Sparse macroinvertebrate community, with no species sensitive to pollution found.
Riparian zone invaded by exotic trees and woody weeds.
Treated effluent regularly discharged into waterway.
Area map
About the location
Hahndorf Creek rises near Hahndorf in the central Mount Lofty Ranges, and flows through a small catchment area into the Onkaparinga River just south of Verdun, near the South Eastern Freeway. Livestock grazing (57%) is the main land use but there are also extensive areas of urban development (26%) and some dairying (5%). The Hahndorf Wastewater Treatment Plant regularly discharges chlorinated effluent into the stream.
The site selected for monitoring was located downstream of the treatment plant, off Main Road, on the eastern boundary of Hahndorf.
The river was given a Poor rating at this site because the ecosystem showed evidence of major changes in the animal community and plant life, and moderate changes to the way the ecosystem functions because of nutrient enrichment and presence of fine sediment.
Findings
A series of pool habitats, set within a channel three to four metres wide, and connected by small areas of flowing riffles, formed the creek at this site when it was sampled in October 2008.
A sparse community of 25 macroinvertebrate species was collected. The community comprised mainly species tolerant of high nutrient levels such as chironomids, worms, mites and snails. Chironomids (including Dicrotendipes and Polypedilum) were the most abundant species collected. No sensitive species were found, and no stoneflies, mayflies or caddisflies were seen.
The water was fresh (salinity of 900 mg/L), moderately well oxygenated (57% saturation), and slightly cloudy, or turbid. It contained high concentrations of nutrients such as nitrogen (6 mg/L) and phosphorus (0.14 mg/L).
The sediments were mostly clay, detritus and silt; they were blackened and anaerobic below the surface, indicating the presence of too much organic material in the creek.
While the potential for nuisance algal and plant growths exists with this sort of poor water quality, algae and plants were not abundant at the site. This was presumably due to the combined effect of a persistent but slight flow of water, and the dense shading (95%) provided by River Red Gums, exotic trees and woody weeds (hawthorn, blackberries and willows) lining the creek in the riparian zone.
Vegetation in the surrounding area was mostly native eucalypt woodland over acacias and grasses.
Special environmental features
None identified.
Pressures and management responses
Pressures
Management responses
Widespread introduced trees and 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.
Stormwater runoff causing high water velocities, containing nutrients and sediments (causing habitat disturbance, algal growth and aquatic weeds).
The Adelaide and Mount Lofty Ranges NRM Board's 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.
Wastewater discharge, adding excessive nutrients and organic matter (leading to algal growth and aquatic weeds).
SA Water Hahndorf Wastewater Treatment Plant
SA Water assess and undertake scheduled process improvement actions at the wastewater treatment plant, with the aim to reduce environmental risk and ensure operations are compliant with EPA licence conditions.
This aquatic ecosystem condition report is based on monitoring data collected by the EPA and prepared in conjunction with the Adelaide and Mount Lofty Ranges NRM Board.
Observed Condition
Expected Condition
