Tributary of Dry Creek, Banksia Park
2011 Aquatic Ecosystem Condition Report
- Permanently wet, freshwater creek with flowing water in autumn and isolated pools in spring
- Sparse macroinvertebrate community with one rare species
- Obvious signs of gross nutrient enrichment
- Riparian vegetation consisted of planted native trees and weedy understorey
- Fine sediment deposited in the creek
About the location
Tributary of Dry Creek is a small stream in the Southern Mount Lofty Ranges that rises on the western side of Range Road in Lower Hermitage and flows east, where it joins with other tributaries to eventually form the one main channel called Dry Creek in Valley View. The monitoring site was located off Butler Crescent in Banksia Park. The major land uses in the 305 hectare catchment are rural residential living, stock grazing and remnant native vegetation, with smaller areas used for irrigated cropping and roads.
The creek 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, fine sediment deposition and degraded riparian habitats.
A sparse community of at least 23 species of macroinvertebrates was collected from the creek, 1.2-1.8 m wide and up to 28 cm deep, in autumn and spring 2011. Small areas of flowing riffles were present in autumn but only small chironomids were seen in this habitat. The non-flowing channel habitat that dominated the creek in autumn contracted to isolated pools when sampled again in spring.
The community was dominated by moderate numbers of a few species tolerant to poor water quality that frequent temporary waters, such as chironomids, mites, flatworms and an introduced snail (Physa). It also included a few limpets, native snails, worms, amphipods, springtails, beetles, mosquitoes, sciomyzids, waterbugs and odonates. None of the more sensitive insect groups, such as mayflies, stoneflies and caddisflies, were present. The only rare macroinvertebrate found at the site was a single chironomid from the genus Podonomopsis; it has typically been recorded from wetter catchments in the Mount Lofty Ranges but may also be able to colonise newly created, flowing habitats from more ephemeral streams in the region, such as Dry Creek, on occasions. No fish were seen at the site in 2011.
The water was fresh (salinity ranged from 209-598 mg/L), moderately well oxygenated (59-61% saturated), slightly turbid and coloured in autumn when the creek was flowing, and with high concentrations of nutrients such as nitrogen (1.16-1.52 mg/L) and phosphorus (0.1-0.17 mg/L).
The sediments were dominated by detritus and sand, with boulder, cobble, algae, gravel and silt also present. Samples taken from below the surface were well aerated in autumn but anaerobic and sulfidic in spring, indicating the sediments turn into a harsh environment that lacks oxygen when the creek dries. A deposit of 1-5 cm of silt covered the channel in autumn but only about 1 cm was noted in spring; intervening rains had presumably transported large amounts of sediment further downstream in winter.
Moderate growths of phytoplankton and filamentous algae (including Cladophora) were present in spring but were not as abundant earlier in the year. Small growths of aquatic plants covered about 10% of the channel, including submerged (Callitriche) and emergent species (Cyperus and Bolboschoenus). The very narrow riparian zone consisted of planted gums and sheoaks over a range of introduced grasses and weeds. The surrounding vegetation was urban gardens.
Special environmental features
None detected apart from the unexpected presence of one rarely collected chironomid.
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.|
|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.|
|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.