
About the location
The Little Para River is a large stream in the Southern Mount Lofty Ranges that rises south from Inglewood and drains northwards into the Little Para Reservoir; downstream flows head westwards where it eventually discharges into the Port River estuarine environment at Swan Alley Creek. The monitoring site was located off Martins Road in Salisbury. The major land uses in the 9,408 hectare catchment are stock grazing, water supply (Little Para Reservoir), rural residential living and remnant native vegetation, with smaller areas used for a range of irrigated crops and other agricultural activities, quarries and recreation.
The creek was given a Very Poor rating because the site sampled showed evidence of major changes to both the animal and plant life inhabiting the stream, and a significant breakdown in the way the ecosystem functions. There was considerable evidence of human disturbance including nutrient enrichment, bank erosion from stormwater damage, degraded riparian habitats and fine silt deposition in the channel.
A sparse community of at least 14 species of macroinvertebrates was collected from the isolated pools in the creek, 2-2.6 m wide and up to 44 cm deep, in autumn and spring 2011. The community was comprised low numbers of flatworms, introduced and native snails, worms, yabbies, beetles, mosquitoes, chironomids, waterbugs, damselflies and dragonflies. All were among the most tolerant types of macroinvertebrates and no rare or sensitive species were recorded. No fish were seen at the site in 2011.
The water was very fresh (salinity ranged from 171-204 mg/L), well oxygenated (56-89% saturated), slightly coloured but highly turbid, and with moderate to high concentrations of nutrients such as nitrogen (0.45-1.53 mg/L) and phosphorus (0.06-0.16 mg/L).
The sediments were dominated by clay and detritus, with cobble, silt, sand and algae also present. Samples taken from below the surface were blackened in colour which indicates that the sediments occasionally turned anaerobic, or lacked oxygen, however, the sediments appeared well-aerated when assessed in 2011. A large deposit of silt up to 5 cm deep was recorded in spring, when over 10 m of bank showed evidence of erosion caused by recent flood damage.
A large amount of phytoplankton was recorded from the stream in spring, when filamentous algal growths (mostly Spirogyra) covered about 10% of the site. A few patches of emergent plants (Cyperus, Rumex and Persicaria) were present but only covered slightly less than 10% of the available wetted area. The riparian vegetation comprised a few, large River Red Gums and some wattles over an understorey dominated by introduced grasses and weeds. The surrounding vegetation was urban residential land with a recreation part and golf course in the local landscape.
Special environmental features
Pressures and management responses
|Stormwater runoff containing high nutrient and sediment loads discharging to the creek (causing habitat disturbance, algal growth and aquatic weeds).||The Adelaide and Mount Lofty Ranges NRM Board has a well developed stormwater quality improvement, harvesting and reuse program which has installed (and maintains) gross pollutant (and silt) traps in several watercourses across the region to catch litter, debris and silt in order to minimise impacts and damage to seagrass in the receiving marine environment. Stormwater captured is also treated through artificial wetlands across the region which act as suspended solid and nutrient filters; these wetlands also provide important habitat for many native species.|
|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.|
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.