Walkers Creek, 4.5 km south-east from Freeling
2011 Aquatic Ecosystem Condition Report
- Permanently wet, slow-flowing, saline creek in autumn and spring 2011
- Sparse macroinvertebrate community with no rare and sensitive species
- Obvious signs of moderate to gross nutrient enrichment and salinisation effects
- Riparian vegetation limited to introduced grasses and a few gums
- Large deposit of silt in the creek.
About the location
Walkers Creek is a moderate sized stream in the Southern Mount Lofty Ranges that rises near Belvidere in the Nain Range and flows in a south-westerly direction before discharging into the North Para River near Rosedale. The monitoring site was located near Dee Road, about 4.5 km south-east from Freeling. The major land uses in the 6,564 hectare catchment are cereal cropping, legumes and stock grazing, with smaller areas of remnant native vegetation, various other minor agricultural activities and rural residential living.
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, high salinity, degraded riparian vegetation, silt deposition and areas with bank erosion.
A sparse community of at least 15 species of macroinvertebrates was collected from the slightly flowing creek, 2.6-3.2 m wide and up to 38 cm deep, in autumn and spring 2011. A small area of fast-flowing riffle habitat was present in autumn but the creek was only just flowing in spring. The community was dominated by generalists and species tolerant to poor water quality such as chironomids, dytiscid beetles and amphipods (Austrochiltonia). It also included smaller numbers of yabbies, springtails, mosquitoes, soldierflies, waterbugs and damselflies. No sensitive and rare species were recorded, and no flow-dependent macroinvertebrates were detected. No fish were seen at the site in 2011.
The water was saline (salinity ranged from 8,937-11,922 mg/L), well oxygenated (60-98% saturated), clear, and with moderate to high concentrations of nutrients such as nitrogen (0.65-1.23 mg/L) and phosphorus (0.04-0.1 mg/L).
The sediments were dominated by detritus, silt, clay and algae, with cobble, pebble and sand also present. Samples taken from below the surface were blackened, anaerobic and sulfidic, indicating that the sediment lacked oxygen and was a harsh environment for burrowing species to live in. Over 10 cm of fine silt covered the creekbed and more than 10 m of bank showed signs of erosion, caused by past high flow events and sheep damage of the poorly vegetated banks.
More than 10% of the creek was covered by filamentous algae (including Cladophora and Spirogyra) and a similar area was covered by emergent plants (Bolboschoenus and Juncus articulatus). The narrow riparian zone was dominated by introduced grasses under a few scattered River Red Gums. The surrounding vegetation comprised cereal cropping land with patches of remnant native woodland vegetation.
Special environmental features
Pressures and 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.