Tributary of Coolawang Creek, north from Koolah
2011 Aquatic Ecosystem Condition Report
- Permanently wet, slightly flowing, freshwater creek in autumn and spring 2011
- Sparse macroinvertebrate community with two rare and sensitive species
- Obvious signs of gross nutrient enrichment
- Riparian zone well-vegetated and fenced at the site to prevent stock accessing the creek.
About the location
Tributary of Coolawang Creek is a small stream in the Southern Mount Lofty Ranges that rises north-east from Mount Desert and flows in a southerly direction, where it joins with Willow Swamp and ultimately discharges into Coolawang Creek. The monitoring site was located on a track off Willow Creek Road, about 500 metres north from ‘Koolah’ on the Fleurieu Peninsula. The major land uses in the 116 hectare catchment are cropping and stock grazing, with some small areas set aside for remnant native vegetation and roads.
The creek was given a Fair rating because the site sampled showed evidence of moderate changes in ecosystem structure, and some changes to the way the ecosystem functions. There was evidence of human disturbance including nutrient enrichment and excessive growth of aquatic plants at the site sampled. Despite this, the stream still provided habitat for a few rare and sensitive macroinvertebrate species.
A sparse community of at least 20 species of macroinvertebrates was collected from the slightly flowing creek, 2.6-2.8 m wide and only 11 cm deep, in autumn and spring 2011. The community was dominated by generalists and species sensitive to poor water quality such as chironomids, amphipods and immature stoneflies. It also included smaller numbers of flatworms, snails, mites, springtails, beetles, waterbugs and caddisflies. Two rare and sensitive species that typically occur in flowing habitats were collected, including a stonefly (Austrocerca tasmanica) and caddisfly (Taschorema evansi). None of the more commonly found flow-dependent species that occur in the region were detected and no fish were seen at the site in 2011.
The water was fresh (salinity ranged from 202-223 mg/L), well oxygenated (65-66% saturated), clear but strongly coloured, and with very high concentrations of nutrients such as nitrogen (2.52-4.13 mg/L) and phosphorus (0.1-0.2 mg/L). The water was also slightly acidic with a pH ranging from 6.39-6.74, presumably caused decaying vegetation in the creek that released coloured tannins into the water column.
The sediments were dominated by detritus with cobble, pebble, gravel, sand and algae also present. Samples taken from below the surface were slightly black in colour, had a strong manure or anaerobic odour and were sulfidic, indicating that the sediments lacked oxygen and represented a harsh environment for most burrowing species to be able to live in. A small deposit of silt, about 1 cm deep, was recorded in spring but no areas of significant erosion were noted during either survey in 2011; indications that the fencing installed to prevent cattle accessing the banks had been successful.
A large amount of phytoplankton was present in spring when about 10% of the creek was also covered by filamentous algae (including Cladophora). Over 90% of the site was covered by aquatic plants, consisting of extensive growths of rushes (Juncus) and smaller patches of several other emergent species (Persicaria, Eleocharis, Isolepis and Rumex). The 10-40 m wide riparian zone was dominated by bracken, rushes, sedges (mostly Baumea), and introduced grasses and weeds, with a few gums and wattles also present. The surrounding vegetation was mostly comprised cleared grazing paddocks but also included patches of remnant eucalypt woodland in the local landscape.
Special environmental features
The permanently wet, slow-flowing creek provides habitat for at least two rare and sensitive species.
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 to the creek upstream from the site(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.|
|Large nutrient 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’s 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.